+// SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+// SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
#ifndef _URCU_POINTER_STATIC_H
#define _URCU_POINTER_STATIC_H
/*
- * urcu/static/pointer.h
- *
* Userspace RCU header. Operations on pointers.
*
* TO BE INCLUDED ONLY IN CODE THAT IS TO BE RECOMPILED ON EACH LIBURCU
* RELEASE. See urcu.h for linking dynamically with the userspace rcu library.
*
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
- *
- * This 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.
- *
- * This 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 this library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
* IBM's contributions to this file may be relicensed under LGPLv2 or later.
*/
* optimizations are taken care of by the "memory_order_consume" atomic
* load.
*
+ * Use the gcc __atomic_load() rather than C11/C++11 atomic load
+ * explicit because the pointer used as input argument is a pointer,
+ * not an _Atomic type as required by C11/C++11.
+ *
* By defining URCU_DEREFERENCE_USE_VOLATILE, the user requires use of
* volatile access to implement rcu_dereference rather than
* memory_order_consume load from the C11/C++11 standards.
* expanded directly in non-LGPL code.
*/
-#ifdef URCU_DEREFERENCE_USE_VOLATILE
-# define __rcu_dereference(p) CMM_LOAD_SHARED(p)
-#else
-# if defined (__cplusplus)
-# if __cplusplus >= 201103L
-# include <atomic>
-# define __rcu_dereference(p) ((std::atomic<__typeof__(p)>)(p)).load(std::memory_order_consume)
-# else
-# define __rcu_dereference(p) CMM_LOAD_SHARED(x)
-# endif
-# else
-# if (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L)
-# include <stdatomic.h>
-# define __rcu_dereference(p) atomic_load_explicit(&(p), memory_order_consume)
-# else
-# define __rcu_dereference(p) CMM_LOAD_SHARED(p)
-# endif
-# endif
+#if !defined (URCU_DEREFERENCE_USE_VOLATILE) && \
+ ((defined (__cplusplus) && __cplusplus >= 201103L) || \
+ (defined (__STDC_VERSION__) && __STDC_VERSION__ >= 201112L))
+# define __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
#endif
-#define _rcu_dereference(p) \
- __extension__ \
- ({ \
- __typeof__(p) _________p1 = __rcu_dereference(p); \
- cmm_smp_read_barrier_depends(); \
- (_________p1); \
- })
+/*
+ * If p is const (the pointer itself, not what it points to), using
+ * __typeof__(p) would declare a const variable, leading to
+ * -Wincompatible-pointer-types errors. Using the statement expression
+ * makes it an rvalue and gets rid of the const-ness.
+ */
+#ifdef __URCU_DEREFERENCE_USE_ATOMIC_CONSUME
+# define _rcu_dereference(p) __extension__ ({ \
+ __typeof__(__extension__ ({ \
+ __typeof__(p) __attribute__((unused)) _________p0 = { 0 }; \
+ _________p0; \
+ })) _________p1; \
+ __atomic_load(&(p), &_________p1, __ATOMIC_CONSUME); \
+ (_________p1); \
+ })
+#else
+# define _rcu_dereference(p) __extension__ ({ \
+ __typeof__(p) _________p1 = CMM_LOAD_SHARED(p); \
+ cmm_smp_read_barrier_depends(); \
+ (_________p1); \
+ })
+#endif
/**
* _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer