** Description changed: SRU: Backport LLVM 18.1.8 to Ubuntu 24.04 LTS - A test rebuild using these packages was done as described in LP: + [ Impact ] + + * A newer Clang/LLVM version will be available for older releases as a + non-default LLVM selection. + + * On newer releases which had an older LLVM 18 release: some general + bug fixes and improvements that release note may or may not mention: + https://discourse.llvm.org/t/18-1-8-released/79725 (and mostly about + PowerPC fixes in 18.1.7). + + [ Test Plan ] + + * Run autopkgtests on reverse dependencies. + + * On LTS releases which don't currently have LLVM 18, we can just + examine the builtin unittest results, the unit tests don't need to have + a 100% pass rate because that's impossible even for the upstream + sometimes. + + [ Where problems could occur ] + + * LLVM is a very large piece of software with a lot of moving parts. A + lot could go wrong even in a minor release: optimizer misoptimizations, + Clang behavior changes, library linkage changes, C/C++ UB (undefined + behavior) handling changes, on-disk IR format change (maybe + compatible/upgradable), change of "internal" C++ API parameters, and + change of C API behaviors. + + * In the backport, since we will need to apply extra patches for LLVM + to compile in an older LTS, more LLVM breakages may happen unnoticed as + we don't really care about unittests provided by LLVM (because a lot of + them don't function correctly on non-amd64 and non-arm64 platforms; a + lot of LIT tests may require the build system to have the same + environment as the upstream CI, which is by itself a moving target.). + + * In Focal backport, a RISC-V patch was added to fix LLVM code + generation and internal linker behavior when targeting RISC-V. This is + needed because LLVM is by default a cross-compiler that could generate + any supported machine code on any supported platform (we also enabled + LLVM Orc JIT remoting functionality, which allows LLVM JIT to transform + LLVM IR into machine code over the network). This may pose extra risks + since our binutils on Focal only supports RISC-V ABI v2.0 while LLVM 18 + speaks RISC-V ABI v2.1 (whose linker identity string is incompatible + with v2.0, which is quite counter-intuitive). The patch is needed for + older binutils to correctly link the RISC-V binaries when the RISC-V + targets contains these RISC-V standard CPU extensions: +I (i2p0) +M + (i2p0) +A (i2p0) +F (i2p0) +D (i2p0) +Zicsr (i2p0 when using +G with + binutils in 20.04, otherwise not understood with i2p1) +Zifencei + +Zipause + + [ Other Info ] + + * A test rebuild using these packages was done as described in LP: #2076024. - The llvm-18 testsuite run during the build doesn't show regressions. + * The llvm-18 testsuite run during the build doesn't show regressions. - The update exposes an underlinking of bpftrace, which should be SRUed at - the same time. See LP: #2081848 + * The update exposes an underlinking of bpftrace, which should be SRUed + at the same time. See LP: #2081848
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2075477 Title: SRU: Backport LLVM 18.1.8 to Ubuntu LTS To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/llvm-toolchain-18/+bug/2075477/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
