On Fri, Oct 09, 2020 at 03:35:12PM -0400, Steven Rostedt wrote: > On Fri, 9 Oct 2020 09:13:09 -0700 > Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > > This patch series adds support for building x86_64 and arm64 kernels > > with Clang's Link Time Optimization (LTO). > > > > In addition to performance, the primary motivation for LTO is > > to allow Clang's Control-Flow Integrity (CFI) to be used in the > > kernel. Google has shipped millions of Pixel devices running three > > major kernel versions with LTO+CFI since 2018. > > > > Most of the patches are build system changes for handling LLVM > > bitcode, which Clang produces with LTO instead of ELF object files, > > postponing ELF processing until a later stage, and ensuring initcall > > ordering. > > > > Note that this version is based on tip/master to reduce the number > > of prerequisite patches, and to make it easier to manage changes to > > objtool. Patch 1 is from Masahiro's kbuild tree, and while it's not > > directly related to LTO, it makes the module linker script changes > > cleaner. > > > > I went to test this, but it appears that the latest tip/master fails to > build for me. This error is on tip/master, before I even applied a single > patch. > > (config attached) Ah yes, X86_DECODER_SELFTEST seems to be broken in tip/master. If you prefer, I have these patches on top of mainline here: https://github.com/samitolvanen/linux/tree/clang-lto Testing your config with LTO on this tree, it does build and boot for me, although I saw a couple of new objtool warnings, and with LLVM=1, one warning from llvm-objdump. Sami
