[committed] libstdc++: Throw instead of segfaulting in std::thread constructor [PR 67791]

[Jonathan Wakely via Gcc-patches]

This turns a mysterious segfault into an exception with a more useful
message. If the exception isn't caught, the user sees this instead of
just a segfault:

terminate called after throwing an instance of 'std::system_error'
  what():  Enable multithreading to use std::thread: Operation not permitted
Aborted (core dumped)

libstdc++-v3/ChangeLog:

        PR libstdc++/67791
        * src/c++11/thread.cc (thread::_M_start_thread(_State_ptr, void (*)())):
        Check that gthreads is available before calling __gthread_create.

Tested powerpc64le-linux. Committed to trunk.


commit 4bbd5d0c5fb2b7527938ad44a6d8a2f2ef8bbe12
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Nov 24 12:48:31 2020

    libstdc++: Throw instead of segfaulting in std::thread constructor [PR 
67791]
    
    This turns a mysterious segfault into an exception with a more useful
    message. If the exception isn't caught, the user sees this instead of
    just a segfault:
    
    terminate called after throwing an instance of 'std::system_error'
      what():  Enable multithreading to use std::thread: Operation not permitted
    Aborted (core dumped)
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/67791
            * src/c++11/thread.cc (thread::_M_start_thread(_State_ptr, void 
(*)())):
            Check that gthreads is available before calling __gthread_create.

diff --git a/libstdc++-v3/src/c++11/thread.cc b/libstdc++-v3/src/c++11/thread.cc
index e4dd1687a4b2..a9c928049599 100644
--- a/libstdc++-v3/src/c++11/thread.cc
+++ b/libstdc++-v3/src/c++11/thread.cc
@@ -133,6 +133,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   void
   thread::_M_start_thread(_State_ptr state, void (*)())
   {
+    if (!__gthread_active_p())
+      {
+#if __cpp_exceptions
+       throw system_error(make_error_code(errc::operation_not_permitted),
+                          "Enable multithreading to use std::thread");
+#else
+       __builtin_abort();
+#endif
+      }
+
     const int err = __gthread_create(&_M_id._M_thread,
                                     &execute_native_thread_routine,
                                     state.get());