opcodes.c

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/*
 *  linux/arch/arm/kernel/opcodes.c
 *
 *  A32 condition code lookup feature moved from nwfpe/fpopcode.c
 *
 * 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.
 */

#include <linux/module.h>
#include <asm/opcodes.h>

#define ARM_OPCODE_CONDITION_UNCOND 0xf

/*
 * condition code lookup table
 * index into the table is test code: EQ, NE, ... LT, GT, AL, NV
 *
 * bit position in short is condition code: NZCV
 */
static const unsigned short cc_map[16] = {
    0xF0F0,         /* EQ == Z set            */
    0x0F0F,         /* NE                     */
    0xCCCC,         /* CS == C set            */
    0x3333,         /* CC                     */
    0xFF00,         /* MI == N set            */
    0x00FF,         /* PL                     */
    0xAAAA,         /* VS == V set            */
    0x5555,         /* VC                     */
    0x0C0C,         /* HI == C set && Z clear */
    0xF3F3,         /* LS == C clear || Z set */
    0xAA55,         /* GE == (N==V)           */
    0x55AA,         /* LT == (N!=V)           */
    0x0A05,         /* GT == (!Z && (N==V))   */
    0xF5FA,         /* LE == (Z || (N!=V))    */
    0xFFFF,         /* AL always              */
    0           /* NV                     */
};

/*
 * Returns:
 * ARM_OPCODE_CONDTEST_FAIL   - if condition fails
 * ARM_OPCODE_CONDTEST_PASS   - if condition passes (including AL)
 * ARM_OPCODE_CONDTEST_UNCOND - if NV condition, or separate unconditional
 *                              opcode space from v5 onwards
 *
 * Code that tests whether a conditional instruction would pass its condition
 * check should check that return value == ARM_OPCODE_CONDTEST_PASS.
 *
 * Code that tests if a condition means that the instruction would be executed
 * (regardless of conditional or unconditional) should instead check that the
 * return value != ARM_OPCODE_CONDTEST_FAIL.
 */
asmlinkage unsigned int arm_check_condition(u32 opcode, u32 psr)
{
    u32 cc_bits  = opcode >> 28;
    u32 psr_cond = psr >> 28;
    unsigned int ret;

    if (cc_bits != ARM_OPCODE_CONDITION_UNCOND) {
        if ((cc_map[cc_bits] >> (psr_cond)) & 1)
            ret = ARM_OPCODE_CONDTEST_PASS;
        else
            ret = ARM_OPCODE_CONDTEST_FAIL;
    } else {
        ret = ARM_OPCODE_CONDTEST_UNCOND;
    }

    return ret;
}
EXPORT_SYMBOL_GPL(arm_check_condition);