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Rong Xu
9f2aee8f7d
Add distributed ThinLTO build support for the Linux kernel.
This new mode offers several advantages: (1) Increased
flexibility in handling user-specified build options.
(2) Improved user-friendliness for developers. (3) Greater
convenience for integrating with objtool and livepatch.
Note that "distributed" in this context refers to a term
that differentiates in-process ThinLTO builds by invoking
backend compilation through the linker, not necessarily
building in distributed environments.
Distributed ThinLTO is enabled via the
`CONFIG_LTO_CLANG_THIN_DIST` Kconfig option. For example:
> make LLVM=1 defconfig
> scripts/config -e LTO_CLANG_THIN_DIST
> make LLVM=1 oldconfig
> make LLVM=1 vmlinux -j <..>
The build flow proceeds in four stages:
1. Perform FE compilation, mirroring the in-process ThinLTO mode.
2. Thin-link the generated IR files and object files.
3. Find all IR files and perform BE compilation, using the flags
stored in the .*.o.cmd files.
4. Link the BE results to generate the final vmlinux.o.
NOTE: This patch currently implements the build for the main kernel
image (vmlinux) only. Kernel module support is planned for a
subsequent patch.
Tested on the following arch: x86, arm64, loongarch, and
riscv.
The earlier implementation details can be found here:
https://discourse.llvm.org/t/rfc-distributed-thinlto-build-for-kernel/85934
Signed-off-by: Rong Xu <xur@google.com>
Co-developed-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Piotr Gorski <piotrgorski@cachyos.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://patch.msgid.link/20260529185347.2418373-4-xur@google.com
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
41 lines
1.4 KiB
Makefile
41 lines
1.4 KiB
Makefile
PHONY := __default
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__default:
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include include/config/auto.conf
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include $(srctree)/scripts/Kbuild.include
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include $(srctree)/scripts/Makefile.lib
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native-objs := $(patsubst %.o,%.thinlto-native.o,$(call read-file, vmlinux.thinlto-index))
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__default: $(native-objs)
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# Generate .thinlto-native.o (obj) from .o (bitcode) and .thinlto.bc (summary) files
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# ---------------------------------------------------------------------------
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quiet_cmd_cc_o_bc = CC $(quiet_modtag) $@
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be_flags = $(shell sed -n '/saved_c_flags_/s/.*:= //p' \
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$(dir $(<)).$(notdir $(<)).cmd)
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cmd_cc_o_bc = \
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$(CC) $(be_flags) -x ir -fno-lto -Wno-unused-command-line-argument \
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-fthinlto-index=$(word 2, $^) -c -o $@ $<
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targets += $(native-objs)
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$(native-objs): %.thinlto-native.o: %.o %.o.thinlto.bc FORCE
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$(call if_changed,cc_o_bc)
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# Add FORCE to the prerequisites of a target to force it to be always rebuilt.
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# ---------------------------------------------------------------------------
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PHONY += FORCE
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FORCE:
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# Read all saved command lines and dependencies for the $(targets) we
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# may be building above, using $(if_changed{,_dep}). As an
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# optimization, we don't need to read them if the target does not
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# exist, we will rebuild anyway in that case.
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existing-targets := $(wildcard $(sort $(targets)))
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-include $(foreach f, $(existing-targets),$(dir $(f)).$(notdir $(f)).cmd)
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.PHONY: $(PHONY)
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