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

[Carlos O'Donell]

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.