1 \input texinfo @c -*-texinfo-*-
3 @c Free Software Foundation, Inc.
6 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
7 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
13 @setchapternewpage odd
24 @c readline appendices use @vindex
27 @c !!set GDB manual's edition---not the same as GDB version!
30 @c !!set GDB manual's revision date
31 @set DATE February 1999
33 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
36 @c This is a dir.info fragment to support semi-automated addition of
37 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
40 * Gdb: (gdb). The @sc{gnu} debugger.
47 This file documents the @sc{gnu} debugger @value{GDBN}.
50 This is the @value{EDITION} Edition, @value{DATE},
51 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
52 for @value{GDBN} Version @value{GDBVN}.
54 Copyright (C) 1988-1999 Free Software Foundation, Inc.
56 Permission is granted to make and distribute verbatim copies of
57 this manual provided the copyright notice and this permission notice
58 are preserved on all copies.
61 Permission is granted to process this file through TeX and print the
62 results, provided the printed document carries copying permission
63 notice identical to this one except for the removal of this paragraph
64 (this paragraph not being relevant to the printed manual).
67 Permission is granted to copy and distribute modified versions of this
68 manual under the conditions for verbatim copying, provided also that the
69 entire resulting derived work is distributed under the terms of a
70 permission notice identical to this one.
72 Permission is granted to copy and distribute translations of this manual
73 into another language, under the above conditions for modified versions.
77 @title Debugging with @value{GDBN}
78 @subtitle The @sc{gnu} Source-Level Debugger
81 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
82 @subtitle @value{DATE}
83 @author Richard M. Stallman and Roland H. Pesch
86 @subtitle Edition @value{EDITION}, for @value{HPVER} (based on @value{GDBN} @value{GDBVN})
87 @subtitle @value{DATE}
88 @author Richard M. Stallman and Roland H. Pesch (modified by HP)
94 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
95 \hfill {\it Debugging with @value{GDBN}}\par
96 \hfill \TeX{}info \texinfoversion\par
103 \hfill {\it Debugging with @value{GDBN}}\par
104 \hfill \TeX{}info \texinfoversion\par
109 @vskip 0pt plus 1filll
110 Copyright @copyright{} 1988-1999 Free Software Foundation, Inc.
113 Published by the Free Software Foundation @*
114 59 Temple Place - Suite 330, @*
115 Boston, MA 02111-1307 USA @*
116 Printed copies are available for $20 each. @*
117 ISBN 1-882114-11-6 @*
120 Permission is granted to make and distribute verbatim copies of
121 this manual provided the copyright notice and this permission notice
122 are preserved on all copies.
124 Permission is granted to copy and distribute modified versions of this
125 manual under the conditions for verbatim copying, provided also that the
126 entire resulting derived work is distributed under the terms of a
127 permission notice identical to this one.
129 Permission is granted to copy and distribute translations of this manual
130 into another language, under the above conditions for modified versions.
135 @node Top, Summary, (dir), (dir)
136 @top Debugging with @value{GDBN}
138 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
140 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
143 Copyright (C) 1988-1999 Free Software Foundation, Inc.
145 * Summary:: Summary of @value{GDBN}
146 * Sample Session:: A sample @value{GDBN} session
148 * Invocation:: Getting in and out of @value{GDBN}
149 * Commands:: @value{GDBN} commands
150 * Running:: Running programs under @value{GDBN}
151 * Stopping:: Stopping and continuing
152 * Stack:: Examining the stack
153 * Source:: Examining source files
154 * Data:: Examining data
156 * Languages:: Using @value{GDBN} with different languages
157 * C:: C language support
159 * Symbols:: Examining the symbol table
160 * Altering:: Altering execution
161 * GDB Files:: @value{GDBN} files
162 * Targets:: Specifying a debugging target
163 * Controlling GDB:: Controlling @value{GDBN}
164 * Sequences:: Canned sequences of commands
165 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
167 * GDB Bugs:: Reporting bugs in @value{GDBN}
169 @ifclear PRECONFIGURED
171 * Formatting Documentation:: How to format and print @value{GDBN} documentation
176 * Command Line Editing:: Command Line Editing
177 * Using History Interactively:: Using History Interactively
178 * Installing GDB:: Installing GDB
181 --- The Detailed Node Listing ---
183 Summary of @value{GDBN}
185 * Free Software:: Freely redistributable software
186 * Contributors:: Contributors to GDB
188 Getting In and Out of @value{GDBN}
190 * Invoking GDB:: How to start @value{GDBN}
191 * Quitting GDB:: How to quit @value{GDBN}
192 * Shell Commands:: How to use shell commands inside @value{GDBN}
194 Invoking @value{GDBN}
196 * File Options:: Choosing files
197 * Mode Options:: Choosing modes
199 @value{GDBN} Commands
201 * Command Syntax:: How to give commands to @value{GDBN}
202 * Completion:: Command completion
203 * Help:: How to ask @value{GDBN} for help
205 Running Programs Under @value{GDBN}
207 * Compilation:: Compiling for debugging
208 * Starting:: Starting your program
209 * Arguments:: Your program's arguments
210 * Environment:: Your program's environment
211 * Working Directory:: Your program's working directory
212 * Input/Output:: Your program's input and output
213 * Attach:: Debugging an already-running process
214 * Kill Process:: Killing the child process
215 * Process Information:: Additional process information
217 * Threads:: Debugging programs with multiple threads
218 * Processes:: Debugging programs with multiple processes
220 Stopping and Continuing
222 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
223 * Continuing and Stepping:: Resuming execution
225 * Thread Stops:: Stopping and starting multi-thread programs
227 Breakpoints and watchpoints
229 * Set Breaks:: Setting breakpoints
230 * Set Watchpoints:: Setting watchpoints
231 * Set Catchpoints:: Setting catchpoints
232 * Delete Breaks:: Deleting breakpoints
233 * Disabling:: Disabling breakpoints
234 * Conditions:: Break conditions
235 * Break Commands:: Breakpoint command lists
236 * Breakpoint Menus:: Breakpoint menus
240 * Frames:: Stack frames
241 * Backtrace:: Backtraces
242 * Selection:: Selecting a frame
243 * Frame Info:: Information on a frame
244 * Alpha/MIPS Stack:: Alpha and MIPS machines and the function stack
246 Examining Source Files
248 * List:: Printing source lines
249 * Search:: Searching source files
250 * Source Path:: Specifying source directories
251 * Machine Code:: Source and machine code
255 * Expressions:: Expressions
256 * Variables:: Program variables
257 * Arrays:: Artificial arrays
258 * Output Formats:: Output formats
259 * Memory:: Examining memory
260 * Auto Display:: Automatic display
261 * Print Settings:: Print settings
262 * Value History:: Value history
263 * Convenience Vars:: Convenience variables
264 * Registers:: Registers
265 * Floating Point Hardware:: Floating point hardware
267 Using @value{GDBN} with Different Languages
269 * Setting:: Switching between source languages
270 * Show:: Displaying the language
271 * Checks:: Type and range checks
272 * Support:: Supported languages
274 Switching between source languages
276 * Filenames:: Filename extensions and languages.
277 * Manually:: Setting the working language manually
278 * Automatically:: Having @value{GDBN} infer the source language
280 Type and range checking
282 * Type Checking:: An overview of type checking
283 * Range Checking:: An overview of range checking
290 * C Operators:: C and C++ operators
291 * C Constants:: C and C++ constants
292 * C plus plus expressions:: C++ expressions
293 * C Defaults:: Default settings for C and C++
294 * C Checks:: C and C++ type and range checks
295 * Debugging C:: @value{GDBN} and C
296 * Debugging C plus plus:: @value{GDBN} features for C++
300 * M2 Operators:: Built-in operators
301 * Built-In Func/Proc:: Built-in functions and procedures
302 * M2 Constants:: Modula-2 constants
303 * M2 Defaults:: Default settings for Modula-2
304 * Deviations:: Deviations from standard Modula-2
305 * M2 Checks:: Modula-2 type and range checks
306 * M2 Scope:: The scope operators @code{::} and @code{.}
307 * GDB/M2:: @value{GDBN} and Modula-2
311 * Assignment:: Assignment to variables
312 * Jumping:: Continuing at a different address
313 * Signaling:: Giving your program a signal
314 * Returning:: Returning from a function
315 * Calling:: Calling your program's functions
316 * Patching:: Patching your program
320 * Files:: Commands to specify files
321 * Symbol Errors:: Errors reading symbol files
323 Specifying a Debugging Target
325 * Active Targets:: Active targets
326 * Target Commands:: Commands for managing targets
328 * Byte Order:: Choosing target byte order
329 * Remote:: Remote debugging
334 * Remote Serial:: @value{GDBN} remote serial protocol
336 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
338 * UDI29K Remote:: The UDI protocol for AMD29K
340 * EB29K Remote:: The EBMON protocol for AMD29K
342 * VxWorks Remote:: @value{GDBN} and VxWorks
344 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
346 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
348 * MIPS Remote:: @value{GDBN} and MIPS boards
350 * Simulator:: Simulated CPU target
352 Controlling @value{GDBN}
355 * Editing:: Command editing
356 * History:: Command history
357 * Screen Size:: Screen size
359 * Messages/Warnings:: Optional warnings and messages
361 Canned Sequences of Commands
363 * Define:: User-defined commands
364 * Hooks:: User-defined command hooks
365 * Command Files:: Command files
366 * Output:: Commands for controlled output
368 Reporting Bugs in @value{GDBN}
370 * Bug Criteria:: Have you found a bug?
371 * Bug Reporting:: How to report bugs
373 Installing @value{GDBN}
375 * Separate Objdir:: Compiling @value{GDBN} in another directory
376 * Config Names:: Specifying names for hosts and targets
377 * Configure Options:: Summary of options for configure
382 @node Summary, Sample Session, Top, Top
383 @unnumbered Summary of @value{GDBN}
385 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
386 going on ``inside'' another program while it executes---or what another
387 program was doing at the moment it crashed.
389 @value{GDBN} can do four main kinds of things (plus other things in support of
390 these) to help you catch bugs in the act:
394 Start your program, specifying anything that might affect its behavior.
397 Make your program stop on specified conditions.
400 Examine what has happened, when your program has stopped.
403 Change things in your program, so you can experiment with correcting the
404 effects of one bug and go on to learn about another.
407 You can use @value{GDBN} to debug programs written in C and C++.
408 For more information, see @ref{Support,,Supported languages}.
409 For more information, see @ref{C,,C and C++}.
413 Support for Modula-2 and Chill is partial. For information on Modula-2,
414 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
417 Debugging Pascal programs which use sets, subranges, file variables, or
418 nested functions does not currently work. @value{GDBN} does not support
419 entering expressions, printing values, or similar features using Pascal
423 @value{GDBN} can be used to debug programs written in Fortran, although
424 It may be necessary to refer to some variables with a trailing
428 This version of the manual documents HP Wildebeest (WDB) Version 0.75,
429 implemented on HP 9000 systems running Release 10.20, 10.30, or 11.0 of
430 the HP-UX operating system. HP WDB 0.75 can be used to debug code
431 generated by the HP ANSI C and HP ANSI C++ compilers as well as the
432 @sc{gnu} C and C++ compilers. It does not support the debugging of
433 Fortran, Modula-2, or Chill programs.
437 * Free Software:: Freely redistributable software
438 * Contributors:: Contributors to GDB
441 @node Free Software, Contributors, Summary, Summary
442 @unnumberedsec Free software
444 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
445 General Public License
446 (GPL). The GPL gives you the freedom to copy or adapt a licensed
447 program---but every person getting a copy also gets with it the
448 freedom to modify that copy (which means that they must get access to
449 the source code), and the freedom to distribute further copies.
450 Typical software companies use copyrights to limit your freedoms; the
451 Free Software Foundation uses the GPL to preserve these freedoms.
453 Fundamentally, the General Public License is a license which says that
454 you have these freedoms and that you cannot take these freedoms away
457 @node Contributors, , Free Software, Summary
458 @unnumberedsec Contributors to GDB
460 Richard Stallman was the original author of GDB, and of many other
461 @sc{gnu} programs. Many others have contributed to its development.
462 This section attempts to credit major contributors. One of the virtues
463 of free software is that everyone is free to contribute to it; with
464 regret, we cannot actually acknowledge everyone here. The file
465 @file{ChangeLog} in the @value{GDBN} distribution approximates a
466 blow-by-blow account.
468 Changes much prior to version 2.0 are lost in the mists of time.
471 @emph{Plea:} Additions to this section are particularly welcome. If you
472 or your friends (or enemies, to be evenhanded) have been unfairly
473 omitted from this list, we would like to add your names!
476 So that they may not regard their many labors as thankless, we
477 particularly thank those who shepherded @value{GDBN} through major
479 Jim Blandy (release 4.18);
480 Jason Molenda (release 4.17);
481 Stan Shebs (release 4.14);
482 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
483 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
484 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
485 Jim Kingdon (releases 3.5, 3.4, and 3.3);
486 and Randy Smith (releases 3.2, 3.1, and 3.0).
488 Richard Stallman, assisted at various times by Peter TerMaat, Chris
489 Hanson, and Richard Mlynarik, handled releases through 2.8.
491 Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB,
492 with significant additional contributions from Per Bothner. James
493 Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter
494 TerMaat (who also did much general update work leading to release 3.0).
496 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
497 object-file formats; BFD was a joint project of David V.
498 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
500 David Johnson wrote the original COFF support; Pace Willison did
501 the original support for encapsulated COFF.
503 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
505 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
506 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
508 Jean-Daniel Fekete contributed Sun 386i support.
509 Chris Hanson improved the HP9000 support.
510 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
511 David Johnson contributed Encore Umax support.
512 Jyrki Kuoppala contributed Altos 3068 support.
513 Jeff Law contributed HP PA and SOM support.
514 Keith Packard contributed NS32K support.
515 Doug Rabson contributed Acorn Risc Machine support.
516 Bob Rusk contributed Harris Nighthawk CX-UX support.
517 Chris Smith contributed Convex support (and Fortran debugging).
518 Jonathan Stone contributed Pyramid support.
519 Michael Tiemann contributed SPARC support.
520 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
521 Pace Willison contributed Intel 386 support.
522 Jay Vosburgh contributed Symmetry support.
524 Andreas Schwab contributed M68K Linux support.
526 Rich Schaefer and Peter Schauer helped with support of SunOS shared
529 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
530 about several machine instruction sets.
532 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
533 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
534 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
535 and RDI targets, respectively.
537 Brian Fox is the author of the readline libraries providing
538 command-line editing and command history.
540 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
541 Modula-2 support, and contributed the Languages chapter of this manual.
543 Fred Fish wrote most of the support for Unix System Vr4.
544 He also enhanced the command-completion support to cover C++ overloaded
547 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
550 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
552 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
554 Toshiba sponsored the support for the TX39 Mips processor.
556 Matsushita sponsored the support for the MN10200 and MN10300 processors.
558 Fujitsu sponsored the support for SPARClite and FR30 processors
560 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
563 Michael Snyder added support for tracepoints.
565 Stu Grossman wrote gdbserver.
567 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
568 nearly innumerable bug fixes and cleanups throughout GDB.
570 The following people at the Hewlett-Packard Company contributed
571 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
572 (narrow mode), HP's implementation of kernel threads, HP's aC++
573 compiler, and the terminal user interface: Ben Krepp, Richard Title,
574 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
575 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
576 information in this manual.
578 Cygnus Solutions has sponsored GDB maintenance and much of its
579 development since 1991. Cygnus engineers who have worked on GDB
580 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Edith Epstein,
581 Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu
582 Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey
583 Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan
584 Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian
585 Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ
586 Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David
587 Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke,
588 Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore,
589 Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith,
590 Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron
591 Unrau, Jim Wilson, and David Zuhn have made contributions both large
595 @node Sample Session, Invocation, Summary, Top
596 @chapter A Sample @value{GDBN} Session
598 You can use this manual at your leisure to read all about @value{GDBN}.
599 However, a handful of commands are enough to get started using the
600 debugger. This chapter illustrates those commands.
603 In this sample session, we emphasize user input like this: @b{input},
604 to make it easier to pick out from the surrounding output.
607 @c FIXME: this example may not be appropriate for some configs, where
608 @c FIXME...primary interest is in remote use.
610 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
611 processor) exhibits the following bug: sometimes, when we change its
612 quote strings from the default, the commands used to capture one macro
613 definition within another stop working. In the following short @code{m4}
614 session, we define a macro @code{foo} which expands to @code{0000}; we
615 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
616 same thing. However, when we change the open quote string to
617 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
618 procedure fails to define a new synonym @code{baz}:
627 @b{define(bar,defn(`foo'))}
631 @b{changequote(<QUOTE>,<UNQUOTE>)}
633 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
636 m4: End of input: 0: fatal error: EOF in string
640 Let us use @value{GDBN} to try to see what is going on.
644 $ @b{@value{GDBP} m4}
645 @c FIXME: this falsifies the exact text played out, to permit smallbook
646 @c FIXME... format to come out better.
647 @value{GDBN} is free software and you are welcome to distribute copies
648 of it under certain conditions; type "show copying" to see
650 There is absolutely no warranty for @value{GDBN}; type "show warranty"
653 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
659 $ @b{@value{GDBP} m4}
660 Wildebeest is free software and you are welcome to distribute copies of
661 it under certain conditions; type "show copying" to see the conditions.
662 There is absolutely no warranty for Wildebeest; type "show warranty"
665 Hewlett-Packard Wildebeest 0.75 (based on GDB 4.16)
666 (built for PA-RISC 1.1 or 2.0, HP-UX 10.20)
667 Copyright 1996, 1997 Free Software Foundation, Inc.
673 @value{GDBN} reads only enough symbol data to know where to find the
674 rest when needed; as a result, the first prompt comes up very quickly.
675 We now tell @value{GDBN} to use a narrower display width than usual, so
676 that examples fit in this manual.
679 (@value{GDBP}) @b{set width 70}
683 We need to see how the @code{m4} built-in @code{changequote} works.
684 Having looked at the source, we know the relevant subroutine is
685 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
686 @code{break} command.
689 (@value{GDBP}) @b{break m4_changequote}
690 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
694 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
695 control; as long as control does not reach the @code{m4_changequote}
696 subroutine, the program runs as usual:
699 (@value{GDBP}) @b{run}
700 Starting program: /work/Editorial/gdb/gnu/m4/m4
708 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
709 suspends execution of @code{m4}, displaying information about the
710 context where it stops.
713 @b{changequote(<QUOTE>,<UNQUOTE>)}
715 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
717 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
721 Now we use the command @code{n} (@code{next}) to advance execution to
722 the next line of the current function.
726 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
731 @code{set_quotes} looks like a promising subroutine. We can go into it
732 by using the command @code{s} (@code{step}) instead of @code{next}.
733 @code{step} goes to the next line to be executed in @emph{any}
734 subroutine, so it steps into @code{set_quotes}.
738 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
740 530 if (lquote != def_lquote)
744 The display that shows the subroutine where @code{m4} is now
745 suspended (and its arguments) is called a stack frame display. It
746 shows a summary of the stack. We can use the @code{backtrace}
747 command (which can also be spelled @code{bt}), to see where we are
748 in the stack as a whole: the @code{backtrace} command displays a
749 stack frame for each active subroutine.
752 (@value{GDBP}) @b{bt}
753 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
755 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
757 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
758 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
760 #4 0x79dc in expand_input () at macro.c:40
761 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
765 We step through a few more lines to see what happens. The first two
766 times, we can use @samp{s}; the next two times we use @code{n} to avoid
767 falling into the @code{xstrdup} subroutine.
771 0x3b5c 532 if (rquote != def_rquote)
773 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
774 def_lquote : xstrdup(lq);
776 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
779 538 len_lquote = strlen(rquote);
783 The last line displayed looks a little odd; we can examine the variables
784 @code{lquote} and @code{rquote} to see if they are in fact the new left
785 and right quotes we specified. We use the command @code{p}
786 (@code{print}) to see their values.
789 (@value{GDBP}) @b{p lquote}
790 $1 = 0x35d40 "<QUOTE>"
791 (@value{GDBP}) @b{p rquote}
792 $2 = 0x35d50 "<UNQUOTE>"
796 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
797 To look at some context, we can display ten lines of source
798 surrounding the current line with the @code{l} (@code{list}) command.
804 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
806 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
809 538 len_lquote = strlen(rquote);
810 539 len_rquote = strlen(lquote);
817 Let us step past the two lines that set @code{len_lquote} and
818 @code{len_rquote}, and then examine the values of those variables.
822 539 len_rquote = strlen(lquote);
825 (@value{GDBP}) @b{p len_lquote}
827 (@value{GDBP}) @b{p len_rquote}
832 That certainly looks wrong, assuming @code{len_lquote} and
833 @code{len_rquote} are meant to be the lengths of @code{lquote} and
834 @code{rquote} respectively. We can set them to better values using
835 the @code{p} command, since it can print the value of
836 any expression---and that expression can include subroutine calls and
840 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
842 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
847 Is that enough to fix the problem of using the new quotes with the
848 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
849 executing with the @code{c} (@code{continue}) command, and then try the
850 example that caused trouble initially:
856 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
863 Success! The new quotes now work just as well as the default ones. The
864 problem seems to have been just the two typos defining the wrong
865 lengths. We allow @code{m4} exit by giving it an EOF as input:
869 Program exited normally.
873 The message @samp{Program exited normally.} is from @value{GDBN}; it
874 indicates @code{m4} has finished executing. We can end our @value{GDBN}
875 session with the @value{GDBN} @code{quit} command.
878 (@value{GDBP}) @b{quit}
881 @node Invocation, Commands, Sample Session, Top
882 @chapter Getting In and Out of @value{GDBN}
884 This chapter discusses how to start @value{GDBN}, and how to get out of it.
888 type @samp{@value{GDBP}} to start GDB.
890 type @kbd{quit} or @kbd{C-d} to exit.
894 * Invoking GDB:: How to start @value{GDBN}
895 * Quitting GDB:: How to quit @value{GDBN}
896 * Shell Commands:: How to use shell commands inside @value{GDBN}
899 @node Invoking GDB, Quitting GDB, Invocation, Invocation
900 @section Invoking @value{GDBN}
902 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
903 @value{GDBN} reads commands from the terminal until you tell it to exit.
905 You can also run @code{@value{GDBP}} with a variety of arguments and options,
906 to specify more of your debugging environment at the outset.
908 The command-line options described here are designed
909 to cover a variety of situations; in some environments, some of these
910 options may effectively be unavailable.
912 The most usual way to start @value{GDBN} is with one argument,
913 specifying an executable program:
916 @value{GDBP} @var{program}
920 You can also start with both an executable program and a core file
924 @value{GDBP} @var{program} @var{core}
927 You can, instead, specify a process ID as a second argument, if you want
928 to debug a running process:
931 @value{GDBP} @var{program} 1234
935 would attach @value{GDBN} to process @code{1234} (unless you also have a file
936 named @file{1234}; @value{GDBN} does check for a core file first).
939 Taking advantage of the second command-line argument requires a fairly
940 complete operating system; when you use @value{GDBN} as a remote debugger
941 attached to a bare board, there may not be any notion of ``process'',
942 and there is often no way to get a core dump.
945 You can run @code{gdb} without printing the front material, which describes
946 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
953 You can further control how @value{GDBN} starts up by using command-line
954 options. @value{GDBN} itself can remind you of the options available.
964 to display all available options and briefly describe their use
965 (@samp{@value{GDBP} -h} is a shorter equivalent).
967 All options and command line arguments you give are processed
968 in sequential order. The order makes a difference when the
969 @samp{-x} option is used.
973 * File Options:: Choosing files
974 * Mode Options:: Choosing modes
978 @subsection Choosing files
980 When @value{GDBN} starts, it reads any arguments other than options as
981 specifying an executable file and core file (or process ID). This is
982 the same as if the arguments were specified by the @samp{-se} and
983 @samp{-c} options respectively. (@value{GDBN} reads the first argument
984 that does not have an associated option flag as equivalent to the
985 @samp{-se} option followed by that argument; and the second argument
986 that does not have an associated option flag, if any, as equivalent to
987 the @samp{-c} option followed by that argument.)
989 If @value{GDBN} has not been configured to included core file support,
990 such as for most embedded targets, then it will complain about a second
991 argument and ignore it.
993 Many options have both long and short forms; both are shown in the
994 following list. @value{GDBN} also recognizes the long forms if you truncate
995 them, so long as enough of the option is present to be unambiguous.
996 (If you prefer, you can flag option arguments with @samp{--} rather
997 than @samp{-}, though we illustrate the more usual convention.)
1000 @item -symbols @var{file}
1001 @itemx -s @var{file}
1002 Read symbol table from file @var{file}.
1004 @item -exec @var{file}
1005 @itemx -e @var{file}
1006 Use file @var{file} as the executable file to execute when appropriate,
1007 and for examining pure data in conjunction with a core dump.
1009 @item -se @var{file}
1010 Read symbol table from file @var{file} and use it as the executable
1013 @item -core @var{file}
1014 @itemx -c @var{file}
1015 Use file @var{file} as a core dump to examine.
1017 @item -c @var{number}
1018 Connect to process ID @var{number}, as with the @code{attach} command
1019 (unless there is a file in core-dump format named @var{number}, in which
1020 case @samp{-c} specifies that file as a core dump to read).
1022 @item -command @var{file}
1023 @itemx -x @var{file}
1024 Execute @value{GDBN} commands from file @var{file}. @xref{Command
1025 Files,, Command files}.
1027 @item -directory @var{directory}
1028 @itemx -d @var{directory}
1029 Add @var{directory} to the path to search for source files.
1034 @emph{Warning: this option depends on operating system facilities that are not
1035 supported on all systems.}@*
1036 If memory-mapped files are available on your system through the @code{mmap}
1037 system call, you can use this option
1038 to have @value{GDBN} write the symbols from your
1039 program into a reusable file in the current directory. If the program you are debugging is
1040 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
1041 Future @value{GDBN} debugging sessions notice the presence of this file,
1042 and can quickly map in symbol information from it, rather than reading
1043 the symbol table from the executable program.
1045 The @file{.syms} file is specific to the host machine where @value{GDBN}
1046 is run. It holds an exact image of the internal @value{GDBN} symbol
1047 table. It cannot be shared across multiple host platforms.
1053 Read each symbol file's entire symbol table immediately, rather than
1054 the default, which is to read it incrementally as it is needed.
1055 This makes startup slower, but makes future operations faster.
1060 The @code{-mapped} and @code{-readnow} options are typically combined in
1061 order to build a @file{.syms} file that contains complete symbol
1062 information. (@xref{Files,,Commands to specify files}, for
1063 information on @file{.syms} files.) A simple GDB invocation to do
1064 nothing but build a @file{.syms} file for future use is:
1067 gdb -batch -nx -mapped -readnow programname
1071 @node Mode Options, , File Options, Invoking GDB
1072 @subsection Choosing modes
1074 You can run @value{GDBN} in various alternative modes---for example, in
1075 batch mode or quiet mode.
1080 Do not execute commands from any initialization files (normally called
1081 @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally, the commands in
1082 these files are executed after all the command options and arguments
1083 have been processed. @xref{Command Files,,Command files}.
1087 ``Quiet''. Do not print the introductory and copyright messages. These
1088 messages are also suppressed in batch mode.
1091 Run in batch mode. Exit with status @code{0} after processing all the
1092 command files specified with @samp{-x} (and all commands from
1093 initialization files, if not inhibited with @samp{-n}). Exit with
1094 nonzero status if an error occurs in executing the @value{GDBN} commands
1095 in the command files.
1097 Batch mode may be useful for running @value{GDBN} as a filter, for example to
1098 download and run a program on another computer; in order to make this
1099 more useful, the message
1102 Program exited normally.
1106 (which is ordinarily issued whenever a program running under @value{GDBN} control
1107 terminates) is not issued when running in batch mode.
1109 @item -cd @var{directory}
1110 Run @value{GDBN} using @var{directory} as its working directory,
1111 instead of the current directory.
1115 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
1116 subprocess. It tells @value{GDBN} to output the full file name and line
1117 number in a standard, recognizable fashion each time a stack frame is
1118 displayed (which includes each time your program stops). This
1119 recognizable format looks like two @samp{\032} characters, followed by
1120 the file name, line number and character position separated by colons,
1121 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
1122 @samp{\032} characters as a signal to display the source code for the
1127 Set the line speed (baud rate or bits per second) of any serial
1128 interface used by @value{GDBN} for remote debugging.
1131 @item -tty @var{device}
1132 Run using @var{device} for your program's standard input and output.
1133 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1137 Use a Terminal User Interface. For information, use your Web browser to
1138 read the file @file{TUI.html}, which is usually installed in the
1139 directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
1140 this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
1141 @value{GDBN} under @sc{gnu} Emacs}).
1144 Run in XDB compatibility mode, allowing the use of certain XDB commands.
1145 For information, see the file @file{xdb_trans.html}, which is usually
1146 installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
1151 @node Quitting GDB, Shell Commands, Invoking GDB, Invocation
1152 @section Quitting @value{GDBN}
1153 @cindex exiting @value{GDBN}
1154 @cindex leaving @value{GDBN}
1157 @kindex quit @r{[}@var{expression}@r{]}
1160 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or
1161 type an end-of-file character (usually @kbd{C-d}). If you do not supply
1162 @var{expression}, @value{GDBN} will terminate normally; otherwise it will
1163 terminate using the result of @var{expression} as the error code.
1167 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1168 terminates the action of any @value{GDBN} command that is in progress and
1169 returns to @value{GDBN} command level. It is safe to type the interrupt
1170 character at any time because @value{GDBN} does not allow it to take effect
1171 until a time when it is safe.
1173 If you have been using @value{GDBN} to control an attached process or
1174 device, you can release it with the @code{detach} command
1175 (@pxref{Attach, ,Debugging an already-running process}).
1177 @node Shell Commands, , Quitting GDB, Invocation
1178 @section Shell commands
1180 If you need to execute occasional shell commands during your
1181 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1182 just use the @code{shell} command.
1186 @cindex shell escape
1187 @item shell @var{command string}
1188 Invoke a standard shell to execute @var{command string}.
1189 If it exists, the environment variable @code{SHELL} determines which
1190 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
1193 The utility @code{make} is often needed in development environments.
1194 You do not have to use the @code{shell} command for this purpose in
1199 @cindex calling make
1200 @item make @var{make-args}
1201 Execute the @code{make} program with the specified
1202 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1205 @node Commands, Running, Invocation, Top
1206 @chapter @value{GDBN} Commands
1208 You can abbreviate a @value{GDBN} command to the first few letters of the command
1209 name, if that abbreviation is unambiguous; and you can repeat certain
1210 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1211 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1212 show you the alternatives available, if there is more than one possibility).
1215 * Command Syntax:: How to give commands to @value{GDBN}
1216 * Completion:: Command completion
1217 * Help:: How to ask @value{GDBN} for help
1220 @node Command Syntax, Completion, Commands, Commands
1221 @section Command syntax
1223 A @value{GDBN} command is a single line of input. There is no limit on
1224 how long it can be. It starts with a command name, which is followed by
1225 arguments whose meaning depends on the command name. For example, the
1226 command @code{step} accepts an argument which is the number of times to
1227 step, as in @samp{step 5}. You can also use the @code{step} command
1228 with no arguments. Some command names do not allow any arguments.
1230 @cindex abbreviation
1231 @value{GDBN} command names may always be truncated if that abbreviation is
1232 unambiguous. Other possible command abbreviations are listed in the
1233 documentation for individual commands. In some cases, even ambiguous
1234 abbreviations are allowed; for example, @code{s} is specially defined as
1235 equivalent to @code{step} even though there are other commands whose
1236 names start with @code{s}. You can test abbreviations by using them as
1237 arguments to the @code{help} command.
1239 @cindex repeating commands
1241 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1242 repeat the previous command. Certain commands (for example, @code{run})
1243 will not repeat this way; these are commands whose unintentional
1244 repetition might cause trouble and which you are unlikely to want to
1247 The @code{list} and @code{x} commands, when you repeat them with
1248 @key{RET}, construct new arguments rather than repeating
1249 exactly as typed. This permits easy scanning of source or memory.
1251 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1252 output, in a way similar to the common utility @code{more}
1253 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1254 @key{RET} too many in this situation, @value{GDBN} disables command
1255 repetition after any command that generates this sort of display.
1259 Any text from a @kbd{#} to the end of the line is a comment; it does
1260 nothing. This is useful mainly in command files (@pxref{Command
1261 Files,,Command files}).
1263 @node Completion, Help, Command Syntax, Commands
1264 @section Command completion
1267 @cindex word completion
1268 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1269 only one possibility; it can also show you what the valid possibilities
1270 are for the next word in a command, at any time. This works for @value{GDBN}
1271 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1273 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1274 of a word. If there is only one possibility, @value{GDBN} fills in the
1275 word, and waits for you to finish the command (or press @key{RET} to
1276 enter it). For example, if you type
1278 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1279 @c complete accuracy in these examples; space introduced for clarity.
1280 @c If texinfo enhancements make it unnecessary, it would be nice to
1281 @c replace " @key" by "@key" in the following...
1283 (@value{GDBP}) info bre @key{TAB}
1287 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1288 the only @code{info} subcommand beginning with @samp{bre}:
1291 (@value{GDBP}) info breakpoints
1295 You can either press @key{RET} at this point, to run the @code{info
1296 breakpoints} command, or backspace and enter something else, if
1297 @samp{breakpoints} does not look like the command you expected. (If you
1298 were sure you wanted @code{info breakpoints} in the first place, you
1299 might as well just type @key{RET} immediately after @samp{info bre},
1300 to exploit command abbreviations rather than command completion).
1302 If there is more than one possibility for the next word when you press
1303 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1304 characters and try again, or just press @key{TAB} a second time;
1305 @value{GDBN} displays all the possible completions for that word. For
1306 example, you might want to set a breakpoint on a subroutine whose name
1307 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1308 just sounds the bell. Typing @key{TAB} again displays all the
1309 function names in your program that begin with those characters, for
1313 (@value{GDBP}) b make_ @key{TAB}
1314 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1315 make_a_section_from_file make_environ
1316 make_abs_section make_function_type
1317 make_blockvector make_pointer_type
1318 make_cleanup make_reference_type
1319 make_command make_symbol_completion_list
1320 (@value{GDBP}) b make_
1324 After displaying the available possibilities, @value{GDBN} copies your
1325 partial input (@samp{b make_} in the example) so you can finish the
1328 If you just want to see the list of alternatives in the first place, you
1329 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1330 means @kbd{@key{META} ?}. You can type this either by holding down a
1331 key designated as the @key{META} shift on your keyboard (if there is
1332 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1334 @cindex quotes in commands
1335 @cindex completion of quoted strings
1336 Sometimes the string you need, while logically a ``word'', may contain
1337 parentheses or other characters that @value{GDBN} normally excludes from
1338 its notion of a word. To permit word completion to work in this
1339 situation, you may enclose words in @code{'} (single quote marks) in
1340 @value{GDBN} commands.
1342 The most likely situation where you might need this is in typing the
1343 name of a C++ function. This is because C++ allows function overloading
1344 (multiple definitions of the same function, distinguished by argument
1345 type). For example, when you want to set a breakpoint you may need to
1346 distinguish whether you mean the version of @code{name} that takes an
1347 @code{int} parameter, @code{name(int)}, or the version that takes a
1348 @code{float} parameter, @code{name(float)}. To use the word-completion
1349 facilities in this situation, type a single quote @code{'} at the
1350 beginning of the function name. This alerts @value{GDBN} that it may need to
1351 consider more information than usual when you press @key{TAB} or
1352 @kbd{M-?} to request word completion:
1355 (@value{GDBP}) b 'bubble( @key{M-?}
1356 bubble(double,double) bubble(int,int)
1357 (@value{GDBP}) b 'bubble(
1360 In some cases, @value{GDBN} can tell that completing a name requires using
1361 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1362 completing as much as it can) if you do not type the quote in the first
1366 (@value{GDBP}) b bub @key{TAB}
1367 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1368 (@value{GDBP}) b 'bubble(
1372 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1373 you have not yet started typing the argument list when you ask for
1374 completion on an overloaded symbol.
1376 For more information about overloaded functions, @pxref{C plus plus
1377 expressions, ,C++ expressions}. You can use the command @code{set
1378 overload-resolution off} to disable overload resolution;
1379 @pxref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1382 @node Help, , Completion, Commands
1383 @section Getting help
1384 @cindex online documentation
1387 You can always ask @value{GDBN} itself for information on its commands,
1388 using the command @code{help}.
1394 You can use @code{help} (abbreviated @code{h}) with no arguments to
1395 display a short list of named classes of commands:
1399 List of classes of commands:
1401 running -- Running the program
1402 stack -- Examining the stack
1403 data -- Examining data
1404 breakpoints -- Making program stop at certain points
1405 files -- Specifying and examining files
1406 status -- Status inquiries
1407 support -- Support facilities
1408 user-defined -- User-defined commands
1409 aliases -- Aliases of other commands
1410 obscure -- Obscure features
1412 Type "help" followed by a class name for a list of
1413 commands in that class.
1414 Type "help" followed by command name for full
1416 Command name abbreviations are allowed if unambiguous.
1420 @item help @var{class}
1421 Using one of the general help classes as an argument, you can get a
1422 list of the individual commands in that class. For example, here is the
1423 help display for the class @code{status}:
1426 (@value{GDBP}) help status
1431 @c Line break in "show" line falsifies real output, but needed
1432 @c to fit in smallbook page size.
