On Wed, Nov 15, 2017 at 01:34:10PM -0800, Sami Tolvanen wrote: > This series adds build system support for compiling the kernel with clang > Link Time Optimization (LTO), using GNU gold with the LLVMgold plug-in > for linking. Some background for clang's LTO support is available here: > > https://llvm.org/docs/LinkTimeOptimization.html > > With -flto, clang produces LLVM bitcode instead of object files, and > the compilation to native code happens at link time. In addition, clang > cannot use an external assembler for inline assembly when LTO is enabled, > which causes further compatibility issues. > > The patches in this series remove intermediate linking steps when LTO is > used, postpone processing done on object files until after the LTO link > step, add workarounds for GNU gold incompatibilities, and address inline > assembly incompatibilities for arm64. > > These changes allow arm64 defconfig to be compiled with LTO, but other > architectures are not enabled until compatibility issues have been > addressed. In particular, x86 inline assembly doesn't currently compile > with clang's integrated assembler due to this LLVM bug: > > https://bugs.llvm.org/show_bug.cgi?id=24487 > > Due to recent bug fixes in the toolchain, it's recommended to use clang > 5.0 or later, and GNU gold from binutils 2.27 or later, although older > versions may also work depending on your kernel configuration. So, you don't guarantee that kernel will work with old compiler and toolchain? If so, I would suggest you to add the patch that checks their versions and disables LTO if needed. Yury -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
