futex.h

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/*
 * Copyright (C) 2012 ARM Ltd.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
#ifndef __ASM_FUTEX_H
#define __ASM_FUTEX_H

#ifdef __KERNEL__

#include <linux/futex.h>
#include <linux/uaccess.h>
#include <asm/errno.h>

#define __futex_atomic_op(insn, ret, oldval, uaddr, tmp, oparg)     \
    asm volatile(                           \
"1: ldaxr   %w1, %2\n"                      \
    insn "\n"                           \
"2: stlxr   %w3, %w0, %2\n"                     \
"   cbnz    %w3, 1b\n"                      \
"3:\n"                                  \
"   .pushsection .fixup,\"ax\"\n"                   \
"4: mov %w0, %w5\n"                     \
"   b   3b\n"                           \
"   .popsection\n"                          \
"   .pushsection __ex_table,\"a\"\n"                \
"   .align  3\n"                            \
"   .quad   1b, 4b, 2b, 4b\n"                   \
"   .popsection\n"                          \
    : "=&r" (ret), "=&r" (oldval), "+Q" (*uaddr), "=&r" (tmp)   \
    : "r" (oparg), "Ir" (-EFAULT)                   \
    : "cc")

static inline int
futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
{
    int op = (encoded_op >> 28) & 7;
    int cmp = (encoded_op >> 24) & 15;
    int oparg = (encoded_op << 8) >> 20;
    int cmparg = (encoded_op << 20) >> 20;
    int oldval = 0, ret, tmp;

    if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
        oparg = 1 << oparg;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
        return -EFAULT;

    pagefault_disable();    /* implies preempt_disable() */

    switch (op) {
    case FUTEX_OP_SET:
        __futex_atomic_op("mov  %w0, %w4",
                  ret, oldval, uaddr, tmp, oparg);
        break;
    case FUTEX_OP_ADD:
        __futex_atomic_op("add  %w0, %w1, %w4",
                  ret, oldval, uaddr, tmp, oparg);
        break;
    case FUTEX_OP_OR:
        __futex_atomic_op("orr  %w0, %w1, %w4",
                  ret, oldval, uaddr, tmp, oparg);
        break;
    case FUTEX_OP_ANDN:
        __futex_atomic_op("and  %w0, %w1, %w4",
                  ret, oldval, uaddr, tmp, ~oparg);
        break;
    case FUTEX_OP_XOR:
        __futex_atomic_op("eor  %w0, %w1, %w4",
                  ret, oldval, uaddr, tmp, oparg);
        break;
    default:
        ret = -ENOSYS;
    }

    pagefault_enable(); /* subsumes preempt_enable() */

    if (!ret) {
        switch (cmp) {
        case FUTEX_OP_CMP_EQ: ret = (oldval == cmparg); break;
        case FUTEX_OP_CMP_NE: ret = (oldval != cmparg); break;
        case FUTEX_OP_CMP_LT: ret = (oldval < cmparg); break;
        case FUTEX_OP_CMP_GE: ret = (oldval >= cmparg); break;
        case FUTEX_OP_CMP_LE: ret = (oldval <= cmparg); break;
        case FUTEX_OP_CMP_GT: ret = (oldval > cmparg); break;
        default: ret = -ENOSYS;
        }
    }
    return ret;
}

static inline int
futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
                  u32 oldval, u32 newval)
{
    int ret = 0;
    u32 val, tmp;

    if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
        return -EFAULT;

    asm volatile("// futex_atomic_cmpxchg_inatomic\n"
"1: ldaxr   %w1, %2\n"
"   sub %w3, %w1, %w4\n"
"   cbnz    %w3, 3f\n"
"2: stlxr   %w3, %w5, %2\n"
"   cbnz    %w3, 1b\n"
"3:\n"
"   .pushsection .fixup,\"ax\"\n"
"4: mov %w0, %w6\n"
"   b   3b\n"
"   .popsection\n"
"   .pushsection __ex_table,\"a\"\n"
"   .align  3\n"
"   .quad   1b, 4b, 2b, 4b\n"
"   .popsection\n"
    : "+r" (ret), "=&r" (val), "+Q" (*uaddr), "=&r" (tmp)
    : "r" (oldval), "r" (newval), "Ir" (-EFAULT)
    : "cc", "memory");

    *uval = val;
    return ret;
}

#endif /* __KERNEL__ */
#endif /* __ASM_FUTEX_H */