ANDROID: kbuild: add support for Clang LTO
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>
This commit is contained in:
Sami Tolvanen
parent
548c06ceb9
commit
2e39b40dd2
29
Makefile
29
Makefile
@ -654,6 +654,16 @@ RETPOLINE_VDSO_CFLAGS := $(call cc-option,$(RETPOLINE_VDSO_CFLAGS_GCC),$(call cc
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export RETPOLINE_CFLAGS
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export RETPOLINE_VDSO_CFLAGS
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# Make toolchain changes before including arch/$(SRCARCH)/Makefile to ensure
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# ar/cc/ld-* macros return correct values.
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ifdef CONFIG_LTO_CLANG
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# LTO produces LLVM IR instead of object files. Use llvm-ar and llvm-nm, so we
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# can process these.
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AR := llvm-ar
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LLVM_NM := llvm-nm
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export LLVM_NM
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endif
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include arch/$(SRCARCH)/Makefile
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ifdef need-config
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@ -856,6 +866,22 @@ KBUILD_CFLAGS += $(CC_FLAGS_SCS)
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export CC_FLAGS_SCS
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endif
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ifdef CONFIG_LTO_CLANG
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ifdef CONFIG_THINLTO
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CC_FLAGS_LTO_CLANG := -flto=thin $(call cc-option, -fsplit-lto-unit)
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KBUILD_LDFLAGS += --thinlto-cache-dir=.thinlto-cache
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else
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CC_FLAGS_LTO_CLANG := -flto
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endif
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CC_FLAGS_LTO_CLANG += -fvisibility=default
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endif
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ifdef CONFIG_LTO
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CC_FLAGS_LTO := $(CC_FLAGS_LTO_CLANG)
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KBUILD_CFLAGS += $(CC_FLAGS_LTO)
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export CC_FLAGS_LTO
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endif
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# arch Makefile may override CC so keep this after arch Makefile is included
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NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
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@ -1682,7 +1708,8 @@ clean: $(clean-dirs)
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-o -name modules.builtin -o -name '.tmp_*.o.*' \
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-o -name '*.c.[012]*.*' \
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-o -name '*.ll' \
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-o -name '*.gcno' \) -type f -print | xargs rm -f
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-o -name '*.gcno' \
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-o -name '*.*.symversions' \) -type f -print | xargs rm -f
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# Generate tags for editors
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# ---------------------------------------------------------------------------
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47
arch/Kconfig
47
arch/Kconfig
@ -554,6 +554,53 @@ config SHADOW_CALL_STACK_VMAP
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provides better stack exhaustion protection, but increases per-thread
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memory consumption as a full page is allocated for each shadow stack.
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config LTO
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bool
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config ARCH_SUPPORTS_LTO_CLANG
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bool
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help
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An architecture should select this option if it supports:
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- compiling with Clang,
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- compiling inline assembly with Clang's integrated assembler,
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- and linking with LLD.
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config ARCH_SUPPORTS_THINLTO
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bool
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help
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An architecture should select this if it supports Clang ThinLTO.
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config THINLTO
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bool "Use Clang's ThinLTO (EXPERIMENTAL)"
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depends on LTO_CLANG && ARCH_SUPPORTS_THINLTO
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default y
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help
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Use ThinLTO to speed up Link Time Optimization.
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choice
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prompt "Link-Time Optimization (LTO) (EXPERIMENTAL)"
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default LTO_NONE
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help
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This option turns on Link-Time Optimization (LTO).
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config LTO_NONE
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bool "None"
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config LTO_CLANG
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bool "Use Clang's Link Time Optimization (LTO) (EXPERIMENTAL)"
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depends on ARCH_SUPPORTS_LTO_CLANG
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depends on !KASAN
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depends on !FTRACE_MCOUNT_RECORD
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depends on CC_IS_CLANG && CLANG_VERSION >= 100000 && LD_IS_LLD
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select LTO
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help
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This option enables Clang's Link Time Optimization (LTO), which allows
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the compiler to optimize the kernel globally at link time. If you
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enable this option, the compiler generates LLVM IR instead of object
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files, and the actual compilation from IR occurs at the LTO link step,
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which may take several minutes.
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endchoice
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config HAVE_ARCH_WITHIN_STACK_FRAMES
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bool
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@ -63,10 +63,13 @@
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* .data. We don't want to pull in .data..other sections, which Linux
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* has defined. Same for text and bss.
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*
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* With LTO_CLANG, the linker also splits sections by default, so we need
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* these macros to combine the sections during the final link.
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*
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* RODATA_MAIN is not used because existing code already defines .rodata.x
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* sections to be brought in with rodata.
