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This file describes GDB, the GNU symbolic debugger.

This is the HP Ninth Edition, June 2000, for GDB Version 19991101.

Copyright (C) 1988-2000 Free Software Foundation, Inc.

SummarySummary of GDB
Sample SessionA sample GDB session
InvocationGetting in and out of GDB
CommandsGDB commands
RunningRunning programs under GDB
StoppingStopping and continuing
StackExamining the stack
SourceExamining source files
DataExamining data
LanguagesUsing GDB with different languages
SymbolsExamining the symbol table
AlteringAltering execution
GDB FilesGDB files
TargetsSpecifying a debugging target
HP-UX ConfigurationHP Configuration-specific information
Terminal User InterfaceScreen-based interface to HP WDB 2.0
XDB to WDB Transition GuideAid for XDB users who are learning HP WDB 2.0
Controlling GDBControlling GDB
SequencesCanned sequences of commands
EmacsUsing GDB under GNU Emacs
GDB BugsReporting bugs in GDB
Command Line EditingCommand Line Editing
Using History InteractivelyUsing History Interactively
Installing GDBInstalling GDB
IndexIndex



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Summary of GDB

The purpose of a debugger such as GDB is to allow you to see what is going on "inside" another program while it executes--or what another program was doing at the moment it crashed.

GDB can do four main kinds of things (plus other things in support of these) to help you catch bugs in the act:

You can use GDB to debug programs written in C and C++. For more information, see Support. For more information, see C.

Support for Modula-2 and Chill is partial. For information on Modula-2, see Modula-2. For information on Chill, see Chill.

Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. GDB does not support entering expressions, printing values, or similar features using Pascal syntax.

GDB can be used to debug programs written in Fortran, although it may be necessary to refer to some variables with a trailing underscore. See Fortran.

This version of the manual documents HP WDB 2.0, implemented on HP 9000 systems running Release 10.20, or 11.0 of the HP-UX operating system. HP WDB 2.0 can be used to debug code generated by the HP ANSI C, HP ANSI C++ and HP Fortran compilers as well as the GNU C and C++ compilers. It does not support the debugging of Modula-2 or Chill programs.

Free SoftwareFreely redistributable software
ContributorsContributors to GDB




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Free software

GDB is free software, protected by the GNU General Public License (GPL). The GPL gives you the freedom to copy or adapt a licensed program--but every person getting a copy also gets with it the freedom to modify that copy (which means that they must get access to the source code), and the freedom to distribute further copies. Typical software companies use copyrights to limit your freedoms; the Free Software Foundation uses the GPL to preserve these freedoms.

Fundamentally, the General Public License is a license which says that you have these freedoms and that you cannot take these freedoms away from anyone else.




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Contributors to GDB

Richard Stallman was the original author of GDB, and of many other GNU programs. Many others have contributed to its development. This section attempts to credit major contributors. One of the virtues of free software is that everyone is free to contribute to it; with regret, we cannot actually acknowledge everyone here. The file `ChangeLog' in the GDB distribution approximates a blow-by-blow account.

Changes much prior to version 2.0 are lost in the mists of time.

Plea: Additions to this section are particularly welcome. If you or your friends (or enemies, to be evenhanded) have been unfairly omitted from this list, we would like to add your names!
So that they may not regard their many labors as thankless, we particularly thank those who shepherded GDB through major releases: Jim Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs (release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10, and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5, and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2, 3.1, and 3.0).

Richard Stallman, assisted at various times by Peter TerMaat, Chris Hanson, and Richard Mlynarik, handled releases through 2.8.

Michael Tiemann is the author of most of the GNU C++ support in GDB, with significant additional contributions from Per Bothner. James Clark wrote the GNU C++ demangler. Early work on C++ was by Peter TerMaat (who also did much general update work leading to release 3.0).

GDB 4 uses the BFD subroutine library to examine multiple object-file formats; BFD was a joint project of David V. Henkel-Wallace, Rich Pixley, Steve Chamberlain, and John Gilmore.

David Johnson wrote the original COFF support; Pace Willison did the original support for encapsulated COFF.

Brent Benson of Harris Computer Systems contributed DWARF 2 support.

Adam de Boor and Bradley Davis contributed the ISI Optimum V support. Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS support. Jean-Daniel Fekete contributed Sun 386i support. Chris Hanson improved the HP9000 support. Noboyuki Hikichi and Tomoyuki Hasei contributed Sony/News OS 3 support. David Johnson contributed Encore Umax support. Jyrki Kuoppala contributed Altos 3068 support. Jeff Law contributed HP PA and SOM support. Keith Packard contributed NS32K support. Doug Rabson contributed Acorn Risc Machine support. Bob Rusk contributed Harris Nighthawk CX-UX support. Chris Smith contributed Convex support (and Fortran debugging). Jonathan Stone contributed Pyramid support. Michael Tiemann contributed SPARC support. Tim Tucker contributed support for the Gould NP1 and Gould Powernode. Pace Willison contributed Intel 386 support. Jay Vosburgh contributed Symmetry support.

Andreas Schwab contributed M68K Linux support.

Rich Schaefer and Peter Schauer helped with support of SunOS shared libraries.

Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about several machine instruction sets.

Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped develop remote debugging. Intel Corporation, Wind River Systems, AMD, and ARM contributed remote debugging modules for the i960, VxWorks, A29K UDI, and RDI targets, respectively.

Brian Fox is the author of the readline libraries providing command-line editing and command history.

Andrew Beers of SUNY Buffalo wrote the language-switching code, the Modula-2 support, and contributed the Languages chapter of this manual.

Fred Fish wrote most of the support for Unix System Vr4. He also enhanced the command-completion support to cover C++ overloaded symbols.

Hitachi America, Ltd. sponsored the support for H8/300, H8/500, and Super-H processors.

NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx processors.

Mitsubishi sponsored the support for D10V, D30V, and M32R/D processors.

Toshiba sponsored the support for the TX39 Mips processor.

Matsushita sponsored the support for the MN10200 and MN10300 processors.

Fujitsu sponsored the support for SPARClite and FR30 processors

Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware watchpoints.

Michael Snyder added support for tracepoints.

Stu Grossman wrote gdbserver.

Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly innumerable bug fixes and cleanups throughout GDB.

The following people at the Hewlett-Packard Company contributed support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0 (narrow mode), HP's implementation of kernel threads, HP's aC++ compiler, and the terminal user interface: Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann, Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni. Kim Haase and Rosario de la Torre provided HP-specific information in this manual.

Cygnus Solutions has sponsored GDB maintenance and much of its development since 1991. Cygnus engineers who have worked on GDB fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler, Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni. In addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton, JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner, Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David Zuhn have made contributions both large and small.




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1. A Sample GDB Session

You can use this manual at your leisure to read all about GDB. However, a handful of commands are enough to get started using the debugger. This chapter illustrates those commands.

One of the preliminary versions of GNU m4 (a generic macro processor) exhibits the following bug: sometimes, when we change its quote strings from the default, the commands used to capture one macro definition within another stop working. In the following short m4 session, we define a macro foo which expands to 0000; we then use the m4 built-in defn to define bar as the same thing. However, when we change the open quote string to <QUOTE> and the close quote string to <UNQUOTE>, the same procedure fails to define a new synonym baz:

$ cd gnu/m4
$ ./m4
define(foo,0000)

foo
0000
define(bar,defn(`foo'))

bar
0000
changequote(<QUOTE>,<UNQUOTE>)

define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
C-d
m4: End of input: 0: fatal error: EOF in string
Let us use GDB to try to see what is going on.

$ gdb m4

Copyright 1986 - 2000 Free Software Foundation, Inc.
Hewlett-Packard Wildebeest 2.0 (based on GDB 4.17-hpwdb-980821)
Wildebeest is free software, covered by the GNU General Public License, 
and you are welcome to change it and/or distribute copies of it under 
certain conditions.  Type "show copying" to see the conditions.  
There is absolutely no warranty for Wildebeest.  
Type "show warranty" for details.
Wildebeest was built for PA-RISC 1.1 or 2.0 (narrow), HP-UX 11.00.
GDB reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell GDB to use a narrower display width than usual, so that examples fit in this manual.

(gdb) set width 70
We need to see how the m4 built-in changequote works. Having looked at the source, we know the relevant subroutine is m4_changequote, so we set a breakpoint there with the GDB break command.

(gdb) break m4_changequote
Breakpoint 1 at 0x62f4: file builtin.c, line 879.
Using the run command, we start m4 running under GDB control; as long as control does not reach the m4_changequote subroutine, the program runs as usual:

(gdb) run
Starting program: /work/Editorial/gdb/gnu/m4/m4
define(foo,0000)

foo
0000
To trigger the breakpoint, we call changequote. GDB suspends execution of m4, displaying information about the context where it stops.

changequote(<QUOTE>,<UNQUOTE>)

Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) 
    at builtin.c:879
879         if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3))
Now we use the command n (next) to advance execution to the next line of the current function.

(gdb) n
882         set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\
 : nil,
set_quotes looks like a promising subroutine. We can go into it by using the command s (step) instead of next. step goes to the next line to be executed in any subroutine, so it steps into set_quotes.

(gdb) s
set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
    at input.c:530
530         if (lquote != def_lquote)
The display that shows the subroutine where m4 is now suspended (and its arguments) is called a stack frame display. It shows a summary of the stack. We can use the backtrace command (which can also be spelled bt), to see where we are in the stack as a whole: the backtrace command displays a stack frame for each active subroutine.

(gdb) bt
#0  set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>")
    at input.c:530
#1  0x6344 in m4_changequote (argc=3, argv=0x33c70) 
    at builtin.c:882
#2  0x8174 in expand_macro (sym=0x33320) at macro.c:242
#3  0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30)
    at macro.c:71
#4  0x79dc in expand_input () at macro.c:40
#5  0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195
We step through a few more lines to see what happens. The first two times, we can use `s'; the next two times we use n to avoid falling into the xstrdup subroutine.

(gdb) s
0x3b5c  532         if (rquote != def_rquote)
(gdb) s
0x3b80  535         lquote = (lq == nil || *lq == '\0') ?  \
def_lquote : xstrdup(lq);
(gdb) n
536         rquote = (rq == nil || *rq == '\0') ? def_rquote\
 : xstrdup(rq);
(gdb) n
538         len_lquote = strlen(rquote);
The last line displayed looks a little odd; we can examine the variables lquote and rquote to see if they are in fact the new left and right quotes we specified. We use the command p (print) to see their values.

(gdb) p lquote
$1 = 0x35d40 "<QUOTE>"
(gdb) p rquote
$2 = 0x35d50 "<UNQUOTE>"
lquote and rquote are indeed the new left and right quotes. To look at some context, we can display ten lines of source surrounding the current line with the l (list) command.

(gdb) l
533             xfree(rquote);
534
535         lquote = (lq == nil || *lq == '\0') ? def_lquote\
 : xstrdup (lq);
536         rquote = (rq == nil || *rq == '\0') ? def_rquote\
 : xstrdup (rq);
537
538         len_lquote = strlen(rquote);
539         len_rquote = strlen(lquote);
540     }
541
542     void
Let us step past the two lines that set len_lquote and len_rquote, and then examine the values of those variables.

(gdb) n
539         len_rquote = strlen(lquote);
(gdb) n
540     }
(gdb) p len_lquote
$3 = 9
(gdb) p len_rquote
$4 = 7
That certainly looks wrong, assuming len_lquote and len_rquote are meant to be the lengths of lquote and rquote respectively. We can set them to better values using the p command, since it can print the value of any expression--and that expression can include subroutine calls and assignments.

(gdb) p len_lquote=strlen(lquote)
$5 = 7
(gdb) p len_rquote=strlen(rquote)
$6 = 9
Is that enough to fix the problem of using the new quotes with the m4 built-in defn? We can allow m4 to continue executing with the c (continue) command, and then try the example that caused trouble initially:

(gdb) c
Continuing.

define(baz,defn(<QUOTE>foo<UNQUOTE>))

baz
0000
Success! The new quotes now work just as well as the default ones. The problem seems to have been just the two typos defining the wrong lengths. We allow m4 exit by giving it an EOF as input:

C-d
Program exited normally.
The message `Program exited normally.' is from GDB; it indicates m4 has finished executing. We can end our GDB session with the GDB quit command.

(gdb) quit



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2. Getting In and Out of GDB

This chapter discusses how to start GDB, and how to get out of it. The essentials are:

Invoking GDBHow to start GDB
Quitting GDBHow to quit GDB
Shell CommandsHow to use shell commands inside GDB




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2.1 Invoking GDB

Invoke GDB by running the program gdb. Once started, GDB reads commands from the terminal until you tell it to exit.

You can also run gdb with a variety of arguments and options, to specify more of your debugging environment at the outset.

The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable.

The most usual way to start GDB is with one argument, specifying an executable program:

gdb program
You can also start with both an executable program and a core file specified:

gdb program core
You can, instead, specify a process ID as a second argument, if you want to debug a running process:

gdb program 1234
would attach GDB to process 1234 (unless you also have a file named `1234'; GDB does check for a core file first).

Taking advantage of the second command-line argument requires a fairly complete operating system; when you use GDB as a remote debugger attached to a bare board, there may not be any notion of "process", and there is often no way to get a core dump. GDB will warn you if it is unable to attach or to read core dumps.

You can run gdb without printing the front material, which describes GDB's non-warranty, by specifying -silent:

gdb -silent
You can further control how GDB starts up by using command-line options. GDB itself can remind you of the options available.

Type

gdb -help
to display all available options and briefly describe their use (`gdb -h' is a shorter equivalent).

All options and command line arguments you give are processed in sequential order. The order makes a difference when the `-x' option is used.

File OptionsChoosing files
Mode OptionsChoosing modes
Redirecting to a fileRedirecting WDB input and output to a file




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2.1.1 Choosing files

When GDB starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the `-se' and `-c' options respectively. (GDB reads the first argument that does not have an associated option flag as equivalent to the `-se' option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the `-c' option followed by that argument.)

If GDB has not been configured to included core file support, such as for most embedded targets, then it will complain about a second argument and ignore it.

Many options have both long and short forms; both are shown in the following list. GDB also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with `--' rather than `-', though we illustrate the more usual convention.)

-symbols file
-s file
Read symbol table from file file.

-exec file
-e file
Use file file as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump.

-se file
Read symbol table from file file and use it as the executable file.

-core file
-c file
Use file file as a core dump to examine.

-c number
Connect to process ID number, as with the attach command (unless there is a file in core-dump format named number, in which case `-c' specifies that file as a core dump to read).

-command file
-x file
Execute GDB commands from file file. See Command Files.

-directory directory
-d directory
Add directory to the path to search for source files.

-m
-mapped
Warning: this option depends on operating system facilities that are not supported on all systems.
If memory-mapped files are available on your system through the mmap system call, you can use this option to have GDB write the symbols from your program into a reusable file in the current directory. If the program you are debugging is called `/tmp/fred', the mapped symbol file is `./fred.syms'. Future GDB debugging sessions notice the presence of this file, and can quickly map in symbol information from it, rather than reading the symbol table from the executable program.

The `.syms' file is specific to the host machine where GDB is run. It holds an exact image of the internal GDB symbol table. It cannot be shared across multiple host platforms.

-r
-readnow
Read each symbol file's entire symbol table immediately, rather than the default, which is to read it incrementally as it is needed. This makes startup slower, but makes future operations faster.

You typically combine the -mapped and -readnow options in order to build a `.syms' file that contains complete symbol information. (See Files, for information on `.syms' files.) A simple GDB invocation to do nothing but build a `.syms' file for future use is:

gdb -batch -nx -mapped -readnow programname



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2.1.2 Choosing modes

You can run GDB in various alternative modes--for example, in batch mode or quiet mode.

-nx
-n
Do not execute commands found in any initialization files (normally called `.gdbinit', or `gdb.ini' on PCs). Normally, GDB executes the commands in these files after all the command options and arguments have been processed. See Command Files.

-quiet
-q
"Quiet". Do not print the introductory and copyright messages. These messages are also suppressed in batch mode.

-batch
Run in batch mode. Exit with status 0 after processing all the command files specified with `-x' (and all commands from initialization files, if not inhibited with `-n'). Exit with nonzero status if an error occurs in executing the GDB commands in the command files.

Batch mode may be useful for running GDB as a filter, for example to download and run a program on another computer; in order to make this more useful, the message

Program exited normally.
(which is ordinarily issued whenever a program running under GDB control terminates) is not issued when running in batch mode.

-nowindows
-nw
"No windows". If GDB comes with a graphical user interface (GUI) built in, then this option tells GDB to only use the command-line interface. If no GUI is available, this option has no effect.

-windows
-w
If GDB includes a GUI, then this option requires it to be used if possible.

-cd directory
Run GDB using directory as its working directory, instead of the current directory.

-dbx
Support additional dbx commands, including:

-fullname
-f
GNU Emacs sets this option when it runs GDB as a subprocess. It tells GDB to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time your program stops). This recognizable format looks like two `\032' characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-GDB interface program uses the two `\032' characters as a signal to display the source code for the frame.

-baud bps
-b bps
Set the line speed (baud rate or bits per second) of any serial interface used by GDB for remote debugging.

-tty device
Run using device for your program's standard input and output.

-tui
Use a Terminal User Interface. For information, use your Web browser to read the file `TUI.html', which is usually installed in the directory /opt/langtools/wdb/doc on HP-UX systems. Do not use this option if you run GDB from Emacs (see see Emacs).

-xdb
Run in XDB compatibility mode, allowing the use of certain XDB commands. For information, see the file `xdb_trans.html', which is usually installed in the directory /opt/langtools/wdb/doc on HP-UX systems.




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2.1.3 Redirecting HP WDB 2.0 input and output to a file

To redirect HP WDB 2.0 input and output to a file use either of these commands to start the debugger:

$ script log1
$ gdb
or

$ gdb | tee log1



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2.2 Quitting GDB

quit
To exit GDB, use the quit command (abbreviated q), or type an end-of-file character (usually C-d). If you do not supply expression, GDB will terminate normally; otherwise it will terminate using the result of expression as the error code.

An interrupt (often C-c) does not exit from GDB, but rather terminates the action of any GDB command that is in progress and returns to GDB command level. It is safe to type the interrupt character at any time because GDB does not allow it to take effect until a time when it is safe.

If you have been using GDB to control an attached process or device, you can release it with the detach command (see Attach).




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2.3 Shell commands

If you need to execute occasional shell commands during your debugging session, there is no need to leave or suspend GDB; you can just use the shell command.

shell command string
Invoke a standard shell to execute command string. If it exists, the environment variable SHELL determines which shell to run. Otherwise GDB uses the default shell (`/bin/sh' on Unix systems, `COMMAND.COM' on MS-DOS, etc.).

The utility make is often needed in development environments. You do not have to use the shell command for this purpose in GDB:

make make-args
Execute the make program with the specified arguments. This is equivalent to `shell make make-args'.




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3. GDB Commands

You can abbreviate a GDB command to the first few letters of the command name, if that abbreviation is unambiguous; and you can repeat certain GDB commands by typing just RET. You can also use the TAB key to get GDB to fill out the rest of a word in a command (or to show you the alternatives available, if there is more than one possibility).

Command SyntaxHow to give commands to GDB
CompletionCommand completion
HelpHow to ask GDB for help




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3.1 Command syntax

A GDB command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments whose meaning depends on the command name. For example, the command step accepts an argument which is the number of times to step, as in `step 5'. You can also use the step command with no arguments. Some command names do not allow any arguments.

GDB command names may always be truncated if that abbreviation is unambiguous. Other possible command abbreviations are listed in the documentation for individual commands. In some cases, even ambiguous abbreviations are allowed; for example, s is specially defined as equivalent to step even though there are other commands whose names start with s. You can test abbreviations by using them as arguments to the help command.

A blank line as input to GDB (typing just RET) means to repeat the previous command. Certain commands (for example, run) will not repeat this way; these are commands whose unintentional repetition might cause trouble and which you are unlikely to want to repeat.

The list and x commands, when you repeat them with RET, construct new arguments rather than repeating exactly as typed. This permits easy scanning of source or memory.

GDB can also use RET in another way: to partition lengthy output, in a way similar to the common utility more (see Screen Size). Since it is easy to press one RET too many in this situation, GDB disables command repetition after any command that generates this sort of display.

Any text from a # to the end of the line is a comment; it does nothing. This is useful mainly in command files (see Command Files).




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3.2 Command completion

GDB can fill in the rest of a word in a command for you, if there is only one possibility; it can also show you what the valid possibilities are for the next word in a command, at any time. This works for GDB commands, GDB subcommands, and the names of symbols in your program.

Press the TAB key whenever you want GDB to fill out the rest of a word. If there is only one possibility, GDB fills in the word, and waits for you to finish the command (or press RET to enter it). For example, if you type

(gdb) info bre TAB
GDB fills in the rest of the word `breakpoints', since that is the only info subcommand beginning with `bre':

(gdb) info breakpoints
You can either press RET at this point, to run the info breakpoints command, or backspace and enter something else, if `breakpoints' does not look like the command you expected. (If you were sure you wanted info breakpoints in the first place, you might as well just type RET immediately after `info bre', to exploit command abbreviations rather than command completion).

If there is more than one possibility for the next word when you press TAB, GDB sounds a bell. You can either supply more characters and try again, or just press TAB a second time; GDB displays all the possible completions for that word. For example, you might want to set a breakpoint on a subroutine whose name begins with `make_', but when you type b make_TAB GDB just sounds the bell. Typing TAB again displays all the function names in your program that begin with those characters, for example:

(gdb) b make_ TAB
GDB sounds bell; press TAB again, to see:
make_a_section_from_file     make_environ               
make_abs_section             make_function_type         
make_blockvector             make_pointer_type          
make_cleanup                 make_reference_type        
make_command                 make_symbol_completion_list
(gdb) b make_
After displaying the available possibilities, GDB copies your partial input (`b make_' in the example) so you can finish the command.

If you just want to see the list of alternatives in the first place, you can press M-? rather than pressing TAB twice. M-? means META ?. You can type this either by holding down a key designated as the META shift on your keyboard (if there is one) while typing ?, or as ESC followed by ?.

Sometimes the string you need, while logically a "word", may contain parentheses or other characters that GDB normally excludes from its notion of a word. To permit word completion to work in this situation, you may enclose words in ' (single quote marks) in GDB commands.

The most likely situation where you might need this is in typing the name of a C++ function. This is because C++ allows function overloading (multiple definitions of the same function, distinguished by argument type). For example, when you want to set a breakpoint you may need to distinguish whether you mean the version of name that takes an int parameter, name(int), or the version that takes a float parameter, name(float). To use the word-completion facilities in this situation, type a single quote ' at the beginning of the function name. This alerts GDB that it may need to consider more information than usual when you press TAB or M-? to request word completion:

(gdb) b 'bubble( M-?
bubble(double,double)    bubble(int,int)
(gdb) b 'bubble(
In some cases, GDB can tell that completing a name requires using quotes. When this happens, GDB inserts the quote for you (while completing as much as it can) if you do not type the quote in the first place:

(gdb) b bub TAB
GDB alters your input line to the following, and rings a bell:
(gdb) b 'bubble(
In general, GDB can tell that a quote is needed (and inserts it) if you have not yet started typing the argument list when you ask for completion on an overloaded symbol.

For more information about overloaded functions, see C plus plus expressions. You can use the command set overload-resolution off to disable overload resolution; see Debugging C plus plus.




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3.3 Getting help

You can always ask GDB itself for information on its commands, using the command help.

help
h
You can use help (abbreviated h) with no arguments to display a short list of named classes of commands:

(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of 
commands in that class.
Type "help" followed by command name for full 
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)
help class
Using one of the general help classes as an argument, you can get a list of the individual commands in that class. For example, here is the help display for the class status:

(gdb) help status
Status inquiries.

List of commands:

info -- Generic command for showing things
 about the program being debugged
show -- Generic command for showing things
 about the debugger

Type "help" followed by command name for full 
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)
help command
With a command name as help argument, GDB displays a short paragraph on how to use that command.

complete args
The complete args command lists all the possible completions for the beginning of a command. Use args to specify the beginning of the command you want completed. For example:

complete i
results in:

if
ignore
info
inspect
This is intended for use by GNU Emacs.

In addition to help, you can use the GDB commands info and show to inquire about the state of your program, or the state of GDB itself. Each command supports many topics of inquiry; this manual introduces each of them in the appropriate context. The listings under info and under show in the Index point to all the sub-commands. See Index.

info
This command (abbreviated i) is for describing the state of your program. For example, you can list the arguments given to your program with info args, list the registers currently in use with info registers, or list the breakpoints you have set with info breakpoints. You can get a complete list of the info sub-commands with help info.

set
You can assign the result of an expression to an environment variable with set. For example, you can set the GDB prompt to a $-sign with set prompt $.

show
In contrast to info, show is for describing the state of GDB itself. You can change most of the things you can show, by using the related command set; for example, you can control what number system is used for displays with set radix, or simply inquire which is currently in use with show radix.

To display all the settable parameters and their current values, you can use show with no arguments; you may also use info set. Both commands produce the same display.

Here are three miscellaneous show subcommands, all of which are exceptional in lacking corresponding set commands:

show version
Show what version of GDB is running. You should include this information in GDB bug-reports. If multiple versions of GDB are in use at your site, you may need to determine which version of GDB you are running; as GDB evolves, new commands are introduced, and old ones may wither away. Also, many system vendors ship variant versions of GDB, and there are variant versions of GDB in GNU/Linux distributions as well. The version number is the same as the one announced when you start GDB.

show copying
Display information about permission for copying GDB.

show warranty
Display the GNU "NO WARRANTY" statement, or a warranty, if your version of comes with one.




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4. Running Programs Under GDB

When you run a program under GDB, you must first generate debugging information when you compile it.

You may start GDB with its arguments, if any, in an environment of your choice. If you are doing native debugging, you may redirect your program's input and output, debug an already running process, or kill a child process.

CompilationCompiling for debugging
StartingStarting your program
ArgumentsYour program's arguments
EnvironmentYour program's environment
Working DirectoryYour program's working directory
Input/OutputYour program's input and output
AttachDebugging an already-running process
Kill ProcessKilling the child process
ThreadsDebugging programs with multiple threads
ProcessesDebugging programs with multiple processes




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4.1 Compiling for debugging

In order to debug a program effectively, you need to generate debugging information when you compile it. This debugging information is stored in the object file; it describes the data type of each variable or function and the correspondence between source line numbers and addresses in the executable code.

To request debugging information, specify the `-g' option when you run the compiler.

Many C compilers are unable to handle the `-g' and `-O' options together. Using those compilers, you cannot generate optimized executables containing debugging information.

The HP-UX ANSI C and C++ compilers, as well as GCC, the GNU C compiler, supports `-g' with or without `-O', making it possible to debug optimized code. We recommend that you always use `-g' whenever you compile a program. You may think your program is correct, but there is no sense in pushing your luck.

When you debug a program compiled with `-g -O', remember that the optimizer is rearranging your code; the debugger shows you what is really there. Do not be too surprised when the execution path does not exactly match your source file! An extreme example: if you define a variable, but never use it, GDB might not see that variable--because the compiler might optimize it out of existence.

Some things do not work as well with `-g -O' as with just `-g', particularly on machines with instruction scheduling. If in doubt, recompile with `-g' alone, and if this fixes the problem, please report it to us as a bug (including a test case!).

Older versions of the GNU C compiler permitted a variant option `-gg' for debugging information. GDB no longer supports this format; if your GNU C compiler has this option, do not use it.




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4.2 Starting your program

run
r
Use the run command to start your program under GDB. You must first specify the program name (except on VxWorks) with an argument to GDB (see Invocation), or by using the file or exec-file command (see Files).

If you are running your program in an execution environment that supports processes, run creates an inferior process and makes that process run your program. (In environments without processes, run jumps to the start of your program.)

The execution of a program is affected by certain information it receives from its superior. GDB provides ways to specify this information, which you must do before starting your program. (You can change it after starting your program, but such changes only affect your program the next time you start it.) This information may be divided into four categories:

The arguments.
Specify the arguments to give your program as the arguments of the run command. If a shell is available on your target, the shell is used to pass the arguments, so that you may use normal conventions (such as wildcard expansion or variable substitution) in describing the arguments. In Unix systems, you can control which shell is used with the SHELL environment variable. GDB uses the C shell (/usr/bin/csh). See Arguments.

The environment.
Your program normally inherits its environment from GDB, but you can use the GDB commands set environment and unset environment to change parts of the environment that affect your program. See Environment.

The working directory.
Your program inherits its working directory from GDB. You can set the GDB working directory with the cd command in GDB. See Working Directory.

The standard input and output.
Your program normally uses the same device for standard input and standard output as GDB is using. You can redirect input and output in the run command line, or you can use the tty command to set a different device for your program. See Input/Output.

Warning: While input and output redirection work, you cannot use pipes to pass the output of the program you are debugging to another program; if you attempt this, GDB is likely to wind up debugging the wrong program.

When you issue the run command, your program begins to execute immediately. See Stopping, for discussion of how to arrange for your program to stop. Once your program has stopped, you may call functions in your program, using the print or call commands. See Data.

If the modification time of your symbol file has changed since the last time GDB read its symbols, GDB discards its symbol table, and reads it again. When it does this, GDB tries to retain your current breakpoints.




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4.3 Your program's arguments

The arguments to your program can be specified by the arguments of the run command. On HP-UX, they are passed to the C shell (/usr/bin/csh), which expands wildcard characters and performs redirection of I/O, and thence to your program.

On non-Unix systems, the program is usually invoked directly by GDB, which emulates I/O redirection via the appropriate system calls, and the wildcard characters are expanded by the startup code of the program, not by the shell.

run with no arguments uses the same arguments used by the previous run, or those set by the set args command.

set args
Specify the arguments to be used the next time your program is run. If set args has no arguments, run executes your program with no arguments. Once you have run your program with arguments, using set args before the next run is the only way to run it again without arguments.

show args
Show the arguments to give your program when it is started.




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4.4 Your program's environment

The environment consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start GDB over again.

path directory
Add directory to the front of the PATH environment variable (the search path for executables), for both GDB and your program. You may specify several directory names, separated by white space or by a system-dependent separator character (`:' on Unix, `;' on MS-DOS and MS-Windows). If directory is already in the path, it is moved to the front, so it is searched sooner.

You can use the string `$cwd' to refer to whatever is the current working directory at the time GDB searches the path. If you use `.' instead, it refers to the directory where you executed the path command. GDB replaces `.' in the directory argument (with the current path) before adding directory to the search path.

show paths
Display the list of search paths for executables (the PATH environment variable).

show environment [varname]
Print the value of environment variable varname to be given to your program when it starts. If you do not supply varname, print the names and values of all environment variables to be given to your program. You can abbreviate environment as env.

set environment varname [=value]
Set environment variable varname to value. The value changes for your program only, not for GDB itself. value may be any string; the values of environment variables are just strings, and any interpretation is supplied by your program itself. The value parameter is optional; if it is eliminated, the variable is set to a null value.

For example, this command:

set env USER = foo
tells the debugged program, when subsequently run, that its user is named `foo'. (The spaces around `=' are used for clarity here; they are not actually required.)

unset environment varname
Remove variable varname from the environment to be passed to your program. This is different from `set env varname ='; unset environment removes the variable from the environment, rather than assigning it an empty value.




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4.5 Your program's working directory

Each time you start your program with run, it inherits its working directory from the current working directory of GDB. The GDB working directory is initially whatever it inherited from its parent process (typically the shell), but you can specify a new working directory in GDB with the cd command.

The GDB working directory also serves as a default for the commands that specify files for GDB to operate on. See Files.

cd directory
Set the GDB working directory to directory.

pwd
Print the GDB working directory.




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4.6 Your program's input and output

By default, the program you run under GDB does input and output to the same terminal that GDB uses. GDB switches the terminal to its own terminal modes to interact with you, but it records the terminal modes your program was using and switches back to them when you continue running your program.

info terminal
Displays information recorded by GDB about the terminal modes your program is using.

You can redirect your program's input and/or output using shell redirection with the run command. For example,

run > outfile
starts your program, diverting its output to the file `outfile'.

Another way to specify where your program should do input and output is with the tty command. This command accepts a file name as argument, and causes this file to be the default for future run commands. It also resets the controlling terminal for the child process, for future run commands. For example,

tty /dev/ttyb
directs that processes started with subsequent run commands default to do input and output on the terminal `/dev/ttyb' and have that as their controlling terminal.

An explicit redirection in run overrides the tty command's effect on the input/output device, but not its effect on the controlling terminal.

When you use the tty command or redirect input in the run command, only the input for your program is affected. The input for GDB still comes from your terminal.




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4.7 Debugging an already-running process

attach process-id
This command attaches to a running process--one that was started outside GDB. (info files shows your active targets.) The command takes as argument a process ID. The usual way to find out the process-id of a Unix process is with the ps utility, or with the `jobs -l' shell command.

attach does not repeat if you press RET a second time after executing the command.

To use attach, your program must be running in an environment which supports processes; for example, attach does not work for programs on bare-board targets that lack an operating system. You must also have permission to send the process a signal.

When you use attach, the debugger finds the program running in the process first by looking in the current working directory, then (if the program is not found) by using the source file search path (see Source Path). You can also use the file command to load the program. See Files.

The first thing GDB does after arranging to debug the specified process is to stop it. You can examine and modify an attached process with all the GDB commands that are ordinarily available when you start processes with run. You can insert breakpoints; you can step and continue; you can modify storage. See Breakpoints. If you would rather the process continue running, you may use the continue command after attaching GDB to the process.

detach
When you have finished debugging the attached process, you can use the detach command to release it from GDB control. Detaching the process continues its execution. After the detach command, that process and GDB become completely independent once more, and you are ready to attach another process or start one with run. detach does not repeat if you press RET again after executing the command.

If you exit GDB or use the run command while you have an attached process, you kill that process. By default, GDB asks for confirmation if you try to do either of these things; you can control whether or not you need to confirm by using the set confirm command (see Messages/Warnings).

NOTE: When GDB attaches to a running program you may get a message saying Attaching to process #nnnnn failed."

The most likely cause for this message is that you have attached to a process that was started across an NFS mount. The HP-UX kernel has had a restriction that prevents a debugger from attaching to a process started from an NFS mount, unless the mount was made non-interruptable with the -nointr flag, see mount(1).




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4.8 Killing the child process

kill
Kill the child process in which your program is running under GDB.

This command is useful if you wish to debug a core dump instead of a running process. GDB ignores any core dump file while your program is running.

On some operating systems, a program cannot be executed outside GDB while you have breakpoints set on it inside GDB. You can use the kill command in this situation to permit running your program outside the debugger.

The kill command is also useful if you wish to recompile and relink your program, since on many systems it is impossible to modify an executable file while it is running in a process. In this case, when you next type run, GDB notices that the file has changed, and reads the symbol table again (while trying to preserve your current breakpoint settings).




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4.9 Debugging programs with multiple threads

In some operating systems, such as HP-UX and Solaris, a single program may have more than one thread of execution. The precise semantics of threads differ from one operating system to another, but in general the threads of a single program are akin to multiple processes--except that they share one address space (that is, they can all examine and modify the same variables). On the other hand, each thread has its own registers and execution stack, and perhaps private memory.

GDB provides these facilities for debugging multi-thread programs:

Warning: These facilities are not yet available on every GDB configuration where the operating system supports threads. If your GDB does not support threads, these commands have no effect. For example, a system without thread support shows no output from `info threads', and always rejects the thread command, like this:

(gdb) info threads
(gdb) thread 1
Thread ID 1 not known.  Use the "info threads" command to
see the IDs of currently known threads.

The GDB thread debugging facility allows you to observe all threads while your program runs--but whenever GDB takes control, one thread in particular is always the focus of debugging. This thread is called the current thread. Debugging commands show program information from the perspective of the current thread.

Whenever GDB detects a new thread in your program, it displays the target system's identification for the thread with a message in the form `[New systag]'. systag is a thread identifier whose form varies depending on the particular system. For example, on LynxOS, you might see

[New process 35 thread 27]
when GDB notices a new thread. In contrast, on an SGI system, the systag is simply something like `process 368', with no further qualifier.

For debugging purposes, GDB associates its own thread number--always a single integer--with each thread in your program.

info threads
Display a summary of all threads currently in your program. GDB displays for each thread (in this order):

  1. the thread number assigned by GDB
  2. the target system's thread identifier (systag)
  3. the current stack frame summary for that thread
An asterisk `*' to the left of the GDB thread number indicates the current thread.

For example,

(gdb) info threads
  3 process 35 thread 27  0x34e5 in sigpause ()
  2 process 35 thread 23  0x34e5 in sigpause ()
* 1 process 35 thread 13  main (argc=1, argv=0x7ffffff8)
    at threadtest.c:68
On HP-UX systems:

For debugging purposes, GDB associates its own thread number--a small integer assigned in thread-creation order--with each thread in your program.

Whenever GDB detects a new thread in your program, it displays both GDB's thread number and the target system's identification for the thread with a message in the form `[New systag]'. systag is a thread identifier whose form varies depending on the particular system. For example, on HP-UX, you see

[New thread 2 (system thread 26594)]
when GDB notices a new thread.

On HP-UX systems, you can control the display of thread creation messages.

set threadverbose on
Enable the output of informational messages regarding thread creation. The default setting is on. You can set it to off to stop the display of messages.

set threadverbose off
Disable the output of informational messages regarding thread creation. The default setting is on. You can set it to on to display messages.

show threadverbose
Display whether set threadverbose is on or off.

Here are commands to get more information about threads:

info threads
Display a summary of all threads currently in your program. GDB displays for each thread (in this order):

  1. the thread number assigned by GDB
  2. the target system's thread identifier (systag)
  3. the current stack frame summary for that thread
An asterisk `*' to the left of the GDB thread number indicates the current thread.

For example,

(gdb) info threads
    * 3 system thread 26607  worker (wptr=0x7b09c318 "@") at quicksort.c:137
      2 system thread 26606  0x7b0030d8 in __ksleep () from /usr/lib/libc.2
      1 system thread 27905  0x7b003498 in _brk () from /usr/lib/libc.2
thread threadno
Make thread number threadno the current thread. The command argument threadno is the internal GDB thread number, as shown in the first field of the `info threads' display. GDB responds by displaying the system identifier of the thread you selected, and its current stack frame summary:

(gdb) thread 2
[Switching to thread 2 (system thread 26594)]
0x34e5 in sigpause ()
As with the `[New ...]' message, the form of the text after `Switching to' depends on your system's conventions for identifying threads.

thread apply [threadno] [all] args
The thread apply command allows you to apply a command to one or more threads. Specify the numbers of the threads that you want affected with the command argument threadno. threadno is the internal GDB thread number, as shown in the first field of the `info threads' display. To apply a command to all threads, use thread apply all args.

Whenever GDB stops your program, due to a breakpoint or a signal, it automatically selects the thread where that breakpoint or signal happened. GDB alerts you to the context switch with a message of the form `[Switching to systag]' to identify the thread.

See Thread Stops, for more information about how GDB behaves when you stop and start programs with multiple threads.

See Set Watchpoints, for information about watchpoints in programs with multiple threads.




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4.10 Debugging programs with multiple processes

On most systems, GDB has no special support for debugging programs which create additional processes using the fork function. When a program forks, GDB will continue to debug the parent process and the child process will run unimpeded. If you have set a breakpoint in any code which the child then executes, the child will get a SIGTRAP signal which (unless it catches the signal) will cause it to terminate.

However, if you want to debug the child process there is a workaround which isn't too painful. Put a call to sleep in the code which the child process executes after the fork. It may be useful to sleep only if a certain environment variable is set, or a certain file exists, so that the delay need not occur when you don't want to run GDB on the child. While the child is sleeping, use the ps program to get its process ID. Then tell GDB (a new invocation of GDB if you are also debugging the parent process) to attach to the child process (see Attach). From that point on you can debug the child process just like any other process which you attached to.

On HP-UX (11.x and later only), GDB provides support for debugging programs that create additional processes using the fork or vfork function.

By default, when a program forks, GDB will continue to debug the parent process and the child process will run unimpeded.

If you want to follow the child process instead of the parent process, use the command set follow-fork-mode.

set follow-fork-mode mode
Set the debugger response to a program call of fork or vfork. A call to fork or vfork creates a new process. The mode can be:

parent
The original process is debugged after a fork. The child process runs unimpeded. This is the default.

child
The new process is debugged after a fork. The parent process runs unimpeded.

show follow-fork-mode
Display the current debugger response to a fork or vfork call.

If you ask to debug a child process and a vfork is followed by an exec, GDB executes the new target up to the first breakpoint in the new target. If you have a breakpoint set on main in your original program, the breakpoint will also be set on the child process's main.

When a child process is spawned by vfork, you cannot debug the child or parent until an exec call completes.

If you issue a run command to GDB after an exec call executes, the new target restarts. To restart the parent process, use the file command with the parent executable name as its argument.

You can use the catch command to make GDB stop whenever a fork, vfork, or exec call is made. See Set Catchpoints.




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5. Stopping and Continuing

The principal purposes of using a debugger are so that you can stop your program before it terminates; or so that, if your program runs into trouble, you can investigate and find out why.

