arch/riscv/lib/strcmp.S

Source file repositories/reference/linux-study-clean/arch/riscv/lib/strcmp.S

File Facts

System
Linux kernel
Corpus path
arch/riscv/lib/strcmp.S
Extension
.S
Size
2133 bytes
Lines
126
Domain
Architecture Layer
Bucket
arch/riscv
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/asm.h>
#include <asm/alternative-macros.h>
#include <asm/hwcap.h>

/* int strcmp(const char *cs, const char *ct) */
SYM_FUNC_START(strcmp)

	__ALTERNATIVE_CFG("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB,
		IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB))

	/*
	 * Returns
	 *   a0 - comparison result, value like strcmp
	 *
	 * Parameters
	 *   a0 - string1
	 *   a1 - string2
	 *
	 * Clobbers
	 *   t0, t1
	 */
1:
	lbu	t0, 0(a0)
	lbu	t1, 0(a1)
	addi	a0, a0, 1
	addi	a1, a1, 1
	bne	t0, t1, 2f
	bnez	t0, 1b
	li	a0, 0
	ret
2:
	/*
	 * strcmp only needs to return (< 0, 0, > 0) values
	 * not necessarily -1, 0, +1
	 */
	sub	a0, t0, t1
	ret

/*
 * Variant of strcmp using the ZBB extension if available.
 * The code was published as part of the bitmanip manual
 * in Appendix A.
 */
#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)
strcmp_zbb:

.option push
.option arch,+zbb

	/*
	 * Returns
	 *   a0 - comparison result, value like strcmp
	 *
	 * Parameters
	 *   a0 - string1
	 *   a1 - string2
	 *
	 * Clobbers
	 *   t0, t1, t2, t3, t4
	 */

	or	t2, a0, a1
	li	t4, -1
	and	t2, t2, SZREG-1
	bnez	t2, 3f

	/* Main loop for aligned string.  */
	.p2align 3
1:

Annotation

Implementation Notes