汇编语言-003（LAHF_SAHF 、XCHG、FLAGS、 OFFSET、ALIGN、PTR、LENGTHOF、SIZEOF）

1：LAHF将EFLAGS符号寄存器低8位字节复制到AH，SAHF将AH复制到EFLAGS符号寄存器低8位字节

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
saveflags BYTE ?.code
main PROClahfmov saveflags ,ahmov ah,saveflagssahfINVOKE ExitProcess,0
main ENDP
END main

2：交换两个操作数内容

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCoed:DWORD.data
val1 WORD 1234h
val2 WORD 5678h.code
main PROCmov ax,val1xchg ax,val2mov val1,axINVOKE ExitProcess,0
main ENDP
END main

3：直接寻址，数组名加[]和偏移量访问元素

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCoed:DWORD.data
arrayB BYTE 10h,20h,30h,40h,50h
arrayW WORD 100h,200h,300h,400h,500h
arrayD DWORD 1000h,2000h,3000h,4000h,5000h.code
main PROCmov al,arrayBmov al,[arrayB+1]mov al,[arrayB+2]mov ax,arrayWmov ax,[arrayW+2]mov eax,arrayDmov eax,[arrayD+4]INVOKE ExitProcess,0
main ENDP
END main

4：算术表达式例子 Rval = -Xval + (Yval - Zval)

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
Rval SDWORD ?
Xval SDWORD 26
Yval SDWORD 30
Zval SDWORD 40.code
main PROCmov eax,Xvalneg eaxmov ebx,Yvalsub ebx,Zvaladd eax,ebxmov Rval,eaxINVOKE ExitProcess,0
main ENDP
END main

5：标志位例子展示

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
val1 BYTE 10h.code
main PROC;零标志mov cx,1sub cx,1mov ax,0FFFFhinc ax;符号标志位mov cx,0sub cx,1mov ax,7FFFhadd ax,2;进位标志位mov al,0FFhadd al,1;溢出标志位mov al,+127add al,1mov al,-128sub al,1INVOKE ExitProcess,0
main ENDP
END main

6：OFFSET伪指令，返回数据标号的距离数据段起始地址的偏移量

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
bVal BYTE ?
wVal WORD ?
dVal DWORD ?
dVal2 DWORD ?myArray WORD 1,2,3,4,5.code
main PROCmov esi,OFFSET bValmov esi,OFFSET wValmov esi,OFFSET dValmov esi,OFFSET dVal2;OFFSET访问数组元素mov esi,OFFSET myArray+4INVOKE ExitProcess,0
main ENDP
END main

7：ALIGN伪指令，将一个变量对齐到1，2，4，8，16个字节

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCode:DWORD.data
bVal BYTE ?  ;00404000h
ALIGN 2
wVal WORD ?  ;00404002h
bVal2 BYTE ? ;00404004h
ALIGN 4
dVal DWORD ? ;00404008h
dVal2 DWORD ?;0040400ch.code
main PROCINVOKE ExitProcess,0
main ENDP
END main

8：重写一个已经声明过的操作数的大小类型，就类似指针，指向某地址再取值

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCoed:DWORD.data
myDouble DWORD 12345678h
wordList WORD 5678h,1234h.code
main PROC; mov ax,myDouble ;汇编器不允许这样mov ax,WORD PTR myDoublemov ax,WORD PTR [myDouble+2] ;1234hmov bl,BYTE PTR myDouble  ;78hmov eax,DWORD PTR wordList  ;12345678hINVOKE ExitProcess,0
main ENDP
END main

9：LENGTHOF伪指令，计算数组元素个数

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCoed:DWORD.data
byte1 BYTE 10,20,30        ;LENGTHOF为3
array1 WORD 30 DUP(?),0,0   ;LENGTHOF为30+2
array2 WORD 5 DUP(3 DUP(?))  ;如果嵌套DUP,那LENGTHOF返回的是两个数值的乘积 LENGTHOF为5*3,类似二维数组
array3 DWORD 1,2,3,4             ;LENGTHOF为4
digitStr BYTE "12345678",0      ;LENGTHOF为9myArray BYTE 10,20,30,40,50    ;LENGTHOF为5，占用多行只针对第一行BYTE 60,70,80,90,100myArray2 BYTE 10,20,30,40,50,   ;LENGTHOF为10，第一行用逗号，后面继续初始化60,70,80,90,100.code
main PROCINVOKE ExitProcess,0
main ENDP
END main

10：SIZEOF伪指令，计算数组总字节数,LENGTHOF 与 TYPE 的乘积

.386
.model flat,stdcall.stack 4096
ExitProcess PROTO,dwExitCoed:DWORD.data
intArray WORD 32 DUP(0).code
main PROCmov eax,SIZEOF intArrayINVOKE ExitProcess,0
main ENDP
END main