1 \input texinfo @c -*-texinfo-*-
3 @c Free Software Foundation, Inc.
6 @c makeinfo ignores cmds prev to setfilename, so its arg cannot make use
7 @c of @set vars. However, you can override filename with makeinfo -o.
12 @settitle Debugging with @value{GDBN}
13 @setchapternewpage odd
24 @c readline appendices use @vindex
27 @c !!set GDB manual's edition---not the same as GDB version!
30 @c !!set GDB manual's revision date
31 @set DATE February 1999
33 @c THIS MANUAL REQUIRES TEXINFO-2 macros and info-makers to format properly.
36 @c This is a dir.info fragment to support semi-automated addition of
37 @c manuals to an info tree. zoo@cygnus.com is developing this facility.
40 * Gdb: (gdb). The @sc{gnu} debugger.
47 This file documents the @sc{gnu} debugger @value{GDBN}.
50 This is the @value{EDITION} Edition, @value{DATE},
51 of @cite{Debugging with @value{GDBN}: the @sc{gnu} Source-Level Debugger}
52 for @value{GDBN} Version @value{GDBVN}.
54 Copyright (C) 1988-1999 Free Software Foundation, Inc.
56 Permission is granted to make and distribute verbatim copies of
57 this manual provided the copyright notice and this permission notice
58 are preserved on all copies.
61 Permission is granted to process this file through TeX and print the
62 results, provided the printed document carries copying permission
63 notice identical to this one except for the removal of this paragraph
64 (this paragraph not being relevant to the printed manual).
67 Permission is granted to copy and distribute modified versions of this
68 manual under the conditions for verbatim copying, provided also that the
69 entire resulting derived work is distributed under the terms of a
70 permission notice identical to this one.
72 Permission is granted to copy and distribute translations of this manual
73 into another language, under the above conditions for modified versions.
77 @title Debugging with @value{GDBN}
78 @subtitle The @sc{gnu} Source-Level Debugger
80 @subtitle @value{EDITION} Edition, for @value{GDBN} version @value{GDBVN}
81 @subtitle @value{DATE}
82 @author Richard M. Stallman and Roland H. Pesch
86 \hfill (Send bugs and comments on @value{GDBN} to bug-gdb\@gnu.org.)\par
87 \hfill {\it Debugging with @value{GDBN}}\par
88 \hfill \TeX{}info \texinfoversion\par
92 @c ISBN seems to be wrong...
94 @vskip 0pt plus 1filll
95 Copyright @copyright{} 1988-1999 Free Software Foundation, Inc.
97 Published by the Free Software Foundation @*
98 59 Temple Place - Suite 330, @*
99 Boston, MA 02111-1307 USA @*
100 Printed copies are available for $20 each. @*
101 ISBN 1-882114-11-6 @*
103 Permission is granted to make and distribute verbatim copies of
104 this manual provided the copyright notice and this permission notice
105 are preserved on all copies.
107 Permission is granted to copy and distribute modified versions of this
108 manual under the conditions for verbatim copying, provided also that the
109 entire resulting derived work is distributed under the terms of a
110 permission notice identical to this one.
112 Permission is granted to copy and distribute translations of this manual
113 into another language, under the above conditions for modified versions.
119 @top Debugging with @value{GDBN}
121 This file describes @value{GDBN}, the @sc{gnu} symbolic debugger.
123 This is the @value{EDITION} Edition, @value{DATE}, for @value{GDBN} Version
126 Copyright (C) 1988-1999 Free Software Foundation, Inc.
128 * Summary:: Summary of @value{GDBN}
129 * Sample Session:: A sample @value{GDBN} session
131 * Invocation:: Getting in and out of @value{GDBN}
132 * Commands:: @value{GDBN} commands
133 * Running:: Running programs under @value{GDBN}
134 * Stopping:: Stopping and continuing
135 * Stack:: Examining the stack
136 * Source:: Examining source files
137 * Data:: Examining data
139 * Languages:: Using @value{GDBN} with different languages
141 * Symbols:: Examining the symbol table
142 * Altering:: Altering execution
143 * GDB Files:: @value{GDBN} files
144 * Targets:: Specifying a debugging target
145 * Configurations:: Configuration-specific information
146 * Controlling GDB:: Controlling @value{GDBN}
147 * Sequences:: Canned sequences of commands
148 * Emacs:: Using @value{GDBN} under @sc{gnu} Emacs
149 * Annotations:: @value{GDBN}'s annotations interface.
151 * GDB Bugs:: Reporting bugs in @value{GDBN}
152 * Formatting Documentation:: How to format and print @value{GDBN} documentation
154 * Command Line Editing:: Command Line Editing
155 * Using History Interactively:: Using History Interactively
156 * Installing GDB:: Installing GDB
163 @unnumbered Summary of @value{GDBN}
165 The purpose of a debugger such as @value{GDBN} is to allow you to see what is
166 going on ``inside'' another program while it executes---or what another
167 program was doing at the moment it crashed.
169 @value{GDBN} can do four main kinds of things (plus other things in support of
170 these) to help you catch bugs in the act:
174 Start your program, specifying anything that might affect its behavior.
177 Make your program stop on specified conditions.
180 Examine what has happened, when your program has stopped.
183 Change things in your program, so you can experiment with correcting the
184 effects of one bug and go on to learn about another.
187 You can use @value{GDBN} to debug programs written in C and C++.
188 For more information, see @ref{Support,,Supported languages}.
189 For more information, see @ref{C,,C and C++}.
193 Support for Modula-2 and Chill is partial. For information on Modula-2,
194 see @ref{Modula-2,,Modula-2}. For information on Chill, see @ref{Chill}.
197 Debugging Pascal programs which use sets, subranges, file variables, or
198 nested functions does not currently work. @value{GDBN} does not support
199 entering expressions, printing values, or similar features using Pascal
203 @value{GDBN} can be used to debug programs written in Fortran, although
204 it may be necessary to refer to some variables with a trailing
208 * Free Software:: Freely redistributable software
209 * Contributors:: Contributors to GDB
213 @unnumberedsec Free software
215 @value{GDBN} is @dfn{free software}, protected by the @sc{gnu}
216 General Public License
217 (GPL). The GPL gives you the freedom to copy or adapt a licensed
218 program---but every person getting a copy also gets with it the
219 freedom to modify that copy (which means that they must get access to
220 the source code), and the freedom to distribute further copies.
221 Typical software companies use copyrights to limit your freedoms; the
222 Free Software Foundation uses the GPL to preserve these freedoms.
224 Fundamentally, the General Public License is a license which says that
225 you have these freedoms and that you cannot take these freedoms away
229 @unnumberedsec Contributors to GDB
231 Richard Stallman was the original author of GDB, and of many other
232 @sc{gnu} programs. Many others have contributed to its development.
233 This section attempts to credit major contributors. One of the virtues
234 of free software is that everyone is free to contribute to it; with
235 regret, we cannot actually acknowledge everyone here. The file
236 @file{ChangeLog} in the @value{GDBN} distribution approximates a
237 blow-by-blow account.
239 Changes much prior to version 2.0 are lost in the mists of time.
242 @emph{Plea:} Additions to this section are particularly welcome. If you
243 or your friends (or enemies, to be evenhanded) have been unfairly
244 omitted from this list, we would like to add your names!
247 So that they may not regard their many labors as thankless, we
248 particularly thank those who shepherded @value{GDBN} through major
250 Jim Blandy (release 4.18);
251 Jason Molenda (release 4.17);
252 Stan Shebs (release 4.14);
253 Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9);
254 Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4);
255 John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9);
256 Jim Kingdon (releases 3.5, 3.4, and 3.3);
257 and Randy Smith (releases 3.2, 3.1, and 3.0).
259 Richard Stallman, assisted at various times by Peter TerMaat, Chris
260 Hanson, and Richard Mlynarik, handled releases through 2.8.
262 Michael Tiemann is the author of most of the @sc{gnu} C++ support in GDB,
263 with significant additional contributions from Per Bothner. James
264 Clark wrote the @sc{gnu} C++ demangler. Early work on C++ was by Peter
265 TerMaat (who also did much general update work leading to release 3.0).
267 @value{GDBN} 4 uses the BFD subroutine library to examine multiple
268 object-file formats; BFD was a joint project of David V.
269 Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.
271 David Johnson wrote the original COFF support; Pace Willison did
272 the original support for encapsulated COFF.
274 Brent Benson of Harris Computer Systems contributed DWARF 2 support.
276 Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
277 Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
279 Jean-Daniel Fekete contributed Sun 386i support.
280 Chris Hanson improved the HP9000 support.
281 Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support.
282 David Johnson contributed Encore Umax support.
283 Jyrki Kuoppala contributed Altos 3068 support.
284 Jeff Law contributed HP PA and SOM support.
285 Keith Packard contributed NS32K support.
286 Doug Rabson contributed Acorn Risc Machine support.
287 Bob Rusk contributed Harris Nighthawk CX-UX support.
288 Chris Smith contributed Convex support (and Fortran debugging).
289 Jonathan Stone contributed Pyramid support.
290 Michael Tiemann contributed SPARC support.
291 Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
292 Pace Willison contributed Intel 386 support.
293 Jay Vosburgh contributed Symmetry support.
295 Andreas Schwab contributed M68K Linux support.
297 Rich Schaefer and Peter Schauer helped with support of SunOS shared
300 Jay Fenlason and Roland McGrath ensured that @value{GDBN} and GAS agree
301 about several machine instruction sets.
303 Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop
304 remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM
305 contributed remote debugging modules for the i960, VxWorks, A29K UDI,
306 and RDI targets, respectively.
308 Brian Fox is the author of the readline libraries providing
309 command-line editing and command history.
311 Andrew Beers of SUNY Buffalo wrote the language-switching code, the
312 Modula-2 support, and contributed the Languages chapter of this manual.
314 Fred Fish wrote most of the support for Unix System Vr4.
315 He also enhanced the command-completion support to cover C++ overloaded
318 Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and
321 NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.
323 Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.
325 Toshiba sponsored the support for the TX39 Mips processor.
327 Matsushita sponsored the support for the MN10200 and MN10300 processors.
329 Fujitsu sponsored the support for SPARClite and FR30 processors
331 Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
334 Michael Snyder added support for tracepoints.
336 Stu Grossman wrote gdbserver.
338 Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made
339 nearly innumerable bug fixes and cleanups throughout GDB.
341 The following people at the Hewlett-Packard Company contributed
342 support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
343 (narrow mode), HP's implementation of kernel threads, HP's aC++
344 compiler, and the terminal user interface: Ben Krepp, Richard Title,
345 John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve
346 Rehrauer, and Elena Zannoni. Kim Haase provided HP-specific
347 information in this manual.
349 Cygnus Solutions has sponsored GDB maintenance and much of its
350 development since 1991. Cygnus engineers who have worked on GDB
351 fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
352 Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
353 Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
354 Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
355 Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In
356 addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
357 JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
358 Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
359 Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
360 Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
361 Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
362 Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
363 Zuhn have made contributions both large and small.
367 @chapter A Sample @value{GDBN} Session
369 You can use this manual at your leisure to read all about @value{GDBN}.
370 However, a handful of commands are enough to get started using the
371 debugger. This chapter illustrates those commands.
374 In this sample session, we emphasize user input like this: @b{input},
375 to make it easier to pick out from the surrounding output.
378 @c FIXME: this example may not be appropriate for some configs, where
379 @c FIXME...primary interest is in remote use.
381 One of the preliminary versions of @sc{gnu} @code{m4} (a generic macro
382 processor) exhibits the following bug: sometimes, when we change its
383 quote strings from the default, the commands used to capture one macro
384 definition within another stop working. In the following short @code{m4}
385 session, we define a macro @code{foo} which expands to @code{0000}; we
386 then use the @code{m4} built-in @code{defn} to define @code{bar} as the
387 same thing. However, when we change the open quote string to
388 @code{<QUOTE>} and the close quote string to @code{<UNQUOTE>}, the same
389 procedure fails to define a new synonym @code{baz}:
398 @b{define(bar,defn(`foo'))}
402 @b{changequote(<QUOTE>,<UNQUOTE>)}
404 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
407 m4: End of input: 0: fatal error: EOF in string
411 Let us use @value{GDBN} to try to see what is going on.
414 $ @b{@value{GDBP} m4}
415 @c FIXME: this falsifies the exact text played out, to permit smallbook
416 @c FIXME... format to come out better.
417 @value{GDBN} is free software and you are welcome to distribute copies
418 of it under certain conditions; type "show copying" to see
420 There is absolutely no warranty for @value{GDBN}; type "show warranty"
423 @value{GDBN} @value{GDBVN}, Copyright 1999 Free Software Foundation, Inc...
428 @value{GDBN} reads only enough symbol data to know where to find the
429 rest when needed; as a result, the first prompt comes up very quickly.
430 We now tell @value{GDBN} to use a narrower display width than usual, so
431 that examples fit in this manual.
434 (@value{GDBP}) @b{set width 70}
438 We need to see how the @code{m4} built-in @code{changequote} works.
439 Having looked at the source, we know the relevant subroutine is
440 @code{m4_changequote}, so we set a breakpoint there with the @value{GDBN}
441 @code{break} command.
444 (@value{GDBP}) @b{break m4_changequote}
445 Breakpoint 1 at 0x62f4: file builtin.c, line 879.
449 Using the @code{run} command, we start @code{m4} running under @value{GDBN}
450 control; as long as control does not reach the @code{m4_changequote}
451 subroutine, the program runs as usual:
454 (@value{GDBP}) @b{run}
455 Starting program: /work/Editorial/gdb/gnu/m4/m4
463 To trigger the breakpoint, we call @code{changequote}. @value{GDBN}
464 suspends execution of @code{m4}, displaying information about the
465 context where it stops.
468 @b{changequote(<QUOTE>,<UNQUOTE>)}
470 Breakpoint 1, m4_changequote (argc=3, argv=0x33c70)
472 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
476 Now we use the command @code{n} (@code{next}) to advance execution to
477 the next line of the current function.
481 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
486 @code{set_quotes} looks like a promising subroutine. We can go into it
487 by using the command @code{s} (@code{step}) instead of @code{next}.
488 @code{step} goes to the next line to be executed in @emph{any}
489 subroutine, so it steps into @code{set_quotes}.
493 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
495 530 if (lquote != def_lquote)
499 The display that shows the subroutine where @code{m4} is now
500 suspended (and its arguments) is called a stack frame display. It
501 shows a summary of the stack. We can use the @code{backtrace}
502 command (which can also be spelled @code{bt}), to see where we are
503 in the stack as a whole: the @code{backtrace} command displays a
504 stack frame for each active subroutine.
507 (@value{GDBP}) @b{bt}
508 #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
510 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70)
512 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242
513 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
515 #4 0x79dc in expand_input () at macro.c:40
516 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
520 We step through a few more lines to see what happens. The first two
521 times, we can use @samp{s}; the next two times we use @code{n} to avoid
522 falling into the @code{xstrdup} subroutine.
526 0x3b5c 532 if (rquote != def_rquote)
528 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \
529 def_lquote : xstrdup(lq);
531 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
534 538 len_lquote = strlen(rquote);
538 The last line displayed looks a little odd; we can examine the variables
539 @code{lquote} and @code{rquote} to see if they are in fact the new left
540 and right quotes we specified. We use the command @code{p}
541 (@code{print}) to see their values.
544 (@value{GDBP}) @b{p lquote}
545 $1 = 0x35d40 "<QUOTE>"
546 (@value{GDBP}) @b{p rquote}
547 $2 = 0x35d50 "<UNQUOTE>"
551 @code{lquote} and @code{rquote} are indeed the new left and right quotes.
552 To look at some context, we can display ten lines of source
553 surrounding the current line with the @code{l} (@code{list}) command.
559 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\
561 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\
564 538 len_lquote = strlen(rquote);
565 539 len_rquote = strlen(lquote);
572 Let us step past the two lines that set @code{len_lquote} and
573 @code{len_rquote}, and then examine the values of those variables.
577 539 len_rquote = strlen(lquote);
580 (@value{GDBP}) @b{p len_lquote}
582 (@value{GDBP}) @b{p len_rquote}
587 That certainly looks wrong, assuming @code{len_lquote} and
588 @code{len_rquote} are meant to be the lengths of @code{lquote} and
589 @code{rquote} respectively. We can set them to better values using
590 the @code{p} command, since it can print the value of
591 any expression---and that expression can include subroutine calls and
595 (@value{GDBP}) @b{p len_lquote=strlen(lquote)}
597 (@value{GDBP}) @b{p len_rquote=strlen(rquote)}
602 Is that enough to fix the problem of using the new quotes with the
603 @code{m4} built-in @code{defn}? We can allow @code{m4} to continue
604 executing with the @code{c} (@code{continue}) command, and then try the
605 example that caused trouble initially:
611 @b{define(baz,defn(<QUOTE>foo<UNQUOTE>))}
618 Success! The new quotes now work just as well as the default ones. The
619 problem seems to have been just the two typos defining the wrong
620 lengths. We allow @code{m4} exit by giving it an EOF as input:
624 Program exited normally.
628 The message @samp{Program exited normally.} is from @value{GDBN}; it
629 indicates @code{m4} has finished executing. We can end our @value{GDBN}
630 session with the @value{GDBN} @code{quit} command.
633 (@value{GDBP}) @b{quit}
637 @chapter Getting In and Out of @value{GDBN}
639 This chapter discusses how to start @value{GDBN}, and how to get out of it.
643 type @samp{@value{GDBP}} to start @value{GDBN}.
645 type @kbd{quit} or @kbd{C-d} to exit.
649 * Invoking GDB:: How to start @value{GDBN}
650 * Quitting GDB:: How to quit @value{GDBN}
651 * Shell Commands:: How to use shell commands inside @value{GDBN}
655 @section Invoking @value{GDBN}
657 Invoke @value{GDBN} by running the program @code{@value{GDBP}}. Once started,
658 @value{GDBN} reads commands from the terminal until you tell it to exit.
660 You can also run @code{@value{GDBP}} with a variety of arguments and options,
661 to specify more of your debugging environment at the outset.
663 The command-line options described here are designed
664 to cover a variety of situations; in some environments, some of these
665 options may effectively be unavailable.
667 The most usual way to start @value{GDBN} is with one argument,
668 specifying an executable program:
671 @value{GDBP} @var{program}
675 You can also start with both an executable program and a core file
679 @value{GDBP} @var{program} @var{core}
682 You can, instead, specify a process ID as a second argument, if you want
683 to debug a running process:
686 @value{GDBP} @var{program} 1234
690 would attach @value{GDBN} to process @code{1234} (unless you also have a file
691 named @file{1234}; @value{GDBN} does check for a core file first).
693 Taking advantage of the second command-line argument requires a fairly
694 complete operating system; when you use @value{GDBN} as a remote
695 debugger attached to a bare board, there may not be any notion of
696 ``process'', and there is often no way to get a core dump. @value{GDBN}
697 will warn you if it is unable to attach or to read core dumps.
699 You can run @code{gdb} without printing the front material, which describes
700 @value{GDBN}'s non-warranty, by specifying @code{-silent}:
707 You can further control how @value{GDBN} starts up by using command-line
708 options. @value{GDBN} itself can remind you of the options available.
718 to display all available options and briefly describe their use
719 (@samp{@value{GDBP} -h} is a shorter equivalent).
721 All options and command line arguments you give are processed
722 in sequential order. The order makes a difference when the
723 @samp{-x} option is used.
727 * File Options:: Choosing files
728 * Mode Options:: Choosing modes
732 @subsection Choosing files
734 When @value{GDBN} starts, it reads any arguments other than options as
735 specifying an executable file and core file (or process ID). This is
736 the same as if the arguments were specified by the @samp{-se} and
737 @samp{-c} options respectively. (@value{GDBN} reads the first argument
738 that does not have an associated option flag as equivalent to the
739 @samp{-se} option followed by that argument; and the second argument
740 that does not have an associated option flag, if any, as equivalent to
741 the @samp{-c} option followed by that argument.)
743 If @value{GDBN} has not been configured to included core file support,
744 such as for most embedded targets, then it will complain about a second
745 argument and ignore it.
747 Many options have both long and short forms; both are shown in the
748 following list. @value{GDBN} also recognizes the long forms if you truncate
749 them, so long as enough of the option is present to be unambiguous.
750 (If you prefer, you can flag option arguments with @samp{--} rather
751 than @samp{-}, though we illustrate the more usual convention.)
753 @c NOTE: the @cindex entries here use double dashes ON PURPOSE. This
754 @c way, both those who look for -foo and --foo in the index, will find
758 @item -symbols @var{file}
760 @cindex @code{--symbols}
762 Read symbol table from file @var{file}.
764 @item -exec @var{file}
766 @cindex @code{--exec}
768 Use file @var{file} as the executable file to execute when appropriate,
769 and for examining pure data in conjunction with a core dump.
773 Read symbol table from file @var{file} and use it as the executable
776 @item -core @var{file}
778 @cindex @code{--core}
780 Use file @var{file} as a core dump to examine.
782 @item -c @var{number}
783 Connect to process ID @var{number}, as with the @code{attach} command
784 (unless there is a file in core-dump format named @var{number}, in which
785 case @samp{-c} specifies that file as a core dump to read).
787 @item -command @var{file}
789 @cindex @code{--command}
791 Execute @value{GDBN} commands from file @var{file}. @xref{Command
792 Files,, Command files}.
794 @item -directory @var{directory}
795 @itemx -d @var{directory}
796 @cindex @code{--directory}
798 Add @var{directory} to the path to search for source files.
802 @cindex @code{--mapped}
804 @emph{Warning: this option depends on operating system facilities that are not
805 supported on all systems.}@*
806 If memory-mapped files are available on your system through the @code{mmap}
807 system call, you can use this option
808 to have @value{GDBN} write the symbols from your
809 program into a reusable file in the current directory. If the program you are debugging is
810 called @file{/tmp/fred}, the mapped symbol file is @file{./fred.syms}.
811 Future @value{GDBN} debugging sessions notice the presence of this file,
812 and can quickly map in symbol information from it, rather than reading
813 the symbol table from the executable program.
815 The @file{.syms} file is specific to the host machine where @value{GDBN}
816 is run. It holds an exact image of the internal @value{GDBN} symbol
817 table. It cannot be shared across multiple host platforms.
821 @cindex @code{--readnow}
823 Read each symbol file's entire symbol table immediately, rather than
824 the default, which is to read it incrementally as it is needed.
825 This makes startup slower, but makes future operations faster.
829 You typically combine the @code{-mapped} and @code{-readnow} options in
830 order to build a @file{.syms} file that contains complete symbol
831 information. (@xref{Files,,Commands to specify files}, for information
832 on @file{.syms} files.) A simple @value{GDBN} invocation to do nothing
833 but build a @file{.syms} file for future use is:
836 gdb -batch -nx -mapped -readnow programname
840 @subsection Choosing modes
842 You can run @value{GDBN} in various alternative modes---for example, in
843 batch mode or quiet mode.
850 Do not execute commands found in any initialization files (normally
851 called @file{.gdbinit}, or @file{gdb.ini} on PCs). Normally,
852 @value{GDBN} executes the commands in these files after all the command
853 options and arguments have been processed. @xref{Command Files,,Command
859 @cindex @code{--quiet}
860 @cindex @code{--silent}
862 ``Quiet''. Do not print the introductory and copyright messages. These
863 messages are also suppressed in batch mode.
866 @cindex @code{--batch}
867 Run in batch mode. Exit with status @code{0} after processing all the
868 command files specified with @samp{-x} (and all commands from
869 initialization files, if not inhibited with @samp{-n}). Exit with
870 nonzero status if an error occurs in executing the @value{GDBN} commands
871 in the command files.
873 Batch mode may be useful for running @value{GDBN} as a filter, for
874 example to download and run a program on another computer; in order to
875 make this more useful, the message
878 Program exited normally.
882 (which is ordinarily issued whenever a program running under
883 @value{GDBN} control terminates) is not issued when running in batch
888 @cindex @code{--nowindows}
890 ``No windows''. If @value{GDBN} comes with a graphical user interface
891 (GUI) built in, then this option tells GDB to only use the command-line
892 interface. If no GUI is available, this option has no effect.
896 @cindex @code{--windows}
898 If @value{GDBN} includes a GUI, then this option requires it to be
901 @item -cd @var{directory}
903 Run @value{GDBN} using @var{directory} as its working directory,
904 instead of the current directory.
908 @cindex @code{--fullname}
910 @sc{gnu} Emacs sets this option when it runs @value{GDBN} as a
911 subprocess. It tells @value{GDBN} to output the full file name and line
912 number in a standard, recognizable fashion each time a stack frame is
913 displayed (which includes each time your program stops). This
914 recognizable format looks like two @samp{\032} characters, followed by
915 the file name, line number and character position separated by colons,
916 and a newline. The Emacs-to-@value{GDBN} interface program uses the two
917 @samp{\032} characters as a signal to display the source code for the
921 @cindex @code{--epoch}
922 The Epoch Emacs-@value{GDBN} interface sets this option when it runs
923 @value{GDBN} as a subprocess. It tells @value{GDBN} to modify its print
924 routines so as to allow Epoch to display values of expressions in a
927 @item -annotate @var{level}
928 @cindex @code{--annotate}
929 This option sets the @dfn{annotation level} inside @value{GDBN}. Its
930 effect is identical to using @samp{set annotate @var{level}}
931 (@pxref{Annotations}).
932 Annotation level controls how much information does @value{GDBN} print
933 together with its prompt, values of expressions, source lines, and other
934 types of output. Level 0 is the normal, level 1 is for use when
935 @value{GDBN} is run as a subprocess of @sc{gnu} Emacs, level 2 is the
936 maximum annotation suitable for programs that control @value{GDBN}.
939 @cindex @code{--async}
940 Use the asynchronous event loop for the command-line interface.
941 @value{GDBN} processes all events, such as user keyboard input, via a
942 special event loop. This allows @value{GDBN} to accept and process user
943 commands in parallel with the debugged process being
944 run@footnote{@value{GDBN} built with @sc{djgpp} tools for
945 MS-DOS/MS-Windows supports this mode of operation, but the event loop is
946 suspended when the debuggee runs.}, so you don't need to wait for
947 control to return to @value{GDBN} before you type the next command.
948 (@emph{Note:} as of version 5.0, the target side of the asynchronous
949 operation is not yet in place, so @samp{-async} does not work fully
951 @c FIXME: when the target side of the event loop is done, the above NOTE
952 @c should be removed.
954 When the standard input is connected to a terminal device, @value{GDBN}
955 uses the asynchronous event loop by default, unless disabled by the
956 @samp{-noasync} option.
959 @cindex @code{--noasync}
960 Disable the asynchronous event loop for the command-line interface.
962 @item -baud @var{bps}
964 @cindex @code{--baud}
966 Set the line speed (baud rate or bits per second) of any serial
967 interface used by @value{GDBN} for remote debugging.
969 @item -tty @var{device}
970 @itemx -t @var{device}
973 Run using @var{device} for your program's standard input and output.
974 @c FIXME: kingdon thinks there is more to -tty. Investigate.
976 @c resolve the situation of these eventually
978 @c @cindex @code{--tui}
979 @c Use a Terminal User Interface. For information, use your Web browser to
980 @c read the file @file{TUI.html}, which is usually installed in the
981 @c directory @code{/opt/langtools/wdb/doc} on HP-UX systems. Do not use
982 @c this option if you run @value{GDBN} from Emacs (see @pxref{Emacs, ,Using
983 @c @value{GDBN} under @sc{gnu} Emacs}).
986 @c @cindex @code{--xdb}
987 @c Run in XDB compatibility mode, allowing the use of certain XDB commands.
988 @c For information, see the file @file{xdb_trans.html}, which is usually
989 @c installed in the directory @code{/opt/langtools/wdb/doc} on HP-UX
992 @item -interpreter @var{interp}
993 @cindex @code{--interpreter}
994 Use the interpreter @var{interp} for interface with the controlling
995 program or device. This option is meant to be set by programs which
996 communicate with @value{GDBN} using it as a back end. For example,
997 @samp{--interpreter=mi} causes @value{GDBN} to use the @dfn{gdbmi
999 @c FIXME: There should be an @xref here to the GDB/MI docs, but
1000 @c gdbmi.texi doesn't have a single node to reference!
1003 @cindex @code{--write}
1004 Open the executable and core files for both reading and writing. This
1005 is equivalent to the @samp{set write on} command inside @value{GDBN}
1009 @cindex @code{--statistics}
1010 This option causes @value{GDBN} to print statistics about time and
1011 memory usage after it completes each command and returns to the prompt.
1014 @cindex @code{--version}
1015 This option causes @value{GDBN} to print its version number and
1016 no-warranty blurb, and exit.
1021 @section Quitting @value{GDBN}
1022 @cindex exiting @value{GDBN}
1023 @cindex leaving @value{GDBN}
1026 @kindex quit @r{[}@var{expression}@r{]}
1029 To exit @value{GDBN}, use the @code{quit} command (abbreviated @code{q}), or
1030 type an end-of-file character (usually @kbd{C-d}). If you do not supply
1031 @var{expression}, @value{GDBN} will terminate normally; otherwise it will
1032 terminate using the result of @var{expression} as the error code.
1036 An interrupt (often @kbd{C-c}) does not exit from @value{GDBN}, but rather
1037 terminates the action of any @value{GDBN} command that is in progress and
1038 returns to @value{GDBN} command level. It is safe to type the interrupt
1039 character at any time because @value{GDBN} does not allow it to take effect
1040 until a time when it is safe.
1042 If you have been using @value{GDBN} to control an attached process or
1043 device, you can release it with the @code{detach} command
1044 (@pxref{Attach, ,Debugging an already-running process}).
1046 @node Shell Commands
1047 @section Shell commands
1049 If you need to execute occasional shell commands during your
1050 debugging session, there is no need to leave or suspend @value{GDBN}; you can
1051 just use the @code{shell} command.
1055 @cindex shell escape
1056 @item shell @var{command string}
1057 Invoke a standard shell to execute @var{command string}.
1058 If it exists, the environment variable @code{SHELL} determines which
1059 shell to run. Otherwise @value{GDBN} uses the default shell
1060 (@file{/bin/sh} on Unix systems, @file{COMMAND.COM} on MS-DOS, etc.).
1063 The utility @code{make} is often needed in development environments.
1064 You do not have to use the @code{shell} command for this purpose in
1069 @cindex calling make
1070 @item make @var{make-args}
1071 Execute the @code{make} program with the specified
1072 arguments. This is equivalent to @samp{shell make @var{make-args}}.
1076 @chapter @value{GDBN} Commands
1078 You can abbreviate a @value{GDBN} command to the first few letters of the command
1079 name, if that abbreviation is unambiguous; and you can repeat certain
1080 @value{GDBN} commands by typing just @key{RET}. You can also use the @key{TAB}
1081 key to get @value{GDBN} to fill out the rest of a word in a command (or to
1082 show you the alternatives available, if there is more than one possibility).
1085 * Command Syntax:: How to give commands to @value{GDBN}
1086 * Completion:: Command completion
1087 * Help:: How to ask @value{GDBN} for help
1090 @node Command Syntax
1091 @section Command syntax
1093 A @value{GDBN} command is a single line of input. There is no limit on
1094 how long it can be. It starts with a command name, which is followed by
1095 arguments whose meaning depends on the command name. For example, the
1096 command @code{step} accepts an argument which is the number of times to
1097 step, as in @samp{step 5}. You can also use the @code{step} command
1098 with no arguments. Some command names do not allow any arguments.
1100 @cindex abbreviation
1101 @value{GDBN} command names may always be truncated if that abbreviation is
1102 unambiguous. Other possible command abbreviations are listed in the
1103 documentation for individual commands. In some cases, even ambiguous
1104 abbreviations are allowed; for example, @code{s} is specially defined as
1105 equivalent to @code{step} even though there are other commands whose
1106 names start with @code{s}. You can test abbreviations by using them as
1107 arguments to the @code{help} command.
1109 @cindex repeating commands
1111 A blank line as input to @value{GDBN} (typing just @key{RET}) means to
1112 repeat the previous command. Certain commands (for example, @code{run})
1113 will not repeat this way; these are commands whose unintentional
1114 repetition might cause trouble and which you are unlikely to want to
1117 The @code{list} and @code{x} commands, when you repeat them with
1118 @key{RET}, construct new arguments rather than repeating
1119 exactly as typed. This permits easy scanning of source or memory.
1121 @value{GDBN} can also use @key{RET} in another way: to partition lengthy
1122 output, in a way similar to the common utility @code{more}
1123 (@pxref{Screen Size,,Screen size}). Since it is easy to press one
1124 @key{RET} too many in this situation, @value{GDBN} disables command
1125 repetition after any command that generates this sort of display.
1129 Any text from a @kbd{#} to the end of the line is a comment; it does
1130 nothing. This is useful mainly in command files (@pxref{Command
1131 Files,,Command files}).
1134 @section Command completion
1137 @cindex word completion
1138 @value{GDBN} can fill in the rest of a word in a command for you, if there is
1139 only one possibility; it can also show you what the valid possibilities
1140 are for the next word in a command, at any time. This works for @value{GDBN}
1141 commands, @value{GDBN} subcommands, and the names of symbols in your program.
1143 Press the @key{TAB} key whenever you want @value{GDBN} to fill out the rest
1144 of a word. If there is only one possibility, @value{GDBN} fills in the
1145 word, and waits for you to finish the command (or press @key{RET} to
1146 enter it). For example, if you type
1148 @c FIXME "@key" does not distinguish its argument sufficiently to permit
1149 @c complete accuracy in these examples; space introduced for clarity.
1150 @c If texinfo enhancements make it unnecessary, it would be nice to
1151 @c replace " @key" by "@key" in the following...
1153 (@value{GDBP}) info bre @key{TAB}
1157 @value{GDBN} fills in the rest of the word @samp{breakpoints}, since that is
1158 the only @code{info} subcommand beginning with @samp{bre}:
1161 (@value{GDBP}) info breakpoints
1165 You can either press @key{RET} at this point, to run the @code{info
1166 breakpoints} command, or backspace and enter something else, if
1167 @samp{breakpoints} does not look like the command you expected. (If you
1168 were sure you wanted @code{info breakpoints} in the first place, you
1169 might as well just type @key{RET} immediately after @samp{info bre},
1170 to exploit command abbreviations rather than command completion).
1172 If there is more than one possibility for the next word when you press
1173 @key{TAB}, @value{GDBN} sounds a bell. You can either supply more
1174 characters and try again, or just press @key{TAB} a second time;
1175 @value{GDBN} displays all the possible completions for that word. For
1176 example, you might want to set a breakpoint on a subroutine whose name
1177 begins with @samp{make_}, but when you type @kbd{b make_@key{TAB}} @value{GDBN}
1178 just sounds the bell. Typing @key{TAB} again displays all the
1179 function names in your program that begin with those characters, for
1183 (@value{GDBP}) b make_ @key{TAB}
1184 @exdent @value{GDBN} sounds bell; press @key{TAB} again, to see:
1185 make_a_section_from_file make_environ
1186 make_abs_section make_function_type
1187 make_blockvector make_pointer_type
1188 make_cleanup make_reference_type
1189 make_command make_symbol_completion_list
1190 (@value{GDBP}) b make_
1194 After displaying the available possibilities, @value{GDBN} copies your
1195 partial input (@samp{b make_} in the example) so you can finish the
1198 If you just want to see the list of alternatives in the first place, you
1199 can press @kbd{M-?} rather than pressing @key{TAB} twice. @kbd{M-?}
1200 means @kbd{@key{META} ?}. You can type this either by holding down a
1201 key designated as the @key{META} shift on your keyboard (if there is
1202 one) while typing @kbd{?}, or as @key{ESC} followed by @kbd{?}.
1204 @cindex quotes in commands
1205 @cindex completion of quoted strings
1206 Sometimes the string you need, while logically a ``word'', may contain
1207 parentheses or other characters that @value{GDBN} normally excludes from
1208 its notion of a word. To permit word completion to work in this
1209 situation, you may enclose words in @code{'} (single quote marks) in
1210 @value{GDBN} commands.
1212 The most likely situation where you might need this is in typing the
1213 name of a C++ function. This is because C++ allows function overloading
1214 (multiple definitions of the same function, distinguished by argument
1215 type). For example, when you want to set a breakpoint you may need to
1216 distinguish whether you mean the version of @code{name} that takes an
1217 @code{int} parameter, @code{name(int)}, or the version that takes a
1218 @code{float} parameter, @code{name(float)}. To use the word-completion
1219 facilities in this situation, type a single quote @code{'} at the
1220 beginning of the function name. This alerts @value{GDBN} that it may need to
1221 consider more information than usual when you press @key{TAB} or
1222 @kbd{M-?} to request word completion:
1225 (@value{GDBP}) b 'bubble( @key{M-?}
1226 bubble(double,double) bubble(int,int)
1227 (@value{GDBP}) b 'bubble(
1230 In some cases, @value{GDBN} can tell that completing a name requires using
1231 quotes. When this happens, @value{GDBN} inserts the quote for you (while
1232 completing as much as it can) if you do not type the quote in the first
1236 (@value{GDBP}) b bub @key{TAB}
1237 @exdent @value{GDBN} alters your input line to the following, and rings a bell:
1238 (@value{GDBP}) b 'bubble(
1242 In general, @value{GDBN} can tell that a quote is needed (and inserts it) if
1243 you have not yet started typing the argument list when you ask for
1244 completion on an overloaded symbol.
1246 For more information about overloaded functions, see @ref{C plus plus
1247 expressions, ,C++ expressions}. You can use the command @code{set
1248 overload-resolution off} to disable overload resolution;
1249 see @ref{Debugging C plus plus, ,@value{GDBN} features for C++}.
1253 @section Getting help
1254 @cindex online documentation
1257 You can always ask @value{GDBN} itself for information on its commands,
1258 using the command @code{help}.
1264 You can use @code{help} (abbreviated @code{h}) with no arguments to
1265 display a short list of named classes of commands:
1269 List of classes of commands:
1271 aliases -- Aliases of other commands
1272 breakpoints -- Making program stop at certain points
1273 data -- Examining data
1274 files -- Specifying and examining files
1275 internals -- Maintenance commands
1276 obscure -- Obscure features
1277 running -- Running the program
1278 stack -- Examining the stack
1279 status -- Status inquiries
1280 support -- Support facilities
1281 tracepoints -- Tracing of program execution without stopping the program
1282 user-defined -- User-defined commands
1284 Type "help" followed by a class name for a list of
1285 commands in that class.
1286 Type "help" followed by command name for full
1288 Command name abbreviations are allowed if unambiguous.
1292 @item help @var{class}
1293 Using one of the general help classes as an argument, you can get a
1294 list of the individual commands in that class. For example, here is the
1295 help display for the class @code{status}:
1298 (@value{GDBP}) help status
1303 @c Line break in "show" line falsifies real output, but needed
1304 @c to fit in smallbook page size.
1305 info -- Generic command for showing things
1306 about the program being debugged
1307 show -- Generic command for showing things
1310 Type "help" followed by command name for full
1312 Command name abbreviations are allowed if unambiguous.
1316 @item help @var{command}
1317 With a command name as @code{help} argument, @value{GDBN} displays a
1318 short paragraph on how to use that command.
1321 @item complete @var{args}
1322 The @code{complete @var{args}} command lists all the possible completions
1323 for the beginning of a command. Use @var{args} to specify the beginning of the
1324 command you want completed. For example:
1330 @noindent results in:
1341 @noindent This is intended for use by @sc{gnu} Emacs.
1344 In addition to @code{help}, you can use the @value{GDBN} commands @code{info}
1345 and @code{show} to inquire about the state of your program, or the state
1346 of @value{GDBN} itself. Each command supports many topics of inquiry; this
1347 manual introduces each of them in the appropriate context. The listings
1348 under @code{info} and under @code{show} in the Index point to
1349 all the sub-commands. @xref{Index}.
1356 This command (abbreviated @code{i}) is for describing the state of your
1357 program. For example, you can list the arguments given to your program
1358 with @code{info args}, list the registers currently in use with @code{info
1359 registers}, or list the breakpoints you have set with @code{info breakpoints}.
1360 You can get a complete list of the @code{info} sub-commands with
1361 @w{@code{help info}}.
1365 You can assign the result of an expression to an environment variable with
1366 @code{set}. For example, you can set the @value{GDBN} prompt to a $-sign with
1367 @code{set prompt $}.
1371 In contrast to @code{info}, @code{show} is for describing the state of
1372 @value{GDBN} itself.
1373 You can change most of the things you can @code{show}, by using the
1374 related command @code{set}; for example, you can control what number
1375 system is used for displays with @code{set radix}, or simply inquire
1376 which is currently in use with @code{show radix}.
1379 To display all the settable parameters and their current
1380 values, you can use @code{show} with no arguments; you may also use
1381 @code{info set}. Both commands produce the same display.
1382 @c FIXME: "info set" violates the rule that "info" is for state of
1383 @c FIXME...program. Ck w/ GNU: "info set" to be called something else,
1384 @c FIXME...or change desc of rule---eg "state of prog and debugging session"?
1388 Here are three miscellaneous @code{show} subcommands, all of which are
1389 exceptional in lacking corresponding @code{set} commands:
1392 @kindex show version
1393 @cindex version number
1395 Show what version of @value{GDBN} is running. You should include this
1396 information in @value{GDBN} bug-reports. If multiple versions of
1397 @value{GDBN} are in use at your site, you may need to determine which
1398 version of @value{GDBN} you are running; as @value{GDBN} evolves, new
1399 commands are introduced, and old ones may wither away. Also, many
1400 system vendors ship variant versions of @value{GDBN}, and there are
1401 variant versions of @value{GDBN} in GNU/Linux distributions as well.
1402 The version number is the same as the one announced when you start
1405 @kindex show copying
1407 Display information about permission for copying @value{GDBN}.
1409 @kindex show warranty
1411 Display the @sc{gnu} ``NO WARRANTY'' statement, or a warranty,
1412 if your version of @value{GDB} comes with one.
1417 @chapter Running Programs Under @value{GDBN}
1419 When you run a program under @value{GDBN}, you must first generate
1420 debugging information when you compile it.
1422 You may start @value{GDBN} with its arguments, if any, in an environment
1423 of your choice. If you are doing native debugging, you may redirect
1424 your program's input and output, debug an already running process, or
1425 kill a child process.
1428 * Compilation:: Compiling for debugging
1429 * Starting:: Starting your program
1430 * Arguments:: Your program's arguments
1431 * Environment:: Your program's environment
1433 * Working Directory:: Your program's working directory
1434 * Input/Output:: Your program's input and output
1435 * Attach:: Debugging an already-running process
1436 * Kill Process:: Killing the child process
1438 * Threads:: Debugging programs with multiple threads
1439 * Processes:: Debugging programs with multiple processes
1443 @section Compiling for debugging
1445 In order to debug a program effectively, you need to generate
1446 debugging information when you compile it. This debugging information
1447 is stored in the object file; it describes the data type of each
1448 variable or function and the correspondence between source line numbers
1449 and addresses in the executable code.
1451 To request debugging information, specify the @samp{-g} option when you run
1454 Many C compilers are unable to handle the @samp{-g} and @samp{-O}
1455 options together. Using those compilers, you cannot generate optimized
1456 executables containing debugging information.
1458 @value{NGCC}, the @sc{gnu} C compiler, supports @samp{-g} with or
1459 without @samp{-O}, making it possible to debug optimized code. We
1460 recommend that you @emph{always} use @samp{-g} whenever you compile a
1461 program. You may think your program is correct, but there is no sense
1462 in pushing your luck.
1464 @cindex optimized code, debugging
1465 @cindex debugging optimized code
1466 When you debug a program compiled with @samp{-g -O}, remember that the
1467 optimizer is rearranging your code; the debugger shows you what is
1468 really there. Do not be too surprised when the execution path does not
1469 exactly match your source file! An extreme example: if you define a
1470 variable, but never use it, @value{GDBN} never sees that
1471 variable---because the compiler optimizes it out of existence.
1473 Some things do not work as well with @samp{-g -O} as with just
1474 @samp{-g}, particularly on machines with instruction scheduling. If in
1475 doubt, recompile with @samp{-g} alone, and if this fixes the problem,
1476 please report it to us as a bug (including a test case!).
1478 Older versions of the @sc{gnu} C compiler permitted a variant option
1479 @w{@samp{-gg}} for debugging information. @value{GDBN} no longer supports this
1480 format; if your @sc{gnu} C compiler has this option, do not use it.
1484 @section Starting your program
1492 Use the @code{run} command to start your program under @value{GDBN}.
1493 You must first specify the program name (except on VxWorks) with an
1494 argument to @value{GDBN} (@pxref{Invocation, ,Getting In and Out of
1495 @value{GDBN}}), or by using the @code{file} or @code{exec-file} command
1496 (@pxref{Files, ,Commands to specify files}).
1500 If you are running your program in an execution environment that
1501 supports processes, @code{run} creates an inferior process and makes
1502 that process run your program. (In environments without processes,
1503 @code{run} jumps to the start of your program.)
1505 The execution of a program is affected by certain information it
1506 receives from its superior. @value{GDBN} provides ways to specify this
1507 information, which you must do @emph{before} starting your program. (You
1508 can change it after starting your program, but such changes only affect
1509 your program the next time you start it.) This information may be
1510 divided into four categories:
1513 @item The @emph{arguments.}
1514 Specify the arguments to give your program as the arguments of the
1515 @code{run} command. If a shell is available on your target, the shell
1516 is used to pass the arguments, so that you may use normal conventions
1517 (such as wildcard expansion or variable substitution) in describing
1519 In Unix systems, you can control which shell is used with the
1520 @code{SHELL} environment variable.
1521 @xref{Arguments, ,Your program's arguments}.
1523 @item The @emph{environment.}
1524 Your program normally inherits its environment from @value{GDBN}, but you can
1525 use the @value{GDBN} commands @code{set environment} and @code{unset
1526 environment} to change parts of the environment that affect
1527 your program. @xref{Environment, ,Your program's environment}.
1529 @item The @emph{working directory.}
1530 Your program inherits its working directory from @value{GDBN}. You can set
1531 the @value{GDBN} working directory with the @code{cd} command in @value{GDBN}.
1532 @xref{Working Directory, ,Your program's working directory}.
1534 @item The @emph{standard input and output.}
1535 Your program normally uses the same device for standard input and
1536 standard output as @value{GDBN} is using. You can redirect input and output
1537 in the @code{run} command line, or you can use the @code{tty} command to
1538 set a different device for your program.
1539 @xref{Input/Output, ,Your program's input and output}.
1542 @emph{Warning:} While input and output redirection work, you cannot use
1543 pipes to pass the output of the program you are debugging to another
1544 program; if you attempt this, @value{GDBN} is likely to wind up debugging the
1548 When you issue the @code{run} command, your program begins to execute
1549 immediately. @xref{Stopping, ,Stopping and continuing}, for discussion
1550 of how to arrange for your program to stop. Once your program has
1551 stopped, you may call functions in your program, using the @code{print}
1552 or @code{call} commands. @xref{Data, ,Examining Data}.
1554 If the modification time of your symbol file has changed since the last
1555 time @value{GDBN} read its symbols, @value{GDBN} discards its symbol
1556 table, and reads it again. When it does this, @value{GDBN} tries to retain
1557 your current breakpoints.
1560 @section Your program's arguments
1562 @cindex arguments (to your program)
1563 The arguments to your program can be specified by the arguments of the
1565 They are passed to a shell, which expands wildcard characters and
1566 performs redirection of I/O, and thence to your program. Your
1567 @code{SHELL} environment variable (if it exists) specifies what shell
1568 @value{GDBN} uses. If you do not define @code{SHELL}, @value{GDBN} uses
1569 the default shell (@file{/bin/sh} on Unix).
1571 On non-Unix systems, the program is usually invoked directly by
1572 @value{GDBN}, which emulates I/O redirection via the appropriate system
1573 calls, and the wildcard characters are expanded by the startup code of
1574 the program, not by the shell.
1576 @code{run} with no arguments uses the same arguments used by the previous
1577 @code{run}, or those set by the @code{set args} command.
1582 Specify the arguments to be used the next time your program is run. If
1583 @code{set args} has no arguments, @code{run} executes your program
1584 with no arguments. Once you have run your program with arguments,
1585 using @code{set args} before the next @code{run} is the only way to run
1586 it again without arguments.
1590 Show the arguments to give your program when it is started.
1594 @section Your program's environment
1596 @cindex environment (of your program)
1597 The @dfn{environment} consists of a set of environment variables and
1598 their values. Environment variables conventionally record such things as
1599 your user name, your home directory, your terminal type, and your search
1600 path for programs to run. Usually you set up environment variables with
1601 the shell and they are inherited by all the other programs you run. When
1602 debugging, it can be useful to try running your program with a modified
1603 environment without having to start @value{GDBN} over again.
1607 @item path @var{directory}
1608 Add @var{directory} to the front of the @code{PATH} environment variable
1609 (the search path for executables), for both @value{GDBN} and your program.
1610 You may specify several directory names, separated by whitespace or by a
1611 system-dependent separator character (@samp{:} on Unix, @samp{;} on
1612 MS-DOS and MS-Windows). If @var{directory} is already in the path, it
1613 is moved to the front, so it is searched sooner.
1615 You can use the string @samp{$cwd} to refer to whatever is the current
1616 working directory at the time @value{GDBN} searches the path. If you
1617 use @samp{.} instead, it refers to the directory where you executed the
1618 @code{path} command. @value{GDBN} replaces @samp{.} in the
1619 @var{directory} argument (with the current path) before adding
1620 @var{directory} to the search path.
1621 @c 'path' is explicitly nonrepeatable, but RMS points out it is silly to
1622 @c document that, since repeating it would be a no-op.
1626 Display the list of search paths for executables (the @code{PATH}
1627 environment variable).
1629 @kindex show environment
1630 @item show environment @r{[}@var{varname}@r{]}
1631 Print the value of environment variable @var{varname} to be given to
1632 your program when it starts. If you do not supply @var{varname},
1633 print the names and values of all environment variables to be given to
1634 your program. You can abbreviate @code{environment} as @code{env}.
1636 @kindex set environment
1637 @item set environment @var{varname} @r{[}=@var{value}@r{]}
1638 Set environment variable @var{varname} to @var{value}. The value
1639 changes for your program only, not for @value{GDBN} itself. @var{value} may
1640 be any string; the values of environment variables are just strings, and
1641 any interpretation is supplied by your program itself. The @var{value}
1642 parameter is optional; if it is eliminated, the variable is set to a
1644 @c "any string" here does not include leading, trailing
1645 @c blanks. Gnu asks: does anyone care?
1647 For example, this command:
1654 tells the debugged program, when subsequently run, that its user is named
1655 @samp{foo}. (The spaces around @samp{=} are used for clarity here; they
1656 are not actually required.)
1658 @kindex unset environment
1659 @item unset environment @var{varname}
1660 Remove variable @var{varname} from the environment to be passed to your
1661 program. This is different from @samp{set env @var{varname} =};
1662 @code{unset environment} removes the variable from the environment,
1663 rather than assigning it an empty value.
