arch/arm64/lib/memcmp.S

Source file repositories/reference/linux-study-clean/arch/arm64/lib/memcmp.S

File Facts

System
Linux kernel
Corpus path
arch/arm64/lib/memcmp.S
Extension
.S
Size
2951 bytes
Lines
140
Domain
Architecture Layer
Bucket
arch/arm64
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

#include <linux/linkage.h>
#include <asm/assembler.h>

/* Assumptions:
 *
 * ARMv8-a, AArch64, unaligned accesses.
 */

#define L(label) .L ## label

/* Parameters and result.  */
#define src1		x0
#define src2		x1
#define limit		x2
#define result		w0

/* Internal variables.  */
#define data1		x3
#define data1w		w3
#define data1h		x4
#define data2		x5
#define data2w		w5
#define data2h		x6
#define tmp1		x7
#define tmp2		x8

SYM_FUNC_START(__pi_memcmp)
	subs	limit, limit, 8
	b.lo	L(less8)

	ldr	data1, [src1], 8
	ldr	data2, [src2], 8
	cmp	data1, data2
	b.ne	L(return)

	subs	limit, limit, 8
	b.gt	L(more16)

	ldr	data1, [src1, limit]
	ldr	data2, [src2, limit]
	b	L(return)

L(more16):
	ldr	data1, [src1], 8
	ldr	data2, [src2], 8
	cmp	data1, data2
	bne	L(return)

	/* Jump directly to comparing the last 16 bytes for 32 byte (or less)
	   strings.  */
	subs	limit, limit, 16
	b.ls	L(last_bytes)

	/* We overlap loads between 0-32 bytes at either side of SRC1 when we
	   try to align, so limit it only to strings larger than 128 bytes.  */
	cmp	limit, 96
	b.ls	L(loop16)

	/* Align src1 and adjust src2 with bytes not yet done.  */
	and	tmp1, src1, 15
	add	limit, limit, tmp1
	sub	src1, src1, tmp1
	sub	src2, src2, tmp1

	/* Loop performing 16 bytes per iteration using aligned src1.
	   Limit is pre-decremented by 16 and must be larger than zero.
	   Exit if <= 16 bytes left to do or if the data is not equal.  */
	.p2align 4
L(loop16):
	ldp	data1, data1h, [src1], 16

Annotation

Implementation Notes