In Fedora's rust-ravif package, the test encode8_opaque fails only on s390x, and only in Fedora 43/44. The most obvious common factor here is LLVM 21. I managed to reproduce the test failure in a fedora-rawhide-s390x mock chroot (on x86_64, using qemu-user-static) with a git checkout from upstream, https://github.com/kornelski/cavif-rs.git. I needed to compile tests in release mode, as Fedora does, and specify a single codegen unit: $ git clone https://github.com/kornelski/cavif-rs.git $ cd cavif-rs/ravif $ RUSTFLAGS='-Ccodegen-units=1' cargo test --release I filed a bug upstream, https://github.com/kornelski/cavif-rs/issues/109, which has many more details. Dan Horák reproduced the issue with Rust 1.92, 1.91 and 1.90 (all built with LLVM 21), but not with Rust 1.89 built with LLVM 20. Dan asked me to open a downstream bug on Rust in Fedora – so here it is! Reproducible: Always
for the record, I have been using a rawhide VM on real HW and then downgraded rust + cargo to older builds downloaded from koji, so only rust (and llvm with 1.89) changed
At first try, this test passes with the upstream stable (1.92.0) toolchain. However, Fedora raises the default CPU from z10 to z13, and upstream *does* fail the test with `-Ctarget-cpu=z13`. (This is still with its standard library as-is, not `-Zbuild-std`.)
cargo-bisect-rustc found it passing on nightly-2025-08-06 and failing on nightly-2025-08-07, which does correspond to the LLVM 21 update. https://github.com/rust-lang/rust/compare/ec7c02612527d185c379900b613311bc1dcbf7dc...7d82b83ed57d188ab3f2441a765a6419685a88a3
I found that it is not reproducible with LLVM 22, and I narrowed it down to commit fc12fc635b96 as the fix -- which cites an error in commit cdc7864 from LLVM 21. bug: https://github.com/llvm/llvm-project/commit/cdc786498650c028c9c8ce23dfbff81bf2780d14 fix: https://github.com/llvm/llvm-project/commit/fc12fc635b96e9fa521a33eb31336c539eed1918 I will confirm that with a backport to LLVM 21 and then send an llvm package PR.
Great job, Josh, thanks.
Thank you for investigating this!
FEDORA-2026-2928da47ab (llvm-21.1.8-6.fc44) has been submitted as an update to Fedora 44. https://bodhi.fedoraproject.org/updates/FEDORA-2026-2928da47ab
FEDORA-2026-2928da47ab (llvm-21.1.8-6.fc44) has been pushed to the Fedora 44 stable repository. If problem still persists, please make note of it in this bug report.
To close the loop, I removed the test skip in Rawhide[1] and rebuilt rust-ravif successfully with llvm-21.1.8-6.fc44[2]. [1] https://src.fedoraproject.org/rpms/rust-ravif/c/1c8722507198738b424bcd0ad9ca7e12690321ed?branch=rawhide [2] https://koji.fedoraproject.org/koji/buildinfo?buildID=2923348
FEDORA-2026-537e5ad775 (llvm-21.1.8-4.fc43) has been submitted as an update to Fedora 43. https://bodhi.fedoraproject.org/updates/FEDORA-2026-537e5ad775
FEDORA-2026-537e5ad775 has been pushed to the Fedora 43 testing repository. Soon you'll be able to install the update with the following command: `sudo dnf upgrade --enablerepo=updates-testing --refresh --advisory=FEDORA-2026-537e5ad775` You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2026-537e5ad775 See also https://fedoraproject.org/wiki/QA:Updates_Testing for more information on how to test updates.
FEDORA-2026-537e5ad775 (llvm-21.1.8-4.fc43) has been pushed to the Fedora 43 stable repository. If problem still persists, please make note of it in this bug report.