| Message ID | 20200918201436.2932360-1-samitolvanen@google.com |
|---|---|
| Headers | show |
| Series | Add support for Clang LTO | expand |
On Fri, Sep 18, 2020 at 10:14 PM 'Sami Tolvanen' via Clang Built Linux <clang-built-linux@googlegroups.com> wrote: > > This patch series adds support for building x86_64 and arm64 kernels > with Clang's Link Time Optimization (LTO). > > In addition to performance, the primary motivation for LTO is > to allow Clang's Control-Flow Integrity (CFI) to be used in the > kernel. Google has shipped millions of Pixel devices running three > major kernel versions with LTO+CFI since 2018. > > Most of the patches are build system changes for handling LLVM > bitcode, which Clang produces with LTO instead of ELF object files, > postponing ELF processing until a later stage, and ensuring initcall > ordering. > > Note that patches 1-5 are not directly related to LTO, but are > needed to compile LTO kernels with ToT Clang, so I'm including them > in the series for your convenience: > > - Patches 1-3 fix build issues with LLVM and they are already in > linux-next. > > - Patch 4 fixes x86 builds with LLVM IAS, but it hasn't yet been > picked up by maintainers. > > - Patch 5 is from Masahiro's kbuild tree and makes the LTO linker > script changes much cleaner. > Hi Sami, might be good to point to your GitHub tree and corresponding release-tag for easy fetching. Thanks. Regards, - Sedat - > --- > Changes in v3: > > - Added a separate patch to remove the unused DISABLE_LTO treewide, > as filtering out CC_FLAGS_LTO instead is preferred. > > - Updated the Kconfig help to explain why LTO is behind a choice > and disabled by default. > > - Dropped CC_FLAGS_LTO_CLANG, compiler-specific LTO flags are now > appended directly to CC_FLAGS_LTO. > > - Updated $(AR) flags as KBUILD_ARFLAGS was removed earlier. > > - Fixed ThinLTO cache handling for external module builds. > > - Rebased on top of Masahiro's patch for preprocessing modules.lds, > and moved the contents of module-lto.lds to modules.lds.S. > > - Moved objtool_args to Makefile.lib to avoid duplication of the > command line parameters in Makefile.modfinal. > > - Clarified in the commit message for the initcall ordering patch > that the initcall order remains the same as without LTO. > > - Changed link-vmlinux.sh to use jobserver-exec to control the > number of jobs started by generate_initcall_ordering.pl. > > - Dropped the x86/relocs patch to whitelist L4_PAGE_OFFSET as it's > no longer needed with ToT kernel. > > - Disabled LTO for arch/x86/power/cpu.c to work around a Clang bug > with stack protector attributes. > > Changes in v2: > > - Fixed -Wmissing-prototypes warnings with W=1. > > - Dropped cc-option from -fsplit-lto-unit and added .thinlto-cache > scrubbing to make distclean. > > - Added a comment about Clang >=11 being required. > > - Added a patch to disable LTO for the arm64 KVM nVHE code. > > - Disabled objtool's noinstr validation with LTO unless enabled. > > - Included Peter's proposed objtool mcount patch in the series > and replaced recordmcount with the objtool pass to avoid > whitelisting relocations that are not calls. > > - Updated several commit messages with better explanations. > > > Arvind Sankar (2): > x86/boot/compressed: Disable relocation relaxation > x86/asm: Replace __force_order with memory clobber > > Luca Stefani (1): > RAS/CEC: Fix cec_init() prototype > > Masahiro Yamada (1): > kbuild: preprocess module linker script > > Nick Desaulniers (1): > lib/string.c: implement stpcpy > > Peter Zijlstra (1): > objtool: Add a pass for generating __mcount_loc > > Sami Tolvanen (24): > objtool: Don't autodetect vmlinux.o > kbuild: add support for objtool mcount > x86, build: use objtool mcount > treewide: remove DISABLE_LTO > kbuild: add support for Clang LTO > kbuild: lto: fix module versioning > kbuild: lto: