elflink.h

来自「基于4个mips核的noc设计」· C头文件 代码 · 共 2,075 行 · 第 1/5 页

/* ELF linker support.
   Copyright 1995, 1996, 1997, 1998, 1999, 2000, 2001
   Free Software Foundation, Inc.

This file is part of BFD, the Binary File Descriptor library.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/* ELF linker code.  */

/* This struct is used to pass information to routines called via
   elf_link_hash_traverse which must return failure.  */

struct elf_info_failed
{
  boolean failed;
  struct bfd_link_info *info;
};

static boolean elf_link_add_object_symbols
  PARAMS ((bfd *, struct bfd_link_info *));
static boolean elf_link_add_archive_symbols
  PARAMS ((bfd *, struct bfd_link_info *));
static boolean elf_merge_symbol
  PARAMS ((bfd *, struct bfd_link_info *, const char *, Elf_Internal_Sym *,
	   asection **, bfd_vma *, struct elf_link_hash_entry **,
	   boolean *, boolean *, boolean *, boolean));
static boolean elf_export_symbol
  PARAMS ((struct elf_link_hash_entry *, PTR));
static boolean elf_fix_symbol_flags
  PARAMS ((struct elf_link_hash_entry *, struct elf_info_failed *));
static boolean elf_adjust_dynamic_symbol
  PARAMS ((struct elf_link_hash_entry *, PTR));
static boolean elf_link_find_version_dependencies
  PARAMS ((struct elf_link_hash_entry *, PTR));
static boolean elf_link_find_version_dependencies
  PARAMS ((struct elf_link_hash_entry *, PTR));
static boolean elf_link_assign_sym_version
  PARAMS ((struct elf_link_hash_entry *, PTR));
static boolean elf_collect_hash_codes
  PARAMS ((struct elf_link_hash_entry *, PTR));
static boolean elf_link_read_relocs_from_section
  PARAMS ((bfd *, Elf_Internal_Shdr *, PTR, Elf_Internal_Rela *));
static void elf_link_output_relocs
  PARAMS ((bfd *, asection *, Elf_Internal_Shdr *, Elf_Internal_Rela *));
static boolean elf_link_size_reloc_section
  PARAMS ((bfd *, Elf_Internal_Shdr *, asection *));
static void elf_link_adjust_relocs
  PARAMS ((bfd *, Elf_Internal_Shdr *, unsigned int,
	   struct elf_link_hash_entry **));

/* Given an ELF BFD, add symbols to the global hash table as
   appropriate.  */

boolean
elf_bfd_link_add_symbols (abfd, info)
     bfd *abfd;
     struct bfd_link_info *info;
{
  switch (bfd_get_format (abfd))
    {
    case bfd_object:
      return elf_link_add_object_symbols (abfd, info);
    case bfd_archive:
      return elf_link_add_archive_symbols (abfd, info);
    default:
      bfd_set_error (bfd_error_wrong_format);
      return false;
    }
}

/* Return true iff this is a non-common, definition of a non-function symbol.  */
static boolean
is_global_data_symbol_definition (abfd, sym)
     bfd * abfd ATTRIBUTE_UNUSED;
     Elf_Internal_Sym * sym;
{
  /* Local symbols do not count, but target specific ones might.  */
  if (ELF_ST_BIND (sym->st_info) != STB_GLOBAL
      && ELF_ST_BIND (sym->st_info) < STB_LOOS)
    return false;

  /* Function symbols do not count.  */
  if (ELF_ST_TYPE (sym->st_info) == STT_FUNC)
    return false;

  /* If the section is undefined, then so is the symbol.  */
  if (sym->st_shndx == SHN_UNDEF)
    return false;

  /* If the symbol is defined in the common section, then
     it is a common definition and so does not count.  */
  if (sym->st_shndx == SHN_COMMON)
    return false;

  /* If the symbol is in a target specific section then we
     must rely upon the backend to tell us what it is.  */
  if (sym->st_shndx >= SHN_LORESERVE && sym->st_shndx < SHN_ABS)
    /* FIXME - this function is not coded yet:

       return _bfd_is_global_symbol_definition (abfd, sym);

