How to add the .entrypoint directive to a method (dynamic assembly)

Question

I want to create a simple application using the classes in System.Reflection.Emit. How can I add the enrypoint directive to the Main method?

AssemblyName aName = new AssemblyName("Hello");
AssemblyBuilder aBuilder = AppDomain.CurrentDomain.DefineDynamicAssembly(aName, AssemblyBuilderAccess.Save);

ModuleBuilder mBuilder = aBuilder.DefineDynamicModule("Module");

TypeBuilder tb = mBuilder.DefineType("Program", TypeAttributes.Public);

MethodBuilder methodBuilder = tb.DefineMethod("Main", MethodAttributes.Public | MethodAttributes.Static);

ILGenerator ilGenerator = methodBuilder.GetILGenerator();
ilGenerator.EmitWriteLine("Hello!");

aBuilder.SetEntryPoint(methodBuilder);
tb.CreateType();
aBuilder.Save("Hello.exe");

AssemblyBuilder.SetEntryPoint does not seem to achieve this.

Answer 1

Try this (I've put comments on modified lines):

AssemblyName aName = new AssemblyName("Hello");
AssemblyBuilder aBuilder = AppDomain
    .CurrentDomain
    .DefineDynamicAssembly(aName, AssemblyBuilderAccess.Save);
// When you define a dynamic module and want to save the assembly 
// to the disc you need to specify a filename
ModuleBuilder mBuilder = aBuilder
    .DefineDynamicModule("Module", "Hello.exe", false);
TypeBuilder tb = mBuilder
    .DefineType("Program", TypeAttributes.Public);
MethodBuilder methodBuilder = tb
    .DefineMethod("Main", MethodAttributes.Public | MethodAttributes.Static);

ILGenerator ilGenerator = methodBuilder.GetILGenerator();
ilGenerator.EmitWriteLine("Hello!");

// You need to always emit the return operation from a method 
// otherwise you will get an invalid IL
ilGenerator.Emit(OpCodes.Ret);

aBuilder.SetEntryPoint(methodBuilder);
tb.CreateType();
aBuilder.Save("Hello.exe");