Inside GDB, your program may stop for any of several reasons, such as a signal, a breakpoint, or reaching a new line after a GDB command such as step. You may then examine and change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by GDB provide ample explanation of the status of your program--but you can also explicitly request this information at any time.

info program
Display information about the status of your program: whether it is running or not, what process it is, and why it stopped.

BreakpointsBreakpoints, watchpoints, and catchpoints
Continuing and SteppingResuming execution
SignalsSignals
Thread StopsStopping and starting multi-thread programs




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5.1 Breakpoints, watchpoints, and catchpoints

A breakpoint makes your program stop whenever a certain point in the program is reached. For each breakpoint, you can add conditions to control in finer detail whether your program stops. You can set breakpoints with the break command and its variants (see Set Breaks), to specify the place where your program should stop by line number, function name or exact address in the program.

In HP-UX, SunOS 4.x, SVR4, and Alpha OSF/1 configurations, you can set breakpoints in shared libraries before the executable is run. See Shared library breakpoints.

A watchpoint is a special breakpoint that stops your program when the value of an expression changes. You must use a different command to set watchpoints (see Set Watchpoints), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands.

You can arrange to have values from your program displayed automatically whenever GDB stops at a breakpoint. See Auto Display.

A catchpoint is another special breakpoint that stops your program when a certain kind of event occurs, such as the throwing of a C++ exception or the loading of a library. As with watchpoints, you use a different command to set a catchpoint (see Set Catchpoints), but aside from that, you can manage a catchpoint like any other breakpoint. (To stop when your program receives a signal, use the handle command; see Signals.)

GDB assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be enabled or disabled; if disabled, it has no effect on your program until you enable it again.

Some GDB commands accept a range of breakpoints on which to operate. A breakpoint range is either a single breakpoint number, like `5', or two such numbers, in increasing order, separated by a hyphen, like `5-7'. When a breakpoint range is given to a command, all breakpoint in that range are operated on.

Set BreaksSetting breakpoints
Set WatchpointsSetting watchpoints
Set CatchpointsSetting catchpoints
Delete BreaksDeleting breakpoints
DisablingDisabling breakpoints
ConditionsBreak conditions
Break CommandsBreakpoint command lists
Breakpoint MenusBreakpoint menus
Error in Breakpoints"Cannot insert breakpoints"




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5.1.1 Setting breakpoints

Breakpoints are set with the break command (abbreviated b). The debugger convenience variable `$bpnum' records the number of the breakpoints you've set most recently; see Convenience Vars, for a discussion of what you can do with convenience variables.

You have several ways to say where the breakpoint should go.

break function
Set a breakpoint at entry to function function. When using source languages that permit overloading of symbols, such as C++, function may refer to more than one possible place to break. See Breakpoint Menus, for a discussion of that situation.

break +offset
break -offset
Set a breakpoint some number of lines forward or back from the position at which execution stopped in the currently selected stack frame. (See Frames, for a description of stack frames.)

break linenum
Set a breakpoint at line linenum in the current source file. The current source file is the last file whose source text was printed. The breakpoint will stop your program just before it executes any of the code on that line.

break filename:linenum
Set a breakpoint at line linenum in source file filename.

break filename:function
Set a breakpoint at entry to function function found in file filename. Specifying a file name as well as a function name is superfluous except when multiple files contain similarly named functions.

break *address
Set a breakpoint at address address. You can use this to set breakpoints in parts of your program which do not have debugging information or source files.

break
When called without any arguments, break sets a breakpoint at the next instruction to be executed in the selected stack frame (see Stack). In any selected frame but the innermost, this makes your program stop as soon as control returns to that frame. This is similar to the effect of a finish command in the frame inside the selected frame--except that finish does not leave an active breakpoint. If you use break without an argument in the innermost frame, GDB stops the next time it reaches the current location; this may be useful inside loops.

GDB normally ignores breakpoints when it resumes execution, until at least one instruction has been executed. If it did not do this, you would be unable to proceed past a breakpoint without first disabling the breakpoint. This rule applies whether or not the breakpoint already existed when your program stopped.

break ... if cond
Set a breakpoint with condition cond; evaluate the expression cond each time the breakpoint is reached, and stop only if the value is nonzero--that is, if cond evaluates as true. `...' stands for one of the possible arguments described above (or no argument) specifying where to break. See Conditions, for more information on breakpoint conditions.

tbreak args
Set a breakpoint enabled only for one stop. args are the same as for the break command, and the breakpoint is set in the same way, but the breakpoint is automatically deleted after the first time your program stops there. See Disabling.

hbreak args
Set a hardware-assisted breakpoint. args are the same as for the break command and the breakpoint is set in the same way, but the breakpoint requires hardware support and some target hardware may not have this support. The main purpose of this is EPROM/ROM code debugging, so you can set a breakpoint at an instruction without changing the instruction. This can be used with the new trap-generation provided by SPARClite DSU and some x86-based targets. These targets will generate traps when a program accesses some data or instruction address that is assigned to the debug registers. However the hardware breakpoint registers can take a limited number of breakpoints. For example, on the DSU, only two data breakpoints can be set at a time, and GDB will reject this command if more than two are used. Delete or disable unused hardware breakpoints before setting new ones (see Disabling). See Conditions.

thbreak args
Set a hardware-assisted breakpoint enabled only for one stop. args are the same as for the hbreak command and the breakpoint is set in the same way. However, like the tbreak command, the breakpoint is automatically deleted after the first time your program stops there. Also, like the hbreak command, the breakpoint requires hardware support and some target hardware may not have this support. See Disabling. See also Conditions.

rbreak regex
Set breakpoints on all functions matching the regular expression regex. This command sets an unconditional breakpoint on all matches, printing a list of all breakpoints it set. Once these breakpoints are set, they are treated just like the breakpoints set with the break command. You can delete them, disable them, or make them conditional the same way as any other breakpoint.

The syntax of the regular expression is the standard one used with tools like `grep'. Note that this is different from the syntax used by shells, so for instance foo* matches all functions that include an fo followed by zero or more os. There is an implicit .* leading and trailing the regular expression you supply, so to match only functions that begin with foo, use ^foo.

When debugging C++ programs, rbreak is useful for setting breakpoints on overloaded functions that are not members of any special classes.

info breakpoints [n]
info break [n]
info watchpoints [n]
Print a table of all breakpoints, watchpoints, and catchpoints set and not deleted, with the following columns for each breakpoint:

Breakpoint Numbers
Type
Breakpoint, watchpoint, or catchpoint.
Disposition
Whether the breakpoint is marked to be disabled or deleted when hit.
Enabled or Disabled
Enabled breakpoints are marked with `y'. `n' marks breakpoints that are not enabled.
Address
Where the breakpoint is in your program, as a memory address.
What
Where the breakpoint is in the source for your program, as a file and line number.

If a breakpoint is conditional, info break shows the condition on the line following the affected breakpoint; breakpoint commands, if any, are listed after that.

info break with a breakpoint number n as argument lists only that breakpoint. The convenience variable $_ and the default examining-address for the x command are set to the address of the last breakpoint listed (see Memory).

info break displays a count of the number of times the breakpoint has been hit. This is especially useful in conjunction with the ignore command. You can ignore a large number of breakpoint hits, look at the breakpoint info to see how many times the breakpoint was hit, and then run again, ignoring one less than that number. This will get you quickly to the last hit of that breakpoint.

GDB allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (see Conditions).

GDB itself sometimes sets breakpoints in your program for special purposes, such as proper handling of longjmp (in C programs). These internal breakpoints are assigned negative numbers, starting with -1; `info breakpoints' does not display them.

You can see these breakpoints with the GDB maintenance command `maint info breakpoints'.

maint info breakpoints
Using the same format as `info breakpoints', display both the breakpoints you've set explicitly, and those GDB is using for internal purposes. Internal breakpoints are shown with negative breakpoint numbers. The type column identifies what kind of breakpoint is shown:

breakpoint
Normal, explicitly set breakpoint.

watchpoint
Normal, explicitly set watchpoint.

longjmp
Internal breakpoint, used to handle correctly stepping through longjmp calls.

longjmp resume
Internal breakpoint at the target of a longjmp.

until
Temporary internal breakpoint used by the GDB until command.

finish
Temporary internal breakpoint used by the GDB finish command.

shlib events
Shared library events.




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5.1.1.1 Simulating Hardware Breakpoints

In some situations hardware breakpoints may not be available (e.g. HP-UX 10.20) or you may want to try something other than a hardware watchpoint.

One thing to try is to make a command line call to mprotect() in your program to manually protect the page yourself. See mprotect(2) man page for explicit information and limitations.

A situation where you might choose to use this technique would be if you find that an instruction is being rewritten or a single data value is corrupted by an errant pointer.

The limitation is that since one protects the entire page, this becomes unwieldy if a lot changes on that page. You need to make sure that there are few other access to the page.

An example of this technique might be:

(gdb) dissass myfunction   ; disassemble functions, get address
0x7aefa260 <myfunction>:stw %r19,-0x1c(%sr0,%sp)
0x7aefa264 <myfunction+4>:ldil L'-0x40000000,%r1
...
End of assembler dump.

(gdb) p mprotect(0x7aefa000,0x1000,0x5)  ; protect one page one
Make certain to remove any debugger breakpoints from the page or other reasons the debugger might want to write to the page




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5.1.2 Setting watchpoints

You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen.

Depending on your system, watchpoints may be implemented in software or hardware. GDB does software watchpoints by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.)

On some systems, such as HP-UX 11.x, Linux and some other x86-based targets, GDB includes support for hardware watchpoints, which do not slow down the running of your program.

watch expr
Set a watchpoint for an expression. GDB will break when expr is written into by the program and its value changes.

rwatch expr
Set a watchpoint that will break when watch expr is read by the program.

awatch expr
Set a watchpoint that will break when expr is either read or written into by the program.

info watchpoints
This command prints a list of watchpoints, breakpoints, and catchpoints; it is the same as info break.

GDB sets a hardware watchpoint if possible. Hardware watchpoints execute very quickly, and the debugger reports a change in value at the exact instruction where the change occurs. If GDB cannot set a hardware watchpoint, it sets a software watchpoint, which executes more slowly and reports the change in value at the next statement, not the instruction, after the change occurs.

When you issue the watch command, GDB reports

Hardware watchpoint num: expr
if it was able to set a hardware watchpoint.

NOTE: HP-UX does not support awatch and rwatch but does support hardware watchpoints using page protection.
Currently, the awatch and rwatch commands can only set hardware watchpoints, because accesses to data that don't change the value of the watched expression cannot be detected without examining every instruction as it is being executed, and GDB does not do that currently. If GDB finds that it is unable to set a hardware breakpoint with the awatch or rwatch command, it will print a message like this:

Expression cannot be implemented with read/access watchpoint.
Sometimes, GDB cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints.

If you set too many hardware watchpoints, GDB might be unable to insert all of them when you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, GDB might not be able to warn you about this when you set the watchpoints, and the warning will be printed only when the program is resumed:

Hardware watchpoint num: Could not insert watchpoint
If this happens, delete or disable some of the watchpoints.

The SPARClite DSU will generate traps when a program accesses some data or instruction address that is assigned to the debug registers. For the data addresses, DSU facilitates the watch command. However the hardware breakpoint registers can only take two data watchpoints, and both watchpoints must be the same kind. For example, you can set two watchpoints with watch commands, two with rwatch commands, or two with awatch commands, but you cannot set one watchpoint with one command and the other with a different command. GDB will reject the command if you try to mix watchpoints. Delete or disable unused watchpoint commands before setting new ones.

If you call a function interactively using print or call, any watchpoints you have set will be inactive until GDB reaches another kind of breakpoint or the call completes.

GDB automatically deletes watchpoints that watch local (automatic) variables, or expressions that involve such variables, when they go out of scope, that is, when the execution leaves the block in which these variables were defined. In particular, when the program being debugged terminates, all local variables go out of scope, and so only watchpoints that watch global variables remain set. If you rerun the program, you will need to set all such watchpoints again. One way of doing that would be to set a code breakpoint at the entry to the main function and when it breaks, set all the watchpoints.

Warning: In multi-thread programs, software watchpoints have only limited usefulness. If GDB creates a software watchpoint, it can only watch the value of an expression in a single thread. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use software watchpoints as usual. However, GDB may not notice when a non-current thread's activity changes the expression. (Hardware watchpoints, in contrast, watch an expression in all threads.)




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5.1.3 Setting catchpoints

You can use catchpoints to cause the debugger to stop for certain kinds of program events, such as C++ exceptions or the loading of a shared library. Use the catch command to set a catchpoint.

catch event
Stop when event occurs. event can be any of the following:
throw
The throwing of a C++ exception.

catch
The catching of a C++ exception.

exec
A call to exec. This is currently only available for HP-UX.

fork
A call to fork. This is currently only available for HP-UX.

vfork
A call to vfork. This is currently only available for HP-UX.

load
load libname
The dynamic loading of any shared library, or the loading of the library libname. This is currently only available for HP-UX.

unload
unload libname
The unloading of any dynamically loaded shared library, or the unloading of the library libname. This is currently only available for HP-UX.

tcatch event
Set a catchpoint that is enabled only for one stop. The catchpoint is automatically deleted after the first time the event is caught.

Use the info break command to list the current catchpoints.

There are currently some limitations to C++ exception handling (catch throw and catch catch) in GDB:

Sometimes catch is not the best way to debug exception handling: if you need to know exactly where an exception is raised, it is better to stop before the exception handler is called, since that way you can see the stack before any unwinding takes place. If you set a breakpoint in an exception handler instead, it may not be easy to find out where the exception was raised.

To stop just before an exception handler is called, you need some knowledge of the implementation. In the case of GNU C++, exceptions are raised by calling a library function named __raise_exception which has the following ANSI C interface:

    /* addr is where the exception identifier is stored.
       id is the exception identifier.  */
    void __raise_exception (void **addr, void *id);
To make the debugger catch all exceptions before any stack unwinding takes place, set a breakpoint on __raise_exception (see Breakpoints).

With a conditional breakpoint (see Conditions) that depends on the value of id, you can stop your program when a specific exception is raised. You can use multiple conditional breakpoints to stop your program when any of a number of exceptions are raised.




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5.1.4 Deleting breakpoints

It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done its job and you no longer want your program to stop there. This is called deleting the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten.

With the clear command you can delete breakpoints according to where they are in your program. With the delete command you can delete individual breakpoints, watchpoints, or catchpoints by specifying their breakpoint numbers.

It is not necessary to delete a breakpoint to proceed past it. GDB automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address.

clear
Delete any breakpoints at the next instruction to be executed in the selected stack frame (see Selection). When the innermost frame is selected, this is a good way to delete a breakpoint where your program just stopped.

clear function
clear filename:function
Delete any breakpoints set at entry to the function function.

clear linenum
clear filename:linenum
Delete any breakpoints set at or within the code of the specified line.

delete [breakpoints] [bnums...]
Delete the breakpoints, watchpoints, or catchpoints of the breakpoint ranges specified as arguments. If no argument is specified, delete all breakpoints (GDB asks confirmation, unless you have set confirm off). You can abbreviate this command as d.




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5.1.5 Disabling breakpoints

Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to disable it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can enable it again later.

You disable and enable breakpoints, watchpoints, and catchpoints with the enable and disable commands, optionally specifying one or more breakpoint numbers as arguments. Use info break or info watch to print a list of breakpoints, watchpoints, and catchpoints if you do not know which numbers to use.

A breakpoint, watchpoint, or catchpoint can have any of four different states of enablement:

You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints:

disable [breakpoints] [bnums...]
Disable the specified breakpoints--or all breakpoints, if none are listed. A disabled breakpoint has no effect but is not forgotten. All options such as ignore-counts, conditions and commands are remembered in case the breakpoint is enabled again later. You may abbreviate disable as dis.

enable [breakpoints] [bnums...]
Enable the specified breakpoints (or all defined breakpoints). They become effective once again in stopping your program.

enable [breakpoints] once bnums...
Enable the specified breakpoints temporarily. GDB disables any of these breakpoints immediately after stopping your program.

enable [breakpoints] delete bnums...
Enable the specified breakpoints to work once, then die. GDB deletes any of these breakpoints as soon as your program stops there.

Except for a breakpoint set with tbreak (see Set Breaks), breakpoints that you set are initially enabled; subsequently, they become disabled or enabled only when you use one of the commands above. (The command until can set and delete a breakpoint of its own, but it does not change the state of your other breakpoints; see Continuing and Stepping.)




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5.1.6 Break conditions

The simplest sort of breakpoint breaks every time your program reaches a specified place. You can also specify a condition for a breakpoint. A condition is just a Boolean expression in your programming language (see Expressions). A breakpoint with a condition evaluates the expression each time your program reaches it, and your program stops only if the condition is true.

This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated--that is, when the condition is false. In C, if you want to test an assertion expressed by the condition assert, you should set the condition `! assert' on the appropriate breakpoint.

Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow--but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one.

Break conditions can have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, GDB might see the other breakpoint first and stop your program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached (see Break Commands).

Break conditions can be specified when a breakpoint is set, by using `if' in the arguments to the break command. See Set Breaks. They can also be changed at any time with the condition command.

You can also use the if keyword with the watch command. The catch command does not recognize the if keyword; condition is the only way to impose a further condition on a catchpoint.

condition bnum expression
Specify expression as the break condition for breakpoint, watchpoint, or catchpoint number bnum. After you set a condition, breakpoint bnum stops your program only if the value of expression is true (nonzero, in C). When you use condition, GDB checks expression immediately for syntactic correctness, and to determine whether symbols in it have referents in the context of your breakpoint. If expression uses symbols not referenced in the context of the breakpoint, GDB prints an error message:

No symbol "foo" in current context.
GDB does not actually evaluate expression at the time the condition command (or a command that sets a breakpoint with a condition, like break if ...) is given, however. See Expressions.

condition bnum
Remove the condition from breakpoint number bnum. It becomes an ordinary unconditional breakpoint.

A special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the ignore count of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if your program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is n, the breakpoint does not stop the next n times your program reaches it.

ignore bnum count
Set the ignore count of breakpoint number bnum to count. The next count times the breakpoint is reached, your program's execution does not stop; other than to decrement the ignore count, GDB takes no action.

To make the breakpoint stop the next time it is reached, specify a count of zero.

When you use continue to resume execution of your program from a breakpoint, you can specify an ignore count directly as an argument to continue, rather than using ignore. See Continuing and Stepping.

If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, GDB resumes checking the condition.

You could achieve the effect of the ignore count with a condition such as `$foo-- <= 0' using a debugger convenience variable that is decremented each time. See Convenience Vars.

Ignore counts apply to breakpoints, watchpoints, and catchpoints.




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5.1.7 Breakpoint command lists

You can give any breakpoint (or watchpoint or catchpoint) a series of commands to execute when your program stops due to that breakpoint. For example, you might want to print the values of certain expressions, or enable other breakpoints.

commands [bnum]
... command-list ...
end
Specify a list of commands for breakpoint number bnum. The commands themselves appear on the following lines. Type a line containing just end to terminate the commands.

To remove all commands from a breakpoint, type commands and follow it immediately with end; that is, give no commands.

With no bnum argument, commands refers to the last breakpoint, watchpoint, or catchpoint set (not to the breakpoint most recently encountered).

Pressing RET as a means of repeating the last GDB command is disabled within a command-list.

You can use breakpoint commands to start your program up again. Simply use the continue command, or step, or any other command that resumes execution.

Any other commands in the command list, after a command that resumes execution, are ignored. This is because any time you resume execution (even with a simple next or step), you may encounter another breakpoint--which could have its own command list, leading to ambiguities about which list to execute.

If the first command you specify in a command list is silent, the usual message about stopping at a breakpoint is not printed. This may be desirable for breakpoints that are to print a specific message and then continue. If none of the remaining commands print anything, you see no sign that the breakpoint was reached. silent is meaningful only at the beginning of a breakpoint command list.

The commands echo, output, and printf allow you to print precisely controlled output, and are often useful in silent breakpoints. See Output.

For example, here is how you could use breakpoint commands to print the value of x at entry to foo whenever x is positive.

break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end
One application for breakpoint commands is to compensate for one bug so you can test for another. Put a breakpoint just after the erroneous line of code, give it a condition to detect the case in which something erroneous has been done, and give it commands to assign correct values to any variables that need them. End with the continue command so that your program does not stop, and start with the silent command so that no output is produced. Here is an example:

break 403
commands
silent
set x = y + 4
cont
end



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5.1.8 Breakpoint menus

Some programming languages (notably C++) permit a single function name to be defined several times, for application in different contexts. This is called overloading. When a function name is overloaded, `break function' is not enough to tell GDB where you want a breakpoint. If you realize this is a problem, you can use something like `break function(types)' to specify which particular version of the function you want. Otherwise, GDB offers you a menu of numbered choices for different possible breakpoints, and waits for your selection with the prompt `>'. The first two options are always `[0] cancel' and `[1] all'. Typing 1 sets a breakpoint at each definition of function, and typing 0 aborts the break command without setting any new breakpoints.

For example, the following session excerpt shows an attempt to set a breakpoint at the overloaded symbol String::after. We choose three particular definitions of that function name:

(gdb) b String::after
[0] cancel
[1] all
[2] file:String.cc; line number:867
[3] file:String.cc; line number:860
[4] file:String.cc; line number:875
[5] file:String.cc; line number:853
[6] file:String.cc; line number:846
[7] file:String.cc; line number:735
> 2 4 6
Breakpoint 1 at 0xb26c: file String.cc, line 867.
Breakpoint 2 at 0xb344: file String.cc, line 875.
Breakpoint 3 at 0xafcc: file String.cc, line 846.
Multiple breakpoints were set.
Use the "delete" command to delete unwanted
 breakpoints.
(gdb)



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5.1.9 "Cannot insert breakpoints"

Under some operating systems, breakpoints cannot be used in a program if any other process is running that program. In this situation, attempting to run or continue a program with a breakpoint causes GDB to print an error message:

Cannot insert breakpoints.
The same program may be running in another process.
When this happens, you have three ways to proceed:

  1. Remove or disable the breakpoints, then continue.

  2. Suspend GDB, and copy the file containing your program to a new name. Resume GDB and use the exec-file command to specify that GDB should run your program under that name. Then start your program again.

  3. Relink your program so that the text segment is nonsharable, using the linker option `-N'. The operating system limitation may not apply to nonsharable executables.
A similar message can be printed if you request too many active hardware-assisted breakpoints and watchpoints:

Stopped; cannot insert breakpoints.
You may have requested too many hardware breakpoints and watchpoints.
This message is printed when you attempt to resume the program, since only then GDB knows exactly how many hardware breakpoints and watchpoints it needs to insert.

When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue.




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5.2 Continuing and stepping

Continuing means resuming program execution until your program completes normally. In contrast, stepping means executing just one more "step" of your program, where "step" may mean either one line of source code, or one machine instruction (depending on what particular command you use). Either when continuing or when stepping, your program may stop even sooner, due to a breakpoint or a signal. (If it stops due to a signal, you may want to use handle, or use `signal 0' to resume execution. See Signals.)

continue [ignore-count]
c [ignore-count]
fg [ignore-count]
Resume program execution, at the address where your program last stopped; any breakpoints set at that address are bypassed. The optional argument ignore-count allows you to specify a further number of times to ignore a breakpoint at this location; its effect is like that of ignore (see Conditions).

The argument ignore-count is meaningful only when your program stopped due to a breakpoint. At other times, the argument to continue is ignored.

The synonyms c and fg (for foreground, as the debugged program is deemed to be the foreground program) are provided purely for convenience, and have exactly the same behavior as continue.

To resume execution at a different place, you can use return (see Returning) to go back to the calling function; or jump (see Jumping) to go to an arbitrary location in your program.

A typical technique for using stepping is to set a breakpoint (see Breakpoints) at the beginning of the function or the section of your program where a problem is believed to lie, run your program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen.

step
Continue running your program until control reaches a different source line, then stop it and return control to GDB. This command is abbreviated s.

Warning: If you use the step command while control is within a function that was compiled without debugging information, execution proceeds until control reaches a function that does have debugging information. Likewise, it will not step into a function which is compiled without debugging information. To step through functions without debugging information, use the stepi command, described below.
The step command only stops at the first instruction of a source line. This prevents the multiple stops that could otherwise occur in switch statements, for loops, etc. step continues to stop if a function that has debugging information is called within the line. In other words, step steps inside any functions called within the line.

Also, the step command only enters a function if there is line number information for the function. Otherwise it acts like the next command. This avoids problems when using cc -gl on MIPS machines. Previously, step entered subroutines if there was any debugging information about the routine.

step count
Continue running as in step, but do so count times. If a breakpoint is reached, or a signal not related to stepping occurs before count steps, stepping stops right away.

next [count]
Continue to the next source line in the current (innermost) stack frame. This is similar to step, but function calls that appear within the line of code are executed without stopping. Execution stops when control reaches a different line of code at the original stack level that was executing when you gave the next command. This command is abbreviated n.

An argument count is a repeat count, as for step.

The next command only stops at the first instruction of a source line. This prevents multiple stops that could otherwise occur in switch statements, for loops, etc.

finish
Continue running until just after function in the selected stack frame returns. Print the returned value (if any).

Contrast this with the return command (see Returning).

until
u
Continue running until a source line past the current line, in the current stack frame, is reached. This command is used to avoid single stepping through a loop more than once. It is like the next command, except that when until encounters a jump, it automatically continues execution until the program counter is greater than the address of the jump.

This means that when you reach the end of a loop after single stepping though it, until makes your program continue execution until it exits the loop. In contrast, a next command at the end of a loop simply steps back to the beginning of the loop, which forces you to step through the next iteration.

until always stops your program if it attempts to exit the current stack frame.

until may produce somewhat counterintuitive results if the order of machine code does not match the order of the source lines. For example, in the following excerpt from a debugging session, the f (frame) command shows that execution is stopped at line 206; yet when we use until, we get to line 195:

(gdb) f
#0  main (argc=4, argv=0xf7fffae8) at m4.c:206
206                 expand_input();
(gdb) until
195             for ( ; argc > 0; NEXTARG) {
This happened because, for execution efficiency, the compiler had generated code for the loop closure test at the end, rather than the start, of the loop--even though the test in a C for-loop is written before the body of the loop. The until command appeared to step back to the beginning of the loop when it advanced to this expression; however, it has not really gone to an earlier statement--not in terms of the actual machine code.

until with no argument works by means of single instruction stepping, and hence is slower than until with an argument.

until location
u location
Continue running your program until either the specified location is reached, or the current stack frame returns. location is any of the forms of argument acceptable to break (see Set Breaks). This form of the command uses breakpoints, and hence is quicker than until without an argument.

stepi
si
Execute one machine instruction, then stop and return to the debugger.

It is often useful to do `display/i $pc' when stepping by machine instructions. This makes GDB automatically display the next instruction to be executed, each time your program stops. See Auto Display.

An argument is a repeat count, as in step.

nexti
ni
Execute one machine instruction, but if it is a function call, proceed until the function returns.

An argument is a repeat count, as in next.




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5.3 Signals

A signal is an asynchronous event that can happen in a program. The operating system defines the possible kinds of signals, and gives each kind a name and a number. For example, in Unix SIGINT is the signal a program gets when you type an interrupt character (often C-c); SIGSEGV is the signal a program gets from referencing a place in memory far away from all the areas in use; SIGALRM occurs when the alarm clock timer goes off (which happens only if your program has requested an alarm).

Some signals, including SIGALRM, are a normal part of the functioning of your program. Others, such as SIGSEGV, indicate errors; these signals are fatal (they kill your program immediately) if the program has not specified in advance some other way to handle the signal. SIGINT does not indicate an error in your program, but it is normally fatal so it can carry out the purpose of the interrupt: to kill the program.

GDB has the ability to detect any occurrence of a signal in your program. You can tell GDB in advance what to do for each kind of signal.

Normally, GDB is set up to ignore non-erroneous signals like SIGALRM (so as not to interfere with their role in the functioning of your program) but to stop your program immediately whenever an error signal happens. You can change these settings with the handle command.

info signals
Print a table of all the kinds of signals and how GDB has been told to handle each one. You can use this to see the signal numbers of all the defined types of signals.

info handle is an alias for info signals.

handle signal keywords...
Change the way GDB handles signal signal. signal can be the number of a signal or its name (with or without the `SIG' at the beginning). The keywords say what change to make.

The keywords allowed by the handle command can be abbreviated. Their full names are:

nostop
GDB should not stop your program when this signal happens. It may still print a message telling you that the signal has come in.

stop
GDB should stop your program when this signal happens. This implies the print keyword as well.

print
GDB should print a message when this signal happens.

noprint
GDB should not mention the occurrence of the signal at all. This implies the nostop keyword as well.

pass
GDB should allow your program to see this signal; your program can handle the signal, or else it may terminate if the signal is fatal and not handled.

nopass
GDB should not allow your program to see this signal.

When a signal stops your program, the signal is not visible to the program until you continue. Your program sees the signal then, if pass is in effect for the signal in question at that time. In other words, after GDB reports a signal, you can use the handle command with pass or nopass to control whether your program sees that signal when you continue.

You can also use the signal command to prevent your program from seeing a signal, or cause it to see a signal it normally would not see, or to give it any signal at any time. For example, if your program stopped due to some sort of memory reference error, you might store correct values into the erroneous variables and continue, hoping to see more execution; but your program would probably terminate immediately as a result of the fatal signal once it saw the signal. To prevent this, you can continue with `signal 0'. See Signaling.




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5.4 Stopping and starting multi-thread programs

When your program has multiple threads (see Threads), you can choose whether to set breakpoints on all threads, or on a particular thread.

break linespec thread threadno
break linespec thread threadno if ...
linespec specifies source lines; there are several ways of writing them, but the effect is always to specify some source line.

Use the qualifier `thread threadno' with a breakpoint command to specify that you only want GDB to stop the program when a particular thread reaches this breakpoint. threadno is one of the numeric thread identifiers assigned by GDB, shown in the first column of the `info threads' display.

If you do not specify `thread threadno' when you set a breakpoint, the breakpoint applies to all threads of your program.

You can use the thread qualifier on conditional breakpoints as well; in this case, place `thread threadno' before the breakpoint condition, like this:

(gdb) break frik.c:13 thread 28 if bartab > lim

Whenever your program stops under GDB for any reason, all threads of execution stop, not just the current thread. This allows you to examine the overall state of the program, including switching between threads, without worrying that things may change underfoot.

Conversely, whenever you restart the program, all threads start executing. This is true even when single-stepping with commands like step or next.

In particular, GDB cannot single-step all threads in lockstep. Since thread scheduling is up to your debugging target's operating system (not controlled by GDB), other threads may execute more than one statement while the current thread completes a single step. Moreover, in general other threads stop in the middle of a statement, rather than at a clean statement boundary, when the program stops.

You might even find your program stopped in another thread after continuing or even single-stepping. This happens whenever some other thread runs into a breakpoint, a signal, or an exception before the first thread completes whatever you requested.

On some OSes, you can lock the OS scheduler and thus allow only a single thread to run.

set scheduler-locking mode
Set the scheduler locking mode. If it is off, then there is no locking and any thread may run at any time. If on, then only the current thread may run when the inferior is resumed. The step mode optimizes for single-stepping. It stops other threads from "seizing the prompt" by preempting the current thread while you are stepping. Other threads will only rarely (or never) get a chance to run when you step. They are more likely to run when you `next' over a function call, and they are completely free to run when you use commands like `continue', `until', or `finish'. However, unless another thread hits a breakpoint during its timeslice, they will never steal the GDB prompt away from the thread that you are debugging.

show scheduler-locking
Display the current scheduler locking mode.




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6. Examining the Stack

When your program has stopped, the first thing you need to know is where it stopped and how it got there.

Each time your program performs a function call, information about the call is generated. That information includes the location of the call in your program, the arguments of the call, and the local variables of the function being called. The information is saved in a block of data called a stack frame. The stack frames are allocated in a region of memory called the call stack.

When your program stops, the GDB commands for examining the stack allow you to see all of this information.

One of the stack frames is selected by GDB and many GDB commands refer implicitly to the selected frame. In particular, whenever you ask GDB for the value of a variable in your program, the value is found in the selected frame. There are special GDB commands to select whichever frame you are interested in. See Selection.

When your program stops, GDB automatically selects the currently executing frame and describes it briefly, similar to the frame command (see Frame Info).

FramesStack frames
BacktraceBacktraces
SelectionSelecting a frame
Frame InfoInformation on a frame




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6.1 Stack frames

The call stack is divided up into contiguous pieces called stack frames, or frames for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing.

When your program is started, the stack has only one frame, that of the function main. This is called the initial frame or the outermost frame. Each time a function is called, a new frame is made. Each time a function returns, the frame for that function invocation is eliminated. If a function is recursive, there can be many frames for the same function. The frame for the function in which execution is actually occurring is called the innermost frame. This is the most recently created of all the stack frames that still exist.

Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually this address is kept in a register called the frame pointer register while execution is going on in that frame.

GDB assigns numbers to all existing stack frames, starting with zero for the innermost frame, one for the frame that called it, and so on upward. These numbers do not really exist in your program; they are assigned by GDB to give you a way of designating stack frames in GDB commands.

Some compilers provide a way to compile functions so that they operate without stack frames. (For example, the gcc option `-fomit-frame-pointer' generates functions without a frame.) This is occasionally done with heavily used library functions to save the frame setup time. GDB has limited facilities for dealing with these function invocations. If the innermost function invocation has no stack frame, GDB nevertheless regards it as though it had a separate frame, which is numbered zero as usual, allowing correct tracing of the function call chain. However, GDB has no provision for frameless functions elsewhere in the stack.

frame args
The frame command allows you to move from one stack frame to another, and to print the stack frame you select. args may be either the address of the frame or the stack frame number. Without an argument, frame prints the current stack frame.

select-frame
The select-frame command allows you to move from one stack frame to another without printing the frame. This is the silent version of frame.




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6.2 Backtraces

A backtrace is a summary of how your program got where it is. It shows one line per frame, for many frames, starting with the currently executing frame (frame zero), followed by its caller (frame one), and on up the stack.

backtrace
bt
Print a backtrace of the entire stack: one line per frame for all frames in the stack.

You can stop the backtrace at any time by typing the system interrupt character, normally C-c.

backtrace n
bt n
Similar, but print only the innermost n frames.

backtrace -n
bt -n
Similar, but print only the outermost n frames.

backtrace-other-thread
Print backtrace of all stack frames for a thread with stack pointer SP and program counter PC. This command is useful in cases where the debugger does not support a user thread package fully.

The names where and info stack (abbreviated info s) are additional aliases for backtrace.

Each line in the backtrace shows the frame number and the function name. The program counter value is also shown--unless you use set print address off. The backtrace also shows the source file name and line number, as well as the arguments to the function. The program counter value is omitted if it is at the beginning of the code for that line number.

Here is an example of a backtrace. It was made with the command `bt 3', so it shows the innermost three frames.

#0  m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8) 
    at builtin.c:993
#1  0x6e38 in expand_macro (sym=0x2b600) at macro.c:242
#2  0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
    at macro.c:71
(More stack frames follow...)
The display for frame zero does not begin with a program counter value, indicating that your program has stopped at the beginning of the code for line 993 of builtin.c.




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6.3 Selecting a frame

Most commands for examining the stack and other data in your program work on whichever stack frame is selected at the moment. Here are the commands for selecting a stack frame; all of them finish by printing a brief description of the stack frame just selected.

frame n
f n
Select frame number n. Recall that frame zero is the innermost (currently executing) frame, frame one is the frame that called the innermost one, and so on. The highest-numbered frame is the one for main.

frame addr
f addr
Select the frame at address addr. This is useful mainly if the chaining of stack frames has been damaged by a bug, making it impossible for GDB to assign numbers properly to all frames. In addition, this can be useful when your program has multiple stacks and switches between them.

On the SPARC architecture, frame needs two addresses to select an arbitrary frame: a frame pointer and a stack pointer.

On the MIPS and Alpha architecture, it needs two addresses: a stack pointer and a program counter.

On the 29k architecture, it needs three addresses: a register stack pointer, a program counter, and a memory stack pointer.

up n
Move n frames up the stack. For positive numbers n, this advances toward the outermost frame, to higher frame numbers, to frames that have existed longer. n defaults to one.

down n
Move n frames down the stack. For positive numbers n, this advances toward the innermost frame, to lower frame numbers, to frames that were created more recently. n defaults to one. You may abbreviate down as do.

All of these commands end by printing two lines of output describing the frame. The first line shows the frame number, the function name, the arguments, and the source file and line number of execution in that frame. The second line shows the text of that source line.

For example:

(gdb) up
#1  0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
    at env.c:10
10              read_input_file (argv[i]);
After such a printout, the list command with no arguments prints ten lines centered on the point of execution in the frame. See List.

up-silently n
down-silently n
These two commands are variants of up and down, respectively; they differ in that they do their work silently, without causing display of the new frame. They are intended primarily for use in GDB command scripts, where the output might be unnecessary and distracting.




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6.4 Information about a frame

There are several other commands to print information about the selected stack frame.

frame
f
When used without any argument, this command does not change which frame is selected, but prints a brief description of the currently selected stack frame. It can be abbreviated f. With an argument, this command is used to select a stack frame. See Selection.

info frame
info f
This command prints a verbose description of the selected stack frame, including:

The verbose description is useful when something has gone wrong that has made the stack format fail to fit the usual conventions.

info frame addr
info f addr
Print a verbose description of the frame at address addr, without selecting that frame. The selected frame remains unchanged by this command. This requires the same kind of address (more than one for some architectures) that you specify in the frame command. See Selection.

info args
Print the arguments of the selected frame, each on a separate line.

info locals
Print the local variables of the selected frame, each on a separate line. These are all variables (declared either static or automatic) accessible at the point of execution of the selected frame.

info catch
Print a list of all the exception handlers that are active in the current stack frame at the current point of execution. To see other exception handlers, visit the associated frame (using the up, down, or frame commands); then type info catch. See Set Catchpoints.




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7. Examining Source Files

GDB can print parts of your program's source, since the debugging information recorded in the program tells GDB what source files were used to build it. When your program stops, GDB spontaneously prints the line where it stopped. Likewise, when you select a stack frame (see Selection), GDB prints the line where execution in that frame has stopped. You can print other portions of source files by explicit command.

If you use GDB through its GNU Emacs interface, you may prefer to use Emacs facilities to view source; see Emacs.

ListPrinting source lines
SearchSearching source files
Source PathSpecifying source directories
Machine CodeSource and machine code




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7.1 Printing source lines

To print lines from a source file, use the list command (abbreviated l). By default, ten lines are printed. There are several ways to specify what part of the file you want to print.

Here are the forms of the list command most commonly used:

list linenum
Print lines centered around line number linenum in the current source file.

list function
Print lines centered around the beginning of function function.

list
Print more lines. If the last lines printed were printed with a list command, this prints lines following the last lines printed; however, if the last line printed was a solitary line printed as part of displaying a stack frame (see Stack), this prints lines centered around that line.

list -
Print lines just before the lines last printed.

By default, GDB prints ten source lines with any of these forms of the list command. You can change this using set listsize:

set listsize count
Make the list command display count source lines (unless the list argument explicitly specifies some other number).

show listsize
Display the number of lines that list prints.

Repeating a list command with RET discards the argument, so it is equivalent to typing just list. This is more useful than listing the same lines again. An exception is made for an argument of `-'; that argument is preserved in repetition so that each repetition moves up in the source file.

In general, the list command expects you to supply zero, one or two linespecs. Linespecs specify source lines; there are several ways of writing them, but the effect is always to specify some source line. Here is a complete description of the possible arguments for list:

list linespec
Print lines centered around the line specified by linespec.

list first,last
Print lines from first to last. Both arguments are linespecs.

list ,last
Print lines ending with last.

list first,
Print lines starting with first.

list +
Print lines just after the lines last printed.

list -
Print lines just before the lines last printed.

list
As described in the preceding table.

Here are the ways of specifying a single source line--all the kinds of linespec.

number
Specifies line number of the current source file. When a list command has two linespecs, this refers to the same source file as the first linespec.

+offset
Specifies the line offset lines after the last line printed. When used as the second linespec in a list command that has two, this specifies the line offset lines down from the first linespec.

-offset
Specifies the line offset lines before the last line printed.

filename:number
Specifies line number in the source file filename.

function
Specifies the line that begins the body of the function function. For example: in C, this is the line with the open brace.

filename:function
Specifies the line of the open-brace that begins the body of the function function in the file filename. You only need the file name with a function name to avoid ambiguity when there are identically named functions in different source files.

*address
Specifies the line containing the program address address. address may be any expression.




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7.2 Searching source files

There are two commands for searching through the current source file for a regular expression.

forward-search regexp
search regexp
The command `forward-search regexp' checks each line, starting with the one following the last line listed, for a match for regexp. It lists the line that is found. You can use the synonym `search regexp' or abbreviate the command name as fo.

reverse-search regexp
The command `reverse-search regexp' checks each line, starting with the one before the last line listed and going backward, for a match for regexp. It lists the line that is found. You can abbreviate this command as rev.




