C++11 thread_local destructors support

This feature is specifically for the C++ compiler to offload calling
thread_local object destructors on thread program exit, to glibc.
This is to overcome the possible complication of destructors of
thread_local objects getting called after the DSO in which they're
defined is unloaded by the dynamic linker.  The DSO is marked as
'unloadable' if it has a constructed thread_local object and marked as
'unloadable' again when all the constructed thread_local objects
defined in it are destroyed.

1 files changed, 102 insertions, 0 deletions

diff --git a/stdlib/cxa_thread_atexit_impl.c b/stdlib/cxa_thread_atexit_impl.c
new file mode 100644
index 0000000000..9638efc7a0
--- /dev/null
+++ b/stdlib/cxa_thread_atexit_impl.c
@@ -0,0 +1,102 @@
+/* Register destructors for C++ TLS variables declared with thread_local.
+   Copyright (C) 2012 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <ldsodefs.h>
+
+typedef void (*dtor_func) (void *);
+
+struct dtor_list
+{
+  dtor_func func;
+  void *obj;
+  struct link_map *map;
+  struct dtor_list *next;
+};
+
+static __thread struct dtor_list *tls_dtor_list;
+static __thread void *dso_symbol_cache;
+static __thread struct link_map *lm_cache;
+
+/* Register a destructor for TLS variables declared with the 'thread_local'
+   keyword.  This function is only called from code generated by the C++
+   compiler.  FUNC is the destructor function and OBJ is the object to be
+   passed to the destructor.  DSO_SYMBOL is the __dso_handle symbol that each
+   DSO has at a unique address in its map, added from crtbegin.o during the
+   linking phase.  */
+int
+__cxa_thread_atexit_impl (dtor_func func, void *obj, void *dso_symbol)
+{
+  /* Prepend.  */
+  struct dtor_list *new = calloc (1, sizeof (struct dtor_list));
+  new->func = func;
+  new->obj = obj;
+  new->next = tls_dtor_list;
+  tls_dtor_list = new;
+
+  /* See if we already encountered the DSO.  */
+  __rtld_lock_lock_recursive (GL(dl_load_lock));
+
+  if (__builtin_expect (dso_symbol_cache != dso_symbol, 0))
+    {
+      ElfW(Addr) caller = (ElfW(Addr)) dso_symbol;
+
+      struct link_map *l = _dl_find_dso_for_object (caller);
+
+      /* If the address is not recognized the call comes from the main
+         program (we hope).  */
+      lm_cache = l ? l : GL(dl_ns)[LM_ID_BASE]._ns_loaded;
+    }
+  /* A destructor could result in a thread_local construction and the former
+     could have cleared the flag.  */
+  if (lm_cache->l_type == lt_loaded && lm_cache->l_tls_dtor_count == 0)
+    lm_cache->l_flags_1 |= DF_1_NODELETE;
+
+  new->map = lm_cache;
+  new->map->l_tls_dtor_count++;
+
+  __rtld_lock_unlock_recursive (GL(dl_load_lock));
+
+  return 0;
+}
+
+/* Call the destructors.  This is called either when a thread returns from the
+   initial function or when the process exits via the exit(3) function.  */
+void
+__call_tls_dtors (void)
+{
+  while (tls_dtor_list)
+    {
+      struct dtor_list *cur = tls_dtor_list;
+      tls_dtor_list = tls_dtor_list->next;
+
+      cur->func (cur->obj);
+
+      __rtld_lock_lock_recursive (GL(dl_load_lock));
+
+      /* Allow DSO unload if count drops to zero.  */
+      cur->map->l_tls_dtor_count--;
+      if (cur->map->l_tls_dtor_count == 0 && cur->map->l_type == lt_loaded)
+        cur->map->l_flags_1 &= ~DF_1_NODELETE;
+
+      __rtld_lock_unlock_recursive (GL(dl_load_lock));
+
+      free (cur);
+    }
+}
+libc_hidden_def (__call_tls_dtors)