Search Results: "denis"

13 December 2023

Melissa Wen: 15 Tips for Debugging Issues in the AMD Display Kernel Driver

A self-help guide for examining and debugging the AMD display driver within the Linux kernel/DRM subsystem. It s based on my experience as an external developer working on the driver, and are shared with the goal of helping others navigate the driver code. Acknowledgments: These tips were gathered thanks to the countless help received from AMD developers during the driver development process. The list below was obtained by examining open source code, reviewing public documentation, playing with tools, asking in public forums and also with the help of my former GSoC mentor, Rodrigo Siqueira.

Pre-Debugging Steps: Before diving into an issue, it s crucial to perform two essential steps: 1) Check the latest changes: Ensure you re working with the latest AMD driver modifications located in the amd-staging-drm-next branch maintained by Alex Deucher. You may also find bug fixes for newer kernel versions on branches that have the name pattern drm-fixes-<date>. 2) Examine the issue tracker: Confirm that your issue isn t already documented and addressed in the AMD display driver issue tracker. If you find a similar issue, you can team up with others and speed up the debugging process.

Understanding the issue: Do you really need to change this? Where should you start looking for changes? 3) Is the issue in the AMD kernel driver or in the userspace?: Identifying the source of the issue is essential regardless of the GPU vendor. Sometimes this can be challenging so here are some helpful tips:
  • Record the screen: Capture the screen using a recording app while experiencing the issue. If the bug appears in the capture, it s likely a userspace issue, not the kernel display driver.
  • Analyze the dmesg log: Look for error messages related to the display driver in the dmesg log. If the error message appears before the message [drm] Display Core v... , it s not likely a display driver issue. If this message doesn t appear in your log, the display driver wasn t fully loaded and you will see a notification that something went wrong here.
4) AMD Display Manager vs. AMD Display Core: The AMD display driver consists of two components:
  • Display Manager (DM): This component interacts directly with the Linux DRM infrastructure. Occasionally, issues can arise from misinterpretations of DRM properties or features. If the issue doesn t occur on other platforms with the same AMD hardware - for example, only happens on Linux but not on Windows - it s more likely related to the AMD DM code.
  • Display Core (DC): This is the platform-agnostic part responsible for setting and programming hardware features. Modifications to the DC usually require validation on other platforms, like Windows, to avoid regressions.
5) Identify the DC HW family: Each AMD GPU has variations in its hardware architecture. Features and helpers differ between families, so determining the relevant code for your specific hardware is crucial.
  • Find GPU product information in Linux/AMD GPU documentation
  • Check the dmesg log for the Display Core version (since this commit in Linux kernel 6.3v). For example:
    • [drm] Display Core v3.2.241 initialized on DCN 2.1
    • [drm] Display Core v3.2.237 initialized on DCN 3.0.1

Investigating the relevant driver code: Keep from letting unrelated driver code to affect your investigation. 6) Narrow the code inspection down to one DC HW family: the relevant code resides in a directory named after the DC number. For example, the DCN 3.0.1 driver code is located at drivers/gpu/drm/amd/display/dc/dcn301. We all know that the AMD s shared code is huge and you can use these boundaries to rule out codes unrelated to your issue. 7) Newer families may inherit code from older ones: you can find dcn301 using code from dcn30, dcn20, dcn10 files. It s crucial to verify which hooks and helpers your driver utilizes to investigate the right portion. You can leverage ftrace for supplemental validation. To give an example, it was useful when I was updating DCN3 color mapping to correctly use their new post-blending color capabilities, such as: Additionally, you can use two different HW families to compare behaviours. If you see the issue in one but not in the other, you can compare the code and understand what has changed and if the implementation from a previous family doesn t fit well the new HW resources or design. You can also count on the help of the community on the Linux AMD issue tracker to validate your code on other hardware and/or systems. This approach helped me debug a 2-year-old issue where the cursor gamma adjustment was incorrect in DCN3 hardware, but working correctly for DCN2 family. I solved the issue in two steps, thanks for community feedback and validation: 8) Check the hardware capability screening in the driver: You can currently find a list of display hardware capabilities in the drivers/gpu/drm/amd/display/dc/dcn*/dcn*_resource.c file. More precisely in the dcn*_resource_construct() function. Using DCN301 for illustration, here is the list of its hardware caps:
	/*************************************************
	 *  Resource + asic cap harcoding                *
	 *************************************************/
	pool->base.underlay_pipe_index = NO_UNDERLAY_PIPE;
	pool->base.pipe_count = pool->base.res_cap->num_timing_generator;
	pool->base.mpcc_count = pool->base.res_cap->num_timing_generator;
	dc->caps.max_downscale_ratio = 600;
	dc->caps.i2c_speed_in_khz = 100;
	dc->caps.i2c_speed_in_khz_hdcp = 5; /*1.4 w/a enabled by default*/
	dc->caps.max_cursor_size = 256;
	dc->caps.min_horizontal_blanking_period = 80;
	dc->caps.dmdata_alloc_size = 2048;
	dc->caps.max_slave_planes = 2;
	dc->caps.max_slave_yuv_planes = 2;
	dc->caps.max_slave_rgb_planes = 2;
	dc->caps.is_apu = true;
	dc->caps.post_blend_color_processing = true;
	dc->caps.force_dp_tps4_for_cp2520 = true;
	dc->caps.extended_aux_timeout_support = true;
	dc->caps.dmcub_support = true;
	/* Color pipeline capabilities */
	dc->caps.color.dpp.dcn_arch = 1;
	dc->caps.color.dpp.input_lut_shared = 0;
	dc->caps.color.dpp.icsc = 1;
	dc->caps.color.dpp.dgam_ram = 0; // must use gamma_corr
	dc->caps.color.dpp.dgam_rom_caps.srgb = 1;
	dc->caps.color.dpp.dgam_rom_caps.bt2020 = 1;
	dc->caps.color.dpp.dgam_rom_caps.gamma2_2 = 1;
	dc->caps.color.dpp.dgam_rom_caps.pq = 1;
	dc->caps.color.dpp.dgam_rom_caps.hlg = 1;
	dc->caps.color.dpp.post_csc = 1;
	dc->caps.color.dpp.gamma_corr = 1;
	dc->caps.color.dpp.dgam_rom_for_yuv = 0;
	dc->caps.color.dpp.hw_3d_lut = 1;
	dc->caps.color.dpp.ogam_ram = 1;
	// no OGAM ROM on DCN301
	dc->caps.color.dpp.ogam_rom_caps.srgb = 0;
	dc->caps.color.dpp.ogam_rom_caps.bt2020 = 0;
	dc->caps.color.dpp.ogam_rom_caps.gamma2_2 = 0;
	dc->caps.color.dpp.ogam_rom_caps.pq = 0;
	dc->caps.color.dpp.ogam_rom_caps.hlg = 0;
	dc->caps.color.dpp.ocsc = 0;
	dc->caps.color.mpc.gamut_remap = 1;
	dc->caps.color.mpc.num_3dluts = pool->base.res_cap->num_mpc_3dlut; //2
	dc->caps.color.mpc.ogam_ram = 1;
	dc->caps.color.mpc.ogam_rom_caps.srgb = 0;
	dc->caps.color.mpc.ogam_rom_caps.bt2020 = 0;
	dc->caps.color.mpc.ogam_rom_caps.gamma2_2 = 0;
	dc->caps.color.mpc.ogam_rom_caps.pq = 0;
	dc->caps.color.mpc.ogam_rom_caps.hlg = 0;
	dc->caps.color.mpc.ocsc = 1;
	dc->caps.dp_hdmi21_pcon_support = true;
	/* read VBIOS LTTPR caps */
	if (ctx->dc_bios->funcs->get_lttpr_caps)  
		enum bp_result bp_query_result;
		uint8_t is_vbios_lttpr_enable = 0;
		bp_query_result = ctx->dc_bios->funcs->get_lttpr_caps(ctx->dc_bios, &is_vbios_lttpr_enable);
		dc->caps.vbios_lttpr_enable = (bp_query_result == BP_RESULT_OK) && !!is_vbios_lttpr_enable;
	 
	if (ctx->dc_bios->funcs->get_lttpr_interop)  
		enum bp_result bp_query_result;
		uint8_t is_vbios_interop_enabled = 0;
		bp_query_result = ctx->dc_bios->funcs->get_lttpr_interop(ctx->dc_bios, &is_vbios_interop_enabled);
		dc->caps.vbios_lttpr_aware = (bp_query_result == BP_RESULT_OK) && !!is_vbios_interop_enabled;
	 
Keep in mind that the documentation of color capabilities are available at the Linux kernel Documentation.

Understanding the development history: What has brought us to the current state? 9) Pinpoint relevant commits: Use git log and git blame to identify commits targeting the code section you re interested in. 10) Track regressions: If you re examining the amd-staging-drm-next branch, check for regressions between DC release versions. These are defined by DC_VER in the drivers/gpu/drm/amd/display/dc/dc.h file. Alternatively, find a commit with this format drm/amd/display: 3.2.221 that determines a display release. It s useful for bisecting. This information helps you understand how outdated your branch is and identify potential regressions. You can consider each DC_VER takes around one week to be bumped. Finally, check testing log of each release in the report provided on the amd-gfx mailing list, such as this one Tested-by: Daniel Wheeler:

Reducing the inspection area: Focus on what really matters. 11) Identify involved HW blocks: This helps isolate the issue. You can find more information about DCN HW blocks in the DCN Overview documentation. In summary:
  • Plane issues are closer to HUBP and DPP.
  • Blending/Stream issues are closer to MPC, OPP and OPTC. They are related to DRM CRTC subjects.
This information was useful when debugging a hardware rotation issue where the cursor plane got clipped off in the middle of the screen. Finally, the issue was addressed by two patches: 12) Issues around bandwidth (glitches) and clocks: May be affected by calculations done in these HW blocks and HW specific values. The recalculation equations are found in the DML folder. DML stands for Display Mode Library. It s in charge of all required configuration parameters supported by the hardware for multiple scenarios. See more in the AMD DC Overview kernel docs. It s a math library that optimally configures hardware to find the best balance between power efficiency and performance in a given scenario. Finding some clk variables that affect device behavior may be a sign of it. It s hard for a external developer to debug this part, since it involves information from HW specs and firmware programming that we don t have access. The best option is to provide all relevant debugging information you have and ask AMD developers to check the values from your suspicions.
  • Do a trick: If you suspect the power setup is degrading performance, try setting the amount of power supplied to the GPU to the maximum and see if it affects the system behavior with this command: sudo bash -c "echo high > /sys/class/drm/card0/device/power_dpm_force_performance_level"
I learned it when debugging glitches with hardware cursor rotation on Steam Deck. My first attempt was changing the clock calculation. In the end, Rodrigo Siqueira proposed the right solution targeting bandwidth in two steps:

