@tubetime this is going to save tons of die space and...

@tubetime this is going to save tons of die space and power though. Its one of the major things holding #X86 back. I think this quite fundamental change regarding backward compatibility is a direct response to #riscv . I suspect #ARM will soon follow

Like 26 May 2023 at 6:11 | Wall-to-wall | Open on fosstodon.org

5 comments

Григорий Клюшников

Dantali0n :arch: :i3:, Apple SoCs already only support 64-bit mode from what I can gather. Android also prepares to be able to run on 64-bit-only ARM CPUs.

8 Jul 2023 at 16:52

Dantali0n :arch: :i3:

@grishka @tubetime I don't think this its true, according to both wikichip and wikipedia its just ARMv8.4, so it supports everything that does including thumb-2 instruction mode and the ability to swap endianness with a single instruction

10 Jul 2023 at 10:45 | Open on fosstodon.org

Dantali0n :arch: :i3:

@grishka @tubetime mind you to clarify, just because its a 64bit cpu does not mean it only has a 64bit mode. All modern x86 cpus are 64bit but still start in 16bit mode, het switched to 32bit real mode and only then enter 64bit mode. Although this situation is less awful for arm

10 Jul 2023 at 10:49 | Open on fosstodon.org

Григорий Клюшников

Dantali0n :arch: :i3:, but ARM, to the best of my knowledge, is opposite — it starts in its native mode (so the M1 starts in the 64-bit mode, so do Raspberry Pis) but then, if the OS is 32-bit, the bootloader switches it to the 32-bit mode at some point before the kernel starts. From reading various articles about reverse-engineering the M1 for the purpose of running custom OSes on it, I got the impression that it's incapable of switching to 32-bit mode and so it's safe to assume it doesn't implement it at all. I also remember reading that Yuzu, the Nintendo Switch emulator, when running on Apple Silicon, uses virtualization for 64-bit games but has to emulate the CPU for 32-bit ones for the same reason.

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10 Jul 2023 at 14:13

Dantali0n :arch: :i3:

@grishka @tubetime ah so they basically got to license an ARMv8.4 core and then nuked part of the ISA and ARM was like, sure this seems fine, I believe you but does not seem like something you want from an ISA even if it drastically cuts down on required die space.

I wonder what other features are missing, would it even run thumb-2. Almost tempted to get one now an figure it out. Then again someone probably already investigated this if I dig deep enough

10 Jul 2023 at 14:45 | Open on fosstodon.org