elf/do-lookup.h

   1 /* Look up a symbol in the loaded objects.
   2    Copyright (C) 1995-2002, 2003, 2004 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 /* Inner part of the lookup functions.  We return a value > 0 if we
  21    found the symbol, the value 0 if nothing is found and < 0 if
  22    something bad happened.  */
  23 static int
  24 __attribute_noinline__
  25 do_lookup_x (const char *undef_name, unsigned long int hash,
  26              const ElfW(Sym) *ref, struct sym_val *result,
  27              struct r_scope_elem *scope, size_t i,
  28              const struct r_found_version *const version, int flags,
  29              struct link_map *skip, int type_class)
  30 {
  31   struct link_map **list = scope->r_list;
  32   size_t n = scope->r_nlist;
  33   struct link_map *map;
  34
  35   do
  36     {
  37       const ElfW(Sym) *symtab;
  38       const char *strtab;
  39       const ElfW(Half) *verstab;
  40       Elf_Symndx symidx;
  41       const ElfW(Sym) *sym;
  42       int num_versions = 0;
  43       const ElfW(Sym) *versioned_sym = NULL;
  44
  45       map = list[i]->l_real;
  46
  47       /* Here come the extra test needed for `_dl_lookup_symbol_skip'.  */
  48       if (skip != NULL && map == skip)
  49         continue;
  50
  51       /* Don't search the executable when resolving a copy reloc.  */
  52       if ((type_class & ELF_RTYPE_CLASS_COPY) && map->l_type == lt_executable)
  53         continue;
  54
  55       /* Print some debugging info if wanted.  */
  56       if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_SYMBOLS, 0))
  57         _dl_debug_printf ("symbol=%s;  lookup in file=%s\n",
  58                           undef_name,
  59                           map->l_name[0] ? map->l_name : rtld_progname);
  60
  61       symtab = (const void *) D_PTR (map, l_info[DT_SYMTAB]);
  62       strtab = (const void *) D_PTR (map, l_info[DT_STRTAB]);
  63       verstab = map->l_versyms;
  64
  65       /* Search the appropriate hash bucket in this object's symbol table
  66          for a definition for the same symbol name.  */
  67       for (symidx = map->l_buckets[hash % map->l_nbuckets];
  68            symidx != STN_UNDEF;
  69            symidx = map->l_chain[symidx])
  70         {
  71           sym = &symtab[symidx];
  72
  73           assert (ELF_RTYPE_CLASS_PLT == 1);
  74           if ((sym->st_value == 0 /* No value.  */
  75 #ifdef USE_TLS
  76                && ELFW(ST_TYPE) (sym->st_info) != STT_TLS
  77 #endif
  78                )
  79               || (type_class & (sym->st_shndx == SHN_UNDEF)))
  80             continue;
  81
  82           if (ELFW(ST_TYPE) (sym->st_info) > STT_FUNC
  83 #ifdef USE_TLS
  84               && ELFW(ST_TYPE) (sym->st_info) != STT_TLS
  85 #endif
  86               )
  87             /* Ignore all but STT_NOTYPE, STT_OBJECT and STT_FUNC
  88                entries (and STT_TLS if TLS is supported) since these
  89                are no code/data definitions.  */
  90             continue;
  91
  92           if (sym != ref && strcmp (strtab + sym->st_name, undef_name))
  93             /* Not the symbol we are looking for.  */
  94             continue;
  95
  96           if (version != NULL)
  97             {
  98               if (__builtin_expect (verstab == NULL, 0))
  99                 {
 100                   /* We need a versioned symbol but haven't found any.  If
 101                      this is the object which is referenced in the verneed
 102                      entry it is a bug in the library since a symbol must
 103                      not simply disappear.
 104
 105                      It would also be a bug in the object since it means that
 106                      the list of required versions is incomplete and so the
 107                      tests in dl-version.c haven't found a problem.*/
 108                   assert (version->filename == NULL
 109                           || ! _dl_name_match_p (version->filename, map));
 110
 111                   /* Otherwise we accept the symbol.  */
 112                 }
 113               else
 114                 {
 115                   /* We can match the version information or use the
 116                      default one if it is not hidden.  */
 117                   ElfW(Half) ndx = verstab[symidx] & 0x7fff;
 118                   if ((map->l_versions[ndx].hash != version->hash
 119                        || strcmp (map->l_versions[ndx].name, version->name))
 120                       && (version->hidden || map->l_versions[ndx].hash
 121                           || (verstab[symidx] & 0x8000)))
 122                     /* It's not the version we want.  */
 123                     continue;
 124                 }
 125             }
 126           else
 127             {
 128               /* No specific version is selected.  There are two ways we
 129                  can got here:
 130
 131                  - a binary which does not include versioning information
 132                    is loaded
 133
 134                  - dlsym() instead of dlvsym() is used to get a symbol which
 135                    might exist in more than one form
 136
 137                  If the library does not provide symbol version
 138                  information there is no problem at at: we simply use the
 139                  symbol if it is defined.
 140
 141                  These two lookups need to be handled differently if the
 142                  library defines versions.  In the case of the old
 143                  unversioned application the oldest (default) version
 144                  should be used.  In case of a dlsym() call the latest and
 145                  public interface should be returned.  */
 146               if (verstab != NULL)
 147                 {
 148                   if ((verstab[symidx] & 0x7fff)
 149                       >= ((flags & DL_LOOKUP_RETURN_NEWEST) ? 2 : 3))
 150                     {
 151                       /* Don't accept hidden symbols.  */
 152                       if ((verstab[symidx] & 0x8000) == 0
 153                           && num_versions++ == 0)
 154                         /* No version so far.  */
 155                         versioned_sym = sym;
 156
 157                       continue;
 158                     }
 159                 }
 160             }
 161
 162           /* There cannot be another entry for this symbol so stop here.  */
 163           goto found_it;
 164         }
 165
 166       /* If we have seen exactly one versioned symbol while we are
 167          looking for an unversioned symbol and the version is not the
 168          default version we still accept this symbol since there are
 169          no possible ambiguities.  */
 170       sym = num_versions == 1 ? versioned_sym : NULL;
 171
 172       if (sym != NULL)
 173         {
 174         found_it:
 175           switch (ELFW(ST_BIND) (sym->st_info))
 176             {
 177             case STB_WEAK:
 178               /* Weak definition.  Use this value if we don't find another.  */
 179               if (__builtin_expect (GLRO(dl_dynamic_weak), 0))
 180                 {
 181                   if (! result->s)
 182                     {
 183                       result->s = sym;
 184                       result->m = map;
 185                     }
 186                   break;
 187                 }
 188               /* FALLTHROUGH */
 189             case STB_GLOBAL:
 190               /* Global definition.  Just what we need.  */
 191               result->s = sym;
 192               result->m = map;
 193               return 1;
 194             default:
 195               /* Local symbols are ignored.  */
 196               break;
 197             }
 198         }
 199
 200       /* If this current map is the one mentioned in the verneed entry
 201          and we have not found a weak entry, it is a bug.  */
 202       if (symidx == STN_UNDEF && version != NULL && version->filename != NULL
 203           && __builtin_expect (_dl_name_match_p (version->filename, map), 0))
 204         return -1;
 205     }
 206   while (++i < n);
 207
 208   /* We have not found anything until now.  */
 209   return 0;
 210 }
 211
 212 #undef FCT
 213 #undef ARG
 214 #undef VERSIONED