Dynamically replace the contents of a C# method?

Question

What I want to do is change how a C# method executes when it is called, so that I can write something like this:

[Distributed]
public DTask Solve         


        

Answer 1

you can replace it if the method is non virtual, non generic, not in generic type, not inlined and on x86 plateform:

MethodInfo methodToReplace = ...
RuntimeHelpers.PrepareMetod(methodToReplace.MethodHandle);

var getDynamicHandle = Delegate.CreateDelegate(Metadata>.Type, Metadata.Type.GetMethod("GetMethodDescriptor", BindingFlags.Instance | BindingFlags.NonPublic)) as Func;

var newMethod = new DynamicMethod(...);
var body = newMethod.GetILGenerator();
body.Emit(...) // do what you want.
body.Emit(OpCodes.jmp, methodToReplace);
body.Emit(OpCodes.ret);

var handle = getDynamicHandle(newMethod);
RuntimeHelpers.PrepareMethod(handle);

*((int*)new IntPtr(((int*)methodToReplace.MethodHandle.Value.ToPointer() + 2)).ToPointer()) = handle.GetFunctionPointer().ToInt32();

//all call on methodToReplace redirect to newMethod and methodToReplace is called in newMethod and you can continue to debug it, enjoy.