       Instead for now assume that the definition is not global,
       Even if this is wrong, at least the linker will behave
       in the same way that it used to do.  */
    return false;

  return true;
}

/* Search the symbol table of the archive element of the archive ABFD
   whose archive map contains a mention of SYMDEF, and determine if
   the symbol is defined in this element.  */
static boolean
elf_link_is_defined_archive_symbol (abfd, symdef)
     bfd * abfd;
     carsym * symdef;
{
  Elf_Internal_Shdr * hdr;
  Elf_External_Sym *  esym;
  Elf_External_Sym *  esymend;
  Elf_External_Sym *  buf = NULL;
  size_t symcount;
  size_t extsymcount;
  size_t extsymoff;
  boolean result = false;

  abfd = _bfd_get_elt_at_filepos (abfd, symdef->file_offset);
  if (abfd == (bfd *) NULL)
    return false;

  if (! bfd_check_format (abfd, bfd_object))
    return false;

  /* If we have already included the element containing this symbol in the
     link then we do not need to include it again.  Just claim that any symbol
     it contains is not a definition, so that our caller will not decide to
     (re)include this element.  */
  if (abfd->archive_pass)
    return false;

  /* Select the appropriate symbol table.  */
  if ((abfd->flags & DYNAMIC) == 0 || elf_dynsymtab (abfd) == 0)
    hdr = &elf_tdata (abfd)->symtab_hdr;
  else
    hdr = &elf_tdata (abfd)->dynsymtab_hdr;

  symcount = hdr->sh_size / sizeof (Elf_External_Sym);

  /* The sh_info field of the symtab header tells us where the
     external symbols start.  We don't care about the local symbols.  */
  if (elf_bad_symtab (abfd))
    {
      extsymcount = symcount;
      extsymoff = 0;
    }
  else
    {
      extsymcount = symcount - hdr->sh_info;
      extsymoff = hdr->sh_info;
    }

  buf = ((Elf_External_Sym *)
	 bfd_malloc (extsymcount * sizeof (Elf_External_Sym)));
  if (buf == NULL && extsymcount != 0)
    return false;

  /* Read in the symbol table.
     FIXME:  This ought to be cached somewhere.  */
  if (bfd_seek (abfd,
		hdr->sh_offset + extsymoff * sizeof (Elf_External_Sym),
		SEEK_SET) != 0
      || (bfd_read ((PTR) buf, sizeof (Elf_External_Sym), extsymcount, abfd)
	  != extsymcount * sizeof (Elf_External_Sym)))
    {
      free (buf);
      return false;
    }

  /* Scan the symbol table looking for SYMDEF.  */
  esymend = buf + extsymcount;
  for (esym = buf;
       esym < esymend;
       esym++)
    {
      Elf_Internal_Sym sym;
      const char * name;

      elf_swap_symbol_in (abfd, esym, & sym);

      name = bfd_elf_string_from_elf_section (abfd, hdr->sh_link, sym.st_name);
      if (name == (const char *) NULL)
	break;

      if (strcmp (name, symdef->name) == 0)
	{
	  result = is_global_data_symbol_definition (abfd, & sym);
	  break;
	}
    }

  free (buf);

  return result;
}

/* Add symbols from an ELF archive file to the linker hash table.  We
   don't use _bfd_generic_link_add_archive_symbols because of a
   problem which arises on UnixWare.  The UnixWare libc.so is an
   archive which includes an entry libc.so.1 which defines a bunch of
   symbols.  The libc.so archive also includes a number of other
   object files, which also define symbols, some of which are the same
   as those defined in libc.so.1.  Correct linking requires that we
   consider each object file in turn, and include it if it defines any
   symbols we need.  _bfd_generic_link_add_archive_symbols does not do
   this; it looks through the list of undefined symbols, and includes
   any object file which defines them.  When this algorithm is used on
   UnixWare, it winds up pulling in libc.so.1 early and defining a
   bunch of symbols.  This means that some of the other objects in the
   archive are not included in the link, which is incorrect since they
   precede libc.so.1 in the archive.

   Fortunately, ELF archive handling is simpler than that done by
   _bfd_generic_link_add_archive_symbols, which has to allow for a.out
   oddities.  In ELF, if we find a symbol in the archive map, and the
   symbol is currently undefined, we know that we must pull in that
   object file.

   Unfortunately, we do have to make multiple passes over the symbol
   table until nothing further is resolved.  */

static boolean
elf_link_add_archive_symbols (abfd, info)
     bfd *abfd;
     struct bfd_link_info *info;
{
  symindex c;
  boolean *defined = NULL;
  boolean *included = NULL;
  carsym *symdefs;
  boolean loop;

  if (! bfd_has_map (abfd))
    {
      /* An empty archive is a special case.  */
      if (bfd_openr_next_archived_file (abfd, (bfd *) NULL) == NULL)
	return true;
      bfd_set_error (bfd_error_no_armap);
      return false;
    }

