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From: Vagrant Cascadian <vagrant@debian.org>
To: 36117@debbugs.gnu.org
Subject: bug#36117: qemu-binfmt with non-native chroot
Date: Thu, 06 Jun 2019 10:55:25 -0700	[thread overview]
Message-ID: <87r286zjhu.fsf@yucca> (raw)

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I've been trying to use qemu-binfmt-service-type to build a non-native
chroot of a Debian system on Guix... because, well... because!

In Debian, this works with the qemu-user-static package, where the
binfmt sets these flags:

  $ cat /proc/sys/fs/binfmt_misc/qemu-aarch64
  enabled
  interpreter /usr/bin/qemu-aarch64-static
  flags: OCF
  offset 0
  magic 7f454c460201010000000000000000000200b700
  mask ffffffffffffff00fffffffffffffffffeffffff

In particular, the F flag allows the host system binaries to be used as
the interpreter inside the chroot. But apparently, this only works with
static-built qemu targets, according to the linux's
Documentation/admin-guide/binfmt-misc.rst.

On Guix there are no flags set, and the binary used is a dynamically
linked executable:

  $ cat /proc/sys/fs/binfmt_misc/qemu-aarch64
  enabled
  interpreter
  /gnu/store/sw2rrqmjij73wcy3ajd47ypvmzh12yz6-qemu-3.1.0/bin/qemu-aarch64
  flags:
  offset 0
  magic 7f454c460201010000000000000000000200b700
  mask ffffffffffffff00fffffffffffffffffeffffff


So there are (at least) two things needed to make this work on Guix:

* A way to set the flags on qemu-binfmt-service-type.

* A static build of qemu-user targets

* A way to set which qemu to use for qemu-binfmt-service-type.

The *three* things are...


With this working correctly foreign-architecture chroots would become
trivial:

  # on an amd64 host:
  $ debootstrap --arch=arm64 buster buster-chroot http://deb.debian.org/debian
  ...
  $ chroot buster-chroot /bin/bash


Enabling qemu-binfmt-service-type to operate in this way would obviate
the need for the "guix-support?" qemu-binfmt-configuration option, as
you could simply assemble the build environment without having to
include all of qemu's dependencies in the container.

It's a pretty magical feature.


live well,
  vagrant

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             reply	other threads:[~2019-06-06 17:56 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-06 17:55 Vagrant Cascadian [this message]
2019-06-07 13:00 ` bug#36117: qemu-binfmt with non-native chroot Ludovic Courtès
2019-06-08  6:03   ` Vagrant Cascadian
2019-06-24 12:25     ` Ludovic Courtès
2021-02-22 19:50       ` bug#36117: [PATCH 1/4] gnu: qemu: Fix indentation and remove trailing #t Maxim Cournoyer
2021-02-22 19:50         ` bug#36117: [PATCH 2/4] gnu: Add glib-static Maxim Cournoyer
2021-02-22 19:50         ` bug#36117: [PATCH 3/4] gnu: qemu: Add a static output Maxim Cournoyer
2021-02-23  8:38           ` Ludovic Courtès
2021-02-25 13:57             ` Maxim Cournoyer
2021-02-25 14:50               ` Ludovic Courtès
2021-02-22 19:50         ` bug#36117: [PATCH 4/4] services/qemu-binfmt: Use the F flag and the static output of QEMU Maxim Cournoyer
2021-02-23  8:37           ` Ludovic Courtès
2021-02-25 21:47             ` Maxim Cournoyer
2021-03-15 22:07               ` bug#36117: qemu-binfmt with non-native chroot Maxim Cournoyer

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