JVMCraft

Writing JVM in Rust to play Minecraft.
Ambitious project to learn rust (trying my best).

As of today 28/04/2025, this project has been developed as a side project after work in three weeks => not the best code. :)

After a long pause where I searched for a job (found it), worked on my master thesis, and took care of my mental health (it is important!!!), I finally continued this project and implemented sockets! (10/07/2025)

This is my first "big" rust project !

NOTE: Only tested on openjdk-23.0.2

Current state of the project

Milestones:

• System.out.Println (~2M instructions x.x)
• Sockets
• Multithreading
• Minecraft Server
• Minecraft

Since the goal of the project is to run minecraft, I will first implement opcodes/internals needed to run it, and in a second moment implement what's left.

NOTE: The JVM is really dependent on openjdk-23.0.2 implementation (especially related to MethodHandle)

TODO:

• create class loader logic
• separate class based on the class loader
• init threads
• run initPhase1 and initPhase2 and initPhase3
• handle CallSite/MethodHandle/LambdaMetaFactories
• sockets
• memoization of some boxed values (bool, byte, short, etc.)
• ahead-of-time compilation of some classes (e.g. DirectMethodHandle$Holder) -- falling back to dynamically generated bytecode (slow path)
• continue testing

Some vm properties are obtained from env variables such as :

vm property	env variable	description
java.home	JHOME
user.home	JUHOME
user.dir	JUDIR
java.io.tmpdir	JTMPDIR
java.library.path	JLIB	LD_LIBRARY_PATH

How to run it

Download the java modules:

curl -L -o openjdk.tar.gz https://download.java.net/java/GA/jdk23.0.2/6da2a6609d6e406f85c491fcb119101b/7/GPL/openjdk-23.0.2_linux-x64_bin.tar.gz
mkdir openjdk
tar -xzf openjdk.tar.gz -C openjdk --strip-components=1
./openjdk/bin/jimage extract --dir java_modules ./openjdk/lib/modules

Run it:

javac samples/print/Print.java
JMODS=/path/to/java_modules cargo run -- -u samples -c print.Print -m main -d "()V"

where JMODS is the folder with the java modules just downloaded.

What it is not implemented/supported

• JFR
• Multithreading (Virtual Thread/Carrier Threads)
• Virtual Object (every object is materialized)
• Multi OS support (Only linux supported)
• No hidden classes
• IPv6

Unit testing

In the future, unit tests MUST be written, but at the moment I do not have time for them. :)

Open Questions

During init, initPhase1 and initPhase2 and initPhase3 should always be called ?