On Wed, 15 Nov 2017 13:34:22 -0800 Sami Tolvanen <samitolva...@google.com> wrote:
> This change adds the configuration option CONFIG_LTO_CLANG, and > build system support for clang's Link Time Optimization (LTO). In > preparation for LTO support for other compilers, potentially common > parts of the changes are gated behind CONFIG_LTO instead. > > With -flto, instead of object files, clang produces LLVM bitcode, > which is compiled into a native object at link time, allowing the > final binary to be optimized globally. For more details, see: > > https://llvm.org/docs/LinkTimeOptimization.html > > While the kernel normally uses GNU ld for linking, LLVM supports LTO > only with lld or GNU gold linkers. This patch set assumes gold will > be used with the LLVMgold plug-in to perform the LTO link step. Due > to potential incompatibilities with GNU ld, this change also adds > LDFINAL_vmlinux for using a different linker for the vmlinux_link > step, and defaults to using GNU ld. > > Assuming LLVMgold.so is in LD_LIBRARY_PATH and CONFIG_LTO_CLANG has > been selected, an LTO kernel can be built simply by running make > CC=clang. Recommended versions are >= 5.0 for clang, and >= 2.27 for > binutils. Do you have any kind of numbers for this, out of curiosity? Binary size, performance, build time? Also > @@ -585,6 +585,7 @@ config CC_STACKPROTECTOR_STRONG > endchoice > > config THIN_ARCHIVES > + depends on !LTO_CLANG > def_bool y > help > Select this if the architecture wants to use thin archives Why is this needed? It would have been nice to get rid of the !THIN_ARCHIVES option if you can make the patches work with the thin archives paths. Thanks, Nick
