futex.h

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#ifndef _ASM_ARM_FUTEX_H
#define _ASM_ARM_FUTEX_H

#ifdef __KERNEL__

#if defined(CONFIG_CPU_USE_DOMAINS) && defined(CONFIG_SMP)
/* ARM doesn't provide unprivileged exclusive memory accessors */
#include <asm-generic/futex.h>
#else

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

#define __futex_atomic_ex_table(err_reg)            \
    "3:\n"                          \
    "   .pushsection __ex_table,\"a\"\n"        \
    "   .align  3\n"                    \
    "   .long   1b, 4f, 2b, 4f\n"           \
    "   .popsection\n"                  \
    "   .pushsection .fixup,\"ax\"\n"           \
    "   .align  2\n"                    \
    "4: mov %0, " err_reg "\n"          \
    "   b   3b\n"                   \
    "   .popsection"

#ifdef CONFIG_SMP

#define __futex_atomic_op(insn, ret, oldval, tmp, uaddr, oparg) \
    smp_mb();                       \
    __asm__ __volatile__(                   \
    "1: ldrex   %1, [%3]\n"             \
    "   " insn "\n"                 \
    "2: strex   %2, %0, [%3]\n"             \
    "   teq %2, #0\n"               \
    "   bne 1b\n"                   \
    "   mov %0, #0\n"               \
    __futex_atomic_ex_table("%5")               \
    : "=&r" (ret), "=&r" (oldval), "=&r" (tmp)      \
    : "r" (uaddr), "r" (oparg), "Ir" (-EFAULT)      \
    : "cc", "memory")

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

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

    smp_mb();
    __asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
    "1: ldrex   %1, [%4]\n"
    "   teq %1, %2\n"
    "   ite eq  @ explicit IT needed for the 2b label\n"
    "2: strexeq %0, %3, [%4]\n"
    "   movne   %0, #0\n"
    "   teq %0, #0\n"
    "   bne 1b\n"
    __futex_atomic_ex_table("%5")
    : "=&r" (ret), "=&r" (val)
    : "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
    : "cc", "memory");
    smp_mb();

    *uval = val;
    return ret;
}

#else /* !SMP, we can work around lack of atomic ops by disabling preemption */

#include <linux/preempt.h>
#include <asm/domain.h>

#define __futex_atomic_op(insn, ret, oldval, tmp, uaddr, oparg) \
    __asm__ __volatile__(                   \
    "1: " TUSER(ldr) "  %1, [%3]\n"         \
    "   " insn "\n"                 \
    "2: " TUSER(str) "  %0, [%3]\n"         \
    "   mov %0, #0\n"               \
    __futex_atomic_ex_table("%5")               \
    : "=&r" (ret), "=&r" (oldval), "=&r" (tmp)      \
    : "r" (uaddr), "r" (oparg), "Ir" (-EFAULT)      \
    : "cc", "memory")

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

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

    __asm__ __volatile__("@futex_atomic_cmpxchg_inatomic\n"
    "1: " TUSER(ldr) "  %1, [%4]\n"
    "   teq %1, %2\n"
    "   it  eq  @ explicit IT needed for the 2b label\n"
    "2: " TUSER(streq) "    %3, [%4]\n"
    __futex_atomic_ex_table("%5")
    : "+r" (ret), "=&r" (val)
    : "r" (oldval), "r" (newval), "r" (uaddr), "Ir" (-EFAULT)
    : "cc", "memory");

    *uval = val;
    return ret;
}

#endif /* !SMP */

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  %0, %4", ret, oldval, tmp, uaddr, oparg);
        break;
    case FUTEX_OP_ADD:
        __futex_atomic_op("add  %0, %1, %4", ret, oldval, tmp, uaddr, oparg);
        break;
    case FUTEX_OP_OR:
        __futex_atomic_op("orr  %0, %1, %4", ret, oldval, tmp, uaddr, oparg);
        break;
    case FUTEX_OP_ANDN:
        __futex_atomic_op("and  %0, %1, %4", ret, oldval, tmp, uaddr, ~oparg);
        break;
    case FUTEX_OP_XOR:
        __futex_atomic_op("eor  %0, %1, %4", ret, oldval, tmp, uaddr, 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;
}

#endif /* !(CPU_USE_DOMAINS && SMP) */
#endif /* __KERNEL__ */
#endif /* _ASM_ARM_FUTEX_H */