1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (C) 1988-2017 Free Software Foundation, Inc.
5 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
6 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
23 @c To avoid file-name clashes between index.html and Index.html, when
24 @c the manual is produced on a Posix host and then moved to a
25 @c case-insensitive filesystem (e.g., MS-Windows), we separate the
26 @c indices into two: Concept Index and all the rest.
30 @c readline appendices use @vindex, @findex and @ftable,
31 @c annotate.texi and gdbmi use @findex.
34 @c !!set GDB manual's edition---not the same as GDB version!
35 @c This is updated by GNU Press.
38 @c !!set GDB edit command default editor
41 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
43 @c This is a dir.info fragment to support semi-automated addition of
44 @c manuals to an info tree.
45 @dircategory Software development
47 * Gdb: (gdb). The GNU debugger.
48 * gdbserver: (gdb) Server. The GNU debugging server.
52 @c man begin COPYRIGHT
53 Copyright @copyright{} 1988-2017 Free Software Foundation, Inc.
55 Permission is granted to copy, distribute and/or modify this document
56 under the terms of the GNU Free Documentation License, Version 1.3 or
57 any later version published by the Free Software Foundation; with the
58 Invariant Sections being ``Free Software'' and ``Free Software Needs
59 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
60 and with the Back-Cover Texts as in (a) below.
62 (a) The FSF's Back-Cover Text is: ``You are free to copy and modify
63 this GNU Manual. Buying copies from GNU Press supports the FSF in
64 developing GNU and promoting software freedom.''
69 This file documents the @sc{gnu} debugger @value{GDBN}.
71 This is the @value{EDITION} Edition, of @cite{Debugging with
72 @value{GDBN}: the @sc{gnu} Source-Level Debugger} for @value{GDBN}
73 @ifset VERSION_PACKAGE
74 @value{VERSION_PACKAGE}
76 Version @value{GDBVN}.
82 @title Debugging with @value{GDBN}
83 @subtitle The @sc{gnu} Source-Level Debugger
85 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
86 @ifset VERSION_PACKAGE
88 @subtitle @value{VERSION_PACKAGE}
90 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
94 \hfill (Send bugs and comments on @value{GDBN} to @value{BUGURL}.)\par
95 \hfill {\it Debugging with @value{GDBN}}\par
96 \hfill \TeX{}info \texinfoversion\par
100 @vskip 0pt plus 1filll
101 Published by the Free Software Foundation @*
102 51 Franklin Street, Fifth Floor,
103 Boston, MA 02110-1301, USA@*
104 ISBN 978-0-9831592-3-0 @*
111 @node Top, Summary, (dir), (dir)
113 @top Debugging with @value{GDBN}
115 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
117 This is the @value{EDITION} Edition, for @value{GDBN}
118 @ifset VERSION_PACKAGE
119 @value{VERSION_PACKAGE}
121 Version @value{GDBVN}.
123 Copyright (C) 1988-2017 Free Software Foundation, Inc.
125 This edition of the GDB manual is dedicated to the memory of Fred
126 Fish. Fred was a long-standing contributor to GDB and to Free
127 software in general. We will miss him.
130 * Summary:: Summary of @value{GDBN}
131 * Sample Session:: A sample @value{GDBN} session
133 * Invocation:: Getting in and out of @value{GDBN}
134 * Commands:: @value{GDBN} commands
135 * Running:: Running programs under @value{GDBN}
136 * Stopping:: Stopping and continuing
137 * Reverse Execution:: Running programs backward
138 * Process Record and Replay:: Recording inferior's execution and replaying it
139 * Stack:: Examining the stack
140 * Source:: Examining source files
141 * Data:: Examining data
142 * Optimized Code:: Debugging optimized code
143 * Macros:: Preprocessor Macros
144 * Tracepoints:: Debugging remote targets non-intrusively
145 * Overlays:: Debugging programs that use overlays
147 * Languages:: Using @value{GDBN} with different languages
149 * Symbols:: Examining the symbol table
150 * Altering:: Altering execution
151 * GDB Files:: @value{GDBN} files
152 * Targets:: Specifying a debugging target
153 * Remote Debugging:: Debugging remote programs
154 * Configurations:: Configuration-specific information
155 * Controlling GDB:: Controlling @value{GDBN}
156 * Extending GDB:: Extending @value{GDBN}
157 * Interpreters:: Command Interpreters
158 * TUI:: @value{GDBN} Text User Interface
159 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
160 * GDB/MI:: @value{GDBN}'s Machine Interface.
161 * Annotations:: @value{GDBN}'s annotation interface.
162 * JIT Interface:: Using the JIT debugging interface.
163 * In-Process Agent:: In-Process Agent
165 * GDB Bugs:: Reporting bugs in @value{GDBN}
167 @ifset SYSTEM_READLINE
168 * Command Line Editing: (rluserman). Command Line Editing
169 * Using History Interactively: (history). Using History Interactively
171 @ifclear SYSTEM_READLINE
172 * Command Line Editing:: Command Line Editing
173 * Using History Interactively:: Using History Interactively
175 * In Memoriam:: In Memoriam
176 * Formatting Documentation:: How to format and print @value{GDBN} documentation
177 * Installing GDB:: Installing GDB
178 * Maintenance Commands:: Maintenance Commands
179 * Remote Protocol:: GDB Remote Serial Protocol
180 * Agent Expressions:: The GDB Agent Expression Mechanism
181 * Target Descriptions:: How targets can describe themselves to
183 * Operating System Information:: Getting additional information from
185 * Trace File Format:: GDB trace file format
186 * Index Section Format:: .gdb_index section format
187 * Man Pages:: Manual pages
188 * Copying:: GNU General Public License says
189 how you can copy and share GDB
190 * GNU Free Documentation License:: The license for this documentation
191 * Concept Index:: Index of @value{GDBN} concepts
192 * Command and Variable Index:: Index of @value{GDBN} commands, variables,
193 functions, and Python data types
201 @unnumbered Summary of @value{GDBN}
203 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
204 going on ``inside'' another program while it executes---or what another
205 program was doing at the moment it crashed.
207 @value{GDBN} can do four main kinds of things (plus other things in support of
208 these) to help you catch bugs in the act:
212 Start your program, specifying anything that might affect its behavior.
215 Make your program stop on specified conditions.
218 Examine what has happened, when your program has stopped.
221 Change things in your program, so you can experiment with correcting the
222 effects of one bug and go on to learn about another.
225 You can use @value{GDBN} to debug programs written in C and C@t{++}.
226 For more information, see @ref{Supported Languages,,Supported Languages}.
227 For more information, see @ref{C,,C and C++}.
229 Support for D is partial. For information on D, see
233 Support for Modula-2 is partial. For information on Modula-2, see
234 @ref{Modula-2,,Modula-2}.
236 Support for OpenCL C is partial. For information on OpenCL C, see
237 @ref{OpenCL C,,OpenCL C}.
240 Debugging Pascal programs which use sets, subranges, file variables, or
241 nested functions does not currently work. @value{GDBN} does not support
242 entering expressions, printing values, or similar features using Pascal
246 @value{GDBN} can be used to debug programs written in Fortran, although
247 it may be necessary to refer to some variables with a trailing
250 @value{GDBN} can be used to debug programs written in Objective-C,
251 using either the Apple/NeXT or the GNU Objective-C runtime.
254 * Free Software:: Freely redistributable software
255 * Free Documentation:: Free Software Needs Free Documentation
256 * Contributors:: Contributors to GDB
260 @unnumberedsec Free Software
262 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
263 General Public License
264 (GPL). The GPL gives you the freedom to copy or adapt a licensed
265 program---but every person getting a copy also gets with it the
266 freedom to modify that copy (which means that they must get access to
267 the source code), and the freedom to distribute further copies.
268 Typical software companies use copyrights to limit your freedoms; the
269 Free Software Foundation uses the GPL to preserve these freedoms.
271 Fundamentally, the General Public License is a license which says that
272 you have these freedoms and that you cannot take these freedoms away
275 @node Free Documentation
276 @unnumberedsec Free Software Needs Free Documentation
278 The biggest deficiency in the free software community today is not in
279 the software---it is the lack of good free documentation that we can
280 include with the free software. Many of our most important
281 programs do not come with free reference manuals and free introductory
282 texts. Documentation is an essential part of any software package;
283 when an important free software package does not come with a free
284 manual and a free tutorial, that is a major gap. We have many such
287 Consider Perl, for instance. The tutorial manuals that people
288 normally use are non-free. How did this come about? Because the
289 authors of those manuals published them with restrictive terms---no
290 copying, no modification, source files not available---which exclude
291 them from the free software world.
293 That wasn't the first time this sort of thing happened, and it was far
294 from the last. Many times we have heard a GNU user eagerly describe a
295 manual that he is writing, his intended contribution to the community,
296 only to learn that he had ruined everything by signing a publication
297 contract to make it non-free.
299 Free documentation, like free software, is a matter of freedom, not
300 price. The problem with the non-free manual is not that publishers
301 charge a price for printed copies---that in itself is fine. (The Free
302 Software Foundation sells printed copies of manuals, too.) The
303 problem is the restrictions on the use of the manual. Free manuals
304 are available in source code form, and give you permission to copy and
305 modify. Non-free manuals do not allow this.
307 The criteria of freedom for a free manual are roughly the same as for
308 free software. Redistribution (including the normal kinds of
309 commercial redistribution) must be permitted, so that the manual can
310 accompany every copy of the program, both on-line and on paper.
312 Permission for modification of the technical content is crucial too.
313 When people modify the software, adding or changing features, if they
314 are conscientious they will change the manual too---so they can
315 provide accurate and clear documentation for the modified program. A
316 manual that leaves you no choice but to write a new manual to document
317 a changed version of the program is not really available to our
320 Some kinds of limits on the way modification is handled are
321 acceptable. For example, requirements to preserve the original
322 author's copyright notice, the distribution terms, or the list of
323 authors, are ok. It is also no problem to require modified versions
324 to include notice that they were modified. Even entire sections that
325 may not be deleted or changed are acceptable, as long as they deal
326 with nontechnical topics (like this one). These kinds of restrictions
327 are acceptable because they don't obstruct the community's normal use
330 However, it must be possible to modify all the @emph{technical}
331 content of the manual, and then distribute the result in all the usual
332 media, through all the usual channels. Otherwise, the restrictions
333 obstruct the use of the manual, it is not free, and we need another
334 manual to replace it.
336 Please spread the word about this issue. Our community continues to
337 lose manuals to proprietary publishing. If we spread the word that
338 free software needs free reference manuals and free tutorials, perhaps
339 the next person who wants to contribute by writing documentation will
340 realize, before it is too late, that only free manuals contribute to
341 the free software community.
343 If you are writing documentation, please insist on publishing it under
344 the GNU Free Documentation License or another free documentation
345 license. Remember that this decision requires your approval---you
346 don't have to let the publisher decide. Some commercial publishers
347 will use a free license if you insist, but they will not propose the
348 option; it is up to you to raise the issue and say firmly that this is
349 what you want. If the publisher you are dealing with refuses, please
350 try other publishers. If you're not sure whether a proposed license
351 is free, write to @email{licensing@@gnu.org}.
353 You can encourage commercial publishers to sell more free, copylefted
354 manuals and tutorials by buying them, and particularly by buying
355 copies from the publishers that paid for their writing or for major
356 improvements. Meanwhile, try to avoid buying non-free documentation
357 at all. Check the distribution terms of a manual before you buy it,
358 and insist that whoever seeks your business must respect your freedom.
359 Check the history of the book, and try to reward the publishers that
360 have paid or pay the authors to work on it.
362 The Free Software Foundation maintains a list of free documentation
363 published by other publishers, at
364 @url{http://www.fsf.org/doc/other-free-books.html}.
367 @unnumberedsec Contributors to @value{GDBN}
369 Richard Stallman was the original author of @value{GDBN}, and of many
370 other @sc{gnu} programs. Many others have contributed to its
371 development. This section attempts to credit major contributors. One
372 of the virtues of free software is that everyone is free to contribute
373 to it; with regret, we cannot actually acknowledge everyone here. The
374 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
375 blow-by-blow account.
377 Changes much prior to version 2.0 are lost in the mists of time.
380 @emph{Plea:} Additions to this section are particularly welcome. If you
381 or your friends (or enemies, to be evenhanded) have been unfairly
382 omitted from this list, we would like to add your names!
385 So that they may not regard their many labors as thankless, we
386 particularly thank those who shepherded @value{GDBN} through major
388 Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0);
389 Jim Blandy (release 4.18);
390 Jason Molenda (release 4.17);
391 Stan Shebs (release 4.14);
392 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
393 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
394 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
395 Jim Kingdon (releases 3.5, 3.4, and 3.3);
396 and Randy Smith (releases 3.2, 3.1, and 3.0).
398 Richard Stallman, assisted at various times by Peter TerMaat, Chris
399 Hanson, and Richard Mlynarik, handled releases through 2.8.
401 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
402 in @value{GDBN}, with significant additional contributions from Per
403 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
404 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
405 much general update work leading to release 3.0).
407 @value{GDBN} uses the BFD subroutine library to examine multiple
408 object-file formats; BFD was a joint project of David V.
409 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
411 David Johnson wrote the original COFF support; Pace Willison did
412 the original support for encapsulated COFF.
414 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
416 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
417 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
419 Jean-Daniel Fekete contributed Sun 386i support.
420 Chris Hanson improved the HP9000 support.
421 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
422 David Johnson contributed Encore Umax support.
423 Jyrki Kuoppala contributed Altos 3068 support.
424 Jeff Law contributed HP PA and SOM support.
425 Keith Packard contributed NS32K support.
426 Doug Rabson contributed Acorn Risc Machine support.
427 Bob Rusk contributed Harris Nighthawk CX-UX support.
428 Chris Smith contributed Convex support (and Fortran debugging).
429 Jonathan Stone contributed Pyramid support.
430 Michael Tiemann contributed SPARC support.
431 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
432 Pace Willison contributed Intel 386 support.
433 Jay Vosburgh contributed Symmetry support.
434 Marko Mlinar contributed OpenRISC 1000 support.
436 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
438 Rich Schaefer and Peter Schauer helped with support of SunOS shared
441 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
442 about several machine instruction sets.
444 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
445 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
446 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
447 and RDI targets, respectively.
449 Brian Fox is the author of the readline libraries providing
450 command-line editing and command history.
452 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
453 Modula-2 support, and contributed the Languages chapter of this manual.
455 Fred Fish wrote most of the support for Unix System Vr4.
456 He also enhanced the command-completion support to cover C@t{++} overloaded
459 Hitachi America (now Renesas America), Ltd. sponsored the support for
460 H8/300, H8/500, and Super-H processors.
462 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
464 Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and M32R/D
467 Toshiba sponsored the support for the TX39 Mips processor.
469 Matsushita sponsored the support for the MN10200 and MN10300 processors.
471 Fujitsu sponsored the support for SPARClite and FR30 processors.
473 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
476 Michael Snyder added support for tracepoints.
478 Stu Grossman wrote gdbserver.
480 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
481 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
483 The following people at the Hewlett-Packard Company contributed
484 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
485 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
486 compiler, and the Text User Interface (nee Terminal User Interface):
487 Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
488 Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase
489 provided HP-specific information in this manual.
491 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
492 Robert Hoehne made significant contributions to the DJGPP port.
494 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
495 development since 1991. Cygnus engineers who have worked on @value{GDBN}
496 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
497 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
498 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
499 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
500 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
501 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
502 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
503 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
504 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
505 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
506 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
507 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
508 Zuhn have made contributions both large and small.
510 Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
511 Cygnus Solutions, implemented the original @sc{gdb/mi} interface.
513 Jim Blandy added support for preprocessor macros, while working for Red
516 Andrew Cagney designed @value{GDBN}'s architecture vector. Many
517 people including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick
518 Duffek, Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei
519 Sakamoto, Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason
520 Thorpe, Corinna Vinschen, Ulrich Weigand, and Elena Zannoni, helped
521 with the migration of old architectures to this new framework.
523 Andrew Cagney completely re-designed and re-implemented @value{GDBN}'s
524 unwinder framework, this consisting of a fresh new design featuring
525 frame IDs, independent frame sniffers, and the sentinel frame. Mark
526 Kettenis implemented the @sc{dwarf 2} unwinder, Jeff Johnston the
527 libunwind unwinder, and Andrew Cagney the dummy, sentinel, tramp, and
528 trad unwinders. The architecture-specific changes, each involving a
529 complete rewrite of the architecture's frame code, were carried out by
530 Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
531 Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
532 Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
533 Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
536 Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
537 Tensilica, Inc.@: contributed support for Xtensa processors. Others
538 who have worked on the Xtensa port of @value{GDBN} in the past include
539 Steve Tjiang, John Newlin, and Scott Foehner.
541 Michael Eager and staff of Xilinx, Inc., contributed support for the
542 Xilinx MicroBlaze architecture.
544 Initial support for the FreeBSD/mips target and native configuration
545 was developed by SRI International and the University of Cambridge
546 Computer Laboratory under DARPA/AFRL contract FA8750-10-C-0237
547 ("CTSRD"), as part of the DARPA CRASH research programme.
550 @chapter A Sample @value{GDBN} Session
552 You can use this manual at your leisure to read all about @value{GDBN}.
553 However, a handful of commands are enough to get started using the
554 debugger. This chapter illustrates those commands.
557 In this sample session, we emphasize user input like this: @b{input},
558 to make it easier to pick out from the surrounding output.
561 @c FIXME: this example may not be appropriate for some configs, where
562 @c FIXME...primary interest is in remote use.
564 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
565 processor) exhibits the following bug: sometimes, when we change its
566 quote strings from the default, the commands used to capture one macro
567 definition within another stop working. In the following short @code{m4}
568 session, we define a macro @code{foo} which expands to @code{0000}; we
569 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
570 same thing. However, when we change the open quote string to
571 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
572 procedure fails to define a new synonym @code{baz}:
581 @b{define(bar,defn(`foo'))}
585 @b{changequote(<QUOTE>,<UNQUOTE>)}
587 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
590 m4: End of input: 0: fatal error: EOF in string
594 Let us use @value{GDBN} to try to see what is going on.
597 $ @b{@value{GDBP} m4}
598 @c FIXME: this falsifies the exact text played out, to permit smallbook
599 @c FIXME... format to come out better.
600 @value{GDBN} is free software and you are welcome to distribute copies
601 of it under certain conditions; type "show copying" to see
603 There is absolutely no warranty for @value{GDBN}; type "show warranty"
606 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
611 @value{GDBN} reads only enough symbol data to know where to find the
612 rest when needed; as a result, the first prompt comes up very quickly.
613 We now tell @value{GDBN} to use a narrower display width than usual, so
614 that examples fit in this manual.
617 (@value{GDBP}) @b{set width 70}
621 We need to see how the @code{m4} built-in @code{changequote} works.
622 Having looked at the source, we know the relevant subroutine is
623 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
624 @code{break} command.
627 (@value{GDBP}) @b{break m4_changequote}
628 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
632 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
633 control; as long as control does not reach the @code{m4_changequote}
634 subroutine, the program runs as usual:
637 (@value{GDBP}) @b{run}
638 Starting program: /work/Editorial/gdb/gnu/m4/m4
646 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
647 suspends execution of @code{m4}, displaying information about the
648 context where it stops.
651 @b{changequote(<QUOTE>,<UNQUOTE>)}
653 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
655 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
659 Now we use the command @code{n} (@code{next}) to advance execution to
660 the next line of the current function.
664 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
669 @code{set_quotes} looks like a promising subroutine. We can go into it
670 by using the command @code{s} (@code{step}) instead of @code{next}.
671 @code{step} goes to the next line to be executed in @emph{any}
672 subroutine, so it steps into @code{set_quotes}.
676 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
678 530 if (lquote != def_lquote)
682 The display that shows the subroutine where @code{m4} is now
683 suspended (and its arguments) is called a stack frame display. It
684 shows a summary of the stack. We can use the @code{backtrace}
685 command (which can also be spelled @code{bt}), to see where we are
686 in the stack as a whole: the @code{backtrace} command displays a
687 stack frame for each active subroutine.
690 (@value{GDBP}) @b{bt}
691 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
693 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
695 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
696 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
698 #4 0x79dc in expand_input () at macro.c:40
699 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
703 We step through a few more lines to see what happens. The first two
704 times, we can use @samp{s}; the next two times we use @code{n} to avoid
705 falling into the @code{xstrdup} subroutine.
709 0x3b5c 532 if (rquote != def_rquote)
711 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
712 def_lquote : xstrdup(lq);
714 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
717 538 len_lquote = strlen(rquote);
721 The last line displayed looks a little odd; we can examine the variables
722 @code{lquote} and @code{rquote} to see if they are in fact the new left
723 and right quotes we specified. We use the command @code{p}
724 (@code{print}) to see their values.
727 (@value{GDBP}) @b{p lquote}
728 $1 = 0x35d40 "<QUOTE>"
729 (@value{GDBP}) @b{p rquote}
730 $2 = 0x35d50 "<UNQUOTE>"
734 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
735 To look at some context, we can display ten lines of source
736 surrounding the current line with the @code{l} (@code{list}) command.
742 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
744 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
747 538 len_lquote = strlen(rquote);
748 539 len_rquote = strlen(lquote);
755 Let us step past the two lines that set @code{len_lquote} and
756 @code{len_rquote}, and then examine the values of those variables.
760 539 len_rquote = strlen(lquote);
763 (@value{GDBP}) @b{p len_lquote}
765 (@value{GDBP}) @b{p len_rquote}
770 That certainly looks wrong, assuming @code{len_lquote} and
771 @code{len_rquote} are meant to be the lengths of @code{lquote} and
772 @code{rquote} respectively. We can set them to better values using
773 the @code{p} command, since it can print the value of
774 any expression---and that expression can include subroutine calls and
778 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
780 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
785 Is that enough to fix the problem of using the new quotes with the
786 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
787 executing with the @code{c} (@code{continue}) command, and then try the
788 example that caused trouble initially:
794 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
801 Success! The new quotes now work just as well as the default ones. The
802 problem seems to have been just the two typos defining the wrong
803 lengths. We allow @code{m4} exit by giving it an EOF as input:
807 Program exited normally.
811 The message @samp{Program exited normally.} is from @value{GDBN}; it
812 indicates @code{m4} has finished executing. We can end our @value{GDBN}
813 session with the @value{GDBN} @code{quit} command.
816 (@value{GDBP}) @b{quit}
820 @chapter Getting In and Out of @value{GDBN}
822 This chapter discusses how to start @value{GDBN}, and how to get out of it.
826 type @samp{@value{GDBP}} to start @value{GDBN}.
828 type @kbd{quit} or @kbd{Ctrl-d} to exit.
832 * Invoking GDB:: How to start @value{GDBN}
833 * Quitting GDB:: How to quit @value{GDBN}
834 * Shell Commands:: How to use shell commands inside @value{GDBN}
835 * Logging Output:: How to log @value{GDBN}'s output to a file
839 @section Invoking @value{GDBN}
841 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
842 @value{GDBN} reads commands from the terminal until you tell it to exit.
844 You can also run @code{@value{GDBP}} with a variety of arguments and options,
845 to specify more of your debugging environment at the outset.
847 The command-line options described here are designed
848 to cover a variety of situations; in some environments, some of these
849 options may effectively be unavailable.
851 The most usual way to start @value{GDBN} is with one argument,
852 specifying an executable program:
855 @value{GDBP} @var{program}
859 You can also start with both an executable program and a core file
863 @value{GDBP} @var{program} @var{core}
866 You can, instead, specify a process ID as a second argument, if you want
867 to debug a running process:
870 @value{GDBP} @var{program} 1234
874 would attach @value{GDBN} to process @code{1234} (unless you also have a file
875 named @file{1234}; @value{GDBN} does check for a core file first).
877 Taking advantage of the second command-line argument requires a fairly
878 complete operating system; when you use @value{GDBN} as a remote
879 debugger attached to a bare board, there may not be any notion of
880 ``process'', and there is often no way to get a core dump. @value{GDBN}
881 will warn you if it is unable to attach or to read core dumps.
883 You can optionally have @code{@value{GDBP}} pass any arguments after the
884 executable file to the inferior using @code{--args}. This option stops
887 @value{GDBP} --args gcc -O2 -c foo.c
889 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
890 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
892 You can run @code{@value{GDBP}} without printing the front material, which describes
893 @value{GDBN}'s non-warranty, by specifying @code{--silent}
894 (or @code{-q}/@code{--quiet}):
897 @value{GDBP} --silent
901 You can further control how @value{GDBN} starts up by using command-line
902 options. @value{GDBN} itself can remind you of the options available.
912 to display all available options and briefly describe their use
913 (@samp{@value{GDBP} -h} is a shorter equivalent).
915 All options and command line arguments you give are processed
916 in sequential order. The order makes a difference when the
917 @samp{-x} option is used.
921 * File Options:: Choosing files
922 * Mode Options:: Choosing modes
923 * Startup:: What @value{GDBN} does during startup
927 @subsection Choosing Files
929 When @value{GDBN} starts, it reads any arguments other than options as
930 specifying an executable file and core file (or process ID). This is
931 the same as if the arguments were specified by the @samp{-se} and
932 @samp{-c} (or @samp{-p}) options respectively. (@value{GDBN} reads the
933 first argument that does not have an associated option flag as
934 equivalent to the @samp{-se} option followed by that argument; and the
935 second argument that does not have an associated option flag, if any, as
936 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
937 If the second argument begins with a decimal digit, @value{GDBN} will
938 first attempt to attach to it as a process, and if that fails, attempt
939 to open it as a corefile. If you have a corefile whose name begins with
940 a digit, you can prevent @value{GDBN} from treating it as a pid by
941 prefixing it with @file{./}, e.g.@: @file{./12345}.
943 If @value{GDBN} has not been configured to included core file support,
944 such as for most embedded targets, then it will complain about a second
945 argument and ignore it.
947 Many options have both long and short forms; both are shown in the
948 following list. @value{GDBN} also recognizes the long forms if you truncate
949 them, so long as enough of the option is present to be unambiguous.
950 (If you prefer, you can flag option arguments with @samp{--} rather
951 than @samp{-}, though we illustrate the more usual convention.)
953 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
954 @c way, both those who look for -foo and --foo in the index, will find
958 @item -symbols @var{file}
960 @cindex @code{--symbols}
962 Read symbol table from file @var{file}.
964 @item -exec @var{file}
966 @cindex @code{--exec}
968 Use file @var{file} as the executable file to execute when appropriate,
969 and for examining pure data in conjunction with a core dump.
973 Read symbol table from file @var{file} and use it as the executable
976 @item -core @var{file}
978 @cindex @code{--core}
980 Use file @var{file} as a core dump to examine.
982 @item -pid @var{number}
983 @itemx -p @var{number}
986 Connect to process ID @var{number}, as with the @code{attach} command.
988 @item -command @var{file}
990 @cindex @code{--command}
992 Execute commands from file @var{file}. The contents of this file is
993 evaluated exactly as the @code{source} command would.
994 @xref{Command Files,, Command files}.
996 @item -eval-command @var{command}
997 @itemx -ex @var{command}
998 @cindex @code{--eval-command}
1000 Execute a single @value{GDBN} command.
1002 This option may be used multiple times to call multiple commands. It may
1003 also be interleaved with @samp{-command} as required.
1006 @value{GDBP} -ex 'target sim' -ex 'load' \
1007 -x setbreakpoints -ex 'run' a.out
1010 @item -init-command @var{file}
1011 @itemx -ix @var{file}
1012 @cindex @code{--init-command}
1014 Execute commands from file @var{file} before loading the inferior (but
1015 after loading gdbinit files).
1018 @item -init-eval-command @var{command}
1019 @itemx -iex @var{command}
1020 @cindex @code{--init-eval-command}
1022 Execute a single @value{GDBN} command before loading the inferior (but
1023 after loading gdbinit files).
1026 @item -directory @var{directory}
1027 @itemx -d @var{directory}
1028 @cindex @code{--directory}
1030 Add @var{directory} to the path to search for source and script files.
1034 @cindex @code{--readnow}
1036 Read each symbol file's entire symbol table immediately, rather than
1037 the default, which is to read it incrementally as it is needed.
1038 This makes startup slower, but makes future operations faster.
1043 @subsection Choosing Modes
1045 You can run @value{GDBN} in various alternative modes---for example, in
1046 batch mode or quiet mode.
1054 Do not execute commands found in any initialization file.
1055 There are three init files, loaded in the following order:
1058 @item @file{system.gdbinit}
1059 This is the system-wide init file.
1060 Its location is specified with the @code{--with-system-gdbinit}
1061 configure option (@pxref{System-wide configuration}).
1062 It is loaded first when @value{GDBN} starts, before command line options
1063 have been processed.
1064 @item @file{~/.gdbinit}
1065 This is the init file in your home directory.
1066 It is loaded next, after @file{system.gdbinit}, and before
1067 command options have been processed.
1068 @item @file{./.gdbinit}
1069 This is the init file in the current directory.
1070 It is loaded last, after command line options other than @code{-x} and
1071 @code{-ex} have been processed. Command line options @code{-x} and
1072 @code{-ex} are processed last, after @file{./.gdbinit} has been loaded.
1075 For further documentation on startup processing, @xref{Startup}.
1076 For documentation on how to write command files,
1077 @xref{Command Files,,Command Files}.
1082 Do not execute commands found in @file{~/.gdbinit}, the init file
1083 in your home directory.
1089 @cindex @code{--quiet}
1090 @cindex @code{--silent}
1092 ``Quiet''. Do not print the introductory and copyright messages. These
1093 messages are also suppressed in batch mode.
1096 @cindex @code{--batch}
1097 Run in batch mode. Exit with status @code{0} after processing all the
1098 command files specified with @samp{-x} (and all commands from
1099 initialization files, if not inhibited with @samp{-n}). Exit with
1100 nonzero status if an error occurs in executing the @value{GDBN} commands
1101 in the command files. Batch mode also disables pagination, sets unlimited
1102 terminal width and height @pxref{Screen Size}, and acts as if @kbd{set confirm
1103 off} were in effect (@pxref{Messages/Warnings}).
1105 Batch mode may be useful for running @value{GDBN} as a filter, for
1106 example to download and run a program on another computer; in order to
1107 make this more useful, the message
1110 Program exited normally.
1114 (which is ordinarily issued whenever a program running under
1115 @value{GDBN} control terminates) is not issued when running in batch
1119 @cindex @code{--batch-silent}
1120 Run in batch mode exactly like @samp{-batch}, but totally silently. All
1121 @value{GDBN} output to @code{stdout} is prevented (@code{stderr} is
1122 unaffected). This is much quieter than @samp{-silent} and would be useless
1123 for an interactive session.
1125 This is particularly useful when using targets that give @samp{Loading section}
1126 messages, for example.
1128 Note that targets that give their output via @value{GDBN}, as opposed to
1129 writing directly to @code{stdout}, will also be made silent.
1131 @item -return-child-result
1132 @cindex @code{--return-child-result}
1133 The return code from @value{GDBN} will be the return code from the child
1134 process (the process being debugged), with the following exceptions:
1138 @value{GDBN} exits abnormally. E.g., due to an incorrect argument or an
1139 internal error. In this case the exit code is the same as it would have been
1140 without @samp{-return-child-result}.
1142 The user quits with an explicit value. E.g., @samp{quit 1}.
1144 The child process never runs, or is not allowed to terminate, in which case
1145 the exit code will be -1.
1148 This option is useful in conjunction with @samp{-batch} or @samp{-batch-silent},
1149 when @value{GDBN} is being used as a remote program loader or simulator
1154 @cindex @code{--nowindows}
1156 ``No windows''. If @value{GDBN} comes with a graphical user interface
1157 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1158 interface. If no GUI is available, this option has no effect.
1162 @cindex @code{--windows}
1164 If @value{GDBN} includes a GUI, then this option requires it to be
1167 @item -cd @var{directory}
1169 Run @value{GDBN} using @var{directory} as its working directory,
1170 instead of the current directory.
1172 @item -data-directory @var{directory}
1173 @itemx -D @var{directory}
1174 @cindex @code{--data-directory}
1176 Run @value{GDBN} using @var{directory} as its data directory.
1177 The data directory is where @value{GDBN} searches for its
1178 auxiliary files. @xref{Data Files}.
1182 @cindex @code{--fullname}
1184 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1185 subprocess. It tells @value{GDBN} to output the full file name and line
1186 number in a standard, recognizable fashion each time a stack frame is
1187 displayed (which includes each time your program stops). This
1188 recognizable format looks like two @samp{\032} characters, followed by
1189 the file name, line number and character position separated by colons,
1190 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1191 @samp{\032} characters as a signal to display the source code for the
1194 @item -annotate @var{level}
1195 @cindex @code{--annotate}
1196 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1197 effect is identical to using @samp{set annotate @var{level}}
1198 (@pxref{Annotations}). The annotation @var{level} controls how much
1199 information @value{GDBN} prints together with its prompt, values of
1200 expressions, source lines, and other types of output. Level 0 is the
1201 normal, level 1 is for use when @value{GDBN} is run as a subprocess of
1202 @sc{gnu} Emacs, level 3 is the maximum annotation suitable for programs
1203 that control @value{GDBN}, and level 2 has been deprecated.
1205 The annotation mechanism has largely been superseded by @sc{gdb/mi}
1209 @cindex @code{--args}
1210 Change interpretation of command line so that arguments following the
1211 executable file are passed as command line arguments to the inferior.
1212 This option stops option processing.
1214 @item -baud @var{bps}
1216 @cindex @code{--baud}
1218 Set the line speed (baud rate or bits per second) of any serial
1219 interface used by @value{GDBN} for remote debugging.
1221 @item -l @var{timeout}
1223 Set the timeout (in seconds) of any communication used by @value{GDBN}
1224 for remote debugging.
1226 @item -tty @var{device}
1227 @itemx -t @var{device}
1228 @cindex @code{--tty}
1230 Run using @var{device} for your program's standard input and output.
1231 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1233 @c resolve the situation of these eventually
1235 @cindex @code{--tui}
1236 Activate the @dfn{Text User Interface} when starting. The Text User
1237 Interface manages several text windows on the terminal, showing
1238 source, assembly, registers and @value{GDBN} command outputs
1239 (@pxref{TUI, ,@value{GDBN} Text User Interface}). Do not use this
1240 option if you run @value{GDBN} from Emacs (@pxref{Emacs, ,
1241 Using @value{GDBN} under @sc{gnu} Emacs}).
1243 @item -interpreter @var{interp}
1244 @cindex @code{--interpreter}
1245 Use the interpreter @var{interp} for interface with the controlling
1246 program or device. This option is meant to be set by programs which
1247 communicate with @value{GDBN} using it as a back end.
1248 @xref{Interpreters, , Command Interpreters}.
1250 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1251 @value{GDBN} to use the @dfn{@sc{gdb/mi} interface} (@pxref{GDB/MI, ,
1252 The @sc{gdb/mi} Interface}) included since @value{GDBN} version 6.0. The
1253 previous @sc{gdb/mi} interface, included in @value{GDBN} version 5.3 and
1254 selected with @samp{--interpreter=mi1}, is deprecated. Earlier
1255 @sc{gdb/mi} interfaces are no longer supported.
1258 @cindex @code{--write}
1259 Open the executable and core files for both reading and writing. This
1260 is equivalent to the @samp{set write on} command inside @value{GDBN}
1264 @cindex @code{--statistics}
1265 This option causes @value{GDBN} to print statistics about time and
1266 memory usage after it completes each command and returns to the prompt.
1269 @cindex @code{--version}
1270 This option causes @value{GDBN} to print its version number and
1271 no-warranty blurb, and exit.
1273 @item -configuration
1274 @cindex @code{--configuration}
1275 This option causes @value{GDBN} to print details about its build-time
1276 configuration parameters, and then exit. These details can be
1277 important when reporting @value{GDBN} bugs (@pxref{GDB Bugs}).
1282 @subsection What @value{GDBN} Does During Startup
1283 @cindex @value{GDBN} startup
1285 Here's the description of what @value{GDBN} does during session startup:
1289 Sets up the command interpreter as specified by the command line
1290 (@pxref{Mode Options, interpreter}).
1294 Reads the system-wide @dfn{init file} (if @option{--with-system-gdbinit} was
1295 used when building @value{GDBN}; @pxref{System-wide configuration,
1296 ,System-wide configuration and settings}) and executes all the commands in
1299 @anchor{Home Directory Init File}
1301 Reads the init file (if any) in your home directory@footnote{On
1302 DOS/Windows systems, the home directory is the one pointed to by the
1303 @code{HOME} environment variable.} and executes all the commands in
1306 @anchor{Option -init-eval-command}
1308 Executes commands and command files specified by the @samp{-iex} and
1309 @samp{-ix} options in their specified order. Usually you should use the
1310 @samp{-ex} and @samp{-x} options instead, but this way you can apply
1311 settings before @value{GDBN} init files get executed and before inferior
1315 Processes command line options and operands.
1317 @anchor{Init File in the Current Directory during Startup}
1319 Reads and executes the commands from init file (if any) in the current
1320 working directory as long as @samp{set auto-load local-gdbinit} is set to
1321 @samp{on} (@pxref{Init File in the Current Directory}).
1322 This is only done if the current directory is
1323 different from your home directory. Thus, you can have more than one
1324 init file, one generic in your home directory, and another, specific
1325 to the program you are debugging, in the directory where you invoke
1329 If the command line specified a program to debug, or a process to
1330 attach to, or a core file, @value{GDBN} loads any auto-loaded
1331 scripts provided for the program or for its loaded shared libraries.
1332 @xref{Auto-loading}.
1334 If you wish to disable the auto-loading during startup,
1335 you must do something like the following:
1338 $ gdb -iex "set auto-load python-scripts off" myprogram
1341 Option @samp{-ex} does not work because the auto-loading is then turned
1345 Executes commands and command files specified by the @samp{-ex} and
1346 @samp{-x} options in their specified order. @xref{Command Files}, for
1347 more details about @value{GDBN} command files.
1350 Reads the command history recorded in the @dfn{history file}.
1351 @xref{Command History}, for more details about the command history and the
1352 files where @value{GDBN} records it.
1355 Init files use the same syntax as @dfn{command files} (@pxref{Command
1356 Files}) and are processed by @value{GDBN} in the same way. The init
1357 file in your home directory can set options (such as @samp{set
1358 complaints}) that affect subsequent processing of command line options
1359 and operands. Init files are not executed if you use the @samp{-nx}
1360 option (@pxref{Mode Options, ,Choosing Modes}).
1362 To display the list of init files loaded by gdb at startup, you
1363 can use @kbd{gdb --help}.
1365 @cindex init file name
1366 @cindex @file{.gdbinit}
1367 @cindex @file{gdb.ini}
1368 The @value{GDBN} init files are normally called @file{.gdbinit}.
1369 The DJGPP port of @value{GDBN} uses the name @file{gdb.ini}, due to
1370 the limitations of file names imposed by DOS filesystems. The Windows
1371 port of @value{GDBN} uses the standard name, but if it finds a
1372 @file{gdb.ini} file in your home directory, it warns you about that
1373 and suggests to rename the file to the standard name.
1377 @section Quitting @value{GDBN}
1378 @cindex exiting @value{GDBN}
1379 @cindex leaving @value{GDBN}
1382 @kindex quit @r{[}@var{expression}@r{]}
1383 @kindex q @r{(@code{quit})}
1384 @item quit @r{[}@var{expression}@r{]}
1386 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1387 @code{q}), or type an end-of-file character (usually @kbd{Ctrl-d}). If you
1388 do not supply @var{expression}, @value{GDBN} will terminate normally;
1389 otherwise it will terminate using the result of @var{expression} as the
1394 An interrupt (often @kbd{Ctrl-c}) does not exit from @value{GDBN}, but rather
1395 terminates the action of any @value{GDBN} command that is in progress and
1396 returns to @value{GDBN} command level. It is safe to type the interrupt
1397 character at any time because @value{GDBN} does not allow it to take effect
1398 until a time when it is safe.
1400 If you have been using @value{GDBN} to control an attached process or
1401 device, you can release it with the @code{detach} command
1402 (@pxref{Attach, ,Debugging an Already-running Process}).
1404 @node Shell Commands
1405 @section Shell Commands
1407 If you need to execute occasional shell commands during your
1408 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1409 just use the @code{shell} command.
1414 @cindex shell escape
1415 @item shell @var{command-string}
1416 @itemx !@var{command-string}
1417 Invoke a standard shell to execute @var{command-string}.
1418 Note that no space is needed between @code{!} and @var{command-string}.
1419 If it exists, the environment variable @code{SHELL} determines which
1420 shell to run. Otherwise @value{GDBN} uses the default shell
1421 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1424 The utility @code{make} is often needed in development environments.
1425 You do not have to use the @code{shell} command for this purpose in
1430 @cindex calling make
1431 @item make @var{make-args}
1432 Execute the @code{make} program with the specified
1433 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1436 @node Logging Output
1437 @section Logging Output
1438 @cindex logging @value{GDBN} output
1439 @cindex save @value{GDBN} output to a file
1441 You may want to save the output of @value{GDBN} commands to a file.
1442 There are several commands to control @value{GDBN}'s logging.
1446 @item set logging on
1448 @item set logging off
1450 @cindex logging file name
1451 @item set logging file @var{file}
1452 Change the name of the current logfile. The default logfile is @file{gdb.txt}.
1453 @item set logging overwrite [on|off]
1454 By default, @value{GDBN} will append to the logfile. Set @code{overwrite} if
1455 you want @code{set logging on} to overwrite the logfile instead.
1456 @item set logging redirect [on|off]
1457 By default, @value{GDBN} output will go to both the terminal and the logfile.
1458 Set @code{redirect} if you want output to go only to the log file.
1459 @kindex show logging
1461 Show the current values of the logging settings.
1465 @chapter @value{GDBN} Commands
1467 You can abbreviate a @value{GDBN} command to the first few letters of the command
1468 name, if that abbreviation is unambiguous; and you can repeat certain
1469 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1470 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1471 show you the alternatives available, if there is more than one possibility).
1474 * Command Syntax:: How to give commands to @value{GDBN}
1475 * Completion:: Command completion
1476 * Help:: How to ask @value{GDBN} for help
1479 @node Command Syntax
1480 @section Command Syntax
1482 A @value{GDBN} command is a single line of input. There is no limit on
1483 how long it can be. It starts with a command name, which is followed by
1484 arguments whose meaning depends on the command name. For example, the
1485 command @code{step} accepts an argument which is the number of times to
1486 step, as in @samp{step 5}. You can also use the @code{step} command
1487 with no arguments. Some commands do not allow any arguments.
1489 @cindex abbreviation
1490 @value{GDBN} command names may always be truncated if that abbreviation is
1491 unambiguous. Other possible command abbreviations are listed in the
1492 documentation for individual commands. In some cases, even ambiguous
1493 abbreviations are allowed; for example, @code{s} is specially defined as
1494 equivalent to @code{step} even though there are other commands whose
1495 names start with @code{s}. You can test abbreviations by using them as
1496 arguments to the @code{help} command.
1498 @cindex repeating commands
1499 @kindex RET @r{(repeat last command)}
1500 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1501 repeat the previous command. Certain commands (for example, @code{run})
1502 will not repeat this way; these are commands whose unintentional
1503 repetition might cause trouble and which you are unlikely to want to
1504 repeat. User-defined commands can disable this feature; see
1505 @ref{Define, dont-repeat}.
1507 The @code{list} and @code{x} commands, when you repeat them with
1508 @key{RET}, construct new arguments rather than repeating
1509 exactly as typed. This permits easy scanning of source or memory.
1511 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1512 output, in a way similar to the common utility @code{more}
1513 (@pxref{Screen Size,,Screen Size}). Since it is easy to press one
1514 @key{RET} too many in this situation, @value{GDBN} disables command
1515 repetition after any command that generates this sort of display.
1517 @kindex # @r{(a comment)}
1519 Any text from a @kbd{#} to the end of the line is a comment; it does
1520 nothing. This is useful mainly in command files (@pxref{Command
1521 Files,,Command Files}).
1523 @cindex repeating command sequences
1524 @kindex Ctrl-o @r{(operate-and-get-next)}
1525 The @kbd{Ctrl-o} binding is useful for repeating a complex sequence of
1526 commands. This command accepts the current line, like @key{RET}, and
1527 then fetches the next line relative to the current line from the history
1531 @section Command Completion
1534 @cindex word completion
1535 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1536 only one possibility; it can also show you what the valid possibilities
1537 are for the next word in a command, at any time. This works for @value{GDBN}
1538 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1540 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1541 of a word. If there is only one possibility, @value{GDBN} fills in the
1542 word, and waits for you to finish the command (or press @key{RET} to
1543 enter it). For example, if you type
1545 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1546 @c complete accuracy in these examples; space introduced for clarity.
1547 @c If texinfo enhancements make it unnecessary, it would be nice to
1548 @c replace " @key" by "@key" in the following...
1550 (@value{GDBP}) info bre @key{TAB}
1554 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1555 the only @code{info} subcommand beginning with @samp{bre}:
1558 (@value{GDBP}) info breakpoints
1562 You can either press @key{RET} at this point, to run the @code{info
1563 breakpoints} command, or backspace and enter something else, if
1564 @samp{breakpoints} does not look like the command you expected. (If you
1565 were sure you wanted @code{info breakpoints} in the first place, you
1566 might as well just type @key{RET} immediately after @samp{info bre},
1567 to exploit command abbreviations rather than command completion).
1569 If there is more than one possibility for the next word when you press
1570 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1571 characters and try again, or just press @key{TAB} a second time;
1572 @value{GDBN} displays all the possible completions for that word. For
1573 example, you might want to set a breakpoint on a subroutine whose name
1574 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1575 just sounds the bell. Typing @key{TAB} again displays all the
1576 function names in your program that begin with those characters, for
1580 (@value{GDBP}) b make_ @key{TAB}
1581 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1582 make_a_section_from_file make_environ
1583 make_abs_section make_function_type
1584 make_blockvector make_pointer_type
1585 make_cleanup make_reference_type
1586 make_command make_symbol_completion_list
1587 (@value{GDBP}) b make_
1591 After displaying the available possibilities, @value{GDBN} copies your
1592 partial input (@samp{b make_} in the example) so you can finish the
1595 If you just want to see the list of alternatives in the first place, you
1596 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1597 means @kbd{@key{META} ?}. You can type this either by holding down a
1598 key designated as the @key{META} shift on your keyboard (if there is
1599 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1601 If the number of possible completions is large, @value{GDBN} will
1602 print as much of the list as it has collected, as well as a message
1603 indicating that the list may be truncated.
1606 (@value{GDBP}) b m@key{TAB}@key{TAB}
1608 <... the rest of the possible completions ...>
1609 *** List may be truncated, max-completions reached. ***
1614 This behavior can be controlled with the following commands:
1617 @kindex set max-completions
1618 @item set max-completions @var{limit}
1619 @itemx set max-completions unlimited
1620 Set the maximum number of completion candidates. @value{GDBN} will
1621 stop looking for more completions once it collects this many candidates.
1622 This is useful when completing on things like function names as collecting
1623 all the possible candidates can be time consuming.
1624 The default value is 200. A value of zero disables tab-completion.
1625 Note that setting either no limit or a very large limit can make
1627 @kindex show max-completions
1628 @item show max-completions
1629 Show the maximum number of candidates that @value{GDBN} will collect and show
1633 @cindex quotes in commands
1634 @cindex completion of quoted strings
1635 Sometimes the string you need, while logically a ``word'', may contain
1636 parentheses or other characters that @value{GDBN} normally excludes from
1637 its notion of a word. To permit word completion to work in this
1638 situation, you may enclose words in @code{'} (single quote marks) in
1639 @value{GDBN} commands.
1641 The most likely situation where you might need this is in typing the
1642 name of a C@t{++} function. This is because C@t{++} allows function
1643 overloading (multiple definitions of the same function, distinguished
1644 by argument type). For example, when you want to set a breakpoint you
1645 may need to distinguish whether you mean the version of @code{name}
1646 that takes an @code{int} parameter, @code{name(int)}, or the version
1647 that takes a @code{float} parameter, @code{name(float)}. To use the
1648 word-completion facilities in this situation, type a single quote
1649 @code{'} at the beginning of the function name. This alerts
1650 @value{GDBN} that it may need to consider more information than usual
1651 when you press @key{TAB} or @kbd{M-?} to request word completion:
1654 (@value{GDBP}) b 'bubble( @kbd{M-?}
1655 bubble(double,double) bubble(int,int)
1656 (@value{GDBP}) b 'bubble(
1659 In some cases, @value{GDBN} can tell that completing a name requires using
1660 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1661 completing as much as it can) if you do not type the quote in the first
1665 (@value{GDBP}) b bub @key{TAB}
1666 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1667 (@value{GDBP}) b 'bubble(
1671 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1672 you have not yet started typing the argument list when you ask for
1673 completion on an overloaded symbol.
1675 For more information about overloaded functions, see @ref{C Plus Plus
1676 Expressions, ,C@t{++} Expressions}. You can use the command @code{set
1677 overload-resolution off} to disable overload resolution;
1678 see @ref{Debugging C Plus Plus, ,@value{GDBN} Features for C@t{++}}.
1680 @cindex completion of structure field names
1681 @cindex structure field name completion
1682 @cindex completion of union field names
1683 @cindex union field name completion
1684 When completing in an expression which looks up a field in a
1685 structure, @value{GDBN} also tries@footnote{The completer can be
1686 confused by certain kinds of invalid expressions. Also, it only
1687 examines the static type of the expression, not the dynamic type.} to
1688 limit completions to the field names available in the type of the
1692 (@value{GDBP}) p gdb_stdout.@kbd{M-?}
1693 magic to_fputs to_rewind
1694 to_data to_isatty to_write
1695 to_delete to_put to_write_async_safe
1700 This is because the @code{gdb_stdout} is a variable of the type
1701 @code{struct ui_file} that is defined in @value{GDBN} sources as
1708 ui_file_flush_ftype *to_flush;
1709 ui_file_write_ftype *to_write;
1710 ui_file_write_async_safe_ftype *to_write_async_safe;
1711 ui_file_fputs_ftype *to_fputs;
1712 ui_file_read_ftype *to_read;
1713 ui_file_delete_ftype *to_delete;
1714 ui_file_isatty_ftype *to_isatty;
1715 ui_file_rewind_ftype *to_rewind;
1716 ui_file_put_ftype *to_put;
1723 @section Getting Help
1724 @cindex online documentation
1727 You can always ask @value{GDBN} itself for information on its commands,
1728 using the command @code{help}.
1731 @kindex h @r{(@code{help})}
1734 You can use @code{help} (abbreviated @code{h}) with no arguments to
1735 display a short list of named classes of commands:
1739 List of classes of commands:
1741 aliases -- Aliases of other commands
1742 breakpoints -- Making program stop at certain points
1743 data -- Examining data
1744 files -- Specifying and examining files
1745 internals -- Maintenance commands
1746 obscure -- Obscure features
1747 running -- Running the program
1748 stack -- Examining the stack
1749 status -- Status inquiries
1750 support -- Support facilities
1751 tracepoints -- Tracing of program execution without
1752 stopping the program
1753 user-defined -- User-defined commands
1755 Type "help" followed by a class name for a list of
1756 commands in that class.
1757 Type "help" followed by command name for full
1759 Command name abbreviations are allowed if unambiguous.
1762 @c the above line break eliminates huge line overfull...
1764 @item help @var{class}
1765 Using one of the general help classes as an argument, you can get a
1766 list of the individual commands in that class. For example, here is the
1767 help display for the class @code{status}:
1770 (@value{GDBP}) help status
1775 @c Line break in "show" line falsifies real output, but needed
1776 @c to fit in smallbook page size.
1777 info -- Generic command for showing things
1778 about the program being debugged
1779 show -- Generic command for showing things
1782 Type "help" followed by command name for full
1784 Command name abbreviations are allowed if unambiguous.
1788 @item help @var{command}
1789 With a command name as @code{help} argument, @value{GDBN} displays a
1790 short paragraph on how to use that command.
1793 @item apropos @var{args}
1794 The @code{apropos} command searches through all of the @value{GDBN}
1795 commands, and their documentation, for the regular expression specified in
1796 @var{args}. It prints out all matches found. For example:
1807 alias -- Define a new command that is an alias of an existing command
1808 aliases -- Aliases of other commands
1809 d -- Delete some breakpoints or auto-display expressions
1810 del -- Delete some breakpoints or auto-display expressions
1811 delete -- Delete some breakpoints or auto-display expressions
1816 @item complete @var{args}
1817 The @code{complete @var{args}} command lists all the possible completions
1818 for the beginning of a command. Use @var{args} to specify the beginning of the
1819 command you want completed. For example:
1825 @noindent results in:
1836 @noindent This is intended for use by @sc{gnu} Emacs.
1839 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1840 and @code{show} to inquire about the state of your program, or the state
1841 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1842 manual introduces each of them in the appropriate context. The listings
1843 under @code{info} and under @code{show} in the Command, Variable, and
1844 Function Index point to all the sub-commands. @xref{Command and Variable
1850 @kindex i @r{(@code{info})}
1852 This command (abbreviated @code{i}) is for describing the state of your
1853 program. For example, you can show the arguments passed to a function
1854 with @code{info args}, list the registers currently in use with @code{info
1855 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1856 You can get a complete list of the @code{info} sub-commands with
1857 @w{@code{help info}}.
1861 You can assign the result of an expression to an environment variable with
1862 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1863 @code{set prompt $}.
1867 In contrast to @code{info}, @code{show} is for describing the state of
1868 @value{GDBN} itself.
1869 You can change most of the things you can @code{show}, by using the
1870 related command @code{set}; for example, you can control what number
1871 system is used for displays with @code{set radix}, or simply inquire
1872 which is currently in use with @code{show radix}.
1875 To display all the settable parameters and their current
1876 values, you can use @code{show} with no arguments; you may also use
1877 @code{info set}. Both commands produce the same display.
1878 @c FIXME: "info set" violates the rule that "info" is for state of
1879 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1880 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1884 Here are several miscellaneous @code{show} subcommands, all of which are
1885 exceptional in lacking corresponding @code{set} commands:
1888 @kindex show version
1889 @cindex @value{GDBN} version number
1891 Show what version of @value{GDBN} is running. You should include this
1892 information in @value{GDBN} bug-reports. If multiple versions of
1893 @value{GDBN} are in use at your site, you may need to determine which
1894 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1895 commands are introduced, and old ones may wither away. Also, many
1896 system vendors ship variant versions of @value{GDBN}, and there are
1897 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1898 The version number is the same as the one announced when you start
1901 @kindex show copying
1902 @kindex info copying
1903 @cindex display @value{GDBN} copyright
1906 Display information about permission for copying @value{GDBN}.
1908 @kindex show warranty
1909 @kindex info warranty
1911 @itemx info warranty
1912 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1913 if your version of @value{GDBN} comes with one.
1915 @kindex show configuration
1916 @item show configuration
1917 Display detailed information about the way @value{GDBN} was configured
1918 when it was built. This displays the optional arguments passed to the
1919 @file{configure} script and also configuration parameters detected
1920 automatically by @command{configure}. When reporting a @value{GDBN}
1921 bug (@pxref{GDB Bugs}), it is important to include this information in
1927 @chapter Running Programs Under @value{GDBN}
1929 When you run a program under @value{GDBN}, you must first generate
1930 debugging information when you compile it.
1932 You may start @value{GDBN} with its arguments, if any, in an environment
1933 of your choice. If you are doing native debugging, you may redirect
1934 your program's input and output, debug an already running process, or
1935 kill a child process.
1938 * Compilation:: Compiling for debugging
1939 * Starting:: Starting your program
1940 * Arguments:: Your program's arguments
1941 * Environment:: Your program's environment
1943 * Working Directory:: Your program's working directory
1944 * Input/Output:: Your program's input and output
1945 * Attach:: Debugging an already-running process
1946 * Kill Process:: Killing the child process
1948 * Inferiors and Programs:: Debugging multiple inferiors and programs
1949 * Threads:: Debugging programs with multiple threads
1950 * Forks:: Debugging forks
1951 * Checkpoint/Restart:: Setting a @emph{bookmark} to return to later
1955 @section Compiling for Debugging
1957 In order to debug a program effectively, you need to generate
1958 debugging information when you compile it. This debugging information
1959 is stored in the object file; it describes the data type of each
1960 variable or function and the correspondence between source line numbers
1961 and addresses in the executable code.
1963 To request debugging information, specify the @samp{-g} option when you run
1966 Programs that are to be shipped to your customers are compiled with
1967 optimizations, using the @samp{-O} compiler option. However, some
1968 compilers are unable to handle the @samp{-g} and @samp{-O} options
1969 together. Using those compilers, you cannot generate optimized
1970 executables containing debugging information.
1972 @value{NGCC}, the @sc{gnu} C/C@t{++} compiler, supports @samp{-g} with or
1973 without @samp{-O}, making it possible to debug optimized code. We
1974 recommend that you @emph{always} use @samp{-g} whenever you compile a
1975 program. You may think your program is correct, but there is no sense
1976 in pushing your luck. For more information, see @ref{Optimized Code}.
1978 Older versions of the @sc{gnu} C compiler permitted a variant option
1979 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1980 format; if your @sc{gnu} C compiler has this option, do not use it.
1982 @value{GDBN} knows about preprocessor macros and can show you their
1983 expansion (@pxref{Macros}). Most compilers do not include information
1984 about preprocessor macros in the debugging information if you specify
1985 the @option{-g} flag alone. Version 3.1 and later of @value{NGCC},
1986 the @sc{gnu} C compiler, provides macro information if you are using
1987 the DWARF debugging format, and specify the option @option{-g3}.
1989 @xref{Debugging Options,,Options for Debugging Your Program or GCC,
1990 gcc.info, Using the @sc{gnu} Compiler Collection (GCC)}, for more
1991 information on @value{NGCC} options affecting debug information.
1993 You will have the best debugging experience if you use the latest
1994 version of the DWARF debugging format that your compiler supports.
1995 DWARF is currently the most expressive and best supported debugging
1996 format in @value{GDBN}.
2000 @section Starting your Program
2006 @kindex r @r{(@code{run})}
2009 Use the @code{run} command to start your program under @value{GDBN}.
2010 You must first specify the program name with an argument to
2011 @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
2012 @value{GDBN}}), or by using the @code{file} or @code{exec-file}
2013 command (@pxref{Files, ,Commands to Specify Files}).
2017 If you are running your program in an execution environment that
2018 supports processes, @code{run} creates an inferior process and makes
2019 that process run your program. In some environments without processes,
2020 @code{run} jumps to the start of your program. Other targets,
2021 like @samp{remote}, are always running. If you get an error
2022 message like this one:
2025 The "remote" target does not support "run".
2026 Try "help target" or "continue".
2030 then use @code{continue} to run your program. You may need @code{load}
2031 first (@pxref{load}).
2033 The execution of a program is affected by certain information it
2034 receives from its superior. @value{GDBN} provides ways to specify this
2035 information, which you must do @emph{before} starting your program. (You
2036 can change it after starting your program, but such changes only affect
2037 your program the next time you start it.) This information may be
2038 divided into four categories:
2041 @item The @emph{arguments.}
2042 Specify the arguments to give your program as the arguments of the
2043 @code{run} command. If a shell is available on your target, the shell
2044 is used to pass the arguments, so that you may use normal conventions
2045 (such as wildcard expansion or variable substitution) in describing
2047 In Unix systems, you can control which shell is used with the
2048 @code{SHELL} environment variable. If you do not define @code{SHELL},
2049 @value{GDBN} uses the default shell (@file{/bin/sh}). You can disable
2050 use of any shell with the @code{set startup-with-shell} command (see
2053 @item The @emph{environment.}
2054 Your program normally inherits its environment from @value{GDBN}, but you can
2055 use the @value{GDBN} commands @code{set environment} and @code{unset
2056 environment} to change parts of the environment that affect
2057 your program. @xref{Environment, ,Your Program's Environment}.
2059 @item The @emph{working directory.}
2060 You can set your program's working directory with the command
2061 @kbd{set cwd}. If you do not set any working directory with this
2062 command, your program will inherit @value{GDBN}'s working directory if
2063 native debugging, or the remote server's working directory if remote
2064 debugging. @xref{Working Directory, ,Your Program's Working
2067 @item The @emph{standard input and output.}
2068 Your program normally uses the same device for standard input and
2069 standard output as @value{GDBN} is using. You can redirect input and output
2070 in the @code{run} command line, or you can use the @code{tty} command to
2071 set a different device for your program.
2072 @xref{Input/Output, ,Your Program's Input and Output}.
2075 @emph{Warning:} While input and output redirection work, you cannot use
2076 pipes to pass the output of the program you are debugging to another
2077 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
2081 When you issue the @code{run} command, your program begins to execute
2082 immediately. @xref{Stopping, ,Stopping and Continuing}, for discussion
2083 of how to arrange for your program to stop. Once your program has
2084 stopped, you may call functions in your program, using the @code{print}
2085 or @code{call} commands. @xref{Data, ,Examining Data}.
2087 If the modification time of your symbol file has changed since the last
2088 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
2089 table, and reads it again. When it does this, @value{GDBN} tries to retain
2090 your current breakpoints.
2095 @cindex run to main procedure
2096 The name of the main procedure can vary from language to language.
2097 With C or C@t{++}, the main procedure name is always @code{main}, but
2098 other languages such as Ada do not require a specific name for their
2099 main procedure. The debugger provides a convenient way to start the
2100 execution of the program and to stop at the beginning of the main
2101 procedure, depending on the language used.
2103 The @samp{start} command does the equivalent of setting a temporary
2104 breakpoint at the beginning of the main procedure and then invoking
2105 the @samp{run} command.
2107 @cindex elaboration phase
2108 Some programs contain an @dfn{elaboration} phase where some startup code is
2109 executed before the main procedure is called. This depends on the
2110 languages used to write your program. In C@t{++}, for instance,
2111 constructors for static and global objects are executed before
2112 @code{main} is called. It is therefore possible that the debugger stops
2113 before reaching the main procedure. However, the temporary breakpoint
2114 will remain to halt execution.
2116 Specify the arguments to give to your program as arguments to the
2117 @samp{start} command. These arguments will be given verbatim to the
2118 underlying @samp{run} command. Note that the same arguments will be
2119 reused if no argument is provided during subsequent calls to
2120 @samp{start} or @samp{run}.
2122 It is sometimes necessary to debug the program during elaboration. In
2123 these cases, using the @code{start} command would stop the execution
2124 of your program too late, as the program would have already completed
2125 the elaboration phase. Under these circumstances, either insert
2126 breakpoints in your elaboration code before running your program or
2127 use the @code{starti} command.
2131 @cindex run to first instruction
2132 The @samp{starti} command does the equivalent of setting a temporary
2133 breakpoint at the first instruction of a program's execution and then
2134 invoking the @samp{run} command. For programs containing an
2135 elaboration phase, the @code{starti} command will stop execution at
2136 the start of the elaboration phase.
2138 @anchor{set exec-wrapper}
2139 @kindex set exec-wrapper
2140 @item set exec-wrapper @var{wrapper}
2141 @itemx show exec-wrapper
2142 @itemx unset exec-wrapper
2143 When @samp{exec-wrapper} is set, the specified wrapper is used to
2144 launch programs for debugging. @value{GDBN} starts your program
2145 with a shell command of the form @kbd{exec @var{wrapper}
2146 @var{program}}. Quoting is added to @var{program} and its
2147 arguments, but not to @var{wrapper}, so you should add quotes if
2148 appropriate for your shell. The wrapper runs until it executes
2149 your program, and then @value{GDBN} takes control.
2151 You can use any program that eventually calls @code{execve} with
2152 its arguments as a wrapper. Several standard Unix utilities do
2153 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
2154 with @code{exec "$@@"} will also work.
2156 For example, you can use @code{env} to pass an environment variable to
2157 the debugged program, without setting the variable in your shell's
2161 (@value{GDBP}) set exec-wrapper env 'LD_PRELOAD=libtest.so'
2165 This command is available when debugging locally on most targets, excluding
2166 @sc{djgpp}, Cygwin, MS Windows, and QNX Neutrino.
2168 @kindex set startup-with-shell
2169 @anchor{set startup-with-shell}
2170 @item set startup-with-shell
2171 @itemx set startup-with-shell on
2172 @itemx set startup-with-shell off
2173 @itemx show startup-with-shell
2174 On Unix systems, by default, if a shell is available on your target,
2175 @value{GDBN}) uses it to start your program. Arguments of the
2176 @code{run} command are passed to the shell, which does variable
2177 substitution, expands wildcard characters and performs redirection of
2178 I/O. In some circumstances, it may be useful to disable such use of a
2179 shell, for example, when debugging the shell itself or diagnosing
2180 startup failures such as:
2184 Starting program: ./a.out
2185 During startup program terminated with signal SIGSEGV, Segmentation fault.
2189 which indicates the shell or the wrapper specified with
2190 @samp{exec-wrapper} crashed, not your program. Most often, this is
2191 caused by something odd in your shell's non-interactive mode
2192 initialization file---such as @file{.cshrc} for C-shell,
2193 $@file{.zshenv} for the Z shell, or the file specified in the
2194 @samp{BASH_ENV} environment variable for BASH.
2196 @anchor{set auto-connect-native-target}
2197 @kindex set auto-connect-native-target
2198 @item set auto-connect-native-target
2199 @itemx set auto-connect-native-target on
2200 @itemx set auto-connect-native-target off
2201 @itemx show auto-connect-native-target
2203 By default, if not connected to any target yet (e.g., with
2204 @code{target remote}), the @code{run} command starts your program as a
2205 native process under @value{GDBN}, on your local machine. If you're
2206 sure you don't want to debug programs on your local machine, you can
2207 tell @value{GDBN} to not connect to the native target automatically
2208 with the @code{set auto-connect-native-target off} command.
2210 If @code{on}, which is the default, and if @value{GDBN} is not
2211 connected to a target already, the @code{run} command automaticaly
2212 connects to the native target, if one is available.
2214 If @code{off}, and if @value{GDBN} is not connected to a target
2215 already, the @code{run} command fails with an error:
2219 Don't know how to run. Try "help target".
2222 If @value{GDBN} is already connected to a target, @value{GDBN} always
2223 uses it with the @code{run} command.
2225 In any case, you can explicitly connect to the native target with the
2226 @code{target native} command. For example,
2229 (@value{GDBP}) set auto-connect-native-target off
2231 Don't know how to run. Try "help target".
2232 (@value{GDBP}) target native
2234 Starting program: ./a.out
2235 [Inferior 1 (process 10421) exited normally]
2238 In case you connected explicitly to the @code{native} target,
2239 @value{GDBN} remains connected even if all inferiors exit, ready for
2240 the next @code{run} command. Use the @code{disconnect} command to
2243 Examples of other commands that likewise respect the
2244 @code{auto-connect-native-target} setting: @code{attach}, @code{info
2245 proc}, @code{info os}.
2247 @kindex set disable-randomization
2248 @item set disable-randomization
2249 @itemx set disable-randomization on
2250 This option (enabled by default in @value{GDBN}) will turn off the native
2251 randomization of the virtual address space of the started program. This option
2252 is useful for multiple debugging sessions to make the execution better
2253 reproducible and memory addresses reusable across debugging sessions.
2255 This feature is implemented only on certain targets, including @sc{gnu}/Linux.
2256 On @sc{gnu}/Linux you can get the same behavior using
2259 (@value{GDBP}) set exec-wrapper setarch `uname -m` -R
2262 @item set disable-randomization off
2263 Leave the behavior of the started executable unchanged. Some bugs rear their
2264 ugly heads only when the program is loaded at certain addresses. If your bug
2265 disappears when you run the program under @value{GDBN}, that might be because
2266 @value{GDBN} by default disables the address randomization on platforms, such
2267 as @sc{gnu}/Linux, which do that for stand-alone programs. Use @kbd{set
2268 disable-randomization off} to try to reproduce such elusive bugs.
2270 On targets where it is available, virtual address space randomization
2271 protects the programs against certain kinds of security attacks. In these
2272 cases the attacker needs to know the exact location of a concrete executable
2273 code. Randomizing its location makes it impossible to inject jumps misusing
2274 a code at its expected addresses.
2276 Prelinking shared libraries provides a startup performance advantage but it
2277 makes addresses in these libraries predictable for privileged processes by
2278 having just unprivileged access at the target system. Reading the shared
2279 library binary gives enough information for assembling the malicious code
2280 misusing it. Still even a prelinked shared library can get loaded at a new
2281 random address just requiring the regular relocation process during the
2282 startup. Shared libraries not already prelinked are always loaded at
2283 a randomly chosen address.
2285 Position independent executables (PIE) contain position independent code
2286 similar to the shared libraries and therefore such executables get loaded at
2287 a randomly chosen address upon startup. PIE executables always load even
2288 already prelinked shared libraries at a random address. You can build such
2289 executable using @command{gcc -fPIE -pie}.
2291 Heap (malloc storage), stack and custom mmap areas are always placed randomly
2292 (as long as the randomization is enabled).
2294 @item show disable-randomization
2295 Show the current setting of the explicit disable of the native randomization of
2296 the virtual address space of the started program.
2301 @section Your Program's Arguments
2303 @cindex arguments (to your program)
2304 The arguments to your program can be specified by the arguments of the
2306 They are passed to a shell, which expands wildcard characters and
2307 performs redirection of I/O, and thence to your program. Your
2308 @code{SHELL} environment variable (if it exists) specifies what shell
2309 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
2310 the default shell (@file{/bin/sh} on Unix).
2312 On non-Unix systems, the program is usually invoked directly by
2313 @value{GDBN}, which emulates I/O redirection via the appropriate system
2314 calls, and the wildcard characters are expanded by the startup code of
2315 the program, not by the shell.
2317 @code{run} with no arguments uses the same arguments used by the previous
2318 @code{run}, or those set by the @code{set args} command.
2323 Specify the arguments to be used the next time your program is run. If
2324 @code{set args} has no arguments, @code{run} executes your program
2325 with no arguments. Once you have run your program with arguments,
2326 using @code{set args} before the next @code{run} is the only way to run
2327 it again without arguments.
2331 Show the arguments to give your program when it is started.
2335 @section Your Program's Environment
2337 @cindex environment (of your program)
2338 The @dfn{environment} consists of a set of environment variables and
2339 their values. Environment variables conventionally record such things as
2340 your user name, your home directory, your terminal type, and your search
2341 path for programs to run. Usually you set up environment variables with
2342 the shell and they are inherited by all the other programs you run. When
2343 debugging, it can be useful to try running your program with a modified
2344 environment without having to start @value{GDBN} over again.
2348 @item path @var{directory}
2349 Add @var{directory} to the front of the @code{PATH} environment variable
2350 (the search path for executables) that will be passed to your program.
2351 The value of @code{PATH} used by @value{GDBN} does not change.
2352 You may specify several directory names, separated by whitespace or by a
2353 system-dependent separator character (@samp{:} on Unix, @samp{;} on
2354 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
2355 is moved to the front, so it is searched sooner.
2357 You can use the string @samp{$cwd} to refer to whatever is the current
2358 working directory at the time @value{GDBN} searches the path. If you
2359 use @samp{.} instead, it refers to the directory where you executed the
2360 @code{path} command. @value{GDBN} replaces @samp{.} in the
2361 @var{directory} argument (with the current path) before adding
2362 @var{directory} to the search path.
2363 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
2364 @c document that, since repeating it would be a no-op.
2368 Display the list of search paths for executables (the @code{PATH}
2369 environment variable).
2371 @kindex show environment
2372 @item show environment @r{[}@var{varname}@r{]}
2373 Print the value of environment variable @var{varname} to be given to
2374 your program when it starts. If you do not supply @var{varname},
2375 print the names and values of all environment variables to be given to
2376 your program. You can abbreviate @code{environment} as @code{env}.
2378 @kindex set environment
2379 @anchor{set environment}
2380 @item set environment @var{varname} @r{[}=@var{value}@r{]}
2381 Set environment variable @var{varname} to @var{value}. The value
2382 changes for your program (and the shell @value{GDBN} uses to launch
2383 it), not for @value{GDBN} itself. The @var{value} may be any string; the
2384 values of environment variables are just strings, and any
2385 interpretation is supplied by your program itself. The @var{value}
2386 parameter is optional; if it is eliminated, the variable is set to a
2388 @c "any string" here does not include leading, trailing
2389 @c blanks. Gnu asks: does anyone care?
2391 For example, this command:
2398 tells the debugged program, when subsequently run, that its user is named
2399 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
2400 are not actually required.)
2402 Note that on Unix systems, @value{GDBN} runs your program via a shell,
2403 which also inherits the environment set with @code{set environment}.
2404 If necessary, you can avoid that by using the @samp{env} program as a
2405 wrapper instead of using @code{set environment}. @xref{set
2406 exec-wrapper}, for an example doing just that.
2408 Environment variables that are set by the user are also transmitted to
2409 @command{gdbserver} to be used when starting the remote inferior.
2410 @pxref{QEnvironmentHexEncoded}.
2412 @kindex unset environment
2413 @anchor{unset environment}
2414 @item unset environment @var{varname}
2415 Remove variable @var{varname} from the environment to be passed to your
2416 program. This is different from @samp{set env @var{varname} =};
2417 @code{unset environment} removes the variable from the environment,
2418 rather than assigning it an empty value.
2420 Environment variables that are unset by the user are also unset on
2421 @command{gdbserver} when starting the remote inferior.
2422 @pxref{QEnvironmentUnset}.
2425 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
2426 the shell indicated by your @code{SHELL} environment variable if it
2427 exists (or @code{/bin/sh} if not). If your @code{SHELL} variable
2428 names a shell that runs an initialization file when started
2429 non-interactively---such as @file{.cshrc} for C-shell, $@file{.zshenv}
2430 for the Z shell, or the file specified in the @samp{BASH_ENV}
2431 environment variable for BASH---any variables you set in that file
2432 affect your program. You may wish to move setting of environment
2433 variables to files that are only run when you sign on, such as
2434 @file{.login} or @file{.profile}.
2436 @node Working Directory
2437 @section Your Program's Working Directory
2439 @cindex working directory (of your program)
2440 Each time you start your program with @code{run}, the inferior will be
2441 initialized with the current working directory specified by the
2442 @kbd{set cwd} command. If no directory has been specified by this
2443 command, then the inferior will inherit @value{GDBN}'s current working
2444 directory as its working directory if native debugging, or it will
2445 inherit the remote server's current working directory if remote
2450 @cindex change inferior's working directory
2451 @anchor{set cwd command}
2452 @item set cwd @r{[}@var{directory}@r{]}
2453 Set the inferior's working directory to @var{directory}, which will be
2454 @code{glob}-expanded in order to resolve tildes (@file{~}). If no
2455 argument has been specified, the command clears the setting and resets
2456 it to an empty state. This setting has no effect on @value{GDBN}'s
2457 working directory, and it only takes effect the next time you start
2458 the inferior. The @file{~} in @var{directory} is a short for the
2459 @dfn{home directory}, usually pointed to by the @env{HOME} environment
2460 variable. On MS-Windows, if @env{HOME} is not defined, @value{GDBN}
2461 uses the concatenation of @env{HOMEDRIVE} and @env{HOMEPATH} as
2464 You can also change @value{GDBN}'s current working directory by using
2465 the @code{cd} command.
2469 @cindex show inferior's working directory
2471 Show the inferior's working directory. If no directory has been
2472 specified by @kbd{set cwd}, then the default inferior's working
2473 directory is the same as @value{GDBN}'s working directory.
2476 @cindex change @value{GDBN}'s working directory
2478 @item cd @r{[}@var{directory}@r{]}
2479 Set the @value{GDBN} working directory to @var{directory}. If not
2480 given, @var{directory} uses @file{'~'}.
2482 The @value{GDBN} working directory serves as a default for the
2483 commands that specify files for @value{GDBN} to operate on.
2484 @xref{Files, ,Commands to Specify Files}.
2485 @xref{set cwd command}
2489 Print the @value{GDBN} working directory.
2492 It is generally impossible to find the current working directory of
2493 the process being debugged (since a program can change its directory
2494 during its run). If you work on a system where @value{GDBN} is
2495 configured with the @file{/proc} support, you can use the @code{info
2496 proc} command (@pxref{SVR4 Process Information}) to find out the
2497 current working directory of the debuggee.
2500 @section Your Program's Input and Output
2505 By default, the program you run under @value{GDBN} does input and output to
2506 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
2507 to its own terminal modes to interact with you, but it records the terminal
2508 modes your program was using and switches back to them when you continue
2509 running your program.
2512 @kindex info terminal
2514 Displays information recorded by @value{GDBN} about the terminal modes your
2518 You can redirect your program's input and/or output using shell
2519 redirection with the @code{run} command. For example,
2526 starts your program, diverting its output to the file @file{outfile}.
2529 @cindex controlling terminal
2530 Another way to specify where your program should do input and output is
2531 with the @code{tty} command. This command accepts a file name as
2532 argument, and causes this file to be the default for future @code{run}
2533 commands. It also resets the controlling terminal for the child
2534 process, for future @code{run} commands. For example,
2541 directs that processes started with subsequent @code{run} commands
2542 default to do input and output on the terminal @file{/dev/ttyb} and have
2543 that as their controlling terminal.
2545 An explicit redirection in @code{run} overrides the @code{tty} command's
2546 effect on the input/output device, but not its effect on the controlling
2549 When you use the @code{tty} command or redirect input in the @code{run}
2550 command, only the input @emph{for your program} is affected. The input
2551 for @value{GDBN} still comes from your terminal. @code{tty} is an alias
2552 for @code{set inferior-tty}.
2554 @cindex inferior tty
2555 @cindex set inferior controlling terminal
2556 You can use the @code{show inferior-tty} command to tell @value{GDBN} to
2557 display the name of the terminal that will be used for future runs of your
2561 @item set inferior-tty [ @var{tty} ]
2562 @kindex set inferior-tty
2563 Set the tty for the program being debugged to @var{tty}. Omitting @var{tty}
2564 restores the default behavior, which is to use the same terminal as
2567 @item show inferior-tty
2568 @kindex show inferior-tty
2569 Show the current tty for the program being debugged.
2573 @section Debugging an Already-running Process
2578 @item attach @var{process-id}
2579 This command attaches to a running process---one that was started
2580 outside @value{GDBN}. (@code{info files} shows your active
2581 targets.) The command takes as argument a process ID. The usual way to
2582 find out the @var{process-id} of a Unix process is with the @code{ps} utility,
2583 or with the @samp{jobs -l} shell command.
2585 @code{attach} does not repeat if you press @key{RET} a second time after
2586 executing the command.
2589 To use @code{attach}, your program must be running in an environment
2590 which supports processes; for example, @code{attach} does not work for
2591 programs on bare-board targets that lack an operating system. You must
2592 also have permission to send the process a signal.
2594 When you use @code{attach}, the debugger finds the program running in
2595 the process first by looking in the current working directory, then (if
2596 the program is not found) by using the source file search path
2597 (@pxref{Source Path, ,Specifying Source Directories}). You can also use
2598 the @code{file} command to load the program. @xref{Files, ,Commands to
2601 The first thing @value{GDBN} does after arranging to debug the specified
2602 process is to stop it. You can examine and modify an attached process
2603 with all the @value{GDBN} commands that are ordinarily available when
2604 you start processes with @code{run}. You can insert breakpoints; you
2605 can step and continue; you can modify storage. If you would rather the
2606 process continue running, you may use the @code{continue} command after
2607 attaching @value{GDBN} to the process.
2612 When you have finished debugging the attached process, you can use the
2613 @code{detach} command to release it from @value{GDBN} control. Detaching
2614 the process continues its execution. After the @code{detach} command,
2615 that process and @value{GDBN} become completely independent once more, and you
2616 are ready to @code{attach} another process or start one with @code{run}.
2617 @code{detach} does not repeat if you press @key{RET} again after
2618 executing the command.
2621 If you exit @value{GDBN} while you have an attached process, you detach
2622 that process. If you use the @code{run} command, you kill that process.
2623 By default, @value{GDBN} asks for confirmation if you try to do either of these
2624 things; you can control whether or not you need to confirm by using the
2625 @code{set confirm} command (@pxref{Messages/Warnings, ,Optional Warnings and
2629 @section Killing the Child Process
2634 Kill the child process in which your program is running under @value{GDBN}.
2637 This command is useful if you wish to debug a core dump instead of a
2638 running process. @value{GDBN} ignores any core dump file while your program
2641 On some operating systems, a program cannot be executed outside @value{GDBN}
2642 while you have breakpoints set on it inside @value{GDBN}. You can use the
2643 @code{kill} command in this situation to permit running your program
2644 outside the debugger.
2646 The @code{kill} command is also useful if you wish to recompile and
2647 relink your program, since on many systems it is impossible to modify an
2648 executable file while it is running in a process. In this case, when you
2649 next type @code{run}, @value{GDBN} notices that the file has changed, and
2650 reads the symbol table again (while trying to preserve your current
2651 breakpoint settings).
2653 @node Inferiors and Programs
2654 @section Debugging Multiple Inferiors and Programs
2656 @value{GDBN} lets you run and debug multiple programs in a single
2657 session. In addition, @value{GDBN} on some systems may let you run
2658 several programs simultaneously (otherwise you have to exit from one
2659 before starting another). In the most general case, you can have
2660 multiple threads of execution in each of multiple processes, launched
2661 from multiple executables.
2664 @value{GDBN} represents the state of each program execution with an
2665 object called an @dfn{inferior}. An inferior typically corresponds to
2666 a process, but is more general and applies also to targets that do not
2667 have processes. Inferiors may be created before a process runs, and
2668 may be retained after a process exits. Inferiors have unique
2669 identifiers that are different from process ids. Usually each
2670 inferior will also have its own distinct address space, although some
2671 embedded targets may have several inferiors running in different parts
2672 of a single address space. Each inferior may in turn have multiple
2673 threads running in it.
2675 To find out what inferiors exist at any moment, use @w{@code{info
2679 @kindex info inferiors
2680 @item info inferiors
2681 Print a list of all inferiors currently being managed by @value{GDBN}.
2683 @value{GDBN} displays for each inferior (in this order):
2687 the inferior number assigned by @value{GDBN}
2690 the target system's inferior identifier
2693 the name of the executable the inferior is running.
2698 An asterisk @samp{*} preceding the @value{GDBN} inferior number
2699 indicates the current inferior.
2703 @c end table here to get a little more width for example
2706 (@value{GDBP}) info inferiors
2707 Num Description Executable
2708 2 process 2307 hello
2709 * 1 process 3401 goodbye
2712 To switch focus between inferiors, use the @code{inferior} command:
2715 @kindex inferior @var{infno}
2716 @item inferior @var{infno}
2717 Make inferior number @var{infno} the current inferior. The argument
2718 @var{infno} is the inferior number assigned by @value{GDBN}, as shown
2719 in the first field of the @samp{info inferiors} display.
2722 @vindex $_inferior@r{, convenience variable}
2723 The debugger convenience variable @samp{$_inferior} contains the
2724 number of the current inferior. You may find this useful in writing
2725 breakpoint conditional expressions, command scripts, and so forth.
2726 @xref{Convenience Vars,, Convenience Variables}, for general
2727 information on convenience variables.
2729 You can get multiple executables into a debugging session via the
2730 @code{add-inferior} and @w{@code{clone-inferior}} commands. On some
2731 systems @value{GDBN} can add inferiors to the debug session
2732 automatically by following calls to @code{fork} and @code{exec}. To
2733 remove inferiors from the debugging session use the
2734 @w{@code{remove-inferiors}} command.
2737 @kindex add-inferior
2738 @item add-inferior [ -copies @var{n} ] [ -exec @var{executable} ]
2739 Adds @var{n} inferiors to be run using @var{executable} as the
2740 executable; @var{n} defaults to 1. If no executable is specified,
2741 the inferiors begins empty, with no program. You can still assign or
2742 change the program assigned to the inferior at any time by using the
2743 @code{file} command with the executable name as its argument.
2745 @kindex clone-inferior
2746 @item clone-inferior [ -copies @var{n} ] [ @var{infno} ]
2747 Adds @var{n} inferiors ready to execute the same program as inferior
2748 @var{infno}; @var{n} defaults to 1, and @var{infno} defaults to the
2749 number of the current inferior. This is a convenient command when you
2750 want to run another instance of the inferior you are debugging.
2753 (@value{GDBP}) info inferiors
2754 Num Description Executable
2755 * 1 process 29964 helloworld
2756 (@value{GDBP}) clone-inferior
2759 (@value{GDBP}) info inferiors
2760 Num Description Executable
2762 * 1 process 29964 helloworld
2765 You can now simply switch focus to inferior 2 and run it.
2767 @kindex remove-inferiors
2768 @item remove-inferiors @var{infno}@dots{}
2769 Removes the inferior or inferiors @var{infno}@dots{}. It is not
2770 possible to remove an inferior that is running with this command. For
2771 those, use the @code{kill} or @code{detach} command first.
2775 To quit debugging one of the running inferiors that is not the current
2776 inferior, you can either detach from it by using the @w{@code{detach
2777 inferior}} command (allowing it to run independently), or kill it
2778 using the @w{@code{kill inferiors}} command:
2781 @kindex detach inferiors @var{infno}@dots{}
2782 @item detach inferior @var{infno}@dots{}
2783 Detach from the inferior or inferiors identified by @value{GDBN}
2784 inferior number(s) @var{infno}@dots{}. Note that the inferior's entry
2785 still stays on the list of inferiors shown by @code{info inferiors},
2786 but its Description will show @samp{<null>}.
2788 @kindex kill inferiors @var{infno}@dots{}
2789 @item kill inferiors @var{infno}@dots{}
2790 Kill the inferior or inferiors identified by @value{GDBN} inferior
2791 number(s) @var{infno}@dots{}. Note that the inferior's entry still
2792 stays on the list of inferiors shown by @code{info inferiors}, but its
2793 Description will show @samp{<null>}.
2796 After the successful completion of a command such as @code{detach},
2797 @code{detach inferiors}, @code{kill} or @code{kill inferiors}, or after
2798 a normal process exit, the inferior is still valid and listed with
2799 @code{info inferiors}, ready to be restarted.
2802 To be notified when inferiors are started or exit under @value{GDBN}'s
2803 control use @w{@code{set print inferior-events}}:
2806 @kindex set print inferior-events
2807 @cindex print messages on inferior start and exit
2808 @item set print inferior-events
2809 @itemx set print inferior-events on
2810 @itemx set print inferior-events off
2811 The @code{set print inferior-events} command allows you to enable or
2812 disable printing of messages when @value{GDBN} notices that new
2813 inferiors have started or that inferiors have exited or have been
2814 detached. By default, these messages will not be printed.
2816 @kindex show print inferior-events
2817 @item show print inferior-events
2818 Show whether messages will be printed when @value{GDBN} detects that
2819 inferiors have started, exited or have been detached.
2822 Many commands will work the same with multiple programs as with a
2823 single program: e.g., @code{print myglobal} will simply display the
2824 value of @code{myglobal} in the current inferior.
2827 Occasionaly, when debugging @value{GDBN} itself, it may be useful to
2828 get more info about the relationship of inferiors, programs, address
2829 spaces in a debug session. You can do that with the @w{@code{maint
2830 info program-spaces}} command.
2833 @kindex maint info program-spaces
2834 @item maint info program-spaces
2835 Print a list of all program spaces currently being managed by
2838 @value{GDBN} displays for each program space (in this order):
2842 the program space number assigned by @value{GDBN}
2845 the name of the executable loaded into the program space, with e.g.,
2846 the @code{file} command.
2851 An asterisk @samp{*} preceding the @value{GDBN} program space number
2852 indicates the current program space.
2854 In addition, below each program space line, @value{GDBN} prints extra
2855 information that isn't suitable to display in tabular form. For
2856 example, the list of inferiors bound to the program space.
2859 (@value{GDBP}) maint info program-spaces
2863 Bound inferiors: ID 1 (process 21561)
2866 Here we can see that no inferior is running the program @code{hello},
2867 while @code{process 21561} is running the program @code{goodbye}. On
2868 some targets, it is possible that multiple inferiors are bound to the
2869 same program space. The most common example is that of debugging both
2870 the parent and child processes of a @code{vfork} call. For example,
2873 (@value{GDBP}) maint info program-spaces
2876 Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)
2879 Here, both inferior 2 and inferior 1 are running in the same program
2880 space as a result of inferior 1 having executed a @code{vfork} call.
2884 @section Debugging Programs with Multiple Threads
2886 @cindex threads of execution
2887 @cindex multiple threads
2888 @cindex switching threads
2889 In some operating systems, such as GNU/Linux and Solaris, a single program
2890 may have more than one @dfn{thread} of execution. The precise semantics
2891 of threads differ from one operating system to another, but in general
2892 the threads of a single program are akin to multiple processes---except
2893 that they share one address space (that is, they can all examine and
2894 modify the same variables). On the other hand, each thread has its own
2895 registers and execution stack, and perhaps private memory.
2897 @value{GDBN} provides these facilities for debugging multi-thread
2901 @item automatic notification of new threads
2902 @item @samp{thread @var{thread-id}}, a command to switch among threads
2903 @item @samp{info threads}, a command to inquire about existing threads
2904 @item @samp{thread apply [@var{thread-id-list}] [@var{all}] @var{args}},
2905 a command to apply a command to a list of threads
2906 @item thread-specific breakpoints
2907 @item @samp{set print thread-events}, which controls printing of
2908 messages on thread start and exit.
2909 @item @samp{set libthread-db-search-path @var{path}}, which lets
2910 the user specify which @code{libthread_db} to use if the default choice
2911 isn't compatible with the program.
2914 @cindex focus of debugging
2915 @cindex current thread
2916 The @value{GDBN} thread debugging facility allows you to observe all
2917 threads while your program runs---but whenever @value{GDBN} takes
2918 control, one thread in particular is always the focus of debugging.
2919 This thread is called the @dfn{current thread}. Debugging commands show
2920 program information from the perspective of the current thread.
2922 @cindex @code{New} @var{systag} message
2923 @cindex thread identifier (system)
2924 @c FIXME-implementors!! It would be more helpful if the [New...] message
2925 @c included GDB's numeric thread handle, so you could just go to that
2926 @c thread without first checking `info threads'.
2927 Whenever @value{GDBN} detects a new thread in your program, it displays
2928 the target system's identification for the thread with a message in the
2929 form @samp{[New @var{systag}]}, where @var{systag} is a thread identifier
2930 whose form varies depending on the particular system. For example, on
2931 @sc{gnu}/Linux, you might see
2934 [New Thread 0x41e02940 (LWP 25582)]
2938 when @value{GDBN} notices a new thread. In contrast, on other systems,
2939 the @var{systag} is simply something like @samp{process 368}, with no
2942 @c FIXME!! (1) Does the [New...] message appear even for the very first
2943 @c thread of a program, or does it only appear for the
2944 @c second---i.e.@: when it becomes obvious we have a multithread
2946 @c (2) *Is* there necessarily a first thread always? Or do some
2947 @c multithread systems permit starting a program with multiple
2948 @c threads ab initio?
2950 @anchor{thread numbers}
2951 @cindex thread number, per inferior
2952 @cindex thread identifier (GDB)
2953 For debugging purposes, @value{GDBN} associates its own thread number
2954 ---always a single integer---with each thread of an inferior. This
2955 number is unique between all threads of an inferior, but not unique
2956 between threads of different inferiors.
2958 @cindex qualified thread ID
2959 You can refer to a given thread in an inferior using the qualified
2960 @var{inferior-num}.@var{thread-num} syntax, also known as
2961 @dfn{qualified thread ID}, with @var{inferior-num} being the inferior
2962 number and @var{thread-num} being the thread number of the given
2963 inferior. For example, thread @code{2.3} refers to thread number 3 of
2964 inferior 2. If you omit @var{inferior-num} (e.g., @code{thread 3}),
2965 then @value{GDBN} infers you're referring to a thread of the current
2968 Until you create a second inferior, @value{GDBN} does not show the
2969 @var{inferior-num} part of thread IDs, even though you can always use
2970 the full @var{inferior-num}.@var{thread-num} form to refer to threads
2971 of inferior 1, the initial inferior.
2973 @anchor{thread ID lists}
2974 @cindex thread ID lists
2975 Some commands accept a space-separated @dfn{thread ID list} as
2976 argument. A list element can be:
2980 A thread ID as shown in the first field of the @samp{info threads}
2981 display, with or without an inferior qualifier. E.g., @samp{2.1} or
2985 A range of thread numbers, again with or without an inferior
2986 qualifier, as in @var{inf}.@var{thr1}-@var{thr2} or
2987 @var{thr1}-@var{thr2}. E.g., @samp{1.2-4} or @samp{2-4}.
2990 All threads of an inferior, specified with a star wildcard, with or
2991 without an inferior qualifier, as in @var{inf}.@code{*} (e.g.,
2992 @samp{1.*}) or @code{*}. The former refers to all threads of the
2993 given inferior, and the latter form without an inferior qualifier
2994 refers to all threads of the current inferior.
2998 For example, if the current inferior is 1, and inferior 7 has one
2999 thread with ID 7.1, the thread list @samp{1 2-3 4.5 6.7-9 7.*}
3000 includes threads 1 to 3 of inferior 1, thread 5 of inferior 4, threads
3001 7 to 9 of inferior 6 and all threads of inferior 7. That is, in
3002 expanded qualified form, the same as @samp{1.1 1.2 1.3 4.5 6.7 6.8 6.9
3006 @anchor{global thread numbers}
3007 @cindex global thread number
3008 @cindex global thread identifier (GDB)
3009 In addition to a @emph{per-inferior} number, each thread is also
3010 assigned a unique @emph{global} number, also known as @dfn{global
3011 thread ID}, a single integer. Unlike the thread number component of
3012 the thread ID, no two threads have the same global ID, even when
3013 you're debugging multiple inferiors.
3015 From @value{GDBN}'s perspective, a process always has at least one
3016 thread. In other words, @value{GDBN} assigns a thread number to the
3017 program's ``main thread'' even if the program is not multi-threaded.
3019 @vindex $_thread@r{, convenience variable}
3020 @vindex $_gthread@r{, convenience variable}
3021 The debugger convenience variables @samp{$_thread} and
3022 @samp{$_gthread} contain, respectively, the per-inferior thread number
3023 and the global thread number of the current thread. You may find this
3024 useful in writing breakpoint conditional expressions, command scripts,
3025 and so forth. @xref{Convenience Vars,, Convenience Variables}, for
3026 general information on convenience variables.
3028 If @value{GDBN} detects the program is multi-threaded, it augments the
3029 usual message about stopping at a breakpoint with the ID and name of
3030 the thread that hit the breakpoint.
3033 Thread 2 "client" hit Breakpoint 1, send_message () at client.c:68
3036 Likewise when the program receives a signal:
3039 Thread 1 "main" received signal SIGINT, Interrupt.
3043 @kindex info threads
3044 @item info threads @r{[}@var{thread-id-list}@r{]}
3046 Display information about one or more threads. With no arguments
3047 displays information about all threads. You can specify the list of
3048 threads that you want to display using the thread ID list syntax
3049 (@pxref{thread ID lists}).
3051 @value{GDBN} displays for each thread (in this order):
3055 the per-inferior thread number assigned by @value{GDBN}
3058 the global thread number assigned by @value{GDBN}, if the @samp{-gid}
3059 option was specified
3062 the target system's thread identifier (@var{systag})
3065 the thread's name, if one is known. A thread can either be named by
3066 the user (see @code{thread name}, below), or, in some cases, by the
3070 the current stack frame summary for that thread
3074 An asterisk @samp{*} to the left of the @value{GDBN} thread number
3075 indicates the current thread.
3079 @c end table here to get a little more width for example
3082 (@value{GDBP}) info threads
3084 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
3085 2 process 35 thread 23 0x34e5 in sigpause ()
3086 3 process 35 thread 27 0x34e5 in sigpause ()
3090 If you're debugging multiple inferiors, @value{GDBN} displays thread
3091 IDs using the qualified @var{inferior-num}.@var{thread-num} format.
3092 Otherwise, only @var{thread-num} is shown.
3094 If you specify the @samp{-gid} option, @value{GDBN} displays a column
3095 indicating each thread's global thread ID:
3098 (@value{GDBP}) info threads
3099 Id GId Target Id Frame
3100 1.1 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
3101 1.2 3 process 35 thread 23 0x34e5 in sigpause ()
3102 1.3 4 process 35 thread 27 0x34e5 in sigpause ()
3103 * 2.1 2 process 65 thread 1 main (argc=1, argv=0x7ffffff8)
3106 On Solaris, you can display more information about user threads with a
3107 Solaris-specific command:
3110 @item maint info sol-threads
3111 @kindex maint info sol-threads
3112 @cindex thread info (Solaris)
3113 Display info on Solaris user threads.
3117 @kindex thread @var{thread-id}
3118 @item thread @var{thread-id}
3119 Make thread ID @var{thread-id} the current thread. The command
3120 argument @var{thread-id} is the @value{GDBN} thread ID, as shown in
3121 the first field of the @samp{info threads} display, with or without an
3122 inferior qualifier (e.g., @samp{2.1} or @samp{1}).
3124 @value{GDBN} responds by displaying the system identifier of the
3125 thread you selected, and its current stack frame summary:
3128 (@value{GDBP}) thread 2
3129 [Switching to thread 2 (Thread 0xb7fdab70 (LWP 12747))]
3130 #0 some_function (ignore=0x0) at example.c:8
3131 8 printf ("hello\n");
3135 As with the @samp{[New @dots{}]} message, the form of the text after
3136 @samp{Switching to} depends on your system's conventions for identifying
3139 @kindex thread apply
3140 @cindex apply command to several threads
3141 @item thread apply [@var{thread-id-list} | all [-ascending]] @var{command}
3142 The @code{thread apply} command allows you to apply the named
3143 @var{command} to one or more threads. Specify the threads that you
3144 want affected using the thread ID list syntax (@pxref{thread ID
3145 lists}), or specify @code{all} to apply to all threads. To apply a
3146 command to all threads in descending order, type @kbd{thread apply all
3147 @var{command}}. To apply a command to all threads in ascending order,
3148 type @kbd{thread apply all -ascending @var{command}}.
3152 @cindex name a thread
3153 @item thread name [@var{name}]
3154 This command assigns a name to the current thread. If no argument is
3155 given, any existing user-specified name is removed. The thread name
3156 appears in the @samp{info threads} display.
3158 On some systems, such as @sc{gnu}/Linux, @value{GDBN} is able to
3159 determine the name of the thread as given by the OS. On these
3160 systems, a name specified with @samp{thread name} will override the
3161 system-give name, and removing the user-specified name will cause
3162 @value{GDBN} to once again display the system-specified name.
3165 @cindex search for a thread
3166 @item thread find [@var{regexp}]
3167 Search for and display thread ids whose name or @var{systag}
3168 matches the supplied regular expression.
3170 As well as being the complement to the @samp{thread name} command,
3171 this command also allows you to identify a thread by its target
3172 @var{systag}. For instance, on @sc{gnu}/Linux, the target @var{systag}
3176 (@value{GDBN}) thread find 26688
3177 Thread 4 has target id 'Thread 0x41e02940 (LWP 26688)'
3178 (@value{GDBN}) info thread 4
3180 4 Thread 0x41e02940 (LWP 26688) 0x00000031ca6cd372 in select ()
3183 @kindex set print thread-events
3184 @cindex print messages on thread start and exit
3185 @item set print thread-events
3186 @itemx set print thread-events on
3187 @itemx set print thread-events off
3188 The @code{set print thread-events} command allows you to enable or
3189 disable printing of messages when @value{GDBN} notices that new threads have
3190 started or that threads have exited. By default, these messages will
3191 be printed if detection of these events is supported by the target.
3192 Note that these messages cannot be disabled on all targets.
3194 @kindex show print thread-events
3195 @item show print thread-events
3196 Show whether messages will be printed when @value{GDBN} detects that threads
3197 have started and exited.
3200 @xref{Thread Stops,,Stopping and Starting Multi-thread Programs}, for
3201 more information about how @value{GDBN} behaves when you stop and start
3202 programs with multiple threads.
3204 @xref{Set Watchpoints,,Setting Watchpoints}, for information about
3205 watchpoints in programs with multiple threads.
3207 @anchor{set libthread-db-search-path}
3209 @kindex set libthread-db-search-path
3210 @cindex search path for @code{libthread_db}
3211 @item set libthread-db-search-path @r{[}@var{path}@r{]}
3212 If this variable is set, @var{path} is a colon-separated list of
3213 directories @value{GDBN} will use to search for @code{libthread_db}.
3214 If you omit @var{path}, @samp{libthread-db-search-path} will be reset to
3215 its default value (@code{$sdir:$pdir} on @sc{gnu}/Linux and Solaris systems).
3216 Internally, the default value comes from the @code{LIBTHREAD_DB_SEARCH_PATH}
3219 On @sc{gnu}/Linux and Solaris systems, @value{GDBN} uses a ``helper''
3220 @code{libthread_db} library to obtain information about threads in the
3221 inferior process. @value{GDBN} will use @samp{libthread-db-search-path}
3222 to find @code{libthread_db}. @value{GDBN} also consults first if inferior
3223 specific thread debugging library loading is enabled
3224 by @samp{set auto-load libthread-db} (@pxref{libthread_db.so.1 file}).
3226 A special entry @samp{$sdir} for @samp{libthread-db-search-path}
3227 refers to the default system directories that are
3228 normally searched for loading shared libraries. The @samp{$sdir} entry
3229 is the only kind not needing to be enabled by @samp{set auto-load libthread-db}
3230 (@pxref{libthread_db.so.1 file}).
3232 A special entry @samp{$pdir} for @samp{libthread-db-search-path}
3233 refers to the directory from which @code{libpthread}
3234 was loaded in the inferior process.
3236 For any @code{libthread_db} library @value{GDBN} finds in above directories,
3237 @value{GDBN} attempts to initialize it with the current inferior process.
3238 If this initialization fails (which could happen because of a version
3239 mismatch between @code{libthread_db} and @code{libpthread}), @value{GDBN}
3240 will unload @code{libthread_db}, and continue with the next directory.
3241 If none of @code{libthread_db} libraries initialize successfully,
3242 @value{GDBN} will issue a warning and thread debugging will be disabled.
3244 Setting @code{libthread-db-search-path} is currently implemented
3245 only on some platforms.
3247 @kindex show libthread-db-search-path
3248 @item show libthread-db-search-path
3249 Display current libthread_db search path.
3251 @kindex set debug libthread-db
3252 @kindex show debug libthread-db
3253 @cindex debugging @code{libthread_db}
3254 @item set debug libthread-db
3255 @itemx show debug libthread-db
3256 Turns on or off display of @code{libthread_db}-related events.
3257 Use @code{1} to enable, @code{0} to disable.
3261 @section Debugging Forks
3263 @cindex fork, debugging programs which call
3264 @cindex multiple processes
3265 @cindex processes, multiple
3266 On most systems, @value{GDBN} has no special support for debugging
3267 programs which create additional processes using the @code{fork}
3268 function. When a program forks, @value{GDBN} will continue to debug the
3269 parent process and the child process will run unimpeded. If you have
3270 set a breakpoint in any code which the child then executes, the child
3271 will get a @code{SIGTRAP} signal which (unless it catches the signal)
3272 will cause it to terminate.
3274 However, if you want to debug the child process there is a workaround
3275 which isn't too painful. Put a call to @code{sleep} in the code which
3276 the child process executes after the fork. It may be useful to sleep
3277 only if a certain environment variable is set, or a certain file exists,
3278 so that the delay need not occur when you don't want to run @value{GDBN}
3279 on the child. While the child is sleeping, use the @code{ps} program to
3280 get its process ID. Then tell @value{GDBN} (a new invocation of
3281 @value{GDBN} if you are also debugging the parent process) to attach to
3282 the child process (@pxref{Attach}). From that point on you can debug
3283 the child process just like any other process which you attached to.
3285 On some systems, @value{GDBN} provides support for debugging programs
3286 that create additional processes using the @code{fork} or @code{vfork}
3287 functions. On @sc{gnu}/Linux platforms, this feature is supported
3288 with kernel version 2.5.46 and later.
3290 The fork debugging commands are supported in native mode and when
3291 connected to @code{gdbserver} in either @code{target remote} mode or
3292 @code{target extended-remote} mode.
3294 By default, when a program forks, @value{GDBN} will continue to debug
3295 the parent process and the child process will run unimpeded.
3297 If you want to follow the child process instead of the parent process,
3298 use the command @w{@code{set follow-fork-mode}}.
3301 @kindex set follow-fork-mode
3302 @item set follow-fork-mode @var{mode}
3303 Set the debugger response to a program call of @code{fork} or
3304 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
3305 process. The @var{mode} argument can be:
3309 The original process is debugged after a fork. The child process runs
3310 unimpeded. This is the default.
3313 The new process is debugged after a fork. The parent process runs
3318 @kindex show follow-fork-mode
3319 @item show follow-fork-mode
3320 Display the current debugger response to a @code{fork} or @code{vfork} call.
3323 @cindex debugging multiple processes
3324 On Linux, if you want to debug both the parent and child processes, use the
3325 command @w{@code{set detach-on-fork}}.
3328 @kindex set detach-on-fork
3329 @item set detach-on-fork @var{mode}
3330 Tells gdb whether to detach one of the processes after a fork, or
3331 retain debugger control over them both.
3335 The child process (or parent process, depending on the value of
3336 @code{follow-fork-mode}) will be detached and allowed to run
3337 independently. This is the default.
3340 Both processes will be held under the control of @value{GDBN}.
3341 One process (child or parent, depending on the value of
3342 @code{follow-fork-mode}) is debugged as usual, while the other
3347 @kindex show detach-on-fork
3348 @item show detach-on-fork
3349 Show whether detach-on-fork mode is on/off.
3352 If you choose to set @samp{detach-on-fork} mode off, then @value{GDBN}
3353 will retain control of all forked processes (including nested forks).
3354 You can list the forked processes under the control of @value{GDBN} by
3355 using the @w{@code{info inferiors}} command, and switch from one fork
3356 to another by using the @code{inferior} command (@pxref{Inferiors and
3357 Programs, ,Debugging Multiple Inferiors and Programs}).
3359 To quit debugging one of the forked processes, you can either detach
3360 from it by using the @w{@code{detach inferiors}} command (allowing it
3361 to run independently), or kill it using the @w{@code{kill inferiors}}
3362 command. @xref{Inferiors and Programs, ,Debugging Multiple Inferiors
3365 If you ask to debug a child process and a @code{vfork} is followed by an
3366 @code{exec}, @value{GDBN} executes the new target up to the first
3367 breakpoint in the new target. If you have a breakpoint set on
3368 @code{main} in your original program, the breakpoint will also be set on
3369 the child process's @code{main}.
3371 On some systems, when a child process is spawned by @code{vfork}, you
3372 cannot debug the child or parent until an @code{exec} call completes.
3374 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
3375 call executes, the new target restarts. To restart the parent
3376 process, use the @code{file} command with the parent executable name
3377 as its argument. By default, after an @code{exec} call executes,
3378 @value{GDBN} discards the symbols of the previous executable image.
3379 You can change this behaviour with the @w{@code{set follow-exec-mode}}
3383 @kindex set follow-exec-mode
3384 @item set follow-exec-mode @var{mode}
3386 Set debugger response to a program call of @code{exec}. An
3387 @code{exec} call replaces the program image of a process.
3389 @code{follow-exec-mode} can be:
3393 @value{GDBN} creates a new inferior and rebinds the process to this
3394 new inferior. The program the process was running before the
3395 @code{exec} call can be restarted afterwards by restarting the
3401 (@value{GDBP}) info inferiors
3403 Id Description Executable
3406 process 12020 is executing new program: prog2
3407 Program exited normally.
3408 (@value{GDBP}) info inferiors
3409 Id Description Executable
3415 @value{GDBN} keeps the process bound to the same inferior. The new
3416 executable image replaces the previous executable loaded in the
3417 inferior. Restarting the inferior after the @code{exec} call, with
3418 e.g., the @code{run} command, restarts the executable the process was
3419 running after the @code{exec} call. This is the default mode.
3424 (@value{GDBP}) info inferiors
3425 Id Description Executable
3428 process 12020 is executing new program: prog2
3429 Program exited normally.
3430 (@value{GDBP}) info inferiors
3431 Id Description Executable
3438 @code{follow-exec-mode} is supported in native mode and
3439 @code{target extended-remote} mode.
3441 You can use the @code{catch} command to make @value{GDBN} stop whenever
3442 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
3443 Catchpoints, ,Setting Catchpoints}.
3445 @node Checkpoint/Restart
3446 @section Setting a @emph{Bookmark} to Return to Later
3451 @cindex snapshot of a process
3452 @cindex rewind program state
3454 On certain operating systems@footnote{Currently, only
3455 @sc{gnu}/Linux.}, @value{GDBN} is able to save a @dfn{snapshot} of a
3456 program's state, called a @dfn{checkpoint}, and come back to it
3459 Returning to a checkpoint effectively undoes everything that has
3460 happened in the program since the @code{checkpoint} was saved. This
3461 includes changes in memory, registers, and even (within some limits)
3462 system state. Effectively, it is like going back in time to the
3463 moment when the checkpoint was saved.
3465 Thus, if you're stepping thru a program and you think you're
3466 getting close to the point where things go wrong, you can save
3467 a checkpoint. Then, if you accidentally go too far and miss
3468 the critical statement, instead of having to restart your program
3469 from the beginning, you can just go back to the checkpoint and
3470 start again from there.
3472 This can be especially useful if it takes a lot of time or
3473 steps to reach the point where you think the bug occurs.
3475 To use the @code{checkpoint}/@code{restart} method of debugging:
3480 Save a snapshot of the debugged program's current execution state.
3481 The @code{checkpoint} command takes no arguments, but each checkpoint
3482 is assigned a small integer id, similar to a breakpoint id.
3484 @kindex info checkpoints
3485 @item info checkpoints
3486 List the checkpoints that have been saved in the current debugging
3487 session. For each checkpoint, the following information will be
3494 @item Source line, or label
3497 @kindex restart @var{checkpoint-id}
3498 @item restart @var{checkpoint-id}
3499 Restore the program state that was saved as checkpoint number
3500 @var{checkpoint-id}. All program variables, registers, stack frames
3501 etc.@: will be returned to the values that they had when the checkpoint
3502 was saved. In essence, gdb will ``wind back the clock'' to the point
3503 in time when the checkpoint was saved.
3505 Note that breakpoints, @value{GDBN} variables, command history etc.
3506 are not affected by restoring a checkpoint. In general, a checkpoint
3507 only restores things that reside in the program being debugged, not in
3510 @kindex delete checkpoint @var{checkpoint-id}
3511 @item delete checkpoint @var{checkpoint-id}
3512 Delete the previously-saved checkpoint identified by @var{checkpoint-id}.
3516 Returning to a previously saved checkpoint will restore the user state
3517 of the program being debugged, plus a significant subset of the system
3518 (OS) state, including file pointers. It won't ``un-write'' data from
3519 a file, but it will rewind the file pointer to the previous location,
3520 so that the previously written data can be overwritten. For files
3521 opened in read mode, the pointer will also be restored so that the
3522 previously read data can be read again.
3524 Of course, characters that have been sent to a printer (or other
3525 external device) cannot be ``snatched back'', and characters received
3526 from eg.@: a serial device can be removed from internal program buffers,
3527 but they cannot be ``pushed back'' into the serial pipeline, ready to
3528 be received again. Similarly, the actual contents of files that have
3529 been changed cannot be restored (at this time).
3531 However, within those constraints, you actually can ``rewind'' your
3532 program to a previously saved point in time, and begin debugging it
3533 again --- and you can change the course of events so as to debug a
3534 different execution path this time.
3536 @cindex checkpoints and process id
3537 Finally, there is one bit of internal program state that will be
3538 different when you return to a checkpoint --- the program's process
3539 id. Each checkpoint will have a unique process id (or @var{pid}),
3540 and each will be different from the program's original @var{pid}.
3541 If your program has saved a local copy of its process id, this could
3542 potentially pose a problem.
3544 @subsection A Non-obvious Benefit of Using Checkpoints
3546 On some systems such as @sc{gnu}/Linux, address space randomization
3547 is performed on new processes for security reasons. This makes it
3548 difficult or impossible to set a breakpoint, or watchpoint, on an
3549 absolute address if you have to restart the program, since the
3550 absolute location of a symbol will change from one execution to the
3553 A checkpoint, however, is an @emph{identical} copy of a process.
3554 Therefore if you create a checkpoint at (eg.@:) the start of main,
3555 and simply return to that checkpoint instead of restarting the
3556 process, you can avoid the effects of address randomization and
3557 your symbols will all stay in the same place.
3560 @chapter Stopping and Continuing
3562 The principal purposes of using a debugger are so that you can stop your
3563 program before it terminates; or so that, if your program runs into
3564 trouble, you can investigate and find out why.
3566 Inside @value{GDBN}, your program may stop for any of several reasons,
3567 such as a signal, a breakpoint, or reaching a new line after a
3568 @value{GDBN} command such as @code{step}. You may then examine and
3569 change variables, set new breakpoints or remove old ones, and then
3570 continue execution. Usually, the messages shown by @value{GDBN} provide
3571 ample explanation of the status of your program---but you can also
3572 explicitly request this information at any time.
3575 @kindex info program
3577 Display information about the status of your program: whether it is
3578 running or not, what process it is, and why it stopped.
3582 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
3583 * Continuing and Stepping:: Resuming execution
3584 * Skipping Over Functions and Files::
3585 Skipping over functions and files
3587 * Thread Stops:: Stopping and starting multi-thread programs
3591 @section Breakpoints, Watchpoints, and Catchpoints
3594 A @dfn{breakpoint} makes your program stop whenever a certain point in
3595 the program is reached. For each breakpoint, you can add conditions to
3596 control in finer detail whether your program stops. You can set
3597 breakpoints with the @code{break} command and its variants (@pxref{Set
3598 Breaks, ,Setting Breakpoints}), to specify the place where your program
3599 should stop by line number, function name or exact address in the
3602 On some systems, you can set breakpoints in shared libraries before
3603 the executable is run.
3606 @cindex data breakpoints
3607 @cindex memory tracing
3608 @cindex breakpoint on memory address
3609 @cindex breakpoint on variable modification
3610 A @dfn{watchpoint} is a special breakpoint that stops your program
3611 when the value of an expression changes. The expression may be a value
3612 of a variable, or it could involve values of one or more variables
3613 combined by operators, such as @samp{a + b}. This is sometimes called
3614 @dfn{data breakpoints}. You must use a different command to set
3615 watchpoints (@pxref{Set Watchpoints, ,Setting Watchpoints}), but aside
3616 from that, you can manage a watchpoint like any other breakpoint: you
3617 enable, disable, and delete both breakpoints and watchpoints using the
3620 You can arrange to have values from your program displayed automatically
3621 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
3625 @cindex breakpoint on events
3626 A @dfn{catchpoint} is another special breakpoint that stops your program
3627 when a certain kind of event occurs, such as the throwing of a C@t{++}
3628 exception or the loading of a library. As with watchpoints, you use a
3629 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
3630 Catchpoints}), but aside from that, you can manage a catchpoint like any
3631 other breakpoint. (To stop when your program receives a signal, use the
3632 @code{handle} command; see @ref{Signals, ,Signals}.)
3634 @cindex breakpoint numbers
3635 @cindex numbers for breakpoints
3636 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
3637 catchpoint when you create it; these numbers are successive integers
3638 starting with one. In many of the commands for controlling various
3639 features of breakpoints you use the breakpoint number to say which
3640 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
3641 @dfn{disabled}; if disabled, it has no effect on your program until you
3644 @cindex breakpoint ranges
3645 @cindex breakpoint lists
3646 @cindex ranges of breakpoints
3647 @cindex lists of breakpoints
3648 Some @value{GDBN} commands accept a space-separated list of breakpoints
3649 on which to operate. A list element can be either a single breakpoint number,
3650 like @samp{5}, or a range of such numbers, like @samp{5-7}.
3651 When a breakpoint list is given to a command, all breakpoints in that list
3655 * Set Breaks:: Setting breakpoints
3656 * Set Watchpoints:: Setting watchpoints
3657 * Set Catchpoints:: Setting catchpoints
3658 * Delete Breaks:: Deleting breakpoints
3659 * Disabling:: Disabling breakpoints
3660 * Conditions:: Break conditions
3661 * Break Commands:: Breakpoint command lists
3662 * Dynamic Printf:: Dynamic printf
3663 * Save Breakpoints:: How to save breakpoints in a file
3664 * Static Probe Points:: Listing static probe points
3665 * Error in Breakpoints:: ``Cannot insert breakpoints''
3666 * Breakpoint-related Warnings:: ``Breakpoint address adjusted...''
3670 @subsection Setting Breakpoints
3672 @c FIXME LMB what does GDB do if no code on line of breakpt?
3673 @c consider in particular declaration with/without initialization.
3675 @c FIXME 2 is there stuff on this already? break at fun start, already init?
3678 @kindex b @r{(@code{break})}
3679 @vindex $bpnum@r{, convenience variable}
3680 @cindex latest breakpoint
3681 Breakpoints are set with the @code{break} command (abbreviated
3682 @code{b}). The debugger convenience variable @samp{$bpnum} records the
3683 number of the breakpoint you've set most recently; see @ref{Convenience
3684 Vars,, Convenience Variables}, for a discussion of what you can do with
3685 convenience variables.
3688 @item break @var{location}
3689 Set a breakpoint at the given @var{location}, which can specify a
3690 function name, a line number, or an address of an instruction.
3691 (@xref{Specify Location}, for a list of all the possible ways to
3692 specify a @var{location}.) The breakpoint will stop your program just
3693 before it executes any of the code in the specified @var{location}.
3695 When using source languages that permit overloading of symbols, such as
3696 C@t{++}, a function name may refer to more than one possible place to break.
3697 @xref{Ambiguous Expressions,,Ambiguous Expressions}, for a discussion of
3700 It is also possible to insert a breakpoint that will stop the program
3701 only if a specific thread (@pxref{Thread-Specific Breakpoints})
3702 or a specific task (@pxref{Ada Tasks}) hits that breakpoint.
3705 When called without any arguments, @code{break} sets a breakpoint at
3706 the next instruction to be executed in the selected stack frame
3707 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
3708 innermost, this makes your program stop as soon as control
3709 returns to that frame. This is similar to the effect of a
3710 @code{finish} command in the frame inside the selected frame---except
3711 that @code{finish} does not leave an active breakpoint. If you use
3712 @code{break} without an argument in the innermost frame, @value{GDBN} stops
3713 the next time it reaches the current location; this may be useful
3716 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
3717 least one instruction has been executed. If it did not do this, you
3718 would be unable to proceed past a breakpoint without first disabling the
3719 breakpoint. This rule applies whether or not the breakpoint already
3720 existed when your program stopped.
3722 @item break @dots{} if @var{cond}
3723 Set a breakpoint with condition @var{cond}; evaluate the expression
3724 @var{cond} each time the breakpoint is reached, and stop only if the
3725 value is nonzero---that is, if @var{cond} evaluates as true.
3726 @samp{@dots{}} stands for one of the possible arguments described
3727 above (or no argument) specifying where to break. @xref{Conditions,
3728 ,Break Conditions}, for more information on breakpoint conditions.
3731 @item tbreak @var{args}
3732 Set a breakpoint enabled only for one stop. The @var{args} are the
3733 same as for the @code{break} command, and the breakpoint is set in the same
3734 way, but the breakpoint is automatically deleted after the first time your
3735 program stops there. @xref{Disabling, ,Disabling Breakpoints}.
3738 @cindex hardware breakpoints
3739 @item hbreak @var{args}
3740 Set a hardware-assisted breakpoint. The @var{args} are the same as for the
3741 @code{break} command and the breakpoint is set in the same way, but the
3742 breakpoint requires hardware support and some target hardware may not
3743 have this support. The main purpose of this is EPROM/ROM code
3744 debugging, so you can set a breakpoint at an instruction without
3745 changing the instruction. This can be used with the new trap-generation
3746 provided by SPARClite DSU and most x86-based targets. These targets
3747 will generate traps when a program accesses some data or instruction
3748 address that is assigned to the debug registers. However the hardware
3749 breakpoint registers can take a limited number of breakpoints. For
3750 example, on the DSU, only two data breakpoints can be set at a time, and
3751 @value{GDBN} will reject this command if more than two are used. Delete
3752 or disable unused hardware breakpoints before setting new ones
3753 (@pxref{Disabling, ,Disabling Breakpoints}).
3754 @xref{Conditions, ,Break Conditions}.
3755 For remote targets, you can restrict the number of hardware
3756 breakpoints @value{GDBN} will use, see @ref{set remote
3757 hardware-breakpoint-limit}.
3760 @item thbreak @var{args}
3761 Set a hardware-assisted breakpoint enabled only for one stop. The @var{args}
3762 are the same as for the @code{hbreak} command and the breakpoint is set in
3763 the same way. However, like the @code{tbreak} command,
3764 the breakpoint is automatically deleted after the
3765 first time your program stops there. Also, like the @code{hbreak}
3766 command, the breakpoint requires hardware support and some target hardware
3767 may not have this support. @xref{Disabling, ,Disabling Breakpoints}.
3768 See also @ref{Conditions, ,Break Conditions}.
3771 @cindex regular expression
3772 @cindex breakpoints at functions matching a regexp
3773 @cindex set breakpoints in many functions
3774 @item rbreak @var{regex}
3775 Set breakpoints on all functions matching the regular expression
3776 @var{regex}. This command sets an unconditional breakpoint on all
3777 matches, printing a list of all breakpoints it set. Once these
3778 breakpoints are set, they are treated just like the breakpoints set with
3779 the @code{break} command. You can delete them, disable them, or make
3780 them conditional the same way as any other breakpoint.
3782 The syntax of the regular expression is the standard one used with tools
3783 like @file{grep}. Note that this is different from the syntax used by
3784 shells, so for instance @code{foo*} matches all functions that include
3785 an @code{fo} followed by zero or more @code{o}s. There is an implicit
3786 @code{.*} leading and trailing the regular expression you supply, so to
3787 match only functions that begin with @code{foo}, use @code{^foo}.
3789 @cindex non-member C@t{++} functions, set breakpoint in
3790 When debugging C@t{++} programs, @code{rbreak} is useful for setting
3791 breakpoints on overloaded functions that are not members of any special
3794 @cindex set breakpoints on all functions
3795 The @code{rbreak} command can be used to set breakpoints in
3796 @strong{all} the functions in a program, like this:
3799 (@value{GDBP}) rbreak .
3802 @item rbreak @var{file}:@var{regex}
3803 If @code{rbreak} is called with a filename qualification, it limits
3804 the search for functions matching the given regular expression to the
3805 specified @var{file}. This can be used, for example, to set breakpoints on
3806 every function in a given file:
3809 (@value{GDBP}) rbreak file.c:.
3812 The colon separating the filename qualifier from the regex may
3813 optionally be surrounded by spaces.
3815 @kindex info breakpoints
3816 @cindex @code{$_} and @code{info breakpoints}
3817 @item info breakpoints @r{[}@var{list}@dots{}@r{]}
3818 @itemx info break @r{[}@var{list}@dots{}@r{]}
3819 Print a table of all breakpoints, watchpoints, and catchpoints set and
3820 not deleted. Optional argument @var{n} means print information only
3821 about the specified breakpoint(s) (or watchpoint(s) or catchpoint(s)).
3822 For each breakpoint, following columns are printed:
3825 @item Breakpoint Numbers
3827 Breakpoint, watchpoint, or catchpoint.
3829 Whether the breakpoint is marked to be disabled or deleted when hit.
3830 @item Enabled or Disabled
3831 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
3832 that are not enabled.
3834 Where the breakpoint is in your program, as a memory address. For a
3835 pending breakpoint whose address is not yet known, this field will
3836 contain @samp{<PENDING>}. Such breakpoint won't fire until a shared
3837 library that has the symbol or line referred by breakpoint is loaded.
3838 See below for details. A breakpoint with several locations will
3839 have @samp{<MULTIPLE>} in this field---see below for details.
3841 Where the breakpoint is in the source for your program, as a file and
3842 line number. For a pending breakpoint, the original string passed to
3843 the breakpoint command will be listed as it cannot be resolved until
3844 the appropriate shared library is loaded in the future.
3848 If a breakpoint is conditional, there are two evaluation modes: ``host'' and
3849 ``target''. If mode is ``host'', breakpoint condition evaluation is done by
3850 @value{GDBN} on the host's side. If it is ``target'', then the condition
3851 is evaluated by the target. The @code{info break} command shows
3852 the condition on the line following the affected breakpoint, together with
3853 its condition evaluation mode in between parentheses.
3855 Breakpoint commands, if any, are listed after that. A pending breakpoint is
3856 allowed to have a condition specified for it. The condition is not parsed for
3857 validity until a shared library is loaded that allows the pending
3858 breakpoint to resolve to a valid location.
3861 @code{info break} with a breakpoint
3862 number @var{n} as argument lists only that breakpoint. The
3863 convenience variable @code{$_} and the default examining-address for
3864 the @code{x} command are set to the address of the last breakpoint
3865 listed (@pxref{Memory, ,Examining Memory}).
3868 @code{info break} displays a count of the number of times the breakpoint
3869 has been hit. This is especially useful in conjunction with the
3870 @code{ignore} command. You can ignore a large number of breakpoint
3871 hits, look at the breakpoint info to see how many times the breakpoint
3872 was hit, and then run again, ignoring one less than that number. This
3873 will get you quickly to the last hit of that breakpoint.
3876 For a breakpoints with an enable count (xref) greater than 1,
3877 @code{info break} also displays that count.
3881 @value{GDBN} allows you to set any number of breakpoints at the same place in
3882 your program. There is nothing silly or meaningless about this. When
3883 the breakpoints are conditional, this is even useful
3884 (@pxref{Conditions, ,Break Conditions}).
3886 @cindex multiple locations, breakpoints
3887 @cindex breakpoints, multiple locations
3888 It is possible that a breakpoint corresponds to several locations
3889 in your program. Examples of this situation are:
3893 Multiple functions in the program may have the same name.
3896 For a C@t{++} constructor, the @value{NGCC} compiler generates several
3897 instances of the function body, used in different cases.
3900 For a C@t{++} template function, a given line in the function can
3901 correspond to any number of instantiations.
3904 For an inlined function, a given source line can correspond to
3905 several places where that function is inlined.
3908 In all those cases, @value{GDBN} will insert a breakpoint at all
3909 the relevant locations.
3911 A breakpoint with multiple locations is displayed in the breakpoint
3912 table using several rows---one header row, followed by one row for
3913 each breakpoint location. The header row has @samp{<MULTIPLE>} in the
3914 address column. The rows for individual locations contain the actual
3915 addresses for locations, and show the functions to which those
3916 locations belong. The number column for a location is of the form
3917 @var{breakpoint-number}.@var{location-number}.
3922 Num Type Disp Enb Address What
3923 1 breakpoint keep y <MULTIPLE>
3925 breakpoint already hit 1 time
3926 1.1 y 0x080486a2 in void foo<int>() at t.cc:8
3927 1.2 y 0x080486ca in void foo<double>() at t.cc:8
3930 You cannot delete the individual locations from a breakpoint. However,
3931 each location can be individually enabled or disabled by passing
3932 @var{breakpoint-number}.@var{location-number} as argument to the
3933 @code{enable} and @code{disable} commands. It's also possible to
3934 @code{enable} and @code{disable} a range of @var{location-number}
3935 locations using a @var{breakpoint-number} and two @var{location-number}s,
3936 in increasing order, separated by a hyphen, like
3937 @kbd{@var{breakpoint-number}.@var{location-number1}-@var{location-number2}},
3938 in which case @value{GDBN} acts on all the locations in the range (inclusive).
3939 Disabling or enabling the parent breakpoint (@pxref{Disabling}) affects
3940 all of the locations that belong to that breakpoint.
3942 @cindex pending breakpoints
3943 It's quite common to have a breakpoint inside a shared library.
3944 Shared libraries can be loaded and unloaded explicitly,
3945 and possibly repeatedly, as the program is executed. To support
3946 this use case, @value{GDBN} updates breakpoint locations whenever
3947 any shared library is loaded or unloaded. Typically, you would
3948 set a breakpoint in a shared library at the beginning of your
3949 debugging session, when the library is not loaded, and when the
3950 symbols from the library are not available. When you try to set
3951 breakpoint, @value{GDBN} will ask you if you want to set
3952 a so called @dfn{pending breakpoint}---breakpoint whose address
3953 is not yet resolved.
3955 After the program is run, whenever a new shared library is loaded,
3956 @value{GDBN} reevaluates all the breakpoints. When a newly loaded
3957 shared library contains the symbol or line referred to by some
3958 pending breakpoint, that breakpoint is resolved and becomes an
3959 ordinary breakpoint. When a library is unloaded, all breakpoints
3960 that refer to its symbols or source lines become pending again.
3962 This logic works for breakpoints with multiple locations, too. For
3963 example, if you have a breakpoint in a C@t{++} template function, and
3964 a newly loaded shared library has an instantiation of that template,
3965 a new location is added to the list of locations for the breakpoint.
3967 Except for having unresolved address, pending breakpoints do not
3968 differ from regular breakpoints. You can set conditions or commands,
3969 enable and disable them and perform other breakpoint operations.
3971 @value{GDBN} provides some additional commands for controlling what
3972 happens when the @samp{break} command cannot resolve breakpoint
3973 address specification to an address:
3975 @kindex set breakpoint pending
3976 @kindex show breakpoint pending
3978 @item set breakpoint pending auto
3979 This is the default behavior. When @value{GDBN} cannot find the breakpoint
3980 location, it queries you whether a pending breakpoint should be created.
3982 @item set breakpoint pending on
3983 This indicates that an unrecognized breakpoint location should automatically
3984 result in a pending breakpoint being created.
3986 @item set breakpoint pending off
3987 This indicates that pending breakpoints are not to be created. Any
3988 unrecognized breakpoint location results in an error. This setting does
3989 not affect any pending breakpoints previously created.
3991 @item show breakpoint pending
3992 Show the current behavior setting for creating pending breakpoints.
3995 The settings above only affect the @code{break} command and its
3996 variants. Once breakpoint is set, it will be automatically updated
3997 as shared libraries are loaded and unloaded.
3999 @cindex automatic hardware breakpoints
4000 For some targets, @value{GDBN} can automatically decide if hardware or
4001 software breakpoints should be used, depending on whether the
4002 breakpoint address is read-only or read-write. This applies to
4003 breakpoints set with the @code{break} command as well as to internal
4004 breakpoints set by commands like @code{next} and @code{finish}. For
4005 breakpoints set with @code{hbreak}, @value{GDBN} will always use hardware
4008 You can control this automatic behaviour with the following commands:
4010 @kindex set breakpoint auto-hw
4011 @kindex show breakpoint auto-hw
4013 @item set breakpoint auto-hw on
4014 This is the default behavior. When @value{GDBN} sets a breakpoint, it
4015 will try to use the target memory map to decide if software or hardware
4016 breakpoint must be used.
4018 @item set breakpoint auto-hw off
4019 This indicates @value{GDBN} should not automatically select breakpoint
4020 type. If the target provides a memory map, @value{GDBN} will warn when
4021 trying to set software breakpoint at a read-only address.
4024 @value{GDBN} normally implements breakpoints by replacing the program code
4025 at the breakpoint address with a special instruction, which, when
4026 executed, given control to the debugger. By default, the program
4027 code is so modified only when the program is resumed. As soon as
4028 the program stops, @value{GDBN} restores the original instructions. This
4029 behaviour guards against leaving breakpoints inserted in the
4030 target should gdb abrubptly disconnect. However, with slow remote
4031 targets, inserting and removing breakpoint can reduce the performance.
4032 This behavior can be controlled with the following commands::
4034 @kindex set breakpoint always-inserted
4035 @kindex show breakpoint always-inserted
4037 @item set breakpoint always-inserted off
4038 All breakpoints, including newly added by the user, are inserted in
4039 the target only when the target is resumed. All breakpoints are
4040 removed from the target when it stops. This is the default mode.
4042 @item set breakpoint always-inserted on
4043 Causes all breakpoints to be inserted in the target at all times. If
4044 the user adds a new breakpoint, or changes an existing breakpoint, the
4045 breakpoints in the target are updated immediately. A breakpoint is
4046 removed from the target only when breakpoint itself is deleted.
4049 @value{GDBN} handles conditional breakpoints by evaluating these conditions
4050 when a breakpoint breaks. If the condition is true, then the process being
4051 debugged stops, otherwise the process is resumed.
4053 If the target supports evaluating conditions on its end, @value{GDBN} may
4054 download the breakpoint, together with its conditions, to it.
4056 This feature can be controlled via the following commands:
4058 @kindex set breakpoint condition-evaluation
4059 @kindex show breakpoint condition-evaluation
4061 @item set breakpoint condition-evaluation host
4062 This option commands @value{GDBN} to evaluate the breakpoint
4063 conditions on the host's side. Unconditional breakpoints are sent to
4064 the target which in turn receives the triggers and reports them back to GDB
4065 for condition evaluation. This is the standard evaluation mode.
4067 @item set breakpoint condition-evaluation target
4068 This option commands @value{GDBN} to download breakpoint conditions
4069 to the target at the moment of their insertion. The target
4070 is responsible for evaluating the conditional expression and reporting
4071 breakpoint stop events back to @value{GDBN} whenever the condition
4072 is true. Due to limitations of target-side evaluation, some conditions
4073 cannot be evaluated there, e.g., conditions that depend on local data
4074 that is only known to the host. Examples include
4075 conditional expressions involving convenience variables, complex types
4076 that cannot be handled by the agent expression parser and expressions
4077 that are too long to be sent over to the target, specially when the
4078 target is a remote system. In these cases, the conditions will be
4079 evaluated by @value{GDBN}.
4081 @item set breakpoint condition-evaluation auto
4082 This is the default mode. If the target supports evaluating breakpoint
4083 conditions on its end, @value{GDBN} will download breakpoint conditions to
4084 the target (limitations mentioned previously apply). If the target does
4085 not support breakpoint condition evaluation, then @value{GDBN} will fallback
4086 to evaluating all these conditions on the host's side.
4090 @cindex negative breakpoint numbers
4091 @cindex internal @value{GDBN} breakpoints
4092 @value{GDBN} itself sometimes sets breakpoints in your program for
4093 special purposes, such as proper handling of @code{longjmp} (in C
4094 programs). These internal breakpoints are assigned negative numbers,
4095 starting with @code{-1}; @samp{info breakpoints} does not display them.
4096 You can see these breakpoints with the @value{GDBN} maintenance command
4097 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
4100 @node Set Watchpoints
4101 @subsection Setting Watchpoints
4103 @cindex setting watchpoints
4104 You can use a watchpoint to stop execution whenever the value of an
4105 expression changes, without having to predict a particular place where
4106 this may happen. (This is sometimes called a @dfn{data breakpoint}.)
4107 The expression may be as simple as the value of a single variable, or
4108 as complex as many variables combined by operators. Examples include:
4112 A reference to the value of a single variable.
4115 An address cast to an appropriate data type. For example,
4116 @samp{*(int *)0x12345678} will watch a 4-byte region at the specified
4117 address (assuming an @code{int} occupies 4 bytes).
4120 An arbitrarily complex expression, such as @samp{a*b + c/d}. The
4121 expression can use any operators valid in the program's native
4122 language (@pxref{Languages}).
4125 You can set a watchpoint on an expression even if the expression can
4126 not be evaluated yet. For instance, you can set a watchpoint on
4127 @samp{*global_ptr} before @samp{global_ptr} is initialized.
4128 @value{GDBN} will stop when your program sets @samp{global_ptr} and
4129 the expression produces a valid value. If the expression becomes
4130 valid in some other way than changing a variable (e.g.@: if the memory
4131 pointed to by @samp{*global_ptr} becomes readable as the result of a
4132 @code{malloc} call), @value{GDBN} may not stop until the next time
4133 the expression changes.
4135 @cindex software watchpoints
4136 @cindex hardware watchpoints
4137 Depending on your system, watchpoints may be implemented in software or
4138 hardware. @value{GDBN} does software watchpointing by single-stepping your
4139 program and testing the variable's value each time, which is hundreds of
4140 times slower than normal execution. (But this may still be worth it, to
4141 catch errors where you have no clue what part of your program is the
4144 On some systems, such as most PowerPC or x86-based targets,
4145 @value{GDBN} includes support for hardware watchpoints, which do not
4146 slow down the running of your program.
4150 @item watch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{thread-id}@r{]} @r{[}mask @var{maskvalue}@r{]}
4151 Set a watchpoint for an expression. @value{GDBN} will break when the
4152 expression @var{expr} is written into by the program and its value
4153 changes. The simplest (and the most popular) use of this command is
4154 to watch the value of a single variable:
4157 (@value{GDBP}) watch foo
4160 If the command includes a @code{@r{[}thread @var{thread-id}@r{]}}
4161 argument, @value{GDBN} breaks only when the thread identified by
4162 @var{thread-id} changes the value of @var{expr}. If any other threads
4163 change the value of @var{expr}, @value{GDBN} will not break. Note
4164 that watchpoints restricted to a single thread in this way only work
4165 with Hardware Watchpoints.
4167 Ordinarily a watchpoint respects the scope of variables in @var{expr}
4168 (see below). The @code{-location} argument tells @value{GDBN} to
4169 instead watch the memory referred to by @var{expr}. In this case,
4170 @value{GDBN} will evaluate @var{expr}, take the address of the result,
4171 and watch the memory at that address. The type of the result is used
4172 to determine the size of the watched memory. If the expression's
4173 result does not have an address, then @value{GDBN} will print an
4176 The @code{@r{[}mask @var{maskvalue}@r{]}} argument allows creation
4177 of masked watchpoints, if the current architecture supports this
4178 feature (e.g., PowerPC Embedded architecture, see @ref{PowerPC
4179 Embedded}.) A @dfn{masked watchpoint} specifies a mask in addition
4180 to an address to watch. The mask specifies that some bits of an address
4181 (the bits which are reset in the mask) should be ignored when matching
4182 the address accessed by the inferior against the watchpoint address.
4183 Thus, a masked watchpoint watches many addresses simultaneously---those
4184 addresses whose unmasked bits are identical to the unmasked bits in the
4185 watchpoint address. The @code{mask} argument implies @code{-location}.
4189 (@value{GDBP}) watch foo mask 0xffff00ff
4190 (@value{GDBP}) watch *0xdeadbeef mask 0xffffff00
4194 @item rwatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{thread-id}@r{]} @r{[}mask @var{maskvalue}@r{]}
4195 Set a watchpoint that will break when the value of @var{expr} is read
4199 @item awatch @r{[}-l@r{|}-location@r{]} @var{expr} @r{[}thread @var{thread-id}@r{]} @r{[}mask @var{maskvalue}@r{]}
4200 Set a watchpoint that will break when @var{expr} is either read from
4201 or written into by the program.
4203 @kindex info watchpoints @r{[}@var{list}@dots{}@r{]}
4204 @item info watchpoints @r{[}@var{list}@dots{}@r{]}
4205 This command prints a list of watchpoints, using the same format as
4206 @code{info break} (@pxref{Set Breaks}).
4209 If you watch for a change in a numerically entered address you need to
4210 dereference it, as the address itself is just a constant number which will
4211 never change. @value{GDBN} refuses to create a watchpoint that watches
4212 a never-changing value:
4215 (@value{GDBP}) watch 0x600850
4216 Cannot watch constant value 0x600850.
4217 (@value{GDBP}) watch *(int *) 0x600850
4218 Watchpoint 1: *(int *) 6293584
4221 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
4222 watchpoints execute very quickly, and the debugger reports a change in
4223 value at the exact instruction where the change occurs. If @value{GDBN}
4224 cannot set a hardware watchpoint, it sets a software watchpoint, which
4225 executes more slowly and reports the change in value at the next
4226 @emph{statement}, not the instruction, after the change occurs.
4228 @cindex use only software watchpoints
4229 You can force @value{GDBN} to use only software watchpoints with the
4230 @kbd{set can-use-hw-watchpoints 0} command. With this variable set to
4231 zero, @value{GDBN} will never try to use hardware watchpoints, even if
4232 the underlying system supports them. (Note that hardware-assisted
4233 watchpoints that were set @emph{before} setting
4234 @code{can-use-hw-watchpoints} to zero will still use the hardware
4235 mechanism of watching expression values.)
4238 @item set can-use-hw-watchpoints
4239 @kindex set can-use-hw-watchpoints
4240 Set whether or not to use hardware watchpoints.
4242 @item show can-use-hw-watchpoints
4243 @kindex show can-use-hw-watchpoints
4244 Show the current mode of using hardware watchpoints.
4247 For remote targets, you can restrict the number of hardware
4248 watchpoints @value{GDBN} will use, see @ref{set remote
4249 hardware-breakpoint-limit}.
4251 When you issue the @code{watch} command, @value{GDBN} reports
4254 Hardware watchpoint @var{num}: @var{expr}
4258 if it was able to set a hardware watchpoint.
4260 Currently, the @code{awatch} and @code{rwatch} commands can only set
4261 hardware watchpoints, because accesses to data that don't change the
4262 value of the watched expression cannot be detected without examining
4263 every instruction as it is being executed, and @value{GDBN} does not do
4264 that currently. If @value{GDBN} finds that it is unable to set a
4265 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
4266 will print a message like this:
4269 Expression cannot be implemented with read/access watchpoint.
4272 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
4273 data type of the watched expression is wider than what a hardware
4274 watchpoint on the target machine can handle. For example, some systems
4275 can only watch regions that are up to 4 bytes wide; on such systems you
4276 cannot set hardware watchpoints for an expression that yields a
4277 double-precision floating-point number (which is typically 8 bytes
4278 wide). As a work-around, it might be possible to break the large region
4279 into a series of smaller ones and watch them with separate watchpoints.
4281 If you set too many hardware watchpoints, @value{GDBN} might be unable
4282 to insert all of them when you resume the execution of your program.
4283 Since the precise number of active watchpoints is unknown until such
4284 time as the program is about to be resumed, @value{GDBN} might not be
4285 able to warn you about this when you set the watchpoints, and the
4286 warning will be printed only when the program is resumed:
4289 Hardware watchpoint @var{num}: Could not insert watchpoint
4293 If this happens, delete or disable some of the watchpoints.
4295 Watching complex expressions that reference many variables can also
4296 exhaust the resources available for hardware-assisted watchpoints.
4297 That's because @value{GDBN} needs to watch every variable in the
4298 expression with separately allocated resources.
4300 If you call a function interactively using @code{print} or @code{call},
4301 any watchpoints you have set will be inactive until @value{GDBN} reaches another
4302 kind of breakpoint or the call completes.
4304 @value{GDBN} automatically deletes watchpoints that watch local
4305 (automatic) variables, or expressions that involve such variables, when
4306 they go out of scope, that is, when the execution leaves the block in
4307 which these variables were defined. In particular, when the program
4308 being debugged terminates, @emph{all} local variables go out of scope,
4309 and so only watchpoints that watch global variables remain set. If you
4310 rerun the program, you will need to set all such watchpoints again. One
4311 way of doing that would be to set a code breakpoint at the entry to the
4312 @code{main} function and when it breaks, set all the watchpoints.
4314 @cindex watchpoints and threads
4315 @cindex threads and watchpoints
4316 In multi-threaded programs, watchpoints will detect changes to the
4317 watched expression from every thread.
4320 @emph{Warning:} In multi-threaded programs, software watchpoints
4321 have only limited usefulness. If @value{GDBN} creates a software
4322 watchpoint, it can only watch the value of an expression @emph{in a
4323 single thread}. If you are confident that the expression can only
4324 change due to the current thread's activity (and if you are also
4325 confident that no other thread can become current), then you can use
4326 software watchpoints as usual. However, @value{GDBN} may not notice
4327 when a non-current thread's activity changes the expression. (Hardware
4328 watchpoints, in contrast, watch an expression in all threads.)
4331 @xref{set remote hardware-watchpoint-limit}.
4333 @node Set Catchpoints
4334 @subsection Setting Catchpoints
4335 @cindex catchpoints, setting
4336 @cindex exception handlers
4337 @cindex event handling
4339 You can use @dfn{catchpoints} to cause the debugger to stop for certain
4340 kinds of program events, such as C@t{++} exceptions or the loading of a
4341 shared library. Use the @code{catch} command to set a catchpoint.
4345 @item catch @var{event}
4346 Stop when @var{event} occurs. The @var{event} can be any of the following:
4349 @item throw @r{[}@var{regexp}@r{]}
4350 @itemx rethrow @r{[}@var{regexp}@r{]}
4351 @itemx catch @r{[}@var{regexp}@r{]}
4353 @kindex catch rethrow
4355 @cindex stop on C@t{++} exceptions
4356 The throwing, re-throwing, or catching of a C@t{++} exception.
4358 If @var{regexp} is given, then only exceptions whose type matches the
4359 regular expression will be caught.
4361 @vindex $_exception@r{, convenience variable}
4362 The convenience variable @code{$_exception} is available at an
4363 exception-related catchpoint, on some systems. This holds the
4364 exception being thrown.
4366 There are currently some limitations to C@t{++} exception handling in
4371 The support for these commands is system-dependent. Currently, only
4372 systems using the @samp{gnu-v3} C@t{++} ABI (@pxref{ABI}) are
4376 The regular expression feature and the @code{$_exception} convenience
4377 variable rely on the presence of some SDT probes in @code{libstdc++}.
4378 If these probes are not present, then these features cannot be used.
4379 These probes were first available in the GCC 4.8 release, but whether
4380 or not they are available in your GCC also depends on how it was
4384 The @code{$_exception} convenience variable is only valid at the
4385 instruction at which an exception-related catchpoint is set.
4388 When an exception-related catchpoint is hit, @value{GDBN} stops at a
4389 location in the system library which implements runtime exception
4390 support for C@t{++}, usually @code{libstdc++}. You can use @code{up}
4391 (@pxref{Selection}) to get to your code.
4394 If you call a function interactively, @value{GDBN} normally returns
4395 control to you when the function has finished executing. If the call
4396 raises an exception, however, the call may bypass the mechanism that
4397 returns control to you and cause your program either to abort or to
4398 simply continue running until it hits a breakpoint, catches a signal
4399 that @value{GDBN} is listening for, or exits. This is the case even if
4400 you set a catchpoint for the exception; catchpoints on exceptions are
4401 disabled within interactive calls. @xref{Calling}, for information on
4402 controlling this with @code{set unwind-on-terminating-exception}.
4405 You cannot raise an exception interactively.
4408 You cannot install an exception handler interactively.
4412 @kindex catch exception
4413 @cindex Ada exception catching
4414 @cindex catch Ada exceptions
4415 An Ada exception being raised. If an exception name is specified
4416 at the end of the command (eg @code{catch exception Program_Error}),
4417 the debugger will stop only when this specific exception is raised.
4418 Otherwise, the debugger stops execution when any Ada exception is raised.
4420 When inserting an exception catchpoint on a user-defined exception whose
4421 name is identical to one of the exceptions defined by the language, the
4422 fully qualified name must be used as the exception name. Otherwise,
4423 @value{GDBN} will assume that it should stop on the pre-defined exception
4424 rather than the user-defined one. For instance, assuming an exception
4425 called @code{Constraint_Error} is defined in package @code{Pck}, then
4426 the command to use to catch such exceptions is @kbd{catch exception
4427 Pck.Constraint_Error}.
4429 @item exception unhandled
4430 @kindex catch exception unhandled
4431 An exception that was raised but is not handled by the program.
4434 @kindex catch assert
4435 A failed Ada assertion.
4439 @cindex break on fork/exec
4440 A call to @code{exec}.
4443 @itemx syscall @r{[}@var{name} @r{|} @var{number} @r{|} @r{group:}@var{groupname} @r{|} @r{g:}@var{groupname}@r{]} @dots{}
4444 @kindex catch syscall
4445 @cindex break on a system call.
4446 A call to or return from a system call, a.k.a.@: @dfn{syscall}. A
4447 syscall is a mechanism for application programs to request a service
4448 from the operating system (OS) or one of the OS system services.
4449 @value{GDBN} can catch some or all of the syscalls issued by the
4450 debuggee, and show the related information for each syscall. If no
4451 argument is specified, calls to and returns from all system calls
4454 @var{name} can be any system call name that is valid for the
4455 underlying OS. Just what syscalls are valid depends on the OS. On
4456 GNU and Unix systems, you can find the full list of valid syscall
4457 names on @file{/usr/include/asm/unistd.h}.
4459 @c For MS-Windows, the syscall names and the corresponding numbers
4460 @c can be found, e.g., on this URL:
4461 @c http://www.metasploit.com/users/opcode/syscalls.html
4462 @c but we don't support Windows syscalls yet.
4464 Normally, @value{GDBN} knows in advance which syscalls are valid for
4465 each OS, so you can use the @value{GDBN} command-line completion
4466 facilities (@pxref{Completion,, command completion}) to list the
4469 You may also specify the system call numerically. A syscall's
4470 number is the value passed to the OS's syscall dispatcher to
4471 identify the requested service. When you specify the syscall by its
4472 name, @value{GDBN} uses its database of syscalls to convert the name
4473 into the corresponding numeric code, but using the number directly
4474 may be useful if @value{GDBN}'s database does not have the complete
4475 list of syscalls on your system (e.g., because @value{GDBN} lags
4476 behind the OS upgrades).
4478 You may specify a group of related syscalls to be caught at once using
4479 the @code{group:} syntax (@code{g:} is a shorter equivalent). For
4480 instance, on some platforms @value{GDBN} allows you to catch all
4481 network related syscalls, by passing the argument @code{group:network}
4482 to @code{catch syscall}. Note that not all syscall groups are
4483 available in every system. You can use the command completion
4484 facilities (@pxref{Completion,, command completion}) to list the
4485 syscall groups available on your environment.
4487 The example below illustrates how this command works if you don't provide
4491 (@value{GDBP}) catch syscall
4492 Catchpoint 1 (syscall)
4494 Starting program: /tmp/catch-syscall
4496 Catchpoint 1 (call to syscall 'close'), \
4497 0xffffe424 in __kernel_vsyscall ()
4501 Catchpoint 1 (returned from syscall 'close'), \
4502 0xffffe424 in __kernel_vsyscall ()
4506 Here is an example of catching a system call by name:
4509 (@value{GDBP}) catch syscall chroot
4510 Catchpoint 1 (syscall 'chroot' [61])
4512 Starting program: /tmp/catch-syscall
4514 Catchpoint 1 (call to syscall 'chroot'), \
4515 0xffffe424 in __kernel_vsyscall ()
4519 Catchpoint 1 (returned from syscall 'chroot'), \
4520 0xffffe424 in __kernel_vsyscall ()
4524 An example of specifying a system call numerically. In the case
4525 below, the syscall number has a corresponding entry in the XML
4526 file, so @value{GDBN} finds its name and prints it:
4529 (@value{GDBP}) catch syscall 252
4530 Catchpoint 1 (syscall(s) 'exit_group')
4532 Starting program: /tmp/catch-syscall
4534 Catchpoint 1 (call to syscall 'exit_group'), \
4535 0xffffe424 in __kernel_vsyscall ()
4539 Program exited normally.
4543 Here is an example of catching a syscall group:
4546 (@value{GDBP}) catch syscall group:process
4547 Catchpoint 1 (syscalls 'exit' [1] 'fork' [2] 'waitpid' [7]
4548 'execve' [11] 'wait4' [114] 'clone' [120] 'vfork' [190]
4549 'exit_group' [252] 'waitid' [284] 'unshare' [310])
4551 Starting program: /tmp/catch-syscall
4553 Catchpoint 1 (call to syscall fork), 0x00007ffff7df4e27 in open64 ()
4554 from /lib64/ld-linux-x86-64.so.2
4560 However, there can be situations when there is no corresponding name
4561 in XML file for that syscall number. In this case, @value{GDBN} prints
4562 a warning message saying that it was not able to find the syscall name,
4563 but the catchpoint will be set anyway. See the example below:
4566 (@value{GDBP}) catch syscall 764
4567 warning: The number '764' does not represent a known syscall.
4568 Catchpoint 2 (syscall 764)
4572 If you configure @value{GDBN} using the @samp{--without-expat} option,
4573 it will not be able to display syscall names. Also, if your
4574 architecture does not have an XML file describing its system calls,
4575 you will not be able to see the syscall names. It is important to
4576 notice that these two features are used for accessing the syscall
4577 name database. In either case, you will see a warning like this:
4580 (@value{GDBP}) catch syscall
4581 warning: Could not open "syscalls/i386-linux.xml"
4582 warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'.
4583 GDB will not be able to display syscall names.
4584 Catchpoint 1 (syscall)
4588 Of course, the file name will change depending on your architecture and system.
4590 Still using the example above, you can also try to catch a syscall by its
4591 number. In this case, you would see something like:
4594 (@value{GDBP}) catch syscall 252
4595 Catchpoint 1 (syscall(s) 252)
4598 Again, in this case @value{GDBN} would not be able to display syscall's names.
4602 A call to @code{fork}.
4606 A call to @code{vfork}.
4608 @item load @r{[}regexp@r{]}
4609 @itemx unload @r{[}regexp@r{]}
4611 @kindex catch unload
4612 The loading or unloading of a shared library. If @var{regexp} is
4613 given, then the catchpoint will stop only if the regular expression
4614 matches one of the affected libraries.
4616 @item signal @r{[}@var{signal}@dots{} @r{|} @samp{all}@r{]}
4617 @kindex catch signal
4618 The delivery of a signal.
4620 With no arguments, this catchpoint will catch any signal that is not
4621 used internally by @value{GDBN}, specifically, all signals except
4622 @samp{SIGTRAP} and @samp{SIGINT}.
4624 With the argument @samp{all}, all signals, including those used by
4625 @value{GDBN}, will be caught. This argument cannot be used with other
4628 Otherwise, the arguments are a list of signal names as given to
4629 @code{handle} (@pxref{Signals}). Only signals specified in this list
4632 One reason that @code{catch signal} can be more useful than
4633 @code{handle} is that you can attach commands and conditions to the
4636 When a signal is caught by a catchpoint, the signal's @code{stop} and
4637 @code{print} settings, as specified by @code{handle}, are ignored.
4638 However, whether the signal is still delivered to the inferior depends
4639 on the @code{pass} setting; this can be changed in the catchpoint's
4644 @item tcatch @var{event}
4646 Set a catchpoint that is enabled only for one stop. The catchpoint is
4647 automatically deleted after the first time the event is caught.
4651 Use the @code{info break} command to list the current catchpoints.
4655 @subsection Deleting Breakpoints
4657 @cindex clearing breakpoints, watchpoints, catchpoints
4658 @cindex deleting breakpoints, watchpoints, catchpoints
4659 It is often necessary to eliminate a breakpoint, watchpoint, or
4660 catchpoint once it has done its job and you no longer want your program
4661 to stop there. This is called @dfn{deleting} the breakpoint. A
4662 breakpoint that has been deleted no longer exists; it is forgotten.
4664 With the @code{clear} command you can delete breakpoints according to
4665 where they are in your program. With the @code{delete} command you can
4666 delete individual breakpoints, watchpoints, or catchpoints by specifying
4667 their breakpoint numbers.
4669 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
4670 automatically ignores breakpoints on the first instruction to be executed
4671 when you continue execution without changing the execution address.
4676 Delete any breakpoints at the next instruction to be executed in the
4677 selected stack frame (@pxref{Selection, ,Selecting a Frame}). When
4678 the innermost frame is selected, this is a good way to delete a
4679 breakpoint where your program just stopped.
4681 @item clear @var{location}
4682 Delete any breakpoints set at the specified @var{location}.
4683 @xref{Specify Location}, for the various forms of @var{location}; the
4684 most useful ones are listed below:
4687 @item clear @var{function}
4688 @itemx clear @var{filename}:@var{function}
4689 Delete any breakpoints set at entry to the named @var{function}.
4691 @item clear @var{linenum}
4692 @itemx clear @var{filename}:@var{linenum}
4693 Delete any breakpoints set at or within the code of the specified
4694 @var{linenum} of the specified @var{filename}.
4697 @cindex delete breakpoints
4699 @kindex d @r{(@code{delete})}
4700 @item delete @r{[}breakpoints@r{]} @r{[}@var{list}@dots{}@r{]}
4701 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
4702 list specified as argument. If no argument is specified, delete all
4703 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
4704 confirm off}). You can abbreviate this command as @code{d}.
4708 @subsection Disabling Breakpoints
4710 @cindex enable/disable a breakpoint
4711 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
4712 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
4713 it had been deleted, but remembers the information on the breakpoint so
4714 that you can @dfn{enable} it again later.
4716 You disable and enable breakpoints, watchpoints, and catchpoints with
4717 the @code{enable} and @code{disable} commands, optionally specifying
4718 one or more breakpoint numbers as arguments. Use @code{info break} to
4719 print a list of all breakpoints, watchpoints, and catchpoints if you
4720 do not know which numbers to use.
4722 Disabling and enabling a breakpoint that has multiple locations
4723 affects all of its locations.
4725 A breakpoint, watchpoint, or catchpoint can have any of several
4726 different states of enablement:
4730 Enabled. The breakpoint stops your program. A breakpoint set
4731 with the @code{break} command starts out in this state.
4733 Disabled. The breakpoint has no effect on your program.
4735 Enabled once. The breakpoint stops your program, but then becomes
4738 Enabled for a count. The breakpoint stops your program for the next
4739 N times, then becomes disabled.
4741 Enabled for deletion. The breakpoint stops your program, but
4742 immediately after it does so it is deleted permanently. A breakpoint
4743 set with the @code{tbreak} command starts out in this state.
4746 You can use the following commands to enable or disable breakpoints,
4747 watchpoints, and catchpoints:
4751 @kindex dis @r{(@code{disable})}
4752 @item disable @r{[}breakpoints@r{]} @r{[}@var{list}@dots{}@r{]}
4753 Disable the specified breakpoints---or all breakpoints, if none are
4754 listed. A disabled breakpoint has no effect but is not forgotten. All
4755 options such as ignore-counts, conditions and commands are remembered in
4756 case the breakpoint is enabled again later. You may abbreviate
4757 @code{disable} as @code{dis}.
4760 @item enable @r{[}breakpoints@r{]} @r{[}@var{list}@dots{}@r{]}
4761 Enable the specified breakpoints (or all defined breakpoints). They
4762 become effective once again in stopping your program.
4764 @item enable @r{[}breakpoints@r{]} once @var{list}@dots{}
4765 Enable the specified breakpoints temporarily. @value{GDBN} disables any
4766 of these breakpoints immediately after stopping your program.
4768 @item enable @r{[}breakpoints@r{]} count @var{count} @var{list}@dots{}
4769 Enable the specified breakpoints temporarily. @value{GDBN} records
4770 @var{count} with each of the specified breakpoints, and decrements a
4771 breakpoint's count when it is hit. When any count reaches 0,
4772 @value{GDBN} disables that breakpoint. If a breakpoint has an ignore
4773 count (@pxref{Conditions, ,Break Conditions}), that will be
4774 decremented to 0 before @var{count} is affected.
4776 @item enable @r{[}breakpoints@r{]} delete @var{list}@dots{}
4777 Enable the specified breakpoints to work once, then die. @value{GDBN}
4778 deletes any of these breakpoints as soon as your program stops there.
4779 Breakpoints set by the @code{tbreak} command start out in this state.
4782 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
4783 @c confusing: tbreak is also initially enabled.
4784 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
4785 ,Setting Breakpoints}), breakpoints that you set are initially enabled;
4786 subsequently, they become disabled or enabled only when you use one of
4787 the commands above. (The command @code{until} can set and delete a
4788 breakpoint of its own, but it does not change the state of your other
4789 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
4793 @subsection Break Conditions
4794 @cindex conditional breakpoints
4795 @cindex breakpoint conditions
4797 @c FIXME what is scope of break condition expr? Context where wanted?
4798 @c in particular for a watchpoint?
4799 The simplest sort of breakpoint breaks every time your program reaches a
4800 specified place. You can also specify a @dfn{condition} for a
4801 breakpoint. A condition is just a Boolean expression in your
4802 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
4803 a condition evaluates the expression each time your program reaches it,
4804 and your program stops only if the condition is @emph{true}.
4806 This is the converse of using assertions for program validation; in that
4807 situation, you want to stop when the assertion is violated---that is,
4808 when the condition is false. In C, if you want to test an assertion expressed
4809 by the condition @var{assert}, you should set the condition
4810 @samp{! @var{assert}} on the appropriate breakpoint.
4812 Conditions are also accepted for watchpoints; you may not need them,
4813 since a watchpoint is inspecting the value of an expression anyhow---but
4814 it might be simpler, say, to just set a watchpoint on a variable name,
4815 and specify a condition that tests whether the new value is an interesting
4818 Break conditions can have side effects, and may even call functions in
4819 your program. This can be useful, for example, to activate functions
4820 that log program progress, or to use your own print functions to
4821 format special data structures. The effects are completely predictable
4822 unless there is another enabled breakpoint at the same address. (In
4823 that case, @value{GDBN} might see the other breakpoint first and stop your
4824 program without checking the condition of this one.) Note that
4825 breakpoint commands are usually more convenient and flexible than break
4827 purpose of performing side effects when a breakpoint is reached
4828 (@pxref{Break Commands, ,Breakpoint Command Lists}).
4830 Breakpoint conditions can also be evaluated on the target's side if
4831 the target supports it. Instead of evaluating the conditions locally,
4832 @value{GDBN} encodes the expression into an agent expression
4833 (@pxref{Agent Expressions}) suitable for execution on the target,
4834 independently of @value{GDBN}. Global variables become raw memory
4835 locations, locals become stack accesses, and so forth.
4837 In this case, @value{GDBN} will only be notified of a breakpoint trigger
4838 when its condition evaluates to true. This mechanism may provide faster
4839 response times depending on the performance characteristics of the target
4840 since it does not need to keep @value{GDBN} informed about
4841 every breakpoint trigger, even those with false conditions.
4843 Break conditions can be specified when a breakpoint is set, by using
4844 @samp{if} in the arguments to the @code{break} command. @xref{Set
4845 Breaks, ,Setting Breakpoints}. They can also be changed at any time
4846 with the @code{condition} command.
4848 You can also use the @code{if} keyword with the @code{watch} command.
4849 The @code{catch} command does not recognize the @code{if} keyword;
4850 @code{condition} is the only way to impose a further condition on a
4855 @item condition @var{bnum} @var{expression}
4856 Specify @var{expression} as the break condition for breakpoint,
4857 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
4858 breakpoint @var{bnum} stops your program only if the value of
4859 @var{expression} is true (nonzero, in C). When you use
4860 @code{condition}, @value{GDBN} checks @var{expression} immediately for
4861 syntactic correctness, and to determine whether symbols in it have
4862 referents in the context of your breakpoint. If @var{expression} uses
4863 symbols not referenced in the context of the breakpoint, @value{GDBN}
4864 prints an error message:
4867 No symbol "foo" in current context.
4872 not actually evaluate @var{expression} at the time the @code{condition}
4873 command (or a command that sets a breakpoint with a condition, like
4874 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
4876 @item condition @var{bnum}
4877 Remove the condition from breakpoint number @var{bnum}. It becomes
4878 an ordinary unconditional breakpoint.
4881 @cindex ignore count (of breakpoint)
4882 A special case of a breakpoint condition is to stop only when the
4883 breakpoint has been reached a certain number of times. This is so
4884 useful that there is a special way to do it, using the @dfn{ignore
4885 count} of the breakpoint. Every breakpoint has an ignore count, which
4886 is an integer. Most of the time, the ignore count is zero, and
4887 therefore has no effect. But if your program reaches a breakpoint whose
4888 ignore count is positive, then instead of stopping, it just decrements
4889 the ignore count by one and continues. As a result, if the ignore count
4890 value is @var{n}, the breakpoint does not stop the next @var{n} times
4891 your program reaches it.
4895 @item ignore @var{bnum} @var{count}
4896 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
4897 The next @var{count} times the breakpoint is reached, your program's
4898 execution does not stop; other than to decrement the ignore count, @value{GDBN}
4901 To make the breakpoint stop the next time it is reached, specify
4904 When you use @code{continue} to resume execution of your program from a
4905 breakpoint, you can specify an ignore count directly as an argument to
4906 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
4907 Stepping,,Continuing and Stepping}.
4909 If a breakpoint has a positive ignore count and a condition, the
4910 condition is not checked. Once the ignore count reaches zero,
4911 @value{GDBN} resumes checking the condition.
4913 You could achieve the effect of the ignore count with a condition such
4914 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
4915 is decremented each time. @xref{Convenience Vars, ,Convenience
4919 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
4922 @node Break Commands
4923 @subsection Breakpoint Command Lists
4925 @cindex breakpoint commands
4926 You can give any breakpoint (or watchpoint or catchpoint) a series of
4927 commands to execute when your program stops due to that breakpoint. For
4928 example, you might want to print the values of certain expressions, or
4929 enable other breakpoints.
4933 @kindex end@r{ (breakpoint commands)}
4934 @item commands @r{[}@var{list}@dots{}@r{]}
4935 @itemx @dots{} @var{command-list} @dots{}
4937 Specify a list of commands for the given breakpoints. The commands
4938 themselves appear on the following lines. Type a line containing just
4939 @code{end} to terminate the commands.
4941 To remove all commands from a breakpoint, type @code{commands} and
4942 follow it immediately with @code{end}; that is, give no commands.
4944 With no argument, @code{commands} refers to the last breakpoint,
4945 watchpoint, or catchpoint set (not to the breakpoint most recently
4946 encountered). If the most recent breakpoints were set with a single
4947 command, then the @code{commands} will apply to all the breakpoints
4948 set by that command. This applies to breakpoints set by
4949 @code{rbreak}, and also applies when a single @code{break} command
4950 creates multiple breakpoints (@pxref{Ambiguous Expressions,,Ambiguous
4954 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
4955 disabled within a @var{command-list}.
4957 You can use breakpoint commands to start your program up again. Simply
4958 use the @code{continue} command, or @code{step}, or any other command
4959 that resumes execution.
4961 Any other commands in the command list, after a command that resumes
4962 execution, are ignored. This is because any time you resume execution
4963 (even with a simple @code{next} or @code{step}), you may encounter
4964 another breakpoint---which could have its own command list, leading to
4965 ambiguities about which list to execute.
4968 If the first command you specify in a command list is @code{silent}, the
4969 usual message about stopping at a breakpoint is not printed. This may
4970 be desirable for breakpoints that are to print a specific message and
4971 then continue. If none of the remaining commands print anything, you
4972 see no sign that the breakpoint was reached. @code{silent} is
4973 meaningful only at the beginning of a breakpoint command list.
4975 The commands @code{echo}, @code{output}, and @code{printf} allow you to
4976 print precisely controlled output, and are often useful in silent
4977 breakpoints. @xref{Output, ,Commands for Controlled Output}.
4979 For example, here is how you could use breakpoint commands to print the
4980 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
4986 printf "x is %d\n",x
4991 One application for breakpoint commands is to compensate for one bug so
4992 you can test for another. Put a breakpoint just after the erroneous line
4993 of code, give it a condition to detect the case in which something
4994 erroneous has been done, and give it commands to assign correct values
4995 to any variables that need them. End with the @code{continue} command
4996 so that your program does not stop, and start with the @code{silent}
4997 command so that no output is produced. Here is an example:
5008 @node Dynamic Printf
5009 @subsection Dynamic Printf
5011 @cindex dynamic printf
5013 The dynamic printf command @code{dprintf} combines a breakpoint with
5014 formatted printing of your program's data to give you the effect of
5015 inserting @code{printf} calls into your program on-the-fly, without
5016 having to recompile it.
5018 In its most basic form, the output goes to the GDB console. However,
5019 you can set the variable @code{dprintf-style} for alternate handling.
5020 For instance, you can ask to format the output by calling your
5021 program's @code{printf} function. This has the advantage that the
5022 characters go to the program's output device, so they can recorded in
5023 redirects to files and so forth.
5025 If you are doing remote debugging with a stub or agent, you can also
5026 ask to have the printf handled by the remote agent. In addition to
5027 ensuring that the output goes to the remote program's device along
5028 with any other output the program might produce, you can also ask that
5029 the dprintf remain active even after disconnecting from the remote
5030 target. Using the stub/agent is also more efficient, as it can do
5031 everything without needing to communicate with @value{GDBN}.
5035 @item dprintf @var{location},@var{template},@var{expression}[,@var{expression}@dots{}]
5036 Whenever execution reaches @var{location}, print the values of one or
5037 more @var{expressions} under the control of the string @var{template}.
5038 To print several values, separate them with commas.
5040 @item set dprintf-style @var{style}
5041 Set the dprintf output to be handled in one of several different
5042 styles enumerated below. A change of style affects all existing
5043 dynamic printfs immediately. (If you need individual control over the
5044 print commands, simply define normal breakpoints with
5045 explicitly-supplied command lists.)
5049 @kindex dprintf-style gdb
5050 Handle the output using the @value{GDBN} @code{printf} command.
5053 @kindex dprintf-style call
5054 Handle the output by calling a function in your program (normally
5058 @kindex dprintf-style agent
5059 Have the remote debugging agent (such as @code{gdbserver}) handle
5060 the output itself. This style is only available for agents that
5061 support running commands on the target.
5064 @item set dprintf-function @var{function}
5065 Set the function to call if the dprintf style is @code{call}. By
5066 default its value is @code{printf}. You may set it to any expression.
5067 that @value{GDBN} can evaluate to a function, as per the @code{call}
5070 @item set dprintf-channel @var{channel}
5071 Set a ``channel'' for dprintf. If set to a non-empty value,
5072 @value{GDBN} will evaluate it as an expression and pass the result as
5073 a first argument to the @code{dprintf-function}, in the manner of
5074 @code{fprintf} and similar functions. Otherwise, the dprintf format
5075 string will be the first argument, in the manner of @code{printf}.
5077 As an example, if you wanted @code{dprintf} output to go to a logfile
5078 that is a standard I/O stream assigned to the variable @code{mylog},
5079 you could do the following:
5082 (gdb) set dprintf-style call
5083 (gdb) set dprintf-function fprintf
5084 (gdb) set dprintf-channel mylog
5085 (gdb) dprintf 25,"at line 25, glob=%d\n",glob
5086 Dprintf 1 at 0x123456: file main.c, line 25.
5088 1 dprintf keep y 0x00123456 in main at main.c:25
5089 call (void) fprintf (mylog,"at line 25, glob=%d\n",glob)
5094 Note that the @code{info break} displays the dynamic printf commands
5095 as normal breakpoint commands; you can thus easily see the effect of
5096 the variable settings.
5098 @item set disconnected-dprintf on
5099 @itemx set disconnected-dprintf off
5100 @kindex set disconnected-dprintf
5101 Choose whether @code{dprintf} commands should continue to run if
5102 @value{GDBN} has disconnected from the target. This only applies
5103 if the @code{dprintf-style} is @code{agent}.
5105 @item show disconnected-dprintf off
5106 @kindex show disconnected-dprintf
5107 Show the current choice for disconnected @code{dprintf}.
5111 @value{GDBN} does not check the validity of function and channel,
5112 relying on you to supply values that are meaningful for the contexts
5113 in which they are being used. For instance, the function and channel
5114 may be the values of local variables, but if that is the case, then
5115 all enabled dynamic prints must be at locations within the scope of
5116 those locals. If evaluation fails, @value{GDBN} will report an error.
5118 @node Save Breakpoints
5119 @subsection How to save breakpoints to a file
5121 To save breakpoint definitions to a file use the @w{@code{save
5122 breakpoints}} command.
5125 @kindex save breakpoints
5126 @cindex save breakpoints to a file for future sessions
5127 @item save breakpoints [@var{filename}]
5128 This command saves all current breakpoint definitions together with
5129 their commands and ignore counts, into a file @file{@var{filename}}
5130 suitable for use in a later debugging session. This includes all
5131 types of breakpoints (breakpoints, watchpoints, catchpoints,
5132 tracepoints). To read the saved breakpoint definitions, use the
5133 @code{source} command (@pxref{Command Files}). Note that watchpoints
5134 with expressions involving local variables may fail to be recreated
5135 because it may not be possible to access the context where the
5136 watchpoint is valid anymore. Because the saved breakpoint definitions
5137 are simply a sequence of @value{GDBN} commands that recreate the
5138 breakpoints, you can edit the file in your favorite editing program,
5139 and remove the breakpoint definitions you're not interested in, or
5140 that can no longer be recreated.