Checking implicit programming and hardware limitations: Bring implicit programming to the level of consciousness and recognize hardware limitations. 13) Implicit update types: Check if the selected type for atomic update may affect your issue. The update type depends on the mode settings, since programming some modes demands more time for hardware processing. More details in the source code:
/* Surface update type is used by dc_update_surfaces_and_stream
 * The update type is determined at the very beginning of the function based
 * on parameters passed in and decides how much programming (or updating) is
 * going to be done during the call.
 *
 * UPDATE_TYPE_FAST is used for really fast updates that do not require much
 * logical calculations or hardware register programming. This update MUST be
 * ISR safe on windows. Currently fast update will only be used to flip surface
 * address.
 *
 * UPDATE_TYPE_MED is used for slower updates which require significant hw
 * re-programming however do not affect bandwidth consumption or clock
 * requirements. At present, this is the level at which front end updates
 * that do not require us to run bw_calcs happen. These are in/out transfer func
 * updates, viewport offset changes, recout size changes and pixel
depth changes.
 * This update can be done at ISR, but we want to minimize how often
this happens.
 *
 * UPDATE_TYPE_FULL is slow. Really slow. This requires us to recalculate our
 * bandwidth and clocks, possibly rearrange some pipes and reprogram
anything front
 * end related. Any time viewport dimensions, recout dimensions,
scaling ratios or
 * gamma need to be adjusted or pipe needs to be turned on (or
disconnected) we do
 * a full update. This cannot be done at ISR level and should be a rare event.
 * Unless someone is stress testing mpo enter/exit, playing with
colour or adjusting
 * underscan we don't expect to see this call at all.
 */
enum surface_update_type  
UPDATE_TYPE_FAST, /* super fast, safe to execute in isr */
UPDATE_TYPE_MED,  /* ISR safe, most of programming needed, no bw/clk change*/
UPDATE_TYPE_FULL, /* may need to shuffle resources */
 ;

Using tools: Observe the current state, validate your findings, continue improvements. 14) Use AMD tools to check hardware state and driver programming: help on understanding your driver settings and checking the behavior when changing those settings.
  • DC Visual confirmation: Check multiple planes and pipe split policy.
  • DTN logs: Check display hardware state, including rotation, size, format, underflow, blocks in use, color block values, etc.
  • UMR: Check ASIC info, register values, KMS state - links and elements (framebuffers, planes, CRTCs, connectors). Source: UMR project documentation
15) Use generic DRM/KMS tools:
  • IGT test tools: Use generic KMS tests or develop your own to isolate the issue in the kernel space. Compare results across different GPU vendors to understand their implementations and find potential solutions. Here AMD also has specific IGT tests for its GPUs that is expect to work without failures on any AMD GPU. You can check results of HW-specific tests using different display hardware families or you can compare expected differences between the generic workflow and AMD workflow.
  • drm_info: This tool summarizes the current state of a display driver (capabilities, properties and formats) per element of the DRM/KMS workflow. Output can be helpful when reporting bugs.

Don t give up! Debugging issues in the AMD display driver can be challenging, but by following these tips and leveraging available resources, you can significantly improve your chances of success. Worth mentioning: This blog post builds upon my talk, I m not an AMD expert, but presented at the 2022 XDC. It shares guidelines that helped me debug AMD display issues as an external developer of the driver. Open Source Display Driver: The Linux kernel/AMD display driver is open source, allowing you to actively contribute by addressing issues listed in the official tracker. Tackling existing issues or resolving your own can be a rewarding learning experience and a valuable contribution to the community. Additionally, the tracker serves as a valuable resource for finding similar bugs, troubleshooting tips, and suggestions from AMD developers. Finally, it s a platform for seeking help when needed. Remember, contributing to the open source community through issue resolution and collaboration is mutually beneficial for everyone involved.

8 February 2023

Chris Lamb: Most anticipated films of 2023

Very few highly-anticipated movies appear in January and February, as the bigger releases are timed so they can be considered for the Golden Globes in January and the Oscars in late February or early March, so film fans have the advantage of a few weeks after the New Year to collect their thoughts on the year ahead. In other words, I'm not actually late in outlining below the films I'm most looking forward to in 2023...

Barbie No, seriously! If anyone can make a good film about a doll franchise, it's probably Greta Gerwig. Not only was Little Women (2019) more than admirable, the same could be definitely said for Lady Bird (2017). More importantly, I can't help feel she was the real 'Driver' behind Frances Ha (2012), one of the better modern takes on Claudia Weill's revelatory Girlfriends (1978). Still, whenever I remember that Barbie will be a film about a billion-dollar toy and media franchise with a nettlesome history, I recall I rubbished the "Facebook film" that turned into The Social Network (2010). Anyway, the trailer for Barbie is worth watching, if only because it seems like a parody of itself.

Blitz It's difficult to overstate just how important the aerial bombing of London during World War II is crucial to understanding the British psyche, despite it being a constructed phenomenon from the outset. Without wishing to underplay the deaths of over 40,000 civilian deaths, Angus Calder pointed out in the 1990s that the modern mythology surrounding the event "did not evolve spontaneously; it was a propaganda construct directed as much at [then neutral] American opinion as at British." It will therefore be interesting to see how British Grenadian Trinidadian director Steve McQueen addresses a topic so essential to the British self-conception. (Remember the controversy in right-wing circles about the sole Indian soldier in Christopher Nolan's Dunkirk (2017)?) McQueen is perhaps best known for his 12 Years a Slave (2013), but he recently directed a six-part film anthology for the BBC which addressed the realities of post-Empire immigration to Britain, and this leads me to suspect he sees the Blitz and its surrounding mythology with a more critical perspective. But any attempt to complicate the story of World War II will be vigorously opposed in a way that will make the recent hullabaloo surrounding The Crown seem tame. All this is to say that the discourse surrounding this release may be as interesting as the film itself.

Dune, Part II Coming out of the cinema after the first part of Denis Vileneve's adaptation of Dune (2021), I was struck by the conception that it was less of a fresh adaptation of the 1965 novel by Frank Herbert than an attempt to rehabilitate David Lynch's 1984 version and in a broader sense, it was also an attempt to reestablish the primacy of cinema over streaming TV and the myriad of other distractions in our lives. I must admit I'm not a huge fan of the original novel, finding within it a certain prurience regarding hereditary military regimes and writing about them with a certain sense of glee that belies a secret admiration for them... not to mention an eyebrow-raising allegory for the Middle East. Still, Dune, Part II is going to be a fantastic spectacle.

Ferrari It'll be curious to see how this differs substantially from the recent Ford v Ferrari (2019), but given that Michael Mann's Heat (1995) so effectively re-energised the gangster/heist genre, I'm more than willing to kick the tires of this about the founder of the eponymous car manufacturer. I'm in the minority for preferring Mann's Thief (1981) over Heat, in part because the former deals in more abstract themes, so I'd have perhaps prefered to look forward to a more conceptual film from Mann over a story about one specific guy.

How Do You Live There are a few directors one can look forward to watching almost without qualification, and Hayao Miyazaki (My Neighbor Totoro, Kiki's Delivery Service, Princess Mononoke Howl's Moving Castle, etc.) is one of them. And this is especially so given that The Wind Rises (2013) was meant to be the last collaboration between Miyazaki and Studio Ghibli. Let's hope he is able to come out of retirement in another ten years.

Indiana Jones and the Dial of Destiny Given I had a strong dislike of Indiana Jones and the Kingdom of the Crystal Skull (2008), I seriously doubt I will enjoy anything this film has to show me, but with 1981's Raiders of the Lost Ark remaining one of my most treasured films (read my brief homage), I still feel a strong sense of obligation towards the Indiana Jones name, despite it feeling like the copper is being pulled out of the walls of this franchise today.

Kafka I only know Polish filmmaker Agnieszka Holland through her Spoor (2017), an adaptation of Olga Tokarczuk's 2009 eco-crime novel Drive Your Plow Over the Bones of the Dead. I wasn't an unqualified fan of Spoor (nor the book on which it is based), but I am interested in Holland's take on the life of Czech author Franz Kafka, an author enmeshed with twentieth-century art and philosophy, especially that of central Europe. Holland has mentioned she intends to tell the story "as a kind of collage," and I can hope that it is an adventurous take on the over-furrowed biopic genre. Or perhaps Gregor Samsa will awake from uneasy dreams to find himself transformed in his bed into a huge verminous biopic.

The Killer It'll be interesting to see what path David Fincher is taking today, especially after his puzzling and strangely cold Mank (2020) portraying the writing process behind Orson Welles' Citizen Kane (1941). The Killer is said to be a straight-to-Netflix thriller based on the graphic novel about a hired assassin, which makes me think of Fincher's Zodiac (2007), and, of course, Se7en (1995). I'm not as entranced by Fincher as I used to be, but any film with Michael Fassbender and Tilda Swinton (with a score by Trent Reznor) is always going to get my attention.

Killers of the Flower Moon In Killers of the Flower Moon, Martin Scorsese directs an adaptation of a book about the FBI's investigation into a conspiracy to murder Osage tribe members in the early years of the twentieth century in order to deprive them of their oil-rich land. (The only thing more quintessentially American than apple pie is a conspiracy combined with a genocide.) Separate from learning more about this disquieting chapter of American history, I'd love to discover what attracted Scorsese to this particular story: he's one of the few top-level directors who have the ability to lucidly articulate their intentions and motivations.

Napoleon It often strikes me that, despite all of his achievements and fame, it's somehow still possible to claim that Ridley Scott is relatively underrated compared to other directors working at the top level today. Besides that, though, I'm especially interested in this film, not least of all because I just read Tolstoy's War and Peace (read my recent review) and am working my way through the mind-boggling 431-minute Soviet TV adaptation, but also because several auteur filmmakers (including Stanley Kubrick) have tried to make a Napoleon epic and failed.

Oppenheimer In a way, a biopic about the scientist responsible for the atomic bomb and the Manhattan Project seems almost perfect material for Christopher Nolan. He can certainly rely on stars to queue up to be in his movies (Robert Downey Jr., Matt Damon, Kenneth Branagh, etc.), but whilst I'm certain it will be entertaining on many fronts, I fear it will fall into the well-established Nolan mould of yet another single man struggling with obsession, deception and guilt who is trying in vain to balance order and chaos in the world.

The Way of the Wind Marked by philosophical and spiritual overtones, all of Terrence Malick's films are perfumed with themes of transcendence, nature and the inevitable conflict between instinct and reason. My particular favourite is his stunning Days of Heaven (1978), but The Thin Red Line (1998) and A Hidden Life (2019) also touched me ways difficult to relate, and are one of the few films about the Second World War that don't touch off my sensitivity about them (see my remarks about Blitz above). It is therefore somewhat Malickian that his next film will be a biblical drama about the life of Jesus. Given Malick's filmography, I suspect this will be far more subdued than William Wyler's 1959 Ben-Hur and significantly more equivocal in its conviction compared to Paolo Pasolini's ardently progressive The Gospel According to St. Matthew (1964). However, little beyond that can be guessed, and the film may not even appear until 2024 or even 2025.

