Search Results: "wookey"

10 November 2016

Andrew Cater: Debian Miniconf ARM, Cambridge 10/11/16 - Post 4

As we left at about 1740, Wookey was still working on the Cubietruck I'd left him with but had made progress.

Dispersed to various pubs and eateries: we all ended up talking a great deal, much as last year. Tsk, tsk - you hardly see people for 20 years then you see the same people twice in two years :)

Though I didn't see that much of them through the day, thanks to Jo, Lucy and all who kept front desk running as ever and thanks to all the various ARM staff who were helpful with opening doors for the visitors and all the little things around administration - wifi access, badges and all that goes with hosting.

And why, O why, did I not notice that I'd subconsciously typed 10/11/12 not once but three times

25 July 2016

Martin Michlmayr: Debian on Jetson TK1

Debian on Jetson TK1 I became interested in running Debian on NVIDIA's Tegra platform recently. NVIDIA is doing a great job getting support for Tegra upstream (u-boot, kernel, X.org and other projects). As part of ensuring good Debian support for Tegra, I wanted to install Debian on a Jetson TK1, a development board from NVIDIA based on the Tegra K1 chip (Tegra 124), a 32-bit ARM chip. Ian Campbell enabled u-boot and Linux kernel support and added support in the installer for this device about a year ago. I updated some kernel options since there has been a lot of progress upstream in the meantime, performed a lot of tests and documented the installation process on the Debian wiki. Wookey made substantial improvements to the wiki as well. If you're interested in a good 32-bit ARM development platform, give Debian on the Jetson TK1 a try. There's also a 64-bit board. More on that later...

12 April 2016

Reproducible builds folks: Reproducible builds: week 49 in Stretch cycle

What happened in the reproducible builds effort between March 27th and April 2nd: Toolchain fixes Packages fixed The following packages have become reproducible due to changes in their build dependencies: ctioga2, erlang-bitcask, libcommons-collections3-java, libjgoodies-animation-java, libjide-oss-java, octave-gsl, octave-interval, octave-io, octave-quaternion, octave-signal, octave-stk, segment, service-wrapper-java, sqlline, svnkit, uddi4j, velocity-tools. The following packages became reproducible after getting fixed: Some uploads fixed some reproducibility issues, but not all of them: Patches submitted which have not made their way to the archive yet: tests.reproducible-builds.org The i386 builders are now testing packages on i386 for reproducibility. It will probably take 4 weeks until everything has been build twice, on this arch. (h01ger) Package reviews 52 reviews have been removed, 24 added and 4 updated in the previous week. Chris Lamb reported 13 new FTBFS. New issue: copyright_year_in_comments_generated_by_ckbuilder. Misc. This week's edition was mostly written by Lunar, with some help by Reiner Herrmann and h01ger.

16 October 2015

Norbert Preining: Debian/TeX Live multiarch update

A big update of all related packages (tex-common 6.04, texlive-bin 2015.20150524.37493-7, texlive-base/lang/extra package 2015.20151016-1) due to the move to support multi-arch. Of course, the regular updates of the TeX Live are included, too. With this change it should be possible to run a multi-arch system with only one TeX Live installed. Debian - TeX Live 2015 Thanks to the excellent support and testing of the Multi-arch guys, in particular Thorsten Glaser, Helmut Grohne, Johannes Schauer, and Wookey, I learned a lot about multi-arch, and I hope that the current setup is safe. All the packages but the various lib* packages are tagged as Multi-Arch: foreign, while the lib packages are tagged Multi-Arch: same. Anyway, if you find a bug concerning multi-arch, that is that some of the programs exhibit architecture information, please let us know via a bug report. Updated packages acro, alegreya, amiri, assoccnt, attachfile, babel-french, babel-hungarian, barr, beebe, biblatex-philosophy, bidi, bnumexpr, caption, chemfig, chemformula, chemmacros, cjk-gs-integrate, csplain, dantelogo, dataref, dtxgen, dvipdfmx-def, dvips, eledmac, elements, fcolumn, fithesis, fontspec, genealogytree, gradstudentresume, gtl, jfontmaps, knuth-local, koma-script, kotex-oblivoir, kotex-plain, kotex-utf, kpathsea, l3build, l3experimental, l3kernel, l3packages, latex, latexconfig, ledmac, ltxfileinfo, lualatex-math, luamplib, luatex, luatexbase, luatexja, luatexko, make4ht, mcf2graph, mflogo, modiagram, multiexpand, newtx, odsfile, old-arrows, paracol, pdfpages, pdftex, plain, pst-stru, pxchfon, randomwalk, reledmac, resumecls, rubik, selnolig, showhyphens, siunitx, suftesi, tetex, teubner, tex4ebook, tex4ht, texlive-scripts, tikzsymbols, tipfr, tools, tudscr, uassign, unicode-math, unravel, visualfaq, xepersian, xetex-def, xint. New packages archaeologie, ctablestack, dynamicnumber, exercises, fibeamer, h2020proposal, imfellenglish, lstbayes, tempora, xellipsis. Enjoy.

21 September 2015

Lunar: Reproducible builds: week 21 in Stretch cycle

If you see someone on the Debian ReproducibleBuilds project, buy him/her a beer. This work is awesome. What happened in the reproducible builds effort this week: Media coverage Nathan Willis covered our DebConf15 status update in Linux Weekly News. Access to non-LWN subscribers will be given on Thursday 24th. Linux Journal published a more general piece last Tuesday. Unexpected praise for reproducible builds appeared this week in the form of several iOS applications identified as including spyware. The malware was undetected by Apple screening. This actually happened because application developers had simply downloaded a trojaned version of XCode through an unofficial source. While reproducible builds can't really help users of non-free software, this is exactly the kind of attacks that we are trying to prevent in our systems. Toolchain fixes Niko Tyni wrote and uploaded a better patch for the source order problem in libmodule-build-perl. Tristan Seligmann identified how the code generated by python-cffi could be emitted in random order in some cases. Upstream has already fixed the problem. Packages fixed The following 24 packages became reproducible due to changes in their build dependencies: apache-curator, checkbox-ng, gant, gnome-clocks, hawtjni, jackrabbit, jersey1, libjsr305-java, mathjax-docs, mlpy, moap, octave-geometry, paste, pdf.js, pyinotify, pytango, python-asyncssh, python-mock, python-openid, python-repoze.who, shadow, swift, tcpwatch-httpproxy, transfig. The following packages became reproducible after getting fixed: Some uploads fixed some reproducibility issues but not all of them: Patches submitted which have not made their way to the archive yet: reproducible.debian.net Tests for Coreboot, OpenWrt, NetBSD, and FreeBSD now runs weekly (instead of monthly). diffoscope development Python 3 offers new features (namely yield from and concurrent.futures) that could help implement parallel processing. The clear separation of bytes and unicode strings is also likely to reduce encoding related issues. Mattia Rizolo thus kicked the effort of porting diffoscope to Python 3. tlsh was the only dependency missing a Python 3 module. This got quickly fixed by a new upload. The rest of the code has been moved to the point where only incompatibilities between Python 2.7 and Pyhon 3.4 had to be changed. The commit stream still require some cleanups but all tests are now passing under Python 3. Documentation update The documentation on how to assemble the weekly reports has been updated. (Lunar) The example on how to use SOURCE_DATE_EPOCH with CMake has been improved. (Ben Beockel, Daniel Kahn Gillmor) The solution for timestamps in man pages generated by Sphinx now uses SOURCE_DATE_EPOCH. (Mattia Rizzolo) Package reviews 45 reviews have been removed, 141 added and 62 updated this week. 67 new FTBFS reports have been filled by Chris Lamb, Niko Tyni, and Lisandro Dami n Nicanor P rez Meyer. New issues added this week: randomness_in_r_rdb_rds_databases, python-ply_compiled_parse_tables. Misc. The prebuilder script is now properly testing umask variations again. Santiago Villa started a discussion on debian-devel on how binNMUs would work for reproducible builds.

21 July 2015

Martin Michlmayr: Debian archive rebuild on ARM64 with GCC 5

I recently got access to several ProLiant m400 ARM64 servers at work. Since Debian is currently working on the migration to GCC 5, I thought it would be nice to rebuild the Debian archive on ARM64 to see if GCC 5 is ready. Fortunately, I found no obvious compiler errors. During the process, I noticed several areas where ARM64 support can be improved. First, a lot of packages failed to build due to missing dependencies. Some missing dependencies are libraries or tools that have not been ported to ARM64 yet, but the majority was due to the lack of popular programming languages on ARM64. This requires upstream porting work, which I'm sure is going on already in many cases. Second, over 160 packages failed to build due to out-of-date autoconf and libtool scripts. Most of these bugs have been reported over a year ago by the ARM64 porters (Matthias Klose from Canonical/Ubuntu and Wookey from ARM/Linaro) and the PowerPC porters, but unfortunately they haven't been fixed yet. Finally, I went through all packages that list specific architectures in debian/control and filed wishlist bugs on those that looked relevant to ARM64. This actually prompted some Debian and upstream developers to implement ARM64 support, which is great!

