Re: [gentoo-dev] crossdev: installing _host_ build dependencies not automatic?

[Alexis Ballier <aballier@gentoo.org>]

On Wed, 3 May 2017 22:47:18 +0100
James Le Cuirot <chewi@gentoo.org> wrote:

> On Wed, 3 May 2017 17:56:43 +0200
> Alexis Ballier <aballier@gentoo.org> wrote:
> 
> > On Wed, 3 May 2017 12:05:48 +0200
> > "Paweł Hajdan, Jr." <phajdan.jr@gentoo.org> wrote:
> >   
> > > I encountered <https://bugs.gentoo.org/show_bug.cgi?id=617276>
> > > while working on some cross-compiling project.
> > > 
> > > Admittedly, it may not be that easy to handle host package
> > > dependencies fully automatically.
> > > 
> > > I'm wondering - is it documented what portage guarantees, and
> > > what I'm expected to just manually handle to provide host build
> > > dependencies?
> > > 
> > > Any other advice about properly using crossdev would also be
> > > appreciated. I'd be happy to test and help improve things.    
> > 
> > 
> > From man emerge:
> > 
> > 
> >        --root-deps[=rdeps]
> >               If  no argument is given then build-time dependencies
> > of packages for ROOT are installed to ROOT instead of /.  If the
> >        rdeps argument is given then discard all build-time
> > dependencies of packages for ROOT.  This option is only meaningful
> > when used together with ROOT and it should not be enabled under
> > normal circumstances!
> > 
> >               Does not affect EAPIs that support HDEPEND.
> > Experimental EAPI 5-hdepend provides HDEPEND as a new means to
> > adjust installation into "/" and ROOT.  If ebuilds using EAPIs
> >               which do not support HDEPEND are built  in  the same
> >               emerge run as those using EAPIs which do support
> > HDEPEND, this option affects only the former.
> > 
> > 
> > crossdev wrappers set --root-deps=rdeps (read cross-emerge, this
> > can be overriden), but be careful: If you only care about getting
> > all the deps and maybe more then removing --root-deps might help
> > you. However, when cross compiling you will likely run into broken
> > deps since / and ROOT will not use the same keyword visibility.  
> 
> I was going to point to crossdev's use of --root-deps=rdeps too. I did
> wonder why on earth this was even added. I overrode it for quite a
> while and didn't have any issue. History showed that it was added by
> solar without much of an explanation. He's no longer around to ask. It
> wasn't until I tried to build a brand new ppc64le system recently that
> I finally found a reason for it, though I'm not sure it was the
> original reason. The multilib ABI USE flags start conflicting horribly
> in cross situations and this option seems to be the only way around it
> at present.

there's that and e.g. you might want to enable USE=mmal for cross
compiling to a raspberry pi; raspberrypi-userland will be in DEPEND but
you wont be able to merge it into /

> I doubt keyword visibility is an issue. Portage uses a different
> configuration between / and ROOT when cross-compiling. I don't think
> it tries to force the same package versions beyond what is specified
> in the ebuild. For pure build-time dependencies, the package will
> only be installed to / anyway (i.e. you don't need cmake in ROOT) so
> there is nothing to enforce here.


The issue is that we can't distinguish between target build time
dependencies (libraries, headers, etc.) and host build time
dependencies (cmake, autotools, etc.). While --root-deps=rdeps avoids
most of the problems at the cost of missing host deps, it still fails
horribly for target build time only deps (e.g. pure headers libraries).