source: mainline/uspace/lib/c/arch/arm32/src/atomic.c@ eec201d

/*
 * Copyright (c) 2007 Michal Kebrt
 * Copyright (c) 2018 CZ.NIC, z.s.p.o.
 * 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.
 */

/*
 * Older ARMs don't have atomic instructions, so we need to define a bunch
 * of symbols for GCC to use.
 */

#include <stdbool.h>

extern volatile unsigned *ras_page;

bool __atomic_compare_exchange_4(volatile unsigned *mem, unsigned *expected, unsigned desired, bool weak, int success, int failure)
{
        (void) success;
        (void) failure;
        (void) weak;

        unsigned ov = *expected;
        unsigned ret;

        /*
         * The following instructions between labels 1 and 2 constitute a
         * Restartable Atomic Sequence. 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"
            : [ret] "=&r" (ret),
              [rp0] "=m" (ras_page[0]),
              [rp1] "=m" (ras_page[1]),
              [addr] "+m" (*mem)
            : [ov] "r" (ov),
              [nv] "r" (desired)
            : "memory"
        );

        ras_page[0] = 0;
        ras_page[1] = 0xffffffff;

        if (ret == ov)
                return true;

        *expected = ret;
        return false;
}

unsigned short __atomic_fetch_add_2(volatile unsigned short *mem, unsigned short val, int model)
{
        (void) model;

        unsigned short ret;

        /*
         * 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"
            "   ldrh %[ret], %[addr]\n"
            "   add %[ret], %[ret], %[imm]\n"
            "   strh %[ret], %[addr]\n"
            "2:\n"
            : [ret] "=&r" (ret),
              [rp0] "=m" (ras_page[0]),
              [rp1] "=m" (ras_page[1]),
              [addr] "+m" (*mem)
            : [imm] "r" (val)
        );

        ras_page[0] = 0;
        ras_page[1] = 0xffffffff;

        return ret - val;
}

unsigned __atomic_fetch_add_4(volatile unsigned *mem, unsigned val, int model)
{
        (void) model;

        unsigned ret;

        /*
         * 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" (*mem)
            : [imm] "r" (val)
        );

        ras_page[0] = 0;
        ras_page[1] = 0xffffffff;

        return ret - val;
}

unsigned __atomic_fetch_sub_4(volatile unsigned *mem, unsigned val, int model)
{
        return __atomic_fetch_add_4(mem, -val, model);
}

void __sync_synchronize(void)
{
        // FIXME: Full memory barrier. We might need a syscall for this.
}

unsigned __sync_add_and_fetch_4(volatile void *vptr, unsigned val)
{
        return __atomic_fetch_add_4(vptr, val, __ATOMIC_SEQ_CST) + val;
}

unsigned __sync_sub_and_fetch_4(volatile void *vptr, unsigned val)
{
        return __atomic_fetch_sub_4(vptr, val, __ATOMIC_SEQ_CST) - val;
}

bool __sync_bool_compare_and_swap_4(volatile void *ptr, unsigned old_val, unsigned new_val)
{
        return __atomic_compare_exchange_4(ptr, &old_val, new_val, false,
            __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
}

unsigned __sync_val_compare_and_swap_4(volatile void *ptr, unsigned old_val, unsigned new_val)
{
        __atomic_compare_exchange_4(ptr, &old_val, new_val, false,
            __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
        return old_val;
}