arch/riscv/lib/memset.S

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

File Facts

System
Linux kernel
Corpus path
arch/riscv/lib/memset.S
Extension
.S
Size
2484 bytes
Lines
116
Domain
Architecture Layer
Bucket
arch/riscv
Inferred role
Architecture Layer: arch/riscv
Status
atlas-only

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>

/* void *memset(void *, int, size_t) */
SYM_FUNC_START(__memset)
	move t0, a0  /* Preserve return value */

	/* Defer to byte-oriented fill for small sizes */
	sltiu a3, a2, 16
	bnez a3, 4f

	/*
	 * Round to nearest XLEN-aligned address
	 * greater than or equal to start address
	 */
	addi a3, t0, SZREG-1
	andi a3, a3, ~(SZREG-1)
	beq a3, t0, 2f  /* Skip if already aligned */
	/* Handle initial misalignment */
	sub a4, a3, t0
1:
	sb a1, 0(t0)
	addi t0, t0, 1
	bltu t0, a3, 1b
	sub a2, a2, a4  /* Update count */

2: /* Duff's device with 32 XLEN stores per iteration */
	/* Broadcast value into all bytes */
	andi a1, a1, 0xff
	slli a3, a1, 8
	or a1, a3, a1
	slli a3, a1, 16
	or a1, a3, a1
#ifdef CONFIG_64BIT
	slli a3, a1, 32
	or a1, a3, a1
#endif

	/* Calculate end address */
	andi a4, a2, ~(SZREG-1)
	add a3, t0, a4

	andi a4, a4, 31*SZREG  /* Calculate remainder */
	beqz a4, 3f            /* Shortcut if no remainder */
	neg a4, a4
	addi a4, a4, 32*SZREG  /* Calculate initial offset */

	/* Adjust start address with offset */
	sub t0, t0, a4

	/* Jump into loop body */
	/* Assumes 32-bit instruction lengths */
	la a5, 3f
#ifdef CONFIG_64BIT
	srli a4, a4, 1
#endif
	add a5, a5, a4
	jr a5
3:
	REG_S a1,        0(t0)
	REG_S a1,    SZREG(t0)
	REG_S a1,  2*SZREG(t0)
	REG_S a1,  3*SZREG(t0)
	REG_S a1,  4*SZREG(t0)
	REG_S a1,  5*SZREG(t0)
	REG_S a1,  6*SZREG(t0)
	REG_S a1,  7*SZREG(t0)
	REG_S a1,  8*SZREG(t0)
	REG_S a1,  9*SZREG(t0)
	REG_S a1, 10*SZREG(t0)

Annotation

Implementation Notes