[PATCH 11/11] powerpc64le: Add glibc-hwcaps support

[Florian Weimer]

* Adhemerval Zanella:

> On 02/12/2020 10:51, Florian Weimer wrote:
>> * Adhemerval Zanella:
>> 
>>>> +uint32_t
>>>> +_dl_hwcaps_subdirs_active (void)
>>>> +{
>>>> +  int active = 0;
>>>> +
>>>> +  /* Test in reverse preference order.  Altivec and VSX are implied by
>>>> +     the powerpc64le ABI definition.  */
>>>> +
>>>> +  /* POWER9.  GCC enables float128 hardware support for -mcpu=power9.  */
>>>> +  if ((GLRO (dl_hwcap2) & PPC_FEATURE2_ARCH_3_00) == 0
>>>> +      || (GLRO (dl_hwcap2) & PPC_FEATURE2_HAS_IEEE128) == 0)
>>>> +    return _dl_hwcaps_subdirs_build_bitmask (subdirs_count, active);
>>>> +  ++active;
>>>
>>> Should we test PPC_FEATURE2_DARN as well? I think cryptographic and related
>>> libraries might use it as source of entropy.
>> 
>> It does not show up in the compiler preprocessor macros.  There also
>> have been cases where randomness-generating instructions have been
>> disabled in firmware (but probably not on POWER).  I think it's safer
>> not to include cryptographic stuff.
>
> GCC does provides it through a compiler builtin, only enabled for
> power9 and newer.  And I think hardware entropy instruction are not
> used on cryptographic, but also on different fields as simulations.

Maybe Tulio can comment.  I do not have a strong opinion (although the
x86 precedent is kind of unsettling).

Thanks,
Florian
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