Linux 7.2 raises Clang requirement to version 17, adds distributed thin LTO support

The Linux 7.2 kernel merge window opened with Kbuild updates that bump the minimum LLVM/Clang version from 15 to 17 and introduce support for LLVM's distributed thin link-time optimization mode.

Linux 7.2 will require Clang 17 or newer, up from the previous Clang 15 threshold. The change landed in the Kbuild pull requests submitted ahead of the Linux 7.1 release.

The bump aligns the compiler baseline with GCC 8.1+ capabilities, specifically resolving issues around scope checking and const-qualified variables used in _static_assert and related macros. LLVM/Clang 17 fixed these incompatibilities, and raising the requirement eliminates a year of maintenance workarounds in the kernel build system.

The second major addition: support for LLVM's Distributed ThinLTO (DTLTO) mode. In-process thin LTO already parallelizes optimization across modules, but DTLTO distributes the work across separate processes or machines. Early benchmarks show faster kernel builds compared to the in-process variant, and LLVM has continued improving DTLTO performance since its introduction.

Other Kbuild changes in the 7.2 cycle include:

Hardened Kconfig against null pointer dereferences
A new kconfig-sym-check target to detect dangling Kconfig symbol references
Typo fixes across build infrastructure

The Kbuild pull request is available on the Linux kernel mailing list for review.

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Clang 17 shipped in September 2023. The version requirement bump means distributions still running Clang 15 or 16 will need to upgrade before building the 7.2 kernel, though most active distributions have already moved past Clang 17.

ThinLTO has been part of the Linux kernel build pipeline since version 5.12, when the Kconfig option CONFIG_LTO_CLANG_THIN was introduced. The distributed variant builds on that foundation, splitting module optimization into independent tasks that can run in parallel across a build cluster.

For homelab builders and kernel developers running local builds, DTLTO offers a meaningful speedup when compiling on multi-core systems with sufficient memory. The mode requires LLVM's lld linker and a build environment configured for distributed compilation.

The 7.2 merge window continues through late June, with additional subsystem pull requests expected in the coming days.