1 \input texinfo @c -*-texinfo-*-
2 @c Copyright 1988 1989 1990 1991 1992 1993 1994 1995
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.
13 @settitle Debugging with @value{GDBN}
16 @settitle Debugging with @value{GDBN} (@value{TARGET})
19 @setchapternewpage odd
30 @c readline appendices use @vindex
33 @c !!set GDB manual's edition---not the same as GDB version!
36 @c !!set GDB manual's revision date
37 @set DATE January 1994
39 @c GDB CHANGELOG CONSULTED BETWEEN:
40 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
41 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
43 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
46 @c This is a dir.info fragment to support semi-automated addition of
47 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
50 * Gdb: (gdb). The @sc{gnu} debugger.
57 This file documents the @sc{gnu} debugger @value{GDBN}.
60 This is Edition @value{EDITION}, @value{DATE},
61 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
62 for @value{GDBN} Version @value{GDBVN}.
64 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
65 Free Software Foundation, Inc.
67 Permission is granted to make and distribute verbatim copies of
68 this manual provided the copyright notice and this permission notice
69 are preserved on all copies.
72 Permission is granted to process this file through TeX and print the
73 results, provided the printed document carries copying permission
74 notice identical to this one except for the removal of this paragraph
75 (this paragraph not being relevant to the printed manual).
78 Permission is granted to copy and distribute modified versions of this
79 manual under the conditions for verbatim copying, provided also that the
80 entire resulting derived work is distributed under the terms of a
81 permission notice identical to this one.
83 Permission is granted to copy and distribute translations of this manual
84 into another language, under the above conditions for modified versions.
88 @title Debugging with @value{GDBN}
89 @subtitle The @sc{gnu} Source-Level Debugger
91 @subtitle (@value{TARGET})
94 @subtitle Edition @value{EDITION}, for @value{GDBN} version @value{GDBVN}
95 @subtitle @value{DATE}
96 @author Richard M. Stallman and Roland H. Pesch
100 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
101 \hfill {\it Debugging with @value{GDBN}}\par
102 \hfill \TeX{}info \texinfoversion\par
103 \hfill doc\@cygnus.com\par
107 @vskip 0pt plus 1filll
108 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
109 Free Software Foundation, Inc.
111 Published by the Free Software Foundation @*
112 59 Temple Place - Suite 330, @*
113 Boston, MA 02111-1307 USA @*
114 Printed copies are available for $20 each. @*
115 ISBN 1-882114-11-6 @*
117 Permission is granted to make and distribute verbatim copies of
118 this manual provided the copyright notice and this permission notice
119 are preserved on all copies.
121 Permission is granted to copy and distribute modified versions of this
122 manual under the conditions for verbatim copying, provided also that the
123 entire resulting derived work is distributed under the terms of a
124 permission notice identical to this one.
126 Permission is granted to copy and distribute translations of this manual
127 into another language, under the above conditions for modified versions.
133 @top Debugging with @value{GDBN}
135 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
137 This is Edition @value{EDITION}, @value{DATE}, for @value{GDBN} Version
141 * Summary:: Summary of @value{GDBN}
143 * Sample Session:: A sample @value{GDBN} session
146 * Invocation:: Getting in and out of @value{GDBN}
147 * Commands:: @value{GDBN} commands
148 * Running:: Running programs under @value{GDBN}
149 * Stopping:: Stopping and continuing
150 * Stack:: Examining the stack
151 * Source:: Examining source files
152 * Data:: Examining data
154 * Languages:: Using @value{GDBN} with different languages
157 * C:: C language support
159 @c remnant makeinfo bug, blank line needed after two end-ifs?
161 * Symbols:: Examining the symbol table
162 * Altering:: Altering execution
163 * GDB Files:: @value{GDBN} files
164 * Targets:: Specifying a debugging target
165 * Controlling GDB:: Controlling @value{GDBN}
166 * Sequences:: Canned sequences of commands
168 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
171 * GDB Bugs:: Reporting bugs in @value{GDBN}
172 * Command Line Editing:: Facilities of the readline library
173 * Using History Interactively::
175 @c * Renamed Commands::
177 @ifclear PRECONFIGURED
178 * Formatting Documentation:: How to format and print @value{GDBN} documentation
179 * Installing GDB:: Installing GDB
187 @unnumbered Summary of @value{GDBN}
189 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
190 going on ``inside'' another program while it executes---or what another
191 program was doing at the moment it crashed.
193 @value{GDBN} can do four main kinds of things (plus other things in support of
194 these) to help you catch bugs in the act:
198 Start your program, specifying anything that might affect its behavior.
201 Make your program stop on specified conditions.
204 Examine what has happened, when your program has stopped.
207 Change things in your program, so you can experiment with correcting the
208 effects of one bug and go on to learn about another.
212 You can use @value{GDBN} to debug programs written in C or C++.
213 @c "MOD2" used as a "miscellaneous languages" flag here.
214 @c This is acceptable while there is no real doc for Chill and Pascal.
216 For more information, see @ref{Support,,Supported languages}.
219 For more information, see @ref{C,,C and C++}.
221 Support for Modula-2 and Chill is partial. For information on Modula-2,
222 see @ref{Modula-2,,Modula-2}. There is no further documentation on Chill yet.
224 Debugging Pascal programs which use sets, subranges, file variables, or nested
225 functions does not currently work. @value{GDBN} does not support
226 entering expressions, printing values, or similar features using Pascal syntax.
231 @value{GDBN} can be used to debug programs written in Fortran, although
232 it does not yet support entering expressions, printing values, or
233 similar features using Fortran syntax. It may be necessary to refer to
234 some variables with a trailing underscore.
239 * Free Software:: Freely redistributable software
240 * Contributors:: Contributors to GDB
244 @unnumberedsec Free software
246 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
247 General Public License
248 (GPL). The GPL gives you the freedom to copy or adapt a licensed
249 program---but every person getting a copy also gets with it the
250 freedom to modify that copy (which means that they must get access to
251 the source code), and the freedom to distribute further copies.
252 Typical software companies use copyrights to limit your freedoms; the
253 Free Software Foundation uses the GPL to preserve these freedoms.
255 Fundamentally, the General Public License is a license which says that
256 you have these freedoms and that you cannot take these freedoms away
260 @unnumberedsec Contributors to GDB
262 Richard Stallman was the original author of GDB, and of many other @sc{gnu}
263 programs. Many others have contributed to its development. This
264 section attempts to credit major contributors. One of the virtues of
265 free software is that everyone is free to contribute to it; with
266 regret, we cannot actually acknowledge everyone here. The file
267 @file{ChangeLog} in the @value{GDBN} distribution approximates a blow-by-blow
270 Changes much prior to version 2.0 are lost in the mists of time.
273 @emph{Plea:} Additions to this section are particularly welcome. If you
274 or your friends (or enemies, to be evenhanded) have been unfairly
275 omitted from this list, we would like to add your names!
278 So that they may not regard their long labor as thankless, we
279 particularly thank those who shepherded GDB through major releases:
280 Stan Shebs (release 4.14),
281 Fred Fish (releases 4.13, 4.12, 4.11, 4.10, and 4.9),
282 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4),
283 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
284 Jim Kingdon (releases 3.5, 3.4, and 3.3);
285 and Randy Smith (releases 3.2, 3.1, and 3.0).
286 As major maintainer of @value{GDBN} for some period, each
287 contributed significantly to the structure, stability, and capabilities
288 of the entire debugger.
290 Richard Stallman, assisted at various times by Peter TerMaat, Chris
291 Hanson, and Richard Mlynarik, handled releases through 2.8.
294 Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB,
295 with significant additional contributions from Per Bothner. James
296 Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter
297 TerMaat (who also did much general update work leading to release 3.0).
300 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
301 object-file formats; BFD was a joint project of David V.
302 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
304 David Johnson wrote the original COFF support; Pace Willison did
305 the original support for encapsulated COFF.
307 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
308 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
310 Jean-Daniel Fekete contributed Sun 386i support.
311 Chris Hanson improved the HP9000 support.
312 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
313 David Johnson contributed Encore Umax support.
314 Jyrki Kuoppala contributed Altos 3068 support.
315 Jeff Law contributed HP PA and SOM support.
316 Keith Packard contributed NS32K support.
317 Doug Rabson contributed Acorn Risc Machine support.
318 Bob Rusk contributed Harris Nighthawk CX-UX support.
319 Chris Smith contributed Convex support (and Fortran debugging).
320 Jonathan Stone contributed Pyramid support.
321 Michael Tiemann contributed SPARC support.
322 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
323 Pace Willison contributed Intel 386 support.
324 Jay Vosburgh contributed Symmetry support.
326 Rich Schaefer and Peter Schauer helped with support of SunOS shared
329 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree about
330 several machine instruction sets.
332 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
333 develop remote debugging. Intel Corporation and Wind River Systems
334 contributed remote debugging modules for their products.
336 Brian Fox is the author of the readline libraries providing
337 command-line editing and command history.
339 Andrew Beers of SUNY Buffalo wrote the language-switching code,
341 the Modula-2 support,
343 and contributed the Languages chapter of this manual.
345 Fred Fish wrote most of the support for Unix System Vr4.
347 He also enhanced the command-completion support to cover C++ overloaded
351 Hitachi America, Ltd. sponsored the support for Hitachi microprocessors.
353 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
356 Stu Grossman wrote gdbserver.
358 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
359 nearly innumerable bug fixes and cleanups throughout GDB.
363 @chapter A Sample @value{GDBN} Session
365 You can use this manual at your leisure to read all about @value{GDBN}.
366 However, a handful of commands are enough to get started using the
367 debugger. This chapter illustrates those commands.
370 In this sample session, we emphasize user input like this: @b{input},
371 to make it easier to pick out from the surrounding output.
374 @c FIXME: this example may not be appropriate for some configs, where
375 @c FIXME...primary interest is in remote use.
377 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
378 processor) exhibits the following bug: sometimes, when we change its
379 quote strings from the default, the commands used to capture one macro
380 definition within another stop working. In the following short @code{m4}
381 session, we define a macro @code{foo} which expands to @code{0000}; we
382 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
383 same thing. However, when we change the open quote string to
384 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
385 procedure fails to define a new synonym @code{baz}:
394 @b{define(bar,defn(`foo'))}
398 @b{changequote(<QUOTE>,<UNQUOTE>)}
400 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
403 m4: End of input: 0: fatal error: EOF in string
407 Let us use @value{GDBN} to try to see what is going on.
410 $ @b{@value{GDBP} m4}
411 @c FIXME: this falsifies the exact text played out, to permit smallbook
412 @c FIXME... format to come out better.
413 @value{GDBN} is free software and you are welcome to distribute copies
414 of it under certain conditions; type "show copying" to see
416 There is absolutely no warranty for @value{GDBN}; type "show warranty"
419 @value{GDBN} @value{GDBVN}, Copyright 1995 Free Software Foundation, Inc...
424 @value{GDBN} reads only enough symbol data to know where to find the
425 rest when needed; as a result, the first prompt comes up very quickly.
426 We now tell @value{GDBN} to use a narrower display width than usual, so
427 that examples fit in this manual.
430 (@value{GDBP}) @b{set width 70}
434 We need to see how the @code{m4} built-in @code{changequote} works.
435 Having looked at the source, we know the relevant subroutine is
436 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
437 @code{break} command.
440 (@value{GDBP}) @b{break m4_changequote}
441 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
445 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
446 control; as long as control does not reach the @code{m4_changequote}
447 subroutine, the program runs as usual:
450 (@value{GDBP}) @b{run}
451 Starting program: /work/Editorial/gdb/gnu/m4/m4
459 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
460 suspends execution of @code{m4}, displaying information about the
461 context where it stops.
464 @b{changequote(<QUOTE>,<UNQUOTE>)}
466 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
468 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
472 Now we use the command @code{n} (@code{next}) to advance execution to
473 the next line of the current function.
477 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
482 @code{set_quotes} looks like a promising subroutine. We can go into it
483 by using the command @code{s} (@code{step}) instead of @code{next}.
484 @code{step} goes to the next line to be executed in @emph{any}
485 subroutine, so it steps into @code{set_quotes}.
489 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
491 530 if (lquote != def_lquote)
495 The display that shows the subroutine where @code{m4} is now
496 suspended (and its arguments) is called a stack frame display. It
497 shows a summary of the stack. We can use the @code{backtrace}
498 command (which can also be spelled @code{bt}), to see where we are
499 in the stack as a whole: the @code{backtrace} command displays a
500 stack frame for each active subroutine.
503 (@value{GDBP}) @b{bt}
504 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
506 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
508 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
509 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
511 #4 0x79dc in expand_input () at macro.c:40
512 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
516 We step through a few more lines to see what happens. The first two
517 times, we can use @samp{s}; the next two times we use @code{n} to avoid
518 falling into the @code{xstrdup} subroutine.
522 0x3b5c 532 if (rquote != def_rquote)
524 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
525 def_lquote : xstrdup(lq);
527 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
530 538 len_lquote = strlen(rquote);
534 The last line displayed looks a little odd; we can examine the variables
535 @code{lquote} and @code{rquote} to see if they are in fact the new left
536 and right quotes we specified. We use the command @code{p}
537 (@code{print}) to see their values.
540 (@value{GDBP}) @b{p lquote}
541 $1 = 0x35d40 "<QUOTE>"
542 (@value{GDBP}) @b{p rquote}
543 $2 = 0x35d50 "<UNQUOTE>"
547 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
548 To look at some context, we can display ten lines of source
549 surrounding the current line with the @code{l} (@code{list}) command.
555 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
557 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
560 538 len_lquote = strlen(rquote);
561 539 len_rquote = strlen(lquote);
568 Let us step past the two lines that set @code{len_lquote} and
569 @code{len_rquote}, and then examine the values of those variables.
573 539 len_rquote = strlen(lquote);
576 (@value{GDBP}) @b{p len_lquote}
578 (@value{GDBP}) @b{p len_rquote}
583 That certainly looks wrong, assuming @code{len_lquote} and
584 @code{len_rquote} are meant to be the lengths of @code{lquote} and
585 @code{rquote} respectively. We can set them to better values using
586 the @code{p} command, since it can print the value of
587 any expression---and that expression can include subroutine calls and
591 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
593 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
598 Is that enough to fix the problem of using the new quotes with the
599 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
600 executing with the @code{c} (@code{continue}) command, and then try the
601 example that caused trouble initially:
607 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
614 Success! The new quotes now work just as well as the default ones. The
615 problem seems to have been just the two typos defining the wrong
616 lengths. We allow @code{m4} exit by giving it an EOF as input:
620 Program exited normally.
624 The message @samp{Program exited normally.} is from @value{GDBN}; it
625 indicates @code{m4} has finished executing. We can end our @value{GDBN}
626 session with the @value{GDBN} @code{quit} command.
629 (@value{GDBP}) @b{quit}
634 @chapter Getting In and Out of @value{GDBN}
636 This chapter discusses how to start @value{GDBN}, and how to get out of it.
640 type @samp{@value{GDBP}} to start GDB.
642 type @kbd{quit} or @kbd{C-d} to exit.
646 * Invoking GDB:: How to start @value{GDBN}
647 * Quitting GDB:: How to quit @value{GDBN}
648 * Shell Commands:: How to use shell commands inside @value{GDBN}
652 @section Invoking @value{GDBN}
655 For details on starting up @value{GDBP} as a
656 remote debugger attached to a Hitachi microprocessor, see @ref{Hitachi
657 Remote,,@value{GDBN} and Hitachi Microprocessors}.
660 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
661 @value{GDBN} reads commands from the terminal until you tell it to exit.
663 You can also run @code{@value{GDBP}} with a variety of arguments and options,
664 to specify more of your debugging environment at the outset.
667 The command-line options described here are designed
668 to cover a variety of situations; in some environments, some of these
669 options may effectively be unavailable.
672 The most usual way to start @value{GDBN} is with one argument,
673 specifying an executable program:
676 @value{GDBP} @var{program}
681 You can also start with both an executable program and a core file
685 @value{GDBP} @var{program} @var{core}
688 You can, instead, specify a process ID as a second argument, if you want
689 to debug a running process:
692 @value{GDBP} @var{program} 1234
696 would attach @value{GDBN} to process @code{1234} (unless you also have a file
697 named @file{1234}; @value{GDBN} does check for a core file first).
699 Taking advantage of the second command-line argument requires a fairly
700 complete operating system; when you use @value{GDBN} as a remote debugger
701 attached to a bare board, there may not be any notion of ``process'',
702 and there is often no way to get a core dump.
705 You can run @code{gdb} without printing the front material, which describes
706 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
709 @value{GDBP} @var{-silent}
713 You can further control how @value{GDBN} starts up by using command-line
714 options. @value{GDBN} itself can remind you of the options available.
724 to display all available options and briefly describe their use
725 (@samp{@value{GDBP} -h} is a shorter equivalent).
727 All options and command line arguments you give are processed
728 in sequential order. The order makes a difference when the
729 @samp{-x} option is used.
735 * Remote Serial:: @value{GDBN} remote serial protocol
738 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
741 * UDI29K Remote:: The UDI protocol for AMD29K
742 * EB29K Remote:: The EBMON protocol for AMD29K
745 * VxWorks Remote:: @value{GDBN} and VxWorks
748 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
751 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
754 * MIPS Remote:: @value{GDBN} and MIPS boards
757 * Sparclet Remote:: @value{GDBN} and Sparclet boards
760 * Simulator:: Simulated CPU target
763 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
765 * File Options:: Choosing files
766 * Mode Options:: Choosing modes
774 @subsection Choosing files
777 When @value{GDBN} starts, it reads any arguments other than options as
778 specifying an executable file and core file (or process ID). This is
779 the same as if the arguments were specified by the @samp{-se} and
780 @samp{-c} options respectively. (@value{GDBN} reads the first argument
781 that does not have an associated option flag as equivalent to the
782 @samp{-se} option followed by that argument; and the second argument
783 that does not have an associated option flag, if any, as equivalent to
784 the @samp{-c} option followed by that argument.)
787 When @value{GDBN} starts, it reads any argument other than options as
788 specifying an executable file. This is the same as if the argument was
789 specified by the @samp{-se} option.
792 Many options have both long and short forms; both are shown in the
793 following list. @value{GDBN} also recognizes the long forms if you truncate
794 them, so long as enough of the option is present to be unambiguous.
795 (If you prefer, you can flag option arguments with @samp{--} rather
796 than @samp{-}, though we illustrate the more usual convention.)
799 @item -symbols @var{file}
801 Read symbol table from file @var{file}.
803 @item -exec @var{file}
805 Use file @var{file} as the executable file to execute when
810 appropriate, and for examining pure data in conjunction with a core
815 Read symbol table from file @var{file} and use it as the executable
819 @item -core @var{file}
821 Use file @var{file} as a core dump to examine.
823 @item -c @var{number}
824 Connect to process ID @var{number}, as with the @code{attach} command
825 (unless there is a file in core-dump format named @var{number}, in which
826 case @samp{-c} specifies that file as a core dump to read).
829 @item -command @var{file}
831 Execute @value{GDBN} commands from file @var{file}. @xref{Command
832 Files,, Command files}.
834 @item -directory @var{directory}
835 @itemx -d @var{directory}
836 Add @var{directory} to the path to search for source files.
841 @emph{Warning: this option depends on operating system facilities that are not
842 supported on all systems.}@*
843 If memory-mapped files are available on your system through the @code{mmap}
844 system call, you can use this option
845 to have @value{GDBN} write the symbols from your
846 program into a reusable file in the current directory. If the program you are debugging is
847 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
848 Future @value{GDBN} debugging sessions notice the presence of this file,
849 and can quickly map in symbol information from it, rather than reading
850 the symbol table from the executable program.
852 The @file{.syms} file is specific to the host machine where @value{GDBN}
853 is run. It holds an exact image of the internal @value{GDBN} symbol
854 table. It cannot be shared across multiple host platforms.
859 Read each symbol file's entire symbol table immediately, rather than
860 the default, which is to read it incrementally as it is needed.
861 This makes startup slower, but makes future operations faster.
865 The @code{-mapped} and @code{-readnow} options are typically combined in
866 order to build a @file{.syms} file that contains complete symbol
867 information. (@xref{Files,,Commands to specify files}, for information
869 a @file{.syms} file for future use is:
872 gdb -batch -nx -mapped -readnow programname
877 @subsection Choosing modes
879 You can run @value{GDBN} in various alternative modes---for example, in
880 batch mode or quiet mode.
885 Do not execute commands from any initialization files (normally called
886 @file{@value{GDBINIT}}). Normally, the commands in these files are
887 executed after all the command options and arguments have been
888 processed. @xref{Command Files,,Command files}.
892 ``Quiet''. Do not print the introductory and copyright messages. These
893 messages are also suppressed in batch mode.
896 Run in batch mode. Exit with status @code{0} after processing all the
897 command files specified with @samp{-x} (and all commands from
898 initialization files, if not inhibited with @samp{-n}). Exit with
899 nonzero status if an error occurs in executing the @value{GDBN} commands
900 in the command files.
902 Batch mode may be useful for running @value{GDBN} as a filter, for example to
903 download and run a program on another computer; in order to make this
904 more useful, the message
907 Program exited normally.
911 (which is ordinarily issued whenever a program running under @value{GDBN} control
912 terminates) is not issued when running in batch mode.
914 @item -cd @var{directory}
915 Run @value{GDBN} using @var{directory} as its working directory,
916 instead of the current directory.
919 @item -context @var{authentication}
920 When the Energize programming system starts up @value{GDBN}, it uses this
921 option to trigger an alternate mode of interaction.
922 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
923 as a client in the Energize environment. Avoid this option when you run
924 @value{GDBN} directly from the command line. See @ref{Energize,,Using
925 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
931 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
932 to output the full file name and line number in a standard,
933 recognizable fashion each time a stack frame is displayed (which
934 includes each time your program stops). This recognizable format looks
935 like two @samp{\032} characters, followed by the file name, line number
936 and character position separated by colons, and a newline. The
937 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
938 a signal to display the source code for the frame.
943 Set the line speed (baud rate or bits per second) of any serial
944 interface used by @value{GDBN} for remote debugging.
946 @item -tty @var{device}
947 Run using @var{device} for your program's standard input and output.
948 @c FIXME: kingdon thinks there is more to -tty. Investigate.
953 @section Quitting @value{GDBN}
954 @cindex exiting @value{GDBN}
955 @cindex leaving @value{GDBN}
958 @kindex quit @r{[}@var{expression}@r{]}
961 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or
962 type an end-of-file character (usually @kbd{C-d}). If you do not supply
963 @var{expression}, @value{GDBN} will terminate normally; otherwise it will
964 terminate using the result of @var{expression} as the error code.
968 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
969 terminates the action of any @value{GDBN} command that is in progress and
970 returns to @value{GDBN} command level. It is safe to type the interrupt
971 character at any time because @value{GDBN} does not allow it to take effect
972 until a time when it is safe.
975 If you have been using @value{GDBN} to control an attached process or
976 device, you can release it with the @code{detach} command
977 (@pxref{Attach, ,Debugging an already-running process}).
981 @section Shell commands
983 If you need to execute occasional shell commands during your
984 debugging session, there is no need to leave or suspend @value{GDBN}; you can
985 just use the @code{shell} command.
990 @item shell @var{command string}
991 Invoke a the standard shell to execute @var{command string}.
993 If it exists, the environment variable @code{SHELL} determines which
994 shell to run. Otherwise @value{GDBN} uses @code{/bin/sh}.
998 The utility @code{make} is often needed in development environments.
999 You do not have to use the @code{shell} command for this purpose in
1004 @cindex calling make
1005 @item make @var{make-args}
1006 Execute the @code{make} program with the specified
1007 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1011 @chapter @value{GDBN} Commands
1013 You can abbreviate a @value{GDBN} command to the first few letters of the command
1014 name, if that abbreviation is unambiguous; and you can repeat certain
1015 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1016 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1017 show you the alternatives available, if there is more than one possibility).
1020 * Command Syntax:: How to give commands to @value{GDBN}
1021 * Completion:: Command completion
1022 * Help:: How to ask @value{GDBN} for help
1025 @node Command Syntax
1026 @section Command syntax
1028 A @value{GDBN} command is a single line of input. There is no limit on
1029 how long it can be. It starts with a command name, which is followed by
1030 arguments whose meaning depends on the command name. For example, the
1031 command @code{step} accepts an argument which is the number of times to
1032 step, as in @samp{step 5}. You can also use the @code{step} command
1033 with no arguments. Some command names do not allow any arguments.
1035 @cindex abbreviation
1036 @value{GDBN} command names may always be truncated if that abbreviation is
1037 unambiguous. Other possible command abbreviations are listed in the
1038 documentation for individual commands. In some cases, even ambiguous
1039 abbreviations are allowed; for example, @code{s} is specially defined as
1040 equivalent to @code{step} even though there are other commands whose
1041 names start with @code{s}. You can test abbreviations by using them as
1042 arguments to the @code{help} command.
1044 @cindex repeating commands
1046 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1047 repeat the previous command. Certain commands (for example, @code{run})
1048 will not repeat this way; these are commands whose unintentional
1049 repetition might cause trouble and which you are unlikely to want to
1052 The @code{list} and @code{x} commands, when you repeat them with
1053 @key{RET}, construct new arguments rather than repeating
1054 exactly as typed. This permits easy scanning of source or memory.
1056 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1057 output, in a way similar to the common utility @code{more}
1058 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1059 @key{RET} too many in this situation, @value{GDBN} disables command
1060 repetition after any command that generates this sort of display.
1064 Any text from a @kbd{#} to the end of the line is a comment; it does
1065 nothing. This is useful mainly in command files (@pxref{Command
1066 Files,,Command files}).
1069 @section Command completion
1072 @cindex word completion
1073 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1074 only one possibility; it can also show you what the valid possibilities
1075 are for the next word in a command, at any time. This works for @value{GDBN}
1076 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1078 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1079 of a word. If there is only one possibility, @value{GDBN} fills in the
1080 word, and waits for you to finish the command (or press @key{RET} to
1081 enter it). For example, if you type
1083 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1084 @c complete accuracy in these examples; space introduced for clarity.
1085 @c If texinfo enhancements make it unnecessary, it would be nice to
1086 @c replace " @key" by "@key" in the following...
1088 (@value{GDBP}) info bre @key{TAB}
1092 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1093 the only @code{info} subcommand beginning with @samp{bre}:
1096 (@value{GDBP}) info breakpoints
1100 You can either press @key{RET} at this point, to run the @code{info
1101 breakpoints} command, or backspace and enter something else, if
1102 @samp{breakpoints} does not look like the command you expected. (If you
1103 were sure you wanted @code{info breakpoints} in the first place, you
1104 might as well just type @key{RET} immediately after @samp{info bre},
1105 to exploit command abbreviations rather than command completion).
1107 If there is more than one possibility for the next word when you press
1108 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1109 characters and try again, or just press @key{TAB} a second time;
1110 @value{GDBN} displays all the possible completions for that word. For
1111 example, you might want to set a breakpoint on a subroutine whose name
1112 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1113 just sounds the bell. Typing @key{TAB} again displays all the
1114 function names in your program that begin with those characters, for
1118 (@value{GDBP}) b make_ @key{TAB}
1119 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1120 make_a_section_from_file make_environ
1121 make_abs_section make_function_type
1122 make_blockvector make_pointer_type
1123 make_cleanup make_reference_type
1124 make_command make_symbol_completion_list
1125 (@value{GDBP}) b make_
1129 After displaying the available possibilities, @value{GDBN} copies your
1130 partial input (@samp{b make_} in the example) so you can finish the
1133 If you just want to see the list of alternatives in the first place, you
1134 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1135 means @kbd{@key{META} ?}. You can type this
1137 either by holding down a
1138 key designated as the @key{META} shift on your keyboard (if there is
1139 one) while typing @kbd{?}, or
1141 as @key{ESC} followed by @kbd{?}.
1143 @cindex quotes in commands
1144 @cindex completion of quoted strings
1145 Sometimes the string you need, while logically a ``word'', may contain
1146 parentheses or other characters that @value{GDBN} normally excludes from its
1147 notion of a word. To permit word completion to work in this situation,
1148 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1151 The most likely situation where you might need this is in typing the
1152 name of a C++ function. This is because C++ allows function overloading
1153 (multiple definitions of the same function, distinguished by argument
1154 type). For example, when you want to set a breakpoint you may need to
1155 distinguish whether you mean the version of @code{name} that takes an
1156 @code{int} parameter, @code{name(int)}, or the version that takes a
1157 @code{float} parameter, @code{name(float)}. To use the word-completion
1158 facilities in this situation, type a single quote @code{'} at the
1159 beginning of the function name. This alerts @value{GDBN} that it may need to
1160 consider more information than usual when you press @key{TAB} or
1161 @kbd{M-?} to request word completion:
1164 (@value{GDBP}) b 'bubble( @key{M-?}
1165 bubble(double,double) bubble(int,int)
1166 (@value{GDBP}) b 'bubble(
1169 In some cases, @value{GDBN} can tell that completing a name requires using
1170 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1171 completing as much as it can) if you do not type the quote in the first
1175 (@value{GDBP}) b bub @key{TAB}
1176 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1177 (@value{GDBP}) b 'bubble(
1181 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1182 you have not yet started typing the argument list when you ask for
1183 completion on an overloaded symbol.
1188 @section Getting help
1189 @cindex online documentation
1192 You can always ask @value{GDBN} itself for information on its commands,
1193 using the command @code{help}.
1199 You can use @code{help} (abbreviated @code{h}) with no arguments to
1200 display a short list of named classes of commands:
1204 List of classes of commands:
1206 running -- Running the program
1207 stack -- Examining the stack
1208 data -- Examining data
1209 breakpoints -- Making program stop at certain points
1210 files -- Specifying and examining files
1211 status -- Status inquiries
1212 support -- Support facilities
1213 user-defined -- User-defined commands
1214 aliases -- Aliases of other commands
1215 obscure -- Obscure features
1217 Type "help" followed by a class name for a list of
1218 commands in that class.
1219 Type "help" followed by command name for full
1221 Command name abbreviations are allowed if unambiguous.
1225 @item help @var{class}
1226 Using one of the general help classes as an argument, you can get a
1227 list of the individual commands in that class. For example, here is the
1228 help display for the class @code{status}:
1231 (@value{GDBP}) help status
1236 @c Line break in "show" line falsifies real output, but needed
1237 @c to fit in smallbook page size.
1238 show -- Generic command for showing things set
1240 info -- Generic command for printing status
1242 Type "help" followed by command name for full
1244 Command name abbreviations are allowed if unambiguous.
1248 @item help @var{command}
1249 With a command name as @code{help} argument, @value{GDBN} displays a
1250 short paragraph on how to use that command.
1253 @item complete @var{args}
1254 The @code{complete @var{args}} command lists all the possible completions
1255 for the beginning of a command. Use @var{args} to specify the beginning of the
1256 command you want completed. For example:
1262 @noindent results in:
1270 @noindent This is intended for use by @sc{gnu} Emacs.
1273 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1274 and @code{show} to inquire about the state of your program, or the state
1275 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1276 manual introduces each of them in the appropriate context. The listings
1277 under @code{info} and under @code{show} in the Index point to
1278 all the sub-commands. @xref{Index}.
1285 This command (abbreviated @code{i}) is for describing the state of your
1286 program. For example, you can list the arguments given to your program
1287 with @code{info args}, list the registers currently in use with @code{info
1288 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1289 You can get a complete list of the @code{info} sub-commands with
1290 @w{@code{help info}}.
1294 You can assign the result of an expresson to an environment variable with
1295 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1296 @code{set prompt $}.
1300 In contrast to @code{info}, @code{show} is for describing the state of
1301 @value{GDBN} itself.
1302 You can change most of the things you can @code{show}, by using the
1303 related command @code{set}; for example, you can control what number
1304 system is used for displays with @code{set radix}, or simply inquire
1305 which is currently in use with @code{show radix}.
1308 To display all the settable parameters and their current
1309 values, you can use @code{show} with no arguments; you may also use
1310 @code{info set}. Both commands produce the same display.
1311 @c FIXME: "info set" violates the rule that "info" is for state of
1312 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1313 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1317 Here are three miscellaneous @code{show} subcommands, all of which are
1318 exceptional in lacking corresponding @code{set} commands:
1321 @kindex show version
1322 @cindex version number
1324 Show what version of @value{GDBN} is running. You should include this
1325 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1326 use at your site, you may occasionally want to determine which version
1327 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1328 and old ones may wither away. The version number is also announced
1329 when you start @value{GDBN}.
