atomic.h

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/*
 * Copyright (C) 2005, 2007, 2008  Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
 * PERFORMANCE OF THIS SOFTWARE.
 */

/* $Id: atomic.h,v 1.10 2008/01/24 23:47:00 tbox Exp $ */

#ifndef ISC_ATOMIC_H
#define ISC_ATOMIC_H 1

#include <isc/platform.h>
#include <isc/types.h>

#ifdef ISC_PLATFORM_USEGCCASM
/*
 * This routine atomically increments the value stored in 'p' by 'val', and
 * returns the previous value.
 */
static __inline__ isc_int32_t
isc_atomic_xadd(isc_int32_t *p, isc_int32_t val) {
        isc_int32_t prev = val;

        __asm__ volatile(
#ifdef ISC_PLATFORM_USETHREADS
                "lock;"
#endif
                "xadd %0, %1"
                :"=q"(prev)
                :"m"(*p), "0"(prev)
                :"memory", "cc");

        return (prev);
}

#ifdef ISC_PLATFORM_HAVEXADDQ
static __inline__ isc_int64_t
isc_atomic_xaddq(isc_int64_t *p, isc_int64_t val) {
        isc_int64_t prev = val;

        __asm__ volatile(
#ifdef ISC_PLATFORM_USETHREADS
            "lock;"
#endif
            "xaddq %0, %1"
            :"=q"(prev)
            :"m"(*p), "0"(prev)
            :"memory", "cc");

        return (prev);
}
#endif /* ISC_PLATFORM_HAVEXADDQ */

/*
 * This routine atomically stores the value 'val' in 'p'.
 */
static __inline__ void
isc_atomic_store(isc_int32_t *p, isc_int32_t val) {
        __asm__ volatile(
#ifdef ISC_PLATFORM_USETHREADS
                /*
                 * xchg should automatically lock memory, but we add it
                 * explicitly just in case (it at least doesn't harm)
                 */
                "lock;"
#endif

                "xchgl %1, %0"
                :
                : "r"(val), "m"(*p)
                : "memory");
}

/*
 * This routine atomically replaces the value in 'p' with 'val', if the
 * original value is equal to 'cmpval'.  The original value is returned in any
 * case.
 */
static __inline__ isc_int32_t
isc_atomic_cmpxchg(isc_int32_t *p, isc_int32_t cmpval, isc_int32_t val) {
        __asm__ volatile(
#ifdef ISC_PLATFORM_USETHREADS
                "lock;"
#endif
                "cmpxchgl %1, %2"
                : "=a"(cmpval)
                : "r"(val), "m"(*p), "a"(cmpval)
                : "memory");

        return (cmpval);
}

#elif defined(ISC_PLATFORM_USESTDASM)
/*
 * The followings are "generic" assembly code which implements the same
 * functionality in case the gcc extension cannot be used.  It should be
 * better to avoid inlining below, since we directly refer to specific
 * positions of the stack frame, which would not actually point to the
 * intended address in the embedded mnemonic.
 */
#include <isc/util.h>           /* for 'UNUSED' macro */

static isc_int32_t
isc_atomic_xadd(isc_int32_t *p, isc_int32_t val) {
        UNUSED(p);
        UNUSED(val);

        __asm (
                "movl 8(%ebp), %ecx\n"
                "movl 12(%ebp), %edx\n"
#ifdef ISC_PLATFORM_USETHREADS
                "lock;"
#endif
                "xadd %edx, (%ecx)\n"

                /*
                 * set the return value directly in the register so that we
                 * can avoid guessing the correct position in the stack for a
                 * local variable.
                 */
                "movl %edx, %eax"
                );
}

static void
isc_atomic_store(isc_int32_t *p, isc_int32_t val) {
        UNUSED(p);
        UNUSED(val);

        __asm (
                "movl 8(%ebp), %ecx\n"
                "movl 12(%ebp), %edx\n"
#ifdef ISC_PLATFORM_USETHREADS
                "lock;"
#endif
                "xchgl (%ecx), %edx\n"
                );
}

static isc_int32_t
isc_atomic_cmpxchg(isc_int32_t *p, isc_int32_t cmpval, isc_int32_t val) {
        UNUSED(p);
        UNUSED(cmpval);
        UNUSED(val);

        __asm (
                "movl 8(%ebp), %ecx\n"
                "movl 12(%ebp), %eax\n" /* must be %eax for cmpxchgl */
                "movl 16(%ebp), %edx\n"
#ifdef ISC_PLATFORM_USETHREADS
                "lock;"
#endif

                /*
                 * If (%ecx) == %eax then (%ecx) := %edx.
                 % %eax is set to old (%ecx), which will be the return value.
                 */
                "cmpxchgl %edx, (%ecx)"
                );
}
#else /* !ISC_PLATFORM_USEGCCASM && !ISC_PLATFORM_USESTDASM */

#error "unsupported compiler.  disable atomic ops by --disable-atomic"

#endif
#endif /* ISC_ATOMIC_H */

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