Index: include/std/mutex
===================================================================
--- include/std/mutex	(revision 146799)
+++ include/std/mutex	(working copy)
@@ -729,8 +729,11 @@ namespace std
 #else
   extern function<void()> __once_functor;
 
-  extern unique_lock<mutex>&
-  __get_once_functor_lock();
+  extern void
+  __set_once_functor_lock_ptr(unique_lock<mutex>*);
+
+  extern mutex&
+  __get_once_mutex();
 #endif
 
   extern "C" void __once_proxy();
@@ -745,16 +748,16 @@ namespace std
       __once_callable = &__bound_functor;
       __once_call = &__once_call_impl<decltype(__bound_functor)>;
 #else
-      unique_lock<mutex>& __functor_lock = __get_once_functor_lock();
-      __functor_lock.lock();
+      unique_lock<mutex> __functor_lock(__get_once_mutex());
       __once_functor = bind(__f, __args...);
+      __set_once_functor_lock_ptr(&__functor_lock);
 #endif
 
       int __e = __gthread_once(&(__once._M_once), &__once_proxy);
 
 #ifndef _GLIBCXX_HAVE_TLS
       if (__functor_lock)
-	__functor_lock.unlock();
+        __set_once_functor_lock_ptr(0);
 #endif
 
       if (__e)
Index: src/mutex.cc
===================================================================
--- src/mutex.cc	(revision 146799)
+++ src/mutex.cc	(working copy)
@@ -28,11 +28,11 @@
 #ifndef _GLIBCXX_HAVE_TLS
 namespace
 {
-  std::mutex&
-  get_once_mutex()
+  inline std::unique_lock<std::mutex>*&
+  __get_once_functor_lock_ptr()
   {
-    static std::mutex once_mutex;
-    return once_mutex;
+    static std::unique_lock<std::mutex>* __once_functor_lock_ptr = 0;
+    return __once_functor_lock_ptr;
   }
 }
 #endif
@@ -55,10 +55,25 @@ namespace std
   template class function<void()>;
   function<void()> __once_functor;
 
+  mutex&
+  __get_once_mutex()
+  {
+    static mutex once_mutex;
+    return once_mutex;
+  }
+
+  // code linked against ABI 3.4.12 and later uses this
+  void
+  __set_once_functor_lock_ptr(unique_lock<mutex>* __ptr)
+  {
+    __get_once_functor_lock_ptr() = __ptr;
+  }
+
+  // unsafe - retained for compatibility with ABI 3.4.11
   unique_lock<mutex>&
   __get_once_functor_lock()
   {
-    static unique_lock<mutex> once_functor_lock(get_once_mutex(), defer_lock);
+    static unique_lock<mutex> once_functor_lock(__get_once_mutex(), defer_lock);
     return once_functor_lock;
   }
 #endif
@@ -69,7 +84,14 @@ namespace std
     {
 #ifndef _GLIBCXX_HAVE_TLS
       function<void()> __once_call = std::move(__once_functor);
-      __get_once_functor_lock().unlock();
+      if (unique_lock<mutex>* __lock = __get_once_functor_lock_ptr())
+      {
+        // caller is using new ABI and provided lock ptr
+        __get_once_functor_lock_ptr() = 0;
+        __lock->unlock();
+      }
+      else
+        __get_once_functor_lock().unlock();  // global lock
 #endif
       __once_call();
     }
Index: config/abi/pre/gnu.ver
===================================================================
--- config/abi/pre/gnu.ver	(revision 146799)
+++ config/abi/pre/gnu.ver	(working copy)
@@ -882,6 +882,10 @@ GLIBCXX_3.4.11 {
     _ZSt23__get_once_functor_lockv;
     __once_proxy;
 
+    # TODO move these to new 3.4.12 block
+    _ZSt27__set_once_functor_lock_ptrPSt11unique_lockISt5mutexE;
+    _ZSt16__get_once_mutexv;
+
     # condition_variable
     _ZNSt18condition_variable10notify_allEv;
     _ZNSt18condition_variable10notify_oneEv;