Re: [PATCH 5/5] Defer allocation of R_MIPS_REL32 GOT slots

[Richard Sandiford <rdsandiford at googlemail dot com>]

Richard Sandiford <rdsandiford@googlemail.com> writes:
> The MIPS backend creates a GOT entry for a symbol S when it first sees
> an input relocation that _might_ be turned into a dynamic R_MIPS_REL32
> against S.  However, the code defers the allocation of the relocations
> themselves.
>
> This patch defers both decisions, only allocating the GOT entry when
> we allocate the associated relocations.  It is only safe to do this
> after the previous patches.
>
> Tested on mips64-linux-gnu and mips64el-linux-gnu.  OK to install?
>
>
> That's the end of the GOT-improvement sequence.  FWIW, the patches
> should make it easier to divide the GGA_NORMAL are up into two:
>
>   - symbols that are referenced by 16-bit GOT offsets like
>     R_MIPS_GOT16
>
>   - symbols that are only referenced by 32-bit GOT offsets like
>     R_MIPS_GOT_HI16/R_MIPS_GOT_LO16.
>
> This should avoid the traditional problem with -mxgot: if the whole
> object doesn't use 32-bit offsets, the 16-bit accesses might still be
> out of range.  I think this is the reason Debian compile crtstuff.c
> & co. with -mxgot.
>
> I don't plan to implement that in the near future though. ;)

I've updated the patch for current mainline, taking account of:

   http://sources.redhat.com/ml/binutils/2008-07/msg00350.html

Richard


bfd/
	* elfxx-mips.c (mips_elf_record_relocs): Defer allocation of a
	global GOT entry when deferring allocation of dynamic relocations.
	(allocate_dynrelocs): When allocating deferred dynamic relocations,
	also do the deferred allocation of a GOT entry.

Index: bfd/elfxx-mips.c
===================================================================
--- bfd/elfxx-mips.c	2008-08-06 21:01:03.000000000 +0100
+++ bfd/elfxx-mips.c	2008-08-06 21:01:08.000000000 +0100
@@ -7274,21 +7274,6 @@ _bfd_mips_elf_check_relocs (bfd *abfd, s
 		       are relocations against the text segment.  */
 		    hmips->readonly_reloc = TRUE;
 		}
-
-	      /* Even though we don't directly need a GOT entry for
-		 this symbol, a symbol must have a dynamic symbol
-		 table index greater that DT_MIPS_GOTSYM if there are
-		 dynamic relocations against it.  This does not apply
-		 to VxWorks, which does not have the usual coupling
-		 between global GOT entries and .dynsym entries.  */
-	      if (h != NULL && !htab->is_vxworks)
-		{
-		  struct mips_elf_link_hash_entry *hmips;
-
-		  hmips = (struct mips_elf_link_hash_entry *) h;
-		  if (hmips->global_got_area > GGA_RELOC_ONLY)
-		    hmips->global_got_area = GGA_RELOC_ONLY;
-		}
 	    }
 
 	  if (SGI_COMPAT (abfd))
@@ -7585,6 +7570,12 @@ allocate_dynrelocs (struct elf_link_hash
 
       if (do_copy)
 	{
+	  /* Even though we don't directly need a GOT entry for this symbol,
+	     a symbol must have a dynamic symbol table index greater that
+	     DT_MIPS_GOTSYM if there are dynamic relocations against it.  */
+	  if (hmips->global_got_area > GGA_RELOC_ONLY)
+	    hmips->global_got_area = GGA_RELOC_ONLY;
+
 	  mips_elf_allocate_dynamic_relocations
 	    (dynobj, info, hmips->possibly_dynamic_relocs);
 	  if (hmips->readonly_reloc)