Comment 34 for bug 328035

Here's a recipe for running your X server under valgrind that might be helpful.

$ sudo dpkg-divert --local --rename --divert /usr/bin/X.valgrind-madness /usr/bin/X
$ sudo tee /usr/bin/X
#!/bin/sh
exec valgrind --error-limit=no --log-file=/var/log/Xorg-valgrind.log X.valgrind-madness "$@"
^D
$ sudo chmod a+x /usr/bin/X
$

I think that's sufficient to get X started with the right permissions from gdm. If you're starting it by some other method that depends on X's suid bit, you'll probably need to set valgrind itself suid root (unfortunately) to get the right permissions available.

To unwind, run:

$ sudo rm /usr/bin/X
$ sudo dpkg-divert --remove --local --rename /usr/bin/X
$