lion-tutorial02.htm

内有一些代码

  you will see that it's full of function prototypes for kernel32.dll. If you 
  don't include kernel32.inc, you can still call ExitProcess but only with simple 
  call syntax. You won't be able to invoke the function. The point here is that: 
  in order to invoke a function, you have to put its function prototype somewhere 
  in the source code. In the above example, if you don't include kernel32.inc, 
  you can define the function prototype for ExitProcess anywhere in the source 
  code above the invoke command and it will work. The include files are there 
  to save you the work of typing out the prototypes yourself so use them whenever 
  you can.</font> <br>
  <font face="Arial">Now we encounter a new directive, includelib. includelib 
  doesn't work like include. It 's only a way to tell the assembler what import 
  library your program uses. When the assembler sees an includelib directive, 
  it puts a linker command into the object file so that the linker knows what 
  import libraries your program needs to link with. You're not forced to use includelib 
  though. You can specify the names of the import libraries in the command line 
  of the linker but believe me, it's tedious and the command line can hold only 
  128 characters.</font> 
<p><font face="Arial">Now save the example under the name msgbox.asm. Assuming 
  that ml.exe is in your path, assemble msgbox.asm with:</font> 
<ul>
  <font face="Arial">ml&nbsp; /c&nbsp; /coff&nbsp; /Cp msgbox.asm</font> 
  <li> <font face="Arial">/c tells MASM to assemble only. Do not invoke link.exe. 
    Most of the time, you would not want to call link.exe automatically since 
    you may have to perform some other tasks prior to calling link.exe.</font></li>
  <br>
  <font face="Arial">/coff tells MASM to create .obj file in COFF format. MASM 
  uses a variation of COFF (Common Object File Format) which is used under Unix 
  as its own object and executable file format.</font> <br>
  <font face="Arial">/Cp tells MASM to preserve case of user identifiers. If you 
  use hutch's MASM32 package, you may put "option casemap:none" at the head of 
  your source code, just below .model directive to achieve the same effect.</font> 
</ul>
<font face="Arial">After you successfully assemble msgbox.asm, you will get msgbox.obj. 
msgbox.obj is an object file. An object file is only one step away from an executable 
file. It contains the instructions/data in binary form. What is lacking is some 
fixups of addresses by the linker.</font> 
<p><font face="Arial">Then go on with link:</font> 
<ul>
  <font face="Arial">link /SUBSYSTEM:WINDOWS&nbsp; /LIBPATH:c:\masm32\lib&nbsp; 
  msgbox.obj</font> 
</ul>
<blockquote><font face="Arial">/SUBSYSTEM:WINDOWS&nbsp; informs Link what sort 
  of executable this program is</font> <br>
  <font face="Arial">/LIBPATH:&lt;path to import library> tells Link where the 
  import libraries are. If you use MASM32, they will be in MASM32\lib folder.</font></blockquote>
<font face="Arial">Link reads in the object file and fixes it with addresses from 
the import libraries. When the process is finished you get msgbox.exe.</font> 
<p><font face="Arial">Now you get msgbox.exe. Go on, run it. You'll find that 
  it does nothing. Well, we haven't put anything interesting into it yet. But 
  it's a Windows program nonetheless. And look at its size! In my PC, it is 1,536 
  bytes.</font> 
<p><font face="Arial">Next we're going to put in a message box. Its function prototype 
  is:</font> 
<p><b><font face="Arial">MessageBox PROTO hwnd:DWORD, lpText:DWORD, lpCaption:DWORD, 
  uType:DWORD</font></b> 
<blockquote><font face="Arial">hwnd is the handle to parent window. You can think 
  of a handle as a number that represents the window you're referrring to. Its 
  value is not important to you. You only remember that it represents the window. 
  When you want to do anything with the window, you must refer to it by its handle.</font> 
  <br>
  <font face="Arial">lpText is a pointer to the text you want to display in the 
  client area of the message box. A pointer is really an address of something. 
