Klepton Enables Running Android ARM64 VR APKs on Apple Vision Pro Without JIT

Bridging Android and Apple VR

Klepton is a new runtime environment designed to enable Android ARM64 VR applications to run on Apple Vision Pro. It achieves this by translating Android's shared object (.so) libraries into Apple's dynamic library (.dylib) and framework (.framework) formats, which then link into the Klepton runtime. This process allows Android applications to execute on Apple hardware without requiring Just-In-Time (JIT) compilation.

Technical Translation Details

For graphics rendering, Klepton translates GLES 3.2 calls to a vendored ANGLE GLES 3.0, which utilizes its Metal backend. Vulkan API calls are translated to MoltenVK, further ensuring compatibility with Apple's graphics frameworks. The system currently focuses on Java-thin applications, meaning it does not support Android Runtime (ART) or a full Java Virtual Machine (JVM).

Addressing Compatibility Challenges

A specific compatibility challenge addressed by Klepton involves the x18 register. While both Android and macOS reserve this register, some older Android applications use it, whereas macOS zeros it on context switches. Klepton-ld patches all x18 usage to instead utilize per-library Thread Local Storage (TLS) slots, ensuring proper execution on macOS. The tool also supports runtime loading and patching of .so files using mmap, which is primarily useful on macOS where JIT is permitted.

Current Status and Future Development

As of now, applications like Beat Saber are reported to be working on both macOS and visionOS through Klepton, albeit with minor graphical issues. Ongoing development includes improving generalizability, refining build tooling, and further work on projects like macOS Steam VR Link frontend. The project provides a guide in BUILDING.md for users to compile and run their own Android APKs.