# Debugging with GDB

## Loading the program
To load a program for debugging simply pass it to gdb

    gdb <executable>

### Debugging programs using libtool
To execute gdb for a program using libtool from it's build directory you can
use:

    libtool --mode=execute gdb <executable>

this makes sure *LD_LIBRARY_PATH* etc. is setup correctly.

## Breaking
Once the program is loaded we can start to examin it. To stop program execution
at a certain position we can use a breakpoint. Once the program hits the
breakpoint you can step through the code. First set a breakpoint

    break <file>:<function>
    break <file>:<linenumerber>

## Stepping
Once you broke out of program execution you can step through the code. To show
the source code around the current execution point:

    list

Step to the next statement in the current function:

    next

Step to the next statement following function calls:

    step

Other useful commands:

* finish: run until the function exits and print it's return value
* print: print the value of a variable
* directory: specify source code location
* set substitute-path: define a source path substitution to look for the source at a different location

## Backtrace
The current stacktrace can be inspected using *bt*. *bt full* additionally
includes the values of local variables. In threaded programs use *thread apply
all bt* to see all threads.

## Calling functions
To call functions use:

    call g_hash_table_lookup (priv->sockets_by_msg, msg)

## Configuration
Add this to *~/.gdbinit*

    # save all history into one file
    set history filename ~/.gdb_history
    # save history
    set history save on

# Miscelanous

## Generating a core file

On some systems the limit for core files size is 0, change that to unlimited to
make the system generate core files on e.g. SEGV:

    ulimit -c unlimited

## Aborting on GTK+ warning

To abort on the first encountered glib/GTK+ warning use:

    <program> --g-fatal-warnings

## Printing Glib messages

Print all messages:

    G_MESSAGES_DEBUG=all <program> 

See the [Glib manual][] for details.

# Other tools
* valgrind
* strace,  ltrace

## Packages

Debugging things in a vm is useful if you don't want to hose your production
system. This needs the following packages in the guest:

    aptitude install vim-nox gdb gdb-doc build-essential exuberant-ctags libc6-dbg git git-buildpackage ccache strace valgrind

And when debugging GTK+ related problems:

    aptitude install libglib2.0-0-dbg libgnutls26-dbg libgtk2.0-0-dbg libpcre3-dbg vim-syntax-gtk gtkparasite

[Glib manual]: https://developer.gnome.org/glib/stable/glib-running.html