5143 @node Static Probe Points
5144 @subsection Static Probe Points
5146 @cindex static probe point, SystemTap
5147 @cindex static probe point, DTrace
5148 @value{GDBN} supports @dfn{SDT} probes in the code. @acronym{SDT} stands
5149 for Statically Defined Tracing, and the probes are designed to have a tiny
5150 runtime code and data footprint, and no dynamic relocations.
5152 Currently, the following types of probes are supported on
5153 ELF-compatible systems:
5157 @item @code{SystemTap} (@uref{http://sourceware.org/systemtap/})
5158 @acronym{SDT} probes@footnote{See
5159 @uref{http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps}
5160 for more information on how to add @code{SystemTap} @acronym{SDT}
5161 probes in your applications.}. @code{SystemTap} probes are usable
5162 from assembly, C and C@t{++} languages@footnote{See
5163 @uref{http://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation}
5164 for a good reference on how the @acronym{SDT} probes are implemented.}.
5166 @item @code{DTrace} (@uref{http://oss.oracle.com/projects/DTrace})
5167 @acronym{USDT} probes. @code{DTrace} probes are usable from C and
5171 @cindex semaphores on static probe points
5172 Some @code{SystemTap} probes have an associated semaphore variable;
5173 for instance, this happens automatically if you defined your probe
5174 using a DTrace-style @file{.d} file. If your probe has a semaphore,
5175 @value{GDBN} will automatically enable it when you specify a
5176 breakpoint using the @samp{-probe-stap} notation. But, if you put a
5177 breakpoint at a probe's location by some other method (e.g.,
5178 @code{break file:line}), then @value{GDBN} will not automatically set
5179 the semaphore. @code{DTrace} probes do not support semaphores.
5181 You can examine the available static static probes using @code{info
5182 probes}, with optional arguments:
5186 @item info probes @r{[}@var{type}@r{]} @r{[}@var{provider} @r{[}@var{name} @r{[}@var{objfile}@r{]}@r{]}@r{]}
5187 If given, @var{type} is either @code{stap} for listing
5188 @code{SystemTap} probes or @code{dtrace} for listing @code{DTrace}
5189 probes. If omitted all probes are listed regardless of their types.
5191 If given, @var{provider} is a regular expression used to match against provider
5192 names when selecting which probes to list. If omitted, probes by all
5193 probes from all providers are listed.
5195 If given, @var{name} is a regular expression to match against probe names
5196 when selecting which probes to list. If omitted, probe names are not
5197 considered when deciding whether to display them.
5199 If given, @var{objfile} is a regular expression used to select which
5200 object files (executable or shared libraries) to examine. If not
5201 given, all object files are considered.
5203 @item info probes all
5204 List the available static probes, from all types.
5207 @cindex enabling and disabling probes
5208 Some probe points can be enabled and/or disabled. The effect of
5209 enabling or disabling a probe depends on the type of probe being
5210 handled. Some @code{DTrace} probes can be enabled or
5211 disabled, but @code{SystemTap} probes cannot be disabled.
5213 You can enable (or disable) one or more probes using the following
5214 commands, with optional arguments:
5217 @kindex enable probes
5218 @item enable probes @r{[}@var{provider} @r{[}@var{name} @r{[}@var{objfile}@r{]}@r{]}@r{]}
5219 If given, @var{provider} is a regular expression used to match against
5220 provider names when selecting which probes to enable. If omitted,
5221 all probes from all providers are enabled.
5223 If given, @var{name} is a regular expression to match against probe
5224 names when selecting which probes to enable. If omitted, probe names
5225 are not considered when deciding whether to enable them.
5227 If given, @var{objfile} is a regular expression used to select which
5228 object files (executable or shared libraries) to examine. If not
5229 given, all object files are considered.
5231 @kindex disable probes
5232 @item disable probes @r{[}@var{provider} @r{[}@var{name} @r{[}@var{objfile}@r{]}@r{]}@r{]}
5233 See the @code{enable probes} command above for a description of the
5234 optional arguments accepted by this command.
5237 @vindex $_probe_arg@r{, convenience variable}
5238 A probe may specify up to twelve arguments. These are available at the
5239 point at which the probe is defined---that is, when the current PC is
5240 at the probe's location. The arguments are available using the
5241 convenience variables (@pxref{Convenience Vars})
5242 @code{$_probe_arg0}@dots{}@code{$_probe_arg11}. In @code{SystemTap}
5243 probes each probe argument is an integer of the appropriate size;
5244 types are not preserved. In @code{DTrace} probes types are preserved
5245 provided that they are recognized as such by @value{GDBN}; otherwise
5246 the value of the probe argument will be a long integer. The
5247 convenience variable @code{$_probe_argc} holds the number of arguments
5248 at the current probe point.
5250 These variables are always available, but attempts to access them at
5251 any location other than a probe point will cause @value{GDBN} to give
5255 @c @ifclear BARETARGET
5256 @node Error in Breakpoints
5257 @subsection ``Cannot insert breakpoints''
5259 If you request too many active hardware-assisted breakpoints and
5260 watchpoints, you will see this error message:
5262 @c FIXME: the precise wording of this message may change; the relevant
5263 @c source change is not committed yet (Sep 3, 1999).
5265 Stopped; cannot insert breakpoints.
5266 You may have requested too many hardware breakpoints and watchpoints.
5270 This message is printed when you attempt to resume the program, since
5271 only then @value{GDBN} knows exactly how many hardware breakpoints and
5272 watchpoints it needs to insert.
5274 When this message is printed, you need to disable or remove some of the
5275 hardware-assisted breakpoints and watchpoints, and then continue.
5277 @node Breakpoint-related Warnings
5278 @subsection ``Breakpoint address adjusted...''
5279 @cindex breakpoint address adjusted
5281 Some processor architectures place constraints on the addresses at
5282 which breakpoints may be placed. For architectures thus constrained,
5283 @value{GDBN} will attempt to adjust the breakpoint's address to comply
5284 with the constraints dictated by the architecture.
5286 One example of such an architecture is the Fujitsu FR-V. The FR-V is
5287 a VLIW architecture in which a number of RISC-like instructions may be
5288 bundled together for parallel execution. The FR-V architecture
5289 constrains the location of a breakpoint instruction within such a
5290 bundle to the instruction with the lowest address. @value{GDBN}
5291 honors this constraint by adjusting a breakpoint's address to the
5292 first in the bundle.
5294 It is not uncommon for optimized code to have bundles which contain
5295 instructions from different source statements, thus it may happen that
5296 a breakpoint's address will be adjusted from one source statement to
5297 another. Since this adjustment may significantly alter @value{GDBN}'s
5298 breakpoint related behavior from what the user expects, a warning is
5299 printed when the breakpoint is first set and also when the breakpoint
5302 A warning like the one below is printed when setting a breakpoint
5303 that's been subject to address adjustment:
5306 warning: Breakpoint address adjusted from 0x00010414 to 0x00010410.
5309 Such warnings are printed both for user settable and @value{GDBN}'s
5310 internal breakpoints. If you see one of these warnings, you should
5311 verify that a breakpoint set at the adjusted address will have the
5312 desired affect. If not, the breakpoint in question may be removed and
5313 other breakpoints may be set which will have the desired behavior.
5314 E.g., it may be sufficient to place the breakpoint at a later
5315 instruction. A conditional breakpoint may also be useful in some
5316 cases to prevent the breakpoint from triggering too often.
5318 @value{GDBN} will also issue a warning when stopping at one of these
5319 adjusted breakpoints:
5322 warning: Breakpoint 1 address previously adjusted from 0x00010414
5326 When this warning is encountered, it may be too late to take remedial
5327 action except in cases where the breakpoint is hit earlier or more
5328 frequently than expected.
5330 @node Continuing and Stepping
5331 @section Continuing and Stepping
5335 @cindex resuming execution
5336 @dfn{Continuing} means resuming program execution until your program
5337 completes normally. In contrast, @dfn{stepping} means executing just
5338 one more ``step'' of your program, where ``step'' may mean either one
5339 line of source code, or one machine instruction (depending on what
5340 particular command you use). Either when continuing or when stepping,
5341 your program may stop even sooner, due to a breakpoint or a signal. (If
5342 it stops due to a signal, you may want to use @code{handle}, or use
5343 @samp{signal 0} to resume execution (@pxref{Signals, ,Signals}),
5344 or you may step into the signal's handler (@pxref{stepping and signal
5349 @kindex c @r{(@code{continue})}
5350 @kindex fg @r{(resume foreground execution)}
5351 @item continue @r{[}@var{ignore-count}@r{]}
5352 @itemx c @r{[}@var{ignore-count}@r{]}
5353 @itemx fg @r{[}@var{ignore-count}@r{]}
5354 Resume program execution, at the address where your program last stopped;
5355 any breakpoints set at that address are bypassed. The optional argument
5356 @var{ignore-count} allows you to specify a further number of times to
5357 ignore a breakpoint at this location; its effect is like that of
5358 @code{ignore} (@pxref{Conditions, ,Break Conditions}).
5360 The argument @var{ignore-count} is meaningful only when your program
5361 stopped due to a breakpoint. At other times, the argument to
5362 @code{continue} is ignored.
5364 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
5365 debugged program is deemed to be the foreground program) are provided
5366 purely for convenience, and have exactly the same behavior as
5370 To resume execution at a different place, you can use @code{return}
5371 (@pxref{Returning, ,Returning from a Function}) to go back to the
5372 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
5373 Different Address}) to go to an arbitrary location in your program.
5375 A typical technique for using stepping is to set a breakpoint
5376 (@pxref{Breakpoints, ,Breakpoints; Watchpoints; and Catchpoints}) at the
5377 beginning of the function or the section of your program where a problem
5378 is believed to lie, run your program until it stops at that breakpoint,
5379 and then step through the suspect area, examining the variables that are
5380 interesting, until you see the problem happen.
5384 @kindex s @r{(@code{step})}
5386 Continue running your program until control reaches a different source
5387 line, then stop it and return control to @value{GDBN}. This command is
5388 abbreviated @code{s}.
5391 @c "without debugging information" is imprecise; actually "without line
5392 @c numbers in the debugging information". (gcc -g1 has debugging info but
5393 @c not line numbers). But it seems complex to try to make that
5394 @c distinction here.
5395 @emph{Warning:} If you use the @code{step} command while control is
5396 within a function that was compiled without debugging information,
5397 execution proceeds until control reaches a function that does have
5398 debugging information. Likewise, it will not step into a function which
5399 is compiled without debugging information. To step through functions
5400 without debugging information, use the @code{stepi} command, described
5404 The @code{step} command only stops at the first instruction of a source
5405 line. This prevents the multiple stops that could otherwise occur in
5406 @code{switch} statements, @code{for} loops, etc. @code{step} continues
5407 to stop if a function that has debugging information is called within
5408 the line. In other words, @code{step} @emph{steps inside} any functions
5409 called within the line.
5411 Also, the @code{step} command only enters a function if there is line
5412 number information for the function. Otherwise it acts like the
5413 @code{next} command. This avoids problems when using @code{cc -gl}
5414 on @acronym{MIPS} machines. Previously, @code{step} entered subroutines if there
5415 was any debugging information about the routine.
5417 @item step @var{count}
5418 Continue running as in @code{step}, but do so @var{count} times. If a
5419 breakpoint is reached, or a signal not related to stepping occurs before
5420 @var{count} steps, stepping stops right away.
5423 @kindex n @r{(@code{next})}
5424 @item next @r{[}@var{count}@r{]}
5425 Continue to the next source line in the current (innermost) stack frame.
5426 This is similar to @code{step}, but function calls that appear within
5427 the line of code are executed without stopping. Execution stops when
5428 control reaches a different line of code at the original stack level
5429 that was executing when you gave the @code{next} command. This command
5430 is abbreviated @code{n}.
5432 An argument @var{count} is a repeat count, as for @code{step}.
5435 @c FIX ME!! Do we delete this, or is there a way it fits in with
5436 @c the following paragraph? --- Vctoria
5438 @c @code{next} within a function that lacks debugging information acts like
5439 @c @code{step}, but any function calls appearing within the code of the
5440 @c function are executed without stopping.
5442 The @code{next} command only stops at the first instruction of a
5443 source line. This prevents multiple stops that could otherwise occur in
5444 @code{switch} statements, @code{for} loops, etc.
5446 @kindex set step-mode
5448 @cindex functions without line info, and stepping
5449 @cindex stepping into functions with no line info
5450 @itemx set step-mode on
5451 The @code{set step-mode on} command causes the @code{step} command to
5452 stop at the first instruction of a function which contains no debug line
5453 information rather than stepping over it.
5455 This is useful in cases where you may be interested in inspecting the
5456 machine instructions of a function which has no symbolic info and do not
5457 want @value{GDBN} to automatically skip over this function.
5459 @item set step-mode off
5460 Causes the @code{step} command to step over any functions which contains no
5461 debug information. This is the default.
5463 @item show step-mode
5464 Show whether @value{GDBN} will stop in or step over functions without
5465 source line debug information.
5468 @kindex fin @r{(@code{finish})}
5470 Continue running until just after function in the selected stack frame
5471 returns. Print the returned value (if any). This command can be
5472 abbreviated as @code{fin}.
5474 Contrast this with the @code{return} command (@pxref{Returning,
5475 ,Returning from a Function}).
5478 @kindex u @r{(@code{until})}
5479 @cindex run until specified location
5482 Continue running until a source line past the current line, in the
5483 current stack frame, is reached. This command is used to avoid single
5484 stepping through a loop more than once. It is like the @code{next}
5485 command, except that when @code{until} encounters a jump, it
5486 automatically continues execution until the program counter is greater
5487 than the address of the jump.
5489 This means that when you reach the end of a loop after single stepping
5490 though it, @code{until} makes your program continue execution until it
5491 exits the loop. In contrast, a @code{next} command at the end of a loop
5492 simply steps back to the beginning of the loop, which forces you to step
5493 through the next iteration.
5495 @code{until} always stops your program if it attempts to exit the current
5498 @code{until} may produce somewhat counterintuitive results if the order
5499 of machine code does not match the order of the source lines. For
5500 example, in the following excerpt from a debugging session, the @code{f}
5501 (@code{frame}) command shows that execution is stopped at line
5502 @code{206}; yet when we use @code{until}, we get to line @code{195}:
5506 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
5508 (@value{GDBP}) until
5509 195 for ( ; argc > 0; NEXTARG) @{
5512 This happened because, for execution efficiency, the compiler had
5513 generated code for the loop closure test at the end, rather than the
5514 start, of the loop---even though the test in a C @code{for}-loop is
5515 written before the body of the loop. The @code{until} command appeared
5516 to step back to the beginning of the loop when it advanced to this
5517 expression; however, it has not really gone to an earlier
5518 statement---not in terms of the actual machine code.
5520 @code{until} with no argument works by means of single
5521 instruction stepping, and hence is slower than @code{until} with an
5524 @item until @var{location}
5525 @itemx u @var{location}
5526 Continue running your program until either the specified @var{location} is
5527 reached, or the current stack frame returns. The location is any of
5528 the forms described in @ref{Specify Location}.
5529 This form of the command uses temporary breakpoints, and
5530 hence is quicker than @code{until} without an argument. The specified
5531 location is actually reached only if it is in the current frame. This
5532 implies that @code{until} can be used to skip over recursive function
5533 invocations. For instance in the code below, if the current location is
5534 line @code{96}, issuing @code{until 99} will execute the program up to
5535 line @code{99} in the same invocation of factorial, i.e., after the inner
5536 invocations have returned.
5539 94 int factorial (int value)
5541 96 if (value > 1) @{
5542 97 value *= factorial (value - 1);
5549 @kindex advance @var{location}
5550 @item advance @var{location}
5551 Continue running the program up to the given @var{location}. An argument is
5552 required, which should be of one of the forms described in
5553 @ref{Specify Location}.
5554 Execution will also stop upon exit from the current stack
5555 frame. This command is similar to @code{until}, but @code{advance} will
5556 not skip over recursive function calls, and the target location doesn't
5557 have to be in the same frame as the current one.
5561 @kindex si @r{(@code{stepi})}
5563 @itemx stepi @var{arg}
5565 Execute one machine instruction, then stop and return to the debugger.
5567 It is often useful to do @samp{display/i $pc} when stepping by machine
5568 instructions. This makes @value{GDBN} automatically display the next
5569 instruction to be executed, each time your program stops. @xref{Auto
5570 Display,, Automatic Display}.
5572 An argument is a repeat count, as in @code{step}.
5576 @kindex ni @r{(@code{nexti})}
5578 @itemx nexti @var{arg}
5580 Execute one machine instruction, but if it is a function call,
5581 proceed until the function returns.
5583 An argument is a repeat count, as in @code{next}.
5587 @anchor{range stepping}
5588 @cindex range stepping
5589 @cindex target-assisted range stepping
5590 By default, and if available, @value{GDBN} makes use of
5591 target-assisted @dfn{range stepping}. In other words, whenever you
5592 use a stepping command (e.g., @code{step}, @code{next}), @value{GDBN}
5593 tells the target to step the corresponding range of instruction
5594 addresses instead of issuing multiple single-steps. This speeds up
5595 line stepping, particularly for remote targets. Ideally, there should
5596 be no reason you would want to turn range stepping off. However, it's
5597 possible that a bug in the debug info, a bug in the remote stub (for
5598 remote targets), or even a bug in @value{GDBN} could make line
5599 stepping behave incorrectly when target-assisted range stepping is
5600 enabled. You can use the following command to turn off range stepping
5604 @kindex set range-stepping
5605 @kindex show range-stepping
5606 @item set range-stepping
5607 @itemx show range-stepping
5608 Control whether range stepping is enabled.
5610 If @code{on}, and the target supports it, @value{GDBN} tells the
5611 target to step a range of addresses itself, instead of issuing
5612 multiple single-steps. If @code{off}, @value{GDBN} always issues
5613 single-steps, even if range stepping is supported by the target. The
5614 default is @code{on}.
5618 @node Skipping Over Functions and Files
5619 @section Skipping Over Functions and Files
5620 @cindex skipping over functions and files
5622 The program you are debugging may contain some functions which are
5623 uninteresting to debug. The @code{skip} command lets you tell @value{GDBN} to
5624 skip a function, all functions in a file or a particular function in
5625 a particular file when stepping.
5627 For example, consider the following C function:
5638 Suppose you wish to step into the functions @code{foo} and @code{bar}, but you
5639 are not interested in stepping through @code{boring}. If you run @code{step}
5640 at line 103, you'll enter @code{boring()}, but if you run @code{next}, you'll
5641 step over both @code{foo} and @code{boring}!
5643 One solution is to @code{step} into @code{boring} and use the @code{finish}
5644 command to immediately exit it. But this can become tedious if @code{boring}
5645 is called from many places.
5647 A more flexible solution is to execute @kbd{skip boring}. This instructs
5648 @value{GDBN} never to step into @code{boring}. Now when you execute
5649 @code{step} at line 103, you'll step over @code{boring} and directly into
5652 Functions may be skipped by providing either a function name, linespec
5653 (@pxref{Specify Location}), regular expression that matches the function's
5654 name, file name or a @code{glob}-style pattern that matches the file name.
5656 On Posix systems the form of the regular expression is
5657 ``Extended Regular Expressions''. See for example @samp{man 7 regex}
5658 on @sc{gnu}/Linux systems. On non-Posix systems the form of the regular
5659 expression is whatever is provided by the @code{regcomp} function of
5660 the underlying system.
5661 See for example @samp{man 7 glob} on @sc{gnu}/Linux systems for a
5662 description of @code{glob}-style patterns.
5666 @item skip @r{[}@var{options}@r{]}
5667 The basic form of the @code{skip} command takes zero or more options
5668 that specify what to skip.
5669 The @var{options} argument is any useful combination of the following:
5672 @item -file @var{file}
5673 @itemx -fi @var{file}
5674 Functions in @var{file} will be skipped over when stepping.
5676 @item -gfile @var{file-glob-pattern}
5677 @itemx -gfi @var{file-glob-pattern}
5678 @cindex skipping over files via glob-style patterns
5679 Functions in files matching @var{file-glob-pattern} will be skipped
5683 (gdb) skip -gfi utils/*.c
5686 @item -function @var{linespec}
5687 @itemx -fu @var{linespec}
5688 Functions named by @var{linespec} or the function containing the line
5689 named by @var{linespec} will be skipped over when stepping.
5690 @xref{Specify Location}.
5692 @item -rfunction @var{regexp}
5693 @itemx -rfu @var{regexp}
5694 @cindex skipping over functions via regular expressions
5695 Functions whose name matches @var{regexp} will be skipped over when stepping.
5697 This form is useful for complex function names.
5698 For example, there is generally no need to step into C@t{++} @code{std::string}
5699 constructors or destructors. Plus with C@t{++} templates it can be hard to
5700 write out the full name of the function, and often it doesn't matter what
5701 the template arguments are. Specifying the function to be skipped as a
5702 regular expression makes this easier.
5705 (gdb) skip -rfu ^std::(allocator|basic_string)<.*>::~?\1 *\(
5708 If you want to skip every templated C@t{++} constructor and destructor
5709 in the @code{std} namespace you can do:
5712 (gdb) skip -rfu ^std::([a-zA-z0-9_]+)<.*>::~?\1 *\(
5716 If no options are specified, the function you're currently debugging
5719 @kindex skip function
5720 @item skip function @r{[}@var{linespec}@r{]}
5721 After running this command, the function named by @var{linespec} or the
5722 function containing the line named by @var{linespec} will be skipped over when
5723 stepping. @xref{Specify Location}.
5725 If you do not specify @var{linespec}, the function you're currently debugging
5728 (If you have a function called @code{file} that you want to skip, use
5729 @kbd{skip function file}.)
5732 @item skip file @r{[}@var{filename}@r{]}
5733 After running this command, any function whose source lives in @var{filename}
5734 will be skipped over when stepping.
5737 (gdb) skip file boring.c
5738 File boring.c will be skipped when stepping.
5741 If you do not specify @var{filename}, functions whose source lives in the file
5742 you're currently debugging will be skipped.
5745 Skips can be listed, deleted, disabled, and enabled, much like breakpoints.
5746 These are the commands for managing your list of skips:
5750 @item info skip @r{[}@var{range}@r{]}
5751 Print details about the specified skip(s). If @var{range} is not specified,
5752 print a table with details about all functions and files marked for skipping.
5753 @code{info skip} prints the following information about each skip:
5757 A number identifying this skip.
5758 @item Enabled or Disabled
5759 Enabled skips are marked with @samp{y}.
5760 Disabled skips are marked with @samp{n}.
5762 If the file name is a @samp{glob} pattern this is @samp{y}.
5763 Otherwise it is @samp{n}.
5765 The name or @samp{glob} pattern of the file to be skipped.
5766 If no file is specified this is @samp{<none>}.
5768 If the function name is a @samp{regular expression} this is @samp{y}.
5769 Otherwise it is @samp{n}.
5771 The name or regular expression of the function to skip.
5772 If no function is specified this is @samp{<none>}.
5776 @item skip delete @r{[}@var{range}@r{]}
5777 Delete the specified skip(s). If @var{range} is not specified, delete all
5781 @item skip enable @r{[}@var{range}@r{]}
5782 Enable the specified skip(s). If @var{range} is not specified, enable all
5785 @kindex skip disable
5786 @item skip disable @r{[}@var{range}@r{]}
5787 Disable the specified skip(s). If @var{range} is not specified, disable all
5796 A signal is an asynchronous event that can happen in a program. The
5797 operating system defines the possible kinds of signals, and gives each
5798 kind a name and a number. For example, in Unix @code{SIGINT} is the
5799 signal a program gets when you type an interrupt character (often @kbd{Ctrl-c});
5800 @code{SIGSEGV} is the signal a program gets from referencing a place in
5801 memory far away from all the areas in use; @code{SIGALRM} occurs when
5802 the alarm clock timer goes off (which happens only if your program has
5803 requested an alarm).
5805 @cindex fatal signals
5806 Some signals, including @code{SIGALRM}, are a normal part of the
5807 functioning of your program. Others, such as @code{SIGSEGV}, indicate
5808 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
5809 program has not specified in advance some other way to handle the signal.
5810 @code{SIGINT} does not indicate an error in your program, but it is normally
5811 fatal so it can carry out the purpose of the interrupt: to kill the program.
5813 @value{GDBN} has the ability to detect any occurrence of a signal in your
5814 program. You can tell @value{GDBN} in advance what to do for each kind of
5817 @cindex handling signals
5818 Normally, @value{GDBN} is set up to let the non-erroneous signals like
5819 @code{SIGALRM} be silently passed to your program
5820 (so as not to interfere with their role in the program's functioning)
5821 but to stop your program immediately whenever an error signal happens.
5822 You can change these settings with the @code{handle} command.
5825 @kindex info signals
5829 Print a table of all the kinds of signals and how @value{GDBN} has been told to
5830 handle each one. You can use this to see the signal numbers of all
5831 the defined types of signals.
5833 @item info signals @var{sig}
5834 Similar, but print information only about the specified signal number.
5836 @code{info handle} is an alias for @code{info signals}.
5838 @item catch signal @r{[}@var{signal}@dots{} @r{|} @samp{all}@r{]}
5839 Set a catchpoint for the indicated signals. @xref{Set Catchpoints},
5840 for details about this command.
5843 @item handle @var{signal} @r{[}@var{keywords}@dots{}@r{]}
5844 Change the way @value{GDBN} handles signal @var{signal}. The @var{signal}
5845 can be the number of a signal or its name (with or without the
5846 @samp{SIG} at the beginning); a list of signal numbers of the form
5847 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
5848 known signals. Optional arguments @var{keywords}, described below,
5849 say what change to make.
5853 The keywords allowed by the @code{handle} command can be abbreviated.
5854 Their full names are:
5858 @value{GDBN} should not stop your program when this signal happens. It may
5859 still print a message telling you that the signal has come in.
5862 @value{GDBN} should stop your program when this signal happens. This implies
5863 the @code{print} keyword as well.
5866 @value{GDBN} should print a message when this signal happens.
5869 @value{GDBN} should not mention the occurrence of the signal at all. This
5870 implies the @code{nostop} keyword as well.
5874 @value{GDBN} should allow your program to see this signal; your program
5875 can handle the signal, or else it may terminate if the signal is fatal
5876 and not handled. @code{pass} and @code{noignore} are synonyms.
5880 @value{GDBN} should not allow your program to see this signal.
5881 @code{nopass} and @code{ignore} are synonyms.
5885 When a signal stops your program, the signal is not visible to the
5887 continue. Your program sees the signal then, if @code{pass} is in
5888 effect for the signal in question @emph{at that time}. In other words,
5889 after @value{GDBN} reports a signal, you can use the @code{handle}
5890 command with @code{pass} or @code{nopass} to control whether your
5891 program sees that signal when you continue.
5893 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
5894 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
5895 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
5898 You can also use the @code{signal} command to prevent your program from
5899 seeing a signal, or cause it to see a signal it normally would not see,
5900 or to give it any signal at any time. For example, if your program stopped
5901 due to some sort of memory reference error, you might store correct
5902 values into the erroneous variables and continue, hoping to see more
5903 execution; but your program would probably terminate immediately as
5904 a result of the fatal signal once it saw the signal. To prevent this,
5905 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
5908 @cindex stepping and signal handlers
5909 @anchor{stepping and signal handlers}
5911 @value{GDBN} optimizes for stepping the mainline code. If a signal
5912 that has @code{handle nostop} and @code{handle pass} set arrives while
5913 a stepping command (e.g., @code{stepi}, @code{step}, @code{next}) is
5914 in progress, @value{GDBN} lets the signal handler run and then resumes
5915 stepping the mainline code once the signal handler returns. In other
5916 words, @value{GDBN} steps over the signal handler. This prevents
5917 signals that you've specified as not interesting (with @code{handle
5918 nostop}) from changing the focus of debugging unexpectedly. Note that
5919 the signal handler itself may still hit a breakpoint, stop for another
5920 signal that has @code{handle stop} in effect, or for any other event
5921 that normally results in stopping the stepping command sooner. Also
5922 note that @value{GDBN} still informs you that the program received a
5923 signal if @code{handle print} is set.
5925 @anchor{stepping into signal handlers}
5927 If you set @code{handle pass} for a signal, and your program sets up a
5928 handler for it, then issuing a stepping command, such as @code{step}
5929 or @code{stepi}, when your program is stopped due to the signal will
5930 step @emph{into} the signal handler (if the target supports that).
5932 Likewise, if you use the @code{queue-signal} command to queue a signal
5933 to be delivered to the current thread when execution of the thread
5934 resumes (@pxref{Signaling, ,Giving your Program a Signal}), then a
5935 stepping command will step into the signal handler.
5937 Here's an example, using @code{stepi} to step to the first instruction
5938 of @code{SIGUSR1}'s handler:
5941 (@value{GDBP}) handle SIGUSR1
5942 Signal Stop Print Pass to program Description
5943 SIGUSR1 Yes Yes Yes User defined signal 1
5947 Program received signal SIGUSR1, User defined signal 1.
5948 main () sigusr1.c:28
5951 sigusr1_handler () at sigusr1.c:9
5955 The same, but using @code{queue-signal} instead of waiting for the
5956 program to receive the signal first:
5961 (@value{GDBP}) queue-signal SIGUSR1
5963 sigusr1_handler () at sigusr1.c:9
5968 @cindex extra signal information
5969 @anchor{extra signal information}
5971 On some targets, @value{GDBN} can inspect extra signal information
5972 associated with the intercepted signal, before it is actually
5973 delivered to the program being debugged. This information is exported
5974 by the convenience variable @code{$_siginfo}, and consists of data
5975 that is passed by the kernel to the signal handler at the time of the
5976 receipt of a signal. The data type of the information itself is
5977 target dependent. You can see the data type using the @code{ptype
5978 $_siginfo} command. On Unix systems, it typically corresponds to the
5979 standard @code{siginfo_t} type, as defined in the @file{signal.h}
5982 Here's an example, on a @sc{gnu}/Linux system, printing the stray
5983 referenced address that raised a segmentation fault.
5987 (@value{GDBP}) continue
5988 Program received signal SIGSEGV, Segmentation fault.
5989 0x0000000000400766 in main ()
5991 (@value{GDBP}) ptype $_siginfo
5998 struct @{...@} _kill;
5999 struct @{...@} _timer;
6001 struct @{...@} _sigchld;
6002 struct @{...@} _sigfault;
6003 struct @{...@} _sigpoll;
6006 (@value{GDBP}) ptype $_siginfo._sifields._sigfault
6010 (@value{GDBP}) p $_siginfo._sifields._sigfault.si_addr
6011 $1 = (void *) 0x7ffff7ff7000
6015 Depending on target support, @code{$_siginfo} may also be writable.
6017 @cindex Intel MPX boundary violations
6018 @cindex boundary violations, Intel MPX
6019 On some targets, a @code{SIGSEGV} can be caused by a boundary
6020 violation, i.e., accessing an address outside of the allowed range.
6021 In those cases @value{GDBN} may displays additional information,
6022 depending on how @value{GDBN} has been told to handle the signal.
6023 With @code{handle stop SIGSEGV}, @value{GDBN} displays the violation
6024 kind: "Upper" or "Lower", the memory address accessed and the
6025 bounds, while with @code{handle nostop SIGSEGV} no additional
6026 information is displayed.
6028 The usual output of a segfault is:
6030 Program received signal SIGSEGV, Segmentation fault
6031 0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68
6032 68 value = *(p + len);
6035 While a bound violation is presented as:
6037 Program received signal SIGSEGV, Segmentation fault
6038 Upper bound violation while accessing address 0x7fffffffc3b3
6039 Bounds: [lower = 0x7fffffffc390, upper = 0x7fffffffc3a3]
6040 0x0000000000400d7c in upper () at i386-mpx-sigsegv.c:68
6041 68 value = *(p + len);
6045 @section Stopping and Starting Multi-thread Programs
6047 @cindex stopped threads
6048 @cindex threads, stopped
6050 @cindex continuing threads
6051 @cindex threads, continuing
6053 @value{GDBN} supports debugging programs with multiple threads
6054 (@pxref{Threads,, Debugging Programs with Multiple Threads}). There
6055 are two modes of controlling execution of your program within the
6056 debugger. In the default mode, referred to as @dfn{all-stop mode},
6057 when any thread in your program stops (for example, at a breakpoint
6058 or while being stepped), all other threads in the program are also stopped by
6059 @value{GDBN}. On some targets, @value{GDBN} also supports
6060 @dfn{non-stop mode}, in which other threads can continue to run freely while
6061 you examine the stopped thread in the debugger.
6064 * All-Stop Mode:: All threads stop when GDB takes control
6065 * Non-Stop Mode:: Other threads continue to execute
6066 * Background Execution:: Running your program asynchronously
6067 * Thread-Specific Breakpoints:: Controlling breakpoints
6068 * Interrupted System Calls:: GDB may interfere with system calls
6069 * Observer Mode:: GDB does not alter program behavior
6073 @subsection All-Stop Mode
6075 @cindex all-stop mode
6077 In all-stop mode, whenever your program stops under @value{GDBN} for any reason,
6078 @emph{all} threads of execution stop, not just the current thread. This
6079 allows you to examine the overall state of the program, including
6080 switching between threads, without worrying that things may change
6083 Conversely, whenever you restart the program, @emph{all} threads start
6084 executing. @emph{This is true even when single-stepping} with commands
6085 like @code{step} or @code{next}.
6087 In particular, @value{GDBN} cannot single-step all threads in lockstep.
6088 Since thread scheduling is up to your debugging target's operating
6089 system (not controlled by @value{GDBN}), other threads may
6090 execute more than one statement while the current thread completes a
6091 single step. Moreover, in general other threads stop in the middle of a
6092 statement, rather than at a clean statement boundary, when the program
6095 You might even find your program stopped in another thread after
6096 continuing or even single-stepping. This happens whenever some other
6097 thread runs into a breakpoint, a signal, or an exception before the
6098 first thread completes whatever you requested.
6100 @cindex automatic thread selection
6101 @cindex switching threads automatically
6102 @cindex threads, automatic switching
6103 Whenever @value{GDBN} stops your program, due to a breakpoint or a
6104 signal, it automatically selects the thread where that breakpoint or
6105 signal happened. @value{GDBN} alerts you to the context switch with a
6106 message such as @samp{[Switching to Thread @var{n}]} to identify the
6109 On some OSes, you can modify @value{GDBN}'s default behavior by
6110 locking the OS scheduler to allow only a single thread to run.
6113 @item set scheduler-locking @var{mode}
6114 @cindex scheduler locking mode
6115 @cindex lock scheduler
6116 Set the scheduler locking mode. It applies to normal execution,
6117 record mode, and replay mode. If it is @code{off}, then there is no
6118 locking and any thread may run at any time. If @code{on}, then only
6119 the current thread may run when the inferior is resumed. The
6120 @code{step} mode optimizes for single-stepping; it prevents other
6121 threads from preempting the current thread while you are stepping, so
6122 that the focus of debugging does not change unexpectedly. Other
6123 threads never get a chance to run when you step, and they are
6124 completely free to run when you use commands like @samp{continue},
6125 @samp{until}, or @samp{finish}. However, unless another thread hits a
6126 breakpoint during its timeslice, @value{GDBN} does not change the
6127 current thread away from the thread that you are debugging. The
6128 @code{replay} mode behaves like @code{off} in record mode and like
6129 @code{on} in replay mode.
6131 @item show scheduler-locking
6132 Display the current scheduler locking mode.
6135 @cindex resume threads of multiple processes simultaneously
6136 By default, when you issue one of the execution commands such as
6137 @code{continue}, @code{next} or @code{step}, @value{GDBN} allows only
6138 threads of the current inferior to run. For example, if @value{GDBN}
6139 is attached to two inferiors, each with two threads, the
6140 @code{continue} command resumes only the two threads of the current
6141 inferior. This is useful, for example, when you debug a program that
6142 forks and you want to hold the parent stopped (so that, for instance,
6143 it doesn't run to exit), while you debug the child. In other
6144 situations, you may not be interested in inspecting the current state
6145 of any of the processes @value{GDBN} is attached to, and you may want
6146 to resume them all until some breakpoint is hit. In the latter case,
6147 you can instruct @value{GDBN} to allow all threads of all the
6148 inferiors to run with the @w{@code{set schedule-multiple}} command.
6151 @kindex set schedule-multiple
6152 @item set schedule-multiple
6153 Set the mode for allowing threads of multiple processes to be resumed
6154 when an execution command is issued. When @code{on}, all threads of
6155 all processes are allowed to run. When @code{off}, only the threads
6156 of the current process are resumed. The default is @code{off}. The
6157 @code{scheduler-locking} mode takes precedence when set to @code{on},
6158 or while you are stepping and set to @code{step}.
6160 @item show schedule-multiple
6161 Display the current mode for resuming the execution of threads of
6166 @subsection Non-Stop Mode
6168 @cindex non-stop mode
6170 @c This section is really only a place-holder, and needs to be expanded
6171 @c with more details.
6173 For some multi-threaded targets, @value{GDBN} supports an optional
6174 mode of operation in which you can examine stopped program threads in
6175 the debugger while other threads continue to execute freely. This
6176 minimizes intrusion when debugging live systems, such as programs
6177 where some threads have real-time constraints or must continue to
6178 respond to external events. This is referred to as @dfn{non-stop} mode.
6180 In non-stop mode, when a thread stops to report a debugging event,
6181 @emph{only} that thread is stopped; @value{GDBN} does not stop other
6182 threads as well, in contrast to the all-stop mode behavior. Additionally,
6183 execution commands such as @code{continue} and @code{step} apply by default
6184 only to the current thread in non-stop mode, rather than all threads as
6185 in all-stop mode. This allows you to control threads explicitly in
6186 ways that are not possible in all-stop mode --- for example, stepping
6187 one thread while allowing others to run freely, stepping
6188 one thread while holding all others stopped, or stepping several threads
6189 independently and simultaneously.
6191 To enter non-stop mode, use this sequence of commands before you run
6192 or attach to your program:
6195 # If using the CLI, pagination breaks non-stop.
6198 # Finally, turn it on!
6202 You can use these commands to manipulate the non-stop mode setting:
6205 @kindex set non-stop
6206 @item set non-stop on
6207 Enable selection of non-stop mode.
6208 @item set non-stop off
6209 Disable selection of non-stop mode.
6210 @kindex show non-stop
6212 Show the current non-stop enablement setting.
6215 Note these commands only reflect whether non-stop mode is enabled,
6216 not whether the currently-executing program is being run in non-stop mode.
6217 In particular, the @code{set non-stop} preference is only consulted when
6218 @value{GDBN} starts or connects to the target program, and it is generally
6219 not possible to switch modes once debugging has started. Furthermore,
6220 since not all targets support non-stop mode, even when you have enabled
6221 non-stop mode, @value{GDBN} may still fall back to all-stop operation by
6224 In non-stop mode, all execution commands apply only to the current thread
6225 by default. That is, @code{continue} only continues one thread.
6226 To continue all threads, issue @code{continue -a} or @code{c -a}.
6228 You can use @value{GDBN}'s background execution commands
6229 (@pxref{Background Execution}) to run some threads in the background
6230 while you continue to examine or step others from @value{GDBN}.
6231 The MI execution commands (@pxref{GDB/MI Program Execution}) are
6232 always executed asynchronously in non-stop mode.
6234 Suspending execution is done with the @code{interrupt} command when
6235 running in the background, or @kbd{Ctrl-c} during foreground execution.
6236 In all-stop mode, this stops the whole process;
6237 but in non-stop mode the interrupt applies only to the current thread.
6238 To stop the whole program, use @code{interrupt -a}.
6240 Other execution commands do not currently support the @code{-a} option.
6242 In non-stop mode, when a thread stops, @value{GDBN} doesn't automatically make
6243 that thread current, as it does in all-stop mode. This is because the
6244 thread stop notifications are asynchronous with respect to @value{GDBN}'s
6245 command interpreter, and it would be confusing if @value{GDBN} unexpectedly
6246 changed to a different thread just as you entered a command to operate on the
6247 previously current thread.
6249 @node Background Execution
6250 @subsection Background Execution
6252 @cindex foreground execution
6253 @cindex background execution
6254 @cindex asynchronous execution
6255 @cindex execution, foreground, background and asynchronous
6257 @value{GDBN}'s execution commands have two variants: the normal
6258 foreground (synchronous) behavior, and a background
6259 (asynchronous) behavior. In foreground execution, @value{GDBN} waits for
6260 the program to report that some thread has stopped before prompting for
6261 another command. In background execution, @value{GDBN} immediately gives
6262 a command prompt so that you can issue other commands while your program runs.
6264 If the target doesn't support async mode, @value{GDBN} issues an error
6265 message if you attempt to use the background execution commands.
6267 To specify background execution, add a @code{&} to the command. For example,
6268 the background form of the @code{continue} command is @code{continue&}, or
6269 just @code{c&}. The execution commands that accept background execution
6275 @xref{Starting, , Starting your Program}.
6279 @xref{Attach, , Debugging an Already-running Process}.
6283 @xref{Continuing and Stepping, step}.
6287 @xref{Continuing and Stepping, stepi}.
6291 @xref{Continuing and Stepping, next}.
6295 @xref{Continuing and Stepping, nexti}.
6299 @xref{Continuing and Stepping, continue}.
6303 @xref{Continuing and Stepping, finish}.
6307 @xref{Continuing and Stepping, until}.
6311 Background execution is especially useful in conjunction with non-stop
6312 mode for debugging programs with multiple threads; see @ref{Non-Stop Mode}.
6313 However, you can also use these commands in the normal all-stop mode with
6314 the restriction that you cannot issue another execution command until the
6315 previous one finishes. Examples of commands that are valid in all-stop
6316 mode while the program is running include @code{help} and @code{info break}.
6318 You can interrupt your program while it is running in the background by
6319 using the @code{interrupt} command.
6326 Suspend execution of the running program. In all-stop mode,
6327 @code{interrupt} stops the whole process, but in non-stop mode, it stops
6328 only the current thread. To stop the whole program in non-stop mode,
6329 use @code{interrupt -a}.
6332 @node Thread-Specific Breakpoints
6333 @subsection Thread-Specific Breakpoints
6335 When your program has multiple threads (@pxref{Threads,, Debugging
6336 Programs with Multiple Threads}), you can choose whether to set
6337 breakpoints on all threads, or on a particular thread.
6340 @cindex breakpoints and threads
6341 @cindex thread breakpoints
6342 @kindex break @dots{} thread @var{thread-id}
6343 @item break @var{location} thread @var{thread-id}
6344 @itemx break @var{location} thread @var{thread-id} if @dots{}
6345 @var{location} specifies source lines; there are several ways of
6346 writing them (@pxref{Specify Location}), but the effect is always to
6347 specify some source line.
6349 Use the qualifier @samp{thread @var{thread-id}} with a breakpoint command
6350 to specify that you only want @value{GDBN} to stop the program when a
6351 particular thread reaches this breakpoint. The @var{thread-id} specifier
6352 is one of the thread identifiers assigned by @value{GDBN}, shown
6353 in the first column of the @samp{info threads} display.
6355 If you do not specify @samp{thread @var{thread-id}} when you set a
6356 breakpoint, the breakpoint applies to @emph{all} threads of your
6359 You can use the @code{thread} qualifier on conditional breakpoints as
6360 well; in this case, place @samp{thread @var{thread-id}} before or
6361 after the breakpoint condition, like this:
6364 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
6369 Thread-specific breakpoints are automatically deleted when
6370 @value{GDBN} detects the corresponding thread is no longer in the
6371 thread list. For example:
6375 Thread-specific breakpoint 3 deleted - thread 28 no longer in the thread list.
6378 There are several ways for a thread to disappear, such as a regular
6379 thread exit, but also when you detach from the process with the
6380 @code{detach} command (@pxref{Attach, ,Debugging an Already-running
6381 Process}), or if @value{GDBN} loses the remote connection
6382 (@pxref{Remote Debugging}), etc. Note that with some targets,
6383 @value{GDBN} is only able to detect a thread has exited when the user
6384 explictly asks for the thread list with the @code{info threads}
6387 @node Interrupted System Calls
6388 @subsection Interrupted System Calls
6390 @cindex thread breakpoints and system calls
6391 @cindex system calls and thread breakpoints
6392 @cindex premature return from system calls
6393 There is an unfortunate side effect when using @value{GDBN} to debug
6394 multi-threaded programs. If one thread stops for a
6395 breakpoint, or for some other reason, and another thread is blocked in a
6396 system call, then the system call may return prematurely. This is a
6397 consequence of the interaction between multiple threads and the signals
6398 that @value{GDBN} uses to implement breakpoints and other events that
6401 To handle this problem, your program should check the return value of
6402 each system call and react appropriately. This is good programming
6405 For example, do not write code like this:
6411 The call to @code{sleep} will return early if a different thread stops
6412 at a breakpoint or for some other reason.
6414 Instead, write this:
6419 unslept = sleep (unslept);
6422 A system call is allowed to return early, so the system is still
6423 conforming to its specification. But @value{GDBN} does cause your
6424 multi-threaded program to behave differently than it would without
6427 Also, @value{GDBN} uses internal breakpoints in the thread library to
6428 monitor certain events such as thread creation and thread destruction.
6429 When such an event happens, a system call in another thread may return
6430 prematurely, even though your program does not appear to stop.
6433 @subsection Observer Mode
6435 If you want to build on non-stop mode and observe program behavior
6436 without any chance of disruption by @value{GDBN}, you can set
6437 variables to disable all of the debugger's attempts to modify state,
6438 whether by writing memory, inserting breakpoints, etc. These operate
6439 at a low level, intercepting operations from all commands.
6441 When all of these are set to @code{off}, then @value{GDBN} is said to
6442 be @dfn{observer mode}. As a convenience, the variable
6443 @code{observer} can be set to disable these, plus enable non-stop
6446 Note that @value{GDBN} will not prevent you from making nonsensical
6447 combinations of these settings. For instance, if you have enabled
6448 @code{may-insert-breakpoints} but disabled @code{may-write-memory},
6449 then breakpoints that work by writing trap instructions into the code
6450 stream will still not be able to be placed.
6455 @item set observer on
6456 @itemx set observer off
6457 When set to @code{on}, this disables all the permission variables
6458 below (except for @code{insert-fast-tracepoints}), plus enables
6459 non-stop debugging. Setting this to @code{off} switches back to
6460 normal debugging, though remaining in non-stop mode.
6463 Show whether observer mode is on or off.
6465 @kindex may-write-registers
6466 @item set may-write-registers on
6467 @itemx set may-write-registers off
6468 This controls whether @value{GDBN} will attempt to alter the values of
6469 registers, such as with assignment expressions in @code{print}, or the
6470 @code{jump} command. It defaults to @code{on}.
6472 @item show may-write-registers
6473 Show the current permission to write registers.
6475 @kindex may-write-memory
6476 @item set may-write-memory on
6477 @itemx set may-write-memory off
6478 This controls whether @value{GDBN} will attempt to alter the contents
6479 of memory, such as with assignment expressions in @code{print}. It
6480 defaults to @code{on}.
6482 @item show may-write-memory
6483 Show the current permission to write memory.
6485 @kindex may-insert-breakpoints
6486 @item set may-insert-breakpoints on
6487 @itemx set may-insert-breakpoints off
6488 This controls whether @value{GDBN} will attempt to insert breakpoints.
6489 This affects all breakpoints, including internal breakpoints defined
6490 by @value{GDBN}. It defaults to @code{on}.
6492 @item show may-insert-breakpoints
6493 Show the current permission to insert breakpoints.
6495 @kindex may-insert-tracepoints
6496 @item set may-insert-tracepoints on
6497 @itemx set may-insert-tracepoints off
6498 This controls whether @value{GDBN} will attempt to insert (regular)
6499 tracepoints at the beginning of a tracing experiment. It affects only
6500 non-fast tracepoints, fast tracepoints being under the control of
6501 @code{may-insert-fast-tracepoints}. It defaults to @code{on}.
6503 @item show may-insert-tracepoints
6504 Show the current permission to insert tracepoints.
6506 @kindex may-insert-fast-tracepoints
6507 @item set may-insert-fast-tracepoints on
6508 @itemx set may-insert-fast-tracepoints off
6509 This controls whether @value{GDBN} will attempt to insert fast
6510 tracepoints at the beginning of a tracing experiment. It affects only
6511 fast tracepoints, regular (non-fast) tracepoints being under the
6512 control of @code{may-insert-tracepoints}. It defaults to @code{on}.
6514 @item show may-insert-fast-tracepoints
6515 Show the current permission to insert fast tracepoints.
6517 @kindex may-interrupt
6518 @item set may-interrupt on
6519 @itemx set may-interrupt off
6520 This controls whether @value{GDBN} will attempt to interrupt or stop
6521 program execution. When this variable is @code{off}, the
6522 @code{interrupt} command will have no effect, nor will
6523 @kbd{Ctrl-c}. It defaults to @code{on}.
6525 @item show may-interrupt
6526 Show the current permission to interrupt or stop the program.
6530 @node Reverse Execution
6531 @chapter Running programs backward
6532 @cindex reverse execution
6533 @cindex running programs backward
6535 When you are debugging a program, it is not unusual to realize that
6536 you have gone too far, and some event of interest has already happened.
6537 If the target environment supports it, @value{GDBN} can allow you to
6538 ``rewind'' the program by running it backward.
6540 A target environment that supports reverse execution should be able
6541 to ``undo'' the changes in machine state that have taken place as the
6542 program was executing normally. Variables, registers etc.@: should
6543 revert to their previous values. Obviously this requires a great
6544 deal of sophistication on the part of the target environment; not
6545 all target environments can support reverse execution.
6547 When a program is executed in reverse, the instructions that
6548 have most recently been executed are ``un-executed'', in reverse
6549 order. The program counter runs backward, following the previous
6550 thread of execution in reverse. As each instruction is ``un-executed'',
6551 the values of memory and/or registers that were changed by that
6552 instruction are reverted to their previous states. After executing
6553 a piece of source code in reverse, all side effects of that code
6554 should be ``undone'', and all variables should be returned to their
6555 prior values@footnote{
6556 Note that some side effects are easier to undo than others. For instance,
6557 memory and registers are relatively easy, but device I/O is hard. Some
6558 targets may be able undo things like device I/O, and some may not.
6560 The contract between @value{GDBN} and the reverse executing target
6561 requires only that the target do something reasonable when
6562 @value{GDBN} tells it to execute backwards, and then report the
6563 results back to @value{GDBN}. Whatever the target reports back to
6564 @value{GDBN}, @value{GDBN} will report back to the user. @value{GDBN}
6565 assumes that the memory and registers that the target reports are in a
6566 consistant state, but @value{GDBN} accepts whatever it is given.
6569 If you are debugging in a target environment that supports
6570 reverse execution, @value{GDBN} provides the following commands.
6573 @kindex reverse-continue
6574 @kindex rc @r{(@code{reverse-continue})}
6575 @item reverse-continue @r{[}@var{ignore-count}@r{]}
6576 @itemx rc @r{[}@var{ignore-count}@r{]}
6577 Beginning at the point where your program last stopped, start executing
6578 in reverse. Reverse execution will stop for breakpoints and synchronous
6579 exceptions (signals), just like normal execution. Behavior of
6580 asynchronous signals depends on the target environment.
6582 @kindex reverse-step
6583 @kindex rs @r{(@code{step})}
6584 @item reverse-step @r{[}@var{count}@r{]}
6585 Run the program backward until control reaches the start of a
6586 different source line; then stop it, and return control to @value{GDBN}.
6588 Like the @code{step} command, @code{reverse-step} will only stop
6589 at the beginning of a source line. It ``un-executes'' the previously
6590 executed source line. If the previous source line included calls to
6591 debuggable functions, @code{reverse-step} will step (backward) into
6592 the called function, stopping at the beginning of the @emph{last}
6593 statement in the called function (typically a return statement).
6595 Also, as with the @code{step} command, if non-debuggable functions are
6596 called, @code{reverse-step} will run thru them backward without stopping.
6598 @kindex reverse-stepi
6599 @kindex rsi @r{(@code{reverse-stepi})}
6600 @item reverse-stepi @r{[}@var{count}@r{]}
6601 Reverse-execute one machine instruction. Note that the instruction
6602 to be reverse-executed is @emph{not} the one pointed to by the program
6603 counter, but the instruction executed prior to that one. For instance,
6604 if the last instruction was a jump, @code{reverse-stepi} will take you
6605 back from the destination of the jump to the jump instruction itself.
6607 @kindex reverse-next
6608 @kindex rn @r{(@code{reverse-next})}
6609 @item reverse-next @r{[}@var{count}@r{]}
6610 Run backward to the beginning of the previous line executed in
6611 the current (innermost) stack frame. If the line contains function
6612 calls, they will be ``un-executed'' without stopping. Starting from
6613 the first line of a function, @code{reverse-next} will take you back
6614 to the caller of that function, @emph{before} the function was called,
6615 just as the normal @code{next} command would take you from the last
6616 line of a function back to its return to its caller
6617 @footnote{Unless the code is too heavily optimized.}.
6619 @kindex reverse-nexti
6620 @kindex rni @r{(@code{reverse-nexti})}
6621 @item reverse-nexti @r{[}@var{count}@r{]}
6622 Like @code{nexti}, @code{reverse-nexti} executes a single instruction
6623 in reverse, except that called functions are ``un-executed'' atomically.
6624 That is, if the previously executed instruction was a return from
6625 another function, @code{reverse-nexti} will continue to execute
6626 in reverse until the call to that function (from the current stack
6629 @kindex reverse-finish
6630 @item reverse-finish
6631 Just as the @code{finish} command takes you to the point where the
6632 current function returns, @code{reverse-finish} takes you to the point
6633 where it was called. Instead of ending up at the end of the current
6634 function invocation, you end up at the beginning.
6636 @kindex set exec-direction
6637 @item set exec-direction
6638 Set the direction of target execution.
6639 @item set exec-direction reverse
6640 @cindex execute forward or backward in time
6641 @value{GDBN} will perform all execution commands in reverse, until the
6642 exec-direction mode is changed to ``forward''. Affected commands include
6643 @code{step, stepi, next, nexti, continue, and finish}. The @code{return}
6644 command cannot be used in reverse mode.
6645 @item set exec-direction forward
6646 @value{GDBN} will perform all execution commands in the normal fashion.
6647 This is the default.
6651 @node Process Record and Replay
6652 @chapter Recording Inferior's Execution and Replaying It
6653 @cindex process record and replay
6654 @cindex recording inferior's execution and replaying it
6656 On some platforms, @value{GDBN} provides a special @dfn{process record
6657 and replay} target that can record a log of the process execution, and
6658 replay it later with both forward and reverse execution commands.
6661 When this target is in use, if the execution log includes the record
6662 for the next instruction, @value{GDBN} will debug in @dfn{replay
6663 mode}. In the replay mode, the inferior does not really execute code
6664 instructions. Instead, all the events that normally happen during
6665 code execution are taken from the execution log. While code is not
6666 really executed in replay mode, the values of registers (including the
6667 program counter register) and the memory of the inferior are still
6668 changed as they normally would. Their contents are taken from the
6672 If the record for the next instruction is not in the execution log,
6673 @value{GDBN} will debug in @dfn{record mode}. In this mode, the
6674 inferior executes normally, and @value{GDBN} records the execution log
6677 The process record and replay target supports reverse execution
6678 (@pxref{Reverse Execution}), even if the platform on which the
6679 inferior runs does not. However, the reverse execution is limited in
6680 this case by the range of the instructions recorded in the execution
6681 log. In other words, reverse execution on platforms that don't
6682 support it directly can only be done in the replay mode.
6684 When debugging in the reverse direction, @value{GDBN} will work in
6685 replay mode as long as the execution log includes the record for the
6686 previous instruction; otherwise, it will work in record mode, if the
6687 platform supports reverse execution, or stop if not.
6689 For architecture environments that support process record and replay,
6690 @value{GDBN} provides the following commands:
6693 @kindex target record
6694 @kindex target record-full
6695 @kindex target record-btrace
6698 @kindex record btrace
6699 @kindex record btrace bts
6700 @kindex record btrace pt
6706 @kindex rec btrace bts
6707 @kindex rec btrace pt
6710 @item record @var{method}
6711 This command starts the process record and replay target. The
6712 recording method can be specified as parameter. Without a parameter
6713 the command uses the @code{full} recording method. The following
6714 recording methods are available:
6718 Full record/replay recording using @value{GDBN}'s software record and
6719 replay implementation. This method allows replaying and reverse
6722 @item btrace @var{format}
6723 Hardware-supported instruction recording. This method does not record
6724 data. Further, the data is collected in a ring buffer so old data will
6725 be overwritten when the buffer is full. It allows limited reverse
6726 execution. Variables and registers are not available during reverse
6727 execution. In remote debugging, recording continues on disconnect.
6728 Recorded data can be inspected after reconnecting. The recording may
6729 be stopped using @code{record stop}.
6731 The recording format can be specified as parameter. Without a parameter
6732 the command chooses the recording format. The following recording
6733 formats are available:
6737 @cindex branch trace store
6738 Use the @dfn{Branch Trace Store} (@acronym{BTS}) recording format. In
6739 this format, the processor stores a from/to record for each executed
6740 branch in the btrace ring buffer.
6743 @cindex Intel Processor Trace
6744 Use the @dfn{Intel Processor Trace} recording format. In this
6745 format, the processor stores the execution trace in a compressed form
6746 that is afterwards decoded by @value{GDBN}.
6748 The trace can be recorded with very low overhead. The compressed
6749 trace format also allows small trace buffers to already contain a big
6750 number of instructions compared to @acronym{BTS}.
6752 Decoding the recorded execution trace, on the other hand, is more
6753 expensive than decoding @acronym{BTS} trace. This is mostly due to the
6754 increased number of instructions to process. You should increase the
6755 buffer-size with care.
6758 Not all recording formats may be available on all processors.
6761 The process record and replay target can only debug a process that is
6762 already running. Therefore, you need first to start the process with
6763 the @kbd{run} or @kbd{start} commands, and then start the recording
6764 with the @kbd{record @var{method}} command.
6766 @cindex displaced stepping, and process record and replay
6767 Displaced stepping (@pxref{Maintenance Commands,, displaced stepping})
6768 will be automatically disabled when process record and replay target
6769 is started. That's because the process record and replay target
6770 doesn't support displaced stepping.
6772 @cindex non-stop mode, and process record and replay
6773 @cindex asynchronous execution, and process record and replay
6774 If the inferior is in the non-stop mode (@pxref{Non-Stop Mode}) or in
6775 the asynchronous execution mode (@pxref{Background Execution}), not
6776 all recording methods are available. The @code{full} recording method
6777 does not support these two modes.
6782 Stop the process record and replay target. When process record and
6783 replay target stops, the entire execution log will be deleted and the
6784 inferior will either be terminated, or will remain in its final state.
6786 When you stop the process record and replay target in record mode (at
6787 the end of the execution log), the inferior will be stopped at the
6788 next instruction that would have been recorded. In other words, if
6789 you record for a while and then stop recording, the inferior process
6790 will be left in the same state as if the recording never happened.
6792 On the other hand, if the process record and replay target is stopped
6793 while in replay mode (that is, not at the end of the execution log,
6794 but at some earlier point), the inferior process will become ``live''
6795 at that earlier state, and it will then be possible to continue the
6796 usual ``live'' debugging of the process from that state.
6798 When the inferior process exits, or @value{GDBN} detaches from it,
6799 process record and replay target will automatically stop itself.
6803 Go to a specific location in the execution log. There are several
6804 ways to specify the location to go to:
6807 @item record goto begin
6808 @itemx record goto start
6809 Go to the beginning of the execution log.
6811 @item record goto end
6812 Go to the end of the execution log.
6814 @item record goto @var{n}
6815 Go to instruction number @var{n} in the execution log.
6819 @item record save @var{filename}
6820 Save the execution log to a file @file{@var{filename}}.
6821 Default filename is @file{gdb_record.@var{process_id}}, where
6822 @var{process_id} is the process ID of the inferior.
6824 This command may not be available for all recording methods.
6826 @kindex record restore
6827 @item record restore @var{filename}
6828 Restore the execution log from a file @file{@var{filename}}.
6829 File must have been created with @code{record save}.
6831 @kindex set record full
6832 @item set record full insn-number-max @var{limit}
6833 @itemx set record full insn-number-max unlimited
6834 Set the limit of instructions to be recorded for the @code{full}
6835 recording method. Default value is 200000.
6837 If @var{limit} is a positive number, then @value{GDBN} will start
6838 deleting instructions from the log once the number of the record
6839 instructions becomes greater than @var{limit}. For every new recorded
6840 instruction, @value{GDBN} will delete the earliest recorded
6841 instruction to keep the number of recorded instructions at the limit.
6842 (Since deleting recorded instructions loses information, @value{GDBN}
6843 lets you control what happens when the limit is reached, by means of
6844 the @code{stop-at-limit} option, described below.)
6846 If @var{limit} is @code{unlimited} or zero, @value{GDBN} will never
6847 delete recorded instructions from the execution log. The number of
6848 recorded instructions is limited only by the available memory.
6850 @kindex show record full
6851 @item show record full insn-number-max
6852 Show the limit of instructions to be recorded with the @code{full}
6855 @item set record full stop-at-limit
6856 Control the behavior of the @code{full} recording method when the
6857 number of recorded instructions reaches the limit. If ON (the
6858 default), @value{GDBN} will stop when the limit is reached for the
6859 first time and ask you whether you want to stop the inferior or
6860 continue running it and recording the execution log. If you decide
6861 to continue recording, each new recorded instruction will cause the
6862 oldest one to be deleted.
6864 If this option is OFF, @value{GDBN} will automatically delete the
6865 oldest record to make room for each new one, without asking.
6867 @item show record full stop-at-limit
6868 Show the current setting of @code{stop-at-limit}.
6870 @item set record full memory-query
6871 Control the behavior when @value{GDBN} is unable to record memory
6872 changes caused by an instruction for the @code{full} recording method.
6873 If ON, @value{GDBN} will query whether to stop the inferior in that
6876 If this option is OFF (the default), @value{GDBN} will automatically
6877 ignore the effect of such instructions on memory. Later, when
6878 @value{GDBN} replays this execution log, it will mark the log of this
6879 instruction as not accessible, and it will not affect the replay
6882 @item show record full memory-query
6883 Show the current setting of @code{memory-query}.
6885 @kindex set record btrace
6886 The @code{btrace} record target does not trace data. As a
6887 convenience, when replaying, @value{GDBN} reads read-only memory off
6888 the live program directly, assuming that the addresses of the
6889 read-only areas don't change. This for example makes it possible to
6890 disassemble code while replaying, but not to print variables.
6891 In some cases, being able to inspect variables might be useful.
6892 You can use the following command for that:
6894 @item set record btrace replay-memory-access
6895 Control the behavior of the @code{btrace} recording method when
6896 accessing memory during replay. If @code{read-only} (the default),
6897 @value{GDBN} will only allow accesses to read-only memory.
6898 If @code{read-write}, @value{GDBN} will allow accesses to read-only
6899 and to read-write memory. Beware that the accessed memory corresponds
6900 to the live target and not necessarily to the current replay
6903 @kindex show record btrace
6904 @item show record btrace replay-memory-access
6905 Show the current setting of @code{replay-memory-access}.
6907 @kindex set record btrace bts
6908 @item set record btrace bts buffer-size @var{size}
6909 @itemx set record btrace bts buffer-size unlimited
6910 Set the requested ring buffer size for branch tracing in @acronym{BTS}
6911 format. Default is 64KB.
6913 If @var{size} is a positive number, then @value{GDBN} will try to
6914 allocate a buffer of at least @var{size} bytes for each new thread
6915 that uses the btrace recording method and the @acronym{BTS} format.
6916 The actually obtained buffer size may differ from the requested
6917 @var{size}. Use the @code{info record} command to see the actual
6918 buffer size for each thread that uses the btrace recording method and
6919 the @acronym{BTS} format.
6921 If @var{limit} is @code{unlimited} or zero, @value{GDBN} will try to
6922 allocate a buffer of 4MB.
6924 Bigger buffers mean longer traces. On the other hand, @value{GDBN} will
6925 also need longer to process the branch trace data before it can be used.
6927 @item show record btrace bts buffer-size @var{size}
6928 Show the current setting of the requested ring buffer size for branch
6929 tracing in @acronym{BTS} format.
6931 @kindex set record btrace pt
6932 @item set record btrace pt buffer-size @var{size}
6933 @itemx set record btrace pt buffer-size unlimited
6934 Set the requested ring buffer size for branch tracing in Intel
6935 Processor Trace format. Default is 16KB.
6937 If @var{size} is a positive number, then @value{GDBN} will try to
6938 allocate a buffer of at least @var{size} bytes for each new thread
6939 that uses the btrace recording method and the Intel Processor Trace
6940 format. The actually obtained buffer size may differ from the
6941 requested @var{size}. Use the @code{info record} command to see the
6942 actual buffer size for each thread.
6944 If @var{limit} is @code{unlimited} or zero, @value{GDBN} will try to
6945 allocate a buffer of 4MB.
6947 Bigger buffers mean longer traces. On the other hand, @value{GDBN} will
6948 also need longer to process the branch trace data before it can be used.
6950 @item show record btrace pt buffer-size @var{size}
6951 Show the current setting of the requested ring buffer size for branch
6952 tracing in Intel Processor Trace format.
6956 Show various statistics about the recording depending on the recording
6961 For the @code{full} recording method, it shows the state of process
6962 record and its in-memory execution log buffer, including:
6966 Whether in record mode or replay mode.
6968 Lowest recorded instruction number (counting from when the current execution log started recording instructions).
6970 Highest recorded instruction number.
6972 Current instruction about to be replayed (if in replay mode).
6974 Number of instructions contained in the execution log.
6976 Maximum number of instructions that may be contained in the execution log.
6980 For the @code{btrace} recording method, it shows:
6986 Number of instructions that have been recorded.
6988 Number of blocks of sequential control-flow formed by the recorded
6991 Whether in record mode or replay mode.
6994 For the @code{bts} recording format, it also shows:
6997 Size of the perf ring buffer.
7000 For the @code{pt} recording format, it also shows:
7003 Size of the perf ring buffer.
7007 @kindex record delete
7010 When record target runs in replay mode (``in the past''), delete the
7011 subsequent execution log and begin to record a new execution log starting
7012 from the current address. This means you will abandon the previously
7013 recorded ``future'' and begin recording a new ``future''.
7015 @kindex record instruction-history
7016 @kindex rec instruction-history
7017 @item record instruction-history
7018 Disassembles instructions from the recorded execution log. By
7019 default, ten instructions are disassembled. This can be changed using
7020 the @code{set record instruction-history-size} command. Instructions
7021 are printed in execution order.
7023 It can also print mixed source+disassembly if you specify the the
7024 @code{/m} or @code{/s} modifier, and print the raw instructions in hex
7025 as well as in symbolic form by specifying the @code{/r} modifier.
7027 The current position marker is printed for the instruction at the
7028 current program counter value. This instruction can appear multiple
7029 times in the trace and the current position marker will be printed
7030 every time. To omit the current position marker, specify the
7033 To better align the printed instructions when the trace contains
7034 instructions from more than one function, the function name may be
7035 omitted by specifying the @code{/f} modifier.
7037 Speculatively executed instructions are prefixed with @samp{?}. This
7038 feature is not available for all recording formats.
7040 There are several ways to specify what part of the execution log to
7044 @item record instruction-history @var{insn}
7045 Disassembles ten instructions starting from instruction number
7048 @item record instruction-history @var{insn}, +/-@var{n}
7049 Disassembles @var{n} instructions around instruction number
7050 @var{insn}. If @var{n} is preceded with @code{+}, disassembles
7051 @var{n} instructions after instruction number @var{insn}. If
7052 @var{n} is preceded with @code{-}, disassembles @var{n}
7053 instructions before instruction number @var{insn}.
7055 @item record instruction-history
7056 Disassembles ten more instructions after the last disassembly.
7058 @item record instruction-history -
7059 Disassembles ten more instructions before the last disassembly.
7061 @item record instruction-history @var{begin}, @var{end}
7062 Disassembles instructions beginning with instruction number
7063 @var{begin} until instruction number @var{end}. The instruction
7064 number @var{end} is included.
7067 This command may not be available for all recording methods.
7070 @item set record instruction-history-size @var{size}
7071 @itemx set record instruction-history-size unlimited
7072 Define how many instructions to disassemble in the @code{record
7073 instruction-history} command. The default value is 10.
7074 A @var{size} of @code{unlimited} means unlimited instructions.
7077 @item show record instruction-history-size
7078 Show how many instructions to disassemble in the @code{record
7079 instruction-history} command.
7081 @kindex record function-call-history
7082 @kindex rec function-call-history
7083 @item record function-call-history
7084 Prints the execution history at function granularity. It prints one
7085 line for each sequence of instructions that belong to the same
7086 function giving the name of that function, the source lines
7087 for this instruction sequence (if the @code{/l} modifier is
7088 specified), and the instructions numbers that form the sequence (if
7089 the @code{/i} modifier is specified). The function names are indented
7090 to reflect the call stack depth if the @code{/c} modifier is
7091 specified. The @code{/l}, @code{/i}, and @code{/c} modifiers can be
7095 (@value{GDBP}) @b{list 1, 10}
7106 (@value{GDBP}) @b{record function-call-history /ilc}
7107 1 bar inst 1,4 at foo.c:6,8
7108 2 foo inst 5,10 at foo.c:2,3
7109 3 bar inst 11,13 at foo.c:9,10
7112 By default, ten lines are printed. This can be changed using the
7113 @code{set record function-call-history-size} command. Functions are
7114 printed in execution order. There are several ways to specify what
7118 @item record function-call-history @var{func}
7119 Prints ten functions starting from function number @var{func}.
7121 @item record function-call-history @var{func}, +/-@var{n}
7122 Prints @var{n} functions around function number @var{func}. If
7123 @var{n} is preceded with @code{+}, prints @var{n} functions after
7124 function number @var{func}. If @var{n} is preceded with @code{-},
7125 prints @var{n} functions before function number @var{func}.
7127 @item record function-call-history
7128 Prints ten more functions after the last ten-line print.
7130 @item record function-call-history -
7131 Prints ten more functions before the last ten-line print.
7133 @item record function-call-history @var{begin}, @var{end}
7134 Prints functions beginning with function number @var{begin} until
7135 function number @var{end}. The function number @var{end} is included.
7138 This command may not be available for all recording methods.
7140 @item set record function-call-history-size @var{size}
7141 @itemx set record function-call-history-size unlimited
7142 Define how many lines to print in the
7143 @code{record function-call-history} command. The default value is 10.
7144 A size of @code{unlimited} means unlimited lines.
7146 @item show record function-call-history-size
7147 Show how many lines to print in the
7148 @code{record function-call-history} command.
7153 @chapter Examining the Stack
7155 When your program has stopped, the first thing you need to know is where it
7156 stopped and how it got there.
7159 Each time your program performs a function call, information about the call
7161 That information includes the location of the call in your program,
7162 the arguments of the call,
7163 and the local variables of the function being called.
7164 The information is saved in a block of data called a @dfn{stack frame}.
7165 The stack frames are allocated in a region of memory called the @dfn{call
7168 When your program stops, the @value{GDBN} commands for examining the
7169 stack allow you to see all of this information.
7171 @cindex selected frame
7172 One of the stack frames is @dfn{selected} by @value{GDBN} and many
7173 @value{GDBN} commands refer implicitly to the selected frame. In
7174 particular, whenever you ask @value{GDBN} for the value of a variable in
7175 your program, the value is found in the selected frame. There are
7176 special @value{GDBN} commands to select whichever frame you are
7177 interested in. @xref{Selection, ,Selecting a Frame}.
7179 When your program stops, @value{GDBN} automatically selects the
7180 currently executing frame and describes it briefly, similar to the
7181 @code{frame} command (@pxref{Frame Info, ,Information about a Frame}).
7184 * Frames:: Stack frames
7185 * Backtrace:: Backtraces
7186 * Selection:: Selecting a frame
7187 * Frame Info:: Information on a frame
7188 * Frame Filter Management:: Managing frame filters
7193 @section Stack Frames
7195 @cindex frame, definition
7197 The call stack is divided up into contiguous pieces called @dfn{stack
7198 frames}, or @dfn{frames} for short; each frame is the data associated
7199 with one call to one function. The frame contains the arguments given
7200 to the function, the function's local variables, and the address at
7201 which the function is executing.
7203 @cindex initial frame
7204 @cindex outermost frame
7205 @cindex innermost frame
7206 When your program is started, the stack has only one frame, that of the
7207 function @code{main}. This is called the @dfn{initial} frame or the
7208 @dfn{outermost} frame. Each time a function is called, a new frame is
7209 made. Each time a function returns, the frame for that function invocation
7210 is eliminated. If a function is recursive, there can be many frames for
7211 the same function. The frame for the function in which execution is
7212 actually occurring is called the @dfn{innermost} frame. This is the most
7213 recently created of all the stack frames that still exist.
7215 @cindex frame pointer
7216 Inside your program, stack frames are identified by their addresses. A
7217 stack frame consists of many bytes, each of which has its own address; each
7218 kind of computer has a convention for choosing one byte whose
7219 address serves as the address of the frame. Usually this address is kept
7220 in a register called the @dfn{frame pointer register}
7221 (@pxref{Registers, $fp}) while execution is going on in that frame.
7223 @cindex frame number
7224 @value{GDBN} assigns numbers to all existing stack frames, starting with
7225 zero for the innermost frame, one for the frame that called it,
7226 and so on upward. These numbers do not really exist in your program;
7227 they are assigned by @value{GDBN} to give you a way of designating stack
7228 frames in @value{GDBN} commands.
7230 @c The -fomit-frame-pointer below perennially causes hbox overflow
7231 @c underflow problems.
7232 @cindex frameless execution
7233 Some compilers provide a way to compile functions so that they operate
7234 without stack frames. (For example, the @value{NGCC} option
7236 @samp{-fomit-frame-pointer}
7238 generates functions without a frame.)
7239 This is occasionally done with heavily used library functions to save
7240 the frame setup time. @value{GDBN} has limited facilities for dealing
7241 with these function invocations. If the innermost function invocation
7242 has no stack frame, @value{GDBN} nevertheless regards it as though
7243 it had a separate frame, which is numbered zero as usual, allowing
7244 correct tracing of the function call chain. However, @value{GDBN} has
7245 no provision for frameless functions elsewhere in the stack.
7251 @cindex call stack traces
7252 A backtrace is a summary of how your program got where it is. It shows one
7253 line per frame, for many frames, starting with the currently executing
7254 frame (frame zero), followed by its caller (frame one), and on up the
7257 @anchor{backtrace-command}
7260 @kindex bt @r{(@code{backtrace})}
7263 Print a backtrace of the entire stack: one line per frame for all
7264 frames in the stack.
7266 You can stop the backtrace at any time by typing the system interrupt
7267 character, normally @kbd{Ctrl-c}.
7269 @item backtrace @var{n}
7271 Similar, but print only the innermost @var{n} frames.
7273 @item backtrace -@var{n}
7275 Similar, but print only the outermost @var{n} frames.
7277 @item backtrace full
7279 @itemx bt full @var{n}
7280 @itemx bt full -@var{n}
7281 Print the values of the local variables also. As described above,
7282 @var{n} specifies the number of frames to print.
7284 @item backtrace no-filters
7285 @itemx bt no-filters
7286 @itemx bt no-filters @var{n}
7287 @itemx bt no-filters -@var{n}
7288 @itemx bt no-filters full
7289 @itemx bt no-filters full @var{n}
7290 @itemx bt no-filters full -@var{n}
7291 Do not run Python frame filters on this backtrace. @xref{Frame
7292 Filter API}, for more information. Additionally use @ref{disable
7293 frame-filter all} to turn off all frame filters. This is only
7294 relevant when @value{GDBN} has been configured with @code{Python}
7300 The names @code{where} and @code{info stack} (abbreviated @code{info s})
7301 are additional aliases for @code{backtrace}.
7303 @cindex multiple threads, backtrace
7304 In a multi-threaded program, @value{GDBN} by default shows the
7305 backtrace only for the current thread. To display the backtrace for
7306 several or all of the threads, use the command @code{thread apply}
7307 (@pxref{Threads, thread apply}). For example, if you type @kbd{thread
7308 apply all backtrace}, @value{GDBN} will display the backtrace for all
7309 the threads; this is handy when you debug a core dump of a
7310 multi-threaded program.
7312 Each line in the backtrace shows the frame number and the function name.
7313 The program counter value is also shown---unless you use @code{set
7314 print address off}. The backtrace also shows the source file name and
7315 line number, as well as the arguments to the function. The program
7316 counter value is omitted if it is at the beginning of the code for that
7319 Here is an example of a backtrace. It was made with the command
7320 @samp{bt 3}, so it shows the innermost three frames.
7324 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
7326 #1 0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
7327 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
7329 (More stack frames follow...)
7334 The display for frame zero does not begin with a program counter
7335 value, indicating that your program has stopped at the beginning of the
7336 code for line @code{993} of @code{builtin.c}.
7339 The value of parameter @code{data} in frame 1 has been replaced by
7340 @code{@dots{}}. By default, @value{GDBN} prints the value of a parameter
7341 only if it is a scalar (integer, pointer, enumeration, etc). See command
7342 @kbd{set print frame-arguments} in @ref{Print Settings} for more details
7343 on how to configure the way function parameter values are printed.
7345 @cindex optimized out, in backtrace
7346 @cindex function call arguments, optimized out
7347 If your program was compiled with optimizations, some compilers will
7348 optimize away arguments passed to functions if those arguments are
7349 never used after the call. Such optimizations generate code that
7350 passes arguments through registers, but doesn't store those arguments
7351 in the stack frame. @value{GDBN} has no way of displaying such
7352 arguments in stack frames other than the innermost one. Here's what
7353 such a backtrace might look like:
7357 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
7359 #1 0x6e38 in expand_macro (sym=<optimized out>) at macro.c:242
7360 #2 0x6840 in expand_token (obs=0x0, t=<optimized out>, td=0xf7fffb08)
7362 (More stack frames follow...)
7367 The values of arguments that were not saved in their stack frames are
7368 shown as @samp{<optimized out>}.
7370 If you need to display the values of such optimized-out arguments,
7371 either deduce that from other variables whose values depend on the one
7372 you are interested in, or recompile without optimizations.
7374 @cindex backtrace beyond @code{main} function
7375 @cindex program entry point
7376 @cindex startup code, and backtrace
7377 Most programs have a standard user entry point---a place where system
7378 libraries and startup code transition into user code. For C this is
7379 @code{main}@footnote{
7380 Note that embedded programs (the so-called ``free-standing''
7381 environment) are not required to have a @code{main} function as the
7382 entry point. They could even have multiple entry points.}.
7383 When @value{GDBN} finds the entry function in a backtrace
7384 it will terminate the backtrace, to avoid tracing into highly
7385 system-specific (and generally uninteresting) code.
7387 If you need to examine the startup code, or limit the number of levels
7388 in a backtrace, you can change this behavior:
7391 @item set backtrace past-main
7392 @itemx set backtrace past-main on
7393 @kindex set backtrace
7394 Backtraces will continue past the user entry point.
7396 @item set backtrace past-main off
7397 Backtraces will stop when they encounter the user entry point. This is the
7400 @item show backtrace past-main
7401 @kindex show backtrace
7402 Display the current user entry point backtrace policy.
7404 @item set backtrace past-entry
7405 @itemx set backtrace past-entry on
7406 Backtraces will continue past the internal entry point of an application.
7407 This entry point is encoded by the linker when the application is built,
7408 and is likely before the user entry point @code{main} (or equivalent) is called.
7410 @item set backtrace past-entry off
7411 Backtraces will stop when they encounter the internal entry point of an
7412 application. This is the default.
7414 @item show backtrace past-entry
7415 Display the current internal entry point backtrace policy.
7417 @item set backtrace limit @var{n}
7418 @itemx set backtrace limit 0
7419 @itemx set backtrace limit unlimited
7420 @cindex backtrace limit
7421 Limit the backtrace to @var{n} levels. A value of @code{unlimited}
7422 or zero means unlimited levels.
7424 @item show backtrace limit
7425 Display the current limit on backtrace levels.
7428 You can control how file names are displayed.
7431 @item set filename-display
7432 @itemx set filename-display relative
7433 @cindex filename-display
7434 Display file names relative to the compilation directory. This is the default.
7436 @item set filename-display basename
7437 Display only basename of a filename.
7439 @item set filename-display absolute
7440 Display an absolute filename.
7442 @item show filename-display
7443 Show the current way to display filenames.
7447 @section Selecting a Frame
7449 Most commands for examining the stack and other data in your program work on
7450 whichever stack frame is selected at the moment. Here are the commands for
7451 selecting a stack frame; all of them finish by printing a brief description
7452 of the stack frame just selected.
7455 @kindex frame@r{, selecting}
7456 @kindex f @r{(@code{frame})}
7459 Select frame number @var{n}. Recall that frame zero is the innermost
7460 (currently executing) frame, frame one is the frame that called the
7461 innermost one, and so on. The highest-numbered frame is the one for
7464 @item frame @var{stack-addr} [ @var{pc-addr} ]
7465 @itemx f @var{stack-addr} [ @var{pc-addr} ]
7466 Select the frame at address @var{stack-addr}. This is useful mainly if the
7467 chaining of stack frames has been damaged by a bug, making it
7468 impossible for @value{GDBN} to assign numbers properly to all frames. In
7469 addition, this can be useful when your program has multiple stacks and
7470 switches between them. The optional @var{pc-addr} can also be given to
7471 specify the value of PC for the stack frame.
7475 Move @var{n} frames up the stack; @var{n} defaults to 1. For positive
7476 numbers @var{n}, this advances toward the outermost frame, to higher
7477 frame numbers, to frames that have existed longer.
7480 @kindex do @r{(@code{down})}
7482 Move @var{n} frames down the stack; @var{n} defaults to 1. For
7483 positive numbers @var{n}, this advances toward the innermost frame, to
7484 lower frame numbers, to frames that were created more recently.
7485 You may abbreviate @code{down} as @code{do}.
7488 All of these commands end by printing two lines of output describing the
7489 frame. The first line shows the frame number, the function name, the
7490 arguments, and the source file and line number of execution in that
7491 frame. The second line shows the text of that source line.
7499 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
7501 10 read_input_file (argv[i]);
7505 After such a printout, the @code{list} command with no arguments
7506 prints ten lines centered on the point of execution in the frame.
7507 You can also edit the program at the point of execution with your favorite
7508 editing program by typing @code{edit}.
7509 @xref{List, ,Printing Source Lines},
7513 @kindex select-frame
7515 The @code{select-frame} command is a variant of @code{frame} that does
7516 not display the new frame after selecting it. This command is
7517 intended primarily for use in @value{GDBN} command scripts, where the
7518 output might be unnecessary and distracting.
7520 @kindex down-silently
7522 @item up-silently @var{n}
7523 @itemx down-silently @var{n}
7524 These two commands are variants of @code{up} and @code{down},
7525 respectively; they differ in that they do their work silently, without
7526 causing display of the new frame. They are intended primarily for use
7527 in @value{GDBN} command scripts, where the output might be unnecessary and
7532 @section Information About a Frame
7534 There are several other commands to print information about the selected
7540 When used without any argument, this command does not change which
7541 frame is selected, but prints a brief description of the currently
7542 selected stack frame. It can be abbreviated @code{f}. With an
7543 argument, this command is used to select a stack frame.
7544 @xref{Selection, ,Selecting a Frame}.
7547 @kindex info f @r{(@code{info frame})}
7550 This command prints a verbose description of the selected stack frame,
7555 the address of the frame
7557 the address of the next frame down (called by this frame)
7559 the address of the next frame up (caller of this frame)
7561 the language in which the source code corresponding to this frame is written
7563 the address of the frame's arguments
7565 the address of the frame's local variables
7567 the program counter saved in it (the address of execution in the caller frame)
7569 which registers were saved in the frame
7572 @noindent The verbose description is useful when
7573 something has gone wrong that has made the stack format fail to fit
7574 the usual conventions.
7576 @item info frame @var{addr}
7577 @itemx info f @var{addr}
7578 Print a verbose description of the frame at address @var{addr}, without
7579 selecting that frame. The selected frame remains unchanged by this
7580 command. This requires the same kind of address (more than one for some
7581 architectures) that you specify in the @code{frame} command.
7582 @xref{Selection, ,Selecting a Frame}.
7586 Print the arguments of the selected frame, each on a separate line.
7590 Print the local variables of the selected frame, each on a separate
7591 line. These are all variables (declared either static or automatic)
7592 accessible at the point of execution of the selected frame.
7596 @node Frame Filter Management
7597 @section Management of Frame Filters.
7598 @cindex managing frame filters
7600 Frame filters are Python based utilities to manage and decorate the
7601 output of frames. @xref{Frame Filter API}, for further information.
7603 Managing frame filters is performed by several commands available
7604 within @value{GDBN}, detailed here.
7607 @kindex info frame-filter
7608 @item info frame-filter
7609 Print a list of installed frame filters from all dictionaries, showing
7610 their name, priority and enabled status.
7612 @kindex disable frame-filter
7613 @anchor{disable frame-filter all}
7614 @item disable frame-filter @var{filter-dictionary} @var{filter-name}
7615 Disable a frame filter in the dictionary matching
7616 @var{filter-dictionary} and @var{filter-name}. The
7617 @var{filter-dictionary} may be @code{all}, @code{global},
7618 @code{progspace}, or the name of the object file where the frame filter
7619 dictionary resides. When @code{all} is specified, all frame filters
7620 across all dictionaries are disabled. The @var{filter-name} is the name
7621 of the frame filter and is used when @code{all} is not the option for
7622 @var{filter-dictionary}. A disabled frame-filter is not deleted, it
7623 may be enabled again later.
7625 @kindex enable frame-filter
7626 @item enable frame-filter @var{filter-dictionary} @var{filter-name}
7627 Enable a frame filter in the dictionary matching
7628 @var{filter-dictionary} and @var{filter-name}. The
7629 @var{filter-dictionary} may be @code{all}, @code{global},
7630 @code{progspace} or the name of the object file where the frame filter
7631 dictionary resides. When @code{all} is specified, all frame filters across
7632 all dictionaries are enabled. The @var{filter-name} is the name of the frame
7633 filter and is used when @code{all} is not the option for
7634 @var{filter-dictionary}.
7639 (gdb) info frame-filter
7641 global frame-filters:
7642 Priority Enabled Name
7643 1000 No PrimaryFunctionFilter
7646 progspace /build/test frame-filters:
7647 Priority Enabled Name
7648 100 Yes ProgspaceFilter
7650 objfile /build/test frame-filters:
7651 Priority Enabled Name
7652 999 Yes BuildProgra Filter
7654 (gdb) disable frame-filter /build/test BuildProgramFilter
7655 (gdb) info frame-filter
7657 global frame-filters:
7658 Priority Enabled Name
7659 1000 No PrimaryFunctionFilter
7662 progspace /build/test frame-filters:
7663 Priority Enabled Name
7664 100 Yes ProgspaceFilter
7666 objfile /build/test frame-filters:
7667 Priority Enabled Name
7668 999 No BuildProgramFilter
7670 (gdb) enable frame-filter global PrimaryFunctionFilter
7671 (gdb) info frame-filter
7673 global frame-filters:
7674 Priority Enabled Name
7675 1000 Yes PrimaryFunctionFilter
7678 progspace /build/test frame-filters:
7679 Priority Enabled Name
7680 100 Yes ProgspaceFilter
7682 objfile /build/test frame-filters:
7683 Priority Enabled Name
7684 999 No BuildProgramFilter
7687 @kindex set frame-filter priority
7688 @item set frame-filter priority @var{filter-dictionary} @var{filter-name} @var{priority}
7689 Set the @var{priority} of a frame filter in the dictionary matching
7690 @var{filter-dictionary}, and the frame filter name matching
7691 @var{filter-name}. The @var{filter-dictionary} may be @code{global},
7692 @code{progspace} or the name of the object file where the frame filter
7693 dictionary resides. The @var{priority} is an integer.
7695 @kindex show frame-filter priority
7696 @item show frame-filter priority @var{filter-dictionary} @var{filter-name}
7697 Show the @var{priority} of a frame filter in the dictionary matching
7698 @var{filter-dictionary}, and the frame filter name matching
7699 @var{filter-name}. The @var{filter-dictionary} may be @code{global},
7700 @code{progspace} or the name of the object file where the frame filter
7706 (gdb) info frame-filter
7708 global frame-filters:
7709 Priority Enabled Name
7710 1000 Yes PrimaryFunctionFilter
7713 progspace /build/test frame-filters:
7714 Priority Enabled Name
7715 100 Yes ProgspaceFilter
7717 objfile /build/test frame-filters:
7718 Priority Enabled Name
7719 999 No BuildProgramFilter
7721 (gdb) set frame-filter priority global Reverse 50
7722 (gdb) info frame-filter
7724 global frame-filters:
7725 Priority Enabled Name
7726 1000 Yes PrimaryFunctionFilter
7729 progspace /build/test frame-filters:
7730 Priority Enabled Name
7731 100 Yes ProgspaceFilter
7733 objfile /build/test frame-filters:
7734 Priority Enabled Name
7735 999 No BuildProgramFilter
7740 @chapter Examining Source Files
7742 @value{GDBN} can print parts of your program's source, since the debugging
7743 information recorded in the program tells @value{GDBN} what source files were
7744 used to build it. When your program stops, @value{GDBN} spontaneously prints
7745 the line where it stopped. Likewise, when you select a stack frame
7746 (@pxref{Selection, ,Selecting a Frame}), @value{GDBN} prints the line where
7747 execution in that frame has stopped. You can print other portions of
7748 source files by explicit command.
7750 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
7751 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
7752 @value{GDBN} under @sc{gnu} Emacs}.
7755 * List:: Printing source lines
7756 * Specify Location:: How to specify code locations
7757 * Edit:: Editing source files
7758 * Search:: Searching source files
7759 * Source Path:: Specifying source directories
7760 * Machine Code:: Source and machine code
7764 @section Printing Source Lines
7767 @kindex l @r{(@code{list})}
7768 To print lines from a source file, use the @code{list} command
7769 (abbreviated @code{l}). By default, ten lines are printed.
7770 There are several ways to specify what part of the file you want to
7771 print; see @ref{Specify Location}, for the full list.
7773 Here are the forms of the @code{list} command most commonly used:
7776 @item list @var{linenum}
7777 Print lines centered around line number @var{linenum} in the
7778 current source file.
7780 @item list @var{function}
7781 Print lines centered around the beginning of function
7785 Print more lines. If the last lines printed were printed with a
7786 @code{list} command, this prints lines following the last lines
7787 printed; however, if the last line printed was a solitary line printed
7788 as part of displaying a stack frame (@pxref{Stack, ,Examining the
7789 Stack}), this prints lines centered around that line.
7792 Print lines just before the lines last printed.
7795 @cindex @code{list}, how many lines to display
7796 By default, @value{GDBN} prints ten source lines with any of these forms of
7797 the @code{list} command. You can change this using @code{set listsize}:
7800 @kindex set listsize
7801 @item set listsize @var{count}
7802 @itemx set listsize unlimited
7803 Make the @code{list} command display @var{count} source lines (unless
7804 the @code{list} argument explicitly specifies some other number).
7805 Setting @var{count} to @code{unlimited} or 0 means there's no limit.
7807 @kindex show listsize
7809 Display the number of lines that @code{list} prints.
7812 Repeating a @code{list} command with @key{RET} discards the argument,
7813 so it is equivalent to typing just @code{list}. This is more useful
7814 than listing the same lines again. An exception is made for an
7815 argument of @samp{-}; that argument is preserved in repetition so that
7816 each repetition moves up in the source file.
7818 In general, the @code{list} command expects you to supply zero, one or two
7819 @dfn{locations}. Locations specify source lines; there are several ways
7820 of writing them (@pxref{Specify Location}), but the effect is always
7821 to specify some source line.
7823 Here is a complete description of the possible arguments for @code{list}:
7826 @item list @var{location}
7827 Print lines centered around the line specified by @var{location}.
7829 @item list @var{first},@var{last}
7830 Print lines from @var{first} to @var{last}. Both arguments are
7831 locations. When a @code{list} command has two locations, and the
7832 source file of the second location is omitted, this refers to
7833 the same source file as the first location.
7835 @item list ,@var{last}
7836 Print lines ending with @var{last}.
7838 @item list @var{first},
7839 Print lines starting with @var{first}.
7842 Print lines just after the lines last printed.
7845 Print lines just before the lines last printed.
7848 As described in the preceding table.
7851 @node Specify Location
7852 @section Specifying a Location
7853 @cindex specifying location
7855 @cindex source location
7858 * Linespec Locations:: Linespec locations
7859 * Explicit Locations:: Explicit locations
7860 * Address Locations:: Address locations
7863 Several @value{GDBN} commands accept arguments that specify a location
7864 of your program's code. Since @value{GDBN} is a source-level
7865 debugger, a location usually specifies some line in the source code.
7866 Locations may be specified using three different formats:
7867 linespec locations, explicit locations, or address locations.
7869 @node Linespec Locations
7870 @subsection Linespec Locations
7871 @cindex linespec locations
7873 A @dfn{linespec} is a colon-separated list of source location parameters such
7874 as file name, function name, etc. Here are all the different ways of
7875 specifying a linespec:
7879 Specifies the line number @var{linenum} of the current source file.
7882 @itemx +@var{offset}
7883 Specifies the line @var{offset} lines before or after the @dfn{current
7884 line}. For the @code{list} command, the current line is the last one
7885 printed; for the breakpoint commands, this is the line at which
7886 execution stopped in the currently selected @dfn{stack frame}
7887 (@pxref{Frames, ,Frames}, for a description of stack frames.) When
7888 used as the second of the two linespecs in a @code{list} command,
7889 this specifies the line @var{offset} lines up or down from the first
7892 @item @var{filename}:@var{linenum}
7893 Specifies the line @var{linenum} in the source file @var{filename}.
7894 If @var{filename} is a relative file name, then it will match any
7895 source file name with the same trailing components. For example, if
7896 @var{filename} is @samp{gcc/expr.c}, then it will match source file
7897 name of @file{/build/trunk/gcc/expr.c}, but not
7898 @file{/build/trunk/libcpp/expr.c} or @file{/build/trunk/gcc/x-expr.c}.
7900 @item @var{function}
7901 Specifies the line that begins the body of the function @var{function}.
7902 For example, in C, this is the line with the open brace.
7904 @item @var{function}:@var{label}
7905 Specifies the line where @var{label} appears in @var{function}.
7907 @item @var{filename}:@var{function}
7908 Specifies the line that begins the body of the function @var{function}
7909 in the file @var{filename}. You only need the file name with a
7910 function name to avoid ambiguity when there are identically named
7911 functions in different source files.
7914 Specifies the line at which the label named @var{label} appears
7915 in the function corresponding to the currently selected stack frame.
7916 If there is no current selected stack frame (for instance, if the inferior
7917 is not running), then @value{GDBN} will not search for a label.
7919 @cindex breakpoint at static probe point
7920 @item -pstap|-probe-stap @r{[}@var{objfile}:@r{[}@var{provider}:@r{]}@r{]}@var{name}
7921 The @sc{gnu}/Linux tool @code{SystemTap} provides a way for
7922 applications to embed static probes. @xref{Static Probe Points}, for more
7923 information on finding and using static probes. This form of linespec
7924 specifies the location of such a static probe.
7926 If @var{objfile} is given, only probes coming from that shared library
7927 or executable matching @var{objfile} as a regular expression are considered.
7928 If @var{provider} is given, then only probes from that provider are considered.
7929 If several probes match the spec, @value{GDBN} will insert a breakpoint at
7930 each one of those probes.
7933 @node Explicit Locations
7934 @subsection Explicit Locations
7935 @cindex explicit locations
7937 @dfn{Explicit locations} allow the user to directly specify the source
7938 location's parameters using option-value pairs.
7940 Explicit locations are useful when several functions, labels, or
7941 file names have the same name (base name for files) in the program's
7942 sources. In these cases, explicit locations point to the source
7943 line you meant more accurately and unambiguously. Also, using
7944 explicit locations might be faster in large programs.
7946 For example, the linespec @samp{foo:bar} may refer to a function @code{bar}
7947 defined in the file named @file{foo} or the label @code{bar} in a function
7948 named @code{foo}. @value{GDBN} must search either the file system or
7949 the symbol table to know.
7951 The list of valid explicit location options is summarized in the
7955 @item -source @var{filename}
7956 The value specifies the source file name. To differentiate between
7957 files with the same base name, prepend as many directories as is necessary
7958 to uniquely identify the desired file, e.g., @file{foo/bar/baz.c}. Otherwise
7959 @value{GDBN} will use the first file it finds with the given base
7960 name. This option requires the use of either @code{-function} or @code{-line}.
7962 @item -function @var{function}
7963 The value specifies the name of a function. Operations
7964 on function locations unmodified by other options (such as @code{-label}
7965 or @code{-line}) refer to the line that begins the body of the function.
7966 In C, for example, this is the line with the open brace.
7968 @item -label @var{label}
7969 The value specifies the name of a label. When the function
7970 name is not specified, the label is searched in the function of the currently
7971 selected stack frame.
7973 @item -line @var{number}
7974 The value specifies a line offset for the location. The offset may either
7975 be absolute (@code{-line 3}) or relative (@code{-line +3}), depending on
7976 the command. When specified without any other options, the line offset is
7977 relative to the current line.
7980 Explicit location options may be abbreviated by omitting any non-unique
7981 trailing characters from the option name, e.g., @code{break -s main.c -li 3}.
7983 @node Address Locations
7984 @subsection Address Locations
7985 @cindex address locations
7987 @dfn{Address locations} indicate a specific program address. They have
7988 the generalized form *@var{address}.
7990 For line-oriented commands, such as @code{list} and @code{edit}, this
7991 specifies a source line that contains @var{address}. For @code{break} and
7992 other breakpoint-oriented commands, this can be used to set breakpoints in
7993 parts of your program which do not have debugging information or
7996 Here @var{address} may be any expression valid in the current working
7997 language (@pxref{Languages, working language}) that specifies a code
7998 address. In addition, as a convenience, @value{GDBN} extends the
7999 semantics of expressions used in locations to cover several situations
8000 that frequently occur during debugging. Here are the various forms
8004 @item @var{expression}
8005 Any expression valid in the current working language.
8007 @item @var{funcaddr}
8008 An address of a function or procedure derived from its name. In C,
8009 C@t{++}, Objective-C, Fortran, minimal, and assembly, this is
8010 simply the function's name @var{function} (and actually a special case
8011 of a valid expression). In Pascal and Modula-2, this is
8012 @code{&@var{function}}. In Ada, this is @code{@var{function}'Address}
8013 (although the Pascal form also works).
8015 This form specifies the address of the function's first instruction,
8016 before the stack frame and arguments have been set up.
8018 @item '@var{filename}':@var{funcaddr}
8019 Like @var{funcaddr} above, but also specifies the name of the source
8020 file explicitly. This is useful if the name of the function does not
8021 specify the function unambiguously, e.g., if there are several
8022 functions with identical names in different source files.
8026 @section Editing Source Files
8027 @cindex editing source files
8030 @kindex e @r{(@code{edit})}
8031 To edit the lines in a source file, use the @code{edit} command.
8032 The editing program of your choice
8033 is invoked with the current line set to
8034 the active line in the program.
8035 Alternatively, there are several ways to specify what part of the file you
8036 want to print if you want to see other parts of the program:
8039 @item edit @var{location}
8040 Edit the source file specified by @code{location}. Editing starts at
8041 that @var{location}, e.g., at the specified source line of the
8042 specified file. @xref{Specify Location}, for all the possible forms
8043 of the @var{location} argument; here are the forms of the @code{edit}
8044 command most commonly used:
8047 @item edit @var{number}
8048 Edit the current source file with @var{number} as the active line number.
8050 @item edit @var{function}
8051 Edit the file containing @var{function} at the beginning of its definition.
8056 @subsection Choosing your Editor
8057 You can customize @value{GDBN} to use any editor you want
8059 The only restriction is that your editor (say @code{ex}), recognizes the
8060 following command-line syntax:
8062 ex +@var{number} file
8064 The optional numeric value +@var{number} specifies the number of the line in
8065 the file where to start editing.}.
8066 By default, it is @file{@value{EDITOR}}, but you can change this
8067 by setting the environment variable @code{EDITOR} before using
8068 @value{GDBN}. For example, to configure @value{GDBN} to use the
8069 @code{vi} editor, you could use these commands with the @code{sh} shell:
8075 or in the @code{csh} shell,
8077 setenv EDITOR /usr/bin/vi
8082 @section Searching Source Files
8083 @cindex searching source files
8085 There are two commands for searching through the current source file for a
8090 @kindex forward-search
8091 @kindex fo @r{(@code{forward-search})}
8092 @item forward-search @var{regexp}
8093 @itemx search @var{regexp}
8094 The command @samp{forward-search @var{regexp}} checks each line,
8095 starting with the one following the last line listed, for a match for
8096 @var{regexp}. It lists the line that is found. You can use the
8097 synonym @samp{search @var{regexp}} or abbreviate the command name as
8100 @kindex reverse-search
8101 @item reverse-search @var{regexp}
8102 The command @samp{reverse-search @var{regexp}} checks each line, starting
8103 with the one before the last line listed and going backward, for a match
8104 for @var{regexp}. It lists the line that is found. You can abbreviate
8105 this command as @code{rev}.
8109 @section Specifying Source Directories
8112 @cindex directories for source files
8113 Executable programs sometimes do not record the directories of the source
8114 files from which they were compiled, just the names. Even when they do,
8115 the directories could be moved between the compilation and your debugging
8116 session. @value{GDBN} has a list of directories to search for source files;
8117 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
8118 it tries all the directories in the list, in the order they are present
8119 in the list, until it finds a file with the desired name.
8121 For example, suppose an executable references the file
8122 @file{/usr/src/foo-1.0/lib/foo.c}, and our source path is
8123 @file{/mnt/cross}. The file is first looked up literally; if this
8124 fails, @file{/mnt/cross/usr/src/foo-1.0/lib/foo.c} is tried; if this
8125 fails, @file{/mnt/cross/foo.c} is opened; if this fails, an error
8126 message is printed. @value{GDBN} does not look up the parts of the
8127 source file name, such as @file{/mnt/cross/src/foo-1.0/lib/foo.c}.
8128 Likewise, the subdirectories of the source path are not searched: if
8129 the source path is @file{/mnt/cross}, and the binary refers to
8130 @file{foo.c}, @value{GDBN} would not find it under
8131 @file{/mnt/cross/usr/src/foo-1.0/lib}.
8133 Plain file names, relative file names with leading directories, file
8134 names containing dots, etc.@: are all treated as described above; for
8135 instance, if the source path is @file{/mnt/cross}, and the source file
8136 is recorded as @file{../lib/foo.c}, @value{GDBN} would first try
8137 @file{../lib/foo.c}, then @file{/mnt/cross/../lib/foo.c}, and after
8138 that---@file{/mnt/cross/foo.c}.
8140 Note that the executable search path is @emph{not} used to locate the
8143 Whenever you reset or rearrange the source path, @value{GDBN} clears out
8144 any information it has cached about where source files are found and where
8145 each line is in the file.
8149 When you start @value{GDBN}, its source path includes only @samp{cdir}
8150 and @samp{cwd}, in that order.
8151 To add other directories, use the @code{directory} command.
8153 The search path is used to find both program source files and @value{GDBN}
8154 script files (read using the @samp{-command} option and @samp{source} command).
8156 In addition to the source path, @value{GDBN} provides a set of commands
8157 that manage a list of source path substitution rules. A @dfn{substitution
8158 rule} specifies how to rewrite source directories stored in the program's
8159 debug information in case the sources were moved to a different
8160 directory between compilation and debugging. A rule is made of
8161 two strings, the first specifying what needs to be rewritten in
8162 the path, and the second specifying how it should be rewritten.
8163 In @ref{set substitute-path}, we name these two parts @var{from} and
8164 @var{to} respectively. @value{GDBN} does a simple string replacement
8165 of @var{from} with @var{to} at the start of the directory part of the
8166 source file name, and uses that result instead of the original file
8167 name to look up the sources.
8169 Using the previous example, suppose the @file{foo-1.0} tree has been
8170 moved from @file{/usr/src} to @file{/mnt/cross}, then you can tell
8171 @value{GDBN} to replace @file{/usr/src} in all source path names with
8172 @file{/mnt/cross}. The first lookup will then be
8173 @file{/mnt/cross/foo-1.0/lib/foo.c} in place of the original location
8174 of @file{/usr/src/foo-1.0/lib/foo.c}. To define a source path
8175 substitution rule, use the @code{set substitute-path} command
8176 (@pxref{set substitute-path}).
8178 To avoid unexpected substitution results, a rule is applied only if the
8179 @var{from} part of the directory name ends at a directory separator.
8180 For instance, a rule substituting @file{/usr/source} into
8181 @file{/mnt/cross} will be applied to @file{/usr/source/foo-1.0} but
8182 not to @file{/usr/sourceware/foo-2.0}. And because the substitution
8183 is applied only at the beginning of the directory name, this rule will
8184 not be applied to @file{/root/usr/source/baz.c} either.
8186 In many cases, you can achieve the same result using the @code{directory}
8187 command. However, @code{set substitute-path} can be more efficient in
8188 the case where the sources are organized in a complex tree with multiple
8189 subdirectories. With the @code{directory} command, you need to add each
8190 subdirectory of your project. If you moved the entire tree while
8191 preserving its internal organization, then @code{set substitute-path}
8192 allows you to direct the debugger to all the sources with one single
8195 @code{set substitute-path} is also more than just a shortcut command.
8196 The source path is only used if the file at the original location no
8197 longer exists. On the other hand, @code{set substitute-path} modifies
8198 the debugger behavior to look at the rewritten location instead. So, if
8199 for any reason a source file that is not relevant to your executable is
8200 located at the original location, a substitution rule is the only
8201 method available to point @value{GDBN} at the new location.
8203 @cindex @samp{--with-relocated-sources}
8204 @cindex default source path substitution
8205 You can configure a default source path substitution rule by
8206 configuring @value{GDBN} with the
8207 @samp{--with-relocated-sources=@var{dir}} option. The @var{dir}
8208 should be the name of a directory under @value{GDBN}'s configured
8209 prefix (set with @samp{--prefix} or @samp{--exec-prefix}), and
8210 directory names in debug information under @var{dir} will be adjusted
8211 automatically if the installed @value{GDBN} is moved to a new
8212 location. This is useful if @value{GDBN}, libraries or executables
8213 with debug information and corresponding source code are being moved
8217 @item directory @var{dirname} @dots{}
8218 @item dir @var{dirname} @dots{}
8219 Add directory @var{dirname} to the front of the source path. Several
8220 directory names may be given to this command, separated by @samp{:}
8221 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
8222 part of absolute file names) or
8223 whitespace. You may specify a directory that is already in the source
8224 path; this moves it forward, so @value{GDBN} searches it sooner.
8228 @vindex $cdir@r{, convenience variable}
8229 @vindex $cwd@r{, convenience variable}
8230 @cindex compilation directory
8231 @cindex current directory
8232 @cindex working directory
8233 @cindex directory, current
8234 @cindex directory, compilation
8235 You can use the string @samp{$cdir} to refer to the compilation
8236 directory (if one is recorded), and @samp{$cwd} to refer to the current
8237 working directory. @samp{$cwd} is not the same as @samp{.}---the former
8238 tracks the current working directory as it changes during your @value{GDBN}
8239 session, while the latter is immediately expanded to the current
8240 directory at the time you add an entry to the source path.
8243 Reset the source path to its default value (@samp{$cdir:$cwd} on Unix systems). This requires confirmation.
8245 @c RET-repeat for @code{directory} is explicitly disabled, but since
8246 @c repeating it would be a no-op we do not say that. (thanks to RMS)
8248 @item set directories @var{path-list}
8249 @kindex set directories
8250 Set the source path to @var{path-list}.
8251 @samp{$cdir:$cwd} are added if missing.
8253 @item show directories
8254 @kindex show directories
8255 Print the source path: show which directories it contains.
8257 @anchor{set substitute-path}
8258 @item set substitute-path @var{from} @var{to}
8259 @kindex set substitute-path
8260 Define a source path substitution rule, and add it at the end of the
8261 current list of existing substitution rules. If a rule with the same
8262 @var{from} was already defined, then the old rule is also deleted.
8264 For example, if the file @file{/foo/bar/baz.c} was moved to
8265 @file{/mnt/cross/baz.c}, then the command
8268 (@value{GDBP}) set substitute-path /foo/bar /mnt/cross
8272 will tell @value{GDBN} to replace @samp{/foo/bar} with
8273 @samp{/mnt/cross}, which will allow @value{GDBN} to find the file
8274 @file{baz.c} even though it was moved.
8276 In the case when more than one substitution rule have been defined,
8277 the rules are evaluated one by one in the order where they have been
8278 defined. The first one matching, if any, is selected to perform
8281 For instance, if we had entered the following commands:
8284 (@value{GDBP}) set substitute-path /usr/src/include /mnt/include
8285 (@value{GDBP}) set substitute-path /usr/src /mnt/src
8289 @value{GDBN} would then rewrite @file{/usr/src/include/defs.h} into
8290 @file{/mnt/include/defs.h} by using the first rule. However, it would
8291 use the second rule to rewrite @file{/usr/src/lib/foo.c} into
8292 @file{/mnt/src/lib/foo.c}.
8295 @item unset substitute-path [path]
8296 @kindex unset substitute-path
8297 If a path is specified, search the current list of substitution rules
8298 for a rule that would rewrite that path. Delete that rule if found.
8299 A warning is emitted by the debugger if no rule could be found.
8301 If no path is specified, then all substitution rules are deleted.
8303 @item show substitute-path [path]
8304 @kindex show substitute-path
8305 If a path is specified, then print the source path substitution rule
8306 which would rewrite that path, if any.
8308 If no path is specified, then print all existing source path substitution
8313 If your source path is cluttered with directories that are no longer of
8314 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
8315 versions of source. You can correct the situation as follows:
8319 Use @code{directory} with no argument to reset the source path to its default value.
8322 Use @code{directory} with suitable arguments to reinstall the
8323 directories you want in the source path. You can add all the
8324 directories in one command.
8328 @section Source and Machine Code
8329 @cindex source line and its code address
8331 You can use the command @code{info line} to map source lines to program
8332 addresses (and vice versa), and the command @code{disassemble} to display
8333 a range of addresses as machine instructions. You can use the command
8334 @code{set disassemble-next-line} to set whether to disassemble next
8335 source line when execution stops. When run under @sc{gnu} Emacs
8336 mode, the @code{info line} command causes the arrow to point to the
8337 line specified. Also, @code{info line} prints addresses in symbolic form as
8342 @item info line @var{location}
8343 Print the starting and ending addresses of the compiled code for
8344 source line @var{location}. You can specify source lines in any of
8345 the ways documented in @ref{Specify Location}.
8348 For example, we can use @code{info line} to discover the location of
8349 the object code for the first line of function
8350 @code{m4_changequote}:
8352 @c FIXME: I think this example should also show the addresses in
8353 @c symbolic form, as they usually would be displayed.
8355 (@value{GDBP}) info line m4_changequote
8356 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
8360 @cindex code address and its source line
8361 We can also inquire (using @code{*@var{addr}} as the form for
8362 @var{location}) what source line covers a particular address:
8364 (@value{GDBP}) info line *0x63ff
8365 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
8368 @cindex @code{$_} and @code{info line}
8369 @cindex @code{x} command, default address
8370 @kindex x@r{(examine), and} info line
8371 After @code{info line}, the default address for the @code{x} command
8372 is changed to the starting address of the line, so that @samp{x/i} is
8373 sufficient to begin examining the machine code (@pxref{Memory,
8374 ,Examining Memory}). Also, this address is saved as the value of the
8375 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
8380 @cindex assembly instructions
8381 @cindex instructions, assembly
8382 @cindex machine instructions
8383 @cindex listing machine instructions
8385 @itemx disassemble /m
8386 @itemx disassemble /s
8387 @itemx disassemble /r
8388 This specialized command dumps a range of memory as machine
8389 instructions. It can also print mixed source+disassembly by specifying
8390 the @code{/m} or @code{/s} modifier and print the raw instructions in hex
8391 as well as in symbolic form by specifying the @code{/r} modifier.
8392 The default memory range is the function surrounding the
8393 program counter of the selected frame. A single argument to this
8394 command is a program counter value; @value{GDBN} dumps the function
8395 surrounding this value. When two arguments are given, they should
8396 be separated by a comma, possibly surrounded by whitespace. The
8397 arguments specify a range of addresses to dump, in one of two forms:
8400 @item @var{start},@var{end}
8401 the addresses from @var{start} (inclusive) to @var{end} (exclusive)
8402 @item @var{start},+@var{length}
8403 the addresses from @var{start} (inclusive) to
8404 @code{@var{start}+@var{length}} (exclusive).
8408 When 2 arguments are specified, the name of the function is also
8409 printed (since there could be several functions in the given range).
8411 The argument(s) can be any expression yielding a numeric value, such as
8412 @samp{0x32c4}, @samp{&main+10} or @samp{$pc - 8}.
8414 If the range of memory being disassembled contains current program counter,
8415 the instruction at that location is shown with a @code{=>} marker.
8418 The following example shows the disassembly of a range of addresses of
8419 HP PA-RISC 2.0 code:
8422 (@value{GDBP}) disas 0x32c4, 0x32e4
8423 Dump of assembler code from 0x32c4 to 0x32e4:
8424 0x32c4 <main+204>: addil 0,dp
8425 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
8426 0x32cc <main+212>: ldil 0x3000,r31
8427 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
8428 0x32d4 <main+220>: ldo 0(r31),rp
8429 0x32d8 <main+224>: addil -0x800,dp
8430 0x32dc <main+228>: ldo 0x588(r1),r26
8431 0x32e0 <main+232>: ldil 0x3000,r31
8432 End of assembler dump.
8435 Here is an example showing mixed source+assembly for Intel x86
8436 with @code{/m} or @code{/s}, when the program is stopped just after
8437 function prologue in a non-optimized function with no inline code.
8440 (@value{GDBP}) disas /m main
8441 Dump of assembler code for function main:
8443 0x08048330 <+0>: push %ebp
8444 0x08048331 <+1>: mov %esp,%ebp
8445 0x08048333 <+3>: sub $0x8,%esp
8446 0x08048336 <+6>: and $0xfffffff0,%esp
8447 0x08048339 <+9>: sub $0x10,%esp
8449 6 printf ("Hello.\n");
8450 => 0x0804833c <+12>: movl $0x8048440,(%esp)
8451 0x08048343 <+19>: call 0x8048284 <puts@@plt>
8455 0x08048348 <+24>: mov $0x0,%eax
8456 0x0804834d <+29>: leave
8457 0x0804834e <+30>: ret
8459 End of assembler dump.
8462 The @code{/m} option is deprecated as its output is not useful when
8463 there is either inlined code or re-ordered code.
8464 The @code{/s} option is the preferred choice.
8465 Here is an example for AMD x86-64 showing the difference between
8466 @code{/m} output and @code{/s} output.
8467 This example has one inline function defined in a header file,
8468 and the code is compiled with @samp{-O2} optimization.
8469 Note how the @code{/m} output is missing the disassembly of
8470 several instructions that are present in the @code{/s} output.
8500 (@value{GDBP}) disas /m main
8501 Dump of assembler code for function main:
8505 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y>
8506 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x>
8510 0x000000000040041d <+29>: xor %eax,%eax
8511 0x000000000040041f <+31>: retq
8512 0x0000000000400420 <+32>: add %eax,%eax
8513 0x0000000000400422 <+34>: jmp 0x400417 <main+23>
8515 End of assembler dump.
8516 (@value{GDBP}) disas /s main
8517 Dump of assembler code for function main:
8521 0x0000000000400400 <+0>: mov 0x200c2e(%rip),%eax # 0x601034 <y>
8525 0x0000000000400406 <+6>: test %eax,%eax
8526 0x0000000000400408 <+8>: js 0x400420 <main+32>
8531 0x000000000040040a <+10>: lea 0xa(%rax),%edx
8532 0x000000000040040d <+13>: test %eax,%eax
8533 0x000000000040040f <+15>: mov $0x1,%eax
8534 0x0000000000400414 <+20>: cmovne %edx,%eax
8538 0x0000000000400417 <+23>: mov %eax,0x200c13(%rip) # 0x601030 <x>
8542 0x000000000040041d <+29>: xor %eax,%eax
8543 0x000000000040041f <+31>: retq
8547 0x0000000000400420 <+32>: add %eax,%eax
8548 0x0000000000400422 <+34>: jmp 0x400417 <main+23>
8549 End of assembler dump.
8552 Here is another example showing raw instructions in hex for AMD x86-64,
8555 (gdb) disas /r 0x400281,+10
8556 Dump of assembler code from 0x400281 to 0x40028b:
8557 0x0000000000400281: 38 36 cmp %dh,(%rsi)
8558 0x0000000000400283: 2d 36 34 2e 73 sub $0x732e3436,%eax
8559 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx)
8560 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al
8561 End of assembler dump.
8564 Addresses cannot be specified as a location (@pxref{Specify Location}).
8565 So, for example, if you want to disassemble function @code{bar}
8566 in file @file{foo.c}, you must type @samp{disassemble 'foo.c'::bar}
8567 and not @samp{disassemble foo.c:bar}.
8569 Some architectures have more than one commonly-used set of instruction
8570 mnemonics or other syntax.
8572 For programs that were dynamically linked and use shared libraries,
8573 instructions that call functions or branch to locations in the shared
8574 libraries might show a seemingly bogus location---it's actually a
8575 location of the relocation table. On some architectures, @value{GDBN}
8576 might be able to resolve these to actual function names.
8579 @kindex set disassembler-options
8580 @cindex disassembler options
8581 @item set disassembler-options @var{option1}[,@var{option2}@dots{}]
8582 This command controls the passing of target specific information to
8583 the disassembler. For a list of valid options, please refer to the
8584 @code{-M}/@code{--disassembler-options} section of the @samp{objdump}
8585 manual and/or the output of @kbd{objdump --help}
8586 (@pxref{objdump,,objdump,binutils.info,The GNU Binary Utilities}).
8587 The default value is the empty string.
8589 If it is necessary to specify more than one disassembler option, then
8590 multiple options can be placed together into a comma separated list.
8591 Currently this command is only supported on targets ARM, PowerPC
8594 @kindex show disassembler-options
8595 @item show disassembler-options
8596 Show the current setting of the disassembler options.
8600 @kindex set disassembly-flavor
8601 @cindex Intel disassembly flavor
8602 @cindex AT&T disassembly flavor
8603 @item set disassembly-flavor @var{instruction-set}
8604 Select the instruction set to use when disassembling the
8605 program via the @code{disassemble} or @code{x/i} commands.
8607 Currently this command is only defined for the Intel x86 family. You
8608 can set @var{instruction-set} to either @code{intel} or @code{att}.
8609 The default is @code{att}, the AT&T flavor used by default by Unix
8610 assemblers for x86-based targets.
8612 @kindex show disassembly-flavor
8613 @item show disassembly-flavor
8614 Show the current setting of the disassembly flavor.
8618 @kindex set disassemble-next-line
8619 @kindex show disassemble-next-line
8620 @item set disassemble-next-line
8621 @itemx show disassemble-next-line
8622 Control whether or not @value{GDBN} will disassemble the next source
8623 line or instruction when execution stops. If ON, @value{GDBN} will
8624 display disassembly of the next source line when execution of the
8625 program being debugged stops. This is @emph{in addition} to
8626 displaying the source line itself, which @value{GDBN} always does if
8627 possible. If the next source line cannot be displayed for some reason
8628 (e.g., if @value{GDBN} cannot find the source file, or there's no line
8629 info in the debug info), @value{GDBN} will display disassembly of the
8630 next @emph{instruction} instead of showing the next source line. If
8631 AUTO, @value{GDBN} will display disassembly of next instruction only
8632 if the source line cannot be displayed. This setting causes
8633 @value{GDBN} to display some feedback when you step through a function
8634 with no line info or whose source file is unavailable. The default is
8635 OFF, which means never display the disassembly of the next line or
8641 @chapter Examining Data
8643 @cindex printing data
8644 @cindex examining data
8647 The usual way to examine data in your program is with the @code{print}
8648 command (abbreviated @code{p}), or its synonym @code{inspect}. It
8649 evaluates and prints the value of an expression of the language your
8650 program is written in (@pxref{Languages, ,Using @value{GDBN} with
8651 Different Languages}). It may also print the expression using a
8652 Python-based pretty-printer (@pxref{Pretty Printing}).
8655 @item print @var{expr}
8656 @itemx print /@var{f} @var{expr}
8657 @var{expr} is an expression (in the source language). By default the
8658 value of @var{expr} is printed in a format appropriate to its data type;
8659 you can choose a different format by specifying @samp{/@var{f}}, where
8660 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
8664 @itemx print /@var{f}
8665 @cindex reprint the last value
8666 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
8667 @dfn{value history}; @pxref{Value History, ,Value History}). This allows you to
8668 conveniently inspect the same value in an alternative format.
8671 A more low-level way of examining data is with the @code{x} command.
8672 It examines data in memory at a specified address and prints it in a
8673 specified format. @xref{Memory, ,Examining Memory}.
8675 If you are interested in information about types, or about how the
8676 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
8677 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
8680 @cindex exploring hierarchical data structures
8682 Another way of examining values of expressions and type information is
8683 through the Python extension command @code{explore} (available only if
8684 the @value{GDBN} build is configured with @code{--with-python}). It
8685 offers an interactive way to start at the highest level (or, the most
8686 abstract level) of the data type of an expression (or, the data type
8687 itself) and explore all the way down to leaf scalar values/fields
8688 embedded in the higher level data types.
8691 @item explore @var{arg}
8692 @var{arg} is either an expression (in the source language), or a type
8693 visible in the current context of the program being debugged.
8696 The working of the @code{explore} command can be illustrated with an
8697 example. If a data type @code{struct ComplexStruct} is defined in your
8707 struct ComplexStruct
8709 struct SimpleStruct *ss_p;
8715 followed by variable declarations as
8718 struct SimpleStruct ss = @{ 10, 1.11 @};
8719 struct ComplexStruct cs = @{ &ss, @{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 @} @};
8723 then, the value of the variable @code{cs} can be explored using the
8724 @code{explore} command as follows.
8728 The value of `cs' is a struct/class of type `struct ComplexStruct' with
8729 the following fields:
8731 ss_p = <Enter 0 to explore this field of type `struct SimpleStruct *'>
8732 arr = <Enter 1 to explore this field of type `int [10]'>
8734 Enter the field number of choice:
8738 Since the fields of @code{cs} are not scalar values, you are being
8739 prompted to chose the field you want to explore. Let's say you choose
8740 the field @code{ss_p} by entering @code{0}. Then, since this field is a
8741 pointer, you will be asked if it is pointing to a single value. From
8742 the declaration of @code{cs} above, it is indeed pointing to a single
8743 value, hence you enter @code{y}. If you enter @code{n}, then you will
8744 be asked if it were pointing to an array of values, in which case this
8745 field will be explored as if it were an array.
8748 `cs.ss_p' is a pointer to a value of type `struct SimpleStruct'
8749 Continue exploring it as a pointer to a single value [y/n]: y
8750 The value of `*(cs.ss_p)' is a struct/class of type `struct
8751 SimpleStruct' with the following fields:
8753 i = 10 .. (Value of type `int')
8754 d = 1.1100000000000001 .. (Value of type `double')
8756 Press enter to return to parent value:
8760 If the field @code{arr} of @code{cs} was chosen for exploration by
8761 entering @code{1} earlier, then since it is as array, you will be
8762 prompted to enter the index of the element in the array that you want
8766 `cs.arr' is an array of `int'.
8767 Enter the index of the element you want to explore in `cs.arr': 5
8769 `(cs.arr)[5]' is a scalar value of type `int'.
8773 Press enter to return to parent value:
8776 In general, at any stage of exploration, you can go deeper towards the
8777 leaf values by responding to the prompts appropriately, or hit the
8778 return key to return to the enclosing data structure (the @i{higher}
8779 level data structure).
8781 Similar to exploring values, you can use the @code{explore} command to
8782 explore types. Instead of specifying a value (which is typically a
8783 variable name or an expression valid in the current context of the
8784 program being debugged), you specify a type name. If you consider the
8785 same example as above, your can explore the type
8786 @code{struct ComplexStruct} by passing the argument
8787 @code{struct ComplexStruct} to the @code{explore} command.
8790 (gdb) explore struct ComplexStruct
8794 By responding to the prompts appropriately in the subsequent interactive
8795 session, you can explore the type @code{struct ComplexStruct} in a
8796 manner similar to how the value @code{cs} was explored in the above
8799 The @code{explore} command also has two sub-commands,
8800 @code{explore value} and @code{explore type}. The former sub-command is
8801 a way to explicitly specify that value exploration of the argument is
8802 being invoked, while the latter is a way to explicitly specify that type
8803 exploration of the argument is being invoked.
8806 @item explore value @var{expr}
8807 @cindex explore value
8808 This sub-command of @code{explore} explores the value of the
8809 expression @var{expr} (if @var{expr} is an expression valid in the
8810 current context of the program being debugged). The behavior of this
8811 command is identical to that of the behavior of the @code{explore}
8812 command being passed the argument @var{expr}.
8814 @item explore type @var{arg}
8815 @cindex explore type
8816 This sub-command of @code{explore} explores the type of @var{arg} (if
8817 @var{arg} is a type visible in the current context of program being
8818 debugged), or the type of the value/expression @var{arg} (if @var{arg}
8819 is an expression valid in the current context of the program being
8820 debugged). If @var{arg} is a type, then the behavior of this command is
8821 identical to that of the @code{explore} command being passed the
8822 argument @var{arg}. If @var{arg} is an expression, then the behavior of
8823 this command will be identical to that of the @code{explore} command
8824 being passed the type of @var{arg} as the argument.
8828 * Expressions:: Expressions
8829 * Ambiguous Expressions:: Ambiguous Expressions
8830 * Variables:: Program variables
8831 * Arrays:: Artificial arrays
8832 * Output Formats:: Output formats
8833 * Memory:: Examining memory
8834 * Auto Display:: Automatic display
8835 * Print Settings:: Print settings
8836 * Pretty Printing:: Python pretty printing
8837 * Value History:: Value history
8838 * Convenience Vars:: Convenience variables
8839 * Convenience Funs:: Convenience functions
8840 * Registers:: Registers
8841 * Floating Point Hardware:: Floating point hardware
8842 * Vector Unit:: Vector Unit
8843 * OS Information:: Auxiliary data provided by operating system
8844 * Memory Region Attributes:: Memory region attributes
8845 * Dump/Restore Files:: Copy between memory and a file
8846 * Core File Generation:: Cause a program dump its core
8847 * Character Sets:: Debugging programs that use a different
8848 character set than GDB does
8849 * Caching Target Data:: Data caching for targets
8850 * Searching Memory:: Searching memory for a sequence of bytes
8851 * Value Sizes:: Managing memory allocated for values
8855 @section Expressions
8858 @code{print} and many other @value{GDBN} commands accept an expression and
8859 compute its value. Any kind of constant, variable or operator defined
8860 by the programming language you are using is valid in an expression in
8861 @value{GDBN}. This includes conditional expressions, function calls,
8862 casts, and string constants. It also includes preprocessor macros, if
8863 you compiled your program to include this information; see
8866 @cindex arrays in expressions
8867 @value{GDBN} supports array constants in expressions input by
8868 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
8869 you can use the command @code{print @{1, 2, 3@}} to create an array
8870 of three integers. If you pass an array to a function or assign it
8871 to a program variable, @value{GDBN} copies the array to memory that
8872 is @code{malloc}ed in the target program.
8874 Because C is so widespread, most of the expressions shown in examples in
8875 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
8876 Languages}, for information on how to use expressions in other
8879 In this section, we discuss operators that you can use in @value{GDBN}
8880 expressions regardless of your programming language.
8882 @cindex casts, in expressions
8883 Casts are supported in all languages, not just in C, because it is so
8884 useful to cast a number into a pointer in order to examine a structure
8885 at that address in memory.
8886 @c FIXME: casts supported---Mod2 true?
8888 @value{GDBN} supports these operators, in addition to those common
8889 to programming languages:
8893 @samp{@@} is a binary operator for treating parts of memory as arrays.
8894 @xref{Arrays, ,Artificial Arrays}, for more information.
8897 @samp{::} allows you to specify a variable in terms of the file or
8898 function where it is defined. @xref{Variables, ,Program Variables}.
8900 @cindex @{@var{type}@}
8901 @cindex type casting memory
8902 @cindex memory, viewing as typed object
8903 @cindex casts, to view memory
8904 @item @{@var{type}@} @var{addr}
8905 Refers to an object of type @var{type} stored at address @var{addr} in
8906 memory. The address @var{addr} may be any expression whose value is
8907 an integer or pointer (but parentheses are required around binary
8908 operators, just as in a cast). This construct is allowed regardless
8909 of what kind of data is normally supposed to reside at @var{addr}.
8912 @node Ambiguous Expressions
8913 @section Ambiguous Expressions
8914 @cindex ambiguous expressions
8916 Expressions can sometimes contain some ambiguous elements. For instance,
8917 some programming languages (notably Ada, C@t{++} and Objective-C) permit
8918 a single function name to be defined several times, for application in
8919 different contexts. This is called @dfn{overloading}. Another example
8920 involving Ada is generics. A @dfn{generic package} is similar to C@t{++}
8921 templates and is typically instantiated several times, resulting in
8922 the same function name being defined in different contexts.
8924 In some cases and depending on the language, it is possible to adjust
8925 the expression to remove the ambiguity. For instance in C@t{++}, you
8926 can specify the signature of the function you want to break on, as in
8927 @kbd{break @var{function}(@var{types})}. In Ada, using the fully
8928 qualified name of your function often makes the expression unambiguous
8931 When an ambiguity that needs to be resolved is detected, the debugger
8932 has the capability to display a menu of numbered choices for each
8933 possibility, and then waits for the selection with the prompt @samp{>}.
8934 The first option is always @samp{[0] cancel}, and typing @kbd{0 @key{RET}}
8935 aborts the current command. If the command in which the expression was
8936 used allows more than one choice to be selected, the next option in the
8937 menu is @samp{[1] all}, and typing @kbd{1 @key{RET}} selects all possible
8940 For example, the following session excerpt shows an attempt to set a
8941 breakpoint at the overloaded symbol @code{String::after}.
8942 We choose three particular definitions of that function name:
8944 @c FIXME! This is likely to change to show arg type lists, at least
8947 (@value{GDBP}) b String::after
8950 [2] file:String.cc; line number:867
8951 [3] file:String.cc; line number:860
8952 [4] file:String.cc; line number:875
8953 [5] file:String.cc; line number:853
8954 [6] file:String.cc; line number:846
8955 [7] file:String.cc; line number:735
8957 Breakpoint 1 at 0xb26c: file String.cc, line 867.
8958 Breakpoint 2 at 0xb344: file String.cc, line 875.
8959 Breakpoint 3 at 0xafcc: file String.cc, line 846.
8960 Multiple breakpoints were set.
8961 Use the "delete" command to delete unwanted
8968 @kindex set multiple-symbols
8969 @item set multiple-symbols @var{mode}
8970 @cindex multiple-symbols menu
8972 This option allows you to adjust the debugger behavior when an expression
8975 By default, @var{mode} is set to @code{all}. If the command with which
8976 the expression is used allows more than one choice, then @value{GDBN}
8977 automatically selects all possible choices. For instance, inserting
8978 a breakpoint on a function using an ambiguous name results in a breakpoint
8979 inserted on each possible match. However, if a unique choice must be made,
8980 then @value{GDBN} uses the menu to help you disambiguate the expression.
8981 For instance, printing the address of an overloaded function will result
8982 in the use of the menu.
8984 When @var{mode} is set to @code{ask}, the debugger always uses the menu
8985 when an ambiguity is detected.
8987 Finally, when @var{mode} is set to @code{cancel}, the debugger reports
8988 an error due to the ambiguity and the command is aborted.
8990 @kindex show multiple-symbols
8991 @item show multiple-symbols
8992 Show the current value of the @code{multiple-symbols} setting.
8996 @section Program Variables
8998 The most common kind of expression to use is the name of a variable
9001 Variables in expressions are understood in the selected stack frame
9002 (@pxref{Selection, ,Selecting a Frame}); they must be either:
9006 global (or file-static)
9013 visible according to the scope rules of the
9014 programming language from the point of execution in that frame
9017 @noindent This means that in the function
9032 you can examine and use the variable @code{a} whenever your program is
9033 executing within the function @code{foo}, but you can only use or
9034 examine the variable @code{b} while your program is executing inside
9035 the block where @code{b} is declared.
9037 @cindex variable name conflict
9038 There is an exception: you can refer to a variable or function whose
9039 scope is a single source file even if the current execution point is not
9040 in this file. But it is possible to have more than one such variable or
9041 function with the same name (in different source files). If that
9042 happens, referring to that name has unpredictable effects. If you wish,
9043 you can specify a static variable in a particular function or file by
9044 using the colon-colon (@code{::}) notation:
9046 @cindex colon-colon, context for variables/functions
9048 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
9049 @cindex @code{::}, context for variables/functions
9052 @var{file}::@var{variable}
9053 @var{function}::@var{variable}
9057 Here @var{file} or @var{function} is the name of the context for the
9058 static @var{variable}. In the case of file names, you can use quotes to
9059 make sure @value{GDBN} parses the file name as a single word---for example,
9060 to print a global value of @code{x} defined in @file{f2.c}:
9063 (@value{GDBP}) p 'f2.c'::x
9066 The @code{::} notation is normally used for referring to
9067 static variables, since you typically disambiguate uses of local variables
9068 in functions by selecting the appropriate frame and using the
9069 simple name of the variable. However, you may also use this notation
9070 to refer to local variables in frames enclosing the selected frame:
9079 process (a); /* Stop here */
9090 For example, if there is a breakpoint at the commented line,
9091 here is what you might see
9092 when the program stops after executing the call @code{bar(0)}:
9097 (@value{GDBP}) p bar::a
9100 #2 0x080483d0 in foo (a=5) at foobar.c:12
9103 (@value{GDBP}) p bar::a
9107 @cindex C@t{++} scope resolution
9108 These uses of @samp{::} are very rarely in conflict with the very
9109 similar use of the same notation in C@t{++}. When they are in
9110 conflict, the C@t{++} meaning takes precedence; however, this can be
9111 overridden by quoting the file or function name with single quotes.
9113 For example, suppose the program is stopped in a method of a class
9114 that has a field named @code{includefile}, and there is also an
9115 include file named @file{includefile} that defines a variable,
9119 (@value{GDBP}) p includefile
9121 (@value{GDBP}) p includefile::some_global
9122 A syntax error in expression, near `'.
9123 (@value{GDBP}) p 'includefile'::some_global
9127 @cindex wrong values
9128 @cindex variable values, wrong
9129 @cindex function entry/exit, wrong values of variables
9130 @cindex optimized code, wrong values of variables
9132 @emph{Warning:} Occasionally, a local variable may appear to have the
9133 wrong value at certain points in a function---just after entry to a new
9134 scope, and just before exit.
9136 You may see this problem when you are stepping by machine instructions.
9137 This is because, on most machines, it takes more than one instruction to
9138 set up a stack frame (including local variable definitions); if you are
9139 stepping by machine instructions, variables may appear to have the wrong
9140 values until the stack frame is completely built. On exit, it usually
9141 also takes more than one machine instruction to destroy a stack frame;
9142 after you begin stepping through that group of instructions, local
9143 variable definitions may be gone.
9145 This may also happen when the compiler does significant optimizations.
9146 To be sure of always seeing accurate values, turn off all optimization
9149 @cindex ``No symbol "foo" in current context''
9150 Another possible effect of compiler optimizations is to optimize
9151 unused variables out of existence, or assign variables to registers (as
9152 opposed to memory addresses). Depending on the support for such cases
9153 offered by the debug info format used by the compiler, @value{GDBN}
9154 might not be able to display values for such local variables. If that
9155 happens, @value{GDBN} will print a message like this:
9158 No symbol "foo" in current context.
9161 To solve such problems, either recompile without optimizations, or use a
9162 different debug info format, if the compiler supports several such
9163 formats. @xref{Compilation}, for more information on choosing compiler
9164 options. @xref{C, ,C and C@t{++}}, for more information about debug
9165 info formats that are best suited to C@t{++} programs.
9167 If you ask to print an object whose contents are unknown to
9168 @value{GDBN}, e.g., because its data type is not completely specified
9169 by the debug information, @value{GDBN} will say @samp{<incomplete
9170 type>}. @xref{Symbols, incomplete type}, for more about this.
9172 @cindex no debug info variables
9173 If you try to examine or use the value of a (global) variable for
9174 which @value{GDBN} has no type information, e.g., because the program
9175 includes no debug information, @value{GDBN} displays an error message.
9176 @xref{Symbols, unknown type}, for more about unknown types. If you
9177 cast the variable to its declared type, @value{GDBN} gets the
9178 variable's value using the cast-to type as the variable's type. For
9179 example, in a C program:
9182 (@value{GDBP}) p var
9183 'var' has unknown type; cast it to its declared type
9184 (@value{GDBP}) p (float) var
9188 If you append @kbd{@@entry} string to a function parameter name you get its
9189 value at the time the function got called. If the value is not available an
9190 error message is printed. Entry values are available only with some compilers.
9191 Entry values are normally also printed at the function parameter list according
9192 to @ref{set print entry-values}.
9195 Breakpoint 1, d (i=30) at gdb.base/entry-value.c:29
9201 (gdb) print i@@entry
9205 Strings are identified as arrays of @code{char} values without specified
9206 signedness. Arrays of either @code{signed char} or @code{unsigned char} get
9207 printed as arrays of 1 byte sized integers. @code{-fsigned-char} or
9208 @code{-funsigned-char} @value{NGCC} options have no effect as @value{GDBN}
9209 defines literal string type @code{"char"} as @code{char} without a sign.
9214 signed char var1[] = "A";
9217 You get during debugging
9222 $2 = @{65 'A', 0 '\0'@}
9226 @section Artificial Arrays
9228 @cindex artificial array
9230 @kindex @@@r{, referencing memory as an array}
9231 It is often useful to print out several successive objects of the
9232 same type in memory; a section of an array, or an array of
9233 dynamically determined size for which only a pointer exists in the
9236 You can do this by referring to a contiguous span of memory as an
9237 @dfn{artificial array}, using the binary operator @samp{@@}. The left
9238 operand of @samp{@@} should be the first element of the desired array
9239 and be an individual object. The right operand should be the desired length
9240 of the array. The result is an array value whose elements are all of
9241 the type of the left argument. The first element is actually the left
9242 argument; the second element comes from bytes of memory immediately
9243 following those that hold the first element, and so on. Here is an
9244 example. If a program says
9247 int *array = (int *) malloc (len * sizeof (int));
9251 you can print the contents of @code{array} with
9257 The left operand of @samp{@@} must reside in memory. Array values made
9258 with @samp{@@} in this way behave just like other arrays in terms of
9259 subscripting, and are coerced to pointers when used in expressions.
9260 Artificial arrays most often appear in expressions via the value history
9261 (@pxref{Value History, ,Value History}), after printing one out.
9263 Another way to create an artificial array is to use a cast.
9264 This re-interprets a value as if it were an array.
9265 The value need not be in memory:
9267 (@value{GDBP}) p/x (short[2])0x12345678
9268 $1 = @{0x1234, 0x5678@}
9271 As a convenience, if you leave the array length out (as in
9272 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
9273 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
9275 (@value{GDBP}) p/x (short[])0x12345678
9276 $2 = @{0x1234, 0x5678@}
9279 Sometimes the artificial array mechanism is not quite enough; in
9280 moderately complex data structures, the elements of interest may not
9281 actually be adjacent---for example, if you are interested in the values
9282 of pointers in an array. One useful work-around in this situation is
9283 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
9284 Variables}) as a counter in an expression that prints the first
9285 interesting value, and then repeat that expression via @key{RET}. For
9286 instance, suppose you have an array @code{dtab} of pointers to
9287 structures, and you are interested in the values of a field @code{fv}
9288 in each structure. Here is an example of what you might type:
9298 @node Output Formats
9299 @section Output Formats
9301 @cindex formatted output
9302 @cindex output formats
9303 By default, @value{GDBN} prints a value according to its data type. Sometimes
9304 this is not what you want. For example, you might want to print a number
9305 in hex, or a pointer in decimal. Or you might want to view data in memory
9306 at a certain address as a character string or as an instruction. To do
9307 these things, specify an @dfn{output format} when you print a value.
9309 The simplest use of output formats is to say how to print a value
9310 already computed. This is done by starting the arguments of the
9311 @code{print} command with a slash and a format letter. The format
9312 letters supported are:
9316 Regard the bits of the value as an integer, and print the integer in
9320 Print as integer in signed decimal.
9323 Print as integer in unsigned decimal.
9326 Print as integer in octal.
9329 Print as integer in binary. The letter @samp{t} stands for ``two''.
9330 @footnote{@samp{b} cannot be used because these format letters are also
9331 used with the @code{x} command, where @samp{b} stands for ``byte'';
9332 see @ref{Memory,,Examining Memory}.}
9335 @cindex unknown address, locating
9336 @cindex locate address
9337 Print as an address, both absolute in hexadecimal and as an offset from
9338 the nearest preceding symbol. You can use this format used to discover
9339 where (in what function) an unknown address is located:
9342 (@value{GDBP}) p/a 0x54320
9343 $3 = 0x54320 <_initialize_vx+396>
9347 The command @code{info symbol 0x54320} yields similar results.
9348 @xref{Symbols, info symbol}.
9351 Regard as an integer and print it as a character constant. This
9352 prints both the numerical value and its character representation. The
9353 character representation is replaced with the octal escape @samp{\nnn}
9354 for characters outside the 7-bit @sc{ascii} range.
9356 Without this format, @value{GDBN} displays @code{char},
9357 @w{@code{unsigned char}}, and @w{@code{signed char}} data as character
9358 constants. Single-byte members of vectors are displayed as integer
9362 Regard the bits of the value as a floating point number and print
9363 using typical floating point syntax.
9366 @cindex printing strings
9367 @cindex printing byte arrays
9368 Regard as a string, if possible. With this format, pointers to single-byte
9369 data are displayed as null-terminated strings and arrays of single-byte data
9370 are displayed as fixed-length strings. Other values are displayed in their
9373 Without this format, @value{GDBN} displays pointers to and arrays of
9374 @code{char}, @w{@code{unsigned char}}, and @w{@code{signed char}} as
9375 strings. Single-byte members of a vector are displayed as an integer
9379 Like @samp{x} formatting, the value is treated as an integer and
9380 printed as hexadecimal, but leading zeros are printed to pad the value
9381 to the size of the integer type.
9384 @cindex raw printing
9385 Print using the @samp{raw} formatting. By default, @value{GDBN} will
9386 use a Python-based pretty-printer, if one is available (@pxref{Pretty
9387 Printing}). This typically results in a higher-level display of the
9388 value's contents. The @samp{r} format bypasses any Python
9389 pretty-printer which might exist.
9392 For example, to print the program counter in hex (@pxref{Registers}), type
9399 Note that no space is required before the slash; this is because command
9400 names in @value{GDBN} cannot contain a slash.
9402 To reprint the last value in the value history with a different format,
9403 you can use the @code{print} command with just a format and no
9404 expression. For example, @samp{p/x} reprints the last value in hex.
9407 @section Examining Memory
9409 You can use the command @code{x} (for ``examine'') to examine memory in
9410 any of several formats, independently of your program's data types.
9412 @cindex examining memory
9414 @kindex x @r{(examine memory)}
9415 @item x/@var{nfu} @var{addr}
9418 Use the @code{x} command to examine memory.
9421 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
9422 much memory to display and how to format it; @var{addr} is an
9423 expression giving the address where you want to start displaying memory.
9424 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
9425 Several commands set convenient defaults for @var{addr}.
9428 @item @var{n}, the repeat count
9429 The repeat count is a decimal integer; the default is 1. It specifies
9430 how much memory (counting by units @var{u}) to display. If a negative
9431 number is specified, memory is examined backward from @var{addr}.
9432 @c This really is **decimal**; unaffected by 'set radix' as of GDB
9435 @item @var{f}, the display format
9436 The display format is one of the formats used by @code{print}
9437 (@samp{x}, @samp{d}, @samp{u}, @samp{o}, @samp{t}, @samp{a}, @samp{c},
9438 @samp{f}, @samp{s}), and in addition @samp{i} (for machine instructions).
9439 The default is @samp{x} (hexadecimal) initially. The default changes
9440 each time you use either @code{x} or @code{print}.
9442 @item @var{u}, the unit size
9443 The unit size is any of
9449 Halfwords (two bytes).
9451 Words (four bytes). This is the initial default.
9453 Giant words (eight bytes).
9456 Each time you specify a unit size with @code{x}, that size becomes the
9457 default unit the next time you use @code{x}. For the @samp{i} format,
9458 the unit size is ignored and is normally not written. For the @samp{s} format,
9459 the unit size defaults to @samp{b}, unless it is explicitly given.
9460 Use @kbd{x /hs} to display 16-bit char strings and @kbd{x /ws} to display
9461 32-bit strings. The next use of @kbd{x /s} will again display 8-bit strings.
9462 Note that the results depend on the programming language of the
9463 current compilation unit. If the language is C, the @samp{s}
9464 modifier will use the UTF-16 encoding while @samp{w} will use
9465 UTF-32. The encoding is set by the programming language and cannot
9468 @item @var{addr}, starting display address
9469 @var{addr} is the address where you want @value{GDBN} to begin displaying
9470 memory. The expression need not have a pointer value (though it may);
9471 it is always interpreted as an integer address of a byte of memory.
9472 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
9473 @var{addr} is usually just after the last address examined---but several
9474 other commands also set the default address: @code{info breakpoints} (to
9475 the address of the last breakpoint listed), @code{info line} (to the
9476 starting address of a line), and @code{print} (if you use it to display
9477 a value from memory).
9480 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
9481 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
9482 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
9483 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
9484 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
9486 You can also specify a negative repeat count to examine memory backward
9487 from the given address. For example, @samp{x/-3uh 0x54320} prints three
9488 halfwords (@code{h}) at @code{0x54314}, @code{0x54328}, and @code{0x5431c}.
9490 Since the letters indicating unit sizes are all distinct from the
9491 letters specifying output formats, you do not have to remember whether
9492 unit size or format comes first; either order works. The output
9493 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
9494 (However, the count @var{n} must come first; @samp{wx4} does not work.)
9496 Even though the unit size @var{u} is ignored for the formats @samp{s}
9497 and @samp{i}, you might still want to use a count @var{n}; for example,
9498 @samp{3i} specifies that you want to see three machine instructions,
9499 including any operands. For convenience, especially when used with
9500 the @code{display} command, the @samp{i} format also prints branch delay
9501 slot instructions, if any, beyond the count specified, which immediately
9502 follow the last instruction that is within the count. The command
9503 @code{disassemble} gives an alternative way of inspecting machine
9504 instructions; see @ref{Machine Code,,Source and Machine Code}.
9506 If a negative repeat count is specified for the formats @samp{s} or @samp{i},
9507 the command displays null-terminated strings or instructions before the given
9508 address as many as the absolute value of the given number. For the @samp{i}
9509 format, we use line number information in the debug info to accurately locate
9510 instruction boundaries while disassembling backward. If line info is not
9511 available, the command stops examining memory with an error message.
9513 All the defaults for the arguments to @code{x} are designed to make it
9514 easy to continue scanning memory with minimal specifications each time
9515 you use @code{x}. For example, after you have inspected three machine
9516 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
9517 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
9518 the repeat count @var{n} is used again; the other arguments default as
9519 for successive uses of @code{x}.
9521 When examining machine instructions, the instruction at current program
9522 counter is shown with a @code{=>} marker. For example:
9525 (@value{GDBP}) x/5i $pc-6
9526 0x804837f <main+11>: mov %esp,%ebp
9527 0x8048381 <main+13>: push %ecx
9528 0x8048382 <main+14>: sub $0x4,%esp
9529 => 0x8048385 <main+17>: movl $0x8048460,(%esp)
9530 0x804838c <main+24>: call 0x80482d4 <puts@@plt>
9533 @cindex @code{$_}, @code{$__}, and value history
9534 The addresses and contents printed by the @code{x} command are not saved
9535 in the value history because there is often too much of them and they
9536 would get in the way. Instead, @value{GDBN} makes these values available for
9537 subsequent use in expressions as values of the convenience variables
9538 @code{$_} and @code{$__}. After an @code{x} command, the last address
9539 examined is available for use in expressions in the convenience variable
9540 @code{$_}. The contents of that address, as examined, are available in
9541 the convenience variable @code{$__}.
9543 If the @code{x} command has a repeat count, the address and contents saved
9544 are from the last memory unit printed; this is not the same as the last
9545 address printed if several units were printed on the last line of output.
9547 @anchor{addressable memory unit}
9548 @cindex addressable memory unit
9549 Most targets have an addressable memory unit size of 8 bits. This means
9550 that to each memory address are associated 8 bits of data. Some
9551 targets, however, have other addressable memory unit sizes.
9552 Within @value{GDBN} and this document, the term
9553 @dfn{addressable memory unit} (or @dfn{memory unit} for short) is used
9554 when explicitly referring to a chunk of data of that size. The word
9555 @dfn{byte} is used to refer to a chunk of data of 8 bits, regardless of
9556 the addressable memory unit size of the target. For most systems,
9557 addressable memory unit is a synonym of byte.
9559 @cindex remote memory comparison
9560 @cindex target memory comparison
9561 @cindex verify remote memory image
9562 @cindex verify target memory image
9563 When you are debugging a program running on a remote target machine
9564 (@pxref{Remote Debugging}), you may wish to verify the program's image
9565 in the remote machine's memory against the executable file you
9566 downloaded to the target. Or, on any target, you may want to check
9567 whether the program has corrupted its own read-only sections. The
9568 @code{compare-sections} command is provided for such situations.
9571 @kindex compare-sections
9572 @item compare-sections @r{[}@var{section-name}@r{|}@code{-r}@r{]}
9573 Compare the data of a loadable section @var{section-name} in the
9574 executable file of the program being debugged with the same section in
9575 the target machine's memory, and report any mismatches. With no
9576 arguments, compares all loadable sections. With an argument of
9577 @code{-r}, compares all loadable read-only sections.
9579 Note: for remote targets, this command can be accelerated if the
9580 target supports computing the CRC checksum of a block of memory
9581 (@pxref{qCRC packet}).
9585 @section Automatic Display
9586 @cindex automatic display
9587 @cindex display of expressions
9589 If you find that you want to print the value of an expression frequently
9590 (to see how it changes), you might want to add it to the @dfn{automatic
9591 display list} so that @value{GDBN} prints its value each time your program stops.
9592 Each expression added to the list is given a number to identify it;
9593 to remove an expression from the list, you specify that number.
9594 The automatic display looks like this:
9598 3: bar[5] = (struct hack *) 0x3804
9602 This display shows item numbers, expressions and their current values. As with
9603 displays you request manually using @code{x} or @code{print}, you can
9604 specify the output format you prefer; in fact, @code{display} decides
9605 whether to use @code{print} or @code{x} depending your format
9606 specification---it uses @code{x} if you specify either the @samp{i}
9607 or @samp{s} format, or a unit size; otherwise it uses @code{print}.
9611 @item display @var{expr}
9612 Add the expression @var{expr} to the list of expressions to display
9613 each time your program stops. @xref{Expressions, ,Expressions}.
9615 @code{display} does not repeat if you press @key{RET} again after using it.
9617 @item display/@var{fmt} @var{expr}
9618 For @var{fmt} specifying only a display format and not a size or
9619 count, add the expression @var{expr} to the auto-display list but
9620 arrange to display it each time in the specified format @var{fmt}.
9621 @xref{Output Formats,,Output Formats}.
9623 @item display/@var{fmt} @var{addr}
9624 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
9625 number of units, add the expression @var{addr} as a memory address to
9626 be examined each time your program stops. Examining means in effect
9627 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining Memory}.
9630 For example, @samp{display/i $pc} can be helpful, to see the machine
9631 instruction about to be executed each time execution stops (@samp{$pc}
9632 is a common name for the program counter; @pxref{Registers, ,Registers}).
9635 @kindex delete display
9637 @item undisplay @var{dnums}@dots{}
9638 @itemx delete display @var{dnums}@dots{}
9639 Remove items from the list of expressions to display. Specify the
9640 numbers of the displays that you want affected with the command
9641 argument @var{dnums}. It can be a single display number, one of the
9642 numbers shown in the first field of the @samp{info display} display;
9643 or it could be a range of display numbers, as in @code{2-4}.
9645 @code{undisplay} does not repeat if you press @key{RET} after using it.
9646 (Otherwise you would just get the error @samp{No display number @dots{}}.)
9648 @kindex disable display
9649 @item disable display @var{dnums}@dots{}
9650 Disable the display of item numbers @var{dnums}. A disabled display
9651 item is not printed automatically, but is not forgotten. It may be
9652 enabled again later. Specify the numbers of the displays that you
9653 want affected with the command argument @var{dnums}. It can be a
9654 single display number, one of the numbers shown in the first field of
9655 the @samp{info display} display; or it could be a range of display
9656 numbers, as in @code{2-4}.
9658 @kindex enable display
9659 @item enable display @var{dnums}@dots{}
9660 Enable display of item numbers @var{dnums}. It becomes effective once
9661 again in auto display of its expression, until you specify otherwise.
9662 Specify the numbers of the displays that you want affected with the
9663 command argument @var{dnums}. It can be a single display number, one
9664 of the numbers shown in the first field of the @samp{info display}
9665 display; or it could be a range of display numbers, as in @code{2-4}.
9668 Display the current values of the expressions on the list, just as is
9669 done when your program stops.
9671 @kindex info display
9673 Print the list of expressions previously set up to display
9674 automatically, each one with its item number, but without showing the
9675 values. This includes disabled expressions, which are marked as such.
9676 It also includes expressions which would not be displayed right now
9677 because they refer to automatic variables not currently available.
9680 @cindex display disabled out of scope
9681 If a display expression refers to local variables, then it does not make
9682 sense outside the lexical context for which it was set up. Such an
9683 expression is disabled when execution enters a context where one of its
9684 variables is not defined. For example, if you give the command
9685 @code{display last_char} while inside a function with an argument
9686 @code{last_char}, @value{GDBN} displays this argument while your program
9687 continues to stop inside that function. When it stops elsewhere---where
9688 there is no variable @code{last_char}---the display is disabled
9689 automatically. The next time your program stops where @code{last_char}
9690 is meaningful, you can enable the display expression once again.
9692 @node Print Settings
9693 @section Print Settings
9695 @cindex format options
9696 @cindex print settings
9697 @value{GDBN} provides the following ways to control how arrays, structures,
9698 and symbols are printed.
9701 These settings are useful for debugging programs in any language:
9705 @item set print address
9706 @itemx set print address on
9707 @cindex print/don't print memory addresses
9708 @value{GDBN} prints memory addresses showing the location of stack
9709 traces, structure values, pointer values, breakpoints, and so forth,
9710 even when it also displays the contents of those addresses. The default
9711 is @code{on}. For example, this is what a stack frame display looks like with
9712 @code{set print address on}:
9717 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
9719 530 if (lquote != def_lquote)
9723 @item set print address off
9724 Do not print addresses when displaying their contents. For example,
9725 this is the same stack frame displayed with @code{set print address off}:
9729 (@value{GDBP}) set print addr off
9731 #0 set_quotes (lq="<<", rq=">>") at input.c:530
9732 530 if (lquote != def_lquote)
9736 You can use @samp{set print address off} to eliminate all machine
9737 dependent displays from the @value{GDBN} interface. For example, with
9738 @code{print address off}, you should get the same text for backtraces on
9739 all machines---whether or not they involve pointer arguments.
9742 @item show print address
9743 Show whether or not addresses are to be printed.
9746 When @value{GDBN} prints a symbolic address, it normally prints the
9747 closest earlier symbol plus an offset. If that symbol does not uniquely
9748 identify the address (for example, it is a name whose scope is a single
9749 source file), you may need to clarify. One way to do this is with
9750 @code{info line}, for example @samp{info line *0x4537}. Alternately,
9751 you can set @value{GDBN} to print the source file and line number when
9752 it prints a symbolic address:
9755 @item set print symbol-filename on
9756 @cindex source file and line of a symbol
9757 @cindex symbol, source file and line
9758 Tell @value{GDBN} to print the source file name and line number of a
9759 symbol in the symbolic form of an address.
9761 @item set print symbol-filename off
9762 Do not print source file name and line number of a symbol. This is the
9765 @item show print symbol-filename
9766 Show whether or not @value{GDBN} will print the source file name and
9767 line number of a symbol in the symbolic form of an address.
9770 Another situation where it is helpful to show symbol filenames and line
9771 numbers is when disassembling code; @value{GDBN} shows you the line
9772 number and source file that corresponds to each instruction.
9774 Also, you may wish to see the symbolic form only if the address being
9775 printed is reasonably close to the closest earlier symbol:
9778 @item set print max-symbolic-offset @var{max-offset}
9779 @itemx set print max-symbolic-offset unlimited
9780 @cindex maximum value for offset of closest symbol
9781 Tell @value{GDBN} to only display the symbolic form of an address if the
9782 offset between the closest earlier symbol and the address is less than
9783 @var{max-offset}. The default is @code{unlimited}, which tells @value{GDBN}
9784 to always print the symbolic form of an address if any symbol precedes
9785 it. Zero is equivalent to @code{unlimited}.
9787 @item show print max-symbolic-offset
9788 Ask how large the maximum offset is that @value{GDBN} prints in a
9792 @cindex wild pointer, interpreting
9793 @cindex pointer, finding referent
9794 If you have a pointer and you are not sure where it points, try
9795 @samp{set print symbol-filename on}. Then you can determine the name
9796 and source file location of the variable where it points, using
9797 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
9798 For example, here @value{GDBN} shows that a variable @code{ptt} points
9799 at another variable @code{t}, defined in @file{hi2.c}:
9802 (@value{GDBP}) set print symbol-filename on
9803 (@value{GDBP}) p/a ptt
9804 $4 = 0xe008 <t in hi2.c>
9808 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
9809 does not show the symbol name and filename of the referent, even with
9810 the appropriate @code{set print} options turned on.
9813 You can also enable @samp{/a}-like formatting all the time using
9814 @samp{set print symbol on}:
9817 @item set print symbol on
9818 Tell @value{GDBN} to print the symbol corresponding to an address, if
9821 @item set print symbol off
9822 Tell @value{GDBN} not to print the symbol corresponding to an
9823 address. In this mode, @value{GDBN} will still print the symbol
9824 corresponding to pointers to functions. This is the default.
9826 @item show print symbol
9827 Show whether @value{GDBN} will display the symbol corresponding to an
9831 Other settings control how different kinds of objects are printed:
9834 @item set print array
9835 @itemx set print array on
9836 @cindex pretty print arrays
9837 Pretty print arrays. This format is more convenient to read,
9838 but uses more space. The default is off.
9840 @item set print array off
9841 Return to compressed format for arrays.
9843 @item show print array
9844 Show whether compressed or pretty format is selected for displaying
9847 @cindex print array indexes
9848 @item set print array-indexes
9849 @itemx set print array-indexes on
9850 Print the index of each element when displaying arrays. May be more
9851 convenient to locate a given element in the array or quickly find the
9852 index of a given element in that printed array. The default is off.
9854 @item set print array-indexes off
9855 Stop printing element indexes when displaying arrays.
9857 @item show print array-indexes
9858 Show whether the index of each element is printed when displaying
9861 @item set print elements @var{number-of-elements}
9862 @itemx set print elements unlimited
9863 @cindex number of array elements to print
9864 @cindex limit on number of printed array elements
9865 Set a limit on how many elements of an array @value{GDBN} will print.
9866 If @value{GDBN} is printing a large array, it stops printing after it has
9867 printed the number of elements set by the @code{set print elements} command.
9868 This limit also applies to the display of strings.
9869 When @value{GDBN} starts, this limit is set to 200.
9870 Setting @var{number-of-elements} to @code{unlimited} or zero means
9871 that the number of elements to print is unlimited.
9873 @item show print elements
9874 Display the number of elements of a large array that @value{GDBN} will print.
9875 If the number is 0, then the printing is unlimited.
9877 @item set print frame-arguments @var{value}
9878 @kindex set print frame-arguments
9879 @cindex printing frame argument values
9880 @cindex print all frame argument values
9881 @cindex print frame argument values for scalars only
9882 @cindex do not print frame argument values
9883 This command allows to control how the values of arguments are printed
9884 when the debugger prints a frame (@pxref{Frames}). The possible
9889 The values of all arguments are printed.
9892 Print the value of an argument only if it is a scalar. The value of more
9893 complex arguments such as arrays, structures, unions, etc, is replaced
9894 by @code{@dots{}}. This is the default. Here is an example where
9895 only scalar arguments are shown:
9898 #1 0x08048361 in call_me (i=3, s=@dots{}, ss=0xbf8d508c, u=@dots{}, e=green)
9903 None of the argument values are printed. Instead, the value of each argument
9904 is replaced by @code{@dots{}}. In this case, the example above now becomes:
9907 #1 0x08048361 in call_me (i=@dots{}, s=@dots{}, ss=@dots{}, u=@dots{}, e=@dots{})
9912 By default, only scalar arguments are printed. This command can be used
9913 to configure the debugger to print the value of all arguments, regardless
9914 of their type. However, it is often advantageous to not print the value
9915 of more complex parameters. For instance, it reduces the amount of
9916 information printed in each frame, making the backtrace more readable.
9917 Also, it improves performance when displaying Ada frames, because
9918 the computation of large arguments can sometimes be CPU-intensive,
9919 especially in large applications. Setting @code{print frame-arguments}
9920 to @code{scalars} (the default) or @code{none} avoids this computation,
9921 thus speeding up the display of each Ada frame.
9923 @item show print frame-arguments
9924 Show how the value of arguments should be displayed when printing a frame.
9926 @item set print raw frame-arguments on
9927 Print frame arguments in raw, non pretty-printed, form.
9929 @item set print raw frame-arguments off
9930 Print frame arguments in pretty-printed form, if there is a pretty-printer
9931 for the value (@pxref{Pretty Printing}),
9932 otherwise print the value in raw form.
9933 This is the default.
9935 @item show print raw frame-arguments
9936 Show whether to print frame arguments in raw form.
9938 @anchor{set print entry-values}
9939 @item set print entry-values @var{value}
9940 @kindex set print entry-values
9941 Set printing of frame argument values at function entry. In some cases
9942 @value{GDBN} can determine the value of function argument which was passed by
9943 the function caller, even if the value was modified inside the called function
9944 and therefore is different. With optimized code, the current value could be
9945 unavailable, but the entry value may still be known.
9947 The default value is @code{default} (see below for its description). Older
9948 @value{GDBN} behaved as with the setting @code{no}. Compilers not supporting
9949 this feature will behave in the @code{default} setting the same way as with the
9952 This functionality is currently supported only by DWARF 2 debugging format and
9953 the compiler has to produce @samp{DW_TAG_call_site} tags. With
9954 @value{NGCC}, you need to specify @option{-O -g} during compilation, to get
9957 The @var{value} parameter can be one of the following:
9961 Print only actual parameter values, never print values from function entry
9965 #0 different (val=6)
9966 #0 lost (val=<optimized out>)
9968 #0 invalid (val=<optimized out>)
9972 Print only parameter values from function entry point. The actual parameter
9973 values are never printed.
9975 #0 equal (val@@entry=5)
9976 #0 different (val@@entry=5)
9977 #0 lost (val@@entry=5)
9978 #0 born (val@@entry=<optimized out>)
9979 #0 invalid (val@@entry=<optimized out>)
9983 Print only parameter values from function entry point. If value from function
9984 entry point is not known while the actual value is known, print the actual
9985 value for such parameter.
9987 #0 equal (val@@entry=5)
9988 #0 different (val@@entry=5)
9989 #0 lost (val@@entry=5)
9991 #0 invalid (val@@entry=<optimized out>)
9995 Print actual parameter values. If actual parameter value is not known while
9996 value from function entry point is known, print the entry point value for such
10000 #0 different (val=6)
10001 #0 lost (val@@entry=5)
10003 #0 invalid (val=<optimized out>)
10007 Always print both the actual parameter value and its value from function entry
10008 point, even if values of one or both are not available due to compiler
10011 #0 equal (val=5, val@@entry=5)
10012 #0 different (val=6, val@@entry=5)
10013 #0 lost (val=<optimized out>, val@@entry=5)
10014 #0 born (val=10, val@@entry=<optimized out>)
10015 #0 invalid (val=<optimized out>, val@@entry=<optimized out>)
10019 Print the actual parameter value if it is known and also its value from
10020 function entry point if it is known. If neither is known, print for the actual
10021 value @code{<optimized out>}. If not in MI mode (@pxref{GDB/MI}) and if both
10022 values are known and identical, print the shortened
10023 @code{param=param@@entry=VALUE} notation.
10025 #0 equal (val=val@@entry=5)
10026 #0 different (val=6, val@@entry=5)
10027 #0 lost (val@@entry=5)
10029 #0 invalid (val=<optimized out>)
10033 Always print the actual parameter value. Print also its value from function
10034 entry point, but only if it is known. If not in MI mode (@pxref{GDB/MI}) and
10035 if both values are known and identical, print the shortened
10036 @code{param=param@@entry=VALUE} notation.
10038 #0 equal (val=val@@entry=5)
10039 #0 different (val=6, val@@entry=5)
10040 #0 lost (val=<optimized out>, val@@entry=5)
10042 #0 invalid (val=<optimized out>)
10046 For analysis messages on possible failures of frame argument values at function
10047 entry resolution see @ref{set debug entry-values}.
10049 @item show print entry-values
10050 Show the method being used for printing of frame argument values at function
10053 @item set print repeats @var{number-of-repeats}
10054 @itemx set print repeats unlimited
10055 @cindex repeated array elements
10056 Set the threshold for suppressing display of repeated array
10057 elements. When the number of consecutive identical elements of an
10058 array exceeds the threshold, @value{GDBN} prints the string
10059 @code{"<repeats @var{n} times>"}, where @var{n} is the number of
10060 identical repetitions, instead of displaying the identical elements
10061 themselves. Setting the threshold to @code{unlimited} or zero will
10062 cause all elements to be individually printed. The default threshold
10065 @item show print repeats
10066 Display the current threshold for printing repeated identical
10069 @item set print null-stop
10070 @cindex @sc{null} elements in arrays
10071 Cause @value{GDBN} to stop printing the characters of an array when the first
10072 @sc{null} is encountered. This is useful when large arrays actually
10073 contain only short strings.
10074 The default is off.
10076 @item show print null-stop
10077 Show whether @value{GDBN} stops printing an array on the first
10078 @sc{null} character.
10080 @item set print pretty on
10081 @cindex print structures in indented form
10082 @cindex indentation in structure display
10083 Cause @value{GDBN} to print structures in an indented format with one member
10084 per line, like this:
10099 @item set print pretty off
10100 Cause @value{GDBN} to print structures in a compact format, like this:
10104 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
10105 meat = 0x54 "Pork"@}
10110 This is the default format.
10112 @item show print pretty
10113 Show which format @value{GDBN} is using to print structures.
10115 @item set print sevenbit-strings on
10116 @cindex eight-bit characters in strings
10117 @cindex octal escapes in strings
10118 Print using only seven-bit characters; if this option is set,
10119 @value{GDBN} displays any eight-bit characters (in strings or
10120 character values) using the notation @code{\}@var{nnn}. This setting is
10121 best if you are working in English (@sc{ascii}) and you use the
10122 high-order bit of characters as a marker or ``meta'' bit.
10124 @item set print sevenbit-strings off
10125 Print full eight-bit characters. This allows the use of more
10126 international character sets, and is the default.
10128 @item show print sevenbit-strings
10129 Show whether or not @value{GDBN} is printing only seven-bit characters.
10131 @item set print union on
10132 @cindex unions in structures, printing
10133 Tell @value{GDBN} to print unions which are contained in structures
10134 and other unions. This is the default setting.
10136 @item set print union off
10137 Tell @value{GDBN} not to print unions which are contained in
10138 structures and other unions. @value{GDBN} will print @code{"@{...@}"}
10141 @item show print union
10142 Ask @value{GDBN} whether or not it will print unions which are contained in
10143 structures and other unions.
10145 For example, given the declarations
10148 typedef enum @{Tree, Bug@} Species;
10149 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
10150 typedef enum @{Caterpillar, Cocoon, Butterfly@}
10161 struct thing foo = @{Tree, @{Acorn@}@};
10165 with @code{set print union on} in effect @samp{p foo} would print
10168 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
10172 and with @code{set print union off} in effect it would print
10175 $1 = @{it = Tree, form = @{...@}@}
10179 @code{set print union} affects programs written in C-like languages
10185 These settings are of interest when debugging C@t{++} programs:
10188 @cindex demangling C@t{++} names
10189 @item set print demangle
10190 @itemx set print demangle on
10191 Print C@t{++} names in their source form rather than in the encoded
10192 (``mangled'') form passed to the assembler and linker for type-safe
10193 linkage. The default is on.
10195 @item show print demangle
10196 Show whether C@t{++} names are printed in mangled or demangled form.
10198 @item set print asm-demangle
10199 @itemx set print asm-demangle on
10200 Print C@t{++} names in their source form rather than their mangled form, even
10201 in assembler code printouts such as instruction disassemblies.
10202 The default is off.
10204 @item show print asm-demangle
10205 Show whether C@t{++} names in assembly listings are printed in mangled
10208 @cindex C@t{++} symbol decoding style
10209 @cindex symbol decoding style, C@t{++}
10210 @kindex set demangle-style
10211 @item set demangle-style @var{style}
10212 Choose among several encoding schemes used by different compilers to
10213 represent C@t{++} names. The choices for @var{style} are currently:
10217 Allow @value{GDBN} to choose a decoding style by inspecting your program.
10218 This is the default.
10221 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
10224 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
10227 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
10230 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
10231 @strong{Warning:} this setting alone is not sufficient to allow
10232 debugging @code{cfront}-generated executables. @value{GDBN} would
10233 require further enhancement to permit that.
10236 If you omit @var{style}, you will see a list of possible formats.
10238 @item show demangle-style
10239 Display the encoding style currently in use for decoding C@t{++} symbols.
10241 @item set print object
10242 @itemx set print object on
10243 @cindex derived type of an object, printing
10244 @cindex display derived types
10245 When displaying a pointer to an object, identify the @emph{actual}
10246 (derived) type of the object rather than the @emph{declared} type, using
10247 the virtual function table. Note that the virtual function table is
10248 required---this feature can only work for objects that have run-time
10249 type identification; a single virtual method in the object's declared
10250 type is sufficient. Note that this setting is also taken into account when
10251 working with variable objects via MI (@pxref{GDB/MI}).
10253 @item set print object off
10254 Display only the declared type of objects, without reference to the
10255 virtual function table. This is the default setting.
10257 @item show print object
10258 Show whether actual, or declared, object types are displayed.
10260 @item set print static-members
10261 @itemx set print static-members on
10262 @cindex static members of C@t{++} objects
10263 Print static members when displaying a C@t{++} object. The default is on.
10265 @item set print static-members off
10266 Do not print static members when displaying a C@t{++} object.
10268 @item show print static-members
10269 Show whether C@t{++} static members are printed or not.
10271 @item set print pascal_static-members
10272 @itemx set print pascal_static-members on
10273 @cindex static members of Pascal objects
10274 @cindex Pascal objects, static members display
10275 Print static members when displaying a Pascal object. The default is on.
10277 @item set print pascal_static-members off
10278 Do not print static members when displaying a Pascal object.
10280 @item show print pascal_static-members
10281 Show whether Pascal static members are printed or not.
10283 @c These don't work with HP ANSI C++ yet.
