tweak __ehdr_start visibility and flags for check_relocs

bfd/
	* elf-bfd.h (UNDEFWEAK_NO_DYNAMIC_RELOC): Test linker_def.
ld/
	* ldelf.c (ldelf_before_allocation): Don't force __ehdr_start
	local and hidden here..
	* ldlang.c (lang_symbol_tweaks): ..do so here instead and set
	def_regular and linker_def for check_relocs.  New function
	extracted from lang_process.

bfd/elf-bfd.h

@@ -291,9 +291,12 @@ weakdef (struct elf_link_hash_entry *h)
   _bfd_elf_symbol_refs_local_p (H, INFO, 1)
 
 /* Whether an undefined weak symbol should resolve to its link-time
-   value, even in PIC or PIE objects.  */
+   value, even in PIC or PIE objects.  The linker_def test is to
+   handle symbols like __ehdr_start that may be undefweak in early
+   stages of linking but are guaranteed to be defined later.  */
 #define UNDEFWEAK_NO_DYNAMIC_RELOC(INFO, H)		\
   ((H)->root.type == bfd_link_hash_undefweak		\
+   && !(H)->root.linker_def				\
    && (ELF_ST_VISIBILITY ((H)->other) != STV_DEFAULT	\
        || (INFO)->dynamic_undefined_weak == 0))
 

ld/ldelf.c

@@ -1607,11 +1607,6 @@ ldelf_before_allocation (char *audit, char *depaudit,
 		  || h->root.type == bfd_link_hash_undefweak
 		  || h->root.type == bfd_link_hash_common))
 	    {
-	      const struct elf_backend_data *bed;
-	      bed = get_elf_backend_data (link_info.output_bfd);
-	      (*bed->elf_backend_hide_symbol) (&link_info, h, true);
-	      if (ELF_ST_VISIBILITY (h->other) != STV_INTERNAL)
-		h->other = (h->other & ~ELF_ST_VISIBILITY (-1)) | STV_HIDDEN;
 	      /* Don't leave the symbol undefined.  Undefined hidden
 		 symbols typically won't have dynamic relocations, but
 		 we most likely will need dynamic relocations for

ld/ldlang.c

@@ -6994,6 +6994,43 @@ lang_finalize_start_stop (void)
   foreach_start_stop (set_start_stop);
 }
 
+static void
+lang_symbol_tweaks (void)
+{
+  /* Give initial values for __start and __stop symbols, so that  ELF
+     gc_sections will keep sections referenced by these symbols.  Must
+     be done before lang_do_assignments.  */
+  if (config.build_constructors)
+    lang_init_start_stop ();
+
+  /* Make __ehdr_start hidden, and set def_regular even though it is
+     likely undefined at this stage.  For lang_check_relocs.  */
+  if (is_elf_hash_table (link_info.hash)
+      && !bfd_link_relocatable (&link_info))
+    {
+      struct elf_link_hash_entry *h = (struct elf_link_hash_entry *)
+	bfd_link_hash_lookup (link_info.hash, "__ehdr_start",
+			      false, false, true);
+
+      /* Only adjust the export class if the symbol was referenced
+	 and not defined, otherwise leave it alone.  */
+      if (h != NULL
+	  && (h->root.type == bfd_link_hash_new
+	      || h->root.type == bfd_link_hash_undefined
+	      || h->root.type == bfd_link_hash_undefweak
+	      || h->root.type == bfd_link_hash_common))
+	{
+	  const struct elf_backend_data *bed;
+	  bed = get_elf_backend_data (link_info.output_bfd);
+	  (*bed->elf_backend_hide_symbol) (&link_info, h, true);
+	  if (ELF_ST_VISIBILITY (h->other) != STV_INTERNAL)
+	    h->other = (h->other & ~ELF_ST_VISIBILITY (-1)) | STV_HIDDEN;
+	  h->def_regular = 1;
+	  h->root.linker_def = 1;
+	}
+    }
+}
+
 static void
 lang_end (void)
 {
@@ -8210,11 +8247,7 @@ lang_process (void)
      files.  */
   ldctor_build_sets ();
 
-  /* Give initial values for __start and __stop symbols, so that  ELF
+  lang_symbol_tweaks ();
-     gc_sections will keep sections referenced by these symbols.  Must
-     be done before lang_do_assignments below.  */
-  if (config.build_constructors)
-    lang_init_start_stop ();
 
   /* PR 13683: We must rerun the assignments prior to running garbage
      collection in order to make sure that all symbol aliases are resolved.  */