1433 show -- Generic command for showing things set
1435 info -- Generic command for printing status
1437 Type "help" followed by command name for full
1439 Command name abbreviations are allowed if unambiguous.
1443 @item help @var{command}
1444 With a command name as @code{help} argument, @value{GDBN} displays a
1445 short paragraph on how to use that command.
1448 @item complete @var{args}
1449 The @code{complete @var{args}} command lists all the possible completions
1450 for the beginning of a command. Use @var{args} to specify the beginning of the
1451 command you want completed. For example:
1457 @noindent results in:
1467 @noindent This is intended for use by @sc{gnu} Emacs.
1470 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1471 and @code{show} to inquire about the state of your program, or the state
1472 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1473 manual introduces each of them in the appropriate context. The listings
1474 under @code{info} and under @code{show} in the Index point to
1475 all the sub-commands. @xref{Index}.
1482 This command (abbreviated @code{i}) is for describing the state of your
1483 program. For example, you can list the arguments given to your program
1484 with @code{info args}, list the registers currently in use with @code{info
1485 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1486 You can get a complete list of the @code{info} sub-commands with
1487 @w{@code{help info}}.
1491 You can assign the result of an expression to an environment variable with
1492 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1493 @code{set prompt $}.
1497 In contrast to @code{info}, @code{show} is for describing the state of
1498 @value{GDBN} itself.
1499 You can change most of the things you can @code{show}, by using the
1500 related command @code{set}; for example, you can control what number
1501 system is used for displays with @code{set radix}, or simply inquire
1502 which is currently in use with @code{show radix}.
1505 To display all the settable parameters and their current
1506 values, you can use @code{show} with no arguments; you may also use
1507 @code{info set}. Both commands produce the same display.
1508 @c FIXME: "info set" violates the rule that "info" is for state of
1509 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1510 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1514 Here are three miscellaneous @code{show} subcommands, all of which are
1515 exceptional in lacking corresponding @code{set} commands:
1518 @kindex show version
1519 @cindex version number
1521 Show what version of @value{GDBN} is running. You should include this
1522 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1523 use at your site, you may occasionally want to determine which version
1524 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1525 and old ones may wither away. The version number is also announced
1526 when you start @value{GDBN}.
1528 @kindex show copying
1530 Display information about permission for copying @value{GDBN}.
1532 @kindex show warranty
1534 Display the @sc{gnu} ``NO WARRANTY'' statement.
1537 @node Running, Stopping, Commands, Top
1538 @chapter Running Programs Under @value{GDBN}
1540 When you run a program under @value{GDBN}, you must first generate
1541 debugging information when you compile it.
1543 You may start @value{GDBN} with its arguments, if any, in an environment
1544 of your choice. If you are doing native debugging, you may redirect
1545 your program's input and output, debug an already running process, or
1546 kill a child process.
1549 * Compilation:: Compiling for debugging
1550 * Starting:: Starting your program
1551 * Arguments:: Your program's arguments
1552 * Environment:: Your program's environment
1554 * Working Directory:: Your program's working directory
1555 * Input/Output:: Your program's input and output
1556 * Attach:: Debugging an already-running process
1557 * Kill Process:: Killing the child process
1558 * Process Information:: Additional process information
1560 * Threads:: Debugging programs with multiple threads
1561 * Processes:: Debugging programs with multiple processes
1564 @node Compilation, Starting, Running, Running
1565 @section Compiling for debugging
1567 In order to debug a program effectively, you need to generate
1568 debugging information when you compile it. This debugging information
1569 is stored in the object file; it describes the data type of each
1570 variable or function and the correspondence between source line numbers
1571 and addresses in the executable code.
1573 To request debugging information, specify the @samp{-g} option when you run
1576 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1577 options together. Using those compilers, you cannot generate optimized
1578 executables containing debugging information.
1581 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or without
1584 The HP ANSI C and C++ compilers, as well as @value{NGCC}, the @sc{gnu} C
1585 compiler, support @samp{-g} with or without
1587 @samp{-O}, making it possible to debug optimized code. We recommend
1588 that you @emph{always} use @samp{-g} whenever you compile a program.
1589 You may think your program is correct, but there is no sense in pushing
1592 @cindex optimized code, debugging
1593 @cindex debugging optimized code
1594 When you debug a program compiled with @samp{-g -O}, remember that the
1595 optimizer is rearranging your code; the debugger shows you what is
1596 really there. Do not be too surprised when the execution path does not
1597 exactly match your source file! An extreme example: if you define a
1598 variable, but never use it, @value{GDBN} never sees that
1599 variable---because the compiler optimizes it out of existence.
1601 Some things do not work as well with @samp{-g -O} as with just
1602 @samp{-g}, particularly on machines with instruction scheduling. If in
1603 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1604 please report it to us as a bug (including a test case!).
1606 Older versions of the @sc{gnu} C compiler permitted a variant option
1607 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1608 format; if your @sc{gnu} C compiler has this option, do not use it.
1611 @node Starting, Arguments, Compilation, Running
1612 @section Starting your program
1620 Use the @code{run} command to start your program under @value{GDBN}.
1621 You must first specify the program name (except on VxWorks) with an
1622 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1623 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1624 (@pxref{Files, ,Commands to specify files}).
1628 If you are running your program in an execution environment that
1629 supports processes, @code{run} creates an inferior process and makes
1630 that process run your program. (In environments without processes,
1631 @code{run} jumps to the start of your program.)
1633 The execution of a program is affected by certain information it
1634 receives from its superior. @value{GDBN} provides ways to specify this
1635 information, which you must do @emph{before} starting your program. (You
1636 can change it after starting your program, but such changes only affect
1637 your program the next time you start it.) This information may be
1638 divided into four categories:
1641 @item The @emph{arguments.}
1642 Specify the arguments to give your program as the arguments of the
1643 @code{run} command. If a shell is available on your target, the shell
1644 is used to pass the arguments, so that you may use normal conventions
1645 (such as wildcard expansion or variable substitution) in describing
1647 In Unix systems, you can control which shell is used with the
1648 @code{SHELL} environment variable.
1649 @xref{Arguments, ,Your program's arguments}.
1651 @item The @emph{environment.}
1652 Your program normally inherits its environment from @value{GDBN}, but you can
1653 use the @value{GDBN} commands @code{set environment} and @code{unset
1654 environment} to change parts of the environment that affect
1655 your program. @xref{Environment, ,Your program's environment}.
1657 @item The @emph{working directory.}
1658 Your program inherits its working directory from @value{GDBN}. You can set
1659 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1660 @xref{Working Directory, ,Your program's working directory}.
1662 @item The @emph{standard input and output.}
1663 Your program normally uses the same device for standard input and
1664 standard output as @value{GDBN} is using. You can redirect input and output
1665 in the @code{run} command line, or you can use the @code{tty} command to
1666 set a different device for your program.
1667 @xref{Input/Output, ,Your program's input and output}.
1670 @emph{Warning:} While input and output redirection work, you cannot use
1671 pipes to pass the output of the program you are debugging to another
1672 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1676 When you issue the @code{run} command, your program begins to execute
1677 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1678 of how to arrange for your program to stop. Once your program has
1679 stopped, you may call functions in your program, using the @code{print}
1680 or @code{call} commands. @xref{Data, ,Examining Data}.
1682 If the modification time of your symbol file has changed since the last
1683 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1684 table, and reads it again. When it does this, @value{GDBN} tries to retain
1685 your current breakpoints.
1687 @node Arguments, Environment, Starting, Running
1688 @section Your program's arguments
1690 @cindex arguments (to your program)
1691 The arguments to your program can be specified by the arguments of the
1693 They are passed to a shell, which expands wildcard characters and
1694 performs redirection of I/O, and thence to your program. Your
1695 @code{SHELL} environment variable (if it exists) specifies what shell
1696 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1699 @code{run} with no arguments uses the same arguments used by the previous
1700 @code{run}, or those set by the @code{set args} command.
1705 Specify the arguments to be used the next time your program is run. If
1706 @code{set args} has no arguments, @code{run} executes your program
1707 with no arguments. Once you have run your program with arguments,
1708 using @code{set args} before the next @code{run} is the only way to run
1709 it again without arguments.
1713 Show the arguments to give your program when it is started.
1716 @node Environment, Working Directory, Arguments, Running
1717 @section Your program's environment
1719 @cindex environment (of your program)
1720 The @dfn{environment} consists of a set of environment variables and
1721 their values. Environment variables conventionally record such things as
1722 your user name, your home directory, your terminal type, and your search
1723 path for programs to run. Usually you set up environment variables with
1724 the shell and they are inherited by all the other programs you run. When
1725 debugging, it can be useful to try running your program with a modified
1726 environment without having to start @value{GDBN} over again.
1730 @item path @var{directory}
1731 Add @var{directory} to the front of the @code{PATH} environment variable
1732 (the search path for executables), for both @value{GDBN} and your program.
1733 You may specify several directory names, separated by @samp{:} or
1734 whitespace. If @var{directory} is already in the path, it is moved to
1735 the front, so it is searched sooner.
1737 You can use the string @samp{$cwd} to refer to whatever is the current
1738 working directory at the time @value{GDBN} searches the path. If you
1739 use @samp{.} instead, it refers to the directory where you executed the
1740 @code{path} command. @value{GDBN} replaces @samp{.} in the
1741 @var{directory} argument (with the current path) before adding
1742 @var{directory} to the search path.
1743 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1744 @c document that, since repeating it would be a no-op.
1748 Display the list of search paths for executables (the @code{PATH}
1749 environment variable).
1751 @kindex show environment
1752 @item show environment @r{[}@var{varname}@r{]}
1753 Print the value of environment variable @var{varname} to be given to
1754 your program when it starts. If you do not supply @var{varname},
1755 print the names and values of all environment variables to be given to
1756 your program. You can abbreviate @code{environment} as @code{env}.
1758 @kindex set environment
1759 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1760 Set environment variable @var{varname} to @var{value}. The value
1761 changes for your program only, not for @value{GDBN} itself. @var{value} may
1762 be any string; the values of environment variables are just strings, and
1763 any interpretation is supplied by your program itself. The @var{value}
1764 parameter is optional; if it is eliminated, the variable is set to a
1766 @c "any string" here does not include leading, trailing
1767 @c blanks. Gnu asks: does anyone care?
1769 For example, this command:
1776 tells a Unix program, when subsequently run, that its user is named
1777 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1778 are not actually required.)
1780 @kindex unset environment
1781 @item unset environment @var{varname}
1782 Remove variable @var{varname} from the environment to be passed to your
1783 program. This is different from @samp{set env @var{varname} =};
1784 @code{unset environment} removes the variable from the environment,
1785 rather than assigning it an empty value.
1788 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1789 by your @code{SHELL} environment variable if it exists (or
1790 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1791 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1792 @file{.bashrc} for BASH---any variables you set in that file affect
1793 your program. You may wish to move setting of environment variables to
1794 files that are only run when you sign on, such as @file{.login} or
1797 @node Working Directory, Input/Output, Environment, Running
1798 @section Your program's working directory
1800 @cindex working directory (of your program)
1801 Each time you start your program with @code{run}, it inherits its
1802 working directory from the current working directory of @value{GDBN}.
1803 The @value{GDBN} working directory is initially whatever it inherited
1804 from its parent process (typically the shell), but you can specify a new
1805 working directory in @value{GDBN} with the @code{cd} command.
1807 The @value{GDBN} working directory also serves as a default for the commands
1808 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1813 @item cd @var{directory}
1814 Set the @value{GDBN} working directory to @var{directory}.
1818 Print the @value{GDBN} working directory.
1821 @node Input/Output, Attach, Working Directory, Running
1822 @section Your program's input and output
1827 By default, the program you run under @value{GDBN} does input and output to
1828 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1829 to its own terminal modes to interact with you, but it records the terminal
1830 modes your program was using and switches back to them when you continue
1831 running your program.
1834 @kindex info terminal
1836 Displays information recorded by @value{GDBN} about the terminal modes your
1840 You can redirect your program's input and/or output using shell
1841 redirection with the @code{run} command. For example,
1848 starts your program, diverting its output to the file @file{outfile}.
1851 @cindex controlling terminal
1852 Another way to specify where your program should do input and output is
1853 with the @code{tty} command. This command accepts a file name as
1854 argument, and causes this file to be the default for future @code{run}
1855 commands. It also resets the controlling terminal for the child
1856 process, for future @code{run} commands. For example,
1863 directs that processes started with subsequent @code{run} commands
1864 default to do input and output on the terminal @file{/dev/ttyb} and have
1865 that as their controlling terminal.
1867 An explicit redirection in @code{run} overrides the @code{tty} command's
1868 effect on the input/output device, but not its effect on the controlling
1871 When you use the @code{tty} command or redirect input in the @code{run}
1872 command, only the input @emph{for your program} is affected. The input
1873 for @value{GDBN} still comes from your terminal.
1875 @node Attach, Kill Process, Input/Output, Running
1876 @section Debugging an already-running process
1881 @item attach @var{process-id}
1882 This command attaches to a running process---one that was started
1883 outside @value{GDBN}. (@code{info files} shows your active
1884 targets.) The command takes as argument a process ID. The usual way to
1885 find out the process-id of a Unix process is with the @code{ps} utility,
1886 or with the @samp{jobs -l} shell command.
1888 @code{attach} does not repeat if you press @key{RET} a second time after
1889 executing the command.
1892 To use @code{attach}, your program must be running in an environment
1893 which supports processes; for example, @code{attach} does not work for
1894 programs on bare-board targets that lack an operating system. You must
1895 also have permission to send the process a signal.
1897 When you use @code{attach}, the debugger finds the program running in
1898 the process first by looking in the current working directory, then (if
1899 the program is not found) by using the source file search path
1900 (@pxref{Source Path, ,Specifying source directories}). You can also use
1901 the @code{file} command to load the program. @xref{Files, ,Commands to
1904 The first thing @value{GDBN} does after arranging to debug the specified
1905 process is to stop it. You can examine and modify an attached process
1906 with all the @value{GDBN} commands that are ordinarily available when you start
1908 processes with @code{run}. You can insert breakpoints; you can step and
1911 processes with @code{run}. You can insert breakpoints (except in shared
1912 libraries); you can step and
1914 continue; you can modify storage. If you would rather the process
1915 continue running, you may use the @code{continue} command after
1916 attaching @value{GDBN} to the process.
1921 When you have finished debugging the attached process, you can use the
1922 @code{detach} command to release it from @value{GDBN} control. Detaching
1923 the process continues its execution. After the @code{detach} command,
1924 that process and @value{GDBN} become completely independent once more, and you
1925 are ready to @code{attach} another process or start one with @code{run}.
1926 @code{detach} does not repeat if you press @key{RET} again after
1927 executing the command.
1930 If you exit @value{GDBN} or use the @code{run} command while you have an
1931 attached process, you kill that process. By default, @value{GDBN} asks
1932 for confirmation if you try to do either of these things; you can
1933 control whether or not you need to confirm by using the @code{set
1934 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1937 @node Kill Process, Process Information, Attach, Running
1938 @section Killing the child process
1943 Kill the child process in which your program is running under @value{GDBN}.
1946 This command is useful if you wish to debug a core dump instead of a
1947 running process. @value{GDBN} ignores any core dump file while your program
1950 On some operating systems, a program cannot be executed outside @value{GDBN}
1951 while you have breakpoints set on it inside @value{GDBN}. You can use the
1952 @code{kill} command in this situation to permit running your program
1953 outside the debugger.
1955 The @code{kill} command is also useful if you wish to recompile and
1956 relink your program, since on many systems it is impossible to modify an
1957 executable file while it is running in a process. In this case, when you
1958 next type @code{run}, @value{GDBN} notices that the file has changed, and
1959 reads the symbol table again (while trying to preserve your current
1960 breakpoint settings).
1962 @node Process Information, Threads, Kill Process, Running
1963 @section Additional process information
1966 @cindex process image
1968 Some operating systems provide a facility called @samp{/proc} that can
1969 be used to examine the image of a running process using file-system
1970 subroutines. If @value{GDBN} is configured for an operating system with this
1971 facility, the command @code{info proc} is available to report on several
1972 kinds of information about the process running your program.
1973 @code{info proc} works only on SVR4 systems that support @code{procfs}.
1974 This includes OSF/1 (Digital Unix), Solaris, Irix, and Unixware,
1975 but not HP-UX or Linux, for example.
1980 Summarize available information about the process.
1982 @kindex info proc mappings
1983 @item info proc mappings
1984 Report on the address ranges accessible in the program, with information
1985 on whether your program may read, write, or execute each range.
1987 @kindex info proc times
1988 @item info proc times
1989 Starting time, user CPU time, and system CPU time for your program and
1992 @kindex info proc id
1994 Report on the process IDs related to your program: its own process ID,
1995 the ID of its parent, the process group ID, and the session ID.
1997 @kindex info proc status
1998 @item info proc status
1999 General information on the state of the process. If the process is
2000 stopped, this report includes the reason for stopping, and any signal
2004 Show all the above information about the process.
2007 @node Threads, Processes, Process Information, Running
2008 @section Debugging programs with multiple threads
2010 @cindex threads of execution
2011 @cindex multiple threads
2012 @cindex switching threads
2013 In some operating systems, such as HP-UX and Solaris, a single program
2014 may have more than one @dfn{thread} of execution. The precise semantics
2015 of threads differ from one operating system to another, but in general
2016 the threads of a single program are akin to multiple processes---except
2017 that they share one address space (that is, they can all examine and
2018 modify the same variables). On the other hand, each thread has its own
2019 registers and execution stack, and perhaps private memory.
2021 @value{GDBN} provides these facilities for debugging multi-thread
2025 @item automatic notification of new threads
2026 @item @samp{thread @var{threadno}}, a command to switch among threads
2027 @item @samp{info threads}, a command to inquire about existing threads
2028 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
2029 a command to apply a command to a list of threads
2030 @item thread-specific breakpoints
2035 @emph{Warning:} These facilities are not yet available on every
2036 @value{GDBN} configuration where the operating system supports threads.
2037 If your @value{GDBN} does not support threads, these commands have no
2038 effect. For example, a system without thread support shows no output
2039 from @samp{info threads}, and always rejects the @code{thread} command,
2043 (@value{GDBP}) info threads
2044 (@value{GDBP}) thread 1
2045 Thread ID 1 not known. Use the "info threads" command to
2046 see the IDs of currently known threads.
2048 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
2049 @c doesn't support threads"?
2053 @cindex focus of debugging
2054 @cindex current thread
2055 The @value{GDBN} thread debugging facility allows you to observe all
2056 threads while your program runs---but whenever @value{GDBN} takes
2057 control, one thread in particular is always the focus of debugging.
2058 This thread is called the @dfn{current thread}. Debugging commands show
2059 program information from the perspective of the current thread.
2062 @kindex New @var{systag}
2063 @cindex thread identifier (system)
2064 @c FIXME-implementors!! It would be more helpful if the [New...] message
2065 @c included GDB's numeric thread handle, so you could just go to that
2066 @c thread without first checking `info threads'.
2067 Whenever @value{GDBN} detects a new thread in your program, it displays
2068 the target system's identification for the thread with a message in the
2069 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2070 whose form varies depending on the particular system. For example, on
2071 LynxOS, you might see
2074 [New process 35 thread 27]
2078 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
2079 the @var{systag} is simply something like @samp{process 368}, with no
2082 @c FIXME!! (1) Does the [New...] message appear even for the very first
2083 @c thread of a program, or does it only appear for the
2084 @c second---i.e., when it becomes obvious we have a multithread
2086 @c (2) *Is* there necessarily a first thread always? Or do some
2087 @c multithread systems permit starting a program with multiple
2088 @c threads ab initio?
2090 @cindex thread number
2091 @cindex thread identifier (GDB)
2092 For debugging purposes, @value{GDBN} associates its own thread
2093 number---always a single integer---with each thread in your program.
2096 @kindex info threads
2098 Display a summary of all threads currently in your
2099 program. @value{GDBN} displays for each thread (in this order):
2102 @item the thread number assigned by @value{GDBN}
2104 @item the target system's thread identifier (@var{systag})
2106 @item the current stack frame summary for that thread
2110 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2111 indicates the current thread.
2115 @c end table here to get a little more width for example
2118 (@value{GDBP}) info threads
2119 3 process 35 thread 27 0x34e5 in sigpause ()
2120 2 process 35 thread 23 0x34e5 in sigpause ()
2121 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
2127 @cindex thread number
2128 @cindex thread identifier (GDB)
2129 For debugging purposes, @value{GDBN} associates its own thread
2130 number---a small integer assigned in thread-creation order---with each
2131 thread in your program.
2133 @kindex New @var{systag}
2134 @cindex thread identifier (system)
2135 @c FIXME-implementors!! It would be more helpful if the [New...] message
2136 @c included GDB's numeric thread handle, so you could just go to that
2137 @c thread without first checking `info threads'.
2138 Whenever @value{GDBN} detects a new thread in your program, it displays
2139 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
2140 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
2141 whose form varies depending on the particular system. For example, on
2145 [New thread 2 (system thread 26594)]
2149 when @value{GDBN} notices a new thread.
2152 @kindex info threads
2154 Display a summary of all threads currently in your
2155 program. @value{GDBN} displays for each thread (in this order):
2158 @item the thread number assigned by @value{GDBN}
2160 @item the target system's thread identifier (@var{systag})
2162 @item the current stack frame summary for that thread
2166 An asterisk @samp{*} to the left of the @value{GDBN} thread number
2167 indicates the current thread.
2171 @c end table here to get a little more width for example
2174 (@value{GDBP}) info threads
2175 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") at quicksort.c:137
2176 2 system thread 26606 0x7b0030d8 in __ksleep () from /usr/lib/libc.2
2177 1 system thread 27905 0x7b003498 in _brk () from /usr/lib/libc.2
2182 @kindex thread @var{threadno}
2183 @item thread @var{threadno}
2184 Make thread number @var{threadno} the current thread. The command
2185 argument @var{threadno} is the internal @value{GDBN} thread number, as
2186 shown in the first field of the @samp{info threads} display.
2187 @value{GDBN} responds by displaying the system identifier of the thread
2188 you selected, and its current stack frame summary:
2191 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2192 (@value{GDBP}) thread 2
2194 [Switching to process 35 thread 23]
2197 [Switching to thread 2 (system thread 26594)]
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 @node Processes, , Threads, Running
2235 @section Debugging programs with multiple processes
2237 @cindex fork, debugging programs which call
2238 @cindex multiple processes
2239 @cindex processes, multiple
2240 @value{GDBN} has no special support for debugging programs which create
2241 additional processes using the @code{fork} function. When a program
2242 forks, @value{GDBN} will continue to debug the parent process and the
2243 child process will run unimpeded. If you have set a breakpoint in any
2244 code which the child then executes, the child will get a @code{SIGTRAP}
2245 signal which (unless it catches the signal) 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 (see @ref{Attach}). From that point on you can debug
2256 the child process just like any other process which you attached to.
2259 @node Processes, , Threads, Running
2260 @section Debugging programs with multiple processes
2262 @cindex fork, debugging programs which call
2263 @cindex multiple processes
2264 @cindex processes, multiple
2266 @value{GDBN} provides support for debugging programs that create
2267 additional processes using the @code{fork} or @code{vfork} function.
2269 By default, when a program forks, @value{GDBN} will continue to debug
2270 the parent process and the child process will run unimpeded.
2272 If you want to follow the child process instead of the parent process,
2273 use the command @w{@code{set follow-fork-mode}}.
2276 @kindex set follow-fork-mode
2277 @item set follow-fork-mode @var{mode}
2278 Set the debugger response to a program call of @code{fork} or
2279 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2280 process. The @var{mode} can be:
2284 The original process is debugged after a fork. The child process runs
2288 The new process is debugged after a fork. The parent process runs
2292 The debugger will ask for one of the above choices.
2295 @item show follow-fork-mode
2296 Display the current debugger response to a fork or vfork call.
2299 If you ask to debug a child process and a @code{vfork} is followed by an
2300 @code{exec}, @value{GDBN} executes the new target up to the first
2301 breakpoint in the new target. If you have a breakpoint set on
2302 @code{main} in your original program, the breakpoint will also be set on
2303 the child process's @code{main}.
2305 When a child process is spawned by @code{vfork}, you cannot debug the
2306 child or parent until an @code{exec} call completes.
2308 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2309 call executes, the new target restarts. To restart the parent process,
2310 use the @code{file} command with the parent executable name as its
2313 You can use the @code{catch} command to make @value{GDBN} stop whenever
2314 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2315 Catchpoints, ,Setting catchpoints}.
2318 @node Stopping, Stack, Running, Top
2319 @chapter Stopping and Continuing
2321 The principal purposes of using a debugger are so that you can stop your
2322 program before it terminates; or so that, if your program runs into
2323 trouble, you can investigate and find out why.
2325 Inside @value{GDBN}, your program may stop for any of several reasons,
2326 such as a signal, a breakpoint, or reaching a new line after a
2327 @value{GDBN} command such as @code{step}. You may then examine and
2328 change variables, set new breakpoints or remove old ones, and then
2329 continue execution. Usually, the messages shown by @value{GDBN} provide
2330 ample explanation of the status of your program---but you can also
2331 explicitly request this information at any time.
2334 @kindex info program
2336 Display information about the status of your program: whether it is
2337 running or not, what process it is, and why it stopped.
2341 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2342 * Continuing and Stepping:: Resuming execution
2344 * Thread Stops:: Stopping and starting multi-thread programs
2347 @node Breakpoints, Continuing and Stepping, Stopping, Stopping
2348 @section Breakpoints, watchpoints, and catchpoints
2351 A @dfn{breakpoint} makes your program stop whenever a certain point in
2352 the program is reached. For each breakpoint, you can add conditions to
2353 control in finer detail whether your program stops. You can set
2354 breakpoints with the @code{break} command and its variants (@pxref{Set
2355 Breaks, ,Setting breakpoints}), to specify the place where your program
2356 should stop by line number, function name or exact address in the
2359 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2360 breakpoints in shared libraries before the executable is run. There is
2361 a minor limitation on HP-UX systems: you must wait until the executable
2362 is run in order to set breakpoints in shared library routines that are
2363 not called directly by the program (for example, routines that are
2364 arguments in a @code{pthread_create} call).
2367 @cindex memory tracing
2368 @cindex breakpoint on memory address
2369 @cindex breakpoint on variable modification
2370 A @dfn{watchpoint} is a special breakpoint that stops your program
2371 when the value of an expression changes. You must use a different
2372 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2373 watchpoints}), but aside from that, you can manage a watchpoint like
2374 any other breakpoint: you enable, disable, and delete both breakpoints
2375 and watchpoints using the same commands.
2377 You can arrange to have values from your program displayed automatically
2378 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2382 @cindex breakpoint on events
2383 A @dfn{catchpoint} is another special breakpoint that stops your program
2384 when a certain kind of event occurs, such as the throwing of a C++
2385 exception or the loading of a library. As with watchpoints, you use a
2386 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2387 catchpoints}), but aside from that, you can manage a catchpoint like any
2388 other breakpoint. (To stop when your program receives a signal, use the
2389 @code{handle} command; @pxref{Signals, ,Signals}.)
2391 @cindex breakpoint numbers
2392 @cindex numbers for breakpoints
2393 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2394 catchpoint when you create it; these numbers are successive integers
2395 starting with one. In many of the commands for controlling various
2396 features of breakpoints you use the breakpoint number to say which
2397 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2398 @dfn{disabled}; if disabled, it has no effect on your program until you
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
2411 @c * Error in Breakpoints:: ``Cannot insert breakpoints''
2414 @node Set Breaks, Set Watchpoints, Breakpoints, Breakpoints
2415 @subsection Setting breakpoints
2417 @c FIXME LMB what does GDB do if no code on line of breakpt?
2418 @c consider in particular declaration with/without initialization.
2420 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2425 @cindex latest breakpoint
2426 Breakpoints are set with the @code{break} command (abbreviated
2427 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2428 number of the breakpoints you've set most recently; see @ref{Convenience
2429 Vars,, Convenience variables}, for a discussion of what you can do with
2430 convenience variables.
2432 You have several ways to say where the breakpoint should go.
2435 @item break @var{function}
2436 Set a breakpoint at entry to function @var{function}.
2437 When using source languages that permit overloading of symbols, such as
2438 C++, @var{function} may refer to more than one possible place to break.
2439 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2441 @item break +@var{offset}
2442 @itemx break -@var{offset}
2443 Set a breakpoint some number of lines forward or back from the position
2444 at which execution stopped in the currently selected frame.
2446 @item break @var{linenum}
2447 Set a breakpoint at line @var{linenum} in the current source file.
2448 That file is the last file whose source text was printed. This
2449 breakpoint stops 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}.
2501 @item hbreak @var{args}
2502 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2503 @code{break} command and the breakpoint is set in the same way, but the
2504 breakpoint requires hardware support and some target hardware may not
2505 have this support. The main purpose of this is EPROM/ROM code
2506 debugging, so you can set a breakpoint at an instruction without
2507 changing the instruction. This can be used with the new trap-generation
2508 provided by SPARClite DSU. DSU will generate traps when a program accesses
2509 some data or instruction address that is assigned to the debug registers.
2510 However the hardware breakpoint registers can only take two data breakpoints,
2511 and @value{GDBN} will reject this command if more than two are used.
2512 Delete or disable unused hardware breakpoints before setting
2513 new ones. @xref{Conditions, ,Break conditions}.
2516 @item thbreak @var{args}
2517 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2518 are the same as for the @code{hbreak} command and the breakpoint is set in
2519 the same way. However, like the @code{tbreak} command,
2520 the breakpoint is automatically deleted after the
2521 first time your program stops there. Also, like the @code{hbreak}
2522 command, the breakpoint requires hardware support and some target hardware
2523 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2524 Also @xref{Conditions, ,Break conditions}.
2528 @cindex regular expression
2529 @item rbreak @var{regex}
2530 @c FIXME what kind of regexp?
2531 Set breakpoints on all functions matching the regular expression
2532 @var{regex}. This command
2533 sets an unconditional breakpoint on all matches, printing a list of all
2534 breakpoints it set. Once these breakpoints are set, they are treated
2535 just like the breakpoints set with the @code{break} command. You can
2536 delete them, disable them, or make them conditional the same way as any
2539 When debugging C++ programs, @code{rbreak} is useful for setting
2540 breakpoints on overloaded functions that are not members of any special
2543 @kindex info breakpoints
2544 @cindex @code{$_} and @code{info breakpoints}
2545 @item info breakpoints @r{[}@var{n}@r{]}
2546 @itemx info break @r{[}@var{n}@r{]}
2547 @itemx info watchpoints @r{[}@var{n}@r{]}
2548 Print a table of all breakpoints, watchpoints, and catchpoints set and
2549 not deleted, with the following columns for each breakpoint:
2552 @item Breakpoint Numbers
2554 Breakpoint, watchpoint, or catchpoint.
2556 Whether the breakpoint is marked to be disabled or deleted when hit.
2557 @item Enabled or Disabled
2558 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2559 that are not enabled.
2561 Where the breakpoint is in your program, as a memory address
2563 Where the breakpoint is in the source for your program, as a file and
2568 If a breakpoint is conditional, @code{info break} shows the condition on
2569 the line following the affected breakpoint; breakpoint commands, if any,
2570 are listed after that.
2573 @code{info break} with a breakpoint
2574 number @var{n} as argument lists only that breakpoint. The
2575 convenience variable @code{$_} and the default examining-address for
2576 the @code{x} command are set to the address of the last breakpoint
2577 listed (@pxref{Memory, ,Examining memory}).
2580 @code{info break} displays a count of the number of times the breakpoint
2581 has been hit. This is especially useful in conjunction with the
2582 @code{ignore} command. You can ignore a large number of breakpoint
2583 hits, look at the breakpoint info to see how many times the breakpoint
2584 was hit, and then run again, ignoring one less than that number. This
2585 will get you quickly to the last hit of that breakpoint.
2588 @value{GDBN} allows you to set any number of breakpoints at the same place in
2589 your program. There is nothing silly or meaningless about this. When
2590 the breakpoints are conditional, this is even useful
2591 (@pxref{Conditions, ,Break conditions}).
2593 @cindex negative breakpoint numbers
2594 @cindex internal @value{GDBN} breakpoints
2595 @value{GDBN} itself sometimes sets breakpoints in your program for special
2596 purposes, such as proper handling of @code{longjmp} (in C programs).
2597 These internal breakpoints are assigned negative numbers, starting with
2598 @code{-1}; @samp{info breakpoints} does not display them.
2600 You can see these breakpoints with the @value{GDBN} maintenance command
2601 @samp{maint info breakpoints}.
2604 @kindex maint info breakpoints
2605 @item maint info breakpoints
2606 Using the same format as @samp{info breakpoints}, display both the
2607 breakpoints you've set explicitly, and those @value{GDBN} is using for
2608 internal purposes. Internal breakpoints are shown with negative
2609 breakpoint numbers. The type column identifies what kind of breakpoint
2614 Normal, explicitly set breakpoint.
2617 Normal, explicitly set watchpoint.
2620 Internal breakpoint, used to handle correctly stepping through
2621 @code{longjmp} calls.
2623 @item longjmp resume
2624 Internal breakpoint at the target of a @code{longjmp}.
2627 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2630 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2634 Shared library events.
2640 @node Set Watchpoints, Set Catchpoints, Set Breaks, Breakpoints
2641 @subsection Setting watchpoints
2643 @cindex setting watchpoints
2644 @cindex software watchpoints
2645 @cindex hardware watchpoints
2646 You can use a watchpoint to stop execution whenever the value of an
2647 expression changes, without having to predict a particular place where
2650 Depending on your system, watchpoints may be implemented in software or
2651 hardware. GDB does software watchpointing by single-stepping your
2652 program and testing the variable's value each time, which is hundreds of
2653 times slower than normal execution. (But this may still be worth it, to
2654 catch errors where you have no clue what part of your program is the
2657 On some systems, such as HP-UX and Linux, GDB includes support for
2658 hardware watchpoints, which do not slow down the running of your
2663 @item watch @var{expr}
2664 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2665 is written into by the program and its value changes.
2668 @item rwatch @var{expr}
2669 Set a watchpoint that will break when watch @var{expr} is read by the program.
2672 @item awatch @var{expr}
2673 Set a watchpoint that will break when @var{args} is read and written into
2676 @kindex info watchpoints
2677 @item info watchpoints
2678 This command prints a list of watchpoints, breakpoints, and catchpoints;
2679 it is the same as @code{info break}.
2682 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2683 watchpoints execute very quickly, and the debugger reports a change in
2684 value at the exact instruction where the change occurs. If @value{GDBN}
2685 cannot set a hardware watchpoint, it sets a software watchpoint, which
2686 executes more slowly and reports the change in value at the next
2687 statement, not the instruction, after the change occurs.
2689 When you issue the @code{watch} command, @value{GDBN} reports
2692 Hardware watchpoint @var{num}: @var{expr}
2696 if it was able to set a hardware watchpoint.
2698 Currently, the @code{awatch} and @code{rwatch} commands can only set
2699 hardware watchpoints, because accesses to data that don't change the
2700 value of the watched expression cannot be detected without examining
2701 every instruction as it is being executed, and @value{GDBN} does not do
2702 that currently. If @value{GDBN} finds that it is unable to set a
2703 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2704 will print a message like this:
2707 Expression cannot be implemented with read/access watchpoint.
2710 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2711 data type of the watched expression is wider than what a hardware
2712 watchpoint on the target machine can handle. For example, some systems
2713 can only watch regions that are up to 4 bytes wide; on such systems you
2714 cannot set hardware watchpoints for an expression that yields a
2715 double-precision floating-point number (which is typically 8 bytes
2716 wide). As a work-around, it might be possible to break the large region
2717 into a series of smaller ones and watch them with separate watchpoints.
2719 If you set too many hardware watchpoints, @value{GDBN} might be unable
2720 to insert all of them when you resume the execution of your program.
2721 Since the precise number of active watchpoints is unknown until such
2722 time as the program is about to be resumed, @value{GDBN} might not be
2723 able to warn you about this when you set the watchpoints, and the
2724 warning will be printed only when the program is resumed:
2727 Hardware watchpoint @var{num}: Could not insert watchpoint
2731 If this happens, delete or disable some of the watchpoints.
2733 The SPARClite DSU will generate traps when a program accesses some data
2734 or instruction address that is assigned to the debug registers. For the
2735 data addresses, DSU facilitates the @code{watch} command. However the
2736 hardware breakpoint registers can only take two data watchpoints, and
2737 both watchpoints must be the same kind. For example, you can set two
2738 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2739 @strong{or} two with @code{awatch} commands, but you cannot set one
2740 watchpoint with one command and the other with a different command.
2741 @value{GDBN} will reject the command if you try to mix watchpoints.
2742 Delete or disable unused watchpoint commands before setting new ones.
2744 If you call a function interactively using @code{print} or @code{call},
2745 any watchpoints you have set will be inactive until GDB reaches another
2746 kind of breakpoint or the call completes.
