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[C#, Dnlib] - Constants Data is not being replaced correctly [Help]


r3xq1

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From an old topic: https://forum.tuts4you.com/topic/42934-c-dnlib-how-do-i-change-const-string/?tab=comments#comment-208456

Source Code Stub file:

namespace DlibStub
{
    using System;

    public static class ConstTester
    {
        public const string MYCONST = "1111";
        public const string DNTEST = "2222";

        public static void GetResult()
        { 
            Console.WriteLine($"Result: {MYCONST}");
            Console.WriteLine($"Result: {DNTEST}");
        }
    }
}

IL Code:

field: System.String DlibStub.ConstTester::DNTEST
field: System.String DlibStub.ConstTester::MYCONST
Instruction: IL_0000: ldstr "Dnlib Tester"
Instruction: IL_0000: ldstr "Result: 1111"
Instruction: IL_0005: call System.Void System.Console::set_Title(System.String)
Instruction: IL_0005: call System.Void System.Console::WriteLine(System.String)
Instruction: IL_000A: call System.Void DlibStub.ConstTester::GetResult()
Instruction: IL_000A: ldstr "Result: 2222"
Instruction: IL_000F: call System.String System.Console::ReadLine()
Instruction: IL_000F: call System.Void System.Console::WriteLine(System.String)
Instruction: IL_0014: pop
Instruction: IL_0014: ret
Instruction: IL_0015: ret

Code to replace text:

public static void Inizialize(string fileModule)
{
  using var module = ModuleDefMD.Load(fileModule);
  using var text = File.AppendText("LogDnlib.txt"); // For write to txt
  foreach (TypeDef type in module.GetTypes())
  {
     foreach (FieldDef field in type.Fields)
     {
       text.WriteLine($"Field: {field}");
       text.WriteLine($"FieldName: {field.Name}");
       text.WriteLine($"Field: {field}");

       if (field.HasConstant && field.ElementType.Equals(ElementType.String))
       {
          if (field.Name.String.Contains("MYCONST")) // Find a text named MYCONST
          {
              field.Constant.Value = "test1";
          }
          if (field.Name.String.Contains("DNTEST")) // Find a text named DNTEST
          {
               field.Constant.Value = "test2";
          }
       }            
      }
    }
   module.Write("Patched.exe");
 }

Result (ScreenShots): 

How fix?

 

Screenshot_2.png

Screenshot_1.png

Edited by r3xq1
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Hey, When you compile the program the Compiler it self replace those "Constants" to their value on method body because its Constant values :) so you can't really do that on dnlib.

Edited by CursedLand
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[Update]

I tried replacing both Fields and Ldstr and it worked.

 

foreach (MethodDef method in type.Methods)
{
   if (method.HasBody == false) continue;
   if (method.Body.HasInstructions)
   {
      for (int i = 0; i < method.Body.Instructions.Count; i++)
      {
         if (method.Body.Instructions[i].OpCode == OpCodes.Ldstr && method.Body.Instructions[i].Operand.ToString().Contains("1111"))
         {
             method.Body.Instructions[i].Operand = "test1"; 
         }
         if (method.Body.Instructions[i].OpCode == OpCodes.Ldstr && method.Body.Instructions[i].Operand.ToString().Contains("2222"))
         {
             method.Body.Instructions[i].Operand = "test2";
         } 
         method.Body.SimplifyBranches();
         method.Body.OptimizeMacros();
      }
   }
}

 

Screenshot_1.png

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