[Reproducible-builds] Cross-building across architectures (reproducibly?)

[Steven Chamberlain]

Hi,

I was going to introduce this topic, but it turned into an essay, so
there is some background at:  http://pyro.eu.org/writings/2016010100

The part most relevant to Reproducible Builds is:

For arch-dependent binary packages, our latest breakthrough is that
using Helmut's tool, I've been able to rebootstrap a minimal Debian
linux-i386 chroot (445 binary packages[3]).  These were cross-compiled
from source, by only running kfreebsd-amd64 binaries on a FreeBSD
kernel, and having some Arch:all packages installed.

Ideally we'd like the native and cross-built binaries to be identical,
but for many reasons they're currently not.  They must build
reproducibly in the first place, and Debian has made great progress
there already.

In the future, we'd like to be able to re-bootstrap more architectures,
also in the reverse direction using linux to verify kfreebsd and hurd,
and other combinations.

For the Arch:all (architecture-independent) packages, there was some
discussion recently on the reproducible-builds list[4].  I'd like those
to be reproducible from more than one arch someday, with bonus points if
that also works from different kernels.

That only leaves bootloaders, kernels, and perhaps system firmware like
coreboot;  though they tend to cross-build quite easily actually, grub2
and kfreebsd package builds are mostly reproducible from Linux and
kFreeBSD already.

[3]: http://kfreebsd.eu/rebootstrap/2016010100/rebootstrap_i386_gcc5_nobiarch/
[4]: https://lists.alioth.debian.org/pipermail/reproducible-builds/Week-of-Mon-20151123/003992.html

Regards,
-- 
Steven Chamberlain
steven at pyro.eu.org
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