1666 @emph{Warning:} On Unix systems, @value{GDBN} runs your program using
1668 by your @code{SHELL} environment variable if it exists (or
1669 @code{/bin/sh} if not). If your @code{SHELL} variable names a shell
1670 that runs an initialization file---such as @file{.cshrc} for C-shell, or
1671 @file{.bashrc} for BASH---any variables you set in that file affect
1672 your program. You may wish to move setting of environment variables to
1673 files that are only run when you sign on, such as @file{.login} or
1676 @node Working Directory
1677 @section Your program's working directory
1679 @cindex working directory (of your program)
1680 Each time you start your program with @code{run}, it inherits its
1681 working directory from the current working directory of @value{GDBN}.
1682 The @value{GDBN} working directory is initially whatever it inherited
1683 from its parent process (typically the shell), but you can specify a new
1684 working directory in @value{GDBN} with the @code{cd} command.
1686 The @value{GDBN} working directory also serves as a default for the commands
1687 that specify files for @value{GDBN} to operate on. @xref{Files, ,Commands to
1692 @item cd @var{directory}
1693 Set the @value{GDBN} working directory to @var{directory}.
1697 Print the @value{GDBN} working directory.
1701 @section Your program's input and output
1706 By default, the program you run under @value{GDBN} does input and output to
1707 the same terminal that @value{GDBN} uses. @value{GDBN} switches the terminal
1708 to its own terminal modes to interact with you, but it records the terminal
1709 modes your program was using and switches back to them when you continue
1710 running your program.
1713 @kindex info terminal
1715 Displays information recorded by @value{GDBN} about the terminal modes your
1719 You can redirect your program's input and/or output using shell
1720 redirection with the @code{run} command. For example,
1727 starts your program, diverting its output to the file @file{outfile}.
1730 @cindex controlling terminal
1731 Another way to specify where your program should do input and output is
1732 with the @code{tty} command. This command accepts a file name as
1733 argument, and causes this file to be the default for future @code{run}
1734 commands. It also resets the controlling terminal for the child
1735 process, for future @code{run} commands. For example,
1742 directs that processes started with subsequent @code{run} commands
1743 default to do input and output on the terminal @file{/dev/ttyb} and have
1744 that as their controlling terminal.
1746 An explicit redirection in @code{run} overrides the @code{tty} command's
1747 effect on the input/output device, but not its effect on the controlling
1750 When you use the @code{tty} command or redirect input in the @code{run}
1751 command, only the input @emph{for your program} is affected. The input
1752 for @value{GDBN} still comes from your terminal.
1755 @section Debugging an already-running process
1760 @item attach @var{process-id}
1761 This command attaches to a running process---one that was started
1762 outside @value{GDBN}. (@code{info files} shows your active
1763 targets.) The command takes as argument a process ID. The usual way to
1764 find out the process-id of a Unix process is with the @code{ps} utility,
1765 or with the @samp{jobs -l} shell command.
1767 @code{attach} does not repeat if you press @key{RET} a second time after
1768 executing the command.
1771 To use @code{attach}, your program must be running in an environment
1772 which supports processes; for example, @code{attach} does not work for
1773 programs on bare-board targets that lack an operating system. You must
1774 also have permission to send the process a signal.
1776 When you use @code{attach}, the debugger finds the program running in
1777 the process first by looking in the current working directory, then (if
1778 the program is not found) by using the source file search path
1779 (@pxref{Source Path, ,Specifying source directories}). You can also use
1780 the @code{file} command to load the program. @xref{Files, ,Commands to
1783 The first thing @value{GDBN} does after arranging to debug the specified
1784 process is to stop it. You can examine and modify an attached process
1785 with all the @value{GDBN} commands that are ordinarily available when
1786 you start processes with @code{run}. You can insert breakpoints; you
1787 can step and continue; you can modify storage. If you would rather the
1788 process continue running, you may use the @code{continue} command after
1789 attaching @value{GDBN} to the process.
1794 When you have finished debugging the attached process, you can use the
1795 @code{detach} command to release it from @value{GDBN} control. Detaching
1796 the process continues its execution. After the @code{detach} command,
1797 that process and @value{GDBN} become completely independent once more, and you
1798 are ready to @code{attach} another process or start one with @code{run}.
1799 @code{detach} does not repeat if you press @key{RET} again after
1800 executing the command.
1803 If you exit @value{GDBN} or use the @code{run} command while you have an
1804 attached process, you kill that process. By default, @value{GDBN} asks
1805 for confirmation if you try to do either of these things; you can
1806 control whether or not you need to confirm by using the @code{set
1807 confirm} command (@pxref{Messages/Warnings, ,Optional warnings and
1811 @section Killing the child process
1816 Kill the child process in which your program is running under @value{GDBN}.
1819 This command is useful if you wish to debug a core dump instead of a
1820 running process. @value{GDBN} ignores any core dump file while your program
1823 On some operating systems, a program cannot be executed outside @value{GDBN}
1824 while you have breakpoints set on it inside @value{GDBN}. You can use the
1825 @code{kill} command in this situation to permit running your program
1826 outside the debugger.
1828 The @code{kill} command is also useful if you wish to recompile and
1829 relink your program, since on many systems it is impossible to modify an
1830 executable file while it is running in a process. In this case, when you
1831 next type @code{run}, @value{GDBN} notices that the file has changed, and
1832 reads the symbol table again (while trying to preserve your current
1833 breakpoint settings).
1836 @section Debugging programs with multiple threads
1838 @cindex threads of execution
1839 @cindex multiple threads
1840 @cindex switching threads
1841 In some operating systems, such as HP-UX and Solaris, a single program
1842 may have more than one @dfn{thread} of execution. The precise semantics
1843 of threads differ from one operating system to another, but in general
1844 the threads of a single program are akin to multiple processes---except
1845 that they share one address space (that is, they can all examine and
1846 modify the same variables). On the other hand, each thread has its own
1847 registers and execution stack, and perhaps private memory.
1849 @value{GDBN} provides these facilities for debugging multi-thread
1853 @item automatic notification of new threads
1854 @item @samp{thread @var{threadno}}, a command to switch among threads
1855 @item @samp{info threads}, a command to inquire about existing threads
1856 @item @samp{thread apply [@var{threadno}] [@var{all}] @var{args}},
1857 a command to apply a command to a list of threads
1858 @item thread-specific breakpoints
1862 @emph{Warning:} These facilities are not yet available on every
1863 @value{GDBN} configuration where the operating system supports threads.
1864 If your @value{GDBN} does not support threads, these commands have no
1865 effect. For example, a system without thread support shows no output
1866 from @samp{info threads}, and always rejects the @code{thread} command,
1870 (@value{GDBP}) info threads
1871 (@value{GDBP}) thread 1
1872 Thread ID 1 not known. Use the "info threads" command to
1873 see the IDs of currently known threads.
1875 @c FIXME to implementors: how hard would it be to say "sorry, this GDB
1876 @c doesn't support threads"?
1879 @cindex focus of debugging
1880 @cindex current thread
1881 The @value{GDBN} thread debugging facility allows you to observe all
1882 threads while your program runs---but whenever @value{GDBN} takes
1883 control, one thread in particular is always the focus of debugging.
1884 This thread is called the @dfn{current thread}. Debugging commands show
1885 program information from the perspective of the current thread.
1887 @kindex New @var{systag}
1888 @cindex thread identifier (system)
1889 @c FIXME-implementors!! It would be more helpful if the [New...] message
1890 @c included GDB's numeric thread handle, so you could just go to that
1891 @c thread without first checking `info threads'.
1892 Whenever @value{GDBN} detects a new thread in your program, it displays
1893 the target system's identification for the thread with a message in the
1894 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1895 whose form varies depending on the particular system. For example, on
1896 LynxOS, you might see
1899 [New process 35 thread 27]
1903 when @value{GDBN} notices a new thread. In contrast, on an SGI system,
1904 the @var{systag} is simply something like @samp{process 368}, with no
1907 @c FIXME!! (1) Does the [New...] message appear even for the very first
1908 @c thread of a program, or does it only appear for the
1909 @c second---i.e., when it becomes obvious we have a multithread
1911 @c (2) *Is* there necessarily a first thread always? Or do some
1912 @c multithread systems permit starting a program with multiple
1913 @c threads ab initio?
1915 @cindex thread number
1916 @cindex thread identifier (GDB)
1917 For debugging purposes, @value{GDBN} associates its own thread
1918 number---always a single integer---with each thread in your program.
1921 @kindex info threads
1923 Display a summary of all threads currently in your
1924 program. @value{GDBN} displays for each thread (in this order):
1927 @item the thread number assigned by @value{GDBN}
1929 @item the target system's thread identifier (@var{systag})
1931 @item the current stack frame summary for that thread
1935 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1936 indicates the current thread.
1940 @c end table here to get a little more width for example
1943 (@value{GDBP}) info threads
1944 3 process 35 thread 27 0x34e5 in sigpause ()
1945 2 process 35 thread 23 0x34e5 in sigpause ()
1946 * 1 process 35 thread 13 main (argc=1, argv=0x7ffffff8)
1952 @cindex thread number
1953 @cindex thread identifier (GDB)
1954 For debugging purposes, @value{GDBN} associates its own thread
1955 number---a small integer assigned in thread-creation order---with each
1956 thread in your program.
1958 @kindex New @var{systag}
1959 @cindex thread identifier (system)
1960 @c FIXME-implementors!! It would be more helpful if the [New...] message
1961 @c included GDB's numeric thread handle, so you could just go to that
1962 @c thread without first checking `info threads'.
1963 Whenever @value{GDBN} detects a new thread in your program, it displays
1964 both @value{GDBN}'s thread number and the target system's identification for the thread with a message in the
1965 form @samp{[New @var{systag}]}. @var{systag} is a thread identifier
1966 whose form varies depending on the particular system. For example, on
1970 [New thread 2 (system thread 26594)]
1974 when @value{GDBN} notices a new thread.
1977 @kindex info threads
1979 Display a summary of all threads currently in your
1980 program. @value{GDBN} displays for each thread (in this order):
1983 @item the thread number assigned by @value{GDBN}
1985 @item the target system's thread identifier (@var{systag})
1987 @item the current stack frame summary for that thread
1991 An asterisk @samp{*} to the left of the @value{GDBN} thread number
1992 indicates the current thread.
1996 @c end table here to get a little more width for example
1999 (@value{GDBP}) info threads
2000 * 3 system thread 26607 worker (wptr=0x7b09c318 "@@") at quicksort.c:137
2001 2 system thread 26606 0x7b0030d8 in __ksleep () from /usr/lib/libc.2
2002 1 system thread 27905 0x7b003498 in _brk () from /usr/lib/libc.2
2006 @kindex thread @var{threadno}
2007 @item thread @var{threadno}
2008 Make thread number @var{threadno} the current thread. The command
2009 argument @var{threadno} is the internal @value{GDBN} thread number, as
2010 shown in the first field of the @samp{info threads} display.
2011 @value{GDBN} responds by displaying the system identifier of the thread
2012 you selected, and its current stack frame summary:
2015 @c FIXME!! This example made up; find a @value{GDBN} w/threads and get real one
2016 (@value{GDBP}) thread 2
2017 [Switching to process 35 thread 23]
2018 0x34e5 in sigpause ()
2022 As with the @samp{[New @dots{}]} message, the form of the text after
2023 @samp{Switching to} depends on your system's conventions for identifying
2026 @kindex thread apply
2027 @item thread apply [@var{threadno}] [@var{all}] @var{args}
2028 The @code{thread apply} command allows you to apply a command to one or
2029 more threads. Specify the numbers of the threads that you want affected
2030 with the command argument @var{threadno}. @var{threadno} is the internal
2031 @value{GDBN} thread number, as shown in the first field of the @samp{info
2032 threads} display. To apply a command to all threads, use
2033 @code{thread apply all} @var{args}.
2036 @cindex automatic thread selection
2037 @cindex switching threads automatically
2038 @cindex threads, automatic switching
2039 Whenever @value{GDBN} stops your program, due to a breakpoint or a
2040 signal, it automatically selects the thread where that breakpoint or
2041 signal happened. @value{GDBN} alerts you to the context switch with a
2042 message of the form @samp{[Switching to @var{systag}]} to identify the
2045 @xref{Thread Stops,,Stopping and starting multi-thread programs}, for
2046 more information about how @value{GDBN} behaves when you stop and start
2047 programs with multiple threads.
2049 @xref{Set Watchpoints,,Setting watchpoints}, for information about
2050 watchpoints in programs with multiple threads.
2053 @section Debugging programs with multiple processes
2055 @cindex fork, debugging programs which call
2056 @cindex multiple processes
2057 @cindex processes, multiple
2058 On most systems, @value{GDBN} has no special support for debugging
2059 programs which create additional processes using the @code{fork}
2060 function. When a program forks, @value{GDBN} will continue to debug the
2061 parent process and the child process will run unimpeded. If you have
2062 set a breakpoint in any code which the child then executes, the child
2063 will get a @code{SIGTRAP} signal which (unless it catches the signal)
2064 will cause it to terminate.
2066 However, if you want to debug the child process there is a workaround
2067 which isn't too painful. Put a call to @code{sleep} in the code which
2068 the child process executes after the fork. It may be useful to sleep
2069 only if a certain environment variable is set, or a certain file exists,
2070 so that the delay need not occur when you don't want to run @value{GDBN}
2071 on the child. While the child is sleeping, use the @code{ps} program to
2072 get its process ID. Then tell @value{GDBN} (a new invocation of
2073 @value{GDBN} if you are also debugging the parent process) to attach to
2074 the child process (@pxref{Attach}). From that point on you can debug
2075 the child process just like any other process which you attached to.
2077 On HP-UX (11.x and later only?), @value{GDBN} provides support for
2078 debugging programs that create additional processes using the
2079 @code{fork} or @code{vfork} function.
2081 By default, when a program forks, @value{GDBN} will continue to debug
2082 the parent process and the child process will run unimpeded.
2084 If you want to follow the child process instead of the parent process,
2085 use the command @w{@code{set follow-fork-mode}}.
2088 @kindex set follow-fork-mode
2089 @item set follow-fork-mode @var{mode}
2090 Set the debugger response to a program call of @code{fork} or
2091 @code{vfork}. A call to @code{fork} or @code{vfork} creates a new
2092 process. The @var{mode} can be:
2096 The original process is debugged after a fork. The child process runs
2097 unimpeded. This is the default.
2100 The new process is debugged after a fork. The parent process runs
2104 The debugger will ask for one of the above choices.
2107 @item show follow-fork-mode
2108 Display the current debugger response to a @code{fork} or @code{vfork} call.
2111 If you ask to debug a child process and a @code{vfork} is followed by an
2112 @code{exec}, @value{GDBN} executes the new target up to the first
2113 breakpoint in the new target. If you have a breakpoint set on
2114 @code{main} in your original program, the breakpoint will also be set on
2115 the child process's @code{main}.
2117 When a child process is spawned by @code{vfork}, you cannot debug the
2118 child or parent until an @code{exec} call completes.
2120 If you issue a @code{run} command to @value{GDBN} after an @code{exec}
2121 call executes, the new target restarts. To restart the parent process,
2122 use the @code{file} command with the parent executable name as its
2125 You can use the @code{catch} command to make @value{GDBN} stop whenever
2126 a @code{fork}, @code{vfork}, or @code{exec} call is made. @xref{Set
2127 Catchpoints, ,Setting catchpoints}.
2130 @chapter Stopping and Continuing
2132 The principal purposes of using a debugger are so that you can stop your
2133 program before it terminates; or so that, if your program runs into
2134 trouble, you can investigate and find out why.
2136 Inside @value{GDBN}, your program may stop for any of several reasons,
2137 such as a signal, a breakpoint, or reaching a new line after a
2138 @value{GDBN} command such as @code{step}. You may then examine and
2139 change variables, set new breakpoints or remove old ones, and then
2140 continue execution. Usually, the messages shown by @value{GDBN} provide
2141 ample explanation of the status of your program---but you can also
2142 explicitly request this information at any time.
2145 @kindex info program
2147 Display information about the status of your program: whether it is
2148 running or not, what process it is, and why it stopped.
2152 * Breakpoints:: Breakpoints, watchpoints, and catchpoints
2153 * Continuing and Stepping:: Resuming execution
2155 * Thread Stops:: Stopping and starting multi-thread programs
2159 @section Breakpoints, watchpoints, and catchpoints
2162 A @dfn{breakpoint} makes your program stop whenever a certain point in
2163 the program is reached. For each breakpoint, you can add conditions to
2164 control in finer detail whether your program stops. You can set
2165 breakpoints with the @code{break} command and its variants (@pxref{Set
2166 Breaks, ,Setting breakpoints}), to specify the place where your program
2167 should stop by line number, function name or exact address in the
2170 In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set
2171 breakpoints in shared libraries before the executable is run. There is
2172 a minor limitation on HP-UX systems: you must wait until the executable
2173 is run in order to set breakpoints in shared library routines that are
2174 not called directly by the program (for example, routines that are
2175 arguments in a @code{pthread_create} call).
2178 @cindex memory tracing
2179 @cindex breakpoint on memory address
2180 @cindex breakpoint on variable modification
2181 A @dfn{watchpoint} is a special breakpoint that stops your program
2182 when the value of an expression changes. You must use a different
2183 command to set watchpoints (@pxref{Set Watchpoints, ,Setting
2184 watchpoints}), but aside from that, you can manage a watchpoint like
2185 any other breakpoint: you enable, disable, and delete both breakpoints
2186 and watchpoints using the same commands.
2188 You can arrange to have values from your program displayed automatically
2189 whenever @value{GDBN} stops at a breakpoint. @xref{Auto Display,,
2193 @cindex breakpoint on events
2194 A @dfn{catchpoint} is another special breakpoint that stops your program
2195 when a certain kind of event occurs, such as the throwing of a C++
2196 exception or the loading of a library. As with watchpoints, you use a
2197 different command to set a catchpoint (@pxref{Set Catchpoints, ,Setting
2198 catchpoints}), but aside from that, you can manage a catchpoint like any
2199 other breakpoint. (To stop when your program receives a signal, use the
2200 @code{handle} command; see @ref{Signals, ,Signals}.)
2202 @cindex breakpoint numbers
2203 @cindex numbers for breakpoints
2204 @value{GDBN} assigns a number to each breakpoint, watchpoint, or
2205 catchpoint when you create it; these numbers are successive integers
2206 starting with one. In many of the commands for controlling various
2207 features of breakpoints you use the breakpoint number to say which
2208 breakpoint you want to change. Each breakpoint may be @dfn{enabled} or
2209 @dfn{disabled}; if disabled, it has no effect on your program until you
2212 @cindex breakpoint ranges
2213 @cindex ranges of breakpoints
2214 Some @value{GDBN} commands accept a range of breakpoints on which to
2215 operate. A breakpoint range is either a single breakpoint number, like
2216 @samp{5}, or two such numbers, in increasing order, separated by a
2217 hyphen, like @samp{5-7}. When a breakpoint range is given to a command,
2218 all breakpoint in that range are operated on.
2221 * Set Breaks:: Setting breakpoints
2222 * Set Watchpoints:: Setting watchpoints
2223 * Set Catchpoints:: Setting catchpoints
2224 * Delete Breaks:: Deleting breakpoints
2225 * Disabling:: Disabling breakpoints
2226 * Conditions:: Break conditions
2227 * Break Commands:: Breakpoint command lists
2228 * Breakpoint Menus:: Breakpoint menus
2229 * Error in Breakpoints:: ``Cannot insert breakpoints''
2233 @subsection Setting breakpoints
2235 @c FIXME LMB what does GDB do if no code on line of breakpt?
2236 @c consider in particular declaration with/without initialization.
2238 @c FIXME 2 is there stuff on this already? break at fun start, already init?
2243 @cindex latest breakpoint
2244 Breakpoints are set with the @code{break} command (abbreviated
2245 @code{b}). The debugger convenience variable @samp{$bpnum} records the
2246 number of the breakpoints you've set most recently; see @ref{Convenience
2247 Vars,, Convenience variables}, for a discussion of what you can do with
2248 convenience variables.
2250 You have several ways to say where the breakpoint should go.
2253 @item break @var{function}
2254 Set a breakpoint at entry to function @var{function}.
2255 When using source languages that permit overloading of symbols, such as
2256 C++, @var{function} may refer to more than one possible place to break.
2257 @xref{Breakpoint Menus,,Breakpoint menus}, for a discussion of that situation.
2259 @item break +@var{offset}
2260 @itemx break -@var{offset}
2261 Set a breakpoint some number of lines forward or back from the position
2262 at which execution stopped in the currently selected @dfn{stack frame}.
2263 (@xref{Frames, ,Frames}, for a description of stack frames.)
2265 @item break @var{linenum}
2266 Set a breakpoint at line @var{linenum} in the current source file.
2267 The current source file is the last file whose source text was printed.
2268 The breakpoint will stop your program just before it executes any of the
2271 @item break @var{filename}:@var{linenum}
2272 Set a breakpoint at line @var{linenum} in source file @var{filename}.
2274 @item break @var{filename}:@var{function}
2275 Set a breakpoint at entry to function @var{function} found in file
2276 @var{filename}. Specifying a file name as well as a function name is
2277 superfluous except when multiple files contain similarly named
2280 @item break *@var{address}
2281 Set a breakpoint at address @var{address}. You can use this to set
2282 breakpoints in parts of your program which do not have debugging
2283 information or source files.
2286 When called without any arguments, @code{break} sets a breakpoint at
2287 the next instruction to be executed in the selected stack frame
2288 (@pxref{Stack, ,Examining the Stack}). In any selected frame but the
2289 innermost, this makes your program stop as soon as control
2290 returns to that frame. This is similar to the effect of a
2291 @code{finish} command in the frame inside the selected frame---except
2292 that @code{finish} does not leave an active breakpoint. If you use
2293 @code{break} without an argument in the innermost frame, @value{GDBN} stops
2294 the next time it reaches the current location; this may be useful
2297 @value{GDBN} normally ignores breakpoints when it resumes execution, until at
2298 least one instruction has been executed. If it did not do this, you
2299 would be unable to proceed past a breakpoint without first disabling the
2300 breakpoint. This rule applies whether or not the breakpoint already
2301 existed when your program stopped.
2303 @item break @dots{} if @var{cond}
2304 Set a breakpoint with condition @var{cond}; evaluate the expression
2305 @var{cond} each time the breakpoint is reached, and stop only if the
2306 value is nonzero---that is, if @var{cond} evaluates as true.
2307 @samp{@dots{}} stands for one of the possible arguments described
2308 above (or no argument) specifying where to break. @xref{Conditions,
2309 ,Break conditions}, for more information on breakpoint conditions.
2312 @item tbreak @var{args}
2313 Set a breakpoint enabled only for one stop. @var{args} are the
2314 same as for the @code{break} command, and the breakpoint is set in the same
2315 way, but the breakpoint is automatically deleted after the first time your
2316 program stops there. @xref{Disabling, ,Disabling breakpoints}.
2319 @item hbreak @var{args}
2320 Set a hardware-assisted breakpoint. @var{args} are the same as for the
2321 @code{break} command and the breakpoint is set in the same way, but the
2322 breakpoint requires hardware support and some target hardware may not
2323 have this support. The main purpose of this is EPROM/ROM code
2324 debugging, so you can set a breakpoint at an instruction without
2325 changing the instruction. This can be used with the new trap-generation
2326 provided by SPARClite DSU and some x86-based targets. These targets
2327 will generate traps when a program accesses some data or instruction
2328 address that is assigned to the debug registers. However the hardware
2329 breakpoint registers can take a limited number of breakpoints. For
2330 example, on the DSU, only two data breakpoints can be set at a time, and
2331 @value{GDBN} will reject this command if more than two are used. Delete
2332 or disable unused hardware breakpoints before setting new ones
2333 (@pxref{Disabling, ,Disabling}). @xref{Conditions, ,Break conditions}.
2336 @item thbreak @var{args}
2337 Set a hardware-assisted breakpoint enabled only for one stop. @var{args}
2338 are the same as for the @code{hbreak} command and the breakpoint is set in
2339 the same way. However, like the @code{tbreak} command,
2340 the breakpoint is automatically deleted after the
2341 first time your program stops there. Also, like the @code{hbreak}
2342 command, the breakpoint requires hardware support and some target hardware
2343 may not have this support. @xref{Disabling, ,Disabling breakpoints}.
2344 See also @ref{Conditions, ,Break conditions}.
2347 @cindex regular expression
2348 @item rbreak @var{regex}
2349 Set breakpoints on all functions matching the regular expression
2350 @var{regex}. This command sets an unconditional breakpoint on all
2351 matches, printing a list of all breakpoints it set. Once these
2352 breakpoints are set, they are treated just like the breakpoints set with
2353 the @code{break} command. You can delete them, disable them, or make
2354 them conditional the same way as any other breakpoint.
2356 The syntax of the regular expression is the standard one used with tools
2357 like @file{grep}. Note that this is different from the syntax used by
2358 shells, so for instance @code{foo*} matches all functions that include
2359 an @code{fo} followed by zero or more @code{o}s. There is an implicit
2360 @code{.*} leading and trailing the regular expression you supply, so to
2361 match only functions that begin with @code{foo}, use @code{^foo}.
2363 When debugging C++ programs, @code{rbreak} is useful for setting
2364 breakpoints on overloaded functions that are not members of any special
2367 @kindex info breakpoints
2368 @cindex @code{$_} and @code{info breakpoints}
2369 @item info breakpoints @r{[}@var{n}@r{]}
2370 @itemx info break @r{[}@var{n}@r{]}
2371 @itemx info watchpoints @r{[}@var{n}@r{]}
2372 Print a table of all breakpoints, watchpoints, and catchpoints set and
2373 not deleted, with the following columns for each breakpoint:
2376 @item Breakpoint Numbers
2378 Breakpoint, watchpoint, or catchpoint.
2380 Whether the breakpoint is marked to be disabled or deleted when hit.
2381 @item Enabled or Disabled
2382 Enabled breakpoints are marked with @samp{y}. @samp{n} marks breakpoints
2383 that are not enabled.
2385 Where the breakpoint is in your program, as a memory address.
2387 Where the breakpoint is in the source for your program, as a file and
2392 If a breakpoint is conditional, @code{info break} shows the condition on
2393 the line following the affected breakpoint; breakpoint commands, if any,
2394 are listed after that.
2397 @code{info break} with a breakpoint
2398 number @var{n} as argument lists only that breakpoint. The
2399 convenience variable @code{$_} and the default examining-address for
2400 the @code{x} command are set to the address of the last breakpoint
2401 listed (@pxref{Memory, ,Examining memory}).
2404 @code{info break} displays a count of the number of times the breakpoint
2405 has been hit. This is especially useful in conjunction with the
2406 @code{ignore} command. You can ignore a large number of breakpoint
2407 hits, look at the breakpoint info to see how many times the breakpoint
2408 was hit, and then run again, ignoring one less than that number. This
2409 will get you quickly to the last hit of that breakpoint.
2412 @value{GDBN} allows you to set any number of breakpoints at the same place in
2413 your program. There is nothing silly or meaningless about this. When
2414 the breakpoints are conditional, this is even useful
2415 (@pxref{Conditions, ,Break conditions}).
2417 @cindex negative breakpoint numbers
2418 @cindex internal @value{GDBN} breakpoints
2419 @value{GDBN} itself sometimes sets breakpoints in your program for special
2420 purposes, such as proper handling of @code{longjmp} (in C programs).
2421 These internal breakpoints are assigned negative numbers, starting with
2422 @code{-1}; @samp{info breakpoints} does not display them.
2424 You can see these breakpoints with the @value{GDBN} maintenance command
2425 @samp{maint info breakpoints}.
2428 @kindex maint info breakpoints
2429 @item maint info breakpoints
2430 Using the same format as @samp{info breakpoints}, display both the
2431 breakpoints you've set explicitly, and those @value{GDBN} is using for
2432 internal purposes. Internal breakpoints are shown with negative
2433 breakpoint numbers. The type column identifies what kind of breakpoint
2438 Normal, explicitly set breakpoint.
2441 Normal, explicitly set watchpoint.
2444 Internal breakpoint, used to handle correctly stepping through
2445 @code{longjmp} calls.
2447 @item longjmp resume
2448 Internal breakpoint at the target of a @code{longjmp}.
2451 Temporary internal breakpoint used by the @value{GDBN} @code{until} command.
2454 Temporary internal breakpoint used by the @value{GDBN} @code{finish} command.
2457 Shared library events.
2464 @node Set Watchpoints
2465 @subsection Setting watchpoints
2467 @cindex setting watchpoints
2468 @cindex software watchpoints
2469 @cindex hardware watchpoints
2470 You can use a watchpoint to stop execution whenever the value of an
2471 expression changes, without having to predict a particular place where
2474 Depending on your system, watchpoints may be implemented in software or
2475 hardware. @value{GDBN} does software watchpointing by single-stepping your
2476 program and testing the variable's value each time, which is hundreds of
2477 times slower than normal execution. (But this may still be worth it, to
2478 catch errors where you have no clue what part of your program is the
2481 On some systems, such as HP-UX, Linux and some other x86-based targets,
2482 @value{GDBN} includes support for
2483 hardware watchpoints, which do not slow down the running of your
2488 @item watch @var{expr}
2489 Set a watchpoint for an expression. @value{GDBN} will break when @var{expr}
2490 is written into by the program and its value changes.
2493 @item rwatch @var{expr}
2494 Set a watchpoint that will break when watch @var{expr} is read by the program.
2497 @item awatch @var{expr}
2498 Set a watchpoint that will break when @var{expr} is either read or written into
2501 @kindex info watchpoints
2502 @item info watchpoints
2503 This command prints a list of watchpoints, breakpoints, and catchpoints;
2504 it is the same as @code{info break}.
2507 @value{GDBN} sets a @dfn{hardware watchpoint} if possible. Hardware
2508 watchpoints execute very quickly, and the debugger reports a change in
2509 value at the exact instruction where the change occurs. If @value{GDBN}
2510 cannot set a hardware watchpoint, it sets a software watchpoint, which
2511 executes more slowly and reports the change in value at the next
2512 statement, not the instruction, after the change occurs.
2514 When you issue the @code{watch} command, @value{GDBN} reports
2517 Hardware watchpoint @var{num}: @var{expr}
2521 if it was able to set a hardware watchpoint.
2523 Currently, the @code{awatch} and @code{rwatch} commands can only set
2524 hardware watchpoints, because accesses to data that don't change the
2525 value of the watched expression cannot be detected without examining
2526 every instruction as it is being executed, and @value{GDBN} does not do
2527 that currently. If @value{GDBN} finds that it is unable to set a
2528 hardware breakpoint with the @code{awatch} or @code{rwatch} command, it
2529 will print a message like this:
2532 Expression cannot be implemented with read/access watchpoint.
2535 Sometimes, @value{GDBN} cannot set a hardware watchpoint because the
2536 data type of the watched expression is wider than what a hardware
2537 watchpoint on the target machine can handle. For example, some systems
2538 can only watch regions that are up to 4 bytes wide; on such systems you
2539 cannot set hardware watchpoints for an expression that yields a
2540 double-precision floating-point number (which is typically 8 bytes
2541 wide). As a work-around, it might be possible to break the large region
2542 into a series of smaller ones and watch them with separate watchpoints.
2544 If you set too many hardware watchpoints, @value{GDBN} might be unable
2545 to insert all of them when you resume the execution of your program.
2546 Since the precise number of active watchpoints is unknown until such
2547 time as the program is about to be resumed, @value{GDBN} might not be
2548 able to warn you about this when you set the watchpoints, and the
2549 warning will be printed only when the program is resumed:
2552 Hardware watchpoint @var{num}: Could not insert watchpoint
2556 If this happens, delete or disable some of the watchpoints.
2558 The SPARClite DSU will generate traps when a program accesses some data
2559 or instruction address that is assigned to the debug registers. For the
2560 data addresses, DSU facilitates the @code{watch} command. However the
2561 hardware breakpoint registers can only take two data watchpoints, and
2562 both watchpoints must be the same kind. For example, you can set two
2563 watchpoints with @code{watch} commands, two with @code{rwatch} commands,
2564 @strong{or} two with @code{awatch} commands, but you cannot set one
2565 watchpoint with one command and the other with a different command.
2566 @value{GDBN} will reject the command if you try to mix watchpoints.
2567 Delete or disable unused watchpoint commands before setting new ones.
2569 If you call a function interactively using @code{print} or @code{call},
2570 any watchpoints you have set will be inactive until @value{GDBN} reaches another
2571 kind of breakpoint or the call completes.
2573 @value{GDBN} automatically deletes watchpoints that watch local
2574 (automatic) variables, or expressions that involve such variables, when
2575 they go out of scope, that is, when the execution leaves the block in
2576 which these variables were defined. In particular, when the program
2577 being debugged terminates, @emph{all} local variables go out of scope,
2578 and so only watchpoints that watch global variables remain set. If you
2579 rerun the program, you will need to set all such watchpoints again. One
2580 way of doing that would be to set a code breakpoint at the entry to the
2581 @code{main} function and when it breaks, set all the watchpoints.
2584 @cindex watchpoints and threads
2585 @cindex threads and watchpoints
2586 @emph{Warning:} In multi-thread programs, watchpoints have only limited
2587 usefulness. With the current watchpoint implementation, @value{GDBN}
2588 can only watch the value of an expression @emph{in a single thread}. If
2589 you are confident that the expression can only change due to the current
2590 thread's activity (and if you are also confident that no other thread
2591 can become current), then you can use watchpoints as usual. However,
2592 @value{GDBN} may not notice when a non-current thread's activity changes
2595 @c FIXME: this is almost identical to the previous paragraph.
2596 @emph{HP-UX Warning:} In multi-thread programs, software watchpoints
2597 have only limited usefulness. If @value{GDBN} creates a software
2598 watchpoint, it can only watch the value of an expression @emph{in a
2599 single thread}. If you are confident that the expression can only
2600 change due to the current thread's activity (and if you are also
2601 confident that no other thread can become current), then you can use
2602 software watchpoints as usual. However, @value{GDBN} may not notice
2603 when a non-current thread's activity changes the expression. (Hardware
2604 watchpoints, in contrast, watch an expression in all threads.)
2607 @node Set Catchpoints
2608 @subsection Setting catchpoints
2609 @cindex catchpoints, setting
2610 @cindex exception handlers
2611 @cindex event handling
2613 You can use @dfn{catchpoints} to cause the debugger to stop for certain
2614 kinds of program events, such as C++ exceptions or the loading of a
2615 shared library. Use the @code{catch} command to set a catchpoint.
2619 @item catch @var{event}
2620 Stop when @var{event} occurs. @var{event} can be any of the following:
2624 The throwing of a C++ exception.
2628 The catching of a C++ exception.
2632 A call to @code{exec}. This is currently only available for HP-UX.
2636 A call to @code{fork}. This is currently only available for HP-UX.
2640 A call to @code{vfork}. This is currently only available for HP-UX.
2643 @itemx load @var{libname}
2645 The dynamic loading of any shared library, or the loading of the library
2646 @var{libname}. This is currently only available for HP-UX.
2649 @itemx unload @var{libname}
2650 @kindex catch unload
2651 The unloading of any dynamically loaded shared library, or the unloading
2652 of the library @var{libname}. This is currently only available for HP-UX.
2655 @item tcatch @var{event}
2656 Set a catchpoint that is enabled only for one stop. The catchpoint is
2657 automatically deleted after the first time the event is caught.
2661 Use the @code{info break} command to list the current catchpoints.
2663 There are currently some limitations to C++ exception handling
2664 (@code{catch throw} and @code{catch catch}) in @value{GDBN}:
2668 If you call a function interactively, @value{GDBN} normally returns
2669 control to you when the function has finished executing. If the call
2670 raises an exception, however, the call may bypass the mechanism that
2671 returns control to you and cause your program either to abort or to
2672 simply continue running until it hits a breakpoint, catches a signal
2673 that @value{GDBN} is listening for, or exits. This is the case even if
2674 you set a catchpoint for the exception; catchpoints on exceptions are
2675 disabled within interactive calls.
2678 You cannot raise an exception interactively.
2681 You cannot install an exception handler interactively.
2684 @cindex raise exceptions
2685 Sometimes @code{catch} is not the best way to debug exception handling:
2686 if you need to know exactly where an exception is raised, it is better to
2687 stop @emph{before} the exception handler is called, since that way you
2688 can see the stack before any unwinding takes place. If you set a
2689 breakpoint in an exception handler instead, it may not be easy to find
2690 out where the exception was raised.
2692 To stop just before an exception handler is called, you need some
2693 knowledge of the implementation. In the case of @sc{gnu} C++, exceptions are
2694 raised by calling a library function named @code{__raise_exception}
2695 which has the following ANSI C interface:
2698 /* @var{addr} is where the exception identifier is stored.
2699 @var{id} is the exception identifier. */
2700 void __raise_exception (void **addr, void *id);
2704 To make the debugger catch all exceptions before any stack
2705 unwinding takes place, set a breakpoint on @code{__raise_exception}
2706 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and exceptions}).
2708 With a conditional breakpoint (@pxref{Conditions, ,Break conditions})
2709 that depends on the value of @var{id}, you can stop your program when
2710 a specific exception is raised. You can use multiple conditional
2711 breakpoints to stop your program when any of a number of exceptions are
2716 @subsection Deleting breakpoints
2718 @cindex clearing breakpoints, watchpoints, catchpoints
2719 @cindex deleting breakpoints, watchpoints, catchpoints
2720 It is often necessary to eliminate a breakpoint, watchpoint, or
2721 catchpoint once it has done its job and you no longer want your program
2722 to stop there. This is called @dfn{deleting} the breakpoint. A
2723 breakpoint that has been deleted no longer exists; it is forgotten.
2725 With the @code{clear} command you can delete breakpoints according to
2726 where they are in your program. With the @code{delete} command you can
2727 delete individual breakpoints, watchpoints, or catchpoints by specifying
2728 their breakpoint numbers.
2730 It is not necessary to delete a breakpoint to proceed past it. @value{GDBN}
2731 automatically ignores breakpoints on the first instruction to be executed
2732 when you continue execution without changing the execution address.
2737 Delete any breakpoints at the next instruction to be executed in the
2738 selected stack frame (@pxref{Selection, ,Selecting a frame}). When
2739 the innermost frame is selected, this is a good way to delete a
2740 breakpoint where your program just stopped.
2742 @item clear @var{function}
2743 @itemx clear @var{filename}:@var{function}
2744 Delete any breakpoints set at entry to the function @var{function}.
2746 @item clear @var{linenum}
2747 @itemx clear @var{filename}:@var{linenum}
2748 Delete any breakpoints set at or within the code of the specified line.
2750 @cindex delete breakpoints
2753 @item delete @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2754 Delete the breakpoints, watchpoints, or catchpoints of the breakpoint
2755 ranges specified as arguments. If no argument is specified, delete all
2756 breakpoints (@value{GDBN} asks confirmation, unless you have @code{set
2757 confirm off}). You can abbreviate this command as @code{d}.
2761 @subsection Disabling breakpoints
2763 @kindex disable breakpoints
2764 @kindex enable breakpoints
2765 Rather than deleting a breakpoint, watchpoint, or catchpoint, you might
2766 prefer to @dfn{disable} it. This makes the breakpoint inoperative as if
2767 it had been deleted, but remembers the information on the breakpoint so
2768 that you can @dfn{enable} it again later.
2770 You disable and enable breakpoints, watchpoints, and catchpoints with
2771 the @code{enable} and @code{disable} commands, optionally specifying one
2772 or more breakpoint numbers as arguments. Use @code{info break} or
2773 @code{info watch} to print a list of breakpoints, watchpoints, and
2774 catchpoints if you do not know which numbers to use.
2776 A breakpoint, watchpoint, or catchpoint can have any of four different
2777 states of enablement:
2781 Enabled. The breakpoint stops your program. A breakpoint set
2782 with the @code{break} command starts out in this state.
2784 Disabled. The breakpoint has no effect on your program.
2786 Enabled once. The breakpoint stops your program, but then becomes
2789 Enabled for deletion. The breakpoint stops your program, but
2790 immediately after it does so it is deleted permanently. A breakpoint
2791 set with the @code{tbreak} command starts out in this state.
2794 You can use the following commands to enable or disable breakpoints,
2795 watchpoints, and catchpoints:
2798 @kindex disable breakpoints
2801 @item disable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2802 Disable the specified breakpoints---or all breakpoints, if none are
2803 listed. A disabled breakpoint has no effect but is not forgotten. All
2804 options such as ignore-counts, conditions and commands are remembered in
2805 case the breakpoint is enabled again later. You may abbreviate
2806 @code{disable} as @code{dis}.
2808 @kindex enable breakpoints
2810 @item enable @r{[}breakpoints@r{]} @r{[}@var{range}@dots{}@r{]}
2811 Enable the specified breakpoints (or all defined breakpoints). They
2812 become effective once again in stopping your program.
2814 @item enable @r{[}breakpoints@r{]} once @var{range}@dots{}
2815 Enable the specified breakpoints temporarily. @value{GDBN} disables any
2816 of these breakpoints immediately after stopping your program.
2818 @item enable @r{[}breakpoints@r{]} delete @var{range}@dots{}
2819 Enable the specified breakpoints to work once, then die. @value{GDBN}
2820 deletes any of these breakpoints as soon as your program stops there.
2823 @c FIXME: I think the following ``Except for [...] @code{tbreak}'' is
2824 @c confusing: tbreak is also initially enabled.
2825 Except for a breakpoint set with @code{tbreak} (@pxref{Set Breaks,
2826 ,Setting breakpoints}), breakpoints that you set are initially enabled;
2827 subsequently, they become disabled or enabled only when you use one of
2828 the commands above. (The command @code{until} can set and delete a
2829 breakpoint of its own, but it does not change the state of your other
2830 breakpoints; see @ref{Continuing and Stepping, ,Continuing and
2834 @subsection Break conditions
2835 @cindex conditional breakpoints
2836 @cindex breakpoint conditions
2838 @c FIXME what is scope of break condition expr? Context where wanted?
2839 @c in particular for a watchpoint?
2840 The simplest sort of breakpoint breaks every time your program reaches a
2841 specified place. You can also specify a @dfn{condition} for a
2842 breakpoint. A condition is just a Boolean expression in your
2843 programming language (@pxref{Expressions, ,Expressions}). A breakpoint with
2844 a condition evaluates the expression each time your program reaches it,
2845 and your program stops only if the condition is @emph{true}.
2847 This is the converse of using assertions for program validation; in that
2848 situation, you want to stop when the assertion is violated---that is,
2849 when the condition is false. In C, if you want to test an assertion expressed
2850 by the condition @var{assert}, you should set the condition
2851 @samp{! @var{assert}} on the appropriate breakpoint.
2853 Conditions are also accepted for watchpoints; you may not need them,
2854 since a watchpoint is inspecting the value of an expression anyhow---but
2855 it might be simpler, say, to just set a watchpoint on a variable name,
2856 and specify a condition that tests whether the new value is an interesting
2859 Break conditions can have side effects, and may even call functions in
2860 your program. This can be useful, for example, to activate functions
2861 that log program progress, or to use your own print functions to
2862 format special data structures. The effects are completely predictable
2863 unless there is another enabled breakpoint at the same address. (In
2864 that case, @value{GDBN} might see the other breakpoint first and stop your
2865 program without checking the condition of this one.) Note that
2866 breakpoint commands are usually more convenient and flexible than break
2868 purpose of performing side effects when a breakpoint is reached
2869 (@pxref{Break Commands, ,Breakpoint command lists}).
2871 Break conditions can be specified when a breakpoint is set, by using
2872 @samp{if} in the arguments to the @code{break} command. @xref{Set
2873 Breaks, ,Setting breakpoints}. They can also be changed at any time
2874 with the @code{condition} command.
2876 You can also use the @code{if} keyword with the @code{watch} command.
2877 The @code{catch} command does not recognize the @code{if} keyword;
2878 @code{condition} is the only way to impose a further condition on a
2883 @item condition @var{bnum} @var{expression}
2884 Specify @var{expression} as the break condition for breakpoint,
2885 watchpoint, or catchpoint number @var{bnum}. After you set a condition,
2886 breakpoint @var{bnum} stops your program only if the value of
2887 @var{expression} is true (nonzero, in C). When you use
2888 @code{condition}, @value{GDBN} checks @var{expression} immediately for
2889 syntactic correctness, and to determine whether symbols in it have
2890 referents in the context of your breakpoint. If @var{expression} uses
2891 symbols not referenced in the context of the breakpoint, @value{GDBN}
2892 prints an error message:
2895 No symbol "foo" in current context.
2900 not actually evaluate @var{expression} at the time the @code{condition}
2901 command (or a command that sets a breakpoint with a condition, like
2902 @code{break if @dots{}}) is given, however. @xref{Expressions, ,Expressions}.
2904 @item condition @var{bnum}
2905 Remove the condition from breakpoint number @var{bnum}. It becomes
2906 an ordinary unconditional breakpoint.
2909 @cindex ignore count (of breakpoint)
2910 A special case of a breakpoint condition is to stop only when the
2911 breakpoint has been reached a certain number of times. This is so
2912 useful that there is a special way to do it, using the @dfn{ignore
2913 count} of the breakpoint. Every breakpoint has an ignore count, which
2914 is an integer. Most of the time, the ignore count is zero, and
2915 therefore has no effect. But if your program reaches a breakpoint whose
2916 ignore count is positive, then instead of stopping, it just decrements
2917 the ignore count by one and continues. As a result, if the ignore count
2918 value is @var{n}, the breakpoint does not stop the next @var{n} times
2919 your program reaches it.
2923 @item ignore @var{bnum} @var{count}
2924 Set the ignore count of breakpoint number @var{bnum} to @var{count}.
2925 The next @var{count} times the breakpoint is reached, your program's
2926 execution does not stop; other than to decrement the ignore count, @value{GDBN}
2929 To make the breakpoint stop the next time it is reached, specify
2932 When you use @code{continue} to resume execution of your program from a
2933 breakpoint, you can specify an ignore count directly as an argument to
2934 @code{continue}, rather than using @code{ignore}. @xref{Continuing and
2935 Stepping,,Continuing and stepping}.
2937 If a breakpoint has a positive ignore count and a condition, the
2938 condition is not checked. Once the ignore count reaches zero,
2939 @value{GDBN} resumes checking the condition.
2941 You could achieve the effect of the ignore count with a condition such
2942 as @w{@samp{$foo-- <= 0}} using a debugger convenience variable that
2943 is decremented each time. @xref{Convenience Vars, ,Convenience
2947 Ignore counts apply to breakpoints, watchpoints, and catchpoints.
2950 @node Break Commands
2951 @subsection Breakpoint command lists
2953 @cindex breakpoint commands
2954 You can give any breakpoint (or watchpoint or catchpoint) a series of
2955 commands to execute when your program stops due to that breakpoint. For
2956 example, you might want to print the values of certain expressions, or
2957 enable other breakpoints.
2962 @item commands @r{[}@var{bnum}@r{]}
2963 @itemx @dots{} @var{command-list} @dots{}
2965 Specify a list of commands for breakpoint number @var{bnum}. The commands
2966 themselves appear on the following lines. Type a line containing just
2967 @code{end} to terminate the commands.
2969 To remove all commands from a breakpoint, type @code{commands} and
2970 follow it immediately with @code{end}; that is, give no commands.
2972 With no @var{bnum} argument, @code{commands} refers to the last
2973 breakpoint, watchpoint, or catchpoint set (not to the breakpoint most
2974 recently encountered).
2977 Pressing @key{RET} as a means of repeating the last @value{GDBN} command is
2978 disabled within a @var{command-list}.
2980 You can use breakpoint commands to start your program up again. Simply
2981 use the @code{continue} command, or @code{step}, or any other command
2982 that resumes execution.
2984 Any other commands in the command list, after a command that resumes
2985 execution, are ignored. This is because any time you resume execution
2986 (even with a simple @code{next} or @code{step}), you may encounter
2987 another breakpoint---which could have its own command list, leading to
2988 ambiguities about which list to execute.
2991 If the first command you specify in a command list is @code{silent}, the
2992 usual message about stopping at a breakpoint is not printed. This may
2993 be desirable for breakpoints that are to print a specific message and
2994 then continue. If none of the remaining commands print anything, you
2995 see no sign that the breakpoint was reached. @code{silent} is
2996 meaningful only at the beginning of a breakpoint command list.
2998 The commands @code{echo}, @code{output}, and @code{printf} allow you to
2999 print precisely controlled output, and are often useful in silent
3000 breakpoints. @xref{Output, ,Commands for controlled output}.
3002 For example, here is how you could use breakpoint commands to print the
3003 value of @code{x} at entry to @code{foo} whenever @code{x} is positive.
3009 printf "x is %d\n",x
3014 One application for breakpoint commands is to compensate for one bug so
3015 you can test for another. Put a breakpoint just after the erroneous line
3016 of code, give it a condition to detect the case in which something
3017 erroneous has been done, and give it commands to assign correct values
3018 to any variables that need them. End with the @code{continue} command
3019 so that your program does not stop, and start with the @code{silent}
3020 command so that no output is produced. Here is an example:
3031 @node Breakpoint Menus
3032 @subsection Breakpoint menus
3034 @cindex symbol overloading
3036 Some programming languages (notably C++) permit a single function name
3037 to be defined several times, for application in different contexts.
3038 This is called @dfn{overloading}. When a function name is overloaded,
3039 @samp{break @var{function}} is not enough to tell @value{GDBN} where you want
3040 a breakpoint. If you realize this is a problem, you can use
3041 something like @samp{break @var{function}(@var{types})} to specify which
3042 particular version of the function you want. Otherwise, @value{GDBN} offers
3043 you a menu of numbered choices for different possible breakpoints, and
3044 waits for your selection with the prompt @samp{>}. The first two
3045 options are always @samp{[0] cancel} and @samp{[1] all}. Typing @kbd{1}
3046 sets a breakpoint at each definition of @var{function}, and typing
3047 @kbd{0} aborts the @code{break} command without setting any new
3050 For example, the following session excerpt shows an attempt to set a
3051 breakpoint at the overloaded symbol @code{String::after}.
3052 We choose three particular definitions of that function name:
3054 @c FIXME! This is likely to change to show arg type lists, at least
3057 (@value{GDBP}) b String::after
3060 [2] file:String.cc; line number:867
3061 [3] file:String.cc; line number:860
3062 [4] file:String.cc; line number:875
3063 [5] file:String.cc; line number:853
3064 [6] file:String.cc; line number:846
3065 [7] file:String.cc; line number:735
3067 Breakpoint 1 at 0xb26c: file String.cc, line 867.
3068 Breakpoint 2 at 0xb344: file String.cc, line 875.
3069 Breakpoint 3 at 0xafcc: file String.cc, line 846.
3070 Multiple breakpoints were set.
3071 Use the "delete" command to delete unwanted
3077 @c @ifclear BARETARGET
3078 @node Error in Breakpoints
3079 @subsection ``Cannot insert breakpoints''
3081 @c FIXME!! 14/6/95 Is there a real example of this? Let's use it.
