Windows下反汇编程序例子

Windows下编写的程序经编译链接之后，就可用debug等调试工具调试执行，也能看到反汇编的结果，这很便于理解“汇编指令”是如何翻译成“机器指令”的。对Windows程序，这样的工具有很多，像SoftICE、TRW、W32dasm、IDA、Hiew等。这里准备谈一下W32dasm。

;===============================================================
;例：取命令行参数，并显示到消息框中
;文件名：6.asm

.386
.model flat,stdcall
option casemap:none

include windows.inc ;常量及结构定义

include kernel32.inc ;函数原型声明
include user32.inc

includelib kernel32.lib ;用到的引入库
includelib user32.lib

.data
szCaption db "命令行参数",0

.code
start:
invoke GetCommandLine
invoke MessageBox,NULL,eax,addr szCaption,MB_OK
invoke ExitProcess,NULL
end start
---------------------------------------------------------
用到API函数：
LPTSTR GetCommandLine(VOID)
This function has no parameters.
The return value is a pointer to the command-line string for the current process.
---------------------------------------------------------
编译链接：

---------------------------------------------------------

下面使用W32dasm来反汇编6.exe。

启动W32dasm，从菜单Disassembler中选Open File to Disassemble...，从出现的对话框中选择要进行反汇编的程序，比如6.exe并打开。

若首次使用该反汇编工具，屏幕显示可能有点乱，执行Disassembler/Font.../Select Font选择合适的字体即可解决该问题。执行Disassembler/Font.../Save Default Font，这样下次启动该软件时也不会乱啦。下面是6.exe反汇编后的结果：

Disassembly of File: 6.exe
Code Offset = 00000400, Code Size = 00000200
Data Offset = 00000800, Data Size = 00000200

Number of Objects = 0003 (dec), Imagebase = 00400000h

Object01: .text RVA: 00001000 Offset: 00000400 Size: 00000200 Flags: 60000020
Object02: .rdata RVA: 00002000 Offset: 00000600 Size: 00000200 Flags: 40000040
Object03: .data RVA: 00003000 Offset: 00000800 Size: 00000200 Flags: C0000040

+++++++++++++++++++ MENU INFORMATION ++++++++++++++++++

There Are No Menu Resources in This Application

+++++++++++++++++ DIALOG INFORMATION ++++++++++++++++++

There Are No Dialog Resources in This Application

+++++++++++++++++++ IMPORTED FUNCTIONS ++++++++++++++++++
Number of Imported Modules = 2 (decimal) ;本程序用到两个引入库

Import Module 001: KERNEL32.dll
Import Module 002: USER32.dll

+++++++++++++++++++ IMPORT MODULE DETAILS +++++++++++++++

Import Module 001: KERNEL32.dll ;要用到本库中下面两个函数

Addr:00002072 hint(00B6) Name: GetCommandLineA
Addr:00002064 hint(0075) Name: ExitProcess

Import Module 002: USER32.dll

Addr:00002092 hint(01BB) Name: MessageBoxA

+++++++++++++++++++ EXPORTED FUNCTIONS ++++++++++++++++++
Number of Exported Functions = 0000 (decimal)

+++++++++++++++++++ ASSEMBLY CODE LISTING ++++++++++++++++++
//********************** Start of Code in Object .text **************
Program Entry Point = 00401000 (6.exe File Offset:00001600)

* Reference To: KERNEL32.GetCommandLineA, Ord:00B6h
|

//******************** Program Entry Point ******** ;程序入口点
:00401000 E81D000000 Call 00401022 ;取命令行参数
:00401005 6A00 push 00000000
:00401007 680E304000 push 0040300E
:0040100C 50 push eax
:0040100D 6A00 push 00000000

* Reference To: USER32.MessageBoxA, Ord:01BBh
|
:0040100F E814000000 Call 00401028 ;显示消息框
:00401014 6A00 push 00000000

* Reference To: KERNEL32.ExitProcess, Ord:0075h
|
:00401016 E801000000 Call 0040101C ;结束程序
:0040101B CC int 03

* Referenced by a CALL at Address:
|:00401016
|

* Reference To: KERNEL32.ExitProcess, Ord:0075h
|
:0040101C FF2504204000 Jmp dword ptr [00402004] ;转到ExitProcess去执行

* Referenced by a CALL at Address:
|:00401000
|

* Reference To: KERNEL32.GetCommandLineA, Ord:00B6h
|
:00401022 FF2500204000 Jmp dword ptr [00402000] ;转到GetCommandLine去执行

* Reference To: USER32.MessageBoxA, Ord:01BBh
|
:00401028 FF250C204000 Jmp dword ptr [0040200C] ;转到MessageBoxA去执行

-----------------------------------------------------------------------
问题：为什么invoke GetCommandLine在编译时没直接翻译成Call dword ptr [00402000]而用下面的形式呢？
:00401000 E81D000000 Call 00401022 ;取命令行参数
. .
. .
. .
:00401022 FF2500204000 Jmp dword ptr [00402000] 转到GetCommandLine去执行

注意：加载器在加载程序时，还存在一个重定位的问题，即动态链接库中的函数的地址必须设定好后才能执行。假如某个函数要调用100次，使用第二种方法，加载器只需要修改一个地方的内容；而使用第一种方法，加载器就要修改100个地方的内容。显然增大了加载器的工作量。

执行debug/Load Process，在出现的窗口中输入命令参数（也可不输），确定，出现下面的调试窗口，就象在dos下的debug中操作一样进行操作.