memset_64.S

  1/* SPDX-License-Identifier: GPL-2.0 */
  2/* Copyright 2002 Andi Kleen, SuSE Labs */
  3
  4#include <linux/export.h>
  5#include <linux/linkage.h>
  6#include <linux/cfi_types.h>
  7#include <asm/cpufeatures.h>
  8#include <asm/alternative.h>
  9
 10.section .noinstr.text, "ax"
 11
 12/*
 13 * ISO C memset - set a memory block to a byte value. This function uses fast
 14 * string to get better performance than the original function. The code is
 15 * simpler and shorter than the original function as well.
 16 *
 17 * rdi   destination
 18 * rsi   value (char)
 19 * rdx   count (bytes)
 20 *
 21 * rax   original destination
 22 *
 23 * The FSRS alternative should be done inline (avoiding the call and
 24 * the disgusting return handling), but that would require some help
 25 * from the compiler for better calling conventions.
 26 *
 27 * The 'rep stosb' itself is small enough to replace the call, but all
 28 * the register moves blow up the code. And two of them are "needed"
 29 * only for the return value that is the same as the source input,
 30 * which the compiler could/should do much better anyway.
 31 */
 32SYM_TYPED_FUNC_START(__memset)
 33	ALTERNATIVE "jmp memset_orig", "", X86_FEATURE_FSRS
 34
 35	movq %rdi,%r9
 36	movb %sil,%al
 37	movq %rdx,%rcx
 38	rep stosb
 39	movq %r9,%rax
 40	RET
 41SYM_FUNC_END(__memset)
 42EXPORT_SYMBOL(__memset)
 43
 44SYM_FUNC_ALIAS_MEMFUNC(memset, __memset)
 45SYM_PIC_ALIAS(memset)
 46EXPORT_SYMBOL(memset)
 47
 48SYM_FUNC_START_LOCAL(memset_orig)
 49	movq %rdi,%r10
 50
 51	/* expand byte value  */
 52	movzbl %sil,%ecx
 53	movabs $0x0101010101010101,%rax
 54	imulq  %rcx,%rax
 55
 56	/* align dst */
 57	movl  %edi,%r9d
 58	andl  $7,%r9d
 59	jnz  .Lbad_alignment
 60.Lafter_bad_alignment:
 61
 62	movq  %rdx,%rcx
 63	shrq  $6,%rcx
 64	jz	 .Lhandle_tail
 65
 66	.p2align 4
 67.Lloop_64:
 68	decq  %rcx
 69	movq  %rax,(%rdi)
 70	movq  %rax,8(%rdi)
 71	movq  %rax,16(%rdi)
 72	movq  %rax,24(%rdi)
 73	movq  %rax,32(%rdi)
 74	movq  %rax,40(%rdi)
 75	movq  %rax,48(%rdi)
 76	movq  %rax,56(%rdi)
 77	leaq  64(%rdi),%rdi
 78	jnz    .Lloop_64
 79
 80	/* Handle tail in loops. The loops should be faster than hard
 81	   to predict jump tables. */
 82	.p2align 4
 83.Lhandle_tail:
 84	movl	%edx,%ecx
 85	andl    $63&(~7),%ecx
 86	jz 		.Lhandle_7
 87	shrl	$3,%ecx
 88	.p2align 4
 89.Lloop_8:
 90	decl   %ecx
 91	movq  %rax,(%rdi)
 92	leaq  8(%rdi),%rdi
 93	jnz    .Lloop_8
 94
 95.Lhandle_7:
 96	andl	$7,%edx
 97	jz      .Lende
 98	.p2align 4
 99.Lloop_1:
100	decl    %edx
101	movb 	%al,(%rdi)
102	leaq	1(%rdi),%rdi
103	jnz     .Lloop_1
104
105.Lende:
106	movq	%r10,%rax
107	RET
108
109.Lbad_alignment:
110	cmpq $7,%rdx
111	jbe	.Lhandle_7
112	movq %rax,(%rdi)	/* unaligned store */
113	movq $8,%r8
114	subq %r9,%r8
115	addq %r8,%rdi
116	subq %r8,%rdx
117	jmp .Lafter_bad_alignment
118.Lfinal:
119SYM_FUNC_END(memset_orig)