6 January 2015

Steve McIntyre: Bootstrapping arm64 in Debian

I promised to write about this a long time, ooops... :-) Another ARM port in Debian - yay! arm64 is officially a release architecture for Jessie, aka Debian version 8. That's taken a lot of manual porting and development effort over the last couple of years, and it's also taken a lot of CPU time - there are ~21,000 source packages in Debian Jessie! As is often the case for a brand new architecture like arm64 (or AArch64, to use ARM's own terminology), hardware can be really difficult to get hold of. In time this will cease to be an issue as hardware becomes more commoditised, but in Debian we really struggled to get hold of equipment for a very long time during the early part of the port. First bring-up in Debian Ports To start with, we could use ARM's own AArch64 software models to build the first few packages. This worked, but only very slowly. Then Chen Baozi and the folks running the Tianhe-2 supercomputer project in Guangzhou, China contacted us to offer access to some arm64 hardware, and this is what Wookey used for bootstrapping the new port in the unofficial Debian Ports archive. This has now become the normal way for new architectures to get into Debian. We got most of the archive built in debian-ports this way, and we could then use those results to seed the initial core set of packages in the main Debian archive. Second bring-up - moving into the main Debian archive By the time that first Debian bring-up was done, ARM was starting to produce its own "Juno" development boards, and with the help of my boss^4 James McNiven we managed to acquire a couple of those machines for use as official Debian build machines. The existing machines in China were faster, but for various reasons quite difficult to maintain as official Debian machines. So I set up the Junos as buildds just before going to DebConf in August 2014. They ran very well, and (for dev boards!) were very fast and stable. They built a large chunk of the Debian archive, but as the release freeze for Jessie grew close we weren't quite there. There was a small but persistent backlog of un-built packages that were causing us issues, plus the Juno machines are/were not quite suitable as porter boxes for Debian developers all over the world to use for debugging their packages on the new architecture. More horsepower - Linaro machines This is where Linaro came to our aid. Linaro's goal is to help improve Free and Open Source Software on ARM, and one of the more recent projects in Linaro is a cluster of servers that are made available for software developers to use to get early access to ARMv8 (arm64) hardware. It's a great way for people who are interested in this new architecture to try things out, port their software or indeed just help with the general porting effort. As Debian is seen as such an important part of the FLOSS ecosystem, we managed to negotiate dedicated access to three of the machines in that cluster for Debian's use and we set those up in October, shortly before the freeze for Jessie. Andy Doan spent a lot of his time getting these machines going for us, and then I set up two of them as build machines and one as the porter box we were still needing. With these extra machines available, we quickly caught up with the ever-busy "Needs-Build" queue and we've got sufficient build power now to keep things going for the Jessie release. We were officially added to the list of release architectures at the Cambridge mini-Debconf in November, and all is looking good now! And in the future? I've organised the loan of another arm64 machine from AMD for Debian to use for further porting and/or building. We're also expecting that more and more machines will be coming out soon as vendors move on from prototyping to producing real customer equipment. Once that's happened, more kit will be available and everybody will be able to have arm64-powered computers in the server room, on their desk and even inside their laptop! Mine will be running Debian Jessie... :-) Thanks! There's been a lot of people involved in the Debian arm64 bootstrapping at various stages, so many that I couldn't possibly credit them all! I'll highlight some, though. :-) First of all, Wookey's life has revolved around this port for the last few years, tirelessly porting, fixing and hacking out package builds to get us going. We've had loads of help from other teams in Debian, particularly the massive patience of the DSA folks with getting early machines up and running and the prodding of the ftpmaster, buildd and release teams when we've been grinding our way through ever more package builds and dependency loops. We've also had really good support from toolchain folks in Debian and ARM, fixing bugs as we've found them by stressing new code and new machines. We've had a number of other people helping by filing bugs and posting patches to help us get things built and working. And (last but not least!) thanks to all the folks who've helped us beg and borrow the hardware to make the Debian arm64 port a reality. Rumours of even more ARM ports coming soon are entirely scurrilous... *grin*

9 November 2014

Enrico Zini: fun-and-sanity

Fun and Sanity in Debian A friend of mine recently asked: "is there anything happening in Debian besides systemd?" Of course there is. He asked it 2 days after the freeze, which happened in time, and with an amazingly low RC bug count. The most visible thing right now seems to be this endless init system argument, but there are fun and sane things in Debian. Many of them. I think someone should put the spotlight on them, and here's my attempt. Yesterday I set up a gobby document asking "What is now happening in Debian that is exciting, fun and sane?", and passed the link around the Cambridge Miniconf and some IRC channels. Here are a few quotations that I collected:
The armhf and arm64 ports have for me been wonderful and exciting, and were a great time for me to start getting involved. (Jon "Aardvark" Ward) We have a way of tracking random contributors, and as far as I know no other project has anything like it. (Enrico Zini) codesearch.debian.net is an incredibly important resource, not just for us but for the free software community at large. (Ben Hutchings) sources.debian.net is a very useful resource with lots of interested contributors, it received 10 OPW applicants (Stefano Zacchiroli) It has never been easier to work on new infrastructure project thanks to the awesome work of the DSA team. We have dozens of contribution opportunities outside of just plain packaging. (Rapha l Hertzog) The work on reproducible builds has achieved excellent results with 61.3% of packages being reproducible. (Paul Wise) Porting arm64 has been (peversely) great fun. It's remarkably morish and I like nothing more than a tedious argument with autoconf macros. Working with lots of enthusiastic people from other teams, helping getting the port set up and build has been great - thank you everybody. (Wookey)
And here are random exciting things that were listed:

6 February 2014

Johannes Schauer: botch updates

My last update about ongoing development of botch, the bootstrap/build ordering tool chain, was three months ago with the announcement of bootstrap.debian.net. Since then a number of things happened, so I thought an update was due.

New graphs for port metrics By default, a dependency graph is created by arbitrarily choosing an installation set for binary package installation or source package compilation. Installation set vertices and source vertices are connected according to this arbitrary selection. Niels Thykier approached me at Debconf13 about the possibility of using this graph to create a metric which would be able to tell for each source package, how many other source packages would become uncompilable or how many binary packages would become uninstallable, if that source package was removed from the archive. This could help deciding about the importance of packages. More about this can be found at the thread on debian-devel. For botch, this meant that two new graph graphs can now be generated. Instead of picking an arbitrary installation set for compiling a source package or installing a binary package, botch can now create a minimum graph which is created by letting dose3 calculate strong dependencies and a maximum graph by using the dependency closure.

Build profile syntax in dpkg With dpkg 1.17.2 we now have experimental build profile support in unstable. The syntax which ended up being added was: 
Build-Depends: large (>= 1.0), small <!profile.stage1>
But until packages with that syntax can hit the archive, a few more tools need to understand the syntax. The patch we have for sbuild is very simple because sbuild relies on libdpkg for dependency parsing. We have a patch for apt too, but we have to rebase it for the current apt version and have to adapt it so that it works exactly like the functionality dpkg implements. But before we can do that we have to decide how to handle mixed positive and negative qualifiers or whether to remove this feature altogether because it causes too much confusion. The relevant thread on debian-dpkg starts here.

Update to latest dose3 git Botch heavily depends on libdose3 and unfortunately requires features which are only available in the current git HEAD. The latest version packaged in Debian is 3.1.3 from October 2012. Unfortunately the current dose3 git HEAD also relies on unreleased features from libcudf. On top of that, the GraphML output of the latest ocamlgraph version (1.8.3) is also broken and only fixed in the git. For now everything is set up as git submodules but this is the major blocker preventing any packaging of botch as a Debian package. Hopefully new releases will be done soon for all involved components.

Writing and reading GraphML Botch is a collection of several utilities which are connected together in a shell script. The advantage of this is, that one does not need to understand or hack the OCaml code to use botch for different purposes. In theory it also allows to insert 3rd party tools into a pipe to further modify the data. Until recently this ability was seriously hampered by the fact that many botch tools communicated with each other through marshaled OCaml binary files which prevent everything which is not written in OCaml from modifying them. The data that was passed around like this were the dependency graphs and I initially implemented it like that because I didnt want to write a GraphML parser. I now ended up writing an xmlm based GraphML parser so as of now, botch only reads and writes ASCII text files in XML (for the graphs) and in rfc822 packages format (for Packages and Sources files) which can both easily be modified by 3rd party tools. The ./tools directory contains many Python scripts using the networkx module to modify GraphML and the apt_pkg module to modify rfc822 files.

Splitting of tools To further increase the ability to modify program execution without having to know OCaml, I split up some big tools into multiple smaller ones. Some of the smaller tools are now even written in Python which is probably much more hackable for the general crowd. I converted those tools to Python which did not need any dose3 functionality and which were simple enough so that writing them didnt take much time. I could convert more tools but that might introduce bugs and takes time which I currently dont have much of (who does?).

Gzip instead of bz2 Since around January 14, snapshot.debian.org doesnt offer bzip2 compressed Packages and Sources files anymore but uses xz instead. This is awesome for must purposes but unfortunately I had to discover that there exist no OCaml bindings for libxz. Thus, botch is now using gzip instead of bz2 until either myself or anybody else finds some time to write a libxz OCaml binding.

Self hosting Fedora Paul Wise made me aware of Harald Hoyer's attempts to bootstrap Fedora. I reproduced his steps for the Debian dependency graph and it turns out that they are a little bit bigger. I'm exchanging emails with Harald Hoyer because it might not be too hard to use botch for rpm based distributions as well because dose3 supports rpm. The article also made me aware of the tred tool which is part of graphviz and allows to calculate the transitive reduction of a graph. This can help making horrible situations much better.

