1  /* Look up a symbol in a shared object loaded by `dlopen'.
       2     Copyright (C) 1995-2023 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 */