[binutils-gdb] [bfd] Fix data race in bfd_check_format_matches

[Tom de Vries]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=bd14b62e42e11a374a1f90d194db28c5b37c43fb

commit bd14b62e42e11a374a1f90d194db28c5b37c43fb
Author: Tom de Vries <tdevries@suse.de>
Date:   Tue Jan 27 10:40:06 2026 +0100

    [bfd] Fix data race in bfd_check_format_matches
    
    At the start of bfd_check_format_matches, we have this read of_bfd_section_id:
    ...
      unsigned int initial_section_id = _bfd_section_id;
    ...
    
    In order to access the variable, it is required to hold the global BFD lock.
    
    The function already contains code acquiring the lock:
    ...
      /* Locking is required here in order to manage _bfd_section_id.  */
      if (!bfd_lock ())
        {
          bfd_cache_set_uncloseable (abfd, old_in_format_matches, NULL);
          free (matching_vector);
          return false;
        }
    ...
    so fix this by moving the read after it.
    
    Tested on x86_64-linux.
    
    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33826

Diff:
---
 bfd/format.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/bfd/format.c b/bfd/format.c
index f35230eb28b..2d35f59cd85 100644
--- a/bfd/format.c
+++ b/bfd/format.c
@@ -452,7 +452,7 @@ bfd_check_format_matches (bfd *abfd, bfd_format format, char ***matching)
   const bfd_target *fail_targ;
   int match_count, best_count, best_match;
   int ar_match_index;
-  unsigned int initial_section_id = _bfd_section_id;
+  unsigned int initial_section_id;
   struct bfd_preserve preserve, preserve_match;
   bfd_cleanup cleanup = NULL;
   struct per_xvec_messages messages = { abfd, PER_XVEC_NO_TARGET, NULL, NULL };
@@ -492,6 +492,7 @@ bfd_check_format_matches (bfd *abfd, bfd_format format, char ***matching)
       free (matching_vector);
       return false;
     }
+  initial_section_id = _bfd_section_id;
 
   /* Presume the answer is yes.  */
   abfd->format = format;