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    Thursday, 20 November 2014

    UEFI Debian CDs for Jessie...

    So, my work for Wheezy gave us working amd64 UEFI installer images. Yay! Except: there were a few bugs that remained, and also places where we could deal better with some of the more crappy UEFI implementations out there. But, things have improve since then and we should be better for Jessie in quite a few ways.

    First of all, Colin and the other Grub developers have continued working hard and quite a lot of the old bugs in this area look to be fixed. I'm hoping we're not going to see so many "UEFI boot gives me a blank black screen" type of problems now.

    For those poor unfortunates with Windows 7 on their machines, using BIOS boot despite having UEFI support in their hardware, I've fixed a long-standing bug (#763127) that could leave people with broken systems, unable to dual boot.

    We've fixed a silly potential permissions bug in how the EFI System Partition is mounted: (#770033).

    Next up, I'm hoping to add a workaround for some of the broken UEFI implementations, by adding support in our Grub packages (and in d-i) for forcing the installation of a copy of grub-efi in the removable media path. See #746662 for more of the details. It's horrid to be doing this, but it's just about the best thing we can do to support people with broken firmware.

    Finally, I've been getting lots of requests for adding i386 (32-bit x86) UEFI support in our official images. Back in the Wheezy development cycle, I had test images that worked on i386, but decided not to push that support into the release. There were worries about potentially critical bugs that could be tickled on some hardware, plus there were only very few known i386 UEFI platforms at the time; the risk of damage outweighed the small proportion of users, IMHO. However, I'm now revisiting that decision. The potentially broken machines are now 2 years older, and so less likely to be in use. Also, Intel have released some horrid platform concoction around the Bay Trail CPU: a 64-bit CPU (that really wants a 64-bit kernel), but running a 32-bit UEFI firmware with no BIOS Compatibility Mode. Recent kernels are able to cope with this mess, but at the moment there is no sensible way to install Debian on such a machine. I'm hoping to fix that next (#768461). It's going to be awkward again, needing changes in several places too.

    You can help! Same as 2 years ago, I'll need help testing some of these images. Particularly for the 32-bit UEFI support, I currently have no relevant hardware myself. That's not going to make it easy... :-/

    I'll start pushing unofficial Jessie EFI test images shortly.

    22:59 :: # :: /debian/CDs :: 10 comments

    Friday, 14 November 2014

    Weird things I've noticed in hotels lately...

    I've been crap about blogging lately. Let's see if I can fix that.

    Back in February and March, Jo and I went on vacation for 2 weeks touring California and Nevada. We had an awesome time and we got to see and do lots of fun stuff. I'm not going to go into all the details, as it's a long time ago now...! I've got a massive set of photos online, though.

    However, two things struck me as odd when we were there. I'm travelling quite regularly to the US these days due to my work in Linaro, but these still seemed new when I saw them this February/March. These are, admittedly trivial things, but they really stood out for me. Maybe I'm a little weird? :-)

    Curved shower curtain tracks


    I guess I'm not the only one who's been annoyed by shower curtains sticking to me in the shower, but I'd not really paid much thought to it until now. Suddenly, as of maybe 18 months ago I'm seeing most hotel bathrooms replacing the straight curtain track with a curved one, to stop that happening. This photo shows that process with both tracks visible...

    Waterproof/washable TV remotes


    This one really surprised me. As Jo will attest, I have a little bit of an obsession with TVs and set-top boxes in hotel rooms. This dates from my time working for Amino where we made set-top boxes, and I got into the habit of checking what products were in the hotels I stayed in. I've seen a range of weird and wonderful setups over the years, but never this one before. In two of the hotels on our trip, they had replaced the normal TV remotes with washable/wipe-down ones. Weird...

    01:02 :: # :: /misc :: 4 comments

    Mini-Debconf in Cambridge, November 6-9 2014

    People in the sunshine!

