State of the Debian/Ubuntu arm64 port
=====================================
*** Arm64 lives! ***
Executive summary
-----------------
* There is now a bootable (raring) image to download and run
* Everything has been rebuilt against glibc 2.17 so it works
* A bit more work is needed to make the rootfs useable as a native buildd
* Multiarch crossbuilding and the build-profile mechanism is mature enough to
cross-build
a port from scratch (this is a big deal IMHO)
* All packages, sources and tools are in a public repo and this work should be
reproducible.
* This image is fully multiarched so co-installing armhf for a
64/32 mix should work nicely, as should multiarch crossbuilding to
legacy x86 architectures. :-) (but I haven't tried that yet...)
* Linaro wants 'the distros' to take this work forward from here so people
interested in
Debian and Ubuntu on 64-bit arm hardware need to step up and help out.
Bootable images
---------------
A milestone was reached this week: Enough packages were built for arm64 to
debootstrap an
image which booted to a prompt! After a bit of fettling (and switching to
multistrap) I got
an image with all the packages configured which boots with upstart to a login
prompt (I
admit, I did get quite excited about this, as it represents the coming together
of nearly 3
years work on multiarch, crossbuilding, bootstrapping, cyclic dependencies and
arm64 :-)
The images are available for download:
http://wiki.debian.org/Arm64Port#Pre-built_Rootfs
And there are destructions there for making your own.
All these packages were cross-built on raring, untangling cyclic dependencies
with build
profiles (see wiki.debian.org/DebianBootstrap for how that works), making this
the first
(non x86) self-bootstrapped debian port ever (so far as I know). All (?)
previous ports have
been done using something else like OpenEmbedded (armel, armhf), RedHat/HardHat
(arm, alpha,
mips), something IBMy (s390) to get an initial linux rootfs on which debian
packages are
built.
The new bootstrap process is (almost) just a list of sbuild commands. In
practice there are
still a few rough edges around cross- build-dependencies so of the 140 packages
needed for
the bootstrap, 9 had to be built manually with 'dpkg-buildpackage -aarm64 -d'
(to skip
build-dep checks) instead of 'sbuild --host arm64 <package>'.
The current bootstrap packageset status is here:
http://people.linaro.org/~wookey/buildd/raring-arm64/status-bootstrap.html
There is no armv8 (arm64/aarch64) hardware available yet, so this image can
currently only
be run in a model. ARM provide a free-beer prorietary 'Foundation model' so we
do have
someting to test with. It's sluggish but perfectly useable. Booting the images
takes a
couple of minutes on my fairly average machine.
The images are using the Linaro OE release kernels which seem to work fine for
this purpose.
Thanks to Marcin for modified bootloader lines in .axf files.
Image status
------------
I was impressed that things basically 'just worked' on first boot. There is of
course plenty
of breakage, I'm sure, and I haven't looked very hard yet, but it's a lot
better than I
expected after months of just building stuff and testing nothing. (Things that
are poorly:
nano can't parse it's own syntax-coluring files for example, and multiarch perl
has the
wrong @INC path compiled in; I'm sure there is more). Consider this alpha-grade
until it's
been used a bit more.
Things that are not yet built which would make the images a lot more useful are
apt and a
dhcp client. apt needs gnupg needs curl needs nss. The nss cross-build needs
fixing to
unbung that. A debian chroot without apt turns out to be disappointing quite
quickly :-)
Expect an updated image with more packages very soon.
Multiarch crossbuilding
-----------------------
It's really nice to have building and crossbuilding using exactly the same
mechanisms
and tools, with all files having one canonical location, and dependency
mechanisms that
are reliable. The more I've used this, the more I've been impressed by it.
There is
still work to do to expand the set of cross-buildable stuff, but it's a solid
base to
work from.
Getting this port working has been 'interesting' because it's attempting 4 new
things all at
once: multiarch (file layouts and dependencies), crossbuilding (tools and
packaging support
in a distro that historically was always natively built), arm64 (aarch64)
support in
packages that need it, and build-profiles to linearise the build-order.
The arm64 part of this is a relatively small part as the heavy lifting has been
done
upstream (gcc, (e)glibc, binutils, kernel, libffi, autotools and a lot of minor
fixes in
various packages). Thanks are due to doko (Matthias Klose) for sterling work
getting all
that integrated into the debian and ubuntu toolchain packages, and infinity
(Adam Conrad)
for merging various eglibc branches. There were also hordes of very boring
patches of the
form 'update config.sub and guess before building'.