1331 @kindex show copying
1333 Display information about permission for copying @value{GDBN}.
1335 @kindex show warranty
1337 Display the @sc{gnu} ``NO WARRANTY'' statement.
1341 @chapter Running Programs Under @value{GDBN}
1343 When you run a program under @value{GDBN}, you must first generate
1344 debugging information when you compile it.
1346 You may start @value{GDBN} with its arguments, if any, in an environment
1347 of your choice. You may redirect your program's input and output, debug an
1348 already running process, or kill a child process.
1352 * Compilation:: Compiling for debugging
1353 * Starting:: Starting your program
1355 * Arguments:: Your program's arguments
1356 * Environment:: Your program's environment
1357 * Working Directory:: Your program's working directory
1358 * Input/Output:: Your program's input and output
1359 * Attach:: Debugging an already-running process
1360 * Kill Process:: Killing the child process
1361 * Process Information:: Additional process information
1362 * Threads:: Debugging programs with multiple threads
1363 * Processes:: Debugging programs with multiple processes
1368 @section Compiling for debugging
1370 In order to debug a program effectively, you need to generate
1371 debugging information when you compile it. This debugging information
1372 is stored in the object file; it describes the data type of each
1373 variable or function and the correspondence between source line numbers
1374 and addresses in the executable code.
1376 To request debugging information, specify the @samp{-g} option when you run
1379 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1380 options together. Using those compilers, you cannot generate optimized
1381 executables containing debugging information.
1383 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or without
1384 @samp{-O}, making it possible to debug optimized code. We recommend
1385 that you @emph{always} use @samp{-g} whenever you compile a program.
1386 You may think your program is correct, but there is no sense in pushing
1389 @cindex optimized code, debugging
1390 @cindex debugging optimized code
1391 When you debug a program compiled with @samp{-g -O}, remember that the
1392 optimizer is rearranging your code; the debugger shows you what is
1393 really there. Do not be too surprised when the execution path does not
1394 exactly match your source file! An extreme example: if you define a
1395 variable, but never use it, @value{GDBN} never sees that
1396 variable---because the compiler optimizes it out of existence.
1398 Some things do not work as well with @samp{-g -O} as with just
1399 @samp{-g}, particularly on machines with instruction scheduling. If in
1400 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1401 please report it to us as a bug (including a test case!).
1403 Older versions of the @sc{gnu} C compiler permitted a variant option
1404 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1405 format; if your @sc{gnu} C compiler has this option, do not use it.
1409 @section Starting your program
1417 Use the @code{run} command to start your program under @value{GDBN}. You must
1418 first specify the program name
1422 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1423 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1424 command (@pxref{Files, ,Commands to specify files}).
1429 If you are running your program in an execution environment that
1430 supports processes, @code{run} creates an inferior process and makes
1431 that process run your program. (In environments without processes,
1432 @code{run} jumps to the start of your program.)
1434 The execution of a program is affected by certain information it
1435 receives from its superior. @value{GDBN} provides ways to specify this
1436 information, which you must do @emph{before} starting your program. (You
1437 can change it after starting your program, but such changes only affect
1438 your program the next time you start it.) This information may be
1439 divided into four categories:
1442 @item The @emph{arguments.}
1443 Specify the arguments to give your program as the arguments of the
1444 @code{run} command. If a shell is available on your target, the shell
1445 is used to pass the arguments, so that you may use normal conventions
1446 (such as wildcard expansion or variable substitution) in describing
1447 the arguments. In Unix systems, you can control which shell is used
1448 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1449 program's arguments}.
1451 @item The @emph{environment.}
1452 Your program normally inherits its environment from @value{GDBN}, but you can
1453 use the @value{GDBN} commands @code{set environment} and @code{unset
1454 environment} to change parts of the environment that affect
1455 your program. @xref{Environment, ,Your program's environment}.
1457 @item The @emph{working directory.}
1458 Your program inherits its working directory from @value{GDBN}. You can set
1459 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1460 @xref{Working Directory, ,Your program's working directory}.
1462 @item The @emph{standard input and output.}
1463 Your program normally uses the same device for standard input and
1464 standard output as @value{GDBN} is using. You can redirect input and output
1465 in the @code{run} command line, or you can use the @code{tty} command to
1466 set a different device for your program.
1467 @xref{Input/Output, ,Your program's input and output}.
1470 @emph{Warning:} While input and output redirection work, you cannot use
1471 pipes to pass the output of the program you are debugging to another
1472 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1477 When you issue the @code{run} command, your program begins to execute
1478 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1479 of how to arrange for your program to stop. Once your program has
1480 stopped, you may call functions in your program, using the @code{print}
1481 or @code{call} commands. @xref{Data, ,Examining Data}.
1483 If the modification time of your symbol file has changed since the last
1484 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1485 table, and reads it again. When it does this, @value{GDBN} tries to retain
1486 your current breakpoints.
1490 @section Your program's arguments
1492 @cindex arguments (to your program)
1493 The arguments to your program can be specified by the arguments of the
1494 @code{run} command. They are passed to a shell, which expands wildcard
1495 characters and performs redirection of I/O, and thence to your program.
1496 Your @code{SHELL} environment variable (if it exists) specifies what
1497 shell @value{GDBN} uses. If you do not define @code{SHELL},
1498 @value{GDBN} uses @code{/bin/sh}.
1500 @code{run} with no arguments uses the same arguments used by the previous
1501 @code{run}, or those set by the @code{set args} command.
1506 Specify the arguments to be used the next time your program is run. If
1507 @code{set args} has no arguments, @code{run} executes your program
1508 with no arguments. Once you have run your program with arguments,
1509 using @code{set args} before the next @code{run} is the only way to run
1510 it again without arguments.
1514 Show the arguments to give your program when it is started.
1518 @section Your program's environment
1520 @cindex environment (of your program)
1521 The @dfn{environment} consists of a set of environment variables and
1522 their values. Environment variables conventionally record such things as
1523 your user name, your home directory, your terminal type, and your search
1524 path for programs to run. Usually you set up environment variables with
1525 the shell and they are inherited by all the other programs you run. When
1526 debugging, it can be useful to try running your program with a modified
1527 environment without having to start @value{GDBN} over again.
1531 @item path @var{directory}
1532 Add @var{directory} to the front of the @code{PATH} environment variable
1533 (the search path for executables), for both @value{GDBN} and your program.
1534 You may specify several directory names, separated by @samp{:} or
1535 whitespace. If @var{directory} is already in the path, it is moved to
1536 the front, so it is searched sooner.
1538 You can use the string @samp{$cwd} to refer to whatever is the current
1539 working directory at the time @value{GDBN} searches the path. If you
1540 use @samp{.} instead, it refers to the directory where you executed the
1541 @code{path} command. @value{GDBN} replaces @samp{.} in the
1542 @var{directory} argument (with the current path) before adding
1543 @var{directory} to the search path.
1544 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1545 @c document that, since repeating it would be a no-op.
1549 Display the list of search paths for executables (the @code{PATH}
1550 environment variable).
1552 @kindex show environment
1553 @item show environment @r{[}@var{varname}@r{]}
1554 Print the value of environment variable @var{varname} to be given to
1555 your program when it starts. If you do not supply @var{varname},
1556 print the names and values of all environment variables to be given to
1557 your program. You can abbreviate @code{environment} as @code{env}.
1559 @kindex set environment
1560 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1561 Set environment variable @var{varname} to @var{value}. The value
1562 changes for your program only, not for @value{GDBN} itself. @var{value} may
1563 be any string; the values of environment variables are just strings, and
1564 any interpretation is supplied by your program itself. The @var{value}
1565 parameter is optional; if it is eliminated, the variable is set to a
1567 @c "any string" here does not include leading, trailing
1568 @c blanks. Gnu asks: does anyone care?
1570 For example, this command:
1577 tells a Unix program, when subsequently run, that its user is named
1578 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1579 are not actually required.)
1581 @kindex unset environment
1582 @item unset environment @var{varname}
1583 Remove variable @var{varname} from the environment to be passed to your
1584 program. This is different from @samp{set env @var{varname} =};
1585 @code{unset environment} removes the variable from the environment,
1586 rather than assigning it an empty value.
1589 @emph{Warning:} @value{GDBN} runs your program using the shell indicated
1590 by your @code{SHELL} environment variable if it exists (or
1591 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1592 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1593 @file{.bashrc} for BASH---any variables you set in that file affect
1594 your program. You may wish to move setting of environment variables to
1595 files that are only run when you sign on, such as @file{.login} or
1598 @node Working Directory
1599 @section Your program's working directory
1601 @cindex working directory (of your program)
1602 Each time you start your program with @code{run}, it inherits its
1603 working directory from the current working directory of @value{GDBN}.
1604 The @value{GDBN} working directory is initially whatever it inherited
1605 from its parent process (typically the shell), but you can specify a new
1606 working directory in @value{GDBN} with the @code{cd} command.
1608 The @value{GDBN} working directory also serves as a default for the commands
1609 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1614 @item cd @var{directory}
1615 Set the @value{GDBN} working directory to @var{directory}.
1619 Print the @value{GDBN} working directory.
1623 @section Your program's input and output
1628 By default, the program you run under @value{GDBN} does input and output to
1629 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1630 to its own terminal modes to interact with you, but it records the terminal
1631 modes your program was using and switches back to them when you continue
1632 running your program.
1635 @kindex info terminal
1637 Displays information recorded by @value{GDBN} about the terminal modes your
1641 You can redirect your program's input and/or output using shell
1642 redirection with the @code{run} command. For example,
1649 starts your program, diverting its output to the file @file{outfile}.
1652 @cindex controlling terminal
1653 Another way to specify where your program should do input and output is
1654 with the @code{tty} command. This command accepts a file name as
1655 argument, and causes this file to be the default for future @code{run}
1656 commands. It also resets the controlling terminal for the child
1657 process, for future @code{run} commands. For example,
1664 directs that processes started with subsequent @code{run} commands
1665 default to do input and output on the terminal @file{/dev/ttyb} and have
1666 that as their controlling terminal.
1668 An explicit redirection in @code{run} overrides the @code{tty} command's
1669 effect on the input/output device, but not its effect on the controlling
1672 When you use the @code{tty} command or redirect input in the @code{run}
1673 command, only the input @emph{for your program} is affected. The input
1674 for @value{GDBN} still comes from your terminal.
1677 @section Debugging an already-running process
1682 @item attach @var{process-id}
1683 This command attaches to a running process---one that was started
1684 outside @value{GDBN}. (@code{info files} shows your active
1685 targets.) The command takes as argument a process ID. The usual way to
1686 find out the process-id of a Unix process is with the @code{ps} utility,
1687 or with the @samp{jobs -l} shell command.
1689 @code{attach} does not repeat if you press @key{RET} a second time after
1690 executing the command.
1693 To use @code{attach}, your program must be running in an environment
1694 which supports processes; for example, @code{attach} does not work for
1695 programs on bare-board targets that lack an operating system. You must
1696 also have permission to send the process a signal.
1698 When using @code{attach}, you should first use the @code{file} command
1699 to specify the program running in the process and load its symbol table.
1700 @xref{Files, ,Commands to Specify Files}.
1702 The first thing @value{GDBN} does after arranging to debug the specified
1703 process is to stop it. You can examine and modify an attached process
1704 with all the @value{GDBN} commands that are ordinarily available when you start
1705 processes with @code{run}. You can insert breakpoints; you can step and
1706 continue; you can modify storage. If you would rather the process
1707 continue running, you may use the @code{continue} command after
1708 attaching @value{GDBN} to the process.
1713 When you have finished debugging the attached process, you can use the
1714 @code{detach} command to release it from @value{GDBN} control. Detaching
1715 the process continues its execution. After the @code{detach} command,
1716 that process and @value{GDBN} become completely independent once more, and you
1717 are ready to @code{attach} another process or start one with @code{run}.
1718 @code{detach} does not repeat if you press @key{RET} again after
1719 executing the command.
1722 If you exit @value{GDBN} or use the @code{run} command while you have an
1723 attached process, you kill that process. By default, @value{GDBN} asks
1724 for confirmation if you try to do either of these things; you can
1725 control whether or not you need to confirm by using the @code{set
1726 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1731 @section Killing the child process
1736 Kill the child process in which your program is running under @value{GDBN}.
1739 This command is useful if you wish to debug a core dump instead of a
1740 running process. @value{GDBN} ignores any core dump file while your program
1744 On some operating systems, a program cannot be executed outside @value{GDBN}
1745 while you have breakpoints set on it inside @value{GDBN}. You can use the
1746 @code{kill} command in this situation to permit running your program
1747 outside the debugger.
1749 The @code{kill} command is also useful if you wish to recompile and
1750 relink your program, since on many systems it is impossible to modify an
1751 executable file while it is running in a process. In this case, when you
1752 next type @code{run}, @value{GDBN} notices that the file has changed, and
1753 reads the symbol table again (while trying to preserve your current
1754 breakpoint settings).
1756 @node Process Information
1757 @section Additional process information
1760 @cindex process image
1761 Some operating systems provide a facility called @samp{/proc} that can
1762 be used to examine the image of a running process using file-system
1763 subroutines. If @value{GDBN} is configured for an operating system with this
1764 facility, the command @code{info proc} is available to report on several
1765 kinds of information about the process running your program.
1766 @code{info proc} works only on SVR4 systems that support @code{procfs}.
1771 Summarize available information about the process.
1773 @kindex info proc mappings
1774 @item info proc mappings
1775 Report on the address ranges accessible in the program, with information
1776 on whether your program may read, write, or execute each range.
1778 @kindex info proc times
1779 @item info proc times
1780 Starting time, user CPU time, and system CPU time for your program and
1783 @kindex info proc id
1785 Report on the process IDs related to your program: its own process ID,
1786 the ID of its parent, the process group ID, and the session ID.
1788 @kindex info proc status
1789 @item info proc status
1790 General information on the state of the process. If the process is
1791 stopped, this report includes the reason for stopping, and any signal
1795 Show all the above information about the process.
1799 @section Debugging programs with multiple threads
1801 @cindex threads of execution
1802 @cindex multiple threads
1803 @cindex switching threads
1804 In some operating systems, a single program may have more than one
1805 @dfn{thread} of execution. The precise semantics of threads differ from
1806 one operating system to another, but in general the threads of a single
1807 program are akin to multiple processes---except that they share one
1808 address space (that is, they can all examine and modify the same
1809 variables). On the other hand, each thread has its own registers and
1810 execution stack, and perhaps private memory.
1812 @value{GDBN} provides these facilities for debugging multi-thread
1816 @item automatic notification of new threads
1817 @item @samp{thread @var{threadno}}, a command to switch among threads
1818 @item @samp{info threads}, a command to inquire about existing threads
1819 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1820 a command to apply a command to a list of threads
1821 @item thread-specific breakpoints
1825 @emph{Warning:} These facilities are not yet available on every
1826 @value{GDBN} configuration where the operating system supports threads.
1827 If your @value{GDBN} does not support threads, these commands have no
1828 effect. For example, a system without thread support shows no output
1829 from @samp{info threads}, and always rejects the @code{thread} command,
1833 (@value{GDBP}) info threads
1834 (@value{GDBP}) thread 1
1835 Thread ID 1 not known. Use the "info threads" command to
1836 see the IDs of currently known threads.
1838 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1839 @c doesn't support threads"?
1842 @cindex focus of debugging
1843 @cindex current thread
1844 The @value{GDBN} thread debugging facility allows you to observe all
1845 threads while your program runs---but whenever @value{GDBN} takes
1846 control, one thread in particular is always the focus of debugging.
1847 This thread is called the @dfn{current thread}. Debugging commands show
1848 program information from the perspective of the current thread.
1850 @kindex New @var{systag}
1851 @cindex thread identifier (system)
1852 @c FIXME-implementors!! It would be more helpful if the [New...] message
1853 @c included GDB's numeric thread handle, so you could just go to that
1854 @c thread without first checking `info threads'.
1855 Whenever @value{GDBN} detects a new thread in your program, it displays
1856 the target system's identification for the thread with a message in the
1857 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1858 whose form varies depending on the particular system. For example, on
1859 LynxOS, you might see
1862 [New process 35 thread 27]
1866 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1867 the @var{systag} is simply something like @samp{process 368}, with no
1870 @c FIXME!! (1) Does the [New...] message appear even for the very first
1871 @c thread of a program, or does it only appear for the
1872 @c second---i.e., when it becomes obvious we have a multithread
1874 @c (2) *Is* there necessarily a first thread always? Or do some
1875 @c multithread systems permit starting a program with multiple
1876 @c threads ab initio?
1878 @cindex thread number
1879 @cindex thread identifier (GDB)
1880 For debugging purposes, @value{GDBN} associates its own thread
1881 number---always a single integer---with each thread in your program.
1884 @kindex info threads
1886 Display a summary of all threads currently in your
1887 program. @value{GDBN} displays for each thread (in this order):
1890 @item the thread number assigned by @value{GDBN}
1892 @item the target system's thread identifier (@var{systag})
1894 @item the current stack frame summary for that thread
1898 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1899 indicates the current thread.
1903 @c end table here to get a little more width for example
1906 (@value{GDBP}) info threads
1907 3 process 35 thread 27 0x34e5 in sigpause ()
1908 2 process 35 thread 23 0x34e5 in sigpause ()
1909 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1914 @kindex thread @var{threadno}
1915 @item thread @var{threadno}
1916 Make thread number @var{threadno} the current thread. The command
1917 argument @var{threadno} is the internal @value{GDBN} thread number, as
1918 shown in the first field of the @samp{info threads} display.
1919 @value{GDBN} responds by displaying the system identifier of the thread
1920 you selected, and its current stack frame summary:
1923 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
1924 (@value{GDBP}) thread 2
1925 [Switching to process 35 thread 23]
1926 0x34e5 in sigpause ()
1930 As with the @samp{[New @dots{}]} message, the form of the text after
1931 @samp{Switching to} depends on your system's conventions for identifying
1934 @kindex thread apply
1935 @item thread apply [@var{threadno}] [@var{all}] @var{args}
1936 The @code{thread apply} command allows you to apply a command to one or
1937 more threads. Specify the numbers of the threads that you want affected
1938 with the command argument @var{threadno}. @var{threadno} is the internal
1939 @value{GDBN} thread number, as shown in the first field of the @samp{info
1940 threads} display. To apply a command to all threads, use
1941 @code{thread apply all} @var{args}.
1944 @cindex automatic thread selection
1945 @cindex switching threads automatically
1946 @cindex threads, automatic switching
1947 Whenever @value{GDBN} stops your program, due to a breakpoint or a
1948 signal, it automatically selects the thread where that breakpoint or
1949 signal happened. @value{GDBN} alerts you to the context switch with a
1950 message of the form @samp{[Switching to @var{systag}]} to identify the
1953 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
1954 more information about how @value{GDBN} behaves when you stop and start
1955 programs with multiple threads.
1957 @xref{Set Watchpoints,,Setting watchpoints}, for information about
1958 watchpoints in programs with multiple threads.
1962 @section Debugging programs with multiple processes
1964 @cindex fork, debugging programs which call
1965 @cindex multiple processes
1966 @cindex processes, multiple
1967 @value{GDBN} has no special support for debugging programs which create
1968 additional processes using the @code{fork} function. When a program
1969 forks, @value{GDBN} will continue to debug the parent process and the
1970 child process will run unimpeded. If you have set a breakpoint in any
1971 code which the child then executes, the child will get a @code{SIGTRAP}
1972 signal which (unless it catches the signal) will cause it to terminate.
1974 However, if you want to debug the child process there is a workaround
1975 which isn't too painful. Put a call to @code{sleep} in the code which
1976 the child process executes after the fork. It may be useful to sleep
1977 only if a certain environment variable is set, or a certain file exists,
1978 so that the delay need not occur when you don't want to run @value{GDBN}
1979 on the child. While the child is sleeping, use the @code{ps} program to
1980 get its process ID. Then tell @value{GDBN} (a new invocation of
1981 @value{GDBN} if you are also debugging the parent process) to attach to
1982 the child process (see @ref{Attach}). From that point on you can debug
1983 the child process just like any other process which you attached to.
1986 @chapter Stopping and Continuing
1988 The principal purposes of using a debugger are so that you can stop your
1989 program before it terminates; or so that, if your program runs into
1990 trouble, you can investigate and find out why.
1992 Inside @value{GDBN}, your program may stop for any of several reasons, such
1997 a breakpoint, or reaching a new line after a @value{GDBN}
1998 command such as @code{step}. You may then examine and change
1999 variables, set new breakpoints or remove old ones, and then continue
2000 execution. Usually, the messages shown by @value{GDBN} provide ample
2001 explanation of the status of your program---but you can also explicitly
2002 request this information at any time.
2005 @kindex info program
2007 Display information about the status of your program: whether it is
2017 * Breakpoints:: Breakpoints, watchpoints, and exceptions
2020 * Breakpoints:: Breakpoints and watchpoints
2022 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
2024 * Continuing and Stepping:: Resuming execution
2029 * Thread Stops:: Stopping and starting multi-thread programs
2033 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
2034 @c ...hence distribute @node Breakpoints over two possible @if expansions.
2038 @section Breakpoints, watchpoints, and exceptions
2042 @section Breakpoints and watchpoints
2046 A @dfn{breakpoint} makes your program stop whenever a certain point in
2047 the program is reached. For each breakpoint, you can add
2048 conditions to control in finer detail whether your program stops.
2049 You can set breakpoints with the @code{break} command and its variants
2050 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
2051 your program should stop by line number, function name or exact address
2054 In languages with exception handling (such as @sc{gnu} C++), you can also set
2055 breakpoints where an exception is raised (@pxref{Exception Handling,,
2056 Breakpoints and exceptions}).
2059 In SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can now set
2060 breakpoints in shared libraries before the executable is run.
2063 @cindex memory tracing
2064 @cindex breakpoint on memory address
2065 @cindex breakpoint on variable modification
2066 A @dfn{watchpoint} is a special breakpoint that stops your program
2067 when the value of an expression changes. You must use a different
2068 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2069 watchpoints}), but aside from that, you can manage a watchpoint like
2070 any other breakpoint: you enable, disable, and delete both breakpoints
2071 and watchpoints using the same commands.
2073 You can arrange to have values from your program displayed automatically
2074 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2077 @cindex breakpoint numbers
2078 @cindex numbers for breakpoints
2079 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
2080 create it; these numbers are successive integers starting with one. In
2081 many of the commands for controlling various features of breakpoints you
2082 use the breakpoint number to say which breakpoint you want to change.
2083 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
2084 no effect on your program until you enable it again.
2087 * Set Breaks:: Setting breakpoints
2088 * Set Watchpoints:: Setting watchpoints
2090 * Exception Handling:: Breakpoints and exceptions
2093 * Delete Breaks:: Deleting breakpoints
2094 * Disabling:: Disabling breakpoints
2095 * Conditions:: Break conditions
2096 * Break Commands:: Breakpoint command lists
2098 * Breakpoint Menus:: Breakpoint menus
2100 @c @ifclear BARETARGET
2101 @c * Error in Breakpoints:: ``Cannot insert breakpoints''
2106 @subsection Setting breakpoints
2108 @c FIXME LMB what does GDB do if no code on line of breakpt?
2109 @c consider in particular declaration with/without initialization.
2111 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2116 @cindex latest breakpoint
2117 Breakpoints are set with the @code{break} command (abbreviated
2118 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2119 number of the breakpoints you've set most recently; see @ref{Convenience
2120 Vars,, Convenience variables}, for a discussion of what you can do with
2121 convenience variables.
2123 You have several ways to say where the breakpoint should go.
2126 @item break @var{function}
2127 Set a breakpoint at entry to function @var{function}.
2129 When using source languages that permit overloading of symbols, such as
2130 C++, @var{function} may refer to more than one possible place to break.
2131 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2134 @item break +@var{offset}
2135 @itemx break -@var{offset}
2136 Set a breakpoint some number of lines forward or back from the position
2137 at which execution stopped in the currently selected frame.
2139 @item break @var{linenum}
2140 Set a breakpoint at line @var{linenum} in the current source file.
2141 That file is the last file whose source text was printed. This
2142 breakpoint stops your program just before it executes any of the
2145 @item break @var{filename}:@var{linenum}
2146 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2148 @item break @var{filename}:@var{function}
2149 Set a breakpoint at entry to function @var{function} found in file
2150 @var{filename}. Specifying a file name as well as a function name is
2151 superfluous except when multiple files contain similarly named
2154 @item break *@var{address}
2155 Set a breakpoint at address @var{address}. You can use this to set
2156 breakpoints in parts of your program which do not have debugging
2157 information or source files.
2160 When called without any arguments, @code{break} sets a breakpoint at
2161 the next instruction to be executed in the selected stack frame
2162 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2163 innermost, this makes your program stop as soon as control
2164 returns to that frame. This is similar to the effect of a
2165 @code{finish} command in the frame inside the selected frame---except
2166 that @code{finish} does not leave an active breakpoint. If you use
2167 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2168 the next time it reaches the current location; this may be useful
2171 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2172 least one instruction has been executed. If it did not do this, you
2173 would be unable to proceed past a breakpoint without first disabling the
2174 breakpoint. This rule applies whether or not the breakpoint already
2175 existed when your program stopped.
2177 @item break @dots{} if @var{cond}
2178 Set a breakpoint with condition @var{cond}; evaluate the expression
2179 @var{cond} each time the breakpoint is reached, and stop only if the
2180 value is nonzero---that is, if @var{cond} evaluates as true.
2181 @samp{@dots{}} stands for one of the possible arguments described
2182 above (or no argument) specifying where to break. @xref{Conditions,
2183 ,Break conditions}, for more information on breakpoint conditions.
2186 @item tbreak @var{args}
2187 Set a breakpoint enabled only for one stop. @var{args} are the
2188 same as for the @code{break} command, and the breakpoint is set in the same
2189 way, but the breakpoint is automatically deleted after the first time your
2190 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2193 @item hbreak @var{args}
2194 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2195 @code{break} command and the breakpoint is set in the same way, but the
2196 breakpoint requires hardware support and some target hardware may not
2197 have this support. The main purpose of this is EPROM/ROM code
2198 debugging, so you can set a breakpoint at an instruction without
2199 changing the instruction. This can be used with the new trap-generation
2200 provided by SPARClite DSU. DSU will generate traps when a program accesses
2201 some date or instruction address that is assigned to the debug registers.
2202 However the hardware breakpoint registers can only take two data breakpoints,
2203 and @value{GDBN} will reject this command if more than two are used.
2204 Delete or disable usused hardware breakpoints before setting
2205 new ones. @xref{Conditions, ,Break conditions}.
2208 @item thbreak @var{args}
2209 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2210 are the same as for the @code{hbreak} command and the breakpoint is set in
2211 the same way. However, like the @code{tbreak} command,
2212 the breakpoint is automatically deleted after the
2213 first time your program stops there. Also, like the @code{hbreak}
2214 command, the breakpoint requires hardware support and some target hardware
2215 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2216 Also @xref{Conditions, ,Break conditions}.
2219 @cindex regular expression
2220 @item rbreak @var{regex}
2221 @c FIXME what kind of regexp?
2222 Set breakpoints on all functions matching the regular expression
2223 @var{regex}. This command
2224 sets an unconditional breakpoint on all matches, printing a list of all
2225 breakpoints it set. Once these breakpoints are set, they are treated
2226 just like the breakpoints set with the @code{break} command. You can
2227 delete them, disable them, or make them conditional the same way as any
2231 When debugging C++ programs, @code{rbreak} is useful for setting
2232 breakpoints on overloaded functions that are not members of any special
2236 @kindex info breakpoints
2237 @cindex @code{$_} and @code{info breakpoints}
2238 @item info breakpoints @r{[}@var{n}@r{]}
2239 @itemx info break @r{[}@var{n}@r{]}
2240 @itemx info watchpoints @r{[}@var{n}@r{]}
2241 Print a table of all breakpoints and watchpoints set and not
2242 deleted, with the following columns for each breakpoint:
2245 @item Breakpoint Numbers
2247 Breakpoint or watchpoint.
2249 Whether the breakpoint is marked to be disabled or deleted when hit.
2250 @item Enabled or Disabled
2251 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2252 that are not enabled.
2254 Where the breakpoint is in your program, as a memory address
2256 Where the breakpoint is in the source for your program, as a file and
2261 If a breakpoint is conditional, @code{info break} shows the condition on
2262 the line following the affected breakpoint; breakpoint commands, if any,
2263 are listed after that.
2266 @code{info break} with a breakpoint
2267 number @var{n} as argument lists only that breakpoint. The
2268 convenience variable @code{$_} and the default examining-address for
2269 the @code{x} command are set to the address of the last breakpoint
2270 listed (@pxref{Memory, ,Examining memory}).
2273 @code{info break} now displays a count of the number of times the
2274 breakpoint has been hit. This is especially useful in conjunction with
2275 the @code{ignore} command. You can ignore a large number of breakpoint
2276 hits, look at the breakpoint info to see how many times the
2277 breakpoint was hit, and then run again, ignoring one less than that
2278 number. This will get you quickly to the last hit of that breakpoint.
2281 @value{GDBN} allows you to set any number of breakpoints at the same place in
2282 your program. There is nothing silly or meaningless about this. When
2283 the breakpoints are conditional, this is even useful
2284 (@pxref{Conditions, ,Break conditions}).
2286 @cindex negative breakpoint numbers
2287 @cindex internal @value{GDBN} breakpoints
2288 @value{GDBN} itself sometimes sets breakpoints in your program for special
2289 purposes, such as proper handling of @code{longjmp} (in C programs).
2290 These internal breakpoints are assigned negative numbers, starting with
2291 @code{-1}; @samp{info breakpoints} does not display them.
2293 You can see these breakpoints with the @value{GDBN} maintenance command
2294 @samp{maint info breakpoints}.
2297 @kindex maint info breakpoints
2298 @item maint info breakpoints
2299 Using the same format as @samp{info breakpoints}, display both the
2300 breakpoints you've set explicitly, and those @value{GDBN} is using for
2301 internal purposes. Internal breakpoints are shown with negative
2302 breakpoint numbers. The type column identifies what kind of breakpoint
2307 Normal, explicitly set breakpoint.
2310 Normal, explicitly set watchpoint.
2313 Internal breakpoint, used to handle correctly stepping through
2314 @code{longjmp} calls.
2316 @item longjmp resume
2317 Internal breakpoint at the target of a @code{longjmp}.
2320 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2323 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2329 @node Set Watchpoints
2330 @subsection Setting watchpoints
2331 @cindex setting watchpoints
2333 You can use a watchpoint to stop execution whenever the value of an
2334 expression changes, without having to predict a particular place
2335 where this may happen.
2337 Watchpoints currently execute two orders of magnitude more slowly than
2338 other breakpoints, but this can be well worth it to catch errors where
2339 you have no clue what part of your program is the culprit.
2341 @c FIXME - did Stan mean to @ignore this out?
2343 Some processors provide special hardware to support watchpoint
2344 evaluation; @value{GDBN} will use such hardware if it is available,
2345 and if the support code has been added for that configuration.
2350 @item watch @var{expr}
2351 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2352 is written into by the program and its value changes.
2353 This can be used with the new trap-generation provided by
2354 SPARClite DSU. DSU will generate traps when a program accesses
2355 some date or instruction address that is assigned to the debug registers.
2356 For the data addresses, DSU facilitates the @code{watch} command.
2357 However the hardware breakpoint registers can only take two data watchpoints,
2358 and both watchpoints must be the same kind. For example, you can set two
2359 watchpoints with @code{watch} commands, two with @code{rwatch}
2360 commands, @strong{or} two with @code{awatch} commands, but you cannot set one
2361 watchpoint with one command and the other with a different command.
2362 @value{GBDN} will reject the command if you try to mix watchpoints.
2363 Delete or disable unused watchpoint commands before setting new ones.
2366 @item rwatch @var{expr}
2367 Set a watchpoint that will break when watch @var{args} is read by the program.
2368 If you use both watchpoints, both must be set with the @code{rwatch}
2372 @item awatch @var{expr}
2373 Set a watchpoint that will break when @var{args} is read and written into
2374 by the program. If you use both watchpoints, both must be set with the
2375 @code{awatch} command.
2377 @kindex info watchpoints
2378 @item info watchpoints
2379 This command prints a list of watchpoints and breakpoints; it is the
2380 same as @code{info break}.
