第五章实验四第三题

题目：下面的程序功能是将“mov ax,4c00h"之前的指令复制到内存0:200处，补全程序。上机调试，跟踪运行结果

代码：

assume cs:codesgcodesg segment mov ax,__(1)__ mov ds,ax mov ax,0020h mov es,ax mov bx,0 mov cx,__(2)___ s: mov al,[bx] mov es:[bx],al inc bx loop s mov ax,4c00h int 21hcodesg endsend

 

1分析：这里要复制的是从3~10行的汇编指令。可以肯定的是(1)处填写cs或者codesg都行，因为cs指向了程序指令的开始处。其次我们知道这段程序的代码长度在cx中存放（用debug来调试时）。所以我们可以先在（2)处填上cx，即先让程序能编译链接生成对应的target.exe文件，然后用debug target.exe来对其调试（当然我们并不是真的调试，而是为了查看cx的值是多少），然后输入r后查看cx的值，如果不知道mov ax,4c00h 和int 21h占了多少字节，都可以通过输入u后就可以看到各条命令占了多少字节。获得了总长度之后，再用其减去mov ax,4c00h 和int 21h占用的字节，所得的结果就是（2）出所应该填写的值了。

2.在（1）和（2）出分别填上cs和cx，编译链接之后用debug来调试。

i：代码看起来是这样的：

assume cs:codesgcodesg segment mov ax,cs mov ds,ax mov ax,0020h mov es,ax mov bx,0 mov cx,cx s: mov al,[bx] mov es:[bx],al inc bx loop s mov ax,4c00h int 21hcodesg endsend

ii：debug的数据如下：

-rAX=0000 BX=0000 CX=001B DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B75 ES=0B75 SS=0B85 CS=0B85 IP=0000 NV UP EI PL NZ NA PO NC 0B85:0000 8CC8 MOVAX,CS -u0B85:0000 8CC8 MOVAX,CS 0B85:0002 8ED8 MOVDS,AX 0B85:0004 B82000 MOVAX,0020 0B85:0007 8EC0 MOVES,AX 0B85:0009 BB0000 MOVBX,0000 0B85:000C 8BC9 MOVCX,CX 0B85:000E 8A07 MOVAL,[BX] 0B85:0010 26 ES: 0B85:0011 8807 MOV[BX],AL 0B85:0013 43 INCBX 0B85:0014 E2F8 LOOP000E 0B85:0016 B8004C MOVAX,4C00 0B85:0019 CD21 INT21 0B85:001B 00721F ADD[BP+SI+1F],DH 0B85:001E D1E2 SHLDX,1 -rAX=0000 BX=0000 CX=001B DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B75 ES=0B75 SS=0B85 CS=0B85 IP=0000 NV UP EI PL NZ NA PO NC 0B85:0000 8CC8 MOVAX,CS -

从以上数据可以得出cx=001bh,而mov ax,4c00h 和int 21h占了5字节，所以可以得知(2)处应该填写001b-0005的值，及0017h。

3.用cs填充(1)处，0017h填充(2）处。代码看起来是这样。

assume cs:codesgcodesg segment mov ax,cs mov ds,ax mov ax,0020h mov es,ax mov bx,0 mov cx,0017h s: mov al,[bx] mov es:[bx],al inc bx loop s mov ax,4c00h int 21hcodesg endsend

