Fuzzing the .NET JIT Compiler

I recently came across the excellent ‘Fuzzlyn’ project, created as part of the ‘Language-Based Security’ course at Aarhus University. As per the project description Fuzzlyn is a:

Monitoring and Observability in the .NET Runtime

.NET is a managed runtime, which means that it provides high-level features that ‘manage’ your program for you, from Introduction to the Common Language Runtime (CLR) (written in 2007):

Presentations and Talks covering '.NET Internals'

I’m constantly surprised at just how popular resources related to ‘.NET Internals’ are, for instance take this tweet and the thread that followed:

.NET JIT and CLR - Joined at the Hip

I’ve been digging into .NET Internals for a while now, but never really looked closely at how the ‘Just-in-Time’ (JIT) compiler works. In my mind, the interaction between the .NET Runtime and the JIT has always looked like this:

JIT and EE Interaction - Expected

Tools for Exploring .NET Internals

Whether you want to look at what your code is doing ‘under-the-hood’ or you’re trying to see what the ‘internals’ of the CLR look like, there is a whole range of tools that can help you out.

CoreRT - A .NET Runtime for AOT

Firstly, what exactly is CoreRT? From its GitHub repo

.. a .NET Core runtime optimized for AOT (ahead of time compilation) scenarios, with the accompanying .NET native compiler toolchain

Taking a look at the ECMA-335 Standard for .NET

It turns out that the .NET Runtime has a technical standard (or specification), known by its full name ECMA-335 - Common Language Infrastructure (CLI) (not to be confused with ECMA-334 which is the ‘C# Language Specification’). The latest update is the 6th edition from June 2012.

Exploring the internals of the .NET Runtime

I recently appeared on Herding Code and Stackify ‘Developer Things’ podcasts and in both cases, the first question asked was ‘how do you figure out the internals of the .NET runtime’?

How generics were added to .NET

Before we dive into the technical details, let’s start with a quick history lesson, courtesy of Don Syme who worked on adding generics to .NET and then went on to design and implement F#, which is a pretty impressive set of achievements!!

Resources for Learning about .NET Internals

It all started with a tweet, which seemed to resonate with people: