iOS 18.4 appears to interfere with JIT compilation in sideloaded apps
If you’ve been following along in the app sideloading and game emulation communities for the iPhone and iPad, then you might have heard of something called JIT, which many app developers have been particularly excited about because it can boost performance in certain situations by recompiling code extemporaneously.
Unfortunately, as many have started pointing out this weekend, the first iOS & iPadOS 18.4 developer beta 1 that Apple seeded on Friday appears to lock down JIT capabilities to the debugger only, which means that commonly used utilities like AltJIT, SideJIT, and Jitterbug may soon be impacted on the latest firmware versions.
JIT, which stands for Just In Time compilation, allows sideloaded apps like game emulators to run better on iPhones and iPads than they ever could without. That’s because it simplifies the process of transforming regular programming code into a universal machine code that runs smoothly on most or all devices whether those are desktop computers or mobile devices. Moreover, it’s highly adaptable to whatever is at hand.
Emulators can make good use of this capability because most games are designed for the console they were released to run on and converting that game’s programming code to a universal machine code in real time means that those games can run more efficiently on the new host device, such as an iPhone.
Alternatively, we have AOT, which stands for Ahead Of Time compilation, which Apple seems to prefer. This method compiles code before execution, which makes it easier for Apple’s safety systems to ensure that the code isn’t malicious before it runs, whereas JIT doesn’t give Apple’s safety systems this opportunity due to compiling code during the code execution.
As it would appear, iOS hacker and developer Duy Tran was working on a 32-bit translation layer that utilized JIT, and that too has now been stifled by Apple’s decision to interfere with normal JIT enablement.
While Apple has long wagged the finger at JIT-enabled apps for the App Store, sideloaded apps haven’t been affected since they circumvent the App Store review process. But now that Apple limits JIT via private entitlements that jailbreak commentator @MasterMike best describes as something a “normal sideloaded app would never have,” it seems like sideloaded apps won’t be able to use it in iOS or iPadOS 18.4 and later.
It wouldn’t be particularly viable for ordinary users to tinker with JIT oriented projects in the debugger, so it seems like the only practical way to enable JIT again would be for a jailbreak to become available on the latest firmware, which hasn’t happened for newer arm64e (A12 and later) devices since iOS 16.5.1, and there’s still no newer jailbreak for these devices in sight at this time.
JIT offers many critical use cases for iPhone and iPad owners, especially for those who value emulation, which Apple only began allowing in the official App Store for ‘retro’ consoles starting last Summer with the availability of Delta. The developers behind Delta, which also oversee the AltStore sideloading utility, have been strong proponents of JIT for this reason.
While it may seem like Apple is trying to low-key stifle the emulator community on its platform, this doesn’t appear to be the intent, but rather an unintended side effect. JIT opens users up to security issues, as malware can make just as good use of it as emulated games can. That said, it makes sense why Apple may not want to allow this on their devices.
It’s also worth noting that sideloaded emulator apps that utilized JIT for the performance gains will remain usable even without JIT, but at a perhaps with worse performance than they provided with JIT. That said, it’s more of a user experience gripe than anything else.
Still, we think this should be a user choice thing, just like jailbreaking. That’s because not every iPhone and iPad user needs the big Apple making decisions for them. Some people like lowering their security if it means being able to do cool things on their handsets. So some sort of operating system setup setting that allows the user to choose between heightened or lowered security would be a great thing for Apple to do.
Are you upset to see that Apple is killing viable JIT in iOS & iPadOS 18.4 and later? Let us know your thoughts in the comments section down below.
Source link: https://www.idownloadblog.com/2025/02/23/ios-18-4-jit-blocked-by-apple/
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