[PATCH x86_64][BZ #20139] Don't allow configure with not supporting AVX512 assembler w/o --disable-avx512.

[Florian Weimer]

On 06/27/2016 10:22 PM, Joseph Myers wrote:
> On Mon, 27 Jun 2016, H.J. Lu wrote:
>
>>>> May be it will be the best way.  Needed version is 2.25 and it was
>>>> released at Mon, 5 Jan 2015.
>>>
>>>
>>> It's a fairly recent version.
>>>
>>
>> Binutils 2.24 released in Dec., 2013 supports AVX512.
>
> Time-based updates to the binutils requirements would indicate moving to
> requiring binutils 2.24 for building glibc 2.25 and later rather than
> requiring it now for building glibc 2.24, but given a clear reason for the
> requirement I wouldn't object to bringing it forward.
>
> Note: if we require a version with AVX512 support, we should also remove
> all the configure / preprocessor / makefile conditionals on such support,
> and all places where .byte directives are used for instruction encoding
> because of instructions not supported in older versions.

Alternatively, we could upstream the .byte-based AVX512 hacks we have 
for supporting older binutils in our downstream glibc builds for Red Hat 
Enterprise Linux.  But just requiring the newer glibc version is 
certainly the cleaner approach.

Thanks,
Florian