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/* Copyright 2002 Andi Kleen */
#include <linux/linkage.h>
#include <asm/cpufeature.h>
#include <asm/dwarf2.h>
/*
* memcpy - Copy a memory block.
*
* Input:
* rdi destination
* rsi source
* rdx count
*
* Output:
* rax original destination
*/
/*
* memcpy_c() - fast string ops (REP MOVSQ) based variant.
*
* This gets patched over the unrolled variant (below) via the
* alternative instructions framework:
*/
.section .altinstr_replacement, "ax", @progbits
.Lmemcpy_c:
movq %rdi, %rax
movl %edx, %ecx
shrl $3, %ecx
andl $7, %edx
rep movsq
movl %edx, %ecx
rep movsb
ret
.Lmemcpy_e:
.previous
ENTRY(__memcpy)
ENTRY(memcpy)
CFI_STARTPROC
movq %rdi, %rax
/*
* Use 32bit CMP here to avoid long NOP padding.
*/
cmp $0x20, %edx
jb .Lhandle_tail
/*
* We check whether memory false dependence could occur,
* then jump to corresponding copy mode.
*/
cmp %dil, %sil
jl .Lcopy_backward
subl $0x20, %edx
.Lcopy_forward_loop:
subq $0x20, %rdx
/*
* Move in blocks of 4x8 bytes:
*/
movq 0*8(%rsi), %r8
movq 1*8(%rsi), %r9
movq 2*8(%rsi), %r10
movq 3*8(%rsi), %r11
leaq 4*8(%rsi), %rsi
movq %r8, 0*8(%rdi)
movq %r9, 1*8(%rdi)
movq %r10, 2*8(%rdi)
movq %r11, 3*8(%rdi)
leaq 4*8(%rdi), %rdi
jae .Lcopy_forward_loop
addq $0x20, %rdx
jmp .Lhandle_tail
.Lcopy_backward:
/*
* Calculate copy position to tail.
*/
addq %rdx, %rsi
addq %rdx, %rdi
subq $0x20, %rdx
/*
* At most 3 ALU operations in one cycle,
* so append NOPS in the same 16bytes trunk.
*/
.p2align 4
.Lcopy_backward_loop:
subq $0x20, %rdx
movq -1*8(%rsi), %r8
movq -2*8(%rsi), %r9
movq -3*8(%rsi), %r10
movq -4*8(%rsi), %r11
leaq -4*8(%rsi), %rsi
movq %r8, -1*8(%rdi)
movq %r9, -2*8(%rdi)
movq %r10, -3*8(%rdi)
movq %r11, -4*8(%rdi)
leaq -4*8(%rdi), %rdi
jae .Lcopy_backward_loop
/*
* Calculate copy position to head.
*/
addq $0x20, %rdx
subq %rdx, %rsi
subq %rdx, %rdi
.Lhandle_tail:
cmpq $16, %rdx
jb .Lless_16bytes
/*
* Move data from 16 bytes to 31 bytes.
*/
movq 0*8(%rsi), %r8
movq 1*8(%rsi), %r9
movq -2*8(%rsi, %rdx), %r10
movq -1*8(%rsi, %rdx), %r11
movq %r8, 0*8(%rdi)
movq %r9, 1*8(%rdi)
movq %r10, -2*8(%rdi, %rdx)
movq %r11, -1*8(%rdi, %rdx)
retq
.p2align 4
.Lless_16bytes:
cmpq $8, %rdx
jb .Lless_8bytes
/*
* Move data from 8 bytes to 15 bytes.
*/
movq 0*8(%rsi), %r8
movq -1*8(%rsi, %rdx), %r9
movq %r8, 0*8(%rdi)
movq %r9, -1*8(%rdi, %rdx)
retq
.p2align 4
.Lless_8bytes:
cmpq $4, %rdx
jb .Lless_3bytes
/*
* Move data from 4 bytes to 7 bytes.
*/
movl (%rsi), %ecx
movl -4(%rsi, %rdx), %r8d
movl %ecx, (%rdi)
movl %r8d, -4(%rdi, %rdx)
retq
.p2align 4
.Lless_3bytes:
cmpl $0, %edx
je .Lend
/*
* Move data from 1 bytes to 3 bytes.
*/
.Lloop_1:
movb (%rsi), %r8b
movb %r8b, (%rdi)
incq %rdi
incq %rsi
decl %edx
jnz .Lloop_1
.Lend:
retq
CFI_ENDPROC
ENDPROC(memcpy)
ENDPROC(__memcpy)
/*
* Some CPUs run faster using the string copy instructions.
* It is also a lot simpler. Use this when possible:
*/
.section .altinstructions, "a"
.align 8
.quad memcpy
.quad .Lmemcpy_c
.word X86_FEATURE_REP_GOOD
/*
* Replace only beginning, memcpy is used to apply alternatives,
* so it is silly to overwrite itself with nops - reboot is the
* only outcome...
*/
.byte .Lmemcpy_e - .Lmemcpy_c
.byte .Lmemcpy_e - .Lmemcpy_c
.previous
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