.NET: How to debug or decompile a DanamicMethod with dnSpy?

Question

I have a managed .NET executable that supplies the msil bytecode of a function as raw bytes. It constructs a DynamicMethod object, sets the bytecode with DynamicMethod.DynamicILInfo.SetCode() and invokes it with DynamicMetho.Invoke().

What is the best way to decompile or step into this DynamicMethod thing? How do I reverse it?

DnSyp doc has this to say:

Dynamic modules can be debugged (but not dynamic methods due to CLR limitations)

But there has to be a way to deal with it.

I am new to .NET debugging so there might be a simple solution I am missing.

Answer 1

You can debug DynamicMethod's using the EventPipe API. I've written a library that uses it to allow for code injection via DynamicMethod that can be debugged: https://github.com/damieng/DamienG.Library/blob/master/DamienG.Library/Diagnostics/EventPipe/DynamicMethodInjector.cs

First, create a new DynamicMethodInjector object: var injector = new DynamicMethodInjector("MyTypeName", "MyMethodName");

Then, add some IL to your DynamicMethod: injector.AddMethodBody(ILGenerator il);

You can then invoke the DynamicMethod as normal, adding a breakpoint to the EventPipe.Start method to avoid hitting the breakpoint before the IL is injected: // Inject IL into the process injector.Inject();

// Invoke your DynamicMethod var result = (int)m.Invoke(obj, new object[] { 1, 2 });