1 \input texinfo @c -*-texinfo-*-
2 @c Copyright (c) 1988 1989 1990 1991 1992 1993 Free Software Foundation, Inc.
5 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
6 @c of @set vars. However, you can override filename with makeinfo -o.
9 @include gdb-config.texi
12 @settitle Debugging with @value{GDBN}
15 @settitle Debugging with @value{GDBN} (@value{TARGET})
17 @setchapternewpage odd
25 @c Include the readline documentation in the TeX output,
26 @c but not in the Info output.
27 @c Eventually, we should make a cross reference to the Readline Info
28 @c nodes; but this requires that the nodes exist and be in an expected
29 @c place. Wait for a standard, complete GNU distribution. Meanwhile,
30 @c cross references are only in the printed TeX output, and only when
31 @c `have-readline-appendices' is set.
33 @c The readline documentation is distributed with the readline code
34 @c and consists of the two following files:
38 @set have-readline-appendices
41 @clear have-readline-appendices
47 @c readline appendices use @vindex
51 @c Determine the edition number in *three* places by hand:
52 @c 1. First ifinfo section 2. title page 3. top node
53 @c To find the locations, search for !!set
55 @c GDB CHANGELOG CONSULTED BETWEEN:
56 @c Fri Oct 11 23:27:06 1991 John Gilmore (gnu at cygnus.com)
57 @c Sat Dec 22 02:51:40 1990 John Gilmore (gnu at cygint)
59 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
62 @c This is a dir.info fragment to support semi-automated addition of
63 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
66 * Gdb: (gdb). The GNU debugger.
73 This file documents the GNU debugger @value{GDBN}.
75 @c !!set edition, date, version
76 This is Edition 4.07, January 1993,
77 of @cite{Debugging with @value{GDBN}: the GNU Source-Level Debugger}
78 for GDB Version @value{GDBVN}.
80 Copyright (C) 1988, 1989, 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
82 Permission is granted to make and distribute verbatim copies of
83 this manual provided the copyright notice and this permission notice
84 are preserved on all copies.
87 Permission is granted to process this file through TeX and print the
88 results, provided the printed document carries copying permission
89 notice identical to this one except for the removal of this paragraph
90 (this paragraph not being relevant to the printed manual).
93 Permission is granted to copy and distribute modified versions of this
94 manual under the conditions for verbatim copying, provided also that the
95 section entitled ``GNU General Public License'' is included exactly as
96 in the original, and provided that the entire resulting derived work is
97 distributed under the terms of a permission notice identical to this
100 Permission is granted to copy and distribute translations of this manual
101 into another language, under the above conditions for modified versions,
102 except that the section entitled ``GNU General Public License'' may be
103 included in a translation approved by the Free Software Foundation
104 instead of in the original English.
108 @title Debugging with @value{GDBN}
109 @subtitle The GNU Source-Level Debugger
111 @subtitle on @value{TARGET} Systems
114 @c !!set edition, date, version
115 @subtitle Edition 4.07, for @value{GDBN} version @value{GDBVN}
116 @subtitle January 1993
117 @author by Richard M. Stallman and Roland H. Pesch
121 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@prep.ai.mit.edu.)\par
122 \hfill {\it Debugging with @value{GDBN}}\par
123 \hfill \TeX{}info \texinfoversion\par
124 \hfill pesch\@cygnus.com\par
128 @vskip 0pt plus 1filll
129 Copyright @copyright{} 1988, 1989, 1990, 1991, 1992, 1993 Free Software Foundation, Inc.
131 Permission is granted to make and distribute verbatim copies of
132 this manual provided the copyright notice and this permission notice
133 are preserved on all copies.
135 Permission is granted to copy and distribute modified versions of this
136 manual under the conditions for verbatim copying, provided also that the
137 section entitled ``GNU General Public License'' is included exactly as
138 in the original, and provided that the entire resulting derived work is
139 distributed under the terms of a permission notice identical to this
142 Permission is granted to copy and distribute translations of this manual
143 into another language, under the above conditions for modified versions,
144 except that the section entitled ``GNU General Public License'' may be
145 included in a translation approved by the Free Software Foundation
146 instead of in the original English.
152 @top Debugging with @value{GDBN}
154 This file describes @value{GDBN}, the GNU symbolic debugger.
156 @c !!set edition, date, version
157 This is Edition 4.07, January 1993, for GDB Version @value{GDBVN}.
160 * Summary:: Summary of @value{GDBN}
162 * New Features:: New features since GDB version 3.5
165 * Sample Session:: A sample @value{GDBN} session
168 * Invocation:: Getting in and out of @value{GDBN}
169 * Commands:: @value{GDBN} commands
170 * Running:: Running programs under @value{GDBN}
171 * Stopping:: Stopping and continuing
172 * Stack:: Examining the stack
173 * Source:: Examining source files
174 * Data:: Examining data
176 * Languages:: Using @value{GDBN} with different languages
179 * C:: C language support
181 @c remnant makeinfo bug, blank line needed after two end-ifs?
183 * Symbols:: Examining the symbol table
184 * Altering:: Altering execution
185 * GDB Files:: @value{GDBN} files
186 * Targets:: Specifying a debugging target
187 * Controlling GDB:: Controlling @value{GDBN}
188 * Sequences:: Canned sequences of commands
190 * Emacs:: Using @value{GDBN} under GNU Emacs
193 * GDB Bugs:: Reporting bugs in @value{GDBN}
197 @ifclear PRECONFIGURED
198 * Formatting Documentation:: How to format and print GDB documentation
199 * Installing GDB:: Installing GDB
201 @ifclear AGGLOMERATION
202 * Copying:: GNU GENERAL PUBLIC LICENSE
210 @unnumbered Summary of @value{GDBN}
212 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
213 going on ``inside'' another program while it executes---or what another
214 program was doing at the moment it crashed.
216 @value{GDBN} can do four main kinds of things (plus other things in support of
217 these) to help you catch bugs in the act:
221 Start your program, specifying anything that might affect its behavior.
224 Make your program stop on specified conditions.
227 Examine what has happened, when your program has stopped.
230 Change things in your program, so you can experiment with correcting the
231 effects of one bug and go on to learn about another.
235 You can use @value{GDBN} to debug programs written in C, C++, and Modula-2.
236 Fortran support will be added when a GNU Fortran compiler is ready.
240 * Free Software:: Freely redistributable software
241 * Contributors:: Contributors to GDB
245 @unnumberedsec Free software
247 @value{GDBN} is @dfn{free software}, protected by the GNU 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
259 @ifclear AGGLOMERATION
260 For full details, @pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}.
264 @unnumberedsec Contributors to GDB
266 Richard Stallman was the original author of GDB, and of many other GNU
267 programs. Many others have contributed to its development. This
268 section attempts to credit major contributors. One of the virtues of
269 free software is that everyone is free to contribute to it; with
270 regret, we cannot actually acknowledge everyone here. The file
271 @file{ChangeLog} in the GDB distribution approximates a blow-by-blow
274 Changes much prior to version 2.0 are lost in the mists of time.
277 @emph{Plea:} Additions to this section are particularly welcome. If you
278 or your friends (or enemies, to be evenhanded) have been unfairly
279 omitted from this list, we would like to add your names!
282 So that they may not regard their long labor as thankless, we
283 particularly thank those who shepherded GDB through major releases: Stu
284 Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, 4.4), John Gilmore
285 (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4,
286 3.3); and Randy Smith (releases 3.2, 3.1, 3.0). As major maintainer of
287 GDB for some period, each contributed significantly to the structure,
288 stability, and capabilities of the entire debugger.
290 Richard Stallman, assisted at various times by Pete TerMaat, Chris
291 Hanson, and Richard Mlynarik, handled releases through 2.8.
294 Michael Tiemann is the author of most of the GNU C++ support in GDB,
295 with significant additional contributions from Per Bothner. James
296 Clark wrote the 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 GDB 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
309 support. Jean-Daniel Fekete contributed Sun 386i support. Chris
310 Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki
311 Hasei contributed Sony/News OS 3 support. David Johnson contributed
312 Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support.
313 Keith Packard contributed NS32K support. Doug Rabson contributed
314 Acorn Risc Machine support. Chris Smith contributed Convex support
315 (and Fortran debugging). Jonathan Stone contributed Pyramid support.
316 Michael Tiemann contributed SPARC support. Tim Tucker contributed
317 support for the Gould NP1 and Gould Powernode. Pace Willison
318 contributed Intel 386 support. Jay Vosburgh contributed Symmetry
321 Rich Schaefer and Peter Schauer helped with support of SunOS shared
324 Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
325 several machine instruction sets.
327 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
328 develop remote debugging. Intel Corporation and Wind River Systems
329 contributed remote debugging modules for their products.
331 Brian Fox is the author of the readline libraries providing
332 command-line editing and command history.
334 Andrew Beers of SUNY Buffalo wrote the language-switching code and
335 the Modula-2 support, and contributed the Languages chapter of this
338 Fred Fish wrote most of the support for Unix System Vr4.
340 He also enhanced the command-completion support to cover C++ overloaded
344 Hitachi America, Ltd. sponsored the support for the H8/300 and H8/500.
348 @unnumbered New Features since GDB Version 3.5
352 Using the new command @code{target}, you can select at runtime whether
353 you are debugging local files, local processes, standalone systems over
354 a serial port, realtime systems over a TCP/IP connection, etc. The
355 command @code{load} can download programs into a remote system. Serial
356 stubs are available for Motorola 680x0, Intel 80386, and Sparc remote
357 systems; GDB also supports debugging realtime processes running under
358 VxWorks, using SunRPC Remote Procedure Calls over TCP/IP to talk to a
359 debugger stub on the target system. Internally, GDB now uses a function
360 vector to mediate access to different targets; if you need to add your
361 own support for a remote protocol, this makes it much easier.
364 GDB now sports watchpoints as well as breakpoints. You can use a
365 watchpoint to stop execution whenever the value of an expression
366 changes, without having to predict a particular place in your program
367 where this may happen.
370 Commands that issue wide output now insert newlines at places designed
371 to make the output more readable.
373 @item Object Code Formats
374 GDB uses a new library called the Binary File Descriptor (BFD)
375 Library to permit it to switch dynamically, without reconfiguration or
376 recompilation, between different object-file formats. Formats currently
377 supported are COFF, a.out, and the Intel 960 b.out; files may be read as
378 .o files, archive libraries, or core dumps. BFD is available as a
379 subroutine library so that other programs may take advantage of it, and
380 the other GNU binary utilities are being converted to use it.
382 @item Configuration and Ports
383 Compile-time configuration (to select a particular architecture and
384 operating system) is much easier. The script @code{configure} now
385 allows you to configure GDB as either a native debugger or a
386 cross-debugger. @xref{Installing GDB}, for details on how to
390 The user interface to the GDB control variables is simpler,
391 and is consolidated in two commands, @code{set} and @code{show}. Output
392 lines are now broken at readable places, rather than overflowing onto
393 the next line. You can suppress output of machine-level addresses,
394 displaying only source language information.
397 GDB now supports C++ multiple inheritance (if used with a GCC
398 version 2 compiler), and also has limited support for C++ exception
399 handling, with the commands @code{catch} and @code{info catch}: GDB
400 can break when an exception is raised, before the stack is peeled back
401 to the exception handler's context.
404 GDB now has preliminary support for the GNU Modula-2 compiler, currently
405 under development at the State University of New York at Buffalo.
406 Coordinated development of both GDB and the GNU Modula-2 compiler will
407 continue. Other Modula-2 compilers are currently not supported, and
408 attempting to debug programs compiled with them will likely result in an
409 error as the symbol table of the executable is read in.
411 @item Command Rationalization
412 Many GDB commands have been renamed to make them easier to remember
413 and use. In particular, the subcommands of @code{info} and
414 @code{show}/@code{set} are grouped to make the former refer to the state
415 of your program, and the latter refer to the state of GDB itself.
416 @xref{Renamed Commands}, for details on what commands were renamed.
418 @item Shared Libraries
419 GDB 4 can debug programs and core files that use SunOS, SVR4, or IBM RS/6000
423 GDB 4 has a reference card. @xref{Formatting Documentation,,Formatting
424 the Documentation}, for instructions about how to print it.
426 @item Work in Progress
427 Kernel debugging for BSD and Mach systems; Tahoe and HPPA architecture
434 @chapter A Sample @value{GDBN} Session
436 You can use this manual at your leisure to read all about @value{GDBN}.
437 However, a handful of commands are enough to get started using the
438 debugger. This chapter illustrates those commands.
441 In this sample session, we emphasize user input like this: @b{input},
442 to make it easier to pick out from the surrounding output.
445 @c FIXME: this example may not be appropriate for some configs, where
446 @c FIXME...primary interest is in remote use.
448 One of the preliminary versions of GNU @code{m4} (a generic macro
449 processor) exhibits the following bug: sometimes, when we change its
450 quote strings from the default, the commands used to capture one macro
451 definition within another stop working. In the following short @code{m4}
452 session, we define a macro @code{foo} which expands to @code{0000}; we
453 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
454 same thing. However, when we change the open quote string to
455 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
456 procedure fails to define a new synonym @code{baz}:
465 @b{define(bar,defn(`foo'))}
469 @b{changequote(<QUOTE>,<UNQUOTE>)}
471 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
474 m4: End of input: 0: fatal error: EOF in string
478 Let us use @value{GDBN} to try to see what is going on.
481 $ @b{@value{GDBP} m4}
482 @c FIXME: this falsifies the exact text played out, to permit smallbook
483 @c FIXME... format to come out better.
484 GDB is free software and you are welcome to distribute copies
485 of it under certain conditions; type "show copying" to see
487 There is absolutely no warranty for GDB; type "show warranty"
489 GDB @value{GDBVN}, Copyright 1993 Free Software Foundation, Inc...
494 @value{GDBN} reads only enough symbol data to know where to find the rest when
495 needed; as a result, the first prompt comes up very quickly. We now
496 tell @value{GDBN} to use a narrower display width than usual, so that examples
497 will fit in this manual.
500 (@value{GDBP}) @b{set width 70}
504 We need to see how the @code{m4} built-in @code{changequote} works.
505 Having looked at the source, we know the relevant subroutine is
506 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
507 @code{break} command.
510 (@value{GDBP}) @b{break m4_changequote}
511 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
515 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
516 control; as long as control does not reach the @code{m4_changequote}
517 subroutine, the program runs as usual:
520 (@value{GDBP}) @b{run}
521 Starting program: /work/Editorial/gdb/gnu/m4/m4
529 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
530 suspends execution of @code{m4}, displaying information about the
531 context where it stops.
534 @b{changequote(<QUOTE>,<UNQUOTE>)}
536 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
538 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
542 Now we use the command @code{n} (@code{next}) to advance execution to
543 the next line of the current function.
547 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
552 @code{set_quotes} looks like a promising subroutine. We can go into it
553 by using the command @code{s} (@code{step}) instead of @code{next}.
554 @code{step} goes to the next line to be executed in @emph{any}
555 subroutine, so it steps into @code{set_quotes}.
559 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
561 530 if (lquote != def_lquote)
565 The display that shows the subroutine where @code{m4} is now
566 suspended (and its arguments) is called a stack frame display. It
567 shows a summary of the stack. We can use the @code{backtrace}
568 command (which can also be spelled @code{bt}), to see where we are
569 in the stack as a whole: the @code{backtrace} command displays a
570 stack frame for each active subroutine.
573 (@value{GDBP}) @b{bt}
574 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
576 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
578 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
579 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
581 #4 0x79dc in expand_input () at macro.c:40
582 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
586 We will step through a few more lines to see what happens. The first two
587 times, we can use @samp{s}; the next two times we use @code{n} to avoid
588 falling into the @code{xstrdup} subroutine.
592 0x3b5c 532 if (rquote != def_rquote)
594 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
595 def_lquote : xstrdup(lq);
597 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
600 538 len_lquote = strlen(rquote);
604 The last line displayed looks a little odd; we can examine the variables
605 @code{lquote} and @code{rquote} to see if they are in fact the new left
606 and right quotes we specified. We use the command @code{p}
607 (@code{print}) to see their values.
610 (@value{GDBP}) @b{p lquote}
611 $1 = 0x35d40 "<QUOTE>"
612 (@value{GDBP}) @b{p rquote}
613 $2 = 0x35d50 "<UNQUOTE>"
617 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
618 To look at some context, we can display ten lines of source
619 surrounding the current line with the @code{l} (@code{list}) command.
625 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
627 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
630 538 len_lquote = strlen(rquote);
631 539 len_rquote = strlen(lquote);
638 Let us step past the two lines that set @code{len_lquote} and
639 @code{len_rquote}, and then examine the values of those variables.
643 539 len_rquote = strlen(lquote);
646 (@value{GDBP}) @b{p len_lquote}
648 (@value{GDBP}) @b{p len_rquote}
653 That certainly looks wrong, assuming @code{len_lquote} and
654 @code{len_rquote} are meant to be the lengths of @code{lquote} and
655 @code{rquote} respectively. We can set them to better values using
656 the @code{p} command, since it can print the value of
657 any expression---and that expression can include subroutine calls and
661 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
663 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
668 Is that enough to fix the problem of using the new quotes with the
669 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
670 executing with the @code{c} (@code{continue}) command, and then try the
671 example that caused trouble initially:
677 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
684 Success! The new quotes now work just as well as the default ones. The
685 problem seems to have been just the two typos defining the wrong
686 lengths. We allow @code{m4} exit by giving it an EOF as input:
690 Program exited normally.
694 The message @samp{Program exited normally.} is from @value{GDBN}; it
695 indicates @code{m4} has finished executing. We can end our @value{GDBN}
696 session with the @value{GDBN} @code{quit} command.
699 (@value{GDBP}) @b{quit}
704 @chapter Getting In and Out of @value{GDBN}
706 This chapter discusses how to start @value{GDBN}, and how to get out of it.
707 (The essentials: type @samp{@value{GDBP}} to start GDB, and type @kbd{quit}
708 or @kbd{C-d} to exit.)
711 * Invoking GDB:: How to start @value{GDBN}
712 * Quitting GDB:: How to quit @value{GDBN}
714 * Shell Commands:: How to use shell commands inside @value{GDBN}
719 @section Invoking @value{GDBN}
721 @ifset HviiiEXCLUSIVE
722 For details on starting up @value{GDBP} as a
723 remote debugger attached to a Hitachi H8/300 or H8/500 board, see @ref{Hitachi
724 H8 Remote,,@value{GDBN} and the Hitachi H8/300 and H8/500}.
727 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
728 @value{GDBN} reads commands from the terminal until you tell it to exit.
730 You can also run @code{@value{GDBP}} with a variety of arguments and options,
731 to specify more of your debugging environment at the outset.
734 The command-line options described here are designed
735 to cover a variety of situations; in some environments, some of these
736 options may effectively be unavailable.
739 The most usual way to start @value{GDBN} is with one argument,
740 specifying an executable program:
743 @value{GDBP} @var{program}
748 You can also start with both an executable program and a core file
752 @value{GDBP} @var{program} @var{core}
755 You can, instead, specify a process ID as a second argument, if you want
756 to debug a running process:
759 @value{GDBP} @var{program} 1234
763 would attach @value{GDBN} to process @code{1234} (unless you also have a file
764 named @file{1234}; @value{GDBN} does check for a core file first).
766 Taking advantage of the second command-line argument requires a fairly
767 complete operating system; when you use @value{GDBN} as a remote debugger
768 attached to a bare board, there may not be any notion of ``process'',
769 and there is often no way to get a core dump.
773 You can further control how @value{GDBN} starts up by using command-line
774 options. @value{GDBN} itself can remind you of the options available.
784 to display all available options and briefly describe their use
785 (@samp{@value{GDBP} -h} is a shorter equivalent).
787 All options and command line arguments you give are processed
788 in sequential order. The order makes a difference when the
789 @samp{-x} option is used.
795 * Remote Serial:: @value{GDBN} remote serial protocol
798 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
801 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
802 * EB29K Remote:: @value{GDBN} with a remote EB29K
805 * VxWorks Remote:: @value{GDBN} and VxWorks
808 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
811 * Hitachi H8 Remote:: @value{GDBN} and the Hitachi H8/300 and H8/500
814 * Simulator:: Simulated CPU target
817 @c remnant makeinfo bug requires this blank line after *two* end-ifblahs:
819 * File Options:: Choosing files
820 * Mode Options:: Choosing modes
824 @include gdbinv-s.texi
828 @subsection Choosing files
831 When @value{GDBN} starts, it reads any arguments other than options as
832 specifying an executable file and core file (or process ID). This is
833 the same as if the arguments were specified by the @samp{-se} and
834 @samp{-c} options respectively. (@value{GDBN} reads the first argument
835 that does not have an associated option flag as equivalent to the
836 @samp{-se} option followed by that argument; and the second argument
837 that does not have an associated option flag, if any, as equivalent to
838 the @samp{-c} option followed by that argument.)
841 When @value{GDBN} starts, it reads any argument other than options as
842 specifying an executable file. This is the same as if the argument was
843 specified by the @samp{-se} option.
846 Many options have both long and short forms; both are shown in the
847 following list. @value{GDBN} also recognizes the long forms if you truncate
848 them, so long as enough of the option is present to be unambiguous.
849 (If you prefer, you can flag option arguments with @samp{--} rather
850 than @samp{-}, though we illustrate the more usual convention.)
853 @item -symbols=@var{file}
855 Read symbol table from file @var{file}.
857 @item -exec=@var{file}
859 Use file @var{file} as the executable file to execute when
864 appropriate, and for examining pure data in conjunction with a core
869 Read symbol table from file @var{file} and use it as the executable
873 @item -core=@var{file}
875 Use file @var{file} as a core dump to examine.
878 @item -command=@var{file}
880 Execute @value{GDBN} commands from file @var{file}. @xref{Command
881 Files,, Command files}.
883 @item -directory=@var{directory}
884 @itemx -d @var{directory}
885 Add @var{directory} to the path to search for source files.
890 @emph{Warning: this option depends on operating system facilities that are not
891 supported on all systems.}@*
892 If memory-mapped files are available on your system through the @code{mmap}
893 system call, you can use this option
894 to have @value{GDBN} write the symbols from your
895 program into a reusable file in the current directory. If the program you are debugging is
896 called @file{/tmp/fred}, the mapped symbol file will be @file{./fred.syms}.
897 Future @value{GDBN} debugging sessions will notice the presence of this file,
898 and will quickly map in symbol information from it, rather than reading
899 the symbol table from the executable program.
901 @c FIXME! Really host, not target?
902 The @file{.syms} file is specific to the host machine where @value{GDBN}
903 is run. It holds an exact image of the internal @value{GDBN} symbol
904 table. It cannot be shared across multiple host platforms.
909 Read each symbol file's entire symbol table immediately, rather than
910 the default, which is to read it incrementally as it is needed.
911 This makes startup slower, but makes future operations faster.
915 The @code{-mapped} and @code{-readnow} options are typically combined in
916 order to build a @file{.syms} file that contains complete symbol
917 information. (@xref{Files,,Commands to specify files}, for information
918 on @file{.syms} files.) A simple GDB invocation to do nothing but build
919 a @file{.syms} file for future use is:
922 gdb -batch -nx -mapped -readnow programname
927 @subsection Choosing modes
929 You can run @value{GDBN} in various alternative modes---for example, in
930 batch mode or quiet mode.
935 Do not execute commands from any @file{@value{GDBINIT}} initialization files.
936 Normally, the commands in these files are executed after all the
937 command options and arguments have been processed.
938 @xref{Command Files,,Command files}.
942 ``Quiet''. Do not print the introductory and copyright messages. These
943 messages are also suppressed in batch mode.
946 Run in batch mode. Exit with status @code{0} after processing all the command
947 files specified with @samp{-x} (and @file{@value{GDBINIT}}, if not inhibited).
948 Exit with nonzero status if an error occurs in executing the @value{GDBN}
949 commands in the command files.
951 Batch mode may be useful for running @value{GDBN} as a filter, for example to
952 download and run a program on another computer; in order to make this
953 more useful, the message
956 Program exited normally.
960 (which is ordinarily issued whenever a program running under @value{GDBN} control
961 terminates) is not issued when running in batch mode.
963 @item -cd=@var{directory}
964 Run @value{GDBN} using @var{directory} as its working directory,
965 instead of the current directory.
968 @item -context @var{authentication}
969 When the Energize programming system starts up @value{GDBN}, it uses this
970 option to trigger an alternate mode of interaction.
971 @var{authentication} is a pair of numeric codes that identify @value{GDBN}
972 as a client in the Energize environment. Avoid this option when you run
973 @value{GDBN} directly from the command line. See @ref{Energize,,Using
974 @value{GDBN} with Energize} for more discussion of using @value{GDBN} with Energize.
980 Emacs sets this option when it runs @value{GDBN} as a subprocess. It tells @value{GDBN}
981 to output the full file name and line number in a standard,
982 recognizable fashion each time a stack frame is displayed (which
983 includes each time your program stops). This recognizable format looks
984 like two @samp{\032} characters, followed by the file name, line number
985 and character position separated by colons, and a newline. The
986 Emacs-to-@value{GDBN} interface program uses the two @samp{\032} characters as
987 a signal to display the source code for the frame.
992 Set the line speed (baud rate or bits per second) of any serial
993 interface used by @value{GDBN} for remote debugging.
995 @item -tty=@var{device}
996 Run using @var{device} for your program's standard input and output.
997 @c FIXME: kingdon thinks there is more to -tty. Investigate.
1002 @section Quitting @value{GDBN}
1003 @cindex exiting @value{GDBN}
1004 @cindex leaving @value{GDBN}
1010 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or type
1011 an end-of-file character (usually @kbd{C-d}).
1015 An interrupt (often @kbd{C-c}) will not exit from @value{GDBN}, but rather
1016 will terminate the action of any @value{GDBN} command that is in progress and
1017 return to @value{GDBN} command level. It is safe to type the interrupt
1018 character at any time because @value{GDBN} does not allow it to take effect
1019 until a time when it is safe.
1022 If you have been using @value{GDBN} to control an attached process or
1023 device, you can release it with the @code{detach} command
1024 (@pxref{Attach, ,Debugging an already-running process}).
1028 @node Shell Commands
1029 @section Shell commands
1031 If you need to execute occasional shell commands during your
1032 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1033 just use the @code{shell} command.
1036 @item shell @var{command string}
1038 @cindex shell escape
1039 Directs @value{GDBN} to invoke an inferior shell to execute @var{command
1040 string}. If it exists, the environment variable @code{SHELL} is used
1041 for the name of the shell to run. Otherwise @value{GDBN} uses
1045 The utility @code{make} is often needed in development environments.
1046 You do not have to use the @code{shell} command for this purpose in @value{GDBN}:
1049 @item make @var{make-args}
1051 @cindex calling make
1052 Causes @value{GDBN} to execute an inferior @code{make} program with the specified
1053 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1058 @chapter @value{GDBN} Commands
1060 You can abbreviate a @value{GDBN} command to the first few letters of the command
1061 name, if that abbreviation is unambiguous; and you can repeat certain
1062 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1063 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1064 show you the alternatives available, if there is more than one possibility).
1067 * Command Syntax:: How to give commands to @value{GDBN}
1068 * Completion:: Command completion
1069 * Help:: How to ask @value{GDBN} for help
1072 @node Command Syntax
1073 @section Command syntax
1075 A @value{GDBN} command is a single line of input. There is no limit on
1076 how long it can be. It starts with a command name, which is followed by
1077 arguments whose meaning depends on the command name. For example, the
1078 command @code{step} accepts an argument which is the number of times to
1079 step, as in @samp{step 5}. You can also use the @code{step} command
1080 with no arguments. Some command names do not allow any arguments.
1082 @cindex abbreviation
1083 @value{GDBN} command names may always be truncated if that abbreviation is
1084 unambiguous. Other possible command abbreviations are listed in the
1085 documentation for individual commands. In some cases, even ambiguous
1086 abbreviations are allowed; for example, @code{s} is specially defined as
1087 equivalent to @code{step} even though there are other commands whose
1088 names start with @code{s}. You can test abbreviations by using them as
1089 arguments to the @code{help} command.
1091 @cindex repeating commands
1093 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1094 repeat the previous command. Certain commands (for example, @code{run})
1095 will not repeat this way; these are commands for which unintentional
1096 repetition might cause trouble and which you are unlikely to want to
1099 The @code{list} and @code{x} commands, when you repeat them with
1100 @key{RET}, construct new arguments rather than repeating
1101 exactly as typed. This permits easy scanning of source or memory.
1103 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1104 output, in a way similar to the common utility @code{more}
1105 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1106 @key{RET} too many in this situation, @value{GDBN} disables command
1107 repetition after any command that generates this sort of display.
1111 Any text from a @kbd{#} to the end of the line is a comment; it does
1112 nothing. This is useful mainly in command files (@pxref{Command
1113 Files,,Command files}).
1116 @section Command completion
1119 @cindex word completion
1120 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1121 only one possibility; it can also show you what the valid possibilities
1122 are for the next word in a command, at any time. This works for @value{GDBN}
1123 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1125 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1126 of a word. If there is only one possibility, @value{GDBN} will fill in the
1127 word, and wait for you to finish the command (or press @key{RET} to
1128 enter it). For example, if you type
1130 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1131 @c complete accuracy in these examples; space introduced for clarity.
1132 @c If texinfo enhancements make it unnecessary, it would be nice to
1133 @c replace " @key" by "@key" in the following...
1135 (@value{GDBP}) info bre @key{TAB}
1139 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1140 the only @code{info} subcommand beginning with @samp{bre}:
1143 (@value{GDBP}) info breakpoints
1147 You can either press @key{RET} at this point, to run the @code{info
1148 breakpoints} command, or backspace and enter something else, if
1149 @samp{breakpoints} does not look like the command you expected. (If you
1150 were sure you wanted @code{info breakpoints} in the first place, you
1151 might as well just type @key{RET} immediately after @samp{info bre},
1152 to exploit command abbreviations rather than command completion).
1154 If there is more than one possibility for the next word when you press
1155 @key{TAB}, @value{GDBN} will sound a bell. You can either supply more
1156 characters and try again, or just press @key{TAB} a second time, and
1157 @value{GDBN} will display all the possible completions for that word. For
1158 example, you might want to set a breakpoint on a subroutine whose name
1159 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1160 just sounds the bell. Typing @key{TAB} again will display all the
1161 function names in your program that begin with those characters, for
1165 (@value{GDBP}) b make_ @key{TAB}
1166 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1167 make_a_section_from_file make_environ
1168 make_abs_section make_function_type
1169 make_blockvector make_pointer_type
1170 make_cleanup make_reference_type
1171 make_command make_symbol_completion_list
1172 (@value{GDBP}) b make_
1176 After displaying the available possibilities, @value{GDBN} copies your
1177 partial input (@samp{b make_} in the example) so you can finish the
1180 If you just want to see the list of alternatives in the first place, you
1181 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1182 means @kbd{@key{META} ?}. You can type this
1184 either by holding down a
1185 key designated as the @key{META} shift on your keyboard (if there is
1186 one) while typing @kbd{?}, or
1188 as @key{ESC} followed by @kbd{?}.
1190 @cindex quotes in commands
1191 @cindex completion of quoted strings
1192 Sometimes the string you need, while logically a ``word'', may contain
1193 parentheses or other characters that @value{GDBN} normally excludes from its
1194 notion of a word. To permit word completion to work in this situation,
1195 you may enclose words in @code{'} (single quote marks) in @value{GDBN} commands.
1198 The most likely situation where you might need this is in typing the
1199 name of a C++ function. This is because C++ allows function overloading
1200 (multiple definitions of the same function, distinguished by argument
1201 type). For example, when you want to set a breakpoint you may need to
1202 distinguish whether you mean the version of @code{name} that takes an
1203 @code{int} parameter, @code{name(int)}, or the version that takes a
1204 @code{float} parameter, @code{name(float)}. To use the word-completion
1205 facilities in this situation, type a single quote @code{'} at the
1206 beginning of the function name. This alerts @value{GDBN} that it may need to
1207 consider more information than usual when you press @key{TAB} or
1208 @kbd{M-?} to request word completion:
1211 (@value{GDBP}) b 'bubble( @key{M-?}
1212 bubble(double,double) bubble(int,int)
1213 (@value{GDBP}) b 'bubble(
1216 In some cases, @value{GDBN} can tell that completing a name will require
1217 quotes. When this happens, @value{GDBN} will insert the quote for you (while
1218 completing as much as it can) if you do not type the quote in the first
1222 (@value{GDBP}) b bub @key{TAB}
1223 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1224 (@value{GDBP}) b 'bubble(
1228 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1229 you have not yet started typing the argument list when you ask for
1230 completion on an overloaded symbol.