postpone objtool > kbuild: lto: limit inlining > kbuild: lto: merge module sections > kbuild: lto: remove duplicate dependencies from .mod files > init: lto: ensure initcall ordering > init: lto: fix PREL32 relocations > PCI: Fix PREL32 relocations for LTO > modpost: lto: strip .lto from module names > scripts/mod: disable LTO for empty.c > efi/libstub: disable LTO > drivers/misc/lkdtm: disable LTO for rodata.o > arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY > arm64: vdso: disable LTO > KVM: arm64: disable LTO for the nVHE directory > arm64: allow LTO_CLANG and THINLTO to be selected > x86, vdso: disable LTO only for vDSO > x86, cpu: disable LTO for cpu.c > x86, build: allow LTO_CLANG and THINLTO to be selected > > .gitignore | 1 + > Makefile | 74 ++++- > arch/Kconfig | 68 +++++ > arch/arm/Makefile | 4 - > .../module.lds => include/asm/module.lds.h} | 2 + > arch/arm64/Kconfig | 2 + > arch/arm64/Makefile | 5 +- > .../module.lds => include/asm/module.lds.h} | 2 + > arch/arm64/kernel/vdso/Makefile | 4 +- > arch/arm64/kvm/hyp/nvhe/Makefile | 4 +- > arch/ia64/Makefile | 1 - > .../{module.lds => include/asm/module.lds.h} | 0 > arch/m68k/Makefile | 1 - > .../module.lds => include/asm/module.lds.h} | 0 > arch/powerpc/Makefile | 1 - > .../module.lds => include/asm/module.lds.h} | 0 > arch/riscv/Makefile | 3 - > .../module.lds => include/asm/module.lds.h} | 3 +- > arch/sparc/vdso/Makefile | 2 - > arch/um/include/asm/Kbuild | 1 + > arch/x86/Kconfig | 3 + > arch/x86/Makefile | 5 + > arch/x86/boot/compressed/Makefile | 2 + > arch/x86/boot/compressed/pgtable_64.c | 9 - > arch/x86/entry/vdso/Makefile | 5 +- > arch/x86/include/asm/special_insns.h | 28 +- > arch/x86/kernel/cpu/common.c | 4 +- > arch/x86/power/Makefile | 4 + > drivers/firmware/efi/libstub/Makefile | 2 + > drivers/misc/lkdtm/Makefile | 1 + > drivers/ras/cec.c | 9 +- > include/asm-generic/Kbuild | 1 + > include/asm-generic/module.lds.h | 10 + > include/asm-generic/vmlinux.lds.h | 11 +- > include/linux/init.h | 79 ++++- > include/linux/pci.h | 19 +- > kernel/Makefile | 3 - > kernel/trace/Kconfig | 5 + > lib/string.c | 24 ++ > scripts/.gitignore | 1 + > scripts/Makefile | 3 + > scripts/Makefile.build | 69 +++-- > scripts/Makefile.lib | 17 +- > scripts/Makefile.modfinal | 29 +- > scripts/Makefile.modpost | 22 +- > scripts/generate_initcall_order.pl | 270 ++++++++++++++++++ > scripts/link-vmlinux.sh | 95 +++++- > scripts/mod/Makefile | 1 + > scripts/mod/modpost.c | 16 +- > scripts/mod/modpost.h | 9 + > scripts/mod/sumversion.c | 6 +- > scripts/{module-common.lds => module.lds.S} | 31 ++ > scripts/package/builddeb | 2 +- > tools/objtool/builtin-check.c | 13 +- > tools/objtool/builtin.h | 2 +- > tools/objtool/check.c | 83 ++++++ > tools/objtool/check.h | 1 + > tools/objtool/objtool.h | 1 + > 58 files changed, 919 insertions(+), 154 deletions(-) > rename arch/arm/{kernel/module.lds => include/asm/module.lds.h} (72%) > rename arch/arm64/{kernel/module.lds => include/asm/module.lds.h} (76%) > rename arch/ia64/{module.lds => include/asm/module.lds.h} (100%) > rename arch/m68k/{kernel/module.lds => include/asm/module.lds.h} (100%) > rename arch/powerpc/{kernel/module.lds => include/asm/module.lds.h} (100%) > rename arch/riscv/{kernel/module.lds => include/asm/module.lds.h} (84%) > create mode 100644 include/asm-generic/module.lds.h > create mode 100755 scripts/generate_initcall_order.pl > rename scripts/{module-common.lds => module.lds.S} (59%) > > > base-commit: 92ab97adeefccf375de7ebaad9d5b75d4125fe8b > -- > 2.28.0.681.g6f77f65b4e-goog > > -- > You received this message because you are subscribed to the Google Groups "Clang Built Linux" group. > To unsubscribe from this group and stop receiving emails from it, send an email to clang-built-linux+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20200918201436.2932360-1-samitolvanen%40google.com.
