I want to share the experience I had cross-building linuxcnc using
qemu-arm-user:
It works, it is faster than some actual ARM boards to build, but you
can't usefully run/test linuxcnc in this environment.
After installing some packages like debootstrap and qemu-user-static, I
created a debian armhf chroot:
$ sudo qemu-debootstrap --no-check-gpg --arch=armhf jessie
~/roots/jessie-armhf http://httpredir.debian.org/debian
I then prepared the configuration of schroot in
/etc/schroot/schroot.conf:
[jessie-armhf]
type=directory
description=Jessie armhf
directory=/home/jepler/roots/jessie-armhf
groups=root,sudo
root-groups=root,sudo
aliases=armhf,default
now I could 'sudo schroot', add my jepler user in the chroot, install
packages with apt, etc. Then I could 'schroot' (not as root) to get my
regular home directory, and build linuxcnc in a fresh new git clone. (I
did all git ops in my 'real' system, not the emulated system)
This is a nice fast development system (i7-4970k), it builds linuxcnc
for x86_64 in around 30 seconds (time make -j9). Building linuxcnc for
arm in the schroot takes about 7.5 minutes, or 15x as long. It's
competitive with my odroid U3, where due to having only 2GB memory I
have to build with "-j2" even though the CPU has 4 cores, so it's a
technique I'll keep in my toolbox.
(I haven't tried building a package, but I assume it'll work right but
still take longer than I'd like to routinely wait)
However, when it came time to run the testsuite or linuxcnc itself, I
encountered test failures and even deadlocks between rtapi_app and
halcmd. It appears that qemu-user does not support atomic operations
between separate processes, but linuxcnc needs this for basic
functionality like loading a component. I've filed this bug upstream
with qemu, https://bugs.launchpad.net/qemu/+bug/1585840
Unlike whole-system emulation, one great thing about schroot is that you
can fully share your home directory between the real computer and the
schroot.
Jeff
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