Re: [PATCH v2 00/28] Add support for Clang LTO

Sedat Dilek
2020-09-04T07:53:57Z

On Thu, Sep 3, 2020 at 10:30 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 1-4 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 are required for building the kernel with ToT Clang,
> and IAS, and patch 4 is needed to build allmodconfig with LTO.
>
> - Patches 3-4 are already in linux-next, but not yet in 5.9-rc.
>

I jumped to Sami's clang-cfi Git tree which includes clang-lto v2.

My LLVM toolchain is version 11.0.0.0-rc2+ more precisely git
97ac9e82002d6b12831ca2c78f739cca65a4fa05.

If this is OK, feel free to add my...

Tested-by: Sedat Dilek <sedat.dilek@gmail.com>

- Sedat -

[1] https://github.com/samitolvanen/linux/commits/clang-cfi

> ---
> 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
>
> Nick Desaulniers (1):
> lib/string.c: implement stpcpy
>
> Peter Zijlstra (1):
> objtool: Add a pass for generating __mcount_loc
>
> Sami Tolvanen (23):
> objtool: Don't autodetect vmlinux.o
> kbuild: add support for objtool mcount
> x86, build: use objtool mcount
> 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, relocs: Ignore L4_PAGE_OFFSET relocations
> x86, build: allow LTO_CLANG and THINLTO to be selected
>
> .gitignore | 1 +
> Makefile | 65 ++++++-
> arch/Kconfig | 67 +++++++
> arch/arm64/Kconfig | 2 +
> arch/arm64/Makefile | 1 +
> arch/arm64/kernel/vdso/Makefile | 4 +-
> arch/arm64/kvm/hyp/nvhe/Makefile | 4 +-
> 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/tools/relocs.c | 1 +
> drivers/firmware/efi/libstub/Makefile | 2 +
> drivers/misc/lkdtm/Makefile | 1 +
> drivers/ras/cec.c | 9 +-
> include/asm-generic/vmlinux.lds.h | 11 +-
> include/linux/init.h | 79 +++++++-
> include/linux/pci.h | 19 +-
> kernel/trace/Kconfig | 5 +
> lib/string.c | 24 +++
> scripts/Makefile.build | 55 +++++-
> scripts/Makefile.lib | 6 +-
> scripts/Makefile.modfinal | 31 ++-
> scripts/Makefile.modpost | 26 ++-
> scripts/generate_initcall_order.pl | 270 ++++++++++++++++++++++++++
> scripts/link-vmlinux.sh | 94 ++++++++-
> scripts/mod/Makefile | 1 +
> scripts/mod/modpost.c | 16 +-
> scripts/mod/modpost.h | 9 +
> scripts/mod/sumversion.c | 6 +-
> scripts/module-lto.lds | 26 +++
> 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 +
> 39 files changed, 883 insertions(+), 108 deletions(-)
> create mode 100755 scripts/generate_initcall_order.pl
> create mode 100644 scripts/module-lto.lds
>
>
> base-commit: e28f0104343d0c132fa37f479870c9e43355fee4
> --
> 2.28.0.402.g5ffc5be6b7-goog
>
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