2748 @value{GDBN} automatically deletes watchpoints that watch local
2749 (automatic) variables, or expressions that involve such variables, when
2750 they go out of scope, that is, when the execution leaves the block in
2751 which these variables were defined. In particular, when the program
2752 being debugged terminates, @emph{all} local variables go out of scope,
2753 and so only watchpoints that watch global variables remain set. If you
2754 rerun the program, you will need to set all such watchpoints again. One
2755 way of doing that would be to set a code breakpoint at the entry to the
2756 @code{main} function and when it breaks, set all the watchpoints.
2759 @cindex watchpoints and threads
2760 @cindex threads and watchpoints
2762 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2763 usefulness. With the current watchpoint implementation, @value{GDBN}
2764 can only watch the value of an expression @emph{in a single thread}. If
2765 you are confident that the expression can only change due to the current
2766 thread's activity (and if you are also confident that no other thread
2767 can become current), then you can use watchpoints as usual. However,
2768 @value{GDBN} may not notice when a non-current thread's activity changes
2772 @emph{Warning:} In multi-thread programs, software watchpoints have only
2773 limited usefulness. If @value{GDBN} creates a software watchpoint, it
2774 can only watch the value of an expression @emph{in a single thread}. If
2775 you are confident that the expression can only change due to the current
2776 thread's activity (and if you are also confident that no other thread
2777 can become current), then you can use software watchpoints as usual.
2778 However, @value{GDBN} may not notice when a non-current thread's
2779 activity changes the expression. (Hardware watchpoints, in contrast,
2780 watch an expression in all threads.)
2784 @node Set Catchpoints, Delete Breaks, Set Watchpoints, Breakpoints
2785 @subsection Setting catchpoints
2787 @cindex exception handlers
2788 @cindex event handling
2790 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2791 kinds of program events, such as C++ exceptions or the loading of a
2792 shared library. Use the @code{catch} command to set a catchpoint.
2796 @item catch @var{event}
2797 Stop when @var{event} occurs. @var{event} can be any of the following:
2801 The throwing of a C++ exception.
2805 The catching of a C++ exception.
2809 A call to @code{exec}. This is currently only available for HP-UX.
2813 A call to @code{fork}. This is currently only available for HP-UX.
2817 A call to @code{vfork}. This is currently only available for HP-UX.
2820 @itemx load @var{libname}
2822 The dynamic loading of any shared library, or the loading of the library
2823 @var{libname}. This is currently only available for HP-UX.
2826 @itemx unload @var{libname}
2827 @kindex catch unload
2828 The unloading of any dynamically loaded shared library, or the unloading
2829 of the library @var{libname}. This is currently only available for HP-UX.
2832 @item tcatch @var{event}
2833 Set a catchpoint that is enabled only for one stop. The catchpoint is
2834 automatically deleted after the first time the event is caught.
2838 Use the @code{info break} command to list the current catchpoints.
2840 There are currently some limitations to C++ exception handling
2841 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2845 If you call a function interactively, @value{GDBN} normally returns
2846 control to you when the function has finished executing. If the call
2847 raises an exception, however, the call may bypass the mechanism that
2848 returns control to you and cause your program either to abort or to
2849 simply continue running until it hits a breakpoint, catches a signal
2850 that @value{GDBN} is listening for, or exits. This is the case even if
2851 you set a catchpoint for the exception; catchpoints on exceptions are
2852 disabled within interactive calls.
2855 You cannot raise an exception interactively.
2858 You cannot install an exception handler interactively.
2861 @cindex raise exceptions
2862 Sometimes @code{catch} is not the best way to debug exception handling:
2863 if you need to know exactly where an exception is raised, it is better to
2864 stop @emph{before} the exception handler is called, since that way you
2865 can see the stack before any unwinding takes place. If you set a
2866 breakpoint in an exception handler instead, it may not be easy to find
2867 out where the exception was raised.
2869 To stop just before an exception handler is called, you need some
2870 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2871 raised by calling a library function named @code{__raise_exception}
2872 which has the following ANSI C interface:
2875 /* @var{addr} is where the exception identifier is stored.
2876 ID is the exception identifier. */
2877 void __raise_exception (void **@var{addr}, void *@var{id});
2881 To make the debugger catch all exceptions before any stack
2882 unwinding takes place, set a breakpoint on @code{__raise_exception}
2883 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2885 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2886 that depends on the value of @var{id}, you can stop your program when
2887 a specific exception is raised. You can use multiple conditional
2888 breakpoints to stop your program when any of a number of exceptions are
2892 @node Delete Breaks, Disabling, Set Catchpoints, Breakpoints
2893 @subsection Deleting breakpoints
2895 @cindex clearing breakpoints, watchpoints, catchpoints
2896 @cindex deleting breakpoints, watchpoints, catchpoints
2897 It is often necessary to eliminate a breakpoint, watchpoint, or
2898 catchpoint once it has done its job and you no longer want your program
2899 to stop there. This is called @dfn{deleting} the breakpoint. A
2900 breakpoint that has been deleted no longer exists; it is forgotten.
2902 With the @code{clear} command you can delete breakpoints according to
2903 where they are in your program. With the @code{delete} command you can
2904 delete individual breakpoints, watchpoints, or catchpoints by specifying
2905 their breakpoint numbers.
2907 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2908 automatically ignores breakpoints on the first instruction to be executed
2909 when you continue execution without changing the execution address.
2914 Delete any breakpoints at the next instruction to be executed in the
2915 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2916 the innermost frame is selected, this is a good way to delete a
2917 breakpoint where your program just stopped.
2919 @item clear @var{function}
2920 @itemx clear @var{filename}:@var{function}
2921 Delete any breakpoints set at entry to the function @var{function}.
2923 @item clear @var{linenum}
2924 @itemx clear @var{filename}:@var{linenum}
2925 Delete any breakpoints set at or within the code of the specified line.
2927 @cindex delete breakpoints
2930 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2931 Delete the breakpoints, watchpoints, or catchpoints of the numbers
2932 specified as arguments. If no argument is specified, delete all
2933 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2934 confirm off}). You can abbreviate this command as @code{d}.
2937 @node Disabling, Conditions, Delete Breaks, Breakpoints
2938 @subsection Disabling breakpoints
2940 @kindex disable breakpoints
2941 @kindex enable breakpoints
2942 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2943 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2944 it had been deleted, but remembers the information on the breakpoint so
2945 that you can @dfn{enable} it again later.
2947 You disable and enable breakpoints, watchpoints, and catchpoints with
2948 the @code{enable} and @code{disable} commands, optionally specifying one
2949 or more breakpoint numbers as arguments. Use @code{info break} or
2950 @code{info watch} to print a list of breakpoints, watchpoints, and
2951 catchpoints if you do not know which numbers to use.
2953 A breakpoint, watchpoint, or catchpoint can have any of four different
2954 states of enablement:
2958 Enabled. The breakpoint stops your program. A breakpoint set
2959 with the @code{break} command starts out in this state.
2961 Disabled. The breakpoint has no effect on your program.
2963 Enabled once. The breakpoint stops your program, but then becomes
2964 disabled. A breakpoint set with the @code{tbreak} command starts out in
2967 Enabled for deletion. The breakpoint stops your program, but
2968 immediately after it does so it is deleted permanently.
2971 You can use the following commands to enable or disable breakpoints,
2972 watchpoints, and catchpoints:
2975 @kindex disable breakpoints
2978 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2979 Disable the specified breakpoints---or all breakpoints, if none are
2980 listed. A disabled breakpoint has no effect but is not forgotten. All
2981 options such as ignore-counts, conditions and commands are remembered in
2982 case the breakpoint is enabled again later. You may abbreviate
2983 @code{disable} as @code{dis}.
2985 @kindex enable breakpoints
2987 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2988 Enable the specified breakpoints (or all defined breakpoints). They
2989 become effective once again in stopping your program.
2991 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2992 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2993 of these breakpoints immediately after stopping your program.
2995 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2996 Enable the specified breakpoints to work once, then die. @value{GDBN}
2997 deletes any of these breakpoints as soon as your program stops there.
3000 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
3001 ,Setting breakpoints}), breakpoints that you set are initially enabled;
3002 subsequently, they become disabled or enabled only when you use one of
3003 the commands above. (The command @code{until} can set and delete a
3004 breakpoint of its own, but it does not change the state of your other
3005 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
3008 @node Conditions, Break Commands, Disabling, Breakpoints
3009 @subsection Break conditions
3010 @cindex conditional breakpoints
3011 @cindex breakpoint conditions
3013 @c FIXME what is scope of break condition expr? Context where wanted?
3014 @c in particular for a watchpoint?
3015 The simplest sort of breakpoint breaks every time your program reaches a
3016 specified place. You can also specify a @dfn{condition} for a
3017 breakpoint. A condition is just a Boolean expression in your
3018 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
3019 a condition evaluates the expression each time your program reaches it,
3020 and your program stops only if the condition is @emph{true}.
3022 This is the converse of using assertions for program validation; in that
3023 situation, you want to stop when the assertion is violated---that is,
3024 when the condition is false. In C, if you want to test an assertion expressed
3025 by the condition @var{assert}, you should set the condition
3026 @samp{! @var{assert}} on the appropriate breakpoint.
3028 Conditions are also accepted for watchpoints; you may not need them,
3029 since a watchpoint is inspecting the value of an expression anyhow---but
3030 it might be simpler, say, to just set a watchpoint on a variable name,
3031 and specify a condition that tests whether the new value is an interesting
3034 Break conditions can have side effects, and may even call functions in
3035 your program. This can be useful, for example, to activate functions
3036 that log program progress, or to use your own print functions to
3037 format special data structures. The effects are completely predictable
3038 unless there is another enabled breakpoint at the same address. (In
3039 that case, @value{GDBN} might see the other breakpoint first and stop your
3040 program without checking the condition of this one.) Note that
3041 breakpoint commands are usually more convenient and flexible for the
3042 purpose of performing side effects when a breakpoint is reached
3043 (@pxref{Break Commands, ,Breakpoint command lists}).
3045 Break conditions can be specified when a breakpoint is set, by using
3046 @samp{if} in the arguments to the @code{break} command. @xref{Set
3047 Breaks, ,Setting breakpoints}. They can also be changed at any time
3048 with the @code{condition} command.
3050 @c The watch command now seems to recognize the if keyword.
3051 @c catch doesn't, though.
3052 The @code{watch} command does not recognize the @code{if} keyword;
3053 @code{condition} is the only way to impose a further condition on a
3057 You can also use the @code{if} keyword with the @code{watch} command.
3058 The @code{catch} command does not recognize the @code{if} keyword;
3059 @code{condition} is the only way to impose a further condition on a
3065 @item condition @var{bnum} @var{expression}
3066 Specify @var{expression} as the break condition for breakpoint,
3067 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
3068 breakpoint @var{bnum} stops your program only if the value of
3069 @var{expression} is true (nonzero, in C). When you use
3070 @code{condition}, @value{GDBN} checks @var{expression} immediately for
3071 syntactic correctness, and to determine whether symbols in it have
3072 referents in the context of your breakpoint.
3073 @c FIXME so what does GDB do if there is no referent? Moreover, what
3074 @c about watchpoints?
3076 not actually evaluate @var{expression} at the time the @code{condition}
3077 command is given, however. @xref{Expressions, ,Expressions}.
3079 @item condition @var{bnum}
3080 Remove the condition from breakpoint number @var{bnum}. It becomes
3081 an ordinary unconditional breakpoint.
3084 @cindex ignore count (of breakpoint)
3085 A special case of a breakpoint condition is to stop only when the
3086 breakpoint has been reached a certain number of times. This is so
3087 useful that there is a special way to do it, using the @dfn{ignore
3088 count} of the breakpoint. Every breakpoint has an ignore count, which
3089 is an integer. Most of the time, the ignore count is zero, and
3090 therefore has no effect. But if your program reaches a breakpoint whose
3091 ignore count is positive, then instead of stopping, it just decrements
3092 the ignore count by one and continues. As a result, if the ignore count
3093 value is @var{n}, the breakpoint does not stop the next @var{n} times
3094 your program reaches it.
3098 @item ignore @var{bnum} @var{count}
3099 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
3100 The next @var{count} times the breakpoint is reached, your program's
3101 execution does not stop; other than to decrement the ignore count, @value{GDBN}
3104 To make the breakpoint stop the next time it is reached, specify
3107 When you use @code{continue} to resume execution of your program from a
3108 breakpoint, you can specify an ignore count directly as an argument to
3109 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
3110 Stepping,,Continuing and stepping}.
3112 If a breakpoint has a positive ignore count and a condition, the
3113 condition is not checked. Once the ignore count reaches zero,
3114 @value{GDBN} resumes checking the condition.
3116 You could achieve the effect of the ignore count with a condition such
3117 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
3118 is decremented each time. @xref{Convenience Vars, ,Convenience
3122 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
3125 @node Break Commands, Breakpoint Menus, Conditions, Breakpoints
3126 @subsection Breakpoint command lists
3128 @cindex breakpoint commands
3129 You can give any breakpoint (or watchpoint or catchpoint) a series of
3130 commands to execute when your program stops due to that breakpoint. For
3131 example, you might want to print the values of certain expressions, or
3132 enable other breakpoints.
3137 @item commands @r{[}@var{bnum}@r{]}
3138 @itemx @dots{} @var{command-list} @dots{}
3140 Specify a list of commands for breakpoint number @var{bnum}. The commands
3141 themselves appear on the following lines. Type a line containing just
3142 @code{end} to terminate the commands.
3144 To remove all commands from a breakpoint, type @code{commands} and
3145 follow it immediately with @code{end}; that is, give no commands.
3147 With no @var{bnum} argument, @code{commands} refers to the last
3148 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
3149 recently encountered).
3152 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
3153 disabled within a @var{command-list}.
3155 You can use breakpoint commands to start your program up again. Simply
3156 use the @code{continue} command, or @code{step}, or any other command
3157 that resumes execution.
3159 Any other commands in the command list, after a command that resumes
3160 execution, are ignored. This is because any time you resume execution
3161 (even with a simple @code{next} or @code{step}), you may encounter
3162 another breakpoint---which could have its own command list, leading to
3163 ambiguities about which list to execute.
3166 If the first command you specify in a command list is @code{silent}, the
3167 usual message about stopping at a breakpoint is not printed. This may
3168 be desirable for breakpoints that are to print a specific message and
3169 then continue. If none of the remaining commands print anything, you
3170 see no sign that the breakpoint was reached. @code{silent} is
3171 meaningful only at the beginning of a breakpoint command list.
3173 The commands @code{echo}, @code{output}, and @code{printf} allow you to
3174 print precisely controlled output, and are often useful in silent
3175 breakpoints. @xref{Output, ,Commands for controlled output}.
3177 For example, here is how you could use breakpoint commands to print the
3178 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3184 printf "x is %d\n",x
3189 One application for breakpoint commands is to compensate for one bug so
3190 you can test for another. Put a breakpoint just after the erroneous line
3191 of code, give it a condition to detect the case in which something
3192 erroneous has been done, and give it commands to assign correct values
3193 to any variables that need them. End with the @code{continue} command
3194 so that your program does not stop, and start with the @code{silent}
3195 command so that no output is produced. Here is an example:
3206 @node Breakpoint Menus, , Break Commands, Breakpoints
3207 @subsection Breakpoint menus
3209 @cindex symbol overloading
3211 Some programming languages (notably C++) permit a single function name
3212 to be defined several times, for application in different contexts.
3213 This is called @dfn{overloading}. When a function name is overloaded,
3214 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3215 a breakpoint. If you realize this is a problem, you can use
3216 something like @samp{break @var{function}(@var{types})} to specify which
3217 particular version of the function you want. Otherwise, @value{GDBN} offers
3218 you a menu of numbered choices for different possible breakpoints, and
3219 waits for your selection with the prompt @samp{>}. The first two
3220 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3221 sets a breakpoint at each definition of @var{function}, and typing
3222 @kbd{0} aborts the @code{break} command without setting any new
3225 For example, the following session excerpt shows an attempt to set a
3226 breakpoint at the overloaded symbol @code{String::after}.
3227 We choose three particular definitions of that function name:
3229 @c FIXME! This is likely to change to show arg type lists, at least
3232 (@value{GDBP}) b String::after
3235 [2] file:String.cc; line number:867
3236 [3] file:String.cc; line number:860
3237 [4] file:String.cc; line number:875
3238 [5] file:String.cc; line number:853
3239 [6] file:String.cc; line number:846
3240 [7] file:String.cc; line number:735
3242 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3243 Breakpoint 2 at 0xb344: file String.cc, line 875.
3244 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3245 Multiple breakpoints were set.
3246 Use the "delete" command to delete unwanted
3252 @c @ifclear BARETARGET
3253 @c @node Error in Breakpoints
3254 @c @subsection ``Cannot insert breakpoints''
3256 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3258 @c Under some operating systems, breakpoints cannot be used in a program if
3259 @c any other process is running that program. In this situation,
3260 @c attempting to run or continue a program with a breakpoint causes
3261 @c @value{GDBN} to stop the other process.
3263 @c When this happens, you have three ways to proceed:
3267 @c Remove or disable the breakpoints, then continue.
3270 @c Suspend @value{GDBN}, and copy the file containing your program to a new
3271 @c name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3272 @c that @value{GDBN} should run your program under that name.
3273 @c Then start your program again.
3276 @c Relink your program so that the text segment is nonsharable, using the
3277 @c linker option @samp{-N}. The operating system limitation may not apply
3278 @c to nonsharable executables.
3282 @node Continuing and Stepping, Signals, Breakpoints, Stopping
3283 @section Continuing and stepping
3287 @cindex resuming execution
3288 @dfn{Continuing} means resuming program execution until your program
3289 completes normally. In contrast, @dfn{stepping} means executing just
3290 one more ``step'' of your program, where ``step'' may mean either one
3291 line of source code, or one machine instruction (depending on what
3292 particular command you use). Either when continuing or when stepping,
3293 your program may stop even sooner, due to a breakpoint or a signal. (If
3294 due to a signal, you may want to use @code{handle}, or use @samp{signal
3295 0} to resume execution. @xref{Signals, ,Signals}.)
3301 @item continue @r{[}@var{ignore-count}@r{]}
3302 @itemx c @r{[}@var{ignore-count}@r{]}
3303 @itemx fg @r{[}@var{ignore-count}@r{]}
3304 Resume program execution, at the address where your program last stopped;
3305 any breakpoints set at that address are bypassed. The optional argument
3306 @var{ignore-count} allows you to specify a further number of times to
3307 ignore a breakpoint at this location; its effect is like that of
3308 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3310 The argument @var{ignore-count} is meaningful only when your program
3311 stopped due to a breakpoint. At other times, the argument to
3312 @code{continue} is ignored.
3314 The synonyms @code{c} and @code{fg} are provided purely for convenience,
3315 and have exactly the same behavior as @code{continue}.
3318 To resume execution at a different place, you can use @code{return}
3319 (@pxref{Returning, ,Returning from a function}) to go back to the
3320 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3321 different address}) to go to an arbitrary location in your program.
3323 A typical technique for using stepping is to set a breakpoint
3324 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3325 beginning of the function or the section of your program where a problem
3326 is believed to lie, run your program until it stops at that breakpoint,
3327 and then step through the suspect area, examining the variables that are
3328 interesting, until you see the problem happen.
3334 Continue running your program until control reaches a different source
3335 line, then stop it and return control to @value{GDBN}. This command is
3336 abbreviated @code{s}.
3339 @c "without debugging information" is imprecise; actually "without line
3340 @c numbers in the debugging information". (gcc -g1 has debugging info but
3341 @c not line numbers). But it seems complex to try to make that
3342 @c distinction here.
3343 @emph{Warning:} If you use the @code{step} command while control is
3344 within a function that was compiled without debugging information,
3345 execution proceeds until control reaches a function that does have
3346 debugging information. Likewise, it will not step into a function which
3347 is compiled without debugging information. To step through functions
3348 without debugging information, use the @code{stepi} command, described
3352 The @code{step} command now only stops at the first instruction of a
3353 source line. This prevents the multiple stops that used to occur in
3354 switch statements, for loops, etc. @code{step} continues to stop if a
3355 function that has debugging information is called within the line.
3357 Also, the @code{step} command now only enters a subroutine if there is line
3358 number information for the subroutine. Otherwise it acts like the
3359 @code{next} command. This avoids problems when using @code{cc -gl}
3360 on MIPS machines. Previously, @code{step} entered subroutines if there
3361 was any debugging information about the routine.
3363 @item step @var{count}
3364 Continue running as in @code{step}, but do so @var{count} times. If a
3365 breakpoint is reached, or a signal not related to stepping occurs before
3366 @var{count} steps, stepping stops right away.
3370 @item next @r{[}@var{count}@r{]}
3371 Continue to the next source line in the current (innermost) stack frame.
3372 This is similar to @code{step}, but function calls that appear within
3373 the line of code are executed without stopping. Execution stops when
3374 control reaches a different line of code at the original stack level
3375 that was executing when you gave the @code{next} command. This command
3376 is abbreviated @code{n}.
3378 An argument @var{count} is a repeat count, as for @code{step}.
3381 @c FIX ME!! Do we delete this, or is there a way it fits in with
3382 @c the following paragraph? --- Vctoria
3384 @c @code{next} within a function that lacks debugging information acts like
3385 @c @code{step}, but any function calls appearing within the code of the
3386 @c function are executed without stopping.
3388 The @code{next} command now only stops at the first instruction of a
3389 source line. This prevents the multiple stops that used to occur in
3390 switch statements, for loops, etc.
3394 Continue running until just after function in the selected stack frame
3395 returns. Print the returned value (if any).
3397 Contrast this with the @code{return} command (@pxref{Returning,
3398 ,Returning from a function}).
3404 Continue running until a source line past the current line, in the
3405 current stack frame, is reached. This command is used to avoid single
3406 stepping through a loop more than once. It is like the @code{next}
3407 command, except that when @code{until} encounters a jump, it
3408 automatically continues execution until the program counter is greater
3409 than the address of the jump.
3411 This means that when you reach the end of a loop after single stepping
3412 though it, @code{until} makes your program continue execution until it
3413 exits the loop. In contrast, a @code{next} command at the end of a loop
3414 simply steps back to the beginning of the loop, which forces you to step
3415 through the next iteration.
3417 @code{until} always stops your program if it attempts to exit the current
3420 @code{until} may produce somewhat counterintuitive results if the order
3421 of machine code does not match the order of the source lines. For
3422 example, in the following excerpt from a debugging session, the @code{f}
3423 (@code{frame}) command shows that execution is stopped at line
3424 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3428 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3430 (@value{GDBP}) until
3431 195 for ( ; argc > 0; NEXTARG) @{
3434 This happened because, for execution efficiency, the compiler had
3435 generated code for the loop closure test at the end, rather than the
3436 start, of the loop---even though the test in a C @code{for}-loop is
3437 written before the body of the loop. The @code{until} command appeared
3438 to step back to the beginning of the loop when it advanced to this
3439 expression; however, it has not really gone to an earlier
3440 statement---not in terms of the actual machine code.
3442 @code{until} with no argument works by means of single
3443 instruction stepping, and hence is slower than @code{until} with an
3446 @item until @var{location}
3447 @itemx u @var{location}
3448 Continue running your program until either the specified location is
3449 reached, or the current stack frame returns. @var{location} is any of
3450 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3451 ,Setting breakpoints}). This form of the command uses breakpoints,
3452 and hence is quicker than @code{until} without an argument.
3458 Execute one machine instruction, then stop and return to the debugger.
3460 It is often useful to do @samp{display/i $pc} when stepping by machine
3461 instructions. This makes @value{GDBN} automatically display the next
3462 instruction to be executed, each time your program stops. @xref{Auto
3463 Display,, Automatic display}.
3465 An argument is a repeat count, as in @code{step}.
3472 Execute one machine instruction, but if it is a function call,
3473 proceed until the function returns.
3475 An argument is a repeat count, as in @code{next}.
3478 @node Signals, Thread Stops, Continuing and Stepping, Stopping
3482 A signal is an asynchronous event that can happen in a program. The
3483 operating system defines the possible kinds of signals, and gives each
3484 kind a name and a number. For example, in Unix @code{SIGINT} is the
3485 signal a program gets when you type an interrupt (often @kbd{C-c});
3486 @code{SIGSEGV} is the signal a program gets from referencing a place in
3487 memory far away from all the areas in use; @code{SIGALRM} occurs when
3488 the alarm clock timer goes off (which happens only if your program has
3489 requested an alarm).
3491 @cindex fatal signals
3492 Some signals, including @code{SIGALRM}, are a normal part of the
3493 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3494 errors; these signals are @dfn{fatal} (kill your program immediately) if the
3495 program has not specified in advance some other way to handle the signal.
3496 @code{SIGINT} does not indicate an error in your program, but it is normally
3497 fatal so it can carry out the purpose of the interrupt: to kill the program.
3499 @value{GDBN} has the ability to detect any occurrence of a signal in your
3500 program. You can tell @value{GDBN} in advance what to do for each kind of
3503 @cindex handling signals
3504 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3505 (so as not to interfere with their role in the functioning of your program)
3506 but to stop your program immediately whenever an error signal happens.
3507 You can change these settings with the @code{handle} command.
3510 @kindex info signals
3512 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3513 handle each one. You can use this to see the signal numbers of all
3514 the defined types of signals.
3516 @code{info handle} is the new alias for @code{info signals}.
3519 @item handle @var{signal} @var{keywords}@dots{}
3520 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3521 be the number of a signal or its name (with or without the @samp{SIG} at the
3522 beginning). The @var{keywords} say what change to make.
3526 The keywords allowed by the @code{handle} command can be abbreviated.
3527 Their full names are:
3531 @value{GDBN} should not stop your program when this signal happens. It may
3532 still print a message telling you that the signal has come in.
3535 @value{GDBN} should stop your program when this signal happens. This implies
3536 the @code{print} keyword as well.
3539 @value{GDBN} should print a message when this signal happens.
3542 @value{GDBN} should not mention the occurrence of the signal at all. This
3543 implies the @code{nostop} keyword as well.
3546 @value{GDBN} should allow your program to see this signal; your program
3547 can handle the signal, or else it may terminate if the signal is fatal
3551 @value{GDBN} should not allow your program to see this signal.
3555 When a signal stops your program, the signal is not visible until you
3556 continue. Your program sees the signal then, if @code{pass} is in
3557 effect for the signal in question @emph{at that time}. In other words,
3558 after @value{GDBN} reports a signal, you can use the @code{handle}
3559 command with @code{pass} or @code{nopass} to control whether your
3560 program sees that signal when you continue.
3562 You can also use the @code{signal} command to prevent your program from
3563 seeing a signal, or cause it to see a signal it normally would not see,
3564 or to give it any signal at any time. For example, if your program stopped
3565 due to some sort of memory reference error, you might store correct
3566 values into the erroneous variables and continue, hoping to see more
3567 execution; but your program would probably terminate immediately as
3568 a result of the fatal signal once it saw the signal. To prevent this,
3569 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3572 @node Thread Stops, , Signals, Stopping
3573 @section Stopping and starting multi-thread programs
3575 When your program has multiple threads (@pxref{Threads,, Debugging
3576 programs with multiple threads}), you can choose whether to set
3577 breakpoints on all threads, or on a particular thread.
3580 @cindex breakpoints and threads
3581 @cindex thread breakpoints
3582 @kindex break @dots{} thread @var{threadno}
3583 @item break @var{linespec} thread @var{threadno}
3584 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3585 @var{linespec} specifies source lines; there are several ways of
3586 writing them, but the effect is always to specify some source line.
3588 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3589 to specify that you only want @value{GDBN} to stop the program when a
3590 particular thread reaches this breakpoint. @var{threadno} is one of the
3591 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3592 column of the @samp{info threads} display.
3594 If you do not specify @samp{thread @var{threadno}} when you set a
3595 breakpoint, the breakpoint applies to @emph{all} threads of your
3598 You can use the @code{thread} qualifier on conditional breakpoints as
3599 well; in this case, place @samp{thread @var{threadno}} before the
3600 breakpoint condition, like this:
3603 (gdb) break frik.c:13 thread 28 if bartab > lim
3608 @cindex stopped threads
3609 @cindex threads, stopped
3610 Whenever your program stops under @value{GDBN} for any reason,
3611 @emph{all} threads of execution stop, not just the current thread. This
3612 allows you to examine the overall state of the program, including
3613 switching between threads, without worrying that things may change
3616 @cindex continuing threads
3617 @cindex threads, continuing
3618 Conversely, whenever you restart the program, @emph{all} threads start
3619 executing. @emph{This is true even when single-stepping} with commands
3620 like @code{step} or @code{next}.
3622 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3623 Since thread scheduling is up to your debugging target's operating
3624 system (not controlled by @value{GDBN}), other threads may
3625 execute more than one statement while the current thread completes a
3626 single step. Moreover, in general other threads stop in the middle of a
3627 statement, rather than at a clean statement boundary, when the program
3630 You might even find your program stopped in another thread after
3631 continuing or even single-stepping. This happens whenever some other
3632 thread runs into a breakpoint, a signal, or an exception before the
3633 first thread completes whatever you requested.
3635 On some OSes, you can lock the OS scheduler and thus allow only a single
3639 @item set scheduler-locking @var{mode}
3640 Set the scheduler locking mode. If it is @code{off}, then there is no
3641 locking and any thread may run at any time. If @code{on}, then only the
3642 current thread may run when the inferior is resumed. The @code{step}
3643 mode optimizes for single-stepping. It stops other threads from
3644 ``seizing the prompt'' by preempting the current thread while you are
3645 stepping. Other threads will only rarely (or never) get a chance to run
3646 when you step. They are more likely to run when you ``next'' over a
3647 function call, and they are completely free to run when you use commands
3648 like ``continue'', ``until'', or ``finish''. However, unless another
3649 thread hits a breakpoint during its timeslice, they will never steal the
3650 GDB prompt away from the thread that you are debugging.
3652 @item show scheduler-locking
3653 Display the current scheduler locking mode.
3657 @node Stack, Source, Stopping, Top
3658 @chapter Examining the Stack
3660 When your program has stopped, the first thing you need to know is where it
3661 stopped and how it got there.
3664 Each time your program performs a function call, information about the call
3666 That information includes the location of the call in your program,
3667 the arguments of the call,
3668 and the local variables of the function being called.
3669 The information is saved in a block of data called a @dfn{stack frame}.
3670 The stack frames are allocated in a region of memory called the @dfn{call
3673 When your program stops, the @value{GDBN} commands for examining the
3674 stack allow you to see all of this information.
3676 @cindex selected frame
3677 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3678 @value{GDBN} commands refer implicitly to the selected frame. In
3679 particular, whenever you ask @value{GDBN} for the value of a variable in
3680 your program, the value is found in the selected frame. There are
3681 special @value{GDBN} commands to select whichever frame you are
3682 interested in. @xref{Selection, ,Selecting a frame}.
3684 When your program stops, @value{GDBN} automatically selects the
3685 currently executing frame and describes it briefly, similar to the
3686 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3689 * Frames:: Stack frames
3690 * Backtrace:: Backtraces
3691 * Selection:: Selecting a frame
3692 * Frame Info:: Information on a frame
3693 * Alpha/MIPS Stack:: Alpha and MIPS machines and the function stack
3697 @node Frames, Backtrace, Stack, Stack
3698 @section Stack frames
3702 The call stack is divided up into contiguous pieces called @dfn{stack
3703 frames}, or @dfn{frames} for short; each frame is the data associated
3704 with one call to one function. The frame contains the arguments given
3705 to the function, the function's local variables, and the address at
3706 which the function is executing.
3708 @cindex initial frame
3709 @cindex outermost frame
3710 @cindex innermost frame
3711 When your program is started, the stack has only one frame, that of the
3712 function @code{main}. This is called the @dfn{initial} frame or the
3713 @dfn{outermost} frame. Each time a function is called, a new frame is
3714 made. Each time a function returns, the frame for that function invocation
3715 is eliminated. If a function is recursive, there can be many frames for
3716 the same function. The frame for the function in which execution is
3717 actually occurring is called the @dfn{innermost} frame. This is the most
3718 recently created of all the stack frames that still exist.
3720 @cindex frame pointer
3721 Inside your program, stack frames are identified by their addresses. A
3722 stack frame consists of many bytes, each of which has its own address; each
3723 kind of computer has a convention for choosing one byte whose
3724 address serves as the address of the frame. Usually this address is kept
3725 in a register called the @dfn{frame pointer register} while execution is
3726 going on in that frame.
3728 @cindex frame number
3729 @value{GDBN} assigns numbers to all existing stack frames, starting with
3730 zero for the innermost frame, one for the frame that called it,
3731 and so on upward. These numbers do not really exist in your program;
3732 they are assigned by @value{GDBN} to give you a way of designating stack
3733 frames in @value{GDBN} commands.
3735 @c below produces an acceptable overful hbox. --mew 13aug1993
3736 @cindex frameless execution
3737 Some compilers provide a way to compile functions so that they operate
3738 without stack frames. (For example, the @code{@value{GCC}} option
3739 @samp{-fomit-frame-pointer} generates functions without a frame.)
3740 This is occasionally done with heavily used library functions to save
3741 the frame setup time. @value{GDBN} has limited facilities for dealing
3742 with these function invocations. If the innermost function invocation
3743 has no stack frame, @value{GDBN} nevertheless regards it as though
3744 it had a separate frame, which is numbered zero as usual, allowing
3745 correct tracing of the function call chain. However, @value{GDBN} has
3746 no provision for frameless functions elsewhere in the stack.
3750 @item frame @var{args}
3751 The @code{frame} command allows you to move from one stack frame to another,
3752 and to print the stack frame you select. @var{args} may be either the
3753 address of the frame or the stack frame number. Without an argument,
3754 @code{frame} prints the current stack frame.
3756 @kindex select-frame
3758 The @code{select-frame} command allows you to move from one stack frame
3759 to another without printing the frame. This is the silent version of
3763 @node Backtrace, Selection, Frames, Stack
3768 @cindex stack traces
3769 A backtrace is a summary of how your program got where it is. It shows one
3770 line per frame, for many frames, starting with the currently executing
3771 frame (frame zero), followed by its caller (frame one), and on up the
3779 Print a backtrace of the entire stack: one line per frame for all
3780 frames in the stack.
3782 You can stop the backtrace at any time by typing the system interrupt
3783 character, normally @kbd{C-c}.
3785 @item backtrace @var{n}
3787 Similar, but print only the innermost @var{n} frames.
3789 @item backtrace -@var{n}
3791 Similar, but print only the outermost @var{n} frames.
3797 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3798 are additional aliases for @code{backtrace}.
3800 Each line in the backtrace shows the frame number and the function name.
3801 The program counter value is also shown---unless you use @code{set
3802 print address off}. The backtrace also shows the source file name and
3803 line number, as well as the arguments to the function. The program
3804 counter value is omitted if it is at the beginning of the code for that
3807 Here is an example of a backtrace. It was made with the command
3808 @samp{bt 3}, so it shows the innermost three frames.
3812 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3814 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3815 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3817 (More stack frames follow...)
3822 The display for frame zero does not begin with a program counter
3823 value, indicating that your program has stopped at the beginning of the
3824 code for line @code{993} of @code{builtin.c}.
3826 @node Selection, Frame Info, Backtrace, Stack
3827 @section Selecting a frame
3829 Most commands for examining the stack and other data in your program work on
3830 whichever stack frame is selected at the moment. Here are the commands for
3831 selecting a stack frame; all of them finish by printing a brief description
3832 of the stack frame just selected.
3839 Select frame number @var{n}. Recall that frame zero is the innermost
3840 (currently executing) frame, frame one is the frame that called the
3841 innermost one, and so on. The highest-numbered frame is the one for
3844 @item frame @var{addr}
3846 Select the frame at address @var{addr}. This is useful mainly if the
3847 chaining of stack frames has been damaged by a bug, making it
3848 impossible for @value{GDBN} to assign numbers properly to all frames. In
3849 addition, this can be useful when your program has multiple stacks and
3850 switches between them.
3853 On the SPARC architecture, @code{frame} needs two addresses to
3854 select an arbitrary frame: a frame pointer and a stack pointer.
3856 On the MIPS and Alpha architecture, it needs two addresses: a stack
3857 pointer and a program counter.
3859 On the 29k architecture, it needs three addresses: a register stack
3860 pointer, a program counter, and a memory stack pointer.
3861 @c note to future updaters: this is conditioned on a flag
3862 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3863 @c as of 27 Jan 1994.
3868 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3869 advances toward the outermost frame, to higher frame numbers, to frames
3870 that have existed longer. @var{n} defaults to one.
3875 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3876 advances toward the innermost frame, to lower frame numbers, to frames
3877 that were created more recently. @var{n} defaults to one. You may
3878 abbreviate @code{down} as @code{do}.
3881 All of these commands end by printing two lines of output describing the
3882 frame. The first line shows the frame number, the function name, the
3883 arguments, and the source file and line number of execution in that
3884 frame. The second line shows the text of that source line.
3892 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3894 10 read_input_file (argv[i]);
3898 After such a printout, the @code{list} command with no arguments
3899 prints ten lines centered on the point of execution in the frame.
3900 @xref{List, ,Printing source lines}.
3903 @kindex down-silently
3905 @item up-silently @var{n}
3906 @itemx down-silently @var{n}
3907 These two commands are variants of @code{up} and @code{down},
3908 respectively; they differ in that they do their work silently, without
3909 causing display of the new frame. They are intended primarily for use
3910 in @value{GDBN} command scripts, where the output might be unnecessary and
3914 @node Frame Info, Alpha/MIPS Stack, Selection, Stack
3915 @section Information about a frame
3917 There are several other commands to print information about the selected
3923 When used without any argument, this command does not change which
3924 frame is selected, but prints a brief description of the currently
3925 selected stack frame. It can be abbreviated @code{f}. With an
3926 argument, this command is used to select a stack frame.
