Billy Laws
2edee2855c
The Race: 1. A Reader sets `READ_WAITER_BIT` (Bit 15) and sleeps on the High 16 bits (`Futex+2`). 2. Writer A unlocks. It clears `READ_WAITER_BIT` (in Low 16 bits) and `WRITE_OWNED` (in High 16 bits). 3. Writer B immediately steals the lock. It sets `WRITE_OWNED` but preserves the now-cleared `READ_WAITER_BIT`. 4. The Reader, checking `Futex+2`, sees `WRITE_OWNED` is set. Since it cannot see that Bit 15 was unset (as it is watching High 16 bits), it assumes its wait signal is still valid and sleeps. 5. Writer B unlocks. It sees no `READ_WAITER_BIT` and wakes nobody. Deadlock. The Fix: Move `READ_WAITER_BIT` to Bit 30 (High 16 bits). Now, when Writer A clears the flag, the High 16 bits change value which will prevent the wait from occurring within WaitForAddress
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.