dlfcn/dlsym.c

   1 /* Look up a symbol in a shared object loaded by `dlopen'.
   2    Copyright (C) 1995-2022 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 <dlfcn.h>
  20 #include <ldsodefs.h>
  21 #include <shlib-compat.h>
  22 #include <stddef.h>
  23
  24 struct dlsym_args
  25 {
  26   /* The arguments to dlsym_doit.  */
  27   void *handle;
  28   const char *name;
  29   void *who;
  30
  31   /* The return value of dlsym_doit.  */
  32   void *sym;
  33 };
  34
  35 static void
  36 dlsym_doit (void *a)
  37 {
  38   struct dlsym_args *args = (struct dlsym_args *) a;
  39
  40   args->sym = _dl_sym (args->handle, args->name, args->who);
  41 }
  42
  43 static void *
  44 dlsym_implementation (void *handle, const char *name, void *dl_caller)
  45 {
  46   struct dlsym_args args;
  47   args.who = dl_caller;
  48   args.handle = handle;
  49   args.name = name;
  50
  51   /* Protect against concurrent loads and unloads.  */
  52   __rtld_lock_lock_recursive (GL(dl_load_lock));
  53
  54   void *result = (_dlerror_run (dlsym_doit, &args) ? NULL : args.sym);
  55
  56   __rtld_lock_unlock_recursive (GL(dl_load_lock));
  57
  58   return result;
  59 }
  60
  61 #ifdef SHARED
  62 void *
  63 ___dlsym (void *handle, const char *name)
  64 {
  65   if (GLRO (dl_dlfcn_hook) != NULL)
  66     return GLRO (dl_dlfcn_hook)->dlsym (handle, name, RETURN_ADDRESS (0));
  67   else
  68     return dlsym_implementation (handle, name, RETURN_ADDRESS (0));
  69 }
  70 versioned_symbol (libc, ___dlsym, dlsym, GLIBC_2_34);
  71
  72 # if OTHER_SHLIB_COMPAT (libdl, GLIBC_2_0, GLIBC_2_34)
  73 compat_symbol (libdl, ___dlsym, dlsym, GLIBC_2_0);
  74 # endif
  75
  76 #else /* !SHARED */
  77 /* Also used with _dlfcn_hook.  */
  78 void *
  79 __dlsym (void *handle, const char *name, void *dl_caller)
  80 {
  81   return dlsym_implementation (handle, name, dl_caller);
  82 }
  83
  84 void *
  85 ___dlsym (void *handle, const char *name)
  86 {
  87   return __dlsym (handle, name, RETURN_ADDRESS (0));
  88 }
  89 weak_alias (___dlsym, dlsym)
  90 #endif /* !SHARED */