Zone of Interest I was mesmerised by Jonathan Glazer's Under the Skin (2013), and there is much to admire in his borderline 'revisionist gangster' film Sexy Beast (2000), so I will definitely be on the lookout for this one. The only thing making me hesitate is that Zone of Interest is based on a book by Martin Amis about a romance set inside the Auschwitz concentration camp. I haven't read the book, but Amis has something of a history in his grappling with the history of the twentieth century, and he seems to do it in a way that never sits right with me. But if Paul Verhoeven's Starship Troopers (1997) proves anything at all, it's all in the adaption.

23 December 2022

Louis-Philippe V ronneau: 2022 A Musical Retrospective

With the end of the year approaching fast, I thought putting my year in retrospective via music would be a fun thing to do. Albums In 2022, I added 51 new albums to my collection nearly one a week! I listed them below in the order in which I acquired them. I purchased most of these albums when I could and borrowed the rest at libraries. If you want to browse though, I added links to the album covers pointing either to websites where you can buy them or to Discogs when digital copies weren't available1. Browsing through the albums, I can see my tastes really shifted a lot in the last few years. I used to listen to a lot of Hip-Hop, but the recent trends in this genre2 really turn me off. In fact, it seems I didn't add a single Hip-Hop album to my collection this year... Metal also continues to dominate the list. Many thanks to Angry Metal Guy for being the best metal reviewing website out there. Concerts 2022 was also a big change for me, as I started going to much more concerts than I previously did. metalfinder has been working great and I'm really happy with it. Here are the concerts I went to in 2022: I'm looking forward continuing to go to a lot of concerts in 2023!

  1. Some of the albums especially the O ! ones are pretty underground. For most of those, I actually have physical copies I bought and ripped.
  2. Mostly mumble rap, beats than are less and less sample-based, extreme commercialisation and lyrics that are less and less political and engaged.

16 January 2022

Chris Lamb: Favourite films of 2021

In my four most recent posts, I went over the memoirs and biographies, the non-fiction, the fiction and the 'classic' novels that I enjoyed reading the most in 2021. But in the very last of my 2021 roundup posts, I'll be going over some of my favourite movies. (Saying that, these are perhaps less of my 'favourite films' than the ones worth remarking on after all, nobody needs to hear that The Godfather is a good movie.) It's probably helpful to remark you that I took a self-directed course in film history in 2021, based around the first volume of Roger Ebert's The Great Movies. This collection of 100-odd movie essays aims to make a tour of the landmarks of the first century of cinema, and I watched all but a handul before the year was out. I am slowly making my way through volume two in 2022. This tome was tremendously useful, and not simply due to the background context that Ebert added to each film: it also brought me into contact with films I would have hardly come through some other means. Would I have ever discovered the sly comedy of Trouble in Paradise (1932) or the touching proto-realism of L'Atalante (1934) any other way? It also helped me to 'get around' to watching films I may have put off watching forever the influential Battleship Potemkin (1925), for instance, and the ur-epic Lawrence of Arabia (1962) spring to mind here. Choosing a 'worst' film is perhaps more difficult than choosing the best. There are first those that left me completely dry (Ready or Not, Written on the Wind, etc.), and those that were simply poorly executed. And there are those that failed to meet their own high opinions of themselves, such as the 'made for Reddit' Tenet (2020) or the inscrutable Vanilla Sky (2001) the latter being an almost perfect example of late-20th century cultural exhaustion. But I must save my most severe judgement for those films where I took a visceral dislike how their subjects were portrayed. The sexually problematic Sixteen Candles (1984) and the pseudo-Catholic vigilantism of The Boondock Saints (1999) both spring to mind here, the latter of which combines so many things I dislike into such a short running time I'd need an entire essay to adequately express how much I disliked it.

Dogtooth (2009) A father, a mother, a brother and two sisters live in a large and affluent house behind a very high wall and an always-locked gate. Only the father ever leaves the property, driving to the factory that he happens to own. Dogtooth goes far beyond any allusion to Josef Fritzl's cellar, though, as the children's education is a grotesque parody of home-schooling. Here, the parents deliberately teach their children the wrong meaning of words (e.g. a yellow flower is called a 'zombie'), all of which renders the outside world utterly meaningless and unreadable, and completely mystifying its very existence. It is this creepy strangeness within a 'regular' family unit in Dogtooth that is both socially and epistemically horrific, and I'll say nothing here of its sexual elements as well. Despite its cold, inscrutable and deadpan surreality, Dogtooth invites all manner of potential interpretations. Is this film about the artificiality of the nuclear family that the West insists is the benchmark of normality? Or is it, as I prefer to believe, something more visceral altogether: an allegory for the various forms of ontological violence wrought by fascism, as well a sobering nod towards some of fascism's inherent appeals? (Perhaps it is both. In 1972, French poststructuralists Gilles and F lix Guattari wrote Anti-Oedipus, which plays with the idea of the family unit as a metaphor for the authoritarian state.) The Greek-language Dogtooth, elegantly shot, thankfully provides no easy answers.

Holy Motors (2012) There is an infamous scene in Un Chien Andalou, the 1929 film collaboration between Luis Bu uel and famed artist Salvador Dal . A young woman is cornered in her own apartment by a threatening man, and she reaches for a tennis racquet in self-defence. But the man suddenly picks up two nearby ropes and drags into the frame two large grand pianos... each leaden with a dead donkey, a stone tablet, a pumpkin and a bewildered priest. This bizarre sketch serves as a better introduction to Leos Carax's Holy Motors than any elementary outline of its plot, which ostensibly follows 24 hours in the life of a man who must play a number of extremely diverse roles around Paris... all for no apparent reason. (And is he even a man?) Surrealism as an art movement gets a pretty bad wrap these days, and perhaps justifiably so. But Holy Motors and Un Chien Andalou serve as a good reminder that surrealism can be, well, 'good, actually'. And if not quite high art, Holy Motors at least demonstrates that surrealism can still unnerving and hilariously funny. Indeed, recalling the whimsy of the plot to a close friend, the tears of laughter came unbidden to my eyes once again. ("And then the limousines...!") Still, it is unclear how Holy Motors truly refreshes surrealism for the twenty-first century. Surrealism was, in part, a reaction to the mechanical and unfeeling brutality of World War I and ultimately sought to release the creative potential of the unconscious mind. Holy Motors cannot be responding to another continental conflagration, and so it appears to me to be some kind of commentary on the roles we exhibit in an era of 'post-postmodernity': a sketch on our age of performative authenticity, perhaps, or an idle doodle on the function and psychosocial function of work. Or perhaps not. After all, this film was produced in a time that offers the near-universal availability of mind-altering substances, and this certainly changes the context in which this film was both created. And, how can I put it, was intended to be watched.

Manchester by the Sea (2016) An absolutely devastating portrayal of a character who is unable to forgive himself and is hesitant to engage with anyone ever again. It features a near-ideal balance between portraying unrecoverable anguish and tender warmth, and is paradoxically grandiose in its subtle intimacy. The mechanics of life led me to watch this lying on a bed in a chain hotel by Heathrow Airport, and if this colourless circumstance blunted the film's emotional impact on me, I am probably thankful for it. Indeed, I find myself reduced in this review to fatuously recalling my favourite interactions instead of providing any real commentary. You could write a whole essay about one particular incident: its surfaces, subtexts and angles... all despite nothing of any substance ever being communicated. Truly stunning.

McCabe & Mrs. Miller (1971) Roger Ebert called this movie one of the saddest films I have ever seen, filled with a yearning for love and home that will not ever come. But whilst it is difficult to disagree with his sentiment, Ebert's choice of sad is somehow not quite the right word. Indeed, I've long regretted that our dictionaries don't have more nuanced blends of tragedy and sadness; perhaps the Ancient Greeks can loan us some. Nevertheless, the plot of this film is of a gambler and a prostitute who become business partners in a new and remote mining town called Presbyterian Church. However, as their town and enterprise booms, it comes to the attention of a large mining corporation who want to bully or buy their way into the action. What makes this film stand out is not the plot itself, however, but its mood and tone the town and its inhabitants seem to be thrown together out of raw lumber, covered alternatively in mud or frozen ice, and their days (and their personalities) are both short and dark in equal measure. As a brief aside, if you haven't seen a Roger Altman film before, this has all the trappings of being a good introduction. As Ebert went on to observe: This is not the kind of movie where the characters are introduced. They are all already here. Furthermore, we can see some of Altman's trademark conversations that overlap, a superb handling of ensemble casts, and a quietly subversive view of the tyranny of 'genre'... and the latter in a time when the appetite for revisionist portrays of the West was not very strong. All of these 'Altmanian' trademarks can be ordered in much stronger measures in his later films: in particular, his comedy-drama Nashville (1975) has 24 main characters, and my jejune interpretation of Gosford Park (2001) is that it is purposefully designed to poke fun those who take a reductionist view of 'genre', or at least on the audience's expectations. (In this case, an Edwardian-era English murder mystery in the style of Agatha Christie, but where no real murder or detection really takes place.) On the other hand, McCabe & Mrs. Miller is actually a poor introduction to Altman. The story is told in a suitable deliberate and slow tempo, and the two stars of the film are shown thoroughly defrocked of any 'star status', in both the visual and moral dimensions. All of these traits are, however, this film's strength, adding up to a credible, fascinating and riveting portrayal of the old West.

Detour (1945) Detour was filmed in less than a week, and it's difficult to decide out of the actors and the screenplay which is its weakest point.... Yet it still somehow seemed to drag me in. The plot revolves around luckless Al who is hitchhiking to California. Al gets a lift from a man called Haskell who quickly falls down dead from a heart attack. Al quickly buries the body and takes Haskell's money, car and identification, believing that the police will believe Al murdered him. An unstable element is soon introduced in the guise of Vera, who, through a set of coincidences that stretches credulity, knows that this 'new' Haskell (ie. Al pretending to be him) is not who he seems. Vera then attaches herself to Al in order to blackmail him, and the world starts to spin out of his control. It must be understood that none of this is executed very well. Rather, what makes Detour so interesting to watch is that its 'errors' lend a distinctively creepy and unnatural hue to the film. Indeed, in the early twentieth century, Sigmund Freud used the word unheimlich to describe the experience of something that is not simply mysterious, but something creepy in a strangely familiar way. This is almost the perfect description of watching Detour its eerie nature means that we are not only frequently second-guessed about where the film is going, but are often uncertain whether we are watching the usual objective perspective offered by cinema. In particular, are all the ham-fisted segues, stilted dialogue and inscrutable character motivations actually a product of Al inventing a story for the viewer? Did he murder Haskell after all, despite the film 'showing' us that Haskell died of natural causes? In other words, are we watching what Al wants us to believe? Regardless of the answers to these questions, the film succeeds precisely because of its accidental or inadvertent choices, so it is an implicit reminder that seeking the director's original intention in any piece of art is a complete mirage. Detour is certainly not a good film, but it just might be a great one. (It is a short film too, and, out of copyright, it is available online for free.)

