/DISCARD/ group sections

[Alan Modra <amodra at gmail dot com>]

People have asked for this feature before, and since I was poking at
the bfd code that handles objcopy removal of group sections, I figured
I might as well implement it for ld too.

bfd/
	* elf.c (_bfd_elf_fixup_group_sections): New function, split out from..
	(_bfd_elf_copy_private_header_data): ..here.
	* elflink.c (_bfd_elf_size_group_sections): New function.
	(bfd_elf_size_dynamic_sections): Call it.
	* elf-bfd.h (_bfd_elf_size_group_sections): Declare.
	(_bfd_elf_fixup_group_sections): Declare.
ld/
	* ldlang.c (unique_section_p): Add os param.  Allow group
	sections to match /DISCARD/.  Update all callers.
	* emultempl/genelf.em (gld${EMULATION_NAME}_before_allocation): New.
	(LDEMUL_BEFORE_ALLOCATION): Define.
ld/testsuite/
	* ld-elf/group.ld: Discard .dropme sections.
	* ld-elf/group10.d, * ld-elf/group10.s: New test.

Index: bfd/elf-bfd.h
===================================================================
RCS file: /cvs/src/src/bfd/elf-bfd.h,v
retrieving revision 1.300
diff -u -p -r1.300 elf-bfd.h
--- bfd/elf-bfd.h	9 Feb 2010 12:14:42 -0000	1.300
+++ bfd/elf-bfd.h	18 Feb 2010 12:15:25 -0000
@@ -1773,6 +1773,10 @@ extern void _bfd_elf_link_just_syms
   (asection *, struct bfd_link_info *);
 extern void _bfd_elf_copy_link_hash_symbol_type
   (bfd *, struct bfd_link_hash_entry *, struct bfd_link_hash_entry *);
+extern bfd_boolean _bfd_elf_size_group_sections
+  (struct bfd_link_info *);
+extern bfd_boolean _bfd_elf_fixup_group_sections
+(bfd *, asection *);
 extern bfd_boolean _bfd_elf_copy_private_header_data
   (bfd *, bfd *);
 extern bfd_boolean _bfd_elf_copy_private_symbol_data
Index: bfd/elf.c
===================================================================
RCS file: /cvs/src/src/bfd/elf.c,v
retrieving revision 1.503
diff -u -p -r1.503 elf.c
--- bfd/elf.c	18 Feb 2010 00:09:06 -0000	1.503
+++ bfd/elf.c	18 Feb 2010 12:15:26 -0000
@@ -6137,58 +6134,92 @@ _bfd_elf_copy_private_section_data (bfd 
 					     NULL);
 }
 
-/* Copy private header information.  */
+/* Look at all the SHT_GROUP sections in IBFD, making any adjustments
+   necessary if we are removing either the SHT_GROUP section or any of
+   the group member sections.  DISCARDED is the value that a section's
+   output_section has if the section will be discarded, NULL when this
+   function is called from objcopy, bfd_abs_section_ptr when called
+   from the linker.  */
 
 bfd_boolean
-_bfd_elf_copy_private_header_data (bfd *ibfd, bfd *obfd)
+_bfd_elf_fixup_group_sections (bfd *ibfd, asection *discarded)
 {
   asection *isec;
 
