[PATCH] MIPS/BFD: Fix n64 GOT header size in the ELF backend

Maciej W. Rozycki macro@linux-mips.org
Mon May 7 09:56:00 GMT 2012


Hi,

 I've noticed the MIPS backend does not set the size of the GOT header 
correctly in the ELF backend structure for the n64 ABI.  This is mostly 
harmless because the MIPS backend does not use the value from the 
structure and hardcoded the header size to twice the GOT entry size.  
Furthermore the MIPS backend does not use the generic GOT creation 
function (_bfd_elf_create_got_section) so it escapes damage there too.

 However the size from the ELF backend structure is still used in linker 
garbage collection (bfd_elf_gc_common_finalize_got_offsets) that the MIPS 
backend does use, although GC is not on by default.  Therefore I propose 
to fix it as below and make the MIPS backend use the GOT header size from 
the ELF backend structure too so that there is a central place everything 
depends on and any breakage is easily noticed.  Surprisingly enough this 
is also a bit cheaper as MIPS_ELF_GOT_SIZE implies an extra pointer 
dereference and calculation (the multiplication by 2 should be cancelled 
by any sane compiler though).

 I have no test case available and I don't remember anymore how I spotted 
this, most probably noticed it by inspection while debugging the n64 
compound relocation breakage with GC I have fixed recently.  However I 
believe the change is obvious enough and it does not cause any regressions 
in mips64-gnu-linux testing.  OK to apply?

2012-05-07  Maciej W. Rozycki  <macro@linux-mips.org>

	bfd/
	* elf64-mips.c (elf_backend_got_header_size): Correct definition.
	* elfxx-mips.c (_bfd_mips_elf_adjust_dynamic_symbol): Use the ELF
	backend's GOT header size instead of hardcoding it.

  Maciej

binutils-mips-got-header-size.patch
Index: binutils/bfd/elf64-mips.c
===================================================================
--- binutils.orig/bfd/elf64-mips.c
+++ binutils/bfd/elf64-mips.c
@@ -3261,7 +3261,7 @@ const struct elf_size_info mips_elf64_si
 #define elf_backend_grok_prstatus	elf64_mips_grok_prstatus
 #define elf_backend_grok_psinfo		elf64_mips_grok_psinfo
 
-#define elf_backend_got_header_size	(4 * MIPS_RESERVED_GOTNO)
+#define elf_backend_got_header_size	(8 * MIPS_RESERVED_GOTNO)
 
 /* MIPS ELF64 can use a mixture of REL and RELA, but some Relocations
    work better/work only in RELA, so we default to this.  */
Index: binutils/bfd/elfxx-mips.c
===================================================================
--- binutils.orig/bfd/elfxx-mips.c
+++ binutils/bfd/elfxx-mips.c
@@ -8293,7 +8293,8 @@ _bfd_mips_elf_adjust_dynamic_symbol (str
 	  /* On non-VxWorks targets, the first two entries in .got.plt
 	     are reserved.  */
 	  if (!htab->is_vxworks)
-	    htab->sgotplt->size += 2 * MIPS_ELF_GOT_SIZE (dynobj);
+	    htab->sgotplt->size
+	      += get_elf_backend_data (dynobj)->got_header_size;
 
 	  /* On VxWorks, also allocate room for the header's
 	     .rela.plt.unloaded entries.  */



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