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

[Aurelien Jarno <aurelien@aurel32.net>]

On 2022-10-01 15:11, Noah Goldstein wrote:
> 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

I didn't included those, because 'bzhil' is only used the 'n' case. That
said with the 'shlx' you mentioned in the other email, we should indeed
include that one.

> strrchr
> wcsrchr
> wcscmp

Same for those, I missed 'shlx'. I'll fix that.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net