PR libstdc++/90682 allow set_terminate(0) and set_unexpected(0)

Make these functions restore the default handlers when passed a null
pointer. This is consistent with std::pmr::set_default_resource(0), and
also matches the current behaviour of libc++.

In order to avoid duplicating the preprocessor condition from
eh_term_handler.cc more that into a new eh_term_handler.h header and
define a macro that can be used in both eh_term_handler.cc and
eh_terminate.cc.

Backport from mainline
2019-05-31  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/90682
	* libsupc++/eh_term_handler.cc: Include eh_term_handler.h to get
	definition of _GLIBCXX_DEFAULT_TERM_HANDLER.
	* libsupc++/eh_term_handler.h: New header defining
	_GLIBCXX_DEFAULT_TERM_HANDLER.
	* libsupc++/eh_terminate.cc: Include eh_term_handler.h.
	(set_terminate): Restore default handler when argument is null.
	(set_unexpected): Likewise.
	* testsuite/18_support/set_terminate.cc: New test.
	* testsuite/18_support/set_unexpected.cc: New test.

git-svn-id: https://gcc.gnu.org/svn/gcc/branches/gcc-9-branch@277393 138bc75d-0d04-0410-961f-82ee72b054a4

3 files changed, 48 insertions, 15 deletions

diff --git a/libstdc++-v3/libsupc++/eh_term_handler.cc b/libstdc++-v3/libsupc++/eh_term_handler.cc
index 6a368c0699e..4b330bc9177 100644
--- a/libstdc++-v3/libsupc++/eh_term_handler.cc
+++ b/libstdc++-v3/libsupc++/eh_term_handler.cc
@@ -24,21 +24,8 @@
 
 #include <bits/c++config.h>
 #include "unwind-cxx.h"
+#include "eh_term_handler.h"
 
-/* We default to the talkative, informative handler in a normal hosted
-   library.  This pulls in the demangler, the dyn-string utilities, and
-   elements of the I/O library.  For a low-memory environment, you can return
-   to the earlier "silent death" handler by configuring GCC with
-   --disable-libstdcxx-verbose and rebuilding the library.
-   In a freestanding environment, we default to this latter approach.  */
-
-#if _GLIBCXX_HOSTED && _GLIBCXX_VERBOSE && __cpp_exceptions
 /* The current installed user handler.  */
 std::terminate_handler __cxxabiv1::__terminate_handler =
-	__gnu_cxx::__verbose_terminate_handler;
-#else
-# include <cstdlib>
-/* The current installed user handler.  */
-std::terminate_handler __cxxabiv1::__terminate_handler = std::abort;
-#endif
-
+	_GLIBCXX_DEFAULT_TERM_HANDLER;
diff --git a/libstdc++-v3/libsupc++/eh_term_handler.h b/libstdc++-v3/libsupc++/eh_term_handler.h
new file mode 100644
index 00000000000..e4774bdf9c5
--- /dev/null
+++ b/libstdc++-v3/libsupc++/eh_term_handler.h
@@ -0,0 +1,39 @@
+// -*- C++ -*- default std::terminate handler
+// Copyright (C) 2002-2019 Free Software Foundation, Inc.
+//
+// This file is part of GCC.
+//
+// GCC is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation; either version 3, or (at your option)
+// any later version.
+//
+// GCC 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 General Public License for more details.
+//
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
+// <http://www.gnu.org/licenses/>.
+
+#include <bits/c++config.h>
+
+/* We default to the talkative, informative handler in a normal hosted
+   library.  This pulls in the demangler, the dyn-string utilities, and
+   elements of the I/O library.  For a low-memory environment, you can return
+   to the earlier "silent death" handler by configuring GCC with
+   --disable-libstdcxx-verbose and rebuilding the library.
+   In a freestanding environment, we default to this latter approach.  */
+
+#if _GLIBCXX_HOSTED && _GLIBCXX_VERBOSE && __cpp_exceptions
+# define _GLIBCXX_DEFAULT_TERM_HANDLER __gnu_cxx::__verbose_terminate_handler
+#else
+# include <cstdlib>
+# define _GLIBCXX_DEFAULT_TERM_HANDLER std::abort
+#endif
diff --git a/libstdc++-v3/libsupc++/eh_terminate.cc b/libstdc++-v3/libsupc++/eh_terminate.cc
index 6acae0593ac..d5f24ea1000 100644
--- a/libstdc++-v3/libsupc++/eh_terminate.cc
+++ b/libstdc++-v3/libsupc++/eh_terminate.cc
@@ -26,6 +26,7 @@
 #include "exception"
 #include <cstdlib>
 #include "unwind-cxx.h"
+#include "eh_term_handler.h"
 #include <bits/exception_defines.h>
 #include <bits/atomic_lockfree_defines.h>
 
@@ -73,6 +74,9 @@ std::unexpected ()
 std::terminate_handler
 std::set_terminate (std::terminate_handler func) throw()
 {
+  if (!func)
+    func = _GLIBCXX_DEFAULT_TERM_HANDLER;
+
   std::terminate_handler old;
 #if ATOMIC_POINTER_LOCK_FREE > 1
   __atomic_exchange (&__terminate_handler, &func, &old, __ATOMIC_ACQ_REL);
@@ -100,6 +104,9 @@ std::get_terminate () noexcept
 std::unexpected_handler
 std::set_unexpected (std::unexpected_handler func) throw()
 {
+  if (!func)
+    func = std::terminate;
+
   std::unexpected_handler old;
 #if ATOMIC_POINTER_LOCK_FREE > 1
   __atomic_exchange (&__unexpected_handler, &func, &old, __ATOMIC_ACQ_REL);