glibc/elf/dl-lookup.c

/* Look up a symbol in the loaded objects.
   Copyright (C) 1995, 1996, 1997, 1998 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 Library General Public License as
   published by the Free Software Foundation; either version 2 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
   Library General Public License for more details.

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

#include <alloca.h>
#include <string.h>
#include <unistd.h>
#include <elf/ldsodefs.h>
#include "dl-hash.h"
#include <dl-machine.h>

#include <assert.h>

#define VERSTAG(tag)	(DT_NUM + DT_PROCNUM + 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 = __stpcpy (cp, all[cnt]);					      \
									      \
    result;								      \
  })

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


/* Inner part of the lookup functions.  We return a value > 0 if we
   found the symbol, the value 0 if nothing is found and < 0 if
   something bad happened.  */
static inline int
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, const char *reference_name,
	   const struct r_found_version *version, struct link_map *skip,
	   int reloc_type)
{
  struct link_map **list = scope->r_list;
  size_t n = scope->r_nlist;
  struct link_map *map;

  ++_dl_num_relocations;

  for (; i < n; ++i)
    {
      const ElfW(Sym) *symtab;
      const char *strtab;
      const ElfW(Half) *verstab;
      ElfW(Symndx) symidx;
      int num_versions = 0;
      const ElfW(Sym) *sym;
      const ElfW(Sym) *versioned_sym = NULL;

      map = list[i];

      /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
      if (skip != NULL && map == skip)
	continue;

      /* Skip objects that could not be opened, which can occur in trace
	 mode.  */
      if (map->l_opencount == 0)
	continue;

      /* Don't search the executable when resolving a copy reloc.  */
      if (elf_machine_lookup_noexec_p (reloc_type)
	  && map->l_type == lt_executable)
	continue;

      /* Skip objects without symbol tables.  */
      if (map->l_info[DT_SYMTAB] == NULL)
	continue;

      /* Print some debugging info if wanted.  */
      if (_dl_debug_symbols)
	_dl_debug_message (1, "symbol=", undef_name, ";  lookup in file=",
			   map->l_name[0] ? map->l_name : _dl_argv[0],
			   "\n", NULL);

      symtab = ((void *) map->l_addr + map->l_info[DT_SYMTAB]->d_un.d_ptr);
      strtab = ((void *) map->l_addr + map->l_info[DT_STRTAB]->d_un.d_ptr);
      verstab = map->l_versyms;

      /* Search the appropriate hash bucket in this object's symbol table
	 for a definition for the same symbol name.  */
      for (symidx = map->l_buckets[hash % map->l_nbuckets];
	   symidx != STN_UNDEF;
	   symidx = map->l_chain[symidx])
	{
	  sym = &symtab[symidx];

	  if (sym->st_value == 0 || /* No value.  */
	      (elf_machine_lookup_noplt_p (reloc_type) /* Reject PLT entry.  */
	       && sym->st_shndx == SHN_UNDEF))
	    continue;

	  if (ELFW(ST_TYPE) (sym->st_info) > STT_FUNC)
	    /* Ignore all but STT_NOTYPE, STT_OBJECT and STT_FUNC entries
	       since these are no code/data definitions.  */
	    continue;

	  if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
	    /* Not the symbol we are looking for.  */
	    continue;

	  if (version == NULL)
	    {
	      /* No specific version is selected.  When the object
		 file also does not define a version we have a match.
		 Otherwise we accept the default version, or in case
		 there is only one version defined, this one version.  */
	      if (verstab != NULL)
		{
		  ElfW(Half) ndx = verstab[symidx] & 0x7fff;
		  if (ndx > 2) /* map->l_versions[ndx].hash != 0) */
		    {
		      /* Don't accept hidden symbols.  */
		      if ((verstab[symidx] & 0x8000) == 0
			  && num_versions++ == 0)
			/* No version so far.  */
			versioned_sym = sym;
		      continue;
		    }
		}
	    }
	  else
	    {
	      if (verstab == NULL)
		{
		  /* We need a versioned system but haven't found any.
		     If this is the object which is referenced in the
		     verneed entry it is a bug in the library since a
		     symbol must not simply disappear.  */
		  if (version->filename != NULL
		      && _dl_name_match_p (version->filename, map))
		    return -2;
		  /* Otherwise we accept the symbol.  */
		}
	      else
		{
		  /* We can match the version information or use the
		     default one if it is not hidden.  */
		  ElfW(Half) ndx = verstab[symidx] & 0x7fff;
		  if ((map->l_versions[ndx].hash != version->hash
		       || strcmp (map->l_versions[ndx].name, version->name))
		      && (version->hidden || map->l_versions[ndx].hash
			  || (verstab[symidx] & 0x8000)))
		    /* It's not the version we want.  */
		    continue;
		}
	    }

	  /* There cannot be another entry for this symbol so stop here.  */
	  goto found_it;
	}

