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Message-Id: <20201013003203.4168817-1-samitolvanen@google.com>
Date: Mon, 12 Oct 2020 17:31:38 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Masahiro Yamada <masahiroy@...nel.org>, Steven Rostedt <rostedt@...dmis.org>
Cc: Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Paul E. McKenney" <paulmck@...nel.org>,
Kees Cook <keescook@...omium.org>, Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux@...glegroups.com, kernel-hardening@...ts.openwall.com,
linux-arch@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org, x86@...nel.org,
Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v6 00/25] Add support for Clang LTO
This patch series adds support for building the x86_64 kernel 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-v6
---
Changes in v6:
- Added the missing --mcount flag to patch 5.
- Dropped the arm64 patches from this series and will repost them
later.
Changes in v5:
- Rebased on top of tip/master.
- 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.
- 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 (23):
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
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/Makefile | 4 -
.../module.lds => include/asm/module.lds.h} | 2 +
arch/arm64/kernel/vdso/Makefile | 1 -
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/builtin.h | 2 +-
tools/objtool/check.c | 84 +++++-
tools/objtool/check.h | 1 +
tools/objtool/objtool.c | 1 +
tools/objtool/objtool.h | 1 +
54 files changed, 895 insertions(+), 128 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: a292570e9f694ed50d3e69afd6d54272fd40deca
--
2.28.0.1011.ga647a8990f-goog
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