1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,
3 @c 1999, 2000, 2001, 2002, 2003
4 @c Free Software Foundation, Inc.
7 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
8 @c of @set vars. However, you can override filename with makeinfo -o.
13 @settitle Debugging with @value{GDBN}
14 @setchapternewpage odd
25 @c readline appendices use @vindex, @findex and @ftable,
26 @c annotate.texi and gdbmi use @findex.
30 @c !!set GDB manual's edition---not the same as GDB version!
33 @c !!set GDB manual's revision date
36 @c !!set GDB edit command default editor
39 @c THIS MANUAL REQUIRES TEXINFO 4.0 OR LATER.
41 @c This is a dir.info fragment to support semi-automated addition of
42 @c manuals to an info tree.
43 @dircategory Programming & development tools.
45 * Gdb: (gdb). The @sc{gnu} debugger.
49 This file documents the @sc{gnu} debugger @value{GDBN}.
52 This is the @value{EDITION} Edition, @value{DATE},
53 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
54 for @value{GDBN} Version @value{GDBVN}.
56 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998,@*
57 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
59 Permission is granted to copy, distribute and/or modify this document
60 under the terms of the GNU Free Documentation License, Version 1.1 or
61 any later version published by the Free Software Foundation; with the
62 Invariant Sections being ``Free Software'' and ``Free Software Needs
63 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
64 and with the Back-Cover Texts as in (a) below.
66 (a) The Free Software Foundation's Back-Cover Text is: ``You have
67 freedom to copy and modify this GNU Manual, like GNU software. Copies
68 published by the Free Software Foundation raise funds for GNU
73 @title Debugging with @value{GDBN}
74 @subtitle The @sc{gnu} Source-Level Debugger
76 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
77 @subtitle @value{DATE}
78 @author Richard Stallman, Roland Pesch, Stan Shebs, et al.
82 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
83 \hfill {\it Debugging with @value{GDBN}}\par
84 \hfill \TeX{}info \texinfoversion\par
88 @vskip 0pt plus 1filll
89 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995,
90 1996, 1998, 1999, 2000, 2001, 2002, 2003 Free Software Foundation, Inc.
92 Published by the Free Software Foundation @*
93 59 Temple Place - Suite 330, @*
94 Boston, MA 02111-1307 USA @*
97 Permission is granted to copy, distribute and/or modify this document
98 under the terms of the GNU Free Documentation License, Version 1.1 or
99 any later version published by the Free Software Foundation; with the
100 Invariant Sections being ``Free Software'' and ``Free Software Needs
101 Free Documentation'', with the Front-Cover Texts being ``A GNU Manual,''
102 and with the Back-Cover Texts as in (a) below.
104 (a) The Free Software Foundation's Back-Cover Text is: ``You have
105 freedom to copy and modify this GNU Manual, like GNU software. Copies
106 published by the Free Software Foundation raise funds for GNU
112 @node Top, Summary, (dir), (dir)
114 @top Debugging with @value{GDBN}
116 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
118 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
121 Copyright (C) 1988-2003 Free Software Foundation, Inc.
124 * Summary:: Summary of @value{GDBN}
125 * Sample Session:: A sample @value{GDBN} session
127 * Invocation:: Getting in and out of @value{GDBN}
128 * Commands:: @value{GDBN} commands
129 * Running:: Running programs under @value{GDBN}
130 * Stopping:: Stopping and continuing
131 * Stack:: Examining the stack
132 * Source:: Examining source files
133 * Data:: Examining data
134 * Macros:: Preprocessor Macros
135 * Tracepoints:: Debugging remote targets non-intrusively
136 * Overlays:: Debugging programs that use overlays
138 * Languages:: Using @value{GDBN} with different languages
140 * Symbols:: Examining the symbol table
141 * Altering:: Altering execution
142 * GDB Files:: @value{GDBN} files
143 * Targets:: Specifying a debugging target
144 * Remote Debugging:: Debugging remote programs
145 * Configurations:: Configuration-specific information
146 * Controlling GDB:: Controlling @value{GDBN}
147 * Sequences:: Canned sequences of commands
148 * TUI:: @value{GDBN} Text User Interface
149 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
150 * Annotations:: @value{GDBN}'s annotation interface.
151 * GDB/MI:: @value{GDBN}'s Machine Interface.
153 * GDB Bugs:: Reporting bugs in @value{GDBN}
154 * Formatting Documentation:: How to format and print @value{GDBN} documentation
156 * Command Line Editing:: Command Line Editing
157 * Using History Interactively:: Using History Interactively
158 * Installing GDB:: Installing GDB
159 * Maintenance Commands:: Maintenance Commands
160 * Remote Protocol:: GDB Remote Serial Protocol
161 * Copying:: GNU General Public License says
162 how you can copy and share GDB
163 * GNU Free Documentation License:: The license for this documentation
172 @unnumbered Summary of @value{GDBN}
174 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
175 going on ``inside'' another program while it executes---or what another
176 program was doing at the moment it crashed.
178 @value{GDBN} can do four main kinds of things (plus other things in support of
179 these) to help you catch bugs in the act:
183 Start your program, specifying anything that might affect its behavior.
186 Make your program stop on specified conditions.
189 Examine what has happened, when your program has stopped.
192 Change things in your program, so you can experiment with correcting the
193 effects of one bug and go on to learn about another.
196 You can use @value{GDBN} to debug programs written in C and C++.
197 For more information, see @ref{Support,,Supported languages}.
198 For more information, see @ref{C,,C and C++}.
201 Support for Modula-2 is partial. For information on Modula-2, see
202 @ref{Modula-2,,Modula-2}.
205 Debugging Pascal programs which use sets, subranges, file variables, or
206 nested functions does not currently work. @value{GDBN} does not support
207 entering expressions, printing values, or similar features using Pascal
211 @value{GDBN} can be used to debug programs written in Fortran, although
212 it may be necessary to refer to some variables with a trailing
216 * Free Software:: Freely redistributable software
217 * Contributors:: Contributors to GDB
221 @unnumberedsec Free software
223 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
224 General Public License
225 (GPL). The GPL gives you the freedom to copy or adapt a licensed
226 program---but every person getting a copy also gets with it the
227 freedom to modify that copy (which means that they must get access to
228 the source code), and the freedom to distribute further copies.
229 Typical software companies use copyrights to limit your freedoms; the
230 Free Software Foundation uses the GPL to preserve these freedoms.
232 Fundamentally, the General Public License is a license which says that
233 you have these freedoms and that you cannot take these freedoms away
236 @unnumberedsec Free Software Needs Free Documentation
238 The biggest deficiency in the free software community today is not in
239 the software---it is the lack of good free documentation that we can
240 include with the free software. Many of our most important
241 programs do not come with free reference manuals and free introductory
242 texts. Documentation is an essential part of any software package;
243 when an important free software package does not come with a free
244 manual and a free tutorial, that is a major gap. We have many such
247 Consider Perl, for instance. The tutorial manuals that people
248 normally use are non-free. How did this come about? Because the
249 authors of those manuals published them with restrictive terms---no
250 copying, no modification, source files not available---which exclude
251 them from the free software world.
253 That wasn't the first time this sort of thing happened, and it was far
254 from the last. Many times we have heard a GNU user eagerly describe a
255 manual that he is writing, his intended contribution to the community,
256 only to learn that he had ruined everything by signing a publication
257 contract to make it non-free.
259 Free documentation, like free software, is a matter of freedom, not
260 price. The problem with the non-free manual is not that publishers
261 charge a price for printed copies---that in itself is fine. (The Free
262 Software Foundation sells printed copies of manuals, too.) The
263 problem is the restrictions on the use of the manual. Free manuals
264 are available in source code form, and give you permission to copy and
265 modify. Non-free manuals do not allow this.
267 The criteria of freedom for a free manual are roughly the same as for
268 free software. Redistribution (including the normal kinds of
269 commercial redistribution) must be permitted, so that the manual can
270 accompany every copy of the program, both on-line and on paper.
272 Permission for modification of the technical content is crucial too.
273 When people modify the software, adding or changing features, if they
274 are conscientious they will change the manual too---so they can
275 provide accurate and clear documentation for the modified program. A
276 manual that leaves you no choice but to write a new manual to document
277 a changed version of the program is not really available to our
280 Some kinds of limits on the way modification is handled are
281 acceptable. For example, requirements to preserve the original
282 author's copyright notice, the distribution terms, or the list of
283 authors, are ok. It is also no problem to require modified versions
284 to include notice that they were modified. Even entire sections that
285 may not be deleted or changed are acceptable, as long as they deal
286 with nontechnical topics (like this one). These kinds of restrictions
287 are acceptable because they don't obstruct the community's normal use
290 However, it must be possible to modify all the @emph{technical}
291 content of the manual, and then distribute the result in all the usual
292 media, through all the usual channels. Otherwise, the restrictions
293 obstruct the use of the manual, it is not free, and we need another
294 manual to replace it.
296 Please spread the word about this issue. Our community continues to
297 lose manuals to proprietary publishing. If we spread the word that
298 free software needs free reference manuals and free tutorials, perhaps
299 the next person who wants to contribute by writing documentation will
300 realize, before it is too late, that only free manuals contribute to
301 the free software community.
303 If you are writing documentation, please insist on publishing it under
304 the GNU Free Documentation License or another free documentation
305 license. Remember that this decision requires your approval---you
306 don't have to let the publisher decide. Some commercial publishers
307 will use a free license if you insist, but they will not propose the
308 option; it is up to you to raise the issue and say firmly that this is
309 what you want. If the publisher you are dealing with refuses, please
310 try other publishers. If you're not sure whether a proposed license
311 is free, write to @email{licensing@@gnu.org}.
313 You can encourage commercial publishers to sell more free, copylefted
314 manuals and tutorials by buying them, and particularly by buying
315 copies from the publishers that paid for their writing or for major
316 improvements. Meanwhile, try to avoid buying non-free documentation
317 at all. Check the distribution terms of a manual before you buy it,
318 and insist that whoever seeks your business must respect your freedom.
319 Check the history of the book, and try to reward the publishers that
320 have paid or pay the authors to work on it.
322 The Free Software Foundation maintains a list of free documentation
323 published by other publishers, at
324 @url{http://www.fsf.org/doc/other-free-books.html}.
327 @unnumberedsec Contributors to @value{GDBN}
329 Richard Stallman was the original author of @value{GDBN}, and of many
330 other @sc{gnu} programs. Many others have contributed to its
331 development. This section attempts to credit major contributors. One
332 of the virtues of free software is that everyone is free to contribute
333 to it; with regret, we cannot actually acknowledge everyone here. The
334 file @file{ChangeLog} in the @value{GDBN} distribution approximates a
335 blow-by-blow account.
337 Changes much prior to version 2.0 are lost in the mists of time.
340 @emph{Plea:} Additions to this section are particularly welcome. If you
341 or your friends (or enemies, to be evenhanded) have been unfairly
342 omitted from this list, we would like to add your names!
345 So that they may not regard their many labors as thankless, we
346 particularly thank those who shepherded @value{GDBN} through major
348 Andrew Cagney (releases 5.3, 5.2, 5.1 and 5.0);
349 Jim Blandy (release 4.18);
350 Jason Molenda (release 4.17);
351 Stan Shebs (release 4.14);
352 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
353 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
354 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
355 Jim Kingdon (releases 3.5, 3.4, and 3.3);
356 and Randy Smith (releases 3.2, 3.1, and 3.0).
358 Richard Stallman, assisted at various times by Peter TerMaat, Chris
359 Hanson, and Richard Mlynarik, handled releases through 2.8.
361 Michael Tiemann is the author of most of the @sc{gnu} C@t{++} support
362 in @value{GDBN}, with significant additional contributions from Per
363 Bothner and Daniel Berlin. James Clark wrote the @sc{gnu} C@t{++}
364 demangler. Early work on C@t{++} was by Peter TerMaat (who also did
365 much general update work leading to release 3.0).
367 @value{GDBN} uses the BFD subroutine library to examine multiple
368 object-file formats; BFD was a joint project of David V.
369 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
371 David Johnson wrote the original COFF support; Pace Willison did
372 the original support for encapsulated COFF.
374 Brent Benson of Harris Computer Systems contributed DWARF2 support.
376 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
377 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
379 Jean-Daniel Fekete contributed Sun 386i support.
380 Chris Hanson improved the HP9000 support.
381 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
382 David Johnson contributed Encore Umax support.
383 Jyrki Kuoppala contributed Altos 3068 support.
384 Jeff Law contributed HP PA and SOM support.
385 Keith Packard contributed NS32K support.
386 Doug Rabson contributed Acorn Risc Machine support.
387 Bob Rusk contributed Harris Nighthawk CX-UX support.
388 Chris Smith contributed Convex support (and Fortran debugging).
389 Jonathan Stone contributed Pyramid support.
390 Michael Tiemann contributed SPARC support.
391 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
392 Pace Willison contributed Intel 386 support.
393 Jay Vosburgh contributed Symmetry support.
394 Marko Mlinar contributed OpenRISC 1000 support.
396 Andreas Schwab contributed M68K @sc{gnu}/Linux support.
398 Rich Schaefer and Peter Schauer helped with support of SunOS shared
401 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
402 about several machine instruction sets.
404 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
405 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
406 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
407 and RDI targets, respectively.
409 Brian Fox is the author of the readline libraries providing
410 command-line editing and command history.
412 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
413 Modula-2 support, and contributed the Languages chapter of this manual.
415 Fred Fish wrote most of the support for Unix System Vr4.
416 He also enhanced the command-completion support to cover C@t{++} overloaded
419 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
422 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
424 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
426 Toshiba sponsored the support for the TX39 Mips processor.
428 Matsushita sponsored the support for the MN10200 and MN10300 processors.
430 Fujitsu sponsored the support for SPARClite and FR30 processors.
432 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
435 Michael Snyder added support for tracepoints.
437 Stu Grossman wrote gdbserver.
439 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
440 nearly innumerable bug fixes and cleanups throughout @value{GDBN}.
442 The following people at the Hewlett-Packard Company contributed
443 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
444 (narrow mode), HP's implementation of kernel threads, HP's aC@t{++}
445 compiler, and the terminal user interface: Ben Krepp, Richard Title,
446 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
447 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
448 information in this manual.
450 DJ Delorie ported @value{GDBN} to MS-DOS, for the DJGPP project.
451 Robert Hoehne made significant contributions to the DJGPP port.
453 Cygnus Solutions has sponsored @value{GDBN} maintenance and much of its
454 development since 1991. Cygnus engineers who have worked on @value{GDBN}
455 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
456 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
457 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
458 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
459 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
460 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
461 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
462 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
463 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
464 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
465 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
466 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
467 Zuhn have made contributions both large and small.
469 Jim Blandy added support for preprocessor macros, while working for Red
473 @chapter A Sample @value{GDBN} Session
475 You can use this manual at your leisure to read all about @value{GDBN}.
476 However, a handful of commands are enough to get started using the
477 debugger. This chapter illustrates those commands.
480 In this sample session, we emphasize user input like this: @b{input},
481 to make it easier to pick out from the surrounding output.
484 @c FIXME: this example may not be appropriate for some configs, where
485 @c FIXME...primary interest is in remote use.
487 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
488 processor) exhibits the following bug: sometimes, when we change its
489 quote strings from the default, the commands used to capture one macro
490 definition within another stop working. In the following short @code{m4}
491 session, we define a macro @code{foo} which expands to @code{0000}; we
492 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
493 same thing. However, when we change the open quote string to
494 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
495 procedure fails to define a new synonym @code{baz}:
504 @b{define(bar,defn(`foo'))}
508 @b{changequote(<QUOTE>,<UNQUOTE>)}
510 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
513 m4: End of input: 0: fatal error: EOF in string
517 Let us use @value{GDBN} to try to see what is going on.
520 $ @b{@value{GDBP} m4}
521 @c FIXME: this falsifies the exact text played out, to permit smallbook
522 @c FIXME... format to come out better.
523 @value{GDBN} is free software and you are welcome to distribute copies
524 of it under certain conditions; type "show copying" to see
526 There is absolutely no warranty for @value{GDBN}; type "show warranty"
529 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
534 @value{GDBN} reads only enough symbol data to know where to find the
535 rest when needed; as a result, the first prompt comes up very quickly.
536 We now tell @value{GDBN} to use a narrower display width than usual, so
537 that examples fit in this manual.
540 (@value{GDBP}) @b{set width 70}
544 We need to see how the @code{m4} built-in @code{changequote} works.
545 Having looked at the source, we know the relevant subroutine is
546 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
547 @code{break} command.
550 (@value{GDBP}) @b{break m4_changequote}
551 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
555 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
556 control; as long as control does not reach the @code{m4_changequote}
557 subroutine, the program runs as usual:
560 (@value{GDBP}) @b{run}
561 Starting program: /work/Editorial/gdb/gnu/m4/m4
569 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
570 suspends execution of @code{m4}, displaying information about the
571 context where it stops.
574 @b{changequote(<QUOTE>,<UNQUOTE>)}
576 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
578 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
582 Now we use the command @code{n} (@code{next}) to advance execution to
583 the next line of the current function.
587 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
592 @code{set_quotes} looks like a promising subroutine. We can go into it
593 by using the command @code{s} (@code{step}) instead of @code{next}.
594 @code{step} goes to the next line to be executed in @emph{any}
595 subroutine, so it steps into @code{set_quotes}.
599 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
601 530 if (lquote != def_lquote)
605 The display that shows the subroutine where @code{m4} is now
606 suspended (and its arguments) is called a stack frame display. It
607 shows a summary of the stack. We can use the @code{backtrace}
608 command (which can also be spelled @code{bt}), to see where we are
609 in the stack as a whole: the @code{backtrace} command displays a
610 stack frame for each active subroutine.
613 (@value{GDBP}) @b{bt}
614 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
616 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
618 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
619 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
621 #4 0x79dc in expand_input () at macro.c:40
622 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
626 We step through a few more lines to see what happens. The first two
627 times, we can use @samp{s}; the next two times we use @code{n} to avoid
628 falling into the @code{xstrdup} subroutine.
632 0x3b5c 532 if (rquote != def_rquote)
634 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
635 def_lquote : xstrdup(lq);
637 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
640 538 len_lquote = strlen(rquote);
644 The last line displayed looks a little odd; we can examine the variables
645 @code{lquote} and @code{rquote} to see if they are in fact the new left
646 and right quotes we specified. We use the command @code{p}
647 (@code{print}) to see their values.
650 (@value{GDBP}) @b{p lquote}
651 $1 = 0x35d40 "<QUOTE>"
652 (@value{GDBP}) @b{p rquote}
653 $2 = 0x35d50 "<UNQUOTE>"
657 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
658 To look at some context, we can display ten lines of source
659 surrounding the current line with the @code{l} (@code{list}) command.
665 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
667 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
670 538 len_lquote = strlen(rquote);
671 539 len_rquote = strlen(lquote);
678 Let us step past the two lines that set @code{len_lquote} and
679 @code{len_rquote}, and then examine the values of those variables.
683 539 len_rquote = strlen(lquote);
686 (@value{GDBP}) @b{p len_lquote}
688 (@value{GDBP}) @b{p len_rquote}
693 That certainly looks wrong, assuming @code{len_lquote} and
694 @code{len_rquote} are meant to be the lengths of @code{lquote} and
695 @code{rquote} respectively. We can set them to better values using
696 the @code{p} command, since it can print the value of
697 any expression---and that expression can include subroutine calls and
701 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
703 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
708 Is that enough to fix the problem of using the new quotes with the
709 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
710 executing with the @code{c} (@code{continue}) command, and then try the
711 example that caused trouble initially:
717 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
724 Success! The new quotes now work just as well as the default ones. The
725 problem seems to have been just the two typos defining the wrong
726 lengths. We allow @code{m4} exit by giving it an EOF as input:
730 Program exited normally.
734 The message @samp{Program exited normally.} is from @value{GDBN}; it
735 indicates @code{m4} has finished executing. We can end our @value{GDBN}
736 session with the @value{GDBN} @code{quit} command.
739 (@value{GDBP}) @b{quit}
743 @chapter Getting In and Out of @value{GDBN}
745 This chapter discusses how to start @value{GDBN}, and how to get out of it.
749 type @samp{@value{GDBP}} to start @value{GDBN}.
751 type @kbd{quit} or @kbd{C-d} to exit.
755 * Invoking GDB:: How to start @value{GDBN}
756 * Quitting GDB:: How to quit @value{GDBN}
757 * Shell Commands:: How to use shell commands inside @value{GDBN}
761 @section Invoking @value{GDBN}
763 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
764 @value{GDBN} reads commands from the terminal until you tell it to exit.
766 You can also run @code{@value{GDBP}} with a variety of arguments and options,
767 to specify more of your debugging environment at the outset.
769 The command-line options described here are designed
770 to cover a variety of situations; in some environments, some of these
771 options may effectively be unavailable.
773 The most usual way to start @value{GDBN} is with one argument,
774 specifying an executable program:
777 @value{GDBP} @var{program}
781 You can also start with both an executable program and a core file
785 @value{GDBP} @var{program} @var{core}
788 You can, instead, specify a process ID as a second argument, if you want
789 to debug a running process:
792 @value{GDBP} @var{program} 1234
796 would attach @value{GDBN} to process @code{1234} (unless you also have a file
797 named @file{1234}; @value{GDBN} does check for a core file first).
799 Taking advantage of the second command-line argument requires a fairly
800 complete operating system; when you use @value{GDBN} as a remote
801 debugger attached to a bare board, there may not be any notion of
802 ``process'', and there is often no way to get a core dump. @value{GDBN}
803 will warn you if it is unable to attach or to read core dumps.
805 You can optionally have @code{@value{GDBP}} pass any arguments after the
806 executable file to the inferior using @code{--args}. This option stops
809 gdb --args gcc -O2 -c foo.c
811 This will cause @code{@value{GDBP}} to debug @code{gcc}, and to set
812 @code{gcc}'s command-line arguments (@pxref{Arguments}) to @samp{-O2 -c foo.c}.
814 You can run @code{@value{GDBP}} without printing the front material, which describes
815 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
822 You can further control how @value{GDBN} starts up by using command-line
823 options. @value{GDBN} itself can remind you of the options available.
833 to display all available options and briefly describe their use
834 (@samp{@value{GDBP} -h} is a shorter equivalent).
836 All options and command line arguments you give are processed
837 in sequential order. The order makes a difference when the
838 @samp{-x} option is used.
842 * File Options:: Choosing files
843 * Mode Options:: Choosing modes
847 @subsection Choosing files
849 When @value{GDBN} starts, it reads any arguments other than options as
850 specifying an executable file and core file (or process ID). This is
851 the same as if the arguments were specified by the @samp{-se} and
852 @samp{-c} (or @samp{-p} options respectively. (@value{GDBN} reads the
853 first argument that does not have an associated option flag as
854 equivalent to the @samp{-se} option followed by that argument; and the
855 second argument that does not have an associated option flag, if any, as
856 equivalent to the @samp{-c}/@samp{-p} option followed by that argument.)
857 If the second argument begins with a decimal digit, @value{GDBN} will
858 first attempt to attach to it as a process, and if that fails, attempt
859 to open it as a corefile. If you have a corefile whose name begins with
860 a digit, you can prevent @value{GDBN} from treating it as a pid by
861 prefixing it with @file{./}, eg. @file{./12345}.
863 If @value{GDBN} has not been configured to included core file support,
864 such as for most embedded targets, then it will complain about a second
865 argument and ignore it.
867 Many options have both long and short forms; both are shown in the
868 following list. @value{GDBN} also recognizes the long forms if you truncate
869 them, so long as enough of the option is present to be unambiguous.
870 (If you prefer, you can flag option arguments with @samp{--} rather
871 than @samp{-}, though we illustrate the more usual convention.)
873 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
874 @c way, both those who look for -foo and --foo in the index, will find
878 @item -symbols @var{file}
880 @cindex @code{--symbols}
882 Read symbol table from file @var{file}.
884 @item -exec @var{file}
886 @cindex @code{--exec}
888 Use file @var{file} as the executable file to execute when appropriate,
889 and for examining pure data in conjunction with a core dump.
893 Read symbol table from file @var{file} and use it as the executable
896 @item -core @var{file}
898 @cindex @code{--core}
900 Use file @var{file} as a core dump to examine.
902 @item -c @var{number}
903 @item -pid @var{number}
904 @itemx -p @var{number}
907 Connect to process ID @var{number}, as with the @code{attach} command.
908 If there is no such process, @value{GDBN} will attempt to open a core
909 file named @var{number}.
911 @item -command @var{file}
913 @cindex @code{--command}
915 Execute @value{GDBN} commands from file @var{file}. @xref{Command
916 Files,, Command files}.
918 @item -directory @var{directory}
919 @itemx -d @var{directory}
920 @cindex @code{--directory}
922 Add @var{directory} to the path to search for source files.
926 @cindex @code{--mapped}
928 @emph{Warning: this option depends on operating system facilities that are not
929 supported on all systems.}@*
930 If memory-mapped files are available on your system through the @code{mmap}
931 system call, you can use this option
932 to have @value{GDBN} write the symbols from your
933 program into a reusable file in the current directory. If the program you are debugging is
934 called @file{/tmp/fred}, the mapped symbol file is @file{/tmp/fred.syms}.
935 Future @value{GDBN} debugging sessions notice the presence of this file,
936 and can quickly map in symbol information from it, rather than reading
937 the symbol table from the executable program.
939 The @file{.syms} file is specific to the host machine where @value{GDBN}
940 is run. It holds an exact image of the internal @value{GDBN} symbol
941 table. It cannot be shared across multiple host platforms.
945 @cindex @code{--readnow}
947 Read each symbol file's entire symbol table immediately, rather than
948 the default, which is to read it incrementally as it is needed.
949 This makes startup slower, but makes future operations faster.
953 You typically combine the @code{-mapped} and @code{-readnow} options in
954 order to build a @file{.syms} file that contains complete symbol
955 information. (@xref{Files,,Commands to specify files}, for information
956 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
957 but build a @file{.syms} file for future use is:
960 gdb -batch -nx -mapped -readnow programname
964 @subsection Choosing modes
966 You can run @value{GDBN} in various alternative modes---for example, in
967 batch mode or quiet mode.
974 Do not execute commands found in any initialization files. Normally,
975 @value{GDBN} executes the commands in these files after all the command
976 options and arguments have been processed. @xref{Command Files,,Command
982 @cindex @code{--quiet}
983 @cindex @code{--silent}
985 ``Quiet''. Do not print the introductory and copyright messages. These
986 messages are also suppressed in batch mode.
989 @cindex @code{--batch}
990 Run in batch mode. Exit with status @code{0} after processing all the
991 command files specified with @samp{-x} (and all commands from
992 initialization files, if not inhibited with @samp{-n}). Exit with
993 nonzero status if an error occurs in executing the @value{GDBN} commands
994 in the command files.
996 Batch mode may be useful for running @value{GDBN} as a filter, for
997 example to download and run a program on another computer; in order to
998 make this more useful, the message
1001 Program exited normally.
1005 (which is ordinarily issued whenever a program running under
1006 @value{GDBN} control terminates) is not issued when running in batch
1011 @cindex @code{--nowindows}
1013 ``No windows''. If @value{GDBN} comes with a graphical user interface
1014 (GUI) built in, then this option tells @value{GDBN} to only use the command-line
1015 interface. If no GUI is available, this option has no effect.
1019 @cindex @code{--windows}
1021 If @value{GDBN} includes a GUI, then this option requires it to be
1024 @item -cd @var{directory}
1026 Run @value{GDBN} using @var{directory} as its working directory,
1027 instead of the current directory.
1031 @cindex @code{--fullname}
1033 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1034 subprocess. It tells @value{GDBN} to output the full file name and line
1035 number in a standard, recognizable fashion each time a stack frame is
1036 displayed (which includes each time your program stops). This
1037 recognizable format looks like two @samp{\032} characters, followed by
1038 the file name, line number and character position separated by colons,
1039 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1040 @samp{\032} characters as a signal to display the source code for the
1044 @cindex @code{--epoch}
1045 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
1046 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
1047 routines so as to allow Epoch to display values of expressions in a
1050 @item -annotate @var{level}
1051 @cindex @code{--annotate}
1052 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
1053 effect is identical to using @samp{set annotate @var{level}}
1054 (@pxref{Annotations}).
1055 Annotation level controls how much information does @value{GDBN} print
1056 together with its prompt, values of expressions, source lines, and other
1057 types of output. Level 0 is the normal, level 1 is for use when
1058 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
1059 maximum annotation suitable for programs that control @value{GDBN}.
1062 @cindex @code{--async}
1063 Use the asynchronous event loop for the command-line interface.
1064 @value{GDBN} processes all events, such as user keyboard input, via a
1065 special event loop. This allows @value{GDBN} to accept and process user
1066 commands in parallel with the debugged process being
1067 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
1068 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
1069 suspended when the debuggee runs.}, so you don't need to wait for
1070 control to return to @value{GDBN} before you type the next command.
1071 (@emph{Note:} as of version 5.1, the target side of the asynchronous
1072 operation is not yet in place, so @samp{-async} does not work fully
1074 @c FIXME: when the target side of the event loop is done, the above NOTE
1075 @c should be removed.
1077 When the standard input is connected to a terminal device, @value{GDBN}
1078 uses the asynchronous event loop by default, unless disabled by the
1079 @samp{-noasync} option.
1082 @cindex @code{--noasync}
1083 Disable the asynchronous event loop for the command-line interface.
1086 @cindex @code{--args}
1087 Change interpretation of command line so that arguments following the
1088 executable file are passed as command line arguments to the inferior.
1089 This option stops option processing.
1091 @item -baud @var{bps}
1093 @cindex @code{--baud}
1095 Set the line speed (baud rate or bits per second) of any serial
1096 interface used by @value{GDBN} for remote debugging.
1098 @item -tty @var{device}
1099 @itemx -t @var{device}
1100 @cindex @code{--tty}
1102 Run using @var{device} for your program's standard input and output.
1103 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1105 @c resolve the situation of these eventually
1107 @cindex @code{--tui}
1108 Activate the Terminal User Interface when starting.
1109 The Terminal User Interface manages several text windows on the terminal,
1110 showing source, assembly, registers and @value{GDBN} command outputs
1111 (@pxref{TUI, ,@value{GDBN} Text User Interface}).
1112 Do not use this option if you run @value{GDBN} from Emacs
1113 (@pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}).
1116 @c @cindex @code{--xdb}
1117 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
1118 @c For information, see the file @file{xdb_trans.html}, which is usually
1119 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1122 @item -interpreter @var{interp}
1123 @cindex @code{--interpreter}
1124 Use the interpreter @var{interp} for interface with the controlling
1125 program or device. This option is meant to be set by programs which
1126 communicate with @value{GDBN} using it as a back end.
1128 @samp{--interpreter=mi} (or @samp{--interpreter=mi2}) causes
1129 @value{GDBN} to use the current @dfn{@sc{gdb/mi} interface}
1130 (@pxref{GDB/MI, , The @sc{gdb/mi} Interface}). The previous @sc{gdb/mi}
1131 interface, included in @value{GDBN} version 5.3, can be selected with
1132 @samp{--interpreter=mi1}. Earlier @sc{gdb/mi} interfaces
1136 @cindex @code{--write}
1137 Open the executable and core files for both reading and writing. This
1138 is equivalent to the @samp{set write on} command inside @value{GDBN}
1142 @cindex @code{--statistics}
1143 This option causes @value{GDBN} to print statistics about time and
1144 memory usage after it completes each command and returns to the prompt.
1147 @cindex @code{--version}
1148 This option causes @value{GDBN} to print its version number and
1149 no-warranty blurb, and exit.
1154 @section Quitting @value{GDBN}
1155 @cindex exiting @value{GDBN}
1156 @cindex leaving @value{GDBN}
1159 @kindex quit @r{[}@var{expression}@r{]}
1160 @kindex q @r{(@code{quit})}
1161 @item quit @r{[}@var{expression}@r{]}
1163 To exit @value{GDBN}, use the @code{quit} command (abbreviated
1164 @code{q}), or type an end-of-file character (usually @kbd{C-d}). If you
1165 do not supply @var{expression}, @value{GDBN} will terminate normally;
1166 otherwise it will terminate using the result of @var{expression} as the
1171 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1172 terminates the action of any @value{GDBN} command that is in progress and
1173 returns to @value{GDBN} command level. It is safe to type the interrupt
1174 character at any time because @value{GDBN} does not allow it to take effect
1175 until a time when it is safe.
1177 If you have been using @value{GDBN} to control an attached process or
1178 device, you can release it with the @code{detach} command
1179 (@pxref{Attach, ,Debugging an already-running process}).
1181 @node Shell Commands
1182 @section Shell commands
1184 If you need to execute occasional shell commands during your
1185 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1186 just use the @code{shell} command.
1190 @cindex shell escape
1191 @item shell @var{command string}
1192 Invoke a standard shell to execute @var{command string}.
1193 If it exists, the environment variable @code{SHELL} determines which
1194 shell to run. Otherwise @value{GDBN} uses the default shell
1195 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1198 The utility @code{make} is often needed in development environments.
1199 You do not have to use the @code{shell} command for this purpose in
1204 @cindex calling make
1205 @item make @var{make-args}
1206 Execute the @code{make} program with the specified
1207 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1211 @chapter @value{GDBN} Commands
1213 You can abbreviate a @value{GDBN} command to the first few letters of the command
1214 name, if that abbreviation is unambiguous; and you can repeat certain
1215 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1216 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1217 show you the alternatives available, if there is more than one possibility).
1220 * Command Syntax:: How to give commands to @value{GDBN}
1221 * Completion:: Command completion
1222 * Help:: How to ask @value{GDBN} for help
1225 @node Command Syntax
1226 @section Command syntax
1228 A @value{GDBN} command is a single line of input. There is no limit on
1229 how long it can be. It starts with a command name, which is followed by
1230 arguments whose meaning depends on the command name. For example, the
1231 command @code{step} accepts an argument which is the number of times to
1232 step, as in @samp{step 5}. You can also use the @code{step} command
1233 with no arguments. Some commands do not allow any arguments.
1235 @cindex abbreviation
1236 @value{GDBN} command names may always be truncated if that abbreviation is
1237 unambiguous. Other possible command abbreviations are listed in the
1238 documentation for individual commands. In some cases, even ambiguous
1239 abbreviations are allowed; for example, @code{s} is specially defined as
1240 equivalent to @code{step} even though there are other commands whose
1241 names start with @code{s}. You can test abbreviations by using them as
1242 arguments to the @code{help} command.
1244 @cindex repeating commands
1245 @kindex RET @r{(repeat last command)}
1246 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1247 repeat the previous command. Certain commands (for example, @code{run})
1248 will not repeat this way; these are commands whose unintentional
1249 repetition might cause trouble and which you are unlikely to want to
1252 The @code{list} and @code{x} commands, when you repeat them with
1253 @key{RET}, construct new arguments rather than repeating
1254 exactly as typed. This permits easy scanning of source or memory.
1256 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1257 output, in a way similar to the common utility @code{more}
1258 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1259 @key{RET} too many in this situation, @value{GDBN} disables command
1260 repetition after any command that generates this sort of display.
1262 @kindex # @r{(a comment)}
1264 Any text from a @kbd{#} to the end of the line is a comment; it does
1265 nothing. This is useful mainly in command files (@pxref{Command
1266 Files,,Command files}).
1268 @cindex repeating command sequences
1269 @kindex C-o @r{(operate-and-get-next)}
1270 The @kbd{C-o} binding is useful for repeating a complex sequence of
1271 commands. This command accepts the current line, like @kbd{RET}, and
1272 then fetches the next line relative to the current line from the history
1276 @section Command completion
1279 @cindex word completion
1280 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1281 only one possibility; it can also show you what the valid possibilities
1282 are for the next word in a command, at any time. This works for @value{GDBN}
1283 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1285 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1286 of a word. If there is only one possibility, @value{GDBN} fills in the
1287 word, and waits for you to finish the command (or press @key{RET} to
1288 enter it). For example, if you type
1290 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1291 @c complete accuracy in these examples; space introduced for clarity.
1292 @c If texinfo enhancements make it unnecessary, it would be nice to
1293 @c replace " @key" by "@key" in the following...
1295 (@value{GDBP}) info bre @key{TAB}
1299 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1300 the only @code{info} subcommand beginning with @samp{bre}:
1303 (@value{GDBP}) info breakpoints
1307 You can either press @key{RET} at this point, to run the @code{info
1308 breakpoints} command, or backspace and enter something else, if
1309 @samp{breakpoints} does not look like the command you expected. (If you
1310 were sure you wanted @code{info breakpoints} in the first place, you
1311 might as well just type @key{RET} immediately after @samp{info bre},
1312 to exploit command abbreviations rather than command completion).
1314 If there is more than one possibility for the next word when you press
1315 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1316 characters and try again, or just press @key{TAB} a second time;
1317 @value{GDBN} displays all the possible completions for that word. For
1318 example, you might want to set a breakpoint on a subroutine whose name
1319 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1320 just sounds the bell. Typing @key{TAB} again displays all the
1321 function names in your program that begin with those characters, for
1325 (@value{GDBP}) b make_ @key{TAB}
1326 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1327 make_a_section_from_file make_environ
1328 make_abs_section make_function_type
1329 make_blockvector make_pointer_type
1330 make_cleanup make_reference_type
1331 make_command make_symbol_completion_list
1332 (@value{GDBP}) b make_
1336 After displaying the available possibilities, @value{GDBN} copies your
1337 partial input (@samp{b make_} in the example) so you can finish the
1340 If you just want to see the list of alternatives in the first place, you
1341 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1342 means @kbd{@key{META} ?}. You can type this either by holding down a
1343 key designated as the @key{META} shift on your keyboard (if there is
1344 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1346 @cindex quotes in commands
1347 @cindex completion of quoted strings
1348 Sometimes the string you need, while logically a ``word'', may contain
1349 parentheses or other characters that @value{GDBN} normally excludes from
1350 its notion of a word. To permit word completion to work in this
1351 situation, you may enclose words in @code{'} (single quote marks) in
1352 @value{GDBN} commands.
1354 The most likely situation where you might need this is in typing the
1355 name of a C@t{++} function. This is because C@t{++} allows function
1356 overloading (multiple definitions of the same function, distinguished
1357 by argument type). For example, when you want to set a breakpoint you
1358 may need to distinguish whether you mean the version of @code{name}
1359 that takes an @code{int} parameter, @code{name(int)}, or the version
1360 that takes a @code{float} parameter, @code{name(float)}. To use the
1361 word-completion facilities in this situation, type a single quote
1362 @code{'} at the beginning of the function name. This alerts
1363 @value{GDBN} that it may need to consider more information than usual
1364 when you press @key{TAB} or @kbd{M-?} to request word completion:
1367 (@value{GDBP}) b 'bubble( @kbd{M-?}
1368 bubble(double,double) bubble(int,int)
1369 (@value{GDBP}) b 'bubble(
1372 In some cases, @value{GDBN} can tell that completing a name requires using
1373 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1374 completing as much as it can) if you do not type the quote in the first
1378 (@value{GDBP}) b bub @key{TAB}
1379 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1380 (@value{GDBP}) b 'bubble(
1384 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1385 you have not yet started typing the argument list when you ask for
1386 completion on an overloaded symbol.
1388 For more information about overloaded functions, see @ref{C plus plus
1389 expressions, ,C@t{++} expressions}. You can use the command @code{set
1390 overload-resolution off} to disable overload resolution;
1391 see @ref{Debugging C plus plus, ,@value{GDBN} features for C@t{++}}.
1395 @section Getting help
1396 @cindex online documentation
1399 You can always ask @value{GDBN} itself for information on its commands,
1400 using the command @code{help}.
1403 @kindex h @r{(@code{help})}
1406 You can use @code{help} (abbreviated @code{h}) with no arguments to
1407 display a short list of named classes of commands:
1411 List of classes of commands:
1413 aliases -- Aliases of other commands
1414 breakpoints -- Making program stop at certain points
1415 data -- Examining data
1416 files -- Specifying and examining files
1417 internals -- Maintenance commands
1418 obscure -- Obscure features
1419 running -- Running the program
1420 stack -- Examining the stack
1421 status -- Status inquiries
1422 support -- Support facilities
1423 tracepoints -- Tracing of program execution without@*
1424 stopping the program
1425 user-defined -- User-defined commands
1427 Type "help" followed by a class name for a list of
1428 commands in that class.
1429 Type "help" followed by command name for full
1431 Command name abbreviations are allowed if unambiguous.
1434 @c the above line break eliminates huge line overfull...
1436 @item help @var{class}
1437 Using one of the general help classes as an argument, you can get a
1438 list of the individual commands in that class. For example, here is the
1439 help display for the class @code{status}:
1442 (@value{GDBP}) help status
1447 @c Line break in "show" line falsifies real output, but needed
1448 @c to fit in smallbook page size.
1449 info -- Generic command for showing things
1450 about the program being debugged
1451 show -- Generic command for showing things
1454 Type "help" followed by command name for full
1456 Command name abbreviations are allowed if unambiguous.
1460 @item help @var{command}
1461 With a command name as @code{help} argument, @value{GDBN} displays a
1462 short paragraph on how to use that command.
1465 @item apropos @var{args}
1466 The @code{apropos @var{args}} command searches through all of the @value{GDBN}
1467 commands, and their documentation, for the regular expression specified in
1468 @var{args}. It prints out all matches found. For example:
1479 set symbol-reloading -- Set dynamic symbol table reloading
1480 multiple times in one run
1481 show symbol-reloading -- Show dynamic symbol table reloading
1482 multiple times in one run
1487 @item complete @var{args}
1488 The @code{complete @var{args}} command lists all the possible completions
1489 for the beginning of a command. Use @var{args} to specify the beginning of the
1490 command you want completed. For example:
1496 @noindent results in:
1507 @noindent This is intended for use by @sc{gnu} Emacs.
1510 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1511 and @code{show} to inquire about the state of your program, or the state
1512 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1513 manual introduces each of them in the appropriate context. The listings
1514 under @code{info} and under @code{show} in the Index point to
1515 all the sub-commands. @xref{Index}.
1520 @kindex i @r{(@code{info})}
1522 This command (abbreviated @code{i}) is for describing the state of your
1523 program. For example, you can list the arguments given to your program
1524 with @code{info args}, list the registers currently in use with @code{info
1525 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1526 You can get a complete list of the @code{info} sub-commands with
1527 @w{@code{help info}}.
1531 You can assign the result of an expression to an environment variable with
1532 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1533 @code{set prompt $}.
1537 In contrast to @code{info}, @code{show} is for describing the state of
1538 @value{GDBN} itself.
1539 You can change most of the things you can @code{show}, by using the
1540 related command @code{set}; for example, you can control what number
1541 system is used for displays with @code{set radix}, or simply inquire
1542 which is currently in use with @code{show radix}.
1545 To display all the settable parameters and their current
1546 values, you can use @code{show} with no arguments; you may also use
1547 @code{info set}. Both commands produce the same display.
1548 @c FIXME: "info set" violates the rule that "info" is for state of
1549 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1550 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1554 Here are three miscellaneous @code{show} subcommands, all of which are
1555 exceptional in lacking corresponding @code{set} commands:
1558 @kindex show version
1559 @cindex version number
1561 Show what version of @value{GDBN} is running. You should include this
1562 information in @value{GDBN} bug-reports. If multiple versions of
1563 @value{GDBN} are in use at your site, you may need to determine which
1564 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1565 commands are introduced, and old ones may wither away. Also, many
1566 system vendors ship variant versions of @value{GDBN}, and there are
1567 variant versions of @value{GDBN} in @sc{gnu}/Linux distributions as well.
1568 The version number is the same as the one announced when you start
1571 @kindex show copying
1573 Display information about permission for copying @value{GDBN}.
1575 @kindex show warranty
1577 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1578 if your version of @value{GDBN} comes with one.
1583 @chapter Running Programs Under @value{GDBN}
1585 When you run a program under @value{GDBN}, you must first generate
1586 debugging information when you compile it.
1588 You may start @value{GDBN} with its arguments, if any, in an environment
1589 of your choice. If you are doing native debugging, you may redirect
1590 your program's input and output, debug an already running process, or
1591 kill a child process.
1594 * Compilation:: Compiling for debugging
1595 * Starting:: Starting your program
1596 * Arguments:: Your program's arguments
1597 * Environment:: Your program's environment
1599 * Working Directory:: Your program's working directory
1600 * Input/Output:: Your program's input and output
1601 * Attach:: Debugging an already-running process
1602 * Kill Process:: Killing the child process
1604 * Threads:: Debugging programs with multiple threads
1605 * Processes:: Debugging programs with multiple processes
1609 @section Compiling for debugging
1611 In order to debug a program effectively, you need to generate
1612 debugging information when you compile it. This debugging information
1613 is stored in the object file; it describes the data type of each
1614 variable or function and the correspondence between source line numbers
1615 and addresses in the executable code.
1617 To request debugging information, specify the @samp{-g} option when you run
1620 Most compilers do not include information about preprocessor macros in
1621 the debugging information if you specify the @option{-g} flag alone,
1622 because this information is rather large. Version 3.1 of @value{NGCC},
1623 the @sc{gnu} C compiler, provides macro information if you specify the
1624 options @option{-gdwarf-2} and @option{-g3}; the former option requests
1625 debugging information in the Dwarf 2 format, and the latter requests
1626 ``extra information''. In the future, we hope to find more compact ways
1627 to represent macro information, so that it can be included with
1630 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1631 options together. Using those compilers, you cannot generate optimized
1632 executables containing debugging information.
1634 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1635 without @samp{-O}, making it possible to debug optimized code. We
1636 recommend that you @emph{always} use @samp{-g} whenever you compile a
1637 program. You may think your program is correct, but there is no sense
1638 in pushing your luck.
1640 @cindex optimized code, debugging
1641 @cindex debugging optimized code
1642 When you debug a program compiled with @samp{-g -O}, remember that the
1643 optimizer is rearranging your code; the debugger shows you what is
1644 really there. Do not be too surprised when the execution path does not
1645 exactly match your source file! An extreme example: if you define a
1646 variable, but never use it, @value{GDBN} never sees that
1647 variable---because the compiler optimizes it out of existence.
1649 Some things do not work as well with @samp{-g -O} as with just
1650 @samp{-g}, particularly on machines with instruction scheduling. If in
1651 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1652 please report it to us as a bug (including a test case!).
1654 Older versions of the @sc{gnu} C compiler permitted a variant option
1655 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1656 format; if your @sc{gnu} C compiler has this option, do not use it.
1660 @section Starting your program
1666 @kindex r @r{(@code{run})}
1669 Use the @code{run} command to start your program under @value{GDBN}.
1670 You must first specify the program name (except on VxWorks) with an
1671 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1672 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1673 (@pxref{Files, ,Commands to specify files}).
1677 If you are running your program in an execution environment that
1678 supports processes, @code{run} creates an inferior process and makes
1679 that process run your program. (In environments without processes,
1680 @code{run} jumps to the start of your program.)
1682 The execution of a program is affected by certain information it
1683 receives from its superior. @value{GDBN} provides ways to specify this
1684 information, which you must do @emph{before} starting your program. (You
1685 can change it after starting your program, but such changes only affect
1686 your program the next time you start it.) This information may be
1687 divided into four categories:
1690 @item The @emph{arguments.}
1691 Specify the arguments to give your program as the arguments of the
1692 @code{run} command. If a shell is available on your target, the shell
1693 is used to pass the arguments, so that you may use normal conventions
1694 (such as wildcard expansion or variable substitution) in describing
1696 In Unix systems, you can control which shell is used with the
1697 @code{SHELL} environment variable.
1698 @xref{Arguments, ,Your program's arguments}.
1700 @item The @emph{environment.}
1701 Your program normally inherits its environment from @value{GDBN}, but you can
1702 use the @value{GDBN} commands @code{set environment} and @code{unset
1703 environment} to change parts of the environment that affect
1704 your program. @xref{Environment, ,Your program's environment}.
1706 @item The @emph{working directory.}
1707 Your program inherits its working directory from @value{GDBN}. You can set
1708 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1709 @xref{Working Directory, ,Your program's working directory}.
1711 @item The @emph{standard input and output.}
1712 Your program normally uses the same device for standard input and
1713 standard output as @value{GDBN} is using. You can redirect input and output
1714 in the @code{run} command line, or you can use the @code{tty} command to
1715 set a different device for your program.
1716 @xref{Input/Output, ,Your program's input and output}.
1719 @emph{Warning:} While input and output redirection work, you cannot use
1720 pipes to pass the output of the program you are debugging to another
1721 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1725 When you issue the @code{run} command, your program begins to execute
1726 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1727 of how to arrange for your program to stop. Once your program has
1728 stopped, you may call functions in your program, using the @code{print}
1729 or @code{call} commands. @xref{Data, ,Examining Data}.
1731 If the modification time of your symbol file has changed since the last
1732 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1733 table, and reads it again. When it does this, @value{GDBN} tries to retain
1734 your current breakpoints.
1737 @section Your program's arguments
1739 @cindex arguments (to your program)
1740 The arguments to your program can be specified by the arguments of the
1742 They are passed to a shell, which expands wildcard characters and
1743 performs redirection of I/O, and thence to your program. Your
1744 @code{SHELL} environment variable (if it exists) specifies what shell
1745 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1746 the default shell (@file{/bin/sh} on Unix).
1748 On non-Unix systems, the program is usually invoked directly by
1749 @value{GDBN}, which emulates I/O redirection via the appropriate system
1750 calls, and the wildcard characters are expanded by the startup code of
1751 the program, not by the shell.
1753 @code{run} with no arguments uses the same arguments used by the previous
1754 @code{run}, or those set by the @code{set args} command.
1759 Specify the arguments to be used the next time your program is run. If
1760 @code{set args} has no arguments, @code{run} executes your program
1761 with no arguments. Once you have run your program with arguments,
1762 using @code{set args} before the next @code{run} is the only way to run
1763 it again without arguments.
1767 Show the arguments to give your program when it is started.
1771 @section Your program's environment
1773 @cindex environment (of your program)
1774 The @dfn{environment} consists of a set of environment variables and
1775 their values. Environment variables conventionally record such things as
1776 your user name, your home directory, your terminal type, and your search
1777 path for programs to run. Usually you set up environment variables with
1778 the shell and they are inherited by all the other programs you run. When
1779 debugging, it can be useful to try running your program with a modified
1780 environment without having to start @value{GDBN} over again.
1784 @item path @var{directory}
1785 Add @var{directory} to the front of the @code{PATH} environment variable
1786 (the search path for executables) that will be passed to your program.
1787 The value of @code{PATH} used by @value{GDBN} does not change.
1788 You may specify several directory names, separated by whitespace or by a
1789 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1790 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1791 is moved to the front, so it is searched sooner.
1793 You can use the string @samp{$cwd} to refer to whatever is the current
1794 working directory at the time @value{GDBN} searches the path. If you
1795 use @samp{.} instead, it refers to the directory where you executed the
1796 @code{path} command. @value{GDBN} replaces @samp{.} in the
1797 @var{directory} argument (with the current path) before adding
1798 @var{directory} to the search path.
1799 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1800 @c document that, since repeating it would be a no-op.
1804 Display the list of search paths for executables (the @code{PATH}
1805 environment variable).
1807 @kindex show environment
1808 @item show environment @r{[}@var{varname}@r{]}
1809 Print the value of environment variable @var{varname} to be given to
1810 your program when it starts. If you do not supply @var{varname},
1811 print the names and values of all environment variables to be given to
1812 your program. You can abbreviate @code{environment} as @code{env}.
1814 @kindex set environment
1815 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1816 Set environment variable @var{varname} to @var{value}. The value
1817 changes for your program only, not for @value{GDBN} itself. @var{value} may
1818 be any string; the values of environment variables are just strings, and
1819 any interpretation is supplied by your program itself. The @var{value}
1820 parameter is optional; if it is eliminated, the variable is set to a
1822 @c "any string" here does not include leading, trailing
1823 @c blanks. Gnu asks: does anyone care?
1825 For example, this command:
1832 tells the debugged program, when subsequently run, that its user is named
1833 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1834 are not actually required.)
1836 @kindex unset environment
1837 @item unset environment @var{varname}
1838 Remove variable @var{varname} from the environment to be passed to your
1839 program. This is different from @samp{set env @var{varname} =};
1840 @code{unset environment} removes the variable from the environment,
1841 rather than assigning it an empty value.
1844 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1846 by your @code{SHELL} environment variable if it exists (or
1847 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1848 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1849 @file{.bashrc} for BASH---any variables you set in that file affect
1850 your program. You may wish to move setting of environment variables to
1851 files that are only run when you sign on, such as @file{.login} or
1854 @node Working Directory
1855 @section Your program's working directory
1857 @cindex working directory (of your program)
1858 Each time you start your program with @code{run}, it inherits its
1859 working directory from the current working directory of @value{GDBN}.
1860 The @value{GDBN} working directory is initially whatever it inherited
1861 from its parent process (typically the shell), but you can specify a new
1862 working directory in @value{GDBN} with the @code{cd} command.
1864 The @value{GDBN} working directory also serves as a default for the commands
1865 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1870 @item cd @var{directory}
1871 Set the @value{GDBN} working directory to @var{directory}.
1875 Print the @value{GDBN} working directory.
1879 @section Your program's input and output
1884 By default, the program you run under @value{GDBN} does input and output to
1885 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1886 to its own terminal modes to interact with you, but it records the terminal
1887 modes your program was using and switches back to them when you continue
1888 running your program.
1891 @kindex info terminal
1893 Displays information recorded by @value{GDBN} about the terminal modes your
1897 You can redirect your program's input and/or output using shell
1898 redirection with the @code{run} command. For example,
1905 starts your program, diverting its output to the file @file{outfile}.
1908 @cindex controlling terminal
1909 Another way to specify where your program should do input and output is
1910 with the @code{tty} command. This command accepts a file name as
1911 argument, and causes this file to be the default for future @code{run}
1912 commands. It also resets the controlling terminal for the child
1913 process, for future @code{run} commands. For example,
1920 directs that processes started with subsequent @code{run} commands
1921 default to do input and output on the terminal @file{/dev/ttyb} and have
1922 that as their controlling terminal.
1924 An explicit redirection in @code{run} overrides the @code{tty} command's
1925 effect on the input/output device, but not its effect on the controlling
1928 When you use the @code{tty} command or redirect input in the @code{run}
1929 command, only the input @emph{for your program} is affected. The input
1930 for @value{GDBN} still comes from your terminal.
1933 @section Debugging an already-running process
1938 @item attach @var{process-id}
1939 This command attaches to a running process---one that was started
1940 outside @value{GDBN}. (@code{info files} shows your active
1941 targets.) The command takes as argument a process ID. The usual way to
1942 find out the process-id of a Unix process is with the @code{ps} utility,
1943 or with the @samp{jobs -l} shell command.
1945 @code{attach} does not repeat if you press @key{RET} a second time after
1946 executing the command.
1949 To use @code{attach}, your program must be running in an environment
1950 which supports processes; for example, @code{attach} does not work for
1951 programs on bare-board targets that lack an operating system. You must
1952 also have permission to send the process a signal.
1954 When you use @code{attach}, the debugger finds the program running in
1955 the process first by looking in the current working directory, then (if
1956 the program is not found) by using the source file search path
1957 (@pxref{Source Path, ,Specifying source directories}). You can also use
1958 the @code{file} command to load the program. @xref{Files, ,Commands to
1961 The first thing @value{GDBN} does after arranging to debug the specified
1962 process is to stop it. You can examine and modify an attached process
1963 with all the @value{GDBN} commands that are ordinarily available when
1964 you start processes with @code{run}. You can insert breakpoints; you
1965 can step and continue; you can modify storage. If you would rather the
1966 process continue running, you may use the @code{continue} command after
1967 attaching @value{GDBN} to the process.
1972 When you have finished debugging the attached process, you can use the
1973 @code{detach} command to release it from @value{GDBN} control. Detaching
1974 the process continues its execution. After the @code{detach} command,
1975 that process and @value{GDBN} become completely independent once more, and you
1976 are ready to @code{attach} another process or start one with @code{run}.
1977 @code{detach} does not repeat if you press @key{RET} again after
1978 executing the command.
1981 If you exit @value{GDBN} or use the @code{run} command while you have an
1982 attached process, you kill that process. By default, @value{GDBN} asks
1983 for confirmation if you try to do either of these things; you can
1984 control whether or not you need to confirm by using the @code{set
1985 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1989 @section Killing the child process
1994 Kill the child process in which your program is running under @value{GDBN}.
1997 This command is useful if you wish to debug a core dump instead of a
1998 running process. @value{GDBN} ignores any core dump file while your program
2001 On some operating systems, a program cannot be executed outside @value{GDBN}
2002 while you have breakpoints set on it inside @value{GDBN}. You can use the
2003 @code{kill} command in this situation to permit running your program
2004 outside the debugger.
2006 The @code{kill} command is also useful if you wish to recompile and
2007 relink your program, since on many systems it is impossible to modify an
2008 executable file while it is running in a process. In this case, when you
2009 next type @code{run}, @value{GDBN} notices that the file has changed, and
2010 reads the symbol table again (while trying to preserve your current
2011 breakpoint settings).
2014 @section Debugging programs with multiple threads
2016 @cindex threads of execution
2017 @cindex multiple threads
2018 @cindex switching threads
2019 In some operating systems, such as HP-UX and Solaris, a single program
2020 may have more than one @dfn{thread} of execution. The precise semantics
2021 of threads differ from one operating system to another, but in general
2022 the threads of a single program are akin to multiple processes---except
2023 that they share one address space (that is, they can all examine and
2024 modify the same variables). On the other hand, each thread has its own
2025 registers and execution stack, and perhaps private memory.
2027 @value{GDBN} provides these facilities for debugging multi-thread
2031 @item automatic notification of new threads
2032 @item @samp{thread @var{threadno}}, a command to switch among threads
2033 @item @samp{info threads}, a command to inquire about existing threads
2034 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2035 a command to apply a command to a list of threads
2036 @item thread-specific breakpoints
2040 @emph{Warning:} These facilities are not yet available on every
2041 @value{GDBN} configuration where the operating system supports threads.
2042 If your @value{GDBN} does not support threads, these commands have no
2043 effect. For example, a system without thread support shows no output
2044 from @samp{info threads}, and always rejects the @code{thread} command,
2048 (@value{GDBP}) info threads
2049 (@value{GDBP}) thread 1
2050 Thread ID 1 not known. Use the "info threads" command to
2051 see the IDs of currently known threads.
2053 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2054 @c doesn't support threads"?
2057 @cindex focus of debugging
2058 @cindex current thread
2059 The @value{GDBN} thread debugging facility allows you to observe all
2060 threads while your program runs---but whenever @value{GDBN} takes
2061 control, one thread in particular is always the focus of debugging.
2062 This thread is called the @dfn{current thread}. Debugging commands show
2063 program information from the perspective of the current thread.
2065 @cindex @code{New} @var{systag} message
2066 @cindex thread identifier (system)
2067 @c FIXME-implementors!! It would be more helpful if the [New...] message
2068 @c included GDB's numeric thread handle, so you could just go to that
2069 @c thread without first checking `info threads'.
2070 Whenever @value{GDBN} detects a new thread in your program, it displays
2071 the target system's identification for the thread with a message in the
2072 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2073 whose form varies depending on the particular system. For example, on
2074 LynxOS, you might see
2077 [New process 35 thread 27]
2081 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2082 the @var{systag} is simply something like @samp{process 368}, with no
2085 @c FIXME!! (1) Does the [New...] message appear even for the very first
2086 @c thread of a program, or does it only appear for the
2087 @c second---i.e.@: when it becomes obvious we have a multithread
2089 @c (2) *Is* there necessarily a first thread always? Or do some
2090 @c multithread systems permit starting a program with multiple
2091 @c threads ab initio?
2093 @cindex thread number
2094 @cindex thread identifier (GDB)
2095 For debugging purposes, @value{GDBN} associates its own thread
2096 number---always a single integer---with each thread in your program.
2099 @kindex info threads
2101 Display a summary of all threads currently in your
2102 program. @value{GDBN} displays for each thread (in this order):
2105 @item the thread number assigned by @value{GDBN}
2107 @item the target system's thread identifier (@var{systag})
2109 @item the current stack frame summary for that thread
2113 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2114 indicates the current thread.
2118 @c end table here to get a little more width for example
2121 (@value{GDBP}) info threads
2122 3 process 35 thread 27 0x34e5 in sigpause ()
2123 2 process 35 thread 23 0x34e5 in sigpause ()
2124 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2130 @cindex thread number
2131 @cindex thread identifier (GDB)
2132 For debugging purposes, @value{GDBN} associates its own thread
2133 number---a small integer assigned in thread-creation order---with each
2134 thread in your program.
2136 @cindex @code{New} @var{systag} message, on HP-UX
2137 @cindex thread identifier (system), on HP-UX
2138 @c FIXME-implementors!! It would be more helpful if the [New...] message
2139 @c included GDB's numeric thread handle, so you could just go to that
2140 @c thread without first checking `info threads'.
2141 Whenever @value{GDBN} detects a new thread in your program, it displays
2142 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2143 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2144 whose form varies depending on the particular system. For example, on
2148 [New thread 2 (system thread 26594)]
2152 when @value{GDBN} notices a new thread.
2155 @kindex info threads
2157 Display a summary of all threads currently in your
2158 program. @value{GDBN} displays for each thread (in this order):
2161 @item the thread number assigned by @value{GDBN}
2163 @item the target system's thread identifier (@var{systag})
2165 @item the current stack frame summary for that thread
2169 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2170 indicates the current thread.
2174 @c end table here to get a little more width for example
2177 (@value{GDBP}) info threads
2178 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") \@*
2180 2 system thread 26606 0x7b0030d8 in __ksleep () \@*
2181 from /usr/lib/libc.2
2182 1 system thread 27905 0x7b003498 in _brk () \@*
2183 from /usr/lib/libc.2
2187 @kindex thread @var{threadno}
2188 @item thread @var{threadno}
2189 Make thread number @var{threadno} the current thread. The command
2190 argument @var{threadno} is the internal @value{GDBN} thread number, as
2191 shown in the first field of the @samp{info threads} display.
2192 @value{GDBN} responds by displaying the system identifier of the thread
2193 you selected, and its current stack frame summary:
2196 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2197 (@value{GDBP}) thread 2
2198 [Switching to process 35 thread 23]
2199 0x34e5 in sigpause ()
2203 As with the @samp{[New @dots{}]} message, the form of the text after
2204 @samp{Switching to} depends on your system's conventions for identifying
2207 @kindex thread apply
2208 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2209 The @code{thread apply} command allows you to apply a command to one or
2210 more threads. Specify the numbers of the threads that you want affected
2211 with the command argument @var{threadno}. @var{threadno} is the internal
2212 @value{GDBN} thread number, as shown in the first field of the @samp{info
2213 threads} display. To apply a command to all threads, use
2214 @code{thread apply all} @var{args}.
2217 @cindex automatic thread selection
2218 @cindex switching threads automatically
2219 @cindex threads, automatic switching
2220 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2221 signal, it automatically selects the thread where that breakpoint or
2222 signal happened. @value{GDBN} alerts you to the context switch with a
2223 message of the form @samp{[Switching to @var{systag}]} to identify the
2226 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2227 more information about how @value{GDBN} behaves when you stop and start
2228 programs with multiple threads.
2230 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2231 watchpoints in programs with multiple threads.
2234 @section Debugging programs with multiple processes
2236 @cindex fork, debugging programs which call
2237 @cindex multiple processes
2238 @cindex processes, multiple
2239 On most systems, @value{GDBN} has no special support for debugging
2240 programs which create additional processes using the @code{fork}
2241 function. When a program forks, @value{GDBN} will continue to debug the
2242 parent process and the child process will run unimpeded. If you have
2243 set a breakpoint in any code which the child then executes, the child
2244 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2245 will cause it to terminate.
2247 However, if you want to debug the child process there is a workaround
2248 which isn't too painful. Put a call to @code{sleep} in the code which
2249 the child process executes after the fork. It may be useful to sleep
2250 only if a certain environment variable is set, or a certain file exists,
2251 so that the delay need not occur when you don't want to run @value{GDBN}
2252 on the child. While the child is sleeping, use the @code{ps} program to
2253 get its process ID. Then tell @value{GDBN} (a new invocation of
2254 @value{GDBN} if you are also debugging the parent process) to attach to
2255 the child process (@pxref{Attach}). From that point on you can debug
2256 the child process just like any other process which you attached to.
2258 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2259 debugging programs that create additional processes using the
2260 @code{fork} or @code{vfork} function.
2262 By default, when a program forks, @value{GDBN} will continue to debug
2263 the parent process and the child process will run unimpeded.
2265 If you want to follow the child process instead of the parent process,
2266 use the command @w{@code{set follow-fork-mode}}.
2269 @kindex set follow-fork-mode
2270 @item set follow-fork-mode @var{mode}
2271 Set the debugger response to a program call of @code{fork} or
2272 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2273 process. The @var{mode} can be:
2277 The original process is debugged after a fork. The child process runs
2278 unimpeded. This is the default.
2281 The new process is debugged after a fork. The parent process runs
2285 The debugger will ask for one of the above choices.
2288 @item show follow-fork-mode
2289 Display the current debugger response to a @code{fork} or @code{vfork} call.
2292 If you ask to debug a child process and a @code{vfork} is followed by an
2293 @code{exec}, @value{GDBN} executes the new target up to the first
2294 breakpoint in the new target. If you have a breakpoint set on
2295 @code{main} in your original program, the breakpoint will also be set on
2296 the child process's @code{main}.
2298 When a child process is spawned by @code{vfork}, you cannot debug the
2299 child or parent until an @code{exec} call completes.
2301 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2302 call executes, the new target restarts. To restart the parent process,
2303 use the @code{file} command with the parent executable name as its
2306 You can use the @code{catch} command to make @value{GDBN} stop whenever
2307 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2308 Catchpoints, ,Setting catchpoints}.
2311 @chapter Stopping and Continuing
2313 The principal purposes of using a debugger are so that you can stop your
2314 program before it terminates; or so that, if your program runs into
2315 trouble, you can investigate and find out why.
2317 Inside @value{GDBN}, your program may stop for any of several reasons,
2318 such as a signal, a breakpoint, or reaching a new line after a
2319 @value{GDBN} command such as @code{step}. You may then examine and
2320 change variables, set new breakpoints or remove old ones, and then
2321 continue execution. Usually, the messages shown by @value{GDBN} provide
2322 ample explanation of the status of your program---but you can also
2323 explicitly request this information at any time.
2326 @kindex info program
2328 Display information about the status of your program: whether it is
2329 running or not, what process it is, and why it stopped.
2333 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2334 * Continuing and Stepping:: Resuming execution
2336 * Thread Stops:: Stopping and starting multi-thread programs
2340 @section Breakpoints, watchpoints, and catchpoints
2343 A @dfn{breakpoint} makes your program stop whenever a certain point in
2344 the program is reached. For each breakpoint, you can add conditions to
2345 control in finer detail whether your program stops. You can set
2346 breakpoints with the @code{break} command and its variants (@pxref{Set
2347 Breaks, ,Setting breakpoints}), to specify the place where your program
2348 should stop by line number, function name or exact address in the
2351 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2352 breakpoints in shared libraries before the executable is run. There is
2353 a minor limitation on HP-UX systems: you must wait until the executable
2354 is run in order to set breakpoints in shared library routines that are
2355 not called directly by the program (for example, routines that are
2356 arguments in a @code{pthread_create} call).
2359 @cindex memory tracing
2360 @cindex breakpoint on memory address
2361 @cindex breakpoint on variable modification
2362 A @dfn{watchpoint} is a special breakpoint that stops your program
2363 when the value of an expression changes. You must use a different
2364 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2365 watchpoints}), but aside from that, you can manage a watchpoint like
2366 any other breakpoint: you enable, disable, and delete both breakpoints
2367 and watchpoints using the same commands.
2369 You can arrange to have values from your program displayed automatically
2370 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2374 @cindex breakpoint on events
2375 A @dfn{catchpoint} is another special breakpoint that stops your program
2376 when a certain kind of event occurs, such as the throwing of a C@t{++}
2377 exception or the loading of a library. As with watchpoints, you use a
2378 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2379 catchpoints}), but aside from that, you can manage a catchpoint like any
2380 other breakpoint. (To stop when your program receives a signal, use the
2381 @code{handle} command; see @ref{Signals, ,Signals}.)
2383 @cindex breakpoint numbers
2384 @cindex numbers for breakpoints
2385 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2386 catchpoint when you create it; these numbers are successive integers
2387 starting with one. In many of the commands for controlling various
2388 features of breakpoints you use the breakpoint number to say which
2389 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2390 @dfn{disabled}; if disabled, it has no effect on your program until you
2393 @cindex breakpoint ranges
2394 @cindex ranges of breakpoints
2395 Some @value{GDBN} commands accept a range of breakpoints on which to
2396 operate. A breakpoint range is either a single breakpoint number, like
2397 @samp{5}, or two such numbers, in increasing order, separated by a
2398 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2399 all breakpoint in that range are operated on.
2402 * Set Breaks:: Setting breakpoints
2403 * Set Watchpoints:: Setting watchpoints
2404 * Set Catchpoints:: Setting catchpoints
2405 * Delete Breaks:: Deleting breakpoints
2406 * Disabling:: Disabling breakpoints
2407 * Conditions:: Break conditions
2408 * Break Commands:: Breakpoint command lists
2409 * Breakpoint Menus:: Breakpoint menus
2410 * Error in Breakpoints:: ``Cannot insert breakpoints''
2414 @subsection Setting breakpoints
2416 @c FIXME LMB what does GDB do if no code on line of breakpt?
2417 @c consider in particular declaration with/without initialization.
2419 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2422 @kindex b @r{(@code{break})}
2423 @vindex $bpnum@r{, convenience variable}
2424 @cindex latest breakpoint
2425 Breakpoints are set with the @code{break} command (abbreviated
2426 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2427 number of the breakpoint you've set most recently; see @ref{Convenience
2428 Vars,, Convenience variables}, for a discussion of what you can do with
2429 convenience variables.
2431 You have several ways to say where the breakpoint should go.
2434 @item break @var{function}
2435 Set a breakpoint at entry to function @var{function}.
2436 When using source languages that permit overloading of symbols, such as
2437 C@t{++}, @var{function} may refer to more than one possible place to break.
2438 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2440 @item break +@var{offset}
2441 @itemx break -@var{offset}
2442 Set a breakpoint some number of lines forward or back from the position
2443 at which execution stopped in the currently selected @dfn{stack frame}.
2444 (@xref{Frames, ,Frames}, for a description of stack frames.)
2446 @item break @var{linenum}
2447 Set a breakpoint at line @var{linenum} in the current source file.
2448 The current source file is the last file whose source text was printed.
2449 The breakpoint will stop your program just before it executes any of the
2452 @item break @var{filename}:@var{linenum}
2453 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2455 @item break @var{filename}:@var{function}
2456 Set a breakpoint at entry to function @var{function} found in file
2457 @var{filename}. Specifying a file name as well as a function name is
2458 superfluous except when multiple files contain similarly named
2461 @item break *@var{address}
2462 Set a breakpoint at address @var{address}. You can use this to set
2463 breakpoints in parts of your program which do not have debugging
2464 information or source files.
2467 When called without any arguments, @code{break} sets a breakpoint at
2468 the next instruction to be executed in the selected stack frame
2469 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2470 innermost, this makes your program stop as soon as control
2471 returns to that frame. This is similar to the effect of a
2472 @code{finish} command in the frame inside the selected frame---except
2473 that @code{finish} does not leave an active breakpoint. If you use
2474 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2475 the next time it reaches the current location; this may be useful
2478 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2479 least one instruction has been executed. If it did not do this, you
2480 would be unable to proceed past a breakpoint without first disabling the
2481 breakpoint. This rule applies whether or not the breakpoint already
2482 existed when your program stopped.
2484 @item break @dots{} if @var{cond}
2485 Set a breakpoint with condition @var{cond}; evaluate the expression
2486 @var{cond} each time the breakpoint is reached, and stop only if the
2487 value is nonzero---that is, if @var{cond} evaluates as true.
2488 @samp{@dots{}} stands for one of the possible arguments described
2489 above (or no argument) specifying where to break. @xref{Conditions,
2490 ,Break conditions}, for more information on breakpoint conditions.
2493 @item tbreak @var{args}
2494 Set a breakpoint enabled only for one stop. @var{args} are the
2495 same as for the @code{break} command, and the breakpoint is set in the same
2496 way, but the breakpoint is automatically deleted after the first time your
2497 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2500 @item hbreak @var{args}
2501 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2502 @code{break} command and the breakpoint is set in the same way, but the
2503 breakpoint requires hardware support and some target hardware may not
2504 have this support. The main purpose of this is EPROM/ROM code
2505 debugging, so you can set a breakpoint at an instruction without
2506 changing the instruction. This can be used with the new trap-generation
2507 provided by SPARClite DSU and some x86-based targets. These targets
2508 will generate traps when a program accesses some data or instruction
2509 address that is assigned to the debug registers. However the hardware
2510 breakpoint registers can take a limited number of breakpoints. For
2511 example, on the DSU, only two data breakpoints can be set at a time, and
2512 @value{GDBN} will reject this command if more than two are used. Delete
2513 or disable unused hardware breakpoints before setting new ones
2514 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2517 @item thbreak @var{args}
2518 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2519 are the same as for the @code{hbreak} command and the breakpoint is set in
2520 the same way. However, like the @code{tbreak} command,
2521 the breakpoint is automatically deleted after the
2522 first time your program stops there. Also, like the @code{hbreak}
2523 command, the breakpoint requires hardware support and some target hardware
2524 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2525 See also @ref{Conditions, ,Break conditions}.
2528 @cindex regular expression
2529 @item rbreak @var{regex}
2530 Set breakpoints on all functions matching the regular expression
2531 @var{regex}. This command sets an unconditional breakpoint on all
2532 matches, printing a list of all breakpoints it set. Once these
2533 breakpoints are set, they are treated just like the breakpoints set with
2534 the @code{break} command. You can delete them, disable them, or make
2535 them conditional the same way as any other breakpoint.
2537 The syntax of the regular expression is the standard one used with tools
2538 like @file{grep}. Note that this is different from the syntax used by
2539 shells, so for instance @code{foo*} matches all functions that include
2540 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2541 @code{.*} leading and trailing the regular expression you supply, so to
2542 match only functions that begin with @code{foo}, use @code{^foo}.
2544 When debugging C@t{++} programs, @code{rbreak} is useful for setting
2545 breakpoints on overloaded functions that are not members of any special
2548 @kindex info breakpoints
2549 @cindex @code{$_} and @code{info breakpoints}
2550 @item info breakpoints @r{[}@var{n}@r{]}
2551 @itemx info break @r{[}@var{n}@r{]}
2552 @itemx info watchpoints @r{[}@var{n}@r{]}
2553 Print a table of all breakpoints, watchpoints, and catchpoints set and
2554 not deleted, with the following columns for each breakpoint:
2557 @item Breakpoint Numbers
2559 Breakpoint, watchpoint, or catchpoint.
2561 Whether the breakpoint is marked to be disabled or deleted when hit.
2562 @item Enabled or Disabled
2563 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2564 that are not enabled.
2566 Where the breakpoint is in your program, as a memory address.
2568 Where the breakpoint is in the source for your program, as a file and
2573 If a breakpoint is conditional, @code{info break} shows the condition on
2574 the line following the affected breakpoint; breakpoint commands, if any,
2575 are listed after that.
2578 @code{info break} with a breakpoint
2579 number @var{n} as argument lists only that breakpoint. The
2580 convenience variable @code{$_} and the default examining-address for
2581 the @code{x} command are set to the address of the last breakpoint
2582 listed (@pxref{Memory, ,Examining memory}).
2585 @code{info break} displays a count of the number of times the breakpoint
2586 has been hit. This is especially useful in conjunction with the
2587 @code{ignore} command. You can ignore a large number of breakpoint
2588 hits, look at the breakpoint info to see how many times the breakpoint
2589 was hit, and then run again, ignoring one less than that number. This
2590 will get you quickly to the last hit of that breakpoint.
2593 @value{GDBN} allows you to set any number of breakpoints at the same place in
2594 your program. There is nothing silly or meaningless about this. When
2595 the breakpoints are conditional, this is even useful
2596 (@pxref{Conditions, ,Break conditions}).
2598 @cindex negative breakpoint numbers
2599 @cindex internal @value{GDBN} breakpoints
2600 @value{GDBN} itself sometimes sets breakpoints in your program for
2601 special purposes, such as proper handling of @code{longjmp} (in C
2602 programs). These internal breakpoints are assigned negative numbers,
2603 starting with @code{-1}; @samp{info breakpoints} does not display them.
2604 You can see these breakpoints with the @value{GDBN} maintenance command
2605 @samp{maint info breakpoints} (@pxref{maint info breakpoints}).
2608 @node Set Watchpoints
2609 @subsection Setting watchpoints
2611 @cindex setting watchpoints
2612 @cindex software watchpoints
2613 @cindex hardware watchpoints
2614 You can use a watchpoint to stop execution whenever the value of an
2615 expression changes, without having to predict a particular place where
2618 Depending on your system, watchpoints may be implemented in software or
2619 hardware. @value{GDBN} does software watchpointing by single-stepping your
2620 program and testing the variable's value each time, which is hundreds of
2621 times slower than normal execution. (But this may still be worth it, to
2622 catch errors where you have no clue what part of your program is the
2625 On some systems, such as HP-UX, @sc{gnu}/Linux and some other x86-based targets,
2626 @value{GDBN} includes support for
2627 hardware watchpoints, which do not slow down the running of your
2632 @item watch @var{expr}
2633 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2634 is written into by the program and its value changes.
2637 @item rwatch @var{expr}
2638 Set a watchpoint that will break when watch @var{expr} is read by the program.
2641 @item awatch @var{expr}
2642 Set a watchpoint that will break when @var{expr} is either read or written into
2645 @kindex info watchpoints
2646 @item info watchpoints
2647 This command prints a list of watchpoints, breakpoints, and catchpoints;
2648 it is the same as @code{info break}.
2651 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2652 watchpoints execute very quickly, and the debugger reports a change in
2653 value at the exact instruction where the change occurs. If @value{GDBN}
2654 cannot set a hardware watchpoint, it sets a software watchpoint, which
2655 executes more slowly and reports the change in value at the next
2656 statement, not the instruction, after the change occurs.
2658 When you issue the @code{watch} command, @value{GDBN} reports
2661 Hardware watchpoint @var{num}: @var{expr}
2665 if it was able to set a hardware watchpoint.
2667 Currently, the @code{awatch} and @code{rwatch} commands can only set
2668 hardware watchpoints, because accesses to data that don't change the
2669 value of the watched expression cannot be detected without examining
2670 every instruction as it is being executed, and @value{GDBN} does not do
2671 that currently. If @value{GDBN} finds that it is unable to set a
2672 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2673 will print a message like this:
2676 Expression cannot be implemented with read/access watchpoint.
2679 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2680 data type of the watched expression is wider than what a hardware
2681 watchpoint on the target machine can handle. For example, some systems
2682 can only watch regions that are up to 4 bytes wide; on such systems you
2683 cannot set hardware watchpoints for an expression that yields a
2684 double-precision floating-point number (which is typically 8 bytes
2685 wide). As a work-around, it might be possible to break the large region
2686 into a series of smaller ones and watch them with separate watchpoints.
2688 If you set too many hardware watchpoints, @value{GDBN} might be unable
2689 to insert all of them when you resume the execution of your program.
2690 Since the precise number of active watchpoints is unknown until such
2691 time as the program is about to be resumed, @value{GDBN} might not be
2692 able to warn you about this when you set the watchpoints, and the
2693 warning will be printed only when the program is resumed:
2696 Hardware watchpoint @var{num}: Could not insert watchpoint
2700 If this happens, delete or disable some of the watchpoints.
2702 The SPARClite DSU will generate traps when a program accesses some data
2703 or instruction address that is assigned to the debug registers. For the
2704 data addresses, DSU facilitates the @code{watch} command. However the
2705 hardware breakpoint registers can only take two data watchpoints, and
2706 both watchpoints must be the same kind. For example, you can set two
2707 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2708 @strong{or} two with @code{awatch} commands, but you cannot set one
2709 watchpoint with one command and the other with a different command.
2710 @value{GDBN} will reject the command if you try to mix watchpoints.
2711 Delete or disable unused watchpoint commands before setting new ones.
2713 If you call a function interactively using @code{print} or @code{call},
2714 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2715 kind of breakpoint or the call completes.
2717 @value{GDBN} automatically deletes watchpoints that watch local
2718 (automatic) variables, or expressions that involve such variables, when
2719 they go out of scope, that is, when the execution leaves the block in
2720 which these variables were defined. In particular, when the program
2721 being debugged terminates, @emph{all} local variables go out of scope,
2722 and so only watchpoints that watch global variables remain set. If you
2723 rerun the program, you will need to set all such watchpoints again. One
2724 way of doing that would be to set a code breakpoint at the entry to the
2725 @code{main} function and when it breaks, set all the watchpoints.
2728 @cindex watchpoints and threads
2729 @cindex threads and watchpoints
2730 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2731 usefulness. With the current watchpoint implementation, @value{GDBN}
2732 can only watch the value of an expression @emph{in a single thread}. If
2733 you are confident that the expression can only change due to the current
2734 thread's activity (and if you are also confident that no other thread
2735 can become current), then you can use watchpoints as usual. However,
2736 @value{GDBN} may not notice when a non-current thread's activity changes
2739 @c FIXME: this is almost identical to the previous paragraph.
2740 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2741 have only limited usefulness. If @value{GDBN} creates a software
2742 watchpoint, it can only watch the value of an expression @emph{in a
2743 single thread}. If you are confident that the expression can only
2744 change due to the current thread's activity (and if you are also
2745 confident that no other thread can become current), then you can use
2746 software watchpoints as usual. However, @value{GDBN} may not notice
2747 when a non-current thread's activity changes the expression. (Hardware
2748 watchpoints, in contrast, watch an expression in all threads.)
2751 @node Set Catchpoints
2752 @subsection Setting catchpoints
2753 @cindex catchpoints, setting
2754 @cindex exception handlers
2755 @cindex event handling
2757 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2758 kinds of program events, such as C@t{++} exceptions or the loading of a
2759 shared library. Use the @code{catch} command to set a catchpoint.
2763 @item catch @var{event}
2764 Stop when @var{event} occurs. @var{event} can be any of the following:
2768 The throwing of a C@t{++} exception.
2772 The catching of a C@t{++} exception.
2776 A call to @code{exec}. This is currently only available for HP-UX.
2780 A call to @code{fork}. This is currently only available for HP-UX.
2784 A call to @code{vfork}. This is currently only available for HP-UX.
2787 @itemx load @var{libname}
2789 The dynamic loading of any shared library, or the loading of the library
2790 @var{libname}. This is currently only available for HP-UX.
2793 @itemx unload @var{libname}
2794 @kindex catch unload
2795 The unloading of any dynamically loaded shared library, or the unloading
2796 of the library @var{libname}. This is currently only available for HP-UX.
2799 @item tcatch @var{event}
2800 Set a catchpoint that is enabled only for one stop. The catchpoint is
2801 automatically deleted after the first time the event is caught.
2805 Use the @code{info break} command to list the current catchpoints.
2807 There are currently some limitations to C@t{++} exception handling
2808 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2812 If you call a function interactively, @value{GDBN} normally returns
2813 control to you when the function has finished executing. If the call
2814 raises an exception, however, the call may bypass the mechanism that
2815 returns control to you and cause your program either to abort or to
2816 simply continue running until it hits a breakpoint, catches a signal
2817 that @value{GDBN} is listening for, or exits. This is the case even if
2818 you set a catchpoint for the exception; catchpoints on exceptions are
2819 disabled within interactive calls.
2822 You cannot raise an exception interactively.
2825 You cannot install an exception handler interactively.
2828 @cindex raise exceptions
2829 Sometimes @code{catch} is not the best way to debug exception handling:
2830 if you need to know exactly where an exception is raised, it is better to
2831 stop @emph{before} the exception handler is called, since that way you
2832 can see the stack before any unwinding takes place. If you set a
2833 breakpoint in an exception handler instead, it may not be easy to find
2834 out where the exception was raised.
2836 To stop just before an exception handler is called, you need some
2837 knowledge of the implementation. In the case of @sc{gnu} C@t{++}, exceptions are
2838 raised by calling a library function named @code{__raise_exception}
2839 which has the following ANSI C interface:
2842 /* @var{addr} is where the exception identifier is stored.
2843 @var{id} is the exception identifier. */
2844 void __raise_exception (void **addr, void *id);
2848 To make the debugger catch all exceptions before any stack
2849 unwinding takes place, set a breakpoint on @code{__raise_exception}
2850 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2852 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2853 that depends on the value of @var{id}, you can stop your program when
2854 a specific exception is raised. You can use multiple conditional
2855 breakpoints to stop your program when any of a number of exceptions are
2860 @subsection Deleting breakpoints
2862 @cindex clearing breakpoints, watchpoints, catchpoints
2863 @cindex deleting breakpoints, watchpoints, catchpoints
2864 It is often necessary to eliminate a breakpoint, watchpoint, or
2865 catchpoint once it has done its job and you no longer want your program
2866 to stop there. This is called @dfn{deleting} the breakpoint. A
2867 breakpoint that has been deleted no longer exists; it is forgotten.
2869 With the @code{clear} command you can delete breakpoints according to
2870 where they are in your program. With the @code{delete} command you can
2871 delete individual breakpoints, watchpoints, or catchpoints by specifying
2872 their breakpoint numbers.
2874 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2875 automatically ignores breakpoints on the first instruction to be executed
2876 when you continue execution without changing the execution address.
2881 Delete any breakpoints at the next instruction to be executed in the
2882 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2883 the innermost frame is selected, this is a good way to delete a
2884 breakpoint where your program just stopped.
2886 @item clear @var{function}
2887 @itemx clear @var{filename}:@var{function}
2888 Delete any breakpoints set at entry to the function @var{function}.
2890 @item clear @var{linenum}
2891 @itemx clear @var{filename}:@var{linenum}
2892 Delete any breakpoints set at or within the code of the specified line.
2894 @cindex delete breakpoints
2896 @kindex d @r{(@code{delete})}
2897 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2898 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2899 ranges specified as arguments. If no argument is specified, delete all
2900 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2901 confirm off}). You can abbreviate this command as @code{d}.
2905 @subsection Disabling breakpoints
2907 @kindex disable breakpoints
2908 @kindex enable breakpoints
2909 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2910 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2911 it had been deleted, but remembers the information on the breakpoint so
2912 that you can @dfn{enable} it again later.
2914 You disable and enable breakpoints, watchpoints, and catchpoints with
2915 the @code{enable} and @code{disable} commands, optionally specifying one
2916 or more breakpoint numbers as arguments. Use @code{info break} or
2917 @code{info watch} to print a list of breakpoints, watchpoints, and
2918 catchpoints if you do not know which numbers to use.
2920 A breakpoint, watchpoint, or catchpoint can have any of four different
2921 states of enablement:
2925 Enabled. The breakpoint stops your program. A breakpoint set
2926 with the @code{break} command starts out in this state.
2928 Disabled. The breakpoint has no effect on your program.
2930 Enabled once. The breakpoint stops your program, but then becomes
2933 Enabled for deletion. The breakpoint stops your program, but
2934 immediately after it does so it is deleted permanently. A breakpoint
2935 set with the @code{tbreak} command starts out in this state.
2938 You can use the following commands to enable or disable breakpoints,
2939 watchpoints, and catchpoints:
2942 @kindex disable breakpoints
2944 @kindex dis @r{(@code{disable})}
2945 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2946 Disable the specified breakpoints---or all breakpoints, if none are
2947 listed. A disabled breakpoint has no effect but is not forgotten. All
2948 options such as ignore-counts, conditions and commands are remembered in
2949 case the breakpoint is enabled again later. You may abbreviate
2950 @code{disable} as @code{dis}.
2952 @kindex enable breakpoints
2954 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2955 Enable the specified breakpoints (or all defined breakpoints). They
2956 become effective once again in stopping your program.
2958 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2959 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2960 of these breakpoints immediately after stopping your program.
2962 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2963 Enable the specified breakpoints to work once, then die. @value{GDBN}
2964 deletes any of these breakpoints as soon as your program stops there.
2967 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2968 @c confusing: tbreak is also initially enabled.
2969 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2970 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2971 subsequently, they become disabled or enabled only when you use one of
2972 the commands above. (The command @code{until} can set and delete a
2973 breakpoint of its own, but it does not change the state of your other
2974 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2978 @subsection Break conditions
2979 @cindex conditional breakpoints
2980 @cindex breakpoint conditions
2982 @c FIXME what is scope of break condition expr? Context where wanted?
2983 @c in particular for a watchpoint?
2984 The simplest sort of breakpoint breaks every time your program reaches a
2985 specified place. You can also specify a @dfn{condition} for a
2986 breakpoint. A condition is just a Boolean expression in your
2987 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2988 a condition evaluates the expression each time your program reaches it,
2989 and your program stops only if the condition is @emph{true}.
2991 This is the converse of using assertions for program validation; in that
2992 situation, you want to stop when the assertion is violated---that is,
2993 when the condition is false. In C, if you want to test an assertion expressed
2994 by the condition @var{assert}, you should set the condition
2995 @samp{! @var{assert}} on the appropriate breakpoint.
2997 Conditions are also accepted for watchpoints; you may not need them,
2998 since a watchpoint is inspecting the value of an expression anyhow---but
2999 it might be simpler, say, to just set a watchpoint on a variable name,
3000 and specify a condition that tests whether the new value is an interesting
3003 Break conditions can have side effects, and may even call functions in
3004 your program. This can be useful, for example, to activate functions
3005 that log program progress, or to use your own print functions to
3006 format special data structures. The effects are completely predictable
3007 unless there is another enabled breakpoint at the same address. (In
3008 that case, @value{GDBN} might see the other breakpoint first and stop your
3009 program without checking the condition of this one.) Note that
3010 breakpoint commands are usually more convenient and flexible than break
3012 purpose of performing side effects when a breakpoint is reached
3013 (@pxref{Break Commands, ,Breakpoint command lists}).
3015 Break conditions can be specified when a breakpoint is set, by using
3016 @samp{if} in the arguments to the @code{break} command. @xref{Set
3017 Breaks, ,Setting breakpoints}. They can also be changed at any time
3018 with the @code{condition} command.
3020 You can also use the @code{if} keyword with the @code{watch} command.
3021 The @code{catch} command does not recognize the @code{if} keyword;
3022 @code{condition} is the only way to impose a further condition on a
3027 @item condition @var{bnum} @var{expression}
3028 Specify @var{expression} as the break condition for breakpoint,
3029 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3030 breakpoint @var{bnum} stops your program only if the value of
3031 @var{expression} is true (nonzero, in C). When you use
3032 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3033 syntactic correctness, and to determine whether symbols in it have
3034 referents in the context of your breakpoint. If @var{expression} uses
3035 symbols not referenced in the context of the breakpoint, @value{GDBN}
3036 prints an error message:
3039 No symbol "foo" in current context.
3044 not actually evaluate @var{expression} at the time the @code{condition}
3045 command (or a command that sets a breakpoint with a condition, like
3046 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
3048 @item condition @var{bnum}
3049 Remove the condition from breakpoint number @var{bnum}. It becomes
3050 an ordinary unconditional breakpoint.
3053 @cindex ignore count (of breakpoint)
3054 A special case of a breakpoint condition is to stop only when the
3055 breakpoint has been reached a certain number of times. This is so
3056 useful that there is a special way to do it, using the @dfn{ignore
3057 count} of the breakpoint. Every breakpoint has an ignore count, which
3058 is an integer. Most of the time, the ignore count is zero, and
3059 therefore has no effect. But if your program reaches a breakpoint whose
3060 ignore count is positive, then instead of stopping, it just decrements
3061 the ignore count by one and continues. As a result, if the ignore count
3062 value is @var{n}, the breakpoint does not stop the next @var{n} times
3063 your program reaches it.
3067 @item ignore @var{bnum} @var{count}
3068 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3069 The next @var{count} times the breakpoint is reached, your program's
3070 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3073 To make the breakpoint stop the next time it is reached, specify
3076 When you use @code{continue} to resume execution of your program from a
3077 breakpoint, you can specify an ignore count directly as an argument to
3078 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3079 Stepping,,Continuing and stepping}.
3081 If a breakpoint has a positive ignore count and a condition, the
3082 condition is not checked. Once the ignore count reaches zero,
3083 @value{GDBN} resumes checking the condition.
3085 You could achieve the effect of the ignore count with a condition such
3086 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3087 is decremented each time. @xref{Convenience Vars, ,Convenience
3091 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3094 @node Break Commands
3095 @subsection Breakpoint command lists
3097 @cindex breakpoint commands
3098 You can give any breakpoint (or watchpoint or catchpoint) a series of
3099 commands to execute when your program stops due to that breakpoint. For
3100 example, you might want to print the values of certain expressions, or
3101 enable other breakpoints.
3106 @item commands @r{[}@var{bnum}@r{]}
3107 @itemx @dots{} @var{command-list} @dots{}
3109 Specify a list of commands for breakpoint number @var{bnum}. The commands
3110 themselves appear on the following lines. Type a line containing just
3111 @code{end} to terminate the commands.
3113 To remove all commands from a breakpoint, type @code{commands} and
3114 follow it immediately with @code{end}; that is, give no commands.
3116 With no @var{bnum} argument, @code{commands} refers to the last
3117 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3118 recently encountered).
3121 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3122 disabled within a @var{command-list}.
3124 You can use breakpoint commands to start your program up again. Simply
3125 use the @code{continue} command, or @code{step}, or any other command
3126 that resumes execution.
3128 Any other commands in the command list, after a command that resumes
3129 execution, are ignored. This is because any time you resume execution
3130 (even with a simple @code{next} or @code{step}), you may encounter
3131 another breakpoint---which could have its own command list, leading to
3132 ambiguities about which list to execute.
3135 If the first command you specify in a command list is @code{silent}, the
3136 usual message about stopping at a breakpoint is not printed. This may
3137 be desirable for breakpoints that are to print a specific message and
3138 then continue. If none of the remaining commands print anything, you
3139 see no sign that the breakpoint was reached. @code{silent} is
3140 meaningful only at the beginning of a breakpoint command list.
3142 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3143 print precisely controlled output, and are often useful in silent
3144 breakpoints. @xref{Output, ,Commands for controlled output}.
3146 For example, here is how you could use breakpoint commands to print the
3147 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3153 printf "x is %d\n",x
3158 One application for breakpoint commands is to compensate for one bug so
3159 you can test for another. Put a breakpoint just after the erroneous line
3160 of code, give it a condition to detect the case in which something
3161 erroneous has been done, and give it commands to assign correct values
3162 to any variables that need them. End with the @code{continue} command
3163 so that your program does not stop, and start with the @code{silent}
3164 command so that no output is produced. Here is an example:
3175 @node Breakpoint Menus
3176 @subsection Breakpoint menus
3178 @cindex symbol overloading
3180 Some programming languages (notably C@t{++}) permit a single function name
3181 to be defined several times, for application in different contexts.
3182 This is called @dfn{overloading}. When a function name is overloaded,
3183 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3184 a breakpoint. If you realize this is a problem, you can use
3185 something like @samp{break @var{function}(@var{types})} to specify which
3186 particular version of the function you want. Otherwise, @value{GDBN} offers
3187 you a menu of numbered choices for different possible breakpoints, and
3188 waits for your selection with the prompt @samp{>}. The first two
3189 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3190 sets a breakpoint at each definition of @var{function}, and typing
3191 @kbd{0} aborts the @code{break} command without setting any new
3194 For example, the following session excerpt shows an attempt to set a
3195 breakpoint at the overloaded symbol @code{String::after}.
3196 We choose three particular definitions of that function name:
3198 @c FIXME! This is likely to change to show arg type lists, at least
3201 (@value{GDBP}) b String::after
3204 [2] file:String.cc; line number:867
3205 [3] file:String.cc; line number:860
3206 [4] file:String.cc; line number:875
3207 [5] file:String.cc; line number:853
3208 [6] file:String.cc; line number:846
3209 [7] file:String.cc; line number:735
3211 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3212 Breakpoint 2 at 0xb344: file String.cc, line 875.
3213 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3214 Multiple breakpoints were set.
3215 Use the "delete" command to delete unwanted
3221 @c @ifclear BARETARGET
3222 @node Error in Breakpoints
3223 @subsection ``Cannot insert breakpoints''
3225 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3227 Under some operating systems, breakpoints cannot be used in a program if
3228 any other process is running that program. In this situation,
3229 attempting to run or continue a program with a breakpoint causes
3230 @value{GDBN} to print an error message:
3233 Cannot insert breakpoints.
3234 The same program may be running in another process.
3237 When this happens, you have three ways to proceed:
3241 Remove or disable the breakpoints, then continue.
3244 Suspend @value{GDBN}, and copy the file containing your program to a new
3245 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3246 that @value{GDBN} should run your program under that name.
3247 Then start your program again.
3250 Relink your program so that the text segment is nonsharable, using the
3251 linker option @samp{-N}. The operating system limitation may not apply
3252 to nonsharable executables.
3256 A similar message can be printed if you request too many active
3257 hardware-assisted breakpoints and watchpoints:
3259 @c FIXME: the precise wording of this message may change; the relevant
3260 @c source change is not committed yet (Sep 3, 1999).
3262 Stopped; cannot insert breakpoints.
3263 You may have requested too many hardware breakpoints and watchpoints.
3267 This message is printed when you attempt to resume the program, since
3268 only then @value{GDBN} knows exactly how many hardware breakpoints and
3269 watchpoints it needs to insert.
3271 When this message is printed, you need to disable or remove some of the
3272 hardware-assisted breakpoints and watchpoints, and then continue.
3275 @node Continuing and Stepping
3276 @section Continuing and stepping
3280 @cindex resuming execution
3281 @dfn{Continuing} means resuming program execution until your program
3282 completes normally. In contrast, @dfn{stepping} means executing just
3283 one more ``step'' of your program, where ``step'' may mean either one
3284 line of source code, or one machine instruction (depending on what
3285 particular command you use). Either when continuing or when stepping,
3286 your program may stop even sooner, due to a breakpoint or a signal. (If
3287 it stops due to a signal, you may want to use @code{handle}, or use
3288 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3292 @kindex c @r{(@code{continue})}
3293 @kindex fg @r{(resume foreground execution)}
3294 @item continue @r{[}@var{ignore-count}@r{]}
3295 @itemx c @r{[}@var{ignore-count}@r{]}
3296 @itemx fg @r{[}@var{ignore-count}@r{]}
3297 Resume program execution, at the address where your program last stopped;
3298 any breakpoints set at that address are bypassed. The optional argument
3299 @var{ignore-count} allows you to specify a further number of times to
3300 ignore a breakpoint at this location; its effect is like that of
3301 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3303 The argument @var{ignore-count} is meaningful only when your program
3304 stopped due to a breakpoint. At other times, the argument to
3305 @code{continue} is ignored.
3307 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3308 debugged program is deemed to be the foreground program) are provided
3309 purely for convenience, and have exactly the same behavior as
3313 To resume execution at a different place, you can use @code{return}
3314 (@pxref{Returning, ,Returning from a function}) to go back to the
3315 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3316 different address}) to go to an arbitrary location in your program.
3318 A typical technique for using stepping is to set a breakpoint
3319 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3320 beginning of the function or the section of your program where a problem
3321 is believed to lie, run your program until it stops at that breakpoint,
3322 and then step through the suspect area, examining the variables that are
3323 interesting, until you see the problem happen.
3327 @kindex s @r{(@code{step})}
3329 Continue running your program until control reaches a different source
3330 line, then stop it and return control to @value{GDBN}. This command is
3331 abbreviated @code{s}.
3334 @c "without debugging information" is imprecise; actually "without line
3335 @c numbers in the debugging information". (gcc -g1 has debugging info but
3336 @c not line numbers). But it seems complex to try to make that
3337 @c distinction here.
3338 @emph{Warning:} If you use the @code{step} command while control is
3339 within a function that was compiled without debugging information,
3340 execution proceeds until control reaches a function that does have
3341 debugging information. Likewise, it will not step into a function which
3342 is compiled without debugging information. To step through functions
3343 without debugging information, use the @code{stepi} command, described
3347 The @code{step} command only stops at the first instruction of a source
3348 line. This prevents the multiple stops that could otherwise occur in
3349 @code{switch} statements, @code{for} loops, etc. @code{step} continues
3350 to stop if a function that has debugging information is called within
3351 the line. In other words, @code{step} @emph{steps inside} any functions
3352 called within the line.
3354 Also, the @code{step} command only enters a function if there is line
3355 number information for the function. Otherwise it acts like the
3356 @code{next} command. This avoids problems when using @code{cc -gl}
3357 on MIPS machines. Previously, @code{step} entered subroutines if there
3358 was any debugging information about the routine.
3360 @item step @var{count}
3361 Continue running as in @code{step}, but do so @var{count} times. If a
3362 breakpoint is reached, or a signal not related to stepping occurs before
3363 @var{count} steps, stepping stops right away.
3366 @kindex n @r{(@code{next})}
3367 @item next @r{[}@var{count}@r{]}
3368 Continue to the next source line in the current (innermost) stack frame.
3369 This is similar to @code{step}, but function calls that appear within
3370 the line of code are executed without stopping. Execution stops when
3371 control reaches a different line of code at the original stack level
3372 that was executing when you gave the @code{next} command. This command
3373 is abbreviated @code{n}.
3375 An argument @var{count} is a repeat count, as for @code{step}.
3378 @c FIX ME!! Do we delete this, or is there a way it fits in with
3379 @c the following paragraph? --- Vctoria
3381 @c @code{next} within a function that lacks debugging information acts like
3382 @c @code{step}, but any function calls appearing within the code of the
3383 @c function are executed without stopping.
3385 The @code{next} command only stops at the first instruction of a
3386 source line. This prevents multiple stops that could otherwise occur in
3387 @code{switch} statements, @code{for} loops, etc.
3389 @kindex set step-mode
3391 @cindex functions without line info, and stepping
3392 @cindex stepping into functions with no line info
3393 @itemx set step-mode on
3394 The @code{set step-mode on} command causes the @code{step} command to
3395 stop at the first instruction of a function which contains no debug line
3396 information rather than stepping over it.
3398 This is useful in cases where you may be interested in inspecting the
3399 machine instructions of a function which has no symbolic info and do not
3400 want @value{GDBN} to automatically skip over this function.
3402 @item set step-mode off
3403 Causes the @code{step} command to step over any functions which contains no
3404 debug information. This is the default.
3408 Continue running until just after function in the selected stack frame
3409 returns. Print the returned value (if any).
3411 Contrast this with the @code{return} command (@pxref{Returning,
3412 ,Returning from a function}).
3415 @kindex u @r{(@code{until})}
3418 Continue running until a source line past the current line, in the
3419 current stack frame, is reached. This command is used to avoid single
3420 stepping through a loop more than once. It is like the @code{next}
3421 command, except that when @code{until} encounters a jump, it
3422 automatically continues execution until the program counter is greater
3423 than the address of the jump.
3425 This means that when you reach the end of a loop after single stepping
3426 though it, @code{until} makes your program continue execution until it
3427 exits the loop. In contrast, a @code{next} command at the end of a loop
3428 simply steps back to the beginning of the loop, which forces you to step
3429 through the next iteration.
3431 @code{until} always stops your program if it attempts to exit the current
3434 @code{until} may produce somewhat counterintuitive results if the order
3435 of machine code does not match the order of the source lines. For
3436 example, in the following excerpt from a debugging session, the @code{f}
3437 (@code{frame}) command shows that execution is stopped at line
3438 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3442 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3444 (@value{GDBP}) until
3445 195 for ( ; argc > 0; NEXTARG) @{
3448 This happened because, for execution efficiency, the compiler had
3449 generated code for the loop closure test at the end, rather than the
3450 start, of the loop---even though the test in a C @code{for}-loop is
3451 written before the body of the loop. The @code{until} command appeared
3452 to step back to the beginning of the loop when it advanced to this
3453 expression; however, it has not really gone to an earlier
3454 statement---not in terms of the actual machine code.
3456 @code{until} with no argument works by means of single
3457 instruction stepping, and hence is slower than @code{until} with an
3460 @item until @var{location}
3461 @itemx u @var{location}
3462 Continue running your program until either the specified location is
3463 reached, or the current stack frame returns. @var{location} is any of
3464 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3465 ,Setting breakpoints}). This form of the command uses breakpoints,
3466 and hence is quicker than @code{until} without an argument.
3469 @kindex si @r{(@code{stepi})}
3471 @itemx stepi @var{arg}
3473 Execute one machine instruction, then stop and return to the debugger.
3475 It is often useful to do @samp{display/i $pc} when stepping by machine
3476 instructions. This makes @value{GDBN} automatically display the next
3477 instruction to be executed, each time your program stops. @xref{Auto
3478 Display,, Automatic display}.
3480 An argument is a repeat count, as in @code{step}.
3484 @kindex ni @r{(@code{nexti})}
3486 @itemx nexti @var{arg}
3488 Execute one machine instruction, but if it is a function call,
3489 proceed until the function returns.
3491 An argument is a repeat count, as in @code{next}.
3498 A signal is an asynchronous event that can happen in a program. The
3499 operating system defines the possible kinds of signals, and gives each
3500 kind a name and a number. For example, in Unix @code{SIGINT} is the
3501 signal a program gets when you type an interrupt character (often @kbd{C-c});
3502 @code{SIGSEGV} is the signal a program gets from referencing a place in
3503 memory far away from all the areas in use; @code{SIGALRM} occurs when
3504 the alarm clock timer goes off (which happens only if your program has
3505 requested an alarm).
3507 @cindex fatal signals
3508 Some signals, including @code{SIGALRM}, are a normal part of the
3509 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3510 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3511 program has not specified in advance some other way to handle the signal.
3512 @code{SIGINT} does not indicate an error in your program, but it is normally
3513 fatal so it can carry out the purpose of the interrupt: to kill the program.
3515 @value{GDBN} has the ability to detect any occurrence of a signal in your
3516 program. You can tell @value{GDBN} in advance what to do for each kind of
3519 @cindex handling signals
3520 Normally, @value{GDBN} is set up to let the non-erroneous signals like
3521 @code{SIGALRM} be silently passed to your program
3522 (so as not to interfere with their role in the program's functioning)
3523 but to stop your program immediately whenever an error signal happens.
3524 You can change these settings with the @code{handle} command.
3527 @kindex info signals
3530 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3531 handle each one. You can use this to see the signal numbers of all
3532 the defined types of signals.
3534 @code{info handle} is an alias for @code{info signals}.
3537 @item handle @var{signal} @var{keywords}@dots{}
3538 Change the way @value{GDBN} handles signal @var{signal}. @var{signal}
3539 can be the number of a signal or its name (with or without the
3540 @samp{SIG} at the beginning); a list of signal numbers of the form
3541 @samp{@var{low}-@var{high}}; or the word @samp{all}, meaning all the
3542 known signals. The @var{keywords} say what change to make.
3546 The keywords allowed by the @code{handle} command can be abbreviated.
3547 Their full names are:
3551 @value{GDBN} should not stop your program when this signal happens. It may
3552 still print a message telling you that the signal has come in.
3555 @value{GDBN} should stop your program when this signal happens. This implies
3556 the @code{print} keyword as well.
3559 @value{GDBN} should print a message when this signal happens.
3562 @value{GDBN} should not mention the occurrence of the signal at all. This
3563 implies the @code{nostop} keyword as well.
3567 @value{GDBN} should allow your program to see this signal; your program
3568 can handle the signal, or else it may terminate if the signal is fatal
3569 and not handled. @code{pass} and @code{noignore} are synonyms.
3573 @value{GDBN} should not allow your program to see this signal.
3574 @code{nopass} and @code{ignore} are synonyms.
3578 When a signal stops your program, the signal is not visible to the
3580 continue. Your program sees the signal then, if @code{pass} is in
3581 effect for the signal in question @emph{at that time}. In other words,
3582 after @value{GDBN} reports a signal, you can use the @code{handle}
3583 command with @code{pass} or @code{nopass} to control whether your
3584 program sees that signal when you continue.
3586 The default is set to @code{nostop}, @code{noprint}, @code{pass} for
3587 non-erroneous signals such as @code{SIGALRM}, @code{SIGWINCH} and
3588 @code{SIGCHLD}, and to @code{stop}, @code{print}, @code{pass} for the
3591 You can also use the @code{signal} command to prevent your program from
3592 seeing a signal, or cause it to see a signal it normally would not see,
3593 or to give it any signal at any time. For example, if your program stopped
3594 due to some sort of memory reference error, you might store correct
3595 values into the erroneous variables and continue, hoping to see more
3596 execution; but your program would probably terminate immediately as
3597 a result of the fatal signal once it saw the signal. To prevent this,
3598 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3602 @section Stopping and starting multi-thread programs
3604 When your program has multiple threads (@pxref{Threads,, Debugging
3605 programs with multiple threads}), you can choose whether to set
3606 breakpoints on all threads, or on a particular thread.
3609 @cindex breakpoints and threads
3610 @cindex thread breakpoints
3611 @kindex break @dots{} thread @var{threadno}
3612 @item break @var{linespec} thread @var{threadno}
3613 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3614 @var{linespec} specifies source lines; there are several ways of
3615 writing them, but the effect is always to specify some source line.
3617 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3618 to specify that you only want @value{GDBN} to stop the program when a
3619 particular thread reaches this breakpoint. @var{threadno} is one of the
3620 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3621 column of the @samp{info threads} display.
3623 If you do not specify @samp{thread @var{threadno}} when you set a
3624 breakpoint, the breakpoint applies to @emph{all} threads of your
3627 You can use the @code{thread} qualifier on conditional breakpoints as
3628 well; in this case, place @samp{thread @var{threadno}} before the
3629 breakpoint condition, like this:
3632 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3637 @cindex stopped threads
3638 @cindex threads, stopped
3639 Whenever your program stops under @value{GDBN} for any reason,
3640 @emph{all} threads of execution stop, not just the current thread. This
3641 allows you to examine the overall state of the program, including
3642 switching between threads, without worrying that things may change
3645 @cindex continuing threads
3646 @cindex threads, continuing
3647 Conversely, whenever you restart the program, @emph{all} threads start
3648 executing. @emph{This is true even when single-stepping} with commands
3649 like @code{step} or @code{next}.
3651 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3652 Since thread scheduling is up to your debugging target's operating
3653 system (not controlled by @value{GDBN}), other threads may
3654 execute more than one statement while the current thread completes a
3655 single step. Moreover, in general other threads stop in the middle of a
3656 statement, rather than at a clean statement boundary, when the program
3659 You might even find your program stopped in another thread after
3660 continuing or even single-stepping. This happens whenever some other
3661 thread runs into a breakpoint, a signal, or an exception before the
3662 first thread completes whatever you requested.
3664 On some OSes, you can lock the OS scheduler and thus allow only a single
3668 @item set scheduler-locking @var{mode}
3669 Set the scheduler locking mode. If it is @code{off}, then there is no
3670 locking and any thread may run at any time. If @code{on}, then only the
3671 current thread may run when the inferior is resumed. The @code{step}
3672 mode optimizes for single-stepping. It stops other threads from
3673 ``seizing the prompt'' by preempting the current thread while you are
3674 stepping. Other threads will only rarely (or never) get a chance to run
3675 when you step. They are more likely to run when you @samp{next} over a
3676 function call, and they are completely free to run when you use commands
3677 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3678 thread hits a breakpoint during its timeslice, they will never steal the
3679 @value{GDBN} prompt away from the thread that you are debugging.
3681 @item show scheduler-locking
3682 Display the current scheduler locking mode.
3687 @chapter Examining the Stack
3689 When your program has stopped, the first thing you need to know is where it
3690 stopped and how it got there.
3693 Each time your program performs a function call, information about the call
3695 That information includes the location of the call in your program,
3696 the arguments of the call,
3697 and the local variables of the function being called.
3698 The information is saved in a block of data called a @dfn{stack frame}.
3699 The stack frames are allocated in a region of memory called the @dfn{call
3702 When your program stops, the @value{GDBN} commands for examining the
3703 stack allow you to see all of this information.
3705 @cindex selected frame
3706 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3707 @value{GDBN} commands refer implicitly to the selected frame. In
3708 particular, whenever you ask @value{GDBN} for the value of a variable in
3709 your program, the value is found in the selected frame. There are
3710 special @value{GDBN} commands to select whichever frame you are
3711 interested in. @xref{Selection, ,Selecting a frame}.
3713 When your program stops, @value{GDBN} automatically selects the
3714 currently executing frame and describes it briefly, similar to the
3715 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3718 * Frames:: Stack frames
3719 * Backtrace:: Backtraces
3720 * Selection:: Selecting a frame
3721 * Frame Info:: Information on a frame
3726 @section Stack frames
3728 @cindex frame, definition
3730 The call stack is divided up into contiguous pieces called @dfn{stack
3731 frames}, or @dfn{frames} for short; each frame is the data associated
3732 with one call to one function. The frame contains the arguments given
3733 to the function, the function's local variables, and the address at
3734 which the function is executing.
3736 @cindex initial frame
3737 @cindex outermost frame
3738 @cindex innermost frame
3739 When your program is started, the stack has only one frame, that of the
3740 function @code{main}. This is called the @dfn{initial} frame or the
3741 @dfn{outermost} frame. Each time a function is called, a new frame is
3742 made. Each time a function returns, the frame for that function invocation
3743 is eliminated. If a function is recursive, there can be many frames for
3744 the same function. The frame for the function in which execution is
3745 actually occurring is called the @dfn{innermost} frame. This is the most
3746 recently created of all the stack frames that still exist.
