V4 [PATCH] x86: Add <sys/platform/x86.h>

[Florian Weimer]

* H. J. Lu:

> On Thu, Sep 20, 2018 at 4:41 AM, Florian Weimer <fweimer@redhat.com> wrote:
>> * H. J. Lu:
>>
>>> Add <sys/platform/x86.h> to provide an API to access x86 specific platform
>>> features.  It makes raw and derived CPUID information available to
>>> applications so that programmers can avoid complicated steps to retrieve
>>> the same information with CPUID instructions.
>>
>> Sorry, I still think that this patch semantically depends on delayed
>> IFUNC processing.
>>
>> Furthermore, I strongly prefer a simplified interface, like:
>>
>>   enum {
>>     X86_FEATURE_MMX,
>>     X86_FEATURE_SSE,
>>     X86_FEATURE_SSE2,
>>     …
>>     X86_FEATURE_AVX512F,
>>     …
>>   };
>>
>>   _Bool x86_feature_usable (int index) __attribute__ ((pure));
>>
>> Applications could then do something like this:
>>
>>   if (x86_feature_usable (X86_FEATURE_AVX512F))
>>     return &__matmul_avx512f;
>>
>> I don't think there is value in exposing the CPUID data directly.  If
>> programmers need it, they can use <cpuid.h> from GCC instead, without
>> needing to worry how glibc populates its data structures.
>>
>
> You have 2 concerns.  Which one is the primary concern?  Or
> are both blockers for you?

The design of the API is more important.

We can implement delayed IFUNC processing later to support this feature
(and others).

Thanks,
Florian