2385 @cindex watchpoints and threads
2386 @cindex threads and watchpoints
2387 @emph{Warning:} in multi-thread programs, watchpoints have only limited
2388 usefulness. With the current watchpoint implementation, @value{GDBN}
2389 can only watch the value of an expression @emph{in a single thread}. If
2390 you are confident that the expression can only change due to the current
2391 thread's activity (and if you are also confident that no other thread
2392 can become current), then you can use watchpoints as usual. However,
2393 @value{GDBN} may not notice when a non-current thread's activity changes
2399 @node Exception Handling
2400 @subsection Breakpoints and exceptions
2401 @cindex exception handlers
2403 Some languages, such as @sc{gnu} C++, implement exception handling. You can
2404 use @value{GDBN} to examine what caused your program to raise an exception,
2405 and to list the exceptions your program is prepared to handle at a
2406 given point in time.
2410 @item catch @var{exceptions}
2411 You can set breakpoints at active exception handlers by using the
2412 @code{catch} command. @var{exceptions} is a list of names of exceptions
2416 You can use @code{info catch} to list active exception handlers.
2417 @xref{Frame Info, ,Information about a frame}.
2419 There are currently some limitations to exception handling in @value{GDBN}:
2423 If you call a function interactively, @value{GDBN} normally returns
2424 control to you when the function has finished executing. If the call
2425 raises an exception, however, the call may bypass the mechanism that
2426 returns control to you and cause your program to simply continue
2427 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2428 listening for, or exits.
2431 You cannot raise an exception interactively.
2434 You cannot install an exception handler interactively.
2437 @cindex raise exceptions
2438 Sometimes @code{catch} is not the best way to debug exception handling:
2439 if you need to know exactly where an exception is raised, it is better to
2440 stop @emph{before} the exception handler is called, since that way you
2441 can see the stack before any unwinding takes place. If you set a
2442 breakpoint in an exception handler instead, it may not be easy to find
2443 out where the exception was raised.
2445 To stop just before an exception handler is called, you need some
2446 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2447 raised by calling a library function named @code{__raise_exception}
2448 which has the following ANSI C interface:
2451 /* @var{addr} is where the exception identifier is stored.
2452 ID is the exception identifier. */
2453 void __raise_exception (void **@var{addr}, void *@var{id});
2457 To make the debugger catch all exceptions before any stack
2458 unwinding takes place, set a breakpoint on @code{__raise_exception}
2459 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2461 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2462 that depends on the value of @var{id}, you can stop your program when
2463 a specific exception is raised. You can use multiple conditional
2464 breakpoints to stop your program when any of a number of exceptions are
2469 @subsection Deleting breakpoints
2471 @cindex clearing breakpoints, watchpoints
2472 @cindex deleting breakpoints, watchpoints
2473 It is often necessary to eliminate a breakpoint or watchpoint once it
2474 has done its job and you no longer want your program to stop there. This
2475 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2476 deleted no longer exists; it is forgotten.
2478 With the @code{clear} command you can delete breakpoints according to
2479 where they are in your program. With the @code{delete} command you can
2480 delete individual breakpoints or watchpoints by specifying their
2483 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2484 automatically ignores breakpoints on the first instruction to be executed
2485 when you continue execution without changing the execution address.
2490 Delete any breakpoints at the next instruction to be executed in the
2491 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2492 the innermost frame is selected, this is a good way to delete a
2493 breakpoint where your program just stopped.
2495 @item clear @var{function}
2496 @itemx clear @var{filename}:@var{function}
2497 Delete any breakpoints set at entry to the function @var{function}.
2499 @item clear @var{linenum}
2500 @itemx clear @var{filename}:@var{linenum}
2501 Delete any breakpoints set at or within the code of the specified line.
2503 @cindex delete breakpoints
2506 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2507 Delete the breakpoints or watchpoints of the numbers specified as
2508 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2509 asks confirmation, unless you have @code{set confirm off}). You
2510 can abbreviate this command as @code{d}.
2514 @subsection Disabling breakpoints
2516 @kindex disable breakpoints
2517 @kindex enable breakpoints
2518 Rather than deleting a breakpoint or watchpoint, you might prefer to
2519 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2520 been deleted, but remembers the information on the breakpoint so that
2521 you can @dfn{enable} it again later.
2523 You disable and enable breakpoints and watchpoints with the
2524 @code{enable} and @code{disable} commands, optionally specifying one or
2525 more breakpoint numbers as arguments. Use @code{info break} or
2526 @code{info watch} to print a list of breakpoints or watchpoints if you
2527 do not know which numbers to use.
2529 A breakpoint or watchpoint can have any of four different states of
2534 Enabled. The breakpoint stops your program. A breakpoint set
2535 with the @code{break} command starts out in this state.
2537 Disabled. The breakpoint has no effect on your program.
2539 Enabled once. The breakpoint stops your program, but then becomes
2540 disabled. A breakpoint set with the @code{tbreak} command starts out in
2543 Enabled for deletion. The breakpoint stops your program, but
2544 immediately after it does so it is deleted permanently.
2547 You can use the following commands to enable or disable breakpoints and
2551 @kindex disable breakpoints
2554 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2555 Disable the specified breakpoints---or all breakpoints, if none are
2556 listed. A disabled breakpoint has no effect but is not forgotten. All
2557 options such as ignore-counts, conditions and commands are remembered in
2558 case the breakpoint is enabled again later. You may abbreviate
2559 @code{disable} as @code{dis}.
2561 @kindex enable breakpoints
2563 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2564 Enable the specified breakpoints (or all defined breakpoints). They
2565 become effective once again in stopping your program.
2567 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2568 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2569 of these breakpoints immediately after stopping your program.
2571 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2572 Enable the specified breakpoints to work once, then die. @value{GDBN}
2573 deletes any of these breakpoints as soon as your program stops there.
2576 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2577 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2578 subsequently, they become disabled or enabled only when you use one of
2579 the commands above. (The command @code{until} can set and delete a
2580 breakpoint of its own, but it does not change the state of your other
2581 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2585 @subsection Break conditions
2586 @cindex conditional breakpoints
2587 @cindex breakpoint conditions
2589 @c FIXME what is scope of break condition expr? Context where wanted?
2590 @c in particular for a watchpoint?
2591 The simplest sort of breakpoint breaks every time your program reaches a
2592 specified place. You can also specify a @dfn{condition} for a
2593 breakpoint. A condition is just a Boolean expression in your
2594 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2595 a condition evaluates the expression each time your program reaches it,
2596 and your program stops only if the condition is @emph{true}.
2598 This is the converse of using assertions for program validation; in that
2599 situation, you want to stop when the assertion is violated---that is,
2600 when the condition is false. In C, if you want to test an assertion expressed
2601 by the condition @var{assert}, you should set the condition
2602 @samp{! @var{assert}} on the appropriate breakpoint.
2604 Conditions are also accepted for watchpoints; you may not need them,
2605 since a watchpoint is inspecting the value of an expression anyhow---but
2606 it might be simpler, say, to just set a watchpoint on a variable name,
2607 and specify a condition that tests whether the new value is an interesting
2610 Break conditions can have side effects, and may even call functions in
2611 your program. This can be useful, for example, to activate functions
2612 that log program progress, or to use your own print functions to
2613 format special data structures. The effects are completely predictable
2614 unless there is another enabled breakpoint at the same address. (In
2615 that case, @value{GDBN} might see the other breakpoint first and stop your
2616 program without checking the condition of this one.) Note that
2617 breakpoint commands are usually more convenient and flexible for the
2618 purpose of performing side effects when a breakpoint is reached
2619 (@pxref{Break Commands, ,Breakpoint command lists}).
2621 Break conditions can be specified when a breakpoint is set, by using
2622 @samp{if} in the arguments to the @code{break} command. @xref{Set
2623 Breaks, ,Setting breakpoints}. They can also be changed at any time
2624 with the @code{condition} command. The @code{watch} command does not
2625 recognize the @code{if} keyword; @code{condition} is the only way to
2626 impose a further condition on a watchpoint.
2630 @item condition @var{bnum} @var{expression}
2631 Specify @var{expression} as the break condition for breakpoint or
2632 watchpoint number @var{bnum}. After you set a condition, breakpoint
2633 @var{bnum} stops your program only if the value of @var{expression} is
2634 true (nonzero, in C). When you use @code{condition}, @value{GDBN}
2635 checks @var{expression} immediately for syntactic correctness, and to
2636 determine whether symbols in it have referents in the context of your
2638 @c FIXME so what does GDB do if there is no referent? Moreover, what
2639 @c about watchpoints?
2641 not actually evaluate @var{expression} at the time the @code{condition}
2642 command is given, however. @xref{Expressions, ,Expressions}.
2644 @item condition @var{bnum}
2645 Remove the condition from breakpoint number @var{bnum}. It becomes
2646 an ordinary unconditional breakpoint.
2649 @cindex ignore count (of breakpoint)
2650 A special case of a breakpoint condition is to stop only when the
2651 breakpoint has been reached a certain number of times. This is so
2652 useful that there is a special way to do it, using the @dfn{ignore
2653 count} of the breakpoint. Every breakpoint has an ignore count, which
2654 is an integer. Most of the time, the ignore count is zero, and
2655 therefore has no effect. But if your program reaches a breakpoint whose
2656 ignore count is positive, then instead of stopping, it just decrements
2657 the ignore count by one and continues. As a result, if the ignore count
2658 value is @var{n}, the breakpoint does not stop the next @var{n} times
2659 your program reaches it.
2663 @item ignore @var{bnum} @var{count}
2664 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2665 The next @var{count} times the breakpoint is reached, your program's
2666 execution does not stop; other than to decrement the ignore count, @value{GDBN}
2669 To make the breakpoint stop the next time it is reached, specify
2672 When you use @code{continue} to resume execution of your program from a
2673 breakpoint, you can specify an ignore count directly as an argument to
2674 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2675 Stepping,,Continuing and stepping}.
2677 If a breakpoint has a positive ignore count and a condition, the
2678 condition is not checked. Once the ignore count reaches zero,
2679 @value{GDBN} resumes checking the condition.
2681 You could achieve the effect of the ignore count with a condition such
2682 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2683 is decremented each time. @xref{Convenience Vars, ,Convenience
2687 @node Break Commands
2688 @subsection Breakpoint command lists
2690 @cindex breakpoint commands
2691 You can give any breakpoint (or watchpoint) a series of commands to
2692 execute when your program stops due to that breakpoint. For example, you
2693 might want to print the values of certain expressions, or enable other
2699 @item commands @r{[}@var{bnum}@r{]}
2700 @itemx @dots{} @var{command-list} @dots{}
2702 Specify a list of commands for breakpoint number @var{bnum}. The commands
2703 themselves appear on the following lines. Type a line containing just
2704 @code{end} to terminate the commands.
2706 To remove all commands from a breakpoint, type @code{commands} and
2707 follow it immediately with @code{end}; that is, give no commands.
2709 With no @var{bnum} argument, @code{commands} refers to the last
2710 breakpoint or watchpoint set (not to the breakpoint most recently
2714 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2715 disabled within a @var{command-list}.
2717 You can use breakpoint commands to start your program up again. Simply
2718 use the @code{continue} command, or @code{step}, or any other command
2719 that resumes execution.
2721 Any other commands in the command list, after a command that resumes
2722 execution, are ignored. This is because any time you resume execution
2723 (even with a simple @code{next} or @code{step}), you may encounter
2724 another breakpoint---which could have its own command list, leading to
2725 ambiguities about which list to execute.
2728 If the first command you specify in a command list is @code{silent}, the
2729 usual message about stopping at a breakpoint is not printed. This may
2730 be desirable for breakpoints that are to print a specific message and
2731 then continue. If none of the remaining commands print anything, you
2732 see no sign that the breakpoint was reached. @code{silent} is
2733 meaningful only at the beginning of a breakpoint command list.
2735 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2736 print precisely controlled output, and are often useful in silent
2737 breakpoints. @xref{Output, ,Commands for controlled output}.
2739 For example, here is how you could use breakpoint commands to print the
2740 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2746 printf "x is %d\n",x
2751 One application for breakpoint commands is to compensate for one bug so
2752 you can test for another. Put a breakpoint just after the erroneous line
2753 of code, give it a condition to detect the case in which something
2754 erroneous has been done, and give it commands to assign correct values
2755 to any variables that need them. End with the @code{continue} command
2756 so that your program does not stop, and start with the @code{silent}
2757 command so that no output is produced. Here is an example:
2769 @node Breakpoint Menus
2770 @subsection Breakpoint menus
2772 @cindex symbol overloading
2774 Some programming languages (notably C++) permit a single function name
2775 to be defined several times, for application in different contexts.
2776 This is called @dfn{overloading}. When a function name is overloaded,
2777 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2778 a breakpoint. If you realize this is a problem, you can use
2779 something like @samp{break @var{function}(@var{types})} to specify which
2780 particular version of the function you want. Otherwise, @value{GDBN} offers
2781 you a menu of numbered choices for different possible breakpoints, and
2782 waits for your selection with the prompt @samp{>}. The first two
2783 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2784 sets a breakpoint at each definition of @var{function}, and typing
2785 @kbd{0} aborts the @code{break} command without setting any new
2788 For example, the following session excerpt shows an attempt to set a
2789 breakpoint at the overloaded symbol @code{String::after}.
2790 We choose three particular definitions of that function name:
2792 @c FIXME! This is likely to change to show arg type lists, at least
2794 (@value{GDBP}) b String::after
2797 [2] file:String.cc; line number:867
2798 [3] file:String.cc; line number:860
2799 [4] file:String.cc; line number:875
2800 [5] file:String.cc; line number:853
2801 [6] file:String.cc; line number:846
2802 [7] file:String.cc; line number:735
2804 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2805 Breakpoint 2 at 0xb344: file String.cc, line 875.
2806 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2807 Multiple breakpoints were set.
2808 Use the "delete" command to delete unwanted
2814 @c @ifclear BARETARGET
2815 @c @node Error in Breakpoints
2816 @c @subsection ``Cannot insert breakpoints''
2818 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
2820 @c Under some operating systems, breakpoints cannot be used in a program if
2821 @c any other process is running that program. In this situation,
2822 @c attempting to run or continue a program with a breakpoint causes
2823 @c @value{GDBN} to stop the other process.
2825 @c When this happens, you have three ways to proceed:
2829 @c Remove or disable the breakpoints, then continue.
2832 @c Suspend @value{GDBN}, and copy the file containing your program to a new
2833 @c name. Resume @value{GDBN} and use the @code{exec-file} command to specify
2834 @c that @value{GDBN} should run your program under that name.
2835 @c Then start your program again.
2838 @c Relink your program so that the text segment is nonsharable, using the
2839 @c linker option @samp{-N}. The operating system limitation may not apply
2840 @c to nonsharable executables.
2844 @node Continuing and Stepping
2845 @section Continuing and stepping
2849 @cindex resuming execution
2850 @dfn{Continuing} means resuming program execution until your program
2851 completes normally. In contrast, @dfn{stepping} means executing just
2852 one more ``step'' of your program, where ``step'' may mean either one
2853 line of source code, or one machine instruction (depending on what
2854 particular command you use). Either when continuing
2855 or when stepping, your program may stop even sooner, due to
2860 a breakpoint or a signal. (If due to a signal, you may want to use
2861 @code{handle}, or use @samp{signal 0} to resume execution.
2862 @xref{Signals, ,Signals}.)
2869 @item continue @r{[}@var{ignore-count}@r{]}
2870 @itemx c @r{[}@var{ignore-count}@r{]}
2871 @itemx fg @r{[}@var{ignore-count}@r{]}
2872 Resume program execution, at the address where your program last stopped;
2873 any breakpoints set at that address are bypassed. The optional argument
2874 @var{ignore-count} allows you to specify a further number of times to
2875 ignore a breakpoint at this location; its effect is like that of
2876 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2878 The argument @var{ignore-count} is meaningful only when your program
2879 stopped due to a breakpoint. At other times, the argument to
2880 @code{continue} is ignored.
2882 The synonyms @code{c} and @code{fg} are provided purely for convenience,
2883 and have exactly the same behavior as @code{continue}.
2886 To resume execution at a different place, you can use @code{return}
2887 (@pxref{Returning, ,Returning from a function}) to go back to the
2888 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2889 different address}) to go to an arbitrary location in your program.
2891 A typical technique for using stepping is to set a breakpoint
2893 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2896 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2899 beginning of the function or the section of your program where a
2900 problem is believed to lie, run your program until it stops at that
2901 breakpoint, and then step through the suspect area, examining the
2902 variables that are interesting, until you see the problem happen.
2908 Continue running your program until control reaches a different source
2909 line, then stop it and return control to @value{GDBN}. This command is
2910 abbreviated @code{s}.
2913 @c "without debugging information" is imprecise; actually "without line
2914 @c numbers in the debugging information". (gcc -g1 has debugging info but
2915 @c not line numbers). But it seems complex to try to make that
2916 @c distinction here.
2917 @emph{Warning:} If you use the @code{step} command while control is
2918 within a function that was compiled without debugging information,
2919 execution proceeds until control reaches a function that does have
2920 debugging information. Likewise, it will not step into a function which
2921 is compiled without debugging information. To step through functions
2922 without debugging information, use the @code{stepi} command, described
2926 The @code{step} command now only stops at the first instruction of a
2927 source line. This prevents the multiple stops that used to occur in
2928 switch statements, for loops, etc. @code{step} continues to stop if a
2929 function that has debugging information is called within the line.
2931 Also, the @code{step} command now only enters a subroutine if there is line
2932 number information for the subroutine. Otherwise it acts like the
2933 @code{next} command. This avoids problems when using @code{cc -gl}
2934 on MIPS machines. Previously, @code{step} entered subroutines if there
2935 was any debugging information about the routine.
2937 @item step @var{count}
2938 Continue running as in @code{step}, but do so @var{count} times. If a
2939 breakpoint is reached,
2941 or a signal not related to stepping occurs before @var{count} steps,
2943 stepping stops right away.
2947 @item next @r{[}@var{count}@r{]}
2948 Continue to the next source line in the current (innermost) stack frame.
2949 This is similar to @code{step}, but function calls that appear within the line
2950 of code are executed without stopping. Execution stops when control
2951 reaches a different line of code at the original stack level that was
2952 executing when you gave the @code{next} command. This command is abbreviated
2955 An argument @var{count} is a repeat count, as for @code{step}.
2958 @c FIX ME!! Do we delete this, or is there a way it fits in with
2959 @c the following paragraph? --- Vctoria
2961 @c @code{next} within a function that lacks debugging information acts like
2962 @c @code{step}, but any function calls appearing within the code of the
2963 @c function are executed without stopping.
2965 The @code{next} command now only stops at the first instruction of a
2966 source line. This prevents the multiple stops that used to occur in
2967 swtch statements, for loops, etc.
2971 Continue running until just after function in the selected stack frame
2972 returns. Print the returned value (if any).
2974 Contrast this with the @code{return} command (@pxref{Returning,
2975 ,Returning from a function}).
2981 Continue running until a source line past the current line, in the
2982 current stack frame, is reached. This command is used to avoid single
2983 stepping through a loop more than once. It is like the @code{next}
2984 command, except that when @code{until} encounters a jump, it
2985 automatically continues execution until the program counter is greater
2986 than the address of the jump.
2988 This means that when you reach the end of a loop after single stepping
2989 though it, @code{until} makes your program continue execution until it
2990 exits the loop. In contrast, a @code{next} command at the end of a loop
2991 simply steps back to the beginning of the loop, which forces you to step
2992 through the next iteration.
2994 @code{until} always stops your program if it attempts to exit the current
2997 @code{until} may produce somewhat counterintuitive results if the order
2998 of machine code does not match the order of the source lines. For
2999 example, in the following excerpt from a debugging session, the @code{f}
3000 (@code{frame}) command shows that execution is stopped at line
3001 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3005 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3007 (@value{GDBP}) until
3008 195 for ( ; argc > 0; NEXTARG) @{
3011 This happened because, for execution efficiency, the compiler had
3012 generated code for the loop closure test at the end, rather than the
3013 start, of the loop---even though the test in a C @code{for}-loop is
3014 written before the body of the loop. The @code{until} command appeared
3015 to step back to the beginning of the loop when it advanced to this
3016 expression; however, it has not really gone to an earlier
3017 statement---not in terms of the actual machine code.
3019 @code{until} with no argument works by means of single
3020 instruction stepping, and hence is slower than @code{until} with an
3023 @item until @var{location}
3024 @itemx u @var{location}
3025 Continue running your program until either the specified location is
3026 reached, or the current stack frame returns. @var{location} is any of
3027 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3028 ,Setting breakpoints}). This form of the command uses breakpoints,
3029 and hence is quicker than @code{until} without an argument.
3035 Execute one machine instruction, then stop and return to the debugger.
3037 It is often useful to do @samp{display/i $pc} when stepping by machine
3038 instructions. This makes @value{GDBN} automatically display the next
3039 instruction to be executed, each time your program stops. @xref{Auto
3040 Display,, Automatic display}.
3042 An argument is a repeat count, as in @code{step}.
3049 Execute one machine instruction, but if it is a function call,
3050 proceed until the function returns.
3052 An argument is a repeat count, as in @code{next}.
3060 A signal is an asynchronous event that can happen in a program. The
3061 operating system defines the possible kinds of signals, and gives each
3062 kind a name and a number. For example, in Unix @code{SIGINT} is the
3063 signal a program gets when you type an interrupt (often @kbd{C-c});
3064 @code{SIGSEGV} is the signal a program gets from referencing a place in
3065 memory far away from all the areas in use; @code{SIGALRM} occurs when
3066 the alarm clock timer goes off (which happens only if your program has
3067 requested an alarm).
3069 @cindex fatal signals
3070 Some signals, including @code{SIGALRM}, are a normal part of the
3071 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3072 errors; these signals are @dfn{fatal} (kill your program immediately) if the
3073 program has not specified in advance some other way to handle the signal.
3074 @code{SIGINT} does not indicate an error in your program, but it is normally
3075 fatal so it can carry out the purpose of the interrupt: to kill the program.
3077 @value{GDBN} has the ability to detect any occurrence of a signal in your
3078 program. You can tell @value{GDBN} in advance what to do for each kind of
3081 @cindex handling signals
3082 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3083 (so as not to interfere with their role in the functioning of your program)
3084 but to stop your program immediately whenever an error signal happens.
3085 You can change these settings with the @code{handle} command.
3088 @kindex info signals
3090 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3091 handle each one. You can use this to see the signal numbers of all
3092 the defined types of signals.
3094 @code{info handle} is the new alias for @code{info signals}.
3097 @item handle @var{signal} @var{keywords}@dots{}
3098 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3099 be the number of a signal or its name (with or without the @samp{SIG} at the
3100 beginning). The @var{keywords} say what change to make.
3104 The keywords allowed by the @code{handle} command can be abbreviated.
3105 Their full names are:
3109 @value{GDBN} should not stop your program when this signal happens. It may
3110 still print a message telling you that the signal has come in.
3113 @value{GDBN} should stop your program when this signal happens. This implies
3114 the @code{print} keyword as well.
3117 @value{GDBN} should print a message when this signal happens.
3120 @value{GDBN} should not mention the occurrence of the signal at all. This
3121 implies the @code{nostop} keyword as well.
3124 @value{GDBN} should allow your program to see this signal; your program
3125 can handle the signal, or else it may terminate if the signal is fatal
3129 @value{GDBN} should not allow your program to see this signal.
3133 When a signal stops your program, the signal is not visible until you
3134 continue. Your program sees the signal then, if @code{pass} is in
3135 effect for the signal in question @emph{at that time}. In other words,
3136 after @value{GDBN} reports a signal, you can use the @code{handle}
3137 command with @code{pass} or @code{nopass} to control whether your
3138 program sees that signal when you continue.
3140 You can also use the @code{signal} command to prevent your program from
3141 seeing a signal, or cause it to see a signal it normally would not see,
3142 or to give it any signal at any time. For example, if your program stopped
3143 due to some sort of memory reference error, you might store correct
3144 values into the erroneous variables and continue, hoping to see more
3145 execution; but your program would probably terminate immediately as
3146 a result of the fatal signal once it saw the signal. To prevent this,
3147 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3153 @section Stopping and starting multi-thread programs
3155 When your program has multiple threads (@pxref{Threads,, Debugging
3156 programs with multiple threads}), you can choose whether to set
3157 breakpoints on all threads, or on a particular thread.
3160 @cindex breakpoints and threads
3161 @cindex thread breakpoints
3162 @kindex break @dots{} thread @var{threadno}
3163 @item break @var{linespec} thread @var{threadno}
3164 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3165 @var{linespec} specifies source lines; there are several ways of
3166 writing them, but the effect is always to specify some source line.
3168 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3169 to specify that you only want @value{GDBN} to stop the program when a
3170 particular thread reaches this breakpoint. @var{threadno} is one of the
3171 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3172 column of the @samp{info threads} display.
3174 If you do not specify @samp{thread @var{threadno}} when you set a
3175 breakpoint, the breakpoint applies to @emph{all} threads of your
3178 You can use the @code{thread} qualifier on conditional breakpoints as
3179 well; in this case, place @samp{thread @var{threadno}} before the
3180 breakpoint condition, like this:
3183 (gdb) break frik.c:13 thread 28 if bartab > lim
3188 @cindex stopped threads
3189 @cindex threads, stopped
3190 Whenever your program stops under @value{GDBN} for any reason,
3191 @emph{all} threads of execution stop, not just the current thread. This
3192 allows you to examine the overall state of the program, including
3193 switching between threads, without worrying that things may change
3196 @cindex continuing threads
3197 @cindex threads, continuing
3198 Conversely, whenever you restart the program, @emph{all} threads start
3199 executing. @emph{This is true even when single-stepping} with commands
3200 like @code{step} or @code{next}.
3202 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3203 Since thread scheduling is up to your debugging target's operating
3204 system (not controlled by @value{GDBN}), other threads may
3205 execute more than one statement while the current thread completes a
3206 single step. Moreover, in general other threads stop in the middle of a
3207 statement, rather than at a clean statement boundary, when the program
3210 You might even find your program stopped in another thread after
3211 continuing or even single-stepping. This happens whenever some other
3212 thread runs into a breakpoint, a signal, or an exception before the
3213 first thread completes whatever you requested.
3217 @chapter Examining the Stack
3219 When your program has stopped, the first thing you need to know is where it
3220 stopped and how it got there.
3223 Each time your program performs a function call, information about the call
3225 That information includes the location of the call in your program,
3226 the arguments of the call,
3227 and the local variables of the function being called.
3228 The information is saved in a block of data called a @dfn{stack frame}.
3229 The stack frames are allocated in a region of memory called the @dfn{call
3232 When your program stops, the @value{GDBN} commands for examining the
3233 stack allow you to see all of this information.
3235 @cindex selected frame
3236 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3237 @value{GDBN} commands refer implicitly to the selected frame. In
3238 particular, whenever you ask @value{GDBN} for the value of a variable in
3239 your program, the value is found in the selected frame. There are
3240 special @value{GDBN} commands to select whichever frame you are
3241 interested in. @xref{Selection, ,Selecting a frame}.
3243 When your program stops, @value{GDBN} automatically selects the
3244 currently executing frame and describes it briefly, similar to the
3245 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3248 * Frames:: Stack frames
3249 * Backtrace:: Backtraces
3250 * Selection:: Selecting a frame
3251 * Frame Info:: Information on a frame
3253 * MIPS Stack:: MIPS machines and the function stack
3258 @section Stack frames
3262 The call stack is divided up into contiguous pieces called @dfn{stack
3263 frames}, or @dfn{frames} for short; each frame is the data associated
3264 with one call to one function. The frame contains the arguments given
3265 to the function, the function's local variables, and the address at
3266 which the function is executing.
3268 @cindex initial frame
3269 @cindex outermost frame
3270 @cindex innermost frame
3271 When your program is started, the stack has only one frame, that of the
3272 function @code{main}. This is called the @dfn{initial} frame or the
3273 @dfn{outermost} frame. Each time a function is called, a new frame is
3274 made. Each time a function returns, the frame for that function invocation
3275 is eliminated. If a function is recursive, there can be many frames for
3276 the same function. The frame for the function in which execution is
3277 actually occurring is called the @dfn{innermost} frame. This is the most
3278 recently created of all the stack frames that still exist.
3280 @cindex frame pointer
3281 Inside your program, stack frames are identified by their addresses. A
3282 stack frame consists of many bytes, each of which has its own address; each
3283 kind of computer has a convention for choosing one byte whose
3284 address serves as the address of the frame. Usually this address is kept
3285 in a register called the @dfn{frame pointer register} while execution is
3286 going on in that frame.
3288 @cindex frame number
3289 @value{GDBN} assigns numbers to all existing stack frames, starting with
3290 zero for the innermost frame, one for the frame that called it,
3291 and so on upward. These numbers do not really exist in your program;
3292 they are assigned by @value{GDBN} to give you a way of designating stack
3293 frames in @value{GDBN} commands.
3295 @c below produces an acceptable overful hbox. --mew 13aug1993
3296 @cindex frameless execution
3297 Some compilers provide a way to compile functions so that they operate
3298 without stack frames. (For example, the @code{@value{GCC}} option
3299 @samp{-fomit-frame-pointer} generates functions without a frame.)
3300 This is occasionally done with heavily used library functions to save
3301 the frame setup time. @value{GDBN} has limited facilities for dealing
3302 with these function invocations. If the innermost function invocation
3303 has no stack frame, @value{GDBN} nevertheless regards it as though
3304 it had a separate frame, which is numbered zero as usual, allowing
3305 correct tracing of the function call chain. However, @value{GDBN} has
3306 no provision for frameless functions elsewhere in the stack.
3310 @item frame @var{args}
3311 The @code{frame} command allows you to move from one stack frame to another,
3312 and to print the stack frame you select. @var{args} may be either the
3313 address of the frame or the stack frame number. Without an argument,
3314 @code{frame} prints the current stack frame.
3316 @kindex select-frame
3318 The @code{select-frame} command allows you to move from one stack frame
3319 to another without printing the frame. This is the silent version of
3326 A backtrace is a summary of how your program got where it is. It shows one
3327 line per frame, for many frames, starting with the currently executing
3328 frame (frame zero), followed by its caller (frame one), and on up the
3336 Print a backtrace of the entire stack: one line per frame for all
3337 frames in the stack.
3339 You can stop the backtrace at any time by typing the system interrupt
3340 character, normally @kbd{C-c}.
3342 @item backtrace @var{n}
3344 Similar, but print only the innermost @var{n} frames.
3346 @item backtrace -@var{n}
3348 Similar, but print only the outermost @var{n} frames.
3354 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3355 are additional aliases for @code{backtrace}.
3357 Each line in the backtrace shows the frame number and the function name.
3358 The program counter value is also shown---unless you use @code{set
3359 print address off}. The backtrace also shows the source file name and
3360 line number, as well as the arguments to the function. The program
3361 counter value is omitted if it is at the beginning of the code for that
3364 Here is an example of a backtrace. It was made with the command
3365 @samp{bt 3}, so it shows the innermost three frames.
3369 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3371 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3372 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3374 (More stack frames follow...)
3379 The display for frame zero does not begin with a program counter
3380 value, indicating that your program has stopped at the beginning of the
3381 code for line @code{993} of @code{builtin.c}.
3384 @section Selecting a frame
3386 Most commands for examining the stack and other data in your program work on
3387 whichever stack frame is selected at the moment. Here are the commands for
3388 selecting a stack frame; all of them finish by printing a brief description
3389 of the stack frame just selected.
3396 Select frame number @var{n}. Recall that frame zero is the innermost
3397 (currently executing) frame, frame one is the frame that called the
3398 innermost one, and so on. The highest-numbered frame is the one for
3401 @item frame @var{addr}
3403 Select the frame at address @var{addr}. This is useful mainly if the
3404 chaining of stack frames has been damaged by a bug, making it
3405 impossible for @value{GDBN} to assign numbers properly to all frames. In
3406 addition, this can be useful when your program has multiple stacks and
3407 switches between them.
3409 @ifclear H8EXCLUSIVE
3410 On the SPARC architecture, @code{frame} needs two addresses to
3411 select an arbitrary frame: a frame pointer and a stack pointer.
3413 On the MIPS and Alpha architecture, it needs two addresses: a stack
3414 pointer and a program counter.
3416 On the 29k architecture, it needs three addresses: a register stack
3417 pointer, a program counter, and a memory stack pointer.
3418 @c note to future updaters: this is conditioned on a flag
3419 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3420 @c as of 27 Jan 1994.
3425 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3426 advances toward the outermost frame, to higher frame numbers, to frames
3427 that have existed longer. @var{n} defaults to one.
3432 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3433 advances toward the innermost frame, to lower frame numbers, to frames
3434 that were created more recently. @var{n} defaults to one. You may
3435 abbreviate @code{down} as @code{do}.
3438 All of these commands end by printing two lines of output describing the
3439 frame. The first line shows the frame number, the function name, the
3440 arguments, and the source file and line number of execution in that
3441 frame. The second line shows the text of that source line.
