[binutils-gdb] aarch64: setup_gnu_properties only creates the notes section when none exists

[Matthieu Longo]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=2cf9acb79ffdd1d445eaa492c24825a0bc273536

commit 2cf9acb79ffdd1d445eaa492c24825a0bc273536
Author: Matthieu Longo <matthieu.longo@arm.com>
Date:   Thu Feb 20 16:14:03 2025 +0000

    aarch64: setup_gnu_properties only creates the notes section when none exists
    
    The creation of .note.gnu.property section should not be based on the
    presence of GNU properties, but rather on whether this section exits
    or not.
    However, there is one exception to this: PR23900 [1]. Old linkers were
    treating .note.gnu.property as a generic note section, so old objects
    might contain properties inside .note instead of .note.gnu.property. In
    this case, the section won't be detected but the properties are still
    parsed. So the absence of the .note.gnu.property section is necessary
    but not enough to create the section. The condition of the creation of
    the section has also to include the absence of GNU properties.
    
    [1] PR23900: https://sourceware.org/bugzilla/show_bug.cgi?id=23900

Diff:
---
 bfd/elfxx-aarch64.c | 43 ++++++++++++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 17 deletions(-)

diff --git a/bfd/elfxx-aarch64.c b/bfd/elfxx-aarch64.c
index 2c2424c41db..804d0a5ee13 100644
--- a/bfd/elfxx-aarch64.c
+++ b/bfd/elfxx-aarch64.c
@@ -704,29 +704,29 @@ _bfd_aarch64_elf_write_core_note (bfd *abfd, char *buf, int *bufsiz, int note_ty
 static bfd *
 _bfd_aarch64_elf_find_1st_bfd_input_with_gnu_property (
   struct bfd_link_info *info,
-  bool *has_gnu_property)
+  bool *has_note_section)
 {
-  BFD_ASSERT (has_gnu_property);
-  const struct elf_backend_data *obfd = get_elf_backend_data (info->output_bfd);
+  const struct elf_backend_data *be = get_elf_backend_data (info->output_bfd);
   bfd *pbfd = info->input_bfds;
-  bfd *prev = NULL;
+  bfd *prev_bfd = NULL;
   for (; pbfd != NULL; pbfd = pbfd->link.next)
     if (bfd_get_flavour (pbfd) == bfd_target_elf_flavour
 	&& bfd_count_sections (pbfd) != 0
 	&& (pbfd->flags & (DYNAMIC | BFD_PLUGIN | BFD_LINKER_CREATED)) == 0
-	&& (obfd->elf_machine_code
+	&& (be->elf_machine_code
 	    == get_elf_backend_data (pbfd)->elf_machine_code)
-	&& (obfd->s->elfclass == get_elf_backend_data (pbfd)->s->elfclass))
+	&& (be->s->elfclass == get_elf_backend_data (pbfd)->s->elfclass))
       {
+	prev_bfd = pbfd;
+
 	/* Does the input have a list of GNU properties ? */
 	if (elf_properties (pbfd) != NULL)
-	  {
-	    *has_gnu_property = true;
-	    return pbfd;
-	  }
-	prev = pbfd;
+	  break;
       }
-  return prev;
+  if (prev_bfd != NULL)
+    *has_note_section =
+      bfd_get_section_by_name (prev_bfd, NOTE_GNU_PROPERTY_SECTION_NAME) != NULL;
+  return prev_bfd;
 }
 
 /* Create a GNU property section for the given bfd input.  */
@@ -861,19 +861,28 @@ _bfd_aarch64_elf_link_setup_gnu_properties (struct bfd_link_info *info)
   struct elf_aarch64_obj_tdata *tdata = elf_aarch64_tdata (info->output_bfd);
   uint32_t outprop = tdata->gnu_property_aarch64_feature_1_and;
 
-  bool has_gnu_property = false;
+  bool has_note_section = false;
   bfd *ebfd =
     _bfd_aarch64_elf_find_1st_bfd_input_with_gnu_property (info,
-							   &has_gnu_property);
+							   &has_note_section);
 
   /* If ebfd != NULL it is either an input with property note or the last input.
      Either way if we have an output GNU property that was provided, we should
      add it (by creating a section if needed).  */
   if (ebfd != NULL)
     {
-      /* If no GNU property node was found, create the GNU property note
-	 section.  */
-      if (!has_gnu_property)
+      /* If no GNU property note section was found, create one.
+
+	 Note: If there is no .gnu.note.property section, we might think that
+	 elf_properties (ebfd) is always NULL.  However, this is not always
+	 true.  In PR23900: old linkers were treating .note.gnu.property as a
+	 generic note section, so old objects might contain properties inside
+	 .note instead of .note.gnu.property. In this case, the section won't be
+	 detected but the properties are still parsed. Consequently,
+	 elf_properties (ebfd) is populated and different from NULL (see
+	 https://sourceware.org/bugzilla/show_bug.cgi?id=23900 for more
+	 details).  */
+      if (!has_note_section && elf_properties (ebfd) == NULL)
 	_bfd_aarch64_elf_create_gnu_property_section (info, ebfd);
 
       /* Merge the found input property with output properties. Note: if no