Re: [PATCH v2 12/31] x86: Fix fallback for wcsncmp_avx2 in strcmp-avx2.S [BZ #28896]

Re: [PATCH v2 12/31] x86: Fix fallback for wcsncmp_avx2 in strcmp-avx2.S [BZ #28896]

[Sunil Pandey]

On Thu, Mar 24, 2022 at 2:59 PM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Thu, Mar 24, 2022 at 2:43 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > On Thu, Mar 24, 2022 at 4:26 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > >
> > > On Thu, Mar 24, 2022 at 1:50 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> > > >
> > > > Overflow case for __wcsncmp_avx2_rtm should be __wcscmp_avx2_rtm not
> > > > __wcscmp_avx2.
> > > >
> > > > commit ddf0992cf57a93200e0c782e2a94d0733a5a0b87
> > > > Author: Noah Goldstein <goldstein.w.n@gmail.com>
> > > > Date:   Sun Jan 9 16:02:21 2022 -0600
> > > >
> > > >     x86: Fix __wcsncmp_avx2 in strcmp-avx2.S [BZ# 28755]
> > > >
> > > > Set the wrong fallback function for `__wcsncmp_avx2_rtm`. It was set
> > > > to fallback on to `__wcscmp_avx2` instead of `__wcscmp_avx2_rtm` which
> > > > can cause spurious aborts.
> > > >
> > > > This change will need to be backported.
> > > >
> > > > All string/memory tests pass.
> > > > ---
> > > >  sysdeps/x86/tst-strncmp-rtm.c          | 15 +++++++++++++++
> > > >  sysdeps/x86_64/multiarch/strcmp-avx2.S |  2 +-
> > > >  2 files changed, 16 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/sysdeps/x86/tst-strncmp-rtm.c b/sysdeps/x86/tst-strncmp-rtm.c
> > > > index 300bc8c281..a3b14e72ff 100644
> > > > --- a/sysdeps/x86/tst-strncmp-rtm.c
> > > > +++ b/sysdeps/x86/tst-strncmp-rtm.c
> > > > @@ -70,6 +70,16 @@ function_overflow (void)
> > > >      return 1;
> > > >  }
> > > >
> > > > +__attribute__ ((noinline, noclone))
> > > > +static int
> > > > +function_overflow2 (void)
> > > > +{
> > > > +  if (STRNCMP (string1, string2, SIZE_MAX >> 4) == 0)
> > > > +    return 0;
> > > > +  else
> > > > +    return 1;
> > > > +}
> > > > +
> > > >  static int
> > > >  do_test (void)
> > > >  {
> > > > @@ -77,5 +87,10 @@ do_test (void)
> > > >    if (status != EXIT_SUCCESS)
> > > >      return status;
> > > >    status = do_test_1 (TEST_NAME, LOOP, prepare, function_overflow);
> > > > +  if (status != EXIT_SUCCESS)
> > > > +    return status;
> > > > +  status = do_test_1 (TEST_NAME, LOOP, prepare, function_overflow2);
> > > > +  if (status != EXIT_SUCCESS)
> > > > +    return status;
> > > >    return status;
> > > >  }
> > > > diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > > > index 52ff5ad724..86a86b68e3 100644
> > > > --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > > > +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > > > @@ -122,7 +122,7 @@ ENTRY(STRCMP)
> > > >            are cases where length is large enough that it can never be a
> > > >            bound on valid memory so just use wcscmp.  */
> > > >         shrq    $56, %rcx
> > > > -       jnz     __wcscmp_avx2
> > > > +       jnz     OVERFLOW_STRCMP
> > > >
> > > >         leaq    (, %rdx, 4), %rdx
> > > >  #  endif
> > > > --
> > > > 2.25.1
> > > >
> > >
> > > LGTM.   Verified on AVX2 machine with RTM.  Without the fix,
> > > the new testcase failed.
> >
> > And that w/ the fix it passes?
>
> Yes.
>
> > >
> > > Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
> > >
> > > Thanks.
> > >
> > > --
> > > H.J.
>
>
>
> --
> H.J.

I would like to backport this patch to release branches.
Any comments or objections?

--Sunil