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Re: Group identifier of a comdat group


On Wed, Jun 05, 2002 at 10:39:00AM +0930, Alan Modra wrote:
> Sounds like a problem in the object file itself.

Problem is with the author of this code (ie. me).  This fixes the
symbol problem (which I wasn't seeing due to using .group as the
section name for all SHT_GROUP sections in my local copy of gas).
Also makes objcopy and ld -r work, at least with my simple testcases.

bfd/ChangeLog
	* elf.c (group_signature): Swap in the whole symbol, and handle
	extracting section symbol names.
	(setup_group): Add comment.
	(set_group_contents): When called from objcopy or ld, arrange for
	section contents to be written.  Write group member output section
	indices to allow objcopy to reorganize sections.
	(_bfd_elf_copy_private_section_data): Copy group info.

binutils/ChangeLog
	* objcopy.c (copy_section): Don't copy SEC_GROUP sections.

ld/ChangeLog
	* emultempl/elf32.em (gld${EMULATION_NAME}_place_orphan): Place
	SEC_EXCLUDE sections when doing a relocatable link.

Index: bfd/elf.c
===================================================================
RCS file: /cvs/src/src/bfd/elf.c,v
retrieving revision 1.143
diff -u -p -r1.143 elf.c
--- bfd/elf.c	5 Jun 2002 03:43:09 -0000	1.143
+++ bfd/elf.c	5 Jun 2002 14:00:26 -0000
@@ -372,23 +372,54 @@ group_signature (abfd, ghdr)
 {
   struct elf_backend_data *bed;
   file_ptr pos;
-  unsigned char ename[4];
-  unsigned long iname;
+  bfd_size_type amt;
+  Elf_Internal_Shdr *hdr;
+  Elf_Internal_Shdr *shndx_hdr;
+  unsigned char esym[sizeof (Elf64_External_Sym)];
+  Elf_External_Sym_Shndx eshndx;
+  Elf_Internal_Sym isym;
+  unsigned int iname;
+  unsigned int shindex;
 
   /* First we need to ensure the symbol table is available.  */
   if (! bfd_section_from_shdr (abfd, ghdr->sh_link))
     return NULL;
 
-  /* Fortunately, the name index is at the same place in the external
-     symbol for both 32 and 64 bit ELF.  */
+  /* Go read the symbol.  */
+  hdr = &elf_tdata (abfd)->symtab_hdr;
   bed = get_elf_backend_data (abfd);
-  pos = elf_tdata (abfd)->symtab_hdr.sh_offset;
-  pos += ghdr->sh_info * bed->s->sizeof_sym;
+  amt = bed->s->sizeof_sym;
+  pos = hdr->sh_offset + ghdr->sh_info * amt;
   if (bfd_seek (abfd, pos, SEEK_SET) != 0
-      || bfd_bread (ename, (bfd_size_type) 4, abfd) != 4)
+      || bfd_bread (esym, amt, abfd) != amt)
     return NULL;
-  iname = H_GET_32 (abfd, ename);
-  return elf_string_from_elf_strtab (abfd, iname);
+
+  /* And possibly the symbol section index extension.  */
+  shndx_hdr = &elf_tdata (abfd)->symtab_shndx_hdr;
+  if (elf_elfsections (abfd) != NULL
+      && elf_elfsections (abfd)[shndx_hdr->sh_link] == hdr)
+    {
+      amt = sizeof (Elf_External_Sym_Shndx);
+      pos = shndx_hdr->sh_offset + ghdr->sh_info * amt;
+      if (bfd_seek (abfd, pos, SEEK_SET) != 0
+	  || bfd_bread ((PTR) &eshndx, amt, abfd) != amt)
+	return NULL;
+    }
+
+  /* Convert to internal format.  */
+  (*bed->s->swap_symbol_in) (abfd, (const PTR *) &esym, (const PTR *) &eshndx,
+			     &isym);
+
+  /* Look up the symbol name.  */
+  iname = isym.st_name;
+  shindex = hdr->sh_link;
+  if (iname == 0 && ELF_ST_TYPE (isym.st_info) == STT_SECTION)
+    {
+      iname = elf_elfsections (abfd)[isym.st_shndx]->sh_name;
+      shindex = elf_elfheader (abfd)->e_shstrndx;
+    }
+
+  return bfd_elf_string_from_elf_section (abfd, shindex, iname);
 }
 
 /* Set next_in_group list pointer, and group name for NEWSECT.  */
@@ -536,6 +567,8 @@ setup_group (abfd, hdr, newsect)
 		    elf_next_in_group (newsect) = newsect;
 		  }
 
+		/* If the group section has been created, point to the
+		   new member.  */
 		if (shdr->bfd_section != NULL)
 		  elf_next_in_group (shdr->bfd_section) = newsect;
 
@@ -2357,9 +2390,10 @@ set_group_contents (abfd, sec, failedptr
 {
   boolean *failedptr = (boolean *) failedptrarg;
   unsigned long symindx;
-  asection *elt;
+  asection *elt, *first;
   unsigned char *loc;
   struct bfd_link_order *l;
+  boolean gas;
 
   if (elf_section_data (sec)->this_hdr.sh_type != SHT_GROUP
       || *failedptr)
@@ -2374,10 +2408,15 @@ set_group_contents (abfd, sec, failedptr
     symindx = elf_section_data (sec)->this_idx;
   elf_section_data (sec)->this_hdr.sh_info = symindx;
 
