I'm trying to cross-build a Debian/Ubuntu package on a running amd64 system to mips arch. I've tried several methods, from pubilder to sbuild, but I keep failing. About the latter, on a freshly installed Debian 9 I do:

apt-get -y install sbuild
sbuild-createchroot --arch=mips --make-sbuild-tarball=/srv/chroots/wheezy-sbuild.tgz wheezy /srv/chroots/wheezy http://archive.debian.org/debian/

But in the end I get:

W: Failure trying to run: chroot /srv/chroots/wheezy dpkg-deb -f /var/cache/apt/archives/dpkg_1.16.18_mips.deb Version
W: See /srv/chroots/wheezy/debootstrap/debootstrap.log for details
W: Failure trying to run: chroot /srv/chroots/wheezy mount -t proc proc /proc
W: See /srv/chroots/wheezy/debootstrap/debootstrap.log for details
E: Error running debootstrap at /usr/sbin/sbuild-createchroot line 268.

and the log contains:

chroot: failed to run command 'dpkg-deb': Exec format error
chroot: failed to run command 'mount': Exec format error

All the methods I tried end up with that Exec format error while trying different commands.

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  • Do you have to target Wheezy? It would be much easier if you could target Stretch. – Stephen Kitt May 15 '19 at 21:12
  • Yes, wheezy. I need to compile a package for UniFi Edge Router which is based on that version – Maxxer May 16 '19 at 2:45

Cross-building only became nice and easy with Debian 9 as a target; it’s do-able with Debian 8 too, but targeting Debian 7 is a bit too complex. (EmDebian was dropped before Debian 7.)

There is however a simple setup to build mipsel Wheezy packages on any system capable of running QEMU, and building packages there will still be much faster than building on your router:

  • start an mipsel setup in a chroot using debootstrap:

    sudo debootstrap --arch=mipsel --foreign --variant=buildd \
                     --include=fakeroot,build-essential \
                     wheezy ./wheezy-mipsel-chroot \
  • install QEMU and binfmt_misc support:

    sudo apt install qemu-user-static binfmt-support
  • copy the QEMU binary into the chroot:

    sudo cp /usr/bin/qemu-mipsel-static wheezy-mipsel-chroot/usr/bin

    (it’s statically-linked, so it will work fine)

  • enter the chroot and finish debootstrap:

    sudo chroot wheezy-mipsel-chroot /debootstrap/debootstrap --second-stage

You can now use your chroot to build packages. Manually, copy your package into the chroot, enter it, and build with dpkg-buildpackage after installing the build dependencies.

To build with sbuild, you’ll need to at least register the chroot with schroot; add a file named /etc/schroot/chroot.d/wheezy-mipsel-sbuild with the following contents:

description=Debian wheezy/mipsel autobuilder

There are probably other steps required to get the chroot to work correctly with sbuild, in particular setting up the sbuild group inside the chroot and fixing ownership.

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  • Before running the last commands I had to copy some dirs as stated here. But even if I can enter the chroot when running debootstrap package installation fails because package architecture (mipsel) does not match system (amd64) – Maxxer May 17 '19 at 5:41
  • You’ve destroyed the chroot by copying the directories. (The chroot contained foreign binaries which you overwrote with amd64 binaries.) I ran all those commands before posting my answer, on a Debian 9 system, and it worked as described. (Although I realise now that I got the target arch wrong; I’ll run them again with mipsel...) What failed in your case, that led you to copy the directories? – Stephen Kitt May 17 '19 at 5:46
  • I now have a working mipsel chroot after running the commands in my updated answer. – Stephen Kitt May 17 '19 at 5:53
  • I've accepted the answer because all works. Unfortunately the chroot is not liked by sbuild. If I run sbuild --dist=wheezy --host=mipsel -c /root/wheezy-mipsel-chroot/ I get E: /root/wheezy-mipsel-chroot/: Chroot not found – Maxxer May 17 '19 at 10:17
  • If you want to use the chroot with sbuild in its default schroot mode, you need to register it with schroot. – Stephen Kitt May 17 '19 at 11:00

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