dl-lookup.c

Newlib 嵌入式 C库 标准实现代码

/* Look up a symbol in the loaded objects.
   Copyright (C) 1995,96,97,98,99,2000,2001 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

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

#include <alloca.h>
#include <libintl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <ldsodefs.h>
#include "dl-hash.h"
#include <machine/dl-machine.h>
#include <bits/libc-lock.h>

#include <assert.h>

#define VERSTAG(tag)	(DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGIDX (tag))

/* We need this string more than once.  */
static const char undefined_msg[] = "undefined symbol: ";


struct sym_val
  {
    const ElfW(Sym) *s;
    struct link_map *m;
  };


#define make_string(string, rest...) \
  ({									      \
    const char *all[] = { string, ## rest };				      \
    size_t len, cnt;							      \
    char *result, *cp;							      \
									      \
    len = 1;								      \
    for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)		      \
      len += strlen (all[cnt]);						      \
									      \
    cp = result = alloca (len);						      \
    for (cnt = 0; cnt < sizeof (all) / sizeof (all[0]); ++cnt)		      \
    {                                                                         \
      cp = strcpy (cp, all[cnt]);					      \
      cp += strlen(all[cnt]);                                                 \
    }                                                                         \
									      \
    result;								      \
  })

/* Statistics function.  */
unsigned long int _dl_num_relocations;


/* We have two different situations when looking up a simple: with or
   without versioning.  gcc is not able to optimize a single function
   definition serving for both purposes so we define two functions.  */
#define VERSIONED	0
#include "do-lookup.h"

#define VERSIONED	1
#include "do-lookup.h"


/* Add extra dependency on MAP to UNDEF_MAP.  */
static int
internal_function
add_dependency (struct link_map *undef_map, struct link_map *map)
{
  struct link_map **list;
  struct link_map *runp;
  unsigned int act;
  unsigned int i;
  int result = 0;

  /* Avoid self-references.  */
  if (undef_map == map)
    return 0;

  /* Make sure nobody can unload the object while we are at it.  */
#ifdef HAVE_DD_LOCK
    __lock_acquire(_dl_load_lock);
#endif


  /* Determine whether UNDEF_MAP already has a reference to MAP.  First
     look in the normal dependencies.  */
  if (undef_map->l_searchlist.r_list != NULL)
    {
      list = undef_map->l_initfini;

      for (i = 0; list[i] != NULL; ++i)
	if (list[i] == map)
	  goto out;
    }

  /* No normal dependency.  See whether we already had to add it
     to the special list of dynamic dependencies.  */
  list = undef_map->l_reldeps;
  act = undef_map->l_reldepsact;

  for (i = 0; i < act; ++i)
    if (list[i] == map)
      goto out;

  /* The object is not yet in the dependency list.  Before we add
     it make sure just one more time the object we are about to
     reference is still available.  There is a brief period in
     which the object could have been removed since we found the
     definition.  */
  runp = _dl_loaded;
  while (runp != NULL && runp != map)
    runp = runp->l_next;

  if (runp != NULL)
    {
      /* The object is still available.  Add the reference now.  */
      if (__builtin_expect (act >= undef_map->l_reldepsmax, 0))
	{
	  /* Allocate more memory for the dependency list.  Since this
	     can never happen during the startup phase we can use
	     `realloc'.  */
	  void *newp;

	  undef_map->l_reldepsmax += 5;
	  newp = realloc (undef_map->l_reldeps,
			  undef_map->l_reldepsmax
			  * sizeof (struct link_map *));

	  if (__builtin_expect (newp != NULL, 1))
	    undef_map->l_reldeps = (struct link_map **) newp;
	  else
	    /* Correct the addition.  */
	    undef_map->l_reldepsmax -= 5;
	}

      /* If we didn't manage to allocate memory for the list this is
	 no fatal mistake.  We simply increment the use counter of the
	 referenced object and don't record the dependencies.  This
	 means this increment can never be reverted and the object
	 will never be unloaded.  This is semantically the correct
	 behaviour.  */
      if (__builtin_expect (act < undef_map->l_reldepsmax, 1))
	undef_map->l_reldeps[undef_map->l_reldepsact++] = map;

      if (map->l_searchlist.r_list != NULL)
	/* And increment the counter in the referenced object.  */
	++map->l_opencount;
      else
	/* We have to bump the counts for all dependencies since so far
	   this object was only a normal or transitive dependency.
	   Now it might be closed with _dl_close() directly.  */
	for (list = map->l_initfini; *list != NULL; ++list)
	  ++(*list)->l_opencount;

      /* Display information if we are debugging.  */
      if (__builtin_expect (_dl_debug_mask & DL_DEBUG_FILES, 0))
	_dl_debug_printf ("\
\nfile=%s;  needed by %s (relocation dependency)\n\n",
			  map->l_name[0] ? map->l_name : _dl_argv[0],
			  undef_map->l_name[0]
			  ? undef_map->l_name : _dl_argv[0]);
    }
  else
    /* Whoa, that was bad luck.  We have to search again.  */
    result = -1;

 out:
  /* Release the lock.  */
#ifdef HAVE_DD_LOCK
    __lock_release(_dl_load_lock);
#endif


  return result;
}

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);
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);


/* Search loaded objects' symbol tables for a definition of the symbol
   UNDEF_NAME.  */

lookup_t
internal_function
_dl_lookup_symbol (const char *undef_name, struct link_map *undef_map,
		   const ElfW(Sym) **ref, struct r_scope_elem *symbol_scope[],
		   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)
    if (do_lookup (undef_name, hash, *ref, &current_value, *scope, 0, NULL,
		   type_class))
      {
	/* 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_symbol (undef_name, undef_map, ref, symbol_scope,
				    type_class, 0);

	break;
      }

  if (__builtin_expect (current_value.s == NULL, 0))
    {
      const char *reference_name = undef_map ? undef_map->l_name : NULL;

      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	/* XXX We cannot translate the messages.  */
	_dl_signal_cerror (0, (reference_name && reference_name[0]
			       ? reference_name
			       : (_dl_argv[0] ?: "<main program>")),
			   N_("relocation error"),
			   make_string (undefined_msg, undef_name));
      *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'\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 };

      for (scope = symbol_scope; *scope; ++scope)
	if (_dl_do_lookup (undef_name, hash, *ref, &protected_value, *scope,
			   0, 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);
    }
}


/* This function is nearly the same as `_dl_lookup_symbol' but it
   skips in the first list all objects until SKIP_MAP is found.  I.e.,
   it only considers objects which were loaded after the described
   object.  If there are more search lists the object described by
   SKIP_MAP is only skipped.  */
lookup_t
internal_function
_dl_lookup_symbol_skip (const char *undef_name,
			struct link_map *undef_map, const ElfW(Sym) **ref,
			struct r_scope_elem *symbol_scope[],
			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);