    For the second year running, we held our mini-debconf in Cambridge last weekend. Roughly 70 people turned up this year to the ARM offices in Cambridge over the 4 days.

    Alongside our originally planned general sprint work on Thursday and Friday, the Release Team had their own sprint to work through remaining post-freeze decisions about policies, architectures, naming etc. The rest of us worked through a range of topics all over Debian: installer, admin, ARM arch support etc. We even managed to fix Andy's laptop :-).

    Saturday and Sunday were two days devoted to more traditional conference sessions. Our talks covered a wide range of topics: d-i progress and an update from the Release Team, backup software and an arm64 laptop project to name but a few.

    I was very happy that the Release Team announced Zurg"Stretch" and "Buster" as upcoming release names, and obviously it was lovely to have arm64 and ppc64el confirmed as release architectures for Jessie. It's a shame to see the kfreebsd ports dropped from the official Jessie list, but let's see if the porters can do an unofficial release anyway. I'll help if I can with things like CD builds...

    Several volunteers from the DebConf video team were on hand too, so our talks were recorded and are already online at Yay!

    Again, the mini-conf went well and feedback from attendees was universally positive. We may run again next year. More importantly, I can confirm that we're definitely planning on bidding to host a full DebConf in Cambridge in the summer of 2017.

    Thanks to all our helpers, and of course to our sponsors: ARM for providing the venue and infrastructure for the event, and Codethink for helping with food costs.

    00:25 :: # :: /debian/mini-debconf :: 0 comments

    Monday, 13 October 2014

    Successful Summer of Code in Linaro

    It's past time I wrote about how Linaro's students fared in this year's Google Summer of Code. You might remember me posting earlier in the year when we welcomed our students. We started with 3 student projects at the beginning of the summer. One of the students unfortunately didn't work out, but the other two were hugely successful.

    Gaurav Minocha was a graduate student at the University of British Columbia, Vancouver, Canada. He worked on Linux Flattened Device Tree Self-checking, mentored by Grant Likely from Linaro's Office of the CTO. Gaurav achieved all of his project's goals, and he was invited to Linaro's recent Linaro Connect USAConnect conference in California to meet people and and talk about his project. He and Grant presented a session on their work; it was filmed, and video is online. Grant said he was very happy with Gaurav's "strong, solid performance" during the project.

    Varad Gautam was a student at Birla Institute of Technology and Science, Pilani, India. He succeeded in porting UEFI to the BeagleBone Black. Leif Lindholm from the Linaro Enterprise Group was his mentor for the summer. At the end of the summer, Varad delivered a UEFI port ready for booting Linux and his code was included in Linaro's September UEFI release. Leif said that he was "very pleased with Varad's self sufficiency and ability to pick up an entirely new software project very quickly". We were hoping to invite Gaurad to Connect in California also, but travel document delays got in the way. With luck we'll see him at the next Connect in Hong Kong in February 2015.

    Well done, guys! It was great to work with these young developers for the summer, and we wish them lots more success in their future endeavours.

    Google have also just confirmed that they will be running the Summer of Code program again in 2015. I'm hoping that Linaro will be accepted again next year as a mentoring organisation. I'll post more about that early next year.

    18:06 :: # :: /linaro :: 0 comments

    Tuesday, 22 April 2014

    Linaro welcomes GSOC 2014 students

    After several weeks of review and discussion, the application and selection period for the 2014 Google Summer of Code is over. 4,420 students proposed a total of 6,313 projects for this summer. From those, 1,307 students have been accepted (more details), and Linaro is one of the 190 Open Source projects that will be working with students this year.

    In our first year as a GSOC mentoring organisation, we received 17 applications and Google allocated us 3 slots for student projects. It was quite a challenge to pick just 3 projects from the excellent field, and it's a shame that the limited number of slots meant we had no choice but to disappoint some people. Thanks to all those who applied!