Most of the work has been in making things cross-build (exactly the same fixes
needed for
armel/hf too so I've had plenty of help there from canonical types who want
cross-building
for arm to work nicely), and particular thinks to Neil Williams for taking on
the perl
cross-build challenge and creating the debian-perl-cross package to manage the
cross-configury, whilst also working with upstream to make the whole thing a
bit less 1996.
Multiarchifying has been going on nicely in libraries and -dev packages, but
things like
perl and python needed significant work, along with a lot of boring bugs saying
'mark this
package MA: foreign' and 'build-dep on python:any or perl-base:any'. Thanks are
due to doko
for the python multiarching and Niko Tyni for the perl multiarchification.
Getting all 3
'aspects' of multiarch perl, cross-built perl and arm64 perl config to work at
the same time
was quite hard work, and there are still bugs there. Wider usage of multiarched
perl would
no doubt sort this out reasonably quickly. I started a wiki page to track the
status of
multiarched cross-buildable perl: http://wiki.debian.org/Multiarch/Perl . Help
would be
welcome.
The build-profile work is described on the
http://wiki.debian.org/DebianBootstrap page.
Progress has been greatly helped by GSOC projects last year, with good work on
the tools
(crossbuild-essential packages, build-profile support) from P.J McDermott and
an impressive
contribution from Johannes Schauer on dependency analysis tools around libdose,
and apt
build-profile support.
All of this apart from multiarch perl, crossbuildable perl and build-profile
stuff (and
a few pending patches) is already in raring.
Building stuff yourself
-----------------------
Setting up an arm64 build environment is very simple. Use sbuild-createchroot
or mk-sbuild
and point at the bootstrap repo, with a bit of config and some updated tools
packages from
the repo (amd64 only supplied). Details are given on
https://wiki.linaro.org/Platform/DevPlatform/CrossCompile/arm64bootstrap
Once you've created a tarball chroot builds are simply done with
sbuild -c quantal-amd64-sbuild -d quantal --host=arm64 <package.dsc> or
sbuild -c quantal-amd64-sbuild -d quantal --host=arm64 <package>_<version>
(I'd love it
if sbuild got smart enough to work out the version itself when given a distro
- Roger
says he's working on it)
To deal with the chore of 'find version, run sbuild, sign result, upload to
repo, import to
repo, deal with reprepro bitching if you re-upload the same version of
something' for every
package build, I wrote 'dimstrap' which is a simple-minded tool to wrap that up
and either do
one-off builds or run through a list. It is part of the xbuilder package here:
https://launchpad.net/~linaro-foundations/+archive/cross-build-tools/ It also
includes the
logfile-parsing script ('generate html') which generates the nice status pages:
http://people.linaro.org/~wookey/buildd/raring-arm64/status-bootstrap.html
Image building
--------------
The config and instructions provided (in
http://wiki.debian.org/Arm64Port#Building_your_own_rootfs_image ) is
for multistrap. Debootstrap sort-of produces working images too but
takes a lot longer to unpack/configure, and misses out various vital
packages (like libperl5.14). I'm sure it could be kicked into
submission. In theory multistrap (apt really) should have got all the
arch all packages from the main repo, but in practice it refused to do
that so I had to rebuild them or copy them over anyway (grumble).
Any package that installs replaced conffiles seems to generate invalid
dpkg status entries (ifupdown did this to me). I've not got to the
bottom of that yet. Deleting the offending line gets you an image that
works.
Issues
------
General:
The build-profile patches for dpkg and apt need to be pushed into the distro to
make
that feature permanent. A thread on debian-devel is working on that
(http://debian.2.n7.nabble.com/Bootstrappable-Debian-proposal-of-needed-changes-td2848200.html).
The main issue is what syntax to use '<>' or '[]' and how to deal with multiple
overlapping
profiles. The patches to debian control cannot go in until at least the syntax
is agreed and
the tools will parse them without barfing. Johannes ands I will send an updated
spec
soonish.
The missing piece of bootstrapping with regard to build-deps is packages that
build-dep on
gcc-4.6 or binutils. When cross-building this should be satisfied by
<triplet>-gcc-4.6 or
<triplet>-binutils. Nothing makes that happen currently. A scheme has been
mooted but
nothing is implemented yet.
There is debate about whether cross-toolchains should build against multiarch
libraries
(libgcc, libstdc++) like everything else, or have their own internal copies.
