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Hello-World iOS App in Assembly

(gist.github.com)
169 points pabs3 | 6 comments | 30 Oct 25 02:37 UTC | HN request time: 0.931s | source | bottom
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sanskarix ◴[30 Oct 25 05:49 UTC] No.45756787[source]▶
This kind of thing is how you actually learn what's under the hood. Everyone's building with React Native and Flutter, which is fine until something breaks. Then you're stuck Googling black magic. Starting from assembly teaches you the real cost of abstraction.
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internetter ◴[30 Oct 25 06:45 UTC] No.45757063[source]▶
Is this really low level though? Because its hooking UIKit which is very high level relative to ASM. I'd be really curious to see an app draw on iOS without UIKit. I don't know if thats possible.
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shreddit ◴[30 Oct 25 08:01 UTC] No.45757464[source]▶
Of course it is. You just have to reimplement UIKit in ASM, no big deal…
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pjmlp ◴[30 Oct 25 09:03 UTC] No.45757829[source]▶
And even that won't do it, because within the constraints of iOS, eventually that framebuffer with software rendering has to be displayed on the screen via an OS API, which is UI Kit.
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1. fingerlocks ◴[30 Oct 25 10:41 UTC] No.45758436[source]▶
It should be possible.

If you enable the JIT entitlement for personal development, then bundle a mach-o into an entitled app. Or compile it directly on the app and mprotect-x to execute it. Is there something else you can’t do that I’m not considering? I might give this a try.

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2. pjmlp ◴[30 Oct 25 11:03 UTC] No.45758615[source]▶
The point is what is possible within the constrains of public APIs.
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3. fingerlocks ◴[30 Oct 25 11:14 UTC] No.45758714[source]▶
Everything I described is in a public header right inside your iOS SDK folder
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4. pjmlp ◴[30 Oct 25 12:16 UTC] No.45759186{3}[source]▶
I doubt you can render an UI in pure Assembly and show it on the screen without going through UI Kit in a non-rooted device, given that even the device drivers extension points is quite limited.

Which was the whole discussion point that started the thread, how to make a iOS app with zero references to UI Kit.

This isn't an 8 and 16 bit home computers, or games console, with an address for the framebuffer.

5. Someone ◴[30 Oct 25 12:58 UTC] No.45759556[source]▶
Is syscall a public API on iOS? In the end, you have to call that to get anything on the screen?

Looking at unistd.h, it seems marked as

  __OS_AVAILABILITY_MSG(ios,deprecated=10.0,"syscall(2) is unsupported; "
    "please switch to a supported interface. For SYS_kdebug_trace use kdebug_signpost().")
and syscall numbers seem wrapped by

  #ifdef __APPLE_API_PRIVATE
in *<sys/syscall.h>
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6. pjmlp ◴[30 Oct 25 14:13 UTC] No.45760251{3}[source]▶
Not at all, it is a Linux thing to keep applications doing syscalls, like back in MS-DOS interrupt days.

All other modern OSes give zero guarantees about syscalls.

Indeed, you have to call UI Kit, that is the public API for userspace applications.

Even if via OpenGL ES or Metal, you need a drawing context and a Window to render it.