[Pixman] testsuite fails on power7

[Lennart Sorensen]

I get crashes in the scaling and affinity tests on power7.  The crashes
are always in the vmx code, so building with vmx support disabled makes
the problem go away.

The error is not consistent, so my current guess is that multiple threads
are running and depending on timing one thread manages to sometimes
corrupt another and cause it to fail.

As far as I can tell, it doesn't fail on power5 or power6 machines,
but given the interesting memory model of the powerpc and requirement
for explicit syncs and barriers to ensure things have really made it to
memory and other CPUs, the power7 has managed to show up bugs in glibc
and gcc already where power5 and power6 and other powerpc systems never
failed before.

Any suggestions on how to debug this or where to look?  Any traces or
logs that would be helpful?

I am currently using version 0.26.0-4 debian package on Debian 7 (wheezy).

Interestingly, if I change the version of libc to 2.17 instead of 2.13
that wheezy is using, then the problem also disappears, but again, this
might just be a timing change causing this, or perhaps there is something
relevant changed in the newer libc, although I haven't spotted anything
suspicious looking when doing a diff so far.

-- 
Len Sorensen