  A pointer to text string==The address of that string.</font> <br>
  <font face="Arial">lpCaption is a pointer to the caption of the message box</font> 
  <br>
  <font face="Arial">uType specifies the icon and the number and type of buttons 
  on the message box</font></blockquote>
<font face="Arial">Let's modify msgbox.asm to include the message box.</font> 
<br>
&nbsp; 
<p><font face="Arial">.386</font> <br>
  <font face="Arial">.model flat,stdcall</font> <br>
  <font face="Arial">option casemap:none</font> <br>
  <font face="Arial">include \masm32\include\windows.inc</font> <br>
  <font face="Arial">include \masm32\include\kernel32.inc</font> <br>
  <font face="Arial">includelib \masm32\lib\kernel32.lib</font> <br>
  <font face="Arial">include \masm32\include\user32.inc</font> <br>
  <font face="Arial">includelib \masm32\lib\user32.lib</font> 
<p><font face="Arial">.data</font> <br>
  <font face="Arial">MsgBoxCaption&nbsp; db "Iczelion Tutorial No.2",0</font> 
  <br>
  <font face="Arial">MsgBoxText&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; db "Win32 
  Assembly is Great!",0</font> 
<p><font face="Arial">.code</font> <br>
  <font face="Arial">start:</font> <br>
  <font face="Arial">invoke MessageBox, NULL, addr MsgBoxText, addr MsgBoxCaption, 
  MB_OK</font> <br>
  <font face="Arial">invoke ExitProcess, NULL</font> <br>
  <font face="Arial">end start</font> 
<p><font face="Arial">Assemble and run it. You will see a message box displaying 
  the text "Win32 Assembly is Great!".</font> 
<p><font face="Arial">Let's look again at the source code.</font> <br>
  <font face="Arial">We define two zero-terminated strings in .data section. Remember 
  that every ANSI string in Windows must be terminated by NULL (0 hexadecimal).</font> 
  <br>
  <font face="Arial">We use two constants, NULL and MB_OK. Those constants are 
  documented in windows.inc. So you can refer to them by name instead of the values. 
  This improves readability of your source code.</font> <br>
  <font face="Arial">The addr operator is used to pass the address of a label 
  to the function. It's valid only in the context of invoke directive. You can't 
  use it to assign the address of a label to a register/variable, for example. 
  You can use offset instead of addr in the above example. However, there are 
  some differences between the two:</font> 
<ol>
  <li> <font face="Arial">addr cannot handle forward reference while offset can. 
    For example, if the label is defined somewhere further in the source code 
    than the invoke line, addr will not work.</font></li>
  <blockquote><font face="Arial">invoke MessageBox,NULL, addr MsgBoxText,addr 
    MsgBoxCaption,MB_OK</font> <br>
    <font face="Arial">......</font> <br>
    <font face="Arial">MsgBoxCaption&nbsp; db "Iczelion Tutorial No.2",0</font> 
    <br>
    <font face="Arial">MsgBoxText&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; db "Win32 
    Assembly is Great!",0</font></blockquote>
  <font face="Arial">MASM will report error. If you use offset instead of addr 
  in the above code snippet, MASM will assemble it happily.</font> 
  <li> <font face="Arial">addr can handle local variables while offset cannot. 
    A local variable is only some reserved space in the stack. You will only know 
    its address during runtime. offset is interpreted during assembly time by 
    the assembler. So it's natural that offset won't work for local variables. 
    addr is able to handle local variables because of the fact that the assembler 
    checks first whether the variable referred to by addr is a global or local 
    one. If it's a global variable, it puts the address of that variable into 
    the object file. In this regard, it works like offset. If it's a local variable, 
    it generates an instruction sequence like this before it actually calls the 
    function:</font></li>
  <blockquote><font face="Arial">lea eax, LocalVar</font> <br>
    <font face="Arial">push eax</font></blockquote>
  <p><br>
    <font face="Arial">Since lea can determine the address of a label at runtime, 
    this works fine.</font><font face="Fixedsys"><strong> </strong></font>
</ol>
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