-  /* Nor will the contents be allocated for "ld -r".  */
+  /* Nor will the contents be allocated for "ld -r" or objcopy.  */
+  gas = true;
   if (sec->contents == NULL)
     {
+      gas = false;
       sec->contents = bfd_alloc (abfd, sec->_raw_size);
+
+      /* Arrange for the section to be written out.  */
+      elf_section_data (sec)->this_hdr.contents = sec->contents;
       if (sec->contents == NULL)
 	{
 	  *failedptr = true;
@@ -2387,9 +2426,10 @@ set_group_contents (abfd, sec, failedptr
 
   loc = sec->contents + sec->_raw_size;
 
-  /* Get the pointer to the first section in the group that we
-     squirreled away here.  */
-  elt = elf_next_in_group (sec);
+  /* Get the pointer to the first section in the group that gas
+     squirreled away here.  objcopy arranges for this to be set to the
+     start of the input section group.  */
+  first = elt = elf_next_in_group (sec);
 
   /* First element is a flag word.  Rest of section is elf section
      indices for all the sections of the group.  Write them backwards
@@ -2397,9 +2437,20 @@ set_group_contents (abfd, sec, failedptr
      directives, not that it matters.  */
   while (elt != NULL)
     {
+      asection *s;
+      unsigned int idx;
+
       loc -= 4;
-      H_PUT_32 (abfd, elf_section_data (elt)->this_idx, loc);
+      s = elt;
+      if (!gas)
+	s = s->output_section;
+      idx = 0;
+      if (s != NULL)
+	idx = elf_section_data (s)->this_idx;
+      H_PUT_32 (abfd, idx, loc);
       elt = elf_next_in_group (elt);
+      if (elt == first)
+	break;
     }
 
   /* If this is a relocatable link, then the above did nothing because
@@ -2418,10 +2469,16 @@ set_group_contents (abfd, sec, failedptr
 	}
       while (elt != elf_next_in_group (l->u.indirect.section));
 
-  loc -= 4;
-  H_PUT_32 (abfd, sec->flags & SEC_LINK_ONCE ? GRP_COMDAT : 0, loc);
+  /* With ld -r, merging SHT_GROUP sections results in wasted space
+     due to allowing for the flag word on each input.  We may well
+     duplicate entries too.  */
+  while ((loc -= 4) > sec->contents)
+    H_PUT_32 (abfd, 0, loc);
+
+  if (loc != sec->contents)
+    abort ();
 
-  BFD_ASSERT (loc == sec->contents);
+  H_PUT_32 (abfd, sec->flags & SEC_LINK_ONCE ? GRP_COMDAT : 0, loc);
 }
 
 /* Assign all ELF section numbers.  The dummy first section is handled here
@@ -4940,6 +4997,12 @@ _bfd_elf_copy_private_section_data (ibfd
       || ihdr->sh_type == SHT_GNU_verneed
       || ihdr->sh_type == SHT_GNU_verdef)
     ohdr->sh_info = ihdr->sh_info;
+
+  /* Set things up for objcopy.  The output SHT_GROUP section will
+     have its elf_next_in_group pointing back to the input group
+     members.  */
+  elf_next_in_group (osec) = elf_next_in_group (isec);
+  elf_group_name (osec) = elf_group_name (isec);
 
   elf_section_data (osec)->use_rela_p
     = elf_section_data (isec)->use_rela_p;
Index: binutils/objcopy.c
===================================================================
RCS file: /cvs/src/src/binutils/objcopy.c,v
retrieving revision 1.39
diff -u -p -r1.39 objcopy.c
--- binutils/objcopy.c	21 May 2002 19:34:58 -0000	1.39
+++ binutils/objcopy.c	5 Jun 2002 13:40:33 -0000
@@ -1684,18 +1684,23 @@ copy_section (ibfd, isection, obfdarg)
   sec_ptr osection;
   bfd_size_type size;
   long relsize;
+  flagword flags;
 
   /* If we have already failed earlier on,
      do not keep on generating complaints now.  */
   if (status != 0)
     return;
 
-  if ((bfd_get_section_flags (ibfd, isection) & SEC_DEBUGGING) != 0
+  flags = bfd_get_section_flags (ibfd, isection);
+  if ((flags & SEC_DEBUGGING) != 0
       && (strip_symbols == STRIP_DEBUG
 	  || strip_symbols == STRIP_UNNEEDED
 	  || strip_symbols == STRIP_ALL
 	  || discard_locals == LOCALS_ALL
 	  || convert_debugging))
+    return;
+
+  if ((flags & SEC_GROUP) != 0)
     return;
 
   p = find_section_list (bfd_section_name (ibfd, isection), false);
Index: ld/emultempl/elf32.em
===================================================================
RCS file: /cvs/src/src/ld/emultempl/elf32.em,v
retrieving revision 1.76
diff -u -p -r1.76 elf32.em
--- ld/emultempl/elf32.em	27 May 2002 08:22:08 -0000	1.76
+++ ld/emultempl/elf32.em	5 Jun 2002 14:00:27 -0000
@@ -1107,7 +1107,7 @@ gld${EMULATION_NAME}_place_orphan (file,
 #define HAVE_SECTION(hold, name) \
 (hold.os != NULL || (hold.os = lang_output_section_find (name)) != NULL)
 
-  if (s->flags & SEC_EXCLUDE)
+  if ((s->flags & SEC_EXCLUDE) != 0 && !link_info.relocateable)
     {
       if (s->output_section == NULL)
 	s->output_section = bfd_abs_section_ptr;

-- 
Alan Modra
IBM OzLabs - Linux Technology Centre


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