Fix Hurd getcwd build with GCC >= 13

The build of glibc for i686-gnu has been failing for a while with GCC
mainline / GCC 13:

../sysdeps/mach/hurd/getcwd.c: In function '__hurd_canonicalize_directory_name_internal':
../sysdeps/mach/hurd/getcwd.c:242:48: error: pointer 'file_name' may be used after 'realloc' [-Werror=use-after-free]
  242 |                   file_namep = &buf[file_namep - file_name + size / 2];
      |                                     ~~~~~~~~~~~^~~~~~~~~~~
../sysdeps/mach/hurd/getcwd.c:236:25: note: call to 'realloc' here
  236 |                   buf = realloc (file_name, size);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~~~

Fix by doing the subtraction before the reallocation.

Tested with build-many-glibcs.py for i686-gnu.

[samuel.thibault@ens-lyon.rg: Removed mention of this being a bug]

Message-Id: <18587337-7815-4056-ebd0-724df262d591@codesourcery.com>

diff --git a/sysdeps/mach/hurd/getcwd.c b/sysdeps/mach/hurd/getcwd.c
index f24b35b..cd3aedd 100644 (file)
--- a/sysdeps/mach/hurd/getcwd.c
+++ b/sysdeps/mach/hurd/getcwd.c
@@ -222,8 +222,9 @@ __hurd_canonicalize_directory_name_internal (file_t thisdir,
       found:
        {
          /* Prepend the directory name just discovered.  */
+         size_t offset = file_namep - file_name;
 
-         if (file_namep - file_name < d->d_namlen + 1)
+         if (offset < d->d_namlen + 1)
            {
              if (orig_size > 0)
                {
@@ -239,7 +240,7 @@ __hurd_canonicalize_directory_name_internal (file_t thisdir,
                      free (file_name);
                      return NULL;
                    }
-                 file_namep = &buf[file_namep - file_name + size / 2];
+                 file_namep = &buf[offset + size / 2];
                  file_name = buf;
                  /* Move current contents up to the end of the buffer.
                     This is guaranteed to be non-overlapping.  */