3083 Under some operating systems, breakpoints cannot be used in a program if
3084 any other process is running that program. In this situation,
3085 attempting to run or continue a program with a breakpoint causes
3086 @value{GDBN} to print an error message:
3089 Cannot insert breakpoints.
3090 The same program may be running in another process.
3093 When this happens, you have three ways to proceed:
3097 Remove or disable the breakpoints, then continue.
3100 Suspend @value{GDBN}, and copy the file containing your program to a new
3101 name. Resume @value{GDBN} and use the @code{exec-file} command to specify
3102 that @value{GDBN} should run your program under that name.
3103 Then start your program again.
3106 Relink your program so that the text segment is nonsharable, using the
3107 linker option @samp{-N}. The operating system limitation may not apply
3108 to nonsharable executables.
3112 A similar message can be printed if you request too many active
3113 hardware-assisted breakpoints and watchpoints:
3115 @c FIXME: the precise wording of this message may change; the relevant
3116 @c source change is not committed yet (Sep 3, 1999).
3118 Stopped; cannot insert breakpoints.
3119 You may have requested too many hardware breakpoints and watchpoints.
3123 This message is printed when you attempt to resume the program, since
3124 only then @value{GDBN} knows exactly how many hardware breakpoints and
3125 watchpoints it needs to insert.
3127 When this message is printed, you need to disable or remove some of the
3128 hardware-assisted breakpoints and watchpoints, and then continue.
3131 @node Continuing and Stepping
3132 @section Continuing and stepping
3136 @cindex resuming execution
3137 @dfn{Continuing} means resuming program execution until your program
3138 completes normally. In contrast, @dfn{stepping} means executing just
3139 one more ``step'' of your program, where ``step'' may mean either one
3140 line of source code, or one machine instruction (depending on what
3141 particular command you use). Either when continuing or when stepping,
3142 your program may stop even sooner, due to a breakpoint or a signal. (If
3143 it stops due to a signal, you may want to use @code{handle}, or use
3144 @samp{signal 0} to resume execution. @xref{Signals, ,Signals}.)
3150 @item continue @r{[}@var{ignore-count}@r{]}
3151 @itemx c @r{[}@var{ignore-count}@r{]}
3152 @itemx fg @r{[}@var{ignore-count}@r{]}
3153 Resume program execution, at the address where your program last stopped;
3154 any breakpoints set at that address are bypassed. The optional argument
3155 @var{ignore-count} allows you to specify a further number of times to
3156 ignore a breakpoint at this location; its effect is like that of
3157 @code{ignore} (@pxref{Conditions, ,Break conditions}).
3159 The argument @var{ignore-count} is meaningful only when your program
3160 stopped due to a breakpoint. At other times, the argument to
3161 @code{continue} is ignored.
3163 The synonyms @code{c} and @code{fg} (for @dfn{foreground}, as the
3164 debugged program is deemed to be the foreground program) are provided
3165 purely for convenience, and have exactly the same behavior as
3169 To resume execution at a different place, you can use @code{return}
3170 (@pxref{Returning, ,Returning from a function}) to go back to the
3171 calling function; or @code{jump} (@pxref{Jumping, ,Continuing at a
3172 different address}) to go to an arbitrary location in your program.
3174 A typical technique for using stepping is to set a breakpoint
3175 (@pxref{Breakpoints, ,Breakpoints; watchpoints; and catchpoints}) at the
3176 beginning of the function or the section of your program where a problem
3177 is believed to lie, run your program until it stops at that breakpoint,
3178 and then step through the suspect area, examining the variables that are
3179 interesting, until you see the problem happen.
3185 Continue running your program until control reaches a different source
3186 line, then stop it and return control to @value{GDBN}. This command is
3187 abbreviated @code{s}.
3190 @c "without debugging information" is imprecise; actually "without line
3191 @c numbers in the debugging information". (gcc -g1 has debugging info but
3192 @c not line numbers). But it seems complex to try to make that
3193 @c distinction here.
3194 @emph{Warning:} If you use the @code{step} command while control is
3195 within a function that was compiled without debugging information,
3196 execution proceeds until control reaches a function that does have
3197 debugging information. Likewise, it will not step into a function which
3198 is compiled without debugging information. To step through functions
3199 without debugging information, use the @code{stepi} command, described
3203 The @code{step} command only stops at the first instruction of a
3204 source line. This prevents the multiple stops that could otherwise occur in
3205 switch statements, for loops, etc. @code{step} continues to stop if a
3206 function that has debugging information is called within the line.
3207 In other words, @code{step} @emph{steps inside} any functions called
3210 Also, the @code{step} command only enters a function if there is line
3211 number information for the function. Otherwise it acts like the
3212 @code{next} command. This avoids problems when using @code{cc -gl}
3213 on MIPS machines. Previously, @code{step} entered subroutines if there
3214 was any debugging information about the routine.
3216 @item step @var{count}
3217 Continue running as in @code{step}, but do so @var{count} times. If a
3218 breakpoint is reached, or a signal not related to stepping occurs before
3219 @var{count} steps, stepping stops right away.
3223 @item next @r{[}@var{count}@r{]}
3224 Continue to the next source line in the current (innermost) stack frame.
3225 This is similar to @code{step}, but function calls that appear within
3226 the line of code are executed without stopping. Execution stops when
3227 control reaches a different line of code at the original stack level
3228 that was executing when you gave the @code{next} command. This command
3229 is abbreviated @code{n}.
3231 An argument @var{count} is a repeat count, as for @code{step}.
3234 @c FIX ME!! Do we delete this, or is there a way it fits in with
3235 @c the following paragraph? --- Vctoria
3237 @c @code{next} within a function that lacks debugging information acts like
3238 @c @code{step}, but any function calls appearing within the code of the
3239 @c function are executed without stopping.
3241 The @code{next} command only stops at the first instruction of a
3242 source line. This prevents multiple stops that could otherwise occur in
3243 switch statements, for loops, etc.
3247 Continue running until just after function in the selected stack frame
3248 returns. Print the returned value (if any).
3250 Contrast this with the @code{return} command (@pxref{Returning,
3251 ,Returning from a function}).
3257 Continue running until a source line past the current line, in the
3258 current stack frame, is reached. This command is used to avoid single
3259 stepping through a loop more than once. It is like the @code{next}
3260 command, except that when @code{until} encounters a jump, it
3261 automatically continues execution until the program counter is greater
3262 than the address of the jump.
3264 This means that when you reach the end of a loop after single stepping
3265 though it, @code{until} makes your program continue execution until it
3266 exits the loop. In contrast, a @code{next} command at the end of a loop
3267 simply steps back to the beginning of the loop, which forces you to step
3268 through the next iteration.
3270 @code{until} always stops your program if it attempts to exit the current
3273 @code{until} may produce somewhat counterintuitive results if the order
3274 of machine code does not match the order of the source lines. For
3275 example, in the following excerpt from a debugging session, the @code{f}
3276 (@code{frame}) command shows that execution is stopped at line
3277 @code{206}; yet when we use @code{until}, we get to line @code{195}:
3281 #0 main (argc=4, argv=0xf7fffae8) at m4.c:206
3283 (@value{GDBP}) until
3284 195 for ( ; argc > 0; NEXTARG) @{
3287 This happened because, for execution efficiency, the compiler had
3288 generated code for the loop closure test at the end, rather than the
3289 start, of the loop---even though the test in a C @code{for}-loop is
3290 written before the body of the loop. The @code{until} command appeared
3291 to step back to the beginning of the loop when it advanced to this
3292 expression; however, it has not really gone to an earlier
3293 statement---not in terms of the actual machine code.
3295 @code{until} with no argument works by means of single
3296 instruction stepping, and hence is slower than @code{until} with an
3299 @item until @var{location}
3300 @itemx u @var{location}
3301 Continue running your program until either the specified location is
3302 reached, or the current stack frame returns. @var{location} is any of
3303 the forms of argument acceptable to @code{break} (@pxref{Set Breaks,
3304 ,Setting breakpoints}). This form of the command uses breakpoints,
3305 and hence is quicker than @code{until} without an argument.
3311 Execute one machine instruction, then stop and return to the debugger.
3313 It is often useful to do @samp{display/i $pc} when stepping by machine
3314 instructions. This makes @value{GDBN} automatically display the next
3315 instruction to be executed, each time your program stops. @xref{Auto
3316 Display,, Automatic display}.
3318 An argument is a repeat count, as in @code{step}.
3325 Execute one machine instruction, but if it is a function call,
3326 proceed until the function returns.
3328 An argument is a repeat count, as in @code{next}.
3335 A signal is an asynchronous event that can happen in a program. The
3336 operating system defines the possible kinds of signals, and gives each
3337 kind a name and a number. For example, in Unix @code{SIGINT} is the
3338 signal a program gets when you type an interrupt character (often @kbd{C-c});
3339 @code{SIGSEGV} is the signal a program gets from referencing a place in
3340 memory far away from all the areas in use; @code{SIGALRM} occurs when
3341 the alarm clock timer goes off (which happens only if your program has
3342 requested an alarm).
3344 @cindex fatal signals
3345 Some signals, including @code{SIGALRM}, are a normal part of the
3346 functioning of your program. Others, such as @code{SIGSEGV}, indicate
3347 errors; these signals are @dfn{fatal} (they kill your program immediately) if the
3348 program has not specified in advance some other way to handle the signal.
3349 @code{SIGINT} does not indicate an error in your program, but it is normally
3350 fatal so it can carry out the purpose of the interrupt: to kill the program.
3352 @value{GDBN} has the ability to detect any occurrence of a signal in your
3353 program. You can tell @value{GDBN} in advance what to do for each kind of
3356 @cindex handling signals
3357 Normally, @value{GDBN} is set up to ignore non-erroneous signals like @code{SIGALRM}
3358 (so as not to interfere with their role in the functioning of your program)
3359 but to stop your program immediately whenever an error signal happens.
3360 You can change these settings with the @code{handle} command.
3363 @kindex info signals
3365 Print a table of all the kinds of signals and how @value{GDBN} has been told to
3366 handle each one. You can use this to see the signal numbers of all
3367 the defined types of signals.
3369 @code{info handle} is an alias for @code{info signals}.
3372 @item handle @var{signal} @var{keywords}@dots{}
3373 Change the way @value{GDBN} handles signal @var{signal}. @var{signal} can
3374 be the number of a signal or its name (with or without the @samp{SIG} at the
3375 beginning). The @var{keywords} say what change to make.
3379 The keywords allowed by the @code{handle} command can be abbreviated.
3380 Their full names are:
3384 @value{GDBN} should not stop your program when this signal happens. It may
3385 still print a message telling you that the signal has come in.
3388 @value{GDBN} should stop your program when this signal happens. This implies
3389 the @code{print} keyword as well.
3392 @value{GDBN} should print a message when this signal happens.
3395 @value{GDBN} should not mention the occurrence of the signal at all. This
3396 implies the @code{nostop} keyword as well.
3399 @value{GDBN} should allow your program to see this signal; your program
3400 can handle the signal, or else it may terminate if the signal is fatal
3404 @value{GDBN} should not allow your program to see this signal.
3408 When a signal stops your program, the signal is not visible to the
3410 continue. Your program sees the signal then, if @code{pass} is in
3411 effect for the signal in question @emph{at that time}. In other words,
3412 after @value{GDBN} reports a signal, you can use the @code{handle}
3413 command with @code{pass} or @code{nopass} to control whether your
3414 program sees that signal when you continue.
3416 You can also use the @code{signal} command to prevent your program from
3417 seeing a signal, or cause it to see a signal it normally would not see,
3418 or to give it any signal at any time. For example, if your program stopped
3419 due to some sort of memory reference error, you might store correct
3420 values into the erroneous variables and continue, hoping to see more
3421 execution; but your program would probably terminate immediately as
3422 a result of the fatal signal once it saw the signal. To prevent this,
3423 you can continue with @samp{signal 0}. @xref{Signaling, ,Giving your
3427 @section Stopping and starting multi-thread programs
3429 When your program has multiple threads (@pxref{Threads,, Debugging
3430 programs with multiple threads}), you can choose whether to set
3431 breakpoints on all threads, or on a particular thread.
3434 @cindex breakpoints and threads
3435 @cindex thread breakpoints
3436 @kindex break @dots{} thread @var{threadno}
3437 @item break @var{linespec} thread @var{threadno}
3438 @itemx break @var{linespec} thread @var{threadno} if @dots{}
3439 @var{linespec} specifies source lines; there are several ways of
3440 writing them, but the effect is always to specify some source line.
3442 Use the qualifier @samp{thread @var{threadno}} with a breakpoint command
3443 to specify that you only want @value{GDBN} to stop the program when a
3444 particular thread reaches this breakpoint. @var{threadno} is one of the
3445 numeric thread identifiers assigned by @value{GDBN}, shown in the first
3446 column of the @samp{info threads} display.
3448 If you do not specify @samp{thread @var{threadno}} when you set a
3449 breakpoint, the breakpoint applies to @emph{all} threads of your
3452 You can use the @code{thread} qualifier on conditional breakpoints as
3453 well; in this case, place @samp{thread @var{threadno}} before the
3454 breakpoint condition, like this:
3457 (@value{GDBP}) break frik.c:13 thread 28 if bartab > lim
3462 @cindex stopped threads
3463 @cindex threads, stopped
3464 Whenever your program stops under @value{GDBN} for any reason,
3465 @emph{all} threads of execution stop, not just the current thread. This
3466 allows you to examine the overall state of the program, including
3467 switching between threads, without worrying that things may change
3470 @cindex continuing threads
3471 @cindex threads, continuing
3472 Conversely, whenever you restart the program, @emph{all} threads start
3473 executing. @emph{This is true even when single-stepping} with commands
3474 like @code{step} or @code{next}.
3476 In particular, @value{GDBN} cannot single-step all threads in lockstep.
3477 Since thread scheduling is up to your debugging target's operating
3478 system (not controlled by @value{GDBN}), other threads may
3479 execute more than one statement while the current thread completes a
3480 single step. Moreover, in general other threads stop in the middle of a
3481 statement, rather than at a clean statement boundary, when the program
3484 You might even find your program stopped in another thread after
3485 continuing or even single-stepping. This happens whenever some other
3486 thread runs into a breakpoint, a signal, or an exception before the
3487 first thread completes whatever you requested.
3489 On some OSes, you can lock the OS scheduler and thus allow only a single
3493 @item set scheduler-locking @var{mode}
3494 Set the scheduler locking mode. If it is @code{off}, then there is no
3495 locking and any thread may run at any time. If @code{on}, then only the
3496 current thread may run when the inferior is resumed. The @code{step}
3497 mode optimizes for single-stepping. It stops other threads from
3498 ``seizing the prompt'' by preempting the current thread while you are
3499 stepping. Other threads will only rarely (or never) get a chance to run
3500 when you step. They are more likely to run when you @samp{next} over a
3501 function call, and they are completely free to run when you use commands
3502 like @samp{continue}, @samp{until}, or @samp{finish}. However, unless another
3503 thread hits a breakpoint during its timeslice, they will never steal the
3504 @value{GDBN} prompt away from the thread that you are debugging.
3506 @item show scheduler-locking
3507 Display the current scheduler locking mode.
3512 @chapter Examining the Stack
3514 When your program has stopped, the first thing you need to know is where it
3515 stopped and how it got there.
3518 Each time your program performs a function call, information about the call
3520 That information includes the location of the call in your program,
3521 the arguments of the call,
3522 and the local variables of the function being called.
3523 The information is saved in a block of data called a @dfn{stack frame}.
3524 The stack frames are allocated in a region of memory called the @dfn{call
3527 When your program stops, the @value{GDBN} commands for examining the
3528 stack allow you to see all of this information.
3530 @cindex selected frame
3531 One of the stack frames is @dfn{selected} by @value{GDBN} and many
3532 @value{GDBN} commands refer implicitly to the selected frame. In
3533 particular, whenever you ask @value{GDBN} for the value of a variable in
3534 your program, the value is found in the selected frame. There are
3535 special @value{GDBN} commands to select whichever frame you are
3536 interested in. @xref{Selection, ,Selecting a frame}.
3538 When your program stops, @value{GDBN} automatically selects the
3539 currently executing frame and describes it briefly, similar to the
3540 @code{frame} command (@pxref{Frame Info, ,Information about a frame}).
3543 * Frames:: Stack frames
3544 * Backtrace:: Backtraces
3545 * Selection:: Selecting a frame
3546 * Frame Info:: Information on a frame
3551 @section Stack frames
3553 @cindex frame, definition
3555 The call stack is divided up into contiguous pieces called @dfn{stack
3556 frames}, or @dfn{frames} for short; each frame is the data associated
3557 with one call to one function. The frame contains the arguments given
3558 to the function, the function's local variables, and the address at
3559 which the function is executing.
3561 @cindex initial frame
3562 @cindex outermost frame
3563 @cindex innermost frame
3564 When your program is started, the stack has only one frame, that of the
3565 function @code{main}. This is called the @dfn{initial} frame or the
3566 @dfn{outermost} frame. Each time a function is called, a new frame is
3567 made. Each time a function returns, the frame for that function invocation
3568 is eliminated. If a function is recursive, there can be many frames for
3569 the same function. The frame for the function in which execution is
3570 actually occurring is called the @dfn{innermost} frame. This is the most
3571 recently created of all the stack frames that still exist.
3573 @cindex frame pointer
3574 Inside your program, stack frames are identified by their addresses. A
3575 stack frame consists of many bytes, each of which has its own address; each
3576 kind of computer has a convention for choosing one byte whose
3577 address serves as the address of the frame. Usually this address is kept
3578 in a register called the @dfn{frame pointer register} while execution is
3579 going on in that frame.
3581 @cindex frame number
3582 @value{GDBN} assigns numbers to all existing stack frames, starting with
3583 zero for the innermost frame, one for the frame that called it,
3584 and so on upward. These numbers do not really exist in your program;
3585 they are assigned by @value{GDBN} to give you a way of designating stack
3586 frames in @value{GDBN} commands.
3588 @c below produces an acceptable overful hbox. --mew 13aug1993
3589 @cindex frameless execution
3590 Some compilers provide a way to compile functions so that they operate
3591 without stack frames. (For example, the @code{@value{GCC}} option
3592 @samp{-fomit-frame-pointer} generates functions without a frame.)
3593 This is occasionally done with heavily used library functions to save
3594 the frame setup time. @value{GDBN} has limited facilities for dealing
3595 with these function invocations. If the innermost function invocation
3596 has no stack frame, @value{GDBN} nevertheless regards it as though
3597 it had a separate frame, which is numbered zero as usual, allowing
3598 correct tracing of the function call chain. However, @value{GDBN} has
3599 no provision for frameless functions elsewhere in the stack.
3602 @kindex frame@r{, command}
3603 @item frame @var{args}
3604 The @code{frame} command allows you to move from one stack frame to another,
3605 and to print the stack frame you select. @var{args} may be either the
3606 address of the frame or the stack frame number. Without an argument,
3607 @code{frame} prints the current stack frame.
3609 @kindex select-frame
3611 The @code{select-frame} command allows you to move from one stack frame
3612 to another without printing the frame. This is the silent version of
3621 @cindex stack traces
3622 A backtrace is a summary of how your program got where it is. It shows one
3623 line per frame, for many frames, starting with the currently executing
3624 frame (frame zero), followed by its caller (frame one), and on up the
3632 Print a backtrace of the entire stack: one line per frame for all
3633 frames in the stack.
3635 You can stop the backtrace at any time by typing the system interrupt
3636 character, normally @kbd{C-c}.
3638 @item backtrace @var{n}
3640 Similar, but print only the innermost @var{n} frames.
3642 @item backtrace -@var{n}
3644 Similar, but print only the outermost @var{n} frames.
3650 The names @code{where} and @code{info stack} (abbreviated @code{info s})
3651 are additional aliases for @code{backtrace}.
3653 Each line in the backtrace shows the frame number and the function name.
3654 The program counter value is also shown---unless you use @code{set
3655 print address off}. The backtrace also shows the source file name and
3656 line number, as well as the arguments to the function. The program
3657 counter value is omitted if it is at the beginning of the code for that
3660 Here is an example of a backtrace. It was made with the command
3661 @samp{bt 3}, so it shows the innermost three frames.
3665 #0 m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
3667 #1 0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
3668 #2 0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
3670 (More stack frames follow...)
3675 The display for frame zero does not begin with a program counter
3676 value, indicating that your program has stopped at the beginning of the
3677 code for line @code{993} of @code{builtin.c}.
3680 @section Selecting a frame
3682 Most commands for examining the stack and other data in your program work on
3683 whichever stack frame is selected at the moment. Here are the commands for
3684 selecting a stack frame; all of them finish by printing a brief description
3685 of the stack frame just selected.
3688 @kindex frame@r{, selecting}
3692 Select frame number @var{n}. Recall that frame zero is the innermost
3693 (currently executing) frame, frame one is the frame that called the
3694 innermost one, and so on. The highest-numbered frame is the one for
3697 @item frame @var{addr}
3699 Select the frame at address @var{addr}. This is useful mainly if the
3700 chaining of stack frames has been damaged by a bug, making it
3701 impossible for @value{GDBN} to assign numbers properly to all frames. In
3702 addition, this can be useful when your program has multiple stacks and
3703 switches between them.
3705 On the SPARC architecture, @code{frame} needs two addresses to
3706 select an arbitrary frame: a frame pointer and a stack pointer.
3708 On the MIPS and Alpha architecture, it needs two addresses: a stack
3709 pointer and a program counter.
3711 On the 29k architecture, it needs three addresses: a register stack
3712 pointer, a program counter, and a memory stack pointer.
3713 @c note to future updaters: this is conditioned on a flag
3714 @c SETUP_ARBITRARY_FRAME in the tm-*.h files. The above is up to date
3715 @c as of 27 Jan 1994.
3719 Move @var{n} frames up the stack. For positive numbers @var{n}, this
3720 advances toward the outermost frame, to higher frame numbers, to frames
3721 that have existed longer. @var{n} defaults to one.
3726 Move @var{n} frames down the stack. For positive numbers @var{n}, this
3727 advances toward the innermost frame, to lower frame numbers, to frames
3728 that were created more recently. @var{n} defaults to one. You may
3729 abbreviate @code{down} as @code{do}.
3732 All of these commands end by printing two lines of output describing the
3733 frame. The first line shows the frame number, the function name, the
3734 arguments, and the source file and line number of execution in that
3735 frame. The second line shows the text of that source line.
3743 #1 0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
3745 10 read_input_file (argv[i]);
3749 After such a printout, the @code{list} command with no arguments
3750 prints ten lines centered on the point of execution in the frame.
3751 @xref{List, ,Printing source lines}.
3754 @kindex down-silently
3756 @item up-silently @var{n}
3757 @itemx down-silently @var{n}
3758 These two commands are variants of @code{up} and @code{down},
3759 respectively; they differ in that they do their work silently, without
3760 causing display of the new frame. They are intended primarily for use
3761 in @value{GDBN} command scripts, where the output might be unnecessary and
3766 @section Information about a frame
3768 There are several other commands to print information about the selected
3774 When used without any argument, this command does not change which
3775 frame is selected, but prints a brief description of the currently
3776 selected stack frame. It can be abbreviated @code{f}. With an
3777 argument, this command is used to select a stack frame.
3778 @xref{Selection, ,Selecting a frame}.
3784 This command prints a verbose description of the selected stack frame,
3789 the address of the frame
3791 the address of the next frame down (called by this frame)
3793 the address of the next frame up (caller of this frame)
3795 the language in which the source code corresponding to this frame is written
3797 the address of the frame's arguments
3799 the address of the frame's local variables
3801 the program counter saved in it (the address of execution in the caller frame)
3803 which registers were saved in the frame
3806 @noindent The verbose description is useful when
3807 something has gone wrong that has made the stack format fail to fit
3808 the usual conventions.
3810 @item info frame @var{addr}
3811 @itemx info f @var{addr}
3812 Print a verbose description of the frame at address @var{addr}, without
3813 selecting that frame. The selected frame remains unchanged by this
3814 command. This requires the same kind of address (more than one for some
3815 architectures) that you specify in the @code{frame} command.
3816 @xref{Selection, ,Selecting a frame}.
3820 Print the arguments of the selected frame, each on a separate line.
3824 Print the local variables of the selected frame, each on a separate
3825 line. These are all variables (declared either static or automatic)
3826 accessible at the point of execution of the selected frame.
3829 @cindex catch exceptions, list active handlers
3830 @cindex exception handlers, how to list
3832 Print a list of all the exception handlers that are active in the
3833 current stack frame at the current point of execution. To see other
3834 exception handlers, visit the associated frame (using the @code{up},
3835 @code{down}, or @code{frame} commands); then type @code{info catch}.
3836 @xref{Set Catchpoints, , Setting catchpoints}.
3842 @chapter Examining Source Files
3844 @value{GDBN} can print parts of your program's source, since the debugging
3845 information recorded in the program tells @value{GDBN} what source files were
3846 used to build it. When your program stops, @value{GDBN} spontaneously prints
3847 the line where it stopped. Likewise, when you select a stack frame
3848 (@pxref{Selection, ,Selecting a frame}), @value{GDBN} prints the line where
3849 execution in that frame has stopped. You can print other portions of
3850 source files by explicit command.
3852 If you use @value{GDBN} through its @sc{gnu} Emacs interface, you may
3853 prefer to use Emacs facilities to view source; see @ref{Emacs, ,Using
3854 @value{GDBN} under @sc{gnu} Emacs}.
3857 * List:: Printing source lines
3858 * Search:: Searching source files
3859 * Source Path:: Specifying source directories
3860 * Machine Code:: Source and machine code
3864 @section Printing source lines
3868 To print lines from a source file, use the @code{list} command
3869 (abbreviated @code{l}). By default, ten lines are printed.
3870 There are several ways to specify what part of the file you want to print.
3872 Here are the forms of the @code{list} command most commonly used:
3875 @item list @var{linenum}
3876 Print lines centered around line number @var{linenum} in the
3877 current source file.
3879 @item list @var{function}
3880 Print lines centered around the beginning of function
3884 Print more lines. If the last lines printed were printed with a
3885 @code{list} command, this prints lines following the last lines
3886 printed; however, if the last line printed was a solitary line printed
3887 as part of displaying a stack frame (@pxref{Stack, ,Examining the
3888 Stack}), this prints lines centered around that line.
3891 Print lines just before the lines last printed.
3894 By default, @value{GDBN} prints ten source lines with any of these forms of
3895 the @code{list} command. You can change this using @code{set listsize}:
3898 @kindex set listsize
3899 @item set listsize @var{count}
3900 Make the @code{list} command display @var{count} source lines (unless
3901 the @code{list} argument explicitly specifies some other number).
3903 @kindex show listsize
3905 Display the number of lines that @code{list} prints.
3908 Repeating a @code{list} command with @key{RET} discards the argument,
3909 so it is equivalent to typing just @code{list}. This is more useful
3910 than listing the same lines again. An exception is made for an
3911 argument of @samp{-}; that argument is preserved in repetition so that
3912 each repetition moves up in the source file.
3915 In general, the @code{list} command expects you to supply zero, one or two
3916 @dfn{linespecs}. Linespecs specify source lines; there are several ways
3917 of writing them, but the effect is always to specify some source line.
3918 Here is a complete description of the possible arguments for @code{list}:
3921 @item list @var{linespec}
3922 Print lines centered around the line specified by @var{linespec}.
3924 @item list @var{first},@var{last}
3925 Print lines from @var{first} to @var{last}. Both arguments are
3928 @item list ,@var{last}
3929 Print lines ending with @var{last}.
3931 @item list @var{first},
3932 Print lines starting with @var{first}.
3935 Print lines just after the lines last printed.
3938 Print lines just before the lines last printed.
3941 As described in the preceding table.
3944 Here are the ways of specifying a single source line---all the
3949 Specifies line @var{number} of the current source file.
3950 When a @code{list} command has two linespecs, this refers to
3951 the same source file as the first linespec.
3954 Specifies the line @var{offset} lines after the last line printed.
3955 When used as the second linespec in a @code{list} command that has
3956 two, this specifies the line @var{offset} lines down from the
3960 Specifies the line @var{offset} lines before the last line printed.
3962 @item @var{filename}:@var{number}
3963 Specifies line @var{number} in the source file @var{filename}.
3965 @item @var{function}
3966 Specifies the line that begins the body of the function @var{function}.
3967 For example: in C, this is the line with the open brace.
3969 @item @var{filename}:@var{function}
3970 Specifies the line of the open-brace that begins the body of the
3971 function @var{function} in the file @var{filename}. You only need the
3972 file name with a function name to avoid ambiguity when there are
3973 identically named functions in different source files.
3975 @item *@var{address}
3976 Specifies the line containing the program address @var{address}.
3977 @var{address} may be any expression.
3981 @section Searching source files
3983 @kindex reverse-search
3985 There are two commands for searching through the current source file for a
3990 @kindex forward-search
3991 @item forward-search @var{regexp}
3992 @itemx search @var{regexp}
3993 The command @samp{forward-search @var{regexp}} checks each line,
3994 starting with the one following the last line listed, for a match for
3995 @var{regexp}. It lists the line that is found. You can use the
3996 synonym @samp{search @var{regexp}} or abbreviate the command name as
3999 @item reverse-search @var{regexp}
4000 The command @samp{reverse-search @var{regexp}} checks each line, starting
4001 with the one before the last line listed and going backward, for a match
4002 for @var{regexp}. It lists the line that is found. You can abbreviate
4003 this command as @code{rev}.
4007 @section Specifying source directories
4010 @cindex directories for source files
4011 Executable programs sometimes do not record the directories of the source
4012 files from which they were compiled, just the names. Even when they do,
4013 the directories could be moved between the compilation and your debugging
4014 session. @value{GDBN} has a list of directories to search for source files;
4015 this is called the @dfn{source path}. Each time @value{GDBN} wants a source file,
4016 it tries all the directories in the list, in the order they are present
4017 in the list, until it finds a file with the desired name. Note that
4018 the executable search path is @emph{not} used for this purpose. Neither is
4019 the current working directory, unless it happens to be in the source
4022 If @value{GDBN} cannot find a source file in the source path, and the
4023 object program records a directory, @value{GDBN} tries that directory
4024 too. If the source path is empty, and there is no record of the
4025 compilation directory, @value{GDBN} looks in the current directory as a
4028 Whenever you reset or rearrange the source path, @value{GDBN} clears out
4029 any information it has cached about where source files are found and where
4030 each line is in the file.
4034 When you start @value{GDBN}, its source path includes only @samp{cdir}
4035 and @samp{cwd}, in that order.
4036 To add other directories, use the @code{directory} command.
4039 @item directory @var{dirname} @dots{}
4040 @item dir @var{dirname} @dots{}
4041 Add directory @var{dirname} to the front of the source path. Several
4042 directory names may be given to this command, separated by @samp{:}
4043 (@samp{;} on MS-DOS and MS-Windows, where @samp{:} usually appears as
4044 part of absolute file names) or
4045 whitespace. You may specify a directory that is already in the source
4046 path; this moves it forward, so @value{GDBN} searches it sooner.
4052 @cindex compilation directory
4053 @cindex current directory
4054 @cindex working directory
4055 @cindex directory, current
4056 @cindex directory, compilation
4057 You can use the string @samp{$cdir} to refer to the compilation
4058 directory (if one is recorded), and @samp{$cwd} to refer to the current
4059 working directory. @samp{$cwd} is not the same as @samp{.}---the former
4060 tracks the current working directory as it changes during your @value{GDBN}
4061 session, while the latter is immediately expanded to the current
4062 directory at the time you add an entry to the source path.
4065 Reset the source path to empty again. This requires confirmation.
4067 @c RET-repeat for @code{directory} is explicitly disabled, but since
4068 @c repeating it would be a no-op we do not say that. (thanks to RMS)
4070 @item show directories
4071 @kindex show directories
4072 Print the source path: show which directories it contains.
4075 If your source path is cluttered with directories that are no longer of
4076 interest, @value{GDBN} may sometimes cause confusion by finding the wrong
4077 versions of source. You can correct the situation as follows:
4081 Use @code{directory} with no argument to reset the source path to empty.
4084 Use @code{directory} with suitable arguments to reinstall the
4085 directories you want in the source path. You can add all the
4086 directories in one command.
4090 @section Source and machine code
4092 You can use the command @code{info line} to map source lines to program
4093 addresses (and vice versa), and the command @code{disassemble} to display
4094 a range of addresses as machine instructions. When run under @sc{gnu} Emacs
4095 mode, the @code{info line} command causes the arrow to point to the
4096 line specified. Also, @code{info line} prints addresses in symbolic form as
4101 @item info line @var{linespec}
4102 Print the starting and ending addresses of the compiled code for
4103 source line @var{linespec}. You can specify source lines in any of
4104 the ways understood by the @code{list} command (@pxref{List, ,Printing
4108 For example, we can use @code{info line} to discover the location of
4109 the object code for the first line of function
4110 @code{m4_changequote}:
4112 @c FIXME: I think this example should also show the addresses in
4113 @c symbolic form, as they usually would be displayed.
4115 (@value{GDBP}) info line m4_changecom
4116 Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
4120 We can also inquire (using @code{*@var{addr}} as the form for
4121 @var{linespec}) what source line covers a particular address:
4123 (@value{GDBP}) info line *0x63ff
4124 Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.
4127 @cindex @code{$_} and @code{info line}
4128 @kindex x@r{, and }@code{info line}
4129 After @code{info line}, the default address for the @code{x} command
4130 is changed to the starting address of the line, so that @samp{x/i} is
4131 sufficient to begin examining the machine code (@pxref{Memory,
4132 ,Examining memory}). Also, this address is saved as the value of the
4133 convenience variable @code{$_} (@pxref{Convenience Vars, ,Convenience
4138 @cindex assembly instructions
4139 @cindex instructions, assembly
4140 @cindex machine instructions
4141 @cindex listing machine instructions
4143 This specialized command dumps a range of memory as machine
4144 instructions. The default memory range is the function surrounding the
4145 program counter of the selected frame. A single argument to this
4146 command is a program counter value; @value{GDBN} dumps the function
4147 surrounding this value. Two arguments specify a range of addresses
4148 (first inclusive, second exclusive) to dump.
4151 The following example shows the disassembly of a range of addresses of
4152 HP PA-RISC 2.0 code:
4155 (@value{GDBP}) disas 0x32c4 0x32e4
4156 Dump of assembler code from 0x32c4 to 0x32e4:
4157 0x32c4 <main+204>: addil 0,dp
4158 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26
4159 0x32cc <main+212>: ldil 0x3000,r31
4160 0x32d0 <main+216>: ble 0x3f8(sr4,r31)
4161 0x32d4 <main+220>: ldo 0(r31),rp
4162 0x32d8 <main+224>: addil -0x800,dp
4163 0x32dc <main+228>: ldo 0x588(r1),r26
4164 0x32e0 <main+232>: ldil 0x3000,r31
4165 End of assembler dump.
4168 Some architectures have more than one commonly-used set of instruction
4169 mnemonics or other syntax.
4172 @kindex set disassembly-flavor
4173 @cindex assembly instructions
4174 @cindex instructions, assembly
4175 @cindex machine instructions
4176 @cindex listing machine instructions
4177 @cindex Intel disassembly flavor
4178 @cindex AT&T disassembly flavor
4179 @item set disassembly-flavor @var{instruction-set}
4180 Select the instruction set to use when disassembling the
4181 program via the @code{disassemble} or @code{x/i} commands.
4183 Currently this command is only defined for the Intel x86 family. You
4184 can set @var{instruction-set} to either @code{intel} or @code{att}.
4185 The default is @code{att}, the AT&T flavor used by default by Unix
4186 assemblers for x86-based targets.
4191 @chapter Examining Data
4193 @cindex printing data
4194 @cindex examining data
4197 @c "inspect" is not quite a synonym if you are using Epoch, which we do not
4198 @c document because it is nonstandard... Under Epoch it displays in a
4199 @c different window or something like that.
4200 The usual way to examine data in your program is with the @code{print}
4201 command (abbreviated @code{p}), or its synonym @code{inspect}. It
4202 evaluates and prints the value of an expression of the language your
4203 program is written in (@pxref{Languages, ,Using @value{GDBN} with
4204 Different Languages}).
4207 @item print @var{expr}
4208 @itemx print /@var{f} @var{expr}
4209 @var{expr} is an expression (in the source language). By default the
4210 value of @var{expr} is printed in a format appropriate to its data type;
4211 you can choose a different format by specifying @samp{/@var{f}}, where
4212 @var{f} is a letter specifying the format; see @ref{Output Formats,,Output
4216 @itemx print /@var{f}
4217 If you omit @var{expr}, @value{GDBN} displays the last value again (from the
4218 @dfn{value history}; @pxref{Value History, ,Value history}). This allows you to
4219 conveniently inspect the same value in an alternative format.
4222 A more low-level way of examining data is with the @code{x} command.
4223 It examines data in memory at a specified address and prints it in a
4224 specified format. @xref{Memory, ,Examining memory}.
4226 If you are interested in information about types, or about how the
4227 fields of a struct or a class are declared, use the @code{ptype @var{exp}}
4228 command rather than @code{print}. @xref{Symbols, ,Examining the Symbol
4232 * Expressions:: Expressions
4233 * Variables:: Program variables
4234 * Arrays:: Artificial arrays
4235 * Output Formats:: Output formats
4236 * Memory:: Examining memory
4237 * Auto Display:: Automatic display
4238 * Print Settings:: Print settings
4239 * Value History:: Value history
4240 * Convenience Vars:: Convenience variables
4241 * Registers:: Registers
4242 * Floating Point Hardware:: Floating point hardware
4246 @section Expressions
4249 @code{print} and many other @value{GDBN} commands accept an expression and
4250 compute its value. Any kind of constant, variable or operator defined
4251 by the programming language you are using is valid in an expression in
4252 @value{GDBN}. This includes conditional expressions, function calls, casts
4253 and string constants. It unfortunately does not include symbols defined
4254 by preprocessor @code{#define} commands.
4256 @value{GDBN} supports array constants in expressions input by
4257 the user. The syntax is @{@var{element}, @var{element}@dots{}@}. For example,
4258 you can use the command @code{print @{1, 2, 3@}} to build up an array in
4259 memory that is @code{malloc}ed in the target program.
4261 Because C is so widespread, most of the expressions shown in examples in
4262 this manual are in C. @xref{Languages, , Using @value{GDBN} with Different
4263 Languages}, for information on how to use expressions in other
4266 In this section, we discuss operators that you can use in @value{GDBN}
4267 expressions regardless of your programming language.
4269 Casts are supported in all languages, not just in C, because it is so
4270 useful to cast a number into a pointer in order to examine a structure
4271 at that address in memory.
4272 @c FIXME: casts supported---Mod2 true?
4274 @value{GDBN} supports these operators, in addition to those common
4275 to programming languages:
4279 @samp{@@} is a binary operator for treating parts of memory as arrays.
4280 @xref{Arrays, ,Artificial arrays}, for more information.
4283 @samp{::} allows you to specify a variable in terms of the file or
4284 function where it is defined. @xref{Variables, ,Program variables}.
4286 @cindex @{@var{type}@}
4287 @cindex type casting memory
4288 @cindex memory, viewing as typed object
4289 @cindex casts, to view memory
4290 @item @{@var{type}@} @var{addr}
4291 Refers to an object of type @var{type} stored at address @var{addr} in
4292 memory. @var{addr} may be any expression whose value is an integer or
4293 pointer (but parentheses are required around binary operators, just as in
4294 a cast). This construct is allowed regardless of what kind of data is
4295 normally supposed to reside at @var{addr}.
4299 @section Program variables
4301 The most common kind of expression to use is the name of a variable
4304 Variables in expressions are understood in the selected stack frame
4305 (@pxref{Selection, ,Selecting a frame}); they must be either:
4309 global (or file-static)
4316 visible according to the scope rules of the
4317 programming language from the point of execution in that frame
4320 @noindent This means that in the function
4335 you can examine and use the variable @code{a} whenever your program is
4336 executing within the function @code{foo}, but you can only use or
4337 examine the variable @code{b} while your program is executing inside
4338 the block where @code{b} is declared.
4340 @cindex variable name conflict
4341 There is an exception: you can refer to a variable or function whose
4342 scope is a single source file even if the current execution point is not
4343 in this file. But it is possible to have more than one such variable or
4344 function with the same name (in different source files). If that
4345 happens, referring to that name has unpredictable effects. If you wish,
4346 you can specify a static variable in a particular function or file,
4347 using the colon-colon notation:
4349 @cindex colon-colon, context for variables/functions
4351 @c info cannot cope with a :: index entry, but why deprive hard copy readers?
4355 @var{file}::@var{variable}
4356 @var{function}::@var{variable}
4360 Here @var{file} or @var{function} is the name of the context for the
4361 static @var{variable}. In the case of file names, you can use quotes to
4362 make sure @value{GDBN} parses the file name as a single word---for example,
4363 to print a global value of @code{x} defined in @file{f2.c}:
4366 (@value{GDBP}) p 'f2.c'::x
4369 @cindex C++ scope resolution
4370 This use of @samp{::} is very rarely in conflict with the very similar
4371 use of the same notation in C++. @value{GDBN} also supports use of the C++
4372 scope resolution operator in @value{GDBN} expressions.
4373 @c FIXME: Um, so what happens in one of those rare cases where it's in
4376 @cindex wrong values
4377 @cindex variable values, wrong
4379 @emph{Warning:} Occasionally, a local variable may appear to have the
4380 wrong value at certain points in a function---just after entry to a new
4381 scope, and just before exit.
4383 You may see this problem when you are stepping by machine instructions.
4384 This is because, on most machines, it takes more than one instruction to
4385 set up a stack frame (including local variable definitions); if you are
4386 stepping by machine instructions, variables may appear to have the wrong
4387 values until the stack frame is completely built. On exit, it usually
4388 also takes more than one machine instruction to destroy a stack frame;
4389 after you begin stepping through that group of instructions, local
4390 variable definitions may be gone.
4392 This may also happen when the compiler does significant optimizations.
4393 To be sure of always seeing accurate values, turn off all optimization
4396 @cindex ``No symbol "foo" in current context''
4397 Another possible effect of compiler optimizations is to optimize
4398 unused variables out of existence, or assign variables to registers (as
4399 opposed to memory addresses). Depending on the support for such cases
4400 offered by the debug info format used by the compiler, @value{GDBN}
4401 might not be able to display values for such local variables. If that
4402 happens, @value{GDBN} will print a message like this:
4405 No symbol "foo" in current context.
4408 To solve such problems, either recompile without optimizations, or use a
4409 different debug info format, if the compiler supports several such
4410 formats. For example, @value{NGCC}, the @sc{gnu} C/C++ compiler usually
4411 supports the @samp{-gstabs} option. @samp{-gstabs} produces debug info
4412 in a format that is superior to formats such as COFF. You may be able
4413 to use DWARF-2 (@samp{-gdwarf-2}), which is also an effective form for
4414 debug info. See @ref{Debugging Options,,Options for Debugging Your
4415 Program or @sc{gnu} CC, gcc.info, Using @sc{gnu} CC}, for more
4420 @section Artificial arrays
4422 @cindex artificial array
4424 It is often useful to print out several successive objects of the
4425 same type in memory; a section of an array, or an array of
4426 dynamically determined size for which only a pointer exists in the
4429 You can do this by referring to a contiguous span of memory as an
4430 @dfn{artificial array}, using the binary operator @samp{@@}. The left
4431 operand of @samp{@@} should be the first element of the desired array
4432 and be an individual object. The right operand should be the desired length
4433 of the array. The result is an array value whose elements are all of
4434 the type of the left argument. The first element is actually the left
4435 argument; the second element comes from bytes of memory immediately
4436 following those that hold the first element, and so on. Here is an
4437 example. If a program says
4440 int *array = (int *) malloc (len * sizeof (int));
4444 you can print the contents of @code{array} with
4450 The left operand of @samp{@@} must reside in memory. Array values made
4451 with @samp{@@} in this way behave just like other arrays in terms of
4452 subscripting, and are coerced to pointers when used in expressions.
4453 Artificial arrays most often appear in expressions via the value history
4454 (@pxref{Value History, ,Value history}), after printing one out.
4456 Another way to create an artificial array is to use a cast.
4457 This re-interprets a value as if it were an array.
4458 The value need not be in memory:
4460 (@value{GDBP}) p/x (short[2])0x12345678
4461 $1 = @{0x1234, 0x5678@}
4464 As a convenience, if you leave the array length out (as in
4465 @samp{(@var{type}[])@var{value}}) @value{GDBN} calculates the size to fill
4466 the value (as @samp{sizeof(@var{value})/sizeof(@var{type})}:
4468 (@value{GDBP}) p/x (short[])0x12345678
4469 $2 = @{0x1234, 0x5678@}
4472 Sometimes the artificial array mechanism is not quite enough; in
4473 moderately complex data structures, the elements of interest may not
4474 actually be adjacent---for example, if you are interested in the values
4475 of pointers in an array. One useful work-around in this situation is
4476 to use a convenience variable (@pxref{Convenience Vars, ,Convenience
4477 variables}) as a counter in an expression that prints the first
4478 interesting value, and then repeat that expression via @key{RET}. For
4479 instance, suppose you have an array @code{dtab} of pointers to
4480 structures, and you are interested in the values of a field @code{fv}
4481 in each structure. Here is an example of what you might type:
4491 @node Output Formats
4492 @section Output formats
4494 @cindex formatted output
4495 @cindex output formats
4496 By default, @value{GDBN} prints a value according to its data type. Sometimes
4497 this is not what you want. For example, you might want to print a number
4498 in hex, or a pointer in decimal. Or you might want to view data in memory
4499 at a certain address as a character string or as an instruction. To do
4500 these things, specify an @dfn{output format} when you print a value.
4502 The simplest use of output formats is to say how to print a value
4503 already computed. This is done by starting the arguments of the
4504 @code{print} command with a slash and a format letter. The format
4505 letters supported are:
4509 Regard the bits of the value as an integer, and print the integer in
4513 Print as integer in signed decimal.
4516 Print as integer in unsigned decimal.
4519 Print as integer in octal.
4522 Print as integer in binary. The letter @samp{t} stands for ``two''.
4523 @footnote{@samp{b} cannot be used because these format letters are also
4524 used with the @code{x} command, where @samp{b} stands for ``byte'';
4525 see @ref{Memory,,Examining memory}.}
4528 @cindex unknown address, locating
4529 Print as an address, both absolute in hexadecimal and as an offset from
4530 the nearest preceding symbol. You can use this format used to discover
4531 where (in what function) an unknown address is located:
4534 (@value{GDBP}) p/a 0x54320
4535 $3 = 0x54320 <_initialize_vx+396>
4539 Regard as an integer and print it as a character constant.
4542 Regard the bits of the value as a floating point number and print
4543 using typical floating point syntax.
4546 For example, to print the program counter in hex (@pxref{Registers}), type
4553 Note that no space is required before the slash; this is because command
4554 names in @value{GDBN} cannot contain a slash.
4556 To reprint the last value in the value history with a different format,
4557 you can use the @code{print} command with just a format and no
4558 expression. For example, @samp{p/x} reprints the last value in hex.
4561 @section Examining memory
4563 You can use the command @code{x} (for ``examine'') to examine memory in
4564 any of several formats, independently of your program's data types.
4566 @cindex examining memory
4569 @item x/@var{nfu} @var{addr}
4572 Use the @code{x} command to examine memory.
4575 @var{n}, @var{f}, and @var{u} are all optional parameters that specify how
4576 much memory to display and how to format it; @var{addr} is an
4577 expression giving the address where you want to start displaying memory.
4578 If you use defaults for @var{nfu}, you need not type the slash @samp{/}.
4579 Several commands set convenient defaults for @var{addr}.
4582 @item @var{n}, the repeat count
4583 The repeat count is a decimal integer; the default is 1. It specifies
4584 how much memory (counting by units @var{u}) to display.
4585 @c This really is **decimal**; unaffected by 'set radix' as of GDB
4588 @item @var{f}, the display format
4589 The display format is one of the formats used by @code{print},
4590 @samp{s} (null-terminated string), or @samp{i} (machine instruction).
4591 The default is @samp{x} (hexadecimal) initially.
4592 The default changes each time you use either @code{x} or @code{print}.
4594 @item @var{u}, the unit size
4595 The unit size is any of
4601 Halfwords (two bytes).
4603 Words (four bytes). This is the initial default.
4605 Giant words (eight bytes).
4608 Each time you specify a unit size with @code{x}, that size becomes the
4609 default unit the next time you use @code{x}. (For the @samp{s} and
4610 @samp{i} formats, the unit size is ignored and is normally not written.)
4612 @item @var{addr}, starting display address
4613 @var{addr} is the address where you want @value{GDBN} to begin displaying
4614 memory. The expression need not have a pointer value (though it may);
4615 it is always interpreted as an integer address of a byte of memory.
4616 @xref{Expressions, ,Expressions}, for more information on expressions. The default for
4617 @var{addr} is usually just after the last address examined---but several
4618 other commands also set the default address: @code{info breakpoints} (to
4619 the address of the last breakpoint listed), @code{info line} (to the
4620 starting address of a line), and @code{print} (if you use it to display
4621 a value from memory).
4624 For example, @samp{x/3uh 0x54320} is a request to display three halfwords
4625 (@code{h}) of memory, formatted as unsigned decimal integers (@samp{u}),
4626 starting at address @code{0x54320}. @samp{x/4xw $sp} prints the four
4627 words (@samp{w}) of memory above the stack pointer (here, @samp{$sp};
4628 @pxref{Registers, ,Registers}) in hexadecimal (@samp{x}).
4630 Since the letters indicating unit sizes are all distinct from the
4631 letters specifying output formats, you do not have to remember whether
4632 unit size or format comes first; either order works. The output
4633 specifications @samp{4xw} and @samp{4wx} mean exactly the same thing.
4634 (However, the count @var{n} must come first; @samp{wx4} does not work.)
4636 Even though the unit size @var{u} is ignored for the formats @samp{s}
4637 and @samp{i}, you might still want to use a count @var{n}; for example,
4638 @samp{3i} specifies that you want to see three machine instructions,
4639 including any operands. The command @code{disassemble} gives an
4640 alternative way of inspecting machine instructions; see @ref{Machine
4641 Code,,Source and machine code}.
4643 All the defaults for the arguments to @code{x} are designed to make it
4644 easy to continue scanning memory with minimal specifications each time
4645 you use @code{x}. For example, after you have inspected three machine
4646 instructions with @samp{x/3i @var{addr}}, you can inspect the next seven
4647 with just @samp{x/7}. If you use @key{RET} to repeat the @code{x} command,
4648 the repeat count @var{n} is used again; the other arguments default as
4649 for successive uses of @code{x}.
