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df05c0e949
LLVM versions prior to 11.0.0 have a harder time with dead code elimination, which can cause issues with commonly used expressions such as BUILD_BUG_ON and the bitmask functions/macros in bitfield.h (see the first two issues links below). Whenever there is an issue within LLVM that has been resolved in a later release, the only course of action is to gate the problematic configuration or source code on the toolchain verson or raise the minimum supported version of LLVM for building the kernel, as LLVM has a limited support lifetime compared to GCC. GCC major releases will typically see a few point releases across a two year period on average whereas LLVM major releases are only supported until the next major release and will only see one or two point releases within that timeframe. For example, GCC 8.1 was released in May 2018 and GCC 8.5 was released in May 2021, whereas LLVM 12.0.0 was released in April 2021 and its only point release, 12.0.1, was released in July 2021, giving a minimal window for fixes to be backported. To resolve these build errors around improper dead code elimination, raise the minimum supported version of LLVM for building the kernel to 11.0.0. Doing so is a more proper solution than mucking around with core kernel macros that have always worked with GCC or disabling drivers for using these macros in a proper manner. This type of issue may continue to crop up and require patching, which creates more debt for bumping the minimum supported version in the future. This should have a minimal impact to distributions. Using a script to pull several different Docker images and check the output of 'clang --version': archlinux:latest: clang version 13.0.0 debian:oldoldstable-slim: clang version 3.8.1-24 (tags/RELEASE_381/final) debian:oldstable-slim: clang version 7.0.1-8+deb10u2 (tags/RELEASE_701/final) debian:stable-slim: Debian clang version 11.0.1-2 debian:testing-slim: Debian clang version 11.1.0-4 debian:unstable-slim: Debian clang version 11.1.0-4 fedora:34: clang version 12.0.1 (Fedora 12.0.1-1.fc34) fedora:latest: clang version 13.0.0 (Fedora 13.0.0-3.fc35) fedora:rawhide: clang version 13.0.0 (Fedora 13.0.0-5.fc36) opensuse/leap:15.2: clang version 9.0.1 opensuse/leap:latest: clang version 11.0.1 opensuse/tumbleweed:latest: clang version 13.0.0 ubuntu:bionic: clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final) ubuntu:latest: clang version 10.0.0-4ubuntu1 ubuntu:hirsute: Ubuntu clang version 12.0.0-3ubuntu1~21.04.2 ubuntu:rolling: Ubuntu clang version 13.0.0-2 ubuntu:devel: Ubuntu clang version 13.0.0-9 In every case, the distribution's version of clang is either older than the current minimum supported version of LLVM 10.0.1 or equal to or greater than the proposed 11.0.0 so nothing should change. Another benefit of this change is LLVM=1 works better with arm64 and x86_64 since commit |
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| .. | ||
| 1.Intro.rst | ||
| 2.Process.rst | ||
| 3.Early-stage.rst | ||
| 4.Coding.rst | ||
| 5.Posting.rst | ||
| 6.Followthrough.rst | ||
| 7.AdvancedTopics.rst | ||
| 8.Conclusion.rst | ||
| adding-syscalls.rst | ||
| applying-patches.rst | ||
| botching-up-ioctls.rst | ||
| changes.rst | ||
| clang-format.rst | ||
| code-of-conduct-interpretation.rst | ||
| code-of-conduct.rst | ||
| coding-style.rst | ||
| deprecated.rst | ||
| development-process.rst | ||
| email-clients.rst | ||
| embargoed-hardware-issues.rst | ||
| howto.rst | ||
| index.rst | ||
| kernel-docs.rst | ||
| kernel-driver-statement.rst | ||
| kernel-enforcement-statement.rst | ||
| license-rules.rst | ||
| magic-number.rst | ||
| maintainer-handbooks.rst | ||
| maintainer-pgp-guide.rst | ||
| maintainer-tip.rst | ||
| maintainers.rst | ||
| management-style.rst | ||
| programming-language.rst | ||
| stable-api-nonsense.rst | ||
| stable-kernel-rules.rst | ||
| submit-checklist.rst | ||
| submitting-drivers.rst | ||
| submitting-patches.rst | ||
| volatile-considered-harmful.rst | ||