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7.3 Specifying source directories

Executable programs sometimes do not record the directories of the source files from which they were compiled, just the names. Even when they do, the directories could be moved between the compilation and your debugging session. GDB has a list of directories to search for source files; this is called the source path. Each time GDB wants a source file, it tries all the directories in the list, in the order they are present in the list, until it finds a file with the desired name. Note that the executable search path is not used for this purpose. Neither is the current working directory, unless it happens to be in the source path.

If GDB cannot find a source file in the source path, and the object program records a directory, GDB tries that directory too. If the source path is empty, and there is no record of the compilation directory, GDB looks in the current directory as a last resort.

Whenever you reset or rearrange the source path, GDB clears out any information it has cached about where source files are found and where each line is in the file.

When you start GDB, its source path includes only `cdir' and `cwd', in that order. To add other directories, use the directory command.

directory dirname ...
dir dirname ...
Add directory dirname to the front of the source path. Several directory names may be given to this command, separated by `:' (`;' on MS-DOS and MS-Windows, where `:' usually appears as part of absolute file names) or white space. You may specify a directory that is already in the source path; this moves it forward, so GDB searches it sooner.

You can use the string `$cdir' to refer to the compilation directory (if one is recorded), and `$cwd' to refer to the current working directory. `$cwd' is not the same as `.'---the former tracks the current working directory as it changes during your GDB session, while the latter is immediately expanded to the current directory at the time you add an entry to the source path.

directory
Reset the source path to empty again. This requires confirmation.

show directories
Print the source path: show which directories it contains.

If your source path is cluttered with directories that are no longer of interest, GDB may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows:

  1. Use directory with no argument to reset the source path to empty.

  2. Use directory with suitable arguments to reinstall the directories you want in the source path. You can add all the directories in one command.



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7.4 Source and machine code

You can use the command info line to map source lines to program addresses (and vice versa), and the command disassemble to display a range of addresses as machine instructions. When run under GNU Emacs mode, the info line command causes the arrow to point to the line specified. Also, info line prints addresses in symbolic form as well as hex.

info line linespec
Print the starting and ending addresses of the compiled code for source line linespec. You can specify source lines in any of the ways understood by the list command (see List).

For example, we can use info line to discover the location of the object code for the first line of function m4_changequote:

(gdb) info line m4_changecom
Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350.
We can also inquire (using *addr as the form for linespec) what source line covers a particular address:
(gdb) info line *0x63ff
Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404.

After info line, the default address for the x command is changed to the starting address of the line, so that `x/i' is sufficient to begin examining the machine code (see Memory). Also, this address is saved as the value of the convenience variable $_ (see Convenience Vars).

disassemble
This specialized command dumps a range of memory as machine instructions. The default memory range is the function surrounding the program counter of the selected frame. A single argument to this command is a program counter value; GDB dumps the function surrounding this value. Two arguments specify a range of addresses (first inclusive, second exclusive) to dump.

The following example shows the disassembly of a range of addresses of HP PA-RISC 2.0 code:

(gdb) disas 0x32c4 0x32e4
Dump of assembler code from 0x32c4 to 0x32e4:
0x32c4 <main+204>:      addil 0,dp
0x32c8 <main+208>:      ldw 0x22c(sr0,r1),r26
0x32cc <main+212>:      ldil 0x3000,r31
0x32d0 <main+216>:      ble 0x3f8(sr4,r31)
0x32d4 <main+220>:      ldo 0(r31),rp
0x32d8 <main+224>:      addil -0x800,dp
0x32dc <main+228>:      ldo 0x588(r1),r26
0x32e0 <main+232>:      ldil 0x3000,r31
End of assembler dump.
Some architectures have more than one commonly-used set of instruction mnemonics or other syntax.

set disassembly-flavor instruction-set
Select the instruction set to use when disassembling the program via the disassemble or x/i commands.

Currently this command is only defined for the Intel x86 family. You can set instruction-set to either intel or att. The default is att, the AT&T flavor used by default by Unix assemblers for x86-based targets.




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8. Examining Data

The usual way to examine data in your program is with the print command (abbreviated p), or its synonym inspect. It evaluates and prints the value of an expression of the language your program is written in (see Languages).

print expr
print /f expr
expr is an expression (in the source language). By default the value of expr is printed in a format appropriate to its data type; you can choose a different format by specifying `/f', where f is a letter specifying the format; see Output Formats.

print
print /f
If you omit expr, GDB displays the last value again (from the value history; see Value History). This allows you to conveniently inspect the same value in an alternative format.

A more low-level way of examining data is with the x command. It examines data in memory at a specified address and prints it in a specified format. See Memory.

If you are interested in information about types, or about how the fields of a struct or a class are declared, use the ptype exp command rather than print. See Symbols.

ExpressionsExpressions
VariablesProgram variables
ArraysArtificial arrays
Output FormatsOutput formats
MemoryExamining memory
Auto DisplayAutomatic display
Print SettingsPrint settings
Value HistoryValue history
Convenience VarsConvenience variables
RegistersRegisters
Floating Point HardwareFloating point hardware
Printing Floating Point ValuesPrinting Floating Point Values




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8.1 Expressions

print and many other GDB commands accept an expression and compute its value. Any kind of constant, variable or operator defined by the programming language you are using is valid in an expression in GDB. This includes conditional expressions, function calls, casts and string constants. It unfortunately does not include symbols defined by preprocessor #define commands.

GDB supports array constants in expressions input by the user. The syntax is {element, element...}. For example, you can use the command print {1, 2, 3} to build up an array in memory that is malloced in the target program.

Because C is so widespread, most of the expressions shown in examples in this manual are in C. See Languages, for information on how to use expressions in other languages.

In this section, we discuss operators that you can use in GDB expressions regardless of your programming language.

Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory.

GDB supports these operators, in addition to those common to programming languages:

@
`@' is a binary operator for treating parts of memory as arrays. See Arrays, for more information.

::
`::' allows you to specify a variable in terms of the file or function where it is defined. See Variables.

{type} addr
Refers to an object of type type stored at address addr in memory. addr may be any expression whose value is an integer or pointer (but parentheses are required around binary operators, just as in a cast). This construct is allowed regardless of what kind of data is normally supposed to reside at addr.




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8.2 Program variables

The most common kind of expression to use is the name of a variable in your program.

Variables in expressions are understood in the selected stack frame (see Selection); they must be either:

or

This means that in the function

foo (a)
     int a;
{
  bar (a);
  {
    int b = test ();
    bar (b);
  }
}
you can examine and use the variable a whenever your program is executing within the function foo, but you can only use or examine the variable b while your program is executing inside the block where b is declared.

There is an exception: you can refer to a variable or function whose scope is a single source file even if the current execution point is not in this file. But it is possible to have more than one such variable or function with the same name (in different source files). If that happens, referring to that name has unpredictable effects. If you wish, you can specify a static variable in a particular function or file, using the colon-colon notation:

file::variable
function::variable
Here file or function is the name of the context for the static variable. In the case of file names, you can use quotes to make sure GDB parses the file name as a single word--for example, to print a global value of x defined in `f2.c':

(gdb) p 'f2.c'::x

This use of `::' is very rarely in conflict with the very similar use of the same notation in C++. GDB also supports use of the C++ scope resolution operator in GDB expressions.

Warning: Occasionally, a local variable may appear to have the wrong value at certain points in a function--just after entry to a new scope, and just before exit.
You may see this problem when you are stepping by machine instructions. This is because, on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you are stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone.

This may also happen when the compiler does significant optimizations. To be sure of always seeing accurate values, turn off all optimization when compiling.

Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, GDB might not be able to display values for such local variables. If that happens, GDB will print a message like this:

No symbol "foo" in current context.
To solve such problems, either recompile without optimizations, or use a different debug info format, if the compiler supports several such formats. For example, GCC, the GNU C/C++ compiler usually supports the `-gstabs' option. `-gstabs' produces debug info in a format that is superior to formats such as COFF. You may be able to use DWARF-2 (`-gdwarf-2'), which is also an effective form for debug info. See Compilation.




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8.3 Artificial arrays

It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program.

You can do this by referring to a contiguous span of memory as an artificial array, using the binary operator `@'. The left operand of `@' should be the first element of the desired array and be an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says

int *array = (int *) malloc (len * sizeof (int));
you can print the contents of array with

p *array@len
The left operand of `@' must reside in memory. Array values made with `@' in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (see Value History), after printing one out.

Another way to create an artificial array is to use a cast. This re-interprets a value as if it were an array. The value need not be in memory:

(gdb) p/x (short[2])0x12345678
$1 = {0x1234, 0x5678}
As a convenience, if you leave the array length out (as in `(type[])value') GDB calculates the size to fill the value (as `sizeof(value)/sizeof(type)':
(gdb) p/x (short[])0x12345678
$2 = {0x1234, 0x5678}
Sometimes the artificial array mechanism is not quite enough; in moderately complex data structures, the elements of interest may not actually be adjacent--for example, if you are interested in the values of pointers in an array. One useful work-around in this situation is to use a convenience variable (see Convenience Vars) as a counter in an expression that prints the first interesting value, and then repeat that expression via RET. For instance, suppose you have an array dtab of pointers to structures, and you are interested in the values of a field fv in each structure. Here is an example of what you might type:

set $i = 0
p dtab[$i++]->fv
RET
RET
...



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8.4 Output formats

By default, GDB prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an output format when you print a value.

The simplest use of output formats is to say how to print a value already computed. This is done by starting the arguments of the print command with a slash and a format letter. The format letters supported are:

x
Regard the bits of the value as an integer, and print the integer in hexadecimal.

d
Print as integer in signed decimal.

u
Print as integer in unsigned decimal.

o
Print as integer in octal.

t
Print as integer in binary. The letter `t' stands for "two". (1)

a
Print as an address, both absolute in hexadecimal and as an offset from the nearest preceding symbol. You can use this format used to discover where (in what function) an unknown address is located:

(gdb) p/a 0x54320
$3 = 0x54320 <_initialize_vx+396>
c
Regard as an integer and print it as a character constant.

f
Regard the bits of the value as a floating point number and print using typical floating point syntax.

For example, to print the program counter in hex (see Registers), type

p/x $pc
Note that no space is required before the slash; this is because command names in GDB cannot contain a slash.

To reprint the last value in the value history with a different format, you can use the print command with just a format and no expression. For example, `p/x' reprints the last value in hex.




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8.5 Examining memory

You can use the command x (for "examine") to examine memory in any of several formats, independently of your program's data types.

x/nfu addr
x addr
x
Use the x command to examine memory.

n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash `/'. Several commands set convenient defaults for addr.

n, the repeat count
The repeat count is a decimal integer; the default is 1. It specifies how much memory (counting by units u) to display.

f, the display format
The display format is one of the formats used by print, `s' (null-terminated string), or `i' (machine instruction). The default is `x' (hexadecimal) initially. The default changes each time you use either x or print.

u, the unit size
The unit size is any of

b
Bytes.
h
Halfwords (two bytes).
w
Words (four bytes). This is the initial default.
g
Giant words (eight bytes).

Each time you specify a unit size with x, that size becomes the default unit the next time you use x. (For the `s' and `i' formats, the unit size is ignored and is normally not written.)

addr, starting display address
addr is the address where you want GDB to begin displaying memory. The expression need not have a pointer value (though it may); it is always interpreted as an integer address of a byte of memory. See Expressions, for more information on expressions. The default for addr is usually just after the last address examined--but several other commands also set the default address: info breakpoints (to the address of the last breakpoint listed), info line (to the starting address of a line), and print (if you use it to display a value from memory).

For example, `x/3uh 0x54320' is a request to display three halfwords (h) of memory, formatted as unsigned decimal integers (`u'), starting at address 0x54320. `x/4xw $sp' prints the four words (`w') of memory above the stack pointer (here, `$sp'; see Registers) in hexadecimal (`x').

Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications `4xw' and `4wx' mean exactly the same thing. (However, the count n must come first; `wx4' does not work.)

Even though the unit size u is ignored for the formats `s' and `i', you might still want to use a count n; for example, `3i' specifies that you want to see three machine instructions, including any operands. The command disassemble gives an alternative way of inspecting machine instructions; see Machine Code.

All the defaults for the arguments to x are designed to make it easy to continue scanning memory with minimal specifications each time you use x. For example, after you have inspected three machine instructions with `x/3i addr', you can inspect the next seven with just `x/7'. If you use RET to repeat the x command, the repeat count n is used again; the other arguments default as for successive uses of x.

The addresses and contents printed by the x command are not saved in the value history because there is often too much of them and they would get in the way. Instead, GDB makes these values available for subsequent use in expressions as values of the convenience variables $_ and $__. After an x command, the last address examined is available for use in expressions in the convenience variable $_. The contents of that address, as examined, are available in the convenience variable $__.

If the x command has a repeat count, the address and contents saved are from the last memory unit printed; this is not the same as the last address printed if several units were printed on the last line of output.




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8.6 Automatic display

If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the automatic display list so that GDB prints its value each time your program stops. Each expression added to the list is given a number to identify it; to remove an expression from the list, you specify that number. The automatic display looks like this:

2: foo = 38
3: bar[5] = (struct hack *) 0x3804
This display shows item numbers, expressions and their current values. As with displays you request manually using x or print, you can specify the output format you prefer; in fact, display decides whether to use print or x depending on how elaborate your format specification is--it uses x if you specify a unit size, or one of the two formats (`i' and `s') that are only supported by x; otherwise it uses print.

display expr
Add the expression expr to the list of expressions to display each time your program stops. See Expressions.

display does not repeat if you press RET again after using it.

display/fmt expr
For fmt specifying only a display format and not a size or count, add the expression expr to the auto-display list but arrange to display it each time in the specified format fmt. See Output Formats.

display/fmt addr
For fmt `i' or `s', or including a unit-size or a number of units, add the expression addr as a memory address to be examined each time your program stops. Examining means in effect doing `x/fmt addr'. See Memory.

For example, `display/i $pc' can be helpful, to see the machine instruction about to be executed each time execution stops (`$pc' is a common name for the program counter; see Registers).

undisplay dnums...
delete display dnums...
Remove item numbers dnums from the list of expressions to display.

undisplay does not repeat if you press RET after using it. (Otherwise you would just get the error `No display number ...'.)

disable display dnums...
Disable the display of item numbers dnums. A disabled display item is not printed automatically, but is not forgotten. It may be enabled again later.

enable display dnums...
Enable display of item numbers dnums. It becomes effective once again in auto display of its expression, until you specify otherwise.

display
Display the current values of the expressions on the list, just as is done when your program stops.

info display
Print the list of expressions previously set up to display automatically, each one with its item number, but without showing the values. This includes disabled expressions, which are marked as such. It also includes expressions which would not be displayed right now because they refer to automatic variables not currently available.

If a display expression refers to local variables, then it does not make sense outside the lexical context for which it was set up. Such an expression is disabled when execution enters a context where one of its variables is not defined. For example, if you give the command display last_char while inside a function with an argument last_char, GDB displays this argument while your program continues to stop inside that function. When it stops elsewhere--where there is no variable last_char---the display is disabled automatically. The next time your program stops where last_char is meaningful, you can enable the display expression once again.




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8.7 Print settings

GDB provides the following ways to control how arrays, structures, and symbols are printed.

These settings are useful for debugging programs in any language:

set print address
set print address on
GDB prints memory addresses showing the location of stack traces, structure values, pointer values, breakpoints, and so forth, even when it also displays the contents of those addresses. The default is on. For example, this is what a stack frame display looks like with set print address on:

(gdb) f
#0  set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
    at input.c:530
530         if (lquote != def_lquote)
set print address off
Do not print addresses when displaying their contents. For example, this is the same stack frame displayed with set print address off:

(gdb) set print addr off
(gdb) f
#0  set_quotes (lq="<<", rq=">>") at input.c:530
530         if (lquote != def_lquote)
You can use `set print address off' to eliminate all machine dependent displays from the GDB interface. For example, with print address off, you should get the same text for backtraces on all machines--whether or not they involve pointer arguments.

show print address
Show whether or not addresses are to be printed.

When GDB prints a symbolic address, it normally prints the closest earlier symbol plus an offset. If that symbol does not uniquely identify the address (for example, it is a name whose scope is a single source file), you may need to clarify. One way to do this is with info line, for example `info line *0x4537'. Alternately, you can set GDB to print the source file and line number when it prints a symbolic address:

set print symbol-filename on
Tell GDB to print the source file name and line number of a symbol in the symbolic form of an address.

set print symbol-filename off
Do not print source file name and line number of a symbol. This is the default.

show print symbol-filename
Show whether or not GDB will print the source file name and line number of a symbol in the symbolic form of an address.

Another situation where it is helpful to show symbol filenames and line numbers is when disassembling code; GDB shows you the line number and source file that corresponds to each instruction.

Also, you may wish to see the symbolic form only if the address being printed is reasonably close to the closest earlier symbol:

set print max-symbolic-offset max-offset
Tell GDB to only display the symbolic form of an address if the offset between the closest earlier symbol and the address is less than max-offset. The default is 0, which tells GDB to always print the symbolic form of an address if any symbol precedes it.

show print max-symbolic-offset
Ask how large the maximum offset is that GDB prints in a symbolic address.

If you have a pointer and you are not sure where it points, try `set print symbol-filename on'. Then you can determine the name and source file location of the variable where it points, using `p/a pointer'. This interprets the address in symbolic form. For example, here GDB shows that a variable ptt points at another variable t, defined in `hi2.c':

(gdb) set print symbol-filename on
(gdb) p/a ptt
$4 = 0xe008 <t in hi2.c>
Warning: For pointers that point to a local variable, `p/a' does not show the symbol name and filename of the referent, even with the appropriate set print options turned on.
Other settings control how different kinds of objects are printed:

set print array
set print array on
Pretty print arrays. This format is more convenient to read, but uses more space. The default is off.

set print array off
Return to compressed format for arrays.

show print array
Show whether compressed or pretty format is selected for displaying arrays.

set print elements number-of-elements
Set a limit on how many elements of an array GDB will print. If GDB is printing a large array, it stops printing after it has printed the number of elements set by the set print elements command. This limit also applies to the display of strings. When GDB starts, this limit is set to 200. Setting number-of-elements to zero means that the printing is unlimited.

show print elements
Display the number of elements of a large array that GDB will print. If the number is 0, then the printing is unlimited.

set print null-stop
Cause GDB to stop printing the characters of an array when the first NULL is encountered. This is useful when large arrays actually contain only short strings. The default is off.

set print pretty on
Cause GDB to print structures in an indented format with one member per line, like this:

$1 = {
  next = 0x0,
  flags = {
    sweet = 1,
    sour = 1
  },
  meat = 0x54 "Pork"
}
set print pretty off
Cause GDB to print structures in a compact format, like this:

$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \
meat = 0x54 "Pork"}
This is the default format.

show print pretty
Show which format GDB is using to print structures.

set print sevenbit-strings on
Print using only seven-bit characters; if this option is set, GDB displays any eight-bit characters (in strings or character values) using the notation \nnn. This setting is best if you are working in English (ASCII) and you use the high-order bit of characters as a marker or "meta" bit.

set print sevenbit-strings off
Print full eight-bit characters. This allows the use of more international character sets, and is the default.

show print sevenbit-strings
Show whether or not GDB is printing only seven-bit characters.

set print union on
Tell GDB to print unions which are contained in structures. This is the default setting.

set print union off
Tell GDB not to print unions which are contained in structures.

show print union
Ask GDB whether or not it will print unions which are contained in structures.

For example, given the declarations

typedef enum {Tree, Bug} Species;
typedef enum {Big_tree, Acorn, Seedling} Tree_forms;
typedef enum {Caterpillar, Cocoon, Butterfly} 
              Bug_forms;

struct thing {
  Species it;
  union {
    Tree_forms tree;
    Bug_forms bug;
  } form;
};

struct thing foo = {Tree, {Acorn}};
with set print union on in effect `p foo' would print

$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}
and with set print union off in effect it would print

$1 = {it = Tree, form = {...}}

These settings are of interest when debugging C++ programs:

set print demangle
set print demangle on
Print C++ names in their source form rather than in the encoded ("mangled") form passed to the assembler and linker for type-safe linkage. The default is on.

show print demangle
Show whether C++ names are printed in mangled or demangled form.

set print asm-demangle
set print asm-demangle on
Print C++ names in their source form rather than their mangled form, even in assembler code printouts such as instruction disassemblies. The default is off.

show print asm-demangle
Show whether C++ names in assembly listings are printed in mangled or demangled form.

set demangle-style style
Choose among several encoding schemes used by different compilers to represent C++ names. The choices for style are currently:

auto
Allow GDB to choose a decoding style by inspecting your program.

gnu
Decode based on the GNU C++ compiler (g++) encoding algorithm.

hp
Decode based on the HP ANSI C++ (aCC) encoding algorithm. This is the default.
lucid
Decode based on the Lucid C++ compiler (lcc) encoding algorithm.

arm
Decode using the algorithm in the C++ Annotated Reference Manual. Warning: this setting alone is not sufficient to allow debugging cfront-generated executables. GDB would require further enhancement to permit that.

If you omit style, you will see a list of possible formats.

show demangle-style
Display the encoding style currently in use for decoding C++ symbols.

set print object
set print object on
When displaying a pointer to an object, identify the actual (derived) type of the object rather than the declared type, using the virtual function table.

set print object off
Display only the declared type of objects, without reference to the virtual function table. This is the default setting.

show print object
Show whether actual, or declared, object types are displayed.

set print static-members
set print static-members on
Print static members when displaying a C++ object. The default is on.

set print static-members off
Do not print static members when displaying a C++ object.

show print static-members
Show whether C++ static members are printed, or not.

set print vtbl
set print vtbl on
Pretty print C++ virtual function tables. The default is off. (The vtbl commands do not work on programs compiled with the HP ANSI C++ compiler (aCC).)

set print vtbl off
Do not pretty print C++ virtual function tables.

show print vtbl
Show whether C++ virtual function tables are pretty printed, or not.




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8.8 Value history

Values printed by the print command are saved in the GDB value history. This allows you to refer to them in other expressions. Values are kept until the symbol table is re-read or discarded (for example with the file or symbol-file commands). When the symbol table changes, the value history is discarded, since the values may contain pointers back to the types defined in the symbol table.

The values printed are given history numbers by which you can refer to them. These are successive integers starting with one. print shows you the history number assigned to a value by printing `$num = ' before the value; here num is the history number.

To refer to any previous value, use `$' followed by the value's history number. The way print labels its output is designed to remind you of this. Just $ refers to the most recent value in the history, and $$ refers to the value before that. $$n refers to the nth value from the end; $$2 is the value just prior to $$, $$1 is equivalent to $$, and $$0 is equivalent to $.

For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type

p *$
If you have a chain of structures where the component next points to the next one, you can print the contents of the next one with this:

p *$.next
You can print successive links in the chain by repeating this command--which you can do by just typing RET.

Note that the history records values, not expressions. If the value of x is 4 and you type these commands:

print x
set x=5
then the value recorded in the value history by the print command remains 4 even though the value of x has changed.

show values
Print the last ten values in the value history, with their item numbers. This is like `p $$9' repeated ten times, except that show values does not change the history.

show values n
Print ten history values centered on history item number n.

show values +
Print ten history values just after the values last printed. If no more values are available, show values + produces no display.

Pressing RET to repeat show values n has exactly the same effect as `show values +'.




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8.9 Convenience variables

GDB provides convenience variables that you can use within GDB to hold on to a value and refer to it later. These variables exist entirely within GDB; they are not part of your program, and setting a convenience variable has no direct effect on further execution of your program. That is why you can use them freely.

Convenience variables are prefixed with `$'. Any name preceded by `$' can be used for a convenience variable, unless it is one of the predefined machine-specific register names (see Registers). (Value history references, in contrast, are numbers preceded by `$'. See Value History.)

You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. For example:

set $foo = *object_ptr
would save in $foo the value contained in the object pointed to by object_ptr.

Using a convenience variable for the first time creates it, but its value is void until you assign a new value. You can alter the value with another assignment at any time.

Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value.

show convenience
Print a list of convenience variables used so far, and their values. Abbreviated show conv.

One of the ways to use a convenience variable is as a counter to be incremented or a pointer to be advanced. For example, to print a field from successive elements of an array of structures:

set $i = 0
print bar[$i++]->contents
Repeat that command by typing RET.

Some convenience variables are created automatically by GDB and given values likely to be useful.

$_
The variable $_ is automatically set by the x command to the last address examined (see Memory). Other commands which provide a default address for x to examine also set $_ to that address; these commands include info line and info breakpoint. The type of $_ is void * except when set by the x command, in which case it is a pointer to the type of $__.

$__
The variable $__ is automatically set by the x command to the value found in the last address examined. Its type is chosen to match the format in which the data was printed.

$_exitcode
The variable $_exitcode is automatically set to the exit code when the program being debugged terminates.

On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, GDB searches for a user or system name first, before it searches for a convenience variable.




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8.10 Registers

You can refer to machine register contents, in expressions, as variables with names starting with `$'. The names of registers are different for each machine; use info registers to see the names used on your machine.

info registers
Print the names and values of all registers except floating-point registers (in the selected stack frame).

info all-registers
Print the names and values of all registers, including floating-point registers.

info registers regname ...
Print the relativized value of each specified register regname. As discussed in detail below, register values are normally relative to the selected stack frame. regname may be any register name valid on the machine you are using, with or without the initial `$'.

GDB has four "standard" register names that are available (in expressions) on most machines--whenever they do not conflict with an architecture's canonical mnemonics for registers. The register names $pc and $sp are used for the program counter register and the stack pointer. $fp is used for a register that contains a pointer to the current stack frame, and $ps is used for a register that contains the processor status. For example, you could print the program counter in hex with

p/x $pc
or print the instruction to be executed next with

x/i $pc
or add four to the stack pointer(2) with

set $sp += 4
Whenever possible, these four standard register names are available on your machine even though the machine has different canonical mnemonics, so long as there is no conflict. The info registers command shows the canonical names. For example, on the SPARC, info registers displays the processor status register as $psr but you can also refer to it as $ps, except on Unix systems; and on x86-based machines $ps is an alias for the EFLAGS register.

GDB always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can print it as a floating point value with `print/f $regname').

Some registers have distinct "raw" and "virtual" data formats. This means that the data format in which the register contents are saved by the operating system is not the same one that your program normally sees. For example, the registers of the 68881 floating point coprocessor are always saved in "extended" (raw) format, but all C programs expect to work with "double" (virtual) format. In such cases, GDB normally works with the virtual format only (the format that makes sense for your program), but the info registers command prints the data in both formats.

Normally, register values are relative to the selected stack frame (see Selection). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with `frame 0').

However, GDB must deduce where registers are saved, from the machine code generated by your compiler. If some registers are not saved, or if GDB is unable to locate the saved registers, the selected stack frame makes no difference.




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8.11 Printing Floating Point Values

You can print the values of floating-point registers in different formats.

To print both single- and double-precision values:

(gdb) info reg $fr5
fr5     (single precision)     10.1444092
fr5															     (double precision)     600000
To get the bit pattern, try the following macro:

define pbits
  set *((float *) $sp)=$arg0
  p/x *((int *) $sp)
end
This is what the macro produces:

(gdb) pbits $fr6
$1 = 0x4082852d



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8.12 Floating point hardware

Depending on the configuration, GDB may be able to give you more information about the status of the floating point hardware.

info float
Display hardware-dependent information about the floating point unit. The exact contents and layout vary depending on the floating point chip. Currently, `info float' is supported on the ARM and x86 machines.




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9. Using GDB with Different Languages

Although programming languages generally have common aspects, they are rarely expressed in the same manner. For instance, in ANSI C, dereferencing a pointer p is accomplished by *p, but in Modula-2, it is accomplished by p^. Values can also be represented (and displayed) differently. Hex numbers in C appear as `0x1ae', while in Modula-2 they appear as `1AEH'.

Language-specific information is built into GDB for some languages, allowing you to express operations like the above in your program's native language, and allowing GDB to output values in a manner consistent with the syntax of your program's native language. The language you use to build expressions is called the working language.

SettingSwitching between source languages
ShowDisplaying the language
ChecksType and range checks
SupportSupported languages




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9.1 Switching between source languages

There are two ways to control the working language--either have GDB set it automatically, or select it manually yourself. You can use the set language command for either purpose. On startup, GDB defaults to setting the language automatically. The working language is used to determine how expressions you type are interpreted, how values are printed, etc.

In addition to the working language, every source file that GDB knows about has its own working language. For some object file formats, the compiler might indicate which language a particular source file is in. However, most of the time GDB infers the language from the name of the file. The language of a source file controls whether C++ names are demangled--this way backtrace can show each frame appropriately for its own language. There is no way to set the language of a source file from within GDB, but you can set the language associated with a filename extension. See Show.

This is most commonly a problem when you use a program, such as cfront or f2c, that generates C but is written in another language. In that case, make the program use #line directives in its C output; that way GDB will know the correct language of the source code of the original program, and will display that source code, not the generated C code.

FilenamesFilename extensions and languages.
ManuallySetting the working language manually
AutomaticallyHaving GDB infer the source language




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9.1.1 List of filename extensions and languages

If a source file name ends in one of the following extensions, then GDB infers that its language is the one indicated.

`.c'
C source file

`.C'
`.cc'
`.cp'
`.cpp'
`.cxx'
`.c++'
C++ source file

`.f'
`.F'
`.f90'
Fortran source files. GDB does not distinguish between Fortran 77 and Fortran 90 files. Fortran source file

`.ch'
`.c186'
`.c286'
CHILL source file.

`.mod'
Modula-2 source file

`.s'
`.S'
Assembler source file. This actually behaves almost like C, but GDB does not skip over function prologues when stepping.

In addition, you may set the language associated with a filename extension. See Show.




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9.1.2 Setting the working language

If you allow GDB to set the language automatically, expressions are interpreted the same way in your debugging session and your program.

If you wish, you may set the language manually. To do this, issue the command `set language lang', where lang is the name of a language, such as c or modula-2. For a list of the supported languages, type `set language'.

Setting the language manually prevents GDB from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages--but means different things. For instance, if the current source file were written in C, and GDB was parsing Modula-2, a command such as:

print a = b + c
might not have the effect you intended. In C, this means to add b and c and place the result in a. The result printed would be the value of a. In Modula-2, this means to compare a to the result of b+c, yielding a BOOLEAN value.




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9.1.3 Having GDB infer the source language

To have GDB set the working language automatically, use `set language local' or `set language auto'. GDB then infers the working language. That is, when your program stops in a frame (usually by encountering a breakpoint), GDB sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and GDB issues a warning.

This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using `set language auto' in this case frees you from having to set the working language manually.




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9.2 Displaying the language

The following commands help you find out which language is the working language, and also what language source files were written in.

show language
Display the current working language. This is the language you can use with commands such as print to build and compute expressions that may involve variables in your program.

info frame
Display the source language for this frame. This language becomes the working language if you use an identifier from this frame. See Frame Info, to identify the other information listed here.

info source
Display the source language of this source file. See Symbols, to identify the other information listed here.

In unusual circumstances, you may have source files with extensions not in the standard list. You can then set the extension associated with a language explicitly:

set extension-language .ext language
Set source files with extension .ext to be assumed to be in the source language language. Not valid on Unix systems.

info extensions
List all the filename extensions and the associated languages. Not valid on Unix systems.




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9.3 Type and range checking

Warning: In this release, the GDB commands for type and range checking are included, but they do not yet have any effect. This section documents the intended facilities.
Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators, and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches, and providing active checks for range errors when your program is running.

GDB can check for conditions like the above if you wish. Although GDB does not check the statements in your program, it can check expressions entered directly into GDB for evaluation via the print command, for example. As with the working language, GDB can also decide whether or not to check automatically based on your program's source language. See Support, for the default settings of supported languages.

Type CheckingAn overview of type checking
Range CheckingAn overview of range checking




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9.3.1 An overview of type checking

Some languages, such as Modula-2, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example,

1 + 2 => 3
but
error--> 1 + 2.3
The second example fails because the CARDINAL 1 is not type-compatible with the REAL 2.3.

For the expressions you use in GDB commands, you can tell the GDB type checker to skip checking; to treat any mismatches as errors and abandon the expression; or to only issue warnings when type mismatches occur, but evaluate the expression anyway. When you choose the last of these, GDB evaluates expressions like the second example above, but also issues a warning.

Even if you turn type checking off, there may be other reasons related to type that prevent GDB from evaluating an expression. For instance, GDB does not know how to add an int and a struct foo. These particular type errors have nothing to do with the language in use, and usually arise from expressions, such as the one described above, which make little sense to evaluate anyway.

Each language defines to what degree it is strict about type. For instance, both Modula-2 and C require the arguments to arithmetical operators to be numbers. In C, enumerated types and pointers can be represented as numbers, so that they are valid arguments to mathematical operators. See Support, for further details on specific languages.

GDB provides some additional commands for controlling the type checker:

set check type auto
Set type checking on or off based on the current working language. See Support, for the default settings for each language.

set check type on
set check type off
Set type checking on or off, overriding the default setting for the current working language. Issue a warning if the setting does not match the language default. If any type mismatches occur in evaluating an expression while type checking is on, GDB prints a message and aborts evaluation of the expression.

set check type warn
Cause the type checker to issue warnings, but to always attempt to evaluate the expression. Evaluating the expression may still be impossible for other reasons. For example, GDB cannot add numbers and structures.

show type
Show the current setting of the type checker, and whether or not GDB is setting it automatically.




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9.3.2 An overview of range checking

In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array.

For expressions you use in GDB commands, you can tell GDB to treat range errors in one of three ways: ignore them, always treat them as errors and abandon the expression, or issue warnings but evaluate the expression anyway.

A range error can result from numerical overflow, from exceeding an array index bound, or when you type a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to "wrap around" to lower values--for example, if m is the largest integer value, and s is the smallest, then

m + 1 => s
This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. See Support, for further details on specific languages.

GDB provides some additional commands for controlling the range checker:

set check range auto
Set range checking on or off based on the current working language. See Support, for the default settings for each language.

set check range on
set check range off
Set range checking on or off, overriding the default setting for the current working language. A warning is issued if the setting does not match the language default. If a range error occurs and range checking is on, then a message is printed and evaluation of the expression is aborted.

set check range warn
Output messages when the GDB range checker detects a range error, but attempt to evaluate the expression anyway. Evaluating the expression may still be impossible for other reasons, such as accessing memory that the process does not own (a typical example from many Unix systems).

show range
Show the current setting of the range checker, and whether or not it is being set automatically by GDB.




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9.4 Supported languages

GDB supports C, C++, Fortran, Java, Chill, assembly, and Modula-2.

Fortran for specific information about Fortran.

Some GDB features may be used in expressions regardless of the language you use: the GDB @ and :: operators, and the `{type}addr' construct (see Expressions) can be used with the constructs of any supported language.

The following sections detail to what degree each source language is supported by GDB. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the GDB expression parser accepts, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial.

CC and C++
Modula-2Modula-2
ChillChill
FortranFortran




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9.4.1 C and C++

Since C and C++ are so closely related, many features of GDB apply to both languages. Whenever this is the case, we discuss those languages together.

The C++ debugging facilities are jointly implemented by the C++ compiler and GDB. Therefore, to debug your C++ code effectively, you must compile your C++ programs with a supported C++ compiler, such as GNU g++, or the HP ANSI C++ compiler (aCC).

For best results when using GNU C++, use the stabs debugging format. You can select that format explicitly with the g++ command-line options `-gstabs' or `-gstabs+'. See section `Options for Debugging Your Program or GNU CC' in Using GNU CC, for more information.

C OperatorsC and C++ operators
C ConstantsC and C++ constants
C plus plus expressionsC++ expressions
C DefaultsDefault settings for C and C++
C ChecksC and C++ type and range checks
Debugging CGDB and C
Debugging C plus plusGDB features for C++




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9.4.1.1 C and C++ operators

Operators must be defined on values of specific types. For instance, + is defined on numbers, but not on structures. Operators are often defined on groups of types.

For the purposes of C and C++, the following definitions hold:

The following operators are supported. They are listed here in order of increasing precedence:
,
The comma or sequencing operator. Expressions in a comma-separated list are evaluated from left to right, with the result of the entire expression being the last expression evaluated.

=
Assignment. The value of an assignment expression is the value assigned. Defined on scalar types.

op=
Used in an expression of the form a op= b, and translated to a = a op b. op= and = have the same precedence. op is any one of the operators |, ^, &, <<, >>, +, -, *, /, %.

?:
The ternary operator. a ? b : c can be thought of as: if a then b else c. a should be of an integral type.

||
Logical OR. Defined on integral types.

&&
Logical AND. Defined on integral types.

|
Bitwise OR. Defined on integral types.

^
Bitwise exclusive-OR. Defined on integral types.

&
Bitwise AND. Defined on integral types.

==, !=
Equality and inequality. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true.

<, >, <=, >=
Less than, greater than, less than or equal, greater than or equal. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true.

<<, >>
left shift, and right shift. Defined on integral types.

@
The GDB "artificial array" operator (see Expressions).

+, -
Addition and subtraction. Defined on integral types, floating-point types and pointer types.

*, /, %
Multiplication, division, and modulus. Multiplication and division are defined on integral and floating-point types. Modulus is defined on integral types.

++, --
Increment and decrement. When appearing before a variable, the operation is performed before the variable is used in an expression; when appearing after it, the variable's value is used before the operation takes place.

*
Pointer dereferencing. Defined on pointer types. Same precedence as ++.

&
Address operator. Defined on variables. Same precedence as ++.

For debugging C++, GDB implements a use of `&' beyond what is allowed in the C++ language itself: you can use `&(&ref)' (or, if you prefer, simply `&&ref') to examine the address where a C++ reference variable (declared with `&ref') is stored.

-
Negative. Defined on integral and floating-point types. Same precedence as ++.

!
Logical negation. Defined on integral types. Same precedence as ++.

~
Bitwise complement operator. Defined on integral types. Same precedence as ++.

., ->
Structure member, and pointer-to-structure member. For convenience, GDB regards the two as equivalent, choosing whether to dereference a pointer based on the stored type information. Defined on struct and union data.

.*, ->*
Dereferences of pointers to members.

[]
Array indexing. a[i] is defined as *(a+i). Same precedence as ->.

()
Function parameter list. Same precedence as ->.

::
C++ scope resolution operator. Defined on struct, union, and class types.

::
Doubled colons also represent the GDB scope operator (see Expressions). Same precedence as ::, above.
If an operator is redefined in the user code, GDB usually attempts to invoke the redefined version instead of using the operator's predefined meaning.
9.4.1.2 C and C++ constants



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9.4.1.2 C and C++ constants

GDB allows you to express the constants of C and C++ in the following ways:

9.4.1.3 C++ expressions
9.4.1.4 C and C++ defaults
9.4.1.5 C and C++ type and range checks
9.4.1.6 GDB and C




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9.4.1.3 C++ expressions

GDB expression handling can interpret most C++ expressions.

Warning: GDB can only debug C++ code if you use the proper compiler. Typically, C++ debugging depends on the use of additional debugging information in the symbol table, and thus requires special support. In particular, if your compiler generates a.out, MIPS ECOFF, RS/6000 XCOFF, or ELF with stabs extensions to the symbol table, these facilities are all available. (With GNU CC, you can use the `-gstabs' option to request stabs debugging extensions explicitly.) Where the object code format is standard COFF or DWARF in ELF, on the other hand, most of the C++ support in GDB does not work.
  1. Member function calls are allowed; you can use expressions like

    count = aml->GetOriginal(x, y)
    
  2. While a member function is active (in the selected stack frame), your expressions have the same namespace available as the member function; that is, GDB allows implicit references to the class instance pointer this following the same rules as C++.

  3. You can call overloaded functions; GDB resolves the function call to the right definition, with some restrictions. GDB does not perform overload resolution involving user-defined type conversions, calls to constructors, or instantiations of templates that do not exist in the program. It also cannot handle ellipsis argument lists or default arguments.

    It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, and standard conversions such as those of functions or arrays to pointers; it requires an exact match on the number of function arguments.

    Overload resolution is always performed, unless you have specified set overload-resolution off. See Debugging C plus plus.

    You must specify set overload-resolution off in order to use an explicit function signature to call an overloaded function, as in

    p 'foo(char,int)'('x', 13)
    
    The GDB command-completion facility can simplify this; see Completion.

  4. GDB understands variables declared as C++ references; you can use them in expressions just as you do in C++ source--they are automatically dereferenced.

    In the parameter list shown when GDB displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The address of a reference variable is always shown, unless you have specified `set print address off'.

  5. GDB supports the C++ name resolution operator ::---your expressions can use it just as expressions in your program do. Since one scope may be defined in another, you can use :: repeatedly if necessary, for example in an expression like `scope1::scope2::name'. GDB also allows resolving name scope by reference to source files, in both C and C++ debugging (see Variables).

In addition, when used with HP's C++ compiler, GDB supports calling virtual functions correctly, printing out virtual bases of objects, calling functions in a base subobject, casting objects, and invoking user-defined operators.




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9.4.1.4 C and C++ defaults

If you allow GDB to set type and range checking automatically, they both default to off whenever the working language changes to C or C++. This happens regardless of whether you or GDB selects the working language.