10284 @item set print vtbl
10285 @itemx set print vtbl on
10286 @cindex pretty print C@t{++} virtual function tables
10287 @cindex virtual functions (C@t{++}) display
10288 @cindex VTBL display
10289 Pretty print C@t{++} virtual function tables. The default is off.
10290 (The @code{vtbl} commands do not work on programs compiled with the HP
10291 ANSI C@t{++} compiler (@code{aCC}).)
10293 @item set print vtbl off
10294 Do not pretty print C@t{++} virtual function tables.
10296 @item show print vtbl
10297 Show whether C@t{++} virtual function tables are pretty printed, or not.
10300 @node Pretty Printing
10301 @section Pretty Printing
10303 @value{GDBN} provides a mechanism to allow pretty-printing of values using
10304 Python code. It greatly simplifies the display of complex objects. This
10305 mechanism works for both MI and the CLI.
10308 * Pretty-Printer Introduction:: Introduction to pretty-printers
10309 * Pretty-Printer Example:: An example pretty-printer
10310 * Pretty-Printer Commands:: Pretty-printer commands
10313 @node Pretty-Printer Introduction
10314 @subsection Pretty-Printer Introduction
10316 When @value{GDBN} prints a value, it first sees if there is a pretty-printer
10317 registered for the value. If there is then @value{GDBN} invokes the
10318 pretty-printer to print the value. Otherwise the value is printed normally.
10320 Pretty-printers are normally named. This makes them easy to manage.
10321 The @samp{info pretty-printer} command will list all the installed
10322 pretty-printers with their names.
10323 If a pretty-printer can handle multiple data types, then its
10324 @dfn{subprinters} are the printers for the individual data types.
10325 Each such subprinter has its own name.
10326 The format of the name is @var{printer-name};@var{subprinter-name}.
10328 Pretty-printers are installed by @dfn{registering} them with @value{GDBN}.
10329 Typically they are automatically loaded and registered when the corresponding
10330 debug information is loaded, thus making them available without having to
10331 do anything special.
10333 There are three places where a pretty-printer can be registered.
10337 Pretty-printers registered globally are available when debugging
10341 Pretty-printers registered with a program space are available only
10342 when debugging that program.
10343 @xref{Progspaces In Python}, for more details on program spaces in Python.
10346 Pretty-printers registered with an objfile are loaded and unloaded
10347 with the corresponding objfile (e.g., shared library).
10348 @xref{Objfiles In Python}, for more details on objfiles in Python.
10351 @xref{Selecting Pretty-Printers}, for further information on how
10352 pretty-printers are selected,
10354 @xref{Writing a Pretty-Printer}, for implementing pretty printers
10357 @node Pretty-Printer Example
10358 @subsection Pretty-Printer Example
10360 Here is how a C@t{++} @code{std::string} looks without a pretty-printer:
10363 (@value{GDBP}) print s
10365 static npos = 4294967295,
10367 <std::allocator<char>> = @{
10368 <__gnu_cxx::new_allocator<char>> = @{
10369 <No data fields>@}, <No data fields>
10371 members of std::basic_string<char, std::char_traits<char>,
10372 std::allocator<char> >::_Alloc_hider:
10373 _M_p = 0x804a014 "abcd"
10378 With a pretty-printer for @code{std::string} only the contents are printed:
10381 (@value{GDBP}) print s
10385 @node Pretty-Printer Commands
10386 @subsection Pretty-Printer Commands
10387 @cindex pretty-printer commands
10390 @kindex info pretty-printer
10391 @item info pretty-printer [@var{object-regexp} [@var{name-regexp}]]
10392 Print the list of installed pretty-printers.
10393 This includes disabled pretty-printers, which are marked as such.
10395 @var{object-regexp} is a regular expression matching the objects
10396 whose pretty-printers to list.
10397 Objects can be @code{global}, the program space's file
10398 (@pxref{Progspaces In Python}),
10399 and the object files within that program space (@pxref{Objfiles In Python}).
10400 @xref{Selecting Pretty-Printers}, for details on how @value{GDBN}
10401 looks up a printer from these three objects.
10403 @var{name-regexp} is a regular expression matching the name of the printers
10406 @kindex disable pretty-printer
10407 @item disable pretty-printer [@var{object-regexp} [@var{name-regexp}]]
10408 Disable pretty-printers matching @var{object-regexp} and @var{name-regexp}.
10409 A disabled pretty-printer is not forgotten, it may be enabled again later.
10411 @kindex enable pretty-printer
10412 @item enable pretty-printer [@var{object-regexp} [@var{name-regexp}]]
10413 Enable pretty-printers matching @var{object-regexp} and @var{name-regexp}.
10418 Suppose we have three pretty-printers installed: one from library1.so
10419 named @code{foo} that prints objects of type @code{foo}, and
10420 another from library2.so named @code{bar} that prints two types of objects,
10421 @code{bar1} and @code{bar2}.
10424 (gdb) info pretty-printer
10431 (gdb) info pretty-printer library2
10436 (gdb) disable pretty-printer library1
10438 2 of 3 printers enabled
10439 (gdb) info pretty-printer
10446 (gdb) disable pretty-printer library2 bar:bar1
10448 1 of 3 printers enabled
10449 (gdb) info pretty-printer library2
10456 (gdb) disable pretty-printer library2 bar
10458 0 of 3 printers enabled
10459 (gdb) info pretty-printer library2
10468 Note that for @code{bar} the entire printer can be disabled,
10469 as can each individual subprinter.
10471 @node Value History
10472 @section Value History
10474 @cindex value history
10475 @cindex history of values printed by @value{GDBN}
10476 Values printed by the @code{print} command are saved in the @value{GDBN}
10477 @dfn{value history}. This allows you to refer to them in other expressions.
10478 Values are kept until the symbol table is re-read or discarded
10479 (for example with the @code{file} or @code{symbol-file} commands).
10480 When the symbol table changes, the value history is discarded,
10481 since the values may contain pointers back to the types defined in the
10486 @cindex history number
10487 The values printed are given @dfn{history numbers} by which you can
10488 refer to them. These are successive integers starting with one.
10489 @code{print} shows you the history number assigned to a value by
10490 printing @samp{$@var{num} = } before the value; here @var{num} is the
10493 To refer to any previous value, use @samp{$} followed by the value's
10494 history number. The way @code{print} labels its output is designed to
10495 remind you of this. Just @code{$} refers to the most recent value in
10496 the history, and @code{$$} refers to the value before that.
10497 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
10498 is the value just prior to @code{$$}, @code{$$1} is equivalent to
10499 @code{$$}, and @code{$$0} is equivalent to @code{$}.
10501 For example, suppose you have just printed a pointer to a structure and
10502 want to see the contents of the structure. It suffices to type
10508 If you have a chain of structures where the component @code{next} points
10509 to the next one, you can print the contents of the next one with this:
10516 You can print successive links in the chain by repeating this
10517 command---which you can do by just typing @key{RET}.
10519 Note that the history records values, not expressions. If the value of
10520 @code{x} is 4 and you type these commands:
10528 then the value recorded in the value history by the @code{print} command
10529 remains 4 even though the value of @code{x} has changed.
10532 @kindex show values
10534 Print the last ten values in the value history, with their item numbers.
10535 This is like @samp{p@ $$9} repeated ten times, except that @code{show
10536 values} does not change the history.
10538 @item show values @var{n}
10539 Print ten history values centered on history item number @var{n}.
10541 @item show values +
10542 Print ten history values just after the values last printed. If no more
10543 values are available, @code{show values +} produces no display.
10546 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
10547 same effect as @samp{show values +}.
10549 @node Convenience Vars
10550 @section Convenience Variables
10552 @cindex convenience variables
10553 @cindex user-defined variables
10554 @value{GDBN} provides @dfn{convenience variables} that you can use within
10555 @value{GDBN} to hold on to a value and refer to it later. These variables
10556 exist entirely within @value{GDBN}; they are not part of your program, and
10557 setting a convenience variable has no direct effect on further execution
10558 of your program. That is why you can use them freely.
10560 Convenience variables are prefixed with @samp{$}. Any name preceded by
10561 @samp{$} can be used for a convenience variable, unless it is one of
10562 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
10563 (Value history references, in contrast, are @emph{numbers} preceded
10564 by @samp{$}. @xref{Value History, ,Value History}.)
10566 You can save a value in a convenience variable with an assignment
10567 expression, just as you would set a variable in your program.
10571 set $foo = *object_ptr
10575 would save in @code{$foo} the value contained in the object pointed to by
10578 Using a convenience variable for the first time creates it, but its
10579 value is @code{void} until you assign a new value. You can alter the
10580 value with another assignment at any time.
10582 Convenience variables have no fixed types. You can assign a convenience
10583 variable any type of value, including structures and arrays, even if
10584 that variable already has a value of a different type. The convenience
10585 variable, when used as an expression, has the type of its current value.
10588 @kindex show convenience
10589 @cindex show all user variables and functions
10590 @item show convenience
10591 Print a list of convenience variables used so far, and their values,
10592 as well as a list of the convenience functions.
10593 Abbreviated @code{show conv}.
10595 @kindex init-if-undefined
10596 @cindex convenience variables, initializing
10597 @item init-if-undefined $@var{variable} = @var{expression}
10598 Set a convenience variable if it has not already been set. This is useful
10599 for user-defined commands that keep some state. It is similar, in concept,
10600 to using local static variables with initializers in C (except that
10601 convenience variables are global). It can also be used to allow users to
10602 override default values used in a command script.
10604 If the variable is already defined then the expression is not evaluated so
10605 any side-effects do not occur.
10608 One of the ways to use a convenience variable is as a counter to be
10609 incremented or a pointer to be advanced. For example, to print
10610 a field from successive elements of an array of structures:
10614 print bar[$i++]->contents
10618 Repeat that command by typing @key{RET}.
10620 Some convenience variables are created automatically by @value{GDBN} and given
10621 values likely to be useful.
10624 @vindex $_@r{, convenience variable}
10626 The variable @code{$_} is automatically set by the @code{x} command to
10627 the last address examined (@pxref{Memory, ,Examining Memory}). Other
10628 commands which provide a default address for @code{x} to examine also
10629 set @code{$_} to that address; these commands include @code{info line}
10630 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
10631 except when set by the @code{x} command, in which case it is a pointer
10632 to the type of @code{$__}.
10634 @vindex $__@r{, convenience variable}
10636 The variable @code{$__} is automatically set by the @code{x} command
10637 to the value found in the last address examined. Its type is chosen
10638 to match the format in which the data was printed.
10641 @vindex $_exitcode@r{, convenience variable}
10642 When the program being debugged terminates normally, @value{GDBN}
10643 automatically sets this variable to the exit code of the program, and
10644 resets @code{$_exitsignal} to @code{void}.
10647 @vindex $_exitsignal@r{, convenience variable}
10648 When the program being debugged dies due to an uncaught signal,
10649 @value{GDBN} automatically sets this variable to that signal's number,
10650 and resets @code{$_exitcode} to @code{void}.
10652 To distinguish between whether the program being debugged has exited
10653 (i.e., @code{$_exitcode} is not @code{void}) or signalled (i.e.,
10654 @code{$_exitsignal} is not @code{void}), the convenience function
10655 @code{$_isvoid} can be used (@pxref{Convenience Funs,, Convenience
10656 Functions}). For example, considering the following source code:
10659 #include <signal.h>
10662 main (int argc, char *argv[])
10669 A valid way of telling whether the program being debugged has exited
10670 or signalled would be:
10673 (@value{GDBP}) define has_exited_or_signalled
10674 Type commands for definition of ``has_exited_or_signalled''.
10675 End with a line saying just ``end''.
10676 >if $_isvoid ($_exitsignal)
10677 >echo The program has exited\n
10679 >echo The program has signalled\n
10685 Program terminated with signal SIGALRM, Alarm clock.
10686 The program no longer exists.
10687 (@value{GDBP}) has_exited_or_signalled
10688 The program has signalled
10691 As can be seen, @value{GDBN} correctly informs that the program being
10692 debugged has signalled, since it calls @code{raise} and raises a
10693 @code{SIGALRM} signal. If the program being debugged had not called
10694 @code{raise}, then @value{GDBN} would report a normal exit:
10697 (@value{GDBP}) has_exited_or_signalled
10698 The program has exited
10702 The variable @code{$_exception} is set to the exception object being
10703 thrown at an exception-related catchpoint. @xref{Set Catchpoints}.
10706 @itemx $_probe_arg0@dots{}$_probe_arg11
10707 Arguments to a static probe. @xref{Static Probe Points}.
10710 @vindex $_sdata@r{, inspect, convenience variable}
10711 The variable @code{$_sdata} contains extra collected static tracepoint
10712 data. @xref{Tracepoint Actions,,Tracepoint Action Lists}. Note that
10713 @code{$_sdata} could be empty, if not inspecting a trace buffer, or
10714 if extra static tracepoint data has not been collected.
10717 @vindex $_siginfo@r{, convenience variable}
10718 The variable @code{$_siginfo} contains extra signal information
10719 (@pxref{extra signal information}). Note that @code{$_siginfo}
10720 could be empty, if the application has not yet received any signals.
10721 For example, it will be empty before you execute the @code{run} command.
10724 @vindex $_tlb@r{, convenience variable}
10725 The variable @code{$_tlb} is automatically set when debugging
10726 applications running on MS-Windows in native mode or connected to
10727 gdbserver that supports the @code{qGetTIBAddr} request.
10728 @xref{General Query Packets}.
10729 This variable contains the address of the thread information block.
10732 The number of the current inferior. @xref{Inferiors and
10733 Programs, ,Debugging Multiple Inferiors and Programs}.
10736 The thread number of the current thread. @xref{thread numbers}.
10739 The global number of the current thread. @xref{global thread numbers}.
10743 @node Convenience Funs
10744 @section Convenience Functions
10746 @cindex convenience functions
10747 @value{GDBN} also supplies some @dfn{convenience functions}. These
10748 have a syntax similar to convenience variables. A convenience
10749 function can be used in an expression just like an ordinary function;
10750 however, a convenience function is implemented internally to
10753 These functions do not require @value{GDBN} to be configured with
10754 @code{Python} support, which means that they are always available.
10758 @item $_isvoid (@var{expr})
10759 @findex $_isvoid@r{, convenience function}
10760 Return one if the expression @var{expr} is @code{void}. Otherwise it
10763 A @code{void} expression is an expression where the type of the result
10764 is @code{void}. For example, you can examine a convenience variable
10765 (see @ref{Convenience Vars,, Convenience Variables}) to check whether
10769 (@value{GDBP}) print $_exitcode
10771 (@value{GDBP}) print $_isvoid ($_exitcode)
10774 Starting program: ./a.out
10775 [Inferior 1 (process 29572) exited normally]
10776 (@value{GDBP}) print $_exitcode
10778 (@value{GDBP}) print $_isvoid ($_exitcode)
10782 In the example above, we used @code{$_isvoid} to check whether
10783 @code{$_exitcode} is @code{void} before and after the execution of the
10784 program being debugged. Before the execution there is no exit code to
10785 be examined, therefore @code{$_exitcode} is @code{void}. After the
10786 execution the program being debugged returned zero, therefore
10787 @code{$_exitcode} is zero, which means that it is not @code{void}
10790 The @code{void} expression can also be a call of a function from the
10791 program being debugged. For example, given the following function:
10800 The result of calling it inside @value{GDBN} is @code{void}:
10803 (@value{GDBP}) print foo ()
10805 (@value{GDBP}) print $_isvoid (foo ())
10807 (@value{GDBP}) set $v = foo ()
10808 (@value{GDBP}) print $v
10810 (@value{GDBP}) print $_isvoid ($v)
10816 These functions require @value{GDBN} to be configured with
10817 @code{Python} support.
10821 @item $_memeq(@var{buf1}, @var{buf2}, @var{length})
10822 @findex $_memeq@r{, convenience function}
10823 Returns one if the @var{length} bytes at the addresses given by
10824 @var{buf1} and @var{buf2} are equal.
10825 Otherwise it returns zero.
10827 @item $_regex(@var{str}, @var{regex})
10828 @findex $_regex@r{, convenience function}
10829 Returns one if the string @var{str} matches the regular expression
10830 @var{regex}. Otherwise it returns zero.
10831 The syntax of the regular expression is that specified by @code{Python}'s
10832 regular expression support.
10834 @item $_streq(@var{str1}, @var{str2})
10835 @findex $_streq@r{, convenience function}
10836 Returns one if the strings @var{str1} and @var{str2} are equal.
10837 Otherwise it returns zero.
10839 @item $_strlen(@var{str})
10840 @findex $_strlen@r{, convenience function}
10841 Returns the length of string @var{str}.
10843 @item $_caller_is(@var{name}@r{[}, @var{number_of_frames}@r{]})
10844 @findex $_caller_is@r{, convenience function}
10845 Returns one if the calling function's name is equal to @var{name}.
10846 Otherwise it returns zero.
10848 If the optional argument @var{number_of_frames} is provided,
10849 it is the number of frames up in the stack to look.
10857 at testsuite/gdb.python/py-caller-is.c:21
10858 #1 0x00000000004005a0 in middle_func ()
10859 at testsuite/gdb.python/py-caller-is.c:27
10860 #2 0x00000000004005ab in top_func ()
10861 at testsuite/gdb.python/py-caller-is.c:33
10862 #3 0x00000000004005b6 in main ()
10863 at testsuite/gdb.python/py-caller-is.c:39
10864 (gdb) print $_caller_is ("middle_func")
10866 (gdb) print $_caller_is ("top_func", 2)
10870 @item $_caller_matches(@var{regexp}@r{[}, @var{number_of_frames}@r{]})
10871 @findex $_caller_matches@r{, convenience function}
10872 Returns one if the calling function's name matches the regular expression
10873 @var{regexp}. Otherwise it returns zero.
10875 If the optional argument @var{number_of_frames} is provided,
10876 it is the number of frames up in the stack to look.
10879 @item $_any_caller_is(@var{name}@r{[}, @var{number_of_frames}@r{]})
10880 @findex $_any_caller_is@r{, convenience function}
10881 Returns one if any calling function's name is equal to @var{name}.
10882 Otherwise it returns zero.
10884 If the optional argument @var{number_of_frames} is provided,
10885 it is the number of frames up in the stack to look.
10888 This function differs from @code{$_caller_is} in that this function
10889 checks all stack frames from the immediate caller to the frame specified
10890 by @var{number_of_frames}, whereas @code{$_caller_is} only checks the
10891 frame specified by @var{number_of_frames}.
10893 @item $_any_caller_matches(@var{regexp}@r{[}, @var{number_of_frames}@r{]})
10894 @findex $_any_caller_matches@r{, convenience function}
10895 Returns one if any calling function's name matches the regular expression
10896 @var{regexp}. Otherwise it returns zero.
10898 If the optional argument @var{number_of_frames} is provided,
10899 it is the number of frames up in the stack to look.
10902 This function differs from @code{$_caller_matches} in that this function
10903 checks all stack frames from the immediate caller to the frame specified
10904 by @var{number_of_frames}, whereas @code{$_caller_matches} only checks the
10905 frame specified by @var{number_of_frames}.
10907 @item $_as_string(@var{value})
10908 @findex $_as_string@r{, convenience function}
10909 Return the string representation of @var{value}.
10911 This function is useful to obtain the textual label (enumerator) of an
10912 enumeration value. For example, assuming the variable @var{node} is of
10913 an enumerated type:
10916 (gdb) printf "Visiting node of type %s\n", $_as_string(node)
10917 Visiting node of type NODE_INTEGER
10922 @value{GDBN} provides the ability to list and get help on
10923 convenience functions.
10926 @item help function
10927 @kindex help function
10928 @cindex show all convenience functions
10929 Print a list of all convenience functions.
10936 You can refer to machine register contents, in expressions, as variables
10937 with names starting with @samp{$}. The names of registers are different
10938 for each machine; use @code{info registers} to see the names used on
10942 @kindex info registers
10943 @item info registers
10944 Print the names and values of all registers except floating-point
10945 and vector registers (in the selected stack frame).
10947 @kindex info all-registers
10948 @cindex floating point registers
10949 @item info all-registers
10950 Print the names and values of all registers, including floating-point
10951 and vector registers (in the selected stack frame).
10953 @item info registers @var{regname} @dots{}
10954 Print the @dfn{relativized} value of each specified register @var{regname}.
10955 As discussed in detail below, register values are normally relative to
10956 the selected stack frame. The @var{regname} may be any register name valid on
10957 the machine you are using, with or without the initial @samp{$}.
10960 @anchor{standard registers}
10961 @cindex stack pointer register
10962 @cindex program counter register
10963 @cindex process status register
10964 @cindex frame pointer register
10965 @cindex standard registers
10966 @value{GDBN} has four ``standard'' register names that are available (in
10967 expressions) on most machines---whenever they do not conflict with an
10968 architecture's canonical mnemonics for registers. The register names
10969 @code{$pc} and @code{$sp} are used for the program counter register and
10970 the stack pointer. @code{$fp} is used for a register that contains a
10971 pointer to the current stack frame, and @code{$ps} is used for a
10972 register that contains the processor status. For example,
10973 you could print the program counter in hex with
10980 or print the instruction to be executed next with
10987 or add four to the stack pointer@footnote{This is a way of removing
10988 one word from the stack, on machines where stacks grow downward in
10989 memory (most machines, nowadays). This assumes that the innermost
10990 stack frame is selected; setting @code{$sp} is not allowed when other
10991 stack frames are selected. To pop entire frames off the stack,
10992 regardless of machine architecture, use @code{return};
10993 see @ref{Returning, ,Returning from a Function}.} with
10999 Whenever possible, these four standard register names are available on
11000 your machine even though the machine has different canonical mnemonics,
11001 so long as there is no conflict. The @code{info registers} command
11002 shows the canonical names. For example, on the SPARC, @code{info
11003 registers} displays the processor status register as @code{$psr} but you
11004 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
11005 is an alias for the @sc{eflags} register.
11007 @value{GDBN} always considers the contents of an ordinary register as an
11008 integer when the register is examined in this way. Some machines have
11009 special registers which can hold nothing but floating point; these
11010 registers are considered to have floating point values. There is no way
11011 to refer to the contents of an ordinary register as floating point value
11012 (although you can @emph{print} it as a floating point value with
11013 @samp{print/f $@var{regname}}).
11015 Some registers have distinct ``raw'' and ``virtual'' data formats. This
11016 means that the data format in which the register contents are saved by
11017 the operating system is not the same one that your program normally
11018 sees. For example, the registers of the 68881 floating point
11019 coprocessor are always saved in ``extended'' (raw) format, but all C
11020 programs expect to work with ``double'' (virtual) format. In such
11021 cases, @value{GDBN} normally works with the virtual format only (the format
11022 that makes sense for your program), but the @code{info registers} command
11023 prints the data in both formats.
11025 @cindex SSE registers (x86)
11026 @cindex MMX registers (x86)
11027 Some machines have special registers whose contents can be interpreted
11028 in several different ways. For example, modern x86-based machines
11029 have SSE and MMX registers that can hold several values packed
11030 together in several different formats. @value{GDBN} refers to such
11031 registers in @code{struct} notation:
11034 (@value{GDBP}) print $xmm1
11036 v4_float = @{0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044@},
11037 v2_double = @{9.92129282474342e-303, 2.7585945287983262e-313@},
11038 v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
11039 v8_int16 = @{0, 0, 14072, 315, 11, 0, 13, 0@},
11040 v4_int32 = @{0, 20657912, 11, 13@},
11041 v2_int64 = @{88725056443645952, 55834574859@},
11042 uint128 = 0x0000000d0000000b013b36f800000000
11047 To set values of such registers, you need to tell @value{GDBN} which
11048 view of the register you wish to change, as if you were assigning
11049 value to a @code{struct} member:
11052 (@value{GDBP}) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF
11055 Normally, register values are relative to the selected stack frame
11056 (@pxref{Selection, ,Selecting a Frame}). This means that you get the
11057 value that the register would contain if all stack frames farther in
11058 were exited and their saved registers restored. In order to see the
11059 true contents of hardware registers, you must select the innermost
11060 frame (with @samp{frame 0}).
11062 @cindex caller-saved registers
11063 @cindex call-clobbered registers
11064 @cindex volatile registers
11065 @cindex <not saved> values
11066 Usually ABIs reserve some registers as not needed to be saved by the
11067 callee (a.k.a.: ``caller-saved'', ``call-clobbered'' or ``volatile''
11068 registers). It may therefore not be possible for @value{GDBN} to know
11069 the value a register had before the call (in other words, in the outer
11070 frame), if the register value has since been changed by the callee.
11071 @value{GDBN} tries to deduce where the inner frame saved
11072 (``callee-saved'') registers, from the debug info, unwind info, or the
11073 machine code generated by your compiler. If some register is not
11074 saved, and @value{GDBN} knows the register is ``caller-saved'' (via
11075 its own knowledge of the ABI, or because the debug/unwind info
11076 explicitly says the register's value is undefined), @value{GDBN}
11077 displays @w{@samp{<not saved>}} as the register's value. With targets
11078 that @value{GDBN} has no knowledge of the register saving convention,
11079 if a register was not saved by the callee, then its value and location
11080 in the outer frame are assumed to be the same of the inner frame.
11081 This is usually harmless, because if the register is call-clobbered,
11082 the caller either does not care what is in the register after the
11083 call, or has code to restore the value that it does care about. Note,
11084 however, that if you change such a register in the outer frame, you
11085 may also be affecting the inner frame. Also, the more ``outer'' the
11086 frame is you're looking at, the more likely a call-clobbered
11087 register's value is to be wrong, in the sense that it doesn't actually
11088 represent the value the register had just before the call.
11090 @node Floating Point Hardware
11091 @section Floating Point Hardware
11092 @cindex floating point
11094 Depending on the configuration, @value{GDBN} may be able to give
11095 you more information about the status of the floating point hardware.
11100 Display hardware-dependent information about the floating
11101 point unit. The exact contents and layout vary depending on the
11102 floating point chip. Currently, @samp{info float} is supported on
11103 the ARM and x86 machines.
11107 @section Vector Unit
11108 @cindex vector unit
11110 Depending on the configuration, @value{GDBN} may be able to give you
11111 more information about the status of the vector unit.
11114 @kindex info vector
11116 Display information about the vector unit. The exact contents and
11117 layout vary depending on the hardware.
11120 @node OS Information
11121 @section Operating System Auxiliary Information
11122 @cindex OS information
11124 @value{GDBN} provides interfaces to useful OS facilities that can help
11125 you debug your program.
11127 @cindex auxiliary vector
11128 @cindex vector, auxiliary
11129 Some operating systems supply an @dfn{auxiliary vector} to programs at
11130 startup. This is akin to the arguments and environment that you
11131 specify for a program, but contains a system-dependent variety of
11132 binary values that tell system libraries important details about the
11133 hardware, operating system, and process. Each value's purpose is
11134 identified by an integer tag; the meanings are well-known but system-specific.
11135 Depending on the configuration and operating system facilities,
11136 @value{GDBN} may be able to show you this information. For remote
11137 targets, this functionality may further depend on the remote stub's
11138 support of the @samp{qXfer:auxv:read} packet, see
11139 @ref{qXfer auxiliary vector read}.
11144 Display the auxiliary vector of the inferior, which can be either a
11145 live process or a core dump file. @value{GDBN} prints each tag value
11146 numerically, and also shows names and text descriptions for recognized
11147 tags. Some values in the vector are numbers, some bit masks, and some
11148 pointers to strings or other data. @value{GDBN} displays each value in the
11149 most appropriate form for a recognized tag, and in hexadecimal for
11150 an unrecognized tag.
11153 On some targets, @value{GDBN} can access operating system-specific
11154 information and show it to you. The types of information available
11155 will differ depending on the type of operating system running on the
11156 target. The mechanism used to fetch the data is described in
11157 @ref{Operating System Information}. For remote targets, this
11158 functionality depends on the remote stub's support of the
11159 @samp{qXfer:osdata:read} packet, see @ref{qXfer osdata read}.
11163 @item info os @var{infotype}
11165 Display OS information of the requested type.
11167 On @sc{gnu}/Linux, the following values of @var{infotype} are valid:
11169 @anchor{linux info os infotypes}
11171 @kindex info os cpus
11173 Display the list of all CPUs/cores. For each CPU/core, @value{GDBN} prints
11174 the available fields from /proc/cpuinfo. For each supported architecture
11175 different fields are available. Two common entries are processor which gives
11176 CPU number and bogomips; a system constant that is calculated during
11177 kernel initialization.
11179 @kindex info os files
11181 Display the list of open file descriptors on the target. For each
11182 file descriptor, @value{GDBN} prints the identifier of the process
11183 owning the descriptor, the command of the owning process, the value
11184 of the descriptor, and the target of the descriptor.
11186 @kindex info os modules
11188 Display the list of all loaded kernel modules on the target. For each
11189 module, @value{GDBN} prints the module name, the size of the module in
11190 bytes, the number of times the module is used, the dependencies of the
11191 module, the status of the module, and the address of the loaded module
11194 @kindex info os msg
11196 Display the list of all System V message queues on the target. For each
11197 message queue, @value{GDBN} prints the message queue key, the message
11198 queue identifier, the access permissions, the current number of bytes
11199 on the queue, the current number of messages on the queue, the processes
11200 that last sent and received a message on the queue, the user and group
11201 of the owner and creator of the message queue, the times at which a
11202 message was last sent and received on the queue, and the time at which
11203 the message queue was last changed.
11205 @kindex info os processes
11207 Display the list of processes on the target. For each process,
11208 @value{GDBN} prints the process identifier, the name of the user, the
11209 command corresponding to the process, and the list of processor cores
11210 that the process is currently running on. (To understand what these
11211 properties mean, for this and the following info types, please consult
11212 the general @sc{gnu}/Linux documentation.)
11214 @kindex info os procgroups
11216 Display the list of process groups on the target. For each process,
11217 @value{GDBN} prints the identifier of the process group that it belongs
11218 to, the command corresponding to the process group leader, the process
11219 identifier, and the command line of the process. The list is sorted
11220 first by the process group identifier, then by the process identifier,
11221 so that processes belonging to the same process group are grouped together
11222 and the process group leader is listed first.
11224 @kindex info os semaphores
11226 Display the list of all System V semaphore sets on the target. For each
11227 semaphore set, @value{GDBN} prints the semaphore set key, the semaphore
11228 set identifier, the access permissions, the number of semaphores in the
11229 set, the user and group of the owner and creator of the semaphore set,
11230 and the times at which the semaphore set was operated upon and changed.
11232 @kindex info os shm
11234 Display the list of all System V shared-memory regions on the target.
11235 For each shared-memory region, @value{GDBN} prints the region key,
11236 the shared-memory identifier, the access permissions, the size of the
11237 region, the process that created the region, the process that last
11238 attached to or detached from the region, the current number of live
11239 attaches to the region, and the times at which the region was last
11240 attached to, detach from, and changed.
11242 @kindex info os sockets
11244 Display the list of Internet-domain sockets on the target. For each
11245 socket, @value{GDBN} prints the address and port of the local and
11246 remote endpoints, the current state of the connection, the creator of
11247 the socket, the IP address family of the socket, and the type of the
11250 @kindex info os threads
11252 Display the list of threads running on the target. For each thread,
11253 @value{GDBN} prints the identifier of the process that the thread
11254 belongs to, the command of the process, the thread identifier, and the
11255 processor core that it is currently running on. The main thread of a
11256 process is not listed.
11260 If @var{infotype} is omitted, then list the possible values for
11261 @var{infotype} and the kind of OS information available for each
11262 @var{infotype}. If the target does not return a list of possible
11263 types, this command will report an error.
11266 @node Memory Region Attributes
11267 @section Memory Region Attributes
11268 @cindex memory region attributes
11270 @dfn{Memory region attributes} allow you to describe special handling
11271 required by regions of your target's memory. @value{GDBN} uses
11272 attributes to determine whether to allow certain types of memory
11273 accesses; whether to use specific width accesses; and whether to cache
11274 target memory. By default the description of memory regions is
11275 fetched from the target (if the current target supports this), but the
11276 user can override the fetched regions.
11278 Defined memory regions can be individually enabled and disabled. When a
11279 memory region is disabled, @value{GDBN} uses the default attributes when
11280 accessing memory in that region. Similarly, if no memory regions have
11281 been defined, @value{GDBN} uses the default attributes when accessing
11284 When a memory region is defined, it is given a number to identify it;
11285 to enable, disable, or remove a memory region, you specify that number.
11289 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
11290 Define a memory region bounded by @var{lower} and @var{upper} with
11291 attributes @var{attributes}@dots{}, and add it to the list of regions
11292 monitored by @value{GDBN}. Note that @var{upper} == 0 is a special
11293 case: it is treated as the target's maximum memory address.
11294 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
11297 Discard any user changes to the memory regions and use target-supplied
11298 regions, if available, or no regions if the target does not support.
11301 @item delete mem @var{nums}@dots{}
11302 Remove memory regions @var{nums}@dots{} from the list of regions
11303 monitored by @value{GDBN}.
11305 @kindex disable mem
11306 @item disable mem @var{nums}@dots{}
11307 Disable monitoring of memory regions @var{nums}@dots{}.
11308 A disabled memory region is not forgotten.
11309 It may be enabled again later.
11312 @item enable mem @var{nums}@dots{}
11313 Enable monitoring of memory regions @var{nums}@dots{}.
11317 Print a table of all defined memory regions, with the following columns
11321 @item Memory Region Number
11322 @item Enabled or Disabled.
11323 Enabled memory regions are marked with @samp{y}.
11324 Disabled memory regions are marked with @samp{n}.
11327 The address defining the inclusive lower bound of the memory region.
11330 The address defining the exclusive upper bound of the memory region.
11333 The list of attributes set for this memory region.
11338 @subsection Attributes
11340 @subsubsection Memory Access Mode
11341 The access mode attributes set whether @value{GDBN} may make read or
11342 write accesses to a memory region.
11344 While these attributes prevent @value{GDBN} from performing invalid
11345 memory accesses, they do nothing to prevent the target system, I/O DMA,
11346 etc.@: from accessing memory.
11350 Memory is read only.
11352 Memory is write only.
11354 Memory is read/write. This is the default.
11357 @subsubsection Memory Access Size
11358 The access size attribute tells @value{GDBN} to use specific sized
11359 accesses in the memory region. Often memory mapped device registers
11360 require specific sized accesses. If no access size attribute is
11361 specified, @value{GDBN} may use accesses of any size.
11365 Use 8 bit memory accesses.
11367 Use 16 bit memory accesses.
11369 Use 32 bit memory accesses.
11371 Use 64 bit memory accesses.
11374 @c @subsubsection Hardware/Software Breakpoints
11375 @c The hardware/software breakpoint attributes set whether @value{GDBN}
11376 @c will use hardware or software breakpoints for the internal breakpoints
11377 @c used by the step, next, finish, until, etc. commands.
11381 @c Always use hardware breakpoints
11382 @c @item swbreak (default)
11385 @subsubsection Data Cache
11386 The data cache attributes set whether @value{GDBN} will cache target
11387 memory. While this generally improves performance by reducing debug
11388 protocol overhead, it can lead to incorrect results because @value{GDBN}
11389 does not know about volatile variables or memory mapped device
11394 Enable @value{GDBN} to cache target memory.
11396 Disable @value{GDBN} from caching target memory. This is the default.
11399 @subsection Memory Access Checking
11400 @value{GDBN} can be instructed to refuse accesses to memory that is
11401 not explicitly described. This can be useful if accessing such
11402 regions has undesired effects for a specific target, or to provide
11403 better error checking. The following commands control this behaviour.
11406 @kindex set mem inaccessible-by-default
11407 @item set mem inaccessible-by-default [on|off]
11408 If @code{on} is specified, make @value{GDBN} treat memory not
11409 explicitly described by the memory ranges as non-existent and refuse accesses
11410 to such memory. The checks are only performed if there's at least one
11411 memory range defined. If @code{off} is specified, make @value{GDBN}
11412 treat the memory not explicitly described by the memory ranges as RAM.
11413 The default value is @code{on}.
11414 @kindex show mem inaccessible-by-default
11415 @item show mem inaccessible-by-default
11416 Show the current handling of accesses to unknown memory.
11420 @c @subsubsection Memory Write Verification
11421 @c The memory write verification attributes set whether @value{GDBN}
11422 @c will re-reads data after each write to verify the write was successful.
11426 @c @item noverify (default)
11429 @node Dump/Restore Files
11430 @section Copy Between Memory and a File
11431 @cindex dump/restore files
11432 @cindex append data to a file
11433 @cindex dump data to a file
11434 @cindex restore data from a file
11436 You can use the commands @code{dump}, @code{append}, and
11437 @code{restore} to copy data between target memory and a file. The
11438 @code{dump} and @code{append} commands write data to a file, and the
11439 @code{restore} command reads data from a file back into the inferior's
11440 memory. Files may be in binary, Motorola S-record, Intel hex,
11441 Tektronix Hex, or Verilog Hex format; however, @value{GDBN} can only
11442 append to binary files, and cannot read from Verilog Hex files.
11447 @item dump @r{[}@var{format}@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
11448 @itemx dump @r{[}@var{format}@r{]} value @var{filename} @var{expr}
11449 Dump the contents of memory from @var{start_addr} to @var{end_addr},
11450 or the value of @var{expr}, to @var{filename} in the given format.
11452 The @var{format} parameter may be any one of:
11459 Motorola S-record format.
11461 Tektronix Hex format.
11463 Verilog Hex format.
11466 @value{GDBN} uses the same definitions of these formats as the
11467 @sc{gnu} binary utilities, like @samp{objdump} and @samp{objcopy}. If
11468 @var{format} is omitted, @value{GDBN} dumps the data in raw binary
11472 @item append @r{[}binary@r{]} memory @var{filename} @var{start_addr} @var{end_addr}
11473 @itemx append @r{[}binary@r{]} value @var{filename} @var{expr}
11474 Append the contents of memory from @var{start_addr} to @var{end_addr},
11475 or the value of @var{expr}, to the file @var{filename}, in raw binary form.
11476 (@value{GDBN} can only append data to files in raw binary form.)
11479 @item restore @var{filename} @r{[}binary@r{]} @var{bias} @var{start} @var{end}
11480 Restore the contents of file @var{filename} into memory. The
11481 @code{restore} command can automatically recognize any known @sc{bfd}
11482 file format, except for raw binary. To restore a raw binary file you
11483 must specify the optional keyword @code{binary} after the filename.
11485 If @var{bias} is non-zero, its value will be added to the addresses
11486 contained in the file. Binary files always start at address zero, so
11487 they will be restored at address @var{bias}. Other bfd files have
11488 a built-in location; they will be restored at offset @var{bias}
11489 from that location.
11491 If @var{start} and/or @var{end} are non-zero, then only data between
11492 file offset @var{start} and file offset @var{end} will be restored.
11493 These offsets are relative to the addresses in the file, before
11494 the @var{bias} argument is applied.
11498 @node Core File Generation
11499 @section How to Produce a Core File from Your Program
11500 @cindex dump core from inferior
11502 A @dfn{core file} or @dfn{core dump} is a file that records the memory
11503 image of a running process and its process status (register values
11504 etc.). Its primary use is post-mortem debugging of a program that
11505 crashed while it ran outside a debugger. A program that crashes
11506 automatically produces a core file, unless this feature is disabled by
11507 the user. @xref{Files}, for information on invoking @value{GDBN} in
11508 the post-mortem debugging mode.
11510 Occasionally, you may wish to produce a core file of the program you
11511 are debugging in order to preserve a snapshot of its state.
11512 @value{GDBN} has a special command for that.
11516 @kindex generate-core-file
11517 @item generate-core-file [@var{file}]
11518 @itemx gcore [@var{file}]
11519 Produce a core dump of the inferior process. The optional argument
11520 @var{file} specifies the file name where to put the core dump. If not
11521 specified, the file name defaults to @file{core.@var{pid}}, where
11522 @var{pid} is the inferior process ID.
11524 Note that this command is implemented only for some systems (as of
11525 this writing, @sc{gnu}/Linux, FreeBSD, Solaris, and S390).
11527 On @sc{gnu}/Linux, this command can take into account the value of the
11528 file @file{/proc/@var{pid}/coredump_filter} when generating the core
11529 dump (@pxref{set use-coredump-filter}).
11531 @kindex set use-coredump-filter
11532 @anchor{set use-coredump-filter}
11533 @item set use-coredump-filter on
11534 @itemx set use-coredump-filter off
11535 Enable or disable the use of the file
11536 @file{/proc/@var{pid}/coredump_filter} when generating core dump
11537 files. This file is used by the Linux kernel to decide what types of
11538 memory mappings will be dumped or ignored when generating a core dump
11539 file. @var{pid} is the process ID of a currently running process.
11541 To make use of this feature, you have to write in the
11542 @file{/proc/@var{pid}/coredump_filter} file a value, in hexadecimal,
11543 which is a bit mask representing the memory mapping types. If a bit
11544 is set in the bit mask, then the memory mappings of the corresponding
11545 types will be dumped; otherwise, they will be ignored. This
11546 configuration is inherited by child processes. For more information
11547 about the bits that can be set in the
11548 @file{/proc/@var{pid}/coredump_filter} file, please refer to the
11549 manpage of @code{core(5)}.
11551 By default, this option is @code{on}. If this option is turned
11552 @code{off}, @value{GDBN} does not read the @file{coredump_filter} file
11553 and instead uses the same default value as the Linux kernel in order
11554 to decide which pages will be dumped in the core dump file. This
11555 value is currently @code{0x33}, which means that bits @code{0}
11556 (anonymous private mappings), @code{1} (anonymous shared mappings),
11557 @code{4} (ELF headers) and @code{5} (private huge pages) are active.
11558 This will cause these memory mappings to be dumped automatically.
11561 @node Character Sets
11562 @section Character Sets
11563 @cindex character sets
11565 @cindex translating between character sets
11566 @cindex host character set
11567 @cindex target character set
11569 If the program you are debugging uses a different character set to
11570 represent characters and strings than the one @value{GDBN} uses itself,
11571 @value{GDBN} can automatically translate between the character sets for
11572 you. The character set @value{GDBN} uses we call the @dfn{host
11573 character set}; the one the inferior program uses we call the
11574 @dfn{target character set}.
11576 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
11577 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
11578 remote protocol (@pxref{Remote Debugging}) to debug a program
11579 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
11580 then the host character set is Latin-1, and the target character set is
11581 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
11582 target-charset EBCDIC-US}, then @value{GDBN} translates between
11583 @sc{ebcdic} and Latin 1 as you print character or string values, or use
11584 character and string literals in expressions.
11586 @value{GDBN} has no way to automatically recognize which character set
11587 the inferior program uses; you must tell it, using the @code{set
11588 target-charset} command, described below.
11590 Here are the commands for controlling @value{GDBN}'s character set
11594 @item set target-charset @var{charset}
11595 @kindex set target-charset
11596 Set the current target character set to @var{charset}. To display the
11597 list of supported target character sets, type
11598 @kbd{@w{set target-charset @key{TAB}@key{TAB}}}.
11600 @item set host-charset @var{charset}
11601 @kindex set host-charset
11602 Set the current host character set to @var{charset}.
11604 By default, @value{GDBN} uses a host character set appropriate to the
11605 system it is running on; you can override that default using the
11606 @code{set host-charset} command. On some systems, @value{GDBN} cannot
11607 automatically determine the appropriate host character set. In this
11608 case, @value{GDBN} uses @samp{UTF-8}.
11610 @value{GDBN} can only use certain character sets as its host character
11611 set. If you type @kbd{@w{set host-charset @key{TAB}@key{TAB}}},
11612 @value{GDBN} will list the host character sets it supports.
11614 @item set charset @var{charset}
11615 @kindex set charset
11616 Set the current host and target character sets to @var{charset}. As
11617 above, if you type @kbd{@w{set charset @key{TAB}@key{TAB}}},
11618 @value{GDBN} will list the names of the character sets that can be used
11619 for both host and target.
11622 @kindex show charset
11623 Show the names of the current host and target character sets.
11625 @item show host-charset
11626 @kindex show host-charset
11627 Show the name of the current host character set.
11629 @item show target-charset
11630 @kindex show target-charset
11631 Show the name of the current target character set.
11633 @item set target-wide-charset @var{charset}
11634 @kindex set target-wide-charset
11635 Set the current target's wide character set to @var{charset}. This is
11636 the character set used by the target's @code{wchar_t} type. To
11637 display the list of supported wide character sets, type
11638 @kbd{@w{set target-wide-charset @key{TAB}@key{TAB}}}.
11640 @item show target-wide-charset
11641 @kindex show target-wide-charset
11642 Show the name of the current target's wide character set.
11645 Here is an example of @value{GDBN}'s character set support in action.
11646 Assume that the following source code has been placed in the file
11647 @file{charset-test.c}:
11653 = @{72, 101, 108, 108, 111, 44, 32, 119,
11654 111, 114, 108, 100, 33, 10, 0@};
11655 char ibm1047_hello[]
11656 = @{200, 133, 147, 147, 150, 107, 64, 166,
11657 150, 153, 147, 132, 90, 37, 0@};
11661 printf ("Hello, world!\n");
11665 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
11666 containing the string @samp{Hello, world!} followed by a newline,
11667 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
11669 We compile the program, and invoke the debugger on it:
11672 $ gcc -g charset-test.c -o charset-test
11673 $ gdb -nw charset-test
11674 GNU gdb 2001-12-19-cvs
11675 Copyright 2001 Free Software Foundation, Inc.
11680 We can use the @code{show charset} command to see what character sets
11681 @value{GDBN} is currently using to interpret and display characters and
11685 (@value{GDBP}) show charset
11686 The current host and target character set is `ISO-8859-1'.
11690 For the sake of printing this manual, let's use @sc{ascii} as our
11691 initial character set:
11693 (@value{GDBP}) set charset ASCII
11694 (@value{GDBP}) show charset
11695 The current host and target character set is `ASCII'.
11699 Let's assume that @sc{ascii} is indeed the correct character set for our
11700 host system --- in other words, let's assume that if @value{GDBN} prints
11701 characters using the @sc{ascii} character set, our terminal will display
11702 them properly. Since our current target character set is also
11703 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
11706 (@value{GDBP}) print ascii_hello
11707 $1 = 0x401698 "Hello, world!\n"
11708 (@value{GDBP}) print ascii_hello[0]
11713 @value{GDBN} uses the target character set for character and string
11714 literals you use in expressions:
11717 (@value{GDBP}) print '+'
11722 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
11725 @value{GDBN} relies on the user to tell it which character set the
11726 target program uses. If we print @code{ibm1047_hello} while our target
11727 character set is still @sc{ascii}, we get jibberish:
11730 (@value{GDBP}) print ibm1047_hello
11731 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
11732 (@value{GDBP}) print ibm1047_hello[0]
11737 If we invoke the @code{set target-charset} followed by @key{TAB}@key{TAB},
11738 @value{GDBN} tells us the character sets it supports:
11741 (@value{GDBP}) set target-charset
11742 ASCII EBCDIC-US IBM1047 ISO-8859-1
11743 (@value{GDBP}) set target-charset
11746 We can select @sc{ibm1047} as our target character set, and examine the
11747 program's strings again. Now the @sc{ascii} string is wrong, but
11748 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
11749 target character set, @sc{ibm1047}, to the host character set,
11750 @sc{ascii}, and they display correctly:
11753 (@value{GDBP}) set target-charset IBM1047
11754 (@value{GDBP}) show charset
11755 The current host character set is `ASCII'.
11756 The current target character set is `IBM1047'.
11757 (@value{GDBP}) print ascii_hello
11758 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
11759 (@value{GDBP}) print ascii_hello[0]
11761 (@value{GDBP}) print ibm1047_hello
11762 $8 = 0x4016a8 "Hello, world!\n"
11763 (@value{GDBP}) print ibm1047_hello[0]
11768 As above, @value{GDBN} uses the target character set for character and
11769 string literals you use in expressions:
11772 (@value{GDBP}) print '+'
11777 The @sc{ibm1047} character set uses the number 78 to encode the @samp{+}
11780 @node Caching Target Data
11781 @section Caching Data of Targets
11782 @cindex caching data of targets
11784 @value{GDBN} caches data exchanged between the debugger and a target.
11785 Each cache is associated with the address space of the inferior.
11786 @xref{Inferiors and Programs}, about inferior and address space.
11787 Such caching generally improves performance in remote debugging
11788 (@pxref{Remote Debugging}), because it reduces the overhead of the
11789 remote protocol by bundling memory reads and writes into large chunks.
11790 Unfortunately, simply caching everything would lead to incorrect results,
11791 since @value{GDBN} does not necessarily know anything about volatile
11792 values, memory-mapped I/O addresses, etc. Furthermore, in non-stop mode
11793 (@pxref{Non-Stop Mode}) memory can be changed @emph{while} a gdb command
11795 Therefore, by default, @value{GDBN} only caches data
11796 known to be on the stack@footnote{In non-stop mode, it is moderately
11797 rare for a running thread to modify the stack of a stopped thread
11798 in a way that would interfere with a backtrace, and caching of
11799 stack reads provides a significant speed up of remote backtraces.} or
11800 in the code segment.
11801 Other regions of memory can be explicitly marked as
11802 cacheable; @pxref{Memory Region Attributes}.
11805 @kindex set remotecache
11806 @item set remotecache on
11807 @itemx set remotecache off
11808 This option no longer does anything; it exists for compatibility
11811 @kindex show remotecache
11812 @item show remotecache
11813 Show the current state of the obsolete remotecache flag.
11815 @kindex set stack-cache
11816 @item set stack-cache on
11817 @itemx set stack-cache off
11818 Enable or disable caching of stack accesses. When @code{on}, use
11819 caching. By default, this option is @code{on}.
11821 @kindex show stack-cache
11822 @item show stack-cache
11823 Show the current state of data caching for memory accesses.
11825 @kindex set code-cache
11826 @item set code-cache on
11827 @itemx set code-cache off
11828 Enable or disable caching of code segment accesses. When @code{on},
11829 use caching. By default, this option is @code{on}. This improves
11830 performance of disassembly in remote debugging.
11832 @kindex show code-cache
11833 @item show code-cache
11834 Show the current state of target memory cache for code segment
11837 @kindex info dcache
11838 @item info dcache @r{[}line@r{]}
11839 Print the information about the performance of data cache of the
11840 current inferior's address space. The information displayed
11841 includes the dcache width and depth, and for each cache line, its
11842 number, address, and how many times it was referenced. This
11843 command is useful for debugging the data cache operation.
11845 If a line number is specified, the contents of that line will be
11848 @item set dcache size @var{size}
11849 @cindex dcache size
11850 @kindex set dcache size
11851 Set maximum number of entries in dcache (dcache depth above).
11853 @item set dcache line-size @var{line-size}
11854 @cindex dcache line-size
11855 @kindex set dcache line-size
11856 Set number of bytes each dcache entry caches (dcache width above).
11857 Must be a power of 2.
11859 @item show dcache size
11860 @kindex show dcache size
11861 Show maximum number of dcache entries. @xref{Caching Target Data, info dcache}.
11863 @item show dcache line-size
11864 @kindex show dcache line-size
11865 Show default size of dcache lines.
11869 @node Searching Memory
11870 @section Search Memory
11871 @cindex searching memory
11873 Memory can be searched for a particular sequence of bytes with the
11874 @code{find} command.
11878 @item find @r{[}/@var{sn}@r{]} @var{start_addr}, +@var{len}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
11879 @itemx find @r{[}/@var{sn}@r{]} @var{start_addr}, @var{end_addr}, @var{val1} @r{[}, @var{val2}, @dots{}@r{]}
11880 Search memory for the sequence of bytes specified by @var{val1}, @var{val2},
11881 etc. The search begins at address @var{start_addr} and continues for either
11882 @var{len} bytes or through to @var{end_addr} inclusive.
11885 @var{s} and @var{n} are optional parameters.
11886 They may be specified in either order, apart or together.
11889 @item @var{s}, search query size
11890 The size of each search query value.
11896 halfwords (two bytes)
11900 giant words (eight bytes)
11903 All values are interpreted in the current language.
11904 This means, for example, that if the current source language is C/C@t{++}
11905 then searching for the string ``hello'' includes the trailing '\0'.
11907 If the value size is not specified, it is taken from the
11908 value's type in the current language.
11909 This is useful when one wants to specify the search
11910 pattern as a mixture of types.
11911 Note that this means, for example, that in the case of C-like languages
11912 a search for an untyped 0x42 will search for @samp{(int) 0x42}
11913 which is typically four bytes.
11915 @item @var{n}, maximum number of finds
11916 The maximum number of matches to print. The default is to print all finds.
11919 You can use strings as search values. Quote them with double-quotes
11921 The string value is copied into the search pattern byte by byte,
11922 regardless of the endianness of the target and the size specification.
11924 The address of each match found is printed as well as a count of the
11925 number of matches found.
11927 The address of the last value found is stored in convenience variable
11929 A count of the number of matches is stored in @samp{$numfound}.
11931 For example, if stopped at the @code{printf} in this function:
11937 static char hello[] = "hello-hello";
11938 static struct @{ char c; short s; int i; @}
11939 __attribute__ ((packed)) mixed
11940 = @{ 'c', 0x1234, 0x87654321 @};
11941 printf ("%s\n", hello);
11946 you get during debugging:
11949 (gdb) find &hello[0], +sizeof(hello), "hello"
11950 0x804956d <hello.1620+6>
11952 (gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
11953 0x8049567 <hello.1620>
11954 0x804956d <hello.1620+6>
11956 (gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
11957 0x8049567 <hello.1620>
11959 (gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
11960 0x8049560 <mixed.1625>
11962 (gdb) print $numfound
11965 $2 = (void *) 0x8049560
11969 @section Value Sizes
11971 Whenever @value{GDBN} prints a value memory will be allocated within
11972 @value{GDBN} to hold the contents of the value. It is possible in
11973 some languages with dynamic typing systems, that an invalid program
11974 may indicate a value that is incorrectly large, this in turn may cause
11975 @value{GDBN} to try and allocate an overly large ammount of memory.
11978 @kindex set max-value-size
11979 @item set max-value-size @var{bytes}
11980 @itemx set max-value-size unlimited
11981 Set the maximum size of memory that @value{GDBN} will allocate for the
11982 contents of a value to @var{bytes}, trying to display a value that
11983 requires more memory than that will result in an error.
11985 Setting this variable does not effect values that have already been
11986 allocated within @value{GDBN}, only future allocations.
11988 There's a minimum size that @code{max-value-size} can be set to in
11989 order that @value{GDBN} can still operate correctly, this minimum is
11990 currently 16 bytes.
11992 The limit applies to the results of some subexpressions as well as to
11993 complete expressions. For example, an expression denoting a simple
11994 integer component, such as @code{x.y.z}, may fail if the size of
11995 @var{x.y} is dynamic and exceeds @var{bytes}. On the other hand,
11996 @value{GDBN} is sometimes clever; the expression @code{A[i]}, where
11997 @var{A} is an array variable with non-constant size, will generally
11998 succeed regardless of the bounds on @var{A}, as long as the component
11999 size is less than @var{bytes}.
12001 The default value of @code{max-value-size} is currently 64k.
12003 @kindex show max-value-size
12004 @item show max-value-size
12005 Show the maximum size of memory, in bytes, that @value{GDBN} will
12006 allocate for the contents of a value.
12009 @node Optimized Code
12010 @chapter Debugging Optimized Code
12011 @cindex optimized code, debugging
12012 @cindex debugging optimized code
12014 Almost all compilers support optimization. With optimization
12015 disabled, the compiler generates assembly code that corresponds
12016 directly to your source code, in a simplistic way. As the compiler
12017 applies more powerful optimizations, the generated assembly code
12018 diverges from your original source code. With help from debugging
12019 information generated by the compiler, @value{GDBN} can map from
12020 the running program back to constructs from your original source.
12022 @value{GDBN} is more accurate with optimization disabled. If you
12023 can recompile without optimization, it is easier to follow the
12024 progress of your program during debugging. But, there are many cases
12025 where you may need to debug an optimized version.
12027 When you debug a program compiled with @samp{-g -O}, remember that the
12028 optimizer has rearranged your code; the debugger shows you what is
12029 really there. Do not be too surprised when the execution path does not
12030 exactly match your source file! An extreme example: if you define a
12031 variable, but never use it, @value{GDBN} never sees that
12032 variable---because the compiler optimizes it out of existence.
12034 Some things do not work as well with @samp{-g -O} as with just
12035 @samp{-g}, particularly on machines with instruction scheduling. If in
12036 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
12037 please report it to us as a bug (including a test case!).
12038 @xref{Variables}, for more information about debugging optimized code.
12041 * Inline Functions:: How @value{GDBN} presents inlining
12042 * Tail Call Frames:: @value{GDBN} analysis of jumps to functions
12045 @node Inline Functions
12046 @section Inline Functions
12047 @cindex inline functions, debugging
12049 @dfn{Inlining} is an optimization that inserts a copy of the function
12050 body directly at each call site, instead of jumping to a shared
12051 routine. @value{GDBN} displays inlined functions just like
12052 non-inlined functions. They appear in backtraces. You can view their
12053 arguments and local variables, step into them with @code{step}, skip
12054 them with @code{next}, and escape from them with @code{finish}.
12055 You can check whether a function was inlined by using the
12056 @code{info frame} command.
12058 For @value{GDBN} to support inlined functions, the compiler must
12059 record information about inlining in the debug information ---
12060 @value{NGCC} using the @sc{dwarf 2} format does this, and several
12061 other compilers do also. @value{GDBN} only supports inlined functions
12062 when using @sc{dwarf 2}. Versions of @value{NGCC} before 4.1
12063 do not emit two required attributes (@samp{DW_AT_call_file} and
12064 @samp{DW_AT_call_line}); @value{GDBN} does not display inlined
12065 function calls with earlier versions of @value{NGCC}. It instead
12066 displays the arguments and local variables of inlined functions as
12067 local variables in the caller.
12069 The body of an inlined function is directly included at its call site;
12070 unlike a non-inlined function, there are no instructions devoted to
12071 the call. @value{GDBN} still pretends that the call site and the
12072 start of the inlined function are different instructions. Stepping to
12073 the call site shows the call site, and then stepping again shows
12074 the first line of the inlined function, even though no additional
12075 instructions are executed.
12077 This makes source-level debugging much clearer; you can see both the
12078 context of the call and then the effect of the call. Only stepping by
12079 a single instruction using @code{stepi} or @code{nexti} does not do
12080 this; single instruction steps always show the inlined body.
12082 There are some ways that @value{GDBN} does not pretend that inlined
12083 function calls are the same as normal calls:
12087 Setting breakpoints at the call site of an inlined function may not
12088 work, because the call site does not contain any code. @value{GDBN}
12089 may incorrectly move the breakpoint to the next line of the enclosing
12090 function, after the call. This limitation will be removed in a future
12091 version of @value{GDBN}; until then, set a breakpoint on an earlier line
12092 or inside the inlined function instead.
12095 @value{GDBN} cannot locate the return value of inlined calls after
12096 using the @code{finish} command. This is a limitation of compiler-generated
12097 debugging information; after @code{finish}, you can step to the next line
12098 and print a variable where your program stored the return value.
12102 @node Tail Call Frames
12103 @section Tail Call Frames
12104 @cindex tail call frames, debugging
12106 Function @code{B} can call function @code{C} in its very last statement. In
12107 unoptimized compilation the call of @code{C} is immediately followed by return
12108 instruction at the end of @code{B} code. Optimizing compiler may replace the
12109 call and return in function @code{B} into one jump to function @code{C}
12110 instead. Such use of a jump instruction is called @dfn{tail call}.
12112 During execution of function @code{C}, there will be no indication in the
12113 function call stack frames that it was tail-called from @code{B}. If function
12114 @code{A} regularly calls function @code{B} which tail-calls function @code{C},
12115 then @value{GDBN} will see @code{A} as the caller of @code{C}. However, in
12116 some cases @value{GDBN} can determine that @code{C} was tail-called from
12117 @code{B}, and it will then create fictitious call frame for that, with the
12118 return address set up as if @code{B} called @code{C} normally.
12120 This functionality is currently supported only by DWARF 2 debugging format and
12121 the compiler has to produce @samp{DW_TAG_call_site} tags. With
12122 @value{NGCC}, you need to specify @option{-O -g} during compilation, to get
12125 @kbd{info frame} command (@pxref{Frame Info}) will indicate the tail call frame
12126 kind by text @code{tail call frame} such as in this sample @value{GDBN} output:
12130 0x40066b <b(int, double)+11>: jmp 0x400640 <c(int, double)>
12132 Stack level 1, frame at 0x7fffffffda30:
12133 rip = 0x40066d in b (amd64-entry-value.cc:59); saved rip 0x4004c5
12134 tail call frame, caller of frame at 0x7fffffffda30
12135 source language c++.
12136 Arglist at unknown address.
12137 Locals at unknown address, Previous frame's sp is 0x7fffffffda30
12140 The detection of all the possible code path executions can find them ambiguous.
12141 There is no execution history stored (possible @ref{Reverse Execution} is never
12142 used for this purpose) and the last known caller could have reached the known
12143 callee by multiple different jump sequences. In such case @value{GDBN} still
12144 tries to show at least all the unambiguous top tail callers and all the
12145 unambiguous bottom tail calees, if any.
12148 @anchor{set debug entry-values}
12149 @item set debug entry-values
12150 @kindex set debug entry-values
12151 When set to on, enables printing of analysis messages for both frame argument
12152 values at function entry and tail calls. It will show all the possible valid
12153 tail calls code paths it has considered. It will also print the intersection
12154 of them with the final unambiguous (possibly partial or even empty) code path
12157 @item show debug entry-values
12158 @kindex show debug entry-values
12159 Show the current state of analysis messages printing for both frame argument
12160 values at function entry and tail calls.
12163 The analysis messages for tail calls can for example show why the virtual tail
12164 call frame for function @code{c} has not been recognized (due to the indirect
12165 reference by variable @code{x}):
12168 static void __attribute__((noinline, noclone)) c (void);
12169 void (*x) (void) = c;
12170 static void __attribute__((noinline, noclone)) a (void) @{ x++; @}
12171 static void __attribute__((noinline, noclone)) c (void) @{ a (); @}
12172 int main (void) @{ x (); return 0; @}
12174 Breakpoint 1, DW_OP_entry_value resolving cannot find
12175 DW_TAG_call_site 0x40039a in main
12177 3 static void __attribute__((noinline, noclone)) a (void) @{ x++; @}
12180 #1 0x000000000040039a in main () at t.c:5
12183 Another possibility is an ambiguous virtual tail call frames resolution:
12187 static void __attribute__((noinline, noclone)) f (void) @{ i++; @}
12188 static void __attribute__((noinline, noclone)) e (void) @{ f (); @}
12189 static void __attribute__((noinline, noclone)) d (void) @{ f (); @}
12190 static void __attribute__((noinline, noclone)) c (void) @{ d (); @}
12191 static void __attribute__((noinline, noclone)) b (void)
12192 @{ if (i) c (); else e (); @}
12193 static void __attribute__((noinline, noclone)) a (void) @{ b (); @}
12194 int main (void) @{ a (); return 0; @}
12196 tailcall: initial: 0x4004d2(a) 0x4004ce(b) 0x4004b2(c) 0x4004a2(d)
12197 tailcall: compare: 0x4004d2(a) 0x4004cc(b) 0x400492(e)
12198 tailcall: reduced: 0x4004d2(a) |
12201 #1 0x00000000004004d2 in a () at t.c:8
12202 #2 0x0000000000400395 in main () at t.c:9
12205 @set CALLSEQ1A @code{main@value{ARROW}a@value{ARROW}b@value{ARROW}c@value{ARROW}d@value{ARROW}f}
12206 @set CALLSEQ2A @code{main@value{ARROW}a@value{ARROW}b@value{ARROW}e@value{ARROW}f}
12208 @c Convert CALLSEQ#A to CALLSEQ#B depending on HAVE_MAKEINFO_CLICK.
12209 @ifset HAVE_MAKEINFO_CLICK
12210 @set ARROW @click{}
12211 @set CALLSEQ1B @clicksequence{@value{CALLSEQ1A}}
12212 @set CALLSEQ2B @clicksequence{@value{CALLSEQ2A}}
12214 @ifclear HAVE_MAKEINFO_CLICK
12216 @set CALLSEQ1B @value{CALLSEQ1A}
12217 @set CALLSEQ2B @value{CALLSEQ2A}
12220 Frames #0 and #2 are real, #1 is a virtual tail call frame.
12221 The code can have possible execution paths @value{CALLSEQ1B} or
12222 @value{CALLSEQ2B}, @value{GDBN} cannot find which one from the inferior state.
12224 @code{initial:} state shows some random possible calling sequence @value{GDBN}
12225 has found. It then finds another possible calling sequcen - that one is
12226 prefixed by @code{compare:}. The non-ambiguous intersection of these two is
12227 printed as the @code{reduced:} calling sequence. That one could have many
12228 futher @code{compare:} and @code{reduced:} statements as long as there remain
12229 any non-ambiguous sequence entries.
12231 For the frame of function @code{b} in both cases there are different possible
12232 @code{$pc} values (@code{0x4004cc} or @code{0x4004ce}), therefore this frame is
12233 also ambigous. The only non-ambiguous frame is the one for function @code{a},
12234 therefore this one is displayed to the user while the ambiguous frames are
12237 There can be also reasons why printing of frame argument values at function
12242 static void __attribute__((noinline, noclone)) c (int i) @{ v++; @}
12243 static void __attribute__((noinline, noclone)) a (int i);
12244 static void __attribute__((noinline, noclone)) b (int i) @{ a (i); @}
12245 static void __attribute__((noinline, noclone)) a (int i)
12246 @{ if (i) b (i - 1); else c (0); @}
12247 int main (void) @{ a (5); return 0; @}
12250 #0 c (i=i@@entry=0) at t.c:2
12251 #1 0x0000000000400428 in a (DW_OP_entry_value resolving has found
12252 function "a" at 0x400420 can call itself via tail calls
12253 i=<optimized out>) at t.c:6
12254 #2 0x000000000040036e in main () at t.c:7
12257 @value{GDBN} cannot find out from the inferior state if and how many times did
12258 function @code{a} call itself (via function @code{b}) as these calls would be
12259 tail calls. Such tail calls would modify thue @code{i} variable, therefore
12260 @value{GDBN} cannot be sure the value it knows would be right - @value{GDBN}
12261 prints @code{<optimized out>} instead.
12264 @chapter C Preprocessor Macros
12266 Some languages, such as C and C@t{++}, provide a way to define and invoke
12267 ``preprocessor macros'' which expand into strings of tokens.
12268 @value{GDBN} can evaluate expressions containing macro invocations, show
12269 the result of macro expansion, and show a macro's definition, including
12270 where it was defined.
12272 You may need to compile your program specially to provide @value{GDBN}
12273 with information about preprocessor macros. Most compilers do not
12274 include macros in their debugging information, even when you compile
12275 with the @option{-g} flag. @xref{Compilation}.
12277 A program may define a macro at one point, remove that definition later,
12278 and then provide a different definition after that. Thus, at different
12279 points in the program, a macro may have different definitions, or have
12280 no definition at all. If there is a current stack frame, @value{GDBN}
12281 uses the macros in scope at that frame's source code line. Otherwise,
12282 @value{GDBN} uses the macros in scope at the current listing location;
12285 Whenever @value{GDBN} evaluates an expression, it always expands any
12286 macro invocations present in the expression. @value{GDBN} also provides
12287 the following commands for working with macros explicitly.
12291 @kindex macro expand
12292 @cindex macro expansion, showing the results of preprocessor
12293 @cindex preprocessor macro expansion, showing the results of
12294 @cindex expanding preprocessor macros
12295 @item macro expand @var{expression}
12296 @itemx macro exp @var{expression}
12297 Show the results of expanding all preprocessor macro invocations in
12298 @var{expression}. Since @value{GDBN} simply expands macros, but does
12299 not parse the result, @var{expression} need not be a valid expression;
12300 it can be any string of tokens.
12303 @item macro expand-once @var{expression}
12304 @itemx macro exp1 @var{expression}
12305 @cindex expand macro once
12306 @i{(This command is not yet implemented.)} Show the results of
12307 expanding those preprocessor macro invocations that appear explicitly in
12308 @var{expression}. Macro invocations appearing in that expansion are
12309 left unchanged. This command allows you to see the effect of a
12310 particular macro more clearly, without being confused by further
12311 expansions. Since @value{GDBN} simply expands macros, but does not
12312 parse the result, @var{expression} need not be a valid expression; it
12313 can be any string of tokens.
12316 @cindex macro definition, showing
12317 @cindex definition of a macro, showing
12318 @cindex macros, from debug info
12319 @item info macro [-a|-all] [--] @var{macro}
12320 Show the current definition or all definitions of the named @var{macro},
12321 and describe the source location or compiler command-line where that
12322 definition was established. The optional double dash is to signify the end of
12323 argument processing and the beginning of @var{macro} for non C-like macros where
12324 the macro may begin with a hyphen.
12326 @kindex info macros
12327 @item info macros @var{location}
12328 Show all macro definitions that are in effect at the location specified
12329 by @var{location}, and describe the source location or compiler
12330 command-line where those definitions were established.
12332 @kindex macro define
12333 @cindex user-defined macros
12334 @cindex defining macros interactively
12335 @cindex macros, user-defined
12336 @item macro define @var{macro} @var{replacement-list}
12337 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
12338 Introduce a definition for a preprocessor macro named @var{macro},
12339 invocations of which are replaced by the tokens given in
12340 @var{replacement-list}. The first form of this command defines an
12341 ``object-like'' macro, which takes no arguments; the second form
12342 defines a ``function-like'' macro, which takes the arguments given in
12345 A definition introduced by this command is in scope in every
12346 expression evaluated in @value{GDBN}, until it is removed with the
12347 @code{macro undef} command, described below. The definition overrides
12348 all definitions for @var{macro} present in the program being debugged,
12349 as well as any previous user-supplied definition.
12351 @kindex macro undef
12352 @item macro undef @var{macro}
12353 Remove any user-supplied definition for the macro named @var{macro}.
12354 This command only affects definitions provided with the @code{macro
12355 define} command, described above; it cannot remove definitions present
12356 in the program being debugged.
12360 List all the macros defined using the @code{macro define} command.
12363 @cindex macros, example of debugging with
12364 Here is a transcript showing the above commands in action. First, we
12365 show our source files:
12370 #include "sample.h"
12373 #define ADD(x) (M + x)
12378 printf ("Hello, world!\n");
12380 printf ("We're so creative.\n");
12382 printf ("Goodbye, world!\n");
12389 Now, we compile the program using the @sc{gnu} C compiler,
12390 @value{NGCC}. We pass the @option{-gdwarf-2}@footnote{This is the
12391 minimum. Recent versions of @value{NGCC} support @option{-gdwarf-3}
12392 and @option{-gdwarf-4}; we recommend always choosing the most recent
12393 version of DWARF.} @emph{and} @option{-g3} flags to ensure the compiler
12394 includes information about preprocessor macros in the debugging
12398 $ gcc -gdwarf-2 -g3 sample.c -o sample
12402 Now, we start @value{GDBN} on our sample program:
12406 GNU gdb 2002-05-06-cvs
12407 Copyright 2002 Free Software Foundation, Inc.
12408 GDB is free software, @dots{}
12412 We can expand macros and examine their definitions, even when the
12413 program is not running. @value{GDBN} uses the current listing position
12414 to decide which macro definitions are in scope:
12417 (@value{GDBP}) list main
12420 5 #define ADD(x) (M + x)
12425 10 printf ("Hello, world!\n");
12427 12 printf ("We're so creative.\n");
12428 (@value{GDBP}) info macro ADD
12429 Defined at /home/jimb/gdb/macros/play/sample.c:5
12430 #define ADD(x) (M + x)
12431 (@value{GDBP}) info macro Q
12432 Defined at /home/jimb/gdb/macros/play/sample.h:1
12433 included at /home/jimb/gdb/macros/play/sample.c:2
12435 (@value{GDBP}) macro expand ADD(1)
12436 expands to: (42 + 1)
12437 (@value{GDBP}) macro expand-once ADD(1)
12438 expands to: once (M + 1)
12442 In the example above, note that @code{macro expand-once} expands only
12443 the macro invocation explicit in the original text --- the invocation of
12444 @code{ADD} --- but does not expand the invocation of the macro @code{M},
12445 which was introduced by @code{ADD}.
12447 Once the program is running, @value{GDBN} uses the macro definitions in
12448 force at the source line of the current stack frame:
12451 (@value{GDBP}) break main
12452 Breakpoint 1 at 0x8048370: file sample.c, line 10.
12454 Starting program: /home/jimb/gdb/macros/play/sample
12456 Breakpoint 1, main () at sample.c:10
12457 10 printf ("Hello, world!\n");
12461 At line 10, the definition of the macro @code{N} at line 9 is in force:
12464 (@value{GDBP}) info macro N
12465 Defined at /home/jimb/gdb/macros/play/sample.c:9
12467 (@value{GDBP}) macro expand N Q M
12468 expands to: 28 < 42
12469 (@value{GDBP}) print N Q M
12474 As we step over directives that remove @code{N}'s definition, and then
12475 give it a new definition, @value{GDBN} finds the definition (or lack
12476 thereof) in force at each point:
12479 (@value{GDBP}) next
12481 12 printf ("We're so creative.\n");
12482 (@value{GDBP}) info macro N
12483 The symbol `N' has no definition as a C/C++ preprocessor macro
12484 at /home/jimb/gdb/macros/play/sample.c:12
12485 (@value{GDBP}) next
12487 14 printf ("Goodbye, world!\n");
12488 (@value{GDBP}) info macro N
12489 Defined at /home/jimb/gdb/macros/play/sample.c:13
12491 (@value{GDBP}) macro expand N Q M
12492 expands to: 1729 < 42
12493 (@value{GDBP}) print N Q M
12498 In addition to source files, macros can be defined on the compilation command
12499 line using the @option{-D@var{name}=@var{value}} syntax. For macros defined in
12500 such a way, @value{GDBN} displays the location of their definition as line zero
12501 of the source file submitted to the compiler.
12504 (@value{GDBP}) info macro __STDC__
12505 Defined at /home/jimb/gdb/macros/play/sample.c:0
12512 @chapter Tracepoints
12513 @c This chapter is based on the documentation written by Michael
12514 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
12516 @cindex tracepoints
12517 In some applications, it is not feasible for the debugger to interrupt
12518 the program's execution long enough for the developer to learn
12519 anything helpful about its behavior. If the program's correctness
12520 depends on its real-time behavior, delays introduced by a debugger
12521 might cause the program to change its behavior drastically, or perhaps
12522 fail, even when the code itself is correct. It is useful to be able
12523 to observe the program's behavior without interrupting it.
12525 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
12526 specify locations in the program, called @dfn{tracepoints}, and
12527 arbitrary expressions to evaluate when those tracepoints are reached.
12528 Later, using the @code{tfind} command, you can examine the values
12529 those expressions had when the program hit the tracepoints. The
12530 expressions may also denote objects in memory---structures or arrays,
12531 for example---whose values @value{GDBN} should record; while visiting
12532 a particular tracepoint, you may inspect those objects as if they were
12533 in memory at that moment. However, because @value{GDBN} records these
12534 values without interacting with you, it can do so quickly and
12535 unobtrusively, hopefully not disturbing the program's behavior.
12537 The tracepoint facility is currently available only for remote
12538 targets. @xref{Targets}. In addition, your remote target must know
12539 how to collect trace data. This functionality is implemented in the
12540 remote stub; however, none of the stubs distributed with @value{GDBN}
12541 support tracepoints as of this writing. The format of the remote
12542 packets used to implement tracepoints are described in @ref{Tracepoint
12545 It is also possible to get trace data from a file, in a manner reminiscent
12546 of corefiles; you specify the filename, and use @code{tfind} to search
12547 through the file. @xref{Trace Files}, for more details.
12549 This chapter describes the tracepoint commands and features.
12552 * Set Tracepoints::
12553 * Analyze Collected Data::
12554 * Tracepoint Variables::
12558 @node Set Tracepoints
12559 @section Commands to Set Tracepoints
12561 Before running such a @dfn{trace experiment}, an arbitrary number of
12562 tracepoints can be set. A tracepoint is actually a special type of
12563 breakpoint (@pxref{Set Breaks}), so you can manipulate it using
12564 standard breakpoint commands. For instance, as with breakpoints,
12565 tracepoint numbers are successive integers starting from one, and many
12566 of the commands associated with tracepoints take the tracepoint number
12567 as their argument, to identify which tracepoint to work on.
12569 For each tracepoint, you can specify, in advance, some arbitrary set
12570 of data that you want the target to collect in the trace buffer when
12571 it hits that tracepoint. The collected data can include registers,
12572 local variables, or global data. Later, you can use @value{GDBN}
12573 commands to examine the values these data had at the time the
12574 tracepoint was hit.
12576 Tracepoints do not support every breakpoint feature. Ignore counts on
12577 tracepoints have no effect, and tracepoints cannot run @value{GDBN}
12578 commands when they are hit. Tracepoints may not be thread-specific
12581 @cindex fast tracepoints
12582 Some targets may support @dfn{fast tracepoints}, which are inserted in
12583 a different way (such as with a jump instead of a trap), that is
12584 faster but possibly restricted in where they may be installed.
12586 @cindex static tracepoints
12587 @cindex markers, static tracepoints
12588 @cindex probing markers, static tracepoints
12589 Regular and fast tracepoints are dynamic tracing facilities, meaning
12590 that they can be used to insert tracepoints at (almost) any location
12591 in the target. Some targets may also support controlling @dfn{static
12592 tracepoints} from @value{GDBN}. With static tracing, a set of
12593 instrumentation points, also known as @dfn{markers}, are embedded in
12594 the target program, and can be activated or deactivated by name or
12595 address. These are usually placed at locations which facilitate
12596 investigating what the target is actually doing. @value{GDBN}'s
12597 support for static tracing includes being able to list instrumentation
12598 points, and attach them with @value{GDBN} defined high level
12599 tracepoints that expose the whole range of convenience of
12600 @value{GDBN}'s tracepoints support. Namely, support for collecting
12601 registers values and values of global or local (to the instrumentation
12602 point) variables; tracepoint conditions and trace state variables.
12603 The act of installing a @value{GDBN} static tracepoint on an
12604 instrumentation point, or marker, is referred to as @dfn{probing} a
12605 static tracepoint marker.
12607 @code{gdbserver} supports tracepoints on some target systems.
12608 @xref{Server,,Tracepoints support in @code{gdbserver}}.
12610 This section describes commands to set tracepoints and associated
12611 conditions and actions.
12614 * Create and Delete Tracepoints::
12615 * Enable and Disable Tracepoints::
12616 * Tracepoint Passcounts::
12617 * Tracepoint Conditions::
12618 * Trace State Variables::
12619 * Tracepoint Actions::
12620 * Listing Tracepoints::
12621 * Listing Static Tracepoint Markers::
12622 * Starting and Stopping Trace Experiments::
12623 * Tracepoint Restrictions::
12626 @node Create and Delete Tracepoints
12627 @subsection Create and Delete Tracepoints
12630 @cindex set tracepoint
12632 @item trace @var{location}
12633 The @code{trace} command is very similar to the @code{break} command.
12634 Its argument @var{location} can be any valid location.
12635 @xref{Specify Location}. The @code{trace} command defines a tracepoint,
12636 which is a point in the target program where the debugger will briefly stop,
12637 collect some data, and then allow the program to continue. Setting a tracepoint
12638 or changing its actions takes effect immediately if the remote stub
12639 supports the @samp{InstallInTrace} feature (@pxref{install tracepoint
12641 If remote stub doesn't support the @samp{InstallInTrace} feature, all
12642 these changes don't take effect until the next @code{tstart}
12643 command, and once a trace experiment is running, further changes will
12644 not have any effect until the next trace experiment starts. In addition,
12645 @value{GDBN} supports @dfn{pending tracepoints}---tracepoints whose
12646 address is not yet resolved. (This is similar to pending breakpoints.)
12647 Pending tracepoints are not downloaded to the target and not installed
12648 until they are resolved. The resolution of pending tracepoints requires
12649 @value{GDBN} support---when debugging with the remote target, and
12650 @value{GDBN} disconnects from the remote stub (@pxref{disconnected
12651 tracing}), pending tracepoints can not be resolved (and downloaded to
12652 the remote stub) while @value{GDBN} is disconnected.
12654 Here are some examples of using the @code{trace} command:
12657 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
12659 (@value{GDBP}) @b{trace +2} // 2 lines forward
12661 (@value{GDBP}) @b{trace my_function} // first source line of function
12663 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
12665 (@value{GDBP}) @b{trace *0x2117c4} // an address
12669 You can abbreviate @code{trace} as @code{tr}.
12671 @item trace @var{location} if @var{cond}
12672 Set a tracepoint with condition @var{cond}; evaluate the expression
12673 @var{cond} each time the tracepoint is reached, and collect data only
12674 if the value is nonzero---that is, if @var{cond} evaluates as true.
12675 @xref{Tracepoint Conditions, ,Tracepoint Conditions}, for more
12676 information on tracepoint conditions.
12678 @item ftrace @var{location} [ if @var{cond} ]
12679 @cindex set fast tracepoint
12680 @cindex fast tracepoints, setting
12682 The @code{ftrace} command sets a fast tracepoint. For targets that
12683 support them, fast tracepoints will use a more efficient but possibly
12684 less general technique to trigger data collection, such as a jump
12685 instruction instead of a trap, or some sort of hardware support. It
12686 may not be possible to create a fast tracepoint at the desired
12687 location, in which case the command will exit with an explanatory
12690 @value{GDBN} handles arguments to @code{ftrace} exactly as for
12693 On 32-bit x86-architecture systems, fast tracepoints normally need to
12694 be placed at an instruction that is 5 bytes or longer, but can be
12695 placed at 4-byte instructions if the low 64K of memory of the target
12696 program is available to install trampolines. Some Unix-type systems,
12697 such as @sc{gnu}/Linux, exclude low addresses from the program's
12698 address space; but for instance with the Linux kernel it is possible
12699 to let @value{GDBN} use this area by doing a @command{sysctl} command
12700 to set the @code{mmap_min_addr} kernel parameter, as in
12703 sudo sysctl -w vm.mmap_min_addr=32768
12707 which sets the low address to 32K, which leaves plenty of room for
12708 trampolines. The minimum address should be set to a page boundary.
12710 @item strace @var{location} [ if @var{cond} ]
12711 @cindex set static tracepoint
12712 @cindex static tracepoints, setting
12713 @cindex probe static tracepoint marker
12715 The @code{strace} command sets a static tracepoint. For targets that
12716 support it, setting a static tracepoint probes a static
12717 instrumentation point, or marker, found at @var{location}. It may not
12718 be possible to set a static tracepoint at the desired location, in
12719 which case the command will exit with an explanatory message.
12721 @value{GDBN} handles arguments to @code{strace} exactly as for
12722 @code{trace}, with the addition that the user can also specify
12723 @code{-m @var{marker}} as @var{location}. This probes the marker
12724 identified by the @var{marker} string identifier. This identifier
12725 depends on the static tracepoint backend library your program is
12726 using. You can find all the marker identifiers in the @samp{ID} field
12727 of the @code{info static-tracepoint-markers} command output.
12728 @xref{Listing Static Tracepoint Markers,,Listing Static Tracepoint
12729 Markers}. For example, in the following small program using the UST
12735 trace_mark(ust, bar33, "str %s", "FOOBAZ");
12740 the marker id is composed of joining the first two arguments to the
12741 @code{trace_mark} call with a slash, which translates to:
12744 (@value{GDBP}) info static-tracepoint-markers
12745 Cnt Enb ID Address What
12746 1 n ust/bar33 0x0000000000400ddc in main at stexample.c:22
12752 so you may probe the marker above with:
12755 (@value{GDBP}) strace -m ust/bar33
12758 Static tracepoints accept an extra collect action --- @code{collect
12759 $_sdata}. This collects arbitrary user data passed in the probe point
12760 call to the tracing library. In the UST example above, you'll see
12761 that the third argument to @code{trace_mark} is a printf-like format
12762 string. The user data is then the result of running that formating
12763 string against the following arguments. Note that @code{info
12764 static-tracepoint-markers} command output lists that format string in
12765 the @samp{Data:} field.
12767 You can inspect this data when analyzing the trace buffer, by printing
12768 the $_sdata variable like any other variable available to
12769 @value{GDBN}. @xref{Tracepoint Actions,,Tracepoint Action Lists}.
12772 @cindex last tracepoint number
12773 @cindex recent tracepoint number
12774 @cindex tracepoint number
12775 The convenience variable @code{$tpnum} records the tracepoint number
12776 of the most recently set tracepoint.
12778 @kindex delete tracepoint
12779 @cindex tracepoint deletion
12780 @item delete tracepoint @r{[}@var{num}@r{]}
12781 Permanently delete one or more tracepoints. With no argument, the
12782 default is to delete all tracepoints. Note that the regular
12783 @code{delete} command can remove tracepoints also.
12788 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
12790 (@value{GDBP}) @b{delete trace} // remove all tracepoints
12794 You can abbreviate this command as @code{del tr}.
12797 @node Enable and Disable Tracepoints
12798 @subsection Enable and Disable Tracepoints
12800 These commands are deprecated; they are equivalent to plain @code{disable} and @code{enable}.
12803 @kindex disable tracepoint
12804 @item disable tracepoint @r{[}@var{num}@r{]}
12805 Disable tracepoint @var{num}, or all tracepoints if no argument
12806 @var{num} is given. A disabled tracepoint will have no effect during
12807 a trace experiment, but it is not forgotten. You can re-enable
12808 a disabled tracepoint using the @code{enable tracepoint} command.
12809 If the command is issued during a trace experiment and the debug target
12810 has support for disabling tracepoints during a trace experiment, then the
12811 change will be effective immediately. Otherwise, it will be applied to the
12812 next trace experiment.
12814 @kindex enable tracepoint
12815 @item enable tracepoint @r{[}@var{num}@r{]}
12816 Enable tracepoint @var{num}, or all tracepoints. If this command is
12817 issued during a trace experiment and the debug target supports enabling
12818 tracepoints during a trace experiment, then the enabled tracepoints will
12819 become effective immediately. Otherwise, they will become effective the
12820 next time a trace experiment is run.
12823 @node Tracepoint Passcounts
12824 @subsection Tracepoint Passcounts
12828 @cindex tracepoint pass count
12829 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
12830 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
12831 automatically stop a trace experiment. If a tracepoint's passcount is
12832 @var{n}, then the trace experiment will be automatically stopped on
12833 the @var{n}'th time that tracepoint is hit. If the tracepoint number
12834 @var{num} is not specified, the @code{passcount} command sets the
12835 passcount of the most recently defined tracepoint. If no passcount is
12836 given, the trace experiment will run until stopped explicitly by the
12842 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
12843 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
12845 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
12846 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
12847 (@value{GDBP}) @b{trace foo}
12848 (@value{GDBP}) @b{pass 3}
12849 (@value{GDBP}) @b{trace bar}
12850 (@value{GDBP}) @b{pass 2}
12851 (@value{GDBP}) @b{trace baz}
12852 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
12853 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
12854 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
12855 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
12859 @node Tracepoint Conditions
12860 @subsection Tracepoint Conditions
12861 @cindex conditional tracepoints
12862 @cindex tracepoint conditions
12864 The simplest sort of tracepoint collects data every time your program
12865 reaches a specified place. You can also specify a @dfn{condition} for
12866 a tracepoint. A condition is just a Boolean expression in your
12867 programming language (@pxref{Expressions, ,Expressions}). A
12868 tracepoint with a condition evaluates the expression each time your
12869 program reaches it, and data collection happens only if the condition
12872 Tracepoint conditions can be specified when a tracepoint is set, by
12873 using @samp{if} in the arguments to the @code{trace} command.
12874 @xref{Create and Delete Tracepoints, ,Setting Tracepoints}. They can
12875 also be set or changed at any time with the @code{condition} command,
12876 just as with breakpoints.
12878 Unlike breakpoint conditions, @value{GDBN} does not actually evaluate
12879 the conditional expression itself. Instead, @value{GDBN} encodes the
12880 expression into an agent expression (@pxref{Agent Expressions})
12881 suitable for execution on the target, independently of @value{GDBN}.
12882 Global variables become raw memory locations, locals become stack
12883 accesses, and so forth.
12885 For instance, suppose you have a function that is usually called
12886 frequently, but should not be called after an error has occurred. You
12887 could use the following tracepoint command to collect data about calls
12888 of that function that happen while the error code is propagating
12889 through the program; an unconditional tracepoint could end up
12890 collecting thousands of useless trace frames that you would have to
12894 (@value{GDBP}) @kbd{trace normal_operation if errcode > 0}
12897 @node Trace State Variables
12898 @subsection Trace State Variables
12899 @cindex trace state variables
12901 A @dfn{trace state variable} is a special type of variable that is
12902 created and managed by target-side code. The syntax is the same as
12903 that for GDB's convenience variables (a string prefixed with ``$''),
12904 but they are stored on the target. They must be created explicitly,
12905 using a @code{tvariable} command. They are always 64-bit signed
12908 Trace state variables are remembered by @value{GDBN}, and downloaded
12909 to the target along with tracepoint information when the trace
12910 experiment starts. There are no intrinsic limits on the number of
12911 trace state variables, beyond memory limitations of the target.
12913 @cindex convenience variables, and trace state variables
12914 Although trace state variables are managed by the target, you can use
12915 them in print commands and expressions as if they were convenience
12916 variables; @value{GDBN} will get the current value from the target
12917 while the trace experiment is running. Trace state variables share
12918 the same namespace as other ``$'' variables, which means that you
12919 cannot have trace state variables with names like @code{$23} or
12920 @code{$pc}, nor can you have a trace state variable and a convenience
12921 variable with the same name.
12925 @item tvariable $@var{name} [ = @var{expression} ]
12927 The @code{tvariable} command creates a new trace state variable named
12928 @code{$@var{name}}, and optionally gives it an initial value of
12929 @var{expression}. The @var{expression} is evaluated when this command is
12930 entered; the result will be converted to an integer if possible,
12931 otherwise @value{GDBN} will report an error. A subsequent
12932 @code{tvariable} command specifying the same name does not create a
12933 variable, but instead assigns the supplied initial value to the
12934 existing variable of that name, overwriting any previous initial
12935 value. The default initial value is 0.
12937 @item info tvariables
12938 @kindex info tvariables
12939 List all the trace state variables along with their initial values.
12940 Their current values may also be displayed, if the trace experiment is
12943 @item delete tvariable @r{[} $@var{name} @dots{} @r{]}
12944 @kindex delete tvariable
12945 Delete the given trace state variables, or all of them if no arguments
12950 @node Tracepoint Actions
12951 @subsection Tracepoint Action Lists
12955 @cindex tracepoint actions
12956 @item actions @r{[}@var{num}@r{]}
12957 This command will prompt for a list of actions to be taken when the
12958 tracepoint is hit. If the tracepoint number @var{num} is not
12959 specified, this command sets the actions for the one that was most
12960 recently defined (so that you can define a tracepoint and then say
12961 @code{actions} without bothering about its number). You specify the
12962 actions themselves on the following lines, one action at a time, and
12963 terminate the actions list with a line containing just @code{end}. So
12964 far, the only defined actions are @code{collect}, @code{teval}, and
12965 @code{while-stepping}.
12967 @code{actions} is actually equivalent to @code{commands} (@pxref{Break
12968 Commands, ,Breakpoint Command Lists}), except that only the defined
12969 actions are allowed; any other @value{GDBN} command is rejected.
12971 @cindex remove actions from a tracepoint
12972 To remove all actions from a tracepoint, type @samp{actions @var{num}}
12973 and follow it immediately with @samp{end}.
12976 (@value{GDBP}) @b{collect @var{data}} // collect some data
12978 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
12980 (@value{GDBP}) @b{end} // signals the end of actions.
12983 In the following example, the action list begins with @code{collect}
12984 commands indicating the things to be collected when the tracepoint is
12985 hit. Then, in order to single-step and collect additional data
12986 following the tracepoint, a @code{while-stepping} command is used,
12987 followed by the list of things to be collected after each step in a
12988 sequence of single steps. The @code{while-stepping} command is
12989 terminated by its own separate @code{end} command. Lastly, the action
12990 list is terminated by an @code{end} command.
12993 (@value{GDBP}) @b{trace foo}
12994 (@value{GDBP}) @b{actions}
12995 Enter actions for tracepoint 1, one per line:
12998 > while-stepping 12
12999 > collect $pc, arr[i]
13004 @kindex collect @r{(tracepoints)}
13005 @item collect@r{[}/@var{mods}@r{]} @var{expr1}, @var{expr2}, @dots{}
13006 Collect values of the given expressions when the tracepoint is hit.
13007 This command accepts a comma-separated list of any valid expressions.
13008 In addition to global, static, or local variables, the following
13009 special arguments are supported:
13013 Collect all registers.
13016 Collect all function arguments.
13019 Collect all local variables.
13022 Collect the return address. This is helpful if you want to see more
13025 @emph{Note:} The return address location can not always be reliably
13026 determined up front, and the wrong address / registers may end up
13027 collected instead. On some architectures the reliability is higher
13028 for tracepoints at function entry, while on others it's the opposite.
13029 When this happens, backtracing will stop because the return address is
13030 found unavailable (unless another collect rule happened to match it).
13033 Collects the number of arguments from the static probe at which the
13034 tracepoint is located.
13035 @xref{Static Probe Points}.
13037 @item $_probe_arg@var{n}
13038 @var{n} is an integer between 0 and 11. Collects the @var{n}th argument
13039 from the static probe at which the tracepoint is located.
13040 @xref{Static Probe Points}.
13043 @vindex $_sdata@r{, collect}
13044 Collect static tracepoint marker specific data. Only available for
13045 static tracepoints. @xref{Tracepoint Actions,,Tracepoint Action
13046 Lists}. On the UST static tracepoints library backend, an
13047 instrumentation point resembles a @code{printf} function call. The
13048 tracing library is able to collect user specified data formatted to a
13049 character string using the format provided by the programmer that
13050 instrumented the program. Other backends have similar mechanisms.
13051 Here's an example of a UST marker call:
13054 const char master_name[] = "$your_name";
13055 trace_mark(channel1, marker1, "hello %s", master_name)
13058 In this case, collecting @code{$_sdata} collects the string
13059 @samp{hello $yourname}. When analyzing the trace buffer, you can
13060 inspect @samp{$_sdata} like any other variable available to
13064 You can give several consecutive @code{collect} commands, each one
13065 with a single argument, or one @code{collect} command with several
13066 arguments separated by commas; the effect is the same.
13068 The optional @var{mods} changes the usual handling of the arguments.
13069 @code{s} requests that pointers to chars be handled as strings, in
13070 particular collecting the contents of the memory being pointed at, up
13071 to the first zero. The upper bound is by default the value of the
13072 @code{print elements} variable; if @code{s} is followed by a decimal
13073 number, that is the upper bound instead. So for instance
13074 @samp{collect/s25 mystr} collects as many as 25 characters at
13077 The command @code{info scope} (@pxref{Symbols, info scope}) is
13078 particularly useful for figuring out what data to collect.
13080 @kindex teval @r{(tracepoints)}
13081 @item teval @var{expr1}, @var{expr2}, @dots{}
13082 Evaluate the given expressions when the tracepoint is hit. This
13083 command accepts a comma-separated list of expressions. The results
13084 are discarded, so this is mainly useful for assigning values to trace
13085 state variables (@pxref{Trace State Variables}) without adding those
13086 values to the trace buffer, as would be the case if the @code{collect}
13089 @kindex while-stepping @r{(tracepoints)}
13090 @item while-stepping @var{n}
13091 Perform @var{n} single-step instruction traces after the tracepoint,
13092 collecting new data after each step. The @code{while-stepping}
13093 command is followed by the list of what to collect while stepping
13094 (followed by its own @code{end} command):
13097 > while-stepping 12
13098 > collect $regs, myglobal
13104 Note that @code{$pc} is not automatically collected by
13105 @code{while-stepping}; you need to explicitly collect that register if
13106 you need it. You may abbreviate @code{while-stepping} as @code{ws} or
13109 @item set default-collect @var{expr1}, @var{expr2}, @dots{}
13110 @kindex set default-collect
13111 @cindex default collection action
13112 This variable is a list of expressions to collect at each tracepoint
13113 hit. It is effectively an additional @code{collect} action prepended
13114 to every tracepoint action list. The expressions are parsed
13115 individually for each tracepoint, so for instance a variable named
13116 @code{xyz} may be interpreted as a global for one tracepoint, and a
13117 local for another, as appropriate to the tracepoint's location.
13119 @item show default-collect
13120 @kindex show default-collect
13121 Show the list of expressions that are collected by default at each
13126 @node Listing Tracepoints
13127 @subsection Listing Tracepoints
13130 @kindex info tracepoints @r{[}@var{n}@dots{}@r{]}
13131 @kindex info tp @r{[}@var{n}@dots{}@r{]}
13132 @cindex information about tracepoints
13133 @item info tracepoints @r{[}@var{num}@dots{}@r{]}
13134 Display information about the tracepoint @var{num}. If you don't
13135 specify a tracepoint number, displays information about all the
13136 tracepoints defined so far. The format is similar to that used for
13137 @code{info breakpoints}; in fact, @code{info tracepoints} is the same
13138 command, simply restricting itself to tracepoints.
13140 A tracepoint's listing may include additional information specific to
13145 its passcount as given by the @code{passcount @var{n}} command
13148 the state about installed on target of each location
13152 (@value{GDBP}) @b{info trace}
13153 Num Type Disp Enb Address What
13154 1 tracepoint keep y 0x0804ab57 in foo() at main.cxx:7
13156 collect globfoo, $regs
13161 2 tracepoint keep y <MULTIPLE>
13163 2.1 y 0x0804859c in func4 at change-loc.h:35
13164 installed on target
13165 2.2 y 0xb7ffc480 in func4 at change-loc.h:35
13166 installed on target
13167 2.3 y <PENDING> set_tracepoint
13168 3 tracepoint keep y 0x080485b1 in foo at change-loc.c:29
13169 not installed on target
13174 This command can be abbreviated @code{info tp}.
13177 @node Listing Static Tracepoint Markers
13178 @subsection Listing Static Tracepoint Markers
13181 @kindex info static-tracepoint-markers
13182 @cindex information about static tracepoint markers
13183 @item info static-tracepoint-markers
13184 Display information about all static tracepoint markers defined in the
13187 For each marker, the following columns are printed:
13191 An incrementing counter, output to help readability. This is not a
13194 The marker ID, as reported by the target.
13195 @item Enabled or Disabled
13196 Probed markers are tagged with @samp{y}. @samp{n} identifies marks
13197 that are not enabled.
13199 Where the marker is in your program, as a memory address.
13201 Where the marker is in the source for your program, as a file and line
13202 number. If the debug information included in the program does not
13203 allow @value{GDBN} to locate the source of the marker, this column
13204 will be left blank.
13208 In addition, the following information may be printed for each marker:
13212 User data passed to the tracing library by the marker call. In the
13213 UST backend, this is the format string passed as argument to the
13215 @item Static tracepoints probing the marker
13216 The list of static tracepoints attached to the marker.
13220 (@value{GDBP}) info static-tracepoint-markers
13221 Cnt ID Enb Address What
13222 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25
13223 Data: number1 %d number2 %d
13224 Probed by static tracepoints: #2
13225 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24
13231 @node Starting and Stopping Trace Experiments
13232 @subsection Starting and Stopping Trace Experiments
13235 @kindex tstart [ @var{notes} ]
13236 @cindex start a new trace experiment
13237 @cindex collected data discarded
13239 This command starts the trace experiment, and begins collecting data.
13240 It has the side effect of discarding all the data collected in the
13241 trace buffer during the previous trace experiment. If any arguments
13242 are supplied, they are taken as a note and stored with the trace
13243 experiment's state. The notes may be arbitrary text, and are
13244 especially useful with disconnected tracing in a multi-user context;
13245 the notes can explain what the trace is doing, supply user contact
13246 information, and so forth.
13248 @kindex tstop [ @var{notes} ]
13249 @cindex stop a running trace experiment
13251 This command stops the trace experiment. If any arguments are
13252 supplied, they are recorded with the experiment as a note. This is
13253 useful if you are stopping a trace started by someone else, for
13254 instance if the trace is interfering with the system's behavior and
13255 needs to be stopped quickly.
13257 @strong{Note}: a trace experiment and data collection may stop
13258 automatically if any tracepoint's passcount is reached
13259 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
13262 @cindex status of trace data collection
13263 @cindex trace experiment, status of
13265 This command displays the status of the current trace data
13269 Here is an example of the commands we described so far:
13272 (@value{GDBP}) @b{trace gdb_c_test}
13273 (@value{GDBP}) @b{actions}
13274 Enter actions for tracepoint #1, one per line.
13275 > collect $regs,$locals,$args
13276 > while-stepping 11
13280 (@value{GDBP}) @b{tstart}
13281 [time passes @dots{}]
13282 (@value{GDBP}) @b{tstop}
13285 @anchor{disconnected tracing}
13286 @cindex disconnected tracing
13287 You can choose to continue running the trace experiment even if
13288 @value{GDBN} disconnects from the target, voluntarily or
13289 involuntarily. For commands such as @code{detach}, the debugger will
13290 ask what you want to do with the trace. But for unexpected
13291 terminations (@value{GDBN} crash, network outage), it would be
13292 unfortunate to lose hard-won trace data, so the variable
13293 @code{disconnected-tracing} lets you decide whether the trace should
13294 continue running without @value{GDBN}.
13297 @item set disconnected-tracing on
13298 @itemx set disconnected-tracing off
13299 @kindex set disconnected-tracing
13300 Choose whether a tracing run should continue to run if @value{GDBN}
13301 has disconnected from the target. Note that @code{detach} or
13302 @code{quit} will ask you directly what to do about a running trace no
13303 matter what this variable's setting, so the variable is mainly useful
13304 for handling unexpected situations, such as loss of the network.
13306 @item show disconnected-tracing
13307 @kindex show disconnected-tracing
13308 Show the current choice for disconnected tracing.
13312 When you reconnect to the target, the trace experiment may or may not
13313 still be running; it might have filled the trace buffer in the
13314 meantime, or stopped for one of the other reasons. If it is running,
13315 it will continue after reconnection.
13317 Upon reconnection, the target will upload information about the
13318 tracepoints in effect. @value{GDBN} will then compare that
13319 information to the set of tracepoints currently defined, and attempt
13320 to match them up, allowing for the possibility that the numbers may
13321 have changed due to creation and deletion in the meantime. If one of
13322 the target's tracepoints does not match any in @value{GDBN}, the
13323 debugger will create a new tracepoint, so that you have a number with
13324 which to specify that tracepoint. This matching-up process is
13325 necessarily heuristic, and it may result in useless tracepoints being
13326 created; you may simply delete them if they are of no use.
13328 @cindex circular trace buffer
13329 If your target agent supports a @dfn{circular trace buffer}, then you
13330 can run a trace experiment indefinitely without filling the trace
13331 buffer; when space runs out, the agent deletes already-collected trace
13332 frames, oldest first, until there is enough room to continue
13333 collecting. This is especially useful if your tracepoints are being
13334 hit too often, and your trace gets terminated prematurely because the
13335 buffer is full. To ask for a circular trace buffer, simply set
13336 @samp{circular-trace-buffer} to on. You can set this at any time,
13337 including during tracing; if the agent can do it, it will change
13338 buffer handling on the fly, otherwise it will not take effect until
13342 @item set circular-trace-buffer on
13343 @itemx set circular-trace-buffer off
13344 @kindex set circular-trace-buffer
13345 Choose whether a tracing run should use a linear or circular buffer
13346 for trace data. A linear buffer will not lose any trace data, but may
13347 fill up prematurely, while a circular buffer will discard old trace
13348 data, but it will have always room for the latest tracepoint hits.
13350 @item show circular-trace-buffer
13351 @kindex show circular-trace-buffer
13352 Show the current choice for the trace buffer. Note that this may not
13353 match the agent's current buffer handling, nor is it guaranteed to
13354 match the setting that might have been in effect during a past run,
13355 for instance if you are looking at frames from a trace file.
13360 @item set trace-buffer-size @var{n}
13361 @itemx set trace-buffer-size unlimited
13362 @kindex set trace-buffer-size
13363 Request that the target use a trace buffer of @var{n} bytes. Not all
13364 targets will honor the request; they may have a compiled-in size for
13365 the trace buffer, or some other limitation. Set to a value of
13366 @code{unlimited} or @code{-1} to let the target use whatever size it
13367 likes. This is also the default.
13369 @item show trace-buffer-size
13370 @kindex show trace-buffer-size
13371 Show the current requested size for the trace buffer. Note that this
13372 will only match the actual size if the target supports size-setting,
13373 and was able to handle the requested size. For instance, if the
13374 target can only change buffer size between runs, this variable will
13375 not reflect the change until the next run starts. Use @code{tstatus}
13376 to get a report of the actual buffer size.
13380 @item set trace-user @var{text}
13381 @kindex set trace-user
13383 @item show trace-user
13384 @kindex show trace-user
13386 @item set trace-notes @var{text}
13387 @kindex set trace-notes
13388 Set the trace run's notes.
13390 @item show trace-notes
13391 @kindex show trace-notes
13392 Show the trace run's notes.
13394 @item set trace-stop-notes @var{text}
13395 @kindex set trace-stop-notes
13396 Set the trace run's stop notes. The handling of the note is as for
13397 @code{tstop} arguments; the set command is convenient way to fix a
13398 stop note that is mistaken or incomplete.
13400 @item show trace-stop-notes
13401 @kindex show trace-stop-notes
13402 Show the trace run's stop notes.
13406 @node Tracepoint Restrictions
13407 @subsection Tracepoint Restrictions
13409 @cindex tracepoint restrictions
13410 There are a number of restrictions on the use of tracepoints. As
13411 described above, tracepoint data gathering occurs on the target
13412 without interaction from @value{GDBN}. Thus the full capabilities of
13413 the debugger are not available during data gathering, and then at data
13414 examination time, you will be limited by only having what was
13415 collected. The following items describe some common problems, but it
13416 is not exhaustive, and you may run into additional difficulties not
13422 Tracepoint expressions are intended to gather objects (lvalues). Thus
13423 the full flexibility of GDB's expression evaluator is not available.
13424 You cannot call functions, cast objects to aggregate types, access
13425 convenience variables or modify values (except by assignment to trace
13426 state variables). Some language features may implicitly call
13427 functions (for instance Objective-C fields with accessors), and therefore
13428 cannot be collected either.
13431 Collection of local variables, either individually or in bulk with
13432 @code{$locals} or @code{$args}, during @code{while-stepping} may
13433 behave erratically. The stepping action may enter a new scope (for
13434 instance by stepping into a function), or the location of the variable
13435 may change (for instance it is loaded into a register). The
13436 tracepoint data recorded uses the location information for the
13437 variables that is correct for the tracepoint location. When the
13438 tracepoint is created, it is not possible, in general, to determine
13439 where the steps of a @code{while-stepping} sequence will advance the
13440 program---particularly if a conditional branch is stepped.
13443 Collection of an incompletely-initialized or partially-destroyed object
13444 may result in something that @value{GDBN} cannot display, or displays
13445 in a misleading way.
13448 When @value{GDBN} displays a pointer to character it automatically
13449 dereferences the pointer to also display characters of the string
13450 being pointed to. However, collecting the pointer during tracing does
13451 not automatically collect the string. You need to explicitly
13452 dereference the pointer and provide size information if you want to
13453 collect not only the pointer, but the memory pointed to. For example,
13454 @code{*ptr@@50} can be used to collect the 50 element array pointed to
13458 It is not possible to collect a complete stack backtrace at a
13459 tracepoint. Instead, you may collect the registers and a few hundred
13460 bytes from the stack pointer with something like @code{*(unsigned char *)$esp@@300}
13461 (adjust to use the name of the actual stack pointer register on your
13462 target architecture, and the amount of stack you wish to capture).
13463 Then the @code{backtrace} command will show a partial backtrace when
13464 using a trace frame. The number of stack frames that can be examined
13465 depends on the sizes of the frames in the collected stack. Note that
13466 if you ask for a block so large that it goes past the bottom of the
13467 stack, the target agent may report an error trying to read from an
13471 If you do not collect registers at a tracepoint, @value{GDBN} can
13472 infer that the value of @code{$pc} must be the same as the address of
13473 the tracepoint and use that when you are looking at a trace frame
13474 for that tracepoint. However, this cannot work if the tracepoint has
13475 multiple locations (for instance if it was set in a function that was
13476 inlined), or if it has a @code{while-stepping} loop. In those cases
13477 @value{GDBN} will warn you that it can't infer @code{$pc}, and default
13482 @node Analyze Collected Data
13483 @section Using the Collected Data
13485 After the tracepoint experiment ends, you use @value{GDBN} commands
13486 for examining the trace data. The basic idea is that each tracepoint
13487 collects a trace @dfn{snapshot} every time it is hit and another
13488 snapshot every time it single-steps. All these snapshots are
13489 consecutively numbered from zero and go into a buffer, and you can
13490 examine them later. The way you examine them is to @dfn{focus} on a
13491 specific trace snapshot. When the remote stub is focused on a trace
13492 snapshot, it will respond to all @value{GDBN} requests for memory and
13493 registers by reading from the buffer which belongs to that snapshot,
13494 rather than from @emph{real} memory or registers of the program being
13495 debugged. This means that @strong{all} @value{GDBN} commands
13496 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
13497 behave as if we were currently debugging the program state as it was
13498 when the tracepoint occurred. Any requests for data that are not in
13499 the buffer will fail.
13502 * tfind:: How to select a trace snapshot
13503 * tdump:: How to display all data for a snapshot
13504 * save tracepoints:: How to save tracepoints for a future run
13508 @subsection @code{tfind @var{n}}
13511 @cindex select trace snapshot
13512 @cindex find trace snapshot
13513 The basic command for selecting a trace snapshot from the buffer is
13514 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
13515 counting from zero. If no argument @var{n} is given, the next
13516 snapshot is selected.
13518 Here are the various forms of using the @code{tfind} command.
13522 Find the first snapshot in the buffer. This is a synonym for
13523 @code{tfind 0} (since 0 is the number of the first snapshot).
13526 Stop debugging trace snapshots, resume @emph{live} debugging.
13529 Same as @samp{tfind none}.
13532 No argument means find the next trace snapshot or find the first
13533 one if no trace snapshot is selected.
13536 Find the previous trace snapshot before the current one. This permits
13537 retracing earlier steps.
13539 @item tfind tracepoint @var{num}
13540 Find the next snapshot associated with tracepoint @var{num}. Search
13541 proceeds forward from the last examined trace snapshot. If no
13542 argument @var{num} is given, it means find the next snapshot collected
13543 for the same tracepoint as the current snapshot.
13545 @item tfind pc @var{addr}
13546 Find the next snapshot associated with the value @var{addr} of the
13547 program counter. Search proceeds forward from the last examined trace
13548 snapshot. If no argument @var{addr} is given, it means find the next
13549 snapshot with the same value of PC as the current snapshot.
13551 @item tfind outside @var{addr1}, @var{addr2}
13552 Find the next snapshot whose PC is outside the given range of
13553 addresses (exclusive).
13555 @item tfind range @var{addr1}, @var{addr2}
13556 Find the next snapshot whose PC is between @var{addr1} and
13557 @var{addr2} (inclusive).
13559 @item tfind line @r{[}@var{file}:@r{]}@var{n}
13560 Find the next snapshot associated with the source line @var{n}. If
13561 the optional argument @var{file} is given, refer to line @var{n} in
13562 that source file. Search proceeds forward from the last examined
13563 trace snapshot. If no argument @var{n} is given, it means find the
13564 next line other than the one currently being examined; thus saying
13565 @code{tfind line} repeatedly can appear to have the same effect as
13566 stepping from line to line in a @emph{live} debugging session.
13569 The default arguments for the @code{tfind} commands are specifically
13570 designed to make it easy to scan through the trace buffer. For
13571 instance, @code{tfind} with no argument selects the next trace
13572 snapshot, and @code{tfind -} with no argument selects the previous
13573 trace snapshot. So, by giving one @code{tfind} command, and then
13574 simply hitting @key{RET} repeatedly you can examine all the trace
13575 snapshots in order. Or, by saying @code{tfind -} and then hitting
13576 @key{RET} repeatedly you can examine the snapshots in reverse order.
13577 The @code{tfind line} command with no argument selects the snapshot
13578 for the next source line executed. The @code{tfind pc} command with
13579 no argument selects the next snapshot with the same program counter
13580 (PC) as the current frame. The @code{tfind tracepoint} command with
13581 no argument selects the next trace snapshot collected by the same
13582 tracepoint as the current one.
13584 In addition to letting you scan through the trace buffer manually,
13585 these commands make it easy to construct @value{GDBN} scripts that
13586 scan through the trace buffer and print out whatever collected data
13587 you are interested in. Thus, if we want to examine the PC, FP, and SP
13588 registers from each trace frame in the buffer, we can say this:
13591 (@value{GDBP}) @b{tfind start}
13592 (@value{GDBP}) @b{while ($trace_frame != -1)}
13593 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
13594 $trace_frame, $pc, $sp, $fp
13598 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
13599 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
13600 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
13601 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
13602 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
13603 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
13604 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
13605 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
13606 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
13607 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
13608 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
13611 Or, if we want to examine the variable @code{X} at each source line in
13615 (@value{GDBP}) @b{tfind start}
13616 (@value{GDBP}) @b{while ($trace_frame != -1)}
13617 > printf "Frame %d, X == %d\n", $trace_frame, X
13627 @subsection @code{tdump}
13629 @cindex dump all data collected at tracepoint
13630 @cindex tracepoint data, display
13632 This command takes no arguments. It prints all the data collected at
13633 the current trace snapshot.
13636 (@value{GDBP}) @b{trace 444}
13637 (@value{GDBP}) @b{actions}
13638 Enter actions for tracepoint #2, one per line:
13639 > collect $regs, $locals, $args, gdb_long_test
13642 (@value{GDBP}) @b{tstart}
13644 (@value{GDBP}) @b{tfind line 444}
13645 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
13647 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
13649 (@value{GDBP}) @b{tdump}
13650 Data collected at tracepoint 2, trace frame 1:
13651 d0 0xc4aa0085 -995491707
13655 d4 0x71aea3d 119204413
13658 d7 0x380035 3670069
13659 a0 0x19e24a 1696330
13660 a1 0x3000668 50333288
13662 a3 0x322000 3284992
13663 a4 0x3000698 50333336
13664 a5 0x1ad3cc 1758156
13665 fp 0x30bf3c 0x30bf3c
13666 sp 0x30bf34 0x30bf34
13668 pc 0x20b2c8 0x20b2c8
13672 p = 0x20e5b4 "gdb-test"
13679 gdb_long_test = 17 '\021'
13684 @code{tdump} works by scanning the tracepoint's current collection
13685 actions and printing the value of each expression listed. So
13686 @code{tdump} can fail, if after a run, you change the tracepoint's
13687 actions to mention variables that were not collected during the run.
13689 Also, for tracepoints with @code{while-stepping} loops, @code{tdump}
13690 uses the collected value of @code{$pc} to distinguish between trace
13691 frames that were collected at the tracepoint hit, and frames that were
13692 collected while stepping. This allows it to correctly choose whether
13693 to display the basic list of collections, or the collections from the
13694 body of the while-stepping loop. However, if @code{$pc} was not collected,
13695 then @code{tdump} will always attempt to dump using the basic collection
13696 list, and may fail if a while-stepping frame does not include all the
13697 same data that is collected at the tracepoint hit.
13698 @c This is getting pretty arcane, example would be good.
13700 @node save tracepoints
13701 @subsection @code{save tracepoints @var{filename}}
13702 @kindex save tracepoints
13703 @kindex save-tracepoints
13704 @cindex save tracepoints for future sessions
13706 This command saves all current tracepoint definitions together with
13707 their actions and passcounts, into a file @file{@var{filename}}
13708 suitable for use in a later debugging session. To read the saved
13709 tracepoint definitions, use the @code{source} command (@pxref{Command
13710 Files}). The @w{@code{save-tracepoints}} command is a deprecated
13711 alias for @w{@code{save tracepoints}}
13713 @node Tracepoint Variables
13714 @section Convenience Variables for Tracepoints
13715 @cindex tracepoint variables
13716 @cindex convenience variables for tracepoints
13719 @vindex $trace_frame
13720 @item (int) $trace_frame
13721 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
13722 snapshot is selected.
13724 @vindex $tracepoint
13725 @item (int) $tracepoint
13726 The tracepoint for the current trace snapshot.
13728 @vindex $trace_line
13729 @item (int) $trace_line
13730 The line number for the current trace snapshot.
13732 @vindex $trace_file
13733 @item (char []) $trace_file
13734 The source file for the current trace snapshot.
13736 @vindex $trace_func
13737 @item (char []) $trace_func
13738 The name of the function containing @code{$tracepoint}.
13741 Note: @code{$trace_file} is not suitable for use in @code{printf},
13742 use @code{output} instead.
13744 Here's a simple example of using these convenience variables for
13745 stepping through all the trace snapshots and printing some of their
13746 data. Note that these are not the same as trace state variables,
13747 which are managed by the target.
13750 (@value{GDBP}) @b{tfind start}
13752 (@value{GDBP}) @b{while $trace_frame != -1}
13753 > output $trace_file
13754 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
13760 @section Using Trace Files
13761 @cindex trace files
13763 In some situations, the target running a trace experiment may no
13764 longer be available; perhaps it crashed, or the hardware was needed
13765 for a different activity. To handle these cases, you can arrange to
13766 dump the trace data into a file, and later use that file as a source
13767 of trace data, via the @code{target tfile} command.
13772 @item tsave [ -r ] @var{filename}
13773 @itemx tsave [-ctf] @var{dirname}
13774 Save the trace data to @var{filename}. By default, this command
13775 assumes that @var{filename} refers to the host filesystem, so if
13776 necessary @value{GDBN} will copy raw trace data up from the target and
13777 then save it. If the target supports it, you can also supply the
13778 optional argument @code{-r} (``remote'') to direct the target to save
13779 the data directly into @var{filename} in its own filesystem, which may be
13780 more efficient if the trace buffer is very large. (Note, however, that
13781 @code{target tfile} can only read from files accessible to the host.)
13782 By default, this command will save trace frame in tfile format.
13783 You can supply the optional argument @code{-ctf} to save data in CTF
13784 format. The @dfn{Common Trace Format} (CTF) is proposed as a trace format
13785 that can be shared by multiple debugging and tracing tools. Please go to
13786 @indicateurl{http://www.efficios.com/ctf} to get more information.
13788 @kindex target tfile
13792 @item target tfile @var{filename}
13793 @itemx target ctf @var{dirname}
13794 Use the file named @var{filename} or directory named @var{dirname} as
13795 a source of trace data. Commands that examine data work as they do with
13796 a live target, but it is not possible to run any new trace experiments.
13797 @code{tstatus} will report the state of the trace run at the moment
13798 the data was saved, as well as the current trace frame you are examining.
13799 Both @var{filename} and @var{dirname} must be on a filesystem accessible to
13803 (@value{GDBP}) target ctf ctf.ctf
13804 (@value{GDBP}) tfind
13805 Found trace frame 0, tracepoint 2
13806 39 ++a; /* set tracepoint 1 here */
13807 (@value{GDBP}) tdump
13808 Data collected at tracepoint 2, trace frame 0:
13812 c = @{"123", "456", "789", "123", "456", "789"@}
13813 d = @{@{@{a = 1, b = 2@}, @{a = 3, b = 4@}@}, @{@{a = 5, b = 6@}, @{a = 7, b = 8@}@}@}
13821 @chapter Debugging Programs That Use Overlays
13824 If your program is too large to fit completely in your target system's
13825 memory, you can sometimes use @dfn{overlays} to work around this
13826 problem. @value{GDBN} provides some support for debugging programs that
13830 * How Overlays Work:: A general explanation of overlays.
13831 * Overlay Commands:: Managing overlays in @value{GDBN}.
13832 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
13833 mapped by asking the inferior.
13834 * Overlay Sample Program:: A sample program using overlays.
13837 @node How Overlays Work
13838 @section How Overlays Work
13839 @cindex mapped overlays
13840 @cindex unmapped overlays
13841 @cindex load address, overlay's
13842 @cindex mapped address
13843 @cindex overlay area
13845 Suppose you have a computer whose instruction address space is only 64
13846 kilobytes long, but which has much more memory which can be accessed by
13847 other means: special instructions, segment registers, or memory
13848 management hardware, for example. Suppose further that you want to
13849 adapt a program which is larger than 64 kilobytes to run on this system.
13851 One solution is to identify modules of your program which are relatively
13852 independent, and need not call each other directly; call these modules
13853 @dfn{overlays}. Separate the overlays from the main program, and place
13854 their machine code in the larger memory. Place your main program in
13855 instruction memory, but leave at least enough space there to hold the
13856 largest overlay as well.
13858 Now, to call a function located in an overlay, you must first copy that
13859 overlay's machine code from the large memory into the space set aside
13860 for it in the instruction memory, and then jump to its entry point
13863 @c NB: In the below the mapped area's size is greater or equal to the
13864 @c size of all overlays. This is intentional to remind the developer
13865 @c that overlays don't necessarily need to be the same size.
13869 Data Instruction Larger
13870 Address Space Address Space Address Space
13871 +-----------+ +-----------+ +-----------+
13873 +-----------+ +-----------+ +-----------+<-- overlay 1
13874 | program | | main | .----| overlay 1 | load address
13875 | variables | | program | | +-----------+
13876 | and heap | | | | | |
13877 +-----------+ | | | +-----------+<-- overlay 2
13878 | | +-----------+ | | | load address
13879 +-----------+ | | | .-| overlay 2 |
13881 mapped --->+-----------+ | | +-----------+
13882 address | | | | | |
13883 | overlay | <-' | | |
13884 | area | <---' +-----------+<-- overlay 3
13885 | | <---. | | load address
13886 +-----------+ `--| overlay 3 |
13893 @anchor{A code overlay}A code overlay
13897 The diagram (@pxref{A code overlay}) shows a system with separate data
13898 and instruction address spaces. To map an overlay, the program copies
13899 its code from the larger address space to the instruction address space.
13900 Since the overlays shown here all use the same mapped address, only one
13901 may be mapped at a time. For a system with a single address space for
13902 data and instructions, the diagram would be similar, except that the
13903 program variables and heap would share an address space with the main
13904 program and the overlay area.
13906 An overlay loaded into instruction memory and ready for use is called a
13907 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
13908 instruction memory. An overlay not present (or only partially present)
13909 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
13910 is its address in the larger memory. The mapped address is also called
13911 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
13912 called the @dfn{load memory address}, or @dfn{LMA}.
13914 Unfortunately, overlays are not a completely transparent way to adapt a
13915 program to limited instruction memory. They introduce a new set of
13916 global constraints you must keep in mind as you design your program:
13921 Before calling or returning to a function in an overlay, your program
13922 must make sure that overlay is actually mapped. Otherwise, the call or
13923 return will transfer control to the right address, but in the wrong
13924 overlay, and your program will probably crash.
13927 If the process of mapping an overlay is expensive on your system, you
13928 will need to choose your overlays carefully to minimize their effect on
13929 your program's performance.
13932 The executable file you load onto your system must contain each
13933 overlay's instructions, appearing at the overlay's load address, not its
13934 mapped address. However, each overlay's instructions must be relocated
13935 and its symbols defined as if the overlay were at its mapped address.
13936 You can use GNU linker scripts to specify different load and relocation
13937 addresses for pieces of your program; see @ref{Overlay Description,,,
13938 ld.info, Using ld: the GNU linker}.
13941 The procedure for loading executable files onto your system must be able
13942 to load their contents into the larger address space as well as the
13943 instruction and data spaces.
13947 The overlay system described above is rather simple, and could be
13948 improved in many ways:
13953 If your system has suitable bank switch registers or memory management
13954 hardware, you could use those facilities to make an overlay's load area
13955 contents simply appear at their mapped address in instruction space.
13956 This would probably be faster than copying the overlay to its mapped
13957 area in the usual way.
13960 If your overlays are small enough, you could set aside more than one
13961 overlay area, and have more than one overlay mapped at a time.
13964 You can use overlays to manage data, as well as instructions. In
13965 general, data overlays are even less transparent to your design than
13966 code overlays: whereas code overlays only require care when you call or
13967 return to functions, data overlays require care every time you access
13968 the data. Also, if you change the contents of a data overlay, you
13969 must copy its contents back out to its load address before you can copy a
13970 different data overlay into the same mapped area.
13975 @node Overlay Commands
13976 @section Overlay Commands
13978 To use @value{GDBN}'s overlay support, each overlay in your program must
13979 correspond to a separate section of the executable file. The section's
13980 virtual memory address and load memory address must be the overlay's
13981 mapped and load addresses. Identifying overlays with sections allows
13982 @value{GDBN} to determine the appropriate address of a function or
13983 variable, depending on whether the overlay is mapped or not.
13985 @value{GDBN}'s overlay commands all start with the word @code{overlay};
13986 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
13991 Disable @value{GDBN}'s overlay support. When overlay support is
13992 disabled, @value{GDBN} assumes that all functions and variables are
13993 always present at their mapped addresses. By default, @value{GDBN}'s
13994 overlay support is disabled.
13996 @item overlay manual
13997 @cindex manual overlay debugging
13998 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
13999 relies on you to tell it which overlays are mapped, and which are not,
14000 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
14001 commands described below.
14003 @item overlay map-overlay @var{overlay}
14004 @itemx overlay map @var{overlay}
14005 @cindex map an overlay
14006 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
14007 be the name of the object file section containing the overlay. When an
14008 overlay is mapped, @value{GDBN} assumes it can find the overlay's
14009 functions and variables at their mapped addresses. @value{GDBN} assumes
14010 that any other overlays whose mapped ranges overlap that of
14011 @var{overlay} are now unmapped.
14013 @item overlay unmap-overlay @var{overlay}
14014 @itemx overlay unmap @var{overlay}
14015 @cindex unmap an overlay
14016 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
14017 must be the name of the object file section containing the overlay.
14018 When an overlay is unmapped, @value{GDBN} assumes it can find the
14019 overlay's functions and variables at their load addresses.
14022 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
14023 consults a data structure the overlay manager maintains in the inferior
14024 to see which overlays are mapped. For details, see @ref{Automatic
14025 Overlay Debugging}.
14027 @item overlay load-target
14028 @itemx overlay load
14029 @cindex reloading the overlay table
14030 Re-read the overlay table from the inferior. Normally, @value{GDBN}
14031 re-reads the table @value{GDBN} automatically each time the inferior
14032 stops, so this command should only be necessary if you have changed the
14033 overlay mapping yourself using @value{GDBN}. This command is only
14034 useful when using automatic overlay debugging.
14036 @item overlay list-overlays
14037 @itemx overlay list
14038 @cindex listing mapped overlays
14039 Display a list of the overlays currently mapped, along with their mapped
14040 addresses, load addresses, and sizes.
14044 Normally, when @value{GDBN} prints a code address, it includes the name
14045 of the function the address falls in:
14048 (@value{GDBP}) print main
14049 $3 = @{int ()@} 0x11a0 <main>
14052 When overlay debugging is enabled, @value{GDBN} recognizes code in
14053 unmapped overlays, and prints the names of unmapped functions with
14054 asterisks around them. For example, if @code{foo} is a function in an
14055 unmapped overlay, @value{GDBN} prints it this way:
14058 (@value{GDBP}) overlay list
14059 No sections are mapped.
14060 (@value{GDBP}) print foo
14061 $5 = @{int (int)@} 0x100000 <*foo*>
14064 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
14068 (@value{GDBP}) overlay list
14069 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
14070 mapped at 0x1016 - 0x104a
14071 (@value{GDBP}) print foo
14072 $6 = @{int (int)@} 0x1016 <foo>
14075 When overlay debugging is enabled, @value{GDBN} can find the correct
14076 address for functions and variables in an overlay, whether or not the
14077 overlay is mapped. This allows most @value{GDBN} commands, like
14078 @code{break} and @code{disassemble}, to work normally, even on unmapped
14079 code. However, @value{GDBN}'s breakpoint support has some limitations:
14083 @cindex breakpoints in overlays
14084 @cindex overlays, setting breakpoints in
14085 You can set breakpoints in functions in unmapped overlays, as long as
14086 @value{GDBN} can write to the overlay at its load address.
14088 @value{GDBN} can not set hardware or simulator-based breakpoints in
14089 unmapped overlays. However, if you set a breakpoint at the end of your
14090 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
14091 you are using manual overlay management), @value{GDBN} will re-set its
14092 breakpoints properly.
14096 @node Automatic Overlay Debugging
14097 @section Automatic Overlay Debugging
14098 @cindex automatic overlay debugging
14100 @value{GDBN} can automatically track which overlays are mapped and which
14101 are not, given some simple co-operation from the overlay manager in the
14102 inferior. If you enable automatic overlay debugging with the
14103 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
14104 looks in the inferior's memory for certain variables describing the
14105 current state of the overlays.
14107 Here are the variables your overlay manager must define to support
14108 @value{GDBN}'s automatic overlay debugging:
14112 @item @code{_ovly_table}:
14113 This variable must be an array of the following structures:
14118 /* The overlay's mapped address. */
14121 /* The size of the overlay, in bytes. */
14122 unsigned long size;
14124 /* The overlay's load address. */
14127 /* Non-zero if the overlay is currently mapped;
14129 unsigned long mapped;
14133 @item @code{_novlys}:
14134 This variable must be a four-byte signed integer, holding the total
14135 number of elements in @code{_ovly_table}.
14139 To decide whether a particular overlay is mapped or not, @value{GDBN}
14140 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
14141 @code{lma} members equal the VMA and LMA of the overlay's section in the
14142 executable file. When @value{GDBN} finds a matching entry, it consults
14143 the entry's @code{mapped} member to determine whether the overlay is
14146 In addition, your overlay manager may define a function called
14147 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
14148 will silently set a breakpoint there. If the overlay manager then
14149 calls this function whenever it has changed the overlay table, this
14150 will enable @value{GDBN} to accurately keep track of which overlays
14151 are in program memory, and update any breakpoints that may be set
14152 in overlays. This will allow breakpoints to work even if the
14153 overlays are kept in ROM or other non-writable memory while they
14154 are not being executed.
14156 @node Overlay Sample Program
14157 @section Overlay Sample Program
14158 @cindex overlay example program
14160 When linking a program which uses overlays, you must place the overlays
14161 at their load addresses, while relocating them to run at their mapped
14162 addresses. To do this, you must write a linker script (@pxref{Overlay
14163 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
14164 since linker scripts are specific to a particular host system, target
14165 architecture, and target memory layout, this manual cannot provide
14166 portable sample code demonstrating @value{GDBN}'s overlay support.
14168 However, the @value{GDBN} source distribution does contain an overlaid
14169 program, with linker scripts for a few systems, as part of its test
14170 suite. The program consists of the following files from
14171 @file{gdb/testsuite/gdb.base}:
14175 The main program file.
14177 A simple overlay manager, used by @file{overlays.c}.
14182 Overlay modules, loaded and used by @file{overlays.c}.
14185 Linker scripts for linking the test program on the @code{d10v-elf}
14186 and @code{m32r-elf} targets.
14189 You can build the test program using the @code{d10v-elf} GCC
14190 cross-compiler like this:
14193 $ d10v-elf-gcc -g -c overlays.c
14194 $ d10v-elf-gcc -g -c ovlymgr.c
14195 $ d10v-elf-gcc -g -c foo.c
14196 $ d10v-elf-gcc -g -c bar.c
14197 $ d10v-elf-gcc -g -c baz.c
14198 $ d10v-elf-gcc -g -c grbx.c
14199 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
14200 baz.o grbx.o -Wl,-Td10v.ld -o overlays
14203 The build process is identical for any other architecture, except that
14204 you must substitute the appropriate compiler and linker script for the
14205 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
14209 @chapter Using @value{GDBN} with Different Languages
14212 Although programming languages generally have common aspects, they are
14213 rarely expressed in the same manner. For instance, in ANSI C,
14214 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
14215 Modula-2, it is accomplished by @code{p^}. Values can also be
14216 represented (and displayed) differently. Hex numbers in C appear as
14217 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
14219 @cindex working language
14220 Language-specific information is built into @value{GDBN} for some languages,
14221 allowing you to express operations like the above in your program's
14222 native language, and allowing @value{GDBN} to output values in a manner
14223 consistent with the syntax of your program's native language. The
14224 language you use to build expressions is called the @dfn{working
14228 * Setting:: Switching between source languages
14229 * Show:: Displaying the language
14230 * Checks:: Type and range checks
14231 * Supported Languages:: Supported languages
14232 * Unsupported Languages:: Unsupported languages
14236 @section Switching Between Source Languages
14238 There are two ways to control the working language---either have @value{GDBN}
14239 set it automatically, or select it manually yourself. You can use the
14240 @code{set language} command for either purpose. On startup, @value{GDBN}
14241 defaults to setting the language automatically. The working language is
14242 used to determine how expressions you type are interpreted, how values
14245 In addition to the working language, every source file that
14246 @value{GDBN} knows about has its own working language. For some object
14247 file formats, the compiler might indicate which language a particular
14248 source file is in. However, most of the time @value{GDBN} infers the
14249 language from the name of the file. The language of a source file
14250 controls whether C@t{++} names are demangled---this way @code{backtrace} can
14251 show each frame appropriately for its own language. There is no way to
14252 set the language of a source file from within @value{GDBN}, but you can
14253 set the language associated with a filename extension. @xref{Show, ,
14254 Displaying the Language}.
14256 This is most commonly a problem when you use a program, such
14257 as @code{cfront} or @code{f2c}, that generates C but is written in
14258 another language. In that case, make the
14259 program use @code{#line} directives in its C output; that way
14260 @value{GDBN} will know the correct language of the source code of the original
14261 program, and will display that source code, not the generated C code.
14264 * Filenames:: Filename extensions and languages.
14265 * Manually:: Setting the working language manually
14266 * Automatically:: Having @value{GDBN} infer the source language
14270 @subsection List of Filename Extensions and Languages
14272 If a source file name ends in one of the following extensions, then
14273 @value{GDBN} infers that its language is the one indicated.
14291 C@t{++} source file
14297 Objective-C source file
14301 Fortran source file
14304 Modula-2 source file
14308 Assembler source file. This actually behaves almost like C, but
14309 @value{GDBN} does not skip over function prologues when stepping.
14312 In addition, you may set the language associated with a filename
14313 extension. @xref{Show, , Displaying the Language}.
14316 @subsection Setting the Working Language
14318 If you allow @value{GDBN} to set the language automatically,
14319 expressions are interpreted the same way in your debugging session and
14322 @kindex set language
14323 If you wish, you may set the language manually. To do this, issue the
14324 command @samp{set language @var{lang}}, where @var{lang} is the name of
14325 a language, such as
14326 @code{c} or @code{modula-2}.
14327 For a list of the supported languages, type @samp{set language}.
14329 Setting the language manually prevents @value{GDBN} from updating the working
14330 language automatically. This can lead to confusion if you try
14331 to debug a program when the working language is not the same as the
14332 source language, when an expression is acceptable to both
14333 languages---but means different things. For instance, if the current
14334 source file were written in C, and @value{GDBN} was parsing Modula-2, a
14342 might not have the effect you intended. In C, this means to add
14343 @code{b} and @code{c} and place the result in @code{a}. The result
14344 printed would be the value of @code{a}. In Modula-2, this means to compare
14345 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
14347 @node Automatically
14348 @subsection Having @value{GDBN} Infer the Source Language
14350 To have @value{GDBN} set the working language automatically, use
14351 @samp{set language local} or @samp{set language auto}. @value{GDBN}
14352 then infers the working language. That is, when your program stops in a
14353 frame (usually by encountering a breakpoint), @value{GDBN} sets the
14354 working language to the language recorded for the function in that
14355 frame. If the language for a frame is unknown (that is, if the function
14356 or block corresponding to the frame was defined in a source file that
14357 does not have a recognized extension), the current working language is
14358 not changed, and @value{GDBN} issues a warning.
14360 This may not seem necessary for most programs, which are written
14361 entirely in one source language. However, program modules and libraries
14362 written in one source language can be used by a main program written in
14363 a different source language. Using @samp{set language auto} in this
14364 case frees you from having to set the working language manually.
14367 @section Displaying the Language
14369 The following commands help you find out which language is the
14370 working language, and also what language source files were written in.
14373 @item show language
14374 @anchor{show language}
14375 @kindex show language
14376 Display the current working language. This is the
14377 language you can use with commands such as @code{print} to
14378 build and compute expressions that may involve variables in your program.
14381 @kindex info frame@r{, show the source language}
14382 Display the source language for this frame. This language becomes the
14383 working language if you use an identifier from this frame.
14384 @xref{Frame Info, ,Information about a Frame}, to identify the other
14385 information listed here.
14388 @kindex info source@r{, show the source language}
14389 Display the source language of this source file.
14390 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
14391 information listed here.
14394 In unusual circumstances, you may have source files with extensions
14395 not in the standard list. You can then set the extension associated
14396 with a language explicitly:
14399 @item set extension-language @var{ext} @var{language}
14400 @kindex set extension-language
14401 Tell @value{GDBN} that source files with extension @var{ext} are to be
14402 assumed as written in the source language @var{language}.
14404 @item info extensions
14405 @kindex info extensions
14406 List all the filename extensions and the associated languages.
14410 @section Type and Range Checking
14412 Some languages are designed to guard you against making seemingly common
14413 errors through a series of compile- and run-time checks. These include
14414 checking the type of arguments to functions and operators and making
14415 sure mathematical overflows are caught at run time. Checks such as
14416 these help to ensure a program's correctness once it has been compiled
14417 by eliminating type mismatches and providing active checks for range
14418 errors when your program is running.
14420 By default @value{GDBN} checks for these errors according to the
14421 rules of the current source language. Although @value{GDBN} does not check
14422 the statements in your program, it can check expressions entered directly
14423 into @value{GDBN} for evaluation via the @code{print} command, for example.
14426 * Type Checking:: An overview of type checking
14427 * Range Checking:: An overview of range checking
14430 @cindex type checking
14431 @cindex checks, type
14432 @node Type Checking
14433 @subsection An Overview of Type Checking
14435 Some languages, such as C and C@t{++}, are strongly typed, meaning that the
14436 arguments to operators and functions have to be of the correct type,
14437 otherwise an error occurs. These checks prevent type mismatch
14438 errors from ever causing any run-time problems. For example,
14441 int klass::my_method(char *b) @{ return b ? 1 : 2; @}
14443 (@value{GDBP}) print obj.my_method (0)
14446 (@value{GDBP}) print obj.my_method (0x1234)
14447 Cannot resolve method klass::my_method to any overloaded instance
14450 The second example fails because in C@t{++} the integer constant
14451 @samp{0x1234} is not type-compatible with the pointer parameter type.
14453 For the expressions you use in @value{GDBN} commands, you can tell
14454 @value{GDBN} to not enforce strict type checking or
14455 to treat any mismatches as errors and abandon the expression;
14456 When type checking is disabled, @value{GDBN} successfully evaluates
14457 expressions like the second example above.
14459 Even if type checking is off, there may be other reasons
14460 related to type that prevent @value{GDBN} from evaluating an expression.
14461 For instance, @value{GDBN} does not know how to add an @code{int} and
14462 a @code{struct foo}. These particular type errors have nothing to do
14463 with the language in use and usually arise from expressions which make
14464 little sense to evaluate anyway.
14466 @value{GDBN} provides some additional commands for controlling type checking:
14468 @kindex set check type
14469 @kindex show check type
14471 @item set check type on
14472 @itemx set check type off
14473 Set strict type checking on or off. If any type mismatches occur in
14474 evaluating an expression while type checking is on, @value{GDBN} prints a
14475 message and aborts evaluation of the expression.
14477 @item show check type
14478 Show the current setting of type checking and whether @value{GDBN}
14479 is enforcing strict type checking rules.
14482 @cindex range checking
14483 @cindex checks, range
14484 @node Range Checking
14485 @subsection An Overview of Range Checking
14487 In some languages (such as Modula-2), it is an error to exceed the
14488 bounds of a type; this is enforced with run-time checks. Such range
14489 checking is meant to ensure program correctness by making sure
14490 computations do not overflow, or indices on an array element access do
14491 not exceed the bounds of the array.
14493 For expressions you use in @value{GDBN} commands, you can tell
14494 @value{GDBN} to treat range errors in one of three ways: ignore them,
14495 always treat them as errors and abandon the expression, or issue
14496 warnings but evaluate the expression anyway.
14498 A range error can result from numerical overflow, from exceeding an
14499 array index bound, or when you type a constant that is not a member
14500 of any type. Some languages, however, do not treat overflows as an
14501 error. In many implementations of C, mathematical overflow causes the
14502 result to ``wrap around'' to lower values---for example, if @var{m} is
14503 the largest integer value, and @var{s} is the smallest, then
14506 @var{m} + 1 @result{} @var{s}
14509 This, too, is specific to individual languages, and in some cases
14510 specific to individual compilers or machines. @xref{Supported Languages, ,
14511 Supported Languages}, for further details on specific languages.
14513 @value{GDBN} provides some additional commands for controlling the range checker:
14515 @kindex set check range
14516 @kindex show check range
14518 @item set check range auto
14519 Set range checking on or off based on the current working language.
14520 @xref{Supported Languages, ,Supported Languages}, for the default settings for
14523 @item set check range on
14524 @itemx set check range off
14525 Set range checking on or off, overriding the default setting for the
14526 current working language. A warning is issued if the setting does not
14527 match the language default. If a range error occurs and range checking is on,
14528 then a message is printed and evaluation of the expression is aborted.
14530 @item set check range warn
14531 Output messages when the @value{GDBN} range checker detects a range error,
14532 but attempt to evaluate the expression anyway. Evaluating the
14533 expression may still be impossible for other reasons, such as accessing
14534 memory that the process does not own (a typical example from many Unix
14538 Show the current setting of the range checker, and whether or not it is
14539 being set automatically by @value{GDBN}.
14542 @node Supported Languages
14543 @section Supported Languages
14545 @value{GDBN} supports C, C@t{++}, D, Go, Objective-C, Fortran,
14546 OpenCL C, Pascal, Rust, assembly, Modula-2, and Ada.
14547 @c This is false ...
14548 Some @value{GDBN} features may be used in expressions regardless of the
14549 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
14550 and the @samp{@{type@}addr} construct (@pxref{Expressions,
14551 ,Expressions}) can be used with the constructs of any supported
14554 The following sections detail to what degree each source language is
14555 supported by @value{GDBN}. These sections are not meant to be language
14556 tutorials or references, but serve only as a reference guide to what the
14557 @value{GDBN} expression parser accepts, and what input and output
14558 formats should look like for different languages. There are many good
14559 books written on each of these languages; please look to these for a
14560 language reference or tutorial.
14563 * C:: C and C@t{++}
14566 * Objective-C:: Objective-C
14567 * OpenCL C:: OpenCL C
14568 * Fortran:: Fortran
14571 * Modula-2:: Modula-2
14576 @subsection C and C@t{++}
14578 @cindex C and C@t{++}
14579 @cindex expressions in C or C@t{++}
14581 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
14582 to both languages. Whenever this is the case, we discuss those languages
14586 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
14587 @cindex @sc{gnu} C@t{++}
14588 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
14589 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
14590 effectively, you must compile your C@t{++} programs with a supported
14591 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
14592 compiler (@code{aCC}).
14595 * C Operators:: C and C@t{++} operators
14596 * C Constants:: C and C@t{++} constants
14597 * C Plus Plus Expressions:: C@t{++} expressions
14598 * C Defaults:: Default settings for C and C@t{++}
14599 * C Checks:: C and C@t{++} type and range checks
14600 * Debugging C:: @value{GDBN} and C
14601 * Debugging C Plus Plus:: @value{GDBN} features for C@t{++}
14602 * Decimal Floating Point:: Numbers in Decimal Floating Point format
14606 @subsubsection C and C@t{++} Operators
14608 @cindex C and C@t{++} operators
14610 Operators must be defined on values of specific types. For instance,
14611 @code{+} is defined on numbers, but not on structures. Operators are
14612 often defined on groups of types.
14614 For the purposes of C and C@t{++}, the following definitions hold:
14619 @emph{Integral types} include @code{int} with any of its storage-class
14620 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
14623 @emph{Floating-point types} include @code{float}, @code{double}, and
14624 @code{long double} (if supported by the target platform).
14627 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
14630 @emph{Scalar types} include all of the above.
14635 The following operators are supported. They are listed here
14636 in order of increasing precedence:
14640 The comma or sequencing operator. Expressions in a comma-separated list
14641 are evaluated from left to right, with the result of the entire
14642 expression being the last expression evaluated.
14645 Assignment. The value of an assignment expression is the value
14646 assigned. Defined on scalar types.
14649 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
14650 and translated to @w{@code{@var{a} = @var{a op b}}}.
14651 @w{@code{@var{op}=}} and @code{=} have the same precedence. The operator
14652 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
14653 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
14656 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
14657 of as: if @var{a} then @var{b} else @var{c}. The argument @var{a}
14658 should be of an integral type.
14661 Logical @sc{or}. Defined on integral types.
14664 Logical @sc{and}. Defined on integral types.
14667 Bitwise @sc{or}. Defined on integral types.
14670 Bitwise exclusive-@sc{or}. Defined on integral types.
14673 Bitwise @sc{and}. Defined on integral types.
14676 Equality and inequality. Defined on scalar types. The value of these
14677 expressions is 0 for false and non-zero for true.
14679 @item <@r{, }>@r{, }<=@r{, }>=
14680 Less than, greater than, less than or equal, greater than or equal.
14681 Defined on scalar types. The value of these expressions is 0 for false
14682 and non-zero for true.
14685 left shift, and right shift. Defined on integral types.
14688 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
14691 Addition and subtraction. Defined on integral types, floating-point types and
14694 @item *@r{, }/@r{, }%
14695 Multiplication, division, and modulus. Multiplication and division are
14696 defined on integral and floating-point types. Modulus is defined on
14700 Increment and decrement. When appearing before a variable, the
14701 operation is performed before the variable is used in an expression;
14702 when appearing after it, the variable's value is used before the
14703 operation takes place.
14706 Pointer dereferencing. Defined on pointer types. Same precedence as
14710 Address operator. Defined on variables. Same precedence as @code{++}.
14712 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
14713 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
14714 to examine the address
14715 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
14719 Negative. Defined on integral and floating-point types. Same
14720 precedence as @code{++}.
14723 Logical negation. Defined on integral types. Same precedence as
14727 Bitwise complement operator. Defined on integral types. Same precedence as
14732 Structure member, and pointer-to-structure member. For convenience,
14733 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
14734 pointer based on the stored type information.
14735 Defined on @code{struct} and @code{union} data.
14738 Dereferences of pointers to members.
14741 Array indexing. @code{@var{a}[@var{i}]} is defined as
14742 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
14745 Function parameter list. Same precedence as @code{->}.
14748 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
14749 and @code{class} types.
14752 Doubled colons also represent the @value{GDBN} scope operator
14753 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
14757 If an operator is redefined in the user code, @value{GDBN} usually
14758 attempts to invoke the redefined version instead of using the operator's
14759 predefined meaning.
14762 @subsubsection C and C@t{++} Constants
14764 @cindex C and C@t{++} constants
14766 @value{GDBN} allows you to express the constants of C and C@t{++} in the
14771 Integer constants are a sequence of digits. Octal constants are
14772 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
14773 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
14774 @samp{l}, specifying that the constant should be treated as a
14778 Floating point constants are a sequence of digits, followed by a decimal
14779 point, followed by a sequence of digits, and optionally followed by an
14780 exponent. An exponent is of the form:
14781 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
14782 sequence of digits. The @samp{+} is optional for positive exponents.
14783 A floating-point constant may also end with a letter @samp{f} or
14784 @samp{F}, specifying that the constant should be treated as being of
14785 the @code{float} (as opposed to the default @code{double}) type; or with
14786 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
14790 Enumerated constants consist of enumerated identifiers, or their
14791 integral equivalents.
14794 Character constants are a single character surrounded by single quotes
14795 (@code{'}), or a number---the ordinal value of the corresponding character
14796 (usually its @sc{ascii} value). Within quotes, the single character may
14797 be represented by a letter or by @dfn{escape sequences}, which are of
14798 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
14799 of the character's ordinal value; or of the form @samp{\@var{x}}, where
14800 @samp{@var{x}} is a predefined special character---for example,
14801 @samp{\n} for newline.
14803 Wide character constants can be written by prefixing a character
14804 constant with @samp{L}, as in C. For example, @samp{L'x'} is the wide
14805 form of @samp{x}. The target wide character set is used when
14806 computing the value of this constant (@pxref{Character Sets}).
14809 String constants are a sequence of character constants surrounded by
14810 double quotes (@code{"}). Any valid character constant (as described
14811 above) may appear. Double quotes within the string must be preceded by
14812 a backslash, so for instance @samp{"a\"b'c"} is a string of five
14815 Wide string constants can be written by prefixing a string constant
14816 with @samp{L}, as in C. The target wide character set is used when
14817 computing the value of this constant (@pxref{Character Sets}).
14820 Pointer constants are an integral value. You can also write pointers
14821 to constants using the C operator @samp{&}.
14824 Array constants are comma-separated lists surrounded by braces @samp{@{}
14825 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
14826 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
14827 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
14830 @node C Plus Plus Expressions
14831 @subsubsection C@t{++} Expressions
14833 @cindex expressions in C@t{++}
14834 @value{GDBN} expression handling can interpret most C@t{++} expressions.
14836 @cindex debugging C@t{++} programs
14837 @cindex C@t{++} compilers
14838 @cindex debug formats and C@t{++}
14839 @cindex @value{NGCC} and C@t{++}
14841 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use
14842 the proper compiler and the proper debug format. Currently,
14843 @value{GDBN} works best when debugging C@t{++} code that is compiled
14844 with the most recent version of @value{NGCC} possible. The DWARF
14845 debugging format is preferred; @value{NGCC} defaults to this on most
14846 popular platforms. Other compilers and/or debug formats are likely to
14847 work badly or not at all when using @value{GDBN} to debug C@t{++}
14848 code. @xref{Compilation}.
14853 @cindex member functions
14855 Member function calls are allowed; you can use expressions like
14858 count = aml->GetOriginal(x, y)
14861 @vindex this@r{, inside C@t{++} member functions}
14862 @cindex namespace in C@t{++}
14864 While a member function is active (in the selected stack frame), your
14865 expressions have the same namespace available as the member function;
14866 that is, @value{GDBN} allows implicit references to the class instance
14867 pointer @code{this} following the same rules as C@t{++}. @code{using}
14868 declarations in the current scope are also respected by @value{GDBN}.
14870 @cindex call overloaded functions
14871 @cindex overloaded functions, calling
14872 @cindex type conversions in C@t{++}
14874 You can call overloaded functions; @value{GDBN} resolves the function
14875 call to the right definition, with some restrictions. @value{GDBN} does not
14876 perform overload resolution involving user-defined type conversions,
14877 calls to constructors, or instantiations of templates that do not exist
14878 in the program. It also cannot handle ellipsis argument lists or
14881 It does perform integral conversions and promotions, floating-point
14882 promotions, arithmetic conversions, pointer conversions, conversions of
14883 class objects to base classes, and standard conversions such as those of
14884 functions or arrays to pointers; it requires an exact match on the
14885 number of function arguments.
14887 Overload resolution is always performed, unless you have specified
14888 @code{set overload-resolution off}. @xref{Debugging C Plus Plus,
14889 ,@value{GDBN} Features for C@t{++}}.
14891 You must specify @code{set overload-resolution off} in order to use an
14892 explicit function signature to call an overloaded function, as in
14894 p 'foo(char,int)'('x', 13)
14897 The @value{GDBN} command-completion facility can simplify this;
14898 see @ref{Completion, ,Command Completion}.
14900 @cindex reference declarations
14902 @value{GDBN} understands variables declared as C@t{++} lvalue or rvalue
14903 references; you can use them in expressions just as you do in C@t{++}
14904 source---they are automatically dereferenced.
14906 In the parameter list shown when @value{GDBN} displays a frame, the values of
14907 reference variables are not displayed (unlike other variables); this
14908 avoids clutter, since references are often used for large structures.
14909 The @emph{address} of a reference variable is always shown, unless
14910 you have specified @samp{set print address off}.
14913 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
14914 expressions can use it just as expressions in your program do. Since
14915 one scope may be defined in another, you can use @code{::} repeatedly if
14916 necessary, for example in an expression like
14917 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
14918 resolving name scope by reference to source files, in both C and C@t{++}
14919 debugging (@pxref{Variables, ,Program Variables}).
14922 @value{GDBN} performs argument-dependent lookup, following the C@t{++}
14927 @subsubsection C and C@t{++} Defaults
14929 @cindex C and C@t{++} defaults
14931 If you allow @value{GDBN} to set range checking automatically, it
14932 defaults to @code{off} whenever the working language changes to
14933 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
14934 selects the working language.
14936 If you allow @value{GDBN} to set the language automatically, it
14937 recognizes source files whose names end with @file{.c}, @file{.C}, or
14938 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
14939 these files, it sets the working language to C or C@t{++}.
14940 @xref{Automatically, ,Having @value{GDBN} Infer the Source Language},
14941 for further details.
14944 @subsubsection C and C@t{++} Type and Range Checks
14946 @cindex C and C@t{++} checks
14948 By default, when @value{GDBN} parses C or C@t{++} expressions, strict type
14949 checking is used. However, if you turn type checking off, @value{GDBN}
14950 will allow certain non-standard conversions, such as promoting integer
14951 constants to pointers.
14953 Range checking, if turned on, is done on mathematical operations. Array
14954 indices are not checked, since they are often used to index a pointer
14955 that is not itself an array.
14958 @subsubsection @value{GDBN} and C
14960 The @code{set print union} and @code{show print union} commands apply to
14961 the @code{union} type. When set to @samp{on}, any @code{union} that is
14962 inside a @code{struct} or @code{class} is also printed. Otherwise, it
14963 appears as @samp{@{...@}}.
14965 The @code{@@} operator aids in the debugging of dynamic arrays, formed
14966 with pointers and a memory allocation function. @xref{Expressions,
14969 @node Debugging C Plus Plus
14970 @subsubsection @value{GDBN} Features for C@t{++}
14972 @cindex commands for C@t{++}
14974 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
14975 designed specifically for use with C@t{++}. Here is a summary:
14978 @cindex break in overloaded functions
14979 @item @r{breakpoint menus}
14980 When you want a breakpoint in a function whose name is overloaded,
14981 @value{GDBN} has the capability to display a menu of possible breakpoint
14982 locations to help you specify which function definition you want.
14983 @xref{Ambiguous Expressions,,Ambiguous Expressions}.
14985 @cindex overloading in C@t{++}
14986 @item rbreak @var{regex}
14987 Setting breakpoints using regular expressions is helpful for setting
14988 breakpoints on overloaded functions that are not members of any special
14990 @xref{Set Breaks, ,Setting Breakpoints}.
14992 @cindex C@t{++} exception handling
14994 @itemx catch rethrow
14996 Debug C@t{++} exception handling using these commands. @xref{Set
14997 Catchpoints, , Setting Catchpoints}.
14999 @cindex inheritance
15000 @item ptype @var{typename}
15001 Print inheritance relationships as well as other information for type
15003 @xref{Symbols, ,Examining the Symbol Table}.
15005 @item info vtbl @var{expression}.
15006 The @code{info vtbl} command can be used to display the virtual
15007 method tables of the object computed by @var{expression}. This shows
15008 one entry per virtual table; there may be multiple virtual tables when
15009 multiple inheritance is in use.
15011 @cindex C@t{++} demangling
15012 @item demangle @var{name}
15013 Demangle @var{name}.
15014 @xref{Symbols}, for a more complete description of the @code{demangle} command.
15016 @cindex C@t{++} symbol display
15017 @item set print demangle
15018 @itemx show print demangle
15019 @itemx set print asm-demangle
15020 @itemx show print asm-demangle
15021 Control whether C@t{++} symbols display in their source form, both when
15022 displaying code as C@t{++} source and when displaying disassemblies.
15023 @xref{Print Settings, ,Print Settings}.
15025 @item set print object
15026 @itemx show print object
15027 Choose whether to print derived (actual) or declared types of objects.
15028 @xref{Print Settings, ,Print Settings}.
15030 @item set print vtbl
15031 @itemx show print vtbl
15032 Control the format for printing virtual function tables.
15033 @xref{Print Settings, ,Print Settings}.
15034 (The @code{vtbl} commands do not work on programs compiled with the HP
15035 ANSI C@t{++} compiler (@code{aCC}).)
15037 @kindex set overload-resolution
15038 @cindex overloaded functions, overload resolution
15039 @item set overload-resolution on
15040 Enable overload resolution for C@t{++} expression evaluation. The default
15041 is on. For overloaded functions, @value{GDBN} evaluates the arguments
15042 and searches for a function whose signature matches the argument types,
15043 using the standard C@t{++} conversion rules (see @ref{C Plus Plus
15044 Expressions, ,C@t{++} Expressions}, for details).
15045 If it cannot find a match, it emits a message.
15047 @item set overload-resolution off
15048 Disable overload resolution for C@t{++} expression evaluation. For
15049 overloaded functions that are not class member functions, @value{GDBN}
15050 chooses the first function of the specified name that it finds in the
15051 symbol table, whether or not its arguments are of the correct type. For
15052 overloaded functions that are class member functions, @value{GDBN}
15053 searches for a function whose signature @emph{exactly} matches the
15056 @kindex show overload-resolution
15057 @item show overload-resolution
15058 Show the current setting of overload resolution.
15060 @item @r{Overloaded symbol names}
15061 You can specify a particular definition of an overloaded symbol, using
15062 the same notation that is used to declare such symbols in C@t{++}: type
15063 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
15064 also use the @value{GDBN} command-line word completion facilities to list the
15065 available choices, or to finish the type list for you.
15066 @xref{Completion,, Command Completion}, for details on how to do this.
15069 @node Decimal Floating Point
15070 @subsubsection Decimal Floating Point format
15071 @cindex decimal floating point format
15073 @value{GDBN} can examine, set and perform computations with numbers in
15074 decimal floating point format, which in the C language correspond to the
15075 @code{_Decimal32}, @code{_Decimal64} and @code{_Decimal128} types as
15076 specified by the extension to support decimal floating-point arithmetic.
15078 There are two encodings in use, depending on the architecture: BID (Binary
15079 Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for
15080 PowerPC and S/390. @value{GDBN} will use the appropriate encoding for the
15083 Because of a limitation in @file{libdecnumber}, the library used by @value{GDBN}
15084 to manipulate decimal floating point numbers, it is not possible to convert
15085 (using a cast, for example) integers wider than 32-bit to decimal float.
15087 In addition, in order to imitate @value{GDBN}'s behaviour with binary floating
15088 point computations, error checking in decimal float operations ignores
15089 underflow, overflow and divide by zero exceptions.
15091 In the PowerPC architecture, @value{GDBN} provides a set of pseudo-registers
15092 to inspect @code{_Decimal128} values stored in floating point registers.
15093 See @ref{PowerPC,,PowerPC} for more details.
15099 @value{GDBN} can be used to debug programs written in D and compiled with
15100 GDC, LDC or DMD compilers. Currently @value{GDBN} supports only one D
15101 specific feature --- dynamic arrays.
15106 @cindex Go (programming language)
15107 @value{GDBN} can be used to debug programs written in Go and compiled with
15108 @file{gccgo} or @file{6g} compilers.
15110 Here is a summary of the Go-specific features and restrictions:
15113 @cindex current Go package
15114 @item The current Go package
15115 The name of the current package does not need to be specified when
15116 specifying global variables and functions.
15118 For example, given the program:
15122 var myglob = "Shall we?"
15128 When stopped inside @code{main} either of these work:
15132 (gdb) p main.myglob
15135 @cindex builtin Go types
15136 @item Builtin Go types
15137 The @code{string} type is recognized by @value{GDBN} and is printed
15140 @cindex builtin Go functions
15141 @item Builtin Go functions
15142 The @value{GDBN} expression parser recognizes the @code{unsafe.Sizeof}
15143 function and handles it internally.
15145 @cindex restrictions on Go expressions
15146 @item Restrictions on Go expressions
15147 All Go operators are supported except @code{&^}.
15148 The Go @code{_} ``blank identifier'' is not supported.
15149 Automatic dereferencing of pointers is not supported.
15153 @subsection Objective-C
15155 @cindex Objective-C
15156 This section provides information about some commands and command
15157 options that are useful for debugging Objective-C code. See also
15158 @ref{Symbols, info classes}, and @ref{Symbols, info selectors}, for a
15159 few more commands specific to Objective-C support.
15162 * Method Names in Commands::
15163 * The Print Command with Objective-C::
15166 @node Method Names in Commands
15167 @subsubsection Method Names in Commands
15169 The following commands have been extended to accept Objective-C method
15170 names as line specifications:
15172 @kindex clear@r{, and Objective-C}
15173 @kindex break@r{, and Objective-C}
15174 @kindex info line@r{, and Objective-C}
15175 @kindex jump@r{, and Objective-C}
15176 @kindex list@r{, and Objective-C}
15180 @item @code{info line}
15185 A fully qualified Objective-C method name is specified as
15188 -[@var{Class} @var{methodName}]
15191 where the minus sign is used to indicate an instance method and a
15192 plus sign (not shown) is used to indicate a class method. The class
15193 name @var{Class} and method name @var{methodName} are enclosed in
15194 brackets, similar to the way messages are specified in Objective-C
15195 source code. For example, to set a breakpoint at the @code{create}
15196 instance method of class @code{Fruit} in the program currently being
15200 break -[Fruit create]
15203 To list ten program lines around the @code{initialize} class method,
15207 list +[NSText initialize]
15210 In the current version of @value{GDBN}, the plus or minus sign is
15211 required. In future versions of @value{GDBN}, the plus or minus
15212 sign will be optional, but you can use it to narrow the search. It
15213 is also possible to specify just a method name:
15219 You must specify the complete method name, including any colons. If
15220 your program's source files contain more than one @code{create} method,
15221 you'll be presented with a numbered list of classes that implement that
15222 method. Indicate your choice by number, or type @samp{0} to exit if
15225 As another example, to clear a breakpoint established at the
15226 @code{makeKeyAndOrderFront:} method of the @code{NSWindow} class, enter:
15229 clear -[NSWindow makeKeyAndOrderFront:]
15232 @node The Print Command with Objective-C
15233 @subsubsection The Print Command With Objective-C
15234 @cindex Objective-C, print objects
15235 @kindex print-object
15236 @kindex po @r{(@code{print-object})}
15238 The print command has also been extended to accept methods. For example:
15241 print -[@var{object} hash]
15244 @cindex print an Objective-C object description
15245 @cindex @code{_NSPrintForDebugger}, and printing Objective-C objects
15247 will tell @value{GDBN} to send the @code{hash} message to @var{object}
15248 and print the result. Also, an additional command has been added,
15249 @code{print-object} or @code{po} for short, which is meant to print
15250 the description of an object. However, this command may only work
15251 with certain Objective-C libraries that have a particular hook
15252 function, @code{_NSPrintForDebugger}, defined.
15255 @subsection OpenCL C
15258 This section provides information about @value{GDBN}s OpenCL C support.
15261 * OpenCL C Datatypes::
15262 * OpenCL C Expressions::
15263 * OpenCL C Operators::
15266 @node OpenCL C Datatypes
15267 @subsubsection OpenCL C Datatypes
15269 @cindex OpenCL C Datatypes
15270 @value{GDBN} supports the builtin scalar and vector datatypes specified
15271 by OpenCL 1.1. In addition the half- and double-precision floating point
15272 data types of the @code{cl_khr_fp16} and @code{cl_khr_fp64} OpenCL
15273 extensions are also known to @value{GDBN}.
15275 @node OpenCL C Expressions
15276 @subsubsection OpenCL C Expressions
15278 @cindex OpenCL C Expressions
15279 @value{GDBN} supports accesses to vector components including the access as
15280 lvalue where possible. Since OpenCL C is based on C99 most C expressions
15281 supported by @value{GDBN} can be used as well.
15283 @node OpenCL C Operators
15284 @subsubsection OpenCL C Operators
15286 @cindex OpenCL C Operators
15287 @value{GDBN} supports the operators specified by OpenCL 1.1 for scalar and
15291 @subsection Fortran
15292 @cindex Fortran-specific support in @value{GDBN}
15294 @value{GDBN} can be used to debug programs written in Fortran, but it
15295 currently supports only the features of Fortran 77 language.
15297 @cindex trailing underscore, in Fortran symbols
15298 Some Fortran compilers (@sc{gnu} Fortran 77 and Fortran 95 compilers
15299 among them) append an underscore to the names of variables and
15300 functions. When you debug programs compiled by those compilers, you
15301 will need to refer to variables and functions with a trailing
15305 * Fortran Operators:: Fortran operators and expressions
15306 * Fortran Defaults:: Default settings for Fortran
15307 * Special Fortran Commands:: Special @value{GDBN} commands for Fortran
15310 @node Fortran Operators
15311 @subsubsection Fortran Operators and Expressions
15313 @cindex Fortran operators and expressions
15315 Operators must be defined on values of specific types. For instance,
15316 @code{+} is defined on numbers, but not on characters or other non-
15317 arithmetic types. Operators are often defined on groups of types.
15321 The exponentiation operator. It raises the first operand to the power
15325 The range operator. Normally used in the form of array(low:high) to
15326 represent a section of array.
15329 The access component operator. Normally used to access elements in derived
15330 types. Also suitable for unions. As unions aren't part of regular Fortran,
15331 this can only happen when accessing a register that uses a gdbarch-defined
15335 @node Fortran Defaults
15336 @subsubsection Fortran Defaults
15338 @cindex Fortran Defaults
15340 Fortran symbols are usually case-insensitive, so @value{GDBN} by
15341 default uses case-insensitive matches for Fortran symbols. You can
15342 change that with the @samp{set case-insensitive} command, see
15343 @ref{Symbols}, for the details.
15345 @node Special Fortran Commands
15346 @subsubsection Special Fortran Commands
15348 @cindex Special Fortran commands
15350 @value{GDBN} has some commands to support Fortran-specific features,
15351 such as displaying common blocks.
15354 @cindex @code{COMMON} blocks, Fortran
15355 @kindex info common
15356 @item info common @r{[}@var{common-name}@r{]}
15357 This command prints the values contained in the Fortran @code{COMMON}
15358 block whose name is @var{common-name}. With no argument, the names of
15359 all @code{COMMON} blocks visible at the current program location are
15366 @cindex Pascal support in @value{GDBN}, limitations
15367 Debugging Pascal programs which use sets, subranges, file variables, or
15368 nested functions does not currently work. @value{GDBN} does not support
15369 entering expressions, printing values, or similar features using Pascal
15372 The Pascal-specific command @code{set print pascal_static-members}
15373 controls whether static members of Pascal objects are displayed.
15374 @xref{Print Settings, pascal_static-members}.
15379 @value{GDBN} supports the @url{https://www.rust-lang.org/, Rust
15380 Programming Language}. Type- and value-printing, and expression
15381 parsing, are reasonably complete. However, there are a few
15382 peculiarities and holes to be aware of.
15386 Linespecs (@pxref{Specify Location}) are never relative to the current
15387 crate. Instead, they act as if there were a global namespace of
15388 crates, somewhat similar to the way @code{extern crate} behaves.
15390 That is, if @value{GDBN} is stopped at a breakpoint in a function in
15391 crate @samp{A}, module @samp{B}, then @code{break B::f} will attempt
15392 to set a breakpoint in a function named @samp{f} in a crate named
15395 As a consequence of this approach, linespecs also cannot refer to
15396 items using @samp{self::} or @samp{super::}.
15399 Because @value{GDBN} implements Rust name-lookup semantics in
15400 expressions, it will sometimes prepend the current crate to a name.
15401 For example, if @value{GDBN} is stopped at a breakpoint in the crate
15402 @samp{K}, then @code{print ::x::y} will try to find the symbol
15405 However, since it is useful to be able to refer to other crates when
15406 debugging, @value{GDBN} provides the @code{extern} extension to
15407 circumvent this. To use the extension, just put @code{extern} before
15408 a path expression to refer to the otherwise unavailable ``global''
15411 In the above example, if you wanted to refer to the symbol @samp{y} in
15412 the crate @samp{x}, you would use @code{print extern x::y}.
15415 The Rust expression evaluator does not support ``statement-like''
15416 expressions such as @code{if} or @code{match}, or lambda expressions.
15419 Tuple expressions are not implemented.
15422 The Rust expression evaluator does not currently implement the
15423 @code{Drop} trait. Objects that may be created by the evaluator will
15424 never be destroyed.
15427 @value{GDBN} does not implement type inference for generics. In order
15428 to call generic functions or otherwise refer to generic items, you
15429 will have to specify the type parameters manually.
15432 @value{GDBN} currently uses the C@t{++} demangler for Rust. In most
15433 cases this does not cause any problems. However, in an expression
15434 context, completing a generic function name will give syntactically
15435 invalid results. This happens because Rust requires the @samp{::}
15436 operator between the function name and its generic arguments. For
15437 example, @value{GDBN} might provide a completion like
15438 @code{crate::f<u32>}, where the parser would require
15439 @code{crate::f::<u32>}.
15442 As of this writing, the Rust compiler (version 1.8) has a few holes in
15443 the debugging information it generates. These holes prevent certain
15444 features from being implemented by @value{GDBN}:
15448 Method calls cannot be made via traits.
15451 Trait objects cannot be created or inspected.
15454 Operator overloading is not implemented.
15457 When debugging in a monomorphized function, you cannot use the generic
15461 The type @code{Self} is not available.
15464 @code{use} statements are not available, so some names may not be
15465 available in the crate.
15470 @subsection Modula-2
15472 @cindex Modula-2, @value{GDBN} support
15474 The extensions made to @value{GDBN} to support Modula-2 only support
15475 output from the @sc{gnu} Modula-2 compiler (which is currently being
15476 developed). Other Modula-2 compilers are not currently supported, and
15477 attempting to debug executables produced by them is most likely
15478 to give an error as @value{GDBN} reads in the executable's symbol
15481 @cindex expressions in Modula-2
15483 * M2 Operators:: Built-in operators
15484 * Built-In Func/Proc:: Built-in functions and procedures
15485 * M2 Constants:: Modula-2 constants
15486 * M2 Types:: Modula-2 types
15487 * M2 Defaults:: Default settings for Modula-2
15488 * Deviations:: Deviations from standard Modula-2
15489 * M2 Checks:: Modula-2 type and range checks
15490 * M2 Scope:: The scope operators @code{::} and @code{.}
15491 * GDB/M2:: @value{GDBN} and Modula-2
15495 @subsubsection Operators
15496 @cindex Modula-2 operators
15498 Operators must be defined on values of specific types. For instance,
15499 @code{+} is defined on numbers, but not on structures. Operators are
15500 often defined on groups of types. For the purposes of Modula-2, the
15501 following definitions hold:
15506 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
15510 @emph{Character types} consist of @code{CHAR} and its subranges.
15513 @emph{Floating-point types} consist of @code{REAL}.
15516 @emph{Pointer types} consist of anything declared as @code{POINTER TO
15520 @emph{Scalar types} consist of all of the above.
15523 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
15526 @emph{Boolean types} consist of @code{BOOLEAN}.
15530 The following operators are supported, and appear in order of
15531 increasing precedence:
15535 Function argument or array index separator.
15538 Assignment. The value of @var{var} @code{:=} @var{value} is
15542 Less than, greater than on integral, floating-point, or enumerated
15546 Less than or equal to, greater than or equal to
15547 on integral, floating-point and enumerated types, or set inclusion on
15548 set types. Same precedence as @code{<}.
15550 @item =@r{, }<>@r{, }#
15551 Equality and two ways of expressing inequality, valid on scalar types.
15552 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
15553 available for inequality, since @code{#} conflicts with the script
15557 Set membership. Defined on set types and the types of their members.
15558 Same precedence as @code{<}.
15561 Boolean disjunction. Defined on boolean types.
15564 Boolean conjunction. Defined on boolean types.
15567 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
15570 Addition and subtraction on integral and floating-point types, or union
15571 and difference on set types.
15574 Multiplication on integral and floating-point types, or set intersection
15578 Division on floating-point types, or symmetric set difference on set
15579 types. Same precedence as @code{*}.
15582 Integer division and remainder. Defined on integral types. Same
15583 precedence as @code{*}.
