dl-lookup.c

用于嵌入式Linux系统的标准C的库函数

  if (! _dl_do_lookup (undef_name, hash, *ref, &current_value, *scope, i,
		       skip_map, 0))
    while (*++scope)
      if (_dl_do_lookup (undef_name, hash, *ref, &current_value, *scope, 0,
			 skip_map, 0))
	break;

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_mask & DL_DEBUG_BINDINGS, 0))
    _dl_debug_printf ("binding file %s to %s: %s symbol `%s'\n",
		       (reference_name && reference_name[0]
			? reference_name : (_dl_argv[0] ?: "<main program>")),
		       current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       protected ? "protected" : "normal", undef_name);

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky.  We need to figure out what value to
         return for the protected symbol.  */
      struct sym_val protected_value = { NULL, NULL };

      if (i >= (*scope)->r_nlist
	  || !_dl_do_lookup (undef_name, hash, *ref, &protected_value, *scope,
			     i, skip_map, ELF_RTYPE_CLASS_PLT))
	while (*++scope)
	  if (_dl_do_lookup (undef_name, hash, *ref, &protected_value, *scope,
			     0, skip_map, ELF_RTYPE_CLASS_PLT))
	    break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* This function works like _dl_lookup_symbol but it takes an
   additional arguement with the version number of the requested
   symbol.

   XXX We'll see whether we need this separate function.  */
lookup_t
internal_function
_dl_lookup_versioned_symbol (const char *undef_name,
			     struct link_map *undef_map, const ElfW(Sym) **ref,
			     struct r_scope_elem *symbol_scope[],
			     const struct r_found_version *version,
			     int type_class, int explicit)
{
  unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;
  int protected;

  ++_dl_num_relocations;

  /* Search the relevant loaded objects for a definition.  */
  for (scope = symbol_scope; *scope; ++scope)
    {
      int res = do_lookup_versioned (undef_name, hash, *ref, &current_value,
				     *scope, 0, version, NULL, type_class);
      if (res > 0)
	{
	  /* We have to check whether this would bind UNDEF_MAP to an object
	     in the global scope which was dynamically loaded.  In this case
	     we have to prevent the latter from being unloaded unless the
	     UNDEF_MAP object is also unloaded.  */
	  if (__builtin_expect (current_value.m->l_type == lt_loaded, 0)
	      /* Don't do this for explicit lookups as opposed to implicit
		 runtime lookups.  */
	      && ! explicit
	      /* Add UNDEF_MAP to the dependencies.  */
	      && add_dependency (undef_map, current_value.m) < 0)
	    /* Something went wrong.  Perhaps the object we tried to reference
	       was just removed.  Try finding another definition.  */
	    return _dl_lookup_versioned_symbol (undef_name, undef_map, ref,
						symbol_scope, version,
						type_class, 0);

	  break;
	}

      if (__builtin_expect (res, 0) < 0)
	{
	  /* Oh, oh.  The file named in the relocation entry does not
	     contain the needed symbol.  */
	  const char *reference_name = undef_map ? undef_map->l_name : NULL;

	  /* XXX We cannot translate the message.  */
	  _dl_signal_cerror (0, (reference_name && reference_name[0]
				 ? reference_name
				 : (_dl_argv[0] ?: "<main program>")),
			     N_("relocation error"),
			     make_string ("symbol ", undef_name, ", version ",
					  version->name,
					  " not defined in file ",
					  version->filename,
					  " with link time reference",
					  res == -2
					  ? " (no version symbols)" : ""));
	  *ref = NULL;
	  return 0;
	}
    }

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	{
	  /* We could find no value for a strong reference.  */
	  const char *reference_name = undef_map ? undef_map->l_name : NULL;

	  /* XXX We cannot translate the message.  */
	  _dl_signal_cerror (0, (reference_name && reference_name[0]
				 ? reference_name
				 : (_dl_argv[0] ?: "<main program>")), NULL,
			     make_string (undefined_msg, undef_name,
					  ", version ",
					  version->name ?: NULL));
	}
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_mask & DL_DEBUG_BINDINGS, 0))
    {
      const char *reference_name = undef_map ? undef_map->l_name : NULL;

      _dl_debug_printf ("binding file %s to %s: %s symbol `%s' [%s]\n",
			(reference_name && reference_name[0]
			 ? reference_name : (_dl_argv[0] ?: "<main program>")),
			current_value.m->l_name[0]
			? current_value.m->l_name : _dl_argv[0],
			protected ? "protected" : "normal",
			undef_name, version->name);
    }