3449 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3451 10 read_input_file (argv[i]);
3455 After such a printout, the @code{list} command with no arguments
3456 prints ten lines centered on the point of execution in the frame.
3457 @xref{List, ,Printing source lines}.
3460 @kindex down-silently
3462 @item up-silently @var{n}
3463 @itemx down-silently @var{n}
3464 These two commands are variants of @code{up} and @code{down},
3465 respectively; they differ in that they do their work silently, without
3466 causing display of the new frame. They are intended primarily for use
3467 in @value{GDBN} command scripts, where the output might be unnecessary and
3472 @section Information about a frame
3474 There are several other commands to print information about the selected
3480 When used without any argument, this command does not change which
3481 frame is selected, but prints a brief description of the currently
3482 selected stack frame. It can be abbreviated @code{f}. With an
3483 argument, this command is used to select a stack frame.
3484 @xref{Selection, ,Selecting a frame}.
3490 This command prints a verbose description of the selected stack frame,
3495 the address of the frame
3497 the address of the next frame down (called by this frame)
3499 the address of the next frame up (caller of this frame)
3501 the language in which the source code corresponding to this frame is written
3503 the address of the frame's arguments
3505 the program counter saved in it (the address of execution in the caller frame)
3507 which registers were saved in the frame
3510 @noindent The verbose description is useful when
3511 something has gone wrong that has made the stack format fail to fit
3512 the usual conventions.
3514 @item info frame @var{addr}
3515 @itemx info f @var{addr}
3516 Print a verbose description of the frame at address @var{addr}, without
3517 selecting that frame. The selected frame remains unchanged by this
3518 command. This requires the same kind of address (more than one for some
3519 architectures) that you specify in the @code{frame} command.
3520 @xref{Selection, ,Selecting a frame}.
3524 Print the arguments of the selected frame, each on a separate line.
3528 Print the local variables of the selected frame, each on a separate
3529 line. These are all variables (declared either static or automatic)
3530 accessible at the point of execution of the selected frame.
3534 @cindex catch exceptions
3535 @cindex exception handlers
3537 Print a list of all the exception handlers that are active in the
3538 current stack frame at the current point of execution. To see other
3539 exception handlers, visit the associated frame (using the @code{up},
3540 @code{down}, or @code{frame} commands); then type @code{info catch}.
3541 @xref{Exception Handling, ,Breakpoints and exceptions}.
3547 @section MIPS machines and the function stack
3549 @cindex stack on MIPS
3551 MIPS based computers use an unusual stack frame, which sometimes
3552 requires @value{GDBN} to search backward in the object code to find the
3553 beginning of a function.
3555 @cindex response time, MIPS debugging
3556 To improve response time (especially for embedded applications, where
3557 @value{GDBN} may be restricted to a slow serial line for this search)
3558 you may want to limit the size of this search, using one of these
3562 @cindex @code{heuristic-fence-post} (MIPS)
3563 @item set heuristic-fence-post @var{limit}
3564 Restrict @value{GDBN} to examining at most @var{limit} bytes in its search
3565 for the beginning of a function. A value of @var{0} (the default)
3566 means there is no limit. However, except for @var{0}, the larger the
3567 limit the more bytes @code{heuristic-fence-post} must search and
3568 therefore the longer it takes to run.
3570 @item show heuristic-fence-post
3571 Display the current limit.
3575 These commands are available @emph{only} when @value{GDBN} is configured
3576 for debugging programs on MIPS processors.
3580 @chapter Examining Source Files
3582 @value{GDBN} can print parts of your program's source, since the debugging
3583 information recorded in the program tells @value{GDBN} what source files were
3584 used to build it. When your program stops, @value{GDBN} spontaneously prints
3585 the line where it stopped. Likewise, when you select a stack frame
3586 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3587 execution in that frame has stopped. You can print other portions of
3588 source files by explicit command.
3591 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may prefer
3593 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under @sc{gnu} Emacs}.
3597 * List:: Printing source lines
3599 * Search:: Searching source files
3602 * Source Path:: Specifying source directories
3603 * Machine Code:: Source and machine code
3607 @section Printing source lines
3611 To print lines from a source file, use the @code{list} command
3612 (abbreviated @code{l}). By default, ten lines are printed.
3613 There are several ways to specify what part of the file you want to print.
3615 Here are the forms of the @code{list} command most commonly used:
3618 @item list @var{linenum}
3619 Print lines centered around line number @var{linenum} in the
3620 current source file.
3622 @item list @var{function}
3623 Print lines centered around the beginning of function
3627 Print more lines. If the last lines printed were printed with a
3628 @code{list} command, this prints lines following the last lines
3629 printed; however, if the last line printed was a solitary line printed
3630 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3631 Stack}), this prints lines centered around that line.
3634 Print lines just before the lines last printed.
3637 By default, @value{GDBN} prints ten source lines with any of these forms of
3638 the @code{list} command. You can change this using @code{set listsize}:
3641 @kindex set listsize
3642 @item set listsize @var{count}
3643 Make the @code{list} command display @var{count} source lines (unless
3644 the @code{list} argument explicitly specifies some other number).
3646 @kindex show listsize
3648 Display the number of lines that @code{list} prints.
3651 Repeating a @code{list} command with @key{RET} discards the argument,
3652 so it is equivalent to typing just @code{list}. This is more useful
3653 than listing the same lines again. An exception is made for an
3654 argument of @samp{-}; that argument is preserved in repetition so that
3655 each repetition moves up in the source file.
3658 In general, the @code{list} command expects you to supply zero, one or two
3659 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3660 of writing them but the effect is always to specify some source line.
3661 Here is a complete description of the possible arguments for @code{list}:
3664 @item list @var{linespec}
3665 Print lines centered around the line specified by @var{linespec}.
3667 @item list @var{first},@var{last}
3668 Print lines from @var{first} to @var{last}. Both arguments are
3671 @item list ,@var{last}
3672 Print lines ending with @var{last}.
3674 @item list @var{first},
3675 Print lines starting with @var{first}.
3678 Print lines just after the lines last printed.
3681 Print lines just before the lines last printed.
3684 As described in the preceding table.
3687 Here are the ways of specifying a single source line---all the
3692 Specifies line @var{number} of the current source file.
3693 When a @code{list} command has two linespecs, this refers to
3694 the same source file as the first linespec.
3697 Specifies the line @var{offset} lines after the last line printed.
3698 When used as the second linespec in a @code{list} command that has
3699 two, this specifies the line @var{offset} lines down from the
3703 Specifies the line @var{offset} lines before the last line printed.
3705 @item @var{filename}:@var{number}
3706 Specifies line @var{number} in the source file @var{filename}.
3708 @item @var{function}
3709 Specifies the line that begins the body of the function @var{function}.
3710 For example: in C, this is the line with the open brace.
3712 @item @var{filename}:@var{function}
3713 Specifies the line of the open-brace that begins the body of the
3714 function @var{function} in the file @var{filename}. You only need the
3715 file name with a function name to avoid ambiguity when there are
3716 identically named functions in different source files.
3718 @item *@var{address}
3719 Specifies the line containing the program address @var{address}.
3720 @var{address} may be any expression.
3725 @section Searching source files
3727 @kindex reverse-search
3729 There are two commands for searching through the current source file for a
3734 @kindex forward-search
3735 @item forward-search @var{regexp}
3736 @itemx search @var{regexp}
3737 The command @samp{forward-search @var{regexp}} checks each line,
3738 starting with the one following the last line listed, for a match for
3739 @var{regexp}. It lists the line that is found. You can use the
3740 synonym @samp{search @var{regexp}} or abbreviate the command name as
3743 @item reverse-search @var{regexp}
3744 The command @samp{reverse-search @var{regexp}} checks each line, starting
3745 with the one before the last line listed and going backward, for a match
3746 for @var{regexp}. It lists the line that is found. You can abbreviate
3747 this command as @code{rev}.
3752 @section Specifying source directories
3755 @cindex directories for source files
3756 Executable programs sometimes do not record the directories of the source
3757 files from which they were compiled, just the names. Even when they do,
3758 the directories could be moved between the compilation and your debugging
3759 session. @value{GDBN} has a list of directories to search for source files;
3760 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3761 it tries all the directories in the list, in the order they are present
3762 in the list, until it finds a file with the desired name. Note that
3763 the executable search path is @emph{not} used for this purpose. Neither is
3764 the current working directory, unless it happens to be in the source
3767 If @value{GDBN} cannot find a source file in the source path, and the
3768 object program records a directory, @value{GDBN} tries that directory
3769 too. If the source path is empty, and there is no record of the
3770 compilation directory, @value{GDBN} looks in the current directory as a
3773 Whenever you reset or rearrange the source path, @value{GDBN} clears out
3774 any information it has cached about where source files are found and where
3775 each line is in the file.
3779 When you start @value{GDBN}, its source path is empty.
3780 To add other directories, use the @code{directory} command.
3783 @item directory @var{dirname} @dots{}
3784 @item dir @var{dirname} @dots{}
3785 Add directory @var{dirname} to the front of the source path. Several
3786 directory names may be given to this command, separated by @samp{:} or
3787 whitespace. You may specify a directory that is already in the source
3788 path; this moves it forward, so @value{GDBN} searches it sooner.
3794 @cindex compilation directory
3795 @cindex current directory
3796 @cindex working directory
3797 @cindex directory, current
3798 @cindex directory, compilation
3799 You can use the string @samp{$cdir} to refer to the compilation
3800 directory (if one is recorded), and @samp{$cwd} to refer to the current
3801 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3802 tracks the current working directory as it changes during your @value{GDBN}
3803 session, while the latter is immediately expanded to the current
3804 directory at the time you add an entry to the source path.
3807 Reset the source path to empty again. This requires confirmation.
3809 @c RET-repeat for @code{directory} is explicitly disabled, but since
3810 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3812 @item show directories
3813 @kindex show directories
3814 Print the source path: show which directories it contains.
3817 If your source path is cluttered with directories that are no longer of
3818 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3819 versions of source. You can correct the situation as follows:
3823 Use @code{directory} with no argument to reset the source path to empty.
3826 Use @code{directory} with suitable arguments to reinstall the
3827 directories you want in the source path. You can add all the
3828 directories in one command.
3832 @section Source and machine code
3834 You can use the command @code{info line} to map source lines to program
3835 addresses (and vice versa), and the command @code{disassemble} to display
3836 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
3837 mode, the @code{info line} command now causes the arrow to point to the
3838 line specified. Also, @code{info line} prints addresses in symbolic form as
3843 @item info line @var{linespec}
3844 Print the starting and ending addresses of the compiled code for
3845 source line @var{linespec}. You can specify source lines in any of
3846 the ways understood by the @code{list} command (@pxref{List, ,Printing
3850 For example, we can use @code{info line} to discover the location of
3851 the object code for the first line of function
3852 @code{m4_changequote}:
3855 (@value{GDBP}) info line m4_changecom
3856 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3860 We can also inquire (using @code{*@var{addr}} as the form for
3861 @var{linespec}) what source line covers a particular address:
3863 (@value{GDBP}) info line *0x63ff
3864 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3867 @cindex @code{$_} and @code{info line}
3868 After @code{info line}, the default address for the @code{x} command
3869 is changed to the starting address of the line, so that @samp{x/i} is
3870 sufficient to begin examining the machine code (@pxref{Memory,
3871 ,Examining memory}). Also, this address is saved as the value of the
3872 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3877 @cindex assembly instructions
3878 @cindex instructions, assembly
3879 @cindex machine instructions
3880 @cindex listing machine instructions
3882 This specialized command dumps a range of memory as machine
3883 instructions. The default memory range is the function surrounding the
3884 program counter of the selected frame. A single argument to this
3885 command is a program counter value; @value{GDBN} dumps the function
3886 surrounding this value. Two arguments specify a range of addresses
3887 (first inclusive, second exclusive) to dump.
3890 @ifclear H8EXCLUSIVE
3891 We can use @code{disassemble} to inspect the object code
3892 range shown in the last @code{info line} example (the example
3893 shows SPARC machine instructions):
3897 (@value{GDBP}) disas 0x63e4 0x6404
3898 Dump of assembler code from 0x63e4 to 0x6404:
3899 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3900 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3901 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3902 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3903 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3904 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3905 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3906 0x6400 <builtin_init+5368>: nop
3907 End of assembler dump.
3912 For example, here is the beginning of the output for the
3913 disassembly of a function @code{fact}:
3917 (@value{GDBP}) disas fact
3918 Dump of assembler code for function fact:
3920 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3921 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3922 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3923 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3924 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3925 0x8038 <fact+12> 19 11 sub.w r1,r1
3933 @kindex set assembly-language
3934 @cindex assembly instructions
3935 @cindex instructions, assembly
3936 @cindex machine instructions
3937 @cindex listing machine instructions
3938 @item set assembly-language @var{instruction-set}
3939 This command selects the instruction set to use when disassembling the program via the
3940 @code{disassemble} or @code{x/i} commands. It is useful for architectures that
3941 have more than one native instruction set.
3943 Currently it is only defined for the Intel x86 family. You can set @var{instruction-set}
3944 to either @code{i386} or @code{i8086}. The default is @code{i386}.
3949 @chapter Examining Data
3951 @cindex printing data
3952 @cindex examining data
3955 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3956 @c document because it is nonstandard... Under Epoch it displays in a
3957 @c different window or something like that.
3958 The usual way to examine data in your program is with the @code{print}
3959 command (abbreviated @code{p}), or its synonym @code{inspect}.
3961 It evaluates and prints the value of an expression of the language your
3962 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3967 @item print @var{exp}
3968 @itemx print /@var{f} @var{exp}
3969 @var{exp} is an expression (in the source language). By default the
3970 value of @var{exp} is printed in a format appropriate to its data type;
3971 you can choose a different format by specifying @samp{/@var{f}}, where
3972 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3976 @itemx print /@var{f}
3977 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3978 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3979 conveniently inspect the same value in an alternative format.
3982 A more low-level way of examining data is with the @code{x} command.
3983 It examines data in memory at a specified address and prints it in a
3984 specified format. @xref{Memory, ,Examining memory}.
3986 If you are interested in information about types, or about how the fields
3991 are declared, use the @code{ptype @var{exp}}
3992 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3995 * Expressions:: Expressions
3996 * Variables:: Program variables
3997 * Arrays:: Artificial arrays
3998 * Output Formats:: Output formats
3999 * Memory:: Examining memory
4000 * Auto Display:: Automatic display
4001 * Print Settings:: Print settings
4002 * Value History:: Value history
4003 * Convenience Vars:: Convenience variables
4004 * Registers:: Registers
4006 * Floating Point Hardware:: Floating point hardware
4011 @section Expressions
4014 @code{print} and many other @value{GDBN} commands accept an expression and
4015 compute its value. Any kind of constant, variable or operator defined
4016 by the programming language you are using is valid in an expression in
4017 @value{GDBN}. This includes conditional expressions, function calls, casts
4018 and string constants. It unfortunately does not include symbols defined
4019 by preprocessor @code{#define} commands.
4021 @value{GDBN} now supports array constants in expressions input by
4022 the user. The syntax is @var{@{element, element@dots{}@}}. For example,
4023 you can now use the command @code{print @{1, 2, 3@}} to build up an array in
4024 memory that is malloc'd in the target program.
4027 Because C is so widespread, most of the expressions shown in examples in
4028 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4029 Languages}, for information on how to use expressions in other
4032 In this section, we discuss operators that you can use in @value{GDBN}
4033 expressions regardless of your programming language.
4035 Casts are supported in all languages, not just in C, because it is so
4036 useful to cast a number into a pointer in order to examine a structure
4037 at that address in memory.
4038 @c FIXME: casts supported---Mod2 true?
4041 @value{GDBN} supports these operators, in addition to those common
4042 to programming languages:
4046 @samp{@@} is a binary operator for treating parts of memory as arrays.
4047 @xref{Arrays, ,Artificial arrays}, for more information.
4050 @samp{::} allows you to specify a variable in terms of the file or
4051 function where it is defined. @xref{Variables, ,Program variables}.
4053 @cindex @{@var{type}@}
4054 @cindex type casting memory
4055 @cindex memory, viewing as typed object
4056 @cindex casts, to view memory
4057 @item @{@var{type}@} @var{addr}
4058 Refers to an object of type @var{type} stored at address @var{addr} in
4059 memory. @var{addr} may be any expression whose value is an integer or
4060 pointer (but parentheses are required around binary operators, just as in
4061 a cast). This construct is allowed regardless of what kind of data is
4062 normally supposed to reside at @var{addr}.
4066 @section Program variables
4068 The most common kind of expression to use is the name of a variable
4071 Variables in expressions are understood in the selected stack frame
4072 (@pxref{Selection, ,Selecting a frame}); they must be either:
4083 visible according to the scope rules of the
4084 programming language from the point of execution in that frame
4087 @noindent This means that in the function
4102 you can examine and use the variable @code{a} whenever your program is
4103 executing within the function @code{foo}, but you can only use or
4104 examine the variable @code{b} while your program is executing inside
4105 the block where @code{b} is declared.
4107 @cindex variable name conflict
4108 There is an exception: you can refer to a variable or function whose
4109 scope is a single source file even if the current execution point is not
4110 in this file. But it is possible to have more than one such variable or
4111 function with the same name (in different source files). If that
4112 happens, referring to that name has unpredictable effects. If you wish,
4113 you can specify a static variable in a particular function or file,
4114 using the colon-colon notation:
4118 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4122 @var{file}::@var{variable}
4123 @var{function}::@var{variable}
4127 Here @var{file} or @var{function} is the name of the context for the
4128 static @var{variable}. In the case of file names, you can use quotes to
4129 make sure @value{GDBN} parses the file name as a single word---for example,
4130 to print a global value of @code{x} defined in @file{f2.c}:
4133 (@value{GDBP}) p 'f2.c'::x
4137 @cindex C++ scope resolution
4138 This use of @samp{::} is very rarely in conflict with the very similar
4139 use of the same notation in C++. @value{GDBN} also supports use of the C++
4140 scope resolution operator in @value{GDBN} expressions.
4141 @c FIXME: Um, so what happens in one of those rare cases where it's in
4145 @cindex wrong values
4146 @cindex variable values, wrong
4148 @emph{Warning:} Occasionally, a local variable may appear to have the
4149 wrong value at certain points in a function---just after entry to a new
4150 scope, and just before exit.
4152 You may see this problem when you are stepping by machine instructions.
4153 This is because, on most machines, it takes more than one instruction to
4154 set up a stack frame (including local variable definitions); if you are
4155 stepping by machine instructions, variables may appear to have the wrong
4156 values until the stack frame is completely built. On exit, it usually
4157 also takes more than one machine instruction to destroy a stack frame;
4158 after you begin stepping through that group of instructions, local
4159 variable definitions may be gone.
4162 @section Artificial arrays
4164 @cindex artificial array
4166 It is often useful to print out several successive objects of the
4167 same type in memory; a section of an array, or an array of
4168 dynamically determined size for which only a pointer exists in the
4171 You can do this by referring to a contiguous span of memory as an
4172 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4173 operand of @samp{@@} should be the first element of the desired array
4174 and be an individual object. The right operand should be the desired length
4175 of the array. The result is an array value whose elements are all of
4176 the type of the left argument. The first element is actually the left
4177 argument; the second element comes from bytes of memory immediately
4178 following those that hold the first element, and so on. Here is an
4179 example. If a program says
4182 int *array = (int *) malloc (len * sizeof (int));
4186 you can print the contents of @code{array} with
4192 The left operand of @samp{@@} must reside in memory. Array values made
4193 with @samp{@@} in this way behave just like other arrays in terms of
4194 subscripting, and are coerced to pointers when used in expressions.
4195 Artificial arrays most often appear in expressions via the value history
4196 (@pxref{Value History, ,Value history}), after printing one out.
4198 Another way to create an artificial array is to use a cast.
4199 This re-interprets a value as if it were an array.
4200 The value need not be in memory:
4202 (@value{GDBP}) p/x (short[2])0x12345678
4203 $1 = @{0x1234, 0x5678@}
4206 As a convenience, if you leave the array length out (as in
4207 @samp{(@var{type})[])@var{value}}) gdb calculates the size to fill
4208 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4210 (@value{GDBP}) p/x (short[])0x12345678
4211 $2 = @{0x1234, 0x5678@}
4214 Sometimes the artificial array mechanism is not quite enough; in
4215 moderately complex data structures, the elements of interest may not
4216 actually be adjacent---for example, if you are interested in the values
4217 of pointers in an array. One useful work-around in this situation is
4218 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4219 variables}) as a counter in an expression that prints the first
4220 interesting value, and then repeat that expression via @key{RET}. For
4221 instance, suppose you have an array @code{dtab} of pointers to
4222 structures, and you are interested in the values of a field @code{fv}
4223 in each structure. Here is an example of what you might type:
4233 @node Output Formats
4234 @section Output formats
4236 @cindex formatted output
4237 @cindex output formats
4238 By default, @value{GDBN} prints a value according to its data type. Sometimes
4239 this is not what you want. For example, you might want to print a number
4240 in hex, or a pointer in decimal. Or you might want to view data in memory
4241 at a certain address as a character string or as an instruction. To do
4242 these things, specify an @dfn{output format} when you print a value.
4244 The simplest use of output formats is to say how to print a value
4245 already computed. This is done by starting the arguments of the
4246 @code{print} command with a slash and a format letter. The format
4247 letters supported are:
4251 Regard the bits of the value as an integer, and print the integer in
4255 Print as integer in signed decimal.
4258 Print as integer in unsigned decimal.
4261 Print as integer in octal.
4264 Print as integer in binary. The letter @samp{t} stands for ``two''.
4265 @footnote{@samp{b} cannot be used because these format letters are also
4266 used with the @code{x} command, where @samp{b} stands for ``byte'';
4267 @pxref{Memory,,Examining memory}.}
4270 @cindex unknown address, locating
4271 Print as an address, both absolute in hexadecimal and as an offset from
4272 the nearest preceding symbol. You can use this format used to discover
4273 where (in what function) an unknown address is located:
4276 (@value{GDBP}) p/a 0x54320
4277 $3 = 0x54320 <_initialize_vx+396>
4281 Regard as an integer and print it as a character constant.
4284 Regard the bits of the value as a floating point number and print
4285 using typical floating point syntax.
4288 For example, to print the program counter in hex (@pxref{Registers}), type
4295 Note that no space is required before the slash; this is because command
4296 names in @value{GDBN} cannot contain a slash.
4298 To reprint the last value in the value history with a different format,
4299 you can use the @code{print} command with just a format and no
4300 expression. For example, @samp{p/x} reprints the last value in hex.
4303 @section Examining memory
4305 You can use the command @code{x} (for ``examine'') to examine memory in
4306 any of several formats, independently of your program's data types.
4308 @cindex examining memory
4311 @item x/@var{nfu} @var{addr}
4314 Use the @code{x} command to examine memory.
4317 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4318 much memory to display and how to format it; @var{addr} is an
4319 expression giving the address where you want to start displaying memory.
4320 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4321 Several commands set convenient defaults for @var{addr}.
4324 @item @var{n}, the repeat count
4325 The repeat count is a decimal integer; the default is 1. It specifies
4326 how much memory (counting by units @var{u}) to display.
4327 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4330 @item @var{f}, the display format
4331 The display format is one of the formats used by @code{print},
4332 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4333 The default is @samp{x} (hexadecimal) initially.
4334 The default changes each time you use either @code{x} or @code{print}.
4336 @item @var{u}, the unit size
4337 The unit size is any of
4343 Halfwords (two bytes).
4345 Words (four bytes). This is the initial default.
4347 Giant words (eight bytes).
4350 Each time you specify a unit size with @code{x}, that size becomes the
4351 default unit the next time you use @code{x}. (For the @samp{s} and
4352 @samp{i} formats, the unit size is ignored and is normally not written.)
4354 @item @var{addr}, starting display address
4355 @var{addr} is the address where you want @value{GDBN} to begin displaying
4356 memory. The expression need not have a pointer value (though it may);
4357 it is always interpreted as an integer address of a byte of memory.
4358 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4359 @var{addr} is usually just after the last address examined---but several
4360 other commands also set the default address: @code{info breakpoints} (to
4361 the address of the last breakpoint listed), @code{info line} (to the
4362 starting address of a line), and @code{print} (if you use it to display
4363 a value from memory).
4366 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4367 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4368 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4369 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4370 @pxref{Registers}) in hexadecimal (@samp{x}).
4372 Since the letters indicating unit sizes are all distinct from the
4373 letters specifying output formats, you do not have to remember whether
4374 unit size or format comes first; either order works. The output
4375 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4376 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4378 Even though the unit size @var{u} is ignored for the formats @samp{s}
4379 and @samp{i}, you might still want to use a count @var{n}; for example,
4380 @samp{3i} specifies that you want to see three machine instructions,
4381 including any operands. The command @code{disassemble} gives an
4382 alternative way of inspecting machine instructions; @pxref{Machine
4383 Code,,Source and machine code}.
4385 All the defaults for the arguments to @code{x} are designed to make it
4386 easy to continue scanning memory with minimal specifications each time
4387 you use @code{x}. For example, after you have inspected three machine
4388 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4389 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4390 the repeat count @var{n} is used again; the other arguments default as
4391 for successive uses of @code{x}.
4393 @cindex @code{$_}, @code{$__}, and value history
4394 The addresses and contents printed by the @code{x} command are not saved
4395 in the value history because there is often too much of them and they
4396 would get in the way. Instead, @value{GDBN} makes these values available for
4397 subsequent use in expressions as values of the convenience variables
4398 @code{$_} and @code{$__}. After an @code{x} command, the last address
4399 examined is available for use in expressions in the convenience variable
4400 @code{$_}. The contents of that address, as examined, are available in
4401 the convenience variable @code{$__}.
4403 If the @code{x} command has a repeat count, the address and contents saved
4404 are from the last memory unit printed; this is not the same as the last
4405 address printed if several units were printed on the last line of output.
4408 @section Automatic display
4409 @cindex automatic display
4410 @cindex display of expressions
4412 If you find that you want to print the value of an expression frequently
4413 (to see how it changes), you might want to add it to the @dfn{automatic
4414 display list} so that @value{GDBN} prints its value each time your program stops.
4415 Each expression added to the list is given a number to identify it;
4416 to remove an expression from the list, you specify that number.
4417 The automatic display looks like this:
4421 3: bar[5] = (struct hack *) 0x3804
4425 This display shows item numbers, expressions and their current values. As with
4426 displays you request manually using @code{x} or @code{print}, you can
4427 specify the output format you prefer; in fact, @code{display} decides
4428 whether to use @code{print} or @code{x} depending on how elaborate your
4429 format specification is---it uses @code{x} if you specify a unit size,
4430 or one of the two formats (@samp{i} and @samp{s}) that are only
4431 supported by @code{x}; otherwise it uses @code{print}.
4435 @item display @var{exp}
4436 Add the expression @var{exp} to the list of expressions to display
4437 each time your program stops. @xref{Expressions, ,Expressions}.
4439 @code{display} does not repeat if you press @key{RET} again after using it.
4441 @item display/@var{fmt} @var{exp}
4442 For @var{fmt} specifying only a display format and not a size or
4443 count, add the expression @var{exp} to the auto-display list but
4444 arrange to display it each time in the specified format @var{fmt}.
4445 @xref{Output Formats,,Output formats}.
4447 @item display/@var{fmt} @var{addr}
4448 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4449 number of units, add the expression @var{addr} as a memory address to
4450 be examined each time your program stops. Examining means in effect
4451 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4454 For example, @samp{display/i $pc} can be helpful, to see the machine
4455 instruction about to be executed each time execution stops (@samp{$pc}
4456 is a common name for the program counter; @pxref{Registers}).
4459 @kindex delete display
4461 @item undisplay @var{dnums}@dots{}
4462 @itemx delete display @var{dnums}@dots{}
4463 Remove item numbers @var{dnums} from the list of expressions to display.
4465 @code{undisplay} does not repeat if you press @key{RET} after using it.
4466 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4468 @kindex disable display
4469 @item disable display @var{dnums}@dots{}
4470 Disable the display of item numbers @var{dnums}. A disabled display
4471 item is not printed automatically, but is not forgotten. It may be
4472 enabled again later.
4474 @kindex enable display
4475 @item enable display @var{dnums}@dots{}
4476 Enable display of item numbers @var{dnums}. It becomes effective once
4477 again in auto display of its expression, until you specify otherwise.
4480 Display the current values of the expressions on the list, just as is
4481 done when your program stops.
4483 @kindex info display
4485 Print the list of expressions previously set up to display
4486 automatically, each one with its item number, but without showing the
4487 values. This includes disabled expressions, which are marked as such.
4488 It also includes expressions which would not be displayed right now
4489 because they refer to automatic variables not currently available.
4492 If a display expression refers to local variables, then it does not make
4493 sense outside the lexical context for which it was set up. Such an
4494 expression is disabled when execution enters a context where one of its
4495 variables is not defined. For example, if you give the command
4496 @code{display last_char} while inside a function with an argument
4497 @code{last_char}, @value{GDBN} displays this argument while your program
4498 continues to stop inside that function. When it stops elsewhere---where
4499 there is no variable @code{last_char}---the display is disabled
4500 automatically. The next time your program stops where @code{last_char}
4501 is meaningful, you can enable the display expression once again.
4503 @node Print Settings
4504 @section Print settings
4506 @cindex format options
4507 @cindex print settings
4508 @value{GDBN} provides the following ways to control how arrays, structures,
4509 and symbols are printed.
4512 These settings are useful for debugging programs in any language:
4515 @kindex set print address
4516 @item set print address
4517 @itemx set print address on
4518 @value{GDBN} prints memory addresses showing the location of stack
4519 traces, structure values, pointer values, breakpoints, and so forth,
4520 even when it also displays the contents of those addresses. The default
4521 is @code{on}. For example, this is what a stack frame display looks like with
4522 @code{set print address on}:
4527 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4529 530 if (lquote != def_lquote)
4533 @item set print address off
4534 Do not print addresses when displaying their contents. For example,
4535 this is the same stack frame displayed with @code{set print address off}:
4539 (@value{GDBP}) set print addr off
4541 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4542 530 if (lquote != def_lquote)
4546 You can use @samp{set print address off} to eliminate all machine
4547 dependent displays from the @value{GDBN} interface. For example, with
4548 @code{print address off}, you should get the same text for backtraces on
4549 all machines---whether or not they involve pointer arguments.
4551 @kindex show print address
4552 @item show print address
4553 Show whether or not addresses are to be printed.
4556 When @value{GDBN} prints a symbolic address, it normally prints the
4557 closest earlier symbol plus an offset. If that symbol does not uniquely
4558 identify the address (for example, it is a name whose scope is a single
4559 source file), you may need to clarify. One way to do this is with
4560 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4561 you can set @value{GDBN} to print the source file and line number when
4562 it prints a symbolic address:
4565 @kindex set print symbol-filename
4566 @item set print symbol-filename on
4567 Tell @value{GDBN} to print the source file name and line number of a
4568 symbol in the symbolic form of an address.
4570 @item set print symbol-filename off
4571 Do not print source file name and line number of a symbol. This is the
4574 @kindex show print symbol-filename
4575 @item show print symbol-filename
4576 Show whether or not @value{GDBN} will print the source file name and
4577 line number of a symbol in the symbolic form of an address.
4580 Another situation where it is helpful to show symbol filenames and line
4581 numbers is when disassembling code; @value{GDBN} shows you the line
4582 number and source file that corresponds to each instruction.
4584 Also, you may wish to see the symbolic form only if the address being
4585 printed is reasonably close to the closest earlier symbol:
4588 @kindex set print max-symbolic-offset
4589 @item set print max-symbolic-offset @var{max-offset}
4590 Tell @value{GDBN} to only display the symbolic form of an address if the
4591 offset between the closest earlier symbol and the address is less than
4592 @var{max-offset}. The default is 0, which tells @value{GDBN}
4593 to always print the symbolic form of an address if any symbol precedes it.
4595 @kindex show print max-symbolic-offset
4596 @item show print max-symbolic-offset
4597 Ask how large the maximum offset is that @value{GDBN} prints in a
4601 @cindex wild pointer, interpreting
4602 @cindex pointer, finding referent
4603 If you have a pointer and you are not sure where it points, try
4604 @samp{set print symbol-filename on}. Then you can determine the name
4605 and source file location of the variable where it points, using
4606 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4607 For example, here @value{GDBN} shows that a variable @code{ptt} points
4608 at another variable @code{t}, defined in @file{hi2.c}:
4611 (@value{GDBP}) set print symbol-filename on
4612 (@value{GDBP}) p/a ptt
4613 $4 = 0xe008 <t in hi2.c>
4617 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4618 does not show the symbol name and filename of the referent, even with
4619 the appropriate @code{set print} options turned on.
