Re: [Buildroot] [PATCH 2/2] arch/Config.in.x86: add support for x86-64-v2, x86-64-v3, x86-64-v4

[Romain Naour <romain.naour@smile.fr>]

Hello Thomas, Yann,

Le 09/01/2022 à 11:36, Yann E. MORIN a écrit :
> Thomas, All,
> 
> On 2022-01-09 09:01 +0100, Thomas Petazzoni spake thusly:
>> In the face of the vast amount of x86-64 CPU architecture variants,
>> Linux distributions have worked together to define "micro-architecture
>> levels" in the x86-64 psABI, called x86-64-v2, x86-64-v3 and
>> x86-64-v4. They standardize a set of CPU features, and GCC since its
>> version 11.x has support for these micro-architecture levels as
>> -march= options.
>>
>> It makes sense to support them in Buildroot, especially for those who
>> want to build toolchains that aim at targeting a reasonably broad
>> family of x86-64 processors.
> 
> As for x86-64, I've added a dependency on BR2_x86_64.
> 
>> More details:
>>
>>  https://gitlab.com/x86-psABIs/x86-64-ABI/-/blob/master/x86-64-ABI/low-level-sys-info.tex
>>  https://developers.redhat.com/blog/2021/01/05/building-red-hat-enterprise-linux-9-for-the-x86-64-v2-microarchitecture-level
>>  https://www.phoronix.com/scan.php?page=news_item&px=GCC-11-x86-64-Feature-Levels
> 
> I've added a URL to the upstream commit too.

Sorry I'm late, but I had a look at this series to use x86-64-v3 and x86-64-v4
for Qemu runtime testing.

There are some limitation with the current version of Qemu (6.2.0):

"Note that TCG is not capable of supporting the 2 newest ABI levels
currently:

* x86-64-abi3:

  CPUID.01H:ECX.fma [bit 12]
  CPUID.01H:ECX.avx [bit 28]
  CPUID.01H:ECX.f16c [bit 29]
  CPUID.07H:EBX.avx2 [bit 5]

* x86-64-abi4:

  CPUID.01H:ECX.pcid [bit 17]
  CPUID.01H:ECX.x2apic [bit 21]
  CPUID.01H:ECX.tsc-deadline [bit 24]
  CPUID.07H:EBX.invpcid [bit 10]
  CPUID.07H:EBX.avx512f [bit 16]
  CPUID.07H:EBX.avx512dq [bit 17]
  CPUID.07H:EBX.rdseed [bit 18]
  CPUID.07H:EBX.avx512cd [bit 28]
  CPUID.07H:EBX.avx512bw [bit 30]
  CPUID.07H:EBX.avx512vl [bit 31]
  CPUID.80000001H:ECX.3dnowprefetch [bit 8]
  CPUID.0DH:EAX.xsavec [bit 1]"

https://lists.gnu.org/archive/html/qemu-devel/2021-02/msg00170.html

I wanted to reply to add this info in the commit log.

Best regards,
Romain


> 
>> Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
> 
> Applied to master, thanks.
> 
> Regards,
> Yann E. MORIN.
> 
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