nptl: Add C11 threads call_once functions

This patch adds the call_* definitions from C11 threads (ISO/IEC 9899:2011),
more specifically call_once and required types.

Mostly of the definitions are composed based on POSIX conterparts,including
once_flag (pthread_once_t).  The idea is to make possible to share POSIX
internal implementations for mostly of the code (and making adjustment only
when required).

Checked with a build for all major ABI (aarch64-linux-gnu, alpha-linux-gnu,
arm-linux-gnueabi, i386-linux-gnu, ia64-linux-gnu, m68k-linux-gnu,
microblaze-linux-gnu [1], mips{64}-linux-gnu, nios2-linux-gnu,
powerpc{64le}-linux-gnu, s390{x}-linux-gnu, sparc{64}-linux-gnu,
and x86_64-linux-gnu).

Also ran a full check on aarch64-linux-gnu, x86_64-linux-gnu, i686-linux-gnu,
arm-linux-gnueabhf, and powerpc64le-linux-gnu.

	[BZ #14092]
	* conform/data/threads.h-data (ONCE_FLAG_INIT): New macro.
	(once_flag): New type.
	(call_once): New function.
	* nptl/Makefile (libpthread-routines): Add call_once object.
	* nptl/Versions (libphread) [GLIBC_2.28]: Add call_once symbol.
	* nptl/call_once.c: New file.
	* sysdeps/nptl/threads.h (ONCE_FLAG_INIT): New define.
	(once_flag): New type.
	(call_once): New prototype.

4 files changed, 44 insertions, 1 deletions

diff --git a/nptl/Makefile b/nptl/Makefile
index 4b889ab..d55d24b 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -143,7 +143,7 @@ libpthread-routines = nptl-init nptlfreeres vars events version pt-interp \
 		      pthread_setattr_default_np pthread_getattr_default_np \
 		      thrd_create thrd_detach thrd_exit thrd_join \
 		      mtx_destroy mtx_init mtx_lock mtx_timedlock \
-		      mtx_trylock mtx_unlock
+		      mtx_trylock mtx_unlock call_once
 #		      pthread_setuid pthread_seteuid pthread_setreuid \
 #		      pthread_setresuid \
 #		      pthread_setgid pthread_setegid pthread_setregid \
diff --git a/nptl/Versions b/nptl/Versions
index ca1be37..0fdba18 100644
--- a/nptl/Versions
+++ b/nptl/Versions
@@ -273,6 +273,7 @@ libpthread {
   GLIBC_2.28 {
     thrd_create; thrd_detach; thrd_exit; thrd_join;
     mtx_init; mtx_lock; mtx_timedlock; mtx_trylock; mtx_unlock; mtx_destroy;
+    call_once;
   }
 
   GLIBC_PRIVATE {
diff --git a/nptl/call_once.c b/nptl/call_once.c
new file mode 100644
index 0000000..5bc88cb
--- /dev/null
+++ b/nptl/call_once.c
@@ -0,0 +1,31 @@
+/* C11 threads call once implementation.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   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 <stdalign.h>
+
+#include "thrd_priv.h"
+
+void
+call_once (once_flag *flag, void (*func)(void))
+{
+  _Static_assert (sizeof (once_flag) == sizeof (pthread_once_t),
+		  "sizeof (once_flag) != sizeof (pthread_once_t)");
+  _Static_assert (alignof (once_flag) == alignof (pthread_once_t),
+		  "alignof (once_flag) != alignof (pthread_once_t)");
+  __pthread_once (&flag->__data, func);
+}
diff --git a/nptl/threads.h b/nptl/threads.h
index 13d0075..32f7cf8 100644
--- a/nptl/threads.h
+++ b/nptl/threads.h
@@ -48,6 +48,12 @@ enum
   mtx_timed     = 2
 };
 
+typedef struct
+{
+  int __data __ONCE_ALIGNMENT;
+} once_flag;
+#define ONCE_FLAG_INIT { 0 }
+
 typedef union
 {
   char __size[__SIZEOF_PTHREAD_MUTEX_T];
@@ -129,6 +135,11 @@ extern int mtx_unlock (mtx_t *__mutex);
 /* Destroy the mutex object pointed by __MUTEX.  */
 extern void mtx_destroy (mtx_t *__mutex);
 
+
+/* Call function __FUNC exactly once, even if invoked from several threads.
+   All calls must be made with the same __FLAGS object.  */
+extern void call_once (once_flag *__flag, void (*__func)(void));
+
 __END_DECLS
 
 #endif /* _THREADS_H */