[urcu.git] / compiler.h

#ifndef _COMPILER_H
#define _COMPILER_H

/*
 * compiler.h
 *
 * Compiler definitions.
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
 *
 * 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.
 */

/* The "volatile" is due to gcc bugs */
#define barrier() __asm__ __volatile__("": : :"memory")

#define likely(x)       __builtin_expect(!!(x), 1)
#define unlikely(x)     __builtin_expect(!!(x), 0)

/*
 * Instruct the compiler to perform only a single access to a variable
 * (prohibits merging and refetching). The compiler is also forbidden to reorder
 * successive instances of ACCESS_ONCE(), but only when the compiler is aware of
 * particular ordering. Compiler ordering can be ensured, for example, by
 * putting two ACCESS_ONCE() in separate C statements.
 *
 * This macro does absolutely -nothing- to prevent the CPU from reordering,
 * merging, or refetching absolutely anything at any time.  Its main intended
 * use is to mediate communication between process-level code and irq/NMI
 * handlers, all running on the same CPU.
 */
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x))

#endif /* _COMPILER_H */
Commit	Line	Data
af02d47e MD	1	#ifndef _COMPILER_H
	2	#define _COMPILER_H
	3
	4	/*
	5	* compiler.h
	6	*
	7	* Compiler definitions.
	8	*
	9	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
	10	*
	11	* This library is free software; you can redistribute it and/or
	12	* modify it under the terms of the GNU Lesser General Public
	13	* License as published by the Free Software Foundation; either
	14	* version 2.1 of the License, or (at your option) any later version.
	15	*
	16	* This library is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	19	* Lesser General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU Lesser General Public
	22	* License along with this library; if not, write to the Free Software
	23	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	24	*
	25	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	26	*/
	27
	28	/* The "volatile" is due to gcc bugs */
	29	#define barrier() __asm__ __volatile__("": : :"memory")
	30
	31	#define likely(x) __builtin_expect(!!(x), 1)
	32	#define unlikely(x) __builtin_expect(!!(x), 0)
	33
	34	/*
	35	* Instruct the compiler to perform only a single access to a variable
	36	* (prohibits merging and refetching). The compiler is also forbidden to reorder
	37	* successive instances of ACCESS_ONCE(), but only when the compiler is aware of
	38	* particular ordering. Compiler ordering can be ensured, for example, by
	39	* putting two ACCESS_ONCE() in separate C statements.
	40	*
	41	* This macro does absolutely -nothing- to prevent the CPU from reordering,
	42	* merging, or refetching absolutely anything at any time. Its main intended
	43	* use is to mediate communication between process-level code and irq/NMI
	44	* handlers, all running on the same CPU.
	45	*/
	46	#define ACCESS_ONCE(x) ((volatile typeof(x) )&(x))
	47
	48	#endif /* _COMPILER_H */