1235 @section Getting help
1236 @cindex online documentation
1239 You can always ask @value{GDBN} itself for information on its commands, using the
1240 command @code{help}.
1246 You can use @code{help} (abbreviated @code{h}) with no arguments to
1247 display a short list of named classes of commands:
1251 List of classes of commands:
1253 running -- Running the program
1254 stack -- Examining the stack
1255 data -- Examining data
1256 breakpoints -- Making program stop at certain points
1257 files -- Specifying and examining files
1258 status -- Status inquiries
1259 support -- Support facilities
1260 user-defined -- User-defined commands
1261 aliases -- Aliases of other commands
1262 obscure -- Obscure features
1264 Type "help" followed by a class name for a list of
1265 commands in that class.
1266 Type "help" followed by command name for full
1268 Command name abbreviations are allowed if unambiguous.
1272 @item help @var{class}
1273 Using one of the general help classes as an argument, you can get a
1274 list of the individual commands in that class. For example, here is the
1275 help display for the class @code{status}:
1278 (@value{GDBP}) help status
1283 @c Line break in "show" line falsifies real output, but needed
1284 @c to fit in smallbook page size.
1285 show -- Generic command for showing things set
1287 info -- Generic command for printing status
1289 Type "help" followed by command name for full
1291 Command name abbreviations are allowed if unambiguous.
1295 @item help @var{command}
1296 With a command name as @code{help} argument, @value{GDBN} will display a
1297 short paragraph on how to use that command.
1300 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1301 and @code{show} to inquire about the state of your program, or the state
1302 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1303 manual introduces each of them in the appropriate context. The listings
1304 under @code{info} and under @code{show} in the Index point to
1305 all the sub-commands. @xref{Index}.
1312 This command (abbreviated @code{i}) is for describing the state of your
1313 program. For example, you can list the arguments given to your program
1314 with @code{info args}, list the registers currently in use with @code{info
1315 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1316 You can get a complete list of the @code{info} sub-commands with
1317 @w{@code{help info}}.
1321 In contrast, @code{show} is for describing the state of @value{GDBN} itself.
1322 You can change most of the things you can @code{show}, by using the
1323 related command @code{set}; for example, you can control what number
1324 system is used for displays with @code{set radix}, or simply inquire
1325 which is currently in use with @code{show radix}.
1328 To display all the settable parameters and their current
1329 values, you can use @code{show} with no arguments; you may also use
1330 @code{info set}. Both commands produce the same display.
1331 @c FIXME: "info set" violates the rule that "info" is for state of
1332 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1333 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1337 Here are three miscellaneous @code{show} subcommands, all of which are
1338 exceptional in lacking corresponding @code{set} commands:
1341 @kindex show version
1342 @cindex version number
1344 Show what version of @value{GDBN} is running. You should include this
1345 information in @value{GDBN} bug-reports. If multiple versions of @value{GDBN} are in
1346 use at your site, you may occasionally want to determine which version
1347 of @value{GDBN} you are running; as @value{GDBN} evolves, new commands are introduced,
1348 and old ones may wither away. The version number is also announced
1349 when you start @value{GDBN} with no arguments.
1351 @kindex show copying
1353 Display information about permission for copying @value{GDBN}.
1355 @kindex show warranty
1357 Display the GNU ``NO WARRANTY'' statement.
1361 @chapter Running Programs Under @value{GDBN}
1363 When you run a program under @value{GDBN}, you must first generate
1364 debugging information when you compile it.
1366 You may start it with its arguments, if any, in an environment of your
1367 choice. You may redirect your program's input and output, debug an
1368 already running process, or kill a child process.
1372 * Compilation:: Compiling for debugging
1373 * Starting:: Starting your program
1375 * Arguments:: Your program's arguments
1376 * Environment:: Your program's environment
1377 * Working Directory:: Your program's working directory
1378 * Input/Output:: Your program's input and output
1379 * Attach:: Debugging an already-running process
1380 * Kill Process:: Killing the child process
1381 * Process Information:: Additional process information
1386 @section Compiling for debugging
1388 In order to debug a program effectively, you need to generate
1389 debugging information when you compile it. This debugging information
1390 is stored in the object file; it describes the data type of each
1391 variable or function and the correspondence between source line numbers
1392 and addresses in the executable code.
1394 To request debugging information, specify the @samp{-g} option when you run
1397 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1398 options together. Using those compilers, you cannot generate optimized
1399 executables containing debugging information.
1401 @value{NGCC}, the GNU C compiler, supports @samp{-g} with or without
1402 @samp{-O}, making it possible to debug optimized code. We recommend
1403 that you @emph{always} use @samp{-g} whenever you compile a program.
1404 You may think your program is correct, but there is no sense in pushing
1407 @cindex optimized code, debugging
1408 @cindex debugging optimized code
1409 When you debug a program compiled with @samp{-g -O}, remember that the
1410 optimizer is rearranging your code; the debugger will show you what is
1411 really there. Do not be too surprised when the execution path does not
1412 exactly match your source file! An extreme example: if you define a
1413 variable, but never use it, @value{GDBN} will never see that
1414 variable---because the compiler optimizes it out of existence.
1416 Some things do not work as well with @samp{-g -O} as with just
1417 @samp{-g}, particularly on machines with instruction scheduling. If in
1418 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1419 please report it as a bug (including a test case!).
1421 Older versions of the GNU C compiler permitted a variant option
1422 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1423 format; if your GNU C compiler has this option, do not use it.
1426 @comment As far as I know, there are no cases in which @value{GDBN} will
1427 @comment produce strange output in this case. (but no promises).
1428 If your program includes archives made with the @code{ar} program, and
1429 if the object files used as input to @code{ar} were compiled without the
1430 @samp{-g} option and have names longer than 15 characters, @value{GDBN} will get
1431 confused reading your program's symbol table. No error message will be
1432 given, but @value{GDBN} may behave strangely. The reason for this problem is a
1433 deficiency in the Unix archive file format, which cannot represent file
1434 names longer than 15 characters.
1436 To avoid this problem, compile the archive members with the @samp{-g}
1437 option or use shorter file names. Alternatively, use a version of GNU
1438 @code{ar} dated more recently than August 1989.
1442 @section Starting your program
1450 Use the @code{run} command to start your program under @value{GDBN}. You must
1451 first specify the program name
1455 with an argument to @value{GDBN} (@pxref{Invocation, ,Getting In and
1456 Out of @value{GDBN}}), or by using the @code{file} or @code{exec-file}
1457 command (@pxref{Files, ,Commands to specify files}).
1462 If you are running your program in an execution environment that
1463 supports processes, @code{run} creates an inferior process and makes
1464 that process run your program. (In environments without processes,
1465 @code{run} jumps to the start of your program.)
1467 The execution of a program is affected by certain information it
1468 receives from its superior. @value{GDBN} provides ways to specify this
1469 information, which you must do @emph{before} starting your program. (You
1470 can change it after starting your program, but such changes will only affect
1471 your program the next time you start it.) This information may be
1472 divided into four categories:
1475 @item The @emph{arguments.}
1476 Specify the arguments to give your program as the arguments of the
1477 @code{run} command. If a shell is available on your target, the shell
1478 is used to pass the arguments, so that you may use normal conventions
1479 (such as wildcard expansion or variable substitution) in describing
1480 the arguments. In Unix systems, you can control which shell is used
1481 with the @code{SHELL} environment variable. @xref{Arguments, ,Your
1482 program's arguments}.
1484 @item The @emph{environment.}
1485 Your program normally inherits its environment from @value{GDBN}, but you can
1486 use the @value{GDBN} commands @code{set environment} and @code{unset
1487 environment} to change parts of the environment that will be given to
1488 your program. @xref{Environment, ,Your program's environment}.
1490 @item The @emph{working directory.}
1491 Your program inherits its working directory from @value{GDBN}. You can set
1492 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1493 @xref{Working Directory, ,Your program's working directory}.
1495 @item The @emph{standard input and output.}
1496 Your program normally uses the same device for standard input and
1497 standard output as @value{GDBN} is using. You can redirect input and output
1498 in the @code{run} command line, or you can use the @code{tty} command to
1499 set a different device for your program.
1500 @xref{Input/Output, ,Your program's input and output}.
1503 @emph{Warning:} While input and output redirection work, you cannot use
1504 pipes to pass the output of the program you are debugging to another
1505 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1510 When you issue the @code{run} command, your program begins to execute
1511 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1512 of how to arrange for your program to stop. Once your program has
1513 stopped, you may calls functions in your program, using the @code{print}
1514 or @code{call} commands. @xref{Data, ,Examining Data}.
1516 If the modification time of your symbol file has changed since the
1517 last time @value{GDBN} read its symbols, @value{GDBN} will discard its symbol table and
1518 re-read it. When it does this, @value{GDBN} tries to retain your current
1523 @section Your program's arguments
1525 @cindex arguments (to your program)
1526 The arguments to your program can be specified by the arguments of the
1527 @code{run} command. They are passed to a shell, which expands wildcard
1528 characters and performs redirection of I/O, and thence to your program.
1529 @value{GDBN} uses the shell indicated by your @code{SHELL} environment
1530 variable if it exists; otherwise, @value{GDBN} uses @code{/bin/sh}.
1532 @code{run} with no arguments uses the same arguments used by the previous
1533 @code{run}, or those set by the @code{set args} command.
1538 Specify the arguments to be used the next time your program is run. If
1539 @code{set args} has no arguments, @code{run} will execute your program
1540 with no arguments. Once you have run your program with arguments,
1541 using @code{set args} before the next @code{run} is the only way to run
1542 it again without arguments.
1546 Show the arguments to give your program when it is started.
1550 @section Your program's environment
1552 @cindex environment (of your program)
1553 The @dfn{environment} consists of a set of environment variables and
1554 their values. Environment variables conventionally record such things as
1555 your user name, your home directory, your terminal type, and your search
1556 path for programs to run. Usually you set up environment variables with
1557 the shell and they are inherited by all the other programs you run. When
1558 debugging, it can be useful to try running your program with a modified
1559 environment without having to start @value{GDBN} over again.
1562 @item path @var{directory}
1564 Add @var{directory} to the front of the @code{PATH} environment variable
1565 (the search path for executables), for both @value{GDBN} and your program.
1566 You may specify several directory names, separated by @samp{:} or
1567 whitespace. If @var{directory} is already in the path, it is moved to
1568 the front, so it will be searched sooner.
1570 You can use the string @samp{$cwd} to refer to whatever is the current
1571 working directory at the time @value{GDBN} searches the path. If you use
1572 @samp{.} instead, it refers to the directory where you executed the
1573 @code{path} command. @value{GDBN} fills in the current path where needed in
1574 the @var{directory} argument, before adding it to the search path.
1575 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1576 @c document that, since repeating it would be a no-op.
1580 Display the list of search paths for executables (the @code{PATH}
1581 environment variable).
1583 @item show environment @r{[}@var{varname}@r{]}
1584 @kindex show environment
1585 Print the value of environment variable @var{varname} to be given to
1586 your program when it starts. If you do not supply @var{varname},
1587 print the names and values of all environment variables to be given to
1588 your program. You can abbreviate @code{environment} as @code{env}.
1590 @item set environment @var{varname} @r{[}=@r{]} @var{value}
1591 @kindex set environment
1592 Set environment variable @var{varname} to @var{value}. The value
1593 changes for your program only, not for @value{GDBN} itself. @var{value} may
1594 be any string; the values of environment variables are just strings, and
1595 any interpretation is supplied by your program itself. The @var{value}
1596 parameter is optional; if it is eliminated, the variable is set to a
1598 @c "any string" here does not include leading, trailing
1599 @c blanks. Gnu asks: does anyone care?
1601 For example, this command:
1608 tells a Unix program, when subsequently run, that its user is named
1609 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1610 are not actually required.)
1612 @item unset environment @var{varname}
1613 @kindex unset environment
1614 Remove variable @var{varname} from the environment to be passed to your
1615 program. This is different from @samp{set env @var{varname} =};
1616 @code{unset environment} removes the variable from the environment,
1617 rather than assigning it an empty value.
1620 @node Working Directory
1621 @section Your program's working directory
1623 @cindex working directory (of your program)
1624 Each time you start your program with @code{run}, it inherits its
1625 working directory from the current working directory of @value{GDBN}.
1626 The @value{GDBN} working directory is initially whatever it inherited
1627 from its parent process (typically the shell), but you can specify a new
1628 working directory in @value{GDBN} with the @code{cd} command.
1630 The @value{GDBN} working directory also serves as a default for the commands
1631 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1635 @item cd @var{directory}
1637 Set the @value{GDBN} working directory to @var{directory}.
1641 Print the @value{GDBN} working directory.
1645 @section Your program's input and output
1650 By default, the program you run under @value{GDBN} does input and output to
1651 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal to
1652 its own terminal modes to interact with you, but it records the terminal
1653 modes your program was using and switches back to them when you continue
1654 running your program.
1658 @kindex info terminal
1659 Displays information recorded by @value{GDBN} about the terminal modes your
1663 You can redirect your program's input and/or output using shell
1664 redirection with the @code{run} command. For example,
1671 starts your program, diverting its output to the file @file{outfile}.
1674 @cindex controlling terminal
1675 Another way to specify where your program should do input and output is
1676 with the @code{tty} command. This command accepts a file name as
1677 argument, and causes this file to be the default for future @code{run}
1678 commands. It also resets the controlling terminal for the child
1679 process, for future @code{run} commands. For example,
1686 directs that processes started with subsequent @code{run} commands
1687 default to do input and output on the terminal @file{/dev/ttyb} and have
1688 that as their controlling terminal.
1690 An explicit redirection in @code{run} overrides the @code{tty} command's
1691 effect on the input/output device, but not its effect on the controlling
1694 When you use the @code{tty} command or redirect input in the @code{run}
1695 command, only the input @emph{for your program} is affected. The input
1696 for @value{GDBN} still comes from your terminal.
1699 @section Debugging an already-running process
1704 @item attach @var{process-id}
1705 This command attaches to a running process---one that was started
1706 outside @value{GDBN}. (@code{info files} will show your active
1707 targets.) The command takes as argument a process ID. The usual way to
1708 find out the process-id of a Unix process is with the @code{ps} utility,
1709 or with the @samp{jobs -l} shell command.
1711 @code{attach} will not repeat if you press @key{RET} a second time after
1712 executing the command.
1715 To use @code{attach}, you must be debugging in an environment which
1716 supports processes. You must also have permission to send the process a
1717 signal, and it must have the same effective user ID as the @value{GDBN}
1720 When using @code{attach}, you should first use the @code{file} command
1721 to specify the program running in the process and load its symbol table.
1722 @xref{Files, ,Commands to Specify Files}.
1724 The first thing @value{GDBN} does after arranging to debug the specified
1725 process is to stop it. You can examine and modify an attached process
1726 with all the @value{GDBN} commands that are ordinarily available when you start
1727 processes with @code{run}. You can insert breakpoints; you can step and
1728 continue; you can modify storage. If you would rather the process
1729 continue running, you may use the @code{continue} command after
1730 attaching @value{GDBN} to the process.
1735 When you have finished debugging the attached process, you can use the
1736 @code{detach} command to release it from @value{GDBN} control. Detaching
1737 the process continues its execution. After the @code{detach} command,
1738 that process and @value{GDBN} become completely independent once more, and you
1739 are ready to @code{attach} another process or start one with @code{run}.
1740 @code{detach} will not repeat if you press @key{RET} again after
1741 executing the command.
1744 If you exit @value{GDBN} or use the @code{run} command while you have an attached
1745 process, you kill that process. By default, you will be asked for
1746 confirmation if you try to do either of these things; you can control
1747 whether or not you need to confirm by using the @code{set confirm} command
1748 (@pxref{Messages/Warnings, ,Optional warnings and messages}).
1752 @section Killing the child process
1757 Kill the child process in which your program is running under @value{GDBN}.
1760 This command is useful if you wish to debug a core dump instead of a
1761 running process. @value{GDBN} ignores any core dump file while your program
1765 On some operating systems, a program cannot be executed outside @value{GDBN}
1766 while you have breakpoints set on it inside @value{GDBN}. You can use the
1767 @code{kill} command in this situation to permit running your program
1768 outside the debugger.
1770 The @code{kill} command is also useful if you wish to recompile and
1771 relink your program, since on many systems it is impossible to modify an
1772 executable file while it is running in a process. In this case, when you
1773 next type @code{run}, @value{GDBN} will notice that the file has changed, and
1774 will re-read the symbol table (while trying to preserve your current
1775 breakpoint settings).
1777 @node Process Information
1778 @section Additional process information
1781 @cindex process image
1782 Some operating systems provide a facility called @samp{/proc} that can
1783 be used to examine the image of a running process using file-system
1784 subroutines. If @value{GDBN} is configured for an operating system with this
1785 facility, the command @code{info proc} is available to report on several
1786 kinds of information about the process running your program.
1791 Summarize available information about the process.
1793 @item info proc mappings
1794 @kindex info proc mappings
1795 Report on the address ranges accessible in the program, with information
1796 on whether your program may read, write, or execute each range.
1798 @item info proc times
1799 @kindex info proc times
1800 Starting time, user CPU time, and system CPU time for your program and
1804 @kindex info proc id
1805 Report on the process IDs related to your program: its own process ID,
1806 the ID of its parent, the process group ID, and the session ID.
1808 @item info proc status
1809 @kindex info proc status
1810 General information on the state of the process. If the process is
1811 stopped, this report includes the reason for stopping, and any signal
1815 Show all the above information about the process.
1820 @chapter Stopping and Continuing
1822 The principal purposes of using a debugger are so that you can stop your
1823 program before it terminates; or so that, if your program runs into
1824 trouble, you can investigate and find out why.
1826 Inside @value{GDBN}, your program may stop for any of several reasons, such
1831 a breakpoint, or reaching a new line after a @value{GDBN}
1832 command such as @code{step}. You may then examine and change
1833 variables, set new breakpoints or remove old ones, and then continue
1834 execution. Usually, the messages shown by @value{GDBN} provide ample
1835 explanation of the status of your program---but you can also explicitly
1836 request this information at any time.
1840 @kindex info program
1841 Display information about the status of your program: whether it is
1851 * Breakpoints:: Breakpoints, watchpoints, and exceptions
1854 * Breakpoints:: Breakpoints and watchpoints
1856 @c Remnant makeinfo bug requires blank line after *successful* end-if in menu:
1858 * Continuing and Stepping:: Resuming execution
1864 @c makeinfo node-defaulting requires adjacency of @node and sectioning cmds
1865 @c ...hence distribute @node Breakpoints over two possible @if expansions.
1869 @section Breakpoints, watchpoints, and exceptions
1873 @section Breakpoints and watchpoints
1877 A @dfn{breakpoint} makes your program stop whenever a certain point in
1878 the program is reached. For each breakpoint, you can add various
1879 conditions to control in finer detail whether your program will stop.
1880 You can set breakpoints with the @code{break} command and its variants
1881 (@pxref{Set Breaks, ,Setting breakpoints}), to specify the place where
1882 your program should stop by line number, function name or exact address
1885 In languages with exception handling (such as GNU C++), you can also set
1886 breakpoints where an exception is raised (@pxref{Exception Handling,
1887 ,Breakpoints and exceptions}).
1891 @cindex memory tracing
1892 @cindex breakpoint on memory address
1893 @cindex breakpoint on variable modification
1894 A @dfn{watchpoint} is a special breakpoint that stops your program
1895 when the value of an expression changes. You must use a different
1896 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
1897 watchpoints}), but aside from that, you can manage a watchpoint like
1898 any other breakpoint: you enable, disable, and delete both breakpoints
1899 and watchpoints using the same commands.
1901 You can arrange to have values from your program displayed automatically
1902 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,
1903 ,Automatic display}.
1905 @cindex breakpoint numbers
1906 @cindex numbers for breakpoints
1907 @value{GDBN} assigns a number to each breakpoint or watchpoint when you
1908 create it; these numbers are successive integers starting with one. In
1909 many of the commands for controlling various features of breakpoints you
1910 use the breakpoint number to say which breakpoint you want to change.
1911 Each breakpoint may be @dfn{enabled} or @dfn{disabled}; if disabled, it has
1912 no effect on your program until you enable it again.
1915 * Set Breaks:: Setting breakpoints
1916 * Set Watchpoints:: Setting watchpoints
1918 * Exception Handling:: Breakpoints and exceptions
1921 * Delete Breaks:: Deleting breakpoints
1922 * Disabling:: Disabling breakpoints
1923 * Conditions:: Break conditions
1924 * Break Commands:: Breakpoint command lists
1926 * Breakpoint Menus:: Breakpoint menus
1929 * Error in Breakpoints:: ``Cannot insert breakpoints''
1934 @subsection Setting breakpoints
1936 @c FIXME LMB what does GDB do if no code on line of breakpt?
1937 @c consider in particular declaration with/without initialization.
1939 @c FIXME 2 is there stuff on this already? break at fun start, already init?
1944 @cindex latest breakpoint
1945 Breakpoints are set with the @code{break} command (abbreviated
1946 @code{b}). The debugger convenience variable @samp{$bpnum} records the
1947 number of the beakpoint you've set most recently; see @ref{Convenience
1948 Vars,, Convenience variables}, for a discussion of what you can do with
1949 convenience variables.
1951 You have several ways to say where the breakpoint should go.
1954 @item break @var{function}
1955 Set a breakpoint at entry to function @var{function}.
1957 When using source languages that permit overloading of symbols, such as
1958 C++, @var{function} may refer to more than one possible place to break.
1959 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
1962 @item break +@var{offset}
1963 @itemx break -@var{offset}
1964 Set a breakpoint some number of lines forward or back from the position
1965 at which execution stopped in the currently selected frame.
1967 @item break @var{linenum}
1968 Set a breakpoint at line @var{linenum} in the current source file.
1969 That file is the last file whose source text was printed. This
1970 breakpoint will stop your program just before it executes any of the
1973 @item break @var{filename}:@var{linenum}
1974 Set a breakpoint at line @var{linenum} in source file @var{filename}.
1976 @item break @var{filename}:@var{function}
1977 Set a breakpoint at entry to function @var{function} found in file
1978 @var{filename}. Specifying a file name as well as a function name is
1979 superfluous except when multiple files contain similarly named
1982 @item break *@var{address}
1983 Set a breakpoint at address @var{address}. You can use this to set
1984 breakpoints in parts of your program which do not have debugging
1985 information or source files.
1988 When called without any arguments, @code{break} sets a breakpoint at
1989 the next instruction to be executed in the selected stack frame
1990 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
1991 innermost, this will cause your program to stop as soon as control
1992 returns to that frame. This is similar to the effect of a
1993 @code{finish} command in the frame inside the selected frame---except
1994 that @code{finish} does not leave an active breakpoint. If you use
1995 @code{break} without an argument in the innermost frame, @value{GDBN} will stop
1996 the next time it reaches the current location; this may be useful
1999 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2000 least one instruction has been executed. If it did not do this, you
2001 would be unable to proceed past a breakpoint without first disabling the
2002 breakpoint. This rule applies whether or not the breakpoint already
2003 existed when your program stopped.
2005 @item break @dots{} if @var{cond}
2006 Set a breakpoint with condition @var{cond}; evaluate the expression
2007 @var{cond} each time the breakpoint is reached, and stop only if the
2008 value is nonzero---that is, if @var{cond} evaluates as true.
2009 @samp{@dots{}} stands for one of the possible arguments described
2010 above (or no argument) specifying where to break. @xref{Conditions,
2011 ,Break conditions}, for more information on breakpoint conditions.
2013 @item tbreak @var{args}
2015 Set a breakpoint enabled only for one stop. @var{args} are the
2016 same as for the @code{break} command, and the breakpoint is set in the same
2017 way, but the breakpoint is automatically disabled after the first time your
2018 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2020 @item rbreak @var{regex}
2022 @cindex regular expression
2023 @c FIXME what kind of regexp?
2024 Set breakpoints on all functions matching the regular expression
2025 @var{regex}. This command
2026 sets an unconditional breakpoint on all matches, printing a list of all
2027 breakpoints it set. Once these breakpoints are set, they are treated
2028 just like the breakpoints set with the @code{break} command. They can
2029 be deleted, disabled, made conditional, etc., in the standard ways.
2032 When debugging C++ programs, @code{rbreak} is useful for setting
2033 breakpoints on overloaded functions that are not members of any special
2037 @kindex info breakpoints
2038 @cindex @code{$_} and @code{info breakpoints}
2039 @item info breakpoints @r{[}@var{n}@r{]}
2040 @itemx info break @r{[}@var{n}@r{]}
2041 @itemx info watchpoints @r{[}@var{n}@r{]}
2042 Print a table of all breakpoints and watchpoints set and not
2043 deleted, with the following columns for each breakpoint:
2046 @item Breakpoint Numbers
2048 Breakpoint or watchpoint.
2050 Whether the breakpoint is marked to be disabled or deleted when hit.
2051 @item Enabled or Disabled
2052 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2053 that are not enabled.
2055 Where the breakpoint is in your program, as a memory address
2057 Where the breakpoint is in the source for your program, as a file and
2062 Breakpoint commands, if any, are listed after the line for the
2063 corresponding breakpoint.
2066 @code{info break} with a breakpoint
2067 number @var{n} as argument lists only that breakpoint. The
2068 convenience variable @code{$_} and the default examining-address for
2069 the @code{x} command are set to the address of the last breakpoint
2070 listed (@pxref{Memory, ,Examining memory}).
2073 @value{GDBN} allows you to set any number of breakpoints at the same place in
2074 your program. There is nothing silly or meaningless about this. When
2075 the breakpoints are conditional, this is even useful
2076 (@pxref{Conditions, ,Break conditions}).
2078 @cindex negative breakpoint numbers
2079 @cindex internal @value{GDBN} breakpoints
2080 @value{GDBN} itself sometimes sets breakpoints in your program for special
2081 purposes, such as proper handling of @code{longjmp} (in C programs).
2082 These internal breakpoints are assigned negative numbers, starting with
2083 @code{-1}; @samp{info breakpoints} does not display them.
2085 You can see these breakpoints with the @value{GDBN} maintenance command
2086 @samp{maint info breakpoints}.
2089 @kindex maint info breakpoints
2090 @item maint info breakpoints
2091 Using the same format as @samp{info breakpoints}, display both the
2092 breakpoints you've set explicitly, and those @value{GDBN} is using for
2093 internal purposes. Internal breakpoints are shown with negative
2094 breakpoint numbers. The type column identifies what kind of breakpoint
2099 Normal, explicitly set breakpoint.
2102 Normal, explicitly set watchpoint.
2105 Internal breakpoint, used to handle correctly stepping through
2106 @code{longjmp} calls.
2108 @item longjmp resume
2109 Internal breakpoint at the target of a @code{longjmp}.
2112 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2115 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2121 @node Set Watchpoints
2122 @subsection Setting watchpoints
2123 @cindex setting watchpoints
2125 You can use a watchpoint to stop execution whenever the value of an
2126 expression changes, without having to predict a particular place
2127 where this may happen.
2129 Watchpoints currently execute two orders of magnitude more slowly than
2130 other breakpoints, but this can well be worth it to catch errors where
2131 you have no clue what part of your program is the culprit. Some
2132 processors provide special hardware to support watchpoint evaluation; future
2133 releases of @value{GDBN} will use such hardware if it is available.
2137 @item watch @var{expr}
2138 Set a watchpoint for an expression.
2140 @kindex info watchpoints
2141 @item info watchpoints
2142 This command prints a list of watchpoints and breakpoints; it is the
2143 same as @code{info break}.
2147 @node Exception Handling
2148 @subsection Breakpoints and exceptions
2149 @cindex exception handlers
2151 Some languages, such as GNU C++, implement exception handling. You can
2152 use @value{GDBN} to examine what caused your program to raise an exception,
2153 and to list the exceptions your program is prepared to handle at a
2154 given point in time.
2157 @item catch @var{exceptions}
2159 You can set breakpoints at active exception handlers by using the
2160 @code{catch} command. @var{exceptions} is a list of names of exceptions
2164 You can use @code{info catch} to list active exception handlers.
2165 @xref{Frame Info, ,Information about a frame}.
2167 There are currently some limitations to exception handling in @value{GDBN}.
2168 These will be corrected in a future release.
2172 If you call a function interactively, @value{GDBN} normally returns
2173 control to you when the function has finished executing. If the call
2174 raises an exception, however, the call may bypass the mechanism that
2175 returns control to you and cause your program to simply continue
2176 running until it hits a breakpoint, catches a signal that @value{GDBN} is
2177 listening for, or exits.
2179 You cannot raise an exception interactively.
2181 You cannot interactively install an exception handler.
2184 @cindex raise exceptions
2185 Sometimes @code{catch} is not the best way to debug exception handling:
2186 if you need to know exactly where an exception is raised, it is better to
2187 stop @emph{before} the exception handler is called, since that way you
2188 can see the stack before any unwinding takes place. If you set a
2189 breakpoint in an exception handler instead, it may not be easy to find
2190 out where the exception was raised.
2192 To stop just before an exception handler is called, you need some
2193 knowledge of the implementation. In the case of GNU C++, exceptions are
2194 raised by calling a library function named @code{__raise_exception}
2195 which has the following ANSI C interface:
2198 /* @var{addr} is where the exception identifier is stored.
2199 ID is the exception identifier. */
2200 void __raise_exception (void **@var{addr}, void *@var{id});
2204 To make the debugger catch all exceptions before any stack
2205 unwinding takes place, set a breakpoint on @code{__raise_exception}
2206 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2208 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2209 that depends on the value of @var{id}, you can stop your program when
2210 a specific exception is raised. You can use multiple conditional
2211 breakpoints to stop your program when any of a number of exceptions are
2216 @subsection Deleting breakpoints
2218 @cindex clearing breakpoints, watchpoints
2219 @cindex deleting breakpoints, watchpoints
2220 It is often necessary to eliminate a breakpoint or watchpoint once it
2221 has done its job and you no longer want your program to stop there. This
2222 is called @dfn{deleting} the breakpoint. A breakpoint that has been
2223 deleted no longer exists; it is forgotten.
2225 With the @code{clear} command you can delete breakpoints according to
2226 where they are in your program. With the @code{delete} command you can
2227 delete individual breakpoints or watchpoints by specifying their
2230 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2231 automatically ignores breakpoints on the first instruction to be executed
2232 when you continue execution without changing the execution address.
2237 Delete any breakpoints at the next instruction to be executed in the
2238 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2239 the innermost frame is selected, this is a good way to delete a
2240 breakpoint where your program just stopped.
2242 @item clear @var{function}
2243 @itemx clear @var{filename}:@var{function}
2244 Delete any breakpoints set at entry to the function @var{function}.
2246 @item clear @var{linenum}
2247 @itemx clear @var{filename}:@var{linenum}
2248 Delete any breakpoints set at or within the code of the specified line.
2250 @item delete @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2251 @cindex delete breakpoints
2254 Delete the breakpoints or watchpoints of the numbers specified as
2255 arguments. If no argument is specified, delete all breakpoints (@value{GDBN}
2256 asks confirmation, unless you have @code{set confirm off}). You
2257 can abbreviate this command as @code{d}.
2261 @subsection Disabling breakpoints
2263 @cindex disabled breakpoints
2264 @cindex enabled breakpoints
2265 Rather than deleting a breakpoint or watchpoint, you might prefer to
2266 @dfn{disable} it. This makes the breakpoint inoperative as if it had
2267 been deleted, but remembers the information on the breakpoint so that
2268 you can @dfn{enable} it again later.
2270 You disable and enable breakpoints and watchpoints with the
2271 @code{enable} and @code{disable} commands, optionally specifying one or
2272 more breakpoint numbers as arguments. Use @code{info break} or
2273 @code{info watch} to print a list of breakpoints or watchpoints if you
2274 do not know which numbers to use.
2276 A breakpoint or watchpoint can have any of four different states of
2281 Enabled. The breakpoint will stop your program. A breakpoint set
2282 with the @code{break} command starts out in this state.
2284 Disabled. The breakpoint has no effect on your program.
2286 Enabled once. The breakpoint will stop your program, but
2287 when it does so it will become disabled. A breakpoint set
2288 with the @code{tbreak} command starts out in this state.
2290 Enabled for deletion. The breakpoint will stop your program, but
2291 immediately after it does so it will be deleted permanently.
2294 You can use the following commands to enable or disable breakpoints and
2298 @item disable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2299 @kindex disable breakpoints
2302 Disable the specified breakpoints---or all breakpoints, if none are
2303 listed. A disabled breakpoint has no effect but is not forgotten. All
2304 options such as ignore-counts, conditions and commands are remembered in
2305 case the breakpoint is enabled again later. You may abbreviate
2306 @code{disable} as @code{dis}.
