2e39b40dd2
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>
124 lines
4.0 KiB
Makefile
124 lines
4.0 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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# ===========================================================================
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# Module versions
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# ===========================================================================
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#
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# Stage one of module building created the following:
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# a) The individual .o files used for the module
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# b) A <module>.o file which is the .o files above linked together
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# c) A <module>.mod file, listing the name of the preliminary <module>.o file,
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# plus all .o files
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# d) modules.order, which lists all the modules
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# Stage 2 is handled by this file and does the following
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# 1) Find all modules listed in modules.order
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# 2) modpost is then used to
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# 3) create one <module>.mod.c file pr. module
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# 4) create one Module.symvers file with CRC for all exported symbols
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# Step 3 is used to place certain information in the module's ELF
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# section, including information such as:
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# Version magic (see include/linux/vermagic.h for full details)
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# - Kernel release
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# - SMP is CONFIG_SMP
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# - PREEMPT is CONFIG_PREEMPT[_RT]
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# - GCC Version
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# Module info
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# - Module version (MODULE_VERSION)
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# - Module alias'es (MODULE_ALIAS)
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# - Module license (MODULE_LICENSE)
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# - See include/linux/module.h for more details
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# Step 4 is solely used to allow module versioning in external modules,
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# where the CRC of each module is retrieved from the Module.symvers file.
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# KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
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# symbols in the final module linking stage
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# KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
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# This is solely useful to speed up test compiles
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PHONY := __modpost
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__modpost:
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include include/config/auto.conf
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include scripts/Kbuild.include
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kernelsymfile := $(objtree)/Module.symvers
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modulesymfile := $(firstword $(KBUILD_EXTMOD))/Module.symvers
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MODPOST = scripts/mod/modpost \
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$(if $(CONFIG_MODVERSIONS),-m) \
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$(if $(CONFIG_MODULE_SRCVERSION_ALL),-a) \
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$(if $(KBUILD_EXTMOD),-i,-o) $(kernelsymfile) \
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$(if $(KBUILD_EXTMOD),-I $(modulesymfile)) \
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$(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
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$(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
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$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E) \
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$(if $(KBUILD_MODPOST_WARN),-w) \
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$(if $(filter nsdeps,$(MAKECMDGOALS)),-d)
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ifdef MODPOST_VMLINUX
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quiet_cmd_modpost = MODPOST vmlinux.o
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cmd_modpost = $(MODPOST) vmlinux.o
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__modpost:
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$(call cmd,modpost)
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else
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# When building external modules load the Kbuild file to retrieve EXTRA_SYMBOLS info
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ifneq ($(KBUILD_EXTMOD),)
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# set src + obj - they may be used when building the .mod.c file
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obj := $(KBUILD_EXTMOD)
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src := $(obj)
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# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
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include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
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$(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
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endif
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MODPOST += $(subst -i,-n,$(filter -i,$(MAKEFLAGS))) -s -T - $(wildcard vmlinux)
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# find all modules listed in modules.order
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modules := $(sort $(shell cat $(MODORDER)))
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# With CONFIG_LTO_CLANG, .o files might be LLVM IR, so we need to link them
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# into actual objects before passing them to modpost
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modpost-ext = $(if $(CONFIG_LTO_CLANG),.lto,)
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ifdef CONFIG_LTO_CLANG
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quiet_cmd_cc_lto_link_modules = LTO [M] $@
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cmd_cc_lto_link_modules = \
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$(LD) $(ld_flags) -r -o $(@) \
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$(shell [ -s $(@:$(modpost-ext).o=.o.symversions) ] && \
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echo -T $(@:$(modpost-ext).o=.o.symversions)) \
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--whole-archive $(filter-out FORCE,$^)
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$(modules:.ko=$(modpost-ext).o): %$(modpost-ext).o: %.o FORCE
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$(call if_changed,cc_lto_link_modules)
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PHONY += FORCE
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FORCE:
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endif
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# Read out modules.order instead of expanding $(modules) to pass in modpost.
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# Otherwise, allmodconfig would fail with "Argument list too long".
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quiet_cmd_modpost = MODPOST $(words $(modules)) modules
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cmd_modpost = sed 's/\.ko$$/$(modpost-ext)\.o/' $(MODORDER) | $(MODPOST)
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__modpost: $(modules:.ko=$(modpost-ext).o)
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@$(kecho) ' Building modules, stage 2.'
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$(call cmd,modpost)
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ifneq ($(KBUILD_MODPOST_NOFINAL),1)
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$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal
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endif
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nsdeps: __modpost
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endif
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.PHONY: $(PHONY)
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