mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2026-06-21 15:43:21 +02:00
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>
84 lines
2.3 KiB
Makefile
84 lines
2.3 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0-only
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PHONY := __default
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__default: vmlinux.a
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include include/config/auto.conf
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include $(srctree)/scripts/Kbuild.include
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include $(srctree)/scripts/Makefile.lib
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# Link of built-in-fixup.a
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# ---------------------------------------------------------------------------
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# '$(AR) mPi' needs 'T' to workaround the bug of llvm-ar <= 14
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quiet_cmd_ar_builtin_fixup = AR $@
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cmd_ar_builtin_fixup = \
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rm -f $@; \
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$(AR) cDPrST $@ $(KBUILD_VMLINUX_OBJS); \
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$(AR) mPiT $$($(AR) t $@ | sed -n 1p) $@ $$($(AR) t $@ | grep -F -f $(srctree)/scripts/head-object-list.txt)
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targets += built-in-fixup.a
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built-in-fixup.a: $(KBUILD_VMLINUX_OBJS) scripts/head-object-list.txt FORCE
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$(call if_changed,ar_builtin_fixup)
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ifdef CONFIG_LTO_CLANG_THIN_DIST
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quiet_cmd_builtin.order = GEN $@
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cmd_builtin.order = $(AR) t $< > $@
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targets += builtin.order
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builtin.order: built-in-fixup.a FORCE
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$(call if_changed,builtin.order)
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quiet_cmd_ld_thinlto_index = LD $@
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cmd_ld_thinlto_index = \
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$(LD) $(KBUILD_LDFLAGS) -r --thinlto-index-only=$@ @$<
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targets += vmlinux.thinlto-index
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vmlinux.thinlto-index: builtin.order FORCE
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$(call if_changed,ld_thinlto_index)
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quiet_cmd_ar_vmlinux.a = GEN $@
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cmd_ar_vmlinux.a = \
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rm -f $@; \
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while read -r obj; do \
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if grep -Fqx $${obj} $(word 2, $^); then \
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echo $${obj%.o}.thinlto-native.o; \
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else \
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echo $${obj}; \
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fi; \
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done < $< | xargs $(AR) cDPrS --thin $@
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targets += vmlinux.a
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vmlinux.a: builtin.order vmlinux.thinlto-index FORCE
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$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.thinlto
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$(call if_changed,ar_vmlinux.a)
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else
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# vmlinux.a
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# ---------------------------------------------------------------------------
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targets += vmlinux.a
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vmlinux.a: built-in-fixup.a FORCE
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$(call if_changed,copy)
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endif
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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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