Valgrind#

Valgrind is a programmer tool that allows to track memory related errors in C and C++ programs.

Hint

You can read a full introduction on the Valgrind website.

This page includes some tips on how to proficiently use valgrind on GTK/GNOME programs. Feel free to add your own tricks or expand the page with more detailed explanations.

Memcheck#

Memcheck is the main valgrind tool, it allows to detect memory leaks and other memory management errors. To run a gnome program under memcheck run:

valgrind \
  --leak-check=full \
  --leak-resolution=high \
  --num-callers=20 \
  --log-file=vgdump.txt\
  your-program

If the program you are debugging uses dynamically loaded modules with GModule (for instance it has a GModule based plugin system) you should use G_DEBUG=resident-modules to make sure that the modules do not get unloaded and valgrind can retrieve the function names when writing its log:

G_DEBUG=resident-modules valgrind \
  --leak-check=full \
  --leak-resolution=high \
  --num-callers=20 \
  --log-file=vgdump.txt \
  your-program

Note

If you are still using Autotools as your build system, your binary is really a libtool-generated temporary wrapper, the above command line will run valgrind on your shell which is probably not what you want. You will need to use libtool --mode=execute valgrind ... instead.

After running the program you can inspect the log in the vgdump file. The log contains a list of memory related issues and in particular memory leaks. Memory leaks are marked in three ways: definitely lost, possibly lost and still reachable. For a start, concentrate on the definitely lost ones, which are bits of memory leaked for sure—you can filter for them by passing --show-leak-kinds=definite. For each leak valgrind provides a backtrace which lets you pinpoint exactly where the leaks happens, in particular if your program was compiled with debugging symbols, valgrind will tell you the exact line and file of the leak.

Suppression files#

GLib and other libraries often make one-off allocations that are meant to exist until the end of the lifetime of your application. These are not leaks, but Valgrind will mark them as such. In order to avoid cluttering your reports, you can use “suppression files”, to tell Valgrind to eliminate known one-off allocations. GLib and GTK provide suppression files that you can use.

Assuming your copy of GLib and GTK are installed under /usr, the Valgrind suppression files are located here:

  • /usr/share/glib-2.0/valgrind/glib.supp

  • /usr/share/gtk-4.0/valgrind/gtk.supp

You can use them with the --suppressions argument for the memcheck tool, e.g.:

valgrind \
  --suppressions=/usr/share/glib-2.0/valgrind/glib.supp \
  --suppressions=/usr/share/gtk-4.0/valgrind/gtk.supp \
  your-gtk-app

Hint

You can use multiple --suppressions arguments, one for each suppression file.

If your project has its own one-off allocations you wish to suppress, you can write your own suppression file by following the instructions in the Valgrind documentation.