310afefe71
This change adds the configuration option CONFIG_LTO_CLANG, and build system support for Clang's Link Time Optimization (LTO). In preparation for LTO support with other compilers, potentially common parts of the changes are gated behind CONFIG_LTO instead. With -flto, instead of object files, Clang produces LLVM bitcode, which is compiled into a native object at link time, allowing the final binary to be optimized globally. For more details, see: https://llvm.org/docs/LinkTimeOptimization.html While the kernel normally uses GNU ld for linking, LLVM supports LTO only with LLD or GNU gold linkers. This change assumes LLD is used. Bug: 145210207 Change-Id: If1164ff33d073358ee7d4bba84cbb06c349c4a88 Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
73 lines
2.2 KiB
Text
73 lines
2.2 KiB
Text
# SPDX-License-Identifier: GPL-2.0-only
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# ===========================================================================
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# Module final link
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# ===========================================================================
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PHONY := __modfinal
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__modfinal:
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include $(srctree)/scripts/Kbuild.include
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# for c_flags
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include $(srctree)/scripts/Makefile.lib
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# find all modules listed in modules.order
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modules := $(sort $(shell cat $(MODORDER)))
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__modfinal: $(modules)
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@:
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# modname and part-of-module are set to make c_flags define proper module flags
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modname = $(notdir $(@:.mod.o=))
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part-of-module = y
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quiet_cmd_cc_o_c = CC [M] $@
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cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
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%.mod.o: %.mod.c FORCE
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$(call if_changed_dep,cc_o_c)
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ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
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quiet_cmd_ld_ko_o = LD [M] $@
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ifdef CONFIG_LTO_CLANG
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cmd_ld_ko_o = \
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$(LD) -r $(LDFLAGS) \
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$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
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$(addprefix -T , $(KBUILD_LDS_MODULE)) \
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$(shell [ -s $(@:.ko=.o.symversions) ] && \
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echo -T $(@:.ko=.o.symversions)) \
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-o $@ --whole-archive \
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$(filter-out FORCE,$(^:$(modpost-ext).o=.o)); \
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$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
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else
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cmd_ld_ko_o = \
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$(LD) -r $(KBUILD_LDFLAGS) \
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$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
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$(addprefix -T , $(KBUILD_LDS_MODULE)) \
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-o $@ $(filter %.o, $^); \
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$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
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endif
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$(modules): %.ko: %$(modpost-ext).o %.o %.mod.o $(KBUILD_LDS_MODULE) FORCE
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+$(call if_changed,ld_ko_o)
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targets += $(modules) $(modules:.ko=.mod.o)
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# Add FORCE to the prequisites 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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