(sid_amd64)zumbi@cat:/tmp/hello-2.6$ dpkg-buildpackage -us -uc -rfakeroot -aarmel
[...]
chown -R root:root debian/tmp
chmod -R u+w,go=rX debian/tmp
dpkg --build debian/tmp ..
dpkg-deb: building package `hello' in `../hello_2.6-1_armel.deb'.
 dpkg-genchanges  >../hello_2.6-1_armel.changes
dpkg-genchanges: including full source code in upload
 dpkg-source --after-build hello-2.6
dpkg-buildpackage: full upload (original source is included)


zumbi@cat:~$ sudo sbuild -d sid_amd64 hello_2.6-1

zumbi@cat:~$ ls -l hello_2.6-1_amd64.*
lrwxrwxrwx 1 root emdebian    42 Jan 21 10:47 hello_2.6-1_amd64.build -> /root/logs/hello_2.6-1-amd64-20110121-1047
-rw-r--r-- 1 root emdebian   818 Jan 21 10:48 hello_2.6-1_amd64.changes
-rw-r--r-- 1 root root     59986 Jan 21 10:48 hello_2.6-1_amd64.deb

$ sudo sbuild -d sid_amd64 --debbuildopt="-aarmel" hello_2.6-1
[...]
chmod -R u+w,go=rX debian/tmp
dpkg --build debian/tmp ..
dpkg-deb: building package `hello' in `../hello_2.6-1_armel.deb'.
 dpkg-genchanges -B >../hello_2.6-1_armel.changes
dpkg-genchanges: arch-specific upload - not including arch-independent packages
dpkg-genchanges: binary-only upload - not including any source code
 dpkg-source --after-build hello-2.6
dpkg-buildpackage: binary only upload (no source included)
Build finished at 20110121-1105
Can't find hello_2.6-1_amd64.changes -- can't dump info
âPPackage contents
âFFinishe
Built successfully
Purging /srv/chroot/sid_amd64/build/root-hello_2.6-1-amd64-D9WaOO
Finished at 20110121-1105
Build needed 00:00:12, 4812k disc space

$ ls -l hello*                  
lrwxrwxrwx 1 root emdebian 42 Jan 21 11:04 hello_2.6-1_amd64.build -> /root/logs/hello_2.6-1-amd64-20110121-110

$ sudo sbuild -d sid_amd64 --arch=armel --debbuildopt="-a armel" hello_2.6-1
Chroot sid_amd64 for architecture armel not found

$ sudo vi /usr/share/perl5/Sbuild/Build.pm +1944
# Figure out chroot architecture
sub chroot_arch {
    my $self = shift;
    my $nasty = "armel";

    my $pipe = $self->get('Session')->pipe_command(
        { COMMAND => [$self->get_conf('DPKG'),
                      '--print-architecture'],
          USER => $self->get_conf('USERNAME'),
          CHROOT => 1,
          PRIORITY => 0,
          DIR => '/' }) || return undef;

    chomp(my $chroot_arch = <$pipe>);
    close($pipe);

    die "Can't determine architecture of chroot: $!\n"
        if ($? || !defined($chroot_arch));

    return $nasty;
 #   return $chroot_arch;
}

$ sudo sbuild -d sid_amd64 --debbuildopt="-aarmel" hello_2.6-1
[...]
âFFinished
Built successfully
Purging /srv/chroot/sid_amd64/build/root-hello_2.6-1-armel-LvZgMC
Finished at 20110121-1113
Build needed 00:00:12, 4876k disc space

zumbi@cat:~$ ls -la hello*
lrwxrwxrwx 1 root emdebian    42 Jan 21 11:04 hello_2.6-1_amd64.build -> /root/logs/hello_2.6-1-amd64-20110121-1104
lrwxrwxrwx 1 root emdebian    42 Jan 21 11:13 hello_2.6-1_armel.build -> /root/logs/hello_2.6-1-armel-20110121-1113
-rw-r--r-- 1 root emdebian   818 Jan 21 11:13 hello_2.6-1_armel.changes
-rw-r--r-- 1 root root     61024 Jan 21 11:13 hello_2.6-1_armel.deb

( Following part is not needed, only if you need to pass --arch=armel )

$ sudo vi /usr/share/perl5/Sbuild/ChrootInfo.pm +112
[...]
#       if ($arch_set && !$arch_found && $arch ne "") {
#           # TODO: Return error, rather than die.
#           die "Chroot $distribution for architecture $arch not found\n";
#           return undef;
#       }

$ sudo sbuild -d sid_amd64 --debbuildopt="-aarmel" hello_2.6-1
[...]
Built successfully
Purging /srv/chroot/sid_amd64/build/root-hello_2.6-1-armel-0eV9Yp
Finished at 20110121-1100
Build needed 00:00:12, 4876k disc space

zumbi@cat:~$ ls -la hello_2.6-1_a*
lrwxrwxrwx 1 root emdebian    42 Jan 21 10:50 hello_2.6-1_amd64.build -> /root/logs/hello_2.6-1-amd64-20110121-1050
-rw-r--r-- 1 root emdebian   818 Jan 21 10:48 hello_2.6-1_amd64.changes
-rw-r--r-- 1 root root     59986 Jan 21 10:48 hello_2.6-1_amd64.deb
lrwxrwxrwx 1 root emdebian    42 Jan 21 10:59 hello_2.6-1_armel.build -> /root/logs/hello_2.6-1-armel-20110121-1059
-rw-r--r-- 1 root emdebian   818 Jan 21 11:00 hello_2.6-1_armel.changes
-rw-r--r-- 1 root root     61034 Jan 21 11:00 hello_2.6-1_armel.deb

( Inside hello_2.6-1_armel.deb
/tmp/mc-zumbi/extfsXQiT2jhello: ELF 32-bit LSB executable, ARM, version 1 (SYSV),
 dynamically linked (uses shared libs), for GNU/Linux 2.6.18, stripped )