[PATCH v5] x86: Fallback {str|wcs}cmp RTM in the ncmp overflow case [BZ #28896]

[Sunil Pandey]

On Thu, Feb 17, 2022 at 11:21 AM H.J. Lu via Libc-alpha
<libc-alpha@sourceware.org> wrote:
>
> On Thu, Feb 17, 2022 at 11:15 AM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> > In the overflow fallback strncmp-avx2-rtm and wcsncmp-avx2-rtm would
> > call strcmp-avx2 and wcsncmp-avx2 respectively. This would have
> > not checks around vzeroupper and would trigger spurious
> > aborts. This commit fixes that.
> >
> > test-strcmp, test-strncmp, test-wcscmp, and test-wcsncmp all pass on
> > AVX2 machines with and without RTM.
> >
> > Co-authored-by: H.J. Lu <hjl.tools@gmail.com>
> > ---
> >  sysdeps/x86/Makefile                        |  2 +-
> >  sysdeps/x86/tst-strncmp-rtm.c               | 17 ++++++++++++++++-
> >  sysdeps/x86_64/multiarch/strcmp-avx2.S      |  8 ++------
> >  sysdeps/x86_64/multiarch/strncmp-avx2-rtm.S |  1 +
> >  sysdeps/x86_64/multiarch/strncmp-avx2.S     |  1 +
> >  sysdeps/x86_64/multiarch/wcsncmp-avx2-rtm.S |  2 +-
> >  sysdeps/x86_64/multiarch/wcsncmp-avx2.S     |  2 +-
> >  7 files changed, 23 insertions(+), 10 deletions(-)
> >
> > diff --git a/sysdeps/x86/Makefile b/sysdeps/x86/Makefile
> > index 6cf708335c..d110f7b7f2 100644
> > --- a/sysdeps/x86/Makefile
> > +++ b/sysdeps/x86/Makefile
> > @@ -109,7 +109,7 @@ CFLAGS-tst-memset-rtm.c += -mrtm
> >  CFLAGS-tst-strchr-rtm.c += -mrtm
> >  CFLAGS-tst-strcpy-rtm.c += -mrtm
> >  CFLAGS-tst-strlen-rtm.c += -mrtm
> > -CFLAGS-tst-strncmp-rtm.c += -mrtm
> > +CFLAGS-tst-strncmp-rtm.c += -mrtm -Wno-error
> >  CFLAGS-tst-strrchr-rtm.c += -mrtm
> >  endif
> >
> > diff --git a/sysdeps/x86/tst-strncmp-rtm.c b/sysdeps/x86/tst-strncmp-rtm.c
> > index 09ed6fa0d6..9e20abaacc 100644
> > --- a/sysdeps/x86/tst-strncmp-rtm.c
> > +++ b/sysdeps/x86/tst-strncmp-rtm.c
> > @@ -16,6 +16,7 @@
> >     License along with the GNU C Library; if not, see
> >     <https://www.gnu.org/licenses/>.  */
> >
> > +#include <stdint.h>
> >  #include <tst-string-rtm.h>
> >
> >  #define LOOP 3000
> > @@ -45,8 +46,22 @@ function (void)
> >      return 1;
> >  }
> >
> > +__attribute__ ((noinline, noclone))
> > +static int
> > +function_overflow (void)
> > +{
> > +  if (strncmp (string1, string2, SIZE_MAX) == 0)
> > +    return 0;
> > +  else
> > +    return 1;
> > +}
> > +
> >  static int
> >  do_test (void)
> >  {
> > -  return do_test_1 ("strncmp", LOOP, prepare, function);
> > +  int status = do_test_1 ("strncmp", LOOP, prepare, function);
> > +  if (status != EXIT_SUCCESS)
> > +    return status;
> > +  status = do_test_1 ("strncmp", LOOP, prepare, function_overflow);
> > +  return status;
> >  }
> > diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > index 07a5a2c889..52ff5ad724 100644