4651 @cindex @code{$_}, @code{$__}, and value history
4652 The addresses and contents printed by the @code{x} command are not saved
4653 in the value history because there is often too much of them and they
4654 would get in the way. Instead, @value{GDBN} makes these values available for
4655 subsequent use in expressions as values of the convenience variables
4656 @code{$_} and @code{$__}. After an @code{x} command, the last address
4657 examined is available for use in expressions in the convenience variable
4658 @code{$_}. The contents of that address, as examined, are available in
4659 the convenience variable @code{$__}.
4661 If the @code{x} command has a repeat count, the address and contents saved
4662 are from the last memory unit printed; this is not the same as the last
4663 address printed if several units were printed on the last line of output.
4666 @section Automatic display
4667 @cindex automatic display
4668 @cindex display of expressions
4670 If you find that you want to print the value of an expression frequently
4671 (to see how it changes), you might want to add it to the @dfn{automatic
4672 display list} so that @value{GDBN} prints its value each time your program stops.
4673 Each expression added to the list is given a number to identify it;
4674 to remove an expression from the list, you specify that number.
4675 The automatic display looks like this:
4679 3: bar[5] = (struct hack *) 0x3804
4683 This display shows item numbers, expressions and their current values. As with
4684 displays you request manually using @code{x} or @code{print}, you can
4685 specify the output format you prefer; in fact, @code{display} decides
4686 whether to use @code{print} or @code{x} depending on how elaborate your
4687 format specification is---it uses @code{x} if you specify a unit size,
4688 or one of the two formats (@samp{i} and @samp{s}) that are only
4689 supported by @code{x}; otherwise it uses @code{print}.
4693 @item display @var{expr}
4694 Add the expression @var{expr} to the list of expressions to display
4695 each time your program stops. @xref{Expressions, ,Expressions}.
4697 @code{display} does not repeat if you press @key{RET} again after using it.
4699 @item display/@var{fmt} @var{expr}
4700 For @var{fmt} specifying only a display format and not a size or
4701 count, add the expression @var{expr} to the auto-display list but
4702 arrange to display it each time in the specified format @var{fmt}.
4703 @xref{Output Formats,,Output formats}.
4705 @item display/@var{fmt} @var{addr}
4706 For @var{fmt} @samp{i} or @samp{s}, or including a unit-size or a
4707 number of units, add the expression @var{addr} as a memory address to
4708 be examined each time your program stops. Examining means in effect
4709 doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory, ,Examining memory}.
4712 For example, @samp{display/i $pc} can be helpful, to see the machine
4713 instruction about to be executed each time execution stops (@samp{$pc}
4714 is a common name for the program counter; @pxref{Registers, ,Registers}).
4717 @kindex delete display
4719 @item undisplay @var{dnums}@dots{}
4720 @itemx delete display @var{dnums}@dots{}
4721 Remove item numbers @var{dnums} from the list of expressions to display.
4723 @code{undisplay} does not repeat if you press @key{RET} after using it.
4724 (Otherwise you would just get the error @samp{No display number @dots{}}.)
4726 @kindex disable display
4727 @item disable display @var{dnums}@dots{}
4728 Disable the display of item numbers @var{dnums}. A disabled display
4729 item is not printed automatically, but is not forgotten. It may be
4730 enabled again later.
4732 @kindex enable display
4733 @item enable display @var{dnums}@dots{}
4734 Enable display of item numbers @var{dnums}. It becomes effective once
4735 again in auto display of its expression, until you specify otherwise.
4738 Display the current values of the expressions on the list, just as is
4739 done when your program stops.
4741 @kindex info display
4743 Print the list of expressions previously set up to display
4744 automatically, each one with its item number, but without showing the
4745 values. This includes disabled expressions, which are marked as such.
4746 It also includes expressions which would not be displayed right now
4747 because they refer to automatic variables not currently available.
4750 If a display expression refers to local variables, then it does not make
4751 sense outside the lexical context for which it was set up. Such an
4752 expression is disabled when execution enters a context where one of its
4753 variables is not defined. For example, if you give the command
4754 @code{display last_char} while inside a function with an argument
4755 @code{last_char}, @value{GDBN} displays this argument while your program
4756 continues to stop inside that function. When it stops elsewhere---where
4757 there is no variable @code{last_char}---the display is disabled
4758 automatically. The next time your program stops where @code{last_char}
4759 is meaningful, you can enable the display expression once again.
4761 @node Print Settings
4762 @section Print settings
4764 @cindex format options
4765 @cindex print settings
4766 @value{GDBN} provides the following ways to control how arrays, structures,
4767 and symbols are printed.
4770 These settings are useful for debugging programs in any language:
4773 @kindex set print address
4774 @item set print address
4775 @itemx set print address on
4776 @value{GDBN} prints memory addresses showing the location of stack
4777 traces, structure values, pointer values, breakpoints, and so forth,
4778 even when it also displays the contents of those addresses. The default
4779 is @code{on}. For example, this is what a stack frame display looks like with
4780 @code{set print address on}:
4785 #0 set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
4787 530 if (lquote != def_lquote)
4791 @item set print address off
4792 Do not print addresses when displaying their contents. For example,
4793 this is the same stack frame displayed with @code{set print address off}:
4797 (@value{GDBP}) set print addr off
4799 #0 set_quotes (lq="<<", rq=">>") at input.c:530
4800 530 if (lquote != def_lquote)
4804 You can use @samp{set print address off} to eliminate all machine
4805 dependent displays from the @value{GDBN} interface. For example, with
4806 @code{print address off}, you should get the same text for backtraces on
4807 all machines---whether or not they involve pointer arguments.
4809 @kindex show print address
4810 @item show print address
4811 Show whether or not addresses are to be printed.
4814 When @value{GDBN} prints a symbolic address, it normally prints the
4815 closest earlier symbol plus an offset. If that symbol does not uniquely
4816 identify the address (for example, it is a name whose scope is a single
4817 source file), you may need to clarify. One way to do this is with
4818 @code{info line}, for example @samp{info line *0x4537}. Alternately,
4819 you can set @value{GDBN} to print the source file and line number when
4820 it prints a symbolic address:
4823 @kindex set print symbol-filename
4824 @item set print symbol-filename on
4825 Tell @value{GDBN} to print the source file name and line number of a
4826 symbol in the symbolic form of an address.
4828 @item set print symbol-filename off
4829 Do not print source file name and line number of a symbol. This is the
4832 @kindex show print symbol-filename
4833 @item show print symbol-filename
4834 Show whether or not @value{GDBN} will print the source file name and
4835 line number of a symbol in the symbolic form of an address.
4838 Another situation where it is helpful to show symbol filenames and line
4839 numbers is when disassembling code; @value{GDBN} shows you the line
4840 number and source file that corresponds to each instruction.
4842 Also, you may wish to see the symbolic form only if the address being
4843 printed is reasonably close to the closest earlier symbol:
4846 @kindex set print max-symbolic-offset
4847 @item set print max-symbolic-offset @var{max-offset}
4848 Tell @value{GDBN} to only display the symbolic form of an address if the
4849 offset between the closest earlier symbol and the address is less than
4850 @var{max-offset}. The default is 0, which tells @value{GDBN}
4851 to always print the symbolic form of an address if any symbol precedes it.
4853 @kindex show print max-symbolic-offset
4854 @item show print max-symbolic-offset
4855 Ask how large the maximum offset is that @value{GDBN} prints in a
4859 @cindex wild pointer, interpreting
4860 @cindex pointer, finding referent
4861 If you have a pointer and you are not sure where it points, try
4862 @samp{set print symbol-filename on}. Then you can determine the name
4863 and source file location of the variable where it points, using
4864 @samp{p/a @var{pointer}}. This interprets the address in symbolic form.
4865 For example, here @value{GDBN} shows that a variable @code{ptt} points
4866 at another variable @code{t}, defined in @file{hi2.c}:
4869 (@value{GDBP}) set print symbol-filename on
4870 (@value{GDBP}) p/a ptt
4871 $4 = 0xe008 <t in hi2.c>
4875 @emph{Warning:} For pointers that point to a local variable, @samp{p/a}
4876 does not show the symbol name and filename of the referent, even with
4877 the appropriate @code{set print} options turned on.
4880 Other settings control how different kinds of objects are printed:
4883 @kindex set print array
4884 @item set print array
4885 @itemx set print array on
4886 Pretty print arrays. This format is more convenient to read,
4887 but uses more space. The default is off.
4889 @item set print array off
4890 Return to compressed format for arrays.
4892 @kindex show print array
4893 @item show print array
4894 Show whether compressed or pretty format is selected for displaying
4897 @kindex set print elements
4898 @item set print elements @var{number-of-elements}
4899 Set a limit on how many elements of an array @value{GDBN} will print.
4900 If @value{GDBN} is printing a large array, it stops printing after it has
4901 printed the number of elements set by the @code{set print elements} command.
4902 This limit also applies to the display of strings.
4903 When @value{GDBN} starts, this limit is set to 200.
4904 Setting @var{number-of-elements} to zero means that the printing is unlimited.
4906 @kindex show print elements
4907 @item show print elements
4908 Display the number of elements of a large array that @value{GDBN} will print.
4909 If the number is 0, then the printing is unlimited.
4911 @kindex set print null-stop
4912 @item set print null-stop
4913 Cause @value{GDBN} to stop printing the characters of an array when the first
4914 @sc{null} is encountered. This is useful when large arrays actually
4915 contain only short strings.
4918 @kindex set print pretty
4919 @item set print pretty on
4920 Cause @value{GDBN} to print structures in an indented format with one member
4921 per line, like this:
4936 @item set print pretty off
4937 Cause @value{GDBN} to print structures in a compact format, like this:
4941 $1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, \
4942 meat = 0x54 "Pork"@}
4947 This is the default format.
4949 @kindex show print pretty
4950 @item show print pretty
4951 Show which format @value{GDBN} is using to print structures.
4953 @kindex set print sevenbit-strings
4954 @item set print sevenbit-strings on
4955 Print using only seven-bit characters; if this option is set,
4956 @value{GDBN} displays any eight-bit characters (in strings or
4957 character values) using the notation @code{\}@var{nnn}. This setting is
4958 best if you are working in English (@sc{ascii}) and you use the
4959 high-order bit of characters as a marker or ``meta'' bit.
4961 @item set print sevenbit-strings off
4962 Print full eight-bit characters. This allows the use of more
4963 international character sets, and is the default.
4965 @kindex show print sevenbit-strings
4966 @item show print sevenbit-strings
4967 Show whether or not @value{GDBN} is printing only seven-bit characters.
4969 @kindex set print union
4970 @item set print union on
4971 Tell @value{GDBN} to print unions which are contained in structures. This
4972 is the default setting.
4974 @item set print union off
4975 Tell @value{GDBN} not to print unions which are contained in structures.
4977 @kindex show print union
4978 @item show print union
4979 Ask @value{GDBN} whether or not it will print unions which are contained in
4982 For example, given the declarations
4985 typedef enum @{Tree, Bug@} Species;
4986 typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms;
4987 typedef enum @{Caterpillar, Cocoon, Butterfly@}
4998 struct thing foo = @{Tree, @{Acorn@}@};
5002 with @code{set print union on} in effect @samp{p foo} would print
5005 $1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@}
5009 and with @code{set print union off} in effect it would print
5012 $1 = @{it = Tree, form = @{...@}@}
5018 These settings are of interest when debugging C++ programs:
5022 @kindex set print demangle
5023 @item set print demangle
5024 @itemx set print demangle on
5025 Print C++ names in their source form rather than in the encoded
5026 (``mangled'') form passed to the assembler and linker for type-safe
5027 linkage. The default is on.
5029 @kindex show print demangle
5030 @item show print demangle
5031 Show whether C++ names are printed in mangled or demangled form.
5033 @kindex set print asm-demangle
5034 @item set print asm-demangle
5035 @itemx set print asm-demangle on
5036 Print C++ names in their source form rather than their mangled form, even
5037 in assembler code printouts such as instruction disassemblies.
5040 @kindex show print asm-demangle
5041 @item show print asm-demangle
5042 Show whether C++ names in assembly listings are printed in mangled
5045 @kindex set demangle-style
5046 @cindex C++ symbol decoding style
5047 @cindex symbol decoding style, C++
5048 @item set demangle-style @var{style}
5049 Choose among several encoding schemes used by different compilers to
5050 represent C++ names. The choices for @var{style} are currently:
5054 Allow @value{GDBN} to choose a decoding style by inspecting your program.
5057 Decode based on the @sc{gnu} C++ compiler (@code{g++}) encoding algorithm.
5058 This is the default.
5061 Decode based on the HP ANSI C++ (@code{aCC}) encoding algorithm.
5064 Decode based on the Lucid C++ compiler (@code{lcc}) encoding algorithm.
5067 Decode using the algorithm in the @cite{C++ Annotated Reference Manual}.
5068 @strong{Warning:} this setting alone is not sufficient to allow
5069 debugging @code{cfront}-generated executables. @value{GDBN} would
5070 require further enhancement to permit that.
5073 If you omit @var{style}, you will see a list of possible formats.
5075 @kindex show demangle-style
5076 @item show demangle-style
5077 Display the encoding style currently in use for decoding C++ symbols.
5079 @kindex set print object
5080 @item set print object
5081 @itemx set print object on
5082 When displaying a pointer to an object, identify the @emph{actual}
5083 (derived) type of the object rather than the @emph{declared} type, using
5084 the virtual function table.
5086 @item set print object off
5087 Display only the declared type of objects, without reference to the
5088 virtual function table. This is the default setting.
5090 @kindex show print object
5091 @item show print object
5092 Show whether actual, or declared, object types are displayed.
5094 @kindex set print static-members
5095 @item set print static-members
5096 @itemx set print static-members on
5097 Print static members when displaying a C++ object. The default is on.
5099 @item set print static-members off
5100 Do not print static members when displaying a C++ object.
5102 @kindex show print static-members
5103 @item show print static-members
5104 Show whether C++ static members are printed, or not.
5106 @c These don't work with HP ANSI C++ yet.
5107 @kindex set print vtbl
5108 @item set print vtbl
5109 @itemx set print vtbl on
5110 Pretty print C++ virtual function tables. The default is off.
5111 (The @code{vtbl} commands do not work on programs compiled with the HP
5112 ANSI C++ compiler (@code{aCC}).)
5114 @item set print vtbl off
5115 Do not pretty print C++ virtual function tables.
5117 @kindex show print vtbl
5118 @item show print vtbl
5119 Show whether C++ virtual function tables are pretty printed, or not.
5123 @section Value history
5125 @cindex value history
5126 Values printed by the @code{print} command are saved in the @value{GDBN}
5127 @dfn{value history}. This allows you to refer to them in other expressions.
5128 Values are kept until the symbol table is re-read or discarded
5129 (for example with the @code{file} or @code{symbol-file} commands).
5130 When the symbol table changes, the value history is discarded,
5131 since the values may contain pointers back to the types defined in the
5136 @cindex history number
5137 The values printed are given @dfn{history numbers} by which you can
5138 refer to them. These are successive integers starting with one.
5139 @code{print} shows you the history number assigned to a value by
5140 printing @samp{$@var{num} = } before the value; here @var{num} is the
5143 To refer to any previous value, use @samp{$} followed by the value's
5144 history number. The way @code{print} labels its output is designed to
5145 remind you of this. Just @code{$} refers to the most recent value in
5146 the history, and @code{$$} refers to the value before that.
5147 @code{$$@var{n}} refers to the @var{n}th value from the end; @code{$$2}
5148 is the value just prior to @code{$$}, @code{$$1} is equivalent to
5149 @code{$$}, and @code{$$0} is equivalent to @code{$}.
5151 For example, suppose you have just printed a pointer to a structure and
5152 want to see the contents of the structure. It suffices to type
5158 If you have a chain of structures where the component @code{next} points
5159 to the next one, you can print the contents of the next one with this:
5166 You can print successive links in the chain by repeating this
5167 command---which you can do by just typing @key{RET}.
5169 Note that the history records values, not expressions. If the value of
5170 @code{x} is 4 and you type these commands:
5178 then the value recorded in the value history by the @code{print} command
5179 remains 4 even though the value of @code{x} has changed.
5184 Print the last ten values in the value history, with their item numbers.
5185 This is like @samp{p@ $$9} repeated ten times, except that @code{show
5186 values} does not change the history.
5188 @item show values @var{n}
5189 Print ten history values centered on history item number @var{n}.
5192 Print ten history values just after the values last printed. If no more
5193 values are available, @code{show values +} produces no display.
5196 Pressing @key{RET} to repeat @code{show values @var{n}} has exactly the
5197 same effect as @samp{show values +}.
5199 @node Convenience Vars
5200 @section Convenience variables
5202 @cindex convenience variables
5203 @value{GDBN} provides @dfn{convenience variables} that you can use within
5204 @value{GDBN} to hold on to a value and refer to it later. These variables
5205 exist entirely within @value{GDBN}; they are not part of your program, and
5206 setting a convenience variable has no direct effect on further execution
5207 of your program. That is why you can use them freely.
5209 Convenience variables are prefixed with @samp{$}. Any name preceded by
5210 @samp{$} can be used for a convenience variable, unless it is one of
5211 the predefined machine-specific register names (@pxref{Registers, ,Registers}).
5212 (Value history references, in contrast, are @emph{numbers} preceded
5213 by @samp{$}. @xref{Value History, ,Value history}.)
5215 You can save a value in a convenience variable with an assignment
5216 expression, just as you would set a variable in your program.
5220 set $foo = *object_ptr
5224 would save in @code{$foo} the value contained in the object pointed to by
5227 Using a convenience variable for the first time creates it, but its
5228 value is @code{void} until you assign a new value. You can alter the
5229 value with another assignment at any time.
5231 Convenience variables have no fixed types. You can assign a convenience
5232 variable any type of value, including structures and arrays, even if
5233 that variable already has a value of a different type. The convenience
5234 variable, when used as an expression, has the type of its current value.
5237 @kindex show convenience
5238 @item show convenience
5239 Print a list of convenience variables used so far, and their values.
5240 Abbreviated @code{show conv}.
5243 One of the ways to use a convenience variable is as a counter to be
5244 incremented or a pointer to be advanced. For example, to print
5245 a field from successive elements of an array of structures:
5249 print bar[$i++]->contents
5253 Repeat that command by typing @key{RET}.
5255 Some convenience variables are created automatically by @value{GDBN} and given
5256 values likely to be useful.
5261 The variable @code{$_} is automatically set by the @code{x} command to
5262 the last address examined (@pxref{Memory, ,Examining memory}). Other
5263 commands which provide a default address for @code{x} to examine also
5264 set @code{$_} to that address; these commands include @code{info line}
5265 and @code{info breakpoint}. The type of @code{$_} is @code{void *}
5266 except when set by the @code{x} command, in which case it is a pointer
5267 to the type of @code{$__}.
5271 The variable @code{$__} is automatically set by the @code{x} command
5272 to the value found in the last address examined. Its type is chosen
5273 to match the format in which the data was printed.
5277 The variable @code{$_exitcode} is automatically set to the exit code when
5278 the program being debugged terminates.
5281 On HP-UX systems, if you refer to a function or variable name that
5282 begins with a dollar sign, @value{GDBN} searches for a user or system
5283 name first, before it searches for a convenience variable.
5289 You can refer to machine register contents, in expressions, as variables
5290 with names starting with @samp{$}. The names of registers are different
5291 for each machine; use @code{info registers} to see the names used on
5295 @kindex info registers
5296 @item info registers
5297 Print the names and values of all registers except floating-point
5298 registers (in the selected stack frame).
5300 @kindex info all-registers
5301 @cindex floating point registers
5302 @item info all-registers
5303 Print the names and values of all registers, including floating-point
5306 @item info registers @var{regname} @dots{}
5307 Print the @dfn{relativized} value of each specified register @var{regname}.
5308 As discussed in detail below, register values are normally relative to
5309 the selected stack frame. @var{regname} may be any register name valid on
5310 the machine you are using, with or without the initial @samp{$}.
5313 @value{GDBN} has four ``standard'' register names that are available (in
5314 expressions) on most machines---whenever they do not conflict with an
5315 architecture's canonical mnemonics for registers. The register names
5316 @code{$pc} and @code{$sp} are used for the program counter register and
5317 the stack pointer. @code{$fp} is used for a register that contains a
5318 pointer to the current stack frame, and @code{$ps} is used for a
5319 register that contains the processor status. For example,
5320 you could print the program counter in hex with
5327 or print the instruction to be executed next with
5334 or add four to the stack pointer@footnote{This is a way of removing
5335 one word from the stack, on machines where stacks grow downward in
5336 memory (most machines, nowadays). This assumes that the innermost
5337 stack frame is selected; setting @code{$sp} is not allowed when other
5338 stack frames are selected. To pop entire frames off the stack,
5339 regardless of machine architecture, use @code{return};
5340 see @ref{Returning, ,Returning from a function}.} with
5346 Whenever possible, these four standard register names are available on
5347 your machine even though the machine has different canonical mnemonics,
5348 so long as there is no conflict. The @code{info registers} command
5349 shows the canonical names. For example, on the SPARC, @code{info
5350 registers} displays the processor status register as @code{$psr} but you
5351 can also refer to it as @code{$ps}; and on x86-based machines @code{$ps}
5352 is an alias for the @sc{eflags} register.
5354 @value{GDBN} always considers the contents of an ordinary register as an
5355 integer when the register is examined in this way. Some machines have
5356 special registers which can hold nothing but floating point; these
5357 registers are considered to have floating point values. There is no way
5358 to refer to the contents of an ordinary register as floating point value
5359 (although you can @emph{print} it as a floating point value with
5360 @samp{print/f $@var{regname}}).
5362 Some registers have distinct ``raw'' and ``virtual'' data formats. This
5363 means that the data format in which the register contents are saved by
5364 the operating system is not the same one that your program normally
5365 sees. For example, the registers of the 68881 floating point
5366 coprocessor are always saved in ``extended'' (raw) format, but all C
5367 programs expect to work with ``double'' (virtual) format. In such
5368 cases, @value{GDBN} normally works with the virtual format only (the format
5369 that makes sense for your program), but the @code{info registers} command
5370 prints the data in both formats.
5372 Normally, register values are relative to the selected stack frame
5373 (@pxref{Selection, ,Selecting a frame}). This means that you get the
5374 value that the register would contain if all stack frames farther in
5375 were exited and their saved registers restored. In order to see the
5376 true contents of hardware registers, you must select the innermost
5377 frame (with @samp{frame 0}).
5379 However, @value{GDBN} must deduce where registers are saved, from the machine
5380 code generated by your compiler. If some registers are not saved, or if
5381 @value{GDBN} is unable to locate the saved registers, the selected stack
5382 frame makes no difference.
5384 @node Floating Point Hardware
5385 @section Floating point hardware
5386 @cindex floating point
5388 Depending on the configuration, @value{GDBN} may be able to give
5389 you more information about the status of the floating point hardware.
5394 Display hardware-dependent information about the floating
5395 point unit. The exact contents and layout vary depending on the
5396 floating point chip. Currently, @samp{info float} is supported on
5397 the ARM and x86 machines.
5401 @chapter Using @value{GDBN} with Different Languages
5404 Although programming languages generally have common aspects, they are
5405 rarely expressed in the same manner. For instance, in ANSI C,
5406 dereferencing a pointer @code{p} is accomplished by @code{*p}, but in
5407 Modula-2, it is accomplished by @code{p^}. Values can also be
5408 represented (and displayed) differently. Hex numbers in C appear as
5409 @samp{0x1ae}, while in Modula-2 they appear as @samp{1AEH}.
5411 @cindex working language
5412 Language-specific information is built into @value{GDBN} for some languages,
5413 allowing you to express operations like the above in your program's
5414 native language, and allowing @value{GDBN} to output values in a manner
5415 consistent with the syntax of your program's native language. The
5416 language you use to build expressions is called the @dfn{working
5420 * Setting:: Switching between source languages
5421 * Show:: Displaying the language
5422 * Checks:: Type and range checks
5423 * Support:: Supported languages
5427 @section Switching between source languages
5429 There are two ways to control the working language---either have @value{GDBN}
5430 set it automatically, or select it manually yourself. You can use the
5431 @code{set language} command for either purpose. On startup, @value{GDBN}
5432 defaults to setting the language automatically. The working language is
5433 used to determine how expressions you type are interpreted, how values
5436 In addition to the working language, every source file that
5437 @value{GDBN} knows about has its own working language. For some object
5438 file formats, the compiler might indicate which language a particular
5439 source file is in. However, most of the time @value{GDBN} infers the
5440 language from the name of the file. The language of a source file
5441 controls whether C++ names are demangled---this way @code{backtrace} can
5442 show each frame appropriately for its own language. There is no way to
5443 set the language of a source file from within @value{GDBN}, but you can
5444 set the language associated with a filename extension. @xref{Show, ,
5445 Displaying the language}.
5447 This is most commonly a problem when you use a program, such
5448 as @code{cfront} or @code{f2c}, that generates C but is written in
5449 another language. In that case, make the
5450 program use @code{#line} directives in its C output; that way
5451 @value{GDBN} will know the correct language of the source code of the original
5452 program, and will display that source code, not the generated C code.
5455 * Filenames:: Filename extensions and languages.
5456 * Manually:: Setting the working language manually
5457 * Automatically:: Having @value{GDBN} infer the source language
5461 @subsection List of filename extensions and languages
5463 If a source file name ends in one of the following extensions, then
5464 @value{GDBN} infers that its language is the one indicated.
5489 Modula-2 source file
5493 Assembler source file. This actually behaves almost like C, but
5494 @value{GDBN} does not skip over function prologues when stepping.
5497 In addition, you may set the language associated with a filename
5498 extension. @xref{Show, , Displaying the language}.
5501 @subsection Setting the working language
5503 If you allow @value{GDBN} to set the language automatically,
5504 expressions are interpreted the same way in your debugging session and
5507 @kindex set language
5508 If you wish, you may set the language manually. To do this, issue the
5509 command @samp{set language @var{lang}}, where @var{lang} is the name of
5511 @code{c} or @code{modula-2}.
5512 For a list of the supported languages, type @samp{set language}.
5514 Setting the language manually prevents @value{GDBN} from updating the working
5515 language automatically. This can lead to confusion if you try
5516 to debug a program when the working language is not the same as the
5517 source language, when an expression is acceptable to both
5518 languages---but means different things. For instance, if the current
5519 source file were written in C, and @value{GDBN} was parsing Modula-2, a
5527 might not have the effect you intended. In C, this means to add
5528 @code{b} and @code{c} and place the result in @code{a}. The result
5529 printed would be the value of @code{a}. In Modula-2, this means to compare
5530 @code{a} to the result of @code{b+c}, yielding a @code{BOOLEAN} value.
5533 @subsection Having @value{GDBN} infer the source language
5535 To have @value{GDBN} set the working language automatically, use
5536 @samp{set language local} or @samp{set language auto}. @value{GDBN}
5537 then infers the working language. That is, when your program stops in a
5538 frame (usually by encountering a breakpoint), @value{GDBN} sets the
5539 working language to the language recorded for the function in that
5540 frame. If the language for a frame is unknown (that is, if the function
5541 or block corresponding to the frame was defined in a source file that
5542 does not have a recognized extension), the current working language is
5543 not changed, and @value{GDBN} issues a warning.
5545 This may not seem necessary for most programs, which are written
5546 entirely in one source language. However, program modules and libraries
5547 written in one source language can be used by a main program written in
5548 a different source language. Using @samp{set language auto} in this
5549 case frees you from having to set the working language manually.
5552 @section Displaying the language
5554 The following commands help you find out which language is the
5555 working language, and also what language source files were written in.
5557 @kindex show language
5558 @kindex info frame@r{, show the source language}
5559 @kindex info source@r{, show the source language}
5562 Display the current working language. This is the
5563 language you can use with commands such as @code{print} to
5564 build and compute expressions that may involve variables in your program.
5567 Display the source language for this frame. This language becomes the
5568 working language if you use an identifier from this frame.
5569 @xref{Frame Info, ,Information about a frame}, to identify the other
5570 information listed here.
5573 Display the source language of this source file.
5574 @xref{Symbols, ,Examining the Symbol Table}, to identify the other
5575 information listed here.
5578 In unusual circumstances, you may have source files with extensions
5579 not in the standard list. You can then set the extension associated
5580 with a language explicitly:
5582 @kindex set extension-language
5583 @kindex info extensions
5585 @item set extension-language @var{.ext} @var{language}
5586 Set source files with extension @var{.ext} to be assumed to be in
5587 the source language @var{language}.
5589 @item info extensions
5590 List all the filename extensions and the associated languages.
5594 @section Type and range checking
5597 @emph{Warning:} In this release, the @value{GDBN} commands for type and range
5598 checking are included, but they do not yet have any effect. This
5599 section documents the intended facilities.
5601 @c FIXME remove warning when type/range code added
5603 Some languages are designed to guard you against making seemingly common
5604 errors through a series of compile- and run-time checks. These include
5605 checking the type of arguments to functions and operators, and making
5606 sure mathematical overflows are caught at run time. Checks such as
5607 these help to ensure a program's correctness once it has been compiled
5608 by eliminating type mismatches, and providing active checks for range
5609 errors when your program is running.
5611 @value{GDBN} can check for conditions like the above if you wish.
5612 Although @value{GDBN} does not check the statements in your program, it
5613 can check expressions entered directly into @value{GDBN} for evaluation via
5614 the @code{print} command, for example. As with the working language,
5615 @value{GDBN} can also decide whether or not to check automatically based on
5616 your program's source language. @xref{Support, ,Supported languages},
5617 for the default settings of supported languages.
5620 * Type Checking:: An overview of type checking
5621 * Range Checking:: An overview of range checking
5624 @cindex type checking
5625 @cindex checks, type
5627 @subsection An overview of type checking
5629 Some languages, such as Modula-2, are strongly typed, meaning that the
5630 arguments to operators and functions have to be of the correct type,
5631 otherwise an error occurs. These checks prevent type mismatch
5632 errors from ever causing any run-time problems. For example,
5640 The second example fails because the @code{CARDINAL} 1 is not
5641 type-compatible with the @code{REAL} 2.3.
5643 For the expressions you use in @value{GDBN} commands, you can tell the
5644 @value{GDBN} type checker to skip checking;
5645 to treat any mismatches as errors and abandon the expression;
5646 or to only issue warnings when type mismatches occur,
5647 but evaluate the expression anyway. When you choose the last of
5648 these, @value{GDBN} evaluates expressions like the second example above, but
5649 also issues a warning.
5651 Even if you turn type checking off, there may be other reasons
5652 related to type that prevent @value{GDBN} from evaluating an expression.
5653 For instance, @value{GDBN} does not know how to add an @code{int} and
5654 a @code{struct foo}. These particular type errors have nothing to do
5655 with the language in use, and usually arise from expressions, such as
5656 the one described above, which make little sense to evaluate anyway.
5658 Each language defines to what degree it is strict about type. For
5659 instance, both Modula-2 and C require the arguments to arithmetical
5660 operators to be numbers. In C, enumerated types and pointers can be
5661 represented as numbers, so that they are valid arguments to mathematical
5662 operators. @xref{Support, ,Supported languages}, for further
5663 details on specific languages.
5665 @value{GDBN} provides some additional commands for controlling the type checker:
5667 @kindex set check@r{, type}
5668 @kindex set check type
5669 @kindex show check type
5671 @item set check type auto
5672 Set type checking on or off based on the current working language.
5673 @xref{Support, ,Supported languages}, for the default settings for
5676 @item set check type on
5677 @itemx set check type off
5678 Set type checking on or off, overriding the default setting for the
5679 current working language. Issue a warning if the setting does not
5680 match the language default. If any type mismatches occur in
5681 evaluating an expression while type checking is on, @value{GDBN} prints a
5682 message and aborts evaluation of the expression.
5684 @item set check type warn
5685 Cause the type checker to issue warnings, but to always attempt to
5686 evaluate the expression. Evaluating the expression may still
5687 be impossible for other reasons. For example, @value{GDBN} cannot add
5688 numbers and structures.
5691 Show the current setting of the type checker, and whether or not @value{GDBN}
5692 is setting it automatically.
5695 @cindex range checking
5696 @cindex checks, range
5697 @node Range Checking
5698 @subsection An overview of range checking
5700 In some languages (such as Modula-2), it is an error to exceed the
5701 bounds of a type; this is enforced with run-time checks. Such range
5702 checking is meant to ensure program correctness by making sure
5703 computations do not overflow, or indices on an array element access do
5704 not exceed the bounds of the array.
5706 For expressions you use in @value{GDBN} commands, you can tell
5707 @value{GDBN} to treat range errors in one of three ways: ignore them,
5708 always treat them as errors and abandon the expression, or issue
5709 warnings but evaluate the expression anyway.
5711 A range error can result from numerical overflow, from exceeding an
5712 array index bound, or when you type a constant that is not a member
5713 of any type. Some languages, however, do not treat overflows as an
5714 error. In many implementations of C, mathematical overflow causes the
5715 result to ``wrap around'' to lower values---for example, if @var{m} is
5716 the largest integer value, and @var{s} is the smallest, then
5719 @var{m} + 1 @result{} @var{s}
5722 This, too, is specific to individual languages, and in some cases
5723 specific to individual compilers or machines. @xref{Support, ,
5724 Supported languages}, for further details on specific languages.
5726 @value{GDBN} provides some additional commands for controlling the range checker:
5728 @kindex set check@r{, range}
5729 @kindex set check range
5730 @kindex show check range
5732 @item set check range auto
5733 Set range checking on or off based on the current working language.
5734 @xref{Support, ,Supported languages}, for the default settings for
5737 @item set check range on
5738 @itemx set check range off
5739 Set range checking on or off, overriding the default setting for the
5740 current working language. A warning is issued if the setting does not
5741 match the language default. If a range error occurs and range checking is on,
5742 then a message is printed and evaluation of the expression is aborted.
5744 @item set check range warn
5745 Output messages when the @value{GDBN} range checker detects a range error,
5746 but attempt to evaluate the expression anyway. Evaluating the
5747 expression may still be impossible for other reasons, such as accessing
5748 memory that the process does not own (a typical example from many Unix
5752 Show the current setting of the range checker, and whether or not it is
5753 being set automatically by @value{GDBN}.
5757 @section Supported languages
5759 @value{GDBN} supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.
5760 @c This is false ...
5761 Some @value{GDBN} features may be used in expressions regardless of the
5762 language you use: the @value{GDBN} @code{@@} and @code{::} operators,
5763 and the @samp{@{type@}addr} construct (@pxref{Expressions,
5764 ,Expressions}) can be used with the constructs of any supported
5767 The following sections detail to what degree each source language is
5768 supported by @value{GDBN}. These sections are not meant to be language
5769 tutorials or references, but serve only as a reference guide to what the
5770 @value{GDBN} expression parser accepts, and what input and output
5771 formats should look like for different languages. There are many good
5772 books written on each of these languages; please look to these for a
5773 language reference or tutorial.
5777 * Modula-2:: Modula-2
5782 @subsection C and C++
5785 @cindex expressions in C or C++
5787 Since C and C++ are so closely related, many features of @value{GDBN} apply
5788 to both languages. Whenever this is the case, we discuss those languages
5793 @cindex @sc{gnu} C++
5794 The C++ debugging facilities are jointly implemented by the C++
5795 compiler and @value{GDBN}. Therefore, to debug your C++ code
5796 effectively, you must compile your C++ programs with a supported
5797 C++ compiler, such as @sc{gnu} @code{g++}, or the HP ANSI C++
5798 compiler (@code{aCC}).
5800 For best results when using @sc{gnu} C++, use the stabs debugging
5801 format. You can select that format explicitly with the @code{g++}
5802 command-line options @samp{-gstabs} or @samp{-gstabs+}. See
5803 @ref{Debugging Options,,Options for Debugging Your Program or @sc{gnu}
5804 CC, gcc.info, Using @sc{gnu} CC}, for more information.
5807 * C Operators:: C and C++ operators
5808 * C Constants:: C and C++ constants
5809 * C plus plus expressions:: C++ expressions
5810 * C Defaults:: Default settings for C and C++
5811 * C Checks:: C and C++ type and range checks
5812 * Debugging C:: @value{GDBN} and C
5813 * Debugging C plus plus:: @value{GDBN} features for C++
5817 @subsubsection C and C++ operators
5819 @cindex C and C++ operators
5821 Operators must be defined on values of specific types. For instance,
5822 @code{+} is defined on numbers, but not on structures. Operators are
5823 often defined on groups of types.
5825 For the purposes of C and C++, the following definitions hold:
5830 @emph{Integral types} include @code{int} with any of its storage-class
5831 specifiers; @code{char}; @code{enum}; and, for C++, @code{bool}.
5834 @emph{Floating-point types} include @code{float}, @code{double}, and
5835 @code{long double} (if supported by the target platform).
5838 @emph{Pointer types} include all types defined as @code{(@var{type} *)}.
5841 @emph{Scalar types} include all of the above.
5846 The following operators are supported. They are listed here
5847 in order of increasing precedence:
5851 The comma or sequencing operator. Expressions in a comma-separated list
5852 are evaluated from left to right, with the result of the entire
5853 expression being the last expression evaluated.
5856 Assignment. The value of an assignment expression is the value
5857 assigned. Defined on scalar types.
5860 Used in an expression of the form @w{@code{@var{a} @var{op}= @var{b}}},
5861 and translated to @w{@code{@var{a} = @var{a op b}}}.
5862 @w{@code{@var{op}=}} and @code{=} have the same precedence.
5863 @var{op} is any one of the operators @code{|}, @code{^}, @code{&},
5864 @code{<<}, @code{>>}, @code{+}, @code{-}, @code{*}, @code{/}, @code{%}.
5867 The ternary operator. @code{@var{a} ? @var{b} : @var{c}} can be thought
5868 of as: if @var{a} then @var{b} else @var{c}. @var{a} should be of an
5872 Logical @sc{or}. Defined on integral types.
5875 Logical @sc{and}. Defined on integral types.
5878 Bitwise @sc{or}. Defined on integral types.
5881 Bitwise exclusive-@sc{or}. Defined on integral types.
5884 Bitwise @sc{and}. Defined on integral types.
5887 Equality and inequality. Defined on scalar types. The value of these
5888 expressions is 0 for false and non-zero for true.
5890 @item <@r{, }>@r{, }<=@r{, }>=
5891 Less than, greater than, less than or equal, greater than or equal.
5892 Defined on scalar types. The value of these expressions is 0 for false
5893 and non-zero for true.
5896 left shift, and right shift. Defined on integral types.
5899 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
5902 Addition and subtraction. Defined on integral types, floating-point types and
5905 @item *@r{, }/@r{, }%
5906 Multiplication, division, and modulus. Multiplication and division are
5907 defined on integral and floating-point types. Modulus is defined on
5911 Increment and decrement. When appearing before a variable, the
5912 operation is performed before the variable is used in an expression;
5913 when appearing after it, the variable's value is used before the
5914 operation takes place.
5917 Pointer dereferencing. Defined on pointer types. Same precedence as
5921 Address operator. Defined on variables. Same precedence as @code{++}.
5923 For debugging C++, @value{GDBN} implements a use of @samp{&} beyond what is
5924 allowed in the C++ language itself: you can use @samp{&(&@var{ref})}
5925 (or, if you prefer, simply @samp{&&@var{ref}}) to examine the address
5926 where a C++ reference variable (declared with @samp{&@var{ref}}) is
5930 Negative. Defined on integral and floating-point types. Same
5931 precedence as @code{++}.
5934 Logical negation. Defined on integral types. Same precedence as
5938 Bitwise complement operator. Defined on integral types. Same precedence as
5943 Structure member, and pointer-to-structure member. For convenience,
5944 @value{GDBN} regards the two as equivalent, choosing whether to dereference a
5945 pointer based on the stored type information.
5946 Defined on @code{struct} and @code{union} data.
5949 Dereferences of pointers to members.
5952 Array indexing. @code{@var{a}[@var{i}]} is defined as
5953 @code{*(@var{a}+@var{i})}. Same precedence as @code{->}.
5956 Function parameter list. Same precedence as @code{->}.
5959 C++ scope resolution operator. Defined on @code{struct}, @code{union},
5960 and @code{class} types.
5963 Doubled colons also represent the @value{GDBN} scope operator
5964 (@pxref{Expressions, ,Expressions}). Same precedence as @code{::},
5968 If an operator is redefined in the user code, @value{GDBN} usually
5969 attempts to invoke the redefined version instead of using the operator's
5977 @subsubsection C and C++ constants
5979 @cindex C and C++ constants
5981 @value{GDBN} allows you to express the constants of C and C++ in the
5986 Integer constants are a sequence of digits. Octal constants are
5987 specified by a leading @samp{0} (i.e. zero), and hexadecimal constants by
5988 a leading @samp{0x} or @samp{0X}. Constants may also end with a letter
5989 @samp{l}, specifying that the constant should be treated as a
5993 Floating point constants are a sequence of digits, followed by a decimal
5994 point, followed by a sequence of digits, and optionally followed by an
5995 exponent. An exponent is of the form:
5996 @samp{@w{e@r{[[}+@r{]|}-@r{]}@var{nnn}}}, where @var{nnn} is another
5997 sequence of digits. The @samp{+} is optional for positive exponents.
5998 A floating-point constant may also end with a letter @samp{f} or
5999 @samp{F}, specifying that the constant should be treated as being of
6000 the @code{float} (as opposed to the default @code{double}) type; or with
6001 a letter @samp{l} or @samp{L}, which specifies a @code{long double}
6005 Enumerated constants consist of enumerated identifiers, or their
6006 integral equivalents.
6009 Character constants are a single character surrounded by single quotes
6010 (@code{'}), or a number---the ordinal value of the corresponding character
6011 (usually its @sc{ascii} value). Within quotes, the single character may
6012 be represented by a letter or by @dfn{escape sequences}, which are of
6013 the form @samp{\@var{nnn}}, where @var{nnn} is the octal representation
6014 of the character's ordinal value; or of the form @samp{\@var{x}}, where
6015 @samp{@var{x}} is a predefined special character---for example,
6016 @samp{\n} for newline.
6019 String constants are a sequence of character constants surrounded
6020 by double quotes (@code{"}).
6023 Pointer constants are an integral value. You can also write pointers
6024 to constants using the C operator @samp{&}.
6027 Array constants are comma-separated lists surrounded by braces @samp{@{}
6028 and @samp{@}}; for example, @samp{@{1,2,3@}} is a three-element array of
6029 integers, @samp{@{@{1,2@}, @{3,4@}, @{5,6@}@}} is a three-by-two array,
6030 and @samp{@{&"hi", &"there", &"fred"@}} is a three-element array of pointers.
6034 * C plus plus expressions::
6041 @node C plus plus expressions
6042 @subsubsection C++ expressions
6044 @cindex expressions in C++
6045 @value{GDBN} expression handling can interpret most C++ expressions.
6047 @cindex C++ support, not in @sc{coff}
6048 @cindex @sc{coff} versus C++
6049 @cindex C++ and object formats
6050 @cindex object formats and C++
6051 @cindex a.out and C++
6052 @cindex @sc{ecoff} and C++
6053 @cindex @sc{xcoff} and C++
6054 @cindex @sc{elf}/stabs and C++
6055 @cindex @sc{elf}/@sc{dwarf} and C++
6056 @c FIXME!! GDB may eventually be able to debug C++ using DWARF; check
6057 @c periodically whether this has happened...
6059 @emph{Warning:} @value{GDBN} can only debug C++ code if you use the
6060 proper compiler. Typically, C++ debugging depends on the use of
6061 additional debugging information in the symbol table, and thus requires
6062 special support. In particular, if your compiler generates a.out, MIPS
6063 @sc{ecoff}, RS/6000 @sc{xcoff}, or @sc{elf} with stabs extensions to the
6064 symbol table, these facilities are all available. (With @sc{gnu} CC,
6065 you can use the @samp{-gstabs} option to request stabs debugging
6066 extensions explicitly.) Where the object code format is standard
6067 @sc{coff} or @sc{dwarf} in @sc{elf}, on the other hand, most of the C++
6068 support in @value{GDBN} does @emph{not} work.
6073 @cindex member functions
6075 Member function calls are allowed; you can use expressions like
6078 count = aml->GetOriginal(x, y)
6082 @cindex namespace in C++
6084 While a member function is active (in the selected stack frame), your
6085 expressions have the same namespace available as the member function;
6086 that is, @value{GDBN} allows implicit references to the class instance
6087 pointer @code{this} following the same rules as C++.
6089 @cindex call overloaded functions
6090 @cindex overloaded functions, calling
6091 @cindex type conversions in C++
6093 You can call overloaded functions; @value{GDBN} resolves the function
6094 call to the right definition, with some restrictions. @value{GDBN} does not
6095 perform overload resolution involving user-defined type conversions,
6096 calls to constructors, or instantiations of templates that do not exist
6097 in the program. It also cannot handle ellipsis argument lists or
6100 It does perform integral conversions and promotions, floating-point
6101 promotions, arithmetic conversions, pointer conversions, conversions of
6102 class objects to base classes, and standard conversions such as those of
6103 functions or arrays to pointers; it requires an exact match on the
6104 number of function arguments.
6106 Overload resolution is always performed, unless you have specified
6107 @code{set overload-resolution off}. @xref{Debugging C plus plus,
6108 ,@value{GDBN} features for C++}.
6110 You must specify @code{set overload-resolution off} in order to use an
6111 explicit function signature to call an overloaded function, as in
6113 p 'foo(char,int)'('x', 13)
6116 The @value{GDBN} command-completion facility can simplify this;
6117 see @ref{Completion, ,Command completion}.
6119 @cindex reference declarations
6121 @value{GDBN} understands variables declared as C++ references; you can use
6122 them in expressions just as you do in C++ source---they are automatically
6125 In the parameter list shown when @value{GDBN} displays a frame, the values of
6126 reference variables are not displayed (unlike other variables); this
6127 avoids clutter, since references are often used for large structures.
6128 The @emph{address} of a reference variable is always shown, unless
6129 you have specified @samp{set print address off}.
6132 @value{GDBN} supports the C++ name resolution operator @code{::}---your
6133 expressions can use it just as expressions in your program do. Since
6134 one scope may be defined in another, you can use @code{::} repeatedly if
6135 necessary, for example in an expression like
6136 @samp{@var{scope1}::@var{scope2}::@var{name}}. @value{GDBN} also allows
6137 resolving name scope by reference to source files, in both C and C++
6138 debugging (@pxref{Variables, ,Program variables}).
6141 In addition, when used with HP's C++ compiler, @value{GDBN} supports
6142 calling virtual functions correctly, printing out virtual bases of
6143 objects, calling functions in a base subobject, casting objects, and
6144 invoking user-defined operators.
6147 @subsubsection C and C++ defaults
6149 @cindex C and C++ defaults
6151 If you allow @value{GDBN} to set type and range checking automatically, they
6152 both default to @code{off} whenever the working language changes to
6153 C or C++. This happens regardless of whether you or @value{GDBN}
6154 selects the working language.
6156 If you allow @value{GDBN} to set the language automatically, it
6157 recognizes source files whose names end with @file{.c}, @file{.C}, or
6158 @file{.cc}, etc, and when @value{GDBN} enters code compiled from one of
6159 these files, it sets the working language to C or C++.
6160 @xref{Automatically, ,Having @value{GDBN} infer the source language},
6161 for further details.
6163 @c Type checking is (a) primarily motivated by Modula-2, and (b)
6164 @c unimplemented. If (b) changes, it might make sense to let this node
6165 @c appear even if Mod-2 does not, but meanwhile ignore it. roland 16jul93.
6168 @subsubsection C and C++ type and range checks
6170 @cindex C and C++ checks
6172 By default, when @value{GDBN} parses C or C++ expressions, type checking
6173 is not used. However, if you turn type checking on, @value{GDBN}
6174 considers two variables type equivalent if:
6178 The two variables are structured and have the same structure, union, or
6182 The two variables have the same type name, or types that have been
6183 declared equivalent through @code{typedef}.
6186 @c leaving this out because neither J Gilmore nor R Pesch understand it.
6189 The two @code{struct}, @code{union}, or @code{enum} variables are
6190 declared in the same declaration. (Note: this may not be true for all C
6195 Range checking, if turned on, is done on mathematical operations. Array
6196 indices are not checked, since they are often used to index a pointer
6197 that is not itself an array.
6200 @subsubsection @value{GDBN} and C
6202 The @code{set print union} and @code{show print union} commands apply to
6203 the @code{union} type. When set to @samp{on}, any @code{union} that is
6204 inside a @code{struct} or @code{class} is also printed. Otherwise, it
6205 appears as @samp{@{...@}}.
6207 The @code{@@} operator aids in the debugging of dynamic arrays, formed
6208 with pointers and a memory allocation function. @xref{Expressions,
6212 * Debugging C plus plus::
6215 @node Debugging C plus plus
6216 @subsubsection @value{GDBN} features for C++
6218 @cindex commands for C++
6220 Some @value{GDBN} commands are particularly useful with C++, and some are
6221 designed specifically for use with C++. Here is a summary:
6224 @cindex break in overloaded functions
6225 @item @r{breakpoint menus}
6226 When you want a breakpoint in a function whose name is overloaded,
6227 @value{GDBN} breakpoint menus help you specify which function definition
6228 you want. @xref{Breakpoint Menus,,Breakpoint menus}.
6230 @cindex overloading in C++
6231 @item rbreak @var{regex}
6232 Setting breakpoints using regular expressions is helpful for setting
6233 breakpoints on overloaded functions that are not members of any special
6235 @xref{Set Breaks, ,Setting breakpoints}.
6237 @cindex C++ exception handling
6240 Debug C++ exception handling using these commands. @xref{Set
6241 Catchpoints, , Setting catchpoints}.
6244 @item ptype @var{typename}
6245 Print inheritance relationships as well as other information for type
6247 @xref{Symbols, ,Examining the Symbol Table}.
6249 @cindex C++ symbol display
6250 @item set print demangle
6251 @itemx show print demangle
6252 @itemx set print asm-demangle
6253 @itemx show print asm-demangle
6254 Control whether C++ symbols display in their source form, both when
6255 displaying code as C++ source and when displaying disassemblies.
6256 @xref{Print Settings, ,Print settings}.
6258 @item set print object
6259 @itemx show print object
6260 Choose whether to print derived (actual) or declared types of objects.
6261 @xref{Print Settings, ,Print settings}.
6263 @item set print vtbl
6264 @itemx show print vtbl
6265 Control the format for printing virtual function tables.
6266 @xref{Print Settings, ,Print settings}.
