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20f3337d35
The modern target to use is FSRS (Fast Short REP STOS), and the other cases should only be used for bigger areas (ie mainly things like page clearing). Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
117 lines
2.4 KiB
ArmAsm
117 lines
2.4 KiB
ArmAsm
/* SPDX-License-Identifier: GPL-2.0 */
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/* Copyright 2002 Andi Kleen, SuSE Labs */
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#include <linux/linkage.h>
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#include <asm/cpufeatures.h>
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#include <asm/alternative.h>
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#include <asm/export.h>
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.section .noinstr.text, "ax"
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/*
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* ISO C memset - set a memory block to a byte value. This function uses fast
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* string to get better performance than the original function. The code is
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* simpler and shorter than the original function as well.
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*
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* rdi destination
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* rsi value (char)
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* rdx count (bytes)
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*
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* rax original destination
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*
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* The FSRS alternative should be done inline (avoiding the call and
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* the disgusting return handling), but that would require some help
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* from the compiler for better calling conventions.
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*
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* The 'rep stosb' itself is small enough to replace the call, but all
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* the register moves blow up the code. And two of them are "needed"
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* only for the return value that is the same as the source input,
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* which the compiler could/should do much better anyway.
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*/
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SYM_FUNC_START(__memset)
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ALTERNATIVE "jmp memset_orig", "", X86_FEATURE_FSRS
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movq %rdi,%r9
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movb %sil,%al
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movq %rdx,%rcx
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rep stosb
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movq %r9,%rax
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RET
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SYM_FUNC_END(__memset)
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EXPORT_SYMBOL(__memset)
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SYM_FUNC_ALIAS(memset, __memset)
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EXPORT_SYMBOL(memset)
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SYM_FUNC_START_LOCAL(memset_orig)
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movq %rdi,%r10
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/* expand byte value */
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movzbl %sil,%ecx
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movabs $0x0101010101010101,%rax
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imulq %rcx,%rax
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/* align dst */
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movl %edi,%r9d
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andl $7,%r9d
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jnz .Lbad_alignment
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.Lafter_bad_alignment:
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movq %rdx,%rcx
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shrq $6,%rcx
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jz .Lhandle_tail
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.p2align 4
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.Lloop_64:
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decq %rcx
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movq %rax,(%rdi)
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movq %rax,8(%rdi)
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movq %rax,16(%rdi)
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movq %rax,24(%rdi)
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movq %rax,32(%rdi)
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movq %rax,40(%rdi)
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movq %rax,48(%rdi)
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movq %rax,56(%rdi)
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leaq 64(%rdi),%rdi
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jnz .Lloop_64
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/* Handle tail in loops. The loops should be faster than hard
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to predict jump tables. */
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.p2align 4
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.Lhandle_tail:
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movl %edx,%ecx
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andl $63&(~7),%ecx
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jz .Lhandle_7
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shrl $3,%ecx
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.p2align 4
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.Lloop_8:
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decl %ecx
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movq %rax,(%rdi)
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leaq 8(%rdi),%rdi
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jnz .Lloop_8
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.Lhandle_7:
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andl $7,%edx
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jz .Lende
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.p2align 4
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.Lloop_1:
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decl %edx
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movb %al,(%rdi)
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leaq 1(%rdi),%rdi
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jnz .Lloop_1
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.Lende:
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movq %r10,%rax
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RET
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.Lbad_alignment:
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cmpq $7,%rdx
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jbe .Lhandle_7
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movq %rax,(%rdi) /* unaligned store */
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movq $8,%r8
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subq %r9,%r8
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addq %r8,%rdi
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subq %r8,%rdx
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jmp .Lafter_bad_alignment
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.Lfinal:
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SYM_FUNC_END(memset_orig)
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