jzvm - ARM Jazelle DBX experiments

Project links: repo (mirror), issues, CI: ARM, x86

Introduction

ARM Jazelle DBX ("direct bytecode execution")¹ is a ARM32 instruction set extension that allows running Java bytecode directly on certain CPUs. Jazelle mode is entered by executing a special branch instruction, BXJ.

Jazelle hardware support is rather widespread within a certain timeframe of manufacturing dates, since it was included in the ARM926EJ-S and ARM1176JZF-S CPUs at the heart of many devices.

Jazelle software support is rather rare, because it presumably relies on a proprietary JVM licensed by ARM, and the hardware isn't openly documented like the rest of the ARM architecture(s). This is where jzvm comes in: It is an attempt to create both an open source software implementation, and hardware documentation for Jazelle.

License

The source code in this repository is licensed under the LGPL 2.1

References

• Wikipedia: https://en.wikipedia.org/wiki/Jazelle
• the Hackspire wiki: https://hackspire.org/index.php/Jazelle
• a previous attempt at using Jazelle: https://github.com/SonoSooS/libjz/wiki/About
• and an Advent-of-Code solution: https://github.com/aspargas2/advent-of-code-2022/tree/main/day05-jazelle
• ARMv5 Architecture Reference Manual [DDI0100I]: https://developer.arm.com/documentation/ddi0100/i/

Footnotes

1. The Jazelle brand has later been reused for an unrelated technology, Jazelle RCT. When I say Jazelle it will mean Jazelle DBX most of the time. ↩