3748 @cindex frame pointer
3749 Inside your program, stack frames are identified by their addresses. A
3750 stack frame consists of many bytes, each of which has its own address; each
3751 kind of computer has a convention for choosing one byte whose
3752 address serves as the address of the frame. Usually this address is kept
3753 in a register called the @dfn{frame pointer register} while execution is
3754 going on in that frame.
3756 @cindex frame number
3757 @value{GDBN} assigns numbers to all existing stack frames, starting with
3758 zero for the innermost frame, one for the frame that called it,
3759 and so on upward. These numbers do not really exist in your program;
3760 they are assigned by @value{GDBN} to give you a way of designating stack
3761 frames in @value{GDBN} commands.
3763 @c The -fomit-frame-pointer below perennially causes hbox overflow
3764 @c underflow problems.
3765 @cindex frameless execution
3766 Some compilers provide a way to compile functions so that they operate
3767 without stack frames. (For example, the @value{GCC} option
3769 @samp{-fomit-frame-pointer}
3771 generates functions without a frame.)
3772 This is occasionally done with heavily used library functions to save
3773 the frame setup time. @value{GDBN} has limited facilities for dealing
3774 with these function invocations. If the innermost function invocation
3775 has no stack frame, @value{GDBN} nevertheless regards it as though
3776 it had a separate frame, which is numbered zero as usual, allowing
3777 correct tracing of the function call chain. However, @value{GDBN} has
3778 no provision for frameless functions elsewhere in the stack.
3781 @kindex frame@r{, command}
3782 @cindex current stack frame
3783 @item frame @var{args}
3784 The @code{frame} command allows you to move from one stack frame to another,
3785 and to print the stack frame you select. @var{args} may be either the
3786 address of the frame or the stack frame number. Without an argument,
3787 @code{frame} prints the current stack frame.
3789 @kindex select-frame
3790 @cindex selecting frame silently
3792 The @code{select-frame} command allows you to move from one stack frame
3793 to another without printing the frame. This is the silent version of
3802 @cindex stack traces
3803 A backtrace is a summary of how your program got where it is. It shows one
3804 line per frame, for many frames, starting with the currently executing
3805 frame (frame zero), followed by its caller (frame one), and on up the
3810 @kindex bt @r{(@code{backtrace})}
3813 Print a backtrace of the entire stack: one line per frame for all
3814 frames in the stack.
3816 You can stop the backtrace at any time by typing the system interrupt
3817 character, normally @kbd{C-c}.
3819 @item backtrace @var{n}
3821 Similar, but print only the innermost @var{n} frames.
3823 @item backtrace -@var{n}
3825 Similar, but print only the outermost @var{n} frames.
3830 @kindex info s @r{(@code{info stack})}
3831 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3832 are additional aliases for @code{backtrace}.
3834 Each line in the backtrace shows the frame number and the function name.
3835 The program counter value is also shown---unless you use @code{set
3836 print address off}. The backtrace also shows the source file name and
3837 line number, as well as the arguments to the function. The program
3838 counter value is omitted if it is at the beginning of the code for that
3841 Here is an example of a backtrace. It was made with the command
3842 @samp{bt 3}, so it shows the innermost three frames.
3846 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3848 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3849 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3851 (More stack frames follow...)
3856 The display for frame zero does not begin with a program counter
3857 value, indicating that your program has stopped at the beginning of the
3858 code for line @code{993} of @code{builtin.c}.
3860 @kindex set backtrace-below-main
3861 @kindex show backtrace-below-main
3863 Most programs have a standard entry point---a place where system libraries
3864 and startup code transition into user code. For C this is @code{main}.
3865 When @value{GDBN} finds the entry function in a backtrace it will terminate
3866 the backtrace, to avoid tracing into highly system-specific (and generally
3867 uninteresting) code. If you need to examine the startup code, then you can
3868 change this behavior.
3871 @item set backtrace-below-main off
3872 Backtraces will stop when they encounter the user entry point. This is the
3875 @item set backtrace-below-main
3876 @itemx set backtrace-below-main on
3877 Backtraces will continue past the user entry point to the top of the stack.
3879 @item show backtrace-below-main
3880 Display the current backtrace policy.
3884 @section Selecting a frame
3886 Most commands for examining the stack and other data in your program work on
3887 whichever stack frame is selected at the moment. Here are the commands for
3888 selecting a stack frame; all of them finish by printing a brief description
3889 of the stack frame just selected.
3892 @kindex frame@r{, selecting}
3893 @kindex f @r{(@code{frame})}
3896 Select frame number @var{n}. Recall that frame zero is the innermost
3897 (currently executing) frame, frame one is the frame that called the
3898 innermost one, and so on. The highest-numbered frame is the one for
3901 @item frame @var{addr}
3903 Select the frame at address @var{addr}. This is useful mainly if the
3904 chaining of stack frames has been damaged by a bug, making it
3905 impossible for @value{GDBN} to assign numbers properly to all frames. In
3906 addition, this can be useful when your program has multiple stacks and
3907 switches between them.
3909 On the SPARC architecture, @code{frame} needs two addresses to
3910 select an arbitrary frame: a frame pointer and a stack pointer.
3912 On the MIPS and Alpha architecture, it needs two addresses: a stack
3913 pointer and a program counter.
3915 On the 29k architecture, it needs three addresses: a register stack
3916 pointer, a program counter, and a memory stack pointer.
3917 @c note to future updaters: this is conditioned on a flag
3918 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3919 @c as of 27 Jan 1994.
3923 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3924 advances toward the outermost frame, to higher frame numbers, to frames
3925 that have existed longer. @var{n} defaults to one.
3928 @kindex do @r{(@code{down})}
3930 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3931 advances toward the innermost frame, to lower frame numbers, to frames
3932 that were created more recently. @var{n} defaults to one. You may
3933 abbreviate @code{down} as @code{do}.
3936 All of these commands end by printing two lines of output describing the
3937 frame. The first line shows the frame number, the function name, the
3938 arguments, and the source file and line number of execution in that
3939 frame. The second line shows the text of that source line.
3947 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3949 10 read_input_file (argv[i]);
3953 After such a printout, the @code{list} command with no arguments
3954 prints ten lines centered on the point of execution in the frame.
3955 You can also edit the program at the point of execution with your favorite
3956 editing program by typing @code{edit}.
3957 @xref{List, ,Printing source lines},
3961 @kindex down-silently
3963 @item up-silently @var{n}
3964 @itemx down-silently @var{n}
3965 These two commands are variants of @code{up} and @code{down},
3966 respectively; they differ in that they do their work silently, without
3967 causing display of the new frame. They are intended primarily for use
3968 in @value{GDBN} command scripts, where the output might be unnecessary and
3973 @section Information about a frame
3975 There are several other commands to print information about the selected
3981 When used without any argument, this command does not change which
3982 frame is selected, but prints a brief description of the currently
3983 selected stack frame. It can be abbreviated @code{f}. With an
3984 argument, this command is used to select a stack frame.
3985 @xref{Selection, ,Selecting a frame}.
3988 @kindex info f @r{(@code{info frame})}
3991 This command prints a verbose description of the selected stack frame,
3996 the address of the frame
3998 the address of the next frame down (called by this frame)
4000 the address of the next frame up (caller of this frame)
4002 the language in which the source code corresponding to this frame is written
4004 the address of the frame's arguments
4006 the address of the frame's local variables
4008 the program counter saved in it (the address of execution in the caller frame)
4010 which registers were saved in the frame
4013 @noindent The verbose description is useful when
4014 something has gone wrong that has made the stack format fail to fit
4015 the usual conventions.
4017 @item info frame @var{addr}
4018 @itemx info f @var{addr}
4019 Print a verbose description of the frame at address @var{addr}, without
4020 selecting that frame. The selected frame remains unchanged by this
4021 command. This requires the same kind of address (more than one for some
4022 architectures) that you specify in the @code{frame} command.
4023 @xref{Selection, ,Selecting a frame}.
4027 Print the arguments of the selected frame, each on a separate line.
4031 Print the local variables of the selected frame, each on a separate
4032 line. These are all variables (declared either static or automatic)
4033 accessible at the point of execution of the selected frame.
4036 @cindex catch exceptions, list active handlers
4037 @cindex exception handlers, how to list
4039 Print a list of all the exception handlers that are active in the
4040 current stack frame at the current point of execution. To see other
4041 exception handlers, visit the associated frame (using the @code{up},
4042 @code{down}, or @code{frame} commands); then type @code{info catch}.
4043 @xref{Set Catchpoints, , Setting catchpoints}.
4049 @chapter Examining Source Files
4051 @value{GDBN} can print parts of your program's source, since the debugging
4052 information recorded in the program tells @value{GDBN} what source files were
4053 used to build it. When your program stops, @value{GDBN} spontaneously prints
4054 the line where it stopped. Likewise, when you select a stack frame
4055 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4056 execution in that frame has stopped. You can print other portions of
4057 source files by explicit command.
4059 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4060 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
4061 @value{GDBN} under @sc{gnu} Emacs}.
4064 * List:: Printing source lines
4065 * Edit:: Editing source files
4066 * Search:: Searching source files
4067 * Source Path:: Specifying source directories
4068 * Machine Code:: Source and machine code
4072 @section Printing source lines
4075 @kindex l @r{(@code{list})}
4076 To print lines from a source file, use the @code{list} command
4077 (abbreviated @code{l}). By default, ten lines are printed.
4078 There are several ways to specify what part of the file you want to print.
4080 Here are the forms of the @code{list} command most commonly used:
4083 @item list @var{linenum}
4084 Print lines centered around line number @var{linenum} in the
4085 current source file.
4087 @item list @var{function}
4088 Print lines centered around the beginning of function
4092 Print more lines. If the last lines printed were printed with a
4093 @code{list} command, this prints lines following the last lines
4094 printed; however, if the last line printed was a solitary line printed
4095 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4096 Stack}), this prints lines centered around that line.
4099 Print lines just before the lines last printed.
4102 By default, @value{GDBN} prints ten source lines with any of these forms of
4103 the @code{list} command. You can change this using @code{set listsize}:
4106 @kindex set listsize
4107 @item set listsize @var{count}
4108 Make the @code{list} command display @var{count} source lines (unless
4109 the @code{list} argument explicitly specifies some other number).
4111 @kindex show listsize
4113 Display the number of lines that @code{list} prints.
4116 Repeating a @code{list} command with @key{RET} discards the argument,
4117 so it is equivalent to typing just @code{list}. This is more useful
4118 than listing the same lines again. An exception is made for an
4119 argument of @samp{-}; that argument is preserved in repetition so that
4120 each repetition moves up in the source file.
4123 In general, the @code{list} command expects you to supply zero, one or two
4124 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4125 of writing them, but the effect is always to specify some source line.
4126 Here is a complete description of the possible arguments for @code{list}:
4129 @item list @var{linespec}
4130 Print lines centered around the line specified by @var{linespec}.
4132 @item list @var{first},@var{last}
4133 Print lines from @var{first} to @var{last}. Both arguments are
4136 @item list ,@var{last}
4137 Print lines ending with @var{last}.
4139 @item list @var{first},
4140 Print lines starting with @var{first}.
4143 Print lines just after the lines last printed.
4146 Print lines just before the lines last printed.
4149 As described in the preceding table.
4152 Here are the ways of specifying a single source line---all the
4157 Specifies line @var{number} of the current source file.
4158 When a @code{list} command has two linespecs, this refers to
4159 the same source file as the first linespec.
4162 Specifies the line @var{offset} lines after the last line printed.
4163 When used as the second linespec in a @code{list} command that has
4164 two, this specifies the line @var{offset} lines down from the
4168 Specifies the line @var{offset} lines before the last line printed.
4170 @item @var{filename}:@var{number}
4171 Specifies line @var{number} in the source file @var{filename}.
4173 @item @var{function}
4174 Specifies the line that begins the body of the function @var{function}.
4175 For example: in C, this is the line with the open brace.
4177 @item @var{filename}:@var{function}
4178 Specifies the line of the open-brace that begins the body of the
4179 function @var{function} in the file @var{filename}. You only need the
4180 file name with a function name to avoid ambiguity when there are
4181 identically named functions in different source files.
4183 @item *@var{address}
4184 Specifies the line containing the program address @var{address}.
4185 @var{address} may be any expression.
4189 @section Editing source files
4190 @cindex editing source files
4193 @kindex e @r{(@code{edit})}
4194 To edit the lines in a source file, use the @code{edit} command.
4195 The editing program of your choice
4196 is invoked with the current line set to
4197 the active line in the program.
4198 Alternatively, there are several ways to specify what part of the file you
4199 want to print if you want to see other parts of the program.
4201 Here are the forms of the @code{edit} command most commonly used:
4205 Edit the current source file at the active line number in the program.
4207 @item edit @var{number}
4208 Edit the current source file with @var{number} as the active line number.
4210 @item edit @var{function}
4211 Edit the file containing @var{function} at the beginning of its definition.
4213 @item edit @var{filename}:@var{number}
4214 Specifies line @var{number} in the source file @var{filename}.
4216 @item edit @var{filename}:@var{function}
4217 Specifies the line that begins the body of the
4218 function @var{function} in the file @var{filename}. You only need the
4219 file name with a function name to avoid ambiguity when there are
4220 identically named functions in different source files.
4222 @item edit *@var{address}
4223 Specifies the line containing the program address @var{address}.
4224 @var{address} may be any expression.
4227 @subsection Choosing your editor
4228 You can customize @value{GDBN} to use any editor you want
4230 The only restriction is that your editor (say @code{ex}), recognizes the
4231 following command-line syntax:
4233 ex +@var{number} file
4235 The optional numeric value +@var{number} designates the active line in
4236 the file.}. By default, it is @value{EDITOR}, but you can change this
4237 by setting the environment variable @code{EDITOR} before using
4238 @value{GDBN}. For example, to configure @value{GDBN} to use the
4239 @code{vi} editor, you could use these commands with the @code{sh} shell:
4245 or in the @code{csh} shell,
4247 setenv EDITOR /usr/bin/vi
4252 @section Searching source files
4254 @kindex reverse-search
4256 There are two commands for searching through the current source file for a
4261 @kindex forward-search
4262 @item forward-search @var{regexp}
4263 @itemx search @var{regexp}
4264 The command @samp{forward-search @var{regexp}} checks each line,
4265 starting with the one following the last line listed, for a match for
4266 @var{regexp}. It lists the line that is found. You can use the
4267 synonym @samp{search @var{regexp}} or abbreviate the command name as
4270 @item reverse-search @var{regexp}
4271 The command @samp{reverse-search @var{regexp}} checks each line, starting
4272 with the one before the last line listed and going backward, for a match
4273 for @var{regexp}. It lists the line that is found. You can abbreviate
4274 this command as @code{rev}.
4278 @section Specifying source directories
4281 @cindex directories for source files
4282 Executable programs sometimes do not record the directories of the source
4283 files from which they were compiled, just the names. Even when they do,
4284 the directories could be moved between the compilation and your debugging
4285 session. @value{GDBN} has a list of directories to search for source files;
4286 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4287 it tries all the directories in the list, in the order they are present
4288 in the list, until it finds a file with the desired name. Note that
4289 the executable search path is @emph{not} used for this purpose. Neither is
4290 the current working directory, unless it happens to be in the source
4293 If @value{GDBN} cannot find a source file in the source path, and the
4294 object program records a directory, @value{GDBN} tries that directory
4295 too. If the source path is empty, and there is no record of the
4296 compilation directory, @value{GDBN} looks in the current directory as a
4299 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4300 any information it has cached about where source files are found and where
4301 each line is in the file.
4305 When you start @value{GDBN}, its source path includes only @samp{cdir}
4306 and @samp{cwd}, in that order.
4307 To add other directories, use the @code{directory} command.
4310 @item directory @var{dirname} @dots{}
4311 @item dir @var{dirname} @dots{}
4312 Add directory @var{dirname} to the front of the source path. Several
4313 directory names may be given to this command, separated by @samp{:}
4314 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4315 part of absolute file names) or
4316 whitespace. You may specify a directory that is already in the source
4317 path; this moves it forward, so @value{GDBN} searches it sooner.
4321 @vindex $cdir@r{, convenience variable}
4322 @vindex $cwdr@r{, convenience variable}
4323 @cindex compilation directory
4324 @cindex current directory
4325 @cindex working directory
4326 @cindex directory, current
4327 @cindex directory, compilation
4328 You can use the string @samp{$cdir} to refer to the compilation
4329 directory (if one is recorded), and @samp{$cwd} to refer to the current
4330 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4331 tracks the current working directory as it changes during your @value{GDBN}
4332 session, while the latter is immediately expanded to the current
4333 directory at the time you add an entry to the source path.
4336 Reset the source path to empty again. This requires confirmation.
4338 @c RET-repeat for @code{directory} is explicitly disabled, but since
4339 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4341 @item show directories
4342 @kindex show directories
4343 Print the source path: show which directories it contains.
4346 If your source path is cluttered with directories that are no longer of
4347 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4348 versions of source. You can correct the situation as follows:
4352 Use @code{directory} with no argument to reset the source path to empty.
4355 Use @code{directory} with suitable arguments to reinstall the
4356 directories you want in the source path. You can add all the
4357 directories in one command.
4361 @section Source and machine code
4363 You can use the command @code{info line} to map source lines to program
4364 addresses (and vice versa), and the command @code{disassemble} to display
4365 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4366 mode, the @code{info line} command causes the arrow to point to the
4367 line specified. Also, @code{info line} prints addresses in symbolic form as
4372 @item info line @var{linespec}
4373 Print the starting and ending addresses of the compiled code for
4374 source line @var{linespec}. You can specify source lines in any of
4375 the ways understood by the @code{list} command (@pxref{List, ,Printing
4379 For example, we can use @code{info line} to discover the location of
4380 the object code for the first line of function
4381 @code{m4_changequote}:
4383 @c FIXME: I think this example should also show the addresses in
4384 @c symbolic form, as they usually would be displayed.
4386 (@value{GDBP}) info line m4_changequote
4387 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4391 We can also inquire (using @code{*@var{addr}} as the form for
4392 @var{linespec}) what source line covers a particular address:
4394 (@value{GDBP}) info line *0x63ff
4395 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4398 @cindex @code{$_} and @code{info line}
4399 @kindex x@r{(examine), and} info line
4400 After @code{info line}, the default address for the @code{x} command
4401 is changed to the starting address of the line, so that @samp{x/i} is
4402 sufficient to begin examining the machine code (@pxref{Memory,
4403 ,Examining memory}). Also, this address is saved as the value of the
4404 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4409 @cindex assembly instructions
4410 @cindex instructions, assembly
4411 @cindex machine instructions
4412 @cindex listing machine instructions
4414 This specialized command dumps a range of memory as machine
4415 instructions. The default memory range is the function surrounding the
4416 program counter of the selected frame. A single argument to this
4417 command is a program counter value; @value{GDBN} dumps the function
4418 surrounding this value. Two arguments specify a range of addresses
4419 (first inclusive, second exclusive) to dump.
4422 The following example shows the disassembly of a range of addresses of
4423 HP PA-RISC 2.0 code:
4426 (@value{GDBP}) disas 0x32c4 0x32e4
4427 Dump of assembler code from 0x32c4 to 0x32e4:
4428 0x32c4 <main+204>: addil 0,dp
4429 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4430 0x32cc <main+212>: ldil 0x3000,r31
4431 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4432 0x32d4 <main+220>: ldo 0(r31),rp
4433 0x32d8 <main+224>: addil -0x800,dp
4434 0x32dc <main+228>: ldo 0x588(r1),r26
4435 0x32e0 <main+232>: ldil 0x3000,r31
4436 End of assembler dump.
4439 Some architectures have more than one commonly-used set of instruction
4440 mnemonics or other syntax.
4443 @kindex set disassembly-flavor
4444 @cindex assembly instructions
4445 @cindex instructions, assembly
4446 @cindex machine instructions
4447 @cindex listing machine instructions
4448 @cindex Intel disassembly flavor
4449 @cindex AT&T disassembly flavor
4450 @item set disassembly-flavor @var{instruction-set}
4451 Select the instruction set to use when disassembling the
4452 program via the @code{disassemble} or @code{x/i} commands.
4454 Currently this command is only defined for the Intel x86 family. You
4455 can set @var{instruction-set} to either @code{intel} or @code{att}.
4456 The default is @code{att}, the AT&T flavor used by default by Unix
4457 assemblers for x86-based targets.
4462 @chapter Examining Data
4464 @cindex printing data
4465 @cindex examining data
4468 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4469 @c document because it is nonstandard... Under Epoch it displays in a
4470 @c different window or something like that.
4471 The usual way to examine data in your program is with the @code{print}
4472 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4473 evaluates and prints the value of an expression of the language your
4474 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4475 Different Languages}).
4478 @item print @var{expr}
4479 @itemx print /@var{f} @var{expr}
4480 @var{expr} is an expression (in the source language). By default the
4481 value of @var{expr} is printed in a format appropriate to its data type;
4482 you can choose a different format by specifying @samp{/@var{f}}, where
4483 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4487 @itemx print /@var{f}
4488 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4489 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4490 conveniently inspect the same value in an alternative format.
4493 A more low-level way of examining data is with the @code{x} command.
4494 It examines data in memory at a specified address and prints it in a
4495 specified format. @xref{Memory, ,Examining memory}.
4497 If you are interested in information about types, or about how the
4498 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4499 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4503 * Expressions:: Expressions
4504 * Variables:: Program variables
4505 * Arrays:: Artificial arrays
4506 * Output Formats:: Output formats
4507 * Memory:: Examining memory
4508 * Auto Display:: Automatic display
4509 * Print Settings:: Print settings
4510 * Value History:: Value history
4511 * Convenience Vars:: Convenience variables
4512 * Registers:: Registers
4513 * Floating Point Hardware:: Floating point hardware
4514 * Vector Unit:: Vector Unit
4515 * Memory Region Attributes:: Memory region attributes
4516 * Dump/Restore Files:: Copy between memory and a file
4517 * Character Sets:: Debugging programs that use a different
4518 character set than GDB does
4522 @section Expressions
4525 @code{print} and many other @value{GDBN} commands accept an expression and
4526 compute its value. Any kind of constant, variable or operator defined
4527 by the programming language you are using is valid in an expression in
4528 @value{GDBN}. This includes conditional expressions, function calls,
4529 casts, and string constants. It also includes preprocessor macros, if
4530 you compiled your program to include this information; see
4533 @value{GDBN} supports array constants in expressions input by
4534 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4535 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4536 memory that is @code{malloc}ed in the target program.
4538 Because C is so widespread, most of the expressions shown in examples in
4539 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4540 Languages}, for information on how to use expressions in other
4543 In this section, we discuss operators that you can use in @value{GDBN}
4544 expressions regardless of your programming language.
4546 Casts are supported in all languages, not just in C, because it is so
4547 useful to cast a number into a pointer in order to examine a structure
4548 at that address in memory.
4549 @c FIXME: casts supported---Mod2 true?
4551 @value{GDBN} supports these operators, in addition to those common
4552 to programming languages:
4556 @samp{@@} is a binary operator for treating parts of memory as arrays.
4557 @xref{Arrays, ,Artificial arrays}, for more information.
4560 @samp{::} allows you to specify a variable in terms of the file or
4561 function where it is defined. @xref{Variables, ,Program variables}.
4563 @cindex @{@var{type}@}
4564 @cindex type casting memory
4565 @cindex memory, viewing as typed object
4566 @cindex casts, to view memory
4567 @item @{@var{type}@} @var{addr}
4568 Refers to an object of type @var{type} stored at address @var{addr} in
4569 memory. @var{addr} may be any expression whose value is an integer or
4570 pointer (but parentheses are required around binary operators, just as in
4571 a cast). This construct is allowed regardless of what kind of data is
4572 normally supposed to reside at @var{addr}.
4576 @section Program variables
4578 The most common kind of expression to use is the name of a variable
4581 Variables in expressions are understood in the selected stack frame
4582 (@pxref{Selection, ,Selecting a frame}); they must be either:
4586 global (or file-static)
4593 visible according to the scope rules of the
4594 programming language from the point of execution in that frame
4597 @noindent This means that in the function
4612 you can examine and use the variable @code{a} whenever your program is
4613 executing within the function @code{foo}, but you can only use or
4614 examine the variable @code{b} while your program is executing inside
4615 the block where @code{b} is declared.
4617 @cindex variable name conflict
4618 There is an exception: you can refer to a variable or function whose
4619 scope is a single source file even if the current execution point is not
4620 in this file. But it is possible to have more than one such variable or
4621 function with the same name (in different source files). If that
4622 happens, referring to that name has unpredictable effects. If you wish,
4623 you can specify a static variable in a particular function or file,
4624 using the colon-colon notation:
4626 @cindex colon-colon, context for variables/functions
4628 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4629 @cindex @code{::}, context for variables/functions
4632 @var{file}::@var{variable}
4633 @var{function}::@var{variable}
4637 Here @var{file} or @var{function} is the name of the context for the
4638 static @var{variable}. In the case of file names, you can use quotes to
4639 make sure @value{GDBN} parses the file name as a single word---for example,
4640 to print a global value of @code{x} defined in @file{f2.c}:
4643 (@value{GDBP}) p 'f2.c'::x
4646 @cindex C@t{++} scope resolution
4647 This use of @samp{::} is very rarely in conflict with the very similar
4648 use of the same notation in C@t{++}. @value{GDBN} also supports use of the C@t{++}
4649 scope resolution operator in @value{GDBN} expressions.
4650 @c FIXME: Um, so what happens in one of those rare cases where it's in
4653 @cindex wrong values
4654 @cindex variable values, wrong
4656 @emph{Warning:} Occasionally, a local variable may appear to have the
4657 wrong value at certain points in a function---just after entry to a new
4658 scope, and just before exit.
4660 You may see this problem when you are stepping by machine instructions.
4661 This is because, on most machines, it takes more than one instruction to
4662 set up a stack frame (including local variable definitions); if you are
4663 stepping by machine instructions, variables may appear to have the wrong
4664 values until the stack frame is completely built. On exit, it usually
4665 also takes more than one machine instruction to destroy a stack frame;
4666 after you begin stepping through that group of instructions, local
4667 variable definitions may be gone.
4669 This may also happen when the compiler does significant optimizations.
4670 To be sure of always seeing accurate values, turn off all optimization
4673 @cindex ``No symbol "foo" in current context''
4674 Another possible effect of compiler optimizations is to optimize
4675 unused variables out of existence, or assign variables to registers (as
4676 opposed to memory addresses). Depending on the support for such cases
4677 offered by the debug info format used by the compiler, @value{GDBN}
4678 might not be able to display values for such local variables. If that
4679 happens, @value{GDBN} will print a message like this:
4682 No symbol "foo" in current context.
4685 To solve such problems, either recompile without optimizations, or use a
4686 different debug info format, if the compiler supports several such
4687 formats. For example, @value{NGCC}, the @sc{gnu} C/C@t{++} compiler usually
4688 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4689 in a format that is superior to formats such as COFF. You may be able
4690 to use DWARF2 (@samp{-gdwarf-2}), which is also an effective form for
4691 debug info. See @ref{Debugging Options,,Options for Debugging Your
4692 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4697 @section Artificial arrays
4699 @cindex artificial array
4700 @kindex @@@r{, referencing memory as an array}
4701 It is often useful to print out several successive objects of the
4702 same type in memory; a section of an array, or an array of
4703 dynamically determined size for which only a pointer exists in the
4706 You can do this by referring to a contiguous span of memory as an
4707 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4708 operand of @samp{@@} should be the first element of the desired array
4709 and be an individual object. The right operand should be the desired length
4710 of the array. The result is an array value whose elements are all of
4711 the type of the left argument. The first element is actually the left
4712 argument; the second element comes from bytes of memory immediately
4713 following those that hold the first element, and so on. Here is an
4714 example. If a program says
4717 int *array = (int *) malloc (len * sizeof (int));
4721 you can print the contents of @code{array} with
4727 The left operand of @samp{@@} must reside in memory. Array values made
4728 with @samp{@@} in this way behave just like other arrays in terms of
4729 subscripting, and are coerced to pointers when used in expressions.
4730 Artificial arrays most often appear in expressions via the value history
4731 (@pxref{Value History, ,Value history}), after printing one out.
4733 Another way to create an artificial array is to use a cast.
4734 This re-interprets a value as if it were an array.
4735 The value need not be in memory:
4737 (@value{GDBP}) p/x (short[2])0x12345678
4738 $1 = @{0x1234, 0x5678@}
4741 As a convenience, if you leave the array length out (as in
4742 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4743 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4745 (@value{GDBP}) p/x (short[])0x12345678
4746 $2 = @{0x1234, 0x5678@}
4749 Sometimes the artificial array mechanism is not quite enough; in
4750 moderately complex data structures, the elements of interest may not
4751 actually be adjacent---for example, if you are interested in the values
4752 of pointers in an array. One useful work-around in this situation is
4753 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4754 variables}) as a counter in an expression that prints the first
4755 interesting value, and then repeat that expression via @key{RET}. For
4756 instance, suppose you have an array @code{dtab} of pointers to
4757 structures, and you are interested in the values of a field @code{fv}
4758 in each structure. Here is an example of what you might type:
4768 @node Output Formats
4769 @section Output formats
4771 @cindex formatted output
4772 @cindex output formats
4773 By default, @value{GDBN} prints a value according to its data type. Sometimes
4774 this is not what you want. For example, you might want to print a number
4775 in hex, or a pointer in decimal. Or you might want to view data in memory
4776 at a certain address as a character string or as an instruction. To do
4777 these things, specify an @dfn{output format} when you print a value.
4779 The simplest use of output formats is to say how to print a value
4780 already computed. This is done by starting the arguments of the
4781 @code{print} command with a slash and a format letter. The format
4782 letters supported are:
4786 Regard the bits of the value as an integer, and print the integer in
4790 Print as integer in signed decimal.
4793 Print as integer in unsigned decimal.
4796 Print as integer in octal.
4799 Print as integer in binary. The letter @samp{t} stands for ``two''.
4800 @footnote{@samp{b} cannot be used because these format letters are also
4801 used with the @code{x} command, where @samp{b} stands for ``byte'';
4802 see @ref{Memory,,Examining memory}.}
4805 @cindex unknown address, locating
4806 @cindex locate address
4807 Print as an address, both absolute in hexadecimal and as an offset from
4808 the nearest preceding symbol. You can use this format used to discover
4809 where (in what function) an unknown address is located:
4812 (@value{GDBP}) p/a 0x54320
4813 $3 = 0x54320 <_initialize_vx+396>
4817 The command @code{info symbol 0x54320} yields similar results.
4818 @xref{Symbols, info symbol}.
4821 Regard as an integer and print it as a character constant.
4824 Regard the bits of the value as a floating point number and print
4825 using typical floating point syntax.
4828 For example, to print the program counter in hex (@pxref{Registers}), type
4835 Note that no space is required before the slash; this is because command
4836 names in @value{GDBN} cannot contain a slash.
4838 To reprint the last value in the value history with a different format,
4839 you can use the @code{print} command with just a format and no
4840 expression. For example, @samp{p/x} reprints the last value in hex.
4843 @section Examining memory
4845 You can use the command @code{x} (for ``examine'') to examine memory in
4846 any of several formats, independently of your program's data types.
4848 @cindex examining memory
4850 @kindex x @r{(examine memory)}
4851 @item x/@var{nfu} @var{addr}
4854 Use the @code{x} command to examine memory.
4857 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4858 much memory to display and how to format it; @var{addr} is an
4859 expression giving the address where you want to start displaying memory.
4860 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4861 Several commands set convenient defaults for @var{addr}.
4864 @item @var{n}, the repeat count
4865 The repeat count is a decimal integer; the default is 1. It specifies
4866 how much memory (counting by units @var{u}) to display.
4867 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4870 @item @var{f}, the display format
4871 The display format is one of the formats used by @code{print},
4872 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4873 The default is @samp{x} (hexadecimal) initially.
4874 The default changes each time you use either @code{x} or @code{print}.
4876 @item @var{u}, the unit size
4877 The unit size is any of
4883 Halfwords (two bytes).
4885 Words (four bytes). This is the initial default.
4887 Giant words (eight bytes).
4890 Each time you specify a unit size with @code{x}, that size becomes the
4891 default unit the next time you use @code{x}. (For the @samp{s} and
4892 @samp{i} formats, the unit size is ignored and is normally not written.)
4894 @item @var{addr}, starting display address
4895 @var{addr} is the address where you want @value{GDBN} to begin displaying
4896 memory. The expression need not have a pointer value (though it may);
4897 it is always interpreted as an integer address of a byte of memory.
4898 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4899 @var{addr} is usually just after the last address examined---but several
4900 other commands also set the default address: @code{info breakpoints} (to
4901 the address of the last breakpoint listed), @code{info line} (to the
4902 starting address of a line), and @code{print} (if you use it to display
4903 a value from memory).
4906 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4907 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4908 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4909 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4910 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4912 Since the letters indicating unit sizes are all distinct from the
4913 letters specifying output formats, you do not have to remember whether
4914 unit size or format comes first; either order works. The output
4915 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4916 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4918 Even though the unit size @var{u} is ignored for the formats @samp{s}
4919 and @samp{i}, you might still want to use a count @var{n}; for example,
4920 @samp{3i} specifies that you want to see three machine instructions,
4921 including any operands. The command @code{disassemble} gives an
4922 alternative way of inspecting machine instructions; see @ref{Machine
4923 Code,,Source and machine code}.
4925 All the defaults for the arguments to @code{x} are designed to make it
4926 easy to continue scanning memory with minimal specifications each time
4927 you use @code{x}. For example, after you have inspected three machine
4928 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4929 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4930 the repeat count @var{n} is used again; the other arguments default as
4931 for successive uses of @code{x}.
4933 @cindex @code{$_}, @code{$__}, and value history
4934 The addresses and contents printed by the @code{x} command are not saved
4935 in the value history because there is often too much of them and they
4936 would get in the way. Instead, @value{GDBN} makes these values available for
4937 subsequent use in expressions as values of the convenience variables
4938 @code{$_} and @code{$__}. After an @code{x} command, the last address
4939 examined is available for use in expressions in the convenience variable
4940 @code{$_}. The contents of that address, as examined, are available in
4941 the convenience variable @code{$__}.
4943 If the @code{x} command has a repeat count, the address and contents saved
4944 are from the last memory unit printed; this is not the same as the last
4945 address printed if several units were printed on the last line of output.
4948 @section Automatic display
4949 @cindex automatic display
4950 @cindex display of expressions
4952 If you find that you want to print the value of an expression frequently
4953 (to see how it changes), you might want to add it to the @dfn{automatic
4954 display list} so that @value{GDBN} prints its value each time your program stops.
4955 Each expression added to the list is given a number to identify it;
4956 to remove an expression from the list, you specify that number.
4957 The automatic display looks like this:
4961 3: bar[5] = (struct hack *) 0x3804
4965 This display shows item numbers, expressions and their current values. As with
4966 displays you request manually using @code{x} or @code{print}, you can
4967 specify the output format you prefer; in fact, @code{display} decides
4968 whether to use @code{print} or @code{x} depending on how elaborate your
4969 format specification is---it uses @code{x} if you specify a unit size,
4970 or one of the two formats (@samp{i} and @samp{s}) that are only
4971 supported by @code{x}; otherwise it uses @code{print}.
4975 @item display @var{expr}
4976 Add the expression @var{expr} to the list of expressions to display
4977 each time your program stops. @xref{Expressions, ,Expressions}.
4979 @code{display} does not repeat if you press @key{RET} again after using it.
4981 @item display/@var{fmt} @var{expr}
4982 For @var{fmt} specifying only a display format and not a size or
4983 count, add the expression @var{expr} to the auto-display list but
4984 arrange to display it each time in the specified format @var{fmt}.
4985 @xref{Output Formats,,Output formats}.
4987 @item display/@var{fmt} @var{addr}
4988 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4989 number of units, add the expression @var{addr} as a memory address to
4990 be examined each time your program stops. Examining means in effect
4991 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4994 For example, @samp{display/i $pc} can be helpful, to see the machine
4995 instruction about to be executed each time execution stops (@samp{$pc}
4996 is a common name for the program counter; @pxref{Registers, ,Registers}).
4999 @kindex delete display
5001 @item undisplay @var{dnums}@dots{}
5002 @itemx delete display @var{dnums}@dots{}
5003 Remove item numbers @var{dnums} from the list of expressions to display.
5005 @code{undisplay} does not repeat if you press @key{RET} after using it.
5006 (Otherwise you would just get the error @samp{No display number @dots{}}.)
5008 @kindex disable display
5009 @item disable display @var{dnums}@dots{}
5010 Disable the display of item numbers @var{dnums}. A disabled display
5011 item is not printed automatically, but is not forgotten. It may be
5012 enabled again later.
5014 @kindex enable display
5015 @item enable display @var{dnums}@dots{}
5016 Enable display of item numbers @var{dnums}. It becomes effective once
5017 again in auto display of its expression, until you specify otherwise.
5020 Display the current values of the expressions on the list, just as is
5021 done when your program stops.
5023 @kindex info display
5025 Print the list of expressions previously set up to display
5026 automatically, each one with its item number, but without showing the
5027 values. This includes disabled expressions, which are marked as such.
5028 It also includes expressions which would not be displayed right now
5029 because they refer to automatic variables not currently available.
5032 If a display expression refers to local variables, then it does not make
5033 sense outside the lexical context for which it was set up. Such an
5034 expression is disabled when execution enters a context where one of its
5035 variables is not defined. For example, if you give the command
5036 @code{display last_char} while inside a function with an argument
5037 @code{last_char}, @value{GDBN} displays this argument while your program
5038 continues to stop inside that function. When it stops elsewhere---where
5039 there is no variable @code{last_char}---the display is disabled
5040 automatically. The next time your program stops where @code{last_char}
5041 is meaningful, you can enable the display expression once again.
5043 @node Print Settings
5044 @section Print settings
5046 @cindex format options
5047 @cindex print settings
5048 @value{GDBN} provides the following ways to control how arrays, structures,
5049 and symbols are printed.
5052 These settings are useful for debugging programs in any language:
5055 @kindex set print address
5056 @item set print address
5057 @itemx set print address on
5058 @value{GDBN} prints memory addresses showing the location of stack
5059 traces, structure values, pointer values, breakpoints, and so forth,
5060 even when it also displays the contents of those addresses. The default
5061 is @code{on}. For example, this is what a stack frame display looks like with
5062 @code{set print address on}:
5067 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
5069 530 if (lquote != def_lquote)
5073 @item set print address off
5074 Do not print addresses when displaying their contents. For example,
5075 this is the same stack frame displayed with @code{set print address off}:
5079 (@value{GDBP}) set print addr off
5081 #0 set_quotes (lq="<<", rq=">>") at input.c:530
5082 530 if (lquote != def_lquote)
5086 You can use @samp{set print address off} to eliminate all machine
5087 dependent displays from the @value{GDBN} interface. For example, with
5088 @code{print address off}, you should get the same text for backtraces on
5089 all machines---whether or not they involve pointer arguments.
5091 @kindex show print address
5092 @item show print address
5093 Show whether or not addresses are to be printed.
5096 When @value{GDBN} prints a symbolic address, it normally prints the
5097 closest earlier symbol plus an offset. If that symbol does not uniquely
5098 identify the address (for example, it is a name whose scope is a single
5099 source file), you may need to clarify. One way to do this is with
5100 @code{info line}, for example @samp{info line *0x4537}. Alternately,
5101 you can set @value{GDBN} to print the source file and line number when
5102 it prints a symbolic address:
5105 @kindex set print symbol-filename
5106 @item set print symbol-filename on
5107 Tell @value{GDBN} to print the source file name and line number of a
5108 symbol in the symbolic form of an address.
5110 @item set print symbol-filename off
5111 Do not print source file name and line number of a symbol. This is the
5114 @kindex show print symbol-filename
5115 @item show print symbol-filename
5116 Show whether or not @value{GDBN} will print the source file name and
5117 line number of a symbol in the symbolic form of an address.
5120 Another situation where it is helpful to show symbol filenames and line
5121 numbers is when disassembling code; @value{GDBN} shows you the line
5122 number and source file that corresponds to each instruction.
5124 Also, you may wish to see the symbolic form only if the address being
5125 printed is reasonably close to the closest earlier symbol:
5128 @kindex set print max-symbolic-offset
5129 @item set print max-symbolic-offset @var{max-offset}
5130 Tell @value{GDBN} to only display the symbolic form of an address if the
5131 offset between the closest earlier symbol and the address is less than
5132 @var{max-offset}. The default is 0, which tells @value{GDBN}
5133 to always print the symbolic form of an address if any symbol precedes it.
5135 @kindex show print max-symbolic-offset
5136 @item show print max-symbolic-offset
5137 Ask how large the maximum offset is that @value{GDBN} prints in a
5141 @cindex wild pointer, interpreting
5142 @cindex pointer, finding referent
5143 If you have a pointer and you are not sure where it points, try
5144 @samp{set print symbol-filename on}. Then you can determine the name
5145 and source file location of the variable where it points, using
5146 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5147 For example, here @value{GDBN} shows that a variable @code{ptt} points
5148 at another variable @code{t}, defined in @file{hi2.c}:
5151 (@value{GDBP}) set print symbol-filename on
5152 (@value{GDBP}) p/a ptt
5153 $4 = 0xe008 <t in hi2.c>
5157 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5158 does not show the symbol name and filename of the referent, even with
5159 the appropriate @code{set print} options turned on.
5162 Other settings control how different kinds of objects are printed:
5165 @kindex set print array
5166 @item set print array
5167 @itemx set print array on
5168 Pretty print arrays. This format is more convenient to read,
5169 but uses more space. The default is off.
5171 @item set print array off
5172 Return to compressed format for arrays.
5174 @kindex show print array
5175 @item show print array
5176 Show whether compressed or pretty format is selected for displaying
5179 @kindex set print elements
5180 @item set print elements @var{number-of-elements}
5181 Set a limit on how many elements of an array @value{GDBN} will print.
5182 If @value{GDBN} is printing a large array, it stops printing after it has
5183 printed the number of elements set by the @code{set print elements} command.
5184 This limit also applies to the display of strings.
5185 When @value{GDBN} starts, this limit is set to 200.
5186 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5188 @kindex show print elements
5189 @item show print elements
5190 Display the number of elements of a large array that @value{GDBN} will print.
5191 If the number is 0, then the printing is unlimited.
5193 @kindex set print null-stop
5194 @item set print null-stop
5195 Cause @value{GDBN} to stop printing the characters of an array when the first
5196 @sc{null} is encountered. This is useful when large arrays actually
5197 contain only short strings.
5200 @kindex set print pretty
5201 @item set print pretty on
5202 Cause @value{GDBN} to print structures in an indented format with one member
5203 per line, like this:
5218 @item set print pretty off
5219 Cause @value{GDBN} to print structures in a compact format, like this:
5223 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5224 meat = 0x54 "Pork"@}
5229 This is the default format.
5231 @kindex show print pretty
5232 @item show print pretty
5233 Show which format @value{GDBN} is using to print structures.
5235 @kindex set print sevenbit-strings
5236 @item set print sevenbit-strings on
5237 Print using only seven-bit characters; if this option is set,
5238 @value{GDBN} displays any eight-bit characters (in strings or
5239 character values) using the notation @code{\}@var{nnn}. This setting is
5240 best if you are working in English (@sc{ascii}) and you use the
5241 high-order bit of characters as a marker or ``meta'' bit.
5243 @item set print sevenbit-strings off
5244 Print full eight-bit characters. This allows the use of more
5245 international character sets, and is the default.
5247 @kindex show print sevenbit-strings
5248 @item show print sevenbit-strings
5249 Show whether or not @value{GDBN} is printing only seven-bit characters.
5251 @kindex set print union
5252 @item set print union on
5253 Tell @value{GDBN} to print unions which are contained in structures. This
5254 is the default setting.
5256 @item set print union off
5257 Tell @value{GDBN} not to print unions which are contained in structures.
5259 @kindex show print union
5260 @item show print union
5261 Ask @value{GDBN} whether or not it will print unions which are contained in
5264 For example, given the declarations
5267 typedef enum @{Tree, Bug@} Species;
5268 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5269 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5280 struct thing foo = @{Tree, @{Acorn@}@};
5284 with @code{set print union on} in effect @samp{p foo} would print
5287 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5291 and with @code{set print union off} in effect it would print
5294 $1 = @{it = Tree, form = @{...@}@}
5300 These settings are of interest when debugging C@t{++} programs:
5304 @kindex set print demangle
5305 @item set print demangle
5306 @itemx set print demangle on
5307 Print C@t{++} names in their source form rather than in the encoded
5308 (``mangled'') form passed to the assembler and linker for type-safe
5309 linkage. The default is on.
5311 @kindex show print demangle
5312 @item show print demangle
5313 Show whether C@t{++} names are printed in mangled or demangled form.
5315 @kindex set print asm-demangle
5316 @item set print asm-demangle
5317 @itemx set print asm-demangle on
5318 Print C@t{++} names in their source form rather than their mangled form, even
5319 in assembler code printouts such as instruction disassemblies.
5322 @kindex show print asm-demangle
5323 @item show print asm-demangle
5324 Show whether C@t{++} names in assembly listings are printed in mangled
5327 @kindex set demangle-style
5328 @cindex C@t{++} symbol decoding style
5329 @cindex symbol decoding style, C@t{++}
5330 @item set demangle-style @var{style}
5331 Choose among several encoding schemes used by different compilers to
5332 represent C@t{++} names. The choices for @var{style} are currently:
5336 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5339 Decode based on the @sc{gnu} C@t{++} compiler (@code{g++}) encoding algorithm.
5340 This is the default.
5343 Decode based on the HP ANSI C@t{++} (@code{aCC}) encoding algorithm.
5346 Decode based on the Lucid C@t{++} compiler (@code{lcc}) encoding algorithm.
5349 Decode using the algorithm in the @cite{C@t{++} Annotated Reference Manual}.
5350 @strong{Warning:} this setting alone is not sufficient to allow
5351 debugging @code{cfront}-generated executables. @value{GDBN} would
5352 require further enhancement to permit that.
5355 If you omit @var{style}, you will see a list of possible formats.
5357 @kindex show demangle-style
5358 @item show demangle-style
5359 Display the encoding style currently in use for decoding C@t{++} symbols.
5361 @kindex set print object
5362 @item set print object
5363 @itemx set print object on
5364 When displaying a pointer to an object, identify the @emph{actual}
5365 (derived) type of the object rather than the @emph{declared} type, using
5366 the virtual function table.
5368 @item set print object off
5369 Display only the declared type of objects, without reference to the
5370 virtual function table. This is the default setting.
5372 @kindex show print object
5373 @item show print object
5374 Show whether actual, or declared, object types are displayed.
5376 @kindex set print static-members
5377 @item set print static-members
5378 @itemx set print static-members on
5379 Print static members when displaying a C@t{++} object. The default is on.
5381 @item set print static-members off
5382 Do not print static members when displaying a C@t{++} object.
5384 @kindex show print static-members
5385 @item show print static-members
5386 Show whether C@t{++} static members are printed, or not.
5388 @c These don't work with HP ANSI C++ yet.
5389 @kindex set print vtbl
5390 @item set print vtbl
5391 @itemx set print vtbl on
5392 Pretty print C@t{++} virtual function tables. The default is off.
5393 (The @code{vtbl} commands do not work on programs compiled with the HP
5394 ANSI C@t{++} compiler (@code{aCC}).)
5396 @item set print vtbl off
5397 Do not pretty print C@t{++} virtual function tables.
5399 @kindex show print vtbl
5400 @item show print vtbl
5401 Show whether C@t{++} virtual function tables are pretty printed, or not.
5405 @section Value history
5407 @cindex value history
5408 Values printed by the @code{print} command are saved in the @value{GDBN}
5409 @dfn{value history}. This allows you to refer to them in other expressions.
5410 Values are kept until the symbol table is re-read or discarded
5411 (for example with the @code{file} or @code{symbol-file} commands).
5412 When the symbol table changes, the value history is discarded,
5413 since the values may contain pointers back to the types defined in the
5418 @cindex history number
5419 The values printed are given @dfn{history numbers} by which you can
5420 refer to them. These are successive integers starting with one.
5421 @code{print} shows you the history number assigned to a value by
5422 printing @samp{$@var{num} = } before the value; here @var{num} is the
5425 To refer to any previous value, use @samp{$} followed by the value's
5426 history number. The way @code{print} labels its output is designed to
5427 remind you of this. Just @code{$} refers to the most recent value in
5428 the history, and @code{$$} refers to the value before that.
5429 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5430 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5431 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5433 For example, suppose you have just printed a pointer to a structure and
5434 want to see the contents of the structure. It suffices to type
5440 If you have a chain of structures where the component @code{next} points
5441 to the next one, you can print the contents of the next one with this:
5448 You can print successive links in the chain by repeating this
5449 command---which you can do by just typing @key{RET}.
5451 Note that the history records values, not expressions. If the value of
5452 @code{x} is 4 and you type these commands:
5460 then the value recorded in the value history by the @code{print} command
5461 remains 4 even though the value of @code{x} has changed.
5466 Print the last ten values in the value history, with their item numbers.
5467 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5468 values} does not change the history.
5470 @item show values @var{n}
5471 Print ten history values centered on history item number @var{n}.
5474 Print ten history values just after the values last printed. If no more
5475 values are available, @code{show values +} produces no display.
5478 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5479 same effect as @samp{show values +}.
5481 @node Convenience Vars
5482 @section Convenience variables
5484 @cindex convenience variables
5485 @value{GDBN} provides @dfn{convenience variables} that you can use within
5486 @value{GDBN} to hold on to a value and refer to it later. These variables
5487 exist entirely within @value{GDBN}; they are not part of your program, and
5488 setting a convenience variable has no direct effect on further execution
5489 of your program. That is why you can use them freely.
5491 Convenience variables are prefixed with @samp{$}. Any name preceded by
5492 @samp{$} can be used for a convenience variable, unless it is one of
5493 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5494 (Value history references, in contrast, are @emph{numbers} preceded
5495 by @samp{$}. @xref{Value History, ,Value history}.)
5497 You can save a value in a convenience variable with an assignment
5498 expression, just as you would set a variable in your program.
5502 set $foo = *object_ptr
5506 would save in @code{$foo} the value contained in the object pointed to by
5509 Using a convenience variable for the first time creates it, but its
5510 value is @code{void} until you assign a new value. You can alter the
5511 value with another assignment at any time.
5513 Convenience variables have no fixed types. You can assign a convenience
5514 variable any type of value, including structures and arrays, even if
5515 that variable already has a value of a different type. The convenience
5516 variable, when used as an expression, has the type of its current value.
5519 @kindex show convenience
5520 @item show convenience
5521 Print a list of convenience variables used so far, and their values.
5522 Abbreviated @code{show conv}.
5525 One of the ways to use a convenience variable is as a counter to be
5526 incremented or a pointer to be advanced. For example, to print
5527 a field from successive elements of an array of structures:
5531 print bar[$i++]->contents
5535 Repeat that command by typing @key{RET}.
5537 Some convenience variables are created automatically by @value{GDBN} and given
5538 values likely to be useful.
5541 @vindex $_@r{, convenience variable}
5543 The variable @code{$_} is automatically set by the @code{x} command to
5544 the last address examined (@pxref{Memory, ,Examining memory}). Other
5545 commands which provide a default address for @code{x} to examine also
5546 set @code{$_} to that address; these commands include @code{info line}
5547 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5548 except when set by the @code{x} command, in which case it is a pointer
5549 to the type of @code{$__}.
5551 @vindex $__@r{, convenience variable}
5553 The variable @code{$__} is automatically set by the @code{x} command
5554 to the value found in the last address examined. Its type is chosen
5555 to match the format in which the data was printed.
5558 @vindex $_exitcode@r{, convenience variable}
5559 The variable @code{$_exitcode} is automatically set to the exit code when
5560 the program being debugged terminates.
5563 On HP-UX systems, if you refer to a function or variable name that
5564 begins with a dollar sign, @value{GDBN} searches for a user or system
5565 name first, before it searches for a convenience variable.
5571 You can refer to machine register contents, in expressions, as variables
5572 with names starting with @samp{$}. The names of registers are different
5573 for each machine; use @code{info registers} to see the names used on
5577 @kindex info registers
5578 @item info registers
5579 Print the names and values of all registers except floating-point
5580 and vector registers (in the selected stack frame).
5582 @kindex info all-registers
5583 @cindex floating point registers
5584 @item info all-registers
5585 Print the names and values of all registers, including floating-point
5586 and vector registers (in the selected stack frame).
5588 @item info registers @var{regname} @dots{}
5589 Print the @dfn{relativized} value of each specified register @var{regname}.
5590 As discussed in detail below, register values are normally relative to
5591 the selected stack frame. @var{regname} may be any register name valid on
5592 the machine you are using, with or without the initial @samp{$}.
5595 @value{GDBN} has four ``standard'' register names that are available (in
5596 expressions) on most machines---whenever they do not conflict with an
5597 architecture's canonical mnemonics for registers. The register names
5598 @code{$pc} and @code{$sp} are used for the program counter register and
5599 the stack pointer. @code{$fp} is used for a register that contains a
5600 pointer to the current stack frame, and @code{$ps} is used for a
5601 register that contains the processor status. For example,
5602 you could print the program counter in hex with
5609 or print the instruction to be executed next with
5616 or add four to the stack pointer@footnote{This is a way of removing
5617 one word from the stack, on machines where stacks grow downward in
5618 memory (most machines, nowadays). This assumes that the innermost
5619 stack frame is selected; setting @code{$sp} is not allowed when other
5620 stack frames are selected. To pop entire frames off the stack,
5621 regardless of machine architecture, use @code{return};
5622 see @ref{Returning, ,Returning from a function}.} with
5628 Whenever possible, these four standard register names are available on
5629 your machine even though the machine has different canonical mnemonics,
5630 so long as there is no conflict. The @code{info registers} command
5631 shows the canonical names. For example, on the SPARC, @code{info
5632 registers} displays the processor status register as @code{$psr} but you
5633 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5634 is an alias for the @sc{eflags} register.
5636 @value{GDBN} always considers the contents of an ordinary register as an
5637 integer when the register is examined in this way. Some machines have
5638 special registers which can hold nothing but floating point; these
5639 registers are considered to have floating point values. There is no way
5640 to refer to the contents of an ordinary register as floating point value
5641 (although you can @emph{print} it as a floating point value with
5642 @samp{print/f $@var{regname}}).
5644 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5645 means that the data format in which the register contents are saved by
5646 the operating system is not the same one that your program normally
5647 sees. For example, the registers of the 68881 floating point
5648 coprocessor are always saved in ``extended'' (raw) format, but all C
5649 programs expect to work with ``double'' (virtual) format. In such
5650 cases, @value{GDBN} normally works with the virtual format only (the format
5651 that makes sense for your program), but the @code{info registers} command
5652 prints the data in both formats.
5654 Normally, register values are relative to the selected stack frame
5655 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5656 value that the register would contain if all stack frames farther in
5657 were exited and their saved registers restored. In order to see the
5658 true contents of hardware registers, you must select the innermost
5659 frame (with @samp{frame 0}).
5661 However, @value{GDBN} must deduce where registers are saved, from the machine
5662 code generated by your compiler. If some registers are not saved, or if
5663 @value{GDBN} is unable to locate the saved registers, the selected stack
5664 frame makes no difference.
5666 @node Floating Point Hardware
5667 @section Floating point hardware
5668 @cindex floating point
5670 Depending on the configuration, @value{GDBN} may be able to give
5671 you more information about the status of the floating point hardware.
5676 Display hardware-dependent information about the floating
5677 point unit. The exact contents and layout vary depending on the
5678 floating point chip. Currently, @samp{info float} is supported on
5679 the ARM and x86 machines.
5683 @section Vector Unit
5686 Depending on the configuration, @value{GDBN} may be able to give you
5687 more information about the status of the vector unit.
5692 Display information about the vector unit. The exact contents and
5693 layout vary depending on the hardware.
5696 @node Memory Region Attributes
5697 @section Memory region attributes
5698 @cindex memory region attributes
5700 @dfn{Memory region attributes} allow you to describe special handling
5701 required by regions of your target's memory. @value{GDBN} uses attributes
5702 to determine whether to allow certain types of memory accesses; whether to
5703 use specific width accesses; and whether to cache target memory.
5705 Defined memory regions can be individually enabled and disabled. When a
5706 memory region is disabled, @value{GDBN} uses the default attributes when
5707 accessing memory in that region. Similarly, if no memory regions have
5708 been defined, @value{GDBN} uses the default attributes when accessing
5711 When a memory region is defined, it is given a number to identify it;
5712 to enable, disable, or remove a memory region, you specify that number.