On Fri, Sep 18, 2020 at 1:22 PM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > On Fri, Sep 18, 2020 at 10:14 PM 'Sami Tolvanen' via Clang Built Linux > <clang-built-linux@googlegroups.com> wrote: > > > > This patch series adds support for building x86_64 and arm64 kernels > > with Clang's Link Time Optimization (LTO). > > > > In addition to performance, the primary motivation for LTO is > > to allow Clang's Control-Flow Integrity (CFI) to be used in the > > kernel. Google has shipped millions of Pixel devices running three > > major kernel versions with LTO+CFI since 2018. > > > > Most of the patches are build system changes for handling LLVM > > bitcode, which Clang produces with LTO instead of ELF object files, > > postponing ELF processing until a later stage, and ensuring initcall > > ordering. > > > > Note that patches 1-5 are not directly related to LTO, but are > > needed to compile LTO kernels with ToT Clang, so I'm including them > > in the series for your convenience: > > > > - Patches 1-3 fix build issues with LLVM and they are already in > > linux-next. > > > > - Patch 4 fixes x86 builds with LLVM IAS, but it hasn't yet been > > picked up by maintainers. > > > > - Patch 5 is from Masahiro's kbuild tree and makes the LTO linker > > script changes much cleaner. > > > > Hi Sami, > > might be good to point to your GitHub tree and corresponding > release-tag for easy fetching. Ah, true. You can also pull this series from https://github.com/samitolvanen/linux.git lto-v3 Sami
On Fri, Sep 18, 2020 at 1:50 PM Sami Tolvanen <samitolvanen@google.com> wrote: > > On Fri, Sep 18, 2020 at 1:22 PM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > > > On Fri, Sep 18, 2020 at 10:14 PM 'Sami Tolvanen' via Clang Built Linux > > <clang-built-linux@googlegroups.com> wrote: > > > > > > This patch series adds support for building x86_64 and arm64 kernels > > > with Clang's Link Time Optimization (LTO). > > > > > > In addition to performance, the primary motivation for LTO is > > > to allow Clang's Control-Flow Integrity (CFI) to be used in the > > > kernel. Google has shipped millions of Pixel devices running three > > > major kernel versions with LTO+CFI since 2018. > > > > > > Most of the patches are build system changes for handling LLVM > > > bitcode, which Clang produces with LTO instead of ELF object files, > > > postponing ELF processing until a later stage, and ensuring initcall > > > ordering. > > > > > > Note that patches 1-5 are not directly related to LTO, but are > > > needed to compile LTO kernels with ToT Clang, so I'm including them > > > in the series for your convenience: > > > > > > - Patches 1-3 fix build issues with LLVM and they are already in > > > linux-next. > > > > > > - Patch 4 fixes x86 builds with LLVM IAS, but it hasn't yet been > > > picked up by maintainers. > > > > > > - Patch 5 is from Masahiro's kbuild tree and makes the LTO linker > > > script changes much cleaner. > > > > > > > Hi Sami, > > > > might be good to point to your GitHub tree and corresponding > > release-tag for easy fetching. > > Ah, true. You can also pull this series from > > https://github.com/samitolvanen/linux.git lto-v3 Also, I've been using b4 happily for a short while now. https://people.kernel.org/monsieuricon/introducing-b4-and-patch-attestation My workflow would be: check lore.kernel.org/lkml/ for the series in question. In this case: https://lore.kernel.org/lkml/CABCJKueyWvNB2MQw_PCLtZb8F1+sA1QOLJi_5qMKwdFCcwSMGg@mail.gmail.com/T/#t is the cover letter. Then in my tree: $ b4 am https://lore.kernel.org/lkml/CABCJKueyWvNB2MQw_PCLtZb8F1+sA1QOLJi_5qMKwdFCcwSMGg@mail.gmail.com/T/#t -o - | git am
