Messages in this thread | | | From | Sami Tolvanen <> | Subject | [PATCH 00/15] Add support for clang LTO | Date | Fri, 3 Nov 2017 10:11:44 -0700 |
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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 CLANG_LTO $ make ARCH=arm64 oldconfig $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CC=clang \ LD=aarch64-linux-gnu-ld.gold
You can also define LD_FINAL_VMLINUX to use a different linker for vmlinux_link, which may be necessary for working around GNU gold issues with KASLR, for example.
Greg Hackmann (1): arm64: use -mno-implicit-float instead of -mgeneral-regs-only
Sami Tolvanen (14): kbuild: add ld-name macro and support for GNU gold kbuild: fix LD_DEAD_CODE_DATA_ELIMINATION with GNU gold kbuild: add support for clang LTO kbuild: fix dynamic ftrace with clang LTO scripts/mod: disable LTO for empty.c efi/libstub: disable clang LTO arm64: don't pass -maarch64linux to GNU gold arm64: keep .altinstructions and .altinstr_replacement arm64: disable ARM64_ERRATUM_843419 for clang LTO arm64: explicitly pass --no-fix-cortex-a53-843419 to GNU gold arm64: add a workaround for GNU gold with ARM64_MODULE_PLTS arm64: fix mrs_s/msr_s macros for clang LTO arm64: crypto: disable LTO for aes-ce-cipher.c arm64: select ARCH_SUPPORTS_CLANG_LTO
.gitignore | 2 + Makefile | 21 ++++++- arch/Kconfig | 32 ++++++++++ arch/arm64/Kconfig | 6 +- arch/arm64/Makefile | 17 +++++- arch/arm64/crypto/Makefile | 2 +- arch/arm64/include/asm/kvm_hyp.h | 2 + arch/arm64/include/asm/sysreg.h | 71 ++++++++++++++++------ arch/arm64/kernel/vmlinux.lds.S | 4 +- drivers/firmware/efi/libstub/Makefile | 3 +- include/asm-generic/vmlinux.lds.h | 10 ++-- include/linux/compiler-clang.h | 7 +++ include/linux/compiler.h | 4 ++ kernel/trace/ftrace.c | 6 +- scripts/Kbuild.include | 4 ++ scripts/Makefile.build | 83 +++++++++++++++++++++++++- scripts/Makefile.modpost | 67 ++++++++++++++++++--- scripts/link-vmlinux.sh | 108 ++++++++++++++++++++++++++++++---- scripts/mod/Makefile | 1 + scripts/recordmcount.c | 3 +- 20 files changed, 397 insertions(+), 56 deletions(-)
-- 2.15.0.403.gc27cc4dac6-goog
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