MOV EDI,EDI
摘自KSSDMOVEDI,EDI 就是两个字节的NOP
在程序中与NOP指令的意义相同。
为什么要用MOVEDI,EDI 而不用两个NOP?
我的理解是：
用两个NOP指令耗费的CPU时钟周期要比用MOVEDI,EDI指令要长，为了提高效率，就采用了MOVEDI,EDI
listing.inc文件的内容
;; LISTING.INC
;;
;; This file contains assembler macros and is included by the files created
;; with the -FA compiler switch to be assembled by MASM (Microsoft Macro
;; Assembler).
;;
;; Copyright (c) 1993, Microsoft Corporation. All rights reserved.
;; non destructive nops
npad macro size
if size eq 1
nop
else
if size eq 2
mov edi, edi
else
if size eq 3
; lea ecx,
DB 8DH, 49H, 00H
else
if size eq 4
; lea esp,
DB 8DH, 64H, 24H, 00H
else
if size eq 5
add eax, DWORD PTR 0
else
if size eq 6
; lea ebx,
DB 8DH, 9BH, 00H, 00H, 00H, 00H
else
if size eq 7
; lea esp,
DB 8DH, 0A4H, 24H, 00H, 00H, 00H, 00H
else
%out error: unsupported npad size
.err
endif
endif
endif
endif
endif
endif
endif
endm
;; destructive nops
dpad macro size, reg
if size eq 1
inc reg
else
%out error: unsupported dpad size
.err
endif
endm 除了mov edi,edi以外，还有66 90这种nop。
66 90是在16位状态下运行32位的xchg eax,eax，或者32位状态下运行16位的xchg ax,ax
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