> > --- a/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> > @@ -193,10 +193,10 @@ L(ret_zero):
> >         .p2align 4,, 5
> >  L(one_or_less):
> >         jb      L(ret_zero)
> > -#  ifdef USE_AS_WCSCMP
> >         /* 'nbe' covers the case where length is negative (large
> >            unsigned).  */
> > -       jnbe    __wcscmp_avx2
> > +       jnbe    OVERFLOW_STRCMP
> > +#  ifdef USE_AS_WCSCMP
> >         movl    (%rdi), %edx
> >         xorl    %eax, %eax
> >         cmpl    (%rsi), %edx
> > @@ -205,10 +205,6 @@ L(one_or_less):
> >         negl    %eax
> >         orl     $1, %eax
> >  #  else
> > -       /* 'nbe' covers the case where length is negative (large
> > -          unsigned).  */
> > -
> > -       jnbe    __strcmp_avx2
> >         movzbl  (%rdi), %eax
> >         movzbl  (%rsi), %ecx
> >         subl    %ecx, %eax
> > diff --git a/sysdeps/x86_64/multiarch/strncmp-avx2-rtm.S b/sysdeps/x86_64/multiarch/strncmp-avx2-rtm.S
> > index 37d1224bb9..68bad365ba 100644
> > --- a/sysdeps/x86_64/multiarch/strncmp-avx2-rtm.S
> > +++ b/sysdeps/x86_64/multiarch/strncmp-avx2-rtm.S
> > @@ -1,3 +1,4 @@
> >  #define STRCMP __strncmp_avx2_rtm
> >  #define USE_AS_STRNCMP 1
> > +#define OVERFLOW_STRCMP        __strcmp_avx2_rtm
> >  #include "strcmp-avx2-rtm.S"
> > diff --git a/sysdeps/x86_64/multiarch/strncmp-avx2.S b/sysdeps/x86_64/multiarch/strncmp-avx2.S
> > index 1678bcc235..f138e9f1fd 100644
> > --- a/sysdeps/x86_64/multiarch/strncmp-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/strncmp-avx2.S
> > @@ -1,3 +1,4 @@
> >  #define STRCMP __strncmp_avx2
> >  #define USE_AS_STRNCMP 1
> > +#define OVERFLOW_STRCMP __strcmp_avx2
> >  #include "strcmp-avx2.S"
> > diff --git a/sysdeps/x86_64/multiarch/wcsncmp-avx2-rtm.S b/sysdeps/x86_64/multiarch/wcsncmp-avx2-rtm.S
> > index 4e88c70cc6..f467582cbe 100644
> > --- a/sysdeps/x86_64/multiarch/wcsncmp-avx2-rtm.S
> > +++ b/sysdeps/x86_64/multiarch/wcsncmp-avx2-rtm.S
> > @@ -1,5 +1,5 @@
> >  #define STRCMP __wcsncmp_avx2_rtm
> >  #define USE_AS_STRNCMP 1
> >  #define USE_AS_WCSCMP 1
> > -
> > +#define OVERFLOW_STRCMP        __wcscmp_avx2_rtm
> >  #include "strcmp-avx2-rtm.S"
> > diff --git a/sysdeps/x86_64/multiarch/wcsncmp-avx2.S b/sysdeps/x86_64/multiarch/wcsncmp-avx2.S
> > index 4fa1de4d3f..e9ede522b8 100644
> > --- a/sysdeps/x86_64/multiarch/wcsncmp-avx2.S
> > +++ b/sysdeps/x86_64/multiarch/wcsncmp-avx2.S
> > @@ -1,5 +1,5 @@
> >  #define STRCMP __wcsncmp_avx2
> >  #define USE_AS_STRNCMP 1
> >  #define USE_AS_WCSCMP 1
> > -
> > +#define OVERFLOW_STRCMP        __wcscmp_avx2
> >  #include "strcmp-avx2.S"
> > --
> > 2.25.1
> >
>
> LGTM.
>
> Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
>
> Thanks.
>
> --
> H.J.

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

Patch attached, it fixes BZ# 29127.

--Sunil
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