elf: Add size_relative_relocs and finish_relative_relocs

On some targets, the DT_RELR section size can be computed only after all
symbols addresses can be determined.  Set the preliminary DT_RELR section
size before mapping sections to segments and set the final DT_RELR section
size after regular symbol processing is done.

	* elf-bfd.h (elf_backend_data): Add size_relative_relocs and
	finish_relative_relocs.
	* elf.c (_bfd_elf_map_sections_to_segments): Call
	size_relative_relocs if DT_RELR is enabled.
	* elflink.c (bfd_elf_final_link): Call finish_relative_relocs
	after regular symbol processing is finished if DT_RELR is enabled.
	* elfxx-target.h (elf_backend_size_relative_relocs): New.
	(elf_backend_finish_relative_relocs): Likewise.
	(elfNN_bed): Add elf_backend_size_relative_relocs and
	elf_backend_finish_relative_relocs.

bfd/elf-bfd.h

@@ -1105,6 +1105,16 @@ struct elf_backend_data
     (bfd *abfd, struct bfd_link_info *info, asection *o,
      const Elf_Internal_Rela *relocs);
 
+  /* The SIZE_RELATIVE_RELOCS function is called to size relative
+     relocations when mappig sections to segments.  */
+  bool (*size_relative_relocs)
+    (struct bfd_link_info *info, bool *need_layout);
+
+  /* The FINISH_RELATIVE_RELOCS function is called to finish relative
+     relocations in bfd_elf_final_link.  */
+  bool (*finish_relative_relocs)
+    (struct bfd_link_info *info);
+
   /* The CHECK_DIRECTIVES function is called once per input file by
      the add_symbols phase of the ELF backend linker.  The function
      must inspect the bfd and create any additional symbols according

bfd/elf.c

@@ -4615,7 +4615,7 @@ elf_modify_segment_map (bfd *abfd,
 bool
 _bfd_elf_map_sections_to_segments (bfd *abfd,
 				   struct bfd_link_info *info,
-				   bool *need_layout ATTRIBUTE_UNUSED)
+				   bool *need_layout)
 {
   unsigned int count;
   struct elf_segment_map *m;
@@ -4626,8 +4626,18 @@ _bfd_elf_map_sections_to_segments (bfd *abfd,
   no_user_phdrs = elf_seg_map (abfd) == NULL;
 
   if (info != NULL)
+    {
       info->user_phdrs = !no_user_phdrs;
 
+      /* Size the relative relocations if DT_RELR is enabled.  */
+      if (info->enable_dt_relr
+	  && need_layout != NULL
+	  && bed->size_relative_relocs
+	  && !bed->size_relative_relocs (info, need_layout))
+	info->callbacks->einfo
+	  (_("%F%P: failed to size relative relocations\n"));
+    }
+
   if (no_user_phdrs && bfd_count_sections (abfd) != 0)
     {
       asection *s;

bfd/elflink.c

@@ -12599,6 +12599,14 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
   if (!_bfd_elf_fixup_eh_frame_hdr (info))
     return false;
 
+  /* Finish relative relocations here after regular symbol processing
+     is finished if DT_RELR is enabled.  */
+  if (info->enable_dt_relr
+      && bed->finish_relative_relocs
+      && !bed->finish_relative_relocs (info))
+    info->callbacks->einfo
+      (_("%F%P: %pB: failed to finish relative relocations\n"), abfd);
+
   /* Since ELF permits relocations to be against local symbols, we
      must have the local symbols available when we do the relocations.
      Since we would rather only read the local symbols once, and we

bfd/elfxx-target.h

@@ -478,6 +478,12 @@
 #ifndef elf_backend_check_relocs
 #define elf_backend_check_relocs	0
 #endif
+#ifndef elf_backend_size_relative_relocs
+#define elf_backend_size_relative_relocs 0
+#endif
+#ifndef elf_backend_finish_relative_relocs
+#define elf_backend_finish_relative_relocs 0
+#endif
 #ifndef elf_backend_check_directives
 #define elf_backend_check_directives	0
 #endif
@@ -842,6 +848,8 @@ static const struct elf_backend_data elfNN_bed =
   elf_backend_omit_section_dynsym,
   elf_backend_relocs_compatible,
   elf_backend_check_relocs,
+  elf_backend_size_relative_relocs,
+  elf_backend_finish_relative_relocs,
   elf_backend_check_directives,
   elf_backend_notice_as_needed,
   elf_backend_adjust_dynamic_symbol,