elf/dl-sym.c

   1 /* Look up a symbol in a shared object loaded by `dlopen'.
   2    Copyright (C) 1999-2021 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, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <stddef.h>
  21 #include <setjmp.h>
  22 #include <stdlib.h>
  23 #include <libintl.h>
  24
  25 #include <dlfcn.h>
  26 #include <ldsodefs.h>
  27 #include <dl-hash.h>
  28 #include <sysdep-cancel.h>
  29 #include <dl-tls.h>
  30 #include <dl-irel.h>
  31 #include <dl-sym-post.h>
  32
  33
  34 #ifdef SHARED
  35 /* Systems which do not have tls_index also probably have to define
  36    DONT_USE_TLS_INDEX.  */
  37
  38 # ifndef __TLS_GET_ADDR
  39 #  define __TLS_GET_ADDR __tls_get_addr
  40 # endif
  41
  42 /* Return the symbol address given the map of the module it is in and
  43    the symbol record.  This is used in dl-sym.c.  */
  44 static void *
  45 _dl_tls_symaddr (struct link_map *map, const ElfW(Sym) *ref)
  46 {
  47 # ifndef DONT_USE_TLS_INDEX
  48   tls_index tmp =
  49     {
  50       .ti_module = map->l_tls_modid,
  51       .ti_offset = ref->st_value
  52     };
  53
  54   return __TLS_GET_ADDR (&tmp);
  55 # else
  56   return __TLS_GET_ADDR (map->l_tls_modid, ref->st_value);
  57 # endif
  58 }
  59 #endif
  60
  61
  62 struct call_dl_lookup_args
  63 {
  64   /* Arguments to do_dlsym.  */
  65   struct link_map *map;
  66   const char *name;
  67   struct r_found_version *vers;
  68   int flags;
  69
  70   /* Return values of do_dlsym.  */
  71   lookup_t loadbase;
  72   const ElfW(Sym) **refp;
  73 };
  74
  75 static void
  76 call_dl_lookup (void *ptr)
  77 {
  78   struct call_dl_lookup_args *args = (struct call_dl_lookup_args *) ptr;
  79   args->map = GLRO(dl_lookup_symbol_x) (args->name, args->map, args->refp,
  80                                         args->map->l_scope, args->vers, 0,
  81                                         args->flags, NULL);
  82 }
  83
  84 static void *
  85 do_sym (void *handle, const char *name, void *who,
  86         struct r_found_version *vers, int flags)
  87 {
  88   const ElfW(Sym) *ref = NULL;
  89   lookup_t result;
  90   ElfW(Addr) caller = (ElfW(Addr)) who;
  91
  92   /* Link map of the caller if needed.  */
  93   struct link_map *match = NULL;
  94
  95   if (handle == RTLD_DEFAULT)
  96     {
  97       match = _dl_sym_find_caller_link_map (caller);
  98
  99       /* Search the global scope.  We have the simple case where
 100          we look up in the scope of an object which was part of
 101          the initial binary.  And then the more complex part
 102          where the object is dynamically loaded and the scope
 103          array can change.  */
 104       if (RTLD_SINGLE_THREAD_P)
 105         result = GLRO(dl_lookup_symbol_x) (name, match, &ref,
 106                                            match->l_scope, vers, 0,
 107                                            flags | DL_LOOKUP_ADD_DEPENDENCY,
 108                                            NULL);
 109       else
 110         {
 111           struct call_dl_lookup_args args;
 112           args.name = name;
 113           args.map = match;
 114           args.vers = vers;
 115           args.flags
 116             = flags | DL_LOOKUP_ADD_DEPENDENCY | DL_LOOKUP_GSCOPE_LOCK;
 117           args.refp = &ref;
 118
 119           THREAD_GSCOPE_SET_FLAG ();
 120           struct dl_exception exception;
 121           int err = _dl_catch_exception (&exception, call_dl_lookup, &args);
 122           THREAD_GSCOPE_RESET_FLAG ();
 123           if (__glibc_unlikely (exception.errstring != NULL))
 124             _dl_signal_exception (err, &exception, NULL);
 125
 126           result = args.map;
 127         }
 128     }
 129   else if (handle == RTLD_NEXT)
 130     {
 131       match = _dl_sym_find_caller_link_map (caller);
 132
 133       if (__glibc_unlikely (match == GL(dl_ns)[LM_ID_BASE]._ns_loaded))
 134         {
 135           if (match == NULL
 136               || caller < match->l_map_start
 137               || caller >= match->l_map_end)
 138             _dl_signal_error (0, NULL, NULL, N_("\
 139 RTLD_NEXT used in code not dynamically loaded"));
 140         }
 141
 142       struct link_map *l = match;
 143       while (l->l_loader != NULL)
 144         l = l->l_loader;
 145
 146       result = GLRO(dl_lookup_symbol_x) (name, match, &ref, l->l_local_scope,
 147                                          vers, 0, 0, match);
 148     }
 149   else
 150     {
 151       /* Search the scope of the given object.  */
 152       struct link_map *map = handle;
 153       result = GLRO(dl_lookup_symbol_x) (name, map, &ref, map->l_local_scope,
 154                                          vers, 0, flags, NULL);
 155     }
 156
 157   if (ref != NULL)
 158     {
 159       void *value;
 160
 161 #ifdef SHARED
 162       if (ELFW(ST_TYPE) (ref->st_info) == STT_TLS)
 163         /* The found symbol is a thread-local storage variable.
 164            Return the address for to the current thread.  */
 165         value = _dl_tls_symaddr (result, ref);
 166       else
 167 #endif
 168         value = DL_SYMBOL_ADDRESS (result, ref);
 169
 170       return _dl_sym_post (result, ref, value, caller, match);
 171     }
 172
 173   return NULL;
 174 }
 175
 176
 177 void *
 178 _dl_vsym (void *handle, const char *name, const char *version, void *who)
 179 {
 180   struct r_found_version vers;
 181
 182   /* Compute hash value to the version string.  */
 183   vers.name = version;
 184   vers.hidden = 1;
 185   vers.hash = _dl_elf_hash (version);
 186   /* We don't have a specific file where the symbol can be found.  */
 187   vers.filename = NULL;
 188
 189   return do_sym (handle, name, who, &vers, 0);
 190 }
 191
 192
 193 void *
 194 _dl_sym (void *handle, const char *name, void *who)
 195 {
 196   return do_sym (handle, name, who, NULL, DL_LOOKUP_RETURN_NEWEST);
 197 }