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. Here are the steps for compiling arm64 defconfig with LTO, assuming LLVMgold.so is in LD_LIBRARY_PATH and the rest of the toolchain is in PATH: $ make ARCH=arm64 defconfig $ ./scripts/config -e LTO_CLANG $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CC=clang -- Changes in v2: - Fixed issues found by the 0-day bot. - Moved clang and gold fixes that don't depend on LTO earlier in the patch set. - Added clang support to cc-version. - Renamed CLANG_LTO to LTO_CLANG, added CONFIG_LTO for sharing code with potential gcc LTO work, and added checks for compiler support to prepare-compiler-check. - Added linker selection to Makefile, so LD doesn't have to be passed in make command line. - arm64 specific: - Added -fno-jump-tables to arch/arm64/kvm/hyp to prevent clang from generating jump tables with EL1 virtual addresses for code that runs at EL2. - Adopted Alex's version of the mrs_s / msr_s fix, which uses the same code path for both gcc and clang. - Enabled LLVM bug 30792 workaround only for clang < 6.0. - Instead of disabling PLTs, removed NOLOAD from PLT sections in modules to work around a bug in gold. - Instead of disabling ARM64_ERRATUM_843419 with gold, enabled the previously disabled ADR_PREL_PG_HI21* relocations. - Instead of omitting -m for gold, pass aarch64_elf64_(be|le)_vec. -- Alex Matveev (1): arm64: make mrs_s and msr_s macros work with LTO Greg Hackmann (1): arm64: use -mno-implicit-float instead of -mgeneral-regs-only Sami Tolvanen (16): kbuild: add ld-name macro and support for GNU gold kbuild: fix LD_DEAD_CODE_DATA_ELIMINATION with GNU gold kbuild: move gcc-version.sh to cc-version.sh and add clang support arm64: fix -m for GNU gold arm64: kvm: use -fno-jump-tables with clang arm64: keep .altinstructions and .altinstr_replacement arm64: don't disable ADR_PREL_PG_HI21* with ARM64_ERRATUM_843419 arm64: explicitly pass --no-fix-cortex-a53-843419 to GNU gold arm64: add a workaround for GNU gold with ARM64_MODULE_PLTS kbuild: add support for clang LTO kbuild: fix dynamic ftrace with clang LTO scripts/mod: disable LTO for empty.c efi/libstub: disable LTO arm64: crypto: disable LTO for aes-ce-cipher.c arm64: disable RANDOMIZE_MODULE_REGION_FULL with LTO_CLANG arm64: select ARCH_SUPPORTS_LTO_CLANG .gitignore | 2 + Makefile | 59 ++++++++++++++++++- arch/Kconfig | 32 ++++++++++ arch/arm64/Kconfig | 3 +- arch/arm64/Makefile | 21 ++++++- arch/arm64/crypto/Makefile | 2 +- arch/arm64/include/asm/kvm_hyp.h | 8 ++- arch/arm64/include/asm/sysreg.h | 55 +++++++++++------ arch/arm64/kernel/module.c | 2 - arch/arm64/kernel/module.lds | 4 +- arch/arm64/kernel/vmlinux.lds.S | 4 +- arch/arm64/kvm/hyp/Makefile | 4 ++ drivers/firmware/efi/libstub/Makefile | 3 +- include/asm-generic/vmlinux.lds.h | 9 +-- include/linux/compiler-clang.h | 7 +++ include/linux/compiler_types.h | 4 ++ kernel/trace/ftrace.c | 6 +- scripts/Kbuild.include | 8 ++- scripts/Makefile.build | 80 ++++++++++++++++++++++++- scripts/Makefile.modpost | 67 ++++++++++++++++++--- scripts/cc-version.sh | 45 ++++++++++++++ scripts/gcc-version.sh | 33 ----------- scripts/link-vmlinux.sh | 108 ++++++++++++++++++++++++++++++---- scripts/mod/Makefile | 1 + scripts/recordmcount.c | 3 +- 25 files changed, 475 insertions(+), 95 deletions(-) create mode 100755 scripts/cc-version.sh delete mode 100755 scripts/gcc-version.sh -- 2.15.0.448.gf294e3d99a-goog -- 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