15586 Negative. Defined on @code{INTEGER} and @code{REAL} data.
15589 Pointer dereferencing. Defined on pointer types.
15592 Boolean negation. Defined on boolean types. Same precedence as
15596 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
15597 precedence as @code{^}.
15600 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
15603 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
15607 @value{GDBN} and Modula-2 scope operators.
15611 @emph{Warning:} Set expressions and their operations are not yet supported, so @value{GDBN}
15612 treats the use of the operator @code{IN}, or the use of operators
15613 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
15614 @code{<=}, and @code{>=} on sets as an error.
15618 @node Built-In Func/Proc
15619 @subsubsection Built-in Functions and Procedures
15620 @cindex Modula-2 built-ins
15622 Modula-2 also makes available several built-in procedures and functions.
15623 In describing these, the following metavariables are used:
15628 represents an @code{ARRAY} variable.
15631 represents a @code{CHAR} constant or variable.
15634 represents a variable or constant of integral type.
15637 represents an identifier that belongs to a set. Generally used in the
15638 same function with the metavariable @var{s}. The type of @var{s} should
15639 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
15642 represents a variable or constant of integral or floating-point type.
15645 represents a variable or constant of floating-point type.
15651 represents a variable.
15654 represents a variable or constant of one of many types. See the
15655 explanation of the function for details.
15658 All Modula-2 built-in procedures also return a result, described below.
15662 Returns the absolute value of @var{n}.
15665 If @var{c} is a lower case letter, it returns its upper case
15666 equivalent, otherwise it returns its argument.
15669 Returns the character whose ordinal value is @var{i}.
15672 Decrements the value in the variable @var{v} by one. Returns the new value.
15674 @item DEC(@var{v},@var{i})
15675 Decrements the value in the variable @var{v} by @var{i}. Returns the
15678 @item EXCL(@var{m},@var{s})
15679 Removes the element @var{m} from the set @var{s}. Returns the new
15682 @item FLOAT(@var{i})
15683 Returns the floating point equivalent of the integer @var{i}.
15685 @item HIGH(@var{a})
15686 Returns the index of the last member of @var{a}.
15689 Increments the value in the variable @var{v} by one. Returns the new value.
15691 @item INC(@var{v},@var{i})
15692 Increments the value in the variable @var{v} by @var{i}. Returns the
15695 @item INCL(@var{m},@var{s})
15696 Adds the element @var{m} to the set @var{s} if it is not already
15697 there. Returns the new set.
15700 Returns the maximum value of the type @var{t}.
15703 Returns the minimum value of the type @var{t}.
15706 Returns boolean TRUE if @var{i} is an odd number.
15709 Returns the ordinal value of its argument. For example, the ordinal
15710 value of a character is its @sc{ascii} value (on machines supporting
15711 the @sc{ascii} character set). The argument @var{x} must be of an
15712 ordered type, which include integral, character and enumerated types.
15714 @item SIZE(@var{x})
15715 Returns the size of its argument. The argument @var{x} can be a
15716 variable or a type.
15718 @item TRUNC(@var{r})
15719 Returns the integral part of @var{r}.
15721 @item TSIZE(@var{x})
15722 Returns the size of its argument. The argument @var{x} can be a
15723 variable or a type.
15725 @item VAL(@var{t},@var{i})
15726 Returns the member of the type @var{t} whose ordinal value is @var{i}.
15730 @emph{Warning:} Sets and their operations are not yet supported, so
15731 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
15735 @cindex Modula-2 constants
15737 @subsubsection Constants
15739 @value{GDBN} allows you to express the constants of Modula-2 in the following
15745 Integer constants are simply a sequence of digits. When used in an
15746 expression, a constant is interpreted to be type-compatible with the
15747 rest of the expression. Hexadecimal integers are specified by a
15748 trailing @samp{H}, and octal integers by a trailing @samp{B}.
15751 Floating point constants appear as a sequence of digits, followed by a
15752 decimal point and another sequence of digits. An optional exponent can
15753 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
15754 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
15755 digits of the floating point constant must be valid decimal (base 10)
15759 Character constants consist of a single character enclosed by a pair of
15760 like quotes, either single (@code{'}) or double (@code{"}). They may
15761 also be expressed by their ordinal value (their @sc{ascii} value, usually)
15762 followed by a @samp{C}.
15765 String constants consist of a sequence of characters enclosed by a
15766 pair of like quotes, either single (@code{'}) or double (@code{"}).
15767 Escape sequences in the style of C are also allowed. @xref{C
15768 Constants, ,C and C@t{++} Constants}, for a brief explanation of escape
15772 Enumerated constants consist of an enumerated identifier.
15775 Boolean constants consist of the identifiers @code{TRUE} and
15779 Pointer constants consist of integral values only.
15782 Set constants are not yet supported.
15786 @subsubsection Modula-2 Types
15787 @cindex Modula-2 types
15789 Currently @value{GDBN} can print the following data types in Modula-2
15790 syntax: array types, record types, set types, pointer types, procedure
15791 types, enumerated types, subrange types and base types. You can also
15792 print the contents of variables declared using these type.
15793 This section gives a number of simple source code examples together with
15794 sample @value{GDBN} sessions.
15796 The first example contains the following section of code:
15805 and you can request @value{GDBN} to interrogate the type and value of
15806 @code{r} and @code{s}.
15809 (@value{GDBP}) print s
15811 (@value{GDBP}) ptype s
15813 (@value{GDBP}) print r
15815 (@value{GDBP}) ptype r
15820 Likewise if your source code declares @code{s} as:
15824 s: SET ['A'..'Z'] ;
15828 then you may query the type of @code{s} by:
15831 (@value{GDBP}) ptype s
15832 type = SET ['A'..'Z']
15836 Note that at present you cannot interactively manipulate set
15837 expressions using the debugger.
15839 The following example shows how you might declare an array in Modula-2
15840 and how you can interact with @value{GDBN} to print its type and contents:
15844 s: ARRAY [-10..10] OF CHAR ;
15848 (@value{GDBP}) ptype s
15849 ARRAY [-10..10] OF CHAR
15852 Note that the array handling is not yet complete and although the type
15853 is printed correctly, expression handling still assumes that all
15854 arrays have a lower bound of zero and not @code{-10} as in the example
15857 Here are some more type related Modula-2 examples:
15861 colour = (blue, red, yellow, green) ;
15862 t = [blue..yellow] ;
15870 The @value{GDBN} interaction shows how you can query the data type
15871 and value of a variable.
15874 (@value{GDBP}) print s
15876 (@value{GDBP}) ptype t
15877 type = [blue..yellow]
15881 In this example a Modula-2 array is declared and its contents
15882 displayed. Observe that the contents are written in the same way as
15883 their @code{C} counterparts.
15887 s: ARRAY [1..5] OF CARDINAL ;
15893 (@value{GDBP}) print s
15894 $1 = @{1, 0, 0, 0, 0@}
15895 (@value{GDBP}) ptype s
15896 type = ARRAY [1..5] OF CARDINAL
15899 The Modula-2 language interface to @value{GDBN} also understands
15900 pointer types as shown in this example:
15904 s: POINTER TO ARRAY [1..5] OF CARDINAL ;
15911 and you can request that @value{GDBN} describes the type of @code{s}.
15914 (@value{GDBP}) ptype s
15915 type = POINTER TO ARRAY [1..5] OF CARDINAL
15918 @value{GDBN} handles compound types as we can see in this example.
15919 Here we combine array types, record types, pointer types and subrange
15930 myarray = ARRAY myrange OF CARDINAL ;
15931 myrange = [-2..2] ;
15933 s: POINTER TO ARRAY myrange OF foo ;
15937 and you can ask @value{GDBN} to describe the type of @code{s} as shown
15941 (@value{GDBP}) ptype s
15942 type = POINTER TO ARRAY [-2..2] OF foo = RECORD
15945 f3 : ARRAY [-2..2] OF CARDINAL;
15950 @subsubsection Modula-2 Defaults
15951 @cindex Modula-2 defaults
15953 If type and range checking are set automatically by @value{GDBN}, they
15954 both default to @code{on} whenever the working language changes to
15955 Modula-2. This happens regardless of whether you or @value{GDBN}
15956 selected the working language.
15958 If you allow @value{GDBN} to set the language automatically, then entering
15959 code compiled from a file whose name ends with @file{.mod} sets the
15960 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN}
15961 Infer the Source Language}, for further details.
15964 @subsubsection Deviations from Standard Modula-2
15965 @cindex Modula-2, deviations from
15967 A few changes have been made to make Modula-2 programs easier to debug.
15968 This is done primarily via loosening its type strictness:
15972 Unlike in standard Modula-2, pointer constants can be formed by
15973 integers. This allows you to modify pointer variables during
15974 debugging. (In standard Modula-2, the actual address contained in a
15975 pointer variable is hidden from you; it can only be modified
15976 through direct assignment to another pointer variable or expression that
15977 returned a pointer.)
15980 C escape sequences can be used in strings and characters to represent
15981 non-printable characters. @value{GDBN} prints out strings with these
15982 escape sequences embedded. Single non-printable characters are
15983 printed using the @samp{CHR(@var{nnn})} format.
15986 The assignment operator (@code{:=}) returns the value of its right-hand
15990 All built-in procedures both modify @emph{and} return their argument.
15994 @subsubsection Modula-2 Type and Range Checks
15995 @cindex Modula-2 checks
15998 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
16001 @c FIXME remove warning when type/range checks added
16003 @value{GDBN} considers two Modula-2 variables type equivalent if:
16007 They are of types that have been declared equivalent via a @code{TYPE
16008 @var{t1} = @var{t2}} statement
16011 They have been declared on the same line. (Note: This is true of the
16012 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
16015 As long as type checking is enabled, any attempt to combine variables
16016 whose types are not equivalent is an error.
16018 Range checking is done on all mathematical operations, assignment, array
16019 index bounds, and all built-in functions and procedures.
16022 @subsubsection The Scope Operators @code{::} and @code{.}
16024 @cindex @code{.}, Modula-2 scope operator
16025 @cindex colon, doubled as scope operator
16027 @vindex colon-colon@r{, in Modula-2}
16028 @c Info cannot handle :: but TeX can.
16031 @vindex ::@r{, in Modula-2}
16034 There are a few subtle differences between the Modula-2 scope operator
16035 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
16040 @var{module} . @var{id}
16041 @var{scope} :: @var{id}
16045 where @var{scope} is the name of a module or a procedure,
16046 @var{module} the name of a module, and @var{id} is any declared
16047 identifier within your program, except another module.
16049 Using the @code{::} operator makes @value{GDBN} search the scope
16050 specified by @var{scope} for the identifier @var{id}. If it is not
16051 found in the specified scope, then @value{GDBN} searches all scopes
16052 enclosing the one specified by @var{scope}.
16054 Using the @code{.} operator makes @value{GDBN} search the current scope for
16055 the identifier specified by @var{id} that was imported from the
16056 definition module specified by @var{module}. With this operator, it is
16057 an error if the identifier @var{id} was not imported from definition
16058 module @var{module}, or if @var{id} is not an identifier in
16062 @subsubsection @value{GDBN} and Modula-2
16064 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
16065 Five subcommands of @code{set print} and @code{show print} apply
16066 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
16067 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
16068 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
16069 analogue in Modula-2.
16071 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
16072 with any language, is not useful with Modula-2. Its
16073 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
16074 created in Modula-2 as they can in C or C@t{++}. However, because an
16075 address can be specified by an integral constant, the construct
16076 @samp{@{@var{type}@}@var{adrexp}} is still useful.
16078 @cindex @code{#} in Modula-2
16079 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
16080 interpreted as the beginning of a comment. Use @code{<>} instead.
16086 The extensions made to @value{GDBN} for Ada only support
16087 output from the @sc{gnu} Ada (GNAT) compiler.
16088 Other Ada compilers are not currently supported, and
16089 attempting to debug executables produced by them is most likely
16093 @cindex expressions in Ada
16095 * Ada Mode Intro:: General remarks on the Ada syntax
16096 and semantics supported by Ada mode
16098 * Omissions from Ada:: Restrictions on the Ada expression syntax.
16099 * Additions to Ada:: Extensions of the Ada expression syntax.
16100 * Overloading support for Ada:: Support for expressions involving overloaded
16102 * Stopping Before Main Program:: Debugging the program during elaboration.
16103 * Ada Exceptions:: Ada Exceptions
16104 * Ada Tasks:: Listing and setting breakpoints in tasks.
16105 * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files
16106 * Ravenscar Profile:: Tasking Support when using the Ravenscar
16108 * Ada Glitches:: Known peculiarities of Ada mode.
16111 @node Ada Mode Intro
16112 @subsubsection Introduction
16113 @cindex Ada mode, general
16115 The Ada mode of @value{GDBN} supports a fairly large subset of Ada expression
16116 syntax, with some extensions.
16117 The philosophy behind the design of this subset is
16121 That @value{GDBN} should provide basic literals and access to operations for
16122 arithmetic, dereferencing, field selection, indexing, and subprogram calls,
16123 leaving more sophisticated computations to subprograms written into the
16124 program (which therefore may be called from @value{GDBN}).
16127 That type safety and strict adherence to Ada language restrictions
16128 are not particularly important to the @value{GDBN} user.
16131 That brevity is important to the @value{GDBN} user.
16134 Thus, for brevity, the debugger acts as if all names declared in
16135 user-written packages are directly visible, even if they are not visible
16136 according to Ada rules, thus making it unnecessary to fully qualify most
16137 names with their packages, regardless of context. Where this causes
16138 ambiguity, @value{GDBN} asks the user's intent.
16140 The debugger will start in Ada mode if it detects an Ada main program.
16141 As for other languages, it will enter Ada mode when stopped in a program that
16142 was translated from an Ada source file.
16144 While in Ada mode, you may use `@t{--}' for comments. This is useful
16145 mostly for documenting command files. The standard @value{GDBN} comment
16146 (@samp{#}) still works at the beginning of a line in Ada mode, but not in the
16147 middle (to allow based literals).
16149 @node Omissions from Ada
16150 @subsubsection Omissions from Ada
16151 @cindex Ada, omissions from
16153 Here are the notable omissions from the subset:
16157 Only a subset of the attributes are supported:
16161 @t{'First}, @t{'Last}, and @t{'Length}
16162 on array objects (not on types and subtypes).
16165 @t{'Min} and @t{'Max}.
16168 @t{'Pos} and @t{'Val}.
16174 @t{'Range} on array objects (not subtypes), but only as the right
16175 operand of the membership (@code{in}) operator.
16178 @t{'Access}, @t{'Unchecked_Access}, and
16179 @t{'Unrestricted_Access} (a GNAT extension).
16187 @code{Characters.Latin_1} are not available and
16188 concatenation is not implemented. Thus, escape characters in strings are
16189 not currently available.
16192 Equality tests (@samp{=} and @samp{/=}) on arrays test for bitwise
16193 equality of representations. They will generally work correctly
16194 for strings and arrays whose elements have integer or enumeration types.
16195 They may not work correctly for arrays whose element
16196 types have user-defined equality, for arrays of real values
16197 (in particular, IEEE-conformant floating point, because of negative
16198 zeroes and NaNs), and for arrays whose elements contain unused bits with
16199 indeterminate values.
16202 The other component-by-component array operations (@code{and}, @code{or},
16203 @code{xor}, @code{not}, and relational tests other than equality)
16204 are not implemented.
16207 @cindex array aggregates (Ada)
16208 @cindex record aggregates (Ada)
16209 @cindex aggregates (Ada)
16210 There is limited support for array and record aggregates. They are
16211 permitted only on the right sides of assignments, as in these examples:
16214 (@value{GDBP}) set An_Array := (1, 2, 3, 4, 5, 6)
16215 (@value{GDBP}) set An_Array := (1, others => 0)
16216 (@value{GDBP}) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6)
16217 (@value{GDBP}) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9))
16218 (@value{GDBP}) set A_Record := (1, "Peter", True);
16219 (@value{GDBP}) set A_Record := (Name => "Peter", Id => 1, Alive => True)
16223 discriminant's value by assigning an aggregate has an
16224 undefined effect if that discriminant is used within the record.
16225 However, you can first modify discriminants by directly assigning to
16226 them (which normally would not be allowed in Ada), and then performing an
16227 aggregate assignment. For example, given a variable @code{A_Rec}
16228 declared to have a type such as:
16231 type Rec (Len : Small_Integer := 0) is record
16233 Vals : IntArray (1 .. Len);
16237 you can assign a value with a different size of @code{Vals} with two
16241 (@value{GDBP}) set A_Rec.Len := 4
16242 (@value{GDBP}) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4))
16245 As this example also illustrates, @value{GDBN} is very loose about the usual
16246 rules concerning aggregates. You may leave out some of the
16247 components of an array or record aggregate (such as the @code{Len}
16248 component in the assignment to @code{A_Rec} above); they will retain their
16249 original values upon assignment. You may freely use dynamic values as
16250 indices in component associations. You may even use overlapping or
16251 redundant component associations, although which component values are
16252 assigned in such cases is not defined.
16255 Calls to dispatching subprograms are not implemented.
16258 The overloading algorithm is much more limited (i.e., less selective)
16259 than that of real Ada. It makes only limited use of the context in
16260 which a subexpression appears to resolve its meaning, and it is much
16261 looser in its rules for allowing type matches. As a result, some
16262 function calls will be ambiguous, and the user will be asked to choose
16263 the proper resolution.
16266 The @code{new} operator is not implemented.
16269 Entry calls are not implemented.
16272 Aside from printing, arithmetic operations on the native VAX floating-point
16273 formats are not supported.
16276 It is not possible to slice a packed array.
16279 The names @code{True} and @code{False}, when not part of a qualified name,
16280 are interpreted as if implicitly prefixed by @code{Standard}, regardless of
16282 Should your program
16283 redefine these names in a package or procedure (at best a dubious practice),
16284 you will have to use fully qualified names to access their new definitions.
16287 @node Additions to Ada
16288 @subsubsection Additions to Ada
16289 @cindex Ada, deviations from
16291 As it does for other languages, @value{GDBN} makes certain generic
16292 extensions to Ada (@pxref{Expressions}):
16296 If the expression @var{E} is a variable residing in memory (typically
16297 a local variable or array element) and @var{N} is a positive integer,
16298 then @code{@var{E}@@@var{N}} displays the values of @var{E} and the
16299 @var{N}-1 adjacent variables following it in memory as an array. In
16300 Ada, this operator is generally not necessary, since its prime use is
16301 in displaying parts of an array, and slicing will usually do this in
16302 Ada. However, there are occasional uses when debugging programs in
16303 which certain debugging information has been optimized away.
16306 @code{@var{B}::@var{var}} means ``the variable named @var{var} that
16307 appears in function or file @var{B}.'' When @var{B} is a file name,
16308 you must typically surround it in single quotes.
16311 The expression @code{@{@var{type}@} @var{addr}} means ``the variable of type
16312 @var{type} that appears at address @var{addr}.''
16315 A name starting with @samp{$} is a convenience variable
16316 (@pxref{Convenience Vars}) or a machine register (@pxref{Registers}).
16319 In addition, @value{GDBN} provides a few other shortcuts and outright
16320 additions specific to Ada:
16324 The assignment statement is allowed as an expression, returning
16325 its right-hand operand as its value. Thus, you may enter
16328 (@value{GDBP}) set x := y + 3
16329 (@value{GDBP}) print A(tmp := y + 1)
16333 The semicolon is allowed as an ``operator,'' returning as its value
16334 the value of its right-hand operand.
16335 This allows, for example,
16336 complex conditional breaks:
16339 (@value{GDBP}) break f
16340 (@value{GDBP}) condition 1 (report(i); k += 1; A(k) > 100)
16344 Rather than use catenation and symbolic character names to introduce special
16345 characters into strings, one may instead use a special bracket notation,
16346 which is also used to print strings. A sequence of characters of the form
16347 @samp{["@var{XX}"]} within a string or character literal denotes the
16348 (single) character whose numeric encoding is @var{XX} in hexadecimal. The
16349 sequence of characters @samp{["""]} also denotes a single quotation mark
16350 in strings. For example,
16352 "One line.["0a"]Next line.["0a"]"
16355 contains an ASCII newline character (@code{Ada.Characters.Latin_1.LF})
16359 The subtype used as a prefix for the attributes @t{'Pos}, @t{'Min}, and
16360 @t{'Max} is optional (and is ignored in any case). For example, it is valid
16364 (@value{GDBP}) print 'max(x, y)
16368 When printing arrays, @value{GDBN} uses positional notation when the
16369 array has a lower bound of 1, and uses a modified named notation otherwise.
16370 For example, a one-dimensional array of three integers with a lower bound
16371 of 3 might print as
16378 That is, in contrast to valid Ada, only the first component has a @code{=>}
16382 You may abbreviate attributes in expressions with any unique,
16383 multi-character subsequence of
16384 their names (an exact match gets preference).
16385 For example, you may use @t{a'len}, @t{a'gth}, or @t{a'lh}
16386 in place of @t{a'length}.
16389 @cindex quoting Ada internal identifiers
16390 Since Ada is case-insensitive, the debugger normally maps identifiers you type
16391 to lower case. The GNAT compiler uses upper-case characters for
16392 some of its internal identifiers, which are normally of no interest to users.
16393 For the rare occasions when you actually have to look at them,
16394 enclose them in angle brackets to avoid the lower-case mapping.
16397 (@value{GDBP}) print <JMPBUF_SAVE>[0]
16401 Printing an object of class-wide type or dereferencing an
16402 access-to-class-wide value will display all the components of the object's
16403 specific type (as indicated by its run-time tag). Likewise, component
16404 selection on such a value will operate on the specific type of the
16409 @node Overloading support for Ada
16410 @subsubsection Overloading support for Ada
16411 @cindex overloading, Ada
16413 The debugger supports limited overloading. Given a subprogram call in which
16414 the function symbol has multiple definitions, it will use the number of
16415 actual parameters and some information about their types to attempt to narrow
16416 the set of definitions. It also makes very limited use of context, preferring
16417 procedures to functions in the context of the @code{call} command, and
16418 functions to procedures elsewhere.
16420 If, after narrowing, the set of matching definitions still contains more than
16421 one definition, @value{GDBN} will display a menu to query which one it should
16425 (@value{GDBP}) print f(1)
16426 Multiple matches for f
16428 [1] foo.f (integer) return boolean at foo.adb:23
16429 [2] foo.f (foo.new_integer) return boolean at foo.adb:28
16433 In this case, just select one menu entry either to cancel expression evaluation
16434 (type @kbd{0} and press @key{RET}) or to continue evaluation with a specific
16435 instance (type the corresponding number and press @key{RET}).
16437 Here are a couple of commands to customize @value{GDBN}'s behavior in this
16442 @kindex set ada print-signatures
16443 @item set ada print-signatures
16444 Control whether parameter types and return types are displayed in overloads
16445 selection menus. It is @code{on} by default.
16446 @xref{Overloading support for Ada}.
16448 @kindex show ada print-signatures
16449 @item show ada print-signatures
16450 Show the current setting for displaying parameter types and return types in
16451 overloads selection menu.
16452 @xref{Overloading support for Ada}.
16456 @node Stopping Before Main Program
16457 @subsubsection Stopping at the Very Beginning
16459 @cindex breakpointing Ada elaboration code
16460 It is sometimes necessary to debug the program during elaboration, and
16461 before reaching the main procedure.
16462 As defined in the Ada Reference
16463 Manual, the elaboration code is invoked from a procedure called
16464 @code{adainit}. To run your program up to the beginning of
16465 elaboration, simply use the following two commands:
16466 @code{tbreak adainit} and @code{run}.
16468 @node Ada Exceptions
16469 @subsubsection Ada Exceptions
16471 A command is provided to list all Ada exceptions:
16474 @kindex info exceptions
16475 @item info exceptions
16476 @itemx info exceptions @var{regexp}
16477 The @code{info exceptions} command allows you to list all Ada exceptions
16478 defined within the program being debugged, as well as their addresses.
16479 With a regular expression, @var{regexp}, as argument, only those exceptions
16480 whose names match @var{regexp} are listed.
16483 Below is a small example, showing how the command can be used, first
16484 without argument, and next with a regular expression passed as an
16488 (@value{GDBP}) info exceptions
16489 All defined Ada exceptions:
16490 constraint_error: 0x613da0
16491 program_error: 0x613d20
16492 storage_error: 0x613ce0
16493 tasking_error: 0x613ca0
16494 const.aint_global_e: 0x613b00
16495 (@value{GDBP}) info exceptions const.aint
16496 All Ada exceptions matching regular expression "const.aint":
16497 constraint_error: 0x613da0
16498 const.aint_global_e: 0x613b00
16501 It is also possible to ask @value{GDBN} to stop your program's execution
16502 when an exception is raised. For more details, see @ref{Set Catchpoints}.
16505 @subsubsection Extensions for Ada Tasks
16506 @cindex Ada, tasking
16508 Support for Ada tasks is analogous to that for threads (@pxref{Threads}).
16509 @value{GDBN} provides the following task-related commands:
16514 This command shows a list of current Ada tasks, as in the following example:
16521 (@value{GDBP}) info tasks
16522 ID TID P-ID Pri State Name
16523 1 8088000 0 15 Child Activation Wait main_task
16524 2 80a4000 1 15 Accept Statement b
16525 3 809a800 1 15 Child Activation Wait a
16526 * 4 80ae800 3 15 Runnable c
16531 In this listing, the asterisk before the last task indicates it to be the
16532 task currently being inspected.
16536 Represents @value{GDBN}'s internal task number.
16542 The parent's task ID (@value{GDBN}'s internal task number).
16545 The base priority of the task.
16548 Current state of the task.
16552 The task has been created but has not been activated. It cannot be
16556 The task is not blocked for any reason known to Ada. (It may be waiting
16557 for a mutex, though.) It is conceptually "executing" in normal mode.
16560 The task is terminated, in the sense of ARM 9.3 (5). Any dependents
16561 that were waiting on terminate alternatives have been awakened and have
16562 terminated themselves.
16564 @item Child Activation Wait
16565 The task is waiting for created tasks to complete activation.
16567 @item Accept Statement
16568 The task is waiting on an accept or selective wait statement.
16570 @item Waiting on entry call
16571 The task is waiting on an entry call.
16573 @item Async Select Wait
16574 The task is waiting to start the abortable part of an asynchronous
16578 The task is waiting on a select statement with only a delay
16581 @item Child Termination Wait
16582 The task is sleeping having completed a master within itself, and is
16583 waiting for the tasks dependent on that master to become terminated or
16584 waiting on a terminate Phase.
16586 @item Wait Child in Term Alt
16587 The task is sleeping waiting for tasks on terminate alternatives to
16588 finish terminating.
16590 @item Accepting RV with @var{taskno}
16591 The task is accepting a rendez-vous with the task @var{taskno}.
16595 Name of the task in the program.
16599 @kindex info task @var{taskno}
16600 @item info task @var{taskno}
16601 This command shows detailled informations on the specified task, as in
16602 the following example:
16607 (@value{GDBP}) info tasks
16608 ID TID P-ID Pri State Name
16609 1 8077880 0 15 Child Activation Wait main_task
16610 * 2 807c468 1 15 Runnable task_1
16611 (@value{GDBP}) info task 2
16612 Ada Task: 0x807c468
16615 Parent: 1 (main_task)
16621 @kindex task@r{ (Ada)}
16622 @cindex current Ada task ID
16623 This command prints the ID of the current task.
16629 (@value{GDBP}) info tasks
16630 ID TID P-ID Pri State Name
16631 1 8077870 0 15 Child Activation Wait main_task
16632 * 2 807c458 1 15 Runnable t
16633 (@value{GDBP}) task
16634 [Current task is 2]
16637 @item task @var{taskno}
16638 @cindex Ada task switching
16639 This command is like the @code{thread @var{thread-id}}
16640 command (@pxref{Threads}). It switches the context of debugging
16641 from the current task to the given task.
16647 (@value{GDBP}) info tasks
16648 ID TID P-ID Pri State Name
16649 1 8077870 0 15 Child Activation Wait main_task
16650 * 2 807c458 1 15 Runnable t
16651 (@value{GDBP}) task 1
16652 [Switching to task 1]
16653 #0 0x8067726 in pthread_cond_wait ()
16655 #0 0x8067726 in pthread_cond_wait ()
16656 #1 0x8056714 in system.os_interface.pthread_cond_wait ()
16657 #2 0x805cb63 in system.task_primitives.operations.sleep ()
16658 #3 0x806153e in system.tasking.stages.activate_tasks ()
16659 #4 0x804aacc in un () at un.adb:5
16662 @item break @var{location} task @var{taskno}
16663 @itemx break @var{location} task @var{taskno} if @dots{}
16664 @cindex breakpoints and tasks, in Ada
16665 @cindex task breakpoints, in Ada
16666 @kindex break @dots{} task @var{taskno}@r{ (Ada)}
16667 These commands are like the @code{break @dots{} thread @dots{}}
16668 command (@pxref{Thread Stops}). The
16669 @var{location} argument specifies source lines, as described
16670 in @ref{Specify Location}.
16672 Use the qualifier @samp{task @var{taskno}} with a breakpoint command
16673 to specify that you only want @value{GDBN} to stop the program when a
16674 particular Ada task reaches this breakpoint. The @var{taskno} is one of the
16675 numeric task identifiers assigned by @value{GDBN}, shown in the first
16676 column of the @samp{info tasks} display.
16678 If you do not specify @samp{task @var{taskno}} when you set a
16679 breakpoint, the breakpoint applies to @emph{all} tasks of your
16682 You can use the @code{task} qualifier on conditional breakpoints as
16683 well; in this case, place @samp{task @var{taskno}} before the
16684 breakpoint condition (before the @code{if}).
16692 (@value{GDBP}) info tasks
16693 ID TID P-ID Pri State Name
16694 1 140022020 0 15 Child Activation Wait main_task
16695 2 140045060 1 15 Accept/Select Wait t2
16696 3 140044840 1 15 Runnable t1
16697 * 4 140056040 1 15 Runnable t3
16698 (@value{GDBP}) b 15 task 2
16699 Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
16700 (@value{GDBP}) cont
16705 Breakpoint 5, test_task_debug () at test_task_debug.adb:15
16707 (@value{GDBP}) info tasks
16708 ID TID P-ID Pri State Name
16709 1 140022020 0 15 Child Activation Wait main_task
16710 * 2 140045060 1 15 Runnable t2
16711 3 140044840 1 15 Runnable t1
16712 4 140056040 1 15 Delay Sleep t3
16716 @node Ada Tasks and Core Files
16717 @subsubsection Tasking Support when Debugging Core Files
16718 @cindex Ada tasking and core file debugging
16720 When inspecting a core file, as opposed to debugging a live program,
16721 tasking support may be limited or even unavailable, depending on
16722 the platform being used.
16723 For instance, on x86-linux, the list of tasks is available, but task
16724 switching is not supported.
16726 On certain platforms, the debugger needs to perform some
16727 memory writes in order to provide Ada tasking support. When inspecting
16728 a core file, this means that the core file must be opened with read-write
16729 privileges, using the command @samp{"set write on"} (@pxref{Patching}).
16730 Under these circumstances, you should make a backup copy of the core
16731 file before inspecting it with @value{GDBN}.
16733 @node Ravenscar Profile
16734 @subsubsection Tasking Support when using the Ravenscar Profile
16735 @cindex Ravenscar Profile
16737 The @dfn{Ravenscar Profile} is a subset of the Ada tasking features,
16738 specifically designed for systems with safety-critical real-time
16742 @kindex set ravenscar task-switching on
16743 @cindex task switching with program using Ravenscar Profile
16744 @item set ravenscar task-switching on
16745 Allows task switching when debugging a program that uses the Ravenscar
16746 Profile. This is the default.
16748 @kindex set ravenscar task-switching off
16749 @item set ravenscar task-switching off
16750 Turn off task switching when debugging a program that uses the Ravenscar
16751 Profile. This is mostly intended to disable the code that adds support
16752 for the Ravenscar Profile, in case a bug in either @value{GDBN} or in
16753 the Ravenscar runtime is preventing @value{GDBN} from working properly.
16754 To be effective, this command should be run before the program is started.
16756 @kindex show ravenscar task-switching
16757 @item show ravenscar task-switching
16758 Show whether it is possible to switch from task to task in a program
16759 using the Ravenscar Profile.
16764 @subsubsection Known Peculiarities of Ada Mode
16765 @cindex Ada, problems
16767 Besides the omissions listed previously (@pxref{Omissions from Ada}),
16768 we know of several problems with and limitations of Ada mode in
16770 some of which will be fixed with planned future releases of the debugger
16771 and the GNU Ada compiler.
16775 Static constants that the compiler chooses not to materialize as objects in
16776 storage are invisible to the debugger.
16779 Named parameter associations in function argument lists are ignored (the
16780 argument lists are treated as positional).
16783 Many useful library packages are currently invisible to the debugger.
16786 Fixed-point arithmetic, conversions, input, and output is carried out using
16787 floating-point arithmetic, and may give results that only approximate those on
16791 The GNAT compiler never generates the prefix @code{Standard} for any of
16792 the standard symbols defined by the Ada language. @value{GDBN} knows about
16793 this: it will strip the prefix from names when you use it, and will never
16794 look for a name you have so qualified among local symbols, nor match against
16795 symbols in other packages or subprograms. If you have
16796 defined entities anywhere in your program other than parameters and
16797 local variables whose simple names match names in @code{Standard},
16798 GNAT's lack of qualification here can cause confusion. When this happens,
16799 you can usually resolve the confusion
16800 by qualifying the problematic names with package
16801 @code{Standard} explicitly.
16804 Older versions of the compiler sometimes generate erroneous debugging
16805 information, resulting in the debugger incorrectly printing the value
16806 of affected entities. In some cases, the debugger is able to work
16807 around an issue automatically. In other cases, the debugger is able
16808 to work around the issue, but the work-around has to be specifically
16811 @kindex set ada trust-PAD-over-XVS
16812 @kindex show ada trust-PAD-over-XVS
16815 @item set ada trust-PAD-over-XVS on
16816 Configure GDB to strictly follow the GNAT encoding when computing the
16817 value of Ada entities, particularly when @code{PAD} and @code{PAD___XVS}
16818 types are involved (see @code{ada/exp_dbug.ads} in the GCC sources for
16819 a complete description of the encoding used by the GNAT compiler).
16820 This is the default.
16822 @item set ada trust-PAD-over-XVS off
16823 This is related to the encoding using by the GNAT compiler. If @value{GDBN}
16824 sometimes prints the wrong value for certain entities, changing @code{ada
16825 trust-PAD-over-XVS} to @code{off} activates a work-around which may fix
16826 the issue. It is always safe to set @code{ada trust-PAD-over-XVS} to
16827 @code{off}, but this incurs a slight performance penalty, so it is
16828 recommended to leave this setting to @code{on} unless necessary.
16832 @cindex GNAT descriptive types
16833 @cindex GNAT encoding
16834 Internally, the debugger also relies on the compiler following a number
16835 of conventions known as the @samp{GNAT Encoding}, all documented in
16836 @file{gcc/ada/exp_dbug.ads} in the GCC sources. This encoding describes
16837 how the debugging information should be generated for certain types.
16838 In particular, this convention makes use of @dfn{descriptive types},
16839 which are artificial types generated purely to help the debugger.
16841 These encodings were defined at a time when the debugging information
16842 format used was not powerful enough to describe some of the more complex
16843 types available in Ada. Since DWARF allows us to express nearly all
16844 Ada features, the long-term goal is to slowly replace these descriptive
16845 types by their pure DWARF equivalent. To facilitate that transition,
16846 a new maintenance option is available to force the debugger to ignore
16847 those descriptive types. It allows the user to quickly evaluate how
16848 well @value{GDBN} works without them.
16852 @kindex maint ada set ignore-descriptive-types
16853 @item maintenance ada set ignore-descriptive-types [on|off]
16854 Control whether the debugger should ignore descriptive types.
16855 The default is not to ignore descriptives types (@code{off}).
16857 @kindex maint ada show ignore-descriptive-types
16858 @item maintenance ada show ignore-descriptive-types
16859 Show if descriptive types are ignored by @value{GDBN}.
16863 @node Unsupported Languages
16864 @section Unsupported Languages
16866 @cindex unsupported languages
16867 @cindex minimal language
16868 In addition to the other fully-supported programming languages,
16869 @value{GDBN} also provides a pseudo-language, called @code{minimal}.
16870 It does not represent a real programming language, but provides a set
16871 of capabilities close to what the C or assembly languages provide.
16872 This should allow most simple operations to be performed while debugging
16873 an application that uses a language currently not supported by @value{GDBN}.
16875 If the language is set to @code{auto}, @value{GDBN} will automatically
16876 select this language if the current frame corresponds to an unsupported
16880 @chapter Examining the Symbol Table
16882 The commands described in this chapter allow you to inquire about the
16883 symbols (names of variables, functions and types) defined in your
16884 program. This information is inherent in the text of your program and
16885 does not change as your program executes. @value{GDBN} finds it in your
16886 program's symbol table, in the file indicated when you started @value{GDBN}
16887 (@pxref{File Options, ,Choosing Files}), or by one of the
16888 file-management commands (@pxref{Files, ,Commands to Specify Files}).
16890 @cindex symbol names
16891 @cindex names of symbols
16892 @cindex quoting names
16893 Occasionally, you may need to refer to symbols that contain unusual
16894 characters, which @value{GDBN} ordinarily treats as word delimiters. The
16895 most frequent case is in referring to static variables in other
16896 source files (@pxref{Variables,,Program Variables}). File names
16897 are recorded in object files as debugging symbols, but @value{GDBN} would
16898 ordinarily parse a typical file name, like @file{foo.c}, as the three words
16899 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
16900 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
16907 looks up the value of @code{x} in the scope of the file @file{foo.c}.
16910 @cindex case-insensitive symbol names
16911 @cindex case sensitivity in symbol names
16912 @kindex set case-sensitive
16913 @item set case-sensitive on
16914 @itemx set case-sensitive off
16915 @itemx set case-sensitive auto
16916 Normally, when @value{GDBN} looks up symbols, it matches their names
16917 with case sensitivity determined by the current source language.
16918 Occasionally, you may wish to control that. The command @code{set
16919 case-sensitive} lets you do that by specifying @code{on} for
16920 case-sensitive matches or @code{off} for case-insensitive ones. If
16921 you specify @code{auto}, case sensitivity is reset to the default
16922 suitable for the source language. The default is case-sensitive
16923 matches for all languages except for Fortran, for which the default is
16924 case-insensitive matches.
16926 @kindex show case-sensitive
16927 @item show case-sensitive
16928 This command shows the current setting of case sensitivity for symbols
16931 @kindex set print type methods
16932 @item set print type methods
16933 @itemx set print type methods on
16934 @itemx set print type methods off
16935 Normally, when @value{GDBN} prints a class, it displays any methods
16936 declared in that class. You can control this behavior either by
16937 passing the appropriate flag to @code{ptype}, or using @command{set
16938 print type methods}. Specifying @code{on} will cause @value{GDBN} to
16939 display the methods; this is the default. Specifying @code{off} will
16940 cause @value{GDBN} to omit the methods.
16942 @kindex show print type methods
16943 @item show print type methods
16944 This command shows the current setting of method display when printing
16947 @kindex set print type typedefs
16948 @item set print type typedefs
16949 @itemx set print type typedefs on
16950 @itemx set print type typedefs off
16952 Normally, when @value{GDBN} prints a class, it displays any typedefs
16953 defined in that class. You can control this behavior either by
16954 passing the appropriate flag to @code{ptype}, or using @command{set
16955 print type typedefs}. Specifying @code{on} will cause @value{GDBN} to
16956 display the typedef definitions; this is the default. Specifying
16957 @code{off} will cause @value{GDBN} to omit the typedef definitions.
16958 Note that this controls whether the typedef definition itself is
16959 printed, not whether typedef names are substituted when printing other
16962 @kindex show print type typedefs
16963 @item show print type typedefs
16964 This command shows the current setting of typedef display when
16967 @kindex info address
16968 @cindex address of a symbol
16969 @item info address @var{symbol}
16970 Describe where the data for @var{symbol} is stored. For a register
16971 variable, this says which register it is kept in. For a non-register
16972 local variable, this prints the stack-frame offset at which the variable
16975 Note the contrast with @samp{print &@var{symbol}}, which does not work
16976 at all for a register variable, and for a stack local variable prints
16977 the exact address of the current instantiation of the variable.
16979 @kindex info symbol
16980 @cindex symbol from address
16981 @cindex closest symbol and offset for an address
16982 @item info symbol @var{addr}
16983 Print the name of a symbol which is stored at the address @var{addr}.
16984 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
16985 nearest symbol and an offset from it:
16988 (@value{GDBP}) info symbol 0x54320
16989 _initialize_vx + 396 in section .text
16993 This is the opposite of the @code{info address} command. You can use
16994 it to find out the name of a variable or a function given its address.
16996 For dynamically linked executables, the name of executable or shared
16997 library containing the symbol is also printed:
17000 (@value{GDBP}) info symbol 0x400225
17001 _start + 5 in section .text of /tmp/a.out
17002 (@value{GDBP}) info symbol 0x2aaaac2811cf
17003 __read_nocancel + 6 in section .text of /usr/lib64/libc.so.6
17008 @item demangle @r{[}-l @var{language}@r{]} @r{[}@var{--}@r{]} @var{name}
17009 Demangle @var{name}.
17010 If @var{language} is provided it is the name of the language to demangle
17011 @var{name} in. Otherwise @var{name} is demangled in the current language.
17013 The @samp{--} option specifies the end of options,
17014 and is useful when @var{name} begins with a dash.
17016 The parameter @code{demangle-style} specifies how to interpret the kind
17017 of mangling used. @xref{Print Settings}.
17020 @item whatis[/@var{flags}] [@var{arg}]
17021 Print the data type of @var{arg}, which can be either an expression
17022 or a name of a data type. With no argument, print the data type of
17023 @code{$}, the last value in the value history.
17025 If @var{arg} is an expression (@pxref{Expressions, ,Expressions}), it
17026 is not actually evaluated, and any side-effecting operations (such as
17027 assignments or function calls) inside it do not take place.
17029 If @var{arg} is a variable or an expression, @code{whatis} prints its
17030 literal type as it is used in the source code. If the type was
17031 defined using a @code{typedef}, @code{whatis} will @emph{not} print
17032 the data type underlying the @code{typedef}. If the type of the
17033 variable or the expression is a compound data type, such as
17034 @code{struct} or @code{class}, @code{whatis} never prints their
17035 fields or methods. It just prints the @code{struct}/@code{class}
17036 name (a.k.a.@: its @dfn{tag}). If you want to see the members of
17037 such a compound data type, use @code{ptype}.
17039 If @var{arg} is a type name that was defined using @code{typedef},
17040 @code{whatis} @dfn{unrolls} only one level of that @code{typedef}.
17041 Unrolling means that @code{whatis} will show the underlying type used
17042 in the @code{typedef} declaration of @var{arg}. However, if that
17043 underlying type is also a @code{typedef}, @code{whatis} will not
17046 For C code, the type names may also have the form @samp{class
17047 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
17048 @var{union-tag}} or @samp{enum @var{enum-tag}}.
17050 @var{flags} can be used to modify how the type is displayed.
17051 Available flags are:
17055 Display in ``raw'' form. Normally, @value{GDBN} substitutes template
17056 parameters and typedefs defined in a class when printing the class'
17057 members. The @code{/r} flag disables this.
17060 Do not print methods defined in the class.
17063 Print methods defined in the class. This is the default, but the flag
17064 exists in case you change the default with @command{set print type methods}.
17067 Do not print typedefs defined in the class. Note that this controls
17068 whether the typedef definition itself is printed, not whether typedef
17069 names are substituted when printing other types.
17072 Print typedefs defined in the class. This is the default, but the flag
17073 exists in case you change the default with @command{set print type typedefs}.
17077 @item ptype[/@var{flags}] [@var{arg}]
17078 @code{ptype} accepts the same arguments as @code{whatis}, but prints a
17079 detailed description of the type, instead of just the name of the type.
17080 @xref{Expressions, ,Expressions}.
17082 Contrary to @code{whatis}, @code{ptype} always unrolls any
17083 @code{typedef}s in its argument declaration, whether the argument is
17084 a variable, expression, or a data type. This means that @code{ptype}
17085 of a variable or an expression will not print literally its type as
17086 present in the source code---use @code{whatis} for that. @code{typedef}s at
17087 the pointer or reference targets are also unrolled. Only @code{typedef}s of
17088 fields, methods and inner @code{class typedef}s of @code{struct}s,
17089 @code{class}es and @code{union}s are not unrolled even with @code{ptype}.
17091 For example, for this variable declaration:
17094 typedef double real_t;
17095 struct complex @{ real_t real; double imag; @};
17096 typedef struct complex complex_t;
17098 real_t *real_pointer_var;
17102 the two commands give this output:
17106 (@value{GDBP}) whatis var
17108 (@value{GDBP}) ptype var
17109 type = struct complex @{
17113 (@value{GDBP}) whatis complex_t
17114 type = struct complex
17115 (@value{GDBP}) whatis struct complex
17116 type = struct complex
17117 (@value{GDBP}) ptype struct complex
17118 type = struct complex @{
17122 (@value{GDBP}) whatis real_pointer_var
17124 (@value{GDBP}) ptype real_pointer_var
17130 As with @code{whatis}, using @code{ptype} without an argument refers to
17131 the type of @code{$}, the last value in the value history.
17133 @cindex incomplete type
17134 Sometimes, programs use opaque data types or incomplete specifications
17135 of complex data structure. If the debug information included in the
17136 program does not allow @value{GDBN} to display a full declaration of
17137 the data type, it will say @samp{<incomplete type>}. For example,
17138 given these declarations:
17142 struct foo *fooptr;
17146 but no definition for @code{struct foo} itself, @value{GDBN} will say:
17149 (@value{GDBP}) ptype foo
17150 $1 = <incomplete type>
17154 ``Incomplete type'' is C terminology for data types that are not
17155 completely specified.
17157 @cindex unknown type
17158 Othertimes, information about a variable's type is completely absent
17159 from the debug information included in the program. This most often
17160 happens when the program or library where the variable is defined
17161 includes no debug information at all. @value{GDBN} knows the variable
17162 exists from inspecting the linker/loader symbol table (e.g., the ELF
17163 dynamic symbol table), but such symbols do not contain type
17164 information. Inspecting the type of a (global) variable for which
17165 @value{GDBN} has no type information shows:
17168 (@value{GDBP}) ptype var
17169 type = <data variable, no debug info>
17172 @xref{Variables, no debug info variables}, for how to print the values
17176 @item info types @var{regexp}
17178 Print a brief description of all types whose names match the regular
17179 expression @var{regexp} (or all types in your program, if you supply
17180 no argument). Each complete typename is matched as though it were a
17181 complete line; thus, @samp{i type value} gives information on all
17182 types in your program whose names include the string @code{value}, but
17183 @samp{i type ^value$} gives information only on types whose complete
17184 name is @code{value}.
17186 This command differs from @code{ptype} in two ways: first, like
17187 @code{whatis}, it does not print a detailed description; second, it
17188 lists all source files where a type is defined.
17190 @kindex info type-printers
17191 @item info type-printers
17192 Versions of @value{GDBN} that ship with Python scripting enabled may
17193 have ``type printers'' available. When using @command{ptype} or
17194 @command{whatis}, these printers are consulted when the name of a type
17195 is needed. @xref{Type Printing API}, for more information on writing
17198 @code{info type-printers} displays all the available type printers.
17200 @kindex enable type-printer
17201 @kindex disable type-printer
17202 @item enable type-printer @var{name}@dots{}
17203 @item disable type-printer @var{name}@dots{}
17204 These commands can be used to enable or disable type printers.
17207 @cindex local variables
17208 @item info scope @var{location}
17209 List all the variables local to a particular scope. This command
17210 accepts a @var{location} argument---a function name, a source line, or
17211 an address preceded by a @samp{*}, and prints all the variables local
17212 to the scope defined by that location. (@xref{Specify Location}, for
17213 details about supported forms of @var{location}.) For example:
17216 (@value{GDBP}) @b{info scope command_line_handler}
17217 Scope for command_line_handler:
17218 Symbol rl is an argument at stack/frame offset 8, length 4.
17219 Symbol linebuffer is in static storage at address 0x150a18, length 4.
17220 Symbol linelength is in static storage at address 0x150a1c, length 4.
17221 Symbol p is a local variable in register $esi, length 4.
17222 Symbol p1 is a local variable in register $ebx, length 4.
17223 Symbol nline is a local variable in register $edx, length 4.
17224 Symbol repeat is a local variable at frame offset -8, length 4.
17228 This command is especially useful for determining what data to collect
17229 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
17232 @kindex info source
17234 Show information about the current source file---that is, the source file for
17235 the function containing the current point of execution:
17238 the name of the source file, and the directory containing it,
17240 the directory it was compiled in,
17242 its length, in lines,
17244 which programming language it is written in,
17246 if the debug information provides it, the program that compiled the file
17247 (which may include, e.g., the compiler version and command line arguments),
17249 whether the executable includes debugging information for that file, and
17250 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
17252 whether the debugging information includes information about
17253 preprocessor macros.
17257 @kindex info sources
17259 Print the names of all source files in your program for which there is
17260 debugging information, organized into two lists: files whose symbols
17261 have already been read, and files whose symbols will be read when needed.
17263 @kindex info functions
17264 @item info functions
17265 Print the names and data types of all defined functions.
17267 @item info functions @var{regexp}
17268 Print the names and data types of all defined functions
17269 whose names contain a match for regular expression @var{regexp}.
17270 Thus, @samp{info fun step} finds all functions whose names
17271 include @code{step}; @samp{info fun ^step} finds those whose names
17272 start with @code{step}. If a function name contains characters
17273 that conflict with the regular expression language (e.g.@:
17274 @samp{operator*()}), they may be quoted with a backslash.
17276 @kindex info variables
17277 @item info variables
17278 Print the names and data types of all variables that are defined
17279 outside of functions (i.e.@: excluding local variables).
17281 @item info variables @var{regexp}
17282 Print the names and data types of all variables (except for local
17283 variables) whose names contain a match for regular expression
17286 @kindex info classes
17287 @cindex Objective-C, classes and selectors
17289 @itemx info classes @var{regexp}
17290 Display all Objective-C classes in your program, or
17291 (with the @var{regexp} argument) all those matching a particular regular
17294 @kindex info selectors
17295 @item info selectors
17296 @itemx info selectors @var{regexp}
17297 Display all Objective-C selectors in your program, or
17298 (with the @var{regexp} argument) all those matching a particular regular
17302 This was never implemented.
17303 @kindex info methods
17305 @itemx info methods @var{regexp}
17306 The @code{info methods} command permits the user to examine all defined
17307 methods within C@t{++} program, or (with the @var{regexp} argument) a
17308 specific set of methods found in the various C@t{++} classes. Many
17309 C@t{++} classes provide a large number of methods. Thus, the output
17310 from the @code{ptype} command can be overwhelming and hard to use. The
17311 @code{info-methods} command filters the methods, printing only those
17312 which match the regular-expression @var{regexp}.
17315 @cindex opaque data types
17316 @kindex set opaque-type-resolution
17317 @item set opaque-type-resolution on
17318 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
17319 declared as a pointer to a @code{struct}, @code{class}, or
17320 @code{union}---for example, @code{struct MyType *}---that is used in one
17321 source file although the full declaration of @code{struct MyType} is in
17322 another source file. The default is on.
17324 A change in the setting of this subcommand will not take effect until
17325 the next time symbols for a file are loaded.
17327 @item set opaque-type-resolution off
17328 Tell @value{GDBN} not to resolve opaque types. In this case, the type
17329 is printed as follows:
17331 @{<no data fields>@}
17334 @kindex show opaque-type-resolution
17335 @item show opaque-type-resolution
17336 Show whether opaque types are resolved or not.
17338 @kindex set print symbol-loading
17339 @cindex print messages when symbols are loaded
17340 @item set print symbol-loading
17341 @itemx set print symbol-loading full
17342 @itemx set print symbol-loading brief
17343 @itemx set print symbol-loading off
17344 The @code{set print symbol-loading} command allows you to control the
17345 printing of messages when @value{GDBN} loads symbol information.
17346 By default a message is printed for the executable and one for each
17347 shared library, and normally this is what you want. However, when
17348 debugging apps with large numbers of shared libraries these messages
17350 When set to @code{brief} a message is printed for each executable,
17351 and when @value{GDBN} loads a collection of shared libraries at once
17352 it will only print one message regardless of the number of shared
17353 libraries. When set to @code{off} no messages are printed.
17355 @kindex show print symbol-loading
17356 @item show print symbol-loading
17357 Show whether messages will be printed when a @value{GDBN} command
17358 entered from the keyboard causes symbol information to be loaded.
17360 @kindex maint print symbols
17361 @cindex symbol dump
17362 @kindex maint print psymbols
17363 @cindex partial symbol dump
17364 @kindex maint print msymbols
17365 @cindex minimal symbol dump
17366 @item maint print symbols @r{[}-pc @var{address}@r{]} @r{[}@var{filename}@r{]}
17367 @itemx maint print symbols @r{[}-objfile @var{objfile}@r{]} @r{[}-source @var{source}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]}
17368 @itemx maint print psymbols @r{[}-objfile @var{objfile}@r{]} @r{[}-pc @var{address}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]}
17369 @itemx maint print psymbols @r{[}-objfile @var{objfile}@r{]} @r{[}-source @var{source}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]}
17370 @itemx maint print msymbols @r{[}-objfile @var{objfile}@r{]} @r{[}--@r{]} @r{[}@var{filename}@r{]}
17371 Write a dump of debugging symbol data into the file @var{filename} or
17372 the terminal if @var{filename} is unspecified.
17373 If @code{-objfile @var{objfile}} is specified, only dump symbols for
17375 If @code{-pc @var{address}} is specified, only dump symbols for the file
17376 with code at that address. Note that @var{address} may be a symbol like
17378 If @code{-source @var{source}} is specified, only dump symbols for that
17381 These commands are used to debug the @value{GDBN} symbol-reading code.
17382 These commands do not modify internal @value{GDBN} state, therefore
17383 @samp{maint print symbols} will only print symbols for already expanded symbol
17385 You can use the command @code{info sources} to find out which files these are.
17386 If you use @samp{maint print psymbols} instead, the dump shows information
17387 about symbols that @value{GDBN} only knows partially---that is, symbols
17388 defined in files that @value{GDBN} has skimmed, but not yet read completely.
17389 Finally, @samp{maint print msymbols} just dumps ``minimal symbols'', e.g.,
17392 @xref{Files, ,Commands to Specify Files}, for a discussion of how
17393 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
17395 @kindex maint info symtabs
17396 @kindex maint info psymtabs
17397 @cindex listing @value{GDBN}'s internal symbol tables
17398 @cindex symbol tables, listing @value{GDBN}'s internal
17399 @cindex full symbol tables, listing @value{GDBN}'s internal
17400 @cindex partial symbol tables, listing @value{GDBN}'s internal
17401 @item maint info symtabs @r{[} @var{regexp} @r{]}
17402 @itemx maint info psymtabs @r{[} @var{regexp} @r{]}
17404 List the @code{struct symtab} or @code{struct partial_symtab}
17405 structures whose names match @var{regexp}. If @var{regexp} is not
17406 given, list them all. The output includes expressions which you can
17407 copy into a @value{GDBN} debugging this one to examine a particular
17408 structure in more detail. For example:
17411 (@value{GDBP}) maint info psymtabs dwarf2read
17412 @{ objfile /home/gnu/build/gdb/gdb
17413 ((struct objfile *) 0x82e69d0)
17414 @{ psymtab /home/gnu/src/gdb/dwarf2read.c
17415 ((struct partial_symtab *) 0x8474b10)
17418 text addresses 0x814d3c8 -- 0x8158074
17419 globals (* (struct partial_symbol **) 0x8507a08 @@ 9)
17420 statics (* (struct partial_symbol **) 0x40e95b78 @@ 2882)
17421 dependencies (none)
17424 (@value{GDBP}) maint info symtabs
17428 We see that there is one partial symbol table whose filename contains
17429 the string @samp{dwarf2read}, belonging to the @samp{gdb} executable;
17430 and we see that @value{GDBN} has not read in any symtabs yet at all.
17431 If we set a breakpoint on a function, that will cause @value{GDBN} to
17432 read the symtab for the compilation unit containing that function:
17435 (@value{GDBP}) break dwarf2_psymtab_to_symtab
17436 Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c,
17438 (@value{GDBP}) maint info symtabs
17439 @{ objfile /home/gnu/build/gdb/gdb
17440 ((struct objfile *) 0x82e69d0)
17441 @{ symtab /home/gnu/src/gdb/dwarf2read.c
17442 ((struct symtab *) 0x86c1f38)
17445 blockvector ((struct blockvector *) 0x86c1bd0) (primary)
17446 linetable ((struct linetable *) 0x8370fa0)
17447 debugformat DWARF 2
17453 @kindex maint info line-table
17454 @cindex listing @value{GDBN}'s internal line tables
17455 @cindex line tables, listing @value{GDBN}'s internal
17456 @item maint info line-table @r{[} @var{regexp} @r{]}
17458 List the @code{struct linetable} from all @code{struct symtab}
17459 instances whose name matches @var{regexp}. If @var{regexp} is not
17460 given, list the @code{struct linetable} from all @code{struct symtab}.
17462 @kindex maint set symbol-cache-size
17463 @cindex symbol cache size
17464 @item maint set symbol-cache-size @var{size}
17465 Set the size of the symbol cache to @var{size}.
17466 The default size is intended to be good enough for debugging
17467 most applications. This option exists to allow for experimenting
17468 with different sizes.
17470 @kindex maint show symbol-cache-size
17471 @item maint show symbol-cache-size
17472 Show the size of the symbol cache.
17474 @kindex maint print symbol-cache
17475 @cindex symbol cache, printing its contents
17476 @item maint print symbol-cache
17477 Print the contents of the symbol cache.
17478 This is useful when debugging symbol cache issues.
17480 @kindex maint print symbol-cache-statistics
17481 @cindex symbol cache, printing usage statistics
17482 @item maint print symbol-cache-statistics
17483 Print symbol cache usage statistics.
17484 This helps determine how well the cache is being utilized.
17486 @kindex maint flush-symbol-cache
17487 @cindex symbol cache, flushing
17488 @item maint flush-symbol-cache
17489 Flush the contents of the symbol cache, all entries are removed.
17490 This command is useful when debugging the symbol cache.
17491 It is also useful when collecting performance data.
17496 @chapter Altering Execution
17498 Once you think you have found an error in your program, you might want to
17499 find out for certain whether correcting the apparent error would lead to
17500 correct results in the rest of the run. You can find the answer by
17501 experiment, using the @value{GDBN} features for altering execution of the
17504 For example, you can store new values into variables or memory
17505 locations, give your program a signal, restart it at a different
17506 address, or even return prematurely from a function.
17509 * Assignment:: Assignment to variables
17510 * Jumping:: Continuing at a different address
17511 * Signaling:: Giving your program a signal
17512 * Returning:: Returning from a function
17513 * Calling:: Calling your program's functions
17514 * Patching:: Patching your program
17515 * Compiling and Injecting Code:: Compiling and injecting code in @value{GDBN}
17519 @section Assignment to Variables
17522 @cindex setting variables
17523 To alter the value of a variable, evaluate an assignment expression.
17524 @xref{Expressions, ,Expressions}. For example,
17531 stores the value 4 into the variable @code{x}, and then prints the
17532 value of the assignment expression (which is 4).
17533 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
17534 information on operators in supported languages.
17536 @kindex set variable
17537 @cindex variables, setting
17538 If you are not interested in seeing the value of the assignment, use the
17539 @code{set} command instead of the @code{print} command. @code{set} is
17540 really the same as @code{print} except that the expression's value is
17541 not printed and is not put in the value history (@pxref{Value History,
17542 ,Value History}). The expression is evaluated only for its effects.
17544 If the beginning of the argument string of the @code{set} command
17545 appears identical to a @code{set} subcommand, use the @code{set
17546 variable} command instead of just @code{set}. This command is identical
17547 to @code{set} except for its lack of subcommands. For example, if your
17548 program has a variable @code{width}, you get an error if you try to set
17549 a new value with just @samp{set width=13}, because @value{GDBN} has the
17550 command @code{set width}:
17553 (@value{GDBP}) whatis width
17555 (@value{GDBP}) p width
17557 (@value{GDBP}) set width=47
17558 Invalid syntax in expression.
17562 The invalid expression, of course, is @samp{=47}. In
17563 order to actually set the program's variable @code{width}, use
17566 (@value{GDBP}) set var width=47
17569 Because the @code{set} command has many subcommands that can conflict
17570 with the names of program variables, it is a good idea to use the
17571 @code{set variable} command instead of just @code{set}. For example, if
17572 your program has a variable @code{g}, you run into problems if you try
17573 to set a new value with just @samp{set g=4}, because @value{GDBN} has
17574 the command @code{set gnutarget}, abbreviated @code{set g}:
17578 (@value{GDBP}) whatis g
17582 (@value{GDBP}) set g=4
17586 The program being debugged has been started already.
17587 Start it from the beginning? (y or n) y
17588 Starting program: /home/smith/cc_progs/a.out
17589 "/home/smith/cc_progs/a.out": can't open to read symbols:
17590 Invalid bfd target.
17591 (@value{GDBP}) show g
17592 The current BFD target is "=4".
17597 The program variable @code{g} did not change, and you silently set the
17598 @code{gnutarget} to an invalid value. In order to set the variable
17602 (@value{GDBP}) set var g=4
17605 @value{GDBN} allows more implicit conversions in assignments than C; you can
17606 freely store an integer value into a pointer variable or vice versa,
17607 and you can convert any structure to any other structure that is the
17608 same length or shorter.
17609 @comment FIXME: how do structs align/pad in these conversions?
17610 @comment /doc@cygnus.com 18dec1990
17612 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
17613 construct to generate a value of specified type at a specified address
17614 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
17615 to memory location @code{0x83040} as an integer (which implies a certain size
17616 and representation in memory), and
17619 set @{int@}0x83040 = 4
17623 stores the value 4 into that memory location.
17626 @section Continuing at a Different Address
17628 Ordinarily, when you continue your program, you do so at the place where
17629 it stopped, with the @code{continue} command. You can instead continue at
17630 an address of your own choosing, with the following commands:
17634 @kindex j @r{(@code{jump})}
17635 @item jump @var{location}
17636 @itemx j @var{location}
17637 Resume execution at @var{location}. Execution stops again immediately
17638 if there is a breakpoint there. @xref{Specify Location}, for a description
17639 of the different forms of @var{location}. It is common
17640 practice to use the @code{tbreak} command in conjunction with
17641 @code{jump}. @xref{Set Breaks, ,Setting Breakpoints}.
17643 The @code{jump} command does not change the current stack frame, or
17644 the stack pointer, or the contents of any memory location or any
17645 register other than the program counter. If @var{location} is in
17646 a different function from the one currently executing, the results may
17647 be bizarre if the two functions expect different patterns of arguments or
17648 of local variables. For this reason, the @code{jump} command requests
17649 confirmation if the specified line is not in the function currently
17650 executing. However, even bizarre results are predictable if you are
17651 well acquainted with the machine-language code of your program.
17654 On many systems, you can get much the same effect as the @code{jump}
17655 command by storing a new value into the register @code{$pc}. The
17656 difference is that this does not start your program running; it only
17657 changes the address of where it @emph{will} run when you continue. For
17665 makes the next @code{continue} command or stepping command execute at
17666 address @code{0x485}, rather than at the address where your program stopped.
17667 @xref{Continuing and Stepping, ,Continuing and Stepping}.
17669 The most common occasion to use the @code{jump} command is to back
17670 up---perhaps with more breakpoints set---over a portion of a program
17671 that has already executed, in order to examine its execution in more
17676 @section Giving your Program a Signal
17677 @cindex deliver a signal to a program
17681 @item signal @var{signal}
17682 Resume execution where your program is stopped, but immediately give it the
17683 signal @var{signal}. The @var{signal} can be the name or the number of a
17684 signal. For example, on many systems @code{signal 2} and @code{signal
17685 SIGINT} are both ways of sending an interrupt signal.
17687 Alternatively, if @var{signal} is zero, continue execution without
17688 giving a signal. This is useful when your program stopped on account of
17689 a signal and would ordinarily see the signal when resumed with the
17690 @code{continue} command; @samp{signal 0} causes it to resume without a
17693 @emph{Note:} When resuming a multi-threaded program, @var{signal} is
17694 delivered to the currently selected thread, not the thread that last
17695 reported a stop. This includes the situation where a thread was
17696 stopped due to a signal. So if you want to continue execution
17697 suppressing the signal that stopped a thread, you should select that
17698 same thread before issuing the @samp{signal 0} command. If you issue
17699 the @samp{signal 0} command with another thread as the selected one,
17700 @value{GDBN} detects that and asks for confirmation.
17702 Invoking the @code{signal} command is not the same as invoking the
17703 @code{kill} utility from the shell. Sending a signal with @code{kill}
17704 causes @value{GDBN} to decide what to do with the signal depending on
17705 the signal handling tables (@pxref{Signals}). The @code{signal} command
17706 passes the signal directly to your program.
17708 @code{signal} does not repeat when you press @key{RET} a second time
17709 after executing the command.
17711 @kindex queue-signal
17712 @item queue-signal @var{signal}
17713 Queue @var{signal} to be delivered immediately to the current thread
17714 when execution of the thread resumes. The @var{signal} can be the name or
17715 the number of a signal. For example, on many systems @code{signal 2} and
17716 @code{signal SIGINT} are both ways of sending an interrupt signal.
17717 The handling of the signal must be set to pass the signal to the program,
17718 otherwise @value{GDBN} will report an error.
17719 You can control the handling of signals from @value{GDBN} with the
17720 @code{handle} command (@pxref{Signals}).
17722 Alternatively, if @var{signal} is zero, any currently queued signal
17723 for the current thread is discarded and when execution resumes no signal
17724 will be delivered. This is useful when your program stopped on account
17725 of a signal and would ordinarily see the signal when resumed with the
17726 @code{continue} command.
17728 This command differs from the @code{signal} command in that the signal
17729 is just queued, execution is not resumed. And @code{queue-signal} cannot
17730 be used to pass a signal whose handling state has been set to @code{nopass}
17735 @xref{stepping into signal handlers}, for information on how stepping
17736 commands behave when the thread has a signal queued.
17739 @section Returning from a Function
17742 @cindex returning from a function
17745 @itemx return @var{expression}
17746 You can cancel execution of a function call with the @code{return}
17747 command. If you give an
17748 @var{expression} argument, its value is used as the function's return
17752 When you use @code{return}, @value{GDBN} discards the selected stack frame
17753 (and all frames within it). You can think of this as making the
17754 discarded frame return prematurely. If you wish to specify a value to
17755 be returned, give that value as the argument to @code{return}.
17757 This pops the selected stack frame (@pxref{Selection, ,Selecting a
17758 Frame}), and any other frames inside of it, leaving its caller as the
17759 innermost remaining frame. That frame becomes selected. The
17760 specified value is stored in the registers used for returning values
17763 The @code{return} command does not resume execution; it leaves the
17764 program stopped in the state that would exist if the function had just
17765 returned. In contrast, the @code{finish} command (@pxref{Continuing
17766 and Stepping, ,Continuing and Stepping}) resumes execution until the
17767 selected stack frame returns naturally.
17769 @value{GDBN} needs to know how the @var{expression} argument should be set for
17770 the inferior. The concrete registers assignment depends on the OS ABI and the
17771 type being returned by the selected stack frame. For example it is common for
17772 OS ABI to return floating point values in FPU registers while integer values in
17773 CPU registers. Still some ABIs return even floating point values in CPU
17774 registers. Larger integer widths (such as @code{long long int}) also have
17775 specific placement rules. @value{GDBN} already knows the OS ABI from its
17776 current target so it needs to find out also the type being returned to make the
17777 assignment into the right register(s).
17779 Normally, the selected stack frame has debug info. @value{GDBN} will always
17780 use the debug info instead of the implicit type of @var{expression} when the
17781 debug info is available. For example, if you type @kbd{return -1}, and the
17782 function in the current stack frame is declared to return a @code{long long
17783 int}, @value{GDBN} transparently converts the implicit @code{int} value of -1
17784 into a @code{long long int}:
17787 Breakpoint 1, func () at gdb.base/return-nodebug.c:29
17789 (@value{GDBP}) return -1
17790 Make func return now? (y or n) y
17791 #0 0x004004f6 in main () at gdb.base/return-nodebug.c:43
17792 43 printf ("result=%lld\n", func ());
17796 However, if the selected stack frame does not have a debug info, e.g., if the
17797 function was compiled without debug info, @value{GDBN} has to find out the type
17798 to return from user. Specifying a different type by mistake may set the value
17799 in different inferior registers than the caller code expects. For example,
17800 typing @kbd{return -1} with its implicit type @code{int} would set only a part
17801 of a @code{long long int} result for a debug info less function (on 32-bit
17802 architectures). Therefore the user is required to specify the return type by
17803 an appropriate cast explicitly:
17806 Breakpoint 2, 0x0040050b in func ()
17807 (@value{GDBP}) return -1
17808 Return value type not available for selected stack frame.
17809 Please use an explicit cast of the value to return.
17810 (@value{GDBP}) return (long long int) -1
17811 Make selected stack frame return now? (y or n) y
17812 #0 0x00400526 in main ()
17817 @section Calling Program Functions
17820 @cindex calling functions
17821 @cindex inferior functions, calling
17822 @item print @var{expr}
17823 Evaluate the expression @var{expr} and display the resulting value.
17824 The expression may include calls to functions in the program being
17828 @item call @var{expr}
17829 Evaluate the expression @var{expr} without displaying @code{void}
17832 You can use this variant of the @code{print} command if you want to
17833 execute a function from your program that does not return anything
17834 (a.k.a.@: @dfn{a void function}), but without cluttering the output
17835 with @code{void} returned values that @value{GDBN} will otherwise
17836 print. If the result is not void, it is printed and saved in the
17840 It is possible for the function you call via the @code{print} or
17841 @code{call} command to generate a signal (e.g., if there's a bug in
17842 the function, or if you passed it incorrect arguments). What happens
17843 in that case is controlled by the @code{set unwindonsignal} command.
17845 Similarly, with a C@t{++} program it is possible for the function you
17846 call via the @code{print} or @code{call} command to generate an
17847 exception that is not handled due to the constraints of the dummy
17848 frame. In this case, any exception that is raised in the frame, but has
17849 an out-of-frame exception handler will not be found. GDB builds a
17850 dummy-frame for the inferior function call, and the unwinder cannot
17851 seek for exception handlers outside of this dummy-frame. What happens
17852 in that case is controlled by the
17853 @code{set unwind-on-terminating-exception} command.
17856 @item set unwindonsignal
17857 @kindex set unwindonsignal
17858 @cindex unwind stack in called functions
17859 @cindex call dummy stack unwinding
17860 Set unwinding of the stack if a signal is received while in a function
17861 that @value{GDBN} called in the program being debugged. If set to on,
17862 @value{GDBN} unwinds the stack it created for the call and restores
17863 the context to what it was before the call. If set to off (the
17864 default), @value{GDBN} stops in the frame where the signal was
17867 @item show unwindonsignal
17868 @kindex show unwindonsignal
17869 Show the current setting of stack unwinding in the functions called by
17872 @item set unwind-on-terminating-exception
17873 @kindex set unwind-on-terminating-exception
17874 @cindex unwind stack in called functions with unhandled exceptions
17875 @cindex call dummy stack unwinding on unhandled exception.
17876 Set unwinding of the stack if a C@t{++} exception is raised, but left
17877 unhandled while in a function that @value{GDBN} called in the program being
17878 debugged. If set to on (the default), @value{GDBN} unwinds the stack
17879 it created for the call and restores the context to what it was before
17880 the call. If set to off, @value{GDBN} the exception is delivered to
17881 the default C@t{++} exception handler and the inferior terminated.
17883 @item show unwind-on-terminating-exception
17884 @kindex show unwind-on-terminating-exception
17885 Show the current setting of stack unwinding in the functions called by
17890 @subsection Calling functions with no debug info
17892 @cindex no debug info functions
17893 Sometimes, a function you wish to call is missing debug information.
17894 In such case, @value{GDBN} does not know the type of the function,
17895 including the types of the function's parameters. To avoid calling
17896 the inferior function incorrectly, which could result in the called
17897 function functioning erroneously and even crash, @value{GDBN} refuses
17898 to call the function unless you tell it the type of the function.
17900 For prototyped (i.e.@: ANSI/ISO style) functions, there are two ways
17901 to do that. The simplest is to cast the call to the function's
17902 declared return type. For example:
17905 (@value{GDBP}) p getenv ("PATH")
17906 'getenv' has unknown return type; cast the call to its declared return type
17907 (@value{GDBP}) p (char *) getenv ("PATH")
17908 $1 = 0x7fffffffe7ba "/usr/local/bin:/"...
17911 Casting the return type of a no-debug function is equivalent to
17912 casting the function to a pointer to a prototyped function that has a
17913 prototype that matches the types of the passed-in arguments, and
17914 calling that. I.e., the call above is equivalent to:
17917 (@value{GDBP}) p ((char * (*) (const char *)) getenv) ("PATH")
17921 and given this prototyped C or C++ function with float parameters:
17924 float multiply (float v1, float v2) @{ return v1 * v2; @}
17928 these calls are equivalent:
17931 (@value{GDBP}) p (float) multiply (2.0f, 3.0f)
17932 (@value{GDBP}) p ((float (*) (float, float)) multiply) (2.0f, 3.0f)
17935 If the function you wish to call is declared as unprototyped (i.e.@:
17936 old K&R style), you must use the cast-to-function-pointer syntax, so
17937 that @value{GDBN} knows that it needs to apply default argument
17938 promotions (promote float arguments to double). @xref{ABI, float
17939 promotion}. For example, given this unprototyped C function with
17940 float parameters, and no debug info:
17944 multiply_noproto (v1, v2)
17952 you call it like this:
17955 (@value{GDBP}) p ((float (*) ()) multiply_noproto) (2.0f, 3.0f)
17959 @section Patching Programs
17961 @cindex patching binaries
17962 @cindex writing into executables
17963 @cindex writing into corefiles
17965 By default, @value{GDBN} opens the file containing your program's
17966 executable code (or the corefile) read-only. This prevents accidental
17967 alterations to machine code; but it also prevents you from intentionally
17968 patching your program's binary.
17970 If you'd like to be able to patch the binary, you can specify that
17971 explicitly with the @code{set write} command. For example, you might
17972 want to turn on internal debugging flags, or even to make emergency
17978 @itemx set write off
17979 If you specify @samp{set write on}, @value{GDBN} opens executable and
17980 core files for both reading and writing; if you specify @kbd{set write
17981 off} (the default), @value{GDBN} opens them read-only.
17983 If you have already loaded a file, you must load it again (using the
17984 @code{exec-file} or @code{core-file} command) after changing @code{set
17985 write}, for your new setting to take effect.
17989 Display whether executable files and core files are opened for writing
17990 as well as reading.
17993 @node Compiling and Injecting Code
17994 @section Compiling and injecting code in @value{GDBN}
17995 @cindex injecting code
17996 @cindex writing into executables
17997 @cindex compiling code
17999 @value{GDBN} supports on-demand compilation and code injection into
18000 programs running under @value{GDBN}. GCC 5.0 or higher built with
18001 @file{libcc1.so} must be installed for this functionality to be enabled.
18002 This functionality is implemented with the following commands.
18005 @kindex compile code
18006 @item compile code @var{source-code}
18007 @itemx compile code -raw @var{--} @var{source-code}
18008 Compile @var{source-code} with the compiler language found as the current
18009 language in @value{GDBN} (@pxref{Languages}). If compilation and
18010 injection is not supported with the current language specified in
18011 @value{GDBN}, or the compiler does not support this feature, an error
18012 message will be printed. If @var{source-code} compiles and links
18013 successfully, @value{GDBN} will load the object-code emitted,
18014 and execute it within the context of the currently selected inferior.
18015 It is important to note that the compiled code is executed immediately.
18016 After execution, the compiled code is removed from @value{GDBN} and any
18017 new types or variables you have defined will be deleted.
18019 The command allows you to specify @var{source-code} in two ways.
18020 The simplest method is to provide a single line of code to the command.
18024 compile code printf ("hello world\n");
18027 If you specify options on the command line as well as source code, they
18028 may conflict. The @samp{--} delimiter can be used to separate options
18029 from actual source code. E.g.:
18032 compile code -r -- printf ("hello world\n");
18035 Alternatively you can enter source code as multiple lines of text. To
18036 enter this mode, invoke the @samp{compile code} command without any text
18037 following the command. This will start the multiple-line editor and
18038 allow you to type as many lines of source code as required. When you
18039 have completed typing, enter @samp{end} on its own line to exit the
18044 >printf ("hello\n");
18045 >printf ("world\n");
18049 Specifying @samp{-raw}, prohibits @value{GDBN} from wrapping the
18050 provided @var{source-code} in a callable scope. In this case, you must
18051 specify the entry point of the code by defining a function named
18052 @code{_gdb_expr_}. The @samp{-raw} code cannot access variables of the
18053 inferior. Using @samp{-raw} option may be needed for example when
18054 @var{source-code} requires @samp{#include} lines which may conflict with
18055 inferior symbols otherwise.
18057 @kindex compile file
18058 @item compile file @var{filename}
18059 @itemx compile file -raw @var{filename}
18060 Like @code{compile code}, but take the source code from @var{filename}.
18063 compile file /home/user/example.c
18068 @item compile print @var{expr}
18069 @itemx compile print /@var{f} @var{expr}
18070 Compile and execute @var{expr} with the compiler language found as the
18071 current language in @value{GDBN} (@pxref{Languages}). By default the
18072 value of @var{expr} is printed in a format appropriate to its data type;
18073 you can choose a different format by specifying @samp{/@var{f}}, where
18074 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
18077 @item compile print
18078 @itemx compile print /@var{f}
18079 @cindex reprint the last value
18080 Alternatively you can enter the expression (source code producing it) as
18081 multiple lines of text. To enter this mode, invoke the @samp{compile print}
18082 command without any text following the command. This will start the
18083 multiple-line editor.
18087 The process of compiling and injecting the code can be inspected using:
18090 @anchor{set debug compile}
18091 @item set debug compile
18092 @cindex compile command debugging info
18093 Turns on or off display of @value{GDBN} process of compiling and
18094 injecting the code. The default is off.
18096 @item show debug compile
18097 Displays the current state of displaying @value{GDBN} process of
18098 compiling and injecting the code.
18101 @subsection Compilation options for the @code{compile} command
18103 @value{GDBN} needs to specify the right compilation options for the code
18104 to be injected, in part to make its ABI compatible with the inferior
18105 and in part to make the injected code compatible with @value{GDBN}'s
18109 The options used, in increasing precedence:
18112 @item target architecture and OS options (@code{gdbarch})
18113 These options depend on target processor type and target operating
18114 system, usually they specify at least 32-bit (@code{-m32}) or 64-bit
18115 (@code{-m64}) compilation option.
18117 @item compilation options recorded in the target
18118 @value{NGCC} (since version 4.7) stores the options used for compilation
18119 into @code{DW_AT_producer} part of DWARF debugging information according
18120 to the @value{NGCC} option @code{-grecord-gcc-switches}. One has to
18121 explicitly specify @code{-g} during inferior compilation otherwise
18122 @value{NGCC} produces no DWARF. This feature is only relevant for
18123 platforms where @code{-g} produces DWARF by default, otherwise one may
18124 try to enforce DWARF by using @code{-gdwarf-4}.
18126 @item compilation options set by @code{set compile-args}
18130 You can override compilation options using the following command:
18133 @item set compile-args
18134 @cindex compile command options override
18135 Set compilation options used for compiling and injecting code with the
18136 @code{compile} commands. These options override any conflicting ones
18137 from the target architecture and/or options stored during inferior
18140 @item show compile-args
18141 Displays the current state of compilation options override.
18142 This does not show all the options actually used during compilation,
18143 use @ref{set debug compile} for that.
18146 @subsection Caveats when using the @code{compile} command
18148 There are a few caveats to keep in mind when using the @code{compile}
18149 command. As the caveats are different per language, the table below
18150 highlights specific issues on a per language basis.
18153 @item C code examples and caveats
18154 When the language in @value{GDBN} is set to @samp{C}, the compiler will
18155 attempt to compile the source code with a @samp{C} compiler. The source
18156 code provided to the @code{compile} command will have much the same
18157 access to variables and types as it normally would if it were part of
18158 the program currently being debugged in @value{GDBN}.
18160 Below is a sample program that forms the basis of the examples that
18161 follow. This program has been compiled and loaded into @value{GDBN},
18162 much like any other normal debugging session.
18165 void function1 (void)
18168 printf ("function 1\n");
18171 void function2 (void)
18186 For the purposes of the examples in this section, the program above has
18187 been compiled, loaded into @value{GDBN}, stopped at the function
18188 @code{main}, and @value{GDBN} is awaiting input from the user.
18190 To access variables and types for any program in @value{GDBN}, the
18191 program must be compiled and packaged with debug information. The
18192 @code{compile} command is not an exception to this rule. Without debug
18193 information, you can still use the @code{compile} command, but you will
18194 be very limited in what variables and types you can access.
18196 So with that in mind, the example above has been compiled with debug
18197 information enabled. The @code{compile} command will have access to
18198 all variables and types (except those that may have been optimized
18199 out). Currently, as @value{GDBN} has stopped the program in the
18200 @code{main} function, the @code{compile} command would have access to
18201 the variable @code{k}. You could invoke the @code{compile} command
18202 and type some source code to set the value of @code{k}. You can also
18203 read it, or do anything with that variable you would normally do in
18204 @code{C}. Be aware that changes to inferior variables in the
18205 @code{compile} command are persistent. In the following example:
18208 compile code k = 3;
18212 the variable @code{k} is now 3. It will retain that value until
18213 something else in the example program changes it, or another
18214 @code{compile} command changes it.
18216 Normal scope and access rules apply to source code compiled and
18217 injected by the @code{compile} command. In the example, the variables
18218 @code{j} and @code{k} are not accessible yet, because the program is
18219 currently stopped in the @code{main} function, where these variables
18220 are not in scope. Therefore, the following command
18223 compile code j = 3;
18227 will result in a compilation error message.
18229 Once the program is continued, execution will bring these variables in
18230 scope, and they will become accessible; then the code you specify via
18231 the @code{compile} command will be able to access them.
18233 You can create variables and types with the @code{compile} command as
18234 part of your source code. Variables and types that are created as part
18235 of the @code{compile} command are not visible to the rest of the program for
18236 the duration of its run. This example is valid:
18239 compile code int ff = 5; printf ("ff is %d\n", ff);
18242 However, if you were to type the following into @value{GDBN} after that
18243 command has completed:
18246 compile code printf ("ff is %d\n'', ff);
18250 a compiler error would be raised as the variable @code{ff} no longer
18251 exists. Object code generated and injected by the @code{compile}
18252 command is removed when its execution ends. Caution is advised
18253 when assigning to program variables values of variables created by the
18254 code submitted to the @code{compile} command. This example is valid:
18257 compile code int ff = 5; k = ff;
18260 The value of the variable @code{ff} is assigned to @code{k}. The variable
18261 @code{k} does not require the existence of @code{ff} to maintain the value
18262 it has been assigned. However, pointers require particular care in
18263 assignment. If the source code compiled with the @code{compile} command
18264 changed the address of a pointer in the example program, perhaps to a
18265 variable created in the @code{compile} command, that pointer would point
18266 to an invalid location when the command exits. The following example
18267 would likely cause issues with your debugged program:
18270 compile code int ff = 5; p = &ff;
18273 In this example, @code{p} would point to @code{ff} when the
18274 @code{compile} command is executing the source code provided to it.
18275 However, as variables in the (example) program persist with their
18276 assigned values, the variable @code{p} would point to an invalid
18277 location when the command exists. A general rule should be followed
18278 in that you should either assign @code{NULL} to any assigned pointers,
18279 or restore a valid location to the pointer before the command exits.
18281 Similar caution must be exercised with any structs, unions, and typedefs
18282 defined in @code{compile} command. Types defined in the @code{compile}
18283 command will no longer be available in the next @code{compile} command.
18284 Therefore, if you cast a variable to a type defined in the
18285 @code{compile} command, care must be taken to ensure that any future
18286 need to resolve the type can be achieved.
18289 (gdb) compile code static struct a @{ int a; @} v = @{ 42 @}; argv = &v;
18290 (gdb) compile code printf ("%d\n", ((struct a *) argv)->a);
18291 gdb command line:1:36: error: dereferencing pointer to incomplete type ‘struct a’
18292 Compilation failed.
18293 (gdb) compile code struct a @{ int a; @}; printf ("%d\n", ((struct a *) argv)->a);
18297 Variables that have been optimized away by the compiler are not
18298 accessible to the code submitted to the @code{compile} command.
18299 Access to those variables will generate a compiler error which @value{GDBN}
18300 will print to the console.
18303 @subsection Compiler search for the @code{compile} command
18305 @value{GDBN} needs to find @value{NGCC} for the inferior being debugged
18306 which may not be obvious for remote targets of different architecture
18307 than where @value{GDBN} is running. Environment variable @code{PATH} on
18308 @value{GDBN} host is searched for @value{NGCC} binary matching the
18309 target architecture and operating system. This search can be overriden
18310 by @code{set compile-gcc} @value{GDBN} command below. @code{PATH} is
18311 taken from shell that executed @value{GDBN}, it is not the value set by
18312 @value{GDBN} command @code{set environment}). @xref{Environment}.
18315 Specifically @code{PATH} is searched for binaries matching regular expression
18316 @code{@var{arch}(-[^-]*)?-@var{os}-gcc} according to the inferior target being
18317 debugged. @var{arch} is processor name --- multiarch is supported, so for
18318 example both @code{i386} and @code{x86_64} targets look for pattern
18319 @code{(x86_64|i.86)} and both @code{s390} and @code{s390x} targets look
18320 for pattern @code{s390x?}. @var{os} is currently supported only for
18321 pattern @code{linux(-gnu)?}.
18323 On Posix hosts the compiler driver @value{GDBN} needs to find also
18324 shared library @file{libcc1.so} from the compiler. It is searched in
18325 default shared library search path (overridable with usual environment
18326 variable @code{LD_LIBRARY_PATH}), unrelated to @code{PATH} or @code{set
18327 compile-gcc} settings. Contrary to it @file{libcc1plugin.so} is found
18328 according to the installation of the found compiler --- as possibly
18329 specified by the @code{set compile-gcc} command.
18332 @item set compile-gcc
18333 @cindex compile command driver filename override
18334 Set compilation command used for compiling and injecting code with the
18335 @code{compile} commands. If this option is not set (it is set to
18336 an empty string), the search described above will occur --- that is the
18339 @item show compile-gcc
18340 Displays the current compile command @value{NGCC} driver filename.
18341 If set, it is the main command @command{gcc}, found usually for example
18342 under name @file{x86_64-linux-gnu-gcc}.
18346 @chapter @value{GDBN} Files
18348 @value{GDBN} needs to know the file name of the program to be debugged,
18349 both in order to read its symbol table and in order to start your
18350 program. To debug a core dump of a previous run, you must also tell
18351 @value{GDBN} the name of the core dump file.
18354 * Files:: Commands to specify files
18355 * File Caching:: Information about @value{GDBN}'s file caching
18356 * Separate Debug Files:: Debugging information in separate files
18357 * MiniDebugInfo:: Debugging information in a special section
18358 * Index Files:: Index files speed up GDB
18359 * Symbol Errors:: Errors reading symbol files
18360 * Data Files:: GDB data files
18364 @section Commands to Specify Files
18366 @cindex symbol table
18367 @cindex core dump file
18369 You may want to specify executable and core dump file names. The usual
18370 way to do this is at start-up time, using the arguments to
18371 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
18372 Out of @value{GDBN}}).
18374 Occasionally it is necessary to change to a different file during a
18375 @value{GDBN} session. Or you may run @value{GDBN} and forget to
18376 specify a file you want to use. Or you are debugging a remote target
18377 via @code{gdbserver} (@pxref{Server, file, Using the @code{gdbserver}
18378 Program}). In these situations the @value{GDBN} commands to specify
18379 new files are useful.
18382 @cindex executable file
18384 @item file @var{filename}
18385 Use @var{filename} as the program to be debugged. It is read for its
18386 symbols and for the contents of pure memory. It is also the program
18387 executed when you use the @code{run} command. If you do not specify a
18388 directory and the file is not found in the @value{GDBN} working directory,
18389 @value{GDBN} uses the environment variable @code{PATH} as a list of
18390 directories to search, just as the shell does when looking for a program
18391 to run. You can change the value of this variable, for both @value{GDBN}
18392 and your program, using the @code{path} command.
18394 @cindex unlinked object files
18395 @cindex patching object files
18396 You can load unlinked object @file{.o} files into @value{GDBN} using
18397 the @code{file} command. You will not be able to ``run'' an object
18398 file, but you can disassemble functions and inspect variables. Also,
18399 if the underlying BFD functionality supports it, you could use
18400 @kbd{gdb -write} to patch object files using this technique. Note
18401 that @value{GDBN} can neither interpret nor modify relocations in this
18402 case, so branches and some initialized variables will appear to go to
18403 the wrong place. But this feature is still handy from time to time.
18406 @code{file} with no argument makes @value{GDBN} discard any information it
18407 has on both executable file and the symbol table.
18410 @item exec-file @r{[} @var{filename} @r{]}
18411 Specify that the program to be run (but not the symbol table) is found
18412 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
18413 if necessary to locate your program. Omitting @var{filename} means to
18414 discard information on the executable file.
18416 @kindex symbol-file
18417 @item symbol-file @r{[} @var{filename} @r{]}
18418 Read symbol table information from file @var{filename}. @code{PATH} is
18419 searched when necessary. Use the @code{file} command to get both symbol
18420 table and program to run from the same file.
18422 @code{symbol-file} with no argument clears out @value{GDBN} information on your
18423 program's symbol table.
18425 The @code{symbol-file} command causes @value{GDBN} to forget the contents of
18426 some breakpoints and auto-display expressions. This is because they may
18427 contain pointers to the internal data recording symbols and data types,
18428 which are part of the old symbol table data being discarded inside
18431 @code{symbol-file} does not repeat if you press @key{RET} again after
18434 When @value{GDBN} is configured for a particular environment, it
18435 understands debugging information in whatever format is the standard
18436 generated for that environment; you may use either a @sc{gnu} compiler, or
18437 other compilers that adhere to the local conventions.
18438 Best results are usually obtained from @sc{gnu} compilers; for example,
18439 using @code{@value{NGCC}} you can generate debugging information for
18442 For most kinds of object files, with the exception of old SVR3 systems
18443 using COFF, the @code{symbol-file} command does not normally read the
18444 symbol table in full right away. Instead, it scans the symbol table
18445 quickly to find which source files and which symbols are present. The
18446 details are read later, one source file at a time, as they are needed.
18448 The purpose of this two-stage reading strategy is to make @value{GDBN}
18449 start up faster. For the most part, it is invisible except for
18450 occasional pauses while the symbol table details for a particular source
18451 file are being read. (The @code{set verbose} command can turn these
18452 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
18453 Warnings and Messages}.)
18455 We have not implemented the two-stage strategy for COFF yet. When the
18456 symbol table is stored in COFF format, @code{symbol-file} reads the
18457 symbol table data in full right away. Note that ``stabs-in-COFF''
18458 still does the two-stage strategy, since the debug info is actually
18462 @cindex reading symbols immediately
18463 @cindex symbols, reading immediately
18464 @item symbol-file @r{[} -readnow @r{]} @var{filename}
18465 @itemx file @r{[} -readnow @r{]} @var{filename}
18466 You can override the @value{GDBN} two-stage strategy for reading symbol
18467 tables by using the @samp{-readnow} option with any of the commands that
18468 load symbol table information, if you want to be sure @value{GDBN} has the
18469 entire symbol table available.
18471 @c FIXME: for now no mention of directories, since this seems to be in
18472 @c flux. 13mar1992 status is that in theory GDB would look either in
18473 @c current dir or in same dir as myprog; but issues like competing
18474 @c GDB's, or clutter in system dirs, mean that in practice right now
18475 @c only current dir is used. FFish says maybe a special GDB hierarchy
18476 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
18480 @item core-file @r{[}@var{filename}@r{]}
18482 Specify the whereabouts of a core dump file to be used as the ``contents
18483 of memory''. Traditionally, core files contain only some parts of the
18484 address space of the process that generated them; @value{GDBN} can access the
18485 executable file itself for other parts.
18487 @code{core-file} with no argument specifies that no core file is
18490 Note that the core file is ignored when your program is actually running
18491 under @value{GDBN}. So, if you have been running your program and you
18492 wish to debug a core file instead, you must kill the subprocess in which
18493 the program is running. To do this, use the @code{kill} command
18494 (@pxref{Kill Process, ,Killing the Child Process}).
18496 @kindex add-symbol-file
18497 @cindex dynamic linking
18498 @item add-symbol-file @var{filename} @var{address}
18499 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]}
18500 @itemx add-symbol-file @var{filename} @var{address} -s @var{section} @var{address} @dots{}
18501 The @code{add-symbol-file} command reads additional symbol table
18502 information from the file @var{filename}. You would use this command
18503 when @var{filename} has been dynamically loaded (by some other means)
18504 into the program that is running. The @var{address} should give the memory
18505 address at which the file has been loaded; @value{GDBN} cannot figure
18506 this out for itself. You can additionally specify an arbitrary number
18507 of @samp{-s @var{section} @var{address}} pairs, to give an explicit
18508 section name and base address for that section. You can specify any
18509 @var{address} as an expression.
18511 The symbol table of the file @var{filename} is added to the symbol table
18512 originally read with the @code{symbol-file} command. You can use the
18513 @code{add-symbol-file} command any number of times; the new symbol data
18514 thus read is kept in addition to the old.
18516 Changes can be reverted using the command @code{remove-symbol-file}.
18518 @cindex relocatable object files, reading symbols from
18519 @cindex object files, relocatable, reading symbols from
18520 @cindex reading symbols from relocatable object files
18521 @cindex symbols, reading from relocatable object files
18522 @cindex @file{.o} files, reading symbols from
18523 Although @var{filename} is typically a shared library file, an
18524 executable file, or some other object file which has been fully
18525 relocated for loading into a process, you can also load symbolic
18526 information from relocatable @file{.o} files, as long as:
18530 the file's symbolic information refers only to linker symbols defined in
18531 that file, not to symbols defined by other object files,
18533 every section the file's symbolic information refers to has actually
18534 been loaded into the inferior, as it appears in the file, and
18536 you can determine the address at which every section was loaded, and
18537 provide these to the @code{add-symbol-file} command.
18541 Some embedded operating systems, like Sun Chorus and VxWorks, can load
18542 relocatable files into an already running program; such systems
18543 typically make the requirements above easy to meet. However, it's
18544 important to recognize that many native systems use complex link
18545 procedures (@code{.linkonce} section factoring and C@t{++} constructor table
18546 assembly, for example) that make the requirements difficult to meet. In
18547 general, one cannot assume that using @code{add-symbol-file} to read a
18548 relocatable object file's symbolic information will have the same effect
18549 as linking the relocatable object file into the program in the normal
18552 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
18554 @kindex remove-symbol-file
18555 @item remove-symbol-file @var{filename}
18556 @item remove-symbol-file -a @var{address}
18557 Remove a symbol file added via the @code{add-symbol-file} command. The
18558 file to remove can be identified by its @var{filename} or by an @var{address}
18559 that lies within the boundaries of this symbol file in memory. Example:
18562 (gdb) add-symbol-file /home/user/gdb/mylib.so 0x7ffff7ff9480
18563 add symbol table from file "/home/user/gdb/mylib.so" at
18564 .text_addr = 0x7ffff7ff9480
18566 Reading symbols from /home/user/gdb/mylib.so...done.
18567 (gdb) remove-symbol-file -a 0x7ffff7ff9480
18568 Remove symbol table from file "/home/user/gdb/mylib.so"? (y or n) y
18573 @code{remove-symbol-file} does not repeat if you press @key{RET} after using it.
18575 @kindex add-symbol-file-from-memory
18576 @cindex @code{syscall DSO}
18577 @cindex load symbols from memory
18578 @item add-symbol-file-from-memory @var{address}
18579 Load symbols from the given @var{address} in a dynamically loaded
18580 object file whose image is mapped directly into the inferior's memory.
18581 For example, the Linux kernel maps a @code{syscall DSO} into each
18582 process's address space; this DSO provides kernel-specific code for
18583 some system calls. The argument can be any expression whose
18584 evaluation yields the address of the file's shared object file header.
18585 For this command to work, you must have used @code{symbol-file} or
18586 @code{exec-file} commands in advance.
18589 @item section @var{section} @var{addr}
18590 The @code{section} command changes the base address of the named
18591 @var{section} of the exec file to @var{addr}. This can be used if the
18592 exec file does not contain section addresses, (such as in the
18593 @code{a.out} format), or when the addresses specified in the file
18594 itself are wrong. Each section must be changed separately. The
18595 @code{info files} command, described below, lists all the sections and
18599 @kindex info target
18602 @code{info files} and @code{info target} are synonymous; both print the
18603 current target (@pxref{Targets, ,Specifying a Debugging Target}),
18604 including the names of the executable and core dump files currently in
18605 use by @value{GDBN}, and the files from which symbols were loaded. The
18606 command @code{help target} lists all possible targets rather than
18609 @kindex maint info sections
18610 @item maint info sections
18611 Another command that can give you extra information about program sections
18612 is @code{maint info sections}. In addition to the section information
18613 displayed by @code{info files}, this command displays the flags and file
18614 offset of each section in the executable and core dump files. In addition,
18615 @code{maint info sections} provides the following command options (which
18616 may be arbitrarily combined):
18620 Display sections for all loaded object files, including shared libraries.
18621 @item @var{sections}
18622 Display info only for named @var{sections}.
18623 @item @var{section-flags}
18624 Display info only for sections for which @var{section-flags} are true.
18625 The section flags that @value{GDBN} currently knows about are:
18628 Section will have space allocated in the process when loaded.
18629 Set for all sections except those containing debug information.
18631 Section will be loaded from the file into the child process memory.
18632 Set for pre-initialized code and data, clear for @code{.bss} sections.
18634 Section needs to be relocated before loading.
18636 Section cannot be modified by the child process.
18638 Section contains executable code only.
18640 Section contains data only (no executable code).
18642 Section will reside in ROM.
18644 Section contains data for constructor/destructor lists.
18646 Section is not empty.
18648 An instruction to the linker to not output the section.
18649 @item COFF_SHARED_LIBRARY
18650 A notification to the linker that the section contains
18651 COFF shared library information.
18653 Section contains common symbols.
18656 @kindex set trust-readonly-sections
18657 @cindex read-only sections
18658 @item set trust-readonly-sections on
18659 Tell @value{GDBN} that readonly sections in your object file
18660 really are read-only (i.e.@: that their contents will not change).
18661 In that case, @value{GDBN} can fetch values from these sections
18662 out of the object file, rather than from the target program.
18663 For some targets (notably embedded ones), this can be a significant
18664 enhancement to debugging performance.
18666 The default is off.
18668 @item set trust-readonly-sections off
18669 Tell @value{GDBN} not to trust readonly sections. This means that
18670 the contents of the section might change while the program is running,
18671 and must therefore be fetched from the target when needed.
18673 @item show trust-readonly-sections
18674 Show the current setting of trusting readonly sections.
18677 All file-specifying commands allow both absolute and relative file names
18678 as arguments. @value{GDBN} always converts the file name to an absolute file
18679 name and remembers it that way.
18681 @cindex shared libraries
18682 @anchor{Shared Libraries}
18683 @value{GDBN} supports @sc{gnu}/Linux, MS-Windows, SunOS,
18684 Darwin/Mach-O, SVr4, IBM RS/6000 AIX, QNX Neutrino, FDPIC (FR-V), and
18685 DSBT (TIC6X) shared libraries.
18687 On MS-Windows @value{GDBN} must be linked with the Expat library to support
18688 shared libraries. @xref{Expat}.
18690 @value{GDBN} automatically loads symbol definitions from shared libraries
18691 when you use the @code{run} command, or when you examine a core file.
18692 (Before you issue the @code{run} command, @value{GDBN} does not understand
18693 references to a function in a shared library, however---unless you are
18694 debugging a core file).
18696 @c FIXME: some @value{GDBN} release may permit some refs to undef
18697 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
18698 @c FIXME...lib; check this from time to time when updating manual
18700 There are times, however, when you may wish to not automatically load
18701 symbol definitions from shared libraries, such as when they are
18702 particularly large or there are many of them.
18704 To control the automatic loading of shared library symbols, use the
18708 @kindex set auto-solib-add
18709 @item set auto-solib-add @var{mode}
18710 If @var{mode} is @code{on}, symbols from all shared object libraries
18711 will be loaded automatically when the inferior begins execution, you
18712 attach to an independently started inferior, or when the dynamic linker
18713 informs @value{GDBN} that a new library has been loaded. If @var{mode}
18714 is @code{off}, symbols must be loaded manually, using the
18715 @code{sharedlibrary} command. The default value is @code{on}.
18717 @cindex memory used for symbol tables
18718 If your program uses lots of shared libraries with debug info that
18719 takes large amounts of memory, you can decrease the @value{GDBN}
18720 memory footprint by preventing it from automatically loading the
18721 symbols from shared libraries. To that end, type @kbd{set
18722 auto-solib-add off} before running the inferior, then load each
18723 library whose debug symbols you do need with @kbd{sharedlibrary
18724 @var{regexp}}, where @var{regexp} is a regular expression that matches
18725 the libraries whose symbols you want to be loaded.
18727 @kindex show auto-solib-add
18728 @item show auto-solib-add
18729 Display the current autoloading mode.
18732 @cindex load shared library
18733 To explicitly load shared library symbols, use the @code{sharedlibrary}
18737 @kindex info sharedlibrary
18739 @item info share @var{regex}
18740 @itemx info sharedlibrary @var{regex}
18741 Print the names of the shared libraries which are currently loaded
18742 that match @var{regex}. If @var{regex} is omitted then print
18743 all shared libraries that are loaded.
18746 @item info dll @var{regex}
18747 This is an alias of @code{info sharedlibrary}.
18749 @kindex sharedlibrary
18751 @item sharedlibrary @var{regex}
18752 @itemx share @var{regex}
18753 Load shared object library symbols for files matching a
18754 Unix regular expression.
18755 As with files loaded automatically, it only loads shared libraries
18756 required by your program for a core file or after typing @code{run}. If
18757 @var{regex} is omitted all shared libraries required by your program are
18760 @item nosharedlibrary
18761 @kindex nosharedlibrary
18762 @cindex unload symbols from shared libraries
18763 Unload all shared object library symbols. This discards all symbols
18764 that have been loaded from all shared libraries. Symbols from shared
18765 libraries that were loaded by explicit user requests are not
18769 Sometimes you may wish that @value{GDBN} stops and gives you control
18770 when any of shared library events happen. The best way to do this is
18771 to use @code{catch load} and @code{catch unload} (@pxref{Set
18774 @value{GDBN} also supports the the @code{set stop-on-solib-events}
18775 command for this. This command exists for historical reasons. It is
18776 less useful than setting a catchpoint, because it does not allow for
18777 conditions or commands as a catchpoint does.
18780 @item set stop-on-solib-events
18781 @kindex set stop-on-solib-events
18782 This command controls whether @value{GDBN} should give you control
18783 when the dynamic linker notifies it about some shared library event.
18784 The most common event of interest is loading or unloading of a new
18787 @item show stop-on-solib-events
18788 @kindex show stop-on-solib-events
18789 Show whether @value{GDBN} stops and gives you control when shared
18790 library events happen.
18793 Shared libraries are also supported in many cross or remote debugging
18794 configurations. @value{GDBN} needs to have access to the target's libraries;
18795 this can be accomplished either by providing copies of the libraries
18796 on the host system, or by asking @value{GDBN} to automatically retrieve the
18797 libraries from the target. If copies of the target libraries are
18798 provided, they need to be the same as the target libraries, although the
18799 copies on the target can be stripped as long as the copies on the host are
18802 @cindex where to look for shared libraries
18803 For remote debugging, you need to tell @value{GDBN} where the target
18804 libraries are, so that it can load the correct copies---otherwise, it
18805 may try to load the host's libraries. @value{GDBN} has two variables
18806 to specify the search directories for target libraries.
18809 @cindex prefix for executable and shared library file names
18810 @cindex system root, alternate
18811 @kindex set solib-absolute-prefix
18812 @kindex set sysroot
18813 @item set sysroot @var{path}
18814 Use @var{path} as the system root for the program being debugged. Any
18815 absolute shared library paths will be prefixed with @var{path}; many
18816 runtime loaders store the absolute paths to the shared library in the
18817 target program's memory. When starting processes remotely, and when
18818 attaching to already-running processes (local or remote), their
18819 executable filenames will be prefixed with @var{path} if reported to
18820 @value{GDBN} as absolute by the operating system. If you use
18821 @code{set sysroot} to find executables and shared libraries, they need
18822 to be laid out in the same way that they are on the target, with
18823 e.g.@: a @file{/bin}, @file{/lib} and @file{/usr/lib} hierarchy under
18826 If @var{path} starts with the sequence @file{target:} and the target
18827 system is remote then @value{GDBN} will retrieve the target binaries
18828 from the remote system. This is only supported when using a remote
18829 target that supports the @code{remote get} command (@pxref{File
18830 Transfer,,Sending files to a remote system}). The part of @var{path}
18831 following the initial @file{target:} (if present) is used as system
18832 root prefix on the remote file system. If @var{path} starts with the
18833 sequence @file{remote:} this is converted to the sequence
18834 @file{target:} by @code{set sysroot}@footnote{Historically the
18835 functionality to retrieve binaries from the remote system was
18836 provided by prefixing @var{path} with @file{remote:}}. If you want
18837 to specify a local system root using a directory that happens to be
18838 named @file{target:} or @file{remote:}, you need to use some
18839 equivalent variant of the name like @file{./target:}.
18841 For targets with an MS-DOS based filesystem, such as MS-Windows and
18842 SymbianOS, @value{GDBN} tries prefixing a few variants of the target
18843 absolute file name with @var{path}. But first, on Unix hosts,
18844 @value{GDBN} converts all backslash directory separators into forward
18845 slashes, because the backslash is not a directory separator on Unix:
18848 c:\foo\bar.dll @result{} c:/foo/bar.dll
18851 Then, @value{GDBN} attempts prefixing the target file name with
18852 @var{path}, and looks for the resulting file name in the host file
18856 c:/foo/bar.dll @result{} /path/to/sysroot/c:/foo/bar.dll
18859 If that does not find the binary, @value{GDBN} tries removing
18860 the @samp{:} character from the drive spec, both for convenience, and,
18861 for the case of the host file system not supporting file names with
18865 c:/foo/bar.dll @result{} /path/to/sysroot/c/foo/bar.dll
18868 This makes it possible to have a system root that mirrors a target
18869 with more than one drive. E.g., you may want to setup your local
18870 copies of the target system shared libraries like so (note @samp{c} vs
18874 @file{/path/to/sysroot/c/sys/bin/foo.dll}
18875 @file{/path/to/sysroot/c/sys/bin/bar.dll}
18876 @file{/path/to/sysroot/z/sys/bin/bar.dll}
18880 and point the system root at @file{/path/to/sysroot}, so that
18881 @value{GDBN} can find the correct copies of both
18882 @file{c:\sys\bin\foo.dll}, and @file{z:\sys\bin\bar.dll}.
18884 If that still does not find the binary, @value{GDBN} tries
18885 removing the whole drive spec from the target file name:
18888 c:/foo/bar.dll @result{} /path/to/sysroot/foo/bar.dll
18891 This last lookup makes it possible to not care about the drive name,
18892 if you don't want or need to.
18894 The @code{set solib-absolute-prefix} command is an alias for @code{set
18897 @cindex default system root
18898 @cindex @samp{--with-sysroot}
18899 You can set the default system root by using the configure-time
18900 @samp{--with-sysroot} option. If the system root is inside
18901 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
18902 @samp{--exec-prefix}), then the default system root will be updated
18903 automatically if the installed @value{GDBN} is moved to a new
18906 @kindex show sysroot
18908 Display the current executable and shared library prefix.
18910 @kindex set solib-search-path
18911 @item set solib-search-path @var{path}
18912 If this variable is set, @var{path} is a colon-separated list of
18913 directories to search for shared libraries. @samp{solib-search-path}
18914 is used after @samp{sysroot} fails to locate the library, or if the
18915 path to the library is relative instead of absolute. If you want to
18916 use @samp{solib-search-path} instead of @samp{sysroot}, be sure to set
18917 @samp{sysroot} to a nonexistent directory to prevent @value{GDBN} from
18918 finding your host's libraries. @samp{sysroot} is preferred; setting
18919 it to a nonexistent directory may interfere with automatic loading
18920 of shared library symbols.
18922 @kindex show solib-search-path
18923 @item show solib-search-path
18924 Display the current shared library search path.
18926 @cindex DOS file-name semantics of file names.
18927 @kindex set target-file-system-kind (unix|dos-based|auto)
18928 @kindex show target-file-system-kind
18929 @item set target-file-system-kind @var{kind}
18930 Set assumed file system kind for target reported file names.
18932 Shared library file names as reported by the target system may not
18933 make sense as is on the system @value{GDBN} is running on. For
18934 example, when remote debugging a target that has MS-DOS based file
18935 system semantics, from a Unix host, the target may be reporting to
18936 @value{GDBN} a list of loaded shared libraries with file names such as
18937 @file{c:\Windows\kernel32.dll}. On Unix hosts, there's no concept of
18938 drive letters, so the @samp{c:\} prefix is not normally understood as
18939 indicating an absolute file name, and neither is the backslash
18940 normally considered a directory separator character. In that case,
18941 the native file system would interpret this whole absolute file name
18942 as a relative file name with no directory components. This would make
18943 it impossible to point @value{GDBN} at a copy of the remote target's
18944 shared libraries on the host using @code{set sysroot}, and impractical
18945 with @code{set solib-search-path}. Setting
18946 @code{target-file-system-kind} to @code{dos-based} tells @value{GDBN}
18947 to interpret such file names similarly to how the target would, and to
18948 map them to file names valid on @value{GDBN}'s native file system
18949 semantics. The value of @var{kind} can be @code{"auto"}, in addition
18950 to one of the supported file system kinds. In that case, @value{GDBN}
18951 tries to determine the appropriate file system variant based on the
18952 current target's operating system (@pxref{ABI, ,Configuring the
18953 Current ABI}). The supported file system settings are:
18957 Instruct @value{GDBN} to assume the target file system is of Unix
18958 kind. Only file names starting the forward slash (@samp{/}) character
18959 are considered absolute, and the directory separator character is also
18963 Instruct @value{GDBN} to assume the target file system is DOS based.
18964 File names starting with either a forward slash, or a drive letter
18965 followed by a colon (e.g., @samp{c:}), are considered absolute, and
18966 both the slash (@samp{/}) and the backslash (@samp{\\}) characters are
18967 considered directory separators.
18970 Instruct @value{GDBN} to use the file system kind associated with the
18971 target operating system (@pxref{ABI, ,Configuring the Current ABI}).
18972 This is the default.
18976 @cindex file name canonicalization
18977 @cindex base name differences
18978 When processing file names provided by the user, @value{GDBN}
18979 frequently needs to compare them to the file names recorded in the
18980 program's debug info. Normally, @value{GDBN} compares just the
18981 @dfn{base names} of the files as strings, which is reasonably fast
18982 even for very large programs. (The base name of a file is the last
18983 portion of its name, after stripping all the leading directories.)
18984 This shortcut in comparison is based upon the assumption that files
18985 cannot have more than one base name. This is usually true, but
18986 references to files that use symlinks or similar filesystem
18987 facilities violate that assumption. If your program records files
18988 using such facilities, or if you provide file names to @value{GDBN}
18989 using symlinks etc., you can set @code{basenames-may-differ} to
18990 @code{true} to instruct @value{GDBN} to completely canonicalize each
18991 pair of file names it needs to compare. This will make file-name
18992 comparisons accurate, but at a price of a significant slowdown.
18995 @item set basenames-may-differ
18996 @kindex set basenames-may-differ
18997 Set whether a source file may have multiple base names.
18999 @item show basenames-may-differ
19000 @kindex show basenames-may-differ
19001 Show whether a source file may have multiple base names.
19005 @section File Caching
19006 @cindex caching of opened files
19007 @cindex caching of bfd objects
19009 To speed up file loading, and reduce memory usage, @value{GDBN} will
19010 reuse the @code{bfd} objects used to track open files. @xref{Top, ,
19011 BFD, bfd, The Binary File Descriptor Library}. The following commands
19012 allow visibility and control of the caching behavior.
19015 @kindex maint info bfds
19016 @item maint info bfds
19017 This prints information about each @code{bfd} object that is known to
19020 @kindex maint set bfd-sharing
19021 @kindex maint show bfd-sharing
19022 @kindex bfd caching
19023 @item maint set bfd-sharing
19024 @item maint show bfd-sharing
19025 Control whether @code{bfd} objects can be shared. When sharing is
19026 enabled @value{GDBN} reuses already open @code{bfd} objects rather
19027 than reopening the same file. Turning sharing off does not cause
19028 already shared @code{bfd} objects to be unshared, but all future files
19029 that are opened will create a new @code{bfd} object. Similarly,
19030 re-enabling sharing does not cause multiple existing @code{bfd}
19031 objects to be collapsed into a single shared @code{bfd} object.
19033 @kindex set debug bfd-cache @var{level}
19034 @kindex bfd caching
19035 @item set debug bfd-cache @var{level}
19036 Turns on debugging of the bfd cache, setting the level to @var{level}.
19038 @kindex show debug bfd-cache
19039 @kindex bfd caching
19040 @item show debug bfd-cache
19041 Show the current debugging level of the bfd cache.
19044 @node Separate Debug Files
19045 @section Debugging Information in Separate Files
19046 @cindex separate debugging information files
19047 @cindex debugging information in separate files
19048 @cindex @file{.debug} subdirectories
19049 @cindex debugging information directory, global
19050 @cindex global debugging information directories
19051 @cindex build ID, and separate debugging files
19052 @cindex @file{.build-id} directory
19054 @value{GDBN} allows you to put a program's debugging information in a
19055 file separate from the executable itself, in a way that allows
19056 @value{GDBN} to find and load the debugging information automatically.
19057 Since debugging information can be very large---sometimes larger
19058 than the executable code itself---some systems distribute debugging
19059 information for their executables in separate files, which users can
19060 install only when they need to debug a problem.
19062 @value{GDBN} supports two ways of specifying the separate debug info
19067 The executable contains a @dfn{debug link} that specifies the name of
19068 the separate debug info file. The separate debug file's name is
19069 usually @file{@var{executable}.debug}, where @var{executable} is the
19070 name of the corresponding executable file without leading directories
19071 (e.g., @file{ls.debug} for @file{/usr/bin/ls}). In addition, the
19072 debug link specifies a 32-bit @dfn{Cyclic Redundancy Check} (CRC)
19073 checksum for the debug file, which @value{GDBN} uses to validate that
19074 the executable and the debug file came from the same build.
19077 The executable contains a @dfn{build ID}, a unique bit string that is
19078 also present in the corresponding debug info file. (This is supported
19079 only on some operating systems, when using the ELF or PE file formats
19080 for binary files and the @sc{gnu} Binutils.) For more details about
19081 this feature, see the description of the @option{--build-id}
19082 command-line option in @ref{Options, , Command Line Options, ld.info,
19083 The GNU Linker}. The debug info file's name is not specified
19084 explicitly by the build ID, but can be computed from the build ID, see
19088 Depending on the way the debug info file is specified, @value{GDBN}
19089 uses two different methods of looking for the debug file:
19093 For the ``debug link'' method, @value{GDBN} looks up the named file in
19094 the directory of the executable file, then in a subdirectory of that
19095 directory named @file{.debug}, and finally under each one of the global debug
19096 directories, in a subdirectory whose name is identical to the leading
19097 directories of the executable's absolute file name.
19100 For the ``build ID'' method, @value{GDBN} looks in the
19101 @file{.build-id} subdirectory of each one of the global debug directories for
19102 a file named @file{@var{nn}/@var{nnnnnnnn}.debug}, where @var{nn} are the
19103 first 2 hex characters of the build ID bit string, and @var{nnnnnnnn}
19104 are the rest of the bit string. (Real build ID strings are 32 or more
19105 hex characters, not 10.)
19108 So, for example, suppose you ask @value{GDBN} to debug
19109 @file{/usr/bin/ls}, which has a debug link that specifies the
19110 file @file{ls.debug}, and a build ID whose value in hex is
19111 @code{abcdef1234}. If the list of the global debug directories includes
19112 @file{/usr/lib/debug}, then @value{GDBN} will look for the following
19113 debug information files, in the indicated order:
19117 @file{/usr/lib/debug/.build-id/ab/cdef1234.debug}
19119 @file{/usr/bin/ls.debug}
19121 @file{/usr/bin/.debug/ls.debug}
19123 @file{/usr/lib/debug/usr/bin/ls.debug}.
19126 @anchor{debug-file-directory}
19127 Global debugging info directories default to what is set by @value{GDBN}
19128 configure option @option{--with-separate-debug-dir}. During @value{GDBN} run
19129 you can also set the global debugging info directories, and view the list
19130 @value{GDBN} is currently using.
19134 @kindex set debug-file-directory
19135 @item set debug-file-directory @var{directories}
19136 Set the directories which @value{GDBN} searches for separate debugging
19137 information files to @var{directory}. Multiple path components can be set
19138 concatenating them by a path separator.
19140 @kindex show debug-file-directory
19141 @item show debug-file-directory
19142 Show the directories @value{GDBN} searches for separate debugging
19147 @cindex @code{.gnu_debuglink} sections
19148 @cindex debug link sections
19149 A debug link is a special section of the executable file named
19150 @code{.gnu_debuglink}. The section must contain:
19154 A filename, with any leading directory components removed, followed by
19157 zero to three bytes of padding, as needed to reach the next four-byte
19158 boundary within the section, and
19160 a four-byte CRC checksum, stored in the same endianness used for the
19161 executable file itself. The checksum is computed on the debugging
19162 information file's full contents by the function given below, passing
19163 zero as the @var{crc} argument.
19166 Any executable file format can carry a debug link, as long as it can
19167 contain a section named @code{.gnu_debuglink} with the contents
19170 @cindex @code{.note.gnu.build-id} sections
19171 @cindex build ID sections
19172 The build ID is a special section in the executable file (and in other
19173 ELF binary files that @value{GDBN} may consider). This section is
19174 often named @code{.note.gnu.build-id}, but that name is not mandatory.
19175 It contains unique identification for the built files---the ID remains
19176 the same across multiple builds of the same build tree. The default
19177 algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
19178 content for the build ID string. The same section with an identical
19179 value is present in the original built binary with symbols, in its
19180 stripped variant, and in the separate debugging information file.
19182 The debugging information file itself should be an ordinary
19183 executable, containing a full set of linker symbols, sections, and
19184 debugging information. The sections of the debugging information file
19185 should have the same names, addresses, and sizes as the original file,
19186 but they need not contain any data---much like a @code{.bss} section
19187 in an ordinary executable.
19189 The @sc{gnu} binary utilities (Binutils) package includes the
19190 @samp{objcopy} utility that can produce
19191 the separated executable / debugging information file pairs using the
19192 following commands:
19195 @kbd{objcopy --only-keep-debug foo foo.debug}
19200 These commands remove the debugging
19201 information from the executable file @file{foo} and place it in the file
19202 @file{foo.debug}. You can use the first, second or both methods to link the
19207 The debug link method needs the following additional command to also leave
19208 behind a debug link in @file{foo}:
19211 @kbd{objcopy --add-gnu-debuglink=foo.debug foo}
19214 Ulrich Drepper's @file{elfutils} package, starting with version 0.53, contains
19215 a version of the @code{strip} command such that the command @kbd{strip foo -f
19216 foo.debug} has the same functionality as the two @code{objcopy} commands and
19217 the @code{ln -s} command above, together.
19220 Build ID gets embedded into the main executable using @code{ld --build-id} or
19221 the @value{NGCC} counterpart @code{gcc -Wl,--build-id}. Build ID support plus
19222 compatibility fixes for debug files separation are present in @sc{gnu} binary
19223 utilities (Binutils) package since version 2.18.
19228 @cindex CRC algorithm definition
19229 The CRC used in @code{.gnu_debuglink} is the CRC-32 defined in
19230 IEEE 802.3 using the polynomial:
19232 @c TexInfo requires naked braces for multi-digit exponents for Tex
19233 @c output, but this causes HTML output to barf. HTML has to be set using
19234 @c raw commands. So we end up having to specify this equation in 2
19239 <em>x</em><sup>32</sup> + <em>x</em><sup>26</sup> + <em>x</em><sup>23</sup> + <em>x</em><sup>22</sup> + <em>x</em><sup>16</sup> + <em>x</em><sup>12</sup> + <em>x</em><sup>11</sup>
19240 + <em>x</em><sup>10</sup> + <em>x</em><sup>8</sup> + <em>x</em><sup>7</sup> + <em>x</em><sup>5</sup> + <em>x</em><sup>4</sup> + <em>x</em><sup>2</sup> + <em>x</em> + 1
19246 @math{x^{32} + x^{26} + x^{23} + x^{22} + x^{16} + x^{12} + x^{11}}
19247 @math{+ x^{10} + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1}
19251 The function is computed byte at a time, taking the least
19252 significant bit of each byte first. The initial pattern
19253 @code{0xffffffff} is used, to ensure leading zeros affect the CRC and
19254 the final result is inverted to ensure trailing zeros also affect the
19257 @emph{Note:} This is the same CRC polynomial as used in handling the
19258 @dfn{Remote Serial Protocol} @code{qCRC} packet (@pxref{qCRC packet}).
19259 However in the case of the Remote Serial Protocol, the CRC is computed
19260 @emph{most} significant bit first, and the result is not inverted, so
19261 trailing zeros have no effect on the CRC value.
19263 To complete the description, we show below the code of the function
19264 which produces the CRC used in @code{.gnu_debuglink}. Inverting the
19265 initially supplied @code{crc} argument means that an initial call to
19266 this function passing in zero will start computing the CRC using
19269 @kindex gnu_debuglink_crc32
19272 gnu_debuglink_crc32 (unsigned long crc,
19273 unsigned char *buf, size_t len)
19275 static const unsigned long crc32_table[256] =
19277 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
19278 0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
19279 0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
19280 0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
19281 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, 0x136c9856,
19282 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
19283 0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
19284 0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
19285 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
19286 0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
19287 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
19288 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
19289 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
19290 0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
19291 0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
19292 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
19293 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
19294 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
19295 0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
19296 0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
19297 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
19298 0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
19299 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
19300 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
19301 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
19302 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
19303 0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
19304 0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
19305 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
19306 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
19307 0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
19308 0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
19309 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
19310 0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
19311 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
19312 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
19313 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
19314 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
19315 0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
19316 0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
19317 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
19318 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
19319 0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
19320 0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
19321 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
19322 0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
19323 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
19324 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
19325 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
19326 0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
19327 0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
19330 unsigned char *end;
19332 crc = ~crc & 0xffffffff;
19333 for (end = buf + len; buf < end; ++buf)
19334 crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
19335 return ~crc & 0xffffffff;
19340 This computation does not apply to the ``build ID'' method.
19342 @node MiniDebugInfo
19343 @section Debugging information in a special section
19344 @cindex separate debug sections
19345 @cindex @samp{.gnu_debugdata} section
19347 Some systems ship pre-built executables and libraries that have a
19348 special @samp{.gnu_debugdata} section. This feature is called
19349 @dfn{MiniDebugInfo}. This section holds an LZMA-compressed object and
19350 is used to supply extra symbols for backtraces.
19352 The intent of this section is to provide extra minimal debugging
19353 information for use in simple backtraces. It is not intended to be a
19354 replacement for full separate debugging information (@pxref{Separate
19355 Debug Files}). The example below shows the intended use; however,
19356 @value{GDBN} does not currently put restrictions on what sort of
19357 debugging information might be included in the section.
19359 @value{GDBN} has support for this extension. If the section exists,
19360 then it is used provided that no other source of debugging information
19361 can be found, and that @value{GDBN} was configured with LZMA support.
19363 This section can be easily created using @command{objcopy} and other
19364 standard utilities:
19367 # Extract the dynamic symbols from the main binary, there is no need
19368 # to also have these in the normal symbol table.
19369 nm -D @var{binary} --format=posix --defined-only \
19370 | awk '@{ print $1 @}' | sort > dynsyms
19372 # Extract all the text (i.e. function) symbols from the debuginfo.
19373 # (Note that we actually also accept "D" symbols, for the benefit
19374 # of platforms like PowerPC64 that use function descriptors.)
19375 nm @var{binary} --format=posix --defined-only \
19376 | awk '@{ if ($2 == "T" || $2 == "t" || $2 == "D") print $1 @}' \
19379 # Keep all the function symbols not already in the dynamic symbol
19381 comm -13 dynsyms funcsyms > keep_symbols
19383 # Separate full debug info into debug binary.
19384 objcopy --only-keep-debug @var{binary} debug
19386 # Copy the full debuginfo, keeping only a minimal set of symbols and
19387 # removing some unnecessary sections.
19388 objcopy -S --remove-section .gdb_index --remove-section .comment \
19389 --keep-symbols=keep_symbols debug mini_debuginfo
19391 # Drop the full debug info from the original binary.
19392 strip --strip-all -R .comment @var{binary}
19394 # Inject the compressed data into the .gnu_debugdata section of the
19397 objcopy --add-section .gnu_debugdata=mini_debuginfo.xz @var{binary}
19401 @section Index Files Speed Up @value{GDBN}
19402 @cindex index files
19403 @cindex @samp{.gdb_index} section
19405 When @value{GDBN} finds a symbol file, it scans the symbols in the
19406 file in order to construct an internal symbol table. This lets most
19407 @value{GDBN} operations work quickly---at the cost of a delay early
19408 on. For large programs, this delay can be quite lengthy, so
19409 @value{GDBN} provides a way to build an index, which speeds up
19412 The index is stored as a section in the symbol file. @value{GDBN} can
19413 write the index to a file, then you can put it into the symbol file
19414 using @command{objcopy}.
19416 To create an index file, use the @code{save gdb-index} command:
19419 @item save gdb-index @var{directory}
19420 @kindex save gdb-index
19421 Create an index file for each symbol file currently known by
19422 @value{GDBN}. Each file is named after its corresponding symbol file,
19423 with @samp{.gdb-index} appended, and is written into the given
19427 Once you have created an index file you can merge it into your symbol
19428 file, here named @file{symfile}, using @command{objcopy}:
19431 $ objcopy --add-section .gdb_index=symfile.gdb-index \
19432 --set-section-flags .gdb_index=readonly symfile symfile
19435 @value{GDBN} will normally ignore older versions of @file{.gdb_index}
19436 sections that have been deprecated. Usually they are deprecated because
19437 they are missing a new feature or have performance issues.
19438 To tell @value{GDBN} to use a deprecated index section anyway
19439 specify @code{set use-deprecated-index-sections on}.
19440 The default is @code{off}.
19441 This can speed up startup, but may result in some functionality being lost.
19442 @xref{Index Section Format}.
19444 @emph{Warning:} Setting @code{use-deprecated-index-sections} to @code{on}
19445 must be done before gdb reads the file. The following will not work:
19448 $ gdb -ex "set use-deprecated-index-sections on" <program>
19451 Instead you must do, for example,
19454 $ gdb -iex "set use-deprecated-index-sections on" <program>
19457 There are currently some limitation on indices. They only work when
19458 for DWARF debugging information, not stabs. And, they do not
19459 currently work for programs using Ada.
19461 @node Symbol Errors
19462 @section Errors Reading Symbol Files
19464 While reading a symbol file, @value{GDBN} occasionally encounters problems,
19465 such as symbol types it does not recognize, or known bugs in compiler
19466 output. By default, @value{GDBN} does not notify you of such problems, since
19467 they are relatively common and primarily of interest to people
19468 debugging compilers. If you are interested in seeing information
19469 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
19470 only one message about each such type of problem, no matter how many
19471 times the problem occurs; or you can ask @value{GDBN} to print more messages,
19472 to see how many times the problems occur, with the @code{set
19473 complaints} command (@pxref{Messages/Warnings, ,Optional Warnings and
19476 The messages currently printed, and their meanings, include:
19479 @item inner block not inside outer block in @var{symbol}
19481 The symbol information shows where symbol scopes begin and end
19482 (such as at the start of a function or a block of statements). This
19483 error indicates that an inner scope block is not fully contained
19484 in its outer scope blocks.
19486 @value{GDBN} circumvents the problem by treating the inner block as if it had
19487 the same scope as the outer block. In the error message, @var{symbol}
19488 may be shown as ``@code{(don't know)}'' if the outer block is not a
19491 @item block at @var{address} out of order
19493 The symbol information for symbol scope blocks should occur in
19494 order of increasing addresses. This error indicates that it does not
19497 @value{GDBN} does not circumvent this problem, and has trouble
19498 locating symbols in the source file whose symbols it is reading. (You
19499 can often determine what source file is affected by specifying
19500 @code{set verbose on}. @xref{Messages/Warnings, ,Optional Warnings and
19503 @item bad block start address patched
19505 The symbol information for a symbol scope block has a start address
19506 smaller than the address of the preceding source line. This is known
19507 to occur in the SunOS 4.1.1 (and earlier) C compiler.
19509 @value{GDBN} circumvents the problem by treating the symbol scope block as
19510 starting on the previous source line.
19512 @item bad string table offset in symbol @var{n}
19515 Symbol number @var{n} contains a pointer into the string table which is
19516 larger than the size of the string table.
19518 @value{GDBN} circumvents the problem by considering the symbol to have the
19519 name @code{foo}, which may cause other problems if many symbols end up
19522 @item unknown symbol type @code{0x@var{nn}}
19524 The symbol information contains new data types that @value{GDBN} does
19525 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
19526 uncomprehended information, in hexadecimal.
19528 @value{GDBN} circumvents the error by ignoring this symbol information.
19529 This usually allows you to debug your program, though certain symbols
19530 are not accessible. If you encounter such a problem and feel like
19531 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
19532 on @code{complain}, then go up to the function @code{read_dbx_symtab}
19533 and examine @code{*bufp} to see the symbol.
19535 @item stub type has NULL name
19537 @value{GDBN} could not find the full definition for a struct or class.
19539 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
19540 The symbol information for a C@t{++} member function is missing some
19541 information that recent versions of the compiler should have output for
19544 @item info mismatch between compiler and debugger
19546 @value{GDBN} could not parse a type specification output by the compiler.
19551 @section GDB Data Files
19553 @cindex prefix for data files
19554 @value{GDBN} will sometimes read an auxiliary data file. These files
19555 are kept in a directory known as the @dfn{data directory}.
19557 You can set the data directory's name, and view the name @value{GDBN}
19558 is currently using.
19561 @kindex set data-directory
19562 @item set data-directory @var{directory}
19563 Set the directory which @value{GDBN} searches for auxiliary data files
19564 to @var{directory}.
19566 @kindex show data-directory
19567 @item show data-directory
19568 Show the directory @value{GDBN} searches for auxiliary data files.
19571 @cindex default data directory
19572 @cindex @samp{--with-gdb-datadir}
19573 You can set the default data directory by using the configure-time
19574 @samp{--with-gdb-datadir} option. If the data directory is inside
19575 @value{GDBN}'s configured binary prefix (set with @samp{--prefix} or
19576 @samp{--exec-prefix}), then the default data directory will be updated
19577 automatically if the installed @value{GDBN} is moved to a new
19580 The data directory may also be specified with the
19581 @code{--data-directory} command line option.
19582 @xref{Mode Options}.
19585 @chapter Specifying a Debugging Target
19587 @cindex debugging target
19588 A @dfn{target} is the execution environment occupied by your program.
19590 Often, @value{GDBN} runs in the same host environment as your program;
19591 in that case, the debugging target is specified as a side effect when
19592 you use the @code{file} or @code{core} commands. When you need more
19593 flexibility---for example, running @value{GDBN} on a physically separate
19594 host, or controlling a standalone system over a serial port or a
19595 realtime system over a TCP/IP connection---you can use the @code{target}
19596 command to specify one of the target types configured for @value{GDBN}
19597 (@pxref{Target Commands, ,Commands for Managing Targets}).
19599 @cindex target architecture
19600 It is possible to build @value{GDBN} for several different @dfn{target
19601 architectures}. When @value{GDBN} is built like that, you can choose
19602 one of the available architectures with the @kbd{set architecture}
19606 @kindex set architecture
19607 @kindex show architecture
19608 @item set architecture @var{arch}
19609 This command sets the current target architecture to @var{arch}. The
19610 value of @var{arch} can be @code{"auto"}, in addition to one of the
19611 supported architectures.
19613 @item show architecture
19614 Show the current target architecture.
19616 @item set processor
19618 @kindex set processor
19619 @kindex show processor
19620 These are alias commands for, respectively, @code{set architecture}
19621 and @code{show architecture}.
19625 * Active Targets:: Active targets
19626 * Target Commands:: Commands for managing targets
19627 * Byte Order:: Choosing target byte order
19630 @node Active Targets
19631 @section Active Targets
19633 @cindex stacking targets
19634 @cindex active targets
19635 @cindex multiple targets
19637 There are multiple classes of targets such as: processes, executable files or
19638 recording sessions. Core files belong to the process class, making core file
19639 and process mutually exclusive. Otherwise, @value{GDBN} can work concurrently
19640 on multiple active targets, one in each class. This allows you to (for
19641 example) start a process and inspect its activity, while still having access to
19642 the executable file after the process finishes. Or if you start process
19643 recording (@pxref{Reverse Execution}) and @code{reverse-step} there, you are
19644 presented a virtual layer of the recording target, while the process target
19645 remains stopped at the chronologically last point of the process execution.
19647 Use the @code{core-file} and @code{exec-file} commands to select a new core
19648 file or executable target (@pxref{Files, ,Commands to Specify Files}). To
19649 specify as a target a process that is already running, use the @code{attach}
19650 command (@pxref{Attach, ,Debugging an Already-running Process}).
19652 @node Target Commands
19653 @section Commands for Managing Targets
19656 @item target @var{type} @var{parameters}
19657 Connects the @value{GDBN} host environment to a target machine or
19658 process. A target is typically a protocol for talking to debugging
19659 facilities. You use the argument @var{type} to specify the type or
19660 protocol of the target machine.
19662 Further @var{parameters} are interpreted by the target protocol, but
19663 typically include things like device names or host names to connect
19664 with, process numbers, and baud rates.
19666 The @code{target} command does not repeat if you press @key{RET} again
19667 after executing the command.
19669 @kindex help target
19671 Displays the names of all targets available. To display targets
19672 currently selected, use either @code{info target} or @code{info files}
19673 (@pxref{Files, ,Commands to Specify Files}).
19675 @item help target @var{name}
19676 Describe a particular target, including any parameters necessary to
19679 @kindex set gnutarget
19680 @item set gnutarget @var{args}
19681 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
19682 knows whether it is reading an @dfn{executable},
19683 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
19684 with the @code{set gnutarget} command. Unlike most @code{target} commands,
19685 with @code{gnutarget} the @code{target} refers to a program, not a machine.
19688 @emph{Warning:} To specify a file format with @code{set gnutarget},
19689 you must know the actual BFD name.
19693 @xref{Files, , Commands to Specify Files}.
19695 @kindex show gnutarget
19696 @item show gnutarget
19697 Use the @code{show gnutarget} command to display what file format
19698 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
19699 @value{GDBN} will determine the file format for each file automatically,
19700 and @code{show gnutarget} displays @samp{The current BFD target is "auto"}.
19703 @cindex common targets
19704 Here are some common targets (available, or not, depending on the GDB
19709 @item target exec @var{program}
19710 @cindex executable file target
19711 An executable file. @samp{target exec @var{program}} is the same as
19712 @samp{exec-file @var{program}}.
19714 @item target core @var{filename}
19715 @cindex core dump file target
19716 A core dump file. @samp{target core @var{filename}} is the same as
19717 @samp{core-file @var{filename}}.
19719 @item target remote @var{medium}
19720 @cindex remote target
19721 A remote system connected to @value{GDBN} via a serial line or network
19722 connection. This command tells @value{GDBN} to use its own remote
19723 protocol over @var{medium} for debugging. @xref{Remote Debugging}.
19725 For example, if you have a board connected to @file{/dev/ttya} on the
19726 machine running @value{GDBN}, you could say:
19729 target remote /dev/ttya
19732 @code{target remote} supports the @code{load} command. This is only
19733 useful if you have some other way of getting the stub to the target
19734 system, and you can put it somewhere in memory where it won't get
19735 clobbered by the download.
19737 @item target sim @r{[}@var{simargs}@r{]} @dots{}
19738 @cindex built-in simulator target
19739 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
19747 works; however, you cannot assume that a specific memory map, device
19748 drivers, or even basic I/O is available, although some simulators do
19749 provide these. For info about any processor-specific simulator details,
19750 see the appropriate section in @ref{Embedded Processors, ,Embedded
19753 @item target native
19754 @cindex native target
19755 Setup for local/native process debugging. Useful to make the
19756 @code{run} command spawn native processes (likewise @code{attach},
19757 etc.@:) even when @code{set auto-connect-native-target} is @code{off}
19758 (@pxref{set auto-connect-native-target}).
19762 Different targets are available on different configurations of @value{GDBN};
19763 your configuration may have more or fewer targets.
19765 Many remote targets require you to download the executable's code once
19766 you've successfully established a connection. You may wish to control
19767 various aspects of this process.
19772 @kindex set hash@r{, for remote monitors}
19773 @cindex hash mark while downloading
19774 This command controls whether a hash mark @samp{#} is displayed while
19775 downloading a file to the remote monitor. If on, a hash mark is
19776 displayed after each S-record is successfully downloaded to the
19780 @kindex show hash@r{, for remote monitors}
19781 Show the current status of displaying the hash mark.
19783 @item set debug monitor
19784 @kindex set debug monitor
19785 @cindex display remote monitor communications
19786 Enable or disable display of communications messages between
19787 @value{GDBN} and the remote monitor.
19789 @item show debug monitor
19790 @kindex show debug monitor
19791 Show the current status of displaying communications between
19792 @value{GDBN} and the remote monitor.
19797 @kindex load @var{filename} @var{offset}
19798 @item load @var{filename} @var{offset}
19800 Depending on what remote debugging facilities are configured into
19801 @value{GDBN}, the @code{load} command may be available. Where it exists, it
19802 is meant to make @var{filename} (an executable) available for debugging
19803 on the remote system---by downloading, or dynamic linking, for example.
19804 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
19805 the @code{add-symbol-file} command.
19807 If your @value{GDBN} does not have a @code{load} command, attempting to
19808 execute it gets the error message ``@code{You can't do that when your
19809 target is @dots{}}''
19811 The file is loaded at whatever address is specified in the executable.
19812 For some object file formats, you can specify the load address when you
19813 link the program; for other formats, like a.out, the object file format
19814 specifies a fixed address.
19815 @c FIXME! This would be a good place for an xref to the GNU linker doc.
19817 It is also possible to tell @value{GDBN} to load the executable file at a
19818 specific offset described by the optional argument @var{offset}. When
19819 @var{offset} is provided, @var{filename} must also be provided.
19821 Depending on the remote side capabilities, @value{GDBN} may be able to
19822 load programs into flash memory.
19824 @code{load} does not repeat if you press @key{RET} again after using it.
19829 @kindex flash-erase
19831 @anchor{flash-erase}
19833 Erases all known flash memory regions on the target.
19838 @section Choosing Target Byte Order
19840 @cindex choosing target byte order
19841 @cindex target byte order
19843 Some types of processors, such as the @acronym{MIPS}, PowerPC, and Renesas SH,
19844 offer the ability to run either big-endian or little-endian byte
19845 orders. Usually the executable or symbol will include a bit to
19846 designate the endian-ness, and you will not need to worry about
19847 which to use. However, you may still find it useful to adjust
19848 @value{GDBN}'s idea of processor endian-ness manually.
19852 @item set endian big
19853 Instruct @value{GDBN} to assume the target is big-endian.
19855 @item set endian little
19856 Instruct @value{GDBN} to assume the target is little-endian.
19858 @item set endian auto
19859 Instruct @value{GDBN} to use the byte order associated with the
19863 Display @value{GDBN}'s current idea of the target byte order.
19867 Note that these commands merely adjust interpretation of symbolic
19868 data on the host, and that they have absolutely no effect on the
19872 @node Remote Debugging
19873 @chapter Debugging Remote Programs
19874 @cindex remote debugging
19876 If you are trying to debug a program running on a machine that cannot run
19877 @value{GDBN} in the usual way, it is often useful to use remote debugging.
19878 For example, you might use remote debugging on an operating system kernel,
19879 or on a small system which does not have a general purpose operating system
19880 powerful enough to run a full-featured debugger.
19882 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
19883 to make this work with particular debugging targets. In addition,
19884 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
19885 but not specific to any particular target system) which you can use if you
19886 write the remote stubs---the code that runs on the remote system to
19887 communicate with @value{GDBN}.
19889 Other remote targets may be available in your
19890 configuration of @value{GDBN}; use @code{help target} to list them.
19893 * Connecting:: Connecting to a remote target
19894 * File Transfer:: Sending files to a remote system
19895 * Server:: Using the gdbserver program
19896 * Remote Configuration:: Remote configuration
19897 * Remote Stub:: Implementing a remote stub
19901 @section Connecting to a Remote Target
19902 @cindex remote debugging, connecting
19903 @cindex @code{gdbserver}, connecting
19904 @cindex remote debugging, types of connections
19905 @cindex @code{gdbserver}, types of connections
19906 @cindex @code{gdbserver}, @code{target remote} mode
19907 @cindex @code{gdbserver}, @code{target extended-remote} mode
19909 This section describes how to connect to a remote target, including the
19910 types of connections and their differences, how to set up executable and
19911 symbol files on the host and target, and the commands used for
19912 connecting to and disconnecting from the remote target.
19914 @subsection Types of Remote Connections
19916 @value{GDBN} supports two types of remote connections, @code{target remote}
19917 mode and @code{target extended-remote} mode. Note that many remote targets
19918 support only @code{target remote} mode. There are several major
19919 differences between the two types of connections, enumerated here:
19923 @cindex remote debugging, detach and program exit
19924 @item Result of detach or program exit
19925 @strong{With target remote mode:} When the debugged program exits or you
19926 detach from it, @value{GDBN} disconnects from the target. When using
19927 @code{gdbserver}, @code{gdbserver} will exit.
19929 @strong{With target extended-remote mode:} When the debugged program exits or
19930 you detach from it, @value{GDBN} remains connected to the target, even
19931 though no program is running. You can rerun the program, attach to a
19932 running program, or use @code{monitor} commands specific to the target.
19934 When using @code{gdbserver} in this case, it does not exit unless it was
19935 invoked using the @option{--once} option. If the @option{--once} option
19936 was not used, you can ask @code{gdbserver} to exit using the
19937 @code{monitor exit} command (@pxref{Monitor Commands for gdbserver}).
19939 @item Specifying the program to debug
19940 For both connection types you use the @code{file} command to specify the
19941 program on the host system. If you are using @code{gdbserver} there are
19942 some differences in how to specify the location of the program on the
19945 @strong{With target remote mode:} You must either specify the program to debug
19946 on the @code{gdbserver} command line or use the @option{--attach} option
19947 (@pxref{Attaching to a program,,Attaching to a Running Program}).
19949 @cindex @option{--multi}, @code{gdbserver} option
19950 @strong{With target extended-remote mode:} You may specify the program to debug
19951 on the @code{gdbserver} command line, or you can load the program or attach
19952 to it using @value{GDBN} commands after connecting to @code{gdbserver}.
19954 @anchor{--multi Option in Types of Remote Connnections}
19955 You can start @code{gdbserver} without supplying an initial command to run
19956 or process ID to attach. To do this, use the @option{--multi} command line
19957 option. Then you can connect using @code{target extended-remote} and start
19958 the program you want to debug (see below for details on using the
19959 @code{run} command in this scenario). Note that the conditions under which
19960 @code{gdbserver} terminates depend on how @value{GDBN} connects to it
19961 (@code{target remote} or @code{target extended-remote}). The
19962 @option{--multi} option to @code{gdbserver} has no influence on that.
19964 @item The @code{run} command
19965 @strong{With target remote mode:} The @code{run} command is not
19966 supported. Once a connection has been established, you can use all
19967 the usual @value{GDBN} commands to examine and change data. The
19968 remote program is already running, so you can use commands like
19969 @kbd{step} and @kbd{continue}.
19971 @strong{With target extended-remote mode:} The @code{run} command is
19972 supported. The @code{run} command uses the value set by
19973 @code{set remote exec-file} (@pxref{set remote exec-file}) to select
19974 the program to run. Command line arguments are supported, except for
19975 wildcard expansion and I/O redirection (@pxref{Arguments}).
19977 If you specify the program to debug on the command line, then the
19978 @code{run} command is not required to start execution, and you can
19979 resume using commands like @kbd{step} and @kbd{continue} as with
19980 @code{target remote} mode.
19982 @anchor{Attaching in Types of Remote Connections}
19984 @strong{With target remote mode:} The @value{GDBN} command @code{attach} is
19985 not supported. To attach to a running program using @code{gdbserver}, you
19986 must use the @option{--attach} option (@pxref{Running gdbserver}).
19988 @strong{With target extended-remote mode:} To attach to a running program,
19989 you may use the @code{attach} command after the connection has been
19990 established. If you are using @code{gdbserver}, you may also invoke
19991 @code{gdbserver} using the @option{--attach} option
19992 (@pxref{Running gdbserver}).
19996 @anchor{Host and target files}
19997 @subsection Host and Target Files
19998 @cindex remote debugging, symbol files
19999 @cindex symbol files, remote debugging
20001 @value{GDBN}, running on the host, needs access to symbol and debugging
20002 information for your program running on the target. This requires
20003 access to an unstripped copy of your program, and possibly any associated
20004 symbol files. Note that this section applies equally to both @code{target
20005 remote} mode and @code{target extended-remote} mode.
20007 Some remote targets (@pxref{qXfer executable filename read}, and
20008 @pxref{Host I/O Packets}) allow @value{GDBN} to access program files over
20009 the same connection used to communicate with @value{GDBN}. With such a
20010 target, if the remote program is unstripped, the only command you need is
20011 @code{target remote} (or @code{target extended-remote}).
20013 If the remote program is stripped, or the target does not support remote
20014 program file access, start up @value{GDBN} using the name of the local
20015 unstripped copy of your program as the first argument, or use the
20016 @code{file} command. Use @code{set sysroot} to specify the location (on
20017 the host) of target libraries (unless your @value{GDBN} was compiled with
20018 the correct sysroot using @code{--with-sysroot}). Alternatively, you
20019 may use @code{set solib-search-path} to specify how @value{GDBN} locates
20022 The symbol file and target libraries must exactly match the executable
20023 and libraries on the target, with one exception: the files on the host
20024 system should not be stripped, even if the files on the target system
20025 are. Mismatched or missing files will lead to confusing results
20026 during debugging. On @sc{gnu}/Linux targets, mismatched or missing
20027 files may also prevent @code{gdbserver} from debugging multi-threaded
20030 @subsection Remote Connection Commands
20031 @cindex remote connection commands
20032 @value{GDBN} can communicate with the target over a serial line, or
20033 over an @acronym{IP} network using @acronym{TCP} or @acronym{UDP}. In
20034 each case, @value{GDBN} uses the same protocol for debugging your
20035 program; only the medium carrying the debugging packets varies. The
20036 @code{target remote} and @code{target extended-remote} commands
20037 establish a connection to the target. Both commands accept the same
20038 arguments, which indicate the medium to use:
20042 @item target remote @var{serial-device}
20043 @itemx target extended-remote @var{serial-device}
20044 @cindex serial line, @code{target remote}
20045 Use @var{serial-device} to communicate with the target. For example,
20046 to use a serial line connected to the device named @file{/dev/ttyb}:
20049 target remote /dev/ttyb
20052 If you're using a serial line, you may want to give @value{GDBN} the
20053 @samp{--baud} option, or use the @code{set serial baud} command
20054 (@pxref{Remote Configuration, set serial baud}) before the
20055 @code{target} command.
20057 @item target remote @code{@var{host}:@var{port}}
20058 @itemx target remote @code{tcp:@var{host}:@var{port}}
20059 @itemx target extended-remote @code{@var{host}:@var{port}}
20060 @itemx target extended-remote @code{tcp:@var{host}:@var{port}}
20061 @cindex @acronym{TCP} port, @code{target remote}
20062 Debug using a @acronym{TCP} connection to @var{port} on @var{host}.
20063 The @var{host} may be either a host name or a numeric @acronym{IP}
20064 address; @var{port} must be a decimal number. The @var{host} could be
20065 the target machine itself, if it is directly connected to the net, or
20066 it might be a terminal server which in turn has a serial line to the
20069 For example, to connect to port 2828 on a terminal server named
20073 target remote manyfarms:2828
20076 If your remote target is actually running on the same machine as your
20077 debugger session (e.g.@: a simulator for your target running on the
20078 same host), you can omit the hostname. For example, to connect to
20079 port 1234 on your local machine:
20082 target remote :1234
20086 Note that the colon is still required here.
20088 @item target remote @code{udp:@var{host}:@var{port}}
20089 @itemx target extended-remote @code{udp:@var{host}:@var{port}}
20090 @cindex @acronym{UDP} port, @code{target remote}
20091 Debug using @acronym{UDP} packets to @var{port} on @var{host}. For example, to
20092 connect to @acronym{UDP} port 2828 on a terminal server named @code{manyfarms}:
20095 target remote udp:manyfarms:2828
20098 When using a @acronym{UDP} connection for remote debugging, you should
20099 keep in mind that the `U' stands for ``Unreliable''. @acronym{UDP}
20100 can silently drop packets on busy or unreliable networks, which will
20101 cause havoc with your debugging session.
20103 @item target remote | @var{command}
20104 @itemx target extended-remote | @var{command}
20105 @cindex pipe, @code{target remote} to
20106 Run @var{command} in the background and communicate with it using a
20107 pipe. The @var{command} is a shell command, to be parsed and expanded
20108 by the system's command shell, @code{/bin/sh}; it should expect remote
20109 protocol packets on its standard input, and send replies on its
20110 standard output. You could use this to run a stand-alone simulator
20111 that speaks the remote debugging protocol, to make net connections
20112 using programs like @code{ssh}, or for other similar tricks.
20114 If @var{command} closes its standard output (perhaps by exiting),
20115 @value{GDBN} will try to send it a @code{SIGTERM} signal. (If the
20116 program has already exited, this will have no effect.)
20120 @cindex interrupting remote programs
20121 @cindex remote programs, interrupting
20122 Whenever @value{GDBN} is waiting for the remote program, if you type the
20123 interrupt character (often @kbd{Ctrl-c}), @value{GDBN} attempts to stop the
20124 program. This may or may not succeed, depending in part on the hardware
20125 and the serial drivers the remote system uses. If you type the
20126 interrupt character once again, @value{GDBN} displays this prompt:
20129 Interrupted while waiting for the program.
20130 Give up (and stop debugging it)? (y or n)
20133 In @code{target remote} mode, if you type @kbd{y}, @value{GDBN} abandons
20134 the remote debugging session. (If you decide you want to try again later,
20135 you can use @kbd{target remote} again to connect once more.) If you type
20136 @kbd{n}, @value{GDBN} goes back to waiting.
20138 In @code{target extended-remote} mode, typing @kbd{n} will leave
20139 @value{GDBN} connected to the target.
20142 @kindex detach (remote)
20144 When you have finished debugging the remote program, you can use the
20145 @code{detach} command to release it from @value{GDBN} control.
20146 Detaching from the target normally resumes its execution, but the results
20147 will depend on your particular remote stub. After the @code{detach}
20148 command in @code{target remote} mode, @value{GDBN} is free to connect to
20149 another target. In @code{target extended-remote} mode, @value{GDBN} is
20150 still connected to the target.
20154 The @code{disconnect} command closes the connection to the target, and
20155 the target is generally not resumed. It will wait for @value{GDBN}
20156 (this instance or another one) to connect and continue debugging. After
20157 the @code{disconnect} command, @value{GDBN} is again free to connect to
20160 @cindex send command to remote monitor
20161 @cindex extend @value{GDBN} for remote targets
20162 @cindex add new commands for external monitor
20164 @item monitor @var{cmd}
20165 This command allows you to send arbitrary commands directly to the
20166 remote monitor. Since @value{GDBN} doesn't care about the commands it
20167 sends like this, this command is the way to extend @value{GDBN}---you
20168 can add new commands that only the external monitor will understand
20172 @node File Transfer
20173 @section Sending files to a remote system
20174 @cindex remote target, file transfer
20175 @cindex file transfer
20176 @cindex sending files to remote systems
20178 Some remote targets offer the ability to transfer files over the same
20179 connection used to communicate with @value{GDBN}. This is convenient
20180 for targets accessible through other means, e.g.@: @sc{gnu}/Linux systems
20181 running @code{gdbserver} over a network interface. For other targets,
20182 e.g.@: embedded devices with only a single serial port, this may be
20183 the only way to upload or download files.
20185 Not all remote targets support these commands.
20189 @item remote put @var{hostfile} @var{targetfile}
20190 Copy file @var{hostfile} from the host system (the machine running
20191 @value{GDBN}) to @var{targetfile} on the target system.
20194 @item remote get @var{targetfile} @var{hostfile}
20195 Copy file @var{targetfile} from the target system to @var{hostfile}
20196 on the host system.
20198 @kindex remote delete
20199 @item remote delete @var{targetfile}
20200 Delete @var{targetfile} from the target system.
20205 @section Using the @code{gdbserver} Program
20208 @cindex remote connection without stubs
20209 @code{gdbserver} is a control program for Unix-like systems, which
20210 allows you to connect your program with a remote @value{GDBN} via
20211 @code{target remote} or @code{target extended-remote}---but without
20212 linking in the usual debugging stub.
20214 @code{gdbserver} is not a complete replacement for the debugging stubs,
20215 because it requires essentially the same operating-system facilities
20216 that @value{GDBN} itself does. In fact, a system that can run
20217 @code{gdbserver} to connect to a remote @value{GDBN} could also run
20218 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
20219 because it is a much smaller program than @value{GDBN} itself. It is
20220 also easier to port than all of @value{GDBN}, so you may be able to get
20221 started more quickly on a new system by using @code{gdbserver}.
20222 Finally, if you develop code for real-time systems, you may find that
20223 the tradeoffs involved in real-time operation make it more convenient to
20224 do as much development work as possible on another system, for example
20225 by cross-compiling. You can use @code{gdbserver} to make a similar
20226 choice for debugging.
20228 @value{GDBN} and @code{gdbserver} communicate via either a serial line
20229 or a TCP connection, using the standard @value{GDBN} remote serial
20233 @emph{Warning:} @code{gdbserver} does not have any built-in security.
20234 Do not run @code{gdbserver} connected to any public network; a
20235 @value{GDBN} connection to @code{gdbserver} provides access to the
20236 target system with the same privileges as the user running
20240 @anchor{Running gdbserver}
20241 @subsection Running @code{gdbserver}
20242 @cindex arguments, to @code{gdbserver}
20243 @cindex @code{gdbserver}, command-line arguments
20245 Run @code{gdbserver} on the target system. You need a copy of the
20246 program you want to debug, including any libraries it requires.
20247 @code{gdbserver} does not need your program's symbol table, so you can
20248 strip the program if necessary to save space. @value{GDBN} on the host
20249 system does all the symbol handling.
20251 To use the server, you must tell it how to communicate with @value{GDBN};
20252 the name of your program; and the arguments for your program. The usual
20256 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
20259 @var{comm} is either a device name (to use a serial line), or a TCP
20260 hostname and portnumber, or @code{-} or @code{stdio} to use
20261 stdin/stdout of @code{gdbserver}.
20262 For example, to debug Emacs with the argument
20263 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
20267 target> gdbserver /dev/com1 emacs foo.txt
20270 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
20273 To use a TCP connection instead of a serial line:
20276 target> gdbserver host:2345 emacs foo.txt
20279 The only difference from the previous example is the first argument,
20280 specifying that you are communicating with the host @value{GDBN} via
20281 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
20282 expect a TCP connection from machine @samp{host} to local TCP port 2345.
20283 (Currently, the @samp{host} part is ignored.) You can choose any number
20284 you want for the port number as long as it does not conflict with any
20285 TCP ports already in use on the target system (for example, @code{23} is
20286 reserved for @code{telnet}).@footnote{If you choose a port number that
20287 conflicts with another service, @code{gdbserver} prints an error message
20288 and exits.} You must use the same port number with the host @value{GDBN}
20289 @code{target remote} command.
20291 The @code{stdio} connection is useful when starting @code{gdbserver}
20295 (gdb) target remote | ssh -T hostname gdbserver - hello
20298 The @samp{-T} option to ssh is provided because we don't need a remote pty,
20299 and we don't want escape-character handling. Ssh does this by default when
20300 a command is provided, the flag is provided to make it explicit.
20301 You could elide it if you want to.
20303 Programs started with stdio-connected gdbserver have @file{/dev/null} for
20304 @code{stdin}, and @code{stdout},@code{stderr} are sent back to gdb for
20305 display through a pipe connected to gdbserver.
20306 Both @code{stdout} and @code{stderr} use the same pipe.
20308 @anchor{Attaching to a program}
20309 @subsubsection Attaching to a Running Program
20310 @cindex attach to a program, @code{gdbserver}
20311 @cindex @option{--attach}, @code{gdbserver} option
20313 On some targets, @code{gdbserver} can also attach to running programs.
20314 This is accomplished via the @code{--attach} argument. The syntax is:
20317 target> gdbserver --attach @var{comm} @var{pid}
20320 @var{pid} is the process ID of a currently running process. It isn't
20321 necessary to point @code{gdbserver} at a binary for the running process.
20323 In @code{target extended-remote} mode, you can also attach using the
20324 @value{GDBN} attach command
20325 (@pxref{Attaching in Types of Remote Connections}).
20328 You can debug processes by name instead of process ID if your target has the
20329 @code{pidof} utility:
20332 target> gdbserver --attach @var{comm} `pidof @var{program}`
20335 In case more than one copy of @var{program} is running, or @var{program}
20336 has multiple threads, most versions of @code{pidof} support the
20337 @code{-s} option to only return the first process ID.
20339 @subsubsection TCP port allocation lifecycle of @code{gdbserver}
20341 This section applies only when @code{gdbserver} is run to listen on a TCP
20344 @code{gdbserver} normally terminates after all of its debugged processes have
20345 terminated in @kbd{target remote} mode. On the other hand, for @kbd{target
20346 extended-remote}, @code{gdbserver} stays running even with no processes left.
20347 @value{GDBN} normally terminates the spawned debugged process on its exit,
20348 which normally also terminates @code{gdbserver} in the @kbd{target remote}
20349 mode. Therefore, when the connection drops unexpectedly, and @value{GDBN}
20350 cannot ask @code{gdbserver} to kill its debugged processes, @code{gdbserver}
20351 stays running even in the @kbd{target remote} mode.
20353 When @code{gdbserver} stays running, @value{GDBN} can connect to it again later.
20354 Such reconnecting is useful for features like @ref{disconnected tracing}. For
20355 completeness, at most one @value{GDBN} can be connected at a time.
20357 @cindex @option{--once}, @code{gdbserver} option
20358 By default, @code{gdbserver} keeps the listening TCP port open, so that
20359 subsequent connections are possible. However, if you start @code{gdbserver}
20360 with the @option{--once} option, it will stop listening for any further
20361 connection attempts after connecting to the first @value{GDBN} session. This
20362 means no further connections to @code{gdbserver} will be possible after the
20363 first one. It also means @code{gdbserver} will terminate after the first
20364 connection with remote @value{GDBN} has closed, even for unexpectedly closed
20365 connections and even in the @kbd{target extended-remote} mode. The
20366 @option{--once} option allows reusing the same port number for connecting to
20367 multiple instances of @code{gdbserver} running on the same host, since each
20368 instance closes its port after the first connection.
20370 @anchor{Other Command-Line Arguments for gdbserver}
20371 @subsubsection Other Command-Line Arguments for @code{gdbserver}
20373 You can use the @option{--multi} option to start @code{gdbserver} without
20374 specifying a program to debug or a process to attach to. Then you can
20375 attach in @code{target extended-remote} mode and run or attach to a
20376 program. For more information,
20377 @pxref{--multi Option in Types of Remote Connnections}.
20379 @cindex @option{--debug}, @code{gdbserver} option
20380 The @option{--debug} option tells @code{gdbserver} to display extra
20381 status information about the debugging process.
20382 @cindex @option{--remote-debug}, @code{gdbserver} option
20383 The @option{--remote-debug} option tells @code{gdbserver} to display
20384 remote protocol debug output. These options are intended for
20385 @code{gdbserver} development and for bug reports to the developers.
20387 @cindex @option{--debug-format}, @code{gdbserver} option
20388 The @option{--debug-format=option1[,option2,...]} option tells
20389 @code{gdbserver} to include additional information in each output.
20390 Possible options are:
20394 Turn off all extra information in debugging output.
20396 Turn on all extra information in debugging output.
20398 Include a timestamp in each line of debugging output.
20401 Options are processed in order. Thus, for example, if @option{none}
20402 appears last then no additional information is added to debugging output.
20404 @cindex @option{--wrapper}, @code{gdbserver} option
20405 The @option{--wrapper} option specifies a wrapper to launch programs
20406 for debugging. The option should be followed by the name of the
20407 wrapper, then any command-line arguments to pass to the wrapper, then
20408 @kbd{--} indicating the end of the wrapper arguments.
20410 @code{gdbserver} runs the specified wrapper program with a combined
20411 command line including the wrapper arguments, then the name of the
20412 program to debug, then any arguments to the program. The wrapper
20413 runs until it executes your program, and then @value{GDBN} gains control.
20415 You can use any program that eventually calls @code{execve} with
20416 its arguments as a wrapper. Several standard Unix utilities do
20417 this, e.g.@: @code{env} and @code{nohup}. Any Unix shell script ending
20418 with @code{exec "$@@"} will also work.
20420 For example, you can use @code{env} to pass an environment variable to
20421 the debugged program, without setting the variable in @code{gdbserver}'s
20425 $ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog
20428 @cindex @option{--selftest}
20429 The @option{--selftest} option runs the self tests in @code{gdbserver}:
20432 $ gdbserver --selftest
20433 Ran 2 unit tests, 0 failed
20436 These tests are disabled in release.
20437 @subsection Connecting to @code{gdbserver}
20439 The basic procedure for connecting to the remote target is:
20443 Run @value{GDBN} on the host system.
20446 Make sure you have the necessary symbol files
20447 (@pxref{Host and target files}).
20448 Load symbols for your application using the @code{file} command before you
20449 connect. Use @code{set sysroot} to locate target libraries (unless your
20450 @value{GDBN} was compiled with the correct sysroot using
20451 @code{--with-sysroot}).
20454 Connect to your target (@pxref{Connecting,,Connecting to a Remote Target}).
20455 For TCP connections, you must start up @code{gdbserver} prior to using
20456 the @code{target} command. Otherwise you may get an error whose
20457 text depends on the host system, but which usually looks something like
20458 @samp{Connection refused}. Don't use the @code{load}
20459 command in @value{GDBN} when using @code{target remote} mode, since the
20460 program is already on the target.
20464 @anchor{Monitor Commands for gdbserver}
20465 @subsection Monitor Commands for @code{gdbserver}
20466 @cindex monitor commands, for @code{gdbserver}
20468 During a @value{GDBN} session using @code{gdbserver}, you can use the
20469 @code{monitor} command to send special requests to @code{gdbserver}.
20470 Here are the available commands.
20474 List the available monitor commands.
20476 @item monitor set debug 0
20477 @itemx monitor set debug 1
20478 Disable or enable general debugging messages.
20480 @item monitor set remote-debug 0
20481 @itemx monitor set remote-debug 1
20482 Disable or enable specific debugging messages associated with the remote
20483 protocol (@pxref{Remote Protocol}).
20485 @item monitor set debug-format option1@r{[},option2,...@r{]}
20486 Specify additional text to add to debugging messages.
20487 Possible options are:
20491 Turn off all extra information in debugging output.
20493 Turn on all extra information in debugging output.
20495 Include a timestamp in each line of debugging output.
20498 Options are processed in order. Thus, for example, if @option{none}
20499 appears last then no additional information is added to debugging output.
20501 @item monitor set libthread-db-search-path [PATH]
20502 @cindex gdbserver, search path for @code{libthread_db}
20503 When this command is issued, @var{path} is a colon-separated list of
20504 directories to search for @code{libthread_db} (@pxref{Threads,,set
20505 libthread-db-search-path}). If you omit @var{path},
20506 @samp{libthread-db-search-path} will be reset to its default value.
20508 The special entry @samp{$pdir} for @samp{libthread-db-search-path} is
20509 not supported in @code{gdbserver}.
20512 Tell gdbserver to exit immediately. This command should be followed by
20513 @code{disconnect} to close the debugging session. @code{gdbserver} will
20514 detach from any attached processes and kill any processes it created.
20515 Use @code{monitor exit} to terminate @code{gdbserver} at the end
20516 of a multi-process mode debug session.
20520 @subsection Tracepoints support in @code{gdbserver}
20521 @cindex tracepoints support in @code{gdbserver}
20523 On some targets, @code{gdbserver} supports tracepoints, fast
20524 tracepoints and static tracepoints.
20526 For fast or static tracepoints to work, a special library called the
20527 @dfn{in-process agent} (IPA), must be loaded in the inferior process.
20528 This library is built and distributed as an integral part of
20529 @code{gdbserver}. In addition, support for static tracepoints
20530 requires building the in-process agent library with static tracepoints
20531 support. At present, the UST (LTTng Userspace Tracer,
20532 @url{http://lttng.org/ust}) tracing engine is supported. This support
20533 is automatically available if UST development headers are found in the
20534 standard include path when @code{gdbserver} is built, or if
20535 @code{gdbserver} was explicitly configured using @option{--with-ust}
20536 to point at such headers. You can explicitly disable the support
20537 using @option{--with-ust=no}.
20539 There are several ways to load the in-process agent in your program:
20542 @item Specifying it as dependency at link time
20544 You can link your program dynamically with the in-process agent
20545 library. On most systems, this is accomplished by adding
20546 @code{-linproctrace} to the link command.
20548 @item Using the system's preloading mechanisms
20550 You can force loading the in-process agent at startup time by using
20551 your system's support for preloading shared libraries. Many Unixes
20552 support the concept of preloading user defined libraries. In most
20553 cases, you do that by specifying @code{LD_PRELOAD=libinproctrace.so}
20554 in the environment. See also the description of @code{gdbserver}'s
20555 @option{--wrapper} command line option.
20557 @item Using @value{GDBN} to force loading the agent at run time
20559 On some systems, you can force the inferior to load a shared library,
20560 by calling a dynamic loader function in the inferior that takes care
20561 of dynamically looking up and loading a shared library. On most Unix
20562 systems, the function is @code{dlopen}. You'll use the @code{call}
20563 command for that. For example:
20566 (@value{GDBP}) call dlopen ("libinproctrace.so", ...)
20569 Note that on most Unix systems, for the @code{dlopen} function to be
20570 available, the program needs to be linked with @code{-ldl}.
20573 On systems that have a userspace dynamic loader, like most Unix
20574 systems, when you connect to @code{gdbserver} using @code{target
20575 remote}, you'll find that the program is stopped at the dynamic
20576 loader's entry point, and no shared library has been loaded in the
20577 program's address space yet, including the in-process agent. In that
20578 case, before being able to use any of the fast or static tracepoints
20579 features, you need to let the loader run and load the shared
20580 libraries. The simplest way to do that is to run the program to the
20581 main procedure. E.g., if debugging a C or C@t{++} program, start
20582 @code{gdbserver} like so:
20585 $ gdbserver :9999 myprogram
20588 Start GDB and connect to @code{gdbserver} like so, and run to main:
20592 (@value{GDBP}) target remote myhost:9999
20593 0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2
20594 (@value{GDBP}) b main
20595 (@value{GDBP}) continue
20598 The in-process tracing agent library should now be loaded into the
20599 process; you can confirm it with the @code{info sharedlibrary}
20600 command, which will list @file{libinproctrace.so} as loaded in the
20601 process. You are now ready to install fast tracepoints, list static
20602 tracepoint markers, probe static tracepoints markers, and start
20605 @node Remote Configuration
20606 @section Remote Configuration
20609 @kindex show remote
20610 This section documents the configuration options available when
20611 debugging remote programs. For the options related to the File I/O
20612 extensions of the remote protocol, see @ref{system,
20613 system-call-allowed}.
20616 @item set remoteaddresssize @var{bits}
20617 @cindex address size for remote targets
20618 @cindex bits in remote address
20619 Set the maximum size of address in a memory packet to the specified
20620 number of bits. @value{GDBN} will mask off the address bits above
20621 that number, when it passes addresses to the remote target. The
20622 default value is the number of bits in the target's address.
20624 @item show remoteaddresssize
20625 Show the current value of remote address size in bits.
20627 @item set serial baud @var{n}
20628 @cindex baud rate for remote targets
20629 Set the baud rate for the remote serial I/O to @var{n} baud. The
20630 value is used to set the speed of the serial port used for debugging
20633 @item show serial baud
20634 Show the current speed of the remote connection.
20636 @item set serial parity @var{parity}
20637 Set the parity for the remote serial I/O. Supported values of @var{parity} are:
20638 @code{even}, @code{none}, and @code{odd}. The default is @code{none}.
20640 @item show serial parity
20641 Show the current parity of the serial port.
20643 @item set remotebreak
20644 @cindex interrupt remote programs
20645 @cindex BREAK signal instead of Ctrl-C
20646 @anchor{set remotebreak}
20647 If set to on, @value{GDBN} sends a @code{BREAK} signal to the remote
20648 when you type @kbd{Ctrl-c} to interrupt the program running
20649 on the remote. If set to off, @value{GDBN} sends the @samp{Ctrl-C}
20650 character instead. The default is off, since most remote systems
20651 expect to see @samp{Ctrl-C} as the interrupt signal.
20653 @item show remotebreak
20654 Show whether @value{GDBN} sends @code{BREAK} or @samp{Ctrl-C} to
20655 interrupt the remote program.
20657 @item set remoteflow on
20658 @itemx set remoteflow off
20659 @kindex set remoteflow
20660 Enable or disable hardware flow control (@code{RTS}/@code{CTS})
20661 on the serial port used to communicate to the remote target.
20663 @item show remoteflow
20664 @kindex show remoteflow
20665 Show the current setting of hardware flow control.
20667 @item set remotelogbase @var{base}
20668 Set the base (a.k.a.@: radix) of logging serial protocol
20669 communications to @var{base}. Supported values of @var{base} are:
20670 @code{ascii}, @code{octal}, and @code{hex}. The default is
20673 @item show remotelogbase
20674 Show the current setting of the radix for logging remote serial
20677 @item set remotelogfile @var{file}
20678 @cindex record serial communications on file
20679 Record remote serial communications on the named @var{file}. The
20680 default is not to record at all.
20682 @item show remotelogfile.
20683 Show the current setting of the file name on which to record the
20684 serial communications.
20686 @item set remotetimeout @var{num}
20687 @cindex timeout for serial communications
20688 @cindex remote timeout
20689 Set the timeout limit to wait for the remote target to respond to
20690 @var{num} seconds. The default is 2 seconds.
20692 @item show remotetimeout
20693 Show the current number of seconds to wait for the remote target
20696 @cindex limit hardware breakpoints and watchpoints
20697 @cindex remote target, limit break- and watchpoints
20698 @anchor{set remote hardware-watchpoint-limit}
20699 @anchor{set remote hardware-breakpoint-limit}
20700 @item set remote hardware-watchpoint-limit @var{limit}
20701 @itemx set remote hardware-breakpoint-limit @var{limit}
20702 Restrict @value{GDBN} to using @var{limit} remote hardware breakpoint or
20703 watchpoints. A limit of -1, the default, is treated as unlimited.
