Hello-World iOS App in Assembly

Super cool! Would love to see the build/deploy steps needed.

There is also an iOS app implemented in C here:

https://stackoverflow.com/a/10290255/8427

Even better if build steps are provided

I’m guessing even this still requires that I use XCode.

Is that true? What about the command-line version?

It probably doesn't, as you practically never need Xcode for simple apps. From my experience, currently, you need Xcode to compile storyboards (NIB/XIB files) and bundle Assets.car (macOS BOM files); and compile Xcode projects, btw. I may be missing another important feature used in a lot of apps but otherwise for the most part you can build an iOS app without Xcode (or even macOS).

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.

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.

As low level as it gets.

For lower level one needs something like ESP32, Arduino, retro-coding platforms.

The command line tools are still XCode, in a way.

Of course it is. You just have to reimplement UIKit in ASM, no big deal…

snibbetracker is an example of a C/SDL iOS app. <1MB from the app store which is really wild. https://apps.apple.com/de/app/snibbetracker/id1065797528

No, you’ll have to check in with backboard etc before it will let you do anything useful

This is an excellent argument for not using assembly, actually

xcrun -sdk iphoneos clang yellow.asm, pack it into an IPA and sign it

The Command Line Tools doesn't include the iOS SDK; or a simulator; or any of the other tools required to get it deployed to actual device.

Hmm doesn't work. Here's the error log (I'm on Mac M2):

https://gist.github.com/anta40/60f62c803a091ad0415d60f8cac55...

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.

The argument is that learning assembly is useful, it gives some insights into what happens under the hood. That seems like a no brainer to me.

Would I use it for production iOS app, no, I don't hate myself that much.

Maybe throw in a -framework CoreFoundation

All this teaches is how to put parameters on stack, pass them to functions and use the results. It is pretty much a transliteration of what you would do in C.

<1MB is also relatively easy to reach with swiftui apps. I had two fully working ones in the app store below 1MB. They are removed now since I didnt pay the yearly 100€

It's still very educational. It shows how ObjC method calls work under the hood, because even calling objc_msgSend() from plain C involves a certain amount of non-obvious magic (because of the variable argument list and return types).

And tbh I'm kinda surprised how little assembly code it is, less than most UI framework hello-worlds in high level languages ;)

Very cool, if impractical (it’s likely that you’d never get an ASM app through the App Store Approval process).

ARM Assembly is a much more Byzantine creature, than the old 8- and 16-bit versions I used, way back in the Pleistocene.

I’m always a fan of starting from the “bare metal,” to learn, but these days, it’s a long trip. When I was just a wee sprog, it was only a couple of steps away.

It's likely in future, you won't need app store approval process. I hope that EU will nuke Apple with some huge fines.

And there will be corporate tax per each EU country, it's ridiculous corporates are raking huge money here and paying basically nothing on taxes, well only in Ireland and they're having party.

Anyway, asm is great if you are using iOS emulator and need to do something and since you have root there, well :) (not apple meme simulator)

You can already deploy apps on alternative stores inside of the EU. Apple has some bullshit fee but Epic has promised to cover that for AltStore.

You can write directly to the frame buffer, like a video game. You still need the UIKit import to publish, because it has to be bundled into a .ipa which requires an AppDelegate, a UIBundle, among other things.

If you want to “technically” avoid UIKit, you can drop one step lower. UIKit is implemented on CoreAnimation. A bare UIView is nearly a pass through wrapper around CALayer. It wouldn’t be hard to build your own custom UI on CALayers. The old CA tutorials for implementing a ScrollView from the ground up are still floating around out there.

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.

The point is what is possible within the constrains of public APIs.

Everything I described is in a public header right inside your iOS SDK folder

Assembly is fine until it breaks too

You still have whole Objective-C runtime and CoreAnimation, UIKit abstraction under the hood.