4622 Other settings control how different kinds of objects are printed:
4625 @kindex set print array
4626 @item set print array
4627 @itemx set print array on
4628 Pretty print arrays. This format is more convenient to read,
4629 but uses more space. The default is off.
4631 @item set print array off
4632 Return to compressed format for arrays.
4634 @kindex show print array
4635 @item show print array
4636 Show whether compressed or pretty format is selected for displaying
4639 @kindex set print elements
4640 @item set print elements @var{number-of-elements}
4641 Set a limit on how many elements of an array @value{GDBN} will print.
4642 If @value{GDBN} is printing a large array, it stops printing after it has
4643 printed the number of elements set by the @code{set print elements} command.
4644 This limit also applies to the display of strings.
4645 Setting @var{number-of-elements} to zero means that the printing is unlimited.
4647 @kindex show print elements
4648 @item show print elements
4649 Display the number of elements of a large array that @value{GDBN} will print.
4650 If the number is 0, then the printing is unlimited.
4652 @kindex set print null-stop
4653 @item set print null-stop
4654 Cause @value{GDBN} to stop printing the characters of an array when the first
4655 @sc{NULL} is encountered. This is useful when large arrays actually
4656 contain only short strings.
4658 @kindex set print pretty
4659 @item set print pretty on
4660 Cause @value{GDBN} to print structures in an indented format with one member
4661 per line, like this:
4676 @item set print pretty off
4677 Cause @value{GDBN} to print structures in a compact format, like this:
4681 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4682 meat = 0x54 "Pork"@}
4687 This is the default format.
4689 @kindex show print pretty
4690 @item show print pretty
4691 Show which format @value{GDBN} is using to print structures.
4693 @kindex set print sevenbit-strings
4694 @item set print sevenbit-strings on
4695 Print using only seven-bit characters; if this option is set,
4696 @value{GDBN} displays any eight-bit characters (in strings or
4697 character values) using the notation @code{\}@var{nnn}. This setting is
4698 best if you are working in English (@sc{ascii}) and you use the
4699 high-order bit of characters as a marker or ``meta'' bit.
4701 @item set print sevenbit-strings off
4702 Print full eight-bit characters. This allows the use of more
4703 international character sets, and is the default.
4705 @kindex show print sevenbit-strings
4706 @item show print sevenbit-strings
4707 Show whether or not @value{GDBN} is printing only seven-bit characters.
4709 @kindex set print union
4710 @item set print union on
4711 Tell @value{GDBN} to print unions which are contained in structures. This
4712 is the default setting.
4714 @item set print union off
4715 Tell @value{GDBN} not to print unions which are contained in structures.
4717 @kindex show print union
4718 @item show print union
4719 Ask @value{GDBN} whether or not it will print unions which are contained in
4722 For example, given the declarations
4725 typedef enum @{Tree, Bug@} Species;
4726 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4727 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4738 struct thing foo = @{Tree, @{Acorn@}@};
4742 with @code{set print union on} in effect @samp{p foo} would print
4745 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4749 and with @code{set print union off} in effect it would print
4752 $1 = @{it = Tree, form = @{...@}@}
4759 These settings are of interest when debugging C++ programs:
4763 @kindex set print demangle
4764 @item set print demangle
4765 @itemx set print demangle on
4766 Print C++ names in their source form rather than in the encoded
4767 (``mangled'') form passed to the assembler and linker for type-safe
4768 linkage. The default is @samp{on}.
4770 @kindex show print demangle
4771 @item show print demangle
4772 Show whether C++ names are printed in mangled or demangled form.
4774 @kindex set print asm-demangle
4775 @item set print asm-demangle
4776 @itemx set print asm-demangle on
4777 Print C++ names in their source form rather than their mangled form, even
4778 in assembler code printouts such as instruction disassemblies.
4781 @kindex show print asm-demangle
4782 @item show print asm-demangle
4783 Show whether C++ names in assembly listings are printed in mangled
4786 @kindex set demangle-style
4787 @cindex C++ symbol decoding style
4788 @cindex symbol decoding style, C++
4789 @item set demangle-style @var{style}
4790 Choose among several encoding schemes used by different compilers to
4791 represent C++ names. The choices for @var{style} are currently:
4795 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4798 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
4799 This is the default.
4802 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4805 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4806 @strong{Warning:} this setting alone is not sufficient to allow
4807 debugging @code{cfront}-generated executables. @value{GDBN} would
4808 require further enhancement to permit that.
4811 Show the list of formats.
4814 @kindex show demangle-style
4815 @item show demangle-style
4816 Display the encoding style currently in use for decoding C++ symbols.
4818 @kindex set print object
4819 @item set print object
4820 @itemx set print object on
4821 When displaying a pointer to an object, identify the @emph{actual}
4822 (derived) type of the object rather than the @emph{declared} type, using
4823 the virtual function table.
4825 @item set print object off
4826 Display only the declared type of objects, without reference to the
4827 virtual function table. This is the default setting.
4829 @kindex show print object
4830 @item show print object
4831 Show whether actual, or declared, object types are displayed.
4833 @kindex set print static-members
4834 @item set print static-members
4835 @itemx set print static-members on
4836 Print static members when displaying a C++ object. The default is on.
4838 @item set print static-members off
4839 Do not print static members when displaying a C++ object.
4841 @kindex show print static-members
4842 @item show print static-members
4843 Show whether C++ static members are printed, or not.
4845 @kindex set print vtbl
4846 @item set print vtbl
4847 @itemx set print vtbl on
4848 Pretty print C++ virtual function tables. The default is off.
4850 @item set print vtbl off
4851 Do not pretty print C++ virtual function tables.
4853 @kindex show print vtbl
4854 @item show print vtbl
4855 Show whether C++ virtual function tables are pretty printed, or not.
4860 @section Value history
4862 @cindex value history
4863 Values printed by the @code{print} command are saved in the @value{GDBN}
4864 @dfn{value history}. This allows you to refer to them in other expressions.
4865 Values are kept until the symbol table is re-read or discarded
4866 (for example with the @code{file} or @code{symbol-file} commands).
4867 When the symbol table changes, the value history is discarded,
4868 since the values may contain pointers back to the types defined in the
4873 @cindex history number
4874 The values printed are given @dfn{history numbers} by which you can
4875 refer to them. These are successive integers starting with one.
4876 @code{print} shows you the history number assigned to a value by
4877 printing @samp{$@var{num} = } before the value; here @var{num} is the
4880 To refer to any previous value, use @samp{$} followed by the value's
4881 history number. The way @code{print} labels its output is designed to
4882 remind you of this. Just @code{$} refers to the most recent value in
4883 the history, and @code{$$} refers to the value before that.
4884 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4885 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4886 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4888 For example, suppose you have just printed a pointer to a structure and
4889 want to see the contents of the structure. It suffices to type
4895 If you have a chain of structures where the component @code{next} points
4896 to the next one, you can print the contents of the next one with this:
4903 You can print successive links in the chain by repeating this
4904 command---which you can do by just typing @key{RET}.
4906 Note that the history records values, not expressions. If the value of
4907 @code{x} is 4 and you type these commands:
4915 then the value recorded in the value history by the @code{print} command
4916 remains 4 even though the value of @code{x} has changed.
4921 Print the last ten values in the value history, with their item numbers.
4922 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4923 values} does not change the history.
4925 @item show values @var{n}
4926 Print ten history values centered on history item number @var{n}.
4929 Print ten history values just after the values last printed. If no more
4930 values are available, @code{show values +} produces no display.
4933 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4934 same effect as @samp{show values +}.
4936 @node Convenience Vars
4937 @section Convenience variables
4939 @cindex convenience variables
4940 @value{GDBN} provides @dfn{convenience variables} that you can use within
4941 @value{GDBN} to hold on to a value and refer to it later. These variables
4942 exist entirely within @value{GDBN}; they are not part of your program, and
4943 setting a convenience variable has no direct effect on further execution
4944 of your program. That is why you can use them freely.
4946 Convenience variables are prefixed with @samp{$}. Any name preceded by
4947 @samp{$} can be used for a convenience variable, unless it is one of
4948 the predefined machine-specific register names (@pxref{Registers}).
4949 (Value history references, in contrast, are @emph{numbers} preceded
4950 by @samp{$}. @xref{Value History, ,Value history}.)
4952 You can save a value in a convenience variable with an assignment
4953 expression, just as you would set a variable in your program.
4957 set $foo = *object_ptr
4961 would save in @code{$foo} the value contained in the object pointed to by
4964 Using a convenience variable for the first time creates it, but its
4965 value is @code{void} until you assign a new value. You can alter the
4966 value with another assignment at any time.
4968 Convenience variables have no fixed types. You can assign a convenience
4969 variable any type of value, including structures and arrays, even if
4970 that variable already has a value of a different type. The convenience
4971 variable, when used as an expression, has the type of its current value.
4974 @kindex show convenience
4975 @item show convenience
4976 Print a list of convenience variables used so far, and their values.
4977 Abbreviated @code{show con}.
4980 One of the ways to use a convenience variable is as a counter to be
4981 incremented or a pointer to be advanced. For example, to print
4982 a field from successive elements of an array of structures:
4986 print bar[$i++]->contents
4989 @noindent Repeat that command by typing @key{RET}.
4991 Some convenience variables are created automatically by @value{GDBN} and given
4992 values likely to be useful.
4997 The variable @code{$_} is automatically set by the @code{x} command to
4998 the last address examined (@pxref{Memory, ,Examining memory}). Other
4999 commands which provide a default address for @code{x} to examine also
5000 set @code{$_} to that address; these commands include @code{info line}
5001 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5002 except when set by the @code{x} command, in which case it is a pointer
5003 to the type of @code{$__}.
5007 The variable @code{$__} is automatically set by the @code{x} command
5008 to the value found in the last address examined. Its type is chosen
5009 to match the format in which the data was printed.
5013 The variable @code{$_exitcode} is automatically set to the exit code when
5014 the program being debugged terminates.
5021 You can refer to machine register contents, in expressions, as variables
5022 with names starting with @samp{$}. The names of registers are different
5023 for each machine; use @code{info registers} to see the names used on
5027 @kindex info registers
5028 @item info registers
5029 Print the names and values of all registers except floating-point
5030 registers (in the selected stack frame).
5032 @kindex info all-registers
5033 @cindex floating point registers
5034 @item info all-registers
5035 Print the names and values of all registers, including floating-point
5038 @item info registers @var{regname} @dots{}
5039 Print the @dfn{relativized} value of each specified register @var{regname}.
5040 As discussed in detail below, register values are normally relative to
5041 the selected stack frame. @var{regname} may be any register name valid on
5042 the machine you are using, with or without the initial @samp{$}.
5045 @value{GDBN} has four ``standard'' register names that are available (in
5046 expressions) on most machines---whenever they do not conflict with an
5047 architecture's canonical mnemonics for registers. The register names
5048 @code{$pc} and @code{$sp} are used for the program counter register and
5049 the stack pointer. @code{$fp} is used for a register that contains a
5050 pointer to the current stack frame, and @code{$ps} is used for a
5051 register that contains the processor status. For example,
5052 you could print the program counter in hex with
5059 or print the instruction to be executed next with
5066 or add four to the stack pointer@footnote{This is a way of removing
5067 one word from the stack, on machines where stacks grow downward in
5068 memory (most machines, nowadays). This assumes that the innermost
5069 stack frame is selected; setting @code{$sp} is not allowed when other
5070 stack frames are selected. To pop entire frames off the stack,
5071 regardless of machine architecture, use @code{return};
5072 @pxref{Returning, ,Returning from a function}.} with
5078 Whenever possible, these four standard register names are available on
5079 your machine even though the machine has different canonical mnemonics,
5080 so long as there is no conflict. The @code{info registers} command
5081 shows the canonical names. For example, on the SPARC, @code{info
5082 registers} displays the processor status register as @code{$psr} but you
5083 can also refer to it as @code{$ps}.
5085 @value{GDBN} always considers the contents of an ordinary register as an
5086 integer when the register is examined in this way. Some machines have
5087 special registers which can hold nothing but floating point; these
5088 registers are considered to have floating point values. There is no way
5089 to refer to the contents of an ordinary register as floating point value
5090 (although you can @emph{print} it as a floating point value with
5091 @samp{print/f $@var{regname}}).
5093 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5094 means that the data format in which the register contents are saved by
5095 the operating system is not the same one that your program normally
5096 sees. For example, the registers of the 68881 floating point
5097 coprocessor are always saved in ``extended'' (raw) format, but all C
5098 programs expect to work with ``double'' (virtual) format. In such
5099 cases, @value{GDBN} normally works with the virtual format only (the format
5100 that makes sense for your program), but the @code{info registers} command
5101 prints the data in both formats.
5103 Normally, register values are relative to the selected stack frame
5104 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5105 value that the register would contain if all stack frames farther in
5106 were exited and their saved registers restored. In order to see the
5107 true contents of hardware registers, you must select the innermost
5108 frame (with @samp{frame 0}).
5110 However, @value{GDBN} must deduce where registers are saved, from the machine
5111 code generated by your compiler. If some registers are not saved, or if
5112 @value{GDBN} is unable to locate the saved registers, the selected stack
5113 frame makes no difference.
5117 @kindex set rstack_high_address
5118 @cindex AMD 29K register stack
5119 @cindex register stack, AMD29K
5120 @item set rstack_high_address @var{address}
5121 On AMD 29000 family processors, registers are saved in a separate
5122 ``register stack''. There is no way for @value{GDBN} to determine the extent
5123 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
5124 enough''. This may result in @value{GDBN} referencing memory locations that
5125 do not exist. If necessary, you can get around this problem by
5126 specifying the ending address of the register stack with the @code{set
5127 rstack_high_address} command. The argument should be an address, which
5128 you probably want to precede with @samp{0x} to specify in
5131 @kindex show rstack_high_address
5132 @item show rstack_high_address
5133 Display the current limit of the register stack, on AMD 29000 family
5139 @node Floating Point Hardware
5140 @section Floating point hardware
5141 @cindex floating point
5143 Depending on the configuration, @value{GDBN} may be able to give
5144 you more information about the status of the floating point hardware.
5149 Display hardware-dependent information about the floating
5150 point unit. The exact contents and layout vary depending on the
5151 floating point chip. Currently, @samp{info float} is supported on
5152 the ARM and x86 machines.
5158 @chapter Using @value{GDBN} with Different Languages
5162 Although programming languages generally have common aspects, they are
5163 rarely expressed in the same manner. For instance, in ANSI C,
5164 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5165 Modula-2, it is accomplished by @code{p^}. Values can also be
5166 represented (and displayed) differently. Hex numbers in C appear as
5167 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5170 @cindex working language
5171 Language-specific information is built into @value{GDBN} for some languages,
5172 allowing you to express operations like the above in your program's
5173 native language, and allowing @value{GDBN} to output values in a manner
5174 consistent with the syntax of your program's native language. The
5175 language you use to build expressions is called the @dfn{working
5179 * Setting:: Switching between source languages
5180 * Show:: Displaying the language
5182 * Checks:: Type and range checks
5185 * Support:: Supported languages
5189 @section Switching between source languages
5191 There are two ways to control the working language---either have @value{GDBN}
5192 set it automatically, or select it manually yourself. You can use the
5193 @code{set language} command for either purpose. On startup, @value{GDBN}
5194 defaults to setting the language automatically. The working language is
5195 used to determine how expressions you type are interpreted, how values
5198 In addition to the working language, every source file that
5199 @value{GDBN} knows about has its own working language. For some object
5200 file formats, the compiler might indicate which language a particular
5201 source file is in. However, most of the time @value{GDBN} infers the
5202 language from the name of the file. The language of a source file
5203 controls whether C++ names are demangled---this way @code{backtrace} can
5204 show each frame appropriately for its own language. There is no way to
5205 set the language of a source file from within @value{GDBN}.
5207 This is most commonly a problem when you use a program, such
5208 as @code{cfront} or @code{f2c}, that generates C but is written in
5209 another language. In that case, make the
5210 program use @code{#line} directives in its C output; that way
5211 @value{GDBN} will know the correct language of the source code of the original
5212 program, and will display that source code, not the generated C code.
5215 * Filenames:: Filename extensions and languages.
5216 * Manually:: Setting the working language manually
5217 * Automatically:: Having @value{GDBN} infer the source language
5221 @subsection List of filename extensions and languages
5223 If a source file name ends in one of the following extensions, then
5224 @value{GDBN} infers that its language is the one indicated.
5229 Modula-2 source file
5250 Assembler source file. This actually behaves almost like C, but
5251 @value{GDBN} does not skip over function prologues when stepping.
5255 @subsection Setting the working language
5257 If you allow @value{GDBN} to set the language automatically,
5258 expressions are interpreted the same way in your debugging session and
5261 @kindex set language
5262 If you wish, you may set the language manually. To do this, issue the
5263 command @samp{set language @var{lang}}, where @var{lang} is the name of
5269 @code{c} or @code{modula-2}.
5271 For a list of the supported languages, type @samp{set language}.
5274 Setting the language manually prevents @value{GDBN} from updating the working
5275 language automatically. This can lead to confusion if you try
5276 to debug a program when the working language is not the same as the
5277 source language, when an expression is acceptable to both
5278 languages---but means different things. For instance, if the current
5279 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5287 might not have the effect you intended. In C, this means to add
5288 @code{b} and @code{c} and place the result in @code{a}. The result
5289 printed would be the value of @code{a}. In Modula-2, this means to compare
5290 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5294 @subsection Having @value{GDBN} infer the source language
5296 To have @value{GDBN} set the working language automatically, use
5297 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5298 then infers the working language. That is, when your program stops in a
5299 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5300 working language to the language recorded for the function in that
5301 frame. If the language for a frame is unknown (that is, if the function
5302 or block corresponding to the frame was defined in a source file that
5303 does not have a recognized extension), the current working language is
5304 not changed, and @value{GDBN} issues a warning.
5306 This may not seem necessary for most programs, which are written
5307 entirely in one source language. However, program modules and libraries
5308 written in one source language can be used by a main program written in
5309 a different source language. Using @samp{set language auto} in this
5310 case frees you from having to set the working language manually.
5313 @section Displaying the language
5315 The following commands help you find out which language is the
5316 working language, and also what language source files were written in.
5318 @kindex show language
5323 Display the current working language. This is the
5324 language you can use with commands such as @code{print} to
5325 build and compute expressions that may involve variables in your program.
5328 Display the source language for this frame. This language becomes the
5329 working language if you use an identifier from this frame.
5330 @xref{Frame Info, ,Information about a frame}, to identify the other
5331 information listed here.
5334 Display the source language of this source file.
5335 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5336 information listed here.
5341 @section Type and range checking
5344 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5345 checking are included, but they do not yet have any effect. This
5346 section documents the intended facilities.
5348 @c FIXME remove warning when type/range code added
5350 Some languages are designed to guard you against making seemingly common
5351 errors through a series of compile- and run-time checks. These include
5352 checking the type of arguments to functions and operators, and making
5353 sure mathematical overflows are caught at run time. Checks such as
5354 these help to ensure a program's correctness once it has been compiled
5355 by eliminating type mismatches, and providing active checks for range
5356 errors when your program is running.
5358 @value{GDBN} can check for conditions like the above if you wish.
5359 Although @value{GDBN} does not check the statements in your program, it
5360 can check expressions entered directly into @value{GDBN} for evaluation via
5361 the @code{print} command, for example. As with the working language,
5362 @value{GDBN} can also decide whether or not to check automatically based on
5363 your program's source language. @xref{Support, ,Supported languages},
5364 for the default settings of supported languages.
5367 * Type Checking:: An overview of type checking
5368 * Range Checking:: An overview of range checking
5371 @cindex type checking
5372 @cindex checks, type
5374 @subsection An overview of type checking
5376 Some languages, such as Modula-2, are strongly typed, meaning that the
5377 arguments to operators and functions have to be of the correct type,
5378 otherwise an error occurs. These checks prevent type mismatch
5379 errors from ever causing any run-time problems. For example,
5387 The second example fails because the @code{CARDINAL} 1 is not
5388 type-compatible with the @code{REAL} 2.3.
5390 For the expressions you use in @value{GDBN} commands, you can tell the
5391 @value{GDBN} type checker to skip checking;
5392 to treat any mismatches as errors and abandon the expression;
5393 or to only issue warnings when type mismatches occur,
5394 but evaluate the expression anyway. When you choose the last of
5395 these, @value{GDBN} evaluates expressions like the second example above, but
5396 also issues a warning.
5398 Even if you turn type checking off, there may be other reasons
5399 related to type that prevent @value{GDBN} from evaluating an expression.
5400 For instance, @value{GDBN} does not know how to add an @code{int} and
5401 a @code{struct foo}. These particular type errors have nothing to do
5402 with the language in use, and usually arise from expressions, such as
5403 the one described above, which make little sense to evaluate anyway.
5405 Each language defines to what degree it is strict about type. For
5406 instance, both Modula-2 and C require the arguments to arithmetical
5407 operators to be numbers. In C, enumerated types and pointers can be
5408 represented as numbers, so that they are valid arguments to mathematical
5409 operators. @xref{Support, ,Supported languages}, for further
5410 details on specific languages.
5412 @value{GDBN} provides some additional commands for controlling the type checker:
5415 @kindex set check type
5416 @kindex show check type
5418 @item set check type auto
5419 Set type checking on or off based on the current working language.
5420 @xref{Support, ,Supported languages}, for the default settings for
5423 @item set check type on
5424 @itemx set check type off
5425 Set type checking on or off, overriding the default setting for the
5426 current working language. Issue a warning if the setting does not
5427 match the language default. If any type mismatches occur in
5428 evaluating an expression while typechecking is on, @value{GDBN} prints a
5429 message and aborts evaluation of the expression.
5431 @item set check type warn
5432 Cause the type checker to issue warnings, but to always attempt to
5433 evaluate the expression. Evaluating the expression may still
5434 be impossible for other reasons. For example, @value{GDBN} cannot add
5435 numbers and structures.
5438 Show the current setting of the type checker, and whether or not @value{GDBN}
5439 is setting it automatically.
5442 @cindex range checking
5443 @cindex checks, range
5444 @node Range Checking
5445 @subsection An overview of range checking
5447 In some languages (such as Modula-2), it is an error to exceed the
5448 bounds of a type; this is enforced with run-time checks. Such range
5449 checking is meant to ensure program correctness by making sure
5450 computations do not overflow, or indices on an array element access do
5451 not exceed the bounds of the array.
5453 For expressions you use in @value{GDBN} commands, you can tell
5454 @value{GDBN} to treat range errors in one of three ways: ignore them,
5455 always treat them as errors and abandon the expression, or issue
5456 warnings but evaluate the expression anyway.
5458 A range error can result from numerical overflow, from exceeding an
5459 array index bound, or when you type a constant that is not a member
5460 of any type. Some languages, however, do not treat overflows as an
5461 error. In many implementations of C, mathematical overflow causes the
5462 result to ``wrap around'' to lower values---for example, if @var{m} is
5463 the largest integer value, and @var{s} is the smallest, then
5466 @var{m} + 1 @result{} @var{s}
5469 This, too, is specific to individual languages, and in some cases
5470 specific to individual compilers or machines. @xref{Support, ,
5471 Supported languages}, for further details on specific languages.
5473 @value{GDBN} provides some additional commands for controlling the range checker:
5476 @kindex set check range
5477 @kindex show check range
5479 @item set check range auto
5480 Set range checking on or off based on the current working language.
5481 @xref{Support, ,Supported languages}, for the default settings for
5484 @item set check range on
5485 @itemx set check range off
5486 Set range checking on or off, overriding the default setting for the
5487 current working language. A warning is issued if the setting does not
5488 match the language default. If a range error occurs, then a message
5489 is printed and evaluation of the expression is aborted.
5491 @item set check range warn
5492 Output messages when the @value{GDBN} range checker detects a range error,
5493 but attempt to evaluate the expression anyway. Evaluating the
5494 expression may still be impossible for other reasons, such as accessing
5495 memory that the process does not own (a typical example from many Unix
5499 Show the current setting of the range checker, and whether or not it is
5500 being set automatically by @value{GDBN}.
5505 @section Supported languages
5508 @value{GDBN} 4 supports C, C++, and Modula-2.
5511 @value{GDBN} 4 supports C, and C++.
5513 Some @value{GDBN} features may be used in expressions regardless of the
5514 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5515 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5516 ,Expressions}) can be used with the constructs of any supported
5519 The following sections detail to what degree each source language is
5520 supported by @value{GDBN}. These sections are not meant to be language
5521 tutorials or references, but serve only as a reference guide to what the
5522 @value{GDBN} expression parser accepts, and what input and output
5523 formats should look like for different languages. There are many good
5524 books written on each of these languages; please look to these for a
5525 language reference or tutorial.
5530 * Modula-2:: Modula-2
5534 @subsection C and C++
5536 @cindex expressions in C or C++
5538 Since C and C++ are so closely related, many features of @value{GDBN} apply
5539 to both languages. Whenever this is the case, we discuss those languages
5543 @c Cancel this below, under same condition, at end of this chapter!
5549 @cindex @sc{gnu} C++
5550 The C++ debugging facilities are jointly implemented by the @sc{gnu} C++
5551 compiler and @value{GDBN}. Therefore, to debug your C++ code
5552 effectively, you must compile your C++ programs with the @sc{gnu} C++
5553 compiler, @code{g++}.
5555 For best results when debugging C++ programs, use the stabs debugging
5556 format. You can select that format explicitly with the @code{g++}
5557 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5558 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu} CC,
5559 gcc.info, Using @sc{gnu} CC}, for more information.
5563 @chapter C Language Support
5565 @cindex expressions in C
5567 Information specific to the C language is built into @value{GDBN} so that you
5568 can use C expressions while degugging. This also permits @value{GDBN} to
5569 output values in a manner consistent with C conventions.
5572 * C Operators:: C operators
5573 * C Constants:: C constants
5574 * Debugging C:: @value{GDBN} and C
5579 * C Operators:: C and C++ operators
5580 * C Constants:: C and C++ constants
5581 * Cplus expressions:: C++ expressions
5582 * C Defaults:: Default settings for C and C++
5584 * C Checks:: C and C++ type and range checks
5587 * Debugging C:: @value{GDBN} and C
5588 * Debugging C plus plus:: Special features for C++
5593 @cindex C and C++ operators
5595 @subsubsection C and C++ operators
5600 @section C operators
5603 Operators must be defined on values of specific types. For instance,
5604 @code{+} is defined on numbers, but not on structures. Operators are
5605 often defined on groups of types.
5608 For the purposes of C and C++, the following definitions hold:
5613 @emph{Integral types} include @code{int} with any of its storage-class
5614 specifiers; @code{char}; and @code{enum}.
5617 @emph{Floating-point types} include @code{float} and @code{double}.
5620 @emph{Pointer types} include all types defined as @code{(@var{type}
5624 @emph{Scalar types} include all of the above.
5628 The following operators are supported. They are listed here
5629 in order of increasing precedence:
5633 The comma or sequencing operator. Expressions in a comma-separated list
5634 are evaluated from left to right, with the result of the entire
5635 expression being the last expression evaluated.
5638 Assignment. The value of an assignment expression is the value
5639 assigned. Defined on scalar types.
5642 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5643 and translated to @w{@code{@var{a} = @var{a op b}}}.
5644 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5645 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5646 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5649 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5650 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5654 Logical @sc{or}. Defined on integral types.
5657 Logical @sc{and}. Defined on integral types.
5660 Bitwise @sc{or}. Defined on integral types.
5663 Bitwise exclusive-@sc{or}. Defined on integral types.
5666 Bitwise @sc{and}. Defined on integral types.
5669 Equality and inequality. Defined on scalar types. The value of these
5670 expressions is 0 for false and non-zero for true.
5672 @item <@r{, }>@r{, }<=@r{, }>=
5673 Less than, greater than, less than or equal, greater than or equal.
5674 Defined on scalar types. The value of these expressions is 0 for false
5675 and non-zero for true.
5678 left shift, and right shift. Defined on integral types.
5681 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5684 Addition and subtraction. Defined on integral types, floating-point types and
5687 @item *@r{, }/@r{, }%
5688 Multiplication, division, and modulus. Multiplication and division are
5689 defined on integral and floating-point types. Modulus is defined on
5693 Increment and decrement. When appearing before a variable, the
5694 operation is performed before the variable is used in an expression;
5695 when appearing after it, the variable's value is used before the
5696 operation takes place.
5699 Pointer dereferencing. Defined on pointer types. Same precedence as
5703 Address operator. Defined on variables. Same precedence as @code{++}.
5706 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5707 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5708 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5709 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5714 Negative. Defined on integral and floating-point types. Same
5715 precedence as @code{++}.
5718 Logical negation. Defined on integral types. Same precedence as
5722 Bitwise complement operator. Defined on integral types. Same precedence as
5727 Structure member, and pointer-to-structure member. For convenience,
5728 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5729 pointer based on the stored type information.
5730 Defined on @code{struct} and @code{union} data.
5733 Array indexing. @code{@var{a}[@var{i}]} is defined as
5734 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5737 Function parameter list. Same precedence as @code{->}.
5741 C++ scope resolution operator. Defined on
5742 @code{struct}, @code{union}, and @code{class} types.
5750 represent the @value{GDBN} scope operator (@pxref{Expressions,
5753 Same precedence as @code{::}, above.
5758 @cindex C and C++ constants
5760 @subsubsection C and C++ constants
5762 @value{GDBN} allows you to express the constants of C and C++ in the
5768 @section C constants
5770 @value{GDBN} allows you to express the constants of C in the
5776 Integer constants are a sequence of digits. Octal constants are
5777 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
5778 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5779 @samp{l}, specifying that the constant should be treated as a
5783 Floating point constants are a sequence of digits, followed by a decimal
5784 point, followed by a sequence of digits, and optionally followed by an
5785 exponent. An exponent is of the form:
5786 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5787 sequence of digits. The @samp{+} is optional for positive exponents.
5790 Enumerated constants consist of enumerated identifiers, or their
5791 integral equivalents.
5794 Character constants are a single character surrounded by single quotes
5795 (@code{'}), or a number---the ordinal value of the corresponding character
5796 (usually its @sc{ASCII} value). Within quotes, the single character may
5797 be represented by a letter or by @dfn{escape sequences}, which are of
5798 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5799 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5800 @samp{@var{x}} is a predefined special character---for example,
5801 @samp{\n} for newline.
5804 String constants are a sequence of character constants surrounded
5805 by double quotes (@code{"}).
5808 Pointer constants are an integral value. You can also write pointers
5809 to constants using the C operator @samp{&}.
5812 Array constants are comma-separated lists surrounded by braces @samp{@{}
5813 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5814 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5815 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5819 @node Cplus expressions
5820 @subsubsection C++ expressions
5822 @cindex expressions in C++
5823 @value{GDBN} expression handling has a number of extensions to
5824 interpret a significant subset of C++ expressions.
5826 @cindex C++ support, not in @sc{coff}
5827 @cindex @sc{coff} versus C++
5828 @cindex C++ and object formats
5829 @cindex object formats and C++
5830 @cindex a.out and C++
5831 @cindex @sc{ecoff} and C++
5832 @cindex @sc{xcoff} and C++
5833 @cindex @sc{elf}/stabs and C++
5834 @cindex @sc{elf}/@sc{dwarf} and C++
5835 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
5836 @c periodically whether this has happened...
5838 @emph{Warning:} @value{GDBN} can only debug C++ code if you compile with
5839 the @sc{gnu} C++ compiler. Moreover, C++ debugging depends on the use of
5840 additional debugging information in the symbol table, and thus requires
5841 special support. @value{GDBN} has this support @emph{only} with the
5842 stabs debug format. In particular, if your compiler generates a.out,
5843 MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions
5844 to the symbol table, these facilities are all available. (With @sc{gnu} CC,
5845 you can use the @samp{-gstabs} option to request stabs debugging
5846 extensions explicitly.) Where the object code format is standard
5847 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
5848 support in @value{GDBN} does @emph{not} work.
5853 @cindex member functions
5855 Member function calls are allowed; you can use expressions like
5858 count = aml->GetOriginal(x, y)
5862 @cindex namespace in C++
5864 While a member function is active (in the selected stack frame), your
5865 expressions have the same namespace available as the member function;
5866 that is, @value{GDBN} allows implicit references to the class instance
5867 pointer @code{this} following the same rules as C++.
