[committed] MIPS/BFD: Respect the ELF gABI dynamic symbol table sort requirement

[committed] MIPS/BFD: Respect the ELF gABI dynamic symbol table sort requirement

[Maciej W. Rozycki]

Ensure all local symbols precede external symbols in the dynamic symbol 
table.

No local symbols are expected to make it to the dynamic symbol table 
except for section symbols already taken care of, so this is really a 
safeguard only against a potential BFD bug otherwise not so harmful, 
which may become a grave one due to a symbol table sorting requirement 
violation (see PR ld/20828 for an example).  This means however that no 
test suite coverage is possible for this change as code introduced here 
is not normally expected to trigger.

Logically split then the part of the dynamic symbol table which is not 
global offset table mapped, into a local area at the beginning and an 
external area following.  By the time `mips_elf_sort_hash_table' is 
called we have the number of local dynamic symbol table entries (section 
and non-section) already counted in `local_dynsymcount', so use it to 
offset the external area from the beginning.

	bfd/
	* elfxx-mips.c (mips_elf_hash_sort_data): Add 
	`max_local_dynindx'.
	(mips_elf_sort_hash_table): Handle it.
	(mips_elf_sort_hash_table_f) <GGA_NONE>: For forced local 
	symbols bump up `max_local_dynindx' rather than 
	`max_non_got_dynindx'.
---
binutils-mips-bfd-dynsym-sort.diff
Index: binutils/bfd/elfxx-mips.c
===================================================================
--- binutils.orig/bfd/elfxx-mips.c	2017-02-02 00:56:37.742249694 +0000
+++ binutils/bfd/elfxx-mips.c	2017-02-02 00:56:42.271630635 +0000
@@ -315,7 +315,10 @@ struct mips_elf_hash_sort_data
      with a GOT entry that is not referenced (e.g., a dynamic symbol
      with dynamic relocations pointing to it from non-primary GOTs).  */
   bfd_size_type max_unref_got_dynindx;
-  /* The greatest dynamic symbol table index not corresponding to a
+  /* The greatest dynamic symbol table index corresponding to a local
+     symbol.  */
+  bfd_size_type max_local_dynindx;
+  /* The greatest dynamic symbol table index corresponding to an external
      symbol without a GOT entry.  */
   bfd_size_type max_non_got_dynindx;
 };
@@ -3846,11 +3849,15 @@ mips_elf_sort_hash_table (bfd *abfd, str
   hsd.max_unref_got_dynindx
     = hsd.min_got_dynindx
     = (htab->root.dynsymcount - g->reloc_only_gotno);
-  hsd.max_non_got_dynindx = count_section_dynsyms (abfd, info) + 1;
+  /* Add 1 to local symbol indices to account for the mandatory NULL entry
+     at the head of the table; see `_bfd_elf_link_renumber_dynsyms'.  */
+  hsd.max_local_dynindx = count_section_dynsyms (abfd, info) + 1;
+  hsd.max_non_got_dynindx = htab->root.local_dynsymcount + 1;
   mips_elf_link_hash_traverse (htab, mips_elf_sort_hash_table_f, &hsd);
 
   /* There should have been enough room in the symbol table to
      accommodate both the GOT and non-GOT symbols.  */
+  BFD_ASSERT (hsd.max_local_dynindx <= htab->root.local_dynsymcount + 1);
   BFD_ASSERT (hsd.max_non_got_dynindx <= hsd.min_got_dynindx);
   BFD_ASSERT (hsd.max_unref_got_dynindx == htab->root.dynsymcount);
   BFD_ASSERT (htab->root.dynsymcount - hsd.min_got_dynindx == g->global_gotno);
@@ -3879,7 +3886,10 @@ mips_elf_sort_hash_table_f (struct mips_
   switch (h->global_got_area)
     {
     case GGA_NONE:
-      h->root.dynindx = hsd->max_non_got_dynindx++;
+      if (h->root.forced_local)
+	h->root.dynindx = hsd->max_local_dynindx++;
+      else
+	h->root.dynindx = hsd->max_non_got_dynindx++;
       break;
 
     case GGA_NORMAL:

Re: [committed] MIPS/BFD: Respect the ELF gABI dynamic symbol table sort requirement

[Maciej W. Rozycki]

On Thu, 2 Feb 2017, Maciej W. Rozycki wrote:

> Ensure all local symbols precede external symbols in the dynamic symbol 
> table.
> 
> No local symbols are expected to make it to the dynamic symbol table 
> except for section symbols already taken care of, so this is really a 
> safeguard only against a potential BFD bug otherwise not so harmful, 
> which may become a grave one due to a symbol table sorting requirement 
> violation (see PR ld/20828 for an example).  This means however that no 
> test suite coverage is possible for this change as code introduced here 
> is not normally expected to trigger.
> 
> Logically split then the part of the dynamic symbol table which is not 
> global offset table mapped, into a local area at the beginning and an 
> external area following.  By the time `mips_elf_sort_hash_table' is 
> called we have the number of local dynamic symbol table entries (section 
> and non-section) already counted in `local_dynsymcount', so use it to 
> offset the external area from the beginning.
> 
> 	bfd/
> 	* elfxx-mips.c (mips_elf_hash_sort_data): Add 
> 	`max_local_dynindx'.
> 	(mips_elf_sort_hash_table): Handle it.
> 	(mips_elf_sort_hash_table_f) <GGA_NONE>: For forced local 
> 	symbols bump up `max_local_dynindx' rather than 
> 	`max_non_got_dynindx'.
> ---

 I have been told the issue outstanding with PR ld/20828 and version 
symbols causes non-working executables to be produced such as in the case 
of Firefox.

 I have therefore decided to backport this change (and its 3 preparatory 
cleanups) to 2.28 to make people's life easier, as it makes executables 
work while not making them otherwise any worse than now -- the binding of 
any version symbols remains local, which is incorrect, or at least 
inconsistent, however very unlikely to cause any problem.

  Maciej