[v2] Fix stringop-overflow warning in bug-regex19.c.

  Starting with commit
26492c0a14966c32c43cd6ca1d0dca5e62c6cfef
"Annotate additional APIs with GCC attribute access.",
gcc emits this warning on s390x:
In function ‘do_one_test’,
    inlined from ‘do_mb_tests’ at bug-regex19.c:385:11:
bug-regex19.c:271:9: error: ‘re_search’ specified size 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
  271 |   res = re_search (&regbuf, test->string, strlen (test->string),
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  272 |      test->start, strlen (test->string) - test->start, NULL);
      |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from ../include/regex.h:2,
                 from bug-regex19.c:22:
bug-regex19.c: In function ‘do_mb_tests’:
../posix/regex.h:554:17: note: in a call to function ‘re_search’ declared with attribute ‘read_only (2, 3)’
  554 | extern regoff_t re_search (struct re_pattern_buffer *__buffer,
      |                 ^~~~~~~~~
...

The function do_one_test is inlined into do_mb_tests on s390x (at least with
gcc 10).  If do_one_test is marked with __attribute__ ((noinline)), there are
no warnings on s390x. If do_one_test is marked with
__attribute__ ((always_inline)), there are the same warnings on x86_64.

test->string points to a variable length array on stack of do_mb_tests
and the content is generated based on the passed test struct.

According to Martin Sebor, this is a false positive caused by the same bug as
the one in nss/makedb.c.  It's fixed in GCC 11 and will also be available in
the next GCC 10.4 release.
---
 posix/bug-regex19.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
  

On 17/05/2021 16:19, Stefan Liebler wrote:
> Starting with commit
> 26492c0a14966c32c43cd6ca1d0dca5e62c6cfef
> "Annotate additional APIs with GCC attribute access.",
> gcc emits this warning on s390x:
> In function ‘do_one_test’,
>     inlined from ‘do_mb_tests’ at bug-regex19.c:385:11:
> bug-regex19.c:271:9: error: ‘re_search’ specified size 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Werror=stringop-overflow=]
>   271 |   res = re_search (&regbuf, test->string, strlen (test->string),
>       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   272 |      test->start, strlen (test->string) - test->start, NULL);
>       |      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In file included from ../include/regex.h:2,
>                  from bug-regex19.c:22:
> bug-regex19.c: In function ‘do_mb_tests’:
> ../posix/regex.h:554:17: note: in a call to function ‘re_search’ declared with attribute ‘read_only (2, 3)’
>   554 | extern regoff_t re_search (struct re_pattern_buffer *__buffer,
>       |                 ^~~~~~~~~
> ...
> 
> The function do_one_test is inlined into do_mb_tests on s390x (at least with
> gcc 10).  If do_one_test is marked with __attribute__ ((noinline)), there are
> no warnings on s390x. If do_one_test is marked with
> __attribute__ ((always_inline)), there are the same warnings on x86_64.
> 
> test->string points to a variable length array on stack of do_mb_tests
> and the content is generated based on the passed test struct.
> 
> According to Martin Sebor, this is a false positive caused by the same bug as
> the one in nss/makedb.c.  It's fixed in GCC 11 and will also be available in
> the next GCC 10.4 release.
> ---
>  posix/bug-regex19.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/posix/bug-regex19.c b/posix/bug-regex19.c
> index 9bbffb17e3..b3fee0a730 100644
> --- a/posix/bug-regex19.c
> +++ b/posix/bug-regex19.c
> @@ -24,6 +24,7 @@
>  #include <stdlib.h>
>  #include <string.h>
>  #include <locale.h>
> +#include <libc-diag.h>
>  
>  #define BRE RE_SYNTAX_POSIX_BASIC
>  #define ERE RE_SYNTAX_POSIX_EXTENDED
> @@ -268,8 +269,17 @@ do_one_test (const struct test_s *test, const char *fail)
>        return 1;
>      }
>  
> +#if __GNUC_PREREQ (10, 0) && !__GNUC_PREREQ (11, 0)
> +  DIAG_PUSH_NEEDS_COMMENT;
> +  /* Avoid GCC 10 false positive warning: specified size exceeds maximum
> +     object size.  */
> +  DIAG_IGNORE_NEEDS_COMMENT (10, "-Wstringop-overflow");
> +#endif
>    res = re_search (&regbuf, test->string, strlen (test->string),
>  		   test->start, strlen (test->string) - test->start, NULL);
> +#if __GNUC_PREREQ (10, 0) && !__GNUC_PREREQ (11, 0)
> +  DIAG_POP_NEEDS_COMMENT;
> +#endif
>    if (res != test->res)
>      {
>        printf ("%sre_search \"%s\" \"%s\" failed: %d (expected %d)\n",
> @@ -280,8 +290,17 @@ do_one_test (const struct test_s *test, const char *fail)
>  
>    if (test->res > 0 && test->start == 0)
>      {
> +#if __GNUC_PREREQ (10, 0) && !__GNUC_PREREQ (11, 0)
> +  DIAG_PUSH_NEEDS_COMMENT;
> +  /* Avoid GCC 10 false positive warning: specified size exceeds maximum
> +     object size.  */
> +  DIAG_IGNORE_NEEDS_COMMENT (10, "-Wstringop-overflow");
> +#endif
>        res = re_search (&regbuf, test->string, strlen (test->string),
>  		       test->res, strlen (test->string) - test->res, NULL);
> +#if __GNUC_PREREQ (10, 0) && !__GNUC_PREREQ (11, 0)
> +  DIAG_POP_NEEDS_COMMENT;
> +#endif
>        if (res != test->res)
>  	{
>  	  printf ("%sre_search from expected \"%s\" \"%s\" failed: %d (expected %d)\n",
> 
Committed after response from Martin:
https://sourceware.org/pipermail/libc-alpha/2021-May/126416.html

Thanks,
Stefan