Safe (1995) Safe is a subtly disturbing film about an upper-middle-class housewife who begins to complain about vague symptoms of illness. Initially claiming that she doesn't feel right, Carol starts to have unexplained headaches, a dry cough and nosebleeds, and eventually begins to have trouble breathing. Carol's family doctor treats her concerns with little care, and suggests to her husband that she sees a psychiatrist. Yet Carol's episodes soon escalate. For example, as a 'homemaker' and with nothing else to occupy her, Carol's orders a new couch for a party. But when the store delivers the wrong one (although it is not altogether clear that they did), Carol has a near breakdown. Unsure where to turn, an 'allergist' tells Carol she has "Environmental Illness," and so Carol eventually checks herself into a new-age commune filled with alternative therapies. On the surface, Safe is thus a film about the increasing about of pesticides and chemicals in our lives, something that was clearly felt far more viscerally in the 1990s. But it is also a film about how lack of genuine healthcare for women must be seen as a critical factor in the rise of crank medicine. (Indeed, it made for something of an uncomfortable watch during the coronavirus lockdown.) More interestingly, however, Safe gently-yet-critically examines the psychosocial causes that may be aggravating Carol's illnesses, including her vacant marriage, her hollow friends and the 'empty calorie' stimulus of suburbia. None of this should be especially new to anyone: the gendered Victorian term 'hysterical' is often all but spoken throughout this film, and perhaps from the very invention of modern medicine, women's symptoms have often regularly minimised or outright dismissed. (Hilary Mantel's 2003 memoir, Giving Up the Ghost is especially harrowing on this.) As I opened this review, the film is subtle in its messaging. Just to take one example from many, the sound of the cars is always just a fraction too loud: there's a scene where a group is eating dinner with a road in the background, and the total effect can be seen as representing the toxic fumes of modernity invading our social lives and health. I won't spoiler the conclusion of this quietly devasting film, but don't expect a happy ending.

The Driver (1978) Critics grossly misunderstood The Driver when it was first released. They interpreted the cold and unemotional affect of the characters with the lack of developmental depth, instead of representing their dissociation from the society around them. This reading was encouraged by the fact that the principal actors aren't given real names and are instead known simply by their archetypes instead: 'The Driver', 'The Detective', 'The Player' and so on. This sort of quasi-Jungian erudition is common in many crime films today (Reservoir Dogs, Kill Bill, Layer Cake, Fight Club), so the critics' misconceptions were entirely reasonable in 1978. The plot of The Driver involves the eponymous Driver, a noted getaway driver for robberies in Los Angeles. His exceptional talent has far prevented him from being captured thus far, so the Detective attempts to catch the Driver by pardoning another gang if they help convict the Driver via a set-up robbery. To give himself an edge, however, The Driver seeks help from the femme fatale 'Player' in order to mislead the Detective. If this all sounds eerily familiar, you would not be far wrong. The film was essentially remade by Nicolas Winding Refn as Drive (2011) and in Edgar Wright's 2017 Baby Driver. Yet The Driver offers something that these neon-noir variants do not. In particular, the car chases around Los Angeles are some of the most captivating I've seen: they aren't thrilling in the sense of tyre squeals, explosions and flying boxes, but rather the vehicles come across like wild animals hunting one another. This feels especially so when the police are hunting The Driver, which feels less like a low-stakes game of cat and mouse than a pack of feral animals working together a gang who will tear apart their prey if they find him. In contrast to the undercar neon glow of the Fast & Furious franchise, the urban realism backdrop of the The Driver's LA metropolis contributes to a sincere feeling of artistic fidelity as well. To be sure, most of this is present in the truly-excellent Drive, where the chase scenes do really communicate a credible sense of stakes. But the substitution of The Driver's grit with Drive's soft neon tilts it slightly towards that common affliction of crime movies: style over substance. Nevertheless, I can highly recommend watching The Driver and Drive together, as it can tell you a lot about the disconnected socioeconomic practices of the 1980s compared to the 2010s. More than that, however, the pseudo-1980s synthwave soundtrack of Drive captures something crucial to analysing the world of today. In particular, these 'sounds from the past filtered through the present' bring to mind the increasing role of nostalgia for lost futures in the culture of today, where temporality and pop culture references are almost-exclusively citational and commemorational.

The Souvenir (2019) The ostensible outline of this quietly understated film follows a shy but ambitious film student who falls into an emotionally fraught relationship with a charismatic but untrustworthy older man. But that doesn't quite cover the plot at all, for not only is The Souvenir a film about a young artist who is inspired, derailed and ultimately strengthened by a toxic relationship, it is also partly a coming-of-age drama, a subtle portrait of class and, finally, a film about the making of a film. Still, one of the geniuses of this truly heartbreaking movie is that none of these many elements crowds out the other. It never, ever feels rushed. Indeed, there are many scenes where the camera simply 'sits there' and quietly observes what is going on. Other films might smother themselves through references to 18th-century oil paintings, but The Souvenir somehow evades this too. And there's a certain ring of credibility to the story as well, no doubt in part due to the fact it is based on director Joanna Hogg's own experiences at film school. A beautifully observed and multi-layered film; I'll be happy if the sequel is one-half as good.

The Wrestler (2008) Randy 'The Ram' Robinson is long past his prime, but he is still rarin' to go in the local pro-wrestling circuit. Yet after a brutal beating that seriously threatens his health, Randy hangs up his tights and pursues a serious relationship... and even tries to reconnect with his estranged daughter. But Randy can't resist the lure of the ring, and readies himself for a comeback. The stage is thus set for Darren Aronofsky's The Wrestler, which is essentially about what drives Randy back to the ring. To be sure, Randy derives much of his money from wrestling as well as his 'fitness', self-image, self-esteem and self-worth. Oh, it's no use insisting that wrestling is fake, for the sport is, needless to say, Randy's identity; it's not for nothing that this film is called The Wrestler. In a number of ways, The Sound of Metal (2019) is both a reaction to (and a quiet remake of) The Wrestler, if only because both movies utilise 'cool' professions to explore such questions of identity. But perhaps simply when The Wrestler was produced makes it the superior film. Indeed, the role of time feels very important for the Wrestler. In the first instance, time is clearly taking its toll on Randy's body, but I felt it more strongly in the sense this was very much a pre-2008 film, released on the cliff-edge of the global financial crisis, and the concomitant precarity of the 2010s. Indeed, it is curious to consider that you couldn't make The Wrestler today, although not because the relationship to work has changed in any fundamentalway. (Indeed, isn't it somewhat depressing the realise that, since the start of the pandemic and the 'work from home' trend to one side, we now require even more people to wreck their bodies and mental health to cover their bills?) No, what I mean to say here is that, post-2016, you cannot portray wrestling on-screen without, how can I put it, unwelcome connotations. All of which then reminds me of Minari's notorious red hat... But I digress. The Wrestler is a grittily stark darkly humorous look into the life of a desperate man and a sorrowful world, all through one tragic profession.

Thief (1981) Frank is an expert professional safecracker and specialises in high-profile diamond heists. He plans to use his ill-gotten gains to retire from crime and build a life for himself with a wife and kids, so he signs on with a top gangster for one last big score. This, of course, could be the plot to any number of heist movies, but Thief does something different. Similar to The Wrestler and The Driver (see above) and a number of other films that I watched this year, Thief seems to be saying about our relationship to work and family in modernity and postmodernity. Indeed, the 'heist film', we are told, is an understudied genre, but part of the pleasure of watching these films is said to arise from how they portray our desired relationship to work. In particular, Frank's desire to pull off that last big job feels less about the money it would bring him, but a displacement from (or proxy for) fulfilling some deep-down desire to have a family or indeed any relationship at all. Because in theory, of course, Frank could enter into a fulfilling long-term relationship right away, without stealing millions of dollars in diamonds... but that's kinda the entire point: Frank needing just one more theft is an excuse to not pursue a relationship and put it off indefinitely in favour of 'work'. (And being Federal crimes, it also means Frank cannot put down meaningful roots in a community.) All this is communicated extremely subtly in the justly-lauded lowkey diner scene, by far the best scene in the movie. The visual aesthetic of Thief is as if you set The Warriors (1979) in a similarly-filthy Chicago, with the Xenophon-inspired plot of The Warriors replaced with an almost deliberate lack of plot development... and the allure of The Warriors' fantastical criminal gangs (with their alluringly well-defined social identities) substituted by a bunch of amoral individuals with no solidarity beyond the immediate moment. A tale of our time, perhaps. I should warn you that the ending of Thief is famously weak, but this is a gritty, intelligent and strangely credible heist movie before you get there.

Uncut Gems (2019) The most exhausting film I've seen in years; the cinematic equivalent of four cups of double espresso, I didn't even bother even trying to sleep after downing Uncut Gems late one night. Directed by the two Safdie Brothers, it often felt like I was watching two films that had been made at the same time. (Or do I mean two films at 2X speed?) No, whatever clumsy metaphor you choose to adopt, the unavoidable effect of this film's finely-tuned chaos is an uncompromising and anxiety-inducing piece of cinema. The plot follows Howard as a man lost to his countless vices mostly gambling with a significant side hustle in adultery, but you get the distinct impression he would be happy with anything that will give him another high. A true junkie's junkie, you might say. You know right from the beginning it's going to end in some kind of disaster, the only question remaining is precisely how and what. Portrayed by an (almost unrecognisable) Adam Sandler, there's an uncanny sense of distance in the emotional chasm between 'Sandler-as-junkie' and 'Sandler-as-regular-star-of-goofy-comedies'. Yet instead of being distracting and reducing the film's affect, this possibly-deliberate intertextuality somehow adds to the masterfully-controlled mayhem. My heart races just at the memory. Oof.

Woman in the Dunes (1964) I ended up watching three films that feature sand this year: Denis Villeneuve's Dune (2021), Lawrence of Arabia (1962) and Woman in the Dunes. But it is this last 1964 film by Hiroshi Teshigahara that will stick in my mind in the years to come. Sure, there is none of the Medician intrigue of Dune or the Super Panavision-70 of Lawrence of Arabia (or its quasi-orientalist score, itself likely stolen from Anton Bruckner's 6th Symphony), but Woman in the Dunes doesn't have to assert its confidence so boldly, and it reveals the enormity of its plot slowly and deliberately instead. Woman in the Dunes never rushes to get to the film's central dilemma, and it uncovers its terror in little hints and insights, all whilst establishing the daily rhythm of life. Woman in the Dunes has something of the uncanny horror as Dogtooth (see above), as well as its broad range of potential interpretations. Both films permit a wide array of readings, without resorting to being deliberately obscurantist or being just plain random it is perhaps this reason why I enjoyed them so much. It is true that asking 'So what does the sand mean?' sounds tediously sophomoric shorn of any context, but it somehow applies to this thoughtfully self-contained piece of cinema.

