DOS如何将程序加载到内存中？

问题描述

MS-DOS采取什么步骤将COM或EXE文件加载到内存中？网上仍然有关于这种情况的参考吗？我能想到的最好的方法可能是指dosbox源代码。

What steps does MS-DOS take to load a COM or EXE file into memory? Are there still references online as to how this happens? The best I can think of is possibly referring to dosbox source.

推荐答案

当要求command.com执行.com或.exe文件，它将调用中断服务21h / AH = 4B，即EXEC服务。由调用程序决定：

When command.com is asked to execute a .com or .exe file, it will call the interrupt service 21h/AH=4B, the EXEC service. It is up to the calling program to:

• 构建DOS EXEC参数块（请参阅），并在内存中调整
  远指针


• 设置寄存器值
  
  
  
  
  • AL，AH盘符状态
  
  
  • DS，ES-> PSP段（请参阅）
  
  
  • SS：SP->堆栈指针（已定义
  
  
  • exe header is read for initial register values
  • copy code section from exe into memory
  • relocation table (see http://en.wikipedia.org/wiki/Relocation_table) is read andfar pointers are adjusted in memory
  • setup register values
    • AL,AH drive letter status
    • DS,ES -> PSP segment (see http://en.wikipedia.org/wiki/Program_Segment_Prefix )
    • SS:SP -> stack pointer (defined in exe header)

    com：

    
    
    • 将整个.com文件复制到内存中
    
    
    • 设置寄存器值
      
      
      
      
      • AL，AH驱动器盘符状态
      
      
      • CS，DS，ES，SS-> PSP段
      
      
      • SP =前64k段中可用的最后一个字的偏移量
      
      
      • copy entire .com file into memory
      • setup register values
        • AL,AH drive letter status
        • CS,DS,ES,SS -> PSP segment
        • SP = offset of last word available in first 64k segment

        程序现在应该正在执行。

        Program should now be executing.

        注意：

        在Microsoft的KB文档中查找可执行文件的优先级，它提到
        使用 MS-DOS EXEC函数（21h中断服务4Bh）来执行.com和.exe文件
        

        In Microsoft's KB document "Order of Precedence in Locating Executable Files", it mentions theuse of "MS-DOS EXEC function (interrupt 21h service 4Bh)" for executing .com and .exe fileshttp://support.microsoft.com/kb/35284

        所以我们可以在Int 21 / AH = 4Bh上查看拉尔夫·布朗的中断列表

        So we can look at Ralph Brown's Interrupt List on Int 21/AH=4Bh

        
        
        
        
        • Int 21 / AH = 4Bh
        
        
        • Int 21 / AH = 4Bh
        
        
        • http://www.cs.cmu.edu/~ralf/files.html
        • Int 21/AH=4Bh http://www.delorie.com/djgpp/doc/rbinter/id/51/29.html
        • Int 21/AH=4Bh http://www.ctyme.com/intr/rb-2939.htm

        以及使用示例：

        
        
        • 组装艺术/ 19.1.1.1加载并执行
        
        
        • Art of Assembly / 19.1.1.1 Load and Execute http://webster.cs.ucr.edu/AoA/DOS/ch19/CH19-1.html#HEADING1-10

        和dos exe标头格式：

        and the dos exe header format:

        
        
        
        
        
        
        • http://www.delorie.com/djgpp/doc/rbinter/it/94/15.html
        • http://www.delorie.com/djgpp/doc/exe/

        （这是基于谷歌搜索，所以请免费添加建议）

        (this is based off some googling, so please feel free to add suggestions)

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