[PATCH v2 3/6] objcopy: Remove SHT_LLVM_ADDRSIG sections by default.

[Tatsuyuki Ishi <ishitatsuyuki@gmail.com>]

addrsig entries copied by objcopy has historically been ignored by lld [1],
due to known caveats in case the symbol table is modified without updating
the addrsig section as well.

Now that bfd is able to insert the respective sh_link entry for the
section, the heuristic for broken addrsig section in [1] no longer works
and we need to explicitly remove the section to prevent silent corruption.
We also warn the user about this, so they will be aware of the caveat.

[1]: https://github.com/llvm/llvm-project/blob/09c2b7c35af8c4bad39f03e9f60df8bd07323028/lld/ELF/InputFiles.cpp#L540-L554
---
 binutils/objcopy.c | 26 +++++++++++++++++++++++++-
 1 file changed, 25 insertions(+), 1 deletion(-)

diff --git a/binutils/objcopy.c b/binutils/objcopy.c
index df87712df98..57d39558099 100644
--- a/binutils/objcopy.c
+++ b/binutils/objcopy.c
@@ -1316,10 +1316,20 @@ is_mergeable_note_section (bfd * abfd, asection * sec)
   return false;
 }
 
+static bool
+is_addrsig_section (bfd *abfd, asection *sec)
+{
+  if (bfd_get_flavour (abfd) == bfd_target_elf_flavour
+      && elf_section_data (sec)->this_hdr.sh_type == SHT_LLVM_ADDRSIG)
+    return true;
+
+  return false;
+}
+
 /* See if a non-group section is being removed.  */
 
 static bool
-is_strip_section_1 (bfd *abfd ATTRIBUTE_UNUSED, asection *sec)
+is_strip_section_1 (bfd *abfd, asection *sec)
 {
   if (find_section_list (bfd_section_name (sec), false, SECTION_CONTEXT_KEEP)
       != NULL)
@@ -1348,6 +1358,20 @@ is_strip_section_1 (bfd *abfd ATTRIBUTE_UNUSED, asection *sec)
 	return true;
     }
 
+  /* addrsig needs to be updated if the symtab is altered, but we don't know
+     how to read nor write it, so just throw it away to not confuse
+     downstream tools.  */
+  if (is_addrsig_section (abfd, sec))
+    {
+      non_fatal (_ ("warning: removing section %s to prevent corrupt addrsig "
+                    "information"),
+                 bfd_section_name (sec));
+      non_fatal (_ ("pass --remove-section=%1$s to suppress warning, or "
+                    "--keep-section=%1$s to override"),
+                 bfd_section_name (sec));
+      return true;
+    }
+
   if ((bfd_section_flags (sec) & SEC_DEBUGGING) != 0)
     {
       if (strip_symbols == STRIP_DEBUG
-- 
2.36.1