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Reproducible Build Summit

From: Ludovic Courtès
Subject: Reproducible Build Summit
Date: Fri, 04 Dec 2015 20:54:57 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

Hello, Guix!

Manolis and I had the pleasure to attend the first “Reproducible Build
Summit” this week, wonderfully well organized by Debian hackers Lunar
and Holger, along with other brilliant people, and with the support of
the Linux Foundation, the Open Technology Fund, and Google.

There were around 40 people, including contributors to a variety of free
operating systems and distros, which led to many very insightful
sessions and discussions.

Here are the highlights of the sessions I attended and discussions I
had, off the top of my head; Manolis can complement it:

 * Guix & Nix session

   Eelco Dolstra of Nix and myself held a “geek dating” session where we
   presented Nix/Guix to everyone by groups of 8 people.  That was a fun
   exercise, but also difficult to do without any demo/slides.

   I was glad to learn that Lamby, a Debian developer, had come up with
   <>.  :-)  A later session was
   dedicated to specifying a tool similar to ‘guix challenge’ and dubbed

 * Shared reproducibility issue database

   Currently we have a bunch of patches and open reproducibility issues
   at <>, but they feel lonely!  The Debian
   folks have a Yaml database (recutils would be nice, but hey!) that is
   used to generate the pages at <>.
   They are kindly offering to open it to other distros, so that we can
   all work together instead of duplicating work.  Expect updates on the
   practical details soonish.

 * Distro bootstrapping

   We had a short session on distro bootstrapping, where we discussed
   how each project addresses it, and what we could do to improve the
   situation.  Most distros, including Debian, do not have a clearly
   specified set of bootstrap binaries like we have, but are willing to
   work towards having a more formal set of requirements, to allow the
   distro to be bootstrapped in different contexts.  There were
   discussions about diverse double compilation and whether/how it could
   help, as well as how we could reduce the bootstrap set (I suggested
   something like keeping TinyC, not GCC, as a bootstrap binary, used to
   build GCC 4.6-, used to build a more recent GCC that requires C++.)

 * Hacking sessions

   Eelco, Manolis, and I sat together for the hacking sessions.  I
   focused on shamelessly stealing the Nix daemon’s ability to rebuild a
   derivation and error out if the result differs (commits 07e70f4 and

   I also discussed with Eelco the fact that the daemon was leaking the
   real name of the build directory, meaning that if a build machine

     TMPDIR=/foo/bar guix-daemon

   and the other runs:

     TMPDIR=/tmp guix-daemon

   then the first build process will see a directory called
   /foo/bar/nix-build-xxx.  If it captures the build directory name,
   then we get a discrepancy.  Eelco quickly changed that, such that the
   build process always sees /tmp/nix-build-xxx:
   I’ll merge this commit soon.

   Of course the better fix is for packages to not capture the build
   directory name, and even to error out when that happens.  But that
   seems like a longer-term goal, potentially can-of-wormy (think of
   debugging symbols…)

   Besides, I packaged ‘findnewest’ (commit df7393b) by Thomas Klausner
   of NetBSD minutes after he had tagged it.  ;-) This tool is meant to
   help provide useful *and* reproducible timestamps for packages that
   want it.

 * Testing Guix reproducibility

   Holger of Debian said he would be happy to perform independent builds
   of Guix packages on the ProfitBricks-sponsored machines that are used
   for Debian and other distros.  Manolis will discuss with him to get
   that up and running.

 * Authenticating code from a Git repo

   The Qubes people have a sophisticated process to sign their code in
   Git.  Since they want signatures from both the author and the
   reviewers of a given patch series, they use signed tags (signed
   commits can only have one signature.)  Thus they end up automatically
   creating signed tags for each series of patches that is pushed (a bit
   heavyweight, but it does the job.)

   I’d like to suggest that we do something similar.

I think that’s a lot of food for thought already!  There’ll be other
such meetings in the future, so I hope we can keep making progress
together.  I would also like to get the broader GNU involved in
addressing the issue.

Anyway, that was a great experience, with lots of friendly people to
chat with and have a walk in Athens by night!


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