5869 @cindex call overloaded functions
5870 @cindex type conversions in C++
5872 You can call overloaded functions; @value{GDBN} resolves the function
5873 call to the right definition, with one restriction---you must use
5874 arguments of the type required by the function that you want to call.
5875 @value{GDBN} does not perform conversions requiring constructors or
5876 user-defined type operators.
5878 @cindex reference declarations
5880 @value{GDBN} understands variables declared as C++ references; you can use
5881 them in expressions just as you do in C++ source---they are automatically
5884 In the parameter list shown when @value{GDBN} displays a frame, the values of
5885 reference variables are not displayed (unlike other variables); this
5886 avoids clutter, since references are often used for large structures.
5887 The @emph{address} of a reference variable is always shown, unless
5888 you have specified @samp{set print address off}.
5891 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5892 expressions can use it just as expressions in your program do. Since
5893 one scope may be defined in another, you can use @code{::} repeatedly if
5894 necessary, for example in an expression like
5895 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5896 resolving name scope by reference to source files, in both C and C++
5897 debugging (@pxref{Variables, ,Program variables}).
5901 @subsubsection C and C++ defaults
5902 @cindex C and C++ defaults
5904 If you allow @value{GDBN} to set type and range checking automatically, they
5905 both default to @code{off} whenever the working language changes to
5906 C or C++. This happens regardless of whether you or @value{GDBN}
5907 selects the working language.
5909 If you allow @value{GDBN} to set the language automatically, it recognizes
5910 source files whose names end with @file{.c}, @file{.C}, or @file{.cc}, and
5911 when @value{GDBN} enters code compiled from one of these files,
5912 it sets the working language to C or C++.
5913 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5917 @c Type checking is (a) primarily motivated by Modula-2, and (b)
5918 @c unimplemented. If (b) changes, it might make sense to let this node
5919 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
5921 @subsubsection C and C++ type and range checks
5922 @cindex C and C++ checks
5924 By default, when @value{GDBN} parses C or C++ expressions, type checking
5925 is not used. However, if you turn type checking on, @value{GDBN}
5926 considers two variables type equivalent if:
5930 The two variables are structured and have the same structure, union, or
5934 The two variables have the same type name, or types that have been
5935 declared equivalent through @code{typedef}.
5938 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5941 The two @code{struct}, @code{union}, or @code{enum} variables are
5942 declared in the same declaration. (Note: this may not be true for all C
5947 Range checking, if turned on, is done on mathematical operations. Array
5948 indices are not checked, since they are often used to index a pointer
5949 that is not itself an array.
5955 @subsubsection @value{GDBN} and C
5959 @section @value{GDBN} and C
5962 The @code{set print union} and @code{show print union} commands apply to
5963 the @code{union} type. When set to @samp{on}, any @code{union} that is
5964 inside a @code{struct}
5969 Otherwise, it appears as @samp{@{...@}}.
5971 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5972 with pointers and a memory allocation function. @xref{Expressions,
5976 @node Debugging C plus plus
5977 @subsubsection @value{GDBN} features for C++
5979 @cindex commands for C++
5980 Some @value{GDBN} commands are particularly useful with C++, and some are
5981 designed specifically for use with C++. Here is a summary:
5984 @cindex break in overloaded functions
5985 @item @r{breakpoint menus}
5986 When you want a breakpoint in a function whose name is overloaded,
5987 @value{GDBN} breakpoint menus help you specify which function definition
5988 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5990 @cindex overloading in C++
5991 @item rbreak @var{regex}
5992 Setting breakpoints using regular expressions is helpful for setting
5993 breakpoints on overloaded functions that are not members of any special
5995 @xref{Set Breaks, ,Setting breakpoints}.
5997 @cindex C++ exception handling
5998 @item catch @var{exceptions}
6000 Debug C++ exception handling using these commands. @xref{Exception
6001 Handling, ,Breakpoints and exceptions}.
6004 @item ptype @var{typename}
6005 Print inheritance relationships as well as other information for type
6007 @xref{Symbols, ,Examining the Symbol Table}.
6009 @cindex C++ symbol display
6010 @item set print demangle
6011 @itemx show print demangle
6012 @itemx set print asm-demangle
6013 @itemx show print asm-demangle
6014 Control whether C++ symbols display in their source form, both when
6015 displaying code as C++ source and when displaying disassemblies.
6016 @xref{Print Settings, ,Print settings}.
6018 @item set print object
6019 @itemx show print object
6020 Choose whether to print derived (actual) or declared types of objects.
6021 @xref{Print Settings, ,Print settings}.
6023 @item set print vtbl
6024 @itemx show print vtbl
6025 Control the format for printing virtual function tables.
6026 @xref{Print Settings, ,Print settings}.
6028 @item @r{Overloaded symbol names}
6029 You can specify a particular definition of an overloaded symbol, using
6030 the same notation that is used to declare such symbols in C++: type
6031 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6032 also use the @value{GDBN} command-line word completion facilities to list the
6033 available choices, or to finish the type list for you.
6034 @xref{Completion,, Command completion}, for details on how to do this.
6037 @c cancels "raisesections" under same conditions near bgn of chapter
6043 @subsection Modula-2
6046 The extensions made to @value{GDBN} to support Modula-2 only support
6047 output from the @sc{gnu} Modula-2 compiler (which is currently being
6048 developed). Other Modula-2 compilers are not currently supported, and
6049 attempting to debug executables produced by them is most likely
6050 to give an error as @value{GDBN} reads in the executable's symbol
6053 @cindex expressions in Modula-2
6055 * M2 Operators:: Built-in operators
6056 * Built-In Func/Proc:: Built-in functions and procedures
6057 * M2 Constants:: Modula-2 constants
6058 * M2 Defaults:: Default settings for Modula-2
6059 * Deviations:: Deviations from standard Modula-2
6060 * M2 Checks:: Modula-2 type and range checks
6061 * M2 Scope:: The scope operators @code{::} and @code{.}
6062 * GDB/M2:: @value{GDBN} and Modula-2
6066 @subsubsection Operators
6067 @cindex Modula-2 operators
6069 Operators must be defined on values of specific types. For instance,
6070 @code{+} is defined on numbers, but not on structures. Operators are
6071 often defined on groups of types. For the purposes of Modula-2, the
6072 following definitions hold:
6077 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6081 @emph{Character types} consist of @code{CHAR} and its subranges.
6084 @emph{Floating-point types} consist of @code{REAL}.
6087 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6091 @emph{Scalar types} consist of all of the above.
6094 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6097 @emph{Boolean types} consist of @code{BOOLEAN}.
6101 The following operators are supported, and appear in order of
6102 increasing precedence:
6106 Function argument or array index separator.
6109 Assignment. The value of @var{var} @code{:=} @var{value} is
6113 Less than, greater than on integral, floating-point, or enumerated
6117 Less than, greater than, less than or equal to, greater than or equal to
6118 on integral, floating-point and enumerated types, or set inclusion on
6119 set types. Same precedence as @code{<}.
6121 @item =@r{, }<>@r{, }#
6122 Equality and two ways of expressing inequality, valid on scalar types.
6123 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6124 available for inequality, since @code{#} conflicts with the script
6128 Set membership. Defined on set types and the types of their members.
6129 Same precedence as @code{<}.
6132 Boolean disjunction. Defined on boolean types.
6135 Boolean conjuction. Defined on boolean types.
6138 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6141 Addition and subtraction on integral and floating-point types, or union
6142 and difference on set types.
6145 Multiplication on integral and floating-point types, or set intersection
6149 Division on floating-point types, or symmetric set difference on set
6150 types. Same precedence as @code{*}.
6153 Integer division and remainder. Defined on integral types. Same
6154 precedence as @code{*}.
6157 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6160 Pointer dereferencing. Defined on pointer types.
6163 Boolean negation. Defined on boolean types. Same precedence as
6167 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6168 precedence as @code{^}.
6171 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6174 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6178 @value{GDBN} and Modula-2 scope operators.
6182 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6183 treats the use of the operator @code{IN}, or the use of operators
6184 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6185 @code{<=}, and @code{>=} on sets as an error.
6188 @cindex Modula-2 built-ins
6189 @node Built-In Func/Proc
6190 @subsubsection Built-in functions and procedures
6192 Modula-2 also makes available several built-in procedures and functions.
6193 In describing these, the following metavariables are used:
6198 represents an @code{ARRAY} variable.
6201 represents a @code{CHAR} constant or variable.
6204 represents a variable or constant of integral type.
6207 represents an identifier that belongs to a set. Generally used in the
6208 same function with the metavariable @var{s}. The type of @var{s} should
6209 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6212 represents a variable or constant of integral or floating-point type.
6215 represents a variable or constant of floating-point type.
6221 represents a variable.
6224 represents a variable or constant of one of many types. See the
6225 explanation of the function for details.
6228 All Modula-2 built-in procedures also return a result, described below.
6232 Returns the absolute value of @var{n}.
6235 If @var{c} is a lower case letter, it returns its upper case
6236 equivalent, otherwise it returns its argument
6239 Returns the character whose ordinal value is @var{i}.
6242 Decrements the value in the variable @var{v}. Returns the new value.
6244 @item DEC(@var{v},@var{i})
6245 Decrements the value in the variable @var{v} by @var{i}. Returns the
6248 @item EXCL(@var{m},@var{s})
6249 Removes the element @var{m} from the set @var{s}. Returns the new
6252 @item FLOAT(@var{i})
6253 Returns the floating point equivalent of the integer @var{i}.
6256 Returns the index of the last member of @var{a}.
6259 Increments the value in the variable @var{v}. Returns the new value.
6261 @item INC(@var{v},@var{i})
6262 Increments the value in the variable @var{v} by @var{i}. Returns the
6265 @item INCL(@var{m},@var{s})
6266 Adds the element @var{m} to the set @var{s} if it is not already
6267 there. Returns the new set.
6270 Returns the maximum value of the type @var{t}.
6273 Returns the minimum value of the type @var{t}.
6276 Returns boolean TRUE if @var{i} is an odd number.
6279 Returns the ordinal value of its argument. For example, the ordinal
6280 value of a character is its ASCII value (on machines supporting the
6281 ASCII character set). @var{x} must be of an ordered type, which include
6282 integral, character and enumerated types.
6285 Returns the size of its argument. @var{x} can be a variable or a type.
6287 @item TRUNC(@var{r})
6288 Returns the integral part of @var{r}.
6290 @item VAL(@var{t},@var{i})
6291 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6295 @emph{Warning:} Sets and their operations are not yet supported, so
6296 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6300 @cindex Modula-2 constants
6302 @subsubsection Constants
6304 @value{GDBN} allows you to express the constants of Modula-2 in the following
6310 Integer constants are simply a sequence of digits. When used in an
6311 expression, a constant is interpreted to be type-compatible with the
6312 rest of the expression. Hexadecimal integers are specified by a
6313 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6316 Floating point constants appear as a sequence of digits, followed by a
6317 decimal point and another sequence of digits. An optional exponent can
6318 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6319 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6320 digits of the floating point constant must be valid decimal (base 10)
6324 Character constants consist of a single character enclosed by a pair of
6325 like quotes, either single (@code{'}) or double (@code{"}). They may
6326 also be expressed by their ordinal value (their ASCII value, usually)
6327 followed by a @samp{C}.
6330 String constants consist of a sequence of characters enclosed by a
6331 pair of like quotes, either single (@code{'}) or double (@code{"}).
6332 Escape sequences in the style of C are also allowed. @xref{C
6333 Constants, ,C and C++ constants}, for a brief explanation of escape
6337 Enumerated constants consist of an enumerated identifier.
6340 Boolean constants consist of the identifiers @code{TRUE} and
6344 Pointer constants consist of integral values only.
6347 Set constants are not yet supported.
6351 @subsubsection Modula-2 defaults
6352 @cindex Modula-2 defaults
6354 If type and range checking are set automatically by @value{GDBN}, they
6355 both default to @code{on} whenever the working language changes to
6356 Modula-2. This happens regardless of whether you, or @value{GDBN},
6357 selected the working language.
6359 If you allow @value{GDBN} to set the language automatically, then entering
6360 code compiled from a file whose name ends with @file{.mod} sets the
6361 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6362 the language automatically}, for further details.
6365 @subsubsection Deviations from standard Modula-2
6366 @cindex Modula-2, deviations from
6368 A few changes have been made to make Modula-2 programs easier to debug.
6369 This is done primarily via loosening its type strictness:
6373 Unlike in standard Modula-2, pointer constants can be formed by
6374 integers. This allows you to modify pointer variables during
6375 debugging. (In standard Modula-2, the actual address contained in a
6376 pointer variable is hidden from you; it can only be modified
6377 through direct assignment to another pointer variable or expression that
6378 returned a pointer.)
6381 C escape sequences can be used in strings and characters to represent
6382 non-printable characters. @value{GDBN} prints out strings with these
6383 escape sequences embedded. Single non-printable characters are
6384 printed using the @samp{CHR(@var{nnn})} format.
6387 The assignment operator (@code{:=}) returns the value of its right-hand
6391 All built-in procedures both modify @emph{and} return their argument.
6395 @subsubsection Modula-2 type and range checks
6396 @cindex Modula-2 checks
6399 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6402 @c FIXME remove warning when type/range checks added
6404 @value{GDBN} considers two Modula-2 variables type equivalent if:
6408 They are of types that have been declared equivalent via a @code{TYPE
6409 @var{t1} = @var{t2}} statement
6412 They have been declared on the same line. (Note: This is true of the
6413 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6416 As long as type checking is enabled, any attempt to combine variables
6417 whose types are not equivalent is an error.
6419 Range checking is done on all mathematical operations, assignment, array
6420 index bounds, and all built-in functions and procedures.
6423 @subsubsection The scope operators @code{::} and @code{.}
6426 @cindex colon, doubled as scope operator
6429 @c Info cannot handle :: but TeX can.
6435 There are a few subtle differences between the Modula-2 scope operator
6436 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6441 @var{module} . @var{id}
6442 @var{scope} :: @var{id}
6446 where @var{scope} is the name of a module or a procedure,
6447 @var{module} the name of a module, and @var{id} is any declared
6448 identifier within your program, except another module.
6450 Using the @code{::} operator makes @value{GDBN} search the scope
6451 specified by @var{scope} for the identifier @var{id}. If it is not
6452 found in the specified scope, then @value{GDBN} searches all scopes
6453 enclosing the one specified by @var{scope}.
6455 Using the @code{.} operator makes @value{GDBN} search the current scope for
6456 the identifier specified by @var{id} that was imported from the
6457 definition module specified by @var{module}. With this operator, it is
6458 an error if the identifier @var{id} was not imported from definition
6459 module @var{module}, or if @var{id} is not an identifier in
6463 @subsubsection @value{GDBN} and Modula-2
6465 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6466 Five subcommands of @code{set print} and @code{show print} apply
6467 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6468 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6469 apply to C++, and the last to the C @code{union} type, which has no direct
6470 analogue in Modula-2.
6472 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6473 while using any language, is not useful with Modula-2. Its
6474 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6475 created in Modula-2 as they can in C or C++. However, because an
6476 address can be specified by an integral constant, the construct
6477 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
6479 @cindex @code{#} in Modula-2
6480 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6481 interpreted as the beginning of a comment. Use @code{<>} instead.
6486 @chapter Examining the Symbol Table
6488 The commands described in this section allow you to inquire about the
6489 symbols (names of variables, functions and types) defined in your
6490 program. This information is inherent in the text of your program and
6491 does not change as your program executes. @value{GDBN} finds it in your
6492 program's symbol table, in the file indicated when you started @value{GDBN}
6493 (@pxref{File Options, ,Choosing files}), or by one of the
6494 file-management commands (@pxref{Files, ,Commands to specify files}).
6496 @cindex symbol names
6497 @cindex names of symbols
6498 @cindex quoting names
6499 Occasionally, you may need to refer to symbols that contain unusual
6500 characters, which @value{GDBN} ordinarily treats as word delimiters. The
6501 most frequent case is in referring to static variables in other
6502 source files (@pxref{Variables,,Program variables}). File names
6503 are recorded in object files as debugging symbols, but @value{GDBN} would
6504 ordinarily parse a typical file name, like @file{foo.c}, as the three words
6505 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
6506 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
6513 looks up the value of @code{x} in the scope of the file @file{foo.c}.
6516 @kindex info address
6517 @item info address @var{symbol}
6518 Describe where the data for @var{symbol} is stored. For a register
6519 variable, this says which register it is kept in. For a non-register
6520 local variable, this prints the stack-frame offset at which the variable
6523 Note the contrast with @samp{print &@var{symbol}}, which does not work
6524 at all for a register variable, and for a stack local variable prints
6525 the exact address of the current instantiation of the variable.
6528 @item whatis @var{exp}
6529 Print the data type of expression @var{exp}. @var{exp} is not
6530 actually evaluated, and any side-effecting operations (such as
6531 assignments or function calls) inside it do not take place.
6532 @xref{Expressions, ,Expressions}.
6535 Print the data type of @code{$}, the last value in the value history.
6538 @item ptype @var{typename}
6539 Print a description of data type @var{typename}. @var{typename} may be
6540 the name of a type, or for C code it may have the form
6542 @samp{class @var{class-name}},
6544 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
6545 @samp{enum @var{enum-tag}}.
6547 @item ptype @var{exp}
6549 Print a description of the type of expression @var{exp}. @code{ptype}
6550 differs from @code{whatis} by printing a detailed description, instead
6551 of just the name of the type.
6553 For example, for this variable declaration:
6556 struct complex @{double real; double imag;@} v;
6560 the two commands give this output:
6564 (@value{GDBP}) whatis v
6565 type = struct complex
6566 (@value{GDBP}) ptype v
6567 type = struct complex @{
6575 As with @code{whatis}, using @code{ptype} without an argument refers to
6576 the type of @code{$}, the last value in the value history.
6579 @item info types @var{regexp}
6581 Print a brief description of all types whose name matches @var{regexp}
6582 (or all types in your program, if you supply no argument). Each
6583 complete typename is matched as though it were a complete line; thus,
6584 @samp{i type value} gives information on all types in your program whose
6585 name includes the string @code{value}, but @samp{i type ^value$} gives
6586 information only on types whose complete name is @code{value}.
6588 This command differs from @code{ptype} in two ways: first, like
6589 @code{whatis}, it does not print a detailed description; second, it
6590 lists all source files where a type is defined.
6594 Show the name of the current source file---that is, the source file for
6595 the function containing the current point of execution---and the language
6598 @kindex info sources
6600 Print the names of all source files in your program for which there is
6601 debugging information, organized into two lists: files whose symbols
6602 have already been read, and files whose symbols will be read when needed.
6604 @kindex info functions
6605 @item info functions
6606 Print the names and data types of all defined functions.
6608 @item info functions @var{regexp}
6609 Print the names and data types of all defined functions
6610 whose names contain a match for regular expression @var{regexp}.
6611 Thus, @samp{info fun step} finds all functions whose names
6612 include @code{step}; @samp{info fun ^step} finds those whose names
6613 start with @code{step}.
6615 @kindex info variables
6616 @item info variables
6617 Print the names and data types of all variables that are declared
6618 outside of functions (i.e., excluding local variables).
6620 @item info variables @var{regexp}
6621 Print the names and data types of all variables (except for local
6622 variables) whose names contain a match for regular expression
6626 This was never implemented.
6627 @kindex info methods
6629 @itemx info methods @var{regexp}
6630 The @code{info methods} command permits the user to examine all defined
6631 methods within C++ program, or (with the @var{regexp} argument) a
6632 specific set of methods found in the various C++ classes. Many
6633 C++ classes provide a large number of methods. Thus, the output
6634 from the @code{ptype} command can be overwhelming and hard to use. The
6635 @code{info-methods} command filters the methods, printing only those
6636 which match the regular-expression @var{regexp}.
6639 @cindex reloading symbols
6640 Some systems allow individual object files that make up your program to
6641 be replaced without stopping and restarting your program.
6643 For example, in VxWorks you can simply recompile a defective object file
6644 and keep on running.
6646 If you are running on one of these systems, you can allow @value{GDBN} to
6647 reload the symbols for automatically relinked modules:
6650 @kindex set symbol-reloading
6651 @item set symbol-reloading on
6652 Replace symbol definitions for the corresponding source file when an
6653 object file with a particular name is seen again.
6655 @item set symbol-reloading off
6656 Do not replace symbol definitions when re-encountering object files of
6657 the same name. This is the default state; if you are not running on a
6658 system that permits automatically relinking modules, you should leave
6659 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
6660 when linking large programs, that may contain several modules (from
6661 different directories or libraries) with the same name.
6663 @kindex show symbol-reloading
6664 @item show symbol-reloading
6665 Show the current @code{on} or @code{off} setting.
6668 @kindex maint print symbols
6670 @kindex maint print psymbols
6671 @cindex partial symbol dump
6672 @item maint print symbols @var{filename}
6673 @itemx maint print psymbols @var{filename}
6674 @itemx maint print msymbols @var{filename}
6675 Write a dump of debugging symbol data into the file @var{filename}.
6676 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6677 symbols with debugging data are included. If you use @samp{maint print
6678 symbols}, @value{GDBN} includes all the symbols for which it has already
6679 collected full details: that is, @var{filename} reflects symbols for
6680 only those files whose symbols @value{GDBN} has read. You can use the
6681 command @code{info sources} to find out which files these are. If you
6682 use @samp{maint print psymbols} instead, the dump shows information about
6683 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6684 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6685 @samp{maint print msymbols} dumps just the minimal symbol information
6686 required for each object file from which @value{GDBN} has read some symbols.
6687 @xref{Files, ,Commands to specify files}, for a discussion of how
6688 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
6692 @chapter Altering Execution
6694 Once you think you have found an error in your program, you might want to
6695 find out for certain whether correcting the apparent error would lead to
6696 correct results in the rest of the run. You can find the answer by
6697 experiment, using the @value{GDBN} features for altering execution of the
6700 For example, you can store new values into variables or memory
6703 give your program a signal, restart it
6706 restart your program
6708 at a different address, or even return prematurely from a function.
6711 * Assignment:: Assignment to variables
6712 * Jumping:: Continuing at a different address
6714 * Signaling:: Giving your program a signal
6717 * Returning:: Returning from a function
6718 * Calling:: Calling your program's functions
6719 * Patching:: Patching your program
6723 @section Assignment to variables
6726 @cindex setting variables
6727 To alter the value of a variable, evaluate an assignment expression.
6728 @xref{Expressions, ,Expressions}. For example,
6735 stores the value 4 into the variable @code{x}, and then prints the
6736 value of the assignment expression (which is 4).
6738 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6739 information on operators in supported languages.
6742 @kindex set variable
6743 @cindex variables, setting
6744 If you are not interested in seeing the value of the assignment, use the
6745 @code{set} command instead of the @code{print} command. @code{set} is
6746 really the same as @code{print} except that the expression's value is
6747 not printed and is not put in the value history (@pxref{Value History,
6748 ,Value history}). The expression is evaluated only for its effects.
6750 If the beginning of the argument string of the @code{set} command
6751 appears identical to a @code{set} subcommand, use the @code{set
6752 variable} command instead of just @code{set}. This command is identical
6753 to @code{set} except for its lack of subcommands. For example, if
6754 your program has a variable @code{width}, you get
6755 an error if you try to set a new value with just @samp{set width=13},
6756 because @value{GDBN} has the command @code{set width}:
6759 (@value{GDBP}) whatis width
6761 (@value{GDBP}) p width
6763 (@value{GDBP}) set width=47
6764 Invalid syntax in expression.
6768 The invalid expression, of course, is @samp{=47}. In
6769 order to actually set the program's variable @code{width}, use
6772 (@value{GDBP}) set var width=47
6775 @value{GDBN} allows more implicit conversions in assignments than C; you can
6776 freely store an integer value into a pointer variable or vice versa,
6777 and you can convert any structure to any other structure that is the
6778 same length or shorter.
6779 @comment FIXME: how do structs align/pad in these conversions?
6780 @comment /doc@cygnus.com 18dec1990
6782 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6783 construct to generate a value of specified type at a specified address
6784 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6785 to memory location @code{0x83040} as an integer (which implies a certain size
6786 and representation in memory), and
6789 set @{int@}0x83040 = 4
6793 stores the value 4 into that memory location.
6796 @section Continuing at a different address
6798 Ordinarily, when you continue your program, you do so at the place where
6799 it stopped, with the @code{continue} command. You can instead continue at
6800 an address of your own choosing, with the following commands:
6804 @item jump @var{linespec}
6805 Resume execution at line @var{linespec}. Execution stops again
6806 immediately if there is a breakpoint there. @xref{List, ,Printing
6807 source lines}, for a description of the different forms of
6810 The @code{jump} command does not change the current stack frame, or
6811 the stack pointer, or the contents of any memory location or any
6812 register other than the program counter. If line @var{linespec} is in
6813 a different function from the one currently executing, the results may
6814 be bizarre if the two functions expect different patterns of arguments or
6815 of local variables. For this reason, the @code{jump} command requests
6816 confirmation if the specified line is not in the function currently
6817 executing. However, even bizarre results are predictable if you are
6818 well acquainted with the machine-language code of your program.
6820 @item jump *@var{address}
6821 Resume execution at the instruction at address @var{address}.
6824 You can get much the same effect as the @code{jump} command by storing a
6825 new value into the register @code{$pc}. The difference is that this
6826 does not start your program running; it only changes the address of where it
6827 @emph{will} run when you continue. For example,
6834 makes the next @code{continue} command or stepping command execute at
6835 address @code{0x485}, rather than at the address where your program stopped.
6836 @xref{Continuing and Stepping, ,Continuing and stepping}.
6838 The most common occasion to use the @code{jump} command is to back up--
6839 perhaps with more breakpoints set--over a portion of a program that has
6840 already executed, in order to examine its execution in more detail.
6845 @section Giving your program a signal
6849 @item signal @var{signal}
6850 Resume execution where your program stopped, but immediately give it the
6851 signal @var{signal}. @var{signal} can be the name or the number of a
6852 signal. For example, on many systems @code{signal 2} and @code{signal
6853 SIGINT} are both ways of sending an interrupt signal.
6855 Alternatively, if @var{signal} is zero, continue execution without
6856 giving a signal. This is useful when your program stopped on account of
6857 a signal and would ordinary see the signal when resumed with the
6858 @code{continue} command; @samp{signal 0} causes it to resume without a
6861 @code{signal} does not repeat when you press @key{RET} a second time
6862 after executing the command.
6866 Invoking the @code{signal} command is not the same as invoking the
6867 @code{kill} utility from the shell. Sending a signal with @code{kill}
6868 causes @value{GDBN} to decide what to do with the signal depending on
6869 the signal handling tables (@pxref{Signals}). The @code{signal} command
6870 passes the signal directly to your program.
6875 @section Returning from a function
6878 @cindex returning from a function
6881 @itemx return @var{expression}
6882 You can cancel execution of a function call with the @code{return}
6883 command. If you give an
6884 @var{expression} argument, its value is used as the function's return
6888 When you use @code{return}, @value{GDBN} discards the selected stack frame
6889 (and all frames within it). You can think of this as making the
6890 discarded frame return prematurely. If you wish to specify a value to
6891 be returned, give that value as the argument to @code{return}.
6893 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6894 frame}), and any other frames inside of it, leaving its caller as the
6895 innermost remaining frame. That frame becomes selected. The
6896 specified value is stored in the registers used for returning values
6899 The @code{return} command does not resume execution; it leaves the
6900 program stopped in the state that would exist if the function had just
6901 returned. In contrast, the @code{finish} command (@pxref{Continuing
6902 and Stepping, ,Continuing and stepping}) resumes execution until the
6903 selected stack frame returns naturally.
6906 @section Calling program functions
6908 @cindex calling functions
6911 @item call @var{expr}
6912 Evaluate the expression @var{expr} without displaying @code{void}
6916 You can use this variant of the @code{print} command if you want to
6917 execute a function from your program, but without cluttering the output
6918 with @code{void} returned values. If the result is not void, it
6919 is printed and saved in the value history.
6921 A new user-controlled variable, @var{call_scratch_address}, specifies
6922 the location of a scratch area to be used when @value{GDBN} calls a
6923 function in the target. This is necessary because the usual method
6924 of putting the scratch area on the stack does not work in systems that
6925 have separate instruction and data spaces.
6928 @section Patching programs
6929 @cindex patching binaries
6930 @cindex writing into executables
6932 @cindex writing into corefiles
6935 By default, @value{GDBN} opens the file containing your program's executable
6940 read-only. This prevents accidental alterations
6941 to machine code; but it also prevents you from intentionally patching
6942 your program's binary.
6944 If you'd like to be able to patch the binary, you can specify that
6945 explicitly with the @code{set write} command. For example, you might
6946 want to turn on internal debugging flags, or even to make emergency
6952 @itemx set write off
6953 If you specify @samp{set write on}, @value{GDBN} opens executable
6957 files for both reading and writing; if you specify @samp{set write
6958 off} (the default), @value{GDBN} opens them read-only.
6960 If you have already loaded a file, you must load it again (using the
6965 command) after changing @code{set write}, for your new setting to take
6970 Display whether executable files
6974 are opened for writing as well as reading.
6978 @chapter @value{GDBN} Files
6980 @value{GDBN} needs to know the file name of the program to be debugged, both in
6981 order to read its symbol table and in order to start your program.
6983 To debug a core dump of a previous run, you must also tell @value{GDBN}
6984 the name of the core dump file.
6988 * Files:: Commands to specify files
6989 * Symbol Errors:: Errors reading symbol files
6993 @section Commands to specify files
6994 @cindex symbol table
6997 @cindex core dump file
6998 You may want to specify executable and core dump file names.
6999 The usual way to do this is at start-up time, using the arguments to
7000 @value{GDBN}'s start-up commands (@pxref{Invocation, ,
7001 Getting In and Out of @value{GDBN}}).
7004 The usual way to specify an executable file name is with
7005 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
7006 ,Getting In and Out of @value{GDBN}}.
7009 Occasionally it is necessary to change to a different file during a
7010 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
7011 a file you want to use. In these situations the @value{GDBN} commands
7012 to specify new files are useful.
7015 @cindex executable file
7017 @item file @var{filename}
7018 Use @var{filename} as the program to be debugged. It is read for its
7019 symbols and for the contents of pure memory. It is also the program
7020 executed when you use the @code{run} command. If you do not specify a
7021 directory and the file is not found in the @value{GDBN} working directory,
7022 @value{GDBN} uses the environment variable @code{PATH} as a list of
7023 directories to search, just as the shell does when looking for a program
7024 to run. You can change the value of this variable, for both @value{GDBN}
7025 and your program, using the @code{path} command.
7027 On systems with memory-mapped files, an auxiliary file
7028 @file{@var{filename}.syms} may hold symbol table information for
7029 @var{filename}. If so, @value{GDBN} maps in the symbol table from
7030 @file{@var{filename}.syms}, starting up more quickly. See the
7031 descriptions of the file options @samp{-mapped} and @samp{-readnow}
7032 (available on the command line, and with the commands @code{file},
7033 @code{symbol-file}, or @code{add-symbol-file}, described below),
7034 for more information.
7037 @code{file} with no argument makes @value{GDBN} discard any information it
7038 has on both executable file and the symbol table.
7041 @item exec-file @r{[} @var{filename} @r{]}
7042 Specify that the program to be run (but not the symbol table) is found
7043 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
7044 if necessary to locate your program. Omitting @var{filename} means to
7045 discard information on the executable file.
7048 @item symbol-file @r{[} @var{filename} @r{]}
7049 Read symbol table information from file @var{filename}. @code{PATH} is
7050 searched when necessary. Use the @code{file} command to get both symbol
7051 table and program to run from the same file.
7053 @code{symbol-file} with no argument clears out @value{GDBN} information on your
7054 program's symbol table.
7056 The @code{symbol-file} command causes @value{GDBN} to forget the contents
7057 of its convenience variables, the value history, and all breakpoints and
7058 auto-display expressions. This is because they may contain pointers to
7059 the internal data recording symbols and data types, which are part of
7060 the old symbol table data being discarded inside @value{GDBN}.
7062 @code{symbol-file} does not repeat if you press @key{RET} again after
7065 When @value{GDBN} is configured for a particular environment, it
7066 understands debugging information in whatever format is the standard
7067 generated for that environment; you may use either a @sc{gnu} compiler, or
7068 other compilers that adhere to the local conventions. Best results are
7069 usually obtained from @sc{gnu} compilers; for example, using @code{@value{GCC}}
7070 you can generate debugging information for optimized code.