3927 @xref{Selection, ,Selecting a frame}.
3933 This command prints a verbose description of the selected stack frame,
3938 the address of the frame
3940 the address of the next frame down (called by this frame)
3942 the address of the next frame up (caller of this frame)
3944 the language in which the source code corresponding to this frame is written
3946 the address of the frame's arguments
3948 the program counter saved in it (the address of execution in the caller frame)
3950 which registers were saved in the frame
3953 @noindent The verbose description is useful when
3954 something has gone wrong that has made the stack format fail to fit
3955 the usual conventions.
3957 @item info frame @var{addr}
3958 @itemx info f @var{addr}
3959 Print a verbose description of the frame at address @var{addr}, without
3960 selecting that frame. The selected frame remains unchanged by this
3961 command. This requires the same kind of address (more than one for some
3962 architectures) that you specify in the @code{frame} command.
3963 @xref{Selection, ,Selecting a frame}.
3967 Print the arguments of the selected frame, each on a separate line.
3971 Print the local variables of the selected frame, each on a separate
3972 line. These are all variables (declared either static or automatic)
3973 accessible at the point of execution of the selected frame.
3977 @cindex catch exceptions
3978 @cindex exception handlers
3980 Print a list of all the exception handlers that are active in the
3981 current stack frame at the current point of execution. To see other
3982 exception handlers, visit the associated frame (using the @code{up},
3983 @code{down}, or @code{frame} commands); then type @code{info catch}.
3984 @xref{Set Catchpoints, , Setting catchpoints}.
3988 @node Alpha/MIPS Stack, , Frame Info, Stack
3989 @section MIPS/Alpha machines and the function stack
3991 @cindex stack on Alpha
3992 @cindex stack on MIPS
3995 Alpha- and MIPS-based computers use an unusual stack frame, which
3996 sometimes requires @value{GDBN} to search backward in the object code to
3997 find the beginning of a function.
3999 @cindex response time, MIPS debugging
4000 To improve response time (especially for embedded applications, where
4001 @value{GDBN} may be restricted to a slow serial line for this search)
4002 you may want to limit the size of this search, using one of these
4006 @cindex @code{heuristic-fence-post} (Alpha,MIPS)
4007 @item set heuristic-fence-post @var{limit}
4008 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
4009 for the beginning of a function. A value of @var{0} (the default)
4010 means there is no limit. However, except for @var{0}, the larger the
4011 limit the more bytes @code{heuristic-fence-post} must search and
4012 therefore the longer it takes to run.
4014 @item show heuristic-fence-post
4015 Display the current limit.
4019 These commands are available @emph{only} when @value{GDBN} is configured
4020 for debugging programs on Alpha or MIPS processors.
4023 @node Source, Data, Stack, Top
4024 @chapter Examining Source Files
4026 @value{GDBN} can print parts of your program's source, since the debugging
4027 information recorded in the program tells @value{GDBN} what source files were
4028 used to build it. When your program stops, @value{GDBN} spontaneously prints
4029 the line where it stopped. Likewise, when you select a stack frame
4030 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
4031 execution in that frame has stopped. You can print other portions of
4032 source files by explicit command.
4034 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
4035 prefer to use Emacs facilities to view source; @pxref{Emacs, ,Using
4036 @value{GDBN} under @sc{gnu} Emacs}.
4039 * List:: Printing source lines
4040 * Search:: Searching source files
4041 * Source Path:: Specifying source directories
4042 * Machine Code:: Source and machine code
4045 @node List, Search, Source, Source
4046 @section Printing source lines
4050 To print lines from a source file, use the @code{list} command
4051 (abbreviated @code{l}). By default, ten lines are printed.
4052 There are several ways to specify what part of the file you want to print.
4054 Here are the forms of the @code{list} command most commonly used:
4057 @item list @var{linenum}
4058 Print lines centered around line number @var{linenum} in the
4059 current source file.
4061 @item list @var{function}
4062 Print lines centered around the beginning of function
4066 Print more lines. If the last lines printed were printed with a
4067 @code{list} command, this prints lines following the last lines
4068 printed; however, if the last line printed was a solitary line printed
4069 as part of displaying a stack frame (@pxref{Stack, ,Examining the
4070 Stack}), this prints lines centered around that line.
4073 Print lines just before the lines last printed.
4076 By default, @value{GDBN} prints ten source lines with any of these forms of
4077 the @code{list} command. You can change this using @code{set listsize}:
4080 @kindex set listsize
4081 @item set listsize @var{count}
4082 Make the @code{list} command display @var{count} source lines (unless
4083 the @code{list} argument explicitly specifies some other number).
4085 @kindex show listsize
4087 Display the number of lines that @code{list} prints.
4090 Repeating a @code{list} command with @key{RET} discards the argument,
4091 so it is equivalent to typing just @code{list}. This is more useful
4092 than listing the same lines again. An exception is made for an
4093 argument of @samp{-}; that argument is preserved in repetition so that
4094 each repetition moves up in the source file.
4097 In general, the @code{list} command expects you to supply zero, one or two
4098 @dfn{linespecs}. Linespecs specify source lines; there are several ways
4099 of writing them but the effect is always to specify some source line.
4100 Here is a complete description of the possible arguments for @code{list}:
4103 @item list @var{linespec}
4104 Print lines centered around the line specified by @var{linespec}.
4106 @item list @var{first},@var{last}
4107 Print lines from @var{first} to @var{last}. Both arguments are
4110 @item list ,@var{last}
4111 Print lines ending with @var{last}.
4113 @item list @var{first},
4114 Print lines starting with @var{first}.
4117 Print lines just after the lines last printed.
4120 Print lines just before the lines last printed.
4123 As described in the preceding table.
4126 Here are the ways of specifying a single source line---all the
4131 Specifies line @var{number} of the current source file.
4132 When a @code{list} command has two linespecs, this refers to
4133 the same source file as the first linespec.
4136 Specifies the line @var{offset} lines after the last line printed.
4137 When used as the second linespec in a @code{list} command that has
4138 two, this specifies the line @var{offset} lines down from the
4142 Specifies the line @var{offset} lines before the last line printed.
4144 @item @var{filename}:@var{number}
4145 Specifies line @var{number} in the source file @var{filename}.
4147 @item @var{function}
4148 Specifies the line that begins the body of the function @var{function}.
4149 For example: in C, this is the line with the open brace.
4151 @item @var{filename}:@var{function}
4152 Specifies the line of the open-brace that begins the body of the
4153 function @var{function} in the file @var{filename}. You only need the
4154 file name with a function name to avoid ambiguity when there are
4155 identically named functions in different source files.
4157 @item *@var{address}
4158 Specifies the line containing the program address @var{address}.
4159 @var{address} may be any expression.
4162 @node Search, Source Path, List, Source
4163 @section Searching source files
4165 @kindex reverse-search
4167 There are two commands for searching through the current source file for a
4172 @kindex forward-search
4173 @item forward-search @var{regexp}
4174 @itemx search @var{regexp}
4175 The command @samp{forward-search @var{regexp}} checks each line,
4176 starting with the one following the last line listed, for a match for
4177 @var{regexp}. It lists the line that is found. You can use the
4178 synonym @samp{search @var{regexp}} or abbreviate the command name as
4181 @item reverse-search @var{regexp}
4182 The command @samp{reverse-search @var{regexp}} checks each line, starting
4183 with the one before the last line listed and going backward, for a match
4184 for @var{regexp}. It lists the line that is found. You can abbreviate
4185 this command as @code{rev}.
4188 @node Source Path, Machine Code, Search, Source
4189 @section Specifying source directories
4192 @cindex directories for source files
4193 Executable programs sometimes do not record the directories of the source
4194 files from which they were compiled, just the names. Even when they do,
4195 the directories could be moved between the compilation and your debugging
4196 session. @value{GDBN} has a list of directories to search for source files;
4197 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4198 it tries all the directories in the list, in the order they are present
4199 in the list, until it finds a file with the desired name. Note that
4200 the executable search path is @emph{not} used for this purpose. Neither is
4201 the current working directory, unless it happens to be in the source
4204 If @value{GDBN} cannot find a source file in the source path, and the
4205 object program records a directory, @value{GDBN} tries that directory
4206 too. If the source path is empty, and there is no record of the
4207 compilation directory, @value{GDBN} looks in the current directory as a
4210 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4211 any information it has cached about where source files are found and where
4212 each line is in the file.
4216 When you start @value{GDBN}, its source path is empty.
4217 To add other directories, use the @code{directory} command.
4220 @item directory @var{dirname} @dots{}
4221 @item dir @var{dirname} @dots{}
4222 Add directory @var{dirname} to the front of the source path. Several
4223 directory names may be given to this command, separated by @samp{:} or
4224 whitespace. You may specify a directory that is already in the source
4225 path; this moves it forward, so @value{GDBN} searches it sooner.
4231 @cindex compilation directory
4232 @cindex current directory
4233 @cindex working directory
4234 @cindex directory, current
4235 @cindex directory, compilation
4236 You can use the string @samp{$cdir} to refer to the compilation
4237 directory (if one is recorded), and @samp{$cwd} to refer to the current
4238 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4239 tracks the current working directory as it changes during your @value{GDBN}
4240 session, while the latter is immediately expanded to the current
4241 directory at the time you add an entry to the source path.
4244 Reset the source path to empty again. This requires confirmation.
4246 @c RET-repeat for @code{directory} is explicitly disabled, but since
4247 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4249 @item show directories
4250 @kindex show directories
4251 Print the source path: show which directories it contains.
4254 If your source path is cluttered with directories that are no longer of
4255 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4256 versions of source. You can correct the situation as follows:
4260 Use @code{directory} with no argument to reset the source path to empty.
4263 Use @code{directory} with suitable arguments to reinstall the
4264 directories you want in the source path. You can add all the
4265 directories in one command.
4268 @node Machine Code, , Source Path, Source
4269 @section Source and machine code
4271 You can use the command @code{info line} to map source lines to program
4272 addresses (and vice versa), and the command @code{disassemble} to display
4273 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4274 mode, the @code{info line} command now causes the arrow to point to the
4275 line specified. Also, @code{info line} prints addresses in symbolic form as
4280 @item info line @var{linespec}
4281 Print the starting and ending addresses of the compiled code for
4282 source line @var{linespec}. You can specify source lines in any of
4283 the ways understood by the @code{list} command (@pxref{List, ,Printing
4287 For example, we can use @code{info line} to discover the location of
4288 the object code for the first line of function
4289 @code{m4_changequote}:
4292 (@value{GDBP}) info line m4_changecom
4293 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4297 We can also inquire (using @code{*@var{addr}} as the form for
4298 @var{linespec}) what source line covers a particular address:
4300 (@value{GDBP}) info line *0x63ff
4301 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4304 @cindex @code{$_} and @code{info line}
4305 After @code{info line}, the default address for the @code{x} command
4306 is changed to the starting address of the line, so that @samp{x/i} is
4307 sufficient to begin examining the machine code (@pxref{Memory,
4308 ,Examining memory}). Also, this address is saved as the value of the
4309 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4314 @cindex assembly instructions
4315 @cindex instructions, assembly
4316 @cindex machine instructions
4317 @cindex listing machine instructions
4319 This specialized command dumps a range of memory as machine
4320 instructions. The default memory range is the function surrounding the
4321 program counter of the selected frame. A single argument to this
4322 command is a program counter value; @value{GDBN} dumps the function
4323 surrounding this value. Two arguments specify a range of addresses
4324 (first inclusive, second exclusive) to dump.
4327 The following example shows the disassembly of a range of addresses of
4328 HP PA-RISC 2.0 code:
4331 (@value{GDBP}) disas 0x32c4 0x32e4
4332 Dump of assembler code from 0x32c4 to 0x32e4:
4333 0x32c4 <main+204>: addil 0,dp
4334 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4335 0x32cc <main+212>: ldil 0x3000,r31
4336 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4337 0x32d4 <main+220>: ldo 0(r31),rp
4338 0x32d8 <main+224>: addil -0x800,dp
4339 0x32dc <main+228>: ldo 0x588(r1),r26
4340 0x32e0 <main+232>: ldil 0x3000,r31
4341 End of assembler dump.
4344 Some architectures have more than one commonly-used set of instruction
4345 mnemonics or other syntax.
4348 @kindex set assembly-language
4349 @cindex assembly instructions
4350 @cindex instructions, assembly
4351 @cindex machine instructions
4352 @cindex listing machine instructions
4353 @item set assembly-language @var{instruction-set}
4354 Select the instruction set to use when disassembling the
4355 program via the @code{disassemble} or @code{x/i} commands.
4357 Currently this command is only defined for the Intel x86 family. You
4358 can set @var{instruction-set} to either @code{i386} or @code{i8086}.
4359 The default is @code{i386}.
4363 @node Data, Languages, Source, Top
4364 @chapter Examining Data
4366 @cindex printing data
4367 @cindex examining data
4370 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4371 @c document because it is nonstandard... Under Epoch it displays in a
4372 @c different window or something like that.
4373 The usual way to examine data in your program is with the @code{print}
4374 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4375 evaluates and prints the value of an expression of the language your
4376 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4377 Different Languages}).
4380 @item print @var{exp}
4381 @itemx print /@var{f} @var{exp}
4382 @var{exp} is an expression (in the source language). By default the
4383 value of @var{exp} is printed in a format appropriate to its data type;
4384 you can choose a different format by specifying @samp{/@var{f}}, where
4385 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
4389 @itemx print /@var{f}
4390 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
4391 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4392 conveniently inspect the same value in an alternative format.
4395 A more low-level way of examining data is with the @code{x} command.
4396 It examines data in memory at a specified address and prints it in a
4397 specified format. @xref{Memory, ,Examining memory}.
4399 If you are interested in information about types, or about how the
4400 fields of a struct or class are declared, use the @code{ptype @var{exp}}
4401 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4405 * Expressions:: Expressions
4406 * Variables:: Program variables
4407 * Arrays:: Artificial arrays
4408 * Output Formats:: Output formats
4409 * Memory:: Examining memory
4410 * Auto Display:: Automatic display
4411 * Print Settings:: Print settings
4412 * Value History:: Value history
4413 * Convenience Vars:: Convenience variables
4414 * Registers:: Registers
4415 * Floating Point Hardware:: Floating point hardware
4418 @node Expressions, Variables, Data, Data
4419 @section Expressions
4422 @code{print} and many other @value{GDBN} commands accept an expression and
4423 compute its value. Any kind of constant, variable or operator defined
4424 by the programming language you are using is valid in an expression in
4425 @value{GDBN}. This includes conditional expressions, function calls, casts
4426 and string constants. It unfortunately does not include symbols defined
4427 by preprocessor @code{#define} commands.
4429 @value{GDBN} now supports array constants in expressions input by
4430 the user. The syntax is @var{@{element, element@dots{}@}}. For example,
4431 you can now use the command @code{print @{1, 2, 3@}} to build up an array in
4432 memory that is malloc'd in the target program.
4434 Because C is so widespread, most of the expressions shown in examples in
4435 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4436 Languages}, for information on how to use expressions in other
4439 In this section, we discuss operators that you can use in @value{GDBN}
4440 expressions regardless of your programming language.
4442 Casts are supported in all languages, not just in C, because it is so
4443 useful to cast a number into a pointer in order to examine a structure
4444 at that address in memory.
4445 @c FIXME: casts supported---Mod2 true?
4447 @value{GDBN} supports these operators, in addition to those common
4448 to programming languages:
4452 @samp{@@} is a binary operator for treating parts of memory as arrays.
4453 @xref{Arrays, ,Artificial arrays}, for more information.
4456 @samp{::} allows you to specify a variable in terms of the file or
4457 function where it is defined. @xref{Variables, ,Program variables}.
4459 @cindex @{@var{type}@}
4460 @cindex type casting memory
4461 @cindex memory, viewing as typed object
4462 @cindex casts, to view memory
4463 @item @{@var{type}@} @var{addr}
4464 Refers to an object of type @var{type} stored at address @var{addr} in
4465 memory. @var{addr} may be any expression whose value is an integer or
4466 pointer (but parentheses are required around binary operators, just as in
4467 a cast). This construct is allowed regardless of what kind of data is
4468 normally supposed to reside at @var{addr}.
4471 @node Variables, Arrays, Expressions, Data
4472 @section Program variables
4474 The most common kind of expression to use is the name of a variable
4477 Variables in expressions are understood in the selected stack frame
4478 (@pxref{Selection, ,Selecting a frame}); they must be either:
4482 global (or file-static)
4489 visible according to the scope rules of the
4490 programming language from the point of execution in that frame
4493 @noindent This means that in the function
4508 you can examine and use the variable @code{a} whenever your program is
4509 executing within the function @code{foo}, but you can only use or
4510 examine the variable @code{b} while your program is executing inside
4511 the block where @code{b} is declared.
4513 @cindex variable name conflict
4514 There is an exception: you can refer to a variable or function whose
4515 scope is a single source file even if the current execution point is not
4516 in this file. But it is possible to have more than one such variable or
4517 function with the same name (in different source files). If that
4518 happens, referring to that name has unpredictable effects. If you wish,
4519 you can specify a static variable in a particular function or file,
4520 using the colon-colon notation:
4524 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4528 @var{file}::@var{variable}
4529 @var{function}::@var{variable}
4533 Here @var{file} or @var{function} is the name of the context for the
4534 static @var{variable}. In the case of file names, you can use quotes to
4535 make sure @value{GDBN} parses the file name as a single word---for example,
4536 to print a global value of @code{x} defined in @file{f2.c}:
4539 (@value{GDBP}) p 'f2.c'::x
4542 @cindex C++ scope resolution
4543 This use of @samp{::} is very rarely in conflict with the very similar
4544 use of the same notation in C++. @value{GDBN} also supports use of the C++
4545 scope resolution operator in @value{GDBN} expressions.
4546 @c FIXME: Um, so what happens in one of those rare cases where it's in
4549 @cindex wrong values
4550 @cindex variable values, wrong
4552 @emph{Warning:} Occasionally, a local variable may appear to have the
4553 wrong value at certain points in a function---just after entry to a new
4554 scope, and just before exit.
4556 You may see this problem when you are stepping by machine instructions.
4557 This is because, on most machines, it takes more than one instruction to
4558 set up a stack frame (including local variable definitions); if you are
4559 stepping by machine instructions, variables may appear to have the wrong
4560 values until the stack frame is completely built. On exit, it usually
4561 also takes more than one machine instruction to destroy a stack frame;
4562 after you begin stepping through that group of instructions, local
4563 variable definitions may be gone.
4565 This may also happen when the compiler does significant optimizations.
4566 To be sure of always seeing accurate values, turn off all optimization
4569 @node Arrays, Output Formats, Variables, Data
4570 @section Artificial arrays
4572 @cindex artificial array
4574 It is often useful to print out several successive objects of the
4575 same type in memory; a section of an array, or an array of
4576 dynamically determined size for which only a pointer exists in the
4579 You can do this by referring to a contiguous span of memory as an
4580 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4581 operand of @samp{@@} should be the first element of the desired array
4582 and be an individual object. The right operand should be the desired length
4583 of the array. The result is an array value whose elements are all of
4584 the type of the left argument. The first element is actually the left
4585 argument; the second element comes from bytes of memory immediately
4586 following those that hold the first element, and so on. Here is an
4587 example. If a program says
4590 int *array = (int *) malloc (len * sizeof (int));
4594 you can print the contents of @code{array} with
4600 The left operand of @samp{@@} must reside in memory. Array values made
4601 with @samp{@@} in this way behave just like other arrays in terms of
4602 subscripting, and are coerced to pointers when used in expressions.
4603 Artificial arrays most often appear in expressions via the value history
4604 (@pxref{Value History, ,Value history}), after printing one out.
4606 Another way to create an artificial array is to use a cast.
4607 This re-interprets a value as if it were an array.
4608 The value need not be in memory:
4610 (@value{GDBP}) p/x (short[2])0x12345678
4611 $1 = @{0x1234, 0x5678@}
4614 As a convenience, if you leave the array length out (as in
4615 @samp{(@var{type})[])@var{value}}) gdb calculates the size to fill
4616 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4618 (@value{GDBP}) p/x (short[])0x12345678
4619 $2 = @{0x1234, 0x5678@}
4622 Sometimes the artificial array mechanism is not quite enough; in
4623 moderately complex data structures, the elements of interest may not
4624 actually be adjacent---for example, if you are interested in the values
4625 of pointers in an array. One useful work-around in this situation is
4626 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4627 variables}) as a counter in an expression that prints the first
4628 interesting value, and then repeat that expression via @key{RET}. For
4629 instance, suppose you have an array @code{dtab} of pointers to
4630 structures, and you are interested in the values of a field @code{fv}
4631 in each structure. Here is an example of what you might type:
4641 @node Output Formats, Memory, Arrays, Data
4642 @section Output formats
4644 @cindex formatted output
4645 @cindex output formats
4646 By default, @value{GDBN} prints a value according to its data type. Sometimes
4647 this is not what you want. For example, you might want to print a number
4648 in hex, or a pointer in decimal. Or you might want to view data in memory
4649 at a certain address as a character string or as an instruction. To do
4650 these things, specify an @dfn{output format} when you print a value.
4652 The simplest use of output formats is to say how to print a value
4653 already computed. This is done by starting the arguments of the
4654 @code{print} command with a slash and a format letter. The format
4655 letters supported are:
4659 Regard the bits of the value as an integer, and print the integer in
4663 Print as integer in signed decimal.
4666 Print as integer in unsigned decimal.
4669 Print as integer in octal.
4672 Print as integer in binary. The letter @samp{t} stands for ``two''.
4673 @footnote{@samp{b} cannot be used because these format letters are also
4674 used with the @code{x} command, where @samp{b} stands for ``byte'';
4675 @pxref{Memory,,Examining memory}.}
4678 @cindex unknown address, locating
4679 Print as an address, both absolute in hexadecimal and as an offset from
4680 the nearest preceding symbol. You can use this format used to discover
4681 where (in what function) an unknown address is located:
4684 (@value{GDBP}) p/a 0x54320
4685 $3 = 0x54320 <_initialize_vx+396>
4689 Regard as an integer and print it as a character constant.
4692 Regard the bits of the value as a floating point number and print
4693 using typical floating point syntax.
4696 For example, to print the program counter in hex (@pxref{Registers}), type
4703 Note that no space is required before the slash; this is because command
4704 names in @value{GDBN} cannot contain a slash.
4706 To reprint the last value in the value history with a different format,
4707 you can use the @code{print} command with just a format and no
4708 expression. For example, @samp{p/x} reprints the last value in hex.
4710 @node Memory, Auto Display, Output Formats, Data
4711 @section Examining memory
4713 You can use the command @code{x} (for ``examine'') to examine memory in
4714 any of several formats, independently of your program's data types.
4716 @cindex examining memory
4719 @item x/@var{nfu} @var{addr}
4722 Use the @code{x} command to examine memory.
4725 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4726 much memory to display and how to format it; @var{addr} is an
4727 expression giving the address where you want to start displaying memory.
4728 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4729 Several commands set convenient defaults for @var{addr}.
4732 @item @var{n}, the repeat count
4733 The repeat count is a decimal integer; the default is 1. It specifies
4734 how much memory (counting by units @var{u}) to display.
4735 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4738 @item @var{f}, the display format
4739 The display format is one of the formats used by @code{print},
4740 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4741 The default is @samp{x} (hexadecimal) initially.
4742 The default changes each time you use either @code{x} or @code{print}.
4744 @item @var{u}, the unit size
4745 The unit size is any of
4751 Halfwords (two bytes).
4753 Words (four bytes). This is the initial default.
4755 Giant words (eight bytes).
4758 Each time you specify a unit size with @code{x}, that size becomes the
4759 default unit the next time you use @code{x}. (For the @samp{s} and
4760 @samp{i} formats, the unit size is ignored and is normally not written.)
4762 @item @var{addr}, starting display address
4763 @var{addr} is the address where you want @value{GDBN} to begin displaying
4764 memory. The expression need not have a pointer value (though it may);
4765 it is always interpreted as an integer address of a byte of memory.
4766 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4767 @var{addr} is usually just after the last address examined---but several
4768 other commands also set the default address: @code{info breakpoints} (to
4769 the address of the last breakpoint listed), @code{info line} (to the
4770 starting address of a line), and @code{print} (if you use it to display
4771 a value from memory).
4774 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4775 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4776 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4777 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4778 @pxref{Registers}) in hexadecimal (@samp{x}).
4780 Since the letters indicating unit sizes are all distinct from the
4781 letters specifying output formats, you do not have to remember whether
4782 unit size or format comes first; either order works. The output
4783 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4784 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4786 Even though the unit size @var{u} is ignored for the formats @samp{s}
4787 and @samp{i}, you might still want to use a count @var{n}; for example,
4788 @samp{3i} specifies that you want to see three machine instructions,
4789 including any operands. The command @code{disassemble} gives an
4790 alternative way of inspecting machine instructions; @pxref{Machine
4791 Code,,Source and machine code}.
4793 All the defaults for the arguments to @code{x} are designed to make it
4794 easy to continue scanning memory with minimal specifications each time
4795 you use @code{x}. For example, after you have inspected three machine
4796 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4797 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4798 the repeat count @var{n} is used again; the other arguments default as
4799 for successive uses of @code{x}.
4801 @cindex @code{$_}, @code{$__}, and value history
4802 The addresses and contents printed by the @code{x} command are not saved
4803 in the value history because there is often too much of them and they
4804 would get in the way. Instead, @value{GDBN} makes these values available for
4805 subsequent use in expressions as values of the convenience variables
4806 @code{$_} and @code{$__}. After an @code{x} command, the last address
4807 examined is available for use in expressions in the convenience variable
4808 @code{$_}. The contents of that address, as examined, are available in
4809 the convenience variable @code{$__}.
4811 If the @code{x} command has a repeat count, the address and contents saved
4812 are from the last memory unit printed; this is not the same as the last
4813 address printed if several units were printed on the last line of output.
4815 @node Auto Display, Print Settings, Memory, Data
4816 @section Automatic display
4817 @cindex automatic display
4818 @cindex display of expressions
4820 If you find that you want to print the value of an expression frequently
4821 (to see how it changes), you might want to add it to the @dfn{automatic
4822 display list} so that @value{GDBN} prints its value each time your program stops.
4823 Each expression added to the list is given a number to identify it;
4824 to remove an expression from the list, you specify that number.
4825 The automatic display looks like this:
4829 3: bar[5] = (struct hack *) 0x3804
4833 This display shows item numbers, expressions and their current values. As with
4834 displays you request manually using @code{x} or @code{print}, you can
4835 specify the output format you prefer; in fact, @code{display} decides
4836 whether to use @code{print} or @code{x} depending on how elaborate your
4837 format specification is---it uses @code{x} if you specify a unit size,
4838 or one of the two formats (@samp{i} and @samp{s}) that are only
4839 supported by @code{x}; otherwise it uses @code{print}.
4843 @item display @var{exp}
4844 Add the expression @var{exp} to the list of expressions to display
4845 each time your program stops. @xref{Expressions, ,Expressions}.
4847 @code{display} does not repeat if you press @key{RET} again after using it.
4849 @item display/@var{fmt} @var{exp}
4850 For @var{fmt} specifying only a display format and not a size or
4851 count, add the expression @var{exp} to the auto-display list but
4852 arrange to display it each time in the specified format @var{fmt}.
4853 @xref{Output Formats,,Output formats}.
4855 @item display/@var{fmt} @var{addr}
4856 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4857 number of units, add the expression @var{addr} as a memory address to
4858 be examined each time your program stops. Examining means in effect
4859 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4862 For example, @samp{display/i $pc} can be helpful, to see the machine
4863 instruction about to be executed each time execution stops (@samp{$pc}
4864 is a common name for the program counter; @pxref{Registers}).
4867 @kindex delete display
4869 @item undisplay @var{dnums}@dots{}
4870 @itemx delete display @var{dnums}@dots{}
4871 Remove item numbers @var{dnums} from the list of expressions to display.
4873 @code{undisplay} does not repeat if you press @key{RET} after using it.
4874 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4876 @kindex disable display
4877 @item disable display @var{dnums}@dots{}
4878 Disable the display of item numbers @var{dnums}. A disabled display
4879 item is not printed automatically, but is not forgotten. It may be
4880 enabled again later.
4882 @kindex enable display
4883 @item enable display @var{dnums}@dots{}
4884 Enable display of item numbers @var{dnums}. It becomes effective once
4885 again in auto display of its expression, until you specify otherwise.
4888 Display the current values of the expressions on the list, just as is
4889 done when your program stops.
4891 @kindex info display
4893 Print the list of expressions previously set up to display
4894 automatically, each one with its item number, but without showing the
4895 values. This includes disabled expressions, which are marked as such.
4896 It also includes expressions which would not be displayed right now
4897 because they refer to automatic variables not currently available.
4900 If a display expression refers to local variables, then it does not make
4901 sense outside the lexical context for which it was set up. Such an
4902 expression is disabled when execution enters a context where one of its
4903 variables is not defined. For example, if you give the command
4904 @code{display last_char} while inside a function with an argument
4905 @code{last_char}, @value{GDBN} displays this argument while your program
4906 continues to stop inside that function. When it stops elsewhere---where
4907 there is no variable @code{last_char}---the display is disabled
4908 automatically. The next time your program stops where @code{last_char}
4909 is meaningful, you can enable the display expression once again.
4911 @node Print Settings, Value History, Auto Display, Data
4912 @section Print settings
4914 @cindex format options
4915 @cindex print settings
4916 @value{GDBN} provides the following ways to control how arrays, structures,
4917 and symbols are printed.
4920 These settings are useful for debugging programs in any language:
4923 @kindex set print address
4924 @item set print address
4925 @itemx set print address on
4926 @value{GDBN} prints memory addresses showing the location of stack
4927 traces, structure values, pointer values, breakpoints, and so forth,
4928 even when it also displays the contents of those addresses. The default
4929 is @code{on}. For example, this is what a stack frame display looks like with
4930 @code{set print address on}:
4935 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4937 530 if (lquote != def_lquote)
4941 @item set print address off
4942 Do not print addresses when displaying their contents. For example,
4943 this is the same stack frame displayed with @code{set print address off}:
4947 (@value{GDBP}) set print addr off
4949 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4950 530 if (lquote != def_lquote)
4954 You can use @samp{set print address off} to eliminate all machine
4955 dependent displays from the @value{GDBN} interface. For example, with
4956 @code{print address off}, you should get the same text for backtraces on
4957 all machines---whether or not they involve pointer arguments.
4959 @kindex show print address
4960 @item show print address
4961 Show whether or not addresses are to be printed.
4964 When @value{GDBN} prints a symbolic address, it normally prints the
4965 closest earlier symbol plus an offset. If that symbol does not uniquely
4966 identify the address (for example, it is a name whose scope is a single
4967 source file), you may need to clarify. One way to do this is with
4968 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4969 you can set @value{GDBN} to print the source file and line number when
4970 it prints a symbolic address:
4973 @kindex set print symbol-filename
4974 @item set print symbol-filename on
4975 Tell @value{GDBN} to print the source file name and line number of a
4976 symbol in the symbolic form of an address.
4978 @item set print symbol-filename off
4979 Do not print source file name and line number of a symbol. This is the
4982 @kindex show print symbol-filename
4983 @item show print symbol-filename
4984 Show whether or not @value{GDBN} will print the source file name and
4985 line number of a symbol in the symbolic form of an address.
4988 Another situation where it is helpful to show symbol filenames and line
4989 numbers is when disassembling code; @value{GDBN} shows you the line
4990 number and source file that corresponds to each instruction.
4992 Also, you may wish to see the symbolic form only if the address being
4993 printed is reasonably close to the closest earlier symbol:
4996 @kindex set print max-symbolic-offset
4997 @item set print max-symbolic-offset @var{max-offset}
4998 Tell @value{GDBN} to only display the symbolic form of an address if the
4999 offset between the closest earlier symbol and the address is less than
5000 @var{max-offset}. The default is 0, which tells @value{GDBN}
5001 to always print the symbolic form of an address if any symbol precedes it.
5003 @kindex show print max-symbolic-offset
5004 @item show print max-symbolic-offset
5005 Ask how large the maximum offset is that @value{GDBN} prints in a
5009 @cindex wild pointer, interpreting
5010 @cindex pointer, finding referent
5011 If you have a pointer and you are not sure where it points, try
5012 @samp{set print symbol-filename on}. Then you can determine the name
5013 and source file location of the variable where it points, using
5014 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
5015 For example, here @value{GDBN} shows that a variable @code{ptt} points
5016 at another variable @code{t}, defined in @file{hi2.c}:
5019 (@value{GDBP}) set print symbol-filename on
5020 (@value{GDBP}) p/a ptt
5021 $4 = 0xe008 <t in hi2.c>
5025 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
5026 does not show the symbol name and filename of the referent, even with
5027 the appropriate @code{set print} options turned on.
5030 Other settings control how different kinds of objects are printed:
5033 @kindex set print array
5034 @item set print array
5035 @itemx set print array on
5036 Pretty print arrays. This format is more convenient to read,
5037 but uses more space. The default is off.
5039 @item set print array off
5040 Return to compressed format for arrays.
5042 @kindex show print array
5043 @item show print array
5044 Show whether compressed or pretty format is selected for displaying
5047 @kindex set print elements
5048 @item set print elements @var{number-of-elements}
5049 Set a limit on how many elements of an array @value{GDBN} will print.
5050 If @value{GDBN} is printing a large array, it stops printing after it has
5051 printed the number of elements set by the @code{set print elements} command.
5052 This limit also applies to the display of strings.
5053 Setting @var{number-of-elements} to zero means that the printing is unlimited.
5055 @kindex show print elements
5056 @item show print elements
5057 Display the number of elements of a large array that @value{GDBN} will print.
5058 If the number is 0, then the printing is unlimited.
5060 @kindex set print null-stop
5061 @item set print null-stop
5062 Cause @value{GDBN} to stop printing the characters of an array when the first
5063 @sc{NULL} is encountered. This is useful when large arrays actually
5064 contain only short strings.
5066 @kindex set print pretty
5067 @item set print pretty on
5068 Cause @value{GDBN} to print structures in an indented format with one member
5069 per line, like this:
5084 @item set print pretty off
5085 Cause @value{GDBN} to print structures in a compact format, like this:
5089 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
5090 meat = 0x54 "Pork"@}
5095 This is the default format.
5097 @kindex show print pretty
5098 @item show print pretty
5099 Show which format @value{GDBN} is using to print structures.
5101 @kindex set print sevenbit-strings
5102 @item set print sevenbit-strings on
5103 Print using only seven-bit characters; if this option is set,
5104 @value{GDBN} displays any eight-bit characters (in strings or
5105 character values) using the notation @code{\}@var{nnn}. This setting is
5106 best if you are working in English (@sc{ascii}) and you use the
5107 high-order bit of characters as a marker or ``meta'' bit.
5109 @item set print sevenbit-strings off
5110 Print full eight-bit characters. This allows the use of more
5111 international character sets, and is the default.
5113 @kindex show print sevenbit-strings
5114 @item show print sevenbit-strings
5115 Show whether or not @value{GDBN} is printing only seven-bit characters.
5117 @kindex set print union
5118 @item set print union on
5119 Tell @value{GDBN} to print unions which are contained in structures. This
5120 is the default setting.
5122 @item set print union off
5123 Tell @value{GDBN} not to print unions which are contained in structures.
5125 @kindex show print union
5126 @item show print union
5127 Ask @value{GDBN} whether or not it will print unions which are contained in
5130 For example, given the declarations
5133 typedef enum @{Tree, Bug@} Species;
5134 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
5135 typedef enum @{Caterpillar, Cocoon, Butterfly@}
5146 struct thing foo = @{Tree, @{Acorn@}@};
5150 with @code{set print union on} in effect @samp{p foo} would print
5153 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5157 and with @code{set print union off} in effect it would print
5160 $1 = @{it = Tree, form = @{...@}@}
5166 These settings are of interest when debugging C++ programs:
5170 @kindex set print demangle
5171 @item set print demangle
5172 @itemx set print demangle on
5173 Print C++ names in their source form rather than in the encoded
5174 (``mangled'') form passed to the assembler and linker for type-safe
5175 linkage. The default is @samp{on}.
5177 @kindex show print demangle
5178 @item show print demangle
5179 Show whether C++ names are printed in mangled or demangled form.
5181 @kindex set print asm-demangle
5182 @item set print asm-demangle
5183 @itemx set print asm-demangle on
5184 Print C++ names in their source form rather than their mangled form, even
5185 in assembler code printouts such as instruction disassemblies.
5188 @kindex show print asm-demangle
5189 @item show print asm-demangle
5190 Show whether C++ names in assembly listings are printed in mangled
5193 @kindex set demangle-style
5194 @cindex C++ symbol decoding style
5195 @cindex symbol decoding style, C++
5196 @item set demangle-style @var{style}
5197 Choose among several encoding schemes used by different compilers to
5198 represent C++ names. The choices for @var{style} are currently:
5202 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5205 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5207 This is the default.