-  if (bfd_get_flavour (ibfd) != bfd_target_elf_flavour
-      || bfd_get_flavour (obfd) != bfd_target_elf_flavour)
-    return TRUE;
-
-  /* Copy over private BFD data if it has not already been copied.
-     This must be done here, rather than in the copy_private_bfd_data
-     entry point, because the latter is called after the section
-     contents have been set, which means that the program headers have
-     already been worked out.  */
-  if (elf_tdata (obfd)->segment_map == NULL && elf_tdata (ibfd)->phdr != NULL)
-    {
-      if (! copy_private_bfd_data (ibfd, obfd))
-	return FALSE;
-    }
-
   for (isec = ibfd->sections; isec != NULL; isec = isec->next)
     if (elf_section_type (isec) == SHT_GROUP)
       {
 	asection *first = elf_next_in_group (isec);
 	asection *s = first;
+	bfd_size_type removed = 0;
+
 	while (s != NULL)
 	  {
 	    /* If this member section is being output but the
 	       SHT_GROUP section is not, then clear the group info
 	       set up by _bfd_elf_copy_private_section_data.  */
-	    if (s->output_section != NULL
-		&& isec->output_section == NULL)
+	    if (s->output_section != discarded
+		&& isec->output_section == discarded)
 	      {
 		elf_section_flags (s->output_section) &= ~SHF_GROUP;
 		elf_group_name (s->output_section) = NULL;
 	      }
 	    /* Conversely, if the member section is not being output
 	       but the SHT_GROUP section is, then adjust its size.  */
-	    else if (s->output_section == NULL
-		     && isec->output_section != NULL)
-	      isec->output_section->size -= 4;
+	    else if (s->output_section == discarded
+		     && isec->output_section != discarded)
+	      removed += 4;
 	    s = elf_next_in_group (s);
 	    if (s == first)
 	      break;
 	  }
+	if (removed != 0)
+	  {
+	    if (discarded != NULL)
+	      {
+		/* If we've been called for ld -r, then we need to
+		   adjust the input section size.  This function may
+		   be called multiple times, so save the original
+		   size.  */
+		if (isec->rawsize == 0)
+		  isec->rawsize = isec->size;
+		isec->size = isec->rawsize - removed;
+	      }
+	    else
+	      {
+		/* Adjust the output section size when called from
+		   objcopy. */
+		isec->output_section->size -= removed;
+	      }
+	  }
       }
 
   return TRUE;
 }
 
+/* Copy private header information.  */
+
+bfd_boolean
+_bfd_elf_copy_private_header_data (bfd *ibfd, bfd *obfd)
+{
+  if (bfd_get_flavour (ibfd) != bfd_target_elf_flavour
+      || bfd_get_flavour (obfd) != bfd_target_elf_flavour)
+    return TRUE;
+
+  /* Copy over private BFD data if it has not already been copied.
+     This must be done here, rather than in the copy_private_bfd_data
+     entry point, because the latter is called after the section
+     contents have been set, which means that the program headers have
+     already been worked out.  */
+  if (elf_tdata (obfd)->segment_map == NULL && elf_tdata (ibfd)->phdr != NULL)
+    {
+      if (! copy_private_bfd_data (ibfd, obfd))
+	return FALSE;
+    }
+
+  return _bfd_elf_fixup_group_sections (ibfd, NULL);
+}
+
 /* Copy private symbol information.  If this symbol is in a section
    which we did not map into a BFD section, try to map the section
    index correctly.  We use special macro definitions for the mapped
Index: bfd/elflink.c
===================================================================
RCS file: /cvs/src/src/bfd/elflink.c,v
retrieving revision 1.368
diff -u -p -r1.368 elflink.c
--- bfd/elflink.c	4 Feb 2010 09:16:41 -0000	1.368
+++ bfd/elflink.c	18 Feb 2010 12:15:28 -0000
@@ -5481,6 +5481,20 @@ compute_bucket_count (struct bfd_link_in
   return best_size;
 }
 
+/* Size any SHT_GROUP section for ld -r.  */
+
+bfd_boolean
+_bfd_elf_size_group_sections (struct bfd_link_info *info)
+{
+  bfd *ibfd;
+
+  for (ibfd = info->input_bfds; ibfd != NULL; ibfd = ibfd->link_next)
+    if (bfd_get_flavour (ibfd) == bfd_target_elf_flavour
+	&& !_bfd_elf_fixup_group_sections (ibfd, bfd_abs_section_ptr))
+      return FALSE;
+  return TRUE;
+}
+
 /* Set up the sizes and contents of the ELF dynamic sections.  This is
    called by the ELF linker emulation before_allocation routine.  We
    must set the sizes of the sections before the linker sets the
@@ -5555,6 +5569,10 @@ bfd_elf_size_dynamic_sections (bfd *outp
   elf_hash_table (info)->init_plt_refcount
     = elf_hash_table (info)->init_plt_offset;
 