If you allow GDB to set the language automatically, it recognizes source files whose names end with `.c', `.C', or `.cc', etc, and when GDB enters code compiled from one of these files, it sets the working language to C or C++. See Automatically, for further details.




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9.4.1.5 C and C++ type and range checks

By default, when GDB parses C or C++ expressions, type checking is not used. However, if you turn type checking on, GDB considers two variables type equivalent if:

Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array.


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9.4.1.6 GDB and C

The set print union and show print union commands apply to the union type. When set to `on', any union that is inside a struct or class is also printed. Otherwise, it appears as `{...}'.

The @ operator aids in the debugging of dynamic arrays, formed with pointers and a memory allocation function. See Expressions.

9.4.1.7 GDB features for C++




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9.4.1.7 GDB features for C++

Some GDB commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary:

breakpoint menus
When you want a breakpoint in a function whose name is overloaded, GDB breakpoint menus help you specify which function definition you want. See Breakpoint Menus.

rbreak regex
Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes. See Set Breaks.

catch throw
catch catch
Debug C++ exception handling using these commands. See Set Catchpoints.

ptype typename
Print inheritance relationships as well as other information for type typename. See Symbols.

set print demangle
show print demangle
set print asm-demangle
show print asm-demangle
Control whether C++ symbols display in their source form, both when displaying code as C++ source and when displaying disassemblies. See Print Settings.

set print object
show print object
Choose whether to print derived (actual) or declared types of objects. See Print Settings.

set print vtbl
show print vtbl
Control the format for printing virtual function tables. See Print Settings. (The vtbl commands do not work on programs compiled with the HP ANSI C++ compiler (aCC).)

set overload-resolution on
Enable overload resolution for C++ expression evaluation. The default is on. For overloaded functions, GDB evaluates the arguments and searches for a function whose signature matches the argument types, using the standard C++ conversion rules (see C plus plus expressions, for details). If it cannot find a match, it emits a message.

set overload-resolution off
Disable overload resolution for C++ expression evaluation. For overloaded functions that are not class member functions, GDB chooses the first function of the specified name that it finds in the symbol table, whether or not its arguments are of the correct type. For overloaded functions that are class member functions, GDB searches for a function whose signature exactly matches the argument types.

show overload-resolution
Display current overload resolution setting for C++ expression evaluation.

Overloaded symbol names
You can specify a particular definition of an overloaded symbol, using the same notation that is used to declare such symbols in C++: type symbol(types) rather than just symbol. You can also use the GDB command-line word completion facilities to list the available choices, or to finish the type list for you. See Completion, for details on how to do this.




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9.4.2 Modula-2

The extensions made to GDB to support Modula-2 only support output from the GNU Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as GDB reads in the executable's symbol table.

M2 OperatorsBuilt-in operators
Built-In Func/ProcBuilt-in functions and procedures
M2 ConstantsModula-2 constants
M2 DefaultsDefault settings for Modula-2
DeviationsDeviations from standard Modula-2
M2 ChecksModula-2 type and range checks
M2 ScopeThe scope operators :: and .
GDB/M2GDB and Modula-2




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9.4.2.1 Operators

Operators must be defined on values of specific types. For instance, + is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of Modula-2, the following definitions hold:

The following operators are supported, and appear in order of increasing precedence:

,
Function argument or array index separator.

:=
Assignment. The value of var := value is value.

<, >
Less than, greater than on integral, floating-point, or enumerated types.

<=, >=
Less than, greater than, less than or equal to, greater than or equal to on integral, floating-point and enumerated types, or set inclusion on set types. Same precedence as <.

=, <>, #
Equality and two ways of expressing inequality, valid on scalar types. Same precedence as <. In GDB scripts, only <> is available for inequality, since # conflicts with the script comment character.

IN
Set membership. Defined on set types and the types of their members. Same precedence as <.

OR
Boolean disjunction. Defined on boolean types.

AND, &
Boolean conjunction. Defined on boolean types.

@
The GDB "artificial array" operator (see Expressions).

+, -
Addition and subtraction on integral and floating-point types, or union and difference on set types.

*
Multiplication on integral and floating-point types, or set intersection on set types.

/
Division on floating-point types, or symmetric set difference on set types. Same precedence as *.

DIV, MOD
Integer division and remainder. Defined on integral types. Same precedence as *.

-
Negative. Defined on INTEGER and REAL data.

^
Pointer dereferencing. Defined on pointer types.

NOT
Boolean negation. Defined on boolean types. Same precedence as ^.

.
RECORD field selector. Defined on RECORD data. Same precedence as ^.

[]
Array indexing. Defined on ARRAY data. Same precedence as ^.

()
Procedure argument list. Defined on PROCEDURE objects. Same precedence as ^.

::, .
GDB and Modula-2 scope operators.

Warning: Sets and their operations are not yet supported, so GDB treats the use of the operator IN, or the use of operators +, -, *, /, =, , <>, #, <=, and >= on sets as an error.




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9.4.2.2 Built-in functions and procedures

Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used:

a
represents an ARRAY variable.

c
represents a CHAR constant or variable.

i
represents a variable or constant of integral type.

m
represents an identifier that belongs to a set. Generally used in the same function with the metavariable s. The type of s should be SET OF mtype (where mtype is the type of m).

n
represents a variable or constant of integral or floating-point type.

r
represents a variable or constant of floating-point type.

t
represents a type.

v
represents a variable.

x
represents a variable or constant of one of many types. See the explanation of the function for details.

All Modula-2 built-in procedures also return a result, described below.

ABS(n)
Returns the absolute value of n.

CAP(c)
If c is a lower case letter, it returns its upper case equivalent, otherwise it returns its argument.

CHR(i)
Returns the character whose ordinal value is i.

DEC(v)
Decrements the value in the variable v by one. Returns the new value.

DEC(v,i)
Decrements the value in the variable v by i. Returns the new value.

EXCL(m,s)
Removes the element m from the set s. Returns the new set.

FLOAT(i)
Returns the floating point equivalent of the integer i.

HIGH(a)
Returns the index of the last member of a.

INC(v)
Increments the value in the variable v by one. Returns the new value.

INC(v,i)
Increments the value in the variable v by i. Returns the new value.

INCL(m,s)
Adds the element m to the set s if it is not already there. Returns the new set.

MAX(t)
Returns the maximum value of the type t.

MIN(t)
Returns the minimum value of the type t.

ODD(i)
Returns boolean TRUE if i is an odd number.

ORD(x)
Returns the ordinal value of its argument. For example, the ordinal value of a character is its ASCII value (on machines supporting the ASCII character set). x must be of an ordered type, which include integral, character and enumerated types.

SIZE(x)
Returns the size of its argument. x can be a variable or a type.

TRUNC(r)
Returns the integral part of r.

VAL(t,i)
Returns the member of the type t whose ordinal value is i.

Warning: Sets and their operations are not yet supported, so GDB treats the use of procedures INCL and EXCL as an error.




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9.4.2.3 Constants

GDB allows you to express the constants of Modula-2 in the following ways:




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9.4.2.4 Modula-2 defaults

If type and range checking are set automatically by GDB, they both default to on whenever the working language changes to Modula-2. This happens regardless of whether you or GDB selected the working language.

If you allow GDB to set the language automatically, then entering code compiled from a file whose name ends with `.mod' sets the working language to Modula-2. See Automatically, for further details.




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9.4.2.5 Deviations from standard Modula-2

A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness:




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9.4.2.6 Modula-2 type and range checks

Warning: in this release, GDB does not yet perform type or range checking.
GDB considers two Modula-2 variables type equivalent if:

As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error.

Range checking is done on all mathematical operations, assignment, array index bounds, and all built-in functions and procedures.




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9.4.2.7 The scope operators :: and .

There are a few subtle differences between the Modula-2 scope operator (.) and the GDB scope operator (::). The two have similar syntax:


module . id
scope :: id
where scope is the name of a module or a procedure, module the name of a module, and id is any declared identifier within your program, except another module.

Using the :: operator makes GDB search the scope specified by scope for the identifier id. If it is not found in the specified scope, then GDB searches all scopes enclosing the one specified by scope.

Using the . operator makes GDB search the current scope for the identifier specified by id that was imported from the definition module specified by module. With this operator, it is an error if the identifier id was not imported from definition module module, or if id is not an identifier in module.




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9.4.2.8 GDB and Modula-2

Some GDB commands have little use when debugging Modula-2 programs. Five subcommands of set print and show print apply specifically to C and C++: `vtbl', `demangle', `asm-demangle', `object', and `union'. The first four apply to C++, and the last to the C union type, which has no direct analogue in Modula-2.

The @ operator (see Expressions), while available with any language, is not useful with Modula-2. Its intent is to aid the debugging of dynamic arrays, which cannot be created in Modula-2 as they can in C or C++. However, because an address can be specified by an integral constant, the construct `{type}adrexp' is still useful.

In GDB scripts, the Modula-2 inequality operator # is interpreted as the beginning of a comment. Use <> instead.




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9.4.3 Chill

The extensions made to GDB to support Chill only support output from the GNU Chill compiler. Other Chill compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as GDB reads in the executable's symbol table.

This section covers the Chill related topics and the features of GDB which support these topics.

How modes are displayedHow modes are displayed
LocationsLocations and their accesses
Values and their OperationsValues and their Operations
9.4.3.4 Chill type and range checks
9.4.3.5 Chill defaults




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9.4.3.1 How modes are displayed

The Chill Datatype- (Mode) support of GDB is directly related with the functionality of the GNU Chill compiler, and therefore deviates slightly from the standard specification of the Chill language. The provided modes are:

Discrete modes:
Powerset Mode:
A Powerset Mode is displayed by the keyword POWERSET followed by the member mode of the powerset. The member mode can be any discrete mode.
(gdb) ptype x
type = POWERSET SET (egon, hugo, otto)
Reference Modes:
Procedure mode
The procedure mode is displayed by type = PROC(<parameter list>) <return mode> EXCEPTIONS (<exception list>). The <parameter list> is a list of the parameter modes. <return mode> indicates the mode of the result of the procedure if any. The exceptionlist lists all possible exceptions which can be raised by the procedure.

Synchronization Modes:
Timing Modes:
Real Modes:
Real Modes are predefined with REAL and LONG_REAL.

String Modes:
Array Mode:
The Array Mode is displayed by the keyword ARRAY(<range>) followed by the element mode (which may in turn be an array mode).
(gdb) ptype x
type = ARRAY (1:42) 
          ARRAY (1:20) 
             SET (karli = 10, susi = 20, fritzi = 100)
Structure Mode
The Structure mode is displayed by the keyword STRUCT(<field list>). The <field list> consists of names and modes of fields of the structure. Variant structures have the keyword CASE <field> OF <variant fields> ESAC in their field list. Since the current version of the GNU Chill compiler doesn't implement tag processing (no runtime checks of variant fields, and therefore no debugging info), the output always displays all variant fields.
(gdb) ptype str
type = STRUCT (
    as x,
    bs x,
    CASE bs OF
    (karli):
        cs a
    (ott):
        ds x
    ESAC
)




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9.4.3.2 Locations and their accesses

A location in Chill is an object which can contain values.

A value of a location is generally accessed by the (declared) name of the location. The output conforms to the specification of values in Chill programs. How values are specified is the topic of the next section, Values and their Operations.

The pseudo-location RESULT (or result) can be used to display or change the result of a currently-active procedure:

set result := EXPR
This does the same as the Chill action RESULT EXPR (which is not available in GDB).

Values of reference mode locations are printed by PTR(<hex value>) in case of a free reference mode, and by (REF <reference mode>) (<hex-value>) in case of a bound reference. <hex value> represents the address where the reference points to. To access the value of the location referenced by the pointer, use the dereference operator `->'.

Values of procedure mode locations are displayed by { PROC (<argument modes> ) <return mode> } <address> <name of procedure location>. <argument modes> is a list of modes according to the parameter specification of the procedure and <address> shows the address of the entry point.

Substructures of string mode-, array mode- or structure mode-values (e.g. array slices, fields of structure locations) are accessed using certain operations which are described in the next section, Values and their Operations.

A location value may be interpreted as having a different mode using the location conversion. This mode conversion is written as <mode name>(<location>). The user has to consider that the sizes of the modes have to be equal otherwise an error occurs. Furthermore, no range checking of the location against the destination mode is performed, and therefore the result can be quite confusing.

(gdb) print int (s(3 up 4)) XXX TO be filled in !! XXX



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9.4.3.3 Values and their Operations

Values are used to alter locations, to investigate complex structures in more detail or to filter relevant information out of a large amount of data. There are several (mode dependent) operations defined which enable such investigations. These operations are not only applicable to constant values but also to locations, which can become quite useful when debugging complex structures. During parsing the command line (e.g. evaluating an expression) GDB treats location names as the values behind these locations.

This section describes how values have to be specified and which operations are legal to be used with such values.

Literal Values
Literal values are specified in the same manner as in GNU Chill programs. For detailed specification refer to the GNU Chill implementation Manual chapter 1.5.

Tuple Values
A tuple is specified by <mode name>[<tuple>], where <mode name> can be omitted if the mode of the tuple is unambiguous. This unambiguity is derived from the context of a evaluated expression. <tuple> can be one of the following:

String Element Value
A string element value is specified by <string value>(<index>), where <index> is a integer expression. It delivers a character value which is equivalent to the character indexed by <index> in the string.

String Slice Value
A string slice value is specified by <string value>(<slice spec>), where <slice spec> can be either a range of integer expressions or specified by <start expr> up <size>. <size> denotes the number of elements which the slice contains. The delivered value is a string value, which is part of the specified string.

Array Element Values
An array element value is specified by <array value>(<expr>) and delivers a array element value of the mode of the specified array.

Array Slice Values
An array slice is specified by <array value>(<slice spec>), where <slice spec> can be either a range specified by expressions or by <start expr> up <size>. <size> denotes the number of arrayelements the slice contains. The delivered value is an array value which is part of the specified array.

Structure Field Values
A structure field value is derived by <structure value>.<field name>, where <field name> indicates the name of a field specified in the mode definition of the structure. The mode of the delivered value corresponds to this mode definition in the structure definition.

Procedure Call Value
The procedure call value is derived from the return value of the procedure(3).

Values of duration mode locations are represented by ULONG literals.

Values of time mode locations are represented by TIME(<secs>:<nsecs>).

Zero-adic Operator Value
The zero-adic operator value is derived from the instance value for the current active process.

Expression Values
The value delivered by an expression is the result of the evaluation of the specified expression. If there are error conditions (mode incompatibility, etc.) the evaluation of expressions is aborted with a corresponding error message. Expressions may be parenthesised which causes the evaluation of this expression before any other expression which uses the result of the parenthesised expression. The following operators are supported by GDB:

OR, ORIF, XOR
AND, ANDIF
NOT
Logical operators defined over operands of boolean mode.

=, /=
Equality and inequality operators defined over all modes.

>, >=
<, <=
Relational operators defined over predefined modes.

+, -
*, /, MOD, REM
Arithmetic operators defined over predefined modes.

-
Change sign operator.

//
String concatenation operator.

()
String repetition operator.

->
Referenced location operator which can be used either to take the address of a location (->loc), or to dereference a reference location (loc->).

OR, XOR
AND
NOT
Powerset and bitstring operators.

>, >=
<, <=
Powerset inclusion operators.

IN
Membership operator.




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9.4.3.4 Chill type and range checks

GDB considers two Chill variables mode equivalent if the sizes of the two modes are equal. This rule applies recursively to more complex datatypes which means that complex modes are treated equivalent if all element modes (which also can be complex modes like structures, arrays, etc.) have the same size.

Range checking is done on all mathematical operations, assignment, array index bounds and all built in procedures.

Strong type checks are forced using the GDB command set check strong. This enforces strong type and range checks on all operations where Chill constructs are used (expressions, built in functions, etc.) in respect to the semantics as defined in the z.200 language specification.

All checks can be disabled by the GDB command set check off.




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9.4.3.5 Chill defaults

If type and range checking are set automatically by GDB, they both default to on whenever the working language changes to Chill. This happens regardless of whether you or GDB selected the working language.

If you allow GDB to set the language automatically, then entering code compiled from a file whose name ends with `.ch' sets the working language to Chill. See Automatically, for further details.




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9.4.4 Fortran

You can use HP WDB 2.0 to debug programs written in Fortran. HP WDB 2.0 does not distinguish between Fortran 77 and Fortran 90 files.

HP WDB 2.0 includes an option to control case sensitivity.

case-sensitive [on | off]
The default for Fortran is off, for other languages the default is on.

Other supported features are:

Fortran typesSupported data types
Fortran operatorsSupported operators
Fortran issuesSpecial issues with Fortran




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9.4.4.1 Fortran types

Fortran types supported:

integer*1, integer*2, integer*4, integer*8
logical*1, logical*2, logical*4, logical*8
byte
real*4, real*8, real*16
complex*8, complex*16
character*len, character*(*) [len is a user supplied length]
arrays
Array elements are displays in column-major order Use () for array member access (e.g, arr(i) instead of arr[i]) Use "set print elements" to control the number of elements printed out when specifying a whole array. The default is 200 elements or the number of elements of the array, which ever is smaller.




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9.4.4.2 Fortran operators

The following operators are supported. They are listed here in order of increasing precedence:

=
Assignment

*, -, *, /
Binary operators

+, -
Unary operators

**
Exponentiation

.EQ., =
Equal

.NE., /=
Not equal, or concatenation

.LT., <
Less than

.LE., <=
Less than or equal to

.GT., >
Greater than

.GE., >=
Greater than or equal to

//
Concatenation

.NOT.
Logical negation

.AND.
Logical AND

.OR.
Logical OR

.EQV.
Logical equivalence

.NEQV., .XOR.
Logical non-equivalence

Logical constants are represented as .TRUE. or .FALSE.

GDB includes support for viewing Fortran common blocks.

info common
Lists common blocks visible in the current frame.
info common <common_block_name>
Lists values of variables in the named common block.

Fortran entry points are supported.

You can set a break point specifying an entry point name.




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9.4.4.3 Fortran special issues

Fortran allows main to be a non-main procedure, therefore to set a breakpoint in the main program, use break _MAIN_ or break <program_name>.

Do not use break main unless it is the name of a non-main procedure.




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10. Examining the Symbol Table

The commands described in this chapter allow you to inquire about the symbols (names of variables, functions and types) defined in your program. This information is inherent in the text of your program and does not change as your program executes. GDB finds it in your program's symbol table, in the file indicated when you started GDB (see File Options), or by one of the file-management commands (see Files).

Occasionally, you may need to refer to symbols that contain unusual characters, which GDB ordinarily treats as word delimiters. The most frequent case is in referring to static variables in other source files (see Variables). File names are recorded in object files as debugging symbols, but GDB would ordinarily parse a typical file name, like `foo.c', as the three words `foo' `.' `c'. To allow GDB to recognize `foo.c' as a single symbol, enclose it in single quotes; for example,

p 'foo.c'::x
looks up the value of x in the scope of the file `foo.c'.

info address symbol
Describe where the data for symbol is stored. For a register variable, this says which register it is kept in. For a non-register local variable, this prints the stack-frame offset at which the variable is always stored.

Note the contrast with `print &symbol', which does not work at all for a register variable, and for a stack local variable prints the exact address of the current instantiation of the variable.

whatis expr
Print the data type of expression expr. expr is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place. See Expressions.

whatis
Print the data type of $, the last value in the value history.

ptype typename
Print a description of data type typename. typename may be the name of a type, or for C code it may have the form `class class-name', `struct struct-tag', `union union-tag' or `enum enum-tag'.

ptype expr
ptype
Print a description of the type of expression expr. ptype differs from whatis by printing a detailed description, instead of just the name of the type.

For example, for this variable declaration:

struct complex {double real; double imag;} v;
the two commands give this output:

(gdb) whatis v
type = struct complex
(gdb) ptype v
type = struct complex {
    double real;
    double imag;
}
As with whatis, using ptype without an argument refers to the type of $, the last value in the value history.

info types regexp
info types
Print a brief description of all types whose names match regexp (or all types in your program, if you supply no argument). Each complete typename is matched as though it were a complete line; thus, `i type value' gives information on all types in your program whose names include the string value, but `i type ^value$' gives information only on types whose complete name is value.

This command differs from ptype in two ways: first, like whatis, it does not print a detailed description; second, it lists all source files where a type is defined.

info source
Show the name of the current source file--that is, the source file for the function containing the current point of execution--and the language it was written in.

info sources
Print the names of all source files in your program for which there is debugging information, organized into two lists: files whose symbols have already been read, and files whose symbols will be read when needed.

info functions
Print the names and data types of all defined functions.

info functions regexp
Print the names and data types of all defined functions whose names contain a match for regular expression regexp. Thus, `info fun step' finds all functions whose names include step; `info fun ^step' finds those whose names start with step.

info variables
Print the names and data types of all variables that are declared outside of functions (i.e., excluding local variables).

info variables regexp
Print the names and data types of all variables (except for local variables) whose names contain a match for regular expression regexp.

Some systems allow individual object files that make up your program to be replaced without stopping and restarting your program. For example, in VxWorks you can simply recompile a defective object file and keep on running. If you are running on one of these systems, you can allow GDB to reload the symbols for automatically relinked modules:

set symbol-reloading on
Replace symbol definitions for the corresponding source file when an object file with a particular name is seen again.

set symbol-reloading off
Do not replace symbol definitions when re-encountering object files of the same name. This is the default state; if you are not running on a system that permits automatically relinking modules, you should leave symbol-reloading off, since otherwise GDB may discard symbols when linking large programs, that may contain several modules (from different directories or libraries) with the same name.

show symbol-reloading
Show the current on or off setting.

set opaque-type-resolution on
Tell GDB to resolve opaque types. An opaque type is a type declared as a pointer to a struct, class, or union---for example, struct MyType *---that is used in one source file although the full declaration of struct MyType is in another source file. The default is on.

A change in the setting of this subcommand will not take effect until the next time symbols for a file are loaded.

set opaque-type-resolution off
Tell GDB not to resolve opaque types. In this case, the type is printed as follows:
{<no data fields>}
show opaque-type-resolution
Show whether opaque types are resolved or not.

maint print symbols filename
maint print psymbols filename
maint print msymbols filename
Write a dump of debugging symbol data into the file filename. These commands are used to debug the GDB symbol-reading code. Only symbols with debugging data are included. If you use `maint print symbols', GDB includes all the symbols for which it has already collected full details: that is, filename reflects symbols for only those files whose symbols GDB has read. You can use the command info sources to find out which files these are. If you use `maint print psymbols' instead, the dump shows information about symbols that GDB only knows partially--that is, symbols defined in files that GDB has skimmed, but not yet read completely. Finally, `maint print msymbols' dumps just the minimal symbol information required for each object file from which GDB has read some symbols. See Files, for a discussion of how GDB reads symbols (in the description of symbol-file).




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11. Altering Execution

Once you think you have found an error in your program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the GDB features for altering execution of the program.

For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function.

AssignmentAssignment to variables
JumpingContinuing at a different address
SignalingGiving your program a signal
ReturningReturning from a function
CallingCalling your program's functions
PatchingPatching your program




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11.1 Assignment to variables

To alter the value of a variable, evaluate an assignment expression. See Expressions. For example,

print x=4
stores the value 4 into the variable x, and then prints the value of the assignment expression (which is 4). See Languages, for more information on operators in supported languages.

If you are not interested in seeing the value of the assignment, use the set command instead of the print command. set is really the same as print except that the expression's value is not printed and is not put in the value history (see Value History). The expression is evaluated only for its effects.

If the beginning of the argument string of the set command appears identical to a set subcommand, use the set variable command instead of just set. This command is identical to set except for its lack of subcommands. For example, if your program has a variable width, you get an error if you try to set a new value with just `set width=13', because GDB has the command set width:

(gdb) whatis width
type = double
(gdb) p width
$4 = 13
(gdb) set width=47
Invalid syntax in expression.
The invalid expression, of course, is `=47'. In order to actually set the program's variable width, use

(gdb) set var width=47
Because the set command has many subcommands that can conflict with the names of program variables, it is a good idea to use the set variable command instead of just set. For example, if your program has a variable g, you run into problems if you try to set a new value with just `set g=4', because GDB has the command set gnutarget, abbreviated set g:

(gdb) whatis g
type = double
(gdb) p g
$1 = 1
(gdb) set g=4
(gdb) p g
$2 = 1
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/smith/cc_progs/a.out
"/home/smith/cc_progs/a.out": can't open to read symbols: Invalid bfd target.
(gdb) show g
The current BFD target is "=4".
The program variable g did not change, and you silently set the gnutarget to an invalid value. In order to set the variable g, use

(gdb) set var g=4
GDB allows more implicit conversions in assignments than C; you can freely store an integer value into a pointer variable or vice versa, and you can convert any structure to any other structure that is the same length or shorter.

To store values into arbitrary places in memory, use the `{...}' construct to generate a value of specified type at a specified address (see Expressions). For example, {int}0x83040 refers to memory location 0x83040 as an integer (which implies a certain size and representation in memory), and

set {int}0x83040 = 4
stores the value 4 into that memory location.




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11.2 Continuing at a different address

Ordinarily, when you continue your program, you do so at the place where it stopped, with the continue command. You can instead continue at an address of your own choosing, with the following commands:

jump linespec
Resume execution at line linespec. Execution stops again immediately if there is a breakpoint there. See List, for a description of the different forms of linespec. It is common practice to use the tbreak command in conjunction with jump. See Set Breaks.

The jump command does not change the current stack frame, or the stack pointer, or the contents of any memory location or any register other than the program counter. If line linespec is in a different function from the one currently executing, the results may be bizarre if the two functions expect different patterns of arguments or of local variables. For this reason, the jump command requests confirmation if the specified line is not in the function currently executing. However, even bizarre results are predictable if you are well acquainted with the machine-language code of your program.

jump *address
Resume execution at the instruction at address address.

On many systems, you can get much the same effect as the jump command by storing a new value into the register $pc. The difference is that this does not start your program running; it only changes the address of where it will run when you continue. For example,

set $pc = 0x485
makes the next continue command or stepping command execute at address 0x485, rather than at the address where your program stopped. See Continuing and Stepping.

The most common occasion to use the jump command is to back up--perhaps with more breakpoints set--over a portion of a program that has already executed, in order to examine its execution in more detail.




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11.3 Giving your program a signal

signal signal
Resume execution where your program stopped, but immediately give it the signal signal. signal can be the name or the number of a signal. For example, on many systems signal 2 and signal SIGINT are both ways of sending an interrupt signal.

Alternatively, if signal is zero, continue execution without giving a signal. This is useful when your program stopped on account of a signal and would ordinary see the signal when resumed with the continue command; `signal 0' causes it to resume without a signal.

signal does not repeat when you press RET a second time after executing the command.

Invoking the signal command is not the same as invoking the kill utility from the shell. Sending a signal with kill causes GDB to decide what to do with the signal depending on the signal handling tables (see Signals). The signal command passes the signal directly to your program.




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11.4 Returning from a function

return
return expression
You can cancel execution of a function call with the return command. If you give an expression argument, its value is used as the function's return value.

When you use return, GDB discards the selected stack frame (and all frames within it). You can think of this as making the discarded frame return prematurely. If you wish to specify a value to be returned, give that value as the argument to return.

This pops the selected stack frame (see Selection), and any other frames inside of it, leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions.

The return command does not resume execution; it leaves the program stopped in the state that would exist if the function had just returned. In contrast, the finish command (see Continuing and Stepping) resumes execution until the selected stack frame returns naturally.




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11.5 Calling program functions

call expr
Evaluate the expression expr without displaying void returned values.

You can use this variant of the print command if you want to execute a function from your program, but without cluttering the output with void returned values. If the result is not void, it is printed and saved in the value history.

For the A29K, a user-controlled variable call_scratch_address, specifies the location of a scratch area to be used when GDB calls a function in the target. This is necessary because the usual method of putting the scratch area on the stack does not work in systems that have separate instruction and data spaces.




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11.6 Patching programs

By default, GDB opens the file containing your program's executable code (or the core file) read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary.

If you'd like to be able to patch the binary, you can specify that explicitly with the set write command. For example, you might want to turn on internal debugging flags, or even to make emergency repairs.

set write on
set write off
If you specify `set write on', GDB opens executable and core files for both reading and writing; if you specify `set write off' (the default), GDB opens them read-only.

If you have already loaded a file, you must load it again (using the exec-file or core-file command) after changing set write, for your new setting to take effect.

show write
Display whether executable files and core files are opened for writing as well as reading.




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12. GDB Files

GDB needs to know the file name of the program to be debugged, both in order to read its symbol table and in order to start your program. To debug a core dump of a previous run, you must also tell GDB the name of the core dump file.

FilesCommands to specify files
Symbol ErrorsErrors reading symbol files




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12.1 Commands to specify files

You may want to specify executable and core dump file names. The usual way to do this is at start-up time, using the arguments to GDB's start-up commands (see Invocation).

Occasionally it is necessary to change to a different file during a GDB session. Or you may run GDB and forget to specify a file you want to use. In these situations the GDB commands to specify new files are useful.

file filename
Use filename as the program to be debugged. It is read for its symbols and for the contents of pure memory. It is also the program executed when you use the run command. If you do not specify a directory and the file is not found in the GDB working directory, GDB uses the environment variable PATH as a list of directories to search, just as the shell does when looking for a program to run. You can change the value of this variable, for both GDB and your program, using the path command.

On systems with memory-mapped files, an auxiliary file `filename.syms' may hold symbol table information for filename. If so, GDB maps in the symbol table from `filename.syms', starting up more quickly. See the descriptions of the file options `-mapped' and `-readnow' (available on the command line, and with the commands file, symbol-file, or add-symbol-file, described below), for more information.

file
file with no argument makes GDB discard any information it has on both executable file and the symbol table.

exec-file [ filename ]
Specify that the program to be run (but not the symbol table) is found in filename. GDB searches the environment variable PATH if necessary to locate your program. Omitting filename means to discard information on the executable file.

symbol-file [ filename ]
Read symbol table information from file filename. PATH is searched when necessary. Use the file command to get both symbol table and program to run from the same file.

symbol-file with no argument clears out GDB information on your program's symbol table.

The symbol-file command causes GDB to forget the contents of its convenience variables, the value history, and all breakpoints and auto-display expressions. This is because they may contain pointers to the internal data recording symbols and data types, which are part of the old symbol table data being discarded inside GDB.

symbol-file does not repeat if you press RET again after executing it once.

When GDB is configured for a particular environment, it understands debugging information in whatever format is the standard generated for that environment; you may use either a GNU compiler, or other compilers that adhere to the local conventions.

For most kinds of object files, with the exception of old SVR3 systems using COFF, the symbol-file command does not normally read the symbol table in full right away. Instead, it scans the symbol table quickly to find which source files and which symbols are present. The details are read later, one source file at a time, as they are needed.

The purpose of this two-stage reading strategy is to make GDB start up faster. For the most part, it is invisible except for occasional pauses while the symbol table details for a particular source file are being read. (The set verbose command can turn these pauses into messages if desired. See Messages/Warnings.)

We have not implemented the two-stage strategy for COFF yet. When the symbol table is stored in COFF format, symbol-file reads the symbol table data in full right away. Note that "stabs-in-COFF" still does the two-stage strategy, since the debug info is actually in stabs format.

symbol-file filename [ -readnow ] [ -mapped ]
file filename [ -readnow ] [ -mapped ]
You can override the GDB two-stage strategy for reading symbol tables by using the `-readnow' option with any of the commands that load symbol table information, if you want to be sure GDB has the entire symbol table available.

If memory-mapped files are available on your system (usually not Unix systems, through the mmap system call, you can use another option, `-mapped', to cause GDB to write the symbols for your program into a reusable file. Future GDB debugging sessions map in symbol information from this auxiliary symbol file (if the program has not changed), rather than spending time reading the symbol table from the executable program. Using the `-mapped' option has the same effect as starting GDB with the `-mapped' command-line option.

You can use both options together, to make sure the auxiliary symbol file has all the symbol information for your program.

The auxiliary symbol file for a program called myprog is called `myprog.syms'. Once this file exists (so long as it is newer than the corresponding executable), GDB always attempts to use it when you debug myprog; no special options or commands are needed.

The `.syms' file is specific to the host machine where you run GDB. It holds an exact image of the internal GDB symbol table. It cannot be shared across multiple host platforms.

core-file [ filename ]
Specify the whereabouts of a core dump file to be used as the "contents of memory". Traditionally, core files contain only some parts of the address space of the process that generated them; GDB can access the executable file itself for other parts.

core-file with no argument specifies that no core file is to be used.

Note that the core file is ignored when your program is actually running under GDB. So, if you have been running your program and you wish to debug a core file instead, you must kill the subprocess in which the program is running. To do this, use the kill command (see Kill Process).

add-symbol-file filename address
add-symbol-file filename address [ -readnow ] [ -mapped ]
add-symbol-file filename address data_address bss_address
add-symbol-file filename -Tsection address
The add-symbol-file command reads additional symbol table information from the file filename. You would use this command when filename has been dynamically loaded (by some other means) into the program that is running. address should be the memory address at which the file has been loaded; GDB cannot figure this out for itself. You can specify up to three addresses, in which case they are taken to be the addresses of the text, data, and bss segments respectively. For complicated cases, you can specify an arbitrary number of -Tsection address pairs, to give an explicit section name and base address for that section. You can specify any address as an expression.

The symbol table of the file filename is added to the symbol table originally read with the symbol-file command. You can use the add-symbol-file command any number of times; the new symbol data thus read keeps adding to the old. To discard all old symbol data instead, use the symbol-file command.

add-symbol-file does not repeat if you press RET after using it.

You can use the `-mapped' and `-readnow' options just as with the symbol-file command, to change how GDB manages the symbol table information for filename.

add-shared-symbol-file
The add-shared-symbol-file command can be used only under Harris' CXUX operating system for the Motorola 88k. GDB automatically looks for shared libraries, however if GDB does not find yours, you can run add-shared-symbol-file. It takes no arguments.

section
The section command changes the base address of section SECTION of the exec file to ADDR. This can be used if the exec file does not contain section addresses, (such as in the a.out format), or when the addresses specified in the file itself are wrong. Each section must be changed separately. The info files command, described below, lists all the sections and their addresses.

info files
info target
info files and info target are synonymous; both print the current target (see Targets), including the names of the executable and core dump files currently in use by GDB, and the files from which symbols were loaded. The command help target lists all possible targets rather than current ones.

All file-specifying commands allow both absolute and relative file names as arguments. GDB always converts the file name to an absolute file name and remembers it that way.

GDB supports HP-UX, SunOS, SVR4, Irix 5, and IBM RS/6000 shared libraries.

GDB automatically loads symbol definitions from shared libraries when you use the run command, or when you examine a core file. (Before you issue the run command, GDB does not understand references to a function in a shared library, however--unless you are debugging a core file).

On HP-UX, if the program loads a library explicitly, GDB automatically loads the symbols at the time of the shl_load call. See Breakpoints, for more information.

info share
info sharedlibrary
Print the names of the shared libraries which are currently loaded.

sharedlibrary regex
share regex
Load shared object library symbols for files matching a Unix regular expression. As with files loaded automatically, it only loads shared libraries required by your program for a core file or after typing run. If regex is omitted all shared libraries required by your program are loaded.

On HP-UX systems, GDB detects the loading of a shared library and automatically reads in symbols from the newly loaded library, up to a threshold that is initially set but that you can modify if you wish.

Beyond that threshold, symbols from shared libraries must be explicitly loaded. To load these symbols, use the command sharedlibrary filename. The base address of the shared library is determined automatically by GDB and need not be specified.

To display or set the threshold, use the commands:

set auto-solib-add threshold
Set the autoloading size threshold, in megabytes. If threshold is nonzero, symbols from all shared object libraries will be loaded automatically when the inferior begins execution or when the dynamic linker informs GDB that a new library has been loaded, until the symbol table of the program and libraries exceeds this threshold. Otherwise, symbols must be loaded manually, using the sharedlibrary command. The default threshold is 100 megabytes.

show auto-solib-add
Display the current autoloading size threshold, in megabytes.




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12.2 Errors reading symbol files

While reading a symbol file, GDB occasionally encounters problems, such as symbol types it does not recognize, or known bugs in compiler output. By default, GDB does not notify you of such problems, since they are relatively common and primarily of interest to people debugging compilers. If you are interested in seeing information about ill-constructed symbol tables, you can either ask GDB to print only one message about each such type of problem, no matter how many times the problem occurs; or you can ask GDB to print more messages, to see how many times the problems occur, with the set complaints command (see Messages/Warnings).

The messages currently printed, and their meanings, include:

inner block not inside outer block in symbol
The symbol information shows where symbol scopes begin and end (such as at the start of a function or a block of statements). This error indicates that an inner scope block is not fully contained in its outer scope blocks.

GDB circumvents the problem by treating the inner block as if it had the same scope as the outer block. In the error message, symbol may be shown as "(don't know)" if the outer block is not a function.

block at address out of order
The symbol information for symbol scope blocks should occur in order of increasing addresses. This error indicates that it does not do so.

GDB does not circumvent this problem, and has trouble locating symbols in the source file whose symbols it is reading. (You can often determine what source file is affected by specifying set verbose on. See Messages/Warnings.)

bad block start address patched
The symbol information for a symbol scope block has a start address smaller than the address of the preceding source line. This is known to occur in the SunOS 4.1.1 (and earlier) C compiler.

GDB circumvents the problem by treating the symbol scope block as starting on the previous source line.

bad string table offset in symbol n
Symbol number n contains a pointer into the string table which is larger than the size of the string table.

GDB circumvents the problem by considering the symbol to have the name foo, which may cause other problems if many symbols end up with this name.

unknown symbol type 0xnn
The symbol information contains new data types that GDB does not yet know how to read. 0xnn is the symbol type of the uncomprehended information, in hexadecimal.

GDB circumvents the error by ignoring this symbol information. This usually allows you to debug your program, though certain symbols are not accessible. If you encounter such a problem and feel like debugging it, you can debug gdb with itself, breakpoint on complain, then go up to the function read_dbx_symtab and examine *bufp to see the symbol.

stub type has NULL name
GDB could not find the full definition for a struct or class.

const/volatile indicator missing (ok if using g++ v1.x), got...
The symbol information for a C++ member function is missing some information that recent versions of the compiler should have output for it.

info mismatch between compiler and debugger
GDB could not parse a type specification output by the compiler.




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13. Specifying a Debugging Target

A target is the execution environment occupied by your program.

Often, GDB runs in the same host environment as your program; in that case, the debugging target is specified as a side effect when you use the file or core commands. For HP-UX specific information, See HP-UX Targets. When you need more flexibility--for example, running GDB on a physically separate host, or controlling a standalone system over a serial port or a realtime system over a TCP/IP connection--you can use the target command to specify one of the target types configured for GDB (see Target Commands).

Active TargetsActive targets
Target CommandsCommands for managing targets
Byte OrderChoosing target byte order




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13.1 Active targets

There are three classes of targets: processes, core files, and executable files. GDB can work concurrently on up to three active targets, one in each class. This allows you to (for example) start a process and inspect its activity without abandoning your work on a core file.

For example, if you execute `gdb a.out', then the executable file a.out is the only active target. If you designate a core file as well--presumably from a prior run that crashed and core dumped--then GDB has two active targets and uses them in tandem, looking first in the core file target, then in the executable file, to satisfy requests for memory addresses. (Typically, these two classes of target are complementary, since core files contain only a program's read-write memory--variables and so on--plus machine status, while executable files contain only the program text and initialized data.)

When you type run, your executable file becomes an active process target as well. When a process target is active, all GDB commands requesting memory addresses refer to that target; addresses in an active core file or executable file target are obscured while the process target is active.

Use the core-file and exec-file commands to select a new core file or executable target (see Files). To specify as a target a process that is already running, use the attach command (see Attach).




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13.2 Commands for managing targets

target type parameters
Connects the GDB host environment to a target machine or process. A target is typically a protocol for talking to debugging facilities. You use the argument type to specify the type or protocol of the target machine.

Further parameters are interpreted by the target protocol, but typically include things like device names or host names to connect with, process numbers, and baud rates.

The target command does not repeat if you press RET again after executing the command.

help target
Displays the names of all targets available. To display targets currently selected, use either info target or info files (see Files).

help target name
Describe a particular target, including any parameters necessary to select it.

set gnutarget args
GDB uses its own library BFD to read your files. GDB knows whether it is reading an executable, a core, or a .o file; however, you can specify the file format with the set gnutarget command. Unlike most target commands, with gnutarget the target refers to a program, not a machine.

Warning: To specify a file format with set gnutarget, you must know the actual BFD name.
See Files.

show gnutarget
Use the show gnutarget command to display what file format gnutarget is set to read. If you have not set gnutarget, GDB will determine the file format for each file automatically, and show gnutarget displays `The current BDF target is "auto"'.

Here are some common targets (available, or not, depending on the GDB configuration):

target exec program
An executable file. `target exec program' is the same as `exec-file program'.

target core filename
A core dump file. `target core filename' is the same as `core-file filename'.

target remote dev
Remote serial target in GDB-specific protocol. The argument dev specifies what serial device to use for the connection (e.g. `/dev/ttya'). supports the load command. This is only useful if you have some other way of getting the stub to the target system, and you can put it somewhere in memory where it won't get clobbered by the download.

target sim
Builtin CPU simulator. GDB includes simulators for most architectures. In general,
        target sim
        load
        run
works; however, you cannot assume that a specific memory map, device drivers, or even basic I/O is available, although some simulators do provide these.

