System.Reflection.Emit custom property seems to be identical to my mock up, but I get an InvalidProgramException

Question

To expand on the title, I'm using Reflection to generate a custom subclass that will eventually have an arbitrary number of string properties which they'll internally store in a dictionary. In this case I'm just using one. I've used Ildasm.exe to get the MSIL that I need for the My Set method works, as the debugger shows the value I'm assigning, but when I try to read it back I get an InvalidProgramException, "Common Language Runtime detected an invalid program." which points back to the get method. My get method model is:

/* public class TestWrapper : AttributeWrapper  //This is the source of the following MSIL
            {
                public string Name
                {
                    get { return GetAttribute("Name"); }
                    set { SetAttribute("Name", value); }
                }
            }
*/
    {
      // Code size       17 (0x11)
      .maxstack  2
      .locals init ([0] string V_0)
      IL_0000:  nop
      IL_0001:  ldarg.0
      IL_0002:  ldstr      "Name"
      IL_0007:  call       instance string ConfigXMLParser.frmNodeBuilder/AttributeWrapper::GetAttribute(string)
      IL_000c:  stloc.0
      IL_000d:  br.s       IL_000f

      IL_000f:  ldloc.0
      IL_0010:  ret
    } // end of method TestWrapper::get_Name

And code generating the property in question is:

  public static void CreateSelfNamingProperty(TypeBuilder tb, string propertyName, Type propertyType)
        {
            FieldBuilder fieldBuilder = tb.DefineField("_" + propertyName, propertyType, FieldAttributes.Private);

            PropertyBuilder propertyBuilder = tb.DefineProperty(propertyName, PropertyAttributes.HasDefault, propertyType, null);
            MethodBuilder getPropMthdBldr =
                tb.DefineMethod("get_" + propertyName,
                    MethodAttributes.Public | MethodAttributes.SpecialName | MethodAttributes.HideBySig,
                    typeof(string), Type.EmptyTypes);
            Type[] getAttributeArgs = { typeof(string) };
            Type basetype = tb.BaseType;
            MethodInfo getAttrBase = basetype.GetMethod("GetAttribute", BindingFlags.Instance | BindingFlags.NonPublic);
            Debug.Assert(getAttrBase != null);

            ILGenerator ilGen = getPropMthdBldr.GetILGenerator();
            Label labelReturn = ilGen.DefineLabel();
            ilGen.Emit(OpCodes.Nop);           //The Get function starts here.  
            ilGen.Emit(OpCodes.Ldarg_0);
            ilGen.Emit(OpCodes.Ldstr, "Nope.");
            ilGen.EmitCall(OpCodes.Call, getAttrBase, getAttributeArgs);
            ilGen.Emit(OpCodes.Stloc_0);
            ilGen.Emit(OpCodes.Br_S, labelReturn);
            ilGen.MarkLabel(labelReturn);
            ilGen.Emit(OpCodes.Ldloc_0);
            ilGen.Emit(OpCodes.Ret);

            MethodBuilder setPropMthdBldr =
                tb.DefineMethod("set_" + propertyName,
                    MethodAttributes.Public |
                    MethodAttributes.SpecialName |
                    MethodAttributes.HideBySig,
                    null, new[] { propertyType });

            MethodInfo setAttrBase
                = basetype.GetMethod("SetAttribute", BindingFlags.Instance | BindingFlags.NonPublic);

            ILGenerator setIl = setPropMthdBldr.GetILGenerator();
            Label modifyProperty = setIl.DefineLabel();
            Label exitSet = setIl.DefineLabel();
            Type[] setParamTypes = { typeof(string) , typeof(string) };

            setIl.MarkLabel(modifyProperty);
            setIl.Emit(OpCodes.Nop); //The Set method starts here
            setIl.Emit(OpCodes.Ldarg_0);
            setIl.Emit(OpCodes.Ldstr, propertyName);
            setIl.Emit(OpCodes.Ldarg_1);
            setIl.EmitCall(OpCodes.Call, setAttrBase, setParamTypes);


            setIl.Emit(OpCodes.Nop);
            setIl.MarkLabel(exitSet);
            setIl.Emit(OpCodes.Ret);

            propertyBuilder.SetGetMethod(getPropMthdBldr);
            propertyBuilder.SetSetMethod(setPropMthdBldr);
        }


// And this is what builds the TypeBuilder:

        public static TypeBuilder GetTypeBuilder()
        {
            string typeSignature = "MyDynamicType";
            AssemblyName an = new AssemblyName(typeSignature);
            AssemblyBuilder assemblyBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(an, AssemblyBuilderAccess.Run);
            ModuleBuilder moduleBuilder = assemblyBuilder.DefineDynamicModule("MainModule");
            TypeBuilder tb = moduleBuilder.DefineType(typeSignature,
                    TypeAttributes.Public |
                    TypeAttributes.Class |
                    TypeAttributes.AutoClass |
                    TypeAttributes.AnsiClass |
                    TypeAttributes.BeforeFieldInit |
                    TypeAttributes.AutoLayout,
                    null);
            return tb;
        }

Finally, putting it all together:

            TypeBuilder tb = GetTypeBuilder("TestType");
            CreateSelfNamingProperty(tb, "Name", typeof(string));
            dynamic instance = Activator.CreateInstance(tb.CreateType());
            instance.Name = "Test"; //Debug shows Name is Test, but
            MessageBox.Show(instance.Name);//Exception occurs here

And the base class is pretty straightforward:

  public class AttributeWrapper
        {
            protected Dictionary<string, string> _attributes =
                new Dictionary<string, string>();

            protected void SetAttribute(string attribute, string value)
            {
                if (_attributes.ContainsKey(attribute))
                {
                    _attributes[attribute] = value;
                }
                else
                {
                    _attributes.Add(attribute, value);
                }
            }

            protected string GetAttribute(string attribute)
            {
                return _attributes.ContainsKey(attribute) ? _attributes[attribute] : "";
            }
        }

Answer 1

Your immediate problem is that you are using the stloc.0 and ldloc.0 opcodes to read/write into a local without having defined any locals: You can fix that by calling the following at the top of your method:

ilGen.DeclareLocal(typeof(string));

Now here's the thing, the local isn't really required. The code you disassembled and used as your template was obviously compiled in Debug mode. I can tell this due to the local but mostly from the nop 's. These two things exist in the debug build to aide in the debugging process, allowing you to step in and view the intermediate values. Your getter can be reduced to the following IL:

ldarg.0
ldstr "Nope."
call instance string [AttributeWrapper]::GetAttribute(string)
ret

Similarly, your setter can have its nop 's removed.

Some other side notes:

You are using the wrong method to emit your call instruction. The EmitCall method is for calling varargs methods only and accepts an argument containing the types of the varargs parameters. That's not what you have here. That either involves some p/invoke against an API using the VarCall convention and/or TypedReference / __makeref and __arglist / ArgIterator . The latter of which are "hidden" C# keywords that you will almost never find in code. Way back in the days prior to .NET 2.0 the method threw an exception when the target MethodInfo wasn't varargs but this is not the case anymore.

You should instead use the normal Emit method and pass the appropriate Call or CallVirt * OpCode .

Finally, I'd strongly suggest using SharpLab for this purpose, specifically setting it to Release build and viewing the IL tab. It's a whole lot easier than compiling the code and then disassembling manually.

* Often you will see people use the latter, even when the method isn't virtual .