barrier.h

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/*
 * Copyright (C) 2005 Jakub Jermar
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef __ia32_BARRIER_H__
#define __ia32_BARRIER_H__

/*
 * NOTE:
 * No barriers for critical section (i.e. spinlock) on IA-32 are needed:
 * - spinlock_lock() and spinlock_trylock() use serializing XCHG instruction
 * - writes cannot pass reads on IA-32 => spinlock_unlock() needs no barriers
 */

/*
 * Provisions are made to prevent compiler from reordering instructions itself.
 */

#define CS_ENTER_BARRIER()      __asm__ volatile ("" ::: "memory")
#define CS_LEAVE_BARRIER()      __asm__ volatile ("" ::: "memory")

static inline void cpuid_serialization(void)
{
        __asm__ volatile (
                "xorl %%eax, %%eax\n"
                "cpuid\n"
                ::: "eax", "ebx", "ecx", "edx", "memory"
        );
}

#ifdef CONFIG_FENCES_P4
#       define memory_barrier()         __asm__ volatile ("mfence\n" ::: "memory")
#       define read_barrier()           __asm__ volatile ("lfence\n" ::: "memory")
#       ifdef CONFIG_WEAK_MEMORY
#               define write_barrier()  __asm__ volatile ("sfence\n" ::: "memory")
#       else
#               define write_barrier()  __asm__ volatile( "" ::: "memory");
#       endif
#elif CONFIG_FENCES_P3
#       define memory_barrier()         cpuid_serialization()
#       define read_barrier()           cpuid_serialization()
#       ifdef CONFIG_WEAK_MEMORY
#               define write_barrier()  __asm__ volatile ("sfence\n" ::: "memory")
#       else
#               define write_barrier()  __asm__ volatile( "" ::: "memory");
#       endif
#else
#       define memory_barrier()         cpuid_serialization()
#       define read_barrier()           cpuid_serialization()
#       ifdef CONFIG_WEAK_MEMORY
#               define write_barrier()  cpuid_serialization()
#       else
#               define write_barrier()  __asm__ volatile( "" ::: "memory");
#       endif
#endif

#endif

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