Comment by sitkack
14 hours ago
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.
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.
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...
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.
Nice article on this topic: https://lwn.net/Articles/970907/
There are also RISC-V designs with TSO. If you are targeting x86 workloads, it makes sense to have a per thread TSO mode.
There are a bunch of undocumented flags and instructions beyond TSO.
4 replies →
Box64 already runs on RISC-V. Just, the available processors are so slow it's hard to even play 5-10 year old games.
This means that, when the much faster chips implementing RVA23 arrive next year, they'll be immediately able to run Box64.
> Too bad Arm doesn't allow architectural licenses
QEMU exists. I doubt they want the bad press of suing an Open Source project everyone is using.
ARM were perfectly fine getting the bad press for suing Qualcomm for releasing the Snapdragon that was finally performing enough despite these companies paying them a lot of money.
They seemed quite happy to destroy their eco system if they won.
https://www.rcrwireless.com/20251001/business/qualcomm-arm-2
And GBA emulators. And before that, BBC Accorn ones with Risc OS.
better yet, Apple should make it open-source on github.
> Apple should sell Rosetta to Valve.
Isn't Rosetta kinda bad though? And won't get much better because it's not open source?
Rosetta performance is best in class to my knowledge, although they had the benefit of being able to add custom instructions and modes to the cpu to make some parts easier. Meaning Rosetta would not have helped valve unless they built the frame on apple silicon.
As for not improving, it is likely that Apple no longer feels the need to invest in Rosetta improvements now that Apple silicon is so dominant and software support is already very strong, but nothing is stopping them from investing in it if they need it for example for gaming
Rosetta is abandonware: https://developer.apple.com/documentation/apple-silicon/abou...
Why would a company on its way to the moon, entrust such an important project as translation layer between two major architectures to a single rinky-dinky corp that got rich selling common electronics marketed as luxury fluff, that's on the decline and has head so far stuck up its butt that it thinks it can do whatever it wants, instead of just write it themselves with support of the global developer community?
Apple could never do games because there are no luxury games. That's completely out of their zone of comprehensibility.
2 replies →