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/* SPDX-License-Identifier: GPL-2.0 */
/* Copyright 2002 Andi Kleen, SuSE Labs */
#include <linux/linkage.h>
#include <asm/cpufeatures.h>
#include <asm/alternative.h>
#include <asm/export.h>
.section .noinstr.text, "ax"
/*
* ISO C memset - set a memory block to a byte value. This function uses fast
* string to get better performance than the original function. The code is
* simpler and shorter than the original function as well.
*
* rdi destination
* rsi value (char)
* rdx count (bytes)
*
* rax original destination
*
* The FSRS alternative should be done inline (avoiding the call and
* the disgusting return handling), but that would require some help
* from the compiler for better calling conventions.
*
* The 'rep stosb' itself is small enough to replace the call, but all
* the register moves blow up the code. And two of them are "needed"
* only for the return value that is the same as the source input,
* which the compiler could/should do much better anyway.
*/
SYM_FUNC_START(__memset)
ALTERNATIVE "jmp memset_orig", "", X86_FEATURE_FSRS
movq %rdi,%r9
movb %sil,%al
movq %rdx,%rcx
rep stosb
movq %r9,%rax
RET
SYM_FUNC_END(__memset)
EXPORT_SYMBOL(__memset)
SYM_FUNC_ALIAS(memset, __memset)
EXPORT_SYMBOL(memset)
SYM_FUNC_START_LOCAL(memset_orig)
movq %rdi,%r10
/* expand byte value */
movzbl %sil,%ecx
movabs $0x0101010101010101,%rax
imulq %rcx,%rax
/* align dst */
movl %edi,%r9d
andl $7,%r9d
jnz .Lbad_alignment
.Lafter_bad_alignment:
movq %rdx,%rcx
shrq $6,%rcx
jz .Lhandle_tail
.p2align 4
.Lloop_64:
decq %rcx
movq %rax,(%rdi)
movq %rax,8(%rdi)
movq %rax,16(%rdi)
movq %rax,24(%rdi)
movq %rax,32(%rdi)
movq %rax,40(%rdi)
movq %rax,48(%rdi)
movq %rax,56(%rdi)
leaq 64(%rdi),%rdi
jnz .Lloop_64
/* Handle tail in loops. The loops should be faster than hard
to predict jump tables. */
.p2align 4
.Lhandle_tail:
movl %edx,%ecx
andl $63&(~7),%ecx
jz .Lhandle_7
shrl $3,%ecx
.p2align 4
.Lloop_8:
decl %ecx
movq %rax,(%rdi)
leaq 8(%rdi),%rdi
jnz .Lloop_8
.Lhandle_7:
andl $7,%edx
jz .Lende
.p2align 4
.Lloop_1:
decl %edx
movb %al,(%rdi)
leaq 1(%rdi),%rdi
jnz .Lloop_1
.Lende:
movq %r10,%rax
RET
.Lbad_alignment:
cmpq $7,%rdx
jbe .Lhandle_7
movq %rax,(%rdi) /* unaligned store */
movq $8,%r8
subq %r9,%r8
addq %r8,%rdi
subq %r8,%rdx
jmp .Lafter_bad_alignment
.Lfinal:
SYM_FUNC_END(memset_orig)
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