elf: Strip unreferenced weak undefined symbols

Linker will resolve an undefined symbol only if it is referenced by
relocation.  Unreferenced weak undefined symbols serve no purpose.
Weak undefined symbols appear in the dynamic symbol table only when they
are referenced by dynamic relocation.  Mark symbols with relocation and
strip undefined weak symbols if they don't have relocation and aren't
in the dynamic symbol table.

bfd/

	PR ld/31652
	* elf-bfd.h (elf_link_hash_entry): Add has_reloc.
	* elf-vxworks.c (elf_vxworks_emit_relocs): Set has_reloc.
	* elflink.c (_bfd_elf_link_output_relocs): Likewise.
	(elf_link_output_extsym): Strip undefined weak symbols if they
	don't have relocation and aren't in the dynamic symbol table.

ld/

	PR ld/31652
	* testsuite/ld-elf/elf.exp: Run undefweak tests.
	* testsuite/ld-elf/undefweak-1.rd: New file.
	* testsuite/ld-elf/undefweak-1a.s: Likewise.
	* testsuite/ld-elf/undefweak-1b.s: Likewise.
	* testsuite/ld-x86-64/weakundef-1.nd: Likewise.
	* testsuite/ld-x86-64/weakundef-1a.s: Likewise.
	* testsuite/ld-x86-64/weakundef-1b.s: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run undefweak tests.

3 files changed, 47 insertions, 28 deletions

diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index ef5dcb5..92a0287 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -232,6 +232,8 @@ struct elf_link_hash_entry
      a strong defined symbol alias.  U.ALIAS points to a list of aliases,
      the definition having is_weakalias clear.  */
   unsigned int is_weakalias : 1;
+  /* Symbol has a relocation.  */
+  unsigned int has_reloc : 1;
 
   /* String table index in .dynstr if this is a dynamic symbol.  */
   unsigned long dynstr_index;
diff --git a/bfd/elf-vxworks.c b/bfd/elf-vxworks.c
index 4c172cd..36e5540 100644
--- a/bfd/elf-vxworks.c
+++ b/bfd/elf-vxworks.c
@@ -172,35 +172,39 @@ elf_vxworks_emit_relocs (bfd *output_bfd,
 	   irela += bed->s->int_rels_per_ext_rel,
 	     hash_ptr++)
 	{
-	  if (*hash_ptr
-	      && (*hash_ptr)->def_dynamic
-	      && !(*hash_ptr)->def_regular
-	      && ((*hash_ptr)->root.type == bfd_link_hash_defined
-		  || (*hash_ptr)->root.type == bfd_link_hash_defweak)
-	      && (*hash_ptr)->root.u.def.section->output_section != NULL)
+	  if (*hash_ptr)
 	    {
-	      /* This is a relocation from an executable or shared
-		 library against a symbol in a different shared
-		 library.  We are creating a definition in the output
-		 file but it does not come from any of our normal (.o)
-		 files. ie. a PLT stub.  Normally this would be a
-		 relocation against against SHN_UNDEF with the VMA of
-		 the PLT stub.  This upsets the VxWorks loader.
-		 Convert it to a section-relative relocation.  This
-		 gets some other symbols (for instance .dynbss), but
-		 is conservatively correct.  */
-	      for (j = 0; j < bed->s->int_rels_per_ext_rel; j++)
+	      (*hash_ptr)->has_reloc = 1;
+	      if ((*hash_ptr)->def_dynamic
+		  && !(*hash_ptr)->def_regular
+		  && ((*hash_ptr)->root.type == bfd_link_hash_defined
+		      || (*hash_ptr)->root.type == bfd_link_hash_defweak)
+		  && (*hash_ptr)->root.u.def.section->output_section != NULL)
 		{
-		  asection *sec = (*hash_ptr)->root.u.def.section;
-		  int this_idx = sec->output_section->target_index;
-
-		  irela[j].r_info
-		    = ELF32_R_INFO (this_idx, ELF32_R_TYPE (irela[j].r_info));
-		  irela[j].r_addend += (*hash_ptr)->root.u.def.value;
-		  irela[j].r_addend += sec->output_offset;
+		  /* This is a relocation from an executable or shared
+		     library against a symbol in a different shared
+		     library.  We are creating a definition in the output
+		     file but it does not come from any of our normal (.o)
+		     files. ie. a PLT stub.  Normally this would be a
+		     relocation against against SHN_UNDEF with the VMA of
+		     the PLT stub.  This upsets the VxWorks loader.
+		     Convert it to a section-relative relocation.  This
+		     gets some other symbols (for instance .dynbss), but
+		     is conservatively correct.  */
+		  for (j = 0; j < bed->s->int_rels_per_ext_rel; j++)
+		    {
+		      asection *sec = (*hash_ptr)->root.u.def.section;
+		      int this_idx = sec->output_section->target_index;
+
+		      irela[j].r_info
+			= ELF32_R_INFO (this_idx,
+					ELF32_R_TYPE (irela[j].r_info));
+		      irela[j].r_addend += (*hash_ptr)->root.u.def.value;
+		      irela[j].r_addend += sec->output_offset;
+		    }
+		  /* Stop the generic routine adjusting this entry.  */
+		  *hash_ptr = NULL;
 		}
-	      /* Stop the generic routine adjusting this entry.  */
-	      *hash_ptr = NULL;
 	    }
 	}
     }
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 9c53bfc..4f72d1b 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -2942,8 +2942,7 @@ _bfd_elf_link_output_relocs (bfd *output_bfd,
 			     asection *input_section,
 			     Elf_Internal_Shdr *input_rel_hdr,
 			     Elf_Internal_Rela *internal_relocs,
-			     struct elf_link_hash_entry **rel_hash
-			       ATTRIBUTE_UNUSED)
+			     struct elf_link_hash_entry **rel_hash)
 {
   Elf_Internal_Rela *irela;
   Elf_Internal_Rela *irelaend;
@@ -2986,9 +2985,12 @@ _bfd_elf_link_output_relocs (bfd *output_bfd,
 		      * bed->s->int_rels_per_ext_rel);
   while (irela < irelaend)
     {
+      if (*rel_hash)
+	(*rel_hash)->has_reloc = 1;
       (*swap_out) (output_bfd, irela, erel);
       irela += bed->s->int_rels_per_ext_rel;
       erel += input_rel_hdr->sh_entsize;
+      rel_hash++;
     }
 
   /* Bump the counter, so that we know where to add the next set of
@@ -10769,6 +10771,13 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data)
 	   && (h->root.u.undef.abfd->flags & BFD_PLUGIN) != 0)
     strip = true;
 
+  /* Remember if this symbol should be stripped.  */
+  bool should_strip = strip;
+
+  /* Strip undefined weak symbols link if they don't have relocation.  */
+  if (!strip)
+    strip = !h->has_reloc && h->root.type == bfd_link_hash_undefweak;
+
   type = h->type;
 
   /* If we're stripping it, and it's not a dynamic symbol, there's
@@ -10917,6 +10926,10 @@ elf_link_output_extsym (struct bfd_hash_entry *bh, void *data)
 	  eoinfo->failed = true;
 	  return false;
 	}
+      /* If a symbol is in the dynamic symbol table and isn't a
+	 should-strip symbol, also keep it in the symbol table.  */
+      if (!should_strip)
+	strip = false;
     }
 
   /* If we are marking the symbol as undefined, and there are no