Some configurations may include these targets as well:

target nrom dev
NetROM ROM emulator. This target only supports downloading.

Different targets are available on different configurations of GDB; your configuration may have more or fewer targets.

Many remote targets require you to download the executable's code once you've successfully established a connection.

load filename
Depending on what remote debugging facilities are configured into GDB, the load command may be available. Where it exists, it is meant to make filename (an executable) available for debugging on the remote system--by downloading, or dynamic linking, for example. load also records the filename symbol table in GDB, like the add-symbol-file command.

If your GDB does not have a load command, attempting to execute it gets the error message "You can't do that when your target is ..."

The file is loaded at whatever address is specified in the executable. For some object file formats, you can specify the load address when you link the program; for other formats, like a.out, the object file format specifies a fixed address.

load does not repeat if you press RET again after using it.




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13.3 Choosing target byte order

Some types of processors, such as the MIPS, PowerPC, and Hitachi SH, offer the ability to run either big-endian or little-endian byte orders. Usually the executable or symbol will include a bit to designate the endian-ness, and you will not need to worry about which to use. However, you may still find it useful to adjust GDB's idea of processor endian-ness manually.

set endian big
Instruct GDB to assume the target is big-endian.

set endian little
Instruct GDB to assume the target is little-endian.

set endian auto
Instruct GDB to use the byte order associated with the executable.

show endian
Display GDB's current idea of the target byte order.

Note that these commands merely adjust interpretation of symbolic data on the host, and that they have absolutely no effect on the target system.




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14. Configuration-Specific Information

While nearly all GDB commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations.

There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other.

HP WDB 2.0 provides the following features in addition to the standard GDB features:

HP-UX DependenciesRequirements to support HP Features
HP-UX TargetsValid targets for HP-UX
Fix and ContinueFix and Continue Debugging
Debugging Memory ProblemsDebugging Memory Problems
Heap ProfilingHeap Profiling
Object PathsSpecifying Object File Directories
Shared library breakpointsStopping and starting in shared libraries
Shared library mainShared library as a main program
Non-debug executablesGetting information from a non-debug executable




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14.1 HP-UX Dependencies

Several features available in HP WDB 2.0 depend on specific versions of the linker or compilers.




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14.1.1 Linker patch required for +objdebug

You must install the latest linker patch in order to generate object modules that enable faster linking and smaller executable file sizes for large applications. Refer to the HP WDB 2.0 release notes and your compiler release notes for more details.




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14.1.2 Fix and Continue compiler dependencies

Fix and Continue is supported only on HP-UX 11.x with these compilers:

Refer to the WDB release notes and your compiler release notes for more details.




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14.2 HP-UX Targets

On HP-UX systems, GDB has been configured to support debugging of processes running on the PA-RISC architecture. This means that the only possible targets are:

GDB on HP-UX has not been configured to support remote debugging, or to support programs running on other platforms.

HP WDB 2.0 can only debug programs compiled with HP aC++, HP's ANSI-compatible C++ compiler. You must use HP DDE to debug programs compiled with HP C++, HP's earlier cfront-based C++ compiler.

If you try to debug cfront-compiled programs, HP WDB 2.0 may fail, or produce confusing results. For example, if you try looking looking at a data member, HP WDB 2.0 may generate a message about illegally accessing memory at 0x0.

You can detect a cfront executable by using the following commands.

On HP PA-RISC 32-bit programs:

odump -compunit executable file name
or

On HP PA-RISC 64-bit programs:

elfdump -dc executable
The cfront compiler emits HPCPLUSPLUS while the aCC compiler emits ANSI C++ in the compilation directory.




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14.3 Fix and Continue Debugging

Fix and Continue allows you to see the result of changes you make to a program you are debugging without having to re-compile and re-link the entire program.

For example, you can edit a function and use the fix command, which automatically re-compiles your code, links it into a shared library, and continues execution of the program, without leaving the debugger.

Fix and Continue allows you to experiment with various ways of fixing problems until you are satisfied with the correction, before you exit the debugger.

The advantages include:

Note: Fix and Continue is only supported with the most recent versions of HP C and HP aC++.

In command-line mode, you use the edit command before invoking the fix command.

The edit command has the following syntax:

edit file1 file2

where

file
represents one or more source files for the current executable. If you do not specify a file name, HP WDB 2.0 edits the currently open source file.

The fix command has the following syntax:

fix file1 file2

where

file
represents one or more source files for the current executable. If you do not specify a file name, HP WDB 2.0 re-compiles the currently open source file.

When you edit a file with the edit command and save the changes, the original source file contains the changes, even if you do not use the fix command to re-compile your program in the debugger.




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14.3.1 Fix and Continue Restrictions

Fix and Continue has the following restrictions and behaviors:




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14.3.2 Using Fix and Continue

When HP WDB 2.0 re-compiles a fixed source file, it uses the same compiler and the same options that were used to create the original executable. If the compiler generates any syntax errors or it encounters any of the restrictions, HP WDB 2.0 does not patch your changes into the executable image being debugged.

After you successfully re-compile your changes, HP WDB 2.0 uses the fixed version of your code when you use any of the execution commands such as step, run, or continue.

When you use the edit command, HP WDB 2.0 then monitors any edited source files for additional changes. After you enter the initial fix command, HP WDB 2.0 checks for additional saved changes to a source file each time you enter a program execution command. If a saved source file has been changed, HP WDB 2.0 asks you if you want to fix the changed source, allowing you to apply repeated fixes without explicitly entering the fix command.

Note: You must rebuild your program after you use the fix command because the changes you make are temporarily patched into the executable image. The changes are lost if you load a different executable and are not reflected in the original executable when you exit the debugger.
The Fix and Continue allows you to make the following changes:




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14.3.3 Example Fix and Continue Session

This example shows how you can make and test changes to a function without leaving the debugger session.

Here is a short sample C program with an error.

int sum (num)   int num;
{
  int j, total = 0;
  for (j = 0; j <= num; j++)
    total += num;
}

main()
{
   int num = 10;
   printf("The sum from 1 to %d is = %d\n", num, sum(num));
}
  1. Compile the program.
    cc sum.c -g -o mysum
    
    /usr/ccs/bin/ld: (Warning) At least one PA 2.0 object file (sum.o) was detected.
     The linked output may not run on a PA 1.x system.
    
  2. Run the program.
    ./mysum
    
    The sum from 1 to 10 is = 0
    
    This result is obviously wrong. We need to debug the program.

  3. Run the debugger.
    gdb mysum
    
    Copyright 1986 - 2000 Free Software Foundation, Inc.
    Hewlett-Packard Wildebeest 2.0 (based on GDB 4.17-hpwdb-980821)
    Wildebeest is free software, covered by the GNU General Public License, 
    and you are welcome to change it and/or distribute copies of it under 
    certain  conditions.  Type "show copying" to see the conditions.
    There is absolutely no warranty for Wildebeest.
    Type "show warranty" for details.
    Wildebeest was built for PA-RISC 1.1 or 2.0 (narrow), HP-UX 11.00.
    ..
    
    If your TERM environment variable is not set to hpterm, start the debugger and set the terminal type for editing in HP WDB 2.0 with this command (ksh shell):

    TERM=hpterm gdb mysum
    
  4. Notice that the problem might be that there is no return for the num function. You can correct this without leaving the debugger.

  5. Set a break point at main.
    (gdb) b main
    Breakpoint 1 at 0x23f8: file sum.c, line 11.
    
  6. Run your program
    (gdb) run
    Starting program: /tmp/hmc/mysum
    
    Breakpoint 1, main () at sum.c:11
    11         int num = 10;
    
  7. With the program stopped at the break point, you can make changes to the source file with the edit command.

    Because you are going to edit the current file, you do not need to specify a source file name.

    (gdb) edit
    
    The edit command opens a new terminal session using your environment variable settings for terminal and editor. The debugger automatically loads the source file.

  8. Make the necessary changes. In this case, add
    return total;
    
    to the function named num.

  9. Save the edited source file and exit the editor. This saves the changes in the actual source file for your program.

  10. Use the fix command to re-compile your program to see the results of your changes.

    (gdb) fix
    Compiling /dev/src/sum.c...
    Linking...
    Applying code changes to sum.c.
    Fix succeeded.
    
    The fix command creates a new executable that includes the changes you made to the source file.

    The debugger automatically uses the new executable and picks up the debugging session where you stopped before using the edit command.

    For example, you can continue stepping through your program and you will find the new return total; statement in the source view. You can print the value of total, and see that the result is 110.

  11. When you are finished with your debugging session, you can exit the debugger normally.

    (gdb) q
    The following modules in /dev/src/mysum have been fixed:
    /dev/src/sum.c
    Remember to remake the program.
    
    The debugger message lists the source files that you have changed during your debugging session.

    Note: You must rebuild your program after you use the fix command because the changes you make are temporarily patched into the executable image. The changes are lost when you exit the debugger or you load a different executable.




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14.4 Debugging Memory Problems

You can use HP WDB 2.0 to find leaks, profile heap usage and detect other heap related errors in HP C, HP aC++, and HP Fortran programs written for HP-UX 10.20 or 11.00 (both 32 bit and 64 bit programs are supported).

On HP-UX 11.00, the memory debugging features of HP WDB 2.0 work with both single-threaded and multi-threaded programs that use POSIX threads.




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14.4.1 Memory Debugging Restrictions

Programs with these attributes are not supported:




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14.4.2 Using Memory Debugging

HP WDB 2.0 provides several commands that help expose memory-related problems.

The commands allow you to:

To debug memory problems, use the commands:

set heap-check leaks [on | off]
Controls HP WDB 2.0 memory leak checking.

show heap-check
Displays all current settings for memory checking.

info leaks
Displays a leak report, listing information such as the leaks, size of blocks, number of instances.

info leaks filename
Writes leak report output to the specified file.

info leak leaknumber
Produces detailed information on the specified leak including the allocation call stack.

set heap-check block-size num-bytes
Instructs HP WDB 2.0 to stop the program whenever it tries to allocate a block larger than num-bytes in size.

set heap-check heap-size num-size
Instructs HP WDB 2.0 to stop the program whenever it tries to increase the program heap by at least num-bytes.

set heap-check frame-count num
Controls the depth of the call stack collected. Larger values increase run time. Default value is four (4) stack frames.

set heap-check min-leak-size num
Collects a stack trace only if the size of the leak exceeds the number of bytes you specify for this value. Larger values improve run-time performance. Default value is zero (0) bytes.

set heap-check free [on | off]
When set to on, forces HP WDB 2.0 to stop your program when it detects a call to free() with an improper argument or a call to realloc() that does not point to a valid currently allocated heap block.

set heap-check watch address
Stops the program whenever a block at a specified address is allocated or deallocated.

set heap-check bounds [on | off]
Allocates extra space at the beginning and end of a heap block during allocation and fills it with a specific pattern. When blocks are freed, HP WDB 2.0 checks to see if these patterns are intact. If they are corrupted, an underflow or overflow must have occurred and HP WDB 2.0 reports the problem. This option increases the program's memory requirements.

set heap-check scramble [on | off]
Scrambles a memory block and overwrites it with a specific pattern any time it is allocated or deallocated. This change to the memory contents increases the chance that erroneous behaviors such as attempting to access space that is freed or depending on initial values of malloc() blocks cause the program to fail.




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14.4.3 Stop at the free of unallocated or deallocated blocks

HP WDB 2.0 allows you to locate improper calls to free() and realloc() with the command set heap-check free [on | off].

With this setting on, whenever your program calls free() or realloc() HP WDB 2.0 inspects the parameters to verify that they are pointing to valid currently allocated heap blocks.

If HP WDB 2.0 detects an erroneous call to free(), it stops the program and reports this condition. You can then look at the stack trace to understand where and how the problem occurred.




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14.4.4 Stop when freeing a block if bad writes occurred outside block boundary

HP WDB 2.0 allows you to locate problems caused by heap block overflow or underflow with the command set heap-check bounds [on | off]. When bounds checking is turned on, HP WDB 2.0 allocates extra space at the beginning and end of a block during allocation and fills it up with a specific pattern. When blocks are freed, HP WDB 2.0 checks to see if these patterns are intact. If they are corrupted, an underflow or overflow must have occurred and HP WDB 2.0 reports the problem.

Note:Turning on bounds checking increases the program's memory requirements because the extra guard bytes must be allocated at the beginning and end of each block.




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14.4.5 Stop if a specified block address is allocated or deallocated

To stop a program whenever a block at a specified address is allocated or deallocated use the command:

set heap-check watch address

You could use this to debug situations such as multiple free() calls to the same block.




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14.4.6 Scramble previous memory contents at malloc/free calls

HP WDB 2.0 allows you to potentially expose latent memory access defects with the command set heap-check scramble [on | off].

When this setting is turned on, any time a memory block is allocated or deallocated, HP WDB 2.0 scrambles the space and overwrites it with a specific pattern.

This change to the memory contents increases the chance that erroneous behaviors will cause the program to fail. Examples of such behavior include, attempting to access space that is freed or depending on initial values of malloc() blocks.

You can now look at the stack trace to understand where and how the problem occurred.

Note:Turning on scrambling will slow down the program slightly, because at every malloc() and free() call, the space involved must be overwritten.




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14.4.7 When to suspect a memory leak

You should suspect a memory leak in your code if you notice your system running out of swap space or running slower and slower, or both.

Applications or non-kernel code (including daemons) that have memory leaks can eventually use up all swap space. You can run top(1) to see if your process data space (SIZE, RES) is growing more than you expect.

If your system is running out of swap space, programs will fail with out of memory (ENOMEM) errors or SIGBUS signals. In addition, the system might run slower and slower until it comes to a stop; all processes requiring swap to continue running will wait for it indefinitely.




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14.4.8 Report memory leaks

HP WDB 2.0 allows you to check for memory leaks in applications written for HP-UX 10.20 and 11.00 using C, ANSI C++, FORTRAN 77 and Fortran 90.

You can use two methods to identify heap-related problems:




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14.4.9 Detecting memory leaks in batch mode

Enabling batch mode allows you to detect leaks by exercising your program with a test suite. This mode generates a leak report, but no stack traces, when your program run completes. Note that HP WDB 2.0 generates a leak report only if your program terminates with an explicit call to exit().

You can use the batch mode only with non-threaded programs. Only leak checking is available in batch, all other analysis and diagnostics are disabled.

The leak report is sent to a file named /tmp/gdbrtc.log. Each run appends its output to the end of the file.

To use this feature, you must do the following:

  1. For 32-bit programs, link with /opt/langtools/lib/librtc.a. For 64-bit programs link with /opt/langtools/lib/pa20_64/librtc.a. The file librtc.a must be listed before the C library in the link line.

  2. If your program links with either the archive version of the C library, /usr/lib/libc.a or the core libraries, /usr/lib/libcl.a, you must link with the corresponding shared version instead.

  3. Link your application with the core libraries with the -lcl linker option.

  4. Run your program's test suite.
  5. Review the file named /tmp/gdbrtc.log, which contains a list of memory leaks.




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14.4.10 Configuring memory debugging

Several settings are available to control the amount of detail you can see when debugging memory leaks.




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14.4.10.1 Specifying the stack depth

By default, HP WDB 2.0 reports each memory leak with at most four stack frames from the allocating call stack.

The depth of the call stack can be controlled by the command:

set heap-check frame-count num
Specifying a higher value helps you understand the allocation scenario better. However, the higher the value, the slower your program runs.

Larger stack depth values cause slower performance because HP WDB 2.0 must collect the stack trace for every allocation. The more levels of stack trace you want, the more time it takes to collect the stack trace.

HP WDB 2.0 takes more time because it cannot determine at the time a block is allocated if that block will eventually be leaked by the program.

For many programs, the default value should be appropriate.




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14.4.10.2 Specifying minimum leak size

HP WDB 2.0 allows you to specify the minimum leak size for stack trace collection to improve the program's performance.

Stack trace collection slows down your program because it occurs on every allocation call. Therefore, if your program is allocation intensive, HP WDB 2.0 could spend a substantial amount of time collecting stack traces.

You could speed things up by using the command

set heap-check min-leak-size num
For example, if you use,

set heap-check min-leak-size 100
HP WDB 2.0 does not collect stack traces for allocations less than 100 bytes. HP WDB still reports leaks smaller than this size, but does not include a stack trace.




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14.4.11 Detecting memory leaks interactively

The set heap-check leaks [on | off] command controls HP WDB 2.0 memory leak checking.

With leak checking turned on, you can generate a leak report any time the program is stopped inside the debugger, by using the command:

info leaks

When you use info leaks, HP WDB 2.0 scans for memory leaks in your program and produces a leak report, listing information such as the leaks, size of blocks, number of instances. HP WDB 2.0 assigns each of the leaks a unique number.

For additional leak information, use the command info leak leaknumber to display detailed information on the leak including the allocation call stack.

Use these steps to report leaks:

  1. For 64-bit programs, link your application with /opt/langtools/lib/pa20_64/librtc.sl.

    Note: If you are using the static or dynamic linker version earlier than B.11.17, you must link your 32-bit program with /opt/langtools/lib/librtc.sl.
  2. If your program links with either the archive version of the C library, /usr/lib/libc.a, or the core libraries, /usr/lib/libcl.a, you must link with the corresponding shared version instead.

  3. Invoke HP WDB 2.0 with the command-line option -leaks or use the command set heap-check leaks on after starting the debugger.

  4. Any time your application is stopped in the debugger, you can ask for a leak report with the command info leaks.

    To see detailed information associated with a leak use the command info leak leaknumber




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14.4.11.1 Example

This example describes checking a program running on HP-UX 11.00 using linker version B.11.17 or later.

  1. For a 64-bit program, link your application with /opt/langtools/lib/pa20_64/librtc.sl.

  2. Link your program with /usr/lib/libc.sl instead of libc.a.

  3. Run the debugger and load your program.
    > gdb a.out
    
  4. Turn on leak checking.
    (gdb) set heap-check leaks on
    
  5. Set one or more breakpoints in your code where you want to examine cumulative leaks.

    (gdb) b myfunction
    
  6. Run your program in the debugger.
    (gdb) run
    
  7. Use the info command to show list of memory leaks.
    (gdb) info leaks
    
    Scanning for memory leaks...done 
    
    2439 bytes leaked in 25 blocks 
    
    No.   Total bytes     Blocks     Address     Function 
    0        1234           1       0x40419710   foo() 
    1        333            1       0x40410bf8   main() 
    2        245            8       0x40410838   strdup() 
    
    [...] 
    
    
    The debugger assigns each leak a numeric identifier.

  8. To display a stack trace for a specific leak, use the info leak command and specify the number from the list associated with a leak.

    (gdb) info leak 2
    
    245 bytes leaked in 8 blocks (10.05% of all bytes leaked) 
    These range in size from 26 to 36 bytes and are allocated 
     in strdup () 
     in link_the_list () at test.c:55 
     in main () at test.c:13 
     in _start () 
    




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14.5 Heap Profiling

Seeing the heap profile is useful for identifying how memory is being used by the program. You can use HP WDB 2.0 to profile an application's current heap usage.

info heap
Displays a heap report, listing information such as the heap allocations, size of blocks, number of instances. Note that the report shows heap usage at the point you use the info heap command.

The report does not show allocations that have already been freed. For example, if you make several allocations, free them all, and then you use info heap, the result will not show any allocations.

info heap filename
Writes heap report output to the specified file.

info heap idnumber
Produces detailed information on the specified heap allocation including the allocation call stack.

set heap-check frame-count num
Controls the depth of the call stack collected. Larger values increase run time. Default value is four (4) stack frames.

show heap-check
Displays all current settings for memory checking.

Here is an example that shows how to use this feature on HP-UX 11.00 with linker version B.11.17 or later installed.

  1. Link with /opt/langtools/lib/pa20_64/librtc.sl for PA-64 programs. Note: If your linker version is earlier than B.11.17, and you are debugging a 32-bit program, you must link with /opt/langtools/lib/librtc.sl.

  2. Turn on profiling with the set heap-check on command.
    (gdb) set heap-check on
    
  3. Set a breakpoint.
    (gdb) b myfunction
    
  4. When the program is stopped at a breakpoint, use the info heap command.

    (gdb) info heap
    
    Analyzing heap ...done 
    
    41558 bytes allocated in 28 blocks 
    
    No.   Total bytes     Blocks     Address     Function 
    0        34567          1       0x40411000   foo() 
    1        4096           1       0x7bd63000   bar() 
    2        1234           1       0x40419710   baz() 
    3        245            8       0x404108b0   boo() 
    
    [...] 
    
    The display shows the currently allocated heap blocks. Any blocks that have been allocated and already freed, are not listed.
To look at a specific allocation, specify the allocation number with the info heap command.

(gdb) info heap 1 
4096 bytes at 0x7bd63000 (9.86% of all bytes allocated) 
  in bar () at test.c:108 
  in main () at test.c:17 
  in _start () 
  in $START$ () 
When there are multiple blocks allocated from the same call stack, HP WDB 2.0 displays additional information.

(gdb) info heap 3
245 bytes in 8 blocks (0.59% of all bytes allocated) 
These range in size from 26 to 36 bytes and are allocated 
  in boo () 
  in link_the_list () at test.c:55 
  in main () at test.c:13 
  in _start () 



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14.6 Specifying object file directories

GDB enables automatic loading of debug information from object modules when an application is compiled with the +objdebug option.

GDB uses the full path name to the object module files and searches the same directories for source files.

This behavior transparent, however, you can control over when and how object files are loaded with three commands.

objectdir path

Specify a colon (:) separated list of directories in which GDB searches for object files. These directories are added to the beginning of the existing objectdir path. If you specify a directory that is already in the objectdir path, the specified directory is moved up in the objectdir path so that it is searched earlier.

GDB recognizes two special directory names: $cdir, which refers to the compilation directory (if available) and $cwd, which tracks GDB's current working directory.

objectload file.c
Cause GDB to load the debug information for file.c immediately. The default is to load debug information from object modules on demand.

objectretry file.c
Force GDB to retry loading an object file if GDB encounters a file error while reading an object module. File errors that might cause this include incorrect permissions, file not found, or if the objectdir path changes. By default, GDB does not try to read an object file after an error.

Here are some items to check if the debugger can not find your source files.

  1. Make certain the files were compiled with the -g switch. Type info sources to find the list of files that the debugger knows were compiled with -g.

  2. Make certain that the debugger can find the source file. Type show dir to find the list of directories the debugger uses to search for source files and type set dir to change that path.

    On HP-UX, the debug information does not contain the full path name to the source file, only the relative pathname that was recorded at compile time. Consequently, you may need several dir commands for a complex application with multiple source directories. One way to do this is to place them in a `.gdbinit' file placed in the directory used to debug the application.

    A sample of the `.gdbinit' file might look like the following:

    dir /home/fred/appx/system
    dir /home/fred/appx/display
    dir /home/fred/appx/actor
    dir /home/fred/appx/actor/sys
         ...
    
    Note, When you compile your program with the +objdebug option, the debugger may find your source files without using the dir command. This happens because the debugger stores the full path name to the object files and searches for source files in the same directories.



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14.7 Stopping and starting in shared libraries

On HP-UX, shared libraries are special. Until the library is loaded, GDB does not know the names of symbols. However, GDB gives you two ways to set breakpoints in shared libraries.




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14.7.1 Deferred breakpoints

On HP-UX, GDB automatically loads symbol definitions from shared libraries when you use the run command, or when you examine a core file. (Before you issue the run command, GDB does not understand references to a function in a shared library--unless you are debugging a core file).

When you specify a breakpoint using a name that GDB does not recognize, the debugger warns you with a message that it is setting a deferred breakpoint on the name you specified. If any shared library is loaded with a matching name then GDB sets the breakpoint.

For example, if you type:

`break foo'

the debugger does not know if foo is a misspelled name or if it is the name of a routine that has not yet been loaded from a shared library. The debugger displays a warning message that it is setting a deferred breakpoint on foo. If any shared library is loaded that contains a foo, then GDB sets the breakpoint.

If this is not what you want, for example the name was mis-typed, then you can delete the breakpoint.




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14.7.2 Using catch load

The command `catch load <libname>' causes the debugger to stop when the particular library is loaded. This gives you a chance to set breakpoints before routines are executed.




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14.7.3 Privately mapping shared libraries

In cases where you attach to a running program and you try to set a breakpoint in a shared library, GDB may generated the following message:

The shared libraries were not privately mapped; setting a breakpoint
in a shared library will not work until you rerun the program.
GDB generates this message because the debugger sets breakpoints by replacing an instruction with a BREAK instruction. The debugger can not set a breakpoint in a shared library because doing so can affect other processes on the system in addition to the process being debugged.

To set the breakpoint you must kill the program and then re-run it so that the dynamic linker will map a copy of the shared library. There are two ways to run the program:




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14.8 Using shared library as main program

My main program is in a shared library. I try to load it as follows:

(gdb) symbol-file main.sl
Load new symbol table from "main.sl"? (y or n) y
Reading symbols from main.sl
done.
Things don't appear to work.

This command is not the correct thing to do. This command assumes that `main.sl' is loaded at its link time address. This is not not true for shared libraries.

Do not use symbol-file with shared libraries.

Instead, what you should do is to use the deferred breakpoint feature to set breakpoints on any functions necessary before the program starts running.

	(gdb) b main
	Breakpoint 1 (deferred) at "main" ("main" was not found).
	Breakpoint deferred until a shared library containing "main" is loaded.
	(gdb) r
Once the program has started running, it will hit the breakpoint. In addition, the debugger will then already know about the sources for main, since it gets this information when the shared library is loaded.




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14.9 Getting information from a non-debug executable

You can get some information about the arguments passed to the functions displayed in the stack trace in a non-debug, optimized executable.

GDB has no debug information, it does not know where the arguments are located or even the type of the arguments. There is no way for GDB to infer this in an optimized, non-debug executable.

However, for integer arguments you can find the first four parameters for the top-of-stack frame by looking at the registers. The first parameter will be in $r26, the second in $r25 and so on.




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14.10 Parallel Processing

HP WDB 2.0 supports pthread parallelism.

However, HP WDB 2.0 does not support compiler generated parallelism, e.g. with directives.




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14.11 Support for ddd

GDB works with ddd the free GDB GUI shell available at http://mumm.ibr.cs.tu-bs.de/.

While this is not formally supported by Hewlett-Packard, these two do work together. Note however if you have ddd issues, you'll need to report them to the ddd support channel.



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15. The HP-UX Terminal User Interface

By default, GDB runs in line mode. For users who prefer an interface similar (though not identical) to that of the XDB debugger, HP provides a terminal user interface (TUI), which appears when you invoke the gdb command with the -tui option.

Use the -xdb option to allow the use of a number of XDB commands. See the XDB to WDB Transition Guide.

This guide contains the following topics:

Starting TUIHow to start the Terminal User Interface
Automatically Running ProgramStarting program automatically
Screen LayoutsThe screen layouts
Cycling through windowsCycling through windows
Changing Window FocusChanging Window Focus
Scrolling WindowsScrolling Windows
Changing Reg DisplayChanging the Register Display
Changing Window SizeChanging Window Size
TUI RefreshRefreshing and Updating the Screen



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15.1 Starting the TUI

Invoke the debugger using a command like the following:

gdb -xdb -tui a.out

These examples use the default terminal screen size of 24 by 80 characters. The terminal screen looks something like this.


Figure 1

   |----------------------------------------------------------------------|
   |30      {                                                             |
   |31          /* Try two test cases. */                                 |
   |32          print_average (my_list, first, last);                     |
   |33          print_average (my_list, first, last - 3);                 |
   |34      }                                                             |
   |35                                                                    |
   |36                                                                    |
   |37                                                                    |
   |38                                                                    |
   |39                                                                    |
   |40                                                                    |
   |41                                                                    |
   |42                                                                    |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: ??    Line: ??      pc: ??
Wildebeest is free software, covered by the GNU General Public License, and
you are welcome to change it and/or distribute copies of it under certain
conditions.  Type "show copying" to see the conditions.  There is
absolutely no warranty for Wildebeest.  Type "show warranty" for details.
---Type <return> to continue, or q <return> to quit---
Wildebeest was built for PA-RISC 1.1 or 2.0 (narrow), HP-UX 11.00.
..
(gdb)
The terminal is divided into two windows: a source window at the top and a command window at the bottom. In the middle is a locator bar that shows the current file, procedure, line, and program counter (PC) address, when they are known to the debugger. When you set a breakpoint on the main program by issuing the command b main an asterisk (*) appears opposite the first executable line of the program. When you execute the program up to the first breakpoint by issuing the command run a right angle bracket (>) points to the current location. So after you issue those commands, the screen looks something like this:

Figure 2

   |----------------------------------------------------------------------|
   |27      }                                                             |
   |28                                                                    |
   |29      int main(void)                                                |
   |30      {                                                             |
   |31          /* Try two test cases. */                                 |
 *>|32          print_average (my_list, first, last);                     |
   |33          print_average (my_list, first, last - 3);                 |
   |34      }                                                             |
   |35                                                                    |
   |36                                                                    |
   |37                                                                    |
   |38                                                                    |
   |39                                                                    |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
..
(gdb) b main
Breakpoint 1 at 0x3524: file average.c, line 32.
(gdb) run
Starting program: /home/work/wdb/a.out

Breakpoint 1, main () at average.c:32
(gdb)



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15.2 Automatically running a program at startup

HP WDB 2.0 does not start running the target executable at startup as do `xdb' and HP DDE. This makes it easy to set break points before the target program's main function.

To make HP WDB 2.0 automatically start running the target program add these lines to your startup file, `.gdbinit':

break main
start



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15.3 Screen Layouts

The TUI supports four windows within the terminal screen, in various combinations:

The command window is always present. The possible screen configurations of the other windows are:

The layout command (abbreviated la) allows you to change from one window configuration to another.
Note: You can abbreviate any command to its shortest unambiguous form.
15.3.1 Source Window
15.3.2 Disassembly Window
15.3.3 Source/Disassembly Window
15.3.4 Disassembly/Register Window
15.3.5 Source/Register Window




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15.3.1 Source Window

The Source window, Figure 1, appears by default when you invoke the debugger. You can also make it appear by issuing the command

la src



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15.3.2 Disassembly Window

The Disassembly window appears when you issue the command

la asm
The screen looks like this:


Figure 3

   |----------------------------------------------------------------------|
   |;;;     print_average (my_list, first, last);                         |
 *>|0x3524 <main+8> addil L'-0x800,%dp,%r1                                |
   |0x3528 <main+12>        ldo 0x730(%r1),%r26                           |
   |0x352c <main+16>        ldi 9,%r24                                    |
   |0x3530 <main+20>        ldi 0,%r25                                    |
   |0x3534 <main+24>        ldil L'0x3000,%r31                            |
   |0x3538 <main+28>        be,l 0x498(%sr4,%r31)                         |
   |0x353c <main+32>        copy %r31,%rp                                 |
   |;;;     print_average (my_list, first, last - 3);                     |
   |0x3540 <main+36>        addil L'-0x800,%dp,%r1                        |
   |0x3544 <main+40>        ldo 0x730(%r1),%r26                           |
   |0x3548 <main+44>        ldi 6,%r24                                    |
   |0x354c <main+48>        ldi 0,%r25                                    |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
(gdb) b main
Breakpoint 1 at 0x3524: file average.c, line 32.
(gdb) r
Starting program: /home/work/wdb/a.out

Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb)




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15.3.3 Source/Disassembly Window

The Source/Disassembly window appears when you issue the command

la split
You can also reach this window from the Source window with the XDB command

td
The screen looks like this:

Figure 4

   :......................................................................:
 *>:32          print_average (my_list, first, last);                     :
   :33          print_average (my_list, first, last - 3);                 :
   :34      }                                                             :
   :35                                                                    :
   :36                                                                    :
   :37                                                                    :
   :......................................................................:
   |;;;     print_average (my_list, first, last);                         |
 *>|0x3524 <main+8> addil L'-0x800,%dp,%r1                                |
   |0x3528 <main+12>        ldo 0x730(%r1),%r26                           |
   |0x352c <main+16>        ldi 9,%r24                                    |
   |0x3530 <main+20>        ldi 0,%r25                                    |
   |0x3534 <main+24>        ldil L'0x3000,%r31                            |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
Breakpoint 1 at 0x3524: file average.c, line 32.
(gdb) r
Starting program: /home/work/wdb/a.out

Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb)




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15.3.4 Disassembly/Register Window

The Disassembly/Register window appears when you issue the command

la regs
when the current window is the Source/Disassembly window. By default, the debugger displays the general registers.

The screen looks like this:


Figure 5

:.........................................................................:
:flags 29000041          r1 51a800               rp 7f6ce597              :
:r3 7f7f0000             r4 1                    r5 7f7f06f4              :
:r6 7f7f06fc             r7 7f7f0800             r8 7f7f0800              :
:r9 40006b10             r10 0                   r11 40004b78             :
:r12 1                   r13 0                   r14 0                    :
:r15 0                   r16 40003fb8            r17 4                    :
:.........................................................................:
   |;;;     print_average (my_list, first, last);                         |
 *>|0x3524 <main+8> addil L'-0x800,%dp,%r1                                |
   |0x3528 <main+12>        ldo 0x730(%r1),%r26                           |
   |0x352c <main+16>        ldi 9,%r24                                    |
   |0x3530 <main+20>        ldi 0,%r25                                    |
   |0x3534 <main+24>        ldil L'0x3000,%r31                            |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
(gdb) r
Starting program: /home/work/wdb/a.out

Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb)




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15.3.5 Source/Register Window

The Source/Register window appears when you issue the command

la regs
when the current window is the Source window.

The screen looks like this:


Figure 6

:.........................................................................:
:flags 29000041          r1 51a800               rp 7f6ce597              :
:r3 7f7f0000             r4 1                    r5 7f7f06f4              :
:r6 7f7f06fc             r7 7f7f0800             r8 7f7f0800              :
:r9 40006b10             r10 0                   r11 40004b78             :
:r12 1                   r13 0                   r14 0                    :
:r15 0                   r16 40003fb8            r17 4                    :
:.........................................................................:
 *>|32          print_average (my_list, first, last);                     |
   |33          print_average (my_list, first, last - 3);                 |
   |34      }                                                             |
   |35                                                                    |
   |36                                                                    |
   |37                                                                    |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: main    Line: 32      pc: 0x3524

Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb)




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15.4 Cycling Through the Windows

Use the commands

la next
and

la prev
to move from one screen configuration to another without specifying a window name. If you specify la next repeatedly, the order the debugger uses is

If you invoked the gdb command with the -xdb option as well as the -tui option, you can also use the following commands:

td
Toggle between Source and Disassembly/Register windows.

ts
Toggle split-screen mode.




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15.5 Changing Window Focus

The command window always has keyboard focus, so that you can enter debugger commands. If there is only one other window (Source or Disassembly), the other window has the logical focus, so that you can scroll within that window by using the arrow keys or the Page Up and Page Down keys (on some keyboards these are Prev and Next).

Note: In the command window, the scrolling behavior only works for an `hpterm' and not for an `xterm' or `dtterm'.

If you are in split-screen mode, you may want to change the logical focus of the window. To do so, use the command

focus {win_name | prev | next}
where win_name can be src, asm, regs, or cmd.

Remember, if you change the focus to a window other than the command window, you need to use focus cmd to switch back to the command window to enter or scroll through commands.

For example, with the sequence of commands just issued, you are in split-screen mode with the focus in the Source window.

The window with logical focus has a border constructed from "|" and "-".

A window that does not have logical focus has a border constructed from ":"vand ".":


Figure 7

:.........................................................................:
:flags 29000041          r1 51a800               rp 7f6ce597              :
:r3 7f7f0000             r4 1                    r5 7f7f06f4              :
:r6 7f7f06fc             r7 7f7f0800             r8 7f7f0800              :
:r9 40006b10             r10 0                   r11 40004b78             :
:r12 1                   r13 0                   r14 0                    :
:r15 0                   r16 40003fb8            r17 4                    :
:.........................................................................:
 *>|32          print_average (my_list, first, last);                     |
   |33          print_average (my_list, first, last - 3);                 |
   |34      }                                                             |
   |35                                                                    |
   |36                                                                    |
   |37                                                                    |
   |----------------------------------------------------------------------|
 File: average.c    Procedure: main    Line: 32      pc: 0x3524

Breakpoint 1, main () at average.c:32
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb)

By default, the Source window will scroll. To change the focus so that you can scroll in the Register window, use the focus command (abbreviated foc or fs):
fs regs
or
foc next
If you then use the Page Down key to scroll in the Register window, the screen looks like this:

Figure 8

|-------------------------------------------------------------------------|
|flags 29000041          r1 51a800               rp 7f6ce597              |
|r3 7f7f0000             r4 1                    r5 7f7f06f4              |
|r6 7f7f06fc             r7 7f7f0800             r8 7f7f0800              |
|r9 40006b10             r10 0                   r11 40004b78             |
|r12 1                   r13 0                   r14 0                    |
|r15 0                   r16 40003fb8            r17 4                    |
|-------------------------------------------------------------------------|
 *>:32          print_average (my_list, first, last);                     :
   :33          print_average (my_list, first, last - 3);                 :
   :34      }                                                             :
   :35                                                                    :
   :36                                                                    :
   :37                                                                    :
   :......................................................................:
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
(gdb) la asm
(gdb) la split
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb) foc next
Focus set to REGS window.
(gdb)



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15.6 Scrolling Windows

To scroll a window, you can use the arrow keys or the Page Up and Page Down keys (on some keyboards these are Prev and Next). You can also use the following commands:

{+ | -} [num_lines] [win_name]
Vertically scroll the window forward (+) or backward (-). + or - with no arguments scrolls the window forward or backward one page. Use num_lines to specify how many lines to scroll the window. Use win_name to specify a window other than the one with logical focus.
{< | >}[num_char] [win_name]
Horizontally scroll the window left (<) or right (>) the specified number of characters. If you do not specify num_char, the window is scrolled one character.

Note that a space is required between the +, -, <, or > and the number.

To scroll the command window, use the scroll bars on the terminal window.




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15.7 Changing the Register Display

To look at the floating-point or special registers instead of the general registers, and then to return to the general registers, you can use the following XDB commands:

fr
display $fregs
Display the floating-point registers.

sr
display $sregs
Display the special registers.

gr
display $gregs
Display the general registers.

For example, if you use the fr command, the screen looks like this:


Figure 9

|-------------------------------------------------------------------------|
|flags 29000041          r1 51a800               rp 7f6ce597              |
|r3 7f7f0000             r4 1                    r5 7f7f06f4              |
|r6 7f7f06fc             r7 7f7f0800             r8 7f7f0800              |
|r9 40006b10             r10 0                   r11 40004b78             |
|r12 1                   r13 0                   r14 0                    |
|r15 0                   r16 40003fb8            r17 4                    |
   :......................................................................:
   :30      {                                                             :
   :31          /* Try two test cases. */                                 :
 *>:32          print_average (my_list, first, last);                     :
   :33          print_average (my_list, first, last - 3);                 :
   :34      }                                                             :
   :35                                                                    :
   :......................................................................:
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb) foc next
Focus set to REGS window.
(gdb) fr
#0  main () at average.c:32
(gdb)
The default floating-point register display is single-precision. To change the register display to double-precision and then back again, use the XDB toggle float command:
toggle $fregs
The screen looks like this:

Figure 10

|-------------------------------------------------------------------------|
|fpsr 0                              fpe1 0                               |
|fpe2 0                              fpe3 0                               |
|fpe4 0                              fpe5 0                               |
|fpe6 0                              fpe7 0                               |
|fr4     0                           fr4R    0                            |
|fr5     1.0000000000000011          fr5R    7.00649232e-45               |
|-------------------------------------------------------------------------|
 *>:32          print_average (my_list, first, last);                     :
   :33          print_average (my_list, first, last - 3);                 :
   :34      }                                                             :
   :35                                                                    :
   :36                                                                    :
   :37                                                                    :
   :......................................................................:
 File: average.c    Procedure: main    Line: 32      pc: 0x3524
(gdb) la regs
(gdb) la src
(gdb) la regs
(gdb) foc next
Focus set to REGS window.
(gdb) fr
(gdb) tf
(gdb)




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15.8 Changing Window Size

To specify a new height for a window or to increase or decrease the current height, use the winheight command (abbreviated winh or wh).

The syntax is:

winheight [win_name] [+ | -] num_lines
If you omit win_name, the window with logical focus is resized. When you increase the height of a window, the height of the command window is decreased by the same amount, and vice versa. The height of any other windows remains unchanged.

For example, the command

wh src +3
increases the size of the source window, and decreases the size of the command window, by 3 lines.

To find out the current sizes of all windows, use the info win command. For example, if you have a split-screen layout, the command output might be as follows:

(gdb) i win
        SRC     (8 lines)
        REGS    (8 lines)
        CMD     (8 lines)
If you use the mouse or window menus to resize the terminal window during a debugging session, the screen remains the same size it was when you started. To change the screen size, you must exit the debugger and restart it.