Dose3 bugs I planned to generate such simplified graphs for the neighborhood of each source package on bootstrap.debian.net but then binutils stopped building binutils-gold and instead provided binutils-gold while libc6-dev breaks binutils-gold (<< 2.20.1-11). This unfortunately triggered a dose3 bug and thus bootstrap.debian.net will not generate any new results until this is fixed in dose3. Another dose3 bug affects packages which Conflicts/Replaces/Provides:bar while bar is fully virtual and are Multi-Arch:same. Binaries of different architecture with this property can currently not be co-installed with dose3. Unfortunately linux-libc-dev has this property and thus botch cannot be used to analyze cross builds until that bug is fixed in dose3. I hope I get some free time soon to be able to look at these dose3 issues myself.

More documentation Since I started to like the current set of tools and how they work together I ended up writing over 2600 words of documentation in the past few days. You can start setting up and running botch by reading the first steps and get more detailed information by reading about the 28 tools that botch makes use of as of now. All existing articles, thesis and talks are linked from the wiki home.

17 August 2013

Daniel Pocock: DebConf13: breakthroughs in OTP and WebRTC

Saturday, 17 August was a day that saw groundbreaking new work revealed at DebConf13 and may have been a watershed moment in the emergence of WebRTC for the free software community.
Fabian Gr nbichler, Daniel Pocock, Catalin Constantin Usurelu, Emil Ivov, Yana Stamcheva Advancing the use of One Time Passwords with free software Google Summer of Code (GSoC) student Fabian Gr nbichler has spent the summer enhancing oath-toolkit and dynalogin to support a more diverse range of One Time Password schemes. dynalogin's original 1.0 release supports vanilla HOTP and TOTP authentication schemes. Fabian's work has extended the framework to support the more generic and powerful OCRA approach. To find out about all the benefits this brings, I would strongly encourage you to review his slides and video presentation, with a demo where it is explained thoroughly. While there are existing hardware tokens that support HOTP and TOTP using this open algorithm (Gooze has been kind enough to donate some which were on display), the mutual challenge-response schemes are yet to be widely supported in hardware and this means that Fabian's work is now at the cutting edge of development in this area. WebRTC: premium voice/video chat in modern browsers, no plugin required Another member of Debian's GSoC program, Catalin Constantin Usurelu helped organise and run one of the must-see sessions of DebConf13 (video available). In a demonstration that had all the hallmarks of a magic show, Catalin and I took random members of the audience and invited them to wave a magic wand over their web browsers and effortlessly turn them into Skype-busting softphones. As the grand finale, we took Wookey's blog and showed him how to add a WebRTC "call-me" page in less than 20 seconds, less time than it takes to hand over all your private data to the registration process of those rather uncomfortable alternatives. Anybody else seeking to duplicate this effort is encourage to review options like Drucall for Drupal or just directly use JsSIP Jitsi and the Jitsi Video-bridge The grand-finale of the DebConf13 real-time communications track was our guest speaker, Emil Ivov, founder of the Jitsi softphone project. Jitsi itself has recently been accepted into Debian and is easier than ever before to install and use. Emil's talk (video and slides available) went into some detail about the cutting edge development activities of his team, particularly the new Jitsi Video bridge Subsequent to the talk, we had some out-of-bands discussion about ways to potentially integrate Jitsi Video bridge with the open source dvswitch system used to produce streams and recordings from free software events such as DebConf and FOSDEM. It is hoped that this will provide an additional option for remote participation at free software events of all sizes. Upcoming events Emil and I have been invited to participate in the WebRTC Conference Paris 2013 in December. This will be an excellent opportunity to have further discussion about progress with WebRTC and do more to raise the compelling case for premium quality free software to meet the demanding needs of modern business communications. There are a series of talks for both technical and business-oriented audiences.

16 April 2013

Johannes Schauer: botch - the debian bootstrap software has a name

After nearly one year of development, the "Port bootstrap build-ordering tool" now finally has a name: botch. It stands for Bootstrap/Build Order Tool CHain. Now we dont have to call it "Port bootstrap build-ordering tool" anymore (nobody did that anyways) and also dont have to talk about it by referring to it as "the tools" in email, IRC or in my master thesis which is due in a few weeks. With this, the issue also doesnt block the creation of a Debian package anymore. Since only a handful of people have a clone of it anyway, I also renamed the gitorious git repository url (and updated all links in this blog and left a text file informing about the name change in the old location). The new url is: https://gitorious.org/debian-bootstrap/botch Further improvements since my last post in January include: In the mean time a paper about the theoretical aspects of this topic which Pietro Abate and I submitted to the CBSE 2013 conference got accepted (hurray!) and I will travel to the conference in Canada in June. Botch (yeey, I can call it by a name!) is also an integral part of one of the proposals for a Debian Google Summer of Code project this year, mentored by Wookey and co-mentored by myself. Lets hope it gets accepted and produces good results in the end of the summer!

13 March 2013

Ian Campbell: Linaro Connect Asia 2013

I've just got back from Linaro Connect Asia 2013 in Hong Kong. This was my first time back in Hong Kong since 1995 when I left after living there for 10 years. It was really interesting to see how much the place had changed, as well as how much it hadn't! I started the week by giving a talk together with Stefano Stabellini Introducing Xen on ARM to a full house. The slides can be found on the event page or google docs. There is a video on youtube but due to the cameras being setup for a fish-bowl style panel it is unfortunately mostly of my backside. The reception was excellent and the talk seeded a large number of hallway track conversations with all the many folks who are interested in Xen on the ARM platform. The day after our talk Lars Kurth (Xen.org community manager) and Mark Heath (VP of XenServer Engineering, and my boss) gave a keynote (video) announced Citrix's intention to join the Linaro Enterprise Group (AKA "LEG") on the 1st of April. This is pretty exciting for me since it means I'll get to work much more closely with the Linaro and ARM communities and spend even more of my time hacking on Xen on ARM! At some point Stefano and myself were also video interviewed by Charbax of http://armdevices.net/ but it doesn't appear to have gone online yet. Lars and Mark also gave interviews which are online already. One nice thing about Connect is that the afternoons are left free of talks so I managed to find time in the hackrooms to implement SMP host support and 64-bit domain 0 support for Xen on ARM as well as getting multiarch cross building working for upstream Xen with Wookey's kind assistance (no patches for this yet since I still need to clean them up). It was also useful to catch up with the ARM kernel developers and KVM guys to see what they are up to and share ideas etc. Finally right at the end Stefano and myself showed Xen on ARM at Demo Friday. We had Xen running on the Arndale Board, ARM Chromebook and 64-bit ARMv8 using the emulators (no hardware being available yet). All in all I had an excellent (if tiring) week, there was loads of interest in Xen on ARM and in Citrix joining LEG and everyone was very welcoming. I'm really looking forward to the next Connect in Dublin. Outside of Connect I managed to find time to visit Sham Shui Po at look at all the gadgets but managed to resist buying anything (Stefano got a Thinkpad X230, which was enough retail therapy for both of us!). I caught up with my sister (who lives there again), her boyfriend and my parents (who happened to be visiting her that week). I also managed have some drinks with some old school friends, most of whom I've not seen for nearly twenty years, but it was just like old times ;-). I'm off again to Hong Kong next week with my family to visit my sister (yes, there was some bad planning involved here...). This time I plan to do all the toursity type stuff that I never did while I lived there. I've also got tickets for the Hong Kong Rubgy Sevens and hopefully I'll manage catch up with some more old friends. I probably won't be able to resist buying gadgets this time around though.

1 February 2013

Johannes Schauer: Bootstrappable Debian FOSDEM talk

I will give a talk about the current status of automating Debian bootstrapping at FOSDEM 2013. There will also be a live demo of the developed toolchain. The talk will start 16:30 on Saturday, 2 February 2013 in room H.1302 as part of the Cross distro devroom track and will be half an hour long. Directly after my talk, at 17:00, Wookey will give his about bootstrapping Debian/Ubuntu for arm64 in the same location. The current version of the slides can be downloaded here. The latex beamer source is available in the git repository of the debian bootstrap project. If you can't make it to FOSDEM, then my last post about the topic gives away most of the things I will be talking about.

25 January 2013

Johannes Schauer: Bootstrappable Debian - New Milestone

This post is about the port bootstrap build ordering tool (naming suggestions welcome) which was started as a Debian Google Summer of Code project in 2012 and continued to be developed afterwards. Sources are available through gitorious. In the end of November 2012, I managed to put down an approximation algorithm to the feedback arc set problem which allowed to break the dependency graph into a directed acyclic graph with only few removed build dependencies. I wrote about this effort on our mailinglist but didnt mention it here because it was still too much of a proof-of-concept. Later, in January 2013, I mentioned the result of this algorithm in an email wookey and me wrote to debian-devel mailinglist. Many things happened since November 2012:

Processing pipeline instead of monolithic tools The tools I developed so far tried to accomplish everything by themselves, reusing functionality implemented in a central library. Therefor, if one wanted to try out even trivial new things, it mostly meant to hack some OCaml code. Pietro Abate suggested to instead develop smaller tools which could work independently of each other, would only execute one algorithm each and could easily be connected together in different ways to achieve different effects. This switch is now done and all functionality from the old tools is moved into a new toolset. The exchange format between the tools is either plain text files in deb822 control format (Packages/Sources files) or a dependency graph. The dependency graph is currently marshalled by OCaml but future versions should work with just passing a GraphML (an XML graph format) representation around. This new way of doing things seems close to the UNIX philosophy (each program does one thing well, data is stored as text, every program is a filter). For example the deb822 control output can easily be manipulated using grep-dctrl(1) and there exist many tools which can read, analyze and manipulate GraphML. It is a big improvement over the old, monolithic tools which did not allow to manipulate any intermediate result by external, existing tools. Currently, a shell script (native.sh) will execute all tools in a meaningful order, connecting them together correctly. The same tools will be used for a future cross.sh but they will be connected differently. I wrote about a first proposal of what the individual tools should do and how they should be connected in this email from which I also linked a confusing overview of the pipeline. This overview has recently been improved to be even more confusing and the current version of the lower half (the native part) now looks like this: native reduced Solid arrows represent a flow of binary packages, dottend arrows represent a flow of source packages, ovals represent a set of packages, boxes with rounded corners represent set operations, rectangular boxes represent filters. There is only one input to a filter, which is the arrow connected to the top of the box. Outgoing arrows from the bottom represent the filtered input. Ingoing arrows to either side are arguments to the filter and control how the filter behaves depending on the algorithm. I will explain this better once the pipeline proved to be less in flux. The pipeline is currently executed like this by native.sh.