+  if (info->relocatable
+      && !_bfd_elf_size_group_sections (info))
+    return FALSE;
+
   /* The backend may have to create some sections regardless of whether
      we're dynamic or not.  */
   if (bed->elf_backend_always_size_sections
Index: ld/ldlang.c
===================================================================
RCS file: /cvs/src/src/ld/ldlang.c,v
retrieving revision 1.328
diff -u -p -r1.328 ldlang.c
--- ld/ldlang.c	21 Jan 2010 10:31:32 -0000	1.328
+++ ld/ldlang.c	18 Feb 2010 08:43:16 -0000
@@ -195,7 +195,8 @@ input_statement_is_archive_path (const c
 }
 
 static bfd_boolean
-unique_section_p (const asection *sec)
+unique_section_p (const asection *sec,
+		  const lang_output_section_statement_type *os)
 {
   struct unique_sections *unam;
   const char *secnam;
@@ -203,7 +204,8 @@ unique_section_p (const asection *sec)
   if (link_info.relocatable
       && sec->owner != NULL
       && bfd_is_group_section (sec->owner, sec))
-    return TRUE;
+    return !(os != NULL
+	     && strcmp (os->name, DISCARD_SECTION_NAME) == 0);
 
   secnam = sec->name;
   for (unam = unique_section_list; unam; unam = unam->next)
@@ -445,12 +447,15 @@ output_section_callback_fast (lang_wild_
 			      struct wildcard_list *sec,
 			      asection *section,
 			      lang_input_statement_type *file,
-			      void *output ATTRIBUTE_UNUSED)
+			      void *output)
 {
   lang_section_bst_type *node;
   lang_section_bst_type **tree;
+  lang_output_section_statement_type *os;
 
-  if (unique_section_p (section))
+  os = (lang_output_section_statement_type *) output;
+
+  if (unique_section_p (section, os))
     return;
 
   node = (lang_section_bst_type *) xmalloc (sizeof (lang_section_bst_type));
@@ -2415,9 +2420,12 @@ output_section_callback (lang_wild_state
 			 void *output)
 {
   lang_statement_union_type *before;
+  lang_output_section_statement_type *os;
+
+  os = (lang_output_section_statement_type *) output;
 
   /* Exclude sections that match UNIQUE_SECTION_LIST.  */
-  if (unique_section_p (section))
+  if (unique_section_p (section, os))
     return;
 
   before = wild_sort (ptr, sec, file, section);
@@ -2428,16 +2436,14 @@ output_section_callback (lang_wild_state
      of the current list.  */
 
   if (before == NULL)
-    lang_add_section (&ptr->children, section,
-		      (lang_output_section_statement_type *) output);
+    lang_add_section (&ptr->children, section, os);
   else
     {
       lang_statement_list_type list;
       lang_statement_union_type **pp;
 
       lang_list_init (&list);
-      lang_add_section (&list, section,
-			(lang_output_section_statement_type *) output);
+      lang_add_section (&list, section, os);
 
       /* If we are discarding the section, LIST.HEAD will
 	 be NULL.  */
@@ -2464,14 +2470,18 @@ check_section_callback (lang_wild_statem
 			struct wildcard_list *sec ATTRIBUTE_UNUSED,
 			asection *section,
 			lang_input_statement_type *file ATTRIBUTE_UNUSED,
-			void *data)
+			void *output)
 {
+  lang_output_section_statement_type *os;
+
+  os = (lang_output_section_statement_type *) output;
+
   /* Exclude sections that match UNIQUE_SECTION_LIST.  */
-  if (unique_section_p (section))
+  if (unique_section_p (section, os))
     return;
 
   if (section->output_section == NULL && (section->flags & SEC_READONLY) == 0)
-    ((lang_output_section_statement_type *) data)->all_input_readonly = FALSE;
+    os->all_input_readonly = FALSE;
 }
 
 /* This is passed a file name which must have been seen already and
@@ -5848,7 +5858,8 @@ lang_place_orphans (void)
 		  const char *name = s->name;
 		  int constraint = 0;
 