6267 (The @code{vtbl} commands do not work on programs compiled with the HP
6268 ANSI C++ compiler (@code{aCC}).)
6270 @kindex set overload-resolution
6271 @cindex overloaded functions, overload resolution
6272 @item set overload-resolution on
6273 Enable overload resolution for C++ expression evaluation. The default
6274 is on. For overloaded functions, @value{GDBN} evaluates the arguments
6275 and searches for a function whose signature matches the argument types,
6276 using the standard C++ conversion rules (see @ref{C plus plus expressions, ,C++
6277 expressions}, for details). If it cannot find a match, it emits a
6280 @item set overload-resolution off
6281 Disable overload resolution for C++ expression evaluation. For
6282 overloaded functions that are not class member functions, @value{GDBN}
6283 chooses the first function of the specified name that it finds in the
6284 symbol table, whether or not its arguments are of the correct type. For
6285 overloaded functions that are class member functions, @value{GDBN}
6286 searches for a function whose signature @emph{exactly} matches the
6289 @item @r{Overloaded symbol names}
6290 You can specify a particular definition of an overloaded symbol, using
6291 the same notation that is used to declare such symbols in C++: type
6292 @code{@var{symbol}(@var{types})} rather than just @var{symbol}. You can
6293 also use the @value{GDBN} command-line word completion facilities to list the
6294 available choices, or to finish the type list for you.
6295 @xref{Completion,, Command completion}, for details on how to do this.
6299 @subsection Modula-2
6301 @cindex Modula-2, @value{GDBN} support
6303 The extensions made to @value{GDBN} to support Modula-2 only support
6304 output from the @sc{gnu} Modula-2 compiler (which is currently being
6305 developed). Other Modula-2 compilers are not currently supported, and
6306 attempting to debug executables produced by them is most likely
6307 to give an error as @value{GDBN} reads in the executable's symbol
6310 @cindex expressions in Modula-2
6312 * M2 Operators:: Built-in operators
6313 * Built-In Func/Proc:: Built-in functions and procedures
6314 * M2 Constants:: Modula-2 constants
6315 * M2 Defaults:: Default settings for Modula-2
6316 * Deviations:: Deviations from standard Modula-2
6317 * M2 Checks:: Modula-2 type and range checks
6318 * M2 Scope:: The scope operators @code{::} and @code{.}
6319 * GDB/M2:: @value{GDBN} and Modula-2
6323 @subsubsection Operators
6324 @cindex Modula-2 operators
6326 Operators must be defined on values of specific types. For instance,
6327 @code{+} is defined on numbers, but not on structures. Operators are
6328 often defined on groups of types. For the purposes of Modula-2, the
6329 following definitions hold:
6334 @emph{Integral types} consist of @code{INTEGER}, @code{CARDINAL}, and
6338 @emph{Character types} consist of @code{CHAR} and its subranges.
6341 @emph{Floating-point types} consist of @code{REAL}.
6344 @emph{Pointer types} consist of anything declared as @code{POINTER TO
6348 @emph{Scalar types} consist of all of the above.
6351 @emph{Set types} consist of @code{SET} and @code{BITSET} types.
6354 @emph{Boolean types} consist of @code{BOOLEAN}.
6358 The following operators are supported, and appear in order of
6359 increasing precedence:
6363 Function argument or array index separator.
6366 Assignment. The value of @var{var} @code{:=} @var{value} is
6370 Less than, greater than on integral, floating-point, or enumerated
6374 Less than, greater than, less than or equal to, greater than or equal to
6375 on integral, floating-point and enumerated types, or set inclusion on
6376 set types. Same precedence as @code{<}.
6378 @item =@r{, }<>@r{, }#
6379 Equality and two ways of expressing inequality, valid on scalar types.
6380 Same precedence as @code{<}. In @value{GDBN} scripts, only @code{<>} is
6381 available for inequality, since @code{#} conflicts with the script
6385 Set membership. Defined on set types and the types of their members.
6386 Same precedence as @code{<}.
6389 Boolean disjunction. Defined on boolean types.
6392 Boolean conjunction. Defined on boolean types.
6395 The @value{GDBN} ``artificial array'' operator (@pxref{Expressions, ,Expressions}).
6398 Addition and subtraction on integral and floating-point types, or union
6399 and difference on set types.
6402 Multiplication on integral and floating-point types, or set intersection
6406 Division on floating-point types, or symmetric set difference on set
6407 types. Same precedence as @code{*}.
6410 Integer division and remainder. Defined on integral types. Same
6411 precedence as @code{*}.
6414 Negative. Defined on @code{INTEGER} and @code{REAL} data.
6417 Pointer dereferencing. Defined on pointer types.
6420 Boolean negation. Defined on boolean types. Same precedence as
6424 @code{RECORD} field selector. Defined on @code{RECORD} data. Same
6425 precedence as @code{^}.
6428 Array indexing. Defined on @code{ARRAY} data. Same precedence as @code{^}.
6431 Procedure argument list. Defined on @code{PROCEDURE} objects. Same precedence
6435 @value{GDBN} and Modula-2 scope operators.
6439 @emph{Warning:} Sets and their operations are not yet supported, so @value{GDBN}
6440 treats the use of the operator @code{IN}, or the use of operators
6441 @code{+}, @code{-}, @code{*}, @code{/}, @code{=}, , @code{<>}, @code{#},
6442 @code{<=}, and @code{>=} on sets as an error.
6445 @cindex Modula-2 built-ins
6446 @node Built-In Func/Proc
6447 @subsubsection Built-in functions and procedures
6449 Modula-2 also makes available several built-in procedures and functions.
6450 In describing these, the following metavariables are used:
6455 represents an @code{ARRAY} variable.
6458 represents a @code{CHAR} constant or variable.
6461 represents a variable or constant of integral type.
6464 represents an identifier that belongs to a set. Generally used in the
6465 same function with the metavariable @var{s}. The type of @var{s} should
6466 be @code{SET OF @var{mtype}} (where @var{mtype} is the type of @var{m}).
6469 represents a variable or constant of integral or floating-point type.
6472 represents a variable or constant of floating-point type.
6478 represents a variable.
6481 represents a variable or constant of one of many types. See the
6482 explanation of the function for details.
6485 All Modula-2 built-in procedures also return a result, described below.
6489 Returns the absolute value of @var{n}.
6492 If @var{c} is a lower case letter, it returns its upper case
6493 equivalent, otherwise it returns its argument.
6496 Returns the character whose ordinal value is @var{i}.
6499 Decrements the value in the variable @var{v} by one. Returns the new value.
6501 @item DEC(@var{v},@var{i})
6502 Decrements the value in the variable @var{v} by @var{i}. Returns the
6505 @item EXCL(@var{m},@var{s})
6506 Removes the element @var{m} from the set @var{s}. Returns the new
6509 @item FLOAT(@var{i})
6510 Returns the floating point equivalent of the integer @var{i}.
6513 Returns the index of the last member of @var{a}.
6516 Increments the value in the variable @var{v} by one. Returns the new value.
6518 @item INC(@var{v},@var{i})
6519 Increments the value in the variable @var{v} by @var{i}. Returns the
6522 @item INCL(@var{m},@var{s})
6523 Adds the element @var{m} to the set @var{s} if it is not already
6524 there. Returns the new set.
6527 Returns the maximum value of the type @var{t}.
6530 Returns the minimum value of the type @var{t}.
6533 Returns boolean TRUE if @var{i} is an odd number.
6536 Returns the ordinal value of its argument. For example, the ordinal
6537 value of a character is its @sc{ascii} value (on machines supporting the
6538 @sc{ascii} character set). @var{x} must be of an ordered type, which include
6539 integral, character and enumerated types.
6542 Returns the size of its argument. @var{x} can be a variable or a type.
6544 @item TRUNC(@var{r})
6545 Returns the integral part of @var{r}.
6547 @item VAL(@var{t},@var{i})
6548 Returns the member of the type @var{t} whose ordinal value is @var{i}.
6552 @emph{Warning:} Sets and their operations are not yet supported, so
6553 @value{GDBN} treats the use of procedures @code{INCL} and @code{EXCL} as
6557 @cindex Modula-2 constants
6559 @subsubsection Constants
6561 @value{GDBN} allows you to express the constants of Modula-2 in the following
6567 Integer constants are simply a sequence of digits. When used in an
6568 expression, a constant is interpreted to be type-compatible with the
6569 rest of the expression. Hexadecimal integers are specified by a
6570 trailing @samp{H}, and octal integers by a trailing @samp{B}.
6573 Floating point constants appear as a sequence of digits, followed by a
6574 decimal point and another sequence of digits. An optional exponent can
6575 then be specified, in the form @samp{E@r{[}+@r{|}-@r{]}@var{nnn}}, where
6576 @samp{@r{[}+@r{|}-@r{]}@var{nnn}} is the desired exponent. All of the
6577 digits of the floating point constant must be valid decimal (base 10)
6581 Character constants consist of a single character enclosed by a pair of
6582 like quotes, either single (@code{'}) or double (@code{"}). They may
6583 also be expressed by their ordinal value (their @sc{ascii} value, usually)
6584 followed by a @samp{C}.
6587 String constants consist of a sequence of characters enclosed by a
6588 pair of like quotes, either single (@code{'}) or double (@code{"}).
6589 Escape sequences in the style of C are also allowed. @xref{C
6590 Constants, ,C and C++ constants}, for a brief explanation of escape
6594 Enumerated constants consist of an enumerated identifier.
6597 Boolean constants consist of the identifiers @code{TRUE} and
6601 Pointer constants consist of integral values only.
6604 Set constants are not yet supported.
6608 @subsubsection Modula-2 defaults
6609 @cindex Modula-2 defaults
6611 If type and range checking are set automatically by @value{GDBN}, they
6612 both default to @code{on} whenever the working language changes to
6613 Modula-2. This happens regardless of whether you or @value{GDBN}
6614 selected the working language.
6616 If you allow @value{GDBN} to set the language automatically, then entering
6617 code compiled from a file whose name ends with @file{.mod} sets the
6618 working language to Modula-2. @xref{Automatically, ,Having @value{GDBN} set
6619 the language automatically}, for further details.
6622 @subsubsection Deviations from standard Modula-2
6623 @cindex Modula-2, deviations from
6625 A few changes have been made to make Modula-2 programs easier to debug.
6626 This is done primarily via loosening its type strictness:
6630 Unlike in standard Modula-2, pointer constants can be formed by
6631 integers. This allows you to modify pointer variables during
6632 debugging. (In standard Modula-2, the actual address contained in a
6633 pointer variable is hidden from you; it can only be modified
6634 through direct assignment to another pointer variable or expression that
6635 returned a pointer.)
6638 C escape sequences can be used in strings and characters to represent
6639 non-printable characters. @value{GDBN} prints out strings with these
6640 escape sequences embedded. Single non-printable characters are
6641 printed using the @samp{CHR(@var{nnn})} format.
6644 The assignment operator (@code{:=}) returns the value of its right-hand
6648 All built-in procedures both modify @emph{and} return their argument.
6652 @subsubsection Modula-2 type and range checks
6653 @cindex Modula-2 checks
6656 @emph{Warning:} in this release, @value{GDBN} does not yet perform type or
6659 @c FIXME remove warning when type/range checks added
6661 @value{GDBN} considers two Modula-2 variables type equivalent if:
6665 They are of types that have been declared equivalent via a @code{TYPE
6666 @var{t1} = @var{t2}} statement
6669 They have been declared on the same line. (Note: This is true of the
6670 @sc{gnu} Modula-2 compiler, but it may not be true of other compilers.)
6673 As long as type checking is enabled, any attempt to combine variables
6674 whose types are not equivalent is an error.
6676 Range checking is done on all mathematical operations, assignment, array
6677 index bounds, and all built-in functions and procedures.
6680 @subsubsection The scope operators @code{::} and @code{.}
6683 @cindex colon, doubled as scope operator
6685 @kindex colon-colon@r{, in Modula-2}
6686 @c Info cannot handle :: but TeX can.
6692 There are a few subtle differences between the Modula-2 scope operator
6693 (@code{.}) and the @value{GDBN} scope operator (@code{::}). The two have
6698 @var{module} . @var{id}
6699 @var{scope} :: @var{id}
6703 where @var{scope} is the name of a module or a procedure,
6704 @var{module} the name of a module, and @var{id} is any declared
6705 identifier within your program, except another module.
6707 Using the @code{::} operator makes @value{GDBN} search the scope
6708 specified by @var{scope} for the identifier @var{id}. If it is not
6709 found in the specified scope, then @value{GDBN} searches all scopes
6710 enclosing the one specified by @var{scope}.
6712 Using the @code{.} operator makes @value{GDBN} search the current scope for
6713 the identifier specified by @var{id} that was imported from the
6714 definition module specified by @var{module}. With this operator, it is
6715 an error if the identifier @var{id} was not imported from definition
6716 module @var{module}, or if @var{id} is not an identifier in
6720 @subsubsection @value{GDBN} and Modula-2
6722 Some @value{GDBN} commands have little use when debugging Modula-2 programs.
6723 Five subcommands of @code{set print} and @code{show print} apply
6724 specifically to C and C++: @samp{vtbl}, @samp{demangle},
6725 @samp{asm-demangle}, @samp{object}, and @samp{union}. The first four
6726 apply to C++, and the last to the C @code{union} type, which has no direct
6727 analogue in Modula-2.
6729 The @code{@@} operator (@pxref{Expressions, ,Expressions}), while available
6730 with any language, is not useful with Modula-2. Its
6731 intent is to aid the debugging of @dfn{dynamic arrays}, which cannot be
6732 created in Modula-2 as they can in C or C++. However, because an
6733 address can be specified by an integral constant, the construct
6734 @samp{@{@var{type}@}@var{adrexp}} is still useful.
6736 @cindex @code{#} in Modula-2
6737 In @value{GDBN} scripts, the Modula-2 inequality operator @code{#} is
6738 interpreted as the beginning of a comment. Use @code{<>} instead.
6743 The extensions made to @value{GDBN} to support Chill only support output
6744 from the @sc{gnu} Chill compiler. Other Chill compilers are not currently
6745 supported, and attempting to debug executables produced by them is most
6746 likely to give an error as @value{GDBN} reads in the executable's symbol
6749 @c This used to say "... following Chill related topics ...", but since
6750 @c menus are not shown in the printed manual, it would look awkward.
6751 This section covers the Chill related topics and the features
6752 of @value{GDBN} which support these topics.
6755 * How modes are displayed:: How modes are displayed
6756 * Locations:: Locations and their accesses
6757 * Values and their Operations:: Values and their Operations
6758 * Chill type and range checks::
6762 @node How modes are displayed
6763 @subsubsection How modes are displayed
6765 The Chill Datatype- (Mode) support of @value{GDBN} is directly related
6766 with the functionality of the @sc{gnu} Chill compiler, and therefore deviates
6767 slightly from the standard specification of the Chill language. The
6770 @c FIXME: this @table's contents effectively disable @code by using @r
6771 @c on every @item. So why does it need @code?
6773 @item @r{@emph{Discrete modes:}}
6776 @emph{Integer Modes} which are predefined by @code{BYTE, UBYTE, INT,
6779 @emph{Boolean Mode} which is predefined by @code{BOOL},
6781 @emph{Character Mode} which is predefined by @code{CHAR},
6783 @emph{Set Mode} which is displayed by the keyword @code{SET}.
6785 (@value{GDBP}) ptype x
6786 type = SET (karli = 10, susi = 20, fritzi = 100)
6788 If the type is an unnumbered set the set element values are omitted.
6790 @emph{Range Mode} which is displayed by @code{type = <basemode>
6791 (<lower bound> : <upper bound>)}, where @code{<lower bound>, <upper
6792 bound>} can be of any discrete literal expression (e.g. set element
6796 @item @r{@emph{Powerset Mode:}}
6797 A Powerset Mode is displayed by the keyword @code{POWERSET} followed by
6798 the member mode of the powerset. The member mode can be any discrete mode.
6800 (@value{GDBP}) ptype x
6801 type = POWERSET SET (egon, hugo, otto)
6804 @item @r{@emph{Reference Modes:}}
6807 @emph{Bound Reference Mode} which is displayed by the keyword @code{REF}
6808 followed by the mode name to which the reference is bound.
6810 @emph{Free Reference Mode} which is displayed by the keyword @code{PTR}.
6813 @item @r{@emph{Procedure mode}}
6814 The procedure mode is displayed by @code{type = PROC(<parameter list>)
6815 <return mode> EXCEPTIONS (<exception list>)}. The @code{<parameter
6816 list>} is a list of the parameter modes. @code{<return mode>} indicates
6817 the mode of the result of the procedure if any. The exceptionlist lists
6818 all possible exceptions which can be raised by the procedure.
6821 @item @r{@emph{Instance mode}}
6822 The instance mode is represented by a structure, which has a static
6823 type, and is therefore not really of interest.
6826 @item @r{@emph{Synchronization Modes:}}
6829 @emph{Event Mode} which is displayed by @code{EVENT (<event length>)},
6830 where @code{(<event length>)} is optional.
6832 @emph{Buffer Mode} which is displayed by @code{BUFFER (<buffer length>)
6833 <buffer element mode>}, where @code{(<buffer length>)} is optional.
6836 @item @r{@emph{Timing Modes:}}
6839 @emph{Duration Mode} which is predefined by @code{DURATION}
6841 @emph{Absolute Time Mode} which is predefined by @code{TIME}
6844 @item @r{@emph{Real Modes:}}
6845 Real Modes are predefined with @code{REAL} and @code{LONG_REAL}.
6847 @item @r{@emph{String Modes:}}
6850 @emph{Character String Mode} which is displayed by @code{CHARS(<string
6851 length>)}, followed by the keyword @code{VARYING} if the String Mode is
6854 @emph{Bit String Mode} which is displayed by @code{BOOLS(<string
6858 @item @r{@emph{Array Mode:}}
6859 The Array Mode is displayed by the keyword @code{ARRAY(<range>)}
6860 followed by the element mode (which may in turn be an array mode).
6862 (@value{GDBP}) ptype x
6865 SET (karli = 10, susi = 20, fritzi = 100)
6868 @item @r{@emph{Structure Mode}}
6869 The Structure mode is displayed by the keyword @code{STRUCT(<field
6870 list>)}. The @code{<field list>} consists of names and modes of fields
6871 of the structure. Variant structures have the keyword @code{CASE <field>
6872 OF <variant fields> ESAC} in their field list. Since the current version
6873 of the GNU Chill compiler doesn't implement tag processing (no runtime
6874 checks of variant fields, and therefore no debugging info), the output
6875 always displays all variant fields.
6877 (@value{GDBP}) ptype str
6892 @subsubsection Locations and their accesses
6894 A location in Chill is an object which can contain values.
6896 A value of a location is generally accessed by the (declared) name of
6897 the location. The output conforms to the specification of values in
6898 Chill programs. How values are specified
6899 is the topic of the next section, @ref{Values and their Operations}.
6901 The pseudo-location @code{RESULT} (or @code{result}) can be used to
6902 display or change the result of a currently-active procedure:
6909 This does the same as the Chill action @code{RESULT EXPR} (which
6910 is not available in @value{GDBN}).
6912 Values of reference mode locations are printed by @code{PTR(<hex
6913 value>)} in case of a free reference mode, and by @code{(REF <reference
6914 mode>) (<hex-value>)} in case of a bound reference. @code{<hex value>}
6915 represents the address where the reference points to. To access the
6916 value of the location referenced by the pointer, use the dereference
6919 Values of procedure mode locations are displayed by @code{@{ PROC
6920 (<argument modes> ) <return mode> @} <address> <name of procedure
6921 location>}. @code{<argument modes>} is a list of modes according to the
6922 parameter specification of the procedure and @code{<address>} shows the
6923 address of the entry point.
6926 Locations of instance modes are displayed just like a structure with two
6927 fields specifying the @emph{process type} and the @emph{copy number} of
6928 the investigated instance location@footnote{This comes from the current
6929 implementation of instances. They are implemented as a structure (no
6930 na). The output should be something like @code{[<name of the process>;
6931 <instance number>]}.}. The field names are @code{__proc_type} and
6934 Locations of synchronization modes are displayed like a structure with
6935 the field name @code{__event_data} in case of a event mode location, and
6936 like a structure with the field @code{__buffer_data} in case of a buffer
6937 mode location (refer to previous paragraph).
6939 Structure Mode locations are printed by @code{[.<field name>: <value>,
6940 ...]}. The @code{<field name>} corresponds to the structure mode
6941 definition and the layout of @code{<value>} varies depending of the mode
6942 of the field. If the investigated structure mode location is of variant
6943 structure mode, the variant parts of the structure are enclosed in curled
6944 braces (@samp{@{@}}). Fields enclosed by @samp{@{,@}} are residing
6945 on the same memory location and represent the current values of the
6946 memory location in their specific modes. Since no tag processing is done
6947 all variants are displayed. A variant field is printed by
6948 @code{(<variant name>) = .<field name>: <value>}. (who implements the
6951 (@value{GDBP}) print str1 $4 = [.as: 0, .bs: karli, .<TAG>: { (karli) =
6952 [.cs: []], (susi) = [.ds: susi]}]
6956 Substructures of string mode-, array mode- or structure mode-values
6957 (e.g. array slices, fields of structure locations) are accessed using
6958 certain operations which are described in the next section, @ref{Values
6959 and their Operations}.
6961 A location value may be interpreted as having a different mode using the
6962 location conversion. This mode conversion is written as @code{<mode
6963 name>(<location>)}. The user has to consider that the sizes of the modes
6964 have to be equal otherwise an error occurs. Furthermore, no range
6965 checking of the location against the destination mode is performed, and
6966 therefore the result can be quite confusing.
6969 (@value{GDBP}) print int (s(3 up 4)) XXX TO be filled in !! XXX
6972 @node Values and their Operations
6973 @subsubsection Values and their Operations
6975 Values are used to alter locations, to investigate complex structures in
6976 more detail or to filter relevant information out of a large amount of
6977 data. There are several (mode dependent) operations defined which enable
6978 such investigations. These operations are not only applicable to
6979 constant values but also to locations, which can become quite useful
6980 when debugging complex structures. During parsing the command line
6981 (e.g. evaluating an expression) @value{GDBN} treats location names as
6982 the values behind these locations.
6984 This section describes how values have to be specified and which
6985 operations are legal to be used with such values.
6988 @item Literal Values
6989 Literal values are specified in the same manner as in @sc{gnu} Chill programs.
6990 For detailed specification refer to the @sc{gnu} Chill implementation Manual
6992 @c FIXME: if the Chill Manual is a Texinfo documents, the above should
6993 @c be converted to a @ref.
6998 @emph{Integer Literals} are specified in the same manner as in Chill
6999 programs (refer to the Chill Standard z200/88 chpt 5.2.4.2)
7001 @emph{Boolean Literals} are defined by @code{TRUE} and @code{FALSE}.
7003 @emph{Character Literals} are defined by @code{'<character>'}. (e.g.
7006 @emph{Set Literals} are defined by a name which was specified in a set
7007 mode. The value delivered by a Set Literal is the set value. This is
7008 comparable to an enumeration in C/C++ language.
7010 @emph{Emptiness Literal} is predefined by @code{NULL}. The value of the
7011 emptiness literal delivers either the empty reference value, the empty
7012 procedure value or the empty instance value.
7015 @emph{Character String Literals} are defined by a sequence of characters
7016 enclosed in single- or double quotes. If a single- or double quote has
7017 to be part of the string literal it has to be stuffed (specified twice).
7019 @emph{Bitstring Literals} are specified in the same manner as in Chill
7020 programs (refer z200/88 chpt 5.2.4.8).
7022 @emph{Floating point literals} are specified in the same manner as in
7023 (gnu-)Chill programs (refer @sc{gnu} Chill implementation Manual chapter 1.5).
7028 A tuple is specified by @code{<mode name>[<tuple>]}, where @code{<mode
7029 name>} can be omitted if the mode of the tuple is unambiguous. This
7030 unambiguity is derived from the context of a evaluated expression.
7031 @code{<tuple>} can be one of the following:
7034 @item @emph{Powerset Tuple}
7035 @item @emph{Array Tuple}
7036 @item @emph{Structure Tuple}
7037 Powerset tuples, array tuples and structure tuples are specified in the
7038 same manner as in Chill programs refer to z200/88 chpt 5.2.5.
7041 @item String Element Value
7042 A string element value is specified by @code{<string value>(<index>)},
7043 where @code{<index>} is a integer expression. It delivers a character
7044 value which is equivalent to the character indexed by @code{<index>} in
7047 @item String Slice Value
7048 A string slice value is specified by @code{<string value>(<slice
7049 spec>)}, where @code{<slice spec>} can be either a range of integer
7050 expressions or specified by @code{<start expr> up <size>}.
7051 @code{<size>} denotes the number of elements which the slice contains.
7052 The delivered value is a string value, which is part of the specified
7055 @item Array Element Values
7056 An array element value is specified by @code{<array value>(<expr>)} and
7057 delivers a array element value of the mode of the specified array.
7059 @item Array Slice Values
7060 An array slice is specified by @code{<array value>(<slice spec>)}, where
7061 @code{<slice spec>} can be either a range specified by expressions or by
7062 @code{<start expr> up <size>}. @code{<size>} denotes the number of
7063 arrayelements the slice contains. The delivered value is an array value
7064 which is part of the specified array.
7066 @item Structure Field Values
7067 A structure field value is derived by @code{<structure value>.<field
7068 name>}, where @code{<field name>} indicates the name of a field specified
7069 in the mode definition of the structure. The mode of the delivered value
7070 corresponds to this mode definition in the structure definition.
7072 @item Procedure Call Value
7073 The procedure call value is derived from the return value of the
7074 procedure@footnote{If a procedure call is used for instance in an
7075 expression, then this procedure is called with all its side
7076 effects. This can lead to confusing results if used carelessly.}.
7078 Values of duration mode locations are represented by @code{ULONG} literals.
7080 Values of time mode locations are represented by @code{TIME(<secs>:<nsecs>)}.
7083 This is not implemented yet:
7084 @item Built-in Value
7086 The following built in functions are provided:
7098 @item @code{UPPER()}
7099 @item @code{LOWER()}
7100 @item @code{LENGTH()}
7104 @item @code{ARCSIN()}
7105 @item @code{ARCCOS()}
7106 @item @code{ARCTAN()}
7113 For a detailed description refer to the GNU Chill implementation manual
7117 @item Zero-adic Operator Value
7118 The zero-adic operator value is derived from the instance value for the
7119 current active process.
7121 @item Expression Values
7122 The value delivered by an expression is the result of the evaluation of
7123 the specified expression. If there are error conditions (mode
7124 incompatibility, etc.) the evaluation of expressions is aborted with a
7125 corresponding error message. Expressions may be parenthesised which
7126 causes the evaluation of this expression before any other expression
7127 which uses the result of the parenthesised expression. The following
7128 operators are supported by @value{GDBN}:
7131 @item @code{OR, ORIF, XOR}
7132 @itemx @code{AND, ANDIF}
7134 Logical operators defined over operands of boolean mode.
7137 Equality and inequality operators defined over all modes.
7141 Relational operators defined over predefined modes.
7144 @itemx @code{*, /, MOD, REM}
7145 Arithmetic operators defined over predefined modes.
7148 Change sign operator.
7151 String concatenation operator.
7154 String repetition operator.
7157 Referenced location operator which can be used either to take the
7158 address of a location (@code{->loc}), or to dereference a reference
7159 location (@code{loc->}).
7161 @item @code{OR, XOR}
7164 Powerset and bitstring operators.
7168 Powerset inclusion operators.
7171 Membership operator.
7175 @node Chill type and range checks
7176 @subsubsection Chill type and range checks
7178 @value{GDBN} considers two Chill variables mode equivalent if the sizes
7179 of the two modes are equal. This rule applies recursively to more
7180 complex datatypes which means that complex modes are treated
7181 equivalent if all element modes (which also can be complex modes like
7182 structures, arrays, etc.) have the same size.
7184 Range checking is done on all mathematical operations, assignment, array
7185 index bounds and all built in procedures.
7187 Strong type checks are forced using the @value{GDBN} command @code{set
7188 check strong}. This enforces strong type and range checks on all
7189 operations where Chill constructs are used (expressions, built in
7190 functions, etc.) in respect to the semantics as defined in the z.200
7191 language specification.
7193 All checks can be disabled by the @value{GDBN} command @code{set check
7197 @c Deviations from the Chill Standard Z200/88
7198 see last paragraph ?
7201 @node Chill defaults
7202 @subsubsection Chill defaults
7204 If type and range checking are set automatically by @value{GDBN}, they
7205 both default to @code{on} whenever the working language changes to
7206 Chill. This happens regardless of whether you or @value{GDBN}
7207 selected the working language.
7209 If you allow @value{GDBN} to set the language automatically, then entering
7210 code compiled from a file whose name ends with @file{.ch} sets the
7211 working language to Chill. @xref{Automatically, ,Having @value{GDBN} set
7212 the language automatically}, for further details.
7215 @chapter Examining the Symbol Table
7217 The commands described in this chapter allow you to inquire about the
7218 symbols (names of variables, functions and types) defined in your
7219 program. This information is inherent in the text of your program and
7220 does not change as your program executes. @value{GDBN} finds it in your
7221 program's symbol table, in the file indicated when you started @value{GDBN}
7222 (@pxref{File Options, ,Choosing files}), or by one of the
7223 file-management commands (@pxref{Files, ,Commands to specify files}).
7225 @cindex symbol names
7226 @cindex names of symbols
7227 @cindex quoting names
7228 Occasionally, you may need to refer to symbols that contain unusual
7229 characters, which @value{GDBN} ordinarily treats as word delimiters. The
7230 most frequent case is in referring to static variables in other
7231 source files (@pxref{Variables,,Program variables}). File names
7232 are recorded in object files as debugging symbols, but @value{GDBN} would
7233 ordinarily parse a typical file name, like @file{foo.c}, as the three words
7234 @samp{foo} @samp{.} @samp{c}. To allow @value{GDBN} to recognize
7235 @samp{foo.c} as a single symbol, enclose it in single quotes; for example,
7242 looks up the value of @code{x} in the scope of the file @file{foo.c}.
7245 @kindex info address
7246 @item info address @var{symbol}
7247 Describe where the data for @var{symbol} is stored. For a register
7248 variable, this says which register it is kept in. For a non-register
7249 local variable, this prints the stack-frame offset at which the variable
7252 Note the contrast with @samp{print &@var{symbol}}, which does not work
7253 at all for a register variable, and for a stack local variable prints
7254 the exact address of the current instantiation of the variable.
7257 @item whatis @var{expr}
7258 Print the data type of expression @var{expr}. @var{expr} is not
7259 actually evaluated, and any side-effecting operations (such as
7260 assignments or function calls) inside it do not take place.
7261 @xref{Expressions, ,Expressions}.
7264 Print the data type of @code{$}, the last value in the value history.
7267 @item ptype @var{typename}
7268 Print a description of data type @var{typename}. @var{typename} may be
7269 the name of a type, or for C code it may have the form @samp{class
7270 @var{class-name}}, @samp{struct @var{struct-tag}}, @samp{union
7271 @var{union-tag}} or @samp{enum @var{enum-tag}}.
7273 @item ptype @var{expr}
7275 Print a description of the type of expression @var{expr}. @code{ptype}
7276 differs from @code{whatis} by printing a detailed description, instead
7277 of just the name of the type.
7279 For example, for this variable declaration:
7282 struct complex @{double real; double imag;@} v;
7286 the two commands give this output:
7290 (@value{GDBP}) whatis v
7291 type = struct complex
7292 (@value{GDBP}) ptype v
7293 type = struct complex @{
7301 As with @code{whatis}, using @code{ptype} without an argument refers to
7302 the type of @code{$}, the last value in the value history.
7305 @item info types @var{regexp}
7307 Print a brief description of all types whose names match @var{regexp}
7308 (or all types in your program, if you supply no argument). Each
7309 complete typename is matched as though it were a complete line; thus,
7310 @samp{i type value} gives information on all types in your program whose
7311 names include the string @code{value}, but @samp{i type ^value$} gives
7312 information only on types whose complete name is @code{value}.
7314 This command differs from @code{ptype} in two ways: first, like
7315 @code{whatis}, it does not print a detailed description; second, it
7316 lists all source files where a type is defined.
7320 Show the name of the current source file---that is, the source file for
7321 the function containing the current point of execution---and the language
7324 @kindex info sources
7326 Print the names of all source files in your program for which there is
7327 debugging information, organized into two lists: files whose symbols
7328 have already been read, and files whose symbols will be read when needed.
7330 @kindex info functions
7331 @item info functions
7332 Print the names and data types of all defined functions.
7334 @item info functions @var{regexp}
7335 Print the names and data types of all defined functions
7336 whose names contain a match for regular expression @var{regexp}.
7337 Thus, @samp{info fun step} finds all functions whose names
7338 include @code{step}; @samp{info fun ^step} finds those whose names
7339 start with @code{step}.
7341 @kindex info variables
7342 @item info variables
7343 Print the names and data types of all variables that are declared
7344 outside of functions (i.e., excluding local variables).
7346 @item info variables @var{regexp}
7347 Print the names and data types of all variables (except for local
7348 variables) whose names contain a match for regular expression
7352 This was never implemented.
7353 @kindex info methods
7355 @itemx info methods @var{regexp}
7356 The @code{info methods} command permits the user to examine all defined
7357 methods within C++ program, or (with the @var{regexp} argument) a
7358 specific set of methods found in the various C++ classes. Many
7359 C++ classes provide a large number of methods. Thus, the output
7360 from the @code{ptype} command can be overwhelming and hard to use. The
7361 @code{info-methods} command filters the methods, printing only those
7362 which match the regular-expression @var{regexp}.
7365 @cindex reloading symbols
7366 Some systems allow individual object files that make up your program to
7367 be replaced without stopping and restarting your program. For example,
7368 in VxWorks you can simply recompile a defective object file and keep on
7369 running. If you are running on one of these systems, you can allow
7370 @value{GDBN} to reload the symbols for automatically relinked modules:
7373 @kindex set symbol-reloading
7374 @item set symbol-reloading on
7375 Replace symbol definitions for the corresponding source file when an
7376 object file with a particular name is seen again.
7378 @item set symbol-reloading off
7379 Do not replace symbol definitions when re-encountering object files of
7380 the same name. This is the default state; if you are not running on a
7381 system that permits automatically relinking modules, you should leave
7382 @code{symbol-reloading} off, since otherwise @value{GDBN} may discard symbols
7383 when linking large programs, that may contain several modules (from
7384 different directories or libraries) with the same name.
7386 @kindex show symbol-reloading
7387 @item show symbol-reloading
7388 Show the current @code{on} or @code{off} setting.
7391 @kindex set opaque-type-resolution
7392 @item set opaque-type-resolution on
7393 Tell @value{GDBN} to resolve opaque types. An opaque type is a type
7394 declared as a pointer to a @code{struct}, @code{class}, or
7395 @code{union}---for example, @code{struct MyType *}---that is used in one
7396 source file although the full declaration of @code{struct MyType} is in
7397 another source file. The default is on.
7399 A change in the setting of this subcommand will not take effect until
7400 the next time symbols for a file are loaded.
7402 @item set opaque-type-resolution off
7403 Tell @value{GDBN} not to resolve opaque types. In this case, the type
7404 is printed as follows:
7406 @{<no data fields>@}
7409 @kindex show opaque-type-resolution
7410 @item show opaque-type-resolution
7411 Show whether opaque types are resolved or not.
7413 @kindex maint print symbols
7415 @kindex maint print psymbols
7416 @cindex partial symbol dump
7417 @item maint print symbols @var{filename}
7418 @itemx maint print psymbols @var{filename}
7419 @itemx maint print msymbols @var{filename}
7420 Write a dump of debugging symbol data into the file @var{filename}.
7421 These commands are used to debug the @value{GDBN} symbol-reading code. Only
7422 symbols with debugging data are included. If you use @samp{maint print
7423 symbols}, @value{GDBN} includes all the symbols for which it has already
7424 collected full details: that is, @var{filename} reflects symbols for
7425 only those files whose symbols @value{GDBN} has read. You can use the
7426 command @code{info sources} to find out which files these are. If you
7427 use @samp{maint print psymbols} instead, the dump shows information about
7428 symbols that @value{GDBN} only knows partially---that is, symbols defined in
7429 files that @value{GDBN} has skimmed, but not yet read completely. Finally,
7430 @samp{maint print msymbols} dumps just the minimal symbol information
7431 required for each object file from which @value{GDBN} has read some symbols.
7432 @xref{Files, ,Commands to specify files}, for a discussion of how
7433 @value{GDBN} reads symbols (in the description of @code{symbol-file}).
7437 @chapter Altering Execution
7439 Once you think you have found an error in your program, you might want to
7440 find out for certain whether correcting the apparent error would lead to
7441 correct results in the rest of the run. You can find the answer by
7442 experiment, using the @value{GDBN} features for altering execution of the
7445 For example, you can store new values into variables or memory
7446 locations, give your program a signal, restart it at a different
7447 address, or even return prematurely from a function.
7450 * Assignment:: Assignment to variables
7451 * Jumping:: Continuing at a different address
7452 * Signaling:: Giving your program a signal
7453 * Returning:: Returning from a function
7454 * Calling:: Calling your program's functions
7455 * Patching:: Patching your program
7459 @section Assignment to variables
7462 @cindex setting variables
7463 To alter the value of a variable, evaluate an assignment expression.
7464 @xref{Expressions, ,Expressions}. For example,
7471 stores the value 4 into the variable @code{x}, and then prints the
7472 value of the assignment expression (which is 4).
7473 @xref{Languages, ,Using @value{GDBN} with Different Languages}, for more
7474 information on operators in supported languages.
7476 @kindex set variable
7477 @cindex variables, setting
7478 If you are not interested in seeing the value of the assignment, use the
7479 @code{set} command instead of the @code{print} command. @code{set} is
7480 really the same as @code{print} except that the expression's value is
7481 not printed and is not put in the value history (@pxref{Value History,
7482 ,Value history}). The expression is evaluated only for its effects.
7484 If the beginning of the argument string of the @code{set} command
7485 appears identical to a @code{set} subcommand, use the @code{set
7486 variable} command instead of just @code{set}. This command is identical
7487 to @code{set} except for its lack of subcommands. For example, if your
7488 program has a variable @code{width}, you get an error if you try to set
7489 a new value with just @samp{set width=13}, because @value{GDBN} has the
7490 command @code{set width}:
7493 (@value{GDBP}) whatis width
7495 (@value{GDBP}) p width
7497 (@value{GDBP}) set width=47
7498 Invalid syntax in expression.
7502 The invalid expression, of course, is @samp{=47}. In
7503 order to actually set the program's variable @code{width}, use
7506 (@value{GDBP}) set var width=47
7509 Because the @code{set} command has many subcommands that can conflict
7510 with the names of program variables, it is a good idea to use the
7511 @code{set variable} command instead of just @code{set}. For example, if
7512 your program has a variable @code{g}, you run into problems if you try
7513 to set a new value with just @samp{set g=4}, because @value{GDBN} has
7514 the command @code{set gnutarget}, abbreviated @code{set g}:
7518 (@value{GDBP}) whatis g
7522 (@value{GDBP}) set g=4
7526 The program being debugged has been started already.
7527 Start it from the beginning? (y or n) y
7528 Starting program: /home/smith/cc_progs/a.out
7529 "/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target.
7530 (@value{GDBP}) show g
7531 The current BFD target is "=4".
7536 The program variable @code{g} did not change, and you silently set the
7537 @code{gnutarget} to an invalid value. In order to set the variable
7541 (@value{GDBP}) set var g=4
7544 @value{GDBN} allows more implicit conversions in assignments than C; you can
7545 freely store an integer value into a pointer variable or vice versa,
7546 and you can convert any structure to any other structure that is the
7547 same length or shorter.
7548 @comment FIXME: how do structs align/pad in these conversions?
7549 @comment /doc@cygnus.com 18dec1990
7551 To store values into arbitrary places in memory, use the @samp{@{@dots{}@}}
7552 construct to generate a value of specified type at a specified address
7553 (@pxref{Expressions, ,Expressions}). For example, @code{@{int@}0x83040} refers
7554 to memory location @code{0x83040} as an integer (which implies a certain size
7555 and representation in memory), and
7558 set @{int@}0x83040 = 4
7562 stores the value 4 into that memory location.
7565 @section Continuing at a different address
7567 Ordinarily, when you continue your program, you do so at the place where
7568 it stopped, with the @code{continue} command. You can instead continue at
7569 an address of your own choosing, with the following commands:
7573 @item jump @var{linespec}
7574 Resume execution at line @var{linespec}. Execution stops again
7575 immediately if there is a breakpoint there. @xref{List, ,Printing
7576 source lines}, for a description of the different forms of
7577 @var{linespec}. It is common practice to use the @code{tbreak} command
7578 in conjunction with @code{jump}. @xref{Set Breaks, ,Setting
7581 The @code{jump} command does not change the current stack frame, or
7582 the stack pointer, or the contents of any memory location or any
7583 register other than the program counter. If line @var{linespec} is in
7584 a different function from the one currently executing, the results may
7585 be bizarre if the two functions expect different patterns of arguments or
7586 of local variables. For this reason, the @code{jump} command requests
7587 confirmation if the specified line is not in the function currently
7588 executing. However, even bizarre results are predictable if you are
7589 well acquainted with the machine-language code of your program.
7591 @item jump *@var{address}
7592 Resume execution at the instruction at address @var{address}.
7595 @c Doesn't work on HP-UX; have to set $pcoqh and $pcoqt.
7596 On many systems, you can get much the same effect as the @code{jump}
7597 command by storing a new value into the register @code{$pc}. The
7598 difference is that this does not start your program running; it only
7599 changes the address of where it @emph{will} run when you continue. For
7607 makes the next @code{continue} command or stepping command execute at
7608 address @code{0x485}, rather than at the address where your program stopped.
7609 @xref{Continuing and Stepping, ,Continuing and stepping}.
7611 The most common occasion to use the @code{jump} command is to back
7612 up---perhaps with more breakpoints set---over a portion of a program
7613 that has already executed, in order to examine its execution in more
7618 @section Giving your program a signal
7622 @item signal @var{signal}
7623 Resume execution where your program stopped, but immediately give it the
7624 signal @var{signal}. @var{signal} can be the name or the number of a
7625 signal. For example, on many systems @code{signal 2} and @code{signal
7626 SIGINT} are both ways of sending an interrupt signal.
7628 Alternatively, if @var{signal} is zero, continue execution without
7629 giving a signal. This is useful when your program stopped on account of
7630 a signal and would ordinary see the signal when resumed with the
7631 @code{continue} command; @samp{signal 0} causes it to resume without a
7634 @code{signal} does not repeat when you press @key{RET} a second time
7635 after executing the command.
7639 Invoking the @code{signal} command is not the same as invoking the
7640 @code{kill} utility from the shell. Sending a signal with @code{kill}
7641 causes @value{GDBN} to decide what to do with the signal depending on
7642 the signal handling tables (@pxref{Signals}). The @code{signal} command
7643 passes the signal directly to your program.
7647 @section Returning from a function
7650 @cindex returning from a function
7653 @itemx return @var{expression}
7654 You can cancel execution of a function call with the @code{return}
7655 command. If you give an
7656 @var{expression} argument, its value is used as the function's return
7660 When you use @code{return}, @value{GDBN} discards the selected stack frame
7661 (and all frames within it). You can think of this as making the
7662 discarded frame return prematurely. If you wish to specify a value to
7663 be returned, give that value as the argument to @code{return}.
7665 This pops the selected stack frame (@pxref{Selection, ,Selecting a
7666 frame}), and any other frames inside of it, leaving its caller as the
7667 innermost remaining frame. That frame becomes selected. The
7668 specified value is stored in the registers used for returning values
7671 The @code{return} command does not resume execution; it leaves the
7672 program stopped in the state that would exist if the function had just
7673 returned. In contrast, the @code{finish} command (@pxref{Continuing
7674 and Stepping, ,Continuing and stepping}) resumes execution until the
7675 selected stack frame returns naturally.
7678 @section Calling program functions
7680 @cindex calling functions
7683 @item call @var{expr}
7684 Evaluate the expression @var{expr} without displaying @code{void}
7688 You can use this variant of the @code{print} command if you want to
7689 execute a function from your program, but without cluttering the output
7690 with @code{void} returned values. If the result is not void, it
7691 is printed and saved in the value history.
7693 For the A29K, a user-controlled variable @code{call_scratch_address},
7694 specifies the location of a scratch area to be used when @value{GDBN}
7695 calls a function in the target. This is necessary because the usual
7696 method of putting the scratch area on the stack does not work in systems
7697 that have separate instruction and data spaces.
7700 @section Patching programs
7702 @cindex patching binaries
7703 @cindex writing into executables
7704 @cindex writing into corefiles
7706 By default, @value{GDBN} opens the file containing your program's
7707 executable code (or the corefile) read-only. This prevents accidental
7708 alterations to machine code; but it also prevents you from intentionally
7709 patching your program's binary.
7711 If you'd like to be able to patch the binary, you can specify that
7712 explicitly with the @code{set write} command. For example, you might
7713 want to turn on internal debugging flags, or even to make emergency
7719 @itemx set write off
7720 If you specify @samp{set write on}, @value{GDBN} opens executable and
7721 core files for both reading and writing; if you specify @samp{set write
7722 off} (the default), @value{GDBN} opens them read-only.
7724 If you have already loaded a file, you must load it again (using the
7725 @code{exec-file} or @code{core-file} command) after changing @code{set
7726 write}, for your new setting to take effect.
7730 Display whether executable files and core files are opened for writing
7735 @chapter @value{GDBN} Files
7737 @value{GDBN} needs to know the file name of the program to be debugged,
7738 both in order to read its symbol table and in order to start your
7739 program. To debug a core dump of a previous run, you must also tell
7740 @value{GDBN} the name of the core dump file.
7743 * Files:: Commands to specify files
7744 * Symbol Errors:: Errors reading symbol files
7748 @section Commands to specify files
7750 @cindex symbol table
7751 @cindex core dump file
7753 You may want to specify executable and core dump file names. The usual
7754 way to do this is at start-up time, using the arguments to
7755 @value{GDBN}'s start-up commands (@pxref{Invocation, , Getting In and
7756 Out of @value{GDBN}}).
7758 Occasionally it is necessary to change to a different file during a
7759 @value{GDBN} session. Or you may run @value{GDBN} and forget to specify
7760 a file you want to use. In these situations the @value{GDBN} commands
7761 to specify new files are useful.
7764 @cindex executable file
7766 @item file @var{filename}
7767 Use @var{filename} as the program to be debugged. It is read for its
7768 symbols and for the contents of pure memory. It is also the program
7769 executed when you use the @code{run} command. If you do not specify a
7770 directory and the file is not found in the @value{GDBN} working directory,
7771 @value{GDBN} uses the environment variable @code{PATH} as a list of
7772 directories to search, just as the shell does when looking for a program
7773 to run. You can change the value of this variable, for both @value{GDBN}
7774 and your program, using the @code{path} command.
7776 On systems with memory-mapped files, an auxiliary file
7777 @file{@var{filename}.syms} may hold symbol table information for
7778 @var{filename}. If so, @value{GDBN} maps in the symbol table from
7779 @file{@var{filename}.syms}, starting up more quickly. See the
7780 descriptions of the file options @samp{-mapped} and @samp{-readnow}
7781 (available on the command line, and with the commands @code{file},
7782 @code{symbol-file}, or @code{add-symbol-file}, described below),
7783 for more information.
7786 @code{file} with no argument makes @value{GDBN} discard any information it
7787 has on both executable file and the symbol table.
7790 @item exec-file @r{[} @var{filename} @r{]}
7791 Specify that the program to be run (but not the symbol table) is found
7792 in @var{filename}. @value{GDBN} searches the environment variable @code{PATH}
7793 if necessary to locate your program. Omitting @var{filename} means to
7794 discard information on the executable file.
7797 @item symbol-file @r{[} @var{filename} @r{]}
7798 Read symbol table information from file @var{filename}. @code{PATH} is
7799 searched when necessary. Use the @code{file} command to get both symbol
7800 table and program to run from the same file.
7802 @code{symbol-file} with no argument clears out @value{GDBN} information on your
7803 program's symbol table.
7805 The @code{symbol-file} command causes @value{GDBN} to forget the contents
7806 of its convenience variables, the value history, and all breakpoints and
7807 auto-display expressions. This is because they may contain pointers to
7808 the internal data recording symbols and data types, which are part of
7809 the old symbol table data being discarded inside @value{GDBN}.
7811 @code{symbol-file} does not repeat if you press @key{RET} again after
7814 When @value{GDBN} is configured for a particular environment, it
7815 understands debugging information in whatever format is the standard
7816 generated for that environment; you may use either a @sc{gnu} compiler, or
7817 other compilers that adhere to the local conventions.
7818 Best results are usually obtained from @sc{gnu} compilers; for example,
7819 using @code{@value{GCC}} you can generate debugging information for
7822 For most kinds of object files, with the exception of old SVR3 systems
7823 using COFF, the @code{symbol-file} command does not normally read the
7824 symbol table in full right away. Instead, it scans the symbol table
7825 quickly to find which source files and which symbols are present. The
7826 details are read later, one source file at a time, as they are needed.
7828 The purpose of this two-stage reading strategy is to make @value{GDBN}
7829 start up faster. For the most part, it is invisible except for
7830 occasional pauses while the symbol table details for a particular source
7831 file are being read. (The @code{set verbose} command can turn these
7832 pauses into messages if desired. @xref{Messages/Warnings, ,Optional
7833 warnings and messages}.)
7835 We have not implemented the two-stage strategy for COFF yet. When the
7836 symbol table is stored in COFF format, @code{symbol-file} reads the
7837 symbol table data in full right away. Note that ``stabs-in-COFF''
7838 still does the two-stage strategy, since the debug info is actually
7842 @cindex reading symbols immediately
7843 @cindex symbols, reading immediately
7845 @cindex memory-mapped symbol file
7846 @cindex saving symbol table
7847 @item symbol-file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7848 @itemx file @var{filename} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7849 You can override the @value{GDBN} two-stage strategy for reading symbol
7850 tables by using the @samp{-readnow} option with any of the commands that
7851 load symbol table information, if you want to be sure @value{GDBN} has the
7852 entire symbol table available.
7854 If memory-mapped files are available on your system through the
7855 @code{mmap} system call, you can use another option, @samp{-mapped}, to
7856 cause @value{GDBN} to write the symbols for your program into a reusable
7857 file. Future @value{GDBN} debugging sessions map in symbol information
7858 from this auxiliary symbol file (if the program has not changed), rather
7859 than spending time reading the symbol table from the executable
7860 program. Using the @samp{-mapped} option has the same effect as
7861 starting @value{GDBN} with the @samp{-mapped} command-line option.
7863 You can use both options together, to make sure the auxiliary symbol
7864 file has all the symbol information for your program.
7866 The auxiliary symbol file for a program called @var{myprog} is called
7867 @samp{@var{myprog}.syms}. Once this file exists (so long as it is newer
7868 than the corresponding executable), @value{GDBN} always attempts to use
7869 it when you debug @var{myprog}; no special options or commands are
7872 The @file{.syms} file is specific to the host machine where you run
7873 @value{GDBN}. It holds an exact image of the internal @value{GDBN}
7874 symbol table. It cannot be shared across multiple host platforms.
