On Fri, Oct 9, 2020 at 6:13 PM 'Sami Tolvanen' via Clang Built Linux <clang-built-linux@xxxxxxxxxxxxxxxx> 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 this version is based on tip/master to reduce the number > of prerequisite patches, and to make it easier to manage changes to > objtool. Patch 1 is from Masahiro's kbuild tree, and while it's not > directly related to LTO, it makes the module linker script changes > cleaner. > > Furthermore, patches 2-6 include Peter's patch for generating > __mcount_loc with objtool, and build system changes to enable it on > x86. With these patches, we no longer need to annotate functions > that have non-call references to __fentry__ with LTO, which greatly > simplifies supporting dynamic ftrace. > > You can also pull this series from > > https://github.com/samitolvanen/linux.git lto-v5 > > --- > Changes in v5: > > - Rebased on top of tip/master. > What are the plans to get this into mainline? Linux v5.10 :-) too early - needs more review/testing? Will clang-cfi be based on this, too? > - Changed the command line for objtool to use --vmlinux --duplicate > to disable warnings about retpoline thunks and to fix .orc_unwind > generation for vmlinux.o. > > - Added --noinstr flag to objtool, so we can use --vmlinux without > also enabling noinstr validation. > > - Disabled objtool's unreachable instruction warnings with LTO to > disable false positives for the int3 padding in vmlinux.o. > > - Added ANNOTATE_RETPOLINE_SAFE annotations to the indirect jumps > in x86 assembly code to fix objtool warnings with retpoline. > > - Fixed modpost warnings about missing version information with > CONFIG_MODVERSIONS. > > - Included Makefile.lib into Makefile.modpost for ld_flags. Thanks > to Sedat for pointing this out. > That was a long way to detect this as I had very big Debian Linux debug packages generated with CONFIG_DEBUG_INFO_COMPRESSED=y. Thanks for v5 of clang-lto. - Sedat - [1] https://github.com/ClangBuiltLinux/linux/issues/1086#issuecomment-705754002 > - Updated the help text for ThinLTO to better explain the trade-offs. > > - Updated commit messages with better explanations. > > Changes in v4: > > - Fixed a typo in Makefile.lib to correctly pass --no-fp to objtool. > > - Moved ftrace configs related to generating __mcount_loc to Kconfig, > so they are available also in Makefile.modfinal. > > - Dropped two prerequisite patches that were merged to Linus' tree. > > 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. > > > Masahiro Yamada (1): > kbuild: preprocess module linker script > > Peter Zijlstra (1): > objtool: Add a pass for generating __mcount_loc > > Sami Tolvanen (27): > objtool: Don't autodetect vmlinux.o > tracing: move function tracer options to Kconfig > tracing: 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 > objtool: Split noinstr validation from --vmlinux > 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: vdso: disable LTO > KVM: arm64: disable LTO for the nVHE directory > arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS > arm64: allow LTO_CLANG and THINLTO to be selected > x86/asm: annotate indirect jumps > 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 | 68 +++-- > arch/Kconfig | 74 +++++ > arch/arm/Makefile | 4 - > .../module.lds => include/asm/module.lds.h} | 2 + > arch/arm64/Kconfig | 4 + > arch/arm64/Makefile | 4 - > .../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/entry/vdso/Makefile | 5 +- > arch/x86/kernel/acpi/wakeup_64.S | 2 + > arch/x86/platform/pvh/head.S | 2 + > arch/x86/power/Makefile | 4 + > arch/x86/power/hibernate_asm_64.S | 3 + > drivers/firmware/efi/libstub/Makefile | 2 + > drivers/misc/lkdtm/Makefile | 1 + > 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 | 29 ++ > scripts/.gitignore | 1 + > scripts/Makefile | 3 + > scripts/Makefile.build | 69 +++-- > scripts/Makefile.lib | 17 +- > scripts/Makefile.modfinal | 29 +- > scripts/Makefile.modpost | 25 +- > scripts/generate_initcall_order.pl | 270 ++++++++++++++++++ > scripts/link-vmlinux.sh | 98 ++++++- > 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 | 10 +- > tools/objtool/check.c | 84 +++++- > tools/objtool/include/objtool/builtin.h | 2 +- > tools/objtool/include/objtool/check.h | 1 + > tools/objtool/include/objtool/objtool.h | 1 + > tools/objtool/objtool.c | 1 + > 56 files changed, 903 insertions(+), 131 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: 80396d76da65fc8b82581c0260c25a6aa0a495a3 > -- > 2.28.0.1011.ga647a8990f-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@xxxxxxxxxxxxxxxx. > To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/20201009161338.657380-1-samitolvanen%40google.com.