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky. We need to figure out what value to
         return for the protected symbol */
      struct sym_val protected_value = { NULL, NULL };

      for (scope = symbol_scope; *scope; ++scope)
	if (_dl_do_lookup_versioned (undef_name, hash, *ref, &protected_value,
				     *scope, 0, version, NULL,
				     ELF_RTYPE_CLASS_PLT))
	  break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* Similar to _dl_lookup_symbol_skip but takes an additional argument
   with the version we are looking for.  */
lookup_t
internal_function
_dl_lookup_versioned_symbol_skip (const char *undef_name,
				  struct link_map *undef_map,
				  const ElfW(Sym) **ref,
				  struct r_scope_elem *symbol_scope[],
				  const struct r_found_version *version,
				  struct link_map *skip_map)
{
  const char *reference_name = undef_map ? undef_map->l_name : NULL;
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;
  size_t i;
  int protected;

  ++_dl_num_relocations;

  /* Search the relevant loaded objects for a definition.  */
  scope = symbol_scope;
  for (i = 0; (*scope)->r_list[i] != skip_map; ++i)
    assert (i < (*scope)->r_nlist);

  if (! _dl_do_lookup_versioned (undef_name, hash, *ref, &current_value,
				 *scope, i, version, skip_map, 0))
    while (*++scope)
      if (_dl_do_lookup_versioned (undef_name, hash, *ref, &current_value,
				   *scope, 0, version, skip_map, 0))
	break;

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	{
	  /* We could find no value for a strong reference.  */
	  const size_t len = strlen (undef_name);
	  char buf[sizeof undefined_msg + len];
          char *tmp;
          tmp = memcpy (buf, undefined_msg, sizeof undefined_msg - 1);
          tmp += (sizeof undefined_msg - 1);

	  memcpy (tmp, undef_name, len + 1);

	  /* XXX We cannot translate the messages.  */
	  _dl_signal_cerror (0, (reference_name && reference_name[0]
				 ? reference_name
				 : (_dl_argv[0] ?: "<main program>")),
			     NULL, buf);
	}
      *ref = NULL;
      return 0;
    }

  protected = *ref && ELFW(ST_VISIBILITY) ((*ref)->st_other) == STV_PROTECTED;

  if (__builtin_expect (_dl_debug_mask & DL_DEBUG_BINDINGS, 0))
    _dl_debug_printf ("binding file %s to %s: %s symbol `%s' [%s]\n",
		      (reference_name && reference_name[0]
		       ? reference_name : (_dl_argv[0] ?: "<main program>")),
		      current_value.m->l_name[0]
		      ? current_value.m->l_name : _dl_argv[0],
		      protected ? "protected" : "normal",
		      undef_name, version->name);

  if (__builtin_expect (protected == 0, 1))
    {
      *ref = current_value.s;
      return LOOKUP_VALUE (current_value.m);
    }
  else
    {
      /* It is very tricky. We need to figure out what value to
         return for the protected symbol */
      struct sym_val protected_value = { NULL, NULL };

      if (i >= (*scope)->r_nlist
	  || !_dl_do_lookup_versioned (undef_name, hash, *ref,
				       &protected_value, *scope, i, version,
				       skip_map, ELF_RTYPE_CLASS_PLT))
	while (*++scope)
	  if (_dl_do_lookup_versioned (undef_name, hash, *ref,
				       &protected_value, *scope, 0, version,
				       skip_map, ELF_RTYPE_CLASS_PLT))
	    break;

      if (protected_value.s == NULL || protected_value.m == undef_map)
	{
	  *ref = current_value.s;
	  return LOOKUP_VALUE (current_value.m);
	}

      return LOOKUP_VALUE (undef_map);
    }
}


/* Cache the location of MAP's hash table.  */

void
internal_function
_dl_setup_hash (struct link_map *map)
{
  Elf_Symndx *hash;
  Elf_Symndx nchain;

  if (!map->l_info[DT_HASH])
    return;
  hash = (void *)(map->l_addr + map->l_info[DT_HASH]->d_un.d_ptr);

  map->l_nbuckets = *hash++;
  nchain = *hash++;
  map->l_buckets = hash;
  hash += map->l_nbuckets;
  map->l_chain = hash;
}

/* These are here so that we only inline do_lookup{,_versioned} in the common
   case, not everywhere.  */
static int
internal_function
_dl_do_lookup (const char *undef_name, unsigned long int hash,
	       const ElfW(Sym) *ref, struct sym_val *result,
	       struct r_scope_elem *scope, size_t i,
	       struct link_map *skip, int type_class)
{
  return do_lookup (undef_name, hash, ref, result, scope, i, skip,
		    type_class);
}

static int
internal_function
_dl_do_lookup_versioned (const char *undef_name, unsigned long int hash,
			 const ElfW(Sym) *ref, struct sym_val *result,
			 struct r_scope_elem *scope, size_t i,
			 const struct r_found_version *const version,
			 struct link_map *skip, int type_class)
{
  return do_lookup_versioned (undef_name, hash, ref, result, scope, i,
			      version, skip, type_class);
}