Re: [PATCH v3] x86: Fallback {str|wcs}cmp RTM in the ncmp overflow case [BZ #28896]

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Feb 16, 2022 at 6:08 AM Carlos O'Donell <carlos@redhat.com> wrote:
>
> On 2/16/22 08:17, H.J. Lu via Libc-alpha wrote:
> > On Wed, Feb 16, 2022 at 12:09 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               | 14 +++++++++++++-
> >>  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, 20 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..ebc94a3a6d 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 +46,19 @@ 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);
> >> +  return (do_test_1 ("strncmp", LOOP, prepare, function)
> >> +         || do_test_1 ("strncmp", LOOP, prepare, function_overflow));
> >>  }
> >> diff --git a/sysdeps/x86_64/multiarch/strcmp-avx2.S b/sysdeps/x86_64/multiarch/strcmp-avx2.S
> >> index 99e5349be8..6da0e1a248 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.
> >
>
> This fails CI for i686.
> https://patchwork.sourceware.org/project/glibc/patch/20220216080935.3284536-1-goldstein.w.n@gmail.com/
>
> --
> Cheers,
> Carlos.
>

Hi Noah,

We need this change on top of your patch:

diff --git a/sysdeps/x86/tst-strncmp-rtm.c b/sysdeps/x86/tst-strncmp-rtm.c
index ebc94a3a6d..9e20abaacc 100644
--- a/sysdeps/x86/tst-strncmp-rtm.c
+++ b/sysdeps/x86/tst-strncmp-rtm.c
@@ -59,6 +59,9 @@ function_overflow (void)
 static int
 do_test (void)
 {
-  return (do_test_1 ("strncmp", LOOP, prepare, function)
-    || do_test_1 ("strncmp", LOOP, prepare, function_overflow));
+  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;
 }

-- 
H.J.