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Re: The state of cross building

Hi Colin,

On Sun, Jan 31, 2016 at 04:51:26PM +0000, Colin Watson wrote:
> Thanks for doing this.
> How frequently will these be updated?  It would be nice for people to be
> able to upload fixes and see the effects.

Thus far, these are one-shot rebuilds. It is the second attempt of mine.
I crossed 1000 source packages last year and worked towards fixing
tooling issues.

Doing them more frequently is something I would like to see in the
future. We already expressed that vision at the bootstrap sprint in
2014. I guess that jenkins.d.n could afford a node doing cross builds,
so the missing piece probably just is having someone write the code
(https://anonscm.debian.org/git/qa/jenkins.debian.net.git). I can help,
but not drive that.

> It would also be helpful to publish a dd-list so that maintainers can
> easily look for their own packages here.

I thought about that option as well, but I believe that we still have
too many issues that reside outside the realm of individual packages. A
dd-list could mislead maintainers into thinking all of those failures
were bugs in their packages. With pkg-config shipping the cross wrapper
symlinks now and other examples, this situation is fading. I will keep
this in mind for future rebuilds.

> Could you help me understand
> http://subdivi.de/~helmut/debomatic-logs/groff_1.22.3-5_ppc64el.build ?
> This is reported as "uses build arch compiler", but that is a false
> positive because groff intentionally does two build passes, one for the
> host architecture and one for the build architecture, so that it can use
> its own binaries from the build-architecture pass during a cross-build.

Correct. These reasons are heuristics and for groff that heuristic

> The failure is:
>      dh_shlibdeps -a -O--builddirectory=debian/build -O--parallel
>   dpkg-shlibdeps: error: couldn't find library libstdc++.so.6 needed by debian/groff-base/usr/bin/pic (ELF format: 'elf64-powerpcle'; RPATH: '')

This is usually reported as "dpkg-shlibdeps does not search for
libstdc++6 in a sysroot" for other packages, but I failed to improve the
heuristic without regressing it on too many other packages.

> groff doesn't build-depend on libstdc++-5-dev (which is the correct -dev
> package for libstdc++.so.6, despite the confusing naming) because it's
> build-essential, and libstdc++-5-dev-ppc64el-cross is likewise
> cross-build-essential on ppc64el; I can see it being installed in the
> build log.  So why can't dpkg-shlibdeps find it here?

As a ctte member, you will be aware that there are two ways of building
cross compilers and a split on which is better. While it might seem that
this only affects the gcc packaging at first, it also does affect
dpkg-shlibdeps, whose maintainer has a preference on the other way of
maintaining cross toolchains.

So crossbuild-essential-ppc64el transitively depends on
libstdc++-5-dev-ppc64el-cross, but in your groff build nothing depends
on libstdc++-5-dev:ppc64el. So the latter is not installed. Both
packages essentially contain the same files albeit in different
locations. The former puts files in /usr/powerpc64le-linux-gnu/lib while
the latter uses /usr/lib/powerpc64le-linux-gnu. Now dpkg-shlibdeps does
not consider sysroots anymore since 1.18.0 and my inquiry to revert that
was not met with enthusiasm.

So groff crosses just fine once you add libstdc++-5-dev:ppc64el to your


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