    I'm delighted to announce our 3 chosen interns for 2014:

    • Gaurav Minocha is a graduate student at the University of British Columbia, Vancouver, Canada. His project is Linux Flattened Device Tree Self-checking, mentored by Grant Likely from Linaro's Office of the CTO.
    • Ricardo de Freitas Gesuatto is a student at Federal University of São Carlos (UFSCar), Brazil. He will be working on a project entitled "Lightweight IP Stack on top of OpenDataPlane", mentored by Maxim Uvarov from the Linaro Networking Group.
    • Varad Gautam is a student at Birla Institute of Technology and Science, Pilani, India. He will be Porting UEFI to Low-Cost Embedded Platform (BeagleBoneBlack). Leif Lindholm from the Linaro Enterprise Group will be mentoring.

    Please join me in welcoming these three new engineers to the Linaro team!

    We have a GSOC wiki ready for our students to use at

    and hopefully they will start adding content there soon about themselves and their projects (hint!). In the meantime, we have more information about our original proposals and the GSOC program in the main Linaro wiki.

    Starting today, the next phase of the program is the so-called "bonding period". Students are encouraged to get to know people within Linaro (especially their mentors!) and prepare to start work on their projects, whatever is needed. The official start of the work period for GSOC is May 19th, and it runs through to August 18th. We will give updates on progress through the summer, and we're hoping to talk about our results at the next Linaro Connect in September.

    Good luck, folks!

    12:33 :: # :: /linaro :: 0 comments

    Monday, 25 November 2013

    Mini-Debconf in Cambridge, November 14-17 2013

    Phew, we did it!

    We successfuly ran our mini-conf last weekend. We welcomed roughly 60 people to the ARM offices in Cambridge over the 4 days.

    We started off with two days of sprint time, set aside for focussed hacking. We had a selection of ARM development boards on hand that people were playing with, plus a number of other people working on various other projects. The sprint sessions also saw some lively discussions on a couple of topics: the status of the ARM ports in Debian and automated system testing.

    Saturday and Sunday saw us move over to the more traditional style of conference session. Two full days of talks covered a wide range of topics: system testing to git tools, Debian ftp team work to bootstrapping the new arm64 port, improving ways of tracking and crediting Debian contributions to dealing with the new world of UEFI. Several volunteers from the DebConf video team were on hand too, so our talks were streamed live and recorded too - look out for them online soon!

    The mini-conf went well and feedback from attendees was universally positive, so we're already planning to run another similar event next year and maybe even apply to host a full DebConf in Cambridge soon too. :-)

    Many more details about the conference are in the debconf wiki at . Thanks to the sponsors who helped to make it all happen: ARM, Boston, Open@Citrix/Xen and Codethink/Baserock.

    2013-11-25 UPDATE: Videos are now online at in various formats.

    10:42 :: # :: /debian/mini-debconf :: 0 comments

    Saturday, 30 March 2013

    Scanning for assembly code in Free Software packages

    In the Linaro Enterprise Group, my task for the last several weeks was to work through a huge number of packages looking for assembly code. Why? So that we could identify code that would need porting to work well on AArch64, the new 64-bit execution state coming to the ARM world Real Soon Now.

    Working with some Ubuntu and Fedora developers, we generated a list of packages included in each distribution that seemed to contain assembly code of some sort. Then I worked through that list, checking to see:

    1. if there was actually any assembly there;
    2. if so, what it was for, and
    3. whether it was actually used

    I've written a full report about what I found in the scan, and I'll be writing some more articles based on it shortly.

    03:08 :: # :: /linaro :: 2 comments

    Tuesday, 19 February 2013

    Ladies. And Fire Engines. And all for Charity!

    My lovely wife Jo has signed up for a charity event in May this year. To help support the UK Fire Fighters Charity, she has committed to a sponsored driving challenge. If she can raise enough funds in sponsorship, she'll get to drive a fire engine, a tractor and (it's rumoured) maybe even a combine harvester too! I've chipped in some money towards the total already; I'm sure Jo would love it if some other nice people pledged on her JustGiving page too.

