5 ms·

It seems pretty clear from TFA - there’s a directory share with the host, and given that Rosetta isn’t an emulator, but rather a translation layer, they don’t n

It seems pretty clear from TFA - there’s a directory share with the host, and given that Rosetta isn’t an emulator, but rather a translation layer, they don’t need a Linux version: x86 instructions go in, arm64 come out.

Wowfunhappy 4y ago
But surely that would be too slow? Although Rosetta is great at caching instructions ahead of time, it does need to emulate a lot of code (ie, anything generated at runtime).
- anyfoo 4y ago
  Have you tried Rosetta? It can be pretty impressive.
  - Wowfunhappy 4y ago
    Rosetta is very impressive! I just don't see how they could maintain that by passing instructions back and fourth over a shared drive, that would be a ridiculous amount of latency!
    - my123 4y ago
      The shared drive is just a licensing trick. They do an ioctl over /proc/self/exe as the licensing mechanism. (and that's routed over with virtio-fs to the host)
      - deleted 4y ago
        [deleted]
      - halifaxbeard 4y ago
        Didn’t Apple also implement togglable memory models for m1 (and I’m assuming m2)?
- msbarnett 4y ago
  It’s doing an AOT translation of x86-64 opcodes to ARM64 equivalents. There isn’t really any back and forth, it just digests the binary all at once. This would still be pretty slow (see: Microsoft’s version of this under Windows ARM) due to the need to issue a ton of memory fence instructions to make ARM’s looser memory model behave like Intel’s, except that Apple baked the ability to switch the CPU into an Intel-like memory model directly into the silicon. So in practice it is shockingly fast.
  - Wowfunhappy 4y ago
    > It’s doing an AOT translation of x86-64 opcodes to ARM64 equivalents. There isn’t really any back and forth, it just digests the binary all at once. No it's not. Apple is not immune from fundamental computer science principles whatever their marketing team says, and even the original keynote acknowledged that Rosetta 2 emulates some instructions at runtime. Imagine you're running Python under Rosetta. The original Python interpeter takes Python code, translates it into x86 assembly, and runs that x86 assembly. Those x86 instructions did not exist prior to execution! Even if Rosetta could translate the entire interpreter into ARM code, the interpreter would still be producing x86 assembly. Other types of programs produce code at runtime as well. Rosetta 2 is able to cache a very impressive amount of instructions ahead of time, but it's still doing emulation.
    - anyfoo 4y ago
      AOT (ahead of time) really does work on whole binaries. That is also why the first launch of an Intel app seems longer sometimes. Intel binary in, ARM binary out. You're still right that that's not sufficient, for example anything that generates Intel code will definitely need JIT (just in time) translation. But presumably a lot of code will still hit the happy AOP path. That being said, a JIT does not have to be super slow. The early vwmware products, back before there was virtualization support in Intel products, actually had to do some translation as well: https://www.vmware.com/pdf/asplos235_adams.pdf https://www.vmware.com/pdf/asplos235_adams.pdf
      - Wowfunhappy 4y ago

Wowfunhappy 4y ago

But surely that would be too slow? Although Rosetta is great at caching instructions ahead of time, it does need to emulate a lot of code (ie, anything generated at runtime).

anyfoo 4y ago
Have you tried Rosetta? It can be pretty impressive.
- Wowfunhappy 4y ago
  Rosetta is very impressive! I just don't see how they could maintain that by passing instructions back and fourth over a shared drive, that would be a ridiculous amount of latency!
  - my123 4y ago
    The shared drive is just a licensing trick. They do an ioctl over /proc/self/exe as the licensing mechanism. (and that's routed over with virtio-fs to the host)
    - deleted 4y ago
      [deleted]
    - halifaxbeard 4y ago
      Didn’t Apple also implement togglable memory models for m1 (and I’m assuming m2)?
msbarnett 4y ago
It’s doing an AOT translation of x86-64 opcodes to ARM64 equivalents. There isn’t really any back and forth, it just digests the binary all at once. This would still be pretty slow (see: Microsoft’s version of this under Windows ARM) due to the need to issue a ton of memory fence instructions to make ARM’s looser memory model behave like Intel’s, except that Apple baked the ability to switch the CPU into an Intel-like memory model directly into the silicon. So in practice it is shockingly fast.
- Wowfunhappy 4y ago
  > It’s doing an AOT translation of x86-64 opcodes to ARM64 equivalents. There isn’t really any back and forth, it just digests the binary all at once. No it's not. Apple is not immune from fundamental computer science principles whatever their marketing team says, and even the original keynote acknowledged that Rosetta 2 emulates some instructions at runtime. Imagine you're running Python under Rosetta. The original Python interpeter takes Python code, translates it into x86 assembly, and runs that x86 assembly. Those x86 instructions did not exist prior to execution! Even if Rosetta could translate the entire interpreter into ARM code, the interpreter would still be producing x86 assembly. Other types of programs produce code at runtime as well. Rosetta 2 is able to cache a very impressive amount of instructions ahead of time, but it's still doing emulation.
  - anyfoo 4y ago
    AOT (ahead of time) really does work on whole binaries. That is also why the first launch of an Intel app seems longer sometimes. Intel binary in, ARM binary out. You're still right that that's not sufficient, for example anything that generates Intel code will definitely need JIT (just in time) translation. But presumably a lot of code will still hit the happy AOP path. That being said, a JIT does not have to be super slow. The early vwmware products, back before there was virtualization support in Intel products, actually had to do some translation as well: https://www.vmware.com/pdf/asplos235_adams.pdf https://www.vmware.com/pdf/asplos235_adams.pdf
    - Wowfunhappy 4y ago