On Wed, Jun 24, 2020 at 02:31:36PM -0700, Nick Desaulniers wrote: > On Wed, Jun 24, 2020 at 2:15 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > On Wed, Jun 24, 2020 at 01:31:38PM -0700, Sami Tolvanen 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's > > > Pixel devices have shipped with LTO+CFI kernels 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 first objtool patch in the series is already in linux-next, > > > but as it's needed with LTO, I'm including it also here to make testing > > > easier. > > > > I'm very sad that yet again, memory ordering isn't addressed. LTO vastly > > increases the range of the optimizer to wreck things. > > Hi Peter, could you expand on the issue for the folks on the thread? > I'm happy to try to hack something up in LLVM if we check that X does > or does not happen; maybe we can even come up with some concrete test > cases that can be added to LLVM's codebase? I'm sure Will will respond, but the basic issue is the trainwreck C11 made of dependent loads. Anyway, here's a link to the last time this came up: https://lore.kernel.org/linux-arm-kernel/20171116174830.GX3624@xxxxxxxxxxxxxxxxxx/
