RE: Group identifier of a comdat group

["Jessica Han" <jessica at cup dot hp dot com>]

I noticed that the change you made is in the group_signature, which is
trying to retrieve the group signature information used by objcopy and ld.
Is it possible to change the gas behavior, put the section names into
symtab/strtab directly? thanks.

>-----Original Message-----
>From: Alan Modra [mailto:amodra@bigpond.net.au]
>Sent: Wednesday, June 05, 2002 7:04 AM
>To: Jessica Han; binutils@sources.redhat.com; reva@cup.hp.com
>Subject: 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
>