2308 @item enable @r{[}breakpoints@r{]} @r{[}@var{bnums}@dots{}@r{]}
2309 @kindex enable breakpoints
2311 Enable the specified breakpoints (or all defined breakpoints). They
2312 become effective once again in stopping your program.
2314 @item enable @r{[}breakpoints@r{]} once @var{bnums}@dots{}
2315 Enable the specified breakpoints temporarily. Each will be disabled
2316 again the next time it stops your program.
2318 @item enable @r{[}breakpoints@r{]} delete @var{bnums}@dots{}
2319 Enable the specified breakpoints to work once and then die. Each of
2320 the breakpoints will be deleted the next time it stops your program.
2323 Save for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2324 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2325 subsequently, they become disabled or enabled only when you use one of
2326 the commands above. (The command @code{until} can set and delete a
2327 breakpoint of its own, but it will not change the state of your other
2328 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2332 @subsection Break conditions
2333 @cindex conditional breakpoints
2334 @cindex breakpoint conditions
2336 @c FIXME what is scope of break condition expr? Context where wanted?
2337 @c in particular for a watchpoint?
2338 The simplest sort of breakpoint breaks every time your program reaches a
2339 specified place. You can also specify a @dfn{condition} for a
2340 breakpoint. A condition is just a Boolean expression in your
2341 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2342 a condition evaluates the expression each time your program reaches it,
2343 and your program stops only if the condition is @emph{true}.
2345 This is the converse of using assertions for program validation; in that
2346 situation, you want to stop when the assertion is violated---that is,
2347 when the condition is false. In C, if you want to test an assertion expressed
2348 by the condition @var{assert}, you should set the condition
2349 @samp{! @var{assert}} on the appropriate breakpoint.
2351 Conditions are also accepted for watchpoints; you may not need them,
2352 since a watchpoint is inspecting the value of an expression anyhow---but
2353 it might be simpler, say, to just set a watchpoint on a variable name,
2354 and specify a condition that tests whether the new value is an interesting
2357 Break conditions can have side effects, and may even call functions in
2358 your program. This can be useful, for example, to activate functions
2359 that log program progress, or to use your own print functions to
2360 format special data structures. The effects are completely predictable
2361 unless there is another enabled breakpoint at the same address. (In
2362 that case, @value{GDBN} might see the other breakpoint first and stop your
2363 program without checking the condition of this one.) Note that
2364 breakpoint commands are usually more convenient and flexible for the
2365 purpose of performing side effects when a breakpoint is reached
2366 (@pxref{Break Commands, ,Breakpoint command lists}).
2368 Break conditions can be specified when a breakpoint is set, by using
2369 @samp{if} in the arguments to the @code{break} command. @xref{Set
2370 Breaks, ,Setting breakpoints}. They can also be changed at any time
2371 with the @code{condition} command. The @code{watch} command does not
2372 recognize the @code{if} keyword; @code{condition} is the only way to
2373 impose a further condition on a watchpoint.
2376 @item condition @var{bnum} @var{expression}
2378 Specify @var{expression} as the break condition for breakpoint or
2379 watchpoint number @var{bnum}. From now on, this breakpoint will stop
2380 your program only if the value of @var{expression} is true (nonzero, in
2381 C). When you use @code{condition}, @value{GDBN} checks @var{expression}
2382 immediately for syntactic correctness, and to determine whether symbols
2383 in it have referents in the context of your breakpoint.
2384 @c FIXME so what does GDB do if there is no referent? Moreover, what
2385 @c about watchpoints?
2387 not actually evaluate @var{expression} at the time the @code{condition}
2388 command is given, however. @xref{Expressions, ,Expressions}.
2390 @item condition @var{bnum}
2391 Remove the condition from breakpoint number @var{bnum}. It becomes
2392 an ordinary unconditional breakpoint.
2395 @cindex ignore count (of breakpoint)
2396 A special case of a breakpoint condition is to stop only when the
2397 breakpoint has been reached a certain number of times. This is so
2398 useful that there is a special way to do it, using the @dfn{ignore
2399 count} of the breakpoint. Every breakpoint has an ignore count, which
2400 is an integer. Most of the time, the ignore count is zero, and
2401 therefore has no effect. But if your program reaches a breakpoint whose
2402 ignore count is positive, then instead of stopping, it just decrements
2403 the ignore count by one and continues. As a result, if the ignore count
2404 value is @var{n}, the breakpoint will not stop the next @var{n} times it
2408 @item ignore @var{bnum} @var{count}
2410 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2411 The next @var{count} times the breakpoint is reached, your program's
2412 execution will not stop; other than to decrement the ignore count, @value{GDBN}
2415 To make the breakpoint stop the next time it is reached, specify
2418 @item continue @var{count}
2419 @itemx c @var{count}
2420 @itemx fg @var{count}
2421 @kindex continue @var{count}
2422 Continue execution of your program, setting the ignore count of the
2423 breakpoint where your program stopped to @var{count} minus one.
2424 Thus, your program will not stop at this breakpoint until the
2425 @var{count}'th time it is reached.
2427 An argument to this command is meaningful only when your program stopped
2428 due to a breakpoint. At other times, the argument to @code{continue} is
2431 The synonym @code{fg} is provided purely for convenience, and has
2432 exactly the same behavior as other forms of the command.
2435 If a breakpoint has a positive ignore count and a condition, the condition
2436 is not checked. Once the ignore count reaches zero, the condition will
2439 You could achieve the effect of the ignore count with a condition such
2440 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2441 is decremented each time. @xref{Convenience Vars, ,Convenience
2444 @node Break Commands
2445 @subsection Breakpoint command lists
2447 @cindex breakpoint commands
2448 You can give any breakpoint (or watchpoint) a series of commands to
2449 execute when your program stops due to that breakpoint. For example, you
2450 might want to print the values of certain expressions, or enable other
2454 @item commands @r{[}@var{bnum}@r{]}
2455 @itemx @dots{} @var{command-list} @dots{}
2459 Specify a list of commands for breakpoint number @var{bnum}. The commands
2460 themselves appear on the following lines. Type a line containing just
2461 @code{end} to terminate the commands.
2463 To remove all commands from a breakpoint, type @code{commands} and
2464 follow it immediately with @code{end}; that is, give no commands.
2466 With no @var{bnum} argument, @code{commands} refers to the last
2467 breakpoint or watchpoint set (not to the breakpoint most recently
2471 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2472 disabled within a @var{command-list}.
2474 You can use breakpoint commands to start your program up again. Simply
2475 use the @code{continue} command, or @code{step}, or any other command
2476 that resumes execution.
2478 Any other commands in the command list, after a command that resumes
2479 execution, are ignored. This is because any time you resume execution
2480 (even with a simple @code{next} or @code{step}), you may encounter
2481 another breakpoint---which could have its own command list, leading to
2482 ambiguities about which list to execute.
2485 If the first command you specify in a command list is @code{silent}, the
2486 usual message about stopping at a breakpoint is not printed. This may
2487 be desirable for breakpoints that are to print a specific message and
2488 then continue. If none of the remaining commands print anything, you
2489 will see no sign that the breakpoint was reached. @code{silent} is
2490 meaningful only at the beginning of a breakpoint command list.
2492 The commands @code{echo} and @code{output} that allow you to print
2493 precisely controlled output are often useful in silent breakpoints.
2494 @xref{Output, ,Commands for controlled output}.
2496 For example, here is how you could use breakpoint commands to print the
2497 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
2510 One application for breakpoint commands is to compensate for one bug so
2511 you can test for another. Put a breakpoint just after the erroneous line
2512 of code, give it a condition to detect the case in which something
2513 erroneous has been done, and give it commands to assign correct values
2514 to any variables that need them. End with the @code{continue} command
2515 so that your program does not stop, and start with the @code{silent}
2516 command so that no output is produced. Here is an example:
2528 One deficiency in the operation of automatically continuing breakpoints
2529 under Unix appears when your program uses raw mode for the terminal.
2530 @value{GDBN} switches back to its own terminal modes (not raw) before executing
2531 commands, and then must switch back to raw mode when your program is
2532 continued. This causes any pending terminal input to be lost.
2533 @c FIXME: revisit below when GNU sys avail.
2534 @c In the GNU system, this will be fixed by changing the behavior of
2537 Under Unix, you can get around this problem by writing actions into
2538 the breakpoint condition rather than in commands. For example,
2541 condition 5 (x = y + 4), 0
2545 specifies a condition expression (@pxref{Expressions, ,Expressions}) that will
2546 change @code{x} as needed, then always have the value zero so your
2547 program will not stop. No input is lost here, because @value{GDBN} evaluates
2548 break conditions without changing the terminal modes. When you want
2549 to have nontrivial conditions for performing the side effects, the
2550 operators @samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful.
2553 @node Breakpoint Menus
2554 @subsection Breakpoint menus
2556 @cindex symbol overloading
2558 Some programming languages (notably C++) permit a single function name
2559 to be defined several times, for application in different contexts.
2560 This is called @dfn{overloading}. When a function name is overloaded,
2561 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
2562 a breakpoint. If you realize this will be a problem, you can use
2563 something like @samp{break @var{function}(@var{types})} to specify which
2564 particular version of the function you want. Otherwise, @value{GDBN} offers
2565 you a menu of numbered choices for different possible breakpoints, and
2566 waits for your selection with the prompt @samp{>}. The first two
2567 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
2568 sets a breakpoint at each definition of @var{function}, and typing
2569 @kbd{0} aborts the @code{break} command without setting any new
2572 For example, the following session excerpt shows an attempt to set a
2573 breakpoint at the overloaded symbol @code{String::after}.
2574 We choose three particular definitions of that function name:
2576 @c FIXME! This is likely to change to show arg type lists, at least
2578 (@value{GDBP}) b String::after
2581 [2] file:String.cc; line number:867
2582 [3] file:String.cc; line number:860
2583 [4] file:String.cc; line number:875
2584 [5] file:String.cc; line number:853
2585 [6] file:String.cc; line number:846
2586 [7] file:String.cc; line number:735
2588 Breakpoint 1 at 0xb26c: file String.cc, line 867.
2589 Breakpoint 2 at 0xb344: file String.cc, line 875.
2590 Breakpoint 3 at 0xafcc: file String.cc, line 846.
2591 Multiple breakpoints were set.
2592 Use the "delete" command to delete unwanted breakpoints.
2598 @node Error in Breakpoints
2599 @subsection ``Cannot insert breakpoints''
2601 @c FIXME: "cannot insert breakpoints" error, v unclear.
2602 @c Q in pending mail to Gilmore. ---pesch@cygnus.com, 26mar91
2603 @c some light may be shed by looking at instances of
2604 @c ONE_PROCESS_WRITETEXT. But error message seems possible otherwise
2605 @c too. pesch, 20sep91
2606 Under some operating systems, breakpoints cannot be used in a program if
2607 any other process is running that program. In this situation,
2608 attempting to run or continue a program with a breakpoint causes @value{GDBN}
2609 to stop the other process.
2611 When this happens, you have three ways to proceed:
2615 Remove or disable the breakpoints, then continue.
2618 Suspend @value{GDBN}, and copy the file containing your program to a new name.
2619 Resume @value{GDBN} and use the @code{exec-file} command to specify that @value{GDBN}
2620 should run your program under that name. Then start your program again.
2622 @c FIXME: RMS commented here "Show example". Maybe when someone
2623 @c explains the first FIXME: in this section...
2626 Relink your program so that the text segment is nonsharable, using the
2627 linker option @samp{-N}. The operating system limitation may not apply
2628 to nonsharable executables.
2632 @node Continuing and Stepping
2633 @section Continuing and stepping
2637 @cindex resuming execution
2638 @dfn{Continuing} means resuming program execution until your program
2639 completes normally. In contrast, @dfn{stepping} means executing just
2640 one more ``step'' of your program, where ``step'' may mean either one
2641 line of source code, or one machine instruction (depending on what
2642 particular command you use). Either when continuing
2643 or when stepping, your program may stop even sooner, due to
2648 a breakpoint or to a signal. (If due to a signal, you may want to use
2649 @code{handle}, or use @samp{signal 0} to resume execution.
2650 @xref{Signals, ,Signals}.)
2654 @item continue @r{[}@var{ignore-count}@r{]}
2656 Resume program execution, at the address where your program last stopped;
2657 any breakpoints set at that address are bypassed. The optional argument
2658 @var{ignore-count} allows you to specify a further number of times to
2659 ignore a breakpoint at this location; its effect is like that of
2660 @code{ignore} (@pxref{Conditions, ,Break conditions}).
2662 To resume execution at a different place, you can use @code{return}
2663 (@pxref{Returning, ,Returning from a function}) to go back to the
2664 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
2665 different address}) to go to an arbitrary location in your program.
2668 A typical technique for using stepping is to set a breakpoint
2670 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions})
2673 (@pxref{Breakpoints, ,Breakpoints and watchpoints})
2676 beginning of the function or the section of your program where a
2677 problem is believed to lie, run your program until it stops at that
2678 breakpoint, and then step through the suspect area, examining the
2679 variables that are interesting, until you see the problem happen.
2685 Continue running your program until control reaches a different source
2686 line, then stop it and return control to @value{GDBN}. This command is
2687 abbreviated @code{s}.
2690 @emph{Warning:} If you use the @code{step} command while control is
2691 within a function that was compiled without debugging information,
2692 execution will proceed until control reaches another function.
2695 @item step @var{count}
2696 Continue running as in @code{step}, but do so @var{count} times. If a
2697 breakpoint is reached,
2699 or a signal not related to stepping occurs before @var{count} steps,
2701 stepping stops right away.
2703 @item next @r{[}@var{count}@r{]}
2706 Continue to the next source line in the current (innermost) stack frame.
2707 Similar to @code{step}, but any function calls appearing within the line
2708 of code are executed without stopping. Execution stops when control
2709 reaches a different line of code at the stack level which was executing
2710 when the @code{next} command was given. This command is abbreviated
2713 An argument @var{count} is a repeat count, as for @code{step}.
2715 @code{next} within a function that lacks debugging information acts like
2716 @code{step}, but any function calls appearing within the code of the
2717 function are executed without stopping.
2721 Continue running until just after function in the selected stack frame
2722 returns. Print the returned value (if any).
2724 Contrast this with the @code{return} command (@pxref{Returning,
2725 ,Returning from a function}).
2731 Continue running until a source line past the current line, in the
2732 current stack frame, is reached. This command is used to avoid single
2733 stepping through a loop more than once. It is like the @code{next}
2734 command, except that when @code{until} encounters a jump, it
2735 automatically continues execution until the program counter is greater
2736 than the address of the jump.
2738 This means that when you reach the end of a loop after single stepping
2739 though it, @code{until} will cause your program to continue execution
2740 until the loop is exited. In contrast, a @code{next} command at the end
2741 of a loop will simply step back to the beginning of the loop, which
2742 would force you to step through the next iteration.
2744 @code{until} always stops your program if it attempts to exit the current
2747 @code{until} may produce somewhat counterintuitive results if the order
2748 of machine code does not match the order of the source lines. For
2749 example, in the following excerpt from a debugging session, the @code{f}
2750 (@code{frame}) command shows that execution is stopped at line
2751 @code{206}; yet when we use @code{until}, we get to line @code{195}:
2755 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
2757 (@value{GDBP}) until
2758 195 for ( ; argc > 0; NEXTARG) @{
2761 This happened because, for execution efficiency, the compiler had
2762 generated code for the loop closure test at the end, rather than the
2763 start, of the loop---even though the test in a C @code{for}-loop is
2764 written before the body of the loop. The @code{until} command appeared
2765 to step back to the beginning of the loop when it advanced to this
2766 expression; however, it has not really gone to an earlier
2767 statement---not in terms of the actual machine code.
2769 @code{until} with no argument works by means of single
2770 instruction stepping, and hence is slower than @code{until} with an
2773 @item until @var{location}
2774 @item u @var{location}
2775 Continue running your program until either the specified location is
2776 reached, or the current stack frame returns. @var{location} is any of
2777 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
2778 ,Setting breakpoints}). This form of the command uses breakpoints,
2779 and hence is quicker than @code{until} without an argument.
2785 Execute one machine instruction, then stop and return to the debugger.
2787 It is often useful to do @samp{display/i $pc} when stepping by machine
2788 instructions. This will cause the next instruction to be executed to
2789 be displayed automatically at each stop. @xref{Auto Display,
2790 ,Automatic display}.
2792 An argument is a repeat count, as in @code{step}.
2799 Execute one machine instruction, but if it is a function call,
2800 proceed until the function returns.
2802 An argument is a repeat count, as in @code{next}.
2810 A signal is an asynchronous event that can happen in a program. The
2811 operating system defines the possible kinds of signals, and gives each
2812 kind a name and a number. For example, in Unix @code{SIGINT} is the
2813 signal a program gets when you type an interrupt (often @kbd{C-c});
2814 @code{SIGSEGV} is the signal a program gets from referencing a place in
2815 memory far away from all the areas in use; @code{SIGALRM} occurs when
2816 the alarm clock timer goes off (which happens only if your program has
2817 requested an alarm).
2819 @cindex fatal signals
2820 Some signals, including @code{SIGALRM}, are a normal part of the
2821 functioning of your program. Others, such as @code{SIGSEGV}, indicate
2822 errors; these signals are @dfn{fatal} (kill your program immediately) if the
2823 program has not specified in advance some other way to handle the signal.
2824 @code{SIGINT} does not indicate an error in your program, but it is normally
2825 fatal so it can carry out the purpose of the interrupt: to kill the program.
2827 @value{GDBN} has the ability to detect any occurrence of a signal in your
2828 program. You can tell @value{GDBN} in advance what to do for each kind of
2831 @cindex handling signals
2832 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
2833 (so as not to interfere with their role in the functioning of your program)
2834 but to stop your program immediately whenever an error signal happens.
2835 You can change these settings with the @code{handle} command.
2839 @kindex info signals
2840 Print a table of all the kinds of signals and how @value{GDBN} has been told to
2841 handle each one. You can use this to see the signal numbers of all
2842 the defined types of signals.
2844 @item handle @var{signal} @var{keywords}@dots{}
2846 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can be the
2847 number of a signal or its name (with or without the @samp{SIG} at the
2848 beginning). The @var{keywords} say what change to make.
2852 The keywords allowed by the @code{handle} command can be abbreviated.
2853 Their full names are:
2857 @value{GDBN} should not stop your program when this signal happens. It may
2858 still print a message telling you that the signal has come in.
2861 @value{GDBN} should stop your program when this signal happens. This implies
2862 the @code{print} keyword as well.
2865 @value{GDBN} should print a message when this signal happens.
2868 @value{GDBN} should not mention the occurrence of the signal at all. This
2869 implies the @code{nostop} keyword as well.
2872 @value{GDBN} should allow your program to see this signal; your program will be
2873 able to handle the signal, or may be terminated if the signal is fatal
2877 @value{GDBN} should not allow your program to see this signal.
2881 When a signal stops your program, the signal is not visible until you
2882 continue. Your program will see the signal then, if @code{pass} is in
2883 effect for the signal in question @emph{at that time}. In other words,
2884 after @value{GDBN} reports a signal, you can use the @code{handle}
2885 command with @code{pass} or @code{nopass} to control whether that
2886 signal will be seen by your program when you later continue it.
2888 You can also use the @code{signal} command to prevent your program from
2889 seeing a signal, or cause it to see a signal it normally would not see,
2890 or to give it any signal at any time. For example, if your program stopped
2891 due to some sort of memory reference error, you might store correct
2892 values into the erroneous variables and continue, hoping to see more
2893 execution; but your program would probably terminate immediately as
2894 a result of the fatal signal once it saw the signal. To prevent this,
2895 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
2900 @chapter Examining the Stack
2902 When your program has stopped, the first thing you need to know is where it
2903 stopped and how it got there.
2906 Each time your program performs a function call, the information about
2907 where in your program the call was made from is saved in a block of data
2908 called a @dfn{stack frame}. The frame also contains the arguments of the
2909 call and the local variables of the function that was called. All the
2910 stack frames are allocated in a region of memory called the @dfn{call
2913 When your program stops, the @value{GDBN} commands for examining the
2914 stack allow you to see all of this information.
2916 @cindex selected frame
2917 One of the stack frames is @dfn{selected} by @value{GDBN} and many
2918 @value{GDBN} commands refer implicitly to the selected frame. In
2919 particular, whenever you ask @value{GDBN} for the value of a variable in
2920 your program, the value is found in the selected frame. There are
2921 special @value{GDBN} commands to select whichever frame you are
2924 When your program stops, @value{GDBN} automatically selects the
2925 currently executing frame and describes it briefly as the @code{frame}
2926 command does (@pxref{Frame Info, ,Information about a frame}).
2929 * Frames:: Stack frames
2930 * Backtrace:: Backtraces
2931 * Selection:: Selecting a frame
2932 * Frame Info:: Information on a frame
2936 @section Stack frames
2940 The call stack is divided up into contiguous pieces called @dfn{stack
2941 frames}, or @dfn{frames} for short; each frame is the data associated
2942 with one call to one function. The frame contains the arguments given
2943 to the function, the function's local variables, and the address at
2944 which the function is executing.
2946 @cindex initial frame
2947 @cindex outermost frame
2948 @cindex innermost frame
2949 When your program is started, the stack has only one frame, that of the
2950 function @code{main}. This is called the @dfn{initial} frame or the
2951 @dfn{outermost} frame. Each time a function is called, a new frame is
2952 made. Each time a function returns, the frame for that function invocation
2953 is eliminated. If a function is recursive, there can be many frames for
2954 the same function. The frame for the function in which execution is
2955 actually occurring is called the @dfn{innermost} frame. This is the most
2956 recently created of all the stack frames that still exist.
2958 @cindex frame pointer
2959 Inside your program, stack frames are identified by their addresses. A
2960 stack frame consists of many bytes, each of which has its own address; each
2961 kind of computer has a convention for choosing one of those bytes whose
2962 address serves as the address of the frame. Usually this address is kept
2963 in a register called the @dfn{frame pointer register} while execution is
2964 going on in that frame.
2966 @cindex frame number
2967 @value{GDBN} assigns numbers to all existing stack frames, starting with
2968 zero for the innermost frame, one for the frame that called it,
2969 and so on upward. These numbers do not really exist in your program;
2970 they are assigned by @value{GDBN} to give you a way of designating stack
2971 frames in @value{GDBN} commands.
2973 @cindex frameless execution
2974 Some compilers provide a way to compile functions so that they operate
2975 without stack frames. (For example, the @code{@value{GCC}} option
2976 @samp{-fomit-frame-pointer} will generate functions without a frame.)
2977 This is occasionally done with heavily used library functions to save
2978 the frame setup time. @value{GDBN} has limited facilities for dealing
2979 with these function invocations. If the innermost function invocation
2980 has no stack frame, @value{GDBN} will nevertheless regard it as though
2981 it had a separate frame, which is numbered zero as usual, allowing
2982 correct tracing of the function call chain. However, @value{GDBN} has
2983 no provision for frameless functions elsewhere in the stack.
2988 A backtrace is a summary of how your program got where it is. It shows one
2989 line per frame, for many frames, starting with the currently executing
2990 frame (frame zero), followed by its caller (frame one), and on up the
2998 Print a backtrace of the entire stack: one line per frame for all
2999 frames in the stack.
3001 You can stop the backtrace at any time by typing the system interrupt
3002 character, normally @kbd{C-c}.
3004 @item backtrace @var{n}
3006 Similar, but print only the innermost @var{n} frames.
3008 @item backtrace -@var{n}
3010 Similar, but print only the outermost @var{n} frames.
3016 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3017 are additional aliases for @code{backtrace}.
3019 Each line in the backtrace shows the frame number and the function name.
3020 The program counter value is also shown---unless you use @code{set
3021 print address off}. The backtrace also shows the source file name and
3022 line number, as well as the arguments to the function. The program
3023 counter value is omitted if it is at the beginning of the code for that
3026 Here is an example of a backtrace. It was made with the command
3027 @samp{bt 3}, so it shows the innermost three frames.
3031 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3033 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3034 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3036 (More stack frames follow...)
3041 The display for frame zero does not begin with a program counter
3042 value, indicating that your program has stopped at the beginning of the
3043 code for line @code{993} of @code{builtin.c}.
3046 @section Selecting a frame
3048 Most commands for examining the stack and other data in your program work on
3049 whichever stack frame is selected at the moment. Here are the commands for
3050 selecting a stack frame; all of them finish by printing a brief description
3051 of the stack frame just selected.
3058 Select frame number @var{n}. Recall that frame zero is the innermost
3059 (currently executing) frame, frame one is the frame that called the
3060 innermost one, and so on. The highest-numbered frame is the one for
3063 @item frame @var{addr}
3065 Select the frame at address @var{addr}. This is useful mainly if the
3066 chaining of stack frames has been damaged by a bug, making it
3067 impossible for @value{GDBN} to assign numbers properly to all frames. In
3068 addition, this can be useful when your program has multiple stacks and
3069 switches between them.
3072 On the SPARC architecture, @code{frame} needs two addresses to
3073 select an arbitrary frame: a frame pointer and a stack pointer.
3074 @c note to future updaters: this is conditioned on a flag
3075 @c FRAME_SPECIFICATION_DYADIC in the tm-*.h files, currently only used
3076 @c by SPARC, hence the specific attribution. Generalize or list all
3077 @c possibilities if more supported machines start doing this.
3082 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3083 advances toward the outermost frame, to higher frame numbers, to frames
3084 that have existed longer. @var{n} defaults to one.
3089 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3090 advances toward the innermost frame, to lower frame numbers, to frames
3091 that were created more recently. @var{n} defaults to one. You may
3092 abbreviate @code{down} as @code{do}.
3095 All of these commands end by printing two lines of output describing the
3096 frame. The first line shows the frame number, the function name, the
3097 arguments, and the source file and line number of execution in that
3098 frame. The second line shows the text of that source line.
3104 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3106 10 read_input_file (argv[i]);
3110 After such a printout, the @code{list} command with no arguments will
3111 print ten lines centered on the point of execution in the frame.
3112 @xref{List, ,Printing source lines}.
3115 @item up-silently @var{n}
3116 @itemx down-silently @var{n}
3117 @kindex down-silently
3119 These two commands are variants of @code{up} and @code{down},
3120 respectively; they differ in that they do their work silently, without
3121 causing display of the new frame. They are intended primarily for use
3122 in @value{GDBN} command scripts, where the output might be unnecessary and
3127 @section Information about a frame
3129 There are several other commands to print information about the selected
3135 When used without any argument, this command does not change which
3136 frame is selected, but prints a brief description of the currently
3137 selected stack frame. It can be abbreviated @code{f}. With an
3138 argument, this command is used to select a stack frame.
3139 @xref{Selection, ,Selecting a frame}.
3145 This command prints a verbose description of the selected stack frame,
3146 including the address of the frame, the addresses of the next frame down
3147 (called by this frame) and the next frame up (caller of this frame), the
3148 language that the source code corresponding to this frame was written in,
3149 the address of the frame's arguments, the program counter saved in it
3150 (the address of execution in the caller frame), and which registers
3151 were saved in the frame. The verbose description is useful when
3152 something has gone wrong that has made the stack format fail to fit
3153 the usual conventions.
3155 @item info frame @var{addr}
3156 @itemx info f @var{addr}
3157 Print a verbose description of the frame at address @var{addr},
3158 without selecting that frame. The selected frame remains unchanged by
3163 Print the arguments of the selected frame, each on a separate line.
3167 Print the local variables of the selected frame, each on a separate
3168 line. These are all variables (declared either static or automatic)
3169 accessible at the point of execution of the selected frame.
3174 @cindex catch exceptions
3175 @cindex exception handlers
3176 Print a list of all the exception handlers that are active in the
3177 current stack frame at the current point of execution. To see other
3178 exception handlers, visit the associated frame (using the @code{up},
3179 @code{down}, or @code{frame} commands); then type @code{info catch}.
3180 @xref{Exception Handling, ,Breakpoints and exceptions}.
3185 @chapter Examining Source Files
3187 @value{GDBN} can print parts of your program's source, since the debugging
3188 information recorded in the program tells @value{GDBN} what source files were
3189 used to build it. When your program stops, @value{GDBN} spontaneously prints
3190 the line where it stopped. Likewise, when you select a stack frame
3191 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3192 execution in that frame has stopped. You can print other portions of
3193 source files by explicit command.
3196 If you use @value{GDBN} through its GNU Emacs interface, you may prefer to use
3197 Emacs facilities to view source; @pxref{Emacs, ,Using @value{GDBN} under GNU
3202 * List:: Printing source lines
3204 * Search:: Searching source files
3207 * Source Path:: Specifying source directories
3208 * Machine Code:: Source and machine code
3212 @section Printing source lines
3216 To print lines from a source file, use the @code{list} command
3217 (abbreviated @code{l}). There are several ways to specify what part
3218 of the file you want to print.
3220 Here are the forms of the @code{list} command most commonly used:
3223 @item list @var{linenum}
3224 Print lines centered around line number @var{linenum} in the
3225 current source file.
3227 @item list @var{function}
3228 Print lines centered around the beginning of function
3232 Print more lines. If the last lines printed were printed with a
3233 @code{list} command, this prints lines following the last lines
3234 printed; however, if the last line printed was a solitary line printed
3235 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3236 Stack}), this prints lines centered around that line.
3239 Print lines just before the lines last printed.
3242 By default, @value{GDBN} prints ten source lines with any of these forms of
3243 the @code{list} command. You can change this using @code{set listsize}:
3246 @item set listsize @var{count}
3247 @kindex set listsize
3248 Make the @code{list} command display @var{count} source lines (unless
3249 the @code{list} argument explicitly specifies some other number).
3252 @kindex show listsize
3253 Display the number of lines that @code{list} will currently display by
3257 Repeating a @code{list} command with @key{RET} discards the argument,
3258 so it is equivalent to typing just @code{list}. This is more useful
3259 than listing the same lines again. An exception is made for an
3260 argument of @samp{-}; that argument is preserved in repetition so that
3261 each repetition moves up in the source file.
3264 In general, the @code{list} command expects you to supply zero, one or two
3265 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3266 of writing them but the effect is always to specify some source line.
3267 Here is a complete description of the possible arguments for @code{list}:
3270 @item list @var{linespec}
3271 Print lines centered around the line specified by @var{linespec}.
3273 @item list @var{first},@var{last}
3274 Print lines from @var{first} to @var{last}. Both arguments are
3277 @item list ,@var{last}
3278 Print lines ending with @var{last}.
3280 @item list @var{first},
3281 Print lines starting with @var{first}.
3284 Print lines just after the lines last printed.
3287 Print lines just before the lines last printed.
3290 As described in the preceding table.
3293 Here are the ways of specifying a single source line---all the
3298 Specifies line @var{number} of the current source file.
3299 When a @code{list} command has two linespecs, this refers to
3300 the same source file as the first linespec.
3303 Specifies the line @var{offset} lines after the last line printed.
3304 When used as the second linespec in a @code{list} command that has
3305 two, this specifies the line @var{offset} lines down from the
3309 Specifies the line @var{offset} lines before the last line printed.
3311 @item @var{filename}:@var{number}
3312 Specifies line @var{number} in the source file @var{filename}.
3314 @item @var{function}
3315 @c FIXME: "of the open-brace" is C-centric. When we add other langs...
3316 Specifies the line of the open-brace that begins the body of the
3317 function @var{function}.
3319 @item @var{filename}:@var{function}
3320 Specifies the line of the open-brace that begins the body of the
3321 function @var{function} in the file @var{filename}. You only need the
3322 file name with a function name to avoid ambiguity when there are
3323 identically named functions in different source files.
3325 @item *@var{address}
3326 Specifies the line containing the program address @var{address}.
3327 @var{address} may be any expression.
3332 @section Searching source files
3334 @kindex reverse-search
3336 There are two commands for searching through the current source file for a
3340 @item forward-search @var{regexp}
3341 @itemx search @var{regexp}
3343 @kindex forward-search
3344 The command @samp{forward-search @var{regexp}} checks each line,
3345 starting with the one following the last line listed, for a match for
3346 @var{regexp}. It lists the line that is found. You can use
3347 synonym @samp{search @var{regexp}} or abbreviate the command name as
3350 @item reverse-search @var{regexp}
3351 The command @samp{reverse-search @var{regexp}} checks each line, starting
3352 with the one before the last line listed and going backward, for a match
3353 for @var{regexp}. It lists the line that is found. You can abbreviate
3354 this command as @code{rev}.
