[Soc-coordination] Bootstrappable Debian - Report 2

[P. J. McDermott]

This is report two for the "Bootstrappable Debian" project [1][2]
mentored by Wookey and co-mentored by Jonathan Austin.

A copy of this report is sent to the debian-bootstrap list [3].


Work Done
=========

Staged Build Support in dpkg-dev
--------------------------------

I discussed with the dpkg developers in bug #661538 [4] my ideas regarding:

  * Support for "Build-Depends-StageN" and "Build-Depends-Indep-StageN"
    fields for any value of "N" and
  * A new "Build-Stage" (or similar) field set by dpkg-gencontrol to mark
    staged packages.

I implemented the latter idea in a currently standalone patch [5][6]
against dpkg 1.16.4.

I've been working on implementing the former idea using a new
"%FIELDS_RE" hash for "pattern" fields like "Build-Depends-Stage\d" and
one or two new subroutines for accessing field elements by key, all in
Dpkg::Control::Fields.  Unfortunately, this has proven a bit more
complex than I initially expected, since keys and values in the %FIELDS
hash are used in various direct and indirect ways outside of the
Dpkg::Control::Fields module, including in dpkg-gencontrol, dpkg-source,
and Dpkg::Control.  My lack of prior experience with writing Perl code
and with the dpkg-dev codebase has not helped in this matter.

Perl Cross Building Support
---------------------------

Due to my work on another project, I knew that Perl's build system
doesn't support cross compilation in a way that can be easily supported
by a distribution such as Debian.  This is a problem because perl-base
has a "Priority: required" field and is therefore one of the packages
that must be cross built to form a base system that can natively build
other packages.

I found in bug #633884 [7] a patch by Peter Pearse and Steve McIntyre that:

  * Adds cross configurations for armel and armhf,
  * Adds a new "Configure" file in Cross/,
  * Modifies Makefile.SH, and
  * Enables cross building (by using the Perl installation on the build
    system) in debian/rules.

I also found a similar but more intrusive patch in Cross LFS - Sysroot
and a tar archive containing an alternative cross build system on Perl's
upstream development mailing list.

I sent a full report [8] of my findings to the debian-bootstrap and
debian-embedded mailing lists.  More details and references in this
matter may be found there.

Following the report, I reviewed the archive with the alternative build
system and found that it was fairly invasive and not very well documented.

Investigation of sbuild 0.63.1's Cross Building Support
-------------------------------------------------------

I compared the source code of versions 0.62.6 and 0.63.1 of sbuild to
learn about the new cross building support.  I noted the new
command-line interface for defining build and host architectures and
observed the way sbuild now works with and configures tools like dpkg,
APT, xapt, dpkg-cross, and cross toolchains to cross build packages.


Next Steps
==========

Staged Build Support in dpkg-dev
--------------------------------

Upon finishing my work on "pattern" fields like "Build-Depends-Stage\d"
in dpkg-dev, I will refresh the patch proposed by Wookey and add to it
my work on control fields, including my "Build-Stage" field patch.

I will then submit the complete patch for review and hopeful inclusion
in dpkg pending consensus from debian-devel on the design aspects of
staged package builds.

Perl Cross Building Support
---------------------------

I plan to look through Perl's build system and the debian/rules file of
src:perl to see what's changed between the version 5.12.4-1 on which the
patch in #633884 is based and the newer versions 5.14.2-11 and 5.16.0-1
in Debian sid and experimental.  With that knowledge, I can refresh the
patch to apply to the new src:perl versions, forward the updated patch
upstream for comments (as requested by the src:perl maintainers), and
submit it for inclusion in src:perl.

sbuild Chroot for Cross Building
--------------------------------

Finally, I plan to set up a new sbuild chroot and use Thibaut Girka's
multiarch cross toolchain packages to begin attempting to cross build
packages.


[1]: http://wiki.debian.org/SummerOfCode2012/Projects#Bootstrappable_Debian
[2]: http://wiki.debian.org/SummerOfCode2012/StudentApplications/PJMcDermott
[3]: http://lists.mister-muffin.de/cgi-bin/mailman/listinfo/debian-bootstrap
[4]: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=661538#71
[5]:
http://odin1.pehjota.net/~pj/debian-bootstrap/dpkg/dpkg-gencontrol.patch
[6]: http://odin1.pehjota.net/~pj/debian-bootstrap/dpkg/notes.txt
[7]: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=633884
[8]: https://lists.debian.org/debian-embedded/2012/06/msg00011.html

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