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[198.145.64.163]) by smtp.gmail.com with ESMTPSA id y10sm8724624pjm.34.2020.11.21.12.11.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 21 Nov 2020 12:11:26 -0800 (PST) Date: Sat, 21 Nov 2020 12:11:25 -0800 From: Kees Cook To: Sami Tolvanen Cc: Nathan Chancellor , Nick Desaulniers , Masahiro Yamada , Steven Rostedt , Will Deacon , Josh Poimboeuf , Peter Zijlstra , Greg Kroah-Hartman , "Paul E. McKenney" , clang-built-linux , Kernel Hardening , linux-arch , Linux ARM , Linux Kbuild mailing list , LKML , linux-pci@vger.kernel.org Subject: Re: [PATCH v7 02/17] kbuild: add support for Clang LTO Message-ID: <202011211204.211E2B12@keescook> References: <20201118220731.925424-1-samitolvanen@google.com> <20201118220731.925424-3-samitolvanen@google.com> <202011201144.3F2BB70C@keescook> <20201120202935.GA1220359@ubuntu-m3-large-x86> <202011201241.B159562D7@keescook> <202011201556.3B910EF@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Fri, Nov 20, 2020 at 05:46:44PM -0800, Sami Tolvanen wrote: > Sure, this looks good to me, I'll use this in v8. The only minor > concern I have is that ThinLTO cannot be set as the default LTO mode, > but I assume anyone who selects LTO is also capable of deciding which > mode is better for them. It could be re-arranged similar to what you had before, but like: config LTO bool "..." depends on HAS_LTO help ... choice prompt "LTO mode" if LTO default LTO_GCC if HAS_LTO_GCC default LTO_CLANG_THIN if HAS_LTO_CLANG default LTO_CLANG_FULL help ... config LTO_CLANG_THIN ... config LTO_CLANG_FULL endchoice Then the LTO is top-level yes/no, but depends on detected capabilities, and the mode is visible if LTO is chosen, etc. I'm not really sure which is better... > > +config LTO_CLANG_THIN > > + bool "Clang ThinLTO (EXPERIMENTAL)" > > + depends on ARCH_SUPPORTS_LTO_CLANG_THIN > > + select LTO_CLANG > > + help > > + This option enables Clang's ThinLTO, which allows for parallel > > + optimization and faster incremental compiles compared to the > > + CONFIG_LTO_CLANG_FULL option. More information can be found > > + from Clang's documentation: > > + > > + https://clang.llvm.org/docs/ThinLTO.html > > + > > + If unsure, say Y. > > endchoice > > The two LTO_CLANG_* options need to depend on HAS_LTO_CLANG, of course. Whoops, yes. Thanks for catching that. :) -- Kees Cook