[binutils-gdb] aarch64: Fix out-of-range branch veneers when --fix-cortex-a53-843419

[Richard Earnshaw]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d3af4016a645db372ba6812eee651ac5e3eb9159

commit d3af4016a645db372ba6812eee651ac5e3eb9159
Author: Richard Earnshaw <rearnsha@arm.com>
Date:   Tue Dec 16 14:08:10 2025 +0000

    aarch64: Fix out-of-range branch veneers when --fix-cortex-a53-843419
    
    The erratum mitigation support for the Cortex-A53 843419 erratum
    inserts a new stub for every possible instance of the erratum.  Since
    each stub ends up inserting 4k of space into the binary, in order to
    avoid perturbing the alignment of other potential erratum sequences we
    can end up adding substantially more space than the distance to the
    next long-branch stub that we've prepared for.
    
    The problem is, fundamentally a phase ordering problem, but that's
    easily resolvable by running the 843419 erratum pass first and then
    creating the stub groups once that is done.  In this way we take into
    account the additional padding when forming the groups to ensure that
    they remain within range.

Diff:
---
 bfd/elfnn-aarch64.c | 44 +++++++++++++++++++++++++-------------------
 1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index a3fd1dd7561..00a4f171cf1 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -4772,49 +4772,55 @@ elfNN_aarch64_size_stubs (bfd *output_bfd,
       stub_group_size = 127 * 1024 * 1024;
     }
 
-  group_sections (htab, stub_group_size, stubs_always_before_branch);
-
-  (*htab->layout_sections_again) ();
-
-  if (htab->fix_erratum_835769)
+  /* The 843419 erratum fix inserts stub sections in place, not in
+     the section groups.  Running this after we have created the stub
+     groups can perturb the calculations and cause the stub groups
+     that have been created to be out of range.  Avoid this by running
+     this pass first and then creating the groups once we know how much
+     code this mitigation will insert.  */
+  if (htab->fix_erratum_843419 != ERRAT_NONE)
     {
       bfd *input_bfd;
 
       for (input_bfd = info->input_bfds;
-	   input_bfd != NULL; input_bfd = input_bfd->link.next)
+	   input_bfd != NULL;
+	   input_bfd = input_bfd->link.next)
 	{
+	  asection *section;
+
 	  if (!is_aarch64_elf (input_bfd)
 	      || (input_bfd->flags & BFD_LINKER_CREATED) != 0)
 	    continue;
 
-	  if (!_bfd_aarch64_erratum_835769_scan (input_bfd, info,
-						 &num_erratum_835769_fixes))
-	    return false;
+	  for (section = input_bfd->sections;
+	       section != NULL;
+	       section = section->next)
+	    if (!_bfd_aarch64_erratum_843419_scan (input_bfd, section, info))
+	      return false;
 	}
 
       _bfd_aarch64_resize_stubs (htab);
       (*htab->layout_sections_again) ();
     }
 
-  if (htab->fix_erratum_843419 != ERRAT_NONE)
+  group_sections (htab, stub_group_size, stubs_always_before_branch);
+
+  (*htab->layout_sections_again) ();
+
+  if (htab->fix_erratum_835769)
     {
       bfd *input_bfd;
 
       for (input_bfd = info->input_bfds;
-	   input_bfd != NULL;
-	   input_bfd = input_bfd->link.next)
+	   input_bfd != NULL; input_bfd = input_bfd->link.next)
 	{
-	  asection *section;
-
 	  if (!is_aarch64_elf (input_bfd)
 	      || (input_bfd->flags & BFD_LINKER_CREATED) != 0)
 	    continue;
 
-	  for (section = input_bfd->sections;
-	       section != NULL;
-	       section = section->next)
-	    if (!_bfd_aarch64_erratum_843419_scan (input_bfd, section, info))
-	      return false;
+	  if (!_bfd_aarch64_erratum_835769_scan (input_bfd, info,
+						 &num_erratum_835769_fixes))
+	    return false;
 	}
 
       _bfd_aarch64_resize_stubs (htab);