    Go on, it's for a good cause! :-)

    00:11 :: # :: /misc :: 0 comments

    Tuesday, 13 November 2012

    Spoiling my vote

    Ever since I passed the age of 18, I've used my legal right in the UK to vote in every poll I could: local council, British Parliament, European Parliament and even the messed-up referendum on the Alternative Vote that we had last year. In each of those cases, I made a point of considering my available options and I voted accordingly. I went along and marked my ballot paper in person where possible, or I filled in a postal vote for the last Westminster election in 2010 as I was on vacation in Florida when it was held.

    Unfortunately, it seems that my diligence in voting makes me unusual amongst the UK population these days. The long-term trend for voter turnout is downwards (as you can see).

    However, the latest election that's happening in the UK (well, England and Wales outside London) this week is for the newly-created posts of Police and Crime Commissioners. It's a textbook example of how not to organise an election, as pointed out eloquently by the Electoral Reform Society. This election has been incredibly badly managed and publicised by the Government, and lots of early polls are suggesting a tiny turnout of less than 20%. Despite the political crap about "democracy" being spouted by some Tory ministers, it's clear that very few people want this change in how the police are run, and it has simply been imposed from the top. Too few people care about the results of these elections for them to be valid - most people don't want the police politicised.

    After a lot of thought about the issue, I've decided how I'm going to vote this time. For the first time ever, I'm explicitly going to turn up and spoil my ballot paper as a protest - I do not want this crap. I urge other people in England and Wales to consider doing the same.

    23:50 :: # :: /misc/politics :: 4 comments

    Friday, 28 September 2012


    We've been thinking about getting a dog for ages, but it's been difficult to work out the logistics when we've been travelling so much. Well, today's the day!

    Pepper, day one

    Pepper is a Parson Russell Terrier, and she's 3 years old. We just collected her from the lovely people at Wood Green Animals Shelter. Her previous owner passed away recently, so she was looking for a new home.

    We've just brought her home and things are going great - she's very well behaved (so far!) and is loving a new place with lots of fuss and cuddles.

    17:14 :: # :: /misc :: 4 comments

    Anniversary trip to Scotland

    Back at the beginning of September, Jo and I were invited up to Aberdeen for a weekend for a party to celebrate the 50th wedding anniversary of some friends. Then we decided to stay around for a few days - it was our 1st anniversary just two days later. :-)

    We had a great time at the party, and had some awesome weather for the weekend (especially considering the time of year!). We travelled around a bit for the next few days, visiting Crathes Castle, John O' Groats and Culloden amongst other places. We stayed in a hotel overlooking Loch Ness for the evening of our own anniversary, but no sign of Nessie! We headed back via Gretna Green and visited the famous (if tacky!) Blacksmith's there, then headed home. Having done both Land's End and John O' Groats in one year, we've covered the length of Great Britain.

    We thoroughly enjoyed ourselves for a few days, especially the lovely roads with very few people on them! Also we got to see some very unusual road signs that made us chuckle...



    We'll definitely go back again soon!

    16:59 :: # :: /travel :: 0 comments

    Monday, 03 September 2012

    EFI Debian CDs, step 4: i386 support

    Continuing on from my third EFI progress report...

    I've added some i386 EFI support in debian-cd and built new images. Alongside a new amd64 image, we now have an i386 image and a mixed image which should hopefully boot and work on both 32-bit and 64-bit machines. The i386 support is more experimental at this point, and it's more difficult for me to test due to a lack of physical hardware. If you've got an older 32-bit EFI machine, this might work for you...

    Grab the images from if you'd like to help test. Please do, and let me know via debian-boot/debian-cd how you get on.

    As previously, the "bits" subdirectory contains all the tweaked d-i packages I've played with, in both source and binary form. My debian-cd changes are still in my branch but are just about ready for merging I think. I've posted my full set of d-i patches to the debian-boot list for review now, and hopefully we'll be able to get those changes merged in after the Wheezy d-i beta 2 build is done. Full speed ahead for EFI in beta 3!

