I get why Apple wants to remove it but it genuinely sucks. I can't imagine it costs them a lot to put it into maintenance mode and just support 20 years of macOS games and apps going forward. They want developers to fully move to ARM but older titles or software whose developers have moved on/passed will be lost to the sands of time.
If they choose to discontinue it, it would be nice to have them opensource it so that the community could have a go at maintaining it tbh. Surely that's better than letting it rot (both rosetta and the old software that it runs).
That would be ideal, but given Apple's general hostility towards Open Source, it sounds extremely unlikely. I wonder what it would take to re-implement it. If it's "just software," I suppose there is a chance, not that I'm volunteering :)
Apple really isn't as hostile towards OSS as people think. With that being said, the reason to discontinue Rosetta 2 is to push developers to upgrade their software. Allowing others to continue using Rosetta 2 by way of 3rd party maintainers works against that goal :(
I imagine that the area it takes up on the chip is non-trivial and so it'd cost them a ton to continue to have it.
I thought Rosetta 2 was a purely software layer
Rosetta 2 is software, but there are design decisions made for the M-series chips that are specifically made to improve the ability of Rosetta to work in a performant way. The main one I'm aware of is the x86-TSO memory-ordering mode - most ARM chips don't support this, but the M-series have it so that Rosetta can toggle it on for x86 emulation.
I'm not sure what the total cost of these are, but it's not zero.
> There are only a handful of different instructions that account for 90% of all operations executed, and, near the top of that list are addition and subtraction. On ARM these can optionally set the four-bit NZCV register, whereas on x86 these always set six flag bits: CF, ZF, SF and OF (which correspond well-enough to NZCV), as well as PF (the parity flag) and AF (the adjust flag).
> Emulating the last two in software is possible (and seems to be supported by Rosetta 2 for Linux), but can be rather expensive. Most software won’t notice if you get these wrong, but some software will. The Apple M1 has an undocumented extension that, when enabled, ensures instructions like ADDS, SUBS and CMP compute PF and AF and store them as bits 26 and 27 of NZCV respectively, providing accurate emulation with no performance penalty.
https://dougallj.wordpress.com/2022/11/09/why-is-rosetta-2-f...
There's another big one, 4K page support. The MMU can be told to set up a virtual address space with smaller, x86-compatible 4096-byte memory pages instead of the default 16384-byte pages.
Those are still needed for the Rosetta use-cases that are sticking around (old games, Linux binaries)
It’s software.