A Quiet Place (2018) Although A Quiet Place was not actually one of the best films I saw this year, I'm including it here as it is certainly one of the better 'mainstream' Hollywood franchises I came across. Not only is the film very ably constructed and engages on a visceral level, I should point out that it is rare that I can empathise with the peril of conventional horror movies (and perhaps prefer to focus on its cultural and political aesthetics), but I did here. The conceit of this particular post-apocalyptic world is that a family is forced to live in almost complete silence while hiding from creatures that hunt by sound alone. Still, A Quiet Place engages on an intellectual level too, and this probably works in tandem with the pure 'horrorific' elements and make it stick into your mind. In particular, and to my mind at least, A Quiet Place a deeply American conservative film below the surface: it exalts the family structure and a certain kind of sacrifice for your family. (The music often had a passacaglia-like strain too, forming a tombeau for America.) Moreover, you survive in this dystopia by staying quiet that is to say, by staying stoic suggesting that in the wake of any conflict that might beset the world, the best thing to do is to keep quiet. Even communicating with your loved ones can be deadly to both of you, so not emote, acquiesce quietly to your fate, and don't, whatever you do, speak up. (Or join a union.) I could go on, but The Quiet Place is more than this. It's taut and brief, and despite cinema being an increasingly visual medium, it encourages its audience to develop a new relationship with sound.

30 June 2020

Norbert Preining: TeX Live Debian update 20200629

More than a month has passed since the last update of TeX Live packages in Debian, so here is a new checkout!
All arch all packages have been updated to the tlnet state as of 2020-06-29, see the detailed update list below. Enjoy. New packages akshar, beamertheme-pure-minimalistic, biblatex-unified, biblatex-vancouver, bookshelf, commutative-diagrams, conditext, courierten, ektype-tanka, hvarabic, kpfonts-otf, marathi, menucard, namedef, pgf-pie, pwebmac, qrbill, semantex, shtthesis, tikz-lake-fig, tile-graphic, utf8add. Updated packages abnt, achemso, algolrevived, amiri, amscls, animate, antanilipsum, apa7, babel, bangtex, baskervillef, beamerappendixnote, beamerswitch, beamertheme-focus, bengali, bib2gls, biblatex-apa, biblatex-philosophy, biblatex-phys, biblatex-software, biblatex-swiss-legal, bibleref, bookshelf, bxjscls, caption, ccool, cellprops, changes, chemfig, circuitikz, cloze, cnltx, cochineal, commutative-diagrams, comprehensive, context, context-vim, cquthesis, crop, crossword, ctex, cweb, denisbdoc, dijkstra, doclicense, domitian, dps, draftwatermark, dvipdfmx, ebong, ellipsis, emoji, endofproofwd, eqexam, erewhon, erewhon-math, erw-l3, etbb, euflag, examplep, fancyvrb, fbb, fbox, fei, fira, fontools, fontsetup, fontsize, forest-quickstart, gbt7714, genealogytree, haranoaji, haranoaji-extra, hitszthesis, hvarabic, hyperxmp, icon-appr, kpfonts, kpfonts-otf, l3backend, l3build, l3experimental, l3kernel, latex-amsmath-dev, latexbangla, latex-base-dev, latexdemo, latexdiff, latex-graphics-dev, latexindent, latex-make, latexmp, latex-mr, latex-tools-dev, libertinus-fonts, libertinust1math, lion-msc, listings, logix, lshort-czech, lshort-german, lshort-polish, lshort-portuguese, lshort-russian, lshort-slovenian, lshort-thai, lshort-ukr, lshort-vietnamese, luamesh, lua-uca, luavlna, lwarp, marathi, memoir, mnras, moderntimeline, na-position, newcomputermodern, newpx, nicematrix, nodetree, ocgx2, oldstandard, optex, parskip, pdfcrop, pdfpc, pdftexcmds, pdfxup, pgf, pgfornament, pgf-pie, pgf-umlcd, pgf-umlsd, pict2e, plautopatch, poemscol, pst-circ, pst-eucl, pst-func, pstricks, pwebmac, pxjahyper, quran, rec-thy, reledmac, rest-api, sanskrit, sanskrit-t1, scholax, semantex, showexpl, shtthesis, suftesi, svg, tcolorbox, tex4ht, texinfo, thesis-ekf, thuthesis, tkz-doc, tlshell, toptesi, tuda-ci, tudscr, twemoji-colr, univie-ling, updmap-map, vancouver, velthuis, witharrows, wtref, xecjk, xepersian-hm, xetex-itrans, xfakebold, xindex, xindy, xltabular, yathesis, ydoc, yquant, zref.

28 July 2017

Joachim Breitner: How is coinduction the dual of induction?

Earlier today, I demonstrated how to work with coinduction in the theorem provers Isabelle, Coq and Agda, with a very simple example. This reminded me of a discussion I had in Karlsruhe with my then colleague Denis Lohner: If coinduction is the dual of induction, why do the induction principles look so different? I like what we observed there, so I d like to share this. The following is mostly based on my naive understanding of coinduction based on what I observe in the implementation in Isabelle. I am sure that a different, more categorial presentation of datatypes (as initial resp. terminal objects in some category of algebras) makes the duality more obvious, but that does not necessarily help the working Isabelle user who wants to make sense of coninduction.

Inductive lists I will use the usual polymorphic list data type as an example. So on the one hand, we have normal, finite inductive lists:
datatype 'a list = nil   cons (hd : 'a) (tl : "'a list")
with the well-known induction principle that many of my readers know by heart (syntax slightly un-isabellized):
P nil   ( x xs. P xs   P (cons x xs))     xs. P xs

Coinductive lists In contrast, if we define our lists coinductively to get possibly infinite, Haskell-style lists, by writing
codatatype 'a llist = lnil   lcons (hd : 'a)  (tl : "'a llist")
we get the following coinduction principle:
(  xs ys.
    R xs ys'   (xs = lnil) = (ys = lnil)  
               (xs   lnil   ys'   lnil  
	         hd xs = hd ys   R (tl xs) (tl ys)))  
  (  xs ys. R xs ys   xs = ys)
This is less scary that it looks at first. It tell you if you give me a relation R between lists which implies that either both lists are empty or both lists are nonempty, and furthermore if both are non-empty, that they have the same head and tails related by R, then any two lists related by R are actually equal. If you think of the infinte list as a series of states of a computer program, then this is nothing else than a bisimulation. So we have two proof principles, both of which make intuitive sense. But how are they related? They look very different! In one, we have a predicate P, in the other a relation R, to point out just one difference.

Relation induction To see how they are dual to each other, we have to recognize that both these theorems are actually specializations of a more general (co)induction principle. The datatype declaration automatically creates a relator:
rel_list :: ('a   'b   bool)   'a list   'b list   bool
The definition of rel_list R xs ys is that xs and ys have the same shape (i.e. length), and that the corresponding elements are pairwise related by R. You might have defined this relation yourself at some time, and if so, you probably introduced it as an inductive predicate. So it is not surprising that the following induction principle characterizes this relation:
Q nil nil  
( x xs y ys. R x y   Q xs ys   Q (cons x xs) (cons y ys))  
( xs ys   rel_list R xs ys   Q xs ys)
Note how how similar this lemma is in shape to the normal induction for lists above! And indeed, if we choose Q xs ys (P xs xs = ys) and R x y (x = y), then we obtain exactly that. In that sense, the relation induction is a generalization of the normal induction.

Relation coinduction The same observation can be made in the coinductive world. Here, as well, the codatatype declaration introduces a function
rel_llist :: ('a   'b   bool)   'a llist   'b llist   bool
which relates lists of the same shape with related elements only that this one also relates infinite lists, and therefore is a coinductive relation. The corresponding rule for proof by coinduction is not surprising and should remind you of bisimulation, too:
( xs ys.
    R xs ys   (xs = lnil) = (ys = lnil)  
              (xs   lnil   ys   lnil  
	        Q (hd xs) (hd ys)   R (tl xs) (tl ys)))  
(  xs ys   R xs ys   rel_llist Q xs ys)
It is even more obvious that this is a generalization of the standard coinduction principle shown above: Just instantiate Q with equality, which turns rel_llist Q into equality on the lists, and you have the theorem above.

The duality With our induction and coinduction principle generalized to relations, suddenly a duality emerges: If you turn around the implication in the conclusion of one you get the conclusion of the other one. This is an example of cosomething is something with arrows reversed . But what about the premise(s) of the rules? What happens if we turn around the arrow here? Although slighty less immediate, it turns out that they are the same as well. To see that, we start with the premise of the coinduction rule, reverse the implication and then show that to be equivalent to the two premises of the induction rule:
( xs ys.
    R xs ys   (xs = lnil) = (ys = lnil)  
              (xs   lnil   ys   lnil  
	        Q (hd xs) (hd ys)   R (tl xs) (tl ys)))
=   case analysis (the other two cases are vacuously true)  
  ( xs ys.
    xs = lnil   ys = lnil  
    R xs ys   (xs = lnil) = (ys = lnil)  
              (xs   lnil   ys   lnil  
	        Q (hd xs) (hd ys)   R (tl xs) (tl ys)))
  ( xs ys.
    xs   lnil   ys   lnil
    R xs ys   (xs = lnil) = (ys = lnil)  
              (xs   lnil   ys   lnil  
	        Q (hd xs) (hd ys)   R (tl xs) (tl ys)))
=   simplification  
  ( xs ys.  xs = lnil   ys = lnil   R xs ys
  ( x xs y ys.  R (cons x xs) (cons y ys)   (Q x y   R xs ys))
=   more rewriting  
  R nil nil
  ( x xs y ys. Q x y   R xs ys   R (cons x xs) (cons y ys))

Conclusion The coinduction rule is not the direct dual of the induction rule, but both are specializations of more general, relational proof methods, where the duality is clearly present. More generally, this little excursion shows that it is often beneficial to think of types less as sets, and more as relations this way of thinking is surprisingly fruitful, and led to proofs of parametricity and free theorems and other nice things.

31 March 2017

Chris Lamb: Free software activities in March 2017

Here is my monthly update covering what I have been doing in the free software world (previous month):
Reproducible builds

Whilst anyone can inspect the source code of free software for malicious flaws, most software is distributed pre-compiled to end users. The motivation behind the Reproducible Builds effort is to permit verification that no flaws have been introduced either maliciously or accidentally during this compilation process by promising identical results are always generated from a given source, thus allowing multiple third-parties to come to a consensus on whether a build was compromised. I have generously been awarded a grant from the Core Infrastructure Initiative to fund my work in this area. This month I:
I also made the following changes to our tooling:
diffoscope

diffoscope is our in-depth and content-aware diff utility that can locate and diagnose reproducibility issues.

  • New features/optimisations:
    • Extract squashfs archive in one go rather than per-file, speeding up ISO comparison by ~10x.
    • Add support for .docx and .odt files via docx2txt & odt2txt. (#859056).
    • Add support for PGP files via pgpdump. (#859034).
    • Add support for comparing Pcap files. (#858867).
    • Compare GIF images using gifbuild. (#857610).
  • Bug fixes:
    • Ensure that we really are using ImageMagick and not the GraphicsMagick compatibility layer. (#857940).
    • Fix and add test for meaningless 1234-content metadata when introspecting archives. (#858223).
    • Fix detection of ISO9660 images processed with isohybrid.
    • Skip icc tests if the Debian-specific patch is not present. (#856447).
    • Support newer versions of cbfstool to avoid test failures. (#856446).
    • Update the progress bar prior to working to ensure filename is in sync.
  • Cleanups:
    • Use /usr/share/dpkg/pkg-info.mk over manual calls to dpkg-parsechangelog in debian/rules.
    • Ensure tests and the runtime environment can locate binaries in /usr/sbin (eg. tcpdump).

strip-nondeterminism

strip-nondeterminism is our tool to remove specific non-deterministic results from a completed build.

