NAME
gdb - The GNU Debugger
SYNOPSIS
gdb [ -help ] [ -nx ] [ -q ] [ -batch ] [ -cd=dir ] [ -f ] [ -b bps ] [ -tty=dev ]
[ -s symfile ] [ -e prog ] [ -se prog ] [ -c core ] [ -x cmds ] [ -d dir ]
[ prog[ core | procID]]
DESCRIPTION
The purpose of a debugger such as GDB is to allow you to see what is going on ``inside''
another program while it executesor 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:
· Start your program, specifying anything that might affect its behavior.
· Make your program stop on specified conditions.
· Examine what has happened, when your program has stopped.
· Change things in your program, so you can experiment with correcting
the effects of one bug and go on to learn about another.
You can use GDB to debug programs written in C, C++, and Modula2. Fortran support will
be added when a GNU Fortran compiler is ready.
GDB is invoked with the shell command gdb. Once started, it reads commands from the
terminal until you tell it to exit with the GDB command quit. You can get online help from
gdb itself by using the command help.
You can run gdb with no arguments or options; but the most usual way to start GDB is with
one argument or two, specifying an executable program as the argument:
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).
Here are some of the most frequently needed GDB commands:
break [ file: ]function
Set a breakpoint at function (in file).
run [ arglist ] Start your program (with arglist, if specified).
bt Backtrace: display the program stack.
print expr Display the value of an expression.
c Continue running your program (after stopping, e.g. at a breakpoint).
next Execute next program line (after stopping); step over any function calls
in the line.
step Execute next program line (after stopping); step into any function calls
in the line.
help [ name ] Show information about GDB command name, or general information
about using GDB.
quit Exit from GDB.
For full details on GDB, see Using GDB: A Guide to the GNU SourceLevel Debugger, by
Richard M. Stallman and Roland H. Pesch. The same text is available online as the gdb entry
in the info program.
OPTIONS
Any arguments other than options specify an executable file and core file (or process ID);
that is, the first argument encountered with no associated option flag is equivalent to a ` -se '
option, and the second, if any, is equivalent to a ` -c ' option if it's the name of a file. Many
options have both long and short forms; both are shown here. The long forms are also
recognized 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.)
All the options and command line arguments you give are processed in sequential order. The
order makes a difference when the ` -x ' option is used.
-help
-h List all options, with brief explanations.
-symbols=file
-s file Read symbol table from file file.
-write Enable writing into executable and core files.
-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.
-command=file
-x file Execute GDB commands from file file.
-directory=directory
-d directory Add directory to the path to search for source files.
-nx
-n Do not execute commands from any ` .gdbinit ' initialization files.
Normally, the commands in these files are executed after all the
command options and arguments have been processed.
-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 ` .gdbinit ', if not inhibited). 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.
-cd=directory Run GDB using directory as its working directory, instead of the
current directory.
-fullname
-f 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
the program stops). This recognizable format looks like two ` 32 '
characters, followed by the file name, line number and character
position separated by colons, and a newline. The EmacstoGDB
interface program uses the two ` 32 ' characters as a signal to display
the source code for the frame.
-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.
SEE ALSO
` gdb ' entry in info; Using GDB: A Guide to the GNU SourceLevel Debugger, Richard M.
Stallman and Roland H. Pesch, July 1991.
COPYING
Copyright (c) 1991 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this manual provided the
copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this manual under the
conditions for verbatim copying, provided that the entire resulting derived work is distributed
under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this manual into another language,
under the above conditions for modified versions, except that this permission notice may be
included in translations approved by the Free Software Foundation instead of in the original
English.