Re: [PATCH 0/4] x86: Fix AVX2 string functions requiring BMI2 or LZCNT (BZ #29611)

[Noah Goldstein <goldstein.w.n@gmail.com>]

On Sat, Oct 1, 2022 at 12:09 PM Aurelien Jarno <aurelien@aurel32.net> wrote:
>
> Some early Intel Haswell CPU have AVX2 instructions, but do not have
> BMI2 instructions. Some AVX2 string functions only check for AVX2, but
> use BMI2 or LZCNT instructions. This patchset tries to fix that.
>
> While most fixes only change ifunc-impl-list.c, and thus only concerns
> the testsuite, the strn(case)cmp is a real issue affecting early Intel
> Haswell CPU, reported to affect Debian Sid and Fedora Rawhide.
>
> On the other hand, the check for LZCNT in memrchr is purely for
> correctness, I am not aware of a CPU implementing AVX2 without LZCNT.
>
> This has been tested by remplacing all BMI2 and LZCNT instruction in the
> source code by the "ud2" instruction and disabling the BMI1, BMI2
> feature detection, and running the testsuite.
>
> Resolves: BZ #29611
>
> Aurelien Jarno (4):
>   x86: include BMI1 and BMI2 in x86-64-v3 level
>   x86-64: Require BMI2 for AVX2 strn(case)cmp and wcsncmp
>     implementations
>   x86-64: Require BMI2 for AVX2 (raw|w)memchr implementations
>   x86-64: Require LZCNT for AVX2 memrchr implementation
>

We also need BMI2 check in ifunc-impl-list for:
strcasecmp
strcmp
strcasecmp_l
strrchr
wcsrchr
wcscmp

If you want you can make patches, otherwise I can.
>  sysdeps/x86/get-isa-level.h                 |  2 +
>  sysdeps/x86_64/multiarch/ifunc-avx2.h       |  1 +
>  sysdeps/x86_64/multiarch/ifunc-impl-list.c  | 44 +++++++++++++++------
>  sysdeps/x86_64/multiarch/ifunc-strcasecmp.h |  1 +
>  sysdeps/x86_64/multiarch/strncmp.c          |  4 +-
>  5 files changed, 38 insertions(+), 14 deletions(-)
>
> --
> 2.35.1
>