7876 @c FIXME: for now no mention of directories, since this seems to be in
7877 @c flux. 13mar1992 status is that in theory GDB would look either in
7878 @c current dir or in same dir as myprog; but issues like competing
7879 @c GDB's, or clutter in system dirs, mean that in practice right now
7880 @c only current dir is used. FFish says maybe a special GDB hierarchy
7881 @c (eg rooted in val of env var GDBSYMS) could exist for mappable symbol
7886 @item core-file @r{[} @var{filename} @r{]}
7887 Specify the whereabouts of a core dump file to be used as the ``contents
7888 of memory''. Traditionally, core files contain only some parts of the
7889 address space of the process that generated them; @value{GDBN} can access the
7890 executable file itself for other parts.
7892 @code{core-file} with no argument specifies that no core file is
7895 Note that the core file is ignored when your program is actually running
7896 under @value{GDBN}. So, if you have been running your program and you
7897 wish to debug a core file instead, you must kill the subprocess in which
7898 the program is running. To do this, use the @code{kill} command
7899 (@pxref{Kill Process, ,Killing the child process}).
7901 @kindex add-symbol-file
7902 @cindex dynamic linking
7903 @item add-symbol-file @var{filename} @var{address}
7904 @itemx add-symbol-file @var{filename} @var{address} @r{[} -readnow @r{]} @r{[} -mapped @r{]}
7905 @itemx add-symbol-file @var{filename} @var{address} @var{data_address} @var{bss_address}
7906 @itemx add-symbol-file @var{filename} @r{-T}@var{section} @var{address}
7907 The @code{add-symbol-file} command reads additional symbol table information
7908 from the file @var{filename}. You would use this command when @var{filename}
7909 has been dynamically loaded (by some other means) into the program that
7910 is running. @var{address} should be the memory address at which the
7911 file has been loaded; @value{GDBN} cannot figure this out for itself.
7912 You can specify up to three addresses, in which case they are taken to be
7913 the addresses of the text, data, and bss segments respectively.
7914 For complicated cases, you can specify an arbitrary number of @r{-T}@var{section} @var{address}
7915 pairs, to give an explicit section name and base address for that section.
7916 You can specify any @var{address} as an expression.
7918 The symbol table of the file @var{filename} is added to the symbol table
7919 originally read with the @code{symbol-file} command. You can use the
7920 @code{add-symbol-file} command any number of times; the new symbol data thus
7921 read keeps adding to the old. To discard all old symbol data instead,
7922 use the @code{symbol-file} command.
7924 @code{add-symbol-file} does not repeat if you press @key{RET} after using it.
7926 You can use the @samp{-mapped} and @samp{-readnow} options just as with
7927 the @code{symbol-file} command, to change how @value{GDBN} manages the symbol
7928 table information for @var{filename}.
7930 @kindex add-shared-symbol-file
7931 @item add-shared-symbol-file
7932 The @code{add-shared-symbol-file} command can be used only under Harris' CXUX
7933 operating system for the Motorola 88k. @value{GDBN} automatically looks for
7934 shared libraries, however if @value{GDBN} does not find yours, you can run
7935 @code{add-shared-symbol-file}. It takes no arguments.
7939 The @code{section} command changes the base address of section SECTION of
7940 the exec file to ADDR. This can be used if the exec file does not contain
7941 section addresses, (such as in the a.out format), or when the addresses
7942 specified in the file itself are wrong. Each section must be changed
7943 separately. The @code{info files} command, described below, lists all
7944 the sections and their addresses.
7950 @code{info files} and @code{info target} are synonymous; both print the
7951 current target (@pxref{Targets, ,Specifying a Debugging Target}),
7952 including the names of the executable and core dump files currently in
7953 use by @value{GDBN}, and the files from which symbols were loaded. The
7954 command @code{help target} lists all possible targets rather than
7959 All file-specifying commands allow both absolute and relative file names
7960 as arguments. @value{GDBN} always converts the file name to an absolute file
7961 name and remembers it that way.
7963 @cindex shared libraries
7964 @value{GDBN} supports HP-UX, SunOS, SVr4, Irix 5, and IBM RS/6000 shared
7967 @value{GDBN} automatically loads symbol definitions from shared libraries
7968 when you use the @code{run} command, or when you examine a core file.
7969 (Before you issue the @code{run} command, @value{GDBN} does not understand
7970 references to a function in a shared library, however---unless you are
7971 debugging a core file).
7973 On HP-UX, if the program loads a library explicitly, @value{GDBN}
7974 automatically loads the symbols at the time of the @code{shl_load} call.
7976 @c FIXME: some @value{GDBN} release may permit some refs to undef
7977 @c FIXME...symbols---eg in a break cmd---assuming they are from a shared
7978 @c FIXME...lib; check this from time to time when updating manual
7981 @kindex info sharedlibrary
7984 @itemx info sharedlibrary
7985 Print the names of the shared libraries which are currently loaded.
7987 @kindex sharedlibrary
7989 @item sharedlibrary @var{regex}
7990 @itemx share @var{regex}
7991 Load shared object library symbols for files matching a
7992 Unix regular expression.
7993 As with files loaded automatically, it only loads shared libraries
7994 required by your program for a core file or after typing @code{run}. If
7995 @var{regex} is omitted all shared libraries required by your program are
7999 On HP-UX systems, @value{GDBN} detects the loading of a shared library
8000 and automatically reads in symbols from the newly loaded library, up to
8001 a threshold that is initially set but that you can modify if you wish.
8003 Beyond that threshold, symbols from shared libraries must be explicitly
8004 loaded. To load these symbols, use the command @code{sharedlibrary
8005 @var{filename}}. The base address of the shared library is determined
8006 automatically by @value{GDBN} and need not be specified.
8008 To display or set the threshold, use the commands:
8011 @kindex set auto-solib-add
8012 @item set auto-solib-add @var{threshold}
8013 Set the autoloading size threshold, in megabytes. If @var{threshold} is
8014 nonzero, symbols from all shared object libraries will be loaded
8015 automatically when the inferior begins execution or when the dynamic
8016 linker informs @value{GDBN} that a new library has been loaded, until
8017 the symbol table of the program and libraries exceeds this threshold.
8018 Otherwise, symbols must be loaded manually, using the
8019 @code{sharedlibrary} command. The default threshold is 100 megabytes.
8021 @kindex show auto-solib-add
8022 @item show auto-solib-add
8023 Display the current autoloading size threshold, in megabytes.
8027 @section Errors reading symbol files
8029 While reading a symbol file, @value{GDBN} occasionally encounters problems,
8030 such as symbol types it does not recognize, or known bugs in compiler
8031 output. By default, @value{GDBN} does not notify you of such problems, since
8032 they are relatively common and primarily of interest to people
8033 debugging compilers. If you are interested in seeing information
8034 about ill-constructed symbol tables, you can either ask @value{GDBN} to print
8035 only one message about each such type of problem, no matter how many
8036 times the problem occurs; or you can ask @value{GDBN} to print more messages,
8037 to see how many times the problems occur, with the @code{set
8038 complaints} command (@pxref{Messages/Warnings, ,Optional warnings and
8041 The messages currently printed, and their meanings, include:
8044 @item inner block not inside outer block in @var{symbol}
8046 The symbol information shows where symbol scopes begin and end
8047 (such as at the start of a function or a block of statements). This
8048 error indicates that an inner scope block is not fully contained
8049 in its outer scope blocks.
8051 @value{GDBN} circumvents the problem by treating the inner block as if it had
8052 the same scope as the outer block. In the error message, @var{symbol}
8053 may be shown as ``@code{(don't know)}'' if the outer block is not a
8056 @item block at @var{address} out of order
8058 The symbol information for symbol scope blocks should occur in
8059 order of increasing addresses. This error indicates that it does not
8062 @value{GDBN} does not circumvent this problem, and has trouble
8063 locating symbols in the source file whose symbols it is reading. (You
8064 can often determine what source file is affected by specifying
8065 @code{set verbose on}. @xref{Messages/Warnings, ,Optional warnings and
8068 @item bad block start address patched
8070 The symbol information for a symbol scope block has a start address
8071 smaller than the address of the preceding source line. This is known
8072 to occur in the SunOS 4.1.1 (and earlier) C compiler.
8074 @value{GDBN} circumvents the problem by treating the symbol scope block as
8075 starting on the previous source line.
8077 @item bad string table offset in symbol @var{n}
8080 Symbol number @var{n} contains a pointer into the string table which is
8081 larger than the size of the string table.
8083 @value{GDBN} circumvents the problem by considering the symbol to have the
8084 name @code{foo}, which may cause other problems if many symbols end up
8087 @item unknown symbol type @code{0x@var{nn}}
8089 The symbol information contains new data types that @value{GDBN} does
8090 not yet know how to read. @code{0x@var{nn}} is the symbol type of the
8091 uncomprehended information, in hexadecimal.
8093 @value{GDBN} circumvents the error by ignoring this symbol information.
8094 This usually allows you to debug your program, though certain symbols
8095 are not accessible. If you encounter such a problem and feel like
8096 debugging it, you can debug @code{@value{GDBP}} with itself, breakpoint
8097 on @code{complain}, then go up to the function @code{read_dbx_symtab}
8098 and examine @code{*bufp} to see the symbol.
8100 @item stub type has NULL name
8102 @value{GDBN} could not find the full definition for a struct or class.
8104 @item const/volatile indicator missing (ok if using g++ v1.x), got@dots{}
8105 The symbol information for a C++ member function is missing some
8106 information that recent versions of the compiler should have output for
8109 @item info mismatch between compiler and debugger
8111 @value{GDBN} could not parse a type specification output by the compiler.
8116 @chapter Specifying a Debugging Target
8118 @cindex debugging target
8121 A @dfn{target} is the execution environment occupied by your program.
8123 Often, @value{GDBN} runs in the same host environment as your program;
8124 in that case, the debugging target is specified as a side effect when
8125 you use the @code{file} or @code{core} commands. When you need more
8126 flexibility---for example, running @value{GDBN} on a physically separate
8127 host, or controlling a standalone system over a serial port or a
8128 realtime system over a TCP/IP connection---you can use the @code{target}
8129 command to specify one of the target types configured for @value{GDBN}
8130 (@pxref{Target Commands, ,Commands for managing targets}).
8133 * Active Targets:: Active targets
8134 * Target Commands:: Commands for managing targets
8135 * Byte Order:: Choosing target byte order
8136 * Remote:: Remote debugging
8137 * KOD:: Kernel Object Display
8141 @node Active Targets
8142 @section Active targets
8144 @cindex stacking targets
8145 @cindex active targets
8146 @cindex multiple targets
8148 There are three classes of targets: processes, core files, and
8149 executable files. @value{GDBN} can work concurrently on up to three
8150 active targets, one in each class. This allows you to (for example)
8151 start a process and inspect its activity without abandoning your work on
8154 For example, if you execute @samp{gdb a.out}, then the executable file
8155 @code{a.out} is the only active target. If you designate a core file as
8156 well---presumably from a prior run that crashed and coredumped---then
8157 @value{GDBN} has two active targets and uses them in tandem, looking
8158 first in the corefile target, then in the executable file, to satisfy
8159 requests for memory addresses. (Typically, these two classes of target
8160 are complementary, since core files contain only a program's
8161 read-write memory---variables and so on---plus machine status, while
8162 executable files contain only the program text and initialized data.)
8164 When you type @code{run}, your executable file becomes an active process
8165 target as well. When a process target is active, all @value{GDBN}
8166 commands requesting memory addresses refer to that target; addresses in
8167 an active core file or executable file target are obscured while the
8168 process target is active.
8170 Use the @code{core-file} and @code{exec-file} commands to select a new
8171 core file or executable target (@pxref{Files, ,Commands to specify
8172 files}). To specify as a target a process that is already running, use
8173 the @code{attach} command (@pxref{Attach, ,Debugging an already-running
8176 @node Target Commands
8177 @section Commands for managing targets
8180 @item target @var{type} @var{parameters}
8181 Connects the @value{GDBN} host environment to a target machine or
8182 process. A target is typically a protocol for talking to debugging
8183 facilities. You use the argument @var{type} to specify the type or
8184 protocol of the target machine.
8186 Further @var{parameters} are interpreted by the target protocol, but
8187 typically include things like device names or host names to connect
8188 with, process numbers, and baud rates.
8190 The @code{target} command does not repeat if you press @key{RET} again
8191 after executing the command.
8195 Displays the names of all targets available. To display targets
8196 currently selected, use either @code{info target} or @code{info files}
8197 (@pxref{Files, ,Commands to specify files}).
8199 @item help target @var{name}
8200 Describe a particular target, including any parameters necessary to
8203 @kindex set gnutarget
8204 @item set gnutarget @var{args}
8205 @value{GDBN} uses its own library BFD to read your files. @value{GDBN}
8206 knows whether it is reading an @dfn{executable},
8207 a @dfn{core}, or a @dfn{.o} file; however, you can specify the file format
8208 with the @code{set gnutarget} command. Unlike most @code{target} commands,
8209 with @code{gnutarget} the @code{target} refers to a program, not a machine.
8212 @emph{Warning:} To specify a file format with @code{set gnutarget},
8213 you must know the actual BFD name.
8217 @xref{Files, , Commands to specify files}.
8219 @kindex show gnutarget
8220 @item show gnutarget
8221 Use the @code{show gnutarget} command to display what file format
8222 @code{gnutarget} is set to read. If you have not set @code{gnutarget},
8223 @value{GDBN} will determine the file format for each file automatically,
8224 and @code{show gnutarget} displays @samp{The current BDF target is "auto"}.
8227 Here are some common targets (available, or not, depending on the GDB
8232 @item target exec @var{program}
8233 An executable file. @samp{target exec @var{program}} is the same as
8234 @samp{exec-file @var{program}}.
8237 @item target core @var{filename}
8238 A core dump file. @samp{target core @var{filename}} is the same as
8239 @samp{core-file @var{filename}}.
8241 @kindex target remote
8242 @item target remote @var{dev}
8243 Remote serial target in GDB-specific protocol. The argument @var{dev}
8244 specifies what serial device to use for the connection (e.g.
8245 @file{/dev/ttya}). @xref{Remote, ,Remote debugging}. @code{target remote}
8246 supports the @code{load} command. This is only useful if you have
8247 some other way of getting the stub to the target system, and you can put
8248 it somewhere in memory where it won't get clobbered by the download.
8252 Builtin CPU simulator. @value{GDBN} includes simulators for most architectures.
8260 works; however, you cannot assume that a specific memory map, device
8261 drivers, or even basic I/O is available, although some simulators do
8262 provide these. For info about any processor-specific simulator details,
8263 see the appropriate section in @ref{Embedded Processors, ,Embedded
8268 Some configurations may include these targets as well:
8273 @item target nrom @var{dev}
8274 NetROM ROM emulator. This target only supports downloading.
8278 Different targets are available on different configurations of @value{GDBN};
8279 your configuration may have more or fewer targets.
8281 Many remote targets require you to download the executable's code
8282 once you've successfully established a connection.
8286 @kindex load @var{filename}
8287 @item load @var{filename}
8288 Depending on what remote debugging facilities are configured into
8289 @value{GDBN}, the @code{load} command may be available. Where it exists, it
8290 is meant to make @var{filename} (an executable) available for debugging
8291 on the remote system---by downloading, or dynamic linking, for example.
8292 @code{load} also records the @var{filename} symbol table in @value{GDBN}, like
8293 the @code{add-symbol-file} command.
8295 If your @value{GDBN} does not have a @code{load} command, attempting to
8296 execute it gets the error message ``@code{You can't do that when your
8297 target is @dots{}}''
8299 The file is loaded at whatever address is specified in the executable.
8300 For some object file formats, you can specify the load address when you
8301 link the program; for other formats, like a.out, the object file format
8302 specifies a fixed address.
8303 @c FIXME! This would be a good place for an xref to the GNU linker doc.
8305 @code{load} does not repeat if you press @key{RET} again after using it.
8309 @section Choosing target byte order
8311 @cindex choosing target byte order
8312 @cindex target byte order
8313 @kindex set endian big
8314 @kindex set endian little
8315 @kindex set endian auto
8318 Some types of processors, such as the MIPS, PowerPC, and Hitachi SH,
8319 offer the ability to run either big-endian or little-endian byte
8320 orders. Usually the executable or symbol will include a bit to
8321 designate the endian-ness, and you will not need to worry about
8322 which to use. However, you may still find it useful to adjust
8323 @value{GDBN}'s idea of processor endian-ness manually.
8326 @kindex set endian big
8327 @item set endian big
8328 Instruct @value{GDBN} to assume the target is big-endian.
8330 @kindex set endian little
8331 @item set endian little
8332 Instruct @value{GDBN} to assume the target is little-endian.
8334 @kindex set endian auto
8335 @item set endian auto
8336 Instruct @value{GDBN} to use the byte order associated with the
8340 Display @value{GDBN}'s current idea of the target byte order.
8344 Note that these commands merely adjust interpretation of symbolic
8345 data on the host, and that they have absolutely no effect on the
8349 @section Remote debugging
8350 @cindex remote debugging
8352 If you are trying to debug a program running on a machine that cannot run
8353 @value{GDBN} in the usual way, it is often useful to use remote debugging.
8354 For example, you might use remote debugging on an operating system kernel,
8355 or on a small system which does not have a general purpose operating system
8356 powerful enough to run a full-featured debugger.
8358 Some configurations of @value{GDBN} have special serial or TCP/IP interfaces
8359 to make this work with particular debugging targets. In addition,
8360 @value{GDBN} comes with a generic serial protocol (specific to @value{GDBN},
8361 but not specific to any particular target system) which you can use if you
8362 write the remote stubs---the code that runs on the remote system to
8363 communicate with @value{GDBN}.
8365 Other remote targets may be available in your
8366 configuration of @value{GDBN}; use @code{help target} to list them.
8369 * Remote Serial:: @value{GDBN} remote serial protocol
8373 @subsection The @value{GDBN} remote serial protocol
8375 @cindex remote serial debugging, overview
8376 To debug a program running on another machine (the debugging
8377 @dfn{target} machine), you must first arrange for all the usual
8378 prerequisites for the program to run by itself. For example, for a C
8383 A startup routine to set up the C runtime environment; these usually
8384 have a name like @file{crt0}. The startup routine may be supplied by
8385 your hardware supplier, or you may have to write your own.
8388 A C subroutine library to support your program's
8389 subroutine calls, notably managing input and output.
8392 A way of getting your program to the other machine---for example, a
8393 download program. These are often supplied by the hardware
8394 manufacturer, but you may have to write your own from hardware
8398 The next step is to arrange for your program to use a serial port to
8399 communicate with the machine where @value{GDBN} is running (the @dfn{host}
8400 machine). In general terms, the scheme looks like this:
8404 @value{GDBN} already understands how to use this protocol; when everything
8405 else is set up, you can simply use the @samp{target remote} command
8406 (@pxref{Targets,,Specifying a Debugging Target}).
8408 @item On the target,
8409 you must link with your program a few special-purpose subroutines that
8410 implement the @value{GDBN} remote serial protocol. The file containing these
8411 subroutines is called a @dfn{debugging stub}.
8413 On certain remote targets, you can use an auxiliary program
8414 @code{gdbserver} instead of linking a stub into your program.
8415 @xref{Server,,Using the @code{gdbserver} program}, for details.
8418 The debugging stub is specific to the architecture of the remote
8419 machine; for example, use @file{sparc-stub.c} to debug programs on
8422 @cindex remote serial stub list
8423 These working remote stubs are distributed with @value{GDBN}:
8431 For Intel 386 and compatible architectures.
8435 @cindex Motorola 680x0
8437 For Motorola 680x0 architectures.
8443 For Hitachi SH architectures.
8446 @kindex sparc-stub.c
8448 For @sc{sparc} architectures.
8451 @kindex sparcl-stub.c
8454 For Fujitsu @sc{sparclite} architectures.
8458 The @file{README} file in the @value{GDBN} distribution may list other
8459 recently added stubs.
8462 * Stub Contents:: What the stub can do for you
8463 * Bootstrapping:: What you must do for the stub
8464 * Debug Session:: Putting it all together
8465 * Protocol:: Definition of the communication protocol
8466 * Server:: Using the `gdbserver' program
8467 * NetWare:: Using the `gdbserve.nlm' program
8471 @subsubsection What the stub can do for you
8473 @cindex remote serial stub
8474 The debugging stub for your architecture supplies these three
8478 @item set_debug_traps
8479 @kindex set_debug_traps
8480 @cindex remote serial stub, initialization
8481 This routine arranges for @code{handle_exception} to run when your
8482 program stops. You must call this subroutine explicitly near the
8483 beginning of your program.
8485 @item handle_exception
8486 @kindex handle_exception
8487 @cindex remote serial stub, main routine
8488 This is the central workhorse, but your program never calls it
8489 explicitly---the setup code arranges for @code{handle_exception} to
8490 run when a trap is triggered.
8492 @code{handle_exception} takes control when your program stops during
8493 execution (for example, on a breakpoint), and mediates communications
8494 with @value{GDBN} on the host machine. This is where the communications
8495 protocol is implemented; @code{handle_exception} acts as the @value{GDBN}
8496 representative on the target machine. It begins by sending summary
8497 information on the state of your program, then continues to execute,
8498 retrieving and transmitting any information @value{GDBN} needs, until you
8499 execute a @value{GDBN} command that makes your program resume; at that point,
8500 @code{handle_exception} returns control to your own code on the target
8504 @cindex @code{breakpoint} subroutine, remote
8505 Use this auxiliary subroutine to make your program contain a
8506 breakpoint. Depending on the particular situation, this may be the only
8507 way for @value{GDBN} to get control. For instance, if your target
8508 machine has some sort of interrupt button, you won't need to call this;
8509 pressing the interrupt button transfers control to
8510 @code{handle_exception}---in effect, to @value{GDBN}. On some machines,
8511 simply receiving characters on the serial port may also trigger a trap;
8512 again, in that situation, you don't need to call @code{breakpoint} from
8513 your own program---simply running @samp{target remote} from the host
8514 @value{GDBN} session gets control.
8516 Call @code{breakpoint} if none of these is true, or if you simply want
8517 to make certain your program stops at a predetermined point for the
8518 start of your debugging session.
8522 @subsubsection What you must do for the stub
8524 @cindex remote stub, support routines
8525 The debugging stubs that come with @value{GDBN} are set up for a particular
8526 chip architecture, but they have no information about the rest of your
8527 debugging target machine.
8529 First of all you need to tell the stub how to communicate with the
8533 @item int getDebugChar()
8534 @kindex getDebugChar
8535 Write this subroutine to read a single character from the serial port.
8536 It may be identical to @code{getchar} for your target system; a
8537 different name is used to allow you to distinguish the two if you wish.
8539 @item void putDebugChar(int)
8540 @kindex putDebugChar
8541 Write this subroutine to write a single character to the serial port.
8542 It may be identical to @code{putchar} for your target system; a
8543 different name is used to allow you to distinguish the two if you wish.
8546 @cindex control C, and remote debugging
8547 @cindex interrupting remote targets
8548 If you want @value{GDBN} to be able to stop your program while it is
8549 running, you need to use an interrupt-driven serial driver, and arrange
8550 for it to stop when it receives a @code{^C} (@samp{\003}, the control-C
8551 character). That is the character which @value{GDBN} uses to tell the
8552 remote system to stop.
8554 Getting the debugging target to return the proper status to @value{GDBN}
8555 probably requires changes to the standard stub; one quick and dirty way
8556 is to just execute a breakpoint instruction (the ``dirty'' part is that
8557 @value{GDBN} reports a @code{SIGTRAP} instead of a @code{SIGINT}).
8559 Other routines you need to supply are:
8562 @item void exceptionHandler (int @var{exception_number}, void *@var{exception_address})
8563 @kindex exceptionHandler
8564 Write this function to install @var{exception_address} in the exception
8565 handling tables. You need to do this because the stub does not have any
8566 way of knowing what the exception handling tables on your target system
8567 are like (for example, the processor's table might be in @sc{rom},
8568 containing entries which point to a table in @sc{ram}).
8569 @var{exception_number} is the exception number which should be changed;
8570 its meaning is architecture-dependent (for example, different numbers
8571 might represent divide by zero, misaligned access, etc). When this
8572 exception occurs, control should be transferred directly to
8573 @var{exception_address}, and the processor state (stack, registers,
8574 and so on) should be just as it is when a processor exception occurs. So if
8575 you want to use a jump instruction to reach @var{exception_address}, it
8576 should be a simple jump, not a jump to subroutine.
8578 For the 386, @var{exception_address} should be installed as an interrupt
8579 gate so that interrupts are masked while the handler runs. The gate
8580 should be at privilege level 0 (the most privileged level). The
8581 @sc{sparc} and 68k stubs are able to mask interrupts themselves without
8582 help from @code{exceptionHandler}.
8584 @item void flush_i_cache()
8585 @kindex flush_i_cache
8586 On @sc{sparc} and @sc{sparclite} only, write this subroutine to flush the
8587 instruction cache, if any, on your target machine. If there is no
8588 instruction cache, this subroutine may be a no-op.
8590 On target machines that have instruction caches, @value{GDBN} requires this
8591 function to make certain that the state of your program is stable.
8595 You must also make sure this library routine is available:
8598 @item void *memset(void *, int, int)
8600 This is the standard library function @code{memset} that sets an area of
8601 memory to a known value. If you have one of the free versions of
8602 @code{libc.a}, @code{memset} can be found there; otherwise, you must
8603 either obtain it from your hardware manufacturer, or write your own.
8606 If you do not use the GNU C compiler, you may need other standard
8607 library subroutines as well; this varies from one stub to another,
8608 but in general the stubs are likely to use any of the common library
8609 subroutines which @code{@value{GCC}} generates as inline code.
8613 @subsubsection Putting it all together
8615 @cindex remote serial debugging summary
8616 In summary, when your program is ready to debug, you must follow these
8621 Make sure you have the supporting low-level routines
8622 (@pxref{Bootstrapping,,What you must do for the stub}):
8624 @code{getDebugChar}, @code{putDebugChar},
8625 @code{flush_i_cache}, @code{memset}, @code{exceptionHandler}.
8629 Insert these lines near the top of your program:
8637 For the 680x0 stub only, you need to provide a variable called
8638 @code{exceptionHook}. Normally you just use:
8641 void (*exceptionHook)() = 0;
8645 but if before calling @code{set_debug_traps}, you set it to point to a
8646 function in your program; that function is called when
8647 @code{@value{GDBN}} continues after stopping on a trap (for example, bus
8648 error). The function indicated by @code{exceptionHook} is called with
8649 one parameter: an @code{int} which is the exception number.
8652 Compile and link together: your program, the @value{GDBN} debugging stub for
8653 your target architecture, and the supporting subroutines.
8656 Make sure you have a serial connection between your target machine and
8657 the @value{GDBN} host, and identify the serial port on the host.
8660 @c The "remote" target now provides a `load' command, so we should
8661 @c document that. FIXME.
8662 Download your program to your target machine (or get it there by
8663 whatever means the manufacturer provides), and start it.
8666 To start remote debugging, run @value{GDBN} on the host machine, and specify
8667 as an executable file the program that is running in the remote machine.
8668 This tells @value{GDBN} how to find your program's symbols and the contents
8672 @cindex serial line, @code{target remote}
8673 Establish communication using the @code{target remote} command.
8674 Its argument specifies how to communicate with the target
8675 machine---either via a devicename attached to a direct serial line, or a
8676 TCP port (usually to a terminal server which in turn has a serial line
8677 to the target). For example, to use a serial line connected to the
8678 device named @file{/dev/ttyb}:
8681 target remote /dev/ttyb
8684 @cindex TCP port, @code{target remote}
8685 To use a TCP connection, use an argument of the form
8686 @code{@var{host}:port}. For example, to connect to port 2828 on a
8687 terminal server named @code{manyfarms}:
8690 target remote manyfarms:2828
8694 Now you can use all the usual commands to examine and change data and to
8695 step and continue the remote program.
8697 To resume the remote program and stop debugging it, use the @code{detach}
8700 @cindex interrupting remote programs
8701 @cindex remote programs, interrupting
8702 Whenever @value{GDBN} is waiting for the remote program, if you type the
8703 interrupt character (often @key{C-C}), @value{GDBN} attempts to stop the
8704 program. This may or may not succeed, depending in part on the hardware
8705 and the serial drivers the remote system uses. If you type the
8706 interrupt character once again, @value{GDBN} displays this prompt:
8709 Interrupted while waiting for the program.
8710 Give up (and stop debugging it)? (y or n)
8713 If you type @kbd{y}, @value{GDBN} abandons the remote debugging session.
8714 (If you decide you want to try again later, you can use @samp{target
8715 remote} again to connect once more.) If you type @kbd{n}, @value{GDBN}
8716 goes back to waiting.
8719 @subsubsection Communication protocol
8721 @cindex debugging stub, example
8722 @cindex remote stub, example
8723 @cindex stub example, remote debugging
8724 The stub files provided with @value{GDBN} implement the target side of the
8725 communication protocol, and the @value{GDBN} side is implemented in the
8726 @value{GDBN} source file @file{remote.c}. Normally, you can simply allow
8727 these subroutines to communicate, and ignore the details. (If you're
8728 implementing your own stub file, you can still ignore the details: start
8729 with one of the existing stub files. @file{sparc-stub.c} is the best
8730 organized, and therefore the easiest to read.)
8732 However, there may be occasions when you need to know something about
8733 the protocol---for example, if there is only one serial port to your
8734 target machine, you might want your program to do something special if
8735 it recognizes a packet meant for @value{GDBN}.
8737 In the examples below, @samp{<-} and @samp{->} are used to indicate
8738 transmitted and received data respectfully.
8740 @cindex protocol, @value{GDBN} remote serial
8741 @cindex serial protocol, @value{GDBN} remote
8742 @cindex remote serial protocol
8743 All @value{GDBN} commands and responses (other than acknowledgments)
8744 are sent as a @var{packet}. A @var{packet} is introduced with the
8745 character @samp{$}, this is followed by an optional two-digit
8746 @var{sequence-id} and the character @samp{:}, the actual
8747 @var{packet-data}, and the terminating character @samp{#} followed by a
8748 two-digit @var{checksum}:
8751 @code{$}@var{packet-data}@code{#}@var{checksum}
8754 or, with the optional @var{sequence-id}:
8756 @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
8759 @cindex checksum, for @value{GDBN} remote
8761 The two-digit @var{checksum} is computed as the modulo 256 sum of all
8762 characters between the leading @samp{$} and the trailing @samp{#} (that
8763 consisting of both the optional @var{sequence-id}@code{:} and the actual
8764 @var{packet-data}) (an eight bit unsigned checksum).
8766 @cindex sequence-id, for @value{GDBN} remote
8768 The two-digit @var{sequence-id}, when present, is returned with the
8769 acknowledgment. Beyond that its meaning is poorly defined.
8770 @value{GDBN} is not known to output @var{sequence-id}s.
8772 When either the host or the target machine receives a packet, the first
8773 response expected is an acknowledgment: either @samp{+} (to indicate
8774 the package was received correctly) or @samp{-} (to request
8778 <- @code{$}@var{packet-data}@code{#}@var{checksum}
8782 If the received packet included a @var{sequence-id} than that is
8783 appended to a positive acknowledgment:
8786 <- @code{$}@var{sequence-id}@code{:}@var{packet-data}@code{#}@var{checksum}
8787 -> @code{+}@var{sequence-id}
8790 The host (@value{GDBN}) sends @var{command}s, and the target (the
8791 debugging stub incorporated in your program) sends a @var{response}. In
8792 the case of step and continue @var{command}s, the response is only sent
8793 when the operation has completed (the target has again stopped).
8795 @var{packet-data} consists of a sequence of characters with the
8796 exception of @samp{#} and @samp{$} (see @samp{X} packet for an
8797 exception). @samp{:} can not appear as the third character in a packet.
8798 Fields within the packet should be separated using @samp{,} and @samp{;}
8799 (unfortunately some packets chose to use @samp{:}). Except where
8800 otherwise noted all numbers are represented in HEX with leading zeros
8803 Response @var{data} can be run-length encoded to save space. A @samp{*}
8804 means that the next character is an @sc{ascii} encoding giving a repeat count
8805 which stands for that many repetitions of the character preceding the
8806 @samp{*}. The encoding is @code{n+29}, yielding a printable character
8807 where @code{n >=3} (which is where rle starts to win). The printable
8808 characters @samp{$}, @samp{#}, @samp{+} and @samp{-} or with a numeric
8809 value greater than 126 should not be used.
8811 Some remote systems have used a different run-length encoding mechanism
8812 loosely refered to as the cisco encoding. Following the @samp{*}
8813 character are two hex digits that indicate the size of the packet.
8820 means the same as "0000".
8822 The error response, returned for some packets includes a two character
8823 error number. That number is not well defined.
8825 For any @var{command} not supported by the stub, an empty response
8826 (@samp{$#00}) should be returned. That way it is possible to extend the
8827 protocol. A newer @value{GDBN} can tell if a packet is supported based
8830 Below is a complete list of all currently defined @var{command}s and
8831 their corresponding response @var{data}:
8833 @multitable @columnfractions .30 .30 .40
8838 @item extended ops @emph{(optional)}
8841 Use the extended remote protocol. Sticky---only needs to be set once.
8842 The extended remote protocol support the @samp{R} packet.
8846 Stubs that support the extended remote protocol return @samp{} which,
8847 unfortunately, is identical to the response returned by stubs that do not
8848 support protocol extensions.
8853 Indicate the reason the target halted. The reply is the same as for step
8862 @tab Reserved for future use
8864 @item set program arguments @strong{(reserved)} @emph{(optional)}
8865 @tab @code{A}@var{arglen}@code{,}@var{argnum}@code{,}@var{arg}@code{,...}
8867 Initialized @samp{argv[]} array passed into program. @var{arglen}
8868 specifies the number of bytes in the hex encoded byte stream @var{arg}.
8869 See @file{gdbserver} for more details.
8871 @tab reply @code{OK}
8873 @tab reply @code{E}@var{NN}
8875 @item set baud @strong{(deprecated)}
8876 @tab @code{b}@var{baud}
8878 Change the serial line speed to @var{baud}. JTC: @emph{When does the
8879 transport layer state change? When it's received, or after the ACK is
8880 transmitted. In either case, there are problems if the command or the
8881 acknowledgment packet is dropped.} Stan: @emph{If people really wanted
8882 to add something like this, and get it working for the first time, they
8883 ought to modify ser-unix.c to send some kind of out-of-band message to a
8884 specially-setup stub and have the switch happen "in between" packets, so
8885 that from remote protocol's point of view, nothing actually
8888 @item set breakpoint @strong{(deprecated)}
8889 @tab @code{B}@var{addr},@var{mode}
8891 Set (@var{mode} is @samp{S}) or clear (@var{mode} is @samp{C}) a
8892 breakpoint at @var{addr}. @emph{This has been replaced by the @samp{Z} and
8896 @tab @code{c}@var{addr}
8898 @var{addr} is address to resume. If @var{addr} is omitted, resume at
8904 @item continue with signal @emph{(optional)}
8905 @tab @code{C}@var{sig}@code{;}@var{addr}
8907 Continue with signal @var{sig} (hex signal number). If
8908 @code{;}@var{addr} is omitted, resume at same address.
8913 @item toggle debug @emph{(deprecated)}
8918 @item detach @emph{(optional)}
8921 Detach @value{GDBN} from the remote system. Sent to the remote target before
8922 @value{GDBN} disconnects.
8924 @tab reply @emph{no response}
8926 @value{GDBN} does not check for any response after sending this packet
8930 @tab Reserved for future use
8934 @tab Reserved for future use
8938 @tab Reserved for future use
8942 @tab Reserved for future use
8944 @item read registers
8946 @tab Read general registers.
8948 @tab reply @var{XX...}
8950 Each byte of register data is described by two hex digits. The bytes
8951 with the register are transmitted in target byte order. The size of
8952 each register and their position within the @samp{g} @var{packet} are
8953 determined by the @value{GDBN} internal macros @var{REGISTER_RAW_SIZE} and
8954 @var{REGISTER_NAME} macros. The specification of several standard
8955 @code{g} packets is specified below.
8957 @tab @code{E}@var{NN}
8961 @tab @code{G}@var{XX...}
8963 See @samp{g} for a description of the @var{XX...} data.
8965 @tab reply @code{OK}
8968 @tab reply @code{E}@var{NN}
8973 @tab Reserved for future use
8975 @item set thread @emph{(optional)}
8976 @tab @code{H}@var{c}@var{t...}
8978 Set thread for subsequent operations (@samp{m}, @samp{M}, @samp{g},
8979 @samp{G}, et.al.). @var{c} = @samp{c} for thread used in step and
8980 continue; @var{t...} can be -1 for all threads. @var{c} = @samp{g} for
8981 thread used in other operations. If zero, pick a thread, any thread.
8983 @tab reply @code{OK}
8986 @tab reply @code{E}@var{NN}
8990 @c 'H': How restrictive (or permissive) is the thread model. If a
8991 @c thread is selected and stopped, are other threads allowed
8992 @c to continue to execute? As I mentioned above, I think the
8993 @c semantics of each command when a thread is selected must be
8994 @c described. For example:
8996 @c 'g': If the stub supports threads and a specific thread is
8997 @c selected, returns the register block from that thread;
8998 @c otherwise returns current registers.
9000 @c 'G' If the stub supports threads and a specific thread is
9001 @c selected, sets the registers of the register block of
9002 @c that thread; otherwise sets current registers.
9004 @item cycle step @strong{(draft)} @emph{(optional)}
9005 @tab @code{i}@var{addr}@code{,}@var{nnn}
9007 Step the remote target by a single clock cycle. If @code{,}@var{nnn} is
9008 present, cycle step @var{nnn} cycles. If @var{addr} is present, cycle
9009 step starting at that address.
9011 @item signal then cycle step @strong{(reserved)} @emph{(optional)}
9014 See @samp{i} and @samp{S} for likely syntax and semantics.
9018 @tab Reserved for future use
9022 @tab Reserved for future use
9024 @item kill request @emph{(optional)}
9027 FIXME: @emph{There is no description of how operate when a specific
9028 thread context has been selected (ie. does 'k' kill only that thread?)}.
9032 @tab Reserved for future use
9036 @tab Reserved for future use
9039 @tab @code{m}@var{addr}@code{,}@var{length}
9041 Read @var{length} bytes of memory starting at address @var{addr}.
9042 Neither @value{GDBN} nor the stub assume that sized memory transfers are assumed
9043 using word alligned accesses. FIXME: @emph{A word aligned memory
9044 transfer mechanism is needed.}
9046 @tab reply @var{XX...}
9048 @var{XX...} is mem contents. Can be fewer bytes than requested if able
9049 to read only part of the data. Neither @value{GDBN} nor the stub assume that
9050 sized memory transfers are assumed using word alligned accesses. FIXME:
9051 @emph{A word aligned memory transfer mechanism is needed.}
9053 @tab reply @code{E}@var{NN}
9054 @tab @var{NN} is errno
9057 @tab @code{M}@var{addr},@var{length}@code{:}@var{XX...}
9059 Write @var{length} bytes of memory starting at address @var{addr}.
9060 @var{XX...} is the data.
9062 @tab reply @code{OK}
9065 @tab reply @code{E}@var{NN}
9067 for an error (this includes the case where only part of the data was
9072 @tab Reserved for future use
9076 @tab Reserved for future use
9080 @tab Reserved for future use
9084 @tab Reserved for future use
9086 @item read reg @strong{(reserved)}
9087 @tab @code{p}@var{n...}
9091 @tab return @var{r....}
9092 @tab The hex encoded value of the register in target byte order.
9094 @item write reg @emph{(optional)}
9095 @tab @code{P}@var{n...}@code{=}@var{r...}
9097 Write register @var{n...} with value @var{r...}, which contains two hex
9098 digits for each byte in the register (target byte order).
9100 @tab reply @code{OK}
9103 @tab reply @code{E}@var{NN}
9106 @item general query @emph{(optional)}
9107 @tab @code{q}@var{query}
9109 Request info about @var{query}. In general @value{GDBN} @var{query}'s
9110 have a leading upper case letter. Custom vendor queries should use a
9111 company prefix (in lower case) ex: @samp{qfsf.var}. @var{query} may
9112 optionally be followed by a @samp{,} or @samp{;} separated list. Stubs
9113 must ensure that they match the full @var{query} name.
9115 @tab reply @code{XX...}
9116 @tab Hex encoded data from query. The reply can not be empty.
9118 @tab reply @code{E}@var{NN}
9122 @tab Indicating an unrecognized @var{query}.
9124 @item general set @emph{(optional)}
9125 @tab @code{Q}@var{var}@code{=}@var{val}
9127 Set value of @var{var} to @var{val}. See @samp{q} for a discussing of
9130 @item reset @emph{(deprecated)}
9133 Reset the entire system.
9135 @item remote restart @emph{(optional)}
9136 @tab @code{R}@var{XX}
9138 Restart the remote server. @var{XX} while needed has no clear
9139 definition. FIXME: @emph{An example interaction explaining how this
9140 packet is used in extended-remote mode is needed}.
9142 @item step @emph{(optional)}
9143 @tab @code{s}@var{addr}
9145 @var{addr} is address to resume. If @var{addr} is omitted, resume at
9151 @item step with signal @emph{(optional)}
9152 @tab @code{S}@var{sig}@code{;}@var{addr}
9154 Like @samp{C} but step not continue.
9159 @item search @emph{(optional)}
9160 @tab @code{t}@var{addr}@code{:}@var{PP}@code{,}@var{MM}
9162 Search backwards starting at address @var{addr} for a match with pattern
9163 @var{PP} and mask @var{MM}. @var{PP} and @var{MM} are 4
9164 bytes. @var{addr} must be at least 3 digits.
9166 @item thread alive @emph{(optional)}
9167 @tab @code{T}@var{XX}
9168 @tab Find out if the thread XX is alive.
9170 @tab reply @code{OK}
9171 @tab thread is still alive
9173 @tab reply @code{E}@var{NN}
9178 @tab Reserved for future use
9182 @tab Reserved for future use
9186 @tab Reserved for future use
9190 @tab Reserved for future use
9194 @tab Reserved for future use
9198 @tab Reserved for future use
9202 @tab Reserved for future use
9204 @item write mem (binary) @emph{(optional)}
9205 @tab @code{X}@var{addr}@code{,}@var{length}@var{:}@var{XX...}
9207 @var{addr} is address, @var{length} is number of bytes, @var{XX...} is
9208 binary data. The characters @code{$}, @code{#}, and @code{0x7d} are
9209 escaped using @code{0x7d}.
9211 @tab reply @code{OK}
9214 @tab reply @code{E}@var{NN}
9219 @tab Reserved for future use
9223 @tab Reserved for future use
9225 @item remove break or watchpoint @strong{(draft)} @emph{(optional)}
9226 @tab @code{z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9230 @item insert break or watchpoint @strong{(draft)} @emph{(optional)}
9231 @tab @code{Z}@var{t}@code{,}@var{addr}@code{,}@var{length}
9233 @var{t} is type: @samp{0} - software breakpoint, @samp{1} - hardware
9234 breakpoint, @samp{2} - write watchpoint, @samp{3} - read watchpoint,
9235 @samp{4} - access watchpoint; @var{addr} is address; @var{length} is in
9236 bytes. For a software breakpoint, @var{length} specifies the size of
9237 the instruction to be patched. For hardware breakpoints and watchpoints
9238 @var{length} specifies the memory region to be monitored. To avoid
9239 potential problems with duplicate packets, the operations should be
9240 implemented in an ident-potentent way.
9242 @tab reply @code{E}@var{NN}
9245 @tab reply @code{OK}
9249 @tab If not supported.
9253 @tab Reserved for future use
9257 The @samp{C}, @samp{c}, @samp{S}, @samp{s} and @samp{?} packets can
9258 receive any of the below as a reply. In the case of the @samp{C},
9259 @samp{c}, @samp{S} and @samp{s} packets, that reply is only returned
9260 when the target halts. In the below the exact meaning of @samp{signal
9261 number} is poorly defined. In general one of the UNIX signal numbering
9262 conventions is used.
9264 @multitable @columnfractions .4 .6
9266 @item @code{S}@var{AA}
9267 @tab @var{AA} is the signal number
9269 @item @code{T}@var{AA}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}@var{n...}@code{:}@var{r...}@code{;}
9271 @var{AA} = two hex digit signal number; @var{n...} = register number
9272 (hex), @var{r...} = target byte ordered register contents, size defined
9273 by @code{REGISTER_RAW_SIZE}; @var{n...} = @samp{thread}, @var{r...} =
9274 thread process ID, this is a hex integer; @var{n...} = other string not
9275 starting with valid hex digit. @value{GDBN} should ignore this
9276 @var{n...}, @var{r...} pair and go on to the next. This way we can
9277 extend the protocol.
9279 @item @code{W}@var{AA}
9281 The process exited, and @var{AA} is the exit status. This is only
9282 applicable for certains sorts of targets.
9284 @item @code{X}@var{AA}
9286 The process terminated with signal @var{AA}.
9288 @item @code{N}@var{AA}@code{;}@var{tttttttt}@code{;}@var{dddddddd}@code{;}@var{bbbbbbbb} @strong{(obsolete)}
9290 @var{AA} = signal number; @var{tttttttt} = address of symbol "_start";
9291 @var{dddddddd} = base of data section; @var{bbbbbbbb} = base of bss
9292 section. @emph{Note: only used by Cisco Systems targets. The difference
9293 between this reply and the "qOffsets" query is that the 'N' packet may
9294 arrive spontaneously whereas the 'qOffsets' is a query initiated by the
9297 @item @code{O}@var{XX...}
9299 @var{XX...} is hex encoding of @sc{ascii} data. This can happen at any time
9300 while the program is running and the debugger should continue to wait
9305 The following set and query packets have already been defined.
9307 @multitable @columnfractions .2 .2 .6
9309 @item current thread
9310 @tab @code{q}@code{C}
9311 @tab Return the current thread id.
9313 @tab reply @code{QC}@var{pid}
9315 Where @var{pid} is a HEX encoded 16 bit process id.
9318 @tab Any other reply implies the old pid.
9320 @item compute CRC of memory block
9321 @tab @code{q}@code{CRC:}@var{addr}@code{,}@var{length}
9324 @tab reply @code{E}@var{NN}
9325 @tab An error (such as memory fault)
9327 @tab reply @code{C}@var{CRC32}
9328 @tab A 32 bit cyclic redundancy check of the specified memory region.
9330 @item query @var{LIST} or @var{threadLIST} @strong{(deprecated)}
9331 @tab @code{q}@code{L}@var{startflag}@var{threadcount}@var{nextthread}
9333 Obtain thread information from RTOS. Where: @var{startflag} (one hex
9334 digit) is one to indicate the first query and zero to indicate a
9335 subsequent query; @var{threadcount} (two hex digits) is the maximum
9336 number of threads the response packet can contain; and @var{nextthread}
9337 (eight hex digits), for subsequent queries (@var{startflag} is zero), is
9338 returned in the response as @var{argthread}.
9340 @tab reply @code{q}@code{M}@var{count}@var{done}@var{argthread}@var{thread...}
9342 Where: @var{count} (two hex digits) is the number of threads being
9343 returned; @var{done} (one hex digit) is zero to indicate more threads
9344 and one indicates no further threads; @var{argthreadid} (eight hex
9345 digits) is @var{nextthread} from the request packet; @var{thread...} is
9346 a sequence of thread IDs from the target. @var{threadid} (eight hex
9347 digits). See @code{remote.c:parse_threadlist_response()}.
9349 @item query sect offs
9350 @tab @code{q}@code{Offsets}
9352 Get section offsets that the target used when re-locating the downloaded
9353 image. @emph{Note: while a @code{Bss} offset is included in the
9354 response, @value{GDBN} ignores this and instead applies the @code{Data}
9355 offset to the @code{Bss} section.}
9357 @tab reply @code{Text=}@var{xxx}@code{;Data=}@var{yyy}@code{;Bss=}@var{zzz}
9359 @item thread info request
9360 @tab @code{q}@code{P}@var{mode}@var{threadid}
9362 Returns information on @var{threadid}. Where: @var{mode} is a hex
9363 encoded 32 bit mode; @var{threadid} is a hex encoded 64 bit thread ID.
9367 See @code{remote.c:remote_unpack_thread_info_response()}.
9369 @item remote command
9370 @tab @code{q}@code{Rcmd,}@var{COMMAND}
9372 @var{COMMAND} (hex encoded) is passed to the local interpreter for
9373 execution. Invalid commands should be reported using the output string.
9374 Before the final result packet, the target may also respond with a
9375 number of intermediate @code{O}@var{OUTPUT} console output
9376 packets. @emph{Implementors should note that providing access to a
9377 stubs's interpreter may have security implications}.
9379 @tab reply @code{OK}
9381 A command response with no output.
9383 @tab reply @var{OUTPUT}
9385 A command response with the hex encoded output string @var{OUTPUT}.
9387 @tab reply @code{E}@var{NN}
9389 Indicate a badly formed request.
9394 When @samp{q}@samp{Rcmd} is not recognized.
9398 The following @samp{g}/@samp{G} packets have previously been defined.
9399 In the below, some thirty-two bit registers are transferred as sixty-four
9400 bits. Those registers should be zero/sign extended (which?) to fill the
9401 space allocated. Register bytes are transfered in target byte order.
9402 The two nibbles within a register byte are transfered most-significant -
9405 @multitable @columnfractions .5 .5
9409 All registers are transfered as thirty-two bit quantities in the order:
9410 32 general-purpose; sr; lo; hi; bad; cause; pc; 32 floating-point
9411 registers; fsr; fir; fp.
9415 All registers are transfered as sixty-four bit quantities (including
9416 thirty-two bit registers such as @code{sr}). The ordering is the same
9421 Example sequence of a target being re-started. Notice how the restart
9422 does not get any direct output:
9427 @emph{target restarts}
9430 -> @code{T001:1234123412341234}
9434 Example sequence of a target being stepped by a single instruction:
9442 -> @code{T001:1234123412341234}
9450 @kindex set remotedebug@r{, serial protocol}
9451 @kindex show remotedebug@r{, serial protocol}
9452 @cindex packets, reporting on stdout
9453 @cindex serial connections, debugging
9454 If you have trouble with the serial connection, you can use the command
9455 @code{set remotedebug}. This makes @value{GDBN} report on all packets sent
9456 back and forth across the serial line to the remote machine. The
9457 packet-debugging information is printed on the @value{GDBN} standard output
9458 stream. @code{set remotedebug off} turns it off, and @code{show
9459 remotedebug} shows you its current state.
9462 @subsubsection Using the @code{gdbserver} program
9465 @cindex remote connection without stubs
9466 @code{gdbserver} is a control program for Unix-like systems, which
9467 allows you to connect your program with a remote @value{GDBN} via
9468 @code{target remote}---but without linking in the usual debugging stub.
