x86: Don't check PREFETCHWT1 in tst-cpu-features-cpuinfo.c

[Noah Goldstein]

On Thu, Mar 9, 2023 at 9:43 PM DJ Delorie via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
>
> As not noted in the kernel sources:
>
> > /* Intel-defined CPU features, CPUID level 0x00000007:0 (ECX), word 16 */
> > #define X86_FEATURE_AVX512VBMI          (16*32+ 1) /* AVX512 Vector Bit Manipulation instructions*/
> > #define X86_FEATURE_UMIP                (16*32+ 2) /* User Mode Instruction Protection */
>
> vs glibc:
>
> > /* ECX.  */
> > #define bit_cpu_PREFETCHWT1   (1u << 0)

Does platform/x86.h need to be updated as well? Although that might be harder
to change as its user facing.
> > #define bit_cpu_AVX512_VBMI   (1u << 1)
> > #define bit_cpu_UMIP          (1u << 2)
>
> Tested on the one machine I could find in our inventory that set that flag:
>
> - FAIL: elf/tst-cpu-features-cpuinfo
> - FAIL: elf/tst-cpu-features-cpuinfo-static
> -     27 FAIL
> +     23 FAIL
>
> (there were two unrelated timeouts in the "before" results)
>
> From c4a62abbeac4ced531ced3999a2cd2d4fab6bdc6 Mon Sep 17 00:00:00 2001
> From: DJ Delorie <dj@redhat.com>
> Date: Thu, 9 Mar 2023 22:32:54 -0500
> Subject: x86: Don't check PREFETCHWT1 in tst-cpu-features-cpuinfo.c
>
> Don't check PREFETCHWT1 against /proc/cpuinfo since kernel doesn't report
> PREFETCHWT1 in /proc/cpuinfo.
>
> diff --git a/sysdeps/x86/tst-cpu-features-cpuinfo.c b/sysdeps/x86/tst-cpu-features-cpuinfo.c
> index c25240774e..e963592c4b 100644
> --- a/sysdeps/x86/tst-cpu-features-cpuinfo.c
> +++ b/sysdeps/x86/tst-cpu-features-cpuinfo.c
> @@ -217,7 +217,10 @@ do_test (int argc, char **argv)
>    fails += CHECK_PROC (pku, PKU);
>    fails += CHECK_PROC (popcnt, POPCNT);
>    fails += CHECK_PROC (3dnowprefetch, PREFETCHW);
> +#if 0
> +  /* NB: /proc/cpuinfo doesn't report this feature.  */
>    fails += CHECK_PROC (prefetchwt1, PREFETCHWT1);
> +#endif
>  #if 0
>    /* NB: /proc/cpuinfo doesn't report this feature.  */
>    fails += CHECK_PROC (ptwrite, PTWRITE);
>