(In reply to smoki from comment #2)
>  Well i can but i need first to make a bottle of coffee because one llvm
> build takes 30 minutes on Kabini :D.

It shouldn't take that long after switching between the bisected commit and the
one before it (or just re-applying/reverting it on top of whatever later commit
you may have built last). If you're not using ccache yet, that might help a
little as well.

>  I don't have gdm.log as i don't use it, plain startx is used.

Then something like

startx [...] 2>stderr.txt

should capture the stderr output in a file.