include/isc/atomic.h

/*
 * Copyright (C) 2005, 2007, 2008, 2015-2017  Internet Systems Consortium, Inc. ("ISC")
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */

/* $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' (32-bit version).
 */
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");
}

#ifdef ISC_PLATFORM_HAVEATOMICSTOREQ
/*
 * This routine atomically stores the value 'val' in 'p' (64-bit version).
 */
static __inline__ void
isc_atomic_storeq(isc_int64_t *p, isc_int64_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

        "xchgq %1, %0"
        :
        : "r"(val), "m"(*p)
        : "memory");
}
#endif /* ISC_PLATFORM_HAVEATOMICSTOREQ */

/*
 * 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.
 */
static isc_int32_t
isc_atomic_xadd(isc_int32_t *p, isc_int32_t val) {
    (void)(p);
    (void)(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) {
    (void)(p);
    (void)(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) {
    (void)(p);
    (void)(cmpval);
    (void)(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 */