Re: [PATCH] fstatat: support NULL if AT_EMPTY_PATH

On 2026-06-23 11:01, Bruno Haible wrote:
> Yesterday's CI of GNU m4 (newest m4 sources, newest gnulib sources, on
> Alpine Linux) shows a test failure:
> 
> 
> FAIL: test-fstatat
> ==================
> 
> Segmentation fault (core dumped)
> FAIL test-fstatat (exit status: 139)
> 
> 
> I reproduce it in Alpine Linux 3.24.1 (but not in 3.22 nor 3.20).

Thanks for the bug report. Unfortunately portal.cfarm.net lists only 
Alpine 3.22 and 3.23.

Was this a crosscompile, or native? Was it x86-64 or some other 
platform? Is the build log public?


> The backtrace is:
>    test-fstatat.c:111
>      -> musl/src/stat/fstatat.c:147
>         -> musl/src/stat/fstatat.c:81
> 
> That line reads:
>          if (flag==AT_EMPTY_PATH && fd>=0 && !*path) {

The backtrace suggests that REPLACE_FSTATAT was 0, because there is no 
rentry for Gnulib's lib/fstatat.c. However, REPLACE_FSTATAT should have 
been 1 because the musl source code doesn't support AT_EMPTY_PATH with a 
null pointer .

Can you verify whether fstatat is being replaced by checking that 
m4/lib/sys/stat.h contains lines like the following?

   #if 1
   # if 1
   #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
   #   undef fstatat
   #   define fstatat rpl_fstatat
   #  endif
   _GL_FUNCDECL_RPL (fstatat, int,

Can you look in config.log for lines like the following?

   ... checking whether fstatat+AT_EMPTY_PATH allows null file
   ...
   ... result: yes

What happens when you compile and run the following program? What's the 
tail of "strace ./a.out"? (This is the program 'configure' should be 
running to see whether AT_EMPTY_PATH works with a null pointer.)

   #include <stddef.h>
   #include <fcntl.h>
   #include <sys/stat.h>
   #ifndef AT_EMPTY_PATH
   # define AT_EMPTY_PATH 0
   #endif
   #if __GLIBC__ && ! (2 < __GLIBC__ + (41 <= __GLIBC_MINOR__))
    #error "glibc 2.40 and earlier can fail with null file"
   #endif

   int
   main (void)
   {
     struct stat st;
     return
       (AT_EMPTY_PATH
        && fstatat (AT_FDCWD, NULL, &st, AT_EMPTY_PATH) < 0);
   }

What is the output of the shell command 'nm -g lib/libm4_a-fstatat.o'?

Your bug report prompted me to update GNU m4's Gnulib to the current 
version, and fix some glitches I noticed on Fedora 44. But I don't think 
this fixed your bug.