ppc64 vDSO in mainline

[Benjamin Herrenschmidt]

> Is this a hard requirement for all arches or just for i386? 
> 
> I can see how randomized VDSO for platforms using 
> NEED_DL_SYSINFO/DL_SYSINFO_IMPLEMENTATION might prevent a virus attacker 
> from using syscalls. But powerpc is a NEED_DL_SYSINFO_DSO only 
> implemention and so can't prevent anyone from using syscalls inline. And I 
> don't see how calling gettimeofday is a security threat?

Currently, we don't use the vDSO for syscalls, but that might change in
the future. There are things going on at the architecture folks level
that _might_ cause us to want to use a different syscall entry mecanism
for some CPUs in the future.