Dear Sami,
Am 24.06.20 um 22:31 schrieb Sami Tolvanen:
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.
[…]
Thank you very much for sending these changes.
Do you have a branch, where your current work can be pulled from? Your
branch on GitHub [1] seems 15 months old.
Out of curiosity, I applied the changes, allowed the selection for i386
(x86), and with Clang 1:11~++20200701093119+ffee8040534-1~exp1 from
Debian experimental, it failed with `Invalid absolute R_386_32
relocation: KERNEL_PAGES`:
make -f ./scripts/Makefile.build obj=arch/x86/boot arch/x86/boot/bzImage
make -f ./scripts/Makefile.build obj=arch/x86/boot/compressed arch/x86/boot/compressed/vmlinux
llvm-nm vmlinux | sed -n -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(_text\|__bss_start\|_end\)$/#define VO_ _AC(0x,UL)/p' > arch/x86/boot/compressed/../voffset.h
clang -Wp,-MMD,arch/x86/boot/compressed/.misc.o.d -nostdinc -isystem /usr/lib/llvm-11/lib/clang/11.0.0/include -I./arch/x86/include -I./arch/x86/include/generated -I./include -I./arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I./include/uapi -I./include/generated/uapi -include ./include/linux/kconfig.h -include ./include/linux/compiler_types.h -D__KERNEL__ -Qunused-arguments -m32 -O2 -fno-strict-aliasing -fPIE -DDISABLE_BRANCH_PROFILING -march=i386 -mno-mmx -mno-sse -ffreestanding -fno-stack-protector -Wno-address-of-packed-member -Wno-gnu -Wno-pointer-sign -fmacro-prefix-map=./= -fno-asynchronous-unwind-tables -DKBUILD_MODFILE='"arch/x86/boot/compressed/misc"' -DKBUILD_BASENAME='"misc"' -DKBUILD_MODNAME='"misc"' -D__KBUILD_MODNAME=misc -c -o arch/x86/boot/compressed/misc.o arch/x86/boot/compressed/misc.c
llvm-objcopy -R .comment -S vmlinux arch/x86/boot/compressed/vmlinux.bin
arch/x86/tools/relocs vmlinux > arch/x86/boot/compressed/vmlinux.relocs;arch/x86/tools/relocs --abs-relocs vmlinux
Invalid absolute R_386_32 relocation: KERNEL_PAGES
make[2]: *** [arch/x86/boot/compressed/Makefile:134: arch/x86/boot/compressed/vmlinux.relocs] Error 1
make[2]: *** Deleting file 'arch/x86/boot/compressed/vmlinux.relocs'
make[1]: *** [arch/x86/boot/Makefile:115: arch/x86/boot/compressed/vmlinux] Error 2
make: *** [arch/x86/Makefile:268: bzImage] Error 2
Kind regards,
Paul
[1]: https://github.com/samitolvanen/linux/tree/clang-lto