This patch series adds support for building x86_64 and arm64 kernels with Clang's Link Time Optimization (LTO). In addition to performance, the primary motivation for LTO is to allow Clang's Control-Flow Integrity (CFI) to be used in the kernel. Google has shipped millions of Pixel devices running three major kernel versions with LTO+CFI since 2018. Most of the patches are build system changes for handling LLVM bitcode, which Clang produces with LTO instead of ELF object files, postponing ELF processing until a later stage, and ensuring initcall ordering. Note that patches 1-5 are not directly related to LTO, but are needed to compile LTO kernels with ToT Clang, so I'm including them in the series for your convenience: - Patches 1-3 fix build issues with LLVM and they are already in linux-next. - Patch 4 fixes x86 builds with LLVM IAS, but it hasn't yet been picked up by maintainers. - Patch 5 is from Masahiro's kbuild tree and makes the LTO linker script changes much cleaner. --- Changes in v3: - Added a separate patch to remove the unused DISABLE_LTO treewide, as filtering out CC_FLAGS_LTO instead is preferred. - Updated the Kconfig help to explain why LTO is behind a choice and disabled by default. - Dropped CC_FLAGS_LTO_CLANG, compiler-specific LTO flags are now appended directly to CC_FLAGS_LTO. - Updated $(AR) flags as KBUILD_ARFLAGS was removed earlier. - Fixed ThinLTO cache handling for external module builds. - Rebased on top of Masahiro's patch for preprocessing modules.lds, and moved the contents of module-lto.lds to modules.lds.S. - Moved objtool_args to Makefile.lib to avoid duplication of the command line parameters in Makefile.modfinal. - Clarified in the commit message for the initcall ordering patch that the initcall order remains the same as without LTO. - Changed link-vmlinux.sh to use jobserver-exec to control the number of jobs started by generate_initcall_ordering.pl. - Dropped the x86/relocs patch to whitelist L4_PAGE_OFFSET as it's no longer needed with ToT kernel. - Disabled LTO for arch/x86/power/cpu.c to work around a Clang bug with stack protector attributes. Changes in v2: - Fixed -Wmissing-prototypes warnings with W=1. - Dropped cc-option from -fsplit-lto-unit and added .thinlto-cache scrubbing to make distclean. - Added a comment about Clang >=11 being required. - Added a patch to disable LTO for the arm64 KVM nVHE code. - Disabled objtool's noinstr validation with LTO unless enabled. - Included Peter's proposed objtool mcount patch in the series and replaced recordmcount with the objtool pass to avoid whitelisting relocations that are not calls. - Updated several commit messages with better explanations. Arvind Sankar (2): x86/boot/compressed: Disable relocation relaxation x86/asm: Replace __force_order with memory clobber Luca Stefani (1): RAS/CEC: Fix cec_init() prototype Masahiro Yamada (1): kbuild: preprocess module linker script Nick Desaulniers (1): lib/string.c: implement stpcpy Peter Zijlstra (1): objtool: Add a pass for generating __mcount_loc Sami Tolvanen (24): objtool: Don't autodetect vmlinux.o kbuild: add support for objtool mcount x86, build: use objtool mcount treewide: remove