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Kbuild: add support for ThinLTO

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This change adds support for ThinLTO, which greatly improves build times
over full LTO while retaining most of the performance benefits:

  https://clang.llvm.org/docs/ThinLTO.html

Bug: 145210207
Change-Id: I8bfc19028266077be2bc1fb5c2bc001b599d3214
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: mydongistiny <jaysonedson@gmail.com>
Signed-off-by: DennySPB <dennyspb@gmail.com>
This commit is contained in:
Sami Tolvanen 2019-08-01 12:45:43 -07:00 • committed by xxmustafacooTR
parent 9c537aaffc
commit 76290c95e6
No known key found for this signature in database
GPG key ID: 520B6FE385CBF5C9
4 changed files with 26 additions and 13 deletions
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17
Makefile
View file

@ -694,14 +694,12 @@ ifneq ($(ld-name),lld)
LDFINAL_vmlinux := $(LD)
LD := $(LDGOLD)
KBUILD_LDFLAGS += -plugin LLVMgold.so
KBUILD_LDFLAGS += -plugin-opt=-function-sections
KBUILD_LDFLAGS += -plugin-opt=-data-sections
endif
# use llvm-ar for building symbol tables from IR files, and llvm-dis instead
# use llvm-ar for building symbol tables from IR files, and llvm-nm instead
# of objdump for processing symbol versions and exports
LLVM_AR := llvm-ar
LLVM_DIS := llvm-dis
export LLVM_AR LLVM_DIS
LLVM_NM := llvm-nm
export LLVM_AR LLVM_NM
endif
# The arch Makefile can set ARCH_{CPP,A,C}FLAGS to override the default
@ -752,7 +750,12 @@ KBUILD_CFLAGS += $(call cc-option,-fdata-sections,)
endif
ifdef CONFIG_LTO_CLANG
lto-clang-flags := -flto -fvisibility=hidden
ifdef CONFIG_THINLTO
lto-clang-flags := -flto=thin
else
lto-clang-flags := -flto
endif
lto-clang-flags += -fvisibility=default $(call cc-option, -fsplit-lto-unit)
# Limit inlining across translation units to reduce binary size
LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5
@ -763,7 +766,7 @@ KBUILD_LDFLAGS_MODULE += $(LD_FLAGS_LTO_CLANG)
KBUILD_LDFLAGS_MODULE += -T $(srctree)/scripts/module-lto.lds
# allow disabling only clang LTO where needed
DISABLE_LTO_CLANG := -fno-lto -fvisibility=default
DISABLE_LTO_CLANG := -fno-lto
export DISABLE_LTO_CLANG
endif

12
arch/Kconfig
View file

@ -503,6 +503,18 @@ config ARCH_SUPPORTS_LTO_CLANG
- compiling inline assembly with clang's integrated assembler,
- and linking with either lld or GNU gold w/ LLVMgold.
config ARCH_SUPPORTS_THINLTO
bool
help
An architecture should select this if it supports clang's ThinLTO.
config THINLTO
bool "Use clang ThinLTO (EXPERIMENTAL)"
depends on LTO_CLANG && ARCH_SUPPORTS_THINLTO
default y
help
Use ThinLTO to speed up Link Time Optimization.
choice
prompt "Link-Time Optimization (LTO) (EXPERIMENTAL)"
default LTO_NONE

4
scripts/Makefile.build
View file

@ -218,7 +218,7 @@ cmd_modversions_c = \
> $(@D)/$(@F).symversions; \
fi; \
else \
if $(LLVM_DIS) -o=- $(@D)/.tmp_$(@F) | grep -q __ksymtab; then \
if $(LLVM_NM) $(@D)/.tmp_$(@F) | grep -q __ksymtab; then \
$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
> $(@D)/$(@F).symversions; \
fi; \
@ -570,7 +570,7 @@ cmd_export_list = \
$(filter_export_list) \
>>$(ksyms-lds); \
else \
$(LLVM_DIS) -o=- $$o | \
$(LLVM_NM) $$o | \
$(filter_export_list) \
>>$(ksyms-lds); \
fi; \

4
scripts/Makefile.modpost
View file

@ -138,10 +138,8 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(SRCARCH)/Makefile.postlink)
quiet_cmd_ld_ko_o = LD [M] $@
ifdef CONFIG_LTO_CLANG
bad_ld_flags = -plugin-opt=-function-sections -plugin-opt=-data-sections
filtered_ldflags = $(filter-out $(bad_ld_flags),$(LDFLAGS))
cmd_ld_ko_o = \
$(LD) -r $(filtered_ld_flags) \
$(LD) -r $(KBUILD_LDFLAGS) \
$(KBUILD_LDFLAGS_MODULE) $(LDFLAGS_MODULE) \
$(shell [ -s $(@:.ko=.o.symversions) ] && \
echo -T $(@:.ko=.o.symversions)) \