[committed 2.28 2/2] PR ld/21334: Always call `_bfd_elf_link_renumber_dynsyms' if required

["Maciej W. Rozycki" <macro@imgtec.com>]

Complement commit e17b0c351f0b ("MIPS/BFD: Respect the ELF gABI dynamic 
symbol table sort requirement") and correct an inconsistency in dynamic 
symbol accounting data causing an assertion failure in the MIPS backend:

ld: BFD (GNU Binutils) 2.28.51.20170330 assertion fail
../../binutils-gdb/bfd/elfxx-mips.c:3860

in the course of making a GOT entry in a static binary to satisfy a GOT 
relocation present in input, due to the local dynamic symbol count not 
having been established.

To do so let backends request `_bfd_elf_link_renumber_dynsyms' to be 
always called, rather than where a dynamic binary is linked only, and 
then make this request in the MIPS backend.

	bfd/
	PR ld/21334
	* elf-bfd.h (elf_backend_data): Add `always_renumber_dynsyms' 
	member.
	* elfxx-target.h [!elf_backend_always_renumber_dynsyms]
	(elf_backend_always_renumber_dynsyms): Define.
	(elfNN_bed): Initialize `always_renumber_dynsyms' member.
	* elfxx-mips.h (elf_backend_always_renumber_dynsyms): Define.
	* elflink.c (bfd_elf_size_dynsym_hash_dynstr): Also call
	`_bfd_elf_link_renumber_dynsyms' if the backend has requested 
	it.
	(elf_gc_sweep): Likewise.

(backported from commit 23ec1e32b1ab714649a7c25e49b5d721fe3bd3db)
---
 No regressions against the usual targets.  Committed to 2.28.

  Maciej

binutils-bfd-elf-always-dynsym-renumber-2.28.diff
Index: binutils/bfd/elf-bfd.h
===================================================================
--- binutils.orig/bfd/elf-bfd.h	2017-04-26 13:46:32.000000000 +0100
+++ binutils/bfd/elf-bfd.h	2017-04-26 13:59:01.977164246 +0100
@@ -1478,6 +1478,10 @@ struct elf_backend_data
   /* Address of protected data defined in the shared library may be
      external, i.e., due to copy relocation.   */
   unsigned extern_protected_data : 1;
+
+  /* True if `_bfd_elf_link_renumber_dynsyms' must be called even for
+     static binaries.  */
+  unsigned always_renumber_dynsyms : 1;
 };
 
 /* Information about reloc sections associated with a bfd_elf_section_data
Index: binutils/bfd/elflink.c
===================================================================
--- binutils.orig/bfd/elflink.c	2017-04-26 13:56:16.000000000 +0100
+++ binutils/bfd/elflink.c	2017-04-26 13:59:01.995374303 +0100
@@ -6707,6 +6707,8 @@ bfd_boolean
 bfd_elf_size_dynsym_hash_dynstr (bfd *output_bfd, struct bfd_link_info *info)
 {
   const struct elf_backend_data *bed;
+  unsigned long section_sym_count;
+  bfd_size_type dynsymcount;
 
   if (!is_elf_hash_table (info->hash))
     return TRUE;
@@ -6714,24 +6716,30 @@ bfd_elf_size_dynsym_hash_dynstr (bfd *ou
   bed = get_elf_backend_data (output_bfd);
   (*bed->elf_backend_init_index_section) (output_bfd, info);
 
+  /* Assign dynsym indices.  In a shared library we generate a section
+     symbol for each output section, which come first.  Next come all
+     of the back-end allocated local dynamic syms, followed by the rest
+     of the global symbols.
+
+     This is usually not needed for static binaries, however backends
+     can request to always do it, e.g. the MIPS backend uses dynamic
+     symbol counts to lay out GOT, which will be produced in the
+     presence of GOT relocations even in static binaries (holding fixed
+     data in that case, to satisfy those relocations).  */
+
+  if (elf_hash_table (info)->dynamic_sections_created
+      || bed->always_renumber_dynsyms)
+    dynsymcount = _bfd_elf_link_renumber_dynsyms (output_bfd, info,
+						  &section_sym_count);
+
   if (elf_hash_table (info)->dynamic_sections_created)
     {
       bfd *dynobj;
       asection *s;
-      bfd_size_type dynsymcount;
-      unsigned long section_sym_count;
       unsigned int dtagcount;
 
       dynobj = elf_hash_table (info)->dynobj;
 
-      /* Assign dynsym indicies.  In a shared library we generate a
-	 section symbol for each output section, which come first.
-	 Next come all of the back-end allocated local dynamic syms,
-	 followed by the rest of the global symbols.  */
-
-      dynsymcount = _bfd_elf_link_renumber_dynsyms (output_bfd, info,
-						    &section_sym_count);
-
       /* Work out the size of the symbol version section.  */
       s = bfd_get_linker_section (dynobj, ".gnu.version");
       BFD_ASSERT (s != NULL);
@@ -12983,7 +12991,11 @@ elf_gc_sweep (bfd *abfd, struct bfd_link
   elf_link_hash_traverse (elf_hash_table (info), elf_gc_sweep_symbol,
 			  &sweep_info);
 
-  if (elf_hash_table (info)->dynamic_sections_created)
+  /* We need to reassign dynsym indices now that symbols may have
+     been removed.  See the call in `bfd_elf_size_dynsym_hash_dynstr'
+     for the details of the conditions used here.  */
+  if (elf_hash_table (info)->dynamic_sections_created
+      || bed->always_renumber_dynsyms)
     _bfd_elf_link_renumber_dynsyms (abfd, info, &section_sym_count);
   return TRUE;
 }
Index: binutils/bfd/elfxx-mips.h
===================================================================
--- binutils.orig/bfd/elfxx-mips.h	2017-04-26 13:46:34.000000000 +0100
+++ binutils/bfd/elfxx-mips.h	2017-04-26 13:59:02.001414621 +0100
@@ -196,3 +196,4 @@ literal_reloc_p (int r_type)
 #define elf_backend_post_process_headers _bfd_mips_post_process_headers
 #define elf_backend_compact_eh_encoding _bfd_mips_elf_compact_eh_encoding
 #define elf_backend_cant_unwind_opcode _bfd_mips_elf_cant_unwind_opcode
+#define elf_backend_always_renumber_dynsyms TRUE
Index: binutils/bfd/elfxx-target.h
===================================================================
--- binutils.orig/bfd/elfxx-target.h	2017-04-26 13:46:34.000000000 +0100
+++ binutils/bfd/elfxx-target.h	2017-04-26 13:59:02.008468206 +0100
@@ -126,6 +126,9 @@
 #ifndef elf_backend_extern_protected_data
 #define elf_backend_extern_protected_data 0
 #endif
+#ifndef elf_backend_always_renumber_dynsyms
+#define elf_backend_always_renumber_dynsyms FALSE
+#endif
 #ifndef elf_backend_stack_align
 #define elf_backend_stack_align 16
 #endif
@@ -866,7 +869,8 @@ static struct elf_backend_data elfNN_bed
   elf_backend_no_page_alias,
   elf_backend_default_execstack,
   elf_backend_caches_rawsize,
-  elf_backend_extern_protected_data
+  elf_backend_extern_protected_data,
+  elf_backend_always_renumber_dynsyms
 };
 
 /* Forward declaration for use when initialising alternative_target field.  */