Hi George, thank you for testing the release candidates! I assume this might be caused by the fact that the release artifacts have been generated on new versions of MacOS that we didn't make any release from, yet. Feel free to open an issue! Best Magnus On 6/24/26 16:10, George Colpitts wrote:

Thanks Magnus! I installed it on my MacOS 26.5.1 with an M4 chip. I smoke tested it with llvm 22.1.8 and it works fine.

I did get some mysterious (to me at least) messages at install

* checking for 'ar'... Entering: checking for 'ar'   aarch64-apple-darwin-ar not found in search path   aarch64-apple-darwin-llvm-ar not found in search path * checking for 'ranlib'... Entering: checking for 'ranlib'   aarch64-apple-darwin-ranlib not found in search path   aarch64-apple-darwin-llvm-ranlib not found in search path * Entering: checking for 'nm'   aarch64-apple-darwin-nm not found in search path   aarch64-apple-darwin-llvm-nm not found in search path * checking for linker for merging objects... Entering: checking for linker for merging objects   aarch64-apple-darwin-ld not found in search path

Maybe the above is connected with the following for which I will be reporting a bug in the next day or two:

configure: WARNING: There are some differences between the toolchain configured by "configure" (default.target) and the toolchain configured by the "ghc-toolchain" program (default.target.ghc-toolchain).

16c16 < , tgtCxxCompiler = Cxx {cxxProgram = Program { prgPath =  "g++" , prgFlags = [] }} --- > , tgtCxxCompiler = Cxx {cxxProgram = Program { prgPath =  "g++" , prgFlags = ["--target=arm64-apple-darwin"] }}

Don't worry! This won't affect your ghc in any way. However, in a near future, we will move to configuring toolchains with "ghc-toolchain" by default, so you might have discovered a future bug. In light of it, if you've spotted this difference, please report a GHC bug at https://www.haskell.org/ghc/reportabug

Thanks again, George

On Wed, Jun 24, 2026 at 7:01 AM Magnus Viernickel via ghc-devs <ghc-devs@haskell.org> wrote:

Dear GHC users, distributors and devs,

I'm pleased to announce that the second release candidate for GHC 9.12.5 is now available from downloads.haskell.org <http://downloads.haskell.org> and on GHCup.

GHC 9.12.5 is a bug fix release. For a long form announcement, check out https://discourse.haskell.org/t/ghc-9-12-5-rc2-is-now-available/14313/1.

Mind that the very important overhaul of the semaphore-compat library to v2 is included in this release and that the semaphore feature will only start working with cabal-install 3.18 again, which is sadly a breaking but necessary change.

Your testing of the release is much appreciated. Many thanks to the nixpkgs and stackage package set distributors for testing the first release candidate.

If you find any issues with the candidate, please open an issue on the ghc issue tracker.

If there are no critical regressions are discovered within this release candidate, it will be published in about 2 weeks of time (the week of 8 July 2026).

Best

Magnus

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