20705 @cindex limit hardware watchpoints length
20706 @cindex remote target, limit watchpoints length
20707 @anchor{set remote hardware-watchpoint-length-limit}
20708 @item set remote hardware-watchpoint-length-limit @var{limit}
20709 Restrict @value{GDBN} to using @var{limit} bytes for the maximum length of
20710 a remote hardware watchpoint. A limit of -1, the default, is treated
20713 @item show remote hardware-watchpoint-length-limit
20714 Show the current limit (in bytes) of the maximum length of
20715 a remote hardware watchpoint.
20717 @item set remote exec-file @var{filename}
20718 @itemx show remote exec-file
20719 @anchor{set remote exec-file}
20720 @cindex executable file, for remote target
20721 Select the file used for @code{run} with @code{target
20722 extended-remote}. This should be set to a filename valid on the
20723 target system. If it is not set, the target will use a default
20724 filename (e.g.@: the last program run).
20726 @item set remote interrupt-sequence
20727 @cindex interrupt remote programs
20728 @cindex select Ctrl-C, BREAK or BREAK-g
20729 Allow the user to select one of @samp{Ctrl-C}, a @code{BREAK} or
20730 @samp{BREAK-g} as the
20731 sequence to the remote target in order to interrupt the execution.
20732 @samp{Ctrl-C} is a default. Some system prefers @code{BREAK} which
20733 is high level of serial line for some certain time.
20734 Linux kernel prefers @samp{BREAK-g}, a.k.a Magic SysRq g.
20735 It is @code{BREAK} signal followed by character @code{g}.
20737 @item show interrupt-sequence
20738 Show which of @samp{Ctrl-C}, @code{BREAK} or @code{BREAK-g}
20739 is sent by @value{GDBN} to interrupt the remote program.
20740 @code{BREAK-g} is BREAK signal followed by @code{g} and
20741 also known as Magic SysRq g.
20743 @item set remote interrupt-on-connect
20744 @cindex send interrupt-sequence on start
20745 Specify whether interrupt-sequence is sent to remote target when
20746 @value{GDBN} connects to it. This is mostly needed when you debug
20747 Linux kernel. Linux kernel expects @code{BREAK} followed by @code{g}
20748 which is known as Magic SysRq g in order to connect @value{GDBN}.
20750 @item show interrupt-on-connect
20751 Show whether interrupt-sequence is sent
20752 to remote target when @value{GDBN} connects to it.
20756 @item set tcp auto-retry on
20757 @cindex auto-retry, for remote TCP target
20758 Enable auto-retry for remote TCP connections. This is useful if the remote
20759 debugging agent is launched in parallel with @value{GDBN}; there is a race
20760 condition because the agent may not become ready to accept the connection
20761 before @value{GDBN} attempts to connect. When auto-retry is
20762 enabled, if the initial attempt to connect fails, @value{GDBN} reattempts
20763 to establish the connection using the timeout specified by
20764 @code{set tcp connect-timeout}.
20766 @item set tcp auto-retry off
20767 Do not auto-retry failed TCP connections.
20769 @item show tcp auto-retry
20770 Show the current auto-retry setting.
20772 @item set tcp connect-timeout @var{seconds}
20773 @itemx set tcp connect-timeout unlimited
20774 @cindex connection timeout, for remote TCP target
20775 @cindex timeout, for remote target connection
20776 Set the timeout for establishing a TCP connection to the remote target to
20777 @var{seconds}. The timeout affects both polling to retry failed connections
20778 (enabled by @code{set tcp auto-retry on}) and waiting for connections
20779 that are merely slow to complete, and represents an approximate cumulative
20780 value. If @var{seconds} is @code{unlimited}, there is no timeout and
20781 @value{GDBN} will keep attempting to establish a connection forever,
20782 unless interrupted with @kbd{Ctrl-c}. The default is 15 seconds.
20784 @item show tcp connect-timeout
20785 Show the current connection timeout setting.
20788 @cindex remote packets, enabling and disabling
20789 The @value{GDBN} remote protocol autodetects the packets supported by
20790 your debugging stub. If you need to override the autodetection, you
20791 can use these commands to enable or disable individual packets. Each
20792 packet can be set to @samp{on} (the remote target supports this
20793 packet), @samp{off} (the remote target does not support this packet),
20794 or @samp{auto} (detect remote target support for this packet). They
20795 all default to @samp{auto}. For more information about each packet,
20796 see @ref{Remote Protocol}.
20798 During normal use, you should not have to use any of these commands.
20799 If you do, that may be a bug in your remote debugging stub, or a bug
20800 in @value{GDBN}. You may want to report the problem to the
20801 @value{GDBN} developers.
20803 For each packet @var{name}, the command to enable or disable the
20804 packet is @code{set remote @var{name}-packet}. The available settings
20807 @multitable @columnfractions 0.28 0.32 0.25
20810 @tab Related Features
20812 @item @code{fetch-register}
20814 @tab @code{info registers}
20816 @item @code{set-register}
20820 @item @code{binary-download}
20822 @tab @code{load}, @code{set}
20824 @item @code{read-aux-vector}
20825 @tab @code{qXfer:auxv:read}
20826 @tab @code{info auxv}
20828 @item @code{symbol-lookup}
20829 @tab @code{qSymbol}
20830 @tab Detecting multiple threads
20832 @item @code{attach}
20833 @tab @code{vAttach}
20836 @item @code{verbose-resume}
20838 @tab Stepping or resuming multiple threads
20844 @item @code{software-breakpoint}
20848 @item @code{hardware-breakpoint}
20852 @item @code{write-watchpoint}
20856 @item @code{read-watchpoint}
20860 @item @code{access-watchpoint}
20864 @item @code{pid-to-exec-file}
20865 @tab @code{qXfer:exec-file:read}
20866 @tab @code{attach}, @code{run}
20868 @item @code{target-features}
20869 @tab @code{qXfer:features:read}
20870 @tab @code{set architecture}
20872 @item @code{library-info}
20873 @tab @code{qXfer:libraries:read}
20874 @tab @code{info sharedlibrary}
20876 @item @code{memory-map}
20877 @tab @code{qXfer:memory-map:read}
20878 @tab @code{info mem}
20880 @item @code{read-sdata-object}
20881 @tab @code{qXfer:sdata:read}
20882 @tab @code{print $_sdata}
20884 @item @code{read-spu-object}
20885 @tab @code{qXfer:spu:read}
20886 @tab @code{info spu}
20888 @item @code{write-spu-object}
20889 @tab @code{qXfer:spu:write}
20890 @tab @code{info spu}
20892 @item @code{read-siginfo-object}
20893 @tab @code{qXfer:siginfo:read}
20894 @tab @code{print $_siginfo}
20896 @item @code{write-siginfo-object}
20897 @tab @code{qXfer:siginfo:write}
20898 @tab @code{set $_siginfo}
20900 @item @code{threads}
20901 @tab @code{qXfer:threads:read}
20902 @tab @code{info threads}
20904 @item @code{get-thread-local-@*storage-address}
20905 @tab @code{qGetTLSAddr}
20906 @tab Displaying @code{__thread} variables
20908 @item @code{get-thread-information-block-address}
20909 @tab @code{qGetTIBAddr}
20910 @tab Display MS-Windows Thread Information Block.
20912 @item @code{search-memory}
20913 @tab @code{qSearch:memory}
20916 @item @code{supported-packets}
20917 @tab @code{qSupported}
20918 @tab Remote communications parameters
20920 @item @code{catch-syscalls}
20921 @tab @code{QCatchSyscalls}
20922 @tab @code{catch syscall}
20924 @item @code{pass-signals}
20925 @tab @code{QPassSignals}
20926 @tab @code{handle @var{signal}}
20928 @item @code{program-signals}
20929 @tab @code{QProgramSignals}
20930 @tab @code{handle @var{signal}}
20932 @item @code{hostio-close-packet}
20933 @tab @code{vFile:close}
20934 @tab @code{remote get}, @code{remote put}
20936 @item @code{hostio-open-packet}
20937 @tab @code{vFile:open}
20938 @tab @code{remote get}, @code{remote put}
20940 @item @code{hostio-pread-packet}
20941 @tab @code{vFile:pread}
20942 @tab @code{remote get}, @code{remote put}
20944 @item @code{hostio-pwrite-packet}
20945 @tab @code{vFile:pwrite}
20946 @tab @code{remote get}, @code{remote put}
20948 @item @code{hostio-unlink-packet}
20949 @tab @code{vFile:unlink}
20950 @tab @code{remote delete}
20952 @item @code{hostio-readlink-packet}
20953 @tab @code{vFile:readlink}
20956 @item @code{hostio-fstat-packet}
20957 @tab @code{vFile:fstat}
20960 @item @code{hostio-setfs-packet}
20961 @tab @code{vFile:setfs}
20964 @item @code{noack-packet}
20965 @tab @code{QStartNoAckMode}
20966 @tab Packet acknowledgment
20968 @item @code{osdata}
20969 @tab @code{qXfer:osdata:read}
20970 @tab @code{info os}
20972 @item @code{query-attached}
20973 @tab @code{qAttached}
20974 @tab Querying remote process attach state.
20976 @item @code{trace-buffer-size}
20977 @tab @code{QTBuffer:size}
20978 @tab @code{set trace-buffer-size}
20980 @item @code{trace-status}
20981 @tab @code{qTStatus}
20982 @tab @code{tstatus}
20984 @item @code{traceframe-info}
20985 @tab @code{qXfer:traceframe-info:read}
20986 @tab Traceframe info
20988 @item @code{install-in-trace}
20989 @tab @code{InstallInTrace}
20990 @tab Install tracepoint in tracing
20992 @item @code{disable-randomization}
20993 @tab @code{QDisableRandomization}
20994 @tab @code{set disable-randomization}
20996 @item @code{startup-with-shell}
20997 @tab @code{QStartupWithShell}
20998 @tab @code{set startup-with-shell}
21000 @item @code{environment-hex-encoded}
21001 @tab @code{QEnvironmentHexEncoded}
21002 @tab @code{set environment}
21004 @item @code{environment-unset}
21005 @tab @code{QEnvironmentUnset}
21006 @tab @code{unset environment}
21008 @item @code{environment-reset}
21009 @tab @code{QEnvironmentReset}
21010 @tab @code{Reset the inferior environment (i.e., unset user-set variables)}
21012 @item @code{set-working-dir}
21013 @tab @code{QSetWorkingDir}
21014 @tab @code{set cwd}
21016 @item @code{conditional-breakpoints-packet}
21017 @tab @code{Z0 and Z1}
21018 @tab @code{Support for target-side breakpoint condition evaluation}
21020 @item @code{multiprocess-extensions}
21021 @tab @code{multiprocess extensions}
21022 @tab Debug multiple processes and remote process PID awareness
21024 @item @code{swbreak-feature}
21025 @tab @code{swbreak stop reason}
21028 @item @code{hwbreak-feature}
21029 @tab @code{hwbreak stop reason}
21032 @item @code{fork-event-feature}
21033 @tab @code{fork stop reason}
21036 @item @code{vfork-event-feature}
21037 @tab @code{vfork stop reason}
21040 @item @code{exec-event-feature}
21041 @tab @code{exec stop reason}
21044 @item @code{thread-events}
21045 @tab @code{QThreadEvents}
21046 @tab Tracking thread lifetime.
21048 @item @code{no-resumed-stop-reply}
21049 @tab @code{no resumed thread left stop reply}
21050 @tab Tracking thread lifetime.
21055 @section Implementing a Remote Stub
21057 @cindex debugging stub, example
21058 @cindex remote stub, example
21059 @cindex stub example, remote debugging
21060 The stub files provided with @value{GDBN} implement the target side of the
21061 communication protocol, and the @value{GDBN} side is implemented in the
21062 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
21063 these subroutines to communicate, and ignore the details. (If you're
21064 implementing your own stub file, you can still ignore the details: start
21065 with one of the existing stub files. @file{sparc-stub.c} is the best
21066 organized, and therefore the easiest to read.)
21068 @cindex remote serial debugging, overview
21069 To debug a program running on another machine (the debugging
21070 @dfn{target} machine), you must first arrange for all the usual
21071 prerequisites for the program to run by itself. For example, for a C
21076 A startup routine to set up the C runtime environment; these usually
21077 have a name like @file{crt0}. The startup routine may be supplied by
21078 your hardware supplier, or you may have to write your own.
21081 A C subroutine library to support your program's
21082 subroutine calls, notably managing input and output.
21085 A way of getting your program to the other machine---for example, a
21086 download program. These are often supplied by the hardware
21087 manufacturer, but you may have to write your own from hardware
21091 The next step is to arrange for your program to use a serial port to
21092 communicate with the machine where @value{GDBN} is running (the @dfn{host}
21093 machine). In general terms, the scheme looks like this:
21097 @value{GDBN} already understands how to use this protocol; when everything
21098 else is set up, you can simply use the @samp{target remote} command
21099 (@pxref{Targets,,Specifying a Debugging Target}).
21101 @item On the target,
21102 you must link with your program a few special-purpose subroutines that
21103 implement the @value{GDBN} remote serial protocol. The file containing these
21104 subroutines is called a @dfn{debugging stub}.
21106 On certain remote targets, you can use an auxiliary program
21107 @code{gdbserver} instead of linking a stub into your program.
21108 @xref{Server,,Using the @code{gdbserver} Program}, for details.
21111 The debugging stub is specific to the architecture of the remote
21112 machine; for example, use @file{sparc-stub.c} to debug programs on
21115 @cindex remote serial stub list
21116 These working remote stubs are distributed with @value{GDBN}:
21121 @cindex @file{i386-stub.c}
21124 For Intel 386 and compatible architectures.
21127 @cindex @file{m68k-stub.c}
21128 @cindex Motorola 680x0
21130 For Motorola 680x0 architectures.
21133 @cindex @file{sh-stub.c}
21136 For Renesas SH architectures.
21139 @cindex @file{sparc-stub.c}
21141 For @sc{sparc} architectures.
21143 @item sparcl-stub.c
21144 @cindex @file{sparcl-stub.c}
21147 For Fujitsu @sc{sparclite} architectures.
21151 The @file{README} file in the @value{GDBN} distribution may list other
21152 recently added stubs.
21155 * Stub Contents:: What the stub can do for you
21156 * Bootstrapping:: What you must do for the stub
21157 * Debug Session:: Putting it all together
21160 @node Stub Contents
21161 @subsection What the Stub Can Do for You
21163 @cindex remote serial stub
21164 The debugging stub for your architecture supplies these three
21168 @item set_debug_traps
21169 @findex set_debug_traps
21170 @cindex remote serial stub, initialization
21171 This routine arranges for @code{handle_exception} to run when your
21172 program stops. You must call this subroutine explicitly in your
21173 program's startup code.
21175 @item handle_exception
21176 @findex handle_exception
21177 @cindex remote serial stub, main routine
21178 This is the central workhorse, but your program never calls it
21179 explicitly---the setup code arranges for @code{handle_exception} to
21180 run when a trap is triggered.
21182 @code{handle_exception} takes control when your program stops during
21183 execution (for example, on a breakpoint), and mediates communications
21184 with @value{GDBN} on the host machine. This is where the communications
21185 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
21186 representative on the target machine. It begins by sending summary
21187 information on the state of your program, then continues to execute,
21188 retrieving and transmitting any information @value{GDBN} needs, until you
21189 execute a @value{GDBN} command that makes your program resume; at that point,
21190 @code{handle_exception} returns control to your own code on the target
21194 @cindex @code{breakpoint} subroutine, remote
21195 Use this auxiliary subroutine to make your program contain a
21196 breakpoint. Depending on the particular situation, this may be the only
21197 way for @value{GDBN} to get control. For instance, if your target
21198 machine has some sort of interrupt button, you won't need to call this;
21199 pressing the interrupt button transfers control to
21200 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
21201 simply receiving characters on the serial port may also trigger a trap;
21202 again, in that situation, you don't need to call @code{breakpoint} from
21203 your own program---simply running @samp{target remote} from the host
21204 @value{GDBN} session gets control.
21206 Call @code{breakpoint} if none of these is true, or if you simply want
21207 to make certain your program stops at a predetermined point for the
21208 start of your debugging session.
21211 @node Bootstrapping
21212 @subsection What You Must Do for the Stub
21214 @cindex remote stub, support routines
21215 The debugging stubs that come with @value{GDBN} are set up for a particular
21216 chip architecture, but they have no information about the rest of your
21217 debugging target machine.
21219 First of all you need to tell the stub how to communicate with the
21223 @item int getDebugChar()
21224 @findex getDebugChar
21225 Write this subroutine to read a single character from the serial port.
21226 It may be identical to @code{getchar} for your target system; a
21227 different name is used to allow you to distinguish the two if you wish.
21229 @item void putDebugChar(int)
21230 @findex putDebugChar
21231 Write this subroutine to write a single character to the serial port.
21232 It may be identical to @code{putchar} for your target system; a
21233 different name is used to allow you to distinguish the two if you wish.
21236 @cindex control C, and remote debugging
21237 @cindex interrupting remote targets
21238 If you want @value{GDBN} to be able to stop your program while it is
21239 running, you need to use an interrupt-driven serial driver, and arrange
21240 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
21241 character). That is the character which @value{GDBN} uses to tell the
21242 remote system to stop.
21244 Getting the debugging target to return the proper status to @value{GDBN}
21245 probably requires changes to the standard stub; one quick and dirty way
21246 is to just execute a breakpoint instruction (the ``dirty'' part is that
21247 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
21249 Other routines you need to supply are:
21252 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
21253 @findex exceptionHandler
21254 Write this function to install @var{exception_address} in the exception
21255 handling tables. You need to do this because the stub does not have any
21256 way of knowing what the exception handling tables on your target system
21257 are like (for example, the processor's table might be in @sc{rom},
21258 containing entries which point to a table in @sc{ram}).
21259 The @var{exception_number} specifies the exception which should be changed;
21260 its meaning is architecture-dependent (for example, different numbers
21261 might represent divide by zero, misaligned access, etc). When this
21262 exception occurs, control should be transferred directly to
21263 @var{exception_address}, and the processor state (stack, registers,
21264 and so on) should be just as it is when a processor exception occurs. So if
21265 you want to use a jump instruction to reach @var{exception_address}, it
21266 should be a simple jump, not a jump to subroutine.
21268 For the 386, @var{exception_address} should be installed as an interrupt
21269 gate so that interrupts are masked while the handler runs. The gate
21270 should be at privilege level 0 (the most privileged level). The
21271 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
21272 help from @code{exceptionHandler}.
21274 @item void flush_i_cache()
21275 @findex flush_i_cache
21276 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
21277 instruction cache, if any, on your target machine. If there is no
21278 instruction cache, this subroutine may be a no-op.
21280 On target machines that have instruction caches, @value{GDBN} requires this
21281 function to make certain that the state of your program is stable.
21285 You must also make sure this library routine is available:
21288 @item void *memset(void *, int, int)
21290 This is the standard library function @code{memset} that sets an area of
21291 memory to a known value. If you have one of the free versions of
21292 @code{libc.a}, @code{memset} can be found there; otherwise, you must
21293 either obtain it from your hardware manufacturer, or write your own.
21296 If you do not use the GNU C compiler, you may need other standard
21297 library subroutines as well; this varies from one stub to another,
21298 but in general the stubs are likely to use any of the common library
21299 subroutines which @code{@value{NGCC}} generates as inline code.
21302 @node Debug Session
21303 @subsection Putting it All Together
21305 @cindex remote serial debugging summary
21306 In summary, when your program is ready to debug, you must follow these
21311 Make sure you have defined the supporting low-level routines
21312 (@pxref{Bootstrapping,,What You Must Do for the Stub}):
21314 @code{getDebugChar}, @code{putDebugChar},
21315 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
21319 Insert these lines in your program's startup code, before the main
21320 procedure is called:
21327 On some machines, when a breakpoint trap is raised, the hardware
21328 automatically makes the PC point to the instruction after the
21329 breakpoint. If your machine doesn't do that, you may need to adjust
21330 @code{handle_exception} to arrange for it to return to the instruction
21331 after the breakpoint on this first invocation, so that your program
21332 doesn't keep hitting the initial breakpoint instead of making
21336 For the 680x0 stub only, you need to provide a variable called
21337 @code{exceptionHook}. Normally you just use:
21340 void (*exceptionHook)() = 0;
21344 but if before calling @code{set_debug_traps}, you set it to point to a
21345 function in your program, that function is called when
21346 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
21347 error). The function indicated by @code{exceptionHook} is called with
21348 one parameter: an @code{int} which is the exception number.
21351 Compile and link together: your program, the @value{GDBN} debugging stub for
21352 your target architecture, and the supporting subroutines.
21355 Make sure you have a serial connection between your target machine and
21356 the @value{GDBN} host, and identify the serial port on the host.
21359 @c The "remote" target now provides a `load' command, so we should
21360 @c document that. FIXME.
21361 Download your program to your target machine (or get it there by
21362 whatever means the manufacturer provides), and start it.
21365 Start @value{GDBN} on the host, and connect to the target
21366 (@pxref{Connecting,,Connecting to a Remote Target}).
21370 @node Configurations
21371 @chapter Configuration-Specific Information
21373 While nearly all @value{GDBN} commands are available for all native and
21374 cross versions of the debugger, there are some exceptions. This chapter
21375 describes things that are only available in certain configurations.
21377 There are three major categories of configurations: native
21378 configurations, where the host and target are the same, embedded
21379 operating system configurations, which are usually the same for several
21380 different processor architectures, and bare embedded processors, which
21381 are quite different from each other.
21386 * Embedded Processors::
21393 This section describes details specific to particular native
21397 * BSD libkvm Interface:: Debugging BSD kernel memory images
21398 * SVR4 Process Information:: SVR4 process information
21399 * DJGPP Native:: Features specific to the DJGPP port
21400 * Cygwin Native:: Features specific to the Cygwin port
21401 * Hurd Native:: Features specific to @sc{gnu} Hurd
21402 * Darwin:: Features specific to Darwin
21405 @node BSD libkvm Interface
21406 @subsection BSD libkvm Interface
21409 @cindex kernel memory image
21410 @cindex kernel crash dump
21412 BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory
21413 interface that provides a uniform interface for accessing kernel virtual
21414 memory images, including live systems and crash dumps. @value{GDBN}
21415 uses this interface to allow you to debug live kernels and kernel crash
21416 dumps on many native BSD configurations. This is implemented as a
21417 special @code{kvm} debugging target. For debugging a live system, load
21418 the currently running kernel into @value{GDBN} and connect to the
21422 (@value{GDBP}) @b{target kvm}
21425 For debugging crash dumps, provide the file name of the crash dump as an
21429 (@value{GDBP}) @b{target kvm /var/crash/bsd.0}
21432 Once connected to the @code{kvm} target, the following commands are
21438 Set current context from the @dfn{Process Control Block} (PCB) address.
21441 Set current context from proc address. This command isn't available on
21442 modern FreeBSD systems.
21445 @node SVR4 Process Information
21446 @subsection SVR4 Process Information
21448 @cindex examine process image
21449 @cindex process info via @file{/proc}
21451 Many versions of SVR4 and compatible systems provide a facility called
21452 @samp{/proc} that can be used to examine the image of a running
21453 process using file-system subroutines.
21455 If @value{GDBN} is configured for an operating system with this
21456 facility, the command @code{info proc} is available to report
21457 information about the process running your program, or about any
21458 process running on your system. This includes, as of this writing,
21459 @sc{gnu}/Linux and Solaris, for example.
21461 This command may also work on core files that were created on a system
21462 that has the @samp{/proc} facility.
21468 @itemx info proc @var{process-id}
21469 Summarize available information about any running process. If a
21470 process ID is specified by @var{process-id}, display information about
21471 that process; otherwise display information about the program being
21472 debugged. The summary includes the debugged process ID, the command
21473 line used to invoke it, its current working directory, and its
21474 executable file's absolute file name.
21476 On some systems, @var{process-id} can be of the form
21477 @samp{[@var{pid}]/@var{tid}} which specifies a certain thread ID
21478 within a process. If the optional @var{pid} part is missing, it means
21479 a thread from the process being debugged (the leading @samp{/} still
21480 needs to be present, or else @value{GDBN} will interpret the number as
21481 a process ID rather than a thread ID).
21483 @item info proc cmdline
21484 @cindex info proc cmdline
21485 Show the original command line of the process. This command is
21486 specific to @sc{gnu}/Linux.
21488 @item info proc cwd
21489 @cindex info proc cwd
21490 Show the current working directory of the process. This command is
21491 specific to @sc{gnu}/Linux.
21493 @item info proc exe
21494 @cindex info proc exe
21495 Show the name of executable of the process. This command is specific
21498 @item info proc mappings
21499 @cindex memory address space mappings
21500 Report the memory address space ranges accessible in the program, with
21501 information on whether the process has read, write, or execute access
21502 rights to each range. On @sc{gnu}/Linux systems, each memory range
21503 includes the object file which is mapped to that range, instead of the
21504 memory access rights to that range.
21506 @item info proc stat
21507 @itemx info proc status
21508 @cindex process detailed status information
21509 These subcommands are specific to @sc{gnu}/Linux systems. They show
21510 the process-related information, including the user ID and group ID;
21511 how many threads are there in the process; its virtual memory usage;
21512 the signals that are pending, blocked, and ignored; its TTY; its
21513 consumption of system and user time; its stack size; its @samp{nice}
21514 value; etc. For more information, see the @samp{proc} man page
21515 (type @kbd{man 5 proc} from your shell prompt).
21517 @item info proc all
21518 Show all the information about the process described under all of the
21519 above @code{info proc} subcommands.
21522 @comment These sub-options of 'info proc' were not included when
21523 @comment procfs.c was re-written. Keep their descriptions around
21524 @comment against the day when someone finds the time to put them back in.
21525 @kindex info proc times
21526 @item info proc times
21527 Starting time, user CPU time, and system CPU time for your program and
21530 @kindex info proc id
21532 Report on the process IDs related to your program: its own process ID,
21533 the ID of its parent, the process group ID, and the session ID.
21536 @item set procfs-trace
21537 @kindex set procfs-trace
21538 @cindex @code{procfs} API calls
21539 This command enables and disables tracing of @code{procfs} API calls.
21541 @item show procfs-trace
21542 @kindex show procfs-trace
21543 Show the current state of @code{procfs} API call tracing.
21545 @item set procfs-file @var{file}
21546 @kindex set procfs-file
21547 Tell @value{GDBN} to write @code{procfs} API trace to the named
21548 @var{file}. @value{GDBN} appends the trace info to the previous
21549 contents of the file. The default is to display the trace on the
21552 @item show procfs-file
21553 @kindex show procfs-file
21554 Show the file to which @code{procfs} API trace is written.
21556 @item proc-trace-entry
21557 @itemx proc-trace-exit
21558 @itemx proc-untrace-entry
21559 @itemx proc-untrace-exit
21560 @kindex proc-trace-entry
21561 @kindex proc-trace-exit
21562 @kindex proc-untrace-entry
21563 @kindex proc-untrace-exit
21564 These commands enable and disable tracing of entries into and exits
21565 from the @code{syscall} interface.
21568 @kindex info pidlist
21569 @cindex process list, QNX Neutrino
21570 For QNX Neutrino only, this command displays the list of all the
21571 processes and all the threads within each process.
21574 @kindex info meminfo
21575 @cindex mapinfo list, QNX Neutrino
21576 For QNX Neutrino only, this command displays the list of all mapinfos.
21580 @subsection Features for Debugging @sc{djgpp} Programs
21581 @cindex @sc{djgpp} debugging
21582 @cindex native @sc{djgpp} debugging
21583 @cindex MS-DOS-specific commands
21586 @sc{djgpp} is a port of the @sc{gnu} development tools to MS-DOS and
21587 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
21588 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
21589 top of real-mode DOS systems and their emulations.
21591 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
21592 defines a few commands specific to the @sc{djgpp} port. This
21593 subsection describes those commands.
21598 This is a prefix of @sc{djgpp}-specific commands which print
21599 information about the target system and important OS structures.
21602 @cindex MS-DOS system info
21603 @cindex free memory information (MS-DOS)
21604 @item info dos sysinfo
21605 This command displays assorted information about the underlying
21606 platform: the CPU type and features, the OS version and flavor, the
21607 DPMI version, and the available conventional and DPMI memory.
21612 @cindex segment descriptor tables
21613 @cindex descriptor tables display
21615 @itemx info dos ldt
21616 @itemx info dos idt
21617 These 3 commands display entries from, respectively, Global, Local,
21618 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
21619 tables are data structures which store a descriptor for each segment
21620 that is currently in use. The segment's selector is an index into a
21621 descriptor table; the table entry for that index holds the
21622 descriptor's base address and limit, and its attributes and access
21625 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
21626 segment (used for both data and the stack), and a DOS segment (which
21627 allows access to DOS/BIOS data structures and absolute addresses in
21628 conventional memory). However, the DPMI host will usually define
21629 additional segments in order to support the DPMI environment.
21631 @cindex garbled pointers
21632 These commands allow to display entries from the descriptor tables.
21633 Without an argument, all entries from the specified table are
21634 displayed. An argument, which should be an integer expression, means
21635 display a single entry whose index is given by the argument. For
21636 example, here's a convenient way to display information about the
21637 debugged program's data segment:
21640 @exdent @code{(@value{GDBP}) info dos ldt $ds}
21641 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
21645 This comes in handy when you want to see whether a pointer is outside
21646 the data segment's limit (i.e.@: @dfn{garbled}).
21648 @cindex page tables display (MS-DOS)
21650 @itemx info dos pte
21651 These two commands display entries from, respectively, the Page
21652 Directory and the Page Tables. Page Directories and Page Tables are
21653 data structures which control how virtual memory addresses are mapped
21654 into physical addresses. A Page Table includes an entry for every
21655 page of memory that is mapped into the program's address space; there
21656 may be several Page Tables, each one holding up to 4096 entries. A
21657 Page Directory has up to 4096 entries, one each for every Page Table
21658 that is currently in use.
21660 Without an argument, @kbd{info dos pde} displays the entire Page
21661 Directory, and @kbd{info dos pte} displays all the entries in all of
21662 the Page Tables. An argument, an integer expression, given to the
21663 @kbd{info dos pde} command means display only that entry from the Page
21664 Directory table. An argument given to the @kbd{info dos pte} command
21665 means display entries from a single Page Table, the one pointed to by
21666 the specified entry in the Page Directory.
21668 @cindex direct memory access (DMA) on MS-DOS
21669 These commands are useful when your program uses @dfn{DMA} (Direct
21670 Memory Access), which needs physical addresses to program the DMA
21673 These commands are supported only with some DPMI servers.
21675 @cindex physical address from linear address
21676 @item info dos address-pte @var{addr}
21677 This command displays the Page Table entry for a specified linear
21678 address. The argument @var{addr} is a linear address which should
21679 already have the appropriate segment's base address added to it,
21680 because this command accepts addresses which may belong to @emph{any}
21681 segment. For example, here's how to display the Page Table entry for
21682 the page where a variable @code{i} is stored:
21685 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
21686 @exdent @code{Page Table entry for address 0x11a00d30:}
21687 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
21691 This says that @code{i} is stored at offset @code{0xd30} from the page
21692 whose physical base address is @code{0x02698000}, and shows all the
21693 attributes of that page.
21695 Note that you must cast the addresses of variables to a @code{char *},
21696 since otherwise the value of @code{__djgpp_base_address}, the base
21697 address of all variables and functions in a @sc{djgpp} program, will
21698 be added using the rules of C pointer arithmetics: if @code{i} is
21699 declared an @code{int}, @value{GDBN} will add 4 times the value of
21700 @code{__djgpp_base_address} to the address of @code{i}.
21702 Here's another example, it displays the Page Table entry for the
21706 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
21707 @exdent @code{Page Table entry for address 0x29110:}
21708 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
21712 (The @code{+ 3} offset is because the transfer buffer's address is the
21713 3rd member of the @code{_go32_info_block} structure.) The output
21714 clearly shows that this DPMI server maps the addresses in conventional
21715 memory 1:1, i.e.@: the physical (@code{0x00029000} + @code{0x110}) and
21716 linear (@code{0x29110}) addresses are identical.
21718 This command is supported only with some DPMI servers.
21721 @cindex DOS serial data link, remote debugging
21722 In addition to native debugging, the DJGPP port supports remote
21723 debugging via a serial data link. The following commands are specific
21724 to remote serial debugging in the DJGPP port of @value{GDBN}.
21727 @kindex set com1base
21728 @kindex set com1irq
21729 @kindex set com2base
21730 @kindex set com2irq
21731 @kindex set com3base
21732 @kindex set com3irq
21733 @kindex set com4base
21734 @kindex set com4irq
21735 @item set com1base @var{addr}
21736 This command sets the base I/O port address of the @file{COM1} serial
21739 @item set com1irq @var{irq}
21740 This command sets the @dfn{Interrupt Request} (@code{IRQ}) line to use
21741 for the @file{COM1} serial port.
21743 There are similar commands @samp{set com2base}, @samp{set com3irq},
21744 etc.@: for setting the port address and the @code{IRQ} lines for the
21747 @kindex show com1base
21748 @kindex show com1irq
21749 @kindex show com2base
21750 @kindex show com2irq
21751 @kindex show com3base
21752 @kindex show com3irq
21753 @kindex show com4base
21754 @kindex show com4irq
21755 The related commands @samp{show com1base}, @samp{show com1irq} etc.@:
21756 display the current settings of the base address and the @code{IRQ}
21757 lines used by the COM ports.
21760 @kindex info serial
21761 @cindex DOS serial port status
21762 This command prints the status of the 4 DOS serial ports. For each
21763 port, it prints whether it's active or not, its I/O base address and
21764 IRQ number, whether it uses a 16550-style FIFO, its baudrate, and the
21765 counts of various errors encountered so far.
21769 @node Cygwin Native
21770 @subsection Features for Debugging MS Windows PE Executables
21771 @cindex MS Windows debugging
21772 @cindex native Cygwin debugging
21773 @cindex Cygwin-specific commands
21775 @value{GDBN} supports native debugging of MS Windows programs, including
21776 DLLs with and without symbolic debugging information.
21778 @cindex Ctrl-BREAK, MS-Windows
21779 @cindex interrupt debuggee on MS-Windows
21780 MS-Windows programs that call @code{SetConsoleMode} to switch off the
21781 special meaning of the @samp{Ctrl-C} keystroke cannot be interrupted
21782 by typing @kbd{C-c}. For this reason, @value{GDBN} on MS-Windows
21783 supports @kbd{C-@key{BREAK}} as an alternative interrupt key
21784 sequence, which can be used to interrupt the debuggee even if it
21787 There are various additional Cygwin-specific commands, described in
21788 this section. Working with DLLs that have no debugging symbols is
21789 described in @ref{Non-debug DLL Symbols}.
21794 This is a prefix of MS Windows-specific commands which print
21795 information about the target system and important OS structures.
21797 @item info w32 selector
21798 This command displays information returned by
21799 the Win32 API @code{GetThreadSelectorEntry} function.
21800 It takes an optional argument that is evaluated to
21801 a long value to give the information about this given selector.
21802 Without argument, this command displays information
21803 about the six segment registers.
21805 @item info w32 thread-information-block
21806 This command displays thread specific information stored in the
21807 Thread Information Block (readable on the X86 CPU family using @code{$fs}
21808 selector for 32-bit programs and @code{$gs} for 64-bit programs).
21810 @kindex signal-event
21811 @item signal-event @var{id}
21812 This command signals an event with user-provided @var{id}. Used to resume
21813 crashing process when attached to it using MS-Windows JIT debugging (AeDebug).
21815 To use it, create or edit the following keys in
21816 @code{HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\AeDebug} and/or
21817 @code{HKLM\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\AeDebug}
21818 (for x86_64 versions):
21822 @code{Debugger} (REG_SZ) --- a command to launch the debugger.
21823 Suggested command is: @code{@var{fully-qualified-path-to-gdb.exe} -ex
21824 "attach %ld" -ex "signal-event %ld" -ex "continue"}.
21826 The first @code{%ld} will be replaced by the process ID of the
21827 crashing process, the second @code{%ld} will be replaced by the ID of
21828 the event that blocks the crashing process, waiting for @value{GDBN}
21832 @code{Auto} (REG_SZ) --- either @code{1} or @code{0}. @code{1} will
21833 make the system run debugger specified by the Debugger key
21834 automatically, @code{0} will cause a dialog box with ``OK'' and
21835 ``Cancel'' buttons to appear, which allows the user to either
21836 terminate the crashing process (OK) or debug it (Cancel).
21839 @kindex set cygwin-exceptions
21840 @cindex debugging the Cygwin DLL
21841 @cindex Cygwin DLL, debugging
21842 @item set cygwin-exceptions @var{mode}
21843 If @var{mode} is @code{on}, @value{GDBN} will break on exceptions that
21844 happen inside the Cygwin DLL. If @var{mode} is @code{off},
21845 @value{GDBN} will delay recognition of exceptions, and may ignore some
21846 exceptions which seem to be caused by internal Cygwin DLL
21847 ``bookkeeping''. This option is meant primarily for debugging the
21848 Cygwin DLL itself; the default value is @code{off} to avoid annoying
21849 @value{GDBN} users with false @code{SIGSEGV} signals.
21851 @kindex show cygwin-exceptions
21852 @item show cygwin-exceptions
21853 Displays whether @value{GDBN} will break on exceptions that happen
21854 inside the Cygwin DLL itself.
21856 @kindex set new-console
21857 @item set new-console @var{mode}
21858 If @var{mode} is @code{on} the debuggee will
21859 be started in a new console on next start.
21860 If @var{mode} is @code{off}, the debuggee will
21861 be started in the same console as the debugger.
21863 @kindex show new-console
21864 @item show new-console
21865 Displays whether a new console is used
21866 when the debuggee is started.
21868 @kindex set new-group
21869 @item set new-group @var{mode}
21870 This boolean value controls whether the debuggee should
21871 start a new group or stay in the same group as the debugger.
21872 This affects the way the Windows OS handles
21875 @kindex show new-group
21876 @item show new-group
21877 Displays current value of new-group boolean.
21879 @kindex set debugevents
21880 @item set debugevents
21881 This boolean value adds debug output concerning kernel events related
21882 to the debuggee seen by the debugger. This includes events that
21883 signal thread and process creation and exit, DLL loading and
21884 unloading, console interrupts, and debugging messages produced by the
21885 Windows @code{OutputDebugString} API call.
21887 @kindex set debugexec
21888 @item set debugexec
21889 This boolean value adds debug output concerning execute events
21890 (such as resume thread) seen by the debugger.
21892 @kindex set debugexceptions
21893 @item set debugexceptions
21894 This boolean value adds debug output concerning exceptions in the
21895 debuggee seen by the debugger.
21897 @kindex set debugmemory
21898 @item set debugmemory
21899 This boolean value adds debug output concerning debuggee memory reads
21900 and writes by the debugger.
21904 This boolean values specifies whether the debuggee is called
21905 via a shell or directly (default value is on).
21909 Displays if the debuggee will be started with a shell.
21914 * Non-debug DLL Symbols:: Support for DLLs without debugging symbols
21917 @node Non-debug DLL Symbols
21918 @subsubsection Support for DLLs without Debugging Symbols
21919 @cindex DLLs with no debugging symbols
21920 @cindex Minimal symbols and DLLs
21922 Very often on windows, some of the DLLs that your program relies on do
21923 not include symbolic debugging information (for example,
21924 @file{kernel32.dll}). When @value{GDBN} doesn't recognize any debugging
21925 symbols in a DLL, it relies on the minimal amount of symbolic
21926 information contained in the DLL's export table. This section
21927 describes working with such symbols, known internally to @value{GDBN} as
21928 ``minimal symbols''.
21930 Note that before the debugged program has started execution, no DLLs
21931 will have been loaded. The easiest way around this problem is simply to
21932 start the program --- either by setting a breakpoint or letting the
21933 program run once to completion.
21935 @subsubsection DLL Name Prefixes
21937 In keeping with the naming conventions used by the Microsoft debugging
21938 tools, DLL export symbols are made available with a prefix based on the
21939 DLL name, for instance @code{KERNEL32!CreateFileA}. The plain name is
21940 also entered into the symbol table, so @code{CreateFileA} is often
21941 sufficient. In some cases there will be name clashes within a program
21942 (particularly if the executable itself includes full debugging symbols)
21943 necessitating the use of the fully qualified name when referring to the
21944 contents of the DLL. Use single-quotes around the name to avoid the
21945 exclamation mark (``!'') being interpreted as a language operator.
21947 Note that the internal name of the DLL may be all upper-case, even
21948 though the file name of the DLL is lower-case, or vice-versa. Since
21949 symbols within @value{GDBN} are @emph{case-sensitive} this may cause
21950 some confusion. If in doubt, try the @code{info functions} and
21951 @code{info variables} commands or even @code{maint print msymbols}
21952 (@pxref{Symbols}). Here's an example:
21955 (@value{GDBP}) info function CreateFileA
21956 All functions matching regular expression "CreateFileA":
21958 Non-debugging symbols:
21959 0x77e885f4 CreateFileA
21960 0x77e885f4 KERNEL32!CreateFileA
21964 (@value{GDBP}) info function !
21965 All functions matching regular expression "!":
21967 Non-debugging symbols:
21968 0x6100114c cygwin1!__assert
21969 0x61004034 cygwin1!_dll_crt0@@0
21970 0x61004240 cygwin1!dll_crt0(per_process *)
21974 @subsubsection Working with Minimal Symbols
21976 Symbols extracted from a DLL's export table do not contain very much
21977 type information. All that @value{GDBN} can do is guess whether a symbol
21978 refers to a function or variable depending on the linker section that
21979 contains the symbol. Also note that the actual contents of the memory
21980 contained in a DLL are not available unless the program is running. This
21981 means that you cannot examine the contents of a variable or disassemble
21982 a function within a DLL without a running program.
21984 Variables are generally treated as pointers and dereferenced
21985 automatically. For this reason, it is often necessary to prefix a
21986 variable name with the address-of operator (``&'') and provide explicit
21987 type information in the command. Here's an example of the type of
21991 (@value{GDBP}) print 'cygwin1!__argv'
21992 'cygwin1!__argv' has unknown type; cast it to its declared type
21996 (@value{GDBP}) x 'cygwin1!__argv'
21997 'cygwin1!__argv' has unknown type; cast it to its declared type
22000 And two possible solutions:
22003 (@value{GDBP}) print ((char **)'cygwin1!__argv')[0]
22004 $2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"
22008 (@value{GDBP}) x/2x &'cygwin1!__argv'
22009 0x610c0aa8 <cygwin1!__argv>: 0x10021608 0x00000000
22010 (@value{GDBP}) x/x 0x10021608
22011 0x10021608: 0x0022fd98
22012 (@value{GDBP}) x/s 0x0022fd98
22013 0x22fd98: "/cygdrive/c/mydirectory/myprogram"
22016 Setting a break point within a DLL is possible even before the program
22017 starts execution. However, under these circumstances, @value{GDBN} can't
22018 examine the initial instructions of the function in order to skip the
22019 function's frame set-up code. You can work around this by using ``*&''
22020 to set the breakpoint at a raw memory address:
22023 (@value{GDBP}) break *&'python22!PyOS_Readline'
22024 Breakpoint 1 at 0x1e04eff0
22027 The author of these extensions is not entirely convinced that setting a
22028 break point within a shared DLL like @file{kernel32.dll} is completely
22032 @subsection Commands Specific to @sc{gnu} Hurd Systems
22033 @cindex @sc{gnu} Hurd debugging
22035 This subsection describes @value{GDBN} commands specific to the
22036 @sc{gnu} Hurd native debugging.
22041 @kindex set signals@r{, Hurd command}
22042 @kindex set sigs@r{, Hurd command}
22043 This command toggles the state of inferior signal interception by
22044 @value{GDBN}. Mach exceptions, such as breakpoint traps, are not
22045 affected by this command. @code{sigs} is a shorthand alias for
22050 @kindex show signals@r{, Hurd command}
22051 @kindex show sigs@r{, Hurd command}
22052 Show the current state of intercepting inferior's signals.
22054 @item set signal-thread
22055 @itemx set sigthread
22056 @kindex set signal-thread
22057 @kindex set sigthread
22058 This command tells @value{GDBN} which thread is the @code{libc} signal
22059 thread. That thread is run when a signal is delivered to a running
22060 process. @code{set sigthread} is the shorthand alias of @code{set
22063 @item show signal-thread
22064 @itemx show sigthread
22065 @kindex show signal-thread
22066 @kindex show sigthread
22067 These two commands show which thread will run when the inferior is
22068 delivered a signal.
22071 @kindex set stopped@r{, Hurd command}
22072 This commands tells @value{GDBN} that the inferior process is stopped,
22073 as with the @code{SIGSTOP} signal. The stopped process can be
22074 continued by delivering a signal to it.
22077 @kindex show stopped@r{, Hurd command}
22078 This command shows whether @value{GDBN} thinks the debuggee is
22081 @item set exceptions
22082 @kindex set exceptions@r{, Hurd command}
22083 Use this command to turn off trapping of exceptions in the inferior.
22084 When exception trapping is off, neither breakpoints nor
22085 single-stepping will work. To restore the default, set exception
22088 @item show exceptions
22089 @kindex show exceptions@r{, Hurd command}
22090 Show the current state of trapping exceptions in the inferior.
22092 @item set task pause
22093 @kindex set task@r{, Hurd commands}
22094 @cindex task attributes (@sc{gnu} Hurd)
22095 @cindex pause current task (@sc{gnu} Hurd)
22096 This command toggles task suspension when @value{GDBN} has control.
22097 Setting it to on takes effect immediately, and the task is suspended
22098 whenever @value{GDBN} gets control. Setting it to off will take
22099 effect the next time the inferior is continued. If this option is set
22100 to off, you can use @code{set thread default pause on} or @code{set
22101 thread pause on} (see below) to pause individual threads.
22103 @item show task pause
22104 @kindex show task@r{, Hurd commands}
22105 Show the current state of task suspension.
22107 @item set task detach-suspend-count
22108 @cindex task suspend count
22109 @cindex detach from task, @sc{gnu} Hurd
22110 This command sets the suspend count the task will be left with when
22111 @value{GDBN} detaches from it.
22113 @item show task detach-suspend-count
22114 Show the suspend count the task will be left with when detaching.
22116 @item set task exception-port
22117 @itemx set task excp
22118 @cindex task exception port, @sc{gnu} Hurd
22119 This command sets the task exception port to which @value{GDBN} will
22120 forward exceptions. The argument should be the value of the @dfn{send
22121 rights} of the task. @code{set task excp} is a shorthand alias.
22123 @item set noninvasive
22124 @cindex noninvasive task options
22125 This command switches @value{GDBN} to a mode that is the least
22126 invasive as far as interfering with the inferior is concerned. This
22127 is the same as using @code{set task pause}, @code{set exceptions}, and
22128 @code{set signals} to values opposite to the defaults.
22130 @item info send-rights
22131 @itemx info receive-rights
22132 @itemx info port-rights
22133 @itemx info port-sets
22134 @itemx info dead-names
22137 @cindex send rights, @sc{gnu} Hurd
22138 @cindex receive rights, @sc{gnu} Hurd
22139 @cindex port rights, @sc{gnu} Hurd
22140 @cindex port sets, @sc{gnu} Hurd
22141 @cindex dead names, @sc{gnu} Hurd
22142 These commands display information about, respectively, send rights,
22143 receive rights, port rights, port sets, and dead names of a task.
22144 There are also shorthand aliases: @code{info ports} for @code{info
22145 port-rights} and @code{info psets} for @code{info port-sets}.
22147 @item set thread pause
22148 @kindex set thread@r{, Hurd command}
22149 @cindex thread properties, @sc{gnu} Hurd
22150 @cindex pause current thread (@sc{gnu} Hurd)
22151 This command toggles current thread suspension when @value{GDBN} has
22152 control. Setting it to on takes effect immediately, and the current
22153 thread is suspended whenever @value{GDBN} gets control. Setting it to
22154 off will take effect the next time the inferior is continued.
22155 Normally, this command has no effect, since when @value{GDBN} has
22156 control, the whole task is suspended. However, if you used @code{set
22157 task pause off} (see above), this command comes in handy to suspend
22158 only the current thread.
22160 @item show thread pause
22161 @kindex show thread@r{, Hurd command}
22162 This command shows the state of current thread suspension.
22164 @item set thread run
22165 This command sets whether the current thread is allowed to run.
22167 @item show thread run
22168 Show whether the current thread is allowed to run.
22170 @item set thread detach-suspend-count
22171 @cindex thread suspend count, @sc{gnu} Hurd
22172 @cindex detach from thread, @sc{gnu} Hurd
22173 This command sets the suspend count @value{GDBN} will leave on a
22174 thread when detaching. This number is relative to the suspend count
22175 found by @value{GDBN} when it notices the thread; use @code{set thread
22176 takeover-suspend-count} to force it to an absolute value.
22178 @item show thread detach-suspend-count
22179 Show the suspend count @value{GDBN} will leave on the thread when
22182 @item set thread exception-port
22183 @itemx set thread excp
22184 Set the thread exception port to which to forward exceptions. This
22185 overrides the port set by @code{set task exception-port} (see above).
22186 @code{set thread excp} is the shorthand alias.
22188 @item set thread takeover-suspend-count
22189 Normally, @value{GDBN}'s thread suspend counts are relative to the
22190 value @value{GDBN} finds when it notices each thread. This command
22191 changes the suspend counts to be absolute instead.
22193 @item set thread default
22194 @itemx show thread default
22195 @cindex thread default settings, @sc{gnu} Hurd
22196 Each of the above @code{set thread} commands has a @code{set thread
22197 default} counterpart (e.g., @code{set thread default pause}, @code{set
22198 thread default exception-port}, etc.). The @code{thread default}
22199 variety of commands sets the default thread properties for all
22200 threads; you can then change the properties of individual threads with
22201 the non-default commands.
22208 @value{GDBN} provides the following commands specific to the Darwin target:
22211 @item set debug darwin @var{num}
22212 @kindex set debug darwin
22213 When set to a non zero value, enables debugging messages specific to
22214 the Darwin support. Higher values produce more verbose output.
22216 @item show debug darwin
22217 @kindex show debug darwin
22218 Show the current state of Darwin messages.
22220 @item set debug mach-o @var{num}
22221 @kindex set debug mach-o
22222 When set to a non zero value, enables debugging messages while
22223 @value{GDBN} is reading Darwin object files. (@dfn{Mach-O} is the
22224 file format used on Darwin for object and executable files.) Higher
22225 values produce more verbose output. This is a command to diagnose
22226 problems internal to @value{GDBN} and should not be needed in normal
22229 @item show debug mach-o
22230 @kindex show debug mach-o
22231 Show the current state of Mach-O file messages.
22233 @item set mach-exceptions on
22234 @itemx set mach-exceptions off
22235 @kindex set mach-exceptions
22236 On Darwin, faults are first reported as a Mach exception and are then
22237 mapped to a Posix signal. Use this command to turn on trapping of
22238 Mach exceptions in the inferior. This might be sometimes useful to
22239 better understand the cause of a fault. The default is off.
22241 @item show mach-exceptions
22242 @kindex show mach-exceptions
22243 Show the current state of exceptions trapping.
22248 @section Embedded Operating Systems
22250 This section describes configurations involving the debugging of
22251 embedded operating systems that are available for several different
22254 @value{GDBN} includes the ability to debug programs running on
22255 various real-time operating systems.
22257 @node Embedded Processors
22258 @section Embedded Processors
22260 This section goes into details specific to particular embedded
22263 @cindex send command to simulator
22264 Whenever a specific embedded processor has a simulator, @value{GDBN}
22265 allows to send an arbitrary command to the simulator.
22268 @item sim @var{command}
22269 @kindex sim@r{, a command}
22270 Send an arbitrary @var{command} string to the simulator. Consult the
22271 documentation for the specific simulator in use for information about
22272 acceptable commands.
22277 * ARC:: Synopsys ARC
22279 * M68K:: Motorola M68K
22280 * MicroBlaze:: Xilinx MicroBlaze
22281 * MIPS Embedded:: MIPS Embedded
22282 * PowerPC Embedded:: PowerPC Embedded
22285 * Super-H:: Renesas Super-H
22289 @subsection Synopsys ARC
22290 @cindex Synopsys ARC
22291 @cindex ARC specific commands
22297 @value{GDBN} provides the following ARC-specific commands:
22300 @item set debug arc
22301 @kindex set debug arc
22302 Control the level of ARC specific debug messages. Use 0 for no messages (the
22303 default), 1 for debug messages, and 2 for even more debug messages.
22305 @item show debug arc
22306 @kindex show debug arc
22307 Show the level of ARC specific debugging in operation.
22309 @item maint print arc arc-instruction @var{address}
22310 @kindex maint print arc arc-instruction
22311 Print internal disassembler information about instruction at a given address.
22318 @value{GDBN} provides the following ARM-specific commands:
22321 @item set arm disassembler
22323 This commands selects from a list of disassembly styles. The
22324 @code{"std"} style is the standard style.
22326 @item show arm disassembler
22328 Show the current disassembly style.
22330 @item set arm apcs32
22331 @cindex ARM 32-bit mode
22332 This command toggles ARM operation mode between 32-bit and 26-bit.
22334 @item show arm apcs32
22335 Display the current usage of the ARM 32-bit mode.
22337 @item set arm fpu @var{fputype}
22338 This command sets the ARM floating-point unit (FPU) type. The
22339 argument @var{fputype} can be one of these:
22343 Determine the FPU type by querying the OS ABI.
22345 Software FPU, with mixed-endian doubles on little-endian ARM
22348 GCC-compiled FPA co-processor.
22350 Software FPU with pure-endian doubles.
22356 Show the current type of the FPU.
22359 This command forces @value{GDBN} to use the specified ABI.
22362 Show the currently used ABI.
22364 @item set arm fallback-mode (arm|thumb|auto)
22365 @value{GDBN} uses the symbol table, when available, to determine
22366 whether instructions are ARM or Thumb. This command controls
22367 @value{GDBN}'s default behavior when the symbol table is not
22368 available. The default is @samp{auto}, which causes @value{GDBN} to
22369 use the current execution mode (from the @code{T} bit in the @code{CPSR}
22372 @item show arm fallback-mode
22373 Show the current fallback instruction mode.
22375 @item set arm force-mode (arm|thumb|auto)
22376 This command overrides use of the symbol table to determine whether
22377 instructions are ARM or Thumb. The default is @samp{auto}, which
22378 causes @value{GDBN} to use the symbol table and then the setting
22379 of @samp{set arm fallback-mode}.
22381 @item show arm force-mode
22382 Show the current forced instruction mode.
22384 @item set debug arm
22385 Toggle whether to display ARM-specific debugging messages from the ARM
22386 target support subsystem.
22388 @item show debug arm
22389 Show whether ARM-specific debugging messages are enabled.
22393 @item target sim @r{[}@var{simargs}@r{]} @dots{}
22394 The @value{GDBN} ARM simulator accepts the following optional arguments.
22397 @item --swi-support=@var{type}
22398 Tell the simulator which SWI interfaces to support. The argument
22399 @var{type} may be a comma separated list of the following values.
22400 The default value is @code{all}.
22415 The Motorola m68k configuration includes ColdFire support.
22418 @subsection MicroBlaze
22419 @cindex Xilinx MicroBlaze
22420 @cindex XMD, Xilinx Microprocessor Debugger
22422 The MicroBlaze is a soft-core processor supported on various Xilinx
22423 FPGAs, such as Spartan or Virtex series. Boards with these processors
22424 usually have JTAG ports which connect to a host system running the Xilinx
22425 Embedded Development Kit (EDK) or Software Development Kit (SDK).
22426 This host system is used to download the configuration bitstream to
22427 the target FPGA. The Xilinx Microprocessor Debugger (XMD) program
22428 communicates with the target board using the JTAG interface and
22429 presents a @code{gdbserver} interface to the board. By default
22430 @code{xmd} uses port @code{1234}. (While it is possible to change
22431 this default port, it requires the use of undocumented @code{xmd}
22432 commands. Contact Xilinx support if you need to do this.)
22434 Use these GDB commands to connect to the MicroBlaze target processor.
22437 @item target remote :1234
22438 Use this command to connect to the target if you are running @value{GDBN}
22439 on the same system as @code{xmd}.
22441 @item target remote @var{xmd-host}:1234
22442 Use this command to connect to the target if it is connected to @code{xmd}
22443 running on a different system named @var{xmd-host}.
22446 Use this command to download a program to the MicroBlaze target.
22448 @item set debug microblaze @var{n}
22449 Enable MicroBlaze-specific debugging messages if non-zero.
22451 @item show debug microblaze @var{n}
22452 Show MicroBlaze-specific debugging level.
22455 @node MIPS Embedded
22456 @subsection @acronym{MIPS} Embedded
22459 @value{GDBN} supports these special commands for @acronym{MIPS} targets:
22462 @item set mipsfpu double
22463 @itemx set mipsfpu single
22464 @itemx set mipsfpu none
22465 @itemx set mipsfpu auto
22466 @itemx show mipsfpu
22467 @kindex set mipsfpu
22468 @kindex show mipsfpu
22469 @cindex @acronym{MIPS} remote floating point
22470 @cindex floating point, @acronym{MIPS} remote
22471 If your target board does not support the @acronym{MIPS} floating point
22472 coprocessor, you should use the command @samp{set mipsfpu none} (if you
22473 need this, you may wish to put the command in your @value{GDBN} init
22474 file). This tells @value{GDBN} how to find the return value of
22475 functions which return floating point values. It also allows
22476 @value{GDBN} to avoid saving the floating point registers when calling
22477 functions on the board. If you are using a floating point coprocessor
22478 with only single precision floating point support, as on the @sc{r4650}
22479 processor, use the command @samp{set mipsfpu single}. The default
22480 double precision floating point coprocessor may be selected using
22481 @samp{set mipsfpu double}.
22483 In previous versions the only choices were double precision or no
22484 floating point, so @samp{set mipsfpu on} will select double precision
22485 and @samp{set mipsfpu off} will select no floating point.
22487 As usual, you can inquire about the @code{mipsfpu} variable with
22488 @samp{show mipsfpu}.
22491 @node PowerPC Embedded
22492 @subsection PowerPC Embedded
22494 @cindex DVC register
22495 @value{GDBN} supports using the DVC (Data Value Compare) register to
22496 implement in hardware simple hardware watchpoint conditions of the form:
22499 (@value{GDBP}) watch @var{ADDRESS|VARIABLE} \
22500 if @var{ADDRESS|VARIABLE} == @var{CONSTANT EXPRESSION}
22503 The DVC register will be automatically used when @value{GDBN} detects
22504 such pattern in a condition expression, and the created watchpoint uses one
22505 debug register (either the @code{exact-watchpoints} option is on and the
22506 variable is scalar, or the variable has a length of one byte). This feature
22507 is available in native @value{GDBN} running on a Linux kernel version 2.6.34
22510 When running on PowerPC embedded processors, @value{GDBN} automatically uses
22511 ranged hardware watchpoints, unless the @code{exact-watchpoints} option is on,
22512 in which case watchpoints using only one debug register are created when
22513 watching variables of scalar types.
22515 You can create an artificial array to watch an arbitrary memory
22516 region using one of the following commands (@pxref{Expressions}):
22519 (@value{GDBP}) watch *((char *) @var{address})@@@var{length}
22520 (@value{GDBP}) watch @{char[@var{length}]@} @var{address}
22523 PowerPC embedded processors support masked watchpoints. See the discussion
22524 about the @code{mask} argument in @ref{Set Watchpoints}.
22526 @cindex ranged breakpoint
22527 PowerPC embedded processors support hardware accelerated
22528 @dfn{ranged breakpoints}. A ranged breakpoint stops execution of
22529 the inferior whenever it executes an instruction at any address within
22530 the range it specifies. To set a ranged breakpoint in @value{GDBN},
22531 use the @code{break-range} command.
22533 @value{GDBN} provides the following PowerPC-specific commands:
22536 @kindex break-range
22537 @item break-range @var{start-location}, @var{end-location}
22538 Set a breakpoint for an address range given by
22539 @var{start-location} and @var{end-location}, which can specify a function name,
22540 a line number, an offset of lines from the current line or from the start
22541 location, or an address of an instruction (see @ref{Specify Location},
22542 for a list of all the possible ways to specify a @var{location}.)
22543 The breakpoint will stop execution of the inferior whenever it
22544 executes an instruction at any address within the specified range,
22545 (including @var{start-location} and @var{end-location}.)
22547 @kindex set powerpc
22548 @item set powerpc soft-float
22549 @itemx show powerpc soft-float
22550 Force @value{GDBN} to use (or not use) a software floating point calling
22551 convention. By default, @value{GDBN} selects the calling convention based
22552 on the selected architecture and the provided executable file.
22554 @item set powerpc vector-abi
22555 @itemx show powerpc vector-abi
22556 Force @value{GDBN} to use the specified calling convention for vector
22557 arguments and return values. The valid options are @samp{auto};
22558 @samp{generic}, to avoid vector registers even if they are present;
22559 @samp{altivec}, to use AltiVec registers; and @samp{spe} to use SPE
22560 registers. By default, @value{GDBN} selects the calling convention
22561 based on the selected architecture and the provided executable file.
22563 @item set powerpc exact-watchpoints
22564 @itemx show powerpc exact-watchpoints
22565 Allow @value{GDBN} to use only one debug register when watching a variable
22566 of scalar type, thus assuming that the variable is accessed through the
22567 address of its first byte.
22572 @subsection Atmel AVR
22575 When configured for debugging the Atmel AVR, @value{GDBN} supports the
22576 following AVR-specific commands:
22579 @item info io_registers
22580 @kindex info io_registers@r{, AVR}
22581 @cindex I/O registers (Atmel AVR)
22582 This command displays information about the AVR I/O registers. For
22583 each register, @value{GDBN} prints its number and value.
22590 When configured for debugging CRIS, @value{GDBN} provides the
22591 following CRIS-specific commands:
22594 @item set cris-version @var{ver}
22595 @cindex CRIS version
22596 Set the current CRIS version to @var{ver}, either @samp{10} or @samp{32}.
22597 The CRIS version affects register names and sizes. This command is useful in
22598 case autodetection of the CRIS version fails.
22600 @item show cris-version
22601 Show the current CRIS version.
22603 @item set cris-dwarf2-cfi
22604 @cindex DWARF-2 CFI and CRIS
22605 Set the usage of DWARF-2 CFI for CRIS debugging. The default is @samp{on}.
22606 Change to @samp{off} when using @code{gcc-cris} whose version is below
22609 @item show cris-dwarf2-cfi
22610 Show the current state of using DWARF-2 CFI.
22612 @item set cris-mode @var{mode}
22614 Set the current CRIS mode to @var{mode}. It should only be changed when
22615 debugging in guru mode, in which case it should be set to
22616 @samp{guru} (the default is @samp{normal}).
22618 @item show cris-mode
22619 Show the current CRIS mode.
22623 @subsection Renesas Super-H
22626 For the Renesas Super-H processor, @value{GDBN} provides these
22630 @item set sh calling-convention @var{convention}
22631 @kindex set sh calling-convention
22632 Set the calling-convention used when calling functions from @value{GDBN}.
22633 Allowed values are @samp{gcc}, which is the default setting, and @samp{renesas}.
22634 With the @samp{gcc} setting, functions are called using the @value{NGCC} calling
22635 convention. If the DWARF-2 information of the called function specifies
22636 that the function follows the Renesas calling convention, the function
22637 is called using the Renesas calling convention. If the calling convention
22638 is set to @samp{renesas}, the Renesas calling convention is always used,
22639 regardless of the DWARF-2 information. This can be used to override the
22640 default of @samp{gcc} if debug information is missing, or the compiler
22641 does not emit the DWARF-2 calling convention entry for a function.
22643 @item show sh calling-convention
22644 @kindex show sh calling-convention
22645 Show the current calling convention setting.
22650 @node Architectures
22651 @section Architectures
22653 This section describes characteristics of architectures that affect
22654 all uses of @value{GDBN} with the architecture, both native and cross.
22661 * HPPA:: HP PA architecture
22662 * SPU:: Cell Broadband Engine SPU architecture
22669 @subsection AArch64
22670 @cindex AArch64 support
22672 When @value{GDBN} is debugging the AArch64 architecture, it provides the
22673 following special commands:
22676 @item set debug aarch64
22677 @kindex set debug aarch64
22678 This command determines whether AArch64 architecture-specific debugging
22679 messages are to be displayed.
22681 @item show debug aarch64
22682 Show whether AArch64 debugging messages are displayed.
22687 @subsection x86 Architecture-specific Issues
22690 @item set struct-convention @var{mode}
22691 @kindex set struct-convention
22692 @cindex struct return convention
22693 @cindex struct/union returned in registers
22694 Set the convention used by the inferior to return @code{struct}s and
22695 @code{union}s from functions to @var{mode}. Possible values of
22696 @var{mode} are @code{"pcc"}, @code{"reg"}, and @code{"default"} (the
22697 default). @code{"default"} or @code{"pcc"} means that @code{struct}s
22698 are returned on the stack, while @code{"reg"} means that a
22699 @code{struct} or a @code{union} whose size is 1, 2, 4, or 8 bytes will
22700 be returned in a register.
22702 @item show struct-convention
22703 @kindex show struct-convention
22704 Show the current setting of the convention to return @code{struct}s
22709 @subsubsection Intel @dfn{Memory Protection Extensions} (MPX).
22710 @cindex Intel Memory Protection Extensions (MPX).
22712 Memory Protection Extension (MPX) adds the bound registers @samp{BND0}
22713 @footnote{The register named with capital letters represent the architecture
22714 registers.} through @samp{BND3}. Bound registers store a pair of 64-bit values
22715 which are the lower bound and upper bound. Bounds are effective addresses or
22716 memory locations. The upper bounds are architecturally represented in 1's
22717 complement form. A bound having lower bound = 0, and upper bound = 0
22718 (1's complement of all bits set) will allow access to the entire address space.
22720 @samp{BND0} through @samp{BND3} are represented in @value{GDBN} as @samp{bnd0raw}
22721 through @samp{bnd3raw}. Pseudo registers @samp{bnd0} through @samp{bnd3}
22722 display the upper bound performing the complement of one operation on the
22723 upper bound value, i.e.@ when upper bound in @samp{bnd0raw} is 0 in the
22724 @value{GDBN} @samp{bnd0} it will be @code{0xfff@dots{}}. In this sense it
22725 can also be noted that the upper bounds are inclusive.
22727 As an example, assume that the register BND0 holds bounds for a pointer having
22728 access allowed for the range between 0x32 and 0x71. The values present on
22729 bnd0raw and bnd registers are presented as follows:
22732 bnd0raw = @{0x32, 0xffffffff8e@}
22733 bnd0 = @{lbound = 0x32, ubound = 0x71@} : size 64
22736 This way the raw value can be accessed via bnd0raw@dots{}bnd3raw. Any
22737 change on bnd0@dots{}bnd3 or bnd0raw@dots{}bnd3raw is reflect on its
22738 counterpart. When the bnd0@dots{}bnd3 registers are displayed via
22739 Python, the display includes the memory size, in bits, accessible to
22742 Bounds can also be stored in bounds tables, which are stored in
22743 application memory. These tables store bounds for pointers by specifying
22744 the bounds pointer's value along with its bounds. Evaluating and changing
22745 bounds located in bound tables is therefore interesting while investigating
22746 bugs on MPX context. @value{GDBN} provides commands for this purpose:
22749 @item show mpx bound @var{pointer}
22750 @kindex show mpx bound
22751 Display bounds of the given @var{pointer}.
22753 @item set mpx bound @var{pointer}, @var{lbound}, @var{ubound}
22754 @kindex set mpx bound
22755 Set the bounds of a pointer in the bound table.
22756 This command takes three parameters: @var{pointer} is the pointers
22757 whose bounds are to be changed, @var{lbound} and @var{ubound} are new values
22758 for lower and upper bounds respectively.
22761 When you call an inferior function on an Intel MPX enabled program,
22762 GDB sets the inferior's bound registers to the init (disabled) state
22763 before calling the function. As a consequence, bounds checks for the
22764 pointer arguments passed to the function will always pass.
22766 This is necessary because when you call an inferior function, the
22767 program is usually in the middle of the execution of other function.
22768 Since at that point bound registers are in an arbitrary state, not
22769 clearing them would lead to random bound violations in the called
22772 You can still examine the influence of the bound registers on the
22773 execution of the called function by stopping the execution of the
22774 called function at its prologue, setting bound registers, and
22775 continuing the execution. For example:
22779 Breakpoint 2 at 0x4009de: file i386-mpx-call.c, line 47.
22780 $ print upper (a, b, c, d, 1)
22781 Breakpoint 2, upper (a=0x0, b=0x6e0000005b, c=0x0, d=0x0, len=48)....
22783 @{lbound = 0x0, ubound = ffffffff@} : size -1
22786 At this last step the value of bnd0 can be changed for investigation of bound
22787 violations caused along the execution of the call. In order to know how to
22788 set the bound registers or bound table for the call consult the ABI.
22793 See the following section.
22796 @subsection @acronym{MIPS}
22798 @cindex stack on Alpha
22799 @cindex stack on @acronym{MIPS}
22800 @cindex Alpha stack
22801 @cindex @acronym{MIPS} stack
22802 Alpha- and @acronym{MIPS}-based computers use an unusual stack frame, which
22803 sometimes requires @value{GDBN} to search backward in the object code to
22804 find the beginning of a function.
22806 @cindex response time, @acronym{MIPS} debugging
22807 To improve response time (especially for embedded applications, where
22808 @value{GDBN} may be restricted to a slow serial line for this search)
22809 you may want to limit the size of this search, using one of these
22813 @cindex @code{heuristic-fence-post} (Alpha, @acronym{MIPS})
22814 @item set heuristic-fence-post @var{limit}
22815 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
22816 search for the beginning of a function. A value of @var{0} (the
22817 default) means there is no limit. However, except for @var{0}, the
22818 larger the limit the more bytes @code{heuristic-fence-post} must search
22819 and therefore the longer it takes to run. You should only need to use
22820 this command when debugging a stripped executable.
22822 @item show heuristic-fence-post
22823 Display the current limit.
22827 These commands are available @emph{only} when @value{GDBN} is configured
22828 for debugging programs on Alpha or @acronym{MIPS} processors.
22830 Several @acronym{MIPS}-specific commands are available when debugging @acronym{MIPS}
22834 @item set mips abi @var{arg}
22835 @kindex set mips abi
22836 @cindex set ABI for @acronym{MIPS}
22837 Tell @value{GDBN} which @acronym{MIPS} ABI is used by the inferior. Possible
22838 values of @var{arg} are:
22842 The default ABI associated with the current binary (this is the
22852 @item show mips abi
22853 @kindex show mips abi
22854 Show the @acronym{MIPS} ABI used by @value{GDBN} to debug the inferior.
22856 @item set mips compression @var{arg}
22857 @kindex set mips compression
22858 @cindex code compression, @acronym{MIPS}
22859 Tell @value{GDBN} which @acronym{MIPS} compressed
22860 @acronym{ISA, Instruction Set Architecture} encoding is used by the
22861 inferior. @value{GDBN} uses this for code disassembly and other
22862 internal interpretation purposes. This setting is only referred to
22863 when no executable has been associated with the debugging session or
22864 the executable does not provide information about the encoding it uses.
22865 Otherwise this setting is automatically updated from information
22866 provided by the executable.
22868 Possible values of @var{arg} are @samp{mips16} and @samp{micromips}.
22869 The default compressed @acronym{ISA} encoding is @samp{mips16}, as
22870 executables containing @acronym{MIPS16} code frequently are not
22871 identified as such.
22873 This setting is ``sticky''; that is, it retains its value across
22874 debugging sessions until reset either explicitly with this command or
22875 implicitly from an executable.
22877 The compiler and/or assembler typically add symbol table annotations to
22878 identify functions compiled for the @acronym{MIPS16} or
22879 @acronym{microMIPS} @acronym{ISA}s. If these function-scope annotations
22880 are present, @value{GDBN} uses them in preference to the global
22881 compressed @acronym{ISA} encoding setting.
22883 @item show mips compression
22884 @kindex show mips compression
22885 Show the @acronym{MIPS} compressed @acronym{ISA} encoding used by
22886 @value{GDBN} to debug the inferior.
22889 @itemx show mipsfpu
22890 @xref{MIPS Embedded, set mipsfpu}.
22892 @item set mips mask-address @var{arg}
22893 @kindex set mips mask-address
22894 @cindex @acronym{MIPS} addresses, masking
22895 This command determines whether the most-significant 32 bits of 64-bit
22896 @acronym{MIPS} addresses are masked off. The argument @var{arg} can be
22897 @samp{on}, @samp{off}, or @samp{auto}. The latter is the default
22898 setting, which lets @value{GDBN} determine the correct value.
22900 @item show mips mask-address
22901 @kindex show mips mask-address
22902 Show whether the upper 32 bits of @acronym{MIPS} addresses are masked off or
22905 @item set remote-mips64-transfers-32bit-regs
22906 @kindex set remote-mips64-transfers-32bit-regs
22907 This command controls compatibility with 64-bit @acronym{MIPS} targets that
22908 transfer data in 32-bit quantities. If you have an old @acronym{MIPS} 64 target
22909 that transfers 32 bits for some registers, like @sc{sr} and @sc{fsr},
22910 and 64 bits for other registers, set this option to @samp{on}.
22912 @item show remote-mips64-transfers-32bit-regs
22913 @kindex show remote-mips64-transfers-32bit-regs
22914 Show the current setting of compatibility with older @acronym{MIPS} 64 targets.
22916 @item set debug mips
22917 @kindex set debug mips
22918 This command turns on and off debugging messages for the @acronym{MIPS}-specific
22919 target code in @value{GDBN}.
22921 @item show debug mips
22922 @kindex show debug mips
22923 Show the current setting of @acronym{MIPS} debugging messages.
22929 @cindex HPPA support
22931 When @value{GDBN} is debugging the HP PA architecture, it provides the
22932 following special commands:
22935 @item set debug hppa
22936 @kindex set debug hppa
22937 This command determines whether HPPA architecture-specific debugging
22938 messages are to be displayed.
22940 @item show debug hppa
22941 Show whether HPPA debugging messages are displayed.
22943 @item maint print unwind @var{address}
22944 @kindex maint print unwind@r{, HPPA}
22945 This command displays the contents of the unwind table entry at the
22946 given @var{address}.
22952 @subsection Cell Broadband Engine SPU architecture
22953 @cindex Cell Broadband Engine
22956 When @value{GDBN} is debugging the Cell Broadband Engine SPU architecture,
22957 it provides the following special commands:
22960 @item info spu event
22962 Display SPU event facility status. Shows current event mask
22963 and pending event status.
22965 @item info spu signal
22966 Display SPU signal notification facility status. Shows pending
22967 signal-control word and signal notification mode of both signal
22968 notification channels.
22970 @item info spu mailbox
22971 Display SPU mailbox facility status. Shows all pending entries,
22972 in order of processing, in each of the SPU Write Outbound,
22973 SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes.
22976 Display MFC DMA status. Shows all pending commands in the MFC
22977 DMA queue. For each entry, opcode, tag, class IDs, effective
22978 and local store addresses and transfer size are shown.
22980 @item info spu proxydma
22981 Display MFC Proxy-DMA status. Shows all pending commands in the MFC
22982 Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective
22983 and local store addresses and transfer size are shown.
22987 When @value{GDBN} is debugging a combined PowerPC/SPU application
22988 on the Cell Broadband Engine, it provides in addition the following
22992 @item set spu stop-on-load @var{arg}
22994 Set whether to stop for new SPE threads. When set to @code{on}, @value{GDBN}
22995 will give control to the user when a new SPE thread enters its @code{main}
22996 function. The default is @code{off}.
22998 @item show spu stop-on-load
23000 Show whether to stop for new SPE threads.
23002 @item set spu auto-flush-cache @var{arg}
23003 Set whether to automatically flush the software-managed cache. When set to
23004 @code{on}, @value{GDBN} will automatically cause the SPE software-managed
23005 cache to be flushed whenever SPE execution stops. This provides a consistent
23006 view of PowerPC memory that is accessed via the cache. If an application
23007 does not use the software-managed cache, this option has no effect.
23009 @item show spu auto-flush-cache
23010 Show whether to automatically flush the software-managed cache.
23015 @subsection PowerPC
23016 @cindex PowerPC architecture
23018 When @value{GDBN} is debugging the PowerPC architecture, it provides a set of
23019 pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point
23020 numbers stored in the floating point registers. These values must be stored
23021 in two consecutive registers, always starting at an even register like
23022 @code{f0} or @code{f2}.
23024 The pseudo-registers go from @code{$dl0} through @code{$dl15}, and are formed
23025 by joining the even/odd register pairs @code{f0} and @code{f1} for @code{$dl0},
23026 @code{f2} and @code{f3} for @code{$dl1} and so on.
23028 For POWER7 processors, @value{GDBN} provides a set of pseudo-registers, the 64-bit
23029 wide Extended Floating Point Registers (@samp{f32} through @samp{f63}).
23032 @subsection Nios II
23033 @cindex Nios II architecture
23035 When @value{GDBN} is debugging the Nios II architecture,
23036 it provides the following special commands:
23040 @item set debug nios2
23041 @kindex set debug nios2
23042 This command turns on and off debugging messages for the Nios II
23043 target code in @value{GDBN}.
23045 @item show debug nios2
23046 @kindex show debug nios2
23047 Show the current setting of Nios II debugging messages.
23051 @subsection Sparc64
23052 @cindex Sparc64 support
23053 @cindex Application Data Integrity
23054 @subsubsection ADI Support
23056 The M7 processor supports an Application Data Integrity (ADI) feature that
23057 detects invalid data accesses. When software allocates memory and enables
23058 ADI on the allocated memory, it chooses a 4-bit version number, sets the
23059 version in the upper 4 bits of the 64-bit pointer to that data, and stores
23060 the 4-bit version in every cacheline of that data. Hardware saves the latter
23061 in spare bits in the cache and memory hierarchy. On each load and store,
23062 the processor compares the upper 4 VA (virtual address) bits to the
23063 cacheline's version. If there is a mismatch, the processor generates a
23064 version mismatch trap which can be either precise or disrupting. The trap
23065 is an error condition which the kernel delivers to the process as a SIGSEGV
23068 Note that only 64-bit applications can use ADI and need to be built with
23071 Values of the ADI version tags, which are in granularity of a
23072 cacheline (64 bytes), can be viewed or modified.
23076 @kindex adi examine
23077 @item adi (examine | x) [ / @var{n} ] @var{addr}
23079 The @code{adi examine} command displays the value of one ADI version tag per
23082 @var{n} is a decimal integer specifying the number in bytes; the default
23083 is 1. It specifies how much ADI version information, at the ratio of 1:ADI
23084 block size, to display.
23086 @var{addr} is the address in user address space where you want @value{GDBN}
23087 to begin displaying the ADI version tags.
23089 Below is an example of displaying ADI versions of variable "shmaddr".
23092 (@value{GDBP}) adi x/100 shmaddr
23093 0xfff800010002c000: 0 0
23097 @item adi (assign | a) [ / @var{n} ] @var{addr} = @var{tag}
23099 The @code{adi assign} command is used to assign new ADI version tag
23102 @var{n} is a decimal integer specifying the number in bytes;
23103 the default is 1. It specifies how much ADI version information, at the
23104 ratio of 1:ADI block size, to modify.
23106 @var{addr} is the address in user address space where you want @value{GDBN}
23107 to begin modifying the ADI version tags.
23109 @var{tag} is the new ADI version tag.
23111 For example, do the following to modify then verify ADI versions of
23112 variable "shmaddr":
23115 (@value{GDBP}) adi a/100 shmaddr = 7
23116 (@value{GDBP}) adi x/100 shmaddr
23117 0xfff800010002c000: 7 7
23122 @node Controlling GDB
23123 @chapter Controlling @value{GDBN}
23125 You can alter the way @value{GDBN} interacts with you by using the
23126 @code{set} command. For commands controlling how @value{GDBN} displays
23127 data, see @ref{Print Settings, ,Print Settings}. Other settings are
23132 * Editing:: Command editing
23133 * Command History:: Command history
23134 * Screen Size:: Screen size
23135 * Numbers:: Numbers
23136 * ABI:: Configuring the current ABI
23137 * Auto-loading:: Automatically loading associated files
23138 * Messages/Warnings:: Optional warnings and messages
23139 * Debugging Output:: Optional messages about internal happenings
23140 * Other Misc Settings:: Other Miscellaneous Settings
23148 @value{GDBN} indicates its readiness to read a command by printing a string
23149 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
23150 can change the prompt string with the @code{set prompt} command. For
23151 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
23152 the prompt in one of the @value{GDBN} sessions so that you can always tell
23153 which one you are talking to.
23155 @emph{Note:} @code{set prompt} does not add a space for you after the
23156 prompt you set. This allows you to set a prompt which ends in a space
23157 or a prompt that does not.
23161 @item set prompt @var{newprompt}
23162 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
23164 @kindex show prompt
23166 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
23169 Versions of @value{GDBN} that ship with Python scripting enabled have
23170 prompt extensions. The commands for interacting with these extensions
23174 @kindex set extended-prompt
23175 @item set extended-prompt @var{prompt}
23176 Set an extended prompt that allows for substitutions.
23177 @xref{gdb.prompt}, for a list of escape sequences that can be used for
23178 substitution. Any escape sequences specified as part of the prompt
23179 string are replaced with the corresponding strings each time the prompt
23185 set extended-prompt Current working directory: \w (gdb)
23188 Note that when an extended-prompt is set, it takes control of the
23189 @var{prompt_hook} hook. @xref{prompt_hook}, for further information.
23191 @kindex show extended-prompt
23192 @item show extended-prompt
23193 Prints the extended prompt. Any escape sequences specified as part of
23194 the prompt string with @code{set extended-prompt}, are replaced with the
23195 corresponding strings each time the prompt is displayed.
23199 @section Command Editing
23201 @cindex command line editing
23203 @value{GDBN} reads its input commands via the @dfn{Readline} interface. This
23204 @sc{gnu} library provides consistent behavior for programs which provide a
23205 command line interface to the user. Advantages are @sc{gnu} Emacs-style
23206 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
23207 substitution, and a storage and recall of command history across
23208 debugging sessions.
23210 You may control the behavior of command line editing in @value{GDBN} with the
23211 command @code{set}.
23214 @kindex set editing
23217 @itemx set editing on
23218 Enable command line editing (enabled by default).
23220 @item set editing off
23221 Disable command line editing.
23223 @kindex show editing
23225 Show whether command line editing is enabled.
23228 @ifset SYSTEM_READLINE
23229 @xref{Command Line Editing, , , rluserman, GNU Readline Library},
23231 @ifclear SYSTEM_READLINE
23232 @xref{Command Line Editing},
23234 for more details about the Readline
23235 interface. Users unfamiliar with @sc{gnu} Emacs or @code{vi} are
23236 encouraged to read that chapter.
23238 @node Command History
23239 @section Command History
23240 @cindex command history
23242 @value{GDBN} can keep track of the commands you type during your
23243 debugging sessions, so that you can be certain of precisely what
23244 happened. Use these commands to manage the @value{GDBN} command
23247 @value{GDBN} uses the @sc{gnu} History library, a part of the Readline
23248 package, to provide the history facility.
23249 @ifset SYSTEM_READLINE
23250 @xref{Using History Interactively, , , history, GNU History Library},
23252 @ifclear SYSTEM_READLINE
23253 @xref{Using History Interactively},
23255 for the detailed description of the History library.
23257 To issue a command to @value{GDBN} without affecting certain aspects of
23258 the state which is seen by users, prefix it with @samp{server }
23259 (@pxref{Server Prefix}). This
23260 means that this command will not affect the command history, nor will it
23261 affect @value{GDBN}'s notion of which command to repeat if @key{RET} is
23262 pressed on a line by itself.
23264 @cindex @code{server}, command prefix
23265 The server prefix does not affect the recording of values into the value
23266 history; to print a value without recording it into the value history,
23267 use the @code{output} command instead of the @code{print} command.
23269 Here is the description of @value{GDBN} commands related to command
23273 @cindex history substitution
23274 @cindex history file
23275 @kindex set history filename
23276 @cindex @env{GDBHISTFILE}, environment variable
23277 @item set history filename @var{fname}
23278 Set the name of the @value{GDBN} command history file to @var{fname}.
23279 This is the file where @value{GDBN} reads an initial command history
23280 list, and where it writes the command history from this session when it
23281 exits. You can access this list through history expansion or through
23282 the history command editing characters listed below. This file defaults
23283 to the value of the environment variable @code{GDBHISTFILE}, or to
23284 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
23287 @cindex save command history
23288 @kindex set history save
23289 @item set history save
23290 @itemx set history save on
23291 Record command history in a file, whose name may be specified with the
23292 @code{set history filename} command. By default, this option is disabled.
23294 @item set history save off
23295 Stop recording command history in a file.
23297 @cindex history size
23298 @kindex set history size
23299 @cindex @env{GDBHISTSIZE}, environment variable
23300 @item set history size @var{size}
23301 @itemx set history size unlimited
23302 Set the number of commands which @value{GDBN} keeps in its history list.
23303 This defaults to the value of the environment variable @env{GDBHISTSIZE}, or
23304 to 256 if this variable is not set. Non-numeric values of @env{GDBHISTSIZE}
23305 are ignored. If @var{size} is @code{unlimited} or if @env{GDBHISTSIZE} is
23306 either a negative number or the empty string, then the number of commands
23307 @value{GDBN} keeps in the history list is unlimited.
23309 @cindex remove duplicate history
23310 @kindex set history remove-duplicates
23311 @item set history remove-duplicates @var{count}
23312 @itemx set history remove-duplicates unlimited
23313 Control the removal of duplicate history entries in the command history list.
23314 If @var{count} is non-zero, @value{GDBN} will look back at the last @var{count}
23315 history entries and remove the first entry that is a duplicate of the current
23316 entry being added to the command history list. If @var{count} is
23317 @code{unlimited} then this lookbehind is unbounded. If @var{count} is 0, then
23318 removal of duplicate history entries is disabled.
23320 Only history entries added during the current session are considered for
23321 removal. This option is set to 0 by default.
23325 History expansion assigns special meaning to the character @kbd{!}.
23326 @ifset SYSTEM_READLINE
23327 @xref{Event Designators, , , history, GNU History Library},
23329 @ifclear SYSTEM_READLINE
23330 @xref{Event Designators},
23334 @cindex history expansion, turn on/off
23335 Since @kbd{!} is also the logical not operator in C, history expansion
23336 is off by default. If you decide to enable history expansion with the
23337 @code{set history expansion on} command, you may sometimes need to
23338 follow @kbd{!} (when it is used as logical not, in an expression) with
23339 a space or a tab to prevent it from being expanded. The readline
23340 history facilities do not attempt substitution on the strings
23341 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
23343 The commands to control history expansion are:
23346 @item set history expansion on
23347 @itemx set history expansion
23348 @kindex set history expansion
23349 Enable history expansion. History expansion is off by default.
23351 @item set history expansion off
23352 Disable history expansion.
23355 @kindex show history
23357 @itemx show history filename
23358 @itemx show history save
23359 @itemx show history size
23360 @itemx show history expansion
23361 These commands display the state of the @value{GDBN} history parameters.
23362 @code{show history} by itself displays all four states.
23367 @kindex show commands
23368 @cindex show last commands
23369 @cindex display command history
23370 @item show commands
23371 Display the last ten commands in the command history.
23373 @item show commands @var{n}
23374 Print ten commands centered on command number @var{n}.
23376 @item show commands +
23377 Print ten commands just after the commands last printed.
23381 @section Screen Size
23382 @cindex size of screen
23383 @cindex screen size
23386 @cindex pauses in output
23388 Certain commands to @value{GDBN} may produce large amounts of
23389 information output to the screen. To help you read all of it,
23390 @value{GDBN} pauses and asks you for input at the end of each page of
23391 output. Type @key{RET} when you want to continue the output, or @kbd{q}
23392 to discard the remaining output. Also, the screen width setting
23393 determines when to wrap lines of output. Depending on what is being
23394 printed, @value{GDBN} tries to break the line at a readable place,
23395 rather than simply letting it overflow onto the following line.
23397 Normally @value{GDBN} knows the size of the screen from the terminal
23398 driver software. For example, on Unix @value{GDBN} uses the termcap data base
23399 together with the value of the @code{TERM} environment variable and the
23400 @code{stty rows} and @code{stty cols} settings. If this is not correct,
23401 you can override it with the @code{set height} and @code{set
23408 @kindex show height
23409 @item set height @var{lpp}
23410 @itemx set height unlimited
23412 @itemx set width @var{cpl}
23413 @itemx set width unlimited
23415 These @code{set} commands specify a screen height of @var{lpp} lines and
23416 a screen width of @var{cpl} characters. The associated @code{show}
23417 commands display the current settings.
23419 If you specify a height of either @code{unlimited} or zero lines,
23420 @value{GDBN} does not pause during output no matter how long the
23421 output is. This is useful if output is to a file or to an editor
23424 Likewise, you can specify @samp{set width unlimited} or @samp{set
23425 width 0} to prevent @value{GDBN} from wrapping its output.
23427 @item set pagination on
23428 @itemx set pagination off
23429 @kindex set pagination
23430 Turn the output pagination on or off; the default is on. Turning
23431 pagination off is the alternative to @code{set height unlimited}. Note that
23432 running @value{GDBN} with the @option{--batch} option (@pxref{Mode
23433 Options, -batch}) also automatically disables pagination.
23435 @item show pagination
23436 @kindex show pagination
23437 Show the current pagination mode.
23442 @cindex number representation
23443 @cindex entering numbers
23445 You can always enter numbers in octal, decimal, or hexadecimal in
23446 @value{GDBN} by the usual conventions: octal numbers begin with
23447 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
23448 begin with @samp{0x}. Numbers that neither begin with @samp{0} or
23449 @samp{0x}, nor end with a @samp{.} are, by default, entered in base
23450 10; likewise, the default display for numbers---when no particular
23451 format is specified---is base 10. You can change the default base for
23452 both input and output with the commands described below.
23455 @kindex set input-radix
23456 @item set input-radix @var{base}
23457 Set the default base for numeric input. Supported choices
23458 for @var{base} are decimal 8, 10, or 16. The base must itself be
23459 specified either unambiguously or using the current input radix; for
23463 set input-radix 012
23464 set input-radix 10.
23465 set input-radix 0xa
23469 sets the input base to decimal. On the other hand, @samp{set input-radix 10}
23470 leaves the input radix unchanged, no matter what it was, since
23471 @samp{10}, being without any leading or trailing signs of its base, is
23472 interpreted in the current radix. Thus, if the current radix is 16,
23473 @samp{10} is interpreted in hex, i.e.@: as 16 decimal, which doesn't
23476 @kindex set output-radix
23477 @item set output-radix @var{base}
23478 Set the default base for numeric display. Supported choices
23479 for @var{base} are decimal 8, 10, or 16. The base must itself be
23480 specified either unambiguously or using the current input radix.
23482 @kindex show input-radix
23483 @item show input-radix
23484 Display the current default base for numeric input.
23486 @kindex show output-radix
23487 @item show output-radix
23488 Display the current default base for numeric display.
23490 @item set radix @r{[}@var{base}@r{]}
23494 These commands set and show the default base for both input and output
23495 of numbers. @code{set radix} sets the radix of input and output to
23496 the same base; without an argument, it resets the radix back to its
23497 default value of 10.
23502 @section Configuring the Current ABI
23504 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
23505 application automatically. However, sometimes you need to override its
23506 conclusions. Use these commands to manage @value{GDBN}'s view of the
23512 @cindex Newlib OS ABI and its influence on the longjmp handling
23514 One @value{GDBN} configuration can debug binaries for multiple operating
23515 system targets, either via remote debugging or native emulation.
23516 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
23517 but you can override its conclusion using the @code{set osabi} command.
23518 One example where this is useful is in debugging of binaries which use
23519 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
23520 not have the same identifying marks that the standard C library for your
23523 When @value{GDBN} is debugging the AArch64 architecture, it provides a
23524 ``Newlib'' OS ABI. This is useful for handling @code{setjmp} and
23525 @code{longjmp} when debugging binaries that use the @sc{newlib} C library.
23526 The ``Newlib'' OS ABI can be selected by @code{set osabi Newlib}.
23530 Show the OS ABI currently in use.
23533 With no argument, show the list of registered available OS ABI's.
23535 @item set osabi @var{abi}
23536 Set the current OS ABI to @var{abi}.
23539 @cindex float promotion
23541 Generally, the way that an argument of type @code{float} is passed to a
23542 function depends on whether the function is prototyped. For a prototyped
23543 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
23544 according to the architecture's convention for @code{float}. For unprototyped
23545 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
23546 @code{double} and then passed.
23548 Unfortunately, some forms of debug information do not reliably indicate whether
23549 a function is prototyped. If @value{GDBN} calls a function that is not marked
23550 as prototyped, it consults @kbd{set coerce-float-to-double}.
23553 @kindex set coerce-float-to-double
23554 @item set coerce-float-to-double
23555 @itemx set coerce-float-to-double on
23556 Arguments of type @code{float} will be promoted to @code{double} when passed
23557 to an unprototyped function. This is the default setting.
23559 @item set coerce-float-to-double off
23560 Arguments of type @code{float} will be passed directly to unprototyped
23563 @kindex show coerce-float-to-double
23564 @item show coerce-float-to-double
23565 Show the current setting of promoting @code{float} to @code{double}.
23569 @kindex show cp-abi
23570 @value{GDBN} needs to know the ABI used for your program's C@t{++}
23571 objects. The correct C@t{++} ABI depends on which C@t{++} compiler was
23572 used to build your application. @value{GDBN} only fully supports
23573 programs with a single C@t{++} ABI; if your program contains code using
23574 multiple C@t{++} ABI's or if @value{GDBN} can not identify your
23575 program's ABI correctly, you can tell @value{GDBN} which ABI to use.
23576 Currently supported ABI's include ``gnu-v2'', for @code{g++} versions
23577 before 3.0, ``gnu-v3'', for @code{g++} versions 3.0 and later, and
23578 ``hpaCC'' for the HP ANSI C@t{++} compiler. Other C@t{++} compilers may
23579 use the ``gnu-v2'' or ``gnu-v3'' ABI's as well. The default setting is
23584 Show the C@t{++} ABI currently in use.
23587 With no argument, show the list of supported C@t{++} ABI's.
23589 @item set cp-abi @var{abi}
23590 @itemx set cp-abi auto
23591 Set the current C@t{++} ABI to @var{abi}, or return to automatic detection.
23595 @section Automatically loading associated files
23596 @cindex auto-loading
23598 @value{GDBN} sometimes reads files with commands and settings automatically,
23599 without being explicitly told so by the user. We call this feature
23600 @dfn{auto-loading}. While auto-loading is useful for automatically adapting
23601 @value{GDBN} to the needs of your project, it can sometimes produce unexpected
23602 results or introduce security risks (e.g., if the file comes from untrusted
23606 * Init File in the Current Directory:: @samp{set/show/info auto-load local-gdbinit}
23607 * libthread_db.so.1 file:: @samp{set/show/info auto-load libthread-db}
23609 * Auto-loading safe path:: @samp{set/show/info auto-load safe-path}
23610 * Auto-loading verbose mode:: @samp{set/show debug auto-load}
23613 There are various kinds of files @value{GDBN} can automatically load.
23614 In addition to these files, @value{GDBN} supports auto-loading code written
23615 in various extension languages. @xref{Auto-loading extensions}.
23617 Note that loading of these associated files (including the local @file{.gdbinit}
23618 file) requires accordingly configured @code{auto-load safe-path}
23619 (@pxref{Auto-loading safe path}).
23621 For these reasons, @value{GDBN} includes commands and options to let you
23622 control when to auto-load files and which files should be auto-loaded.
23625 @anchor{set auto-load off}
23626 @kindex set auto-load off
23627 @item set auto-load off
23628 Globally disable loading of all auto-loaded files.
23629 You may want to use this command with the @samp{-iex} option
23630 (@pxref{Option -init-eval-command}) such as:
23632 $ @kbd{gdb -iex "set auto-load off" untrusted-executable corefile}
23635 Be aware that system init file (@pxref{System-wide configuration})
23636 and init files from your home directory (@pxref{Home Directory Init File})
23637 still get read (as they come from generally trusted directories).
23638 To prevent @value{GDBN} from auto-loading even those init files, use the
23639 @option{-nx} option (@pxref{Mode Options}), in addition to
23640 @code{set auto-load no}.
23642 @anchor{show auto-load}
23643 @kindex show auto-load
23644 @item show auto-load
23645 Show whether auto-loading of each specific @samp{auto-load} file(s) is enabled
23649 (gdb) show auto-load
23650 gdb-scripts: Auto-loading of canned sequences of commands scripts is on.
23651 libthread-db: Auto-loading of inferior specific libthread_db is on.
23652 local-gdbinit: Auto-loading of .gdbinit script from current directory
23654 python-scripts: Auto-loading of Python scripts is on.
23655 safe-path: List of directories from which it is safe to auto-load files
23656 is $debugdir:$datadir/auto-load.
23657 scripts-directory: List of directories from which to load auto-loaded scripts
23658 is $debugdir:$datadir/auto-load.
23661 @anchor{info auto-load}
23662 @kindex info auto-load
23663 @item info auto-load
23664 Print whether each specific @samp{auto-load} file(s) have been auto-loaded or
23668 (gdb) info auto-load
23671 Yes /home/user/gdb/gdb-gdb.gdb
23672 libthread-db: No auto-loaded libthread-db.
23673 local-gdbinit: Local .gdbinit file "/home/user/gdb/.gdbinit" has been
23677 Yes /home/user/gdb/gdb-gdb.py
23681 These are @value{GDBN} control commands for the auto-loading:
23683 @multitable @columnfractions .5 .5
23684 @item @xref{set auto-load off}.
23685 @tab Disable auto-loading globally.
23686 @item @xref{show auto-load}.
23687 @tab Show setting of all kinds of files.
23688 @item @xref{info auto-load}.
23689 @tab Show state of all kinds of files.
23690 @item @xref{set auto-load gdb-scripts}.
23691 @tab Control for @value{GDBN} command scripts.
23692 @item @xref{show auto-load gdb-scripts}.
23693 @tab Show setting of @value{GDBN} command scripts.
23694 @item @xref{info auto-load gdb-scripts}.
23695 @tab Show state of @value{GDBN} command scripts.
23696 @item @xref{set auto-load python-scripts}.
23697 @tab Control for @value{GDBN} Python scripts.
23698 @item @xref{show auto-load python-scripts}.
23699 @tab Show setting of @value{GDBN} Python scripts.
23700 @item @xref{info auto-load python-scripts}.
23701 @tab Show state of @value{GDBN} Python scripts.
23702 @item @xref{set auto-load guile-scripts}.
23703 @tab Control for @value{GDBN} Guile scripts.
23704 @item @xref{show auto-load guile-scripts}.
23705 @tab Show setting of @value{GDBN} Guile scripts.
23706 @item @xref{info auto-load guile-scripts}.
23707 @tab Show state of @value{GDBN} Guile scripts.
23708 @item @xref{set auto-load scripts-directory}.
23709 @tab Control for @value{GDBN} auto-loaded scripts location.
23710 @item @xref{show auto-load scripts-directory}.
23711 @tab Show @value{GDBN} auto-loaded scripts location.
23712 @item @xref{add-auto-load-scripts-directory}.
23713 @tab Add directory for auto-loaded scripts location list.
23714 @item @xref{set auto-load local-gdbinit}.
23715 @tab Control for init file in the current directory.
23716 @item @xref{show auto-load local-gdbinit}.
23717 @tab Show setting of init file in the current directory.
23718 @item @xref{info auto-load local-gdbinit}.
23719 @tab Show state of init file in the current directory.
23720 @item @xref{set auto-load libthread-db}.
23721 @tab Control for thread debugging library.
23722 @item @xref{show auto-load libthread-db}.
23723 @tab Show setting of thread debugging library.
23724 @item @xref{info auto-load libthread-db}.
23725 @tab Show state of thread debugging library.
23726 @item @xref{set auto-load safe-path}.
23727 @tab Control directories trusted for automatic loading.
23728 @item @xref{show auto-load safe-path}.
23729 @tab Show directories trusted for automatic loading.
23730 @item @xref{add-auto-load-safe-path}.
23731 @tab Add directory trusted for automatic loading.
23734 @node Init File in the Current Directory
23735 @subsection Automatically loading init file in the current directory
23736 @cindex auto-loading init file in the current directory
23738 By default, @value{GDBN} reads and executes the canned sequences of commands
23739 from init file (if any) in the current working directory,
23740 see @ref{Init File in the Current Directory during Startup}.
23742 Note that loading of this local @file{.gdbinit} file also requires accordingly
23743 configured @code{auto-load safe-path} (@pxref{Auto-loading safe path}).
23746 @anchor{set auto-load local-gdbinit}
23747 @kindex set auto-load local-gdbinit
23748 @item set auto-load local-gdbinit [on|off]
23749 Enable or disable the auto-loading of canned sequences of commands
23750 (@pxref{Sequences}) found in init file in the current directory.
23752 @anchor{show auto-load local-gdbinit}
23753 @kindex show auto-load local-gdbinit
23754 @item show auto-load local-gdbinit
23755 Show whether auto-loading of canned sequences of commands from init file in the
23756 current directory is enabled or disabled.
23758 @anchor{info auto-load local-gdbinit}
23759 @kindex info auto-load local-gdbinit
23760 @item info auto-load local-gdbinit
23761 Print whether canned sequences of commands from init file in the
23762 current directory have been auto-loaded.
23765 @node libthread_db.so.1 file
23766 @subsection Automatically loading thread debugging library
23767 @cindex auto-loading libthread_db.so.1
23769 This feature is currently present only on @sc{gnu}/Linux native hosts.
23771 @value{GDBN} reads in some cases thread debugging library from places specific
23772 to the inferior (@pxref{set libthread-db-search-path}).
23774 The special @samp{libthread-db-search-path} entry @samp{$sdir} is processed
23775 without checking this @samp{set auto-load libthread-db} switch as system
23776 libraries have to be trusted in general. In all other cases of
23777 @samp{libthread-db-search-path} entries @value{GDBN} checks first if @samp{set
23778 auto-load libthread-db} is enabled before trying to open such thread debugging
23781 Note that loading of this debugging library also requires accordingly configured
23782 @code{auto-load safe-path} (@pxref{Auto-loading safe path}).
23785 @anchor{set auto-load libthread-db}
23786 @kindex set auto-load libthread-db
23787 @item set auto-load libthread-db [on|off]
23788 Enable or disable the auto-loading of inferior specific thread debugging library.
23790 @anchor{show auto-load libthread-db}
23791 @kindex show auto-load libthread-db
23792 @item show auto-load libthread-db
23793 Show whether auto-loading of inferior specific thread debugging library is
23794 enabled or disabled.
23796 @anchor{info auto-load libthread-db}
23797 @kindex info auto-load libthread-db
23798 @item info auto-load libthread-db
23799 Print the list of all loaded inferior specific thread debugging libraries and
23800 for each such library print list of inferior @var{pid}s using it.
23803 @node Auto-loading safe path
23804 @subsection Security restriction for auto-loading
23805 @cindex auto-loading safe-path
23807 As the files of inferior can come from untrusted source (such as submitted by
23808 an application user) @value{GDBN} does not always load any files automatically.
23809 @value{GDBN} provides the @samp{set auto-load safe-path} setting to list
23810 directories trusted for loading files not explicitly requested by user.
23811 Each directory can also be a shell wildcard pattern.
23813 If the path is not set properly you will see a warning and the file will not
23818 Reading symbols from /home/user/gdb/gdb...done.
23819 warning: File "/home/user/gdb/gdb-gdb.gdb" auto-loading has been
23820 declined by your `auto-load safe-path' set
23821 to "$debugdir:$datadir/auto-load".
23822 warning: File "/home/user/gdb/gdb-gdb.py" auto-loading has been
23823 declined by your `auto-load safe-path' set
23824 to "$debugdir:$datadir/auto-load".
23828 To instruct @value{GDBN} to go ahead and use the init files anyway,
23829 invoke @value{GDBN} like this:
23832 $ gdb -q -iex "set auto-load safe-path /home/user/gdb" ./gdb
23835 The list of trusted directories is controlled by the following commands:
23838 @anchor{set auto-load safe-path}
23839 @kindex set auto-load safe-path
23840 @item set auto-load safe-path @r{[}@var{directories}@r{]}
23841 Set the list of directories (and their subdirectories) trusted for automatic
23842 loading and execution of scripts. You can also enter a specific trusted file.
23843 Each directory can also be a shell wildcard pattern; wildcards do not match
23844 directory separator - see @code{FNM_PATHNAME} for system function @code{fnmatch}
23845 (@pxref{Wildcard Matching, fnmatch, , libc, GNU C Library Reference Manual}).
23846 If you omit @var{directories}, @samp{auto-load safe-path} will be reset to
23847 its default value as specified during @value{GDBN} compilation.
23849 The list of directories uses path separator (@samp{:} on GNU and Unix
23850 systems, @samp{;} on MS-Windows and MS-DOS) to separate directories, similarly
23851 to the @env{PATH} environment variable.
23853 @anchor{show auto-load safe-path}
23854 @kindex show auto-load safe-path
23855 @item show auto-load safe-path
23856 Show the list of directories trusted for automatic loading and execution of
23859 @anchor{add-auto-load-safe-path}
23860 @kindex add-auto-load-safe-path
23861 @item add-auto-load-safe-path
23862 Add an entry (or list of entries) to the list of directories trusted for
23863 automatic loading and execution of scripts. Multiple entries may be delimited
23864 by the host platform path separator in use.
23867 This variable defaults to what @code{--with-auto-load-dir} has been configured
23868 to (@pxref{with-auto-load-dir}). @file{$debugdir} and @file{$datadir}
23869 substitution applies the same as for @ref{set auto-load scripts-directory}.
23870 The default @code{set auto-load safe-path} value can be also overriden by
23871 @value{GDBN} configuration option @option{--with-auto-load-safe-path}.
23873 Setting this variable to @file{/} disables this security protection,
23874 corresponding @value{GDBN} configuration option is
23875 @option{--without-auto-load-safe-path}.
23876 This variable is supposed to be set to the system directories writable by the
23877 system superuser only. Users can add their source directories in init files in
23878 their home directories (@pxref{Home Directory Init File}). See also deprecated
23879 init file in the current directory
23880 (@pxref{Init File in the Current Directory during Startup}).
23882 To force @value{GDBN} to load the files it declined to load in the previous
23883 example, you could use one of the following ways:
23886 @item @file{~/.gdbinit}: @samp{add-auto-load-safe-path ~/src/gdb}
23887 Specify this trusted directory (or a file) as additional component of the list.
23888 You have to specify also any existing directories displayed by
23889 by @samp{show auto-load safe-path} (such as @samp{/usr:/bin} in this example).
23891 @item @kbd{gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" @dots{}}
23892 Specify this directory as in the previous case but just for a single
23893 @value{GDBN} session.
23895 @item @kbd{gdb -iex "set auto-load safe-path /" @dots{}}
23896 Disable auto-loading safety for a single @value{GDBN} session.
23897 This assumes all the files you debug during this @value{GDBN} session will come
23898 from trusted sources.
23900 @item @kbd{./configure --without-auto-load-safe-path}
23901 During compilation of @value{GDBN} you may disable any auto-loading safety.
23902 This assumes all the files you will ever debug with this @value{GDBN} come from
23906 On the other hand you can also explicitly forbid automatic files loading which
23907 also suppresses any such warning messages:
23910 @item @kbd{gdb -iex "set auto-load no" @dots{}}
23911 You can use @value{GDBN} command-line option for a single @value{GDBN} session.
23913 @item @file{~/.gdbinit}: @samp{set auto-load no}
23914 Disable auto-loading globally for the user
23915 (@pxref{Home Directory Init File}). While it is improbable, you could also
23916 use system init file instead (@pxref{System-wide configuration}).
23919 This setting applies to the file names as entered by user. If no entry matches
23920 @value{GDBN} tries as a last resort to also resolve all the file names into
23921 their canonical form (typically resolving symbolic links) and compare the
23922 entries again. @value{GDBN} already canonicalizes most of the filenames on its
23923 own before starting the comparison so a canonical form of directories is
23924 recommended to be entered.
23926 @node Auto-loading verbose mode
23927 @subsection Displaying files tried for auto-load
23928 @cindex auto-loading verbose mode
23930 For better visibility of all the file locations where you can place scripts to
23931 be auto-loaded with inferior --- or to protect yourself against accidental
23932 execution of untrusted scripts --- @value{GDBN} provides a feature for printing
23933 all the files attempted to be loaded. Both existing and non-existing files may
23936 For example the list of directories from which it is safe to auto-load files
23937 (@pxref{Auto-loading safe path}) applies also to canonicalized filenames which
23938 may not be too obvious while setting it up.
23941 (gdb) set debug auto-load on
23942 (gdb) file ~/src/t/true
23943 auto-load: Loading canned sequences of commands script "/tmp/true-gdb.gdb"
23944 for objfile "/tmp/true".
23945 auto-load: Updating directories of "/usr:/opt".
23946 auto-load: Using directory "/usr".
23947 auto-load: Using directory "/opt".
23948 warning: File "/tmp/true-gdb.gdb" auto-loading has been declined
23949 by your `auto-load safe-path' set to "/usr:/opt".
23953 @anchor{set debug auto-load}
23954 @kindex set debug auto-load
23955 @item set debug auto-load [on|off]
23956 Set whether to print the filenames attempted to be auto-loaded.
23958 @anchor{show debug auto-load}
23959 @kindex show debug auto-load
23960 @item show debug auto-load
23961 Show whether printing of the filenames attempted to be auto-loaded is turned
23965 @node Messages/Warnings
23966 @section Optional Warnings and Messages
23968 @cindex verbose operation
23969 @cindex optional warnings
23970 By default, @value{GDBN} is silent about its inner workings. If you are
23971 running on a slow machine, you may want to use the @code{set verbose}
23972 command. This makes @value{GDBN} tell you when it does a lengthy
23973 internal operation, so you will not think it has crashed.
23975 Currently, the messages controlled by @code{set verbose} are those
23976 which announce that the symbol table for a source file is being read;
23977 see @code{symbol-file} in @ref{Files, ,Commands to Specify Files}.
23980 @kindex set verbose
23981 @item set verbose on
23982 Enables @value{GDBN} output of certain informational messages.
23984 @item set verbose off
23985 Disables @value{GDBN} output of certain informational messages.
23987 @kindex show verbose
23989 Displays whether @code{set verbose} is on or off.
23992 By default, if @value{GDBN} encounters bugs in the symbol table of an
23993 object file, it is silent; but if you are debugging a compiler, you may
23994 find this information useful (@pxref{Symbol Errors, ,Errors Reading
23999 @kindex set complaints
24000 @item set complaints @var{limit}
24001 Permits @value{GDBN} to output @var{limit} complaints about each type of
24002 unusual symbols before becoming silent about the problem. Set
24003 @var{limit} to zero to suppress all complaints; set it to a large number
24004 to prevent complaints from being suppressed.
24006 @kindex show complaints
24007 @item show complaints
24008 Displays how many symbol complaints @value{GDBN} is permitted to produce.
24012 @anchor{confirmation requests}
24013 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
24014 lot of stupid questions to confirm certain commands. For example, if
24015 you try to run a program which is already running:
24019 The program being debugged has been started already.
24020 Start it from the beginning? (y or n)
24023 If you are willing to unflinchingly face the consequences of your own
24024 commands, you can disable this ``feature'':
24028 @kindex set confirm
24030 @cindex confirmation
24031 @cindex stupid questions
24032 @item set confirm off
24033 Disables confirmation requests. Note that running @value{GDBN} with
24034 the @option{--batch} option (@pxref{Mode Options, -batch}) also
24035 automatically disables confirmation requests.
24037 @item set confirm on
24038 Enables confirmation requests (the default).
24040 @kindex show confirm
24042 Displays state of confirmation requests.
24046 @cindex command tracing
24047 If you need to debug user-defined commands or sourced files you may find it
24048 useful to enable @dfn{command tracing}. In this mode each command will be
24049 printed as it is executed, prefixed with one or more @samp{+} symbols, the
24050 quantity denoting the call depth of each command.
24053 @kindex set trace-commands
24054 @cindex command scripts, debugging
24055 @item set trace-commands on
24056 Enable command tracing.
24057 @item set trace-commands off
24058 Disable command tracing.
24059 @item show trace-commands
24060 Display the current state of command tracing.
24063 @node Debugging Output
24064 @section Optional Messages about Internal Happenings
24065 @cindex optional debugging messages
24067 @value{GDBN} has commands that enable optional debugging messages from
24068 various @value{GDBN} subsystems; normally these commands are of
24069 interest to @value{GDBN} maintainers, or when reporting a bug. This
24070 section documents those commands.
24073 @kindex set exec-done-display
24074 @item set exec-done-display
24075 Turns on or off the notification of asynchronous commands'
24076 completion. When on, @value{GDBN} will print a message when an
24077 asynchronous command finishes its execution. The default is off.
24078 @kindex show exec-done-display
24079 @item show exec-done-display
24080 Displays the current setting of asynchronous command completion
24083 @cindex ARM AArch64
24084 @item set debug aarch64
24085 Turns on or off display of debugging messages related to ARM AArch64.
24086 The default is off.
24088 @item show debug aarch64
24089 Displays the current state of displaying debugging messages related to
24091 @cindex gdbarch debugging info
24092 @cindex architecture debugging info
24093 @item set debug arch
24094 Turns on or off display of gdbarch debugging info. The default is off
24095 @item show debug arch
24096 Displays the current state of displaying gdbarch debugging info.
24097 @item set debug aix-solib
24098 @cindex AIX shared library debugging
24099 Control display of debugging messages from the AIX shared library
24100 support module. The default is off.
24101 @item show debug aix-thread
24102 Show the current state of displaying AIX shared library debugging messages.
24103 @item set debug aix-thread
24104 @cindex AIX threads
24105 Display debugging messages about inner workings of the AIX thread
24107 @item show debug aix-thread
24108 Show the current state of AIX thread debugging info display.
24109 @item set debug check-physname
24111 Check the results of the ``physname'' computation. When reading DWARF
24112 debugging information for C@t{++}, @value{GDBN} attempts to compute
24113 each entity's name. @value{GDBN} can do this computation in two
24114 different ways, depending on exactly what information is present.
24115 When enabled, this setting causes @value{GDBN} to compute the names
24116 both ways and display any discrepancies.
24117 @item show debug check-physname
24118 Show the current state of ``physname'' checking.
24119 @item set debug coff-pe-read
24120 @cindex COFF/PE exported symbols
24121 Control display of debugging messages related to reading of COFF/PE
24122 exported symbols. The default is off.
24123 @item show debug coff-pe-read
24124 Displays the current state of displaying debugging messages related to
24125 reading of COFF/PE exported symbols.
24126 @item set debug dwarf-die
24128 Dump DWARF DIEs after they are read in.
24129 The value is the number of nesting levels to print.
24130 A value of zero turns off the display.
24131 @item show debug dwarf-die
24132 Show the current state of DWARF DIE debugging.
24133 @item set debug dwarf-line
24134 @cindex DWARF Line Tables
24135 Turns on or off display of debugging messages related to reading
24136 DWARF line tables. The default is 0 (off).
24137 A value of 1 provides basic information.
24138 A value greater than 1 provides more verbose information.
24139 @item show debug dwarf-line
24140 Show the current state of DWARF line table debugging.
24141 @item set debug dwarf-read
24142 @cindex DWARF Reading
24143 Turns on or off display of debugging messages related to reading
24144 DWARF debug info. The default is 0 (off).
24145 A value of 1 provides basic information.
24146 A value greater than 1 provides more verbose information.
24147 @item show debug dwarf-read
24148 Show the current state of DWARF reader debugging.
24149 @item set debug displaced
24150 @cindex displaced stepping debugging info
24151 Turns on or off display of @value{GDBN} debugging info for the
24152 displaced stepping support. The default is off.
24153 @item show debug displaced
24154 Displays the current state of displaying @value{GDBN} debugging info
24155 related to displaced stepping.
24156 @item set debug event
24157 @cindex event debugging info
24158 Turns on or off display of @value{GDBN} event debugging info. The
24160 @item show debug event
24161 Displays the current state of displaying @value{GDBN} event debugging
24163 @item set debug expression
24164 @cindex expression debugging info
24165 Turns on or off display of debugging info about @value{GDBN}
24166 expression parsing. The default is off.
24167 @item show debug expression
24168 Displays the current state of displaying debugging info about
24169 @value{GDBN} expression parsing.
24170 @item set debug fbsd-lwp
24171 @cindex FreeBSD LWP debug messages
24172 Turns on or off debugging messages from the FreeBSD LWP debug support.
24173 @item show debug fbsd-lwp
24174 Show the current state of FreeBSD LWP debugging messages.
24175 @item set debug frame
24176 @cindex frame debugging info
24177 Turns on or off display of @value{GDBN} frame debugging info. The
24179 @item show debug frame
24180 Displays the current state of displaying @value{GDBN} frame debugging
24182 @item set debug gnu-nat
24183 @cindex @sc{gnu}/Hurd debug messages
24184 Turn on or off debugging messages from the @sc{gnu}/Hurd debug support.
24185 @item show debug gnu-nat
24186 Show the current state of @sc{gnu}/Hurd debugging messages.
24187 @item set debug infrun
24188 @cindex inferior debugging info
24189 Turns on or off display of @value{GDBN} debugging info for running the inferior.
24190 The default is off. @file{infrun.c} contains GDB's runtime state machine used
24191 for implementing operations such as single-stepping the inferior.
24192 @item show debug infrun
24193 Displays the current state of @value{GDBN} inferior debugging.
24194 @item set debug jit
24195 @cindex just-in-time compilation, debugging messages
24196 Turn on or off debugging messages from JIT debug support.
24197 @item show debug jit
24198 Displays the current state of @value{GDBN} JIT debugging.
24199 @item set debug lin-lwp
24200 @cindex @sc{gnu}/Linux LWP debug messages
24201 @cindex Linux lightweight processes
24202 Turn on or off debugging messages from the Linux LWP debug support.
24203 @item show debug lin-lwp
24204 Show the current state of Linux LWP debugging messages.
24205 @item set debug linux-namespaces
24206 @cindex @sc{gnu}/Linux namespaces debug messages
24207 Turn on or off debugging messages from the Linux namespaces debug support.
24208 @item show debug linux-namespaces
24209 Show the current state of Linux namespaces debugging messages.
24210 @item set debug mach-o
24211 @cindex Mach-O symbols processing
24212 Control display of debugging messages related to Mach-O symbols
24213 processing. The default is off.
24214 @item show debug mach-o
24215 Displays the current state of displaying debugging messages related to
24216 reading of COFF/PE exported symbols.
24217 @item set debug notification
24218 @cindex remote async notification debugging info
24219 Turn on or off debugging messages about remote async notification.
24220 The default is off.
24221 @item show debug notification
24222 Displays the current state of remote async notification debugging messages.
24223 @item set debug observer
24224 @cindex observer debugging info
24225 Turns on or off display of @value{GDBN} observer debugging. This
24226 includes info such as the notification of observable events.
24227 @item show debug observer
24228 Displays the current state of observer debugging.
24229 @item set debug overload
24230 @cindex C@t{++} overload debugging info
24231 Turns on or off display of @value{GDBN} C@t{++} overload debugging
24232 info. This includes info such as ranking of functions, etc. The default
24234 @item show debug overload
24235 Displays the current state of displaying @value{GDBN} C@t{++} overload
24237 @cindex expression parser, debugging info
24238 @cindex debug expression parser
24239 @item set debug parser
24240 Turns on or off the display of expression parser debugging output.
24241 Internally, this sets the @code{yydebug} variable in the expression
24242 parser. @xref{Tracing, , Tracing Your Parser, bison, Bison}, for
24243 details. The default is off.
24244 @item show debug parser
24245 Show the current state of expression parser debugging.
24246 @cindex packets, reporting on stdout
24247 @cindex serial connections, debugging
24248 @cindex debug remote protocol
24249 @cindex remote protocol debugging
24250 @cindex display remote packets
24251 @item set debug remote
24252 Turns on or off display of reports on all packets sent back and forth across
24253 the serial line to the remote machine. The info is printed on the
24254 @value{GDBN} standard output stream. The default is off.
24255 @item show debug remote
24256 Displays the state of display of remote packets.
24258 @item set debug separate-debug-file
24259 Turns on or off display of debug output about separate debug file search.
24260 @item show debug separate-debug-file
24261 Displays the state of separate debug file search debug output.
24263 @item set debug serial
24264 Turns on or off display of @value{GDBN} serial debugging info. The
24266 @item show debug serial
24267 Displays the current state of displaying @value{GDBN} serial debugging
24269 @item set debug solib-frv
24270 @cindex FR-V shared-library debugging
24271 Turn on or off debugging messages for FR-V shared-library code.
24272 @item show debug solib-frv
24273 Display the current state of FR-V shared-library code debugging
24275 @item set debug symbol-lookup
24276 @cindex symbol lookup
24277 Turns on or off display of debugging messages related to symbol lookup.
24278 The default is 0 (off).
24279 A value of 1 provides basic information.
24280 A value greater than 1 provides more verbose information.
24281 @item show debug symbol-lookup
24282 Show the current state of symbol lookup debugging messages.
24283 @item set debug symfile
24284 @cindex symbol file functions
24285 Turns on or off display of debugging messages related to symbol file functions.
24286 The default is off. @xref{Files}.
24287 @item show debug symfile
24288 Show the current state of symbol file debugging messages.
24289 @item set debug symtab-create
24290 @cindex symbol table creation
24291 Turns on or off display of debugging messages related to symbol table creation.
24292 The default is 0 (off).
24293 A value of 1 provides basic information.
24294 A value greater than 1 provides more verbose information.
24295 @item show debug symtab-create
24296 Show the current state of symbol table creation debugging.
24297 @item set debug target
24298 @cindex target debugging info
24299 Turns on or off display of @value{GDBN} target debugging info. This info
24300 includes what is going on at the target level of GDB, as it happens. The
24301 default is 0. Set it to 1 to track events, and to 2 to also track the
24302 value of large memory transfers.
24303 @item show debug target
24304 Displays the current state of displaying @value{GDBN} target debugging
24306 @item set debug timestamp
24307 @cindex timestampping debugging info
24308 Turns on or off display of timestamps with @value{GDBN} debugging info.
24309 When enabled, seconds and microseconds are displayed before each debugging
24311 @item show debug timestamp
24312 Displays the current state of displaying timestamps with @value{GDBN}
24314 @item set debug varobj
24315 @cindex variable object debugging info
24316 Turns on or off display of @value{GDBN} variable object debugging
24317 info. The default is off.
24318 @item show debug varobj
24319 Displays the current state of displaying @value{GDBN} variable object
24321 @item set debug xml
24322 @cindex XML parser debugging
24323 Turn on or off debugging messages for built-in XML parsers.
24324 @item show debug xml
24325 Displays the current state of XML debugging messages.
24328 @node Other Misc Settings
24329 @section Other Miscellaneous Settings
24330 @cindex miscellaneous settings
24333 @kindex set interactive-mode
24334 @item set interactive-mode
24335 If @code{on}, forces @value{GDBN} to assume that GDB was started
24336 in a terminal. In practice, this means that @value{GDBN} should wait
24337 for the user to answer queries generated by commands entered at
24338 the command prompt. If @code{off}, forces @value{GDBN} to operate
24339 in the opposite mode, and it uses the default answers to all queries.
24340 If @code{auto} (the default), @value{GDBN} tries to determine whether
24341 its standard input is a terminal, and works in interactive-mode if it
24342 is, non-interactively otherwise.
24344 In the vast majority of cases, the debugger should be able to guess
24345 correctly which mode should be used. But this setting can be useful
24346 in certain specific cases, such as running a MinGW @value{GDBN}
24347 inside a cygwin window.
24349 @kindex show interactive-mode
24350 @item show interactive-mode
24351 Displays whether the debugger is operating in interactive mode or not.
24354 @node Extending GDB
24355 @chapter Extending @value{GDBN}
24356 @cindex extending GDB
24358 @value{GDBN} provides several mechanisms for extension.
24359 @value{GDBN} also provides the ability to automatically load
24360 extensions when it reads a file for debugging. This allows the
24361 user to automatically customize @value{GDBN} for the program
24365 * Sequences:: Canned Sequences of @value{GDBN} Commands
24366 * Python:: Extending @value{GDBN} using Python
24367 * Guile:: Extending @value{GDBN} using Guile
24368 * Auto-loading extensions:: Automatically loading extensions
24369 * Multiple Extension Languages:: Working with multiple extension languages
24370 * Aliases:: Creating new spellings of existing commands
24373 To facilitate the use of extension languages, @value{GDBN} is capable
24374 of evaluating the contents of a file. When doing so, @value{GDBN}
24375 can recognize which extension language is being used by looking at
24376 the filename extension. Files with an unrecognized filename extension
24377 are always treated as a @value{GDBN} Command Files.
24378 @xref{Command Files,, Command files}.
24380 You can control how @value{GDBN} evaluates these files with the following
24384 @kindex set script-extension
24385 @kindex show script-extension
24386 @item set script-extension off
24387 All scripts are always evaluated as @value{GDBN} Command Files.
24389 @item set script-extension soft
24390 The debugger determines the scripting language based on filename
24391 extension. If this scripting language is supported, @value{GDBN}
24392 evaluates the script using that language. Otherwise, it evaluates
24393 the file as a @value{GDBN} Command File.
24395 @item set script-extension strict
24396 The debugger determines the scripting language based on filename
24397 extension, and evaluates the script using that language. If the
24398 language is not supported, then the evaluation fails.
24400 @item show script-extension
24401 Display the current value of the @code{script-extension} option.
24406 @section Canned Sequences of Commands
24408 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
24409 Command Lists}), @value{GDBN} provides two ways to store sequences of
24410 commands for execution as a unit: user-defined commands and command
24414 * Define:: How to define your own commands
24415 * Hooks:: Hooks for user-defined commands
24416 * Command Files:: How to write scripts of commands to be stored in a file
24417 * Output:: Commands for controlled output
24418 * Auto-loading sequences:: Controlling auto-loaded command files
24422 @subsection User-defined Commands
24424 @cindex user-defined command
24425 @cindex arguments, to user-defined commands
24426 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
24427 which you assign a new name as a command. This is done with the
24428 @code{define} command. User commands may accept an unlimited number of arguments
24429 separated by whitespace. Arguments are accessed within the user command
24430 via @code{$arg0@dots{}$argN}. A trivial example:
24434 print $arg0 + $arg1 + $arg2
24439 To execute the command use:
24446 This defines the command @code{adder}, which prints the sum of
24447 its three arguments. Note the arguments are text substitutions, so they may
24448 reference variables, use complex expressions, or even perform inferior
24451 @cindex argument count in user-defined commands
24452 @cindex how many arguments (user-defined commands)
24453 In addition, @code{$argc} may be used to find out how many arguments have
24459 print $arg0 + $arg1
24462 print $arg0 + $arg1 + $arg2
24467 Combining with the @code{eval} command (@pxref{eval}) makes it easier
24468 to process a variable number of arguments:
24475 eval "set $sum = $sum + $arg%d", $i
24485 @item define @var{commandname}
24486 Define a command named @var{commandname}. If there is already a command
24487 by that name, you are asked to confirm that you want to redefine it.
24488 The argument @var{commandname} may be a bare command name consisting of letters,
24489 numbers, dashes, and underscores. It may also start with any predefined
24490 prefix command. For example, @samp{define target my-target} creates
24491 a user-defined @samp{target my-target} command.
24493 The definition of the command is made up of other @value{GDBN} command lines,
24494 which are given following the @code{define} command. The end of these
24495 commands is marked by a line containing @code{end}.
24498 @kindex end@r{ (user-defined commands)}
24499 @item document @var{commandname}
24500 Document the user-defined command @var{commandname}, so that it can be
24501 accessed by @code{help}. The command @var{commandname} must already be
24502 defined. This command reads lines of documentation just as @code{define}
24503 reads the lines of the command definition, ending with @code{end}.
24504 After the @code{document} command is finished, @code{help} on command
24505 @var{commandname} displays the documentation you have written.
24507 You may use the @code{document} command again to change the
24508 documentation of a command. Redefining the command with @code{define}
24509 does not change the documentation.
24511 @kindex dont-repeat
24512 @cindex don't repeat command
24514 Used inside a user-defined command, this tells @value{GDBN} that this
24515 command should not be repeated when the user hits @key{RET}
24516 (@pxref{Command Syntax, repeat last command}).
24518 @kindex help user-defined
24519 @item help user-defined
24520 List all user-defined commands and all python commands defined in class
24521 COMAND_USER. The first line of the documentation or docstring is
24526 @itemx show user @var{commandname}
24527 Display the @value{GDBN} commands used to define @var{commandname} (but
24528 not its documentation). If no @var{commandname} is given, display the
24529 definitions for all user-defined commands.
24530 This does not work for user-defined python commands.
24532 @cindex infinite recursion in user-defined commands
24533 @kindex show max-user-call-depth
24534 @kindex set max-user-call-depth
24535 @item show max-user-call-depth
24536 @itemx set max-user-call-depth
24537 The value of @code{max-user-call-depth} controls how many recursion
24538 levels are allowed in user-defined commands before @value{GDBN} suspects an
24539 infinite recursion and aborts the command.
24540 This does not apply to user-defined python commands.
24543 In addition to the above commands, user-defined commands frequently
24544 use control flow commands, described in @ref{Command Files}.
24546 When user-defined commands are executed, the
24547 commands of the definition are not printed. An error in any command
24548 stops execution of the user-defined command.
24550 If used interactively, commands that would ask for confirmation proceed
24551 without asking when used inside a user-defined command. Many @value{GDBN}
24552 commands that normally print messages to say what they are doing omit the
24553 messages when used in a user-defined command.
24556 @subsection User-defined Command Hooks
24557 @cindex command hooks
24558 @cindex hooks, for commands
24559 @cindex hooks, pre-command
24562 You may define @dfn{hooks}, which are a special kind of user-defined
24563 command. Whenever you run the command @samp{foo}, if the user-defined
24564 command @samp{hook-foo} exists, it is executed (with no arguments)
24565 before that command.
24567 @cindex hooks, post-command
24569 A hook may also be defined which is run after the command you executed.
24570 Whenever you run the command @samp{foo}, if the user-defined command
24571 @samp{hookpost-foo} exists, it is executed (with no arguments) after
24572 that command. Post-execution hooks may exist simultaneously with
24573 pre-execution hooks, for the same command.
24575 It is valid for a hook to call the command which it hooks. If this
24576 occurs, the hook is not re-executed, thereby avoiding infinite recursion.
24578 @c It would be nice if hookpost could be passed a parameter indicating
24579 @c if the command it hooks executed properly or not. FIXME!
24581 @kindex stop@r{, a pseudo-command}
24582 In addition, a pseudo-command, @samp{stop} exists. Defining
24583 (@samp{hook-stop}) makes the associated commands execute every time
24584 execution stops in your program: before breakpoint commands are run,
24585 displays are printed, or the stack frame is printed.
24587 For example, to ignore @code{SIGALRM} signals while
24588 single-stepping, but treat them normally during normal execution,
24593 handle SIGALRM nopass
24597 handle SIGALRM pass
24600 define hook-continue
24601 handle SIGALRM pass
24605 As a further example, to hook at the beginning and end of the @code{echo}
24606 command, and to add extra text to the beginning and end of the message,
24614 define hookpost-echo
24618 (@value{GDBP}) echo Hello World
24619 <<<---Hello World--->>>
24624 You can define a hook for any single-word command in @value{GDBN}, but
24625 not for command aliases; you should define a hook for the basic command
24626 name, e.g.@: @code{backtrace} rather than @code{bt}.
24627 @c FIXME! So how does Joe User discover whether a command is an alias
24629 You can hook a multi-word command by adding @code{hook-} or
24630 @code{hookpost-} to the last word of the command, e.g.@:
24631 @samp{define target hook-remote} to add a hook to @samp{target remote}.
24633 If an error occurs during the execution of your hook, execution of
24634 @value{GDBN} commands stops and @value{GDBN} issues a prompt
24635 (before the command that you actually typed had a chance to run).
24637 If you try to define a hook which does not match any known command, you
24638 get a warning from the @code{define} command.
24640 @node Command Files
24641 @subsection Command Files
24643 @cindex command files
24644 @cindex scripting commands
24645 A command file for @value{GDBN} is a text file made of lines that are
24646 @value{GDBN} commands. Comments (lines starting with @kbd{#}) may
24647 also be included. An empty line in a command file does nothing; it
24648 does not mean to repeat the last command, as it would from the
24651 You can request the execution of a command file with the @code{source}
24652 command. Note that the @code{source} command is also used to evaluate
24653 scripts that are not Command Files. The exact behavior can be configured
24654 using the @code{script-extension} setting.
24655 @xref{Extending GDB,, Extending GDB}.
24659 @cindex execute commands from a file
24660 @item source [-s] [-v] @var{filename}
24661 Execute the command file @var{filename}.
24664 The lines in a command file are generally executed sequentially,
24665 unless the order of execution is changed by one of the
24666 @emph{flow-control commands} described below. The commands are not
24667 printed as they are executed. An error in any command terminates
24668 execution of the command file and control is returned to the console.
24670 @value{GDBN} first searches for @var{filename} in the current directory.
24671 If the file is not found there, and @var{filename} does not specify a
24672 directory, then @value{GDBN} also looks for the file on the source search path
24673 (specified with the @samp{directory} command);
24674 except that @file{$cdir} is not searched because the compilation directory
24675 is not relevant to scripts.
24677 If @code{-s} is specified, then @value{GDBN} searches for @var{filename}
24678 on the search path even if @var{filename} specifies a directory.
24679 The search is done by appending @var{filename} to each element of the
24680 search path. So, for example, if @var{filename} is @file{mylib/myscript}
24681 and the search path contains @file{/home/user} then @value{GDBN} will
24682 look for the script @file{/home/user/mylib/myscript}.
24683 The search is also done if @var{filename} is an absolute path.
24684 For example, if @var{filename} is @file{/tmp/myscript} and
24685 the search path contains @file{/home/user} then @value{GDBN} will
24686 look for the script @file{/home/user/tmp/myscript}.
24687 For DOS-like systems, if @var{filename} contains a drive specification,
24688 it is stripped before concatenation. For example, if @var{filename} is
24689 @file{d:myscript} and the search path contains @file{c:/tmp} then @value{GDBN}
24690 will look for the script @file{c:/tmp/myscript}.
24692 If @code{-v}, for verbose mode, is given then @value{GDBN} displays
24693 each command as it is executed. The option must be given before
24694 @var{filename}, and is interpreted as part of the filename anywhere else.
24696 Commands that would ask for confirmation if used interactively proceed
24697 without asking when used in a command file. Many @value{GDBN} commands that
24698 normally print messages to say what they are doing omit the messages
24699 when called from command files.
24701 @value{GDBN} also accepts command input from standard input. In this
24702 mode, normal output goes to standard output and error output goes to
24703 standard error. Errors in a command file supplied on standard input do
24704 not terminate execution of the command file---execution continues with
24708 gdb < cmds > log 2>&1
24711 (The syntax above will vary depending on the shell used.) This example
24712 will execute commands from the file @file{cmds}. All output and errors
24713 would be directed to @file{log}.
24715 Since commands stored on command files tend to be more general than
24716 commands typed interactively, they frequently need to deal with
24717 complicated situations, such as different or unexpected values of
24718 variables and symbols, changes in how the program being debugged is
24719 built, etc. @value{GDBN} provides a set of flow-control commands to
24720 deal with these complexities. Using these commands, you can write
24721 complex scripts that loop over data structures, execute commands
24722 conditionally, etc.
24729 This command allows to include in your script conditionally executed
24730 commands. The @code{if} command takes a single argument, which is an
24731 expression to evaluate. It is followed by a series of commands that
24732 are executed only if the expression is true (its value is nonzero).
24733 There can then optionally be an @code{else} line, followed by a series
24734 of commands that are only executed if the expression was false. The
24735 end of the list is marked by a line containing @code{end}.
24739 This command allows to write loops. Its syntax is similar to
24740 @code{if}: the command takes a single argument, which is an expression
24741 to evaluate, and must be followed by the commands to execute, one per
24742 line, terminated by an @code{end}. These commands are called the
24743 @dfn{body} of the loop. The commands in the body of @code{while} are
24744 executed repeatedly as long as the expression evaluates to true.
24748 This command exits the @code{while} loop in whose body it is included.
24749 Execution of the script continues after that @code{while}s @code{end}
24752 @kindex loop_continue
24753 @item loop_continue
24754 This command skips the execution of the rest of the body of commands
24755 in the @code{while} loop in whose body it is included. Execution
24756 branches to the beginning of the @code{while} loop, where it evaluates
24757 the controlling expression.
24759 @kindex end@r{ (if/else/while commands)}
24761 Terminate the block of commands that are the body of @code{if},
24762 @code{else}, or @code{while} flow-control commands.
24767 @subsection Commands for Controlled Output
24769 During the execution of a command file or a user-defined command, normal
24770 @value{GDBN} output is suppressed; the only output that appears is what is
24771 explicitly printed by the commands in the definition. This section
24772 describes three commands useful for generating exactly the output you
24777 @item echo @var{text}
24778 @c I do not consider backslash-space a standard C escape sequence
24779 @c because it is not in ANSI.
24780 Print @var{text}. Nonprinting characters can be included in
24781 @var{text} using C escape sequences, such as @samp{\n} to print a
24782 newline. @strong{No newline is printed unless you specify one.}
24783 In addition to the standard C escape sequences, a backslash followed
24784 by a space stands for a space. This is useful for displaying a
24785 string with spaces at the beginning or the end, since leading and
24786 trailing spaces are otherwise trimmed from all arguments.
24787 To print @samp{@w{ }and foo =@w{ }}, use the command
24788 @samp{echo \@w{ }and foo = \@w{ }}.
24790 A backslash at the end of @var{text} can be used, as in C, to continue
24791 the command onto subsequent lines. For example,
24794 echo This is some text\n\
24795 which is continued\n\
24796 onto several lines.\n
24799 produces the same output as
24802 echo This is some text\n
24803 echo which is continued\n
24804 echo onto several lines.\n
24808 @item output @var{expression}
24809 Print the value of @var{expression} and nothing but that value: no
24810 newlines, no @samp{$@var{nn} = }. The value is not entered in the
24811 value history either. @xref{Expressions, ,Expressions}, for more information
24814 @item output/@var{fmt} @var{expression}
24815 Print the value of @var{expression} in format @var{fmt}. You can use
24816 the same formats as for @code{print}. @xref{Output Formats,,Output
24817 Formats}, for more information.
24820 @item printf @var{template}, @var{expressions}@dots{}
24821 Print the values of one or more @var{expressions} under the control of
24822 the string @var{template}. To print several values, make
24823 @var{expressions} be a comma-separated list of individual expressions,
24824 which may be either numbers or pointers. Their values are printed as
24825 specified by @var{template}, exactly as a C program would do by
24826 executing the code below:
24829 printf (@var{template}, @var{expressions}@dots{});
24832 As in @code{C} @code{printf}, ordinary characters in @var{template}
24833 are printed verbatim, while @dfn{conversion specification} introduced
24834 by the @samp{%} character cause subsequent @var{expressions} to be
24835 evaluated, their values converted and formatted according to type and
24836 style information encoded in the conversion specifications, and then
24839 For example, you can print two values in hex like this:
24842 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
24845 @code{printf} supports all the standard @code{C} conversion
24846 specifications, including the flags and modifiers between the @samp{%}
24847 character and the conversion letter, with the following exceptions:
24851 The argument-ordering modifiers, such as @samp{2$}, are not supported.
24854 The modifier @samp{*} is not supported for specifying precision or
24858 The @samp{'} flag (for separation of digits into groups according to
24859 @code{LC_NUMERIC'}) is not supported.
24862 The type modifiers @samp{hh}, @samp{j}, @samp{t}, and @samp{z} are not
24866 The conversion letter @samp{n} (as in @samp{%n}) is not supported.
24869 The conversion letters @samp{a} and @samp{A} are not supported.
24873 Note that the @samp{ll} type modifier is supported only if the
24874 underlying @code{C} implementation used to build @value{GDBN} supports
24875 the @code{long long int} type, and the @samp{L} type modifier is
24876 supported only if @code{long double} type is available.
24878 As in @code{C}, @code{printf} supports simple backslash-escape
24879 sequences, such as @code{\n}, @samp{\t}, @samp{\\}, @samp{\"},
24880 @samp{\a}, and @samp{\f}, that consist of backslash followed by a
24881 single character. Octal and hexadecimal escape sequences are not
24884 Additionally, @code{printf} supports conversion specifications for DFP
24885 (@dfn{Decimal Floating Point}) types using the following length modifiers
24886 together with a floating point specifier.
24891 @samp{H} for printing @code{Decimal32} types.
24894 @samp{D} for printing @code{Decimal64} types.
24897 @samp{DD} for printing @code{Decimal128} types.
24900 If the underlying @code{C} implementation used to build @value{GDBN} has
24901 support for the three length modifiers for DFP types, other modifiers
24902 such as width and precision will also be available for @value{GDBN} to use.
24904 In case there is no such @code{C} support, no additional modifiers will be
24905 available and the value will be printed in the standard way.
24907 Here's an example of printing DFP types using the above conversion letters:
24909 printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl
24914 @item eval @var{template}, @var{expressions}@dots{}
24915 Convert the values of one or more @var{expressions} under the control of
24916 the string @var{template} to a command line, and call it.
24920 @node Auto-loading sequences
24921 @subsection Controlling auto-loading native @value{GDBN} scripts
24922 @cindex native script auto-loading
24924 When a new object file is read (for example, due to the @code{file}
24925 command, or because the inferior has loaded a shared library),
24926 @value{GDBN} will look for the command file @file{@var{objfile}-gdb.gdb}.
24927 @xref{Auto-loading extensions}.
24929 Auto-loading can be enabled or disabled,
24930 and the list of auto-loaded scripts can be printed.
24933 @anchor{set auto-load gdb-scripts}
24934 @kindex set auto-load gdb-scripts
24935 @item set auto-load gdb-scripts [on|off]
24936 Enable or disable the auto-loading of canned sequences of commands scripts.
24938 @anchor{show auto-load gdb-scripts}
24939 @kindex show auto-load gdb-scripts
24940 @item show auto-load gdb-scripts
24941 Show whether auto-loading of canned sequences of commands scripts is enabled or
24944 @anchor{info auto-load gdb-scripts}
24945 @kindex info auto-load gdb-scripts
24946 @cindex print list of auto-loaded canned sequences of commands scripts
24947 @item info auto-load gdb-scripts [@var{regexp}]
24948 Print the list of all canned sequences of commands scripts that @value{GDBN}
24952 If @var{regexp} is supplied only canned sequences of commands scripts with
24953 matching names are printed.
24955 @c Python docs live in a separate file.
24956 @include python.texi
24958 @c Guile docs live in a separate file.
24959 @include guile.texi
24961 @node Auto-loading extensions
24962 @section Auto-loading extensions
24963 @cindex auto-loading extensions
24965 @value{GDBN} provides two mechanisms for automatically loading extensions
24966 when a new object file is read (for example, due to the @code{file}
24967 command, or because the inferior has loaded a shared library):
24968 @file{@var{objfile}-gdb.@var{ext}} and the @code{.debug_gdb_scripts}
24969 section of modern file formats like ELF.
24972 * objfile-gdb.ext file: objfile-gdbdotext file. The @file{@var{objfile}-gdb.@var{ext}} file
24973 * .debug_gdb_scripts section: dotdebug_gdb_scripts section. The @code{.debug_gdb_scripts} section
24974 * Which flavor to choose?::
24977 The auto-loading feature is useful for supplying application-specific
24978 debugging commands and features.
24980 Auto-loading can be enabled or disabled,
24981 and the list of auto-loaded scripts can be printed.
24982 See the @samp{auto-loading} section of each extension language
24983 for more information.
24984 For @value{GDBN} command files see @ref{Auto-loading sequences}.
24985 For Python files see @ref{Python Auto-loading}.
24987 Note that loading of this script file also requires accordingly configured
24988 @code{auto-load safe-path} (@pxref{Auto-loading safe path}).
24990 @node objfile-gdbdotext file
24991 @subsection The @file{@var{objfile}-gdb.@var{ext}} file
24992 @cindex @file{@var{objfile}-gdb.gdb}
24993 @cindex @file{@var{objfile}-gdb.py}
24994 @cindex @file{@var{objfile}-gdb.scm}
24996 When a new object file is read, @value{GDBN} looks for a file named
24997 @file{@var{objfile}-gdb.@var{ext}} (we call it @var{script-name} below),
24998 where @var{objfile} is the object file's name and
24999 where @var{ext} is the file extension for the extension language:
25002 @item @file{@var{objfile}-gdb.gdb}
25003 GDB's own command language
25004 @item @file{@var{objfile}-gdb.py}
25006 @item @file{@var{objfile}-gdb.scm}
25010 @var{script-name} is formed by ensuring that the file name of @var{objfile}
25011 is absolute, following all symlinks, and resolving @code{.} and @code{..}
25012 components, and appending the @file{-gdb.@var{ext}} suffix.
25013 If this file exists and is readable, @value{GDBN} will evaluate it as a
25014 script in the specified extension language.
25016 If this file does not exist, then @value{GDBN} will look for
25017 @var{script-name} file in all of the directories as specified below.
25019 Note that loading of these files requires an accordingly configured
25020 @code{auto-load safe-path} (@pxref{Auto-loading safe path}).
25022 For object files using @file{.exe} suffix @value{GDBN} tries to load first the
25023 scripts normally according to its @file{.exe} filename. But if no scripts are
25024 found @value{GDBN} also tries script filenames matching the object file without
25025 its @file{.exe} suffix. This @file{.exe} stripping is case insensitive and it
25026 is attempted on any platform. This makes the script filenames compatible
25027 between Unix and MS-Windows hosts.
25030 @anchor{set auto-load scripts-directory}
25031 @kindex set auto-load scripts-directory
25032 @item set auto-load scripts-directory @r{[}@var{directories}@r{]}
25033 Control @value{GDBN} auto-loaded scripts location. Multiple directory entries
25034 may be delimited by the host platform path separator in use
25035 (@samp{:} on Unix, @samp{;} on MS-Windows and MS-DOS).
25037 Each entry here needs to be covered also by the security setting
25038 @code{set auto-load safe-path} (@pxref{set auto-load safe-path}).
25040 @anchor{with-auto-load-dir}
25041 This variable defaults to @file{$debugdir:$datadir/auto-load}. The default
25042 @code{set auto-load safe-path} value can be also overriden by @value{GDBN}
25043 configuration option @option{--with-auto-load-dir}.
25045 Any reference to @file{$debugdir} will get replaced by
25046 @var{debug-file-directory} value (@pxref{Separate Debug Files}) and any
25047 reference to @file{$datadir} will get replaced by @var{data-directory} which is
25048 determined at @value{GDBN} startup (@pxref{Data Files}). @file{$debugdir} and
25049 @file{$datadir} must be placed as a directory component --- either alone or
25050 delimited by @file{/} or @file{\} directory separators, depending on the host
25053 The list of directories uses path separator (@samp{:} on GNU and Unix
25054 systems, @samp{;} on MS-Windows and MS-DOS) to separate directories, similarly
25055 to the @env{PATH} environment variable.
25057 @anchor{show auto-load scripts-directory}
25058 @kindex show auto-load scripts-directory
25059 @item show auto-load scripts-directory
25060 Show @value{GDBN} auto-loaded scripts location.
25062 @anchor{add-auto-load-scripts-directory}
25063 @kindex add-auto-load-scripts-directory
25064 @item add-auto-load-scripts-directory @r{[}@var{directories}@dots{}@r{]}
25065 Add an entry (or list of entries) to the list of auto-loaded scripts locations.
25066 Multiple entries may be delimited by the host platform path separator in use.
25069 @value{GDBN} does not track which files it has already auto-loaded this way.
25070 @value{GDBN} will load the associated script every time the corresponding
25071 @var{objfile} is opened.
25072 So your @file{-gdb.@var{ext}} file should be careful to avoid errors if it
25073 is evaluated more than once.
25075 @node dotdebug_gdb_scripts section
25076 @subsection The @code{.debug_gdb_scripts} section
25077 @cindex @code{.debug_gdb_scripts} section
25079 For systems using file formats like ELF and COFF,
25080 when @value{GDBN} loads a new object file
25081 it will look for a special section named @code{.debug_gdb_scripts}.
25082 If this section exists, its contents is a list of null-terminated entries
25083 specifying scripts to load. Each entry begins with a non-null prefix byte that
25084 specifies the kind of entry, typically the extension language and whether the
25085 script is in a file or inlined in @code{.debug_gdb_scripts}.
25087 The following entries are supported:
25090 @item SECTION_SCRIPT_ID_PYTHON_FILE = 1
25091 @item SECTION_SCRIPT_ID_SCHEME_FILE = 3
25092 @item SECTION_SCRIPT_ID_PYTHON_TEXT = 4
25093 @item SECTION_SCRIPT_ID_SCHEME_TEXT = 6
25096 @subsubsection Script File Entries
25098 If the entry specifies a file, @value{GDBN} will look for the file first
25099 in the current directory and then along the source search path
25100 (@pxref{Source Path, ,Specifying Source Directories}),
25101 except that @file{$cdir} is not searched, since the compilation
25102 directory is not relevant to scripts.
25104 File entries can be placed in section @code{.debug_gdb_scripts} with,
25105 for example, this GCC macro for Python scripts.
25108 /* Note: The "MS" section flags are to remove duplicates. */
25109 #define DEFINE_GDB_PY_SCRIPT(script_name) \
25111 .pushsection \".debug_gdb_scripts\", \"MS\",@@progbits,1\n\
25112 .byte 1 /* Python */\n\
25113 .asciz \"" script_name "\"\n\
25119 For Guile scripts, replace @code{.byte 1} with @code{.byte 3}.
25120 Then one can reference the macro in a header or source file like this:
25123 DEFINE_GDB_PY_SCRIPT ("my-app-scripts.py")
25126 The script name may include directories if desired.
25128 Note that loading of this script file also requires accordingly configured
25129 @code{auto-load safe-path} (@pxref{Auto-loading safe path}).
25131 If the macro invocation is put in a header, any application or library
25132 using this header will get a reference to the specified script,
25133 and with the use of @code{"MS"} attributes on the section, the linker
25134 will remove duplicates.
25136 @subsubsection Script Text Entries
25138 Script text entries allow to put the executable script in the entry
25139 itself instead of loading it from a file.
25140 The first line of the entry, everything after the prefix byte and up to
25141 the first newline (@code{0xa}) character, is the script name, and must not
25142 contain any kind of space character, e.g., spaces or tabs.
25143 The rest of the entry, up to the trailing null byte, is the script to
25144 execute in the specified language. The name needs to be unique among
25145 all script names, as @value{GDBN} executes each script only once based
25148 Here is an example from file @file{py-section-script.c} in the @value{GDBN}
25152 #include "symcat.h"
25153 #include "gdb/section-scripts.h"
25155 ".pushsection \".debug_gdb_scripts\", \"MS\",@@progbits,1\n"
25156 ".byte " XSTRING (SECTION_SCRIPT_ID_PYTHON_TEXT) "\n"
25157 ".ascii \"gdb.inlined-script\\n\"\n"
25158 ".ascii \"class test_cmd (gdb.Command):\\n\"\n"
25159 ".ascii \" def __init__ (self):\\n\"\n"
25160 ".ascii \" super (test_cmd, self).__init__ ("
25161 "\\\"test-cmd\\\", gdb.COMMAND_OBSCURE)\\n\"\n"
25162 ".ascii \" def invoke (self, arg, from_tty):\\n\"\n"
25163 ".ascii \" print (\\\"test-cmd output, arg = %s\\\" % arg)\\n\"\n"
25164 ".ascii \"test_cmd ()\\n\"\n"
25170 Loading of inlined scripts requires a properly configured
25171 @code{auto-load safe-path} (@pxref{Auto-loading safe path}).
25172 The path to specify in @code{auto-load safe-path} is the path of the file
25173 containing the @code{.debug_gdb_scripts} section.
25175 @node Which flavor to choose?
25176 @subsection Which flavor to choose?
25178 Given the multiple ways of auto-loading extensions, it might not always
25179 be clear which one to choose. This section provides some guidance.
25182 Benefits of the @file{-gdb.@var{ext}} way:
25186 Can be used with file formats that don't support multiple sections.
25189 Ease of finding scripts for public libraries.
25191 Scripts specified in the @code{.debug_gdb_scripts} section are searched for
25192 in the source search path.
25193 For publicly installed libraries, e.g., @file{libstdc++}, there typically
25194 isn't a source directory in which to find the script.
25197 Doesn't require source code additions.
25201 Benefits of the @code{.debug_gdb_scripts} way:
25205 Works with static linking.
25207 Scripts for libraries done the @file{-gdb.@var{ext}} way require an objfile to
25208 trigger their loading. When an application is statically linked the only
25209 objfile available is the executable, and it is cumbersome to attach all the
25210 scripts from all the input libraries to the executable's
25211 @file{-gdb.@var{ext}} script.
25214 Works with classes that are entirely inlined.
25216 Some classes can be entirely inlined, and thus there may not be an associated
25217 shared library to attach a @file{-gdb.@var{ext}} script to.
25220 Scripts needn't be copied out of the source tree.
25222 In some circumstances, apps can be built out of large collections of internal
25223 libraries, and the build infrastructure necessary to install the
25224 @file{-gdb.@var{ext}} scripts in a place where @value{GDBN} can find them is
25225 cumbersome. It may be easier to specify the scripts in the
25226 @code{.debug_gdb_scripts} section as relative paths, and add a path to the
25227 top of the source tree to the source search path.
25230 @node Multiple Extension Languages
25231 @section Multiple Extension Languages
25233 The Guile and Python extension languages do not share any state,
25234 and generally do not interfere with each other.
25235 There are some things to be aware of, however.
25237 @subsection Python comes first
25239 Python was @value{GDBN}'s first extension language, and to avoid breaking
25240 existing behaviour Python comes first. This is generally solved by the
25241 ``first one wins'' principle. @value{GDBN} maintains a list of enabled
25242 extension languages, and when it makes a call to an extension language,
25243 (say to pretty-print a value), it tries each in turn until an extension
25244 language indicates it has performed the request (e.g., has returned the
25245 pretty-printed form of a value).
25246 This extends to errors while performing such requests: If an error happens
25247 while, for example, trying to pretty-print an object then the error is
25248 reported and any following extension languages are not tried.
25251 @section Creating new spellings of existing commands
25252 @cindex aliases for commands
25254 It is often useful to define alternate spellings of existing commands.
25255 For example, if a new @value{GDBN} command defined in Python has
25256 a long name to type, it is handy to have an abbreviated version of it
25257 that involves less typing.
25259 @value{GDBN} itself uses aliases. For example @samp{s} is an alias
25260 of the @samp{step} command even though it is otherwise an ambiguous
25261 abbreviation of other commands like @samp{set} and @samp{show}.
25263 Aliases are also used to provide shortened or more common versions
25264 of multi-word commands. For example, @value{GDBN} provides the
25265 @samp{tty} alias of the @samp{set inferior-tty} command.
25267 You can define a new alias with the @samp{alias} command.
25272 @item alias [-a] [--] @var{ALIAS} = @var{COMMAND}
25276 @var{ALIAS} specifies the name of the new alias.
25277 Each word of @var{ALIAS} must consist of letters, numbers, dashes and
25280 @var{COMMAND} specifies the name of an existing command
25281 that is being aliased.
25283 The @samp{-a} option specifies that the new alias is an abbreviation
25284 of the command. Abbreviations are not shown in command
25285 lists displayed by the @samp{help} command.
25287 The @samp{--} option specifies the end of options,
25288 and is useful when @var{ALIAS} begins with a dash.
25290 Here is a simple example showing how to make an abbreviation
25291 of a command so that there is less to type.
25292 Suppose you were tired of typing @samp{disas}, the current
25293 shortest unambiguous abbreviation of the @samp{disassemble} command
25294 and you wanted an even shorter version named @samp{di}.
25295 The following will accomplish this.
25298 (gdb) alias -a di = disas
25301 Note that aliases are different from user-defined commands.
25302 With a user-defined command, you also need to write documentation
25303 for it with the @samp{document} command.
25304 An alias automatically picks up the documentation of the existing command.
25306 Here is an example where we make @samp{elms} an abbreviation of
25307 @samp{elements} in the @samp{set print elements} command.
25308 This is to show that you can make an abbreviation of any part
25312 (gdb) alias -a set print elms = set print elements
25313 (gdb) alias -a show print elms = show print elements
25314 (gdb) set p elms 20
25316 Limit on string chars or array elements to print is 200.
25319 Note that if you are defining an alias of a @samp{set} command,
25320 and you want to have an alias for the corresponding @samp{show}
25321 command, then you need to define the latter separately.
25323 Unambiguously abbreviated commands are allowed in @var{COMMAND} and
25324 @var{ALIAS}, just as they are normally.
25327 (gdb) alias -a set pr elms = set p ele
25330 Finally, here is an example showing the creation of a one word
25331 alias for a more complex command.
25332 This creates alias @samp{spe} of the command @samp{set print elements}.
25335 (gdb) alias spe = set print elements
25340 @chapter Command Interpreters
25341 @cindex command interpreters
25343 @value{GDBN} supports multiple command interpreters, and some command
25344 infrastructure to allow users or user interface writers to switch
25345 between interpreters or run commands in other interpreters.
25347 @value{GDBN} currently supports two command interpreters, the console
25348 interpreter (sometimes called the command-line interpreter or @sc{cli})
25349 and the machine interface interpreter (or @sc{gdb/mi}). This manual
25350 describes both of these interfaces in great detail.
25352 By default, @value{GDBN} will start with the console interpreter.
25353 However, the user may choose to start @value{GDBN} with another
25354 interpreter by specifying the @option{-i} or @option{--interpreter}
25355 startup options. Defined interpreters include:
25359 @cindex console interpreter
25360 The traditional console or command-line interpreter. This is the most often
25361 used interpreter with @value{GDBN}. With no interpreter specified at runtime,
25362 @value{GDBN} will use this interpreter.
25365 @cindex mi interpreter
25366 The newest @sc{gdb/mi} interface (currently @code{mi2}). Used primarily
25367 by programs wishing to use @value{GDBN} as a backend for a debugger GUI
25368 or an IDE. For more information, see @ref{GDB/MI, ,The @sc{gdb/mi}
25372 @cindex mi2 interpreter
25373 The current @sc{gdb/mi} interface.
25376 @cindex mi1 interpreter
25377 The @sc{gdb/mi} interface included in @value{GDBN} 5.1, 5.2, and 5.3.
25381 @cindex invoke another interpreter
25383 @kindex interpreter-exec
25384 You may execute commands in any interpreter from the current
25385 interpreter using the appropriate command. If you are running the
25386 console interpreter, simply use the @code{interpreter-exec} command:
25389 interpreter-exec mi "-data-list-register-names"
25392 @sc{gdb/mi} has a similar command, although it is only available in versions of
25393 @value{GDBN} which support @sc{gdb/mi} version 2 (or greater).
25395 Note that @code{interpreter-exec} only changes the interpreter for the
25396 duration of the specified command. It does not change the interpreter
25399 @cindex start a new independent interpreter
25401 Although you may only choose a single interpreter at startup, it is
25402 possible to run an independent interpreter on a specified input/output
25403 device (usually a tty).
25405 For example, consider a debugger GUI or IDE that wants to provide a
25406 @value{GDBN} console view. It may do so by embedding a terminal
25407 emulator widget in its GUI, starting @value{GDBN} in the traditional
25408 command-line mode with stdin/stdout/stderr redirected to that
25409 terminal, and then creating an MI interpreter running on a specified
25410 input/output device. The console interpreter created by @value{GDBN}
25411 at startup handles commands the user types in the terminal widget,
25412 while the GUI controls and synchronizes state with @value{GDBN} using
25413 the separate MI interpreter.
25415 To start a new secondary @dfn{user interface} running MI, use the
25416 @code{new-ui} command:
25419 @cindex new user interface
25421 new-ui @var{interpreter} @var{tty}
25424 The @var{interpreter} parameter specifies the interpreter to run.
25425 This accepts the same values as the @code{interpreter-exec} command.
25426 For example, @samp{console}, @samp{mi}, @samp{mi2}, etc. The
25427 @var{tty} parameter specifies the name of the bidirectional file the
25428 interpreter uses for input/output, usually the name of a
25429 pseudoterminal slave on Unix systems. For example:
25432 (@value{GDBP}) new-ui mi /dev/pts/9
25436 runs an MI interpreter on @file{/dev/pts/9}.
25439 @chapter @value{GDBN} Text User Interface
25441 @cindex Text User Interface
25444 * TUI Overview:: TUI overview
25445 * TUI Keys:: TUI key bindings
25446 * TUI Single Key Mode:: TUI single key mode
25447 * TUI Commands:: TUI-specific commands
25448 * TUI Configuration:: TUI configuration variables
25451 The @value{GDBN} Text User Interface (TUI) is a terminal
25452 interface which uses the @code{curses} library to show the source
25453 file, the assembly output, the program registers and @value{GDBN}
25454 commands in separate text windows. The TUI mode is supported only
25455 on platforms where a suitable version of the @code{curses} library
25458 The TUI mode is enabled by default when you invoke @value{GDBN} as
25459 @samp{@value{GDBP} -tui}.
25460 You can also switch in and out of TUI mode while @value{GDBN} runs by
25461 using various TUI commands and key bindings, such as @command{tui
25462 enable} or @kbd{C-x C-a}. @xref{TUI Commands, ,TUI Commands}, and
25463 @ref{TUI Keys, ,TUI Key Bindings}.
25466 @section TUI Overview
25468 In TUI mode, @value{GDBN} can display several text windows:
25472 This window is the @value{GDBN} command window with the @value{GDBN}
25473 prompt and the @value{GDBN} output. The @value{GDBN} input is still
25474 managed using readline.
25477 The source window shows the source file of the program. The current
25478 line and active breakpoints are displayed in this window.
25481 The assembly window shows the disassembly output of the program.
25484 This window shows the processor registers. Registers are highlighted
25485 when their values change.
25488 The source and assembly windows show the current program position
25489 by highlighting the current line and marking it with a @samp{>} marker.
25490 Breakpoints are indicated with two markers. The first marker
25491 indicates the breakpoint type:
25495 Breakpoint which was hit at least once.
25498 Breakpoint which was never hit.
25501 Hardware breakpoint which was hit at least once.
25504 Hardware breakpoint which was never hit.
25507 The second marker indicates whether the breakpoint is enabled or not:
25511 Breakpoint is enabled.
25514 Breakpoint is disabled.
25517 The source, assembly and register windows are updated when the current
25518 thread changes, when the frame changes, or when the program counter
25521 These windows are not all visible at the same time. The command
25522 window is always visible. The others can be arranged in several
25533 source and assembly,
25536 source and registers, or
25539 assembly and registers.
25542 A status line above the command window shows the following information:
25546 Indicates the current @value{GDBN} target.
25547 (@pxref{Targets, ,Specifying a Debugging Target}).
25550 Gives the current process or thread number.
25551 When no process is being debugged, this field is set to @code{No process}.
25554 Gives the current function name for the selected frame.
25555 The name is demangled if demangling is turned on (@pxref{Print Settings}).
25556 When there is no symbol corresponding to the current program counter,
25557 the string @code{??} is displayed.
25560 Indicates the current line number for the selected frame.
25561 When the current line number is not known, the string @code{??} is displayed.
25564 Indicates the current program counter address.
25568 @section TUI Key Bindings
25569 @cindex TUI key bindings
25571 The TUI installs several key bindings in the readline keymaps
25572 @ifset SYSTEM_READLINE
25573 (@pxref{Command Line Editing, , , rluserman, GNU Readline Library}).
25575 @ifclear SYSTEM_READLINE
25576 (@pxref{Command Line Editing}).
25578 The following key bindings are installed for both TUI mode and the
25579 @value{GDBN} standard mode.
25588 Enter or leave the TUI mode. When leaving the TUI mode,
25589 the curses window management stops and @value{GDBN} operates using
25590 its standard mode, writing on the terminal directly. When reentering
25591 the TUI mode, control is given back to the curses windows.
25592 The screen is then refreshed.
25596 Use a TUI layout with only one window. The layout will
25597 either be @samp{source} or @samp{assembly}. When the TUI mode
25598 is not active, it will switch to the TUI mode.
25600 Think of this key binding as the Emacs @kbd{C-x 1} binding.
25604 Use a TUI layout with at least two windows. When the current
25605 layout already has two windows, the next layout with two windows is used.
25606 When a new layout is chosen, one window will always be common to the
25607 previous layout and the new one.
25609 Think of it as the Emacs @kbd{C-x 2} binding.
25613 Change the active window. The TUI associates several key bindings
25614 (like scrolling and arrow keys) with the active window. This command
25615 gives the focus to the next TUI window.
25617 Think of it as the Emacs @kbd{C-x o} binding.
25621 Switch in and out of the TUI SingleKey mode that binds single
25622 keys to @value{GDBN} commands (@pxref{TUI Single Key Mode}).
25625 The following key bindings only work in the TUI mode:
25630 Scroll the active window one page up.
25634 Scroll the active window one page down.
25638 Scroll the active window one line up.
25642 Scroll the active window one line down.
25646 Scroll the active window one column left.
25650 Scroll the active window one column right.
25654 Refresh the screen.
25657 Because the arrow keys scroll the active window in the TUI mode, they
25658 are not available for their normal use by readline unless the command
25659 window has the focus. When another window is active, you must use
25660 other readline key bindings such as @kbd{C-p}, @kbd{C-n}, @kbd{C-b}
25661 and @kbd{C-f} to control the command window.
25663 @node TUI Single Key Mode
25664 @section TUI Single Key Mode
25665 @cindex TUI single key mode
25667 The TUI also provides a @dfn{SingleKey} mode, which binds several
25668 frequently used @value{GDBN} commands to single keys. Type @kbd{C-x s} to
25669 switch into this mode, where the following key bindings are used:
25672 @kindex c @r{(SingleKey TUI key)}
25676 @kindex d @r{(SingleKey TUI key)}
25680 @kindex f @r{(SingleKey TUI key)}
25684 @kindex n @r{(SingleKey TUI key)}
25688 @kindex o @r{(SingleKey TUI key)}
25690 nexti. The shortcut letter @samp{o} stands for ``step Over''.
25692 @kindex q @r{(SingleKey TUI key)}
25694 exit the SingleKey mode.
25696 @kindex r @r{(SingleKey TUI key)}
25700 @kindex s @r{(SingleKey TUI key)}
25704 @kindex i @r{(SingleKey TUI key)}
25706 stepi. The shortcut letter @samp{i} stands for ``step Into''.
25708 @kindex u @r{(SingleKey TUI key)}
25712 @kindex v @r{(SingleKey TUI key)}
25716 @kindex w @r{(SingleKey TUI key)}
25721 Other keys temporarily switch to the @value{GDBN} command prompt.
25722 The key that was pressed is inserted in the editing buffer so that
25723 it is possible to type most @value{GDBN} commands without interaction
25724 with the TUI SingleKey mode. Once the command is entered the TUI
25725 SingleKey mode is restored. The only way to permanently leave
25726 this mode is by typing @kbd{q} or @kbd{C-x s}.
25730 @section TUI-specific Commands
25731 @cindex TUI commands
25733 The TUI has specific commands to control the text windows.
25734 These commands are always available, even when @value{GDBN} is not in
25735 the TUI mode. When @value{GDBN} is in the standard mode, most
25736 of these commands will automatically switch to the TUI mode.
25738 Note that if @value{GDBN}'s @code{stdout} is not connected to a
25739 terminal, or @value{GDBN} has been started with the machine interface
25740 interpreter (@pxref{GDB/MI, ,The @sc{gdb/mi} Interface}), most of
25741 these commands will fail with an error, because it would not be
25742 possible or desirable to enable curses window management.
25747 Activate TUI mode. The last active TUI window layout will be used if
25748 TUI mode has prevsiouly been used in the current debugging session,
25749 otherwise a default layout is used.
25752 @kindex tui disable
25753 Disable TUI mode, returning to the console interpreter.
25757 List and give the size of all displayed windows.
25759 @item layout @var{name}
25761 Changes which TUI windows are displayed. In each layout the command
25762 window is always displayed, the @var{name} parameter controls which
25763 additional windows are displayed, and can be any of the following:
25767 Display the next layout.
25770 Display the previous layout.
25773 Display the source and command windows.
25776 Display the assembly and command windows.
25779 Display the source, assembly, and command windows.
25782 When in @code{src} layout display the register, source, and command
25783 windows. When in @code{asm} or @code{split} layout display the
25784 register, assembler, and command windows.
25787 @item focus @var{name}
25789 Changes which TUI window is currently active for scrolling. The
25790 @var{name} parameter can be any of the following:
25794 Make the next window active for scrolling.
25797 Make the previous window active for scrolling.
25800 Make the source window active for scrolling.
25803 Make the assembly window active for scrolling.
25806 Make the register window active for scrolling.
25809 Make the command window active for scrolling.
25814 Refresh the screen. This is similar to typing @kbd{C-L}.
25816 @item tui reg @var{group}
25818 Changes the register group displayed in the tui register window to
25819 @var{group}. If the register window is not currently displayed this
25820 command will cause the register window to be displayed. The list of
25821 register groups, as well as their order is target specific. The
25822 following groups are available on most targets:
25825 Repeatedly selecting this group will cause the display to cycle
25826 through all of the available register groups.
25829 Repeatedly selecting this group will cause the display to cycle
25830 through all of the available register groups in the reverse order to
25834 Display the general registers.
25836 Display the floating point registers.
25838 Display the system registers.
25840 Display the vector registers.
25842 Display all registers.
25847 Update the source window and the current execution point.
25849 @item winheight @var{name} +@var{count}
25850 @itemx winheight @var{name} -@var{count}
25852 Change the height of the window @var{name} by @var{count}
25853 lines. Positive counts increase the height, while negative counts
25854 decrease it. The @var{name} parameter can be one of @code{src} (the
25855 source window), @code{cmd} (the command window), @code{asm} (the
25856 disassembly window), or @code{regs} (the register display window).
25858 @item tabset @var{nchars}
25860 Set the width of tab stops to be @var{nchars} characters. This
25861 setting affects the display of TAB characters in the source and
25865 @node TUI Configuration
25866 @section TUI Configuration Variables
25867 @cindex TUI configuration variables
25869 Several configuration variables control the appearance of TUI windows.
25872 @item set tui border-kind @var{kind}
25873 @kindex set tui border-kind
25874 Select the border appearance for the source, assembly and register windows.
25875 The possible values are the following:
25878 Use a space character to draw the border.
25881 Use @sc{ascii} characters @samp{+}, @samp{-} and @samp{|} to draw the border.
25884 Use the Alternate Character Set to draw the border. The border is
25885 drawn using character line graphics if the terminal supports them.
25888 @item set tui border-mode @var{mode}
25889 @kindex set tui border-mode
25890 @itemx set tui active-border-mode @var{mode}
25891 @kindex set tui active-border-mode
25892 Select the display attributes for the borders of the inactive windows
25893 or the active window. The @var{mode} can be one of the following:
25896 Use normal attributes to display the border.
25902 Use reverse video mode.
25905 Use half bright mode.
25907 @item half-standout
25908 Use half bright and standout mode.
25911 Use extra bright or bold mode.
25913 @item bold-standout
25914 Use extra bright or bold and standout mode.
25919 @chapter Using @value{GDBN} under @sc{gnu} Emacs
25922 @cindex @sc{gnu} Emacs
25923 A special interface allows you to use @sc{gnu} Emacs to view (and
25924 edit) the source files for the program you are debugging with
25927 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
25928 executable file you want to debug as an argument. This command starts
25929 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
25930 created Emacs buffer.
25931 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
25933 Running @value{GDBN} under Emacs can be just like running @value{GDBN} normally except for two
25938 All ``terminal'' input and output goes through an Emacs buffer, called
25941 This applies both to @value{GDBN} commands and their output, and to the input
25942 and output done by the program you are debugging.
