Re: Cross-building GuixSD (and maybe using pre-built toolchains)

[Ludovic Courtès]

Hello,

Paul Boddie <address@hidden> skribis:

> I was looking at the documentation, which is rather more helpful than most 
> distributions when it comes to describing how the actual distribution 
> archives 
> are built, and I figured a few things out about guix-daemon. However, I'm 
> doing all my work in a chroot - I don't want to "make install" and populate 
> various locations on my main system - and this doesn't seem to be entirely 
> compatible with the recommended way the daemon is used. Specifically, the 
> daemon does not seem to be able to build anything unless I specify the --
> disable-chroot flag.

How does guix-daemon fail exactly?  If needed, could you strace it to
get more details on what’s going on?

> Are there any recommended methods of running guix-daemon in a chroot and have 
> it create new chroots, or do I have to use some kind of virtualisation or 
> container technology? Is any kind of fakeroot/fakechroot mechanism supported?

I think few people do this, on the grounds that Guix is rather
non-intrusive: it stores all its stuff in /gnu/store and /var/guix.  So
if you want to get rid of it, all you have to do is delete those two
directories.  The rest of the system is untouched.

Now, if you really want it, I can’t think of any reason why guix-daemon
wouldn’t run in a chroot.  It currently requires root privileges,
precisely so that it can set up a chroot, separate name spaces, and so
on, but that could work in a chroot too.

> One thing that looks very promising is the ability to cross-bootstrap the 
> system, and I did manage to get that started for a new architecture (mipsel) 
> by performing some modifications suggested in the documentation [1], running 
> guix-daemon with the --disable-chroot flag, and then running this:
>
> guix build --target=mipsel-linux-gnu bootstrap-tarballs
>
> However, not wanting to leave my computer switched on all night, I stopped 
> the 
> build after a while. I can understand the need to bootstrap things like 
> toolchains, but given that I am running Debian which has cross-toolchains for 
> mipsel, I wondered if I could short-circuit this process by employing pre-
> built toolchains. Would this be possible?

No.  The approach we’re taking is to have a self-contained distro, and
that’s where we get all the fruits of the “functional paradigm”
described in the manual.

It’s surely an annoyance when bootstrapping an architecture for the
first time.  Once it’s in place though, it’s OK.  You could have build
machines for that architecture publishing binaries to users (via ‘guix
publish’).

> Finally, it seems to be the case that the workflow involves building a 
> bootstrapped minimal system and then natively building packages. Or have I 
> misunderstood the process?

Correct, this is the process to port the distro to a new platform.

> Is it possible to cross-build all of the packages in the distribution?

That’s also an option: you can simply cross-build the packages that you
need and copy them to the target machine.

We make sure core packages can be cross-built to the architectures we
support (currently x86_64, i686, armhf, and mips64el).  However, there’s
no guarantee that cross-building works for other targets, or that
non-core packages cross-build at all.  We’d definitely welcome patches
in this area, though.  :-)

HTH!

Ludo’.