Doko and I
disagree on this matter. That will need to be worked out at some point.
We won't get that much further with fixing cross- object-introspection, which
is a
non-trivial job.
Image-related:
The images do essentially work but very little has been tested so far.
Multiarch perl still needs work.
nss needs cross-building in order to get apt cross-built
I've not got networking working yet. Info is here:
https://fedoraproject.org/wiki/Architectures/ARM/AArch64/FoundationModel_Networking
lack of a dhcp client in the image hasn't helped there.
More info
---------
The canonical arm64 port info page is:
http://wiki.debian.org/Arm64Port
Full arm64 cross-build status (i.e everything that has been tried) is here:
http://people.linaro.org/~wookey/buildd/raring-arm64/status.html
All the patches generated so far are here:
http://people.debian.org/~wookey/bootstrap/patches/
(most that can, have been filed as bugs - there is a backlog of stuff
filed in Launchpad but not yet forwarded to the Debian BTS - yes I am
a bad boy - blame the fact that you can't use reportbug or bts from
inside ARM due to their idiotic email policies).
Future work
-----------
Firstly we should say thank you to Linaro for sponsoring this work in various
ways over
the last 3 years. We wouldn't be at this point now if it wasn't for that.
However
Linaro has a lot of things to do and is trying hard not to do distro's work for
them,
concentrating on upstream things. This makes sense for commercially-backed
distros like
Red Hat and Ubuntu, but rather less for Debian where we _are_ the distro just
as much
as anyone else is, and ultimately someone has to spend the time to get stuff
working.
Anyway, I was supposed to stop work on this some time back, but have largely
failed to
do so (cross-building is so moreish - there is always one more build to try
before
bedtime!) and appreciate being given enough slack to get this to a point of
actual
utility. However I expect to have much less time to spend on this from now on,
except
insofar as it still co-oncides with things Linaro wants doing. I'd love to hear
from
people who actually want to use this, to get more packages built, the Debian
cross-toolchains sorted, build-profiles finalised, and a whole pile of stuff
fixed once
Wheezy is released. I'm pretty sure there are quite a lot of people who want
multiarch
Debian or Ubuntu on their arm64 machines (or models).
I hear rumours that actual hardware may appear sometime around the middle of
the year
with some bagsied for Debian. Setting up the ports infrastructure for that
would be
good. I don't know if anyone is interested in building slowly on models in the
meantime, or if we should just carry on crossing and see how far we get. This
table
shows that 471 packages in raring can be expected to cross-build already:
http://people.canonical.com/~cjwatson/cross/armhf/raring/
Todo:
Fix up multiarch/cross perl
Fix nss
Build missing packages for apt
Build missing packages for build-essential
Build Debian cross-toolchain
Get all this working in unstable as well as raring
Setup buildds
Build all the other packages
Set up automated bootstraping runs (eventually)
Current setup
-------------
Builds have all been run locally using the sbuild/chroot setup described above
and on
the Arm64Port page, which should be easy for anyone to reproduce. The main
irritation
is keeping up with raring: out of sync libraries are not MA-installable. Logs
are
uploaded to people.linaro.org (rsync). The reprepro repo is on people.debian.org
(dupload). This stuff should probably move to ports.debian.org and
ports.ubuntu.com,
but neither of those are set up for cross-building so I'm not quite sure how
this will
work.
I could go on at great length about the machinery of profiled bootstrap builds,
and
interactions between tools, but it's not very exciting, so will resist. Suffice
it to
say that whilst it's all pretty slick I'd still like better buildd tools.
Build-profile changes
---------------------
The build-profile patches are not yet upstreamable so are collecting in the
repo.
The patch set so far is here:
http://people.debian.org/~wookey/bootstrap/patches/profiles/packages/
Other thanks:
Other people who have helped make this happen in various ways but not got a
mention above:
Colin Watson, Dmitry Ledkovs, Steve Langasek, Harry Leibel, Thibaut Girka,
Roger Leigh,
Marcus Shawcroft, James Morrisey, Jonathan Austin, Steve McIntyre, Peter
Pearse, Aurelien
Jarno, and whoever does sysadmin at people.{linaro,debian}.org
I hope I didn't forget anyone, or any important information.
Feedback from anyone attempting to get this working outside my computer is very
welcome. I have almost certainly forgotten to write down some things, and upload
correct versions of some other things.
Wookey
--
Principal hats: Linaro, Emdebian, Wookware, Balloonboard, ARM
http://wookware.org/
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