RoastVM

A Java Virtual Machine (JVM) implementation written in Rust.

Overview

RoastVM is an educational/experimental JVM implementation that executes Java bytecode. It supports class file parsing, bytecode interpretation, JNI native methods, and includes a boot image system for loading the Java standard library.

Features

Class File Parsing - Full .class file support using deku for binary parsing
Bytecode Interpreter - 200+ JVM instructions implemented
Object Model - Objects, arrays, monitors, and string interning
JNI Support - 250+ JNI functions for native method integration
Boot Image - Load JDK classes from 7z module archives
Native FFI - Dynamic library loading via libffi

Project Structure

roast-vm/
├── crates/
│   ├── core/                    # Main VM implementation
│   │   └── src/
│   │       ├── main.rs          # Entry point
│   │       ├── vm.rs            # VM controller
│   │       ├── thread.rs        # Thread execution
│   │       ├── class_loader.rs  # Class loading
│   │       ├── bimage.rs        # Boot image reader
│   │       ├── frame/           # Stack frames & interpreter
│   │       ├── class_file/      # Class file parser
│   │       ├── objects/         # Object/array model
│   │       └── native/          # JNI infrastructure
│   │
│   └── roast-vm-sys/            # Native methods (cdylib)
│       └── src/                 # JNI implementations
│
├── lib/                         # Boot image location
├── data/                        # Default classpath
└── docs/                        # Detailed documentation

Documentation

Detailed implementation docs are in the docs/ folder:

Class File Parsing - Binary format, constant pool, attributes
Frame & Interpreter - Stack frames, opcode dispatch
Object Management - Objects, arrays, monitors
JNI - JNIEnv structure, native invocation
Native/FFI - Library loading, libffi integration
roast-vm-sys - Native method implementations
Class Loading - Boot image, classpath, RuntimeClass

Building

cargo build
cargo build --release
cargo test

Running

# Run with default classpath (./data)
cargo run

# Run with custom classpath
cargo run -- /path/to/classes

# With debug logging
RUST_LOG=debug cargo run

Dependencies

Crate	Purpose
deku	Binary class file parsing
dashmap	Concurrent maps
jni	JNI type definitions
libloading	Dynamic library loading
libffi	Native function calls
sevenz-rust2	Boot image archives
parking_lot	Synchronization

Status

Early development (v0.2.0). Core class loading, bytecode execution, and JNI are functional. Exception handling and GC are in progress.

Vendor: infernap12

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