[PATCH] Linker fix for data-only sections

[Daniel Gutson <dgutson at codesourcery dot com>]

The attached patch fixes a bug that caused the linker to incorrectly 
mark parts of the output as containing code, rather than data,
when linking data-only sections not explicitly tagged as such.
The bug resulted in incorrect disassembly.

Technical details:
The bug occurred when a data-only section (without a $d mapping symbol,
which is permitted) was inserted after a section containing mapping
symbols (where the last one wasn't a $d), inside the same output
section. So, the data-only 'inherited' the effect of the last mapping
symbol since it didn't provide one.

The attached patch attempts to fix this issue by always adding a $d at
the beginning of data sections that don't have a mapping symbol. This 
may result in (harmless) redundancy of mapping symbols.
I added this fix in the elf_backend_output_arch_local_syms hook, since 
it looks for this purpose:
[elflink.c, calling the hook:]
  /* If backend needs to output some local symbols not present in the hash
     table, do it now.  */

I tested this fix by running the following test suites:
    * binutils
    * gas
    * ld (with a new test case)
    * gcc
    * g++
    * libstdc++

Please let me know if OK to commit.

ChangeLog:

2010-02-02  Daniel Gutson  <dgutson@codesourcery.com>

	bfd/
	* elf32-arm.c (elf32_arm_output_arch_local_syms): add
	missing mapping symbol to data only sections.

	ld/testsuite/
	* ld-arm/arm-elf.exp (armelftests): New test case added.
	* ld-arm/data-only-map.s: New file.
	* ld-arm/data-only-map.d: New file.

Thanks!
	Daniel.

--
Daniel Gutson
CodeSourcery
www.codesourcery.com

? data-only-map.patch
Index: bfd/elf32-arm.c
===================================================================
RCS file: /cvs/src/src/bfd/elf32-arm.c,v
retrieving revision 1.219
diff -u -p -r1.219 elf32-arm.c
--- bfd/elf32-arm.c	19 Jan 2010 03:49:43 -0000	1.219
+++ bfd/elf32-arm.c	2 Feb 2010 17:26:35 -0000
@@ -12942,7 +12942,9 @@ arm_map_one_stub (struct bfd_hash_entry 
   return TRUE;
 }
 
-/* Output mapping symbols for linker generated sections.  */
+/* Output mapping symbols for linker generated sections,
+   and for those data-only sections that do not have a
+   $d.  */
 
 static bfd_boolean
 elf32_arm_output_arch_local_syms (bfd *output_bfd,
@@ -12957,6 +12959,7 @@ elf32_arm_output_arch_local_syms (bfd *o
   struct elf32_arm_link_hash_table *htab;
   bfd_vma offset;
   bfd_size_type size;
+  bfd *input_bfd;
 
   htab = elf32_arm_hash_table (info);
   check_use_blx (htab);
@@ -12965,6 +12968,32 @@ elf32_arm_output_arch_local_syms (bfd *o
   osi.info = info;
   osi.func = func;
 
+  /* Add a $d mapping symbol to data-only sections that
+     don't have any mapping symbol.  This may result in (harmless) redundant
+     mapping symbols.  */
+  for (input_bfd = info->input_bfds;
+       input_bfd != NULL;
+       input_bfd = input_bfd->link_next)
+    {
+      if ((input_bfd->flags & (BFD_LINKER_CREATED | HAS_SYMS)) == HAS_SYMS)
+	for (osi.sec = input_bfd->sections;
+	     osi.sec != NULL;
+	     osi.sec = osi.sec->next)
+	  {
+	    if (osi.sec->output_section != NULL
+		&& (osi.sec->flags & (SEC_HAS_CONTENTS | SEC_LINKER_CREATED))
+		   == SEC_HAS_CONTENTS
+		&& get_arm_elf_section_data (osi.sec) != NULL
+		&& get_arm_elf_section_data (osi.sec)->mapcount == 0)
+	      {
+		osi.sec_shndx = _bfd_elf_section_from_bfd_section
+		  (output_bfd, osi.sec->output_section);
+		if (osi.sec_shndx != (int)SHN_BAD)
+		  elf32_arm_output_map_sym (&osi, ARM_MAP_DATA, 0);
+	      }
+	  }
+    }
+
   /* ARM->Thumb glue.  */
   if (htab->arm_glue_size > 0)
     {
Index: ld/testsuite/ld-arm/arm-elf.exp
===================================================================
RCS file: /cvs/src/src/ld/testsuite/ld-arm/arm-elf.exp,v
retrieving revision 1.69
diff -u -p -r1.69 arm-elf.exp
--- ld/testsuite/ld-arm/arm-elf.exp	1 Feb 2010 10:33:16 -0000	1.69
+++ ld/testsuite/ld-arm/arm-elf.exp	2 Feb 2010 17:26:35 -0000
@@ -241,6 +241,9 @@ set armelftests {
     {"Relocation boundaries" "-defsym x=0 -defsym y=0 -defsym _start=0" "" {reloc-boundaries.s}
      {{objdump -s reloc-boundaries.d}}
      "reloc-boundaries"}
+    {"Data only mapping symbols" "-T data-only-map.ld -Map map" "" {data-only-map.s}
+     {{objdump -dr data-only-map.d}}
+     "data-only-map"}
 }
 
 run_ld_link_tests $armelftests
Index: ld/testsuite/ld-arm/data-only-map.d
===================================================================
RCS file: ld/testsuite/ld-arm/data-only-map.d
diff -N ld/testsuite/ld-arm/data-only-map.d
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-arm/data-only-map.d	2 Feb 2010 17:26:35 -0000
@@ -0,0 +1,13 @@
+
+[^:]*:     file format elf32-littlearm
+
+
+Disassembly of section \.text:
+
+00000000 <_start>:
+   0:	eb01 0002 	add\.w	r0, r1, r2
+   4:	eb010002 	\.word	0xeb010002
+   8:	eb01 0002 	add\.w	r0, r1, r2
+   c:	eb01 0200 	add\.w	r2, r1, r0
+  10:	eb010002 	\.word	0xeb010002
+  14:	eb010002 	\.word	0xeb010002
Index: ld/testsuite/ld-arm/data-only-map.ld
===================================================================
RCS file: ld/testsuite/ld-arm/data-only-map.ld
diff -N ld/testsuite/ld-arm/data-only-map.ld
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-arm/data-only-map.ld	2 Feb 2010 17:26:35 -0000
@@ -0,0 +1,16 @@
+/* Script for ld testsuite */
+OUTPUT_ARCH(arm)
+ENTRY(_start)
+SECTIONS
+{
+  .text :
+  {
+    *(.text)
+    *(.after1)
+    *(.after2)
+    *(.after3)
+    *(.after4)
+    *(.after5)
+  } =0
+}
+
Index: ld/testsuite/ld-arm/data-only-map.s
===================================================================
RCS file: ld/testsuite/ld-arm/data-only-map.s
diff -N ld/testsuite/ld-arm/data-only-map.s
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-arm/data-only-map.s	2 Feb 2010 17:26:35 -0000
@@ -0,0 +1,20 @@
+.syntax unified
+.thumb
+.global _start
+_start:
+add.w r0, r1, r2
+
+.section .after1
+.word 0xeb010002
+
+.section .after2
+add.w r0, r1, r2
+
+.section .after3
+add.w r2, r1, r0
+
+.section .after4
+.word 0xeb010002
+
+.section .after5
+.word 0xeb010002