atomic.h

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/*
 * Copyright (c) 2007 Michal Kebrt
 * 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 LIBC_arm32_ATOMIC_H_
#define LIBC_arm32_ATOMIC_H_

#define LIBC_ARCH_ATOMIC_H_
#define CAS

#include <atomicdflt.h>
#include <bool.h>
#include <sys/types.h>

extern uintptr_t *ras_page;

static inline bool cas(atomic_t *val, atomic_count_t ov, atomic_count_t nv)
{
        atomic_count_t ret = 0;
        
        /*
         * The following instructions between labels 1 and 2 constitute a
         * Restartable Atomic Seqeunce. Should the sequence be non-atomic,
         * the kernel will restart it.
         */
        asm volatile (
                "1:\n"
                "       adr %[ret], 1b\n"
                "       str %[ret], %[rp0]\n"
                "       adr %[ret], 2f\n"
                "       str %[ret], %[rp1]\n"
                "       ldr %[ret], %[addr]\n"
                "       cmp %[ret], %[ov]\n"
                "       streq %[nv], %[addr]\n"
                "2:\n"
                "       moveq %[ret], #1\n"
                "       movne %[ret], #0\n"
                : [ret] "+&r" (ret),
                  [rp0] "=m" (ras_page[0]),
                  [rp1] "=m" (ras_page[1]),
                  [addr] "+m" (val->count)
                : [ov] "r" (ov),
                  [nv] "r" (nv)
                : "memory"
        );
        
        ras_page[0] = 0;
        asm volatile (
                "" ::: "memory"
        );
        ras_page[1] = 0xffffffff;
        
        return (bool) ret;
}

static inline atomic_count_t atomic_add(atomic_t *val, atomic_count_t i)
{
        atomic_count_t ret = 0;
        
        /*
         * The following instructions between labels 1 and 2 constitute a
         * Restartable Atomic Seqeunce. Should the sequence be non-atomic,
         * the kernel will restart it.
         */
        asm volatile (
                "1:\n"
                "       adr %[ret], 1b\n"
                "       str %[ret], %[rp0]\n"
                "       adr %[ret], 2f\n"
                "       str %[ret], %[rp1]\n"
                "       ldr %[ret], %[addr]\n"
                "       add %[ret], %[ret], %[imm]\n"
                "       str %[ret], %[addr]\n"
                "2:\n"
                : [ret] "+&r" (ret),
                  [rp0] "=m" (ras_page[0]),
                  [rp1] "=m" (ras_page[1]),
                  [addr] "+m" (val->count)
                : [imm] "r" (i)
        );
        
        ras_page[0] = 0;
        asm volatile (
                "" ::: "memory"
        );
        ras_page[1] = 0xffffffff;
        
        return ret;
}


static inline void atomic_inc(atomic_t *val)
{
        atomic_add(val, 1);
}


static inline void atomic_dec(atomic_t *val)
{
        atomic_add(val, -1);
}


static inline atomic_count_t atomic_preinc(atomic_t *val)
{
        return atomic_add(val, 1);
}


static inline atomic_count_t atomic_predec(atomic_t *val)
{
        return atomic_add(val, -1);
}


static inline atomic_count_t atomic_postinc(atomic_t *val)
{
        return atomic_add(val, 1) - 1;
}


static inline atomic_count_t atomic_postdec(atomic_t *val)
{
        return atomic_add(val, -1) + 1;
}


#endif

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