5211 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5214 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5217 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5218 @strong{Warning:} this setting alone is not sufficient to allow
5219 debugging @code{cfront}-generated executables. @value{GDBN} would
5220 require further enhancement to permit that.
5223 If you omit @var{style}, you will see a list of possible formats.
5225 @kindex show demangle-style
5226 @item show demangle-style
5227 Display the encoding style currently in use for decoding C++ symbols.
5229 @kindex set print object
5230 @item set print object
5231 @itemx set print object on
5232 When displaying a pointer to an object, identify the @emph{actual}
5233 (derived) type of the object rather than the @emph{declared} type, using
5234 the virtual function table.
5236 @item set print object off
5237 Display only the declared type of objects, without reference to the
5238 virtual function table. This is the default setting.
5240 @kindex show print object
5241 @item show print object
5242 Show whether actual, or declared, object types are displayed.
5244 @kindex set print static-members
5245 @item set print static-members
5246 @itemx set print static-members on
5247 Print static members when displaying a C++ object. The default is on.
5249 @item set print static-members off
5250 Do not print static members when displaying a C++ object.
5252 @kindex show print static-members
5253 @item show print static-members
5254 Show whether C++ static members are printed, or not.
5256 @c These don't work with HP ANSI C++ yet.
5257 @kindex set print vtbl
5258 @item set print vtbl
5259 @itemx set print vtbl on
5260 Pretty print C++ virtual function tables. The default is off.
5262 (The @code{vtbl} commands do not work on programs compiled with the HP
5263 ANSI C++ compiler (@code{aCC}).)
5266 @item set print vtbl off
5267 Do not pretty print C++ virtual function tables.
5269 @kindex show print vtbl
5270 @item show print vtbl
5271 Show whether C++ virtual function tables are pretty printed, or not.
5274 @node Value History, Convenience Vars, Print Settings, Data
5275 @section Value history
5277 @cindex value history
5278 Values printed by the @code{print} command are saved in the @value{GDBN}
5279 @dfn{value history}. This allows you to refer to them in other expressions.
5280 Values are kept until the symbol table is re-read or discarded
5281 (for example with the @code{file} or @code{symbol-file} commands).
5282 When the symbol table changes, the value history is discarded,
5283 since the values may contain pointers back to the types defined in the
5288 @cindex history number
5289 The values printed are given @dfn{history numbers} by which you can
5290 refer to them. These are successive integers starting with one.
5291 @code{print} shows you the history number assigned to a value by
5292 printing @samp{$@var{num} = } before the value; here @var{num} is the
5295 To refer to any previous value, use @samp{$} followed by the value's
5296 history number. The way @code{print} labels its output is designed to
5297 remind you of this. Just @code{$} refers to the most recent value in
5298 the history, and @code{$$} refers to the value before that.
5299 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5300 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5301 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5303 For example, suppose you have just printed a pointer to a structure and
5304 want to see the contents of the structure. It suffices to type
5310 If you have a chain of structures where the component @code{next} points
5311 to the next one, you can print the contents of the next one with this:
5318 You can print successive links in the chain by repeating this
5319 command---which you can do by just typing @key{RET}.
5321 Note that the history records values, not expressions. If the value of
5322 @code{x} is 4 and you type these commands:
5330 then the value recorded in the value history by the @code{print} command
5331 remains 4 even though the value of @code{x} has changed.
5336 Print the last ten values in the value history, with their item numbers.
5337 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5338 values} does not change the history.
5340 @item show values @var{n}
5341 Print ten history values centered on history item number @var{n}.
5344 Print ten history values just after the values last printed. If no more
5345 values are available, @code{show values +} produces no display.
5348 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5349 same effect as @samp{show values +}.
5351 @node Convenience Vars, Registers, Value History, Data
5352 @section Convenience variables
5354 @cindex convenience variables
5355 @value{GDBN} provides @dfn{convenience variables} that you can use within
5356 @value{GDBN} to hold on to a value and refer to it later. These variables
5357 exist entirely within @value{GDBN}; they are not part of your program, and
5358 setting a convenience variable has no direct effect on further execution
5359 of your program. That is why you can use them freely.
5361 Convenience variables are prefixed with @samp{$}. Any name preceded by
5362 @samp{$} can be used for a convenience variable, unless it is one of
5363 the predefined machine-specific register names (@pxref{Registers}).
5364 (Value history references, in contrast, are @emph{numbers} preceded
5365 by @samp{$}. @xref{Value History, ,Value history}.)
5367 You can save a value in a convenience variable with an assignment
5368 expression, just as you would set a variable in your program.
5372 set $foo = *object_ptr
5376 would save in @code{$foo} the value contained in the object pointed to by
5379 Using a convenience variable for the first time creates it, but its
5380 value is @code{void} until you assign a new value. You can alter the
5381 value with another assignment at any time.
5383 Convenience variables have no fixed types. You can assign a convenience
5384 variable any type of value, including structures and arrays, even if
5385 that variable already has a value of a different type. The convenience
5386 variable, when used as an expression, has the type of its current value.
5389 @kindex show convenience
5390 @item show convenience
5391 Print a list of convenience variables used so far, and their values.
5392 Abbreviated @code{show con}.
5395 One of the ways to use a convenience variable is as a counter to be
5396 incremented or a pointer to be advanced. For example, to print
5397 a field from successive elements of an array of structures:
5401 print bar[$i++]->contents
5404 @noindent Repeat that command by typing @key{RET}.
5406 Some convenience variables are created automatically by @value{GDBN} and given
5407 values likely to be useful.
5412 The variable @code{$_} is automatically set by the @code{x} command to
5413 the last address examined (@pxref{Memory, ,Examining memory}). Other
5414 commands which provide a default address for @code{x} to examine also
5415 set @code{$_} to that address; these commands include @code{info line}
5416 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5417 except when set by the @code{x} command, in which case it is a pointer
5418 to the type of @code{$__}.
5422 The variable @code{$__} is automatically set by the @code{x} command
5423 to the value found in the last address examined. Its type is chosen
5424 to match the format in which the data was printed.
5428 The variable @code{$_exitcode} is automatically set to the exit code when
5429 the program being debugged terminates.
5433 If you refer to a function or variable name that begins with a dollar
5434 sign, @value{GDBN} searches for a user or system name first, before it
5435 searches for a convenience variable.
5438 @node Registers, Floating Point Hardware, Convenience Vars, Data
5442 You can refer to machine register contents, in expressions, as variables
5443 with names starting with @samp{$}. The names of registers are different
5444 for each machine; use @code{info registers} to see the names used on
5448 @kindex info registers
5449 @item info registers
5450 Print the names and values of all registers except floating-point
5451 registers (in the selected stack frame).
5453 @kindex info all-registers
5454 @cindex floating point registers
5455 @item info all-registers
5456 Print the names and values of all registers, including floating-point
5459 @item info registers @var{regname} @dots{}
5460 Print the @dfn{relativized} value of each specified register @var{regname}.
5461 As discussed in detail below, register values are normally relative to
5462 the selected stack frame. @var{regname} may be any register name valid on
5463 the machine you are using, with or without the initial @samp{$}.
5466 @value{GDBN} has four ``standard'' register names that are available (in
5467 expressions) on most machines---whenever they do not conflict with an
5468 architecture's canonical mnemonics for registers. The register names
5469 @code{$pc} and @code{$sp} are used for the program counter register and
5470 the stack pointer. @code{$fp} is used for a register that contains a
5471 pointer to the current stack frame, and @code{$ps} is used for a
5472 register that contains the processor status. For example,
5473 you could print the program counter in hex with
5480 or print the instruction to be executed next with
5487 or add four to the stack pointer@footnote{This is a way of removing
5488 one word from the stack, on machines where stacks grow downward in
5489 memory (most machines, nowadays). This assumes that the innermost
5490 stack frame is selected; setting @code{$sp} is not allowed when other
5491 stack frames are selected. To pop entire frames off the stack,
5492 regardless of machine architecture, use @code{return};
5493 @pxref{Returning, ,Returning from a function}.} with
5499 Whenever possible, these four standard register names are available on
5500 your machine even though the machine has different canonical mnemonics,
5501 so long as there is no conflict. The @code{info registers} command
5502 shows the canonical names. For example, on the SPARC, @code{info
5503 registers} displays the processor status register as @code{$psr} but you
5504 can also refer to it as @code{$ps}.
5506 @value{GDBN} always considers the contents of an ordinary register as an
5507 integer when the register is examined in this way. Some machines have
5508 special registers which can hold nothing but floating point; these
5509 registers are considered to have floating point values. There is no way
5510 to refer to the contents of an ordinary register as floating point value
5511 (although you can @emph{print} it as a floating point value with
5512 @samp{print/f $@var{regname}}).
5514 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5515 means that the data format in which the register contents are saved by
5516 the operating system is not the same one that your program normally
5517 sees. For example, the registers of the 68881 floating point
5518 coprocessor are always saved in ``extended'' (raw) format, but all C
5519 programs expect to work with ``double'' (virtual) format. In such
5520 cases, @value{GDBN} normally works with the virtual format only (the format
5521 that makes sense for your program), but the @code{info registers} command
5522 prints the data in both formats.
5524 Normally, register values are relative to the selected stack frame
5525 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5526 value that the register would contain if all stack frames farther in
5527 were exited and their saved registers restored. In order to see the
5528 true contents of hardware registers, you must select the innermost
5529 frame (with @samp{frame 0}).
5531 However, @value{GDBN} must deduce where registers are saved, from the machine
5532 code generated by your compiler. If some registers are not saved, or if
5533 @value{GDBN} is unable to locate the saved registers, the selected stack
5534 frame makes no difference.
5537 @kindex set rstack_high_address
5538 @cindex AMD 29K register stack
5539 @cindex register stack, AMD29K
5540 @item set rstack_high_address @var{address}
5541 On AMD 29000 family processors, registers are saved in a separate
5542 ``register stack''. There is no way for @value{GDBN} to determine the extent
5543 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
5544 enough''. This may result in @value{GDBN} referencing memory locations that
5545 do not exist. If necessary, you can get around this problem by
5546 specifying the ending address of the register stack with the @code{set
5547 rstack_high_address} command. The argument should be an address, which
5548 you probably want to precede with @samp{0x} to specify in
5551 @kindex show rstack_high_address
5552 @item show rstack_high_address
5553 Display the current limit of the register stack, on AMD 29000 family
5557 @node Floating Point Hardware, , Registers, Data
5558 @section Floating point hardware
5559 @cindex floating point
5561 Depending on the configuration, @value{GDBN} may be able to give
5562 you more information about the status of the floating point hardware.
5567 Display hardware-dependent information about the floating
5568 point unit. The exact contents and layout vary depending on the
5569 floating point chip. Currently, @samp{info float} is supported on
5570 the ARM and x86 machines.
5573 @node Languages, Symbols, Data, Top
5574 @chapter Using @value{GDBN} with Different Languages
5577 Although programming languages generally have common aspects, they are
5578 rarely expressed in the same manner. For instance, in ANSI C,
5579 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5580 Modula-2, it is accomplished by @code{p^}. Values can also be
5581 represented (and displayed) differently. Hex numbers in C appear as
5582 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5584 @cindex working language
5585 Language-specific information is built into @value{GDBN} for some languages,
5586 allowing you to express operations like the above in your program's
5587 native language, and allowing @value{GDBN} to output values in a manner
5588 consistent with the syntax of your program's native language. The
5589 language you use to build expressions is called the @dfn{working
5593 * Setting:: Switching between source languages
5594 * Show:: Displaying the language
5595 * Checks:: Type and range checks
5596 * Support:: Supported languages
5599 @node Setting, Show, Languages, Languages
5600 @section Switching between source languages
5602 There are two ways to control the working language---either have @value{GDBN}
5603 set it automatically, or select it manually yourself. You can use the
5604 @code{set language} command for either purpose. On startup, @value{GDBN}
5605 defaults to setting the language automatically. The working language is
5606 used to determine how expressions you type are interpreted, how values
5609 In addition to the working language, every source file that
5610 @value{GDBN} knows about has its own working language. For some object
5611 file formats, the compiler might indicate which language a particular
5612 source file is in. However, most of the time @value{GDBN} infers the
5613 language from the name of the file. The language of a source file
5614 controls whether C++ names are demangled---this way @code{backtrace} can
5615 show each frame appropriately for its own language. There is no way to
5616 set the language of a source file from within @value{GDBN}.
5618 This is most commonly a problem when you use a program, such
5619 as @code{cfront} or @code{f2c}, that generates C but is written in
5620 another language. In that case, make the
5621 program use @code{#line} directives in its C output; that way
5622 @value{GDBN} will know the correct language of the source code of the original
5623 program, and will display that source code, not the generated C code.
5626 * Filenames:: Filename extensions and languages.
5627 * Manually:: Setting the working language manually
5628 * Automatically:: Having @value{GDBN} infer the source language
5631 @node Filenames, Manually, Setting, Setting
5632 @subsection List of filename extensions and languages
5634 If a source file name ends in one of the following extensions, then
5635 @value{GDBN} infers that its language is the one indicated.
5662 Modula-2 source file
5666 Assembler source file. This actually behaves almost like C, but
5667 @value{GDBN} does not skip over function prologues when stepping.
5670 In addition, you may set the language associated with a filename
5671 extension. @xref{Show, , Displaying the language}.
5673 @node Manually, Automatically, Filenames, Setting
5674 @subsection Setting the working language
5676 If you allow @value{GDBN} to set the language automatically,
5677 expressions are interpreted the same way in your debugging session and
5680 @kindex set language
5681 If you wish, you may set the language manually. To do this, issue the
5682 command @samp{set language @var{lang}}, where @var{lang} is the name of
5684 @code{c} or @code{modula-2}.
5685 For a list of the supported languages, type @samp{set language}.
5687 Setting the language manually prevents @value{GDBN} from updating the working
5688 language automatically. This can lead to confusion if you try
5689 to debug a program when the working language is not the same as the
5690 source language, when an expression is acceptable to both
5691 languages---but means different things. For instance, if the current
5692 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5700 might not have the effect you intended. In C, this means to add
5701 @code{b} and @code{c} and place the result in @code{a}. The result
5702 printed would be the value of @code{a}. In Modula-2, this means to compare
5703 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5705 @node Automatically, , Manually, Setting
5706 @subsection Having @value{GDBN} infer the source language
5708 To have @value{GDBN} set the working language automatically, use
5709 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5710 then infers the working language. That is, when your program stops in a
5711 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5712 working language to the language recorded for the function in that
5713 frame. If the language for a frame is unknown (that is, if the function
5714 or block corresponding to the frame was defined in a source file that
5715 does not have a recognized extension), the current working language is
5716 not changed, and @value{GDBN} issues a warning.
5718 This may not seem necessary for most programs, which are written
5719 entirely in one source language. However, program modules and libraries
5720 written in one source language can be used by a main program written in
5721 a different source language. Using @samp{set language auto} in this
5722 case frees you from having to set the working language manually.
5724 @node Show, Checks, Setting, Languages
5725 @section Displaying the language
5727 The following commands help you find out which language is the
5728 working language, and also what language source files were written in.
5730 @kindex show language
5735 Display the current working language. This is the
5736 language you can use with commands such as @code{print} to
5737 build and compute expressions that may involve variables in your program.
5740 Display the source language for this frame. This language becomes the
5741 working language if you use an identifier from this frame.
5742 @xref{Frame Info, ,Information about a frame}, to identify the other
5743 information listed here.
5746 Display the source language of this source file.
5747 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5748 information listed here.
5751 In unusual circumstances, you may have source files with extensions
5752 not in the standard list. You can then set the extension associated
5753 with a language explicitly:
5755 @kindex set extension-language
5756 @kindex info extensions
5758 @item set extension-language @var{.ext} @var{language}
5759 Set source files with extension @var{.ext} to be assumed to be in
5760 the source language @var{language}.
5762 @item info extensions
5763 List all the filename extensions and the associated languages.
5766 @node Checks, Support, Show, Languages
5767 @section Type and range checking
5770 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5771 checking are included, but they do not yet have any effect. This
5772 section documents the intended facilities.
5774 @c FIXME remove warning when type/range code added
5776 Some languages are designed to guard you against making seemingly common
5777 errors through a series of compile- and run-time checks. These include
5778 checking the type of arguments to functions and operators, and making
5779 sure mathematical overflows are caught at run time. Checks such as
5780 these help to ensure a program's correctness once it has been compiled
5781 by eliminating type mismatches, and providing active checks for range
5782 errors when your program is running.
5784 @value{GDBN} can check for conditions like the above if you wish.
5785 Although @value{GDBN} does not check the statements in your program, it
5786 can check expressions entered directly into @value{GDBN} for evaluation via
5787 the @code{print} command, for example. As with the working language,
5788 @value{GDBN} can also decide whether or not to check automatically based on
5789 your program's source language. @xref{Support, ,Supported languages},
5790 for the default settings of supported languages.
5793 * Type Checking:: An overview of type checking
5794 * Range Checking:: An overview of range checking
5797 @cindex type checking
5798 @cindex checks, type
5799 @node Type Checking, Range Checking, Checks, Checks
5800 @subsection An overview of type checking
5802 Some languages, such as Modula-2, are strongly typed, meaning that the
5803 arguments to operators and functions have to be of the correct type,
5804 otherwise an error occurs. These checks prevent type mismatch
5805 errors from ever causing any run-time problems. For example,
5813 The second example fails because the @code{CARDINAL} 1 is not
5814 type-compatible with the @code{REAL} 2.3.
5816 For the expressions you use in @value{GDBN} commands, you can tell the
5817 @value{GDBN} type checker to skip checking;
5818 to treat any mismatches as errors and abandon the expression;
5819 or to only issue warnings when type mismatches occur,
5820 but evaluate the expression anyway. When you choose the last of
5821 these, @value{GDBN} evaluates expressions like the second example above, but
5822 also issues a warning.
5824 Even if you turn type checking off, there may be other reasons
5825 related to type that prevent @value{GDBN} from evaluating an expression.
5826 For instance, @value{GDBN} does not know how to add an @code{int} and
5827 a @code{struct foo}. These particular type errors have nothing to do
5828 with the language in use, and usually arise from expressions, such as
5829 the one described above, which make little sense to evaluate anyway.
5831 Each language defines to what degree it is strict about type. For
5832 instance, both Modula-2 and C require the arguments to arithmetical
5833 operators to be numbers. In C, enumerated types and pointers can be
5834 represented as numbers, so that they are valid arguments to mathematical
5835 operators. @xref{Support, ,Supported languages}, for further
5836 details on specific languages.
5838 @value{GDBN} provides some additional commands for controlling the type checker:
5841 @kindex set check type
5842 @kindex show check type
5844 @item set check type auto
5845 Set type checking on or off based on the current working language.
5846 @xref{Support, ,Supported languages}, for the default settings for
5849 @item set check type on
5850 @itemx set check type off
5851 Set type checking on or off, overriding the default setting for the
5852 current working language. Issue a warning if the setting does not
5853 match the language default. If any type mismatches occur in
5854 evaluating an expression while typechecking is on, @value{GDBN} prints a
5855 message and aborts evaluation of the expression.
5857 @item set check type warn
5858 Cause the type checker to issue warnings, but to always attempt to
5859 evaluate the expression. Evaluating the expression may still
5860 be impossible for other reasons. For example, @value{GDBN} cannot add
5861 numbers and structures.
5864 Show the current setting of the type checker, and whether or not @value{GDBN}
5865 is setting it automatically.
5868 @cindex range checking
5869 @cindex checks, range
5870 @node Range Checking, , Type Checking, Checks
5871 @subsection An overview of range checking
5873 In some languages (such as Modula-2), it is an error to exceed the
5874 bounds of a type; this is enforced with run-time checks. Such range
5875 checking is meant to ensure program correctness by making sure
5876 computations do not overflow, or indices on an array element access do
5877 not exceed the bounds of the array.
5879 For expressions you use in @value{GDBN} commands, you can tell
5880 @value{GDBN} to treat range errors in one of three ways: ignore them,
5881 always treat them as errors and abandon the expression, or issue
5882 warnings but evaluate the expression anyway.
5884 A range error can result from numerical overflow, from exceeding an
5885 array index bound, or when you type a constant that is not a member
5886 of any type. Some languages, however, do not treat overflows as an
5887 error. In many implementations of C, mathematical overflow causes the
5888 result to ``wrap around'' to lower values---for example, if @var{m} is
5889 the largest integer value, and @var{s} is the smallest, then
5892 @var{m} + 1 @result{} @var{s}
5895 This, too, is specific to individual languages, and in some cases
5896 specific to individual compilers or machines. @xref{Support, ,
5897 Supported languages}, for further details on specific languages.
5899 @value{GDBN} provides some additional commands for controlling the range checker:
5902 @kindex set check range
5903 @kindex show check range
5905 @item set check range auto
5906 Set range checking on or off based on the current working language.
5907 @xref{Support, ,Supported languages}, for the default settings for
5910 @item set check range on
5911 @itemx set check range off
5912 Set range checking on or off, overriding the default setting for the
5913 current working language. A warning is issued if the setting does not
5914 match the language default. If a range error occurs, then a message
5915 is printed and evaluation of the expression is aborted.
5917 @item set check range warn
5918 Output messages when the @value{GDBN} range checker detects a range error,
5919 but attempt to evaluate the expression anyway. Evaluating the
5920 expression may still be impossible for other reasons, such as accessing
5921 memory that the process does not own (a typical example from many Unix
5925 Show the current setting of the range checker, and whether or not it is
5926 being set automatically by @value{GDBN}.
5929 @node Support, , Checks, Languages
5930 @section Supported languages
5932 @value{GDBN} supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.
5933 @c This is false ...
5934 Some @value{GDBN} features may be used in expressions regardless of the
5935 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5936 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5937 ,Expressions}) can be used with the constructs of any supported
5940 The following sections detail to what degree each source language is
5941 supported by @value{GDBN}. These sections are not meant to be language
5942 tutorials or references, but serve only as a reference guide to what the
5943 @value{GDBN} expression parser accepts, and what input and output
5944 formats should look like for different languages. There are many good
5945 books written on each of these languages; please look to these for a
5946 language reference or tutorial.
5950 * Modula-2:: Modula-2
5954 @node C, Modula-2, , Support
5955 @subsection C and C++
5958 @cindex expressions in C or C++
5960 Since C and C++ are so closely related, many features of @value{GDBN} apply
5961 to both languages. Whenever this is the case, we discuss those languages
5967 @cindex @sc{gnu} C++
5968 The C++ debugging facilities are jointly implemented by the C++
5969 compiler and @value{GDBN}. Therefore, to debug your C++ code
5970 effectively, you must compile your C++ programs with a supported
5971 C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++
5972 compiler (@code{aCC}).
5974 For best results when using @sc{gnu} C++, use the stabs debugging
5975 format. You can select that format explicitly with the @code{g++}
5976 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5977 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
5978 CC, gcc.info, Using @sc{gnu} CC}, for more information.
5983 @cindex @sc{gnu} C++
5984 You can use @value{GDBN} to debug C programs compiled with either the HP
5985 C compiler (@code{cc}) or the GNU C compiler (@code{gcc}), and to debug
5986 programs compiled with either the HP ANSI C++ compiler (@code{aCC}) or
5987 the @sc{gnu} C++ compiler (@code{g++}).
5989 If you compile with the @sc{gnu} C++ compiler, use the stabs debugging
5990 format for best results when debugging. You can select that format
5991 explicitly with the @code{g++} command-line options @samp{-gstabs} or
5992 @samp{-gstabs+}. See @ref{Debugging Options,,Options for Debugging Your
5993 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
5998 * C Operators:: C and C++ operators
5999 * C Constants:: C and C++ constants
6000 * C plus plus expressions:: C++ expressions
6001 * C Defaults:: Default settings for C and C++
6002 * C Checks:: C and C++ type and range checks
6003 * Debugging C:: @value{GDBN} and C
6004 * Debugging C plus plus:: @value{GDBN} features for C++
6007 @node C Operators, C Constants, , C
6008 @subsubsection C and C++ operators
6010 @cindex C and C++ operators
6012 Operators must be defined on values of specific types. For instance,
6013 @code{+} is defined on numbers, but not on structures. Operators are
6014 often defined on groups of types.
6016 For the purposes of C and C++, the following definitions hold:
6021 @emph{Integral types} include @code{int} with any of its storage-class
6022 specifiers; @code{char}; and @code{enum}.
6025 @emph{Integral types} include @code{int} with any of its storage-class
6026 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
6030 @emph{Floating-point types} include @code{float} and @code{double}.
6033 @emph{Pointer types} include all types defined as @code{(@var{type}
6037 @emph{Scalar types} include all of the above.
6041 The following operators are supported. They are listed here
6042 in order of increasing precedence:
6046 The comma or sequencing operator. Expressions in a comma-separated list
6047 are evaluated from left to right, with the result of the entire
6048 expression being the last expression evaluated.
6051 Assignment. The value of an assignment expression is the value
6052 assigned. Defined on scalar types.
6055 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
6056 and translated to @w{@code{@var{a} = @var{a op b}}}.
6057 @w{@code{@var{op}=}} and @code{=} have the same precendence.
6058 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
6059 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
6062 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
6063 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
6067 Logical @sc{or}. Defined on integral types.
6070 Logical @sc{and}. Defined on integral types.
6073 Bitwise @sc{or}. Defined on integral types.
6076 Bitwise exclusive-@sc{or}. Defined on integral types.
6079 Bitwise @sc{and}. Defined on integral types.
6082 Equality and inequality. Defined on scalar types. The value of these
6083 expressions is 0 for false and non-zero for true.
6085 @item <@r{, }>@r{, }<=@r{, }>=
6086 Less than, greater than, less than or equal, greater than or equal.
6087 Defined on scalar types. The value of these expressions is 0 for false
6088 and non-zero for true.
6091 left shift, and right shift. Defined on integral types.
6094 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6097 Addition and subtraction. Defined on integral types, floating-point types and
6100 @item *@r{, }/@r{, }%
6101 Multiplication, division, and modulus. Multiplication and division are
6102 defined on integral and floating-point types. Modulus is defined on
6106 Increment and decrement. When appearing before a variable, the
6107 operation is performed before the variable is used in an expression;
6108 when appearing after it, the variable's value is used before the
6109 operation takes place.
6112 Pointer dereferencing. Defined on pointer types. Same precedence as
6116 Address operator. Defined on variables. Same precedence as @code{++}.
6118 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
6119 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
6120 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
6121 where a C++ reference variable (declared with @samp{&@var{ref}}) is
6125 Negative. Defined on integral and floating-point types. Same
6126 precedence as @code{++}.
6129 Logical negation. Defined on integral types. Same precedence as
6133 Bitwise complement operator. Defined on integral types. Same precedence as
6138 Structure member, and pointer-to-structure member. For convenience,
6139 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
6140 pointer based on the stored type information.
6141 Defined on @code{struct} and @code{union} data.
6145 Dereferences of pointers to members.
6149 Array indexing. @code{@var{a}[@var{i}]} is defined as
6150 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
6153 Function parameter list. Same precedence as @code{->}.
6156 C++ scope resolution operator. Defined on @code{struct}, @code{union},
6157 and @code{class} types.
6160 Doubled colons also represent the @value{GDBN} scope operator
6161 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
6166 If an operator is redefined in the user code, @value{GDBN} usually
6167 attempts to invoke the redefined version instead of using the operator's
6175 @node C Constants, C plus plus expressions, C Operators, C
6176 @subsubsection C and C++ constants
6178 @cindex C and C++ constants
6180 @value{GDBN} allows you to express the constants of C and C++ in the
6185 Integer constants are a sequence of digits. Octal constants are
6186 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
6187 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
6188 @samp{l}, specifying that the constant should be treated as a
6192 Floating point constants are a sequence of digits, followed by a decimal
6193 point, followed by a sequence of digits, and optionally followed by an
6194 exponent. An exponent is of the form:
6195 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
6196 sequence of digits. The @samp{+} is optional for positive exponents.
6199 Enumerated constants consist of enumerated identifiers, or their
6200 integral equivalents.
6203 Character constants are a single character surrounded by single quotes
6204 (@code{'}), or a number---the ordinal value of the corresponding character
6205 (usually its @sc{ASCII} value). Within quotes, the single character may
6206 be represented by a letter or by @dfn{escape sequences}, which are of
6207 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6208 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6209 @samp{@var{x}} is a predefined special character---for example,
6210 @samp{\n} for newline.
6213 String constants are a sequence of character constants surrounded
6214 by double quotes (@code{"}).
6217 Pointer constants are an integral value. You can also write pointers
6218 to constants using the C operator @samp{&}.
6221 Array constants are comma-separated lists surrounded by braces @samp{@{}
6222 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6223 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6224 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6228 * C plus plus expressions::
6235 @node C plus plus expressions, C Defaults, C Constants, C
6236 @subsubsection C++ expressions
6238 @cindex expressions in C++
6239 @value{GDBN} expression handling can interpret most C++ expressions.
6242 @cindex C++ support, not in @sc{coff}
6243 @cindex @sc{coff} versus C++
6244 @cindex C++ and object formats
6245 @cindex object formats and C++
6246 @cindex a.out and C++
6247 @cindex @sc{ecoff} and C++
6248 @cindex @sc{xcoff} and C++
6249 @cindex @sc{elf}/stabs and C++
6250 @cindex @sc{elf}/@sc{dwarf} and C++
6251 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6252 @c periodically whether this has happened...
6254 @emph{Warning:} @value{GDBN} can only debug C++ code if you use the
6255 proper compiler. Typically, C++ debugging depends on the use of
6256 additional debugging information in the symbol table, and thus requires
6257 special support. In particular, if your compiler generates a.out, MIPS
6258 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6259 symbol table, these facilities are all available. (With @sc{gnu} CC,
6260 you can use the @samp{-gstabs} option to request stabs debugging
6261 extensions explicitly.) Where the object code format is standard
6262 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6263 support in @value{GDBN} does @emph{not} work.
6269 @cindex member functions
6271 Member function calls are allowed; you can use expressions like
6274 count = aml->GetOriginal(x, y)
6278 @cindex namespace in C++
6280 While a member function is active (in the selected stack frame), your
6281 expressions have the same namespace available as the member function;
6282 that is, @value{GDBN} allows implicit references to the class instance
6283 pointer @code{this} following the same rules as C++.
6286 @cindex call overloaded functions
6287 @cindex type conversions in C++
6289 You can call overloaded functions; @value{GDBN} resolves the function
6290 call to the right definition, with one restriction---you must use
6291 arguments of the type required by the function that you want to call.
6292 @value{GDBN} does not perform conversions requiring constructors or
6293 user-defined type operators.
6296 @cindex call overloaded functions
6297 @cindex overloaded functions
6298 @cindex type conversions in C++
6300 You can call overloaded functions; @value{GDBN} resolves the function
6301 call to the right definition, with some restrictions. GDB does not
6302 perform overload resolution involving user-defined type conversions,
6303 calls to constructors, or instantiations of templates that do not exist
6304 in the program. It also cannot handle ellipsis argument lists or
6307 It does perform integral conversions and promotions, floating-point
6308 promotions, arithmetic conversions, pointer conversions, conversions of
6309 class objects to base classes, and standard conversions such as those of
6310 functions or arrays to pointers; it requires an exact match on the
6311 number of function arguments.
6313 Overload resolution is always performed, unless you have specified
6314 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6315 ,@value{GDBN} features for C++}.
6317 You must specify@code{set overload-resolution off} in order to use an
6318 explicit function signature to call an overloaded function, as in
6320 p 'foo(char,int)'('x', 13)
6322 The @value{GDBN} command-completion facility can simplify this;
6323 @pxref{Completion, ,Command completion}.
6327 @cindex reference declarations
6329 @value{GDBN} understands variables declared as C++ references; you can use
6330 them in expressions just as you do in C++ source---they are automatically
6333 In the parameter list shown when @value{GDBN} displays a frame, the values of
6334 reference variables are not displayed (unlike other variables); this
6335 avoids clutter, since references are often used for large structures.
6336 The @emph{address} of a reference variable is always shown, unless
6337 you have specified @samp{set print address off}.
6340 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6341 expressions can use it just as expressions in your program do. Since
6342 one scope may be defined in another, you can use @code{::} repeatedly if
6343 necessary, for example in an expression like
6344 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6345 resolving name scope by reference to source files, in both C and C++
6346 debugging (@pxref{Variables, ,Program variables}).
6350 In addition, @value{GDBN} supports calling virtual functions correctly,
6351 printing out virtual bases of objects, calling functions in a base
6352 subobject, casting objects, and invoking user-defined operators.
6355 @node C Defaults, C Checks, C plus plus expressions, C
6356 @subsubsection C and C++ defaults
6358 @cindex C and C++ defaults
6361 If you allow @value{GDBN} to set type and range checking automatically, they
6362 both default to @code{off} whenever the working language changes to
6363 C or C++. This happens regardless of whether you or @value{GDBN}
6364 selects the working language.
6367 If you allow @value{GDBN} to set the language automatically, it
6368 recognizes source files whose names end with @file{.c}, @file{.C}, or
6369 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
6370 these files, it sets the working language to C or C++.
6371 @xref{Automatically, ,Having @value{GDBN} infer the source language},
6372 for further details.
6374 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6375 @c unimplemented. If (b) changes, it might make sense to let this node
6376 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6378 @node C Checks, Debugging C, C Defaults, C Constants
6379 @subsubsection C and C++ type and range checks
6381 @cindex C and C++ checks
6383 By default, when @value{GDBN} parses C or C++ expressions, type checking
6384 is not used. However, if you turn type checking on, @value{GDBN}
6385 considers two variables type equivalent if:
6389 The two variables are structured and have the same structure, union, or
6393 The two variables have the same type name, or types that have been
6394 declared equivalent through @code{typedef}.
6397 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6400 The two @code{struct}, @code{union}, or @code{enum} variables are
6401 declared in the same declaration. (Note: this may not be true for all C
6406 Range checking, if turned on, is done on mathematical operations. Array
6407 indices are not checked, since they are often used to index a pointer
6408 that is not itself an array.
6410 @node Debugging C, Debugging C plus plus, C Checks, C
6411 @subsubsection @value{GDBN} and C
6413 The @code{set print union} and @code{show print union} commands apply to
6414 the @code{union} type. When set to @samp{on}, any @code{union} that is
6415 inside a @code{struct} or @code{class} is also printed. Otherwise, it
6416 appears as @samp{@{...@}}.
6418 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6419 with pointers and a memory allocation function. @xref{Expressions,
6423 * Debugging C plus plus::
6426 @node Debugging C plus plus, , Debugging C, C
6427 @subsubsection @value{GDBN} features for C++
6429 @cindex commands for C++
6431 Some @value{GDBN} commands are particularly useful with C++, and some are
6432 designed specifically for use with C++. Here is a summary:
6435 @cindex break in overloaded functions
6436 @item @r{breakpoint menus}
6437 When you want a breakpoint in a function whose name is overloaded,
6438 @value{GDBN} breakpoint menus help you specify which function definition
6439 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6441 @cindex overloading in C++
6442 @item rbreak @var{regex}
6443 Setting breakpoints using regular expressions is helpful for setting
6444 breakpoints on overloaded functions that are not members of any special
6446 @xref{Set Breaks, ,Setting breakpoints}.
6448 @cindex C++ exception handling
6451 Debug C++ exception handling using these commands. @xref{Set
6452 Catchpoints, , Setting catchpoints}.
6455 @item ptype @var{typename}
6456 Print inheritance relationships as well as other information for type
6458 @xref{Symbols, ,Examining the Symbol Table}.
6460 @cindex C++ symbol display
6461 @item set print demangle
6462 @itemx show print demangle
6463 @itemx set print asm-demangle
6464 @itemx show print asm-demangle
6465 Control whether C++ symbols display in their source form, both when
6466 displaying code as C++ source and when displaying disassemblies.
6467 @xref{Print Settings, ,Print settings}.
6469 @item set print object
6470 @itemx show print object
6471 Choose whether to print derived (actual) or declared types of objects.
6472 @xref{Print Settings, ,Print settings}.
6474 @item set print vtbl
6475 @itemx show print vtbl
6476 Control the format for printing virtual function tables.
6477 @xref{Print Settings, ,Print settings}.
6479 (The @code{vtbl} commands do not work on programs compiled with the HP
6480 ANSI C++ compiler (@code{aCC}).)
6482 @kindex set overload-resolution
6483 @cindex overloaded functions
6484 @item set overload-resolution on
6485 Enable overload resolution for C++ expression evaluation. The default
6486 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6487 and searches for a function whose signature matches the argument types,
6488 using the standard C++ conversion rules (@pxref{C plus plus expressions, ,C++
6489 expressions} for details). If it cannot find a match, it emits a
6492 @item set overload-resolution off
6493 Disable overload resolution for C++ expression evaluation. For
6494 overloaded functions that are not class member functions, @value{GDBN}
6495 chooses the first function of the specified name that it finds in the
6496 symbol table, whether or not its arguments are of the correct type. For
6497 overloaded functions that are class member functions, @value{GDBN}
6498 searches for a function whose signature @emph{exactly} matches the
6502 @item @r{Overloaded symbol names}
6503 You can specify a particular definition of an overloaded symbol, using
6504 the same notation that is used to declare such symbols in C++: type
6505 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6506 also use the @value{GDBN} command-line word completion facilities to list the
6507 available choices, or to finish the type list for you.
