Philpax

https://fosdem.org/2026/schedule/event/3ZRNDY-fex/

• Tony has always had an interest in running games in places where they weren't meant to be run
• Professionally, studying physics, but didn't really work out
• Working on graphics drivers, like Vulkan drivers for AMD
• The airport express from Berlin is also called FEX ^_^
• FEX was started by Ryan Houdek seven years ago, Tony joined 4 years ago
• FEX is a translation layer between x86 and ARM to allow people to play games
• By default: game running atop engine atop [...] atop OS atop x86 CPU
• The standard solution is a binary recompiler that translates x86 to ARM
• For eah instruction, emit corresponding intermediate representation that fully specifies the semantics, then optimise that, then compile that to ARM
  • "My mouse cursor died. Linux moment."
• But it's not always that easy
  • A simple loop explodes in complexity
  • Each basic block has some translation overhead to set the stage for the following code
  • The dec instruction, for example, translates to three instructions: one to do the actual subtraction, and two for managing the flags before and after it
• There are, by some counts, 6,000 instructions. How do you even manage that?
• The x86 memory model also doesn't match to ARM
  • x86 offers strong consistency between threads; ARM does not
• System call wrappers - relatively straightforward, but there are hundreds, and some of them are quite tricky
• With a reasonably complete kernel compatibility layer + recompiler, everything else above works
• Can take more steps, like replacing the Vulkan x86 interface with a bridge to Vulkan ARM instead, removing a step
• The demo was that the slide was running in x86 Firefox in FEX, but the slides broke by this point, which was a bit awkward
• Yooka Laylee demo
• For Windows, can run x86 WINE atop FEX, but exploring integration with Windows ARM64EC