C#/.Net CIL - ldarga.s how to get index/argument (ldarga.s vs ldarga vs ldarga.0 opcode)?

Question

I'm trying to interpret a CIL instruction by instruction. I'm using Mono.Reflection to get a list of instructions and I don't know how to interpret 'ldarga.s'.

I know "ldarga" - Load the argument address to the evaluation stack." but what is the argument / index of 'ldarga.s', i.e. load / push on stack? - the instruction is under IL_0004 the following list of assemblers.

another instruction "ldarg.0" (without "a") argumet load / push "first" on the stack, "ldarg.1" argumet load / push secound on the stack In another example, "ldloca.s" - "Loads the address of the local variable at the specified index into the evaluation stack.") index is in the instruction operand.

Here is my code I have function "Funkcja1" in class Test

public int Funkcja1(int p1, string p2, ProcesTest p3)
    {
        var zmienalokaln1 = p1;
        var zmiennaLokaln2 = p2 + p1.ToString();
        Metoda1();
        var zmienna3 = zmienalokaln1 + zmiennaLokaln2;
        return zmienna + p1 + p2.Length + zmienna3.Length;
    }

Function assembler (generated by JetBrains dotPeek):

.method public hidebysig instance int32
Funkcja1(
  int32 p1,
  string p2,
  class Cvl.VirtualMachine.Test.ProcesTest p3
) cil managed
{
.maxstack 2
.locals init (
  [0] int32 zmienalokaln1,
  [1] string zmiennaLokaln2,
  [2] string zmienna3,
  [3] int32 V_3
)

// [18 9 - 18 10]
IL_0000: nop

// [19 13 - 19 36]
IL_0001: ldarg.1      // p1
IL_0002: stloc.0      // zmienalokaln1

// [20 13 - 20 53]
IL_0003: ldarg.2      // p2
IL_0004: ldarga.s     p1
IL_0006: call         instance string [System.Runtime]System.Int32::ToString()
IL_000b: call         string [System.Runtime]System.String::Concat(string, string)
IL_0010: stloc.1      // zmiennaLokaln2

// [22 13 - 22 23]
IL_0011: ldarg.0      // this
IL_0012: call         instance void Cvl.VirtualMachine.Test.ProcesTest::Metoda1()
IL_0017: nop

// [24 13 - 24 59]
IL_0018: ldloca.s     zmienalokaln1
IL_001a: call         instance string [System.Runtime]System.Int32::ToString()
IL_001f: ldloc.1      // zmiennaLokaln2
IL_0020: call         string [System.Runtime]System.String::Concat(string, string)
IL_0025: stloc.2      // zmienna3

// [26 13 - 26 63]
IL_0026: ldarg.0      // this
IL_0027: ldfld        int32 Cvl.VirtualMachine.Test.ProcesTest::zmienna
IL_002c: ldarg.1      // p1
IL_002d: add
IL_002e: ldarg.2      // p2
IL_002f: callvirt     instance int32 [System.Runtime]System.String::get_Length()
IL_0034: add
IL_0035: ldloc.2      // zmienna3
IL_0036: callvirt     instance int32 [System.Runtime]System.String::get_Length()
IL_003b: add
IL_003c: stloc.3      // V_3
IL_003d: br.s         IL_003f

// [27 9 - 27 10]
IL_003f: ldloc.3      // V_3
IL_0040: ret

} // end of method ProcesTest::Funkcja1

From Mono.Reflection.Disassembler.GetInstructions(this MethodBase self)

Operand is 'p1'

I need to somehow specify the index of this parameter ('p1') in the function parameter list, which in this case is equal to 0 (first parameter)

Answer 1

Operand in ldarga.s can by System.Reflection.ParameterInfo.

and index = parameterInfo.Position;

if (instruction.Operand is System.Reflection.ParameterInfo parameterInfo)
{
   Index = parameterInfo.Position;
}