IL assembly ldarg instruction learning

IL assembly code,

.assembly  extern  mscorlib {}
.assembly MathLib
{
    .ver  1 : 0 : 1 : 0
}

.module MathLib.dll

.namespace  MyMath
{    
    .class   public  ansi auto MathClass extends [mscorlib]System.Object
    {        
        .method  public  int32 GetSquare(int32) cil managed
        {
            .maxstack  3
            ldarg.0     //  加载对象的 this 指针到堆栈上
            ldarg.1     //  实例方法的实际的参数索引总是从 1 开始
            ldarg.1
            mul
            ret        
        }
    }
}

Build as a dll as follows; the dll contains a method that calculates the square of an integer and returns the value;

 Then make a test program;

using System;
using MyMath;
 
class Program
{
 
static void Main(string[] args)
{
 
    int a=9;
    int i = MathClass.GetSquare(a); 
    Console.WriteLine(i); 
    Console.ReadKey();
}
}

Build this test program from the command line;

To reference an external dll when building from the command line, you need to use /r to specify the dll file name, see, 

C# csc builds dll and specifies dll when csc is built_bcbobo21cn's blog-CSDN blog

Then the following error occurs;

 I still don't know how to do it;

First learn about IL assembly instructions;

ldarg.n

    Load the nth parameter into the stack; in a non-static function, the 0th parameter is an implicit parameter representing this;

    The mul instruction is multiplication;