Canonical Experimented With Rebuilding Its Ubuntu 25.04 Packages Under LLVM/Clang

This morning the first test rebuild results of the "Plucky Puffin" for Ubuntu 25.04 were shared on the mailing list... While typically not interesting to outsiders, one interesting bit is that as a "bonus" they rebuilt the main components of Ubuntu 25.04 packages with the LLVM Clang compiler compared to the usual GCC compiler.

The Ubuntu test rebuild messages on the mailing list are typically not too interesting unless you are an Ubuntu maintainer/packager. Typically they just indicate what packages are failing to build either due to new compiler/toolchain upgrades and/or any issues with more niche CPU architectures, etc. It's also the first of several planned test rebuilds for Ubuntu 25.04 after making other GNU toolchain upgrades.

But what made this Plucky Puffin test rebuild more interesting is this:

"As a bonus, we tried to build the main component of plucky using LLVM, see

https://people.canonical.com/~ginggs/ftbfs-report/test-rebuild-20241219-plucky-llvm-plucky.html"

This appears to be the first time Canonical has experimented with rebuilding Ubuntu under the LLVM/Clang compiler rather than the standard GCC compiler. Indeed checking prior test rebuild mailing list messages didn't mention any "bonus" LLVM build.

That Ubuntu 25.04 test rebuild using the LLVM/Clang compiler did turn up many package build failures: for the main archive, 176 packages failed to build on x86_64, 205 packages failed building on armhf, and 131 packages failed building on ARM64, among the other architectures.

There is no indication of Canonical planning say to switch over to LLVM/Clang as its default C/C++ compiler in the near-term or anything like that, but interesting nevertheless especially as they have begun exploring more low-level improvements to make to the distribution and focusing more on out-of-the-box performance and other areas.

Those interested in the Ubuntu 25.04 test rebuild results can see this Ubuntu devel message.