IL (MSIL) And Inside Of dll

Question

I researched about MSIL (IL) and CLR and the other thing like processing path from source code through the OS

We can see Intermediate Language in the third step. I want to know are .dll files written exactly with Intermediate Language?

this is a .dll file insider code example, is this code called Intermediate Language?

I searched in the internet for MSIL code example and I saw this image below

these are different and because it i doubted.

thanks

Answer 1

You can actually test this yourself. Create a new Library project, and a single function:

public class Class1 {
    public static int Add(int a, int b) {
        return a + b;
    }
}

Compile into a DLL, and open the DLL in ILSpy. Navigate to your Add() function, and change the dropdown from C# to IL. You'll see something like this:

    IL_0001: ldarg.0
    IL_0002: ldarg.1
    IL_0003: add
    IL_0004: stloc.0

These are the human-readable representation of your IL. In ILSpy you can click on each of the instructions (e.g. ldarg.0) to see what they do, and their hexadecimal instruction code. Wikipedia has a full list of them.

So our Add() function in CIL would be the following:

opcode	instruction	description
0x02	ldarg.0	Load argument 0 onto the stack.
0x03	ldarg.1	Load argument 1 onto the stack.
0x58	add	Add two values, returning a new value.
0x0A	stloc.0	Pop a value from stack into local variable 0.

Notice the hexadecimal opcodes there. Now open up the DLL in a hex editor. If you look here, you'll notice that the top parts are not actual code.

If your hex editor has a search, go look for the hex sequence of our opcodes, and you'll see that in the middle of your file, you would find:

02 03 58 0a

Which is what your IL would look like inside a DLL!