3359 @section Specifying source directories
3362 @cindex directories for source files
3363 Executable programs sometimes do not record the directories of the source
3364 files from which they were compiled, just the names. Even when they do,
3365 the directories could be moved between the compilation and your debugging
3366 session. @value{GDBN} has a list of directories to search for source files;
3367 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
3368 it tries all the directories in the list, in the order they are present
3369 in the list, until it finds a file with the desired name. Note that
3370 the executable search path is @emph{not} used for this purpose. Neither is
3371 the current working directory, unless it happens to be in the source
3374 If @value{GDBN} cannot find a source file in the source path, and the object
3375 program records a directory, @value{GDBN} tries that directory too. If the
3376 source path is empty, and there is no record of the compilation
3377 directory, @value{GDBN} will, as a last resort, look in the current
3380 Whenever you reset or rearrange the source path, @value{GDBN} will clear out
3381 any information it has cached about where source files are found, where
3382 each line is in the file, etc.
3385 When you start @value{GDBN}, its source path is empty.
3386 To add other directories, use the @code{directory} command.
3389 @item directory @var{dirname} @dots{}
3390 Add directory @var{dirname} to the front of the source path. Several
3391 directory names may be given to this command, separated by @samp{:} or
3392 whitespace. You may specify a directory that is already in the source
3393 path; this moves it forward, so it will be searched sooner.
3395 You can use the string @samp{$cdir} to refer to the compilation
3396 directory (if one is recorded), and @samp{$cwd} to refer to the current
3397 working directory. @samp{$cwd} is not the same as @samp{.}---the former
3398 tracks the current working directory as it changes during your @value{GDBN}
3399 session, while the latter is immediately expanded to the current
3400 directory at the time you add an entry to the source path.
3403 Reset the source path to empty again. This requires confirmation.
3405 @c RET-repeat for @code{directory} is explicitly disabled, but since
3406 @c repeating it would be a no-op we do not say that. (thanks to RMS)
3408 @item show directories
3409 @kindex show directories
3410 Print the source path: show which directories it contains.
3413 If your source path is cluttered with directories that are no longer of
3414 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
3415 versions of source. You can correct the situation as follows:
3419 Use @code{directory} with no argument to reset the source path to empty.
3422 Use @code{directory} with suitable arguments to reinstall the
3423 directories you want in the source path. You can add all the
3424 directories in one command.
3428 @section Source and machine code
3430 You can use the command @code{info line} to map source lines to program
3431 addresses (and vice versa), and the command @code{disassemble} to display
3432 a range of addresses as machine instructions.
3435 @item info line @var{linespec}
3437 Print the starting and ending addresses of the compiled code for
3438 source line @var{linespec}. You can specify source lines in any of
3439 the ways understood by the @code{list} command (@pxref{List, ,Printing
3443 For example, we can use @code{info line} to discover the location of
3444 the object code for the first line of function
3445 @code{m4_changequote}:
3448 (@value{GDBP}) info line m4_changecom
3449 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
3453 We can also inquire (using @code{*@var{addr}} as the form for
3454 @var{linespec}) what source line covers a particular address:
3456 (@value{GDBP}) info line *0x63ff
3457 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
3460 @cindex @code{$_} and @code{info line}
3461 After @code{info line}, the default address for the @code{x} command
3462 is changed to the starting address of the line, so that @samp{x/i} is
3463 sufficient to begin examining the machine code (@pxref{Memory,
3464 ,Examining memory}). Also, this address is saved as the value of the
3465 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
3471 This specialized command dumps a range of memory as machine
3472 instructions. The default memory range is the function surrounding the
3473 program counter of the selected frame. A single argument to this
3474 command is a program counter value; the function surrounding this value
3475 will be dumped. Two arguments specify a range of addresses (first
3476 inclusive, second exclusive) to dump.
3479 @ifclear HviiiEXCLUSIVE
3480 We can use @code{disassemble} to inspect the object code
3481 range shown in the last @code{info line} example (the example
3482 shows SPARC machine instructions):
3486 (@value{GDBP}) disas 0x63e4 0x6404
3487 Dump of assembler code from 0x63e4 to 0x6404:
3488 0x63e4 <builtin_init+5340>: ble 0x63f8 <builtin_init+5360>
3489 0x63e8 <builtin_init+5344>: sethi %hi(0x4c00), %o0
3490 0x63ec <builtin_init+5348>: ld [%i1+4], %o0
3491 0x63f0 <builtin_init+5352>: b 0x63fc <builtin_init+5364>
3492 0x63f4 <builtin_init+5356>: ld [%o0+4], %o0
3493 0x63f8 <builtin_init+5360>: or %o0, 0x1a4, %o0
3494 0x63fc <builtin_init+5364>: call 0x9288 <path_search>
3495 0x6400 <builtin_init+5368>: nop
3496 End of assembler dump.
3500 @ifset HviiiEXCLUSIVE
3501 For example, here is the beginning of the output for the
3502 disassembly of a function @code{fact}:
3506 (@value{GDBP}) disas fact
3507 Dump of assembler code for function fact:
3509 0x802c <fact>: 6d f2 mov.w r2,@@-r7
3510 0x802e <fact+2>: 6d f3 mov.w r3,@@-r7
3511 0x8030 <fact+4>: 6d f6 mov.w r6,@@-r7
3512 0x8032 <fact+6>: 0d 76 mov.w r7,r6
3513 0x8034 <fact+8>: 6f 70 00 08 mov.w @@(0x8,r7),r0
3514 0x8038 <fact+12> 19 11 sub.w r1,r1
3522 @chapter Examining Data
3524 @cindex printing data
3525 @cindex examining data
3528 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
3529 @c document because it is nonstandard... Under Epoch it displays in a
3530 @c different window or something like that.
3531 The usual way to examine data in your program is with the @code{print}
3532 command (abbreviated @code{p}), or its synonym @code{inspect}.
3534 It evaluates and prints the value of an expression of the language your
3535 program is written in (@pxref{Languages, ,Using @value{GDBN} with Different
3540 @item print @var{exp}
3541 @itemx print /@var{f} @var{exp}
3542 @var{exp} is an expression (in the source language). By default the
3543 value of @var{exp} is printed in a format appropriate to its data type;
3544 you can choose a different format by specifying @samp{/@var{f}}, where
3545 @var{f} is a letter specifying the format; @pxref{Output Formats,,Output
3549 @itemx print /@var{f}
3550 If you omit @var{exp}, @value{GDBN} displays the last value again (from the
3551 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
3552 conveniently inspect the same value in an alternative format.
3555 A more low-level way of examining data is with the @code{x} command.
3556 It examines data in memory at a specified address and prints it in a
3557 specified format. @xref{Memory, ,Examining memory}.
3559 If you are interested in information about types, or about how the fields
3564 are declared, use the @code{ptype @var{exp}}
3565 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol Table}.
3568 * Expressions:: Expressions
3569 * Variables:: Program variables
3570 * Arrays:: Artificial arrays
3571 * Output Formats:: Output formats
3572 * Memory:: Examining memory
3573 * Auto Display:: Automatic display
3574 * Print Settings:: Print settings
3575 * Value History:: Value history
3576 * Convenience Vars:: Convenience variables
3577 * Registers:: Registers
3578 @ifclear HviiiEXCLUSIVE
3579 * Floating Point Hardware:: Floating point hardware
3584 @section Expressions
3587 @code{print} and many other @value{GDBN} commands accept an expression and
3588 compute its value. Any kind of constant, variable or operator defined
3589 by the programming language you are using is valid in an expression in
3590 @value{GDBN}. This includes conditional expressions, function calls, casts
3591 and string constants. It unfortunately does not include symbols defined
3592 by preprocessor @code{#define} commands.
3595 Because C is so widespread, most of the expressions shown in examples in
3596 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
3597 Languages}, for information on how to use expressions in other
3600 In this section, we discuss operators that you can use in @value{GDBN}
3601 expressions regardless of your programming language.
3603 Casts are supported in all languages, not just in C, because it is so
3604 useful to cast a number into a pointer so as to examine a structure
3605 at that address in memory.
3606 @c FIXME: casts supported---Mod2 true?
3609 @value{GDBN} supports these operators in addition to those of programming
3614 @samp{@@} is a binary operator for treating parts of memory as arrays.
3615 @xref{Arrays, ,Artificial arrays}, for more information.
3618 @samp{::} allows you to specify a variable in terms of the file or
3619 function where it is defined. @xref{Variables, ,Program variables}.
3621 @item @{@var{type}@} @var{addr}
3622 @cindex @{@var{type}@}
3623 @cindex type casting memory
3624 @cindex memory, viewing as typed object
3625 @cindex casts, to view memory
3626 Refers to an object of type @var{type} stored at address @var{addr} in
3627 memory. @var{addr} may be any expression whose value is an integer or
3628 pointer (but parentheses are required around binary operators, just as in
3629 a cast). This construct is allowed regardless of what kind of data is
3630 normally supposed to reside at @var{addr}.
3634 @section Program variables
3636 The most common kind of expression to use is the name of a variable
3639 Variables in expressions are understood in the selected stack frame
3640 (@pxref{Selection, ,Selecting a frame}); they must either be global
3641 (or static) or be visible according to the scope rules of the
3642 programming language from the point of execution in that frame. This
3643 means that in the function
3658 you can examine and use the variable @code{a} whenever your program is
3659 executing within the function @code{foo}, but you can only use or
3660 examine the variable @code{b} while your program is executing inside
3661 the block where @code{b} is declared.
3663 @cindex variable name conflict
3664 There is an exception: you can refer to a variable or function whose
3665 scope is a single source file even if the current execution point is not
3666 in this file. But it is possible to have more than one such variable or
3667 function with the same name (in different source files). If that
3668 happens, referring to that name has unpredictable effects. If you wish,
3669 you can specify a static variable in a particular function or file,
3670 using the colon-colon notation:
3674 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
3678 @var{file}::@var{variable}
3679 @var{function}::@var{variable}
3683 Here @var{file} or @var{function} is the name of the context for the
3684 static @var{variable}. In the case of file names, you can use quotes to
3685 make sure @value{GDBN} parses the file name as a single word---for example,
3686 to print a global value of @code{x} defined in @file{f2.c}:
3689 (@value{GDBP}) p 'f2.c'::x
3693 @cindex C++ scope resolution
3694 This use of @samp{::} is very rarely in conflict with the very similar
3695 use of the same notation in C++. @value{GDBN} also supports use of the C++
3696 scope resolution operator in @value{GDBN} expressions.
3697 @c FIXME: Um, so what happens in one of those rare cases where it's in
3701 @cindex wrong values
3702 @cindex variable values, wrong
3704 @emph{Warning:} Occasionally, a local variable may appear to have the
3705 wrong value at certain points in a function---just after entry to a new
3706 scope, and just before exit.
3708 You may see this problem when you are stepping by machine instructions.
3709 This is because on most machines, it takes more than one instruction to
3710 set up a stack frame (including local variable definitions); if you are
3711 stepping by machine instructions, variables may appear to have the wrong
3712 values until the stack frame is completely built. On exit, it usually
3713 also takes more than one machine instruction to destroy a stack frame;
3714 after you begin stepping through that group of instructions, local
3715 variable definitions may be gone.
3718 @section Artificial arrays
3720 @cindex artificial array
3722 It is often useful to print out several successive objects of the
3723 same type in memory; a section of an array, or an array of
3724 dynamically determined size for which only a pointer exists in the
3727 You can do this by referring to a contiguous span of memory as an
3728 @dfn{artificial array}, using the binary operator @samp{@@}. The left
3729 operand of @samp{@@} should be the first element of the desired array,
3730 as an individual object. The right operand should be the desired length
3731 of the array. The result is an array value whose elements are all of
3732 the type of the left argument. The first element is actually the left
3733 argument; the second element comes from bytes of memory immediately
3734 following those that hold the first element, and so on. Here is an
3735 example. If a program says
3738 int *array = (int *) malloc (len * sizeof (int));
3742 you can print the contents of @code{array} with
3748 The left operand of @samp{@@} must reside in memory. Array values made
3749 with @samp{@@} in this way behave just like other arrays in terms of
3750 subscripting, and are coerced to pointers when used in expressions.
3751 Artificial arrays most often appear in expressions via the value history
3752 (@pxref{Value History, ,Value history}), after printing one out.)
3754 Sometimes the artificial array mechanism is not quite enough; in
3755 moderately complex data structures, the elements of interest may not
3756 actually be adjacent---for example, if you are interested in the values
3757 of pointers in an array. One useful work-around in this situation is
3758 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
3759 variables}) as a counter in an expression that prints the first
3760 interesting value, and then repeat that expression via @key{RET}. For
3761 instance, suppose you have an array @code{dtab} of pointers to
3762 structures, and you are interested in the values of a field @code{fv}
3763 in each structure. Here is an example of what you might type:
3773 @node Output Formats
3774 @section Output formats
3776 @cindex formatted output
3777 @cindex output formats
3778 By default, @value{GDBN} prints a value according to its data type. Sometimes
3779 this is not what you want. For example, you might want to print a number
3780 in hex, or a pointer in decimal. Or you might want to view data in memory
3781 at a certain address as a character string or as an instruction. To do
3782 these things, specify an @dfn{output format} when you print a value.
3784 The simplest use of output formats is to say how to print a value
3785 already computed. This is done by starting the arguments of the
3786 @code{print} command with a slash and a format letter. The format
3787 letters supported are:
3791 Regard the bits of the value as an integer, and print the integer in
3795 Print as integer in signed decimal.
3798 Print as integer in unsigned decimal.
3801 Print as integer in octal.
3804 Print as integer in binary. The letter @samp{t} stands for ``two''.
3805 @footnote{@samp{b} cannot be used because these format letters are also
3806 used with the @code{x} command, where @samp{b} stands for ``byte'';
3807 @pxref{Memory,,Examining memory}.}
3810 Print as an address, both absolute in hex and as an offset from the
3811 nearest preceding symbol. This format can be used to discover where (in
3812 what function) an unknown address is located:
3815 (@value{GDBP}) p/a 0x54320
3816 $3 = 0x54320 <_initialize_vx+396>
3820 Regard as an integer and print it as a character constant.
3823 Regard the bits of the value as a floating point number and print
3824 using typical floating point syntax.
3827 For example, to print the program counter in hex (@pxref{Registers}), type
3834 Note that no space is required before the slash; this is because command
3835 names in @value{GDBN} cannot contain a slash.
3837 To reprint the last value in the value history with a different format,
3838 you can use the @code{print} command with just a format and no
3839 expression. For example, @samp{p/x} reprints the last value in hex.
3842 @section Examining memory
3844 You can use the command @code{x} (for ``examine'') to examine memory in
3845 any of several formats, independently of your program's data types.
3847 @cindex examining memory
3850 @item x/@var{nfu} @var{addr}
3853 Use the @code{x} command to examine memory.
3856 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
3857 much memory to display and how to format it; @var{addr} is an
3858 expression giving the address where you want to start displaying memory.
3859 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
3860 Several commands set convenient defaults for @var{addr}.
3863 @item @var{n}, the repeat count
3864 The repeat count is a decimal integer; the default is 1. It specifies
3865 how much memory (counting by units @var{u}) to display.
3866 @c This really is **decimal**; unaffected by 'set radix' as of GDB
3869 @item @var{f}, the display format
3870 The display format is one of the formats used by @code{print},
3871 or @samp{s} (null-terminated string) or @samp{i} (machine instruction).
3872 The default is @samp{x} (hexadecimal) initially, or the format from the
3873 last time you used either @code{x} or @code{print}.
3875 @item @var{u}, the unit size
3876 The unit size is any of
3882 Halfwords (two bytes).
3884 Words (four bytes). This is the initial default.
3886 Giant words (eight bytes).
3889 Each time you specify a unit size with @code{x}, that size becomes the
3890 default unit the next time you use @code{x}. (For the @samp{s} and
3891 @samp{i} formats, the unit size is ignored and is normally not written.)
3893 @item @var{addr}, starting display address
3894 @var{addr} is the address where you want @value{GDBN} to begin displaying
3895 memory. The expression need not have a pointer value (though it may);
3896 it is always interpreted as an integer address of a byte of memory.
3897 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
3898 @var{addr} is usually just after the last address examined---but several
3899 other commands also set the default address: @code{info breakpoints} (to
3900 the address of the last breakpoint listed), @code{info line} (to the
3901 starting address of a line), and @code{print} (if you use it to display
3902 a value from memory).
3905 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
3906 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
3907 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
3908 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
3909 @pxref{Registers}) in hexadecimal (@samp{x}).
3911 Since the letters indicating unit sizes are all distinct from the
3912 letters specifying output formats, you do not have to remember whether
3913 unit size or format comes first; either order will work. The output
3914 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
3915 (However, the count @var{n} must come first; @samp{wx4} will not work.)
3917 Even though the unit size @var{u} is ignored for the formats @samp{s}
3918 and @samp{i}, you might still want to use a count @var{n}; for example,
3919 @samp{3i} specifies that you want to see three machine instructions,
3920 including any operands. The command @code{disassemble} gives an
3921 alternative way of inspecting machine instructions; @pxref{Machine
3922 Code,,Source and machine code}.
3924 All the defaults for the arguments to @code{x} are designed to make it
3925 easy to continue scanning memory with minimal specifications each time
3926 you use @code{x}. For example, after you have inspected three machine
3927 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
3928 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
3929 the repeat count @var{n} is used again; the other arguments default as
3930 for successive uses of @code{x}.
3932 @cindex @code{$_}, @code{$__}, and value history
3933 The addresses and contents printed by the @code{x} command are not saved
3934 in the value history because there is often too much of them and they
3935 would get in the way. Instead, @value{GDBN} makes these values available for
3936 subsequent use in expressions as values of the convenience variables
3937 @code{$_} and @code{$__}. After an @code{x} command, the last address
3938 examined is available for use in expressions in the convenience variable
3939 @code{$_}. The contents of that address, as examined, are available in
3940 the convenience variable @code{$__}.
3942 If the @code{x} command has a repeat count, the address and contents saved
3943 are from the last memory unit printed; this is not the same as the last
3944 address printed if several units were printed on the last line of output.
3947 @section Automatic display
3948 @cindex automatic display
3949 @cindex display of expressions
3951 If you find that you want to print the value of an expression frequently
3952 (to see how it changes), you might want to add it to the @dfn{automatic
3953 display list} so that @value{GDBN} will print its value each time your program stops.
3954 Each expression added to the list is given a number to identify it;
3955 to remove an expression from the list, you specify that number.
3956 The automatic display looks like this:
3960 3: bar[5] = (struct hack *) 0x3804
3964 This display shows item numbers, expressions and their current values. As with
3965 displays you request manually using @code{x} or @code{print}, you can
3966 specify the output format you prefer; in fact, @code{display} decides
3967 whether to use @code{print} or @code{x} depending on how elaborate your
3968 format specification is---it uses @code{x} if you specify a unit size,
3969 or one of the two formats (@samp{i} and @samp{s}) that are only
3970 supported by @code{x}; otherwise it uses @code{print}.
3973 @item display @var{exp}
3975 Add the expression @var{exp} to the list of expressions to display
3976 each time your program stops. @xref{Expressions, ,Expressions}.
3978 @code{display} will not repeat if you press @key{RET} again after using it.
3980 @item display/@var{fmt} @var{exp}
3981 For @var{fmt} specifying only a display format and not a size or
3982 count, add the expression @var{exp} to the auto-display list but
3983 arranges to display it each time in the specified format @var{fmt}.
3984 @xref{Output Formats,,Output formats}.
3986 @item display/@var{fmt} @var{addr}
3987 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
3988 number of units, add the expression @var{addr} as a memory address to
3989 be examined each time your program stops. Examining means in effect
3990 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
3993 For example, @samp{display/i $pc} can be helpful, to see the machine
3994 instruction about to be executed each time execution stops (@samp{$pc}
3995 is a common name for the program counter; @pxref{Registers}).
3998 @item undisplay @var{dnums}@dots{}
3999 @itemx delete display @var{dnums}@dots{}
4000 @kindex delete display
4002 Remove item numbers @var{dnums} from the list of expressions to display.
4004 @code{undisplay} will not repeat if you press @key{RET} after using it.
4005 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4007 @item disable display @var{dnums}@dots{}
4008 @kindex disable display
4009 Disable the display of item numbers @var{dnums}. A disabled display
4010 item is not printed automatically, but is not forgotten. It may be
4011 enabled again later.
4013 @item enable display @var{dnums}@dots{}
4014 @kindex enable display
4015 Enable display of item numbers @var{dnums}. It becomes effective once
4016 again in auto display of its expression, until you specify otherwise.
4019 Display the current values of the expressions on the list, just as is
4020 done when your program stops.
4023 @kindex info display
4024 Print the list of expressions previously set up to display
4025 automatically, each one with its item number, but without showing the
4026 values. This includes disabled expressions, which are marked as such.
4027 It also includes expressions which would not be displayed right now
4028 because they refer to automatic variables not currently available.
4031 If a display expression refers to local variables, then it does not make
4032 sense outside the lexical context for which it was set up. Such an
4033 expression is disabled when execution enters a context where one of its
4034 variables is not defined. For example, if you give the command
4035 @code{display last_char} while inside a function with an argument
4036 @code{last_char}, then this argument will be displayed while your program
4037 continues to stop inside that function. When it stops elsewhere---where
4038 there is no variable @code{last_char}---display is disabled. The next time
4039 your program stops where @code{last_char} is meaningful, you can enable the
4040 display expression once again.
4042 @node Print Settings
4043 @section Print settings
4045 @cindex format options
4046 @cindex print settings
4047 @value{GDBN} provides the following ways to control how arrays, structures,
4048 and symbols are printed.
4051 These settings are useful for debugging programs in any language:
4054 @item set print address
4055 @item set print address on
4056 @kindex set print address
4057 @value{GDBN} will print memory addresses showing the location of stack
4058 traces, structure values, pointer values, breakpoints, and so forth,
4059 even when it also displays the contents of those addresses. The default
4060 is on. For example, this is what a stack frame display looks like, with
4061 @code{set print address on}:
4066 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4068 530 if (lquote != def_lquote)
4072 @item set print address off
4073 Do not print addresses when displaying their contents. For example,
4074 this is the same stack frame displayed with @code{set print address off}:
4078 (@value{GDBP}) set print addr off
4080 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4081 530 if (lquote != def_lquote)
4085 You can use @samp{set print address off} to eliminate all machine
4086 dependent displays from the @value{GDBN} interface. For example, with
4087 @code{print address off}, you should get the same text for backtraces on
4088 all machines---whether or not they involve pointer arguments.
4090 @item show print address
4091 @kindex show print address
4092 Show whether or not addresses are to be printed.
4094 @item set print array
4095 @itemx set print array on
4096 @kindex set print array
4097 @value{GDBN} will pretty-print arrays. This format is more convenient to read,
4098 but uses more space. The default is off.
4100 @item set print array off
4101 Return to compressed format for arrays.
4103 @item show print array
4104 @kindex show print array
4105 Show whether compressed or pretty format is selected for displaying
4108 @item set print elements @var{number-of-elements}
4109 @kindex set print elements
4110 If @value{GDBN} is printing a large array, it will stop printing after it has
4111 printed the number of elements set by the @code{set print elements} command.
4112 This limit also applies to the display of strings.
4114 @item show print elements
4115 @kindex show print elements
4116 Display the number of elements of a large array that @value{GDBN} will print
4117 before losing patience.
4119 @item set print pretty on
4120 @kindex set print pretty
4121 Cause @value{GDBN} to print structures in an indented format with one member per
4137 @item set print pretty off
4138 Cause @value{GDBN} to print structures in a compact format, like this:
4142 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4143 meat = 0x54 "Pork"@}
4148 This is the default format.
4150 @item show print pretty
4151 @kindex show print pretty
4152 Show which format @value{GDBN} will use to print structures.
4154 @item set print sevenbit-strings on
4155 @kindex set print sevenbit-strings
4156 Print using only seven-bit characters; if this option is set,
4157 @value{GDBN} will display any eight-bit characters (in strings or character
4158 values) using the notation @code{\}@var{nnn}. For example, @kbd{M-a} is
4159 displayed as @code{\341}.
4161 @item set print sevenbit-strings off
4162 Print using either seven-bit or eight-bit characters, as required. This
4165 @item show print sevenbit-strings
4166 @kindex show print sevenbit-strings
4167 Show whether or not @value{GDBN} will print only seven-bit characters.
4169 @item set print union on
4170 @kindex set print union
4171 Tell @value{GDBN} to print unions which are contained in structures. This is the
4174 @item set print union off
4175 Tell @value{GDBN} not to print unions which are contained in structures.
4177 @item show print union
4178 @kindex show print union
4179 Ask @value{GDBN} whether or not it will print unions which are contained in
4182 For example, given the declarations
4185 typedef enum @{Tree, Bug@} Species;
4186 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4187 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4198 struct thing foo = @{Tree, @{Acorn@}@};
4202 with @code{set print union on} in effect @samp{p foo} would print
4205 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
4209 and with @code{set print union off} in effect it would print
4212 $1 = @{it = Tree, form = @{...@}@}
4215 @item set print max-symbolic-offset @var{maxoff}
4216 @kindex set print max-symbolic-offset
4217 Tell @value{GDBN} to only display the symbolic form of an address if the
4218 offset between the closest earlier symbol and the address is less than
4219 @var{maxoff}. The default is 0, which means to always print the
4220 symbolic form of an address, if any symbol precedes it.
4222 @item show print max-symbolic-offset
4223 @kindex show print max-symbolic-offset
4224 Ask how large the maximum offset is that @value{GDBN} will print in a
4231 These settings are of interest when debugging C++ programs:
4234 @item set print demangle
4235 @itemx set print demangle on
4236 @kindex set print demangle
4237 Print C++ names in their source form rather than in the encoded
4238 (``mangled'') form passed to the assembler and linker for type-safe
4239 linkage. The default is @samp{on}.
4241 @item show print demangle
4242 @kindex show print demangle
4243 Show whether C++ names will be printed in mangled or demangled form.
4245 @item set print asm-demangle
4246 @itemx set print asm-demangle on
4247 @kindex set print asm-demangle
4248 Print C++ names in their source form rather than their mangled form, even
4249 in assembler code printouts such as instruction disassemblies.
4252 @item show print asm-demangle
4253 @kindex show print asm-demangle
4254 Show whether C++ names in assembly listings will be printed in mangled
4257 @item set demangle-style @var{style}
4258 @kindex set demangle-style
4259 @cindex C++ symbol decoding style
4260 @cindex symbol decoding style, C++
4261 Choose among several encoding schemes used by different compilers to
4262 represent C++ names. The choices for @var{style} are currently:
4266 Allow @value{GDBN} to choose a decoding style by inspecting your program.
4269 Decode based on the GNU C++ compiler (@code{g++}) encoding algorithm.
4272 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
4275 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
4276 @strong{Warning:} despite the name, this setting alone is not sufficient
4277 to allow debugging @code{cfront}-generated executables. @value{GDBN}
4278 would require further enhancement to permit that.
4281 @item show demangle-style
4282 @kindex show demangle-style
4283 Display the encoding style currently in use for decoding C++ symbols.
4285 @item set print object
4286 @itemx set print object on
4287 @kindex set print object
4288 When displaying a pointer to an object, identify the @emph{actual}
4289 (derived) type of the object rather than the @emph{declared} type, using
4290 the virtual function table.
4292 @item set print object off
4293 Display only the declared type of objects, without reference to the
4294 virtual function table. This is the default setting.
4296 @item show print object
4297 @kindex show print object
4298 Show whether actual, or declared, object types will be displayed.
4300 @item set print vtbl
4301 @itemx set print vtbl on
4302 @kindex set print vtbl
4303 Pretty print C++ virtual function tables. The default is off.
4305 @item set print vtbl off
4306 Do not pretty print C++ virtual function tables.
4308 @item show print vtbl
4309 @kindex show print vtbl
4310 Show whether C++ virtual function tables are pretty printed, or not.
4315 @section Value history
4317 @cindex value history
4318 Values printed by the @code{print} command are saved in the @value{GDBN} @dfn{value
4319 history} so that you can refer to them in other expressions. Values are
4320 kept until the symbol table is re-read or discarded (for example with
4321 the @code{file} or @code{symbol-file} commands). When the symbol table
4322 changes, the value history is discarded, since the values may contain
4323 pointers back to the types defined in the symbol table.
4327 @cindex history number
4328 The values printed are given @dfn{history numbers} for you to refer to them
4329 by. These are successive integers starting with one. @code{print} shows you
4330 the history number assigned to a value by printing @samp{$@var{num} = }
4331 before the value; here @var{num} is the history number.
4333 To refer to any previous value, use @samp{$} followed by the value's
4334 history number. The way @code{print} labels its output is designed to
4335 remind you of this. Just @code{$} refers to the most recent value in
4336 the history, and @code{$$} refers to the value before that.
4337 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
4338 is the value just prior to @code{$$}, @code{$$1} is equivalent to
4339 @code{$$}, and @code{$$0} is equivalent to @code{$}.
4341 For example, suppose you have just printed a pointer to a structure and
4342 want to see the contents of the structure. It suffices to type
4348 If you have a chain of structures where the component @code{next} points
4349 to the next one, you can print the contents of the next one with this:
4356 You can print successive links in the chain by repeating this
4357 command---which you can do by just typing @key{RET}.
4359 Note that the history records values, not expressions. If the value of
4360 @code{x} is 4 and you type these commands:
4368 then the value recorded in the value history by the @code{print} command
4369 remains 4 even though the value of @code{x} has changed.
4374 Print the last ten values in the value history, with their item numbers.
4375 This is like @samp{p@ $$9} repeated ten times, except that @code{show
4376 values} does not change the history.
4378 @item show values @var{n}
4379 Print ten history values centered on history item number @var{n}.
4382 Print ten history values just after the values last printed. If no more
4383 values are available, produces no display.
4386 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
4387 same effect as @samp{show values +}.
4389 @node Convenience Vars
4390 @section Convenience variables
4392 @cindex convenience variables
4393 @value{GDBN} provides @dfn{convenience variables} that you can use within
4394 @value{GDBN} to hold on to a value and refer to it later. These variables
4395 exist entirely within @value{GDBN}; they are not part of your program, and
4396 setting a convenience variable has no direct effect on further execution
4397 of your program. That is why you can use them freely.
4399 Convenience variables are prefixed with @samp{$}. Any name preceded by
4400 @samp{$} can be used for a convenience variable, unless it is one of
4401 the predefined machine-specific register names (@pxref{Registers}).
4402 (Value history references, in contrast, are @emph{numbers} preceded
4403 by @samp{$}. @xref{Value History, ,Value history}.)
4405 You can save a value in a convenience variable with an assignment
4406 expression, just as you would set a variable in your program.
4410 set $foo = *object_ptr
4414 would save in @code{$foo} the value contained in the object pointed to by
4417 Using a convenience variable for the first time creates it; but its value
4418 is @code{void} until you assign a new value. You can alter the value with
4419 another assignment at any time.
4421 Convenience variables have no fixed types. You can assign a convenience
4422 variable any type of value, including structures and arrays, even if
4423 that variable already has a value of a different type. The convenience
4424 variable, when used as an expression, has the type of its current value.
4427 @item show convenience
4428 @kindex show convenience
4429 Print a list of convenience variables used so far, and their values.
4430 Abbreviated @code{show con}.
4433 One of the ways to use a convenience variable is as a counter to be
4434 incremented or a pointer to be advanced. For example, to print
4435 a field from successive elements of an array of structures:
4439 print bar[$i++]->contents
4440 @i{@dots{} repeat that command by typing @key{RET}.}
4443 Some convenience variables are created automatically by @value{GDBN} and given
4444 values likely to be useful.
4449 The variable @code{$_} is automatically set by the @code{x} command to
4450 the last address examined (@pxref{Memory, ,Examining memory}). Other
4451 commands which provide a default address for @code{x} to examine also
4452 set @code{$_} to that address; these commands include @code{info line}
4453 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
4454 except when set by the @code{x} command, in which case it is a pointer
4455 to the type of @code{$__}.
4459 The variable @code{$__} is automatically set by the @code{x} command
4460 to the value found in the last address examined. Its type is chosen
4461 to match the format in which the data was printed.
4468 You can refer to machine register contents, in expressions, as variables
4469 with names starting with @samp{$}. The names of registers are different
4470 for each machine; use @code{info registers} to see the names used on
4474 @item info registers
4475 @kindex info registers
4476 Print the names and values of all registers except floating-point
4477 registers (in the selected stack frame).
4479 @item info all-registers
4480 @kindex info all-registers
4481 @cindex floating point registers
4482 Print the names and values of all registers, including floating-point
4485 @item info registers @var{regname} @dots{}
4486 Print the relativized value of each specified register @var{regname}.
4487 @var{regname} may be any register name valid on the machine you are using, with
4488 or without the initial @samp{$}.
