arch/arm/kernel/opcodes.c

Source file repositories/reference/linux-study-clean/arch/arm/kernel/opcodes.c

File Facts

System
Linux kernel
Corpus path
arch/arm/kernel/opcodes.c
Extension
.c
Size
2127 bytes
Lines
70
Domain
Architecture Layer
Bucket
arch/arm
Inferred role
Architecture Layer: exported/initcall integration point
Status
integration implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/arch/arm/kernel/opcodes.c
 *
 *  A32 condition code lookup feature moved from nwfpe/fpopcode.c
 */

#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);

Annotation

Implementation Notes