Can we enable JIT on ios >= 14.2?

[rigor789]

https://groups.google.com/g/v8-users/c/3qStq2YtxYo

Can we remove --jitless if running ios >=14.2? Would app store allow apps that use JIT?

[NathanaelA]

When 14.2 was released and this twitter thread (https://twitter.com/altstoreio/status/1324473755062599680) was posted back at the beginning of Nov -- I did a bit of research into this, because this really excited me getting JIT and WASM on iOS.

Unfortunately the TLDR is; Nope. ;-(

Basically in 14.2 if you build the app in Debug mode, then one of the things that is allowed by the debugger is JIT because the debugger itself needs to be able to remap segments, so it has special privs to allow it to be JITTED. So technically our debug engines could be without the --jitless flag and any debug apps that you build and install directly to the phone. BUT once you send it to be released to the store; the special provisioning that the XCode has is stripped and --jitless won't work and the app will crash on startup as v8 won't run.

However, it does appear that Apple has changed some of the store guidelines about dynamic download/update content, going in this direction. So maybe in the future, or maybe because of the anti-trust stuff going on they will open up allowing --jitless with the v8 and other engines because Google, MS, and Mozilla all want it and they can apply some pressure...

[rigor789]

However, it does appear that Apple has changed some of the store guidelines about dynamic download/update content, going in this direction. So maybe in the future, or maybe because of the anti-trust stuff going on they will open up allowing --jitless with the v8 and other engines because Google, MS, and Mozilla all want it and they can apply some pressure...

I hope that is the case and we can eventually get jit! Until then.... The waiting game

[erikchi]

Thanks for the detailed information! I'm wondering if the policy has changed, are we able to use JIT somehow in the release mode now given that Delta is now approved on App Store?

[edusperoni]

Unfortunately no. Apple has been fighting tooth and nail to keep JIT disabled. For one thing, enabling JIT would enable Chrome to fully enter the iOS space with their own rendering and control over the browser, which goes against Apple's 30ft walled garden philosophy. (It'd also enable emulators and awesome apps that can leverage JIT for performance, like any NativeScript app)

I thought the EU and Epic games would finally make them concede this, but, alas, not this time...

[erikchi]

I'm wondering if Apple still doesn't allow it, why can the Delta game emulator app be approved in App Store. Are they not using JIT in that version?

[edusperoni]

Apparently, the app store version is jitless, but you can enable JIT with AltStore (https://www.reddit.com/r/Delta_Emulator/comments/s6a85c/enabling_jit/). My guess is current processors are good enough to fully emulate without JIT some older systems.