dlfcn/dlsym.c

   1 /* Look up a symbol in a shared object loaded by `dlopen'.
   2    Copyright (C) 1995-2017 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 <dlfcn.h>
  20 #include <stddef.h>
  21
  22 #include <ldsodefs.h>
  23
  24 #if !defined SHARED && IS_IN (libdl)
  25
  26 void *
  27 dlsym (void *handle, const char *name)
  28 {
  29   return __dlsym (handle, name, RETURN_ADDRESS (0));
  30 }
  31
  32 #else
  33
  34 struct dlsym_args
  35 {
  36   /* The arguments to dlsym_doit.  */
  37   void *handle;
  38   const char *name;
  39   void *who;
  40
  41   /* The return value of dlsym_doit.  */
  42   void *sym;
  43 };
  44
  45 static void
  46 dlsym_doit (void *a)
  47 {
  48   struct dlsym_args *args = (struct dlsym_args *) a;
  49
  50   args->sym = _dl_sym (args->handle, args->name, args->who);
  51 }
  52
  53
  54 void *
  55 __dlsym (void *handle, const char *name DL_CALLER_DECL)
  56 {
  57 # ifdef SHARED
  58   if (__glibc_unlikely (_dlfcn_hook != NULL))
  59     return _dlfcn_hook->dlsym (handle, name, DL_CALLER);
  60 # endif
  61
  62   struct dlsym_args args;
  63   args.who = DL_CALLER;
  64   args.handle = handle;
  65   args.name = name;
  66
  67   /* Protect against concurrent loads and unloads.  */
  68   __rtld_lock_lock_recursive (GL(dl_load_lock));
  69
  70   void *result = (_dlerror_run (dlsym_doit, &args) ? NULL : args.sym);
  71
  72   __rtld_lock_unlock_recursive (GL(dl_load_lock));
  73
  74   return result;
  75 }
  76 # ifdef SHARED
  77 strong_alias (__dlsym, dlsym)
  78 # endif
  79 #endif