5716 @item mem @var{lower} @var{upper} @var{attributes}@dots{}
5717 Define memory region bounded by @var{lower} and @var{upper} with
5718 attributes @var{attributes}@dots{}. Note that @var{upper} == 0 is a
5719 special case: it is treated as the the target's maximum memory address.
5720 (0xffff on 16 bit targets, 0xffffffff on 32 bit targets, etc.)
5723 @item delete mem @var{nums}@dots{}
5724 Remove memory regions @var{nums}@dots{}.
5727 @item disable mem @var{nums}@dots{}
5728 Disable memory regions @var{nums}@dots{}.
5729 A disabled memory region is not forgotten.
5730 It may be enabled again later.
5733 @item enable mem @var{nums}@dots{}
5734 Enable memory regions @var{nums}@dots{}.
5738 Print a table of all defined memory regions, with the following columns
5742 @item Memory Region Number
5743 @item Enabled or Disabled.
5744 Enabled memory regions are marked with @samp{y}.
5745 Disabled memory regions are marked with @samp{n}.
5748 The address defining the inclusive lower bound of the memory region.
5751 The address defining the exclusive upper bound of the memory region.
5754 The list of attributes set for this memory region.
5759 @subsection Attributes
5761 @subsubsection Memory Access Mode
5762 The access mode attributes set whether @value{GDBN} may make read or
5763 write accesses to a memory region.
5765 While these attributes prevent @value{GDBN} from performing invalid
5766 memory accesses, they do nothing to prevent the target system, I/O DMA,
5767 etc. from accessing memory.
5771 Memory is read only.
5773 Memory is write only.
5775 Memory is read/write. This is the default.
5778 @subsubsection Memory Access Size
5779 The acccess size attributes tells @value{GDBN} to use specific sized
5780 accesses in the memory region. Often memory mapped device registers
5781 require specific sized accesses. If no access size attribute is
5782 specified, @value{GDBN} may use accesses of any size.
5786 Use 8 bit memory accesses.
5788 Use 16 bit memory accesses.
5790 Use 32 bit memory accesses.
5792 Use 64 bit memory accesses.
5795 @c @subsubsection Hardware/Software Breakpoints
5796 @c The hardware/software breakpoint attributes set whether @value{GDBN}
5797 @c will use hardware or software breakpoints for the internal breakpoints
5798 @c used by the step, next, finish, until, etc. commands.
5802 @c Always use hardware breakpoints
5803 @c @item swbreak (default)
5806 @subsubsection Data Cache
5807 The data cache attributes set whether @value{GDBN} will cache target
5808 memory. While this generally improves performance by reducing debug
5809 protocol overhead, it can lead to incorrect results because @value{GDBN}
5810 does not know about volatile variables or memory mapped device
5815 Enable @value{GDBN} to cache target memory.
5817 Disable @value{GDBN} from caching target memory. This is the default.
5820 @c @subsubsection Memory Write Verification
5821 @c The memory write verification attributes set whether @value{GDBN}
5822 @c will re-reads data after each write to verify the write was successful.
5826 @c @item noverify (default)
5829 @node Dump/Restore Files
5830 @section Copy between memory and a file
5831 @cindex dump/restore files
5832 @cindex append data to a file
5833 @cindex dump data to a file
5834 @cindex restore data from a file
5839 The commands @code{dump}, @code{append}, and @code{restore} are used
5840 for copying data between target memory and a file. Data is written
5841 into a file using @code{dump} or @code{append}, and restored from a
5842 file into memory by using @code{restore}. Files may be binary, srec,
5843 intel hex, or tekhex (but only binary files can be appended).
5847 @kindex append binary
5848 @item dump binary memory @var{filename} @var{start_addr} @var{end_addr}
5849 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5850 raw binary format file @var{filename}.
5852 @item append binary memory @var{filename} @var{start_addr} @var{end_addr}
5853 Append contents of memory from @var{start_addr} to @var{end_addr} to
5854 raw binary format file @var{filename}.
5856 @item dump binary value @var{filename} @var{expression}
5857 Dump value of @var{expression} into raw binary format file @var{filename}.
5859 @item append binary memory @var{filename} @var{expression}
5860 Append value of @var{expression} to raw binary format file @var{filename}.
5863 @item dump ihex memory @var{filename} @var{start_addr} @var{end_addr}
5864 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5865 intel hex format file @var{filename}.
5867 @item dump ihex value @var{filename} @var{expression}
5868 Dump value of @var{expression} into intel hex format file @var{filename}.
5871 @item dump srec memory @var{filename} @var{start_addr} @var{end_addr}
5872 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5873 srec format file @var{filename}.
5875 @item dump srec value @var{filename} @var{expression}
5876 Dump value of @var{expression} into srec format file @var{filename}.
5879 @item dump tekhex memory @var{filename} @var{start_addr} @var{end_addr}
5880 Dump contents of memory from @var{start_addr} to @var{end_addr} into
5881 tekhex format file @var{filename}.
5883 @item dump tekhex value @var{filename} @var{expression}
5884 Dump value of @var{expression} into tekhex format file @var{filename}.
5886 @item restore @var{filename} [@var{binary}] @var{bias} @var{start} @var{end}
5887 Restore the contents of file @var{filename} into memory. The @code{restore}
5888 command can automatically recognize any known bfd file format, except for
5889 raw binary. To restore a raw binary file you must use the optional argument
5890 @var{binary} after the filename.
5892 If @var{bias} is non-zero, its value will be added to the addresses
5893 contained in the file. Binary files always start at address zero, so
5894 they will be restored at address @var{bias}. Other bfd files have
5895 a built-in location; they will be restored at offset @var{bias}
5898 If @var{start} and/or @var{end} are non-zero, then only data between
5899 file offset @var{start} and file offset @var{end} will be restored.
5900 These offsets are relative to the addresses in the file, before
5901 the @var{bias} argument is applied.
5905 @node Character Sets
5906 @section Character Sets
5907 @cindex character sets
5909 @cindex translating between character sets
5910 @cindex host character set
5911 @cindex target character set
5913 If the program you are debugging uses a different character set to
5914 represent characters and strings than the one @value{GDBN} uses itself,
5915 @value{GDBN} can automatically translate between the character sets for
5916 you. The character set @value{GDBN} uses we call the @dfn{host
5917 character set}; the one the inferior program uses we call the
5918 @dfn{target character set}.
5920 For example, if you are running @value{GDBN} on a @sc{gnu}/Linux system, which
5921 uses the ISO Latin 1 character set, but you are using @value{GDBN}'s
5922 remote protocol (@pxref{Remote,Remote Debugging}) to debug a program
5923 running on an IBM mainframe, which uses the @sc{ebcdic} character set,
5924 then the host character set is Latin-1, and the target character set is
5925 @sc{ebcdic}. If you give @value{GDBN} the command @code{set
5926 target-charset ebcdic-us}, then @value{GDBN} translates between
5927 @sc{ebcdic} and Latin 1 as you print character or string values, or use
5928 character and string literals in expressions.
5930 @value{GDBN} has no way to automatically recognize which character set
5931 the inferior program uses; you must tell it, using the @code{set
5932 target-charset} command, described below.
5934 Here are the commands for controlling @value{GDBN}'s character set
5938 @item set target-charset @var{charset}
5939 @kindex set target-charset
5940 Set the current target character set to @var{charset}. We list the
5941 character set names @value{GDBN} recognizes below, but if you invoke the
5942 @code{set target-charset} command with no argument, @value{GDBN} lists
5943 the character sets it supports.
5947 @item set host-charset @var{charset}
5948 @kindex set host-charset
5949 Set the current host character set to @var{charset}.
5951 By default, @value{GDBN} uses a host character set appropriate to the
5952 system it is running on; you can override that default using the
5953 @code{set host-charset} command.
5955 @value{GDBN} can only use certain character sets as its host character
5956 set. We list the character set names @value{GDBN} recognizes below, and
5957 indicate which can be host character sets, but if you invoke the
5958 @code{set host-charset} command with no argument, @value{GDBN} lists the
5959 character sets it supports, placing an asterisk (@samp{*}) after those
5960 it can use as a host character set.
5962 @item set charset @var{charset}
5964 Set the current host and target character sets to @var{charset}. If you
5965 invoke the @code{set charset} command with no argument, it lists the
5966 character sets it supports. @value{GDBN} can only use certain character
5967 sets as its host character set; it marks those in the list with an
5968 asterisk (@samp{*}).
5971 @itemx show host-charset
5972 @itemx show target-charset
5973 @kindex show charset
5974 @kindex show host-charset
5975 @kindex show target-charset
5976 Show the current host and target charsets. The @code{show host-charset}
5977 and @code{show target-charset} commands are synonyms for @code{show
5982 @value{GDBN} currently includes support for the following character
5988 @cindex ASCII character set
5989 Seven-bit U.S. @sc{ascii}. @value{GDBN} can use this as its host
5993 @cindex ISO 8859-1 character set
5994 @cindex ISO Latin 1 character set
5995 The ISO Latin 1 character set. This extends ASCII with accented
5996 characters needed for French, German, and Spanish. @value{GDBN} can use
5997 this as its host character set.
6001 @cindex EBCDIC character set
6002 @cindex IBM1047 character set
6003 Variants of the @sc{ebcdic} character set, used on some of IBM's
6004 mainframe operating systems. (@sc{gnu}/Linux on the S/390 uses U.S. @sc{ascii}.)
6005 @value{GDBN} cannot use these as its host character set.
6009 Note that these are all single-byte character sets. More work inside
6010 GDB is needed to support multi-byte or variable-width character
6011 encodings, like the UTF-8 and UCS-2 encodings of Unicode.
6013 Here is an example of @value{GDBN}'s character set support in action.
6014 Assume that the following source code has been placed in the file
6015 @file{charset-test.c}:
6021 = @{72, 101, 108, 108, 111, 44, 32, 119,
6022 111, 114, 108, 100, 33, 10, 0@};
6023 char ibm1047_hello[]
6024 = @{200, 133, 147, 147, 150, 107, 64, 166,
6025 150, 153, 147, 132, 90, 37, 0@};
6029 printf ("Hello, world!\n");
6033 In this program, @code{ascii_hello} and @code{ibm1047_hello} are arrays
6034 containing the string @samp{Hello, world!} followed by a newline,
6035 encoded in the @sc{ascii} and @sc{ibm1047} character sets.
6037 We compile the program, and invoke the debugger on it:
6040 $ gcc -g charset-test.c -o charset-test
6041 $ gdb -nw charset-test
6042 GNU gdb 2001-12-19-cvs
6043 Copyright 2001 Free Software Foundation, Inc.
6048 We can use the @code{show charset} command to see what character sets
6049 @value{GDBN} is currently using to interpret and display characters and
6054 The current host and target character set is `iso-8859-1'.
6058 For the sake of printing this manual, let's use @sc{ascii} as our
6059 initial character set:
6061 (gdb) set charset ascii
6063 The current host and target character set is `ascii'.
6067 Let's assume that @sc{ascii} is indeed the correct character set for our
6068 host system --- in other words, let's assume that if @value{GDBN} prints
6069 characters using the @sc{ascii} character set, our terminal will display
6070 them properly. Since our current target character set is also
6071 @sc{ascii}, the contents of @code{ascii_hello} print legibly:
6074 (gdb) print ascii_hello
6075 $1 = 0x401698 "Hello, world!\n"
6076 (gdb) print ascii_hello[0]
6081 @value{GDBN} uses the target character set for character and string
6082 literals you use in expressions:
6090 The @sc{ascii} character set uses the number 43 to encode the @samp{+}
6093 @value{GDBN} relies on the user to tell it which character set the
6094 target program uses. If we print @code{ibm1047_hello} while our target
6095 character set is still @sc{ascii}, we get jibberish:
6098 (gdb) print ibm1047_hello
6099 $4 = 0x4016a8 "\310\205\223\223\226k@@\246\226\231\223\204Z%"
6100 (gdb) print ibm1047_hello[0]
6105 If we invoke the @code{set target-charset} command without an argument,
6106 @value{GDBN} tells us the character sets it supports:
6109 (gdb) set target-charset
6110 Valid character sets are:
6115 * - can be used as a host character set
6118 We can select @sc{ibm1047} as our target character set, and examine the
6119 program's strings again. Now the @sc{ascii} string is wrong, but
6120 @value{GDBN} translates the contents of @code{ibm1047_hello} from the
6121 target character set, @sc{ibm1047}, to the host character set,
6122 @sc{ascii}, and they display correctly:
6125 (gdb) set target-charset ibm1047
6127 The current host character set is `ascii'.
6128 The current target character set is `ibm1047'.
6129 (gdb) print ascii_hello
6130 $6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
6131 (gdb) print ascii_hello[0]
6133 (gdb) print ibm1047_hello
6134 $8 = 0x4016a8 "Hello, world!\n"
6135 (gdb) print ibm1047_hello[0]
6140 As above, @value{GDBN} uses the target character set for character and
6141 string literals you use in expressions:
6149 The IBM1047 character set uses the number 78 to encode the @samp{+}
6154 @chapter C Preprocessor Macros
6156 Some languages, such as C and C++, provide a way to define and invoke
6157 ``preprocessor macros'' which expand into strings of tokens.
6158 @value{GDBN} can evaluate expressions containing macro invocations, show
6159 the result of macro expansion, and show a macro's definition, including
6160 where it was defined.
6162 You may need to compile your program specially to provide @value{GDBN}
6163 with information about preprocessor macros. Most compilers do not
6164 include macros in their debugging information, even when you compile
6165 with the @option{-g} flag. @xref{Compilation}.
6167 A program may define a macro at one point, remove that definition later,
6168 and then provide a different definition after that. Thus, at different
6169 points in the program, a macro may have different definitions, or have
6170 no definition at all. If there is a current stack frame, @value{GDBN}
6171 uses the macros in scope at that frame's source code line. Otherwise,
6172 @value{GDBN} uses the macros in scope at the current listing location;
6175 At the moment, @value{GDBN} does not support the @code{##}
6176 token-splicing operator, the @code{#} stringification operator, or
6177 variable-arity macros.
6179 Whenever @value{GDBN} evaluates an expression, it always expands any
6180 macro invocations present in the expression. @value{GDBN} also provides
6181 the following commands for working with macros explicitly.
6185 @kindex macro expand
6186 @cindex macro expansion, showing the results of preprocessor
6187 @cindex preprocessor macro expansion, showing the results of
6188 @cindex expanding preprocessor macros
6189 @item macro expand @var{expression}
6190 @itemx macro exp @var{expression}
6191 Show the results of expanding all preprocessor macro invocations in
6192 @var{expression}. Since @value{GDBN} simply expands macros, but does
6193 not parse the result, @var{expression} need not be a valid expression;
6194 it can be any string of tokens.
6196 @kindex macro expand-once
6197 @item macro expand-once @var{expression}
6198 @itemx macro exp1 @var{expression}
6199 @i{(This command is not yet implemented.)} Show the results of
6200 expanding those preprocessor macro invocations that appear explicitly in
6201 @var{expression}. Macro invocations appearing in that expansion are
6202 left unchanged. This command allows you to see the effect of a
6203 particular macro more clearly, without being confused by further
6204 expansions. Since @value{GDBN} simply expands macros, but does not
6205 parse the result, @var{expression} need not be a valid expression; it
6206 can be any string of tokens.
6209 @cindex macro definition, showing
6210 @cindex definition, showing a macro's
6211 @item info macro @var{macro}
6212 Show the definition of the macro named @var{macro}, and describe the
6213 source location where that definition was established.
6215 @kindex macro define
6216 @cindex user-defined macros
6217 @cindex defining macros interactively
6218 @cindex macros, user-defined
6219 @item macro define @var{macro} @var{replacement-list}
6220 @itemx macro define @var{macro}(@var{arglist}) @var{replacement-list}
6221 @i{(This command is not yet implemented.)} Introduce a definition for a
6222 preprocessor macro named @var{macro}, invocations of which are replaced
6223 by the tokens given in @var{replacement-list}. The first form of this
6224 command defines an ``object-like'' macro, which takes no arguments; the
6225 second form defines a ``function-like'' macro, which takes the arguments
6226 given in @var{arglist}.
6228 A definition introduced by this command is in scope in every expression
6229 evaluated in @value{GDBN}, until it is removed with the @command{macro
6230 undef} command, described below. The definition overrides all
6231 definitions for @var{macro} present in the program being debugged, as
6232 well as any previous user-supplied definition.
6235 @item macro undef @var{macro}
6236 @i{(This command is not yet implemented.)} Remove any user-supplied
6237 definition for the macro named @var{macro}. This command only affects
6238 definitions provided with the @command{macro define} command, described
6239 above; it cannot remove definitions present in the program being
6244 @cindex macros, example of debugging with
6245 Here is a transcript showing the above commands in action. First, we
6246 show our source files:
6254 #define ADD(x) (M + x)
6259 printf ("Hello, world!\n");
6261 printf ("We're so creative.\n");
6263 printf ("Goodbye, world!\n");
6270 Now, we compile the program using the @sc{gnu} C compiler, @value{NGCC}.
6271 We pass the @option{-gdwarf-2} and @option{-g3} flags to ensure the
6272 compiler includes information about preprocessor macros in the debugging
6276 $ gcc -gdwarf-2 -g3 sample.c -o sample
6280 Now, we start @value{GDBN} on our sample program:
6284 GNU gdb 2002-05-06-cvs
6285 Copyright 2002 Free Software Foundation, Inc.
6286 GDB is free software, @dots{}
6290 We can expand macros and examine their definitions, even when the
6291 program is not running. @value{GDBN} uses the current listing position
6292 to decide which macro definitions are in scope:
6298 5 #define ADD(x) (M + x)
6303 10 printf ("Hello, world!\n");
6305 12 printf ("We're so creative.\n");
6306 (gdb) info macro ADD
6307 Defined at /home/jimb/gdb/macros/play/sample.c:5
6308 #define ADD(x) (M + x)
6310 Defined at /home/jimb/gdb/macros/play/sample.h:1
6311 included at /home/jimb/gdb/macros/play/sample.c:2
6313 (gdb) macro expand ADD(1)
6314 expands to: (42 + 1)
6315 (gdb) macro expand-once ADD(1)
6316 expands to: once (M + 1)
6320 In the example above, note that @command{macro expand-once} expands only
6321 the macro invocation explicit in the original text --- the invocation of
6322 @code{ADD} --- but does not expand the invocation of the macro @code{M},
6323 which was introduced by @code{ADD}.
6325 Once the program is running, GDB uses the macro definitions in force at
6326 the source line of the current stack frame:
6330 Breakpoint 1 at 0x8048370: file sample.c, line 10.
6332 Starting program: /home/jimb/gdb/macros/play/sample
6334 Breakpoint 1, main () at sample.c:10
6335 10 printf ("Hello, world!\n");
6339 At line 10, the definition of the macro @code{N} at line 9 is in force:
6343 Defined at /home/jimb/gdb/macros/play/sample.c:9
6345 (gdb) macro expand N Q M
6352 As we step over directives that remove @code{N}'s definition, and then
6353 give it a new definition, @value{GDBN} finds the definition (or lack
6354 thereof) in force at each point:
6359 12 printf ("We're so creative.\n");
6361 The symbol `N' has no definition as a C/C++ preprocessor macro
6362 at /home/jimb/gdb/macros/play/sample.c:12
6365 14 printf ("Goodbye, world!\n");
6367 Defined at /home/jimb/gdb/macros/play/sample.c:13
6369 (gdb) macro expand N Q M
6370 expands to: 1729 < 42
6378 @chapter Tracepoints
6379 @c This chapter is based on the documentation written by Michael
6380 @c Snyder, David Taylor, Jim Blandy, and Elena Zannoni.
6383 In some applications, it is not feasible for the debugger to interrupt
6384 the program's execution long enough for the developer to learn
6385 anything helpful about its behavior. If the program's correctness
6386 depends on its real-time behavior, delays introduced by a debugger
6387 might cause the program to change its behavior drastically, or perhaps
6388 fail, even when the code itself is correct. It is useful to be able
6389 to observe the program's behavior without interrupting it.
6391 Using @value{GDBN}'s @code{trace} and @code{collect} commands, you can
6392 specify locations in the program, called @dfn{tracepoints}, and
6393 arbitrary expressions to evaluate when those tracepoints are reached.
6394 Later, using the @code{tfind} command, you can examine the values
6395 those expressions had when the program hit the tracepoints. The
6396 expressions may also denote objects in memory---structures or arrays,
6397 for example---whose values @value{GDBN} should record; while visiting
6398 a particular tracepoint, you may inspect those objects as if they were
6399 in memory at that moment. However, because @value{GDBN} records these
6400 values without interacting with you, it can do so quickly and
6401 unobtrusively, hopefully not disturbing the program's behavior.
6403 The tracepoint facility is currently available only for remote
6404 targets. @xref{Targets}. In addition, your remote target must know how
6405 to collect trace data. This functionality is implemented in the remote
6406 stub; however, none of the stubs distributed with @value{GDBN} support
6407 tracepoints as of this writing.
6409 This chapter describes the tracepoint commands and features.
6413 * Analyze Collected Data::
6414 * Tracepoint Variables::
6417 @node Set Tracepoints
6418 @section Commands to Set Tracepoints
6420 Before running such a @dfn{trace experiment}, an arbitrary number of
6421 tracepoints can be set. Like a breakpoint (@pxref{Set Breaks}), a
6422 tracepoint has a number assigned to it by @value{GDBN}. Like with
6423 breakpoints, tracepoint numbers are successive integers starting from
6424 one. Many of the commands associated with tracepoints take the
6425 tracepoint number as their argument, to identify which tracepoint to
6428 For each tracepoint, you can specify, in advance, some arbitrary set
6429 of data that you want the target to collect in the trace buffer when
6430 it hits that tracepoint. The collected data can include registers,
6431 local variables, or global data. Later, you can use @value{GDBN}
6432 commands to examine the values these data had at the time the
6435 This section describes commands to set tracepoints and associated
6436 conditions and actions.
6439 * Create and Delete Tracepoints::
6440 * Enable and Disable Tracepoints::
6441 * Tracepoint Passcounts::
6442 * Tracepoint Actions::
6443 * Listing Tracepoints::
6444 * Starting and Stopping Trace Experiment::
6447 @node Create and Delete Tracepoints
6448 @subsection Create and Delete Tracepoints
6451 @cindex set tracepoint
6454 The @code{trace} command is very similar to the @code{break} command.
6455 Its argument can be a source line, a function name, or an address in
6456 the target program. @xref{Set Breaks}. The @code{trace} command
6457 defines a tracepoint, which is a point in the target program where the
6458 debugger will briefly stop, collect some data, and then allow the
6459 program to continue. Setting a tracepoint or changing its commands
6460 doesn't take effect until the next @code{tstart} command; thus, you
6461 cannot change the tracepoint attributes once a trace experiment is
6464 Here are some examples of using the @code{trace} command:
6467 (@value{GDBP}) @b{trace foo.c:121} // a source file and line number
6469 (@value{GDBP}) @b{trace +2} // 2 lines forward
6471 (@value{GDBP}) @b{trace my_function} // first source line of function
6473 (@value{GDBP}) @b{trace *my_function} // EXACT start address of function
6475 (@value{GDBP}) @b{trace *0x2117c4} // an address
6479 You can abbreviate @code{trace} as @code{tr}.
6482 @cindex last tracepoint number
6483 @cindex recent tracepoint number
6484 @cindex tracepoint number
6485 The convenience variable @code{$tpnum} records the tracepoint number
6486 of the most recently set tracepoint.
6488 @kindex delete tracepoint
6489 @cindex tracepoint deletion
6490 @item delete tracepoint @r{[}@var{num}@r{]}
6491 Permanently delete one or more tracepoints. With no argument, the
6492 default is to delete all tracepoints.
6497 (@value{GDBP}) @b{delete trace 1 2 3} // remove three tracepoints
6499 (@value{GDBP}) @b{delete trace} // remove all tracepoints
6503 You can abbreviate this command as @code{del tr}.
6506 @node Enable and Disable Tracepoints
6507 @subsection Enable and Disable Tracepoints
6510 @kindex disable tracepoint
6511 @item disable tracepoint @r{[}@var{num}@r{]}
6512 Disable tracepoint @var{num}, or all tracepoints if no argument
6513 @var{num} is given. A disabled tracepoint will have no effect during
6514 the next trace experiment, but it is not forgotten. You can re-enable
6515 a disabled tracepoint using the @code{enable tracepoint} command.
6517 @kindex enable tracepoint
6518 @item enable tracepoint @r{[}@var{num}@r{]}
6519 Enable tracepoint @var{num}, or all tracepoints. The enabled
6520 tracepoints will become effective the next time a trace experiment is
6524 @node Tracepoint Passcounts
6525 @subsection Tracepoint Passcounts
6529 @cindex tracepoint pass count
6530 @item passcount @r{[}@var{n} @r{[}@var{num}@r{]]}
6531 Set the @dfn{passcount} of a tracepoint. The passcount is a way to
6532 automatically stop a trace experiment. If a tracepoint's passcount is
6533 @var{n}, then the trace experiment will be automatically stopped on
6534 the @var{n}'th time that tracepoint is hit. If the tracepoint number
6535 @var{num} is not specified, the @code{passcount} command sets the
6536 passcount of the most recently defined tracepoint. If no passcount is
6537 given, the trace experiment will run until stopped explicitly by the
6543 (@value{GDBP}) @b{passcount 5 2} // Stop on the 5th execution of
6544 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// tracepoint 2}
6546 (@value{GDBP}) @b{passcount 12} // Stop on the 12th execution of the
6547 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// most recently defined tracepoint.}
6548 (@value{GDBP}) @b{trace foo}
6549 (@value{GDBP}) @b{pass 3}
6550 (@value{GDBP}) @b{trace bar}
6551 (@value{GDBP}) @b{pass 2}
6552 (@value{GDBP}) @b{trace baz}
6553 (@value{GDBP}) @b{pass 1} // Stop tracing when foo has been
6554 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// executed 3 times OR when bar has}
6555 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// been executed 2 times}
6556 @exdent @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @code{// OR when baz has been executed 1 time.}
6560 @node Tracepoint Actions
6561 @subsection Tracepoint Action Lists
6565 @cindex tracepoint actions
6566 @item actions @r{[}@var{num}@r{]}
6567 This command will prompt for a list of actions to be taken when the
6568 tracepoint is hit. If the tracepoint number @var{num} is not
6569 specified, this command sets the actions for the one that was most
6570 recently defined (so that you can define a tracepoint and then say
6571 @code{actions} without bothering about its number). You specify the
6572 actions themselves on the following lines, one action at a time, and
6573 terminate the actions list with a line containing just @code{end}. So
6574 far, the only defined actions are @code{collect} and
6575 @code{while-stepping}.
6577 @cindex remove actions from a tracepoint
6578 To remove all actions from a tracepoint, type @samp{actions @var{num}}
6579 and follow it immediately with @samp{end}.
6582 (@value{GDBP}) @b{collect @var{data}} // collect some data
6584 (@value{GDBP}) @b{while-stepping 5} // single-step 5 times, collect data
6586 (@value{GDBP}) @b{end} // signals the end of actions.
6589 In the following example, the action list begins with @code{collect}
6590 commands indicating the things to be collected when the tracepoint is
6591 hit. Then, in order to single-step and collect additional data
6592 following the tracepoint, a @code{while-stepping} command is used,
6593 followed by the list of things to be collected while stepping. The
6594 @code{while-stepping} command is terminated by its own separate
6595 @code{end} command. Lastly, the action list is terminated by an
6599 (@value{GDBP}) @b{trace foo}
6600 (@value{GDBP}) @b{actions}
6601 Enter actions for tracepoint 1, one per line:
6610 @kindex collect @r{(tracepoints)}
6611 @item collect @var{expr1}, @var{expr2}, @dots{}
6612 Collect values of the given expressions when the tracepoint is hit.
6613 This command accepts a comma-separated list of any valid expressions.
6614 In addition to global, static, or local variables, the following
6615 special arguments are supported:
6619 collect all registers
6622 collect all function arguments
6625 collect all local variables.
6628 You can give several consecutive @code{collect} commands, each one
6629 with a single argument, or one @code{collect} command with several
6630 arguments separated by commas: the effect is the same.
6632 The command @code{info scope} (@pxref{Symbols, info scope}) is
6633 particularly useful for figuring out what data to collect.
6635 @kindex while-stepping @r{(tracepoints)}
6636 @item while-stepping @var{n}
6637 Perform @var{n} single-step traces after the tracepoint, collecting
6638 new data at each step. The @code{while-stepping} command is
6639 followed by the list of what to collect while stepping (followed by
6640 its own @code{end} command):
6644 > collect $regs, myglobal
6650 You may abbreviate @code{while-stepping} as @code{ws} or
6654 @node Listing Tracepoints
6655 @subsection Listing Tracepoints
6658 @kindex info tracepoints
6659 @cindex information about tracepoints
6660 @item info tracepoints @r{[}@var{num}@r{]}
6661 Display information about the tracepoint @var{num}. If you don't specify
6662 a tracepoint number, displays information about all the tracepoints
6663 defined so far. For each tracepoint, the following information is
6670 whether it is enabled or disabled
6674 its passcount as given by the @code{passcount @var{n}} command
6676 its step count as given by the @code{while-stepping @var{n}} command
6678 where in the source files is the tracepoint set
6680 its action list as given by the @code{actions} command
6684 (@value{GDBP}) @b{info trace}
6685 Num Enb Address PassC StepC What
6686 1 y 0x002117c4 0 0 <gdb_asm>
6687 2 y 0x0020dc64 0 0 in g_test at g_test.c:1375
6688 3 y 0x0020b1f4 0 0 in get_data at ../foo.c:41
6693 This command can be abbreviated @code{info tp}.
6696 @node Starting and Stopping Trace Experiment
6697 @subsection Starting and Stopping Trace Experiment
6701 @cindex start a new trace experiment
6702 @cindex collected data discarded
6704 This command takes no arguments. It starts the trace experiment, and
6705 begins collecting data. This has the side effect of discarding all
6706 the data collected in the trace buffer during the previous trace
6710 @cindex stop a running trace experiment
6712 This command takes no arguments. It ends the trace experiment, and
6713 stops collecting data.
6715 @strong{Note:} a trace experiment and data collection may stop
6716 automatically if any tracepoint's passcount is reached
6717 (@pxref{Tracepoint Passcounts}), or if the trace buffer becomes full.
6720 @cindex status of trace data collection
6721 @cindex trace experiment, status of
6723 This command displays the status of the current trace data
6727 Here is an example of the commands we described so far:
6730 (@value{GDBP}) @b{trace gdb_c_test}
6731 (@value{GDBP}) @b{actions}
6732 Enter actions for tracepoint #1, one per line.
6733 > collect $regs,$locals,$args
6738 (@value{GDBP}) @b{tstart}
6739 [time passes @dots{}]
6740 (@value{GDBP}) @b{tstop}
6744 @node Analyze Collected Data
6745 @section Using the collected data
6747 After the tracepoint experiment ends, you use @value{GDBN} commands
6748 for examining the trace data. The basic idea is that each tracepoint
6749 collects a trace @dfn{snapshot} every time it is hit and another
6750 snapshot every time it single-steps. All these snapshots are
6751 consecutively numbered from zero and go into a buffer, and you can
6752 examine them later. The way you examine them is to @dfn{focus} on a
6753 specific trace snapshot. When the remote stub is focused on a trace
6754 snapshot, it will respond to all @value{GDBN} requests for memory and
6755 registers by reading from the buffer which belongs to that snapshot,
6756 rather than from @emph{real} memory or registers of the program being
6757 debugged. This means that @strong{all} @value{GDBN} commands
6758 (@code{print}, @code{info registers}, @code{backtrace}, etc.) will
6759 behave as if we were currently debugging the program state as it was
6760 when the tracepoint occurred. Any requests for data that are not in
6761 the buffer will fail.
6764 * tfind:: How to select a trace snapshot
6765 * tdump:: How to display all data for a snapshot
6766 * save-tracepoints:: How to save tracepoints for a future run
6770 @subsection @code{tfind @var{n}}
6773 @cindex select trace snapshot
6774 @cindex find trace snapshot
6775 The basic command for selecting a trace snapshot from the buffer is
6776 @code{tfind @var{n}}, which finds trace snapshot number @var{n},
6777 counting from zero. If no argument @var{n} is given, the next
6778 snapshot is selected.
6780 Here are the various forms of using the @code{tfind} command.
6784 Find the first snapshot in the buffer. This is a synonym for
6785 @code{tfind 0} (since 0 is the number of the first snapshot).
6788 Stop debugging trace snapshots, resume @emph{live} debugging.
6791 Same as @samp{tfind none}.
6794 No argument means find the next trace snapshot.
6797 Find the previous trace snapshot before the current one. This permits
6798 retracing earlier steps.
6800 @item tfind tracepoint @var{num}
6801 Find the next snapshot associated with tracepoint @var{num}. Search
6802 proceeds forward from the last examined trace snapshot. If no
6803 argument @var{num} is given, it means find the next snapshot collected
6804 for the same tracepoint as the current snapshot.
6806 @item tfind pc @var{addr}
6807 Find the next snapshot associated with the value @var{addr} of the
6808 program counter. Search proceeds forward from the last examined trace
6809 snapshot. If no argument @var{addr} is given, it means find the next
6810 snapshot with the same value of PC as the current snapshot.
6812 @item tfind outside @var{addr1}, @var{addr2}
6813 Find the next snapshot whose PC is outside the given range of
6816 @item tfind range @var{addr1}, @var{addr2}
6817 Find the next snapshot whose PC is between @var{addr1} and
6818 @var{addr2}. @c FIXME: Is the range inclusive or exclusive?
6820 @item tfind line @r{[}@var{file}:@r{]}@var{n}
6821 Find the next snapshot associated with the source line @var{n}. If
6822 the optional argument @var{file} is given, refer to line @var{n} in
6823 that source file. Search proceeds forward from the last examined
6824 trace snapshot. If no argument @var{n} is given, it means find the
6825 next line other than the one currently being examined; thus saying
6826 @code{tfind line} repeatedly can appear to have the same effect as
6827 stepping from line to line in a @emph{live} debugging session.
6830 The default arguments for the @code{tfind} commands are specifically
6831 designed to make it easy to scan through the trace buffer. For
6832 instance, @code{tfind} with no argument selects the next trace
6833 snapshot, and @code{tfind -} with no argument selects the previous
6834 trace snapshot. So, by giving one @code{tfind} command, and then
6835 simply hitting @key{RET} repeatedly you can examine all the trace
6836 snapshots in order. Or, by saying @code{tfind -} and then hitting
6837 @key{RET} repeatedly you can examine the snapshots in reverse order.
6838 The @code{tfind line} command with no argument selects the snapshot
6839 for the next source line executed. The @code{tfind pc} command with
6840 no argument selects the next snapshot with the same program counter
6841 (PC) as the current frame. The @code{tfind tracepoint} command with
6842 no argument selects the next trace snapshot collected by the same
6843 tracepoint as the current one.
6845 In addition to letting you scan through the trace buffer manually,
6846 these commands make it easy to construct @value{GDBN} scripts that
6847 scan through the trace buffer and print out whatever collected data
6848 you are interested in. Thus, if we want to examine the PC, FP, and SP
6849 registers from each trace frame in the buffer, we can say this:
6852 (@value{GDBP}) @b{tfind start}
6853 (@value{GDBP}) @b{while ($trace_frame != -1)}
6854 > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \
6855 $trace_frame, $pc, $sp, $fp
6859 Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44
6860 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44
6861 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44
6862 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44
6863 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44
6864 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44
6865 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44
6866 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44
6867 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44
6868 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44
6869 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14
6872 Or, if we want to examine the variable @code{X} at each source line in
6876 (@value{GDBP}) @b{tfind start}
6877 (@value{GDBP}) @b{while ($trace_frame != -1)}
6878 > printf "Frame %d, X == %d\n", $trace_frame, X
6888 @subsection @code{tdump}
6890 @cindex dump all data collected at tracepoint
6891 @cindex tracepoint data, display
6893 This command takes no arguments. It prints all the data collected at
6894 the current trace snapshot.
6897 (@value{GDBP}) @b{trace 444}
6898 (@value{GDBP}) @b{actions}
6899 Enter actions for tracepoint #2, one per line:
6900 > collect $regs, $locals, $args, gdb_long_test
6903 (@value{GDBP}) @b{tstart}
6905 (@value{GDBP}) @b{tfind line 444}
6906 #0 gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
6908 444 printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )
6910 (@value{GDBP}) @b{tdump}
6911 Data collected at tracepoint 2, trace frame 1:
6912 d0 0xc4aa0085 -995491707
6916 d4 0x71aea3d 119204413
6921 a1 0x3000668 50333288
6924 a4 0x3000698 50333336
6926 fp 0x30bf3c 0x30bf3c
6927 sp 0x30bf34 0x30bf34
6929 pc 0x20b2c8 0x20b2c8
6933 p = 0x20e5b4 "gdb-test"
6940 gdb_long_test = 17 '\021'
6945 @node save-tracepoints
6946 @subsection @code{save-tracepoints @var{filename}}
6947 @kindex save-tracepoints
6948 @cindex save tracepoints for future sessions
6950 This command saves all current tracepoint definitions together with
6951 their actions and passcounts, into a file @file{@var{filename}}
6952 suitable for use in a later debugging session. To read the saved
6953 tracepoint definitions, use the @code{source} command (@pxref{Command
6956 @node Tracepoint Variables
6957 @section Convenience Variables for Tracepoints
6958 @cindex tracepoint variables
6959 @cindex convenience variables for tracepoints
6962 @vindex $trace_frame
6963 @item (int) $trace_frame
6964 The current trace snapshot (a.k.a.@: @dfn{frame}) number, or -1 if no
6965 snapshot is selected.
6968 @item (int) $tracepoint
6969 The tracepoint for the current trace snapshot.
6972 @item (int) $trace_line
6973 The line number for the current trace snapshot.
6976 @item (char []) $trace_file
6977 The source file for the current trace snapshot.
6980 @item (char []) $trace_func
6981 The name of the function containing @code{$tracepoint}.
6984 Note: @code{$trace_file} is not suitable for use in @code{printf},
6985 use @code{output} instead.
6987 Here's a simple example of using these convenience variables for
6988 stepping through all the trace snapshots and printing some of their
6992 (@value{GDBP}) @b{tfind start}
6994 (@value{GDBP}) @b{while $trace_frame != -1}
6995 > output $trace_file
6996 > printf ", line %d (tracepoint #%d)\n", $trace_line, $tracepoint
7002 @chapter Debugging Programs That Use Overlays
7005 If your program is too large to fit completely in your target system's
7006 memory, you can sometimes use @dfn{overlays} to work around this
7007 problem. @value{GDBN} provides some support for debugging programs that
7011 * How Overlays Work:: A general explanation of overlays.
7012 * Overlay Commands:: Managing overlays in @value{GDBN}.
7013 * Automatic Overlay Debugging:: @value{GDBN} can find out which overlays are
7014 mapped by asking the inferior.
7015 * Overlay Sample Program:: A sample program using overlays.
7018 @node How Overlays Work
7019 @section How Overlays Work
7020 @cindex mapped overlays
7021 @cindex unmapped overlays
7022 @cindex load address, overlay's
7023 @cindex mapped address
7024 @cindex overlay area
7026 Suppose you have a computer whose instruction address space is only 64
7027 kilobytes long, but which has much more memory which can be accessed by
7028 other means: special instructions, segment registers, or memory
7029 management hardware, for example. Suppose further that you want to
7030 adapt a program which is larger than 64 kilobytes to run on this system.
7032 One solution is to identify modules of your program which are relatively
7033 independent, and need not call each other directly; call these modules
7034 @dfn{overlays}. Separate the overlays from the main program, and place
7035 their machine code in the larger memory. Place your main program in
7036 instruction memory, but leave at least enough space there to hold the
7037 largest overlay as well.
7039 Now, to call a function located in an overlay, you must first copy that
7040 overlay's machine code from the large memory into the space set aside
7041 for it in the instruction memory, and then jump to its entry point
7044 @c NB: In the below the mapped area's size is greater or equal to the
7045 @c size of all overlays. This is intentional to remind the developer
7046 @c that overlays don't necessarily need to be the same size.
7050 Data Instruction Larger
7051 Address Space Address Space Address Space
7052 +-----------+ +-----------+ +-----------+
7054 +-----------+ +-----------+ +-----------+<-- overlay 1
7055 | program | | main | .----| overlay 1 | load address
7056 | variables | | program | | +-----------+
7057 | and heap | | | | | |
7058 +-----------+ | | | +-----------+<-- overlay 2
7059 | | +-----------+ | | | load address
7060 +-----------+ | | | .-| overlay 2 |
7062 mapped --->+-----------+ | | +-----------+
7064 | overlay | <-' | | |
7065 | area | <---' +-----------+<-- overlay 3
7066 | | <---. | | load address
7067 +-----------+ `--| overlay 3 |
7074 @anchor{A code overlay}A code overlay
7078 The diagram (@pxref{A code overlay}) shows a system with separate data
7079 and instruction address spaces. To map an overlay, the program copies
7080 its code from the larger address space to the instruction address space.
7081 Since the overlays shown here all use the same mapped address, only one
7082 may be mapped at a time. For a system with a single address space for
7083 data and instructions, the diagram would be similar, except that the
7084 program variables and heap would share an address space with the main
7085 program and the overlay area.
7087 An overlay loaded into instruction memory and ready for use is called a
7088 @dfn{mapped} overlay; its @dfn{mapped address} is its address in the
7089 instruction memory. An overlay not present (or only partially present)
7090 in instruction memory is called @dfn{unmapped}; its @dfn{load address}
7091 is its address in the larger memory. The mapped address is also called
7092 the @dfn{virtual memory address}, or @dfn{VMA}; the load address is also
7093 called the @dfn{load memory address}, or @dfn{LMA}.
7095 Unfortunately, overlays are not a completely transparent way to adapt a
7096 program to limited instruction memory. They introduce a new set of
7097 global constraints you must keep in mind as you design your program:
7102 Before calling or returning to a function in an overlay, your program
7103 must make sure that overlay is actually mapped. Otherwise, the call or
7104 return will transfer control to the right address, but in the wrong
7105 overlay, and your program will probably crash.
7108 If the process of mapping an overlay is expensive on your system, you
7109 will need to choose your overlays carefully to minimize their effect on
7110 your program's performance.
7113 The executable file you load onto your system must contain each
7114 overlay's instructions, appearing at the overlay's load address, not its
7115 mapped address. However, each overlay's instructions must be relocated
7116 and its symbols defined as if the overlay were at its mapped address.
7117 You can use GNU linker scripts to specify different load and relocation
7118 addresses for pieces of your program; see @ref{Overlay Description,,,
7119 ld.info, Using ld: the GNU linker}.
7122 The procedure for loading executable files onto your system must be able
7123 to load their contents into the larger address space as well as the
7124 instruction and data spaces.
7128 The overlay system described above is rather simple, and could be
7129 improved in many ways:
7134 If your system has suitable bank switch registers or memory management
7135 hardware, you could use those facilities to make an overlay's load area
7136 contents simply appear at their mapped address in instruction space.
7137 This would probably be faster than copying the overlay to its mapped
7138 area in the usual way.
7141 If your overlays are small enough, you could set aside more than one
7142 overlay area, and have more than one overlay mapped at a time.
7145 You can use overlays to manage data, as well as instructions. In
7146 general, data overlays are even less transparent to your design than
7147 code overlays: whereas code overlays only require care when you call or
7148 return to functions, data overlays require care every time you access
7149 the data. Also, if you change the contents of a data overlay, you
7150 must copy its contents back out to its load address before you can copy a
7151 different data overlay into the same mapped area.
7156 @node Overlay Commands
7157 @section Overlay Commands
7159 To use @value{GDBN}'s overlay support, each overlay in your program must
7160 correspond to a separate section of the executable file. The section's
7161 virtual memory address and load memory address must be the overlay's
7162 mapped and load addresses. Identifying overlays with sections allows
7163 @value{GDBN} to determine the appropriate address of a function or
7164 variable, depending on whether the overlay is mapped or not.
7166 @value{GDBN}'s overlay commands all start with the word @code{overlay};
7167 you can abbreviate this as @code{ov} or @code{ovly}. The commands are:
7172 Disable @value{GDBN}'s overlay support. When overlay support is
7173 disabled, @value{GDBN} assumes that all functions and variables are
7174 always present at their mapped addresses. By default, @value{GDBN}'s
7175 overlay support is disabled.
7177 @item overlay manual
7178 @kindex overlay manual
7179 @cindex manual overlay debugging
7180 Enable @dfn{manual} overlay debugging. In this mode, @value{GDBN}
7181 relies on you to tell it which overlays are mapped, and which are not,
7182 using the @code{overlay map-overlay} and @code{overlay unmap-overlay}
7183 commands described below.
7185 @item overlay map-overlay @var{overlay}
7186 @itemx overlay map @var{overlay}
7187 @kindex overlay map-overlay
7188 @cindex map an overlay
7189 Tell @value{GDBN} that @var{overlay} is now mapped; @var{overlay} must
7190 be the name of the object file section containing the overlay. When an
7191 overlay is mapped, @value{GDBN} assumes it can find the overlay's
7192 functions and variables at their mapped addresses. @value{GDBN} assumes
7193 that any other overlays whose mapped ranges overlap that of
7194 @var{overlay} are now unmapped.
7196 @item overlay unmap-overlay @var{overlay}
7197 @itemx overlay unmap @var{overlay}
7198 @kindex overlay unmap-overlay
7199 @cindex unmap an overlay
7200 Tell @value{GDBN} that @var{overlay} is no longer mapped; @var{overlay}
7201 must be the name of the object file section containing the overlay.
7202 When an overlay is unmapped, @value{GDBN} assumes it can find the
7203 overlay's functions and variables at their load addresses.
7206 @kindex overlay auto
7207 Enable @dfn{automatic} overlay debugging. In this mode, @value{GDBN}
7208 consults a data structure the overlay manager maintains in the inferior
7209 to see which overlays are mapped. For details, see @ref{Automatic
7212 @item overlay load-target
7214 @kindex overlay load-target
7215 @cindex reloading the overlay table
7216 Re-read the overlay table from the inferior. Normally, @value{GDBN}
7217 re-reads the table @value{GDBN} automatically each time the inferior
7218 stops, so this command should only be necessary if you have changed the
7219 overlay mapping yourself using @value{GDBN}. This command is only
7220 useful when using automatic overlay debugging.
7222 @item overlay list-overlays
7224 @cindex listing mapped overlays
7225 Display a list of the overlays currently mapped, along with their mapped
7226 addresses, load addresses, and sizes.
7230 Normally, when @value{GDBN} prints a code address, it includes the name
7231 of the function the address falls in:
7235 $3 = @{int ()@} 0x11a0 <main>
7238 When overlay debugging is enabled, @value{GDBN} recognizes code in
7239 unmapped overlays, and prints the names of unmapped functions with
7240 asterisks around them. For example, if @code{foo} is a function in an
7241 unmapped overlay, @value{GDBN} prints it this way:
7245 No sections are mapped.
7247 $5 = @{int (int)@} 0x100000 <*foo*>
7250 When @code{foo}'s overlay is mapped, @value{GDBN} prints the function's
7255 Section .ov.foo.text, loaded at 0x100000 - 0x100034,
7256 mapped at 0x1016 - 0x104a
7258 $6 = @{int (int)@} 0x1016 <foo>
7261 When overlay debugging is enabled, @value{GDBN} can find the correct
7262 address for functions and variables in an overlay, whether or not the
7263 overlay is mapped. This allows most @value{GDBN} commands, like
7264 @code{break} and @code{disassemble}, to work normally, even on unmapped
7265 code. However, @value{GDBN}'s breakpoint support has some limitations:
7269 @cindex breakpoints in overlays
7270 @cindex overlays, setting breakpoints in
7271 You can set breakpoints in functions in unmapped overlays, as long as
7272 @value{GDBN} can write to the overlay at its load address.
7274 @value{GDBN} can not set hardware or simulator-based breakpoints in
7275 unmapped overlays. However, if you set a breakpoint at the end of your
7276 overlay manager (and tell @value{GDBN} which overlays are now mapped, if
7277 you are using manual overlay management), @value{GDBN} will re-set its
7278 breakpoints properly.
7282 @node Automatic Overlay Debugging
7283 @section Automatic Overlay Debugging
7284 @cindex automatic overlay debugging
7286 @value{GDBN} can automatically track which overlays are mapped and which
7287 are not, given some simple co-operation from the overlay manager in the
7288 inferior. If you enable automatic overlay debugging with the
7289 @code{overlay auto} command (@pxref{Overlay Commands}), @value{GDBN}
7290 looks in the inferior's memory for certain variables describing the
7291 current state of the overlays.
7293 Here are the variables your overlay manager must define to support
7294 @value{GDBN}'s automatic overlay debugging:
7298 @item @code{_ovly_table}:
7299 This variable must be an array of the following structures:
7304 /* The overlay's mapped address. */
7307 /* The size of the overlay, in bytes. */
7310 /* The overlay's load address. */
7313 /* Non-zero if the overlay is currently mapped;
7315 unsigned long mapped;
7319 @item @code{_novlys}:
7320 This variable must be a four-byte signed integer, holding the total
7321 number of elements in @code{_ovly_table}.
7325 To decide whether a particular overlay is mapped or not, @value{GDBN}
7326 looks for an entry in @w{@code{_ovly_table}} whose @code{vma} and
7327 @code{lma} members equal the VMA and LMA of the overlay's section in the
7328 executable file. When @value{GDBN} finds a matching entry, it consults
7329 the entry's @code{mapped} member to determine whether the overlay is
7332 In addition, your overlay manager may define a function called
7333 @code{_ovly_debug_event}. If this function is defined, @value{GDBN}
7334 will silently set a breakpoint there. If the overlay manager then
7335 calls this function whenever it has changed the overlay table, this
7336 will enable @value{GDBN} to accurately keep track of which overlays
7337 are in program memory, and update any breakpoints that may be set
7338 in overlays. This will allow breakpoints to work even if the
7339 overlays are kept in ROM or other non-writable memory while they
7340 are not being executed.
7342 @node Overlay Sample Program
7343 @section Overlay Sample Program
7344 @cindex overlay example program
7346 When linking a program which uses overlays, you must place the overlays
7347 at their load addresses, while relocating them to run at their mapped
7348 addresses. To do this, you must write a linker script (@pxref{Overlay
7349 Description,,, ld.info, Using ld: the GNU linker}). Unfortunately,
7350 since linker scripts are specific to a particular host system, target
7351 architecture, and target memory layout, this manual cannot provide
7352 portable sample code demonstrating @value{GDBN}'s overlay support.
7354 However, the @value{GDBN} source distribution does contain an overlaid
7355 program, with linker scripts for a few systems, as part of its test
7356 suite. The program consists of the following files from
7357 @file{gdb/testsuite/gdb.base}:
7361 The main program file.
7363 A simple overlay manager, used by @file{overlays.c}.
7368 Overlay modules, loaded and used by @file{overlays.c}.
7371 Linker scripts for linking the test program on the @code{d10v-elf}
7372 and @code{m32r-elf} targets.
7375 You can build the test program using the @code{d10v-elf} GCC
7376 cross-compiler like this:
7379 $ d10v-elf-gcc -g -c overlays.c
7380 $ d10v-elf-gcc -g -c ovlymgr.c
7381 $ d10v-elf-gcc -g -c foo.c
7382 $ d10v-elf-gcc -g -c bar.c
7383 $ d10v-elf-gcc -g -c baz.c
7384 $ d10v-elf-gcc -g -c grbx.c
7385 $ d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \
7386 baz.o grbx.o -Wl,-Td10v.ld -o overlays
7389 The build process is identical for any other architecture, except that
7390 you must substitute the appropriate compiler and linker script for the
7391 target system for @code{d10v-elf-gcc} and @code{d10v.ld}.
7395 @chapter Using @value{GDBN} with Different Languages
7398 Although programming languages generally have common aspects, they are
7399 rarely expressed in the same manner. For instance, in ANSI C,
7400 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
7401 Modula-2, it is accomplished by @code{p^}. Values can also be
7402 represented (and displayed) differently. Hex numbers in C appear as
7403 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
7405 @cindex working language
7406 Language-specific information is built into @value{GDBN} for some languages,
7407 allowing you to express operations like the above in your program's
7408 native language, and allowing @value{GDBN} to output values in a manner
7409 consistent with the syntax of your program's native language. The
7410 language you use to build expressions is called the @dfn{working
7414 * Setting:: Switching between source languages
7415 * Show:: Displaying the language
7416 * Checks:: Type and range checks
7417 * Support:: Supported languages
7421 @section Switching between source languages
7423 There are two ways to control the working language---either have @value{GDBN}
7424 set it automatically, or select it manually yourself. You can use the
7425 @code{set language} command for either purpose. On startup, @value{GDBN}
7426 defaults to setting the language automatically. The working language is
7427 used to determine how expressions you type are interpreted, how values
7430 In addition to the working language, every source file that
7431 @value{GDBN} knows about has its own working language. For some object
7432 file formats, the compiler might indicate which language a particular
7433 source file is in. However, most of the time @value{GDBN} infers the
7434 language from the name of the file. The language of a source file
7435 controls whether C@t{++} names are demangled---this way @code{backtrace} can
7436 show each frame appropriately for its own language. There is no way to
7437 set the language of a source file from within @value{GDBN}, but you can
7438 set the language associated with a filename extension. @xref{Show, ,
7439 Displaying the language}.
7441 This is most commonly a problem when you use a program, such
7442 as @code{cfront} or @code{f2c}, that generates C but is written in
7443 another language. In that case, make the
7444 program use @code{#line} directives in its C output; that way
7445 @value{GDBN} will know the correct language of the source code of the original
7446 program, and will display that source code, not the generated C code.
7449 * Filenames:: Filename extensions and languages.
7450 * Manually:: Setting the working language manually
7451 * Automatically:: Having @value{GDBN} infer the source language
7455 @subsection List of filename extensions and languages
7457 If a source file name ends in one of the following extensions, then
7458 @value{GDBN} infers that its language is the one indicated.
7478 Modula-2 source file
7482 Assembler source file. This actually behaves almost like C, but
7483 @value{GDBN} does not skip over function prologues when stepping.
7486 In addition, you may set the language associated with a filename
7487 extension. @xref{Show, , Displaying the language}.
7490 @subsection Setting the working language
7492 If you allow @value{GDBN} to set the language automatically,
7493 expressions are interpreted the same way in your debugging session and
7496 @kindex set language
7497 If you wish, you may set the language manually. To do this, issue the
7498 command @samp{set language @var{lang}}, where @var{lang} is the name of
7500 @code{c} or @code{modula-2}.
7501 For a list of the supported languages, type @samp{set language}.
7503 Setting the language manually prevents @value{GDBN} from updating the working
7504 language automatically. This can lead to confusion if you try
7505 to debug a program when the working language is not the same as the
7506 source language, when an expression is acceptable to both
7507 languages---but means different things. For instance, if the current
7508 source file were written in C, and @value{GDBN} was parsing Modula-2, a
7516 might not have the effect you intended. In C, this means to add
7517 @code{b} and @code{c} and place the result in @code{a}. The result
7518 printed would be the value of @code{a}. In Modula-2, this means to compare
7519 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
7522 @subsection Having @value{GDBN} infer the source language
7524 To have @value{GDBN} set the working language automatically, use
7525 @samp{set language local} or @samp{set language auto}. @value{GDBN}
7526 then infers the working language. That is, when your program stops in a
7527 frame (usually by encountering a breakpoint), @value{GDBN} sets the
7528 working language to the language recorded for the function in that
7529 frame. If the language for a frame is unknown (that is, if the function
7530 or block corresponding to the frame was defined in a source file that
7531 does not have a recognized extension), the current working language is
7532 not changed, and @value{GDBN} issues a warning.
7534 This may not seem necessary for most programs, which are written
7535 entirely in one source language. However, program modules and libraries
7536 written in one source language can be used by a main program written in
7537 a different source language. Using @samp{set language auto} in this
7538 case frees you from having to set the working language manually.
7541 @section Displaying the language
7543 The following commands help you find out which language is the
7544 working language, and also what language source files were written in.
7546 @kindex show language
7547 @kindex info frame@r{, show the source language}
7548 @kindex info source@r{, show the source language}
7551 Display the current working language. This is the
7552 language you can use with commands such as @code{print} to
7553 build and compute expressions that may involve variables in your program.
7556 Display the source language for this frame. This language becomes the
7557 working language if you use an identifier from this frame.
7558 @xref{Frame Info, ,Information about a frame}, to identify the other
7559 information listed here.
7562 Display the source language of this source file.
7563 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
7564 information listed here.
7567 In unusual circumstances, you may have source files with extensions
7568 not in the standard list. You can then set the extension associated
7569 with a language explicitly:
7571 @kindex set extension-language
7572 @kindex info extensions
7574 @item set extension-language @var{.ext} @var{language}
7575 Set source files with extension @var{.ext} to be assumed to be in
7576 the source language @var{language}.
