Ryan Houdek
b7c7789a01
ARM64 branches have fairly small relative distances they can encode. These can be +-1MB, or even +-32KB. The largest relative branch is +-128MB, which we already set as an upper limit of our block JIT cache size. We have for a long time just compiled these without checking with the expectation that things just happen to work. We didn't hit the asserts so it was relatively low priority. Apparently now with Steam and a MaxInst limit of 5000, we are now hitting an assert where we are encoding too large of a range. Implement support for long jumping from anywhere in the JIT for when a long jump tries to be encoded and fails, allowing us to restart the JIT at any moment. This is implemented as a long jump when this singular feature could have gotten away with some sort of invasive check and early exit path for two reasons. For one, that would be even more invasive, effectively doing try-catch logic manually. And two, the next step is supporting JIT buffer overflow for when our block size heuristic fails. This next step will mandate longjump on SIGSEGV (with cooperative interaction with the frontend) from effectively /anywhere/ in the JIT. One of the design goals of the CodeEmitter is that every code emission function doesn't do a size remaining check to allow the compiler to do some very effective optimization of emitting code blocks to memory (and it works!). But we lose the ability to sanely size check. When writing the emitter I knew we were going to need to write this cooperative guard page handler, and we're finally at a point where it needs to be done. This will be in the next PR although.
FEX: Emulate x86 Programs on ARM64
FEX allows you to run x86 applications on ARM64 Linux devices, similar to qemu-user and box64. It offers broad compatibility with both 32-bit and 64-bit binaries, and it can be used alongside Wine/Proton to play Windows games.
It supports forwarding API calls to host system libraries like OpenGL or Vulkan to reduce emulation overhead. An experimental code cache helps minimize in-game stuttering as much as possible. Furthermore, a per-app configuration system allows tweaking performance per game, e.g. by skipping costly memory model emulation. We also provide a user-friendly FEXConfig GUI to explore and change these settings.
Prerequisites
FEX requires ARMv8.0+ hardware. It has been tested with the following Linux distributions, though others are likely to work as well:
- Arch Linux
- Fedora Linux
- openSUSE
- Ubuntu 22.04/24.04/24.10/25.04
An x86-64 RootFS is required and can be downloaded using our FEXRootFSFetcher tool for many distributions.
For other distributions you will need to generate your own RootFS (our wiki page might help).
Quick Start
For Ubuntu 22.04, 24.04, 24.10 and 25.04
Execute the following command in the terminal to install FEX through a PPA.
curl --silent https://raw.githubusercontent.com/FEX-Emu/FEX/main/Scripts/InstallFEX.py | python3
This command will walk you through installing FEX through a PPA, and downloading a RootFS for use with FEX.
For other Distributions
Follow the guide on the official FEX-Emu Wiki here.
Navigating the Source
See the Source Outline for more information.