ARTICLE

Modest Introduction to IL Assembly Language

Posted by Filip Bulovic Articles | Articles C# September 03, 2001
Since I received copy of Visual Studio .NET Beta 2 and did not manage to find “ILAssemblyLanguageProgrammersReference.doc” which was included in beta 1 I decided to share my experience with other assembly enthusiasts.
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To compile and run the code you must have installed Microsoft .NET Framework Beta 2 available for download from http://msdn.Microsoft.com. Since I received copy of Visual Studio .NET Beta 2 and did not manage to find "ILAssemblyLanguageProgrammersReference.doc" which was included in beta 1 I decided to share my experience with other assembly enthusiasts. Documents for somebody interested  in intermediate language could be find in : "C:\ProgramFiles\Microsoft.NET\FrameworkSDK\Tool Developers Guide\docs". Typically work with assembler is from command line and using notepad. To open command line in some directory I'm creating registry entry (key) in "HKEY_CLASSES_ROOT\Folder\shell" called CmdLine and  again new entry in CmdLine called command where we are changing (Default) to string value REG_SZ "cmd.exe %1". In that way we are opening command line using context menu (right click on folder icon and select CmdLine). Also it comes handy to create shortcut to NOTEPAD.EXE and ildasm.exe in "C:\Documents and Settings\whatever your name is\SendTo" so that you can send .il files to notepad and .exe files to  disassembler.

First we will write client and from client send string to ArgIn.dll which will show our string in message box. Copy following, paste it in notepad and  save as client.il

.assembly extern mscorlib{}
.assembly extern ArgIn{}
.assembly go{}
.method public static void GO2() cil managed //any name starting with letter is ok
{
      .entrypoint  //must
      .maxstack  1
 //you can safely comment out .maxstack  1 or set it on 2 but if it is insufficient results in run-time error
      .locals ([0] class [ArgIn]ArgIn.Class1 q)
      //.locals  [init] ( <localsSignature> ) Defines a set of local variables for this method.
      ldstr      "Hello from client"
 //72 <T> ldstr string push a string object for the literal string
      newobj     instance void [ArgIn]ArgIn.Class1::.ctor(string)
 //73 <T> newobj ctor allocate an uninitialized object and call ctor
      stloc.0
 //0A stloc.0 Pop value from stack into local variable 0. //pop will also do here (we won't use it again)
      ret   //return is a must


Do not compile yet, first we must compile library. Following is what we are going to compile to ArgIn.dll :

.assembly extern mscorlib
{}
.assembly extern System.Windows.Forms
{
  .publickeytoken = (B7 7A 5C 56 19 34 E0 89 )                       
  .ver 1:0:2411:0
}
.assembly ArgIn
{}
.namespace ArgIn
{
  .class public auto ansi beforefieldinit Class1
         extends [mscorlib]System.Object
  {
    .method public hidebysig specialname rtspecialname
            instance void  .ctor(string msg) cil managed
    {
        //.maxstack  8
        ldarg.0
        call       instance void [mscorlib]System.Object::.ctor()
        ldarg.1
        ldstr      "From dll"
        call       valuetype [System.Windows.Forms]System.Windows.Forms.DialogResult [System.Windows.Forms]System.Windows.Forms.MessageBox::Show(string,string)
        pop
        ret
    }     }   } 

Save this as ArgIn.il. To compile we will type on command line "ilasm ArgIn /dll". Reference .assembly extern System.Windows.Forms deserves additional explanation. This is value on my machine, if it does not work on  yours copy and paste in notepad following:

using System;
using System.Windows.Forms;
class try1
{
public static void Main()
{
MessageBox.Show ("Test", "Test app");
}


Save it as test.cs and compile from command line typing "csc test.cs". Send test.exe to ildasm and check what is in MANIFEST (double click on it). If it is necessary copy values and apply it in your code.

Now is a time to compile client application. ArgIn.dll must be in the same folder .From command line execute "ilasm client.il" and run client.exe. You will see message box with message "Hello from client" and title "From dll".  I hope that you will find that IL assembler is very friendly and write some code on your own.

At the end I wish to thank Microsoft for making .NET platform available to public, my company Objectronics for providing me with their copy of  .NET Framework Beta 2 and finally to my dear friend Dmitri Vibornov for idea and his help on coding and preparing this article.

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