Comment by thfuran
8 hours ago
Because Intel/AMD regularly contribute kernel changes to maintain support for their own hardware, whereas Apple keeps making undocumented changes that Asahi has to reverse engineer.
8 hours ago
Because Intel/AMD regularly contribute kernel changes to maintain support for their own hardware, whereas Apple keeps making undocumented changes that Asahi has to reverse engineer.
I don't think that's it, as we usually don't even have to update the kernel: when I get a new PC, my old software still boots and runs. The answer has to also provide some analogous note that, unlike new x86 hardware having an interest in still being able to run old versions of Windows, new Apple hardware (maybe... one must presume for the story to be consistent) must not really care about being able to boot old copies of macOS.
> unlike new x86 hardware having an interest in still being able to run old versions of Windows
The "secret sauce" is... we're not speaking about "x86" systems, at least as long as UEFI doesn't enter the game. In fact what we're talking about is "IBM PC-compatible x86" and its BIOS that provides ultra-low-level interfaces for input and output (including a very very basic USB stack). These can then be used to continuously load higher level systems.
Basically what you start with in the BIOS land is the boot sector, you got barely enough code capacity that you have input from the disk and text console output. That you can use to load a second stage bootloader (e.g. GRUB, NTLDR) which now has better knowledge of filesystems, maybe even enough of the driver to bring the GPU up with the basic VESA interface. And that then loads the actual operating system which brings up the rest of the system - proper GPU, a full featured USB stack, you name it. And layered in between that is ACPI for dynamic hardware discovery.
UEFI based systems can skip a lot of the slow early code used to boot in BIOS - it hands over directly to the OS itself in the best case, or to a high-level bootloader such as the modern Windows bootloader that can do all sorts of magic.
In contrast, the ARM world sucks hardcore - there are no standards for board bringup and boundaries, there is only DeviceTree which replaces a very small part of the wonder/hellscape that is ACPI. And that is something even Apple couldn't get rid of. Hell, you can't even be sure it's the CPU that brings everything up - there are weird systems like Broadcom's VideoCore architecture that underpins the Raspberry Pi, where the video chip part of the SoC handles bringing up the ARM CPU.
Basically, x86 has a ton of legacy and warts but for that, backwards compatibility and to a degree even forwards compatibility is a thing. ARM in contrast... it's like if you let a bunch of drugged up monkeys loose.
> In contrast, the ARM world sucks hardcore - there are no standards for board bringup and boundaries
There are standards for ARM, and they are called UEFI, ACPI, and SMBIOS. ARM the company is now pushing hard for their adoption in non-embedded aarch64 world - see ARM SBBR, SBSA, and PC-BSA specs.
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I've definitely ran older kernels of Linux on new Intel/AMD CPUs where the kernel release vastly pre-date the CPU release.
I've found that doing this on laptops is often more problematic, the OS itself will usually boot fine, but you might have issues with drivers for supporting hardware like the GPU, audio, etc.