V5 [PATCH 1/2] x86: Add <sys/platform/x86.h>

[Florian Weimer]

* H. J. Lu:

> On 10/24/18, Florian Weimer <fweimer@redhat.com> wrote:
>> * H. J. Lu:
>>
>>> +@defmac HAS_CPU_FEATURE(name)
>>> +
>>> +Evaluate to true if the CPU feature @code{name} is supported as
>>> indicated
>>> +by @code{CPUID} instruction.  The available features are:
>>
>> I'm still puzzled why we expose this function.  It will only confuse
>> programmers.
>
> A use case:  AVX512 bits can be used to tell Xeon Phi from Skylake
> sever even if AVX512 instructions aren't used/needed at all.

Do you mean checking fore AVX512ER?  Would you consider this good
practice?

It is actually future-proof?  What if Skylake successors implement
AVX512ER?  Do you really want applications to select the Xeon Phi
workarounds in this case?

I still think if you care about Xeon Phi, you should use <cpuid.h> from
GCC and make the checks as explicit as possible.  The <cpuid.h>
facilities should not be too difficult to use for that purpose.

Thanks,
Florian