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15.9 Refreshing and Updating the Screen

If the screen display is disrupted for some reason, use the refresh command (ref) to restore the windows to their previous state:

ref
If you use stack-navigation commands such as up, down, and frame to change your source location, and you wish to return the display to the current point of execution, use the update command (upd):

upd



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16. XDB to WDB Transition Guide

This is a transition aid designed for XDB users who are learning HP WDB 2.0, an HP-supported version of the industry-standard GDB debugger. Select one of these lists for a table that shows HP WDB 2.0 equivalents for many common XDB commands and other features.

Invoke HP WDB 2.0 with the command gdb -tui to obtain a terminal user interface (TUI) similar to that provided by XDB. Commands marked "(with -tui)" are valid when you use the -tui option.

Invoke HP WDB 2.0 with the command gdb -xdb to turn on XDB compatibility mode, which allows you to use many XDB commands as synonyms for GDB commands. Commands marked "(with -xdb)" are valid when you use the -xdb option.

You may use both -xdb and -tui at the same time. Some commands are valid only when you use both options.

For a tutorial introduction to HP WDB 2.0, see Getting Started with HP WDB 2.0

16. XDB to WDB Transition Guide
16.1 By-Function Lists of XDB Commands and HP WDB Equivalents
16.2 Overall Breakpoint Commands
16.3 XDB Data Formats and HP WDB Equivalents
16.4 XDB Location Syntax and HP WDB Equivalents
16.5 XDB Special Language Operators and HP WDB Equivalents
16.6 XDB Special Variables and HP WDB Equivalents
16.7 XDB Variable Identifiers and HP WDB Equivalents
16.8 Alphabetical Lists of XDB Commands and HP WDB Equivalents




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16.1 By-Function Lists of XDB Commands and HP WDB Equivalents

16.1.1 Invocation Commands
16.1.2 Window Mode Commands
16.1.3 File Viewing Commands
16.1.4 Source Directory Mapping Commands
16.1.5 Data Viewing and Modification Commands
16.1.6 Stack Viewing Commands
16.1.7 Status Viewing Command
16.1.8 Job Control Commands




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16.1.1 Invocation Commands

By default, HP WDB runs in line mode. To run it with a terminal user interface similar to that of XDB, use the -tui option.

XDB Command HP WDB 2.0 Equivalent Meaning
xdb program gdb -xdb program, gdb -xdb -tui program Debug program
xdb program corefile gdb -xdb program -c corefile Debug core file
xdb -d dir gdb -xdb -d dir Specify alternate directory to search for source files
xdb -P pid program gdb -xdb program pid Attach to running program at invocation
xdb -i (after starting) run < file Specify input to target program
xdb -o (after starting) run > file Specify output from target program




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16.1.2 Window Mode Commands

These commands are all TUI mode commands and/or XDB compatibility mode commands. They are available when you invoke HP WDB 2.0 by using the -tui or -xdb or both options.

XDB Command HP WDB 2.0 Equivalent Meaning
{+ | -}r {+ | -}r (with -xdb -tui), {+ | -} data (with -tui) Scroll floating-point registers forward or backward (src, cmd, and asm are also valid window names)
fr fr (with -xdb -tui), display $fregs (with -tui) Display floating-point registers
gr gr (with -xdb -tui), display $regs (with -tui) Display general registers
sr sr (with -xdb -tui), display $sregs (with -tui) Display special registers
td td (with -xdb -tui) Toggle disassembly mode
tf tf (with -xdb -tui), toggle $fregs (with -tui) Toggle float register display precision
ts ts (with -xdb -tui) Toggle split-screen mode
u u (with -xdb -tui), update (with -tui) Update screen to current execution point
U U (with -xdb -tui), refresh (with -tui) Refresh all windows
w number w number (with -xdb -tui), winheight src number (with -tui) Set size of source window




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16.1.3 File Viewing Commands

XDB Command HP WDB 2.0 Equivalent Meaning
{+ | -}[number] {+ | -}[ number] (with -tui; note that a space is required between + or - and the number) Move view location forward or backward in source file number lines
/[string] /[string] (with -xdb), search regexp, forw regexp Search source forward for [last] string
?[string] ?[string] (with -xdb), rev regexp Search source backward for [last] string
D "dir" D "dir" (with -xdb), dir pathname Add a directory search path for source files
L L (with -xdb) Show current viewing location or current point of execution
ld ld (with -xdb), show directories List source directory search path (list all directories)
lf lf (with -xdb), info sources List all source files
lf [string] No equivalent List matching files
n fo or rev Repeat previous search
N fo or rev Repeat previous search in opposite direction
v v (with -xdb), list Show one source window forward from current
v location v location (with -xdb), list location View source at location in source window
va address va address (with -xdb), disas address View address in disassembly window
va label va label (with -xdb), disas label View label in disassembly window (label is a location)
va label + offset va label + offset (with -xdb), disas label + offset View label + offset in disassembly window




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16.1.4 Source Directory Mapping Commands

Use the D or dir command to add new directories to be searched for source files. See See XDB-fil.

GDB does not provide a source directory mapping capability and therefore does not have any equivalent of the apm, dpm, and lpm commands.




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16.1.5 Data Viewing and Modification Commands

There are many info commands in addition to those shown here. Use help info to get a list.

XDB Command HP WDB 2.0 Equivalent Meaning
l l (with -xdb), info args followed by info locals List all parameters and locals of current procedure
lc [string] lc [string] (with -xdb), info common string List all (or matching) commons
lg [string] lg [string] (with -xdb), info variables [string] List all (or matching) globals
ll [string] info functions [string], info variables [string], maint print msymbols file List the contents of the linker symbol table
lm show user List all string macros
lm string show user string List matching string macros
lo [[class]::][string] info func [[class]::][string] List all (or matching) overloaded functions
lp info functions Show current scope, list program blocks, list names (symbols)
lp [[class]::]string info func [[class]::]string info addr [[class]::]string List all (or matching) procedures
lr lr (with -xdb), info all-reg List all registers
lr string lr string (with -xdb), info reg string List matching registers
ls [string] No equivalent List all (or matching) special variables
mm info sharedlibrary Show memory map of all loaded shared libraries
mm string No equivalent Show memory map of matching loaded shared libraries
p expr[\format p[/format expr [Note: The count and size portions of formats are not allowed in the p (print) command. They are allowed in the x command (examine memory).] Print value using the specified format
p expr?format p/format &amp;expr Print address using specified format
p class:: No equivalent Print static members of class
p $lang show language Inquire what language is used
p {+ | -}[\format Use x/format command to obtain initial value, then use x with no argument to obtain value of next memory location. To obtain value of previous memory location, use "x $_ - 1". Print value of next/previous memory location using format
pq expr set expr, set var expr Evaluate using the specified format
pq expr?format No equivalent Determine address using specified format
pq class:: No equivalent Evaluate static members of class
pq {+ | -}[\format No equivalent Evaluate next/previous memory location using format




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16.1.6 Stack Viewing Commands

The GDB concept of the top and bottom of the stack is the opposite of XDB's, so XDB's up is GDB's down.

XDB Command HP WDB 2.0 Equivalent Meaning
down up View procedure one level nearer outermost frame of stack (higher number)
down number up number View procedure number levels nearer outermost frame of stack
t [depth] t [depth] (with -xdb), bt [depth] Print stack trace to depth
T [depth] T [depth] (with -xdb), bt full [depth] Print stack trace and show local vars
top frame 0 View procedure at innermost frame of stack
up down View procedure one level nearer innermost frame of stack (lower number)
up number down number View procedure number levels nearer innermost frame of stack
V [depth] V [depth] (with -xdb), frame [depth] Display text for current active procedure or at specified depth on stack




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16.1.7 Status Viewing Command

Type show with no arguments to get a list of current debugger settings.

XDB Command HP WDB 2.0 Equivalent Meaning
I info (many kinds), show (many kinds) Display state of debugger and program




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16.1.8 Job Control Commands

XDB Command HP WDB 2.0 Equivalent Meaning
c c, continue Continue from breakpoint, ignoring any pending signal
c location until location Continue from breakpoint, ignoring any pending signal, set temporary breakpoint at location
C c, continue Continue, allowing any pending signal
C [location] until location Continue, allowing any pending signal, set temporary breakpoint at location
g line g line (with -xdb), go line, tb line followed by jump line Go to line in current procedure
g #label No equivalent Go to label in current procedure
g {+ | -}lines g {+ | -}lines (with -xdb), go {+ | -}lines, tb {+ | -}lines followed by jump {+ | -}lines Go forward or back given # lines
g {+ | -} g {+ | -} (with -xdb), go {+ | -}1, tb {+ | -}1 followed by jump {+ | -}1 Go forward or back 1 line
k k Detach and terminate target
r [arguments] r [arguments] Run with last arguments [or with new arguments]
R R (with -xdb), r Rerun with no arguments
s s, si Single step (into procedures) (si: step by instruction)
s number s number, si number Single step number steps (into procedures) (si: step by instruction)
S S (with -xdb), n, ni Step over (ni: step over by instruction)
S number S number (with -xdb), n number, ninumber Step over by number statements or instructions (ni: step over by instruction)




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16.2 Overall Breakpoint Commands

16.2.1 Auxiliary Breakpoint Commands
16.2.2 Breakpoint Creation Commands
16.2.3 Breakpoint Status Commands
16.2.4 All-Procedures Breakpoint Commands
16.2.5 Global Breakpoint Commands
16.2.6 Assertion Control Commands
16.2.7 Record and Playback Commands
16.2.8 Macro Facility Commands
16.2.9 Signal Control Commands
16.2.10 Miscellaneous Commands

XDB Command HP WDB 2.0 Equivalent Meaning
lb lb (with -xdb), i b List breakpoints
tb No equivalent Toggle overall breakpoint state




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16.2.1 Auxiliary Breakpoint Commands

XDB Command HP WDB 2.0 Equivalent Meaning
"any_string" p "any_string" Print any_string
if expr {cmds} [{cmds}] if expr cmds [else cmds] end Conditionally execute cmds
Q Q (with -xdb), silent (must be first command in a commands list) Quiet breakpoints




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16.2.2 Breakpoint Creation Commands

The GDB equivalent of the count and cmds arguments is to use the commandsbnum command to set an ignore count and/or to specify commands to be executed for that breakpoint.

For C++ programs, you can use the regular-expression breakpoint command rbreak to set breakpoints on all the member functions of a class or on overloaded functions outside a class.

XDB Command HP WDB 2.0 Equivalent Meaning
b loc b loc Set a breakpoint at the specified location
b b Set a breakpoint at the current line
ba address ba address (with -xdb), b *address Set breakpoint at a code address
bb [depth] No equivalent (use b proc) Set breakpoint at procedure beginning
bi expr.proc b class::proc cond bnum (this == expr) Set an instance breakpoint at the first executable line of expr.proc
bi -c expr No equivalent Set an instance breakpoint at first executable line of all non-static member functions of the instance's class (no base classes)
bi -C expr No equivalent Set an instance breakpoint at first executable line of all non-static member functions of the instance's class (base classes included)
bpc -c class rb ^class::* Set a class breakpoint at first executable line of all member functions of the instance's class (no base classes)
bpc -C class Use rb ^class::* for base classes also Set a class breakpoint at first executable line of all member functions of the class (base classes included)
bpo proc rb proc Set breakpoints on overloaded functions outside a class
bpo class::proc b class::proc Set breakpoints on overloaded functions in a class
bt [depth] No equivalent Set trace breakpoint at procedure at specified depth on program stack
bt proc b proc commands bnum finish c end Set trace breakpoint at proc
bu [depth] bu [depth] (with -xdb). The finish command is equivalent to the sequence bu, c, db (to continue out of the current routine). Set up-level breakpoint
bx [depth] bx [depth] (with -xdb) Set a breakpoint at procedure exit




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16.2.3 Breakpoint Status Commands

XDB Command HP WDB 2.0 Equivalent Meaning
ab number enable number Activate suspended breakpoint of the given number
ab * enable Activate all suspended breakpoints
ab @shared-library No equivalent Activate suspended breakpoints in named shared library
bc number expr bc number expr (with -xdb), ignorenumber expr (within a commands list) Set a breakpoint count
db clear Delete breakpoint at current line
db number delete number Delete breakpoint of the given number
db * delete Delete all breakpoints
sb number disable number Suspend breakpoint of the given number
sb * disable Suspend all breakpoints
sb @shared-library No equivalent Suspend breakpoints in named shared library




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16.2.4 All-Procedures Breakpoint Commands

GDB does not provide the ability to set breakpoints on all procedures with a single command. Therefore, it does not have any equivalent of the following commands:

bpt
bpx
dp
Dpt
Dpx



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16.2.5 Global Breakpoint Commands

XDB Command HP WDB 2.0 Equivalent Meaning
abc cmds No exact equivalent, but display expr is equivalent to abc print expr Set or delete cmds to execute at every stop
dbc undisplay Stop displaying values at each stop




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16.2.6 Assertion Control Commands

GDB does not provide the ability to trace by instruction. Watchpoints, however, provide similar functionality to xdb assertions.

For example, watchpoints can be:

HP WDB 2.0 does not have explicit equivalents for the following commands:

a
aa
da
la
sa
ta
x



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16.2.7 Record and Playback Commands

Use the source command to read commands from a file. GDB does not provide a recording capability like XDB's, but you can use the set history save command to record all GDB commands in the file ./.gdb_history (similar to the $HOME/.xdbhist file). The history file is not saved until the end of your debugging session.

To change the name of the history file, use set history filename.

To stop recording, use set history save off.

To display the current history status, use show history.

For an equivalent of the XDB record-all facility, pipe the output of the gdb command to the tee(1) command. For example:

gdb a.out | tee mylogfile
This solution works with the default line-mode user interface, not with the terminal user interface.




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16.2.8 Macro Facility Commands

Use the show user or help user-defined command to obtain a list of all user-defined commands.

XDB Command HP WDB 2.0 Equivalent Meaning
def name replacement-text def name [GDB prompts for commands] Define a user-defined command
tm No equivalent Toggle the macro substitution mechanism
undef name def name [follow with empty command list] Remove the macro definition for name
undef * No equivalent Remove all macro definitions




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16.2.9 Signal Control Commands

XDB Command HP WDB 2.0 Equivalent Meaning
lz lz (with -xdb), info signals List signal handling
z number s z number s (with -xdb), handle numberstop, handle number nostop Toggle stop flag for signal number
z number i z number i (with -xdb), handle numbernopass, handle number pass Toggle ignore flag for signal number
z number r z number r (with -xdb), handle number print, handle number noprint Toggle report flag for signal number
z number Q z number Q (with -xdb), handle number noprint Do not print the new state of the signal




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16.2.10 Miscellaneous Commands

XDB Command HP WDB 2.0 Equivalent Meaning
Return Return Repeat previous command
~ Return Repeat previous command
; No equivalent (one command per line in command list) Separate commands in command list
! cmd_line ! cmd_line (with -xdb), she cmd_line Invoke a shell
{cmd_list} commands [number] ... end Execute command list (group commands)
Control-C Control-C Interrupt the program
# [text] # [text] A comment
am am (with -xdb), set height num Activate more (turn on pagination)
f ["printf-style-fmt"] No equivalent Set address printing format
h h Help
M[{t | c} [expr[; expr...]]] No equivalent Print object or corefile map
q q Quit debugger
sm sm (with -xdb), set height 0 Suspend more (turn off pagination)
ss file No equivalent Save (breakpoint, macro, assertion) state
tc No equivalent Toggle case sensitivity in searches




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16.3 XDB Data Formats and HP WDB Equivalents

The format of the print command is different in XDB and GDB:

XDB:  p expr\fmt
GDB:  p/fmt expr
Use the GDB command set print pretty to obtain a structure display formatted similarly to the default XDB display.

XDB Command HP WDB 2.0 Equivalent Meaning
b d Byte in decimal
B (1) d Byte in decimal
c c Character
C (1) c Wide character
d d Decimal integer
D (1) d Long decimal integer
e No equivalent e floating-point notation as float
E (1) No equivalent e floating-point notation as double
f No equivalent f floating-point notation as float
F (1) No equivalent f floating-point notation as double
g f g floating-point notation as float
G (1) f g floating-point notation as double
i Use x/i command Machine instruction (disassembly)
k No equivalent Formatted structure display
K (1) No equivalent Formatted structure display with base classes
n print Normal (default) format, based on type
o o Expression in octal as integer
O (1) o Expression in octal as long integer
p a Print name of procedure containing address
s No equivalent String
S No equivalent Formatted structure display
t whatis, ptype Show type of the expression
T (1) ptype Show type of expression, including base class information
u u Expression in unsigned decimal format
U (1) u Expression in long unsigned decimal format
w No equivalent Wide character string
W (1) No equivalent Address of wide character string
x x Print in hexadecimal
X (1) x Print in long hexadecimal
z t Print in binary
Z (1) t Print in long binary

(1) HP WDB will display data in the size appropriate for the data. It will not extend the length displayed in response to one of the uppercase formchars (e.g. O, D, F).




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16.4 XDB Location Syntax and HP WDB Equivalents

XDB Location Syntax HP WDB 2.0 Equivalent Meaning
line line Source line and code address
file[:line] file[:line] Source line and code address
proc proc Procedure name
[file:]proc[:proc[...]][:line] No equivalent Source line and code address
[file:]proc[:proc[...]][:#label] No equivalent Source line and code address
[class]::proc [class]::proc Source line and code address
[class]::proc[:line] No equivalent Source line and code address
[class]::proc[#label] No equivalent Source line and code address
proc#line No equivalent Code address
[class]::proc#line No equivalent Code address
#label No equivalent Source line and code address
name@shared-library No equivalent Address of name in shared library shared-library




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16.5 XDB Special Language Operators and HP WDB Equivalents

XDB Language Operator HP WDB 2.0 Equivalent Meaning
$addr Depends on language Unary operator, address of object
$in No equivalent Unary Boolean operator, execution in procedure
$sizeof sizeof Unary operator, size of object




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16.6 XDB Special Variables and HP WDB Equivalents

GDB does not provide special variables of the kind that XDB has, but you can use show and set to display and modify many debugger settings.

XDB Special Variable HP WDB 2.0 Equivalent Meaning
$cplusplus No equivalent C++ feature control flags
$depth No equivalent Default stack depth for local variables
$fpa No equivalent Treat FPA sequence as one instruction
$fpa_reg No equivalent Address register for FPA sequences
$lang show language Current language for expression evaluation
$line No equivalent Current source line number
$malloc No equivalent Debugger memory allocation (bytes)
$print No equivalent Display mode for character data
$regname $regname Hardware registers
$result Use $n (value history number assigned to the desired result) Return value of last command line procedure call
$signal No equivalent Current child procedure signal number
$step No equivalent Number of instructions debugger will step in non-debuggable procedures before free-running
$var $var Define or use special variable (convenience variable)




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16.7 XDB Variable Identifiers and HP WDB Equivalents

XDB Variable Identifier HP WDB 2.0 Equivalent Meaning
var var Search for var
class::var class::var Search class for var (bug: not yet)
[[class]::]proc:[class::]var proc::var Search proc for var (static variables only)
[[class]::]proc:depth:[class::] No equivalent Search proc for depth on stack
. (dot) Empty string; for example, p is the equivalent of p . Shorthand for last thing you looked at
:var or ::var ::var to distinguish a global from a local variable with same name Search for global variable only




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16.8 Alphabetical Lists of XDB Commands and HP WDB Equivalents

16.8.1 A
16.8.2 B
16.8.3 C through D
16.8.4 F through K
16.8.5 L
16.8.6 M through P
16.8.7 Q through S
16.8.8 T
16.8.9 U through Z
16.8.10 Symbols




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16.8.1 A

XDB Command Equivalent HP WDB 2.0 Command
a [cmds] No equivalent
aa number No equivalent
aa * No equivalent
ab number enable number
ab * enable
ab @shared-library No equivalent
abc cmds No exact equivalent, but display expr is equivalent to abc print expr
am am (with -xdb), set height num
apm oldpath [newpath] No equivalent
apm "" [newpath] No equivalent




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16.8.2 B

XDB Command Equivalent HP WDB 2.0 Command
b loc b loc
b b
ba address ba address (with -xdb), b *address
bb [depth] No equivalent (use b proc)
bc number expr bc number expr (with -xdb), ignore number expr (within a commands list)
bi expr.proc b class::proc cond bnum (this == expr)
bi -c expr No equivalent
bi -C expr No equivalent
bp No equivalent
bp cmds No equivalent
bpc -c class rb ^class::*
bpc -C class Use rb ^class::* for base classes also
bpo proc rb proc
bpo class::proc b class::proc
bpt No equivalent
bpt cmds No equivalent
bpx No equivalent
bpx cmds No equivalent
bt [depth] No equivalent
bt proc b proc commands bnum
finish
c
end
bu [depth] bu [depth] (with -xdb). The finish command is equivalent to the sequence bu, c, db (to continue out of the current routine).
bx [depth] bx [depth] (with -xdb)




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16.8.3 C through D

XDB Command Equivalent HP WDB 2.0 Command
c c, continue
c location until location
C c, continue
C location until location
D "dir" D "dir" (with -xdb), dir pathname
da number No equivalent
da * No equivalent
db clear
db number delete number
db * delete
dbc undisplay
def name replacement-text def name [GDB prompts for commands]
down up
down number up number
dp No equivalent
dpm index No equivalent
dpm * No equivalent
Dpt No equivalent
Dpx No equivalent




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16.8.4 F through K

XDB Command Equivalent HP WDB 2.0 Command
f ["printf-style-fmt"] No equivalent
fr fr (with -xdb -tui), display $fregs (with -tui)
g line g line (with -xdb), go line, tb line followed by jump line
g #label No equivalent
g {+ | -}lines g {+ | -}lines (with -xdb), go {+ | -}lines tb {+ | -}lines followed by jump {+ | -}lines
g {+ | -} g {+ | -} (with -xdb), go {+ | -}1, tb {+ | -}1 followed by jump {+ | -}1
gr gr (with -xdb -tui), display $regs (with -tui)
h h
if expr {cmds} [{cmds}] if expr cmds [else cmds] end
I info (many kinds), show (many kinds)
k k




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16.8.5 L

XDB Command Equivalent HP WDB 2.0 Command
l l (with -xdb), info args followed by info locals
L L (with -xdb)
la No equivalent
lb lb (with -xdb), i b
lc [string] lc [string] (with -xdb), info common string
ld ld (with -xdb), show directories
lf lf (with -xdb), info sources
lf [string] No equivalent
lg [string] lg [string] (with -xdb), info variables [string]
ll [string] info functions [string], info variables [string], maint print msymbols file
lm [string] show user [string]
lo [[class]::][string] info func [[class]::][string]
lp info functions
lp [[class]::]string info func [[class]::]string info addr [[class]::]string
lpm No equivalent
lr lr (with -xdb), info all-reg
lr string lr string (with -xdb), info reg string
ls [string] No equivalent
lz lz (with -xdb), info signals




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16.8.6 M through P

XDB Command Equivalent HP WDB 2.0 Command
M[{t | c} [expr[; expr...]]] No equivalent
mm info sharedlibrary
mm string No equivalent
N fo or rev
n fo or rev
p expr[\format] p[/format] expr [Note: The count and size portions of formats are not allowed in the p (print) command. They are allowed in the x command (examine memory).]
p expr?format p/format &amp;expr
p class:: No equivalent
p $lang show language
p {+ | -}[\format Use x/format command to obtain initial value, then use x with no argument to obtain value of next memory location. To obtain value of previous memory location, use "x $_ - 1".
pq expr set expr, set var expr
pq expr?format No equivalent
pq class:: No equivalent
pq [+ | -][\format No equivalent




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16.8.7 Q through S

XDB Command Equivalent HP WDB 2.0 Command
q q
Q Q (with -xdb), silent (must be first command in a commands list)
r [arguments] r [arguments]
R R (with -xdb), r
s s, si
s number s number, si number
S S (with -xdb), n, ni
S number S number (with -xdb), n number, ninumber
sa number No equivalent
sa * No equivalent
sb number disable number
sb * disable
sb @shared-library No equivalent
sm sm (with -xdb), set height 0
sr sr (with -xdb -tui), display $sregs (with -tui)
ss file No equivalent




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16.8.8 T

XDB Command Equivalent HP WDB 2.0 Command
t [depth] t [depth] (with -xdb), bt [depth]
T [depth] T [depth] (with -xdb), bt full [depth]
ta No equivalent
tb No equivalent
tc No equivalent
td td (with -xdb -tui)
tf tf (with -xdb -tui), toggle $fregs (with -tui)
tm No equivalent
top frame 0
tr [@] No equivalent
ts ts (with -xdb -tui)




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16.8.9 U through Z

XDB Command Equivalent HP WDB 2.0 Command
u u (with -xdb -tui), update (with -tui)
U U (with -xdb -tui), refresh (with -tui)
undef name def name [follow with empty command list]
undef * No equivalent
up down
up number down number
v v (with -xdb), list
v location v location (with -xdb), list location
V [depth] V [depth] (with -xdb), frame [depth]
va address va address (with -xdb), disas address
va label va label (with -xdb), disas label
va label + offset va label + offset (with -xdb), disas label + offset
w number w number (with -xdb -tui), winheight src number (with -tui)
x [expr] No equivalent
xdb program gdb -xdb program, gdb -xdb -tui program
xdb program corefile gdb -xdb program -c corefile
xdb -d dir gdb -xdb -d dir
xdb -P pid program gdb -xdb program pid
xdb -i (after starting) run < file
xdb -o (after starting) run > file
z number s z number s (with -xdb), handle number stop, handle number nostop
z number i z number i (with -xdb), handle number nopass, handle number pass
z number r z number r (with -xdb), handle number print, handle number noprint
z number Q z number Q (with -xdb), handle number noprint




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16.8.10 Symbols

>@[c | f | t]
XDB Symbol Equivalent HP WDB Symbol
line line
file[:line] file[:line]
proc proc
[file:]proc[:proc[...]][:line] No equivalent
[file:]proc[:proc[...]][:#label] No equivalent
[class]::proc [class]::proc
[class]::proc[:line] No equivalent
[class]::proc[#label] No equivalent
proc#line No equivalent
[class]::proc#line No equivalent
name@shared-library No equivalent
var var
class::var class::var (bug: not yet)
[[class]::]proc:[class::]var proc::var (static variables only)
[[class]::]proc:depth:[class::]var No equivalent
Return Return
"any_string" p "any_string"
. (dot) Empty string; for example, p is the equivalent of p .
~ Return
{+ | -}r {+ | -}r (with -xdb -tui), {+ | -} data (with -tui)
{+ | -}[number] {+ | -}[ number] (with -tui; note that a space is required between + or - and the number)
/[string] /[string] (with -xdb), search regexp, forw regexp
?[string] ?[string] (with -xdb), rev regexp
; No equivalent (one command per line in command list)
:var or ::var ::var
! cmd_line ! cmd_line (with -xdb), she cmd_line
{cmd_list} commands [number] ... end
<file source file
<<file No equivalent
> No equivalent
>file No equivalent
>c No equivalent
>f No equivalent
>t No equivalent
No equivalent
>@file No equivalent
>> No equivalent
>>file No equivalent
>>@ No equivalent
>>@file No equivalent
Control-C Control-C
# [text] # [text]
#label No equivalent




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17. Controlling GDB

You can alter the way GDB interacts with you by using the set command. For commands controlling how GDB displays data, see Print Settings. Other settings are described here.

PromptPrompt
EditingCommand editing
HistoryCommand history
Screen SizeScreen size
NumbersNumbers
Messages/WarningsOptional warnings and messages




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17.1 Prompt

GDB indicates its readiness to read a command by printing a string called the prompt. This string is normally `(gdb)'. You can change the prompt string with the set prompt command. For instance, when debugging GDB with GDB, it is useful to change the prompt in one of the GDB sessions so that you can always tell which one you are talking to.

Note: set prompt does not add a space for you after the prompt you set. This allows you to set a prompt which ends in a space or a prompt that does not.

set prompt newprompt
Directs GDB to use newprompt as its prompt string henceforth.

show prompt
Prints a line of the form: `Gdb's prompt is: your-prompt'




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17.2 Command editing

GDB reads its input commands via the readline interface. This GNU library provides consistent behavior for programs which provide a command line interface to the user. Advantages are GNU Emacs-style or vi-style inline editing of commands, csh-like history substitution, and a storage and recall of command history across debugging sessions.

You may control the behavior of command line editing in GDB with the command set.

set editing
set editing on
Enable command line editing (enabled by default).

set editing off
Disable command line editing.

show editing
Show whether command line editing is enabled.




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17.3 Command history

GDB can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the GDB command history facility.

To make command history understand your vi key bindings you need to create a `~/.inputrc' file with the following contents:

set editing-mode vi
The readline interface uses the `.inputrc' file to control the settings.

set history filename fname
Set the name of the GDB command history file to fname. This is the file where GDB reads an initial command history list, and where it writes the command history from this session when it exits. You can access this list through history expansion or through the history command editing characters listed below. This file defaults to the value of the environment variable GDBHISTFILE, or to `./.gdb_history' (`./_gdb_history' on MS-DOS) if this variable is not set.

set history save
set history save on
Record command history in a file, whose name may be specified with the set history filename command. By default, this option is disabled.

set history save off
Stop recording command history in a file.

set history size size
Set the number of commands which GDB keeps in its history list. This defaults to the value of the environment variable HISTSIZE, or to 256 if this variable is not set.

History expansion assigns special meaning to the character !.

Since ! is also the logical not operator in C, history expansion is off by default. If you decide to enable history expansion with the set history expansion on command, you may sometimes need to follow ! (when it is used as logical not, in an expression) with a space or a tab to prevent it from being expanded. The readline history facilities do not attempt substitution on the strings != and !(, even when history expansion is enabled.

The commands to control history expansion are:

set history expansion on
set history expansion
Enable history expansion. History expansion is off by default.

set history expansion off
Disable history expansion.

The readline code comes with more complete documentation of editing and history expansion features. Users unfamiliar with GNU Emacs or vi may wish to read it.

show history
show history filename
show history save
show history size
show history expansion
These commands display the state of the GDB history parameters. show history by itself displays all four states.

show commands
Display the last ten commands in the command history.

show commands n
Print ten commands centered on command number n.

show commands +
Print ten commands just after the commands last printed.




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17.4 Screen size

Certain commands to GDB may produce large amounts of information output to the screen. To help you read all of it, GDB pauses and asks you for input at the end of each page of output. Type RET when you want to continue the output, or q to discard the remaining output. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, GDB tries to break the line at a readable place, rather than simply letting it overflow onto the following line.

Normally GDB knows the size of the screen from the terminal driver software. For example, on Unix GDB uses the termcap data base together with the value of the TERM environment variable and the stty rows and stty cols settings. If this is not correct, you can override it with the set height and set width commands:

set height lpp
show height
set width cpl
show width
These set commands specify a screen height of lpp lines and a screen width of cpl characters. The associated show commands display the current settings.

If you specify a height of zero lines, GDB does not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer.

Likewise, you can specify `set width 0' to prevent GDB from wrapping its output.




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17.5 Numbers

You can always enter numbers in octal, decimal, or hexadecimal in GDB by the usual conventions: octal numbers begin with `0', decimal numbers end with `.', and hexadecimal numbers begin with `0x'. Numbers that begin with none of these are, by default, entered in base 10; likewise, the default display for numbers--when no particular format is specified--is base 10. You can change the default base for both input and output with the set radix command.

set input-radix base
Set the default base for numeric input. Supported choices for base are decimal 8, 10, or 16. base must itself be specified either unambiguously or using the current default radix; for example, any of

set radix 012
set radix 10.
set radix 0xa
sets the base to decimal. On the other hand, `set radix 10' leaves the radix unchanged no matter what it was.

set output-radix base
Set the default base for numeric display. Supported choices for base are decimal 8, 10, or 16. base must itself be specified either unambiguously or using the current default radix.

show input-radix
Display the current default base for numeric input.

show output-radix
Display the current default base for numeric display.




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17.6 Optional warnings and messages

By default, GDB is silent about its inner workings. If you are running on a slow machine, you may want to use the set verbose command. This makes GDB tell you when it does a lengthy internal operation, so you will not think it has crashed.

Currently, the messages controlled by set verbose are those which announce that the symbol table for a source file is being read; see symbol-file in Files.

set verbose on
Enables GDB output of certain informational messages.

set verbose off
Disables GDB output of certain informational messages.

show verbose
Displays whether set verbose is on or off.

By default, if GDB encounters bugs in the symbol table of an object file, it is silent; but if you are debugging a compiler, you may find this information useful (see Symbol Errors).

set complaints limit
Permits GDB to output limit complaints about each type of unusual symbols before becoming silent about the problem. Set limit to zero to suppress all complaints; set it to a large number to prevent complaints from being suppressed.

show complaints
Displays how many symbol complaints GDB is permitted to produce.

By default, GDB is cautious, and asks what sometimes seems to be a lot of stupid questions to confirm certain commands. For example, if you try to run a program which is already running:

(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n)
If you are willing to unflinchingly face the consequences of your own commands, you can disable this "feature":

set confirm off
Disables confirmation requests.

set confirm on
Enables confirmation requests (the default).

show confirm
Displays state of confirmation requests.




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18. Canned Sequences of Commands

Aside from breakpoint commands (see Break Commands), GDB provides two ways to store sequences of commands for execution as a unit: user-defined commands and command files.

DefineUser-defined commands
HooksUser-defined command hooks
Command FilesCommand files
OutputCommands for controlled output




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18.1 User-defined commands

A user-defined command is a sequence of GDB commands to which you assign a new name as a command. This is done with the define command. User commands may accept up to 10 arguments separated by white space. Arguments are accessed within the user command via $arg0...$arg9. A trivial example:

define adder
  print $arg0 + $arg1 + $arg2
To execute the command use:

adder 1 2 3
This defines the command adder, which prints the sum of its three arguments. Note the arguments are text substitutions, so they may reference variables, use complex expressions, or even perform inferior functions calls.

define commandname
Define a command named commandname. If there is already a command by that name, you are asked to confirm that you want to redefine it.

The definition of the command is made up of other GDB command lines, which are given following the define command. The end of these commands is marked by a line containing end.

if
Takes a single argument, which is an expression to evaluate. It is followed by a series of commands that are executed only if the expression is true (nonzero). There can then optionally be a line else, followed by a series of commands that are only executed if the expression was false. The end of the list is marked by a line containing end.

while
The syntax is similar to if: the command takes a single argument, which is an expression to evaluate, and must be followed by the commands to execute, one per line, terminated by an end. The commands are executed repeatedly as long as the expression evaluates to true.

document commandname
Document the user-defined command commandname, so that it can be accessed by help. The command commandname must already be defined. This command reads lines of documentation just as define reads the lines of the command definition, ending with end. After the document command is finished, help on command commandname displays the documentation you have written.

You may use the document command again to change the documentation of a command. Redefining the command with define does not change the documentation.

help user-defined
List all user-defined commands, with the first line of the documentation (if any) for each.

show user
show user commandname
Display the GDB commands used to define commandname (but not its documentation). If no commandname is given, display the definitions for all user-defined commands.

When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command.

If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many GDB commands that normally print messages to say what they are doing omit the messages when used in a user-defined command.




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18.2 User-defined command hooks

You may define hooks, which are a special kind of user-defined command. Whenever you run the command `foo', if the user-defined command `hook-foo' exists, it is executed (with no arguments) before that command.

In addition, a pseudo-command, `stop' exists. Defining (`hook-stop') makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed.

For example, to ignore SIGALRM signals while single-stepping, but treat them normally during normal execution, you could define:

define hook-stop
handle SIGALRM nopass
end

define hook-run
handle SIGALRM pass
end

define hook-continue
handle SIGLARM pass
end
You can define a hook for any single-word command in GDB, but not for command aliases; you should define a hook for the basic command name, e.g. backtrace rather than bt. If an error occurs during the execution of your hook, execution of GDB commands stops and GDB issues a prompt (before the command that you actually typed had a chance to run).

If you try to define a hook which does not match any known command, you get a warning from the define command.




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18.3 Command files

A command file for GDB is a file of lines that are GDB commands. Comments (lines starting with #) may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal.

When you start GDB, it automatically executes commands from its init files. These are files named `.gdbinit' on Unix, or `gdb.ini' on DOS/Windows. GDB reads the init file (if any) in your home directory(4), then processes command line options and operands, and then reads the init file (if any) in the current working directory. This is so the init file in your home directory can set options (such as set complaints) which affect the processing of the command line options and operands. The init files are not executed if you use the `-nx' option; see Mode Options.

It can be useful to create a `.gdbinit' file in the directory where you are debugging an application. This file will set the set of actions that apply for this application.

For example, one might add lines like:

dir /usr/src/path/to/source/files
to add source directories or:

break fatal
to set breakpoints on fatal error routines or diagnostic routines.

On some configurations of GDB, the init file is known by a different name (these are typically environments where a specialized form of GDB may need to coexist with other forms, hence a different name for the specialized version's init file). These are the environments with special init file names:

You can also request the execution of a command file with the source command:

source filename
Execute the command file filename.

The lines in a command file are executed sequentially. They are not printed as they are executed. An error in any command terminates execution of the command file.

Commands that would ask for confirmation if used interactively proceed without asking when used in a command file. Many GDB commands that normally print messages to say what they are doing omit the messages when called from command files.




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18.4 Commands for controlled output

During the execution of a command file or a user-defined command, normal GDB output is suppressed; the only output that appears is what is explicitly printed by the commands in the definition. This section describes three commands useful for generating exactly the output you want.

echo text
Print text. Nonprinting characters can be included in text using C escape sequences, such as `\n' to print a newline. No newline is printed unless you specify one. In addition to the standard C escape sequences, a backslash followed by a space stands for a space. This is useful for displaying a string with spaces at the beginning or the end, since leading and trailing spaces are otherwise trimmed from all arguments. To print ` and foo = ', use the command `echo \ and foo = \ '.

A backslash at the end of text can be used, as in C, to continue the command onto subsequent lines. For example,

echo This is some text\n\
which is continued\n\
onto several lines.\n
produces the same output as

echo This is some text\n
echo which is continued\n
echo onto several lines.\n
output expression
Print the value of expression and nothing but that value: no newlines, no `$nn = '. The value is not entered in the value history either. See Expressions, for more information on expressions.

output/fmt expression
Print the value of expression in format fmt. You can use the same formats as for print. See Output Formats, for more information.

printf string, expressions...
Print the values of the expressions under the control of string. The expressions are separated by commas and may be either numbers or pointers. Their values are printed as specified by string, exactly as if your program were to execute the C subroutine

printf (string, expressions...);
For example, you can print two values in hex like this:

printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo
The only backslash-escape sequences that you can use in the format string are the simple ones that consist of backslash followed by a letter.




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19. Using GDB under GNU Emacs

A special interface allows you to use GNU Emacs to view (and edit) the source files for the program you are debugging with GDB.

To use this interface, use the command M-x gdb in Emacs. Give the executable file you want to debug as an argument. This command starts GDB as a subprocess of Emacs, with input and output through a newly created Emacs buffer. (Do not use the -tui option to run GDB from Emacs.)

Using GDB under Emacs is just like using GDB normally except for two things:

This applies both to GDB commands and their output, and to the input and output done by the program you are debugging.

This is useful because it means that you can copy the text of previous commands and input them again; you can even use parts of the output in this way.

All the facilities of Emacs' Shell mode are available for interacting with your program. In particular, you can send signals the usual way--for example, C-c C-c for an interrupt, C-c C-z for a stop.

Each time GDB displays a stack frame, Emacs automatically finds the source file for that frame and puts an arrow (`=>') at the left margin of the current line. Emacs uses a separate buffer for source display, and splits the screen to show both your GDB session and the source.

Explicit GDB list or search commands still produce output as usual, but you probably have no reason to use them from Emacs.

Warning: If the directory where your program resides is not your current directory, it can be easy to confuse Emacs about the location of the source files, in which case the auxiliary display buffer does not appear to show your source. GDB can find programs by searching your environment's PATH variable, so the GDB input and output session proceeds normally; but Emacs does not get enough information back from GDB to locate the source files in this situation. To avoid this problem, either start GDB mode from the directory where your program resides, or specify an absolute file name when prompted for the M-x gdb argument.

A similar confusion can result if you use the GDB file command to switch to debugging a program in some other location, from an existing GDB buffer in Emacs.

By default, M-x gdb calls the program called `gdb'. If you need to call GDB by a different name (for example, if you keep several configurations around, with different names) you can set the Emacs variable gdb-command-name; for example,

(setq gdb-command-name "mygdb")
(preceded by M-: or ESC :, or typed in the *scratch* buffer, or in your `.emacs' file) makes Emacs call the program named "mygdb" instead.

In the GDB I/O buffer, you can use these special Emacs commands in addition to the standard Shell mode commands:

C-h m
Describe the features of Emacs' GDB Mode.

M-s
Execute to another source line, like the GDB step command; also update the display window to show the current file and location.

M-n
Execute to next source line in this function, skipping all function calls, like the GDB next command. Then update the display window to show the current file and location.

