[PATCH v2] x86-64: Update _dl_tlsdesc_dynamic to preserve vector registers

[Florian Weimer]

* H. J. Lu:

>> the TLSDESC call?  Or does current GCC already assume that all scalar
>> registers are preserved?
>
> GCC assumes that only FLAGS_REG is reserved and RAX is the destination
> register.  Everything else must be preserved.
>
>> The other way to fix this is to preallocate everything, so that the need
>> for the slow path goes away.
>
> True.

I susppose we could start saving pretty much all register state for now,
and announce a plan to move to TLS data preallocation later, globally,
for all architectures.

That would need agreement from all active architecture maintainers,
though.

Thanks,
Florian