  /* Keep track of all symbols we know to be already defined, and all
     files we know to be already included.  This is to speed up the
     second and subsequent passes.  */
  c = bfd_ardata (abfd)->symdef_count;
  if (c == 0)
    return true;
  defined = (boolean *) bfd_malloc (c * sizeof (boolean));
  included = (boolean *) bfd_malloc (c * sizeof (boolean));
  if (defined == (boolean *) NULL || included == (boolean *) NULL)
    goto error_return;
  memset (defined, 0, c * sizeof (boolean));
  memset (included, 0, c * sizeof (boolean));

  symdefs = bfd_ardata (abfd)->symdefs;

  do
    {
      file_ptr last;
      symindex i;
      carsym *symdef;
      carsym *symdefend;

      loop = false;
      last = -1;

      symdef = symdefs;
      symdefend = symdef + c;
      for (i = 0; symdef < symdefend; symdef++, i++)
	{
	  struct elf_link_hash_entry *h;
	  bfd *element;
	  struct bfd_link_hash_entry *undefs_tail;
	  symindex mark;

	  if (defined[i] || included[i])
	    continue;
	  if (symdef->file_offset == last)
	    {
	      included[i] = true;
	      continue;
	    }

	  h = elf_link_hash_lookup (elf_hash_table (info), symdef->name,
				    false, false, false);

	  if (h == NULL)
	    {
	      char *p, *copy;

	      /* If this is a default version (the name contains @@),
		 look up the symbol again without the version.  The
		 effect is that references to the symbol without the
		 version will be matched by the default symbol in the
		 archive.  */

	      p = strchr (symdef->name, ELF_VER_CHR);
	      if (p == NULL || p[1] != ELF_VER_CHR)
		continue;

	      copy = bfd_alloc (abfd, p - symdef->name + 1);
	      if (copy == NULL)
		goto error_return;
	      memcpy (copy, symdef->name, p - symdef->name);
	      copy[p - symdef->name] = '\0';

	      h = elf_link_hash_lookup (elf_hash_table (info), copy,
					false, false, false);

	      bfd_release (abfd, copy);
	    }

	  if (h == NULL)
	    continue;

	  if (h->root.type == bfd_link_hash_common)
	    {
	      /* We currently have a common symbol.  The archive map contains
		 a reference to this symbol, so we may want to include it.  We
		 only want to include it however, if this archive element
		 contains a definition of the symbol, not just another common
		 declaration of it.

		 Unfortunately some archivers (including GNU ar) will put
		 declarations of common symbols into their archive maps, as
		 well as real definitions, so we cannot just go by the archive
		 map alone.  Instead we must read in the element's symbol
		 table and check that to see what kind of symbol definition
		 this is.  */
	      if (! elf_link_is_defined_archive_symbol (abfd, symdef))
		continue;
	    }
	  else if (h->root.type != bfd_link_hash_undefined)
	    {
	      if (h->root.type != bfd_link_hash_undefweak)
		defined[i] = true;
	      continue;
	    }

	  /* We need to include this archive member.  */
	  element = _bfd_get_elt_at_filepos (abfd, symdef->file_offset);
	  if (element == (bfd *) NULL)
	    goto error_return;

	  if (! bfd_check_format (element, bfd_object))
	    goto error_return;

	  /* Doublecheck that we have not included this object
	     already--it should be impossible, but there may be
	     something wrong with the archive.  */
	  if (element->archive_pass != 0)
	    {
	      bfd_set_error (bfd_error_bad_value);
	      goto error_return;
	    }
	  element->archive_pass = 1;

	  undefs_tail = info->hash->undefs_tail;

	  if (! (*info->callbacks->add_archive_element) (info, element,
							 symdef->name))
	    goto error_return;
	  if (! elf_link_add_object_symbols (element, info))
	    goto error_return;

	  /* If there are any new undefined symbols, we need to make
	     another pass through the archive in order to see whether
	     they can be defined.  FIXME: This isn't perfect, because
	     common symbols wind up on undefs_tail and because an
	     undefined symbol which is defined later on in this pass
	     does not require another pass.  This isn't a bug, but it
	     does make the code less efficient than it could be.  */
	  if (undefs_tail != info->hash->undefs_tail)
	    loop = true;

	  /* Look backward to mark all symbols from this object file
	     which we have already seen in this pass.  */
	  mark = i;
	  do
	    {
	      included[mark] = true;
	      if (mark == 0)
		break;
	      --mark;
	    }
	  while (symdefs[mark].file_offset == symdef->file_offset);

	  /* We mark subsequent symbols from this object file as we go
	     on through the loop.  */
	  last = symdef->file_offset;
	}
    }
  while (loop);