7578 @item info extensions
7579 List all the filename extensions and the associated languages.
7583 @section Type and range checking
7586 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
7587 checking are included, but they do not yet have any effect. This
7588 section documents the intended facilities.
7590 @c FIXME remove warning when type/range code added
7592 Some languages are designed to guard you against making seemingly common
7593 errors through a series of compile- and run-time checks. These include
7594 checking the type of arguments to functions and operators, and making
7595 sure mathematical overflows are caught at run time. Checks such as
7596 these help to ensure a program's correctness once it has been compiled
7597 by eliminating type mismatches, and providing active checks for range
7598 errors when your program is running.
7600 @value{GDBN} can check for conditions like the above if you wish.
7601 Although @value{GDBN} does not check the statements in your program, it
7602 can check expressions entered directly into @value{GDBN} for evaluation via
7603 the @code{print} command, for example. As with the working language,
7604 @value{GDBN} can also decide whether or not to check automatically based on
7605 your program's source language. @xref{Support, ,Supported languages},
7606 for the default settings of supported languages.
7609 * Type Checking:: An overview of type checking
7610 * Range Checking:: An overview of range checking
7613 @cindex type checking
7614 @cindex checks, type
7616 @subsection An overview of type checking
7618 Some languages, such as Modula-2, are strongly typed, meaning that the
7619 arguments to operators and functions have to be of the correct type,
7620 otherwise an error occurs. These checks prevent type mismatch
7621 errors from ever causing any run-time problems. For example,
7629 The second example fails because the @code{CARDINAL} 1 is not
7630 type-compatible with the @code{REAL} 2.3.
7632 For the expressions you use in @value{GDBN} commands, you can tell the
7633 @value{GDBN} type checker to skip checking;
7634 to treat any mismatches as errors and abandon the expression;
7635 or to only issue warnings when type mismatches occur,
7636 but evaluate the expression anyway. When you choose the last of
7637 these, @value{GDBN} evaluates expressions like the second example above, but
7638 also issues a warning.
7640 Even if you turn type checking off, there may be other reasons
7641 related to type that prevent @value{GDBN} from evaluating an expression.
7642 For instance, @value{GDBN} does not know how to add an @code{int} and
7643 a @code{struct foo}. These particular type errors have nothing to do
7644 with the language in use, and usually arise from expressions, such as
7645 the one described above, which make little sense to evaluate anyway.
7647 Each language defines to what degree it is strict about type. For
7648 instance, both Modula-2 and C require the arguments to arithmetical
7649 operators to be numbers. In C, enumerated types and pointers can be
7650 represented as numbers, so that they are valid arguments to mathematical
7651 operators. @xref{Support, ,Supported languages}, for further
7652 details on specific languages.
7654 @value{GDBN} provides some additional commands for controlling the type checker:
7656 @kindex set check@r{, type}
7657 @kindex set check type
7658 @kindex show check type
7660 @item set check type auto
7661 Set type checking on or off based on the current working language.
7662 @xref{Support, ,Supported languages}, for the default settings for
7665 @item set check type on
7666 @itemx set check type off
7667 Set type checking on or off, overriding the default setting for the
7668 current working language. Issue a warning if the setting does not
7669 match the language default. If any type mismatches occur in
7670 evaluating an expression while type checking is on, @value{GDBN} prints a
7671 message and aborts evaluation of the expression.
7673 @item set check type warn
7674 Cause the type checker to issue warnings, but to always attempt to
7675 evaluate the expression. Evaluating the expression may still
7676 be impossible for other reasons. For example, @value{GDBN} cannot add
7677 numbers and structures.
7680 Show the current setting of the type checker, and whether or not @value{GDBN}
7681 is setting it automatically.
7684 @cindex range checking
7685 @cindex checks, range
7686 @node Range Checking
7687 @subsection An overview of range checking
7689 In some languages (such as Modula-2), it is an error to exceed the
7690 bounds of a type; this is enforced with run-time checks. Such range
7691 checking is meant to ensure program correctness by making sure
7692 computations do not overflow, or indices on an array element access do
7693 not exceed the bounds of the array.
7695 For expressions you use in @value{GDBN} commands, you can tell
7696 @value{GDBN} to treat range errors in one of three ways: ignore them,
7697 always treat them as errors and abandon the expression, or issue
7698 warnings but evaluate the expression anyway.
7700 A range error can result from numerical overflow, from exceeding an
7701 array index bound, or when you type a constant that is not a member
7702 of any type. Some languages, however, do not treat overflows as an
7703 error. In many implementations of C, mathematical overflow causes the
7704 result to ``wrap around'' to lower values---for example, if @var{m} is
7705 the largest integer value, and @var{s} is the smallest, then
7708 @var{m} + 1 @result{} @var{s}
7711 This, too, is specific to individual languages, and in some cases
7712 specific to individual compilers or machines. @xref{Support, ,
7713 Supported languages}, for further details on specific languages.
7715 @value{GDBN} provides some additional commands for controlling the range checker:
7717 @kindex set check@r{, range}
7718 @kindex set check range
7719 @kindex show check range
7721 @item set check range auto
7722 Set range checking on or off based on the current working language.
7723 @xref{Support, ,Supported languages}, for the default settings for
7726 @item set check range on
7727 @itemx set check range off
7728 Set range checking on or off, overriding the default setting for the
7729 current working language. A warning is issued if the setting does not
7730 match the language default. If a range error occurs and range checking is on,
7731 then a message is printed and evaluation of the expression is aborted.
7733 @item set check range warn
7734 Output messages when the @value{GDBN} range checker detects a range error,
7735 but attempt to evaluate the expression anyway. Evaluating the
7736 expression may still be impossible for other reasons, such as accessing
7737 memory that the process does not own (a typical example from many Unix
7741 Show the current setting of the range checker, and whether or not it is
7742 being set automatically by @value{GDBN}.
7746 @section Supported languages
7748 @value{GDBN} supports C, C@t{++}, Fortran, Java, assembly, and Modula-2.
7749 @c This is false ...
7750 Some @value{GDBN} features may be used in expressions regardless of the
7751 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
7752 and the @samp{@{type@}addr} construct (@pxref{Expressions,
7753 ,Expressions}) can be used with the constructs of any supported
7756 The following sections detail to what degree each source language is
7757 supported by @value{GDBN}. These sections are not meant to be language
7758 tutorials or references, but serve only as a reference guide to what the
7759 @value{GDBN} expression parser accepts, and what input and output
7760 formats should look like for different languages. There are many good
7761 books written on each of these languages; please look to these for a
7762 language reference or tutorial.
7766 * Modula-2:: Modula-2
7770 @subsection C and C@t{++}
7772 @cindex C and C@t{++}
7773 @cindex expressions in C or C@t{++}
7775 Since C and C@t{++} are so closely related, many features of @value{GDBN} apply
7776 to both languages. Whenever this is the case, we discuss those languages
7780 @cindex @code{g++}, @sc{gnu} C@t{++} compiler
7781 @cindex @sc{gnu} C@t{++}
7782 The C@t{++} debugging facilities are jointly implemented by the C@t{++}
7783 compiler and @value{GDBN}. Therefore, to debug your C@t{++} code
7784 effectively, you must compile your C@t{++} programs with a supported
7785 C@t{++} compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C@t{++}
7786 compiler (@code{aCC}).
7788 For best results when using @sc{gnu} C@t{++}, use the stabs debugging
7789 format. You can select that format explicitly with the @code{g++}
7790 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
7791 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
7792 CC, gcc.info, Using @sc{gnu} CC}, for more information.
7795 * C Operators:: C and C@t{++} operators
7796 * C Constants:: C and C@t{++} constants
7797 * C plus plus expressions:: C@t{++} expressions
7798 * C Defaults:: Default settings for C and C@t{++}
7799 * C Checks:: C and C@t{++} type and range checks
7800 * Debugging C:: @value{GDBN} and C
7801 * Debugging C plus plus:: @value{GDBN} features for C@t{++}
7805 @subsubsection C and C@t{++} operators
7807 @cindex C and C@t{++} operators
7809 Operators must be defined on values of specific types. For instance,
7810 @code{+} is defined on numbers, but not on structures. Operators are
7811 often defined on groups of types.
7813 For the purposes of C and C@t{++}, the following definitions hold:
7818 @emph{Integral types} include @code{int} with any of its storage-class
7819 specifiers; @code{char}; @code{enum}; and, for C@t{++}, @code{bool}.
7822 @emph{Floating-point types} include @code{float}, @code{double}, and
7823 @code{long double} (if supported by the target platform).
7826 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
7829 @emph{Scalar types} include all of the above.
7834 The following operators are supported. They are listed here
7835 in order of increasing precedence:
7839 The comma or sequencing operator. Expressions in a comma-separated list
7840 are evaluated from left to right, with the result of the entire
7841 expression being the last expression evaluated.
7844 Assignment. The value of an assignment expression is the value
7845 assigned. Defined on scalar types.
7848 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
7849 and translated to @w{@code{@var{a} = @var{a op b}}}.
7850 @w{@code{@var{op}=}} and @code{=} have the same precedence.
7851 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
7852 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
7855 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
7856 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
7860 Logical @sc{or}. Defined on integral types.
7863 Logical @sc{and}. Defined on integral types.
7866 Bitwise @sc{or}. Defined on integral types.
7869 Bitwise exclusive-@sc{or}. Defined on integral types.
7872 Bitwise @sc{and}. Defined on integral types.
7875 Equality and inequality. Defined on scalar types. The value of these
7876 expressions is 0 for false and non-zero for true.
7878 @item <@r{, }>@r{, }<=@r{, }>=
7879 Less than, greater than, less than or equal, greater than or equal.
7880 Defined on scalar types. The value of these expressions is 0 for false
7881 and non-zero for true.
7884 left shift, and right shift. Defined on integral types.
7887 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
7890 Addition and subtraction. Defined on integral types, floating-point types and
7893 @item *@r{, }/@r{, }%
7894 Multiplication, division, and modulus. Multiplication and division are
7895 defined on integral and floating-point types. Modulus is defined on
7899 Increment and decrement. When appearing before a variable, the
7900 operation is performed before the variable is used in an expression;
7901 when appearing after it, the variable's value is used before the
7902 operation takes place.
7905 Pointer dereferencing. Defined on pointer types. Same precedence as
7909 Address operator. Defined on variables. Same precedence as @code{++}.
7911 For debugging C@t{++}, @value{GDBN} implements a use of @samp{&} beyond what is
7912 allowed in the C@t{++} language itself: you can use @samp{&(&@var{ref})}
7913 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
7914 where a C@t{++} reference variable (declared with @samp{&@var{ref}}) is
7918 Negative. Defined on integral and floating-point types. Same
7919 precedence as @code{++}.
7922 Logical negation. Defined on integral types. Same precedence as
7926 Bitwise complement operator. Defined on integral types. Same precedence as
7931 Structure member, and pointer-to-structure member. For convenience,
7932 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
7933 pointer based on the stored type information.
7934 Defined on @code{struct} and @code{union} data.
7937 Dereferences of pointers to members.
7940 Array indexing. @code{@var{a}[@var{i}]} is defined as
7941 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
7944 Function parameter list. Same precedence as @code{->}.
7947 C@t{++} scope resolution operator. Defined on @code{struct}, @code{union},
7948 and @code{class} types.
7951 Doubled colons also represent the @value{GDBN} scope operator
7952 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
7956 If an operator is redefined in the user code, @value{GDBN} usually
7957 attempts to invoke the redefined version instead of using the operator's
7965 @subsubsection C and C@t{++} constants
7967 @cindex C and C@t{++} constants
7969 @value{GDBN} allows you to express the constants of C and C@t{++} in the
7974 Integer constants are a sequence of digits. Octal constants are
7975 specified by a leading @samp{0} (i.e.@: zero), and hexadecimal constants
7976 by a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
7977 @samp{l}, specifying that the constant should be treated as a
7981 Floating point constants are a sequence of digits, followed by a decimal
7982 point, followed by a sequence of digits, and optionally followed by an
7983 exponent. An exponent is of the form:
7984 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
7985 sequence of digits. The @samp{+} is optional for positive exponents.
7986 A floating-point constant may also end with a letter @samp{f} or
7987 @samp{F}, specifying that the constant should be treated as being of
7988 the @code{float} (as opposed to the default @code{double}) type; or with
7989 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
7993 Enumerated constants consist of enumerated identifiers, or their
7994 integral equivalents.
7997 Character constants are a single character surrounded by single quotes
7998 (@code{'}), or a number---the ordinal value of the corresponding character
7999 (usually its @sc{ascii} value). Within quotes, the single character may
8000 be represented by a letter or by @dfn{escape sequences}, which are of
8001 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
8002 of the character's ordinal value; or of the form @samp{\@var{x}}, where
8003 @samp{@var{x}} is a predefined special character---for example,
8004 @samp{\n} for newline.
8007 String constants are a sequence of character constants surrounded by
8008 double quotes (@code{"}). Any valid character constant (as described
8009 above) may appear. Double quotes within the string must be preceded by
8010 a backslash, so for instance @samp{"a\"b'c"} is a string of five
8014 Pointer constants are an integral value. You can also write pointers
8015 to constants using the C operator @samp{&}.
8018 Array constants are comma-separated lists surrounded by braces @samp{@{}
8019 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
8020 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
8021 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
8025 * C plus plus expressions::
8032 @node C plus plus expressions
8033 @subsubsection C@t{++} expressions
8035 @cindex expressions in C@t{++}
8036 @value{GDBN} expression handling can interpret most C@t{++} expressions.
8038 @cindex C@t{++} support, not in @sc{coff}
8039 @cindex @sc{coff} versus C@t{++}
8040 @cindex C@t{++} and object formats
8041 @cindex object formats and C@t{++}
8042 @cindex a.out and C@t{++}
8043 @cindex @sc{ecoff} and C@t{++}
8044 @cindex @sc{xcoff} and C@t{++}
8045 @cindex @sc{elf}/stabs and C@t{++}
8046 @cindex @sc{elf}/@sc{dwarf} and C@t{++}
8047 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
8048 @c periodically whether this has happened...
8050 @emph{Warning:} @value{GDBN} can only debug C@t{++} code if you use the
8051 proper compiler. Typically, C@t{++} debugging depends on the use of
8052 additional debugging information in the symbol table, and thus requires
8053 special support. In particular, if your compiler generates a.out, MIPS
8054 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
8055 symbol table, these facilities are all available. (With @sc{gnu} CC,
8056 you can use the @samp{-gstabs} option to request stabs debugging
8057 extensions explicitly.) Where the object code format is standard
8058 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C@t{++}
8059 support in @value{GDBN} does @emph{not} work.
8064 @cindex member functions
8066 Member function calls are allowed; you can use expressions like
8069 count = aml->GetOriginal(x, y)
8072 @vindex this@r{, inside C@t{++} member functions}
8073 @cindex namespace in C@t{++}
8075 While a member function is active (in the selected stack frame), your
8076 expressions have the same namespace available as the member function;
8077 that is, @value{GDBN} allows implicit references to the class instance
8078 pointer @code{this} following the same rules as C@t{++}.
8080 @cindex call overloaded functions
8081 @cindex overloaded functions, calling
8082 @cindex type conversions in C@t{++}
8084 You can call overloaded functions; @value{GDBN} resolves the function
8085 call to the right definition, with some restrictions. @value{GDBN} does not
8086 perform overload resolution involving user-defined type conversions,
8087 calls to constructors, or instantiations of templates that do not exist
8088 in the program. It also cannot handle ellipsis argument lists or
8091 It does perform integral conversions and promotions, floating-point
8092 promotions, arithmetic conversions, pointer conversions, conversions of
8093 class objects to base classes, and standard conversions such as those of
8094 functions or arrays to pointers; it requires an exact match on the
8095 number of function arguments.
8097 Overload resolution is always performed, unless you have specified
8098 @code{set overload-resolution off}. @xref{Debugging C plus plus,
8099 ,@value{GDBN} features for C@t{++}}.
8101 You must specify @code{set overload-resolution off} in order to use an
8102 explicit function signature to call an overloaded function, as in
8104 p 'foo(char,int)'('x', 13)
8107 The @value{GDBN} command-completion facility can simplify this;
8108 see @ref{Completion, ,Command completion}.
8110 @cindex reference declarations
8112 @value{GDBN} understands variables declared as C@t{++} references; you can use
8113 them in expressions just as you do in C@t{++} source---they are automatically
8116 In the parameter list shown when @value{GDBN} displays a frame, the values of
8117 reference variables are not displayed (unlike other variables); this
8118 avoids clutter, since references are often used for large structures.
8119 The @emph{address} of a reference variable is always shown, unless
8120 you have specified @samp{set print address off}.
8123 @value{GDBN} supports the C@t{++} name resolution operator @code{::}---your
8124 expressions can use it just as expressions in your program do. Since
8125 one scope may be defined in another, you can use @code{::} repeatedly if
8126 necessary, for example in an expression like
8127 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
8128 resolving name scope by reference to source files, in both C and C@t{++}
8129 debugging (@pxref{Variables, ,Program variables}).
8132 In addition, when used with HP's C@t{++} compiler, @value{GDBN} supports
8133 calling virtual functions correctly, printing out virtual bases of
8134 objects, calling functions in a base subobject, casting objects, and
8135 invoking user-defined operators.
8138 @subsubsection C and C@t{++} defaults
8140 @cindex C and C@t{++} defaults
8142 If you allow @value{GDBN} to set type and range checking automatically, they
8143 both default to @code{off} whenever the working language changes to
8144 C or C@t{++}. This happens regardless of whether you or @value{GDBN}
8145 selects the working language.
8147 If you allow @value{GDBN} to set the language automatically, it
8148 recognizes source files whose names end with @file{.c}, @file{.C}, or
8149 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
8150 these files, it sets the working language to C or C@t{++}.
8151 @xref{Automatically, ,Having @value{GDBN} infer the source language},
8152 for further details.
8154 @c Type checking is (a) primarily motivated by Modula-2, and (b)
8155 @c unimplemented. If (b) changes, it might make sense to let this node
8156 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
8159 @subsubsection C and C@t{++} type and range checks
8161 @cindex C and C@t{++} checks
8163 By default, when @value{GDBN} parses C or C@t{++} expressions, type checking
8164 is not used. However, if you turn type checking on, @value{GDBN}
8165 considers two variables type equivalent if:
8169 The two variables are structured and have the same structure, union, or
8173 The two variables have the same type name, or types that have been
8174 declared equivalent through @code{typedef}.
8177 @c leaving this out because neither J Gilmore nor R Pesch understand it.
8180 The two @code{struct}, @code{union}, or @code{enum} variables are
8181 declared in the same declaration. (Note: this may not be true for all C
8186 Range checking, if turned on, is done on mathematical operations. Array
8187 indices are not checked, since they are often used to index a pointer
8188 that is not itself an array.
8191 @subsubsection @value{GDBN} and C
8193 The @code{set print union} and @code{show print union} commands apply to
8194 the @code{union} type. When set to @samp{on}, any @code{union} that is
8195 inside a @code{struct} or @code{class} is also printed. Otherwise, it
8196 appears as @samp{@{...@}}.
8198 The @code{@@} operator aids in the debugging of dynamic arrays, formed
8199 with pointers and a memory allocation function. @xref{Expressions,
8203 * Debugging C plus plus::
8206 @node Debugging C plus plus
8207 @subsubsection @value{GDBN} features for C@t{++}
8209 @cindex commands for C@t{++}
8211 Some @value{GDBN} commands are particularly useful with C@t{++}, and some are
8212 designed specifically for use with C@t{++}. Here is a summary:
8215 @cindex break in overloaded functions
8216 @item @r{breakpoint menus}
8217 When you want a breakpoint in a function whose name is overloaded,
8218 @value{GDBN} breakpoint menus help you specify which function definition
8219 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
8221 @cindex overloading in C@t{++}
8222 @item rbreak @var{regex}
8223 Setting breakpoints using regular expressions is helpful for setting
8224 breakpoints on overloaded functions that are not members of any special
8226 @xref{Set Breaks, ,Setting breakpoints}.
8228 @cindex C@t{++} exception handling
8231 Debug C@t{++} exception handling using these commands. @xref{Set
8232 Catchpoints, , Setting catchpoints}.
8235 @item ptype @var{typename}
8236 Print inheritance relationships as well as other information for type
8238 @xref{Symbols, ,Examining the Symbol Table}.
8240 @cindex C@t{++} symbol display
8241 @item set print demangle
8242 @itemx show print demangle
8243 @itemx set print asm-demangle
8244 @itemx show print asm-demangle
8245 Control whether C@t{++} symbols display in their source form, both when
8246 displaying code as C@t{++} source and when displaying disassemblies.
8247 @xref{Print Settings, ,Print settings}.
8249 @item set print object
8250 @itemx show print object
8251 Choose whether to print derived (actual) or declared types of objects.
8252 @xref{Print Settings, ,Print settings}.
8254 @item set print vtbl
8255 @itemx show print vtbl
8256 Control the format for printing virtual function tables.
8257 @xref{Print Settings, ,Print settings}.
8258 (The @code{vtbl} commands do not work on programs compiled with the HP
8259 ANSI C@t{++} compiler (@code{aCC}).)
8261 @kindex set overload-resolution
8262 @cindex overloaded functions, overload resolution
8263 @item set overload-resolution on
8264 Enable overload resolution for C@t{++} expression evaluation. The default
8265 is on. For overloaded functions, @value{GDBN} evaluates the arguments
8266 and searches for a function whose signature matches the argument types,
8267 using the standard C@t{++} conversion rules (see @ref{C plus plus expressions, ,C@t{++}
8268 expressions}, for details). If it cannot find a match, it emits a
8271 @item set overload-resolution off
8272 Disable overload resolution for C@t{++} expression evaluation. For
8273 overloaded functions that are not class member functions, @value{GDBN}
8274 chooses the first function of the specified name that it finds in the
8275 symbol table, whether or not its arguments are of the correct type. For
8276 overloaded functions that are class member functions, @value{GDBN}
8277 searches for a function whose signature @emph{exactly} matches the
8280 @item @r{Overloaded symbol names}
8281 You can specify a particular definition of an overloaded symbol, using
8282 the same notation that is used to declare such symbols in C@t{++}: type
8283 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
8284 also use the @value{GDBN} command-line word completion facilities to list the
8285 available choices, or to finish the type list for you.
8286 @xref{Completion,, Command completion}, for details on how to do this.
8290 @subsection Modula-2
8292 @cindex Modula-2, @value{GDBN} support
8294 The extensions made to @value{GDBN} to support Modula-2 only support
8295 output from the @sc{gnu} Modula-2 compiler (which is currently being
8296 developed). Other Modula-2 compilers are not currently supported, and
8297 attempting to debug executables produced by them is most likely
8298 to give an error as @value{GDBN} reads in the executable's symbol
8301 @cindex expressions in Modula-2
8303 * M2 Operators:: Built-in operators
8304 * Built-In Func/Proc:: Built-in functions and procedures
8305 * M2 Constants:: Modula-2 constants
8306 * M2 Defaults:: Default settings for Modula-2
8307 * Deviations:: Deviations from standard Modula-2
8308 * M2 Checks:: Modula-2 type and range checks
8309 * M2 Scope:: The scope operators @code{::} and @code{.}
8310 * GDB/M2:: @value{GDBN} and Modula-2
8314 @subsubsection Operators
8315 @cindex Modula-2 operators
8317 Operators must be defined on values of specific types. For instance,
8318 @code{+} is defined on numbers, but not on structures. Operators are
8319 often defined on groups of types. For the purposes of Modula-2, the
8320 following definitions hold:
8325 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
8329 @emph{Character types} consist of @code{CHAR} and its subranges.
8332 @emph{Floating-point types} consist of @code{REAL}.
8335 @emph{Pointer types} consist of anything declared as @code{POINTER TO
8339 @emph{Scalar types} consist of all of the above.
8342 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
8345 @emph{Boolean types} consist of @code{BOOLEAN}.
8349 The following operators are supported, and appear in order of
8350 increasing precedence:
8354 Function argument or array index separator.
8357 Assignment. The value of @var{var} @code{:=} @var{value} is
8361 Less than, greater than on integral, floating-point, or enumerated
8365 Less than or equal to, greater than or equal to
8366 on integral, floating-point and enumerated types, or set inclusion on
8367 set types. Same precedence as @code{<}.
8369 @item =@r{, }<>@r{, }#
8370 Equality and two ways of expressing inequality, valid on scalar types.
8371 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
8372 available for inequality, since @code{#} conflicts with the script
8376 Set membership. Defined on set types and the types of their members.
8377 Same precedence as @code{<}.
8380 Boolean disjunction. Defined on boolean types.
8383 Boolean conjunction. Defined on boolean types.
8386 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
8389 Addition and subtraction on integral and floating-point types, or union
8390 and difference on set types.
8393 Multiplication on integral and floating-point types, or set intersection
8397 Division on floating-point types, or symmetric set difference on set
8398 types. Same precedence as @code{*}.
8401 Integer division and remainder. Defined on integral types. Same
8402 precedence as @code{*}.
8405 Negative. Defined on @code{INTEGER} and @code{REAL} data.
8408 Pointer dereferencing. Defined on pointer types.
8411 Boolean negation. Defined on boolean types. Same precedence as
8415 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
8416 precedence as @code{^}.
8419 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
8422 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
8426 @value{GDBN} and Modula-2 scope operators.
8430 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
8431 treats the use of the operator @code{IN}, or the use of operators
8432 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
8433 @code{<=}, and @code{>=} on sets as an error.
8437 @node Built-In Func/Proc
8438 @subsubsection Built-in functions and procedures
8439 @cindex Modula-2 built-ins
8441 Modula-2 also makes available several built-in procedures and functions.
8442 In describing these, the following metavariables are used:
8447 represents an @code{ARRAY} variable.
8450 represents a @code{CHAR} constant or variable.
8453 represents a variable or constant of integral type.
8456 represents an identifier that belongs to a set. Generally used in the
8457 same function with the metavariable @var{s}. The type of @var{s} should
8458 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
8461 represents a variable or constant of integral or floating-point type.
8464 represents a variable or constant of floating-point type.
8470 represents a variable.
8473 represents a variable or constant of one of many types. See the
8474 explanation of the function for details.
8477 All Modula-2 built-in procedures also return a result, described below.
8481 Returns the absolute value of @var{n}.
8484 If @var{c} is a lower case letter, it returns its upper case
8485 equivalent, otherwise it returns its argument.
8488 Returns the character whose ordinal value is @var{i}.
8491 Decrements the value in the variable @var{v} by one. Returns the new value.
8493 @item DEC(@var{v},@var{i})
8494 Decrements the value in the variable @var{v} by @var{i}. Returns the
8497 @item EXCL(@var{m},@var{s})
8498 Removes the element @var{m} from the set @var{s}. Returns the new
8501 @item FLOAT(@var{i})
8502 Returns the floating point equivalent of the integer @var{i}.
8505 Returns the index of the last member of @var{a}.
8508 Increments the value in the variable @var{v} by one. Returns the new value.
8510 @item INC(@var{v},@var{i})
8511 Increments the value in the variable @var{v} by @var{i}. Returns the
8514 @item INCL(@var{m},@var{s})
8515 Adds the element @var{m} to the set @var{s} if it is not already
8516 there. Returns the new set.
8519 Returns the maximum value of the type @var{t}.
8522 Returns the minimum value of the type @var{t}.
8525 Returns boolean TRUE if @var{i} is an odd number.
8528 Returns the ordinal value of its argument. For example, the ordinal
8529 value of a character is its @sc{ascii} value (on machines supporting the
8530 @sc{ascii} character set). @var{x} must be of an ordered type, which include
8531 integral, character and enumerated types.
8534 Returns the size of its argument. @var{x} can be a variable or a type.
8536 @item TRUNC(@var{r})
8537 Returns the integral part of @var{r}.
8539 @item VAL(@var{t},@var{i})
8540 Returns the member of the type @var{t} whose ordinal value is @var{i}.
8544 @emph{Warning:} Sets and their operations are not yet supported, so
8545 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
8549 @cindex Modula-2 constants
8551 @subsubsection Constants
8553 @value{GDBN} allows you to express the constants of Modula-2 in the following
8559 Integer constants are simply a sequence of digits. When used in an
8560 expression, a constant is interpreted to be type-compatible with the
8561 rest of the expression. Hexadecimal integers are specified by a
8562 trailing @samp{H}, and octal integers by a trailing @samp{B}.
8565 Floating point constants appear as a sequence of digits, followed by a
8566 decimal point and another sequence of digits. An optional exponent can
8567 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
8568 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
8569 digits of the floating point constant must be valid decimal (base 10)
8573 Character constants consist of a single character enclosed by a pair of
8574 like quotes, either single (@code{'}) or double (@code{"}). They may
8575 also be expressed by their ordinal value (their @sc{ascii} value, usually)
8576 followed by a @samp{C}.
8579 String constants consist of a sequence of characters enclosed by a
8580 pair of like quotes, either single (@code{'}) or double (@code{"}).
8581 Escape sequences in the style of C are also allowed. @xref{C
8582 Constants, ,C and C@t{++} constants}, for a brief explanation of escape
8586 Enumerated constants consist of an enumerated identifier.
8589 Boolean constants consist of the identifiers @code{TRUE} and
8593 Pointer constants consist of integral values only.
8596 Set constants are not yet supported.
8600 @subsubsection Modula-2 defaults
8601 @cindex Modula-2 defaults
8603 If type and range checking are set automatically by @value{GDBN}, they
8604 both default to @code{on} whenever the working language changes to
8605 Modula-2. This happens regardless of whether you or @value{GDBN}
8606 selected the working language.
8608 If you allow @value{GDBN} to set the language automatically, then entering
8609 code compiled from a file whose name ends with @file{.mod} sets the
8610 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
8611 the language automatically}, for further details.
8614 @subsubsection Deviations from standard Modula-2
8615 @cindex Modula-2, deviations from
8617 A few changes have been made to make Modula-2 programs easier to debug.
8618 This is done primarily via loosening its type strictness:
8622 Unlike in standard Modula-2, pointer constants can be formed by
8623 integers. This allows you to modify pointer variables during
8624 debugging. (In standard Modula-2, the actual address contained in a
8625 pointer variable is hidden from you; it can only be modified
8626 through direct assignment to another pointer variable or expression that
8627 returned a pointer.)
8630 C escape sequences can be used in strings and characters to represent
8631 non-printable characters. @value{GDBN} prints out strings with these
8632 escape sequences embedded. Single non-printable characters are
8633 printed using the @samp{CHR(@var{nnn})} format.
8636 The assignment operator (@code{:=}) returns the value of its right-hand
8640 All built-in procedures both modify @emph{and} return their argument.
8644 @subsubsection Modula-2 type and range checks
8645 @cindex Modula-2 checks
8648 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
8651 @c FIXME remove warning when type/range checks added
8653 @value{GDBN} considers two Modula-2 variables type equivalent if:
8657 They are of types that have been declared equivalent via a @code{TYPE
8658 @var{t1} = @var{t2}} statement
8661 They have been declared on the same line. (Note: This is true of the
8662 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
8665 As long as type checking is enabled, any attempt to combine variables
8666 whose types are not equivalent is an error.
8668 Range checking is done on all mathematical operations, assignment, array
8669 index bounds, and all built-in functions and procedures.
8672 @subsubsection The scope operators @code{::} and @code{.}
8674 @cindex @code{.}, Modula-2 scope operator
8675 @cindex colon, doubled as scope operator
8677 @vindex colon-colon@r{, in Modula-2}
8678 @c Info cannot handle :: but TeX can.
8681 @vindex ::@r{, in Modula-2}
8684 There are a few subtle differences between the Modula-2 scope operator
8685 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
8690 @var{module} . @var{id}
8691 @var{scope} :: @var{id}
8695 where @var{scope} is the name of a module or a procedure,
8696 @var{module} the name of a module, and @var{id} is any declared
8697 identifier within your program, except another module.
8699 Using the @code{::} operator makes @value{GDBN} search the scope
8700 specified by @var{scope} for the identifier @var{id}. If it is not
8701 found in the specified scope, then @value{GDBN} searches all scopes
8702 enclosing the one specified by @var{scope}.
8704 Using the @code{.} operator makes @value{GDBN} search the current scope for
8705 the identifier specified by @var{id} that was imported from the
8706 definition module specified by @var{module}. With this operator, it is
8707 an error if the identifier @var{id} was not imported from definition
8708 module @var{module}, or if @var{id} is not an identifier in
8712 @subsubsection @value{GDBN} and Modula-2
8714 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
8715 Five subcommands of @code{set print} and @code{show print} apply
8716 specifically to C and C@t{++}: @samp{vtbl}, @samp{demangle},
8717 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
8718 apply to C@t{++}, and the last to the C @code{union} type, which has no direct
8719 analogue in Modula-2.
8721 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
8722 with any language, is not useful with Modula-2. Its
8723 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
8724 created in Modula-2 as they can in C or C@t{++}. However, because an
8725 address can be specified by an integral constant, the construct
8726 @samp{@{@var{type}@}@var{adrexp}} is still useful.
8728 @cindex @code{#} in Modula-2
8729 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
8730 interpreted as the beginning of a comment. Use @code{<>} instead.
8733 @chapter Examining the Symbol Table
8735 The commands described in this chapter allow you to inquire about the
8736 symbols (names of variables, functions and types) defined in your
8737 program. This information is inherent in the text of your program and
8738 does not change as your program executes. @value{GDBN} finds it in your
8739 program's symbol table, in the file indicated when you started @value{GDBN}
8740 (@pxref{File Options, ,Choosing files}), or by one of the
8741 file-management commands (@pxref{Files, ,Commands to specify files}).
8743 @cindex symbol names
8744 @cindex names of symbols
8745 @cindex quoting names
8746 Occasionally, you may need to refer to symbols that contain unusual
8747 characters, which @value{GDBN} ordinarily treats as word delimiters. The
8748 most frequent case is in referring to static variables in other
8749 source files (@pxref{Variables,,Program variables}). File names
8750 are recorded in object files as debugging symbols, but @value{GDBN} would
8751 ordinarily parse a typical file name, like @file{foo.c}, as the three words
8752 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
8753 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
8760 looks up the value of @code{x} in the scope of the file @file{foo.c}.
8763 @kindex info address
8764 @cindex address of a symbol
8765 @item info address @var{symbol}
8766 Describe where the data for @var{symbol} is stored. For a register
8767 variable, this says which register it is kept in. For a non-register
8768 local variable, this prints the stack-frame offset at which the variable
8771 Note the contrast with @samp{print &@var{symbol}}, which does not work
8772 at all for a register variable, and for a stack local variable prints
8773 the exact address of the current instantiation of the variable.
8776 @cindex symbol from address
8777 @item info symbol @var{addr}
8778 Print the name of a symbol which is stored at the address @var{addr}.
8779 If no symbol is stored exactly at @var{addr}, @value{GDBN} prints the
8780 nearest symbol and an offset from it:
8783 (@value{GDBP}) info symbol 0x54320
8784 _initialize_vx + 396 in section .text
8788 This is the opposite of the @code{info address} command. You can use
8789 it to find out the name of a variable or a function given its address.
8792 @item whatis @var{expr}
8793 Print the data type of expression @var{expr}. @var{expr} is not
8794 actually evaluated, and any side-effecting operations (such as
8795 assignments or function calls) inside it do not take place.
8796 @xref{Expressions, ,Expressions}.
8799 Print the data type of @code{$}, the last value in the value history.
8802 @item ptype @var{typename}
8803 Print a description of data type @var{typename}. @var{typename} may be
8804 the name of a type, or for C code it may have the form @samp{class
8805 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
8806 @var{union-tag}} or @samp{enum @var{enum-tag}}.
8808 @item ptype @var{expr}
8810 Print a description of the type of expression @var{expr}. @code{ptype}
8811 differs from @code{whatis} by printing a detailed description, instead
8812 of just the name of the type.
8814 For example, for this variable declaration:
8817 struct complex @{double real; double imag;@} v;
8821 the two commands give this output:
8825 (@value{GDBP}) whatis v
8826 type = struct complex
8827 (@value{GDBP}) ptype v
8828 type = struct complex @{
8836 As with @code{whatis}, using @code{ptype} without an argument refers to
8837 the type of @code{$}, the last value in the value history.
8840 @item info types @var{regexp}
8842 Print a brief description of all types whose names match @var{regexp}
8843 (or all types in your program, if you supply no argument). Each
8844 complete typename is matched as though it were a complete line; thus,
8845 @samp{i type value} gives information on all types in your program whose
8846 names include the string @code{value}, but @samp{i type ^value$} gives
8847 information only on types whose complete name is @code{value}.
8849 This command differs from @code{ptype} in two ways: first, like
8850 @code{whatis}, it does not print a detailed description; second, it
8851 lists all source files where a type is defined.
8854 @cindex local variables
8855 @item info scope @var{addr}
8856 List all the variables local to a particular scope. This command
8857 accepts a location---a function name, a source line, or an address
8858 preceded by a @samp{*}, and prints all the variables local to the
8859 scope defined by that location. For example:
8862 (@value{GDBP}) @b{info scope command_line_handler}
8863 Scope for command_line_handler:
8864 Symbol rl is an argument at stack/frame offset 8, length 4.
8865 Symbol linebuffer is in static storage at address 0x150a18, length 4.
8866 Symbol linelength is in static storage at address 0x150a1c, length 4.
8867 Symbol p is a local variable in register $esi, length 4.
8868 Symbol p1 is a local variable in register $ebx, length 4.
8869 Symbol nline is a local variable in register $edx, length 4.
8870 Symbol repeat is a local variable at frame offset -8, length 4.
8874 This command is especially useful for determining what data to collect
8875 during a @dfn{trace experiment}, see @ref{Tracepoint Actions,
8880 Show information about the current source file---that is, the source file for
8881 the function containing the current point of execution:
8884 the name of the source file, and the directory containing it,
8886 the directory it was compiled in,
8888 its length, in lines,
8890 which programming language it is written in,
8892 whether the executable includes debugging information for that file, and
8893 if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and
8895 whether the debugging information includes information about
8896 preprocessor macros.
8900 @kindex info sources
8902 Print the names of all source files in your program for which there is
8903 debugging information, organized into two lists: files whose symbols
8904 have already been read, and files whose symbols will be read when needed.
8906 @kindex info functions
8907 @item info functions
8908 Print the names and data types of all defined functions.
8910 @item info functions @var{regexp}
8911 Print the names and data types of all defined functions
8912 whose names contain a match for regular expression @var{regexp}.
8913 Thus, @samp{info fun step} finds all functions whose names
8914 include @code{step}; @samp{info fun ^step} finds those whose names
8915 start with @code{step}. If a function name contains characters
8916 that conflict with the regular expression language (eg.
8917 @samp{operator*()}), they may be quoted with a backslash.
8919 @kindex info variables
8920 @item info variables
8921 Print the names and data types of all variables that are declared
8922 outside of functions (i.e.@: excluding local variables).
8924 @item info variables @var{regexp}
8925 Print the names and data types of all variables (except for local
8926 variables) whose names contain a match for regular expression
8930 This was never implemented.
8931 @kindex info methods
8933 @itemx info methods @var{regexp}
8934 The @code{info methods} command permits the user to examine all defined
8935 methods within C@t{++} program, or (with the @var{regexp} argument) a
8936 specific set of methods found in the various C@t{++} classes. Many
8937 C@t{++} classes provide a large number of methods. Thus, the output
8938 from the @code{ptype} command can be overwhelming and hard to use. The
8939 @code{info-methods} command filters the methods, printing only those
8940 which match the regular-expression @var{regexp}.
8943 @cindex reloading symbols
8944 Some systems allow individual object files that make up your program to
8945 be replaced without stopping and restarting your program. For example,
8946 in VxWorks you can simply recompile a defective object file and keep on
8947 running. If you are running on one of these systems, you can allow
8948 @value{GDBN} to reload the symbols for automatically relinked modules:
8951 @kindex set symbol-reloading
8952 @item set symbol-reloading on
8953 Replace symbol definitions for the corresponding source file when an
8954 object file with a particular name is seen again.
8956 @item set symbol-reloading off
8957 Do not replace symbol definitions when encountering object files of the
8958 same name more than once. This is the default state; if you are not
8959 running on a system that permits automatic relinking of modules, you
8960 should leave @code{symbol-reloading} off, since otherwise @value{GDBN}
8961 may discard symbols when linking large programs, that may contain
8962 several modules (from different directories or libraries) with the same
8965 @kindex show symbol-reloading
8966 @item show symbol-reloading
8967 Show the current @code{on} or @code{off} setting.
8970 @kindex set opaque-type-resolution
8971 @item set opaque-type-resolution on
8972 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
8973 declared as a pointer to a @code{struct}, @code{class}, or
8974 @code{union}---for example, @code{struct MyType *}---that is used in one
8975 source file although the full declaration of @code{struct MyType} is in
8976 another source file. The default is on.
8978 A change in the setting of this subcommand will not take effect until
8979 the next time symbols for a file are loaded.
8981 @item set opaque-type-resolution off
8982 Tell @value{GDBN} not to resolve opaque types. In this case, the type
8983 is printed as follows:
8985 @{<no data fields>@}
8988 @kindex show opaque-type-resolution
8989 @item show opaque-type-resolution
8990 Show whether opaque types are resolved or not.
8992 @kindex maint print symbols
8994 @kindex maint print psymbols
8995 @cindex partial symbol dump
8996 @item maint print symbols @var{filename}
8997 @itemx maint print psymbols @var{filename}
8998 @itemx maint print msymbols @var{filename}
8999 Write a dump of debugging symbol data into the file @var{filename}.
9000 These commands are used to debug the @value{GDBN} symbol-reading code. Only
9001 symbols with debugging data are included. If you use @samp{maint print
9002 symbols}, @value{GDBN} includes all the symbols for which it has already
9003 collected full details: that is, @var{filename} reflects symbols for
9004 only those files whose symbols @value{GDBN} has read. You can use the
9005 command @code{info sources} to find out which files these are. If you
9006 use @samp{maint print psymbols} instead, the dump shows information about
9007 symbols that @value{GDBN} only knows partially---that is, symbols defined in
9008 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
9009 @samp{maint print msymbols} dumps just the minimal symbol information
9010 required for each object file from which @value{GDBN} has read some symbols.
9011 @xref{Files, ,Commands to specify files}, for a discussion of how
9012 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
9016 @chapter Altering Execution
9018 Once you think you have found an error in your program, you might want to
9019 find out for certain whether correcting the apparent error would lead to
9020 correct results in the rest of the run. You can find the answer by
9021 experiment, using the @value{GDBN} features for altering execution of the
9024 For example, you can store new values into variables or memory
9025 locations, give your program a signal, restart it at a different
9026 address, or even return prematurely from a function.
9029 * Assignment:: Assignment to variables
9030 * Jumping:: Continuing at a different address
9031 * Signaling:: Giving your program a signal
9032 * Returning:: Returning from a function
9033 * Calling:: Calling your program's functions
9034 * Patching:: Patching your program
9038 @section Assignment to variables
9041 @cindex setting variables
9042 To alter the value of a variable, evaluate an assignment expression.
9043 @xref{Expressions, ,Expressions}. For example,
9050 stores the value 4 into the variable @code{x}, and then prints the
9051 value of the assignment expression (which is 4).
9052 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
9053 information on operators in supported languages.
9055 @kindex set variable
9056 @cindex variables, setting
9057 If you are not interested in seeing the value of the assignment, use the
9058 @code{set} command instead of the @code{print} command. @code{set} is
9059 really the same as @code{print} except that the expression's value is
9060 not printed and is not put in the value history (@pxref{Value History,
9061 ,Value history}). The expression is evaluated only for its effects.
9063 If the beginning of the argument string of the @code{set} command
9064 appears identical to a @code{set} subcommand, use the @code{set
9065 variable} command instead of just @code{set}. This command is identical
9066 to @code{set} except for its lack of subcommands. For example, if your
9067 program has a variable @code{width}, you get an error if you try to set
9068 a new value with just @samp{set width=13}, because @value{GDBN} has the
9069 command @code{set width}:
9072 (@value{GDBP}) whatis width
9074 (@value{GDBP}) p width
9076 (@value{GDBP}) set width=47
9077 Invalid syntax in expression.
9081 The invalid expression, of course, is @samp{=47}. In
9082 order to actually set the program's variable @code{width}, use
9085 (@value{GDBP}) set var width=47
9088 Because the @code{set} command has many subcommands that can conflict
9089 with the names of program variables, it is a good idea to use the
9090 @code{set variable} command instead of just @code{set}. For example, if
9091 your program has a variable @code{g}, you run into problems if you try
9092 to set a new value with just @samp{set g=4}, because @value{GDBN} has
9093 the command @code{set gnutarget}, abbreviated @code{set g}:
9097 (@value{GDBP}) whatis g
9101 (@value{GDBP}) set g=4
9105 The program being debugged has been started already.
9106 Start it from the beginning? (y or n) y
9107 Starting program: /home/smith/cc_progs/a.out
9108 "/home/smith/cc_progs/a.out": can't open to read symbols:
9110 (@value{GDBP}) show g
9111 The current BFD target is "=4".
9116 The program variable @code{g} did not change, and you silently set the
9117 @code{gnutarget} to an invalid value. In order to set the variable
9121 (@value{GDBP}) set var g=4
9124 @value{GDBN} allows more implicit conversions in assignments than C; you can
9125 freely store an integer value into a pointer variable or vice versa,
9126 and you can convert any structure to any other structure that is the
9127 same length or shorter.
9128 @comment FIXME: how do structs align/pad in these conversions?
9129 @comment /doc@cygnus.com 18dec1990
9131 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
9132 construct to generate a value of specified type at a specified address
9133 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
9134 to memory location @code{0x83040} as an integer (which implies a certain size
9135 and representation in memory), and
9138 set @{int@}0x83040 = 4
9142 stores the value 4 into that memory location.
9145 @section Continuing at a different address
9147 Ordinarily, when you continue your program, you do so at the place where
9148 it stopped, with the @code{continue} command. You can instead continue at
9149 an address of your own choosing, with the following commands:
9153 @item jump @var{linespec}
9154 Resume execution at line @var{linespec}. Execution stops again
9155 immediately if there is a breakpoint there. @xref{List, ,Printing
9156 source lines}, for a description of the different forms of
9157 @var{linespec}. It is common practice to use the @code{tbreak} command
9158 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
9161 The @code{jump} command does not change the current stack frame, or
9162 the stack pointer, or the contents of any memory location or any
9163 register other than the program counter. If line @var{linespec} is in
9164 a different function from the one currently executing, the results may
9165 be bizarre if the two functions expect different patterns of arguments or
9166 of local variables. For this reason, the @code{jump} command requests
9167 confirmation if the specified line is not in the function currently
9168 executing. However, even bizarre results are predictable if you are
9169 well acquainted with the machine-language code of your program.
9171 @item jump *@var{address}
9172 Resume execution at the instruction at address @var{address}.
9175 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
9176 On many systems, you can get much the same effect as the @code{jump}
9177 command by storing a new value into the register @code{$pc}. The
9178 difference is that this does not start your program running; it only
9179 changes the address of where it @emph{will} run when you continue. For
9187 makes the next @code{continue} command or stepping command execute at
9188 address @code{0x485}, rather than at the address where your program stopped.
9189 @xref{Continuing and Stepping, ,Continuing and stepping}.
9191 The most common occasion to use the @code{jump} command is to back
9192 up---perhaps with more breakpoints set---over a portion of a program
9193 that has already executed, in order to examine its execution in more
9198 @section Giving your program a signal
9202 @item signal @var{signal}
9203 Resume execution where your program stopped, but immediately give it the
9204 signal @var{signal}. @var{signal} can be the name or the number of a
9205 signal. For example, on many systems @code{signal 2} and @code{signal
9206 SIGINT} are both ways of sending an interrupt signal.
9208 Alternatively, if @var{signal} is zero, continue execution without
9209 giving a signal. This is useful when your program stopped on account of
9210 a signal and would ordinary see the signal when resumed with the
9211 @code{continue} command; @samp{signal 0} causes it to resume without a
9214 @code{signal} does not repeat when you press @key{RET} a second time
9215 after executing the command.
9219 Invoking the @code{signal} command is not the same as invoking the
9220 @code{kill} utility from the shell. Sending a signal with @code{kill}
9221 causes @value{GDBN} to decide what to do with the signal depending on
9222 the signal handling tables (@pxref{Signals}). The @code{signal} command
9223 passes the signal directly to your program.
9227 @section Returning from a function
9230 @cindex returning from a function
9233 @itemx return @var{expression}
9234 You can cancel execution of a function call with the @code{return}
9235 command. If you give an
9236 @var{expression} argument, its value is used as the function's return
9240 When you use @code{return}, @value{GDBN} discards the selected stack frame
9241 (and all frames within it). You can think of this as making the
9242 discarded frame return prematurely. If you wish to specify a value to
9243 be returned, give that value as the argument to @code{return}.
9245 This pops the selected stack frame (@pxref{Selection, ,Selecting a
9246 frame}), and any other frames inside of it, leaving its caller as the
9247 innermost remaining frame. That frame becomes selected. The
9248 specified value is stored in the registers used for returning values
9251 The @code{return} command does not resume execution; it leaves the
9252 program stopped in the state that would exist if the function had just
9253 returned. In contrast, the @code{finish} command (@pxref{Continuing
9254 and Stepping, ,Continuing and stepping}) resumes execution until the
9255 selected stack frame returns naturally.
9258 @section Calling program functions
9260 @cindex calling functions
9263 @item call @var{expr}
9264 Evaluate the expression @var{expr} without displaying @code{void}
9268 You can use this variant of the @code{print} command if you want to
9269 execute a function from your program, but without cluttering the output
9270 with @code{void} returned values. If the result is not void, it
9271 is printed and saved in the value history.
9274 @section Patching programs
9276 @cindex patching binaries
9277 @cindex writing into executables
9278 @cindex writing into corefiles
9280 By default, @value{GDBN} opens the file containing your program's
9281 executable code (or the corefile) read-only. This prevents accidental
9282 alterations to machine code; but it also prevents you from intentionally
9283 patching your program's binary.
9285 If you'd like to be able to patch the binary, you can specify that
9286 explicitly with the @code{set write} command. For example, you might
9287 want to turn on internal debugging flags, or even to make emergency
9293 @itemx set write off
9294 If you specify @samp{set write on}, @value{GDBN} opens executable and
9295 core files for both reading and writing; if you specify @samp{set write
9296 off} (the default), @value{GDBN} opens them read-only.
9298 If you have already loaded a file, you must load it again (using the
9299 @code{exec-file} or @code{core-file} command) after changing @code{set
9300 write}, for your new setting to take effect.
9304 Display whether executable files and core files are opened for writing
9309 @chapter @value{GDBN} Files
9311 @value{GDBN} needs to know the file name of the program to be debugged,
9312 both in order to read its symbol table and in order to start your
9313 program. To debug a core dump of a previous run, you must also tell
9314 @value{GDBN} the name of the core dump file.
9317 * Files:: Commands to specify files
9318 * Symbol Errors:: Errors reading symbol files
9322 @section Commands to specify files
9324 @cindex symbol table
9325 @cindex core dump file
9327 You may want to specify executable and core dump file names. The usual
9328 way to do this is at start-up time, using the arguments to
9329 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
9330 Out of @value{GDBN}}).
9332 Occasionally it is necessary to change to a different file during a
9333 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
9334 a file you want to use. In these situations the @value{GDBN} commands
9335 to specify new files are useful.
9338 @cindex executable file
9340 @item file @var{filename}
9341 Use @var{filename} as the program to be debugged. It is read for its
9342 symbols and for the contents of pure memory. It is also the program
9343 executed when you use the @code{run} command. If you do not specify a
9344 directory and the file is not found in the @value{GDBN} working directory,
9345 @value{GDBN} uses the environment variable @code{PATH} as a list of
9346 directories to search, just as the shell does when looking for a program
9347 to run. You can change the value of this variable, for both @value{GDBN}
9348 and your program, using the @code{path} command.
9350 On systems with memory-mapped files, an auxiliary file named
9351 @file{@var{filename}.syms} may hold symbol table information for
9352 @var{filename}. If so, @value{GDBN} maps in the symbol table from
9353 @file{@var{filename}.syms}, starting up more quickly. See the
9354 descriptions of the file options @samp{-mapped} and @samp{-readnow}
9355 (available on the command line, and with the commands @code{file},
9356 @code{symbol-file}, or @code{add-symbol-file}, described below),
9357 for more information.
9360 @code{file} with no argument makes @value{GDBN} discard any information it
9361 has on both executable file and the symbol table.
9364 @item exec-file @r{[} @var{filename} @r{]}
9365 Specify that the program to be run (but not the symbol table) is found
9366 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
9367 if necessary to locate your program. Omitting @var{filename} means to
9368 discard information on the executable file.
9371 @item symbol-file @r{[} @var{filename} @r{]}
9372 Read symbol table information from file @var{filename}. @code{PATH} is
9373 searched when necessary. Use the @code{file} command to get both symbol
9374 table and program to run from the same file.
9376 @code{symbol-file} with no argument clears out @value{GDBN} information on your
9377 program's symbol table.
9379 The @code{symbol-file} command causes @value{GDBN} to forget the contents
9380 of its convenience variables, the value history, and all breakpoints and
9381 auto-display expressions. This is because they may contain pointers to
9382 the internal data recording symbols and data types, which are part of
9383 the old symbol table data being discarded inside @value{GDBN}.
9385 @code{symbol-file} does not repeat if you press @key{RET} again after
9388 When @value{GDBN} is configured for a particular environment, it
9389 understands debugging information in whatever format is the standard
9390 generated for that environment; you may use either a @sc{gnu} compiler, or
9391 other compilers that adhere to the local conventions.
9392 Best results are usually obtained from @sc{gnu} compilers; for example,
9393 using @code{@value{GCC}} you can generate debugging information for
9396 For most kinds of object files, with the exception of old SVR3 systems
9397 using COFF, the @code{symbol-file} command does not normally read the
9398 symbol table in full right away. Instead, it scans the symbol table
9399 quickly to find which source files and which symbols are present. The
9400 details are read later, one source file at a time, as they are needed.
9402 The purpose of this two-stage reading strategy is to make @value{GDBN}
9403 start up faster. For the most part, it is invisible except for
9404 occasional pauses while the symbol table details for a particular source
9405 file are being read. (The @code{set verbose} command can turn these
9406 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
9407 warnings and messages}.)
9409 We have not implemented the two-stage strategy for COFF yet. When the
9410 symbol table is stored in COFF format, @code{symbol-file} reads the
9411 symbol table data in full right away. Note that ``stabs-in-COFF''
9412 still does the two-stage strategy, since the debug info is actually
9416 @cindex reading symbols immediately
9417 @cindex symbols, reading immediately
9419 @cindex memory-mapped symbol file
9420 @cindex saving symbol table
9421 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9422 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9423 You can override the @value{GDBN} two-stage strategy for reading symbol
9424 tables by using the @samp{-readnow} option with any of the commands that
9425 load symbol table information, if you want to be sure @value{GDBN} has the
9426 entire symbol table available.
9428 If memory-mapped files are available on your system through the
9429 @code{mmap} system call, you can use another option, @samp{-mapped}, to
9430 cause @value{GDBN} to write the symbols for your program into a reusable
9431 file. Future @value{GDBN} debugging sessions map in symbol information
9432 from this auxiliary symbol file (if the program has not changed), rather
9433 than spending time reading the symbol table from the executable
9434 program. Using the @samp{-mapped} option has the same effect as
9435 starting @value{GDBN} with the @samp{-mapped} command-line option.
9437 You can use both options together, to make sure the auxiliary symbol
9438 file has all the symbol information for your program.
9440 The auxiliary symbol file for a program called @var{myprog} is called
9441 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
9442 than the corresponding executable), @value{GDBN} always attempts to use
9443 it when you debug @var{myprog}; no special options or commands are
9446 The @file{.syms} file is specific to the host machine where you run
9447 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
9448 symbol table. It cannot be shared across multiple host platforms.
9450 @c FIXME: for now no mention of directories, since this seems to be in
9451 @c flux. 13mar1992 status is that in theory GDB would look either in
9452 @c current dir or in same dir as myprog; but issues like competing
9453 @c GDB's, or clutter in system dirs, mean that in practice right now
9454 @c only current dir is used. FFish says maybe a special GDB hierarchy
9455 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
9460 @item core-file @r{[} @var{filename} @r{]}
9461 Specify the whereabouts of a core dump file to be used as the ``contents
9462 of memory''. Traditionally, core files contain only some parts of the
9463 address space of the process that generated them; @value{GDBN} can access the
9464 executable file itself for other parts.
9466 @code{core-file} with no argument specifies that no core file is
9469 Note that the core file is ignored when your program is actually running
9470 under @value{GDBN}. So, if you have been running your program and you
9471 wish to debug a core file instead, you must kill the subprocess in which
9472 the program is running. To do this, use the @code{kill} command
9473 (@pxref{Kill Process, ,Killing the child process}).