You have a very long way between assembly and RN/Flutter. I do agree that it helps to know these things, but you need to learn a lot more before it becomes more generally applicable.

Do you need to pay the license to keep your apps in store? Or did they deprecate some APIs and therefore removed your apps?

Honestly wild if you need to upkeep the license just to have it in store once it is published.

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.

How would that impact the App Store approval? AFAIK they review binaries anyway…

Feels like a disassembly of a boilerplate app, as opposed to handcrafted, minimal assembly code.

For instance I’m pretty sure the autorelease pool is unnecessary as long as you don’t use the autorelease mechanism of Objective-C, which you’re most likely not going to do if you’re writing assembly in the first place.

They do, but ASM doesn't have the guardrails that the compiled languages have, so it's almost certain that private APIs would get accessed.

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>

Yes. I have a bike helmet with integrated cameras. The company (Cyclevision) that made it is gone. So no Apple account. So no app for my helmet anymore.

Looks more sensible than having to use XCode and Apple's atrocious developer documentation.

When I was in second or third year of computer science in 1971 or '72, we (of course) learned IBM 360 assembler, but we also had to design a simple binary adder using AND OR and XOR gates. All on paper - no need for any soldering or electronics, which I regret. I cannot remember how many bits of input - probably 4 but may have been 6. But I did do quite a bit of asm programming, including a routine for calculating square roots using Chebyschev polynomials and newtons algorithm.

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.

Complete bogus. This is programmers machismo that's completely detached from reality.

What? That doesn’t make any sense. The only guard rails normal Obj-C has against calling private APIs is that they aren’t listed in the public headers, otherwise you can still easily call them. If you don’t explicitly make calls to private APIs from ASM, the won’t be called. I have no idea why you think “it’s almost certain that private APIs would get accessed.”

Would love to see equivalent in C, not ObjectiveC... plain C.

I'm not sure this is entirely fair though I think you're mostly right. The comment you're replying to is right in terms of the value of understanding one or more levels of abstraction below the one you're working in. Conversely you're right in that learning assembler isn't going to do much to help you debug a failing Flutter app. It's just attacking the abstraction stack in detail from the opposite end - equally myopic.

But none the less valuable because of the additional perspective it brings. That's the real point of it, another lens through which to view and understand the mechanics of the application.

> so it's almost certain that private APIs would get accessed

No it's not. Just like with ObjC or Swift, in ASM you have to be explicit about the APIs you want to call. I don't see how you would accidentally call a private API in ASM.

IMO the bigger risk is attempting to call a method that does not actually exist. ObjC or Swift would protect you from that, but ASM would not and may just crash at runtime.

For folks who are curious about this sort of thing and want an approachable starting point, I would recommend:

https://www.goodreads.com/book/show/44882.Code

It would be way cool to see an actual application which wanted this sort of speed optimization --- the last significant assembly language program I can recall using was WriteNow, which was ~100,000 lines of assembly and to this day is my favourite word-processor (well, the NeXT version --- the Mac, even v2.0 suffered in comparison for not having access to Display PostScript and Services).

Really wish that there was a writeup of it at folklore.org --- unfortunately, it only gets a single mention:

https://www.folklore.org/The_Grand_Unified_Model_The_Finder....

(or that there was an equivalent site for the early history of NeXT)

Tell you guys what.

We’ll just leave things as they are.

I’ll forfeit the game.

The field is yours.

Have a great day!

This is the most HN comment I’ve seen in a while. The real abstraction here is coding with LLMs btw!!!

I just tested this on my computer.

  1. Make a new Xcode iOS project and delete all files except for Info.plist
  2. Remove all keys from Info.plist
  3. In the build settings search for "storyboard" and remove all keys
  4. Add yellow.asm to project
  5. Link UIKit, and Foundation

After all that you can build and run on a simulator

That would be great if iOS supported a GUI in C.

The real optimization here is to move off UIKit and interact with the GPU more directly