[mbreese]

But if they are doing that, then why do they need to use the Mac Hypervisor Framework to setup the VM? That wouldn't be required if you were using qemu, would it?

(How you mention it would be the simplest possible thing that would work)

[vocram]

A Linux VM is still needed because these are Linux containers, ie. they need namespaces, cgroups, layered rootfs, etc.

[mbreese]

Of course, but my question is how is it created... MacOS has a Hypervisor framework for creating VMs, which Docker is using. But I don’t know enough about those internals to understand how they are getting an x86 VM on an ARM host. I know it can be done with qemu emulation, but does that still need the MacOS hypervisor framework or does it run as a normal user process?

These are the questions I’m trying to figure out...

[sirn]

       (5) Docker Image      (amd64)
                ^
                |
       (4) QEMU Binfmt       (arm64 <-> amd64 binary emulation layer)
                ^
                |
        (3) Linux VM         (arm64)
                ^
                |
   (2) Hypervisor.framework  (arm64, macOS native virtualization framework)
                ^
                |
      (1) Docker for Mac

Linux Kernel has a feature to allow using a wrapper to execute userspace program based on file header (binfmt[1]). In this case, Linux VM in (3) has QEMU user mode emulation registered as binfmt, so any amd64 binaries are automatically wrapped into `qemu-x86_64-static /path/to/bin` and run. Docker Image itself doesn't run a Linux kernel but use one from the VM host, so this scenario is possible.

This is also how multiarch[2] works (for amd64 to arm64/ppc64le/etc.) which might even be what Docker is using. In case of multiarch, the qemu-*-static binary is provided as a container running in privileged mode.

[1]: https://www.kernel.org/doc/html/latest/admin-guide/binfmt-mi...

[2]: https://github.com/multiarch/qemu-user-static

[mbreese]

Step 4 was what I was missing.

[cpuguy83]

The VM is an arm64 VM.

[wmf]

Docker Desktop uses Hypervisor.framework to run ARM containers on ARM. Docker Desktop uses QEMU to run x86 containers on ARM.

[cpuguy83]

Docker Desktop uses Hyperbisor.framework to run an arm vm, which runs arm containers natively, or x86 containers via qemu (in the arm VM).