9475 @kindex add-symbol-file
9476 @cindex dynamic linking
9477 @item add-symbol-file @var{filename} @var{address}
9478 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
9479 @itemx add-symbol-file @var{filename} @r{-s}@var{section} @var{address} @dots{}
9480 The @code{add-symbol-file} command reads additional symbol table
9481 information from the file @var{filename}. You would use this command
9482 when @var{filename} has been dynamically loaded (by some other means)
9483 into the program that is running. @var{address} should be the memory
9484 address at which the file has been loaded; @value{GDBN} cannot figure
9485 this out for itself. You can additionally specify an arbitrary number
9486 of @samp{@r{-s}@var{section} @var{address}} pairs, to give an explicit
9487 section name and base address for that section. You can specify any
9488 @var{address} as an expression.
9490 The symbol table of the file @var{filename} is added to the symbol table
9491 originally read with the @code{symbol-file} command. You can use the
9492 @code{add-symbol-file} command any number of times; the new symbol data
9493 thus read keeps adding to the old. To discard all old symbol data
9494 instead, use the @code{symbol-file} command without any arguments.
9496 @cindex relocatable object files, reading symbols from
9497 @cindex object files, relocatable, reading symbols from
9498 @cindex reading symbols from relocatable object files
9499 @cindex symbols, reading from relocatable object files
9500 @cindex @file{.o} files, reading symbols from
9501 Although @var{filename} is typically a shared library file, an
9502 executable file, or some other object file which has been fully
9503 relocated for loading into a process, you can also load symbolic
9504 information from relocatable @file{.o} files, as long as:
9508 the file's symbolic information refers only to linker symbols defined in
9509 that file, not to symbols defined by other object files,
9511 every section the file's symbolic information refers to has actually
9512 been loaded into the inferior, as it appears in the file, and
9514 you can determine the address at which every section was loaded, and
9515 provide these to the @code{add-symbol-file} command.
9519 Some embedded operating systems, like Sun Chorus and VxWorks, can load
9520 relocatable files into an already running program; such systems
9521 typically make the requirements above easy to meet. However, it's
9522 important to recognize that many native systems use complex link
9523 procedures (@code{.linkonce} section factoring and C++ constructor table
9524 assembly, for example) that make the requirements difficult to meet. In
9525 general, one cannot assume that using @code{add-symbol-file} to read a
9526 relocatable object file's symbolic information will have the same effect
9527 as linking the relocatable object file into the program in the normal
9530 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
9532 You can use the @samp{-mapped} and @samp{-readnow} options just as with
9533 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
9534 table information for @var{filename}.
9536 @kindex add-shared-symbol-file
9537 @item add-shared-symbol-file
9538 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
9539 operating system for the Motorola 88k. @value{GDBN} automatically looks for
9540 shared libraries, however if @value{GDBN} does not find yours, you can run
9541 @code{add-shared-symbol-file}. It takes no arguments.
9545 The @code{section} command changes the base address of section SECTION of
9546 the exec file to ADDR. This can be used if the exec file does not contain
9547 section addresses, (such as in the a.out format), or when the addresses
9548 specified in the file itself are wrong. Each section must be changed
9549 separately. The @code{info files} command, described below, lists all
9550 the sections and their addresses.
9556 @code{info files} and @code{info target} are synonymous; both print the
9557 current target (@pxref{Targets, ,Specifying a Debugging Target}),
9558 including the names of the executable and core dump files currently in
9559 use by @value{GDBN}, and the files from which symbols were loaded. The
9560 command @code{help target} lists all possible targets rather than
9563 @kindex maint info sections
9564 @item maint info sections
9565 Another command that can give you extra information about program sections
9566 is @code{maint info sections}. In addition to the section information
9567 displayed by @code{info files}, this command displays the flags and file
9568 offset of each section in the executable and core dump files. In addition,
9569 @code{maint info sections} provides the following command options (which
9570 may be arbitrarily combined):
9574 Display sections for all loaded object files, including shared libraries.
9575 @item @var{sections}
9576 Display info only for named @var{sections}.
9577 @item @var{section-flags}
9578 Display info only for sections for which @var{section-flags} are true.
9579 The section flags that @value{GDBN} currently knows about are:
9582 Section will have space allocated in the process when loaded.
9583 Set for all sections except those containing debug information.
9585 Section will be loaded from the file into the child process memory.
9586 Set for pre-initialized code and data, clear for @code{.bss} sections.
9588 Section needs to be relocated before loading.
9590 Section cannot be modified by the child process.
9592 Section contains executable code only.
9594 Section contains data only (no executable code).
9596 Section will reside in ROM.
9598 Section contains data for constructor/destructor lists.
9600 Section is not empty.
9602 An instruction to the linker to not output the section.
9603 @item COFF_SHARED_LIBRARY
9604 A notification to the linker that the section contains
9605 COFF shared library information.
9607 Section contains common symbols.
9610 @kindex set trust-readonly-sections
9611 @item set trust-readonly-sections on
9612 Tell @value{GDBN} that readonly sections in your object file
9613 really are read-only (i.e.@: that their contents will not change).
9614 In that case, @value{GDBN} can fetch values from these sections
9615 out of the object file, rather than from the target program.
9616 For some targets (notably embedded ones), this can be a significant
9617 enhancement to debugging performance.
9621 @item set trust-readonly-sections off
9622 Tell @value{GDBN} not to trust readonly sections. This means that
9623 the contents of the section might change while the program is running,
9624 and must therefore be fetched from the target when needed.
9627 All file-specifying commands allow both absolute and relative file names
9628 as arguments. @value{GDBN} always converts the file name to an absolute file
9629 name and remembers it that way.
9631 @cindex shared libraries
9632 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
9635 @value{GDBN} automatically loads symbol definitions from shared libraries
9636 when you use the @code{run} command, or when you examine a core file.
9637 (Before you issue the @code{run} command, @value{GDBN} does not understand
9638 references to a function in a shared library, however---unless you are
9639 debugging a core file).
9641 On HP-UX, if the program loads a library explicitly, @value{GDBN}
9642 automatically loads the symbols at the time of the @code{shl_load} call.
9644 @c FIXME: some @value{GDBN} release may permit some refs to undef
9645 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
9646 @c FIXME...lib; check this from time to time when updating manual
9648 There are times, however, when you may wish to not automatically load
9649 symbol definitions from shared libraries, such as when they are
9650 particularly large or there are many of them.
9652 To control the automatic loading of shared library symbols, use the
9656 @kindex set auto-solib-add
9657 @item set auto-solib-add @var{mode}
9658 If @var{mode} is @code{on}, symbols from all shared object libraries
9659 will be loaded automatically when the inferior begins execution, you
9660 attach to an independently started inferior, or when the dynamic linker
9661 informs @value{GDBN} that a new library has been loaded. If @var{mode}
9662 is @code{off}, symbols must be loaded manually, using the
9663 @code{sharedlibrary} command. The default value is @code{on}.
9665 @kindex show auto-solib-add
9666 @item show auto-solib-add
9667 Display the current autoloading mode.
9670 To explicitly load shared library symbols, use the @code{sharedlibrary}
9674 @kindex info sharedlibrary
9677 @itemx info sharedlibrary
9678 Print the names of the shared libraries which are currently loaded.
9680 @kindex sharedlibrary
9682 @item sharedlibrary @var{regex}
9683 @itemx share @var{regex}
9684 Load shared object library symbols for files matching a
9685 Unix regular expression.
9686 As with files loaded automatically, it only loads shared libraries
9687 required by your program for a core file or after typing @code{run}. If
9688 @var{regex} is omitted all shared libraries required by your program are
9692 On some systems, such as HP-UX systems, @value{GDBN} supports
9693 autoloading shared library symbols until a limiting threshold size is
9694 reached. This provides the benefit of allowing autoloading to remain on
9695 by default, but avoids autoloading excessively large shared libraries,
9696 up to a threshold that is initially set, but which you can modify if you
9699 Beyond that threshold, symbols from shared libraries must be explicitly
9700 loaded. To load these symbols, use the command @code{sharedlibrary
9701 @var{filename}}. The base address of the shared library is determined
9702 automatically by @value{GDBN} and need not be specified.
9704 To display or set the threshold, use the commands:
9707 @kindex set auto-solib-limit
9708 @item set auto-solib-limit @var{threshold}
9709 Set the autoloading size threshold, in an integral number of megabytes.
9710 If @var{threshold} is nonzero and shared library autoloading is enabled,
9711 symbols from all shared object libraries will be loaded until the total
9712 size of the loaded shared library symbols exceeds this threshold.
9713 Otherwise, symbols must be loaded manually, using the
9714 @code{sharedlibrary} command. The default threshold is 100 (i.e.@: 100
9717 @kindex show auto-solib-limit
9718 @item show auto-solib-limit
9719 Display the current autoloading size threshold, in megabytes.
9722 Shared libraries are also supported in many cross or remote debugging
9723 configurations. A copy of the target's libraries need to be present on the
9724 host system; they need to be the same as the target libraries, although the
9725 copies on the target can be stripped as long as the copies on the host are
9728 You need to tell @value{GDBN} where the target libraries are, so that it can
9729 load the correct copies---otherwise, it may try to load the host's libraries.
9730 @value{GDBN} has two variables to specify the search directories for target
9734 @kindex set solib-absolute-prefix
9735 @item set solib-absolute-prefix @var{path}
9736 If this variable is set, @var{path} will be used as a prefix for any
9737 absolute shared library paths; many runtime loaders store the absolute
9738 paths to the shared library in the target program's memory. If you use
9739 @samp{solib-absolute-prefix} to find shared libraries, they need to be laid
9740 out in the same way that they are on the target, with e.g.@: a
9741 @file{/usr/lib} hierarchy under @var{path}.
9743 You can set the default value of @samp{solib-absolute-prefix} by using the
9744 configure-time @samp{--with-sysroot} option.
9746 @kindex show solib-absolute-prefix
9747 @item show solib-absolute-prefix
9748 Display the current shared library prefix.
9750 @kindex set solib-search-path
9751 @item set solib-search-path @var{path}
9752 If this variable is set, @var{path} is a colon-separated list of directories
9753 to search for shared libraries. @samp{solib-search-path} is used after
9754 @samp{solib-absolute-prefix} fails to locate the library, or if the path to
9755 the library is relative instead of absolute. If you want to use
9756 @samp{solib-search-path} instead of @samp{solib-absolute-prefix}, be sure to
9757 set @samp{solib-absolute-prefix} to a nonexistant directory to prevent
9758 @value{GDBN} from finding your host's libraries.
9760 @kindex show solib-search-path
9761 @item show solib-search-path
9762 Display the current shared library search path.
9766 @section Errors reading symbol files
9768 While reading a symbol file, @value{GDBN} occasionally encounters problems,
9769 such as symbol types it does not recognize, or known bugs in compiler
9770 output. By default, @value{GDBN} does not notify you of such problems, since
9771 they are relatively common and primarily of interest to people
9772 debugging compilers. If you are interested in seeing information
9773 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
9774 only one message about each such type of problem, no matter how many
9775 times the problem occurs; or you can ask @value{GDBN} to print more messages,
9776 to see how many times the problems occur, with the @code{set
9777 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
9780 The messages currently printed, and their meanings, include:
9783 @item inner block not inside outer block in @var{symbol}
9785 The symbol information shows where symbol scopes begin and end
9786 (such as at the start of a function or a block of statements). This
9787 error indicates that an inner scope block is not fully contained
9788 in its outer scope blocks.
9790 @value{GDBN} circumvents the problem by treating the inner block as if it had
9791 the same scope as the outer block. In the error message, @var{symbol}
9792 may be shown as ``@code{(don't know)}'' if the outer block is not a
9795 @item block at @var{address} out of order
9797 The symbol information for symbol scope blocks should occur in
9798 order of increasing addresses. This error indicates that it does not
9801 @value{GDBN} does not circumvent this problem, and has trouble
9802 locating symbols in the source file whose symbols it is reading. (You
9803 can often determine what source file is affected by specifying
9804 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
9807 @item bad block start address patched
9809 The symbol information for a symbol scope block has a start address
9810 smaller than the address of the preceding source line. This is known
9811 to occur in the SunOS 4.1.1 (and earlier) C compiler.
9813 @value{GDBN} circumvents the problem by treating the symbol scope block as
9814 starting on the previous source line.
9816 @item bad string table offset in symbol @var{n}
9819 Symbol number @var{n} contains a pointer into the string table which is
9820 larger than the size of the string table.
9822 @value{GDBN} circumvents the problem by considering the symbol to have the
9823 name @code{foo}, which may cause other problems if many symbols end up
9826 @item unknown symbol type @code{0x@var{nn}}
9828 The symbol information contains new data types that @value{GDBN} does
9829 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
9830 uncomprehended information, in hexadecimal.
9832 @value{GDBN} circumvents the error by ignoring this symbol information.
9833 This usually allows you to debug your program, though certain symbols
9834 are not accessible. If you encounter such a problem and feel like
9835 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
9836 on @code{complain}, then go up to the function @code{read_dbx_symtab}
9837 and examine @code{*bufp} to see the symbol.
9839 @item stub type has NULL name
9841 @value{GDBN} could not find the full definition for a struct or class.
9843 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
9844 The symbol information for a C@t{++} member function is missing some
9845 information that recent versions of the compiler should have output for
9848 @item info mismatch between compiler and debugger
9850 @value{GDBN} could not parse a type specification output by the compiler.
9855 @chapter Specifying a Debugging Target
9857 @cindex debugging target
9860 A @dfn{target} is the execution environment occupied by your program.
9862 Often, @value{GDBN} runs in the same host environment as your program;
9863 in that case, the debugging target is specified as a side effect when
9864 you use the @code{file} or @code{core} commands. When you need more
9865 flexibility---for example, running @value{GDBN} on a physically separate
9866 host, or controlling a standalone system over a serial port or a
9867 realtime system over a TCP/IP connection---you can use the @code{target}
9868 command to specify one of the target types configured for @value{GDBN}
9869 (@pxref{Target Commands, ,Commands for managing targets}).
9872 * Active Targets:: Active targets
9873 * Target Commands:: Commands for managing targets
9874 * Byte Order:: Choosing target byte order
9875 * Remote:: Remote debugging
9876 * KOD:: Kernel Object Display
9880 @node Active Targets
9881 @section Active targets
9883 @cindex stacking targets
9884 @cindex active targets
9885 @cindex multiple targets
9887 There are three classes of targets: processes, core files, and
9888 executable files. @value{GDBN} can work concurrently on up to three
9889 active targets, one in each class. This allows you to (for example)
9890 start a process and inspect its activity without abandoning your work on
9893 For example, if you execute @samp{gdb a.out}, then the executable file
9894 @code{a.out} is the only active target. If you designate a core file as
9895 well---presumably from a prior run that crashed and coredumped---then
9896 @value{GDBN} has two active targets and uses them in tandem, looking
9897 first in the corefile target, then in the executable file, to satisfy
9898 requests for memory addresses. (Typically, these two classes of target
9899 are complementary, since core files contain only a program's
9900 read-write memory---variables and so on---plus machine status, while
9901 executable files contain only the program text and initialized data.)
9903 When you type @code{run}, your executable file becomes an active process
9904 target as well. When a process target is active, all @value{GDBN}
9905 commands requesting memory addresses refer to that target; addresses in
9906 an active core file or executable file target are obscured while the
9907 process target is active.
9909 Use the @code{core-file} and @code{exec-file} commands to select a new
9910 core file or executable target (@pxref{Files, ,Commands to specify
9911 files}). To specify as a target a process that is already running, use
9912 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
9915 @node Target Commands
9916 @section Commands for managing targets
9919 @item target @var{type} @var{parameters}
9920 Connects the @value{GDBN} host environment to a target machine or
9921 process. A target is typically a protocol for talking to debugging
9922 facilities. You use the argument @var{type} to specify the type or
9923 protocol of the target machine.
9925 Further @var{parameters} are interpreted by the target protocol, but
9926 typically include things like device names or host names to connect
9927 with, process numbers, and baud rates.
9929 The @code{target} command does not repeat if you press @key{RET} again
9930 after executing the command.
9934 Displays the names of all targets available. To display targets
9935 currently selected, use either @code{info target} or @code{info files}
9936 (@pxref{Files, ,Commands to specify files}).
9938 @item help target @var{name}
9939 Describe a particular target, including any parameters necessary to
9942 @kindex set gnutarget
9943 @item set gnutarget @var{args}
9944 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
9945 knows whether it is reading an @dfn{executable},
9946 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
9947 with the @code{set gnutarget} command. Unlike most @code{target} commands,
9948 with @code{gnutarget} the @code{target} refers to a program, not a machine.
9951 @emph{Warning:} To specify a file format with @code{set gnutarget},
9952 you must know the actual BFD name.
9956 @xref{Files, , Commands to specify files}.
9958 @kindex show gnutarget
9959 @item show gnutarget
9960 Use the @code{show gnutarget} command to display what file format
9961 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
9962 @value{GDBN} will determine the file format for each file automatically,
9963 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
9966 Here are some common targets (available, or not, depending on the GDB
9971 @item target exec @var{program}
9972 An executable file. @samp{target exec @var{program}} is the same as
9973 @samp{exec-file @var{program}}.
9976 @item target core @var{filename}
9977 A core dump file. @samp{target core @var{filename}} is the same as
9978 @samp{core-file @var{filename}}.
9980 @kindex target remote
9981 @item target remote @var{dev}
9982 Remote serial target in GDB-specific protocol. The argument @var{dev}
9983 specifies what serial device to use for the connection (e.g.
9984 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
9985 supports the @code{load} command. This is only useful if you have
9986 some other way of getting the stub to the target system, and you can put
9987 it somewhere in memory where it won't get clobbered by the download.
9991 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
9999 works; however, you cannot assume that a specific memory map, device
10000 drivers, or even basic I/O is available, although some simulators do
10001 provide these. For info about any processor-specific simulator details,
10002 see the appropriate section in @ref{Embedded Processors, ,Embedded
10007 Some configurations may include these targets as well:
10011 @kindex target nrom
10012 @item target nrom @var{dev}
10013 NetROM ROM emulator. This target only supports downloading.
10017 Different targets are available on different configurations of @value{GDBN};
10018 your configuration may have more or fewer targets.
10020 Many remote targets require you to download the executable's code
10021 once you've successfully established a connection.
10025 @kindex load @var{filename}
10026 @item load @var{filename}
10027 Depending on what remote debugging facilities are configured into
10028 @value{GDBN}, the @code{load} command may be available. Where it exists, it
10029 is meant to make @var{filename} (an executable) available for debugging
10030 on the remote system---by downloading, or dynamic linking, for example.
10031 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
10032 the @code{add-symbol-file} command.
10034 If your @value{GDBN} does not have a @code{load} command, attempting to
10035 execute it gets the error message ``@code{You can't do that when your
10036 target is @dots{}}''
10038 The file is loaded at whatever address is specified in the executable.
10039 For some object file formats, you can specify the load address when you
10040 link the program; for other formats, like a.out, the object file format
10041 specifies a fixed address.
10042 @c FIXME! This would be a good place for an xref to the GNU linker doc.
10044 @code{load} does not repeat if you press @key{RET} again after using it.
10048 @section Choosing target byte order
10050 @cindex choosing target byte order
10051 @cindex target byte order
10053 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
10054 offer the ability to run either big-endian or little-endian byte
10055 orders. Usually the executable or symbol will include a bit to
10056 designate the endian-ness, and you will not need to worry about
10057 which to use. However, you may still find it useful to adjust
10058 @value{GDBN}'s idea of processor endian-ness manually.
10061 @kindex set endian big
10062 @item set endian big
10063 Instruct @value{GDBN} to assume the target is big-endian.
10065 @kindex set endian little
10066 @item set endian little
10067 Instruct @value{GDBN} to assume the target is little-endian.
10069 @kindex set endian auto
10070 @item set endian auto
10071 Instruct @value{GDBN} to use the byte order associated with the
10075 Display @value{GDBN}'s current idea of the target byte order.
10079 Note that these commands merely adjust interpretation of symbolic
10080 data on the host, and that they have absolutely no effect on the
10084 @section Remote debugging
10085 @cindex remote debugging
10087 If you are trying to debug a program running on a machine that cannot run
10088 @value{GDBN} in the usual way, it is often useful to use remote debugging.
10089 For example, you might use remote debugging on an operating system kernel,
10090 or on a small system which does not have a general purpose operating system
10091 powerful enough to run a full-featured debugger.
10093 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
10094 to make this work with particular debugging targets. In addition,
10095 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
10096 but not specific to any particular target system) which you can use if you
10097 write the remote stubs---the code that runs on the remote system to
10098 communicate with @value{GDBN}.
10100 Other remote targets may be available in your
10101 configuration of @value{GDBN}; use @code{help target} to list them.
10104 @section Kernel Object Display
10106 @cindex kernel object display
10107 @cindex kernel object
10110 Some targets support kernel object display. Using this facility,
10111 @value{GDBN} communicates specially with the underlying operating system
10112 and can display information about operating system-level objects such as
10113 mutexes and other synchronization objects. Exactly which objects can be
10114 displayed is determined on a per-OS basis.
10116 Use the @code{set os} command to set the operating system. This tells
10117 @value{GDBN} which kernel object display module to initialize:
10120 (@value{GDBP}) set os cisco
10123 If @code{set os} succeeds, @value{GDBN} will display some information
10124 about the operating system, and will create a new @code{info} command
10125 which can be used to query the target. The @code{info} command is named
10126 after the operating system:
10129 (@value{GDBP}) info cisco
10130 List of Cisco Kernel Objects
10132 any Any and all objects
10135 Further subcommands can be used to query about particular objects known
10138 There is currently no way to determine whether a given operating system
10139 is supported other than to try it.
10142 @node Remote Debugging
10143 @chapter Debugging remote programs
10146 * Server:: Using the gdbserver program
10147 * NetWare:: Using the gdbserve.nlm program
10148 * remote stub:: Implementing a remote stub
10152 @section Using the @code{gdbserver} program
10155 @cindex remote connection without stubs
10156 @code{gdbserver} is a control program for Unix-like systems, which
10157 allows you to connect your program with a remote @value{GDBN} via
10158 @code{target remote}---but without linking in the usual debugging stub.
10160 @code{gdbserver} is not a complete replacement for the debugging stubs,
10161 because it requires essentially the same operating-system facilities
10162 that @value{GDBN} itself does. In fact, a system that can run
10163 @code{gdbserver} to connect to a remote @value{GDBN} could also run
10164 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
10165 because it is a much smaller program than @value{GDBN} itself. It is
10166 also easier to port than all of @value{GDBN}, so you may be able to get
10167 started more quickly on a new system by using @code{gdbserver}.
10168 Finally, if you develop code for real-time systems, you may find that
10169 the tradeoffs involved in real-time operation make it more convenient to
10170 do as much development work as possible on another system, for example
10171 by cross-compiling. You can use @code{gdbserver} to make a similar
10172 choice for debugging.
10174 @value{GDBN} and @code{gdbserver} communicate via either a serial line
10175 or a TCP connection, using the standard @value{GDBN} remote serial
10179 @item On the target machine,
10180 you need to have a copy of the program you want to debug.
10181 @code{gdbserver} does not need your program's symbol table, so you can
10182 strip the program if necessary to save space. @value{GDBN} on the host
10183 system does all the symbol handling.
10185 To use the server, you must tell it how to communicate with @value{GDBN};
10186 the name of your program; and the arguments for your program. The usual
10190 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
10193 @var{comm} is either a device name (to use a serial line) or a TCP
10194 hostname and portnumber. For example, to debug Emacs with the argument
10195 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
10199 target> gdbserver /dev/com1 emacs foo.txt
10202 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
10205 To use a TCP connection instead of a serial line:
10208 target> gdbserver host:2345 emacs foo.txt
10211 The only difference from the previous example is the first argument,
10212 specifying that you are communicating with the host @value{GDBN} via
10213 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
10214 expect a TCP connection from machine @samp{host} to local TCP port 2345.
10215 (Currently, the @samp{host} part is ignored.) You can choose any number
10216 you want for the port number as long as it does not conflict with any
10217 TCP ports already in use on the target system (for example, @code{23} is
10218 reserved for @code{telnet}).@footnote{If you choose a port number that
10219 conflicts with another service, @code{gdbserver} prints an error message
10220 and exits.} You must use the same port number with the host @value{GDBN}
10221 @code{target remote} command.
10223 On some targets, @code{gdbserver} can also attach to running programs.
10224 This is accomplished via the @code{--attach} argument. The syntax is:
10227 target> gdbserver @var{comm} --attach @var{pid}
10230 @var{pid} is the process ID of a currently running process. It isn't necessary
10231 to point @code{gdbserver} at a binary for the running process.
10233 @item On the @value{GDBN} host machine,
10234 you need an unstripped copy of your program, since @value{GDBN} needs
10235 symbols and debugging information. Start up @value{GDBN} as usual,
10236 using the name of the local copy of your program as the first argument.
10237 (You may also need the @w{@samp{--baud}} option if the serial line is
10238 running at anything other than 9600@dmn{bps}.) After that, use @code{target
10239 remote} to establish communications with @code{gdbserver}. Its argument
10240 is either a device name (usually a serial device, like
10241 @file{/dev/ttyb}), or a TCP port descriptor in the form
10242 @code{@var{host}:@var{PORT}}. For example:
10245 (@value{GDBP}) target remote /dev/ttyb
10249 communicates with the server via serial line @file{/dev/ttyb}, and
10252 (@value{GDBP}) target remote the-target:2345
10256 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
10257 For TCP connections, you must start up @code{gdbserver} prior to using
10258 the @code{target remote} command. Otherwise you may get an error whose
10259 text depends on the host system, but which usually looks something like
10260 @samp{Connection refused}.
10264 @section Using the @code{gdbserve.nlm} program
10266 @kindex gdbserve.nlm
10267 @code{gdbserve.nlm} is a control program for NetWare systems, which
10268 allows you to connect your program with a remote @value{GDBN} via
10269 @code{target remote}.
10271 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
10272 using the standard @value{GDBN} remote serial protocol.
10275 @item On the target machine,
10276 you need to have a copy of the program you want to debug.
10277 @code{gdbserve.nlm} does not need your program's symbol table, so you
10278 can strip the program if necessary to save space. @value{GDBN} on the
10279 host system does all the symbol handling.
10281 To use the server, you must tell it how to communicate with
10282 @value{GDBN}; the name of your program; and the arguments for your
10283 program. The syntax is:
10286 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
10287 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
10290 @var{board} and @var{port} specify the serial line; @var{baud} specifies
10291 the baud rate used by the connection. @var{port} and @var{node} default
10292 to 0, @var{baud} defaults to 9600@dmn{bps}.
10294 For example, to debug Emacs with the argument @samp{foo.txt}and
10295 communicate with @value{GDBN} over serial port number 2 or board 1
10296 using a 19200@dmn{bps} connection:
10299 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
10302 @item On the @value{GDBN} host machine,
10303 you need an unstripped copy of your program, since @value{GDBN} needs
10304 symbols and debugging information. Start up @value{GDBN} as usual,
10305 using the name of the local copy of your program as the first argument.
10306 (You may also need the @w{@samp{--baud}} option if the serial line is
10307 running at anything other than 9600@dmn{bps}. After that, use @code{target
10308 remote} to establish communications with @code{gdbserve.nlm}. Its
10309 argument is a device name (usually a serial device, like
10310 @file{/dev/ttyb}). For example:
10313 (@value{GDBP}) target remote /dev/ttyb
10317 communications with the server via serial line @file{/dev/ttyb}.
10321 @section Implementing a remote stub
10323 @cindex debugging stub, example
10324 @cindex remote stub, example
10325 @cindex stub example, remote debugging
10326 The stub files provided with @value{GDBN} implement the target side of the
10327 communication protocol, and the @value{GDBN} side is implemented in the
10328 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
10329 these subroutines to communicate, and ignore the details. (If you're
10330 implementing your own stub file, you can still ignore the details: start
10331 with one of the existing stub files. @file{sparc-stub.c} is the best
10332 organized, and therefore the easiest to read.)
10334 @cindex remote serial debugging, overview
10335 To debug a program running on another machine (the debugging
10336 @dfn{target} machine), you must first arrange for all the usual
10337 prerequisites for the program to run by itself. For example, for a C
10342 A startup routine to set up the C runtime environment; these usually
10343 have a name like @file{crt0}. The startup routine may be supplied by
10344 your hardware supplier, or you may have to write your own.
10347 A C subroutine library to support your program's
10348 subroutine calls, notably managing input and output.
10351 A way of getting your program to the other machine---for example, a
10352 download program. These are often supplied by the hardware
10353 manufacturer, but you may have to write your own from hardware
10357 The next step is to arrange for your program to use a serial port to
10358 communicate with the machine where @value{GDBN} is running (the @dfn{host}
10359 machine). In general terms, the scheme looks like this:
10363 @value{GDBN} already understands how to use this protocol; when everything
10364 else is set up, you can simply use the @samp{target remote} command
10365 (@pxref{Targets,,Specifying a Debugging Target}).
10367 @item On the target,
10368 you must link with your program a few special-purpose subroutines that
10369 implement the @value{GDBN} remote serial protocol. The file containing these
10370 subroutines is called a @dfn{debugging stub}.
10372 On certain remote targets, you can use an auxiliary program
10373 @code{gdbserver} instead of linking a stub into your program.
10374 @xref{Server,,Using the @code{gdbserver} program}, for details.
10377 The debugging stub is specific to the architecture of the remote
10378 machine; for example, use @file{sparc-stub.c} to debug programs on
10381 @cindex remote serial stub list
10382 These working remote stubs are distributed with @value{GDBN}:
10387 @cindex @file{i386-stub.c}
10390 For Intel 386 and compatible architectures.
10393 @cindex @file{m68k-stub.c}
10394 @cindex Motorola 680x0
10396 For Motorola 680x0 architectures.
10399 @cindex @file{sh-stub.c}
10402 For Hitachi SH architectures.
10405 @cindex @file{sparc-stub.c}
10407 For @sc{sparc} architectures.
10409 @item sparcl-stub.c
10410 @cindex @file{sparcl-stub.c}
10413 For Fujitsu @sc{sparclite} architectures.
10417 The @file{README} file in the @value{GDBN} distribution may list other
10418 recently added stubs.
10421 * Stub Contents:: What the stub can do for you
10422 * Bootstrapping:: What you must do for the stub
10423 * Debug Session:: Putting it all together
10426 @node Stub Contents
10427 @subsection What the stub can do for you
10429 @cindex remote serial stub
10430 The debugging stub for your architecture supplies these three
10434 @item set_debug_traps
10435 @kindex set_debug_traps
10436 @cindex remote serial stub, initialization
10437 This routine arranges for @code{handle_exception} to run when your
10438 program stops. You must call this subroutine explicitly near the
10439 beginning of your program.
10441 @item handle_exception
10442 @kindex handle_exception
10443 @cindex remote serial stub, main routine
10444 This is the central workhorse, but your program never calls it
10445 explicitly---the setup code arranges for @code{handle_exception} to
10446 run when a trap is triggered.
10448 @code{handle_exception} takes control when your program stops during
10449 execution (for example, on a breakpoint), and mediates communications
10450 with @value{GDBN} on the host machine. This is where the communications
10451 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
10452 representative on the target machine. It begins by sending summary
10453 information on the state of your program, then continues to execute,
10454 retrieving and transmitting any information @value{GDBN} needs, until you
10455 execute a @value{GDBN} command that makes your program resume; at that point,
10456 @code{handle_exception} returns control to your own code on the target
10460 @cindex @code{breakpoint} subroutine, remote
10461 Use this auxiliary subroutine to make your program contain a
10462 breakpoint. Depending on the particular situation, this may be the only
10463 way for @value{GDBN} to get control. For instance, if your target
10464 machine has some sort of interrupt button, you won't need to call this;
10465 pressing the interrupt button transfers control to
10466 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
10467 simply receiving characters on the serial port may also trigger a trap;
10468 again, in that situation, you don't need to call @code{breakpoint} from
10469 your own program---simply running @samp{target remote} from the host
10470 @value{GDBN} session gets control.
10472 Call @code{breakpoint} if none of these is true, or if you simply want
10473 to make certain your program stops at a predetermined point for the
10474 start of your debugging session.
10477 @node Bootstrapping
10478 @subsection What you must do for the stub
10480 @cindex remote stub, support routines
10481 The debugging stubs that come with @value{GDBN} are set up for a particular
10482 chip architecture, but they have no information about the rest of your
10483 debugging target machine.
10485 First of all you need to tell the stub how to communicate with the
10489 @item int getDebugChar()
10490 @kindex getDebugChar
10491 Write this subroutine to read a single character from the serial port.
10492 It may be identical to @code{getchar} for your target system; a
10493 different name is used to allow you to distinguish the two if you wish.
10495 @item void putDebugChar(int)
10496 @kindex putDebugChar
10497 Write this subroutine to write a single character to the serial port.
10498 It may be identical to @code{putchar} for your target system; a
10499 different name is used to allow you to distinguish the two if you wish.
10502 @cindex control C, and remote debugging
10503 @cindex interrupting remote targets
10504 If you want @value{GDBN} to be able to stop your program while it is
10505 running, you need to use an interrupt-driven serial driver, and arrange
10506 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
10507 character). That is the character which @value{GDBN} uses to tell the
10508 remote system to stop.
10510 Getting the debugging target to return the proper status to @value{GDBN}
10511 probably requires changes to the standard stub; one quick and dirty way
10512 is to just execute a breakpoint instruction (the ``dirty'' part is that
10513 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
10515 Other routines you need to supply are:
10518 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
10519 @kindex exceptionHandler
10520 Write this function to install @var{exception_address} in the exception
10521 handling tables. You need to do this because the stub does not have any
10522 way of knowing what the exception handling tables on your target system
10523 are like (for example, the processor's table might be in @sc{rom},
10524 containing entries which point to a table in @sc{ram}).
10525 @var{exception_number} is the exception number which should be changed;
10526 its meaning is architecture-dependent (for example, different numbers
10527 might represent divide by zero, misaligned access, etc). When this
10528 exception occurs, control should be transferred directly to
10529 @var{exception_address}, and the processor state (stack, registers,
10530 and so on) should be just as it is when a processor exception occurs. So if
10531 you want to use a jump instruction to reach @var{exception_address}, it
10532 should be a simple jump, not a jump to subroutine.
10534 For the 386, @var{exception_address} should be installed as an interrupt
10535 gate so that interrupts are masked while the handler runs. The gate
10536 should be at privilege level 0 (the most privileged level). The
10537 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
10538 help from @code{exceptionHandler}.
10540 @item void flush_i_cache()
10541 @kindex flush_i_cache
10542 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
10543 instruction cache, if any, on your target machine. If there is no
10544 instruction cache, this subroutine may be a no-op.
10546 On target machines that have instruction caches, @value{GDBN} requires this
10547 function to make certain that the state of your program is stable.
10551 You must also make sure this library routine is available:
10554 @item void *memset(void *, int, int)
10556 This is the standard library function @code{memset} that sets an area of
10557 memory to a known value. If you have one of the free versions of
10558 @code{libc.a}, @code{memset} can be found there; otherwise, you must
10559 either obtain it from your hardware manufacturer, or write your own.
10562 If you do not use the GNU C compiler, you may need other standard
10563 library subroutines as well; this varies from one stub to another,
10564 but in general the stubs are likely to use any of the common library
10565 subroutines which @code{@value{GCC}} generates as inline code.
10568 @node Debug Session
10569 @subsection Putting it all together
10571 @cindex remote serial debugging summary
10572 In summary, when your program is ready to debug, you must follow these
10577 Make sure you have defined the supporting low-level routines
10578 (@pxref{Bootstrapping,,What you must do for the stub}):
10580 @code{getDebugChar}, @code{putDebugChar},
10581 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
10585 Insert these lines near the top of your program:
10593 For the 680x0 stub only, you need to provide a variable called
10594 @code{exceptionHook}. Normally you just use:
10597 void (*exceptionHook)() = 0;
10601 but if before calling @code{set_debug_traps}, you set it to point to a
10602 function in your program, that function is called when
10603 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
10604 error). The function indicated by @code{exceptionHook} is called with
10605 one parameter: an @code{int} which is the exception number.
10608 Compile and link together: your program, the @value{GDBN} debugging stub for
10609 your target architecture, and the supporting subroutines.
10612 Make sure you have a serial connection between your target machine and
10613 the @value{GDBN} host, and identify the serial port on the host.
10616 @c The "remote" target now provides a `load' command, so we should
10617 @c document that. FIXME.
10618 Download your program to your target machine (or get it there by
10619 whatever means the manufacturer provides), and start it.
10622 To start remote debugging, run @value{GDBN} on the host machine, and specify
10623 as an executable file the program that is running in the remote machine.
10624 This tells @value{GDBN} how to find your program's symbols and the contents
10628 @cindex serial line, @code{target remote}
10629 Establish communication using the @code{target remote} command.
10630 Its argument specifies how to communicate with the target
10631 machine---either via a devicename attached to a direct serial line, or a
10632 TCP or UDP port (usually to a terminal server which in turn has a serial line
10633 to the target). For example, to use a serial line connected to the
10634 device named @file{/dev/ttyb}:
10637 target remote /dev/ttyb
10640 @cindex TCP port, @code{target remote}
10641 To use a TCP connection, use an argument of the form
10642 @code{@var{host}:@var{port}} or @code{tcp:@var{host}:@var{port}}.
10643 For example, to connect to port 2828 on a
10644 terminal server named @code{manyfarms}:
10647 target remote manyfarms:2828
10650 If your remote target is actually running on the same machine as
10651 your debugger session (e.g.@: a simulator of your target running on
10652 the same host), you can omit the hostname. For example, to connect
10653 to port 1234 on your local machine:
10656 target remote :1234
10660 Note that the colon is still required here.
10662 @cindex UDP port, @code{target remote}
10663 To use a UDP connection, use an argument of the form
10664 @code{udp:@var{host}:@var{port}}. For example, to connect to UDP port 2828
10665 on a terminal server named @code{manyfarms}:
10668 target remote udp:manyfarms:2828
10671 When using a UDP connection for remote debugging, you should keep in mind
10672 that the `U' stands for ``Unreliable''. UDP can silently drop packets on
10673 busy or unreliable networks, which will cause havoc with your debugging
10678 Now you can use all the usual commands to examine and change data and to
10679 step and continue the remote program.
10681 To resume the remote program and stop debugging it, use the @code{detach}
10684 @cindex interrupting remote programs
10685 @cindex remote programs, interrupting
10686 Whenever @value{GDBN} is waiting for the remote program, if you type the
10687 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
10688 program. This may or may not succeed, depending in part on the hardware
10689 and the serial drivers the remote system uses. If you type the
10690 interrupt character once again, @value{GDBN} displays this prompt:
10693 Interrupted while waiting for the program.
10694 Give up (and stop debugging it)? (y or n)
10697 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
10698 (If you decide you want to try again later, you can use @samp{target
10699 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
10700 goes back to waiting.
10703 @node Configurations
10704 @chapter Configuration-Specific Information
10706 While nearly all @value{GDBN} commands are available for all native and
10707 cross versions of the debugger, there are some exceptions. This chapter
10708 describes things that are only available in certain configurations.
10710 There are three major categories of configurations: native
10711 configurations, where the host and target are the same, embedded
10712 operating system configurations, which are usually the same for several
10713 different processor architectures, and bare embedded processors, which
10714 are quite different from each other.
10719 * Embedded Processors::
10726 This section describes details specific to particular native
10731 * SVR4 Process Information:: SVR4 process information
10732 * DJGPP Native:: Features specific to the DJGPP port
10733 * Cygwin Native:: Features specific to the Cygwin port
10739 On HP-UX systems, if you refer to a function or variable name that
10740 begins with a dollar sign, @value{GDBN} searches for a user or system
10741 name first, before it searches for a convenience variable.
10743 @node SVR4 Process Information
10744 @subsection SVR4 process information
10747 @cindex process image
10749 Many versions of SVR4 provide a facility called @samp{/proc} that can be
10750 used to examine the image of a running process using file-system
10751 subroutines. If @value{GDBN} is configured for an operating system with
10752 this facility, the command @code{info proc} is available to report on
10753 several kinds of information about the process running your program.
10754 @code{info proc} works only on SVR4 systems that include the
10755 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
10756 and Unixware, but not HP-UX or @sc{gnu}/Linux, for example.
10761 Summarize available information about the process.
10763 @kindex info proc mappings
10764 @item info proc mappings
10765 Report on the address ranges accessible in the program, with information
10766 on whether your program may read, write, or execute each range.
10768 @comment These sub-options of 'info proc' were not included when
10769 @comment procfs.c was re-written. Keep their descriptions around
10770 @comment against the day when someone finds the time to put them back in.
10771 @kindex info proc times
10772 @item info proc times
10773 Starting time, user CPU time, and system CPU time for your program and
10776 @kindex info proc id
10778 Report on the process IDs related to your program: its own process ID,
10779 the ID of its parent, the process group ID, and the session ID.
10781 @kindex info proc status
10782 @item info proc status
10783 General information on the state of the process. If the process is
10784 stopped, this report includes the reason for stopping, and any signal
10787 @item info proc all
10788 Show all the above information about the process.
10793 @subsection Features for Debugging @sc{djgpp} Programs
10794 @cindex @sc{djgpp} debugging
10795 @cindex native @sc{djgpp} debugging
10796 @cindex MS-DOS-specific commands
10798 @sc{djgpp} is the port of @sc{gnu} development tools to MS-DOS and
10799 MS-Windows. @sc{djgpp} programs are 32-bit protected-mode programs
10800 that use the @dfn{DPMI} (DOS Protected-Mode Interface) API to run on
10801 top of real-mode DOS systems and their emulations.
10803 @value{GDBN} supports native debugging of @sc{djgpp} programs, and
10804 defines a few commands specific to the @sc{djgpp} port. This
10805 subsection describes those commands.
10810 This is a prefix of @sc{djgpp}-specific commands which print
10811 information about the target system and important OS structures.
10814 @cindex MS-DOS system info
10815 @cindex free memory information (MS-DOS)
10816 @item info dos sysinfo
10817 This command displays assorted information about the underlying
10818 platform: the CPU type and features, the OS version and flavor, the
10819 DPMI version, and the available conventional and DPMI memory.
10824 @cindex segment descriptor tables
10825 @cindex descriptor tables display
10827 @itemx info dos ldt
10828 @itemx info dos idt
10829 These 3 commands display entries from, respectively, Global, Local,
10830 and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor
10831 tables are data structures which store a descriptor for each segment
10832 that is currently in use. The segment's selector is an index into a
10833 descriptor table; the table entry for that index holds the
10834 descriptor's base address and limit, and its attributes and access
10837 A typical @sc{djgpp} program uses 3 segments: a code segment, a data
10838 segment (used for both data and the stack), and a DOS segment (which
10839 allows access to DOS/BIOS data structures and absolute addresses in
10840 conventional memory). However, the DPMI host will usually define
10841 additional segments in order to support the DPMI environment.
10843 @cindex garbled pointers
10844 These commands allow to display entries from the descriptor tables.
10845 Without an argument, all entries from the specified table are
10846 displayed. An argument, which should be an integer expression, means
10847 display a single entry whose index is given by the argument. For
10848 example, here's a convenient way to display information about the
10849 debugged program's data segment:
10852 @exdent @code{(@value{GDBP}) info dos ldt $ds}
10853 @exdent @code{0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)}
10857 This comes in handy when you want to see whether a pointer is outside
10858 the data segment's limit (i.e.@: @dfn{garbled}).
10860 @cindex page tables display (MS-DOS)
10862 @itemx info dos pte
10863 These two commands display entries from, respectively, the Page
10864 Directory and the Page Tables. Page Directories and Page Tables are
10865 data structures which control how virtual memory addresses are mapped
10866 into physical addresses. A Page Table includes an entry for every
10867 page of memory that is mapped into the program's address space; there
10868 may be several Page Tables, each one holding up to 4096 entries. A
10869 Page Directory has up to 4096 entries, one each for every Page Table
10870 that is currently in use.
10872 Without an argument, @kbd{info dos pde} displays the entire Page
10873 Directory, and @kbd{info dos pte} displays all the entries in all of
10874 the Page Tables. An argument, an integer expression, given to the
10875 @kbd{info dos pde} command means display only that entry from the Page
10876 Directory table. An argument given to the @kbd{info dos pte} command
10877 means display entries from a single Page Table, the one pointed to by
10878 the specified entry in the Page Directory.
10880 @cindex direct memory access (DMA) on MS-DOS
10881 These commands are useful when your program uses @dfn{DMA} (Direct
10882 Memory Access), which needs physical addresses to program the DMA
10885 These commands are supported only with some DPMI servers.
10887 @cindex physical address from linear address
10888 @item info dos address-pte @var{addr}
10889 This command displays the Page Table entry for a specified linear
10890 address. The argument linear address @var{addr} should already have the
10891 appropriate segment's base address added to it, because this command
10892 accepts addresses which may belong to @emph{any} segment. For
10893 example, here's how to display the Page Table entry for the page where
10894 the variable @code{i} is stored:
10897 @exdent @code{(@value{GDBP}) info dos address-pte __djgpp_base_address + (char *)&i}
10898 @exdent @code{Page Table entry for address 0x11a00d30:}
10899 @exdent @code{Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30}
10903 This says that @code{i} is stored at offset @code{0xd30} from the page
10904 whose physical base address is @code{0x02698000}, and prints all the
10905 attributes of that page.
10907 Note that you must cast the addresses of variables to a @code{char *},
10908 since otherwise the value of @code{__djgpp_base_address}, the base
10909 address of all variables and functions in a @sc{djgpp} program, will
10910 be added using the rules of C pointer arithmetics: if @code{i} is
10911 declared an @code{int}, @value{GDBN} will add 4 times the value of
10912 @code{__djgpp_base_address} to the address of @code{i}.
10914 Here's another example, it displays the Page Table entry for the
10918 @exdent @code{(@value{GDBP}) info dos address-pte *((unsigned *)&_go32_info_block + 3)}
10919 @exdent @code{Page Table entry for address 0x29110:}
10920 @exdent @code{Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110}
10924 (The @code{+ 3} offset is because the transfer buffer's address is the
10925 3rd member of the @code{_go32_info_block} structure.) The output of
10926 this command clearly shows that addresses in conventional memory are
10927 mapped 1:1, i.e.@: the physical and linear addresses are identical.
10929 This command is supported only with some DPMI servers.
10932 @node Cygwin Native
10933 @subsection Features for Debugging MS Windows PE executables
10934 @cindex MS Windows debugging
10935 @cindex native Cygwin debugging
10936 @cindex Cygwin-specific commands
10938 @value{GDBN} supports native debugging of MS Windows programs, and
10939 defines a few commands specific to the Cygwin port. This
10940 subsection describes those commands.
10945 This is a prefix of MS Windows specific commands which print
10946 information about the target system and important OS structures.
10948 @item info w32 selector
10949 This command displays information returned by
10950 the Win32 API @code{GetThreadSelectorEntry} function.
10951 It takes an optional argument that is evaluated to
10952 a long value to give the information about this given selector.
10953 Without argument, this command displays information
10954 about the the six segment registers.
10958 This is a Cygwin specific alias of info shared.
10960 @kindex dll-symbols
10962 This command loads symbols from a dll similarly to
10963 add-sym command but without the need to specify a base address.
10965 @kindex set new-console
10966 @item set new-console @var{mode}
10967 If @var{mode} is @code{on} the debuggee will
10968 be started in a new console on next start.
10969 If @var{mode} is @code{off}i, the debuggee will
10970 be started in the same console as the debugger.
10972 @kindex show new-console
10973 @item show new-console
10974 Displays whether a new console is used
10975 when the debuggee is started.
10977 @kindex set new-group
10978 @item set new-group @var{mode}
10979 This boolean value controls whether the debuggee should
10980 start a new group or stay in the same group as the debugger.
10981 This affects the way the Windows OS handles
10984 @kindex show new-group
10985 @item show new-group
10986 Displays current value of new-group boolean.
10988 @kindex set debugevents
10989 @item set debugevents
10990 This boolean value adds debug output concerning events seen by the debugger.
10992 @kindex set debugexec
10993 @item set debugexec
10994 This boolean value adds debug output concerning execute events
10995 seen by the debugger.
10997 @kindex set debugexceptions
10998 @item set debugexceptions
10999 This boolean value adds debug ouptut concerning exception events
11000 seen by the debugger.
11002 @kindex set debugmemory
11003 @item set debugmemory
11004 This boolean value adds debug ouptut concerning memory events
11005 seen by the debugger.
11009 This boolean values specifies whether the debuggee is called
11010 via a shell or directly (default value is on).
11014 Displays if the debuggee will be started with a shell.
11019 @section Embedded Operating Systems
11021 This section describes configurations involving the debugging of
11022 embedded operating systems that are available for several different
11026 * VxWorks:: Using @value{GDBN} with VxWorks
11029 @value{GDBN} includes the ability to debug programs running on
11030 various real-time operating systems.
11033 @subsection Using @value{GDBN} with VxWorks
11039 @kindex target vxworks
11040 @item target vxworks @var{machinename}
11041 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
11042 is the target system's machine name or IP address.
11046 On VxWorks, @code{load} links @var{filename} dynamically on the
11047 current target system as well as adding its symbols in @value{GDBN}.
11049 @value{GDBN} enables developers to spawn and debug tasks running on networked
11050 VxWorks targets from a Unix host. Already-running tasks spawned from
11051 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
11052 both the Unix host and on the VxWorks target. The program
11053 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
11054 installed with the name @code{vxgdb}, to distinguish it from a
11055 @value{GDBN} for debugging programs on the host itself.)
11058 @item VxWorks-timeout @var{args}
11059 @kindex vxworks-timeout
11060 All VxWorks-based targets now support the option @code{vxworks-timeout}.
11061 This option is set by the user, and @var{args} represents the number of
11062 seconds @value{GDBN} waits for responses to rpc's. You might use this if
11063 your VxWorks target is a slow software simulator or is on the far side
11064 of a thin network line.
11067 The following information on connecting to VxWorks was current when
11068 this manual was produced; newer releases of VxWorks may use revised
11071 @kindex INCLUDE_RDB
11072 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
11073 to include the remote debugging interface routines in the VxWorks
11074 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
11075 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
11076 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
11077 source debugging task @code{tRdbTask} when VxWorks is booted. For more
11078 information on configuring and remaking VxWorks, see the manufacturer's
11080 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
11082 Once you have included @file{rdb.a} in your VxWorks system image and set
11083 your Unix execution search path to find @value{GDBN}, you are ready to
11084 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or
11085 @code{vxgdb}, depending on your installation).
11087 @value{GDBN} comes up showing the prompt:
11094 * VxWorks Connection:: Connecting to VxWorks
11095 * VxWorks Download:: VxWorks download
11096 * VxWorks Attach:: Running tasks
11099 @node VxWorks Connection
11100 @subsubsection Connecting to VxWorks
11102 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
11103 network. To connect to a target whose host name is ``@code{tt}'', type:
11106 (vxgdb) target vxworks tt
11110 @value{GDBN} displays messages like these:
11113 Attaching remote machine across net...
11118 @value{GDBN} then attempts to read the symbol tables of any object modules
11119 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
11120 these files by searching the directories listed in the command search
11121 path (@pxref{Environment, ,Your program's environment}); if it fails
11122 to find an object file, it displays a message such as:
11125 prog.o: No such file or directory.
11128 When this happens, add the appropriate directory to the search path with
11129 the @value{GDBN} command @code{path}, and execute the @code{target}
11132 @node VxWorks Download
11133 @subsubsection VxWorks download
11135 @cindex download to VxWorks
11136 If you have connected to the VxWorks target and you want to debug an
11137 object that has not yet been loaded, you can use the @value{GDBN}
11138 @code{load} command to download a file from Unix to VxWorks
11139 incrementally. The object file given as an argument to the @code{load}
11140 command is actually opened twice: first by the VxWorks target in order
11141 to download the code, then by @value{GDBN} in order to read the symbol
11142 table. This can lead to problems if the current working directories on
11143 the two systems differ. If both systems have NFS mounted the same
11144 filesystems, you can avoid these problems by using absolute paths.
11145 Otherwise, it is simplest to set the working directory on both systems
11146 to the directory in which the object file resides, and then to reference
11147 the file by its name, without any path. For instance, a program
11148 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
11149 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
11150 program, type this on VxWorks:
11153 -> cd "@var{vxpath}/vw/demo/rdb"
11157 Then, in @value{GDBN}, type:
11160 (vxgdb) cd @var{hostpath}/vw/demo/rdb
11161 (vxgdb) load prog.o
11164 @value{GDBN} displays a response similar to this:
11167 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
11170 You can also use the @code{load} command to reload an object module
11171 after editing and recompiling the corresponding source file. Note that
11172 this makes @value{GDBN} delete all currently-defined breakpoints,
11173 auto-displays, and convenience variables, and to clear the value
11174 history. (This is necessary in order to preserve the integrity of
11175 debugger's data structures that reference the target system's symbol
11178 @node VxWorks Attach
11179 @subsubsection Running tasks
11181 @cindex running VxWorks tasks
11182 You can also attach to an existing task using the @code{attach} command as
11186 (vxgdb) attach @var{task}
11190 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
11191 or suspended when you attach to it. Running tasks are suspended at
11192 the time of attachment.
11194 @node Embedded Processors
11195 @section Embedded Processors
11197 This section goes into details specific to particular embedded
11203 * H8/300:: Hitachi H8/300
11204 * H8/500:: Hitachi H8/500
11205 * i960:: Intel i960
11206 * M32R/D:: Mitsubishi M32R/D
11207 * M68K:: Motorola M68K
11208 * MIPS Embedded:: MIPS Embedded
11209 * OpenRISC 1000:: OpenRisc 1000
11210 * PA:: HP PA Embedded
11213 * Sparclet:: Tsqware Sparclet
11214 * Sparclite:: Fujitsu Sparclite
11215 * ST2000:: Tandem ST2000
11216 * Z8000:: Zilog Z8000
11225 @item target rdi @var{dev}
11226 ARM Angel monitor, via RDI library interface to ADP protocol. You may
11227 use this target to communicate with both boards running the Angel
11228 monitor, or with the EmbeddedICE JTAG debug device.
11231 @item target rdp @var{dev}
11237 @subsection Hitachi H8/300
11241 @kindex target hms@r{, with H8/300}
11242 @item target hms @var{dev}
11243 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
11244 Use special commands @code{device} and @code{speed} to control the serial
11245 line and the communications speed used.
11247 @kindex target e7000@r{, with H8/300}
11248 @item target e7000 @var{dev}
11249 E7000 emulator for Hitachi H8 and SH.
11251 @kindex target sh3@r{, with H8/300}
11252 @kindex target sh3e@r{, with H8/300}
11253 @item target sh3 @var{dev}
11254 @itemx target sh3e @var{dev}
11255 Hitachi SH-3 and SH-3E target systems.
11259 @cindex download to H8/300 or H8/500
11260 @cindex H8/300 or H8/500 download
11261 @cindex download to Hitachi SH
11262 @cindex Hitachi SH download
11263 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
11264 board, the @code{load} command downloads your program to the Hitachi
11265 board and also opens it as the current executable target for
11266 @value{GDBN} on your host (like the @code{file} command).
11268 @value{GDBN} needs to know these things to talk to your
11269 Hitachi SH, H8/300, or H8/500:
11273 that you want to use @samp{target hms}, the remote debugging interface
11274 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
11275 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
11276 the default when @value{GDBN} is configured specifically for the Hitachi SH,
11277 H8/300, or H8/500.)
11280 what serial device connects your host to your Hitachi board (the first
11281 serial device available on your host is the default).
11284 what speed to use over the serial device.
11288 * Hitachi Boards:: Connecting to Hitachi boards.
11289 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
11290 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
11293 @node Hitachi Boards
11294 @subsubsection Connecting to Hitachi boards
11296 @c only for Unix hosts
11298 @cindex serial device, Hitachi micros
11299 Use the special @code{@value{GDBN}} command @samp{device @var{port}} if you
11300 need to explicitly set the serial device. The default @var{port} is the
11301 first available port on your host. This is only necessary on Unix
11302 hosts, where it is typically something like @file{/dev/ttya}.
11305 @cindex serial line speed, Hitachi micros
11306 @code{@value{GDBN}} has another special command to set the communications
11307 speed: @samp{speed @var{bps}}. This command also is only used from Unix
11308 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
11309 the DOS @code{mode} command (for instance,
11310 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
11312 The @samp{device} and @samp{speed} commands are available only when you
11313 use a Unix host to debug your Hitachi microprocessor programs. If you
11315 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
11316 called @code{asynctsr} to communicate with the development board
11317 through a PC serial port. You must also use the DOS @code{mode} command
11318 to set up the serial port on the DOS side.
11320 The following sample session illustrates the steps needed to start a
11321 program under @value{GDBN} control on an H8/300. The example uses a
11322 sample H8/300 program called @file{t.x}. The procedure is the same for
11323 the Hitachi SH and the H8/500.
