elf/dlsym.c

   1 /* Look up a symbol in a shared object loaded by `dlopen'.
   2    Copyright (C) 1995, 1996, 1997 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 Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    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    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 02111-1307, USA.  */
  19
  20 #include <stddef.h>
  21 #include <link.h>
  22 #include <dlfcn.h>
  23 #include <setjmp.h>
  24
  25 struct dlsym_args
  26 {
  27   /* The arguments to dlsym_doit.  */
  28   void *handle;
  29   const char *name;
  30   struct r_found_version version;
  31   ElfW(Addr) caller;
  32   /* The return values of dlsym_doit.  */
  33   ElfW(Addr) loadbase;
  34   const ElfW(Sym) *ref;
  35 };
  36
  37
  38 static void
  39 dlsym_doit (void *a)
  40 {
  41   struct dlsym_args *args = (struct dlsym_args *) a;
  42   args->ref = NULL;
  43
  44   if (args->handle == NULL)
  45     /* Search the global scope.  */
  46     args->loadbase = _dl_lookup_symbol (args->name, &args->ref,
  47                                         &(_dl_global_scope
  48                                           ?: _dl_default_scope)[2],
  49                                         NULL, 0);
  50   else if (args->handle == RTLD_NEXT)
  51     {
  52       struct link_map *l, *match;
  53
  54       /* Find the highest-addressed object that CALLER is not below.  */
  55       match = NULL;
  56       for (l = _dl_loaded; l; l = l->l_next)
  57         if (args->caller >= l->l_addr && (!match || match->l_addr < l->l_addr))
  58           match = l;
  59
  60       if (! match)
  61         _dl_signal_error (0, NULL, _("\
  62 RTLD_NEXT used in code not dynamically loaded"));
  63
  64       l = match;
  65       while (l->l_loader)
  66         l = l->l_loader;
  67
  68       args->loadbase = _dl_lookup_symbol_skip (args->name, &args->ref,
  69                                                &_dl_loaded, NULL, l);
  70     }
  71   else
  72     {
  73       /* Search the scope of the given object.  */
  74       struct link_map *map = args->handle;
  75       struct link_map *mapscope[2] = { map, NULL };
  76       args->loadbase = _dl_lookup_symbol (args->name, &args->ref, mapscope,
  77                                           map->l_name, 0);
  78     }
  79 }
  80
  81
  82 void *
  83 dlsym (void *handle, const char *name)
  84 {
  85   struct dlsym_args args;
  86   args.caller = (ElfW(Addr)) __builtin_return_address (0);
  87   args.handle = handle;
  88   args.name = name;
  89
  90   return (_dlerror_run (dlsym_doit, &args)
  91           ? NULL : (void *) (args.loadbase + args.ref->st_value));
  92 }