JVM

Oct 2022 - Present

A from-scratch Java Virtual Machine (and accompanying tools) in Rust.

The Problem

Back in 2022, I found out that the JVM is actually fully specified, and as someone interested in the language, I wanted to see if I could understand it enough to create a JVM of my own.

It started as a small experiment: could I write a .class file parser? That experiment took off. I ended up spending years building everything: the class loader, the bytecode interpreter, reimplementing the native libraries, etc.

This is a complete, from-scratch JVM. It uses nothing from OpenJDK except for the standard classes file. I even recreated the entire java CLI and built my own Rust crates for handling JImage and JMod files.

Where It is Today

The JVM is capable of quite a bit today, it can:

Complete all 3 init stages of OpenJDK
Handle Java modules
Run basic apps like hello world

And it does so quite quickly, despite currently being fully interpreted.

Where It’s Headed

Fully Implement the JNI

A decent chunk of it has been implemented so far, with new methods being added as-needed.

Remove All Runtime Dependencies

I’ve always wanted to make the JVM have zero dependencies, with the exception of std and libc. Periodically, I’ll choose a crate to remove, and reimplement the functionality I need from scratch. Obviously, this makes the project significantly more complex, but I’m interested in owning the entire stack and understanding every detail of the process.