  • Fix a possible endless loop while stripping .ar files due to trusting the file's own file size data. (#857975).
  • Add support for testing files we should reject and include the filename when evaluating fixtures.

buildinfo.debian.net

buildinfo.debian.net is my experiment into how to process, store and distribute .buildinfo files after the Debian archive software has processed them.

  • Add support for Format: 1.0. (#20).
  • Don't parse Format: header as the source package version. (#21).
  • Show the reproducible status of packages.


Debian


I submitted my platform for the 2017 Debian Project Leader Elections. This was subsequently covered on LWN and I have been participating in the discussions on the debian-vote mailing list since then.


Debian LTS

This month I have been paid to work 14.75 hours on Debian Long Term Support (LTS). In that time I did the following:
  • "Frontdesk" duties, triaging CVEs, etc.
  • Issued DLA 848-1 for the freetype font library fixing a denial of service vulnerability.
  • Issued DLA 851-1 for wget preventing a header injection attack.
  • Issued DLA 863-1 for the deluge BitTorrent client correcting a cross-site request forgery vulnerability.
  • Issued DLA 864-1 for jhead (an EXIF metadata tool) patching an arbitrary code execution vulnerability.
  • Issued DLA 865-1 for the suricata intrusion detection system, fixing an IP protocol matching error.
  • Issued DLA 871-1 for python3.2 fixing a TLS stripping vulnerability in the smptlib library.
  • Issued DLA 873-1 for apt-cacher preventing a HTTP response splitting vulnerability.
  • Issued DLA 876-1 for eject to prevent an issue regarding the checking of setuid(2) and setgid(2) return values.

Uploads
  • python-django:
    • 1:1.10.6-1 New upstream bugfix release.
    • 1:1.11~rc1-1 New upstream release candidate.
  • redis:
    • 3:3.2.8-2 Avoid conflict between RuntimeDirectory and tmpfiles.d(5) both attempting to create /run/redis with differing permissions. (#856116)
    • 3:3.2.8-3 Revert the creation of a /usr/bin/redis-check-rdb to /usr/bin/redis-server symlink to avoid a dangling symlink if only the redis-tools package is installed. (#858519)
  • gunicorn 19.7.0-1 & 19.7.1-1 New upstream releases.
  • adminer 4.3.0-1 New upstream release.

Finally, I also made the following non-maintainer uploads (NMUs):


FTP Team

As a Debian FTP assistant I ACCEPTed 121 packages: 4pane, adql, android-platform-system-core, android-sdk-helper, braillegraph, deepnano, dh-runit, django-auth-ldap, django-dirtyfields, drf-extensions, gammaray, gcc-7, gnome-keysign, golang-code.gitea-sdk, golang-github-bluebreezecf-opentsdb-goclient, golang-github-bsm-redeo, golang-github-cupcake-rdb, golang-github-denisenkom-go-mssqldb, golang-github-exponent-io-jsonpath, golang-github-facebookgo-ensure, golang-github-facebookgo-freeport, golang-github-facebookgo-grace, golang-github-facebookgo-httpdown, golang-github-facebookgo-stack, golang-github-facebookgo-subset, golang-github-go-openapi-loads, golang-github-go-openapi-runtime, golang-github-go-openapi-strfmt, golang-github-go-openapi-validate, golang-github-golang-geo, golang-github-gorilla-pat, golang-github-gorilla-securecookie, golang-github-issue9-assert, golang-github-issue9-identicon, golang-github-jaytaylor-html2text, golang-github-joho-godotenv, golang-github-juju-errors, golang-github-kisielk-gotool, golang-github-kubernetes-gengo, golang-github-lpabon-godbc, golang-github-lunny-log, golang-github-makenowjust-heredoc, golang-github-mrjones-oauth, golang-github-nbutton23-zxcvbn-go, golang-github-neelance-sourcemap, golang-github-ngaut-deadline, golang-github-ngaut-go-zookeeper, golang-github-ngaut-log, golang-github-ngaut-pools, golang-github-ngaut-sync2, golang-github-optiopay-kafka, golang-github-quobyte-api, golang-github-renstrom-dedent, golang-github-sergi-go-diff, golang-github-siddontang-go, golang-github-smartystreets-go-aws-auth, golang-github-xanzy-go-cloudstack, golang-github-xtaci-kcp, golang-github-yohcop-openid-go, graywolf, haskell-raaz, hfst-ospell, hikaricp, iptraf-ng, kanboard-cli, kcptun, kreport, libbluray, libcatmandu-store-elasticsearch-perl, libcsfml, libnet-prometheus-perl, libosmocore, libpandoc-wrapper-perl, libseqlib, matrix-synapse, mockldap, nfs-ganesha, node-buffer, node-pako, nose-el, nvptx-tools, nx-libs, open-ath9k-htc-firmware, pagein, paleomix, pgsql-ogr-fdw, profanity, pyosmium, python-biotools, python-django-extra-views, python-django-otp, python-django-push-notifications, python-dnslib, python-gmpy, python-gmpy2, python-holidays, python-kanboard, python-line-profiler, python-pgpy, python-pweave, python-raven, python-xapian-haystack, python-xopen, r-cran-v8, repetier-host, ruby-jar-dependencies, ruby-maven-libs, ruby-psych, ruby-retriable, seafile-client, spyder-unittest, stressant, systray-mdstat, telegram-desktop, thawab, tigris, tnseq-transit, typesafe-config, vibe.d, x2goserver & xmlrpc-c. I additionally filed 14 RC bugs against packages that had incomplete debian/copyright files against: golang-github-cupcake-rdb, golang-github-sergi-go-diff, graywolf, hfst-ospell, libbluray, pgsql-ogr-fdw, python-gmpy, python-gmpy2, python-pgpy, python-xapian-haystack, repetier-host, telegram-desktop, tigris & xmlrpc-c.

1 March 2017

Paul Wise: FLOSS Activities February 2017

Changes

Issues

Review

Administration
  • Debian: do the samhain dance, ask for new local contacts at one site, ask local admins to reset one machine, powercycle 2 dead machines, redirect 1 user to the support channels, redirect 1 user to a service admin, redirect 1 spam reporter to the right mechanisms, investigate mail logs for a missing bug report, ping bugs-search.d.o service admin about moving off glinka and remove data, poke cdimage-search.d.o service admin about moving off glinka, update a cron job on denis.d.o for the rename of letsencrypt.sh to dehydrated, debug planet.d.o issue and remove stray cron job lock file, check if ftp is used on a couple of security.d.o mirrors, discuss storage upgrade for LeaseWeb for snapshot.d.o/deriv.d.n/etc, investigate SSD SMART error and ignore the unknown attribute, ask 9 users to restart their processes, investigate apt-get update failure in nagios, swapoff/swapon a swap file to drain it, restart/disable some failed services, help restore the backup server, debug stretch /dev/log issue,
  • Debian QA: deploy merged PTS/tracker patches,
  • Debian wiki: answer 1 IP-blocked VPN user, pinged 1 user on IRC about their bouncing mail, disabled 4 accounts due to bouncing mail, redirect 1 person to documentation/lists, whitelist 5 email addresses, forward 1 password reset token, killed 1 spammer account, reverted 1 spammer edit,
  • Debian mentors: security upgrades, check which email a user signed up with
  • Openmoko: security upgrades, daemon restarts, reboot

Debian derivatives
  • Turned off the census cron job because it ran out of disk space
  • Update Armbian sources.list
  • Ping siduction folks about updating their sources.list
  • Start a discussion about DebConf17
  • Notify the derivatives based on jessie or older that stretch is frozen
  • Invite Rebellin Linux (again)

Sponsors The libesedb Debian backport was sponsored by my employer. All other work was done on a volunteer basis.

18 January 2017

Norbert Preining: Debian/TeX Live January 2017

As the freeze of the next release is closing in, I have updated a bunch of packages around TeX: All of the TeX Live packages (binaries and arch independent ones) and tex-common. I might see whether I get some updates of ConTeXt out, too.
texlive2016-debian The changes in the binaries are mostly cosmetic: one removal of a non-free (unclear-free) file, and several upstream patches got cherrypicked (dvips, tltexjp contact email, upmendex, dvipdfmx). I played around with including LuaTeX v1.0, but that breaks horribly with the current packages in TeX Live, so I refrained from it. The infrastructure package tex-common got a bugfix for updates from previous releases, and for the other packages there is the usual bunch of updates and new packages. Enjoy! New packages arimo, arphic-ttf, babel-japanese, conv-xkv, css-colors, dtxdescribe, fgruler, footmisx, halloweenmath, keyfloat, luahyphenrules, math-into-latex-4, mendex-doc, missaali, mpostinl, padauk, platexcheat, pstring, pst-shell, ptex-fontmaps, scsnowman, stanli, tinos, undergradmath, yaletter. Updated packages acmart, animate, apxproof, arabluatex, arsclassica, babel-french, babel-russian, baskervillef, beamer, beebe, biber, biber.x86_64-linux, biblatex, biblatex-apa, biblatex-chem, biblatex-dw, biblatex-gb7714-2015, biblatex-ieee, biblatex-philosophy, biblatex-sbl, bidi, calxxxx-yyyy, chemgreek, churchslavonic, cochineal, comicneue, cquthesis, csquotes, ctanify, ctex, cweb, dataref, denisbdoc, diagbox, dozenal, dtk, dvipdfmx, dvipng, elocalloc, epstopdf, erewhon, etoolbox, exam-n, fbb, fei, fithesis, forest, glossaries, glossaries-extra, glossaries-french, gost, gzt, historische-zeitschrift, inconsolata, japanese-otf, japanese-otf-uptex, jsclasses, latex-bin, latex-make, latexmk, lt3graph, luatexja, markdown, mathspec, mcf2graph, media9, mendex-doc, metafont, mhchem, mweights, nameauth, noto, nwejm, old-arrows, omegaware, onlyamsmath, optidef, pdfpages, pdftools, perception, phonrule, platex-tools, polynom, preview, prooftrees, pst-geo, pstricks, pst-solides3d, ptex, ptex2pdf, ptex-fonts, qcircuit, quran, raleway, reledmac, resphilosophica, sanskrit, scalerel, scanpages, showexpl, siunitx, skdoc, skmath, skrapport, smartdiagram, sourcesanspro, sparklines, tabstackengine, tetex, tex, tex4ht, texlive-scripts, tikzsymbols, tocdata, uantwerpendocs, updmap-map, uplatex, uptex, uptex-fonts, withargs, wtref, xcharter, xcntperchap, xecjk, xellipsis, xepersian, xint, xlop, yathesis.