11325 First hook up your development board. In this example, we use a
11326 board attached to serial port @code{COM2}; if you use a different serial
11327 port, substitute its name in the argument of the @code{mode} command.
11328 When you call @code{asynctsr}, the auxiliary comms program used by the
11329 debugger, you give it just the numeric part of the serial port's name;
11330 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
11334 C:\H8300\TEST> asynctsr 2
11335 C:\H8300\TEST> mode com2:9600,n,8,1,p
11337 Resident portion of MODE loaded
11339 COM2: 9600, n, 8, 1, p
11344 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
11345 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
11346 disable it, or even boot without it, to use @code{asynctsr} to control
11347 your development board.
11350 @kindex target hms@r{, and serial protocol}
11351 Now that serial communications are set up, and the development board is
11352 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
11353 the name of your program as the argument. @code{@value{GDBN}} prompts
11354 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
11355 commands to begin your debugging session: @samp{target hms} to specify
11356 cross-debugging to the Hitachi board, and the @code{load} command to
11357 download your program to the board. @code{load} displays the names of
11358 the program's sections, and a @samp{*} for each 2K of data downloaded.
11359 (If you want to refresh @value{GDBN} data on symbols or on the
11360 executable file without downloading, use the @value{GDBN} commands
11361 @code{file} or @code{symbol-file}. These commands, and @code{load}
11362 itself, are described in @ref{Files,,Commands to specify files}.)
11365 (eg-C:\H8300\TEST) @value{GDBP} t.x
11366 @value{GDBN} is free software and you are welcome to distribute copies
11367 of it under certain conditions; type "show copying" to see
11369 There is absolutely no warranty for @value{GDBN}; type "show warranty"
11371 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
11372 (@value{GDBP}) target hms
11373 Connected to remote H8/300 HMS system.
11374 (@value{GDBP}) load t.x
11375 .text : 0x8000 .. 0xabde ***********
11376 .data : 0xabde .. 0xad30 *
11377 .stack : 0xf000 .. 0xf014 *
11380 At this point, you're ready to run or debug your program. From here on,
11381 you can use all the usual @value{GDBN} commands. The @code{break} command
11382 sets breakpoints; the @code{run} command starts your program;
11383 @code{print} or @code{x} display data; the @code{continue} command
11384 resumes execution after stopping at a breakpoint. You can use the
11385 @code{help} command at any time to find out more about @value{GDBN} commands.
11387 Remember, however, that @emph{operating system} facilities aren't
11388 available on your development board; for example, if your program hangs,
11389 you can't send an interrupt---but you can press the @sc{reset} switch!
11391 Use the @sc{reset} button on the development board
11394 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
11395 no way to pass an interrupt signal to the development board); and
11398 to return to the @value{GDBN} command prompt after your program finishes
11399 normally. The communications protocol provides no other way for @value{GDBN}
11400 to detect program completion.
11403 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
11404 development board as a ``normal exit'' of your program.
11407 @subsubsection Using the E7000 in-circuit emulator
11409 @kindex target e7000@r{, with Hitachi ICE}
11410 You can use the E7000 in-circuit emulator to develop code for either the
11411 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
11412 e7000} command to connect @value{GDBN} to your E7000:
11415 @item target e7000 @var{port} @var{speed}
11416 Use this form if your E7000 is connected to a serial port. The
11417 @var{port} argument identifies what serial port to use (for example,
11418 @samp{com2}). The third argument is the line speed in bits per second
11419 (for example, @samp{9600}).
11421 @item target e7000 @var{hostname}
11422 If your E7000 is installed as a host on a TCP/IP network, you can just
11423 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
11426 @node Hitachi Special
11427 @subsubsection Special @value{GDBN} commands for Hitachi micros
11429 Some @value{GDBN} commands are available only for the H8/300:
11433 @kindex set machine
11434 @kindex show machine
11435 @item set machine h8300
11436 @itemx set machine h8300h
11437 Condition @value{GDBN} for one of the two variants of the H8/300
11438 architecture with @samp{set machine}. You can use @samp{show machine}
11439 to check which variant is currently in effect.
11448 @kindex set memory @var{mod}
11449 @cindex memory models, H8/500
11450 @item set memory @var{mod}
11452 Specify which H8/500 memory model (@var{mod}) you are using with
11453 @samp{set memory}; check which memory model is in effect with @samp{show
11454 memory}. The accepted values for @var{mod} are @code{small},
11455 @code{big}, @code{medium}, and @code{compact}.
11460 @subsection Intel i960
11464 @kindex target mon960
11465 @item target mon960 @var{dev}
11466 MON960 monitor for Intel i960.
11468 @kindex target nindy
11469 @item target nindy @var{devicename}
11470 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
11471 the name of the serial device to use for the connection, e.g.
11478 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
11479 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
11480 tell @value{GDBN} how to connect to the 960 in several ways:
11484 Through command line options specifying serial port, version of the
11485 Nindy protocol, and communications speed;
11488 By responding to a prompt on startup;
11491 By using the @code{target} command at any point during your @value{GDBN}
11492 session. @xref{Target Commands, ,Commands for managing targets}.
11496 @cindex download to Nindy-960
11497 With the Nindy interface to an Intel 960 board, @code{load}
11498 downloads @var{filename} to the 960 as well as adding its symbols in
11502 * Nindy Startup:: Startup with Nindy
11503 * Nindy Options:: Options for Nindy
11504 * Nindy Reset:: Nindy reset command
11507 @node Nindy Startup
11508 @subsubsection Startup with Nindy
11510 If you simply start @code{@value{GDBP}} without using any command-line
11511 options, you are prompted for what serial port to use, @emph{before} you
11512 reach the ordinary @value{GDBN} prompt:
11515 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
11519 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
11520 identifies the serial port you want to use. You can, if you choose,
11521 simply start up with no Nindy connection by responding to the prompt
11522 with an empty line. If you do this and later wish to attach to Nindy,
11523 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
11525 @node Nindy Options
11526 @subsubsection Options for Nindy
11528 These are the startup options for beginning your @value{GDBN} session with a
11529 Nindy-960 board attached:
11532 @item -r @var{port}
11533 Specify the serial port name of a serial interface to be used to connect
11534 to the target system. This option is only available when @value{GDBN} is
11535 configured for the Intel 960 target architecture. You may specify
11536 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
11537 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
11538 suffix for a specific @code{tty} (e.g. @samp{-r a}).
11541 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
11542 the ``old'' Nindy monitor protocol to connect to the target system.
11543 This option is only available when @value{GDBN} is configured for the Intel 960
11544 target architecture.
11547 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
11548 connect to a target system that expects the newer protocol, the connection
11549 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
11550 attempts to reconnect at several different line speeds. You can abort
11551 this process with an interrupt.
11555 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
11556 system, in an attempt to reset it, before connecting to a Nindy target.
11559 @emph{Warning:} Many target systems do not have the hardware that this
11560 requires; it only works with a few boards.
11564 The standard @samp{-b} option controls the line speed used on the serial
11569 @subsubsection Nindy reset command
11574 For a Nindy target, this command sends a ``break'' to the remote target
11575 system; this is only useful if the target has been equipped with a
11576 circuit to perform a hard reset (or some other interesting action) when
11577 a break is detected.
11582 @subsection Mitsubishi M32R/D
11586 @kindex target m32r
11587 @item target m32r @var{dev}
11588 Mitsubishi M32R/D ROM monitor.
11595 The Motorola m68k configuration includes ColdFire support, and
11596 target command for the following ROM monitors.
11600 @kindex target abug
11601 @item target abug @var{dev}
11602 ABug ROM monitor for M68K.
11604 @kindex target cpu32bug
11605 @item target cpu32bug @var{dev}
11606 CPU32BUG monitor, running on a CPU32 (M68K) board.
11608 @kindex target dbug
11609 @item target dbug @var{dev}
11610 dBUG ROM monitor for Motorola ColdFire.
11613 @item target est @var{dev}
11614 EST-300 ICE monitor, running on a CPU32 (M68K) board.
11616 @kindex target rom68k
11617 @item target rom68k @var{dev}
11618 ROM 68K monitor, running on an M68K IDP board.
11622 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
11623 instead have only a single special target command:
11627 @kindex target es1800
11628 @item target es1800 @var{dev}
11629 ES-1800 emulator for M68K.
11637 @kindex target rombug
11638 @item target rombug @var{dev}
11639 ROMBUG ROM monitor for OS/9000.
11643 @node MIPS Embedded
11644 @subsection MIPS Embedded
11646 @cindex MIPS boards
11647 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
11648 MIPS board attached to a serial line. This is available when
11649 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
11652 Use these @value{GDBN} commands to specify the connection to your target board:
11655 @item target mips @var{port}
11656 @kindex target mips @var{port}
11657 To run a program on the board, start up @code{@value{GDBP}} with the
11658 name of your program as the argument. To connect to the board, use the
11659 command @samp{target mips @var{port}}, where @var{port} is the name of
11660 the serial port connected to the board. If the program has not already
11661 been downloaded to the board, you may use the @code{load} command to
11662 download it. You can then use all the usual @value{GDBN} commands.
11664 For example, this sequence connects to the target board through a serial
11665 port, and loads and runs a program called @var{prog} through the
11669 host$ @value{GDBP} @var{prog}
11670 @value{GDBN} is free software and @dots{}
11671 (@value{GDBP}) target mips /dev/ttyb
11672 (@value{GDBP}) load @var{prog}
11676 @item target mips @var{hostname}:@var{portnumber}
11677 On some @value{GDBN} host configurations, you can specify a TCP
11678 connection (for instance, to a serial line managed by a terminal
11679 concentrator) instead of a serial port, using the syntax
11680 @samp{@var{hostname}:@var{portnumber}}.
11682 @item target pmon @var{port}
11683 @kindex target pmon @var{port}
11686 @item target ddb @var{port}
11687 @kindex target ddb @var{port}
11688 NEC's DDB variant of PMON for Vr4300.
11690 @item target lsi @var{port}
11691 @kindex target lsi @var{port}
11692 LSI variant of PMON.
11694 @kindex target r3900
11695 @item target r3900 @var{dev}
11696 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
11698 @kindex target array
11699 @item target array @var{dev}
11700 Array Tech LSI33K RAID controller board.
11706 @value{GDBN} also supports these special commands for MIPS targets:
11709 @item set processor @var{args}
11710 @itemx show processor
11711 @kindex set processor @var{args}
11712 @kindex show processor
11713 Use the @code{set processor} command to set the type of MIPS
11714 processor when you want to access processor-type-specific registers.
11715 For example, @code{set processor @var{r3041}} tells @value{GDBN}
11716 to use the CPU registers appropriate for the 3041 chip.
11717 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
11718 is using. Use the @code{info reg} command to see what registers
11719 @value{GDBN} is using.
11721 @item set mipsfpu double
11722 @itemx set mipsfpu single
11723 @itemx set mipsfpu none
11724 @itemx show mipsfpu
11725 @kindex set mipsfpu
11726 @kindex show mipsfpu
11727 @cindex MIPS remote floating point
11728 @cindex floating point, MIPS remote
11729 If your target board does not support the MIPS floating point
11730 coprocessor, you should use the command @samp{set mipsfpu none} (if you
11731 need this, you may wish to put the command in your @value{GDBN} init
11732 file). This tells @value{GDBN} how to find the return value of
11733 functions which return floating point values. It also allows
11734 @value{GDBN} to avoid saving the floating point registers when calling
11735 functions on the board. If you are using a floating point coprocessor
11736 with only single precision floating point support, as on the @sc{r4650}
11737 processor, use the command @samp{set mipsfpu single}. The default
11738 double precision floating point coprocessor may be selected using
11739 @samp{set mipsfpu double}.
11741 In previous versions the only choices were double precision or no
11742 floating point, so @samp{set mipsfpu on} will select double precision
11743 and @samp{set mipsfpu off} will select no floating point.
11745 As usual, you can inquire about the @code{mipsfpu} variable with
11746 @samp{show mipsfpu}.
11748 @item set remotedebug @var{n}
11749 @itemx show remotedebug
11750 @kindex set remotedebug@r{, MIPS protocol}
11751 @kindex show remotedebug@r{, MIPS protocol}
11752 @cindex @code{remotedebug}, MIPS protocol
11753 @cindex MIPS @code{remotedebug} protocol
11754 @c FIXME! For this to be useful, you must know something about the MIPS
11755 @c FIXME...protocol. Where is it described?
11756 You can see some debugging information about communications with the board
11757 by setting the @code{remotedebug} variable. If you set it to @code{1} using
11758 @samp{set remotedebug 1}, every packet is displayed. If you set it
11759 to @code{2}, every character is displayed. You can check the current value
11760 at any time with the command @samp{show remotedebug}.
11762 @item set timeout @var{seconds}
11763 @itemx set retransmit-timeout @var{seconds}
11764 @itemx show timeout
11765 @itemx show retransmit-timeout
11766 @cindex @code{timeout}, MIPS protocol
11767 @cindex @code{retransmit-timeout}, MIPS protocol
11768 @kindex set timeout
11769 @kindex show timeout
11770 @kindex set retransmit-timeout
11771 @kindex show retransmit-timeout
11772 You can control the timeout used while waiting for a packet, in the MIPS
11773 remote protocol, with the @code{set timeout @var{seconds}} command. The
11774 default is 5 seconds. Similarly, you can control the timeout used while
11775 waiting for an acknowledgement of a packet with the @code{set
11776 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
11777 You can inspect both values with @code{show timeout} and @code{show
11778 retransmit-timeout}. (These commands are @emph{only} available when
11779 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
11781 The timeout set by @code{set timeout} does not apply when @value{GDBN}
11782 is waiting for your program to stop. In that case, @value{GDBN} waits
11783 forever because it has no way of knowing how long the program is going
11784 to run before stopping.
11787 @node OpenRISC 1000
11788 @subsection OpenRISC 1000
11789 @cindex OpenRISC 1000
11791 @cindex or1k boards
11792 See OR1k Architecture document (@uref{www.opencores.org}) for more information
11793 about platform and commands.
11797 @kindex target jtag
11798 @item target jtag jtag://@var{host}:@var{port}
11800 Connects to remote JTAG server.
11801 JTAG remote server can be either an or1ksim or JTAG server,
11802 connected via parallel port to the board.
11804 Example: @code{target jtag jtag://localhost:9999}
11807 @item or1ksim @var{command}
11808 If connected to @code{or1ksim} OpenRISC 1000 Architectural
11809 Simulator, proprietary commands can be executed.
11811 @kindex info or1k spr
11812 @item info or1k spr
11813 Displays spr groups.
11815 @item info or1k spr @var{group}
11816 @itemx info or1k spr @var{groupno}
11817 Displays register names in selected group.
11819 @item info or1k spr @var{group} @var{register}
11820 @itemx info or1k spr @var{register}
11821 @itemx info or1k spr @var{groupno} @var{registerno}
11822 @itemx info or1k spr @var{registerno}
11823 Shows information about specified spr register.
11826 @item spr @var{group} @var{register} @var{value}
11827 @itemx spr @var{register @var{value}}
11828 @itemx spr @var{groupno} @var{registerno @var{value}}
11829 @itemx spr @var{registerno @var{value}}
11830 Writes @var{value} to specified spr register.
11833 Some implementations of OpenRISC 1000 Architecture also have hardware trace.
11834 It is very similar to @value{GDBN} trace, except it does not interfere with normal
11835 program execution and is thus much faster. Hardware breakpoints/watchpoint
11836 triggers can be set using:
11839 Load effective address/data
11841 Store effective address/data
11843 Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA)
11848 When triggered, it can capture low level data, like: @code{PC}, @code{LSEA},
11849 @code{LDATA}, @code{SDATA}, @code{READSPR}, @code{WRITESPR}, @code{INSTR}.
11851 @code{htrace} commands:
11852 @cindex OpenRISC 1000 htrace
11855 @item hwatch @var{conditional}
11856 Set hardware watchpoint on combination of Load/Store Effecive Address(es)
11857 or Data. For example:
11859 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
11861 @code{hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)}
11863 @kindex htrace info
11865 Display information about current HW trace configuration.
11867 @kindex htrace trigger
11868 @item htrace trigger @var{conditional}
11869 Set starting criteria for HW trace.
11871 @kindex htrace qualifier
11872 @item htrace qualifier @var{conditional}
11873 Set acquisition qualifier for HW trace.
11875 @kindex htrace stop
11876 @item htrace stop @var{conditional}
11877 Set HW trace stopping criteria.
11879 @kindex htrace record
11880 @item htrace record @var{[data]*}
11881 Selects the data to be recorded, when qualifier is met and HW trace was
11884 @kindex htrace enable
11885 @item htrace enable
11886 @kindex htrace disable
11887 @itemx htrace disable
11888 Enables/disables the HW trace.
11890 @kindex htrace rewind
11891 @item htrace rewind @var{[filename]}
11892 Clears currently recorded trace data.
11894 If filename is specified, new trace file is made and any newly collected data
11895 will be written there.
11897 @kindex htrace print
11898 @item htrace print @var{[start [len]]}
11899 Prints trace buffer, using current record configuration.
11901 @kindex htrace mode continuous
11902 @item htrace mode continuous
11903 Set continuous trace mode.
11905 @kindex htrace mode suspend
11906 @item htrace mode suspend
11907 Set suspend trace mode.
11912 @subsection PowerPC
11916 @kindex target dink32
11917 @item target dink32 @var{dev}
11918 DINK32 ROM monitor.
11920 @kindex target ppcbug
11921 @item target ppcbug @var{dev}
11922 @kindex target ppcbug1
11923 @item target ppcbug1 @var{dev}
11924 PPCBUG ROM monitor for PowerPC.
11927 @item target sds @var{dev}
11928 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
11933 @subsection HP PA Embedded
11937 @kindex target op50n
11938 @item target op50n @var{dev}
11939 OP50N monitor, running on an OKI HPPA board.
11941 @kindex target w89k
11942 @item target w89k @var{dev}
11943 W89K monitor, running on a Winbond HPPA board.
11948 @subsection Hitachi SH
11952 @kindex target hms@r{, with Hitachi SH}
11953 @item target hms @var{dev}
11954 A Hitachi SH board attached via serial line to your host. Use special
11955 commands @code{device} and @code{speed} to control the serial line and
11956 the communications speed used.
11958 @kindex target e7000@r{, with Hitachi SH}
11959 @item target e7000 @var{dev}
11960 E7000 emulator for Hitachi SH.
11962 @kindex target sh3@r{, with SH}
11963 @kindex target sh3e@r{, with SH}
11964 @item target sh3 @var{dev}
11965 @item target sh3e @var{dev}
11966 Hitachi SH-3 and SH-3E target systems.
11971 @subsection Tsqware Sparclet
11975 @value{GDBN} enables developers to debug tasks running on
11976 Sparclet targets from a Unix host.
11977 @value{GDBN} uses code that runs on
11978 both the Unix host and on the Sparclet target. The program
11979 @code{@value{GDBP}} is installed and executed on the Unix host.
11982 @item remotetimeout @var{args}
11983 @kindex remotetimeout
11984 @value{GDBN} supports the option @code{remotetimeout}.
11985 This option is set by the user, and @var{args} represents the number of
11986 seconds @value{GDBN} waits for responses.
11989 @cindex compiling, on Sparclet
11990 When compiling for debugging, include the options @samp{-g} to get debug
11991 information and @samp{-Ttext} to relocate the program to where you wish to
11992 load it on the target. You may also want to add the options @samp{-n} or
11993 @samp{-N} in order to reduce the size of the sections. Example:
11996 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
11999 You can use @code{objdump} to verify that the addresses are what you intended:
12002 sparclet-aout-objdump --headers --syms prog
12005 @cindex running, on Sparclet
12007 your Unix execution search path to find @value{GDBN}, you are ready to
12008 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
12009 (or @code{sparclet-aout-gdb}, depending on your installation).
12011 @value{GDBN} comes up showing the prompt:
12018 * Sparclet File:: Setting the file to debug
12019 * Sparclet Connection:: Connecting to Sparclet
12020 * Sparclet Download:: Sparclet download
12021 * Sparclet Execution:: Running and debugging
12024 @node Sparclet File
12025 @subsubsection Setting file to debug
12027 The @value{GDBN} command @code{file} lets you choose with program to debug.
12030 (gdbslet) file prog
12034 @value{GDBN} then attempts to read the symbol table of @file{prog}.
12035 @value{GDBN} locates
12036 the file by searching the directories listed in the command search
12038 If the file was compiled with debug information (option "-g"), source
12039 files will be searched as well.
12040 @value{GDBN} locates
12041 the source files by searching the directories listed in the directory search
12042 path (@pxref{Environment, ,Your program's environment}).
12044 to find a file, it displays a message such as:
12047 prog: No such file or directory.
12050 When this happens, add the appropriate directories to the search paths with
12051 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
12052 @code{target} command again.
12054 @node Sparclet Connection
12055 @subsubsection Connecting to Sparclet
12057 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
12058 To connect to a target on serial port ``@code{ttya}'', type:
12061 (gdbslet) target sparclet /dev/ttya
12062 Remote target sparclet connected to /dev/ttya
12063 main () at ../prog.c:3
12067 @value{GDBN} displays messages like these:
12073 @node Sparclet Download
12074 @subsubsection Sparclet download
12076 @cindex download to Sparclet
12077 Once connected to the Sparclet target,
12078 you can use the @value{GDBN}
12079 @code{load} command to download the file from the host to the target.
12080 The file name and load offset should be given as arguments to the @code{load}
12082 Since the file format is aout, the program must be loaded to the starting
12083 address. You can use @code{objdump} to find out what this value is. The load
12084 offset is an offset which is added to the VMA (virtual memory address)
12085 of each of the file's sections.
12086 For instance, if the program
12087 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
12088 and bss at 0x12010170, in @value{GDBN}, type:
12091 (gdbslet) load prog 0x12010000
12092 Loading section .text, size 0xdb0 vma 0x12010000
12095 If the code is loaded at a different address then what the program was linked
12096 to, you may need to use the @code{section} and @code{add-symbol-file} commands
12097 to tell @value{GDBN} where to map the symbol table.
12099 @node Sparclet Execution
12100 @subsubsection Running and debugging
12102 @cindex running and debugging Sparclet programs
12103 You can now begin debugging the task using @value{GDBN}'s execution control
12104 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
12105 manual for the list of commands.
12109 Breakpoint 1 at 0x12010000: file prog.c, line 3.
12111 Starting program: prog
12112 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
12113 3 char *symarg = 0;
12115 4 char *execarg = "hello!";
12120 @subsection Fujitsu Sparclite
12124 @kindex target sparclite
12125 @item target sparclite @var{dev}
12126 Fujitsu sparclite boards, used only for the purpose of loading.
12127 You must use an additional command to debug the program.
12128 For example: target remote @var{dev} using @value{GDBN} standard
12134 @subsection Tandem ST2000
12136 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
12139 To connect your ST2000 to the host system, see the manufacturer's
12140 manual. Once the ST2000 is physically attached, you can run:
12143 target st2000 @var{dev} @var{speed}
12147 to establish it as your debugging environment. @var{dev} is normally
12148 the name of a serial device, such as @file{/dev/ttya}, connected to the
12149 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
12150 connection (for example, to a serial line attached via a terminal
12151 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
12153 The @code{load} and @code{attach} commands are @emph{not} defined for
12154 this target; you must load your program into the ST2000 as you normally
12155 would for standalone operation. @value{GDBN} reads debugging information
12156 (such as symbols) from a separate, debugging version of the program
12157 available on your host computer.
12158 @c FIXME!! This is terribly vague; what little content is here is
12159 @c basically hearsay.
12161 @cindex ST2000 auxiliary commands
12162 These auxiliary @value{GDBN} commands are available to help you with the ST2000
12166 @item st2000 @var{command}
12167 @kindex st2000 @var{cmd}
12168 @cindex STDBUG commands (ST2000)
12169 @cindex commands to STDBUG (ST2000)
12170 Send a @var{command} to the STDBUG monitor. See the manufacturer's
12171 manual for available commands.
12174 @cindex connect (to STDBUG)
12175 Connect the controlling terminal to the STDBUG command monitor. When
12176 you are done interacting with STDBUG, typing either of two character
12177 sequences gets you back to the @value{GDBN} command prompt:
12178 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
12179 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
12183 @subsection Zilog Z8000
12186 @cindex simulator, Z8000
12187 @cindex Zilog Z8000 simulator
12189 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
12192 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
12193 unsegmented variant of the Z8000 architecture) or the Z8001 (the
12194 segmented variant). The simulator recognizes which architecture is
12195 appropriate by inspecting the object code.
12198 @item target sim @var{args}
12200 @kindex target sim@r{, with Z8000}
12201 Debug programs on a simulated CPU. If the simulator supports setup
12202 options, specify them via @var{args}.
12206 After specifying this target, you can debug programs for the simulated
12207 CPU in the same style as programs for your host computer; use the
12208 @code{file} command to load a new program image, the @code{run} command
12209 to run your program, and so on.
12211 As well as making available all the usual machine registers
12212 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
12213 additional items of information as specially named registers:
12218 Counts clock-ticks in the simulator.
12221 Counts instructions run in the simulator.
12224 Execution time in 60ths of a second.
12228 You can refer to these values in @value{GDBN} expressions with the usual
12229 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
12230 conditional breakpoint that suspends only after at least 5000
12231 simulated clock ticks.
12233 @node Architectures
12234 @section Architectures
12236 This section describes characteristics of architectures that affect
12237 all uses of @value{GDBN} with the architecture, both native and cross.
12250 @kindex set rstack_high_address
12251 @cindex AMD 29K register stack
12252 @cindex register stack, AMD29K
12253 @item set rstack_high_address @var{address}
12254 On AMD 29000 family processors, registers are saved in a separate
12255 @dfn{register stack}. There is no way for @value{GDBN} to determine the
12256 extent of this stack. Normally, @value{GDBN} just assumes that the
12257 stack is ``large enough''. This may result in @value{GDBN} referencing
12258 memory locations that do not exist. If necessary, you can get around
12259 this problem by specifying the ending address of the register stack with
12260 the @code{set rstack_high_address} command. The argument should be an
12261 address, which you probably want to precede with @samp{0x} to specify in
12264 @kindex show rstack_high_address
12265 @item show rstack_high_address
12266 Display the current limit of the register stack, on AMD 29000 family
12274 See the following section.
12279 @cindex stack on Alpha
12280 @cindex stack on MIPS
12281 @cindex Alpha stack
12283 Alpha- and MIPS-based computers use an unusual stack frame, which
12284 sometimes requires @value{GDBN} to search backward in the object code to
12285 find the beginning of a function.
12287 @cindex response time, MIPS debugging
12288 To improve response time (especially for embedded applications, where
12289 @value{GDBN} may be restricted to a slow serial line for this search)
12290 you may want to limit the size of this search, using one of these
12294 @cindex @code{heuristic-fence-post} (Alpha, MIPS)
12295 @item set heuristic-fence-post @var{limit}
12296 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
12297 search for the beginning of a function. A value of @var{0} (the
12298 default) means there is no limit. However, except for @var{0}, the
12299 larger the limit the more bytes @code{heuristic-fence-post} must search
12300 and therefore the longer it takes to run.
12302 @item show heuristic-fence-post
12303 Display the current limit.
12307 These commands are available @emph{only} when @value{GDBN} is configured
12308 for debugging programs on Alpha or MIPS processors.
12311 @node Controlling GDB
12312 @chapter Controlling @value{GDBN}
12314 You can alter the way @value{GDBN} interacts with you by using the
12315 @code{set} command. For commands controlling how @value{GDBN} displays
12316 data, see @ref{Print Settings, ,Print settings}. Other settings are
12321 * Editing:: Command editing
12322 * History:: Command history
12323 * Screen Size:: Screen size
12324 * Numbers:: Numbers
12325 * ABI:: Configuring the current ABI
12326 * Messages/Warnings:: Optional warnings and messages
12327 * Debugging Output:: Optional messages about internal happenings
12335 @value{GDBN} indicates its readiness to read a command by printing a string
12336 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
12337 can change the prompt string with the @code{set prompt} command. For
12338 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
12339 the prompt in one of the @value{GDBN} sessions so that you can always tell
12340 which one you are talking to.
12342 @emph{Note:} @code{set prompt} does not add a space for you after the
12343 prompt you set. This allows you to set a prompt which ends in a space
12344 or a prompt that does not.
12348 @item set prompt @var{newprompt}
12349 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
12351 @kindex show prompt
12353 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
12357 @section Command editing
12359 @cindex command line editing
12361 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
12362 @sc{gnu} library provides consistent behavior for programs which provide a
12363 command line interface to the user. Advantages are @sc{gnu} Emacs-style
12364 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
12365 substitution, and a storage and recall of command history across
12366 debugging sessions.
12368 You may control the behavior of command line editing in @value{GDBN} with the
12369 command @code{set}.
12372 @kindex set editing
12375 @itemx set editing on
12376 Enable command line editing (enabled by default).
12378 @item set editing off
12379 Disable command line editing.
12381 @kindex show editing
12383 Show whether command line editing is enabled.
12387 @section Command history
12389 @value{GDBN} can keep track of the commands you type during your
12390 debugging sessions, so that you can be certain of precisely what
12391 happened. Use these commands to manage the @value{GDBN} command
12395 @cindex history substitution
12396 @cindex history file
12397 @kindex set history filename
12398 @kindex GDBHISTFILE
12399 @item set history filename @var{fname}
12400 Set the name of the @value{GDBN} command history file to @var{fname}.
12401 This is the file where @value{GDBN} reads an initial command history
12402 list, and where it writes the command history from this session when it
12403 exits. You can access this list through history expansion or through
12404 the history command editing characters listed below. This file defaults
12405 to the value of the environment variable @code{GDBHISTFILE}, or to
12406 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
12409 @cindex history save
12410 @kindex set history save
12411 @item set history save
12412 @itemx set history save on
12413 Record command history in a file, whose name may be specified with the
12414 @code{set history filename} command. By default, this option is disabled.
12416 @item set history save off
12417 Stop recording command history in a file.
12419 @cindex history size
12420 @kindex set history size
12421 @item set history size @var{size}
12422 Set the number of commands which @value{GDBN} keeps in its history list.
12423 This defaults to the value of the environment variable
12424 @code{HISTSIZE}, or to 256 if this variable is not set.
12427 @cindex history expansion
12428 History expansion assigns special meaning to the character @kbd{!}.
12429 @ifset have-readline-appendices
12430 @xref{Event Designators}.
12433 Since @kbd{!} is also the logical not operator in C, history expansion
12434 is off by default. If you decide to enable history expansion with the
12435 @code{set history expansion on} command, you may sometimes need to
12436 follow @kbd{!} (when it is used as logical not, in an expression) with
12437 a space or a tab to prevent it from being expanded. The readline
12438 history facilities do not attempt substitution on the strings
12439 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
12441 The commands to control history expansion are:
12444 @kindex set history expansion
12445 @item set history expansion on
12446 @itemx set history expansion
12447 Enable history expansion. History expansion is off by default.
12449 @item set history expansion off
12450 Disable history expansion.
12452 The readline code comes with more complete documentation of
12453 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
12454 or @code{vi} may wish to read it.
12455 @ifset have-readline-appendices
12456 @xref{Command Line Editing}.
12460 @kindex show history
12462 @itemx show history filename
12463 @itemx show history save
12464 @itemx show history size
12465 @itemx show history expansion
12466 These commands display the state of the @value{GDBN} history parameters.
12467 @code{show history} by itself displays all four states.
12473 @item show commands
12474 Display the last ten commands in the command history.
12476 @item show commands @var{n}
12477 Print ten commands centered on command number @var{n}.
12479 @item show commands +
12480 Print ten commands just after the commands last printed.
12484 @section Screen size
12485 @cindex size of screen
12486 @cindex pauses in output
12488 Certain commands to @value{GDBN} may produce large amounts of
12489 information output to the screen. To help you read all of it,
12490 @value{GDBN} pauses and asks you for input at the end of each page of
12491 output. Type @key{RET} when you want to continue the output, or @kbd{q}
12492 to discard the remaining output. Also, the screen width setting
12493 determines when to wrap lines of output. Depending on what is being
12494 printed, @value{GDBN} tries to break the line at a readable place,
12495 rather than simply letting it overflow onto the following line.
12497 Normally @value{GDBN} knows the size of the screen from the terminal
12498 driver software. For example, on Unix @value{GDBN} uses the termcap data base
12499 together with the value of the @code{TERM} environment variable and the
12500 @code{stty rows} and @code{stty cols} settings. If this is not correct,
12501 you can override it with the @code{set height} and @code{set
12508 @kindex show height
12509 @item set height @var{lpp}
12511 @itemx set width @var{cpl}
12513 These @code{set} commands specify a screen height of @var{lpp} lines and
12514 a screen width of @var{cpl} characters. The associated @code{show}
12515 commands display the current settings.
12517 If you specify a height of zero lines, @value{GDBN} does not pause during
12518 output no matter how long the output is. This is useful if output is to a
12519 file or to an editor buffer.
12521 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
12522 from wrapping its output.
12527 @cindex number representation
12528 @cindex entering numbers
12530 You can always enter numbers in octal, decimal, or hexadecimal in
12531 @value{GDBN} by the usual conventions: octal numbers begin with
12532 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
12533 begin with @samp{0x}. Numbers that begin with none of these are, by
12534 default, entered in base 10; likewise, the default display for
12535 numbers---when no particular format is specified---is base 10. You can
12536 change the default base for both input and output with the @code{set
12540 @kindex set input-radix
12541 @item set input-radix @var{base}
12542 Set the default base for numeric input. Supported choices
12543 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12544 specified either unambiguously or using the current default radix; for
12554 sets the base to decimal. On the other hand, @samp{set radix 10}
12555 leaves the radix unchanged no matter what it was.
12557 @kindex set output-radix
12558 @item set output-radix @var{base}
12559 Set the default base for numeric display. Supported choices
12560 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
12561 specified either unambiguously or using the current default radix.
12563 @kindex show input-radix
12564 @item show input-radix
12565 Display the current default base for numeric input.
12567 @kindex show output-radix
12568 @item show output-radix
12569 Display the current default base for numeric display.
12573 @section Configuring the current ABI
12575 @value{GDBN} can determine the @dfn{ABI} (Application Binary Interface) of your
12576 application automatically. However, sometimes you need to override its
12577 conclusions. Use these commands to manage @value{GDBN}'s view of the
12584 One @value{GDBN} configuration can debug binaries for multiple operating
12585 system targets, either via remote debugging or native emulation.
12586 @value{GDBN} will autodetect the @dfn{OS ABI} (Operating System ABI) in use,
12587 but you can override its conclusion using the @code{set osabi} command.
12588 One example where this is useful is in debugging of binaries which use
12589 an alternate C library (e.g.@: @sc{uClibc} for @sc{gnu}/Linux) which does
12590 not have the same identifying marks that the standard C library for your
12595 Show the OS ABI currently in use.
12598 With no argument, show the list of registered available OS ABI's.
12600 @item set osabi @var{abi}
12601 Set the current OS ABI to @var{abi}.
12604 @cindex float promotion
12605 @kindex set coerce-float-to-double
12607 Generally, the way that an argument of type @code{float} is passed to a
12608 function depends on whether the function is prototyped. For a prototyped
12609 (i.e.@: ANSI/ISO style) function, @code{float} arguments are passed unchanged,
12610 according to the architecture's convention for @code{float}. For unprototyped
12611 (i.e.@: K&R style) functions, @code{float} arguments are first promoted to type
12612 @code{double} and then passed.
12614 Unfortunately, some forms of debug information do not reliably indicate whether
12615 a function is prototyped. If @value{GDBN} calls a function that is not marked
12616 as prototyped, it consults @kbd{set coerce-float-to-double}.
12619 @item set coerce-float-to-double
12620 @itemx set coerce-float-to-double on
12621 Arguments of type @code{float} will be promoted to @code{double} when passed
12622 to an unprototyped function. This is the default setting.
12624 @item set coerce-float-to-double off
12625 Arguments of type @code{float} will be passed directly to unprototyped
12629 @node Messages/Warnings
12630 @section Optional warnings and messages
12632 By default, @value{GDBN} is silent about its inner workings. If you are
12633 running on a slow machine, you may want to use the @code{set verbose}
12634 command. This makes @value{GDBN} tell you when it does a lengthy
12635 internal operation, so you will not think it has crashed.
12637 Currently, the messages controlled by @code{set verbose} are those
12638 which announce that the symbol table for a source file is being read;
12639 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
12642 @kindex set verbose
12643 @item set verbose on
12644 Enables @value{GDBN} output of certain informational messages.
12646 @item set verbose off
12647 Disables @value{GDBN} output of certain informational messages.
12649 @kindex show verbose
12651 Displays whether @code{set verbose} is on or off.
12654 By default, if @value{GDBN} encounters bugs in the symbol table of an
12655 object file, it is silent; but if you are debugging a compiler, you may
12656 find this information useful (@pxref{Symbol Errors, ,Errors reading
12661 @kindex set complaints
12662 @item set complaints @var{limit}
12663 Permits @value{GDBN} to output @var{limit} complaints about each type of
12664 unusual symbols before becoming silent about the problem. Set
12665 @var{limit} to zero to suppress all complaints; set it to a large number
12666 to prevent complaints from being suppressed.
12668 @kindex show complaints
12669 @item show complaints
12670 Displays how many symbol complaints @value{GDBN} is permitted to produce.
12674 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
12675 lot of stupid questions to confirm certain commands. For example, if
12676 you try to run a program which is already running:
12680 The program being debugged has been started already.
12681 Start it from the beginning? (y or n)
12684 If you are willing to unflinchingly face the consequences of your own
12685 commands, you can disable this ``feature'':
12689 @kindex set confirm
12691 @cindex confirmation
12692 @cindex stupid questions
12693 @item set confirm off
12694 Disables confirmation requests.
12696 @item set confirm on
12697 Enables confirmation requests (the default).
12699 @kindex show confirm
12701 Displays state of confirmation requests.
12705 @node Debugging Output
12706 @section Optional messages about internal happenings
12708 @kindex set debug arch
12709 @item set debug arch
12710 Turns on or off display of gdbarch debugging info. The default is off
12711 @kindex show debug arch
12712 @item show debug arch
12713 Displays the current state of displaying gdbarch debugging info.
12714 @kindex set debug event
12715 @item set debug event
12716 Turns on or off display of @value{GDBN} event debugging info. The
12718 @kindex show debug event
12719 @item show debug event
12720 Displays the current state of displaying @value{GDBN} event debugging
12722 @kindex set debug expression
12723 @item set debug expression
12724 Turns on or off display of @value{GDBN} expression debugging info. The
12726 @kindex show debug expression
12727 @item show debug expression
12728 Displays the current state of displaying @value{GDBN} expression
12730 @kindex set debug overload
12731 @item set debug overload
12732 Turns on or off display of @value{GDBN} C@t{++} overload debugging
12733 info. This includes info such as ranking of functions, etc. The default
12735 @kindex show debug overload
12736 @item show debug overload
12737 Displays the current state of displaying @value{GDBN} C@t{++} overload
12739 @kindex set debug remote
12740 @cindex packets, reporting on stdout
12741 @cindex serial connections, debugging
12742 @item set debug remote
12743 Turns on or off display of reports on all packets sent back and forth across
12744 the serial line to the remote machine. The info is printed on the
12745 @value{GDBN} standard output stream. The default is off.
12746 @kindex show debug remote
12747 @item show debug remote
12748 Displays the state of display of remote packets.
12749 @kindex set debug serial
12750 @item set debug serial
12751 Turns on or off display of @value{GDBN} serial debugging info. The
12753 @kindex show debug serial
12754 @item show debug serial
12755 Displays the current state of displaying @value{GDBN} serial debugging
12757 @kindex set debug target
12758 @item set debug target
12759 Turns on or off display of @value{GDBN} target debugging info. This info
12760 includes what is going on at the target level of GDB, as it happens. The
12762 @kindex show debug target
12763 @item show debug target
12764 Displays the current state of displaying @value{GDBN} target debugging
12766 @kindex set debug varobj
12767 @item set debug varobj
12768 Turns on or off display of @value{GDBN} variable object debugging
12769 info. The default is off.
12770 @kindex show debug varobj
12771 @item show debug varobj
12772 Displays the current state of displaying @value{GDBN} variable object
12777 @chapter Canned Sequences of Commands
12779 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
12780 command lists}), @value{GDBN} provides two ways to store sequences of
12781 commands for execution as a unit: user-defined commands and command
12785 * Define:: User-defined commands
12786 * Hooks:: User-defined command hooks
12787 * Command Files:: Command files
12788 * Output:: Commands for controlled output
12792 @section User-defined commands
12794 @cindex user-defined command
12795 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
12796 which you assign a new name as a command. This is done with the
12797 @code{define} command. User commands may accept up to 10 arguments
12798 separated by whitespace. Arguments are accessed within the user command
12799 via @var{$arg0@dots{}$arg9}. A trivial example:
12803 print $arg0 + $arg1 + $arg2
12807 To execute the command use:
12814 This defines the command @code{adder}, which prints the sum of
12815 its three arguments. Note the arguments are text substitutions, so they may
12816 reference variables, use complex expressions, or even perform inferior
12822 @item define @var{commandname}
12823 Define a command named @var{commandname}. If there is already a command
12824 by that name, you are asked to confirm that you want to redefine it.
12826 The definition of the command is made up of other @value{GDBN} command lines,
12827 which are given following the @code{define} command. The end of these
12828 commands is marked by a line containing @code{end}.
12833 Takes a single argument, which is an expression to evaluate.
12834 It is followed by a series of commands that are executed
12835 only if the expression is true (nonzero).
12836 There can then optionally be a line @code{else}, followed
12837 by a series of commands that are only executed if the expression
12838 was false. The end of the list is marked by a line containing @code{end}.
12842 The syntax is similar to @code{if}: the command takes a single argument,
12843 which is an expression to evaluate, and must be followed by the commands to
12844 execute, one per line, terminated by an @code{end}.
12845 The commands are executed repeatedly as long as the expression
12849 @item document @var{commandname}
12850 Document the user-defined command @var{commandname}, so that it can be
12851 accessed by @code{help}. The command @var{commandname} must already be
12852 defined. This command reads lines of documentation just as @code{define}
12853 reads the lines of the command definition, ending with @code{end}.
12854 After the @code{document} command is finished, @code{help} on command
12855 @var{commandname} displays the documentation you have written.
12857 You may use the @code{document} command again to change the
12858 documentation of a command. Redefining the command with @code{define}
12859 does not change the documentation.
12861 @kindex help user-defined
12862 @item help user-defined
12863 List all user-defined commands, with the first line of the documentation
12868 @itemx show user @var{commandname}
12869 Display the @value{GDBN} commands used to define @var{commandname} (but
12870 not its documentation). If no @var{commandname} is given, display the
12871 definitions for all user-defined commands.
12873 @kindex show max-user-call-depth
12874 @kindex set max-user-call-depth
12875 @item show max-user-call-depth
12876 @itemx set max-user-call-depth
12877 The value of @code{max-user-call-depth} controls how many recursion
12878 levels are allowed in user-defined commands before GDB suspects an
12879 infinite recursion and aborts the command.
12883 When user-defined commands are executed, the
12884 commands of the definition are not printed. An error in any command
12885 stops execution of the user-defined command.
12887 If used interactively, commands that would ask for confirmation proceed
12888 without asking when used inside a user-defined command. Many @value{GDBN}
12889 commands that normally print messages to say what they are doing omit the
12890 messages when used in a user-defined command.
12893 @section User-defined command hooks
12894 @cindex command hooks
12895 @cindex hooks, for commands
12896 @cindex hooks, pre-command
12900 You may define @dfn{hooks}, which are a special kind of user-defined
12901 command. Whenever you run the command @samp{foo}, if the user-defined
12902 command @samp{hook-foo} exists, it is executed (with no arguments)
12903 before that command.
12905 @cindex hooks, post-command
12908 A hook may also be defined which is run after the command you executed.
12909 Whenever you run the command @samp{foo}, if the user-defined command
12910 @samp{hookpost-foo} exists, it is executed (with no arguments) after
12911 that command. Post-execution hooks may exist simultaneously with
12912 pre-execution hooks, for the same command.
12914 It is valid for a hook to call the command which it hooks. If this
12915 occurs, the hook is not re-executed, thereby avoiding infinte recursion.
12917 @c It would be nice if hookpost could be passed a parameter indicating
12918 @c if the command it hooks executed properly or not. FIXME!
12920 @kindex stop@r{, a pseudo-command}
12921 In addition, a pseudo-command, @samp{stop} exists. Defining
12922 (@samp{hook-stop}) makes the associated commands execute every time
12923 execution stops in your program: before breakpoint commands are run,
12924 displays are printed, or the stack frame is printed.
12926 For example, to ignore @code{SIGALRM} signals while
12927 single-stepping, but treat them normally during normal execution,
12932 handle SIGALRM nopass
12936 handle SIGALRM pass
12939 define hook-continue
12940 handle SIGLARM pass
12944 As a further example, to hook at the begining and end of the @code{echo}
12945 command, and to add extra text to the beginning and end of the message,
12953 define hookpost-echo
12957 (@value{GDBP}) echo Hello World
12958 <<<---Hello World--->>>
12963 You can define a hook for any single-word command in @value{GDBN}, but
12964 not for command aliases; you should define a hook for the basic command
12965 name, e.g. @code{backtrace} rather than @code{bt}.
12966 @c FIXME! So how does Joe User discover whether a command is an alias
12968 If an error occurs during the execution of your hook, execution of
12969 @value{GDBN} commands stops and @value{GDBN} issues a prompt
12970 (before the command that you actually typed had a chance to run).
12972 If you try to define a hook which does not match any known command, you
12973 get a warning from the @code{define} command.
12975 @node Command Files
12976 @section Command files
12978 @cindex command files
12979 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
12980 commands. Comments (lines starting with @kbd{#}) may also be included.
12981 An empty line in a command file does nothing; it does not mean to repeat
12982 the last command, as it would from the terminal.
12985 @cindex @file{.gdbinit}
12986 @cindex @file{gdb.ini}
12987 When you start @value{GDBN}, it automatically executes commands from its
12988 @dfn{init files}, normally called @file{.gdbinit}@footnote{The DJGPP
12989 port of @value{GDBN} uses the name @file{gdb.ini} instead, due to the
12990 limitations of file names imposed by DOS filesystems.}.
12991 During startup, @value{GDBN} does the following:
12995 Reads the init file (if any) in your home directory@footnote{On
12996 DOS/Windows systems, the home directory is the one pointed to by the
12997 @code{HOME} environment variable.}.
13000 Processes command line options and operands.
13003 Reads the init file (if any) in the current working directory.
13006 Reads command files specified by the @samp{-x} option.
13009 The init file in your home directory can set options (such as @samp{set
13010 complaints}) that affect subsequent processing of command line options
13011 and operands. Init files are not executed if you use the @samp{-nx}
13012 option (@pxref{Mode Options, ,Choosing modes}).
13014 @cindex init file name
13015 On some configurations of @value{GDBN}, the init file is known by a
13016 different name (these are typically environments where a specialized
13017 form of @value{GDBN} may need to coexist with other forms, hence a
13018 different name for the specialized version's init file). These are the
13019 environments with special init file names:
13021 @cindex @file{.vxgdbinit}
13024 VxWorks (Wind River Systems real-time OS): @file{.vxgdbinit}
13026 @cindex @file{.os68gdbinit}
13028 OS68K (Enea Data Systems real-time OS): @file{.os68gdbinit}
13030 @cindex @file{.esgdbinit}
13032 ES-1800 (Ericsson Telecom AB M68000 emulator): @file{.esgdbinit}
13035 You can also request the execution of a command file with the
13036 @code{source} command:
13040 @item source @var{filename}
13041 Execute the command file @var{filename}.
13044 The lines in a command file are executed sequentially. They are not
13045 printed as they are executed. An error in any command terminates
13046 execution of the command file and control is returned to the console.
13048 Commands that would ask for confirmation if used interactively proceed
13049 without asking when used in a command file. Many @value{GDBN} commands that
13050 normally print messages to say what they are doing omit the messages
13051 when called from command files.
13053 @value{GDBN} also accepts command input from standard input. In this
13054 mode, normal output goes to standard output and error output goes to
13055 standard error. Errors in a command file supplied on standard input do
13056 not terminate execution of the command file --- execution continues with
13060 gdb < cmds > log 2>&1
13063 (The syntax above will vary depending on the shell used.) This example
13064 will execute commands from the file @file{cmds}. All output and errors
13065 would be directed to @file{log}.
13068 @section Commands for controlled output
13070 During the execution of a command file or a user-defined command, normal
13071 @value{GDBN} output is suppressed; the only output that appears is what is
13072 explicitly printed by the commands in the definition. This section
13073 describes three commands useful for generating exactly the output you
13078 @item echo @var{text}
13079 @c I do not consider backslash-space a standard C escape sequence
13080 @c because it is not in ANSI.
13081 Print @var{text}. Nonprinting characters can be included in
13082 @var{text} using C escape sequences, such as @samp{\n} to print a
13083 newline. @strong{No newline is printed unless you specify one.}
13084 In addition to the standard C escape sequences, a backslash followed
13085 by a space stands for a space. This is useful for displaying a
13086 string with spaces at the beginning or the end, since leading and
13087 trailing spaces are otherwise trimmed from all arguments.
13088 To print @samp{@w{ }and foo =@w{ }}, use the command
13089 @samp{echo \@w{ }and foo = \@w{ }}.
13091 A backslash at the end of @var{text} can be used, as in C, to continue
13092 the command onto subsequent lines. For example,
13095 echo This is some text\n\
13096 which is continued\n\
13097 onto several lines.\n
13100 produces the same output as
13103 echo This is some text\n
13104 echo which is continued\n
13105 echo onto several lines.\n
13109 @item output @var{expression}
13110 Print the value of @var{expression} and nothing but that value: no
13111 newlines, no @samp{$@var{nn} = }. The value is not entered in the
13112 value history either. @xref{Expressions, ,Expressions}, for more information
13115 @item output/@var{fmt} @var{expression}
13116 Print the value of @var{expression} in format @var{fmt}. You can use
13117 the same formats as for @code{print}. @xref{Output Formats,,Output
13118 formats}, for more information.
13121 @item printf @var{string}, @var{expressions}@dots{}
13122 Print the values of the @var{expressions} under the control of
13123 @var{string}. The @var{expressions} are separated by commas and may be
13124 either numbers or pointers. Their values are printed as specified by
13125 @var{string}, exactly as if your program were to execute the C
13127 @c FIXME: the above implies that at least all ANSI C formats are
13128 @c supported, but it isn't true: %E and %G don't work (or so it seems).
13129 @c Either this is a bug, or the manual should document what formats are
13133 printf (@var{string}, @var{expressions}@dots{});
13136 For example, you can print two values in hex like this:
13139 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
13142 The only backslash-escape sequences that you can use in the format
13143 string are the simple ones that consist of backslash followed by a
13148 @chapter @value{GDBN} Text User Interface
13152 * TUI Overview:: TUI overview
13153 * TUI Keys:: TUI key bindings
13154 * TUI Single Key Mode:: TUI single key mode
13155 * TUI Commands:: TUI specific commands
13156 * TUI Configuration:: TUI configuration variables
13159 The @value{GDBN} Text User Interface, TUI in short,
13160 is a terminal interface which uses the @code{curses} library
13161 to show the source file, the assembly output, the program registers
13162 and @value{GDBN} commands in separate text windows.
13163 The TUI is available only when @value{GDBN} is configured
13164 with the @code{--enable-tui} configure option (@pxref{Configure Options}).
13167 @section TUI overview
13169 The TUI has two display modes that can be switched while
13174 A curses (or TUI) mode in which it displays several text
13175 windows on the terminal.
13178 A standard mode which corresponds to the @value{GDBN} configured without
13182 In the TUI mode, @value{GDBN} can display several text window
13187 This window is the @value{GDBN} command window with the @value{GDBN}
13188 prompt and the @value{GDBN} outputs. The @value{GDBN} input is still
13189 managed using readline but through the TUI. The @emph{command}
13190 window is always visible.
13193 The source window shows the source file of the program. The current
13194 line as well as active breakpoints are displayed in this window.
13197 The assembly window shows the disassembly output of the program.
13200 This window shows the processor registers. It detects when
13201 a register is changed and when this is the case, registers that have
13202 changed are highlighted.
13206 The source and assembly windows show the current program position
13207 by highlighting the current line and marking them with the @samp{>} marker.
13208 Breakpoints are also indicated with two markers. A first one
13209 indicates the breakpoint type:
13213 Breakpoint which was hit at least once.
13216 Breakpoint which was never hit.
13219 Hardware breakpoint which was hit at least once.
13222 Hardware breakpoint which was never hit.
13226 The second marker indicates whether the breakpoint is enabled or not:
13230 Breakpoint is enabled.
13233 Breakpoint is disabled.
13237 The source, assembly and register windows are attached to the thread
13238 and the frame position. They are updated when the current thread
13239 changes, when the frame changes or when the program counter changes.
13240 These three windows are arranged by the TUI according to several
13241 layouts. The layout defines which of these three windows are visible.
13242 The following layouts are available:
13252 source and assembly
13255 source and registers
13258 assembly and registers
13262 On top of the command window a status line gives various information
13263 concerning the current process begin debugged. The status line is
13264 updated when the information it shows changes. The following fields
13269 Indicates the current gdb target
13270 (@pxref{Targets, ,Specifying a Debugging Target}).
13273 Gives information about the current process or thread number.
13274 When no process is being debugged, this field is set to @code{No process}.
13277 Gives the current function name for the selected frame.
13278 The name is demangled if demangling is turned on (@pxref{Print Settings}).
13279 When there is no symbol corresponding to the current program counter
13280 the string @code{??} is displayed.
13283 Indicates the current line number for the selected frame.
13284 When the current line number is not known the string @code{??} is displayed.
13287 Indicates the current program counter address.
13292 @section TUI Key Bindings
13293 @cindex TUI key bindings
13295 The TUI installs several key bindings in the readline keymaps
13296 (@pxref{Command Line Editing}).
13297 They allow to leave or enter in the TUI mode or they operate
13298 directly on the TUI layout and windows. The TUI also provides
13299 a @emph{SingleKey} keymap which binds several keys directly to
13300 @value{GDBN} commands. The following key bindings
13301 are installed for both TUI mode and the @value{GDBN} standard mode.
13310 Enter or leave the TUI mode. When the TUI mode is left,
13311 the curses window management is left and @value{GDBN} operates using
13312 its standard mode writing on the terminal directly. When the TUI
13313 mode is entered, the control is given back to the curses windows.
13314 The screen is then refreshed.
13318 Use a TUI layout with only one window. The layout will
13319 either be @samp{source} or @samp{assembly}. When the TUI mode
13320 is not active, it will switch to the TUI mode.
13322 Think of this key binding as the Emacs @kbd{C-x 1} binding.
13326 Use a TUI layout with at least two windows. When the current
13327 layout shows already two windows, a next layout with two windows is used.
13328 When a new layout is chosen, one window will always be common to the
13329 previous layout and the new one.
13331 Think of it as the Emacs @kbd{C-x 2} binding.
13335 Use the TUI @emph{SingleKey} keymap that binds single key to gdb commands
13336 (@pxref{TUI Single Key Mode}).
13340 The following key bindings are handled only by the TUI mode:
13345 Scroll the active window one page up.
13349 Scroll the active window one page down.
13353 Scroll the active window one line up.
13357 Scroll the active window one line down.
13361 Scroll the active window one column left.
13365 Scroll the active window one column right.
13369 Refresh the screen.
13373 In the TUI mode, the arrow keys are used by the active window
13374 for scrolling. This means they are not available for readline. It is
13375 necessary to use other readline key bindings such as @key{C-p}, @key{C-n},
13376 @key{C-b} and @key{C-f}.
13378 @node TUI Single Key Mode
13379 @section TUI Single Key Mode
13380 @cindex TUI single key mode
13382 The TUI provides a @emph{SingleKey} mode in which it installs a particular
13383 key binding in the readline keymaps to connect single keys to
13387 @kindex c @r{(SingleKey TUI key)}
13391 @kindex d @r{(SingleKey TUI key)}
13395 @kindex f @r{(SingleKey TUI key)}
13399 @kindex n @r{(SingleKey TUI key)}
13403 @kindex q @r{(SingleKey TUI key)}
13405 exit the @emph{SingleKey} mode.
13407 @kindex r @r{(SingleKey TUI key)}
13411 @kindex s @r{(SingleKey TUI key)}
13415 @kindex u @r{(SingleKey TUI key)}
13419 @kindex v @r{(SingleKey TUI key)}
13423 @kindex w @r{(SingleKey TUI key)}
13429 Other keys temporarily switch to the @value{GDBN} command prompt.
13430 The key that was pressed is inserted in the editing buffer so that
13431 it is possible to type most @value{GDBN} commands without interaction
13432 with the TUI @emph{SingleKey} mode. Once the command is entered the TUI
13433 @emph{SingleKey} mode is restored. The only way to permanently leave
13434 this mode is by hitting @key{q} or @samp{@key{C-x} @key{s}}.