Two new ways to break dependency cycles have been discovered So far, we knew of three ways to formally break dependency cycles:
  • remove build dependencies through build profiles
  • find out that the build dependency is only used to build arch:all packages and therefor put it into Build-Depends-Indep
  • cross compile some source packages
Two new methods can be added to the above:

Dependency graph definition changed Back in September when I was visiting irill, Pietro found a flaw in how the dependency graph used to be generated. He supplied a new definition of the dependency graph which does away with the problem he found. After fixing some small issues with his code, I changed all the existing algorithms to use the new graph definition. The old graph is as of today removed from the repository. Thanks to Pietro for supplying the new graph definition - I must still admit that my OCaml foo is not strong enough to have come up with his code.

Added complexity for profile built source packages As mentioned in the introduction, wookey and me addressed the debian-devel list with a proposal on necessary changes for an automated bootstrapping of Debian. During the discussiong, two important things came up which are to be considered by the dependency graph algorithms:
  • profile built source packages may not create all binary packages
  • profile built source packages may need additional build dependencies
Both things make it necessary to alter the dependency graph during the generation of a feedback arc set and feedback vertex set beyond the simple removal of edges. Luckily, the developed approximation algorithms can be extended to support such changes in the graph.

Different feedback arc set algorithms The initially developed feedback arc set algorithm is well suited to discover build dependency edges which should be dropped. It performs far worse when creating the final build order because it only considers edges by itself and not how many edges of a source package can be dropped by profile building it. The adjusted algorithm for generating a build order is more of a feedback vertex set algorithm because instead of greedily finding the edge with most cycles through it, it greedily finds the source package which would break most cycles if it was profile built.

Generating a build order with less profile built source packages After implementing all the features above I now feel more confident to publish the current status of the tools to a wider audience. The following test shows a run of the aforementioned ./native.sh shell script. Its final output is a list of source packages which have to be profile built and a build order. Using the resulting build order, starting from a minimal build system (essential:yes, build-essential and debhelper), all source packages will be compiled which are needed to compile all binary packages in the system. The result will therefor be a list of source and binary packages which fulfill the following property:
  • all binary packages can be built from the available source packages
  • all source packages can be built with the available binary packages
I called this a "reduceded distribution" in earlier posts. The interesting property of this specific selection is, that it contains the biggest problem set of Debian when bootstrapping it: a 900 to 1000 nodes big strongly connected component. Here is a visualization of the problem: hideous mess Source packages do not yet come with build profiles and the cross build situation can not yet be analyzed, so the following assumptions were made: The last point is about 14 build dependencies which were decided to be broken by the feedback arc set algorithm but for which other data sources did not indicate that they are actually breakable. Those 14 are dynamically generated by native.sh. If above assumptions should not be too far from the actual situation, then not more than 73 source packages have to be modified to bootstrap a reduced distribution. This reduced distribution even includes dependency-wise "big" packages like webkit, metacity, iceweasel, network-manager, tracker, gnome-panel, evolution-data-server, kde-runtime, libav and nautilus. By changing one line in native.sh one could easily develop a build order which generates gnome-desktop or really any given (meta-)package selection. All of native.sh takes only 80 seconds to execute on my system (Core i5, 2.5 GHz, singlethreaded). Here is the final build order which creates 2044 binary packages from 613 source packages.
  1. nspr, libio-pty-perl, libmcrypt, unzip, libdbi-perl, cdparanoia, libelf, c-ares, liblocale-gettext-perl, libibverbs, numactl, ilmbase, tbb, check, libogg, libatomic-ops, libnl($), orc($), libaio, tcl8.4, kmod, libgsm, lame, opencore-amr, tcl8.5, exuberant-ctags, mhash, libtext-iconv-perl, libutempter, pciutils, gperf, hspell, recode, tcp-wrappers, fdupes, chrpath, libbsd, zip, procps, wireless-tools, cpufrequtils, ed, libjpeg8, hesiod, pax, less, dietlibc, netkit-telnet, psmisc, docbook-to-man, libhtml-parser-perl, libonig, opensp($), libterm-size-perl, linux86, libxmltok, db-defaults, java-common, sharutils, libgpg-error, hardening-wrapper, cvsps, p11-kit, libyaml, diffstat, m4
  2. openexr, enca, help2man, speex, libvorbis, libid3tag, patch, openjade1.3, openjade, expat, fakeroot, libgcrypt11($), ustr, sysvinit, netcat, libirman, html2text, libmad, pth, clucene-core, libdaemon($), texinfo, popt, net-tools, tar, libsigsegv, gmp, patchutils($), dirac, cunit, bridge-utils, expect, libgc, nettle, elfutils, jade, bison
  3. sed, indent, findutils, fastjar, cpio, chicken, bzip2, aspell, realpath, dctrl-tools, rsync, ctdb, pkg-config($), libarchive, gpgme1.0, exempi, pump, re2c, klibc, gzip, gawk, flex-old, original-awk, mawk, libtasn1-3($), flex($), libtool
  4. libcap2, mksh, readline6, libcdio, libpipeline, libcroco, schroedinger, desktop-file-utils, eina, fribidi, libusb, binfmt-support, silgraphite2.0, atk1.0($), perl, gnutls26($), netcat-openbsd, ossp-uuid, gsl, libnfnetlink, sg3-utils, jbigkit, lua5.1, unixodbc, sqlite, wayland, radvd, open-iscsi, libpcap, linux-atm, gdbm, id3lib3.8.3, vo-aacenc, vo-amrwbenc, fam, faad2, hunspell, dpkg, tslib, libart-lgpl, libidl, dh-exec, giflib, openslp-dfsg, ppl($), xutils-dev, blcr, bc, time, libdatrie, libpthread-stubs, guile-1.8, libev, attr, libsigc++-2.0, pixman, libpng, libssh2, sqlite3, acpica-unix, acl, a52dec
  5. json-c, cloog-ppl, libverto, glibmm2.4, rtmpdump, libdbd-sqlite3-perl, nss, freetds, slang2, libpciaccess, iptables, e2fsprogs, libnetfilter-conntrack, bash, libthai, python2.6($), libice($), libpaper, libfontenc($), libxau, libxdmcp($), openldap($), cyrus-sasl2($), openssl, python2.7($)
  6. psutils, libevent, stunnel4, libnet-ssleay-perl, libffi, readline5, file, libvoikko, gamin, libieee1284, build-essential, libcap-ng($), lcms($), keyutils, libxml2, libxml++2.6, gcc-4.6($), binutils, dbus($), libsm($), libxslt, doxygen($)
  7. liblqr, rarian, xmlto, policykit-1($), libxml-parser-perl, tdb, devscripts, eet, libasyncns, libusbx, icu, linux, libmng, shadow, xmlstarlet, tidy, gavl, flac, dbus-glib($), libxcb, apr, krb5, alsa-lib
  8. usbutils, enchant, neon27, uw-imap, libsndfile, yasm, xcb-util, gconf($), shared-mime-info($), audiofile, ijs($), jbig2dec, libx11($)
  9. esound, freetype, libxkbfile, xvidcore, xcb-util-image, udev($), libxfixes, libxext($), libxt, libxrender
  10. tk8.4, startup-notification, libatasmart, fontconfig, libxp, libdmx, libvdpau, libdrm, libxres, directfb, libxv, libxxf86dga, libxxf86vm, pcsc-lite, libxss, libxcomposite, libxcursor, libxdamage, libxi($), libxinerama, libxrandr, libxmu($), libxpm, libxfont($)
  11. xfonts-utils, libxvmc, xauth, libxtst($), libxaw($)
  12. pmake, corosync, x11-xserver-utils, x11-xkb-utils, coreutils, xft, nas, cairo
  13. libedit, cairomm, tk8.5, openais, pango1.0($)
  14. ocaml, blt, ruby1.8, firebird2.5, heimdal, lvm2($)
  15. cvs($), python-stdlib-extensions, parted, llvm-2.9, ruby1.9.1, findlib, qt4-x11($)
  16. xen, mesa, audit($), avahi($)
  17. x11-utils, xorg-server, freeglut, libva
  18. jasper, tiff3, python3.2($)
  19. openjpeg, qt-assistant-compat, v4l-utils, qca2, jinja2, markupsafe, lcms2, sip4, imlib2, netpbm-free, cracklib2, cups($), postgresql-9.1
  20. py3cairo, pycairo, pam, libgnomecups, gobject-introspection($)
  21. gdk-pixbuf, libgnomeprint, gnome-menus, gsettings-desktop-schemas, pangomm, consolekit, vala-0.16($), colord($), atkmm1.6
  22. libgee, gtk+3.0($), gtk+2.0($)
  23. gtkmm2.4, poppler($), openssh, libglade2, libiodbc2, gcr($), libwmf, systemd($), gcj-4.7, java-atk-wrapper($)
  24. torque, ecj($), vala-0.14, gnome-keyring($), gcc-defaults, gnome-vfs($)
  25. libidn, libgnome-keyring($), openmpi
  26. mpi-defaults, dnsmasq, wget, lynx-cur, ghostscript, curl
  27. fftw3, gnupg, libquvi, xmlrpc-c, raptor, liboauth, groff, fftw, boost1.49, apt
  28. boost-defaults, libsamplerate, cmake, python-apt
  29. qjson, qtzeitgeist, libssh, qimageblitz, pkg-kde-tools, libical, dwarves-dfsg, automoc, attica, yajl, source-highlight, pygobject, pygobject-2, mysql-5.5($)
  30. libdbd-mysql-perl, polkit-qt-1, libdbusmenu-qt, raptor2, dbus-python, apr-util
  31. rasqal, serf, subversion($), apache2
  32. git, redland
  33. xz-utils, util-linux, rpm, man-db, make-dfsg, libvisual, cryptsetup, libgd2, gstreamer0.10
  34. mscgen, texlive-bin
  35. dvipng, luatex
  36. libconfig, transfig, augeas, blas, libcaca, autogen, libdbi, linuxdoc-tools, gdb, gpm
  37. ncurses, python-numpy($), rrdtool, w3m, iproute, gcc-4.7, libtheora($), gcc-4.4
  38. libraw1394, base-passwd, lm-sensors, netcf, eglibc, gst-plugins-base0.10
  39. libiec61883, qtwebkit, libvirt, libdc1394-22, net-snmp, jack-audio-connection-kit($), bluez
  40. redhat-cluster, gvfs($), pulseaudio($)
  41. phonon, libsdl1.2, openjdk-6($)
  42. phonon-backend-gstreamer($), gettext, libbluray, db, swi-prolog, qdbm, swig2.0($)
  43. highlight, libselinux, talloc, libhdate, libftdi, libplist, python-qt4, libprelude, libsemanage, php5
  44. samba, usbmuxd, libvpx, lirc, bsdmainutils, libiptcdata, libgtop2, libgsf, telepathy-glib, libwnck3, libnotify, libunique3, gnome-desktop3, gmime, glib2.0, json-glib, libgnomecanvas, libcanberra, orbit2, udisks, d-conf, libgusb
  45. libgnomeprintui, libimobiledevice, nautilus($), libbonobo, librsvg
  46. evas, wxwidgets2.8, upower, gnome-disk-utility, libgnome
  47. ecore, libbonoboui
  48. libgnomeui
  49. graphviz
  50. exiv2, libexif, lapack, soprano, libnl3, dbus-c++
  51. atlas, libffado, graphicsmagick, libgphoto2, network-manager
  52. pygtk, jackd2, sane-backends, djvulibre
  53. libav($), gpac($), ntrack, python-imaging, imagemagick, dia
  54. x264($), matplotlib, iceweasel
  55. strigi, opencv, libproxy($), ffms2
  56. kde4libs, frei0r, glib-networking
  57. kde-baseapps, kate, libsoup2.4
  58. geoclue, kde-runtime, totem-pl-parser, libgweather, librest, libgdata
  59. webkit
  60. zenity, gnome-online-accounts
  61. metacity, evolution-data-server
  62. gnome-panel
  63. tracker
The final recompilation of profile built source packages is omitted. Source packages marked with a ($) are selected to be profile built. All source packages listed in the same line can be built in parallel as they do not depend upon each other. This order looks convincing as it first compiles a multitude of source packages which have no or only few build dependencies lacking. Later steps allow fewer source packages to be compiled in parallel. The amount of needed build dependencies is highest in the source packages that are built last.

