I tried out FEX on a modern ARM board with a discrete GPU. Really impressed with the performance.
https://interfacinglinux.com/2025/06/30/fex-emu-gaming-on-th...
FEX-emu – Run x86 applications on ARM64 Linux devices
11–20 of 145 posts
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#12Earlier quoted context omitted.
Too bad Arm doesn't allow architectural licenses, because this is exactly the kind of thing Valve and the FEX developers would want to extend the ISA to support. I bet we see a RISC-V backend to FEX in the next 6 months, it probably already exists in a private repo. FEX is the shootstring, extra special discount budget (not maligning) version of Rosetta. Apple should sell Rosetta to Valve.
My understanding is that Rosetta sidesteps a bunch of tricky memory model issues by using non-standard hardware extensions only present in Apple Silicon, so even if Apple did share Rosetta, which they certainly won't, it wouldn't work properly on Valves hardware anyway.
yeah that is correct. The m series chips can turn on total store ordering memory model solely for Rosetta. There's also some hardware extensions to arm to support x86 condition codes in the hardware because it's way more instruction efficient that way.
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#13How does fex deal with the fact that the memory model on arm is weak and x86 is total store ordering. It seems like would need to hammer performance by putting memory barriers everywhere to handle all cases. Perhaps fex only works when there are well defined mutexes it can gain visibility into? anyone know?
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#14How does fex deal with the fact that the memory model on arm is weak and x86 is total store ordering. It seems like would need to hammer performance by putting memory barriers everywhere to handle all cases. Perhaps fex only works when there are well defined mutexes it can gain visibility into? anyone know?
I think that's right, there is no better way than just adding barriers. On Apple hardware it can probably make use of the special memory ordering mode, but on normal ARM64 there's probably nothing it can do.
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#15How does fex deal with the fact that the memory model on arm is weak and x86 is total store ordering. It seems like would need to hammer performance by putting memory barriers everywhere to handle all cases. Perhaps fex only works when there are well defined mutexes it can gain visibility into? anyone know?
Looks like they do expensive conservative TSO emulation by default, but they're able to piggyback on compiler work that Microsoft did to make newer Windows x86 binaries easier to emulate. Since MSVC 2019 they annotate the executable with metadata that informs an emulator of when TSO is or isn't needed for correctness.
FEX also has settings which weaken or disable TSO altogether, favoring performance over correctness. You wouldn't want to rely on those for anything important but a game possibly crashing isn't the end of the world.
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#16Earlier quoted context omitted.
Too bad Arm doesn't allow architectural licenses, because this is exactly the kind of thing Valve and the FEX developers would want to extend the ISA to support. I bet we see a RISC-V backend to FEX in the next 6 months, it probably already exists in a private repo. FEX is the shootstring, extra special discount budget (not maligning) version of Rosetta. Apple should sell Rosetta to Valve.
My understanding is that Rosetta sidesteps a bunch of tricky memory model issues by using non-standard hardware extensions only present in Apple Silicon, so even if Apple did share Rosetta, which they certainly won't, it wouldn't work properly on Valves hardware anyway.
It's not only present in Apple Silicon, it's just not required by the ARM standard. Fujitsu also has an ARM64 CPU with TSO.
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#17Earlier quoted context omitted.
My understanding is that Rosetta sidesteps a bunch of tricky memory model issues by using non-standard hardware extensions only present in Apple Silicon, so even if Apple did share Rosetta, which they certainly won't, it wouldn't work properly on Valves hardware anyway.
yeah that is correct. The m series chips can turn on total store ordering memory model solely for Rosetta. There's also some hardware extensions to arm to support x86 condition codes in the hardware because it's way more instruction efficient that way.
If you mean FEAT_FlagM, that's standard in ARMv8.4. (There's also FlagM2 and AFP that are optional.)
The JavaScript instruction is cooler though.
https://developer.arm.com/documentation/dui0801/g/A64-Floati...
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#18Earlier quoted context omitted.
My understanding is that Rosetta sidesteps a bunch of tricky memory model issues by using non-standard hardware extensions only present in Apple Silicon, so even if Apple did share Rosetta, which they certainly won't, it wouldn't work properly on Valves hardware anyway.
yeah that is correct. The m series chips can turn on total store ordering memory model solely for Rosetta. There's also some hardware extensions to arm to support x86 condition codes in the hardware because it's way more instruction efficient that way.
The latter is now an optional feature in the mainstream Arm ISA now (FEAT_FlagM and FEAT_FlagM2). Similarly the “alternate floating point mode” that Apple uses to match nuances of x86 FP semantics is a standard architectural feature as well. The TSO option though is Apples own thing.
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#19Now we just need a decent ARM Linux laptop.
Re: FEX-emu – Run x86 applications on ARM64 Linux devices
#20I'n incredibly impressed by valve's commitment to playing the long game. It makes sense to have the frame by arm since the system is lighter and its clear this is just the trojan horse to get arm linux into every gamer's house. I wouldn't be surprised if we end up with an arm steamdeck 1-2 version from now when the tech is ready.
Too bad Arm doesn't allow architectural licenses, because this is exactly the kind of thing Valve and the FEX developers would want to extend the ISA to support. I bet we see a RISC-V backend to FEX in the next 6 months, it probably already exists in a private repo. FEX is the shootstring, extra special discount budget (not maligning) version of Rosetta. Apple should sell Rosetta to Valve.
better yet, Apple should make it open-source on github.