-		  if (config.unique_orphan_sections || unique_section_p (s))
+		  if (config.unique_orphan_sections
+		      || unique_section_p (s, NULL))
 		    constraint = SPECIAL;
 
 		  if (!ldemul_place_orphan (s, name, constraint))
Index: ld/emultempl/genelf.em
===================================================================
RCS file: /cvs/src/src/ld/emultempl/genelf.em,v
retrieving revision 1.6
diff -u -p -r1.6 genelf.em
--- ld/emultempl/genelf.em	2 Sep 2009 07:25:35 -0000	1.6
+++ ld/emultempl/genelf.em	18 Feb 2010 08:43:17 -0000
@@ -48,6 +48,15 @@ gld${EMULATION_NAME}_after_open (void)
 }
 
 static void
+gld${EMULATION_NAME}_before_allocation (void)
+{
+  if (link_info.relocatable
+      && !_bfd_elf_size_group_sections (&link_info))
+    einfo ("%X%P: can not size group sections: %E\n");
+  before_allocation_default ();
+}
+
+static void
 gld${EMULATION_NAME}_after_allocation (void)
 {
   gld${EMULATION_NAME}_map_segments (FALSE);
@@ -56,4 +65,5 @@ EOF
 # Put these extra routines in ld_${EMULATION_NAME}_emulation
 #
 LDEMUL_AFTER_OPEN=gld${EMULATION_NAME}_after_open
+LDEMUL_BEFORE_ALLOCATION=gld${EMULATION_NAME}_before_allocation
 LDEMUL_AFTER_ALLOCATION=gld${EMULATION_NAME}_after_allocation
Index: ld/testsuite/ld-elf/group.ld
===================================================================
RCS file: /cvs/src/src/ld/testsuite/ld-elf/group.ld,v
retrieving revision 1.3
diff -u -p -r1.3 group.ld
--- ld/testsuite/ld-elf/group.ld	18 May 2007 19:04:51 -0000	1.3
+++ ld/testsuite/ld-elf/group.ld	18 Feb 2010 08:43:17 -0000
@@ -2,5 +2,5 @@ SECTIONS
 {
   . = 0x1000;
   .text : { *(.text) *(.rodata.brlt) }
-  /DISCARD/ : { *(.reginfo) }
+  /DISCARD/ : { *(.dropme) *(.reginfo) }
 }
Index: ld/testsuite/ld-elf/group10.d
===================================================================
RCS file: ld/testsuite/ld-elf/group10.d
diff -N ld/testsuite/ld-elf/group10.d
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-elf/group10.d	18 Feb 2010 08:53:48 -0000
@@ -0,0 +1,11 @@
+#source: group10.s
+#ld: -r -T group.ld
+#readelf: -Sg --wide
+
+#...
+group section \[[ 0-9]+\] `foo_group' \[foo_group\] contains 4 sections:
+   \[Index\]    Name
+   \[[ 0-9]+\]   \.text.*
+   \[[ 0-9]+\]   \.rodata\.str.*
+   \[[ 0-9]+\]   \.data.*
+   \[[ 0-9]+\]   \.keepme.*
Index: ld/testsuite/ld-elf/group10.s
===================================================================
RCS file: ld/testsuite/ld-elf/group10.s
diff -N ld/testsuite/ld-elf/group10.s
--- /dev/null	1 Jan 1970 00:00:00 -0000
+++ ld/testsuite/ld-elf/group10.s	18 Feb 2010 08:53:48 -0000
@@ -0,0 +1,14 @@
+	.section .text.foo,"axG",%progbits,foo_group
+	.word 0
+
+	.section .rodata.str.1,"aMSG",%progbits,1,foo_group
+	.asciz "abc"
+
+	.section .data.foo,"waG",%progbits,foo_group
+	.word 1
+
+	.section .dropme,"G",%progbits,foo_group
+	.word 2
+
+	.section .keepme,"G",%progbits,foo_group
+	.word 3

-- 
Alan Modra
Australia Development Lab, IBM