diff --git a/ap/libc/glibc/glibc-2.23/nptl/tst-stdio2.c b/ap/libc/glibc/glibc-2.23/nptl/tst-stdio2.c
new file mode 100644
index 0000000..6168d27
--- /dev/null
+++ b/ap/libc/glibc/glibc-2.23/nptl/tst-stdio2.c
@@ -0,0 +1,81 @@
+/* Copyright (C) 2002-2016 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   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 <pthread.h>
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+
+static void *tf (void *a)
+{
+  puts ("start tf");
+
+  /* Multiple locking, implicitly or explicitly, must be possible.  */
+  flockfile (stdout);
+
+  puts ("after first flockfile");
+
+  flockfile (stdout);
+
+  puts ("foo");
+
+  funlockfile (stdout);
+
+  puts ("after first funlockfile");
+
+  funlockfile (stdout);
+
+  puts ("all done");
+
+  return a;
+}
+
+
+int
+do_test (void)
+{
+  pthread_t th;
+
+  if (pthread_create (&th, NULL, tf, NULL) != 0)
+    {
+      write (2, "create failed\n", 14);
+      _exit (1);
+    }
+
+  void *result;
+  if (pthread_join (th, &result) != 0)
+    {
+      puts ("join failed");
+      exit (1);
+    }
+  else if (result != NULL)
+    {
+      printf ("wrong return value: %p, expected %p\n", result, NULL);
+      exit (1);
+    }
+
+  puts ("join returned succsefully");
+
+  return 0;
+}
+
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"