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[patch] libstdc++/61841 odr-use pthread_create in std::thread constructor

This patch causes the std::thread constructor that launches a new
thread to odr-use pthread_create on glibc-based targets, so that the
program depends directly on pthread_create (and must be linked to
libpthread) not just on the weak symbol in gthr-posix.h

This should fix the Hurd bug in PR61841 as well as the problem
described in

Tested x86_64-linux, committed to trunk.

This is not suitable for the branches as it requires a new exported
symbol. We could maybe just add some other odr-use of pthread_create,
but it would probably be optimized away anyway.

commit 79c721b72b7f9288256cc4bf388cf6b60b65e838
Author: Jonathan Wakely <>
Date:   Fri Jul 18 15:35:49 2014 +0100

    	PR libstdc++/61841
    	* include/std/thread (thread::_M_start_thread): Declare new overload.
    	(thread::thread<_Callable, _Args...>): Call new overload with an
    	explicit reference to pthread_create.
    	* src/c++11/ (thread::_M_start_thread): Add new overload.
    	* config/abi/pre/gnu.ver: Export new function.

diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver
index ed7a93f..41fac71 100644
--- a/libstdc++-v3/config/abi/pre/gnu.ver
+++ b/libstdc++-v3/config/abi/pre/gnu.ver
@@ -1372,6 +1372,9 @@ GLIBCXX_3.4.21 {
     # std::regex_error::regex_error(std::regex_constants::error_type)
+    # void std::thread::_M_start_thread(__shared_base_type, void(*)())
+    _ZNSt6thread15_M_start_threadESt10shared_ptrINS_10_Impl_baseEEPFvvE;
 } GLIBCXX_3.4.20;
diff --git a/libstdc++-v3/include/std/thread b/libstdc++-v3/include/std/thread
index efcb101..0576347 100644
--- a/libstdc++-v3/include/std/thread
+++ b/libstdc++-v3/include/std/thread
       thread(_Callable&& __f, _Args&&... __args)
+	// Create a reference to pthread_create, not just the gthr weak symbol
+        _M_start_thread(_M_make_routine(std::__bind_simple(
+                std::forward<_Callable>(__f),
+                std::forward<_Args>(__args)...)),
+	    reinterpret_cast<void(*)()>(&pthread_create));
+    _M_start_thread(__shared_base_type, void (*)());
+    void
     template<typename _Callable>
diff --git a/libstdc++-v3/src/c++11/ b/libstdc++-v3/src/c++11/
index 49aacb5..bbcc99c 100644
--- a/libstdc++-v3/src/c++11/
+++ b/libstdc++-v3/src/c++11/
+    _M_start_thread(__b, nullptr);
+  }
+  void
+  thread::_M_start_thread(__shared_base_type __b, void (*)())
+  {
     __b->_M_this_ptr = __b;
     int __e = __gthread_create(&_M_id._M_thread,
 			       &execute_native_thread_routine, __b.get());

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