      /* If we have seem exactly one versioned symbol while we are
	 looking for an unversioned symbol and the version is not the
	 default version we still accept this symbol since there are
	 no possible ambiguities.  */
      sym = num_versions == 1 ? versioned_sym : NULL;

      if (sym != NULL)
	{
	found_it:
	  switch (ELFW(ST_BIND) (sym->st_info))
	    {
	    case STB_GLOBAL:
	      /* Global definition.  Just what we need.  */
	      result->s = sym;
	      result->m = map;
	      return 1;
	    case STB_WEAK:
	      /* Weak definition.  Use this value if we don't find another.  */
	      if (! result->s)
		{
		  result->s = sym;
		  result->m = map;
		}
	      break;
	    default:
	      /* Local symbols are ignored.  */
	      break;
	    }
	}

      /* If this current map is the one mentioned in the verneed entry
	 and we have not found a weak entry, it is a bug.  */
      if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
	  && _dl_name_match_p (version->filename, map))
	return -1;
    }

  /* We have not found anything until now.  */
  return 0;
}

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

ElfW(Addr)
internal_function
_dl_lookup_symbol (const char *undef_name, const ElfW(Sym) **ref,
		   struct r_scope_elem *symbol_scope[],
		   const char *reference_name,
		   int reloc_type)
{
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;

  /* 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, reference_name, NULL, NULL, reloc_type))
      break;

  if (current_value.s == NULL)
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	_dl_signal_error (0, (reference_name  && reference_name[0]
			      ? reference_name
			      : (_dl_argv[0] ?: "<main program>")),
			  make_string (undefined_msg, undef_name));
      *ref = NULL;
      return 0;
    }

  if (_dl_debug_bindings)
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": symbol `", undef_name, "'\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


/* 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.  */
ElfW(Addr)
internal_function
_dl_lookup_symbol_skip (const char *undef_name, const ElfW(Sym) **ref,
			struct r_scope_elem *symbol_scope[],
			const char *reference_name,
			struct link_map *skip_map)
{
  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;

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

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

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

  if (_dl_debug_bindings)
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": symbol `", undef_name, "' (skip)\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


/* 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.  */
ElfW(Addr)
internal_function
_dl_lookup_versioned_symbol (const char *undef_name, const ElfW(Sym) **ref,
			     struct r_scope_elem *symbol_scope[],
			     const char *reference_name,
			     const struct r_found_version *version,
			     int reloc_type)
{
  const unsigned long int hash = _dl_elf_hash (undef_name);
  struct sym_val current_value = { NULL, NULL };
  struct r_scope_elem **scope;

  /* Search the relevant loaded objects for a definition.  */
  for (scope = symbol_scope; *scope; ++scope)
    {
      int res = do_lookup (undef_name, hash, *ref, &current_value,
			   *scope, 0, reference_name, version, NULL, reloc_type);
      if (res > 0)
	break;

      if (res < 0)
	/* Oh, oh.  The file named in the relocation entry does not
	   contain the needed symbol.  */
	_dl_signal_error (0, (reference_name && reference_name[0]
			      ? reference_name
			      : (_dl_argv[0] ?: "<main program>")),
			  make_string ("symbol ", undef_name, ", version ",
				       version->name,
				       " not defined in file ",
				       version->filename,
				       " with link time reference",
				       res == -2
				       ? " (no version symbols)" : ""));
    }

  if (current_value.s == NULL)
    {
      if (*ref == NULL || ELFW(ST_BIND) ((*ref)->st_info) != STB_WEAK)
	/* We could find no value for a strong reference.  */
	_dl_signal_error (0, (reference_name && reference_name[0]
			      ? reference_name
			      : (_dl_argv[0] ?: "<main program>")),
			  make_string (undefined_msg, undef_name,
				       ", version ", version->name ?: NULL));
      *ref = NULL;
      return 0;
    }

  if (_dl_debug_bindings)
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ", current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": symbol `", undef_name, "' [", version->name,
		       "]\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


/* Similar to _dl_lookup_symbol_skip but takes an additional argument
   with the version we are looking for.  */
ElfW(Addr)
internal_function
_dl_lookup_versioned_symbol_skip (const char *undef_name,
				  const ElfW(Sym) **ref,
				  struct r_scope_elem *symbol_scope[],
				  const char *reference_name,
				  const struct r_found_version *version,
				  struct link_map *skip_map)
{
  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;

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

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

  if (current_value.s == NULL)
    {
      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];
	  __mempcpy (__mempcpy (buf, undefined_msg, sizeof undefined_msg - 1),
		     undef_name, len + 1);
	  _dl_signal_error (0, (reference_name && reference_name[0]
				? reference_name
				: (_dl_argv[0] ?: "<main program>")), buf);
	}
      *ref = NULL;
      return 0;
    }

  if (_dl_debug_bindings)
    _dl_debug_message (1, "binding file ",
		       (reference_name && reference_name[0]
			? reference_name
			: (_dl_argv[0] ?: "<main program>")),
		       " to ",
		       current_value.m->l_name[0]
		       ? current_value.m->l_name : _dl_argv[0],
		       ": symbol `", undef_name, "' [", version->name,
		       "] (skip)\n", NULL);

  *ref = current_value.s;
  return current_value.m->l_addr;
}


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

void
internal_function
_dl_setup_hash (struct link_map *map)
{
  ElfW(Symndx) *hash;
  ElfW(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;
}