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Comment by blank_pattern | Hacker News Reader

Apple even open sources their XNU kernel: https://opensource.apple.com/

There's some delay between when a new macOS version comes out and when sources get published, but it's great to see how they use the Mach kernel in practice.

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I dont recall if it was Apple that did this, but theres trick one can pull with an "open source"codebase thats part of a proprietary product.

One can have said codebase effectively outsource functionality to function calls on closed source libraries.

Google does something similar with android except in that case its moreso coupling functionality to their services:

https://arstechnica.com/gadgets/2018/07/googles-iron-grip-on...

Apple does not need to do that because of the BSD license, but I've done that with AGPL3 software before. It was the suggested solution by the original developer of the project, whom we hired

It's also mirrored on Github! [1]

[1]: http://github.com/apple/darwin-xnu

Why do they update the macOS XNU Kernel and not iOS?

They seem really big on keeping iOS things secret-ish, but the XNU kernel for both iOS and macOS seem to be built from the same code base.

Up until a couple years ago, they'd strip out ARM specific things from the releases macOS XNU code. Then they started leaving that stuff in!

What about their embedded OS? Like one they're running on T2 chip or inside Airpods? Is it still based on XNU kernel?

T2 is a variant of A10 and runs XNU for the main CPU.

Firmware cores and AirPods run Apple RTKit.

They use L4 in the Secure Enclave. Perhaps they do the same for other embedded devices

I would be surprised if that was the case. Low-power micro-controllers, such as ARM's Cortex-M series usually do not have support for virtual memory, which is required for running XNU.

IIRC they share the exact same kernel, so they don't need to.

They’re not quite the same, which is why the lack of iOS sources was a minor annoyance for a while.

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