[Buildroot] update --march= for x86_64

[Vincent Fazio]

On 3/6/20 9:00 AM, Vincent Fazio wrote:
> Louis-Paul,
>
> On 3/6/20 8:42 AM, lpdev at cordier.org wrote:
>> Hi all,
>>
>> GCC has evolved a lot since 4.x versions. It seems that some target 
>> architectures are not available anymore (like corei7 and corei7-avx). 
>> GCC has moved to processor family names (like sandybridge, ivybridge) 
>> for the --march= parameter.
>>
>> These new nqmes can be checked here:
>>
>> - For old gcc: 
>> https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/i386-and-x86-64-Options.html#i386-and-x86-64-Options
>> - For gcc 7: 
>> https://gcc.gnu.org/onlinedocs/gcc-7.5.0/gcc/x86-Options.html#x86-Options
>>
>> I can send a serie of patches for moving (or adding) from old march 
>> to new march syntax, by adding some of the most used intel processors 
>> that are used for embedded systems (low power cores i3/i5/i7-U, some 
>> atom x series and intel mXXX series).
> Considering BR still supports GCC 4.8, this would have to be 
> conditional on the selected GCC version.
Also, the old names are still functional and are equivalent (at least on 
7.4.0):

vfazio at vfazio1 ~/development/buildroot :( $ diff <(gcc -march=corei7-avx 
-Q --help=target) <(gcc -march=sandybridge -Q --help=target)
24c24
<   -march=                             corei7-avx
---
 >   -march=                             sandybridge
150c150
<   -mtune=                             corei7-avx
---
 >   -mtune=                             sandybridge
vfazio at vfazio1 ~/development/buildroot :( $ diff <(gcc -march=core-avx2 
-Q --help=target) <(gcc -march=haswell -Q --help=target)
24c24
<   -march=                             core-avx2
---
 >   -march=                             haswell
150c150
<   -mtune=                             core-avx2
---
 >   -mtune=                             haswell

>> Before working on this, I would like to have an advice from a 
>> toolchain guru if possible.
>>
>> Thanks!
>>
>> Louis-Paul CORDIER
>>
>>
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>
-- 
Vincent Fazio
Embedded Software Engineer - Linux
Extreme Engineering Solutions, Inc
http://www.xes-inc.com