    07:24 :: # :: /debian/CDs :: 19 comments

    Friday, 24 August 2012

    Even more progress on EFI Debian CDs

    Continuing on from my second EFI progress report...

    My second alpha release of a Wheezy netinst CD for amd64 EFI seemed to work OK for me and a few others, but it wasn't 100% good, with (at least) two issues:

    • It didn't work as a hybrid (CD or USB) image, just working from CD for EFI
    • It didn't work for BIOS booting due to a silly bug

    In the couple of days since then, I've fixed both of these issues. Yay! Hybrid boot was easier than I expected - I've just added a tiny FAT partition to the image containing the grub EFI bootloader and that seems to work fine. I also found that I made a mistake in the ordering of the El Torito boot records in the last image. BIOS boot seems to be limited to just the first image available on the machines I've tested with, wherease EFI will happily work as a secondary image. I've swapped them around in my code, and things look much better now. So, time for another CD alpha release for testing.

    Grab the image from if you'd like to help test it. Please do, and let me know via debian-boot/debian-cd how you get on.

    As previously, the "bits" subdirectory contains all the tweaked d-i packages I've played with, in both source and binary form. My debian-cd changes are still in my branch but are just about ready for merging I think. I've posted my full set of d-i patches to the debian-boot list for review now, and hopefully we'll be able to get those changes merged in after the Wheezy d-i beta 2 build is done. Full speed ahead for EFI in beta 3!

    03:16 :: # :: /debian/CDs :: 16 comments

    Wednesday, 22 August 2012

    More progress on EFI Debian CDs

    Continuing on from my first EFI progress report...

    My first alpha release of a Wheezy netinst CD for amd64 EFI worked OK for me and a few others, with reasonable feedback. But it was far from complete, with (at least) three outstanding issues:

    • It didn't work as a hybrid (CD or USB) image, just working from CD for EFI
    • The initial grub display was really ugly, with no graphics
    • I hadn't been able to get grub-efi to work, so it only allowed use of elilo.

    In the days since then, I've carried on hacking on things. I've not yet sorted out hybrid boot, but I've fixed the other issues. To make graphics work on the grub boot menu was a simple case of loading the right module from grub.cfg ("insmod png"). Getting grub-efi to work took quite a lot more effort, though. I've been looking through Ubuntu's version of debian-installer code and merged a fair amount of their code into my local builds, adding tweaks as necessary. Result? I've got another CD alpha release ready for testing. Yay!

    Grab the image from if you'd like to help test it. Please do, and let me know via debian-boot/debian-cd how you get on.

    As previously, the "bits" subdirectory contains all the tweaked d-i packages I've played with, in both source and binary form. My debian-cd changes are still in my branch but are just about ready for merging I think. I'll post more d-i patches to the debian-boot list for review shortly.

    13:57 :: # :: /debian/CDs :: 0 comments

    Sunday, 12 August 2012

    EFI installation progress

    As promised last month at DebConf, I've been working on adding EFI support to debian-cd and debian-installer, hopefully to get it up and running. At the moment, this is basic support only for booting and setting up the installed system via UEFI. I'm not worrying about "Secure" (better named "Restricted"?) Boot yet - that comes later, and depends on the basic stuff working first.

    So, how is it going? Quite well, really. I've got a debian-cd branch that I'm working on locally, and with a relatively small amount of work there I've got a locally-built CD that boots in EFI mode, using grub-efi as a boot loader. I've borrowed a script called efi-image from Colin Watson which generates the necessary EFI boot image from bits out of the grub-efi-amd64-bin package. For some reason, this grub image isn't working with all the normal graphics code so I've not got a pretty branded startup screen yet. But, nonetheless, I do have a working EFI boot CD. Yay!