6508 @xref{Completion,, Command completion}, for details on how to do this.
6511 @node Modula-2, Chill, C, Support
6512 @subsection Modula-2
6516 The extensions made to @value{GDBN} to support Modula-2 only support
6517 output from the @sc{gnu} Modula-2 compiler (which is currently being
6518 developed). Other Modula-2 compilers are not currently supported, and
6519 attempting to debug executables produced by them is most likely
6520 to give an error as @value{GDBN} reads in the executable's symbol
6523 @cindex expressions in Modula-2
6525 * M2 Operators:: Built-in operators
6526 * Built-In Func/Proc:: Built-in functions and procedures
6527 * M2 Constants:: Modula-2 constants
6528 * M2 Defaults:: Default settings for Modula-2
6529 * Deviations:: Deviations from standard Modula-2
6530 * M2 Checks:: Modula-2 type and range checks
6531 * M2 Scope:: The scope operators @code{::} and @code{.}
6532 * GDB/M2:: @value{GDBN} and Modula-2
6535 @node M2 Operators, Built-In Func/Proc, Modula-2, Modula-2
6536 @subsubsection Operators
6537 @cindex Modula-2 operators
6539 Operators must be defined on values of specific types. For instance,
6540 @code{+} is defined on numbers, but not on structures. Operators are
6541 often defined on groups of types. For the purposes of Modula-2, the
6542 following definitions hold:
6547 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6551 @emph{Character types} consist of @code{CHAR} and its subranges.
6554 @emph{Floating-point types} consist of @code{REAL}.
6557 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6561 @emph{Scalar types} consist of all of the above.
6564 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6567 @emph{Boolean types} consist of @code{BOOLEAN}.
6571 The following operators are supported, and appear in order of
6572 increasing precedence:
6576 Function argument or array index separator.
6579 Assignment. The value of @var{var} @code{:=} @var{value} is
6583 Less than, greater than on integral, floating-point, or enumerated
6587 Less than, greater than, less than or equal to, greater than or equal to
6588 on integral, floating-point and enumerated types, or set inclusion on
6589 set types. Same precedence as @code{<}.
6591 @item =@r{, }<>@r{, }#
6592 Equality and two ways of expressing inequality, valid on scalar types.
6593 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6594 available for inequality, since @code{#} conflicts with the script
6598 Set membership. Defined on set types and the types of their members.
6599 Same precedence as @code{<}.
6602 Boolean disjunction. Defined on boolean types.
6605 Boolean conjuction. Defined on boolean types.
6608 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6611 Addition and subtraction on integral and floating-point types, or union
6612 and difference on set types.
6615 Multiplication on integral and floating-point types, or set intersection
6619 Division on floating-point types, or symmetric set difference on set
6620 types. Same precedence as @code{*}.
6623 Integer division and remainder. Defined on integral types. Same
6624 precedence as @code{*}.
6627 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6630 Pointer dereferencing. Defined on pointer types.
6633 Boolean negation. Defined on boolean types. Same precedence as
6637 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6638 precedence as @code{^}.
6641 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6644 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6648 @value{GDBN} and Modula-2 scope operators.
6652 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6653 treats the use of the operator @code{IN}, or the use of operators
6654 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6655 @code{<=}, and @code{>=} on sets as an error.
6658 @cindex Modula-2 built-ins
6659 @node Built-In Func/Proc, M2 Constants, M2 Operators, Modula-2
6660 @subsubsection Built-in functions and procedures
6662 Modula-2 also makes available several built-in procedures and functions.
6663 In describing these, the following metavariables are used:
6668 represents an @code{ARRAY} variable.
6671 represents a @code{CHAR} constant or variable.
6674 represents a variable or constant of integral type.
6677 represents an identifier that belongs to a set. Generally used in the
6678 same function with the metavariable @var{s}. The type of @var{s} should
6679 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6682 represents a variable or constant of integral or floating-point type.
6685 represents a variable or constant of floating-point type.
6691 represents a variable.
6694 represents a variable or constant of one of many types. See the
6695 explanation of the function for details.
6698 All Modula-2 built-in procedures also return a result, described below.
6702 Returns the absolute value of @var{n}.
6705 If @var{c} is a lower case letter, it returns its upper case
6706 equivalent, otherwise it returns its argument
6709 Returns the character whose ordinal value is @var{i}.
6712 Decrements the value in the variable @var{v}. Returns the new value.
6714 @item DEC(@var{v},@var{i})
6715 Decrements the value in the variable @var{v} by @var{i}. Returns the
6718 @item EXCL(@var{m},@var{s})
6719 Removes the element @var{m} from the set @var{s}. Returns the new
6722 @item FLOAT(@var{i})
6723 Returns the floating point equivalent of the integer @var{i}.
6726 Returns the index of the last member of @var{a}.
6729 Increments the value in the variable @var{v}. Returns the new value.
6731 @item INC(@var{v},@var{i})
6732 Increments the value in the variable @var{v} by @var{i}. Returns the
6735 @item INCL(@var{m},@var{s})
6736 Adds the element @var{m} to the set @var{s} if it is not already
6737 there. Returns the new set.
6740 Returns the maximum value of the type @var{t}.
6743 Returns the minimum value of the type @var{t}.
6746 Returns boolean TRUE if @var{i} is an odd number.
6749 Returns the ordinal value of its argument. For example, the ordinal
6750 value of a character is its ASCII value (on machines supporting the
6751 ASCII character set). @var{x} must be of an ordered type, which include
6752 integral, character and enumerated types.
6755 Returns the size of its argument. @var{x} can be a variable or a type.
6757 @item TRUNC(@var{r})
6758 Returns the integral part of @var{r}.
6760 @item VAL(@var{t},@var{i})
6761 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6765 @emph{Warning:} Sets and their operations are not yet supported, so
6766 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6770 @cindex Modula-2 constants
6771 @node M2 Constants, M2 Defaults, Built-In Func/Proc, Modula-2
6772 @subsubsection Constants
6774 @value{GDBN} allows you to express the constants of Modula-2 in the following
6780 Integer constants are simply a sequence of digits. When used in an
6781 expression, a constant is interpreted to be type-compatible with the
6782 rest of the expression. Hexadecimal integers are specified by a
6783 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6786 Floating point constants appear as a sequence of digits, followed by a
6787 decimal point and another sequence of digits. An optional exponent can
6788 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6789 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6790 digits of the floating point constant must be valid decimal (base 10)
6794 Character constants consist of a single character enclosed by a pair of
6795 like quotes, either single (@code{'}) or double (@code{"}). They may
6796 also be expressed by their ordinal value (their ASCII value, usually)
6797 followed by a @samp{C}.
6800 String constants consist of a sequence of characters enclosed by a
6801 pair of like quotes, either single (@code{'}) or double (@code{"}).
6802 Escape sequences in the style of C are also allowed. @xref{C
6803 Constants, ,C and C++ constants}, for a brief explanation of escape
6807 Enumerated constants consist of an enumerated identifier.
6810 Boolean constants consist of the identifiers @code{TRUE} and
6814 Pointer constants consist of integral values only.
6817 Set constants are not yet supported.
6820 @node M2 Defaults, Deviations, M2 Constants, Modula-2
6821 @subsubsection Modula-2 defaults
6822 @cindex Modula-2 defaults
6824 If type and range checking are set automatically by @value{GDBN}, they
6825 both default to @code{on} whenever the working language changes to
6826 Modula-2. This happens regardless of whether you, or @value{GDBN},
6827 selected the working language.
6829 If you allow @value{GDBN} to set the language automatically, then entering
6830 code compiled from a file whose name ends with @file{.mod} sets the
6831 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6832 the language automatically}, for further details.
6834 @node Deviations, M2 Checks, M2 Defaults, Modula-2
6835 @subsubsection Deviations from standard Modula-2
6836 @cindex Modula-2, deviations from
6838 A few changes have been made to make Modula-2 programs easier to debug.
6839 This is done primarily via loosening its type strictness:
6843 Unlike in standard Modula-2, pointer constants can be formed by
6844 integers. This allows you to modify pointer variables during
6845 debugging. (In standard Modula-2, the actual address contained in a
6846 pointer variable is hidden from you; it can only be modified
6847 through direct assignment to another pointer variable or expression that
6848 returned a pointer.)
6851 C escape sequences can be used in strings and characters to represent
6852 non-printable characters. @value{GDBN} prints out strings with these
6853 escape sequences embedded. Single non-printable characters are
6854 printed using the @samp{CHR(@var{nnn})} format.
6857 The assignment operator (@code{:=}) returns the value of its right-hand
6861 All built-in procedures both modify @emph{and} return their argument.
6864 @node M2 Checks, M2 Scope, Deviations, Modula-2
6865 @subsubsection Modula-2 type and range checks
6866 @cindex Modula-2 checks
6869 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6872 @c FIXME remove warning when type/range checks added
6874 @value{GDBN} considers two Modula-2 variables type equivalent if:
6878 They are of types that have been declared equivalent via a @code{TYPE
6879 @var{t1} = @var{t2}} statement
6882 They have been declared on the same line. (Note: This is true of the
6883 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6886 As long as type checking is enabled, any attempt to combine variables
6887 whose types are not equivalent is an error.
6889 Range checking is done on all mathematical operations, assignment, array
6890 index bounds, and all built-in functions and procedures.
6892 @node M2 Scope, GDB/M2, M2 Checks, Modula-2
6893 @subsubsection The scope operators @code{::} and @code{.}
6896 @cindex colon, doubled as scope operator
6899 @c Info cannot handle :: but TeX can.
6905 There are a few subtle differences between the Modula-2 scope operator
6906 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6911 @var{module} . @var{id}
6912 @var{scope} :: @var{id}
6916 where @var{scope} is the name of a module or a procedure,
6917 @var{module} the name of a module, and @var{id} is any declared
6918 identifier within your program, except another module.
6920 Using the @code{::} operator makes @value{GDBN} search the scope
6921 specified by @var{scope} for the identifier @var{id}. If it is not
6922 found in the specified scope, then @value{GDBN} searches all scopes
6923 enclosing the one specified by @var{scope}.
6925 Using the @code{.} operator makes @value{GDBN} search the current scope for
6926 the identifier specified by @var{id} that was imported from the
6927 definition module specified by @var{module}. With this operator, it is
6928 an error if the identifier @var{id} was not imported from definition
6929 module @var{module}, or if @var{id} is not an identifier in
6932 @node GDB/M2, , M2 Scope, Modula-2
6933 @subsubsection @value{GDBN} and Modula-2
6935 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6936 Five subcommands of @code{set print} and @code{show print} apply
6937 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6938 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6939 apply to C++, and the last to the C @code{union} type, which has no direct
6940 analogue in Modula-2.
6942 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6943 while using any language, is not useful with Modula-2. Its
6944 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6945 created in Modula-2 as they can in C or C++. However, because an
6946 address can be specified by an integral constant, the construct
6947 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
6949 @cindex @code{#} in Modula-2
6950 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6951 interpreted as the beginning of a comment. Use @code{<>} instead.
6953 @node Chill, , Modula-2, Support
6956 The extensions made to @value{GDBN} to support Chill only support output
6957 from the GNU Chill compiler. Other Chill compilers are not currently
6958 supported, and attempting to debug executables produced by them is most
6959 likely to give an error as @value{GDBN} reads in the executable's symbol
6962 This section covers the following Chill related topics and the features
6963 of @value{GDBN} which support these topics.
6966 * How modes are displayed:: How modes are displayed
6967 * Locations:: Locations and their accesses
6968 * Values and their Operations:: Values and their Operations
6971 @node How modes are displayed
6972 @subsubsection How modes are displayed
6974 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
6975 with the functionality of the GNU Chill compiler, and therefore deviates
6976 slightly from the standard specification of the Chill language. The
6979 @item @r{@emph{Discrete modes:}}
6982 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
6985 @emph{Boolean Mode} which is predefined by @code{BOOL},
6987 @emph{Character Mode} which is predefined by @code{CHAR},
6989 @emph{Set Mode} which is displayed by the keyword @code{SET}.
6991 (@value{GDBP}) ptype x
6992 type = SET (karli = 10, susi = 20, fritzi = 100)
6994 If the type is an unnumbered set the set element values are omitted.
6996 @emph{Range Mode} which is displayed by @code{type = <basemode>
6997 (<lower bound> : <upper bound>)}, where @code{<lower bound>, <upper
6998 bound>} can be of any discrete literal expression (e.g. set element
7002 @item @r{@emph{Powerset Mode:}}
7003 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
7004 the member mode of the powerset. The member mode can be any discrete mode.
7006 (@value{GDBP}) ptype x
7007 type = POWERSET SET (egon, hugo, otto)
7010 @item @r{@emph{Reference Modes:}}
7013 @emph{Bound Reference Mode} which is diplayed by the keyword @code{REF}
7014 followed by the mode name to which the reference is bound.
7016 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
7019 @item @r{@emph{Procedure mode}}
7020 The procedure mode is displayed by @code{type = PROC(<parameter list>)
7021 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
7022 list>} is a list of the parameter modes. @code{<return mode>} indicates
7023 the mode of the result of the procedure if any. The exceptionlist lists
7024 all possible exceptions which can be raised by the procedure.
7027 @item @r{@emph{Instance mode}}
7028 The instance mode is represented by a structure, which has a static
7029 type, and is therefore not really of interest.
7032 @item @r{@emph{Synchronization Modes:}}
7035 @emph{Event Mode} which is displayed by @code{EVENT (<event length>)},
7036 where @code{(<event length>)} is optional.
7038 @emph{Buffer Mode} which is displayed by @code{BUFFER (<buffer length>)
7039 <buffer element mode>}, where @code{(<buffer length>)} is optional.
7042 @item @r{@emph{Timing Modes:}}
7045 @emph{Duration Mode} which is predefined by @code{DURATION}
7047 @emph{Absolute Time Mode} which is predefined by @code{TIME}
7050 @item @r{@emph{Real Modes:}}
7051 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
7053 @item @r{@emph{String Modes:}}
7056 @emph{Character String Mode} which is displayed by @code{CHARS(<string
7057 length>)}, followed by the keyword @code{VARYING} if the String Mode is
7060 @emph{Bit String Mode} which is displayed by @code{BOOLS(<string
7064 @item @r{@emph{Array Mode:}}
7065 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
7066 followed by the element mode (which may in turn be an array mode).
7068 (@value{GDBP}) ptype x
7071 SET (karli = 10, susi = 20, fritzi = 100)
7074 @item @r{@emph{Structure Mode}}
7075 The Structure mode is displayed by the keyword @code{STRUCT(<field
7076 list>)}. The @code{<field list>} consists of names and modes of fields
7077 of the structure. Variant structures have the keyword @code{CASE <field>
7078 OF <variant fields> ESAC} in their field list. Since the current version
7079 of the GNU Chill compiler doesn't implement tag processing (no runtime
7080 checks of variant fields, and therefore no debugging info), the output
7081 always displays all variant fields.
7083 (@value{GDBP}) ptype str
7098 @subsubsection Locations and their accesses
7100 A location in Chill is an object which can contain values.
7102 A value of a location is generally accessed by the (declared) name of
7103 the location. The output conforms to the specification of values in
7104 Chill programs. How values are specified, and which operations are valid
7105 is the topic of the next section.
7107 The pseudo-location @code{RESULT} (or @code{result}) can be used to
7108 display or change the result of a currently-active procedure:
7112 - does the same as the Chill action @code{RESULT EXPR} (which
7113 is not available in gdb).
7115 Values of reference mode locations are printed by @code{PTR(<hex
7116 value>)} in case of a free reference mode, and by @code{(REF <reference
7117 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
7118 represents the address where the reference points to. To access the
7119 value of the location referenced by the pointer, use the dereference
7120 operator `@code{->}'.
7122 Values of procedure mode locations are displayed by @code{@{ PROC
7123 (<argument modes> ) <return mode> @} <address> <name of procedure
7124 location>}. @code{<argument modes>} is a list of modes according to the
7125 parameter specification of the procedure and @code{<address>} shows the
7126 address of the entry point.
7129 Locations of instance modes are displayed just like a structure with two
7130 fields specifying the @emph{process type} and the @emph{copy number} of
7131 the investigated instance location@footnote{This comes from the current
7132 implementation of instances. They are implemented as a structure (no
7133 na). The output should be something like @code{[<name of the process>;
7134 <instance number>]}.}. The field names are @code{__proc_type} and
7137 Locations of synchronization modes are displayed like a structure with
7138 the field name @code{__event_data} in case of a event mode location, and
7139 like a structure with the field @code{__buffer_data} in case of a buffer
7140 mode location (refer to previous paragraph).
7142 Structure Mode locations are printed by @code{[.<field name>: <value>,
7143 ...]}. The @code{<field name>} corresponds to the structure mode
7144 definition and the layout of @code{<value>} varies depending of the mode
7145 of the field. If the investigated structure mode location is of variant
7146 structure mode the variant parts of the structure are enclosed in curled
7147 braces (`@code{@{@}}'). Fields enclosed by `@code{@{,@}}' are residing
7148 on the same memory location and represent the current values of the
7149 memory location in their specific modes. Since no tag processing is done
7150 all variants are displayed. A variant field is printed by
7151 @code{(<variant name>) = .<field name>: <value>}. (who implements the
7154 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
7155 [.cs: []], (susi) = [.ds: susi]}]
7159 Substructures of string mode-, array mode- or structure mode-values
7160 (e.g. array slices, fields of structure locations) are accessed using
7161 certain operations which are descibed in the next chapter.
7163 A location value may be interpreted as having a different mode using the
7164 location conversion. This mode conversion is written as @code{<mode
7165 name>(<location>)}. The user has to consider that the sizes of the modes
7166 have to be equal otherwise an error message occurs. Further no range
7167 checking of the location against the destination mode is performed and
7168 therefore the result can be quite confusing.
7170 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
7173 @node Values and their Operations
7174 @subsubsection Values and their Operations
7176 Values are used to alter locations, to investigate complex structures in
7177 more detail or to filter relevant information out of a large amount of
7178 data. There are several (mode dependent) operations defined which enable
7179 such investigations. These operations are not only applicable to
7180 constant values but also to locations, which can become quite useful
7181 when debugging complex structures. During parsing the command line
7182 (e.g. evaluating an expression) @value{GDBN} treats location names as
7183 the values behind these locations.
7185 This subchapters describes how values have to be specified and which
7186 operations are legal to be used with such values.
7189 @item Literal Values
7190 Literal values are specified in the same manner as in GNU Chill programs.
7191 For detailed specification refer to the GNU Chill implementation Manual
7197 @emph{Integer Literals} are specified in the same manner as in Chill
7198 programs (refer z200/88 chpt 5.2.4.2)
7200 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7202 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7205 @emph{Set Literals} are defined by a name which was specified in a set
7206 mode. The value delivered by a Set Literal is the set value. This is
7207 comparable to an enumaration in C/C++ language.
7209 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7210 emptiness literal delivers either the empty reference value, the empty
7211 procedure value or the empty instance value.
7214 @emph{Character String Literals} are defined by a sequence of characters
7215 enclosed in single- or double quotes. If a single- or double quote has
7216 to be part of the string literal it has to be stuffed (specified twice).
7218 @emph{Bitstring Literals} are specified in the same manner as in Chill
7219 programs (refer z200/88 chpt 5.2.4.8).
7221 @emph{Floating point literals} are specified in the same manner as in
7222 (gnu-)Chill programs (refer GNU Chill implementation Manual chapter 1.5).
7227 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7228 name>} can be omitted if the mode of the tuple is unambigous. This
7229 unambiguity is derived from the context of a evaluated expression.
7230 @code{<tuple>} can be one of the following:
7232 @item @emph{Powerset Tuple}
7233 @item @emph{Array Tuple}
7234 @item @emph{Structure Tuple}
7235 Powerset tuples, array tuples and structure tuples are specified in the
7236 same manner as in Chill programs refer z200/88 chpt 5.2.5.
7239 @item String Element Value
7240 A string element value is specified by @code{<string value>(<index>)},
7241 where @code{<index>} is a integer expression. It delivers a character
7242 value which is equivalent to the character indexed by @code{<index>} in
7245 @item String Slice Value
7246 A string slice value is specified by @code{<string value>(<slice
7247 spec>)}, where @code{<slice spec>} can be either a range of integer
7248 expressions or specified by @code{<start expr> up <size>}.
7249 @code{<size>} denotes the number of elements which the slice contains.
7250 The delivered value is a string value, which is part of the specified
7253 @item Array Element Values
7254 An array element value is specified by @code{<array value>(<expr>)} and
7255 delivers a array element value of the mode of the specified array.
7257 @item Array Slice Values
7258 An array slice is specified by @code{<array value>(<slice spec>)}, where
7259 @code{<slice spec>} can be either a range specified by expressions or by
7260 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7261 arrayelements the slice contains. The delivered value is an array value
7262 which is part of the specified array.
7264 @item Structure Field Values
7265 A structure field value is derived by @code{<structure value>.<field
7266 name>}, where @code{<field name>} indcates the name of a field specified
7267 in the mode definition of the structure. The mode of the delivered value
7268 corresponds to this mode definition in the structure definition.
7270 @item Procedure Call Value
7271 The procedure call value is derived from the return value of the
7272 procedure@footnote{If a procedure call is used for instance in an
7273 expression, then this procedure is called with all its side
7274 effects. This can lead to confusing results if used carelessly.}.
7276 Values of duration mode locations are represented by ULONG literals.
7278 Values of time mode locations are represented by TIME(<secs>:<nsecs>).
7281 This is not implemented yet:
7282 @item Built-in Value
7284 The following built in functions are provided:
7295 @item @code{UPPER()}
7296 @item @code{LOWER()}
7297 @item @code{LENGTH()}
7301 @item @code{ARCSIN()}
7302 @item @code{ARCCOS()}
7303 @item @code{ARCTAN()}
7310 For a detailed description refer to the GNU Chill implementation manual
7314 @item Zero-adic Operator Value
7315 The zero-adic operator value is derived from the instance value for the
7316 current active process.
7318 @item Expression Values
7319 The value delivered by an expression is the result of the evaluation of
7320 the specified expression. If there are error conditions (mode
7321 incompatibility, etc.) the evaluation of expressions is aborted with a
7322 corresponding error message. Expressions may be paranthesised which
7323 causes the evaluation of this expression before any other expression
7324 which uses the result of the paranthesised expression. The following
7325 operators are supported by @value{GDBN}:
7327 @item @code{OR, ORIF, XOR}
7328 @item @code{AND, ANDIF}
7330 Logical operators defined over operands of boolean mode.
7332 Equality and inequality operators defined over all modes.
7335 Relational operators defined over predefined modes.
7337 @item @code{*, /, MOD, REM}
7338 Arithmetic operators defined over predefined modes.
7340 Change sign operator.
7342 String concatenation operator.
7344 String repetition operator.
7346 Referenced location operator which can be used either to take the
7347 address of a location (@code{->loc}), or to dereference a reference
7348 location (@code{loc->}).
7349 @item @code{OR, XOR}
7352 Powerset and bitstring operators.
7355 Powerset inclusion operators.
7357 Membership operator.
7361 @subsubsection Chill type and range checks
7363 @value{GDBN} considers two Chill variables mode equivalent if the sizes
7364 of the two modes are equal. This rule applies recursively to more
7365 complex datatypes which means that complex modes are treated
7366 eqivalent if all element modes (which also can be complex modes like
7367 structures, arrays, etc.) have the same size.
7369 Range checking is done on all mathematical operations, assignment, array
7370 index bounds and all built in procedures.
7372 Strong type checks are forced using the @value{GDBN} command @code{set
7373 check strong}. This enforces strong type and range checks on all
7374 operations where Chill constructs are used (expressions, built in
7375 functions, etc.) in respect to the semantics as defined in the z.200
7376 language specification.
7379 All checks can be disabled by the @value{GDBN} command @code{set check
7383 @subsubsection Deviations from the Chill Standard Z200/88
7384 see last paragraph ?
7387 @subsubsection Chill defaults
7389 If type and range checking are set automatically by @value{GDBN}, they
7390 both default to @code{on} whenever the working language changes to
7391 Chill. This happens regardless of whether you, or @value{GDBN},
7392 selected the working language.
7394 If you allow @value{GDBN} to set the language automatically, then entering
7395 code compiled from a file whose name ends with @file{.ch} sets the
7396 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
7397 the language automatically}, for further details.
7399 @node Symbols, Altering, Languages, Top
7400 @chapter Examining the Symbol Table
7402 The commands described in this section allow you to inquire about the
7403 symbols (names of variables, functions and types) defined in your
7404 program. This information is inherent in the text of your program and
7405 does not change as your program executes. @value{GDBN} finds it in your
7406 program's symbol table, in the file indicated when you started @value{GDBN}
7407 (@pxref{File Options, ,Choosing files}), or by one of the
7408 file-management commands (@pxref{Files, ,Commands to specify files}).
7410 @cindex symbol names
7411 @cindex names of symbols
7412 @cindex quoting names
7413 Occasionally, you may need to refer to symbols that contain unusual
7414 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7415 most frequent case is in referring to static variables in other
7416 source files (@pxref{Variables,,Program variables}). File names
7417 are recorded in object files as debugging symbols, but @value{GDBN} would
7418 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7419 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7420 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7427 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7430 @kindex info address
7431 @item info address @var{symbol}
7432 Describe where the data for @var{symbol} is stored. For a register
7433 variable, this says which register it is kept in. For a non-register
7434 local variable, this prints the stack-frame offset at which the variable
7437 Note the contrast with @samp{print &@var{symbol}}, which does not work
7438 at all for a register variable, and for a stack local variable prints
7439 the exact address of the current instantiation of the variable.
7442 @item whatis @var{exp}
7443 Print the data type of expression @var{exp}. @var{exp} is not
7444 actually evaluated, and any side-effecting operations (such as
7445 assignments or function calls) inside it do not take place.
7446 @xref{Expressions, ,Expressions}.
7449 Print the data type of @code{$}, the last value in the value history.
7452 @item ptype @var{typename}
7453 Print a description of data type @var{typename}. @var{typename} may be
7454 the name of a type, or for C code it may have the form @samp{class
7455 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
7456 @var{union-tag}} or @samp{enum @var{enum-tag}}.
7458 @item ptype @var{exp}
7460 Print a description of the type of expression @var{exp}. @code{ptype}
7461 differs from @code{whatis} by printing a detailed description, instead
7462 of just the name of the type.
7464 For example, for this variable declaration:
7467 struct complex @{double real; double imag;@} v;
7471 the two commands give this output:
7475 (@value{GDBP}) whatis v
7476 type = struct complex
7477 (@value{GDBP}) ptype v
7478 type = struct complex @{
7486 As with @code{whatis}, using @code{ptype} without an argument refers to
7487 the type of @code{$}, the last value in the value history.
7490 @item info types @var{regexp}
7492 Print a brief description of all types whose name matches @var{regexp}
7493 (or all types in your program, if you supply no argument). Each
7494 complete typename is matched as though it were a complete line; thus,
7495 @samp{i type value} gives information on all types in your program whose
7496 name includes the string @code{value}, but @samp{i type ^value$} gives
7497 information only on types whose complete name is @code{value}.
7499 This command differs from @code{ptype} in two ways: first, like
7500 @code{whatis}, it does not print a detailed description; second, it
7501 lists all source files where a type is defined.
7505 Show the name of the current source file---that is, the source file for
7506 the function containing the current point of execution---and the language
7509 @kindex info sources
7511 Print the names of all source files in your program for which there is
7512 debugging information, organized into two lists: files whose symbols
7513 have already been read, and files whose symbols will be read when needed.
7515 @kindex info functions
7516 @item info functions
7517 Print the names and data types of all defined functions.
7519 @item info functions @var{regexp}
7520 Print the names and data types of all defined functions
7521 whose names contain a match for regular expression @var{regexp}.
7522 Thus, @samp{info fun step} finds all functions whose names
7523 include @code{step}; @samp{info fun ^step} finds those whose names
7524 start with @code{step}.
7526 @kindex info variables
7527 @item info variables
7528 Print the names and data types of all variables that are declared
7529 outside of functions (i.e., excluding local variables).
7531 @item info variables @var{regexp}
7532 Print the names and data types of all variables (except for local
7533 variables) whose names contain a match for regular expression
7537 This was never implemented.
7538 @kindex info methods
7540 @itemx info methods @var{regexp}
7541 The @code{info methods} command permits the user to examine all defined
7542 methods within C++ program, or (with the @var{regexp} argument) a
7543 specific set of methods found in the various C++ classes. Many
7544 C++ classes provide a large number of methods. Thus, the output
7545 from the @code{ptype} command can be overwhelming and hard to use. The
7546 @code{info-methods} command filters the methods, printing only those
7547 which match the regular-expression @var{regexp}.
7551 @cindex reloading symbols
7552 Some systems allow individual object files that make up your program to
7553 be replaced without stopping and restarting your program. For example,
7554 in VxWorks you can simply recompile a defective object file and keep on
7555 running. If you are running on one of these systems, you can allow
7556 @value{GDBN} to reload the symbols for automatically relinked modules:
7559 @kindex set symbol-reloading
7560 @item set symbol-reloading on
7561 Replace symbol definitions for the corresponding source file when an
7562 object file with a particular name is seen again.
7564 @item set symbol-reloading off
7565 Do not replace symbol definitions when re-encountering object files of
7566 the same name. This is the default state; if you are not running on a
7567 system that permits automatically relinking modules, you should leave
7568 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7569 when linking large programs, that may contain several modules (from
7570 different directories or libraries) with the same name.
7572 @kindex show symbol-reloading
7573 @item show symbol-reloading
7574 Show the current @code{on} or @code{off} setting.
7579 @kindex set opaque-type-resolution
7580 @item set opaque-type-resolution on
7581 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7582 declared as a pointer to a @code{struct}, @code{class}, or
7583 @code{union}---for example, @code{struct MyType *}---that is used in one
7584 source file although the full declaration of @code{struct MyType} is in
7585 another source file. The default is on.
7587 A change in the setting of this subcommand will not take effect until
7588 the next time symbols for a file are loaded.
7590 @item set opaque-type-resolution off
7591 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7592 is printed as follows:
7594 @{<no data fields>@}
7597 @kindex show opaque-type-resolution
7598 @item show opaque-type-resolution
7599 Show whether opaque types are resolved or not.
7602 @kindex maint print symbols
7604 @kindex maint print psymbols
7605 @cindex partial symbol dump
7606 @item maint print symbols @var{filename}
7607 @itemx maint print psymbols @var{filename}
7608 @itemx maint print msymbols @var{filename}
7609 Write a dump of debugging symbol data into the file @var{filename}.
7610 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7611 symbols with debugging data are included. If you use @samp{maint print
7612 symbols}, @value{GDBN} includes all the symbols for which it has already
7613 collected full details: that is, @var{filename} reflects symbols for
7614 only those files whose symbols @value{GDBN} has read. You can use the
7615 command @code{info sources} to find out which files these are. If you
7616 use @samp{maint print psymbols} instead, the dump shows information about
7617 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7618 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7619 @samp{maint print msymbols} dumps just the minimal symbol information
7620 required for each object file from which @value{GDBN} has read some symbols.
7621 @xref{Files, ,Commands to specify files}, for a discussion of how
7622 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7625 @node Altering, GDB Files, Symbols, Top
7626 @chapter Altering Execution
7628 Once you think you have found an error in your program, you might want to
7629 find out for certain whether correcting the apparent error would lead to
7630 correct results in the rest of the run. You can find the answer by
7631 experiment, using the @value{GDBN} features for altering execution of the
7634 For example, you can store new values into variables or memory
7635 locations, give your program a signal, restart it at a different
7636 address, or even return prematurely from a function.
7639 * Assignment:: Assignment to variables
7640 * Jumping:: Continuing at a different address
7641 * Signaling:: Giving your program a signal
7642 * Returning:: Returning from a function
7643 * Calling:: Calling your program's functions
7644 * Patching:: Patching your program
7647 @node Assignment, Jumping, Altering, Altering
7648 @section Assignment to variables
7651 @cindex setting variables
7652 To alter the value of a variable, evaluate an assignment expression.
7653 @xref{Expressions, ,Expressions}. For example,
7660 stores the value 4 into the variable @code{x}, and then prints the
7661 value of the assignment expression (which is 4).
7662 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7663 information on operators in supported languages.
7665 @kindex set variable
7666 @cindex variables, setting
7667 If you are not interested in seeing the value of the assignment, use the
7668 @code{set} command instead of the @code{print} command. @code{set} is
7669 really the same as @code{print} except that the expression's value is
7670 not printed and is not put in the value history (@pxref{Value History,
7671 ,Value history}). The expression is evaluated only for its effects.
7674 If the beginning of the argument string of the @code{set} command
7675 appears identical to a @code{set} subcommand, use the @code{set
7676 variable} command instead of just @code{set}. This command is identical
7677 to @code{set} except for its lack of subcommands. For example, if your
7678 program has a variable @code{width}, you get an error if you try to set
7679 a new value with just @samp{set width=13}, because @value{GDBN} has the
7680 command @code{set width}:
7683 (@value{GDBP}) whatis width
7685 (@value{GDBP}) p width
7687 (@value{GDBP}) set width=47
7688 Invalid syntax in expression.
7692 The invalid expression, of course, is @samp{=47}. In
7693 order to actually set the program's variable @code{width}, use
7696 (@value{GDBP}) set var width=47
7700 Because the @code{set} command has many subcommands that can conflict
7701 with the names of program variables, it is a good idea to use the
7702 @code{set variable} command instead of just @code{set}. For example, if
7703 your program has a variable @code{g}, you run into problems if you try
7704 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7705 the command @code{set gnutarget}, abbreviated @code{set g}:
7709 (@value{GDBP}) whatis g
7713 (@value{GDBP}) set g=4
7717 The program being debugged has been started already.
7718 Start it from the beginning? (y or n) y
7719 Starting program: /home/smith/cc_progs/a.out
7720 "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target.
7721 (@value{GDBP}) show g
7722 The current BFD target is "=4".
7727 The program variable @code{g} did not change, and you silently set the
7728 @code{gnutarget} to an invalid value. In order to set the variable
7732 (@value{GDBP}) set var g=4
7736 @value{GDBN} allows more implicit conversions in assignments than C; you can
7737 freely store an integer value into a pointer variable or vice versa,
7738 and you can convert any structure to any other structure that is the
7739 same length or shorter.
7740 @comment FIXME: how do structs align/pad in these conversions?
7741 @comment /doc@cygnus.com 18dec1990
7743 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7744 construct to generate a value of specified type at a specified address
7745 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7746 to memory location @code{0x83040} as an integer (which implies a certain size
7747 and representation in memory), and
7750 set @{int@}0x83040 = 4
7754 stores the value 4 into that memory location.
7756 @node Jumping, Signaling, Assignment, Altering
7757 @section Continuing at a different address
7759 Ordinarily, when you continue your program, you do so at the place where
7760 it stopped, with the @code{continue} command. You can instead continue at
7761 an address of your own choosing, with the following commands:
7765 @item jump @var{linespec}
7766 Resume execution at line @var{linespec}. Execution stops again
7767 immediately if there is a breakpoint there. @xref{List, ,Printing
7768 source lines}, for a description of the different forms of
7769 @var{linespec}. It is common practice to use the @code{tbreak} command
7770 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7773 The @code{jump} command does not change the current stack frame, or
7774 the stack pointer, or the contents of any memory location or any
7775 register other than the program counter. If line @var{linespec} is in
7776 a different function from the one currently executing, the results may
7777 be bizarre if the two functions expect different patterns of arguments or
7778 of local variables. For this reason, the @code{jump} command requests
7779 confirmation if the specified line is not in the function currently
7780 executing. However, even bizarre results are predictable if you are
7781 well acquainted with the machine-language code of your program.
7783 @item jump *@var{address}
7784 Resume execution at the instruction at address @var{address}.
7788 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7789 You can get much the same effect as the @code{jump} command by storing a
7790 new value into the register @code{$pc}. The difference is that this
7791 does not start your program running; it only changes the address of where it
7792 @emph{will} run when you continue. For example,
7799 makes the next @code{continue} command or stepping command execute at
7800 address @code{0x485}, rather than at the address where your program stopped.
7801 @xref{Continuing and Stepping, ,Continuing and stepping}.
7804 The most common occasion to use the @code{jump} command is to back
7805 up---perhaps with more breakpoints set---over a portion of a program
7806 that has already executed, in order to examine its execution in more
7810 @node Signaling, Returning, Jumping, Altering
7811 @section Giving your program a signal
7815 @item signal @var{signal}
7816 Resume execution where your program stopped, but immediately give it the
7817 signal @var{signal}. @var{signal} can be the name or the number of a
7818 signal. For example, on many systems @code{signal 2} and @code{signal
7819 SIGINT} are both ways of sending an interrupt signal.
7821 Alternatively, if @var{signal} is zero, continue execution without
7822 giving a signal. This is useful when your program stopped on account of
7823 a signal and would ordinary see the signal when resumed with the
7824 @code{continue} command; @samp{signal 0} causes it to resume without a
7827 @code{signal} does not repeat when you press @key{RET} a second time
7828 after executing the command.
7832 Invoking the @code{signal} command is not the same as invoking the
7833 @code{kill} utility from the shell. Sending a signal with @code{kill}
7834 causes @value{GDBN} to decide what to do with the signal depending on
7835 the signal handling tables (@pxref{Signals}). The @code{signal} command
7836 passes the signal directly to your program.
