stdlib/cxa_thread_atexit_impl.c

   1 /* Register destructors for C++ TLS variables declared with thread_local.
   2    Copyright (C) 2013-2015 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 <stdlib.h>
  20 #include <ldsodefs.h>
  21
  22 typedef void (*dtor_func) (void *);
  23
  24 struct dtor_list
  25 {
  26   dtor_func func;
  27   void *obj;
  28   struct link_map *map;
  29   struct dtor_list *next;
  30 };
  31
  32 static __thread struct dtor_list *tls_dtor_list;
  33 static __thread void *dso_symbol_cache;
  34 static __thread struct link_map *lm_cache;
  35
  36 /* Register a destructor for TLS variables declared with the 'thread_local'
  37    keyword.  This function is only called from code generated by the C++
  38    compiler.  FUNC is the destructor function and OBJ is the object to be
  39    passed to the destructor.  DSO_SYMBOL is the __dso_handle symbol that each
  40    DSO has at a unique address in its map, added from crtbegin.o during the
  41    linking phase.  */
  42 int
  43 __cxa_thread_atexit_impl (dtor_func func, void *obj, void *dso_symbol)
  44 {
  45   /* Prepend.  */
  46   struct dtor_list *new = calloc (1, sizeof (struct dtor_list));
  47   new->func = func;
  48   new->obj = obj;
  49   new->next = tls_dtor_list;
  50   tls_dtor_list = new;
  51
  52   /* See if we already encountered the DSO.  */
  53   __rtld_lock_lock_recursive (GL(dl_load_lock));
  54
  55   if (__glibc_unlikely (dso_symbol_cache != dso_symbol))
  56     {
  57       ElfW(Addr) caller = (ElfW(Addr)) dso_symbol;
  58
  59       struct link_map *l = _dl_find_dso_for_object (caller);
  60
  61       /* If the address is not recognized the call comes from the main
  62          program (we hope).  */
  63       lm_cache = l ? l : GL(dl_ns)[LM_ID_BASE]._ns_loaded;
  64     }
  65   /* A destructor could result in a thread_local construction and the former
  66      could have cleared the flag.  */
  67   if (lm_cache->l_type == lt_loaded && lm_cache->l_tls_dtor_count == 0)
  68     lm_cache->l_flags_1 |= DF_1_NODELETE;
  69
  70   new->map = lm_cache;
  71   new->map->l_tls_dtor_count++;
  72
  73   __rtld_lock_unlock_recursive (GL(dl_load_lock));
  74
  75   return 0;
  76 }
  77
  78 /* Call the destructors.  This is called either when a thread returns from the
  79    initial function or when the process exits via the exit function.  */
  80 void
  81 __call_tls_dtors (void)
  82 {
  83   while (tls_dtor_list)
  84     {
  85       struct dtor_list *cur = tls_dtor_list;
  86       tls_dtor_list = tls_dtor_list->next;
  87
  88       cur->func (cur->obj);
  89
  90       __rtld_lock_lock_recursive (GL(dl_load_lock));
  91
  92       /* Allow DSO unload if count drops to zero.  */
  93       cur->map->l_tls_dtor_count--;
  94       if (cur->map->l_tls_dtor_count == 0 && cur->map->l_type == lt_loaded)
  95         cur->map->l_flags_1 &= ~DF_1_NODELETE;
  96
  97       __rtld_lock_unlock_recursive (GL(dl_load_lock));
  98
  99       free (cur);
 100     }
 101 }
 102 libc_hidden_def (__call_tls_dtors)