Comment by SirMaster
6 hours ago
Is there a reason why it's so hard to support newer M chips after supporting an older one? Like so much harder than supporting a new generation Intel or AMD chip doesn't seem too hard in comparison.
6 hours ago
Is there a reason why it's so hard to support newer M chips after supporting an older one? Like so much harder than supporting a new generation Intel or AMD chip doesn't seem too hard in comparison.
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.
3 replies →
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.
M1/M2 were pretty similar.
M3 had gigantic GPU changes.
M4 had some security stuff added, and M5 much more so. Not sure how/if those can be disabled. Others can be explain why this matters better than I can.
They change the arch and add new features all the time. In M4 they added new kernel protections which now they need to somehow emulate.
1) Intel and AMD help to implement support in Linux before their chips even ship. Actually a sanitized version of the Intel graphics ISA bspec is actually available to the OSS community too.
Apple on the other hand provides no support. The one nice thing they did do is allow their bootloader to boot non-apple signed OSes. They do not do this on iPhones, iPads, Apple TVs, Watches, or homepods btw.
2) The GPU ISA changes drastically and often. Its not entirely uncommon for the entire instruction set to change entirely within one generation. Every change to the ISA would require an entire round of new reverse engineering (I suspect, ive never reversed).
I do wonder why Apple chooses not to lock down the Mac to just Mac OS like all their other hardware? I'm sure the sales from people who intend to run something other than MacOS look like a floating-point error on the scales Apple operates.
I don't think it is possible to have a locked down development machine. You have to be able to run arbitrary code on a development machine so they can never lock it down like iOS is.
There are plenty of other ways they can be less open and hackable than Linux but it can never get to the point of the iPhone.
You replied to your own question. Locking down the system for 3 users worldwide and making sure it stays locked is not worth the effort.
Just not publishing the specs is enough to delay so much the effort that those machines are out of warranty and have depreciated so much by the time they are supported that they aren't competitors to the mac ecosystem anymore.
They don't because it's a floating-point error now. But with the continued enshitification of MacOS, it likely won't be in the future, and they just may lock it down. But being so hostile to the hacking community would do more harm than good, so I doubt that they would do so even if Linux use on Macs grew to >1%.