7839 @node Returning, Calling, Signaling, Altering
7840 @section Returning from a function
7843 @cindex returning from a function
7846 @itemx return @var{expression}
7847 You can cancel execution of a function call with the @code{return}
7848 command. If you give an
7849 @var{expression} argument, its value is used as the function's return
7853 When you use @code{return}, @value{GDBN} discards the selected stack frame
7854 (and all frames within it). You can think of this as making the
7855 discarded frame return prematurely. If you wish to specify a value to
7856 be returned, give that value as the argument to @code{return}.
7858 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7859 frame}), and any other frames inside of it, leaving its caller as the
7860 innermost remaining frame. That frame becomes selected. The
7861 specified value is stored in the registers used for returning values
7864 The @code{return} command does not resume execution; it leaves the
7865 program stopped in the state that would exist if the function had just
7866 returned. In contrast, the @code{finish} command (@pxref{Continuing
7867 and Stepping, ,Continuing and stepping}) resumes execution until the
7868 selected stack frame returns naturally.
7870 @node Calling, Patching, Returning, Altering
7871 @section Calling program functions
7873 @cindex calling functions
7876 @item call @var{expr}
7877 Evaluate the expression @var{expr} without displaying @code{void}
7881 You can use this variant of the @code{print} command if you want to
7882 execute a function from your program, but without cluttering the output
7883 with @code{void} returned values. If the result is not void, it
7884 is printed and saved in the value history.
7887 For the A29K, a user-controlled variable @code{call_scratch_address},
7888 specifies the location of a scratch area to be used when @value{GDBN}
7889 calls a function in the target. This is necessary because the usual
7890 method of putting the scratch area on the stack does not work in systems
7891 that have separate instruction and data spaces.
7894 @node Patching, , Calling, Altering
7895 @section Patching programs
7897 @cindex patching binaries
7898 @cindex writing into executables
7899 @cindex writing into corefiles
7901 By default, @value{GDBN} opens the file containing your program's
7902 executable code (or the corefile) read-only. This prevents accidental
7903 alterations to machine code; but it also prevents you from intentionally
7904 patching your program's binary.
7906 If you'd like to be able to patch the binary, you can specify that
7907 explicitly with the @code{set write} command. For example, you might
7908 want to turn on internal debugging flags, or even to make emergency
7914 @itemx set write off
7915 If you specify @samp{set write on}, @value{GDBN} opens executable and
7916 core files for both reading and writing; if you specify @samp{set write
7917 off} (the default), @value{GDBN} opens them read-only.
7919 If you have already loaded a file, you must load it again (using the
7920 @code{exec-file} or @code{core-file} command) after changing @code{set
7921 write}, for your new setting to take effect.
7925 Display whether executable files and core files are opened for writing
7929 @node GDB Files, Targets, Altering, Top
7930 @chapter @value{GDBN} Files
7932 @value{GDBN} needs to know the file name of the program to be debugged,
7933 both in order to read its symbol table and in order to start your
7934 program. To debug a core dump of a previous run, you must also tell
7935 @value{GDBN} the name of the core dump file.
7938 * Files:: Commands to specify files
7939 * Symbol Errors:: Errors reading symbol files
7942 @node Files, Symbol Errors, GDB Files, GDB Files
7943 @section Commands to specify files
7945 @cindex symbol table
7946 @cindex core dump file
7948 You may want to specify executable and core dump file names. The usual
7949 way to do this is at start-up time, using the arguments to
7950 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
7951 Out of @value{GDBN}}).
7953 Occasionally it is necessary to change to a different file during a
7954 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
7955 a file you want to use. In these situations the @value{GDBN} commands
7956 to specify new files are useful.
7959 @cindex executable file
7961 @item file @var{filename}
7962 Use @var{filename} as the program to be debugged. It is read for its
7963 symbols and for the contents of pure memory. It is also the program
7964 executed when you use the @code{run} command. If you do not specify a
7965 directory and the file is not found in the @value{GDBN} working directory,
7966 @value{GDBN} uses the environment variable @code{PATH} as a list of
7967 directories to search, just as the shell does when looking for a program
7968 to run. You can change the value of this variable, for both @value{GDBN}
7969 and your program, using the @code{path} command.
7972 On systems with memory-mapped files, an auxiliary file
7973 @file{@var{filename}.syms} may hold symbol table information for
7974 @var{filename}. If so, @value{GDBN} maps in the symbol table from
7975 @file{@var{filename}.syms}, starting up more quickly. See the
7976 descriptions of the file options @samp{-mapped} and @samp{-readnow}
7977 (available on the command line, and with the commands @code{file},
7978 @code{symbol-file}, or @code{add-symbol-file}, described below),
7979 for more information.
7983 @code{file} with no argument makes @value{GDBN} discard any information it
7984 has on both executable file and the symbol table.
7987 @item exec-file @r{[} @var{filename} @r{]}
7988 Specify that the program to be run (but not the symbol table) is found
7989 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
7990 if necessary to locate your program. Omitting @var{filename} means to
7991 discard information on the executable file.
7994 @item symbol-file @r{[} @var{filename} @r{]}
7995 Read symbol table information from file @var{filename}. @code{PATH} is
7996 searched when necessary. Use the @code{file} command to get both symbol
7997 table and program to run from the same file.
7999 @code{symbol-file} with no argument clears out @value{GDBN} information on your
8000 program's symbol table.
8002 The @code{symbol-file} command causes @value{GDBN} to forget the contents
8003 of its convenience variables, the value history, and all breakpoints and
8004 auto-display expressions. This is because they may contain pointers to
8005 the internal data recording symbols and data types, which are part of
8006 the old symbol table data being discarded inside @value{GDBN}.
8008 @code{symbol-file} does not repeat if you press @key{RET} again after
8011 When @value{GDBN} is configured for a particular environment, it
8012 understands debugging information in whatever format is the standard
8013 generated for that environment; you may use either a @sc{gnu} compiler, or
8014 other compilers that adhere to the local conventions.
8016 Best results are usually obtained from @sc{gnu} compilers; for example,
8017 using @code{@value{GCC}} you can generate debugging information for
8021 For most kinds of object files, with the exception of old SVR3 systems
8022 using COFF, the @code{symbol-file} command does not normally read the
8023 symbol table in full right away. Instead, it scans the symbol table
8024 quickly to find which source files and which symbols are present. The
8025 details are read later, one source file at a time, as they are needed.
8027 The purpose of this two-stage reading strategy is to make @value{GDBN}
8028 start up faster. For the most part, it is invisible except for
8029 occasional pauses while the symbol table details for a particular source
8030 file are being read. (The @code{set verbose} command can turn these
8031 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
8032 warnings and messages}.)
8035 We have not implemented the two-stage strategy for COFF yet. When the
8036 symbol table is stored in COFF format, @code{symbol-file} reads the
8037 symbol table data in full right away. Note that ``stabs-in-COFF''
8038 still does the two-stage strategy, since the debug info is actually
8042 @cindex reading symbols immediately
8043 @cindex symbols, reading immediately
8045 @cindex memory-mapped symbol file
8046 @cindex saving symbol table
8047 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8048 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8049 You can override the @value{GDBN} two-stage strategy for reading symbol
8050 tables by using the @samp{-readnow} option with any of the commands that
8051 load symbol table information, if you want to be sure @value{GDBN} has the
8052 entire symbol table available.
8056 If memory-mapped files are available on your system through the
8057 @code{mmap} system call, you can use another option, @samp{-mapped}, to
8058 cause @value{GDBN} to write the symbols for your program into a reusable
8059 file. Future @value{GDBN} debugging sessions map in symbol information
8060 from this auxiliary symbol file (if the program has not changed), rather
8061 than spending time reading the symbol table from the executable
8062 program. Using the @samp{-mapped} option has the same effect as
8063 starting @value{GDBN} with the @samp{-mapped} command-line option.
8065 You can use both options together, to make sure the auxiliary symbol
8066 file has all the symbol information for your program.
8068 The auxiliary symbol file for a program called @var{myprog} is called
8069 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
8070 than the corresponding executable), @value{GDBN} always attempts to use
8071 it when you debug @var{myprog}; no special options or commands are
8074 The @file{.syms} file is specific to the host machine where you run
8075 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
8076 symbol table. It cannot be shared across multiple host platforms.
8078 @c FIXME: for now no mention of directories, since this seems to be in
8079 @c flux. 13mar1992 status is that in theory GDB would look either in
8080 @c current dir or in same dir as myprog; but issues like competing
8081 @c GDB's, or clutter in system dirs, mean that in practice right now
8082 @c only current dir is used. FFish says maybe a special GDB hierarchy
8083 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
8088 @item core-file @r{[} @var{filename} @r{]}
8089 Specify the whereabouts of a core dump file to be used as the ``contents
8090 of memory''. Traditionally, core files contain only some parts of the
8091 address space of the process that generated them; @value{GDBN} can access the
8092 executable file itself for other parts.
8094 @code{core-file} with no argument specifies that no core file is
8097 Note that the core file is ignored when your program is actually running
8098 under @value{GDBN}. So, if you have been running your program and you
8099 wish to debug a core file instead, you must kill the subprocess in which
8100 the program is running. To do this, use the @code{kill} command
8101 (@pxref{Kill Process, ,Killing the child process}).
8105 @kindex add-symbol-file
8106 @cindex dynamic linking
8107 @item add-symbol-file @var{filename} @var{address}
8108 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
8109 The @code{add-symbol-file} command reads additional symbol table information
8110 from the file @var{filename}. You would use this command when @var{filename}
8111 has been dynamically loaded (by some other means) into the program that
8112 is running. @var{address} should be the memory address at which the
8113 file has been loaded; @value{GDBN} cannot figure this out for itself.
8114 You can specify @var{address} as an expression.
8116 The symbol table of the file @var{filename} is added to the symbol table
8117 originally read with the @code{symbol-file} command. You can use the
8118 @code{add-symbol-file} command any number of times; the new symbol data thus
8119 read keeps adding to the old. To discard all old symbol data instead,
8120 use the @code{symbol-file} command.
8122 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
8124 You can use the @samp{-mapped} and @samp{-readnow} options just as with
8125 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
8126 table information for @var{filename}.
8128 @kindex add-shared-symbol-file
8129 @item add-shared-symbol-file
8130 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
8131 operating system for the Motorola 88k. @value{GDBN} automatically looks for
8132 shared libraries, however if @value{GDBN} does not find yours, you can run
8133 @code{add-shared-symbol-file}. It takes no arguments.
8139 The @code{section} command changes the base address of section SECTION of
8140 the exec file to ADDR. This can be used if the exec file does not contain
8141 section addresses, (such as in the a.out format), or when the addresses
8142 specified in the file itself are wrong. Each section must be changed
8143 separately. The ``info files'' command lists all the sections and their
8151 @code{info files} and @code{info target} are synonymous; both print the
8152 current target (@pxref{Targets, ,Specifying a Debugging Target}),
8153 including the names of the executable and core dump files currently in
8154 use by @value{GDBN}, and the files from which symbols were loaded. The
8155 command @code{help target} lists all possible targets rather than
8160 All file-specifying commands allow both absolute and relative file names
8161 as arguments. @value{GDBN} always converts the file name to an absolute file
8162 name and remembers it that way.
8164 @cindex shared libraries
8166 @c added HP-UX -- Kim (HP writer)
8167 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
8171 @value{GDBN} supports HP-UX shared libraries.
8173 @value{GDBN} automatically loads symbol definitions from shared libraries
8174 when you use the @code{run} command, or when you examine a core file.
8175 (Before you issue the @code{run} command, @value{GDBN} does not understand
8176 references to a function in a shared library, however---unless you are
8177 debugging a core file).
8179 If the program loads a library explicitly, @value{GDBN} automatically
8180 loads the symbols at the time of the @code{shl_load} call.
8182 @c FIXME: some @value{GDBN} release may permit some refs to undef
8183 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
8184 @c FIXME...lib; check this from time to time when updating manual
8187 @kindex info sharedlibrary
8190 @itemx info sharedlibrary
8191 Print the names of the shared libraries which are currently loaded.
8193 @kindex sharedlibrary
8195 @item sharedlibrary @var{regex}
8196 @itemx share @var{regex}
8198 Load shared object library symbols for files matching a
8199 Unix regular expression.
8200 As with files loaded automatically, it only loads shared libraries
8201 required by your program for a core file or after typing @code{run}. If
8202 @var{regex} is omitted all shared libraries required by your program are
8207 @value{GDBN} detects the loading of a shared library and automatically
8208 reads in symbols from the newly loaded library, up to a threshold that
8209 is initially set but that you can modify if you wish.
8211 Beyond that threshold, symbols from shared libraries must be explicitly
8212 loaded. To load these symbols, use the command @code{sharedlibrary}
8213 @var{filename}. The base address of the shared library is determined
8214 automatically by @value{GDBN} and need not be specified.
8216 To display or set the threshold, use the commands:
8219 @kindex set auto-solib-add
8220 @item set auto-solib-add @var{threshold}
8221 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8222 nonzero, symbols from all shared object libraries will be loaded
8223 automatically when the inferior begins execution or when the dynamic
8224 linker informs @value{GDBN} that a new library has been loaded, until
8225 the symbol table of the program and libraries exceeds this threshold.
8226 Otherwise, symbols must be loaded manually, using the
8227 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8229 @kindex show auto-solib-add
8230 @item show auto-solib-add
8231 Display the current autoloading size threshold, in megabytes.
8235 @node Symbol Errors, , Files, GDB Files
8236 @section Errors reading symbol files
8238 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8239 such as symbol types it does not recognize, or known bugs in compiler
8240 output. By default, @value{GDBN} does not notify you of such problems, since
8241 they are relatively common and primarily of interest to people
8242 debugging compilers. If you are interested in seeing information
8243 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8244 only one message about each such type of problem, no matter how many
8245 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8246 to see how many times the problems occur, with the @code{set
8247 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8250 The messages currently printed, and their meanings, include:
8253 @item inner block not inside outer block in @var{symbol}
8255 The symbol information shows where symbol scopes begin and end
8256 (such as at the start of a function or a block of statements). This
8257 error indicates that an inner scope block is not fully contained
8258 in its outer scope blocks.
8260 @value{GDBN} circumvents the problem by treating the inner block as if it had
8261 the same scope as the outer block. In the error message, @var{symbol}
8262 may be shown as ``@code{(don't know)}'' if the outer block is not a
8265 @item block at @var{address} out of order
8267 The symbol information for symbol scope blocks should occur in
8268 order of increasing addresses. This error indicates that it does not
8271 @value{GDBN} does not circumvent this problem, and has trouble
8272 locating symbols in the source file whose symbols it is reading. (You
8273 can often determine what source file is affected by specifying
8274 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8277 @item bad block start address patched
8279 The symbol information for a symbol scope block has a start address
8280 smaller than the address of the preceding source line. This is known
8281 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8283 @value{GDBN} circumvents the problem by treating the symbol scope block as
8284 starting on the previous source line.
8286 @item bad string table offset in symbol @var{n}
8289 Symbol number @var{n} contains a pointer into the string table which is
8290 larger than the size of the string table.
8292 @value{GDBN} circumvents the problem by considering the symbol to have the
8293 name @code{foo}, which may cause other problems if many symbols end up
8296 @item unknown symbol type @code{0x@var{nn}}
8298 The symbol information contains new data types that @value{GDBN} does
8299 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
8300 misunderstood information, in hexadecimal.
8302 @value{GDBN} circumvents the error by ignoring this symbol information.
8303 This usually allows you to debug your program, though certain symbols
8304 are not accessible. If you encounter such a problem and feel like
8305 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
8306 on @code{complain}, then go up to the function @code{read_dbx_symtab}
8307 and examine @code{*bufp} to see the symbol.
8309 @item stub type has NULL name
8311 @value{GDBN} could not find the full definition for a struct or class.
8313 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8314 The symbol information for a C++ member function is missing some
8315 information that recent versions of the compiler should have output for
8318 @item info mismatch between compiler and debugger
8320 @value{GDBN} could not parse a type specification output by the compiler.
8324 @node Targets, Controlling GDB, GDB Files, Top
8325 @chapter Specifying a Debugging Target
8327 @cindex debugging target
8330 A @dfn{target} is the execution environment occupied by your program.
8332 Often, @value{GDBN} runs in the same host environment as your program; in
8333 that case, the debugging target is specified as a side effect when you
8334 use the @code{file} or @code{core} commands. When you need more
8335 flexibility---for example, running @value{GDBN} on a physically separate
8336 host, or controlling a standalone system over a serial port or a
8337 realtime system over a TCP/IP connection---you
8340 On HP-UX systems, @value{GDBN} has been configured to support debugging
8341 of processes running on the PA-RISC architecture. This means that the
8342 only possible targets are:
8346 An executable that has been compiled and linked to run on HP-UX
8349 A live HP-UX process, either started by @value{GDBN} (with the
8350 @code{run} command) or started outside of @value{GDBN} and attached to
8351 (with the @code{attach} command)
8354 A core file generated by an HP-UX process that previously aborted
8358 @value{GDBN} on HP-UX has not been configured to support remote
8359 debugging, or to support programs running on other platforms. You
8360 can use the @code{target} command to specify one of the target types
8361 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
8366 * Active Targets:: Active targets
8367 * Target Commands:: Commands for managing targets
8368 * Byte Order:: Choosing target byte order
8369 * Remote:: Remote debugging
8370 * KOD:: Kernel Object Display
8374 @node Active Targets, Target Commands, Targets, Targets
8375 @section Active targets
8377 @cindex stacking targets
8378 @cindex active targets
8379 @cindex multiple targets
8381 There are three classes of targets: processes, core files, and
8382 executable files. @value{GDBN} can work concurrently on up to three
8383 active targets, one in each class. This allows you to (for example)
8384 start a process and inspect its activity without abandoning your work on
8387 For example, if you execute @samp{gdb a.out}, then the executable file
8388 @code{a.out} is the only active target. If you designate a core file as
8389 well---presumably from a prior run that crashed and coredumped---then
8390 @value{GDBN} has two active targets and uses them in tandem, looking
8391 first in the corefile target, then in the executable file, to satisfy
8392 requests for memory addresses. (Typically, these two classes of target
8393 are complementary, since core files contain only a program's
8394 read-write memory---variables and so on---plus machine status, while
8395 executable files contain only the program text and initialized data.)
8397 When you type @code{run}, your executable file becomes an active process
8398 target as well. When a process target is active, all @value{GDBN}
8399 commands requesting memory addresses refer to that target; addresses in
8400 an active core file or executable file target are obscured while the
8401 process target is active.
8403 Use the @code{core-file} and @code{exec-file} commands to select a new
8404 core file or executable target (@pxref{Files, ,Commands to specify
8405 files}). To specify as a target a process that is already running, use
8406 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
8409 @node Target Commands, Byte Order, Active Targets, Targets
8410 @section Commands for managing targets
8413 @item target @var{type} @var{parameters}
8414 Connects the @value{GDBN} host environment to a target machine or
8415 process. A target is typically a protocol for talking to debugging
8416 facilities. You use the argument @var{type} to specify the type or
8417 protocol of the target machine.
8419 Further @var{parameters} are interpreted by the target protocol, but
8420 typically include things like device names or host names to connect
8421 with, process numbers, and baud rates.
8423 The @code{target} command does not repeat if you press @key{RET} again
8424 after executing the command.
8428 Displays the names of all targets available. To display targets
8429 currently selected, use either @code{info target} or @code{info files}
8430 (@pxref{Files, ,Commands to specify files}).
8432 @item help target @var{name}
8433 Describe a particular target, including any parameters necessary to
8436 @kindex set gnutarget
8437 @item set gnutarget @var{args}
8438 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8439 knows whether it is reading an @dfn{executable},
8440 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8441 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8442 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8444 @emph{Warning:} To specify a file format with @code{set gnutarget},
8445 you must know the actual BFD name.
8447 @noindent @xref{Files, , Commands to specify files}.
8449 @kindex show gnutarget
8450 @item show gnutarget
8451 Use the @code{show gnutarget} command to display what file format
8452 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8453 @value{GDBN} will determine the file format for each file automatically,
8454 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8458 Here are some common targets (available, or not, depending on the GDB
8462 These are the valid targets on HP-UX systems:
8467 @item target exec @var{program}
8468 An executable file. @samp{target exec @var{program}} is the same as
8469 @samp{exec-file @var{program}}.
8472 @item target core @var{filename}
8473 A core dump file. @samp{target core @var{filename}} is the same as
8474 @samp{core-file @var{filename}}.
8476 @kindex target remote
8477 @item target remote @var{dev}
8478 Remote serial target in GDB-specific protocol. The argument @var{dev}
8479 specifies what serial device to use for the connection (e.g.
8480 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8481 now supports the @code{load} command. This is only useful if you have
8482 some other way of getting the stub to the target system, and you can put
8483 it somewhere in memory where it won't get clobbered by the download.
8488 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
8492 The following targets are all CPU-specific, and only available for
8493 specific configurations.
8494 @c should organize by CPU
8499 @item target abug @var{dev}
8500 ABug ROM monitor for M68K.
8502 @kindex target adapt
8503 @item target adapt @var{dev}
8504 Adapt monitor for A29K.
8506 @kindex target amd-eb
8507 @item target amd-eb @var{dev} @var{speed} @var{PROG}
8509 Remote PC-resident AMD EB29K board, attached over serial lines.
8510 @var{dev} is the serial device, as for @code{target remote};
8511 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
8512 name of the program to be debugged, as it appears to DOS on the PC.
8513 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
8515 @kindex target array
8516 @item target array @var{dev}
8517 Array Tech LSI33K RAID controller board.
8520 @item target bug @var{dev}
8521 BUG monitor, running on a MVME187 (m88k) board.
8523 @kindex target cpu32bug
8524 @item target cpu32bug @var{dev}
8525 CPU32BUG monitor, running on a CPU32 (M68K) board.
8528 @item target dbug @var{dev}
8529 dBUG ROM monitor for Motorola ColdFire.
8532 @item target ddb @var{dev}
8533 NEC's DDB monitor for Mips Vr4300.
8535 @kindex target dink32
8536 @item target dink32 @var{dev}
8537 DINK32 ROM monitor for PowerPC.
8539 @kindex target e7000
8540 @item target e7000 @var{dev}
8541 E7000 emulator for Hitachi H8 and SH.
8543 @kindex target es1800
8544 @item target es1800 @var{dev}
8545 ES-1800 emulator for M68K.
8548 @item target est @var{dev}
8549 EST-300 ICE monitor, running on a CPU32 (M68K) board.
8552 @item target hms @var{dev}
8553 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
8554 Use special commands @code{device} and @code{speed} to control the serial
8555 line and the communications speed used.
8556 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
8559 @item target lsi @var{dev}
8560 LSI ROM monitor for Mips.
8563 @item target m32r @var{dev}
8564 Mitsubishi M32R/D ROM monitor.
8567 @item target mips @var{dev}
8568 IDT/SIM ROM monitor for Mips.
8570 @kindex target mon960
8571 @item target mon960 @var{dev}
8572 MON960 monitor for Intel i960.
8574 @kindex target nindy
8575 @item target nindy @var{devicename}
8576 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
8577 the name of the serial device to use for the connection, e.g.
8578 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
8581 @item target nrom @var{dev}
8582 NetROM ROM emulator. This target only supports downloading.
8584 @kindex target op50n
8585 @item target op50n @var{dev}
8586 OP50N monitor, running on an OKI HPPA board.
8589 @item target pmon @var{dev}
8590 PMON ROM monitor for Mips.
8592 @kindex target ppcbug
8593 @item target ppcbug @var{dev}
8594 @kindex target ppcbug1
8595 @item target ppcbug1 @var{dev}
8596 PPCBUG ROM monitor for PowerPC.
8598 @kindex target r3900
8599 @item target r3900 @var{dev}
8600 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
8603 @item target rdi @var{dev}
8604 ARM Angel monitor, via RDI library interface.
8607 @item target rdp @var{dev}
8610 @kindex target rom68k
8611 @item target rom68k @var{dev}
8612 ROM 68K monitor, running on an M68K IDP board.
8614 @kindex target rombug
8615 @item target rombug @var{dev}
8616 ROMBUG ROM monitor for OS/9000.
8619 @item target sds @var{dev}
8620 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
8622 @kindex target sparclite
8623 @item target sparclite @var{dev}
8624 Fujitsu sparclite boards, used only for the purpose of loading.
8625 You must use an additional command to debug the program.
8626 For example: target remote @var{dev} using @value{GDBN} standard
8631 @item target sh3 @var{dev}
8632 @item target sh3e @var{dev}
8633 Hitachi SH-3 and SH-3E target systems.
8635 @kindex target st2000
8636 @item target st2000 @var{dev} @var{speed}
8637 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
8638 is the name of the device attached to the ST2000 serial line;
8639 @var{speed} is the communication line speed. The arguments are not used
8640 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
8641 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
8644 @item target udi @var{keyword}
8645 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
8646 argument specifies which 29K board or simulator to use. @xref{UDI29K
8647 Remote,,The UDI protocol for AMD29K}.
8649 @kindex target vxworks
8650 @item target vxworks @var{machinename}
8651 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
8652 is the target system's machine name or IP address.
8653 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
8656 @item target w89k @var{dev}
8657 W89K monitor, running on a Winbond HPPA board.
8661 Different targets are available on different configurations of @value{GDBN};
8662 your configuration may have more or fewer targets.
8664 Many remote targets require you to download the executable's code
8665 once you've successfully established a connection.
8669 @kindex load @var{filename}
8670 @item load @var{filename}
8671 Depending on what remote debugging facilities are configured into
8672 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8673 is meant to make @var{filename} (an executable) available for debugging
8674 on the remote system---by downloading, or dynamic linking, for example.
8675 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8676 the @code{add-symbol-file} command.
8678 If your @value{GDBN} does not have a @code{load} command, attempting to
8679 execute it gets the error message ``@code{You can't do that when your
8680 target is @dots{}}''
8682 The file is loaded at whatever address is specified in the executable.
8683 For some object file formats, you can specify the load address when you
8684 link the program; for other formats, like a.out, the object file format
8685 specifies a fixed address.
8686 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8688 On VxWorks, @code{load} links @var{filename} dynamically on the
8689 current target system as well as adding its symbols in @value{GDBN}.
8691 @cindex download to Nindy-960
8692 With the Nindy interface to an Intel 960 board, @code{load}
8693 downloads @var{filename} to the 960 as well as adding its symbols in
8696 @cindex download to H8/300 or H8/500
8697 @cindex H8/300 or H8/500 download
8698 @cindex download to Hitachi SH
8699 @cindex Hitachi SH download
8700 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
8701 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
8702 the @code{load} command downloads your program to the Hitachi board and also
8703 opens it as the current executable target for @value{GDBN} on your host
8704 (like the @code{file} command).
8706 @code{load} does not repeat if you press @key{RET} again after using it.
8709 @node Byte Order, Remote, Target Commands, Targets
8710 @section Choosing target byte order
8712 @cindex choosing target byte order
8713 @cindex target byte order
8714 @kindex set endian big
8715 @kindex set endian little
8716 @kindex set endian auto
8719 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
8720 offer the ability to run either big-endian or little-endian byte
8721 orders. Usually the executable or symbol will include a bit to
8722 designate the endian-ness, and you will not need to worry about
8723 which to use. However, you may still find it useful to adjust
8724 GDB's idea of processor endian-ness manually.
8727 @kindex set endian big
8728 @item set endian big
8729 Instruct @value{GDBN} to assume the target is big-endian.
8731 @kindex set endian little
8732 @item set endian little
8733 Instruct @value{GDBN} to assume the target is little-endian.
8735 @kindex set endian auto
8736 @item set endian auto
8737 Instruct @value{GDBN} to use the byte order associated with the
8741 Display @value{GDBN}'s current idea of the target byte order.
8745 Note that these commands merely adjust interpretation of symbolic
8746 data on the host, and that they have absolutely no effect on the
8749 @node Remote, KOD, Byte Order, Targets
8750 @section Remote debugging
8751 @cindex remote debugging
8753 If you are trying to debug a program running on a machine that cannot run
8754 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8755 For example, you might use remote debugging on an operating system kernel,
8756 or on a small system which does not have a general purpose operating system
8757 powerful enough to run a full-featured debugger.
8759 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8760 to make this work with particular debugging targets. In addition,
8761 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8762 but not specific to any particular target system) which you can use if you
8763 write the remote stubs---the code that runs on the remote system to
8764 communicate with @value{GDBN}.
8766 Other remote targets may be available in your
8767 configuration of @value{GDBN}; use @code{help target} to list them.
8769 @c Text on starting up GDB in various specific cases; it goes up front
8770 @c in manuals configured for any of those particular situations, here
8773 * Remote Serial:: @value{GDBN} remote serial protocol
8774 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
8775 * UDI29K Remote:: The UDI protocol for AMD29K
8776 * EB29K Remote:: The EBMON protocol for AMD29K
8777 * VxWorks Remote:: @value{GDBN} and VxWorks
8778 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
8779 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
8780 * MIPS Remote:: @value{GDBN} and MIPS boards
8781 * Sparclet Remote:: @value{GDBN} and Sparclet boards
8782 * Simulator:: Simulated CPU target
8785 @include remote.texi
8788 @node KOD, , Remote, Targets
8789 @section Kernel Object Display
8790 @cindex kernel object display
8791 @cindex kernel object
8794 Some targets support kernel object display. Using this facility,
8795 @value{GDBN} communicates specially with the underlying operating system
8796 and can display information about operating system-level objects such as
8797 mutexes and other synchronization objects. Exactly which objects can be
8798 displayed is determined on a per-OS basis.
8800 Use the @code{set os} command to set the operating system. This tells
8801 @value{GDBN} which kernel object display module to initialize:
8807 If @code{set os} succeeds, @value{GDBN} will display some information
8808 about the operating system, and will create a new @code{info} command
8809 which can be used to query the target. The @code{info} command is named
8810 after the operating system:
8814 List of Cisco Kernel Objects
8816 any Any and all objects
8819 Further subcommands can be used to query about particular objects known
8822 There is currently no way to determine whether a given operating system
8823 is supported other than to try it.
8826 @node Controlling GDB
8827 @chapter Controlling @value{GDBN}
8829 You can alter the way @value{GDBN} interacts with you by using
8830 the @code{set} command. For commands controlling how @value{GDBN} displays
8831 data, @pxref{Print Settings, ,Print settings}; other settings are described
8836 * Editing:: Command editing
8837 * History:: Command history
8838 * Screen Size:: Screen size
8840 * Messages/Warnings:: Optional warnings and messages
8843 @node Prompt, Editing, Controlling GDB, Controlling GDB
8848 @value{GDBN} indicates its readiness to read a command by printing a string
8849 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
8850 can change the prompt string with the @code{set prompt} command. For
8851 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
8852 the prompt in one of the @value{GDBN} sessions so that you can always tell
8853 which one you are talking to.
8855 @emph{Note:} @code{set prompt} no longer adds a space for you after the
8856 prompt you set. This allows you to set a prompt which ends in a space
8857 or a prompt that does not.
8861 @item set prompt @var{newprompt}
8862 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
8866 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
8869 @node Editing, History, Prompt, Controlling GDB
8870 @section Command editing
8872 @cindex command line editing
8874 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
8875 @sc{gnu} library provides consistent behavior for programs which provide a
8876 command line interface to the user. Advantages are @sc{gnu} Emacs-style
8877 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
8878 substitution, and a storage and recall of command history across
8881 You may control the behavior of command line editing in @value{GDBN} with the
8888 @itemx set editing on
8889 Enable command line editing (enabled by default).
8891 @item set editing off
8892 Disable command line editing.
8894 @kindex show editing
8896 Show whether command line editing is enabled.
8899 @node History, Screen Size, Editing, Controlling GDB
8900 @section Command history
8902 @value{GDBN} can keep track of the commands you type during your
8903 debugging sessions, so that you can be certain of precisely what
8904 happened. Use these commands to manage the @value{GDBN} command
8908 @cindex history substitution
8909 @cindex history file
8910 @kindex set history filename
8912 @item set history filename @var{fname}
8913 Set the name of the @value{GDBN} command history file to @var{fname}.
8914 This is the file where @value{GDBN} reads an initial command history
8915 list, and where it writes the command history from this session when it
8916 exits. You can access this list through history expansion or through
8917 the history command editing characters listed below. This file defaults
8918 to the value of the environment variable @code{GDBHISTFILE}, or to
8919 @file{./.gdb_history} if this variable is not set.
8921 @cindex history save
8922 @kindex set history save
8923 @item set history save
8924 @itemx set history save on
8925 Record command history in a file, whose name may be specified with the
8926 @code{set history filename} command. By default, this option is disabled.
8928 @item set history save off
8929 Stop recording command history in a file.
8931 @cindex history size
8932 @kindex set history size
8933 @item set history size @var{size}
8934 Set the number of commands which @value{GDBN} keeps in its history list.
8935 This defaults to the value of the environment variable
8936 @code{HISTSIZE}, or to 256 if this variable is not set.
8939 @cindex history expansion
8940 History expansion assigns special meaning to the character @kbd{!}.
8941 @ifset have-readline-appendices
8942 @xref{Event Designators}.
8945 Since @kbd{!} is also the logical not operator in C, history expansion
8946 is off by default. If you decide to enable history expansion with the
8947 @code{set history expansion on} command, you may sometimes need to
8948 follow @kbd{!} (when it is used as logical not, in an expression) with
8949 a space or a tab to prevent it from being expanded. The readline
8950 history facilities do not attempt substitution on the strings
8951 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
8953 The commands to control history expansion are:
8956 @kindex set history expansion
8957 @item set history expansion on
8958 @itemx set history expansion
8959 Enable history expansion. History expansion is off by default.
8961 @item set history expansion off
8962 Disable history expansion.
8964 The readline code comes with more complete documentation of
8965 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
8966 or @code{vi} may wish to read it.
8967 @ifset have-readline-appendices
8968 @xref{Command Line Editing}.
8972 @kindex show history
8974 @itemx show history filename
8975 @itemx show history save
8976 @itemx show history size
8977 @itemx show history expansion
8978 These commands display the state of the @value{GDBN} history parameters.
8979 @code{show history} by itself displays all four states.
8984 @kindex show commands
8986 Display the last ten commands in the command history.
8988 @item show commands @var{n}
8989 Print ten commands centered on command number @var{n}.
8991 @item show commands +
8992 Print ten commands just after the commands last printed.
8995 @node Screen Size, Numbers, History, Controlling GDB
8996 @section Screen size
8997 @cindex size of screen
8998 @cindex pauses in output
9000 Certain commands to @value{GDBN} may produce large amounts of
9001 information output to the screen. To help you read all of it,
9002 @value{GDBN} pauses and asks you for input at the end of each page of
9003 output. Type @key{RET} when you want to continue the output, or @kbd{q}
9004 to discard the remaining output. Also, the screen width setting
9005 determines when to wrap lines of output. Depending on what is being
9006 printed, @value{GDBN} tries to break the line at a readable place,
9007 rather than simply letting it overflow onto the following line.
9009 Normally @value{GDBN} knows the size of the screen from the termcap data base
9010 together with the value of the @code{TERM} environment variable and the
9011 @code{stty rows} and @code{stty cols} settings. If this is not correct,
9012 you can override it with the @code{set height} and @code{set
9020 @item set height @var{lpp}
9022 @itemx set width @var{cpl}
9024 These @code{set} commands specify a screen height of @var{lpp} lines and
9025 a screen width of @var{cpl} characters. The associated @code{show}
9026 commands display the current settings.
9028 If you specify a height of zero lines, @value{GDBN} does not pause during
9029 output no matter how long the output is. This is useful if output is to a
9030 file or to an editor buffer.
9032 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
9033 from wrapping its output.
9036 @node Numbers, Messages/Warnings, Screen Size, Controlling GDB
9038 @cindex number representation
9039 @cindex entering numbers
9041 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
9042 the usual conventions: octal numbers begin with @samp{0}, decimal
9043 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
9044 Numbers that begin with none of these are, by default, entered in base
9045 10; likewise, the default display for numbers---when no particular
9046 format is specified---is base 10. You can change the default base for
9047 both input and output with the @code{set radix} command.
9050 @kindex set input-radix
9051 @item set input-radix @var{base}
9052 Set the default base for numeric input. Supported choices
9053 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
9054 specified either unambiguously or using the current default radix; for
9064 sets the base to decimal. On the other hand, @samp{set radix 10}
9065 leaves the radix unchanged no matter what it was.
9067 @kindex set output-radix
9068 @item set output-radix @var{base}
9069 Set the default base for numeric display. Supported choices
9070 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
9071 specified either unambiguously or using the current default radix.
9073 @kindex show input-radix
9074 @item show input-radix
9075 Display the current default base for numeric input.
9077 @kindex show output-radix
9078 @item show output-radix
9079 Display the current default base for numeric display.
9082 @node Messages/Warnings, , Numbers, Controlling GDB
9083 @section Optional warnings and messages
9085 By default, @value{GDBN} is silent about its inner workings. If you are running
9086 on a slow machine, you may want to use the @code{set verbose} command.
9087 This makes @value{GDBN} tell you when it does a lengthy internal operation, so
9088 you will not think it has crashed.