    Next step: the installer. At the moment, generic amd64 and i386 machines are assumed to use need dos-style partitioning, and then either lilo or grub as a bootloader. I've patched and rebuilt some of the d-i packages locally to add a new sub-architecture of "efi" for both amd64 and i386, alongside the existing "generic" and "mac" variants. Using that new sub-architecture, it's possible to add checks for amd/efi and i386/efi in various places to make the necessary changes:

    • choose the GPT partition type for blank disks
    • tweak the auto-partitioner to add an EFI (fat32) boot partition on the front of the first hard disk
    • install the elilo bootloader

    Why elilo? It's the default for current ia64 systems, and for EFI Macs. I tried to get grub-efi working with the grub-installer package, but with little success so far. I'll try again with grub-efi, but for now elilo is much simpler and (importantly!) it works for me.

    So, I have a netinst CD built that works for me in local testing in a qemu VM using James Bottomley's OVMF build of Tianocore. It's not pretty, but it works fine, covering all the normal Debian installation steps and giving me a UEFI system at the end of the process. I'm about to start testing on real hardware now, so I think it's worth sharing this netinst image with others too. Grab it from . The "bits" subdirectory contains all the tweaked d-i packages I've played with, in both source and binary form. If you have an EFI system and would like to help us get it supported well in Debian, please download this image and play with it! Feedback to the debian-cd and/or debian-boot lists, please!

    16:22 :: # :: /debian/CDs :: 10 comments

    Monday, 09 July 2012

    CD work at DebCamp

    Great productive couple of days hacking on debian-cd with Joey. I don't do DebCamp often enough - it's great fun...

    18:20 :: # :: /debian/dc12 :: 0 comments

    Friday, 06 July 2012


    Yay, got to Nicaragua OK last night. It's the first time I've managed to get to DebCamp in quite a while, and I'm making the most of it. I've got slides ready for two of my BoF sessions next week (both ARM-related), and I'm preparing for the other four now. Why did I sign up to run six sessions? Maybe because I'm a bit silly, or maybe because they needed doing and other people hadn't registered them. Maybe both. :-)

    BTW: these are all BoF (Birds of a Feather) sessions, not lectures. While I have an interest in each topic, I'm neither wanting nor expecting to just talk at a room full of people - I'm wanting to provoke discussions in each case. If you're interested, please join in those discussions, either physically in Managua or virtually using the live video streaming and IRC back-channels:

    See you there...!

    00:00 :: # :: /debian/dc12 :: 1 comment

    Monday, 04 June 2012

    Small children on long-haul flights...

    ...should be banned. On the flight back from Hong Kong to London, a collection of about half a dozen small children conspired to cry, shout, wail and shriek nigh-on constantly. For twelve hours. :-(

    I think it's incredibly selfish to take kids on planes when they're too young to understand what's going on, or to behave reliably. Children make noise, that's natural and expected. Forcing hundreds of other people around you to deal with that noise in an enclosed space for extended periods with no way to escape is just wrong, in my opinion.


    22:20 :: # :: /travel :: 21 comments

    Wandering around Hong Kong

    Jo and I flew in to HK a few days early for the Linaro conference, so we got some time to ourselves for doing touristy stuff. That was a good plan - we got to see quite a lot of Kowloon for a couple of days, then we wandered over to Hong Kong island itself for a day. Jo also had more time during the week while I was in the sessions at the conference.

    Hong Kong is a busy place, very densely packed at all times of day and night that we could see. The first impression we got on the taxi from the airport on day one was that it was a city full of tower blocks - huge numbers of apartments stacked very closely together for living space. That makes sense, I guess, with the large population in such a small space. There are houses around with more space for people to live, but they are understandably very expensive.

    Later on in Kowloon, we got to meet lots of the local street vendors, mostly offering us "Copy Rolex", "Fake handbag" and the like. Even "Sharp trousers" at one point. We decided not to try them out... :-) We saw lots and lots of very expensive shops downtown, crammed into huge shopping centres in the tourist area. As an antidote for all of that, we headed up to the "Golden Computer Arcade" to go browsing around the vast array of tiny technology stalls and shops there. Picked up some nice cheap laptop memory and some SD cards there. Yay!