4491 @value{GDBN} has four ``standard'' register names that are available (in
4492 expressions) on most machines---whenever they do not conflict with an
4493 architecture's canonical mnemonics for registers. The register names
4494 @code{$pc} and @code{$sp} are used for the program counter register and
4495 the stack pointer. @code{$fp} is used for a register that contains a
4496 pointer to the current stack frame, and @code{$ps} is used for a
4497 register that contains the processor status. For example,
4498 you could print the program counter in hex with
4505 or print the instruction to be executed next with
4512 or add four to the stack pointer@footnote{This is a way of removing
4513 one word from the stack, on machines where stacks grow downward in
4514 memory (most machines, nowadays). This assumes that the innermost
4515 stack frame is selected; setting @code{$sp} is not allowed when other
4516 stack frames are selected. To pop entire frames off the stack,
4517 regardless of machine architecture, use @code{return};
4518 @pxref{Returning, ,Returning from a function}.} with
4524 Whenever possible, these four standard register names are available on
4525 your machine even though the machine has different canonical mnemonics,
4526 so long as there is no conflict. The @code{info registers} command
4527 shows the canonical names. For example, on the SPARC, @code{info
4528 registers} displays the processor status register as @code{$psr} but you
4529 can also refer to it as @code{$ps}.
4531 @value{GDBN} always considers the contents of an ordinary register as an
4532 integer when the register is examined in this way. Some machines have
4533 special registers which can hold nothing but floating point; these
4534 registers are considered to have floating point values. There is no way
4535 to refer to the contents of an ordinary register as floating point value
4536 (although you can @emph{print} it as a floating point value with
4537 @samp{print/f $@var{regname}}).
4539 Some registers have distinct ``raw'' and ``virtual'' data formats. This
4540 means that the data format in which the register contents are saved by
4541 the operating system is not the same one that your program normally
4542 sees. For example, the registers of the 68881 floating point
4543 coprocessor are always saved in ``extended'' (raw) format, but all C
4544 programs expect to work with ``double'' (virtual) format. In such
4545 cases, @value{GDBN} normally works with the virtual format only (the format that
4546 makes sense for your program), but the @code{info registers} command
4547 prints the data in both formats.
4549 Normally, register values are relative to the selected stack frame
4550 (@pxref{Selection, ,Selecting a frame}). This means that you get the
4551 value that the register would contain if all stack frames farther in
4552 were exited and their saved registers restored. In order to see the
4553 true contents of hardware registers, you must select the innermost
4554 frame (with @samp{frame 0}).
4556 However, @value{GDBN} must deduce where registers are saved, from the machine
4557 code generated by your compiler. If some registers are not saved, or if
4558 @value{GDBN} is unable to locate the saved registers, the selected stack
4559 frame will make no difference.
4563 @item set rstack_high_address @var{address}
4564 @kindex set rstack_high_address
4565 @cindex AMD 29K register stack
4566 @cindex register stack, AMD29K
4567 On AMD 29000 family processors, registers are saved in a separate
4568 ``register stack''. There is no way for @value{GDBN} to determine the extent
4569 of this stack. Normally, @value{GDBN} just assumes that the stack is ``large
4570 enough''. This may result in @value{GDBN} referencing memory locations that
4571 do not exist. If necessary, you can get around this problem by
4572 specifying the ending address of the register stack with the @code{set
4573 rstack_high_address} command. The argument should be an address, which
4574 you will probably want to precede with @samp{0x} to specify in
4577 @item show rstack_high_address
4578 @kindex show rstack_high_address
4579 Display the current limit of the register stack, on AMD 29000 family
4584 @ifclear HviiiEXCLUSIVE
4585 @node Floating Point Hardware
4586 @section Floating point hardware
4587 @cindex floating point
4589 @c FIXME! Really host, not target?
4590 Depending on the host machine architecture, @value{GDBN} may be able to give
4591 you more information about the status of the floating point hardware.
4596 Display hardware-dependent information about the floating
4597 point unit. The exact contents and layout vary depending on the
4598 floating point chip; on some platforms, @samp{info float} is not
4601 @c FIXME: this is a cop-out. Try to get examples, explanations. Only
4602 @c FIXME...supported currently on arm's and 386's. Mark properly with
4603 @c FIXME... m4 macros to isolate general statements from hardware-dep,
4604 @c FIXME... at that point.
4609 @chapter Using @value{GDBN} with Different Languages
4612 Although programming languages generally have common aspects, they are
4613 rarely expressed in the same manner. For instance, in ANSI C,
4614 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
4615 Modula-2, it is accomplished by @code{p^}. Values can also be
4616 represented (and displayed) differently. Hex numbers in C are written
4617 like @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
4619 @cindex working language
4620 Language-specific information is built into @value{GDBN} for some languages,
4621 allowing you to express operations like the above in your program's
4622 native language, and allowing @value{GDBN} to output values in a manner
4623 consistent with the syntax of your program's native language. The
4624 language you use to build expressions, called the @dfn{working
4625 language}, can be selected manually, or @value{GDBN} can set it
4629 * Setting:: Switching between source languages
4630 * Show:: Displaying the language
4631 * Checks:: Type and range checks
4632 * Support:: Supported languages
4636 @section Switching between source languages
4638 There are two ways to control the working language---either have @value{GDBN}
4639 set it automatically, or select it manually yourself. You can use the
4640 @code{set language} command for either purpose. On startup, @value{GDBN}
4641 defaults to setting the language automatically.
4644 * Manually:: Setting the working language manually
4645 * Automatically:: Having @value{GDBN} infer the source language
4649 @subsection Setting the working language
4651 If you allow @value{GDBN} to set the language automatically,
4652 expressions are interpreted the same way in your debugging session and
4655 @kindex set language
4656 If you wish, you may set the language manually. To do this, issue the
4657 command @samp{set language @var{lang}}, where @var{lang} is the name of
4658 a language, such as @code{c} or @code{modula-2}. For a list of the supported
4659 languages, type @samp{set language}.
4660 @c FIXME: rms: eventually this command should be "help set language".
4662 Setting the language manually prevents @value{GDBN} from updating the working
4663 language automatically. This can lead to confusion if you try
4664 to debug a program when the working language is not the same as the
4665 source language, when an expression is acceptable to both
4666 languages---but means different things. For instance, if the current
4667 source file were written in C, and @value{GDBN} was parsing Modula-2, a
4675 might not have the effect you intended. In C, this means to add
4676 @code{b} and @code{c} and place the result in @code{a}. The result
4677 printed would be the value of @code{a}. In Modula-2, this means to compare
4678 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
4681 @subsection Having @value{GDBN} infer the source language
4683 To have @value{GDBN} set the working language automatically, use @samp{set
4684 language local} or @samp{set language auto}. @value{GDBN} then infers the
4685 language that a program was written in by looking at the name of its
4686 source files, and examining their extensions:
4690 Modula-2 source file
4700 This information is recorded for each function or procedure in a source
4701 file. When your program stops in a frame (usually by encountering a
4702 breakpoint), @value{GDBN} sets the working language to the language recorded
4703 for the function in that frame. If the language for a frame is unknown
4704 (that is, if the function or block corresponding to the frame was
4705 defined in a source file that does not have a recognized extension), the
4706 current working language is not changed, and @value{GDBN} issues a warning.
4708 This may not seem necessary for most programs, which are written
4709 entirely in one source language. However, program modules and libraries
4710 written in one source language can be used by a main program written in
4711 a different source language. Using @samp{set language auto} in this
4712 case frees you from having to set the working language manually.
4715 @section Displaying the language
4717 The following commands will help you find out which language is the
4718 working language, and also what language source files were written in.
4720 @kindex show language
4725 Display the current working language. This is the
4726 language you can use with commands such as @code{print} to
4727 build and compute expressions that may involve variables in your program.
4730 Among the other information listed here (@pxref{Frame Info, ,Information
4731 about a frame}) is the source language for this frame. This is the
4732 language that will become the working language if you ever use an
4733 identifier that is in this frame.
4736 Among the other information listed here (@pxref{Symbols, ,Examining the
4737 Symbol Table}) is the source language of this source file.
4741 @section Type and range checking
4744 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
4745 checking are included, but they do not yet have any effect. This
4746 section documents the intended facilities.
4748 @c FIXME remove warning when type/range code added
4750 Some languages are designed to guard you against making seemingly common
4751 errors through a series of compile- and run-time checks. These include
4752 checking the type of arguments to functions and operators, and making
4753 sure mathematical overflows are caught at run time. Checks such as
4754 these help to ensure a program's correctness once it has been compiled
4755 by eliminating type mismatches, and providing active checks for range
4756 errors when your program is running.
4758 @value{GDBN} can check for conditions like the above if you wish.
4759 Although @value{GDBN} will not check the statements in your program, it
4760 can check expressions entered directly into @value{GDBN} for evaluation via
4761 the @code{print} command, for example. As with the working language,
4762 @value{GDBN} can also decide whether or not to check automatically based on
4763 your program's source language. @xref{Support, ,Supported languages},
4764 for the default settings of supported languages.
4767 * Type Checking:: An overview of type checking
4768 * Range Checking:: An overview of range checking
4771 @cindex type checking
4772 @cindex checks, type
4774 @subsection An overview of type checking
4776 Some languages, such as Modula-2, are strongly typed, meaning that the
4777 arguments to operators and functions have to be of the correct type,
4778 otherwise an error occurs. These checks prevent type mismatch
4779 errors from ever causing any run-time problems. For example,
4787 The second example fails because the @code{CARDINAL} 1 is not
4788 type-compatible with the @code{REAL} 2.3.
4790 For expressions you use in @value{GDBN} commands, you can tell the @value{GDBN}
4791 type checker to skip checking; to treat any mismatches as errors and
4792 abandon the expression; or only issue warnings when type mismatches
4793 occur, but evaluate the expression anyway. When you choose the last of
4794 these, @value{GDBN} evaluates expressions like the second example above, but
4795 also issues a warning.
4797 Even though you may turn type checking off, other type-based reasons may
4798 prevent @value{GDBN} from evaluating an expression. For instance, @value{GDBN} does not
4799 know how to add an @code{int} and a @code{struct foo}. These particular
4800 type errors have nothing to do with the language in use, and usually
4801 arise from expressions, such as the one described above, which make
4802 little sense to evaluate anyway.
4804 Each language defines to what degree it is strict about type. For
4805 instance, both Modula-2 and C require the arguments to arithmetical
4806 operators to be numbers. In C, enumerated types and pointers can be
4807 represented as numbers, so that they are valid arguments to mathematical
4808 operators. @xref{Support, ,Supported languages}, for further
4809 details on specific languages.
4811 @value{GDBN} provides some additional commands for controlling the type checker:
4814 @kindex set check type
4815 @kindex show check type
4817 @item set check type auto
4818 Set type checking on or off based on the current working language.
4819 @xref{Support, ,Supported languages}, for the default settings for
4822 @item set check type on
4823 @itemx set check type off
4824 Set type checking on or off, overriding the default setting for the
4825 current working language. Issue a warning if the setting does not
4826 match the language default. If any type mismatches occur in
4827 evaluating an expression while typechecking is on, @value{GDBN} prints a
4828 message and aborts evaluation of the expression.
4830 @item set check type warn
4831 Cause the type checker to issue warnings, but to always attempt to
4832 evaluate the expression. Evaluating the expression may still
4833 be impossible for other reasons. For example, @value{GDBN} cannot add
4834 numbers and structures.
4837 Show the current setting of the type checker, and whether or not @value{GDBN} is
4838 setting it automatically.
4841 @cindex range checking
4842 @cindex checks, range
4843 @node Range Checking
4844 @subsection An overview of range checking
4846 In some languages (such as Modula-2), it is an error to exceed the
4847 bounds of a type; this is enforced with run-time checks. Such range
4848 checking is meant to ensure program correctness by making sure
4849 computations do not overflow, or indices on an array element access do
4850 not exceed the bounds of the array.
4852 For expressions you use in @value{GDBN} commands, you can tell
4853 @value{GDBN} to treat range errors in one of three ways: ignore them,
4854 always treat them as errors and abandon the expression, or issue
4855 warnings but evaluate the expression anyway.
4857 A range error can result from numerical overflow, from exceeding an
4858 array index bound, or when you type a constant that is not a member
4859 of any type. Some languages, however, do not treat overflows as an
4860 error. In many implementations of C, mathematical overflow causes the
4861 result to ``wrap around'' to lower values---for example, if @var{m} is
4862 the largest integer value, and @var{s} is the smallest, then
4865 @var{m} + 1 @result{} @var{s}
4868 This, too, is specific to individual languages, and in some cases
4869 specific to individual compilers or machines. @xref{Support, ,
4870 Supported languages}, for further details on specific languages.
4872 @value{GDBN} provides some additional commands for controlling the range checker:
4875 @kindex set check range
4876 @kindex show check range
4878 @item set check range auto
4879 Set range checking on or off based on the current working language.
4880 @xref{Support, ,Supported languages}, for the default settings for
4883 @item set check range on
4884 @itemx set check range off
4885 Set range checking on or off, overriding the default setting for the
4886 current working language. A warning is issued if the setting does not
4887 match the language default. If a range error occurs, then a message
4888 is printed and evaluation of the expression is aborted.
4890 @item set check range warn
4891 Output messages when the @value{GDBN} range checker detects a range error,
4892 but attempt to evaluate the expression anyway. Evaluating the
4893 expression may still be impossible for other reasons, such as accessing
4894 memory that the process does not own (a typical example from many UNIX
4898 Show the current setting of the range checker, and whether or not it is
4899 being set automatically by @value{GDBN}.
4903 @section Supported languages
4905 @value{GDBN} 4 supports C, C++, and Modula-2. Some @value{GDBN}
4906 features may be used in expressions regardless of the language you
4907 use: the @value{GDBN} @code{@@} and @code{::} operators, and the
4908 @samp{@{type@}addr} construct (@pxref{Expressions, ,Expressions}) can be
4909 used with the constructs of any of the supported languages.
4911 The following sections detail to what degree each of these
4912 source languages is supported by @value{GDBN}. These sections are
4913 not meant to be language tutorials or references, but serve only as a
4914 reference guide to what the @value{GDBN} expression parser will accept, and
4915 what input and output formats should look like for different languages.
4916 There are many good books written on each of these languages; please
4917 look to these for a language reference or tutorial.
4921 * Modula-2:: Modula-2
4925 @subsection C and C++
4927 @cindex expressions in C or C++
4929 Since C and C++ are so closely related, many features of @value{GDBN} apply
4930 to both languages. Whenever this is the case, we discuss both languages
4936 The C++ debugging facilities are jointly implemented by the GNU C++
4937 compiler and @value{GDBN}. Therefore, to debug your C++ code effectively,
4938 you must compile your C++ programs with the GNU C++ compiler,
4943 @chapter C Language Support
4945 @cindex expressions in C
4947 Information specific to the C language is built into @value{GDBN} so that you
4948 can use C expressions while degugging. This also permits @value{GDBN} to
4949 output values in a manner consistent with C conventions.
4952 * C Operators:: C operators
4953 * C Constants:: C constants
4954 * Debugging C:: @value{GDBN} and C
4959 * C Operators:: C and C++ operators
4960 * C Constants:: C and C++ constants
4961 * Cplus expressions:: C++ expressions
4962 * C Defaults:: Default settings for C and C++
4963 * C Checks:: C and C++ type and range checks
4964 * Debugging C:: @value{GDBN} and C
4965 * Debugging C plus plus:: Special features for C++
4970 @cindex C and C++ operators
4972 @subsubsection C and C++ operators
4977 @section C operators
4980 Operators must be defined on values of specific types. For instance,
4981 @code{+} is defined on numbers, but not on structures. Operators are
4982 often defined on groups of types.
4985 For the purposes of C and C++, the following definitions hold:
4990 @emph{Integral types} include @code{int} with any of its storage-class
4991 specifiers; @code{char}; and @code{enum}.
4994 @emph{Floating-point types} include @code{float} and @code{double}.
4997 @emph{Pointer types} include all types defined as @code{(@var{type}
5001 @emph{Scalar types} include all of the above.
5005 The following operators are supported. They are listed here
5006 in order of increasing precedence:
5010 The comma or sequencing operator. Expressions in a comma-separated list
5011 are evaluated from left to right, with the result of the entire
5012 expression being the last expression evaluated.
5015 Assignment. The value of an assignment expression is the value
5016 assigned. Defined on scalar types.
5019 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5020 and translated to @w{@code{@var{a} = @var{a op b}}}.
5021 @w{@code{@var{op}=}} and @code{=} have the same precendence.
5022 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5023 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5026 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5027 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5031 Logical @sc{or}. Defined on integral types.
5034 Logical @sc{and}. Defined on integral types.
5037 Bitwise @sc{or}. Defined on integral types.
5040 Bitwise exclusive-@sc{or}. Defined on integral types.
5043 Bitwise @sc{and}. Defined on integral types.
5046 Equality and inequality. Defined on scalar types. The value of these
5047 expressions is 0 for false and non-zero for true.
5049 @item <@r{, }>@r{, }<=@r{, }>=
5050 Less than, greater than, less than or equal, greater than or equal.
5051 Defined on scalar types. The value of these expressions is 0 for false
5052 and non-zero for true.
5055 left shift, and right shift. Defined on integral types.
5058 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5061 Addition and subtraction. Defined on integral types, floating-point types and
5064 @item *@r{, }/@r{, }%
5065 Multiplication, division, and modulus. Multiplication and division are
5066 defined on integral and floating-point types. Modulus is defined on
5070 Increment and decrement. When appearing before a variable, the
5071 operation is performed before the variable is used in an expression;
5072 when appearing after it, the variable's value is used before the
5073 operation takes place.
5076 Pointer dereferencing. Defined on pointer types. Same precedence as
5080 Address operator. Defined on variables. Same precedence as @code{++}.
5083 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5084 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5085 (or, if you prefer, simply @samp{&&@var{ref}} to examine the address
5086 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5091 Negative. Defined on integral and floating-point types. Same
5092 precedence as @code{++}.
5095 Logical negation. Defined on integral types. Same precedence as
5099 Bitwise complement operator. Defined on integral types. Same precedence as
5104 Structure member, and pointer-to-structure member. For convenience,
5105 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5106 pointer based on the stored type information.
5107 Defined on @code{struct} and @code{union} data.
5110 Array indexing. @code{@var{a}[@var{i}]} is defined as
5111 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5114 Function parameter list. Same precedence as @code{->}.
5118 C++ scope resolution operator. Defined on
5119 @code{struct}, @code{union}, and @code{class} types.
5127 represent the @value{GDBN} scope operator (@pxref{Expressions,
5130 Same precedence as @code{::}, above.
5135 @cindex C and C++ constants
5137 @subsubsection C and C++ constants
5139 @value{GDBN} allows you to express the constants of C and C++ in the
5145 @section C constants
5147 @value{GDBN} allows you to express the constants of C in the
5153 Integer constants are a sequence of digits. Octal constants are
5154 specified by a leading @samp{0} (ie. zero), and hexadecimal constants by
5155 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5156 @samp{l}, specifying that the constant should be treated as a
5160 Floating point constants are a sequence of digits, followed by a decimal
5161 point, followed by a sequence of digits, and optionally followed by an
5162 exponent. An exponent is of the form:
5163 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5164 sequence of digits. The @samp{+} is optional for positive exponents.
5167 Enumerated constants consist of enumerated identifiers, or their
5168 integral equivalents.
5171 Character constants are a single character surrounded by single quotes
5172 (@code{'}), or a number---the ordinal value of the corresponding character
5173 (usually its @sc{ASCII} value). Within quotes, the single character may
5174 be represented by a letter or by @dfn{escape sequences}, which are of
5175 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
5176 of the character's ordinal value; or of the form @samp{\@var{x}}, where
5177 @samp{@var{x}} is a predefined special character---for example,
5178 @samp{\n} for newline.
5181 String constants are a sequence of character constants surrounded
5182 by double quotes (@code{"}).
5185 Pointer constants are an integral value. You can also write pointers
5186 to constants using the C operator @samp{&}.
5189 Array constants are comma-separated lists surrounded by braces @samp{@{}
5190 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
5191 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
5192 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
5196 @node Cplus expressions
5197 @subsubsection C++ expressions
5199 @cindex expressions in C++
5200 @value{GDBN} expression handling has a number of extensions to
5201 interpret a significant subset of C++ expressions.
5203 @cindex C++ support, not in @sc{coff}
5204 @cindex @sc{coff} versus C++
5205 @cindex C++ and object formats
5206 @cindex object formats and C++
5207 @cindex a.out and C++
5208 @cindex @sc{ecoff} and C++
5209 @cindex @sc{xcoff} and C++
5210 @cindex @sc{elf}/stabs and C++
5211 @cindex @sc{elf}/@sc{dwarf} and C++
5213 @emph{Warning:} Most of these extensions depend on the use of additional
5214 debugging information in the symbol table, and thus require a rich,
5215 extendable object code format. In particular, if your system uses
5216 a.out, MIPS @sc{ecoff}, RS/6000 @sc{xcoff}, or Sun @sc{elf} with stabs
5217 extensions to the symbol table, these facilities are all available.
5218 Where the object code format is standard @sc{coff}, on the other hand,
5219 most of the C++ support in @value{GDBN} will @emph{not} work, nor can it.
5220 For the standard SVr4 debugging format, @sc{dwarf} in @sc{elf}, the
5221 standard is still evolving, so the C++ support in @value{GDBN} is still
5222 fragile; when this debugging format stabilizes, however, C++ support
5223 will also be available on systems that use it.
5228 @cindex member functions
5230 Member function calls are allowed; you can use expressions like
5233 count = aml->GetOriginal(x, y)
5237 @cindex namespace in C++
5239 While a member function is active (in the selected stack frame), your
5240 expressions have the same namespace available as the member function;
5241 that is, @value{GDBN} allows implicit references to the class instance
5242 pointer @code{this} following the same rules as C++.
5244 @cindex call overloaded functions
5245 @cindex type conversions in C++
5247 You can call overloaded functions; @value{GDBN} will resolve the function
5248 call to the right definition, with one restriction---you must use
5249 arguments of the type required by the function that you want to call.
5250 @value{GDBN} will not perform conversions requiring constructors or
5251 user-defined type operators.
5253 @cindex reference declarations
5255 @value{GDBN} understands variables declared as C++ references; you can use them in
5256 expressions just as you do in C++ source---they are automatically
5259 In the parameter list shown when @value{GDBN} displays a frame, the values of
5260 reference variables are not displayed (unlike other variables); this
5261 avoids clutter, since references are often used for large structures.
5262 The @emph{address} of a reference variable is always shown, unless
5263 you have specified @samp{set print address off}.
5266 @value{GDBN} supports the C++ name resolution operator @code{::}---your
5267 expressions can use it just as expressions in your program do. Since
5268 one scope may be defined in another, you can use @code{::} repeatedly if
5269 necessary, for example in an expression like
5270 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
5271 resolving name scope by reference to source files, in both C and C++
5272 debugging (@pxref{Variables, ,Program variables}).
5276 @subsubsection C and C++ defaults
5277 @cindex C and C++ defaults
5279 If you allow @value{GDBN} to set type and range checking automatically, they
5280 both default to @code{off} whenever the working language changes to
5281 C or C++. This happens regardless of whether you, or @value{GDBN},
5282 selected the working language.
5284 If you allow @value{GDBN} to set the language automatically, it sets the
5285 working language to C or C++ on entering code compiled from a source file
5286 whose name ends with @file{.c}, @file{.C}, or @file{.cc}.
5287 @xref{Automatically, ,Having @value{GDBN} infer the source language}, for
5291 @subsubsection C and C++ type and range checks
5292 @cindex C and C++ checks
5294 By default, when @value{GDBN} parses C or C++ expressions, type checking
5295 is not used. However, if you turn type checking on, @value{GDBN} will
5296 consider two variables type equivalent if:
5300 The two variables are structured and have the same structure, union, or
5304 Two two variables have the same type name, or types that have been
5305 declared equivalent through @code{typedef}.
5308 @c leaving this out because neither J Gilmore nor R Pesch understand it.
5311 The two @code{struct}, @code{union}, or @code{enum} variables are
5312 declared in the same declaration. (Note: this may not be true for all C
5317 Range checking, if turned on, is done on mathematical operations. Array
5318 indices are not checked, since they are often used to index a pointer
5319 that is not itself an array.
5324 @subsubsection @value{GDBN} and C
5328 @section @value{GDBN} and C
5331 The @code{set print union} and @code{show print union} commands apply to
5332 the @code{union} type. When set to @samp{on}, any @code{union} that is
5333 inside a @code{struct}
5337 will also be printed.
5338 Otherwise, it will appear as @samp{@{...@}}.
5340 The @code{@@} operator aids in the debugging of dynamic arrays, formed
5341 with pointers and a memory allocation function. @xref{Expressions,
5345 @node Debugging C plus plus
5346 @subsubsection @value{GDBN} features for C++
5348 @cindex commands for C++
5349 Some @value{GDBN} commands are particularly useful with C++, and some are
5350 designed specifically for use with C++. Here is a summary:
5353 @cindex break in overloaded functions
5354 @item @r{breakpoint menus}
5355 When you want a breakpoint in a function whose name is overloaded,
5356 @value{GDBN} breakpoint menus help you specify which function definition
5357 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
5359 @cindex overloading in C++
5360 @item rbreak @var{regex}
5361 Setting breakpoints using regular expressions is helpful for setting
5362 breakpoints on overloaded functions that are not members of any special
5364 @xref{Set Breaks, ,Setting breakpoints}.
5366 @cindex C++ exception handling
5367 @item catch @var{exceptions}
5369 Debug C++ exception handling using these commands. @xref{Exception
5370 Handling, ,Breakpoints and exceptions}.
5373 @item ptype @var{typename}
5374 Print inheritance relationships as well as other information for type
5376 @xref{Symbols, ,Examining the Symbol Table}.
5378 @cindex C++ symbol display
5379 @item set print demangle
5380 @itemx show print demangle
5381 @itemx set print asm-demangle
5382 @itemx show print asm-demangle
5383 Control whether C++ symbols display in their source form, both when
5384 displaying code as C++ source and when displaying disassemblies.
5385 @xref{Print Settings, ,Print settings}.
5387 @item set print object
5388 @itemx show print object
5389 Choose whether to print derived (actual) or declared types of objects.
5390 @xref{Print Settings, ,Print settings}.
5392 @item set print vtbl
5393 @itemx show print vtbl
5394 Control the format for printing virtual function tables.
5395 @xref{Print Settings, ,Print settings}.
5397 @item @r{Overloaded symbol names}
5398 You can specify a particular definition of an overloaded symbol, using
5399 the same notation that is used to declare such symbols in C++: type
5400 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
5401 also use the @value{GDBN} command-line word completion facilities to list the
5402 available choices, or to finish the type list for you.
5403 @xref{Completion,, Command completion}, for details on how to do this.
5407 @subsection Modula-2
5410 The extensions made to @value{GDBN} to support Modula-2 only support
5411 output from the GNU Modula-2 compiler (which is currently being
5412 developed). Other Modula-2 compilers are not currently supported, and
5413 attempting to debug executables produced by them will most likely
5414 result in an error as @value{GDBN} reads in the executable's symbol
5417 @cindex expressions in Modula-2
5419 * M2 Operators:: Built-in operators
5420 * Built-In Func/Proc:: Built-in functions and procedures
5421 * M2 Constants:: Modula-2 constants
5422 * M2 Defaults:: Default settings for Modula-2
5423 * Deviations:: Deviations from standard Modula-2
5424 * M2 Checks:: Modula-2 type and range checks
5425 * M2 Scope:: The scope operators @code{::} and @code{.}
5426 * GDB/M2:: @value{GDBN} and Modula-2
5430 @subsubsection Operators
5431 @cindex Modula-2 operators
5433 Operators must be defined on values of specific types. For instance,
5434 @code{+} is defined on numbers, but not on structures. Operators are
5435 often defined on groups of types. For the purposes of Modula-2, the
5436 following definitions hold:
5441 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
5445 @emph{Character types} consist of @code{CHAR} and its subranges.
5448 @emph{Floating-point types} consist of @code{REAL}.
5451 @emph{Pointer types} consist of anything declared as @code{POINTER TO
5455 @emph{Scalar types} consist of all of the above.
5458 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
5461 @emph{Boolean types} consist of @code{BOOLEAN}.
5465 The following operators are supported, and appear in order of
5466 increasing precedence:
5470 Function argument or array index separator.
5473 Assignment. The value of @var{var} @code{:=} @var{value} is
5477 Less than, greater than on integral, floating-point, or enumerated
5481 Less than, greater than, less than or equal to, greater than or equal to
5482 on integral, floating-point and enumerated types, or set inclusion on
5483 set types. Same precedence as @code{<}.
5485 @item =@r{, }<>@r{, }#
5486 Equality and two ways of expressing inequality, valid on scalar types.
5487 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
5488 available for inequality, since @code{#} conflicts with the script
5492 Set membership. Defined on set types and the types of their members.
5493 Same precedence as @code{<}.
5496 Boolean disjunction. Defined on boolean types.
5499 Boolean conjuction. Defined on boolean types.
5502 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5505 Addition and subtraction on integral and floating-point types, or union
5506 and difference on set types.
5509 Multiplication on integral and floating-point types, or set intersection
5513 Division on floating-point types, or symmetric set difference on set
5514 types. Same precedence as @code{*}.
5517 Integer division and remainder. Defined on integral types. Same
5518 precedence as @code{*}.
5521 Negative. Defined on @code{INTEGER} and @code{REAL} data.
5524 Pointer dereferencing. Defined on pointer types.
5527 Boolean negation. Defined on boolean types. Same precedence as
5531 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
5532 precedence as @code{^}.
5535 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
5538 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
5542 @value{GDBN} and Modula-2 scope operators.
5546 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
5547 will treat the use of the operator @code{IN}, or the use of operators
5548 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
5549 @code{<=}, and @code{>=} on sets as an error.
5552 @cindex Modula-2 built-ins
5553 @node Built-In Func/Proc
5554 @subsubsection Built-in functions and procedures
5556 Modula-2 also makes available several built-in procedures and functions.
5557 In describing these, the following metavariables are used:
5562 represents an @code{ARRAY} variable.
5565 represents a @code{CHAR} constant or variable.
5568 represents a variable or constant of integral type.
5571 represents an identifier that belongs to a set. Generally used in the
5572 same function with the metavariable @var{s}. The type of @var{s} should
5573 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}.
5576 represents a variable or constant of integral or floating-point type.
5579 represents a variable or constant of floating-point type.
5585 represents a variable.
5588 represents a variable or constant of one of many types. See the
5589 explanation of the function for details.
5592 All Modula-2 built-in procedures also return a result, described below.
5596 Returns the absolute value of @var{n}.
5599 If @var{c} is a lower case letter, it returns its upper case
5600 equivalent, otherwise it returns its argument
5603 Returns the character whose ordinal value is @var{i}.
5606 Decrements the value in the variable @var{v}. Returns the new value.
5608 @item DEC(@var{v},@var{i})
5609 Decrements the value in the variable @var{v} by @var{i}. Returns the
5612 @item EXCL(@var{m},@var{s})
5613 Removes the element @var{m} from the set @var{s}. Returns the new
5616 @item FLOAT(@var{i})
5617 Returns the floating point equivalent of the integer @var{i}.
5620 Returns the index of the last member of @var{a}.
5623 Increments the value in the variable @var{v}. Returns the new value.
5625 @item INC(@var{v},@var{i})
5626 Increments the value in the variable @var{v} by @var{i}. Returns the
5629 @item INCL(@var{m},@var{s})
5630 Adds the element @var{m} to the set @var{s} if it is not already
5631 there. Returns the new set.
5634 Returns the maximum value of the type @var{t}.
5637 Returns the minimum value of the type @var{t}.
5640 Returns boolean TRUE if @var{i} is an odd number.
5643 Returns the ordinal value of its argument. For example, the ordinal
5644 value of a character is its ASCII value (on machines supporting the
5645 ASCII character set). @var{x} must be of an ordered type, which include
5646 integral, character and enumerated types.
5649 Returns the size of its argument. @var{x} can be a variable or a type.
5651 @item TRUNC(@var{r})
5652 Returns the integral part of @var{r}.
5654 @item VAL(@var{t},@var{i})
5655 Returns the member of the type @var{t} whose ordinal value is @var{i}.
5659 @emph{Warning:} Sets and their operations are not yet supported, so
5660 @value{GDBN} will treat the use of procedures @code{INCL} and @code{EXCL} as
5664 @cindex Modula-2 constants
5666 @subsubsection Constants
5668 @value{GDBN} allows you to express the constants of Modula-2 in the following
5674 Integer constants are simply a sequence of digits. When used in an
5675 expression, a constant is interpreted to be type-compatible with the
5676 rest of the expression. Hexadecimal integers are specified by a
5677 trailing @samp{H}, and octal integers by a trailing @samp{B}.