3 November 2016

Norbert Preining: Debian/TeX Live 2016.20161103-1

This month s update falls onto a national holiday in Japan. My recent start as a normal company employee in Japan doesn t leave me enough time during normal days to work on Debian, so things have to wait for holidays. There have been a few notable changes in the current packages, and above all I wanted to fix an RC bug and on the way fixed also several other (sometimes rather old) bugs.
texlive2016-debian From the list of new packages I want to pick apxproof: I have written something myself for one of my rather long papers (with proofs about 60pp), where at times I had to factor out the proofs into an appendix. I did this my own way, but I would have preferred to have a nice package! Another interesting change is the upstream merge of collection-mathextra (which translated to the Debian package texlive-math-extra) and collection-science (Debian: texlive-science) into a new collection collection-mathscience. Since introducing new packages and phasing out old ones is generally a pain in Debian, I decided to digress from the upstream naming convention and use texlive-science for the new collection-mathscience. In the end Mathematics is the most important science of all  Finally also a word about removals: Several ConTeXt packages have been removed due to the fact that they are outdated. These removals will find their way in an update of the Debian ConTeXt package in near future. The TeX Live packages lost voss-mathmode, which was retracted by the author due to various reasons. He is working on an updated version that will hopeful reappear in both TeX Live and Debian in near future. Well, that s it for now. Here now the full list with links. Enjoy. New packages apxproof, bangorexam, biblatex-gb7714-2015, biblatex-lni, biblatex-sbl, context-cmscbf, context-cmttbf, context-inifile, context-layout, delimset, latex2nemeth, latexbangla, latex-papersize, ling-macros, notex-bst, platex-tools, testidx, uppunctlm, wtref, xcolor-material. Removed packages voss-mathmode. Updated packages apa6, autoaligne, babel-german, biblatex-abnt, biblatex-anonymous, biblatex-apa, biblatex-manuscripts-philology, biblatex-nature, biblatex-realauthor, bibtex, bidi, boondox, bxcjkjatype, chickenize, churchslavonic, cjk-gs-integrate, context-filter, cooking-units, ctex, denisbdoc, dvips, europasscv, fixme, glossaries, gzt, handout, imakeidx, ipaex-type1, jsclasses, jslectureplanner, kpathsea, l3build, l3experimental, l3kernel, l3packages, latexindent, latexmk, listofitems, luatexja, marginnote, mcf2graph, minted, multirow, nameauth, newpx, newtx, noto, nucleardata, optidef, overlays, pdflatexpicscale, pst-eucl, reledmac, repere, scanpages, semantic-markup, tableaux, tcolorbox, tetex, texlive-scripts, ticket, todonotes, tracklang, tudscr, turabian-formatting, updmap-map, uspace, visualtikz, xassoccnt, xecjk, yathesis.

24 June 2016

Norbert Preining: Debian/TeX Live 2016.20160623-1

About one month has passed since we did release TeX Live 2016, and more than a month since the last Debian packages, so it is high time to ship out a new checkout of upstream. Nothing spectacular new here, just lots and lots of updates since the freeze. texlive2016-debian I am dedicating this release to those intelligent beings who voted against the stupid Brexit and for remaining in the EC! I am still optimist! New packages aucklandthesis, autobreak, cquthesis, getargs, hustthesis, ietfbibs, linop, markdown, olsak-misc, optidef, sanitize-umlaut, umbclegislation, wordcount, xcntperchap. Updated packages academicons, achemso, acmart, acro, animate, apa6, arabluatex, archaeologie, babel-hungarian, beamertheme-epyt, beebe, biblatex-abnt, biblatex-anonymous, biblatex-bookinother, biblatex-caspervector, biblatex-chicago, biblatex-manuscripts-philology, biblatex-morenames, biblatex-opcit-booktitle, biblatex-philosophy, biblatex-realauthor, biblatex-source-division, biblatex-subseries, bidi, bookcover, bxjscls, caption, chemformula, chemmacros, circuitikz, cloze, cochineal, context, csplain, cstex, datetime2, denisbdoc, dvipdfmx-def, epstopdf, erewhon, exsol, fbb, fibeamer, fithesis, fontawesome, fontspec, fonts-tlwg, geschichtsfrkl, getmap, glossaries, glossaries-extra, graphics, graphics-cfg, gregoriotex, gzt, he-she, hook-pre-commit-pkg, hyperref, ifluatex, keyvaltable, koma-script, l3build, latex, latex-bin, limap, lollipop, lshort-chinese, luaotfload, luatex85, luatex-def, luatexja, lua-visual-debug, marginnote, mcf2graph, media9, minted, mptopdf, msu-thesis, musixtex, navigator, nwejm, oberdiek, patchcmd, pdfcomment, pdftex-def, pdfx, pkuthss, platex, pstricks, ptex, ptex2pdf, ptex-base, ptex-ng, reledmac, repere, scheme-xml, sduthesis, showlabels, tableaux, tcolorbox, tex4ht, texinfo, texlive-scripts, tex-overview, textpos, tools, translations, tudscr, unicode-data, uplatex, uptex, xassoccnt, xcharter, xetex, xindy, yathesis, ycbook. Enjoy.

18 April 2016

Norbert Preining: TeX Live 2016 pretest and Debian packages

Preparation for the release of TeX Live 2016 have started some time ago with the freeze of updates in TeX Live 2015. Yesterday we announced the official start of the pretest period. That means that we invite people to test the new release and help fixing bugs. At the same time I have uploaded the first set of packages of TeX Live 2016 for Debian to the experimental suite. texlive-2016-debian-pretest Concerning the binaries we do expect a few further changes, but hopefully nothing drastic. The most invasive change on the tlmgr side is that cryptographic signatures are now verified to guarantee authenticity of the packages downloaded, but this is rather irrelevant for Debian users (though I will look into how that works in user mode). Other than that, many packages have been updated or added since the last Debian packages, here is the unified list: acro, animate, appendixnumberbeamer, arabluatex, asapsym, asciilist, babel-belarusian, bibarts, biblatex-bookinarticle, biblatex-bookinother, biblatex-caspervector, biblatex-chicago, biblatex-gost, biblatex-ieee, biblatex-morenames, biblatex-opcit-booktitle, bibtexperllibs, bxdvidriver, bxenclose, bxjscls, bxnewfont, bxpapersize, chemnum, cjk-ko, cochineal, csplain, cstex, datetime2-finnish, denisbdoc, dtx, dvipdfmx-def, ejpecp, emisa, fithesis, fnpct, font-change-xetex, forest, formation-latex-ul, gregoriotex, gzt, hausarbeit-jura, hyperxmp, imakeidx, jacow, l3, l3kernel, l3packages, latex2e, latex2e-help-texinfo-fr, latex-bib2-ex, libertinust1math, lollipop, lt3graph, lua-check-hyphen, lualibs, luamplib, luatexja, mathalfa, mathastext, mcf2graph, media9, metrix, nameauth, ndsu-thesis, newtx, normalcolor, noto, nucleardata, nwejm, ocgx2, pdfcomment, pdfpages, pkuthss, polyglossia, proposal, qcircuit, reledmac, rmathbr, savetrees, scanpages, stex, suftesi, svrsymbols, teubner, tex4ebook, tex-ini-files, tikzmark, tikzsymbols, titlesec, tudscr, typed-checklist, ulthese, visualtikz, xespotcolor, xetex-def, xetexko, ycbook, yinit-otf. Enjoy.

20 December 2015

Lunar: Reproducible builds: week 34 in Stretch cycle

What happened in the reproducible builds effort between December 13th to December 19th: Infrastructure Niels Thykier started implementing support for .buildinfo files in dak. A very preliminary commit was made by Ansgar Burchardt to prevent .buildinfo files from being removed from the upload queue. Toolchain fixes Mattia Rizzolo rebased our experimental debhelper with the changes from the latest upload. New fixes have been merged by OCaml upstream. Packages fixed The following 39 packages have become reproducible due to changes in their build dependencies: apache-mime4j, avahi-sharp, blam, bless, cecil-flowanalysis, cecil, coco-cs, cowbell, cppformat, dbus-sharp-glib, dbus-sharp, gdcm, gnome-keyring-sharp, gudev-sharp-1.0, jackson-annotations, jackson-core, jboss-classfilewriter, jboss-jdeparser2, jetty8, json-spirit, lat, leveldb-sharp, libdecentxml-java, libjavaewah-java, libkarma, mono.reflection, monobristol, nuget, pinta, snakeyaml, taglib-sharp, tangerine, themonospot, tomboy-latex, widemargin, wordpress, xsddiagram, xsp, zeitgeist-sharp. 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 Packages in experimental are now tested on armhf. (h01ger) Arch Linux packages in the multilib and community repositories (4,000 more source packages) are also being tested. All of these test results are better analyzed and nicely displayed together with each package. (h01ger) For Fedora, build jobs can now run in parallel. Two are currently running, now testing reproducibility of 785 source packages from Fedora 23. mock/1.2.3-1.1 has been uploaded to experimental to better build RPMs. (h01ger) Work has started on having automatic build node pools to maximize use of armhf build nodes. (Vagrant Cascadian) diffoscope development Version 43 has been released on December 15th. It has been dubbed as epic! as it contains many contributions that were written around the summit in Athens. Baptiste Daroussin found that running diffoscope on some Tar archives could overwrite arbitrary files. This has been fixed by using libarchive instead of Python internal Tar library and adding a sanity check for destination paths. In any cases, until proper sandboxing is implemented, don't run diffosope on unstrusted inputs outside an isolated, throw-away system. Mike Hommey identified that the CBFS comparator would needlessly waste time scanning big files. It will now not consider any files bigger than 24 MiB 8 MiB more than the largest ROM created by coreboot at this time. An encoding issue related to Zip files has also been fixed. (Lunar) New comparators have been added: Android dex files (Reiner Herrmann), filesystem images using libguestfs (Reiner Herrmann), icons and JPEG images using libcaca (Chris Lamb), and OS X binaries (Clemens Lang). The comparator for Free Pascal Compilation Unit will now only be used when the unit version matches the compiler one. (Levente Polyak) A new multi-file HTML output with on-demand loading of long diffs is available through the --html-dir option. On-demand loading requires jQuery which path can be specified through the --jquery option. The diffs can also be simply browsed for non-JavaScript users or when jQuery is not available. (Joachim Breitner) Example of on-demand loading in diffosope Portability toward other systems has been improved: old versions of GNU diff are now supported (Mike McQuaid), suggestion of the appropriate locale is now the more generic en_US.UTF-8 (Ed Maste), the --list-tools option can now support multiple systems (Mattia Rizzolo, Levente Polyak, Lunar). Many internal changes and code clean-ups have been made, paving the way for parallel processing. (Lunar) Version 44 was released on December 18th fixing an issue affecting .deb lacking a md5sums file introduced in a previous refactoring (Lunar). Support has been added for Mozilla optimized Zip files. (Mike Hommey). The HTML output has been optimized in size (Mike Hommey, Esa Peuha, Lunar), speed (Lunar), and will now properly number lines (Mike Hommey). A message will always be displayed when lines are ignored at the end of a diff (Lunar). For portability and consistency, Python os.walk() function is now used instead of find to perform directory listing. (Lunar) Documentation update Package reviews 143 reviews have been removed, 69 added and 22 updated in the previous week. Chris Lamb reported 12 new FTBFS issues. News issues identified this week: random_order_in_init_py_generated_by_python-genpy, timestamps_in_copyright_added_by_perl_dist_zilla, random_contents_in_dat_files_generated_by_chasen-dictutils_makemat, timestamps_in_documentation_generated_by_pandoc. Chris West did some improvements on the scripts used to manage notes in the misc repository. Misc. Accounts of the reproducible builds summit in Athens were written by Thomas Klausner from NetBSD and Hans-Christoph Steiner from The Guardian Project. Some openSUSE developers are working on a hackweek on reproducible builds which was discussed on the opensuse-packaging mailing-list.

