Date: Thu, 25 Jun 2020 09:27:06 +0100 From: Will Deacon <will@...nel.org> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: Peter Zijlstra <peterz@...radead.org>, Masahiro Yamada <masahiroy@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Paul E. McKenney" <paulmck@...nel.org>, Kees Cook <keescook@...omium.org>, Nick Desaulniers <ndesaulniers@...gle.com>, clang-built-linux@...glegroups.com, kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, x86@...nel.org Subject: Re: [PATCH 00/22] add support for Clang LTO On Wed, Jun 24, 2020 at 02:30:14PM -0700, Sami Tolvanen wrote: > On Wed, Jun 24, 2020 at 11:15:40PM +0200, Peter Zijlstra 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. > > I believe Will has some thoughts about this, and patches, but I'll let > him talk about it. Thanks for reminding me! I will get patches out ASAP (I've been avoiding the rebase from hell, but this is the motivation I need). Will
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