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Subject[GIT PULL v2] clang-lto for v5.12-rc1
Hi Linus,

Please pull this Clang Link Time Optimization series for v5.12-rc1.
This has been in linux-next for the entire last development cycle,
and is built on the work done preparing[0] for LTO by arm64 folks,
tracing folks, etc. This series includes the core changes as well as
the remaining pieces for arm64 (LTO has been the default build method on
Android for about 3 years now, as it is the prerequisite for the Control
Flow Integrity protections).

While x86 LTO enablement is done[1], it depends on some objtool
clean-ups[2], though it appears those actually have been in linux-next
(via tip/objtool/core), so it's possible that if that tree lands, I'll
send a "part 2" pull request for LTO that includes x86 support (though
I guess that depends on the length of the merge window).

For merge log posterity, and as detailed in commit dc5723b02e52 ("kbuild:
add support for Clang LTO"), here is the lt;dr to do an LTO build:

make LLVM=1 LLVM_IAS=1 defconfig
scripts/config -e LTO_CLANG_THIN
make LLVM=1 LLVM_IAS=1

(To do a cross-compile of arm64, add "CROSS_COMPILE=aarch64-linux-gnu-"
and "ARCH=arm64" to the "make" command lines.)

Thanks!

-Kees

[0] https://git.kernel.org/linus/3c09ec59cdea5b132212d97154d625fd34e436dd
[1] https://github.com/samitolvanen/linux/commits/clang-lto
[2] https://lore.kernel.org/lkml/cover.1611263461.git.jpoimboe@redhat.com/

The following changes since commit e71ba9452f0b5b2e8dc8aa5445198cd9214a6a62:

Linux 5.11-rc2 (2021-01-03 15:55:30 -0800)

are available in the Git repository at:

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git tags/clang-lto-v5.12-rc1

for you to fetch changes up to 2b8689520520175075ca97bc4eaf51ff3f7253aa:

kbuild: prevent CC_FLAGS_LTO self-bloating on recursive rebuilds (2021-02-17 10:10:37 -0800)

----------------------------------------------------------------
clang-lto series for v5.12-rc1

- Clang LTO build infrastructure and arm64-specific enablement (Sami Tolvanen)
- Recursive build CC_FLAGS_LTO fix (Alexander Lobakin)

----------------------------------------------------------------
Alexander Lobakin (1):
kbuild: prevent CC_FLAGS_LTO self-bloating on recursive rebuilds

Sami Tolvanen (16):
tracing: move function tracer options to Kconfig
kbuild: add support for Clang LTO
kbuild: lto: fix module versioning
kbuild: lto: limit inlining
kbuild: lto: merge module sections
kbuild: lto: add a default list of used symbols
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
arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS
arm64: allow LTO to be selected

.gitignore | 1 +
Makefile | 45 ++++--
arch/Kconfig | 90 ++++++++++++
arch/arm64/Kconfig | 4 +
arch/arm64/kernel/vdso/Makefile | 3 +-
drivers/firmware/efi/libstub/Makefile | 2 +
drivers/misc/lkdtm/Makefile | 1 +
include/asm-generic/vmlinux.lds.h | 11 +-
include/linux/init.h | 79 ++++++++--
include/linux/pci.h | 27 +++-
init/Kconfig | 1 +
kernel/trace/Kconfig | 16 ++
scripts/Makefile.build | 48 +++++-
scripts/Makefile.lib | 6 +-
scripts/Makefile.modfinal | 9 +-
scripts/Makefile.modpost | 25 +++-
scripts/generate_initcall_order.pl | 270 ++++++++++++++++++++++++++++++++++
scripts/link-vmlinux.sh | 70 +++++++--
scripts/lto-used-symbollist.txt | 5 +
scripts/mod/Makefile | 1 +
scripts/mod/modpost.c | 16 +-
scripts/mod/modpost.h | 9 ++
scripts/mod/sumversion.c | 6 +-
scripts/module.lds.S | 24 +++
24 files changed, 707 insertions(+), 62 deletions(-)
create mode 100755 scripts/generate_initcall_order.pl
create mode 100644 scripts/lto-used-symbollist.txt

--
Kees Cook

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