[llvm-dev] New x86-64 micro-architecture levels

[H.J. Lu via llvm-dev]

On Wed, Jul 15, 2020 at 7:38 AM Mark Wielaard <mark at klomp.org> wrote:
>
> Hi Florian,
>
> I understand you want to discuss the x86_64 micro-architecture levels
> only in this thread, but it would be nice to have a similar discussion
> for other architectures.
>
> One thing that wasn't clear to me from this proposal is how the glibc
> dynamic loader checks for the CPU feature flags. This is important for
> valgrind since it can communicate those through different means. cpuid
> interception, auxv AT_HWCAP/AT_HWCAP2 interception (but not AT_PLATFORM
> at the moment) and of course we can generate SIGILL for unsupported
> instructions. We currently don't intercept /proc/cpuinfo (but could).

In library, we can use <sys/platform/x86.h>:

https://sourceware.org/pipermail/libc-alpha/2020-June/115546.html

In GCC, we can use __builtin_cpu_supports.

<sys/platform/x86.h> supports all features and __builtin_cpu_supports in
GCC 11 supports all features which GCC has codegen for.

> I think it is important to be precise here, because in the past this
> has sometimes caused confusion. For example for how to check correctly
> for avx, lzcnt, or fma[4] support.
>
> Thanks,
>
> Mark
>
> P.S. I don't particular like the numbered names, but well, bike-shed...



-- 
H.J.