25944 This is useful because it means that you can copy the text of previous
25945 commands and input them again; you can even use parts of the output
25948 All the facilities of Emacs' Shell mode are available for interacting
25949 with your program. In particular, you can send signals the usual
25950 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
25954 @value{GDBN} displays source code through Emacs.
25956 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
25957 source file for that frame and puts an arrow (@samp{=>}) at the
25958 left margin of the current line. Emacs uses a separate buffer for
25959 source display, and splits the screen to show both your @value{GDBN} session
25962 Explicit @value{GDBN} @code{list} or search commands still produce output as
25963 usual, but you probably have no reason to use them from Emacs.
25966 We call this @dfn{text command mode}. Emacs 22.1, and later, also uses
25967 a graphical mode, enabled by default, which provides further buffers
25968 that can control the execution and describe the state of your program.
25969 @xref{GDB Graphical Interface,,, Emacs, The @sc{gnu} Emacs Manual}.
25971 If you specify an absolute file name when prompted for the @kbd{M-x
25972 gdb} argument, then Emacs sets your current working directory to where
25973 your program resides. If you only specify the file name, then Emacs
25974 sets your current working directory to the directory associated
25975 with the previous buffer. In this case, @value{GDBN} may find your
25976 program by searching your environment's @code{PATH} variable, but on
25977 some operating systems it might not find the source. So, although the
25978 @value{GDBN} input and output session proceeds normally, the auxiliary
25979 buffer does not display the current source and line of execution.
25981 The initial working directory of @value{GDBN} is printed on the top
25982 line of the GUD buffer and this serves as a default for the commands
25983 that specify files for @value{GDBN} to operate on. @xref{Files,
25984 ,Commands to Specify Files}.
25986 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If you
25987 need to call @value{GDBN} by a different name (for example, if you
25988 keep several configurations around, with different names) you can
25989 customize the Emacs variable @code{gud-gdb-command-name} to run the
25992 In the GUD buffer, you can use these special Emacs commands in
25993 addition to the standard Shell mode commands:
25997 Describe the features of Emacs' GUD Mode.
26000 Execute to another source line, like the @value{GDBN} @code{step} command; also
26001 update the display window to show the current file and location.
26004 Execute to next source line in this function, skipping all function
26005 calls, like the @value{GDBN} @code{next} command. Then update the display window
26006 to show the current file and location.
26009 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
26010 display window accordingly.
26013 Execute until exit from the selected stack frame, like the @value{GDBN}
26014 @code{finish} command.
26017 Continue execution of your program, like the @value{GDBN} @code{continue}
26021 Go up the number of frames indicated by the numeric argument
26022 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
26023 like the @value{GDBN} @code{up} command.
26026 Go down the number of frames indicated by the numeric argument, like the
26027 @value{GDBN} @code{down} command.
26030 In any source file, the Emacs command @kbd{C-x @key{SPC}} (@code{gud-break})
26031 tells @value{GDBN} to set a breakpoint on the source line point is on.
26033 In text command mode, if you type @kbd{M-x speedbar}, Emacs displays a
26034 separate frame which shows a backtrace when the GUD buffer is current.
26035 Move point to any frame in the stack and type @key{RET} to make it
26036 become the current frame and display the associated source in the
26037 source buffer. Alternatively, click @kbd{Mouse-2} to make the
26038 selected frame become the current one. In graphical mode, the
26039 speedbar displays watch expressions.
26041 If you accidentally delete the source-display buffer, an easy way to get
26042 it back is to type the command @code{f} in the @value{GDBN} buffer, to
26043 request a frame display; when you run under Emacs, this recreates
26044 the source buffer if necessary to show you the context of the current
26047 The source files displayed in Emacs are in ordinary Emacs buffers
26048 which are visiting the source files in the usual way. You can edit
26049 the files with these buffers if you wish; but keep in mind that @value{GDBN}
26050 communicates with Emacs in terms of line numbers. If you add or
26051 delete lines from the text, the line numbers that @value{GDBN} knows cease
26052 to correspond properly with the code.
26054 A more detailed description of Emacs' interaction with @value{GDBN} is
26055 given in the Emacs manual (@pxref{Debuggers,,, Emacs, The @sc{gnu}
26059 @chapter The @sc{gdb/mi} Interface
26061 @unnumberedsec Function and Purpose
26063 @cindex @sc{gdb/mi}, its purpose
26064 @sc{gdb/mi} is a line based machine oriented text interface to
26065 @value{GDBN} and is activated by specifying using the
26066 @option{--interpreter} command line option (@pxref{Mode Options}). It
26067 is specifically intended to support the development of systems which
26068 use the debugger as just one small component of a larger system.
26070 This chapter is a specification of the @sc{gdb/mi} interface. It is written
26071 in the form of a reference manual.
26073 Note that @sc{gdb/mi} is still under construction, so some of the
26074 features described below are incomplete and subject to change
26075 (@pxref{GDB/MI Development and Front Ends, , @sc{gdb/mi} Development and Front Ends}).
26077 @unnumberedsec Notation and Terminology
26079 @cindex notational conventions, for @sc{gdb/mi}
26080 This chapter uses the following notation:
26084 @code{|} separates two alternatives.
26087 @code{[ @var{something} ]} indicates that @var{something} is optional:
26088 it may or may not be given.
26091 @code{( @var{group} )*} means that @var{group} inside the parentheses
26092 may repeat zero or more times.
26095 @code{( @var{group} )+} means that @var{group} inside the parentheses
26096 may repeat one or more times.
26099 @code{"@var{string}"} means a literal @var{string}.
26103 @heading Dependencies
26107 * GDB/MI General Design::
26108 * GDB/MI Command Syntax::
26109 * GDB/MI Compatibility with CLI::
26110 * GDB/MI Development and Front Ends::
26111 * GDB/MI Output Records::
26112 * GDB/MI Simple Examples::
26113 * GDB/MI Command Description Format::
26114 * GDB/MI Breakpoint Commands::
26115 * GDB/MI Catchpoint Commands::
26116 * GDB/MI Program Context::
26117 * GDB/MI Thread Commands::
26118 * GDB/MI Ada Tasking Commands::
26119 * GDB/MI Program Execution::
26120 * GDB/MI Stack Manipulation::
26121 * GDB/MI Variable Objects::
26122 * GDB/MI Data Manipulation::
26123 * GDB/MI Tracepoint Commands::
26124 * GDB/MI Symbol Query::
26125 * GDB/MI File Commands::
26127 * GDB/MI Kod Commands::
26128 * GDB/MI Memory Overlay Commands::
26129 * GDB/MI Signal Handling Commands::
26131 * GDB/MI Target Manipulation::
26132 * GDB/MI File Transfer Commands::
26133 * GDB/MI Ada Exceptions Commands::
26134 * GDB/MI Support Commands::
26135 * GDB/MI Miscellaneous Commands::
26138 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26139 @node GDB/MI General Design
26140 @section @sc{gdb/mi} General Design
26141 @cindex GDB/MI General Design
26143 Interaction of a @sc{GDB/MI} frontend with @value{GDBN} involves three
26144 parts---commands sent to @value{GDBN}, responses to those commands
26145 and notifications. Each command results in exactly one response,
26146 indicating either successful completion of the command, or an error.
26147 For the commands that do not resume the target, the response contains the
26148 requested information. For the commands that resume the target, the
26149 response only indicates whether the target was successfully resumed.
26150 Notifications is the mechanism for reporting changes in the state of the
26151 target, or in @value{GDBN} state, that cannot conveniently be associated with
26152 a command and reported as part of that command response.
26154 The important examples of notifications are:
26158 Exec notifications. These are used to report changes in
26159 target state---when a target is resumed, or stopped. It would not
26160 be feasible to include this information in response of resuming
26161 commands, because one resume commands can result in multiple events in
26162 different threads. Also, quite some time may pass before any event
26163 happens in the target, while a frontend needs to know whether the resuming
26164 command itself was successfully executed.
26167 Console output, and status notifications. Console output
26168 notifications are used to report output of CLI commands, as well as
26169 diagnostics for other commands. Status notifications are used to
26170 report the progress of a long-running operation. Naturally, including
26171 this information in command response would mean no output is produced
26172 until the command is finished, which is undesirable.
26175 General notifications. Commands may have various side effects on
26176 the @value{GDBN} or target state beyond their official purpose. For example,
26177 a command may change the selected thread. Although such changes can
26178 be included in command response, using notification allows for more
26179 orthogonal frontend design.
26183 There's no guarantee that whenever an MI command reports an error,
26184 @value{GDBN} or the target are in any specific state, and especially,
26185 the state is not reverted to the state before the MI command was
26186 processed. Therefore, whenever an MI command results in an error,
26187 we recommend that the frontend refreshes all the information shown in
26188 the user interface.
26192 * Context management::
26193 * Asynchronous and non-stop modes::
26197 @node Context management
26198 @subsection Context management
26200 @subsubsection Threads and Frames
26202 In most cases when @value{GDBN} accesses the target, this access is
26203 done in context of a specific thread and frame (@pxref{Frames}).
26204 Often, even when accessing global data, the target requires that a thread
26205 be specified. The CLI interface maintains the selected thread and frame,
26206 and supplies them to target on each command. This is convenient,
26207 because a command line user would not want to specify that information
26208 explicitly on each command, and because user interacts with
26209 @value{GDBN} via a single terminal, so no confusion is possible as
26210 to what thread and frame are the current ones.
26212 In the case of MI, the concept of selected thread and frame is less
26213 useful. First, a frontend can easily remember this information
26214 itself. Second, a graphical frontend can have more than one window,
26215 each one used for debugging a different thread, and the frontend might
26216 want to access additional threads for internal purposes. This
26217 increases the risk that by relying on implicitly selected thread, the
26218 frontend may be operating on a wrong one. Therefore, each MI command
26219 should explicitly specify which thread and frame to operate on. To
26220 make it possible, each MI command accepts the @samp{--thread} and
26221 @samp{--frame} options, the value to each is @value{GDBN} global
26222 identifier for thread and frame to operate on.
26224 Usually, each top-level window in a frontend allows the user to select
26225 a thread and a frame, and remembers the user selection for further
26226 operations. However, in some cases @value{GDBN} may suggest that the
26227 current thread or frame be changed. For example, when stopping on a
26228 breakpoint it is reasonable to switch to the thread where breakpoint is
26229 hit. For another example, if the user issues the CLI @samp{thread} or
26230 @samp{frame} commands via the frontend, it is desirable to change the
26231 frontend's selection to the one specified by user. @value{GDBN}
26232 communicates the suggestion to change current thread and frame using the
26233 @samp{=thread-selected} notification.
26235 Note that historically, MI shares the selected thread with CLI, so
26236 frontends used the @code{-thread-select} to execute commands in the
26237 right context. However, getting this to work right is cumbersome. The
26238 simplest way is for frontend to emit @code{-thread-select} command
26239 before every command. This doubles the number of commands that need
26240 to be sent. The alternative approach is to suppress @code{-thread-select}
26241 if the selected thread in @value{GDBN} is supposed to be identical to the
26242 thread the frontend wants to operate on. However, getting this
26243 optimization right can be tricky. In particular, if the frontend
26244 sends several commands to @value{GDBN}, and one of the commands changes the
26245 selected thread, then the behaviour of subsequent commands will
26246 change. So, a frontend should either wait for response from such
26247 problematic commands, or explicitly add @code{-thread-select} for
26248 all subsequent commands. No frontend is known to do this exactly
26249 right, so it is suggested to just always pass the @samp{--thread} and
26250 @samp{--frame} options.
26252 @subsubsection Language
26254 The execution of several commands depends on which language is selected.
26255 By default, the current language (@pxref{show language}) is used.
26256 But for commands known to be language-sensitive, it is recommended
26257 to use the @samp{--language} option. This option takes one argument,
26258 which is the name of the language to use while executing the command.
26262 -data-evaluate-expression --language c "sizeof (void*)"
26267 The valid language names are the same names accepted by the
26268 @samp{set language} command (@pxref{Manually}), excluding @samp{auto},
26269 @samp{local} or @samp{unknown}.
26271 @node Asynchronous and non-stop modes
26272 @subsection Asynchronous command execution and non-stop mode
26274 On some targets, @value{GDBN} is capable of processing MI commands
26275 even while the target is running. This is called @dfn{asynchronous
26276 command execution} (@pxref{Background Execution}). The frontend may
26277 specify a preferrence for asynchronous execution using the
26278 @code{-gdb-set mi-async 1} command, which should be emitted before
26279 either running the executable or attaching to the target. After the
26280 frontend has started the executable or attached to the target, it can
26281 find if asynchronous execution is enabled using the
26282 @code{-list-target-features} command.
26285 @item -gdb-set mi-async on
26286 @item -gdb-set mi-async off
26287 Set whether MI is in asynchronous mode.
26289 When @code{off}, which is the default, MI execution commands (e.g.,
26290 @code{-exec-continue}) are foreground commands, and @value{GDBN} waits
26291 for the program to stop before processing further commands.
26293 When @code{on}, MI execution commands are background execution
26294 commands (e.g., @code{-exec-continue} becomes the equivalent of the
26295 @code{c&} CLI command), and so @value{GDBN} is capable of processing
26296 MI commands even while the target is running.
26298 @item -gdb-show mi-async
26299 Show whether MI asynchronous mode is enabled.
26302 Note: In @value{GDBN} version 7.7 and earlier, this option was called
26303 @code{target-async} instead of @code{mi-async}, and it had the effect
26304 of both putting MI in asynchronous mode and making CLI background
26305 commands possible. CLI background commands are now always possible
26306 ``out of the box'' if the target supports them. The old spelling is
26307 kept as a deprecated alias for backwards compatibility.
26309 Even if @value{GDBN} can accept a command while target is running,
26310 many commands that access the target do not work when the target is
26311 running. Therefore, asynchronous command execution is most useful
26312 when combined with non-stop mode (@pxref{Non-Stop Mode}). Then,
26313 it is possible to examine the state of one thread, while other threads
26316 When a given thread is running, MI commands that try to access the
26317 target in the context of that thread may not work, or may work only on
26318 some targets. In particular, commands that try to operate on thread's
26319 stack will not work, on any target. Commands that read memory, or
26320 modify breakpoints, may work or not work, depending on the target. Note
26321 that even commands that operate on global state, such as @code{print},
26322 @code{set}, and breakpoint commands, still access the target in the
26323 context of a specific thread, so frontend should try to find a
26324 stopped thread and perform the operation on that thread (using the
26325 @samp{--thread} option).
26327 Which commands will work in the context of a running thread is
26328 highly target dependent. However, the two commands
26329 @code{-exec-interrupt}, to stop a thread, and @code{-thread-info},
26330 to find the state of a thread, will always work.
26332 @node Thread groups
26333 @subsection Thread groups
26334 @value{GDBN} may be used to debug several processes at the same time.
26335 On some platfroms, @value{GDBN} may support debugging of several
26336 hardware systems, each one having several cores with several different
26337 processes running on each core. This section describes the MI
26338 mechanism to support such debugging scenarios.
26340 The key observation is that regardless of the structure of the
26341 target, MI can have a global list of threads, because most commands that
26342 accept the @samp{--thread} option do not need to know what process that
26343 thread belongs to. Therefore, it is not necessary to introduce
26344 neither additional @samp{--process} option, nor an notion of the
26345 current process in the MI interface. The only strictly new feature
26346 that is required is the ability to find how the threads are grouped
26349 To allow the user to discover such grouping, and to support arbitrary
26350 hierarchy of machines/cores/processes, MI introduces the concept of a
26351 @dfn{thread group}. Thread group is a collection of threads and other
26352 thread groups. A thread group always has a string identifier, a type,
26353 and may have additional attributes specific to the type. A new
26354 command, @code{-list-thread-groups}, returns the list of top-level
26355 thread groups, which correspond to processes that @value{GDBN} is
26356 debugging at the moment. By passing an identifier of a thread group
26357 to the @code{-list-thread-groups} command, it is possible to obtain
26358 the members of specific thread group.
26360 To allow the user to easily discover processes, and other objects, he
26361 wishes to debug, a concept of @dfn{available thread group} is
26362 introduced. Available thread group is an thread group that
26363 @value{GDBN} is not debugging, but that can be attached to, using the
26364 @code{-target-attach} command. The list of available top-level thread
26365 groups can be obtained using @samp{-list-thread-groups --available}.
26366 In general, the content of a thread group may be only retrieved only
26367 after attaching to that thread group.
26369 Thread groups are related to inferiors (@pxref{Inferiors and
26370 Programs}). Each inferior corresponds to a thread group of a special
26371 type @samp{process}, and some additional operations are permitted on
26372 such thread groups.
26374 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26375 @node GDB/MI Command Syntax
26376 @section @sc{gdb/mi} Command Syntax
26379 * GDB/MI Input Syntax::
26380 * GDB/MI Output Syntax::
26383 @node GDB/MI Input Syntax
26384 @subsection @sc{gdb/mi} Input Syntax
26386 @cindex input syntax for @sc{gdb/mi}
26387 @cindex @sc{gdb/mi}, input syntax
26389 @item @var{command} @expansion{}
26390 @code{@var{cli-command} | @var{mi-command}}
26392 @item @var{cli-command} @expansion{}
26393 @code{[ @var{token} ] @var{cli-command} @var{nl}}, where
26394 @var{cli-command} is any existing @value{GDBN} CLI command.
26396 @item @var{mi-command} @expansion{}
26397 @code{[ @var{token} ] "-" @var{operation} ( " " @var{option} )*
26398 @code{[} " --" @code{]} ( " " @var{parameter} )* @var{nl}}
26400 @item @var{token} @expansion{}
26401 "any sequence of digits"
26403 @item @var{option} @expansion{}
26404 @code{"-" @var{parameter} [ " " @var{parameter} ]}
26406 @item @var{parameter} @expansion{}
26407 @code{@var{non-blank-sequence} | @var{c-string}}
26409 @item @var{operation} @expansion{}
26410 @emph{any of the operations described in this chapter}
26412 @item @var{non-blank-sequence} @expansion{}
26413 @emph{anything, provided it doesn't contain special characters such as
26414 "-", @var{nl}, """ and of course " "}
26416 @item @var{c-string} @expansion{}
26417 @code{""" @var{seven-bit-iso-c-string-content} """}
26419 @item @var{nl} @expansion{}
26428 The CLI commands are still handled by the @sc{mi} interpreter; their
26429 output is described below.
26432 The @code{@var{token}}, when present, is passed back when the command
26436 Some @sc{mi} commands accept optional arguments as part of the parameter
26437 list. Each option is identified by a leading @samp{-} (dash) and may be
26438 followed by an optional argument parameter. Options occur first in the
26439 parameter list and can be delimited from normal parameters using
26440 @samp{--} (this is useful when some parameters begin with a dash).
26447 We want easy access to the existing CLI syntax (for debugging).
26450 We want it to be easy to spot a @sc{mi} operation.
26453 @node GDB/MI Output Syntax
26454 @subsection @sc{gdb/mi} Output Syntax
26456 @cindex output syntax of @sc{gdb/mi}
26457 @cindex @sc{gdb/mi}, output syntax
26458 The output from @sc{gdb/mi} consists of zero or more out-of-band records
26459 followed, optionally, by a single result record. This result record
26460 is for the most recent command. The sequence of output records is
26461 terminated by @samp{(gdb)}.
26463 If an input command was prefixed with a @code{@var{token}} then the
26464 corresponding output for that command will also be prefixed by that same
26468 @item @var{output} @expansion{}
26469 @code{( @var{out-of-band-record} )* [ @var{result-record} ] "(gdb)" @var{nl}}
26471 @item @var{result-record} @expansion{}
26472 @code{ [ @var{token} ] "^" @var{result-class} ( "," @var{result} )* @var{nl}}
26474 @item @var{out-of-band-record} @expansion{}
26475 @code{@var{async-record} | @var{stream-record}}
26477 @item @var{async-record} @expansion{}
26478 @code{@var{exec-async-output} | @var{status-async-output} | @var{notify-async-output}}
26480 @item @var{exec-async-output} @expansion{}
26481 @code{[ @var{token} ] "*" @var{async-output nl}}
26483 @item @var{status-async-output} @expansion{}
26484 @code{[ @var{token} ] "+" @var{async-output nl}}
26486 @item @var{notify-async-output} @expansion{}
26487 @code{[ @var{token} ] "=" @var{async-output nl}}
26489 @item @var{async-output} @expansion{}
26490 @code{@var{async-class} ( "," @var{result} )*}
26492 @item @var{result-class} @expansion{}
26493 @code{"done" | "running" | "connected" | "error" | "exit"}
26495 @item @var{async-class} @expansion{}
26496 @code{"stopped" | @var{others}} (where @var{others} will be added
26497 depending on the needs---this is still in development).
26499 @item @var{result} @expansion{}
26500 @code{ @var{variable} "=" @var{value}}
26502 @item @var{variable} @expansion{}
26503 @code{ @var{string} }
26505 @item @var{value} @expansion{}
26506 @code{ @var{const} | @var{tuple} | @var{list} }
26508 @item @var{const} @expansion{}
26509 @code{@var{c-string}}
26511 @item @var{tuple} @expansion{}
26512 @code{ "@{@}" | "@{" @var{result} ( "," @var{result} )* "@}" }
26514 @item @var{list} @expansion{}
26515 @code{ "[]" | "[" @var{value} ( "," @var{value} )* "]" | "["
26516 @var{result} ( "," @var{result} )* "]" }
26518 @item @var{stream-record} @expansion{}
26519 @code{@var{console-stream-output} | @var{target-stream-output} | @var{log-stream-output}}
26521 @item @var{console-stream-output} @expansion{}
26522 @code{"~" @var{c-string nl}}
26524 @item @var{target-stream-output} @expansion{}
26525 @code{"@@" @var{c-string nl}}
26527 @item @var{log-stream-output} @expansion{}
26528 @code{"&" @var{c-string nl}}
26530 @item @var{nl} @expansion{}
26533 @item @var{token} @expansion{}
26534 @emph{any sequence of digits}.
26542 All output sequences end in a single line containing a period.
26545 The @code{@var{token}} is from the corresponding request. Note that
26546 for all async output, while the token is allowed by the grammar and
26547 may be output by future versions of @value{GDBN} for select async
26548 output messages, it is generally omitted. Frontends should treat
26549 all async output as reporting general changes in the state of the
26550 target and there should be no need to associate async output to any
26554 @cindex status output in @sc{gdb/mi}
26555 @var{status-async-output} contains on-going status information about the
26556 progress of a slow operation. It can be discarded. All status output is
26557 prefixed by @samp{+}.
26560 @cindex async output in @sc{gdb/mi}
26561 @var{exec-async-output} contains asynchronous state change on the target
26562 (stopped, started, disappeared). All async output is prefixed by
26566 @cindex notify output in @sc{gdb/mi}
26567 @var{notify-async-output} contains supplementary information that the
26568 client should handle (e.g., a new breakpoint information). All notify
26569 output is prefixed by @samp{=}.
26572 @cindex console output in @sc{gdb/mi}
26573 @var{console-stream-output} is output that should be displayed as is in the
26574 console. It is the textual response to a CLI command. All the console
26575 output is prefixed by @samp{~}.
26578 @cindex target output in @sc{gdb/mi}
26579 @var{target-stream-output} is the output produced by the target program.
26580 All the target output is prefixed by @samp{@@}.
26583 @cindex log output in @sc{gdb/mi}
26584 @var{log-stream-output} is output text coming from @value{GDBN}'s internals, for
26585 instance messages that should be displayed as part of an error log. All
26586 the log output is prefixed by @samp{&}.
26589 @cindex list output in @sc{gdb/mi}
26590 New @sc{gdb/mi} commands should only output @var{lists} containing
26596 @xref{GDB/MI Stream Records, , @sc{gdb/mi} Stream Records}, for more
26597 details about the various output records.
26599 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26600 @node GDB/MI Compatibility with CLI
26601 @section @sc{gdb/mi} Compatibility with CLI
26603 @cindex compatibility, @sc{gdb/mi} and CLI
26604 @cindex @sc{gdb/mi}, compatibility with CLI
26606 For the developers convenience CLI commands can be entered directly,
26607 but there may be some unexpected behaviour. For example, commands
26608 that query the user will behave as if the user replied yes, breakpoint
26609 command lists are not executed and some CLI commands, such as
26610 @code{if}, @code{when} and @code{define}, prompt for further input with
26611 @samp{>}, which is not valid MI output.
26613 This feature may be removed at some stage in the future and it is
26614 recommended that front ends use the @code{-interpreter-exec} command
26615 (@pxref{-interpreter-exec}).
26617 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26618 @node GDB/MI Development and Front Ends
26619 @section @sc{gdb/mi} Development and Front Ends
26620 @cindex @sc{gdb/mi} development
26622 The application which takes the MI output and presents the state of the
26623 program being debugged to the user is called a @dfn{front end}.
26625 Although @sc{gdb/mi} is still incomplete, it is currently being used
26626 by a variety of front ends to @value{GDBN}. This makes it difficult
26627 to introduce new functionality without breaking existing usage. This
26628 section tries to minimize the problems by describing how the protocol
26631 Some changes in MI need not break a carefully designed front end, and
26632 for these the MI version will remain unchanged. The following is a
26633 list of changes that may occur within one level, so front ends should
26634 parse MI output in a way that can handle them:
26638 New MI commands may be added.
26641 New fields may be added to the output of any MI command.
26644 The range of values for fields with specified values, e.g.,
26645 @code{in_scope} (@pxref{-var-update}) may be extended.
26647 @c The format of field's content e.g type prefix, may change so parse it
26648 @c at your own risk. Yes, in general?
26650 @c The order of fields may change? Shouldn't really matter but it might
26651 @c resolve inconsistencies.
26654 If the changes are likely to break front ends, the MI version level
26655 will be increased by one. This will allow the front end to parse the
26656 output according to the MI version. Apart from mi0, new versions of
26657 @value{GDBN} will not support old versions of MI and it will be the
26658 responsibility of the front end to work with the new one.
26660 @c Starting with mi3, add a new command -mi-version that prints the MI
26663 The best way to avoid unexpected changes in MI that might break your front
26664 end is to make your project known to @value{GDBN} developers and
26665 follow development on @email{gdb@@sourceware.org} and
26666 @email{gdb-patches@@sourceware.org}.
26667 @cindex mailing lists
26669 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
26670 @node GDB/MI Output Records
26671 @section @sc{gdb/mi} Output Records
26674 * GDB/MI Result Records::
26675 * GDB/MI Stream Records::
26676 * GDB/MI Async Records::
26677 * GDB/MI Breakpoint Information::
26678 * GDB/MI Frame Information::
26679 * GDB/MI Thread Information::
26680 * GDB/MI Ada Exception Information::
26683 @node GDB/MI Result Records
26684 @subsection @sc{gdb/mi} Result Records
26686 @cindex result records in @sc{gdb/mi}
26687 @cindex @sc{gdb/mi}, result records
26688 In addition to a number of out-of-band notifications, the response to a
26689 @sc{gdb/mi} command includes one of the following result indications:
26693 @item "^done" [ "," @var{results} ]
26694 The synchronous operation was successful, @code{@var{results}} are the return
26699 This result record is equivalent to @samp{^done}. Historically, it
26700 was output instead of @samp{^done} if the command has resumed the
26701 target. This behaviour is maintained for backward compatibility, but
26702 all frontends should treat @samp{^done} and @samp{^running}
26703 identically and rely on the @samp{*running} output record to determine
26704 which threads are resumed.
26708 @value{GDBN} has connected to a remote target.
26710 @item "^error" "," "msg=" @var{c-string} [ "," "code=" @var{c-string} ]
26712 The operation failed. The @code{msg=@var{c-string}} variable contains
26713 the corresponding error message.
26715 If present, the @code{code=@var{c-string}} variable provides an error
26716 code on which consumers can rely on to detect the corresponding
26717 error condition. At present, only one error code is defined:
26720 @item "undefined-command"
26721 Indicates that the command causing the error does not exist.
26726 @value{GDBN} has terminated.
26730 @node GDB/MI Stream Records
26731 @subsection @sc{gdb/mi} Stream Records
26733 @cindex @sc{gdb/mi}, stream records
26734 @cindex stream records in @sc{gdb/mi}
26735 @value{GDBN} internally maintains a number of output streams: the console, the
26736 target, and the log. The output intended for each of these streams is
26737 funneled through the @sc{gdb/mi} interface using @dfn{stream records}.
26739 Each stream record begins with a unique @dfn{prefix character} which
26740 identifies its stream (@pxref{GDB/MI Output Syntax, , @sc{gdb/mi} Output
26741 Syntax}). In addition to the prefix, each stream record contains a
26742 @code{@var{string-output}}. This is either raw text (with an implicit new
26743 line) or a quoted C string (which does not contain an implicit newline).
26746 @item "~" @var{string-output}
26747 The console output stream contains text that should be displayed in the
26748 CLI console window. It contains the textual responses to CLI commands.
26750 @item "@@" @var{string-output}
26751 The target output stream contains any textual output from the running
26752 target. This is only present when GDB's event loop is truly
26753 asynchronous, which is currently only the case for remote targets.
26755 @item "&" @var{string-output}
26756 The log stream contains debugging messages being produced by @value{GDBN}'s
26760 @node GDB/MI Async Records
26761 @subsection @sc{gdb/mi} Async Records
26763 @cindex async records in @sc{gdb/mi}
26764 @cindex @sc{gdb/mi}, async records
26765 @dfn{Async} records are used to notify the @sc{gdb/mi} client of
26766 additional changes that have occurred. Those changes can either be a
26767 consequence of @sc{gdb/mi} commands (e.g., a breakpoint modified) or a result of
26768 target activity (e.g., target stopped).
26770 The following is the list of possible async records:
26774 @item *running,thread-id="@var{thread}"
26775 The target is now running. The @var{thread} field can be the global
26776 thread ID of the the thread that is now running, and it can be
26777 @samp{all} if all threads are running. The frontend should assume
26778 that no interaction with a running thread is possible after this
26779 notification is produced. The frontend should not assume that this
26780 notification is output only once for any command. @value{GDBN} may
26781 emit this notification several times, either for different threads,
26782 because it cannot resume all threads together, or even for a single
26783 thread, if the thread must be stepped though some code before letting
26786 @item *stopped,reason="@var{reason}",thread-id="@var{id}",stopped-threads="@var{stopped}",core="@var{core}"
26787 The target has stopped. The @var{reason} field can have one of the
26791 @item breakpoint-hit
26792 A breakpoint was reached.
26793 @item watchpoint-trigger
26794 A watchpoint was triggered.
26795 @item read-watchpoint-trigger
26796 A read watchpoint was triggered.
26797 @item access-watchpoint-trigger
26798 An access watchpoint was triggered.
26799 @item function-finished
26800 An -exec-finish or similar CLI command was accomplished.
26801 @item location-reached
26802 An -exec-until or similar CLI command was accomplished.
26803 @item watchpoint-scope
26804 A watchpoint has gone out of scope.
26805 @item end-stepping-range
26806 An -exec-next, -exec-next-instruction, -exec-step, -exec-step-instruction or
26807 similar CLI command was accomplished.
26808 @item exited-signalled
26809 The inferior exited because of a signal.
26811 The inferior exited.
26812 @item exited-normally
26813 The inferior exited normally.
26814 @item signal-received
26815 A signal was received by the inferior.
26817 The inferior has stopped due to a library being loaded or unloaded.
26818 This can happen when @code{stop-on-solib-events} (@pxref{Files}) is
26819 set or when a @code{catch load} or @code{catch unload} catchpoint is
26820 in use (@pxref{Set Catchpoints}).
26822 The inferior has forked. This is reported when @code{catch fork}
26823 (@pxref{Set Catchpoints}) has been used.
26825 The inferior has vforked. This is reported in when @code{catch vfork}
26826 (@pxref{Set Catchpoints}) has been used.
26827 @item syscall-entry
26828 The inferior entered a system call. This is reported when @code{catch
26829 syscall} (@pxref{Set Catchpoints}) has been used.
26830 @item syscall-return
26831 The inferior returned from a system call. This is reported when
26832 @code{catch syscall} (@pxref{Set Catchpoints}) has been used.
26834 The inferior called @code{exec}. This is reported when @code{catch exec}
26835 (@pxref{Set Catchpoints}) has been used.
26838 The @var{id} field identifies the global thread ID of the thread
26839 that directly caused the stop -- for example by hitting a breakpoint.
26840 Depending on whether all-stop
26841 mode is in effect (@pxref{All-Stop Mode}), @value{GDBN} may either
26842 stop all threads, or only the thread that directly triggered the stop.
26843 If all threads are stopped, the @var{stopped} field will have the
26844 value of @code{"all"}. Otherwise, the value of the @var{stopped}
26845 field will be a list of thread identifiers. Presently, this list will
26846 always include a single thread, but frontend should be prepared to see
26847 several threads in the list. The @var{core} field reports the
26848 processor core on which the stop event has happened. This field may be absent
26849 if such information is not available.
26851 @item =thread-group-added,id="@var{id}"
26852 @itemx =thread-group-removed,id="@var{id}"
26853 A thread group was either added or removed. The @var{id} field
26854 contains the @value{GDBN} identifier of the thread group. When a thread
26855 group is added, it generally might not be associated with a running
26856 process. When a thread group is removed, its id becomes invalid and
26857 cannot be used in any way.
26859 @item =thread-group-started,id="@var{id}",pid="@var{pid}"
26860 A thread group became associated with a running program,
26861 either because the program was just started or the thread group
26862 was attached to a program. The @var{id} field contains the
26863 @value{GDBN} identifier of the thread group. The @var{pid} field
26864 contains process identifier, specific to the operating system.
26866 @item =thread-group-exited,id="@var{id}"[,exit-code="@var{code}"]
26867 A thread group is no longer associated with a running program,
26868 either because the program has exited, or because it was detached
26869 from. The @var{id} field contains the @value{GDBN} identifier of the
26870 thread group. The @var{code} field is the exit code of the inferior; it exists
26871 only when the inferior exited with some code.
26873 @item =thread-created,id="@var{id}",group-id="@var{gid}"
26874 @itemx =thread-exited,id="@var{id}",group-id="@var{gid}"
26875 A thread either was created, or has exited. The @var{id} field
26876 contains the global @value{GDBN} identifier of the thread. The @var{gid}
26877 field identifies the thread group this thread belongs to.
26879 @item =thread-selected,id="@var{id}"[,frame="@var{frame}"]
26880 Informs that the selected thread or frame were changed. This notification
26881 is not emitted as result of the @code{-thread-select} or
26882 @code{-stack-select-frame} commands, but is emitted whenever an MI command
26883 that is not documented to change the selected thread and frame actually
26884 changes them. In particular, invoking, directly or indirectly
26885 (via user-defined command), the CLI @code{thread} or @code{frame} commands,
26886 will generate this notification. Changing the thread or frame from another
26887 user interface (see @ref{Interpreters}) will also generate this notification.
26889 The @var{frame} field is only present if the newly selected thread is
26890 stopped. See @ref{GDB/MI Frame Information} for the format of its value.
26892 We suggest that in response to this notification, front ends
26893 highlight the selected thread and cause subsequent commands to apply to
26896 @item =library-loaded,...
26897 Reports that a new library file was loaded by the program. This
26898 notification has 5 fields---@var{id}, @var{target-name},
26899 @var{host-name}, @var{symbols-loaded} and @var{ranges}. The @var{id} field is an
26900 opaque identifier of the library. For remote debugging case,
26901 @var{target-name} and @var{host-name} fields give the name of the
26902 library file on the target, and on the host respectively. For native
26903 debugging, both those fields have the same value. The
26904 @var{symbols-loaded} field is emitted only for backward compatibility
26905 and should not be relied on to convey any useful information. The
26906 @var{thread-group} field, if present, specifies the id of the thread
26907 group in whose context the library was loaded. If the field is
26908 absent, it means the library was loaded in the context of all present
26909 thread groups. The @var{ranges} field specifies the ranges of addresses belonging
26912 @item =library-unloaded,...
26913 Reports that a library was unloaded by the program. This notification
26914 has 3 fields---@var{id}, @var{target-name} and @var{host-name} with
26915 the same meaning as for the @code{=library-loaded} notification.
26916 The @var{thread-group} field, if present, specifies the id of the
26917 thread group in whose context the library was unloaded. If the field is
26918 absent, it means the library was unloaded in the context of all present
26921 @item =traceframe-changed,num=@var{tfnum},tracepoint=@var{tpnum}
26922 @itemx =traceframe-changed,end
26923 Reports that the trace frame was changed and its new number is
26924 @var{tfnum}. The number of the tracepoint associated with this trace
26925 frame is @var{tpnum}.
26927 @item =tsv-created,name=@var{name},initial=@var{initial}
26928 Reports that the new trace state variable @var{name} is created with
26929 initial value @var{initial}.
26931 @item =tsv-deleted,name=@var{name}
26932 @itemx =tsv-deleted
26933 Reports that the trace state variable @var{name} is deleted or all
26934 trace state variables are deleted.
26936 @item =tsv-modified,name=@var{name},initial=@var{initial}[,current=@var{current}]
26937 Reports that the trace state variable @var{name} is modified with
26938 the initial value @var{initial}. The current value @var{current} of
26939 trace state variable is optional and is reported if the current
26940 value of trace state variable is known.
26942 @item =breakpoint-created,bkpt=@{...@}
26943 @itemx =breakpoint-modified,bkpt=@{...@}
26944 @itemx =breakpoint-deleted,id=@var{number}
26945 Reports that a breakpoint was created, modified, or deleted,
26946 respectively. Only user-visible breakpoints are reported to the MI
26949 The @var{bkpt} argument is of the same form as returned by the various
26950 breakpoint commands; @xref{GDB/MI Breakpoint Commands}. The
26951 @var{number} is the ordinal number of the breakpoint.
26953 Note that if a breakpoint is emitted in the result record of a
26954 command, then it will not also be emitted in an async record.
26956 @item =record-started,thread-group="@var{id}",method="@var{method}"[,format="@var{format}"]
26957 @itemx =record-stopped,thread-group="@var{id}"
26958 Execution log recording was either started or stopped on an
26959 inferior. The @var{id} is the @value{GDBN} identifier of the thread
26960 group corresponding to the affected inferior.
26962 The @var{method} field indicates the method used to record execution. If the
26963 method in use supports multiple recording formats, @var{format} will be present
26964 and contain the currently used format. @xref{Process Record and Replay},
26965 for existing method and format values.
26967 @item =cmd-param-changed,param=@var{param},value=@var{value}
26968 Reports that a parameter of the command @code{set @var{param}} is
26969 changed to @var{value}. In the multi-word @code{set} command,
26970 the @var{param} is the whole parameter list to @code{set} command.
26971 For example, In command @code{set check type on}, @var{param}
26972 is @code{check type} and @var{value} is @code{on}.
26974 @item =memory-changed,thread-group=@var{id},addr=@var{addr},len=@var{len}[,type="code"]
26975 Reports that bytes from @var{addr} to @var{data} + @var{len} were
26976 written in an inferior. The @var{id} is the identifier of the
26977 thread group corresponding to the affected inferior. The optional
26978 @code{type="code"} part is reported if the memory written to holds
26982 @node GDB/MI Breakpoint Information
26983 @subsection @sc{gdb/mi} Breakpoint Information
26985 When @value{GDBN} reports information about a breakpoint, a
26986 tracepoint, a watchpoint, or a catchpoint, it uses a tuple with the
26991 The breakpoint number. For a breakpoint that represents one location
26992 of a multi-location breakpoint, this will be a dotted pair, like
26996 The type of the breakpoint. For ordinary breakpoints this will be
26997 @samp{breakpoint}, but many values are possible.
27000 If the type of the breakpoint is @samp{catchpoint}, then this
27001 indicates the exact type of catchpoint.
27004 This is the breakpoint disposition---either @samp{del}, meaning that
27005 the breakpoint will be deleted at the next stop, or @samp{keep},
27006 meaning that the breakpoint will not be deleted.
27009 This indicates whether the breakpoint is enabled, in which case the
27010 value is @samp{y}, or disabled, in which case the value is @samp{n}.
27011 Note that this is not the same as the field @code{enable}.
27014 The address of the breakpoint. This may be a hexidecimal number,
27015 giving the address; or the string @samp{<PENDING>}, for a pending
27016 breakpoint; or the string @samp{<MULTIPLE>}, for a breakpoint with
27017 multiple locations. This field will not be present if no address can
27018 be determined. For example, a watchpoint does not have an address.
27021 If known, the function in which the breakpoint appears.
27022 If not known, this field is not present.
27025 The name of the source file which contains this function, if known.
27026 If not known, this field is not present.
27029 The full file name of the source file which contains this function, if
27030 known. If not known, this field is not present.
27033 The line number at which this breakpoint appears, if known.
27034 If not known, this field is not present.
27037 If the source file is not known, this field may be provided. If
27038 provided, this holds the address of the breakpoint, possibly followed
27042 If this breakpoint is pending, this field is present and holds the
27043 text used to set the breakpoint, as entered by the user.
27046 Where this breakpoint's condition is evaluated, either @samp{host} or
27050 If this is a thread-specific breakpoint, then this identifies the
27051 thread in which the breakpoint can trigger.
27054 If this breakpoint is restricted to a particular Ada task, then this
27055 field will hold the task identifier.
27058 If the breakpoint is conditional, this is the condition expression.
27061 The ignore count of the breakpoint.
27064 The enable count of the breakpoint.
27066 @item traceframe-usage
27069 @item static-tracepoint-marker-string-id
27070 For a static tracepoint, the name of the static tracepoint marker.
27073 For a masked watchpoint, this is the mask.
27076 A tracepoint's pass count.
27078 @item original-location
27079 The location of the breakpoint as originally specified by the user.
27080 This field is optional.
27083 The number of times the breakpoint has been hit.
27086 This field is only given for tracepoints. This is either @samp{y},
27087 meaning that the tracepoint is installed, or @samp{n}, meaning that it
27091 Some extra data, the exact contents of which are type-dependent.
27095 For example, here is what the output of @code{-break-insert}
27096 (@pxref{GDB/MI Breakpoint Commands}) might be:
27099 -> -break-insert main
27100 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
27101 enabled="y",addr="0x08048564",func="main",file="myprog.c",
27102 fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"],
27107 @node GDB/MI Frame Information
27108 @subsection @sc{gdb/mi} Frame Information
27110 Response from many MI commands includes an information about stack
27111 frame. This information is a tuple that may have the following
27116 The level of the stack frame. The innermost frame has the level of
27117 zero. This field is always present.
27120 The name of the function corresponding to the frame. This field may
27121 be absent if @value{GDBN} is unable to determine the function name.
27124 The code address for the frame. This field is always present.
27127 The name of the source files that correspond to the frame's code
27128 address. This field may be absent.
27131 The source line corresponding to the frames' code address. This field
27135 The name of the binary file (either executable or shared library) the
27136 corresponds to the frame's code address. This field may be absent.
27140 @node GDB/MI Thread Information
27141 @subsection @sc{gdb/mi} Thread Information
27143 Whenever @value{GDBN} has to report an information about a thread, it
27144 uses a tuple with the following fields. The fields are always present unless
27149 The global numeric id assigned to the thread by @value{GDBN}.
27152 The target-specific string identifying the thread.
27155 Additional information about the thread provided by the target.
27156 It is supposed to be human-readable and not interpreted by the
27157 frontend. This field is optional.
27160 The name of the thread. If the user specified a name using the
27161 @code{thread name} command, then this name is given. Otherwise, if
27162 @value{GDBN} can extract the thread name from the target, then that
27163 name is given. If @value{GDBN} cannot find the thread name, then this
27167 The execution state of the thread, either @samp{stopped} or @samp{running},
27168 depending on whether the thread is presently running.
27171 The stack frame currently executing in the thread. This field is only present
27172 if the thread is stopped. Its format is documented in
27173 @ref{GDB/MI Frame Information}.
27176 The value of this field is an integer number of the processor core the
27177 thread was last seen on. This field is optional.
27180 @node GDB/MI Ada Exception Information
27181 @subsection @sc{gdb/mi} Ada Exception Information
27183 Whenever a @code{*stopped} record is emitted because the program
27184 stopped after hitting an exception catchpoint (@pxref{Set Catchpoints}),
27185 @value{GDBN} provides the name of the exception that was raised via
27186 the @code{exception-name} field.
27188 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27189 @node GDB/MI Simple Examples
27190 @section Simple Examples of @sc{gdb/mi} Interaction
27191 @cindex @sc{gdb/mi}, simple examples
27193 This subsection presents several simple examples of interaction using
27194 the @sc{gdb/mi} interface. In these examples, @samp{->} means that the
27195 following line is passed to @sc{gdb/mi} as input, while @samp{<-} means
27196 the output received from @sc{gdb/mi}.
27198 Note the line breaks shown in the examples are here only for
27199 readability, they don't appear in the real output.
27201 @subheading Setting a Breakpoint
27203 Setting a breakpoint generates synchronous output which contains detailed
27204 information of the breakpoint.
27207 -> -break-insert main
27208 <- ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
27209 enabled="y",addr="0x08048564",func="main",file="myprog.c",
27210 fullname="/home/nickrob/myprog.c",line="68",thread-groups=["i1"],
27215 @subheading Program Execution
27217 Program execution generates asynchronous records and MI gives the
27218 reason that execution stopped.
27224 <- *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
27225 frame=@{addr="0x08048564",func="main",
27226 args=[@{name="argc",value="1"@},@{name="argv",value="0xbfc4d4d4"@}],
27227 file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"@}
27232 <- *stopped,reason="exited-normally"
27236 @subheading Quitting @value{GDBN}
27238 Quitting @value{GDBN} just prints the result class @samp{^exit}.
27246 Please note that @samp{^exit} is printed immediately, but it might
27247 take some time for @value{GDBN} to actually exit. During that time, @value{GDBN}
27248 performs necessary cleanups, including killing programs being debugged
27249 or disconnecting from debug hardware, so the frontend should wait till
27250 @value{GDBN} exits and should only forcibly kill @value{GDBN} if it
27251 fails to exit in reasonable time.
27253 @subheading A Bad Command
27255 Here's what happens if you pass a non-existent command:
27259 <- ^error,msg="Undefined MI command: rubbish"
27264 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27265 @node GDB/MI Command Description Format
27266 @section @sc{gdb/mi} Command Description Format
27268 The remaining sections describe blocks of commands. Each block of
27269 commands is laid out in a fashion similar to this section.
27271 @subheading Motivation
27273 The motivation for this collection of commands.
27275 @subheading Introduction
27277 A brief introduction to this collection of commands as a whole.
27279 @subheading Commands
27281 For each command in the block, the following is described:
27283 @subsubheading Synopsis
27286 -command @var{args}@dots{}
27289 @subsubheading Result
27291 @subsubheading @value{GDBN} Command
27293 The corresponding @value{GDBN} CLI command(s), if any.
27295 @subsubheading Example
27297 Example(s) formatted for readability. Some of the described commands have
27298 not been implemented yet and these are labeled N.A.@: (not available).
27301 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27302 @node GDB/MI Breakpoint Commands
27303 @section @sc{gdb/mi} Breakpoint Commands
27305 @cindex breakpoint commands for @sc{gdb/mi}
27306 @cindex @sc{gdb/mi}, breakpoint commands
27307 This section documents @sc{gdb/mi} commands for manipulating
27310 @subheading The @code{-break-after} Command
27311 @findex -break-after
27313 @subsubheading Synopsis
27316 -break-after @var{number} @var{count}
27319 The breakpoint number @var{number} is not in effect until it has been
27320 hit @var{count} times. To see how this is reflected in the output of
27321 the @samp{-break-list} command, see the description of the
27322 @samp{-break-list} command below.
27324 @subsubheading @value{GDBN} Command
27326 The corresponding @value{GDBN} command is @samp{ignore}.
27328 @subsubheading Example
27333 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
27334 enabled="y",addr="0x000100d0",func="main",file="hello.c",
27335 fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],
27343 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
27344 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27345 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27346 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27347 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27348 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27349 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27350 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27351 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
27352 line="5",thread-groups=["i1"],times="0",ignore="3"@}]@}
27357 @subheading The @code{-break-catch} Command
27358 @findex -break-catch
27361 @subheading The @code{-break-commands} Command
27362 @findex -break-commands
27364 @subsubheading Synopsis
27367 -break-commands @var{number} [ @var{command1} ... @var{commandN} ]
27370 Specifies the CLI commands that should be executed when breakpoint
27371 @var{number} is hit. The parameters @var{command1} to @var{commandN}
27372 are the commands. If no command is specified, any previously-set
27373 commands are cleared. @xref{Break Commands}. Typical use of this
27374 functionality is tracing a program, that is, printing of values of
27375 some variables whenever breakpoint is hit and then continuing.
27377 @subsubheading @value{GDBN} Command
27379 The corresponding @value{GDBN} command is @samp{commands}.
27381 @subsubheading Example
27386 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",
27387 enabled="y",addr="0x000100d0",func="main",file="hello.c",
27388 fullname="/home/foo/hello.c",line="5",thread-groups=["i1"],
27391 -break-commands 1 "print v" "continue"
27396 @subheading The @code{-break-condition} Command
27397 @findex -break-condition
27399 @subsubheading Synopsis
27402 -break-condition @var{number} @var{expr}
27405 Breakpoint @var{number} will stop the program only if the condition in
27406 @var{expr} is true. The condition becomes part of the
27407 @samp{-break-list} output (see the description of the @samp{-break-list}
27410 @subsubheading @value{GDBN} Command
27412 The corresponding @value{GDBN} command is @samp{condition}.
27414 @subsubheading Example
27418 -break-condition 1 1
27422 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
27423 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27424 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27425 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27426 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27427 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27428 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27429 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27430 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
27431 line="5",cond="1",thread-groups=["i1"],times="0",ignore="3"@}]@}
27435 @subheading The @code{-break-delete} Command
27436 @findex -break-delete
27438 @subsubheading Synopsis
27441 -break-delete ( @var{breakpoint} )+
27444 Delete the breakpoint(s) whose number(s) are specified in the argument
27445 list. This is obviously reflected in the breakpoint list.
27447 @subsubheading @value{GDBN} Command
27449 The corresponding @value{GDBN} command is @samp{delete}.
27451 @subsubheading Example
27459 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
27460 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27461 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27462 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27463 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27464 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27465 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27470 @subheading The @code{-break-disable} Command
27471 @findex -break-disable
27473 @subsubheading Synopsis
27476 -break-disable ( @var{breakpoint} )+
27479 Disable the named @var{breakpoint}(s). The field @samp{enabled} in the
27480 break list is now set to @samp{n} for the named @var{breakpoint}(s).
27482 @subsubheading @value{GDBN} Command
27484 The corresponding @value{GDBN} command is @samp{disable}.
27486 @subsubheading Example
27494 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
27495 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27496 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27497 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27498 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27499 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27500 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27501 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="n",
27502 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
27503 line="5",thread-groups=["i1"],times="0"@}]@}
27507 @subheading The @code{-break-enable} Command
27508 @findex -break-enable
27510 @subsubheading Synopsis
27513 -break-enable ( @var{breakpoint} )+
27516 Enable (previously disabled) @var{breakpoint}(s).
27518 @subsubheading @value{GDBN} Command
27520 The corresponding @value{GDBN} command is @samp{enable}.
27522 @subsubheading Example
27530 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
27531 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27532 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27533 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27534 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27535 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27536 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27537 body=[bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
27538 addr="0x000100d0",func="main",file="hello.c",fullname="/home/foo/hello.c",
27539 line="5",thread-groups=["i1"],times="0"@}]@}
27543 @subheading The @code{-break-info} Command
27544 @findex -break-info
27546 @subsubheading Synopsis
27549 -break-info @var{breakpoint}
27553 Get information about a single breakpoint.
27555 The result is a table of breakpoints. @xref{GDB/MI Breakpoint
27556 Information}, for details on the format of each breakpoint in the
27559 @subsubheading @value{GDBN} Command
27561 The corresponding @value{GDBN} command is @samp{info break @var{breakpoint}}.
27563 @subsubheading Example
27566 @subheading The @code{-break-insert} Command
27567 @findex -break-insert
27568 @anchor{-break-insert}
27570 @subsubheading Synopsis
27573 -break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ]
27574 [ -c @var{condition} ] [ -i @var{ignore-count} ]
27575 [ -p @var{thread-id} ] [ @var{location} ]
27579 If specified, @var{location}, can be one of:
27582 @item linespec location
27583 A linespec location. @xref{Linespec Locations}.
27585 @item explicit location
27586 An explicit location. @sc{gdb/mi} explicit locations are
27587 analogous to the CLI's explicit locations using the option names
27588 listed below. @xref{Explicit Locations}.
27591 @item --source @var{filename}
27592 The source file name of the location. This option requires the use
27593 of either @samp{--function} or @samp{--line}.
27595 @item --function @var{function}
27596 The name of a function or method.
27598 @item --label @var{label}
27599 The name of a label.
27601 @item --line @var{lineoffset}
27602 An absolute or relative line offset from the start of the location.
27605 @item address location
27606 An address location, *@var{address}. @xref{Address Locations}.
27610 The possible optional parameters of this command are:
27614 Insert a temporary breakpoint.
27616 Insert a hardware breakpoint.
27618 If @var{location} cannot be parsed (for example if it
27619 refers to unknown files or functions), create a pending
27620 breakpoint. Without this flag, @value{GDBN} will report
27621 an error, and won't create a breakpoint, if @var{location}
27624 Create a disabled breakpoint.
27626 Create a tracepoint. @xref{Tracepoints}. When this parameter
27627 is used together with @samp{-h}, a fast tracepoint is created.
27628 @item -c @var{condition}
27629 Make the breakpoint conditional on @var{condition}.
27630 @item -i @var{ignore-count}
27631 Initialize the @var{ignore-count}.
27632 @item -p @var{thread-id}
27633 Restrict the breakpoint to the thread with the specified global
27637 @subsubheading Result
27639 @xref{GDB/MI Breakpoint Information}, for details on the format of the
27640 resulting breakpoint.
27642 Note: this format is open to change.
27643 @c An out-of-band breakpoint instead of part of the result?
27645 @subsubheading @value{GDBN} Command
27647 The corresponding @value{GDBN} commands are @samp{break}, @samp{tbreak},
27648 @samp{hbreak}, and @samp{thbreak}. @c and @samp{rbreak}.
27650 @subsubheading Example
27655 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",
27656 fullname="/home/foo/recursive2.c,line="4",thread-groups=["i1"],
27659 -break-insert -t foo
27660 ^done,bkpt=@{number="2",addr="0x00010774",file="recursive2.c",
27661 fullname="/home/foo/recursive2.c,line="11",thread-groups=["i1"],
27665 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27666 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27667 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27668 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27669 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27670 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27671 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27672 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27673 addr="0x0001072c", func="main",file="recursive2.c",
27674 fullname="/home/foo/recursive2.c,"line="4",thread-groups=["i1"],
27676 bkpt=@{number="2",type="breakpoint",disp="del",enabled="y",
27677 addr="0x00010774",func="foo",file="recursive2.c",
27678 fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"],
27681 @c -break-insert -r foo.*
27682 @c ~int foo(int, int);
27683 @c ^done,bkpt=@{number="3",addr="0x00010774",file="recursive2.c,
27684 @c "fullname="/home/foo/recursive2.c",line="11",thread-groups=["i1"],
27689 @subheading The @code{-dprintf-insert} Command
27690 @findex -dprintf-insert
27692 @subsubheading Synopsis
27695 -dprintf-insert [ -t ] [ -f ] [ -d ]
27696 [ -c @var{condition} ] [ -i @var{ignore-count} ]
27697 [ -p @var{thread-id} ] [ @var{location} ] [ @var{format} ]
27702 If supplied, @var{location} may be specified the same way as for
27703 the @code{-break-insert} command. @xref{-break-insert}.
27705 The possible optional parameters of this command are:
27709 Insert a temporary breakpoint.
27711 If @var{location} cannot be parsed (for example, if it
27712 refers to unknown files or functions), create a pending
27713 breakpoint. Without this flag, @value{GDBN} will report
27714 an error, and won't create a breakpoint, if @var{location}
27717 Create a disabled breakpoint.
27718 @item -c @var{condition}
27719 Make the breakpoint conditional on @var{condition}.
27720 @item -i @var{ignore-count}
27721 Set the ignore count of the breakpoint (@pxref{Conditions, ignore count})
27722 to @var{ignore-count}.
27723 @item -p @var{thread-id}
27724 Restrict the breakpoint to the thread with the specified global
27728 @subsubheading Result
27730 @xref{GDB/MI Breakpoint Information}, for details on the format of the
27731 resulting breakpoint.
27733 @c An out-of-band breakpoint instead of part of the result?
27735 @subsubheading @value{GDBN} Command
27737 The corresponding @value{GDBN} command is @samp{dprintf}.
27739 @subsubheading Example
27743 4-dprintf-insert foo "At foo entry\n"
27744 4^done,bkpt=@{number="1",type="dprintf",disp="keep",enabled="y",
27745 addr="0x000000000040061b",func="foo",file="mi-dprintf.c",
27746 fullname="mi-dprintf.c",line="25",thread-groups=["i1"],
27747 times="0",script=@{"printf \"At foo entry\\n\"","continue"@},
27748 original-location="foo"@}
27750 5-dprintf-insert 26 "arg=%d, g=%d\n" arg g
27751 5^done,bkpt=@{number="2",type="dprintf",disp="keep",enabled="y",
27752 addr="0x000000000040062a",func="foo",file="mi-dprintf.c",
27753 fullname="mi-dprintf.c",line="26",thread-groups=["i1"],
27754 times="0",script=@{"printf \"arg=%d, g=%d\\n\", arg, g","continue"@},
27755 original-location="mi-dprintf.c:26"@}
27759 @subheading The @code{-break-list} Command
27760 @findex -break-list
27762 @subsubheading Synopsis
27768 Displays the list of inserted breakpoints, showing the following fields:
27772 number of the breakpoint
27774 type of the breakpoint: @samp{breakpoint} or @samp{watchpoint}
27776 should the breakpoint be deleted or disabled when it is hit: @samp{keep}
27779 is the breakpoint enabled or no: @samp{y} or @samp{n}
27781 memory location at which the breakpoint is set
27783 logical location of the breakpoint, expressed by function name, file
27785 @item Thread-groups
27786 list of thread groups to which this breakpoint applies
27788 number of times the breakpoint has been hit
27791 If there are no breakpoints or watchpoints, the @code{BreakpointTable}
27792 @code{body} field is an empty list.
27794 @subsubheading @value{GDBN} Command
27796 The corresponding @value{GDBN} command is @samp{info break}.
27798 @subsubheading Example
27803 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27804 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27805 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27806 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27807 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27808 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27809 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27810 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27811 addr="0x000100d0",func="main",file="hello.c",line="5",thread-groups=["i1"],
27813 bkpt=@{number="2",type="breakpoint",disp="keep",enabled="y",
27814 addr="0x00010114",func="foo",file="hello.c",fullname="/home/foo/hello.c",
27815 line="13",thread-groups=["i1"],times="0"@}]@}
27819 Here's an example of the result when there are no breakpoints:
27824 ^done,BreakpointTable=@{nr_rows="0",nr_cols="6",
27825 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27826 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27827 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27828 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27829 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27830 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27835 @subheading The @code{-break-passcount} Command
27836 @findex -break-passcount
27838 @subsubheading Synopsis
27841 -break-passcount @var{tracepoint-number} @var{passcount}
27844 Set the passcount for tracepoint @var{tracepoint-number} to
27845 @var{passcount}. If the breakpoint referred to by @var{tracepoint-number}
27846 is not a tracepoint, error is emitted. This corresponds to CLI
27847 command @samp{passcount}.
27849 @subheading The @code{-break-watch} Command
27850 @findex -break-watch
27852 @subsubheading Synopsis
27855 -break-watch [ -a | -r ]
27858 Create a watchpoint. With the @samp{-a} option it will create an
27859 @dfn{access} watchpoint, i.e., a watchpoint that triggers either on a
27860 read from or on a write to the memory location. With the @samp{-r}
27861 option, the watchpoint created is a @dfn{read} watchpoint, i.e., it will
27862 trigger only when the memory location is accessed for reading. Without
27863 either of the options, the watchpoint created is a regular watchpoint,
27864 i.e., it will trigger when the memory location is accessed for writing.
27865 @xref{Set Watchpoints, , Setting Watchpoints}.
27867 Note that @samp{-break-list} will report a single list of watchpoints and
27868 breakpoints inserted.
27870 @subsubheading @value{GDBN} Command
27872 The corresponding @value{GDBN} commands are @samp{watch}, @samp{awatch}, and
27875 @subsubheading Example
27877 Setting a watchpoint on a variable in the @code{main} function:
27882 ^done,wpt=@{number="2",exp="x"@}
27887 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="x"@},
27888 value=@{old="-268439212",new="55"@},
27889 frame=@{func="main",args=[],file="recursive2.c",
27890 fullname="/home/foo/bar/recursive2.c",line="5"@}
27894 Setting a watchpoint on a variable local to a function. @value{GDBN} will stop
27895 the program execution twice: first for the variable changing value, then
27896 for the watchpoint going out of scope.
27901 ^done,wpt=@{number="5",exp="C"@}
27906 *stopped,reason="watchpoint-trigger",
27907 wpt=@{number="5",exp="C"@},value=@{old="-276895068",new="3"@},
27908 frame=@{func="callee4",args=[],
27909 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27910 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
27915 *stopped,reason="watchpoint-scope",wpnum="5",
27916 frame=@{func="callee3",args=[@{name="strarg",
27917 value="0x11940 \"A string argument.\""@}],
27918 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27919 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
27923 Listing breakpoints and watchpoints, at different points in the program
27924 execution. Note that once the watchpoint goes out of scope, it is
27930 ^done,wpt=@{number="2",exp="C"@}
27933 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27934 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27935 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27936 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27937 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27938 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27939 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27940 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27941 addr="0x00010734",func="callee4",
27942 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27943 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",thread-groups=["i1"],
27945 bkpt=@{number="2",type="watchpoint",disp="keep",
27946 enabled="y",addr="",what="C",thread-groups=["i1"],times="0"@}]@}
27951 *stopped,reason="watchpoint-trigger",wpt=@{number="2",exp="C"@},
27952 value=@{old="-276895068",new="3"@},
27953 frame=@{func="callee4",args=[],
27954 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27955 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"@}
27958 ^done,BreakpointTable=@{nr_rows="2",nr_cols="6",
27959 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27960 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27961 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27962 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27963 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27964 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27965 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27966 addr="0x00010734",func="callee4",
27967 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27968 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",thread-groups=["i1"],
27970 bkpt=@{number="2",type="watchpoint",disp="keep",
27971 enabled="y",addr="",what="C",thread-groups=["i1"],times="-5"@}]@}
27975 ^done,reason="watchpoint-scope",wpnum="2",
27976 frame=@{func="callee3",args=[@{name="strarg",
27977 value="0x11940 \"A string argument.\""@}],
27978 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27979 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
27982 ^done,BreakpointTable=@{nr_rows="1",nr_cols="6",
27983 hdr=[@{width="3",alignment="-1",col_name="number",colhdr="Num"@},
27984 @{width="14",alignment="-1",col_name="type",colhdr="Type"@},
27985 @{width="4",alignment="-1",col_name="disp",colhdr="Disp"@},
27986 @{width="3",alignment="-1",col_name="enabled",colhdr="Enb"@},
27987 @{width="10",alignment="-1",col_name="addr",colhdr="Address"@},
27988 @{width="40",alignment="2",col_name="what",colhdr="What"@}],
27989 body=[bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
27990 addr="0x00010734",func="callee4",
27991 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
27992 fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
27993 thread-groups=["i1"],times="1"@}]@}
27998 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
27999 @node GDB/MI Catchpoint Commands
28000 @section @sc{gdb/mi} Catchpoint Commands
28002 This section documents @sc{gdb/mi} commands for manipulating
28006 * Shared Library GDB/MI Catchpoint Commands::
28007 * Ada Exception GDB/MI Catchpoint Commands::
28010 @node Shared Library GDB/MI Catchpoint Commands
28011 @subsection Shared Library @sc{gdb/mi} Catchpoints
28013 @subheading The @code{-catch-load} Command
28014 @findex -catch-load
28016 @subsubheading Synopsis
28019 -catch-load [ -t ] [ -d ] @var{regexp}
28022 Add a catchpoint for library load events. If the @samp{-t} option is used,
28023 the catchpoint is a temporary one (@pxref{Set Breaks, ,Setting
28024 Breakpoints}). If the @samp{-d} option is used, the catchpoint is created
28025 in a disabled state. The @samp{regexp} argument is a regular
28026 expression used to match the name of the loaded library.
28029 @subsubheading @value{GDBN} Command
28031 The corresponding @value{GDBN} command is @samp{catch load}.
28033 @subsubheading Example
28036 -catch-load -t foo.so
28037 ^done,bkpt=@{number="1",type="catchpoint",disp="del",enabled="y",
28038 what="load of library matching foo.so",catch-type="load",times="0"@}
28043 @subheading The @code{-catch-unload} Command
28044 @findex -catch-unload
28046 @subsubheading Synopsis
28049 -catch-unload [ -t ] [ -d ] @var{regexp}
28052 Add a catchpoint for library unload events. If the @samp{-t} option is
28053 used, the catchpoint is a temporary one (@pxref{Set Breaks, ,Setting
28054 Breakpoints}). If the @samp{-d} option is used, the catchpoint is
28055 created in a disabled state. The @samp{regexp} argument is a regular
28056 expression used to match the name of the unloaded library.
28058 @subsubheading @value{GDBN} Command
28060 The corresponding @value{GDBN} command is @samp{catch unload}.
28062 @subsubheading Example
28065 -catch-unload -d bar.so
28066 ^done,bkpt=@{number="2",type="catchpoint",disp="keep",enabled="n",
28067 what="load of library matching bar.so",catch-type="unload",times="0"@}
28071 @node Ada Exception GDB/MI Catchpoint Commands
28072 @subsection Ada Exception @sc{gdb/mi} Catchpoints
28074 The following @sc{gdb/mi} commands can be used to create catchpoints
28075 that stop the execution when Ada exceptions are being raised.
28077 @subheading The @code{-catch-assert} Command
28078 @findex -catch-assert
28080 @subsubheading Synopsis
28083 -catch-assert [ -c @var{condition}] [ -d ] [ -t ]
28086 Add a catchpoint for failed Ada assertions.
28088 The possible optional parameters for this command are:
28091 @item -c @var{condition}
28092 Make the catchpoint conditional on @var{condition}.
28094 Create a disabled catchpoint.
28096 Create a temporary catchpoint.
28099 @subsubheading @value{GDBN} Command
28101 The corresponding @value{GDBN} command is @samp{catch assert}.
28103 @subsubheading Example
28107 ^done,bkptno="5",bkpt=@{number="5",type="breakpoint",disp="keep",
28108 enabled="y",addr="0x0000000000404888",what="failed Ada assertions",
28109 thread-groups=["i1"],times="0",
28110 original-location="__gnat_debug_raise_assert_failure"@}
28114 @subheading The @code{-catch-exception} Command
28115 @findex -catch-exception
28117 @subsubheading Synopsis
28120 -catch-exception [ -c @var{condition}] [ -d ] [ -e @var{exception-name} ]
28124 Add a catchpoint stopping when Ada exceptions are raised.
28125 By default, the command stops the program when any Ada exception
28126 gets raised. But it is also possible, by using some of the
28127 optional parameters described below, to create more selective
28130 The possible optional parameters for this command are:
28133 @item -c @var{condition}
28134 Make the catchpoint conditional on @var{condition}.
28136 Create a disabled catchpoint.
28137 @item -e @var{exception-name}
28138 Only stop when @var{exception-name} is raised. This option cannot
28139 be used combined with @samp{-u}.
28141 Create a temporary catchpoint.
28143 Stop only when an unhandled exception gets raised. This option
28144 cannot be used combined with @samp{-e}.
28147 @subsubheading @value{GDBN} Command
28149 The corresponding @value{GDBN} commands are @samp{catch exception}
28150 and @samp{catch exception unhandled}.
28152 @subsubheading Example
28155 -catch-exception -e Program_Error
28156 ^done,bkptno="4",bkpt=@{number="4",type="breakpoint",disp="keep",
28157 enabled="y",addr="0x0000000000404874",
28158 what="`Program_Error' Ada exception", thread-groups=["i1"],
28159 times="0",original-location="__gnat_debug_raise_exception"@}
28163 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28164 @node GDB/MI Program Context
28165 @section @sc{gdb/mi} Program Context
28167 @subheading The @code{-exec-arguments} Command
28168 @findex -exec-arguments
28171 @subsubheading Synopsis
28174 -exec-arguments @var{args}
28177 Set the inferior program arguments, to be used in the next
28180 @subsubheading @value{GDBN} Command
28182 The corresponding @value{GDBN} command is @samp{set args}.
28184 @subsubheading Example
28188 -exec-arguments -v word
28195 @subheading The @code{-exec-show-arguments} Command
28196 @findex -exec-show-arguments
28198 @subsubheading Synopsis
28201 -exec-show-arguments
28204 Print the arguments of the program.
28206 @subsubheading @value{GDBN} Command
28208 The corresponding @value{GDBN} command is @samp{show args}.
28210 @subsubheading Example
28215 @subheading The @code{-environment-cd} Command
28216 @findex -environment-cd
28218 @subsubheading Synopsis
28221 -environment-cd @var{pathdir}
28224 Set @value{GDBN}'s working directory.
28226 @subsubheading @value{GDBN} Command
28228 The corresponding @value{GDBN} command is @samp{cd}.
28230 @subsubheading Example
28234 -environment-cd /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
28240 @subheading The @code{-environment-directory} Command
28241 @findex -environment-directory
28243 @subsubheading Synopsis
28246 -environment-directory [ -r ] [ @var{pathdir} ]+
28249 Add directories @var{pathdir} to beginning of search path for source files.
28250 If the @samp{-r} option is used, the search path is reset to the default
28251 search path. If directories @var{pathdir} are supplied in addition to the
28252 @samp{-r} option, the search path is first reset and then addition
28254 Multiple directories may be specified, separated by blanks. Specifying
28255 multiple directories in a single command
28256 results in the directories added to the beginning of the
28257 search path in the same order they were presented in the command.
28258 If blanks are needed as
28259 part of a directory name, double-quotes should be used around
28260 the name. In the command output, the path will show up separated
28261 by the system directory-separator character. The directory-separator
28262 character must not be used
28263 in any directory name.
28264 If no directories are specified, the current search path is displayed.
28266 @subsubheading @value{GDBN} Command
28268 The corresponding @value{GDBN} command is @samp{dir}.
28270 @subsubheading Example
28274 -environment-directory /kwikemart/marge/ezannoni/flathead-dev/devo/gdb
28275 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
28277 -environment-directory ""
28278 ^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
28280 -environment-directory -r /home/jjohnstn/src/gdb /usr/src
28281 ^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
28283 -environment-directory -r
28284 ^done,source-path="$cdir:$cwd"
28289 @subheading The @code{-environment-path} Command
28290 @findex -environment-path
28292 @subsubheading Synopsis
28295 -environment-path [ -r ] [ @var{pathdir} ]+
28298 Add directories @var{pathdir} to beginning of search path for object files.
28299 If the @samp{-r} option is used, the search path is reset to the original
28300 search path that existed at gdb start-up. If directories @var{pathdir} are
28301 supplied in addition to the
28302 @samp{-r} option, the search path is first reset and then addition
28304 Multiple directories may be specified, separated by blanks. Specifying
28305 multiple directories in a single command
28306 results in the directories added to the beginning of the
28307 search path in the same order they were presented in the command.
28308 If blanks are needed as
28309 part of a directory name, double-quotes should be used around
28310 the name. In the command output, the path will show up separated
28311 by the system directory-separator character. The directory-separator
28312 character must not be used
28313 in any directory name.
28314 If no directories are specified, the current path is displayed.
28317 @subsubheading @value{GDBN} Command
28319 The corresponding @value{GDBN} command is @samp{path}.
28321 @subsubheading Example
28326 ^done,path="/usr/bin"
28328 -environment-path /kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb /bin
28329 ^done,path="/kwikemart/marge/ezannoni/flathead-dev/ppc-eabi/gdb:/bin:/usr/bin"
28331 -environment-path -r /usr/local/bin
28332 ^done,path="/usr/local/bin:/usr/bin"
28337 @subheading The @code{-environment-pwd} Command
28338 @findex -environment-pwd
28340 @subsubheading Synopsis
28346 Show the current working directory.
28348 @subsubheading @value{GDBN} Command
28350 The corresponding @value{GDBN} command is @samp{pwd}.
28352 @subsubheading Example
28357 ^done,cwd="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb"
28361 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28362 @node GDB/MI Thread Commands
28363 @section @sc{gdb/mi} Thread Commands
28366 @subheading The @code{-thread-info} Command
28367 @findex -thread-info
28369 @subsubheading Synopsis
28372 -thread-info [ @var{thread-id} ]
28375 Reports information about either a specific thread, if the
28376 @var{thread-id} parameter is present, or about all threads.
28377 @var{thread-id} is the thread's global thread ID. When printing
28378 information about all threads, also reports the global ID of the
28381 @subsubheading @value{GDBN} Command
28383 The @samp{info thread} command prints the same information
28386 @subsubheading Result
28388 The result contains the following attributes:
28392 A list of threads. The format of the elements of the list is described in
28393 @ref{GDB/MI Thread Information}.
28395 @item current-thread-id
28396 The global id of the currently selected thread. This field is omitted if there
28397 is no selected thread (for example, when the selected inferior is not running,
28398 and therefore has no threads) or if a @var{thread-id} argument was passed to
28403 @subsubheading Example
28408 @{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
28409 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",
28410 args=[]@},state="running"@},
28411 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
28412 frame=@{level="0",addr="0x0804891f",func="foo",
28413 args=[@{name="i",value="10"@}],
28414 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},
28415 state="running"@}],
28416 current-thread-id="1"
28420 @subheading The @code{-thread-list-ids} Command
28421 @findex -thread-list-ids
28423 @subsubheading Synopsis
28429 Produces a list of the currently known global @value{GDBN} thread ids.
28430 At the end of the list it also prints the total number of such
28433 This command is retained for historical reasons, the
28434 @code{-thread-info} command should be used instead.
28436 @subsubheading @value{GDBN} Command
28438 Part of @samp{info threads} supplies the same information.
28440 @subsubheading Example
28445 ^done,thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
28446 current-thread-id="1",number-of-threads="3"
28451 @subheading The @code{-thread-select} Command
28452 @findex -thread-select
28454 @subsubheading Synopsis
28457 -thread-select @var{thread-id}
28460 Make thread with global thread number @var{thread-id} the current
28461 thread. It prints the number of the new current thread, and the
28462 topmost frame for that thread.
28464 This command is deprecated in favor of explicitly using the
28465 @samp{--thread} option to each command.
28467 @subsubheading @value{GDBN} Command
28469 The corresponding @value{GDBN} command is @samp{thread}.
28471 @subsubheading Example
28478 *stopped,reason="end-stepping-range",thread-id="2",line="187",
28479 file="../../../devo/gdb/testsuite/gdb.threads/linux-dp.c"
28483 thread-ids=@{thread-id="3",thread-id="2",thread-id="1"@},
28484 number-of-threads="3"
28487 ^done,new-thread-id="3",
28488 frame=@{level="0",func="vprintf",
28489 args=[@{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""@},
28490 @{name="arg",value="0x2"@}],file="vprintf.c",line="31"@}
28494 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28495 @node GDB/MI Ada Tasking Commands
28496 @section @sc{gdb/mi} Ada Tasking Commands
28498 @subheading The @code{-ada-task-info} Command
28499 @findex -ada-task-info
28501 @subsubheading Synopsis
28504 -ada-task-info [ @var{task-id} ]
28507 Reports information about either a specific Ada task, if the
28508 @var{task-id} parameter is present, or about all Ada tasks.
28510 @subsubheading @value{GDBN} Command
28512 The @samp{info tasks} command prints the same information
28513 about all Ada tasks (@pxref{Ada Tasks}).
28515 @subsubheading Result
28517 The result is a table of Ada tasks. The following columns are
28518 defined for each Ada task:
28522 This field exists only for the current thread. It has the value @samp{*}.
28525 The identifier that @value{GDBN} uses to refer to the Ada task.
28528 The identifier that the target uses to refer to the Ada task.
28531 The global thread identifier of the thread corresponding to the Ada
28534 This field should always exist, as Ada tasks are always implemented
28535 on top of a thread. But if @value{GDBN} cannot find this corresponding
28536 thread for any reason, the field is omitted.
28539 This field exists only when the task was created by another task.
28540 In this case, it provides the ID of the parent task.
28543 The base priority of the task.
28546 The current state of the task. For a detailed description of the
28547 possible states, see @ref{Ada Tasks}.
28550 The name of the task.
28554 @subsubheading Example
28558 ^done,tasks=@{nr_rows="3",nr_cols="8",
28559 hdr=[@{width="1",alignment="-1",col_name="current",colhdr=""@},
28560 @{width="3",alignment="1",col_name="id",colhdr="ID"@},
28561 @{width="9",alignment="1",col_name="task-id",colhdr="TID"@},
28562 @{width="4",alignment="1",col_name="thread-id",colhdr=""@},
28563 @{width="4",alignment="1",col_name="parent-id",colhdr="P-ID"@},
28564 @{width="3",alignment="1",col_name="priority",colhdr="Pri"@},
28565 @{width="22",alignment="-1",col_name="state",colhdr="State"@},
28566 @{width="1",alignment="2",col_name="name",colhdr="Name"@}],
28567 body=[@{current="*",id="1",task-id=" 644010",thread-id="1",priority="48",
28568 state="Child Termination Wait",name="main_task"@}]@}
28572 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
28573 @node GDB/MI Program Execution
28574 @section @sc{gdb/mi} Program Execution
28576 These are the asynchronous commands which generate the out-of-band
28577 record @samp{*stopped}. Currently @value{GDBN} only really executes
28578 asynchronously with remote targets and this interaction is mimicked in
28581 @subheading The @code{-exec-continue} Command
28582 @findex -exec-continue
28584 @subsubheading Synopsis
28587 -exec-continue [--reverse] [--all|--thread-group N]
28590 Resumes the execution of the inferior program, which will continue
28591 to execute until it reaches a debugger stop event. If the
28592 @samp{--reverse} option is specified, execution resumes in reverse until
28593 it reaches a stop event. Stop events may include
28596 breakpoints or watchpoints
28598 signals or exceptions
28600 the end of the process (or its beginning under @samp{--reverse})
28602 the end or beginning of a replay log if one is being used.
28604 In all-stop mode (@pxref{All-Stop
28605 Mode}), may resume only one thread, or all threads, depending on the
28606 value of the @samp{scheduler-locking} variable. If @samp{--all} is
28607 specified, all threads (in all inferiors) will be resumed. The @samp{--all} option is
28608 ignored in all-stop mode. If the @samp{--thread-group} options is
28609 specified, then all threads in that thread group are resumed.
28611 @subsubheading @value{GDBN} Command
28613 The corresponding @value{GDBN} corresponding is @samp{continue}.
28615 @subsubheading Example
28622 *stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame=@{
28623 func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
28629 @subheading The @code{-exec-finish} Command
28630 @findex -exec-finish
28632 @subsubheading Synopsis
28635 -exec-finish [--reverse]
28638 Resumes the execution of the inferior program until the current
28639 function is exited. Displays the results returned by the function.
28640 If the @samp{--reverse} option is specified, resumes the reverse
28641 execution of the inferior program until the point where current
28642 function was called.
28644 @subsubheading @value{GDBN} Command
28646 The corresponding @value{GDBN} command is @samp{finish}.
28648 @subsubheading Example
28650 Function returning @code{void}.
28657 *stopped,reason="function-finished",frame=@{func="main",args=[],
28658 file="hello.c",fullname="/home/foo/bar/hello.c",line="7"@}
28662 Function returning other than @code{void}. The name of the internal
28663 @value{GDBN} variable storing the result is printed, together with the
28670 *stopped,reason="function-finished",frame=@{addr="0x000107b0",func="foo",
28671 args=[@{name="a",value="1"],@{name="b",value="9"@}@},
28672 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
28673 gdb-result-var="$1",return-value="0"
28678 @subheading The @code{-exec-interrupt} Command
28679 @findex -exec-interrupt
28681 @subsubheading Synopsis
28684 -exec-interrupt [--all|--thread-group N]
28687 Interrupts the background execution of the target. Note how the token
28688 associated with the stop message is the one for the execution command
28689 that has been interrupted. The token for the interrupt itself only
28690 appears in the @samp{^done} output. If the user is trying to
28691 interrupt a non-running program, an error message will be printed.
28693 Note that when asynchronous execution is enabled, this command is
28694 asynchronous just like other execution commands. That is, first the
28695 @samp{^done} response will be printed, and the target stop will be
28696 reported after that using the @samp{*stopped} notification.
28698 In non-stop mode, only the context thread is interrupted by default.
28699 All threads (in all inferiors) will be interrupted if the
28700 @samp{--all} option is specified. If the @samp{--thread-group}
28701 option is specified, all threads in that group will be interrupted.
28703 @subsubheading @value{GDBN} Command
28705 The corresponding @value{GDBN} command is @samp{interrupt}.
28707 @subsubheading Example
28718 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt",
28719 frame=@{addr="0x00010140",func="foo",args=[],file="try.c",
28720 fullname="/home/foo/bar/try.c",line="13"@}
28725 ^error,msg="mi_cmd_exec_interrupt: Inferior not executing."
28729 @subheading The @code{-exec-jump} Command
28732 @subsubheading Synopsis
28735 -exec-jump @var{location}
28738 Resumes execution of the inferior program at the location specified by
28739 parameter. @xref{Specify Location}, for a description of the
28740 different forms of @var{location}.
28742 @subsubheading @value{GDBN} Command
28744 The corresponding @value{GDBN} command is @samp{jump}.
28746 @subsubheading Example
28749 -exec-jump foo.c:10
28750 *running,thread-id="all"
28755 @subheading The @code{-exec-next} Command
28758 @subsubheading Synopsis
28761 -exec-next [--reverse]
28764 Resumes execution of the inferior program, stopping when the beginning
28765 of the next source line is reached.
28767 If the @samp{--reverse} option is specified, resumes reverse execution
28768 of the inferior program, stopping at the beginning of the previous
28769 source line. If you issue this command on the first line of a
28770 function, it will take you back to the caller of that function, to the
28771 source line where the function was called.
28774 @subsubheading @value{GDBN} Command
28776 The corresponding @value{GDBN} command is @samp{next}.
28778 @subsubheading Example
28784 *stopped,reason="end-stepping-range",line="8",file="hello.c"
28789 @subheading The @code{-exec-next-instruction} Command
28790 @findex -exec-next-instruction
28792 @subsubheading Synopsis
28795 -exec-next-instruction [--reverse]
28798 Executes one machine instruction. If the instruction is a function
28799 call, continues until the function returns. If the program stops at an
28800 instruction in the middle of a source line, the address will be
28803 If the @samp{--reverse} option is specified, resumes reverse execution
28804 of the inferior program, stopping at the previous instruction. If the
28805 previously executed instruction was a return from another function,
28806 it will continue to execute in reverse until the call to that function
28807 (from the current stack frame) is reached.
28809 @subsubheading @value{GDBN} Command
28811 The corresponding @value{GDBN} command is @samp{nexti}.
28813 @subsubheading Example
28817 -exec-next-instruction
28821 *stopped,reason="end-stepping-range",
28822 addr="0x000100d4",line="5",file="hello.c"
28827 @subheading The @code{-exec-return} Command
28828 @findex -exec-return
28830 @subsubheading Synopsis
28836 Makes current function return immediately. Doesn't execute the inferior.
28837 Displays the new current frame.
28839 @subsubheading @value{GDBN} Command
28841 The corresponding @value{GDBN} command is @samp{return}.
28843 @subsubheading Example
28847 200-break-insert callee4
28848 200^done,bkpt=@{number="1",addr="0x00010734",
28849 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
28854 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
28855 frame=@{func="callee4",args=[],
28856 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28857 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@}
28863 111^done,frame=@{level="0",func="callee3",
28864 args=[@{name="strarg",
28865 value="0x11940 \"A string argument.\""@}],
28866 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
28867 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"@}
28872 @subheading The @code{-exec-run} Command
28875 @subsubheading Synopsis
28878 -exec-run [ --all | --thread-group N ] [ --start ]
28881 Starts execution of the inferior from the beginning. The inferior
28882 executes until either a breakpoint is encountered or the program
28883 exits. In the latter case the output will include an exit code, if
28884 the program has exited exceptionally.
28886 When neither the @samp{--all} nor the @samp{--thread-group} option
28887 is specified, the current inferior is started. If the
28888 @samp{--thread-group} option is specified, it should refer to a thread
28889 group of type @samp{process}, and that thread group will be started.
28890 If the @samp{--all} option is specified, then all inferiors will be started.
28892 Using the @samp{--start} option instructs the debugger to stop
28893 the execution at the start of the inferior's main subprogram,
28894 following the same behavior as the @code{start} command
28895 (@pxref{Starting}).
28897 @subsubheading @value{GDBN} Command
28899 The corresponding @value{GDBN} command is @samp{run}.
28901 @subsubheading Examples
28906 ^done,bkpt=@{number="1",addr="0x0001072c",file="recursive2.c",line="4"@}
28911 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",
28912 frame=@{func="main",args=[],file="recursive2.c",
28913 fullname="/home/foo/bar/recursive2.c",line="4"@}
28918 Program exited normally:
28926 *stopped,reason="exited-normally"
28931 Program exited exceptionally:
28939 *stopped,reason="exited",exit-code="01"
28943 Another way the program can terminate is if it receives a signal such as
28944 @code{SIGINT}. In this case, @sc{gdb/mi} displays this:
28948 *stopped,reason="exited-signalled",signal-name="SIGINT",
28949 signal-meaning="Interrupt"
28953 @c @subheading -exec-signal
28956 @subheading The @code{-exec-step} Command
28959 @subsubheading Synopsis
28962 -exec-step [--reverse]
28965 Resumes execution of the inferior program, stopping when the beginning
28966 of the next source line is reached, if the next source line is not a
28967 function call. If it is, stop at the first instruction of the called
28968 function. If the @samp{--reverse} option is specified, resumes reverse
28969 execution of the inferior program, stopping at the beginning of the
28970 previously executed source line.
28972 @subsubheading @value{GDBN} Command
28974 The corresponding @value{GDBN} command is @samp{step}.
28976 @subsubheading Example
28978 Stepping into a function:
28984 *stopped,reason="end-stepping-range",
28985 frame=@{func="foo",args=[@{name="a",value="10"@},
28986 @{name="b",value="0"@}],file="recursive2.c",
28987 fullname="/home/foo/bar/recursive2.c",line="11"@}
28997 *stopped,reason="end-stepping-range",line="14",file="recursive2.c"
29002 @subheading The @code{-exec-step-instruction} Command
29003 @findex -exec-step-instruction
29005 @subsubheading Synopsis
29008 -exec-step-instruction [--reverse]
29011 Resumes the inferior which executes one machine instruction. If the
29012 @samp{--reverse} option is specified, resumes reverse execution of the
29013 inferior program, stopping at the previously executed instruction.
29014 The output, once @value{GDBN} has stopped, will vary depending on
29015 whether we have stopped in the middle of a source line or not. In the
29016 former case, the address at which the program stopped will be printed
29019 @subsubheading @value{GDBN} Command
29021 The corresponding @value{GDBN} command is @samp{stepi}.
29023 @subsubheading Example
29027 -exec-step-instruction
29031 *stopped,reason="end-stepping-range",
29032 frame=@{func="foo",args=[],file="try.c",
29033 fullname="/home/foo/bar/try.c",line="10"@}
29035 -exec-step-instruction
29039 *stopped,reason="end-stepping-range",
29040 frame=@{addr="0x000100f4",func="foo",args=[],file="try.c",
29041 fullname="/home/foo/bar/try.c",line="10"@}
29046 @subheading The @code{-exec-until} Command
29047 @findex -exec-until
29049 @subsubheading Synopsis
29052 -exec-until [ @var{location} ]
29055 Executes the inferior until the @var{location} specified in the
29056 argument is reached. If there is no argument, the inferior executes
29057 until a source line greater than the current one is reached. The
29058 reason for stopping in this case will be @samp{location-reached}.
29060 @subsubheading @value{GDBN} Command
29062 The corresponding @value{GDBN} command is @samp{until}.
29064 @subsubheading Example
29068 -exec-until recursive2.c:6
29072 *stopped,reason="location-reached",frame=@{func="main",args=[],
29073 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"@}
29078 @subheading -file-clear
29079 Is this going away????
29082 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29083 @node GDB/MI Stack Manipulation
29084 @section @sc{gdb/mi} Stack Manipulation Commands
29086 @subheading The @code{-enable-frame-filters} Command
29087 @findex -enable-frame-filters
29090 -enable-frame-filters
29093 @value{GDBN} allows Python-based frame filters to affect the output of
29094 the MI commands relating to stack traces. As there is no way to
29095 implement this in a fully backward-compatible way, a front end must
29096 request that this functionality be enabled.
29098 Once enabled, this feature cannot be disabled.
29100 Note that if Python support has not been compiled into @value{GDBN},
29101 this command will still succeed (and do nothing).
29103 @subheading The @code{-stack-info-frame} Command
29104 @findex -stack-info-frame
29106 @subsubheading Synopsis
29112 Get info on the selected frame.
29114 @subsubheading @value{GDBN} Command
29116 The corresponding @value{GDBN} command is @samp{info frame} or @samp{frame}
29117 (without arguments).
29119 @subsubheading Example
29124 ^done,frame=@{level="1",addr="0x0001076c",func="callee3",
29125 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
29126 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@}
29130 @subheading The @code{-stack-info-depth} Command
29131 @findex -stack-info-depth
29133 @subsubheading Synopsis
29136 -stack-info-depth [ @var{max-depth} ]
29139 Return the depth of the stack. If the integer argument @var{max-depth}
29140 is specified, do not count beyond @var{max-depth} frames.
29142 @subsubheading @value{GDBN} Command
29144 There's no equivalent @value{GDBN} command.
29146 @subsubheading Example
29148 For a stack with frame levels 0 through 11:
29155 -stack-info-depth 4
29158 -stack-info-depth 12
29161 -stack-info-depth 11
29164 -stack-info-depth 13
29169 @anchor{-stack-list-arguments}
29170 @subheading The @code{-stack-list-arguments} Command
29171 @findex -stack-list-arguments
29173 @subsubheading Synopsis
29176 -stack-list-arguments [ --no-frame-filters ] [ --skip-unavailable ] @var{print-values}
29177 [ @var{low-frame} @var{high-frame} ]
29180 Display a list of the arguments for the frames between @var{low-frame}
29181 and @var{high-frame} (inclusive). If @var{low-frame} and
29182 @var{high-frame} are not provided, list the arguments for the whole
29183 call stack. If the two arguments are equal, show the single frame
29184 at the corresponding level. It is an error if @var{low-frame} is
29185 larger than the actual number of frames. On the other hand,
29186 @var{high-frame} may be larger than the actual number of frames, in
29187 which case only existing frames will be returned.
29189 If @var{print-values} is 0 or @code{--no-values}, print only the names of
29190 the variables; if it is 1 or @code{--all-values}, print also their
29191 values; and if it is 2 or @code{--simple-values}, print the name,
29192 type and value for simple data types, and the name and type for arrays,
29193 structures and unions. If the option @code{--no-frame-filters} is
29194 supplied, then Python frame filters will not be executed.
29196 If the @code{--skip-unavailable} option is specified, arguments that
29197 are not available are not listed. Partially available arguments
29198 are still displayed, however.
29200 Use of this command to obtain arguments in a single frame is
29201 deprecated in favor of the @samp{-stack-list-variables} command.
29203 @subsubheading @value{GDBN} Command
29205 @value{GDBN} does not have an equivalent command. @code{gdbtk} has a
29206 @samp{gdb_get_args} command which partially overlaps with the
29207 functionality of @samp{-stack-list-arguments}.
29209 @subsubheading Example
29216 frame=@{level="0",addr="0x00010734",func="callee4",
29217 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
29218 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"@},
29219 frame=@{level="1",addr="0x0001076c",func="callee3",
29220 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
29221 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"@},
29222 frame=@{level="2",addr="0x0001078c",func="callee2",
29223 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
29224 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"@},
29225 frame=@{level="3",addr="0x000107b4",func="callee1",
29226 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
29227 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"@},
29228 frame=@{level="4",addr="0x000107e0",func="main",
29229 file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
29230 fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"@}]
29232 -stack-list-arguments 0
29235 frame=@{level="0",args=[]@},
29236 frame=@{level="1",args=[name="strarg"]@},
29237 frame=@{level="2",args=[name="intarg",name="strarg"]@},
29238 frame=@{level="3",args=[name="intarg",name="strarg",name="fltarg"]@},
29239 frame=@{level="4",args=[]@}]
29241 -stack-list-arguments 1
29244 frame=@{level="0",args=[]@},
29246 args=[@{name="strarg",value="0x11940 \"A string argument.\""@}]@},
29247 frame=@{level="2",args=[
29248 @{name="intarg",value="2"@},
29249 @{name="strarg",value="0x11940 \"A string argument.\""@}]@},
29250 @{frame=@{level="3",args=[
29251 @{name="intarg",value="2"@},
29252 @{name="strarg",value="0x11940 \"A string argument.\""@},
29253 @{name="fltarg",value="3.5"@}]@},
29254 frame=@{level="4",args=[]@}]
29256 -stack-list-arguments 0 2 2
29257 ^done,stack-args=[frame=@{level="2",args=[name="intarg",name="strarg"]@}]
29259 -stack-list-arguments 1 2 2
29260 ^done,stack-args=[frame=@{level="2",
29261 args=[@{name="intarg",value="2"@},
29262 @{name="strarg",value="0x11940 \"A string argument.\""@}]@}]
29266 @c @subheading -stack-list-exception-handlers
29269 @anchor{-stack-list-frames}
29270 @subheading The @code{-stack-list-frames} Command
29271 @findex -stack-list-frames
29273 @subsubheading Synopsis
29276 -stack-list-frames [ --no-frame-filters @var{low-frame} @var{high-frame} ]
29279 List the frames currently on the stack. For each frame it displays the
29284 The frame number, 0 being the topmost frame, i.e., the innermost function.
29286 The @code{$pc} value for that frame.
29290 File name of the source file where the function lives.
29291 @item @var{fullname}
29292 The full file name of the source file where the function lives.
29294 Line number corresponding to the @code{$pc}.
29296 The shared library where this function is defined. This is only given
29297 if the frame's function is not known.
29300 If invoked without arguments, this command prints a backtrace for the
29301 whole stack. If given two integer arguments, it shows the frames whose
29302 levels are between the two arguments (inclusive). If the two arguments
29303 are equal, it shows the single frame at the corresponding level. It is
29304 an error if @var{low-frame} is larger than the actual number of
29305 frames. On the other hand, @var{high-frame} may be larger than the
29306 actual number of frames, in which case only existing frames will be
29307 returned. If the option @code{--no-frame-filters} is supplied, then
29308 Python frame filters will not be executed.
29310 @subsubheading @value{GDBN} Command
29312 The corresponding @value{GDBN} commands are @samp{backtrace} and @samp{where}.
29314 @subsubheading Example
29316 Full stack backtrace:
29322 [frame=@{level="0",addr="0x0001076c",func="foo",
29323 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"@},
29324 frame=@{level="1",addr="0x000107a4",func="foo",
29325 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29326 frame=@{level="2",addr="0x000107a4",func="foo",
29327 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29328 frame=@{level="3",addr="0x000107a4",func="foo",
29329 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29330 frame=@{level="4",addr="0x000107a4",func="foo",
29331 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29332 frame=@{level="5",addr="0x000107a4",func="foo",
29333 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29334 frame=@{level="6",addr="0x000107a4",func="foo",
29335 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29336 frame=@{level="7",addr="0x000107a4",func="foo",
29337 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29338 frame=@{level="8",addr="0x000107a4",func="foo",
29339 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29340 frame=@{level="9",addr="0x000107a4",func="foo",
29341 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29342 frame=@{level="10",addr="0x000107a4",func="foo",
29343 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29344 frame=@{level="11",addr="0x00010738",func="main",
29345 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"@}]
29349 Show frames between @var{low_frame} and @var{high_frame}:
29353 -stack-list-frames 3 5
29355 [frame=@{level="3",addr="0x000107a4",func="foo",
29356 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29357 frame=@{level="4",addr="0x000107a4",func="foo",
29358 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@},
29359 frame=@{level="5",addr="0x000107a4",func="foo",
29360 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
29364 Show a single frame:
29368 -stack-list-frames 3 3
29370 [frame=@{level="3",addr="0x000107a4",func="foo",
29371 file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"@}]
29376 @subheading The @code{-stack-list-locals} Command
29377 @findex -stack-list-locals
29378 @anchor{-stack-list-locals}
29380 @subsubheading Synopsis
29383 -stack-list-locals [ --no-frame-filters ] [ --skip-unavailable ] @var{print-values}
29386 Display the local variable names for the selected frame. If
29387 @var{print-values} is 0 or @code{--no-values}, print only the names of
29388 the variables; if it is 1 or @code{--all-values}, print also their
29389 values; and if it is 2 or @code{--simple-values}, print the name,
29390 type and value for simple data types, and the name and type for arrays,
29391 structures and unions. In this last case, a frontend can immediately
29392 display the value of simple data types and create variable objects for
29393 other data types when the user wishes to explore their values in
29394 more detail. If the option @code{--no-frame-filters} is supplied, then
29395 Python frame filters will not be executed.
29397 If the @code{--skip-unavailable} option is specified, local variables
29398 that are not available are not listed. Partially available local
29399 variables are still displayed, however.
29401 This command is deprecated in favor of the
29402 @samp{-stack-list-variables} command.
29404 @subsubheading @value{GDBN} Command
29406 @samp{info locals} in @value{GDBN}, @samp{gdb_get_locals} in @code{gdbtk}.
29408 @subsubheading Example
29412 -stack-list-locals 0
29413 ^done,locals=[name="A",name="B",name="C"]
29415 -stack-list-locals --all-values
29416 ^done,locals=[@{name="A",value="1"@},@{name="B",value="2"@},
29417 @{name="C",value="@{1, 2, 3@}"@}]
29418 -stack-list-locals --simple-values
29419 ^done,locals=[@{name="A",type="int",value="1"@},
29420 @{name="B",type="int",value="2"@},@{name="C",type="int [3]"@}]
29424 @anchor{-stack-list-variables}
29425 @subheading The @code{-stack-list-variables} Command
29426 @findex -stack-list-variables
29428 @subsubheading Synopsis
29431 -stack-list-variables [ --no-frame-filters ] [ --skip-unavailable ] @var{print-values}
29434 Display the names of local variables and function arguments for the selected frame. If
29435 @var{print-values} is 0 or @code{--no-values}, print only the names of
29436 the variables; if it is 1 or @code{--all-values}, print also their
29437 values; and if it is 2 or @code{--simple-values}, print the name,
29438 type and value for simple data types, and the name and type for arrays,
29439 structures and unions. If the option @code{--no-frame-filters} is
29440 supplied, then Python frame filters will not be executed.
29442 If the @code{--skip-unavailable} option is specified, local variables
29443 and arguments that are not available are not listed. Partially
29444 available arguments and local variables are still displayed, however.
29446 @subsubheading Example
29450 -stack-list-variables --thread 1 --frame 0 --all-values
29451 ^done,variables=[@{name="x",value="11"@},@{name="s",value="@{a = 1, b = 2@}"@}]
29456 @subheading The @code{-stack-select-frame} Command
29457 @findex -stack-select-frame
29459 @subsubheading Synopsis
29462 -stack-select-frame @var{framenum}
29465 Change the selected frame. Select a different frame @var{framenum} on
29468 This command in deprecated in favor of passing the @samp{--frame}
29469 option to every command.
29471 @subsubheading @value{GDBN} Command
29473 The corresponding @value{GDBN} commands are @samp{frame}, @samp{up},
29474 @samp{down}, @samp{select-frame}, @samp{up-silent}, and @samp{down-silent}.
29476 @subsubheading Example
29480 -stack-select-frame 2
29485 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
29486 @node GDB/MI Variable Objects
29487 @section @sc{gdb/mi} Variable Objects
29491 @subheading Motivation for Variable Objects in @sc{gdb/mi}
29493 For the implementation of a variable debugger window (locals, watched
29494 expressions, etc.), we are proposing the adaptation of the existing code
29495 used by @code{Insight}.
29497 The two main reasons for that are:
29501 It has been proven in practice (it is already on its second generation).
29504 It will shorten development time (needless to say how important it is
29508 The original interface was designed to be used by Tcl code, so it was
29509 slightly changed so it could be used through @sc{gdb/mi}. This section
29510 describes the @sc{gdb/mi} operations that will be available and gives some
29511 hints about their use.
29513 @emph{Note}: In addition to the set of operations described here, we
29514 expect the @sc{gui} implementation of a variable window to require, at
29515 least, the following operations:
29518 @item @code{-gdb-show} @code{output-radix}
29519 @item @code{-stack-list-arguments}
29520 @item @code{-stack-list-locals}
29521 @item @code{-stack-select-frame}
29526 @subheading Introduction to Variable Objects
29528 @cindex variable objects in @sc{gdb/mi}
29530 Variable objects are "object-oriented" MI interface for examining and
29531 changing values of expressions. Unlike some other MI interfaces that
29532 work with expressions, variable objects are specifically designed for
29533 simple and efficient presentation in the frontend. A variable object
29534 is identified by string name. When a variable object is created, the
29535 frontend specifies the expression for that variable object. The
29536 expression can be a simple variable, or it can be an arbitrary complex
29537 expression, and can even involve CPU registers. After creating a
29538 variable object, the frontend can invoke other variable object
29539 operations---for example to obtain or change the value of a variable
29540 object, or to change display format.
29542 Variable objects have hierarchical tree structure. Any variable object
29543 that corresponds to a composite type, such as structure in C, has
29544 a number of child variable objects, for example corresponding to each
29545 element of a structure. A child variable object can itself have
29546 children, recursively. Recursion ends when we reach
29547 leaf variable objects, which always have built-in types. Child variable
29548 objects are created only by explicit request, so if a frontend
29549 is not interested in the children of a particular variable object, no
29550 child will be created.
29552 For a leaf variable object it is possible to obtain its value as a
29553 string, or set the value from a string. String value can be also
29554 obtained for a non-leaf variable object, but it's generally a string
29555 that only indicates the type of the object, and does not list its
29556 contents. Assignment to a non-leaf variable object is not allowed.
29558 A frontend does not need to read the values of all variable objects each time
29559 the program stops. Instead, MI provides an update command that lists all
29560 variable objects whose values has changed since the last update
29561 operation. This considerably reduces the amount of data that must
29562 be transferred to the frontend. As noted above, children variable
29563 objects are created on demand, and only leaf variable objects have a
29564 real value. As result, gdb will read target memory only for leaf
29565 variables that frontend has created.
29567 The automatic update is not always desirable. For example, a frontend
29568 might want to keep a value of some expression for future reference,
29569 and never update it. For another example, fetching memory is
29570 relatively slow for embedded targets, so a frontend might want
29571 to disable automatic update for the variables that are either not
29572 visible on the screen, or ``closed''. This is possible using so
29573 called ``frozen variable objects''. Such variable objects are never
29574 implicitly updated.
29576 Variable objects can be either @dfn{fixed} or @dfn{floating}. For the
29577 fixed variable object, the expression is parsed when the variable
29578 object is created, including associating identifiers to specific
29579 variables. The meaning of expression never changes. For a floating
29580 variable object the values of variables whose names appear in the
29581 expressions are re-evaluated every time in the context of the current
29582 frame. Consider this example:
29587 struct work_state state;
29594 If a fixed variable object for the @code{state} variable is created in
29595 this function, and we enter the recursive call, the variable
29596 object will report the value of @code{state} in the top-level
29597 @code{do_work} invocation. On the other hand, a floating variable
29598 object will report the value of @code{state} in the current frame.
29600 If an expression specified when creating a fixed variable object
29601 refers to a local variable, the variable object becomes bound to the
29602 thread and frame in which the variable object is created. When such
29603 variable object is updated, @value{GDBN} makes sure that the
29604 thread/frame combination the variable object is bound to still exists,
29605 and re-evaluates the variable object in context of that thread/frame.
29607 The following is the complete set of @sc{gdb/mi} operations defined to
29608 access this functionality:
29610 @multitable @columnfractions .4 .6
29611 @item @strong{Operation}
29612 @tab @strong{Description}
29614 @item @code{-enable-pretty-printing}
29615 @tab enable Python-based pretty-printing
29616 @item @code{-var-create}
29617 @tab create a variable object
29618 @item @code{-var-delete}
29619 @tab delete the variable object and/or its children
29620 @item @code{-var-set-format}
29621 @tab set the display format of this variable
29622 @item @code{-var-show-format}
29623 @tab show the display format of this variable
29624 @item @code{-var-info-num-children}
29625 @tab tells how many children this object has
29626 @item @code{-var-list-children}
29627 @tab return a list of the object's children
29628 @item @code{-var-info-type}
29629 @tab show the type of this variable object
29630 @item @code{-var-info-expression}
29631 @tab print parent-relative expression that this variable object represents
29632 @item @code{-var-info-path-expression}
29633 @tab print full expression that this variable object represents
29634 @item @code{-var-show-attributes}
29635 @tab is this variable editable? does it exist here?
29636 @item @code{-var-evaluate-expression}
29637 @tab get the value of this variable
29638 @item @code{-var-assign}
29639 @tab set the value of this variable
29640 @item @code{-var-update}
29641 @tab update the variable and its children
29642 @item @code{-var-set-frozen}
29643 @tab set frozeness attribute
29644 @item @code{-var-set-update-range}
29645 @tab set range of children to display on update
29648 In the next subsection we describe each operation in detail and suggest
29649 how it can be used.
29651 @subheading Description And Use of Operations on Variable Objects
29653 @subheading The @code{-enable-pretty-printing} Command
29654 @findex -enable-pretty-printing
29657 -enable-pretty-printing
29660 @value{GDBN} allows Python-based visualizers to affect the output of the
29661 MI variable object commands. However, because there was no way to
29662 implement this in a fully backward-compatible way, a front end must
29663 request that this functionality be enabled.
29665 Once enabled, this feature cannot be disabled.
29667 Note that if Python support has not been compiled into @value{GDBN},
29668 this command will still succeed (and do nothing).
29670 This feature is currently (as of @value{GDBN} 7.0) experimental, and
29671 may work differently in future versions of @value{GDBN}.
29673 @subheading The @code{-var-create} Command
29674 @findex -var-create
29676 @subsubheading Synopsis
29679 -var-create @{@var{name} | "-"@}
29680 @{@var{frame-addr} | "*" | "@@"@} @var{expression}
29683 This operation creates a variable object, which allows the monitoring of
29684 a variable, the result of an expression, a memory cell or a CPU
29687 The @var{name} parameter is the string by which the object can be
29688 referenced. It must be unique. If @samp{-} is specified, the varobj
29689 system will generate a string ``varNNNNNN'' automatically. It will be
29690 unique provided that one does not specify @var{name} of that format.
29691 The command fails if a duplicate name is found.
29693 The frame under which the expression should be evaluated can be
29694 specified by @var{frame-addr}. A @samp{*} indicates that the current
29695 frame should be used. A @samp{@@} indicates that a floating variable
29696 object must be created.
29698 @var{expression} is any expression valid on the current language set (must not
29699 begin with a @samp{*}), or one of the following:
29703 @samp{*@var{addr}}, where @var{addr} is the address of a memory cell
29706 @samp{*@var{addr}-@var{addr}} --- a memory address range (TBD)
29709 @samp{$@var{regname}} --- a CPU register name
29712 @cindex dynamic varobj
29713 A varobj's contents may be provided by a Python-based pretty-printer. In this
29714 case the varobj is known as a @dfn{dynamic varobj}. Dynamic varobjs
29715 have slightly different semantics in some cases. If the
29716 @code{-enable-pretty-printing} command is not sent, then @value{GDBN}
29717 will never create a dynamic varobj. This ensures backward
29718 compatibility for existing clients.
29720 @subsubheading Result
29722 This operation returns attributes of the newly-created varobj. These
29727 The name of the varobj.
29730 The number of children of the varobj. This number is not necessarily
29731 reliable for a dynamic varobj. Instead, you must examine the
29732 @samp{has_more} attribute.
29735 The varobj's scalar value. For a varobj whose type is some sort of
29736 aggregate (e.g., a @code{struct}), or for a dynamic varobj, this value
29737 will not be interesting.
29740 The varobj's type. This is a string representation of the type, as
29741 would be printed by the @value{GDBN} CLI. If @samp{print object}
29742 (@pxref{Print Settings, set print object}) is set to @code{on}, the
29743 @emph{actual} (derived) type of the object is shown rather than the
29744 @emph{declared} one.
29747 If a variable object is bound to a specific thread, then this is the
29748 thread's global identifier.
29751 For a dynamic varobj, this indicates whether there appear to be any
29752 children available. For a non-dynamic varobj, this will be 0.
29755 This attribute will be present and have the value @samp{1} if the
29756 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
29757 then this attribute will not be present.
29760 A dynamic varobj can supply a display hint to the front end. The
29761 value comes directly from the Python pretty-printer object's
29762 @code{display_hint} method. @xref{Pretty Printing API}.
29765 Typical output will look like this:
29768 name="@var{name}",numchild="@var{N}",type="@var{type}",thread-id="@var{M}",
29769 has_more="@var{has_more}"
29773 @subheading The @code{-var-delete} Command
29774 @findex -var-delete
29776 @subsubheading Synopsis
29779 -var-delete [ -c ] @var{name}
29782 Deletes a previously created variable object and all of its children.
29783 With the @samp{-c} option, just deletes the children.
29785 Returns an error if the object @var{name} is not found.
29788 @subheading The @code{-var-set-format} Command
29789 @findex -var-set-format
29791 @subsubheading Synopsis
29794 -var-set-format @var{name} @var{format-spec}
29797 Sets the output format for the value of the object @var{name} to be
29800 @anchor{-var-set-format}
29801 The syntax for the @var{format-spec} is as follows:
29804 @var{format-spec} @expansion{}
29805 @{binary | decimal | hexadecimal | octal | natural | zero-hexadecimal@}
29808 The natural format is the default format choosen automatically
29809 based on the variable type (like decimal for an @code{int}, hex
29810 for pointers, etc.).
29812 The zero-hexadecimal format has a representation similar to hexadecimal
29813 but with padding zeroes to the left of the value. For example, a 32-bit
29814 hexadecimal value of 0x1234 would be represented as 0x00001234 in the
29815 zero-hexadecimal format.
29817 For a variable with children, the format is set only on the
29818 variable itself, and the children are not affected.
29820 @subheading The @code{-var-show-format} Command
29821 @findex -var-show-format
29823 @subsubheading Synopsis
29826 -var-show-format @var{name}
29829 Returns the format used to display the value of the object @var{name}.
29832 @var{format} @expansion{}
29837 @subheading The @code{-var-info-num-children} Command
29838 @findex -var-info-num-children
29840 @subsubheading Synopsis
29843 -var-info-num-children @var{name}
29846 Returns the number of children of a variable object @var{name}:
29852 Note that this number is not completely reliable for a dynamic varobj.
29853 It will return the current number of children, but more children may
29857 @subheading The @code{-var-list-children} Command
29858 @findex -var-list-children
29860 @subsubheading Synopsis
29863 -var-list-children [@var{print-values}] @var{name} [@var{from} @var{to}]
29865 @anchor{-var-list-children}
29867 Return a list of the children of the specified variable object and
29868 create variable objects for them, if they do not already exist. With
29869 a single argument or if @var{print-values} has a value of 0 or
29870 @code{--no-values}, print only the names of the variables; if
29871 @var{print-values} is 1 or @code{--all-values}, also print their
29872 values; and if it is 2 or @code{--simple-values} print the name and
29873 value for simple data types and just the name for arrays, structures
29876 @var{from} and @var{to}, if specified, indicate the range of children
29877 to report. If @var{from} or @var{to} is less than zero, the range is
29878 reset and all children will be reported. Otherwise, children starting
29879 at @var{from} (zero-based) and up to and excluding @var{to} will be
29882 If a child range is requested, it will only affect the current call to
29883 @code{-var-list-children}, but not future calls to @code{-var-update}.
29884 For this, you must instead use @code{-var-set-update-range}. The
29885 intent of this approach is to enable a front end to implement any
29886 update approach it likes; for example, scrolling a view may cause the
29887 front end to request more children with @code{-var-list-children}, and
29888 then the front end could call @code{-var-set-update-range} with a
29889 different range to ensure that future updates are restricted to just
29892 For each child the following results are returned:
29897 Name of the variable object created for this child.
29900 The expression to be shown to the user by the front end to designate this child.
29901 For example this may be the name of a structure member.
29903 For a dynamic varobj, this value cannot be used to form an
29904 expression. There is no way to do this at all with a dynamic varobj.
29906 For C/C@t{++} structures there are several pseudo children returned to
29907 designate access qualifiers. For these pseudo children @var{exp} is
29908 @samp{public}, @samp{private}, or @samp{protected}. In this case the
29909 type and value are not present.
29911 A dynamic varobj will not report the access qualifying
29912 pseudo-children, regardless of the language. This information is not
29913 available at all with a dynamic varobj.
29916 Number of children this child has. For a dynamic varobj, this will be
29920 The type of the child. If @samp{print object}
29921 (@pxref{Print Settings, set print object}) is set to @code{on}, the
29922 @emph{actual} (derived) type of the object is shown rather than the
29923 @emph{declared} one.
29926 If values were requested, this is the value.
29929 If this variable object is associated with a thread, this is the
29930 thread's global thread id. Otherwise this result is not present.
29933 If the variable object is frozen, this variable will be present with a value of 1.
29936 A dynamic varobj can supply a display hint to the front end. The
29937 value comes directly from the Python pretty-printer object's
29938 @code{display_hint} method. @xref{Pretty Printing API}.
29941 This attribute will be present and have the value @samp{1} if the
29942 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
29943 then this attribute will not be present.
29947 The result may have its own attributes:
29951 A dynamic varobj can supply a display hint to the front end. The
29952 value comes directly from the Python pretty-printer object's
29953 @code{display_hint} method. @xref{Pretty Printing API}.
29956 This is an integer attribute which is nonzero if there are children
29957 remaining after the end of the selected range.
29960 @subsubheading Example
29964 -var-list-children n
29965 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
29966 numchild=@var{n},type=@var{type}@},@r{(repeats N times)}]
29968 -var-list-children --all-values n
29969 ^done,numchild=@var{n},children=[child=@{name=@var{name},exp=@var{exp},
29970 numchild=@var{n},value=@var{value},type=@var{type}@},@r{(repeats N times)}]
29974 @subheading The @code{-var-info-type} Command
29975 @findex -var-info-type
29977 @subsubheading Synopsis
29980 -var-info-type @var{name}
29983 Returns the type of the specified variable @var{name}. The type is
29984 returned as a string in the same format as it is output by the
29988 type=@var{typename}
29992 @subheading The @code{-var-info-expression} Command
29993 @findex -var-info-expression
29995 @subsubheading Synopsis
29998 -var-info-expression @var{name}
30001 Returns a string that is suitable for presenting this
30002 variable object in user interface. The string is generally
30003 not valid expression in the current language, and cannot be evaluated.
30005 For example, if @code{a} is an array, and variable object
30006 @code{A} was created for @code{a}, then we'll get this output:
30009 (gdb) -var-info-expression A.1
30010 ^done,lang="C",exp="1"
30014 Here, the value of @code{lang} is the language name, which can be
30015 found in @ref{Supported Languages}.
30017 Note that the output of the @code{-var-list-children} command also
30018 includes those expressions, so the @code{-var-info-expression} command
30021 @subheading The @code{-var-info-path-expression} Command
30022 @findex -var-info-path-expression
30024 @subsubheading Synopsis
30027 -var-info-path-expression @var{name}
30030 Returns an expression that can be evaluated in the current
30031 context and will yield the same value that a variable object has.
30032 Compare this with the @code{-var-info-expression} command, which
30033 result can be used only for UI presentation. Typical use of
30034 the @code{-var-info-path-expression} command is creating a
30035 watchpoint from a variable object.
30037 This command is currently not valid for children of a dynamic varobj,
30038 and will give an error when invoked on one.
30040 For example, suppose @code{C} is a C@t{++} class, derived from class
30041 @code{Base}, and that the @code{Base} class has a member called
30042 @code{m_size}. Assume a variable @code{c} is has the type of
30043 @code{C} and a variable object @code{C} was created for variable
30044 @code{c}. Then, we'll get this output:
30046 (gdb) -var-info-path-expression C.Base.public.m_size
30047 ^done,path_expr=((Base)c).m_size)
30050 @subheading The @code{-var-show-attributes} Command
30051 @findex -var-show-attributes
30053 @subsubheading Synopsis
30056 -var-show-attributes @var{name}
30059 List attributes of the specified variable object @var{name}:
30062 status=@var{attr} [ ( ,@var{attr} )* ]
30066 where @var{attr} is @code{@{ @{ editable | noneditable @} | TBD @}}.
30068 @subheading The @code{-var-evaluate-expression} Command
30069 @findex -var-evaluate-expression
30071 @subsubheading Synopsis
30074 -var-evaluate-expression [-f @var{format-spec}] @var{name}
30077 Evaluates the expression that is represented by the specified variable
30078 object and returns its value as a string. The format of the string
30079 can be specified with the @samp{-f} option. The possible values of
30080 this option are the same as for @code{-var-set-format}
30081 (@pxref{-var-set-format}). If the @samp{-f} option is not specified,
30082 the current display format will be used. The current display format
30083 can be changed using the @code{-var-set-format} command.
30089 Note that one must invoke @code{-var-list-children} for a variable
30090 before the value of a child variable can be evaluated.
30092 @subheading The @code{-var-assign} Command
30093 @findex -var-assign
30095 @subsubheading Synopsis
30098 -var-assign @var{name} @var{expression}
30101 Assigns the value of @var{expression} to the variable object specified
30102 by @var{name}. The object must be @samp{editable}. If the variable's
30103 value is altered by the assign, the variable will show up in any
30104 subsequent @code{-var-update} list.
30106 @subsubheading Example
30114 ^done,changelist=[@{name="var1",in_scope="true",type_changed="false"@}]
30118 @subheading The @code{-var-update} Command
30119 @findex -var-update
30121 @subsubheading Synopsis
30124 -var-update [@var{print-values}] @{@var{name} | "*"@}
30127 Reevaluate the expressions corresponding to the variable object
30128 @var{name} and all its direct and indirect children, and return the
30129 list of variable objects whose values have changed; @var{name} must
30130 be a root variable object. Here, ``changed'' means that the result of
30131 @code{-var-evaluate-expression} before and after the
30132 @code{-var-update} is different. If @samp{*} is used as the variable
30133 object names, all existing variable objects are updated, except
30134 for frozen ones (@pxref{-var-set-frozen}). The option
30135 @var{print-values} determines whether both names and values, or just
30136 names are printed. The possible values of this option are the same
30137 as for @code{-var-list-children} (@pxref{-var-list-children}). It is
30138 recommended to use the @samp{--all-values} option, to reduce the
30139 number of MI commands needed on each program stop.
30141 With the @samp{*} parameter, if a variable object is bound to a
30142 currently running thread, it will not be updated, without any
30145 If @code{-var-set-update-range} was previously used on a varobj, then
30146 only the selected range of children will be reported.
30148 @code{-var-update} reports all the changed varobjs in a tuple named
30151 Each item in the change list is itself a tuple holding:
30155 The name of the varobj.
30158 If values were requested for this update, then this field will be
30159 present and will hold the value of the varobj.
30162 @anchor{-var-update}
30163 This field is a string which may take one of three values:
30167 The variable object's current value is valid.
30170 The variable object does not currently hold a valid value but it may
30171 hold one in the future if its associated expression comes back into
30175 The variable object no longer holds a valid value.
30176 This can occur when the executable file being debugged has changed,
30177 either through recompilation or by using the @value{GDBN} @code{file}
30178 command. The front end should normally choose to delete these variable
30182 In the future new values may be added to this list so the front should
30183 be prepared for this possibility. @xref{GDB/MI Development and Front Ends, ,@sc{GDB/MI} Development and Front Ends}.
30186 This is only present if the varobj is still valid. If the type
30187 changed, then this will be the string @samp{true}; otherwise it will
30190 When a varobj's type changes, its children are also likely to have
30191 become incorrect. Therefore, the varobj's children are automatically
30192 deleted when this attribute is @samp{true}. Also, the varobj's update
30193 range, when set using the @code{-var-set-update-range} command, is
30197 If the varobj's type changed, then this field will be present and will
30200 @item new_num_children
30201 For a dynamic varobj, if the number of children changed, or if the
30202 type changed, this will be the new number of children.
30204 The @samp{numchild} field in other varobj responses is generally not
30205 valid for a dynamic varobj -- it will show the number of children that
30206 @value{GDBN} knows about, but because dynamic varobjs lazily
30207 instantiate their children, this will not reflect the number of
30208 children which may be available.
30210 The @samp{new_num_children} attribute only reports changes to the
30211 number of children known by @value{GDBN}. This is the only way to
30212 detect whether an update has removed children (which necessarily can
30213 only happen at the end of the update range).
30216 The display hint, if any.
30219 This is an integer value, which will be 1 if there are more children
30220 available outside the varobj's update range.
30223 This attribute will be present and have the value @samp{1} if the
30224 varobj is a dynamic varobj. If the varobj is not a dynamic varobj,
30225 then this attribute will not be present.
30228 If new children were added to a dynamic varobj within the selected
30229 update range (as set by @code{-var-set-update-range}), then they will
30230 be listed in this attribute.
30233 @subsubheading Example
30240 -var-update --all-values var1
30241 ^done,changelist=[@{name="var1",value="3",in_scope="true",
30242 type_changed="false"@}]
30246 @subheading The @code{-var-set-frozen} Command
30247 @findex -var-set-frozen
30248 @anchor{-var-set-frozen}
30250 @subsubheading Synopsis
30253 -var-set-frozen @var{name} @var{flag}
30256 Set the frozenness flag on the variable object @var{name}. The
30257 @var{flag} parameter should be either @samp{1} to make the variable
30258 frozen or @samp{0} to make it unfrozen. If a variable object is
30259 frozen, then neither itself, nor any of its children, are
30260 implicitly updated by @code{-var-update} of
30261 a parent variable or by @code{-var-update *}. Only
30262 @code{-var-update} of the variable itself will update its value and
30263 values of its children. After a variable object is unfrozen, it is
30264 implicitly updated by all subsequent @code{-var-update} operations.
30265 Unfreezing a variable does not update it, only subsequent
30266 @code{-var-update} does.
30268 @subsubheading Example
30272 -var-set-frozen V 1
30277 @subheading The @code{-var-set-update-range} command
30278 @findex -var-set-update-range
30279 @anchor{-var-set-update-range}
30281 @subsubheading Synopsis
30284 -var-set-update-range @var{name} @var{from} @var{to}
30287 Set the range of children to be returned by future invocations of
30288 @code{-var-update}.
30290 @var{from} and @var{to} indicate the range of children to report. If
30291 @var{from} or @var{to} is less than zero, the range is reset and all
30292 children will be reported. Otherwise, children starting at @var{from}
30293 (zero-based) and up to and excluding @var{to} will be reported.
30295 @subsubheading Example
30299 -var-set-update-range V 1 2
30303 @subheading The @code{-var-set-visualizer} command
30304 @findex -var-set-visualizer
30305 @anchor{-var-set-visualizer}
30307 @subsubheading Synopsis
30310 -var-set-visualizer @var{name} @var{visualizer}
30313 Set a visualizer for the variable object @var{name}.
30315 @var{visualizer} is the visualizer to use. The special value
30316 @samp{None} means to disable any visualizer in use.
30318 If not @samp{None}, @var{visualizer} must be a Python expression.
30319 This expression must evaluate to a callable object which accepts a
30320 single argument. @value{GDBN} will call this object with the value of
30321 the varobj @var{name} as an argument (this is done so that the same
30322 Python pretty-printing code can be used for both the CLI and MI).
30323 When called, this object must return an object which conforms to the
30324 pretty-printing interface (@pxref{Pretty Printing API}).
30326 The pre-defined function @code{gdb.default_visualizer} may be used to
30327 select a visualizer by following the built-in process
30328 (@pxref{Selecting Pretty-Printers}). This is done automatically when
30329 a varobj is created, and so ordinarily is not needed.
30331 This feature is only available if Python support is enabled. The MI
30332 command @code{-list-features} (@pxref{GDB/MI Support Commands})
30333 can be used to check this.
30335 @subsubheading Example
30337 Resetting the visualizer:
30341 -var-set-visualizer V None
30345 Reselecting the default (type-based) visualizer:
30349 -var-set-visualizer V gdb.default_visualizer
30353 Suppose @code{SomeClass} is a visualizer class. A lambda expression
30354 can be used to instantiate this class for a varobj:
30358 -var-set-visualizer V "lambda val: SomeClass()"
30362 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
30363 @node GDB/MI Data Manipulation
30364 @section @sc{gdb/mi} Data Manipulation
30366 @cindex data manipulation, in @sc{gdb/mi}
30367 @cindex @sc{gdb/mi}, data manipulation
30368 This section describes the @sc{gdb/mi} commands that manipulate data:
30369 examine memory and registers, evaluate expressions, etc.
30371 For details about what an addressable memory unit is,
30372 @pxref{addressable memory unit}.
30374 @c REMOVED FROM THE INTERFACE.
30375 @c @subheading -data-assign
30376 @c Change the value of a program variable. Plenty of side effects.
30377 @c @subsubheading GDB Command
30379 @c @subsubheading Example
30382 @subheading The @code{-data-disassemble} Command
30383 @findex -data-disassemble
30385 @subsubheading Synopsis
30389 [ -s @var{start-addr} -e @var{end-addr} ]
30390 | [ -f @var{filename} -l @var{linenum} [ -n @var{lines} ] ]
30398 @item @var{start-addr}
30399 is the beginning address (or @code{$pc})
30400 @item @var{end-addr}
30402 @item @var{filename}
30403 is the name of the file to disassemble
30404 @item @var{linenum}
30405 is the line number to disassemble around
30407 is the number of disassembly lines to be produced. If it is -1,
30408 the whole function will be disassembled, in case no @var{end-addr} is
30409 specified. If @var{end-addr} is specified as a non-zero value, and
30410 @var{lines} is lower than the number of disassembly lines between
30411 @var{start-addr} and @var{end-addr}, only @var{lines} lines are
30412 displayed; if @var{lines} is higher than the number of lines between
30413 @var{start-addr} and @var{end-addr}, only the lines up to @var{end-addr}
30418 @item 0 disassembly only
30419 @item 1 mixed source and disassembly (deprecated)
30420 @item 2 disassembly with raw opcodes
30421 @item 3 mixed source and disassembly with raw opcodes (deprecated)
30422 @item 4 mixed source and disassembly
30423 @item 5 mixed source and disassembly with raw opcodes
30426 Modes 1 and 3 are deprecated. The output is ``source centric''
30427 which hasn't proved useful in practice.
30428 @xref{Machine Code}, for a discussion of the difference between
30429 @code{/m} and @code{/s} output of the @code{disassemble} command.
30432 @subsubheading Result
30434 The result of the @code{-data-disassemble} command will be a list named
30435 @samp{asm_insns}, the contents of this list depend on the @var{mode}
30436 used with the @code{-data-disassemble} command.
30438 For modes 0 and 2 the @samp{asm_insns} list contains tuples with the
30443 The address at which this instruction was disassembled.
30446 The name of the function this instruction is within.
30449 The decimal offset in bytes from the start of @samp{func-name}.
30452 The text disassembly for this @samp{address}.
30455 This field is only present for modes 2, 3 and 5. This contains the raw opcode
30456 bytes for the @samp{inst} field.
30460 For modes 1, 3, 4 and 5 the @samp{asm_insns} list contains tuples named
30461 @samp{src_and_asm_line}, each of which has the following fields:
30465 The line number within @samp{file}.
30468 The file name from the compilation unit. This might be an absolute
30469 file name or a relative file name depending on the compile command
30473 Absolute file name of @samp{file}. It is converted to a canonical form
30474 using the source file search path
30475 (@pxref{Source Path, ,Specifying Source Directories})
30476 and after resolving all the symbolic links.
30478 If the source file is not found this field will contain the path as
30479 present in the debug information.
30481 @item line_asm_insn
30482 This is a list of tuples containing the disassembly for @samp{line} in
30483 @samp{file}. The fields of each tuple are the same as for
30484 @code{-data-disassemble} in @var{mode} 0 and 2, so @samp{address},
30485 @samp{func-name}, @samp{offset}, @samp{inst}, and optionally
30490 Note that whatever included in the @samp{inst} field, is not
30491 manipulated directly by @sc{gdb/mi}, i.e., it is not possible to
30494 @subsubheading @value{GDBN} Command
30496 The corresponding @value{GDBN} command is @samp{disassemble}.
30498 @subsubheading Example
30500 Disassemble from the current value of @code{$pc} to @code{$pc + 20}:
30504 -data-disassemble -s $pc -e "$pc + 20" -- 0
30507 @{address="0x000107c0",func-name="main",offset="4",
30508 inst="mov 2, %o0"@},
30509 @{address="0x000107c4",func-name="main",offset="8",
30510 inst="sethi %hi(0x11800), %o2"@},
30511 @{address="0x000107c8",func-name="main",offset="12",
30512 inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"@},
30513 @{address="0x000107cc",func-name="main",offset="16",
30514 inst="sethi %hi(0x11800), %o2"@},
30515 @{address="0x000107d0",func-name="main",offset="20",
30516 inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"@}]
30520 Disassemble the whole @code{main} function. Line 32 is part of
30524 -data-disassemble -f basics.c -l 32 -- 0
30526 @{address="0x000107bc",func-name="main",offset="0",
30527 inst="save %sp, -112, %sp"@},
30528 @{address="0x000107c0",func-name="main",offset="4",
30529 inst="mov 2, %o0"@},
30530 @{address="0x000107c4",func-name="main",offset="8",
30531 inst="sethi %hi(0x11800), %o2"@},
30533 @{address="0x0001081c",func-name="main",offset="96",inst="ret "@},
30534 @{address="0x00010820",func-name="main",offset="100",inst="restore "@}]
30538 Disassemble 3 instructions from the start of @code{main}:
30542 -data-disassemble -f basics.c -l 32 -n 3 -- 0
30544 @{address="0x000107bc",func-name="main",offset="0",
30545 inst="save %sp, -112, %sp"@},
30546 @{address="0x000107c0",func-name="main",offset="4",
30547 inst="mov 2, %o0"@},
30548 @{address="0x000107c4",func-name="main",offset="8",
30549 inst="sethi %hi(0x11800), %o2"@}]
30553 Disassemble 3 instructions from the start of @code{main} in mixed mode:
30557 -data-disassemble -f basics.c -l 32 -n 3 -- 1
30559 src_and_asm_line=@{line="31",
30560 file="../../../src/gdb/testsuite/gdb.mi/basics.c",
30561 fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c",
30562 line_asm_insn=[@{address="0x000107bc",
30563 func-name="main",offset="0",inst="save %sp, -112, %sp"@}]@},
30564 src_and_asm_line=@{line="32",
30565 file="../../../src/gdb/testsuite/gdb.mi/basics.c",
30566 fullname="/absolute/path/to/src/gdb/testsuite/gdb.mi/basics.c",
30567 line_asm_insn=[@{address="0x000107c0",
30568 func-name="main",offset="4",inst="mov 2, %o0"@},
30569 @{address="0x000107c4",func-name="main",offset="8",
30570 inst="sethi %hi(0x11800), %o2"@}]@}]
30575 @subheading The @code{-data-evaluate-expression} Command
30576 @findex -data-evaluate-expression
30578 @subsubheading Synopsis
30581 -data-evaluate-expression @var{expr}
30584 Evaluate @var{expr} as an expression. The expression could contain an
30585 inferior function call. The function call will execute synchronously.
30586 If the expression contains spaces, it must be enclosed in double quotes.
30588 @subsubheading @value{GDBN} Command
30590 The corresponding @value{GDBN} commands are @samp{print}, @samp{output}, and
30591 @samp{call}. In @code{gdbtk} only, there's a corresponding
30592 @samp{gdb_eval} command.
30594 @subsubheading Example
30596 In the following example, the numbers that precede the commands are the
30597 @dfn{tokens} described in @ref{GDB/MI Command Syntax, ,@sc{gdb/mi}
30598 Command Syntax}. Notice how @sc{gdb/mi} returns the same tokens in its
30602 211-data-evaluate-expression A
30605 311-data-evaluate-expression &A
30606 311^done,value="0xefffeb7c"
30608 411-data-evaluate-expression A+3
30611 511-data-evaluate-expression "A + 3"
30617 @subheading The @code{-data-list-changed-registers} Command
30618 @findex -data-list-changed-registers
30620 @subsubheading Synopsis
30623 -data-list-changed-registers
30626 Display a list of the registers that have changed.
30628 @subsubheading @value{GDBN} Command
30630 @value{GDBN} doesn't have a direct analog for this command; @code{gdbtk}
30631 has the corresponding command @samp{gdb_changed_register_list}.
30633 @subsubheading Example
30635 On a PPC MBX board:
30643 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame=@{
30644 func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c",
30647 -data-list-changed-registers
30648 ^done,changed-registers=["0","1","2","4","5","6","7","8","9",
30649 "10","11","13","14","15","16","17","18","19","20","21","22","23",
30650 "24","25","26","27","28","30","31","64","65","66","67","69"]
30655 @subheading The @code{-data-list-register-names} Command
30656 @findex -data-list-register-names
30658 @subsubheading Synopsis
30661 -data-list-register-names [ ( @var{regno} )+ ]
30664 Show a list of register names for the current target. If no arguments
30665 are given, it shows a list of the names of all the registers. If
30666 integer numbers are given as arguments, it will print a list of the
30667 names of the registers corresponding to the arguments. To ensure
30668 consistency between a register name and its number, the output list may
30669 include empty register names.
30671 @subsubheading @value{GDBN} Command
30673 @value{GDBN} does not have a command which corresponds to
30674 @samp{-data-list-register-names}. In @code{gdbtk} there is a
30675 corresponding command @samp{gdb_regnames}.
30677 @subsubheading Example
30679 For the PPC MBX board:
30682 -data-list-register-names
30683 ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7",
30684 "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18",
30685 "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29",
30686 "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9",
30687 "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20",
30688 "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31",
30689 "", "pc","ps","cr","lr","ctr","xer"]
30691 -data-list-register-names 1 2 3
30692 ^done,register-names=["r1","r2","r3"]
30696 @subheading The @code{-data-list-register-values} Command
30697 @findex -data-list-register-values
30699 @subsubheading Synopsis
30702 -data-list-register-values
30703 [ @code{--skip-unavailable} ] @var{fmt} [ ( @var{regno} )*]
30706 Display the registers' contents. The format according to which the
30707 registers' contents are to be returned is given by @var{fmt}, followed
30708 by an optional list of numbers specifying the registers to display. A
30709 missing list of numbers indicates that the contents of all the
30710 registers must be returned. The @code{--skip-unavailable} option
30711 indicates that only the available registers are to be returned.
30713 Allowed formats for @var{fmt} are:
30730 @subsubheading @value{GDBN} Command
30732 The corresponding @value{GDBN} commands are @samp{info reg}, @samp{info
30733 all-reg}, and (in @code{gdbtk}) @samp{gdb_fetch_registers}.
30735 @subsubheading Example
30737 For a PPC MBX board (note: line breaks are for readability only, they
30738 don't appear in the actual output):
30742 -data-list-register-values r 64 65
30743 ^done,register-values=[@{number="64",value="0xfe00a300"@},
30744 @{number="65",value="0x00029002"@}]
30746 -data-list-register-values x
30747 ^done,register-values=[@{number="0",value="0xfe0043c8"@},
30748 @{number="1",value="0x3fff88"@},@{number="2",value="0xfffffffe"@},
30749 @{number="3",value="0x0"@},@{number="4",value="0xa"@},
30750 @{number="5",value="0x3fff68"@},@{number="6",value="0x3fff58"@},
30751 @{number="7",value="0xfe011e98"@},@{number="8",value="0x2"@},
30752 @{number="9",value="0xfa202820"@},@{number="10",value="0xfa202808"@},
30753 @{number="11",value="0x1"@},@{number="12",value="0x0"@},
30754 @{number="13",value="0x4544"@},@{number="14",value="0xffdfffff"@},
30755 @{number="15",value="0xffffffff"@},@{number="16",value="0xfffffeff"@},
30756 @{number="17",value="0xefffffed"@},@{number="18",value="0xfffffffe"@},
30757 @{number="19",value="0xffffffff"@},@{number="20",value="0xffffffff"@},
30758 @{number="21",value="0xffffffff"@},@{number="22",value="0xfffffff7"@},
30759 @{number="23",value="0xffffffff"@},@{number="24",value="0xffffffff"@},
30760 @{number="25",value="0xffffffff"@},@{number="26",value="0xfffffffb"@},
30761 @{number="27",value="0xffffffff"@},@{number="28",value="0xf7bfffff"@},
30762 @{number="29",value="0x0"@},@{number="30",value="0xfe010000"@},
30763 @{number="31",value="0x0"@},@{number="32",value="0x0"@},
30764 @{number="33",value="0x0"@},@{number="34",value="0x0"@},
30765 @{number="35",value="0x0"@},@{number="36",value="0x0"@},
30766 @{number="37",value="0x0"@},@{number="38",value="0x0"@},
30767 @{number="39",value="0x0"@},@{number="40",value="0x0"@},
30768 @{number="41",value="0x0"@},@{number="42",value="0x0"@},
30769 @{number="43",value="0x0"@},@{number="44",value="0x0"@},
30770 @{number="45",value="0x0"@},@{number="46",value="0x0"@},
30771 @{number="47",value="0x0"@},@{number="48",value="0x0"@},
30772 @{number="49",value="0x0"@},@{number="50",value="0x0"@},
30773 @{number="51",value="0x0"@},@{number="52",value="0x0"@},
30774 @{number="53",value="0x0"@},@{number="54",value="0x0"@},
30775 @{number="55",value="0x0"@},@{number="56",value="0x0"@},
30776 @{number="57",value="0x0"@},@{number="58",value="0x0"@},
30777 @{number="59",value="0x0"@},@{number="60",value="0x0"@},
30778 @{number="61",value="0x0"@},@{number="62",value="0x0"@},
30779 @{number="63",value="0x0"@},@{number="64",value="0xfe00a300"@},
30780 @{number="65",value="0x29002"@},@{number="66",value="0x202f04b5"@},
30781 @{number="67",value="0xfe0043b0"@},@{number="68",value="0xfe00b3e4"@},
30782 @{number="69",value="0x20002b03"@}]
30787 @subheading The @code{-data-read-memory} Command
30788 @findex -data-read-memory
30790 This command is deprecated, use @code{-data-read-memory-bytes} instead.
30792 @subsubheading Synopsis
30795 -data-read-memory [ -o @var{byte-offset} ]
30796 @var{address} @var{word-format} @var{word-size}
30797 @var{nr-rows} @var{nr-cols} [ @var{aschar} ]
30804 @item @var{address}
30805 An expression specifying the address of the first memory word to be
30806 read. Complex expressions containing embedded white space should be
30807 quoted using the C convention.
30809 @item @var{word-format}
30810 The format to be used to print the memory words. The notation is the
30811 same as for @value{GDBN}'s @code{print} command (@pxref{Output Formats,
30814 @item @var{word-size}
30815 The size of each memory word in bytes.
30817 @item @var{nr-rows}
30818 The number of rows in the output table.
30820 @item @var{nr-cols}
30821 The number of columns in the output table.
30824 If present, indicates that each row should include an @sc{ascii} dump. The
30825 value of @var{aschar} is used as a padding character when a byte is not a
30826 member of the printable @sc{ascii} character set (printable @sc{ascii}
30827 characters are those whose code is between 32 and 126, inclusively).
30829 @item @var{byte-offset}
30830 An offset to add to the @var{address} before fetching memory.
30833 This command displays memory contents as a table of @var{nr-rows} by
30834 @var{nr-cols} words, each word being @var{word-size} bytes. In total,
30835 @code{@var{nr-rows} * @var{nr-cols} * @var{word-size}} bytes are read
30836 (returned as @samp{total-bytes}). Should less than the requested number
30837 of bytes be returned by the target, the missing words are identified
30838 using @samp{N/A}. The number of bytes read from the target is returned
30839 in @samp{nr-bytes} and the starting address used to read memory in
30842 The address of the next/previous row or page is available in
30843 @samp{next-row} and @samp{prev-row}, @samp{next-page} and
30846 @subsubheading @value{GDBN} Command
30848 The corresponding @value{GDBN} command is @samp{x}. @code{gdbtk} has
30849 @samp{gdb_get_mem} memory read command.
30851 @subsubheading Example
30853 Read six bytes of memory starting at @code{bytes+6} but then offset by
30854 @code{-6} bytes. Format as three rows of two columns. One byte per
30855 word. Display each word in hex.
30859 9-data-read-memory -o -6 -- bytes+6 x 1 3 2
30860 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6",
30861 next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396",
30862 prev-page="0x0000138a",memory=[
30863 @{addr="0x00001390",data=["0x00","0x01"]@},
30864 @{addr="0x00001392",data=["0x02","0x03"]@},
30865 @{addr="0x00001394",data=["0x04","0x05"]@}]
30869 Read two bytes of memory starting at address @code{shorts + 64} and
30870 display as a single word formatted in decimal.
30874 5-data-read-memory shorts+64 d 2 1 1
30875 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2",
30876 next-row="0x00001512",prev-row="0x0000150e",
30877 next-page="0x00001512",prev-page="0x0000150e",memory=[
30878 @{addr="0x00001510",data=["128"]@}]
30882 Read thirty two bytes of memory starting at @code{bytes+16} and format
30883 as eight rows of four columns. Include a string encoding with @samp{x}
30884 used as the non-printable character.
30888 4-data-read-memory bytes+16 x 1 8 4 x
30889 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32",
30890 next-row="0x000013c0",prev-row="0x0000139c",
30891 next-page="0x000013c0",prev-page="0x00001380",memory=[
30892 @{addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"@},
30893 @{addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"@},
30894 @{addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"@},
30895 @{addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"@},
30896 @{addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"@},
30897 @{addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"@},
30898 @{addr="0x000013b8",data=["0x28","0x29","0x2a","0x2b"],ascii="()*+"@},
30899 @{addr="0x000013bc",data=["0x2c","0x2d","0x2e","0x2f"],ascii=",-./"@}]
30903 @subheading The @code{-data-read-memory-bytes} Command
30904 @findex -data-read-memory-bytes
30906 @subsubheading Synopsis
30909 -data-read-memory-bytes [ -o @var{offset} ]
30910 @var{address} @var{count}
30917 @item @var{address}
30918 An expression specifying the address of the first addressable memory unit
30919 to be read. Complex expressions containing embedded white space should be
30920 quoted using the C convention.
30923 The number of addressable memory units to read. This should be an integer
30927 The offset relative to @var{address} at which to start reading. This
30928 should be an integer literal. This option is provided so that a frontend
30929 is not required to first evaluate address and then perform address
30930 arithmetics itself.
30934 This command attempts to read all accessible memory regions in the
30935 specified range. First, all regions marked as unreadable in the memory
30936 map (if one is defined) will be skipped. @xref{Memory Region
30937 Attributes}. Second, @value{GDBN} will attempt to read the remaining
30938 regions. For each one, if reading full region results in an errors,
30939 @value{GDBN} will try to read a subset of the region.
30941 In general, every single memory unit in the region may be readable or not,
30942 and the only way to read every readable unit is to try a read at
30943 every address, which is not practical. Therefore, @value{GDBN} will
30944 attempt to read all accessible memory units at either beginning or the end
30945 of the region, using a binary division scheme. This heuristic works
30946 well for reading accross a memory map boundary. Note that if a region
30947 has a readable range that is neither at the beginning or the end,
30948 @value{GDBN} will not read it.
30950 The result record (@pxref{GDB/MI Result Records}) that is output of
30951 the command includes a field named @samp{memory} whose content is a
30952 list of tuples. Each tuple represent a successfully read memory block
30953 and has the following fields:
30957 The start address of the memory block, as hexadecimal literal.
30960 The end address of the memory block, as hexadecimal literal.
30963 The offset of the memory block, as hexadecimal literal, relative to
30964 the start address passed to @code{-data-read-memory-bytes}.
30967 The contents of the memory block, in hex.
30973 @subsubheading @value{GDBN} Command
30975 The corresponding @value{GDBN} command is @samp{x}.
30977 @subsubheading Example
30981 -data-read-memory-bytes &a 10
30982 ^done,memory=[@{begin="0xbffff154",offset="0x00000000",
30984 contents="01000000020000000300"@}]
30989 @subheading The @code{-data-write-memory-bytes} Command
30990 @findex -data-write-memory-bytes
30992 @subsubheading Synopsis
30995 -data-write-memory-bytes @var{address} @var{contents}
30996 -data-write-memory-bytes @var{address} @var{contents} @r{[}@var{count}@r{]}
31003 @item @var{address}
31004 An expression specifying the address of the first addressable memory unit
31005 to be written. Complex expressions containing embedded white space should
31006 be quoted using the C convention.
31008 @item @var{contents}
31009 The hex-encoded data to write. It is an error if @var{contents} does
31010 not represent an integral number of addressable memory units.
31013 Optional argument indicating the number of addressable memory units to be
31014 written. If @var{count} is greater than @var{contents}' length,
31015 @value{GDBN} will repeatedly write @var{contents} until it fills
31016 @var{count} memory units.
31020 @subsubheading @value{GDBN} Command
31022 There's no corresponding @value{GDBN} command.
31024 @subsubheading Example
31028 -data-write-memory-bytes &a "aabbccdd"
31035 -data-write-memory-bytes &a "aabbccdd" 16e
31040 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31041 @node GDB/MI Tracepoint Commands
31042 @section @sc{gdb/mi} Tracepoint Commands
31044 The commands defined in this section implement MI support for
31045 tracepoints. For detailed introduction, see @ref{Tracepoints}.
31047 @subheading The @code{-trace-find} Command
31048 @findex -trace-find
31050 @subsubheading Synopsis
31053 -trace-find @var{mode} [@var{parameters}@dots{}]
31056 Find a trace frame using criteria defined by @var{mode} and
31057 @var{parameters}. The following table lists permissible
31058 modes and their parameters. For details of operation, see @ref{tfind}.
31063 No parameters are required. Stops examining trace frames.
31066 An integer is required as parameter. Selects tracepoint frame with
31069 @item tracepoint-number
31070 An integer is required as parameter. Finds next
31071 trace frame that corresponds to tracepoint with the specified number.
31074 An address is required as parameter. Finds
31075 next trace frame that corresponds to any tracepoint at the specified
31078 @item pc-inside-range
31079 Two addresses are required as parameters. Finds next trace
31080 frame that corresponds to a tracepoint at an address inside the
31081 specified range. Both bounds are considered to be inside the range.
31083 @item pc-outside-range
31084 Two addresses are required as parameters. Finds
31085 next trace frame that corresponds to a tracepoint at an address outside
31086 the specified range. Both bounds are considered to be inside the range.
31089 Line specification is required as parameter. @xref{Specify Location}.
31090 Finds next trace frame that corresponds to a tracepoint at
31091 the specified location.
31095 If @samp{none} was passed as @var{mode}, the response does not
31096 have fields. Otherwise, the response may have the following fields:
31100 This field has either @samp{0} or @samp{1} as the value, depending
31101 on whether a matching tracepoint was found.
31104 The index of the found traceframe. This field is present iff
31105 the @samp{found} field has value of @samp{1}.
31108 The index of the found tracepoint. This field is present iff
31109 the @samp{found} field has value of @samp{1}.
31112 The information about the frame corresponding to the found trace
31113 frame. This field is present only if a trace frame was found.
31114 @xref{GDB/MI Frame Information}, for description of this field.
31118 @subsubheading @value{GDBN} Command
31120 The corresponding @value{GDBN} command is @samp{tfind}.
31122 @subheading -trace-define-variable
31123 @findex -trace-define-variable
31125 @subsubheading Synopsis
31128 -trace-define-variable @var{name} [ @var{value} ]
31131 Create trace variable @var{name} if it does not exist. If
31132 @var{value} is specified, sets the initial value of the specified
31133 trace variable to that value. Note that the @var{name} should start
31134 with the @samp{$} character.
31136 @subsubheading @value{GDBN} Command
31138 The corresponding @value{GDBN} command is @samp{tvariable}.
31140 @subheading The @code{-trace-frame-collected} Command
31141 @findex -trace-frame-collected
31143 @subsubheading Synopsis
31146 -trace-frame-collected
31147 [--var-print-values @var{var_pval}]
31148 [--comp-print-values @var{comp_pval}]
31149 [--registers-format @var{regformat}]
31150 [--memory-contents]
31153 This command returns the set of collected objects, register names,
31154 trace state variable names, memory ranges and computed expressions
31155 that have been collected at a particular trace frame. The optional
31156 parameters to the command affect the output format in different ways.
31157 See the output description table below for more details.
31159 The reported names can be used in the normal manner to create
31160 varobjs and inspect the objects themselves. The items returned by
31161 this command are categorized so that it is clear which is a variable,
31162 which is a register, which is a trace state variable, which is a
31163 memory range and which is a computed expression.
31165 For instance, if the actions were
31167 collect myVar, myArray[myIndex], myObj.field, myPtr->field, myCount + 2
31168 collect *(int*)0xaf02bef0@@40
31172 the object collected in its entirety would be @code{myVar}. The
31173 object @code{myArray} would be partially collected, because only the
31174 element at index @code{myIndex} would be collected. The remaining
31175 objects would be computed expressions.
31177 An example output would be:
31181 -trace-frame-collected
31183 explicit-variables=[@{name="myVar",value="1"@}],
31184 computed-expressions=[@{name="myArray[myIndex]",value="0"@},
31185 @{name="myObj.field",value="0"@},
31186 @{name="myPtr->field",value="1"@},
31187 @{name="myCount + 2",value="3"@},
31188 @{name="$tvar1 + 1",value="43970027"@}],
31189 registers=[@{number="0",value="0x7fe2c6e79ec8"@},
31190 @{number="1",value="0x0"@},
31191 @{number="2",value="0x4"@},
31193 @{number="125",value="0x0"@}],
31194 tvars=[@{name="$tvar1",current="43970026"@}],
31195 memory=[@{address="0x0000000000602264",length="4"@},
31196 @{address="0x0000000000615bc0",length="4"@}]
31203 @item explicit-variables
31204 The set of objects that have been collected in their entirety (as
31205 opposed to collecting just a few elements of an array or a few struct
31206 members). For each object, its name and value are printed.
31207 The @code{--var-print-values} option affects how or whether the value
31208 field is output. If @var{var_pval} is 0, then print only the names;
31209 if it is 1, print also their values; and if it is 2, print the name,
31210 type and value for simple data types, and the name and type for
31211 arrays, structures and unions.
31213 @item computed-expressions
31214 The set of computed expressions that have been collected at the
31215 current trace frame. The @code{--comp-print-values} option affects
31216 this set like the @code{--var-print-values} option affects the
31217 @code{explicit-variables} set. See above.
31220 The registers that have been collected at the current trace frame.
31221 For each register collected, the name and current value are returned.
31222 The value is formatted according to the @code{--registers-format}
31223 option. See the @command{-data-list-register-values} command for a
31224 list of the allowed formats. The default is @samp{x}.
31227 The trace state variables that have been collected at the current
31228 trace frame. For each trace state variable collected, the name and
31229 current value are returned.
31232 The set of memory ranges that have been collected at the current trace
31233 frame. Its content is a list of tuples. Each tuple represents a
31234 collected memory range and has the following fields:
31238 The start address of the memory range, as hexadecimal literal.
31241 The length of the memory range, as decimal literal.
31244 The contents of the memory block, in hex. This field is only present
31245 if the @code{--memory-contents} option is specified.
31251 @subsubheading @value{GDBN} Command
31253 There is no corresponding @value{GDBN} command.
31255 @subsubheading Example
31257 @subheading -trace-list-variables
31258 @findex -trace-list-variables
31260 @subsubheading Synopsis
31263 -trace-list-variables
31266 Return a table of all defined trace variables. Each element of the
31267 table has the following fields:
31271 The name of the trace variable. This field is always present.
31274 The initial value. This is a 64-bit signed integer. This
31275 field is always present.
31278 The value the trace variable has at the moment. This is a 64-bit
31279 signed integer. This field is absent iff current value is
31280 not defined, for example if the trace was never run, or is
31285 @subsubheading @value{GDBN} Command
31287 The corresponding @value{GDBN} command is @samp{tvariables}.
31289 @subsubheading Example
31293 -trace-list-variables
31294 ^done,trace-variables=@{nr_rows="1",nr_cols="3",
31295 hdr=[@{width="15",alignment="-1",col_name="name",colhdr="Name"@},
31296 @{width="11",alignment="-1",col_name="initial",colhdr="Initial"@},
31297 @{width="11",alignment="-1",col_name="current",colhdr="Current"@}],
31298 body=[variable=@{name="$trace_timestamp",initial="0"@}
31299 variable=@{name="$foo",initial="10",current="15"@}]@}
31303 @subheading -trace-save
31304 @findex -trace-save
31306 @subsubheading Synopsis
31309 -trace-save [ -r ] [ -ctf ] @var{filename}
31312 Saves the collected trace data to @var{filename}. Without the
31313 @samp{-r} option, the data is downloaded from the target and saved
31314 in a local file. With the @samp{-r} option the target is asked
31315 to perform the save.
31317 By default, this command will save the trace in the tfile format. You can
31318 supply the optional @samp{-ctf} argument to save it the CTF format. See
31319 @ref{Trace Files} for more information about CTF.
31321 @subsubheading @value{GDBN} Command
31323 The corresponding @value{GDBN} command is @samp{tsave}.
31326 @subheading -trace-start
31327 @findex -trace-start
31329 @subsubheading Synopsis
31335 Starts a tracing experiment. The result of this command does not
31338 @subsubheading @value{GDBN} Command
31340 The corresponding @value{GDBN} command is @samp{tstart}.
31342 @subheading -trace-status
31343 @findex -trace-status
31345 @subsubheading Synopsis
31351 Obtains the status of a tracing experiment. The result may include
31352 the following fields:
31357 May have a value of either @samp{0}, when no tracing operations are
31358 supported, @samp{1}, when all tracing operations are supported, or
31359 @samp{file} when examining trace file. In the latter case, examining
31360 of trace frame is possible but new tracing experiement cannot be
31361 started. This field is always present.
31364 May have a value of either @samp{0} or @samp{1} depending on whether
31365 tracing experiement is in progress on target. This field is present
31366 if @samp{supported} field is not @samp{0}.
31369 Report the reason why the tracing was stopped last time. This field
31370 may be absent iff tracing was never stopped on target yet. The
31371 value of @samp{request} means the tracing was stopped as result of
31372 the @code{-trace-stop} command. The value of @samp{overflow} means
31373 the tracing buffer is full. The value of @samp{disconnection} means
31374 tracing was automatically stopped when @value{GDBN} has disconnected.
31375 The value of @samp{passcount} means tracing was stopped when a
31376 tracepoint was passed a maximal number of times for that tracepoint.
31377 This field is present if @samp{supported} field is not @samp{0}.
31379 @item stopping-tracepoint
31380 The number of tracepoint whose passcount as exceeded. This field is
31381 present iff the @samp{stop-reason} field has the value of
31385 @itemx frames-created
31386 The @samp{frames} field is a count of the total number of trace frames
31387 in the trace buffer, while @samp{frames-created} is the total created
31388 during the run, including ones that were discarded, such as when a
31389 circular trace buffer filled up. Both fields are optional.
31393 These fields tell the current size of the tracing buffer and the
31394 remaining space. These fields are optional.
31397 The value of the circular trace buffer flag. @code{1} means that the
31398 trace buffer is circular and old trace frames will be discarded if
31399 necessary to make room, @code{0} means that the trace buffer is linear
31403 The value of the disconnected tracing flag. @code{1} means that
31404 tracing will continue after @value{GDBN} disconnects, @code{0} means
31405 that the trace run will stop.
31408 The filename of the trace file being examined. This field is
31409 optional, and only present when examining a trace file.
31413 @subsubheading @value{GDBN} Command
31415 The corresponding @value{GDBN} command is @samp{tstatus}.
31417 @subheading -trace-stop
31418 @findex -trace-stop
31420 @subsubheading Synopsis
31426 Stops a tracing experiment. The result of this command has the same
31427 fields as @code{-trace-status}, except that the @samp{supported} and
31428 @samp{running} fields are not output.
31430 @subsubheading @value{GDBN} Command
31432 The corresponding @value{GDBN} command is @samp{tstop}.
31435 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31436 @node GDB/MI Symbol Query
31437 @section @sc{gdb/mi} Symbol Query Commands
31441 @subheading The @code{-symbol-info-address} Command
31442 @findex -symbol-info-address
31444 @subsubheading Synopsis
31447 -symbol-info-address @var{symbol}
31450 Describe where @var{symbol} is stored.
31452 @subsubheading @value{GDBN} Command
31454 The corresponding @value{GDBN} command is @samp{info address}.
31456 @subsubheading Example
31460 @subheading The @code{-symbol-info-file} Command
31461 @findex -symbol-info-file
31463 @subsubheading Synopsis
31469 Show the file for the symbol.
31471 @subsubheading @value{GDBN} Command
31473 There's no equivalent @value{GDBN} command. @code{gdbtk} has
31474 @samp{gdb_find_file}.
31476 @subsubheading Example
31480 @subheading The @code{-symbol-info-function} Command
31481 @findex -symbol-info-function
31483 @subsubheading Synopsis
31486 -symbol-info-function
31489 Show which function the symbol lives in.
31491 @subsubheading @value{GDBN} Command
31493 @samp{gdb_get_function} in @code{gdbtk}.
31495 @subsubheading Example
31499 @subheading The @code{-symbol-info-line} Command
31500 @findex -symbol-info-line
31502 @subsubheading Synopsis
31508 Show the core addresses of the code for a source line.
31510 @subsubheading @value{GDBN} Command
31512 The corresponding @value{GDBN} command is @samp{info line}.
31513 @code{gdbtk} has the @samp{gdb_get_line} and @samp{gdb_get_file} commands.
31515 @subsubheading Example
31519 @subheading The @code{-symbol-info-symbol} Command
31520 @findex -symbol-info-symbol
31522 @subsubheading Synopsis
31525 -symbol-info-symbol @var{addr}
31528 Describe what symbol is at location @var{addr}.
31530 @subsubheading @value{GDBN} Command
31532 The corresponding @value{GDBN} command is @samp{info symbol}.
31534 @subsubheading Example
31538 @subheading The @code{-symbol-list-functions} Command
31539 @findex -symbol-list-functions
31541 @subsubheading Synopsis
31544 -symbol-list-functions
31547 List the functions in the executable.
31549 @subsubheading @value{GDBN} Command
31551 @samp{info functions} in @value{GDBN}, @samp{gdb_listfunc} and
31552 @samp{gdb_search} in @code{gdbtk}.
31554 @subsubheading Example
31559 @subheading The @code{-symbol-list-lines} Command
31560 @findex -symbol-list-lines
31562 @subsubheading Synopsis
31565 -symbol-list-lines @var{filename}
31568 Print the list of lines that contain code and their associated program
31569 addresses for the given source filename. The entries are sorted in
31570 ascending PC order.
31572 @subsubheading @value{GDBN} Command
31574 There is no corresponding @value{GDBN} command.
31576 @subsubheading Example
31579 -symbol-list-lines basics.c
31580 ^done,lines=[@{pc="0x08048554",line="7"@},@{pc="0x0804855a",line="8"@}]
31586 @subheading The @code{-symbol-list-types} Command
31587 @findex -symbol-list-types
31589 @subsubheading Synopsis
31595 List all the type names.
31597 @subsubheading @value{GDBN} Command
31599 The corresponding commands are @samp{info types} in @value{GDBN},
31600 @samp{gdb_search} in @code{gdbtk}.
31602 @subsubheading Example
31606 @subheading The @code{-symbol-list-variables} Command
31607 @findex -symbol-list-variables
31609 @subsubheading Synopsis
31612 -symbol-list-variables
31615 List all the global and static variable names.
31617 @subsubheading @value{GDBN} Command
31619 @samp{info variables} in @value{GDBN}, @samp{gdb_search} in @code{gdbtk}.
31621 @subsubheading Example
31625 @subheading The @code{-symbol-locate} Command
31626 @findex -symbol-locate
31628 @subsubheading Synopsis
31634 @subsubheading @value{GDBN} Command
31636 @samp{gdb_loc} in @code{gdbtk}.
31638 @subsubheading Example
31642 @subheading The @code{-symbol-type} Command
31643 @findex -symbol-type
31645 @subsubheading Synopsis
31648 -symbol-type @var{variable}
31651 Show type of @var{variable}.
31653 @subsubheading @value{GDBN} Command
31655 The corresponding @value{GDBN} command is @samp{ptype}, @code{gdbtk} has
31656 @samp{gdb_obj_variable}.
31658 @subsubheading Example
31663 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31664 @node GDB/MI File Commands
31665 @section @sc{gdb/mi} File Commands
31667 This section describes the GDB/MI commands to specify executable file names
31668 and to read in and obtain symbol table information.
31670 @subheading The @code{-file-exec-and-symbols} Command
31671 @findex -file-exec-and-symbols
31673 @subsubheading Synopsis
31676 -file-exec-and-symbols @var{file}
31679 Specify the executable file to be debugged. This file is the one from
31680 which the symbol table is also read. If no file is specified, the
31681 command clears the executable and symbol information. If breakpoints
31682 are set when using this command with no arguments, @value{GDBN} will produce
31683 error messages. Otherwise, no output is produced, except a completion
31686 @subsubheading @value{GDBN} Command
31688 The corresponding @value{GDBN} command is @samp{file}.
31690 @subsubheading Example
31694 -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
31700 @subheading The @code{-file-exec-file} Command
31701 @findex -file-exec-file
31703 @subsubheading Synopsis
31706 -file-exec-file @var{file}
31709 Specify the executable file to be debugged. Unlike
31710 @samp{-file-exec-and-symbols}, the symbol table is @emph{not} read
31711 from this file. If used without argument, @value{GDBN} clears the information
31712 about the executable file. No output is produced, except a completion
31715 @subsubheading @value{GDBN} Command
31717 The corresponding @value{GDBN} command is @samp{exec-file}.
31719 @subsubheading Example
31723 -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
31730 @subheading The @code{-file-list-exec-sections} Command
31731 @findex -file-list-exec-sections
31733 @subsubheading Synopsis
31736 -file-list-exec-sections
31739 List the sections of the current executable file.
31741 @subsubheading @value{GDBN} Command
31743 The @value{GDBN} command @samp{info file} shows, among the rest, the same
31744 information as this command. @code{gdbtk} has a corresponding command
31745 @samp{gdb_load_info}.
31747 @subsubheading Example
31752 @subheading The @code{-file-list-exec-source-file} Command
31753 @findex -file-list-exec-source-file
31755 @subsubheading Synopsis
31758 -file-list-exec-source-file
31761 List the line number, the current source file, and the absolute path
31762 to the current source file for the current executable. The macro
31763 information field has a value of @samp{1} or @samp{0} depending on
31764 whether or not the file includes preprocessor macro information.
31766 @subsubheading @value{GDBN} Command
31768 The @value{GDBN} equivalent is @samp{info source}
31770 @subsubheading Example
31774 123-file-list-exec-source-file
31775 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1"
31780 @subheading The @code{-file-list-exec-source-files} Command
31781 @findex -file-list-exec-source-files
31783 @subsubheading Synopsis
31786 -file-list-exec-source-files
31789 List the source files for the current executable.
31791 It will always output both the filename and fullname (absolute file
31792 name) of a source file.
31794 @subsubheading @value{GDBN} Command
31796 The @value{GDBN} equivalent is @samp{info sources}.
31797 @code{gdbtk} has an analogous command @samp{gdb_listfiles}.
31799 @subsubheading Example
31802 -file-list-exec-source-files
31804 @{file=foo.c,fullname=/home/foo.c@},
31805 @{file=/home/bar.c,fullname=/home/bar.c@},
31806 @{file=gdb_could_not_find_fullpath.c@}]
31810 @subheading The @code{-file-list-shared-libraries} Command
31811 @findex -file-list-shared-libraries
31813 @subsubheading Synopsis
31816 -file-list-shared-libraries [ @var{regexp} ]
31819 List the shared libraries in the program.
31820 With a regular expression @var{regexp}, only those libraries whose
31821 names match @var{regexp} are listed.
31823 @subsubheading @value{GDBN} Command
31825 The corresponding @value{GDBN} command is @samp{info shared}. The fields
31826 have a similar meaning to the @code{=library-loaded} notification.
31827 The @code{ranges} field specifies the multiple segments belonging to this
31828 library. Each range has the following fields:
31832 The address defining the inclusive lower bound of the segment.
31834 The address defining the exclusive upper bound of the segment.
31837 @subsubheading Example
31840 -file-list-exec-source-files
31841 ^done,shared-libraries=[
31842 @{id="/lib/libfoo.so",target-name="/lib/libfoo.so",host-name="/lib/libfoo.so",symbols-loaded="1",thread-group="i1",ranges=[@{from="0x72815989",to="0x728162c0"@}]@},
31843 @{id="/lib/libbar.so",target-name="/lib/libbar.so",host-name="/lib/libbar.so",symbols-loaded="1",thread-group="i1",ranges=[@{from="0x76ee48c0",to="0x76ee9160"@}]@}]
31849 @subheading The @code{-file-list-symbol-files} Command
31850 @findex -file-list-symbol-files
31852 @subsubheading Synopsis
31855 -file-list-symbol-files
31860 @subsubheading @value{GDBN} Command
31862 The corresponding @value{GDBN} command is @samp{info file} (part of it).
31864 @subsubheading Example
31869 @subheading The @code{-file-symbol-file} Command
31870 @findex -file-symbol-file
31872 @subsubheading Synopsis
31875 -file-symbol-file @var{file}
31878 Read symbol table info from the specified @var{file} argument. When
31879 used without arguments, clears @value{GDBN}'s symbol table info. No output is
31880 produced, except for a completion notification.
31882 @subsubheading @value{GDBN} Command
31884 The corresponding @value{GDBN} command is @samp{symbol-file}.
31886 @subsubheading Example
31890 -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx
31896 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31897 @node GDB/MI Memory Overlay Commands
31898 @section @sc{gdb/mi} Memory Overlay Commands
31900 The memory overlay commands are not implemented.
31902 @c @subheading -overlay-auto
31904 @c @subheading -overlay-list-mapping-state
31906 @c @subheading -overlay-list-overlays
31908 @c @subheading -overlay-map
31910 @c @subheading -overlay-off
31912 @c @subheading -overlay-on
31914 @c @subheading -overlay-unmap
31916 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31917 @node GDB/MI Signal Handling Commands
31918 @section @sc{gdb/mi} Signal Handling Commands
31920 Signal handling commands are not implemented.
31922 @c @subheading -signal-handle
31924 @c @subheading -signal-list-handle-actions
31926 @c @subheading -signal-list-signal-types
31930 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
31931 @node GDB/MI Target Manipulation
31932 @section @sc{gdb/mi} Target Manipulation Commands
31935 @subheading The @code{-target-attach} Command
31936 @findex -target-attach
31938 @subsubheading Synopsis
31941 -target-attach @var{pid} | @var{gid} | @var{file}
31944 Attach to a process @var{pid} or a file @var{file} outside of
31945 @value{GDBN}, or a thread group @var{gid}. If attaching to a thread
31946 group, the id previously returned by
31947 @samp{-list-thread-groups --available} must be used.
31949 @subsubheading @value{GDBN} Command
31951 The corresponding @value{GDBN} command is @samp{attach}.
31953 @subsubheading Example
31957 =thread-created,id="1"
31958 *stopped,thread-id="1",frame=@{addr="0xb7f7e410",func="bar",args=[]@}
31964 @subheading The @code{-target-compare-sections} Command
31965 @findex -target-compare-sections
31967 @subsubheading Synopsis
31970 -target-compare-sections [ @var{section} ]
31973 Compare data of section @var{section} on target to the exec file.
31974 Without the argument, all sections are compared.
31976 @subsubheading @value{GDBN} Command
31978 The @value{GDBN} equivalent is @samp{compare-sections}.
31980 @subsubheading Example
31985 @subheading The @code{-target-detach} Command
31986 @findex -target-detach
31988 @subsubheading Synopsis
31991 -target-detach [ @var{pid} | @var{gid} ]
31994 Detach from the remote target which normally resumes its execution.
31995 If either @var{pid} or @var{gid} is specified, detaches from either
31996 the specified process, or specified thread group. There's no output.
31998 @subsubheading @value{GDBN} Command
32000 The corresponding @value{GDBN} command is @samp{detach}.
32002 @subsubheading Example
32012 @subheading The @code{-target-disconnect} Command
32013 @findex -target-disconnect
32015 @subsubheading Synopsis
32021 Disconnect from the remote target. There's no output and the target is
32022 generally not resumed.
32024 @subsubheading @value{GDBN} Command
32026 The corresponding @value{GDBN} command is @samp{disconnect}.
32028 @subsubheading Example
32038 @subheading The @code{-target-download} Command
32039 @findex -target-download
32041 @subsubheading Synopsis
32047 Loads the executable onto the remote target.
32048 It prints out an update message every half second, which includes the fields:
32052 The name of the section.
32054 The size of what has been sent so far for that section.
32056 The size of the section.
32058 The total size of what was sent so far (the current and the previous sections).
32060 The size of the overall executable to download.
32064 Each message is sent as status record (@pxref{GDB/MI Output Syntax, ,
32065 @sc{gdb/mi} Output Syntax}).
32067 In addition, it prints the name and size of the sections, as they are
32068 downloaded. These messages include the following fields:
32072 The name of the section.
32074 The size of the section.
32076 The size of the overall executable to download.
32080 At the end, a summary is printed.
32082 @subsubheading @value{GDBN} Command
32084 The corresponding @value{GDBN} command is @samp{load}.
32086 @subsubheading Example
32088 Note: each status message appears on a single line. Here the messages
32089 have been broken down so that they can fit onto a page.
32094 +download,@{section=".text",section-size="6668",total-size="9880"@}
32095 +download,@{section=".text",section-sent="512",section-size="6668",
32096 total-sent="512",total-size="9880"@}
32097 +download,@{section=".text",section-sent="1024",section-size="6668",
32098 total-sent="1024",total-size="9880"@}
32099 +download,@{section=".text",section-sent="1536",section-size="6668",
32100 total-sent="1536",total-size="9880"@}
32101 +download,@{section=".text",section-sent="2048",section-size="6668",
32102 total-sent="2048",total-size="9880"@}
32103 +download,@{section=".text",section-sent="2560",section-size="6668",
32104 total-sent="2560",total-size="9880"@}
32105 +download,@{section=".text",section-sent="3072",section-size="6668",
32106 total-sent="3072",total-size="9880"@}
32107 +download,@{section=".text",section-sent="3584",section-size="6668",
32108 total-sent="3584",total-size="9880"@}
32109 +download,@{section=".text",section-sent="4096",section-size="6668",
32110 total-sent="4096",total-size="9880"@}
32111 +download,@{section=".text",section-sent="4608",section-size="6668",
32112 total-sent="4608",total-size="9880"@}
32113 +download,@{section=".text",section-sent="5120",section-size="6668",
32114 total-sent="5120",total-size="9880"@}
32115 +download,@{section=".text",section-sent="5632",section-size="6668",
32116 total-sent="5632",total-size="9880"@}
32117 +download,@{section=".text",section-sent="6144",section-size="6668",
32118 total-sent="6144",total-size="9880"@}
32119 +download,@{section=".text",section-sent="6656",section-size="6668",
32120 total-sent="6656",total-size="9880"@}
32121 +download,@{section=".init",section-size="28",total-size="9880"@}
32122 +download,@{section=".fini",section-size="28",total-size="9880"@}
32123 +download,@{section=".data",section-size="3156",total-size="9880"@}
32124 +download,@{section=".data",section-sent="512",section-size="3156",
32125 total-sent="7236",total-size="9880"@}
32126 +download,@{section=".data",section-sent="1024",section-size="3156",
32127 total-sent="7748",total-size="9880"@}
32128 +download,@{section=".data",section-sent="1536",section-size="3156",
32129 total-sent="8260",total-size="9880"@}
32130 +download,@{section=".data",section-sent="2048",section-size="3156",
32131 total-sent="8772",total-size="9880"@}
32132 +download,@{section=".data",section-sent="2560",section-size="3156",
32133 total-sent="9284",total-size="9880"@}
32134 +download,@{section=".data",section-sent="3072",section-size="3156",
32135 total-sent="9796",total-size="9880"@}
32136 ^done,address="0x10004",load-size="9880",transfer-rate="6586",
32143 @subheading The @code{-target-exec-status} Command
32144 @findex -target-exec-status
32146 @subsubheading Synopsis
32149 -target-exec-status
32152 Provide information on the state of the target (whether it is running or
32153 not, for instance).
