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.

ChangeLog

@@ -1,5 +1,16 @@
 2018-07-24  Adhemerval Zanella  <adhemerval.zanella@linaro.org>
 
+	[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.
+
 	[BZ #14092]
 	* conform/data/threads.h-data (mtx_plain): New constant.
 	(mtx_recursive): Likewise.

conform/data/threads.h-data

@@ -1,5 +1,7 @@
 #if defined ISO11
 
+macro ONCE_FLAG_INIT
+
 constant thrd_success
 constant thrd_busy
 constant thrd_error
@@ -13,6 +15,7 @@ constant mtx_timed
 type thrd_t
 type thrd_start_t
 type mtx_t
+type once_flag
 
 function int thrd_create (thrd_t*, thrd_start_t, void*)
 function int thrd_equal (thrd_t, thrd_t)
@@ -30,6 +33,8 @@ function int mtx_trylock (mtx_t*)
 function int mtx_unlock (mtx_t*)
 function void mtx_destroy (mtx_t*)
 
+function void call_once (once_flag*, void (*)(void))
+
 #include "time.h-data"
 
 #endif

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 \

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 {

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);
+}

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 */