7072 On some kinds of object files, the @code{symbol-file} command does not
7073 normally read the symbol table in full right away. Instead, it scans
7074 the symbol table quickly to find which source files and which symbols
7075 are present. The details are read later, one source file at a time,
7078 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
7079 faster. For the most part, it is invisible except for occasional
7080 pauses while the symbol table details for a particular source file are
7081 being read. (The @code{set verbose} command can turn these pauses
7082 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
7085 We have not implemented the two-stage strategy for COFF yet. When the
7086 symbol table is stored in COFF format, @code{symbol-file} reads the
7087 symbol table data in full right away.
7090 @cindex reading symbols immediately
7091 @cindex symbols, reading immediately
7093 @cindex memory-mapped symbol file
7094 @cindex saving symbol table
7095 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7096 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7097 You can override the @value{GDBN} two-stage strategy for reading symbol
7098 tables by using the @samp{-readnow} option with any of the commands that
7099 load symbol table information, if you want to be sure @value{GDBN} has the
7100 entire symbol table available.
7103 If memory-mapped files are available on your system through the
7104 @code{mmap} system call, you can use another option, @samp{-mapped}, to
7105 cause @value{GDBN} to write the symbols for your program into a reusable
7106 file. Future @value{GDBN} debugging sessions map in symbol information
7107 from this auxiliary symbol file (if the program has not changed), rather
7108 than spending time reading the symbol table from the executable
7109 program. Using the @samp{-mapped} option has the same effect as
7110 starting @value{GDBN} with the @samp{-mapped} command-line option.
7112 You can use both options together, to make sure the auxiliary symbol
7113 file has all the symbol information for your program.
7115 The auxiliary symbol file for a program called @var{myprog} is called
7116 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
7117 than the corresponding executable), @value{GDBN} always attempts to use
7118 it when you debug @var{myprog}; no special options or commands are
7121 The @file{.syms} file is specific to the host machine where you run
7122 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
7123 symbol table. It cannot be shared across multiple host platforms.
7125 @c FIXME: for now no mention of directories, since this seems to be in
7126 @c flux. 13mar1992 status is that in theory GDB would look either in
7127 @c current dir or in same dir as myprog; but issues like competing
7128 @c GDB's, or clutter in system dirs, mean that in practice right now
7129 @c only current dir is used. FFish says maybe a special GDB hierarchy
7130 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
7135 @item core-file @r{[} @var{filename} @r{]}
7136 Specify the whereabouts of a core dump file to be used as the ``contents
7137 of memory''. Traditionally, core files contain only some parts of the
7138 address space of the process that generated them; @value{GDBN} can access the
7139 executable file itself for other parts.
7141 @code{core-file} with no argument specifies that no core file is
7144 Note that the core file is ignored when your program is actually running
7145 under @value{GDBN}. So, if you have been running your program and you wish to
7146 debug a core file instead, you must kill the subprocess in which the
7147 program is running. To do this, use the @code{kill} command
7148 (@pxref{Kill Process, ,Killing the child process}).
7151 @kindex load @var{filename}
7152 @item load @var{filename}
7154 Depending on what remote debugging facilities are configured into
7155 @value{GDBN}, the @code{load} command may be available. Where it exists, it
7156 is meant to make @var{filename} (an executable) available for debugging
7157 on the remote system---by downloading, or dynamic linking, for example.
7158 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
7159 the @code{add-symbol-file} command.
7161 If your @value{GDBN} does not have a @code{load} command, attempting to
7162 execute it gets the error message ``@code{You can't do that when your
7163 target is @dots{}}''
7166 The file is loaded at whatever address is specified in the executable.
7167 For some object file formats, you can specify the load address when you
7168 link the program; for other formats, like a.out, the object file format
7169 specifies a fixed address.
7170 @c FIXME! This would be a good place for an xref to the GNU linker doc.
7173 On VxWorks, @code{load} links @var{filename} dynamically on the
7174 current target system as well as adding its symbols in @value{GDBN}.
7178 @cindex download to Nindy-960
7179 With the Nindy interface to an Intel 960 board, @code{load}
7180 downloads @var{filename} to the 960 as well as adding its symbols in
7185 @cindex download to H8/300 or H8/500
7186 @cindex H8/300 or H8/500 download
7187 @cindex download to Hitachi SH
7188 @cindex Hitachi SH download
7189 When you select remote debugging to a Hitachi SH, H8/300, or H8/500 board
7190 (@pxref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}),
7191 the @code{load} command downloads your program to the Hitachi board and also
7192 opens it as the current executable target for @value{GDBN} on your host
7193 (like the @code{file} command).
7196 @code{load} does not repeat if you press @key{RET} again after using it.
7199 @kindex add-symbol-file
7200 @cindex dynamic linking
7201 @item add-symbol-file @var{filename} @var{address}
7202 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7203 The @code{add-symbol-file} command reads additional symbol table information
7204 from the file @var{filename}. You would use this command when @var{filename}
7205 has been dynamically loaded (by some other means) into the program that
7206 is running. @var{address} should be the memory address at which the
7207 file has been loaded; @value{GDBN} cannot figure this out for itself.
7208 You can specify @var{address} as an expression.
7210 The symbol table of the file @var{filename} is added to the symbol table
7211 originally read with the @code{symbol-file} command. You can use the
7212 @code{add-symbol-file} command any number of times; the new symbol data thus
7213 read keeps adding to the old. To discard all old symbol data instead,
7214 use the @code{symbol-file} command.
7216 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
7218 You can use the @samp{-mapped} and @samp{-readnow} options just as with
7219 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
7220 table information for @var{filename}.
7222 @kindex add-shared-symbol-file
7223 @item add-shared-symbol-file
7224 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
7225 operating system for the Motorola 88k. @value{GDBN} automatically looks for
7226 shared libraries, however if @value{GDBN} does not find yours, you can run
7227 @code{add-shared-symbol-file}. It takes no arguments.
7232 The @code{section} command changes the base address of section SECTION of
7233 the exec file to ADDR. This can be used if the exec file does not contain
7234 section addresses, (such as in the a.out format), or when the addresses
7235 specified in the file itself are wrong. Each section must be changed
7236 separately. The ``info files'' command lists all the sections and their
7243 @code{info files} and @code{info target} are synonymous; both print
7244 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
7247 names of the executable and core dump files
7250 name of the executable file
7252 currently in use by @value{GDBN}, and the files from which symbols were
7253 loaded. The command @code{help target} lists all possible targets
7254 rather than current ones.
7257 All file-specifying commands allow both absolute and relative file names
7258 as arguments. @value{GDBN} always converts the file name to an absolute file
7259 name and remembers it that way.
7262 @cindex shared libraries
7263 @value{GDBN} supports SunOS, SVr4, Irix 5, and IBM RS/6000 shared libraries.
7264 @value{GDBN} automatically loads symbol definitions from shared libraries
7265 when you use the @code{run} command, or when you examine a core file.
7266 (Before you issue the @code{run} command, @value{GDBN} does not understand
7267 references to a function in a shared library, however---unless you are
7268 debugging a core file).
7269 @c FIXME: some @value{GDBN} release may permit some refs to undef
7270 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
7271 @c FIXME...lib; check this from time to time when updating manual
7274 @kindex info sharedlibrary
7277 @itemx info sharedlibrary
7278 Print the names of the shared libraries which are currently loaded.
7280 @kindex sharedlibrary
7282 @item sharedlibrary @var{regex}
7283 @itemx share @var{regex}
7285 Load shared object library symbols for files matching a
7286 Unix regular expression.
7287 As with files loaded automatically, it only loads shared libraries
7288 required by your program for a core file or after typing @code{run}. If
7289 @var{regex} is omitted all shared libraries required by your program are
7295 @section Errors reading symbol files
7297 While reading a symbol file, @value{GDBN} occasionally encounters problems,
7298 such as symbol types it does not recognize, or known bugs in compiler
7299 output. By default, @value{GDBN} does not notify you of such problems, since
7300 they are relatively common and primarily of interest to people
7301 debugging compilers. If you are interested in seeing information
7302 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
7303 only one message about each such type of problem, no matter how many
7304 times the problem occurs; or you can ask @value{GDBN} to print more messages,
7305 to see how many times the problems occur, with the @code{set
7306 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
7309 The messages currently printed, and their meanings, include:
7312 @item inner block not inside outer block in @var{symbol}
7314 The symbol information shows where symbol scopes begin and end
7315 (such as at the start of a function or a block of statements). This
7316 error indicates that an inner scope block is not fully contained
7317 in its outer scope blocks.
7319 @value{GDBN} circumvents the problem by treating the inner block as if it had
7320 the same scope as the outer block. In the error message, @var{symbol}
7321 may be shown as ``@code{(don't know)}'' if the outer block is not a
7324 @item block at @var{address} out of order
7326 The symbol information for symbol scope blocks should occur in
7327 order of increasing addresses. This error indicates that it does not
7330 @value{GDBN} does not circumvent this problem, and has trouble
7331 locating symbols in the source file whose symbols it is reading. (You
7332 can often determine what source file is affected by specifying
7333 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
7336 @item bad block start address patched
7338 The symbol information for a symbol scope block has a start address
7339 smaller than the address of the preceding source line. This is known
7340 to occur in the SunOS 4.1.1 (and earlier) C compiler.
7342 @value{GDBN} circumvents the problem by treating the symbol scope block as
7343 starting on the previous source line.
7345 @item bad string table offset in symbol @var{n}
7348 Symbol number @var{n} contains a pointer into the string table which is
7349 larger than the size of the string table.
7351 @value{GDBN} circumvents the problem by considering the symbol to have the
7352 name @code{foo}, which may cause other problems if many symbols end up
7355 @item unknown symbol type @code{0x@var{nn}}
7357 The symbol information contains new data types that @value{GDBN} does not yet
7358 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
7359 information, in hexadecimal.
7361 @value{GDBN} circumvents the error by ignoring this symbol information. This
7362 usually allows you to debug your program, though certain symbols
7363 are not accessible. If you encounter such a problem and feel like
7364 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
7365 @code{complain}, then go up to the function @code{read_dbx_symtab} and
7366 examine @code{*bufp} to see the symbol.
7368 @item stub type has NULL name
7369 @value{GDBN} could not find the full definition for
7378 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
7380 The symbol information for a C++ member function is missing some
7381 information that recent versions of the compiler should have output
7385 @item info mismatch between compiler and debugger
7387 @value{GDBN} could not parse a type specification output by the compiler.
7391 @chapter Specifying a Debugging Target
7392 @cindex debugging target
7395 A @dfn{target} is the execution environment occupied by your program.
7397 Often, @value{GDBN} runs in the same host environment as your program; in
7398 that case, the debugging target is specified as a side effect when you
7399 use the @code{file} or @code{core} commands. When you need more
7400 flexibility---for example, running @value{GDBN} on a physically separate
7401 host, or controlling a standalone system over a serial port or a
7402 realtime system over a TCP/IP connection---you
7407 can use the @code{target} command to specify one of the target types
7408 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
7412 * Active Targets:: Active targets
7413 * Target Commands:: Commands for managing targets
7414 * Remote:: Remote debugging
7417 @node Active Targets
7418 @section Active targets
7419 @cindex stacking targets
7420 @cindex active targets
7421 @cindex multiple targets
7424 There are three classes of targets: processes, core files, and
7425 executable files. @value{GDBN} can work concurrently on up to three active
7426 targets, one in each class. This allows you to (for example) start a
7427 process and inspect its activity without abandoning your work on a core
7430 For example, if you execute @samp{gdb a.out}, then the executable file
7431 @code{a.out} is the only active target. If you designate a core file as
7432 well---presumably from a prior run that crashed and coredumped---then
7433 @value{GDBN} has two active targets and uses them in tandem, looking
7434 first in the corefile target, then in the executable file, to satisfy
7435 requests for memory addresses. (Typically, these two classes of target
7436 are complementary, since core files contain only a program's
7437 read-write memory---variables and so on---plus machine status, while
7438 executable files contain only the program text and initialized data.)
7441 When you type @code{run}, your executable file becomes an active process
7442 target as well. When a process target is active, all @value{GDBN} commands
7443 requesting memory addresses refer to that target; addresses in an
7447 executable file target are obscured while the process
7451 Use the @code{exec-file} command to select a
7452 new executable target (@pxref{Files, ,Commands to specify
7456 Use the @code{core-file} and @code{exec-file} commands to select a
7457 new core file or executable target (@pxref{Files, ,Commands to specify
7458 files}). To specify as a target a process that is already running, use
7459 the @code{attach} command (@pxref{Attach, ,Debugging an
7460 already-running process}).
7463 @node Target Commands
7464 @section Commands for managing targets
7467 @item target @var{type} @var{parameters}
7468 Connects the @value{GDBN} host environment to a target
7473 machine or process. A target is typically a protocol for talking to
7474 debugging facilities. You use the argument @var{type} to specify the
7475 type or protocol of the target machine.
7477 Further @var{parameters} are interpreted by the target protocol, but
7478 typically include things like device names or host names to connect
7479 with, process numbers, and baud rates.
7482 The @code{target} command does not repeat if you press @key{RET} again
7483 after executing the command.
7487 Displays the names of all targets available. To display targets
7488 currently selected, use either @code{info target} or @code{info files}
7489 (@pxref{Files, ,Commands to specify files}).
7491 @item help target @var{name}
7492 Describe a particular target, including any parameters necessary to
7495 @kindex set gnutarget
7496 @item set gnutarget @var{args}
7497 @value{GDBN}uses its own library BFD to read your files. @value{GDBN}
7498 knows whether it is reading an @dfn{executable},
7499 a @dfn{core}, or a @dfn{.o} file, however you can specify the file format
7500 with the @code{set gnutarget} command. Unlike most @code{target} commands,
7501 with @code{gnutarget} the @code{target} refers to a program, not a machine.
7503 @emph{Warning:} To specify a file format with @code{set gnutarget},
7504 you must know the actual BFD name.
7506 @noindent @xref{Files, , Commands to specify files}.
7508 @kindex show gnutarget
7509 @item show gnutarget
7510 Use the @code{show gnutarget} command to display what file format
7511 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
7512 @value{GDBN} will determine the file format for each file automatically
7513 and @code{show gnutarget} displays @code{The current BDF target is "auto"}.
7516 Here are some common targets (available, or not, depending on the GDB
7521 @item target exec @var{program}
7522 An executable file. @samp{target exec @var{program}} is the same as
7523 @samp{exec-file @var{program}}.
7527 @item target core @var{filename}
7528 A core dump file. @samp{target core @var{filename}} is the same as
7529 @samp{core-file @var{filename}}.
7533 @kindex target remote
7534 @item target remote @var{dev}
7535 Remote serial target in GDB-specific protocol. The argument @var{dev}
7536 specifies what serial device to use for the connection (e.g.
7537 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
7538 now supports the @code{load} command. This is only useful if you have
7539 some other way of getting the stub to the target system, and you can put
7540 it somewhere in memory where it won't get clobbered by the download.
7546 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
7551 @item target udi @var{keyword}
7552 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
7553 argument specifies which 29K board or simulator to use. @xref{UDI29K
7554 Remote,,The UDI protocol for AMD29K}.
7556 @kindex target amd-eb
7557 @item target amd-eb @var{dev} @var{speed} @var{PROG}
7559 Remote PC-resident AMD EB29K board, attached over serial lines.
7560 @var{dev} is the serial device, as for @code{target remote};
7561 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
7562 name of the program to be debugged, as it appears to DOS on the PC.
7563 @xref{EB29K Remote, ,The EBMON protocol for AMD29K}.
7568 @item target hms @var{dev}
7569 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
7570 @ifclear H8EXCLUSIVE
7571 Use special commands @code{device} and @code{speed} to control the serial
7572 line and the communications speed used.
7574 @xref{Hitachi Remote,,@value{GDBN} and Hitachi Microprocessors}.
7578 @kindex target nindy
7579 @item target nindy @var{devicename}
7580 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
7581 the name of the serial device to use for the connection, e.g.
7582 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
7586 @kindex target st2000
7587 @item target st2000 @var{dev} @var{speed}
7588 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
7589 is the name of the device attached to the ST2000 serial line;
7590 @var{speed} is the communication line speed. The arguments are not used
7591 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
7592 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
7596 @kindex target vxworks
7597 @item target vxworks @var{machinename}
7598 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
7599 is the target system's machine name or IP address.
7600 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
7603 @kindex target cpu32bug
7604 @item target cpu32bug @var{dev}
7605 CPU32BUG monitor, running on a CPU32 (M68K) board.
7607 @kindex target op50n
7608 @item target op50n @var{dev}
7609 OP50N monitor, running on an OKI HPPA board.
7612 @item target w89k @var{dev}
7613 W89K monitor, running on a Winbond HPPA board.
7616 @item target est @var{dev}
7617 EST-300 ICE monitor, running on a CPU32 (M68K) board.
7619 @kindex target rom68k
7620 @item target rom68k @var{dev}
7621 ROM 68K monitor, running on an IDP board.
7623 @kindex target array
7624 @item target array @var{dev}
7625 Array Tech LSI33K RAID controller board.
7627 @kindex target sparclite
7628 @item target sparclite @var{dev}
7629 Fujitsu sparclite boards, used only for the purpose of loading.
7630 You must use an additional command to debug the program.
7631 For example: target remote @var{dev} using @value{GDBN} standard
7636 Different targets are available on different configurations of @value{GDBN};
7637 your configuration may have more or fewer targets.
7640 @section Choosing target byte order
7641 @cindex choosing target byte order
7642 @cindex target byte order
7643 @kindex set endian big
7644 @kindex set endian little
7645 @kindex set endian auto
7648 You can now choose which byte order to use with a target system.
7649 Use the @code{set endian big} and @code{set endian little} commands.
7650 Use the @code{set endian auto} command to instruct
7651 @value{GDBN} to use the byte order associated with the executable.
7652 You can see the current setting for byte order with the @code{show endian}
7655 @emph{Warning:} Currently, only embedded MIPS configurations support
7656 dynamic selection of target byte order.
7659 @section Remote debugging
7660 @cindex remote debugging
7662 If you are trying to debug a program running on a machine that cannot run
7663 @value{GDBN} in the usual way, it is often useful to use remote debugging.
7664 For example, you might use remote debugging on an operating system kernel,
7665 or on a small system which does not have a general purpose operating system
7666 powerful enough to run a full-featured debugger.
7668 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
7669 to make this work with particular debugging targets. In addition,
7670 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
7671 but not specific to any particular target system) which you can use if you
7672 write the remote stubs---the code that runs on the remote system to
7673 communicate with @value{GDBN}.
7675 Other remote targets may be available in your
7676 configuration of @value{GDBN}; use @code{help target} to list them.
7679 @c Text on starting up GDB in various specific cases; it goes up front
7680 @c in manuals configured for any of those particular situations, here
7684 * Remote Serial:: @value{GDBN} remote serial protocol
7687 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
7690 * UDI29K Remote:: The UDI protocol for AMD29K
7691 * EB29K Remote:: The EBMON protocol for AMD29K
7694 * VxWorks Remote:: @value{GDBN} and VxWorks
7697 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
7700 * Hitachi Remote:: @value{GDBN} and Hitachi Microprocessors
7703 * MIPS Remote:: @value{GDBN} and MIPS boards
7706 * Sparclet Remote:: @value{GDBN} and Sparclet boards
7709 * Simulator:: Simulated CPU target
7713 @include remote.texi
7716 @node Controlling GDB
7717 @chapter Controlling @value{GDBN}
7719 You can alter the way @value{GDBN} interacts with you by using
7720 the @code{set} command. For commands controlling how @value{GDBN} displays
7721 data, @pxref{Print Settings, ,Print settings}; other settings are described
7726 * Editing:: Command editing
7727 * History:: Command history
7728 * Screen Size:: Screen size
7730 * Messages/Warnings:: Optional warnings and messages
7738 @value{GDBN} indicates its readiness to read a command by printing a string
7739 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
7740 can change the prompt string with the @code{set prompt} command. For
7741 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
7742 the prompt in one of the @value{GDBN} sessions so that you can always tell
7743 which one you are talking to.
7745 @emph{Note:} @code{set prompt} no longer adds a space for you after the
7746 prompt you set. This allows you to set a prompt which ends in a space
7747 or a prompt that does not.
7751 @item set prompt @var{newprompt}
7752 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
7756 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
7760 @section Command editing
7762 @cindex command line editing
7764 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
7765 @sc{gnu} library provides consistent behavior for programs which provide a
7766 command line interface to the user. Advantages are @sc{gnu} Emacs-style
7767 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
7768 substitution, and a storage and recall of command history across
7771 You may control the behavior of command line editing in @value{GDBN} with the
7778 @itemx set editing on
7779 Enable command line editing (enabled by default).
7781 @item set editing off
7782 Disable command line editing.
7784 @kindex show editing
7786 Show whether command line editing is enabled.
7790 @section Command history
7792 @value{GDBN} can keep track of the commands you type during your
7793 debugging sessions, so that you can be certain of precisely what
7794 happened. Use these commands to manage the @value{GDBN} command
7798 @cindex history substitution
7799 @cindex history file
7800 @kindex set history filename
7802 @item set history filename @var{fname}
7803 Set the name of the @value{GDBN} command history file to @var{fname}.
7804 This is the file where @value{GDBN} reads an initial command history
7805 list, and where it writes the command history from this session when it
7806 exits. You can access this list through history expansion or through
7807 the history command editing characters listed below. This file defaults
7808 to the value of the environment variable @code{GDBHISTFILE}, or to
7809 @file{./.gdb_history} if this variable is not set.
7811 @cindex history save
7812 @kindex set history save
7813 @item set history save
7814 @itemx set history save on
7815 Record command history in a file, whose name may be specified with the
7816 @code{set history filename} command. By default, this option is disabled.
7818 @item set history save off
7819 Stop recording command history in a file.
7821 @cindex history size
7822 @kindex set history size
7823 @item set history size @var{size}
7824 Set the number of commands which @value{GDBN} keeps in its history list.
7825 This defaults to the value of the environment variable
7826 @code{HISTSIZE}, or to 256 if this variable is not set.
7829 @cindex history expansion
7830 History expansion assigns special meaning to the character @kbd{!}.
7831 @ifset have-readline-appendices
7832 @xref{Event Designators}.
7835 Since @kbd{!} is also the logical not operator in C, history expansion
7836 is off by default. If you decide to enable history expansion with the
7837 @code{set history expansion on} command, you may sometimes need to
7838 follow @kbd{!} (when it is used as logical not, in an expression) with
7839 a space or a tab to prevent it from being expanded. The readline
7840 history facilities do not attempt substitution on the strings
7841 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7843 The commands to control history expansion are:
7846 @kindex set history expansion
7847 @item set history expansion on
7848 @itemx set history expansion
7849 Enable history expansion. History expansion is off by default.
7851 @item set history expansion off
7852 Disable history expansion.
7854 The readline code comes with more complete documentation of
7855 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
7856 or @code{vi} may wish to read it.
7857 @ifset have-readline-appendices
7858 @xref{Command Line Editing}.
7862 @kindex show history
7864 @itemx show history filename
7865 @itemx show history save
7866 @itemx show history size
7867 @itemx show history expansion
7868 These commands display the state of the @value{GDBN} history parameters.
7869 @code{show history} by itself displays all four states.
7874 @kindex show commands
7876 Display the last ten commands in the command history.
7878 @item show commands @var{n}
7879 Print ten commands centered on command number @var{n}.
7881 @item show commands +
7882 Print ten commands just after the commands last printed.
7886 @section Screen size
7887 @cindex size of screen
7888 @cindex pauses in output
7890 Certain commands to @value{GDBN} may produce large amounts of
7891 information output to the screen. To help you read all of it,
7892 @value{GDBN} pauses and asks you for input at the end of each page of
7893 output. Type @key{RET} when you want to continue the output, or @kbd{q}
7894 to discard the remaining output. Also, the screen width setting
7895 determines when to wrap lines of output. Depending on what is being
7896 printed, @value{GDBN} tries to break the line at a readable place,
7897 rather than simply letting it overflow onto the following line.
7899 Normally @value{GDBN} knows the size of the screen from the termcap data base
7900 together with the value of the @code{TERM} environment variable and the
7901 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7902 you can override it with the @code{set height} and @code{set
7910 @item set height @var{lpp}
7912 @itemx set width @var{cpl}
7914 These @code{set} commands specify a screen height of @var{lpp} lines and
7915 a screen width of @var{cpl} characters. The associated @code{show}
7916 commands display the current settings.
7918 If you specify a height of zero lines, @value{GDBN} does not pause during
7919 output no matter how long the output is. This is useful if output is to a
7920 file or to an editor buffer.
7922 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
7923 from wrapping its output.
7928 @cindex number representation
7929 @cindex entering numbers
7931 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7932 the usual conventions: octal numbers begin with @samp{0}, decimal
7933 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7934 Numbers that begin with none of these are, by default, entered in base
7935 10; likewise, the default display for numbers---when no particular
7936 format is specified---is base 10. You can change the default base for
7937 both input and output with the @code{set radix} command.
7940 @kindex set input-radix
7941 @item set input-radix @var{base}
7942 Set the default base for numeric input. Supported choices
7943 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7944 specified either unambiguously or using the current default radix; for
7954 sets the base to decimal. On the other hand, @samp{set radix 10}
7955 leaves the radix unchanged no matter what it was.
7957 @kindex set output-radix
7958 @item set output-radix @var{base}
7959 Set the default base for numeric display. Supported choices
7960 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
7961 specified either unambiguously or using the current default radix.
7963 @kindex show input-radix
7964 @item show input-radix
7965 Display the current default base for numeric input.
7967 @kindex show output-radix
7968 @item show output-radix
7969 Display the current default base for numeric display.
7972 @node Messages/Warnings
7973 @section Optional warnings and messages
7975 By default, @value{GDBN} is silent about its inner workings. If you are running
7976 on a slow machine, you may want to use the @code{set verbose} command.
7977 This makes @value{GDBN} tell you when it does a lengthy internal operation, so
7978 you will not think it has crashed.
7980 Currently, the messages controlled by @code{set verbose} are those
7981 which announce that the symbol table for a source file is being read;
7982 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7986 @item set verbose on
7987 Enables @value{GDBN} output of certain informational messages.
7989 @item set verbose off
7990 Disables @value{GDBN} output of certain informational messages.
7992 @kindex show verbose
7994 Displays whether @code{set verbose} is on or off.
7997 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7998 file, it is silent; but if you are debugging a compiler, you may find
7999 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
8002 @kindex set complaints
8003 @item set complaints @var{limit}
8004 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
8005 symbols before becoming silent about the problem. Set @var{limit} to
8006 zero to suppress all complaints; set it to a large number to prevent
8007 complaints from being suppressed.
8009 @kindex show complaints
8010 @item show complaints
8011 Displays how many symbol complaints @value{GDBN} is permitted to produce.
8014 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
8015 lot of stupid questions to confirm certain commands. For example, if
8016 you try to run a program which is already running:
8020 The program being debugged has been started already.
8021 Start it from the beginning? (y or n)
8024 If you are willing to unflinchingly face the consequences of your own
8025 commands, you can disable this ``feature'':
8030 @cindex confirmation
8031 @cindex stupid questions
8032 @item set confirm off
8033 Disables confirmation requests.
8035 @item set confirm on
8036 Enables confirmation requests (the default).
8038 @kindex show confirm
8040 Displays state of confirmation requests.
8044 @chapter Canned Sequences of Commands
8046 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
8047 command lists}), @value{GDBN} provides two ways to store sequences of commands
8048 for execution as a unit: user-defined commands and command files.
8051 * Define:: User-defined commands
8052 * Hooks:: User-defined command hooks
8053 * Command Files:: Command files
8054 * Output:: Commands for controlled output
8058 @section User-defined commands
8060 @cindex user-defined command
8061 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which
8062 you assign a new name as a command. This is done with the @code{define}
8063 command. User commands may accept up to 10 arguments separated by whitespace.
8064 Arguments are accessed within the user command via @var{$arg0@dots{}$arg9}.
8069 print $arg0 + $arg1 + $arg2
8072 @noindent To execute the command use:
8078 @noindent This defines the command @code{adder}, which prints the sum of
8079 its three arguments. Note the arguments are text substitutions, so they may
8080 reference variables, use complex expressions, or even perform inferior
8085 @item define @var{commandname}
8086 Define a command named @var{commandname}. If there is already a command
8087 by that name, you are asked to confirm that you want to redefine it.
8089 The definition of the command is made up of other @value{GDBN} command lines,
8090 which are given following the @code{define} command. The end of these
8091 commands is marked by a line containing @code{end}.
8096 Takes a single argument, which is an expression to evaluate.
8097 It is followed by a series of commands that are executed
8098 only if the expression is true (nonzero).
8099 There can then optionally be a line @code{else}, followed
8100 by a series of commands that are only executed if the expression
8101 was false. The end of the list is marked by a line containing @code{end}.
8105 The syntax is similar to @code{if}: the command takes a single argument,
8106 which is an expression to evaluate, and must be followed by the commands to
8107 execute, one per line, terminated by an @code{end}.
8108 The commands are executed repeatedly as long as the expression
8112 @item document @var{commandname}
8113 Document the user-defined command @var{commandname}, so that it can be
8114 accessed by @code{help}. The command @var{commandname} must already be
8115 defined. This command reads lines of documentation just as @code{define}
8116 reads the lines of the command definition, ending with @code{end}.
8117 After the @code{document} command is finished, @code{help} on command
8118 @var{commandname} displays the documentation you have written.
8120 You may use the @code{document} command again to change the
8121 documentation of a command. Redefining the command with @code{define}
8122 does not change the documentation.
8124 @kindex help user-defined
8125 @item help user-defined
8126 List all user-defined commands, with the first line of the documentation
8131 @itemx show user @var{commandname}
8132 Display the @value{GDBN} commands used to define @var{commandname} (but not its
8133 documentation). If no @var{commandname} is given, display the
8134 definitions for all user-defined commands.
8137 When user-defined commands are executed, the
8138 commands of the definition are not printed. An error in any command
8139 stops execution of the user-defined command.
8141 If used interactively, commands that would ask for confirmation proceed
8142 without asking when used inside a user-defined command. Many @value{GDBN}
8143 commands that normally print messages to say what they are doing omit the
8144 messages when used in a user-defined command.
8147 @section User-defined command hooks
8148 @cindex command files
8150 You may define @emph{hooks}, which are a special kind of user-defined
8151 command. Whenever you run the command @samp{foo}, if the user-defined
8152 command @samp{hook-foo} exists, it is executed (with no arguments)
8153 before that command.
8155 In addition, a pseudo-command, @samp{stop} exists. Defining
8156 (@samp{hook-stop}) makes the associated commands execute every time
8157 execution stops in your program: before breakpoint commands are run,
8158 displays are printed, or the stack frame is printed.
8161 For example, to ignore @code{SIGALRM} signals while
8162 single-stepping, but treat them normally during normal execution,
8167 handle SIGALRM nopass
8174 define hook-continue
8180 You can define a hook for any single-word command in @value{GDBN}, but
8181 not for command aliases; you should define a hook for the basic command
8182 name, e.g. @code{backtrace} rather than @code{bt}.
8183 @c FIXME! So how does Joe User discover whether a command is an alias
8185 If an error occurs during the execution of your hook, execution of
8186 @value{GDBN} commands stops and @value{GDBN} issues a prompt
8187 (before the command that you actually typed had a chance to run).
8189 If you try to define a hook which does not match any known command, you
8190 get a warning from the @code{define} command.
8193 @section Command files
8195 @cindex command files
8196 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
8197 commands. Comments (lines starting with @kbd{#}) may also be included.
8198 An empty line in a command file does nothing; it does not mean to repeat
8199 the last command, as it would from the terminal.
8202 @cindex @file{@value{GDBINIT}}
8203 When you start @value{GDBN}, it automatically executes commands from its
8204 @dfn{init files}. These are files named @file{@value{GDBINIT}}.
8205 @value{GDBN} reads the init file (if any) in your home directory, then
8206 processes command line options and operands, and then reads the init
8207 file (if any) in the current working directory. This is so the init
8208 file in your home directory can set options (such as @code{set
8209 complaints}) which affect the processing of the command line options and
8210 operands. The init files are not executed if you use the @samp{-nx}
8211 option; @pxref{Mode Options, ,Choosing modes}.
8214 @cindex init file name
8215 On some configurations of @value{GDBN}, the init file is known by a
8216 different name (these are typically environments where a specialized
8217 form of @value{GDBN} may need to coexist with other forms,
8218 hence a different name
8219 for the specialized version's init file). These are the environments
8220 with special init file names:
8225 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
8227 @kindex .os68gdbinit
8229 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
8233 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
8237 You can also request the execution of a command file with the
8238 @code{source} command:
8242 @item source @var{filename}
8243 Execute the command file @var{filename}.
8246 The lines in a command file are executed sequentially. They are not
8247 printed as they are executed. An error in any command terminates execution
8248 of the command file.
