Re: [PATCH v2 3/3] powerpc64le: Add glibc-hwcaps support

[Florian Weimer <fweimer@redhat.com>]

* Tulio Magno Quites Machado Filho:

> Florian Weimer <fweimer@redhat.com> writes:
>
>> I think we need documentation what it means for a processor to implement
>> ISA 3.0, and not altivec.  Or for that matter, what an implementation of
>> powerpc64le-*-linux-gnu without altivec looks like.  Presumably, it will
>> be different yet again from the original hardware used during
>> architecture bring-up.
>
> I think we already have this documented in a couple of places in different
> documents from the OpenPOWER Foundation.

Yes, but all those documents say that Altivec + VSX are required for
powerpc64le-*-linux-gnu.  Your summary below seems to re-confirm that.

My point was that if we want powerpc64le-*-linux-gnu to stand for
something different (without Altivec/VSX), we need (new) documentation
that says what it means.

>> ISA features that cannot automatically and pervasively used by compilers
>> can be excluded as well.  MMA could be in that category, and I think
>> cryptography-related instructions generally are.
>
> MMA is indeed optional for Linux.
> AFAICS, cryptography-related instructions are part of SIMD and should be
> required for Linux.

Then I think we should change GCC not to enable MMA with -mcpu=power10.

The other change is that I should check for PPC_FEATURE2_HAS_IEEE128 for
power9, and add a comment that ALTIVEC and VSX are implied by the place
in the source tree (I deliberately made all this specific to
powerpc64le-*-linux-gnu on the glibc side, like we didn't define new ABI
levels for i386).

Thanks,
Florian
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