6 January 2013

Neil Williams: bootstrapping arm64

I'm still working on perl-cross-debian (just uploaded 0.0.2) and there's more to do on that with upstream but part of the reason to work on perl cross-building is to do what I can to help with the ARM64 port.

So, I went back to Wookey's talk at DebConf12 which leads to the current list of cross-build results for arm64 and started through the list.

coreutils is listed as failing but that was an archive error (MD5sum hash mismatch), so that just needs a retry. I don't have access to that buildd, yet, so nothing I can do there.

Next on the list (excluding those just waiting for build-deps) was klibc. 


  aarch64-linux-gnu-gcc -Wp,-MD,usr/klibc/.__static_init.o.d  -nostdinc -iwithprefix 

include -I/ PKGBUILDDIR /usr/include/arch/x86_64 -Iusr/include/arch/x86_64 

-I/ PKGBUILDDIR /usr/include/bits64 

-Iusr/include/bits64 -I/ PKGBUILDDIR /usr/klibc/../include 

-Iusr/klibc/../include -I/ PKGBUILDDIR /usr/include -Iusr/include 

-I/ PKGBUILDDIR /linux/include -Ilinux/include 

-I/ PKGBUILDDIR /linux/arch/x86/include -Ilinux/arch/x86/include 

-D__KLIBC__=2 -D__KLIBC_MINOR__=0 -D_BITSIZE=64 -fno-stack-protector -fwrapv -m64 -Os 

-fno-asynchronous-unwind-tables -fomit-frame-pointer -falign-functions=1 -falign-jumps=1 -falign-loops=1 

-W -Wall -Wno-sign-compare -Wno-unused-parameter -c -o usr/klibc/__static_init.o usr/klibc/__static_init.c

aarch64-linux-gnu-gcc: error: unrecognized command line option '-m64'

make[4]: *** [usr/klibc/__static_init.o] Error 1


Turns out that this is a build failure I understood, at least initially. A little digging and a trivial patch was begun:


--- a/usr/klibc/arch/arm/MCONFIG

+++ b/usr/klibc/arch/arm/MCONFIG

@@ -30,6 +30,13 @@

 ifeq ($(CONFIG_AEABI),y)

 KLIBCREQFLAGS += -mabi=aapcs-linux -mno-thumb-interwork

 else

+# aarch64

+ifeq ($(CONFIG_AARCH64),y)

+KLIBCREQFLAGS +=

+KLIBCOPTFLAGS += -mgeneral-regs-only

+else

 KLIBCREQFLAGS += -mabi=apcs-gnu -mno-thumb-interwork

 endif

 endif

+endif

+

Alongside a trivial change to debian/rules


ifeq ($(DEB_HOST_ARCH),arm64)

DEB_MAKE_ENVVARS := ARCH=arm CONFIG_AARCH64=y CPU_ARCH=armv8-a CPU_TUNE=generic

endif

OK, then things get a bit more awkward, 


....

code/debian/cross/klibc/klibc-2.0.1/linux/arch/arm/include -Ilinux/arch/arm/include -D__KLIBC__=2 

-D__KLIBC_MINOR__=0 -D_BITSIZE=32 -fno-stack-protector -fwrapv -fno-exceptions -Os 

-march=armv8-a -mtune=generic -mgeneral-regs-only -W -Wall -Wno-sign-compare -Wno-unused-parameter 

-c -o ../foo.o usr/klibc/arch/arm/crt0.S

usr/klibc/arch/arm/crt0.S: Assembler messages:

usr/klibc/arch/arm/crt0.S:19: Error: operand 1 should be an integer register --  mov r0,sp'

usr/klibc/arch/arm/crt0.S:20: Error: operand 1 should be an integer register --  mov r1,#0'

Hmm. Assembly, well, yes, I've done assembly before, I know what mov should normally do, sp is likely to be the stack pointer .... where's my AARCH64 assembly PDF again... PRD03-GENC-010197 ...

OK, so maybe the r0 and r1 should be x0 and x1, hmm, that at least doesn't raise assembly errors. So a tentative change:


--- a/usr/klibc/arch/arm/crt0.S

+++ b/usr/klibc/arch/arm/crt0.S

@@ -15,9 +15,13 @@

 #ifdef __thumb__

 	.thumb_func

 #endif

-

+#ifdef __aarch64__

+_start: mov x0, sp

+	mov x1, #0

+	bl __libc_init

+#else

 _start:	mov	r0, sp

 	mov	r1, #0

 	bl	__libc_init

-

+#endif

 	.size _start,.-_start

Next stage, however, leaves me quite a bit more lost:


....

klibc-2.0.1/linux/arch/arm/include -Ilinux/arch/arm/include 

-D__KLIBC__=2 -D__KLIBC_MINOR__=0 -D_BITSIZE=32 -fno-stack-protector -fwrapv -fno-exceptions -Os 

-march=armv8-a -mtune=generic -mgeneral-regs-only -W -Wall -Wno-sign-compare -Wno-unused-parameter 

-c -o usr/klibc/arch/arm/setjmp.o usr/klibc/arch/arm/setjmp.S

usr/klibc/arch/arm/setjmp.S: Assembler messages:

usr/klibc/arch/arm/setjmp.S:32: Error: unknown mnemonic  stmia' --  stmia r0, r4,r5,r6,r7,r8,r9,r10,fp,sp,lr '

usr/klibc/arch/arm/setjmp.S:33: Error: operand 1 should be an integer register --  mov r0,#0'

usr/klibc/arch/arm/setjmp.S:34: Error: operand 1 should be an integer register --  mov pc,lr'

usr/klibc/arch/arm/setjmp.S:42: Error: unknown mnemonic  ldmia' --  ldmia r0, r4,r5,r6,r7,r8,r9,r10,fp,sp,lr '

usr/klibc/arch/arm/setjmp.S:43: Error: unknown mnemonic  movs' --  movs r0,r1'

usr/klibc/arch/arm/setjmp.S:44: Error: unknown mnemonic  moveq' --  moveq r0,#1'

usr/klibc/arch/arm/setjmp.S:45: Error: operand 1 should be an integer register --  mov pc,lr'

make[5]: *** [usr/klibc/arch/arm/setjmp.o] Error 1


So now I'm out of my depth of AARCH64 assembly (apart from the recurrence of mov r0 vs mov x0 etc.). If the above is useful then maybe someone can work out what is wrong with setjmp.S or whether AARCH64 just means that klibc needs to gain a arch/arm64/ directory and not try to duplicate each entire assembly block within #ifdef clauses.