5680 Floating point constants appear as a sequence of digits, followed by a
5681 decimal point and another sequence of digits. An optional exponent can
5682 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
5683 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
5684 digits of the floating point constant must be valid decimal (base 10)
5688 Character constants consist of a single character enclosed by a pair of
5689 like quotes, either single (@code{'}) or double (@code{"}). They may
5690 also be expressed by their ordinal value (their ASCII value, usually)
5691 followed by a @samp{C}.
5694 String constants consist of a sequence of characters enclosed by a
5695 pair of like quotes, either single (@code{'}) or double (@code{"}).
5696 Escape sequences in the style of C are also allowed. @xref{C
5697 Constants, ,C and C++ constants}, for a brief explanation of escape
5701 Enumerated constants consist of an enumerated identifier.
5704 Boolean constants consist of the identifiers @code{TRUE} and
5708 Pointer constants consist of integral values only.
5711 Set constants are not yet supported.
5715 @subsubsection Modula-2 defaults
5716 @cindex Modula-2 defaults
5718 If type and range checking are set automatically by @value{GDBN}, they
5719 both default to @code{on} whenever the working language changes to
5720 Modula-2. This happens regardless of whether you, or @value{GDBN},
5721 selected the working language.
5723 If you allow @value{GDBN} to set the language automatically, then entering
5724 code compiled from a file whose name ends with @file{.mod} will set the
5725 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
5726 the language automatically}, for further details.
5729 @subsubsection Deviations from standard Modula-2
5730 @cindex Modula-2, deviations from
5732 A few changes have been made to make Modula-2 programs easier to debug.
5733 This is done primarily via loosening its type strictness:
5737 Unlike in standard Modula-2, pointer constants can be formed by
5738 integers. This allows you to modify pointer variables during
5739 debugging. (In standard Modula-2, the actual address contained in a
5740 pointer variable is hidden from you; it can only be modified
5741 through direct assignment to another pointer variable or expression that
5742 returned a pointer.)
5745 C escape sequences can be used in strings and characters to represent
5746 non-printable characters. @value{GDBN} will print out strings with these
5747 escape sequences embedded. Single non-printable characters are
5748 printed using the @samp{CHR(@var{nnn})} format.
5751 The assignment operator (@code{:=}) returns the value of its right-hand
5755 All built-in procedures both modify @emph{and} return their argument.
5759 @subsubsection Modula-2 type and range checks
5760 @cindex Modula-2 checks
5763 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
5766 @c FIXME remove warning when type/range checks added
5768 @value{GDBN} considers two Modula-2 variables type equivalent if:
5772 They are of types that have been declared equivalent via a @code{TYPE
5773 @var{t1} = @var{t2}} statement
5776 They have been declared on the same line. (Note: This is true of the
5777 GNU Modula-2 compiler, but it may not be true of other compilers.)
5780 As long as type checking is enabled, any attempt to combine variables
5781 whose types are not equivalent is an error.
5783 Range checking is done on all mathematical operations, assignment, array
5784 index bounds, and all built-in functions and procedures.
5787 @subsubsection The scope operators @code{::} and @code{.}
5790 @cindex colon, doubled as scope operator
5793 @c Info cannot handle :: but TeX can.
5799 There are a few subtle differences between the Modula-2 scope operator
5800 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
5805 @var{module} . @var{id}
5806 @var{scope} :: @var{id}
5810 where @var{scope} is the name of a module or a procedure,
5811 @var{module} the name of a module, and @var{id} is any declared
5812 identifier within your program, except another module.
5814 Using the @code{::} operator makes @value{GDBN} search the scope
5815 specified by @var{scope} for the identifier @var{id}. If it is not
5816 found in the specified scope, then @value{GDBN} will search all scopes
5817 enclosing the one specified by @var{scope}.
5819 Using the @code{.} operator makes @value{GDBN} search the current scope for
5820 the identifier specified by @var{id} that was imported from the
5821 definition module specified by @var{module}. With this operator, it is
5822 an error if the identifier @var{id} was not imported from definition
5823 module @var{module}, or if @var{id} is not an identifier in
5827 @subsubsection @value{GDBN} and Modula-2
5829 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
5830 Five subcommands of @code{set print} and @code{show print} apply
5831 specifically to C and C++: @samp{vtbl}, @samp{demangle},
5832 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
5833 apply to C++, and the last to the C @code{union} type, which has no direct
5834 analogue in Modula-2.
5836 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
5837 while using any language, is not useful with Modula-2. Its
5838 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
5839 created in Modula-2 as they can in C or C++. However, because an
5840 address can be specified by an integral constant, the construct
5841 @samp{@{@var{type}@}@var{adrexp}} is still useful. (@pxref{Expressions, ,Expressions})
5843 @cindex @code{#} in Modula-2
5844 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
5845 interpreted as the beginning of a comment. Use @code{<>} instead.
5850 @chapter Examining the Symbol Table
5852 The commands described in this section allow you to inquire about the
5853 symbols (names of variables, functions and types) defined in your
5854 program. This information is inherent in the text of your program and
5855 does not change as your program executes. @value{GDBN} finds it in your
5856 program's symbol table, in the file indicated when you started @value{GDBN}
5857 (@pxref{File Options, ,Choosing files}), or by one of the
5858 file-management commands (@pxref{Files, ,Commands to specify files}).
5860 @c FIXME! This might be intentionally specific to C and C++; if so, move
5861 @c to someplace in C section of lang chapter.
5862 @cindex symbol names
5863 @cindex names of symbols
5864 @cindex quoting names
5865 Occasionally, you may need to refer to symbols that contain unusual
5866 characters, which @value{GDBN} ordinarily treats as word delimiters. The
5867 most frequent case is in referring to static variables in other
5868 source files (@pxref{Variables,,Program variables}). File names
5869 are recorded in object files as debugging symbols, but @value{GDBN} would
5870 ordinarily parse a typical file name, like @file{foo.c}, as the three words
5871 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
5872 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
5879 looks up the value of @code{x} in the scope of the file @file{foo.c}.
5882 @item info address @var{symbol}
5883 @kindex info address
5884 Describe where the data for @var{symbol} is stored. For a register
5885 variable, this says which register it is kept in. For a non-register
5886 local variable, this prints the stack-frame offset at which the variable
5889 Note the contrast with @samp{print &@var{symbol}}, which does not work
5890 at all for a register variables, and for a stack local variable prints
5891 the exact address of the current instantiation of the variable.
5893 @item whatis @var{exp}
5895 Print the data type of expression @var{exp}. @var{exp} is not
5896 actually evaluated, and any side-effecting operations (such as
5897 assignments or function calls) inside it do not take place.
5898 @xref{Expressions, ,Expressions}.
5901 Print the data type of @code{$}, the last value in the value history.
5903 @item ptype @var{typename}
5905 Print a description of data type @var{typename}. @var{typename} may be
5906 the name of a type, or for C code it may have the form
5907 @samp{struct @var{struct-tag}}, @samp{union @var{union-tag}} or
5908 @samp{enum @var{enum-tag}}.
5910 @item ptype @var{exp}
5912 Print a description of the type of expression @var{exp}. @code{ptype}
5913 differs from @code{whatis} by printing a detailed description, instead
5914 of just the name of the type.
5916 For example, for this variable declaration:
5919 struct complex @{double real; double imag;@} v;
5923 the two commands give this output:
5927 (@value{GDBP}) whatis v
5928 type = struct complex
5929 (@value{GDBP}) ptype v
5930 type = struct complex @{
5938 As with @code{whatis}, using @code{ptype} without an argument refers to
5939 the type of @code{$}, the last value in the value history.
5941 @item info types @var{regexp}
5944 Print a brief description of all types whose name matches @var{regexp}
5945 (or all types in your program, if you supply no argument). Each
5946 complete typename is matched as though it were a complete line; thus,
5947 @samp{i type value} gives information on all types in your program whose
5948 name includes the string @code{value}, but @samp{i type ^value$} gives
5949 information only on types whose complete name is @code{value}.
5951 This command differs from @code{ptype} in two ways: first, like
5952 @code{whatis}, it does not print a detailed description; second, it
5953 lists all source files where a type is defined.
5957 Show the name of the current source file---that is, the source file for
5958 the function containing the current point of execution---and the language
5962 @kindex info sources
5963 Print the names of all source files in your program for which there is
5964 debugging information, organized into two lists: files whose symbols
5965 have already been read, and files whose symbols will be read when needed.
5967 @item info functions
5968 @kindex info functions
5969 Print the names and data types of all defined functions.
5971 @item info functions @var{regexp}
5972 Print the names and data types of all defined functions
5973 whose names contain a match for regular expression @var{regexp}.
5974 Thus, @samp{info fun step} finds all functions whose names
5975 include @code{step}; @samp{info fun ^step} finds those whose names
5976 start with @code{step}.
5978 @item info variables
5979 @kindex info variables
5980 Print the names and data types of all variables that are declared
5981 outside of functions (i.e., excluding local variables).
5983 @item info variables @var{regexp}
5984 Print the names and data types of all variables (except for local
5985 variables) whose names contain a match for regular expression
5989 This was never implemented.
5991 @itemx info methods @var{regexp}
5992 @kindex info methods
5993 The @code{info methods} command permits the user to examine all defined
5994 methods within C++ program, or (with the @var{regexp} argument) a
5995 specific set of methods found in the various C++ classes. Many
5996 C++ classes provide a large number of methods. Thus, the output
5997 from the @code{ptype} command can be overwhelming and hard to use. The
5998 @code{info-methods} command filters the methods, printing only those
5999 which match the regular-expression @var{regexp}.
6002 @item maint print symbols @var{filename}
6003 @itemx maint print psymbols @var{filename}
6004 @itemx maint print msymbols @var{filename}
6005 @kindex maint print symbols
6007 @kindex maint print psymbols
6008 @cindex partial symbol dump
6009 Write a dump of debugging symbol data into the file @var{filename}.
6010 These commands are used to debug the @value{GDBN} symbol-reading code. Only
6011 symbols with debugging data are included. If you use @samp{maint print
6012 symbols}, @value{GDBN} includes all the symbols for which it has already
6013 collected full details: that is, @var{filename} reflects symbols for
6014 only those files whose symbols @value{GDBN} has read. You can use the
6015 command @code{info sources} to find out which files these are. If you
6016 use @samp{maint print psymbols} instead, the dump shows information about
6017 symbols that @value{GDBN} only knows partially---that is, symbols defined in
6018 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
6019 @samp{maint print msymbols} dumps just the minimal symbol information
6020 required for each object file from which @value{GDBN} has read some symbols.
6021 The description of @code{symbol-file} explains how @value{GDBN} reads
6022 symbols; both @code{info source} and @code{symbol-file} are described in
6023 @ref{Files, ,Commands to specify files}.
6027 @chapter Altering Execution
6029 Once you think you have found an error in your program, you might want to
6030 find out for certain whether correcting the apparent error would lead to
6031 correct results in the rest of the run. You can find the answer by
6032 experiment, using the @value{GDBN} features for altering execution of the
6035 For example, you can store new values into variables or memory
6038 give your program a signal, restart it
6041 restart your program
6043 at a different address, or even return prematurely from a function to
6047 * Assignment:: Assignment to variables
6048 * Jumping:: Continuing at a different address
6050 * Signaling:: Giving your program a signal
6053 * Returning:: Returning from a function
6054 * Calling:: Calling your program's functions
6055 * Patching:: Patching your program
6059 @section Assignment to variables
6062 @cindex setting variables
6063 To alter the value of a variable, evaluate an assignment expression.
6064 @xref{Expressions, ,Expressions}. For example,
6071 stores the value 4 into the variable @code{x}, and then prints the
6072 value of the assignment expression (which is 4).
6074 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
6075 information on operators in supported languages.
6078 @kindex set variable
6079 @cindex variables, setting
6080 If you are not interested in seeing the value of the assignment, use the
6081 @code{set} command instead of the @code{print} command. @code{set} is
6082 really the same as @code{print} except that the expression's value is
6083 not printed and is not put in the value history (@pxref{Value History,
6084 ,Value history}). The expression is evaluated only for its effects.
6086 If the beginning of the argument string of the @code{set} command
6087 appears identical to a @code{set} subcommand, use the @code{set
6088 variable} command instead of just @code{set}. This command is identical
6089 to @code{set} except for its lack of subcommands. For example, if
6090 your program has a variable @code{width}, you get
6091 an error if you try to set a new value with just @samp{set width=13},
6092 because @value{GDBN} has the command @code{set width}:
6095 (@value{GDBP}) whatis width
6097 (@value{GDBP}) p width
6099 (@value{GDBP}) set width=47
6100 Invalid syntax in expression.
6104 The invalid expression, of course, is @samp{=47}. In
6105 order to actually set the program's variable @code{width}, use
6108 (@value{GDBP}) set var width=47
6111 @value{GDBN} allows more implicit conversions in assignments than C; you can
6112 freely store an integer value into a pointer variable or vice versa,
6113 and you can convert any structure to any other structure that is the
6114 same length or shorter.
6115 @comment FIXME: how do structs align/pad in these conversions?
6116 @comment /pesch@cygnus.com 18dec1990
6118 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
6119 construct to generate a value of specified type at a specified address
6120 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
6121 to memory location @code{0x83040} as an integer (which implies a certain size
6122 and representation in memory), and
6125 set @{int@}0x83040 = 4
6129 stores the value 4 into that memory location.
6132 @section Continuing at a different address
6134 Ordinarily, when you continue your program, you do so at the place where
6135 it stopped, with the @code{continue} command. You can instead continue at
6136 an address of your own choosing, with the following commands:
6139 @item jump @var{linespec}
6141 Resume execution at line @var{linespec}. Execution will stop
6142 immediately if there is a breakpoint there. @xref{List, ,Printing
6143 source lines}, for a description of the different forms of
6146 The @code{jump} command does not change the current stack frame, or
6147 the stack pointer, or the contents of any memory location or any
6148 register other than the program counter. If line @var{linespec} is in
6149 a different function from the one currently executing, the results may
6150 be bizarre if the two functions expect different patterns of arguments or
6151 of local variables. For this reason, the @code{jump} command requests
6152 confirmation if the specified line is not in the function currently
6153 executing. However, even bizarre results are predictable if you are
6154 well acquainted with the machine-language code of your program.
6156 @item jump *@var{address}
6157 Resume execution at the instruction at address @var{address}.
6160 You can get much the same effect as the @code{jump} command by storing a
6161 new value into the register @code{$pc}. The difference is that this
6162 does not start your program running; it only changes the address where it
6163 @emph{will} run when it is continued. For example,
6170 causes the next @code{continue} command or stepping command to execute at
6171 address @code{0x485}, rather than at the address where your program stopped.
6172 @xref{Continuing and Stepping, ,Continuing and stepping}.
6174 The most common occasion to use the @code{jump} command is to back up,
6175 perhaps with more breakpoints set, over a portion of a program that has
6176 already executed, in order to examine its execution in more detail.
6181 @section Giving your program a signal
6184 @item signal @var{signalnum}
6186 Resume execution where your program stopped, but give it immediately the
6187 signal number @var{signalnum}.
6189 Alternatively, if @var{signalnum} is zero, continue execution without
6190 giving a signal. This is useful when your program stopped on account of
6191 a signal and would ordinary see the signal when resumed with the
6192 @code{continue} command; @samp{signal 0} causes it to resume without a
6195 @code{signal} does not repeat when you press @key{RET} a second time
6196 after executing the command.
6202 @section Returning from a function
6206 @itemx return @var{expression}
6207 @cindex returning from a function
6209 You can cancel execution of a function call with the @code{return}
6210 command. If you give an
6211 @var{expression} argument, its value is used as the function's return
6215 When you use @code{return}, @value{GDBN} discards the selected stack frame
6216 (and all frames within it). You can think of this as making the
6217 discarded frame return prematurely. If you wish to specify a value to
6218 be returned, give that value as the argument to @code{return}.
6220 This pops the selected stack frame (@pxref{Selection, ,Selecting a
6221 frame}), and any other frames inside of it, leaving its caller as the
6222 innermost remaining frame. That frame becomes selected. The
6223 specified value is stored in the registers used for returning values
6226 The @code{return} command does not resume execution; it leaves the
6227 program stopped in the state that would exist if the function had just
6228 returned. In contrast, the @code{finish} command (@pxref{Continuing
6229 and Stepping, ,Continuing and stepping}) resumes execution until the
6230 selected stack frame returns naturally.
6233 @section Calling program functions
6235 @cindex calling functions
6238 @item call @var{expr}
6239 Evaluate the expression @var{expr} without displaying @code{void}
6243 You can use this variant of the @code{print} command if you want to
6244 execute a function from your program, but without cluttering the output
6245 with @code{void} returned values. The result is printed and saved in
6246 the value history, if it is not void.
6249 @section Patching programs
6250 @cindex patching binaries
6251 @cindex writing into executables
6253 @cindex writing into corefiles
6256 By default, @value{GDBN} opens the file containing your program's executable
6261 read-only. This prevents accidental alterations
6262 to machine code; but it also prevents you from intentionally patching
6263 your program's binary.
6265 If you'd like to be able to patch the binary, you can specify that
6266 explicitly with the @code{set write} command. For example, you might
6267 want to turn on internal debugging flags, or even to make emergency
6272 @itemx set write off
6274 If you specify @samp{set write on}, @value{GDBN} will open executable
6278 files for both reading and writing; if you specify @samp{set write
6279 off} (the default), @value{GDBN} will open them read-only.
6281 If you have already loaded a file, you must load it again (using the
6286 command) after changing @code{set write}, for your new setting to take
6291 Display whether executable files
6295 will be opened for writing as well as reading.
6299 @chapter @value{GDBN} Files
6301 @value{GDBN} needs to know the file name of the program to be debugged, both in
6302 order to read its symbol table and in order to start your program.
6304 To debug a core dump of a previous run, you must also tell @value{GDBN}
6305 the name of the core dump file.
6309 * Files:: Commands to specify files
6310 * Symbol Errors:: Errors reading symbol files
6314 @section Commands to specify files
6315 @cindex symbol table
6318 @cindex core dump file
6319 The usual way to specify executable and core dump file names is with
6320 the command arguments given when you start @value{GDBN} (@pxref{Invocation,
6321 ,Getting In and Out of @value{GDBN}}.
6324 The usual way to specify an executable file name is with
6325 the command argument given when you start @value{GDBN}, (@pxref{Invocation,
6326 ,Getting In and Out of @value{GDBN}}.
6329 Occasionally it is necessary to change to a different file during a
6330 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
6331 a file you want to use. In these situations the @value{GDBN} commands
6332 to specify new files are useful.
6335 @item file @var{filename}
6336 @cindex executable file
6338 Use @var{filename} as the program to be debugged. It is read for its
6339 symbols and for the contents of pure memory. It is also the program
6340 executed when you use the @code{run} command. If you do not specify a
6341 directory and the file is not found in the @value{GDBN} working directory, @value{GDBN}
6342 uses the environment variable @code{PATH} as a list of directories to
6343 search, just as the shell does when looking for a program to run. You
6344 can change the value of this variable, for both @value{GDBN} and your program,
6345 using the @code{path} command.
6347 On systems with memory-mapped files, an auxiliary symbol table file
6348 @file{@var{filename}.syms} may be available for @var{filename}. If it
6349 is, @value{GDBN} will map in the symbol table from
6350 @file{@var{filename}.syms}, starting up more quickly. See the
6351 descriptions of the options @samp{-mapped} and @samp{-readnow} (available
6352 on the command line, and with the commands @code{file}, @code{symbol-file},
6353 or @code{add-symbol-file}), for more information.
6356 @code{file} with no argument makes @value{GDBN} discard any information it
6357 has on both executable file and the symbol table.
6359 @item exec-file @r{[} @var{filename} @r{]}
6361 Specify that the program to be run (but not the symbol table) is found
6362 in @var{filename}. @value{GDBN} will search the environment variable @code{PATH}
6363 if necessary to locate your program. Omitting @var{filename} means to
6364 discard information on the executable file.
6366 @item symbol-file @r{[} @var{filename} @r{]}
6368 Read symbol table information from file @var{filename}. @code{PATH} is
6369 searched when necessary. Use the @code{file} command to get both symbol
6370 table and program to run from the same file.
6372 @code{symbol-file} with no argument clears out @value{GDBN} information on your
6373 program's symbol table.
6375 The @code{symbol-file} command causes @value{GDBN} to forget the contents of its
6376 convenience variables, the value history, and all breakpoints and
6377 auto-display expressions. This is because they may contain pointers to
6378 the internal data recording symbols and data types, which are part of
6379 the old symbol table data being discarded inside @value{GDBN}.
6381 @code{symbol-file} will not repeat if you press @key{RET} again after
6384 When @value{GDBN} is configured for a particular environment, it will
6385 understand debugging information in whatever format is the standard
6386 generated for that environment; you may use either a GNU compiler, or
6387 other compilers that adhere to the local conventions. Best results are
6388 usually obtained from GNU compilers; for example, using @code{@value{GCC}}
6389 you can generate debugging information for optimized code.
6391 On some kinds of object files, the @code{symbol-file} command does not
6392 normally read the symbol table in full right away. Instead, it scans
6393 the symbol table quickly to find which source files and which symbols
6394 are present. The details are read later, one source file at a time,
6397 The purpose of this two-stage reading strategy is to make @value{GDBN} start up
6398 faster. For the most part, it is invisible except for occasional
6399 pauses while the symbol table details for a particular source file are
6400 being read. (The @code{set verbose} command can turn these pauses
6401 into messages if desired. @xref{Messages/Warnings, ,Optional warnings
6404 We have not implemented the two-stage strategy for COFF yet. When the
6405 symbol table is stored in COFF format, @code{symbol-file} reads the
6406 symbol table data in full right away.
6408 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6409 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6411 @cindex reading symbols immediately
6412 @cindex symbols, reading immediately
6414 @cindex memory-mapped symbol file
6415 @cindex saving symbol table
6416 You can override the @value{GDBN} two-stage strategy for reading symbol
6417 tables by using the @samp{-readnow} option with any of the commands that
6418 load symbol table information, if you want to be sure @value{GDBN} has the
6419 entire symbol table available.
6422 If memory-mapped files are available on your system through the
6423 @code{mmap} system call, you can use another option, @samp{-mapped}, to
6424 cause @value{GDBN} to write the symbols for your program into a reusable
6425 file. Future @value{GDBN} debugging sessions will map in symbol information
6426 from this auxiliary symbol file (if the program has not changed), rather
6427 than spending time reading the symbol table from the executable
6428 program. Using the @samp{-mapped} option has the same effect as
6429 starting @value{GDBN} with the @samp{-mapped} command-line option.
6431 You can use both options together, to make sure the auxiliary symbol
6432 file has all the symbol information for your program.
6434 The auxiliary symbol file for a program called @var{myprog} is called
6435 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
6436 than the corresponding executable), @value{GDBN} will always attempt to use
6437 it when you debug @var{myprog}; no special options or commands are
6440 The @file{.syms} file is specific to the host machine where you run
6441 @value{GDBN}. It holds an exact image of the internal @value{GDB}
6442 symbol table. It cannot be shared across multiple host platforms.
6444 @c FIXME: for now no mention of directories, since this seems to be in
6445 @c flux. 13mar1992 status is that in theory GDB would look either in
6446 @c current dir or in same dir as myprog; but issues like competing
6447 @c GDB's, or clutter in system dirs, mean that in practice right now
6448 @c only current dir is used. FFish says maybe a special GDB hierarchy
6449 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
6452 @item core-file @r{[} @var{filename} @r{]}
6455 Specify the whereabouts of a core dump file to be used as the ``contents
6456 of memory''. Traditionally, core files contain only some parts of the
6457 address space of the process that generated them; @value{GDBN} can access the
6458 executable file itself for other parts.
6460 @code{core-file} with no argument specifies that no core file is
6463 Note that the core file is ignored when your program is actually running
6464 under @value{GDBN}. So, if you have been running your program and you wish to
6465 debug a core file instead, you must kill the subprocess in which the
6466 program is running. To do this, use the @code{kill} command
6467 (@pxref{Kill Process, ,Killing the child process}).
6470 @item load @var{filename}
6473 Depending on what remote debugging facilities are configured into
6474 @value{GDBN}, the @code{load} command may be available. Where it exists, it
6475 is meant to make @var{filename} (an executable) available for debugging
6476 on the remote system---by downloading, or dynamic linking, for example.
6477 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
6478 the @code{add-symbol-file} command.
6480 If your @value{GDBN} does not have a @code{load} command, attempting to
6481 execute it gets the error message ``@code{You can't do that when your
6482 target is @dots{}}''
6486 On VxWorks, @code{load} will dynamically link @var{filename} on the
6487 current target system as well as adding its symbols in @value{GDBN}.
6491 @cindex download to Nindy-960
6492 With the Nindy interface to an Intel 960 board, @code{load} will
6493 download @var{filename} to the 960 as well as adding its symbols in
6498 @cindex download to H8/300 or H8/500
6499 @cindex H8/300 or H8/500 download
6500 When you select remote debugging to a Hitachi H8/300 or H8/500 board
6501 (@pxref{Hitachi H8 Remote,,@value{GDBN} and the Hitachi H8/300 and H8/500}),
6502 the @code{load} command downloads your program to the Hitachi board and also
6503 opens it as the current executable target for @value{GDBN} on your host
6504 (like the @code{file} command).
6507 @code{load} will not repeat if you press @key{RET} again after using it.
6510 @item add-symbol-file @var{filename} @var{address}
6511 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
6512 @kindex add-symbol-file
6513 @cindex dynamic linking
6514 The @code{add-symbol-file} command reads additional symbol table information
6515 from the file @var{filename}. You would use this command when @var{filename}
6516 has been dynamically loaded (by some other means) into the program that
6517 is running. @var{address} should be the memory address at which the
6518 file has been loaded; @value{GDBN} cannot figure this out for itself.
6520 The symbol table of the file @var{filename} is added to the symbol table
6521 originally read with the @code{symbol-file} command. You can use the
6522 @code{add-symbol-file} command any number of times; the new symbol data thus
6523 read keeps adding to the old. To discard all old symbol data instead,
6524 use the @code{symbol-file} command.
6526 @code{add-symbol-file} will not repeat if you press @key{RET} after using it.
6528 You can use the @samp{-mapped} and @samp{-readnow} options just as with
6529 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
6530 table information for @var{filename}.
6537 @code{info files} and @code{info target} are synonymous; both print
6538 the current target (@pxref{Targets, ,Specifying a Debugging Target}),
6541 names of the executable and core dump files
6544 name of the executable file
6546 currently in use by @value{GDBN}, and the files from which symbols were
6547 loaded. The command @code{help targets} lists all possible targets
6548 rather than current ones.
6551 All file-specifying commands allow both absolute and relative file names
6552 as arguments. @value{GDBN} always converts the file name to an absolute path
6553 name and remembers it that way.
6556 @cindex shared libraries
6557 @value{GDBN} supports SunOS, SVR4, and IBM RS/6000 shared libraries.
6558 @value{GDBN} automatically loads symbol definitions from shared libraries
6559 when you use the @code{run} command, or when you examine a core file.
6560 (Before you issue the @code{run} command, @value{GDBN} will not understand
6561 references to a function in a shared library, however---unless you are
6562 debugging a core file).
6563 @c FIXME: next @value{GDBN} release should permit some refs to undef
6564 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared lib
6568 @itemx info sharedlibrary
6569 @kindex info sharedlibrary
6571 Print the names of the shared libraries which are currently loaded.
6573 @item sharedlibrary @var{regex}
6574 @itemx share @var{regex}
6575 @kindex sharedlibrary
6577 This is an obsolescent command; you can use it to explicitly
6578 load shared object library symbols for files matching a UNIX regular
6579 expression, but as with files loaded automatically, it will only load
6580 shared libraries required by your program for a core file or after
6581 typing @code{run}. If @var{regex} is omitted all shared libraries
6582 required by your program are loaded.
6587 @section Errors reading symbol files
6589 While reading a symbol file, @value{GDBN} will occasionally encounter problems,
6590 such as symbol types it does not recognize, or known bugs in compiler
6591 output. By default, @value{GDBN} does not notify you of such problems, since
6592 they are relatively common and primarily of interest to people
6593 debugging compilers. If you are interested in seeing information
6594 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
6595 only one message about each such type of problem, no matter how many
6596 times the problem occurs; or you can ask @value{GDBN} to print more messages,
6597 to see how many times the problems occur, with the @code{set
6598 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
6601 The messages currently printed, and their meanings, are:
6604 @item inner block not inside outer block in @var{symbol}
6606 The symbol information shows where symbol scopes begin and end
6607 (such as at the start of a function or a block of statements). This
6608 error indicates that an inner scope block is not fully contained
6609 in its outer scope blocks.
6611 @value{GDBN} circumvents the problem by treating the inner block as if it had
6612 the same scope as the outer block. In the error message, @var{symbol}
6613 may be shown as ``@code{(don't know)}'' if the outer block is not a
6616 @item block at @var{address} out of order
6618 The symbol information for symbol scope blocks should occur in
6619 order of increasing addresses. This error indicates that it does not
6622 @value{GDBN} does not circumvent this problem, and will have trouble
6623 locating symbols in the source file whose symbols it is reading. (You
6624 can often determine what source file is affected by specifying
6625 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
6628 @item bad block start address patched
6630 The symbol information for a symbol scope block has a start address
6631 smaller than the address of the preceding source line. This is known
6632 to occur in the SunOS 4.1.1 (and earlier) C compiler.
6634 @value{GDBN} circumvents the problem by treating the symbol scope block as
6635 starting on the previous source line.
6637 @item bad string table offset in symbol @var{n}
6640 Symbol number @var{n} contains a pointer into the string table which is
6641 larger than the size of the string table.
6643 @value{GDBN} circumvents the problem by considering the symbol to have the
6644 name @code{foo}, which may cause other problems if many symbols end up
6647 @item unknown symbol type @code{0x@var{nn}}
6649 The symbol information contains new data types that @value{GDBN} does not yet
6650 know how to read. @code{0x@var{nn}} is the symbol type of the misunderstood
6651 information, in hexadecimal.
6653 @value{GDBN} circumvents the error by ignoring this symbol information. This
6654 will usually allow your program to be debugged, though certain symbols
6655 will not be accessible. If you encounter such a problem and feel like
6656 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint on
6657 @code{complain}, then go up to the function @code{read_dbx_symtab} and
6658 examine @code{*bufp} to see the symbol.
6660 @item stub type has NULL name
6661 @value{GDBN} could not find the full definition for
6670 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
6672 The symbol information for a C++ member function is missing some
6673 information that recent versions of the compiler should have output
6677 @item info mismatch between compiler and debugger
6679 @value{GDBN} could not parse a type specification output by the compiler.
6683 @chapter Specifying a Debugging Target
6684 @cindex debugging target
6687 A @dfn{target} is the execution environment occupied by your program.
6689 Often, @value{GDBN} runs in the same host environment as your program; in
6690 that case, the debugging target is specified as a side effect when you
6691 use the @code{file} or @code{core} commands. When you need more
6692 flexibility---for example, running @value{GDBN} on a physically separate
6693 host, or controlling a standalone system over a serial port or a
6694 realtime system over a TCP/IP connection---you
6699 can use the @code{target} command to specify one of the target types
6700 configured for @value{GDBN} (@pxref{Target Commands, ,Commands for managing
6704 * Active Targets:: Active targets
6705 * Target Commands:: Commands for managing targets
6706 * Remote:: Remote debugging
6709 @node Active Targets
6710 @section Active targets
6711 @cindex stacking targets
6712 @cindex active targets
6713 @cindex multiple targets
6716 There are three classes of targets: processes, core files, and
6717 executable files. @value{GDBN} can work concurrently on up to three active
6718 targets, one in each class. This allows you to (for example) start a
6719 process and inspect its activity without abandoning your work on a core
6722 For example, if you execute @samp{gdb a.out}, then the executable file
6723 @code{a.out} is the only active target. If you designate a core file as
6724 well---presumably from a prior run that crashed and coredumped---then
6725 @value{GDBN} has two active targets and will use them in tandem, looking
6726 first in the corefile target, then in the executable file, to satisfy
6727 requests for memory addresses. (Typically, these two classes of target
6728 are complementary, since core files contain only a program's
6729 read-write memory---variables and so on---plus machine status, while
6730 executable files contain only the program text and initialized data.)
6733 When you type @code{run}, your executable file becomes an active process
6734 target as well. When a process target is active, all @value{GDBN} commands
6735 requesting memory addresses refer to that target; addresses in an
6739 executable file target are obscured while the process
6743 Use the @code{exec-file} command to select a
6744 new executable target (@pxref{Files, ,Commands to specify
6748 Use the @code{core-file} and @code{exec-file} commands to select a
6749 new core file or executable target (@pxref{Files, ,Commands to specify
6750 files}). To specify as a target a process that is already running, use
6751 the @code{attach} command (@pxref{Attach, ,Debugging an
6752 already-running process}).
