Re: [SPU] bugs in .fixup section code

[Alan Modra <amodra at gmail dot com>]

Hi Trevor,
  I was going through old email in my inbox, and I don't think I
replied to this email.  Apologies for that, and hope to make amends by
the patch I'm about to apply.

On Tue, Feb 02, 2010 at 06:09:12PM -0800, Trevor_Smigiel@playstation.sony.com wrote:
> Hi,
> 
> I noticed a couple of issues with the .fixup code for the SPU target.
> The patch was discussed and commited here:
>   http://sourceware.org/ml/binutils/2009-08/msg00052.html
> 
> The first issues is that it allocates fixup records for debug sections.
> I think that testing the SEC_ALLOC flag is the best way to filter them
> and other sections out.  Is that correct
[snip]

Yes.

> The second problem is that the contents of the fixup output section are
> getting set too soon.  The fixup section is attached to the first input
> bfd, which causes it to get copied to the output section early in
> bfd_elf_final_link while it is relocating sections, but the fixup
> section contents are still being updated while relocating later
> sections.
> 
> Here are 2 approaches I'm considering to fix this.  They both have the
> effect of calling bfd_set_section_contents for the fixup section after
> all section relocations have been completed.
> 
> First approach, create the .fixup section as a dynamic section.  Set the
> SEC_LINKER_CREATED flag and set htab->elf.dynobj to be the first input
> bfd, where the .fixup section was created.  In this case, I am not sure
> of all the effects of setting htab->elf.dynobj.   If there aren't any
> issues, I think this is the slightly better solution.
[snip]

Agreed.

> And a final question about testing.  To create a test case for this I
> will need at least 2 source files.  Is the correct approach to write
> explicit commands for this test in ld-spu/spu.exp?  Similar to
> embed_test that is in the same file.

You can specify multiple source files in the .d file.  See
ld/testsuite/ld-elf/warn1.d for an example.

	* elf32-spu.c (spu_elf_size_sections): Omit fixups for non-alloc
	sections.
	(spu_elf_create_sections): Mark .fixup with SEC_LINKER_CREATED and
	set dynobj.
	(spu_elf_finish_dynamic_sections): New function.
	(elf_backend_finish_dynamic_sections): Define.
	
Index: bfd/elf32-spu.c
===================================================================
RCS file: /cvs/src/src/bfd/elf32-spu.c,v
retrieving revision 1.97
diff -u -p -r1.97 elf32-spu.c
--- bfd/elf32-spu.c	25 Aug 2010 14:53:44 -0000	1.97
+++ bfd/elf32-spu.c	16 Sep 2010 10:31:09 -0000
@@ -602,9 +602,12 @@ spu_elf_create_sections (struct bfd_link
     {
       asection *s;
       flagword flags;
-      ibfd = info->input_bfds;
-      flags = SEC_LOAD | SEC_ALLOC | SEC_READONLY | SEC_HAS_CONTENTS
-	      | SEC_IN_MEMORY;
+
+      if (htab->elf.dynobj == NULL)
+	htab->elf.dynobj = ibfd;
+      ibfd = htab->elf.dynobj;
+      flags = (SEC_LOAD | SEC_ALLOC | SEC_READONLY | SEC_HAS_CONTENTS
+	       | SEC_IN_MEMORY | SEC_LINKER_CREATED);
       s = bfd_make_section_anyway_with_flags (ibfd, ".fixup", flags);
       if (s == NULL || !bfd_set_section_alignment (ibfd, s, 2))
 	return FALSE;
@@ -5096,6 +5099,13 @@ spu_elf_relocate_section (bfd *output_bf
   return ret;
 }
 
+static bfd_boolean
+spu_elf_finish_dynamic_sections (bfd *output_bfd ATTRIBUTE_UNUSED,
+				 struct bfd_link_info *info ATTRIBUTE_UNUSED)
+{
+  return TRUE;
+}
+
 /* Adjust _SPUEAR_ syms to point at their overlay stubs.  */
 
 static int
@@ -5402,7 +5412,8 @@ spu_elf_size_sections (bfd * output_bfd,
 
 	      /* If there aren't any relocs, then there's nothing more
 	         to do.  */
-	      if ((isec->flags & SEC_RELOC) == 0
+	      if ((isec->flags & SEC_ALLOC) == 0
+		  || (isec->flags & SEC_RELOC) == 0
 		  || isec->reloc_count == 0)
 		continue;
 
@@ -5457,6 +5468,7 @@ spu_elf_size_sections (bfd * output_bfd,
 #define elf_info_to_howto			spu_elf_info_to_howto
 #define elf_backend_count_relocs		spu_elf_count_relocs
 #define elf_backend_relocate_section		spu_elf_relocate_section
+#define elf_backend_finish_dynamic_sections	spu_elf_finish_dynamic_sections
 #define elf_backend_symbol_processing		spu_elf_backend_symbol_processing
 #define elf_backend_link_output_symbol_hook	spu_elf_output_symbol_hook
 #define elf_backend_object_p			spu_elf_object_p

-- 
Alan Modra
Australia Development Lab, IBM