9470 @code{gdbserver} is not a complete replacement for the debugging stubs,
9471 because it requires essentially the same operating-system facilities
9472 that @value{GDBN} itself does. In fact, a system that can run
9473 @code{gdbserver} to connect to a remote @value{GDBN} could also run
9474 @value{GDBN} locally! @code{gdbserver} is sometimes useful nevertheless,
9475 because it is a much smaller program than @value{GDBN} itself. It is
9476 also easier to port than all of @value{GDBN}, so you may be able to get
9477 started more quickly on a new system by using @code{gdbserver}.
9478 Finally, if you develop code for real-time systems, you may find that
9479 the tradeoffs involved in real-time operation make it more convenient to
9480 do as much development work as possible on another system, for example
9481 by cross-compiling. You can use @code{gdbserver} to make a similar
9482 choice for debugging.
9484 @value{GDBN} and @code{gdbserver} communicate via either a serial line
9485 or a TCP connection, using the standard @value{GDBN} remote serial
9489 @item On the target machine,
9490 you need to have a copy of the program you want to debug.
9491 @code{gdbserver} does not need your program's symbol table, so you can
9492 strip the program if necessary to save space. @value{GDBN} on the host
9493 system does all the symbol handling.
9495 To use the server, you must tell it how to communicate with @value{GDBN};
9496 the name of your program; and the arguments for your program. The
9500 target> gdbserver @var{comm} @var{program} [ @var{args} @dots{} ]
9503 @var{comm} is either a device name (to use a serial line) or a TCP
9504 hostname and portnumber. For example, to debug Emacs with the argument
9505 @samp{foo.txt} and communicate with @value{GDBN} over the serial port
9509 target> gdbserver /dev/com1 emacs foo.txt
9512 @code{gdbserver} waits passively for the host @value{GDBN} to communicate
9515 To use a TCP connection instead of a serial line:
9518 target> gdbserver host:2345 emacs foo.txt
9521 The only difference from the previous example is the first argument,
9522 specifying that you are communicating with the host @value{GDBN} via
9523 TCP. The @samp{host:2345} argument means that @code{gdbserver} is to
9524 expect a TCP connection from machine @samp{host} to local TCP port 2345.
9525 (Currently, the @samp{host} part is ignored.) You can choose any number
9526 you want for the port number as long as it does not conflict with any
9527 TCP ports already in use on the target system (for example, @code{23} is
9528 reserved for @code{telnet}).@footnote{If you choose a port number that
9529 conflicts with another service, @code{gdbserver} prints an error message
9530 and exits.} You must use the same port number with the host @value{GDBN}
9531 @code{target remote} command.
9533 @item On the @value{GDBN} host machine,
9534 you need an unstripped copy of your program, since @value{GDBN} needs
9535 symbols and debugging information. Start up @value{GDBN} as usual,
9536 using the name of the local copy of your program as the first argument.
9537 (You may also need the @w{@samp{--baud}} option if the serial line is
9538 running at anything other than 9600@dmn{bps}.) After that, use @code{target
9539 remote} to establish communications with @code{gdbserver}. Its argument
9540 is either a device name (usually a serial device, like
9541 @file{/dev/ttyb}), or a TCP port descriptor in the form
9542 @code{@var{host}:@var{PORT}}. For example:
9545 (@value{GDBP}) target remote /dev/ttyb
9549 communicates with the server via serial line @file{/dev/ttyb}, and
9552 (@value{GDBP}) target remote the-target:2345
9556 communicates via a TCP connection to port 2345 on host @w{@file{the-target}}.
9557 For TCP connections, you must start up @code{gdbserver} prior to using
9558 the @code{target remote} command. Otherwise you may get an error whose
9559 text depends on the host system, but which usually looks something like
9560 @samp{Connection refused}.
9564 @subsubsection Using the @code{gdbserve.nlm} program
9566 @kindex gdbserve.nlm
9567 @code{gdbserve.nlm} is a control program for NetWare systems, which
9568 allows you to connect your program with a remote @value{GDBN} via
9569 @code{target remote}.
9571 @value{GDBN} and @code{gdbserve.nlm} communicate via a serial line,
9572 using the standard @value{GDBN} remote serial protocol.
9575 @item On the target machine,
9576 you need to have a copy of the program you want to debug.
9577 @code{gdbserve.nlm} does not need your program's symbol table, so you
9578 can strip the program if necessary to save space. @value{GDBN} on the
9579 host system does all the symbol handling.
9581 To use the server, you must tell it how to communicate with
9582 @value{GDBN}; the name of your program; and the arguments for your
9583 program. The syntax is:
9586 load gdbserve [ BOARD=@var{board} ] [ PORT=@var{port} ]
9587 [ BAUD=@var{baud} ] @var{program} [ @var{args} @dots{} ]
9590 @var{board} and @var{port} specify the serial line; @var{baud} specifies
9591 the baud rate used by the connection. @var{port} and @var{node} default
9592 to 0, @var{baud} defaults to 9600@dmn{bps}.
9594 For example, to debug Emacs with the argument @samp{foo.txt}and
9595 communicate with @value{GDBN} over serial port number 2 or board 1
9596 using a 19200@dmn{bps} connection:
9599 load gdbserve BOARD=1 PORT=2 BAUD=19200 emacs foo.txt
9602 @item On the @value{GDBN} host machine,
9603 you need an unstripped copy of your program, since @value{GDBN} needs
9604 symbols and debugging information. Start up @value{GDBN} as usual,
9605 using the name of the local copy of your program as the first argument.
9606 (You may also need the @w{@samp{--baud}} option if the serial line is
9607 running at anything other than 9600@dmn{bps}. After that, use @code{target
9608 remote} to establish communications with @code{gdbserve.nlm}. Its
9609 argument is a device name (usually a serial device, like
9610 @file{/dev/ttyb}). For example:
9613 (@value{GDBP}) target remote /dev/ttyb
9617 communications with the server via serial line @file{/dev/ttyb}.
9621 @section Kernel Object Display
9623 @cindex kernel object display
9624 @cindex kernel object
9627 Some targets support kernel object display. Using this facility,
9628 @value{GDBN} communicates specially with the underlying operating system
9629 and can display information about operating system-level objects such as
9630 mutexes and other synchronization objects. Exactly which objects can be
9631 displayed is determined on a per-OS basis.
9633 Use the @code{set os} command to set the operating system. This tells
9634 @value{GDBN} which kernel object display module to initialize:
9637 (@value{GDBP}) set os cisco
9640 If @code{set os} succeeds, @value{GDBN} will display some information
9641 about the operating system, and will create a new @code{info} command
9642 which can be used to query the target. The @code{info} command is named
9643 after the operating system:
9646 (@value{GDBP}) info cisco
9647 List of Cisco Kernel Objects
9649 any Any and all objects
9652 Further subcommands can be used to query about particular objects known
9655 There is currently no way to determine whether a given operating system
9656 is supported other than to try it.
9659 @node Configurations
9660 @chapter Configuration-Specific Information
9662 While nearly all @value{GDBN} commands are available for all native and
9663 cross versions of the debugger, there are some exceptions. This chapter
9664 describes things that are only available in certain configurations.
9666 There are three major categories of configurations: native
9667 configurations, where the host and target are the same, embedded
9668 operating system configurations, which are usually the same for several
9669 different processor architectures, and bare embedded processors, which
9670 are quite different from each other.
9675 * Embedded Processors::
9682 This section describes details specific to particular native
9687 * SVR4 Process Information:: SVR4 process information
9693 On HP-UX systems, if you refer to a function or variable name that
9694 begins with a dollar sign, @value{GDBN} searches for a user or system
9695 name first, before it searches for a convenience variable.
9697 @node SVR4 Process Information
9698 @subsection SVR4 process information
9701 @cindex process image
9703 Many versions of SVR4 provide a facility called @samp{/proc} that can be
9704 used to examine the image of a running process using file-system
9705 subroutines. If @value{GDBN} is configured for an operating system with
9706 this facility, the command @code{info proc} is available to report on
9707 several kinds of information about the process running your program.
9708 @code{info proc} works only on SVR4 systems that include the
9709 @code{procfs} code. This includes OSF/1 (Digital Unix), Solaris, Irix,
9710 and Unixware, but not HP-UX or Linux, for example.
9715 Summarize available information about the process.
9717 @kindex info proc mappings
9718 @item info proc mappings
9719 Report on the address ranges accessible in the program, with information
9720 on whether your program may read, write, or execute each range.
9722 @kindex info proc times
9723 @item info proc times
9724 Starting time, user CPU time, and system CPU time for your program and
9727 @kindex info proc id
9729 Report on the process IDs related to your program: its own process ID,
9730 the ID of its parent, the process group ID, and the session ID.
9732 @kindex info proc status
9733 @item info proc status
9734 General information on the state of the process. If the process is
9735 stopped, this report includes the reason for stopping, and any signal
9739 Show all the above information about the process.
9743 @section Embedded Operating Systems
9745 This section describes configurations involving the debugging of
9746 embedded operating systems that are available for several different
9750 * VxWorks:: Using @value{GDBN} with VxWorks
9753 @value{GDBN} includes the ability to debug programs running on
9754 various real-time operating systems.
9757 @subsection Using @value{GDBN} with VxWorks
9763 @kindex target vxworks
9764 @item target vxworks @var{machinename}
9765 A VxWorks system, attached via TCP/IP. The argument @var{machinename}
9766 is the target system's machine name or IP address.
9770 On VxWorks, @code{load} links @var{filename} dynamically on the
9771 current target system as well as adding its symbols in @value{GDBN}.
9773 @value{GDBN} enables developers to spawn and debug tasks running on networked
9774 VxWorks targets from a Unix host. Already-running tasks spawned from
9775 the VxWorks shell can also be debugged. @value{GDBN} uses code that runs on
9776 both the Unix host and on the VxWorks target. The program
9777 @code{@value{GDBP}} is installed and executed on the Unix host. (It may be
9778 installed with the name @code{vxgdb}, to distinguish it from a
9779 @value{GDB} for debugging programs on the host itself.)
9782 @item VxWorks-timeout @var{args}
9783 @kindex vxworks-timeout
9784 All VxWorks-based targets now support the option @code{vxworks-timeout}.
9785 This option is set by the user, and @var{args} represents the number of
9786 seconds @value{GDBN} waits for responses to rpc's. You might use this if
9787 your VxWorks target is a slow software simulator or is on the far side
9788 of a thin network line.
9791 The following information on connecting to VxWorks was current when
9792 this manual was produced; newer releases of VxWorks may use revised
9796 To use @value{GDBN} with VxWorks, you must rebuild your VxWorks kernel
9797 to include the remote debugging interface routines in the VxWorks
9798 library @file{rdb.a}. To do this, define @code{INCLUDE_RDB} in the
9799 VxWorks configuration file @file{configAll.h} and rebuild your VxWorks
9800 kernel. The resulting kernel contains @file{rdb.a}, and spawns the
9801 source debugging task @code{tRdbTask} when VxWorks is booted. For more
9802 information on configuring and remaking VxWorks, see the manufacturer's
9804 @c VxWorks, see the @cite{VxWorks Programmer's Guide}.
9806 Once you have included @file{rdb.a} in your VxWorks system image and set
9807 your Unix execution search path to find @value{GDBN}, you are ready to
9808 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}} (or @code{vxgdb},
9809 depending on your installation).
9811 @value{GDBN} comes up showing the prompt:
9818 * VxWorks Connection:: Connecting to VxWorks
9819 * VxWorks Download:: VxWorks download
9820 * VxWorks Attach:: Running tasks
9823 @node VxWorks Connection
9824 @subsubsection Connecting to VxWorks
9826 The @value{GDBN} command @code{target} lets you connect to a VxWorks target on the
9827 network. To connect to a target whose host name is ``@code{tt}'', type:
9830 (vxgdb) target vxworks tt
9834 @value{GDBN} displays messages like these:
9837 Attaching remote machine across net...
9842 @value{GDBN} then attempts to read the symbol tables of any object modules
9843 loaded into the VxWorks target since it was last booted. @value{GDBN} locates
9844 these files by searching the directories listed in the command search
9845 path (@pxref{Environment, ,Your program's environment}); if it fails
9846 to find an object file, it displays a message such as:
9849 prog.o: No such file or directory.
9852 When this happens, add the appropriate directory to the search path with
9853 the @value{GDBN} command @code{path}, and execute the @code{target}
9856 @node VxWorks Download
9857 @subsubsection VxWorks download
9859 @cindex download to VxWorks
9860 If you have connected to the VxWorks target and you want to debug an
9861 object that has not yet been loaded, you can use the @value{GDBN}
9862 @code{load} command to download a file from Unix to VxWorks
9863 incrementally. The object file given as an argument to the @code{load}
9864 command is actually opened twice: first by the VxWorks target in order
9865 to download the code, then by @value{GDBN} in order to read the symbol
9866 table. This can lead to problems if the current working directories on
9867 the two systems differ. If both systems have NFS mounted the same
9868 filesystems, you can avoid these problems by using absolute paths.
9869 Otherwise, it is simplest to set the working directory on both systems
9870 to the directory in which the object file resides, and then to reference
9871 the file by its name, without any path. For instance, a program
9872 @file{prog.o} may reside in @file{@var{vxpath}/vw/demo/rdb} in VxWorks
9873 and in @file{@var{hostpath}/vw/demo/rdb} on the host. To load this
9874 program, type this on VxWorks:
9877 -> cd "@var{vxpath}/vw/demo/rdb"
9881 Then, in @value{GDBN}, type:
9884 (vxgdb) cd @var{hostpath}/vw/demo/rdb
9888 @value{GDBN} displays a response similar to this:
9891 Reading symbol data from wherever/vw/demo/rdb/prog.o... done.
9894 You can also use the @code{load} command to reload an object module
9895 after editing and recompiling the corresponding source file. Note that
9896 this makes @value{GDBN} delete all currently-defined breakpoints,
9897 auto-displays, and convenience variables, and to clear the value
9898 history. (This is necessary in order to preserve the integrity of
9899 debugger's data structures that reference the target system's symbol
9902 @node VxWorks Attach
9903 @subsubsection Running tasks
9905 @cindex running VxWorks tasks
9906 You can also attach to an existing task using the @code{attach} command as
9910 (vxgdb) attach @var{task}
9914 where @var{task} is the VxWorks hexadecimal task ID. The task can be running
9915 or suspended when you attach to it. Running tasks are suspended at
9916 the time of attachment.
9918 @node Embedded Processors
9919 @section Embedded Processors
9921 This section goes into details specific to particular embedded
9925 * A29K Embedded:: AMD A29K Embedded
9927 * H8/300:: Hitachi H8/300
9928 * H8/500:: Hitachi H8/500
9930 * M32R/D:: Mitsubishi M32R/D
9931 * M68K:: Motorola M68K
9932 * M88K:: Motorola M88K
9933 * MIPS Embedded:: MIPS Embedded
9934 * PA:: HP PA Embedded
9937 * Sparclet:: Tsqware Sparclet
9938 * Sparclite:: Fujitsu Sparclite
9939 * ST2000:: Tandem ST2000
9940 * Z8000:: Zilog Z8000
9944 @subsection AMD A29K Embedded
9949 * Comms (EB29K):: Communications setup
9950 * gdb-EB29K:: EB29K cross-debugging
9951 * Remote Log:: Remote log
9956 @kindex target adapt
9957 @item target adapt @var{dev}
9958 Adapt monitor for A29K.
9960 @kindex target amd-eb
9961 @item target amd-eb @var{dev} @var{speed} @var{PROG}
9963 Remote PC-resident AMD EB29K board, attached over serial lines.
9964 @var{dev} is the serial device, as for @code{target remote};
9965 @var{speed} allows you to specify the linespeed; and @var{PROG} is the
9966 name of the program to be debugged, as it appears to DOS on the PC.
9967 @xref{A29K EB29K, ,EBMON protocol for AMD29K}.
9972 @subsubsection A29K UDI
9975 @cindex AMD29K via UDI
9977 @value{GDBN} supports AMD's UDI (``Universal Debugger Interface'')
9978 protocol for debugging the a29k processor family. To use this
9979 configuration with AMD targets running the MiniMON monitor, you need the
9980 program @code{MONTIP}, available from AMD at no charge. You can also
9981 use @value{GDBN} with the UDI-conformant a29k simulator program
9982 @code{ISSTIP}, also available from AMD.
9985 @item target udi @var{keyword}
9987 Select the UDI interface to a remote a29k board or simulator, where
9988 @var{keyword} is an entry in the AMD configuration file @file{udi_soc}.
9989 This file contains keyword entries which specify parameters used to
9990 connect to a29k targets. If the @file{udi_soc} file is not in your
9991 working directory, you must set the environment variable @samp{UDICONF}
9996 @subsubsection EBMON protocol for AMD29K
9999 @cindex running 29K programs
10001 AMD distributes a 29K development board meant to fit in a PC, together
10002 with a DOS-hosted monitor program called @code{EBMON}. As a shorthand
10003 term, this development system is called the ``EB29K''. To use
10004 @value{GDBN} from a Unix system to run programs on the EB29K board, you
10005 must first connect a serial cable between the PC (which hosts the EB29K
10006 board) and a serial port on the Unix system. In the following, we
10007 assume you've hooked the cable between the PC's @file{COM1} port and
10008 @file{/dev/ttya} on the Unix system.
10010 @node Comms (EB29K)
10011 @subsubsection Communications setup
10013 The next step is to set up the PC's port, by doing something like this
10017 C:\> MODE com1:9600,n,8,1,none
10021 This example---run on an MS DOS 4.0 system---sets the PC port to 9600
10022 bps, no parity, eight data bits, one stop bit, and no ``retry'' action;
10023 you must match the communications parameters when establishing the Unix
10024 end of the connection as well.
10025 @c FIXME: Who knows what this "no retry action" crud from the DOS manual may
10026 @c mean? It's optional; leave it out? ---doc@cygnus.com, 25feb91
10028 @c It's optional, but it's unwise to omit it: who knows what is the
10029 @c default value set when the DOS machines boots? "No retry" means that
10030 @c the DOS serial device driver won't retry the operation if it fails;
10031 @c I understand that this is needed because the GDB serial protocol
10032 @c handles any errors and retransmissions itself. ---Eli Zaretskii, 3sep99
10034 To give control of the PC to the Unix side of the serial line, type
10035 the following at the DOS console:
10042 (Later, if you wish to return control to the DOS console, you can use
10043 the command @code{CTTY con}---but you must send it over the device that
10044 had control, in our example over the @file{COM1} serial line).
10046 From the Unix host, use a communications program such as @code{tip} or
10047 @code{cu} to communicate with the PC; for example,
10050 cu -s 9600 -l /dev/ttya
10054 The @code{cu} options shown specify, respectively, the linespeed and the
10055 serial port to use. If you use @code{tip} instead, your command line
10056 may look something like the following:
10059 tip -9600 /dev/ttya
10063 Your system may require a different name where we show
10064 @file{/dev/ttya} as the argument to @code{tip}. The communications
10065 parameters, including which port to use, are associated with the
10066 @code{tip} argument in the ``remote'' descriptions file---normally the
10067 system table @file{/etc/remote}.
10068 @c FIXME: What if anything needs doing to match the "n,8,1,none" part of
10069 @c the DOS side's comms setup? cu can support -o (odd
10070 @c parity), -e (even parity)---apparently no settings for no parity or
10071 @c for character size. Taken from stty maybe...? John points out tip
10072 @c can set these as internal variables, eg ~s parity=none; man stty
10073 @c suggests that it *might* work to stty these options with stdin or
10074 @c stdout redirected... ---doc@cygnus.com, 25feb91
10076 @c There's nothing to be done for the "none" part of the DOS MODE
10077 @c command. The rest of the parameters should be matched by the
10078 @c baudrate, bits, and parity used by the Unix side. ---Eli Zaretskii, 3Sep99
10081 Using the @code{tip} or @code{cu} connection, change the DOS working
10082 directory to the directory containing a copy of your 29K program, then
10083 start the PC program @code{EBMON} (an EB29K control program supplied
10084 with your board by AMD). You should see an initial display from
10085 @code{EBMON} similar to the one that follows, ending with the
10086 @code{EBMON} prompt @samp{#}---
10091 G:\> CD \usr\joe\work29k
10093 G:\USR\JOE\WORK29K> EBMON
10094 Am29000 PC Coprocessor Board Monitor, version 3.0-18
10095 Copyright 1990 Advanced Micro Devices, Inc.
10096 Written by Gibbons and Associates, Inc.
10098 Enter '?' or 'H' for help
10100 PC Coprocessor Type = EB29K
10102 Memory Base = 0xd0000
10104 Data Memory Size = 2048KB
10105 Available I-RAM Range = 0x8000 to 0x1fffff
10106 Available D-RAM Range = 0x80002000 to 0x801fffff
10109 Register Stack Size = 0x800
10110 Memory Stack Size = 0x1800
10113 Am29027 Available = No
10114 Byte Write Available = Yes
10119 Then exit the @code{cu} or @code{tip} program (done in the example by
10120 typing @code{~.} at the @code{EBMON} prompt). @code{EBMON} keeps
10121 running, ready for @value{GDBN} to take over.
10123 For this example, we've assumed what is probably the most convenient
10124 way to make sure the same 29K program is on both the PC and the Unix
10125 system: a PC/NFS connection that establishes ``drive @file{G:}'' on the
10126 PC as a file system on the Unix host. If you do not have PC/NFS or
10127 something similar connecting the two systems, you must arrange some
10128 other way---perhaps floppy-disk transfer---of getting the 29K program
10129 from the Unix system to the PC; @value{GDBN} does @emph{not} download it over the
10133 @subsubsection EB29K cross-debugging
10135 Finally, @code{cd} to the directory containing an image of your 29K
10136 program on the Unix system, and start @value{GDBN}---specifying as argument the
10137 name of your 29K program:
10140 cd /usr/joe/work29k
10145 Now you can use the @code{target} command:
10148 target amd-eb /dev/ttya 9600 MYFOO
10149 @c FIXME: test above 'target amd-eb' as spelled, with caps! caps are meant to
10150 @c emphasize that this is the name as seen by DOS (since I think DOS is
10151 @c single-minded about case of letters). ---doc@cygnus.com, 25feb91
10155 In this example, we've assumed your program is in a file called
10156 @file{myfoo}. Note that the filename given as the last argument to
10157 @code{target amd-eb} should be the name of the program as it appears to DOS.
10158 In our example this is simply @code{MYFOO}, but in general it can include
10159 a DOS path, and depending on your transfer mechanism may not resemble
10160 the name on the Unix side.
10162 At this point, you can set any breakpoints you wish; when you are ready
10163 to see your program run on the 29K board, use the @value{GDBN} command
10166 To stop debugging the remote program, use the @value{GDBN} @code{detach}
10169 To return control of the PC to its console, use @code{tip} or @code{cu}
10170 once again, after your @value{GDBN} session has concluded, to attach to
10171 @code{EBMON}. You can then type the command @code{q} to shut down
10172 @code{EBMON}, returning control to the DOS command-line interpreter.
10173 Type @kbd{CTTY con} to return command input to the main DOS console,
10174 and type @kbd{~.} to leave @code{tip} or @code{cu}.
10177 @subsubsection Remote log
10179 @cindex log file for EB29K
10181 The @code{target amd-eb} command creates a file @file{eb.log} in the
10182 current working directory, to help debug problems with the connection.
10183 @file{eb.log} records all the output from @code{EBMON}, including echoes
10184 of the commands sent to it. Running @samp{tail -f} on this file in
10185 another window often helps to understand trouble with @code{EBMON}, or
10186 unexpected events on the PC side of the connection.
10194 @item target rdi @var{dev}
10195 ARM Angel monitor, via RDI library interface to ADP protocol. You may
10196 use this target to communicate with both boards running the Angel
10197 monitor, or with the EmbeddedICE JTAG debug device.
10200 @item target rdp @var{dev}
10206 @subsection Hitachi H8/300
10210 @kindex target hms@r{, with H8/300}
10211 @item target hms @var{dev}
10212 A Hitachi SH, H8/300, or H8/500 board, attached via serial line to your host.
10213 Use special commands @code{device} and @code{speed} to control the serial
10214 line and the communications speed used.
10216 @kindex target e7000@r{, with H8/300}
10217 @item target e7000 @var{dev}
10218 E7000 emulator for Hitachi H8 and SH.
10220 @kindex target sh3@r{, with H8/300}
10221 @kindex target sh3e@r{, with H8/300}
10222 @item target sh3 @var{dev}
10223 @item target sh3e @var{dev}
10224 Hitachi SH-3 and SH-3E target systems.
10228 @cindex download to H8/300 or H8/500
10229 @cindex H8/300 or H8/500 download
10230 @cindex download to Hitachi SH
10231 @cindex Hitachi SH download
10232 When you select remote debugging to a Hitachi SH, H8/300, or H8/500
10233 board, the @code{load} command downloads your program to the Hitachi
10234 board and also opens it as the current executable target for
10235 @value{GDBN} on your host (like the @code{file} command).
10237 @value{GDBN} needs to know these things to talk to your
10238 Hitachi SH, H8/300, or H8/500:
10242 that you want to use @samp{target hms}, the remote debugging interface
10243 for Hitachi microprocessors, or @samp{target e7000}, the in-circuit
10244 emulator for the Hitachi SH and the Hitachi 300H. (@samp{target hms} is
10245 the default when @value{GDBN} is configured specifically for the Hitachi SH,
10246 H8/300, or H8/500.)
10249 what serial device connects your host to your Hitachi board (the first
10250 serial device available on your host is the default).
10253 what speed to use over the serial device.
10257 * Hitachi Boards:: Connecting to Hitachi boards.
10258 * Hitachi ICE:: Using the E7000 In-Circuit Emulator.
10259 * Hitachi Special:: Special @value{GDBN} commands for Hitachi micros.
10262 @node Hitachi Boards
10263 @subsubsection Connecting to Hitachi boards
10265 @c only for Unix hosts
10267 @cindex serial device, Hitachi micros
10268 Use the special @code{@value{GDBP}} command @samp{device @var{port}} if you
10269 need to explicitly set the serial device. The default @var{port} is the
10270 first available port on your host. This is only necessary on Unix
10271 hosts, where it is typically something like @file{/dev/ttya}.
10274 @cindex serial line speed, Hitachi micros
10275 @code{@value{GDBP}} has another special command to set the communications
10276 speed: @samp{speed @var{bps}}. This command also is only used from Unix
10277 hosts; on DOS hosts, set the line speed as usual from outside @value{GDBN} with
10278 the DOS @code{mode} command (for instance,
10279 @w{@kbd{mode com2:9600,n,8,1,p}} for a 9600@dmn{bps} connection).
10281 The @samp{device} and @samp{speed} commands are available only when you
10282 use a Unix host to debug your Hitachi microprocessor programs. If you
10284 @value{GDBN} depends on an auxiliary terminate-and-stay-resident program
10285 called @code{asynctsr} to communicate with the development board
10286 through a PC serial port. You must also use the DOS @code{mode} command
10287 to set up the serial port on the DOS side.
10289 The following sample session illustrates the steps needed to start a
10290 program under @value{GDBN} control on an H8/300. The example uses a
10291 sample H8/300 program called @file{t.x}. The procedure is the same for
10292 the Hitachi SH and the H8/500.
10294 First hook up your development board. In this example, we use a
10295 board attached to serial port @code{COM2}; if you use a different serial
10296 port, substitute its name in the argument of the @code{mode} command.
10297 When you call @code{asynctsr}, the auxiliary comms program used by the
10298 debugger, you give it just the numeric part of the serial port's name;
10299 for example, @samp{asyncstr 2} below runs @code{asyncstr} on
10303 C:\H8300\TEST> asynctsr 2
10304 C:\H8300\TEST> mode com2:9600,n,8,1,p
10306 Resident portion of MODE loaded
10308 COM2: 9600, n, 8, 1, p
10313 @emph{Warning:} We have noticed a bug in PC-NFS that conflicts with
10314 @code{asynctsr}. If you also run PC-NFS on your DOS host, you may need to
10315 disable it, or even boot without it, to use @code{asynctsr} to control
10316 your development board.
10319 @kindex target hms@r{, and serial protocol}
10320 Now that serial communications are set up, and the development board is
10321 connected, you can start up @value{GDBN}. Call @code{@value{GDBP}} with
10322 the name of your program as the argument. @code{@value{GDBP}} prompts
10323 you, as usual, with the prompt @samp{(@value{GDBP})}. Use two special
10324 commands to begin your debugging session: @samp{target hms} to specify
10325 cross-debugging to the Hitachi board, and the @code{load} command to
10326 download your program to the board. @code{load} displays the names of
10327 the program's sections, and a @samp{*} for each 2K of data downloaded.
10328 (If you want to refresh @value{GDBN} data on symbols or on the
10329 executable file without downloading, use the @value{GDBN} commands
10330 @code{file} or @code{symbol-file}. These commands, and @code{load}
10331 itself, are described in @ref{Files,,Commands to specify files}.)
10334 (eg-C:\H8300\TEST) @value{GDBP} t.x
10335 @value{GDBN} is free software and you are welcome to distribute copies
10336 of it under certain conditions; type "show copying" to see
10338 There is absolutely no warranty for @value{GDBN}; type "show warranty"
10340 @value{GDBN} @value{GDBVN}, Copyright 1992 Free Software Foundation, Inc...
10341 (@value{GDBP}) target hms
10342 Connected to remote H8/300 HMS system.
10343 (@value{GDBP}) load t.x
10344 .text : 0x8000 .. 0xabde ***********
10345 .data : 0xabde .. 0xad30 *
10346 .stack : 0xf000 .. 0xf014 *
10349 At this point, you're ready to run or debug your program. From here on,
10350 you can use all the usual @value{GDBN} commands. The @code{break} command
10351 sets breakpoints; the @code{run} command starts your program;
10352 @code{print} or @code{x} display data; the @code{continue} command
10353 resumes execution after stopping at a breakpoint. You can use the
10354 @code{help} command at any time to find out more about @value{GDBN} commands.
10356 Remember, however, that @emph{operating system} facilities aren't
10357 available on your development board; for example, if your program hangs,
10358 you can't send an interrupt---but you can press the @sc{reset} switch!
10360 Use the @sc{reset} button on the development board
10363 to interrupt your program (don't use @kbd{ctl-C} on the DOS host---it has
10364 no way to pass an interrupt signal to the development board); and
10367 to return to the @value{GDBN} command prompt after your program finishes
10368 normally. The communications protocol provides no other way for @value{GDBN}
10369 to detect program completion.
10372 In either case, @value{GDBN} sees the effect of a @sc{reset} on the
10373 development board as a ``normal exit'' of your program.
10376 @subsubsection Using the E7000 in-circuit emulator
10378 @kindex target e7000@r{, with Hitachi ICE}
10379 You can use the E7000 in-circuit emulator to develop code for either the
10380 Hitachi SH or the H8/300H. Use one of these forms of the @samp{target
10381 e7000} command to connect @value{GDBN} to your E7000:
10384 @item target e7000 @var{port} @var{speed}
10385 Use this form if your E7000 is connected to a serial port. The
10386 @var{port} argument identifies what serial port to use (for example,
10387 @samp{com2}). The third argument is the line speed in bits per second
10388 (for example, @samp{9600}).
10390 @item target e7000 @var{hostname}
10391 If your E7000 is installed as a host on a TCP/IP network, you can just
10392 specify its hostname; @value{GDBN} uses @code{telnet} to connect.
10395 @node Hitachi Special
10396 @subsubsection Special @value{GDBN} commands for Hitachi micros
10398 Some @value{GDBN} commands are available only for the H8/300:
10402 @kindex set machine
10403 @kindex show machine
10404 @item set machine h8300
10405 @itemx set machine h8300h
10406 Condition @value{GDBN} for one of the two variants of the H8/300
10407 architecture with @samp{set machine}. You can use @samp{show machine}
10408 to check which variant is currently in effect.
10417 @kindex set memory @var{mod}
10418 @cindex memory models, H8/500
10419 @item set memory @var{mod}
10421 Specify which H8/500 memory model (@var{mod}) you are using with
10422 @samp{set memory}; check which memory model is in effect with @samp{show
10423 memory}. The accepted values for @var{mod} are @code{small},
10424 @code{big}, @code{medium}, and @code{compact}.
10429 @subsection Intel i960
10433 @kindex target mon960
10434 @item target mon960 @var{dev}
10435 MON960 monitor for Intel i960.
10437 @item target nindy @var{devicename}
10438 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10439 the name of the serial device to use for the connection, e.g.
10446 @dfn{Nindy} is a ROM Monitor program for Intel 960 target systems. When
10447 @value{GDBN} is configured to control a remote Intel 960 using Nindy, you can
10448 tell @value{GDBN} how to connect to the 960 in several ways:
10452 Through command line options specifying serial port, version of the
10453 Nindy protocol, and communications speed;
10456 By responding to a prompt on startup;
10459 By using the @code{target} command at any point during your @value{GDBN}
10460 session. @xref{Target Commands, ,Commands for managing targets}.
10462 @kindex target nindy
10463 @item target nindy @var{devicename}
10464 An Intel 960 board controlled by a Nindy Monitor. @var{devicename} is
10465 the name of the serial device to use for the connection, e.g.
10470 @cindex download to Nindy-960
10471 With the Nindy interface to an Intel 960 board, @code{load}
10472 downloads @var{filename} to the 960 as well as adding its symbols in
10476 * Nindy Startup:: Startup with Nindy
10477 * Nindy Options:: Options for Nindy
10478 * Nindy Reset:: Nindy reset command
10481 @node Nindy Startup
10482 @subsubsection Startup with Nindy
10484 If you simply start @code{@value{GDBP}} without using any command-line
10485 options, you are prompted for what serial port to use, @emph{before} you
10486 reach the ordinary @value{GDBN} prompt:
10489 Attach /dev/ttyNN -- specify NN, or "quit" to quit:
10493 Respond to the prompt with whatever suffix (after @samp{/dev/tty})
10494 identifies the serial port you want to use. You can, if you choose,
10495 simply start up with no Nindy connection by responding to the prompt
10496 with an empty line. If you do this and later wish to attach to Nindy,
10497 use @code{target} (@pxref{Target Commands, ,Commands for managing targets}).
10499 @node Nindy Options
10500 @subsubsection Options for Nindy
10502 These are the startup options for beginning your @value{GDBN} session with a
10503 Nindy-960 board attached:
10506 @item -r @var{port}
10507 Specify the serial port name of a serial interface to be used to connect
10508 to the target system. This option is only available when @value{GDBN} is
10509 configured for the Intel 960 target architecture. You may specify
10510 @var{port} as any of: a full pathname (e.g. @samp{-r /dev/ttya}), a
10511 device name in @file{/dev} (e.g. @samp{-r ttya}), or simply the unique
10512 suffix for a specific @code{tty} (e.g. @samp{-r a}).
10515 (An uppercase letter ``O'', not a zero.) Specify that @value{GDBN} should use
10516 the ``old'' Nindy monitor protocol to connect to the target system.
10517 This option is only available when @value{GDBN} is configured for the Intel 960
10518 target architecture.
10521 @emph{Warning:} if you specify @samp{-O}, but are actually trying to
10522 connect to a target system that expects the newer protocol, the connection
10523 fails, appearing to be a speed mismatch. @value{GDBN} repeatedly
10524 attempts to reconnect at several different line speeds. You can abort
10525 this process with an interrupt.
10529 Specify that @value{GDBN} should first send a @code{BREAK} signal to the target
10530 system, in an attempt to reset it, before connecting to a Nindy target.
10533 @emph{Warning:} Many target systems do not have the hardware that this
10534 requires; it only works with a few boards.
10538 The standard @samp{-b} option controls the line speed used on the serial
10543 @subsubsection Nindy reset command
10548 For a Nindy target, this command sends a ``break'' to the remote target
10549 system; this is only useful if the target has been equipped with a
10550 circuit to perform a hard reset (or some other interesting action) when
10551 a break is detected.
10556 @subsection Mitsubishi M32R/D
10560 @kindex target m32r
10561 @item target m32r @var{dev}
10562 Mitsubishi M32R/D ROM monitor.
10569 The Motorola m68k configuration includes ColdFire support, and
10570 target command for the following ROM monitors.
10574 @kindex target abug
10575 @item target abug @var{dev}
10576 ABug ROM monitor for M68K.
10578 @kindex target cpu32bug
10579 @item target cpu32bug @var{dev}
10580 CPU32BUG monitor, running on a CPU32 (M68K) board.
10582 @kindex target dbug
10583 @item target dbug @var{dev}
10584 dBUG ROM monitor for Motorola ColdFire.
10587 @item target est @var{dev}
10588 EST-300 ICE monitor, running on a CPU32 (M68K) board.
10590 @kindex target rom68k
10591 @item target rom68k @var{dev}
10592 ROM 68K monitor, running on an M68K IDP board.
10596 If @value{GDBN} is configured with @code{m68*-ericsson-*}, it will
10597 instead have only a single special target command:
10601 @kindex target es1800
10602 @item target es1800 @var{dev}
10603 ES-1800 emulator for M68K.
10611 @kindex target rombug
10612 @item target rombug @var{dev}
10613 ROMBUG ROM monitor for OS/9000.
10623 @item target bug @var{dev}
10624 BUG monitor, running on a MVME187 (m88k) board.
10628 @node MIPS Embedded
10629 @subsection MIPS Embedded
10631 @cindex MIPS boards
10632 @value{GDBN} can use the MIPS remote debugging protocol to talk to a
10633 MIPS board attached to a serial line. This is available when
10634 you configure @value{GDBN} with @samp{--target=mips-idt-ecoff}.
10637 Use these @value{GDBN} commands to specify the connection to your target board:
10640 @item target mips @var{port}
10641 @kindex target mips @var{port}
10642 To run a program on the board, start up @code{@value{GDBP}} with the
10643 name of your program as the argument. To connect to the board, use the
10644 command @samp{target mips @var{port}}, where @var{port} is the name of
10645 the serial port connected to the board. If the program has not already
10646 been downloaded to the board, you may use the @code{load} command to
10647 download it. You can then use all the usual @value{GDBN} commands.
10649 For example, this sequence connects to the target board through a serial
10650 port, and loads and runs a program called @var{prog} through the
10654 host$ @value{GDBP} @var{prog}
10655 @value{GDBN} is free software and @dots{}
10656 (@value{GDBP}) target mips /dev/ttyb
10657 (@value{GDBP}) load @var{prog}
10661 @item target mips @var{hostname}:@var{portnumber}
10662 On some @value{GDBN} host configurations, you can specify a TCP
10663 connection (for instance, to a serial line managed by a terminal
10664 concentrator) instead of a serial port, using the syntax
10665 @samp{@var{hostname}:@var{portnumber}}.
10667 @item target pmon @var{port}
10668 @kindex target pmon @var{port}
10671 @item target ddb @var{port}
10672 @kindex target ddb @var{port}
10673 NEC's DDB variant of PMON for Vr4300.
10675 @item target lsi @var{port}
10676 @kindex target lsi @var{port}
10677 LSI variant of PMON.
10679 @kindex target r3900
10680 @item target r3900 @var{dev}
10681 Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips.
10683 @kindex target array
10684 @item target array @var{dev}
10685 Array Tech LSI33K RAID controller board.
10691 @value{GDBN} also supports these special commands for MIPS targets:
10694 @item set processor @var{args}
10695 @itemx show processor
10696 @kindex set processor @var{args}
10697 @kindex show processor
10698 Use the @code{set processor} command to set the type of MIPS
10699 processor when you want to access processor-type-specific registers.
10700 For example, @code{set processor @var{r3041}} tells @value{GDBN}
10701 to use the CPO registers appropriate for the 3041 chip.
10702 Use the @code{show processor} command to see what MIPS processor @value{GDBN}
10703 is using. Use the @code{info reg} command to see what registers
10704 @value{GDBN} is using.
10706 @item set mipsfpu double
10707 @itemx set mipsfpu single
10708 @itemx set mipsfpu none
10709 @itemx show mipsfpu
10710 @kindex set mipsfpu
10711 @kindex show mipsfpu
10712 @cindex MIPS remote floating point
10713 @cindex floating point, MIPS remote
10714 If your target board does not support the MIPS floating point
10715 coprocessor, you should use the command @samp{set mipsfpu none} (if you
10716 need this, you may wish to put the command in your @value{GDBINIT}
10717 file). This tells @value{GDBN} how to find the return value of
10718 functions which return floating point values. It also allows
10719 @value{GDBN} to avoid saving the floating point registers when calling
10720 functions on the board. If you are using a floating point coprocessor
10721 with only single precision floating point support, as on the @sc{r4650}
10722 processor, use the command @samp{set mipsfpu single}. The default
10723 double precision floating point coprocessor may be selected using
10724 @samp{set mipsfpu double}.
10726 In previous versions the only choices were double precision or no
10727 floating point, so @samp{set mipsfpu on} will select double precision
10728 and @samp{set mipsfpu off} will select no floating point.
10730 As usual, you can inquire about the @code{mipsfpu} variable with
10731 @samp{show mipsfpu}.
10733 @item set remotedebug @var{n}
10734 @itemx show remotedebug
10735 @kindex set remotedebug@r{, MIPS protocol}
10736 @kindex show remotedebug@r{, MIPS protocol}
10737 @cindex @code{remotedebug}, MIPS protocol
10738 @cindex MIPS @code{remotedebug} protocol
10739 @c FIXME! For this to be useful, you must know something about the MIPS
10740 @c FIXME...protocol. Where is it described?
10741 You can see some debugging information about communications with the board
10742 by setting the @code{remotedebug} variable. If you set it to @code{1} using
10743 @samp{set remotedebug 1}, every packet is displayed. If you set it
10744 to @code{2}, every character is displayed. You can check the current value
10745 at any time with the command @samp{show remotedebug}.
10747 @item set timeout @var{seconds}
10748 @itemx set retransmit-timeout @var{seconds}
10749 @itemx show timeout
10750 @itemx show retransmit-timeout
10751 @cindex @code{timeout}, MIPS protocol
10752 @cindex @code{retransmit-timeout}, MIPS protocol
10753 @kindex set timeout
10754 @kindex show timeout
10755 @kindex set retransmit-timeout
10756 @kindex show retransmit-timeout
10757 You can control the timeout used while waiting for a packet, in the MIPS
10758 remote protocol, with the @code{set timeout @var{seconds}} command. The
10759 default is 5 seconds. Similarly, you can control the timeout used while
10760 waiting for an acknowledgement of a packet with the @code{set
10761 retransmit-timeout @var{seconds}} command. The default is 3 seconds.
10762 You can inspect both values with @code{show timeout} and @code{show
10763 retransmit-timeout}. (These commands are @emph{only} available when
10764 @value{GDBN} is configured for @samp{--target=mips-idt-ecoff}.)
10766 The timeout set by @code{set timeout} does not apply when @value{GDBN}
10767 is waiting for your program to stop. In that case, @value{GDBN} waits
10768 forever because it has no way of knowing how long the program is going
10769 to run before stopping.
10773 @subsection PowerPC
10777 @kindex target dink32
10778 @item target dink32 @var{dev}
10779 DINK32 ROM monitor.
10781 @kindex target ppcbug
10782 @item target ppcbug @var{dev}
10783 @kindex target ppcbug1
10784 @item target ppcbug1 @var{dev}
10785 PPCBUG ROM monitor for PowerPC.
10788 @item target sds @var{dev}
10789 SDS monitor, running on a PowerPC board (such as Motorola's ADS).
10794 @subsection HP PA Embedded
10798 @kindex target op50n
10799 @item target op50n @var{dev}
10800 OP50N monitor, running on an OKI HPPA board.
10802 @kindex target w89k
10803 @item target w89k @var{dev}
10804 W89K monitor, running on a Winbond HPPA board.
10809 @subsection Hitachi SH
10813 @kindex target hms@r{, with Hitachi SH}
10814 @item target hms @var{dev}
10815 A Hitachi SH board attached via serial line to your host. Use special
10816 commands @code{device} and @code{speed} to control the serial line and
10817 the communications speed used.
10819 @kindex target e7000@r{, with Hitachi SH}
10820 @item target e7000 @var{dev}
10821 E7000 emulator for Hitachi SH.
10823 @kindex target sh3@r{, with SH}
10824 @kindex target sh3e@r{, with SH}
10825 @item target sh3 @var{dev}
10826 @item target sh3e @var{dev}
10827 Hitachi SH-3 and SH-3E target systems.
10832 @subsection Tsqware Sparclet
10836 @value{GDBN} enables developers to debug tasks running on
10837 Sparclet targets from a Unix host.
10838 @value{GDBN} uses code that runs on
10839 both the Unix host and on the Sparclet target. The program
10840 @code{@value{GDBP}} is installed and executed on the Unix host.
10843 @item timeout @var{args}
10844 @kindex remotetimeout
10845 @value{GDBN} supports the option @code{remotetimeout}.
10846 This option is set by the user, and @var{args} represents the number of
10847 seconds @value{GDBN} waits for responses.
10851 When compiling for debugging, include the options @samp{-g} to get debug
10852 information and @samp{-Ttext} to relocate the program to where you wish to
10853 load it on the target. You may also want to add the options @samp{-n} or
10854 @samp{-N} in order to reduce the size of the sections. Example:
10857 sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N
10860 You can use @code{objdump} to verify that the addresses are what you intended:
10863 sparclet-aout-objdump --headers --syms prog
10868 your Unix execution search path to find @value{GDBN}, you are ready to
10869 run @value{GDBN}. From your Unix host, run @code{@value{GDBP}}
10870 (or @code{sparclet-aout-gdb}, depending on your installation).
10872 @value{GDBN} comes up showing the prompt:
10879 * Sparclet File:: Setting the file to debug
10880 * Sparclet Connection:: Connecting to Sparclet
10881 * Sparclet Download:: Sparclet download
10882 * Sparclet Execution:: Running and debugging
10885 @node Sparclet File
10886 @subsubsection Setting file to debug
10888 The @value{GDBN} command @code{file} lets you choose with program to debug.
10891 (gdbslet) file prog
10895 @value{GDBN} then attempts to read the symbol table of @file{prog}.
10896 @value{GDBN} locates
10897 the file by searching the directories listed in the command search
10899 If the file was compiled with debug information (option "-g"), source
10900 files will be searched as well.
10901 @value{GDBN} locates
10902 the source files by searching the directories listed in the directory search
10903 path (@pxref{Environment, ,Your program's environment}).
10905 to find a file, it displays a message such as:
10908 prog: No such file or directory.
10911 When this happens, add the appropriate directories to the search paths with
10912 the @value{GDBN} commands @code{path} and @code{dir}, and execute the
10913 @code{target} command again.
10915 @node Sparclet Connection
10916 @subsubsection Connecting to Sparclet
10918 The @value{GDBN} command @code{target} lets you connect to a Sparclet target.
10919 To connect to a target on serial port ``@code{ttya}'', type:
10922 (gdbslet) target sparclet /dev/ttya
10923 Remote target sparclet connected to /dev/ttya
10924 main () at ../prog.c:3
10928 @value{GDBN} displays messages like these:
10934 @node Sparclet Download
10935 @subsubsection Sparclet download
10937 @cindex download to Sparclet
10938 Once connected to the Sparclet target,
10939 you can use the @value{GDBN}
10940 @code{load} command to download the file from the host to the target.
10941 The file name and load offset should be given as arguments to the @code{load}
10943 Since the file format is aout, the program must be loaded to the starting
10944 address. You can use @code{objdump} to find out what this value is. The load
10945 offset is an offset which is added to the VMA (virtual memory address)
10946 of each of the file's sections.
10947 For instance, if the program
10948 @file{prog} was linked to text address 0x1201000, with data at 0x12010160
10949 and bss at 0x12010170, in @value{GDBN}, type:
10952 (gdbslet) load prog 0x12010000
10953 Loading section .text, size 0xdb0 vma 0x12010000
10956 If the code is loaded at a different address then what the program was linked
10957 to, you may need to use the @code{section} and @code{add-symbol-file} commands
10958 to tell @value{GDBN} where to map the symbol table.
10960 @node Sparclet Execution
10961 @subsubsection Running and debugging
10963 @cindex running and debugging Sparclet programs
10964 You can now begin debugging the task using @value{GDBN}'s execution control
10965 commands, @code{b}, @code{step}, @code{run}, etc. See the @value{GDBN}
10966 manual for the list of commands.
10970 Breakpoint 1 at 0x12010000: file prog.c, line 3.
10972 Starting program: prog
10973 Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
10974 3 char *symarg = 0;
10976 4 char *execarg = "hello!";
10981 @subsection Fujitsu Sparclite
10985 @kindex target sparclite
10986 @item target sparclite @var{dev}
10987 Fujitsu sparclite boards, used only for the purpose of loading.
10988 You must use an additional command to debug the program.
10989 For example: target remote @var{dev} using @value{GDBN} standard
10995 @subsection Tandem ST2000
10997 @value{GDBN} may be used with a Tandem ST2000 phone switch, running Tandem's
11000 To connect your ST2000 to the host system, see the manufacturer's
11001 manual. Once the ST2000 is physically attached, you can run:
11004 target st2000 @var{dev} @var{speed}
11008 to establish it as your debugging environment. @var{dev} is normally
11009 the name of a serial device, such as @file{/dev/ttya}, connected to the
11010 ST2000 via a serial line. You can instead specify @var{dev} as a TCP
11011 connection (for example, to a serial line attached via a terminal
11012 concentrator) using the syntax @code{@var{hostname}:@var{portnumber}}.
11014 The @code{load} and @code{attach} commands are @emph{not} defined for
11015 this target; you must load your program into the ST2000 as you normally
11016 would for standalone operation. @value{GDBN} reads debugging information
11017 (such as symbols) from a separate, debugging version of the program
11018 available on your host computer.
11019 @c FIXME!! This is terribly vague; what little content is here is
11020 @c basically hearsay.
11022 @cindex ST2000 auxiliary commands
11023 These auxiliary @value{GDBN} commands are available to help you with the ST2000
11027 @item st2000 @var{command}
11028 @kindex st2000 @var{cmd}
11029 @cindex STDBUG commands (ST2000)
11030 @cindex commands to STDBUG (ST2000)
11031 Send a @var{command} to the STDBUG monitor. See the manufacturer's
11032 manual for available commands.
11035 @cindex connect (to STDBUG)
11036 Connect the controlling terminal to the STDBUG command monitor. When
11037 you are done interacting with STDBUG, typing either of two character
11038 sequences gets you back to the @value{GDBN} command prompt:
11039 @kbd{@key{RET}~.} (Return, followed by tilde and period) or
11040 @kbd{@key{RET}~@key{C-d}} (Return, followed by tilde and control-D).
11044 @subsection Zilog Z8000
11047 @cindex simulator, Z8000
11048 @cindex Zilog Z8000 simulator
11050 When configured for debugging Zilog Z8000 targets, @value{GDBN} includes
11053 For the Z8000 family, @samp{target sim} simulates either the Z8002 (the
11054 unsegmented variant of the Z8000 architecture) or the Z8001 (the
11055 segmented variant). The simulator recognizes which architecture is
11056 appropriate by inspecting the object code.