6755 @node Target Commands
6756 @section Commands for managing targets
6759 @item target @var{type} @var{parameters}
6760 Connects the @value{GDBN} host environment to a target
6765 machine or process. A target is typically a protocol for talking to
6766 debugging facilities. You use the argument @var{type} to specify the
6767 type or protocol of the target machine.
6769 Further @var{parameters} are interpreted by the target protocol, but
6770 typically include things like device names or host names to connect
6771 with, process numbers, and baud rates.
6774 The @code{target} command will not repeat if you press @key{RET} again
6775 after executing the command.
6779 Displays the names of all targets available. To display targets
6780 currently selected, use either @code{info target} or @code{info files}
6781 (@pxref{Files, ,Commands to specify files}).
6783 @item help target @var{name}
6784 Describe a particular target, including any parameters necessary to
6788 Here are some common targets (available, or not, depending on the GDB
6792 @item target exec @var{program}
6794 An executable file. @samp{target exec @var{program}} is the same as
6795 @samp{exec-file @var{program}}.
6798 @item target core @var{filename}
6800 A core dump file. @samp{target core @var{filename}} is the same as
6801 @samp{core-file @var{filename}}.
6805 @item target remote @var{dev}
6806 @kindex target remote
6807 Remote serial target in GDB-specific protocol. The argument @var{dev}
6808 specifies what serial device to use for the connection (e.g.
6809 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}.
6815 CPU simulator. @xref{Simulator,,Simulated CPU Target}.
6819 @item target udi @var{keyword}
6821 Remote AMD29K target, using the AMD UDI protocol. The @var{keyword}
6822 argument specifies which 29K board or simulator to use. @xref{UDI29K
6823 Remote,,@value{GDBN} and the UDI protocol for AMD29K}.
6825 @item target amd-eb @var{dev} @var{speed} @var{PROG}
6826 @kindex target amd-eb
6828 Remote PC-resident AMD EB29K board, attached over serial lines.
6829 @var{dev} is the serial device, as for @code{target remote};
6830 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
6831 name of the program to be debugged, as it appears to DOS on the PC.
6832 @xref{EB29K Remote, ,@value{GDBN} with a remote EB29K}.
6838 A Hitachi H8/300 or H8/500 board, attached via serial line to your host. Use
6839 special commands @code{device} and @code{speed} to control the serial
6840 line and the communications speed used. @xref{Hitachi H8
6841 Remote,,@value{GDBN} and the Hitachi H8/300 and H8/500}.
6845 @item target nindy @var{devicename}
6846 @kindex target nindy
6847 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
6848 the name of the serial device to use for the connection, e.g.
6849 @file{/dev/ttya}. @xref{i960-Nindy Remote, ,@value{GDBN} with a remote i960 (Nindy)}.
6853 @item target st2000 @var{dev} @var{speed}
6854 @kindex target st2000
6855 A Tandem ST2000 phone switch, running Tandem's STDBUG protocol. @var{dev}
6856 is the name of the device attached to the ST2000 serial line;
6857 @var{speed} is the communication line speed. The arguments are not used
6858 if @value{GDBN} is configured to connect to the ST2000 using TCP or Telnet.
6859 @xref{ST2000 Remote,,@value{GDBN} with a Tandem ST2000}.
6863 @item target vxworks @var{machinename}
6864 @kindex target vxworks
6865 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
6866 is the target system's machine name or IP address.
6867 @xref{VxWorks Remote, ,@value{GDBN} and VxWorks}.
6872 Different targets are available on different configurations of @value{GDBN}; your
6873 configuration may have more or fewer targets.
6877 @section Remote debugging
6878 @cindex remote debugging
6880 If you are trying to debug a program running on a machine that cannot run
6881 GDB in the usual way, it is often useful to use remote debugging. For
6882 example, you might use remote debugging on an operating system kernel, or on
6883 a small system which does not have a general purpose operating system
6884 powerful enough to run a full-featured debugger.
6886 Some configurations of GDB have special serial or TCP/IP interfaces
6887 to make this work with particular debugging targets. In addition,
6888 GDB comes with a generic serial protocol (specific to GDB, but
6889 not specific to any particular target system) which you can use if you
6890 write the remote stubs---the code that will run on the remote system to
6891 communicate with GDB.
6893 Other remote targets may be available in your
6894 configuration of GDB; use @code{help targets} to list them.
6897 @c Text on starting up GDB in various specific cases; it goes up front
6898 @c in manuals configured for any of those particular situations, here
6902 * Remote Serial:: @value{GDBN} remote serial protocol
6905 * i960-Nindy Remote:: @value{GDBN} with a remote i960 (Nindy)
6908 * UDI29K Remote:: @value{GDBN} and the UDI protocol for AMD29K
6909 * EB29K Remote:: @value{GDBN} with a remote EB29K
6912 * VxWorks Remote:: @value{GDBN} and VxWorks
6915 * ST2000 Remote:: @value{GDBN} with a Tandem ST2000
6918 * Hitachi H8 Remote:: @value{GDBN} and the Hitachi H8/300 and H8/500
6921 * Simulator:: Simulated CPU target
6925 @include gdbinv-s.texi
6928 @node Controlling GDB
6929 @chapter Controlling @value{GDBN}
6931 You can alter the way @value{GDBN} interacts with you by using
6932 the @code{set} command. For commands controlling how @value{GDBN} displays
6933 data, @pxref{Print Settings, ,Print settings}; other settings are described here.
6937 * Editing:: Command editing
6938 * History:: Command history
6939 * Screen Size:: Screen size
6941 * Messages/Warnings:: Optional warnings and messages
6948 @value{GDBN} indicates its readiness to read a command by printing a string
6949 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
6950 can change the prompt string with the @code{set prompt} command. For
6951 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
6952 the prompt in one of the @value{GDBN} sessions so that you can always tell which
6953 one you are talking to.
6956 @item set prompt @var{newprompt}
6958 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
6961 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
6965 @section Command editing
6967 @cindex command line editing
6969 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
6970 GNU library provides consistent behavior for programs which provide a
6971 command line interface to the user. Advantages are @code{emacs}-style
6972 or @code{vi}-style inline editing of commands, @code{csh}-like history
6973 substitution, and a storage and recall of command history across
6976 You may control the behavior of command line editing in @value{GDBN} with the
6983 @itemx set editing on
6984 Enable command line editing (enabled by default).
6986 @item set editing off
6987 Disable command line editing.
6989 @kindex show editing
6991 Show whether command line editing is enabled.
6995 @section Command history
6997 @value{GDBN} can keep track of the commands you type during your
6998 debugging sessions, so that you can be certain of precisely what
6999 happened. Use these commands to manage the @value{GDBN} command
7003 @cindex history substitution
7004 @cindex history file
7005 @kindex set history filename
7006 @item set history filename @var{fname}
7007 Set the name of the @value{GDBN} command history file to @var{fname}. This is
7008 the file from which @value{GDBN} will read an initial command history
7009 list or to which it will write this list when it exits. This list is
7010 accessed through history expansion or through the history
7011 command editing characters listed below. This file defaults to the
7012 value of the environment variable @code{GDBHISTFILE}, or to
7013 @file{./.gdb_history} if this variable is not set.
7015 @cindex history save
7016 @kindex set history save
7017 @item set history save
7018 @itemx set history save on
7019 Record command history in a file, whose name may be specified with the
7020 @code{set history filename} command. By default, this option is disabled.
7022 @item set history save off
7023 Stop recording command history in a file.
7025 @cindex history size
7026 @kindex set history size
7027 @item set history size @var{size}
7028 Set the number of commands which @value{GDBN} will keep in its history list.
7029 This defaults to the value of the environment variable
7030 @code{HISTSIZE}, or to 256 if this variable is not set.
7033 @cindex history expansion
7034 History expansion assigns special meaning to the character @kbd{!}.
7035 @ifset have-readline-appendices
7036 @xref{Event Designators}.
7039 Since @kbd{!} is also the logical not operator in C, history expansion
7040 is off by default. If you decide to enable history expansion with the
7041 @code{set history expansion on} command, you may sometimes need to
7042 follow @kbd{!} (when it is used as logical not, in an expression) with
7043 a space or a tab to prevent it from being expanded. The readline
7044 history facilities will not attempt substitution on the strings
7045 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
7047 The commands to control history expansion are:
7051 @kindex set history expansion
7052 @item set history expansion on
7053 @itemx set history expansion
7054 Enable history expansion. History expansion is off by default.
7056 @item set history expansion off
7057 Disable history expansion.
7059 The readline code comes with more complete documentation of
7060 editing and history expansion features. Users unfamiliar with @code{emacs}
7061 or @code{vi} may wish to read it.
7062 @ifset have-readline-appendices
7063 @xref{Command Line Editing}.
7067 @kindex show history
7069 @itemx show history filename
7070 @itemx show history save
7071 @itemx show history size
7072 @itemx show history expansion
7073 These commands display the state of the @value{GDBN} history parameters.
7074 @code{show history} by itself displays all four states.
7079 @kindex show commands
7081 Display the last ten commands in the command history.
7083 @item show commands @var{n}
7084 Print ten commands centered on command number @var{n}.
7086 @item show commands +
7087 Print ten commands just after the commands last printed.
7091 @section Screen size
7092 @cindex size of screen
7093 @cindex pauses in output
7095 Certain commands to @value{GDBN} may produce large amounts of information
7096 output to the screen. To help you read all of it, @value{GDBN} pauses and
7097 asks you for input at the end of each page of output. Type @key{RET}
7098 when you want to continue the output. @value{GDBN} also uses the screen
7099 width setting to determine when to wrap lines of output. Depending on
7100 what is being printed, it tries to break the line at a readable place,
7101 rather than simply letting it overflow onto the following line.
7103 Normally @value{GDBN} knows the size of the screen from the termcap data base
7104 together with the value of the @code{TERM} environment variable and the
7105 @code{stty rows} and @code{stty cols} settings. If this is not correct,
7106 you can override it with the @code{set height} and @code{set
7110 @item set height @var{lpp}
7112 @itemx set width @var{cpl}
7118 These @code{set} commands specify a screen height of @var{lpp} lines and
7119 a screen width of @var{cpl} characters. The associated @code{show}
7120 commands display the current settings.
7122 If you specify a height of zero lines, @value{GDBN} will not pause during output
7123 no matter how long the output is. This is useful if output is to a file
7124 or to an editor buffer.
7129 @cindex number representation
7130 @cindex entering numbers
7132 You can always enter numbers in octal, decimal, or hexadecimal in @value{GDBN} by
7133 the usual conventions: octal numbers begin with @samp{0}, decimal
7134 numbers end with @samp{.}, and hexadecimal numbers begin with @samp{0x}.
7135 Numbers that begin with none of these are, by default, entered in base
7136 10; likewise, the default display for numbers---when no particular
7137 format is specified---is base 10. You can change the default base for
7138 both input and output with the @code{set radix} command.
7142 @item set radix @var{base}
7143 Set the default base for numeric input and display. Supported choices
7144 for @var{base} are decimal 2, 8, 10, 16. @var{base} must itself be
7145 specified either unambiguously or using the current default radix; for
7156 will set the base to decimal. On the other hand, @samp{set radix 10}
7157 will leave the radix unchanged no matter what it was.
7161 Display the current default base for numeric input and display.
7164 @node Messages/Warnings
7165 @section Optional warnings and messages
7167 By default, @value{GDBN} is silent about its inner workings. If you are running
7168 on a slow machine, you may want to use the @code{set verbose} command.
7169 It will make @value{GDBN} tell you when it does a lengthy internal operation, so
7170 you will not think it has crashed.
7172 Currently, the messages controlled by @code{set verbose} are those
7173 which announce that the symbol table for a source file is being read;
7174 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
7178 @item set verbose on
7179 Enables @value{GDBN} output of certain informational messages.
7181 @item set verbose off
7182 Disables @value{GDBN} output of certain informational messages.
7184 @kindex show verbose
7186 Displays whether @code{set verbose} is on or off.
7189 By default, if @value{GDBN} encounters bugs in the symbol table of an object
7190 file, it is silent; but if you are debugging a compiler, you may find
7191 this information useful (@pxref{Symbol Errors, ,Errors reading symbol files}).
7194 @kindex set complaints
7195 @item set complaints @var{limit}
7196 Permits @value{GDBN} to output @var{limit} complaints about each type of unusual
7197 symbols before becoming silent about the problem. Set @var{limit} to
7198 zero to suppress all complaints; set it to a large number to prevent
7199 complaints from being suppressed.
7201 @kindex show complaints
7202 @item show complaints
7203 Displays how many symbol complaints @value{GDBN} is permitted to produce.
7206 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
7207 lot of stupid questions to confirm certain commands. For example, if
7208 you try to run a program which is already running:
7212 The program being debugged has been started already.
7213 Start it from the beginning? (y or n)
7216 If you are willing to unflinchingly face the consequences of your own
7217 commands, you can disable this ``feature'':
7222 @cindex confirmation
7223 @cindex stupid questions
7224 @item set confirm off
7225 Disables confirmation requests.
7227 @item set confirm on
7228 Enables confirmation requests (the default).
7231 @kindex show confirm
7232 Displays state of confirmation requests.
7235 @c FIXME this does not really belong here. But where *does* it belong?
7236 @cindex reloading symbols
7237 Some systems allow individual object files that make up your program to
7238 be replaced without stopping and restarting your program.
7240 For example, in VxWorks you can simply recompile a defective object file
7241 and keep on running.
7243 If you are running on one of these systems, you can allow @value{GDBN} to
7244 reload the symbols for automatically relinked modules:
7247 @kindex set symbol-reloading
7248 @item set symbol-reloading on
7249 Replace symbol definitions for the corresponding source file when an
7250 object file with a particular name is seen again.
7252 @item set symbol-reloading off
7253 Do not replace symbol definitions when re-encountering object files of
7254 the same name. This is the default state; if you are not running on a
7255 system that permits automatically relinking modules, you should leave
7256 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7257 when linking large programs, that may contain several modules (from
7258 different directories or libraries) with the same name.
7260 @item show symbol-reloading
7261 Show the current @code{on} or @code{off} setting.
7265 @chapter Canned Sequences of Commands
7267 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
7268 command lists}), @value{GDBN} provides two ways to store sequences of commands
7269 for execution as a unit: user-defined commands and command files.
7272 * Define:: User-defined commands
7273 * Hooks:: User-defined command hooks
7274 * Command Files:: Command files
7275 * Output:: Commands for controlled output
7279 @section User-defined commands
7281 @cindex user-defined command
7282 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to which you
7283 assign a new name as a command. This is done with the @code{define}
7287 @item define @var{commandname}
7289 Define a command named @var{commandname}. If there is already a command
7290 by that name, you are asked to confirm that you want to redefine it.
7292 The definition of the command is made up of other @value{GDBN} command lines,
7293 which are given following the @code{define} command. The end of these
7294 commands is marked by a line containing @code{end}.
7296 @item document @var{commandname}
7298 Give documentation to the user-defined command @var{commandname}. The
7299 command @var{commandname} must already be defined. This command reads
7300 lines of documentation just as @code{define} reads the lines of the
7301 command definition, ending with @code{end}. After the @code{document}
7302 command is finished, @code{help} on command @var{commandname} will print
7303 the documentation you have specified.
7305 You may use the @code{document} command again to change the
7306 documentation of a command. Redefining the command with @code{define}
7307 does not change the documentation.
7309 @item help user-defined
7310 @kindex help user-defined
7311 List all user-defined commands, with the first line of the documentation
7315 @itemx show user @var{commandname}
7317 Display the @value{GDBN} commands used to define @var{commandname} (but not its
7318 documentation). If no @var{commandname} is given, display the
7319 definitions for all user-defined commands.
7322 User-defined commands do not take arguments. When they are executed, the
7323 commands of the definition are not printed. An error in any command
7324 stops execution of the user-defined command.
7326 Commands that would ask for confirmation if used interactively proceed
7327 without asking when used inside a user-defined command. Many @value{GDBN} commands
7328 that normally print messages to say what they are doing omit the messages
7329 when used in a user-defined command.
7332 @section User-defined command hooks
7333 @cindex command files
7335 You may define @emph{hooks}, which are a special kind of user-defined
7336 command. Whenever you run the command @samp{foo}, if the user-defined
7337 command @samp{hook-foo} exists, it is executed (with no arguments)
7338 before that command.
7340 In addition, a pseudo-command, @samp{stop} exists. Defining
7341 (@samp{hook-stop}) makes the associated commands execute every time
7342 execution stops in your program: before breakpoint commands are run,
7343 displays are printed, or the stack frame is printed.
7346 For example, to ignore @code{SIGALRM} signals while
7347 single-stepping, but treat them normally during normal execution,
7352 handle SIGALRM nopass
7359 define hook-continue
7365 You can define a hook for any single-word command in @value{GDBN}, but
7366 not for command aliases; you should define a hook for the basic command
7367 name, e.g. @code{backtrace} rather than @code{bt}.
7368 @c FIXME! So how does Joe User discover whether a command is an alias
7370 If an error occurs during the execution of your hook, execution of
7371 @value{GDBN} commands stops and @value{GDBN} issues a prompt
7372 (before the command that you actually typed had a chance to run).
7374 If you try to define a hook which does not match any known command, you
7375 will get a warning from the @code{define} command.
7378 @section Command files
7380 @cindex command files
7381 A command file for @value{GDBN} is a file of lines that are @value{GDBN} commands. Comments
7382 (lines starting with @kbd{#}) may also be included. An empty line in a
7383 command file does nothing; it does not mean to repeat the last command, as
7384 it would from the terminal.
7387 @cindex @file{@value{GDBINIT}}
7388 When you start @value{GDBN}, it automatically executes commands from its
7389 @dfn{init files}. These are files named @file{@value{GDBINIT}}. @value{GDBN} reads
7390 the init file (if any) in your home directory and then the init file
7391 (if any) in the current working directory. (The init files are not
7392 executed if you use the @samp{-nx} option; @pxref{Mode Options,
7396 @cindex init file name
7397 On some configurations of @value{GDBN}, the init file is known by a
7398 different name (these are typically environments where a specialized
7399 form of GDB may need to coexist with other forms, hence a different name
7400 for the specialized version's init file). These are the environments
7401 with special init file names:
7406 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
7408 @kindex .os68gdbinit
7410 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
7414 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
7418 You can also request the execution of a command file with the
7419 @code{source} command:
7422 @item source @var{filename}
7424 Execute the command file @var{filename}.
7427 The lines in a command file are executed sequentially. They are not
7428 printed as they are executed. An error in any command terminates execution
7429 of the command file.
7431 Commands that would ask for confirmation if used interactively proceed
7432 without asking when used in a command file. Many @value{GDBN} commands that
7433 normally print messages to say what they are doing omit the messages
7434 when called from command files.
7437 @section Commands for controlled output
7439 During the execution of a command file or a user-defined command, normal
7440 @value{GDBN} output is suppressed; the only output that appears is what is
7441 explicitly printed by the commands in the definition. This section
7442 describes three commands useful for generating exactly the output you
7446 @item echo @var{text}
7448 @c I do not consider backslash-space a standard C escape sequence
7449 @c because it is not in ANSI.
7450 Print @var{text}. Nonprinting characters can be included in
7451 @var{text} using C escape sequences, such as @samp{\n} to print a
7452 newline. @strong{No newline will be printed unless you specify one.}
7453 In addition to the standard C escape sequences, a backslash followed
7454 by a space stands for a space. This is useful for displaying a
7455 string with spaces at the beginning or the end, since leading and
7456 trailing spaces are otherwise trimmed from all arguments.
7457 To print @samp{@w{ }and foo =@w{ }}, use the command
7458 @samp{echo \@w{ }and foo = \@w{ }}.
7460 A backslash at the end of @var{text} can be used, as in C, to continue
7461 the command onto subsequent lines. For example,
7464 echo This is some text\n\
7465 which is continued\n\
7466 onto several lines.\n
7469 produces the same output as
7472 echo This is some text\n
7473 echo which is continued\n
7474 echo onto several lines.\n
7477 @item output @var{expression}
7479 Print the value of @var{expression} and nothing but that value: no
7480 newlines, no @samp{$@var{nn} = }. The value is not entered in the
7481 value history either. @xref{Expressions, ,Expressions}, for more information on
7484 @item output/@var{fmt} @var{expression}
7485 Print the value of @var{expression} in format @var{fmt}. You can use
7486 the same formats as for @code{print}. @xref{Output Formats,,Output
7487 formats}, for more information.
7489 @item printf @var{string}, @var{expressions}@dots{}
7491 Print the values of the @var{expressions} under the control of
7492 @var{string}. The @var{expressions} are separated by commas and may
7493 be either numbers or pointers. Their values are printed as specified
7494 by @var{string}, exactly as if your program were to execute
7497 printf (@var{string}, @var{expressions}@dots{});
7500 For example, you can print two values in hex like this:
7503 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
7506 The only backslash-escape sequences that you can use in the format
7507 string are the simple ones that consist of backslash followed by a
7513 @chapter Using @value{GDBN} under GNU Emacs
7516 A special interface allows you to use GNU Emacs to view (and
7517 edit) the source files for the program you are debugging with
7520 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
7521 executable file you want to debug as an argument. This command starts
7522 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
7523 created Emacs buffer.
7525 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
7530 All ``terminal'' input and output goes through the Emacs buffer.
7533 This applies both to @value{GDBN} commands and their output, and to the input
7534 and output done by the program you are debugging.
7536 This is useful because it means that you can copy the text of previous
7537 commands and input them again; you can even use parts of the output
7540 All the facilities of Emacs' Shell mode are available for interacting
7541 with your program. In particular, you can send signals the usual
7542 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
7547 @value{GDBN} displays source code through Emacs.
7550 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
7551 source file for that frame and puts an arrow (@samp{=>}) at the
7552 left margin of the current line. Emacs uses a separate buffer for
7553 source display, and splits the screen to show both your @value{GDBN} session
7556 Explicit @value{GDBN} @code{list} or search commands still produce output as
7557 usual, but you probably will have no reason to use them.
7560 @emph{Warning:} If the directory where your program resides is not your
7561 current directory, it can be easy to confuse Emacs about the location of
7562 the source files, in which case the auxiliary display buffer will not
7563 appear to show your source. @value{GDBN} can find programs by searching your
7564 environment's @code{PATH} variable, so the @value{GDBN} input and output
7565 session will proceed normally; but Emacs does not get enough information
7566 back from @value{GDBN} to locate the source files in this situation. To
7567 avoid this problem, either start @value{GDBN} mode from the directory where
7568 your program resides, or specify a full path name when prompted for the
7569 @kbd{M-x gdb} argument.
7571 A similar confusion can result if you use the @value{GDBN} @code{file} command to
7572 switch to debugging a program in some other location, from an existing
7573 @value{GDBN} buffer in Emacs.
7576 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
7577 you need to call @value{GDBN} by a different name (for example, if you keep
7578 several configurations around, with different names) you can set the
7579 Emacs variable @code{gdb-command-name}; for example,
7582 (setq gdb-command-name "mygdb")
7586 (preceded by @kbd{ESC ESC}, or typed in the @code{*scratch*} buffer, or
7587 in your @file{.emacs} file) will make Emacs call the program named
7588 ``@code{mygdb}'' instead.
7590 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
7591 addition to the standard Shell mode commands:
7595 Describe the features of Emacs' @value{GDBN} Mode.
7598 Execute to another source line, like the @value{GDBN} @code{step} command; also
7599 update the display window to show the current file and location.
7602 Execute to next source line in this function, skipping all function
7603 calls, like the @value{GDBN} @code{next} command. Then update the display window
7604 to show the current file and location.
7607 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
7608 display window accordingly.
7611 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
7612 display window accordingly.
7615 Execute until exit from the selected stack frame, like the @value{GDBN}
7616 @code{finish} command.
7619 Continue execution of your program, like the @value{GDBN} @code{continue}
7622 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
7625 Go up the number of frames indicated by the numeric argument
7626 (@pxref{Arguments, , Numeric Arguments, emacs, The GNU Emacs Manual}),
7627 like the @value{GDBN} @code{up} command.
7629 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
7632 Go down the number of frames indicated by the numeric argument, like the
7633 @value{GDBN} @code{down} command.
7635 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
7638 Read the number where the cursor is positioned, and insert it at the end
7639 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
7640 around an address that was displayed earlier, type @kbd{disassemble};
7641 then move the cursor to the address display, and pick up the
7642 argument for @code{disassemble} by typing @kbd{C-x &}.
7644 You can customize this further by defining elements of the list
7645 @code{gdb-print-command}; once it is defined, you can format or
7646 otherwise process numbers picked up by @kbd{C-x &} before they are
7647 inserted. A numeric argument to @kbd{C-x &} will both indicate that you
7648 wish special formatting, and act as an index to pick an element of the
7649 list. If the list element is a string, the number to be inserted is
7650 formatted using the Emacs function @code{format}; otherwise the number
7651 is passed as an argument to the corresponding list element.
7654 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
7655 tells @value{GDBN} to set a breakpoint on the source line point is on.
7657 If you accidentally delete the source-display buffer, an easy way to get
7658 it back is to type the command @code{f} in the @value{GDBN} buffer, to
7659 request a frame display; when you run under Emacs, this will recreate
7660 the source buffer if necessary to show you the context of the current
7663 The source files displayed in Emacs are in ordinary Emacs buffers
7664 which are visiting the source files in the usual way. You can edit
7665 the files with these buffers if you wish; but keep in mind that @value{GDBN}
7666 communicates with Emacs in terms of line numbers. If you add or
7667 delete lines from the text, the line numbers that @value{GDBN} knows will cease
7668 to correspond properly with the code.
7670 @c The following dropped because Epoch is nonstandard. Reactivate
7671 @c if/when v19 does something similar. ---pesch@cygnus.com 19dec1990
7673 @kindex emacs epoch environment
7677 Version 18 of Emacs has a built-in window system called the @code{epoch}
7678 environment. Users of this environment can use a new command,
7679 @code{inspect} which performs identically to @code{print} except that
7680 each value is printed in its own window.
7686 @chapter Using @value{GDBN} with Energize
7689 The Energize Programming System is an integrated development environment
7690 that includes a point-and-click interface to many programming tools.
7691 When you use @value{GDBN} in this environment, you can use the standard
7692 Energize graphical interface to drive @value{GDBN}; you can also, if you
7693 choose, type @value{GDBN} commands as usual in a debugging window. Even if
7694 you use the graphical interface, the debugging window (which uses Emacs,
7695 and resembles the standard Emacs interface to @value{GDBN}) displays the
7696 equivalent commands, so that the history of your debugging session is
7699 When Energize starts up a @value{GDBN} session, it uses one of the
7700 command-line options @samp{-energize} or @samp{-cadillac} (``cadillac''
7701 is the name of the communications protocol used by the Energize system).
7702 This option makes @value{GDBN} run as one of the tools in the Energize Tool
7703 Set: it sends all output to the Energize kernel, and accept input from
7706 See the user manual for the Energize Programming System for
7707 information on how to use the Energize graphical interface and the other
7708 development tools that Energize integrates with @value{GDBN}.
7713 @chapter Reporting Bugs in @value{GDBN}
7714 @cindex bugs in @value{GDBN}
7715 @cindex reporting bugs in @value{GDBN}
7717 Your bug reports play an essential role in making @value{GDBN} reliable.
7719 Reporting a bug may help you by bringing a solution to your problem, or it
7720 may not. But in any case the principal function of a bug report is to help
7721 the entire community by making the next version of @value{GDBN} work better. Bug
7722 reports are your contribution to the maintenance of @value{GDBN}.
7724 In order for a bug report to serve its purpose, you must include the
7725 information that enables us to fix the bug.
7728 * Bug Criteria:: Have you found a bug?
7729 * Bug Reporting:: How to report bugs
7733 @section Have you found a bug?
7734 @cindex bug criteria
7736 If you are not sure whether you have found a bug, here are some guidelines:
7740 @cindex fatal signal
7741 @cindex debugger crash
7742 @cindex crash of debugger
7743 If the debugger gets a fatal signal, for any input whatever, that is a
7744 @value{GDBN} bug. Reliable debuggers never crash.
7747 @cindex error on valid input
7748 If @value{GDBN} produces an error message for valid input, that is a bug.
7751 @cindex invalid input
7752 If @value{GDBN} does not produce an error message for invalid input,
7753 that is a bug. However, you should note that your idea of
7754 ``invalid input'' might be our idea of ``an extension'' or ``support
7755 for traditional practice''.
7758 If you are an experienced user of debugging tools, your suggestions
7759 for improvement of @value{GDBN} are welcome in any case.
7763 @section How to report bugs
7765 @cindex @value{GDBN} bugs, reporting
7767 A number of companies and individuals offer support for GNU products.
7768 If you obtained @value{GDBN} from a support organization, we recommend you
7769 contact that organization first.
7771 You can find contact information for many support companies and
7772 individuals in the file @file{etc/SERVICE} in the GNU Emacs
7775 In any event, we also recommend that you send bug reports for @value{GDBN} to one
7779 bug-gdb@@prep.ai.mit.edu
7780 @{ucbvax|mit-eddie|uunet@}!prep.ai.mit.edu!bug-gdb
7783 @strong{Do not send bug reports to @samp{info-gdb}, or to
7784 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do not want to
7785 receive bug reports. Those that do, have arranged to receive @samp{bug-gdb}.
7787 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
7788 serves as a repeater. The mailing list and the newsgroup carry exactly
7789 the same messages. Often people think of posting bug reports to the
7790 newsgroup instead of mailing them. This appears to work, but it has one
7791 problem which can be crucial: a newsgroup posting often lacks a mail
7792 path back to the sender. Thus, if we need to ask for more information,
7793 we may be unable to reach you. For this reason, it is better to send
7794 bug reports to the mailing list.
7796 As a last resort, send bug reports on paper to:
7800 Free Software Foundation
7805 The fundamental principle of reporting bugs usefully is this:
7806 @strong{report all the facts}. If you are not sure whether to state a
7807 fact or leave it out, state it!
7809 Often people omit facts because they think they know what causes the
7810 problem and assume that some details do not matter. Thus, you might
7811 assume that the name of the variable you use in an example does not matter.
7812 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
7813 stray memory reference which happens to fetch from the location where that
7814 name is stored in memory; perhaps, if the name were different, the contents
7815 of that location would fool the debugger into doing the right thing despite
7816 the bug. Play it safe and give a specific, complete example. That is the
7817 easiest thing for you to do, and the most helpful.
7819 Keep in mind that the purpose of a bug report is to enable us to fix
7820 the bug if it is new to us. It is not as important as what happens if
7821 the bug is already known. Therefore, always write your bug reports on
7822 the assumption that the bug has not been reported previously.
7824 Sometimes people give a few sketchy facts and ask, ``Does this ring a
7825 bell?'' Those bug reports are useless, and we urge everyone to
7826 @emph{refuse to respond to them} except to chide the sender to report
7829 To enable us to fix the bug, you should include all these things:
7833 The version of @value{GDBN}. @value{GDBN} announces it if you start with no
7834 arguments; you can also print it at any time using @code{show version}.
7836 Without this, we will not know whether there is any point in looking for
7837 the bug in the current version of @value{GDBN}.
7840 The type of machine you are using, and the operating system name and
7844 What compiler (and its version) was used to compile @value{GDBN}---e.g.
7845 ``@value{GCC}--2.0''.
7848 What compiler (and its version) was used to compile the program you
7849 are debugging---e.g. ``@value{GCC}--2.0''.
7852 The command arguments you gave the compiler to compile your example and
7853 observe the bug. For example, did you use @samp{-O}? To guarantee
7854 you will not omit something important, list them all. A copy of the
7855 Makefile (or the output from make) is sufficient.
7857 If we were to try to guess the arguments, we would probably guess wrong
7858 and then we might not encounter the bug.
7861 A complete input script, and all necessary source files, that will
7865 A description of what behavior you observe that you believe is
7866 incorrect. For example, ``It gets a fatal signal.''
7868 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we will
7869 certainly notice it. But if the bug is incorrect output, we might not
7870 notice unless it is glaringly wrong. We are human, after all. You
7871 might as well not give us a chance to make a mistake.
7873 Even if the problem you experience is a fatal signal, you should still
7874 say so explicitly. Suppose something strange is going on, such as,
7875 your copy of @value{GDBN} is out of synch, or you have encountered a
7876 bug in the C library on your system. (This has happened!) Your copy
7877 might crash and ours would not. If you told us to expect a crash,
7878 then when ours fails to crash, we would know that the bug was not
7879 happening for us. If you had not told us to expect a crash, then we
7880 would not be able to draw any conclusion from our observations.