I don't really know where else to put an incomplete investigation like this, so it's here for anyone to find.

(Oh, and if you're reading those arm64 cross-build logs, then a few hundred occurrences of ldconfig: /usr/lib/aarch64-linux-gnu/*.so is for unknown machine 183. in every build log (success or fail) is apparently entirely normal until more packages get fixed. Really slows down scanning the build log. :-(

I may try busybox or libusb next. libusb looks like a classic "you might have told me to cross-compile but I'm going to use g++ anyway because I know best" cross-building problem, indicative of yet another BDBS. sigh.

Resources:
Getting started with 64-bit ARM development
ARMv8 images for developers
AArch64 for everyone, Marcin Juszkiewicz
Howto/HelloAarch64 - Linaro wiki
AArch64 gcc options

25 November 2012

Pietro Abate: Mini Debian Conf 2012 in Paris : Bootstrapping Debian for a new architecture

I just finished to address the awesome debian crowd at the Mini Deb conf in paris. My presentation was about a few challenges we have ahead to bootstrap debian on a new architecture. Johannes Schauer and Wookey did a lot of work in the last few months particularly focusing on Linaro/Ubuntu. After Wheezy I think it is important to catch up with their work and integrate it in debian. The two main take away messages from my presentation : This week we just reached an important milestone toward a fully automatic bootstrap procedure. Hopefully we are going to tell you more about this work during fosdem 2013 My slides are attached.
AttachmentSize
debminiconf2012.pdf271.56 KB

18 November 2012

Neil Williams: Long term maintenance of perl cross-build support in Debian

After prompts from Wookey and Steve McIntyre, I decided to look at #285559 and #633884 for perl cross-build support and then port that support forward to the current perl in Wheezy and on to the version of perl currently in experimental. The first patch is for perl 5.8, the second for perl 5.12, neither of which is available currently in Debian. snapshot.debian.org provided the 5.12 source but then that no longer cross-builds with the patch.

The problem, as with any cross build, is that the build must avoid trying to execute binaries compiled within the build to achieve the test results required by ./configure (or in the case of perl, Configure). dpkg-cross has one collection of cache values but the intention was always to migrate the package-specific support data into the packages themselves and keep the architecture-specific data in dpkg-cross or dpkg-dev. Therefore, the approach taken in #633884 would be correct, if only there was a way of ensuring that the cached values remain in sync with the relevant Debian package.

I'll note here that I am aware of other ways of cross-building perl, this is particularly concerned with cross-building the Debian configuration of perl as a Debian package and using Debian or Emdebian cross-compilers. After all, the objective is to support bootstrapping Debian onto new architectures. However, I fully expect this to be just as usable with Ubuntu packages of perl compiled with, e.g. Linaro cross-compilers but I haven't yet looked at the differences between perl in Debian vs Ubuntu in any detail.

I've just got perl 5.14.2 cross-building for armel using the Emdebian gcc-4.4 cross-compiler (4.4.5-8) on a Debian sid amd64 machine without errors (it needs testing, which I'll look at later), so now is the time to document how it is done and what needs to be fixed. I've already discussed part of this with the current perl maintainers in Debian and, subject to just how the update mechanism works, have outline approval for pushing these changes into the Debian package and working with upstream where appropriate. The cache data itself might live in a separate source package which will use a strict dependency on perl to ensure that it remains in sync with the version which it can cross-build. Alternatively, if I can correctly partition the cache data between architecture-specific (and therefore generated from the existing files) and package_$version specific, then it may be possible to push a much smaller patch into the Debian perl package. This would start with some common data, calculate the arch-specific data and then look for some version-specific data, gleaned from Debian porter boxes whilst the version is in Debian experimental.

The key point is that I've offered to provide this support for the long term, ensuring that we don't end up with future stable releases of Debian having a perl package which cannot be cross-built. (To achieve that, we will also end up with versions of perl in Debian testing which also cross-build.)

This cross-build is still using dpkg-cross paths, not MultiArch paths, and this will need to be changed eventually. (e.g. by the source package providing two binaries, one which uses MultiArch and one which expects dpkg-cross paths.) The changes include patches for the upstream Makefile.SH, debian/rules and the cache data itself. Depending on where the cache data finally lives, the new support might or might not use the upstream Cross/ directory as the current contents date from the Zaurus support and don't appear to be that useful for current versions of perl.

The cache data itself has several problems:

  1. It is tightly tied to the version of perl which generated it.

  2. It is, as expected, architecture-dependent

  3. It is, unfortunately, very sensitive to the specific configuration used by the distribution itself


That last point is important because it means that the cache data is not useful upstream as a block. It also means that generating the cache data for a specific Debian package means running the generation code on the native architecture with all of the Debian build-dependencies installed for the full perl build. This is going to complicate the use of this method for new architectures like arm64.

My objective for the long term maintenance of this code is to create sufficient data that a new architecture can be bootstrapped by judicious use of some form of template. Quite how that works out, only time will tell. I expect that this will involve isolating the data which is truly architecture-specific which doesn't change between perl versions from the data which is related to the tests for build-dependencies which does change between perl versions and then work out how to deal with any remainder. A new architecture for a specific perl version should then just be a case of populating the arch-specific data such as the size of a pointer/char and the format specifiers for long long etc. alongside the existing (and correct) data for the current version of perl.

Generating the cache data natively

The perl build repeats twice (three builds in total) and each build provides and requires slightly different cache data - static, debug and shared. Therefore, the maintenance code will need to provide a script which can run the correct configuration step for each mode, copy out the cache data for each one and clean up. The script will need to run inside a buildd chroot on a porter box (I'm looking at using abel.debian.org and harris.debian.org for this work so far) so that the derived data matches what the corresponding Debian native build would use. The data then needs slight modification - typically to replace the absolute paths with PERL_BUILD_DIR. It may also be necessary to change the value of cc, ranlib and other compiler-related values to the relevant cross-compiler executables. That should be possible to arrange within the build of the cache data support package itself, allowing new cache files to be dropped in directly from the porter box.

The configuration step may need to be optimised within debian/rules of perl itself as it currently proceeds on from the bare configuration to do some actual building but I need to compare the data to see if a bare config is modified later. The test step can be omitted already. Each step is performed as:


DEB_BUILD_OPTIONS="nocheck" fakeroot debian/rules perl.static


That is repeated for perl.debug and libperl.so.$(VERSION) where $VERSION comes from :


/bin/bash debian/config.debian --full-version


The files to be copied out are:


There is a lot of scope for templating of some form here, e.g. config.h.debug is 4,686 lines long but only 41 of those lines differ between amd64 and armhf for the same version of perl (and some of those can be identified from existing architecture-specific constants) which should make for a much smaller patch.

Architecture-specific cache data for perl

So far, the existing patches only deal with armel and armhf. If I compare the differences between armel & armhf, it comes down to:

  1. compiler names (config.h.*)

  2. architecture names (config.sh.*)

  3. architecture-based paths (config.sh.*)


However, comparing armel and armhf doesn't provide sufficient info for deriving arm64 or mips etc. Comparing the same versions for armhf and amd64 shows the range of differences more clearly. Typical architecture differences exist like the size of a long, flags to denote if the compiler can cast negative floats to 32bit ints and the sprintf format specifier strings for handling floats and doubles. The data also includes some less expected ones like:


armhf: #define Netdb_host_t		const void * /**/

amd64: #define Netdb_host_t		char * /**/


I'm not at all sure why that is arch-specific - if anyone knows, email codehelp @ d.o - same address if anyone fancies helping out ....

Cross-builds and debclean

When playing with the cross-build, remember to use the cross-build clean support, not just debclean:



dpkg-architecture -aarmel -c fakeroot debian/rules clean


That wasted quite a bit of my time initially with having to blow away the entire tree, unpack it from original apt sources and repatch it. (Once Wheezy is out, may actually investigate getting debclean to support the -a switch).

OK, that's an introduction, I'm planning on pushing the cross-build support code onto github soon-ish and doing some testing of the cross-built perl binaries in a chroot on an armel box. I'll detail that in another blog post when it's available.

Next step is to look at perl 5.16 and then current perl upstream git to see how to get Makefile.SH fixed for the long term.

