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)
120

source code of linux/tools/arch/x86/lib/memset_64.S