7883 If you wish to suggest changes to the @value{GDBN} source, send us context
7884 diffs. If you even discuss something in the @value{GDBN} source, refer to
7885 it by context, not by line number.
7887 The line numbers in our development sources will not match those in your
7888 sources. Your line numbers would convey no useful information to us.
7891 Here are some things that are not necessary:
7895 A description of the envelope of the bug.
7897 Often people who encounter a bug spend a lot of time investigating
7898 which changes to the input file will make the bug go away and which
7899 changes will not affect it.
7901 This is often time consuming and not very useful, because the way we
7902 will find the bug is by running a single example under the debugger
7903 with breakpoints, not by pure deduction from a series of examples.
7904 We recommend that you save your time for something else.
7906 Of course, if you can find a simpler example to report @emph{instead}
7907 of the original one, that is a convenience for us. Errors in the
7908 output will be easier to spot, running under the debugger will take
7911 However, simplification is not vital; if you do not want to do this,
7912 report the bug anyway and send us the entire test case you used.
7915 A patch for the bug.
7917 A patch for the bug does help us if it is a good one. But do not omit
7918 the necessary information, such as the test case, on the assumption that
7919 a patch is all we need. We might see problems with your patch and decide
7920 to fix the problem another way, or we might not understand it at all.
7922 Sometimes with a program as complicated as @value{GDBN} it is very hard to
7923 construct an example that will make the program follow a certain path
7924 through the code. If you do not send us the example, we will not be able
7925 to construct one, so we will not be able to verify that the bug is fixed.
7927 And if we cannot understand what bug you are trying to fix, or why your
7928 patch should be an improvement, we will not install it. A test case will
7929 help us to understand.
7932 A guess about what the bug is or what it depends on.
7934 Such guesses are usually wrong. Even we cannot guess right about such
7935 things without first using the debugger to find the facts.
7938 @ifset have-readline-appendices
7939 @include rluser.texinfo
7940 @include inc-hist.texi
7944 @node Renamed Commands
7945 @appendix Renamed Commands
7947 The following commands were renamed in GDB 4, in order to make the
7948 command set as a whole more consistent and easier to use and remember:
7951 @kindex delete environment
7952 @kindex info copying
7953 @kindex info convenience
7954 @kindex info directories
7955 @kindex info editing
7956 @kindex info history
7957 @kindex info targets
7959 @kindex info version
7960 @kindex info warranty
7961 @kindex set addressprint
7962 @kindex set arrayprint
7963 @kindex set prettyprint
7964 @kindex set screen-height
7965 @kindex set screen-width
7966 @kindex set unionprint
7967 @kindex set vtblprint
7968 @kindex set demangle
7969 @kindex set asm-demangle
7970 @kindex set sevenbit-strings
7971 @kindex set array-max
7973 @kindex set history write
7974 @kindex show addressprint
7975 @kindex show arrayprint
7976 @kindex show prettyprint
7977 @kindex show screen-height
7978 @kindex show screen-width
7979 @kindex show unionprint
7980 @kindex show vtblprint
7981 @kindex show demangle
7982 @kindex show asm-demangle
7983 @kindex show sevenbit-strings
7984 @kindex show array-max
7985 @kindex show caution
7986 @kindex show history write
7991 @c END TEXI2ROFF-KILL
7993 OLD COMMAND NEW COMMAND
7995 --------------- -------------------------------
7996 @c END TEXI2ROFF-KILL
7997 add-syms add-symbol-file
7998 delete environment unset environment
7999 info convenience show convenience
8000 info copying show copying
8001 info directories show directories
8002 info editing show commands
8003 info history show values
8004 info targets help target
8005 info values show values
8006 info version show version
8007 info warranty show warranty
8008 set/show addressprint set/show print address
8009 set/show array-max set/show print elements
8010 set/show arrayprint set/show print array
8011 set/show asm-demangle set/show print asm-demangle
8012 set/show caution set/show confirm
8013 set/show demangle set/show print demangle
8014 set/show history write set/show history save
8015 set/show prettyprint set/show print pretty
8016 set/show screen-height set/show height
8017 set/show screen-width set/show width
8018 set/show sevenbit-strings set/show print sevenbit-strings
8019 set/show unionprint set/show print union
8020 set/show vtblprint set/show print vtbl
8022 unset [No longer an alias for delete]
8028 \vskip \parskip\vskip \baselineskip
8029 \halign{\tt #\hfil &\qquad#&\tt #\hfil\cr
8030 {\bf Old Command} &&{\bf New Command}\cr
8031 add-syms &&add-symbol-file\cr
8032 delete environment &&unset environment\cr
8033 info convenience &&show convenience\cr
8034 info copying &&show copying\cr
8035 info directories &&show directories \cr
8036 info editing &&show commands\cr
8037 info history &&show values\cr
8038 info targets &&help target\cr
8039 info values &&show values\cr
8040 info version &&show version\cr
8041 info warranty &&show warranty\cr
8042 set{\rm / }show addressprint &&set{\rm / }show print address\cr
8043 set{\rm / }show array-max &&set{\rm / }show print elements\cr
8044 set{\rm / }show arrayprint &&set{\rm / }show print array\cr
8045 set{\rm / }show asm-demangle &&set{\rm / }show print asm-demangle\cr
8046 set{\rm / }show caution &&set{\rm / }show confirm\cr
8047 set{\rm / }show demangle &&set{\rm / }show print demangle\cr
8048 set{\rm / }show history write &&set{\rm / }show history save\cr
8049 set{\rm / }show prettyprint &&set{\rm / }show print pretty\cr
8050 set{\rm / }show screen-height &&set{\rm / }show height\cr
8051 set{\rm / }show screen-width &&set{\rm / }show width\cr
8052 set{\rm / }show sevenbit-strings &&set{\rm / }show print sevenbit-strings\cr
8053 set{\rm / }show unionprint &&set{\rm / }show print union\cr
8054 set{\rm / }show vtblprint &&set{\rm / }show print vtbl\cr
8056 unset &&\rm(No longer an alias for delete)\cr
8059 @c END TEXI2ROFF-KILL
8062 @ifclear PRECONFIGURED
8063 @node Formatting Documentation
8064 @appendix Formatting Documentation
8066 @cindex GDB reference card
8067 @cindex reference card
8068 The GDB 4 release includes an already-formatted reference card, ready
8069 for printing with PostScript or GhostScript, in the @file{gdb}
8070 subdirectory of the main source directory@footnote{In
8071 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
8072 release.}. If you can use PostScript or GhostScript with your printer,
8073 you can print the reference card immediately with @file{refcard.ps}.
8075 The release also includes the source for the reference card. You
8076 can format it, using @TeX{}, by typing:
8082 The GDB reference card is designed to print in landscape mode on US
8083 ``letter'' size paper; that is, on a sheet 11 inches wide by 8.5 inches
8084 high. You will need to specify this form of printing as an option to
8085 your @sc{dvi} output program.
8087 @cindex documentation
8089 All the documentation for GDB comes as part of the machine-readable
8090 distribution. The documentation is written in Texinfo format, which is
8091 a documentation system that uses a single source file to produce both
8092 on-line information and a printed manual. You can use one of the Info
8093 formatting commands to create the on-line version of the documentation
8094 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
8096 GDB includes an already formatted copy of the on-line Info version of
8097 this manual in the @file{gdb} subdirectory. The main Info file is
8098 @file{gdb-@var{version-number}/gdb/gdb.info}, and it refers to
8099 subordinate files matching @samp{gdb.info*} in the same directory. If
8100 necessary, you can print out these files, or read them with any editor;
8101 but they are easier to read using the @code{info} subsystem in GNU Emacs
8102 or the standalone @code{info} program, available as part of the GNU
8103 Texinfo distribution.
8105 If you want to format these Info files yourself, you need one of the
8106 Info formatting programs, such as @code{texinfo-format-buffer} or
8109 If you have @code{makeinfo} installed, and are in the top level GDB
8110 source directory (@file{gdb-@value{GDBVN}}, in the case of version @value{GDBVN}), you can
8111 make the Info file by typing:
8118 If you want to typeset and print copies of this manual, you need @TeX{},
8119 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
8120 Texinfo definitions file.
8122 @TeX{} is a typesetting program; it does not print files directly, but
8123 produces output files called @sc{dvi} files. To print a typeset
8124 document, you need a program to print @sc{dvi} files. If your system
8125 has @TeX{} installed, chances are it has such a program. The precise
8126 command to use depends on your system; @kbd{lpr -d} is common; another
8127 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
8128 require a file name without any extension or a @samp{.dvi} extension.
8130 @TeX{} also requires a macro definitions file called
8131 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
8132 written in Texinfo format. On its own, @TeX{} cannot read, much less
8133 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
8134 and is located in the @file{gdb-@var{version-number}/texinfo}
8137 If you have @TeX{} and a @sc{dvi} printer program installed, you can
8138 typeset and print this manual. First switch to the the @file{gdb}
8139 subdirectory of the main source directory (for example, to
8140 @file{gdb-@value{GDBVN}/gdb}) and then type:
8146 @node Installing GDB
8147 @appendix Installing GDB
8148 @cindex configuring GDB
8149 @cindex installation
8151 GDB comes with a @code{configure} script that automates the process
8152 of preparing GDB for installation; you can then use @code{make} to
8153 build the @code{gdb} program.
8155 @c irrelevant in info file; it's as current as the code it lives with.
8156 @footnote{If you have a more recent version of GDB than @value{GDBVN},
8157 look at the @file{README} file in the sources; we may have improved the
8158 installation procedures since publishing this manual.}
8161 The GDB distribution includes all the source code you need for GDB in
8162 a single directory, whose name is usually composed by appending the
8163 version number to @samp{gdb}.
8165 For example, the GDB version @value{GDBVN} distribution is in the
8166 @file{gdb-@value{GDBVN}} directory. That directory contains:
8169 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
8170 script for configuring GDB and all its supporting libraries.
8172 @item gdb-@value{GDBVN}/gdb
8173 the source specific to GDB itself
8175 @item gdb-@value{GDBVN}/bfd
8176 source for the Binary File Descriptor library
8178 @item gdb-@value{GDBVN}/include
8181 @item gdb-@value{GDBVN}/libiberty
8182 source for the @samp{-liberty} free software library
8184 @item gdb-@value{GDBVN}/opcodes
8185 source for the library of opcode tables and disassemblers
8187 @item gdb-@value{GDBVN}/readline
8188 source for the GNU command-line interface
8190 @item gdb-@value{GDBVN}/glob
8191 source for the GNU filename pattern-matching subroutine
8193 @item gdb-@value{GDBVN}/mmalloc
8194 source for the GNU memory-mapped malloc package
8197 The simplest way to configure and build GDB is to run @code{configure}
8198 from the @file{gdb-@var{version-number}} source directory, which in
8199 this example is the @file{gdb-@value{GDBVN}} directory.
8201 First switch to the @file{gdb-@var{version-number}} source directory
8202 if you are not already in it; then run @code{configure}. Pass the
8203 identifier for the platform on which GDB will run as an
8209 cd gdb-@value{GDBVN}
8210 ./configure @var{host}
8215 where @var{host} is an identifier such as @samp{sun4} or
8216 @samp{decstation}, that identifies the platform where GDB will run.
8218 Running @samp{configure @var{host}} and then running @code{make} builds the
8219 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
8220 libraries, then @code{gdb} itself. The configured source files, and the
8221 binaries, are left in the corresponding source directories.
8223 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
8224 system does not recognize this automatically when you run a different
8225 shell, you may need to run @code{sh} on it explicitly:
8228 sh configure @var{host}
8231 If you run @code{configure} from a directory that contains source
8232 directories for multiple libraries or programs, such as the
8233 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
8234 creates configuration files for every directory level underneath (unless
8235 you tell it not to, with the @samp{--norecursion} option).
8237 You can run the @code{configure} script from any of the
8238 subordinate directories in the GDB distribution, if you only want to
8239 configure that subdirectory; but be sure to specify a path to it.
8241 For example, with version @value{GDBVN}, type the following to configure only
8242 the @code{bfd} subdirectory:
8246 cd gdb-@value{GDBVN}/bfd
8247 ../configure @var{host}
8251 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
8252 However, you should make sure that the shell on your path (named by
8253 the @samp{SHELL} environment variable) is publicly readable. Remember
8254 that GDB uses the shell to start your program---some systems refuse to
8255 let GDB debug child processes whose programs are not readable.
8258 * Separate Objdir:: Compiling GDB in another directory
8259 * Config Names:: Specifying names for hosts and targets
8260 * configure Options:: Summary of options for configure
8263 @node Separate Objdir
8264 @section Compiling GDB in another directory
8266 If you want to run GDB versions for several host or target machines,
8267 you need a different @code{gdb} compiled for each combination of
8268 host and target. @code{configure} is designed to make this easy by
8269 allowing you to generate each configuration in a separate subdirectory,
8270 rather than in the source directory. If your @code{make} program
8271 handles the @samp{VPATH} feature (GNU @code{make} does), running
8272 @code{make} in each of these directories builds the @code{gdb}
8273 program specified there.
8275 To build @code{gdb} in a separate directory, run @code{configure}
8276 with the @samp{--srcdir} option to specify where to find the source.
8277 (You also need to specify a path to find @code{configure}
8278 itself from your working directory. If the path to @code{configure}
8279 would be the same as the argument to @samp{--srcdir}, you can leave out
8280 the @samp{--srcdir} option; it will be assumed.)
8282 For example, with version @value{GDBVN}, you can build GDB in a separate
8283 directory for a Sun 4 like this:
8287 cd gdb-@value{GDBVN}
8290 ../gdb-@value{GDBVN}/configure sun4
8295 When @code{configure} builds a configuration using a remote source
8296 directory, it creates a tree for the binaries with the same structure
8297 (and using the same names) as the tree under the source directory. In
8298 the example, you'd find the Sun 4 library @file{libiberty.a} in the
8299 directory @file{gdb-sun4/libiberty}, and GDB itself in
8300 @file{gdb-sun4/gdb}.
8302 One popular reason to build several GDB configurations in separate
8303 directories is to configure GDB for cross-compiling (where GDB
8304 runs on one machine---the host---while debugging programs that run on
8305 another machine---the target). You specify a cross-debugging target by
8306 giving the @samp{--target=@var{target}} option to @code{configure}.
8308 When you run @code{make} to build a program or library, you must run
8309 it in a configured directory---whatever directory you were in when you
8310 called @code{configure} (or one of its subdirectories).
8312 The @code{Makefile} that @code{configure} generates in each source
8313 directory also runs recursively. If you type @code{make} in a source
8314 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
8315 directory configured with @samp{--srcdir=@var{path}/gdb-@value{GDBVN}}), you
8316 will build all the required libraries, and then build GDB.
8318 When you have multiple hosts or targets configured in separate
8319 directories, you can run @code{make} on them in parallel (for example,
8320 if they are NFS-mounted on each of the hosts); they will not interfere
8324 @section Specifying names for hosts and targets
8326 The specifications used for hosts and targets in the @code{configure}
8327 script are based on a three-part naming scheme, but some short predefined
8328 aliases are also supported. The full naming scheme encodes three pieces
8329 of information in the following pattern:
8332 @var{architecture}-@var{vendor}-@var{os}
8335 For example, you can use the alias @code{sun4} as a @var{host} argument,
8336 or as the value for @var{target} in a @code{--target=@var{target}}
8337 option. The equivalent full name is @samp{sparc-sun-sunos4}.
8339 The @code{configure} script accompanying GDB does not provide
8340 any query facility to list all supported host and target names or
8341 aliases. @code{configure} calls the Bourne shell script
8342 @code{config.sub} to map abbreviations to full names; you can read the
8343 script, if you wish, or you can use it to test your guesses on
8344 abbreviations---for example:
8347 % sh config.sub sun4
8349 % sh config.sub sun3
8351 % sh config.sub decstation
8353 % sh config.sub hp300bsd
8355 % sh config.sub i386v
8357 % sh config.sub i786v
8358 Invalid configuration `i786v': machine `i786v' not recognized
8362 @code{config.sub} is also distributed in the GDB source
8363 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
8365 @node configure Options
8366 @section @code{configure} options
8368 Here is a summary of the @code{configure} options and arguments that
8369 are most often useful for building @value{GDBN}. @code{configure} also has
8370 several other options not listed here. @inforef{What Configure
8371 Does,,configure.info}, for a full explanation of @code{configure}.
8372 @c FIXME: Would this be more, or less, useful as an xref (ref to printed
8373 @c manual in the printed manual, ref to info file only from the info file)?
8376 configure @r{[}--help@r{]}
8377 @r{[}--prefix=@var{dir}@r{]}
8378 @r{[}--srcdir=@var{path}@r{]}
8379 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
8380 @r{[}--target=@var{target}@r{]} @var{host}
8384 You may introduce options with a single @samp{-} rather than
8385 @samp{--} if you prefer; but you may abbreviate option names if you use
8390 Display a quick summary of how to invoke @code{configure}.
8392 @item -prefix=@var{dir}
8393 Configure the source to install programs and files under directory
8396 @item --srcdir=@var{path}
8397 @strong{Warning: using this option requires GNU @code{make}, or another
8398 @code{make} that implements the @code{VPATH} feature.}@*
8399 Use this option to make configurations in directories separate from the
8400 GDB source directories. Among other things, you can use this to
8401 build (or maintain) several configurations simultaneously, in separate
8402 directories. @code{configure} writes configuration specific files in
8403 the current directory, but arranges for them to use the source in the
8404 directory @var{path}. @code{configure} will create directories under
8405 the working directory in parallel to the source directories below
8409 Configure only the directory level where @code{configure} is executed; do not
8410 propagate configuration to subdirectories.
8413 Remove the configuration that the other arguments specify.
8415 @c This does not work (yet if ever). FIXME.
8416 @c @item --parse=@var{lang} @dots{}
8417 @c Configure the GDB expression parser to parse the listed languages.
8418 @c @samp{all} configures GDB for all supported languages. To get a
8419 @c list of all supported languages, omit the argument. Without this
8420 @c option, GDB is configured to parse all supported languages.
8422 @item --target=@var{target}
8423 Configure GDB for cross-debugging programs running on the specified
8424 @var{target}. Without this option, GDB is configured to debug
8425 programs that run on the same machine (@var{host}) as GDB itself.
8427 There is no convenient way to generate a list of all available targets.
8429 @item @var{host} @dots{}
8430 Configure GDB to run on the specified @var{host}.
8432 There is no convenient way to generate a list of all available hosts.
8436 @code{configure} accepts other options, for compatibility with
8437 configuring other GNU tools recursively; but these are the only
8438 options that affect GDB or its supporting libraries.
8441 @ifclear AGGLOMERATION
8443 @unnumbered GNU GENERAL PUBLIC LICENSE
8444 @center Version 2, June 1991
8447 Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
8448 675 Mass Ave, Cambridge, MA 02139, USA
8450 Everyone is permitted to copy and distribute verbatim copies
8451 of this license document, but changing it is not allowed.
8454 @unnumberedsec Preamble
8456 The licenses for most software are designed to take away your
8457 freedom to share and change it. By contrast, the GNU General Public
8458 License is intended to guarantee your freedom to share and change free
8459 software---to make sure the software is free for all its users. This
8460 General Public License applies to most of the Free Software
8461 Foundation's software and to any other program whose authors commit to
8462 using it. (Some other Free Software Foundation software is covered by
8463 the GNU Library General Public License instead.) You can apply it to
8466 When we speak of free software, we are referring to freedom, not
8467 price. Our General Public Licenses are designed to make sure that you
8468 have the freedom to distribute copies of free software (and charge for
8469 this service if you wish), that you receive source code or can get it
8470 if you want it, that you can change the software or use pieces of it
8471 in new free programs; and that you know you can do these things.
8473 To protect your rights, we need to make restrictions that forbid
8474 anyone to deny you these rights or to ask you to surrender the rights.
8475 These restrictions translate to certain responsibilities for you if you
8476 distribute copies of the software, or if you modify it.
8478 For example, if you distribute copies of such a program, whether
8479 gratis or for a fee, you must give the recipients all the rights that
8480 you have. You must make sure that they, too, receive or can get the
8481 source code. And you must show them these terms so they know their
8484 We protect your rights with two steps: (1) copyright the software, and
8485 (2) offer you this license which gives you legal permission to copy,
8486 distribute and/or modify the software.
8488 Also, for each author's protection and ours, we want to make certain
8489 that everyone understands that there is no warranty for this free
8490 software. If the software is modified by someone else and passed on, we
8491 want its recipients to know that what they have is not the original, so
8492 that any problems introduced by others will not reflect on the original
8493 authors' reputations.
8495 Finally, any free program is threatened constantly by software
8496 patents. We wish to avoid the danger that redistributors of a free
8497 program will individually obtain patent licenses, in effect making the
8498 program proprietary. To prevent this, we have made it clear that any
8499 patent must be licensed for everyone's free use or not licensed at all.
8501 The precise terms and conditions for copying, distribution and
8502 modification follow.
8505 @unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
8508 @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
8513 This License applies to any program or other work which contains
8514 a notice placed by the copyright holder saying it may be distributed
8515 under the terms of this General Public License. The ``Program'', below,
8516 refers to any such program or work, and a ``work based on the Program''
8517 means either the Program or any derivative work under copyright law:
8518 that is to say, a work containing the Program or a portion of it,
8519 either verbatim or with modifications and/or translated into another
8520 language. (Hereinafter, translation is included without limitation in
8521 the term ``modification''.) Each licensee is addressed as ``you''.
8523 Activities other than copying, distribution and modification are not
8524 covered by this License; they are outside its scope. The act of
8525 running the Program is not restricted, and the output from the Program
8526 is covered only if its contents constitute a work based on the
8527 Program (independent of having been made by running the Program).
8528 Whether that is true depends on what the Program does.
8531 You may copy and distribute verbatim copies of the Program's
8532 source code as you receive it, in any medium, provided that you
8533 conspicuously and appropriately publish on each copy an appropriate
8534 copyright notice and disclaimer of warranty; keep intact all the
8535 notices that refer to this License and to the absence of any warranty;
8536 and give any other recipients of the Program a copy of this License
8537 along with the Program.
8539 You may charge a fee for the physical act of transferring a copy, and
8540 you may at your option offer warranty protection in exchange for a fee.
8543 You may modify your copy or copies of the Program or any portion
8544 of it, thus forming a work based on the Program, and copy and
8545 distribute such modifications or work under the terms of Section 1
8546 above, provided that you also meet all of these conditions:
8550 You must cause the modified files to carry prominent notices
8551 stating that you changed the files and the date of any change.
8554 You must cause any work that you distribute or publish, that in
8555 whole or in part contains or is derived from the Program or any
8556 part thereof, to be licensed as a whole at no charge to all third
8557 parties under the terms of this License.
8560 If the modified program normally reads commands interactively
8561 when run, you must cause it, when started running for such
8562 interactive use in the most ordinary way, to print or display an
8563 announcement including an appropriate copyright notice and a
8564 notice that there is no warranty (or else, saying that you provide
8565 a warranty) and that users may redistribute the program under
8566 these conditions, and telling the user how to view a copy of this
8567 License. (Exception: if the Program itself is interactive but
8568 does not normally print such an announcement, your work based on
8569 the Program is not required to print an announcement.)
8572 These requirements apply to the modified work as a whole. If
8573 identifiable sections of that work are not derived from the Program,
8574 and can be reasonably considered independent and separate works in
8575 themselves, then this License, and its terms, do not apply to those
8576 sections when you distribute them as separate works. But when you
8577 distribute the same sections as part of a whole which is a work based
8578 on the Program, the distribution of the whole must be on the terms of
8579 this License, whose permissions for other licensees extend to the
8580 entire whole, and thus to each and every part regardless of who wrote it.
8582 Thus, it is not the intent of this section to claim rights or contest
8583 your rights to work written entirely by you; rather, the intent is to
8584 exercise the right to control the distribution of derivative or
8585 collective works based on the Program.
8587 In addition, mere aggregation of another work not based on the Program
8588 with the Program (or with a work based on the Program) on a volume of
8589 a storage or distribution medium does not bring the other work under
8590 the scope of this License.
8593 You may copy and distribute the Program (or a work based on it,
8594 under Section 2) in object code or executable form under the terms of
8595 Sections 1 and 2 above provided that you also do one of the following:
8599 Accompany it with the complete corresponding machine-readable
8600 source code, which must be distributed under the terms of Sections
8601 1 and 2 above on a medium customarily used for software interchange; or,
8604 Accompany it with a written offer, valid for at least three
8605 years, to give any third party, for a charge no more than your
8606 cost of physically performing source distribution, a complete
8607 machine-readable copy of the corresponding source code, to be
8608 distributed under the terms of Sections 1 and 2 above on a medium
8609 customarily used for software interchange; or,
8612 Accompany it with the information you received as to the offer
8613 to distribute corresponding source code. (This alternative is
8614 allowed only for noncommercial distribution and only if you
8615 received the program in object code or executable form with such
8616 an offer, in accord with Subsection b above.)
8619 The source code for a work means the preferred form of the work for
8620 making modifications to it. For an executable work, complete source
8621 code means all the source code for all modules it contains, plus any
8622 associated interface definition files, plus the scripts used to
8623 control compilation and installation of the executable. However, as a
8624 special exception, the source code distributed need not include
8625 anything that is normally distributed (in either source or binary
8626 form) with the major components (compiler, kernel, and so on) of the
8627 operating system on which the executable runs, unless that component
8628 itself accompanies the executable.
8630 If distribution of executable or object code is made by offering
8631 access to copy from a designated place, then offering equivalent
8632 access to copy the source code from the same place counts as
8633 distribution of the source code, even though third parties are not
8634 compelled to copy the source along with the object code.
8637 You may not copy, modify, sublicense, or distribute the Program
8638 except as expressly provided under this License. Any attempt
8639 otherwise to copy, modify, sublicense or distribute the Program is
8640 void, and will automatically terminate your rights under this License.
8641 However, parties who have received copies, or rights, from you under
8642 this License will not have their licenses terminated so long as such
8643 parties remain in full compliance.
8646 You are not required to accept this License, since you have not
8647 signed it. However, nothing else grants you permission to modify or
8648 distribute the Program or its derivative works. These actions are
8649 prohibited by law if you do not accept this License. Therefore, by
8650 modifying or distributing the Program (or any work based on the
8651 Program), you indicate your acceptance of this License to do so, and
8652 all its terms and conditions for copying, distributing or modifying
8653 the Program or works based on it.
8656 Each time you redistribute the Program (or any work based on the
8657 Program), the recipient automatically receives a license from the
8658 original licensor to copy, distribute or modify the Program subject to
8659 these terms and conditions. You may not impose any further
8660 restrictions on the recipients' exercise of the rights granted herein.
8661 You are not responsible for enforcing compliance by third parties to
8665 If, as a consequence of a court judgment or allegation of patent
8666 infringement or for any other reason (not limited to patent issues),
8667 conditions are imposed on you (whether by court order, agreement or
8668 otherwise) that contradict the conditions of this License, they do not
8669 excuse you from the conditions of this License. If you cannot
8670 distribute so as to satisfy simultaneously your obligations under this
8671 License and any other pertinent obligations, then as a consequence you
8672 may not distribute the Program at all. For example, if a patent
8673 license would not permit royalty-free redistribution of the Program by
8674 all those who receive copies directly or indirectly through you, then
8675 the only way you could satisfy both it and this License would be to
8676 refrain entirely from distribution of the Program.
8678 If any portion of this section is held invalid or unenforceable under
8679 any particular circumstance, the balance of the section is intended to
8680 apply and the section as a whole is intended to apply in other
8683 It is not the purpose of this section to induce you to infringe any
8684 patents or other property right claims or to contest validity of any
8685 such claims; this section has the sole purpose of protecting the
8686 integrity of the free software distribution system, which is
8687 implemented by public license practices. Many people have made
8688 generous contributions to the wide range of software distributed
8689 through that system in reliance on consistent application of that
8690 system; it is up to the author/donor to decide if he or she is willing
8691 to distribute software through any other system and a licensee cannot
8694 This section is intended to make thoroughly clear what is believed to
8695 be a consequence of the rest of this License.
8698 If the distribution and/or use of the Program is restricted in
8699 certain countries either by patents or by copyrighted interfaces, the
8700 original copyright holder who places the Program under this License
8701 may add an explicit geographical distribution limitation excluding
8702 those countries, so that distribution is permitted only in or among
8703 countries not thus excluded. In such case, this License incorporates
8704 the limitation as if written in the body of this License.
8707 The Free Software Foundation may publish revised and/or new versions
8708 of the General Public License from time to time. Such new versions will
8709 be similar in spirit to the present version, but may differ in detail to
8710 address new problems or concerns.
8712 Each version is given a distinguishing version number. If the Program
8713 specifies a version number of this License which applies to it and ``any
8714 later version'', you have the option of following the terms and conditions
8715 either of that version or of any later version published by the Free
8716 Software Foundation. If the Program does not specify a version number of
8717 this License, you may choose any version ever published by the Free Software
8721 If you wish to incorporate parts of the Program into other free
8722 programs whose distribution conditions are different, write to the author
8723 to ask for permission. For software which is copyrighted by the Free
8724 Software Foundation, write to the Free Software Foundation; we sometimes
8725 make exceptions for this. Our decision will be guided by the two goals
8726 of preserving the free status of all derivatives of our free software and
8727 of promoting the sharing and reuse of software generally.
8730 @heading NO WARRANTY
8737 BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
8738 FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN
8739 OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
8740 PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
8741 OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
8742 MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS
8743 TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE
8744 PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
8745 REPAIR OR CORRECTION.
8748 IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
8749 WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
8750 REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
8751 INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
8752 OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
8753 TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
8754 YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
8755 PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
8756 POSSIBILITY OF SUCH DAMAGES.
8760 @heading END OF TERMS AND CONDITIONS
8763 @center END OF TERMS AND CONDITIONS
8767 @unnumberedsec Applying These Terms to Your New Programs
8769 If you develop a new program, and you want it to be of the greatest
8770 possible use to the public, the best way to achieve this is to make it
8771 free software which everyone can redistribute and change under these terms.
8773 To do so, attach the following notices to the program. It is safest
8774 to attach them to the start of each source file to most effectively
8775 convey the exclusion of warranty; and each file should have at least
8776 the ``copyright'' line and a pointer to where the full notice is found.
8779 @var{one line to give the program's name and an idea of what it does.}
8780 Copyright (C) 19@var{yy} @var{name of author}
8782 This program is free software; you can redistribute it and/or
8783 modify it under the terms of the GNU General Public License
8784 as published by the Free Software Foundation; either version 2
8785 of the License, or (at your option) any later version.
8787 This program is distributed in the hope that it will be useful,
8788 but WITHOUT ANY WARRANTY; without even the implied warranty of
8789 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
8790 GNU General Public License for more details.
8792 You should have received a copy of the GNU General Public License
8793 along with this program; if not, write to the
8794 Free Software Foundation, Inc., 675 Mass Ave,
8795 Cambridge, MA 02139, USA.
8798 Also add information on how to contact you by electronic and paper mail.
8800 If the program is interactive, make it output a short notice like this
8801 when it starts in an interactive mode:
8804 Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
8805 Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
8806 type `show w'. This is free software, and you are welcome
8807 to redistribute it under certain conditions; type `show c'
8811 The hypothetical commands @samp{show w} and @samp{show c} should show
8812 the appropriate parts of the General Public License. Of course, the
8813 commands you use may be called something other than @samp{show w} and
8814 @samp{show c}; they could even be mouse-clicks or menu items---whatever
8817 You should also get your employer (if you work as a programmer) or your
8818 school, if any, to sign a ``copyright disclaimer'' for the program, if
8819 necessary. Here is a sample; alter the names:
8822 Yoyodyne, Inc., hereby disclaims all copyright
8823 interest in the program `Gnomovision'
8824 (which makes passes at compilers) written
8827 @var{signature of Ty Coon}, 1 April 1989
8828 Ty Coon, President of Vice
8831 This General Public License does not permit incorporating your program into
8832 proprietary programs. If your program is a subroutine library, you may
8833 consider it more useful to permit linking proprietary applications with the
8834 library. If this is what you want to do, use the GNU Library General
8835 Public License instead of this License.
8844 % I think something like @colophon should be in texinfo. In the
8846 \long\def\colophon{\hbox to0pt{}\vfill
8847 \centerline{The body of this manual is set in}
8848 \centerline{\fontname\tenrm,}
8849 \centerline{with headings in {\bf\fontname\tenbf}}
8850 \centerline{and examples in {\tt\fontname\tentt}.}
8851 \centerline{{\it\fontname\tenit\/},}
8852 \centerline{{\bf\fontname\tenbf}, and}
8853 \centerline{{\sl\fontname\tensl\/}}
8854 \centerline{are used for emphasis.}\vfill}
8856 % Blame: pesch@cygnus.com, 1991.