9090 Currently, the messages controlled by @code{set verbose} are those
9091 which announce that the symbol table for a source file is being read;
9092 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
9096 @item set verbose on
9097 Enables @value{GDBN} output of certain informational messages.
9099 @item set verbose off
9100 Disables @value{GDBN} output of certain informational messages.
9102 @kindex show verbose
9104 Displays whether @code{set verbose} is on or off.
9107 By default, if @value{GDBN} encounters bugs in the symbol table of an object
9108 file, it is silent; but if you are debugging a compiler, you may find
9109 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
9112 @kindex set complaints
9113 @item set complaints @var{limit}
9114 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
9115 symbols before becoming silent about the problem. Set @var{limit} to
9116 zero to suppress all complaints; set it to a large number to prevent
9117 complaints from being suppressed.
9119 @kindex show complaints
9120 @item show complaints
9121 Displays how many symbol complaints @value{GDBN} is permitted to produce.
9124 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
9125 lot of stupid questions to confirm certain commands. For example, if
9126 you try to run a program which is already running:
9130 The program being debugged has been started already.
9131 Start it from the beginning? (y or n)
9134 If you are willing to unflinchingly face the consequences of your own
9135 commands, you can disable this ``feature'':
9140 @cindex confirmation
9141 @cindex stupid questions
9142 @item set confirm off
9143 Disables confirmation requests.
9145 @item set confirm on
9146 Enables confirmation requests (the default).
9148 @kindex show confirm
9150 Displays state of confirmation requests.
9153 @node Sequences, Emacs, Controlling GDB, Top
9154 @chapter Canned Sequences of Commands
9156 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
9157 command lists}), @value{GDBN} provides two ways to store sequences of commands
9158 for execution as a unit: user-defined commands and command files.
9161 * Define:: User-defined commands
9162 * Hooks:: User-defined command hooks
9163 * Command Files:: Command files
9164 * Output:: Commands for controlled output
9167 @node Define, Hooks, Sequences, Sequences
9168 @section User-defined commands
9170 @cindex user-defined command
9171 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which
9172 you assign a new name as a command. This is done with the @code{define}
9173 command. User commands may accept up to 10 arguments separated by whitespace.
9174 Arguments are accessed within the user command via @var{$arg0@dots{}$arg9}.
9179 print $arg0 + $arg1 + $arg2
9182 @noindent To execute the command use:
9188 @noindent This defines the command @code{adder}, which prints the sum of
9189 its three arguments. Note the arguments are text substitutions, so they may
9190 reference variables, use complex expressions, or even perform inferior
9195 @item define @var{commandname}
9196 Define a command named @var{commandname}. If there is already a command
9197 by that name, you are asked to confirm that you want to redefine it.
9199 The definition of the command is made up of other @value{GDBN} command lines,
9200 which are given following the @code{define} command. The end of these
9201 commands is marked by a line containing @code{end}.
9206 Takes a single argument, which is an expression to evaluate.
9207 It is followed by a series of commands that are executed
9208 only if the expression is true (nonzero).
9209 There can then optionally be a line @code{else}, followed
9210 by a series of commands that are only executed if the expression
9211 was false. The end of the list is marked by a line containing @code{end}.
9215 The syntax is similar to @code{if}: the command takes a single argument,
9216 which is an expression to evaluate, and must be followed by the commands to
9217 execute, one per line, terminated by an @code{end}.
9218 The commands are executed repeatedly as long as the expression
9222 @item document @var{commandname}
9223 Document the user-defined command @var{commandname}, so that it can be
9224 accessed by @code{help}. The command @var{commandname} must already be
9225 defined. This command reads lines of documentation just as @code{define}
9226 reads the lines of the command definition, ending with @code{end}.
9227 After the @code{document} command is finished, @code{help} on command
9228 @var{commandname} displays the documentation you have written.
9230 You may use the @code{document} command again to change the
9231 documentation of a command. Redefining the command with @code{define}
9232 does not change the documentation.
9234 @kindex help user-defined
9235 @item help user-defined
9236 List all user-defined commands, with the first line of the documentation
9241 @itemx show user @var{commandname}
9242 Display the @value{GDBN} commands used to define @var{commandname} (but not its
9243 documentation). If no @var{commandname} is given, display the
9244 definitions for all user-defined commands.
9247 When user-defined commands are executed, the
9248 commands of the definition are not printed. An error in any command
9249 stops execution of the user-defined command.
9251 If used interactively, commands that would ask for confirmation proceed
9252 without asking when used inside a user-defined command. Many @value{GDBN}
9253 commands that normally print messages to say what they are doing omit the
9254 messages when used in a user-defined command.
9256 @node Hooks, Command Files, Define, Sequences
9257 @section User-defined command hooks
9258 @cindex command files
9260 You may define @emph{hooks}, which are a special kind of user-defined
9261 command. Whenever you run the command @samp{foo}, if the user-defined
9262 command @samp{hook-foo} exists, it is executed (with no arguments)
9263 before that command.
9265 In addition, a pseudo-command, @samp{stop} exists. Defining
9266 (@samp{hook-stop}) makes the associated commands execute every time
9267 execution stops in your program: before breakpoint commands are run,
9268 displays are printed, or the stack frame is printed.
9270 For example, to ignore @code{SIGALRM} signals while
9271 single-stepping, but treat them normally during normal execution,
9276 handle SIGALRM nopass
9283 define hook-continue
9288 You can define a hook for any single-word command in @value{GDBN}, but
9289 not for command aliases; you should define a hook for the basic command
9290 name, e.g. @code{backtrace} rather than @code{bt}.
9291 @c FIXME! So how does Joe User discover whether a command is an alias
9293 If an error occurs during the execution of your hook, execution of
9294 @value{GDBN} commands stops and @value{GDBN} issues a prompt
9295 (before the command that you actually typed had a chance to run).
9297 If you try to define a hook which does not match any known command, you
9298 get a warning from the @code{define} command.
9300 @node Command Files, Output, Hooks, Sequences
9301 @section Command files
9303 @cindex command files
9304 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
9305 commands. Comments (lines starting with @kbd{#}) may also be included.
9306 An empty line in a command file does nothing; it does not mean to repeat
9307 the last command, as it would from the terminal.
9310 @cindex @file{.gdbinit}
9311 When you start @value{GDBN}, it automatically executes commands from its
9312 @dfn{init files}. These are files named @file{.gdbinit} on Unix, or
9313 @file{gdb.ini} on DOS/Windows. @value{GDBN} reads the init file (if
9314 any) in your home directory, then processes command line options and
9315 operands, and then reads the init file (if any) in the current working
9316 directory. This is so the init file in your home directory can set
9317 options (such as @code{set complaints}) which affect the processing of
9318 the command line options and operands. The init files are not executed
9319 if you use the @samp{-nx} option; @pxref{Mode Options, ,Choosing modes}.
9321 @cindex init file name
9322 On some configurations of @value{GDBN}, the init file is known by a
9323 different name (these are typically environments where a specialized
9324 form of @value{GDBN} may need to coexist with other forms, hence a
9325 different name for the specialized version's init file). These are the
9326 environments with special init file names:
9331 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
9333 @kindex .os68gdbinit
9335 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
9339 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
9342 You can also request the execution of a command file with the
9343 @code{source} command:
9347 @item source @var{filename}
9348 Execute the command file @var{filename}.
9351 The lines in a command file are executed sequentially. They are not
9352 printed as they are executed. An error in any command terminates execution
9353 of the command file.
9355 Commands that would ask for confirmation if used interactively proceed
9356 without asking when used in a command file. Many @value{GDBN} commands that
9357 normally print messages to say what they are doing omit the messages
9358 when called from command files.
9360 @node Output, , Command Files, Sequences
9361 @section Commands for controlled output
9363 During the execution of a command file or a user-defined command, normal
9364 @value{GDBN} output is suppressed; the only output that appears is what is
9365 explicitly printed by the commands in the definition. This section
9366 describes three commands useful for generating exactly the output you
9371 @item echo @var{text}
9372 @c I do not consider backslash-space a standard C escape sequence
9373 @c because it is not in ANSI.
9374 Print @var{text}. Nonprinting characters can be included in
9375 @var{text} using C escape sequences, such as @samp{\n} to print a
9376 newline. @strong{No newline is printed unless you specify one.}
9377 In addition to the standard C escape sequences, a backslash followed
9378 by a space stands for a space. This is useful for displaying a
9379 string with spaces at the beginning or the end, since leading and
9380 trailing spaces are otherwise trimmed from all arguments.
9381 To print @samp{@w{ }and foo =@w{ }}, use the command
9382 @samp{echo \@w{ }and foo = \@w{ }}.
9384 A backslash at the end of @var{text} can be used, as in C, to continue
9385 the command onto subsequent lines. For example,
9388 echo This is some text\n\
9389 which is continued\n\
9390 onto several lines.\n
9393 produces the same output as
9396 echo This is some text\n
9397 echo which is continued\n
9398 echo onto several lines.\n
9402 @item output @var{expression}
9403 Print the value of @var{expression} and nothing but that value: no
9404 newlines, no @samp{$@var{nn} = }. The value is not entered in the
9405 value history either. @xref{Expressions, ,Expressions}, for more information
9408 @item output/@var{fmt} @var{expression}
9409 Print the value of @var{expression} in format @var{fmt}. You can use
9410 the same formats as for @code{print}. @xref{Output Formats,,Output
9411 formats}, for more information.
9414 @item printf @var{string}, @var{expressions}@dots{}
9415 Print the values of the @var{expressions} under the control of
9416 @var{string}. The @var{expressions} are separated by commas and may be
9417 either numbers or pointers. Their values are printed as specified by
9418 @var{string}, exactly as if your program were to execute the C
9422 printf (@var{string}, @var{expressions}@dots{});
9425 For example, you can print two values in hex like this:
9428 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
9431 The only backslash-escape sequences that you can use in the format
9432 string are the simple ones that consist of backslash followed by a
9436 @node Emacs, GDB Bugs, Sequences, Top
9437 @chapter Using @value{GDBN} under @sc{gnu} Emacs
9440 @cindex @sc{gnu} Emacs
9441 A special interface allows you to use @sc{gnu} Emacs to view (and
9442 edit) the source files for the program you are debugging with
9445 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
9446 executable file you want to debug as an argument. This command starts
9447 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
9448 created Emacs buffer.
9450 (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
9453 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
9458 All ``terminal'' input and output goes through the Emacs buffer.
9461 This applies both to @value{GDBN} commands and their output, and to the input
9462 and output done by the program you are debugging.
9464 This is useful because it means that you can copy the text of previous
9465 commands and input them again; you can even use parts of the output
9468 All the facilities of Emacs' Shell mode are available for interacting
9469 with your program. In particular, you can send signals the usual
9470 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
9475 @value{GDBN} displays source code through Emacs.
9478 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
9479 source file for that frame and puts an arrow (@samp{=>}) at the
9480 left margin of the current line. Emacs uses a separate buffer for
9481 source display, and splits the screen to show both your @value{GDBN} session
9484 Explicit @value{GDBN} @code{list} or search commands still produce output as
9485 usual, but you probably have no reason to use them from Emacs.
9488 @emph{Warning:} If the directory where your program resides is not your
9489 current directory, it can be easy to confuse Emacs about the location of
9490 the source files, in which case the auxiliary display buffer does not
9491 appear to show your source. @value{GDBN} can find programs by searching your
9492 environment's @code{PATH} variable, so the @value{GDBN} input and output
9493 session proceeds normally; but Emacs does not get enough information
9494 back from @value{GDBN} to locate the source files in this situation. To
9495 avoid this problem, either start @value{GDBN} mode from the directory where
9496 your program resides, or specify an absolute file name when prompted for the
9497 @kbd{M-x gdb} argument.
9499 A similar confusion can result if you use the @value{GDBN} @code{file} command to
9500 switch to debugging a program in some other location, from an existing
9501 @value{GDBN} buffer in Emacs.
9504 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
9505 you need to call @value{GDBN} by a different name (for example, if you keep
9506 several configurations around, with different names) you can set the
9507 Emacs variable @code{gdb-command-name}; for example,
9510 (setq gdb-command-name "mygdb")
9514 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
9515 in your @file{.emacs} file) makes Emacs call the program named
9516 ``@code{mygdb}'' instead.
9518 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
9519 addition to the standard Shell mode commands:
9523 Describe the features of Emacs' @value{GDBN} Mode.
9526 Execute to another source line, like the @value{GDBN} @code{step} command; also
9527 update the display window to show the current file and location.
9530 Execute to next source line in this function, skipping all function
9531 calls, like the @value{GDBN} @code{next} command. Then update the display window
9532 to show the current file and location.
9535 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
9536 display window accordingly.
9539 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
9540 display window accordingly.
9543 Execute until exit from the selected stack frame, like the @value{GDBN}
9544 @code{finish} command.
9547 Continue execution of your program, like the @value{GDBN} @code{continue}
9550 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
9553 Go up the number of frames indicated by the numeric argument
9554 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
9555 like the @value{GDBN} @code{up} command.
9557 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
9560 Go down the number of frames indicated by the numeric argument, like the
9561 @value{GDBN} @code{down} command.
9563 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
9566 Read the number where the cursor is positioned, and insert it at the end
9567 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
9568 around an address that was displayed earlier, type @kbd{disassemble};
9569 then move the cursor to the address display, and pick up the
9570 argument for @code{disassemble} by typing @kbd{C-x &}.
9572 You can customize this further by defining elements of the list
9573 @code{gdb-print-command}; once it is defined, you can format or
9574 otherwise process numbers picked up by @kbd{C-x &} before they are
9575 inserted. A numeric argument to @kbd{C-x &} indicates that you
9576 wish special formatting, and also acts as an index to pick an element of the
9577 list. If the list element is a string, the number to be inserted is
9578 formatted using the Emacs function @code{format}; otherwise the number
9579 is passed as an argument to the corresponding list element.
9582 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
9583 tells @value{GDBN} to set a breakpoint on the source line point is on.
9585 If you accidentally delete the source-display buffer, an easy way to get
9586 it back is to type the command @code{f} in the @value{GDBN} buffer, to
9587 request a frame display; when you run under Emacs, this recreates
9588 the source buffer if necessary to show you the context of the current
9591 The source files displayed in Emacs are in ordinary Emacs buffers
9592 which are visiting the source files in the usual way. You can edit
9593 the files with these buffers if you wish; but keep in mind that @value{GDBN}
9594 communicates with Emacs in terms of line numbers. If you add or
9595 delete lines from the text, the line numbers that @value{GDBN} knows cease
9596 to correspond properly with the code.
9598 @c The following dropped because Epoch is nonstandard. Reactivate
9599 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
9601 @kindex Emacs Epoch environment
9605 Version 18 of @sc{gnu} Emacs has a built-in window system
9606 called the @code{epoch}
9607 environment. Users of this environment can use a new command,
9608 @code{inspect} which performs identically to @code{print} except that
9609 each value is printed in its own window.
9613 @c links whacked to pacify makeinfo
9614 @c , Command Line Editing, Emacs, Top
9615 @chapter Reporting Bugs in @value{GDBN}
9616 @cindex bugs in @value{GDBN}
9617 @cindex reporting bugs in @value{GDBN}
9619 Your bug reports play an essential role in making @value{GDBN} reliable.
9621 Reporting a bug may help you by bringing a solution to your problem, or it
9622 may not. But in any case the principal function of a bug report is to help
9623 the entire community by making the next version of @value{GDBN} work better. Bug
9624 reports are your contribution to the maintenance of @value{GDBN}.
9626 In order for a bug report to serve its purpose, you must include the
9627 information that enables us to fix the bug.
9630 * Bug Criteria:: Have you found a bug?
9631 * Bug Reporting:: How to report bugs
9634 @node Bug Criteria, Bug Reporting, GDB Bugs, GDB Bugs
9635 @section Have you found a bug?
9636 @cindex bug criteria
9638 If you are not sure whether you have found a bug, here are some guidelines:
9641 @cindex fatal signal
9642 @cindex debugger crash
9643 @cindex crash of debugger
9645 If the debugger gets a fatal signal, for any input whatever, that is a
9646 @value{GDBN} bug. Reliable debuggers never crash.
9648 @cindex error on valid input
9650 If @value{GDBN} produces an error message for valid input, that is a
9651 bug. (Note that if you're cross debugging, the problem may also be
9652 somewhere in the connection to the target.)
9654 @cindex invalid input
9656 If @value{GDBN} does not produce an error message for invalid input,
9657 that is a bug. However, you should note that your idea of
9658 ``invalid input'' might be our idea of ``an extension'' or ``support
9659 for traditional practice''.
9662 If you are an experienced user of debugging tools, your suggestions
9663 for improvement of @value{GDBN} are welcome in any case.
9666 @node Bug Reporting, , Bug Criteria, GDB Bugs
9667 @section How to report bugs
9669 @cindex @value{GDBN} bugs, reporting
9672 A number of companies and individuals offer support for @sc{gnu} products.
9673 If you obtained @value{GDBN} from a support organization, we recommend you
9674 contact that organization first.
9676 You can find contact information for many support companies and
9677 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
9679 @c should add a web page ref...
9681 In any event, we also recommend that you send bug reports for
9682 @value{GDBN} to this addresses:
9685 bug-gdb@@prep.ai.mit.edu
9688 @strong{Do not send bug reports to @samp{info-gdb}, or to
9689 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
9690 not want to receive bug reports. Those that do have arranged to receive
9693 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
9694 serves as a repeater. The mailing list and the newsgroup carry exactly
9695 the same messages. Often people think of posting bug reports to the
9696 newsgroup instead of mailing them. This appears to work, but it has one
9697 problem which can be crucial: a newsgroup posting often lacks a mail
9698 path back to the sender. Thus, if we need to ask for more information,
9699 we may be unable to reach you. For this reason, it is better to send
9700 bug reports to the mailing list.
9702 As a last resort, send bug reports on paper to:
9705 @sc{gnu} Debugger Bugs
9706 Free Software Foundation Inc.
9707 59 Temple Place - Suite 330
9708 Boston, MA 02111-1307
9714 If you obtained HP GDB as part of your HP ANSI C or HP ANSI C++ compiler
9715 kit, report problems to your HP Support Representative.
9717 If you obtained HP GDB from the Hewlett-Packard Web site, report
9718 problems by electronic mail to @code{wdb-www@@ch.hp.com}.
9721 The fundamental principle of reporting bugs usefully is this:
9722 @strong{report all the facts}. If you are not sure whether to state a
9723 fact or leave it out, state it!
9725 Often people omit facts because they think they know what causes the
9726 problem and assume that some details do not matter. Thus, you might
9727 assume that the name of the variable you use in an example does not matter.
9728 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
9729 stray memory reference which happens to fetch from the location where that
9730 name is stored in memory; perhaps, if the name were different, the contents
9731 of that location would fool the debugger into doing the right thing despite
9732 the bug. Play it safe and give a specific, complete example. That is the
9733 easiest thing for you to do, and the most helpful.
9735 Keep in mind that the purpose of a bug report is to enable us to fix the
9736 bug. It may be that the bug has been reported previously, but neither
9737 you nor we can know that unless your bug report is complete and
9740 Sometimes people give a few sketchy facts and ask, ``Does this ring a
9741 bell?'' Those bug reports are useless, and we urge everyone to
9742 @emph{refuse to respond to them} except to chide the sender to report
9745 To enable us to fix the bug, you should include all these things:
9749 The version of @value{GDBN}. @value{GDBN} announces it if you start
9750 with no arguments; you can also print it at any time using @code{show
9753 Without this, we will not know whether there is any point in looking for
9754 the bug in the current version of @value{GDBN}.
9757 The type of machine you are using, and the operating system name and
9762 What compiler (and its version) was used to compile @value{GDBN}---e.g.
9763 ``@value{GCC}--2.8.1''.
9767 What compiler (and its version) was used to compile the program you are
9768 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
9769 C Compiler''. For GCC, you can say @code{gcc --version} to get this
9770 information; for other compilers, see the documentation for those
9774 The command arguments you gave the compiler to compile your example and
9775 observe the bug. For example, did you use @samp{-O}? To guarantee
9776 you will not omit something important, list them all. A copy of the
9777 Makefile (or the output from make) is sufficient.
9779 If we were to try to guess the arguments, we would probably guess wrong
9780 and then we might not encounter the bug.
9783 A complete input script, and all necessary source files, that will
9787 A description of what behavior you observe that you believe is
9788 incorrect. For example, ``It gets a fatal signal.''
9790 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
9791 will certainly notice it. But if the bug is incorrect output, we might
9792 not notice unless it is glaringly wrong. You might as well not give us
9793 a chance to make a mistake.
9795 Even if the problem you experience is a fatal signal, you should still
9796 say so explicitly. Suppose something strange is going on, such as, your
9797 copy of @value{GDBN} is out of synch, or you have encountered a bug in
9798 the C library on your system. (This has happened!) Your copy might
9799 crash and ours would not. If you told us to expect a crash, then when
9800 ours fails to crash, we would know that the bug was not happening for
9801 us. If you had not told us to expect a crash, then we would not be able
9802 to draw any conclusion from our observations.
9806 If you wish to suggest changes to the @value{GDBN} source, send us context
9807 diffs. If you even discuss something in the @value{GDBN} source, refer to
9808 it by context, not by line number.
9810 The line numbers in our development sources will not match those in your
9811 sources. Your line numbers would convey no useful information to us.
9815 Here are some things that are not necessary:
9819 A description of the envelope of the bug.
9821 Often people who encounter a bug spend a lot of time investigating
9822 which changes to the input file will make the bug go away and which
9823 changes will not affect it.
9825 This is often time consuming and not very useful, because the way we
9826 will find the bug is by running a single example under the debugger
9827 with breakpoints, not by pure deduction from a series of examples.
9828 We recommend that you save your time for something else.
9830 Of course, if you can find a simpler example to report @emph{instead}
9831 of the original one, that is a convenience for us. Errors in the
9832 output will be easier to spot, running under the debugger will take
9833 less time, and so on.
9835 However, simplification is not vital; if you do not want to do this,
9836 report the bug anyway and send us the entire test case you used.
9839 A patch for the bug.
9841 A patch for the bug does help us if it is a good one. But do not omit
9842 the necessary information, such as the test case, on the assumption that
9843 a patch is all we need. We might see problems with your patch and decide
9844 to fix the problem another way, or we might not understand it at all.
9846 Sometimes with a program as complicated as @value{GDBN} it is very hard to
9847 construct an example that will make the program follow a certain path
9848 through the code. If you do not send us the example, we will not be able
9849 to construct one, so we will not be able to verify that the bug is fixed.
9851 And if we cannot understand what bug you are trying to fix, or why your
9852 patch should be an improvement, we will not install it. A test case will
9853 help us to understand.
9856 A guess about what the bug is or what it depends on.
9858 Such guesses are usually wrong. Even we cannot guess right about such
9859 things without first using the debugger to find the facts.
9862 @c The readline documentation is distributed with the readline code
9863 @c and consists of the two following files:
9866 @c Use -I with makeinfo to point to the appropriate directory,
9867 @c environment var TEXINPUTS with TeX.
9868 @include rluser.texinfo
9869 @include inc-hist.texinfo
9872 @ifclear PRECONFIGURED
9874 @node Formatting Documentation
9875 @c links whacked to pacify makeinfo
9876 @c , Installing GDB, Renamed Commands, Top
9877 @appendix Formatting Documentation
9879 @cindex @value{GDBN} reference card
9880 @cindex reference card
9881 The @value{GDBN} 4 release includes an already-formatted reference card, ready
9882 for printing with PostScript or Ghostscript, in the @file{gdb}
9883 subdirectory of the main source directory@footnote{In
9884 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
9885 release.}. If you can use PostScript or Ghostscript with your printer,
9886 you can print the reference card immediately with @file{refcard.ps}.
9888 The release also includes the source for the reference card. You
9889 can format it, using @TeX{}, by typing:
9895 The @value{GDBN} reference card is designed to print in @dfn{landscape}
9896 mode on US ``letter'' size paper;
9897 that is, on a sheet 11 inches wide by 8.5 inches
9898 high. You will need to specify this form of printing as an option to
9899 your @sc{dvi} output program.
9901 @cindex documentation
9903 All the documentation for @value{GDBN} comes as part of the machine-readable
9904 distribution. The documentation is written in Texinfo format, which is
9905 a documentation system that uses a single source file to produce both
9906 on-line information and a printed manual. You can use one of the Info
9907 formatting commands to create the on-line version of the documentation
9908 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
9910 @value{GDBN} includes an already formatted copy of the on-line Info
9911 version of this manual in the @file{gdb} subdirectory. The main Info
9912 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
9913 subordinate files matching @samp{gdb.info*} in the same directory. If
9914 necessary, you can print out these files, or read them with any editor;
9915 but they are easier to read using the @code{info} subsystem in @sc{gnu}
9916 Emacs or the standalone @code{info} program, available as part of the
9917 @sc{gnu} Texinfo distribution.
9919 If you want to format these Info files yourself, you need one of the
9920 Info formatting programs, such as @code{texinfo-format-buffer} or
9923 If you have @code{makeinfo} installed, and are in the top level
9924 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
9925 version @value{GDBVN}), you can make the Info file by typing:
9932 If you want to typeset and print copies of this manual, you need @TeX{},
9933 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
9934 Texinfo definitions file.
9936 @TeX{} is a typesetting program; it does not print files directly, but
9937 produces output files called @sc{dvi} files. To print a typeset
9938 document, you need a program to print @sc{dvi} files. If your system
9939 has @TeX{} installed, chances are it has such a program. The precise
9940 command to use depends on your system; @kbd{lpr -d} is common; another
9941 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
9942 require a file name without any extension or a @samp{.dvi} extension.
9944 @TeX{} also requires a macro definitions file called
9945 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
9946 written in Texinfo format. On its own, @TeX{} cannot either read or
9947 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
9948 and is located in the @file{gdb-@var{version-number}/texinfo}
9951 If you have @TeX{} and a @sc{dvi} printer program installed, you can
9952 typeset and print this manual. First switch to the the @file{gdb}
9953 subdirectory of the main source directory (for example, to
9954 @file{gdb-@value{GDBVN}/gdb}) and type:
9960 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
9963 @node Installing GDB, Index, Using History Interactively, Top
9964 @appendix Installing @value{GDBN}
9965 @cindex configuring @value{GDBN}
9966 @cindex installation
9969 If you obtain @value{GDBN} (HP WDB 0.75) as part of your HP ANSI C or
9970 HP ANSI C++ Developer's Kit at HP-UX Release 11.0, you do not have to
9971 take any special action to build or install @value{GDBN}.
9973 If you obtain @value{GDBN} (HP WDB 0.75) from an HP web site, you may
9974 download either a @code{swinstall}-able package or a source tree, or
9977 Most customers will want to install the @value{GDBN} binary that is part
9978 of the @code{swinstall}-able package. To do so, use a command of the
9982 /usr/sbin/swinstall -s @var{package-name} WDB
9985 Alternatively, it is possible to build @value{GDBN} from the source
9986 distribution. Sophisticated customers who want to modify the debugger
9987 sources to tailor @value{GDBN} to their their needs may wish to do this.
9988 The source distribution consists of a @code{tar}'ed source tree rooted
9989 at @file{gdb-4.16/...}. The instructions that follow describe how to
9990 build a @file{gdb} executable from this source tree. HP believes that
9991 these instructions apply to the WDB source tree that it distributes.
9992 However, HP does not explicitly support building a @file{gdb} for any
9993 non-HP platform from the WDB source tree. It may work, but HP has not
9994 tested it for any platforms other than those described in the WDB 0.75
9998 @value{GDBN} comes with a @code{configure} script that automates the process
9999 of preparing @value{GDBN} for installation; you can then use @code{make} to
10000 build the @code{gdb} program.
10002 @c irrelevant in info file; it's as current as the code it lives with.
10003 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
10004 look at the @file{README} file in the sources; we may have improved the
10005 installation procedures since publishing this manual.}
10008 The @value{GDBN} distribution includes all the source code you need for
10009 @value{GDBN} in a single directory, whose name is usually composed by
10010 appending the version number to @samp{gdb}.
10012 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
10013 @file{gdb-@value{GDBVN}} directory. That directory contains:
10016 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
10017 script for configuring @value{GDBN} and all its supporting libraries
10019 @item gdb-@value{GDBVN}/gdb
10020 the source specific to @value{GDBN} itself
10022 @item gdb-@value{GDBVN}/bfd
10023 source for the Binary File Descriptor library
10025 @item gdb-@value{GDBVN}/include
10026 @sc{gnu} include files
10028 @item gdb-@value{GDBVN}/libiberty
10029 source for the @samp{-liberty} free software library
10031 @item gdb-@value{GDBVN}/opcodes
10032 source for the library of opcode tables and disassemblers
10034 @item gdb-@value{GDBVN}/readline
10035 source for the @sc{gnu} command-line interface
10037 @item gdb-@value{GDBVN}/glob
10038 source for the @sc{gnu} filename pattern-matching subroutine
10040 @item gdb-@value{GDBVN}/mmalloc
10041 source for the @sc{gnu} memory-mapped malloc package
10044 The simplest way to configure and build @value{GDBN} is to run @code{configure}
10045 from the @file{gdb-@var{version-number}} source directory, which in
10046 this example is the @file{gdb-@value{GDBVN}} directory.
10048 First switch to the @file{gdb-@var{version-number}} source directory
10049 if you are not already in it; then run @code{configure}. Pass the
10050 identifier for the platform on which @value{GDBN} will run as an
10056 cd gdb-@value{GDBVN}
10057 ./configure @var{host}
10062 where @var{host} is an identifier such as @samp{sun4} or
10063 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
10064 (You can often leave off @var{host}; @code{configure} tries to guess the
10065 correct value by examining your system.)
10067 Running @samp{configure @var{host}} and then running @code{make} builds the
10068 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
10069 libraries, then @code{gdb} itself. The configured source files, and the
10070 binaries, are left in the corresponding source directories.
10073 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
10074 system does not recognize this automatically when you run a different
10075 shell, you may need to run @code{sh} on it explicitly:
10078 sh configure @var{host}
10081 If you run @code{configure} from a directory that contains source
10082 directories for multiple libraries or programs, such as the
10083 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
10084 creates configuration files for every directory level underneath (unless
10085 you tell it not to, with the @samp{--norecursion} option).
10087 You can run the @code{configure} script from any of the
10088 subordinate directories in the @value{GDBN} distribution if you only want to
10089 configure that subdirectory, but be sure to specify a path to it.
10091 For example, with version @value{GDBVN}, type the following to configure only
10092 the @code{bfd} subdirectory:
10096 cd gdb-@value{GDBVN}/bfd
10097 ../configure @var{host}
10101 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
10102 However, you should make sure that the shell on your path (named by
10103 the @samp{SHELL} environment variable) is publicly readable. Remember
10104 that @value{GDBN} uses the shell to start your program---some systems refuse to
10105 let @value{GDBN} debug child processes whose programs are not readable.
10108 * Separate Objdir:: Compiling @value{GDBN} in another directory
10109 * Config Names:: Specifying names for hosts and targets
10110 * Configure Options:: Summary of options for configure
10113 @node Separate Objdir, Config Names, Installing GDB, Installing GDB
10114 @section Compiling @value{GDBN} in another directory
10116 If you want to run @value{GDBN} versions for several host or target machines,
10117 you need a different @code{gdb} compiled for each combination of
10118 host and target. @code{configure} is designed to make this easy by
10119 allowing you to generate each configuration in a separate subdirectory,
10120 rather than in the source directory. If your @code{make} program
10121 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
10122 @code{make} in each of these directories builds the @code{gdb}
10123 program specified there.
10125 To build @code{gdb} in a separate directory, run @code{configure}
10126 with the @samp{--srcdir} option to specify where to find the source.
10127 (You also need to specify a path to find @code{configure}
10128 itself from your working directory. If the path to @code{configure}
10129 would be the same as the argument to @samp{--srcdir}, you can leave out
10130 the @samp{--srcdir} option; it is assumed.)
10132 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
10133 separate directory for a Sun 4 like this:
10137 cd gdb-@value{GDBVN}
10140 ../gdb-@value{GDBVN}/configure sun4
10145 When @code{configure} builds a configuration using a remote source
10146 directory, it creates a tree for the binaries with the same structure
10147 (and using the same names) as the tree under the source directory. In
10148 the example, you'd find the Sun 4 library @file{libiberty.a} in the
10149 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
10150 @file{gdb-sun4/gdb}.
10152 One popular reason to build several @value{GDBN} configurations in separate
10153 directories is to configure @value{GDBN} for cross-compiling (where
10154 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
10155 programs that run on another machine---the @dfn{target}).
10156 You specify a cross-debugging target by
10157 giving the @samp{--target=@var{target}} option to @code{configure}.
10159 When you run @code{make} to build a program or library, you must run
10160 it in a configured directory---whatever directory you were in when you
10161 called @code{configure} (or one of its subdirectories).
10163 The @code{Makefile} that @code{configure} generates in each source
10164 directory also runs recursively. If you type @code{make} in a source
10165 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
10166 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
10167 will build all the required libraries, and then build GDB.
10169 When you have multiple hosts or targets configured in separate
10170 directories, you can run @code{make} on them in parallel (for example,
10171 if they are NFS-mounted on each of the hosts); they will not interfere
10174 @node Config Names, Configure Options, Separate Objdir, Installing GDB
10175 @section Specifying names for hosts and targets
10177 The specifications used for hosts and targets in the @code{configure}
10178 script are based on a three-part naming scheme, but some short predefined
10179 aliases are also supported. The full naming scheme encodes three pieces
10180 of information in the following pattern:
10183 @var{architecture}-@var{vendor}-@var{os}
10186 For example, you can use the alias @code{sun4} as a @var{host} argument,
10187 or as the value for @var{target} in a @code{--target=@var{target}}
10188 option. The equivalent full name is @samp{sparc-sun-sunos4}.
10190 The @code{configure} script accompanying @value{GDBN} does not provide
10191 any query facility to list all supported host and target names or
10192 aliases. @code{configure} calls the Bourne shell script
10193 @code{config.sub} to map abbreviations to full names; you can read the
10194 script, if you wish, or you can use it to test your guesses on
10195 abbreviations---for example:
10198 % sh config.sub i386-linux
10200 % sh config.sub alpha-linux
10201 alpha-unknown-linux-gnu
10202 % sh config.sub hp9k700
10204 % sh config.sub sun4
10205 sparc-sun-sunos4.1.1
10206 % sh config.sub sun3
10207 m68k-sun-sunos4.1.1
10208 % sh config.sub i986v
10209 Invalid configuration `i986v': machine `i986v' not recognized
10213 @code{config.sub} is also distributed in the @value{GDBN} source
10214 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
10216 @node Configure Options, , Config Names, Installing GDB
10217 @section @code{configure} options
10219 Here is a summary of the @code{configure} options and arguments that
10220 are most often useful for building @value{GDBN}. @code{configure} also has
10221 several other options not listed here. @inforef{What Configure
10222 Does,,configure.info}, for a full explanation of @code{configure}.
10225 configure @r{[}--help@r{]}
10226 @r{[}--prefix=@var{dir}@r{]}
10227 @r{[}--exec-prefix=@var{dir}@r{]}
10228 @r{[}--srcdir=@var{dirname}@r{]}
10229 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
10230 @r{[}--target=@var{target}@r{]}
10235 You may introduce options with a single @samp{-} rather than
10236 @samp{--} if you prefer; but you may abbreviate option names if you use
10241 Display a quick summary of how to invoke @code{configure}.
10243 @item --prefix=@var{dir}
10244 Configure the source to install programs and files under directory
10247 @item --exec-prefix=@var{dir}
10248 Configure the source to install programs under directory
10251 @c avoid splitting the warning from the explanation:
10253 @item --srcdir=@var{dirname}
10254 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
10255 @code{make} that implements the @code{VPATH} feature.}@*
10256 Use this option to make configurations in directories separate from the
10257 @value{GDBN} source directories. Among other things, you can use this to
10258 build (or maintain) several configurations simultaneously, in separate
10259 directories. @code{configure} writes configuration specific files in
10260 the current directory, but arranges for them to use the source in the
10261 directory @var{dirname}. @code{configure} creates directories under
10262 the working directory in parallel to the source directories below
10265 @item --norecursion
10266 Configure only the directory level where @code{configure} is executed; do not
10267 propagate configuration to subdirectories.
10269 @item --target=@var{target}
10270 Configure @value{GDBN} for cross-debugging programs running on the specified
10271 @var{target}. Without this option, @value{GDBN} is configured to debug
10272 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
10274 There is no convenient way to generate a list of all available targets.
10276 @item @var{host} @dots{}
10277 Configure @value{GDBN} to run on the specified @var{host}.
10279 There is no convenient way to generate a list of all available hosts.
10282 There are many other options available as well, but they are generally
10283 needed for special purposes only.
10287 @node Index, , Installing GDB, Top
10293 % I think something like @colophon should be in texinfo. In the
10295 \long\def\colophon{\hbox to0pt{}\vfill
10296 \centerline{The body of this manual is set in}
10297 \centerline{\fontname\tenrm,}
10298 \centerline{with headings in {\bf\fontname\tenbf}}
10299 \centerline{and examples in {\tt\fontname\tentt}.}
10300 \centerline{{\it\fontname\tenit\/},}
10301 \centerline{{\bf\fontname\tenbf}, and}
10302 \centerline{{\sl\fontname\tensl\/}}
10303 \centerline{are used for emphasis.}\vfill}
10305 % Blame: doc@cygnus.com, 1991.