32155 @subsubheading @value{GDBN} Command
32157 There's no equivalent @value{GDBN} command.
32159 @subsubheading Example
32163 @subheading The @code{-target-list-available-targets} Command
32164 @findex -target-list-available-targets
32166 @subsubheading Synopsis
32169 -target-list-available-targets
32172 List the possible targets to connect to.
32174 @subsubheading @value{GDBN} Command
32176 The corresponding @value{GDBN} command is @samp{help target}.
32178 @subsubheading Example
32182 @subheading The @code{-target-list-current-targets} Command
32183 @findex -target-list-current-targets
32185 @subsubheading Synopsis
32188 -target-list-current-targets
32191 Describe the current target.
32193 @subsubheading @value{GDBN} Command
32195 The corresponding information is printed by @samp{info file} (among
32198 @subsubheading Example
32202 @subheading The @code{-target-list-parameters} Command
32203 @findex -target-list-parameters
32205 @subsubheading Synopsis
32208 -target-list-parameters
32214 @subsubheading @value{GDBN} Command
32218 @subsubheading Example
32221 @subheading The @code{-target-flash-erase} Command
32222 @findex -target-flash-erase
32224 @subsubheading Synopsis
32227 -target-flash-erase
32230 Erases all known flash memory regions on the target.
32232 The corresponding @value{GDBN} command is @samp{flash-erase}.
32234 The output is a list of flash regions that have been erased, with starting
32235 addresses and memory region sizes.
32239 -target-flash-erase
32240 ^done,erased-regions=@{address="0x0",size="0x40000"@}
32244 @subheading The @code{-target-select} Command
32245 @findex -target-select
32247 @subsubheading Synopsis
32250 -target-select @var{type} @var{parameters @dots{}}
32253 Connect @value{GDBN} to the remote target. This command takes two args:
32257 The type of target, for instance @samp{remote}, etc.
32258 @item @var{parameters}
32259 Device names, host names and the like. @xref{Target Commands, ,
32260 Commands for Managing Targets}, for more details.
32263 The output is a connection notification, followed by the address at
32264 which the target program is, in the following form:
32267 ^connected,addr="@var{address}",func="@var{function name}",
32268 args=[@var{arg list}]
32271 @subsubheading @value{GDBN} Command
32273 The corresponding @value{GDBN} command is @samp{target}.
32275 @subsubheading Example
32279 -target-select remote /dev/ttya
32280 ^connected,addr="0xfe00a300",func="??",args=[]
32284 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
32285 @node GDB/MI File Transfer Commands
32286 @section @sc{gdb/mi} File Transfer Commands
32289 @subheading The @code{-target-file-put} Command
32290 @findex -target-file-put
32292 @subsubheading Synopsis
32295 -target-file-put @var{hostfile} @var{targetfile}
32298 Copy file @var{hostfile} from the host system (the machine running
32299 @value{GDBN}) to @var{targetfile} on the target system.
32301 @subsubheading @value{GDBN} Command
32303 The corresponding @value{GDBN} command is @samp{remote put}.
32305 @subsubheading Example
32309 -target-file-put localfile remotefile
32315 @subheading The @code{-target-file-get} Command
32316 @findex -target-file-get
32318 @subsubheading Synopsis
32321 -target-file-get @var{targetfile} @var{hostfile}
32324 Copy file @var{targetfile} from the target system to @var{hostfile}
32325 on the host system.
32327 @subsubheading @value{GDBN} Command
32329 The corresponding @value{GDBN} command is @samp{remote get}.
32331 @subsubheading Example
32335 -target-file-get remotefile localfile
32341 @subheading The @code{-target-file-delete} Command
32342 @findex -target-file-delete
32344 @subsubheading Synopsis
32347 -target-file-delete @var{targetfile}
32350 Delete @var{targetfile} from the target system.
32352 @subsubheading @value{GDBN} Command
32354 The corresponding @value{GDBN} command is @samp{remote delete}.
32356 @subsubheading Example
32360 -target-file-delete remotefile
32366 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
32367 @node GDB/MI Ada Exceptions Commands
32368 @section Ada Exceptions @sc{gdb/mi} Commands
32370 @subheading The @code{-info-ada-exceptions} Command
32371 @findex -info-ada-exceptions
32373 @subsubheading Synopsis
32376 -info-ada-exceptions [ @var{regexp}]
32379 List all Ada exceptions defined within the program being debugged.
32380 With a regular expression @var{regexp}, only those exceptions whose
32381 names match @var{regexp} are listed.
32383 @subsubheading @value{GDBN} Command
32385 The corresponding @value{GDBN} command is @samp{info exceptions}.
32387 @subsubheading Result
32389 The result is a table of Ada exceptions. The following columns are
32390 defined for each exception:
32394 The name of the exception.
32397 The address of the exception.
32401 @subsubheading Example
32404 -info-ada-exceptions aint
32405 ^done,ada-exceptions=@{nr_rows="2",nr_cols="2",
32406 hdr=[@{width="1",alignment="-1",col_name="name",colhdr="Name"@},
32407 @{width="1",alignment="-1",col_name="address",colhdr="Address"@}],
32408 body=[@{name="constraint_error",address="0x0000000000613da0"@},
32409 @{name="const.aint_global_e",address="0x0000000000613b00"@}]@}
32412 @subheading Catching Ada Exceptions
32414 The commands describing how to ask @value{GDBN} to stop when a program
32415 raises an exception are described at @ref{Ada Exception GDB/MI
32416 Catchpoint Commands}.
32419 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
32420 @node GDB/MI Support Commands
32421 @section @sc{gdb/mi} Support Commands
32423 Since new commands and features get regularly added to @sc{gdb/mi},
32424 some commands are available to help front-ends query the debugger
32425 about support for these capabilities. Similarly, it is also possible
32426 to query @value{GDBN} about target support of certain features.
32428 @subheading The @code{-info-gdb-mi-command} Command
32429 @cindex @code{-info-gdb-mi-command}
32430 @findex -info-gdb-mi-command
32432 @subsubheading Synopsis
32435 -info-gdb-mi-command @var{cmd_name}
32438 Query support for the @sc{gdb/mi} command named @var{cmd_name}.
32440 Note that the dash (@code{-}) starting all @sc{gdb/mi} commands
32441 is technically not part of the command name (@pxref{GDB/MI Input
32442 Syntax}), and thus should be omitted in @var{cmd_name}. However,
32443 for ease of use, this command also accepts the form with the leading
32446 @subsubheading @value{GDBN} Command
32448 There is no corresponding @value{GDBN} command.
32450 @subsubheading Result
32452 The result is a tuple. There is currently only one field:
32456 This field is equal to @code{"true"} if the @sc{gdb/mi} command exists,
32457 @code{"false"} otherwise.
32461 @subsubheading Example
32463 Here is an example where the @sc{gdb/mi} command does not exist:
32466 -info-gdb-mi-command unsupported-command
32467 ^done,command=@{exists="false"@}
32471 And here is an example where the @sc{gdb/mi} command is known
32475 -info-gdb-mi-command symbol-list-lines
32476 ^done,command=@{exists="true"@}
32479 @subheading The @code{-list-features} Command
32480 @findex -list-features
32481 @cindex supported @sc{gdb/mi} features, list
32483 Returns a list of particular features of the MI protocol that
32484 this version of gdb implements. A feature can be a command,
32485 or a new field in an output of some command, or even an
32486 important bugfix. While a frontend can sometimes detect presence
32487 of a feature at runtime, it is easier to perform detection at debugger
32490 The command returns a list of strings, with each string naming an
32491 available feature. Each returned string is just a name, it does not
32492 have any internal structure. The list of possible feature names
32498 (gdb) -list-features
32499 ^done,result=["feature1","feature2"]
32502 The current list of features is:
32505 @item frozen-varobjs
32506 Indicates support for the @code{-var-set-frozen} command, as well
32507 as possible presense of the @code{frozen} field in the output
32508 of @code{-varobj-create}.
32509 @item pending-breakpoints
32510 Indicates support for the @option{-f} option to the @code{-break-insert}
32513 Indicates Python scripting support, Python-based
32514 pretty-printing commands, and possible presence of the
32515 @samp{display_hint} field in the output of @code{-var-list-children}
32517 Indicates support for the @code{-thread-info} command.
32518 @item data-read-memory-bytes
32519 Indicates support for the @code{-data-read-memory-bytes} and the
32520 @code{-data-write-memory-bytes} commands.
32521 @item breakpoint-notifications
32522 Indicates that changes to breakpoints and breakpoints created via the
32523 CLI will be announced via async records.
32524 @item ada-task-info
32525 Indicates support for the @code{-ada-task-info} command.
32526 @item language-option
32527 Indicates that all @sc{gdb/mi} commands accept the @option{--language}
32528 option (@pxref{Context management}).
32529 @item info-gdb-mi-command
32530 Indicates support for the @code{-info-gdb-mi-command} command.
32531 @item undefined-command-error-code
32532 Indicates support for the "undefined-command" error code in error result
32533 records, produced when trying to execute an undefined @sc{gdb/mi} command
32534 (@pxref{GDB/MI Result Records}).
32535 @item exec-run-start-option
32536 Indicates that the @code{-exec-run} command supports the @option{--start}
32537 option (@pxref{GDB/MI Program Execution}).
32540 @subheading The @code{-list-target-features} Command
32541 @findex -list-target-features
32543 Returns a list of particular features that are supported by the
32544 target. Those features affect the permitted MI commands, but
32545 unlike the features reported by the @code{-list-features} command, the
32546 features depend on which target GDB is using at the moment. Whenever
32547 a target can change, due to commands such as @code{-target-select},
32548 @code{-target-attach} or @code{-exec-run}, the list of target features
32549 may change, and the frontend should obtain it again.
32553 (gdb) -list-target-features
32554 ^done,result=["async"]
32557 The current list of features is:
32561 Indicates that the target is capable of asynchronous command
32562 execution, which means that @value{GDBN} will accept further commands
32563 while the target is running.
32566 Indicates that the target is capable of reverse execution.
32567 @xref{Reverse Execution}, for more information.
32571 @c %%%%%%%%%%%%%%%%%%%%%%%%%%%% SECTION %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
32572 @node GDB/MI Miscellaneous Commands
32573 @section Miscellaneous @sc{gdb/mi} Commands
32575 @c @subheading -gdb-complete
32577 @subheading The @code{-gdb-exit} Command
32580 @subsubheading Synopsis
32586 Exit @value{GDBN} immediately.
32588 @subsubheading @value{GDBN} Command
32590 Approximately corresponds to @samp{quit}.
32592 @subsubheading Example
32602 @subheading The @code{-exec-abort} Command
32603 @findex -exec-abort
32605 @subsubheading Synopsis
32611 Kill the inferior running program.
32613 @subsubheading @value{GDBN} Command
32615 The corresponding @value{GDBN} command is @samp{kill}.
32617 @subsubheading Example
32622 @subheading The @code{-gdb-set} Command
32625 @subsubheading Synopsis
32631 Set an internal @value{GDBN} variable.
32632 @c IS THIS A DOLLAR VARIABLE? OR SOMETHING LIKE ANNOTATE ?????
32634 @subsubheading @value{GDBN} Command
32636 The corresponding @value{GDBN} command is @samp{set}.
32638 @subsubheading Example
32648 @subheading The @code{-gdb-show} Command
32651 @subsubheading Synopsis
32657 Show the current value of a @value{GDBN} variable.
32659 @subsubheading @value{GDBN} Command
32661 The corresponding @value{GDBN} command is @samp{show}.
32663 @subsubheading Example
32672 @c @subheading -gdb-source
32675 @subheading The @code{-gdb-version} Command
32676 @findex -gdb-version
32678 @subsubheading Synopsis
32684 Show version information for @value{GDBN}. Used mostly in testing.
32686 @subsubheading @value{GDBN} Command
32688 The @value{GDBN} equivalent is @samp{show version}. @value{GDBN} by
32689 default shows this information when you start an interactive session.
32691 @subsubheading Example
32693 @c This example modifies the actual output from GDB to avoid overfull
32699 ~Copyright 2000 Free Software Foundation, Inc.
32700 ~GDB is free software, covered by the GNU General Public License, and
32701 ~you are welcome to change it and/or distribute copies of it under
32702 ~ certain conditions.
32703 ~Type "show copying" to see the conditions.
32704 ~There is absolutely no warranty for GDB. Type "show warranty" for
32706 ~This GDB was configured as
32707 "--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
32712 @subheading The @code{-list-thread-groups} Command
32713 @findex -list-thread-groups
32715 @subheading Synopsis
32718 -list-thread-groups [ --available ] [ --recurse 1 ] [ @var{group} ... ]
32721 Lists thread groups (@pxref{Thread groups}). When a single thread
32722 group is passed as the argument, lists the children of that group.
32723 When several thread group are passed, lists information about those
32724 thread groups. Without any parameters, lists information about all
32725 top-level thread groups.
32727 Normally, thread groups that are being debugged are reported.
32728 With the @samp{--available} option, @value{GDBN} reports thread groups
32729 available on the target.
32731 The output of this command may have either a @samp{threads} result or
32732 a @samp{groups} result. The @samp{thread} result has a list of tuples
32733 as value, with each tuple describing a thread (@pxref{GDB/MI Thread
32734 Information}). The @samp{groups} result has a list of tuples as value,
32735 each tuple describing a thread group. If top-level groups are
32736 requested (that is, no parameter is passed), or when several groups
32737 are passed, the output always has a @samp{groups} result. The format
32738 of the @samp{group} result is described below.
32740 To reduce the number of roundtrips it's possible to list thread groups
32741 together with their children, by passing the @samp{--recurse} option
32742 and the recursion depth. Presently, only recursion depth of 1 is
32743 permitted. If this option is present, then every reported thread group
32744 will also include its children, either as @samp{group} or
32745 @samp{threads} field.
32747 In general, any combination of option and parameters is permitted, with
32748 the following caveats:
32752 When a single thread group is passed, the output will typically
32753 be the @samp{threads} result. Because threads may not contain
32754 anything, the @samp{recurse} option will be ignored.
32757 When the @samp{--available} option is passed, limited information may
32758 be available. In particular, the list of threads of a process might
32759 be inaccessible. Further, specifying specific thread groups might
32760 not give any performance advantage over listing all thread groups.
32761 The frontend should assume that @samp{-list-thread-groups --available}
32762 is always an expensive operation and cache the results.
32766 The @samp{groups} result is a list of tuples, where each tuple may
32767 have the following fields:
32771 Identifier of the thread group. This field is always present.
32772 The identifier is an opaque string; frontends should not try to
32773 convert it to an integer, even though it might look like one.
32776 The type of the thread group. At present, only @samp{process} is a
32780 The target-specific process identifier. This field is only present
32781 for thread groups of type @samp{process} and only if the process exists.
32784 The exit code of this group's last exited thread, formatted in octal.
32785 This field is only present for thread groups of type @samp{process} and
32786 only if the process is not running.
32789 The number of children this thread group has. This field may be
32790 absent for an available thread group.
32793 This field has a list of tuples as value, each tuple describing a
32794 thread. It may be present if the @samp{--recurse} option is
32795 specified, and it's actually possible to obtain the threads.
32798 This field is a list of integers, each identifying a core that one
32799 thread of the group is running on. This field may be absent if
32800 such information is not available.
32803 The name of the executable file that corresponds to this thread group.
32804 The field is only present for thread groups of type @samp{process},
32805 and only if there is a corresponding executable file.
32809 @subheading Example
32813 -list-thread-groups
32814 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2"@}]
32815 -list-thread-groups 17
32816 ^done,threads=[@{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
32817 frame=@{level="0",addr="0xffffe410",func="__kernel_vsyscall",args=[]@},state="running"@},
32818 @{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
32819 frame=@{level="0",addr="0x0804891f",func="foo",args=[@{name="i",value="10"@}],
32820 file="/tmp/a.c",fullname="/tmp/a.c",line="158"@},state="running"@}]]
32821 -list-thread-groups --available
32822 ^done,groups=[@{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]@}]
32823 -list-thread-groups --available --recurse 1
32824 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
32825 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
32826 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},..]
32827 -list-thread-groups --available --recurse 1 17 18
32828 ^done,groups=[@{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
32829 threads=[@{id="1",target-id="Thread 0xb7e14b90",cores=[1]@},
32830 @{id="2",target-id="Thread 0xb7e14b90",cores=[2]@}]@},...]
32833 @subheading The @code{-info-os} Command
32836 @subsubheading Synopsis
32839 -info-os [ @var{type} ]
32842 If no argument is supplied, the command returns a table of available
32843 operating-system-specific information types. If one of these types is
32844 supplied as an argument @var{type}, then the command returns a table
32845 of data of that type.
32847 The types of information available depend on the target operating
32850 @subsubheading @value{GDBN} Command
32852 The corresponding @value{GDBN} command is @samp{info os}.
32854 @subsubheading Example
32856 When run on a @sc{gnu}/Linux system, the output will look something
32862 ^done,OSDataTable=@{nr_rows="10",nr_cols="3",
32863 hdr=[@{width="10",alignment="-1",col_name="col0",colhdr="Type"@},
32864 @{width="10",alignment="-1",col_name="col1",colhdr="Description"@},
32865 @{width="10",alignment="-1",col_name="col2",colhdr="Title"@}],
32866 body=[item=@{col0="cpus",col1="Listing of all cpus/cores on the system",
32868 item=@{col0="files",col1="Listing of all file descriptors",
32869 col2="File descriptors"@},
32870 item=@{col0="modules",col1="Listing of all loaded kernel modules",
32871 col2="Kernel modules"@},
32872 item=@{col0="msg",col1="Listing of all message queues",
32873 col2="Message queues"@},
32874 item=@{col0="processes",col1="Listing of all processes",
32875 col2="Processes"@},
32876 item=@{col0="procgroups",col1="Listing of all process groups",
32877 col2="Process groups"@},
32878 item=@{col0="semaphores",col1="Listing of all semaphores",
32879 col2="Semaphores"@},
32880 item=@{col0="shm",col1="Listing of all shared-memory regions",
32881 col2="Shared-memory regions"@},
32882 item=@{col0="sockets",col1="Listing of all internet-domain sockets",
32884 item=@{col0="threads",col1="Listing of all threads",
32888 ^done,OSDataTable=@{nr_rows="190",nr_cols="4",
32889 hdr=[@{width="10",alignment="-1",col_name="col0",colhdr="pid"@},
32890 @{width="10",alignment="-1",col_name="col1",colhdr="user"@},
32891 @{width="10",alignment="-1",col_name="col2",colhdr="command"@},
32892 @{width="10",alignment="-1",col_name="col3",colhdr="cores"@}],
32893 body=[item=@{col0="1",col1="root",col2="/sbin/init",col3="0"@},
32894 item=@{col0="2",col1="root",col2="[kthreadd]",col3="1"@},
32895 item=@{col0="3",col1="root",col2="[ksoftirqd/0]",col3="0"@},
32897 item=@{col0="26446",col1="stan",col2="bash",col3="0"@},
32898 item=@{col0="28152",col1="stan",col2="bash",col3="1"@}]@}
32902 (Note that the MI output here includes a @code{"Title"} column that
32903 does not appear in command-line @code{info os}; this column is useful
32904 for MI clients that want to enumerate the types of data, such as in a
32905 popup menu, but is needless clutter on the command line, and
32906 @code{info os} omits it.)
32908 @subheading The @code{-add-inferior} Command
32909 @findex -add-inferior
32911 @subheading Synopsis
32917 Creates a new inferior (@pxref{Inferiors and Programs}). The created
32918 inferior is not associated with any executable. Such association may
32919 be established with the @samp{-file-exec-and-symbols} command
32920 (@pxref{GDB/MI File Commands}). The command response has a single
32921 field, @samp{inferior}, whose value is the identifier of the
32922 thread group corresponding to the new inferior.
32924 @subheading Example
32929 ^done,inferior="i3"
32932 @subheading The @code{-interpreter-exec} Command
32933 @findex -interpreter-exec
32935 @subheading Synopsis
32938 -interpreter-exec @var{interpreter} @var{command}
32940 @anchor{-interpreter-exec}
32942 Execute the specified @var{command} in the given @var{interpreter}.
32944 @subheading @value{GDBN} Command
32946 The corresponding @value{GDBN} command is @samp{interpreter-exec}.
32948 @subheading Example
32952 -interpreter-exec console "break main"
32953 &"During symbol reading, couldn't parse type; debugger out of date?.\n"
32954 &"During symbol reading, bad structure-type format.\n"
32955 ~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
32960 @subheading The @code{-inferior-tty-set} Command
32961 @findex -inferior-tty-set
32963 @subheading Synopsis
32966 -inferior-tty-set /dev/pts/1
32969 Set terminal for future runs of the program being debugged.
32971 @subheading @value{GDBN} Command
32973 The corresponding @value{GDBN} command is @samp{set inferior-tty} /dev/pts/1.
32975 @subheading Example
32979 -inferior-tty-set /dev/pts/1
32984 @subheading The @code{-inferior-tty-show} Command
32985 @findex -inferior-tty-show
32987 @subheading Synopsis
32993 Show terminal for future runs of program being debugged.
32995 @subheading @value{GDBN} Command
32997 The corresponding @value{GDBN} command is @samp{show inferior-tty}.
32999 @subheading Example
33003 -inferior-tty-set /dev/pts/1
33007 ^done,inferior_tty_terminal="/dev/pts/1"
33011 @subheading The @code{-enable-timings} Command
33012 @findex -enable-timings
33014 @subheading Synopsis
33017 -enable-timings [yes | no]
33020 Toggle the printing of the wallclock, user and system times for an MI
33021 command as a field in its output. This command is to help frontend
33022 developers optimize the performance of their code. No argument is
33023 equivalent to @samp{yes}.
33025 @subheading @value{GDBN} Command
33029 @subheading Example
33037 ^done,bkpt=@{number="1",type="breakpoint",disp="keep",enabled="y",
33038 addr="0x080484ed",func="main",file="myprog.c",
33039 fullname="/home/nickrob/myprog.c",line="73",thread-groups=["i1"],
33041 time=@{wallclock="0.05185",user="0.00800",system="0.00000"@}
33049 *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",thread-id="0",
33050 frame=@{addr="0x080484ed",func="main",args=[@{name="argc",value="1"@},
33051 @{name="argv",value="0xbfb60364"@}],file="myprog.c",
33052 fullname="/home/nickrob/myprog.c",line="73"@}
33057 @chapter @value{GDBN} Annotations
33059 This chapter describes annotations in @value{GDBN}. Annotations were
33060 designed to interface @value{GDBN} to graphical user interfaces or other
33061 similar programs which want to interact with @value{GDBN} at a
33062 relatively high level.
33064 The annotation mechanism has largely been superseded by @sc{gdb/mi}
33068 This is Edition @value{EDITION}, @value{DATE}.
33072 * Annotations Overview:: What annotations are; the general syntax.
33073 * Server Prefix:: Issuing a command without affecting user state.
33074 * Prompting:: Annotations marking @value{GDBN}'s need for input.
33075 * Errors:: Annotations for error messages.
33076 * Invalidation:: Some annotations describe things now invalid.
33077 * Annotations for Running::
33078 Whether the program is running, how it stopped, etc.
33079 * Source Annotations:: Annotations describing source code.
33082 @node Annotations Overview
33083 @section What is an Annotation?
33084 @cindex annotations
33086 Annotations start with a newline character, two @samp{control-z}
33087 characters, and the name of the annotation. If there is no additional
33088 information associated with this annotation, the name of the annotation
33089 is followed immediately by a newline. If there is additional
33090 information, the name of the annotation is followed by a space, the
33091 additional information, and a newline. The additional information
33092 cannot contain newline characters.
33094 Any output not beginning with a newline and two @samp{control-z}
33095 characters denotes literal output from @value{GDBN}. Currently there is
33096 no need for @value{GDBN} to output a newline followed by two
33097 @samp{control-z} characters, but if there was such a need, the
33098 annotations could be extended with an @samp{escape} annotation which
33099 means those three characters as output.
33101 The annotation @var{level}, which is specified using the
33102 @option{--annotate} command line option (@pxref{Mode Options}), controls
33103 how much information @value{GDBN} prints together with its prompt,
33104 values of expressions, source lines, and other types of output. Level 0
33105 is for no annotations, level 1 is for use when @value{GDBN} is run as a
33106 subprocess of @sc{gnu} Emacs, level 3 is the maximum annotation suitable
33107 for programs that control @value{GDBN}, and level 2 annotations have
33108 been made obsolete (@pxref{Limitations, , Limitations of the Annotation
33109 Interface, annotate, GDB's Obsolete Annotations}).
33112 @kindex set annotate
33113 @item set annotate @var{level}
33114 The @value{GDBN} command @code{set annotate} sets the level of
33115 annotations to the specified @var{level}.
33117 @item show annotate
33118 @kindex show annotate
33119 Show the current annotation level.
33122 This chapter describes level 3 annotations.
33124 A simple example of starting up @value{GDBN} with annotations is:
33127 $ @kbd{gdb --annotate=3}
33129 Copyright 2003 Free Software Foundation, Inc.
33130 GDB is free software, covered by the GNU General Public License,
33131 and you are welcome to change it and/or distribute copies of it
33132 under certain conditions.
33133 Type "show copying" to see the conditions.
33134 There is absolutely no warranty for GDB. Type "show warranty"
33136 This GDB was configured as "i386-pc-linux-gnu"
33147 Here @samp{quit} is input to @value{GDBN}; the rest is output from
33148 @value{GDBN}. The three lines beginning @samp{^Z^Z} (where @samp{^Z}
33149 denotes a @samp{control-z} character) are annotations; the rest is
33150 output from @value{GDBN}.
33152 @node Server Prefix
33153 @section The Server Prefix
33154 @cindex server prefix
33156 If you prefix a command with @samp{server } then it will not affect
33157 the command history, nor will it affect @value{GDBN}'s notion of which
33158 command to repeat if @key{RET} is pressed on a line by itself. This
33159 means that commands can be run behind a user's back by a front-end in
33160 a transparent manner.
33162 The @code{server } prefix does not affect the recording of values into
33163 the value history; to print a value without recording it into the
33164 value history, use the @code{output} command instead of the
33165 @code{print} command.
33167 Using this prefix also disables confirmation requests
33168 (@pxref{confirmation requests}).
33171 @section Annotation for @value{GDBN} Input
33173 @cindex annotations for prompts
33174 When @value{GDBN} prompts for input, it annotates this fact so it is possible
33175 to know when to send output, when the output from a given command is
33178 Different kinds of input each have a different @dfn{input type}. Each
33179 input type has three annotations: a @code{pre-} annotation, which
33180 denotes the beginning of any prompt which is being output, a plain
33181 annotation, which denotes the end of the prompt, and then a @code{post-}
33182 annotation which denotes the end of any echo which may (or may not) be
33183 associated with the input. For example, the @code{prompt} input type
33184 features the following annotations:
33192 The input types are
33195 @findex pre-prompt annotation
33196 @findex prompt annotation
33197 @findex post-prompt annotation
33199 When @value{GDBN} is prompting for a command (the main @value{GDBN} prompt).
33201 @findex pre-commands annotation
33202 @findex commands annotation
33203 @findex post-commands annotation
33205 When @value{GDBN} prompts for a set of commands, like in the @code{commands}
33206 command. The annotations are repeated for each command which is input.
33208 @findex pre-overload-choice annotation
33209 @findex overload-choice annotation
33210 @findex post-overload-choice annotation
33211 @item overload-choice
33212 When @value{GDBN} wants the user to select between various overloaded functions.
33214 @findex pre-query annotation
33215 @findex query annotation
33216 @findex post-query annotation
33218 When @value{GDBN} wants the user to confirm a potentially dangerous operation.
33220 @findex pre-prompt-for-continue annotation
33221 @findex prompt-for-continue annotation
33222 @findex post-prompt-for-continue annotation
33223 @item prompt-for-continue
33224 When @value{GDBN} is asking the user to press return to continue. Note: Don't
33225 expect this to work well; instead use @code{set height 0} to disable
33226 prompting. This is because the counting of lines is buggy in the
33227 presence of annotations.
33232 @cindex annotations for errors, warnings and interrupts
33234 @findex quit annotation
33239 This annotation occurs right before @value{GDBN} responds to an interrupt.
33241 @findex error annotation
33246 This annotation occurs right before @value{GDBN} responds to an error.
33248 Quit and error annotations indicate that any annotations which @value{GDBN} was
33249 in the middle of may end abruptly. For example, if a
33250 @code{value-history-begin} annotation is followed by a @code{error}, one
33251 cannot expect to receive the matching @code{value-history-end}. One
33252 cannot expect not to receive it either, however; an error annotation
33253 does not necessarily mean that @value{GDBN} is immediately returning all the way
33256 @findex error-begin annotation
33257 A quit or error annotation may be preceded by
33263 Any output between that and the quit or error annotation is the error
33266 Warning messages are not yet annotated.
33267 @c If we want to change that, need to fix warning(), type_error(),
33268 @c range_error(), and possibly other places.
33271 @section Invalidation Notices
33273 @cindex annotations for invalidation messages
33274 The following annotations say that certain pieces of state may have
33278 @findex frames-invalid annotation
33279 @item ^Z^Zframes-invalid
33281 The frames (for example, output from the @code{backtrace} command) may
33284 @findex breakpoints-invalid annotation
33285 @item ^Z^Zbreakpoints-invalid
33287 The breakpoints may have changed. For example, the user just added or
33288 deleted a breakpoint.
33291 @node Annotations for Running
33292 @section Running the Program
33293 @cindex annotations for running programs
33295 @findex starting annotation
33296 @findex stopping annotation
33297 When the program starts executing due to a @value{GDBN} command such as
33298 @code{step} or @code{continue},
33304 is output. When the program stops,
33310 is output. Before the @code{stopped} annotation, a variety of
33311 annotations describe how the program stopped.
33314 @findex exited annotation
33315 @item ^Z^Zexited @var{exit-status}
33316 The program exited, and @var{exit-status} is the exit status (zero for
33317 successful exit, otherwise nonzero).
33319 @findex signalled annotation
33320 @findex signal-name annotation
33321 @findex signal-name-end annotation
33322 @findex signal-string annotation
33323 @findex signal-string-end annotation
33324 @item ^Z^Zsignalled
33325 The program exited with a signal. After the @code{^Z^Zsignalled}, the
33326 annotation continues:
33332 ^Z^Zsignal-name-end
33336 ^Z^Zsignal-string-end
33341 where @var{name} is the name of the signal, such as @code{SIGILL} or
33342 @code{SIGSEGV}, and @var{string} is the explanation of the signal, such
33343 as @code{Illegal Instruction} or @code{Segmentation fault}. The arguments
33344 @var{intro-text}, @var{middle-text}, and @var{end-text} are for the
33345 user's benefit and have no particular format.
33347 @findex signal annotation
33349 The syntax of this annotation is just like @code{signalled}, but @value{GDBN} is
33350 just saying that the program received the signal, not that it was
33351 terminated with it.
33353 @findex breakpoint annotation
33354 @item ^Z^Zbreakpoint @var{number}
33355 The program hit breakpoint number @var{number}.
33357 @findex watchpoint annotation
33358 @item ^Z^Zwatchpoint @var{number}
33359 The program hit watchpoint number @var{number}.
33362 @node Source Annotations
33363 @section Displaying Source
33364 @cindex annotations for source display
33366 @findex source annotation
33367 The following annotation is used instead of displaying source code:
33370 ^Z^Zsource @var{filename}:@var{line}:@var{character}:@var{middle}:@var{addr}
33373 where @var{filename} is an absolute file name indicating which source
33374 file, @var{line} is the line number within that file (where 1 is the
33375 first line in the file), @var{character} is the character position
33376 within the file (where 0 is the first character in the file) (for most
33377 debug formats this will necessarily point to the beginning of a line),
33378 @var{middle} is @samp{middle} if @var{addr} is in the middle of the
33379 line, or @samp{beg} if @var{addr} is at the beginning of the line, and
33380 @var{addr} is the address in the target program associated with the
33381 source which is being displayed. The @var{addr} is in the form @samp{0x}
33382 followed by one or more lowercase hex digits (note that this does not
33383 depend on the language).
33385 @node JIT Interface
33386 @chapter JIT Compilation Interface
33387 @cindex just-in-time compilation
33388 @cindex JIT compilation interface
33390 This chapter documents @value{GDBN}'s @dfn{just-in-time} (JIT) compilation
33391 interface. A JIT compiler is a program or library that generates native
33392 executable code at runtime and executes it, usually in order to achieve good
33393 performance while maintaining platform independence.
33395 Programs that use JIT compilation are normally difficult to debug because
33396 portions of their code are generated at runtime, instead of being loaded from
33397 object files, which is where @value{GDBN} normally finds the program's symbols
33398 and debug information. In order to debug programs that use JIT compilation,
33399 @value{GDBN} has an interface that allows the program to register in-memory
33400 symbol files with @value{GDBN} at runtime.
33402 If you are using @value{GDBN} to debug a program that uses this interface, then
33403 it should work transparently so long as you have not stripped the binary. If
33404 you are developing a JIT compiler, then the interface is documented in the rest
33405 of this chapter. At this time, the only known client of this interface is the
33408 Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
33409 JIT compiler communicates with @value{GDBN} by writing data into a global
33410 variable and calling a fuction at a well-known symbol. When @value{GDBN}
33411 attaches, it reads a linked list of symbol files from the global variable to
33412 find existing code, and puts a breakpoint in the function so that it can find
33413 out about additional code.
33416 * Declarations:: Relevant C struct declarations
33417 * Registering Code:: Steps to register code
33418 * Unregistering Code:: Steps to unregister code
33419 * Custom Debug Info:: Emit debug information in a custom format
33423 @section JIT Declarations
33425 These are the relevant struct declarations that a C program should include to
33426 implement the interface:
33436 struct jit_code_entry
33438 struct jit_code_entry *next_entry;
33439 struct jit_code_entry *prev_entry;
33440 const char *symfile_addr;
33441 uint64_t symfile_size;
33444 struct jit_descriptor
33447 /* This type should be jit_actions_t, but we use uint32_t
33448 to be explicit about the bitwidth. */
33449 uint32_t action_flag;
33450 struct jit_code_entry *relevant_entry;
33451 struct jit_code_entry *first_entry;
33454 /* GDB puts a breakpoint in this function. */
33455 void __attribute__((noinline)) __jit_debug_register_code() @{ @};
33457 /* Make sure to specify the version statically, because the
33458 debugger may check the version before we can set it. */
33459 struct jit_descriptor __jit_debug_descriptor = @{ 1, 0, 0, 0 @};
33462 If the JIT is multi-threaded, then it is important that the JIT synchronize any
33463 modifications to this global data properly, which can easily be done by putting
33464 a global mutex around modifications to these structures.
33466 @node Registering Code
33467 @section Registering Code
33469 To register code with @value{GDBN}, the JIT should follow this protocol:
33473 Generate an object file in memory with symbols and other desired debug
33474 information. The file must include the virtual addresses of the sections.
33477 Create a code entry for the file, which gives the start and size of the symbol
33481 Add it to the linked list in the JIT descriptor.
33484 Point the relevant_entry field of the descriptor at the entry.
33487 Set @code{action_flag} to @code{JIT_REGISTER} and call
33488 @code{__jit_debug_register_code}.
33491 When @value{GDBN} is attached and the breakpoint fires, @value{GDBN} uses the
33492 @code{relevant_entry} pointer so it doesn't have to walk the list looking for
33493 new code. However, the linked list must still be maintained in order to allow
33494 @value{GDBN} to attach to a running process and still find the symbol files.
33496 @node Unregistering Code
33497 @section Unregistering Code
33499 If code is freed, then the JIT should use the following protocol:
33503 Remove the code entry corresponding to the code from the linked list.
33506 Point the @code{relevant_entry} field of the descriptor at the code entry.
33509 Set @code{action_flag} to @code{JIT_UNREGISTER} and call
33510 @code{__jit_debug_register_code}.
33513 If the JIT frees or recompiles code without unregistering it, then @value{GDBN}
33514 and the JIT will leak the memory used for the associated symbol files.
33516 @node Custom Debug Info
33517 @section Custom Debug Info
33518 @cindex custom JIT debug info
33519 @cindex JIT debug info reader
33521 Generating debug information in platform-native file formats (like ELF
33522 or COFF) may be an overkill for JIT compilers; especially if all the
33523 debug info is used for is displaying a meaningful backtrace. The
33524 issue can be resolved by having the JIT writers decide on a debug info
33525 format and also provide a reader that parses the debug info generated
33526 by the JIT compiler. This section gives a brief overview on writing
33527 such a parser. More specific details can be found in the source file
33528 @file{gdb/jit-reader.in}, which is also installed as a header at
33529 @file{@var{includedir}/gdb/jit-reader.h} for easy inclusion.
33531 The reader is implemented as a shared object (so this functionality is
33532 not available on platforms which don't allow loading shared objects at
33533 runtime). Two @value{GDBN} commands, @code{jit-reader-load} and
33534 @code{jit-reader-unload} are provided, to be used to load and unload
33535 the readers from a preconfigured directory. Once loaded, the shared
33536 object is used the parse the debug information emitted by the JIT
33540 * Using JIT Debug Info Readers:: How to use supplied readers correctly
33541 * Writing JIT Debug Info Readers:: Creating a debug-info reader
33544 @node Using JIT Debug Info Readers
33545 @subsection Using JIT Debug Info Readers
33546 @kindex jit-reader-load
33547 @kindex jit-reader-unload
33549 Readers can be loaded and unloaded using the @code{jit-reader-load}
33550 and @code{jit-reader-unload} commands.
33553 @item jit-reader-load @var{reader}
33554 Load the JIT reader named @var{reader}, which is a shared
33555 object specified as either an absolute or a relative file name. In
33556 the latter case, @value{GDBN} will try to load the reader from a
33557 pre-configured directory, usually @file{@var{libdir}/gdb/} on a UNIX
33558 system (here @var{libdir} is the system library directory, often
33559 @file{/usr/local/lib}).
33561 Only one reader can be active at a time; trying to load a second
33562 reader when one is already loaded will result in @value{GDBN}
33563 reporting an error. A new JIT reader can be loaded by first unloading
33564 the current one using @code{jit-reader-unload} and then invoking
33565 @code{jit-reader-load}.
33567 @item jit-reader-unload
33568 Unload the currently loaded JIT reader.
33572 @node Writing JIT Debug Info Readers
33573 @subsection Writing JIT Debug Info Readers
33574 @cindex writing JIT debug info readers
33576 As mentioned, a reader is essentially a shared object conforming to a
33577 certain ABI. This ABI is described in @file{jit-reader.h}.
33579 @file{jit-reader.h} defines the structures, macros and functions
33580 required to write a reader. It is installed (along with
33581 @value{GDBN}), in @file{@var{includedir}/gdb} where @var{includedir} is
33582 the system include directory.
33584 Readers need to be released under a GPL compatible license. A reader
33585 can be declared as released under such a license by placing the macro
33586 @code{GDB_DECLARE_GPL_COMPATIBLE_READER} in a source file.
33588 The entry point for readers is the symbol @code{gdb_init_reader},
33589 which is expected to be a function with the prototype
33591 @findex gdb_init_reader
33593 extern struct gdb_reader_funcs *gdb_init_reader (void);
33596 @cindex @code{struct gdb_reader_funcs}
33598 @code{struct gdb_reader_funcs} contains a set of pointers to callback
33599 functions. These functions are executed to read the debug info
33600 generated by the JIT compiler (@code{read}), to unwind stack frames
33601 (@code{unwind}) and to create canonical frame IDs
33602 (@code{get_Frame_id}). It also has a callback that is called when the
33603 reader is being unloaded (@code{destroy}). The struct looks like this
33606 struct gdb_reader_funcs
33608 /* Must be set to GDB_READER_INTERFACE_VERSION. */
33609 int reader_version;
33611 /* For use by the reader. */
33614 gdb_read_debug_info *read;
33615 gdb_unwind_frame *unwind;
33616 gdb_get_frame_id *get_frame_id;
33617 gdb_destroy_reader *destroy;
33621 @cindex @code{struct gdb_symbol_callbacks}
33622 @cindex @code{struct gdb_unwind_callbacks}
33624 The callbacks are provided with another set of callbacks by
33625 @value{GDBN} to do their job. For @code{read}, these callbacks are
33626 passed in a @code{struct gdb_symbol_callbacks} and for @code{unwind}
33627 and @code{get_frame_id}, in a @code{struct gdb_unwind_callbacks}.
33628 @code{struct gdb_symbol_callbacks} has callbacks to create new object
33629 files and new symbol tables inside those object files. @code{struct
33630 gdb_unwind_callbacks} has callbacks to read registers off the current
33631 frame and to write out the values of the registers in the previous
33632 frame. Both have a callback (@code{target_read}) to read bytes off the
33633 target's address space.
33635 @node In-Process Agent
33636 @chapter In-Process Agent
33637 @cindex debugging agent
33638 The traditional debugging model is conceptually low-speed, but works fine,
33639 because most bugs can be reproduced in debugging-mode execution. However,
33640 as multi-core or many-core processors are becoming mainstream, and
33641 multi-threaded programs become more and more popular, there should be more
33642 and more bugs that only manifest themselves at normal-mode execution, for
33643 example, thread races, because debugger's interference with the program's
33644 timing may conceal the bugs. On the other hand, in some applications,
33645 it is not feasible for the debugger to interrupt the program's execution
33646 long enough for the developer to learn anything helpful about its behavior.
33647 If the program's correctness depends on its real-time behavior, delays
33648 introduced by a debugger might cause the program to fail, even when the
33649 code itself is correct. It is useful to be able to observe the program's
33650 behavior without interrupting it.
33652 Therefore, traditional debugging model is too intrusive to reproduce
33653 some bugs. In order to reduce the interference with the program, we can
33654 reduce the number of operations performed by debugger. The
33655 @dfn{In-Process Agent}, a shared library, is running within the same
33656 process with inferior, and is able to perform some debugging operations
33657 itself. As a result, debugger is only involved when necessary, and
33658 performance of debugging can be improved accordingly. Note that
33659 interference with program can be reduced but can't be removed completely,
33660 because the in-process agent will still stop or slow down the program.
33662 The in-process agent can interpret and execute Agent Expressions
33663 (@pxref{Agent Expressions}) during performing debugging operations. The
33664 agent expressions can be used for different purposes, such as collecting
33665 data in tracepoints, and condition evaluation in breakpoints.
33667 @anchor{Control Agent}
33668 You can control whether the in-process agent is used as an aid for
33669 debugging with the following commands:
33672 @kindex set agent on
33674 Causes the in-process agent to perform some operations on behalf of the
33675 debugger. Just which operations requested by the user will be done
33676 by the in-process agent depends on the its capabilities. For example,
33677 if you request to evaluate breakpoint conditions in the in-process agent,
33678 and the in-process agent has such capability as well, then breakpoint
33679 conditions will be evaluated in the in-process agent.
33681 @kindex set agent off
33682 @item set agent off
33683 Disables execution of debugging operations by the in-process agent. All
33684 of the operations will be performed by @value{GDBN}.
33688 Display the current setting of execution of debugging operations by
33689 the in-process agent.
33693 * In-Process Agent Protocol::
33696 @node In-Process Agent Protocol
33697 @section In-Process Agent Protocol
33698 @cindex in-process agent protocol
33700 The in-process agent is able to communicate with both @value{GDBN} and
33701 GDBserver (@pxref{In-Process Agent}). This section documents the protocol
33702 used for communications between @value{GDBN} or GDBserver and the IPA.
33703 In general, @value{GDBN} or GDBserver sends commands
33704 (@pxref{IPA Protocol Commands}) and data to in-process agent, and then
33705 in-process agent replies back with the return result of the command, or
33706 some other information. The data sent to in-process agent is composed
33707 of primitive data types, such as 4-byte or 8-byte type, and composite
33708 types, which are called objects (@pxref{IPA Protocol Objects}).
33711 * IPA Protocol Objects::
33712 * IPA Protocol Commands::
33715 @node IPA Protocol Objects
33716 @subsection IPA Protocol Objects
33717 @cindex ipa protocol objects
33719 The commands sent to and results received from agent may contain some
33720 complex data types called @dfn{objects}.
33722 The in-process agent is running on the same machine with @value{GDBN}
33723 or GDBserver, so it doesn't have to handle as much differences between
33724 two ends as remote protocol (@pxref{Remote Protocol}) tries to handle.
33725 However, there are still some differences of two ends in two processes:
33729 word size. On some 64-bit machines, @value{GDBN} or GDBserver can be
33730 compiled as a 64-bit executable, while in-process agent is a 32-bit one.
33732 ABI. Some machines may have multiple types of ABI, @value{GDBN} or
33733 GDBserver is compiled with one, and in-process agent is compiled with
33737 Here are the IPA Protocol Objects:
33741 agent expression object. It represents an agent expression
33742 (@pxref{Agent Expressions}).
33743 @anchor{agent expression object}
33745 tracepoint action object. It represents a tracepoint action
33746 (@pxref{Tracepoint Actions,,Tracepoint Action Lists}) to collect registers,
33747 memory, static trace data and to evaluate expression.
33748 @anchor{tracepoint action object}
33750 tracepoint object. It represents a tracepoint (@pxref{Tracepoints}).
33751 @anchor{tracepoint object}
33755 The following table describes important attributes of each IPA protocol
33758 @multitable @columnfractions .30 .20 .50
33759 @headitem Name @tab Size @tab Description
33760 @item @emph{agent expression object} @tab @tab
33761 @item length @tab 4 @tab length of bytes code
33762 @item byte code @tab @var{length} @tab contents of byte code
33763 @item @emph{tracepoint action for collecting memory} @tab @tab
33764 @item 'M' @tab 1 @tab type of tracepoint action
33765 @item addr @tab 8 @tab if @var{basereg} is @samp{-1}, @var{addr} is the
33766 address of the lowest byte to collect, otherwise @var{addr} is the offset
33767 of @var{basereg} for memory collecting.
33768 @item len @tab 8 @tab length of memory for collecting
33769 @item basereg @tab 4 @tab the register number containing the starting
33770 memory address for collecting.
33771 @item @emph{tracepoint action for collecting registers} @tab @tab
33772 @item 'R' @tab 1 @tab type of tracepoint action
33773 @item @emph{tracepoint action for collecting static trace data} @tab @tab
33774 @item 'L' @tab 1 @tab type of tracepoint action
33775 @item @emph{tracepoint action for expression evaluation} @tab @tab
33776 @item 'X' @tab 1 @tab type of tracepoint action
33777 @item agent expression @tab length of @tab @ref{agent expression object}
33778 @item @emph{tracepoint object} @tab @tab
33779 @item number @tab 4 @tab number of tracepoint
33780 @item address @tab 8 @tab address of tracepoint inserted on
33781 @item type @tab 4 @tab type of tracepoint
33782 @item enabled @tab 1 @tab enable or disable of tracepoint
33783 @item step_count @tab 8 @tab step
33784 @item pass_count @tab 8 @tab pass
33785 @item numactions @tab 4 @tab number of tracepoint actions
33786 @item hit count @tab 8 @tab hit count
33787 @item trace frame usage @tab 8 @tab trace frame usage
33788 @item compiled_cond @tab 8 @tab compiled condition
33789 @item orig_size @tab 8 @tab orig size
33790 @item condition @tab 4 if condition is NULL otherwise length of
33791 @ref{agent expression object}
33792 @tab zero if condition is NULL, otherwise is
33793 @ref{agent expression object}
33794 @item actions @tab variable
33795 @tab numactions number of @ref{tracepoint action object}
33798 @node IPA Protocol Commands
33799 @subsection IPA Protocol Commands
33800 @cindex ipa protocol commands
33802 The spaces in each command are delimiters to ease reading this commands
33803 specification. They don't exist in real commands.
33807 @item FastTrace:@var{tracepoint_object} @var{gdb_jump_pad_head}
33808 Installs a new fast tracepoint described by @var{tracepoint_object}
33809 (@pxref{tracepoint object}). The @var{gdb_jump_pad_head}, 8-byte long, is the
33810 head of @dfn{jumppad}, which is used to jump to data collection routine
33815 @item OK @var{target_address} @var{gdb_jump_pad_head} @var{fjump_size} @var{fjump}
33816 @var{target_address} is address of tracepoint in the inferior.
33817 The @var{gdb_jump_pad_head} is updated head of jumppad. Both of
33818 @var{target_address} and @var{gdb_jump_pad_head} are 8-byte long.
33819 The @var{fjump} contains a sequence of instructions jump to jumppad entry.
33820 The @var{fjump_size}, 4-byte long, is the size of @var{fjump}.
33827 Closes the in-process agent. This command is sent when @value{GDBN} or GDBserver
33828 is about to kill inferiors.
33836 @item probe_marker_at:@var{address}
33837 Asks in-process agent to probe the marker at @var{address}.
33844 @item unprobe_marker_at:@var{address}
33845 Asks in-process agent to unprobe the marker at @var{address}.
33849 @chapter Reporting Bugs in @value{GDBN}
33850 @cindex bugs in @value{GDBN}
33851 @cindex reporting bugs in @value{GDBN}
33853 Your bug reports play an essential role in making @value{GDBN} reliable.
33855 Reporting a bug may help you by bringing a solution to your problem, or it
33856 may not. But in any case the principal function of a bug report is to help
33857 the entire community by making the next version of @value{GDBN} work better. Bug
33858 reports are your contribution to the maintenance of @value{GDBN}.
33860 In order for a bug report to serve its purpose, you must include the
33861 information that enables us to fix the bug.
33864 * Bug Criteria:: Have you found a bug?
33865 * Bug Reporting:: How to report bugs
33869 @section Have You Found a Bug?
33870 @cindex bug criteria
33872 If you are not sure whether you have found a bug, here are some guidelines:
33875 @cindex fatal signal
33876 @cindex debugger crash
33877 @cindex crash of debugger
33879 If the debugger gets a fatal signal, for any input whatever, that is a
33880 @value{GDBN} bug. Reliable debuggers never crash.
33882 @cindex error on valid input
33884 If @value{GDBN} produces an error message for valid input, that is a
33885 bug. (Note that if you're cross debugging, the problem may also be
33886 somewhere in the connection to the target.)
33888 @cindex invalid input
33890 If @value{GDBN} does not produce an error message for invalid input,
33891 that is a bug. However, you should note that your idea of
33892 ``invalid input'' might be our idea of ``an extension'' or ``support
33893 for traditional practice''.
33896 If you are an experienced user of debugging tools, your suggestions
33897 for improvement of @value{GDBN} are welcome in any case.
33900 @node Bug Reporting
33901 @section How to Report Bugs
33902 @cindex bug reports
33903 @cindex @value{GDBN} bugs, reporting
33905 A number of companies and individuals offer support for @sc{gnu} products.
33906 If you obtained @value{GDBN} from a support organization, we recommend you
33907 contact that organization first.
33909 You can find contact information for many support companies and
33910 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
33912 @c should add a web page ref...
33915 @ifset BUGURL_DEFAULT
33916 In any event, we also recommend that you submit bug reports for
33917 @value{GDBN}. The preferred method is to submit them directly using
33918 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
33919 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
33922 @strong{Do not send bug reports to @samp{info-gdb}, or to
33923 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
33924 not want to receive bug reports. Those that do have arranged to receive
33927 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
33928 serves as a repeater. The mailing list and the newsgroup carry exactly
33929 the same messages. Often people think of posting bug reports to the
33930 newsgroup instead of mailing them. This appears to work, but it has one
33931 problem which can be crucial: a newsgroup posting often lacks a mail
33932 path back to the sender. Thus, if we need to ask for more information,
33933 we may be unable to reach you. For this reason, it is better to send
33934 bug reports to the mailing list.
33936 @ifclear BUGURL_DEFAULT
33937 In any event, we also recommend that you submit bug reports for
33938 @value{GDBN} to @value{BUGURL}.
33942 The fundamental principle of reporting bugs usefully is this:
33943 @strong{report all the facts}. If you are not sure whether to state a
33944 fact or leave it out, state it!
33946 Often people omit facts because they think they know what causes the
33947 problem and assume that some details do not matter. Thus, you might
33948 assume that the name of the variable you use in an example does not matter.
33949 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
33950 stray memory reference which happens to fetch from the location where that
33951 name is stored in memory; perhaps, if the name were different, the contents
33952 of that location would fool the debugger into doing the right thing despite
33953 the bug. Play it safe and give a specific, complete example. That is the
33954 easiest thing for you to do, and the most helpful.
33956 Keep in mind that the purpose of a bug report is to enable us to fix the
33957 bug. It may be that the bug has been reported previously, but neither
33958 you nor we can know that unless your bug report is complete and
33961 Sometimes people give a few sketchy facts and ask, ``Does this ring a
33962 bell?'' Those bug reports are useless, and we urge everyone to
33963 @emph{refuse to respond to them} except to chide the sender to report
33966 To enable us to fix the bug, you should include all these things:
33970 The version of @value{GDBN}. @value{GDBN} announces it if you start
33971 with no arguments; you can also print it at any time using @code{show
33974 Without this, we will not know whether there is any point in looking for
33975 the bug in the current version of @value{GDBN}.
33978 The type of machine you are using, and the operating system name and
33982 The details of the @value{GDBN} build-time configuration.
33983 @value{GDBN} shows these details if you invoke it with the
33984 @option{--configuration} command-line option, or if you type
33985 @code{show configuration} at @value{GDBN}'s prompt.
33988 What compiler (and its version) was used to compile @value{GDBN}---e.g.@:
33989 ``@value{GCC}--2.8.1''.
33992 What compiler (and its version) was used to compile the program you are
33993 debugging---e.g.@: ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
33994 C Compiler''. For @value{NGCC}, you can say @kbd{@value{GCC} --version}
33995 to get this information; for other compilers, see the documentation for
33999 The command arguments you gave the compiler to compile your example and
34000 observe the bug. For example, did you use @samp{-O}? To guarantee
34001 you will not omit something important, list them all. A copy of the
34002 Makefile (or the output from make) is sufficient.
34004 If we were to try to guess the arguments, we would probably guess wrong
34005 and then we might not encounter the bug.
34008 A complete input script, and all necessary source files, that will
34012 A description of what behavior you observe that you believe is
34013 incorrect. For example, ``It gets a fatal signal.''
34015 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
34016 will certainly notice it. But if the bug is incorrect output, we might
34017 not notice unless it is glaringly wrong. You might as well not give us
34018 a chance to make a mistake.
34020 Even if the problem you experience is a fatal signal, you should still
34021 say so explicitly. Suppose something strange is going on, such as, your
34022 copy of @value{GDBN} is out of synch, or you have encountered a bug in
34023 the C library on your system. (This has happened!) Your copy might
34024 crash and ours would not. If you told us to expect a crash, then when
34025 ours fails to crash, we would know that the bug was not happening for
34026 us. If you had not told us to expect a crash, then we would not be able
34027 to draw any conclusion from our observations.
34030 @cindex recording a session script
34031 To collect all this information, you can use a session recording program
34032 such as @command{script}, which is available on many Unix systems.
34033 Just run your @value{GDBN} session inside @command{script} and then
34034 include the @file{typescript} file with your bug report.
34036 Another way to record a @value{GDBN} session is to run @value{GDBN}
34037 inside Emacs and then save the entire buffer to a file.
34040 If you wish to suggest changes to the @value{GDBN} source, send us context
34041 diffs. If you even discuss something in the @value{GDBN} source, refer to
34042 it by context, not by line number.
34044 The line numbers in our development sources will not match those in your
34045 sources. Your line numbers would convey no useful information to us.
34049 Here are some things that are not necessary:
34053 A description of the envelope of the bug.
34055 Often people who encounter a bug spend a lot of time investigating
34056 which changes to the input file will make the bug go away and which
34057 changes will not affect it.
34059 This is often time consuming and not very useful, because the way we
34060 will find the bug is by running a single example under the debugger
34061 with breakpoints, not by pure deduction from a series of examples.
34062 We recommend that you save your time for something else.
34064 Of course, if you can find a simpler example to report @emph{instead}
34065 of the original one, that is a convenience for us. Errors in the
34066 output will be easier to spot, running under the debugger will take
34067 less time, and so on.
34069 However, simplification is not vital; if you do not want to do this,
34070 report the bug anyway and send us the entire test case you used.
34073 A patch for the bug.
34075 A patch for the bug does help us if it is a good one. But do not omit
34076 the necessary information, such as the test case, on the assumption that
34077 a patch is all we need. We might see problems with your patch and decide
34078 to fix the problem another way, or we might not understand it at all.
34080 Sometimes with a program as complicated as @value{GDBN} it is very hard to
34081 construct an example that will make the program follow a certain path
34082 through the code. If you do not send us the example, we will not be able
34083 to construct one, so we will not be able to verify that the bug is fixed.
34085 And if we cannot understand what bug you are trying to fix, or why your
34086 patch should be an improvement, we will not install it. A test case will
34087 help us to understand.
34090 A guess about what the bug is or what it depends on.
34092 Such guesses are usually wrong. Even we cannot guess right about such
34093 things without first using the debugger to find the facts.
34096 @c The readline documentation is distributed with the readline code
34097 @c and consists of the two following files:
34100 @c Use -I with makeinfo to point to the appropriate directory,
34101 @c environment var TEXINPUTS with TeX.
34102 @ifclear SYSTEM_READLINE
34103 @include rluser.texi
34104 @include hsuser.texi
34108 @appendix In Memoriam
34110 The @value{GDBN} project mourns the loss of the following long-time
34115 Fred was a long-standing contributor to @value{GDBN} (1991-2006), and
34116 to Free Software in general. Outside of @value{GDBN}, he was known in
34117 the Amiga world for his series of Fish Disks, and the GeekGadget project.
34119 @item Michael Snyder
34120 Michael was one of the Global Maintainers of the @value{GDBN} project,
34121 with contributions recorded as early as 1996, until 2011. In addition
34122 to his day to day participation, he was a large driving force behind
34123 adding Reverse Debugging to @value{GDBN}.
34126 Beyond their technical contributions to the project, they were also
34127 enjoyable members of the Free Software Community. We will miss them.
34129 @node Formatting Documentation
34130 @appendix Formatting Documentation
34132 @cindex @value{GDBN} reference card
34133 @cindex reference card
34134 The @value{GDBN} 4 release includes an already-formatted reference card, ready
34135 for printing with PostScript or Ghostscript, in the @file{gdb}
34136 subdirectory of the main source directory@footnote{In
34137 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
34138 release.}. If you can use PostScript or Ghostscript with your printer,
34139 you can print the reference card immediately with @file{refcard.ps}.
34141 The release also includes the source for the reference card. You
34142 can format it, using @TeX{}, by typing:
34148 The @value{GDBN} reference card is designed to print in @dfn{landscape}
34149 mode on US ``letter'' size paper;
34150 that is, on a sheet 11 inches wide by 8.5 inches
34151 high. You will need to specify this form of printing as an option to
34152 your @sc{dvi} output program.
34154 @cindex documentation
34156 All the documentation for @value{GDBN} comes as part of the machine-readable
34157 distribution. The documentation is written in Texinfo format, which is
34158 a documentation system that uses a single source file to produce both
34159 on-line information and a printed manual. You can use one of the Info
34160 formatting commands to create the on-line version of the documentation
34161 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
34163 @value{GDBN} includes an already formatted copy of the on-line Info
34164 version of this manual in the @file{gdb} subdirectory. The main Info
34165 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
34166 subordinate files matching @samp{gdb.info*} in the same directory. If
34167 necessary, you can print out these files, or read them with any editor;
34168 but they are easier to read using the @code{info} subsystem in @sc{gnu}
34169 Emacs or the standalone @code{info} program, available as part of the
34170 @sc{gnu} Texinfo distribution.
34172 If you want to format these Info files yourself, you need one of the
34173 Info formatting programs, such as @code{texinfo-format-buffer} or
34176 If you have @code{makeinfo} installed, and are in the top level
34177 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
34178 version @value{GDBVN}), you can make the Info file by typing:
34185 If you want to typeset and print copies of this manual, you need @TeX{},
34186 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
34187 Texinfo definitions file.
34189 @TeX{} is a typesetting program; it does not print files directly, but
34190 produces output files called @sc{dvi} files. To print a typeset
34191 document, you need a program to print @sc{dvi} files. If your system
34192 has @TeX{} installed, chances are it has such a program. The precise
34193 command to use depends on your system; @kbd{lpr -d} is common; another
34194 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
34195 require a file name without any extension or a @samp{.dvi} extension.
34197 @TeX{} also requires a macro definitions file called
34198 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
34199 written in Texinfo format. On its own, @TeX{} cannot either read or
34200 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
34201 and is located in the @file{gdb-@var{version-number}/texinfo}
34204 If you have @TeX{} and a @sc{dvi} printer program installed, you can
34205 typeset and print this manual. First switch to the @file{gdb}
34206 subdirectory of the main source directory (for example, to
34207 @file{gdb-@value{GDBVN}/gdb}) and type:
34213 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
34215 @node Installing GDB
34216 @appendix Installing @value{GDBN}
34217 @cindex installation
34220 * Requirements:: Requirements for building @value{GDBN}
34221 * Running Configure:: Invoking the @value{GDBN} @file{configure} script
34222 * Separate Objdir:: Compiling @value{GDBN} in another directory
34223 * Config Names:: Specifying names for hosts and targets
34224 * Configure Options:: Summary of options for configure
34225 * System-wide configuration:: Having a system-wide init file
34229 @section Requirements for Building @value{GDBN}
34230 @cindex building @value{GDBN}, requirements for
34232 Building @value{GDBN} requires various tools and packages to be available.
34233 Other packages will be used only if they are found.
34235 @heading Tools/Packages Necessary for Building @value{GDBN}
34237 @item ISO C90 compiler
34238 @value{GDBN} is written in ISO C90. It should be buildable with any
34239 working C90 compiler, e.g.@: GCC.
34243 @heading Tools/Packages Optional for Building @value{GDBN}
34247 @value{GDBN} can use the Expat XML parsing library. This library may be
34248 included with your operating system distribution; if it is not, you
34249 can get the latest version from @url{http://expat.sourceforge.net}.
34250 The @file{configure} script will search for this library in several
34251 standard locations; if it is installed in an unusual path, you can
34252 use the @option{--with-libexpat-prefix} option to specify its location.
34258 Remote protocol memory maps (@pxref{Memory Map Format})
34260 Target descriptions (@pxref{Target Descriptions})
34262 Remote shared library lists (@xref{Library List Format},
34263 or alternatively @pxref{Library List Format for SVR4 Targets})
34265 MS-Windows shared libraries (@pxref{Shared Libraries})
34267 Traceframe info (@pxref{Traceframe Info Format})
34269 Branch trace (@pxref{Branch Trace Format},
34270 @pxref{Branch Trace Configuration Format})
34274 @cindex compressed debug sections
34275 @value{GDBN} will use the @samp{zlib} library, if available, to read
34276 compressed debug sections. Some linkers, such as GNU gold, are capable
34277 of producing binaries with compressed debug sections. If @value{GDBN}
34278 is compiled with @samp{zlib}, it will be able to read the debug
34279 information in such binaries.
34281 The @samp{zlib} library is likely included with your operating system
34282 distribution; if it is not, you can get the latest version from
34283 @url{http://zlib.net}.
34286 @value{GDBN}'s features related to character sets (@pxref{Character
34287 Sets}) require a functioning @code{iconv} implementation. If you are
34288 on a GNU system, then this is provided by the GNU C Library. Some
34289 other systems also provide a working @code{iconv}.
34291 If @value{GDBN} is using the @code{iconv} program which is installed
34292 in a non-standard place, you will need to tell @value{GDBN} where to find it.
34293 This is done with @option{--with-iconv-bin} which specifies the
34294 directory that contains the @code{iconv} program.
34296 On systems without @code{iconv}, you can install GNU Libiconv. If you
34297 have previously installed Libiconv, you can use the
34298 @option{--with-libiconv-prefix} option to configure.
34300 @value{GDBN}'s top-level @file{configure} and @file{Makefile} will
34301 arrange to build Libiconv if a directory named @file{libiconv} appears
34302 in the top-most source directory. If Libiconv is built this way, and
34303 if the operating system does not provide a suitable @code{iconv}
34304 implementation, then the just-built library will automatically be used
34305 by @value{GDBN}. One easy way to set this up is to download GNU
34306 Libiconv, unpack it, and then rename the directory holding the
34307 Libiconv source code to @samp{libiconv}.
34310 @node Running Configure
34311 @section Invoking the @value{GDBN} @file{configure} Script
34312 @cindex configuring @value{GDBN}
34313 @value{GDBN} comes with a @file{configure} script that automates the process
34314 of preparing @value{GDBN} for installation; you can then use @code{make} to
34315 build the @code{gdb} program.
34317 @c irrelevant in info file; it's as current as the code it lives with.
34318 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
34319 look at the @file{README} file in the sources; we may have improved the
34320 installation procedures since publishing this manual.}
34323 The @value{GDBN} distribution includes all the source code you need for
34324 @value{GDBN} in a single directory, whose name is usually composed by
34325 appending the version number to @samp{gdb}.
34327 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
34328 @file{gdb-@value{GDBVN}} directory. That directory contains:
34331 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
34332 script for configuring @value{GDBN} and all its supporting libraries
34334 @item gdb-@value{GDBVN}/gdb
34335 the source specific to @value{GDBN} itself
34337 @item gdb-@value{GDBVN}/bfd
34338 source for the Binary File Descriptor library
34340 @item gdb-@value{GDBVN}/include
34341 @sc{gnu} include files
34343 @item gdb-@value{GDBVN}/libiberty
34344 source for the @samp{-liberty} free software library
34346 @item gdb-@value{GDBVN}/opcodes
34347 source for the library of opcode tables and disassemblers
34349 @item gdb-@value{GDBVN}/readline
34350 source for the @sc{gnu} command-line interface
34352 @item gdb-@value{GDBVN}/glob
34353 source for the @sc{gnu} filename pattern-matching subroutine
34355 @item gdb-@value{GDBVN}/mmalloc
34356 source for the @sc{gnu} memory-mapped malloc package
34359 The simplest way to configure and build @value{GDBN} is to run @file{configure}
34360 from the @file{gdb-@var{version-number}} source directory, which in
34361 this example is the @file{gdb-@value{GDBVN}} directory.
34363 First switch to the @file{gdb-@var{version-number}} source directory
34364 if you are not already in it; then run @file{configure}. Pass the
34365 identifier for the platform on which @value{GDBN} will run as an
34371 cd gdb-@value{GDBVN}
34372 ./configure @var{host}
34377 where @var{host} is an identifier such as @samp{sun4} or
34378 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
34379 (You can often leave off @var{host}; @file{configure} tries to guess the
34380 correct value by examining your system.)
34382 Running @samp{configure @var{host}} and then running @code{make} builds the
34383 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
34384 libraries, then @code{gdb} itself. The configured source files, and the
34385 binaries, are left in the corresponding source directories.
34388 @file{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
34389 system does not recognize this automatically when you run a different
34390 shell, you may need to run @code{sh} on it explicitly:
34393 sh configure @var{host}
34396 If you run @file{configure} from a directory that contains source
34397 directories for multiple libraries or programs, such as the
34398 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN},
34400 creates configuration files for every directory level underneath (unless
34401 you tell it not to, with the @samp{--norecursion} option).
34403 You should run the @file{configure} script from the top directory in the
34404 source tree, the @file{gdb-@var{version-number}} directory. If you run
34405 @file{configure} from one of the subdirectories, you will configure only
34406 that subdirectory. That is usually not what you want. In particular,
34407 if you run the first @file{configure} from the @file{gdb} subdirectory
34408 of the @file{gdb-@var{version-number}} directory, you will omit the
34409 configuration of @file{bfd}, @file{readline}, and other sibling
34410 directories of the @file{gdb} subdirectory. This leads to build errors
34411 about missing include files such as @file{bfd/bfd.h}.
34413 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
34414 However, you should make sure that the shell on your path (named by
34415 the @samp{SHELL} environment variable) is publicly readable. Remember
34416 that @value{GDBN} uses the shell to start your program---some systems refuse to
34417 let @value{GDBN} debug child processes whose programs are not readable.
34419 @node Separate Objdir
34420 @section Compiling @value{GDBN} in Another Directory
34422 If you want to run @value{GDBN} versions for several host or target machines,
34423 you need a different @code{gdb} compiled for each combination of
34424 host and target. @file{configure} is designed to make this easy by
34425 allowing you to generate each configuration in a separate subdirectory,
34426 rather than in the source directory. If your @code{make} program
34427 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
34428 @code{make} in each of these directories builds the @code{gdb}
34429 program specified there.
34431 To build @code{gdb} in a separate directory, run @file{configure}
34432 with the @samp{--srcdir} option to specify where to find the source.
34433 (You also need to specify a path to find @file{configure}
34434 itself from your working directory. If the path to @file{configure}
34435 would be the same as the argument to @samp{--srcdir}, you can leave out
34436 the @samp{--srcdir} option; it is assumed.)
34438 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
34439 separate directory for a Sun 4 like this:
34443 cd gdb-@value{GDBVN}
34446 ../gdb-@value{GDBVN}/configure sun4
34451 When @file{configure} builds a configuration using a remote source
34452 directory, it creates a tree for the binaries with the same structure
34453 (and using the same names) as the tree under the source directory. In
34454 the example, you'd find the Sun 4 library @file{libiberty.a} in the
34455 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
34456 @file{gdb-sun4/gdb}.
34458 Make sure that your path to the @file{configure} script has just one
34459 instance of @file{gdb} in it. If your path to @file{configure} looks
34460 like @file{../gdb-@value{GDBVN}/gdb/configure}, you are configuring only
34461 one subdirectory of @value{GDBN}, not the whole package. This leads to
34462 build errors about missing include files such as @file{bfd/bfd.h}.
34464 One popular reason to build several @value{GDBN} configurations in separate
34465 directories is to configure @value{GDBN} for cross-compiling (where
34466 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
34467 programs that run on another machine---the @dfn{target}).
34468 You specify a cross-debugging target by
34469 giving the @samp{--target=@var{target}} option to @file{configure}.
34471 When you run @code{make} to build a program or library, you must run
34472 it in a configured directory---whatever directory you were in when you
34473 called @file{configure} (or one of its subdirectories).
34475 The @code{Makefile} that @file{configure} generates in each source
34476 directory also runs recursively. If you type @code{make} in a source
34477 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
34478 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
34479 will build all the required libraries, and then build GDB.
34481 When you have multiple hosts or targets configured in separate
34482 directories, you can run @code{make} on them in parallel (for example,
34483 if they are NFS-mounted on each of the hosts); they will not interfere
34487 @section Specifying Names for Hosts and Targets
34489 The specifications used for hosts and targets in the @file{configure}
34490 script are based on a three-part naming scheme, but some short predefined
34491 aliases are also supported. The full naming scheme encodes three pieces
34492 of information in the following pattern:
34495 @var{architecture}-@var{vendor}-@var{os}
34498 For example, you can use the alias @code{sun4} as a @var{host} argument,
34499 or as the value for @var{target} in a @code{--target=@var{target}}
34500 option. The equivalent full name is @samp{sparc-sun-sunos4}.
34502 The @file{configure} script accompanying @value{GDBN} does not provide
34503 any query facility to list all supported host and target names or
34504 aliases. @file{configure} calls the Bourne shell script
34505 @code{config.sub} to map abbreviations to full names; you can read the
34506 script, if you wish, or you can use it to test your guesses on
34507 abbreviations---for example:
34510 % sh config.sub i386-linux
34512 % sh config.sub alpha-linux
34513 alpha-unknown-linux-gnu
34514 % sh config.sub hp9k700
34516 % sh config.sub sun4
34517 sparc-sun-sunos4.1.1
34518 % sh config.sub sun3
34519 m68k-sun-sunos4.1.1
34520 % sh config.sub i986v
34521 Invalid configuration `i986v': machine `i986v' not recognized
34525 @code{config.sub} is also distributed in the @value{GDBN} source
34526 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
34528 @node Configure Options
34529 @section @file{configure} Options
34531 Here is a summary of the @file{configure} options and arguments that
34532 are most often useful for building @value{GDBN}. @file{configure} also has
34533 several other options not listed here. @inforef{What Configure
34534 Does,,configure.info}, for a full explanation of @file{configure}.
34537 configure @r{[}--help@r{]}
34538 @r{[}--prefix=@var{dir}@r{]}
34539 @r{[}--exec-prefix=@var{dir}@r{]}
34540 @r{[}--srcdir=@var{dirname}@r{]}
34541 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
34542 @r{[}--target=@var{target}@r{]}
34547 You may introduce options with a single @samp{-} rather than
34548 @samp{--} if you prefer; but you may abbreviate option names if you use
34553 Display a quick summary of how to invoke @file{configure}.
34555 @item --prefix=@var{dir}
34556 Configure the source to install programs and files under directory
34559 @item --exec-prefix=@var{dir}
34560 Configure the source to install programs under directory
34563 @c avoid splitting the warning from the explanation:
34565 @item --srcdir=@var{dirname}
34566 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
34567 @code{make} that implements the @code{VPATH} feature.}@*
34568 Use this option to make configurations in directories separate from the
34569 @value{GDBN} source directories. Among other things, you can use this to
34570 build (or maintain) several configurations simultaneously, in separate
34571 directories. @file{configure} writes configuration-specific files in
34572 the current directory, but arranges for them to use the source in the
34573 directory @var{dirname}. @file{configure} creates directories under
34574 the working directory in parallel to the source directories below
34577 @item --norecursion
34578 Configure only the directory level where @file{configure} is executed; do not
34579 propagate configuration to subdirectories.
34581 @item --target=@var{target}
34582 Configure @value{GDBN} for cross-debugging programs running on the specified
34583 @var{target}. Without this option, @value{GDBN} is configured to debug
34584 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
34586 There is no convenient way to generate a list of all available targets.
34588 @item @var{host} @dots{}
34589 Configure @value{GDBN} to run on the specified @var{host}.
34591 There is no convenient way to generate a list of all available hosts.
34594 There are many other options available as well, but they are generally
34595 needed for special purposes only.
34597 @node System-wide configuration
34598 @section System-wide configuration and settings
34599 @cindex system-wide init file
34601 @value{GDBN} can be configured to have a system-wide init file;
34602 this file will be read and executed at startup (@pxref{Startup, , What
34603 @value{GDBN} does during startup}).
34605 Here is the corresponding configure option:
34608 @item --with-system-gdbinit=@var{file}
34609 Specify that the default location of the system-wide init file is
34613 If @value{GDBN} has been configured with the option @option{--prefix=$prefix},
34614 it may be subject to relocation. Two possible cases:
34618 If the default location of this init file contains @file{$prefix},
34619 it will be subject to relocation. Suppose that the configure options
34620 are @option{--prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit};
34621 if @value{GDBN} is moved from @file{$prefix} to @file{$install}, the system
34622 init file is looked for as @file{$install/etc/gdbinit} instead of
34623 @file{$prefix/etc/gdbinit}.
34626 By contrast, if the default location does not contain the prefix,
34627 it will not be relocated. E.g.@: if @value{GDBN} has been configured with
34628 @option{--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit},
34629 then @value{GDBN} will always look for @file{/usr/share/gdb/gdbinit},
34630 wherever @value{GDBN} is installed.
34633 If the configured location of the system-wide init file (as given by the
34634 @option{--with-system-gdbinit} option at configure time) is in the
34635 data-directory (as specified by @option{--with-gdb-datadir} at configure
34636 time) or in one of its subdirectories, then @value{GDBN} will look for the
34637 system-wide init file in the directory specified by the
34638 @option{--data-directory} command-line option.
34639 Note that the system-wide init file is only read once, during @value{GDBN}
34640 initialization. If the data-directory is changed after @value{GDBN} has
34641 started with the @code{set data-directory} command, the file will not be
34645 * System-wide Configuration Scripts:: Installed System-wide Configuration Scripts
34648 @node System-wide Configuration Scripts
34649 @subsection Installed System-wide Configuration Scripts
34650 @cindex system-wide configuration scripts
34652 The @file{system-gdbinit} directory, located inside the data-directory
34653 (as specified by @option{--with-gdb-datadir} at configure time) contains
34654 a number of scripts which can be used as system-wide init files. To
34655 automatically source those scripts at startup, @value{GDBN} should be
34656 configured with @option{--with-system-gdbinit}. Otherwise, any user
34657 should be able to source them by hand as needed.
34659 The following scripts are currently available:
34662 @item @file{elinos.py}
34664 @cindex ELinOS system-wide configuration script
34665 This script is useful when debugging a program on an ELinOS target.
34666 It takes advantage of the environment variables defined in a standard
34667 ELinOS environment in order to determine the location of the system
34668 shared libraries, and then sets the @samp{solib-absolute-prefix}
34669 and @samp{solib-search-path} variables appropriately.
34671 @item @file{wrs-linux.py}
34672 @pindex wrs-linux.py
34673 @cindex Wind River Linux system-wide configuration script
34674 This script is useful when debugging a program on a target running
34675 Wind River Linux. It expects the @env{ENV_PREFIX} to be set to
34676 the host-side sysroot used by the target system.
34680 @node Maintenance Commands
34681 @appendix Maintenance Commands
34682 @cindex maintenance commands
34683 @cindex internal commands
34685 In addition to commands intended for @value{GDBN} users, @value{GDBN}
34686 includes a number of commands intended for @value{GDBN} developers,
34687 that are not documented elsewhere in this manual. These commands are
34688 provided here for reference. (For commands that turn on debugging
34689 messages, see @ref{Debugging Output}.)
34692 @kindex maint agent
34693 @kindex maint agent-eval
34694 @item maint agent @r{[}-at @var{location}@r{,}@r{]} @var{expression}
34695 @itemx maint agent-eval @r{[}-at @var{location}@r{,}@r{]} @var{expression}
34696 Translate the given @var{expression} into remote agent bytecodes.
34697 This command is useful for debugging the Agent Expression mechanism
34698 (@pxref{Agent Expressions}). The @samp{agent} version produces an
34699 expression useful for data collection, such as by tracepoints, while
34700 @samp{maint agent-eval} produces an expression that evaluates directly
34701 to a result. For instance, a collection expression for @code{globa +
34702 globb} will include bytecodes to record four bytes of memory at each
34703 of the addresses of @code{globa} and @code{globb}, while discarding
34704 the result of the addition, while an evaluation expression will do the
34705 addition and return the sum.
34706 If @code{-at} is given, generate remote agent bytecode for @var{location}.
34707 If not, generate remote agent bytecode for current frame PC address.
34709 @kindex maint agent-printf
34710 @item maint agent-printf @var{format},@var{expr},...
34711 Translate the given format string and list of argument expressions
34712 into remote agent bytecodes and display them as a disassembled list.
34713 This command is useful for debugging the agent version of dynamic
34714 printf (@pxref{Dynamic Printf}).
34716 @kindex maint info breakpoints
34717 @item @anchor{maint info breakpoints}maint info breakpoints
34718 Using the same format as @samp{info breakpoints}, display both the
34719 breakpoints you've set explicitly, and those @value{GDBN} is using for
34720 internal purposes. Internal breakpoints are shown with negative
34721 breakpoint numbers. The type column identifies what kind of breakpoint
34726 Normal, explicitly set breakpoint.
34729 Normal, explicitly set watchpoint.
34732 Internal breakpoint, used to handle correctly stepping through
34733 @code{longjmp} calls.
34735 @item longjmp resume
34736 Internal breakpoint at the target of a @code{longjmp}.
34739 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
34742 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
34745 Shared library events.
34749 @kindex maint info btrace
34750 @item maint info btrace
34751 Pint information about raw branch tracing data.
34753 @kindex maint btrace packet-history
34754 @item maint btrace packet-history
34755 Print the raw branch trace packets that are used to compute the
34756 execution history for the @samp{record btrace} command. Both the
34757 information and the format in which it is printed depend on the btrace
34762 For the BTS recording format, print a list of blocks of sequential
34763 code. For each block, the following information is printed:
34767 Newer blocks have higher numbers. The oldest block has number zero.
34768 @item Lowest @samp{PC}
34769 @item Highest @samp{PC}
34773 For the Intel Processor Trace recording format, print a list of
34774 Intel Processor Trace packets. For each packet, the following
34775 information is printed:
34778 @item Packet number
34779 Newer packets have higher numbers. The oldest packet has number zero.
34781 The packet's offset in the trace stream.
34782 @item Packet opcode and payload
34786 @kindex maint btrace clear-packet-history
34787 @item maint btrace clear-packet-history
34788 Discards the cached packet history printed by the @samp{maint btrace
34789 packet-history} command. The history will be computed again when
34792 @kindex maint btrace clear
34793 @item maint btrace clear
34794 Discard the branch trace data. The data will be fetched anew and the
34795 branch trace will be recomputed when needed.
34797 This implicitly truncates the branch trace to a single branch trace
34798 buffer. When updating branch trace incrementally, the branch trace
34799 available to @value{GDBN} may be bigger than a single branch trace
34802 @kindex maint set btrace pt skip-pad
34803 @item maint set btrace pt skip-pad
34804 @kindex maint show btrace pt skip-pad
34805 @item maint show btrace pt skip-pad
34806 Control whether @value{GDBN} will skip PAD packets when computing the
34809 @kindex set displaced-stepping
34810 @kindex show displaced-stepping
34811 @cindex displaced stepping support
34812 @cindex out-of-line single-stepping
34813 @item set displaced-stepping
34814 @itemx show displaced-stepping
34815 Control whether or not @value{GDBN} will do @dfn{displaced stepping}
34816 if the target supports it. Displaced stepping is a way to single-step
34817 over breakpoints without removing them from the inferior, by executing
34818 an out-of-line copy of the instruction that was originally at the
34819 breakpoint location. It is also known as out-of-line single-stepping.
34822 @item set displaced-stepping on
34823 If the target architecture supports it, @value{GDBN} will use
34824 displaced stepping to step over breakpoints.
34826 @item set displaced-stepping off
34827 @value{GDBN} will not use displaced stepping to step over breakpoints,
34828 even if such is supported by the target architecture.
34830 @cindex non-stop mode, and @samp{set displaced-stepping}
34831 @item set displaced-stepping auto
34832 This is the default mode. @value{GDBN} will use displaced stepping
34833 only if non-stop mode is active (@pxref{Non-Stop Mode}) and the target
34834 architecture supports displaced stepping.
34837 @kindex maint check-psymtabs
34838 @item maint check-psymtabs
34839 Check the consistency of currently expanded psymtabs versus symtabs.
34840 Use this to check, for example, whether a symbol is in one but not the other.
34842 @kindex maint check-symtabs
34843 @item maint check-symtabs
34844 Check the consistency of currently expanded symtabs.
34846 @kindex maint expand-symtabs
34847 @item maint expand-symtabs [@var{regexp}]
34848 Expand symbol tables.
34849 If @var{regexp} is specified, only expand symbol tables for file
34850 names matching @var{regexp}.
34852 @kindex maint set catch-demangler-crashes
34853 @kindex maint show catch-demangler-crashes
34854 @cindex demangler crashes
34855 @item maint set catch-demangler-crashes [on|off]
34856 @itemx maint show catch-demangler-crashes
34857 Control whether @value{GDBN} should attempt to catch crashes in the
34858 symbol name demangler. The default is to attempt to catch crashes.
34859 If enabled, the first time a crash is caught, a core file is created,
34860 the offending symbol is displayed and the user is presented with the
34861 option to terminate the current session.
34863 @kindex maint cplus first_component
34864 @item maint cplus first_component @var{name}
34865 Print the first C@t{++} class/namespace component of @var{name}.
34867 @kindex maint cplus namespace
34868 @item maint cplus namespace
34869 Print the list of possible C@t{++} namespaces.
34871 @kindex maint deprecate
34872 @kindex maint undeprecate
34873 @cindex deprecated commands
34874 @item maint deprecate @var{command} @r{[}@var{replacement}@r{]}
34875 @itemx maint undeprecate @var{command}
34876 Deprecate or undeprecate the named @var{command}. Deprecated commands
34877 cause @value{GDBN} to issue a warning when you use them. The optional
34878 argument @var{replacement} says which newer command should be used in
34879 favor of the deprecated one; if it is given, @value{GDBN} will mention
34880 the replacement as part of the warning.
34882 @kindex maint dump-me
34883 @item maint dump-me
34884 @cindex @code{SIGQUIT} signal, dump core of @value{GDBN}
34885 Cause a fatal signal in the debugger and force it to dump its core.
34886 This is supported only on systems which support aborting a program
34887 with the @code{SIGQUIT} signal.
34889 @kindex maint internal-error
34890 @kindex maint internal-warning
34891 @kindex maint demangler-warning
34892 @cindex demangler crashes
34893 @item maint internal-error @r{[}@var{message-text}@r{]}
34894 @itemx maint internal-warning @r{[}@var{message-text}@r{]}
34895 @itemx maint demangler-warning @r{[}@var{message-text}@r{]}
34897 Cause @value{GDBN} to call the internal function @code{internal_error},
34898 @code{internal_warning} or @code{demangler_warning} and hence behave
34899 as though an internal problem has been detected. In addition to
34900 reporting the internal problem, these functions give the user the
34901 opportunity to either quit @value{GDBN} or (for @code{internal_error}
34902 and @code{internal_warning}) create a core file of the current
34903 @value{GDBN} session.
34905 These commands take an optional parameter @var{message-text} that is
34906 used as the text of the error or warning message.
34908 Here's an example of using @code{internal-error}:
34911 (@value{GDBP}) @kbd{maint internal-error testing, 1, 2}
34912 @dots{}/maint.c:121: internal-error: testing, 1, 2
34913 A problem internal to GDB has been detected. Further
34914 debugging may prove unreliable.
34915 Quit this debugging session? (y or n) @kbd{n}
34916 Create a core file? (y or n) @kbd{n}
34920 @cindex @value{GDBN} internal error
34921 @cindex internal errors, control of @value{GDBN} behavior
34922 @cindex demangler crashes
34924 @kindex maint set internal-error
34925 @kindex maint show internal-error
34926 @kindex maint set internal-warning
34927 @kindex maint show internal-warning
34928 @kindex maint set demangler-warning
34929 @kindex maint show demangler-warning
34930 @item maint set internal-error @var{action} [ask|yes|no]
34931 @itemx maint show internal-error @var{action}
34932 @itemx maint set internal-warning @var{action} [ask|yes|no]
34933 @itemx maint show internal-warning @var{action}
34934 @itemx maint set demangler-warning @var{action} [ask|yes|no]
34935 @itemx maint show demangler-warning @var{action}
34936 When @value{GDBN} reports an internal problem (error or warning) it
34937 gives the user the opportunity to both quit @value{GDBN} and create a
34938 core file of the current @value{GDBN} session. These commands let you
34939 override the default behaviour for each particular @var{action},
34940 described in the table below.
34944 You can specify that @value{GDBN} should always (yes) or never (no)
34945 quit. The default is to ask the user what to do.
34948 You can specify that @value{GDBN} should always (yes) or never (no)
34949 create a core file. The default is to ask the user what to do. Note
34950 that there is no @code{corefile} option for @code{demangler-warning}:
34951 demangler warnings always create a core file and this cannot be
34955 @kindex maint packet
34956 @item maint packet @var{text}
34957 If @value{GDBN} is talking to an inferior via the serial protocol,
34958 then this command sends the string @var{text} to the inferior, and
34959 displays the response packet. @value{GDBN} supplies the initial
34960 @samp{$} character, the terminating @samp{#} character, and the
34963 @kindex maint print architecture
34964 @item maint print architecture @r{[}@var{file}@r{]}
34965 Print the entire architecture configuration. The optional argument
34966 @var{file} names the file where the output goes.
34968 @kindex maint print c-tdesc @r{[}@var{file}@r{]}
34969 @item maint print c-tdesc
34970 Print the target description (@pxref{Target Descriptions}) as
34971 a C source file. By default, the target description is for the current
34972 target, but if the optional argument @var{file} is provided, that file
34973 is used to produce the description. The @var{file} should be an XML
34974 document, of the form described in @ref{Target Description Format}.
34975 The created source file is built into @value{GDBN} when @value{GDBN} is
34976 built again. This command is used by developers after they add or
34977 modify XML target descriptions.
34979 @kindex maint check xml-descriptions
34980 @item maint check xml-descriptions @var{dir}
34981 Check that the target descriptions dynamically created by @value{GDBN}
34982 equal the descriptions created from XML files found in @var{dir}.
34984 @kindex maint print dummy-frames
34985 @item maint print dummy-frames
34986 Prints the contents of @value{GDBN}'s internal dummy-frame stack.
34989 (@value{GDBP}) @kbd{b add}
34991 (@value{GDBP}) @kbd{print add(2,3)}
34992 Breakpoint 2, add (a=2, b=3) at @dots{}
34994 The program being debugged stopped while in a function called from GDB.
34996 (@value{GDBP}) @kbd{maint print dummy-frames}
34997 0xa8206d8: id=@{stack=0xbfffe734,code=0xbfffe73f,!special@}, ptid=process 9353
35001 Takes an optional file parameter.
35003 @kindex maint print registers
35004 @kindex maint print raw-registers
35005 @kindex maint print cooked-registers
35006 @kindex maint print register-groups
35007 @kindex maint print remote-registers
35008 @item maint print registers @r{[}@var{file}@r{]}
35009 @itemx maint print raw-registers @r{[}@var{file}@r{]}
35010 @itemx maint print cooked-registers @r{[}@var{file}@r{]}
35011 @itemx maint print register-groups @r{[}@var{file}@r{]}
35012 @itemx maint print remote-registers @r{[}@var{file}@r{]}
35013 Print @value{GDBN}'s internal register data structures.
35015 The command @code{maint print raw-registers} includes the contents of
35016 the raw register cache; the command @code{maint print
35017 cooked-registers} includes the (cooked) value of all registers,
35018 including registers which aren't available on the target nor visible
35019 to user; the command @code{maint print register-groups} includes the
35020 groups that each register is a member of; and the command @code{maint
35021 print remote-registers} includes the remote target's register numbers
35022 and offsets in the `G' packets.
35024 These commands take an optional parameter, a file name to which to
35025 write the information.
35027 @kindex maint print reggroups
35028 @item maint print reggroups @r{[}@var{file}@r{]}
35029 Print @value{GDBN}'s internal register group data structures. The
35030 optional argument @var{file} tells to what file to write the
35033 The register groups info looks like this:
35036 (@value{GDBP}) @kbd{maint print reggroups}
35049 This command forces @value{GDBN} to flush its internal register cache.
35051 @kindex maint print objfiles
35052 @cindex info for known object files
35053 @item maint print objfiles @r{[}@var{regexp}@r{]}
35054 Print a dump of all known object files.
35055 If @var{regexp} is specified, only print object files whose names
35056 match @var{regexp}. For each object file, this command prints its name,
35057 address in memory, and all of its psymtabs and symtabs.
35059 @kindex maint print user-registers
35060 @cindex user registers
35061 @item maint print user-registers
35062 List all currently available @dfn{user registers}. User registers
35063 typically provide alternate names for actual hardware registers. They
35064 include the four ``standard'' registers @code{$fp}, @code{$pc},
35065 @code{$sp}, and @code{$ps}. @xref{standard registers}. User
35066 registers can be used in expressions in the same way as the canonical
35067 register names, but only the latter are listed by the @code{info
35068 registers} and @code{maint print registers} commands.
35070 @kindex maint print section-scripts
35071 @cindex info for known .debug_gdb_scripts-loaded scripts
35072 @item maint print section-scripts [@var{regexp}]
35073 Print a dump of scripts specified in the @code{.debug_gdb_section} section.
35074 If @var{regexp} is specified, only print scripts loaded by object files
35075 matching @var{regexp}.
35076 For each script, this command prints its name as specified in the objfile,
35077 and the full path if known.
35078 @xref{dotdebug_gdb_scripts section}.
35080 @kindex maint print statistics
35081 @cindex bcache statistics
35082 @item maint print statistics
35083 This command prints, for each object file in the program, various data
35084 about that object file followed by the byte cache (@dfn{bcache})
35085 statistics for the object file. The objfile data includes the number
35086 of minimal, partial, full, and stabs symbols, the number of types
35087 defined by the objfile, the number of as yet unexpanded psym tables,
35088 the number of line tables and string tables, and the amount of memory
35089 used by the various tables. The bcache statistics include the counts,
35090 sizes, and counts of duplicates of all and unique objects, max,
35091 average, and median entry size, total memory used and its overhead and
35092 savings, and various measures of the hash table size and chain
35095 @kindex maint print target-stack
35096 @cindex target stack description
35097 @item maint print target-stack
35098 A @dfn{target} is an interface between the debugger and a particular
35099 kind of file or process. Targets can be stacked in @dfn{strata},
35100 so that more than one target can potentially respond to a request.
35101 In particular, memory accesses will walk down the stack of targets
35102 until they find a target that is interested in handling that particular
35105 This command prints a short description of each layer that was pushed on
35106 the @dfn{target stack}, starting from the top layer down to the bottom one.
35108 @kindex maint print type
35109 @cindex type chain of a data type
35110 @item maint print type @var{expr}
35111 Print the type chain for a type specified by @var{expr}. The argument
35112 can be either a type name or a symbol. If it is a symbol, the type of
35113 that symbol is described. The type chain produced by this command is
35114 a recursive definition of the data type as stored in @value{GDBN}'s
35115 data structures, including its flags and contained types.
35117 @kindex maint selftest
35119 @item maint selftest @r{[}@var{filter}@r{]}
35120 Run any self tests that were compiled in to @value{GDBN}. This will
35121 print a message showing how many tests were run, and how many failed.
35122 If a @var{filter} is passed, only the tests with @var{filter} in their
35125 @kindex "maint info selftests"
35127 @item maint info selftests
35128 List the selftests compiled in to @value{GDBN}.
35130 @kindex maint set dwarf always-disassemble
35131 @kindex maint show dwarf always-disassemble
35132 @item maint set dwarf always-disassemble
35133 @item maint show dwarf always-disassemble
35134 Control the behavior of @code{info address} when using DWARF debugging
35137 The default is @code{off}, which means that @value{GDBN} should try to
35138 describe a variable's location in an easily readable format. When
35139 @code{on}, @value{GDBN} will instead display the DWARF location
35140 expression in an assembly-like format. Note that some locations are
35141 too complex for @value{GDBN} to describe simply; in this case you will
35142 always see the disassembly form.
35144 Here is an example of the resulting disassembly:
35147 (gdb) info addr argc
35148 Symbol "argc" is a complex DWARF expression:
35152 For more information on these expressions, see
35153 @uref{http://www.dwarfstd.org/, the DWARF standard}.
35155 @kindex maint set dwarf max-cache-age
35156 @kindex maint show dwarf max-cache-age
35157 @item maint set dwarf max-cache-age
35158 @itemx maint show dwarf max-cache-age
35159 Control the DWARF compilation unit cache.
35161 @cindex DWARF compilation units cache
35162 In object files with inter-compilation-unit references, such as those
35163 produced by the GCC option @samp{-feliminate-dwarf2-dups}, the DWARF
35164 reader needs to frequently refer to previously read compilation units.
35165 This setting controls how long a compilation unit will remain in the
35166 cache if it is not referenced. A higher limit means that cached
35167 compilation units will be stored in memory longer, and more total
35168 memory will be used. Setting it to zero disables caching, which will
35169 slow down @value{GDBN} startup, but reduce memory consumption.
35171 @kindex maint set profile
35172 @kindex maint show profile
35173 @cindex profiling GDB
35174 @item maint set profile
35175 @itemx maint show profile
35176 Control profiling of @value{GDBN}.
35178 Profiling will be disabled until you use the @samp{maint set profile}
35179 command to enable it. When you enable profiling, the system will begin
35180 collecting timing and execution count data; when you disable profiling or
35181 exit @value{GDBN}, the results will be written to a log file. Remember that
35182 if you use profiling, @value{GDBN} will overwrite the profiling log file
35183 (often called @file{gmon.out}). If you have a record of important profiling
35184 data in a @file{gmon.out} file, be sure to move it to a safe location.
35186 Configuring with @samp{--enable-profiling} arranges for @value{GDBN} to be
35187 compiled with the @samp{-pg} compiler option.
35189 @kindex maint set show-debug-regs
35190 @kindex maint show show-debug-regs
35191 @cindex hardware debug registers
35192 @item maint set show-debug-regs
35193 @itemx maint show show-debug-regs
35194 Control whether to show variables that mirror the hardware debug
35195 registers. Use @code{on} to enable, @code{off} to disable. If
35196 enabled, the debug registers values are shown when @value{GDBN} inserts or
35197 removes a hardware breakpoint or watchpoint, and when the inferior
35198 triggers a hardware-assisted breakpoint or watchpoint.
35200 @kindex maint set show-all-tib
35201 @kindex maint show show-all-tib
35202 @item maint set show-all-tib
35203 @itemx maint show show-all-tib
35204 Control whether to show all non zero areas within a 1k block starting
35205 at thread local base, when using the @samp{info w32 thread-information-block}
35208 @kindex maint set target-async
35209 @kindex maint show target-async
35210 @item maint set target-async
35211 @itemx maint show target-async
35212 This controls whether @value{GDBN} targets operate in synchronous or
35213 asynchronous mode (@pxref{Background Execution}). Normally the
35214 default is asynchronous, if it is available; but this can be changed
35215 to more easily debug problems occurring only in synchronous mode.
35217 @kindex maint set target-non-stop @var{mode} [on|off|auto]
35218 @kindex maint show target-non-stop
35219 @item maint set target-non-stop
35220 @itemx maint show target-non-stop
35222 This controls whether @value{GDBN} targets always operate in non-stop
35223 mode even if @code{set non-stop} is @code{off} (@pxref{Non-Stop
35224 Mode}). The default is @code{auto}, meaning non-stop mode is enabled
35225 if supported by the target.
35228 @item maint set target-non-stop auto
35229 This is the default mode. @value{GDBN} controls the target in
35230 non-stop mode if the target supports it.
35232 @item maint set target-non-stop on
35233 @value{GDBN} controls the target in non-stop mode even if the target
35234 does not indicate support.
35236 @item maint set target-non-stop off
35237 @value{GDBN} does not control the target in non-stop mode even if the
35238 target supports it.
35241 @kindex maint set per-command
35242 @kindex maint show per-command
35243 @item maint set per-command
35244 @itemx maint show per-command
35245 @cindex resources used by commands
35247 @value{GDBN} can display the resources used by each command.
35248 This is useful in debugging performance problems.
35251 @item maint set per-command space [on|off]
35252 @itemx maint show per-command space
35253 Enable or disable the printing of the memory used by GDB for each command.
35254 If enabled, @value{GDBN} will display how much memory each command
35255 took, following the command's own output.
35256 This can also be requested by invoking @value{GDBN} with the
35257 @option{--statistics} command-line switch (@pxref{Mode Options}).
35259 @item maint set per-command time [on|off]
35260 @itemx maint show per-command time
35261 Enable or disable the printing of the execution time of @value{GDBN}
35263 If enabled, @value{GDBN} will display how much time it
35264 took to execute each command, following the command's own output.
35265 Both CPU time and wallclock time are printed.
35266 Printing both is useful when trying to determine whether the cost is
35267 CPU or, e.g., disk/network latency.
35268 Note that the CPU time printed is for @value{GDBN} only, it does not include
35269 the execution time of the inferior because there's no mechanism currently
35270 to compute how much time was spent by @value{GDBN} and how much time was
35271 spent by the program been debugged.
35272 This can also be requested by invoking @value{GDBN} with the
35273 @option{--statistics} command-line switch (@pxref{Mode Options}).
35275 @item maint set per-command symtab [on|off]
35276 @itemx maint show per-command symtab
35277 Enable or disable the printing of basic symbol table statistics
35279 If enabled, @value{GDBN} will display the following information:
35283 number of symbol tables
35285 number of primary symbol tables
35287 number of blocks in the blockvector
35291 @kindex maint space
35292 @cindex memory used by commands
35293 @item maint space @var{value}
35294 An alias for @code{maint set per-command space}.
35295 A non-zero value enables it, zero disables it.
35298 @cindex time of command execution
35299 @item maint time @var{value}
35300 An alias for @code{maint set per-command time}.
35301 A non-zero value enables it, zero disables it.
35303 @kindex maint translate-address
35304 @item maint translate-address @r{[}@var{section}@r{]} @var{addr}
35305 Find the symbol stored at the location specified by the address
35306 @var{addr} and an optional section name @var{section}. If found,
35307 @value{GDBN} prints the name of the closest symbol and an offset from
35308 the symbol's location to the specified address. This is similar to
35309 the @code{info address} command (@pxref{Symbols}), except that this
35310 command also allows to find symbols in other sections.
35312 If section was not specified, the section in which the symbol was found
35313 is also printed. For dynamically linked executables, the name of
35314 executable or shared library containing the symbol is printed as well.
35318 The following command is useful for non-interactive invocations of
35319 @value{GDBN}, such as in the test suite.
35322 @item set watchdog @var{nsec}
35323 @kindex set watchdog
35324 @cindex watchdog timer
35325 @cindex timeout for commands
35326 Set the maximum number of seconds @value{GDBN} will wait for the
35327 target operation to finish. If this time expires, @value{GDBN}
35328 reports and error and the command is aborted.
35330 @item show watchdog
35331 Show the current setting of the target wait timeout.
35334 @node Remote Protocol
35335 @appendix @value{GDBN} Remote Serial Protocol
35340 * Stop Reply Packets::
35341 * General Query Packets::
35342 * Architecture-Specific Protocol Details::
35343 * Tracepoint Packets::
35344 * Host I/O Packets::
35346 * Notification Packets::
35347 * Remote Non-Stop::
35348 * Packet Acknowledgment::
35350 * File-I/O Remote Protocol Extension::
35351 * Library List Format::
35352 * Library List Format for SVR4 Targets::
35353 * Memory Map Format::
35354 * Thread List Format::
35355 * Traceframe Info Format::
35356 * Branch Trace Format::
35357 * Branch Trace Configuration Format::
35363 There may be occasions when you need to know something about the
35364 protocol---for example, if there is only one serial port to your target
35365 machine, you might want your program to do something special if it
35366 recognizes a packet meant for @value{GDBN}.
35368 In the examples below, @samp{->} and @samp{<-} are used to indicate
35369 transmitted and received data, respectively.
35371 @cindex protocol, @value{GDBN} remote serial
35372 @cindex serial protocol, @value{GDBN} remote
35373 @cindex remote serial protocol
35374 All @value{GDBN} commands and responses (other than acknowledgments
35375 and notifications, see @ref{Notification Packets}) are sent as a
35376 @var{packet}. A @var{packet} is introduced with the character
35377 @samp{$}, the actual @var{packet-data}, and the terminating character
35378 @samp{#} followed by a two-digit @var{checksum}:
35381 @code{$}@var{packet-data}@code{#}@var{checksum}
35385 @cindex checksum, for @value{GDBN} remote
35387 The two-digit @var{checksum} is computed as the modulo 256 sum of all
35388 characters between the leading @samp{$} and the trailing @samp{#} (an
35389 eight bit unsigned checksum).
35391 Implementors should note that prior to @value{GDBN} 5.0 the protocol
35392 specification also included an optional two-digit @var{sequence-id}:
35395 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
35398 @cindex sequence-id, for @value{GDBN} remote
35400 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
35401 has never output @var{sequence-id}s. Stubs that handle packets added
35402 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
35404 When either the host or the target machine receives a packet, the first
35405 response expected is an acknowledgment: either @samp{+} (to indicate
35406 the package was received correctly) or @samp{-} (to request
35410 -> @code{$}@var{packet-data}@code{#}@var{checksum}
35415 The @samp{+}/@samp{-} acknowledgments can be disabled
35416 once a connection is established.
35417 @xref{Packet Acknowledgment}, for details.
35419 The host (@value{GDBN}) sends @var{command}s, and the target (the
35420 debugging stub incorporated in your program) sends a @var{response}. In
35421 the case of step and continue @var{command}s, the response is only sent
35422 when the operation has completed, and the target has again stopped all
35423 threads in all attached processes. This is the default all-stop mode
35424 behavior, but the remote protocol also supports @value{GDBN}'s non-stop
35425 execution mode; see @ref{Remote Non-Stop}, for details.
35427 @var{packet-data} consists of a sequence of characters with the
35428 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
35431 @cindex remote protocol, field separator
35432 Fields within the packet should be separated using @samp{,} @samp{;} or
35433 @samp{:}. Except where otherwise noted all numbers are represented in
35434 @sc{hex} with leading zeros suppressed.
35436 Implementors should note that prior to @value{GDBN} 5.0, the character
35437 @samp{:} could not appear as the third character in a packet (as it
35438 would potentially conflict with the @var{sequence-id}).
35440 @cindex remote protocol, binary data
35441 @anchor{Binary Data}
35442 Binary data in most packets is encoded either as two hexadecimal
35443 digits per byte of binary data. This allowed the traditional remote
35444 protocol to work over connections which were only seven-bit clean.
35445 Some packets designed more recently assume an eight-bit clean
35446 connection, and use a more efficient encoding to send and receive
35449 The binary data representation uses @code{7d} (@sc{ascii} @samp{@}})
35450 as an escape character. Any escaped byte is transmitted as the escape
35451 character followed by the original character XORed with @code{0x20}.
35452 For example, the byte @code{0x7d} would be transmitted as the two
35453 bytes @code{0x7d 0x5d}. The bytes @code{0x23} (@sc{ascii} @samp{#}),
35454 @code{0x24} (@sc{ascii} @samp{$}), and @code{0x7d} (@sc{ascii}
35455 @samp{@}}) must always be escaped. Responses sent by the stub
35456 must also escape @code{0x2a} (@sc{ascii} @samp{*}), so that it
35457 is not interpreted as the start of a run-length encoded sequence
35460 Response @var{data} can be run-length encoded to save space.
35461 Run-length encoding replaces runs of identical characters with one
35462 instance of the repeated character, followed by a @samp{*} and a
35463 repeat count. The repeat count is itself sent encoded, to avoid
35464 binary characters in @var{data}: a value of @var{n} is sent as
35465 @code{@var{n}+29}. For a repeat count greater or equal to 3, this
35466 produces a printable @sc{ascii} character, e.g.@: a space (@sc{ascii}
35467 code 32) for a repeat count of 3. (This is because run-length
35468 encoding starts to win for counts 3 or more.) Thus, for example,
35469 @samp{0* } is a run-length encoding of ``0000'': the space character
35470 after @samp{*} means repeat the leading @code{0} @w{@code{32 - 29 =
35473 The printable characters @samp{#} and @samp{$} or with a numeric value
35474 greater than 126 must not be used. Runs of six repeats (@samp{#}) or
35475 seven repeats (@samp{$}) can be expanded using a repeat count of only
35476 five (@samp{"}). For example, @samp{00000000} can be encoded as
35479 The error response returned for some packets includes a two character
35480 error number. That number is not well defined.
35482 @cindex empty response, for unsupported packets
35483 For any @var{command} not supported by the stub, an empty response
35484 (@samp{$#00}) should be returned. That way it is possible to extend the
35485 protocol. A newer @value{GDBN} can tell if a packet is supported based
35488 At a minimum, a stub is required to support the @samp{g} and @samp{G}
35489 commands for register access, and the @samp{m} and @samp{M} commands
35490 for memory access. Stubs that only control single-threaded targets
35491 can implement run control with the @samp{c} (continue), and @samp{s}
35492 (step) commands. Stubs that support multi-threading targets should
35493 support the @samp{vCont} command. All other commands are optional.
35498 The following table provides a complete list of all currently defined
35499 @var{command}s and their corresponding response @var{data}.
35500 @xref{File-I/O Remote Protocol Extension}, for details about the File
35501 I/O extension of the remote protocol.
35503 Each packet's description has a template showing the packet's overall
35504 syntax, followed by an explanation of the packet's meaning. We
35505 include spaces in some of the templates for clarity; these are not
35506 part of the packet's syntax. No @value{GDBN} packet uses spaces to
35507 separate its components. For example, a template like @samp{foo
35508 @var{bar} @var{baz}} describes a packet beginning with the three ASCII
35509 bytes @samp{foo}, followed by a @var{bar}, followed directly by a
35510 @var{baz}. @value{GDBN} does not transmit a space character between the
35511 @samp{foo} and the @var{bar}, or between the @var{bar} and the
35514 @cindex @var{thread-id}, in remote protocol
35515 @anchor{thread-id syntax}
35516 Several packets and replies include a @var{thread-id} field to identify
35517 a thread. Normally these are positive numbers with a target-specific
35518 interpretation, formatted as big-endian hex strings. A @var{thread-id}
35519 can also be a literal @samp{-1} to indicate all threads, or @samp{0} to
35522 In addition, the remote protocol supports a multiprocess feature in
35523 which the @var{thread-id} syntax is extended to optionally include both
35524 process and thread ID fields, as @samp{p@var{pid}.@var{tid}}.
35525 The @var{pid} (process) and @var{tid} (thread) components each have the
35526 format described above: a positive number with target-specific
35527 interpretation formatted as a big-endian hex string, literal @samp{-1}
35528 to indicate all processes or threads (respectively), or @samp{0} to
35529 indicate an arbitrary process or thread. Specifying just a process, as
35530 @samp{p@var{pid}}, is equivalent to @samp{p@var{pid}.-1}. It is an
35531 error to specify all processes but a specific thread, such as
35532 @samp{p-1.@var{tid}}. Note that the @samp{p} prefix is @emph{not} used
35533 for those packets and replies explicitly documented to include a process
35534 ID, rather than a @var{thread-id}.
35536 The multiprocess @var{thread-id} syntax extensions are only used if both
35537 @value{GDBN} and the stub report support for the @samp{multiprocess}
35538 feature using @samp{qSupported}. @xref{multiprocess extensions}, for
35541 Note that all packet forms beginning with an upper- or lower-case
35542 letter, other than those described here, are reserved for future use.
35544 Here are the packet descriptions.
35549 @cindex @samp{!} packet
35550 @anchor{extended mode}
35551 Enable extended mode. In extended mode, the remote server is made
35552 persistent. The @samp{R} packet is used to restart the program being
35558 The remote target both supports and has enabled extended mode.
35562 @cindex @samp{?} packet
35564 Indicate the reason the target halted. The reply is the same as for
35565 step and continue. This packet has a special interpretation when the
35566 target is in non-stop mode; see @ref{Remote Non-Stop}.
35569 @xref{Stop Reply Packets}, for the reply specifications.
35571 @item A @var{arglen},@var{argnum},@var{arg},@dots{}
35572 @cindex @samp{A} packet
35573 Initialized @code{argv[]} array passed into program. @var{arglen}
35574 specifies the number of bytes in the hex encoded byte stream
35575 @var{arg}. See @code{gdbserver} for more details.
35580 The arguments were set.
35586 @cindex @samp{b} packet
35587 (Don't use this packet; its behavior is not well-defined.)
35588 Change the serial line speed to @var{baud}.
35590 JTC: @emph{When does the transport layer state change? When it's
35591 received, or after the ACK is transmitted. In either case, there are
35592 problems if the command or the acknowledgment packet is dropped.}
35594 Stan: @emph{If people really wanted to add something like this, and get
35595 it working for the first time, they ought to modify ser-unix.c to send
35596 some kind of out-of-band message to a specially-setup stub and have the
35597 switch happen "in between" packets, so that from remote protocol's point
35598 of view, nothing actually happened.}
35600 @item B @var{addr},@var{mode}
35601 @cindex @samp{B} packet
35602 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
35603 breakpoint at @var{addr}.
35605 Don't use this packet. Use the @samp{Z} and @samp{z} packets instead
35606 (@pxref{insert breakpoint or watchpoint packet}).
35608 @cindex @samp{bc} packet
35611 Backward continue. Execute the target system in reverse. No parameter.
35612 @xref{Reverse Execution}, for more information.
35615 @xref{Stop Reply Packets}, for the reply specifications.
35617 @cindex @samp{bs} packet
35620 Backward single step. Execute one instruction in reverse. No parameter.
35621 @xref{Reverse Execution}, for more information.
35624 @xref{Stop Reply Packets}, for the reply specifications.
35626 @item c @r{[}@var{addr}@r{]}
35627 @cindex @samp{c} packet
35628 Continue at @var{addr}, which is the address to resume. If @var{addr}
35629 is omitted, resume at current address.
35631 This packet is deprecated for multi-threading support. @xref{vCont
35635 @xref{Stop Reply Packets}, for the reply specifications.
35637 @item C @var{sig}@r{[};@var{addr}@r{]}
35638 @cindex @samp{C} packet
35639 Continue with signal @var{sig} (hex signal number). If
35640 @samp{;@var{addr}} is omitted, resume at same address.
35642 This packet is deprecated for multi-threading support. @xref{vCont
35646 @xref{Stop Reply Packets}, for the reply specifications.
35649 @cindex @samp{d} packet
35652 Don't use this packet; instead, define a general set packet
35653 (@pxref{General Query Packets}).
35657 @cindex @samp{D} packet
35658 The first form of the packet is used to detach @value{GDBN} from the
35659 remote system. It is sent to the remote target
35660 before @value{GDBN} disconnects via the @code{detach} command.
35662 The second form, including a process ID, is used when multiprocess
35663 protocol extensions are enabled (@pxref{multiprocess extensions}), to
35664 detach only a specific process. The @var{pid} is specified as a
35665 big-endian hex string.
35675 @item F @var{RC},@var{EE},@var{CF};@var{XX}
35676 @cindex @samp{F} packet
35677 A reply from @value{GDBN} to an @samp{F} packet sent by the target.
35678 This is part of the File-I/O protocol extension. @xref{File-I/O
35679 Remote Protocol Extension}, for the specification.
35682 @anchor{read registers packet}
35683 @cindex @samp{g} packet
35684 Read general registers.
35688 @item @var{XX@dots{}}
35689 Each byte of register data is described by two hex digits. The bytes
35690 with the register are transmitted in target byte order. The size of
35691 each register and their position within the @samp{g} packet are
35692 determined by the @value{GDBN} internal gdbarch functions
35693 @code{DEPRECATED_REGISTER_RAW_SIZE} and @code{gdbarch_register_name}.
35695 When reading registers from a trace frame (@pxref{Analyze Collected
35696 Data,,Using the Collected Data}), the stub may also return a string of
35697 literal @samp{x}'s in place of the register data digits, to indicate
35698 that the corresponding register has not been collected, thus its value
35699 is unavailable. For example, for an architecture with 4 registers of
35700 4 bytes each, the following reply indicates to @value{GDBN} that
35701 registers 0 and 2 have not been collected, while registers 1 and 3
35702 have been collected, and both have zero value:
35706 <- @code{xxxxxxxx00000000xxxxxxxx00000000}
35713 @item G @var{XX@dots{}}
35714 @cindex @samp{G} packet
35715 Write general registers. @xref{read registers packet}, for a
35716 description of the @var{XX@dots{}} data.
35726 @item H @var{op} @var{thread-id}
35727 @cindex @samp{H} packet
35728 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
35729 @samp{G}, et.al.). Depending on the operation to be performed, @var{op}
35730 should be @samp{c} for step and continue operations (note that this
35731 is deprecated, supporting the @samp{vCont} command is a better
35732 option), and @samp{g} for other operations. The thread designator
35733 @var{thread-id} has the format and interpretation described in
35734 @ref{thread-id syntax}.
35745 @c 'H': How restrictive (or permissive) is the thread model. If a
35746 @c thread is selected and stopped, are other threads allowed
35747 @c to continue to execute? As I mentioned above, I think the
35748 @c semantics of each command when a thread is selected must be
35749 @c described. For example:
35751 @c 'g': If the stub supports threads and a specific thread is
35752 @c selected, returns the register block from that thread;
35753 @c otherwise returns current registers.
35755 @c 'G' If the stub supports threads and a specific thread is
35756 @c selected, sets the registers of the register block of
35757 @c that thread; otherwise sets current registers.
35759 @item i @r{[}@var{addr}@r{[},@var{nnn}@r{]]}
35760 @anchor{cycle step packet}
35761 @cindex @samp{i} packet
35762 Step the remote target by a single clock cycle. If @samp{,@var{nnn}} is
35763 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
35764 step starting at that address.
35767 @cindex @samp{I} packet
35768 Signal, then cycle step. @xref{step with signal packet}. @xref{cycle
35772 @cindex @samp{k} packet
35775 The exact effect of this packet is not specified.
35777 For a bare-metal target, it may power cycle or reset the target
35778 system. For that reason, the @samp{k} packet has no reply.
35780 For a single-process target, it may kill that process if possible.
35782 A multiple-process target may choose to kill just one process, or all
35783 that are under @value{GDBN}'s control. For more precise control, use
35784 the vKill packet (@pxref{vKill packet}).
35786 If the target system immediately closes the connection in response to
35787 @samp{k}, @value{GDBN} does not consider the lack of packet
35788 acknowledgment to be an error, and assumes the kill was successful.
35790 If connected using @kbd{target extended-remote}, and the target does
35791 not close the connection in response to a kill request, @value{GDBN}
35792 probes the target state as if a new connection was opened
35793 (@pxref{? packet}).
35795 @item m @var{addr},@var{length}
35796 @cindex @samp{m} packet
35797 Read @var{length} addressable memory units starting at address @var{addr}
35798 (@pxref{addressable memory unit}). Note that @var{addr} may not be aligned to
35799 any particular boundary.
35801 The stub need not use any particular size or alignment when gathering
35802 data from memory for the response; even if @var{addr} is word-aligned
35803 and @var{length} is a multiple of the word size, the stub is free to
35804 use byte accesses, or not. For this reason, this packet may not be
35805 suitable for accessing memory-mapped I/O devices.
35806 @cindex alignment of remote memory accesses
35807 @cindex size of remote memory accesses
35808 @cindex memory, alignment and size of remote accesses
35812 @item @var{XX@dots{}}
35813 Memory contents; each byte is transmitted as a two-digit hexadecimal number.
35814 The reply may contain fewer addressable memory units than requested if the
35815 server was able to read only part of the region of memory.
35820 @item M @var{addr},@var{length}:@var{XX@dots{}}
35821 @cindex @samp{M} packet
35822 Write @var{length} addressable memory units starting at address @var{addr}
35823 (@pxref{addressable memory unit}). The data is given by @var{XX@dots{}}; each
35824 byte is transmitted as a two-digit hexadecimal number.
35831 for an error (this includes the case where only part of the data was
35836 @cindex @samp{p} packet
35837 Read the value of register @var{n}; @var{n} is in hex.
35838 @xref{read registers packet}, for a description of how the returned
35839 register value is encoded.
35843 @item @var{XX@dots{}}
35844 the register's value
35848 Indicating an unrecognized @var{query}.
35851 @item P @var{n@dots{}}=@var{r@dots{}}
35852 @anchor{write register packet}
35853 @cindex @samp{P} packet
35854 Write register @var{n@dots{}} with value @var{r@dots{}}. The register
35855 number @var{n} is in hexadecimal, and @var{r@dots{}} contains two hex
35856 digits for each byte in the register (target byte order).
35866 @item q @var{name} @var{params}@dots{}
35867 @itemx Q @var{name} @var{params}@dots{}
35868 @cindex @samp{q} packet
35869 @cindex @samp{Q} packet
35870 General query (@samp{q}) and set (@samp{Q}). These packets are
35871 described fully in @ref{General Query Packets}.
35874 @cindex @samp{r} packet
35875 Reset the entire system.
35877 Don't use this packet; use the @samp{R} packet instead.
35880 @cindex @samp{R} packet
35881 Restart the program being debugged. The @var{XX}, while needed, is ignored.
35882 This packet is only available in extended mode (@pxref{extended mode}).
35884 The @samp{R} packet has no reply.
35886 @item s @r{[}@var{addr}@r{]}
35887 @cindex @samp{s} packet
35888 Single step, resuming at @var{addr}. If
35889 @var{addr} is omitted, resume at same address.
35891 This packet is deprecated for multi-threading support. @xref{vCont
35895 @xref{Stop Reply Packets}, for the reply specifications.
35897 @item S @var{sig}@r{[};@var{addr}@r{]}
35898 @anchor{step with signal packet}
35899 @cindex @samp{S} packet
35900 Step with signal. This is analogous to the @samp{C} packet, but
35901 requests a single-step, rather than a normal resumption of execution.
35903 This packet is deprecated for multi-threading support. @xref{vCont
35907 @xref{Stop Reply Packets}, for the reply specifications.
35909 @item t @var{addr}:@var{PP},@var{MM}
35910 @cindex @samp{t} packet
35911 Search backwards starting at address @var{addr} for a match with pattern
35912 @var{PP} and mask @var{MM}, both of which are are 4 byte long.
35913 There must be at least 3 digits in @var{addr}.
35915 @item T @var{thread-id}
35916 @cindex @samp{T} packet
35917 Find out if the thread @var{thread-id} is alive. @xref{thread-id syntax}.
35922 thread is still alive
35928 Packets starting with @samp{v} are identified by a multi-letter name,
35929 up to the first @samp{;} or @samp{?} (or the end of the packet).
35931 @item vAttach;@var{pid}
35932 @cindex @samp{vAttach} packet
35933 Attach to a new process with the specified process ID @var{pid}.
35934 The process ID is a
35935 hexadecimal integer identifying the process. In all-stop mode, all
35936 threads in the attached process are stopped; in non-stop mode, it may be
35937 attached without being stopped if that is supported by the target.
35939 @c In non-stop mode, on a successful vAttach, the stub should set the
35940 @c current thread to a thread of the newly-attached process. After
35941 @c attaching, GDB queries for the attached process's thread ID with qC.
35942 @c Also note that, from a user perspective, whether or not the
35943 @c target is stopped on attach in non-stop mode depends on whether you
35944 @c use the foreground or background version of the attach command, not
35945 @c on what vAttach does; GDB does the right thing with respect to either
35946 @c stopping or restarting threads.
35948 This packet is only available in extended mode (@pxref{extended mode}).
35954 @item @r{Any stop packet}
35955 for success in all-stop mode (@pxref{Stop Reply Packets})
35957 for success in non-stop mode (@pxref{Remote Non-Stop})
35960 @item vCont@r{[};@var{action}@r{[}:@var{thread-id}@r{]]}@dots{}
35961 @cindex @samp{vCont} packet
35962 @anchor{vCont packet}
35963 Resume the inferior, specifying different actions for each thread.
35965 For each inferior thread, the leftmost action with a matching
35966 @var{thread-id} is applied. Threads that don't match any action
35967 remain in their current state. Thread IDs are specified using the
35968 syntax described in @ref{thread-id syntax}. If multiprocess
35969 extensions (@pxref{multiprocess extensions}) are supported, actions
35970 can be specified to match all threads in a process by using the
35971 @samp{p@var{pid}.-1} form of the @var{thread-id}. An action with no
35972 @var{thread-id} matches all threads. Specifying no actions is an
35975 Currently supported actions are:
35981 Continue with signal @var{sig}. The signal @var{sig} should be two hex digits.
35985 Step with signal @var{sig}. The signal @var{sig} should be two hex digits.
35988 @item r @var{start},@var{end}
35989 Step once, and then keep stepping as long as the thread stops at
35990 addresses between @var{start} (inclusive) and @var{end} (exclusive).
35991 The remote stub reports a stop reply when either the thread goes out
35992 of the range or is stopped due to an unrelated reason, such as hitting
35993 a breakpoint. @xref{range stepping}.
35995 If the range is empty (@var{start} == @var{end}), then the action
35996 becomes equivalent to the @samp{s} action. In other words,
35997 single-step once, and report the stop (even if the stepped instruction
35998 jumps to @var{start}).
36000 (A stop reply may be sent at any point even if the PC is still within
36001 the stepping range; for example, it is valid to implement this packet
36002 in a degenerate way as a single instruction step operation.)
36006 The optional argument @var{addr} normally associated with the
36007 @samp{c}, @samp{C}, @samp{s}, and @samp{S} packets is
36008 not supported in @samp{vCont}.
36010 The @samp{t} action is only relevant in non-stop mode
36011 (@pxref{Remote Non-Stop}) and may be ignored by the stub otherwise.
36012 A stop reply should be generated for any affected thread not already stopped.
36013 When a thread is stopped by means of a @samp{t} action,
36014 the corresponding stop reply should indicate that the thread has stopped with
36015 signal @samp{0}, regardless of whether the target uses some other signal
36016 as an implementation detail.
36018 The server must ignore @samp{c}, @samp{C}, @samp{s}, @samp{S}, and
36019 @samp{r} actions for threads that are already running. Conversely,
36020 the server must ignore @samp{t} actions for threads that are already
36023 @emph{Note:} In non-stop mode, a thread is considered running until
36024 @value{GDBN} acknowleges an asynchronous stop notification for it with
36025 the @samp{vStopped} packet (@pxref{Remote Non-Stop}).
36027 The stub must support @samp{vCont} if it reports support for
36028 multiprocess extensions (@pxref{multiprocess extensions}).
36031 @xref{Stop Reply Packets}, for the reply specifications.
36034 @cindex @samp{vCont?} packet
36035 Request a list of actions supported by the @samp{vCont} packet.
36039 @item vCont@r{[};@var{action}@dots{}@r{]}
36040 The @samp{vCont} packet is supported. Each @var{action} is a supported
36041 command in the @samp{vCont} packet.
36043 The @samp{vCont} packet is not supported.
36046 @anchor{vCtrlC packet}
36048 @cindex @samp{vCtrlC} packet
36049 Interrupt remote target as if a control-C was pressed on the remote
36050 terminal. This is the equivalent to reacting to the @code{^C}
36051 (@samp{\003}, the control-C character) character in all-stop mode
36052 while the target is running, except this works in non-stop mode.
36053 @xref{interrupting remote targets}, for more info on the all-stop
36064 @item vFile:@var{operation}:@var{parameter}@dots{}
36065 @cindex @samp{vFile} packet
36066 Perform a file operation on the target system. For details,
36067 see @ref{Host I/O Packets}.
36069 @item vFlashErase:@var{addr},@var{length}
36070 @cindex @samp{vFlashErase} packet
36071 Direct the stub to erase @var{length} bytes of flash starting at
36072 @var{addr}. The region may enclose any number of flash blocks, but
36073 its start and end must fall on block boundaries, as indicated by the
36074 flash block size appearing in the memory map (@pxref{Memory Map
36075 Format}). @value{GDBN} groups flash memory programming operations
36076 together, and sends a @samp{vFlashDone} request after each group; the
36077 stub is allowed to delay erase operation until the @samp{vFlashDone}
36078 packet is received.
36088 @item vFlashWrite:@var{addr}:@var{XX@dots{}}
36089 @cindex @samp{vFlashWrite} packet
36090 Direct the stub to write data to flash address @var{addr}. The data
36091 is passed in binary form using the same encoding as for the @samp{X}
36092 packet (@pxref{Binary Data}). The memory ranges specified by
36093 @samp{vFlashWrite} packets preceding a @samp{vFlashDone} packet must
36094 not overlap, and must appear in order of increasing addresses
36095 (although @samp{vFlashErase} packets for higher addresses may already
36096 have been received; the ordering is guaranteed only between
36097 @samp{vFlashWrite} packets). If a packet writes to an address that was
36098 neither erased by a preceding @samp{vFlashErase} packet nor by some other
36099 target-specific method, the results are unpredictable.
36107 for vFlashWrite addressing non-flash memory
36113 @cindex @samp{vFlashDone} packet
36114 Indicate to the stub that flash programming operation is finished.
36115 The stub is permitted to delay or batch the effects of a group of
36116 @samp{vFlashErase} and @samp{vFlashWrite} packets until a
36117 @samp{vFlashDone} packet is received. The contents of the affected
36118 regions of flash memory are unpredictable until the @samp{vFlashDone}
36119 request is completed.
36121 @item vKill;@var{pid}
36122 @cindex @samp{vKill} packet
36123 @anchor{vKill packet}
36124 Kill the process with the specified process ID @var{pid}, which is a
36125 hexadecimal integer identifying the process. This packet is used in
36126 preference to @samp{k} when multiprocess protocol extensions are
36127 supported; see @ref{multiprocess extensions}.
36137 @item vMustReplyEmpty
36138 @cindex @samp{vMustReplyEmpty} packet
36139 The correct reply to an unknown @samp{v} packet is to return the empty
36140 string, however, some older versions of @command{gdbserver} would
36141 incorrectly return @samp{OK} for unknown @samp{v} packets.
36143 The @samp{vMustReplyEmpty} is used as a feature test to check how
36144 @command{gdbserver} handles unknown packets, it is important that this
36145 packet be handled in the same way as other unknown @samp{v} packets.
36146 If this packet is handled differently to other unknown @samp{v}
36147 packets then it is possile that @value{GDBN} may run into problems in
36148 other areas, specifically around use of @samp{vFile:setfs:}.
36150 @item vRun;@var{filename}@r{[};@var{argument}@r{]}@dots{}
36151 @cindex @samp{vRun} packet
36152 Run the program @var{filename}, passing it each @var{argument} on its
36153 command line. The file and arguments are hex-encoded strings. If
36154 @var{filename} is an empty string, the stub may use a default program
36155 (e.g.@: the last program run). The program is created in the stopped
36158 @c FIXME: What about non-stop mode?
36160 This packet is only available in extended mode (@pxref{extended mode}).
36166 @item @r{Any stop packet}
36167 for success (@pxref{Stop Reply Packets})
36171 @cindex @samp{vStopped} packet
36172 @xref{Notification Packets}.
36174 @item X @var{addr},@var{length}:@var{XX@dots{}}
36176 @cindex @samp{X} packet
36177 Write data to memory, where the data is transmitted in binary.
36178 Memory is specified by its address @var{addr} and number of addressable memory
36179 units @var{length} (@pxref{addressable memory unit});
36180 @samp{@var{XX}@dots{}} is binary data (@pxref{Binary Data}).
36190 @item z @var{type},@var{addr},@var{kind}
36191 @itemx Z @var{type},@var{addr},@var{kind}
36192 @anchor{insert breakpoint or watchpoint packet}
36193 @cindex @samp{z} packet
36194 @cindex @samp{Z} packets
36195 Insert (@samp{Z}) or remove (@samp{z}) a @var{type} breakpoint or
36196 watchpoint starting at address @var{address} of kind @var{kind}.
36198 Each breakpoint and watchpoint packet @var{type} is documented
36201 @emph{Implementation notes: A remote target shall return an empty string
36202 for an unrecognized breakpoint or watchpoint packet @var{type}. A
36203 remote target shall support either both or neither of a given
36204 @samp{Z@var{type}@dots{}} and @samp{z@var{type}@dots{}} packet pair. To
36205 avoid potential problems with duplicate packets, the operations should
36206 be implemented in an idempotent way.}
36208 @item z0,@var{addr},@var{kind}
36209 @itemx Z0,@var{addr},@var{kind}@r{[};@var{cond_list}@dots{}@r{]}@r{[};cmds:@var{persist},@var{cmd_list}@dots{}@r{]}
36210 @cindex @samp{z0} packet
36211 @cindex @samp{Z0} packet
36212 Insert (@samp{Z0}) or remove (@samp{z0}) a software breakpoint at address
36213 @var{addr} of type @var{kind}.
36215 A software breakpoint is implemented by replacing the instruction at
36216 @var{addr} with a software breakpoint or trap instruction. The
36217 @var{kind} is target-specific and typically indicates the size of the
36218 breakpoint in bytes that should be inserted. E.g., the @sc{arm} and
36219 @sc{mips} can insert either a 2 or 4 byte breakpoint. Some
36220 architectures have additional meanings for @var{kind}
36221 (@pxref{Architecture-Specific Protocol Details}); if no
36222 architecture-specific value is being used, it should be @samp{0}.
36223 @var{kind} is hex-encoded. @var{cond_list} is an optional list of
36224 conditional expressions in bytecode form that should be evaluated on
36225 the target's side. These are the conditions that should be taken into
36226 consideration when deciding if the breakpoint trigger should be
36227 reported back to @value{GDBN}.
36229 See also the @samp{swbreak} stop reason (@pxref{swbreak stop reason})
36230 for how to best report a software breakpoint event to @value{GDBN}.
36232 The @var{cond_list} parameter is comprised of a series of expressions,
36233 concatenated without separators. Each expression has the following form:
36237 @item X @var{len},@var{expr}
36238 @var{len} is the length of the bytecode expression and @var{expr} is the
36239 actual conditional expression in bytecode form.
36243 The optional @var{cmd_list} parameter introduces commands that may be
36244 run on the target, rather than being reported back to @value{GDBN}.
36245 The parameter starts with a numeric flag @var{persist}; if the flag is
36246 nonzero, then the breakpoint may remain active and the commands
36247 continue to be run even when @value{GDBN} disconnects from the target.
36248 Following this flag is a series of expressions concatenated with no
36249 separators. Each expression has the following form:
36253 @item X @var{len},@var{expr}
36254 @var{len} is the length of the bytecode expression and @var{expr} is the
36255 actual commands expression in bytecode form.
36259 @emph{Implementation note: It is possible for a target to copy or move
36260 code that contains software breakpoints (e.g., when implementing
36261 overlays). The behavior of this packet, in the presence of such a
36262 target, is not defined.}
36274 @item z1,@var{addr},@var{kind}
36275 @itemx Z1,@var{addr},@var{kind}@r{[};@var{cond_list}@dots{}@r{]}@r{[};cmds:@var{persist},@var{cmd_list}@dots{}@r{]}
36276 @cindex @samp{z1} packet
36277 @cindex @samp{Z1} packet
36278 Insert (@samp{Z1}) or remove (@samp{z1}) a hardware breakpoint at
36279 address @var{addr}.
36281 A hardware breakpoint is implemented using a mechanism that is not
36282 dependent on being able to modify the target's memory. The
36283 @var{kind}, @var{cond_list}, and @var{cmd_list} arguments have the
36284 same meaning as in @samp{Z0} packets.
36286 @emph{Implementation note: A hardware breakpoint is not affected by code
36299 @item z2,@var{addr},@var{kind}
36300 @itemx Z2,@var{addr},@var{kind}
36301 @cindex @samp{z2} packet
36302 @cindex @samp{Z2} packet
36303 Insert (@samp{Z2}) or remove (@samp{z2}) a write watchpoint at @var{addr}.
36304 The number of bytes to watch is specified by @var{kind}.
36316 @item z3,@var{addr},@var{kind}
36317 @itemx Z3,@var{addr},@var{kind}
36318 @cindex @samp{z3} packet
36319 @cindex @samp{Z3} packet
36320 Insert (@samp{Z3}) or remove (@samp{z3}) a read watchpoint at @var{addr}.
36321 The number of bytes to watch is specified by @var{kind}.
36333 @item z4,@var{addr},@var{kind}
36334 @itemx Z4,@var{addr},@var{kind}
36335 @cindex @samp{z4} packet
36336 @cindex @samp{Z4} packet
36337 Insert (@samp{Z4}) or remove (@samp{z4}) an access watchpoint at @var{addr}.
36338 The number of bytes to watch is specified by @var{kind}.
36352 @node Stop Reply Packets
36353 @section Stop Reply Packets
36354 @cindex stop reply packets
36356 The @samp{C}, @samp{c}, @samp{S}, @samp{s}, @samp{vCont},
36357 @samp{vAttach}, @samp{vRun}, @samp{vStopped}, and @samp{?} packets can
36358 receive any of the below as a reply. Except for @samp{?}
36359 and @samp{vStopped}, that reply is only returned
36360 when the target halts. In the below the exact meaning of @dfn{signal
36361 number} is defined by the header @file{include/gdb/signals.h} in the
36362 @value{GDBN} source code.
36364 In non-stop mode, the server will simply reply @samp{OK} to commands
36365 such as @samp{vCont}; any stop will be the subject of a future
36366 notification. @xref{Remote Non-Stop}.
36368 As in the description of request packets, we include spaces in the
36369 reply templates for clarity; these are not part of the reply packet's
36370 syntax. No @value{GDBN} stop reply packet uses spaces to separate its
36376 The program received signal number @var{AA} (a two-digit hexadecimal
36377 number). This is equivalent to a @samp{T} response with no
36378 @var{n}:@var{r} pairs.
36380 @item T @var{AA} @var{n1}:@var{r1};@var{n2}:@var{r2};@dots{}
36381 @cindex @samp{T} packet reply
36382 The program received signal number @var{AA} (a two-digit hexadecimal
36383 number). This is equivalent to an @samp{S} response, except that the
36384 @samp{@var{n}:@var{r}} pairs can carry values of important registers
36385 and other information directly in the stop reply packet, reducing
36386 round-trip latency. Single-step and breakpoint traps are reported
36387 this way. Each @samp{@var{n}:@var{r}} pair is interpreted as follows:
36391 If @var{n} is a hexadecimal number, it is a register number, and the
36392 corresponding @var{r} gives that register's value. The data @var{r} is a
36393 series of bytes in target byte order, with each byte given by a
36394 two-digit hex number.
36397 If @var{n} is @samp{thread}, then @var{r} is the @var{thread-id} of
36398 the stopped thread, as specified in @ref{thread-id syntax}.
36401 If @var{n} is @samp{core}, then @var{r} is the hexadecimal number of
36402 the core on which the stop event was detected.
36405 If @var{n} is a recognized @dfn{stop reason}, it describes a more
36406 specific event that stopped the target. The currently defined stop
36407 reasons are listed below. The @var{aa} should be @samp{05}, the trap
36408 signal. At most one stop reason should be present.
36411 Otherwise, @value{GDBN} should ignore this @samp{@var{n}:@var{r}} pair
36412 and go on to the next; this allows us to extend the protocol in the
36416 The currently defined stop reasons are:
36422 The packet indicates a watchpoint hit, and @var{r} is the data address, in
36425 @item syscall_entry
36426 @itemx syscall_return
36427 The packet indicates a syscall entry or return, and @var{r} is the
36428 syscall number, in hex.
36430 @cindex shared library events, remote reply
36432 The packet indicates that the loaded libraries have changed.
36433 @value{GDBN} should use @samp{qXfer:libraries:read} to fetch a new
36434 list of loaded libraries. The @var{r} part is ignored.
36436 @cindex replay log events, remote reply
36438 The packet indicates that the target cannot continue replaying
36439 logged execution events, because it has reached the end (or the
36440 beginning when executing backward) of the log. The value of @var{r}
36441 will be either @samp{begin} or @samp{end}. @xref{Reverse Execution},
36442 for more information.
36445 @anchor{swbreak stop reason}
36446 The packet indicates a software breakpoint instruction was executed,
36447 irrespective of whether it was @value{GDBN} that planted the
36448 breakpoint or the breakpoint is hardcoded in the program. The @var{r}
36449 part must be left empty.
36451 On some architectures, such as x86, at the architecture level, when a
36452 breakpoint instruction executes the program counter points at the
36453 breakpoint address plus an offset. On such targets, the stub is
36454 responsible for adjusting the PC to point back at the breakpoint
36457 This packet should not be sent by default; older @value{GDBN} versions
36458 did not support it. @value{GDBN} requests it, by supplying an
36459 appropriate @samp{qSupported} feature (@pxref{qSupported}). The
36460 remote stub must also supply the appropriate @samp{qSupported} feature
36461 indicating support.
36463 This packet is required for correct non-stop mode operation.
36466 The packet indicates the target stopped for a hardware breakpoint.
36467 The @var{r} part must be left empty.
36469 The same remarks about @samp{qSupported} and non-stop mode above
36472 @cindex fork events, remote reply
36474 The packet indicates that @code{fork} was called, and @var{r}
36475 is the thread ID of the new child process. Refer to
36476 @ref{thread-id syntax} for the format of the @var{thread-id}
36477 field. This packet is only applicable to targets that support
36480 This packet should not be sent by default; older @value{GDBN} versions
36481 did not support it. @value{GDBN} requests it, by supplying an
36482 appropriate @samp{qSupported} feature (@pxref{qSupported}). The
36483 remote stub must also supply the appropriate @samp{qSupported} feature
36484 indicating support.
36486 @cindex vfork events, remote reply
36488 The packet indicates that @code{vfork} was called, and @var{r}
36489 is the thread ID of the new child process. Refer to
36490 @ref{thread-id syntax} for the format of the @var{thread-id}
36491 field. This packet is only applicable to targets that support
36494 This packet should not be sent by default; older @value{GDBN} versions
36495 did not support it. @value{GDBN} requests it, by supplying an
36496 appropriate @samp{qSupported} feature (@pxref{qSupported}). The
36497 remote stub must also supply the appropriate @samp{qSupported} feature
36498 indicating support.
36500 @cindex vforkdone events, remote reply
36502 The packet indicates that a child process created by a vfork
36503 has either called @code{exec} or terminated, so that the
36504 address spaces of the parent and child process are no longer
36505 shared. The @var{r} part is ignored. This packet is only
36506 applicable to targets that support vforkdone events.
36508 This packet should not be sent by default; older @value{GDBN} versions
36509 did not support it. @value{GDBN} requests it, by supplying an
36510 appropriate @samp{qSupported} feature (@pxref{qSupported}). The
36511 remote stub must also supply the appropriate @samp{qSupported} feature
36512 indicating support.
36514 @cindex exec events, remote reply
36516 The packet indicates that @code{execve} was called, and @var{r}
36517 is the absolute pathname of the file that was executed, in hex.
36518 This packet is only applicable to targets that support exec events.
36520 This packet should not be sent by default; older @value{GDBN} versions
36521 did not support it. @value{GDBN} requests it, by supplying an
36522 appropriate @samp{qSupported} feature (@pxref{qSupported}). The
36523 remote stub must also supply the appropriate @samp{qSupported} feature
36524 indicating support.
36526 @cindex thread create event, remote reply
36527 @anchor{thread create event}
36529 The packet indicates that the thread was just created. The new thread
36530 is stopped until @value{GDBN} sets it running with a resumption packet
36531 (@pxref{vCont packet}). This packet should not be sent by default;
36532 @value{GDBN} requests it with the @ref{QThreadEvents} packet. See
36533 also the @samp{w} (@pxref{thread exit event}) remote reply below. The
36534 @var{r} part is ignored.
36539 @itemx W @var{AA} ; process:@var{pid}
36540 The process exited, and @var{AA} is the exit status. This is only
36541 applicable to certain targets.
36543 The second form of the response, including the process ID of the
36544 exited process, can be used only when @value{GDBN} has reported
36545 support for multiprocess protocol extensions; see @ref{multiprocess
36546 extensions}. Both @var{AA} and @var{pid} are formatted as big-endian
36550 @itemx X @var{AA} ; process:@var{pid}
36551 The process terminated with signal @var{AA}.
36553 The second form of the response, including the process ID of the
36554 terminated process, can be used only when @value{GDBN} has reported
36555 support for multiprocess protocol extensions; see @ref{multiprocess
36556 extensions}. Both @var{AA} and @var{pid} are formatted as big-endian
36559 @anchor{thread exit event}
36560 @cindex thread exit event, remote reply
36561 @item w @var{AA} ; @var{tid}
36563 The thread exited, and @var{AA} is the exit status. This response
36564 should not be sent by default; @value{GDBN} requests it with the
36565 @ref{QThreadEvents} packet. See also @ref{thread create event} above.
36566 @var{AA} is formatted as a big-endian hex string.
36569 There are no resumed threads left in the target. In other words, even
36570 though the process is alive, the last resumed thread has exited. For
36571 example, say the target process has two threads: thread 1 and thread
36572 2. The client leaves thread 1 stopped, and resumes thread 2, which
36573 subsequently exits. At this point, even though the process is still
36574 alive, and thus no @samp{W} stop reply is sent, no thread is actually
36575 executing either. The @samp{N} stop reply thus informs the client
36576 that it can stop waiting for stop replies. This packet should not be
36577 sent by default; older @value{GDBN} versions did not support it.
36578 @value{GDBN} requests it, by supplying an appropriate
36579 @samp{qSupported} feature (@pxref{qSupported}). The remote stub must
36580 also supply the appropriate @samp{qSupported} feature indicating
36583 @item O @var{XX}@dots{}
36584 @samp{@var{XX}@dots{}} is hex encoding of @sc{ascii} data, to be
36585 written as the program's console output. This can happen at any time
36586 while the program is running and the debugger should continue to wait
36587 for @samp{W}, @samp{T}, etc. This reply is not permitted in non-stop mode.
36589 @item F @var{call-id},@var{parameter}@dots{}
36590 @var{call-id} is the identifier which says which host system call should
36591 be called. This is just the name of the function. Translation into the
36592 correct system call is only applicable as it's defined in @value{GDBN}.
36593 @xref{File-I/O Remote Protocol Extension}, for a list of implemented
36596 @samp{@var{parameter}@dots{}} is a list of parameters as defined for
36597 this very system call.
36599 The target replies with this packet when it expects @value{GDBN} to
36600 call a host system call on behalf of the target. @value{GDBN} replies
36601 with an appropriate @samp{F} packet and keeps up waiting for the next
36602 reply packet from the target. The latest @samp{C}, @samp{c}, @samp{S}
36603 or @samp{s} action is expected to be continued. @xref{File-I/O Remote
36604 Protocol Extension}, for more details.
36608 @node General Query Packets
36609 @section General Query Packets
36610 @cindex remote query requests
36612 Packets starting with @samp{q} are @dfn{general query packets};
36613 packets starting with @samp{Q} are @dfn{general set packets}. General
36614 query and set packets are a semi-unified form for retrieving and
36615 sending information to and from the stub.
36617 The initial letter of a query or set packet is followed by a name
36618 indicating what sort of thing the packet applies to. For example,
36619 @value{GDBN} may use a @samp{qSymbol} packet to exchange symbol
36620 definitions with the stub. These packet names follow some
36625 The name must not contain commas, colons or semicolons.
36627 Most @value{GDBN} query and set packets have a leading upper case
36630 The names of custom vendor packets should use a company prefix, in
36631 lower case, followed by a period. For example, packets designed at
36632 the Acme Corporation might begin with @samp{qacme.foo} (for querying
36633 foos) or @samp{Qacme.bar} (for setting bars).
36636 The name of a query or set packet should be separated from any
36637 parameters by a @samp{:}; the parameters themselves should be
36638 separated by @samp{,} or @samp{;}. Stubs must be careful to match the
36639 full packet name, and check for a separator or the end of the packet,
36640 in case two packet names share a common prefix. New packets should not begin
36641 with @samp{qC}, @samp{qP}, or @samp{qL}@footnote{The @samp{qP} and @samp{qL}
36642 packets predate these conventions, and have arguments without any terminator
36643 for the packet name; we suspect they are in widespread use in places that
36644 are difficult to upgrade. The @samp{qC} packet has no arguments, but some
36645 existing stubs (e.g.@: RedBoot) are known to not check for the end of the
36648 Like the descriptions of the other packets, each description here
36649 has a template showing the packet's overall syntax, followed by an
36650 explanation of the packet's meaning. We include spaces in some of the
36651 templates for clarity; these are not part of the packet's syntax. No
36652 @value{GDBN} packet uses spaces to separate its components.
36654 Here are the currently defined query and set packets:
36660 Turn on or off the agent as a helper to perform some debugging operations
36661 delegated from @value{GDBN} (@pxref{Control Agent}).
36663 @item QAllow:@var{op}:@var{val}@dots{}
36664 @cindex @samp{QAllow} packet
36665 Specify which operations @value{GDBN} expects to request of the
36666 target, as a semicolon-separated list of operation name and value
36667 pairs. Possible values for @var{op} include @samp{WriteReg},
36668 @samp{WriteMem}, @samp{InsertBreak}, @samp{InsertTrace},
36669 @samp{InsertFastTrace}, and @samp{Stop}. @var{val} is either 0,
36670 indicating that @value{GDBN} will not request the operation, or 1,
36671 indicating that it may. (The target can then use this to set up its
36672 own internals optimally, for instance if the debugger never expects to
36673 insert breakpoints, it may not need to install its own trap handler.)
36676 @cindex current thread, remote request
36677 @cindex @samp{qC} packet
36678 Return the current thread ID.
36682 @item QC @var{thread-id}
36683 Where @var{thread-id} is a thread ID as documented in
36684 @ref{thread-id syntax}.
36685 @item @r{(anything else)}
36686 Any other reply implies the old thread ID.
36689 @item qCRC:@var{addr},@var{length}
36690 @cindex CRC of memory block, remote request
36691 @cindex @samp{qCRC} packet
36692 @anchor{qCRC packet}
36693 Compute the CRC checksum of a block of memory using CRC-32 defined in
36694 IEEE 802.3. The CRC is computed byte at a time, taking the most
36695 significant bit of each byte first. The initial pattern code
36696 @code{0xffffffff} is used to ensure leading zeros affect the CRC.
36698 @emph{Note:} This is the same CRC used in validating separate debug
36699 files (@pxref{Separate Debug Files, , Debugging Information in Separate
36700 Files}). However the algorithm is slightly different. When validating
36701 separate debug files, the CRC is computed taking the @emph{least}
36702 significant bit of each byte first, and the final result is inverted to
36703 detect trailing zeros.
36708 An error (such as memory fault)
36709 @item C @var{crc32}
36710 The specified memory region's checksum is @var{crc32}.
36713 @item QDisableRandomization:@var{value}
36714 @cindex disable address space randomization, remote request
36715 @cindex @samp{QDisableRandomization} packet
36716 Some target operating systems will randomize the virtual address space
36717 of the inferior process as a security feature, but provide a feature
36718 to disable such randomization, e.g.@: to allow for a more deterministic
36719 debugging experience. On such systems, this packet with a @var{value}
36720 of 1 directs the target to disable address space randomization for
36721 processes subsequently started via @samp{vRun} packets, while a packet
36722 with a @var{value} of 0 tells the target to enable address space
36725 This packet is only available in extended mode (@pxref{extended mode}).
36730 The request succeeded.
36733 An error occurred. The error number @var{nn} is given as hex digits.
36736 An empty reply indicates that @samp{QDisableRandomization} is not supported
36740 This packet is not probed by default; the remote stub must request it,
36741 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
36742 This should only be done on targets that actually support disabling
36743 address space randomization.
36745 @item QStartupWithShell:@var{value}
36746 @cindex startup with shell, remote request
36747 @cindex @samp{QStartupWithShell} packet
36748 On UNIX-like targets, it is possible to start the inferior using a
36749 shell program. This is the default behavior on both @value{GDBN} and
36750 @command{gdbserver} (@pxref{set startup-with-shell}). This packet is
36751 used to inform @command{gdbserver} whether it should start the
36752 inferior using a shell or not.
36754 If @var{value} is @samp{0}, @command{gdbserver} will not use a shell
36755 to start the inferior. If @var{value} is @samp{1},
36756 @command{gdbserver} will use a shell to start the inferior. All other
36757 values are considered an error.
36759 This packet is only available in extended mode (@pxref{extended
36765 The request succeeded.
36768 An error occurred. The error number @var{nn} is given as hex digits.
36771 This packet is not probed by default; the remote stub must request it,
36772 by supplying an appropriate @samp{qSupported} response
36773 (@pxref{qSupported}). This should only be done on targets that
36774 actually support starting the inferior using a shell.
36776 Use of this packet is controlled by the @code{set startup-with-shell}
36777 command; @pxref{set startup-with-shell}.
36779 @item QEnvironmentHexEncoded:@var{hex-value}
36780 @anchor{QEnvironmentHexEncoded}
36781 @cindex set environment variable, remote request
36782 @cindex @samp{QEnvironmentHexEncoded} packet
36783 On UNIX-like targets, it is possible to set environment variables that
36784 will be passed to the inferior during the startup process. This
36785 packet is used to inform @command{gdbserver} of an environment
36786 variable that has been defined by the user on @value{GDBN} (@pxref{set
36789 The packet is composed by @var{hex-value}, an hex encoded
36790 representation of the @var{name=value} format representing an
36791 environment variable. The name of the environment variable is
36792 represented by @var{name}, and the value to be assigned to the
36793 environment variable is represented by @var{value}. If the variable
36794 has no value (i.e., the value is @code{null}), then @var{value} will
36797 This packet is only available in extended mode (@pxref{extended
36803 The request succeeded.
36806 This packet is not probed by default; the remote stub must request it,
36807 by supplying an appropriate @samp{qSupported} response
36808 (@pxref{qSupported}). This should only be done on targets that
36809 actually support passing environment variables to the starting
36812 This packet is related to the @code{set environment} command;
36813 @pxref{set environment}.
36815 @item QEnvironmentUnset:@var{hex-value}
36816 @anchor{QEnvironmentUnset}
36817 @cindex unset environment variable, remote request
36818 @cindex @samp{QEnvironmentUnset} packet
36819 On UNIX-like targets, it is possible to unset environment variables
36820 before starting the inferior in the remote target. This packet is
36821 used to inform @command{gdbserver} of an environment variable that has
36822 been unset by the user on @value{GDBN} (@pxref{unset environment}).
36824 The packet is composed by @var{hex-value}, an hex encoded
36825 representation of the name of the environment variable to be unset.
36827 This packet is only available in extended mode (@pxref{extended
36833 The request succeeded.
36836 This packet is not probed by default; the remote stub must request it,
36837 by supplying an appropriate @samp{qSupported} response
36838 (@pxref{qSupported}). This should only be done on targets that
36839 actually support passing environment variables to the starting
36842 This packet is related to the @code{unset environment} command;
36843 @pxref{unset environment}.
36845 @item QEnvironmentReset
36846 @anchor{QEnvironmentReset}
36847 @cindex reset environment, remote request
36848 @cindex @samp{QEnvironmentReset} packet
36849 On UNIX-like targets, this packet is used to reset the state of
36850 environment variables in the remote target before starting the
36851 inferior. In this context, reset means unsetting all environment
36852 variables that were previously set by the user (i.e., were not
36853 initially present in the environment). It is sent to
36854 @command{gdbserver} before the @samp{QEnvironmentHexEncoded}
36855 (@pxref{QEnvironmentHexEncoded}) and the @samp{QEnvironmentUnset}
36856 (@pxref{QEnvironmentUnset}) packets.
36858 This packet is only available in extended mode (@pxref{extended
36864 The request succeeded.
36867 This packet is not probed by default; the remote stub must request it,
36868 by supplying an appropriate @samp{qSupported} response
36869 (@pxref{qSupported}). This should only be done on targets that
36870 actually support passing environment variables to the starting
36873 @item QSetWorkingDir:@r{[}@var{directory}@r{]}
36874 @anchor{QSetWorkingDir packet}
36875 @cindex set working directory, remote request
36876 @cindex @samp{QSetWorkingDir} packet
36877 This packet is used to inform the remote server of the intended
36878 current working directory for programs that are going to be executed.
36880 The packet is composed by @var{directory}, an hex encoded
36881 representation of the directory that the remote inferior will use as
36882 its current working directory. If @var{directory} is an empty string,
36883 the remote server should reset the inferior's current working
36884 directory to its original, empty value.
36886 This packet is only available in extended mode (@pxref{extended
36892 The request succeeded.
36896 @itemx qsThreadInfo
36897 @cindex list active threads, remote request
36898 @cindex @samp{qfThreadInfo} packet
36899 @cindex @samp{qsThreadInfo} packet
36900 Obtain a list of all active thread IDs from the target (OS). Since there
36901 may be too many active threads to fit into one reply packet, this query
36902 works iteratively: it may require more than one query/reply sequence to
36903 obtain the entire list of threads. The first query of the sequence will
36904 be the @samp{qfThreadInfo} query; subsequent queries in the
36905 sequence will be the @samp{qsThreadInfo} query.
36907 NOTE: This packet replaces the @samp{qL} query (see below).
36911 @item m @var{thread-id}
36913 @item m @var{thread-id},@var{thread-id}@dots{}
36914 a comma-separated list of thread IDs
36916 (lower case letter @samp{L}) denotes end of list.
36919 In response to each query, the target will reply with a list of one or
36920 more thread IDs, separated by commas.
36921 @value{GDBN} will respond to each reply with a request for more thread
36922 ids (using the @samp{qs} form of the query), until the target responds
36923 with @samp{l} (lower-case ell, for @dfn{last}).
36924 Refer to @ref{thread-id syntax}, for the format of the @var{thread-id}
36927 @emph{Note: @value{GDBN} will send the @code{qfThreadInfo} query during the
36928 initial connection with the remote target, and the very first thread ID
36929 mentioned in the reply will be stopped by @value{GDBN} in a subsequent
36930 message. Therefore, the stub should ensure that the first thread ID in
36931 the @code{qfThreadInfo} reply is suitable for being stopped by @value{GDBN}.}
36933 @item qGetTLSAddr:@var{thread-id},@var{offset},@var{lm}
36934 @cindex get thread-local storage address, remote request
36935 @cindex @samp{qGetTLSAddr} packet
36936 Fetch the address associated with thread local storage specified
36937 by @var{thread-id}, @var{offset}, and @var{lm}.
36939 @var{thread-id} is the thread ID associated with the
36940 thread for which to fetch the TLS address. @xref{thread-id syntax}.
36942 @var{offset} is the (big endian, hex encoded) offset associated with the
36943 thread local variable. (This offset is obtained from the debug
36944 information associated with the variable.)
36946 @var{lm} is the (big endian, hex encoded) OS/ABI-specific encoding of the
36947 load module associated with the thread local storage. For example,
36948 a @sc{gnu}/Linux system will pass the link map address of the shared
36949 object associated with the thread local storage under consideration.
36950 Other operating environments may choose to represent the load module
36951 differently, so the precise meaning of this parameter will vary.
36955 @item @var{XX}@dots{}
36956 Hex encoded (big endian) bytes representing the address of the thread
36957 local storage requested.
36960 An error occurred. The error number @var{nn} is given as hex digits.
36963 An empty reply indicates that @samp{qGetTLSAddr} is not supported by the stub.
36966 @item qGetTIBAddr:@var{thread-id}
36967 @cindex get thread information block address
36968 @cindex @samp{qGetTIBAddr} packet
36969 Fetch address of the Windows OS specific Thread Information Block.
36971 @var{thread-id} is the thread ID associated with the thread.
36975 @item @var{XX}@dots{}
36976 Hex encoded (big endian) bytes representing the linear address of the
36977 thread information block.
36980 An error occured. This means that either the thread was not found, or the
36981 address could not be retrieved.
36984 An empty reply indicates that @samp{qGetTIBAddr} is not supported by the stub.
36987 @item qL @var{startflag} @var{threadcount} @var{nextthread}
36988 Obtain thread information from RTOS. Where: @var{startflag} (one hex
36989 digit) is one to indicate the first query and zero to indicate a
36990 subsequent query; @var{threadcount} (two hex digits) is the maximum
36991 number of threads the response packet can contain; and @var{nextthread}
36992 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
36993 returned in the response as @var{argthread}.
36995 Don't use this packet; use the @samp{qfThreadInfo} query instead (see above).
36999 @item qM @var{count} @var{done} @var{argthread} @var{thread}@dots{}
37000 Where: @var{count} (two hex digits) is the number of threads being
37001 returned; @var{done} (one hex digit) is zero to indicate more threads
37002 and one indicates no further threads; @var{argthreadid} (eight hex
37003 digits) is @var{nextthread} from the request packet; @var{thread}@dots{}
37004 is a sequence of thread IDs, @var{threadid} (eight hex
37005 digits), from the target. See @code{remote.c:parse_threadlist_response()}.
37009 @cindex section offsets, remote request
37010 @cindex @samp{qOffsets} packet
37011 Get section offsets that the target used when relocating the downloaded
37016 @item Text=@var{xxx};Data=@var{yyy}@r{[};Bss=@var{zzz}@r{]}
37017 Relocate the @code{Text} section by @var{xxx} from its original address.
37018 Relocate the @code{Data} section by @var{yyy} from its original address.
37019 If the object file format provides segment information (e.g.@: @sc{elf}
37020 @samp{PT_LOAD} program headers), @value{GDBN} will relocate entire
37021 segments by the supplied offsets.
37023 @emph{Note: while a @code{Bss} offset may be included in the response,
37024 @value{GDBN} ignores this and instead applies the @code{Data} offset
37025 to the @code{Bss} section.}
37027 @item TextSeg=@var{xxx}@r{[};DataSeg=@var{yyy}@r{]}
37028 Relocate the first segment of the object file, which conventionally
37029 contains program code, to a starting address of @var{xxx}. If
37030 @samp{DataSeg} is specified, relocate the second segment, which
37031 conventionally contains modifiable data, to a starting address of
37032 @var{yyy}. @value{GDBN} will report an error if the object file
37033 does not contain segment information, or does not contain at least
37034 as many segments as mentioned in the reply. Extra segments are
37035 kept at fixed offsets relative to the last relocated segment.
37038 @item qP @var{mode} @var{thread-id}
37039 @cindex thread information, remote request
37040 @cindex @samp{qP} packet
37041 Returns information on @var{thread-id}. Where: @var{mode} is a hex
37042 encoded 32 bit mode; @var{thread-id} is a thread ID
37043 (@pxref{thread-id syntax}).
37045 Don't use this packet; use the @samp{qThreadExtraInfo} query instead
37048 Reply: see @code{remote.c:remote_unpack_thread_info_response()}.
37052 @cindex non-stop mode, remote request
37053 @cindex @samp{QNonStop} packet
37055 Enter non-stop (@samp{QNonStop:1}) or all-stop (@samp{QNonStop:0}) mode.
37056 @xref{Remote Non-Stop}, for more information.
37061 The request succeeded.
37064 An error occurred. The error number @var{nn} is given as hex digits.
37067 An empty reply indicates that @samp{QNonStop} is not supported by
37071 This packet is not probed by default; the remote stub must request it,
37072 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
37073 Use of this packet is controlled by the @code{set non-stop} command;
37074 @pxref{Non-Stop Mode}.
37076 @item QCatchSyscalls:1 @r{[};@var{sysno}@r{]}@dots{}
37077 @itemx QCatchSyscalls:0
37078 @cindex catch syscalls from inferior, remote request
37079 @cindex @samp{QCatchSyscalls} packet
37080 @anchor{QCatchSyscalls}
37081 Enable (@samp{QCatchSyscalls:1}) or disable (@samp{QCatchSyscalls:0})
37082 catching syscalls from the inferior process.
37084 For @samp{QCatchSyscalls:1}, each listed syscall @var{sysno} (encoded
37085 in hex) should be reported to @value{GDBN}. If no syscall @var{sysno}
37086 is listed, every system call should be reported.
37088 Note that if a syscall not in the list is reported, @value{GDBN} will
37089 still filter the event according to its own list from all corresponding
37090 @code{catch syscall} commands. However, it is more efficient to only
37091 report the requested syscalls.
37093 Multiple @samp{QCatchSyscalls:1} packets do not combine; any earlier
37094 @samp{QCatchSyscalls:1} list is completely replaced by the new list.
37096 If the inferior process execs, the state of @samp{QCatchSyscalls} is
37097 kept for the new process too. On targets where exec may affect syscall
37098 numbers, for example with exec between 32 and 64-bit processes, the
37099 client should send a new packet with the new syscall list.
37104 The request succeeded.
37107 An error occurred. @var{nn} are hex digits.
37110 An empty reply indicates that @samp{QCatchSyscalls} is not supported by
37114 Use of this packet is controlled by the @code{set remote catch-syscalls}
37115 command (@pxref{Remote Configuration, set remote catch-syscalls}).
37116 This packet is not probed by default; the remote stub must request it,
37117 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
37119 @item QPassSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
37120 @cindex pass signals to inferior, remote request
37121 @cindex @samp{QPassSignals} packet
37122 @anchor{QPassSignals}
37123 Each listed @var{signal} should be passed directly to the inferior process.
37124 Signals are numbered identically to continue packets and stop replies
37125 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
37126 strictly greater than the previous item. These signals do not need to stop
37127 the inferior, or be reported to @value{GDBN}. All other signals should be
37128 reported to @value{GDBN}. Multiple @samp{QPassSignals} packets do not
37129 combine; any earlier @samp{QPassSignals} list is completely replaced by the
37130 new list. This packet improves performance when using @samp{handle
37131 @var{signal} nostop noprint pass}.
37136 The request succeeded.
37139 An error occurred. The error number @var{nn} is given as hex digits.
37142 An empty reply indicates that @samp{QPassSignals} is not supported by
37146 Use of this packet is controlled by the @code{set remote pass-signals}
37147 command (@pxref{Remote Configuration, set remote pass-signals}).
37148 This packet is not probed by default; the remote stub must request it,
37149 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
37151 @item QProgramSignals: @var{signal} @r{[};@var{signal}@r{]}@dots{}
37152 @cindex signals the inferior may see, remote request
37153 @cindex @samp{QProgramSignals} packet
37154 @anchor{QProgramSignals}
37155 Each listed @var{signal} may be delivered to the inferior process.
37156 Others should be silently discarded.
37158 In some cases, the remote stub may need to decide whether to deliver a
37159 signal to the program or not without @value{GDBN} involvement. One
37160 example of that is while detaching --- the program's threads may have
37161 stopped for signals that haven't yet had a chance of being reported to
37162 @value{GDBN}, and so the remote stub can use the signal list specified
37163 by this packet to know whether to deliver or ignore those pending
37166 This does not influence whether to deliver a signal as requested by a
37167 resumption packet (@pxref{vCont packet}).
37169 Signals are numbered identically to continue packets and stop replies
37170 (@pxref{Stop Reply Packets}). Each @var{signal} list item should be
37171 strictly greater than the previous item. Multiple
37172 @samp{QProgramSignals} packets do not combine; any earlier
37173 @samp{QProgramSignals} list is completely replaced by the new list.
37178 The request succeeded.
37181 An error occurred. The error number @var{nn} is given as hex digits.
37184 An empty reply indicates that @samp{QProgramSignals} is not supported
37188 Use of this packet is controlled by the @code{set remote program-signals}
37189 command (@pxref{Remote Configuration, set remote program-signals}).
37190 This packet is not probed by default; the remote stub must request it,
37191 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
37193 @anchor{QThreadEvents}
37194 @item QThreadEvents:1
37195 @itemx QThreadEvents:0
37196 @cindex thread create/exit events, remote request
37197 @cindex @samp{QThreadEvents} packet
37199 Enable (@samp{QThreadEvents:1}) or disable (@samp{QThreadEvents:0})
37200 reporting of thread create and exit events. @xref{thread create
37201 event}, for the reply specifications. For example, this is used in
37202 non-stop mode when @value{GDBN} stops a set of threads and
37203 synchronously waits for the their corresponding stop replies. Without
37204 exit events, if one of the threads exits, @value{GDBN} would hang
37205 forever not knowing that it should no longer expect a stop for that
37206 same thread. @value{GDBN} does not enable this feature unless the
37207 stub reports that it supports it by including @samp{QThreadEvents+} in
37208 its @samp{qSupported} reply.
37213 The request succeeded.
37216 An error occurred. The error number @var{nn} is given as hex digits.
37219 An empty reply indicates that @samp{QThreadEvents} is not supported by
37223 Use of this packet is controlled by the @code{set remote thread-events}
37224 command (@pxref{Remote Configuration, set remote thread-events}).
37226 @item qRcmd,@var{command}
37227 @cindex execute remote command, remote request
37228 @cindex @samp{qRcmd} packet
37229 @var{command} (hex encoded) is passed to the local interpreter for
37230 execution. Invalid commands should be reported using the output
37231 string. Before the final result packet, the target may also respond
37232 with a number of intermediate @samp{O@var{output}} console output
37233 packets. @emph{Implementors should note that providing access to a
37234 stubs's interpreter may have security implications}.
37239 A command response with no output.
37241 A command response with the hex encoded output string @var{OUTPUT}.
37243 Indicate a badly formed request.
37245 An empty reply indicates that @samp{qRcmd} is not recognized.
37248 (Note that the @code{qRcmd} packet's name is separated from the
37249 command by a @samp{,}, not a @samp{:}, contrary to the naming
37250 conventions above. Please don't use this packet as a model for new
37253 @item qSearch:memory:@var{address};@var{length};@var{search-pattern}
37254 @cindex searching memory, in remote debugging
37256 @cindex @samp{qSearch:memory} packet
37258 @cindex @samp{qSearch memory} packet
37259 @anchor{qSearch memory}
37260 Search @var{length} bytes at @var{address} for @var{search-pattern}.
37261 Both @var{address} and @var{length} are encoded in hex;
37262 @var{search-pattern} is a sequence of bytes, also hex encoded.
37267 The pattern was not found.
37269 The pattern was found at @var{address}.
37271 A badly formed request or an error was encountered while searching memory.
37273 An empty reply indicates that @samp{qSearch:memory} is not recognized.
37276 @item QStartNoAckMode
37277 @cindex @samp{QStartNoAckMode} packet
37278 @anchor{QStartNoAckMode}
37279 Request that the remote stub disable the normal @samp{+}/@samp{-}
37280 protocol acknowledgments (@pxref{Packet Acknowledgment}).
37285 The stub has switched to no-acknowledgment mode.
37286 @value{GDBN} acknowledges this reponse,
37287 but neither the stub nor @value{GDBN} shall send or expect further
37288 @samp{+}/@samp{-} acknowledgments in the current connection.
37290 An empty reply indicates that the stub does not support no-acknowledgment mode.
37293 @item qSupported @r{[}:@var{gdbfeature} @r{[};@var{gdbfeature}@r{]}@dots{} @r{]}
37294 @cindex supported packets, remote query
37295 @cindex features of the remote protocol
37296 @cindex @samp{qSupported} packet
37297 @anchor{qSupported}
37298 Tell the remote stub about features supported by @value{GDBN}, and
37299 query the stub for features it supports. This packet allows
37300 @value{GDBN} and the remote stub to take advantage of each others'
37301 features. @samp{qSupported} also consolidates multiple feature probes
37302 at startup, to improve @value{GDBN} performance---a single larger
37303 packet performs better than multiple smaller probe packets on
37304 high-latency links. Some features may enable behavior which must not
37305 be on by default, e.g.@: because it would confuse older clients or
37306 stubs. Other features may describe packets which could be
37307 automatically probed for, but are not. These features must be
37308 reported before @value{GDBN} will use them. This ``default
37309 unsupported'' behavior is not appropriate for all packets, but it
37310 helps to keep the initial connection time under control with new
37311 versions of @value{GDBN} which support increasing numbers of packets.
37315 @item @var{stubfeature} @r{[};@var{stubfeature}@r{]}@dots{}
37316 The stub supports or does not support each returned @var{stubfeature},
37317 depending on the form of each @var{stubfeature} (see below for the
37320 An empty reply indicates that @samp{qSupported} is not recognized,
37321 or that no features needed to be reported to @value{GDBN}.
37324 The allowed forms for each feature (either a @var{gdbfeature} in the
37325 @samp{qSupported} packet, or a @var{stubfeature} in the response)
37329 @item @var{name}=@var{value}
37330 The remote protocol feature @var{name} is supported, and associated
37331 with the specified @var{value}. The format of @var{value} depends
37332 on the feature, but it must not include a semicolon.
37334 The remote protocol feature @var{name} is supported, and does not
37335 need an associated value.
37337 The remote protocol feature @var{name} is not supported.
37339 The remote protocol feature @var{name} may be supported, and
37340 @value{GDBN} should auto-detect support in some other way when it is
37341 needed. This form will not be used for @var{gdbfeature} notifications,
37342 but may be used for @var{stubfeature} responses.
37345 Whenever the stub receives a @samp{qSupported} request, the
37346 supplied set of @value{GDBN} features should override any previous
37347 request. This allows @value{GDBN} to put the stub in a known
37348 state, even if the stub had previously been communicating with
37349 a different version of @value{GDBN}.