8 August 2012

Johannes Schauer: Bootstrappable Debian - How to help

TLDR: multiarch, multiarch, multiarch, cross buildability, staged build dependencies, wiki page, corrections/hints/requests to debian-bootstrap at lists.mister-muffin.de This summer (and this year's GSoC) is nearing its end and to make it easier for people to make use of the information my tools produced so far, I created a page in the Debian wiki. It lists not only the open issues I see but also statistics that I gathered using the output of my GSoC project. I want to use this blog post to make people aware of that page as well as to get some feedback on it and anything related to it. The biggest blocker my tools face, is that many packages are still missing multiarch information. As long as at least the basic packages do not have their cross build dependencies satisfied via multiarch for an existing foreign architecture, automated tools can not properly analyze the dependency situation in the bootstrapping case, when many packages of the new foreign architecture do not even exist yet. If Debian is supposed to be bootstrappable, then the first stage is to make a set of basic packages cross compile for an existing foreign architecture. Once this is possible, a tool of mine can analyze the cyclic build dependency situation that might occur when cross compiling for an architecture that does not exist yet. Then, staged cross builds can be used to cross compile a minimal foreign system. Due to missing multiarch classification, it is not known yet how big the cyclic build dependency situation is for the base packages. It is not only the conversion of packages to multiarch that is needed but also the adding of the :any (and rare cases :native) qualifier to build dependencies on M-A: allowed packages. Prominent build dependencies that should (but are not yet) be M-A: allowed are python and gettext. Both are needed as a build dependency by many packages of the base system. Unfortunately wanna-build does not understand qualifiers like :any and :native yet. Until it does, no package can be marked :any or :native and cross compilation of many base packages can not succeed. Once the point is reached, where a base system can be cross compiled from nothing, native compilation can start. Since native compilation doesnt depend on multiarch, the dependency situation when trying to natively compiling all of Debian from nothing is understood much better. Unfortunately, the cyclic build dependency situation is also much worse in the native case and there exists a big 1000 node strongly connected component of binary and source packages that all interdepend on each other. This dependency mess can be solved using three approaches: The wiki page gives many hints on how to find packages that each method can be applied to. Stage building is a tool that might be useful for cross building (we dont know for sure yet) but is definitely needed for native compilation. It is needed for native compilation because after all possible dependencies are moved to Build-Depends-Indep, the only other alternative to stage building for breaking dependency cycles is to cross build source packages. Since building a package without one of its build dependencies "staged" is often much easier than making the package in question cross compile, it is a preferred alternative. Once more packages have been made multiarch, it might be possible to prove that there is no alternative to introducing a notion of staged builds. Some people (wookey, Patrick McDermott, Guillem Jover, myself) decided that the following format to mark staged build dependencies would be preferred over others: 
Build-Depends: huge (>= 1.0) [i386 arm] <!embedded !bootstrap>, tiny
The <> format was proposed by Guillem Jover in bug#661538. Patches for dpkg and dose3 are done. More people need to discuss about this format for a final decision on how to indicate staged build dependencies. For more information on the topic, have a look at the corresponding wiki page. Feel free to direct any comments/critique/hints to debian-bootstrap at lists.mister-muffin.de or directly to me.

30 July 2012

Johannes Schauer: port bootstrap build-ordering tool report 4

A copy of this post is sent to soc-coordination@lists.alioth.debian.org as well as to debian-bootstrap@lists.mister-muffin.de.

Diary

July 2
  • playing around with syntactic dependency graphs and how to use them to flatten dependencies

July 4
  • make work with dose 3.0.2
  • add linux-amd64 to source architectures
  • remove printing in build_compile_rounds
  • catch Not_found exception and print warning
  • use the whole installation set in crosseverything.ml instead of flattened dependencies
  • detect infinite loop and quit in crosseverything.ml
  • use globbing in _tags file
  • use wildcards and patsubst in makefile

July 5
  • throw a warning if there exist binary packages without source packages
  • add string_of_list and string_of_pkglist and adapt print_pkg_list and print_pkg_list_full to use them
  • fix and extend flatten_deps - now also tested with Debian Sid

July 6
  • do not exclude the crosscompiled packages from being compiled in crosseverything.ml
  • clean up basebuildsystem.ml, remove old code, use BootstrapCommon code
  • clean up basenocycles.ml, remove unused code and commented out code
  • add option to print statistics about the generated dependency graph
  • implement most_needed_fast_wrong as well as most_needed_slow_correct and make both available through the menu

July 7
  • allow to investigate all scc, not only the full graph and the scc containing the investigated package
  • handle Not_found in src_list_from_bin_list with warning message
  • handle the event of the whole archive actually being buildable
  • replace raise Failure with failwith
  • handle incorrectly typed package names
  • add first version of reduced_dist.ml to create a self-contained mini distribution out of a big one

July 8
  • add script to quickly check for binary packages without source package
  • make Debian Sid default in makefile
  • add *.d.byte files to .gitignore
  • README is helpful now
  • more pattern matching and recursiveness everywhere

July 9
  • fix termination condition of reduced_dist.ml
  • have precise as default ubuntu distribution
  • do not allow to investigate an already installable package

July 10
  • milestone: show all cycles in a graph
  • add copyright info (LGPL3+)

July 11
  • advice to use dose tools in README

July 16
  • write apt_pkg based python filter script replacing grep-dctrl

July 17
  • use Depsolver.listcheck more often
  • add dist_graph.ml
  • refactor dependency graph code into its own module

July 18
  • improve package selection for reduced_dist.ml
  • improve performance of cycle enumeration code

July 20
  • implement buildprofile support into dose3

July 22
  • let dist_graph.ml use commandline arguments

July 23
  • allow dose3 to generate source package lists without Build- Depends Conflicts -Indep

July 29
  • implement crosscompile support into dose3

Results

Readme There is not yet a writeup on how everything works and how all the pieces of the code work together but the current README file provides a short introduction on how to use the tools.
  • build and runtime dependencies
  • compile instructions
  • execution examples for each program
  • step by step guide how to analyze the dependency situation
  • explanation of general commandline options
A detailed writeup about the inner workings of everything will be part of a final documentation stage.

License All my code is now released under the terms of the LGPL either version 3, or (at your option) any later version. A special linking exception is made to the license which can be read at the top of the provided COPYING file. The exception is necessary because Ocaml links statically, which means that without that exception, the conditions of distribution would basically equal GPL3+.

reduced_dist.ml Especially the Debian archive is huge and one might want to work on a reduced selection of packages first. Having a smaller selection of the archive would be significantly faster and would also not add thousands of packages that are not important for an extended base system. I call a reduced distribution a set of source packages A and a set of binary packages B which fulfill the following three properties:
  • all source packages A must be buildable with only binary packages B being available
  • all binary packages B except for architecture:all packages must be buildable from source packages A
The set of binary packages B and source packages A can be retrieved using the reduced_dist program. It allows to either build the most minimal reduced distribution or one that includes a certain package selection. To filter out the package control stanzas for a reduced distribution from a full distribution, I originally used a call to grep-dctrl but later replaced that by a custom python script called filter-packages.py. This script uses python-apt to filter Packages and Sources files for a certain package selection.

dist_graph.ml It soon became obvious that there were not many independent dependency cycle situation but just one big scc that would contain 96% of the packages that are involved in build dependency cycles. Therefor it made sense to write a program that does not iteratively build the dependency graph starting from a single package, but which builds a dependency graph for a whole archive.

Cycles I can now enumerate all cycles in the dependency graph. I covered the theoretical part in another blog post and wrote an email about the achievement to the list. Both resources contain more links to the respective sourcecode. The dependency graph generated for Debian Sid has 39486 vertices. It has only one central scc with 1027 vertices and only eight other scc with 2 to 7 vertices. All the other source and binary packages in the dependency graph for the archive are degenerate components of length one. Obtaining the attached result took 4 hours on my machine (Core i5 @ 2.53GHz). 1.5 h of that were needed to build the dependency graph, the other 2.5 hours were needed to run johnson's algorithm on the result. Memory consumption of the program was at about 700 MB. It is to my joy that apparently the runtime of the cycle finding algorithm for a whole Debian Sid repository as well as the memory requirements are within orders of magnitude that are justifiable when being run on off-the-shelf hardware. It must also be noted that nothing is optimized for performance yet. A list of all cycles in Debian Sid up to length 4 can be retrieved from this email. This cycle analysis assumes that only essential packages, build-essential and dependencies and debhelper are available. Debhelper is not an essential or build-essential package but 79% of the archive build-depends on it. The most interesting cycles are probably those of length 2 that need packages that they build themselves. Noticeable examples for these situations are vala, python, mlton, fpc, sbcl and ghc. Languages seem love to need themselves to be built.

Buildprofiles There is a long discussion of how to encode staged build dependency information in source packages. While the initial idea was to use Build-Depends-StageN fields, this solution would duplicate large parts of the Build-Depends field, which leads to bitrot as well as it is inflexible to possible other build "profiles". To remedy the situation it was proposed to use field names like Build-Depends[stage1 embedded] but this would also duplicate information and would break with the rfc822 format of package description files. A document maintained by Guillem Jover gives even more ideas and details. Internally, Patrick and me decided for another idea of Guillem Jover to annotate staged build dependencies. The format reads like: 
Build-Depends: huge (>= 1.0) [i386 arm] <!embedded !bootstrap>, tiny
So each build profile would follow a dependency in <> "brackets" an have a similar format as architecture options. Patrick has a patch for dpkg that implements this functionality while I patched dose3.

Dropping Build-Depends-Indep and Build-Conflicts-Indep When representing the dependencies of a source package, dose3 concatenates its Build-Depends and Build-Depends-Indep dependency information. So up to now, a source package could only be compiled, if it manages to compile all of its binary packages including architecture:all packages. But when bootstrapping a new architecture, it should be sufficient to only build the architecture dependent packages and therefor to only build the build-arch target in debian/rules and not the build-indep target. Only considering the Build-Depends field and dismissing the Build-Depends-Indep field, reduced the main scc from 1027 vertices to 979 vertices. The amount of cycles up to length four reduced from 276 to 206. Especially the cycles containing gtk-doc-tools, doxygen, debiandoc-sgml and texlive-latex-base got much less. Patrick managed to add a Build-Depends-Indep field to four packages so far which reduced the scc further by 14 vertices down to 965 vertices. So besides staged build dependencies and cross building there is now a third method that can be applied to break dependency cycles: add Build-Depends-Indep information to them or update existing information. I submitted a list of packages that have a binary-indep and/or a build-indep target in their debian/rules to the list. I also submitted a patch for dose3 to be able to specify to ignore Build-Depends-Indep and Build-Conflicts-Indep information.