25 November 2015

Daniel Pocock: Drone strikes coming to Molenbeek?

The St Denis siege last week and the Brussels lockdown this week provides all of us in Europe with an opportunity to reflect on why over ten thousand refugees per day have been coming here from the middle east, especially Syria. At this moment, French warplanes and American drones are striking cities and villages in Syria, killing whole families in their effort to shortcut the justice system and execute a small number of very bad people without putting them on trial. Some observers estimate air strikes and drones kill twenty innocent people for every one bad guy. Women, children, the sick, elderly and even pets are most vulnerable. The leak of the collateral murder video simultaneously brought Wikileaks into the public eye and demonstrated how the crew of a US attack helicopter had butchered unarmed civilians and journalists like they were playing a video game. Just imagine that the French president had sent the fighter jets to St Denis and Molenbeek instead of using law enforcement. After all, how are the terrorists there any better or worse than those in Syria, don't they deserve the same fate? Or what if Obama had offered to help out with a few drone strikes on suburban Brussels? After all, if the drones are such a credible solution for Syria's future, why won't they solve Brussels' (perceived) problems too? If the aerial bombing "solution" had been attempted in a western country, it would have lead to chaos. Half the population of Paris and Brussels would find themselves camping at the migrant camps in Calais, hoping to sneak into the UK in the back of a truck. Over a hundred years ago, Russian leaders proposed a treaty agreeing never to drop bombs from balloons and the US and UK happily signed it. Sadly, the treaty wasn't updated after the invention of fighter jets, attack helicopters, rockets, inter-continental ballistic missiles, satellites and drones. The reality is that asymmetric warfare hasn't worked and never will work in the middle east and as long as it is continued, experts warn that Europe may continue to face the consequences of refugees, terrorists and those who sympathize with their methods. By definition, these people can easily move from place to place and it is ordinary citizens and small businesses who will suffer a lot more under lockdowns and other security measures. In our modern world, people often look to technology for shortcuts. The use of drones in the middle east is a shortcut from a country that spent enormous money on ground invasions of Iraq and Afghanistan and doesn't want to do it again. Unfortunately, technological shortcuts can't always replace the role played by real human beings, whether it is bringing law and order to the streets or in any other domain. Aerial bombardment - by warplane or by drone - carries an implicitly racist message, that the people abused by these drone attacks are not equivalent to the rest of us, they can't benefit from the normal procedures of justice, they don't have rights, they are not innocent until proven guilty and they are expendable. The French police deserve significant credit for the relatively low loss of life in the St Denis siege. If their methods and results were replicated in Syria and other middle eastern hotspots, would it be more likely to improve the situation in the long term than drone strikes?

21 August 2015

Simon Kainz: DUCK challenge: Final week

Well, here are the stats for the final week of the DUCK challenge as well as DebConf15: So we had 21 packages fixed and uploaded by 14 different uploaders. People were really working hard on this during DebConf. A big "Thank You" to you!! Since the start of this challenge, a total of 89 packages, were fixed. Here is a quick overview:
Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7
# Packages 10 15 10 14 10 9 21
Total 10 25 35 49 59 68 89
Thank you all for participating - either on purpose or "accidentially": Some people were really surprised as i sneaked up on them at DebConf15, confronting them with a green lighter! I just tried to put even more fun into Debian, i hope this worked out Pevious articles are here: Week 1, Week 2, Week 3, Week 4, Week 5,Week 6.

16 August 2015

Lunar: Reproducible builds: week 16 in Stretch cycle

What happened in the reproducible builds effort this week: Toolchain fixes Valentin Lorentz sent a patch for ispell to initialize memory structures before dumping their content. In our experimental repository, qt4-x11 has been rebased on the latest version (Dhole), as was doxygen (akira). Packages fixed The following packages became reproducible due to changes in their build dependencies: backup-manager, cheese, coinor-csdp, coinor-dylp, ebook-speaker, freefem, indent, libjbcrypt-java, qtquick1-opensource-src, ruby-coffee-script, ruby-distribution, schroot, twittering-mode. 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: akira found another embedded code copy of texi2html in maxima. reproducible.debian.net Work on testing several architectures has continued. (Mattia/h01ger) Package reviews 29 reviews have been removed, 187 added and 34 updated this week. 172 new FTBFS reports were filled, 137 solely by Chris West (Faux). josch spent time investigating the issue with fonts in PDF files. Chris Lamb documented the issue affecting documentation generated by ocamldoc. Misc. Lunar presented a general Reproducible builds HOWTO talk at the Chaos Communication Camp 2015 in Germany on August 13th. Recordings are already available, as well as slides and script. h01ger and Lunar also used CCCamp15 as an opportunity to have discussions with members of several different projects about reproducible builds. Good news should be coming soon.

16 July 2013

Joachim Breitner: Ultimate Tic Tac Toe is always won by X

The blog Math with Bad Drawings recently featured an article about Ultimate Tic Tac Toe, a variant of Tic Tac Toe where each of the nine fields is a separate game of Tic Tac Toe. To mark a field of the large game as your, you have to win the small game therein. If you chose a field in the small game, this position determines the small field that the other play may play next. See the linked article for a full explanation. As far as I know, the question of who wins this game was open; at least nothing definite was known on Hacker News or on the Board Games StackExchange site. We discussed this a bit in our office, and my coworker Denis Lohner came up with what seems to be a winning strategy. Update: Not surprising, but with these variants of the rule, the winning strategy was already known.
Strategy Assume Denis ( ) plays against me ( ). Like most suggestions for a winning strategy for the first player, Denis (X) starts with the middle:
           
           
           
 
           
           
           
 
           
           
           
Now I have to put my in the center field of the center game. No matter where I place it, Denis will send me back ot the middle, until one field of the center game is free. Doing this eight times inevitably puts us in a position like this:
           
           
           
 
       
       
    
 
           
           
           
The only way I can influence the game is by chosing which I place last; this determines where Denis goes now. But (and please verify that carefully) it will not matter: The only thing required from that field is that there is a second field that, together with the center, forms a row (or column or diagonal); all fields satisfy that. Assume I placed the top-left last, and Denis has to go there. He will send me to that field:
           
           
           
 
       
       
    
 
           
           
           
Now the game of the first field is repeated: Whereever I send him, he will send me back. This works great for all fields but the middle field. The middle field is special: When I send him there, he has the free choice. He will pick the bottom-right game. In any case we will end up in this situation: I won the center game; I likely have a few in the top-left game. To be precise: I have a there if and only if the he has a in the top-left corner of the corresponding game. He also has the diagonal of the lower-right game. For example:
      
         
          
 
      
       
    
 
          
           
           
I have to put my mark in the lower-right game now. From now on, whereever I go, he will send me to either to the top-left or bottom-right game. I can do nothing about it (I cannot send him to the diagonal any more, and whereever I send him there is at least one of the top-left or bottom-right fields fee), so he wil easily win all the other games by getting the diagonal. Eventually, he wins the whole game with the bottom row or the right column:
      
         
        
 
      
       
    
 
         
         
      
This is not a formal proof yet, but hopefully close enough to convince you, or alternatively allow you to precisely describe how you can prevent losing against Denis strategy.

6 July 2012

Christian Perrier: DebConf running: take 4 (Masaya volcano)

Yet another Grand Plan today: run in Masaya Volcan National Park. Masaya Volcano is one of the most active volcanoes in Nicaragua. It is located only 20km south-east of Managua, so going there is as easy as renting a taxi. The original plan was to drive to the entrance of the National park (on the road to Masaya city), then run up to the volcan, so from 250m altitude up to about 600m. I therefore rented a taxi with the kind help of Norman, and we agreed to meet up at 08:30 at the hotel, along with No l and Daniel (who was planning to walk up, not running). After discussing here or there, Kurt and Gaudenz joined, both with the intent of running up. Others would also have liked to join, but I wasn't in the mood of organizing a full bus of Debconfers..:-). My plan was to enjoy pyself the hike...not to manage several taxis, etc. We thus packed in Denis blue taxi...a fancy and very visible customized blue car that looked like it had been the topic of on episode of the "Pimp My Ride" TV show..:-) Sitting 4 people at the back of a regular car without hitting some blue neon lights, or 7" TV screens is kinda tricky, but we made it. When arriving at the park's entrance, we however learned that it is forbidden to walk or hike up the road by foot, because of potential high concentrations of Carbon Dioxide. Sadly, we then had to pack again in the car and go up with it. After reaching the parking close to the volcano's active crater (that is said to have a small lava lake at its bottom, one of the very few in the world), we decided to head up for going round the Nindira crater, an inactive crater located slightly above. Unfortunately, again, the path around the Masaya crater is forbidden to walk on, because of landslides. We indeed still had great fun by running around this crater (which is about a 2.5 kilometers round trip, very very hilly and sometimes hard to run on such as a mountain path. After about 50 minutes and two laps (after all, we had a giant stadium!), we headed back to the parking, packed 5 sweating geeks in the car and went back to the hotel. Full GPS trace is here. I also put a few pictures on Facebook, supposedly visible by anybody : Masaya crater and Nindiri crater.

24 April 2012

David Bremner: Free OpenCL Implementations

It's spring, and young(ish?) hackers' minds turn to OpenCL. What is the state of things? I haven't the faintest idea, but I thought I'd try to share what I find out. So far, just some links. Details to be filled in later, particularly if you, dear reader, tell them to me. Specification LLVM based front ends Mesa backend Rumours/hopes of something working in mesa 8.1? Other projects

22 April 2012

Gregor Herrmann: RC bugs 2012/16

this week I've started to look at the (not yet release critical) gcc 4.7 bugs. luckily there are still enough patches for them in the BTS but at the time of writing, at least 138 are not fixed & don't have a patch yet. so still some work ahead.

& for those who prefer to fix debian/rules files, lucas' last archive rebuild (where build-arch was used) still leaves enough work, & many bugs are not difficult to fix with a basic understanding of makefiles & debian build sytems.

Next.