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*/
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#ifdef CONFIG_LD_DEAD_CODE_DATA_ELIMINATION
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#if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG)
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#define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
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#define DATA_MAIN .data .data.[0-9a-zA-Z_]* .data..LPBX*
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#define SDATA_MAIN .sdata .sdata.[0-9a-zA-Z_]*
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@ -93,7 +93,7 @@ endif
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# ---------------------------------------------------------------------------
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quiet_cmd_cc_s_c = CC $(quiet_modtag) $@
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cmd_cc_s_c = $(CC) $(filter-out $(DEBUG_CFLAGS), $(c_flags)) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
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cmd_cc_s_c = $(CC) $(filter-out $(DEBUG_CFLAGS) $(CC_FLAGS_LTO), $(c_flags)) $(DISABLE_LTO) -fverbose-asm -S -o $@ $<
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$(obj)/%.s: $(src)/%.c FORCE
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$(call if_changed_dep,cc_s_c)
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@ -148,6 +148,15 @@ ifdef CONFIG_MODVERSIONS
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# the actual value of the checksum generated by genksyms
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# o remove .tmp_<file>.o to <file>.o
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ifdef CONFIG_LTO_CLANG
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# Generate .o.symversions files for each .o with exported symbols, and link these
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# to the kernel and/or modules at the end.
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cmd_modversions_c = \
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if $(LLVM_NM) $@ | grep -q __ksymtab; then \
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$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
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> $@.symversions; \
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fi;
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else
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cmd_modversions_c = \
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if $(OBJDUMP) -h $@ | grep -q __ksymtab; then \
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$(call cmd_gensymtypes_c,$(KBUILD_SYMTYPES),$(@:.o=.symtypes)) \
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@ -159,6 +168,7 @@ cmd_modversions_c = \
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rm -f $(@D)/.tmp_$(@F:.o=.ver); \
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fi
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endif
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endif
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ifdef CONFIG_FTRACE_MCOUNT_RECORD
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ifndef CC_USING_RECORD_MCOUNT
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@ -383,6 +393,21 @@ $(obj)/%.asn1.c $(obj)/%.asn1.h: $(src)/%.asn1 $(objtree)/scripts/asn1_compiler
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# To build objects in subdirs, we need to descend into the directories
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$(sort $(subdir-obj-y)): $(subdir-ym) ;
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# combine symversions for later processing
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quiet_cmd_update_lto_symversions = SYMVER $@
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ifeq ($(CONFIG_LTO_CLANG) $(CONFIG_MODVERSIONS),y y)
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cmd_update_lto_symversions = \
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rm -f $@.symversions; \
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for i in $(filter-out FORCE,$^); do \
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if [ -f $$i.symversions ]; then \
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cat $$i.symversions \
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>> $@.symversions; \
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fi; \
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done
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else
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cmd_update_lto_symversions = echo >/dev/null
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endif
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#
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# Rule to compile a set of .o files into one .a file (without symbol table)
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#
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@ -391,8 +416,11 @@ ifdef builtin-target
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quiet_cmd_ar_builtin = AR $@
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cmd_ar_builtin = rm -f $@; $(AR) cDPrST $@ $(real-prereqs)
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quiet_cmd_ar_and_symver = AR $@
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cmd_ar_and_symver = $(cmd_update_lto_symversions); $(cmd_ar_builtin)
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$(builtin-target): $(real-obj-y) FORCE
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$(call if_changed,ar_builtin)
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$(call if_changed,ar_and_symver)
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targets += $(builtin-target)
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endif # builtin-target
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@ -412,16 +440,26 @@ $(modorder-target): $(subdir-ym) FORCE
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#
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ifdef lib-target
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quiet_cmd_ar_lib = AR $@
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cmd_ar_lib = $(cmd_update_lto_symversions); $(cmd_ar)
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$(lib-target): $(lib-y) FORCE
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$(call if_changed,ar)
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$(call if_changed,ar_lib)
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targets += $(lib-target)
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dummy-object = $(obj)/.lib_exports.o
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ksyms-lds = $(dot-target).lds
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ifdef CONFIG_LTO_CLANG
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# Objdump doesn't understand LLVM IR. Use llvm-nm to dump symbols.