8250 Commands that would ask for confirmation if used interactively proceed
8251 without asking when used in a command file. Many @value{GDBN} commands that
8252 normally print messages to say what they are doing omit the messages
8253 when called from command files.
8256 @section Commands for controlled output
8258 During the execution of a command file or a user-defined command, normal
8259 @value{GDBN} output is suppressed; the only output that appears is what is
8260 explicitly printed by the commands in the definition. This section
8261 describes three commands useful for generating exactly the output you
8266 @item echo @var{text}
8267 @c I do not consider backslash-space a standard C escape sequence
8268 @c because it is not in ANSI.
8269 Print @var{text}. Nonprinting characters can be included in
8270 @var{text} using C escape sequences, such as @samp{\n} to print a
8271 newline. @strong{No newline is printed unless you specify one.}
8272 In addition to the standard C escape sequences, a backslash followed
8273 by a space stands for a space. This is useful for displaying a
8274 string with spaces at the beginning or the end, since leading and
8275 trailing spaces are otherwise trimmed from all arguments.
8276 To print @samp{@w{ }and foo =@w{ }}, use the command
8277 @samp{echo \@w{ }and foo = \@w{ }}.
8279 A backslash at the end of @var{text} can be used, as in C, to continue
8280 the command onto subsequent lines. For example,
8283 echo This is some text\n\
8284 which is continued\n\
8285 onto several lines.\n
8288 produces the same output as
8291 echo This is some text\n
8292 echo which is continued\n
8293 echo onto several lines.\n
8297 @item output @var{expression}
8298 Print the value of @var{expression} and nothing but that value: no
8299 newlines, no @samp{$@var{nn} = }. The value is not entered in the
8300 value history either. @xref{Expressions, ,Expressions}, for more information
8303 @item output/@var{fmt} @var{expression}
8304 Print the value of @var{expression} in format @var{fmt}. You can use
8305 the same formats as for @code{print}. @xref{Output Formats,,Output
8306 formats}, for more information.
8309 @item printf @var{string}, @var{expressions}@dots{}
8310 Print the values of the @var{expressions} under the control of
8311 @var{string}. The @var{expressions} are separated by commas and may be
8312 either numbers or pointers. Their values are printed as specified by
8313 @var{string}, exactly as if your program were to execute the C
8317 printf (@var{string}, @var{expressions}@dots{});
8320 For example, you can print two values in hex like this:
8323 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
8326 The only backslash-escape sequences that you can use in the format
8327 string are the simple ones that consist of backslash followed by a
8333 @chapter Using @value{GDBN} under @sc{gnu} Emacs
8336 @cindex @sc{gnu} Emacs
8337 A special interface allows you to use @sc{gnu} Emacs to view (and
8338 edit) the source files for the program you are debugging with
8341 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
8342 executable file you want to debug as an argument. This command starts
8343 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
8344 created Emacs buffer.
8346 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
8351 All ``terminal'' input and output goes through the Emacs buffer.
8354 This applies both to @value{GDBN} commands and their output, and to the input
8355 and output done by the program you are debugging.
8357 This is useful because it means that you can copy the text of previous
8358 commands and input them again; you can even use parts of the output
8361 All the facilities of Emacs' Shell mode are available for interacting
8362 with your program. In particular, you can send signals the usual
8363 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
8368 @value{GDBN} displays source code through Emacs.
8371 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
8372 source file for that frame and puts an arrow (@samp{=>}) at the
8373 left margin of the current line. Emacs uses a separate buffer for
8374 source display, and splits the screen to show both your @value{GDBN} session
8377 Explicit @value{GDBN} @code{list} or search commands still produce output as
8378 usual, but you probably have no reason to use them from Emacs.
8381 @emph{Warning:} If the directory where your program resides is not your
8382 current directory, it can be easy to confuse Emacs about the location of
8383 the source files, in which case the auxiliary display buffer does not
8384 appear to show your source. @value{GDBN} can find programs by searching your
8385 environment's @code{PATH} variable, so the @value{GDBN} input and output
8386 session proceeds normally; but Emacs does not get enough information
8387 back from @value{GDBN} to locate the source files in this situation. To
8388 avoid this problem, either start @value{GDBN} mode from the directory where
8389 your program resides, or specify an absolute file name when prompted for the
8390 @kbd{M-x gdb} argument.
8392 A similar confusion can result if you use the @value{GDBN} @code{file} command to
8393 switch to debugging a program in some other location, from an existing
8394 @value{GDBN} buffer in Emacs.
8397 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
8398 you need to call @value{GDBN} by a different name (for example, if you keep
8399 several configurations around, with different names) you can set the
8400 Emacs variable @code{gdb-command-name}; for example,
8403 (setq gdb-command-name "mygdb")
8407 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
8408 in your @file{.emacs} file) makes Emacs call the program named
8409 ``@code{mygdb}'' instead.
8411 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
8412 addition to the standard Shell mode commands:
8416 Describe the features of Emacs' @value{GDBN} Mode.
8419 Execute to another source line, like the @value{GDBN} @code{step} command; also
8420 update the display window to show the current file and location.
8423 Execute to next source line in this function, skipping all function
8424 calls, like the @value{GDBN} @code{next} command. Then update the display window
8425 to show the current file and location.
8428 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
8429 display window accordingly.
8432 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
8433 display window accordingly.
8436 Execute until exit from the selected stack frame, like the @value{GDBN}
8437 @code{finish} command.
8440 Continue execution of your program, like the @value{GDBN} @code{continue}
8443 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
8446 Go up the number of frames indicated by the numeric argument
8447 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
8448 like the @value{GDBN} @code{up} command.
8450 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
8453 Go down the number of frames indicated by the numeric argument, like the
8454 @value{GDBN} @code{down} command.
8456 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
8459 Read the number where the cursor is positioned, and insert it at the end
8460 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
8461 around an address that was displayed earlier, type @kbd{disassemble};
8462 then move the cursor to the address display, and pick up the
8463 argument for @code{disassemble} by typing @kbd{C-x &}.
8465 You can customize this further by defining elements of the list
8466 @code{gdb-print-command}; once it is defined, you can format or
8467 otherwise process numbers picked up by @kbd{C-x &} before they are
8468 inserted. A numeric argument to @kbd{C-x &} indicates that you
8469 wish special formatting, and also acts as an index to pick an element of the
8470 list. If the list element is a string, the number to be inserted is
8471 formatted using the Emacs function @code{format}; otherwise the number
8472 is passed as an argument to the corresponding list element.
8475 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
8476 tells @value{GDBN} to set a breakpoint on the source line point is on.
8478 If you accidentally delete the source-display buffer, an easy way to get
8479 it back is to type the command @code{f} in the @value{GDBN} buffer, to
8480 request a frame display; when you run under Emacs, this recreates
8481 the source buffer if necessary to show you the context of the current
8484 The source files displayed in Emacs are in ordinary Emacs buffers
8485 which are visiting the source files in the usual way. You can edit
8486 the files with these buffers if you wish; but keep in mind that @value{GDBN}
8487 communicates with Emacs in terms of line numbers. If you add or
8488 delete lines from the text, the line numbers that @value{GDBN} knows cease
8489 to correspond properly with the code.
8491 @c The following dropped because Epoch is nonstandard. Reactivate
8492 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
8494 @kindex Emacs Epoch environment
8498 Version 18 of @sc{gnu} Emacs has a built-in window system
8499 called the @code{epoch}
8500 environment. Users of this environment can use a new command,
8501 @code{inspect} which performs identically to @code{print} except that
8502 each value is printed in its own window.
8508 @chapter Using @value{GDBN} with Energize
8511 The Energize Programming System is an integrated development environment
8512 that includes a point-and-click interface to many programming tools.
8513 When you use @value{GDBN} in this environment, you can use the standard
8514 Energize graphical interface to drive @value{GDBN}; you can also, if you
8515 choose, type @value{GDBN} commands as usual in a debugging window. Even if
8516 you use the graphical interface, the debugging window (which uses Emacs,
8517 and resembles the standard @sc{gnu} Emacs interface to
8518 @value{GDBN}) displays the
8519 equivalent commands, so that the history of your debugging session is
8522 When Energize starts up a @value{GDBN} session, it uses one of the
8523 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
8524 is the name of the communications protocol used by the Energize system).
8525 This option makes @value{GDBN} run as one of the tools in the Energize Tool
8526 Set: it sends all output to the Energize kernel, and accept input from
8529 See the user manual for the Energize Programming System for
8530 information on how to use the Energize graphical interface and the other
8531 development tools that Energize integrates with @value{GDBN}.
8536 @chapter Reporting Bugs in @value{GDBN}
8537 @cindex bugs in @value{GDBN}
8538 @cindex reporting bugs in @value{GDBN}
8540 Your bug reports play an essential role in making @value{GDBN} reliable.
8542 Reporting a bug may help you by bringing a solution to your problem, or it
8543 may not. But in any case the principal function of a bug report is to help
8544 the entire community by making the next version of @value{GDBN} work better. Bug
8545 reports are your contribution to the maintenance of @value{GDBN}.
8547 In order for a bug report to serve its purpose, you must include the
8548 information that enables us to fix the bug.
8551 * Bug Criteria:: Have you found a bug?
8552 * Bug Reporting:: How to report bugs
8556 @section Have you found a bug?
8557 @cindex bug criteria
8559 If you are not sure whether you have found a bug, here are some guidelines:
8562 @cindex fatal signal
8563 @cindex debugger crash
8564 @cindex crash of debugger
8566 If the debugger gets a fatal signal, for any input whatever, that is a
8567 @value{GDBN} bug. Reliable debuggers never crash.
8569 @cindex error on valid input
8571 If @value{GDBN} produces an error message for valid input, that is a bug.
8573 @cindex invalid input
8575 If @value{GDBN} does not produce an error message for invalid input,
8576 that is a bug. However, you should note that your idea of
8577 ``invalid input'' might be our idea of ``an extension'' or ``support
8578 for traditional practice''.
8581 If you are an experienced user of debugging tools, your suggestions
8582 for improvement of @value{GDBN} are welcome in any case.
8586 @section How to report bugs
8588 @cindex @value{GDBN} bugs, reporting
8590 A number of companies and individuals offer support for @sc{gnu} products.
8591 If you obtained @value{GDBN} from a support organization, we recommend you
8592 contact that organization first.
8594 You can find contact information for many support companies and
8595 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
8598 In any event, we also recommend that you send bug reports for @value{GDBN} to one
8602 bug-gdb@@prep.ai.mit.edu
8603 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
8606 @strong{Do not send bug reports to @samp{info-gdb}, or to
8607 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
8608 receive bug reports. Those that do have arranged to receive @samp{bug-gdb}.
8610 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
8611 serves as a repeater. The mailing list and the newsgroup carry exactly
8612 the same messages. Often people think of posting bug reports to the
8613 newsgroup instead of mailing them. This appears to work, but it has one
8614 problem which can be crucial: a newsgroup posting often lacks a mail
8615 path back to the sender. Thus, if we need to ask for more information,
8616 we may be unable to reach you. For this reason, it is better to send
8617 bug reports to the mailing list.
8619 As a last resort, send bug reports on paper to:
8622 @sc{gnu} Debugger Bugs
8623 Free Software Foundation Inc.
8624 59 Temple Place - Suite 330
8625 Boston, MA 02111-1307
8629 The fundamental principle of reporting bugs usefully is this:
8630 @strong{report all the facts}. If you are not sure whether to state a
8631 fact or leave it out, state it!
8633 Often people omit facts because they think they know what causes the
8634 problem and assume that some details do not matter. Thus, you might
8635 assume that the name of the variable you use in an example does not matter.
8636 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
8637 stray memory reference which happens to fetch from the location where that
8638 name is stored in memory; perhaps, if the name were different, the contents
8639 of that location would fool the debugger into doing the right thing despite
8640 the bug. Play it safe and give a specific, complete example. That is the
8641 easiest thing for you to do, and the most helpful.
8643 Keep in mind that the purpose of a bug report is to enable us to fix
8644 the bug if it is new to us.
8646 @c FIX ME!!--What the heck does the following sentence mean,
8647 @c in the context of the one above?
8649 @c It is not as important as what happens if the bug is already known.
8651 Therefore, always write your bug reports on
8652 the assumption that the bug has not been reported previously.
8654 Sometimes people give a few sketchy facts and ask, ``Does this ring a
8655 bell?'' Those bug reports are useless, and we urge everyone to
8656 @emph{refuse to respond to them} except to chide the sender to report
8659 To enable us to fix the bug, you should include all these things:
8663 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
8664 arguments; you can also print it at any time using @code{show version}.
8666 Without this, we will not know whether there is any point in looking for
8667 the bug in the current version of @value{GDBN}.
8670 The type of machine you are using, and the operating system name and
8674 What compiler (and its version) was used to compile @value{GDBN}---e.g.
8675 ``@value{GCC}--2.0''.
8678 What compiler (and its version) was used to compile the program you
8679 are debugging---e.g. ``@value{GCC}--2.0''.
8682 The command arguments you gave the compiler to compile your example and
8683 observe the bug. For example, did you use @samp{-O}? To guarantee
8684 you will not omit something important, list them all. A copy of the
8685 Makefile (or the output from make) is sufficient.
8687 If we were to try to guess the arguments, we would probably guess wrong
8688 and then we might not encounter the bug.
8691 A complete input script, and all necessary source files, that will
8695 A description of what behavior you observe that you believe is
8696 incorrect. For example, ``It gets a fatal signal.''
8698 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
8699 certainly notice it. But if the bug is incorrect output, we might not
8700 notice unless it is glaringly wrong. You might as well not give us a
8701 chance to make a mistake.
8703 Even if the problem you experience is a fatal signal, you should still
8704 say so explicitly. Suppose something strange is going on, such as,
8705 your copy of @value{GDBN} is out of synch, or you have encountered a
8706 bug in the C library on your system. (This has happened!) Your copy
8707 might crash and ours would not. If you told us to expect a crash,
8708 then when ours fails to crash, we would know that the bug was not
8709 happening for us. If you had not told us to expect a crash, then we
8710 would not be able to draw any conclusion from our observations.
8713 If you wish to suggest changes to the @value{GDBN} source, send us context
8714 diffs. If you even discuss something in the @value{GDBN} source, refer to
8715 it by context, not by line number.
8717 The line numbers in our development sources will not match those in your
8718 sources. Your line numbers would convey no useful information to us.
8721 Here are some things that are not necessary:
8725 A description of the envelope of the bug.
8727 Often people who encounter a bug spend a lot of time investigating
8728 which changes to the input file will make the bug go away and which
8729 changes will not affect it.
8731 This is often time consuming and not very useful, because the way we
8732 will find the bug is by running a single example under the debugger
8733 with breakpoints, not by pure deduction from a series of examples.
8734 We recommend that you save your time for something else.
8736 Of course, if you can find a simpler example to report @emph{instead}
8737 of the original one, that is a convenience for us. Errors in the
8738 output will be easier to spot, running under the debugger will take
8739 less time, and so on.
8741 However, simplification is not vital; if you do not want to do this,
8742 report the bug anyway and send us the entire test case you used.
8745 A patch for the bug.
8747 A patch for the bug does help us if it is a good one. But do not omit
8748 the necessary information, such as the test case, on the assumption that
8749 a patch is all we need. We might see problems with your patch and decide
8750 to fix the problem another way, or we might not understand it at all.
8752 Sometimes with a program as complicated as @value{GDBN} it is very hard to
8753 construct an example that will make the program follow a certain path
8754 through the code. If you do not send us the example, we will not be able
8755 to construct one, so we will not be able to verify that the bug is fixed.
8757 And if we cannot understand what bug you are trying to fix, or why your
8758 patch should be an improvement, we will not install it. A test case will
8759 help us to understand.
8762 A guess about what the bug is or what it depends on.
8764 Such guesses are usually wrong. Even we cannot guess right about such
8765 things without first using the debugger to find the facts.
8768 @c The readline documentation is distributed with the readline code
8769 @c and consists of the two following files:
8772 @c Use -I with makeinfo to point to the appropriate directory,
8773 @c environment var TEXINPUTS with TeX.
8774 @include rluser.texinfo
8775 @include inc-hist.texi
8779 @node Renamed Commands
8780 @appendix Renamed Commands
8782 The following commands were renamed in @value{GDBN} 4, in order to make the
8783 command set as a whole more consistent and easier to use and remember:
8786 @kindex delete environment
8787 @kindex info copying
8788 @kindex info convenience
8789 @kindex info directories
8790 @kindex info editing
8791 @kindex info history
8792 @kindex info targets
8794 @kindex info version
8795 @kindex info warranty
8796 @kindex set addressprint
8797 @kindex set arrayprint
8798 @kindex set prettyprint
8799 @kindex set screen-height
8800 @kindex set screen-width
8801 @kindex set unionprint
8802 @kindex set vtblprint
8803 @kindex set demangle
8804 @kindex set asm-demangle
8805 @kindex set sevenbit-strings
8806 @kindex set array-max
8808 @kindex set history write
8809 @kindex show addressprint
8810 @kindex show arrayprint
8811 @kindex show prettyprint
8812 @kindex show screen-height
8813 @kindex show screen-width
8814 @kindex show unionprint
8815 @kindex show vtblprint
8816 @kindex show demangle
8817 @kindex show asm-demangle
8818 @kindex show sevenbit-strings
8819 @kindex show array-max
8820 @kindex show caution
8821 @kindex show history write
8826 @c END TEXI2ROFF-KILL
8828 OLD COMMAND NEW COMMAND
8830 --------------- -------------------------------
8831 @c END TEXI2ROFF-KILL
8832 add-syms add-symbol-file
8833 delete environment unset environment
8834 info convenience show convenience
8835 info copying show copying
8836 info directories show directories
8837 info editing show commands
8838 info history show values
8839 info targets help target
8840 info values show values
8841 info version show version
8842 info warranty show warranty
8843 set/show addressprint set/show print address
8844 set/show array-max set/show print elements
8845 set/show arrayprint set/show print array
8846 set/show asm-demangle set/show print asm-demangle
8847 set/show caution set/show confirm
8848 set/show demangle set/show print demangle
8849 set/show history write set/show history save
8850 set/show prettyprint set/show print pretty
8851 set/show screen-height set/show height
8852 set/show screen-width set/show width
8853 set/show sevenbit-strings set/show print sevenbit-strings
8854 set/show unionprint set/show print union
8855 set/show vtblprint set/show print vtbl
8857 unset [No longer an alias for delete]
8863 \vskip \parskip\vskip \baselineskip
8864 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8865 {\bf Old Command} &&{\bf New Command}\cr
8866 add-syms &&add-symbol-file\cr
8867 delete environment &&unset environment\cr
8868 info convenience &&show convenience\cr
8869 info copying &&show copying\cr
8870 info directories &&show directories \cr
8871 info editing &&show commands\cr
8872 info history &&show values\cr
8873 info targets &&help target\cr
8874 info values &&show values\cr
8875 info version &&show version\cr
8876 info warranty &&show warranty\cr
8877 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8878 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8879 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8880 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8881 set{\rm / }show caution &&set{\rm / }show confirm\cr
8882 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8883 set{\rm / }show history write &&set{\rm / }show history save\cr
8884 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8885 set{\rm / }show screen-height &&set{\rm / }show height\cr
8886 set{\rm / }show screen-width &&set{\rm / }show width\cr
8887 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8888 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8889 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8891 unset &&\rm(No longer an alias for delete)\cr
8894 @c END TEXI2ROFF-KILL
8898 @ifclear PRECONFIGURED
8899 @node Formatting Documentation
8900 @appendix Formatting Documentation
8902 @cindex @value{GDBN} reference card
8903 @cindex reference card
8904 The @value{GDBN} 4 release includes an already-formatted reference card, ready
8905 for printing with PostScript or Ghostscript, in the @file{gdb}
8906 subdirectory of the main source directory@footnote{In
8907 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8908 release.}. If you can use PostScript or Ghostscript with your printer,
8909 you can print the reference card immediately with @file{refcard.ps}.
8911 The release also includes the source for the reference card. You
8912 can format it, using @TeX{}, by typing:
8918 The @value{GDBN} reference card is designed to print in @dfn{landscape}
8919 mode on US ``letter'' size paper;
8920 that is, on a sheet 11 inches wide by 8.5 inches
8921 high. You will need to specify this form of printing as an option to
8922 your @sc{dvi} output program.
8924 @cindex documentation
8926 All the documentation for @value{GDBN} comes as part of the machine-readable
8927 distribution. The documentation is written in Texinfo format, which is
8928 a documentation system that uses a single source file to produce both
8929 on-line information and a printed manual. You can use one of the Info
8930 formatting commands to create the on-line version of the documentation
8931 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8933 @value{GDBN} includes an already formatted copy of the on-line Info version of
8934 this manual in the @file{gdb} subdirectory. The main Info file is
8935 @file{gdb-@r{version-number}/gdb/gdb.info}, and it refers to
8936 subordinate files matching @samp{gdb.info*} in the same directory. If
8937 necessary, you can print out these files, or read them with any editor;
8938 but they are easier to read using the @code{info} subsystem in @sc{gnu} Emacs
8939 or the standalone @code{info} program, available as part of the @sc{gnu}
8940 Texinfo distribution.
8942 If you want to format these Info files yourself, you need one of the
8943 Info formatting programs, such as @code{texinfo-format-buffer} or
8946 If you have @code{makeinfo} installed, and are in the top level @value{GDBN}
8947 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8948 make the Info file by typing:
8955 If you want to typeset and print copies of this manual, you need @TeX{},
8956 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8957 Texinfo definitions file.
8959 @TeX{} is a typesetting program; it does not print files directly, but
8960 produces output files called @sc{dvi} files. To print a typeset
8961 document, you need a program to print @sc{dvi} files. If your system
8962 has @TeX{} installed, chances are it has such a program. The precise
8963 command to use depends on your system; @kbd{lpr -d} is common; another
8964 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8965 require a file name without any extension or a @samp{.dvi} extension.
8967 @TeX{} also requires a macro definitions file called
8968 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8969 written in Texinfo format. On its own, @TeX{} cannot either read or
8970 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8971 and is located in the @file{gdb-@var{version-number}/texinfo}
8974 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8975 typeset and print this manual. First switch to the the @file{gdb}
8976 subdirectory of the main source directory (for example, to
8977 @file{gdb-@value{GDBVN}/gdb}) and then type:
8983 @node Installing GDB
8984 @appendix Installing @value{GDBN}
8985 @cindex configuring @value{GDBN}
8986 @cindex installation
8988 @value{GDBN} comes with a @code{configure} script that automates the process
8989 of preparing @value{GDBN} for installation; you can then use @code{make} to
8990 build the @code{gdb} program.
8992 @c irrelevant in info file; it's as current as the code it lives with.
8993 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
8994 look at the @file{README} file in the sources; we may have improved the
8995 installation procedures since publishing this manual.}
8998 The @value{GDBN} distribution includes all the source code you need for
8999 @value{GDBN} in a single directory, whose name is usually composed by
9000 appending the version number to @samp{gdb}.
9002 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
9003 @file{gdb-@value{GDBVN}} directory. That directory contains:
9006 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
9007 script for configuring @value{GDBN} and all its supporting libraries
9009 @item gdb-@value{GDBVN}/gdb
9010 the source specific to @value{GDBN} itself
9012 @item gdb-@value{GDBVN}/bfd
9013 source for the Binary File Descriptor library
9015 @item gdb-@value{GDBVN}/include
9016 @sc{gnu} include files
9018 @item gdb-@value{GDBVN}/libiberty
9019 source for the @samp{-liberty} free software library
9021 @item gdb-@value{GDBVN}/opcodes
9022 source for the library of opcode tables and disassemblers
9024 @item gdb-@value{GDBVN}/readline
9025 source for the @sc{gnu} command-line interface
9027 @item gdb-@value{GDBVN}/glob
9028 source for the @sc{gnu} filename pattern-matching subroutine
9030 @item gdb-@value{GDBVN}/mmalloc
9031 source for the @sc{gnu} memory-mapped malloc package
9034 The simplest way to configure and build @value{GDBN} is to run @code{configure}
9035 from the @file{gdb-@var{version-number}} source directory, which in
9036 this example is the @file{gdb-@value{GDBVN}} directory.
9038 First switch to the @file{gdb-@var{version-number}} source directory
9039 if you are not already in it; then run @code{configure}. Pass the
9040 identifier for the platform on which @value{GDBN} will run as an
9046 cd gdb-@value{GDBVN}
9047 ./configure @var{host}
9052 where @var{host} is an identifier such as @samp{sun4} or
9053 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
9054 (You can often leave off @var{host}; @code{configure} tries to guess the
9055 correct value by examining your system.)
9057 Running @samp{configure @var{host}} and then running @code{make} builds the
9058 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
9059 libraries, then @code{gdb} itself. The configured source files, and the
9060 binaries, are left in the corresponding source directories.
9063 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
9064 system does not recognize this automatically when you run a different
9065 shell, you may need to run @code{sh} on it explicitly:
9068 sh configure @var{host}
9071 If you run @code{configure} from a directory that contains source
9072 directories for multiple libraries or programs, such as the
9073 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
9074 creates configuration files for every directory level underneath (unless
9075 you tell it not to, with the @samp{--norecursion} option).
9077 You can run the @code{configure} script from any of the
9078 subordinate directories in the @value{GDBN} distribution if you only want to
9079 configure that subdirectory, but be sure to specify a path to it.
9081 For example, with version @value{GDBVN}, type the following to configure only
9082 the @code{bfd} subdirectory:
9086 cd gdb-@value{GDBVN}/bfd
9087 ../configure @var{host}
9091 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
9092 However, you should make sure that the shell on your path (named by
9093 the @samp{SHELL} environment variable) is publicly readable. Remember
9094 that @value{GDBN} uses the shell to start your program---some systems refuse to
9095 let @value{GDBN} debug child processes whose programs are not readable.
9098 * Separate Objdir:: Compiling @value{GDBN} in another directory
9099 * Config Names:: Specifying names for hosts and targets
9100 * configure Options:: Summary of options for configure
9103 @node Separate Objdir
9104 @section Compiling @value{GDBN} in another directory
9106 If you want to run @value{GDBN} versions for several host or target machines,
9107 you need a different @code{gdb} compiled for each combination of
9108 host and target. @code{configure} is designed to make this easy by
9109 allowing you to generate each configuration in a separate subdirectory,
9110 rather than in the source directory. If your @code{make} program
9111 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
9112 @code{make} in each of these directories builds the @code{gdb}
9113 program specified there.
9115 To build @code{gdb} in a separate directory, run @code{configure}
9116 with the @samp{--srcdir} option to specify where to find the source.
9117 (You also need to specify a path to find @code{configure}
9118 itself from your working directory. If the path to @code{configure}
9119 would be the same as the argument to @samp{--srcdir}, you can leave out
9120 the @samp{--srcdir} option; it is assumed.)
9122 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
9123 separate directory for a Sun 4 like this:
9127 cd gdb-@value{GDBVN}
9130 ../gdb-@value{GDBVN}/configure sun4
9135 When @code{configure} builds a configuration using a remote source
9136 directory, it creates a tree for the binaries with the same structure
9137 (and using the same names) as the tree under the source directory. In
9138 the example, you'd find the Sun 4 library @file{libiberty.a} in the
9139 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
9140 @file{gdb-sun4/gdb}.
9142 One popular reason to build several @value{GDBN} configurations in separate
9143 directories is to configure @value{GDBN} for cross-compiling (where
9144 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
9145 programs that run on another machine---the @dfn{target}).
9146 You specify a cross-debugging target by
9147 giving the @samp{--target=@var{target}} option to @code{configure}.
9149 When you run @code{make} to build a program or library, you must run
9150 it in a configured directory---whatever directory you were in when you
9151 called @code{configure} (or one of its subdirectories).
9153 The @code{Makefile} that @code{configure} generates in each source
9154 directory also runs recursively. If you type @code{make} in a source
9155 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
9156 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
9157 will build all the required libraries, and then build GDB.
9159 When you have multiple hosts or targets configured in separate
9160 directories, you can run @code{make} on them in parallel (for example,
9161 if they are NFS-mounted on each of the hosts); they will not interfere
9165 @section Specifying names for hosts and targets
9167 The specifications used for hosts and targets in the @code{configure}
9168 script are based on a three-part naming scheme, but some short predefined
9169 aliases are also supported. The full naming scheme encodes three pieces
9170 of information in the following pattern:
9173 @var{architecture}-@var{vendor}-@var{os}
9176 For example, you can use the alias @code{sun4} as a @var{host} argument,
9177 or as the value for @var{target} in a @code{--target=@var{target}}
9178 option. The equivalent full name is @samp{sparc-sun-sunos4}.
9180 The @code{configure} script accompanying @value{GDBN} does not provide
9181 any query facility to list all supported host and target names or
9182 aliases. @code{configure} calls the Bourne shell script
9183 @code{config.sub} to map abbreviations to full names; you can read the
9184 script, if you wish, or you can use it to test your guesses on
9185 abbreviations---for example:
9188 % sh config.sub sun4
9189 sparc-sun-sunos4.1.1
9190 % sh config.sub sun3
9192 % sh config.sub decstation
9194 % sh config.sub hp300bsd
9196 % sh config.sub i386v
9198 % sh config.sub i786v
9199 Invalid configuration `i786v': machine `i786v' not recognized
9203 @code{config.sub} is also distributed in the @value{GDBN} source
9204 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
9206 @node configure Options
9207 @section @code{configure} options
9209 Here is a summary of the @code{configure} options and arguments that
9210 are most often useful for building @value{GDBN}. @code{configure} also has
9211 several other options not listed here. @inforef{What Configure
9212 Does,,configure.info}, for a full explanation of @code{configure}.
9215 configure @r{[}--help@r{]}
9216 @r{[}--prefix=@var{dir}@r{]}
9217 @r{[}--srcdir=@var{dirname}@r{]}
9218 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
9219 @r{[}--target=@var{target}@r{]} @var{host}
9223 You may introduce options with a single @samp{-} rather than
9224 @samp{--} if you prefer; but you may abbreviate option names if you use
9229 Display a quick summary of how to invoke @code{configure}.
9231 @item -prefix=@var{dir}
9232 Configure the source to install programs and files under directory
9235 @c avoid splitting the warning from the explanation:
9237 @item --srcdir=@var{dirname}
9238 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
9239 @code{make} that implements the @code{VPATH} feature.}@*
9240 Use this option to make configurations in directories separate from the
9241 @value{GDBN} source directories. Among other things, you can use this to
9242 build (or maintain) several configurations simultaneously, in separate
9243 directories. @code{configure} writes configuration specific files in
9244 the current directory, but arranges for them to use the source in the
9245 directory @var{dirname}. @code{configure} creates directories under
9246 the working directory in parallel to the source directories below
9250 Configure only the directory level where @code{configure} is executed; do not
9251 propagate configuration to subdirectories.
9254 @emph{Remove} files otherwise built during configuration.
9256 @c This does not work (yet if ever). FIXME.
9257 @c @item --parse=@var{lang} @dots{}
9258 @c Configure the @value{GDBN} expression parser to parse the listed languages.
9259 @c @samp{all} configures @value{GDBN} for all supported languages. To get a
9260 @c list of all supported languages, omit the argument. Without this
9261 @c option, @value{GDBN} is configured to parse all supported languages.
9263 @item --target=@var{target}
9264 Configure @value{GDBN} for cross-debugging programs running on the specified
9265 @var{target}. Without this option, @value{GDBN} is configured to debug
9266 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
9268 There is no convenient way to generate a list of all available targets.
9270 @item @var{host} @dots{}
9271 Configure @value{GDBN} to run on the specified @var{host}.
9273 There is no convenient way to generate a list of all available hosts.
9277 @code{configure} accepts other options, for compatibility with
9278 configuring other @sc{gnu} tools recursively; but these are the only
9279 options that affect @value{GDBN} or its supporting libraries.
9288 % I think something like @colophon should be in texinfo. In the
9290 \long\def\colophon{\hbox to0pt{}\vfill
9291 \centerline{The body of this manual is set in}
9292 \centerline{\fontname\tenrm,}
9293 \centerline{with headings in {\bf\fontname\tenbf}}
9294 \centerline{and examples in {\tt\fontname\tentt}.}
9295 \centerline{{\it\fontname\tenit\/},}
9296 \centerline{{\bf\fontname\tenbf}, and}
9297 \centerline{{\sl\fontname\tensl\/}}
9298 \centerline{are used for emphasis.}\vfill}
9300 % Blame: doc@cygnus.com, 1991.