Thanks for your random guess.
The following workaround seems to fix the crashes on powerpc.
However, this patch is clearly not what we want for other architectures,
as they might need -fno-omit-frame-pointer to function properly.

Well, and -pg requires it, even on powerpc, so that won't work for
ftrace. Any chance you can try the workaround that segher proposed
though ?

http://penguinppc.de/~segher/0001-powerpc-Workaround-for-the-ftrace-problem.patch

His workaround only kicks in with CONFIG_FTRACE, that would have to be
fixed of course. Also, I suspect the bits that have -pg in a flag
"remove" section should have also "fno-omit-frame-pointer" in that
remove section too.

I reproduced the random crashes of kernel and userspace applications
(without the following patch) on a vanilla 2.6.26 and 2.6.27-rc{1-4}
kernel. I did _not_ try a 2.6.25 kernel with -fno-omit-frame-pointer, so
I don't know if it would also crash then.

I'm currently running more tests on a patched 2.6.27-rc4 kernel, but it
didn't crash, yet. I already did 5 complete kernel tree compilations. It
should have crashed by now, but it didn't :)

Thanks !

Ben.