DISABLE_LTO kbuild: add support for Clang LTO kbuild: lto: fix module versioning kbuild: lto: postpone objtool kbuild: lto: limit inlining kbuild: lto: merge module sections kbuild: lto: remove duplicate dependencies from .mod files init: lto: ensure initcall ordering init: lto: fix PREL32 relocations PCI: Fix PREL32 relocations for LTO modpost: lto: strip .lto from module names scripts/mod: disable LTO for empty.c efi/libstub: disable LTO drivers/misc/lkdtm: disable LTO for rodata.o arm64: export CC_USING_PATCHABLE_FUNCTION_ENTRY arm64: vdso: disable LTO KVM: arm64: disable LTO for the nVHE directory arm64: allow LTO_CLANG and THINLTO to be selected x86, vdso: disable LTO only for vDSO x86, cpu: disable LTO for cpu.c x86, build: allow LTO_CLANG and THINLTO to be selected .gitignore | 1 + Makefile | 74 ++++- arch/Kconfig | 68 +++++ arch/arm/Makefile | 4 - .../module.lds => include/asm/module.lds.h} | 2 + arch/arm64/Kconfig | 2 + arch/arm64/Makefile | 5 +- .../module.lds => include/asm/module.lds.h} | 2 + arch/arm64/kernel/vdso/Makefile | 4 +- arch/arm64/kvm/hyp/nvhe/Makefile | 4 +- arch/ia64/Makefile | 1 - .../{module.lds => include/asm/module.lds.h} | 0 arch/m68k/Makefile | 1 - .../module.lds => include/asm/module.lds.h} | 0 arch/powerpc/Makefile | 1 - .../module.lds => include/asm/module.lds.h} | 0 arch/riscv/Makefile | 3 - .../module.lds => include/asm/module.lds.h} | 3 +- arch/sparc/vdso/Makefile | 2 - arch/um/include/asm/Kbuild | 1 + arch/x86/Kconfig | 3 + arch/x86/Makefile | 5 + arch/x86/boot/compressed/Makefile | 2 + arch/x86/boot/compressed/pgtable_64.c | 9 - arch/x86/entry/vdso/Makefile | 5 +- arch/x86/include/asm/special_insns.h | 28 +- arch/x86/kernel/cpu/common.c | 4 +- arch/x86/power/Makefile | 4 + drivers/firmware/efi/libstub/Makefile | 2 + drivers/misc/lkdtm/Makefile | 1 + drivers/ras/cec.c | 9 +- include/asm-generic/Kbuild | 1 + include/asm-generic/module.lds.h | 10 + include/asm-generic/vmlinux.lds.h | 11 +- include/linux/init.h | 79 ++++- include/linux/pci.h | 19 +- kernel/Makefile | 3 - kernel/trace/Kconfig | 5 + lib/string.c | 24 ++ scripts/.gitignore | 1 + scripts/Makefile | 3 + scripts/Makefile.build | 69 +++-- scripts/Makefile.lib | 17 +- scripts/Makefile.modfinal | 29 +- scripts/Makefile.modpost | 22 +- scripts/generate_initcall_order.pl | 270 ++++++++++++++++++ scripts/link-vmlinux.sh | 95 +++++- scripts/mod/Makefile | 1 + scripts/mod/modpost.c | 16 +- scripts/mod/modpost.h | 9 + scripts/mod/sumversion.c | 6 +- scripts/{module-common.lds => module.lds.S} | 31 ++ scripts/package/builddeb | 2 +- tools/objtool/builtin-check.c | 13 +- tools/objtool/builtin.h | 2 +- tools/objtool/check.c | 83 ++++++ tools/objtool/check.h | 1 + tools/objtool/objtool.h | 1 + 58 files changed, 919 insertions(+), 154 deletions(-) rename arch/arm/{kernel/module.lds => include/asm/module.lds.h} (72%) rename arch/arm64/{kernel/module.lds => include/asm/module.lds.h} (76%) rename arch/ia64/{module.lds => include/asm/module.lds.h} (100%) rename arch/m68k/{kernel/module.lds => include/asm/module.lds.h} (100%) rename arch/powerpc/{kernel/module.lds => include/asm/module.lds.h} (100%) rename arch/riscv/{kernel/module.lds => include/asm/module.lds.h} (84%) create mode 100644 include/asm-generic/module.lds.h create mode 100755 scripts/generate_initcall_order.pl rename scripts/{module-common.lds => module.lds.S} (59%) base-commit: 92ab97adeefccf375de7ebaad9d5b75d4125fe8b