M-i
Execute one instruction, like the GDB stepi command; update display window accordingly.

M-x gdb-nexti
Execute to next instruction, using the GDB nexti command; update display window accordingly.

C-c C-f
Execute until exit from the selected stack frame, like the GDB finish command.

M-c
Continue execution of your program, like the GDB continue command.

Warning: In Emacs v19, this command is C-c C-p.

M-u
Go up the number of frames indicated by the numeric argument (see section `Numeric Arguments' in The GNU Emacs Manual), like the GDB up command.

Warning: In Emacs v19, this command is C-c C-u.

M-d
Go down the number of frames indicated by the numeric argument, like the GDB down command.

Warning: In Emacs v19, this command is C-c C-d.

C-x &
Read the number where the cursor is positioned, and insert it at the end of the GDB I/O buffer. For example, if you wish to disassemble code around an address that was displayed earlier, type disassemble; then move the cursor to the address display, and pick up the argument for disassemble by typing C-x &.

You can customize this further by defining elements of the list gdb-print-command; once it is defined, you can format or otherwise process numbers picked up by C-x & before they are inserted. A numeric argument to C-x & indicates that you wish special formatting, and also acts as an index to pick an element of the list. If the list element is a string, the number to be inserted is formatted using the Emacs function format; otherwise the number is passed as an argument to the corresponding list element.

In any source file, the Emacs command C-x SPC (gdb-break) tells GDB to set a breakpoint on the source line point is on.

If you accidentally delete the source-display buffer, an easy way to get it back is to type the command f in the GDB buffer, to request a frame display; when you run under Emacs, this recreates the source buffer if necessary to show you the context of the current frame.

The source files displayed in Emacs are in ordinary Emacs buffers which are visiting the source files in the usual way. You can edit the files with these buffers if you wish; but keep in mind that GDB communicates with Emacs in terms of line numbers. If you add or delete lines from the text, the line numbers that GDB knows cease to correspond properly with the code.




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20. Reporting Bugs in GDB

Your bug reports play an essential role in making GDB reliable.

Reporting a bug may help you by bringing a solution to your problem, or it may not. But in any case the principal function of a bug report is to help the entire community by making the next version of GDB work better. Bug reports are your contribution to the maintenance of GDB.

In order for a bug report to serve its purpose, you must include the information that enables us to fix the bug.

Bug CriteriaHave you found a bug?
Bug ReportingHow to report bugs




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20.1 Have you found a bug?

If you are not sure whether you have found a bug, here are some guidelines:




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20.2 How to report bugs

If you obtained GDB (Hewlett-Packard Wildebeest (based on GDB 4.17-hpwdb-980821)) as part of your HP ANSI C, HP ANSI C++, or HP Fortran compiler kit, report problems to your HP Support Representative.

If you obtained GDB (Hewlett-Packard Wildebeest (based on GDB 4.17-hpwdb-980821)) from the Hewlett-Packard Web site, report problems to your HP Support Representative. Support is covered under the support contract for your HP compiler.

The fundamental principle of reporting bugs usefully is this: report all the facts. If you are not sure whether to state a fact or leave it out, state it!

Often people omit facts because they think they know what causes the problem and assume that some details do not matter. Thus, you might assume that the name of the variable you use in an example does not matter. Well, probably it does not, but one cannot be sure. Perhaps the bug is a stray memory reference which happens to fetch from the location where that name is stored in memory; perhaps, if the name were different, the contents of that location would fool the debugger into doing the right thing despite the bug. Play it safe and give a specific, complete example. That is the easiest thing for you to do, and the most helpful.

Keep in mind that the purpose of a bug report is to enable us to fix the bug. It may be that the bug has been reported previously, but neither you nor we can know that unless your bug report is complete and self-contained.

Sometimes people give a few sketchy facts and ask, "Does this ring a bell?" Those bug reports are useless, and we urge everyone to refuse to respond to them except to chide the sender to report bugs properly.

To enable us to fix the bug, you should include all these things:

Here are some things that are not necessary:


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21. Command Line Editing

This chapter describes the basic features of the GNU command line editing interface.

available for binding behave like the vi editor.
Introduction and NotationNotation used in this text.
Readline InteractionThe minimum set of commands for editing a line.
Readline Init FileCustomizing Readline from a user's view.
Bindable Readline CommandsA description of most of the Readline commands
Readline vi ModeA short description of how to make Readline




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21.1 Introduction to Line Editing

The following paragraphs describe the notation used to represent keystrokes.

The text C-k is read as `Control-K' and describes the character produced when the k key is pressed while the Control key is depressed.

The text M-k is read as `Meta-K' and describes the character produced when the meta key (if you have one) is depressed, and the k key is pressed. If you do not have a meta key, the identical keystroke can be generated by typing ESC first, and then typing k. Either process is known as metafying the k key.

The text M-C-k is read as `Meta-Control-k' and describes the character produced by metafying C-k.

In addition, several keys have their own names. Specifically, DEL, ESC, LFD, SPC, RET, and TAB all stand for themselves when seen in this text, or in an init file (see Readline Init File).




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21.2 Readline Interaction

Often during an interactive session you type in a long line of text, only to notice that the first word on the line is misspelled. The Readline library gives you a set of commands for manipulating the text as you type it in, allowing you to just fix your typo, and not forcing you to retype the majority of the line. Using these editing commands, you move the cursor to the place that needs correction, and delete or insert the text of the corrections. Then, when you are satisfied with the line, you simply press RETURN. You do not have to be at the end of the line to press RETURN; the entire line is accepted regardless of the location of the cursor within the line.

Readline Bare EssentialsThe least you need to know about Readline.
Readline Movement CommandsMoving about the input line.
Readline Killing CommandsHow to delete text, and how to get it back!
Readline ArgumentsGiving numeric arguments to commands.
SearchingSearching through previous lines.




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21.2.1 Readline Bare Essentials

In order to enter characters into the line, simply type them. The typed character appears where the cursor was, and then the cursor moves one space to the right. If you mistype a character, you can use your erase character to back up and delete the mistyped character.

Sometimes you may miss typing a character that you wanted to type, and not notice your error until you have typed several other characters. In that case, you can type C-b to move the cursor to the left, and then correct your mistake. Afterwards, you can move the cursor to the right with C-f.

When you add text in the middle of a line, you will notice that characters to the right of the cursor are `pushed over' to make room for the text that you have inserted. Likewise, when you delete text behind the cursor, characters to the right of the cursor are `pulled back' to fill in the blank space created by the removal of the text. A list of the basic bare essentials for editing the text of an input line follows.

C-b
Move back one character.
C-f
Move forward one character.
DEL
Delete the character to the left of the cursor.
C-d
Delete the character underneath the cursor.
Printing characters
Insert the character into the line at the cursor.
C-_
Undo the last editing command. You can undo all the way back to an empty line.




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21.2.2 Readline Movement Commands

The above table describes the most basic possible keystrokes that you need in order to do editing of the input line. For your convenience, many other commands have been added in addition to C-b, C-f, C-d, and DEL. Here are some commands for moving more rapidly about the line.

C-a
Move to the start of the line.
C-e
Move to the end of the line.
M-f
Move forward a word, where a word is composed of letters and digits.
M-b
Move backward a word.
C-l
Clear the screen, reprinting the current line at the top.

Notice how C-f moves forward a character, while M-f moves forward a word. It is a loose convention that control keystrokes operate on characters while meta keystrokes operate on words.




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21.2.3 Readline Killing Commands

Killing text means to delete the text from the line, but to save it away for later use, usually by yanking (re-inserting) it back into the line. If the description for a command says that it `kills' text, then you can be sure that you can get the text back in a different (or the same) place later.

When you use a kill command, the text is saved in a kill-ring. Any number of consecutive kills save all of the killed text together, so that when you yank it back, you get it all. The kill ring is not line specific; the text that you killed on a previously typed line is available to be yanked back later, when you are typing another line.

Here is the list of commands for killing text.

C-k
Kill the text from the current cursor position to the end of the line.

M-d
Kill from the cursor to the end of the current word, or if between words, to the end of the next word.

M-DEL
Kill from the cursor the start of the previous word, or if between words, to the start of the previous word.

C-w
Kill from the cursor to the previous whitespace. This is different than M-DEL because the word boundaries differ.

Here is how to yank the text back into the line. Yanking means to copy the most-recently-killed text from the kill buffer.

C-y
Yank the most recently killed text back into the buffer at the cursor.

M-y
Rotate the kill-ring, and yank the new top. You can only do this if the prior command is C-y or M-y.




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21.2.4 Readline Arguments

You can pass numeric arguments to Readline commands. Sometimes the argument acts as a repeat count, other times it is the sign of the argument that is significant. If you pass a negative argument to a command which normally acts in a forward direction, that command will act in a backward direction. For example, to kill text back to the start of the line, you might type `M-- C-k'.

The general way to pass numeric arguments to a command is to type meta digits before the command. If the first `digit' typed is a minus sign (-), then the sign of the argument will be negative. Once you have typed one meta digit to get the argument started, you can type the remainder of the digits, and then the command. For example, to give the C-d command an argument of 10, you could type `M-1 0 C-d'.




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21.2.5 Searching for Commands in the History

Readline provides commands for searching through the command history for lines containing a specified string. There are two search modes: incremental and non-incremental.

Incremental searches begin before the user has finished typing the search string. As each character of the search string is typed, Readline displays the next entry from the history matching the string typed so far. An incremental search requires only as many characters as needed to find the desired history entry. The characters present in the value of the isearch-terminators variable are used to terminate an incremental search. If that variable has not been assigned a value, the ESC and C-J characters will terminate an incremental search. C-g will abort an incremental search and restore the original line. When the search is terminated, the history entry containing the search string becomes the current line. To find other matching entries in the history list, type C-s or C-r as appropriate. This will search backward or forward in the history for the next entry matching the search string typed so far. Any other key sequence bound to a Readline command will terminate the search and execute that command. For instance, a RET will terminate the search and accept the line, thereby executing the command from the history list.

Non-incremental searches read the entire search string before starting to search for matching history lines. The search string may be typed by the user or be part of the contents of the current line.




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21.3 Readline Init File

Although the Readline library comes with a set of emacs-like keybindings installed by default, it is possible to use a different set of keybindings. Any user can customize programs that use Readline by putting commands in an inputrc file in his home directory. The name of this file is taken from the value of the environment variable INPUTRC. If that variable is unset, the default is `~/.inputrc'.

When a program which uses the Readline library starts up, the init file is read, and the key bindings are set.

In addition, the C-x C-r command re-reads this init file, thus incorporating any changes that you might have made to it.

Readline Init File SyntaxSyntax for the commands in the inputrc file.
Conditional Init ConstructsConditional key bindings in the inputrc file.
Sample Init FileAn example inputrc file.




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21.3.1 Readline Init File Syntax

There are only a few basic constructs allowed in the Readline init file. Blank lines are ignored. Lines beginning with a `#' are comments. Lines beginning with a `$' indicate conditional constructs (see Conditional Init Constructs). Other lines denote variable settings and key bindings.

Variable Settings
You can modify the run-time behavior of Readline by altering the values of variables in Readline using the set command within the init file. Here is how to change from the default Emacs-like key binding to use vi line editing commands:

set editing-mode vi
A great deal of run-time behavior is changeable with the following variables.

bell-style
Controls what happens when Readline wants to ring the terminal bell. If set to `none', Readline never rings the bell. If set to `visible', Readline uses a visible bell if one is available. If set to `audible' (the default), Readline attempts to ring the terminal's bell.

comment-begin
The string to insert at the beginning of the line when the insert-comment command is executed. The default value is "#".

completion-ignore-case
If set to `on', Readline performs filename matching and completion in a case-insensitive fashion. The default value is `off'.

completion-query-items
The number of possible completions that determines when the user is asked whether he wants to see the list of possibilities. If the number of possible completions is greater than this value, Readline will ask the user whether or not he wishes to view them; otherwise, they are simply listed. The default limit is 100.

convert-meta
If set to `on', Readline will convert characters with the eighth bit set to an ASCII key sequence by stripping the eighth bit and prepending an ESC character, converting them to a meta-prefixed key sequence. The default value is `on'.

disable-completion
If set to `On', Readline will inhibit word completion. Completion characters will be inserted into the line as if they had been mapped to self-insert. The default is `off'.

editing-mode
The editing-mode variable controls which default set of key bindings is used. By default, Readline starts up in Emacs editing mode, where the keystrokes are most similar to Emacs. This variable can be set to either `emacs' or `vi'.

enable-keypad
When set to `on', Readline will try to enable the application keypad when it is called. Some systems need this to enable the arrow keys. The default is `off'.

expand-tilde
If set to `on', tilde expansion is performed when Readline attempts word completion. The default is `off'.

horizontal-scroll-mode
This variable can be set to either `on' or `off'. Setting it to `on' means that the text of the lines being edited will scroll horizontally on a single screen line when they are longer than the width of the screen, instead of wrapping onto a new screen line. By default, this variable is set to `off'.

input-meta
If set to `on', Readline will enable eight-bit input (it will not strip the eighth bit from the characters it reads), regardless of what the terminal claims it can support. The default value is `off'. The name meta-flag is a synonym for this variable.

isearch-terminators
The string of characters that should terminate an incremental search without subsequently executing the character as a command (see Searching). If this variable has not been given a value, the characters ESC and C-J will terminate an incremental search.

keymap
Sets Readline's idea of the current keymap for key binding commands. Acceptable keymap names are emacs, emacs-standard, emacs-meta, emacs-ctlx, vi, vi-command, and vi-insert. vi is equivalent to vi-command; emacs is equivalent to emacs-standard. The default value is emacs. The value of the editing-mode variable also affects the default keymap.

mark-directories
If set to `on', completed directory names have a slash appended. The default is `on'.

mark-modified-lines
This variable, when set to `on', causes Readline to display an asterisk (`*') at the start of history lines which have been modified. This variable is `off' by default.

output-meta
If set to `on', Readline will display characters with the eighth bit set directly rather than as a meta-prefixed escape sequence. The default is `off'.

print-completions-horizontally
If set to `on', Readline will display completions with matches sorted horizontally in alphabetical order, rather than down the screen. The default is `off'.

show-all-if-ambiguous
This alters the default behavior of the completion functions. If set to `on', words which have more than one possible completion cause the matches to be listed immediately instead of ringing the bell. The default value is `off'.

visible-stats
If set to `on', a character denoting a file's type is appended to the filename when listing possible completions. The default is `off'.

Key Bindings
The syntax for controlling key bindings in the init file is simple. First you have to know the name of the command that you want to change. The following sections contain tables of the command name, the default keybinding, if any, and a short description of what the command does.

Once you know the name of the command, simply place the name of the key you wish to bind the command to, a colon, and then the name of the command on a line in the init file. The name of the key can be expressed in different ways, depending on which is most comfortable for you.

keyname: function-name or macro
keyname is the name of a key spelled out in English. For example:
Control-u: universal-argument
Meta-Rubout: backward-kill-word
Control-o: "> output"
In the above example, C-u is bound to the function universal-argument, and C-o is bound to run the macro expressed on the right hand side (that is, to insert the text `> output' into the line).

"keyseq": function-name or macro
keyseq differs from keyname above in that strings denoting an entire key sequence can be specified, by placing the key sequence in double quotes. Some GNU Emacs style key escapes can be used, as in the following example, but the special character names are not recognized.

"\C-u": universal-argument
"\C-x\C-r": re-read-init-file
"\e[11~": "Function Key 1"
In the above example, C-u is bound to the function universal-argument (just as it was in the first example), `C-x C-r' is bound to the function re-read-init-file, and `ESC [ 1 1 ~' is bound to insert the text `Function Key 1'.

The following GNU Emacs style escape sequences are available when specifying key sequences:

\C-
control prefix
\M-
meta prefix
\e
an escape character
\\
backslash
\"
"
\'
'

In addition to the GNU Emacs style escape sequences, a second set of backslash escapes is available:

\a
alert (bell)
\b
backspace
\d
delete
\f
form feed
\n
newline
\r
carriage return
\t
horizontal tab
\v
vertical tab
\nnn
the character whose ASCII code is the octal value nnn (one to three digits)
\xnnn
the character whose ASCII code is the hexadecimal value nnn (one to three digits)

When entering the text of a macro, single or double quotes must be used to indicate a macro definition. Unquoted text is assumed to be a function name. In the macro body, the backslash escapes described above are expanded. Backslash will quote any other character in the macro text, including `"' and `''. For example, the following binding will make `C-x \' insert a single `\' into the line:

"\C-x\\": "\\"




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21.3.2 Conditional Init Constructs

Readline implements a facility similar in spirit to the conditional compilation features of the C preprocessor which allows key bindings and variable settings to be performed as the result of tests. There are four parser directives used.

$if
The $if construct allows bindings to be made based on the editing mode, the terminal being used, or the application using Readline. The text of the test extends to the end of the line; no characters are required to isolate it.

mode
The mode= form of the $if directive is used to test whether Readline is in emacs or vi mode. This may be used in conjunction with the `set keymap' command, for instance, to set bindings in the emacs-standard and emacs-ctlx keymaps only if Readline is starting out in emacs mode.

term
The term= form may be used to include terminal-specific key bindings, perhaps to bind the key sequences output by the terminal's function keys. The word on the right side of the `=' is tested against both the full name of the terminal and the portion of the terminal name before the first `-'. This allows sun to match both sun and sun-cmd, for instance.

application
The application construct is used to include application-specific settings. Each program using the Readline library sets the application name, and you can test for it. This could be used to bind key sequences to functions useful for a specific program. For instance, the following command adds a key sequence that quotes the current or previous word in Bash:
$if Bash
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
$endif

$endif
This command, as seen in the previous example, terminates an $if command.

$else
Commands in this branch of the $if directive are executed if the test fails.

$include
This directive takes a single filename as an argument and reads commands and bindings from that file.
$include /etc/inputrc




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21.3.3 Sample Init File

Here is an example of an inputrc file. This illustrates key binding, variable assignment, and conditional syntax.

# This file controls the behaviour of line input editing for
# programs that use the Gnu Readline library.  Existing programs
# include FTP, Bash, and Gdb.
#
# You can re-read the inputrc file with C-x C-r.
# Lines beginning with '#' are comments.
#
# First, include any systemwide bindings and variable assignments from
# /etc/Inputrc
$include /etc/Inputrc

#
# Set various bindings for emacs mode.

set editing-mode emacs 

$if mode=emacs

Meta-Control-h:	backward-kill-word	Text after the function name is ignored

#
# Arrow keys in keypad mode
#
#"\M-OD":        backward-char
#"\M-OC":        forward-char
#"\M-OA":        previous-history
#"\M-OB":        next-history
#
# Arrow keys in ANSI mode
#
"\M-[D":        backward-char
"\M-[C":        forward-char
"\M-[A":        previous-history
"\M-[B":        next-history
#
# Arrow keys in 8 bit keypad mode
#
#"\M-\C-OD":       backward-char
#"\M-\C-OC":       forward-char
#"\M-\C-OA":       previous-history
#"\M-\C-OB":       next-history
#
# Arrow keys in 8 bit ANSI mode
#
#"\M-\C-[D":       backward-char
#"\M-\C-[C":       forward-char
#"\M-\C-[A":       previous-history
#"\M-\C-[B":       next-history

C-q: quoted-insert

$endif

# An old-style binding.  This happens to be the default.
TAB: complete

# Macros that are convenient for shell interaction
$if Bash
# edit the path
"\C-xp": "PATH=${PATH}\e\C-e\C-a\ef\C-f"
# prepare to type a quoted word -- insert open and close double quotes
# and move to just after the open quote
"\C-x\"": "\"\"\C-b"
# insert a backslash (testing backslash escapes in sequences and macros)
"\C-x\\": "\\"
# Quote the current or previous word
"\C-xq": "\eb\"\ef\""
# Add a binding to refresh the line, which is unbound
"\C-xr": redraw-current-line
# Edit variable on current line.
"\M-\C-v": "\C-a\C-k$\C-y\M-\C-e\C-a\C-y="
$endif

# use a visible bell if one is available
set bell-style visible

# don't strip characters to 7 bits when reading
set input-meta on

# allow iso-latin1 characters to be inserted rather than converted to
# prefix-meta sequences
set convert-meta off

# display characters with the eighth bit set directly rather than
# as meta-prefixed characters
set output-meta on

# if there are more than 150 possible completions for a word, ask the
# user if he wants to see all of them
set completion-query-items 150

# For FTP
$if Ftp
"\C-xg": "get \M-?"
"\C-xt": "put \M-?"
"\M-.": yank-last-arg
$endif



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21.4 Bindable Readline Commands

Commands For MovingMoving about the line.
Commands For HistoryGetting at previous lines.
Commands For TextCommands for changing text.
Commands For KillingCommands for killing and yanking.
Numeric ArgumentsSpecifying numeric arguments, repeat counts.
Commands For CompletionGetting Readline to do the typing for you.
Keyboard MacrosSaving and re-executing typed characters
Miscellaneous CommandsOther miscellaneous commands.

This section describes Readline commands that may be bound to key sequences.




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21.4.1 Commands For Moving

beginning-of-line (C-a)
Move to the start of the current line.

end-of-line (C-e)
Move to the end of the line.

forward-char (C-f)
Move forward a character.

backward-char (C-b)
Move back a character.

forward-word (M-f)
Move forward to the end of the next word. Words are composed of letters and digits.

backward-word (M-b)
Move back to the start of this, or the previous, word. Words are composed of letters and digits.

clear-screen (C-l)
Clear the screen and redraw the current line, leaving the current line at the top of the screen.

redraw-current-line ()
Refresh the current line. By default, this is unbound.




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21.4.2 Commands For Manipulating The History

accept-line (Newline, Return)
Accept the line regardless of where the cursor is. If this line is non-empty, add it to the history list. If this line was a history line, then restore the history line to its original state.

previous-history (C-p)
Move `up' through the history list.

next-history (C-n)
Move `down' through the history list.

beginning-of-history (M-<)
Move to the first line in the history.

end-of-history (M->)
Move to the end of the input history, i.e., the line currently being entered.

reverse-search-history (C-r)
Search backward starting at the current line and moving `up' through the history as necessary. This is an incremental search.

forward-search-history (C-s)
Search forward starting at the current line and moving `down' through the the history as necessary. This is an incremental search.

non-incremental-reverse-search-history (M-p)
Search backward starting at the current line and moving `up' through the history as necessary using a non-incremental search for a string supplied by the user.

non-incremental-forward-search-history (M-n)
Search forward starting at the current line and moving `down' through the the history as necessary using a non-incremental search for a string supplied by the user.

history-search-forward ()
Search forward through the history for the string of characters between the start of the current line and the current cursor position (the point). This is a non-incremental search. By default, this command is unbound.

history-search-backward ()
Search backward through the history for the string of characters between the start of the current line and the point. This is a non-incremental search. By default, this command is unbound.

yank-nth-arg (M-C-y)
Insert the first argument to the previous command (usually the second word on the previous line). With an argument n, insert the nth word from the previous command (the words in the previous command begin with word 0). A negative argument inserts the nth word from the end of the previous command.

yank-last-arg (M-., M-_)
Insert last argument to the previous command (the last word of the previous history entry). With an argument, behave exactly like yank-nth-arg. Successive calls to yank-last-arg move back through the history list, inserting the last argument of each line in turn.




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21.4.3 Commands For Changing Text

delete-char (C-d)
Delete the character under the cursor. If the cursor is at the beginning of the line, there are no characters in the line, and the last character typed was not bound to delete-char, then return EOF.

backward-delete-char (Rubout)
Delete the character behind the cursor. A numeric argument means to kill the characters instead of deleting them.

forward-backward-delete-char ()
Delete the character under the cursor, unless the cursor is at the end of the line, in which case the character behind the cursor is deleted. By default, this is not bound to a key.

quoted-insert (C-q, C-v)
Add the next character typed to the line verbatim. This is how to insert key sequences like C-q, for example.

tab-insert (M-TAB)
Insert a tab character.

self-insert (a, b, A, 1, !, ...)
Insert yourself.

transpose-chars (C-t)
Drag the character before the cursor forward over the character at the cursor, moving the cursor forward as well. If the insertion point is at the end of the line, then this transposes the last two characters of the line. Negative arguments don't work.

transpose-words (M-t)
Drag the word behind the cursor past the word in front of the cursor moving the cursor over that word as well.

upcase-word (M-u)
Uppercase the current (or following) word. With a negative argument, uppercase the previous word, but do not move the cursor.

downcase-word (M-l)
Lowercase the current (or following) word. With a negative argument, lowercase the previous word, but do not move the cursor.

capitalize-word (M-c)
Capitalize the current (or following) word. With a negative argument, capitalize the previous word, but do not move the cursor.




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21.4.4 Killing And Yanking

kill-line (C-k)
Kill the text from the current cursor position to the end of the line.

backward-kill-line (C-x Rubout)
Kill backward to the beginning of the line.

unix-line-discard (C-u)
Kill backward from the cursor to the beginning of the current line. The killed text is saved on the kill-ring.

kill-whole-line ()
Kill all characters on the current line, no matter where the cursor is. By default, this is unbound.

kill-word (M-d)
Kill from the cursor to the end of the current word, or if between words, to the end of the next word. Word boundaries are the same as forward-word.

backward-kill-word (M-DEL)
Kill the word behind the cursor. Word boundaries are the same as backward-word.

unix-word-rubout (C-w)
Kill the word behind the cursor, using white space as a word boundary. The killed text is saved on the kill-ring.

delete-horizontal-space ()
Delete all spaces and tabs around point. By default, this is unbound.

kill-region ()
Kill the text between the point and the mark (saved cursor position). This text is referred to as the region. By default, this command is unbound.

copy-region-as-kill ()
Copy the text in the region to the kill buffer, so it can be yanked right away. By default, this command is unbound.

copy-backward-word ()
Copy the word before point to the kill buffer. The word boundaries are the same as backward-word. By default, this command is unbound.

copy-forward-word ()
Copy the word following point to the kill buffer. The word boundaries are the same as forward-word. By default, this command is unbound.

yank (C-y)
Yank the top of the kill ring into the buffer at the current cursor position.

yank-pop (M-y)
Rotate the kill-ring, and yank the new top. You can only do this if the prior command is yank or yank-pop.




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21.4.5 Specifying Numeric Arguments

digit-argument (M-0, M-1, ... M--)
Add this digit to the argument already accumulating, or start a new argument. M-- starts a negative argument.

universal-argument ()
This is another way to specify an argument. If this command is followed by one or more digits, optionally with a leading minus sign, those digits define the argument. If the command is followed by digits, executing universal-argument again ends the numeric argument, but is otherwise ignored. As a special case, if this command is immediately followed by a character that is neither a digit or minus sign, the argument count for the next command is multiplied by four. The argument count is initially one, so executing this function the first time makes the argument count four, a second time makes the argument count sixteen, and so on. By default, this is not bound to a key.




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21.4.6 Letting Readline Type For You

complete (TAB)
Attempt to do completion on the text before the cursor. This is application-specific. Generally, if you are typing a filename argument, you can do filename completion; if you are typing a command, you can do command completion; if you are typing in a symbol to GDB, you can do symbol name completion; if you are typing in a variable to Bash, you can do variable name completion, and so on.

possible-completions (M-?)
List the possible completions of the text before the cursor.

insert-completions (M-*)
Insert all completions of the text before point that would have been generated by possible-completions.

menu-complete ()
Similar to complete, but replaces the word to be completed with a single match from the list of possible completions. Repeated execution of menu-complete steps through the list of possible completions, inserting each match in turn. At the end of the list of completions, the bell is rung and the original text is restored. An argument of n moves n positions forward in the list of matches; a negative argument may be used to move backward through the list. This command is intended to be bound to TAB, but is unbound by default.

delete-char-or-list ()
Deletes the character under the cursor if not at the beginning or end of the line (like delete-char). If at the end of the line, behaves identically to possible-completions. This command is unbound by default.




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21.4.7 Keyboard Macros

start-kbd-macro (C-x ()
Begin saving the characters typed into the current keyboard macro.

end-kbd-macro (C-x ))
Stop saving the characters typed into the current keyboard macro and save the definition.

call-last-kbd-macro (C-x e)
Re-execute the last keyboard macro defined, by making the characters in the macro appear as if typed at the keyboard.




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21.4.8 Some Miscellaneous Commands

re-read-init-file (C-x C-r)
Read in the contents of the inputrc file, and incorporate any bindings or variable assignments found there.

abort (C-g)
Abort the current editing command and ring the terminal's bell (subject to the setting of bell-style).

do-uppercase-version (M-a, M-b, M-x, ...)
If the metafied character x is lowercase, run the command that is bound to the corresponding uppercase character.

prefix-meta (ESC)
Make the next character typed be metafied. This is for keyboards without a meta key. Typing `ESC f' is equivalent to typing `M-f'.

undo (C-_, C-x C-u)
Incremental undo, separately remembered for each line.

revert-line (M-r)
Undo all changes made to this line. This is like executing the undo command enough times to get back to the beginning.

tilde-expand (M-~)
Perform tilde expansion on the current word.

set-mark (C-@)
Set the mark to the current point. If a numeric argument is supplied, the mark is set to that position.

exchange-point-and-mark (C-x C-x)
Swap the point with the mark. The current cursor position is set to the saved position, and the old cursor position is saved as the mark.

character-search (C-])
A character is read and point is moved to the next occurrence of that character. A negative count searches for previous occurrences.

character-search-backward (M-C-])
A character is read and point is moved to the previous occurrence of that character. A negative count searches for subsequent occurrences.

insert-comment (M-#)
The value of the comment-begin variable is inserted at the beginning of the current line, and the line is accepted as if a newline had been typed.

dump-functions ()
Print all of the functions and their key bindings to the Readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. This command is unbound by default.

dump-variables ()
Print all of the settable variables and their values to the Readline output stream. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. This command is unbound by default.

dump-macros ()
Print all of the Readline key sequences bound to macros and the strings they ouput. If a numeric argument is supplied, the output is formatted in such a way that it can be made part of an inputrc file. This command is unbound by default.




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21.5 Readline vi Mode

While the Readline library does not have a full set of vi editing functions, it does contain enough to allow simple editing of the line. The Readline vi mode behaves as specified in the POSIX 1003.2 standard.

In order to switch interactively between emacs and vi editing modes, use the command M-C-j (toggle-editing-mode). The Readline default is emacs mode.

When you enter a line in vi mode, you are already placed in `insertion' mode, as if you had typed an `i'. Pressing ESC switches you into `command' mode, where you can edit the text of the line with the standard vi movement keys, move to previous history lines with `k' and subsequent lines with `j', and so forth.




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22. Using History Interactively

This chapter describes how to use the GNU History Library interactively, from a user's standpoint. It should be considered a user's guide.

History InteractionWhat it feels like using History as a user.




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22.1 History Expansion

The History library provides a history expansion feature that is similar to the history expansion provided by csh. This section describes the syntax used to manipulate the history information.

History expansions introduce words from the history list into the input stream, making it easy to repeat commands, insert the arguments to a previous command into the current input line, or fix errors in previous commands quickly.

History expansion takes place in two parts. The first is to determine which line from the history list should be used during substitution. The second is to select portions of that line for inclusion into the current one. The line selected from the history is called the event, and the portions of that line that are acted upon are called words. Various modifiers are available to manipulate the selected words. The line is broken into words in the same fashion that Bash does, so that several words surrounded by quotes are considered one word. History expansions are introduced by the appearance of the history expansion character, which is `!' by default.

Event DesignatorsHow to specify which history line to use.
Word DesignatorsSpecifying which words are of interest.
ModifiersModifying the results of substitution.




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22.1.1 Event Designators

An event designator is a reference to a command line entry in the history list.

!
Start a history substitution, except when followed by a space, tab, the end of the line, `=' or `('.

!n
Refer to command line n.

!-n
Refer to the command n lines back.

!!
Refer to the previous command. This is a synonym for `!-1'.

!string
Refer to the most recent command starting with string.

!?string[?]
Refer to the most recent command containing string. The trailing `?' may be omitted if the string is followed immediately by a newline.

^string1^string2^
Quick Substitution. Repeat the last command, replacing string1 with string2. Equivalent to !!:s/string1/string2/.

!#
The entire command line typed so far.




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22.1.2 Word Designators

Word designators are used to select desired words from the event. A `:' separates the event specification from the word designator. It may be omitted if the word designator begins with a `^', `$', `*', `-', or `%'. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces.

0 (zero)
The 0th word. For many applications, this is the command word.

n
The nth word.

^
The first argument; that is, word 1.

$
The last argument.

%
The word matched by the most recent `?string?' search.

x-y
A range of words; `-y' abbreviates `0-y'.

*
All of the words, except the 0th. This is a synonym for `1-$'. It is not an error to use `*' if there is just one word in the event; the empty string is returned in that case.

x*
Abbreviates `x-$'

x-
Abbreviates `x-$' like `x*', but omits the last word.

If a word designator is supplied without an event specification, the previous command is used as the event.




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22.1.3 Modifiers

After the optional word designator, you can add a sequence of one or more of the following modifiers, each preceded by a `:'.

h
Remove a trailing pathname component, leaving only the head.

t
Remove all leading pathname components, leaving the tail.

r
Remove a trailing suffix of the form `.suffix', leaving the basename.

e
Remove all but the trailing suffix.

p
Print the new command but do not execute it.

s/old/new/
Substitute new for the first occurrence of old in the event line. Any delimiter may be used in place of `/'. The delimiter may be quoted in old and new with a single backslash. If `&' appears in new, it is replaced by old. A single backslash will quote the `&'. The final delimiter is optional if it is the last character on the input line.

&
Repeat the previous substitution.

g
Cause changes to be applied over the entire event line. Used in conjunction with `s', as in gs/old/new/, or with `&'.




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A. Installing GDB

If you obtain GDB (HP WDB 2.0) as part of the HP ANSI C, HP ANSI C++ Developer's Kit for HP-UX Release 11.0, or HP Fortran, you do not have to take any special action to build or install GDB.

If you obtain GDB (HP WDB 2.0) from an HP web site, you may download either an swinstall package or a source tree, or both.

Most customers will want to install the GDB binary that is part of the swinstall package. To do so, use a command of the form

/usr/sbin/swinstall -s package-name WDB
Alternatively, it is possible to build GDB from the source distribution. If you who want to modify the debugger sources to tailor GDB to your needs you may wish to do this. The source distribution consists of a tar file containing the source tree rooted at `gdb-4.17/...'. The instructions that follow describe how to build a `gdb' executable from this source tree. HP believes that these instructions apply to the HP WDB 2.0 source tree that it distributes. However, HP does not explicitly support building a `gdb' for any non-HP platform from the HP WDB 2.0 source tree. It may work, but HP has not tested it for any platforms other than those described in the HP WDB 2.0 Release Notes.

You can find additional information specific to Hewlett-Packard in the `README.HP.WDB' file at the root of the source tree.

GDB comes with a configure script that automates the process of preparing GDB for installation; you can then use make to build the gdb program.

The GDB distribution includes all the source code you need for GDB in a single directory, whose name is usually composed by appending the version number to `gdb'.

For example, the GDB version 19991101 distribution is in the `gdb-19991101' directory. That directory contains:

gdb-19991101/configure (and supporting files)
script for configuring GDB and all its supporting libraries

gdb-19991101/gdb
the source specific to GDB itself

gdb-19991101/bfd
source for the Binary File Descriptor library

gdb-19991101/include
GNU include files

gdb-19991101/libiberty
source for the `-liberty' free software library

gdb-19991101/opcodes
source for the library of opcode tables and disassemblers

gdb-19991101/readline
source for the GNU command-line interface

gdb-19991101/glob
source for the GNU filename pattern-matching subroutine

gdb-19991101/mmalloc
source for the GNU memory-mapped malloc package

The simplest way to configure and build GDB is to run configure from the `gdb-version-number' source directory, which in this example is the `gdb-19991101' directory.

First switch to the `gdb-version-number' source directory if you are not already in it; then run configure. Pass the identifier for the platform on which GDB will run as an argument.

For example:

cd gdb-19991101
./configure host
make
where host is an identifier such as `sun4' or `decstation', that identifies the platform where GDB will run. (You can often leave off host; configure tries to guess the correct value by examining your system.)

Running `configure host' and then running make builds the `bfd', `readline', `mmalloc', and `libiberty' libraries, then gdb itself. The configured source files, and the binaries, are left in the corresponding source directories.

configure is a Bourne-shell (/bin/sh) script; if your system does not recognize this automatically when you run a different shell, you may need to run sh on it explicitly:

sh configure host
If you run configure from a directory that contains source directories for multiple libraries or programs, such as the `gdb-19991101' source directory for version 19991101, configure creates configuration files for every directory level underneath (unless you tell it not to, with the `--norecursion' option).

You can run the configure script from any of the subordinate directories in the GDB distribution if you only want to configure that subdirectory, but be sure to specify a path to it.

For example, with version 19991101, type the following to configure only the bfd subdirectory:

cd gdb-19991101/bfd
../configure host
You can install gdb anywhere; it has no hardwired paths. However, you should make sure that the shell on your path (named by the `SHELL' environment variable) is publicly readable. Remember that GDB uses the shell to start your program--some systems refuse to let GDB debug child processes whose programs are not readable.

Separate ObjdirCompiling GDB in another directory
Config NamesSpecifying names for hosts and targets
Configure OptionsSummary of options for configure




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A.1 Compiling GDB in another directory

If you want to run GDB versions for several host or target machines, you need a different gdb compiled for each combination of host and target. configure is designed to make this easy by allowing you to generate each configuration in a separate subdirectory, rather than in the source directory. If your make program handles the `VPATH' feature (GNU make does), running make in each of these directories builds the gdb program specified there.

To build gdb in a separate directory, run configure with the `--srcdir' option to specify where to find the source. (You also need to specify a path to find configure itself from your working directory. If the path to configure would be the same as the argument to `--srcdir', you can leave out the `--srcdir' option; it is assumed.)

For example, with version 19991101, you can build GDB in a separate directory for a Sun 4 like this:

cd gdb-19991101
mkdir ../gdb-sun4
cd ../gdb-sun4
../gdb-19991101/configure sun4
make
When configure builds a configuration using a remote source directory, it creates a tree for the binaries with the same structure (and using the same names) as the tree under the source directory. In the example, you'd find the Sun 4 library `libiberty.a' in the directory `gdb-sun4/libiberty', and GDB itself in `gdb-sun4/gdb'.

One popular reason to build several GDB configurations in separate directories is to configure GDB for cross-compiling (where GDB runs on one machine--the host---while debugging programs that run on another machine--the target). You specify a cross-debugging target by giving the `--target=target' option to configure.

When you run make to build a program or library, you must run it in a configured directory--whatever directory you were in when you called configure (or one of its subdirectories).

The Makefile that configure generates in each source directory also runs recursively. If you type make in a source directory such as `gdb-19991101' (or in a separate configured directory configured with `--srcdir=dirname/gdb-19991101'), you will build all the required libraries, and then build GDB.

When you have multiple hosts or targets configured in separate directories, you can run make on them in parallel (for example, if they are NFS-mounted on each of the hosts); they will not interfere with each other.




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A.2 Specifying names for hosts and targets

The specifications used for hosts and targets in the configure script are based on a three-part naming scheme, but some short predefined aliases are also supported. The full naming scheme encodes three pieces of information in the following pattern:

architecture-vendor-os
For example, you can use the alias sun4 as a host argument, or as the value for target in a --target=target option. The equivalent full name is `sparc-sun-sunos4'.

The configure script accompanying GDB does not provide any query facility to list all supported host and target names or aliases. configure calls the Bourne shell script config.sub to map abbreviations to full names; you can read the script, if you wish, or you can use it to test your guesses on abbreviations--for example:

% sh config.sub i386-linux
i386-pc-linux-gnu
% sh config.sub alpha-linux
alpha-unknown-linux-gnu
% sh config.sub hp9k700
hppa1.1-hp-hpux
% sh config.sub sun4
sparc-sun-sunos4.1.1
% sh config.sub sun3
m68k-sun-sunos4.1.1
% sh config.sub i986v
Invalid configuration `i986v': machine `i986v' not recognized
config.sub is also distributed in the GDB source directory (`gdb-19991101', for version 19991101).




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A.3 configure options

Here is a summary of the configure options and arguments that are most often useful for building GDB. configure also has several other options not listed here. See Info file `configure.info', node `What Configure Does', for a full explanation of configure.

configure [--help]
          [--prefix=dir]
          [--exec-prefix=dir]
          [--srcdir=dirname]
          [--norecursion] [--rm]
          [--target=target]
          host
You may introduce options with a single `-' rather than `--' if you prefer; but you may abbreviate option names if you use `--'.

--help
Display a quick summary of how to invoke configure.

--prefix=dir
Configure the source to install programs and files under directory `dir'.

--exec-prefix=dir
Configure the source to install programs under directory `dir'.

--srcdir=dirname
Warning: using this option requires GNU make, or another make that implements the VPATH feature.
Use this option to make configurations in directories separate from the GDB source directories. Among other things, you can use this to build (or maintain) several configurations simultaneously, in separate directories. configure writes configuration specific files in the current directory, but arranges for them to use the source in the directory dirname. configure creates directories under the working directory in parallel to the source directories below dirname.

