Compiling aarch64-linux packages on x86_64-linux

[Ian Eure <ian@retrospec.tv>]

In "(guix) Additional Build Options", documenting the --system 
option,
the Guix manual says:

    Similarly, when transparent emulation with QEMU and 
    ‘binfmt_misc’
    is enabled (*note ‘qemu-binfmt-service-type’: Virtualization
    Services.), you can build for any system for which a QEMU
    ‘binfmt_misc’ handler is installed.

So, I added this -- the exact configuration from "(guix) 
Virtualization Services" in the manual -- to my operating-system’s 
services:

	 (service qemu-binfmt-service-type
			  (qemu-binfmt-configuration
               (platforms (lookup-qemu-platforms "arm" 
               "aarch64"))))

And `guix system reconfigure'd.  The service is running:

    # herd status qemu-binfmt
    Status of qemu-binfmt:
      It is running since Mon Dec 30 20:47:07 2024 (6 days ago).
      Running value is #t.
      It is enabled.
      Provides: qemu-binfmt
      Requires: file-system-/proc/sys/fs/binfmt_misc
      Will be respawned.

If I try to build a package with --system specified, it fails due 
to the wrong architecture:

    $ guix build --system=aarch64-linux guix
    The following derivation will be built:
      /gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv
    building 
    /gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv...
    @ unsupported-platform 
    /gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv 
    aarch64-linux
    while setting up the build environment: a `aarch64-linux' is 
    required to build 
    `/gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv', 
    but I am a `x86_64-linux'
    builder for 
    `/gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv' 
    failed with exit code 1
    build of 
    /gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv 
    failed
    View build log at 
    '/var/log/guix/drvs/6w/wbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv.gz'.
    guix build: error: build of 
    `/gnu/store/6wwbzsry0c3sm5s0aifgj4sfzahmkk30-guix-1.4.0-31.121e96d.drv' 
    failed

The "(guix) Native Builds" part of the manual mentions that this 
error will occur "If the ‘binfmt_misc’ mechanism is not setup 
correctly..."

What is the correct way to set Guix up so I can build 
aarch64-linux packages on x86_64-linux?

Thanks,

  -- Ian