elf/dl-sym.c

   1 /* Look up a symbol in a shared object loaded by `dlopen'.
   2    Copyright (C) 1999-2017 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    <http://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
  32
  33 #ifdef SHARED
  34 /* Systems which do not have tls_index also probably have to define
  35    DONT_USE_TLS_INDEX.  */
  36
  37 # ifndef __TLS_GET_ADDR
  38 #  define __TLS_GET_ADDR __tls_get_addr
  39 # endif
  40
  41 /* Return the symbol address given the map of the module it is in and
  42    the symbol record.  This is used in dl-sym.c.  */
  43 static void *
  44 _dl_tls_symaddr (struct link_map *map, const ElfW(Sym) *ref)
  45 {
  46 # ifndef DONT_USE_TLS_INDEX
  47   tls_index tmp =
  48     {
  49       .ti_module = map->l_tls_modid,
  50       .ti_offset = ref->st_value
  51     };
  52
  53   return __TLS_GET_ADDR (&tmp);
  54 # else
  55   return __TLS_GET_ADDR (map->l_tls_modid, ref->st_value);
  56 # endif
  57 }
  58 #endif
  59
  60
  61 struct call_dl_lookup_args
  62 {
  63   /* Arguments to do_dlsym.  */
  64   struct link_map *map;
  65   const char *name;
  66   struct r_found_version *vers;
  67   int flags;
  68
  69   /* Return values of do_dlsym.  */
  70   lookup_t loadbase;
  71   const ElfW(Sym) **refp;
  72 };
  73
  74 static void
  75 call_dl_lookup (void *ptr)
  76 {
  77   struct call_dl_lookup_args *args = (struct call_dl_lookup_args *) ptr;
  78   args->map = GLRO(dl_lookup_symbol_x) (args->name, args->map, args->refp,
  79                                         args->map->l_scope, args->vers, 0,
  80                                         args->flags, NULL);
  81 }
  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   struct link_map *l = _dl_find_dso_for_object (caller);
  93   /* If the address is not recognized the call comes from the main
  94      program (we hope).  */
  95   struct link_map *match = l ? l : GL(dl_ns)[LM_ID_BASE]._ns_loaded;
  96
  97   if (handle == RTLD_DEFAULT)
  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       if (__glibc_unlikely (match == GL(dl_ns)[LM_ID_BASE]._ns_loaded))
 132         {
 133           if (match == NULL
 134               || caller < match->l_map_start
 135               || caller >= match->l_map_end)
 136             _dl_signal_error (0, NULL, NULL, N_("\
 137 RTLD_NEXT used in code not dynamically loaded"));
 138         }
 139
 140       struct link_map *l = match;
 141       while (l->l_loader != NULL)
 142         l = l->l_loader;
 143
 144       result = GLRO(dl_lookup_symbol_x) (name, match, &ref, l->l_local_scope,
 145                                          vers, 0, 0, match);
 146     }
 147   else
 148     {
 149       /* Search the scope of the given object.  */
 150       struct link_map *map = handle;
 151       result = GLRO(dl_lookup_symbol_x) (name, map, &ref, map->l_local_scope,
 152                                          vers, 0, flags, NULL);
 153     }
 154
 155   if (ref != NULL)
 156     {
 157       void *value;
 158
 159 #ifdef SHARED
 160       if (ELFW(ST_TYPE) (ref->st_info) == STT_TLS)
 161         /* The found symbol is a thread-local storage variable.
 162            Return the address for to the current thread.  */
 163         value = _dl_tls_symaddr (result, ref);
 164       else
 165 #endif
 166         value = DL_SYMBOL_ADDRESS (result, ref);
 167
 168       /* Resolve indirect function address.  */
 169       if (__glibc_unlikely (ELFW(ST_TYPE) (ref->st_info) == STT_GNU_IFUNC))
 170         {
 171           DL_FIXUP_VALUE_TYPE fixup
 172             = DL_FIXUP_MAKE_VALUE (result, (ElfW(Addr)) value);
 173           fixup = elf_ifunc_invoke (DL_FIXUP_VALUE_ADDR (fixup));
 174           value = (void *) DL_FIXUP_VALUE_CODE_ADDR (fixup);
 175         }
 176
 177 #ifdef SHARED
 178       /* Auditing checkpoint: we have a new binding.  Provide the
 179          auditing libraries the possibility to change the value and
 180          tell us whether further auditing is wanted.  */
 181       if (__glibc_unlikely (GLRO(dl_naudit) > 0))
 182         {
 183           const char *strtab = (const char *) D_PTR (result,
 184                                                      l_info[DT_STRTAB]);
 185           /* Compute index of the symbol entry in the symbol table of
 186              the DSO with the definition.  */
 187           unsigned int ndx = (ref - (ElfW(Sym) *) D_PTR (result,
 188                                                          l_info[DT_SYMTAB]));
 189
 190           if ((match->l_audit_any_plt | result->l_audit_any_plt) != 0)
 191             {
 192               unsigned int altvalue = 0;
 193               struct audit_ifaces *afct = GLRO(dl_audit);
 194               /* Synthesize a symbol record where the st_value field is
 195                  the result.  */
 196               ElfW(Sym) sym = *ref;
 197               sym.st_value = (ElfW(Addr)) value;
 198
 199               for (unsigned int cnt = 0; cnt < GLRO(dl_naudit); ++cnt)
 200                 {
 201                   if (afct->symbind != NULL
 202                       && ((match->l_audit[cnt].bindflags & LA_FLG_BINDFROM)
 203                           != 0
 204                           || ((result->l_audit[cnt].bindflags & LA_FLG_BINDTO)
 205                               != 0)))
 206                     {
 207                       unsigned int flags = altvalue | LA_SYMB_DLSYM;
 208                       uintptr_t new_value
 209                         = afct->symbind (&sym, ndx,
 210                                          &match->l_audit[cnt].cookie,
 211                                          &result->l_audit[cnt].cookie,
 212                                          &flags, strtab + ref->st_name);
 213                       if (new_value != (uintptr_t) sym.st_value)
 214                         {
 215                           altvalue = LA_SYMB_ALTVALUE;
 216                           sym.st_value = new_value;
 217                         }
 218                     }
 219
 220                   afct = afct->next;
 221                 }
 222
 223               value = (void *) sym.st_value;
 224             }
 225         }
 226 #endif
 227
 228       return value;
 229     }
 230
 231   return NULL;
 232 }
 233
 234
 235 void *
 236 _dl_vsym (void *handle, const char *name, const char *version, void *who)
 237 {
 238   struct r_found_version vers;
 239
 240   /* Compute hash value to the version string.  */
 241   vers.name = version;
 242   vers.hidden = 1;
 243   vers.hash = _dl_elf_hash (version);
 244   /* We don't have a specific file where the symbol can be found.  */
 245   vers.filename = NULL;
 246
 247   return do_sym (handle, name, who, &vers, 0);
 248 }
 249
 250
 251 void *
 252 _dl_sym (void *handle, const char *name, void *who)
 253 {
 254   return do_sym (handle, name, who, NULL, DL_LOOKUP_RETURN_NEWEST);
 255 }