--norecursion
Configure only the directory level where configure is executed; do not propagate configuration to subdirectories.

--target=target
Configure GDB for cross-debugging programs running on the specified target. Without this option, GDB is configured to debug programs that run on the same machine (host) as GDB itself.

There is no convenient way to generate a list of all available targets.

host ...
Configure GDB to run on the specified host.

There is no convenient way to generate a list of all available hosts.

There are many other options available as well, but they are generally needed for special purposes only.



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Index

Jump to:

"   #   $   .   /   @  
A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   {

Index Entry Section

"
"No symbol "foo" in current context"8.2 Program variables

#
#3.1 Command syntax
# in Modula-29.4.2.8 GDB and Modula-2

$
$8.8 Value history
$$8.8 Value history
$, variable names starting with8.9 Convenience variables
$_8.9 Convenience variables
$_ and info breakpoints5.1.1 Setting breakpoints
$_ and info line7.4 Source and machine code
$_, $__, and value history8.5 Examining memory
$__8.9 Convenience variables
$_exitcode8.9 Convenience variables
$bpnum5.1.1 Setting breakpoints
$cdir7.3 Specifying source directories
$cwd7.3 Specifying source directories

.
.esgdbinit18.3 Command files
`.gdbinit'14.6 Specifying object file directories
`.gdbinit'18.3 Command files
.gdbinit, application specific18.3 Command files
.inputrc17.3 Command history
.os68gdbinit18.3 Command files
.vxgdbinit18.3 Command files

/
/tmp/gdbrtc.log, memory leaks list14.4.9 Detecting memory leaks in batch mode

@
@8.3 Artificial arrays

A
a.out and C++9.4.1.3 C++ expressions
abbreviation3.1 Command syntax
active targets13.1 Active targets
add-shared-symbol-file12.1 Commands to specify files
add-symbol-file12.1 Commands to specify files
address, memory leak14.3.3 Example Fix and Continue Session
alloca(), Fix and Continue14.3.1 Fix and Continue Restrictions
allocation, memory14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
application specific settings18.3 Command files
arguments (to your program)4.3 Your program's arguments
Arguments, Calling Fortran functions9.4.4 Fortran
artificial array8.3 Artificial arrays
Assembler language file name extensions9.1.1 List of filename extensions and languages
assembly instructions7.4 Source and machine code
assembly instructions7.4 Source and machine code
assertion control, xdb16.2.5 Global Breakpoint Commands
assignment11.1 Assignment to variables
AT&T disassembly flavor7.4 Source and machine code
attach4.7 Debugging an already-running process
attach4.7 Debugging an already-running process
automatic display8.6 Automatic display
automatic thread selection4.9 Debugging programs with multiple threads
awatch5.1.2 Setting watchpoints

B
b5.1.1 Setting breakpoints
backtrace6.2 Backtraces
backtrace-other-thread6.2 Backtraces
backtraces6.2 Backtraces
batch memory leak checking14.4.8 Report memory leaks
bell-style21.3.1 Readline Init File Syntax
break5.1.1 Setting breakpoints
break ... thread threadno5.4 Stopping and starting multi-thread programs
break in overloaded functions9.4.1.7 GDB features for C++
breakpoint commands5.1.7 Breakpoint command lists
breakpoint conditions5.1.6 Break conditions
breakpoint numbers5.1 Breakpoints, watchpoints, and catchpoints
breakpoint on events5.1 Breakpoints, watchpoints, and catchpoints
breakpoint on memory address5.1 Breakpoints, watchpoints, and catchpoints
breakpoint on variable modification5.1 Breakpoints, watchpoints, and catchpoints
breakpoint ranges5.1 Breakpoints, watchpoints, and catchpoints
breakpoints5.1 Breakpoints, watchpoints, and catchpoints
breakpoints and threads5.4 Stopping and starting multi-thread programs
breakpoints, deferred14.7 Stopping and starting in shared libraries
breakpoints, Fix and Continue14.3.1 Fix and Continue Restrictions
breakpoints, simulating hardware5.1.1 Setting breakpoints
bt6.2 Backtraces
bug criteria20.1 Have you found a bug?
bug reports20.2 How to report bugs
bugs in GDB20. Reporting Bugs in GDB

C
c5.2 Continuing and stepping
C and C++9.4.1 C and C++
C and C++ checks9.4.1.5 C and C++ type and range checks
C and C++ constants9.4.1.2 C and C++ constants
C and C++ defaults9.4.1.4 C and C++ defaults
C and C++ operators9.4.1.1 C and C++ operators
c language file name extensions9.1.1 List of filename extensions and languages
C++9.4.1 C and C++
C++ and object formats9.4.1.3 C++ expressions
C++ exception handling9.4.1.7 GDB features for C++
C++ language file name extensions9.1.1 List of filename extensions and languages
C++ scope resolution8.2 Program variables
C++ support14.2 HP-UX Targets
C++ support, not in COFF9.4.1.3 C++ expressions
C++ symbol decoding style8.7 Print settings
C++ symbol display9.4.1.7 GDB features for C++
call11.5 Calling program functions
call overloaded functions9.4.1.3 C++ expressions
call stack6. Examining the Stack
call stack depth, memory leaks14.4.10 Configuring memory debugging
calling functions11.5 Calling program functions
calling make2.3 Shell commands
case-sensitive9.4.4 Fortran
casts, to view memory8.1 Expressions
catch5.1.3 Setting catchpoints
catch5.1.3 Setting catchpoints
catch catch5.1.3 Setting catchpoints
catch exceptions, list active handlers6.4 Information about a frame
catch exec5.1.3 Setting catchpoints
catch fork5.1.3 Setting catchpoints
catch load5.1.3 Setting catchpoints
catch load14.7.1 Deferred breakpoints
catch throw5.1.3 Setting catchpoints
catch unload5.1.3 Setting catchpoints
catch vfork5.1.3 Setting catchpoints
catchpoint set for one stop5.1.3 Setting catchpoints
catchpoints5.1 Breakpoints, watchpoints, and catchpoints
catchpoints, setting5.1.3 Setting catchpoints
cd4.5 Your program's working directory
cdir7.3 Specifying source directories
cfront C++ support14.2 HP-UX Targets
changing, TUI window focus15.5 Changing Window Focus
checks, range9.3.1 An overview of type checking
checks, type9.3 Type and range checking
ChillSummary of GDB
choosing target byte order13.3 Choosing target byte order
clear5.1.4 Deleting breakpoints
clearing breakpoints, watchpoints, catchpoints5.1.4 Deleting breakpoints
CMA threads, memory debugging restrictions14.4.1 Memory Debugging Restrictions
COFF versus C++9.4.1.3 C++ expressions
colon-colon, context for variables/functions8.2 Program variables
command editing21.2.1 Readline Bare Essentials
command files18.3 Command files
command history17.2 Command editing
command hooks18.2 User-defined command hooks
command line editing17.2 Command editing
command window, TUI15.5 Changing Window Focus
commands5.1.7 Breakpoint command lists
commands for C++9.4.1.7 GDB features for C++
comment3.1 Command syntax
comment-begin21.3.1 Readline Init File Syntax
compilation directory7.3 Specifying source directories
compiler version20.2 How to report bugs
complete3.3 Getting help
completion3.2 Command completion
completion of quoted strings3.2 Command completion
completion-query-items21.3.1 Readline Init File Syntax
condition5.1.6 Break conditions
conditional breakpoints5.1.6 Break conditions
configuring GDBA. Installing GDB
configuring memory debugging14.4.9 Detecting memory leaks in batch mode
confirmation17.6 Optional warnings and messages
continue5.2 Continuing and stepping
continuing5.2 Continuing and stepping
continuing threads5.4 Stopping and starting multi-thread programs
controlling assertions, xdb16.2.5 Global Breakpoint Commands
controlling terminal4.6 Your program's input and output
convenience variables8.9 Convenience variables
convert-meta21.3.1 Readline Init File Syntax
core12.1 Commands to specify files
core dump file12.1 Commands to specify files
core-file12.1 Commands to specify files
crash of debugger20.1 Have you found a bug?
current directory7.3 Specifying source directories
current thread4.9 Debugging programs with multiple threads
cwd7.3 Specifying source directories

D
d5.1.4 Deleting breakpoints
DCE threads, memory debugging restrictions14.4.1 Memory Debugging Restrictions
ddd14.10 Parallel Processing
deallocation, memory14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
debugger crash20.1 Have you found a bug?
debugging memory leaks14.4.9 Detecting memory leaks in batch mode
debugging optimized code4.1 Compiling for debugging
debugging sessions12.1 Commands to specify files
debugging sessions17.1 Prompt
debugging sessions17.2 Command editing
debugging target13. Specifying a Debugging Target
deferred breakpoints14.7 Stopping and starting in shared libraries
define18.1 User-defined commands
delete5.1.4 Deleting breakpoints
delete breakpoints5.1.4 Deleting breakpoints
delete display8.6 Automatic display
deleting breakpoints, watchpoints, catchpoints5.1.4 Deleting breakpoints
demangling8.7 Print settings
dependencies, Fix and Continue14.1.1 Linker patch required for +objdebug
detach4.7 Debugging an already-running process
detecting memory leaks14.3.3 Example Fix and Continue Session
dir7.3 Specifying source directories
dir14.6 Specifying object file directories
directories for source files7.3 Specifying source directories
directory7.3 Specifying source directories
directory, compilation7.3 Specifying source directories
directory, current7.3 Specifying source directories
dis5.1.5 Disabling breakpoints
disable5.1.5 Disabling breakpoints
disable breakpoints5.1.5 Disabling breakpoints
disable breakpoints5.1.5 Disabling breakpoints
disable display8.6 Automatic display
disable-completion21.3.1 Readline Init File Syntax
disassemble7.4 Source and machine code
display8.6 Automatic display
display of expressions8.6 Automatic display
do6.3 Selecting a frame
document18.1 User-defined commands
down6.3 Selecting a frame
down-silently6.3 Selecting a frame
dynamic linking12.1 Commands to specify files

E
echo18.4 Commands for controlled output
ECOFF and C++9.4.1.3 C++ expressions
edit14.3 Fix and Continue Debugging
editing17.2 Command editing
editing command lines21.2.1 Readline Bare Essentials
editing-mode21.3.1 Readline Init File Syntax
ELF/DWARF and C++9.4.1.3 C++ expressions
ELF/stabs and C++9.4.1.3 C++ expressions
else18.1 User-defined commands
enable5.1.5 Disabling breakpoints
enable breakpoints5.1.5 Disabling breakpoints
enable breakpoints5.1.5 Disabling breakpoints
enable display8.6 Automatic display
enable-keypad21.3.1 Readline Init File Syntax
end5.1.7 Breakpoint command lists
ENOMEM errors14.4.7 When to suspect a memory leak
entering numbers17.5 Numbers
environment (of your program)4.4 Your program's environment
environment variable, setting for Fix and Continue14.3.3 Example Fix and Continue Session
error on valid input20.1 Have you found a bug?
event designators22.1.1 Event Designators
event handling5.1.3 Setting catchpoints
examining data8. Examining Data
examining memory8.5 Examining memory
exception handlers5.1.3 Setting catchpoints
exception handlers, how to list6.4 Information about a frame
exec5.1.3 Setting catchpoints
exec-file12.1 Commands to specify files
EXEC_MAGIC, memory debugging restrictions14.4.1 Memory Debugging Restrictions
executable file12.1 Commands to specify files
execution, threads4.9 Debugging programs with multiple threads
exit()14.4.8 Report memory leaks
exiting GDB2.2 Quitting GDB
expand-tilde21.3.1 Readline Init File Syntax
expressions8.1 Expressions
expressions in C or C++9.4.1 C and C++
expressions in C++9.4.1.3 C++ expressions
expressions in Modula-29.4.2 Modula-2
extenstions, file names9.1.1 List of filename extensions and languages

F
f6.3 Selecting a frame
fatal signal20.1 Have you found a bug?
fatal signals5.3 Signals
fg5.2 Continuing and stepping
file12.1 Commands to specify files
file names, extensions9.1.1 List of filename extensions and languages
files, missing14.6 Specifying object file directories
files, object14.6 Specifying object file directories
finding files14.6 Specifying object file directories
finish5.2 Continuing and stepping
fix14.3 Fix and Continue Debugging
Fix and Continue14.2 HP-UX Targets
Fix and Continue dependencies14.1.1 Linker patch required for +objdebug
Fix and Continue restrictions14.3 Fix and Continue Debugging
Fix and Continue, example14.3.2 Using Fix and Continue
flinching17.6 Optional warnings and messages
floating point8.12 Floating point hardware
floating point registers8.10 Registers
floating point registers, printing8.10 Registers
focus15.5 Changing Window Focus
focus of debugging4.9 Debugging programs with multiple threads
focus, TUI window15.5 Changing Window Focus
foo12.2 Errors reading symbol files
fork5.1.3 Setting catchpoints
fork, debugging programs which call4.10 Debugging programs with multiple processes
format options8.7 Print settings
formatted output8.4 Output formats
FortranSummary of GDB
Fortran common blocks9.4.4.2 Fortran operators
Fortran entry points9.4.4.2 Fortran operators
Fortran language file name extensions9.1.1 List of filename extensions and languages
Fortran operators9.4.4.2 Fortran operators
Fortran support9.4.4 Fortran
Fortran types9.4.4.1 Fortran types
Fortran variables9.4.4.2 Fortran operators
forward-search7.2 Searching source files
frame count, memory leaks14.4.10 Configuring memory debugging
frame number6.1 Stack frames
frame pointer6.1 Stack frames
frame, command6.1 Stack frames
frame, definition6.1 Stack frames
frame, selecting6.3 Selecting a frame
frameless execution6.1 Stack frames
free(), memory checking14.4.2 Using Memory Debugging
free(), memory checking14.4.5 Stop if a specified block address is allocated or deallocated
free(), memory leaks14.3.3 Example Fix and Continue Session
free, memory checking14.4.5 Stop if a specified block address is allocated or deallocated
function calls, Fix and Continue14.3.1 Fix and Continue Restrictions
function names, Fix and Continue14.3.1 Fix and Continue Restrictions

G
g++9.4.1 C and C++
GDB bugs, reporting20.2 How to report bugs
`gdb.ini'18.3 Command files
GDBHISTFILE17.3 Command history
gdbinit14.6 Specifying object file directories
GNU C++9.4.1 C and C++
GNU Emacs19. Using GDB under Emacs
Graphical User Interface, ddd14.10 Parallel Processing
graphics applications, memory debugging restrictions14.4.1 Memory Debugging Restrictions
GUI14.10 Parallel Processing

H
h3.3 Getting help
handle5.3 Signals
handling signals5.3 Signals
hardware breakpoints, simulating5.1.1 Setting breakpoints
hardware watchpoints5.1.2 Setting watchpoints
hbreak5.1.1 Setting breakpoints
heap block overflow, detecting14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
heap profiling14.4.11.1 Example
heap, memory leaks14.3.3 Example Fix and Continue Session
heap, reporting memory leaks14.4.7 When to suspect a memory leak
help3.3 Getting help
help target13.2 Commands for managing targets
help user-defined18.1 User-defined commands
history events22.1.1 Event Designators
history expansion17.3 Command history
history expansion22.1 History Expansion
history file17.3 Command history
history number8.8 Value history
history save17.3 Command history
history size17.3 Command history
history substitution17.3 Command history
history vi key bindings17.3 Command history
hooks, for commands18.2 User-defined command hooks
horizontal-scroll-mode21.3.1 Readline Init File Syntax
HP C++9.4.1 C and C++
HP-UX case sensitivity9.4.4 Fortran
HP-UX demangle-style8.7 Print settings
HP-UX Fix and Continue14.1.1 Linker patch required for +objdebug
HP-UX fork function4.10 Debugging programs with multiple processes
HP-UX hardware watchpoints5.1.2 Setting watchpoints
HP-UX key bindings17.3 Command history
HP-UX linker patch14. Configuration-Specific Information
HP-UX loading shared library12.1 Commands to specify files
HP-UX optimized code4.1 Compiling for debugging
HP-UX Setting catchpoints5.1.3 Setting catchpoints
HP-UX shared library breakpoints5.1 Breakpoints, watchpoints, and catchpoints
HP-UX source files14.6 Specifying object file directories
HP-UX specific information14.1.2 Fix and Continue compiler dependencies
HP-UX support20.2 How to report bugs
HP-UX supported versionsSummary of GDB
HP-UX targets14.1.2 Fix and Continue compiler dependencies
HP-UX Terminal User Interface2.1.2 Choosing modes
HP-UX Terminal User Interface15. The HP-UX Terminal User Interface
HP-UX thread numbers4.9 Debugging programs with multiple threads
HP-UX TUI and Emacs19. Using GDB under Emacs
HP-UX variable names8.9 Convenience variables
HP-UX virtual functions9.4.1.3 C++ expressions
HP-UX XDB compatibility2.1.2 Choosing modes
HP-UX, shared libraries12.1 Commands to specify files
HP-UX, simulating hardware breakpoints5.1.1 Setting breakpoints

I
i3.3 Getting help
i/o4.6 Your program's input and output
if18.1 User-defined commands
ignore5.1.6 Break conditions
ignore count (of breakpoint)5.1.6 Break conditions
info3.3 Getting help
info address10. Examining the Symbol Table
info all-registers8.10 Registers
info args6.4 Information about a frame
info breakpoints5.1.1 Setting breakpoints
info catch6.4 Information about a frame
info display8.6 Automatic display
info extensions9.2 Displaying the language
info f6.4 Information about a frame
info files12.1 Commands to specify files
info float8.12 Floating point hardware
info frame6.4 Information about a frame
info frame, show the source language9.2 Displaying the language
info functions10. Examining the Symbol Table
info heap14.5 Heap Profiling
info heap filename14.5 Heap Profiling
info heap idnumber14.5 Heap Profiling
info leak leaknumber14.4.2 Using Memory Debugging
info leak leaknumber14.4.11 Detecting memory leaks interactively
info leaks14.4.2 Using Memory Debugging
info leaks14.4.11 Detecting memory leaks interactively
info leaks filename14.4.2 Using Memory Debugging
info line7.4 Source and machine code
info locals6.4 Information about a frame
info program5. Stopping and Continuing
info registers8.10 Registers
info s6.2 Backtraces
info set3.3 Getting help
info share12.1 Commands to specify files
info sharedlibrary12.1 Commands to specify files
info signals5.3 Signals
info source10. Examining the Symbol Table
info source, show the source language9.2 Displaying the language
info sources10. Examining the Symbol Table
info stack6.2 Backtraces
info target12.1 Commands to specify files
info terminal4.6 Your program's input and output
info threads4.9 Debugging programs with multiple threads
info threads4.9 Debugging programs with multiple threads
info types10. Examining the Symbol Table
info variables10. Examining the Symbol Table
info watchpoints5.1.2 Setting watchpoints
inheritance9.4.1.7 GDB features for C++
init file14.6 Specifying object file directories
init file18.3 Command files
init file name18.3 Command files
initial frame6.1 Stack frames
initialization file, readline21.3 Readline Init File
innermost frame6.1 Stack frames
input-meta21.3.1 Readline Init File Syntax
inputrc17.3 Command history
inspect8. Examining Data
installationA. Installing GDB
instructions, assembly7.4 Source and machine code
instructions, assembly7.4 Source and machine code
Intel disassembly flavor7.4 Source and machine code
interaction, readline21.2 Readline Interaction
interactive memory leak checking14.4.10.2 Specifying minimum leak size
internal GDB breakpoints5.1.1 Setting breakpoints
interrupt2.2 Quitting GDB
invalid input20.1 Have you found a bug?
isearch-terminators21.3.1 Readline Init File Syntax

J
jump11.2 Continuing at a different address

K
keymap21.3.1 Readline Init File Syntax
kill4.8 Killing the child process
kill ring21.2.3 Readline Killing Commands
killing text21.2.3 Readline Killing Commands

L
l7.1 Printing source lines
language, file name extensions9.1.1 List of filename extensions and languages
languages9. Using GDB with Different Languages
latest breakpoint5.1.1 Setting breakpoints
leak checking, interactive14.4.10.2 Specifying minimum leak size
leak checking, turning on14.4.10.2 Specifying minimum leak size
leak size, memory leak configuration14.4.10.1 Specifying the stack depth
leaks, memory14.3.3 Example Fix and Continue Session
leaks, memory14.4.6 Scramble previous memory contents at malloc/free calls
leaks, reporting memory14.4.7 When to suspect a memory leak
leaving GDB2.2 Quitting GDB
libc.sl memory debugging restrictions14.4.1 Memory Debugging Restrictions
libcl.a memory debugging restrictions14.4.1 Memory Debugging Restrictions
linespec7.1 Printing source lines
linker patch14. Configuration-Specific Information
list7.1 Printing source lines
listing machine instructions7.4 Source and machine code
listing machine instructions7.4 Source and machine code
load5.1.3 Setting catchpoints
load filename13.2 Commands for managing targets
loading shared libraries12.1 Commands to specify files

M
machine instructions7.4 Source and machine code
machine instructions7.4 Source and machine code
main in Fortran9.4.4.3 Fortran special issues
maint info breakpoints5.1.1 Setting breakpoints
maint print psymbols10. Examining the Symbol Table
maint print symbols10. Examining the Symbol Table
make2.3 Shell commands
malloc memory debugging restrictions14.4.1 Memory Debugging Restrictions
malloc(), memory checking14.4.5 Stop if a specified block address is allocated or deallocated
malloc(), memory leaks14.3.3 Example Fix and Continue Session
mapped12.1 Commands to specify files
mark-modified-lines21.3.1 Readline Init File Syntax
member functions9.4.1.3 C++ expressions
memory corruption, detecting14.3.3 Example Fix and Continue Session
memory debugging, restrictions14.4 Debugging Memory Problems
memory heap profiling14.4.11.1 Example
memory leak checking, interactive14.4.10.2 Specifying minimum leak size
memory leak checking, turning on14.4.10.2 Specifying minimum leak size
memory leak size, memory leak configuration14.4.10.1 Specifying the stack depth
memory leaks14.3.3 Example Fix and Continue Session
memory leaks, debugging14.4.9 Detecting memory leaks in batch mode
memory leaks, reporting14.4.7 When to suspect a memory leak
memory leaks, when to suspect14.4.6 Scramble previous memory contents at malloc/free calls
memory tracing5.1 Breakpoints, watchpoints, and catchpoints
memory, allocation14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
memory, bad calls to free()14.3.3 Example Fix and Continue Session
memory, deallocation14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
memory, viewing as typed object8.1 Expressions
memory-mapped symbol file12.1 Commands to specify files
meta-flag21.3.1 Readline Init File Syntax
missing files14.6 Specifying object file directories
Modula-2Summary of GDB
Modula-2 built-ins9.4.2.1 Operators
Modula-2 checks9.4.2.6 Modula-2 type and range checks
Modula-2 constants9.4.2.2 Built-in functions and procedures
Modula-2 defaults9.4.2.4 Modula-2 defaults
Modula-2 operators9.4.2.1 Operators
Modula-2, deviations from9.4.2.5 Deviations from standard Modula-2
Modula-2, GDB support9.4.2 Modula-2
mount, process started across NFS4.7 Debugging an already-running process
mprotect()5.1.1 Setting breakpoints
multiple processes4.10 Debugging programs with multiple processes
multiple targets13.1 Active targets
multiple threads4.9 Debugging programs with multiple threads

N
n5.2 Continuing and stepping
names of symbols10. Examining the Symbol Table
namespace in C++9.4.1.3 C++ expressions
negative breakpoint numbers5.1.1 Setting breakpoints
New systag4.9 Debugging programs with multiple threads
New systag4.9 Debugging programs with multiple threads
next5.2 Continuing and stepping
nexti5.2 Continuing and stepping
NFS mounts4.7 Debugging an already-running process
ni5.2 Continuing and stepping
non-debug executable, getting information14.9 Getting information from a non-debug executable
notation, readline21.2.1 Readline Bare Essentials
number representation17.5 Numbers
numbers for breakpoints5.1 Breakpoints, watchpoints, and catchpoints

O
object files14.6 Specifying object file directories
object formats and C++9.4.1.3 C++ expressions
objectdir14.6 Specifying object file directories
objectload14.6 Specifying object file directories
objectretry14.6 Specifying object file directories
online documentation3.3 Getting help
Open Graphics Applications, memory debugging restrictions14.4.1 Memory Debugging Restrictions
optimization, Fix and Continue14.3 Fix and Continue Debugging
optimized code4.1 Compiling for debugging
optimized code, debugging4.1 Compiling for debugging
out of memory errors14.4.6 Scramble previous memory contents at malloc/free calls
outermost frame6.1 Stack frames
output18.4 Commands for controlled output
output formats8.4 Output formats
output-meta21.3.1 Readline Init File Syntax
overflow, heap14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
overload resolution9.4.1.7 GDB features for C++
overloaded functions9.4.1.7 GDB features for C++
overloaded functions, calling9.4.1.3 C++ expressions
overloading5.1.8 Breakpoint menus
overloading in C++9.4.1.7 GDB features for C++

P
parallel processing14.9 Getting information from a non-debug executable
partial symbol dump10. Examining the Symbol Table
PascalSummary of GDB
patching binaries11.6 Patching programs
path4.4 Your program's environment
path names14.6 Specifying object file directories
path, object file14.6 Specifying object file directories
path, object files14.6 Specifying object file directories
path, source file14.6 Specifying object file directories
pauses in output17.4 Screen size
performance, memory checking configuration14.4.10 Configuring memory debugging
performance, memory checking configuration14.4.10.1 Specifying the stack depth
permission denied, attach to a running program4.7 Debugging an already-running process
pipes4.2 Starting your program
pointer, finding referent8.7 Print settings
pointers, Fix and Continue14.3.1 Fix and Continue Restrictions
Pointers, Fortran9.4.4 Fortran
POSIX threads memory debugging14.4 Debugging Memory Problems
print8. Examining Data
print settings8.7 Print settings
printf18.4 Commands for controlled output
printing data8. Examining Data
printing floating point registers8.10 Registers
problems, memory14.3.3 Example Fix and Continue Session
processes, multiple4.10 Debugging programs with multiple processes
profiling, heap14.4.11.1 Example
program counter, Fix and Continue14.3.1 Fix and Continue Restrictions
program speed, memory checking configuration14.4.10 Configuring memory debugging
program speed, memory checking configuration14.4.10.1 Specifying the stack depth
prompt17.1 Prompt
pthreads debugging14.4 Debugging Memory Problems
ptype10. Examining the Symbol Table
pwd4.5 Your program's working directory

Q
q2.2 Quitting GDB
quit [expression]2.2 Quitting GDB
quotes in commands3.2 Command completion
quoting names10. Examining the Symbol Table

R
raise exceptions5.1.3 Setting catchpoints
range checking9.3.1 An overview of type checking
ranges of breakpoints5.1 Breakpoints, watchpoints, and catchpoints
rbreak5.1.1 Setting breakpoints
reading symbols immediately12.1 Commands to specify files
readline17.2 Command editing
readnow12.1 Commands to specify files
redirection4.6 Your program's input and output
reference declarations9.4.1.3 C++ expressions
register variables14.3.1 Fix and Continue Restrictions
registers8.10 Registers
regular expression5.1.1 Setting breakpoints
reloading symbols10. Examining the Symbol Table
repeating commands3.1 Command syntax
reporting bugs in GDB20. Reporting Bugs in GDB
reporting, memory leaks14.4.7 When to suspect a memory leak
restrictions, Fix and Continue14.3 Fix and Continue Debugging
restrictions, memory debugging14.4 Debugging Memory Problems
resuming execution5.2 Continuing and stepping
RET3.1 Command syntax
return11.4 Returning from a function
returning from a function11.4 Returning from a function
reverse-search7.2 Searching source files
run4.2 Starting your program
running4.2 Starting your program
rwatch5.1.2 Setting watchpoints

S
s5.2 Continuing and stepping
saving symbol table12.1 Commands to specify files
scramble memory, to check for memory leaks14.4.5 Stop if a specified block address is allocated or deallocated
scrolling, TUI command window15.5 Changing Window Focus
search7.2 Searching source files
searching7.2 Searching source files
section12.1 Commands to specify files
select-frame6.1 Stack frames
selected frame6. Examining the Stack
sessions, debugging12.1 Commands to specify files
sessions, debugging17.1 Prompt
sessions, debugging17.2 Command editing
set3.3 Getting help
set args4.3 Your program's arguments
set auto-solib-add12.1 Commands to specify files
set check range9.3.2 An overview of range checking
set check type9.3.1 An overview of type checking
set check, range9.3.2 An overview of range checking
set check, type9.3.1 An overview of type checking
set complaints17.6 Optional warnings and messages
set confirm17.6 Optional warnings and messages
set demangle-style8.7 Print settings
set disassembly-flavor7.4 Source and machine code
set editing17.2 Command editing
set endian auto13.3 Choosing target byte order
set endian auto13.3 Choosing target byte order
set endian big13.3 Choosing target byte order
set endian big13.3 Choosing target byte order
set endian little13.3 Choosing target byte order
set endian little13.3 Choosing target byte order
set environment4.4 Your program's environment
set extension-language9.2 Displaying the language
set follow-fork-mode4.10 Debugging programs with multiple processes
set gnutarget13.2 Commands for managing targets
set heap-check block-size num-bytes14.4.2 Using Memory Debugging
set heap-check bounds [on | off]14.4.2 Using Memory Debugging
set heap-check frame-count num14.4.2 Using Memory Debugging
set heap-check frame-count num14.5 Heap Profiling
set heap-check free [on | off]14.4.2 Using Memory Debugging
set heap-check heap-size num-size14.4.2 Using Memory Debugging
set heap-check leaks14.4.2 Using Memory Debugging
set heap-check min-leak-size num14.4.2 Using Memory Debugging
set heap-check scramble [on | off]14.4.2 Using Memory Debugging
set heap-check watch address14.4.2 Using Memory Debugging
set height17.4 Screen size
set history expansion17.3 Command history
set history filename17.3 Command history
set history save17.3 Command history
set history size17.3 Command history
set input-radix17.5 Numbers
set language9.1.2 Setting the working language
set listsize7.1 Printing source lines
set opaque-type-resolution10. Examining the Symbol Table
set output-radix17.5 Numbers
set overload-resolution9.4.1.7 GDB features for C++
set print address8.7 Print settings
set print array8.7 Print settings
set print asm-demangle8.7 Print settings
set print demangle8.7 Print settings
set print elements8.7 Print settings
set print max-symbolic-offset8.7 Print settings
set print null-stop8.7 Print settings
set print object8.7 Print settings
set print pretty8.7 Print settings
set print sevenbit-strings8.7 Print settings
set print static-members8.7 Print settings
set print symbol-filename8.7 Print settings
set print union8.7 Print settings
set print vtbl8.7 Print settings
set prompt17.1 Prompt
set symbol-reloading10. Examining the Symbol Table
set threadverbose4.9 Debugging programs with multiple threads
set variable11.1 Assignment to variables
set verbose17.6 Optional warnings and messages
set width17.4 Screen size
set write11.6 Patching programs
setting variables11.1 Assignment to variables
setting watchpoints5.1.2 Setting watchpoints
settings, application specific18.3 Command files
share12.1 Commands to specify files
shared libraries12.1 Commands to specify files
shared library breakpoints5.1 Breakpoints, watchpoints, and catchpoints
shared library loading12.1 Commands to specify files
sharedlibrary12.1 Commands to specify files
shell2.3 Shell commands
shell escape2.3 Shell commands
SHMEM_MAGIC14.1.2 Fix and Continue compiler dependencies
show3.3 Getting help
show args4.3 Your program's arguments
show auto-solib-add12.1 Commands to specify files
show check range9.3.2 An overview of range checking
show check type9.3.1 An overview of type checking
show commands17.3 Command history
show complaints17.6 Optional warnings and messages
show confirm17.6 Optional warnings and messages
show convenience8.9 Convenience variables
show copying3.3 Getting help
show demangle-style8.7 Print settings
show directories7.3 Specifying source directories
show editing17.2 Command editing
show endian13.3 Choosing target byte order
show environment4.4 Your program's environment
show gnutarget13.2 Commands for managing targets
show heap-check14.4.2 Using Memory Debugging
show heap-check14.5 Heap Profiling
show height17.4 Screen size
show history17.3 Command history
show input-radix17.5 Numbers
show language9.2 Displaying the language
show listsize7.1 Printing source lines
show opaque-type-resolution10. Examining the Symbol Table
show output-radix17.5 Numbers
show overload-resolution9.4.1.7 GDB features for C++
show paths4.4 Your program's environment
show print address8.7 Print settings
show print array8.7 Print settings
show print asm-demangle8.7 Print settings
show print demangle8.7 Print settings
show print elements8.7 Print settings
show print max-symbolic-offset8.7 Print settings
show print object8.7 Print settings
show print pretty8.7 Print settings
show print sevenbit-strings8.7 Print settings
show print static-members8.7 Print settings
show print symbol-filename8.7 Print settings
show print union8.7 Print settings
show print vtbl8.7 Print settings
show prompt17.1 Prompt
show symbol-reloading10. Examining the Symbol Table
show threadverbose4.9 Debugging programs with multiple threads
show user18.1 User-defined commands
show values8.8 Value history
show verbose17.6 Optional warnings and messages
show version3.3 Getting help
show warranty3.3 Getting help
show width17.4 Screen size
show write11.6 Patching programs
show-all-if-ambiguous21.3.1 Readline Init File Syntax
si5.2 Continuing and stepping
SIGBUS errors14.4.7 When to suspect a memory leak
signal11.3 Giving your program a signal
signals5.3 Signals
SIGSEV, Fix and Continue14.3.1 Fix and Continue Restrictions
silent5.1.7 Breakpoint command lists
size of screen17.4 Screen size
slow program performance, memory checking configuration14.4.10 Configuring memory debugging
slow program performance, memory checking configuration14.4.10.1 Specifying the stack depth
software watchpoints5.1.2 Setting watchpoints
source18.3 Command files
source files14.6 Specifying object file directories
source path7.3 Specifying source directories
source path14.6 Specifying object file directories
stack depth, memory leaks14.4.10 Configuring memory debugging
stack frame6.1 Stack frames
stack traces6.2 Backtraces
stacking targets13.1 Active targets
starting4.2 Starting your program
step5.2 Continuing and stepping
stepi5.2 Continuing and stepping
stepping5.2 Continuing and stepping
stop, a pseudo-command18.2 User-defined command hooks
stopped threads5.4 Stopping and starting multi-thread programs
structure fields, Fix and Continue14.3.1 Fix and Continue Restrictions
Structures, Fortran9.4.4 Fortran
stupid questions17.6 Optional warnings and messages
support20.2 How to report bugs
swap space, memory leak symptoms14.4.6 Scramble previous memory contents at malloc/free calls
switching threads4.9 Debugging programs with multiple threads
switching threads automatically4.9 Debugging programs with multiple threads
symbol decoding style, C++8.7 Print settings
symbol dump10. Examining the Symbol Table
symbol names10. Examining the Symbol Table
symbol overloading5.1.8 Breakpoint menus
symbol table12.1 Commands to specify files
symbol-file12.1 Commands to specify files
symbols, reading immediately12.1 Commands to specify files
symptoms, memory leak14.4.6 Scramble previous memory contents at malloc/free calls

T
target13. Specifying a Debugging Target
target byte order13.3 Choosing target byte order
target core13.2 Commands for managing targets
target exec13.2 Commands for managing targets
target nrom13.2 Commands for managing targets
target remote13.2 Commands for managing targets
target sim13.2 Commands for managing targets
targets14.1.2 Fix and Continue compiler dependencies
tbreak5.1.1 Setting breakpoints
tcatch5.1.3 Setting catchpoints
TERM, setting for Fix and Continue14.3.3 Example Fix and Continue Session
terminal4.6 Your program's input and output
Terminal User Interface2.1.2 Choosing modes
Terminal User Interface15. The HP-UX Terminal User Interface
thbreak5.1.1 Setting breakpoints
this9.4.1.3 C++ expressions
thread apply4.9 Debugging programs with multiple threads
thread breakpoints5.4 Stopping and starting multi-thread programs
thread identifier (GDB)4.9 Debugging programs with multiple threads
thread identifier (GDB)4.9 Debugging programs with multiple threads
thread identifier (system)4.9 Debugging programs with multiple threads
thread identifier (system)4.9 Debugging programs with multiple threads
thread number4.9 Debugging programs with multiple threads
thread number4.9 Debugging programs with multiple threads
thread threadno4.9 Debugging programs with multiple threads
threads and watchpoints5.1.2 Setting watchpoints
threads of execution4.9 Debugging programs with multiple threads
threads, automatic switching4.9 Debugging programs with multiple threads
threads, backtrace6.2 Backtraces
threads, continuing5.4 Stopping and starting multi-thread programs
threads, memory debugging CMA, DCE restrictions14.4.1 Memory Debugging Restrictions
threads, POSIX memory debugging14.4 Debugging Memory Problems
threads, stopped5.4 Stopping and starting multi-thread programs
threadverbose4.9 Debugging programs with multiple threads
throw5.1.3 Setting catchpoints
tracebacks6.2 Backtraces
tty4.6 Your program's input and output
TUI2.1.2 Choosing modes
TUI15. The HP-UX Terminal User Interface
TUI and Emacs19. Using GDB under Emacs
TUI, command window15.5 Changing Window Focus
turning on memory leak checking14.4.10.2 Specifying minimum leak size
type casting memory8.1 Expressions
type checking9.3 Type and range checking
type conversions in C++9.4.1.3 C++ expressions
types, Fortran9.4.4.1 Fortran types

U
u5.2 Continuing and stepping
underflow, heap14.4.4 Stop when freeing a block if bad writes occurred outside block boundary
undisplay8.6 Automatic display
Unions, Fortran9.4.4 Fortran
unknown address, locating8.4 Output formats
unload5.1.3 Setting catchpoints
unset environment4.4 Your program's environment
until5.2 Continuing and stepping
up6.3 Selecting a frame
up-silently6.3 Selecting a frame
user-defined command18.1 User-defined commands
Using Fix and Continue14.3.1 Fix and Continue Restrictions

V
value history8.8 Value history
variable name conflict8.2 Program variables
variable names8.9 Convenience variables
variable values, wrong8.2 Program variables
variables, Fix and Continue restrictions14.3.1 Fix and Continue Restrictions
variables, setting11.1 Assignment to variables
version number3.3 Getting help
versions, compiler20.2 How to report bugs
vfork5.1.3 Setting catchpoints
vi key bindings17.3 Command history
virtual functions9.4.1.3 C++ expressions
visible-stats21.3.1 Readline Init File Syntax

W
watch5.1.2 Setting watchpoints
watchpoints5.1 Breakpoints, watchpoints, and catchpoints
watchpoints and threads5.1.2 Setting watchpoints
watchpoints, xdb assertion control16.2.5 Global Breakpoint Commands
whatis10. Examining the Symbol Table
where6.2 Backtraces
while18.1 User-defined commands
wild pointer, interpreting8.7 Print settings
window, changing focus in TUI15.5 Changing Window Focus
word completion3.2 Command completion
working directory7.3 Specifying source directories
working directory (of your program)4.5 Your program's working directory
working language9. Using GDB with Different Languages
writing into core files11.6 Patching programs
writing into executables11.6 Patching programs
wrong values8.2 Program variables

X
x8.5 Examining memory
x, and info line7.4 Source and machine code
XCOFF and C++9.4.1.3 C++ expressions
XDB compatibility2.1.2 Choosing modes
XDB transition guide16. XDB to WDB Transition Guide

Y
yanking text21.2.3 Readline Killing Commands

{
{type}8.1 Expressions




[Top] [Contents] [Index] [ ? ]

Footnotes

(1)

`b' cannot be used because these format letters are also used with the x command, where `b' stands for "byte"; see Memory.

(2)

This is a way of removing one word from the stack, on machines where stacks grow downward in memory (most machines, nowadays). This assumes that the innermost stack frame is selected; setting $sp is not allowed when other stack frames are selected. To pop entire frames off the stack, regardless of machine architecture, use return; see Returning.

(3)

If a procedure call is used for instance in an expression, then this procedure is called with all its side effects. This can lead to confusing results if used carelessly.

(4)

On DOS/Windows systems, the home directory is the one pointed to by the HOME environment variable.



[Top] [Contents] [Index] [ ? ]

Table of Contents



[Top] [Contents] [Index] [ ? ]

Overview (Short Table of Contents)

Summary of GDB
1. A Sample GDB Session
2. Getting In and Out of GDB
3. GDB Commands
4. Running Programs Under GDB
5. Stopping and Continuing
6. Examining the Stack
7. Examining Source Files
8. Examining Data
9. Using GDB with Different Languages
10. Examining the Symbol Table
11. Altering Execution
12. GDB Files
13. Specifying a Debugging Target
14. Configuration-Specific Information
15. The HP-UX Terminal User Interface
16. XDB to WDB Transition Guide
17. Controlling GDB
18. Canned Sequences of Commands
19. Using GDB under GNU Emacs
20. Reporting Bugs in GDB
21. Command Line Editing
22. Using History Interactively
A. Installing GDB
Index


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