    Across on Hong Kong island itself on Sunday, we found my grandfather's grave then rode around on the trams for a while to get a good view of the city, including a democracy protest that happened to be on that day! We had a quick look around Tin Hau Temple, where we found a very specific set of rules for visitors:

    temple rules

    I can only guess that they must have been terrified by gangs of kids racing their RC cars at one point!

    We finished the day by heading up to Victoria Peak for the sunset view and some dinner, then back to the hotel. Killing time in a shopping centre waiting for the bus to turn up, we found a truly astonishing little item on sale, a Solar Queen!

    solar queen

    Apparently this gift has a solar panel on the handbag to provide power to a little motor in the Queen's hand to make her wave to her subjects. We decided that we'd somehow have to live without such a delight in our lives... :-)

    HK was a cool place to visit. It still feels very British in some ways, as you'd expect from an ex-colony (power sockets are still the same as ours, driving on the left, everybody spoke English, etc.) but utterly alien in others (the climate, working public transport *grin*). I look forwards to heading out there again!

    22:12 :: # :: /travel :: 0 comments

    Linaro Connect in Hong Kong, 2012: Ruby bug squashed!

    Connect logoSometimes conferences can be dull and boring, but sometimes they can be just awesome in terms of finding the right people to collaborate with. Linaro Connect in Hong Kong last week was definitely one of the great ones!

    I chaired my my usual sessions (armhf status and cross-distro ARM) and we had some lively discussion in both. We're probably just about done with the armhf sessions, as most distros have accepted a hard-float ARMv7 port now and there's not so much specific work left there now that future sessions will be necessary. The cross-distro work for ARM ports is likely to continue into the future, but we're going to be concentrating on bootstrapping work for ARMv8 soon.

    Talking v8, there were a lot of meetings discussing the various work topics for this new 64-bit ARM architecture: kernel, toolchains, bootstrapping etc. More to come on that soon!

    On top of all this useful discussion and planning, we also found time during the week for some hacking. This was the highlight of the week for me, as I found some expert help to solve my long-standing Ruby on ARM bug (Debian bug #652674, ruby1.9.1: FTBFS on armhf: test suite segfaults). Ulrich Weigand (an IBM toolchain wizard seconded into the Linaro team) sat with me for a couple of hours while we worked through reproducing the problem, only to find that he could not reproduce it! The crash had looked very much like a pthreads locking bug, which was scaring me. After some digging, we worked out where the problem was, and how it was now fixed.

    For a long time on ARM, the Linux getcontext/setcontext system calls have never been implemented; apparently nobody really missed them, so they have never been a priority. In Ruby 1.9.x, the implementation of the new "fiber" primitive wanted to use getcontext/setcontext to control stack state etc. in different threads of control. In cases where they are not available or known not to work well, Ruby has fallback code to implement similar functionality. It seems that fallback code is buggy. Maybe it was correct at some point and has bit-rotted due to not being exercised, or maybe it was buggy as written, but it clearly does not work correctly for us now. In the last few months, getcontext/setcontext have finally been implemented for ARM in glibc trunk (by Michael Hope, also in the Linaro toolchain team!) and backported into current Debian and Ubuntu eglibc versions. Re-running configure and rebuilding Ruby against the most recent code in both Sid and Precise fixed the test suite crash we were seeing earlier. Yay! We could also provoke the bug again at will by quickly hacking around the Ruby source to force it to switch back to the fallback code, thereby verifying the fix.

    Why does this matter? As we're expecting ARM servers to enter the market soon, web apps written in Ruby on Rails are going to be an important part of the software stack that customers will want to run. Broken fibers and threading would not help here!

    It's great to meet up and work with talented folks like this; Linaro Connect is an excellent event for getting stuff done!

    20:22 :: # :: /linaro :: 0 comments