11059 @item target sim @var{args}
11061 @kindex target sim@r{, with Z8000}
11062 Debug programs on a simulated CPU. If the simulator supports setup
11063 options, specify them via @var{args}.
11067 After specifying this target, you can debug programs for the simulated
11068 CPU in the same style as programs for your host computer; use the
11069 @code{file} command to load a new program image, the @code{run} command
11070 to run your program, and so on.
11072 As well as making available all the usual machine registers
11073 (@pxref{Registers, ,Registers}), the Z8000 simulator provides three
11074 additional items of information as specially named registers:
11079 Counts clock-ticks in the simulator.
11082 Counts instructions run in the simulator.
11085 Execution time in 60ths of a second.
11089 You can refer to these values in @value{GDBN} expressions with the usual
11090 conventions; for example, @w{@samp{b fputc if $cycles>5000}} sets a
11091 conditional breakpoint that suspends only after at least 5000
11092 simulated clock ticks.
11094 @node Architectures
11095 @section Architectures
11097 This section describes characteristics of architectures that affect
11098 all uses of @value{GDBN} with the architecture, both native and cross.
11111 @kindex set rstack_high_address
11112 @cindex AMD 29K register stack
11113 @cindex register stack, AMD29K
11114 @item set rstack_high_address @var{address}
11115 On AMD 29000 family processors, registers are saved in a separate
11116 @dfn{register stack}. There is no way for @value{GDBN} to determine the
11117 extent of this stack. Normally, @value{GDBN} just assumes that the
11118 stack is ``large enough''. This may result in @value{GDBN} referencing
11119 memory locations that do not exist. If necessary, you can get around
11120 this problem by specifying the ending address of the register stack with
11121 the @code{set rstack_high_address} command. The argument should be an
11122 address, which you probably want to precede with @samp{0x} to specify in
11125 @kindex show rstack_high_address
11126 @item show rstack_high_address
11127 Display the current limit of the register stack, on AMD 29000 family
11135 See the following section.
11140 @cindex stack on Alpha
11141 @cindex stack on MIPS
11142 @cindex Alpha stack
11144 Alpha- and MIPS-based computers use an unusual stack frame, which
11145 sometimes requires @value{GDBN} to search backward in the object code to
11146 find the beginning of a function.
11148 @cindex response time, MIPS debugging
11149 To improve response time (especially for embedded applications, where
11150 @value{GDBN} may be restricted to a slow serial line for this search)
11151 you may want to limit the size of this search, using one of these
11155 @cindex @code{heuristic-fence-post} (Alpha,MIPS)
11156 @item set heuristic-fence-post @var{limit}
11157 Restrict @value{GDBN} to examining at most @var{limit} bytes in its
11158 search for the beginning of a function. A value of @var{0} (the
11159 default) means there is no limit. However, except for @var{0}, the
11160 larger the limit the more bytes @code{heuristic-fence-post} must search
11161 and therefore the longer it takes to run.
11163 @item show heuristic-fence-post
11164 Display the current limit.
11168 These commands are available @emph{only} when @value{GDBN} is configured
11169 for debugging programs on Alpha or MIPS processors.
11172 @node Controlling GDB
11173 @chapter Controlling @value{GDBN}
11175 You can alter the way @value{GDBN} interacts with you by using the
11176 @code{set} command. For commands controlling how @value{GDBN} displays
11177 data, see @ref{Print Settings, ,Print settings}. Other settings are
11182 * Editing:: Command editing
11183 * History:: Command history
11184 * Screen Size:: Screen size
11185 * Numbers:: Numbers
11186 * Messages/Warnings:: Optional warnings and messages
11194 @value{GDBN} indicates its readiness to read a command by printing a string
11195 called the @dfn{prompt}. This string is normally @samp{(@value{GDBP})}. You
11196 can change the prompt string with the @code{set prompt} command. For
11197 instance, when debugging @value{GDBN} with @value{GDBN}, it is useful to change
11198 the prompt in one of the @value{GDBN} sessions so that you can always tell
11199 which one you are talking to.
11201 @emph{Note:} @code{set prompt} does not add a space for you after the
11202 prompt you set. This allows you to set a prompt which ends in a space
11203 or a prompt that does not.
11207 @item set prompt @var{newprompt}
11208 Directs @value{GDBN} to use @var{newprompt} as its prompt string henceforth.
11210 @kindex show prompt
11212 Prints a line of the form: @samp{Gdb's prompt is: @var{your-prompt}}
11216 @section Command editing
11218 @cindex command line editing
11220 @value{GDBN} reads its input commands via the @dfn{readline} interface. This
11221 @sc{gnu} library provides consistent behavior for programs which provide a
11222 command line interface to the user. Advantages are @sc{gnu} Emacs-style
11223 or @dfn{vi}-style inline editing of commands, @code{csh}-like history
11224 substitution, and a storage and recall of command history across
11225 debugging sessions.
11227 You may control the behavior of command line editing in @value{GDBN} with the
11228 command @code{set}.
11231 @kindex set editing
11234 @itemx set editing on
11235 Enable command line editing (enabled by default).
11237 @item set editing off
11238 Disable command line editing.
11240 @kindex show editing
11242 Show whether command line editing is enabled.
11246 @section Command history
11248 @value{GDBN} can keep track of the commands you type during your
11249 debugging sessions, so that you can be certain of precisely what
11250 happened. Use these commands to manage the @value{GDBN} command
11254 @cindex history substitution
11255 @cindex history file
11256 @kindex set history filename
11257 @kindex GDBHISTFILE
11258 @item set history filename @var{fname}
11259 Set the name of the @value{GDBN} command history file to @var{fname}.
11260 This is the file where @value{GDBN} reads an initial command history
11261 list, and where it writes the command history from this session when it
11262 exits. You can access this list through history expansion or through
11263 the history command editing characters listed below. This file defaults
11264 to the value of the environment variable @code{GDBHISTFILE}, or to
11265 @file{./.gdb_history} (@file{./_gdb_history} on MS-DOS) if this variable
11268 @cindex history save
11269 @kindex set history save
11270 @item set history save
11271 @itemx set history save on
11272 Record command history in a file, whose name may be specified with the
11273 @code{set history filename} command. By default, this option is disabled.
11275 @item set history save off
11276 Stop recording command history in a file.
11278 @cindex history size
11279 @kindex set history size
11280 @item set history size @var{size}
11281 Set the number of commands which @value{GDBN} keeps in its history list.
11282 This defaults to the value of the environment variable
11283 @code{HISTSIZE}, or to 256 if this variable is not set.
11286 @cindex history expansion
11287 History expansion assigns special meaning to the character @kbd{!}.
11288 @ifset have-readline-appendices
11289 @xref{Event Designators}.
11292 Since @kbd{!} is also the logical not operator in C, history expansion
11293 is off by default. If you decide to enable history expansion with the
11294 @code{set history expansion on} command, you may sometimes need to
11295 follow @kbd{!} (when it is used as logical not, in an expression) with
11296 a space or a tab to prevent it from being expanded. The readline
11297 history facilities do not attempt substitution on the strings
11298 @kbd{!=} and @kbd{!(}, even when history expansion is enabled.
11300 The commands to control history expansion are:
11303 @kindex set history expansion
11304 @item set history expansion on
11305 @itemx set history expansion
11306 Enable history expansion. History expansion is off by default.
11308 @item set history expansion off
11309 Disable history expansion.
11311 The readline code comes with more complete documentation of
11312 editing and history expansion features. Users unfamiliar with @sc{gnu} Emacs
11313 or @code{vi} may wish to read it.
11314 @ifset have-readline-appendices
11315 @xref{Command Line Editing}.
11319 @kindex show history
11321 @itemx show history filename
11322 @itemx show history save
11323 @itemx show history size
11324 @itemx show history expansion
11325 These commands display the state of the @value{GDBN} history parameters.
11326 @code{show history} by itself displays all four states.
11331 @kindex show commands
11332 @item show commands
11333 Display the last ten commands in the command history.
11335 @item show commands @var{n}
11336 Print ten commands centered on command number @var{n}.
11338 @item show commands +
11339 Print ten commands just after the commands last printed.
11343 @section Screen size
11344 @cindex size of screen
11345 @cindex pauses in output
11347 Certain commands to @value{GDBN} may produce large amounts of
11348 information output to the screen. To help you read all of it,
11349 @value{GDBN} pauses and asks you for input at the end of each page of
11350 output. Type @key{RET} when you want to continue the output, or @kbd{q}
11351 to discard the remaining output. Also, the screen width setting
11352 determines when to wrap lines of output. Depending on what is being
11353 printed, @value{GDBN} tries to break the line at a readable place,
11354 rather than simply letting it overflow onto the following line.
11356 Normally @value{GDBN} knows the size of the screen from the terminal
11357 driver software. For example, on Unix @value{GDBN} uses the termcap data base
11358 together with the value of the @code{TERM} environment variable and the
11359 @code{stty rows} and @code{stty cols} settings. If this is not correct,
11360 you can override it with the @code{set height} and @code{set
11367 @kindex show height
11368 @item set height @var{lpp}
11370 @itemx set width @var{cpl}
11372 These @code{set} commands specify a screen height of @var{lpp} lines and
11373 a screen width of @var{cpl} characters. The associated @code{show}
11374 commands display the current settings.
11376 If you specify a height of zero lines, @value{GDBN} does not pause during
11377 output no matter how long the output is. This is useful if output is to a
11378 file or to an editor buffer.
11380 Likewise, you can specify @samp{set width 0} to prevent @value{GDBN}
11381 from wrapping its output.
11386 @cindex number representation
11387 @cindex entering numbers
11389 You can always enter numbers in octal, decimal, or hexadecimal in
11390 @value{GDBN} by the usual conventions: octal numbers begin with
11391 @samp{0}, decimal numbers end with @samp{.}, and hexadecimal numbers
11392 begin with @samp{0x}. Numbers that begin with none of these are, by
11393 default, entered in base 10; likewise, the default display for
11394 numbers---when no particular format is specified---is base 10. You can
11395 change the default base for both input and output with the @code{set
11399 @kindex set input-radix
11400 @item set input-radix @var{base}
11401 Set the default base for numeric input. Supported choices
11402 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11403 specified either unambiguously or using the current default radix; for
11413 sets the base to decimal. On the other hand, @samp{set radix 10}
11414 leaves the radix unchanged no matter what it was.
11416 @kindex set output-radix
11417 @item set output-radix @var{base}
11418 Set the default base for numeric display. Supported choices
11419 for @var{base} are decimal 8, 10, or 16. @var{base} must itself be
11420 specified either unambiguously or using the current default radix.
11422 @kindex show input-radix
11423 @item show input-radix
11424 Display the current default base for numeric input.
11426 @kindex show output-radix
11427 @item show output-radix
11428 Display the current default base for numeric display.
11431 @node Messages/Warnings
11432 @section Optional warnings and messages
11434 By default, @value{GDBN} is silent about its inner workings. If you are
11435 running on a slow machine, you may want to use the @code{set verbose}
11436 command. This makes @value{GDBN} tell you when it does a lengthy
11437 internal operation, so you will not think it has crashed.
11439 Currently, the messages controlled by @code{set verbose} are those
11440 which announce that the symbol table for a source file is being read;
11441 see @code{symbol-file} in @ref{Files, ,Commands to specify files}.
11444 @kindex set verbose
11445 @item set verbose on
11446 Enables @value{GDBN} output of certain informational messages.
11448 @item set verbose off
11449 Disables @value{GDBN} output of certain informational messages.
11451 @kindex show verbose
11453 Displays whether @code{set verbose} is on or off.
11456 By default, if @value{GDBN} encounters bugs in the symbol table of an
11457 object file, it is silent; but if you are debugging a compiler, you may
11458 find this information useful (@pxref{Symbol Errors, ,Errors reading
11463 @kindex set complaints
11464 @item set complaints @var{limit}
11465 Permits @value{GDBN} to output @var{limit} complaints about each type of
11466 unusual symbols before becoming silent about the problem. Set
11467 @var{limit} to zero to suppress all complaints; set it to a large number
11468 to prevent complaints from being suppressed.
11470 @kindex show complaints
11471 @item show complaints
11472 Displays how many symbol complaints @value{GDBN} is permitted to produce.
11476 By default, @value{GDBN} is cautious, and asks what sometimes seems to be a
11477 lot of stupid questions to confirm certain commands. For example, if
11478 you try to run a program which is already running:
11482 The program being debugged has been started already.
11483 Start it from the beginning? (y or n)
11486 If you are willing to unflinchingly face the consequences of your own
11487 commands, you can disable this ``feature'':
11491 @kindex set confirm
11493 @cindex confirmation
11494 @cindex stupid questions
11495 @item set confirm off
11496 Disables confirmation requests.
11498 @item set confirm on
11499 Enables confirmation requests (the default).
11501 @kindex show confirm
11503 Displays state of confirmation requests.
11508 @chapter Canned Sequences of Commands
11510 Aside from breakpoint commands (@pxref{Break Commands, ,Breakpoint
11511 command lists}), @value{GDBN} provides two ways to store sequences of
11512 commands for execution as a unit: user-defined commands and command
11516 * Define:: User-defined commands
11517 * Hooks:: User-defined command hooks
11518 * Command Files:: Command files
11519 * Output:: Commands for controlled output
11523 @section User-defined commands
11525 @cindex user-defined command
11526 A @dfn{user-defined command} is a sequence of @value{GDBN} commands to
11527 which you assign a new name as a command. This is done with the
11528 @code{define} command. User commands may accept up to 10 arguments
11529 separated by whitespace. Arguments are accessed within the user command
11530 via @var{$arg0@dots{}$arg9}. A trivial example:
11534 print $arg0 + $arg1 + $arg2
11538 To execute the command use:
11545 This defines the command @code{adder}, which prints the sum of
11546 its three arguments. Note the arguments are text substitutions, so they may
11547 reference variables, use complex expressions, or even perform inferior
11553 @item define @var{commandname}
11554 Define a command named @var{commandname}. If there is already a command
11555 by that name, you are asked to confirm that you want to redefine it.
11557 The definition of the command is made up of other @value{GDBN} command lines,
11558 which are given following the @code{define} command. The end of these
11559 commands is marked by a line containing @code{end}.
11564 Takes a single argument, which is an expression to evaluate.
11565 It is followed by a series of commands that are executed
11566 only if the expression is true (nonzero).
11567 There can then optionally be a line @code{else}, followed
11568 by a series of commands that are only executed if the expression
11569 was false. The end of the list is marked by a line containing @code{end}.
11573 The syntax is similar to @code{if}: the command takes a single argument,
11574 which is an expression to evaluate, and must be followed by the commands to
11575 execute, one per line, terminated by an @code{end}.
11576 The commands are executed repeatedly as long as the expression
11580 @item document @var{commandname}
11581 Document the user-defined command @var{commandname}, so that it can be
11582 accessed by @code{help}. The command @var{commandname} must already be
11583 defined. This command reads lines of documentation just as @code{define}
11584 reads the lines of the command definition, ending with @code{end}.
11585 After the @code{document} command is finished, @code{help} on command
11586 @var{commandname} displays the documentation you have written.
11588 You may use the @code{document} command again to change the
11589 documentation of a command. Redefining the command with @code{define}
11590 does not change the documentation.
11592 @kindex help user-defined
11593 @item help user-defined
11594 List all user-defined commands, with the first line of the documentation
11599 @itemx show user @var{commandname}
11600 Display the @value{GDBN} commands used to define @var{commandname} (but
11601 not its documentation). If no @var{commandname} is given, display the
11602 definitions for all user-defined commands.
11606 When user-defined commands are executed, the
11607 commands of the definition are not printed. An error in any command
11608 stops execution of the user-defined command.
11610 If used interactively, commands that would ask for confirmation proceed
11611 without asking when used inside a user-defined command. Many @value{GDBN}
11612 commands that normally print messages to say what they are doing omit the
11613 messages when used in a user-defined command.
11616 @section User-defined command hooks
11617 @cindex command hooks
11618 @cindex hooks, for commands
11620 You may define @emph{hooks}, which are a special kind of user-defined
11621 command. Whenever you run the command @samp{foo}, if the user-defined
11622 command @samp{hook-foo} exists, it is executed (with no arguments)
11623 before that command.
11625 @kindex stop@r{, a pseudo-command}
11626 In addition, a pseudo-command, @samp{stop} exists. Defining
11627 (@samp{hook-stop}) makes the associated commands execute every time
11628 execution stops in your program: before breakpoint commands are run,
11629 displays are printed, or the stack frame is printed.
11631 For example, to ignore @code{SIGALRM} signals while
11632 single-stepping, but treat them normally during normal execution,
11637 handle SIGALRM nopass
11641 handle SIGALRM pass
11644 define hook-continue
11645 handle SIGLARM pass
11649 You can define a hook for any single-word command in @value{GDBN}, but
11650 not for command aliases; you should define a hook for the basic command
11651 name, e.g. @code{backtrace} rather than @code{bt}.
11652 @c FIXME! So how does Joe User discover whether a command is an alias
11654 If an error occurs during the execution of your hook, execution of
11655 @value{GDBN} commands stops and @value{GDBN} issues a prompt
11656 (before the command that you actually typed had a chance to run).
11658 If you try to define a hook which does not match any known command, you
11659 get a warning from the @code{define} command.
11661 @node Command Files
11662 @section Command files
11664 @cindex command files
11665 A command file for @value{GDBN} is a file of lines that are @value{GDBN}
11666 commands. Comments (lines starting with @kbd{#}) may also be included.
11667 An empty line in a command file does nothing; it does not mean to repeat
11668 the last command, as it would from the terminal.
11671 @cindex @file{.gdbinit}
11672 @cindex @file{gdb.ini}
11673 When you start @value{GDBN}, it automatically executes commands from its
11674 @dfn{init files}. These are files named @file{.gdbinit} on Unix, or
11675 @file{gdb.ini} on DOS/Windows. @value{GDBN} reads the init file (if
11676 any) in your home directory@footnote{On DOS/Windows systems, the home
11677 directory is the one pointed to by the @code{HOME} environment
11678 variable.}, then processes command line options and operands, and then
11679 reads the init file (if any) in the current working directory. This is
11680 so the init file in your home directory can set options (such as
11681 @code{set complaints}) which affect the processing of the command line
11682 options and operands. The init files are not executed if you use the
11683 @samp{-nx} option; @pxref{Mode Options, ,Choosing modes}.
11685 @cindex init file name
11686 On some configurations of @value{GDBN}, the init file is known by a
11687 different name (these are typically environments where a specialized
11688 form of @value{GDBN} may need to coexist with other forms, hence a
11689 different name for the specialized version's init file). These are the
11690 environments with special init file names:
11695 VxWorks (Wind River Systems real-time OS): @samp{.vxgdbinit}
11697 @kindex .os68gdbinit
11699 OS68K (Enea Data Systems real-time OS): @samp{.os68gdbinit}
11703 ES-1800 (Ericsson Telecom AB M68000 emulator): @samp{.esgdbinit}
11706 You can also request the execution of a command file with the
11707 @code{source} command:
11711 @item source @var{filename}
11712 Execute the command file @var{filename}.
11715 The lines in a command file are executed sequentially. They are not
11716 printed as they are executed. An error in any command terminates execution
11717 of the command file.
11719 Commands that would ask for confirmation if used interactively proceed
11720 without asking when used in a command file. Many @value{GDBN} commands that
11721 normally print messages to say what they are doing omit the messages
11722 when called from command files.
11725 @section Commands for controlled output
11727 During the execution of a command file or a user-defined command, normal
11728 @value{GDBN} output is suppressed; the only output that appears is what is
11729 explicitly printed by the commands in the definition. This section
11730 describes three commands useful for generating exactly the output you
11735 @item echo @var{text}
11736 @c I do not consider backslash-space a standard C escape sequence
11737 @c because it is not in ANSI.
11738 Print @var{text}. Nonprinting characters can be included in
11739 @var{text} using C escape sequences, such as @samp{\n} to print a
11740 newline. @strong{No newline is printed unless you specify one.}
11741 In addition to the standard C escape sequences, a backslash followed
11742 by a space stands for a space. This is useful for displaying a
11743 string with spaces at the beginning or the end, since leading and
11744 trailing spaces are otherwise trimmed from all arguments.
11745 To print @samp{@w{ }and foo =@w{ }}, use the command
11746 @samp{echo \@w{ }and foo = \@w{ }}.
11748 A backslash at the end of @var{text} can be used, as in C, to continue
11749 the command onto subsequent lines. For example,
11752 echo This is some text\n\
11753 which is continued\n\
11754 onto several lines.\n
11757 produces the same output as
11760 echo This is some text\n
11761 echo which is continued\n
11762 echo onto several lines.\n
11766 @item output @var{expression}
11767 Print the value of @var{expression} and nothing but that value: no
11768 newlines, no @samp{$@var{nn} = }. The value is not entered in the
11769 value history either. @xref{Expressions, ,Expressions}, for more information
11772 @item output/@var{fmt} @var{expression}
11773 Print the value of @var{expression} in format @var{fmt}. You can use
11774 the same formats as for @code{print}. @xref{Output Formats,,Output
11775 formats}, for more information.
11778 @item printf @var{string}, @var{expressions}@dots{}
11779 Print the values of the @var{expressions} under the control of
11780 @var{string}. The @var{expressions} are separated by commas and may be
11781 either numbers or pointers. Their values are printed as specified by
11782 @var{string}, exactly as if your program were to execute the C
11784 @c FIXME: the above implies that at least all ANSI C formats are
11785 @c supported, but it isn't true: %E and %G don't work (or so it seems).
11786 @c Either this is a bug, or the manual should document what formats are
11790 printf (@var{string}, @var{expressions}@dots{});
11793 For example, you can print two values in hex like this:
11796 printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
11799 The only backslash-escape sequences that you can use in the format
11800 string are the simple ones that consist of backslash followed by a
11805 @chapter Using @value{GDBN} under @sc{gnu} Emacs
11808 @cindex @sc{gnu} Emacs
11809 A special interface allows you to use @sc{gnu} Emacs to view (and
11810 edit) the source files for the program you are debugging with
11813 To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the
11814 executable file you want to debug as an argument. This command starts
11815 @value{GDBN} as a subprocess of Emacs, with input and output through a newly
11816 created Emacs buffer.
11817 @c (Do not use the @code{-tui} option to run @value{GDBN} from Emacs.)
11819 Using @value{GDBN} under Emacs is just like using @value{GDBN} normally except for two
11824 All ``terminal'' input and output goes through the Emacs buffer.
11827 This applies both to @value{GDBN} commands and their output, and to the input
11828 and output done by the program you are debugging.
11830 This is useful because it means that you can copy the text of previous
11831 commands and input them again; you can even use parts of the output
11834 All the facilities of Emacs' Shell mode are available for interacting
11835 with your program. In particular, you can send signals the usual
11836 way---for example, @kbd{C-c C-c} for an interrupt, @kbd{C-c C-z} for a
11841 @value{GDBN} displays source code through Emacs.
11844 Each time @value{GDBN} displays a stack frame, Emacs automatically finds the
11845 source file for that frame and puts an arrow (@samp{=>}) at the
11846 left margin of the current line. Emacs uses a separate buffer for
11847 source display, and splits the screen to show both your @value{GDBN} session
11850 Explicit @value{GDBN} @code{list} or search commands still produce output as
11851 usual, but you probably have no reason to use them from Emacs.
11854 @emph{Warning:} If the directory where your program resides is not your
11855 current directory, it can be easy to confuse Emacs about the location of
11856 the source files, in which case the auxiliary display buffer does not
11857 appear to show your source. @value{GDBN} can find programs by searching your
11858 environment's @code{PATH} variable, so the @value{GDBN} input and output
11859 session proceeds normally; but Emacs does not get enough information
11860 back from @value{GDBN} to locate the source files in this situation. To
11861 avoid this problem, either start @value{GDBN} mode from the directory where
11862 your program resides, or specify an absolute file name when prompted for the
11863 @kbd{M-x gdb} argument.
11865 A similar confusion can result if you use the @value{GDBN} @code{file} command to
11866 switch to debugging a program in some other location, from an existing
11867 @value{GDBN} buffer in Emacs.
11870 By default, @kbd{M-x gdb} calls the program called @file{gdb}. If
11871 you need to call @value{GDBN} by a different name (for example, if you keep
11872 several configurations around, with different names) you can set the
11873 Emacs variable @code{gdb-command-name}; for example,
11876 (setq gdb-command-name "mygdb")
11880 (preceded by @kbd{M-:} or @kbd{ESC :}, or typed in the @code{*scratch*} buffer, or
11881 in your @file{.emacs} file) makes Emacs call the program named
11882 ``@code{mygdb}'' instead.
11884 In the @value{GDBN} I/O buffer, you can use these special Emacs commands in
11885 addition to the standard Shell mode commands:
11889 Describe the features of Emacs' @value{GDBN} Mode.
11892 Execute to another source line, like the @value{GDBN} @code{step} command; also
11893 update the display window to show the current file and location.
11896 Execute to next source line in this function, skipping all function
11897 calls, like the @value{GDBN} @code{next} command. Then update the display window
11898 to show the current file and location.
11901 Execute one instruction, like the @value{GDBN} @code{stepi} command; update
11902 display window accordingly.
11904 @item M-x gdb-nexti
11905 Execute to next instruction, using the @value{GDBN} @code{nexti} command; update
11906 display window accordingly.
11909 Execute until exit from the selected stack frame, like the @value{GDBN}
11910 @code{finish} command.
11913 Continue execution of your program, like the @value{GDBN} @code{continue}
11916 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-p}.
11919 Go up the number of frames indicated by the numeric argument
11920 (@pxref{Arguments, , Numeric Arguments, Emacs, The @sc{gnu} Emacs Manual}),
11921 like the @value{GDBN} @code{up} command.
11923 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-u}.
11926 Go down the number of frames indicated by the numeric argument, like the
11927 @value{GDBN} @code{down} command.
11929 @emph{Warning:} In Emacs v19, this command is @kbd{C-c C-d}.
11932 Read the number where the cursor is positioned, and insert it at the end
11933 of the @value{GDBN} I/O buffer. For example, if you wish to disassemble code
11934 around an address that was displayed earlier, type @kbd{disassemble};
11935 then move the cursor to the address display, and pick up the
11936 argument for @code{disassemble} by typing @kbd{C-x &}.
11938 You can customize this further by defining elements of the list
11939 @code{gdb-print-command}; once it is defined, you can format or
11940 otherwise process numbers picked up by @kbd{C-x &} before they are
11941 inserted. A numeric argument to @kbd{C-x &} indicates that you
11942 wish special formatting, and also acts as an index to pick an element of the
11943 list. If the list element is a string, the number to be inserted is
11944 formatted using the Emacs function @code{format}; otherwise the number
11945 is passed as an argument to the corresponding list element.
11948 In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break})
11949 tells @value{GDBN} to set a breakpoint on the source line point is on.
11951 If you accidentally delete the source-display buffer, an easy way to get
11952 it back is to type the command @code{f} in the @value{GDBN} buffer, to
11953 request a frame display; when you run under Emacs, this recreates
11954 the source buffer if necessary to show you the context of the current
11957 The source files displayed in Emacs are in ordinary Emacs buffers
11958 which are visiting the source files in the usual way. You can edit
11959 the files with these buffers if you wish; but keep in mind that @value{GDBN}
11960 communicates with Emacs in terms of line numbers. If you add or
11961 delete lines from the text, the line numbers that @value{GDBN} knows cease
11962 to correspond properly with the code.
11964 @c The following dropped because Epoch is nonstandard. Reactivate
11965 @c if/when v19 does something similar. ---doc@cygnus.com 19dec1990
11967 @kindex Emacs Epoch environment
11971 Version 18 of @sc{gnu} Emacs has a built-in window system
11972 called the @code{epoch}
11973 environment. Users of this environment can use a new command,
11974 @code{inspect} which performs identically to @code{print} except that
11975 each value is printed in its own window.
11978 @include annotate.texi
11981 @chapter Reporting Bugs in @value{GDBN}
11982 @cindex bugs in @value{GDBN}
11983 @cindex reporting bugs in @value{GDBN}
11985 Your bug reports play an essential role in making @value{GDBN} reliable.
11987 Reporting a bug may help you by bringing a solution to your problem, or it
11988 may not. But in any case the principal function of a bug report is to help
11989 the entire community by making the next version of @value{GDBN} work better. Bug
11990 reports are your contribution to the maintenance of @value{GDBN}.
11992 In order for a bug report to serve its purpose, you must include the
11993 information that enables us to fix the bug.
11996 * Bug Criteria:: Have you found a bug?
11997 * Bug Reporting:: How to report bugs
12001 @section Have you found a bug?
12002 @cindex bug criteria
12004 If you are not sure whether you have found a bug, here are some guidelines:
12007 @cindex fatal signal
12008 @cindex debugger crash
12009 @cindex crash of debugger
12011 If the debugger gets a fatal signal, for any input whatever, that is a
12012 @value{GDBN} bug. Reliable debuggers never crash.
12014 @cindex error on valid input
12016 If @value{GDBN} produces an error message for valid input, that is a
12017 bug. (Note that if you're cross debugging, the problem may also be
12018 somewhere in the connection to the target.)
12020 @cindex invalid input
12022 If @value{GDBN} does not produce an error message for invalid input,
12023 that is a bug. However, you should note that your idea of
12024 ``invalid input'' might be our idea of ``an extension'' or ``support
12025 for traditional practice''.
12028 If you are an experienced user of debugging tools, your suggestions
12029 for improvement of @value{GDBN} are welcome in any case.
12032 @node Bug Reporting
12033 @section How to report bugs
12034 @cindex bug reports
12035 @cindex @value{GDBN} bugs, reporting
12037 A number of companies and individuals offer support for @sc{gnu} products.
12038 If you obtained @value{GDBN} from a support organization, we recommend you
12039 contact that organization first.
12041 You can find contact information for many support companies and
12042 individuals in the file @file{etc/SERVICE} in the @sc{gnu} Emacs
12044 @c should add a web page ref...
12046 In any event, we also recommend that you send bug reports for
12047 @value{GDBN} to this addresses:
12053 @strong{Do not send bug reports to @samp{info-gdb}, or to
12054 @samp{help-gdb}, or to any newsgroups.} Most users of @value{GDBN} do
12055 not want to receive bug reports. Those that do have arranged to receive
12058 The mailing list @samp{bug-gdb} has a newsgroup @samp{gnu.gdb.bug} which
12059 serves as a repeater. The mailing list and the newsgroup carry exactly
12060 the same messages. Often people think of posting bug reports to the
12061 newsgroup instead of mailing them. This appears to work, but it has one
12062 problem which can be crucial: a newsgroup posting often lacks a mail
12063 path back to the sender. Thus, if we need to ask for more information,
12064 we may be unable to reach you. For this reason, it is better to send
12065 bug reports to the mailing list.
12067 As a last resort, send bug reports on paper to:
12070 @sc{gnu} Debugger Bugs
12071 Free Software Foundation Inc.
12072 59 Temple Place - Suite 330
12073 Boston, MA 02111-1307
12077 The fundamental principle of reporting bugs usefully is this:
12078 @strong{report all the facts}. If you are not sure whether to state a
12079 fact or leave it out, state it!
12081 Often people omit facts because they think they know what causes the
12082 problem and assume that some details do not matter. Thus, you might
12083 assume that the name of the variable you use in an example does not matter.
12084 Well, probably it does not, but one cannot be sure. Perhaps the bug is a
12085 stray memory reference which happens to fetch from the location where that
12086 name is stored in memory; perhaps, if the name were different, the contents
12087 of that location would fool the debugger into doing the right thing despite
12088 the bug. Play it safe and give a specific, complete example. That is the
12089 easiest thing for you to do, and the most helpful.
12091 Keep in mind that the purpose of a bug report is to enable us to fix the
12092 bug. It may be that the bug has been reported previously, but neither
12093 you nor we can know that unless your bug report is complete and
12096 Sometimes people give a few sketchy facts and ask, ``Does this ring a
12097 bell?'' Those bug reports are useless, and we urge everyone to
12098 @emph{refuse to respond to them} except to chide the sender to report
12101 To enable us to fix the bug, you should include all these things:
12105 The version of @value{GDBN}. @value{GDBN} announces it if you start
12106 with no arguments; you can also print it at any time using @code{show
12109 Without this, we will not know whether there is any point in looking for
12110 the bug in the current version of @value{GDBN}.
12113 The type of machine you are using, and the operating system name and
12117 What compiler (and its version) was used to compile @value{GDBN}---e.g.
12118 ``@value{GCC}--2.8.1''.
12121 What compiler (and its version) was used to compile the program you are
12122 debugging---e.g. ``@value{GCC}--2.8.1'', or ``HP92453-01 A.10.32.03 HP
12123 C Compiler''. For GCC, you can say @code{gcc --version} to get this
12124 information; for other compilers, see the documentation for those
12128 The command arguments you gave the compiler to compile your example and
12129 observe the bug. For example, did you use @samp{-O}? To guarantee
12130 you will not omit something important, list them all. A copy of the
12131 Makefile (or the output from make) is sufficient.
12133 If we were to try to guess the arguments, we would probably guess wrong
12134 and then we might not encounter the bug.
12137 A complete input script, and all necessary source files, that will
12141 A description of what behavior you observe that you believe is
12142 incorrect. For example, ``It gets a fatal signal.''
12144 Of course, if the bug is that @value{GDBN} gets a fatal signal, then we
12145 will certainly notice it. But if the bug is incorrect output, we might
12146 not notice unless it is glaringly wrong. You might as well not give us
12147 a chance to make a mistake.
12149 Even if the problem you experience is a fatal signal, you should still
12150 say so explicitly. Suppose something strange is going on, such as, your
12151 copy of @value{GDBN} is out of synch, or you have encountered a bug in
12152 the C library on your system. (This has happened!) Your copy might
12153 crash and ours would not. If you told us to expect a crash, then when
12154 ours fails to crash, we would know that the bug was not happening for
12155 us. If you had not told us to expect a crash, then we would not be able
12156 to draw any conclusion from our observations.
12159 If you wish to suggest changes to the @value{GDBN} source, send us context
12160 diffs. If you even discuss something in the @value{GDBN} source, refer to
12161 it by context, not by line number.
12163 The line numbers in our development sources will not match those in your
12164 sources. Your line numbers would convey no useful information to us.
12168 Here are some things that are not necessary:
12172 A description of the envelope of the bug.
12174 Often people who encounter a bug spend a lot of time investigating
12175 which changes to the input file will make the bug go away and which
12176 changes will not affect it.
12178 This is often time consuming and not very useful, because the way we
12179 will find the bug is by running a single example under the debugger
12180 with breakpoints, not by pure deduction from a series of examples.
12181 We recommend that you save your time for something else.
12183 Of course, if you can find a simpler example to report @emph{instead}
12184 of the original one, that is a convenience for us. Errors in the
12185 output will be easier to spot, running under the debugger will take
12186 less time, and so on.
12188 However, simplification is not vital; if you do not want to do this,
12189 report the bug anyway and send us the entire test case you used.
12192 A patch for the bug.
12194 A patch for the bug does help us if it is a good one. But do not omit
12195 the necessary information, such as the test case, on the assumption that
12196 a patch is all we need. We might see problems with your patch and decide
12197 to fix the problem another way, or we might not understand it at all.
12199 Sometimes with a program as complicated as @value{GDBN} it is very hard to
12200 construct an example that will make the program follow a certain path
12201 through the code. If you do not send us the example, we will not be able
12202 to construct one, so we will not be able to verify that the bug is fixed.
12204 And if we cannot understand what bug you are trying to fix, or why your
12205 patch should be an improvement, we will not install it. A test case will
12206 help us to understand.
12209 A guess about what the bug is or what it depends on.
12211 Such guesses are usually wrong. Even we cannot guess right about such
12212 things without first using the debugger to find the facts.
12215 @c The readline documentation is distributed with the readline code
12216 @c and consists of the two following files:
12218 @c inc-hist.texinfo
12219 @c Use -I with makeinfo to point to the appropriate directory,
12220 @c environment var TEXINPUTS with TeX.
12221 @include rluser.texinfo
12222 @include inc-hist.texinfo
12225 @node Formatting Documentation
12226 @appendix Formatting Documentation
12228 @cindex @value{GDBN} reference card
12229 @cindex reference card
12230 The @value{GDBN} 4 release includes an already-formatted reference card, ready
12231 for printing with PostScript or Ghostscript, in the @file{gdb}
12232 subdirectory of the main source directory@footnote{In
12233 @file{gdb-@value{GDBVN}/gdb/refcard.ps} of the version @value{GDBVN}
12234 release.}. If you can use PostScript or Ghostscript with your printer,
12235 you can print the reference card immediately with @file{refcard.ps}.
12237 The release also includes the source for the reference card. You
12238 can format it, using @TeX{}, by typing:
12244 The @value{GDBN} reference card is designed to print in @dfn{landscape}
12245 mode on US ``letter'' size paper;
12246 that is, on a sheet 11 inches wide by 8.5 inches
12247 high. You will need to specify this form of printing as an option to
12248 your @sc{dvi} output program.
12250 @cindex documentation
12252 All the documentation for @value{GDBN} comes as part of the machine-readable
12253 distribution. The documentation is written in Texinfo format, which is
12254 a documentation system that uses a single source file to produce both
12255 on-line information and a printed manual. You can use one of the Info
12256 formatting commands to create the on-line version of the documentation
12257 and @TeX{} (or @code{texi2roff}) to typeset the printed version.
12259 @value{GDBN} includes an already formatted copy of the on-line Info
12260 version of this manual in the @file{gdb} subdirectory. The main Info
12261 file is @file{gdb-@value{GDBVN}/gdb/gdb.info}, and it refers to
12262 subordinate files matching @samp{gdb.info*} in the same directory. If
12263 necessary, you can print out these files, or read them with any editor;
12264 but they are easier to read using the @code{info} subsystem in @sc{gnu}
12265 Emacs or the standalone @code{info} program, available as part of the
12266 @sc{gnu} Texinfo distribution.
12268 If you want to format these Info files yourself, you need one of the
12269 Info formatting programs, such as @code{texinfo-format-buffer} or
12272 If you have @code{makeinfo} installed, and are in the top level
12273 @value{GDBN} source directory (@file{gdb-@value{GDBVN}}, in the case of
12274 version @value{GDBVN}), you can make the Info file by typing:
12281 If you want to typeset and print copies of this manual, you need @TeX{},
12282 a program to print its @sc{dvi} output files, and @file{texinfo.tex}, the
12283 Texinfo definitions file.
12285 @TeX{} is a typesetting program; it does not print files directly, but
12286 produces output files called @sc{dvi} files. To print a typeset
12287 document, you need a program to print @sc{dvi} files. If your system
12288 has @TeX{} installed, chances are it has such a program. The precise
12289 command to use depends on your system; @kbd{lpr -d} is common; another
12290 (for PostScript devices) is @kbd{dvips}. The @sc{dvi} print command may
12291 require a file name without any extension or a @samp{.dvi} extension.
12293 @TeX{} also requires a macro definitions file called
12294 @file{texinfo.tex}. This file tells @TeX{} how to typeset a document
12295 written in Texinfo format. On its own, @TeX{} cannot either read or
12296 typeset a Texinfo file. @file{texinfo.tex} is distributed with GDB
12297 and is located in the @file{gdb-@var{version-number}/texinfo}
12300 If you have @TeX{} and a @sc{dvi} printer program installed, you can
12301 typeset and print this manual. First switch to the the @file{gdb}
12302 subdirectory of the main source directory (for example, to
12303 @file{gdb-@value{GDBVN}/gdb}) and type:
12309 Then give @file{gdb.dvi} to your @sc{dvi} printing program.
12311 @node Installing GDB
12312 @appendix Installing @value{GDBN}
12313 @cindex configuring @value{GDBN}
12314 @cindex installation
12316 @value{GDBN} comes with a @code{configure} script that automates the process
12317 of preparing @value{GDBN} for installation; you can then use @code{make} to
12318 build the @code{gdb} program.
12320 @c irrelevant in info file; it's as current as the code it lives with.
12321 @footnote{If you have a more recent version of @value{GDBN} than @value{GDBVN},
12322 look at the @file{README} file in the sources; we may have improved the
12323 installation procedures since publishing this manual.}
12326 The @value{GDBN} distribution includes all the source code you need for
12327 @value{GDBN} in a single directory, whose name is usually composed by
12328 appending the version number to @samp{gdb}.
12330 For example, the @value{GDBN} version @value{GDBVN} distribution is in the
12331 @file{gdb-@value{GDBVN}} directory. That directory contains:
12334 @item gdb-@value{GDBVN}/configure @r{(and supporting files)}
12335 script for configuring @value{GDBN} and all its supporting libraries
12337 @item gdb-@value{GDBVN}/gdb
12338 the source specific to @value{GDBN} itself
12340 @item gdb-@value{GDBVN}/bfd
12341 source for the Binary File Descriptor library
12343 @item gdb-@value{GDBVN}/include
12344 @sc{gnu} include files
12346 @item gdb-@value{GDBVN}/libiberty
12347 source for the @samp{-liberty} free software library
12349 @item gdb-@value{GDBVN}/opcodes
12350 source for the library of opcode tables and disassemblers
12352 @item gdb-@value{GDBVN}/readline
12353 source for the @sc{gnu} command-line interface
12355 @item gdb-@value{GDBVN}/glob
12356 source for the @sc{gnu} filename pattern-matching subroutine
12358 @item gdb-@value{GDBVN}/mmalloc
12359 source for the @sc{gnu} memory-mapped malloc package
12362 The simplest way to configure and build @value{GDBN} is to run @code{configure}
12363 from the @file{gdb-@var{version-number}} source directory, which in
12364 this example is the @file{gdb-@value{GDBVN}} directory.
12366 First switch to the @file{gdb-@var{version-number}} source directory
12367 if you are not already in it; then run @code{configure}. Pass the
12368 identifier for the platform on which @value{GDBN} will run as an
12374 cd gdb-@value{GDBVN}
12375 ./configure @var{host}
12380 where @var{host} is an identifier such as @samp{sun4} or
12381 @samp{decstation}, that identifies the platform where @value{GDBN} will run.
12382 (You can often leave off @var{host}; @code{configure} tries to guess the
12383 correct value by examining your system.)
12385 Running @samp{configure @var{host}} and then running @code{make} builds the
12386 @file{bfd}, @file{readline}, @file{mmalloc}, and @file{libiberty}
12387 libraries, then @code{gdb} itself. The configured source files, and the
12388 binaries, are left in the corresponding source directories.
12391 @code{configure} is a Bourne-shell (@code{/bin/sh}) script; if your
12392 system does not recognize this automatically when you run a different
12393 shell, you may need to run @code{sh} on it explicitly:
12396 sh configure @var{host}
12399 If you run @code{configure} from a directory that contains source
12400 directories for multiple libraries or programs, such as the
12401 @file{gdb-@value{GDBVN}} source directory for version @value{GDBVN}, @code{configure}
12402 creates configuration files for every directory level underneath (unless
12403 you tell it not to, with the @samp{--norecursion} option).
12405 You can run the @code{configure} script from any of the
12406 subordinate directories in the @value{GDBN} distribution if you only want to
12407 configure that subdirectory, but be sure to specify a path to it.
12409 For example, with version @value{GDBVN}, type the following to configure only
12410 the @code{bfd} subdirectory:
12414 cd gdb-@value{GDBVN}/bfd
12415 ../configure @var{host}
12419 You can install @code{@value{GDBP}} anywhere; it has no hardwired paths.
12420 However, you should make sure that the shell on your path (named by
12421 the @samp{SHELL} environment variable) is publicly readable. Remember
12422 that @value{GDBN} uses the shell to start your program---some systems refuse to
12423 let @value{GDBN} debug child processes whose programs are not readable.
12426 * Separate Objdir:: Compiling @value{GDBN} in another directory
12427 * Config Names:: Specifying names for hosts and targets
12428 * Configure Options:: Summary of options for configure
12431 @node Separate Objdir
12432 @section Compiling @value{GDBN} in another directory
12434 If you want to run @value{GDBN} versions for several host or target machines,
12435 you need a different @code{gdb} compiled for each combination of
12436 host and target. @code{configure} is designed to make this easy by
12437 allowing you to generate each configuration in a separate subdirectory,
12438 rather than in the source directory. If your @code{make} program
12439 handles the @samp{VPATH} feature (@sc{gnu} @code{make} does), running
12440 @code{make} in each of these directories builds the @code{gdb}
12441 program specified there.
12443 To build @code{gdb} in a separate directory, run @code{configure}
12444 with the @samp{--srcdir} option to specify where to find the source.
12445 (You also need to specify a path to find @code{configure}
12446 itself from your working directory. If the path to @code{configure}
12447 would be the same as the argument to @samp{--srcdir}, you can leave out
12448 the @samp{--srcdir} option; it is assumed.)
12450 For example, with version @value{GDBVN}, you can build @value{GDBN} in a
12451 separate directory for a Sun 4 like this:
12455 cd gdb-@value{GDBVN}
12458 ../gdb-@value{GDBVN}/configure sun4
12463 When @code{configure} builds a configuration using a remote source
12464 directory, it creates a tree for the binaries with the same structure
12465 (and using the same names) as the tree under the source directory. In
12466 the example, you'd find the Sun 4 library @file{libiberty.a} in the
12467 directory @file{gdb-sun4/libiberty}, and @value{GDBN} itself in
12468 @file{gdb-sun4/gdb}.
12470 One popular reason to build several @value{GDBN} configurations in separate
12471 directories is to configure @value{GDBN} for cross-compiling (where
12472 @value{GDBN} runs on one machine---the @dfn{host}---while debugging
12473 programs that run on another machine---the @dfn{target}).
12474 You specify a cross-debugging target by
12475 giving the @samp{--target=@var{target}} option to @code{configure}.
12477 When you run @code{make} to build a program or library, you must run
12478 it in a configured directory---whatever directory you were in when you
12479 called @code{configure} (or one of its subdirectories).
12481 The @code{Makefile} that @code{configure} generates in each source
12482 directory also runs recursively. If you type @code{make} in a source
12483 directory such as @file{gdb-@value{GDBVN}} (or in a separate configured
12484 directory configured with @samp{--srcdir=@var{dirname}/gdb-@value{GDBVN}}), you
12485 will build all the required libraries, and then build GDB.
12487 When you have multiple hosts or targets configured in separate
12488 directories, you can run @code{make} on them in parallel (for example,
12489 if they are NFS-mounted on each of the hosts); they will not interfere
12493 @section Specifying names for hosts and targets
12495 The specifications used for hosts and targets in the @code{configure}
12496 script are based on a three-part naming scheme, but some short predefined
12497 aliases are also supported. The full naming scheme encodes three pieces
12498 of information in the following pattern:
12501 @var{architecture}-@var{vendor}-@var{os}
12504 For example, you can use the alias @code{sun4} as a @var{host} argument,
12505 or as the value for @var{target} in a @code{--target=@var{target}}
12506 option. The equivalent full name is @samp{sparc-sun-sunos4}.
12508 The @code{configure} script accompanying @value{GDBN} does not provide
12509 any query facility to list all supported host and target names or
12510 aliases. @code{configure} calls the Bourne shell script
12511 @code{config.sub} to map abbreviations to full names; you can read the
12512 script, if you wish, or you can use it to test your guesses on
12513 abbreviations---for example:
12516 % sh config.sub i386-linux
12518 % sh config.sub alpha-linux
12519 alpha-unknown-linux-gnu
12520 % sh config.sub hp9k700
12522 % sh config.sub sun4
12523 sparc-sun-sunos4.1.1
12524 % sh config.sub sun3
12525 m68k-sun-sunos4.1.1
12526 % sh config.sub i986v
12527 Invalid configuration `i986v': machine `i986v' not recognized
12531 @code{config.sub} is also distributed in the @value{GDBN} source
12532 directory (@file{gdb-@value{GDBVN}}, for version @value{GDBVN}).
12534 @node Configure Options
12535 @section @code{configure} options
12537 Here is a summary of the @code{configure} options and arguments that
12538 are most often useful for building @value{GDBN}. @code{configure} also has
12539 several other options not listed here. @inforef{What Configure
12540 Does,,configure.info}, for a full explanation of @code{configure}.
12543 configure @r{[}--help@r{]}
12544 @r{[}--prefix=@var{dir}@r{]}
12545 @r{[}--exec-prefix=@var{dir}@r{]}
12546 @r{[}--srcdir=@var{dirname}@r{]}
12547 @r{[}--norecursion@r{]} @r{[}--rm@r{]}
12548 @r{[}--target=@var{target}@r{]}
12553 You may introduce options with a single @samp{-} rather than
12554 @samp{--} if you prefer; but you may abbreviate option names if you use
12559 Display a quick summary of how to invoke @code{configure}.
12561 @item --prefix=@var{dir}
12562 Configure the source to install programs and files under directory
12565 @item --exec-prefix=@var{dir}
12566 Configure the source to install programs under directory
12569 @c avoid splitting the warning from the explanation:
12571 @item --srcdir=@var{dirname}
12572 @strong{Warning: using this option requires @sc{gnu} @code{make}, or another
12573 @code{make} that implements the @code{VPATH} feature.}@*
12574 Use this option to make configurations in directories separate from the
12575 @value{GDBN} source directories. Among other things, you can use this to
12576 build (or maintain) several configurations simultaneously, in separate
12577 directories. @code{configure} writes configuration specific files in
12578 the current directory, but arranges for them to use the source in the
12579 directory @var{dirname}. @code{configure} creates directories under
12580 the working directory in parallel to the source directories below
12583 @item --norecursion
12584 Configure only the directory level where @code{configure} is executed; do not
12585 propagate configuration to subdirectories.
12587 @item --target=@var{target}
12588 Configure @value{GDBN} for cross-debugging programs running on the specified
12589 @var{target}. Without this option, @value{GDBN} is configured to debug
12590 programs that run on the same machine (@var{host}) as @value{GDBN} itself.
12592 There is no convenient way to generate a list of all available targets.
12594 @item @var{host} @dots{}
12595 Configure @value{GDBN} to run on the specified @var{host}.
12597 There is no convenient way to generate a list of all available hosts.
12600 There are many other options available as well, but they are generally
12601 needed for special purposes only.
12609 % I think something like @colophon should be in texinfo. In the
12611 \long\def\colophon{\hbox to0pt{}\vfill
12612 \centerline{The body of this manual is set in}
12613 \centerline{\fontname\tenrm,}
12614 \centerline{with headings in {\bf\fontname\tenbf}}
12615 \centerline{and examples in {\tt\fontname\tentt}.}
12616 \centerline{{\it\fontname\tenit\/},}
12617 \centerline{{\bf\fontname\tenbf}, and}
12618 \centerline{{\sl\fontname\tensl\/}}
12619 \centerline{are used for emphasis.}\vfill}
12621 % Blame: doc@cygnus.com, 1991.