4.调试过程

 -rAX=0000 BX=0000 CX=001C DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B75 ES=0B75 SS=0B85 CS=0B85 IP=0000 NV UP EI PL NZ NA PO NC 0B85:0000 8CC8 MOVAX,CS -u0B85:0000 8CC8 MOVAX,CS 0B85:0002 8ED8 MOVDS,AX 0B85:0004 B82000 MOVAX,0020 0B85:0007 8EC0 MOVES,AX 0B85:0009 BB0000 MOVBX,0000 0B85:000C B91700 MOVCX,0017 0B85:000F 8A07 MOVAL,[BX] 0B85:0011 26 ES: 0B85:0012 8807 MOV[BX],AL 0B85:0014 43 INCBX 0B85:0015 E2F8 LOOP000F 0B85:0017 B8004C MOVAX,4C00 0B85:001A CD21 INT21 0B85:001C 721F JB003D 0B85:001E D1E2 SHLDX,1 -tAX=0B85 BX=0000 CX=001C DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B75 ES=0B75 SS=0B85 CS=0B85 IP=0002 NV UP EI PL NZ NA PO NC 0B85:0002 8ED8 MOVDS,AX -tAX=0B85 BX=0000 CX=001C DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0B75 SS=0B85 CS=0B85 IP=0004 NV UP EI PL NZ NA PO NC 0B85:0004 B82000 MOVAX,0020 -tAX=0020 BX=0000 CX=001C DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0B75 SS=0B85 CS=0B85 IP=0007 NV UP EI PL NZ NA PO NC 0B85:0007 8EC0 MOVES,AX -tAX=0020 BX=0000 CX=001C DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0009 NV UP EI PL NZ NA PO NC 0B85:0009 BB0000 MOVBX,0000 -tAX=0020 BX=0000 CX=001C DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=000C NV UP EI PL NZ NA PO NC 0B85:000C B91700 MOVCX,0017 -d es:00020:0000 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0010 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0020 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0030 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0040 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0050 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0060 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0070 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................-tAX=0020 BX=0000 CX=0017 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=000F NV UP EI PL NZ NA PO NC 0B85:000F 8A07 MOVAL,[BX] DS:0000=8C-tAX=008C BX=0000 CX=0017 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0011 NV UP EI PL NZ NA PO NC 0B85:0011 26 ES: 0B85:0012 8807 MOV[BX],AL ES:0000=00-tAX=008C BX=0000 CX=0017 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0014 NV UP EI PL NZ NA PO NC 0B85:0014 43 INCBX -tAX=008C BX=0001 CX=0017 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0015 NV UP EI PL NZ NA PO NC 0B85:0015 E2F8 LOOP000F -tAX=008C BX=0001 CX=0016 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=000F NV UP EI PL NZ NA PO NC 0B85:000F 8A07 MOVAL,[BX] DS:0001=C8-pAX=00C8 BX=0001 CX=0016 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0011 NV UP EI PL NZ NA PO NC 0B85:0011 26 ES: 0B85:0012 8807 MOV[BX],AL ES:0001=00-pAX=00C8 BX=0001 CX=0016 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0014 NV UP EI PL NZ NA PO NC 0B85:0014 43 INCBX -pAX=00C8 BX=0002 CX=0016 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0015 NV UP EI PL NZ NA PO NC 0B85:0015 E2F8 LOOP000F -pAX=00F8 BX=0017 CX=0000 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=0017 NV UP EI PL NZ NA PE NC 0B85:0017 B8004C MOVAX,4C00 -d es:00020:0000 8C C8 8E D8 B8 20 00 8E-C0 BB 00 00 B9 17 00 8A ..... ..........0020:0010 07 26 88 07 43 E2 F8 00-00 00 00 00 00 00 00 00 .&..C...........0020:0020 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0030 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0040 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0050 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0060 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................0020:0070 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................-u es:00020:0000 8CC8 MOVAX,CS 0020:0002 8ED8 MOVDS,AX 0020:0004 B82000 MOVAX,0020 0020:0007 8EC0 MOVES,AX 0020:0009 BB0000 MOVBX,0000 0020:000C B91700 MOVCX,0017 0020:000F 8A07 MOVAL,[BX] 0020:0011 26 ES: 0020:0012 8807 MOV[BX],AL 0020:0014 43 INCBX 0020:0015 E2F8 LOOP000F 0020:0017 0000 ADD[BX+SI],AL 0020:0019 0000 ADD[BX+SI],AL 0020:001B 0000 ADD[BX+SI],AL 0020:001D 0000 ADD[BX+SI],AL 0020:001F 0000 ADD[BX+SI],AL -tAX=4C00 BX=0017 CX=0000 DX=0000 SP=0000 BP=0000 SI=0000 DI=0000 DS=0B85 ES=0020 SS=0B85 CS=0B85 IP=001A NV UP EI PL NZ NA PE NC 0B85:001A CD21 INT21 -pProgram terminated normally-q

5.小结：这里关键的是就是确定复制时的开始地址和结束地址，