Dose3 crossbuilding So far I only looked at dependency situations in the native case. While the native case contains a huge scc of about 1000 packages, the dependency situation will be much nicer when cross building. But dose3 was so far not able to simulate cross building of source packages. I wrote a patch that implements this functionality and will allow me to write programs that help analyze the cross-situation as well.

Debconf Presentation Wookey was giving a talk at debconf12 for which I was supplying him with slides. The slides in their final version can be downloaded here

Future Patrick maintains a list of "weak" build dependencies. Those are dependencies that are very likely to be droppable in either a staged build or using Build-Depends-Indep. I must make use of this list to make it easier to find packages that can easily be removed of their dependencies. I will have to implement support for resolving the main scc using staged build dependencies. Since it is unlikely that Patrick will be fast enough in supplying me with modified packages, I will need to create myself a database of dummy packages. Another open task is to allow to analyze the crossbuilding dependency situation. What I'm currently more or less waiting on is the inclusion of my patches into dose3 as well as a decision on the buildprofile format. More people need to discuss about it until it can be included into tools as well as policy. Every maintainer of a package can help making bootstrapping easier by making sure that as many dependencies as possible are part of the Build-Depends-Indep field.

2 July 2012

Johannes Schauer: port bootstrap build-ordering tool report 3

A copy of this post is sent to soc-coordination@lists.alioth.debian.org as well as to debian-bootstrap@lists.mister-muffin.de.

Diary

June 18 Pietro suggests a faster way to generate installation sets for a list of packages. In my case, I need an installation set for every source package in the archive to find out how often a binary package is needed to build a source package. As a result, the speed is doubled in contrast to the original approach.

June 19
  • adapt code to work with new dose release 3.0
  • remove unneeded parts of code
  • add different possibilities to find amount of source packages that need a binary package
  • add code to get multiple installation sets using Depsolver_int.solve

June 20
  • add ~global_constraints:false to Depsolver.listcheck, Depsolver.trim and Depsolver.edos_install calls
  • adapt output graph to limited xdot capabilities

June 21 I formulate an email to the list, reporting of dependency graphs of debhelper, cdbs, pkg-config and libgtk2.0-dev. My current technique gets an installation set for a source package, removes all those that are already installable and adds the others as a dependency of that source package. This dependency will include an installation set of that binary as well minus all packages that are already available. The problem with that approach are dependency cycles created by long dependency chains. Example: src:A needs B needs C needs A. B and C would both be added as a dependency of src:A. B as well as C would also include their installation set which in both cases includes A. So now there are two cycles: src:A->B->A and src:A->C->A. For a real life example, look at the following situation of cdbs and src:sqlite3. cdbs old situation It is created because src:sqlite3 needs cdbs needs python-scour needs python needs python2.7 needs libsqlite3-0. Therfor libsqlite3-0 is in the installation set of cdbs, python-scour, python and python2.7. This creates five cycles in the graph even though there is only one. It would be better to reduce the dependencies added to src:sqlite3 to its direct dependency which is cdbs. Package dependencies are disjunctions from which the solver chooses one or the other to build an installation set. To solve the problem above I would need to know which disjunction the solver chose and then only add the direct dependency of a package to the dependency graph.
  • improve build_compile_rounds performance
  • big overhaul of menu structure
  • fix subgraph extraction code

June 22
  • do not create a universe if not needed - use hashtables instead
  • for sorting packages, generating difference of package sets and otherwise comparing packages, always use CudfAdd.compare
  • as a custom list membership function, use List.exists instead of trying List.find
  • more speedup for build_compile_rounds
  • the number of source packages that can be built does NOT include the cross built packages
  • print closure members in graph
  • refactor code and move common functions to bootstrapCommon.ml
  • add breakcycles.ml for future code to break cycles using staged build dependencies
  • use more extlib functionality
  • extended package list input format

June 23 After several emails with Pietro I learn about syntactic dependency graphs. To document my progress and prove my efforts I committed the code as commit 6684c13. But this code was soon found out to be unecessary so it will be removed later and just serves as documentation.

June 24 I came up with another (better?) solution to get the chosen disjunctions. It simply uses the calculated installation set to decide for each disjunction which one was taken by the solver. I reported that important step and the open questions involved with it in an email to the list. The problem always was, that an installation set can easily contain more than one package of a disjunction. In this case it is not clear which branch was chosen by the solver. I found, that in Ubuntu Natty there are only 6 such packages and for each of them the situation can be solved. It can be solved because in all of those cases it is that either one package of a disjunction provides the other or that both packages depend upon each other, which means that both have to be included.

June 27
  • use installation set to flatten build dependencies of source packages
  • refactor code and move common functions to bootstrapCommon.ml

June 25 I have to have an algorithm that finds all circuits in a given graph. This is necessary so that:
  1. cycles can be enumerated for huge dependency graphs where cycles are hard to see
  2. cycles can be enumerated to find a cycle that can be broken using staged build dependencies
It seems that Johnson's algorithm is the best way to do this complexity wise and Pietro already blogged about the problem together with an implementation of the algorithm in ocaml. Unfortunately it turns out that his code doesnt implement the algorithm correctly and hence misses out on some cycles. The fix seems not to be too trivial so I'm still investigating it.

June 28
  • add crosseverything.ml to obtain a list of source packages that, if cross compiled, would make the whole archive available

Results While the first week was productive as usual, I had to work some time on a University project during the second week as well as attend a family meeting. I will catch up with the lost time over the course of the next week.

dose3 Using dose 3.0 (which fixes a bug about essential packages) the output of the algorithms is now likely less wrong then before.

performance Performance was improved in the generation of installation sets as well as in the code that tries out how many packages can be built in multiple rounds. This was achieved by more caching, less unnecessary operations in looping constructs, replacing lists with hashtables, not creating universes where not necessary.

user interface The main program, basenocycles.ml now has a much better menu structure.

input format The programs take two package file inputs. The list of source packages that has to be cross built for a minimal build system and the list of source packages that was chosen to be cross compiled in addition to that. Both files list one source package per line and now allow comments.

refactoring As more and more scripts are added, more and more functionality is moved to bootstrapCommon.ml which makes each script much cleaner.

what to test for cross building As discussed in the "Future" section of the last report, I now automated the process of finding out which packages, if they were cross compiled, would make the whole archive available because they break all cycles and allow native compilation of the rest. The outcome: to build 3333 out of 3339 packages in natty natively, at most 186 source packages must be cross compiled. The other six cannot be compiled because of version mismatches in the Natty Sources.bz2 and Packages.bz2. The code can be run from crosseverything.ml.

limit source dependencies to direct dependencies Reducing the dependencies of source packages from their full installation set to their direct dependencies by finding out which disjunction of their dependency list were taken, greatly simplifies the dependency graphs. The dependency graph created for libgtk2.0-dev could be reduced from 491 to 247 vertices for a depth of three. For cdbs it is now clearly visible that cdbs depends on libsqlite3-0 which builds from src:sqlite3 which depends on cdbs. Before: cdbs old situation After: cdbs new situation For pkg-config the graph also has been reduced to the one single cycle that matters: src:pkg-config needs libglib2.0-dev which depends on pkg-config which builds from src:pkg-config. Before: pkg-config old situation After: pkg-config old situation

Future I will prepare content for wookey's debconf talk on crossbuilding and bootstrapping. As this will include directions how to use the current code, I will kill two birds with one stone and write some proper documentation for my current source. The following two lists will be displayed after a dependency graph is calculated and reduced to its scc:
  • those source packages that have the least build dependencies not fulfilled. Those might be candidates for easy staged build dependencies. Since the source package is part of the scc, it will definitely be involved in some cycle somewhere.
  • those binary packages that most source packages depend upon. Those could be candidates for cross compilation as it might be easier to cross compile the source package than using staged build dependencies.
Patrick managed to cross build packages with sbuild now. So the list of packages that crosseverything.ml produces can now be checked efficiently for cross buildability. With this list, potentially more cycles can be broken out of the box. A feature will be added that allows the user to remove all packages from a dependency graph that can be cross compiled without any additional effort. Version mismatches between source and binary packages in Sources.bz2 and Packages.bz2 respectively in Ubuntu make the scripts fail and/or produce wrong results. Debian (even Sid) doesnt have this problem so I should find out where to report this problem to Ubuntu. I need to write a working version of Johnson's algorithm because much functionality depends upon it. I have the option to improve Pietro's version or write one from scratch. Writing one from scratch might be easier as I have Pietro's code as template as well as a Java implementation of Johnson's algorithm which seems to work. The following functionalities need working cycle enumeration:
  • given source packages with staged build dependencies, an enumeration of cycles is needed to find out which cycles can be broken by building packages staged. It makes less sense to blindly build a package stage and then check if this makes more packages available.
  • display cycles of a dependency graph to the user. After obtaining all cycles in the graph it makes sense to sort them by their length. The user would then investigate the situation of the smallest cycles first. This makes sense because breaking small cycles can potentially break bigger cycles. Since in the end, all cycles have to be eliminated anyway, it makes sense for the user to first tackle the small ones.
  • display the feedback arc set to the user. The packages in the feedback arc set might be very good candidates for reduced build dependencies or cross compilation.

Next.