13438 @section TUI specific commands
13439 @cindex TUI commands
13441 The TUI has specific commands to control the text windows.
13442 These commands are always available, that is they do not depend on
13443 the current terminal mode in which @value{GDBN} runs. When @value{GDBN}
13444 is in the standard mode, using these commands will automatically switch
13450 List and give the size of all displayed windows.
13453 @kindex layout next
13454 Display the next layout.
13457 @kindex layout prev
13458 Display the previous layout.
13462 Display the source window only.
13466 Display the assembly window only.
13469 @kindex layout split
13470 Display the source and assembly window.
13473 @kindex layout regs
13474 Display the register window together with the source or assembly window.
13476 @item focus next | prev | src | asm | regs | split
13478 Set the focus to the named window.
13479 This command allows to change the active window so that scrolling keys
13480 can be affected to another window.
13484 Refresh the screen. This is similar to using @key{C-L} key.
13488 Update the source window and the current execution point.
13490 @item winheight @var{name} +@var{count}
13491 @itemx winheight @var{name} -@var{count}
13493 Change the height of the window @var{name} by @var{count}
13494 lines. Positive counts increase the height, while negative counts
13499 @node TUI Configuration
13500 @section TUI configuration variables
13501 @cindex TUI configuration variables
13503 The TUI has several configuration variables that control the
13504 appearance of windows on the terminal.
13507 @item set tui border-kind @var{kind}
13508 @kindex set tui border-kind
13509 Select the border appearance for the source, assembly and register windows.
13510 The possible values are the following:
13513 Use a space character to draw the border.
13516 Use ascii characters + - and | to draw the border.
13519 Use the Alternate Character Set to draw the border. The border is
13520 drawn using character line graphics if the terminal supports them.
13524 @item set tui active-border-mode @var{mode}
13525 @kindex set tui active-border-mode
13526 Select the attributes to display the border of the active window.
13527 The possible values are @code{normal}, @code{standout}, @code{reverse},
13528 @code{half}, @code{half-standout}, @code{bold} and @code{bold-standout}.
13530 @item set tui border-mode @var{mode}
13531 @kindex set tui border-mode
13532 Select the attributes to display the border of other windows.
13533 The @var{mode} can be one of the following:
13536 Use normal attributes to display the border.
13542 Use reverse video mode.
13545 Use half bright mode.
13547 @item half-standout
13548 Use half bright and standout mode.
13551 Use extra bright or bold mode.
13553 @item bold-standout
13554 Use extra bright or bold and standout mode.
13561 @chapter Using @value{GDBN} under @sc{gnu} Emacs
13564 @cindex @sc{gnu} Emacs
13565 A special interface allows you to use @sc{gnu} Emacs to view (and
13566 edit) the source files for the program you are debugging with
13569 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
13570 executable file you want to debug as an argument. This command starts
13571 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
13572 created Emacs buffer.
13573 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
13575 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
13580 All ``terminal'' input and output goes through the Emacs buffer.
13583 This applies both to @value{GDBN} commands and their output, and to the input
13584 and output done by the program you are debugging.
13586 This is useful because it means that you can copy the text of previous
13587 commands and input them again; you can even use parts of the output
13590 All the facilities of Emacs' Shell mode are available for interacting
13591 with your program. In particular, you can send signals the usual
13592 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
13597 @value{GDBN} displays source code through Emacs.
13600 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
13601 source file for that frame and puts an arrow (@samp{=>}) at the
13602 left margin of the current line. Emacs uses a separate buffer for
13603 source display, and splits the screen to show both your @value{GDBN} session
13606 Explicit @value{GDBN} @code{list} or search commands still produce output as
13607 usual, but you probably have no reason to use them from Emacs.
13610 @emph{Warning:} If the directory where your program resides is not your
13611 current directory, it can be easy to confuse Emacs about the location of
13612 the source files, in which case the auxiliary display buffer does not
13613 appear to show your source. @value{GDBN} can find programs by searching your
13614 environment's @code{PATH} variable, so the @value{GDBN} input and output
13615 session proceeds normally; but Emacs does not get enough information
13616 back from @value{GDBN} to locate the source files in this situation. To
13617 avoid this problem, either start @value{GDBN} mode from the directory where
13618 your program resides, or specify an absolute file name when prompted for the
13619 @kbd{M-x gdb} argument.
13621 A similar confusion can result if you use the @value{GDBN} @code{file} command to
13622 switch to debugging a program in some other location, from an existing
13623 @value{GDBN} buffer in Emacs.
13626 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
13627 you need to call @value{GDBN} by a different name (for example, if you keep
13628 several configurations around, with different names) you can set the
13629 Emacs variable @code{gdb-command-name}; for example,
13632 (setq gdb-command-name "mygdb")
13636 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
13637 in your @file{.emacs} file) makes Emacs call the program named
13638 ``@code{mygdb}'' instead.
13640 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
13641 addition to the standard Shell mode commands:
13645 Describe the features of Emacs' @value{GDBN} Mode.
13648 Execute to another source line, like the @value{GDBN} @code{step} command; also
13649 update the display window to show the current file and location.
13652 Execute to next source line in this function, skipping all function
13653 calls, like the @value{GDBN} @code{next} command. Then update the display window
13654 to show the current file and location.
13657 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
13658 display window accordingly.
13660 @item M-x gdb-nexti
13661 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
13662 display window accordingly.
13665 Execute until exit from the selected stack frame, like the @value{GDBN}
13666 @code{finish} command.
13669 Continue execution of your program, like the @value{GDBN} @code{continue}
13672 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
13675 Go up the number of frames indicated by the numeric argument
13676 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
13677 like the @value{GDBN} @code{up} command.
13679 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
13682 Go down the number of frames indicated by the numeric argument, like the
13683 @value{GDBN} @code{down} command.
13685 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
13688 Read the number where the cursor is positioned, and insert it at the end
13689 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
13690 around an address that was displayed earlier, type @kbd{disassemble};
13691 then move the cursor to the address display, and pick up the
13692 argument for @code{disassemble} by typing @kbd{C-x &}.
13694 You can customize this further by defining elements of the list
13695 @code{gdb-print-command}; once it is defined, you can format or
13696 otherwise process numbers picked up by @kbd{C-x &} before they are
13697 inserted. A numeric argument to @kbd{C-x &} indicates that you
13698 wish special formatting, and also acts as an index to pick an element of the
13699 list. If the list element is a string, the number to be inserted is
13700 formatted using the Emacs function @code{format}; otherwise the number
13701 is passed as an argument to the corresponding list element.
13704 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
13705 tells @value{GDBN} to set a breakpoint on the source line point is on.
13707 If you accidentally delete the source-display buffer, an easy way to get
13708 it back is to type the command @code{f} in the @value{GDBN} buffer, to
13709 request a frame display; when you run under Emacs, this recreates
13710 the source buffer if necessary to show you the context of the current
13713 The source files displayed in Emacs are in ordinary Emacs buffers
13714 which are visiting the source files in the usual way. You can edit
13715 the files with these buffers if you wish; but keep in mind that @value{GDBN}
13716 communicates with Emacs in terms of line numbers. If you add or
13717 delete lines from the text, the line numbers that @value{GDBN} knows cease
13718 to correspond properly with the code.
13720 @c The following dropped because Epoch is nonstandard. Reactivate
13721 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
13723 @kindex Emacs Epoch environment
13727 Version 18 of @sc{gnu} Emacs has a built-in window system
13728 called the @code{epoch}
13729 environment. Users of this environment can use a new command,
13730 @code{inspect} which performs identically to @code{print} except that
13731 each value is printed in its own window.
13734 @include annotate.texi
13735 @include gdbmi.texinfo
13738 @chapter Reporting Bugs in @value{GDBN}
13739 @cindex bugs in @value{GDBN}
13740 @cindex reporting bugs in @value{GDBN}
13742 Your bug reports play an essential role in making @value{GDBN} reliable.
13744 Reporting a bug may help you by bringing a solution to your problem, or it
13745 may not. But in any case the principal function of a bug report is to help
13746 the entire community by making the next version of @value{GDBN} work better. Bug
13747 reports are your contribution to the maintenance of @value{GDBN}.
13749 In order for a bug report to serve its purpose, you must include the
13750 information that enables us to fix the bug.
13753 * Bug Criteria:: Have you found a bug?
13754 * Bug Reporting:: How to report bugs
13758 @section Have you found a bug?
13759 @cindex bug criteria
13761 If you are not sure whether you have found a bug, here are some guidelines:
13764 @cindex fatal signal
13765 @cindex debugger crash
13766 @cindex crash of debugger
13768 If the debugger gets a fatal signal, for any input whatever, that is a
13769 @value{GDBN} bug. Reliable debuggers never crash.
13771 @cindex error on valid input
13773 If @value{GDBN} produces an error message for valid input, that is a
13774 bug. (Note that if you're cross debugging, the problem may also be
13775 somewhere in the connection to the target.)
13777 @cindex invalid input
13779 If @value{GDBN} does not produce an error message for invalid input,
13780 that is a bug. However, you should note that your idea of
13781 ``invalid input'' might be our idea of ``an extension'' or ``support
13782 for traditional practice''.
13785 If you are an experienced user of debugging tools, your suggestions
13786 for improvement of @value{GDBN} are welcome in any case.
13789 @node Bug Reporting
13790 @section How to report bugs
13791 @cindex bug reports
13792 @cindex @value{GDBN} bugs, reporting
13794 A number of companies and individuals offer support for @sc{gnu} products.
13795 If you obtained @value{GDBN} from a support organization, we recommend you
13796 contact that organization first.
13798 You can find contact information for many support companies and
13799 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
13801 @c should add a web page ref...
13803 In any event, we also recommend that you submit bug reports for
13804 @value{GDBN}. The prefered method is to submit them directly using
13805 @uref{http://www.gnu.org/software/gdb/bugs/, @value{GDBN}'s Bugs web
13806 page}. Alternatively, the @email{bug-gdb@@gnu.org, e-mail gateway} can
13809 @strong{Do not send bug reports to @samp{info-gdb}, or to
13810 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
13811 not want to receive bug reports. Those that do have arranged to receive
13814 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
13815 serves as a repeater. The mailing list and the newsgroup carry exactly
13816 the same messages. Often people think of posting bug reports to the
13817 newsgroup instead of mailing them. This appears to work, but it has one
13818 problem which can be crucial: a newsgroup posting often lacks a mail
13819 path back to the sender. Thus, if we need to ask for more information,
13820 we may be unable to reach you. For this reason, it is better to send
13821 bug reports to the mailing list.
13823 The fundamental principle of reporting bugs usefully is this:
13824 @strong{report all the facts}. If you are not sure whether to state a
13825 fact or leave it out, state it!
13827 Often people omit facts because they think they know what causes the
13828 problem and assume that some details do not matter. Thus, you might
13829 assume that the name of the variable you use in an example does not matter.
13830 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
13831 stray memory reference which happens to fetch from the location where that
13832 name is stored in memory; perhaps, if the name were different, the contents
13833 of that location would fool the debugger into doing the right thing despite
13834 the bug. Play it safe and give a specific, complete example. That is the
13835 easiest thing for you to do, and the most helpful.
13837 Keep in mind that the purpose of a bug report is to enable us to fix the
13838 bug. It may be that the bug has been reported previously, but neither
13839 you nor we can know that unless your bug report is complete and
13842 Sometimes people give a few sketchy facts and ask, ``Does this ring a
13843 bell?'' Those bug reports are useless, and we urge everyone to
13844 @emph{refuse to respond to them} except to chide the sender to report
13847 To enable us to fix the bug, you should include all these things:
13851 The version of @value{GDBN}. @value{GDBN} announces it if you start
13852 with no arguments; you can also print it at any time using @code{show
13855 Without this, we will not know whether there is any point in looking for
13856 the bug in the current version of @value{GDBN}.
13859 The type of machine you are using, and the operating system name and
13863 What compiler (and its version) was used to compile @value{GDBN}---e.g.
13864 ``@value{GCC}--2.8.1''.
13867 What compiler (and its version) was used to compile the program you are
13868 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
13869 C Compiler''. For GCC, you can say @code{gcc --version} to get this
13870 information; for other compilers, see the documentation for those
13874 The command arguments you gave the compiler to compile your example and
13875 observe the bug. For example, did you use @samp{-O}? To guarantee
13876 you will not omit something important, list them all. A copy of the
13877 Makefile (or the output from make) is sufficient.
13879 If we were to try to guess the arguments, we would probably guess wrong
13880 and then we might not encounter the bug.
13883 A complete input script, and all necessary source files, that will
13887 A description of what behavior you observe that you believe is
13888 incorrect. For example, ``It gets a fatal signal.''
13890 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
13891 will certainly notice it. But if the bug is incorrect output, we might
13892 not notice unless it is glaringly wrong. You might as well not give us
13893 a chance to make a mistake.
13895 Even if the problem you experience is a fatal signal, you should still
13896 say so explicitly. Suppose something strange is going on, such as, your
13897 copy of @value{GDBN} is out of synch, or you have encountered a bug in
13898 the C library on your system. (This has happened!) Your copy might
13899 crash and ours would not. If you told us to expect a crash, then when
13900 ours fails to crash, we would know that the bug was not happening for
13901 us. If you had not told us to expect a crash, then we would not be able
13902 to draw any conclusion from our observations.
13905 If you wish to suggest changes to the @value{GDBN} source, send us context
13906 diffs. If you even discuss something in the @value{GDBN} source, refer to
13907 it by context, not by line number.
13909 The line numbers in our development sources will not match those in your
13910 sources. Your line numbers would convey no useful information to us.
13914 Here are some things that are not necessary:
13918 A description of the envelope of the bug.
13920 Often people who encounter a bug spend a lot of time investigating
13921 which changes to the input file will make the bug go away and which
13922 changes will not affect it.
13924 This is often time consuming and not very useful, because the way we
13925 will find the bug is by running a single example under the debugger
13926 with breakpoints, not by pure deduction from a series of examples.
13927 We recommend that you save your time for something else.
13929 Of course, if you can find a simpler example to report @emph{instead}
13930 of the original one, that is a convenience for us. Errors in the
13931 output will be easier to spot, running under the debugger will take
13932 less time, and so on.
13934 However, simplification is not vital; if you do not want to do this,
13935 report the bug anyway and send us the entire test case you used.
13938 A patch for the bug.
13940 A patch for the bug does help us if it is a good one. But do not omit
13941 the necessary information, such as the test case, on the assumption that
13942 a patch is all we need. We might see problems with your patch and decide
13943 to fix the problem another way, or we might not understand it at all.
13945 Sometimes with a program as complicated as @value{GDBN} it is very hard to
13946 construct an example that will make the program follow a certain path
13947 through the code. If you do not send us the example, we will not be able
13948 to construct one, so we will not be able to verify that the bug is fixed.
13950 And if we cannot understand what bug you are trying to fix, or why your
13951 patch should be an improvement, we will not install it. A test case will
13952 help us to understand.
13955 A guess about what the bug is or what it depends on.
13957 Such guesses are usually wrong. Even we cannot guess right about such
13958 things without first using the debugger to find the facts.
13961 @c The readline documentation is distributed with the readline code
13962 @c and consists of the two following files:
13964 @c inc-hist.texinfo
13965 @c Use -I with makeinfo to point to the appropriate directory,
13966 @c environment var TEXINPUTS with TeX.
13967 @include rluser.texinfo
13968 @include inc-hist.texinfo
13971 @node Formatting Documentation
13972 @appendix Formatting Documentation
13974 @cindex @value{GDBN} reference card
13975 @cindex reference card
13976 The @value{GDBN} 4 release includes an already-formatted reference card, ready
13977 for printing with PostScript or Ghostscript, in the @file{gdb}
13978 subdirectory of the main source directory@footnote{In
13979 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
13980 release.}. If you can use PostScript or Ghostscript with your printer,
13981 you can print the reference card immediately with @file{refcard.ps}.
13983 The release also includes the source for the reference card. You
13984 can format it, using @TeX{}, by typing:
13990 The @value{GDBN} reference card is designed to print in @dfn{landscape}
13991 mode on US ``letter'' size paper;
13992 that is, on a sheet 11 inches wide by 8.5 inches
13993 high. You will need to specify this form of printing as an option to
13994 your @sc{dvi} output program.
13996 @cindex documentation
13998 All the documentation for @value{GDBN} comes as part of the machine-readable
13999 distribution. The documentation is written in Texinfo format, which is
14000 a documentation system that uses a single source file to produce both
14001 on-line information and a printed manual. You can use one of the Info
14002 formatting commands to create the on-line version of the documentation
14003 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
14005 @value{GDBN} includes an already formatted copy of the on-line Info
14006 version of this manual in the @file{gdb} subdirectory. The main Info
14007 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
14008 subordinate files matching @samp{gdb.info*} in the same directory. If
14009 necessary, you can print out these files, or read them with any editor;
14010 but they are easier to read using the @code{info} subsystem in @sc{gnu}
14011 Emacs or the standalone @code{info} program, available as part of the
14012 @sc{gnu} Texinfo distribution.
14014 If you want to format these Info files yourself, you need one of the
14015 Info formatting programs, such as @code{texinfo-format-buffer} or
14018 If you have @code{makeinfo} installed, and are in the top level
14019 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
14020 version @value{GDBVN}), you can make the Info file by typing:
14027 If you want to typeset and print copies of this manual, you need @TeX{},
14028 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
14029 Texinfo definitions file.
14031 @TeX{} is a typesetting program; it does not print files directly, but
14032 produces output files called @sc{dvi} files. To print a typeset
14033 document, you need a program to print @sc{dvi} files. If your system
14034 has @TeX{} installed, chances are it has such a program. The precise
14035 command to use depends on your system; @kbd{lpr -d} is common; another
14036 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
14037 require a file name without any extension or a @samp{.dvi} extension.
14039 @TeX{} also requires a macro definitions file called
14040 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
14041 written in Texinfo format. On its own, @TeX{} cannot either read or
14042 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
14043 and is located in the @file{gdb-@var{version-number}/texinfo}
14046 If you have @TeX{} and a @sc{dvi} printer program installed, you can
14047 typeset and print this manual. First switch to the the @file{gdb}
14048 subdirectory of the main source directory (for example, to
14049 @file{gdb-@value{GDBVN}/gdb}) and type:
14055 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
14057 @node Installing GDB
14058 @appendix Installing @value{GDBN}
14059 @cindex configuring @value{GDBN}
14060 @cindex installation
14062 @value{GDBN} comes with a @code{configure} script that automates the process
14063 of preparing @value{GDBN} for installation; you can then use @code{make} to
14064 build the @code{gdb} program.
14066 @c irrelevant in info file; it's as current as the code it lives with.
14067 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
14068 look at the @file{README} file in the sources; we may have improved the
14069 installation procedures since publishing this manual.}
14072 The @value{GDBN} distribution includes all the source code you need for
14073 @value{GDBN} in a single directory, whose name is usually composed by
14074 appending the version number to @samp{gdb}.
14076 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
14077 @file{gdb-@value{GDBVN}} directory. That directory contains:
14080 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
14081 script for configuring @value{GDBN} and all its supporting libraries
14083 @item gdb-@value{GDBVN}/gdb
14084 the source specific to @value{GDBN} itself
14086 @item gdb-@value{GDBVN}/bfd
14087 source for the Binary File Descriptor library
14089 @item gdb-@value{GDBVN}/include
14090 @sc{gnu} include files
14092 @item gdb-@value{GDBVN}/libiberty
14093 source for the @samp{-liberty} free software library
14095 @item gdb-@value{GDBVN}/opcodes
14096 source for the library of opcode tables and disassemblers
14098 @item gdb-@value{GDBVN}/readline
14099 source for the @sc{gnu} command-line interface
14101 @item gdb-@value{GDBVN}/glob
14102 source for the @sc{gnu} filename pattern-matching subroutine
14104 @item gdb-@value{GDBVN}/mmalloc
14105 source for the @sc{gnu} memory-mapped malloc package
14108 The simplest way to configure and build @value{GDBN} is to run @code{configure}
14109 from the @file{gdb-@var{version-number}} source directory, which in
14110 this example is the @file{gdb-@value{GDBVN}} directory.
14112 First switch to the @file{gdb-@var{version-number}} source directory
14113 if you are not already in it; then run @code{configure}. Pass the
14114 identifier for the platform on which @value{GDBN} will run as an
14120 cd gdb-@value{GDBVN}
14121 ./configure @var{host}
14126 where @var{host} is an identifier such as @samp{sun4} or
14127 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
14128 (You can often leave off @var{host}; @code{configure} tries to guess the
14129 correct value by examining your system.)
14131 Running @samp{configure @var{host}} and then running @code{make} builds the
14132 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
14133 libraries, then @code{gdb} itself. The configured source files, and the
14134 binaries, are left in the corresponding source directories.
14137 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
14138 system does not recognize this automatically when you run a different
14139 shell, you may need to run @code{sh} on it explicitly:
14142 sh configure @var{host}
14145 If you run @code{configure} from a directory that contains source
14146 directories for multiple libraries or programs, such as the
14147 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
14148 creates configuration files for every directory level underneath (unless
14149 you tell it not to, with the @samp{--norecursion} option).
14151 You can run the @code{configure} script from any of the
14152 subordinate directories in the @value{GDBN} distribution if you only want to
14153 configure that subdirectory, but be sure to specify a path to it.
14155 For example, with version @value{GDBVN}, type the following to configure only
14156 the @code{bfd} subdirectory:
14160 cd gdb-@value{GDBVN}/bfd
14161 ../configure @var{host}
14165 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
14166 However, you should make sure that the shell on your path (named by
14167 the @samp{SHELL} environment variable) is publicly readable. Remember
14168 that @value{GDBN} uses the shell to start your program---some systems refuse to
14169 let @value{GDBN} debug child processes whose programs are not readable.
14172 * Separate Objdir:: Compiling @value{GDBN} in another directory
14173 * Config Names:: Specifying names for hosts and targets
14174 * Configure Options:: Summary of options for configure
14177 @node Separate Objdir
14178 @section Compiling @value{GDBN} in another directory
14180 If you want to run @value{GDBN} versions for several host or target machines,
14181 you need a different @code{gdb} compiled for each combination of
14182 host and target. @code{configure} is designed to make this easy by
14183 allowing you to generate each configuration in a separate subdirectory,
14184 rather than in the source directory. If your @code{make} program
14185 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
14186 @code{make} in each of these directories builds the @code{gdb}
14187 program specified there.
14189 To build @code{gdb} in a separate directory, run @code{configure}
14190 with the @samp{--srcdir} option to specify where to find the source.
14191 (You also need to specify a path to find @code{configure}
14192 itself from your working directory. If the path to @code{configure}
14193 would be the same as the argument to @samp{--srcdir}, you can leave out
14194 the @samp{--srcdir} option; it is assumed.)
14196 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
14197 separate directory for a Sun 4 like this:
14201 cd gdb-@value{GDBVN}
14204 ../gdb-@value{GDBVN}/configure sun4
14209 When @code{configure} builds a configuration using a remote source
14210 directory, it creates a tree for the binaries with the same structure
14211 (and using the same names) as the tree under the source directory. In
14212 the example, you'd find the Sun 4 library @file{libiberty.a} in the
14213 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
14214 @file{gdb-sun4/gdb}.
14216 One popular reason to build several @value{GDBN} configurations in separate
14217 directories is to configure @value{GDBN} for cross-compiling (where
14218 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
14219 programs that run on another machine---the @dfn{target}).
14220 You specify a cross-debugging target by
14221 giving the @samp{--target=@var{target}} option to @code{configure}.
14223 When you run @code{make} to build a program or library, you must run
14224 it in a configured directory---whatever directory you were in when you
14225 called @code{configure} (or one of its subdirectories).
14227 The @code{Makefile} that @code{configure} generates in each source
14228 directory also runs recursively. If you type @code{make} in a source
14229 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
14230 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
14231 will build all the required libraries, and then build GDB.
14233 When you have multiple hosts or targets configured in separate
14234 directories, you can run @code{make} on them in parallel (for example,
14235 if they are NFS-mounted on each of the hosts); they will not interfere
14239 @section Specifying names for hosts and targets
14241 The specifications used for hosts and targets in the @code{configure}
14242 script are based on a three-part naming scheme, but some short predefined
14243 aliases are also supported. The full naming scheme encodes three pieces
14244 of information in the following pattern:
14247 @var{architecture}-@var{vendor}-@var{os}
14250 For example, you can use the alias @code{sun4} as a @var{host} argument,
14251 or as the value for @var{target} in a @code{--target=@var{target}}
14252 option. The equivalent full name is @samp{sparc-sun-sunos4}.
14254 The @code{configure} script accompanying @value{GDBN} does not provide
14255 any query facility to list all supported host and target names or
14256 aliases. @code{configure} calls the Bourne shell script
14257 @code{config.sub} to map abbreviations to full names; you can read the
14258 script, if you wish, or you can use it to test your guesses on
14259 abbreviations---for example:
14262 % sh config.sub i386-linux
14264 % sh config.sub alpha-linux
14265 alpha-unknown-linux-gnu
14266 % sh config.sub hp9k700
14268 % sh config.sub sun4
14269 sparc-sun-sunos4.1.1
14270 % sh config.sub sun3
14271 m68k-sun-sunos4.1.1
14272 % sh config.sub i986v
14273 Invalid configuration `i986v': machine `i986v' not recognized
14277 @code{config.sub} is also distributed in the @value{GDBN} source
14278 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
14280 @node Configure Options
14281 @section @code{configure} options
14283 Here is a summary of the @code{configure} options and arguments that
14284 are most often useful for building @value{GDBN}. @code{configure} also has
14285 several other options not listed here. @inforef{What Configure
14286 Does,,configure.info}, for a full explanation of @code{configure}.
14289 configure @r{[}--help@r{]}
14290 @r{[}--prefix=@var{dir}@r{]}
14291 @r{[}--exec-prefix=@var{dir}@r{]}
14292 @r{[}--srcdir=@var{dirname}@r{]}
14293 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
14294 @r{[}--target=@var{target}@r{]}
14299 You may introduce options with a single @samp{-} rather than
14300 @samp{--} if you prefer; but you may abbreviate option names if you use
14305 Display a quick summary of how to invoke @code{configure}.
14307 @item --prefix=@var{dir}
14308 Configure the source to install programs and files under directory
14311 @item --exec-prefix=@var{dir}
14312 Configure the source to install programs under directory
14315 @c avoid splitting the warning from the explanation:
14317 @item --srcdir=@var{dirname}
14318 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
14319 @code{make} that implements the @code{VPATH} feature.}@*
14320 Use this option to make configurations in directories separate from the
14321 @value{GDBN} source directories. Among other things, you can use this to
14322 build (or maintain) several configurations simultaneously, in separate
14323 directories. @code{configure} writes configuration specific files in
14324 the current directory, but arranges for them to use the source in the
14325 directory @var{dirname}. @code{configure} creates directories under
14326 the working directory in parallel to the source directories below
14329 @item --norecursion
14330 Configure only the directory level where @code{configure} is executed; do not
14331 propagate configuration to subdirectories.
14333 @item --target=@var{target}
14334 Configure @value{GDBN} for cross-debugging programs running on the specified
14335 @var{target}. Without this option, @value{GDBN} is configured to debug
14336 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
14338 There is no convenient way to generate a list of all available targets.
14340 @item @var{host} @dots{}
14341 Configure @value{GDBN} to run on the specified @var{host}.
14343 There is no convenient way to generate a list of all available hosts.
14346 There are many other options available as well, but they are generally
14347 needed for special purposes only.
14349 @node Maintenance Commands
14350 @appendix Maintenance Commands
14351 @cindex maintenance commands
14352 @cindex internal commands
14354 In addition to commands intended for @value{GDBN} users, @value{GDBN}
14355 includes a number of commands intended for @value{GDBN} developers.
14356 These commands are provided here for reference.
14359 @kindex maint info breakpoints
14360 @item @anchor{maint info breakpoints}maint info breakpoints
14361 Using the same format as @samp{info breakpoints}, display both the
14362 breakpoints you've set explicitly, and those @value{GDBN} is using for
14363 internal purposes. Internal breakpoints are shown with negative
14364 breakpoint numbers. The type column identifies what kind of breakpoint
14369 Normal, explicitly set breakpoint.
14372 Normal, explicitly set watchpoint.
14375 Internal breakpoint, used to handle correctly stepping through
14376 @code{longjmp} calls.
14378 @item longjmp resume
14379 Internal breakpoint at the target of a @code{longjmp}.
14382 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
14385 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
14388 Shared library events.
14392 @kindex maint internal-error
14393 @kindex maint internal-warning
14394 @item maint internal-error
14395 @itemx maint internal-warning
14396 Cause @value{GDBN} to call the internal function @code{internal_error}
14397 or @code{internal_warning} and hence behave as though an internal error
14398 or internal warning has been detected. In addition to reporting the
14399 internal problem, these functions give the user the opportunity to
14400 either quit @value{GDBN} or create a core file of the current
14401 @value{GDBN} session.
14404 (gdb) @kbd{maint internal-error testing, 1, 2}
14405 @dots{}/maint.c:121: internal-error: testing, 1, 2
14406 A problem internal to GDB has been detected. Further
14407 debugging may prove unreliable.
14408 Quit this debugging session? (y or n) @kbd{n}
14409 Create a core file? (y or n) @kbd{n}
14413 Takes an optional parameter that is used as the text of the error or
14416 @kindex maint print registers
14417 @kindex maint print raw-registers
14418 @kindex maint print cooked-registers
14419 @item maint print registers
14420 @itemx maint print raw-registers
14421 @itemx maint print cooked-registers
14422 Print @value{GDBN}'s internal register data structures.
14424 The command @samp{maint print raw-registers} includes the contents of
14425 the raw register cache; and the command @samp{maint print
14426 cooked-registers} includes the (cooked) value of all registers.
14427 @xref{Registers,, Registers, gdbint, @value{GDBN} Internals}.
14429 Takes an optional file parameter.
14434 @node Remote Protocol
14435 @appendix @value{GDBN} Remote Serial Protocol
14440 * Stop Reply Packets::
14441 * General Query Packets::
14442 * Register Packet Format::
14449 There may be occasions when you need to know something about the
14450 protocol---for example, if there is only one serial port to your target
14451 machine, you might want your program to do something special if it
14452 recognizes a packet meant for @value{GDBN}.
14454 In the examples below, @samp{->} and @samp{<-} are used to indicate
14455 transmitted and received data respectfully.
14457 @cindex protocol, @value{GDBN} remote serial
14458 @cindex serial protocol, @value{GDBN} remote
14459 @cindex remote serial protocol
14460 All @value{GDBN} commands and responses (other than acknowledgments) are
14461 sent as a @var{packet}. A @var{packet} is introduced with the character
14462 @samp{$}, the actual @var{packet-data}, and the terminating character
14463 @samp{#} followed by a two-digit @var{checksum}:
14466 @code{$}@var{packet-data}@code{#}@var{checksum}
14470 @cindex checksum, for @value{GDBN} remote
14472 The two-digit @var{checksum} is computed as the modulo 256 sum of all
14473 characters between the leading @samp{$} and the trailing @samp{#} (an
14474 eight bit unsigned checksum).
14476 Implementors should note that prior to @value{GDBN} 5.0 the protocol
14477 specification also included an optional two-digit @var{sequence-id}:
14480 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
14483 @cindex sequence-id, for @value{GDBN} remote
14485 That @var{sequence-id} was appended to the acknowledgment. @value{GDBN}
14486 has never output @var{sequence-id}s. Stubs that handle packets added
14487 since @value{GDBN} 5.0 must not accept @var{sequence-id}.
14489 @cindex acknowledgment, for @value{GDBN} remote
14490 When either the host or the target machine receives a packet, the first
14491 response expected is an acknowledgment: either @samp{+} (to indicate
14492 the package was received correctly) or @samp{-} (to request
14496 -> @code{$}@var{packet-data}@code{#}@var{checksum}
14501 The host (@value{GDBN}) sends @var{command}s, and the target (the
14502 debugging stub incorporated in your program) sends a @var{response}. In
14503 the case of step and continue @var{command}s, the response is only sent
14504 when the operation has completed (the target has again stopped).
14506 @var{packet-data} consists of a sequence of characters with the
14507 exception of @samp{#} and @samp{$} (see @samp{X} packet for additional
14510 Fields within the packet should be separated using @samp{,} @samp{;} or
14511 @cindex remote protocol, field separator
14512 @samp{:}. Except where otherwise noted all numbers are represented in
14513 @sc{hex} with leading zeros suppressed.
14515 Implementors should note that prior to @value{GDBN} 5.0, the character
14516 @samp{:} could not appear as the third character in a packet (as it
14517 would potentially conflict with the @var{sequence-id}).
14519 Response @var{data} can be run-length encoded to save space. A @samp{*}
14520 means that the next character is an @sc{ascii} encoding giving a repeat count
14521 which stands for that many repetitions of the character preceding the
14522 @samp{*}. The encoding is @code{n+29}, yielding a printable character
14523 where @code{n >=3} (which is where rle starts to win). The printable
14524 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
14525 value greater than 126 should not be used.
14527 Some remote systems have used a different run-length encoding mechanism
14528 loosely refered to as the cisco encoding. Following the @samp{*}
14529 character are two hex digits that indicate the size of the packet.
14536 means the same as "0000".
14538 The error response returned for some packets includes a two character
14539 error number. That number is not well defined.
14541 For any @var{command} not supported by the stub, an empty response
14542 (@samp{$#00}) should be returned. That way it is possible to extend the
14543 protocol. A newer @value{GDBN} can tell if a packet is supported based
14546 A stub is required to support the @samp{g}, @samp{G}, @samp{m}, @samp{M},
14547 @samp{c}, and @samp{s} @var{command}s. All other @var{command}s are
14553 The following table provides a complete list of all currently defined
14554 @var{command}s and their corresponding response @var{data}.
14558 @item @code{!} --- extended mode
14559 @cindex @code{!} packet
14561 Enable extended mode. In extended mode, the remote server is made
14562 persistent. The @samp{R} packet is used to restart the program being
14568 The remote target both supports and has enabled extended mode.
14571 @item @code{?} --- last signal
14572 @cindex @code{?} packet
14574 Indicate the reason the target halted. The reply is the same as for
14578 @xref{Stop Reply Packets}, for the reply specifications.
14580 @item @code{a} --- reserved
14582 Reserved for future use.
14584 @item @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,@dots{}} --- set program arguments @strong{(reserved)}
14585 @cindex @code{A} packet
14587 Initialized @samp{argv[]} array passed into program. @var{arglen}
14588 specifies the number of bytes in the hex encoded byte stream @var{arg}.
14589 See @code{gdbserver} for more details.
14597 @item @code{b}@var{baud} --- set baud @strong{(deprecated)}
14598 @cindex @code{b} packet
14600 Change the serial line speed to @var{baud}.
14602 JTC: @emph{When does the transport layer state change? When it's
14603 received, or after the ACK is transmitted. In either case, there are
14604 problems if the command or the acknowledgment packet is dropped.}
14606 Stan: @emph{If people really wanted to add something like this, and get
14607 it working for the first time, they ought to modify ser-unix.c to send
14608 some kind of out-of-band message to a specially-setup stub and have the
14609 switch happen "in between" packets, so that from remote protocol's point
14610 of view, nothing actually happened.}
14612 @item @code{B}@var{addr},@var{mode} --- set breakpoint @strong{(deprecated)}
14613 @cindex @code{B} packet
14615 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
14616 breakpoint at @var{addr}.
14618 This packet has been replaced by the @samp{Z} and @samp{z} packets
14619 (@pxref{insert breakpoint or watchpoint packet}).
14621 @item @code{c}@var{addr} --- continue
14622 @cindex @code{c} packet
14624 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14628 @xref{Stop Reply Packets}, for the reply specifications.
14630 @item @code{C}@var{sig}@code{;}@var{addr} --- continue with signal
14631 @cindex @code{C} packet
14633 Continue with signal @var{sig} (hex signal number). If
14634 @code{;}@var{addr} is omitted, resume at same address.
14637 @xref{Stop Reply Packets}, for the reply specifications.
14639 @item @code{d} --- toggle debug @strong{(deprecated)}
14640 @cindex @code{d} packet
14644 @item @code{D} --- detach
14645 @cindex @code{D} packet
14647 Detach @value{GDBN} from the remote system. Sent to the remote target
14648 before @value{GDBN} disconnects.
14652 @item @emph{no response}
14653 @value{GDBN} does not check for any response after sending this packet.
14656 @item @code{e} --- reserved
14658 Reserved for future use.
14660 @item @code{E} --- reserved
14662 Reserved for future use.
14664 @item @code{f} --- reserved
14666 Reserved for future use.
14668 @item @code{F} --- reserved
14670 Reserved for future use.
14672 @item @code{g} --- read registers
14673 @anchor{read registers packet}
14674 @cindex @code{g} packet
14676 Read general registers.
14680 @item @var{XX@dots{}}
14681 Each byte of register data is described by two hex digits. The bytes
14682 with the register are transmitted in target byte order. The size of
14683 each register and their position within the @samp{g} @var{packet} are
14684 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE}
14685 and @var{REGISTER_NAME} macros. The specification of several standard
14686 @code{g} packets is specified below.
14691 @item @code{G}@var{XX@dots{}} --- write regs
14692 @cindex @code{G} packet
14694 @xref{read registers packet}, for a description of the @var{XX@dots{}}
14705 @item @code{h} --- reserved
14707 Reserved for future use.
14709 @item @code{H}@var{c}@var{t@dots{}} --- set thread
14710 @cindex @code{H} packet
14712 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
14713 @samp{G}, et.al.). @var{c} depends on the operation to be performed: it
14714 should be @samp{c} for step and continue operations, @samp{g} for other
14715 operations. The thread designator @var{t@dots{}} may be -1, meaning all
14716 the threads, a thread number, or zero which means pick any thread.
14727 @c 'H': How restrictive (or permissive) is the thread model. If a
14728 @c thread is selected and stopped, are other threads allowed
14729 @c to continue to execute? As I mentioned above, I think the
14730 @c semantics of each command when a thread is selected must be
14731 @c described. For example:
14733 @c 'g': If the stub supports threads and a specific thread is
14734 @c selected, returns the register block from that thread;
14735 @c otherwise returns current registers.
14737 @c 'G' If the stub supports threads and a specific thread is
14738 @c selected, sets the registers of the register block of
14739 @c that thread; otherwise sets current registers.
14741 @item @code{i}@var{addr}@code{,}@var{nnn} --- cycle step @strong{(draft)}
14742 @anchor{cycle step packet}
14743 @cindex @code{i} packet
14745 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
14746 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
14747 step starting at that address.
14749 @item @code{I} --- signal then cycle step @strong{(reserved)}
14750 @cindex @code{I} packet
14752 @xref{step with signal packet}. @xref{cycle step packet}.
14754 @item @code{j} --- reserved
14756 Reserved for future use.
14758 @item @code{J} --- reserved
14760 Reserved for future use.
14762 @item @code{k} --- kill request
14763 @cindex @code{k} packet
14765 FIXME: @emph{There is no description of how to operate when a specific
14766 thread context has been selected (i.e.@: does 'k' kill only that
14769 @item @code{K} --- reserved
14771 Reserved for future use.
14773 @item @code{l} --- reserved
14775 Reserved for future use.
14777 @item @code{L} --- reserved
14779 Reserved for future use.
14781 @item @code{m}@var{addr}@code{,}@var{length} --- read memory
14782 @cindex @code{m} packet
14784 Read @var{length} bytes of memory starting at address @var{addr}.
14785 Neither @value{GDBN} nor the stub assume that sized memory transfers are
14786 assumed using word aligned accesses. FIXME: @emph{A word aligned memory
14787 transfer mechanism is needed.}
14791 @item @var{XX@dots{}}
14792 @var{XX@dots{}} is mem contents. Can be fewer bytes than requested if able
14793 to read only part of the data. Neither @value{GDBN} nor the stub assume
14794 that sized memory transfers are assumed using word aligned
14795 accesses. FIXME: @emph{A word aligned memory transfer mechanism is
14801 @item @code{M}@var{addr},@var{length}@code{:}@var{XX@dots{}} --- write mem
14802 @cindex @code{M} packet
14804 Write @var{length} bytes of memory starting at address @var{addr}.
14805 @var{XX@dots{}} is the data.
14812 for an error (this includes the case where only part of the data was
14816 @item @code{n} --- reserved
14818 Reserved for future use.
14820 @item @code{N} --- reserved
14822 Reserved for future use.
14824 @item @code{o} --- reserved
14826 Reserved for future use.
14828 @item @code{O} --- reserved
14830 Reserved for future use.
14832 @item @code{p}@var{n@dots{}} --- read reg @strong{(reserved)}
14833 @cindex @code{p} packet
14835 @xref{write register packet}.
14839 @item @var{r@dots{}.}
14840 The hex encoded value of the register in target byte order.
14843 @item @code{P}@var{n@dots{}}@code{=}@var{r@dots{}} --- write register
14844 @anchor{write register packet}
14845 @cindex @code{P} packet
14847 Write register @var{n@dots{}} with value @var{r@dots{}}, which contains two hex
14848 digits for each byte in the register (target byte order).
14858 @item @code{q}@var{query} --- general query
14859 @anchor{general query packet}
14860 @cindex @code{q} packet
14862 Request info about @var{query}. In general @value{GDBN} queries have a
14863 leading upper case letter. Custom vendor queries should use a company
14864 prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may optionally
14865 be followed by a @samp{,} or @samp{;} separated list. Stubs must ensure
14866 that they match the full @var{query} name.
14870 @item @var{XX@dots{}}
14871 Hex encoded data from query. The reply can not be empty.
14875 Indicating an unrecognized @var{query}.
14878 @item @code{Q}@var{var}@code{=}@var{val} --- general set
14879 @cindex @code{Q} packet
14881 Set value of @var{var} to @var{val}.
14883 @xref{general query packet}, for a discussion of naming conventions.
14885 @item @code{r} --- reset @strong{(deprecated)}
14886 @cindex @code{r} packet
14888 Reset the entire system.
14890 @item @code{R}@var{XX} --- remote restart
14891 @cindex @code{R} packet
14893 Restart the program being debugged. @var{XX}, while needed, is ignored.
14894 This packet is only available in extended mode.
14898 @item @emph{no reply}
14899 The @samp{R} packet has no reply.
14902 @item @code{s}@var{addr} --- step
14903 @cindex @code{s} packet
14905 @var{addr} is address to resume. If @var{addr} is omitted, resume at
14909 @xref{Stop Reply Packets}, for the reply specifications.
14911 @item @code{S}@var{sig}@code{;}@var{addr} --- step with signal
14912 @anchor{step with signal packet}
14913 @cindex @code{S} packet
14915 Like @samp{C} but step not continue.
14918 @xref{Stop Reply Packets}, for the reply specifications.
14920 @item @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM} --- search
14921 @cindex @code{t} packet
14923 Search backwards starting at address @var{addr} for a match with pattern
14924 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4 bytes.
14925 @var{addr} must be at least 3 digits.
14927 @item @code{T}@var{XX} --- thread alive
14928 @cindex @code{T} packet
14930 Find out if the thread XX is alive.
14935 thread is still alive
14940 @item @code{u} --- reserved
14942 Reserved for future use.
14944 @item @code{U} --- reserved
14946 Reserved for future use.
14948 @item @code{v} --- reserved
14950 Reserved for future use.
14952 @item @code{V} --- reserved
14954 Reserved for future use.
14956 @item @code{w} --- reserved
14958 Reserved for future use.
14960 @item @code{W} --- reserved
14962 Reserved for future use.
14964 @item @code{x} --- reserved
14966 Reserved for future use.
14968 @item @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX@dots{}} --- write mem (binary)
14969 @cindex @code{X} packet
14971 @var{addr} is address, @var{length} is number of bytes, @var{XX@dots{}}
14972 is binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
14973 escaped using @code{0x7d}.
14983 @item @code{y} --- reserved
14985 Reserved for future use.
14987 @item @code{Y} reserved
14989 Reserved for future use.
14991 @item @code{z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- remove breakpoint or watchpoint @strong{(draft)}
14992 @itemx @code{Z}@var{type}@code{,}@var{addr}@code{,}@var{length} --- insert breakpoint or watchpoint @strong{(draft)}
14993 @anchor{insert breakpoint or watchpoint packet}
14994 @cindex @code{z} packet
14995 @cindex @code{Z} packets
14997 Insert (@code{Z}) or remove (@code{z}) a @var{type} breakpoint or
14998 watchpoint starting at address @var{address} and covering the next
14999 @var{length} bytes.
15001 Each breakpoint and watchpoint packet @var{type} is documented
15004 @emph{Implementation notes: A remote target shall return an empty string
15005 for an unrecognized breakpoint or watchpoint packet @var{type}. A
15006 remote target shall support either both or neither of a given
15007 @code{Z}@var{type}@dots{} and @code{z}@var{type}@dots{} packet pair. To
15008 avoid potential problems with duplicate packets, the operations should
15009 be implemented in an idempotent way.}
15011 @item @code{z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- remove memory breakpoint @strong{(draft)}
15012 @item @code{Z}@code{0}@code{,}@var{addr}@code{,}@var{length} --- insert memory breakpoint @strong{(draft)}
15013 @cindex @code{z0} packet
15014 @cindex @code{Z0} packet
15016 Insert (@code{Z0}) or remove (@code{z0}) a memory breakpoint at address
15017 @code{addr} of size @code{length}.
15019 A memory breakpoint is implemented by replacing the instruction at
15020 @var{addr} with a software breakpoint or trap instruction. The
15021 @code{length} is used by targets that indicates the size of the
15022 breakpoint (in bytes) that should be inserted (e.g., the @sc{arm} and
15023 @sc{mips} can insert either a 2 or 4 byte breakpoint).
15025 @emph{Implementation note: It is possible for a target to copy or move
15026 code that contains memory breakpoints (e.g., when implementing
15027 overlays). The behavior of this packet, in the presence of such a
15028 target, is not defined.}
15040 @item @code{z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- remove hardware breakpoint @strong{(draft)}
15041 @item @code{Z}@code{1}@code{,}@var{addr}@code{,}@var{length} --- insert hardware breakpoint @strong{(draft)}
15042 @cindex @code{z1} packet
15043 @cindex @code{Z1} packet
15045 Insert (@code{Z1}) or remove (@code{z1}) a hardware breakpoint at
15046 address @code{addr} of size @code{length}.
15048 A hardware breakpoint is implemented using a mechanism that is not
15049 dependant on being able to modify the target's memory.
15051 @emph{Implementation note: A hardware breakpoint is not affected by code
15064 @item @code{z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- remove write watchpoint @strong{(draft)}
15065 @item @code{Z}@code{2}@code{,}@var{addr}@code{,}@var{length} --- insert write watchpoint @strong{(draft)}
15066 @cindex @code{z2} packet
15067 @cindex @code{Z2} packet
15069 Insert (@code{Z2}) or remove (@code{z2}) a write watchpoint.
15081 @item @code{z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- remove read watchpoint @strong{(draft)}
15082 @item @code{Z}@code{3}@code{,}@var{addr}@code{,}@var{length} --- insert read watchpoint @strong{(draft)}
15083 @cindex @code{z3} packet
15084 @cindex @code{Z3} packet
15086 Insert (@code{Z3}) or remove (@code{z3}) a read watchpoint.
15098 @item @code{z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- remove access watchpoint @strong{(draft)}
15099 @item @code{Z}@code{4}@code{,}@var{addr}@code{,}@var{length} --- insert access watchpoint @strong{(draft)}
15100 @cindex @code{z4} packet
15101 @cindex @code{Z4} packet
15103 Insert (@code{Z4}) or remove (@code{z4}) an access watchpoint.
15117 @node Stop Reply Packets
15118 @section Stop Reply Packets
15119 @cindex stop reply packets
15121 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
15122 receive any of the below as a reply. In the case of the @samp{C},
15123 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
15124 when the target halts. In the below the exact meaning of @samp{signal
15125 number} is poorly defined. In general one of the UNIX signal numbering
15126 conventions is used.
15131 @var{AA} is the signal number
15133 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
15134 @cindex @code{T} packet reply
15136 @var{AA} = two hex digit signal number; @var{n...} = register number
15137 (hex), @var{r...} = target byte ordered register contents, size defined
15138 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
15139 thread process ID, this is a hex integer; @var{n...} = (@samp{watch} |
15140 @samp{rwatch} | @samp{awatch}, @var{r...} = data address, this is a hex
15141 integer; @var{n...} = other string not starting with valid hex digit.
15142 @value{GDBN} should ignore this @var{n...}, @var{r...} pair and go on
15143 to the next. This way we can extend the protocol.
15147 The process exited, and @var{AA} is the exit status. This is only
15148 applicable to certain targets.
15152 The process terminated with signal @var{AA}.
15154 @item N@var{AA};@var{t@dots{}};@var{d@dots{}};@var{b@dots{}} @strong{(obsolete)}
15156 @var{AA} = signal number; @var{t@dots{}} = address of symbol
15157 @code{_start}; @var{d@dots{}} = base of data section; @var{b@dots{}} =
15158 base of bss section. @emph{Note: only used by Cisco Systems targets.
15159 The difference between this reply and the @samp{qOffsets} query is that
15160 the @samp{N} packet may arrive spontaneously whereas the @samp{qOffsets}
15161 is a query initiated by the host debugger.}
15163 @item O@var{XX@dots{}}
15165 @var{XX@dots{}} is hex encoding of @sc{ascii} data. This can happen at
15166 any time while the program is running and the debugger should continue
15167 to wait for @samp{W}, @samp{T}, etc.
15171 @node General Query Packets
15172 @section General Query Packets
15174 The following set and query packets have already been defined.
15178 @item @code{q}@code{C} --- current thread
15180 Return the current thread id.
15184 @item @code{QC}@var{pid}
15185 Where @var{pid} is a HEX encoded 16 bit process id.
15187 Any other reply implies the old pid.
15190 @item @code{q}@code{fThreadInfo} -- all thread ids
15192 @code{q}@code{sThreadInfo}
15194 Obtain a list of active thread ids from the target (OS). Since there
15195 may be too many active threads to fit into one reply packet, this query
15196 works iteratively: it may require more than one query/reply sequence to
15197 obtain the entire list of threads. The first query of the sequence will
15198 be the @code{qf}@code{ThreadInfo} query; subsequent queries in the
15199 sequence will be the @code{qs}@code{ThreadInfo} query.
15201 NOTE: replaces the @code{qL} query (see below).
15205 @item @code{m}@var{id}
15207 @item @code{m}@var{id},@var{id}@dots{}
15208 a comma-separated list of thread ids
15210 (lower case 'el') denotes end of list.
15213 In response to each query, the target will reply with a list of one or
15214 more thread ids, in big-endian hex, separated by commas. @value{GDBN}
15215 will respond to each reply with a request for more thread ids (using the
15216 @code{qs} form of the query), until the target responds with @code{l}
15217 (lower-case el, for @code{'last'}).
15219 @item @code{q}@code{ThreadExtraInfo}@code{,}@var{id} --- extra thread info
15221 Where @var{id} is a thread-id in big-endian hex. Obtain a printable
15222 string description of a thread's attributes from the target OS. This
15223 string may contain anything that the target OS thinks is interesting for
15224 @value{GDBN} to tell the user about the thread. The string is displayed
15225 in @value{GDBN}'s @samp{info threads} display. Some examples of
15226 possible thread extra info strings are ``Runnable'', or ``Blocked on
15231 @item @var{XX@dots{}}
15232 Where @var{XX@dots{}} is a hex encoding of @sc{ascii} data, comprising
15233 the printable string containing the extra information about the thread's
15237 @item @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread} --- query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
15239 Obtain thread information from RTOS. Where: @var{startflag} (one hex
15240 digit) is one to indicate the first query and zero to indicate a
15241 subsequent query; @var{threadcount} (two hex digits) is the maximum
15242 number of threads the response packet can contain; and @var{nextthread}
15243 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
15244 returned in the response as @var{argthread}.
15246 NOTE: this query is replaced by the @code{q}@code{fThreadInfo} query
15251 @item @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread@dots{}}
15252 Where: @var{count} (two hex digits) is the number of threads being
15253 returned; @var{done} (one hex digit) is zero to indicate more threads
15254 and one indicates no further threads; @var{argthreadid} (eight hex
15255 digits) is @var{nextthread} from the request packet; @var{thread@dots{}}
15256 is a sequence of thread IDs from the target. @var{threadid} (eight hex
15257 digits). See @code{remote.c:parse_threadlist_response()}.
15260 @item @code{q}@code{CRC:}@var{addr}@code{,}@var{length} --- compute CRC of memory block
15264 @item @code{E}@var{NN}
15265 An error (such as memory fault)
15266 @item @code{C}@var{CRC32}
15267 A 32 bit cyclic redundancy check of the specified memory region.
15270 @item @code{q}@code{Offsets} --- query sect offs
15272 Get section offsets that the target used when re-locating the downloaded
15273 image. @emph{Note: while a @code{Bss} offset is included in the
15274 response, @value{GDBN} ignores this and instead applies the @code{Data}
15275 offset to the @code{Bss} section.}
15279 @item @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
15282 @item @code{q}@code{P}@var{mode}@var{threadid} --- thread info request
15284 Returns information on @var{threadid}. Where: @var{mode} is a hex
15285 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
15292 See @code{remote.c:remote_unpack_thread_info_response()}.
15294 @item @code{q}@code{Rcmd,}@var{command} --- remote command
15296 @var{command} (hex encoded) is passed to the local interpreter for
15297 execution. Invalid commands should be reported using the output string.
15298 Before the final result packet, the target may also respond with a
15299 number of intermediate @code{O}@var{output} console output packets.
15300 @emph{Implementors should note that providing access to a stubs's
15301 interpreter may have security implications}.
15306 A command response with no output.
15308 A command response with the hex encoded output string @var{OUTPUT}.
15309 @item @code{E}@var{NN}
15310 Indicate a badly formed request.
15312 When @samp{q}@samp{Rcmd} is not recognized.
15315 @item @code{qSymbol::} --- symbol lookup
15317 Notify the target that @value{GDBN} is prepared to serve symbol lookup
15318 requests. Accept requests from the target for the values of symbols.
15323 The target does not need to look up any (more) symbols.
15324 @item @code{qSymbol:}@var{sym_name}
15325 The target requests the value of symbol @var{sym_name} (hex encoded).
15326 @value{GDBN} may provide the value by using the
15327 @code{qSymbol:}@var{sym_value}:@var{sym_name} message, described below.
15330 @item @code{qSymbol:}@var{sym_value}:@var{sym_name} --- symbol value
15332 Set the value of @var{sym_name} to @var{sym_value}.
15334 @var{sym_name} (hex encoded) is the name of a symbol whose value the
15335 target has previously requested.
15337 @var{sym_value} (hex) is the value for symbol @var{sym_name}. If
15338 @value{GDBN} cannot supply a value for @var{sym_name}, then this field
15344 The target does not need to look up any (more) symbols.
15345 @item @code{qSymbol:}@var{sym_name}
15346 The target requests the value of a new symbol @var{sym_name} (hex
15347 encoded). @value{GDBN} will continue to supply the values of symbols
15348 (if available), until the target ceases to request them.
15353 @node Register Packet Format
15354 @section Register Packet Format
15356 The following @samp{g}/@samp{G} packets have previously been defined.
15357 In the below, some thirty-two bit registers are transferred as
15358 sixty-four bits. Those registers should be zero/sign extended (which?)
15359 to fill the space allocated. Register bytes are transfered in target
15360 byte order. The two nibbles within a register byte are transfered
15361 most-significant - least-significant.
15367 All registers are transfered as thirty-two bit quantities in the order:
15368 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
15369 registers; fsr; fir; fp.
15373 All registers are transfered as sixty-four bit quantities (including
15374 thirty-two bit registers such as @code{sr}). The ordering is the same
15382 Example sequence of a target being re-started. Notice how the restart
15383 does not get any direct output:
15388 @emph{target restarts}
15391 <- @code{T001:1234123412341234}
15395 Example sequence of a target being stepped by a single instruction:
15398 -> @code{G1445@dots{}}
15403 <- @code{T001:1234123412341234}
15407 <- @code{1455@dots{}}
15421 % I think something like @colophon should be in texinfo. In the
15423 \long\def\colophon{\hbox to0pt{}\vfill
15424 \centerline{The body of this manual is set in}
15425 \centerline{\fontname\tenrm,}
15426 \centerline{with headings in {\bf\fontname\tenbf}}
15427 \centerline{and examples in {\tt\fontname\tentt}.}
15428 \centerline{{\it\fontname\tenit\/},}
15429 \centerline{{\bf\fontname\tenbf}, and}
15430 \centerline{{\sl\fontname\tensl\/}}
15431 \centerline{are used for emphasis.}\vfill}
15433 % Blame: doc@cygnus.com, 1991.