[PATCH 00/22] add support for Clang LTO

Sami Tolvanen
2020-06-24T20:33:07Z

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's
Pixel devices have shipped with LTO+CFI kernels 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 first objtool patch in the series is already in linux-next,
but as it's needed with LTO, I'm including it also here to make testing
easier.

Sami Tolvanen (22):
objtool: use sh_info to find the base for .rela sections
kbuild: add support for Clang LTO
kbuild: lto: fix module versioning
kbuild: lto: fix recordmcount
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: lto: fix PREL32 relocations
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
arm64: allow LTO_CLANG and THINLTO to be selected
x86, vdso: disable LTO only for vDSO
x86, ftrace: disable recordmcount for ftrace_make_nop
x86, relocs: Ignore L4_PAGE_OFFSET relocations
x86, build: allow LTO_CLANG and THINLTO to be selected

.gitignore | 1 +
Makefile | 27 ++-
arch/Kconfig | 65 +++++++
arch/arm64/Kconfig | 2 +
arch/arm64/Makefile | 1 +
arch/arm64/kernel/vdso/Makefile | 4 +-
arch/x86/Kconfig | 2 +
arch/x86/Makefile | 5 +
arch/x86/entry/vdso/Makefile | 5 +-
arch/x86/kernel/ftrace.c | 1 +
arch/x86/tools/relocs.c | 1 +
drivers/firmware/efi/libstub/Makefile | 2 +
drivers/misc/lkdtm/Makefile | 1 +
include/asm-generic/vmlinux.lds.h | 12 +-
include/linux/compiler-clang.h | 4 +
include/linux/compiler.h | 2 +-
include/linux/compiler_types.h | 4 +
include/linux/init.h | 78 +++++++-
include/linux/pci.h | 15 +-
kernel/trace/ftrace.c | 1 +
lib/Kconfig.debug | 2 +-
scripts/Makefile.build | 55 +++++-
scripts/Makefile.lib | 6 +-
scripts/Makefile.modfinal | 40 +++-
scripts/Makefile.modpost | 26 ++-
scripts/generate_initcall_order.pl | 270 ++++++++++++++++++++++++++
scripts/link-vmlinux.sh | 100 +++++++++-
scripts/mod/Makefile | 1 +
scripts/mod/modpost.c | 16 +-
scripts/mod/modpost.h | 9 +
scripts/mod/sumversion.c | 6 +-
scripts/module-lto.lds | 26 +++
scripts/recordmcount.c | 3 +-
tools/objtool/elf.c | 2 +-
34 files changed, 737 insertions(+), 58 deletions(-)
create mode 100755 scripts/generate_initcall_order.pl
create mode 100644 scripts/module-lto.lds

base-commit: 26e122e97a3d0390ebec389347f64f3730fdf48f
--
2.27.0.212.ge8ba1cc988-goog