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setNumCapabilities 257 crashes a program
by Artem Leshchev 06 Dec '24

06 Dec '24

Hi, I was going to report this bug on GitLab as wiki suggests, but this requires my account to be manually approved, so I'm going to write it down here. (But if you can approve "matshch" on GitLab I will appreciate it.) Consider the next program: import GHC.Conc main = setNumCapabilities 257 Compiling it with recent GHC and running it causes segmentation faults sometimes, depending on the compiler version and the environment. Here is the setup that works for me every time: $ printf "import GHC.Conc\nmain = setNumCapabilities 257" | docker run -i --rm haskell:9.10.1-bullseye runghc; echo $? 139 I first discovered this issue in Nix builds, and the next setup also crashes every time for me (it uses GHC 9.6.6 under the hood): $ nix run nixpkgs/b681065d0919f7eb5309a93cea2cfa84dec9aa88#ghc -- -threaded conc.hs; ./conc [1] 311106 segmentation fault (core dumped) ./conc For this fail I have a stack trace that is showing that crash happens somewhere in RTS: Program terminated with signal SIGSEGV, Segmentation fault. #0 0x000000000049d34f in assignNurseriesToCapabilities () [Current thread is 1 (LWP 311106)] (gdb) bt #0 0x000000000049d34f in assignNurseriesToCapabilities () #1 0x000000000049d96c in storageAddCapabilities () #2 0x000000000047eaea in setNumCapabilities () #3 0x000000000041042d in base_GHCziConcziSync_setNumCapabilities1_info () #4 0x0000000000000000 in ?? () I have tried reproducing it with GHCup versions of GHC and have found that it requires more capabilities to cause a crash. If you bump the setNumCapabilities argument to 259, it causes the program to crash under both ghc and runghc of versions 9.6.6, 9.8.4 and 9.10.1. I have also encountered cases (with 258 capabilities IIRC) when it crashes not on every program launch, and also noticed that ghci and runghc looks more susceptible to the problem. I first discovered this issue while upgrading our platform to NixOS 24.11, builds were failing on hedgehog tests. As I have discovered, it was seeing that our build machine has 256 cores, planning to run 256 workers, so it set capabilities to number of cores + 2 (so 258 in our case) to make some room for IO threads, and was crashing as I have shown above. -- Artem Leshchev

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Updating the migration guide for GHC 9.12
by Teofil Camarasu 06 Dec '24

06 Dec '24

Hi folks, With GHC 9.12 around the corner, I just wanted to give folks a gentle nudge to continue filling out the 9.12 migration guide <https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.12>. Ideally we would have an entry for each change that can break user code. And each entry would explain: - what the change is - what error messages caused by the change look like - how users can fix their code Though if you are aware of a breaking change and don't have the time to fill out a full entry, a stub is also appreciated and I (or someone else) can try to fill out the rest. I was also wondering if we should better integrate the migration guide into our processes. Maybe it should be mentioned in the MR template, so entries are added as part of the MR flow? I think that's the point when folks have stuff paged in and have the most context, but I also don't want to add extra hoops to jump through. Any thoughts? Cheers, Teo

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Re: Missing Enum instance for IoSubSystem
by Ben Gamari 06 Dec '24

06 Dec '24

Ben Gamari <ben(a)smart-cactus.org> writes: >> On Wed, Dec 04, 2024 at 10:44:13AM +0000, Tom Ellis wrote: >>> There is test in place to confirm that the API of base does not change >>> accidentally. >> [...] >> >> Just so everyone here is in the loop: >> >> My guess is that the CLC will consider this an unapproved change that >> should be reverted before release. >> > Unfortunately it appears that the situation is a bit worse than just an > Enum instance. > Thankfully it appears I was wrong here. The additional changes I report below are approved under CLC#263. The only problem here is the missing `Enum` and `Show` instances for `IoSubSystem`. I have amended the merge request (!13683) to address this. Cheers, - Ben

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Missing Enum instance for IoSubSystem
by Adithya Kumar 05 Dec '24

05 Dec '24

Hi all, In ghc 9.12-alpha the Enum instance for IoSubSystem no longer exists. I don't see this change mentioned anywhere in the docs (release notes/changelog) here: https://downloads.haskell.org/ghc/9.12.1-alpha1/docs/users_guide/9.12.1-not… Was this change intended or was it a refactoring issue? The datatype itself was moved from GHC.Internal.RTS.Flags to GHC.Internal.IO.SubSystem. The enum instance was earlier defined in GHC.Internal.RTS.Flags but now isn't defined in either of the modules. Best, Adithya

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GHC 9.8.4 is now available
by Ben Gamari 03 Dec '24

03 Dec '24

The GHC developers are happy to announce the availability of GHC 9.8.4. Binary distributions, source distributions, and documentation are available on the [release] page. This release is a small release fixing a few issues noted in 9.8.3, including: * Update the `filepath` submodule to avoid a misbehavior of `splitFileName` under Windows. * Update the `unix` submodule to fix a compilation issue on `musl` platforms * Fix a potential source of miscompilation when building large projects on 32-bit platforms * Fix unsound optimisation of `prompt#` uses A full accounting of changes can be found in the [release notes]. As some of the fixed issues do affect correctness users are encouraged to upgrade promptly. We would like to thank Microsoft Azure, GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, Haskell Foundation, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do give this release a try and open a [ticket] if you see anything amiss. Happy compiling! - Ben [release]: https://www.haskell.org/ghc/download_ghc_9_8_4.html [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [release notes]: https://downloads.haskell.org/~ghc/9.8.4/docs/users_guide/9.8.4-notes.html

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Beginning of GitLab maintenance
by Ben Gamari 03 Dec '24

03 Dec '24

Just a reminder that GitLab will be going down in just a moment. Cheers, - Ben

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GitLab downtime in 55 minutes
by Ben Gamari 03 Dec '24

03 Dec '24

Hi all, At 18:00 EST I will take GitLab down for a few minutes to complete a filesystem migration, hopefully at last freeing us from the disk space issue which has been plauguing us lately. I will sent notification when the migration is finished and things are back to normal. Cheers, - Ben

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Cannot get nightly builds of GHC
by Facundo Domínguez 02 Dec '24

02 Dec '24

Dear devs, Nightly builds of Liquid Haskell seem to be failing because https://ghc.gitlab.haskell.org gives 502 bad gateway. LH needs https://ghc.gitlab.haskell.org/ghcup-metadata/ghcup-nightlies-0.0.7.yaml Is there anyone I should tell about it? Thanks, Facundo -- All views and opinions expressed in this email message are the personal opinions of the author and do not represent those of the organization or its customers.

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[ANNOUNCE] GHC 9.12.1-rc1 is now available
by Zubin Duggal 29 Nov '24

29 Nov '24

The GHC developers are very pleased to announce the availability of the release candidate for GHC 9.12.1. Binary distributions, source distributions, and documentation are available at [downloads.haskell.org][]. We hope to have this release available via ghcup shortly. GHC 9.12 will bring a number of new features and improvements, including: * The new language extension [OrPatterns] allowing you to combine multiple pattern clauses into one. * The [MultilineStrings] language extension to allow you to more easily write strings spanning multiple lines in your source code. * Improvements to the OverloadedRecordDot extension, allowing the built-in `HasField` class to be used for records with fields of non lifted representations. * The [NamedDefaults] language extension has been introduced allowing you to define defaults for typeclasses other than `Num`. * More deterministic object code output, controlled by the `-fobject-determinism` flag, which improves determinism of builds a lot (though does not fully do so) at the cost of some compiler performance (1-2%). See #12935 for the details * GHC now accepts type syntax in expressions as part of [GHC Proposal #281]. * The WASM backend now has support for TemplateHaskell. * ... and many more A full accounting of changes can be found in the [release notes][]. As always, GHC's release status, including planned future releases, can be found on the GHC Wiki [status][]. We would like to thank GitHub, IOG, the Zw3rk stake pool, Well-Typed, Tweag I/O, Serokell, Equinix, SimSpace, the Haskell Foundation, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Finally, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do give this release a try and open a [ticket][] if you see anything amiss. Cheers, Zubin [release notes]: https://downloads.haskell.org/ghc/9.12.1-rc1/docs/users_guide/9.12.1-notes.… [status]: https://gitlab.haskell.org/ghc/ghc/-/wikis/GHC-status [downloads.haskell.org] https://downloads.haskell.org/ghc/9.12.1-rc1 [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new [OrPatterns]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0522-o… [MultilineStrings]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0569-m… [GHC Proposal #281]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0281-v… [NamedDefaults]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0409-e…

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GHC 9.12.1 updates and rc1 status
by Zubin Duggal 27 Nov '24

27 Nov '24

Hi all, We had planned to release 9.12.1-rc1 today. Unfortunately, we discovered a few regressions and bugs which need to be fixed before we can publish a release candidate, including #25382, #25375 and !13633. I am currently waiting for some of these fixes to land in master before backporting them to the release branch. I will try to have the release candidate out on Monday the 25th. The final release is currently scheduled for December 6th. We will inform you if there are any changes to this schedule. Cheers, Zubin.

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