37351 The following values of @var{gdbfeature} (for the packet sent by @value{GDBN})
37356 This feature indicates whether @value{GDBN} supports multiprocess
37357 extensions to the remote protocol. @value{GDBN} does not use such
37358 extensions unless the stub also reports that it supports them by
37359 including @samp{multiprocess+} in its @samp{qSupported} reply.
37360 @xref{multiprocess extensions}, for details.
37363 This feature indicates that @value{GDBN} supports the XML target
37364 description. If the stub sees @samp{xmlRegisters=} with target
37365 specific strings separated by a comma, it will report register
37369 This feature indicates whether @value{GDBN} supports the
37370 @samp{qRelocInsn} packet (@pxref{Tracepoint Packets,,Relocate
37371 instruction reply packet}).
37374 This feature indicates whether @value{GDBN} supports the swbreak stop
37375 reason in stop replies. @xref{swbreak stop reason}, for details.
37378 This feature indicates whether @value{GDBN} supports the hwbreak stop
37379 reason in stop replies. @xref{swbreak stop reason}, for details.
37382 This feature indicates whether @value{GDBN} supports fork event
37383 extensions to the remote protocol. @value{GDBN} does not use such
37384 extensions unless the stub also reports that it supports them by
37385 including @samp{fork-events+} in its @samp{qSupported} reply.
37388 This feature indicates whether @value{GDBN} supports vfork event
37389 extensions to the remote protocol. @value{GDBN} does not use such
37390 extensions unless the stub also reports that it supports them by
37391 including @samp{vfork-events+} in its @samp{qSupported} reply.
37394 This feature indicates whether @value{GDBN} supports exec event
37395 extensions to the remote protocol. @value{GDBN} does not use such
37396 extensions unless the stub also reports that it supports them by
37397 including @samp{exec-events+} in its @samp{qSupported} reply.
37399 @item vContSupported
37400 This feature indicates whether @value{GDBN} wants to know the
37401 supported actions in the reply to @samp{vCont?} packet.
37404 Stubs should ignore any unknown values for
37405 @var{gdbfeature}. Any @value{GDBN} which sends a @samp{qSupported}
37406 packet supports receiving packets of unlimited length (earlier
37407 versions of @value{GDBN} may reject overly long responses). Additional values
37408 for @var{gdbfeature} may be defined in the future to let the stub take
37409 advantage of new features in @value{GDBN}, e.g.@: incompatible
37410 improvements in the remote protocol---the @samp{multiprocess} feature is
37411 an example of such a feature. The stub's reply should be independent
37412 of the @var{gdbfeature} entries sent by @value{GDBN}; first @value{GDBN}
37413 describes all the features it supports, and then the stub replies with
37414 all the features it supports.
37416 Similarly, @value{GDBN} will silently ignore unrecognized stub feature
37417 responses, as long as each response uses one of the standard forms.
37419 Some features are flags. A stub which supports a flag feature
37420 should respond with a @samp{+} form response. Other features
37421 require values, and the stub should respond with an @samp{=}
37424 Each feature has a default value, which @value{GDBN} will use if
37425 @samp{qSupported} is not available or if the feature is not mentioned
37426 in the @samp{qSupported} response. The default values are fixed; a
37427 stub is free to omit any feature responses that match the defaults.
37429 Not all features can be probed, but for those which can, the probing
37430 mechanism is useful: in some cases, a stub's internal
37431 architecture may not allow the protocol layer to know some information
37432 about the underlying target in advance. This is especially common in
37433 stubs which may be configured for multiple targets.
37435 These are the currently defined stub features and their properties:
37437 @multitable @columnfractions 0.35 0.2 0.12 0.2
37438 @c NOTE: The first row should be @headitem, but we do not yet require
37439 @c a new enough version of Texinfo (4.7) to use @headitem.
37441 @tab Value Required
37445 @item @samp{PacketSize}
37450 @item @samp{qXfer:auxv:read}
37455 @item @samp{qXfer:btrace:read}
37460 @item @samp{qXfer:btrace-conf:read}
37465 @item @samp{qXfer:exec-file:read}
37470 @item @samp{qXfer:features:read}
37475 @item @samp{qXfer:libraries:read}
37480 @item @samp{qXfer:libraries-svr4:read}
37485 @item @samp{augmented-libraries-svr4-read}
37490 @item @samp{qXfer:memory-map:read}
37495 @item @samp{qXfer:sdata:read}
37500 @item @samp{qXfer:spu:read}
37505 @item @samp{qXfer:spu:write}
37510 @item @samp{qXfer:siginfo:read}
37515 @item @samp{qXfer:siginfo:write}
37520 @item @samp{qXfer:threads:read}
37525 @item @samp{qXfer:traceframe-info:read}
37530 @item @samp{qXfer:uib:read}
37535 @item @samp{qXfer:fdpic:read}
37540 @item @samp{Qbtrace:off}
37545 @item @samp{Qbtrace:bts}
37550 @item @samp{Qbtrace:pt}
37555 @item @samp{Qbtrace-conf:bts:size}
37560 @item @samp{Qbtrace-conf:pt:size}
37565 @item @samp{QNonStop}
37570 @item @samp{QCatchSyscalls}
37575 @item @samp{QPassSignals}
37580 @item @samp{QStartNoAckMode}
37585 @item @samp{multiprocess}
37590 @item @samp{ConditionalBreakpoints}
37595 @item @samp{ConditionalTracepoints}
37600 @item @samp{ReverseContinue}
37605 @item @samp{ReverseStep}
37610 @item @samp{TracepointSource}
37615 @item @samp{QAgent}
37620 @item @samp{QAllow}
37625 @item @samp{QDisableRandomization}
37630 @item @samp{EnableDisableTracepoints}
37635 @item @samp{QTBuffer:size}
37640 @item @samp{tracenz}
37645 @item @samp{BreakpointCommands}
37650 @item @samp{swbreak}
37655 @item @samp{hwbreak}
37660 @item @samp{fork-events}
37665 @item @samp{vfork-events}
37670 @item @samp{exec-events}
37675 @item @samp{QThreadEvents}
37680 @item @samp{no-resumed}
37687 These are the currently defined stub features, in more detail:
37690 @cindex packet size, remote protocol
37691 @item PacketSize=@var{bytes}
37692 The remote stub can accept packets up to at least @var{bytes} in
37693 length. @value{GDBN} will send packets up to this size for bulk
37694 transfers, and will never send larger packets. This is a limit on the
37695 data characters in the packet, including the frame and checksum.
37696 There is no trailing NUL byte in a remote protocol packet; if the stub
37697 stores packets in a NUL-terminated format, it should allow an extra
37698 byte in its buffer for the NUL. If this stub feature is not supported,
37699 @value{GDBN} guesses based on the size of the @samp{g} packet response.
37701 @item qXfer:auxv:read
37702 The remote stub understands the @samp{qXfer:auxv:read} packet
37703 (@pxref{qXfer auxiliary vector read}).
37705 @item qXfer:btrace:read
37706 The remote stub understands the @samp{qXfer:btrace:read}
37707 packet (@pxref{qXfer btrace read}).
37709 @item qXfer:btrace-conf:read
37710 The remote stub understands the @samp{qXfer:btrace-conf:read}
37711 packet (@pxref{qXfer btrace-conf read}).
37713 @item qXfer:exec-file:read
37714 The remote stub understands the @samp{qXfer:exec-file:read} packet
37715 (@pxref{qXfer executable filename read}).
37717 @item qXfer:features:read
37718 The remote stub understands the @samp{qXfer:features:read} packet
37719 (@pxref{qXfer target description read}).
37721 @item qXfer:libraries:read
37722 The remote stub understands the @samp{qXfer:libraries:read} packet
37723 (@pxref{qXfer library list read}).
37725 @item qXfer:libraries-svr4:read
37726 The remote stub understands the @samp{qXfer:libraries-svr4:read} packet
37727 (@pxref{qXfer svr4 library list read}).
37729 @item augmented-libraries-svr4-read
37730 The remote stub understands the augmented form of the
37731 @samp{qXfer:libraries-svr4:read} packet
37732 (@pxref{qXfer svr4 library list read}).
37734 @item qXfer:memory-map:read
37735 The remote stub understands the @samp{qXfer:memory-map:read} packet
37736 (@pxref{qXfer memory map read}).
37738 @item qXfer:sdata:read
37739 The remote stub understands the @samp{qXfer:sdata:read} packet
37740 (@pxref{qXfer sdata read}).
37742 @item qXfer:spu:read
37743 The remote stub understands the @samp{qXfer:spu:read} packet
37744 (@pxref{qXfer spu read}).
37746 @item qXfer:spu:write
37747 The remote stub understands the @samp{qXfer:spu:write} packet
37748 (@pxref{qXfer spu write}).
37750 @item qXfer:siginfo:read
37751 The remote stub understands the @samp{qXfer:siginfo:read} packet
37752 (@pxref{qXfer siginfo read}).
37754 @item qXfer:siginfo:write
37755 The remote stub understands the @samp{qXfer:siginfo:write} packet
37756 (@pxref{qXfer siginfo write}).
37758 @item qXfer:threads:read
37759 The remote stub understands the @samp{qXfer:threads:read} packet
37760 (@pxref{qXfer threads read}).
37762 @item qXfer:traceframe-info:read
37763 The remote stub understands the @samp{qXfer:traceframe-info:read}
37764 packet (@pxref{qXfer traceframe info read}).
37766 @item qXfer:uib:read
37767 The remote stub understands the @samp{qXfer:uib:read}
37768 packet (@pxref{qXfer unwind info block}).
37770 @item qXfer:fdpic:read
37771 The remote stub understands the @samp{qXfer:fdpic:read}
37772 packet (@pxref{qXfer fdpic loadmap read}).
37775 The remote stub understands the @samp{QNonStop} packet
37776 (@pxref{QNonStop}).
37778 @item QCatchSyscalls
37779 The remote stub understands the @samp{QCatchSyscalls} packet
37780 (@pxref{QCatchSyscalls}).
37783 The remote stub understands the @samp{QPassSignals} packet
37784 (@pxref{QPassSignals}).
37786 @item QStartNoAckMode
37787 The remote stub understands the @samp{QStartNoAckMode} packet and
37788 prefers to operate in no-acknowledgment mode. @xref{Packet Acknowledgment}.
37791 @anchor{multiprocess extensions}
37792 @cindex multiprocess extensions, in remote protocol
37793 The remote stub understands the multiprocess extensions to the remote
37794 protocol syntax. The multiprocess extensions affect the syntax of
37795 thread IDs in both packets and replies (@pxref{thread-id syntax}), and
37796 add process IDs to the @samp{D} packet and @samp{W} and @samp{X}
37797 replies. Note that reporting this feature indicates support for the
37798 syntactic extensions only, not that the stub necessarily supports
37799 debugging of more than one process at a time. The stub must not use
37800 multiprocess extensions in packet replies unless @value{GDBN} has also
37801 indicated it supports them in its @samp{qSupported} request.
37803 @item qXfer:osdata:read
37804 The remote stub understands the @samp{qXfer:osdata:read} packet
37805 ((@pxref{qXfer osdata read}).
37807 @item ConditionalBreakpoints
37808 The target accepts and implements evaluation of conditional expressions
37809 defined for breakpoints. The target will only report breakpoint triggers
37810 when such conditions are true (@pxref{Conditions, ,Break Conditions}).
37812 @item ConditionalTracepoints
37813 The remote stub accepts and implements conditional expressions defined
37814 for tracepoints (@pxref{Tracepoint Conditions}).
37816 @item ReverseContinue
37817 The remote stub accepts and implements the reverse continue packet
37821 The remote stub accepts and implements the reverse step packet
37824 @item TracepointSource
37825 The remote stub understands the @samp{QTDPsrc} packet that supplies
37826 the source form of tracepoint definitions.
37829 The remote stub understands the @samp{QAgent} packet.
37832 The remote stub understands the @samp{QAllow} packet.
37834 @item QDisableRandomization
37835 The remote stub understands the @samp{QDisableRandomization} packet.
37837 @item StaticTracepoint
37838 @cindex static tracepoints, in remote protocol
37839 The remote stub supports static tracepoints.
37841 @item InstallInTrace
37842 @anchor{install tracepoint in tracing}
37843 The remote stub supports installing tracepoint in tracing.
37845 @item EnableDisableTracepoints
37846 The remote stub supports the @samp{QTEnable} (@pxref{QTEnable}) and
37847 @samp{QTDisable} (@pxref{QTDisable}) packets that allow tracepoints
37848 to be enabled and disabled while a trace experiment is running.
37850 @item QTBuffer:size
37851 The remote stub supports the @samp{QTBuffer:size} (@pxref{QTBuffer-size})
37852 packet that allows to change the size of the trace buffer.
37855 @cindex string tracing, in remote protocol
37856 The remote stub supports the @samp{tracenz} bytecode for collecting strings.
37857 See @ref{Bytecode Descriptions} for details about the bytecode.
37859 @item BreakpointCommands
37860 @cindex breakpoint commands, in remote protocol
37861 The remote stub supports running a breakpoint's command list itself,
37862 rather than reporting the hit to @value{GDBN}.
37865 The remote stub understands the @samp{Qbtrace:off} packet.
37868 The remote stub understands the @samp{Qbtrace:bts} packet.
37871 The remote stub understands the @samp{Qbtrace:pt} packet.
37873 @item Qbtrace-conf:bts:size
37874 The remote stub understands the @samp{Qbtrace-conf:bts:size} packet.
37876 @item Qbtrace-conf:pt:size
37877 The remote stub understands the @samp{Qbtrace-conf:pt:size} packet.
37880 The remote stub reports the @samp{swbreak} stop reason for memory
37884 The remote stub reports the @samp{hwbreak} stop reason for hardware
37888 The remote stub reports the @samp{fork} stop reason for fork events.
37891 The remote stub reports the @samp{vfork} stop reason for vfork events
37892 and vforkdone events.
37895 The remote stub reports the @samp{exec} stop reason for exec events.
37897 @item vContSupported
37898 The remote stub reports the supported actions in the reply to
37899 @samp{vCont?} packet.
37901 @item QThreadEvents
37902 The remote stub understands the @samp{QThreadEvents} packet.
37905 The remote stub reports the @samp{N} stop reply.
37910 @cindex symbol lookup, remote request
37911 @cindex @samp{qSymbol} packet
37912 Notify the target that @value{GDBN} is prepared to serve symbol lookup
37913 requests. Accept requests from the target for the values of symbols.
37918 The target does not need to look up any (more) symbols.
37919 @item qSymbol:@var{sym_name}
37920 The target requests the value of symbol @var{sym_name} (hex encoded).
37921 @value{GDBN} may provide the value by using the
37922 @samp{qSymbol:@var{sym_value}:@var{sym_name}} message, described
37926 @item qSymbol:@var{sym_value}:@var{sym_name}
37927 Set the value of @var{sym_name} to @var{sym_value}.
37929 @var{sym_name} (hex encoded) is the name of a symbol whose value the
37930 target has previously requested.
37932 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
37933 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
37939 The target does not need to look up any (more) symbols.
37940 @item qSymbol:@var{sym_name}
37941 The target requests the value of a new symbol @var{sym_name} (hex
37942 encoded). @value{GDBN} will continue to supply the values of symbols
37943 (if available), until the target ceases to request them.
37948 @itemx QTDisconnected
37955 @itemx qTMinFTPILen
37957 @xref{Tracepoint Packets}.
37959 @item qThreadExtraInfo,@var{thread-id}
37960 @cindex thread attributes info, remote request
37961 @cindex @samp{qThreadExtraInfo} packet
37962 Obtain from the target OS a printable string description of thread
37963 attributes for the thread @var{thread-id}; see @ref{thread-id syntax},
37964 for the forms of @var{thread-id}. This
37965 string may contain anything that the target OS thinks is interesting
37966 for @value{GDBN} to tell the user about the thread. The string is
37967 displayed in @value{GDBN}'s @code{info threads} display. Some
37968 examples of possible thread extra info strings are @samp{Runnable}, or
37969 @samp{Blocked on Mutex}.
37973 @item @var{XX}@dots{}
37974 Where @samp{@var{XX}@dots{}} is a hex encoding of @sc{ascii} data,
37975 comprising the printable string containing the extra information about
37976 the thread's attributes.
37979 (Note that the @code{qThreadExtraInfo} packet's name is separated from
37980 the command by a @samp{,}, not a @samp{:}, contrary to the naming
37981 conventions above. Please don't use this packet as a model for new
38000 @xref{Tracepoint Packets}.
38002 @item qXfer:@var{object}:read:@var{annex}:@var{offset},@var{length}
38003 @cindex read special object, remote request
38004 @cindex @samp{qXfer} packet
38005 @anchor{qXfer read}
38006 Read uninterpreted bytes from the target's special data area
38007 identified by the keyword @var{object}. Request @var{length} bytes
38008 starting at @var{offset} bytes into the data. The content and
38009 encoding of @var{annex} is specific to @var{object}; it can supply
38010 additional details about what data to access.
38015 Data @var{data} (@pxref{Binary Data}) has been read from the
38016 target. There may be more data at a higher address (although
38017 it is permitted to return @samp{m} even for the last valid
38018 block of data, as long as at least one byte of data was read).
38019 It is possible for @var{data} to have fewer bytes than the @var{length} in the
38023 Data @var{data} (@pxref{Binary Data}) has been read from the target.
38024 There is no more data to be read. It is possible for @var{data} to
38025 have fewer bytes than the @var{length} in the request.
38028 The @var{offset} in the request is at the end of the data.
38029 There is no more data to be read.
38032 The request was malformed, or @var{annex} was invalid.
38035 The offset was invalid, or there was an error encountered reading the data.
38036 The @var{nn} part is a hex-encoded @code{errno} value.
38039 An empty reply indicates the @var{object} string was not recognized by
38040 the stub, or that the object does not support reading.
38043 Here are the specific requests of this form defined so far. All the
38044 @samp{qXfer:@var{object}:read:@dots{}} requests use the same reply
38045 formats, listed above.
38048 @item qXfer:auxv:read::@var{offset},@var{length}
38049 @anchor{qXfer auxiliary vector read}
38050 Access the target's @dfn{auxiliary vector}. @xref{OS Information,
38051 auxiliary vector}. Note @var{annex} must be empty.
38053 This packet is not probed by default; the remote stub must request it,
38054 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38056 @item qXfer:btrace:read:@var{annex}:@var{offset},@var{length}
38057 @anchor{qXfer btrace read}
38059 Return a description of the current branch trace.
38060 @xref{Branch Trace Format}. The annex part of the generic @samp{qXfer}
38061 packet may have one of the following values:
38065 Returns all available branch trace.
38068 Returns all available branch trace if the branch trace changed since
38069 the last read request.
38072 Returns the new branch trace since the last read request. Adds a new
38073 block to the end of the trace that begins at zero and ends at the source
38074 location of the first branch in the trace buffer. This extra block is
38075 used to stitch traces together.
38077 If the trace buffer overflowed, returns an error indicating the overflow.
38080 This packet is not probed by default; the remote stub must request it
38081 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38083 @item qXfer:btrace-conf:read::@var{offset},@var{length}
38084 @anchor{qXfer btrace-conf read}
38086 Return a description of the current branch trace configuration.
38087 @xref{Branch Trace Configuration Format}.
38089 This packet is not probed by default; the remote stub must request it
38090 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38092 @item qXfer:exec-file:read:@var{annex}:@var{offset},@var{length}
38093 @anchor{qXfer executable filename read}
38094 Return the full absolute name of the file that was executed to create
38095 a process running on the remote system. The annex specifies the
38096 numeric process ID of the process to query, encoded as a hexadecimal
38097 number. If the annex part is empty the remote stub should return the
38098 filename corresponding to the currently executing process.
38100 This packet is not probed by default; the remote stub must request it,
38101 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38103 @item qXfer:features:read:@var{annex}:@var{offset},@var{length}
38104 @anchor{qXfer target description read}
38105 Access the @dfn{target description}. @xref{Target Descriptions}. The
38106 annex specifies which XML document to access. The main description is
38107 always loaded from the @samp{target.xml} annex.
38109 This packet is not probed by default; the remote stub must request it,
38110 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38112 @item qXfer:libraries:read:@var{annex}:@var{offset},@var{length}
38113 @anchor{qXfer library list read}
38114 Access the target's list of loaded libraries. @xref{Library List Format}.
38115 The annex part of the generic @samp{qXfer} packet must be empty
38116 (@pxref{qXfer read}).
38118 Targets which maintain a list of libraries in the program's memory do
38119 not need to implement this packet; it is designed for platforms where
38120 the operating system manages the list of loaded libraries.
38122 This packet is not probed by default; the remote stub must request it,
38123 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38125 @item qXfer:libraries-svr4:read:@var{annex}:@var{offset},@var{length}
38126 @anchor{qXfer svr4 library list read}
38127 Access the target's list of loaded libraries when the target is an SVR4
38128 platform. @xref{Library List Format for SVR4 Targets}. The annex part
38129 of the generic @samp{qXfer} packet must be empty unless the remote
38130 stub indicated it supports the augmented form of this packet
38131 by supplying an appropriate @samp{qSupported} response
38132 (@pxref{qXfer read}, @ref{qSupported}).
38134 This packet is optional for better performance on SVR4 targets.
38135 @value{GDBN} uses memory read packets to read the SVR4 library list otherwise.
38137 This packet is not probed by default; the remote stub must request it,
38138 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38140 If the remote stub indicates it supports the augmented form of this
38141 packet then the annex part of the generic @samp{qXfer} packet may
38142 contain a semicolon-separated list of @samp{@var{name}=@var{value}}
38143 arguments. The currently supported arguments are:
38146 @item start=@var{address}
38147 A hexadecimal number specifying the address of the @samp{struct
38148 link_map} to start reading the library list from. If unset or zero
38149 then the first @samp{struct link_map} in the library list will be
38150 chosen as the starting point.
38152 @item prev=@var{address}
38153 A hexadecimal number specifying the address of the @samp{struct
38154 link_map} immediately preceding the @samp{struct link_map}
38155 specified by the @samp{start} argument. If unset or zero then
38156 the remote stub will expect that no @samp{struct link_map}
38157 exists prior to the starting point.
38161 Arguments that are not understood by the remote stub will be silently
38164 @item qXfer:memory-map:read::@var{offset},@var{length}
38165 @anchor{qXfer memory map read}
38166 Access the target's @dfn{memory-map}. @xref{Memory Map Format}. The
38167 annex part of the generic @samp{qXfer} packet must be empty
38168 (@pxref{qXfer read}).
38170 This packet is not probed by default; the remote stub must request it,
38171 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38173 @item qXfer:sdata:read::@var{offset},@var{length}
38174 @anchor{qXfer sdata read}
38176 Read contents of the extra collected static tracepoint marker
38177 information. The annex part of the generic @samp{qXfer} packet must
38178 be empty (@pxref{qXfer read}). @xref{Tracepoint Actions,,Tracepoint
38181 This packet is not probed by default; the remote stub must request it,
38182 by supplying an appropriate @samp{qSupported} response
38183 (@pxref{qSupported}).
38185 @item qXfer:siginfo:read::@var{offset},@var{length}
38186 @anchor{qXfer siginfo read}
38187 Read contents of the extra signal information on the target
38188 system. The annex part of the generic @samp{qXfer} packet must be
38189 empty (@pxref{qXfer read}).
38191 This packet is not probed by default; the remote stub must request it,
38192 by supplying an appropriate @samp{qSupported} response
38193 (@pxref{qSupported}).
38195 @item qXfer:spu:read:@var{annex}:@var{offset},@var{length}
38196 @anchor{qXfer spu read}
38197 Read contents of an @code{spufs} file on the target system. The
38198 annex specifies which file to read; it must be of the form
38199 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
38200 in the target process, and @var{name} identifes the @code{spufs} file
38201 in that context to be accessed.
38203 This packet is not probed by default; the remote stub must request it,
38204 by supplying an appropriate @samp{qSupported} response
38205 (@pxref{qSupported}).
38207 @item qXfer:threads:read::@var{offset},@var{length}
38208 @anchor{qXfer threads read}
38209 Access the list of threads on target. @xref{Thread List Format}. The
38210 annex part of the generic @samp{qXfer} packet must be empty
38211 (@pxref{qXfer read}).
38213 This packet is not probed by default; the remote stub must request it,
38214 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38216 @item qXfer:traceframe-info:read::@var{offset},@var{length}
38217 @anchor{qXfer traceframe info read}
38219 Return a description of the current traceframe's contents.
38220 @xref{Traceframe Info Format}. The annex part of the generic
38221 @samp{qXfer} packet must be empty (@pxref{qXfer read}).
38223 This packet is not probed by default; the remote stub must request it,
38224 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38226 @item qXfer:uib:read:@var{pc}:@var{offset},@var{length}
38227 @anchor{qXfer unwind info block}
38229 Return the unwind information block for @var{pc}. This packet is used
38230 on OpenVMS/ia64 to ask the kernel unwind information.
38232 This packet is not probed by default.
38234 @item qXfer:fdpic:read:@var{annex}:@var{offset},@var{length}
38235 @anchor{qXfer fdpic loadmap read}
38236 Read contents of @code{loadmap}s on the target system. The
38237 annex, either @samp{exec} or @samp{interp}, specifies which @code{loadmap},
38238 executable @code{loadmap} or interpreter @code{loadmap} to read.
38240 This packet is not probed by default; the remote stub must request it,
38241 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38243 @item qXfer:osdata:read::@var{offset},@var{length}
38244 @anchor{qXfer osdata read}
38245 Access the target's @dfn{operating system information}.
38246 @xref{Operating System Information}.
38250 @item qXfer:@var{object}:write:@var{annex}:@var{offset}:@var{data}@dots{}
38251 @cindex write data into object, remote request
38252 @anchor{qXfer write}
38253 Write uninterpreted bytes into the target's special data area
38254 identified by the keyword @var{object}, starting at @var{offset} bytes
38255 into the data. The binary-encoded data (@pxref{Binary Data}) to be
38256 written is given by @var{data}@dots{}. The content and encoding of @var{annex}
38257 is specific to @var{object}; it can supply additional details about what data
38263 @var{nn} (hex encoded) is the number of bytes written.
38264 This may be fewer bytes than supplied in the request.
38267 The request was malformed, or @var{annex} was invalid.
38270 The offset was invalid, or there was an error encountered writing the data.
38271 The @var{nn} part is a hex-encoded @code{errno} value.
38274 An empty reply indicates the @var{object} string was not
38275 recognized by the stub, or that the object does not support writing.
38278 Here are the specific requests of this form defined so far. All the
38279 @samp{qXfer:@var{object}:write:@dots{}} requests use the same reply
38280 formats, listed above.
38283 @item qXfer:siginfo:write::@var{offset}:@var{data}@dots{}
38284 @anchor{qXfer siginfo write}
38285 Write @var{data} to the extra signal information on the target system.
38286 The annex part of the generic @samp{qXfer} packet must be
38287 empty (@pxref{qXfer write}).
38289 This packet is not probed by default; the remote stub must request it,
38290 by supplying an appropriate @samp{qSupported} response
38291 (@pxref{qSupported}).
38293 @item qXfer:spu:write:@var{annex}:@var{offset}:@var{data}@dots{}
38294 @anchor{qXfer spu write}
38295 Write @var{data} to an @code{spufs} file on the target system. The
38296 annex specifies which file to write; it must be of the form
38297 @file{@var{id}/@var{name}}, where @var{id} specifies an SPU context ID
38298 in the target process, and @var{name} identifes the @code{spufs} file
38299 in that context to be accessed.
38301 This packet is not probed by default; the remote stub must request it,
38302 by supplying an appropriate @samp{qSupported} response (@pxref{qSupported}).
38305 @item qXfer:@var{object}:@var{operation}:@dots{}
38306 Requests of this form may be added in the future. When a stub does
38307 not recognize the @var{object} keyword, or its support for
38308 @var{object} does not recognize the @var{operation} keyword, the stub
38309 must respond with an empty packet.
38311 @item qAttached:@var{pid}
38312 @cindex query attached, remote request
38313 @cindex @samp{qAttached} packet
38314 Return an indication of whether the remote server attached to an
38315 existing process or created a new process. When the multiprocess
38316 protocol extensions are supported (@pxref{multiprocess extensions}),
38317 @var{pid} is an integer in hexadecimal format identifying the target
38318 process. Otherwise, @value{GDBN} will omit the @var{pid} field and
38319 the query packet will be simplified as @samp{qAttached}.
38321 This query is used, for example, to know whether the remote process
38322 should be detached or killed when a @value{GDBN} session is ended with
38323 the @code{quit} command.
38328 The remote server attached to an existing process.
38330 The remote server created a new process.
38332 A badly formed request or an error was encountered.
38336 Enable branch tracing for the current thread using Branch Trace Store.
38341 Branch tracing has been enabled.
38343 A badly formed request or an error was encountered.
38347 Enable branch tracing for the current thread using Intel Processor Trace.
38352 Branch tracing has been enabled.
38354 A badly formed request or an error was encountered.
38358 Disable branch tracing for the current thread.
38363 Branch tracing has been disabled.
38365 A badly formed request or an error was encountered.
38368 @item Qbtrace-conf:bts:size=@var{value}
38369 Set the requested ring buffer size for new threads that use the
38370 btrace recording method in bts format.
38375 The ring buffer size has been set.
38377 A badly formed request or an error was encountered.
38380 @item Qbtrace-conf:pt:size=@var{value}
38381 Set the requested ring buffer size for new threads that use the
38382 btrace recording method in pt format.
38387 The ring buffer size has been set.
38389 A badly formed request or an error was encountered.
38394 @node Architecture-Specific Protocol Details
38395 @section Architecture-Specific Protocol Details
38397 This section describes how the remote protocol is applied to specific
38398 target architectures. Also see @ref{Standard Target Features}, for
38399 details of XML target descriptions for each architecture.
38402 * ARM-Specific Protocol Details::
38403 * MIPS-Specific Protocol Details::
38406 @node ARM-Specific Protocol Details
38407 @subsection @acronym{ARM}-specific Protocol Details
38410 * ARM Breakpoint Kinds::
38413 @node ARM Breakpoint Kinds
38414 @subsubsection @acronym{ARM} Breakpoint Kinds
38415 @cindex breakpoint kinds, @acronym{ARM}
38417 These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets.
38422 16-bit Thumb mode breakpoint.
38425 32-bit Thumb mode (Thumb-2) breakpoint.
38428 32-bit @acronym{ARM} mode breakpoint.
38432 @node MIPS-Specific Protocol Details
38433 @subsection @acronym{MIPS}-specific Protocol Details
38436 * MIPS Register packet Format::
38437 * MIPS Breakpoint Kinds::
38440 @node MIPS Register packet Format
38441 @subsubsection @acronym{MIPS} Register Packet Format
38442 @cindex register packet format, @acronym{MIPS}
38444 The following @code{g}/@code{G} packets have previously been defined.
38445 In the below, some thirty-two bit registers are transferred as
38446 sixty-four bits. Those registers should be zero/sign extended (which?)
38447 to fill the space allocated. Register bytes are transferred in target
38448 byte order. The two nibbles within a register byte are transferred
38449 most-significant -- least-significant.
38454 All registers are transferred as thirty-two bit quantities in the order:
38455 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
38456 registers; fsr; fir; fp.
38459 All registers are transferred as sixty-four bit quantities (including
38460 thirty-two bit registers such as @code{sr}). The ordering is the same
38465 @node MIPS Breakpoint Kinds
38466 @subsubsection @acronym{MIPS} Breakpoint Kinds
38467 @cindex breakpoint kinds, @acronym{MIPS}
38469 These breakpoint kinds are defined for the @samp{Z0} and @samp{Z1} packets.
38474 16-bit @acronym{MIPS16} mode breakpoint.
38477 16-bit @acronym{microMIPS} mode breakpoint.
38480 32-bit standard @acronym{MIPS} mode breakpoint.
38483 32-bit @acronym{microMIPS} mode breakpoint.
38487 @node Tracepoint Packets
38488 @section Tracepoint Packets
38489 @cindex tracepoint packets
38490 @cindex packets, tracepoint
38492 Here we describe the packets @value{GDBN} uses to implement
38493 tracepoints (@pxref{Tracepoints}).
38497 @item QTDP:@var{n}:@var{addr}:@var{ena}:@var{step}:@var{pass}[:F@var{flen}][:X@var{len},@var{bytes}]@r{[}-@r{]}
38498 @cindex @samp{QTDP} packet
38499 Create a new tracepoint, number @var{n}, at @var{addr}. If @var{ena}
38500 is @samp{E}, then the tracepoint is enabled; if it is @samp{D}, then
38501 the tracepoint is disabled. The @var{step} gives the tracepoint's step
38502 count, and @var{pass} gives its pass count. If an @samp{F} is present,
38503 then the tracepoint is to be a fast tracepoint, and the @var{flen} is
38504 the number of bytes that the target should copy elsewhere to make room
38505 for the tracepoint. If an @samp{X} is present, it introduces a
38506 tracepoint condition, which consists of a hexadecimal length, followed
38507 by a comma and hex-encoded bytes, in a manner similar to action
38508 encodings as described below. If the trailing @samp{-} is present,
38509 further @samp{QTDP} packets will follow to specify this tracepoint's
38515 The packet was understood and carried out.
38517 @xref{Tracepoint Packets,,Relocate instruction reply packet}.
38519 The packet was not recognized.
38522 @item QTDP:-@var{n}:@var{addr}:@r{[}S@r{]}@var{action}@dots{}@r{[}-@r{]}
38523 Define actions to be taken when a tracepoint is hit. The @var{n} and
38524 @var{addr} must be the same as in the initial @samp{QTDP} packet for
38525 this tracepoint. This packet may only be sent immediately after
38526 another @samp{QTDP} packet that ended with a @samp{-}. If the
38527 trailing @samp{-} is present, further @samp{QTDP} packets will follow,
38528 specifying more actions for this tracepoint.
38530 In the series of action packets for a given tracepoint, at most one
38531 can have an @samp{S} before its first @var{action}. If such a packet
38532 is sent, it and the following packets define ``while-stepping''
38533 actions. Any prior packets define ordinary actions --- that is, those
38534 taken when the tracepoint is first hit. If no action packet has an
38535 @samp{S}, then all the packets in the series specify ordinary
38536 tracepoint actions.
38538 The @samp{@var{action}@dots{}} portion of the packet is a series of
38539 actions, concatenated without separators. Each action has one of the
38545 Collect the registers whose bits are set in @var{mask},
38546 a hexadecimal number whose @var{i}'th bit is set if register number
38547 @var{i} should be collected. (The least significant bit is numbered
38548 zero.) Note that @var{mask} may be any number of digits long; it may
38549 not fit in a 32-bit word.
38551 @item M @var{basereg},@var{offset},@var{len}
38552 Collect @var{len} bytes of memory starting at the address in register
38553 number @var{basereg}, plus @var{offset}. If @var{basereg} is
38554 @samp{-1}, then the range has a fixed address: @var{offset} is the
38555 address of the lowest byte to collect. The @var{basereg},
38556 @var{offset}, and @var{len} parameters are all unsigned hexadecimal
38557 values (the @samp{-1} value for @var{basereg} is a special case).
38559 @item X @var{len},@var{expr}
38560 Evaluate @var{expr}, whose length is @var{len}, and collect memory as
38561 it directs. The agent expression @var{expr} is as described in
38562 @ref{Agent Expressions}. Each byte of the expression is encoded as a
38563 two-digit hex number in the packet; @var{len} is the number of bytes
38564 in the expression (and thus one-half the number of hex digits in the
38569 Any number of actions may be packed together in a single @samp{QTDP}
38570 packet, as long as the packet does not exceed the maximum packet
38571 length (400 bytes, for many stubs). There may be only one @samp{R}
38572 action per tracepoint, and it must precede any @samp{M} or @samp{X}
38573 actions. Any registers referred to by @samp{M} and @samp{X} actions
38574 must be collected by a preceding @samp{R} action. (The
38575 ``while-stepping'' actions are treated as if they were attached to a
38576 separate tracepoint, as far as these restrictions are concerned.)
38581 The packet was understood and carried out.
38583 @xref{Tracepoint Packets,,Relocate instruction reply packet}.
38585 The packet was not recognized.
38588 @item QTDPsrc:@var{n}:@var{addr}:@var{type}:@var{start}:@var{slen}:@var{bytes}
38589 @cindex @samp{QTDPsrc} packet
38590 Specify a source string of tracepoint @var{n} at address @var{addr}.
38591 This is useful to get accurate reproduction of the tracepoints
38592 originally downloaded at the beginning of the trace run. The @var{type}
38593 is the name of the tracepoint part, such as @samp{cond} for the
38594 tracepoint's conditional expression (see below for a list of types), while
38595 @var{bytes} is the string, encoded in hexadecimal.
38597 @var{start} is the offset of the @var{bytes} within the overall source
38598 string, while @var{slen} is the total length of the source string.
38599 This is intended for handling source strings that are longer than will
38600 fit in a single packet.
38601 @c Add detailed example when this info is moved into a dedicated
38602 @c tracepoint descriptions section.
38604 The available string types are @samp{at} for the location,
38605 @samp{cond} for the conditional, and @samp{cmd} for an action command.
38606 @value{GDBN} sends a separate packet for each command in the action
38607 list, in the same order in which the commands are stored in the list.
38609 The target does not need to do anything with source strings except
38610 report them back as part of the replies to the @samp{qTfP}/@samp{qTsP}
38613 Although this packet is optional, and @value{GDBN} will only send it
38614 if the target replies with @samp{TracepointSource} @xref{General
38615 Query Packets}, it makes both disconnected tracing and trace files
38616 much easier to use. Otherwise the user must be careful that the
38617 tracepoints in effect while looking at trace frames are identical to
38618 the ones in effect during the trace run; even a small discrepancy
38619 could cause @samp{tdump} not to work, or a particular trace frame not
38622 @item QTDV:@var{n}:@var{value}:@var{builtin}:@var{name}
38623 @cindex define trace state variable, remote request
38624 @cindex @samp{QTDV} packet
38625 Create a new trace state variable, number @var{n}, with an initial
38626 value of @var{value}, which is a 64-bit signed integer. Both @var{n}
38627 and @var{value} are encoded as hexadecimal values. @value{GDBN} has
38628 the option of not using this packet for initial values of zero; the
38629 target should simply create the trace state variables as they are
38630 mentioned in expressions. The value @var{builtin} should be 1 (one)
38631 if the trace state variable is builtin and 0 (zero) if it is not builtin.
38632 @value{GDBN} only sets @var{builtin} to 1 if a previous @samp{qTfV} or
38633 @samp{qTsV} packet had it set. The contents of @var{name} is the
38634 hex-encoded name (without the leading @samp{$}) of the trace state
38637 @item QTFrame:@var{n}
38638 @cindex @samp{QTFrame} packet
38639 Select the @var{n}'th tracepoint frame from the buffer, and use the
38640 register and memory contents recorded there to answer subsequent
38641 request packets from @value{GDBN}.
38643 A successful reply from the stub indicates that the stub has found the
38644 requested frame. The response is a series of parts, concatenated
38645 without separators, describing the frame we selected. Each part has
38646 one of the following forms:
38650 The selected frame is number @var{n} in the trace frame buffer;
38651 @var{f} is a hexadecimal number. If @var{f} is @samp{-1}, then there
38652 was no frame matching the criteria in the request packet.
38655 The selected trace frame records a hit of tracepoint number @var{t};
38656 @var{t} is a hexadecimal number.
38660 @item QTFrame:pc:@var{addr}
38661 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
38662 currently selected frame whose PC is @var{addr};
38663 @var{addr} is a hexadecimal number.
38665 @item QTFrame:tdp:@var{t}
38666 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
38667 currently selected frame that is a hit of tracepoint @var{t}; @var{t}
38668 is a hexadecimal number.
38670 @item QTFrame:range:@var{start}:@var{end}
38671 Like @samp{QTFrame:@var{n}}, but select the first tracepoint frame after the
38672 currently selected frame whose PC is between @var{start} (inclusive)
38673 and @var{end} (inclusive); @var{start} and @var{end} are hexadecimal
38676 @item QTFrame:outside:@var{start}:@var{end}
38677 Like @samp{QTFrame:range:@var{start}:@var{end}}, but select the first
38678 frame @emph{outside} the given range of addresses (exclusive).
38681 @cindex @samp{qTMinFTPILen} packet
38682 This packet requests the minimum length of instruction at which a fast
38683 tracepoint (@pxref{Set Tracepoints}) may be placed. For instance, on
38684 the 32-bit x86 architecture, it is possible to use a 4-byte jump, but
38685 it depends on the target system being able to create trampolines in
38686 the first 64K of memory, which might or might not be possible for that
38687 system. So the reply to this packet will be 4 if it is able to
38694 The minimum instruction length is currently unknown.
38696 The minimum instruction length is @var{length}, where @var{length}
38697 is a hexadecimal number greater or equal to 1. A reply
38698 of 1 means that a fast tracepoint may be placed on any instruction
38699 regardless of size.
38701 An error has occurred.
38703 An empty reply indicates that the request is not supported by the stub.
38707 @cindex @samp{QTStart} packet
38708 Begin the tracepoint experiment. Begin collecting data from
38709 tracepoint hits in the trace frame buffer. This packet supports the
38710 @samp{qRelocInsn} reply (@pxref{Tracepoint Packets,,Relocate
38711 instruction reply packet}).
38714 @cindex @samp{QTStop} packet
38715 End the tracepoint experiment. Stop collecting trace frames.
38717 @item QTEnable:@var{n}:@var{addr}
38719 @cindex @samp{QTEnable} packet
38720 Enable tracepoint @var{n} at address @var{addr} in a started tracepoint
38721 experiment. If the tracepoint was previously disabled, then collection
38722 of data from it will resume.
38724 @item QTDisable:@var{n}:@var{addr}
38726 @cindex @samp{QTDisable} packet
38727 Disable tracepoint @var{n} at address @var{addr} in a started tracepoint
38728 experiment. No more data will be collected from the tracepoint unless
38729 @samp{QTEnable:@var{n}:@var{addr}} is subsequently issued.
38732 @cindex @samp{QTinit} packet
38733 Clear the table of tracepoints, and empty the trace frame buffer.
38735 @item QTro:@var{start1},@var{end1}:@var{start2},@var{end2}:@dots{}
38736 @cindex @samp{QTro} packet
38737 Establish the given ranges of memory as ``transparent''. The stub
38738 will answer requests for these ranges from memory's current contents,
38739 if they were not collected as part of the tracepoint hit.
38741 @value{GDBN} uses this to mark read-only regions of memory, like those
38742 containing program code. Since these areas never change, they should
38743 still have the same contents they did when the tracepoint was hit, so
38744 there's no reason for the stub to refuse to provide their contents.
38746 @item QTDisconnected:@var{value}
38747 @cindex @samp{QTDisconnected} packet
38748 Set the choice to what to do with the tracing run when @value{GDBN}
38749 disconnects from the target. A @var{value} of 1 directs the target to
38750 continue the tracing run, while 0 tells the target to stop tracing if
38751 @value{GDBN} is no longer in the picture.
38754 @cindex @samp{qTStatus} packet
38755 Ask the stub if there is a trace experiment running right now.
38757 The reply has the form:
38761 @item T@var{running}@r{[};@var{field}@r{]}@dots{}
38762 @var{running} is a single digit @code{1} if the trace is presently
38763 running, or @code{0} if not. It is followed by semicolon-separated
38764 optional fields that an agent may use to report additional status.
38768 If the trace is not running, the agent may report any of several
38769 explanations as one of the optional fields:
38774 No trace has been run yet.
38776 @item tstop[:@var{text}]:0
38777 The trace was stopped by a user-originated stop command. The optional
38778 @var{text} field is a user-supplied string supplied as part of the
38779 stop command (for instance, an explanation of why the trace was
38780 stopped manually). It is hex-encoded.
38783 The trace stopped because the trace buffer filled up.
38785 @item tdisconnected:0
38786 The trace stopped because @value{GDBN} disconnected from the target.
38788 @item tpasscount:@var{tpnum}
38789 The trace stopped because tracepoint @var{tpnum} exceeded its pass count.
38791 @item terror:@var{text}:@var{tpnum}
38792 The trace stopped because tracepoint @var{tpnum} had an error. The
38793 string @var{text} is available to describe the nature of the error
38794 (for instance, a divide by zero in the condition expression); it
38798 The trace stopped for some other reason.
38802 Additional optional fields supply statistical and other information.
38803 Although not required, they are extremely useful for users monitoring
38804 the progress of a trace run. If a trace has stopped, and these
38805 numbers are reported, they must reflect the state of the just-stopped
38810 @item tframes:@var{n}
38811 The number of trace frames in the buffer.
38813 @item tcreated:@var{n}
38814 The total number of trace frames created during the run. This may
38815 be larger than the trace frame count, if the buffer is circular.
38817 @item tsize:@var{n}
38818 The total size of the trace buffer, in bytes.
38820 @item tfree:@var{n}
38821 The number of bytes still unused in the buffer.
38823 @item circular:@var{n}
38824 The value of the circular trace buffer flag. @code{1} means that the
38825 trace buffer is circular and old trace frames will be discarded if
38826 necessary to make room, @code{0} means that the trace buffer is linear
38829 @item disconn:@var{n}
38830 The value of the disconnected tracing flag. @code{1} means that
38831 tracing will continue after @value{GDBN} disconnects, @code{0} means
38832 that the trace run will stop.
38836 @item qTP:@var{tp}:@var{addr}
38837 @cindex tracepoint status, remote request
38838 @cindex @samp{qTP} packet
38839 Ask the stub for the current state of tracepoint number @var{tp} at
38840 address @var{addr}.
38844 @item V@var{hits}:@var{usage}
38845 The tracepoint has been hit @var{hits} times so far during the trace
38846 run, and accounts for @var{usage} in the trace buffer. Note that
38847 @code{while-stepping} steps are not counted as separate hits, but the
38848 steps' space consumption is added into the usage number.
38852 @item qTV:@var{var}
38853 @cindex trace state variable value, remote request
38854 @cindex @samp{qTV} packet
38855 Ask the stub for the value of the trace state variable number @var{var}.
38860 The value of the variable is @var{value}. This will be the current
38861 value of the variable if the user is examining a running target, or a
38862 saved value if the variable was collected in the trace frame that the
38863 user is looking at. Note that multiple requests may result in
38864 different reply values, such as when requesting values while the
38865 program is running.
38868 The value of the variable is unknown. This would occur, for example,
38869 if the user is examining a trace frame in which the requested variable
38874 @cindex @samp{qTfP} packet
38876 @cindex @samp{qTsP} packet
38877 These packets request data about tracepoints that are being used by
38878 the target. @value{GDBN} sends @code{qTfP} to get the first piece
38879 of data, and multiple @code{qTsP} to get additional pieces. Replies
38880 to these packets generally take the form of the @code{QTDP} packets
38881 that define tracepoints. (FIXME add detailed syntax)
38884 @cindex @samp{qTfV} packet
38886 @cindex @samp{qTsV} packet
38887 These packets request data about trace state variables that are on the
38888 target. @value{GDBN} sends @code{qTfV} to get the first vari of data,
38889 and multiple @code{qTsV} to get additional variables. Replies to
38890 these packets follow the syntax of the @code{QTDV} packets that define
38891 trace state variables.
38897 @cindex @samp{qTfSTM} packet
38898 @cindex @samp{qTsSTM} packet
38899 These packets request data about static tracepoint markers that exist
38900 in the target program. @value{GDBN} sends @code{qTfSTM} to get the
38901 first piece of data, and multiple @code{qTsSTM} to get additional
38902 pieces. Replies to these packets take the following form:
38906 @item m @var{address}:@var{id}:@var{extra}
38908 @item m @var{address}:@var{id}:@var{extra},@var{address}:@var{id}:@var{extra}@dots{}
38909 a comma-separated list of markers
38911 (lower case letter @samp{L}) denotes end of list.
38913 An error occurred. The error number @var{nn} is given as hex digits.
38915 An empty reply indicates that the request is not supported by the
38919 The @var{address} is encoded in hex;
38920 @var{id} and @var{extra} are strings encoded in hex.
38922 In response to each query, the target will reply with a list of one or
38923 more markers, separated by commas. @value{GDBN} will respond to each
38924 reply with a request for more markers (using the @samp{qs} form of the
38925 query), until the target responds with @samp{l} (lower-case ell, for
38928 @item qTSTMat:@var{address}
38930 @cindex @samp{qTSTMat} packet
38931 This packets requests data about static tracepoint markers in the
38932 target program at @var{address}. Replies to this packet follow the
38933 syntax of the @samp{qTfSTM} and @code{qTsSTM} packets that list static
38934 tracepoint markers.
38936 @item QTSave:@var{filename}
38937 @cindex @samp{QTSave} packet
38938 This packet directs the target to save trace data to the file name
38939 @var{filename} in the target's filesystem. The @var{filename} is encoded
38940 as a hex string; the interpretation of the file name (relative vs
38941 absolute, wild cards, etc) is up to the target.
38943 @item qTBuffer:@var{offset},@var{len}
38944 @cindex @samp{qTBuffer} packet
38945 Return up to @var{len} bytes of the current contents of trace buffer,
38946 starting at @var{offset}. The trace buffer is treated as if it were
38947 a contiguous collection of traceframes, as per the trace file format.
38948 The reply consists as many hex-encoded bytes as the target can deliver
38949 in a packet; it is not an error to return fewer than were asked for.
38950 A reply consisting of just @code{l} indicates that no bytes are
38953 @item QTBuffer:circular:@var{value}
38954 This packet directs the target to use a circular trace buffer if
38955 @var{value} is 1, or a linear buffer if the value is 0.
38957 @item QTBuffer:size:@var{size}
38958 @anchor{QTBuffer-size}
38959 @cindex @samp{QTBuffer size} packet
38960 This packet directs the target to make the trace buffer be of size
38961 @var{size} if possible. A value of @code{-1} tells the target to
38962 use whatever size it prefers.
38964 @item QTNotes:@r{[}@var{type}:@var{text}@r{]}@r{[};@var{type}:@var{text}@r{]}@dots{}
38965 @cindex @samp{QTNotes} packet
38966 This packet adds optional textual notes to the trace run. Allowable
38967 types include @code{user}, @code{notes}, and @code{tstop}, the
38968 @var{text} fields are arbitrary strings, hex-encoded.
38972 @subsection Relocate instruction reply packet
38973 When installing fast tracepoints in memory, the target may need to
38974 relocate the instruction currently at the tracepoint address to a
38975 different address in memory. For most instructions, a simple copy is
38976 enough, but, for example, call instructions that implicitly push the
38977 return address on the stack, and relative branches or other
38978 PC-relative instructions require offset adjustment, so that the effect
38979 of executing the instruction at a different address is the same as if
38980 it had executed in the original location.
38982 In response to several of the tracepoint packets, the target may also
38983 respond with a number of intermediate @samp{qRelocInsn} request
38984 packets before the final result packet, to have @value{GDBN} handle
38985 this relocation operation. If a packet supports this mechanism, its
38986 documentation will explicitly say so. See for example the above
38987 descriptions for the @samp{QTStart} and @samp{QTDP} packets. The
38988 format of the request is:
38991 @item qRelocInsn:@var{from};@var{to}
38993 This requests @value{GDBN} to copy instruction at address @var{from}
38994 to address @var{to}, possibly adjusted so that executing the
38995 instruction at @var{to} has the same effect as executing it at
38996 @var{from}. @value{GDBN} writes the adjusted instruction to target
38997 memory starting at @var{to}.
39002 @item qRelocInsn:@var{adjusted_size}
39003 Informs the stub the relocation is complete. The @var{adjusted_size} is
39004 the length in bytes of resulting relocated instruction sequence.
39006 A badly formed request was detected, or an error was encountered while
39007 relocating the instruction.
39010 @node Host I/O Packets
39011 @section Host I/O Packets
39012 @cindex Host I/O, remote protocol
39013 @cindex file transfer, remote protocol
39015 The @dfn{Host I/O} packets allow @value{GDBN} to perform I/O
39016 operations on the far side of a remote link. For example, Host I/O is
39017 used to upload and download files to a remote target with its own
39018 filesystem. Host I/O uses the same constant values and data structure
39019 layout as the target-initiated File-I/O protocol. However, the
39020 Host I/O packets are structured differently. The target-initiated
39021 protocol relies on target memory to store parameters and buffers.
39022 Host I/O requests are initiated by @value{GDBN}, and the
39023 target's memory is not involved. @xref{File-I/O Remote Protocol
39024 Extension}, for more details on the target-initiated protocol.
39026 The Host I/O request packets all encode a single operation along with
39027 its arguments. They have this format:
39031 @item vFile:@var{operation}: @var{parameter}@dots{}
39032 @var{operation} is the name of the particular request; the target
39033 should compare the entire packet name up to the second colon when checking
39034 for a supported operation. The format of @var{parameter} depends on
39035 the operation. Numbers are always passed in hexadecimal. Negative
39036 numbers have an explicit minus sign (i.e.@: two's complement is not
39037 used). Strings (e.g.@: filenames) are encoded as a series of
39038 hexadecimal bytes. The last argument to a system call may be a
39039 buffer of escaped binary data (@pxref{Binary Data}).
39043 The valid responses to Host I/O packets are:
39047 @item F @var{result} [, @var{errno}] [; @var{attachment}]
39048 @var{result} is the integer value returned by this operation, usually
39049 non-negative for success and -1 for errors. If an error has occured,
39050 @var{errno} will be included in the result specifying a
39051 value defined by the File-I/O protocol (@pxref{Errno Values}). For
39052 operations which return data, @var{attachment} supplies the data as a
39053 binary buffer. Binary buffers in response packets are escaped in the
39054 normal way (@pxref{Binary Data}). See the individual packet
39055 documentation for the interpretation of @var{result} and
39059 An empty response indicates that this operation is not recognized.
39063 These are the supported Host I/O operations:
39066 @item vFile:open: @var{filename}, @var{flags}, @var{mode}
39067 Open a file at @var{filename} and return a file descriptor for it, or
39068 return -1 if an error occurs. The @var{filename} is a string,
39069 @var{flags} is an integer indicating a mask of open flags
39070 (@pxref{Open Flags}), and @var{mode} is an integer indicating a mask
39071 of mode bits to use if the file is created (@pxref{mode_t Values}).
39072 @xref{open}, for details of the open flags and mode values.
39074 @item vFile:close: @var{fd}
39075 Close the open file corresponding to @var{fd} and return 0, or
39076 -1 if an error occurs.
39078 @item vFile:pread: @var{fd}, @var{count}, @var{offset}
39079 Read data from the open file corresponding to @var{fd}. Up to
39080 @var{count} bytes will be read from the file, starting at @var{offset}
39081 relative to the start of the file. The target may read fewer bytes;
39082 common reasons include packet size limits and an end-of-file
39083 condition. The number of bytes read is returned. Zero should only be
39084 returned for a successful read at the end of the file, or if
39085 @var{count} was zero.
39087 The data read should be returned as a binary attachment on success.
39088 If zero bytes were read, the response should include an empty binary
39089 attachment (i.e.@: a trailing semicolon). The return value is the
39090 number of target bytes read; the binary attachment may be longer if
39091 some characters were escaped.
39093 @item vFile:pwrite: @var{fd}, @var{offset}, @var{data}
39094 Write @var{data} (a binary buffer) to the open file corresponding
39095 to @var{fd}. Start the write at @var{offset} from the start of the
39096 file. Unlike many @code{write} system calls, there is no
39097 separate @var{count} argument; the length of @var{data} in the
39098 packet is used. @samp{vFile:write} returns the number of bytes written,
39099 which may be shorter than the length of @var{data}, or -1 if an
39102 @item vFile:fstat: @var{fd}
39103 Get information about the open file corresponding to @var{fd}.
39104 On success the information is returned as a binary attachment
39105 and the return value is the size of this attachment in bytes.
39106 If an error occurs the return value is -1. The format of the
39107 returned binary attachment is as described in @ref{struct stat}.
39109 @item vFile:unlink: @var{filename}
39110 Delete the file at @var{filename} on the target. Return 0,
39111 or -1 if an error occurs. The @var{filename} is a string.
39113 @item vFile:readlink: @var{filename}
39114 Read value of symbolic link @var{filename} on the target. Return
39115 the number of bytes read, or -1 if an error occurs.
39117 The data read should be returned as a binary attachment on success.
39118 If zero bytes were read, the response should include an empty binary
39119 attachment (i.e.@: a trailing semicolon). The return value is the
39120 number of target bytes read; the binary attachment may be longer if
39121 some characters were escaped.
39123 @item vFile:setfs: @var{pid}
39124 Select the filesystem on which @code{vFile} operations with
39125 @var{filename} arguments will operate. This is required for
39126 @value{GDBN} to be able to access files on remote targets where
39127 the remote stub does not share a common filesystem with the
39130 If @var{pid} is nonzero, select the filesystem as seen by process
39131 @var{pid}. If @var{pid} is zero, select the filesystem as seen by
39132 the remote stub. Return 0 on success, or -1 if an error occurs.
39133 If @code{vFile:setfs:} indicates success, the selected filesystem
39134 remains selected until the next successful @code{vFile:setfs:}
39140 @section Interrupts
39141 @cindex interrupts (remote protocol)
39142 @anchor{interrupting remote targets}
39144 In all-stop mode, when a program on the remote target is running,
39145 @value{GDBN} may attempt to interrupt it by sending a @samp{Ctrl-C},
39146 @code{BREAK} or a @code{BREAK} followed by @code{g}, control of which
39147 is specified via @value{GDBN}'s @samp{interrupt-sequence}.
39149 The precise meaning of @code{BREAK} is defined by the transport
39150 mechanism and may, in fact, be undefined. @value{GDBN} does not
39151 currently define a @code{BREAK} mechanism for any of the network
39152 interfaces except for TCP, in which case @value{GDBN} sends the
39153 @code{telnet} BREAK sequence.
39155 @samp{Ctrl-C}, on the other hand, is defined and implemented for all
39156 transport mechanisms. It is represented by sending the single byte
39157 @code{0x03} without any of the usual packet overhead described in
39158 the Overview section (@pxref{Overview}). When a @code{0x03} byte is
39159 transmitted as part of a packet, it is considered to be packet data
39160 and does @emph{not} represent an interrupt. E.g., an @samp{X} packet
39161 (@pxref{X packet}), used for binary downloads, may include an unescaped
39162 @code{0x03} as part of its packet.
39164 @code{BREAK} followed by @code{g} is also known as Magic SysRq g.
39165 When Linux kernel receives this sequence from serial port,
39166 it stops execution and connects to gdb.
39168 In non-stop mode, because packet resumptions are asynchronous
39169 (@pxref{vCont packet}), @value{GDBN} is always free to send a remote
39170 command to the remote stub, even when the target is running. For that
39171 reason, @value{GDBN} instead sends a regular packet (@pxref{vCtrlC
39172 packet}) with the usual packet framing instead of the single byte
39175 Stubs are not required to recognize these interrupt mechanisms and the
39176 precise meaning associated with receipt of the interrupt is
39177 implementation defined. If the target supports debugging of multiple
39178 threads and/or processes, it should attempt to interrupt all
39179 currently-executing threads and processes.
39180 If the stub is successful at interrupting the
39181 running program, it should send one of the stop
39182 reply packets (@pxref{Stop Reply Packets}) to @value{GDBN} as a result
39183 of successfully stopping the program in all-stop mode, and a stop reply
39184 for each stopped thread in non-stop mode.
39185 Interrupts received while the
39186 program is stopped are queued and the program will be interrupted when
39187 it is resumed next time.
39189 @node Notification Packets
39190 @section Notification Packets
39191 @cindex notification packets
39192 @cindex packets, notification
39194 The @value{GDBN} remote serial protocol includes @dfn{notifications},
39195 packets that require no acknowledgment. Both the GDB and the stub
39196 may send notifications (although the only notifications defined at
39197 present are sent by the stub). Notifications carry information
39198 without incurring the round-trip latency of an acknowledgment, and so
39199 are useful for low-impact communications where occasional packet loss
39202 A notification packet has the form @samp{% @var{data} #
39203 @var{checksum}}, where @var{data} is the content of the notification,
39204 and @var{checksum} is a checksum of @var{data}, computed and formatted
39205 as for ordinary @value{GDBN} packets. A notification's @var{data}
39206 never contains @samp{$}, @samp{%} or @samp{#} characters. Upon
39207 receiving a notification, the recipient sends no @samp{+} or @samp{-}
39208 to acknowledge the notification's receipt or to report its corruption.
39210 Every notification's @var{data} begins with a name, which contains no
39211 colon characters, followed by a colon character.
39213 Recipients should silently ignore corrupted notifications and
39214 notifications they do not understand. Recipients should restart
39215 timeout periods on receipt of a well-formed notification, whether or
39216 not they understand it.
39218 Senders should only send the notifications described here when this
39219 protocol description specifies that they are permitted. In the
39220 future, we may extend the protocol to permit existing notifications in
39221 new contexts; this rule helps older senders avoid confusing newer
39224 (Older versions of @value{GDBN} ignore bytes received until they see
39225 the @samp{$} byte that begins an ordinary packet, so new stubs may
39226 transmit notifications without fear of confusing older clients. There
39227 are no notifications defined for @value{GDBN} to send at the moment, but we
39228 assume that most older stubs would ignore them, as well.)
39230 Each notification is comprised of three parts:
39232 @item @var{name}:@var{event}
39233 The notification packet is sent by the side that initiates the
39234 exchange (currently, only the stub does that), with @var{event}
39235 carrying the specific information about the notification, and
39236 @var{name} specifying the name of the notification.
39238 The acknowledge sent by the other side, usually @value{GDBN}, to
39239 acknowledge the exchange and request the event.
39242 The purpose of an asynchronous notification mechanism is to report to
39243 @value{GDBN} that something interesting happened in the remote stub.
39245 The remote stub may send notification @var{name}:@var{event}
39246 at any time, but @value{GDBN} acknowledges the notification when
39247 appropriate. The notification event is pending before @value{GDBN}
39248 acknowledges. Only one notification at a time may be pending; if
39249 additional events occur before @value{GDBN} has acknowledged the
39250 previous notification, they must be queued by the stub for later
39251 synchronous transmission in response to @var{ack} packets from
39252 @value{GDBN}. Because the notification mechanism is unreliable,
39253 the stub is permitted to resend a notification if it believes
39254 @value{GDBN} may not have received it.
39256 Specifically, notifications may appear when @value{GDBN} is not
39257 otherwise reading input from the stub, or when @value{GDBN} is
39258 expecting to read a normal synchronous response or a
39259 @samp{+}/@samp{-} acknowledgment to a packet it has sent.
39260 Notification packets are distinct from any other communication from
39261 the stub so there is no ambiguity.
39263 After receiving a notification, @value{GDBN} shall acknowledge it by
39264 sending a @var{ack} packet as a regular, synchronous request to the
39265 stub. Such acknowledgment is not required to happen immediately, as
39266 @value{GDBN} is permitted to send other, unrelated packets to the
39267 stub first, which the stub should process normally.
39269 Upon receiving a @var{ack} packet, if the stub has other queued
39270 events to report to @value{GDBN}, it shall respond by sending a
39271 normal @var{event}. @value{GDBN} shall then send another @var{ack}
39272 packet to solicit further responses; again, it is permitted to send
39273 other, unrelated packets as well which the stub should process
39276 If the stub receives a @var{ack} packet and there are no additional
39277 @var{event} to report, the stub shall return an @samp{OK} response.
39278 At this point, @value{GDBN} has finished processing a notification
39279 and the stub has completed sending any queued events. @value{GDBN}
39280 won't accept any new notifications until the final @samp{OK} is
39281 received . If further notification events occur, the stub shall send
39282 a new notification, @value{GDBN} shall accept the notification, and
39283 the process shall be repeated.
39285 The process of asynchronous notification can be illustrated by the
39288 <- @code{%Stop:T0505:98e7ffbf;04:4ce6ffbf;08:b1b6e54c;thread:p7526.7526;core:0;}
39291 <- @code{T0505:68f37db7;04:40f37db7;08:63850408;thread:p7526.7528;core:0;}
39293 <- @code{T0505:68e3fdb6;04:40e3fdb6;08:63850408;thread:p7526.7529;core:0;}
39298 The following notifications are defined:
39299 @multitable @columnfractions 0.12 0.12 0.38 0.38
39308 @tab @var{reply}. The @var{reply} has the form of a stop reply, as
39309 described in @ref{Stop Reply Packets}. Refer to @ref{Remote Non-Stop},
39310 for information on how these notifications are acknowledged by
39312 @tab Report an asynchronous stop event in non-stop mode.
39316 @node Remote Non-Stop
39317 @section Remote Protocol Support for Non-Stop Mode
39319 @value{GDBN}'s remote protocol supports non-stop debugging of
39320 multi-threaded programs, as described in @ref{Non-Stop Mode}. If the stub
39321 supports non-stop mode, it should report that to @value{GDBN} by including
39322 @samp{QNonStop+} in its @samp{qSupported} response (@pxref{qSupported}).
39324 @value{GDBN} typically sends a @samp{QNonStop} packet only when
39325 establishing a new connection with the stub. Entering non-stop mode
39326 does not alter the state of any currently-running threads, but targets
39327 must stop all threads in any already-attached processes when entering
39328 all-stop mode. @value{GDBN} uses the @samp{?} packet as necessary to
39329 probe the target state after a mode change.
39331 In non-stop mode, when an attached process encounters an event that
39332 would otherwise be reported with a stop reply, it uses the
39333 asynchronous notification mechanism (@pxref{Notification Packets}) to
39334 inform @value{GDBN}. In contrast to all-stop mode, where all threads
39335 in all processes are stopped when a stop reply is sent, in non-stop
39336 mode only the thread reporting the stop event is stopped. That is,
39337 when reporting a @samp{S} or @samp{T} response to indicate completion
39338 of a step operation, hitting a breakpoint, or a fault, only the
39339 affected thread is stopped; any other still-running threads continue
39340 to run. When reporting a @samp{W} or @samp{X} response, all running
39341 threads belonging to other attached processes continue to run.
39343 In non-stop mode, the target shall respond to the @samp{?} packet as
39344 follows. First, any incomplete stop reply notification/@samp{vStopped}
39345 sequence in progress is abandoned. The target must begin a new
39346 sequence reporting stop events for all stopped threads, whether or not
39347 it has previously reported those events to @value{GDBN}. The first
39348 stop reply is sent as a synchronous reply to the @samp{?} packet, and
39349 subsequent stop replies are sent as responses to @samp{vStopped} packets
39350 using the mechanism described above. The target must not send
39351 asynchronous stop reply notifications until the sequence is complete.
39352 If all threads are running when the target receives the @samp{?} packet,
39353 or if the target is not attached to any process, it shall respond
39356 If the stub supports non-stop mode, it should also support the
39357 @samp{swbreak} stop reason if software breakpoints are supported, and
39358 the @samp{hwbreak} stop reason if hardware breakpoints are supported
39359 (@pxref{swbreak stop reason}). This is because given the asynchronous
39360 nature of non-stop mode, between the time a thread hits a breakpoint
39361 and the time the event is finally processed by @value{GDBN}, the
39362 breakpoint may have already been removed from the target. Due to
39363 this, @value{GDBN} needs to be able to tell whether a trap stop was
39364 caused by a delayed breakpoint event, which should be ignored, as
39365 opposed to a random trap signal, which should be reported to the user.
39366 Note the @samp{swbreak} feature implies that the target is responsible
39367 for adjusting the PC when a software breakpoint triggers, if
39368 necessary, such as on the x86 architecture.
39370 @node Packet Acknowledgment
39371 @section Packet Acknowledgment
39373 @cindex acknowledgment, for @value{GDBN} remote
39374 @cindex packet acknowledgment, for @value{GDBN} remote
39375 By default, when either the host or the target machine receives a packet,
39376 the first response expected is an acknowledgment: either @samp{+} (to indicate
39377 the package was received correctly) or @samp{-} (to request retransmission).
39378 This mechanism allows the @value{GDBN} remote protocol to operate over
39379 unreliable transport mechanisms, such as a serial line.
39381 In cases where the transport mechanism is itself reliable (such as a pipe or
39382 TCP connection), the @samp{+}/@samp{-} acknowledgments are redundant.
39383 It may be desirable to disable them in that case to reduce communication
39384 overhead, or for other reasons. This can be accomplished by means of the
39385 @samp{QStartNoAckMode} packet; @pxref{QStartNoAckMode}.
39387 When in no-acknowledgment mode, neither the stub nor @value{GDBN} shall send or
39388 expect @samp{+}/@samp{-} protocol acknowledgments. The packet
39389 and response format still includes the normal checksum, as described in
39390 @ref{Overview}, but the checksum may be ignored by the receiver.
39392 If the stub supports @samp{QStartNoAckMode} and prefers to operate in
39393 no-acknowledgment mode, it should report that to @value{GDBN}
39394 by including @samp{QStartNoAckMode+} in its response to @samp{qSupported};
39395 @pxref{qSupported}.
39396 If @value{GDBN} also supports @samp{QStartNoAckMode} and it has not been
39397 disabled via the @code{set remote noack-packet off} command
39398 (@pxref{Remote Configuration}),
39399 @value{GDBN} may then send a @samp{QStartNoAckMode} packet to the stub.
39400 Only then may the stub actually turn off packet acknowledgments.
39401 @value{GDBN} sends a final @samp{+} acknowledgment of the stub's @samp{OK}
39402 response, which can be safely ignored by the stub.
39404 Note that @code{set remote noack-packet} command only affects negotiation
39405 between @value{GDBN} and the stub when subsequent connections are made;
39406 it does not affect the protocol acknowledgment state for any current
39408 Since @samp{+}/@samp{-} acknowledgments are enabled by default when a
39409 new connection is established,
39410 there is also no protocol request to re-enable the acknowledgments
39411 for the current connection, once disabled.
39416 Example sequence of a target being re-started. Notice how the restart
39417 does not get any direct output:
39422 @emph{target restarts}
39425 <- @code{T001:1234123412341234}
39429 Example sequence of a target being stepped by a single instruction:
39432 -> @code{G1445@dots{}}
39437 <- @code{T001:1234123412341234}
39441 <- @code{1455@dots{}}
39445 @node File-I/O Remote Protocol Extension
39446 @section File-I/O Remote Protocol Extension
39447 @cindex File-I/O remote protocol extension
39450 * File-I/O Overview::
39451 * Protocol Basics::
39452 * The F Request Packet::
39453 * The F Reply Packet::
39454 * The Ctrl-C Message::
39456 * List of Supported Calls::
39457 * Protocol-specific Representation of Datatypes::
39459 * File-I/O Examples::
39462 @node File-I/O Overview
39463 @subsection File-I/O Overview
39464 @cindex file-i/o overview
39466 The @dfn{File I/O remote protocol extension} (short: File-I/O) allows the
39467 target to use the host's file system and console I/O to perform various
39468 system calls. System calls on the target system are translated into a
39469 remote protocol packet to the host system, which then performs the needed
39470 actions and returns a response packet to the target system.
39471 This simulates file system operations even on targets that lack file systems.
39473 The protocol is defined to be independent of both the host and target systems.
39474 It uses its own internal representation of datatypes and values. Both
39475 @value{GDBN} and the target's @value{GDBN} stub are responsible for
39476 translating the system-dependent value representations into the internal
39477 protocol representations when data is transmitted.
39479 The communication is synchronous. A system call is possible only when
39480 @value{GDBN} is waiting for a response from the @samp{C}, @samp{c}, @samp{S}
39481 or @samp{s} packets. While @value{GDBN} handles the request for a system call,
39482 the target is stopped to allow deterministic access to the target's
39483 memory. Therefore File-I/O is not interruptible by target signals. On
39484 the other hand, it is possible to interrupt File-I/O by a user interrupt
39485 (@samp{Ctrl-C}) within @value{GDBN}.
39487 The target's request to perform a host system call does not finish
39488 the latest @samp{C}, @samp{c}, @samp{S} or @samp{s} action. That means,
39489 after finishing the system call, the target returns to continuing the
39490 previous activity (continue, step). No additional continue or step
39491 request from @value{GDBN} is required.
39494 (@value{GDBP}) continue
39495 <- target requests 'system call X'
39496 target is stopped, @value{GDBN} executes system call
39497 -> @value{GDBN} returns result
39498 ... target continues, @value{GDBN} returns to wait for the target
39499 <- target hits breakpoint and sends a Txx packet
39502 The protocol only supports I/O on the console and to regular files on
39503 the host file system. Character or block special devices, pipes,
39504 named pipes, sockets or any other communication method on the host
39505 system are not supported by this protocol.
39507 File I/O is not supported in non-stop mode.
39509 @node Protocol Basics
39510 @subsection Protocol Basics
39511 @cindex protocol basics, file-i/o
39513 The File-I/O protocol uses the @code{F} packet as the request as well
39514 as reply packet. Since a File-I/O system call can only occur when
39515 @value{GDBN} is waiting for a response from the continuing or stepping target,
39516 the File-I/O request is a reply that @value{GDBN} has to expect as a result
39517 of a previous @samp{C}, @samp{c}, @samp{S} or @samp{s} packet.
39518 This @code{F} packet contains all information needed to allow @value{GDBN}
39519 to call the appropriate host system call:
39523 A unique identifier for the requested system call.
39526 All parameters to the system call. Pointers are given as addresses
39527 in the target memory address space. Pointers to strings are given as
39528 pointer/length pair. Numerical values are given as they are.
39529 Numerical control flags are given in a protocol-specific representation.
39533 At this point, @value{GDBN} has to perform the following actions.
39537 If the parameters include pointer values to data needed as input to a
39538 system call, @value{GDBN} requests this data from the target with a
39539 standard @code{m} packet request. This additional communication has to be
39540 expected by the target implementation and is handled as any other @code{m}
39544 @value{GDBN} translates all value from protocol representation to host
39545 representation as needed. Datatypes are coerced into the host types.
39548 @value{GDBN} calls the system call.
39551 It then coerces datatypes back to protocol representation.
39554 If the system call is expected to return data in buffer space specified
39555 by pointer parameters to the call, the data is transmitted to the
39556 target using a @code{M} or @code{X} packet. This packet has to be expected
39557 by the target implementation and is handled as any other @code{M} or @code{X}
39562 Eventually @value{GDBN} replies with another @code{F} packet which contains all
39563 necessary information for the target to continue. This at least contains
39570 @code{errno}, if has been changed by the system call.
39577 After having done the needed type and value coercion, the target continues
39578 the latest continue or step action.
39580 @node The F Request Packet
39581 @subsection The @code{F} Request Packet
39582 @cindex file-i/o request packet
39583 @cindex @code{F} request packet
39585 The @code{F} request packet has the following format:
39588 @item F@var{call-id},@var{parameter@dots{}}
39590 @var{call-id} is the identifier to indicate the host system call to be called.
39591 This is just the name of the function.
39593 @var{parameter@dots{}} are the parameters to the system call.
39594 Parameters are hexadecimal integer values, either the actual values in case
39595 of scalar datatypes, pointers to target buffer space in case of compound
39596 datatypes and unspecified memory areas, or pointer/length pairs in case
39597 of string parameters. These are appended to the @var{call-id} as a
39598 comma-delimited list. All values are transmitted in ASCII
39599 string representation, pointer/length pairs separated by a slash.
39605 @node The F Reply Packet
39606 @subsection The @code{F} Reply Packet
39607 @cindex file-i/o reply packet
39608 @cindex @code{F} reply packet
39610 The @code{F} reply packet has the following format:
39614 @item F@var{retcode},@var{errno},@var{Ctrl-C flag};@var{call-specific attachment}
39616 @var{retcode} is the return code of the system call as hexadecimal value.
39618 @var{errno} is the @code{errno} set by the call, in protocol-specific
39620 This parameter can be omitted if the call was successful.
39622 @var{Ctrl-C flag} is only sent if the user requested a break. In this
39623 case, @var{errno} must be sent as well, even if the call was successful.
39624 The @var{Ctrl-C flag} itself consists of the character @samp{C}:
39631 or, if the call was interrupted before the host call has been performed:
39638 assuming 4 is the protocol-specific representation of @code{EINTR}.
39643 @node The Ctrl-C Message
39644 @subsection The @samp{Ctrl-C} Message
39645 @cindex ctrl-c message, in file-i/o protocol
39647 If the @samp{Ctrl-C} flag is set in the @value{GDBN}
39648 reply packet (@pxref{The F Reply Packet}),
39649 the target should behave as if it had
39650 gotten a break message. The meaning for the target is ``system call
39651 interrupted by @code{SIGINT}''. Consequentially, the target should actually stop
39652 (as with a break message) and return to @value{GDBN} with a @code{T02}
39655 It's important for the target to know in which
39656 state the system call was interrupted. There are two possible cases:
39660 The system call hasn't been performed on the host yet.
39663 The system call on the host has been finished.
39667 These two states can be distinguished by the target by the value of the
39668 returned @code{errno}. If it's the protocol representation of @code{EINTR}, the system
39669 call hasn't been performed. This is equivalent to the @code{EINTR} handling
39670 on POSIX systems. In any other case, the target may presume that the
39671 system call has been finished --- successfully or not --- and should behave
39672 as if the break message arrived right after the system call.
39674 @value{GDBN} must behave reliably. If the system call has not been called
39675 yet, @value{GDBN} may send the @code{F} reply immediately, setting @code{EINTR} as
39676 @code{errno} in the packet. If the system call on the host has been finished
39677 before the user requests a break, the full action must be finished by
39678 @value{GDBN}. This requires sending @code{M} or @code{X} packets as necessary.
39679 The @code{F} packet may only be sent when either nothing has happened
39680 or the full action has been completed.
39683 @subsection Console I/O
39684 @cindex console i/o as part of file-i/o
39686 By default and if not explicitly closed by the target system, the file
39687 descriptors 0, 1 and 2 are connected to the @value{GDBN} console. Output
39688 on the @value{GDBN} console is handled as any other file output operation
39689 (@code{write(1, @dots{})} or @code{write(2, @dots{})}). Console input is handled
39690 by @value{GDBN} so that after the target read request from file descriptor
39691 0 all following typing is buffered until either one of the following
39696 The user types @kbd{Ctrl-c}. The behaviour is as explained above, and the
39698 system call is treated as finished.
39701 The user presses @key{RET}. This is treated as end of input with a trailing
39705 The user types @kbd{Ctrl-d}. This is treated as end of input. No trailing
39706 character (neither newline nor @samp{Ctrl-D}) is appended to the input.
39710 If the user has typed more characters than fit in the buffer given to
39711 the @code{read} call, the trailing characters are buffered in @value{GDBN} until
39712 either another @code{read(0, @dots{})} is requested by the target, or debugging
39713 is stopped at the user's request.
39716 @node List of Supported Calls
39717 @subsection List of Supported Calls
39718 @cindex list of supported file-i/o calls
39735 @unnumberedsubsubsec open
39736 @cindex open, file-i/o system call
39741 int open(const char *pathname, int flags);
39742 int open(const char *pathname, int flags, mode_t mode);
39746 @samp{Fopen,@var{pathptr}/@var{len},@var{flags},@var{mode}}
39749 @var{flags} is the bitwise @code{OR} of the following values:
39753 If the file does not exist it will be created. The host
39754 rules apply as far as file ownership and time stamps
39758 When used with @code{O_CREAT}, if the file already exists it is
39759 an error and open() fails.
39762 If the file already exists and the open mode allows
39763 writing (@code{O_RDWR} or @code{O_WRONLY} is given) it will be
39764 truncated to zero length.
39767 The file is opened in append mode.
39770 The file is opened for reading only.
39773 The file is opened for writing only.
39776 The file is opened for reading and writing.
39780 Other bits are silently ignored.
39784 @var{mode} is the bitwise @code{OR} of the following values:
39788 User has read permission.
39791 User has write permission.
39794 Group has read permission.
39797 Group has write permission.
39800 Others have read permission.
39803 Others have write permission.
39807 Other bits are silently ignored.
39810 @item Return value:
39811 @code{open} returns the new file descriptor or -1 if an error
39818 @var{pathname} already exists and @code{O_CREAT} and @code{O_EXCL} were used.
39821 @var{pathname} refers to a directory.
39824 The requested access is not allowed.
39827 @var{pathname} was too long.
39830 A directory component in @var{pathname} does not exist.
39833 @var{pathname} refers to a device, pipe, named pipe or socket.
39836 @var{pathname} refers to a file on a read-only filesystem and
39837 write access was requested.
39840 @var{pathname} is an invalid pointer value.
39843 No space on device to create the file.
39846 The process already has the maximum number of files open.
39849 The limit on the total number of files open on the system
39853 The call was interrupted by the user.
39859 @unnumberedsubsubsec close
39860 @cindex close, file-i/o system call
39869 @samp{Fclose,@var{fd}}
39871 @item Return value:
39872 @code{close} returns zero on success, or -1 if an error occurred.
39878 @var{fd} isn't a valid open file descriptor.
39881 The call was interrupted by the user.
39887 @unnumberedsubsubsec read
39888 @cindex read, file-i/o system call
39893 int read(int fd, void *buf, unsigned int count);
39897 @samp{Fread,@var{fd},@var{bufptr},@var{count}}
39899 @item Return value:
39900 On success, the number of bytes read is returned.
39901 Zero indicates end of file. If count is zero, read
39902 returns zero as well. On error, -1 is returned.
39908 @var{fd} is not a valid file descriptor or is not open for
39912 @var{bufptr} is an invalid pointer value.
39915 The call was interrupted by the user.
39921 @unnumberedsubsubsec write
39922 @cindex write, file-i/o system call
39927 int write(int fd, const void *buf, unsigned int count);
39931 @samp{Fwrite,@var{fd},@var{bufptr},@var{count}}
39933 @item Return value:
39934 On success, the number of bytes written are returned.
39935 Zero indicates nothing was written. On error, -1
39942 @var{fd} is not a valid file descriptor or is not open for
39946 @var{bufptr} is an invalid pointer value.
39949 An attempt was made to write a file that exceeds the
39950 host-specific maximum file size allowed.
39953 No space on device to write the data.
39956 The call was interrupted by the user.
39962 @unnumberedsubsubsec lseek
39963 @cindex lseek, file-i/o system call
39968 long lseek (int fd, long offset, int flag);
39972 @samp{Flseek,@var{fd},@var{offset},@var{flag}}
39974 @var{flag} is one of:
39978 The offset is set to @var{offset} bytes.
39981 The offset is set to its current location plus @var{offset}
39985 The offset is set to the size of the file plus @var{offset}
39989 @item Return value:
39990 On success, the resulting unsigned offset in bytes from
39991 the beginning of the file is returned. Otherwise, a
39992 value of -1 is returned.
39998 @var{fd} is not a valid open file descriptor.
40001 @var{fd} is associated with the @value{GDBN} console.
40004 @var{flag} is not a proper value.
40007 The call was interrupted by the user.
40013 @unnumberedsubsubsec rename
40014 @cindex rename, file-i/o system call
40019 int rename(const char *oldpath, const char *newpath);
40023 @samp{Frename,@var{oldpathptr}/@var{len},@var{newpathptr}/@var{len}}
40025 @item Return value:
40026 On success, zero is returned. On error, -1 is returned.
40032 @var{newpath} is an existing directory, but @var{oldpath} is not a
40036 @var{newpath} is a non-empty directory.
40039 @var{oldpath} or @var{newpath} is a directory that is in use by some
40043 An attempt was made to make a directory a subdirectory
40047 A component used as a directory in @var{oldpath} or new
40048 path is not a directory. Or @var{oldpath} is a directory
40049 and @var{newpath} exists but is not a directory.
40052 @var{oldpathptr} or @var{newpathptr} are invalid pointer values.
40055 No access to the file or the path of the file.
40059 @var{oldpath} or @var{newpath} was too long.
40062 A directory component in @var{oldpath} or @var{newpath} does not exist.
40065 The file is on a read-only filesystem.
40068 The device containing the file has no room for the new
40072 The call was interrupted by the user.
40078 @unnumberedsubsubsec unlink
40079 @cindex unlink, file-i/o system call
40084 int unlink(const char *pathname);
40088 @samp{Funlink,@var{pathnameptr}/@var{len}}
40090 @item Return value:
40091 On success, zero is returned. On error, -1 is returned.
40097 No access to the file or the path of the file.
40100 The system does not allow unlinking of directories.
40103 The file @var{pathname} cannot be unlinked because it's
40104 being used by another process.
40107 @var{pathnameptr} is an invalid pointer value.
40110 @var{pathname} was too long.
40113 A directory component in @var{pathname} does not exist.
40116 A component of the path is not a directory.
40119 The file is on a read-only filesystem.
40122 The call was interrupted by the user.
40128 @unnumberedsubsubsec stat/fstat
40129 @cindex fstat, file-i/o system call
40130 @cindex stat, file-i/o system call
40135 int stat(const char *pathname, struct stat *buf);
40136 int fstat(int fd, struct stat *buf);
40140 @samp{Fstat,@var{pathnameptr}/@var{len},@var{bufptr}}@*
40141 @samp{Ffstat,@var{fd},@var{bufptr}}
40143 @item Return value:
40144 On success, zero is returned. On error, -1 is returned.
40150 @var{fd} is not a valid open file.
40153 A directory component in @var{pathname} does not exist or the
40154 path is an empty string.
40157 A component of the path is not a directory.
40160 @var{pathnameptr} is an invalid pointer value.
40163 No access to the file or the path of the file.
40166 @var{pathname} was too long.
40169 The call was interrupted by the user.
40175 @unnumberedsubsubsec gettimeofday
40176 @cindex gettimeofday, file-i/o system call
40181 int gettimeofday(struct timeval *tv, void *tz);
40185 @samp{Fgettimeofday,@var{tvptr},@var{tzptr}}
40187 @item Return value:
40188 On success, 0 is returned, -1 otherwise.
40194 @var{tz} is a non-NULL pointer.
40197 @var{tvptr} and/or @var{tzptr} is an invalid pointer value.
40203 @unnumberedsubsubsec isatty
40204 @cindex isatty, file-i/o system call
40209 int isatty(int fd);
40213 @samp{Fisatty,@var{fd}}
40215 @item Return value:
40216 Returns 1 if @var{fd} refers to the @value{GDBN} console, 0 otherwise.
40222 The call was interrupted by the user.
40227 Note that the @code{isatty} call is treated as a special case: it returns
40228 1 to the target if the file descriptor is attached
40229 to the @value{GDBN} console, 0 otherwise. Implementing through system calls
40230 would require implementing @code{ioctl} and would be more complex than
40235 @unnumberedsubsubsec system
40236 @cindex system, file-i/o system call
40241 int system(const char *command);
40245 @samp{Fsystem,@var{commandptr}/@var{len}}
40247 @item Return value:
40248 If @var{len} is zero, the return value indicates whether a shell is
40249 available. A zero return value indicates a shell is not available.
40250 For non-zero @var{len}, the value returned is -1 on error and the
40251 return status of the command otherwise. Only the exit status of the
40252 command is returned, which is extracted from the host's @code{system}
40253 return value by calling @code{WEXITSTATUS(retval)}. In case
40254 @file{/bin/sh} could not be executed, 127 is returned.
40260 The call was interrupted by the user.
40265 @value{GDBN} takes over the full task of calling the necessary host calls
40266 to perform the @code{system} call. The return value of @code{system} on
40267 the host is simplified before it's returned
40268 to the target. Any termination signal information from the child process
40269 is discarded, and the return value consists
40270 entirely of the exit status of the called command.
40272 Due to security concerns, the @code{system} call is by default refused
40273 by @value{GDBN}. The user has to allow this call explicitly with the
40274 @code{set remote system-call-allowed 1} command.
40277 @item set remote system-call-allowed
40278 @kindex set remote system-call-allowed
40279 Control whether to allow the @code{system} calls in the File I/O
40280 protocol for the remote target. The default is zero (disabled).
40282 @item show remote system-call-allowed
40283 @kindex show remote system-call-allowed
40284 Show whether the @code{system} calls are allowed in the File I/O
40288 @node Protocol-specific Representation of Datatypes
40289 @subsection Protocol-specific Representation of Datatypes
40290 @cindex protocol-specific representation of datatypes, in file-i/o protocol
40293 * Integral Datatypes::
40295 * Memory Transfer::
40300 @node Integral Datatypes
40301 @unnumberedsubsubsec Integral Datatypes
40302 @cindex integral datatypes, in file-i/o protocol
40304 The integral datatypes used in the system calls are @code{int},
40305 @code{unsigned int}, @code{long}, @code{unsigned long},
40306 @code{mode_t}, and @code{time_t}.
40308 @code{int}, @code{unsigned int}, @code{mode_t} and @code{time_t} are
40309 implemented as 32 bit values in this protocol.
40311 @code{long} and @code{unsigned long} are implemented as 64 bit types.
40313 @xref{Limits}, for corresponding MIN and MAX values (similar to those
40314 in @file{limits.h}) to allow range checking on host and target.
40316 @code{time_t} datatypes are defined as seconds since the Epoch.
40318 All integral datatypes transferred as part of a memory read or write of a
40319 structured datatype e.g.@: a @code{struct stat} have to be given in big endian
40322 @node Pointer Values
40323 @unnumberedsubsubsec Pointer Values
40324 @cindex pointer values, in file-i/o protocol
40326 Pointers to target data are transmitted as they are. An exception
40327 is made for pointers to buffers for which the length isn't
40328 transmitted as part of the function call, namely strings. Strings
40329 are transmitted as a pointer/length pair, both as hex values, e.g.@:
40336 which is a pointer to data of length 18 bytes at position 0x1aaf.
40337 The length is defined as the full string length in bytes, including
40338 the trailing null byte. For example, the string @code{"hello world"}
40339 at address 0x123456 is transmitted as
40345 @node Memory Transfer
40346 @unnumberedsubsubsec Memory Transfer
40347 @cindex memory transfer, in file-i/o protocol
40349 Structured data which is transferred using a memory read or write (for
40350 example, a @code{struct stat}) is expected to be in a protocol-specific format
40351 with all scalar multibyte datatypes being big endian. Translation to
40352 this representation needs to be done both by the target before the @code{F}
40353 packet is sent, and by @value{GDBN} before
40354 it transfers memory to the target. Transferred pointers to structured
40355 data should point to the already-coerced data at any time.
40359 @unnumberedsubsubsec struct stat
40360 @cindex struct stat, in file-i/o protocol
40362 The buffer of type @code{struct stat} used by the target and @value{GDBN}
40363 is defined as follows:
40367 unsigned int st_dev; /* device */
40368 unsigned int st_ino; /* inode */
40369 mode_t st_mode; /* protection */
40370 unsigned int st_nlink; /* number of hard links */
40371 unsigned int st_uid; /* user ID of owner */
40372 unsigned int st_gid; /* group ID of owner */
40373 unsigned int st_rdev; /* device type (if inode device) */
40374 unsigned long st_size; /* total size, in bytes */
40375 unsigned long st_blksize; /* blocksize for filesystem I/O */
40376 unsigned long st_blocks; /* number of blocks allocated */
40377 time_t st_atime; /* time of last access */
40378 time_t st_mtime; /* time of last modification */
40379 time_t st_ctime; /* time of last change */
40383 The integral datatypes conform to the definitions given in the
40384 appropriate section (see @ref{Integral Datatypes}, for details) so this
40385 structure is of size 64 bytes.
40387 The values of several fields have a restricted meaning and/or
40393 A value of 0 represents a file, 1 the console.
40396 No valid meaning for the target. Transmitted unchanged.
40399 Valid mode bits are described in @ref{Constants}. Any other
40400 bits have currently no meaning for the target.
40405 No valid meaning for the target. Transmitted unchanged.
40410 These values have a host and file system dependent
40411 accuracy. Especially on Windows hosts, the file system may not
40412 support exact timing values.
40415 The target gets a @code{struct stat} of the above representation and is
40416 responsible for coercing it to the target representation before
40419 Note that due to size differences between the host, target, and protocol
40420 representations of @code{struct stat} members, these members could eventually
40421 get truncated on the target.
40423 @node struct timeval
40424 @unnumberedsubsubsec struct timeval
40425 @cindex struct timeval, in file-i/o protocol
40427 The buffer of type @code{struct timeval} used by the File-I/O protocol
40428 is defined as follows:
40432 time_t tv_sec; /* second */
40433 long tv_usec; /* microsecond */
40437 The integral datatypes conform to the definitions given in the
40438 appropriate section (see @ref{Integral Datatypes}, for details) so this
40439 structure is of size 8 bytes.
40442 @subsection Constants
40443 @cindex constants, in file-i/o protocol
40445 The following values are used for the constants inside of the
40446 protocol. @value{GDBN} and target are responsible for translating these
40447 values before and after the call as needed.
40458 @unnumberedsubsubsec Open Flags
40459 @cindex open flags, in file-i/o protocol
40461 All values are given in hexadecimal representation.
40473 @node mode_t Values
40474 @unnumberedsubsubsec mode_t Values
40475 @cindex mode_t values, in file-i/o protocol
40477 All values are given in octal representation.
40494 @unnumberedsubsubsec Errno Values
40495 @cindex errno values, in file-i/o protocol
40497 All values are given in decimal representation.
40522 @code{EUNKNOWN} is used as a fallback error value if a host system returns
40523 any error value not in the list of supported error numbers.
40526 @unnumberedsubsubsec Lseek Flags
40527 @cindex lseek flags, in file-i/o protocol
40536 @unnumberedsubsubsec Limits
40537 @cindex limits, in file-i/o protocol
40539 All values are given in decimal representation.
40542 INT_MIN -2147483648
40544 UINT_MAX 4294967295
40545 LONG_MIN -9223372036854775808
40546 LONG_MAX 9223372036854775807
40547 ULONG_MAX 18446744073709551615
40550 @node File-I/O Examples
40551 @subsection File-I/O Examples
40552 @cindex file-i/o examples
40554 Example sequence of a write call, file descriptor 3, buffer is at target
40555 address 0x1234, 6 bytes should be written:
40558 <- @code{Fwrite,3,1234,6}
40559 @emph{request memory read from target}
40562 @emph{return "6 bytes written"}
40566 Example sequence of a read call, file descriptor 3, buffer is at target
40567 address 0x1234, 6 bytes should be read:
40570 <- @code{Fread,3,1234,6}
40571 @emph{request memory write to target}
40572 -> @code{X1234,6:XXXXXX}
40573 @emph{return "6 bytes read"}
40577 Example sequence of a read call, call fails on the host due to invalid
40578 file descriptor (@code{EBADF}):
40581 <- @code{Fread,3,1234,6}
40585 Example sequence of a read call, user presses @kbd{Ctrl-c} before syscall on
40589 <- @code{Fread,3,1234,6}
40594 Example sequence of a read call, user presses @kbd{Ctrl-c} after syscall on
40598 <- @code{Fread,3,1234,6}
40599 -> @code{X1234,6:XXXXXX}
40603 @node Library List Format
40604 @section Library List Format
40605 @cindex library list format, remote protocol
40607 On some platforms, a dynamic loader (e.g.@: @file{ld.so}) runs in the
40608 same process as your application to manage libraries. In this case,
40609 @value{GDBN} can use the loader's symbol table and normal memory
40610 operations to maintain a list of shared libraries. On other
40611 platforms, the operating system manages loaded libraries.
40612 @value{GDBN} can not retrieve the list of currently loaded libraries
40613 through memory operations, so it uses the @samp{qXfer:libraries:read}
40614 packet (@pxref{qXfer library list read}) instead. The remote stub
40615 queries the target's operating system and reports which libraries
40618 The @samp{qXfer:libraries:read} packet returns an XML document which
40619 lists loaded libraries and their offsets. Each library has an
40620 associated name and one or more segment or section base addresses,
40621 which report where the library was loaded in memory.
40623 For the common case of libraries that are fully linked binaries, the
40624 library should have a list of segments. If the target supports
40625 dynamic linking of a relocatable object file, its library XML element
40626 should instead include a list of allocated sections. The segment or
40627 section bases are start addresses, not relocation offsets; they do not
40628 depend on the library's link-time base addresses.
40630 @value{GDBN} must be linked with the Expat library to support XML
40631 library lists. @xref{Expat}.
40633 A simple memory map, with one loaded library relocated by a single
40634 offset, looks like this:
40638 <library name="/lib/libc.so.6">
40639 <segment address="0x10000000"/>
40644 Another simple memory map, with one loaded library with three
40645 allocated sections (.text, .data, .bss), looks like this:
40649 <library name="sharedlib.o">
40650 <section address="0x10000000"/>
40651 <section address="0x20000000"/>
40652 <section address="0x30000000"/>
40657 The format of a library list is described by this DTD:
40660 <!-- library-list: Root element with versioning -->
40661 <!ELEMENT library-list (library)*>
40662 <!ATTLIST library-list version CDATA #FIXED "1.0">
40663 <!ELEMENT library (segment*, section*)>
40664 <!ATTLIST library name CDATA #REQUIRED>
40665 <!ELEMENT segment EMPTY>
40666 <!ATTLIST segment address CDATA #REQUIRED>
40667 <!ELEMENT section EMPTY>
40668 <!ATTLIST section address CDATA #REQUIRED>
40671 In addition, segments and section descriptors cannot be mixed within a
40672 single library element, and you must supply at least one segment or
40673 section for each library.
40675 @node Library List Format for SVR4 Targets
40676 @section Library List Format for SVR4 Targets
40677 @cindex library list format, remote protocol
40679 On SVR4 platforms @value{GDBN} can use the symbol table of a dynamic loader
40680 (e.g.@: @file{ld.so}) and normal memory operations to maintain a list of
40681 shared libraries. Still a special library list provided by this packet is
40682 more efficient for the @value{GDBN} remote protocol.
40684 The @samp{qXfer:libraries-svr4:read} packet returns an XML document which lists
40685 loaded libraries and their SVR4 linker parameters. For each library on SVR4
40686 target, the following parameters are reported:
40690 @code{name}, the absolute file name from the @code{l_name} field of
40691 @code{struct link_map}.
40693 @code{lm} with address of @code{struct link_map} used for TLS
40694 (Thread Local Storage) access.
40696 @code{l_addr}, the displacement as read from the field @code{l_addr} of
40697 @code{struct link_map}. For prelinked libraries this is not an absolute
40698 memory address. It is a displacement of absolute memory address against
40699 address the file was prelinked to during the library load.
40701 @code{l_ld}, which is memory address of the @code{PT_DYNAMIC} segment
40704 Additionally the single @code{main-lm} attribute specifies address of
40705 @code{struct link_map} used for the main executable. This parameter is used
40706 for TLS access and its presence is optional.
40708 @value{GDBN} must be linked with the Expat library to support XML
40709 SVR4 library lists. @xref{Expat}.
40711 A simple memory map, with two loaded libraries (which do not use prelink),
40715 <library-list-svr4 version="1.0" main-lm="0xe4f8f8">
40716 <library name="/lib/ld-linux.so.2" lm="0xe4f51c" l_addr="0xe2d000"
40718 <library name="/lib/libc.so.6" lm="0xe4fbe8" l_addr="0x154000"
40720 </library-list-svr>
40723 The format of an SVR4 library list is described by this DTD:
40726 <!-- library-list-svr4: Root element with versioning -->
40727 <!ELEMENT library-list-svr4 (library)*>
40728 <!ATTLIST library-list-svr4 version CDATA #FIXED "1.0">
40729 <!ATTLIST library-list-svr4 main-lm CDATA #IMPLIED>
40730 <!ELEMENT library EMPTY>
40731 <!ATTLIST library name CDATA #REQUIRED>
40732 <!ATTLIST library lm CDATA #REQUIRED>
40733 <!ATTLIST library l_addr CDATA #REQUIRED>
40734 <!ATTLIST library l_ld CDATA #REQUIRED>
40737 @node Memory Map Format
40738 @section Memory Map Format
40739 @cindex memory map format
40741 To be able to write into flash memory, @value{GDBN} needs to obtain a
40742 memory map from the target. This section describes the format of the
40745 The memory map is obtained using the @samp{qXfer:memory-map:read}
40746 (@pxref{qXfer memory map read}) packet and is an XML document that
40747 lists memory regions.
40749 @value{GDBN} must be linked with the Expat library to support XML
40750 memory maps. @xref{Expat}.
40752 The top-level structure of the document is shown below:
40755 <?xml version="1.0"?>
40756 <!DOCTYPE memory-map
40757 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
40758 "http://sourceware.org/gdb/gdb-memory-map.dtd">
40764 Each region can be either:
40769 A region of RAM starting at @var{addr} and extending for @var{length}
40773 <memory type="ram" start="@var{addr}" length="@var{length}"/>
40778 A region of read-only memory:
40781 <memory type="rom" start="@var{addr}" length="@var{length}"/>
40786 A region of flash memory, with erasure blocks @var{blocksize}
40790 <memory type="flash" start="@var{addr}" length="@var{length}">
40791 <property name="blocksize">@var{blocksize}</property>
40797 Regions must not overlap. @value{GDBN} assumes that areas of memory not covered
40798 by the memory map are RAM, and uses the ordinary @samp{M} and @samp{X}
40799 packets to write to addresses in such ranges.
40801 The formal DTD for memory map format is given below:
40804 <!-- ................................................... -->
40805 <!-- Memory Map XML DTD ................................ -->
40806 <!-- File: memory-map.dtd .............................. -->
40807 <!-- .................................... .............. -->
40808 <!-- memory-map.dtd -->
40809 <!-- memory-map: Root element with versioning -->
40810 <!ELEMENT memory-map (memory | property)>
40811 <!ATTLIST memory-map version CDATA #FIXED "1.0.0">
40812 <!ELEMENT memory (property)>
40813 <!-- memory: Specifies a memory region,
40814 and its type, or device. -->
40815 <!ATTLIST memory type CDATA #REQUIRED
40816 start CDATA #REQUIRED
40817 length CDATA #REQUIRED
40818 device CDATA #IMPLIED>
40819 <!-- property: Generic attribute tag -->
40820 <!ELEMENT property (#PCDATA | property)*>
40821 <!ATTLIST property name CDATA #REQUIRED>
40824 @node Thread List Format
40825 @section Thread List Format
40826 @cindex thread list format
40828 To efficiently update the list of threads and their attributes,
40829 @value{GDBN} issues the @samp{qXfer:threads:read} packet
40830 (@pxref{qXfer threads read}) and obtains the XML document with
40831 the following structure:
40834 <?xml version="1.0"?>
40836 <thread id="id" core="0" name="name">
40837 ... description ...
40842 Each @samp{thread} element must have the @samp{id} attribute that
40843 identifies the thread (@pxref{thread-id syntax}). The
40844 @samp{core} attribute, if present, specifies which processor core
40845 the thread was last executing on. The @samp{name} attribute, if
40846 present, specifies the human-readable name of the thread. The content
40847 of the of @samp{thread} element is interpreted as human-readable
40848 auxiliary information. The @samp{handle} attribute, if present,
40849 is a hex encoded representation of the thread handle.
40852 @node Traceframe Info Format
40853 @section Traceframe Info Format
40854 @cindex traceframe info format
40856 To be able to know which objects in the inferior can be examined when
40857 inspecting a tracepoint hit, @value{GDBN} needs to obtain the list of
40858 memory ranges, registers and trace state variables that have been
40859 collected in a traceframe.
40861 This list is obtained using the @samp{qXfer:traceframe-info:read}
40862 (@pxref{qXfer traceframe info read}) packet and is an XML document.
40864 @value{GDBN} must be linked with the Expat library to support XML
40865 traceframe info discovery. @xref{Expat}.
40867 The top-level structure of the document is shown below:
40870 <?xml version="1.0"?>
40871 <!DOCTYPE traceframe-info
40872 PUBLIC "+//IDN gnu.org//DTD GDB Memory Map V1.0//EN"
40873 "http://sourceware.org/gdb/gdb-traceframe-info.dtd">
40879 Each traceframe block can be either:
40884 A region of collected memory starting at @var{addr} and extending for
40885 @var{length} bytes from there:
40888 <memory start="@var{addr}" length="@var{length}"/>
40892 A block indicating trace state variable numbered @var{number} has been
40896 <tvar id="@var{number}"/>
40901 The formal DTD for the traceframe info format is given below:
40904 <!ELEMENT traceframe-info (memory | tvar)* >
40905 <!ATTLIST traceframe-info version CDATA #FIXED "1.0">
40907 <!ELEMENT memory EMPTY>
40908 <!ATTLIST memory start CDATA #REQUIRED
40909 length CDATA #REQUIRED>
40911 <!ATTLIST tvar id CDATA #REQUIRED>
40914 @node Branch Trace Format
40915 @section Branch Trace Format
40916 @cindex branch trace format
40918 In order to display the branch trace of an inferior thread,
40919 @value{GDBN} needs to obtain the list of branches. This list is
40920 represented as list of sequential code blocks that are connected via
40921 branches. The code in each block has been executed sequentially.
40923 This list is obtained using the @samp{qXfer:btrace:read}
40924 (@pxref{qXfer btrace read}) packet and is an XML document.
40926 @value{GDBN} must be linked with the Expat library to support XML
40927 traceframe info discovery. @xref{Expat}.
40929 The top-level structure of the document is shown below:
40932 <?xml version="1.0"?>
40934 PUBLIC "+//IDN gnu.org//DTD GDB Branch Trace V1.0//EN"
40935 "http://sourceware.org/gdb/gdb-btrace.dtd">
40944 A block of sequentially executed instructions starting at @var{begin}
40945 and ending at @var{end}:
40948 <block begin="@var{begin}" end="@var{end}"/>
40953 The formal DTD for the branch trace format is given below:
40956 <!ELEMENT btrace (block* | pt) >
40957 <!ATTLIST btrace version CDATA #FIXED "1.0">
40959 <!ELEMENT block EMPTY>
40960 <!ATTLIST block begin CDATA #REQUIRED
40961 end CDATA #REQUIRED>
40963 <!ELEMENT pt (pt-config?, raw?)>
40965 <!ELEMENT pt-config (cpu?)>
40967 <!ELEMENT cpu EMPTY>
40968 <!ATTLIST cpu vendor CDATA #REQUIRED
40969 family CDATA #REQUIRED
40970 model CDATA #REQUIRED
40971 stepping CDATA #REQUIRED>
40973 <!ELEMENT raw (#PCDATA)>
40976 @node Branch Trace Configuration Format
40977 @section Branch Trace Configuration Format
40978 @cindex branch trace configuration format
40980 For each inferior thread, @value{GDBN} can obtain the branch trace
40981 configuration using the @samp{qXfer:btrace-conf:read}
40982 (@pxref{qXfer btrace-conf read}) packet.
40984 The configuration describes the branch trace format and configuration
40985 settings for that format. The following information is described:
40989 This thread uses the @dfn{Branch Trace Store} (@acronym{BTS}) format.
40992 The size of the @acronym{BTS} ring buffer in bytes.
40995 This thread uses the @dfn{Intel Processor Trace} (@acronym{Intel
40999 The size of the @acronym{Intel PT} ring buffer in bytes.
41003 @value{GDBN} must be linked with the Expat library to support XML
41004 branch trace configuration discovery. @xref{Expat}.
41006 The formal DTD for the branch trace configuration format is given below:
41009 <!ELEMENT btrace-conf (bts?, pt?)>
41010 <!ATTLIST btrace-conf version CDATA #FIXED "1.0">
41012 <!ELEMENT bts EMPTY>
41013 <!ATTLIST bts size CDATA #IMPLIED>
41015 <!ELEMENT pt EMPTY>
41016 <!ATTLIST pt size CDATA #IMPLIED>
41019 @include agentexpr.texi
41021 @node Target Descriptions
41022 @appendix Target Descriptions
41023 @cindex target descriptions
41025 One of the challenges of using @value{GDBN} to debug embedded systems
41026 is that there are so many minor variants of each processor
41027 architecture in use. It is common practice for vendors to start with
41028 a standard processor core --- ARM, PowerPC, or @acronym{MIPS}, for example ---
41029 and then make changes to adapt it to a particular market niche. Some
41030 architectures have hundreds of variants, available from dozens of
41031 vendors. This leads to a number of problems:
41035 With so many different customized processors, it is difficult for
41036 the @value{GDBN} maintainers to keep up with the changes.
41038 Since individual variants may have short lifetimes or limited
41039 audiences, it may not be worthwhile to carry information about every
41040 variant in the @value{GDBN} source tree.
41042 When @value{GDBN} does support the architecture of the embedded system
41043 at hand, the task of finding the correct architecture name to give the
41044 @command{set architecture} command can be error-prone.
41047 To address these problems, the @value{GDBN} remote protocol allows a
41048 target system to not only identify itself to @value{GDBN}, but to
41049 actually describe its own features. This lets @value{GDBN} support
41050 processor variants it has never seen before --- to the extent that the
41051 descriptions are accurate, and that @value{GDBN} understands them.
41053 @value{GDBN} must be linked with the Expat library to support XML
41054 target descriptions. @xref{Expat}.
41057 * Retrieving Descriptions:: How descriptions are fetched from a target.
41058 * Target Description Format:: The contents of a target description.
41059 * Predefined Target Types:: Standard types available for target
41061 * Enum Target Types:: How to define enum target types.
41062 * Standard Target Features:: Features @value{GDBN} knows about.
41065 @node Retrieving Descriptions
41066 @section Retrieving Descriptions
41068 Target descriptions can be read from the target automatically, or
41069 specified by the user manually. The default behavior is to read the
41070 description from the target. @value{GDBN} retrieves it via the remote
41071 protocol using @samp{qXfer} requests (@pxref{General Query Packets,
41072 qXfer}). The @var{annex} in the @samp{qXfer} packet will be
41073 @samp{target.xml}. The contents of the @samp{target.xml} annex are an
41074 XML document, of the form described in @ref{Target Description
41077 Alternatively, you can specify a file to read for the target description.
41078 If a file is set, the target will not be queried. The commands to
41079 specify a file are:
41082 @cindex set tdesc filename
41083 @item set tdesc filename @var{path}
41084 Read the target description from @var{path}.
41086 @cindex unset tdesc filename
41087 @item unset tdesc filename
41088 Do not read the XML target description from a file. @value{GDBN}
41089 will use the description supplied by the current target.
41091 @cindex show tdesc filename
41092 @item show tdesc filename
41093 Show the filename to read for a target description, if any.
41097 @node Target Description Format
41098 @section Target Description Format
41099 @cindex target descriptions, XML format
41101 A target description annex is an @uref{http://www.w3.org/XML/, XML}
41102 document which complies with the Document Type Definition provided in
41103 the @value{GDBN} sources in @file{gdb/features/gdb-target.dtd}. This
41104 means you can use generally available tools like @command{xmllint} to
41105 check that your feature descriptions are well-formed and valid.
41106 However, to help people unfamiliar with XML write descriptions for
41107 their targets, we also describe the grammar here.
41109 Target descriptions can identify the architecture of the remote target
41110 and (for some architectures) provide information about custom register
41111 sets. They can also identify the OS ABI of the remote target.
41112 @value{GDBN} can use this information to autoconfigure for your
41113 target, or to warn you if you connect to an unsupported target.
41115 Here is a simple target description:
41118 <target version="1.0">
41119 <architecture>i386:x86-64</architecture>
41124 This minimal description only says that the target uses
41125 the x86-64 architecture.
41127 A target description has the following overall form, with [ ] marking
41128 optional elements and @dots{} marking repeatable elements. The elements
41129 are explained further below.
41132 <?xml version="1.0"?>
41133 <!DOCTYPE target SYSTEM "gdb-target.dtd">
41134 <target version="1.0">
41135 @r{[}@var{architecture}@r{]}
41136 @r{[}@var{osabi}@r{]}
41137 @r{[}@var{compatible}@r{]}
41138 @r{[}@var{feature}@dots{}@r{]}
41143 The description is generally insensitive to whitespace and line
41144 breaks, under the usual common-sense rules. The XML version
41145 declaration and document type declaration can generally be omitted
41146 (@value{GDBN} does not require them), but specifying them may be
41147 useful for XML validation tools. The @samp{version} attribute for
41148 @samp{<target>} may also be omitted, but we recommend
41149 including it; if future versions of @value{GDBN} use an incompatible
41150 revision of @file{gdb-target.dtd}, they will detect and report
41151 the version mismatch.
41153 @subsection Inclusion
41154 @cindex target descriptions, inclusion
41157 @cindex <xi:include>
41160 It can sometimes be valuable to split a target description up into
41161 several different annexes, either for organizational purposes, or to
41162 share files between different possible target descriptions. You can
41163 divide a description into multiple files by replacing any element of
41164 the target description with an inclusion directive of the form:
41167 <xi:include href="@var{document}"/>
41171 When @value{GDBN} encounters an element of this form, it will retrieve
41172 the named XML @var{document}, and replace the inclusion directive with
41173 the contents of that document. If the current description was read
41174 using @samp{qXfer}, then so will be the included document;
41175 @var{document} will be interpreted as the name of an annex. If the
41176 current description was read from a file, @value{GDBN} will look for
41177 @var{document} as a file in the same directory where it found the
41178 original description.
41180 @subsection Architecture
41181 @cindex <architecture>
41183 An @samp{<architecture>} element has this form:
41186 <architecture>@var{arch}</architecture>
41189 @var{arch} is one of the architectures from the set accepted by
41190 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
41193 @cindex @code{<osabi>}
41195 This optional field was introduced in @value{GDBN} version 7.0.
41196 Previous versions of @value{GDBN} ignore it.
41198 An @samp{<osabi>} element has this form:
41201 <osabi>@var{abi-name}</osabi>
41204 @var{abi-name} is an OS ABI name from the same selection accepted by
41205 @w{@code{set osabi}} (@pxref{ABI, ,Configuring the Current ABI}).
41207 @subsection Compatible Architecture
41208 @cindex @code{<compatible>}
41210 This optional field was introduced in @value{GDBN} version 7.0.
41211 Previous versions of @value{GDBN} ignore it.
41213 A @samp{<compatible>} element has this form:
41216 <compatible>@var{arch}</compatible>
41219 @var{arch} is one of the architectures from the set accepted by
41220 @code{set architecture} (@pxref{Targets, ,Specifying a Debugging Target}).
41222 A @samp{<compatible>} element is used to specify that the target
41223 is able to run binaries in some other than the main target architecture
41224 given by the @samp{<architecture>} element. For example, on the
41225 Cell Broadband Engine, the main architecture is @code{powerpc:common}
41226 or @code{powerpc:common64}, but the system is able to run binaries
41227 in the @code{spu} architecture as well. The way to describe this
41228 capability with @samp{<compatible>} is as follows:
41231 <architecture>powerpc:common</architecture>
41232 <compatible>spu</compatible>
41235 @subsection Features
41238 Each @samp{<feature>} describes some logical portion of the target
41239 system. Features are currently used to describe available CPU
41240 registers and the types of their contents. A @samp{<feature>} element
41244 <feature name="@var{name}">
41245 @r{[}@var{type}@dots{}@r{]}
41251 Each feature's name should be unique within the description. The name
41252 of a feature does not matter unless @value{GDBN} has some special
41253 knowledge of the contents of that feature; if it does, the feature
41254 should have its standard name. @xref{Standard Target Features}.
41258 Any register's value is a collection of bits which @value{GDBN} must
41259 interpret. The default interpretation is a two's complement integer,
41260 but other types can be requested by name in the register description.
41261 Some predefined types are provided by @value{GDBN} (@pxref{Predefined
41262 Target Types}), and the description can define additional composite
41265 Each type element must have an @samp{id} attribute, which gives
41266 a unique (within the containing @samp{<feature>}) name to the type.
41267 Types must be defined before they are used.
41270 Some targets offer vector registers, which can be treated as arrays
41271 of scalar elements. These types are written as @samp{<vector>} elements,
41272 specifying the array element type, @var{type}, and the number of elements,
41276 <vector id="@var{id}" type="@var{type}" count="@var{count}"/>
41280 If a register's value is usefully viewed in multiple ways, define it
41281 with a union type containing the useful representations. The
41282 @samp{<union>} element contains one or more @samp{<field>} elements,
41283 each of which has a @var{name} and a @var{type}:
41286 <union id="@var{id}">
41287 <field name="@var{name}" type="@var{type}"/>
41294 If a register's value is composed from several separate values, define
41295 it with either a structure type or a flags type.
41296 A flags type may only contain bitfields.
41297 A structure type may either contain only bitfields or contain no bitfields.
41298 If the value contains only bitfields, its total size in bytes must be
41301 Non-bitfield values have a @var{name} and @var{type}.
41304 <struct id="@var{id}">
41305 <field name="@var{name}" type="@var{type}"/>
41310 Both @var{name} and @var{type} values are required.
41311 No implicit padding is added.
41313 Bitfield values have a @var{name}, @var{start}, @var{end} and @var{type}.
41316 <struct id="@var{id}" size="@var{size}">
41317 <field name="@var{name}" start="@var{start}" end="@var{end}" type="@var{type}"/>
41323 <flags id="@var{id}" size="@var{size}">
41324 <field name="@var{name}" start="@var{start}" end="@var{end}" type="@var{type}"/>
41329 The @var{name} value is required.
41330 Bitfield values may be named with the empty string, @samp{""},
41331 in which case the field is ``filler'' and its value is not printed.
41332 Not all bits need to be specified, so ``filler'' fields are optional.
41334 The @var{start} and @var{end} values are required, and @var{type}
41336 The field's @var{start} must be less than or equal to its @var{end},
41337 and zero represents the least significant bit.
41339 The default value of @var{type} is @code{bool} for single bit fields,
41340 and an unsigned integer otherwise.
41342 Which to choose? Structures or flags?
41344 Registers defined with @samp{flags} have these advantages over
41345 defining them with @samp{struct}:
41349 Arithmetic may be performed on them as if they were integers.
41351 They are printed in a more readable fashion.
41354 Registers defined with @samp{struct} have one advantage over
41355 defining them with @samp{flags}:
41359 One can fetch individual fields like in @samp{C}.
41362 (gdb) print $my_struct_reg.field3
41368 @subsection Registers
41371 Each register is represented as an element with this form:
41374 <reg name="@var{name}"
41375 bitsize="@var{size}"
41376 @r{[}regnum="@var{num}"@r{]}
41377 @r{[}save-restore="@var{save-restore}"@r{]}
41378 @r{[}type="@var{type}"@r{]}
41379 @r{[}group="@var{group}"@r{]}/>
41383 The components are as follows:
41388 The register's name; it must be unique within the target description.
41391 The register's size, in bits.
41394 The register's number. If omitted, a register's number is one greater
41395 than that of the previous register (either in the current feature or in
41396 a preceding feature); the first register in the target description
41397 defaults to zero. This register number is used to read or write
41398 the register; e.g.@: it is used in the remote @code{p} and @code{P}
41399 packets, and registers appear in the @code{g} and @code{G} packets
41400 in order of increasing register number.
41403 Whether the register should be preserved across inferior function
41404 calls; this must be either @code{yes} or @code{no}. The default is
41405 @code{yes}, which is appropriate for most registers except for
41406 some system control registers; this is not related to the target's
41410 The type of the register. It may be a predefined type, a type
41411 defined in the current feature, or one of the special types @code{int}
41412 and @code{float}. @code{int} is an integer type of the correct size
41413 for @var{bitsize}, and @code{float} is a floating point type (in the
41414 architecture's normal floating point format) of the correct size for
41415 @var{bitsize}. The default is @code{int}.
41418 The register group to which this register belongs. It must
41419 be either @code{general}, @code{float}, or @code{vector}. If no
41420 @var{group} is specified, @value{GDBN} will not display the register
41421 in @code{info registers}.
41425 @node Predefined Target Types
41426 @section Predefined Target Types
41427 @cindex target descriptions, predefined types
41429 Type definitions in the self-description can build up composite types
41430 from basic building blocks, but can not define fundamental types. Instead,
41431 standard identifiers are provided by @value{GDBN} for the fundamental
41432 types. The currently supported types are:
41437 Boolean type, occupying a single bit.
41444 Signed integer types holding the specified number of bits.
41451 Unsigned integer types holding the specified number of bits.
41455 Pointers to unspecified code and data. The program counter and
41456 any dedicated return address register may be marked as code
41457 pointers; printing a code pointer converts it into a symbolic
41458 address. The stack pointer and any dedicated address registers
41459 may be marked as data pointers.
41462 Single precision IEEE floating point.
41465 Double precision IEEE floating point.
41468 The 12-byte extended precision format used by ARM FPA registers.
41471 The 10-byte extended precision format used by x87 registers.
41474 32bit @sc{eflags} register used by x86.
41477 32bit @sc{mxcsr} register used by x86.
41481 @node Enum Target Types
41482 @section Enum Target Types
41483 @cindex target descriptions, enum types
41485 Enum target types are useful in @samp{struct} and @samp{flags}
41486 register descriptions. @xref{Target Description Format}.
41488 Enum types have a name, size and a list of name/value pairs.
41491 <enum id="@var{id}" size="@var{size}">
41492 <evalue name="@var{name}" value="@var{value}"/>
41497 Enums must be defined before they are used.
41500 <enum id="levels_type" size="4">
41501 <evalue name="low" value="0"/>
41502 <evalue name="high" value="1"/>
41504 <flags id="flags_type" size="4">
41505 <field name="X" start="0"/>
41506 <field name="LEVEL" start="1" end="1" type="levels_type"/>
41508 <reg name="flags" bitsize="32" type="flags_type"/>
41511 Given that description, a value of 3 for the @samp{flags} register
41512 would be printed as:
41515 (gdb) info register flags
41516 flags 0x3 [ X LEVEL=high ]
41519 @node Standard Target Features
41520 @section Standard Target Features
41521 @cindex target descriptions, standard features
41523 A target description must contain either no registers or all the
41524 target's registers. If the description contains no registers, then
41525 @value{GDBN} will assume a default register layout, selected based on
41526 the architecture. If the description contains any registers, the
41527 default layout will not be used; the standard registers must be
41528 described in the target description, in such a way that @value{GDBN}
41529 can recognize them.
41531 This is accomplished by giving specific names to feature elements
41532 which contain standard registers. @value{GDBN} will look for features
41533 with those names and verify that they contain the expected registers;
41534 if any known feature is missing required registers, or if any required
41535 feature is missing, @value{GDBN} will reject the target
41536 description. You can add additional registers to any of the
41537 standard features --- @value{GDBN} will display them just as if
41538 they were added to an unrecognized feature.
41540 This section lists the known features and their expected contents.
41541 Sample XML documents for these features are included in the
41542 @value{GDBN} source tree, in the directory @file{gdb/features}.
41544 Names recognized by @value{GDBN} should include the name of the
41545 company or organization which selected the name, and the overall
41546 architecture to which the feature applies; so e.g.@: the feature
41547 containing ARM core registers is named @samp{org.gnu.gdb.arm.core}.
41549 The names of registers are not case sensitive for the purpose
41550 of recognizing standard features, but @value{GDBN} will only display
41551 registers using the capitalization used in the description.
41554 * AArch64 Features::
41558 * MicroBlaze Features::
41562 * Nios II Features::
41563 * PowerPC Features::
41564 * S/390 and System z Features::
41570 @node AArch64 Features
41571 @subsection AArch64 Features
41572 @cindex target descriptions, AArch64 features
41574 The @samp{org.gnu.gdb.aarch64.core} feature is required for AArch64
41575 targets. It should contain registers @samp{x0} through @samp{x30},
41576 @samp{sp}, @samp{pc}, and @samp{cpsr}.
41578 The @samp{org.gnu.gdb.aarch64.fpu} feature is optional. If present,
41579 it should contain registers @samp{v0} through @samp{v31}, @samp{fpsr},
41583 @subsection ARC Features
41584 @cindex target descriptions, ARC Features
41586 ARC processors are highly configurable, so even core registers and their number
41587 are not completely predetermined. In addition flags and PC registers which are
41588 important to @value{GDBN} are not ``core'' registers in ARC. It is required
41589 that one of the core registers features is present.
41590 @samp{org.gnu.gdb.arc.aux-minimal} feature is mandatory.
41592 The @samp{org.gnu.gdb.arc.core.v2} feature is required for ARC EM and ARC HS
41593 targets with a normal register file. It should contain registers @samp{r0}
41594 through @samp{r25}, @samp{gp}, @samp{fp}, @samp{sp}, @samp{r30}, @samp{blink},
41595 @samp{lp_count} and @samp{pcl}. This feature may contain register @samp{ilink}
41596 and any of extension core registers @samp{r32} through @samp{r59/acch}.
41597 @samp{ilink} and extension core registers are not available to read/write, when
41598 debugging GNU/Linux applications, thus @samp{ilink} is made optional.
41600 The @samp{org.gnu.gdb.arc.core-reduced.v2} feature is required for ARC EM and
41601 ARC HS targets with a reduced register file. It should contain registers
41602 @samp{r0} through @samp{r3}, @samp{r10} through @samp{r15}, @samp{gp},
41603 @samp{fp}, @samp{sp}, @samp{r30}, @samp{blink}, @samp{lp_count} and @samp{pcl}.
41604 This feature may contain register @samp{ilink} and any of extension core
41605 registers @samp{r32} through @samp{r59/acch}.
41607 The @samp{org.gnu.gdb.arc.core.arcompact} feature is required for ARCompact
41608 targets with a normal register file. It should contain registers @samp{r0}
41609 through @samp{r25}, @samp{gp}, @samp{fp}, @samp{sp}, @samp{r30}, @samp{blink},
41610 @samp{lp_count} and @samp{pcl}. This feature may contain registers
41611 @samp{ilink1}, @samp{ilink2} and any of extension core registers @samp{r32}
41612 through @samp{r59/acch}. @samp{ilink1} and @samp{ilink2} and extension core
41613 registers are not available when debugging GNU/Linux applications. The only
41614 difference with @samp{org.gnu.gdb.arc.core.v2} feature is in the names of
41615 @samp{ilink1} and @samp{ilink2} registers and that @samp{r30} is mandatory in
41616 ARC v2, but @samp{ilink2} is optional on ARCompact.
41618 The @samp{org.gnu.gdb.arc.aux-minimal} feature is required for all ARC
41619 targets. It should contain registers @samp{pc} and @samp{status32}.
41622 @subsection ARM Features
41623 @cindex target descriptions, ARM features
41625 The @samp{org.gnu.gdb.arm.core} feature is required for non-M-profile
41627 It should contain registers @samp{r0} through @samp{r13}, @samp{sp},
41628 @samp{lr}, @samp{pc}, and @samp{cpsr}.
41630 For M-profile targets (e.g. Cortex-M3), the @samp{org.gnu.gdb.arm.core}
41631 feature is replaced by @samp{org.gnu.gdb.arm.m-profile}. It should contain
41632 registers @samp{r0} through @samp{r13}, @samp{sp}, @samp{lr}, @samp{pc},
41635 The @samp{org.gnu.gdb.arm.fpa} feature is optional. If present, it
41636 should contain registers @samp{f0} through @samp{f7} and @samp{fps}.
41638 The @samp{org.gnu.gdb.xscale.iwmmxt} feature is optional. If present,
41639 it should contain at least registers @samp{wR0} through @samp{wR15} and
41640 @samp{wCGR0} through @samp{wCGR3}. The @samp{wCID}, @samp{wCon},
41641 @samp{wCSSF}, and @samp{wCASF} registers are optional.
41643 The @samp{org.gnu.gdb.arm.vfp} feature is optional. If present, it
41644 should contain at least registers @samp{d0} through @samp{d15}. If
41645 they are present, @samp{d16} through @samp{d31} should also be included.
41646 @value{GDBN} will synthesize the single-precision registers from
41647 halves of the double-precision registers.
41649 The @samp{org.gnu.gdb.arm.neon} feature is optional. It does not
41650 need to contain registers; it instructs @value{GDBN} to display the
41651 VFP double-precision registers as vectors and to synthesize the
41652 quad-precision registers from pairs of double-precision registers.
41653 If this feature is present, @samp{org.gnu.gdb.arm.vfp} must also
41654 be present and include 32 double-precision registers.
41656 @node i386 Features
41657 @subsection i386 Features
41658 @cindex target descriptions, i386 features
41660 The @samp{org.gnu.gdb.i386.core} feature is required for i386/amd64
41661 targets. It should describe the following registers:
41665 @samp{eax} through @samp{edi} plus @samp{eip} for i386
41667 @samp{rax} through @samp{r15} plus @samp{rip} for amd64
41669 @samp{eflags}, @samp{cs}, @samp{ss}, @samp{ds}, @samp{es},
41670 @samp{fs}, @samp{gs}
41672 @samp{st0} through @samp{st7}
41674 @samp{fctrl}, @samp{fstat}, @samp{ftag}, @samp{fiseg}, @samp{fioff},
41675 @samp{foseg}, @samp{fooff} and @samp{fop}
41678 The register sets may be different, depending on the target.
41680 The @samp{org.gnu.gdb.i386.sse} feature is optional. It should
41681 describe registers:
41685 @samp{xmm0} through @samp{xmm7} for i386
41687 @samp{xmm0} through @samp{xmm15} for amd64
41692 The @samp{org.gnu.gdb.i386.avx} feature is optional and requires the
41693 @samp{org.gnu.gdb.i386.sse} feature. It should
41694 describe the upper 128 bits of @sc{ymm} registers:
41698 @samp{ymm0h} through @samp{ymm7h} for i386
41700 @samp{ymm0h} through @samp{ymm15h} for amd64
41703 The @samp{org.gnu.gdb.i386.mpx} is an optional feature representing Intel
41704 Memory Protection Extension (MPX). It should describe the following registers:
41708 @samp{bnd0raw} through @samp{bnd3raw} for i386 and amd64.
41710 @samp{bndcfgu} and @samp{bndstatus} for i386 and amd64.
41713 The @samp{org.gnu.gdb.i386.linux} feature is optional. It should
41714 describe a single register, @samp{orig_eax}.
41716 The @samp{org.gnu.gdb.i386.segments} feature is optional. It should
41717 describe two system registers: @samp{fs_base} and @samp{gs_base}.
41719 The @samp{org.gnu.gdb.i386.avx512} feature is optional and requires the
41720 @samp{org.gnu.gdb.i386.avx} feature. It should
41721 describe additional @sc{xmm} registers:
41725 @samp{xmm16h} through @samp{xmm31h}, only valid for amd64.
41728 It should describe the upper 128 bits of additional @sc{ymm} registers:
41732 @samp{ymm16h} through @samp{ymm31h}, only valid for amd64.
41736 describe the upper 256 bits of @sc{zmm} registers:
41740 @samp{zmm0h} through @samp{zmm7h} for i386.
41742 @samp{zmm0h} through @samp{zmm15h} for amd64.
41746 describe the additional @sc{zmm} registers:
41750 @samp{zmm16h} through @samp{zmm31h}, only valid for amd64.
41753 The @samp{org.gnu.gdb.i386.pkeys} feature is optional. It should
41754 describe a single register, @samp{pkru}. It is a 32-bit register
41755 valid for i386 and amd64.
41757 @node MicroBlaze Features
41758 @subsection MicroBlaze Features
41759 @cindex target descriptions, MicroBlaze features
41761 The @samp{org.gnu.gdb.microblaze.core} feature is required for MicroBlaze
41762 targets. It should contain registers @samp{r0} through @samp{r31},
41763 @samp{rpc}, @samp{rmsr}, @samp{rear}, @samp{resr}, @samp{rfsr}, @samp{rbtr},
41764 @samp{rpvr}, @samp{rpvr1} through @samp{rpvr11}, @samp{redr}, @samp{rpid},
41765 @samp{rzpr}, @samp{rtlbx}, @samp{rtlbsx}, @samp{rtlblo}, and @samp{rtlbhi}.
41767 The @samp{org.gnu.gdb.microblaze.stack-protect} feature is optional.
41768 If present, it should contain registers @samp{rshr} and @samp{rslr}
41770 @node MIPS Features
41771 @subsection @acronym{MIPS} Features
41772 @cindex target descriptions, @acronym{MIPS} features
41774 The @samp{org.gnu.gdb.mips.cpu} feature is required for @acronym{MIPS} targets.
41775 It should contain registers @samp{r0} through @samp{r31}, @samp{lo},
41776 @samp{hi}, and @samp{pc}. They may be 32-bit or 64-bit depending
41779 The @samp{org.gnu.gdb.mips.cp0} feature is also required. It should
41780 contain at least the @samp{status}, @samp{badvaddr}, and @samp{cause}
41781 registers. They may be 32-bit or 64-bit depending on the target.
41783 The @samp{org.gnu.gdb.mips.fpu} feature is currently required, though
41784 it may be optional in a future version of @value{GDBN}. It should
41785 contain registers @samp{f0} through @samp{f31}, @samp{fcsr}, and
41786 @samp{fir}. They may be 32-bit or 64-bit depending on the target.
41788 The @samp{org.gnu.gdb.mips.dsp} feature is optional. It should
41789 contain registers @samp{hi1} through @samp{hi3}, @samp{lo1} through
41790 @samp{lo3}, and @samp{dspctl}. The @samp{dspctl} register should
41791 be 32-bit and the rest may be 32-bit or 64-bit depending on the target.
41793 The @samp{org.gnu.gdb.mips.linux} feature is optional. It should
41794 contain a single register, @samp{restart}, which is used by the
41795 Linux kernel to control restartable syscalls.
41797 @node M68K Features
41798 @subsection M68K Features
41799 @cindex target descriptions, M68K features
41802 @item @samp{org.gnu.gdb.m68k.core}
41803 @itemx @samp{org.gnu.gdb.coldfire.core}
41804 @itemx @samp{org.gnu.gdb.fido.core}
41805 One of those features must be always present.
41806 The feature that is present determines which flavor of m68k is
41807 used. The feature that is present should contain registers
41808 @samp{d0} through @samp{d7}, @samp{a0} through @samp{a5}, @samp{fp},
41809 @samp{sp}, @samp{ps} and @samp{pc}.
41811 @item @samp{org.gnu.gdb.coldfire.fp}
41812 This feature is optional. If present, it should contain registers
41813 @samp{fp0} through @samp{fp7}, @samp{fpcontrol}, @samp{fpstatus} and
41817 @node NDS32 Features
41818 @subsection NDS32 Features
41819 @cindex target descriptions, NDS32 features
41821 The @samp{org.gnu.gdb.nds32.core} feature is required for NDS32
41822 targets. It should contain at least registers @samp{r0} through
41823 @samp{r10}, @samp{r15}, @samp{fp}, @samp{gp}, @samp{lp}, @samp{sp},
41826 The @samp{org.gnu.gdb.nds32.fpu} feature is optional. If present,
41827 it should contain 64-bit double-precision floating-point registers
41828 @samp{fd0} through @emph{fdN}, which should be @samp{fd3}, @samp{fd7},
41829 @samp{fd15}, or @samp{fd31} based on the FPU configuration implemented.
41831 @emph{Note:} The first sixteen 64-bit double-precision floating-point
41832 registers are overlapped with the thirty-two 32-bit single-precision
41833 floating-point registers. The 32-bit single-precision registers, if
41834 not being listed explicitly, will be synthesized from halves of the
41835 overlapping 64-bit double-precision registers. Listing 32-bit
41836 single-precision registers explicitly is deprecated, and the
41837 support to it could be totally removed some day.
41839 @node Nios II Features
41840 @subsection Nios II Features
41841 @cindex target descriptions, Nios II features
41843 The @samp{org.gnu.gdb.nios2.cpu} feature is required for Nios II
41844 targets. It should contain the 32 core registers (@samp{zero},
41845 @samp{at}, @samp{r2} through @samp{r23}, @samp{et} through @samp{ra}),
41846 @samp{pc}, and the 16 control registers (@samp{status} through
41849 @node PowerPC Features
41850 @subsection PowerPC Features
41851 @cindex target descriptions, PowerPC features
41853 The @samp{org.gnu.gdb.power.core} feature is required for PowerPC
41854 targets. It should contain registers @samp{r0} through @samp{r31},
41855 @samp{pc}, @samp{msr}, @samp{cr}, @samp{lr}, @samp{ctr}, and
41856 @samp{xer}. They may be 32-bit or 64-bit depending on the target.
41858 The @samp{org.gnu.gdb.power.fpu} feature is optional. It should
41859 contain registers @samp{f0} through @samp{f31} and @samp{fpscr}.
41861 The @samp{org.gnu.gdb.power.altivec} feature is optional. It should
41862 contain registers @samp{vr0} through @samp{vr31}, @samp{vscr},
41865 The @samp{org.gnu.gdb.power.vsx} feature is optional. It should
41866 contain registers @samp{vs0h} through @samp{vs31h}. @value{GDBN}
41867 will combine these registers with the floating point registers
41868 (@samp{f0} through @samp{f31}) and the altivec registers (@samp{vr0}
41869 through @samp{vr31}) to present the 128-bit wide registers @samp{vs0}
41870 through @samp{vs63}, the set of vector registers for POWER7.
41872 The @samp{org.gnu.gdb.power.spe} feature is optional. It should
41873 contain registers @samp{ev0h} through @samp{ev31h}, @samp{acc}, and
41874 @samp{spefscr}. SPE targets should provide 32-bit registers in
41875 @samp{org.gnu.gdb.power.core} and provide the upper halves in
41876 @samp{ev0h} through @samp{ev31h}. @value{GDBN} will combine
41877 these to present registers @samp{ev0} through @samp{ev31} to the
41880 @node S/390 and System z Features
41881 @subsection S/390 and System z Features
41882 @cindex target descriptions, S/390 features
41883 @cindex target descriptions, System z features
41885 The @samp{org.gnu.gdb.s390.core} feature is required for S/390 and
41886 System z targets. It should contain the PSW and the 16 general
41887 registers. In particular, System z targets should provide the 64-bit
41888 registers @samp{pswm}, @samp{pswa}, and @samp{r0} through @samp{r15}.
41889 S/390 targets should provide the 32-bit versions of these registers.
41890 A System z target that runs in 31-bit addressing mode should provide
41891 32-bit versions of @samp{pswm} and @samp{pswa}, as well as the general
41892 register's upper halves @samp{r0h} through @samp{r15h}, and their
41893 lower halves @samp{r0l} through @samp{r15l}.
41895 The @samp{org.gnu.gdb.s390.fpr} feature is required. It should
41896 contain the 64-bit registers @samp{f0} through @samp{f15}, and
41899 The @samp{org.gnu.gdb.s390.acr} feature is required. It should
41900 contain the 32-bit registers @samp{acr0} through @samp{acr15}.
41902 The @samp{org.gnu.gdb.s390.linux} feature is optional. It should
41903 contain the register @samp{orig_r2}, which is 64-bit wide on System z
41904 targets and 32-bit otherwise. In addition, the feature may contain
41905 the @samp{last_break} register, whose width depends on the addressing
41906 mode, as well as the @samp{system_call} register, which is always
41909 The @samp{org.gnu.gdb.s390.tdb} feature is optional. It should
41910 contain the 64-bit registers @samp{tdb0}, @samp{tac}, @samp{tct},
41911 @samp{atia}, and @samp{tr0} through @samp{tr15}.
41913 The @samp{org.gnu.gdb.s390.vx} feature is optional. It should contain
41914 64-bit wide registers @samp{v0l} through @samp{v15l}, which will be
41915 combined by @value{GDBN} with the floating point registers @samp{f0}
41916 through @samp{f15} to present the 128-bit wide vector registers
41917 @samp{v0} through @samp{v15}. In addition, this feature should
41918 contain the 128-bit wide vector registers @samp{v16} through
41921 The @samp{org.gnu.gdb.s390.gs} feature is optional. It should contain
41922 the 64-bit wide guarded-storage-control registers @samp{gsd},
41923 @samp{gssm}, and @samp{gsepla}.
41925 The @samp{org.gnu.gdb.s390.gsbc} feature is optional. It should contain
41926 the 64-bit wide guarded-storage broadcast control registers
41927 @samp{bc_gsd}, @samp{bc_gssm}, and @samp{bc_gsepla}.
41929 @node Sparc Features
41930 @subsection Sparc Features
41931 @cindex target descriptions, sparc32 features
41932 @cindex target descriptions, sparc64 features
41933 The @samp{org.gnu.gdb.sparc.cpu} feature is required for sparc32/sparc64
41934 targets. It should describe the following registers:
41938 @samp{g0} through @samp{g7}
41940 @samp{o0} through @samp{o7}
41942 @samp{l0} through @samp{l7}
41944 @samp{i0} through @samp{i7}
41947 They may be 32-bit or 64-bit depending on the target.
41949 Also the @samp{org.gnu.gdb.sparc.fpu} feature is required for sparc32/sparc64
41950 targets. It should describe the following registers:
41954 @samp{f0} through @samp{f31}
41956 @samp{f32} through @samp{f62} for sparc64
41959 The @samp{org.gnu.gdb.sparc.cp0} feature is required for sparc32/sparc64
41960 targets. It should describe the following registers:
41964 @samp{y}, @samp{psr}, @samp{wim}, @samp{tbr}, @samp{pc}, @samp{npc},
41965 @samp{fsr}, and @samp{csr} for sparc32
41967 @samp{pc}, @samp{npc}, @samp{state}, @samp{fsr}, @samp{fprs}, and @samp{y}
41971 @node TIC6x Features
41972 @subsection TMS320C6x Features
41973 @cindex target descriptions, TIC6x features
41974 @cindex target descriptions, TMS320C6x features
41975 The @samp{org.gnu.gdb.tic6x.core} feature is required for TMS320C6x
41976 targets. It should contain registers @samp{A0} through @samp{A15},
41977 registers @samp{B0} through @samp{B15}, @samp{CSR} and @samp{PC}.
41979 The @samp{org.gnu.gdb.tic6x.gp} feature is optional. It should
41980 contain registers @samp{A16} through @samp{A31} and @samp{B16}
41981 through @samp{B31}.
41983 The @samp{org.gnu.gdb.tic6x.c6xp} feature is optional. It should
41984 contain registers @samp{TSR}, @samp{ILC} and @samp{RILC}.
41986 @node Operating System Information
41987 @appendix Operating System Information
41988 @cindex operating system information
41994 Users of @value{GDBN} often wish to obtain information about the state of
41995 the operating system running on the target---for example the list of
41996 processes, or the list of open files. This section describes the
41997 mechanism that makes it possible. This mechanism is similar to the
41998 target features mechanism (@pxref{Target Descriptions}), but focuses
41999 on a different aspect of target.
42001 Operating system information is retrived from the target via the
42002 remote protocol, using @samp{qXfer} requests (@pxref{qXfer osdata
42003 read}). The object name in the request should be @samp{osdata}, and
42004 the @var{annex} identifies the data to be fetched.
42007 @appendixsection Process list
42008 @cindex operating system information, process list
42010 When requesting the process list, the @var{annex} field in the
42011 @samp{qXfer} request should be @samp{processes}. The returned data is
42012 an XML document. The formal syntax of this document is defined in
42013 @file{gdb/features/osdata.dtd}.
42015 An example document is:
42018 <?xml version="1.0"?>
42019 <!DOCTYPE target SYSTEM "osdata.dtd">
42020 <osdata type="processes">
42022 <column name="pid">1</column>
42023 <column name="user">root</column>
42024 <column name="command">/sbin/init</column>
42025 <column name="cores">1,2,3</column>
42030 Each item should include a column whose name is @samp{pid}. The value
42031 of that column should identify the process on the target. The
42032 @samp{user} and @samp{command} columns are optional, and will be
42033 displayed by @value{GDBN}. The @samp{cores} column, if present,
42034 should contain a comma-separated list of cores that this process
42035 is running on. Target may provide additional columns,
42036 which @value{GDBN} currently ignores.
42038 @node Trace File Format
42039 @appendix Trace File Format
42040 @cindex trace file format
42042 The trace file comes in three parts: a header, a textual description
42043 section, and a trace frame section with binary data.
42045 The header has the form @code{\x7fTRACE0\n}. The first byte is
42046 @code{0x7f} so as to indicate that the file contains binary data,
42047 while the @code{0} is a version number that may have different values
42050 The description section consists of multiple lines of @sc{ascii} text
42051 separated by newline characters (@code{0xa}). The lines may include a
42052 variety of optional descriptive or context-setting information, such
42053 as tracepoint definitions or register set size. @value{GDBN} will
42054 ignore any line that it does not recognize. An empty line marks the end
42059 Specifies the size of a register block in bytes. This is equal to the
42060 size of a @code{g} packet payload in the remote protocol. @var{size}
42061 is an ascii decimal number. There should be only one such line in
42062 a single trace file.
42064 @item status @var{status}
42065 Trace status. @var{status} has the same format as a @code{qTStatus}
42066 remote packet reply. There should be only one such line in a single trace
42069 @item tp @var{payload}
42070 Tracepoint definition. The @var{payload} has the same format as
42071 @code{qTfP}/@code{qTsP} remote packet reply payload. A single tracepoint
42072 may take multiple lines of definition, corresponding to the multiple
42075 @item tsv @var{payload}
42076 Trace state variable definition. The @var{payload} has the same format as
42077 @code{qTfV}/@code{qTsV} remote packet reply payload. A single variable
42078 may take multiple lines of definition, corresponding to the multiple
42081 @item tdesc @var{payload}
42082 Target description in XML format. The @var{payload} is a single line of
42083 the XML file. All such lines should be concatenated together to get
42084 the original XML file. This file is in the same format as @code{qXfer}
42085 @code{features} payload, and corresponds to the main @code{target.xml}
42086 file. Includes are not allowed.
42090 The trace frame section consists of a number of consecutive frames.
42091 Each frame begins with a two-byte tracepoint number, followed by a
42092 four-byte size giving the amount of data in the frame. The data in
42093 the frame consists of a number of blocks, each introduced by a
42094 character indicating its type (at least register, memory, and trace
42095 state variable). The data in this section is raw binary, not a
42096 hexadecimal or other encoding; its endianness matches the target's
42099 @c FIXME bi-arch may require endianness/arch info in description section
42102 @item R @var{bytes}
42103 Register block. The number and ordering of bytes matches that of a
42104 @code{g} packet in the remote protocol. Note that these are the
42105 actual bytes, in target order, not a hexadecimal encoding.
42107 @item M @var{address} @var{length} @var{bytes}...
42108 Memory block. This is a contiguous block of memory, at the 8-byte
42109 address @var{address}, with a 2-byte length @var{length}, followed by
42110 @var{length} bytes.
42112 @item V @var{number} @var{value}
42113 Trace state variable block. This records the 8-byte signed value
42114 @var{value} of trace state variable numbered @var{number}.
42118 Future enhancements of the trace file format may include additional types
42121 @node Index Section Format
42122 @appendix @code{.gdb_index} section format
42123 @cindex .gdb_index section format
42124 @cindex index section format
42126 This section documents the index section that is created by @code{save
42127 gdb-index} (@pxref{Index Files}). The index section is
42128 DWARF-specific; some knowledge of DWARF is assumed in this
42131 The mapped index file format is designed to be directly
42132 @code{mmap}able on any architecture. In most cases, a datum is
42133 represented using a little-endian 32-bit integer value, called an
42134 @code{offset_type}. Big endian machines must byte-swap the values
42135 before using them. Exceptions to this rule are noted. The data is
42136 laid out such that alignment is always respected.
42138 A mapped index consists of several areas, laid out in order.
42142 The file header. This is a sequence of values, of @code{offset_type}
42143 unless otherwise noted:
42147 The version number, currently 8. Versions 1, 2 and 3 are obsolete.
42148 Version 4 uses a different hashing function from versions 5 and 6.
42149 Version 6 includes symbols for inlined functions, whereas versions 4
42150 and 5 do not. Version 7 adds attributes to the CU indices in the
42151 symbol table. Version 8 specifies that symbols from DWARF type units
42152 (@samp{DW_TAG_type_unit}) refer to the type unit's symbol table and not the
42153 compilation unit (@samp{DW_TAG_comp_unit}) using the type.
42155 @value{GDBN} will only read version 4, 5, or 6 indices
42156 by specifying @code{set use-deprecated-index-sections on}.
42157 GDB has a workaround for potentially broken version 7 indices so it is
42158 currently not flagged as deprecated.
42161 The offset, from the start of the file, of the CU list.
42164 The offset, from the start of the file, of the types CU list. Note
42165 that this area can be empty, in which case this offset will be equal
42166 to the next offset.
42169 The offset, from the start of the file, of the address area.
42172 The offset, from the start of the file, of the symbol table.
42175 The offset, from the start of the file, of the constant pool.
42179 The CU list. This is a sequence of pairs of 64-bit little-endian
42180 values, sorted by the CU offset. The first element in each pair is
42181 the offset of a CU in the @code{.debug_info} section. The second
42182 element in each pair is the length of that CU. References to a CU
42183 elsewhere in the map are done using a CU index, which is just the
42184 0-based index into this table. Note that if there are type CUs, then
42185 conceptually CUs and type CUs form a single list for the purposes of
42189 The types CU list. This is a sequence of triplets of 64-bit
42190 little-endian values. In a triplet, the first value is the CU offset,
42191 the second value is the type offset in the CU, and the third value is
42192 the type signature. The types CU list is not sorted.
42195 The address area. The address area consists of a sequence of address
42196 entries. Each address entry has three elements:
42200 The low address. This is a 64-bit little-endian value.
42203 The high address. This is a 64-bit little-endian value. Like
42204 @code{DW_AT_high_pc}, the value is one byte beyond the end.
42207 The CU index. This is an @code{offset_type} value.
42211 The symbol table. This is an open-addressed hash table. The size of
42212 the hash table is always a power of 2.
42214 Each slot in the hash table consists of a pair of @code{offset_type}
42215 values. The first value is the offset of the symbol's name in the
42216 constant pool. The second value is the offset of the CU vector in the
42219 If both values are 0, then this slot in the hash table is empty. This
42220 is ok because while 0 is a valid constant pool index, it cannot be a
42221 valid index for both a string and a CU vector.
42223 The hash value for a table entry is computed by applying an
42224 iterative hash function to the symbol's name. Starting with an
42225 initial value of @code{r = 0}, each (unsigned) character @samp{c} in
42226 the string is incorporated into the hash using the formula depending on the
42231 The formula is @code{r = r * 67 + c - 113}.
42233 @item Versions 5 to 7
42234 The formula is @code{r = r * 67 + tolower (c) - 113}.
42237 The terminating @samp{\0} is not incorporated into the hash.
42239 The step size used in the hash table is computed via
42240 @code{((hash * 17) & (size - 1)) | 1}, where @samp{hash} is the hash
42241 value, and @samp{size} is the size of the hash table. The step size
42242 is used to find the next candidate slot when handling a hash
42245 The names of C@t{++} symbols in the hash table are canonicalized. We
42246 don't currently have a simple description of the canonicalization
42247 algorithm; if you intend to create new index sections, you must read
42251 The constant pool. This is simply a bunch of bytes. It is organized
42252 so that alignment is correct: CU vectors are stored first, followed by
42255 A CU vector in the constant pool is a sequence of @code{offset_type}
42256 values. The first value is the number of CU indices in the vector.
42257 Each subsequent value is the index and symbol attributes of a CU in
42258 the CU list. This element in the hash table is used to indicate which
42259 CUs define the symbol and how the symbol is used.
42260 See below for the format of each CU index+attributes entry.
42262 A string in the constant pool is zero-terminated.
42265 Attributes were added to CU index values in @code{.gdb_index} version 7.
42266 If a symbol has multiple uses within a CU then there is one
42267 CU index+attributes value for each use.
42269 The format of each CU index+attributes entry is as follows
42275 This is the index of the CU in the CU list.
42277 These bits are reserved for future purposes and must be zero.
42279 The kind of the symbol in the CU.
42283 This value is reserved and should not be used.
42284 By reserving zero the full @code{offset_type} value is backwards compatible
42285 with previous versions of the index.
42287 The symbol is a type.
42289 The symbol is a variable or an enum value.
42291 The symbol is a function.
42293 Any other kind of symbol.
42295 These values are reserved.
42299 This bit is zero if the value is global and one if it is static.
42301 The determination of whether a symbol is global or static is complicated.
42302 The authorative reference is the file @file{dwarf2read.c} in
42303 @value{GDBN} sources.
42307 This pseudo-code describes the computation of a symbol's kind and
42308 global/static attributes in the index.
42311 is_external = get_attribute (die, DW_AT_external);
42312 language = get_attribute (cu_die, DW_AT_language);
42315 case DW_TAG_typedef:
42316 case DW_TAG_base_type:
42317 case DW_TAG_subrange_type:
42321 case DW_TAG_enumerator:
42323 is_static = language != CPLUS;
42325 case DW_TAG_subprogram:
42327 is_static = ! (is_external || language == ADA);
42329 case DW_TAG_constant:
42331 is_static = ! is_external;
42333 case DW_TAG_variable:
42335 is_static = ! is_external;
42337 case DW_TAG_namespace:
42341 case DW_TAG_class_type:
42342 case DW_TAG_interface_type:
42343 case DW_TAG_structure_type:
42344 case DW_TAG_union_type:
42345 case DW_TAG_enumeration_type:
42347 is_static = language != CPLUS;
42355 @appendix Manual pages
42359 * gdb man:: The GNU Debugger man page
42360 * gdbserver man:: Remote Server for the GNU Debugger man page
42361 * gcore man:: Generate a core file of a running program
42362 * gdbinit man:: gdbinit scripts
42368 @c man title gdb The GNU Debugger
42370 @c man begin SYNOPSIS gdb
42371 gdb [@option{-help}] [@option{-nh}] [@option{-nx}] [@option{-q}]
42372 [@option{-batch}] [@option{-cd=}@var{dir}] [@option{-f}]
42373 [@option{-b}@w{ }@var{bps}]
42374 [@option{-tty=}@var{dev}] [@option{-s} @var{symfile}]
42375 [@option{-e}@w{ }@var{prog}] [@option{-se}@w{ }@var{prog}]
42376 [@option{-c}@w{ }@var{core}] [@option{-p}@w{ }@var{procID}]
42377 [@option{-x}@w{ }@var{cmds}] [@option{-d}@w{ }@var{dir}]
42378 [@var{prog}|@var{prog} @var{procID}|@var{prog} @var{core}]
42381 @c man begin DESCRIPTION gdb
42382 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
42383 going on ``inside'' another program while it executes -- or what another
42384 program was doing at the moment it crashed.
42386 @value{GDBN} can do four main kinds of things (plus other things in support of
42387 these) to help you catch bugs in the act:
42391 Start your program, specifying anything that might affect its behavior.
42394 Make your program stop on specified conditions.
42397 Examine what has happened, when your program has stopped.
42400 Change things in your program, so you can experiment with correcting the
42401 effects of one bug and go on to learn about another.
42404 You can use @value{GDBN} to debug programs written in C, C@t{++}, Fortran and
42407 @value{GDBN} is invoked with the shell command @code{gdb}. Once started, it reads
42408 commands from the terminal until you tell it to exit with the @value{GDBN}
42409 command @code{quit}. You can get online help from @value{GDBN} itself
42410 by using the command @code{help}.
42412 You can run @code{gdb} with no arguments or options; but the most
42413 usual way to start @value{GDBN} is with one argument or two, specifying an
42414 executable program as the argument:
42420 You can also start with both an executable program and a core file specified:
42426 You can, instead, specify a process ID as a second argument, if you want
42427 to debug a running process:
42435 would attach @value{GDBN} to process @code{1234} (unless you also have a file
42436 named @file{1234}; @value{GDBN} does check for a core file first).
42437 With option @option{-p} you can omit the @var{program} filename.
42439 Here are some of the most frequently needed @value{GDBN} commands:
42441 @c pod2man highlights the right hand side of the @item lines.
42443 @item break [@var{file}:]@var{function}
42444 Set a breakpoint at @var{function} (in @var{file}).
42446 @item run [@var{arglist}]
42447 Start your program (with @var{arglist}, if specified).
42450 Backtrace: display the program stack.
42452 @item print @var{expr}
42453 Display the value of an expression.
42456 Continue running your program (after stopping, e.g. at a breakpoint).
42459 Execute next program line (after stopping); step @emph{over} any
42460 function calls in the line.
42462 @item edit [@var{file}:]@var{function}
42463 look at the program line where it is presently stopped.
42465 @item list [@var{file}:]@var{function}
42466 type the text of the program in the vicinity of where it is presently stopped.
42469 Execute next program line (after stopping); step @emph{into} any
42470 function calls in the line.
42472 @item help [@var{name}]
42473 Show information about @value{GDBN} command @var{name}, or general information
42474 about using @value{GDBN}.
42477 Exit from @value{GDBN}.
42481 For full details on @value{GDBN},
42482 see @cite{Using GDB: A Guide to the GNU Source-Level Debugger},
42483 by Richard M. Stallman and Roland H. Pesch. The same text is available online
42484 as the @code{gdb} entry in the @code{info} program.
42488 @c man begin OPTIONS gdb
42489 Any arguments other than options specify an executable
42490 file and core file (or process ID); that is, the first argument
42491 encountered with no
42492 associated option flag is equivalent to a @option{-se} option, and the second,
42493 if any, is equivalent to a @option{-c} option if it's the name of a file.
42495 both long and short forms; both are shown here. The long forms are also
42496 recognized if you truncate them, so long as enough of the option is
42497 present to be unambiguous. (If you prefer, you can flag option
42498 arguments with @option{+} rather than @option{-}, though we illustrate the
42499 more usual convention.)
42501 All the options and command line arguments you give are processed
42502 in sequential order. The order makes a difference when the @option{-x}
42508 List all options, with brief explanations.
42510 @item -symbols=@var{file}
42511 @itemx -s @var{file}
42512 Read symbol table from file @var{file}.
42515 Enable writing into executable and core files.
42517 @item -exec=@var{file}
42518 @itemx -e @var{file}
42519 Use file @var{file} as the executable file to execute when
42520 appropriate, and for examining pure data in conjunction with a core
42523 @item -se=@var{file}
42524 Read symbol table from file @var{file} and use it as the executable
42527 @item -core=@var{file}
42528 @itemx -c @var{file}
42529 Use file @var{file} as a core dump to examine.
42531 @item -command=@var{file}
42532 @itemx -x @var{file}
42533 Execute @value{GDBN} commands from file @var{file}.
42535 @item -ex @var{command}
42536 Execute given @value{GDBN} @var{command}.
42538 @item -directory=@var{directory}
42539 @itemx -d @var{directory}
42540 Add @var{directory} to the path to search for source files.
42543 Do not execute commands from @file{~/.gdbinit}.
42547 Do not execute commands from any @file{.gdbinit} initialization files.
42551 ``Quiet''. Do not print the introductory and copyright messages. These
42552 messages are also suppressed in batch mode.
42555 Run in batch mode. Exit with status @code{0} after processing all the command
42556 files specified with @option{-x} (and @file{.gdbinit}, if not inhibited).
42557 Exit with nonzero status if an error occurs in executing the @value{GDBN}
42558 commands in the command files.
42560 Batch mode may be useful for running @value{GDBN} as a filter, for example to
42561 download and run a program on another computer; in order to make this
42562 more useful, the message
42565 Program exited normally.
42569 (which is ordinarily issued whenever a program running under @value{GDBN} control
42570 terminates) is not issued when running in batch mode.
42572 @item -cd=@var{directory}
42573 Run @value{GDBN} using @var{directory} as its working directory,
42574 instead of the current directory.
42578 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells
42579 @value{GDBN} to output the full file name and line number in a standard,
42580 recognizable fashion each time a stack frame is displayed (which
42581 includes each time the program stops). This recognizable format looks
42582 like two @samp{\032} characters, followed by the file name, line number
42583 and character position separated by colons, and a newline. The
42584 Emacs-to-@value{GDBN} interface program uses the two @samp{\032}
42585 characters as a signal to display the source code for the frame.
42588 Set the line speed (baud rate or bits per second) of any serial
42589 interface used by @value{GDBN} for remote debugging.
42591 @item -tty=@var{device}
42592 Run using @var{device} for your program's standard input and output.
42596 @c man begin SEEALSO gdb
42598 The full documentation for @value{GDBN} is maintained as a Texinfo manual.
42599 If the @code{info} and @code{gdb} programs and @value{GDBN}'s Texinfo
42600 documentation are properly installed at your site, the command
42607 should give you access to the complete manual.
42609 @cite{Using GDB: A Guide to the GNU Source-Level Debugger},
42610 Richard M. Stallman and Roland H. Pesch, July 1991.
42614 @node gdbserver man
42615 @heading gdbserver man
42617 @c man title gdbserver Remote Server for the GNU Debugger
42619 @c man begin SYNOPSIS gdbserver
42620 gdbserver @var{comm} @var{prog} [@var{args}@dots{}]
42622 gdbserver --attach @var{comm} @var{pid}
42624 gdbserver --multi @var{comm}
42628 @c man begin DESCRIPTION gdbserver
42629 @command{gdbserver} is a program that allows you to run @value{GDBN} on a different machine
42630 than the one which is running the program being debugged.
42633 @subheading Usage (server (target) side)
42636 Usage (server (target) side):
42639 First, you need to have a copy of the program you want to debug put onto
42640 the target system. The program can be stripped to save space if needed, as
42641 @command{gdbserver} doesn't care about symbols. All symbol handling is taken care of by
42642 the @value{GDBN} running on the host system.
42644 To use the server, you log on to the target system, and run the @command{gdbserver}
42645 program. You must tell it (a) how to communicate with @value{GDBN}, (b) the name of
42646 your program, and (c) its arguments. The general syntax is:
42649 target> gdbserver @var{comm} @var{program} [@var{args} ...]
42652 For example, using a serial port, you might say:
42656 @c @file would wrap it as F</dev/com1>.
42657 target> gdbserver /dev/com1 emacs foo.txt
42660 target> gdbserver @file{/dev/com1} emacs foo.txt
42664 This tells @command{gdbserver} to debug emacs with an argument of foo.txt, and
42665 to communicate with @value{GDBN} via @file{/dev/com1}. @command{gdbserver} now
42666 waits patiently for the host @value{GDBN} to communicate with it.
42668 To use a TCP connection, you could say:
42671 target> gdbserver host:2345 emacs foo.txt
42674 This says pretty much the same thing as the last example, except that we are
42675 going to communicate with the @code{host} @value{GDBN} via TCP. The @code{host:2345} argument means
42676 that we are expecting to see a TCP connection from @code{host} to local TCP port
42677 2345. (Currently, the @code{host} part is ignored.) You can choose any number you
42678 want for the port number as long as it does not conflict with any existing TCP
42679 ports on the target system. This same port number must be used in the host
42680 @value{GDBN}s @code{target remote} command, which will be described shortly. Note that if
42681 you chose a port number that conflicts with another service, @command{gdbserver} will
42682 print an error message and exit.
42684 @command{gdbserver} can also attach to running programs.
42685 This is accomplished via the @option{--attach} argument. The syntax is:
42688 target> gdbserver --attach @var{comm} @var{pid}
42691 @var{pid} is the process ID of a currently running process. It isn't
42692 necessary to point @command{gdbserver} at a binary for the running process.
42694 To start @code{gdbserver} without supplying an initial command to run
42695 or process ID to attach, use the @option{--multi} command line option.
42696 In such case you should connect using @kbd{target extended-remote} to start
42697 the program you want to debug.
42700 target> gdbserver --multi @var{comm}
42704 @subheading Usage (host side)
42710 You need an unstripped copy of the target program on your host system, since
42711 @value{GDBN} needs to examine it's symbol tables and such. Start up @value{GDBN} as you normally
42712 would, with the target program as the first argument. (You may need to use the
42713 @option{--baud} option if the serial line is running at anything except 9600 baud.)
42714 That is @code{gdb TARGET-PROG}, or @code{gdb --baud BAUD TARGET-PROG}. After that, the only
42715 new command you need to know about is @code{target remote}
42716 (or @code{target extended-remote}). Its argument is either
42717 a device name (usually a serial device, like @file{/dev/ttyb}), or a @code{HOST:PORT}
42718 descriptor. For example:
42722 @c @file would wrap it as F</dev/ttyb>.
42723 (gdb) target remote /dev/ttyb
42726 (gdb) target remote @file{/dev/ttyb}
42731 communicates with the server via serial line @file{/dev/ttyb}, and:
42734 (gdb) target remote the-target:2345
42738 communicates via a TCP connection to port 2345 on host `the-target', where
42739 you previously started up @command{gdbserver} with the same port number. Note that for
42740 TCP connections, you must start up @command{gdbserver} prior to using the `target remote'
42741 command, otherwise you may get an error that looks something like
42742 `Connection refused'.
42744 @command{gdbserver} can also debug multiple inferiors at once,
42747 the @value{GDBN} manual in node @code{Inferiors and Programs}
42748 -- shell command @code{info -f gdb -n 'Inferiors and Programs'}.
42751 @ref{Inferiors and Programs}.
42753 In such case use the @code{extended-remote} @value{GDBN} command variant:
42756 (gdb) target extended-remote the-target:2345
42759 The @command{gdbserver} option @option{--multi} may or may not be used in such
42763 @c man begin OPTIONS gdbserver
42764 There are three different modes for invoking @command{gdbserver}:
42769 Debug a specific program specified by its program name:
42772 gdbserver @var{comm} @var{prog} [@var{args}@dots{}]
42775 The @var{comm} parameter specifies how should the server communicate
42776 with @value{GDBN}; it is either a device name (to use a serial line),
42777 a TCP port number (@code{:1234}), or @code{-} or @code{stdio} to use
42778 stdin/stdout of @code{gdbserver}. Specify the name of the program to
42779 debug in @var{prog}. Any remaining arguments will be passed to the
42780 program verbatim. When the program exits, @value{GDBN} will close the
42781 connection, and @code{gdbserver} will exit.
42784 Debug a specific program by specifying the process ID of a running
42788 gdbserver --attach @var{comm} @var{pid}
42791 The @var{comm} parameter is as described above. Supply the process ID
42792 of a running program in @var{pid}; @value{GDBN} will do everything
42793 else. Like with the previous mode, when the process @var{pid} exits,
42794 @value{GDBN} will close the connection, and @code{gdbserver} will exit.
42797 Multi-process mode -- debug more than one program/process:
42800 gdbserver --multi @var{comm}
42803 In this mode, @value{GDBN} can instruct @command{gdbserver} which
42804 command(s) to run. Unlike the other 2 modes, @value{GDBN} will not
42805 close the connection when a process being debugged exits, so you can
42806 debug several processes in the same session.
42809 In each of the modes you may specify these options:
42814 List all options, with brief explanations.
42817 This option causes @command{gdbserver} to print its version number and exit.
42820 @command{gdbserver} will attach to a running program. The syntax is:
42823 target> gdbserver --attach @var{comm} @var{pid}
42826 @var{pid} is the process ID of a currently running process. It isn't
42827 necessary to point @command{gdbserver} at a binary for the running process.
42830 To start @code{gdbserver} without supplying an initial command to run
42831 or process ID to attach, use this command line option.
42832 Then you can connect using @kbd{target extended-remote} and start
42833 the program you want to debug. The syntax is:
42836 target> gdbserver --multi @var{comm}
42840 Instruct @code{gdbserver} to display extra status information about the debugging
42842 This option is intended for @code{gdbserver} development and for bug reports to
42845 @item --remote-debug
42846 Instruct @code{gdbserver} to display remote protocol debug output.
42847 This option is intended for @code{gdbserver} development and for bug reports to
42850 @item --debug-format=option1@r{[},option2,...@r{]}
42851 Instruct @code{gdbserver} to include extra information in each line
42852 of debugging output.
42853 @xref{Other Command-Line Arguments for gdbserver}.
42856 Specify a wrapper to launch programs
42857 for debugging. The option should be followed by the name of the
42858 wrapper, then any command-line arguments to pass to the wrapper, then
42859 @kbd{--} indicating the end of the wrapper arguments.
42862 By default, @command{gdbserver} keeps the listening TCP port open, so that
42863 additional connections are possible. However, if you start @code{gdbserver}
42864 with the @option{--once} option, it will stop listening for any further
42865 connection attempts after connecting to the first @value{GDBN} session.
42867 @c --disable-packet is not documented for users.
42869 @c --disable-randomization and --no-disable-randomization are superseded by
42870 @c QDisableRandomization.
42875 @c man begin SEEALSO gdbserver
42877 The full documentation for @value{GDBN} is maintained as a Texinfo manual.
42878 If the @code{info} and @code{gdb} programs and @value{GDBN}'s Texinfo
42879 documentation are properly installed at your site, the command
42885 should give you access to the complete manual.
42887 @cite{Using GDB: A Guide to the GNU Source-Level Debugger},
42888 Richard M. Stallman and Roland H. Pesch, July 1991.
42895 @c man title gcore Generate a core file of a running program
42898 @c man begin SYNOPSIS gcore
42899 gcore [-o @var{filename}] @var{pid}
42903 @c man begin DESCRIPTION gcore
42904 Generate a core dump of a running program with process ID @var{pid}.
42905 Produced file is equivalent to a kernel produced core file as if the process
42906 crashed (and if @kbd{ulimit -c} were used to set up an appropriate core dump
42907 limit). Unlike after a crash, after @command{gcore} the program remains
42908 running without any change.
42911 @c man begin OPTIONS gcore
42913 @item -o @var{filename}
42914 The optional argument
42915 @var{filename} specifies the file name where to put the core dump.
42916 If not specified, the file name defaults to @file{core.@var{pid}},
42917 where @var{pid} is the running program process ID.
42921 @c man begin SEEALSO gcore
42923 The full documentation for @value{GDBN} is maintained as a Texinfo manual.
42924 If the @code{info} and @code{gdb} programs and @value{GDBN}'s Texinfo
42925 documentation are properly installed at your site, the command
42932 should give you access to the complete manual.
42934 @cite{Using GDB: A Guide to the GNU Source-Level Debugger},
42935 Richard M. Stallman and Roland H. Pesch, July 1991.
42942 @c man title gdbinit GDB initialization scripts
42945 @c man begin SYNOPSIS gdbinit
42946 @ifset SYSTEM_GDBINIT
42947 @value{SYSTEM_GDBINIT}
42956 @c man begin DESCRIPTION gdbinit
42957 These files contain @value{GDBN} commands to automatically execute during
42958 @value{GDBN} startup. The lines of contents are canned sequences of commands,
42961 the @value{GDBN} manual in node @code{Sequences}
42962 -- shell command @code{info -f gdb -n Sequences}.
42968 Please read more in
42970 the @value{GDBN} manual in node @code{Startup}
42971 -- shell command @code{info -f gdb -n Startup}.
42978 @ifset SYSTEM_GDBINIT
42979 @item @value{SYSTEM_GDBINIT}
42981 @ifclear SYSTEM_GDBINIT
42982 @item (not enabled with @code{--with-system-gdbinit} during compilation)
42984 System-wide initialization file. It is executed unless user specified
42985 @value{GDBN} option @code{-nx} or @code{-n}.
42988 the @value{GDBN} manual in node @code{System-wide configuration}
42989 -- shell command @code{info -f gdb -n 'System-wide configuration'}.
42992 @ref{System-wide configuration}.
42996 User initialization file. It is executed unless user specified
42997 @value{GDBN} options @code{-nx}, @code{-n} or @code{-nh}.
43000 Initialization file for current directory. It may need to be enabled with
43001 @value{GDBN} security command @code{set auto-load local-gdbinit}.
43004 the @value{GDBN} manual in node @code{Init File in the Current Directory}
43005 -- shell command @code{info -f gdb -n 'Init File in the Current Directory'}.
43008 @ref{Init File in the Current Directory}.
43013 @c man begin SEEALSO gdbinit
43015 gdb(1), @code{info -f gdb -n Startup}
43017 The full documentation for @value{GDBN} is maintained as a Texinfo manual.
43018 If the @code{info} and @code{gdb} programs and @value{GDBN}'s Texinfo
43019 documentation are properly installed at your site, the command
43025 should give you access to the complete manual.
43027 @cite{Using GDB: A Guide to the GNU Source-Level Debugger},
43028 Richard M. Stallman and Roland H. Pesch, July 1991.
43034 @node GNU Free Documentation License
43035 @appendix GNU Free Documentation License
43038 @node Concept Index
43039 @unnumbered Concept Index
43043 @node Command and Variable Index
43044 @unnumbered Command, Variable, and Function Index
43049 % I think something like @@colophon should be in texinfo. In the
43051 \long\def\colophon{\hbox to0pt{}\vfill
43052 \centerline{The body of this manual is set in}
43053 \centerline{\fontname\tenrm,}
43054 \centerline{with headings in {\bf\fontname\tenbf}}
43055 \centerline{and examples in {\tt\fontname\tentt}.}
43056 \centerline{{\it\fontname\tenit\/},}
43057 \centerline{{\bf\fontname\tenbf}, and}
43058 \centerline{{\sl\fontname\tensl\/}}
43059 \centerline{are used for emphasis.}\vfill}
43061 % Blame: doc@@cygnus.com, 1991.