Gdb/gdb-man
Next: gdbserver man, Up: Man Pages [Contents][Index]
gdb man
gdb man
gdb [-help
] [-nh
] [-nx
] [-q
]
[-batch
] [-cd=
dir
] [-f
]
[-b
bps
]
[-tty=
dev
] [-s
symfile
]
[-e
prog
] [-se
prog
]
[-c
core
] [-p
procID
]
[-x
cmds
] [-d
dir
]
[prog
|prog
procID
|prog
core
]
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:
- 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++
, Fortran and
Modula-2.
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 or use option
-p
, if you want to debug a running process:
gdb program 1234 gdb -p 1234
would attach GDB to process 1234
. With option -p
you
can omit the program
filename.
Here are some of the most frequently needed GDB commands:
break [file:]function
- Set a breakpoint at
function
(infile
). 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.
edit [file:]function
- look at the program line where it is presently stopped.
list [file:]function
- type the text of the program in the vicinity of where it is presently stopped.
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.
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
.-ex command
Execute given GDB
command
.-directory=directory
-d directory
Add
directory
to the path to search for source files.-nh
Do not execute commands from
~/.config/gdb/gdbinit
or~/.gdbinit
.-nx
-n
Do not execute commands from any
.gdbinit
initialization 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.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 ‘
\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.-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.
Next: gdbserver man, Up: Man Pages [Contents][Index]