C# Intermediate Language Disassembler(ILDASM)

This is my first C# article. I searched the net to seewhat articles were available on C# and found that there were none forthe IL disassember, a very useful tool for .NET programmers. Users willfind it to be very important once they start using it.You can get IL disassemble tool as ILDasm.exe in directory C:\ProgramFiles\Microsoft.NET\FrameworkSDK\bin (Windows OS).

So what does this tool do?

The answer to this question is found in the tutorialsupplied with .NET SDK as "The ILDSAM tool parses any .NET FrameworkEXE/DLL module and shows the information in a human-readable format. Itallows user to see the pseudo assembly language for .NET". ILdisassmeber tool shows not only namespace but also types includingtheir interfaces.As its name suggests, it is an intermediate language, so it has its ownspecification. Users can also write programs using this intermediatelanguage, its very similar to assembly language of the old days.

I will use a simple example and use ILDASM.exe

//Hello World Program HelloWorld.cs
using System;

class HelloWorld
{
static void Main()
{
Console.WriteLine("Hello, world!");
}
}

Complier it on command line by using csc HelloWorld.cs

Helloworld.exe file will be generated

Now use the command ildasm HelloWorld.exe

You will see a screen like this.

Here you can see all of the Symbols. The table below explains what each graphic symbol means.Some of them you can find in HelloWorld's members.

The tree in this window shows that manifestinformation contained inside HelloWorld.exe. By double-clicking on anyof the types in the tree, you can see more information about the type.

Double-clicking the ".class public auto ansi" entry shows the following information:

Users can see that the HelloWorld type is derived from the System.Object type.

The first method, .ctor, is a constructor.This particular type has just one constructor but other types may haveseveral constructors each with a different signature. If youdouble-click on the constructor method, a new window appears showingthe IL (intermediate language) contained within the method:

The Common Language Runtime is stack based.So, in order to perform any operations, the operands are first pushedonto a virtual stack and then the operator executes. The operator grabsthe operands off the stack, performs the desired operation and placesthe result back on the stack. At any one time, this method will have nomore than 8 operands pushed onto the virtual stack. We can see thbylooking at the ".maxstack" attribute ( Maximum Stack size ) thatappears just before the IL code.In the above code maxstack is shown as 8.

Lets examine the IL code :

IL_0000: ldarg.0 : Load Object this pointer in stack
IL_0001: call instance void [mscorlib]System.Object::.ctor()
IL_0006: return the value loaded in stack

If user make a double click on main: void()
It will look like this:

If we will examine IL Code:

IL_0000: ldstr "Hello, world!"
IL_0005: call void [mscorlib]System.Console::WriteLine(class System.String)
IL_000a: ret

LDSTR: Load String.
First line indicates load String in stack.
Second Line indicates call method System.Console:: WriteLine as thefetch the value from stack put in this method and again put the resultin stack.
Third line shows fetch the final value from stack and return it.

There are some advance option also available.The extra options are enabled by running ILDASM with the /ADV("ADVanced") command-line switch. When /ADV is specified, ILDASMenables additional command-line switches.For the user convenience I will summarize some basic instructions herebelow.

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