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dump_export_list = $(LLVM_NM)
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else
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dump_export_list = $(OBJDUMP) -h
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endif
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quiet_cmd_export_list = EXPORTS $@
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cmd_export_list = $(OBJDUMP) -h $< | \
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cmd_export_list = $(dump_export_list) $< | \
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sed -ne '/___ksymtab/s/.*+\([^ ]*\).*/EXTERN(\1)/p' >$(ksyms-lds);\
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rm -f $(dummy-object);\
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echo | $(CC) $(a_flags) -c -o $(dummy-object) -x assembler -;\
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@ -439,8 +477,16 @@ endif
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# Do not replace $(filter %.o,^) with $(real-prereqs). When a single object
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# module is turned into a multi object module, $^ will contain header file
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# dependencies recorded in the .*.cmd file.
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ifdef CONFIG_LTO_CLANG
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quiet_cmd_link_multi-m = AR [M] $@
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cmd_link_multi-m = \
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$(cmd_update_lto_symversions); \
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rm -f $@; \
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$(AR) rcsTP$(KBUILD_ARFLAGS) $@ $(filter %.o,$^)
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else
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quiet_cmd_link_multi-m = LD [M] $@
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cmd_link_multi-m = $(LD) $(ld_flags) -r -o $@ $(filter %.o,$^)
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endif
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$(multi-used-m): FORCE
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$(call if_changed,link_multi-m)
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@ -6,6 +6,7 @@
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PHONY := __modfinal
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__modfinal:
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include $(objtree)/include/config/auto.conf
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include $(srctree)/scripts/Kbuild.include
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# for c_flags
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@ -30,12 +31,24 @@ quiet_cmd_cc_o_c = CC [M] $@
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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 $(filter %.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: %.o %.mod.o $(KBUILD_LDS_MODULE) FORCE
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+$(call if_changed,ld_ko_o)
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@ -84,12 +84,32 @@ 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$$/o/' $(MODORDER) | $(MODPOST)
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cmd_modpost = sed 's/\.ko$$/$(modpost-ext)\.o/' $(MODORDER) | $(MODPOST)
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__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 ($(KBUILD_MODPOST_NOFINAL),1)
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@ -39,6 +39,30 @@ info()
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fi
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}
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# If CONFIG_LTO_CLANG is selected, collect generated symbol versions into
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# .tmp_symversions
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modversions()
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{
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if [ -z "${CONFIG_LTO_CLANG}" ]; then
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return
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fi
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if [ -z "${CONFIG_MODVERSIONS}" ]; then
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return
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fi
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rm -f .tmp_symversions
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for a in ${KBUILD_VMLINUX_OBJS} ${KBUILD_VMLINUX_LIBS}; do
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for o in $(${AR} t $a 2>/dev/null); do
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if [ -f ${o}.symversions ]; then
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cat ${o}.symversions >> .tmp_symversions
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fi
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done
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done
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echo "-T .tmp_symversions"
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}
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# Link of vmlinux.o used for section mismatch analysis
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# ${1} output file
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modpost_link()
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@ -52,7 +76,15 @@ modpost_link()
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${KBUILD_VMLINUX_LIBS} \
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--end-group"
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${LD} ${KBUILD_LDFLAGS} -r -o ${1} ${objects}
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if [ -n "${CONFIG_LTO_CLANG}" ]; then
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# This might take a while, so indicate that we're doing
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# an LTO link
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info LTO ${1}
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else
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info LD ${1}
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fi
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${LD} ${KBUILD_LDFLAGS} -r -o ${1} $(modversions) ${objects}
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}
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# Link of vmlinux
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@ -70,13 +102,22 @@ vmlinux_link()
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shift
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if [ "${SRCARCH}" != "um" ]; then
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objects="--whole-archive \
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${KBUILD_VMLINUX_OBJS} \
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--no-whole-archive \
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--start-group \
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${KBUILD_VMLINUX_LIBS} \
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--end-group \
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${@}"
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if [ -n "${CONFIG_LTO_CLANG}" ]; then
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# Use vmlinux.o instead of performing the slow LTO
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# link again.
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objects="--whole-archive \
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vmlinux.o \
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--no-whole-archive \
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${@}"
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else
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objects="--whole-archive \
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${KBUILD_VMLINUX_OBJS} \
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--no-whole-archive \
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--start-group \
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${KBUILD_VMLINUX_LIBS} \
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--end-group \
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${@}"
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fi
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${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux} \
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-o ${output} \
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@ -189,6 +230,7 @@ cleanup()
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rm -f .btf.*
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rm -f .tmp_System.map
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rm -f .tmp_kallsyms*
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rm -f .tmp_symversions
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rm -f .tmp_vmlinux*
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rm -f System.map
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rm -f vmlinux
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@ -240,7 +282,6 @@ fi;
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${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init
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#link vmlinux.o
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info LD vmlinux.o
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modpost_link vmlinux.o
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# modpost vmlinux.o to check for section mismatches
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@ -146,6 +146,9 @@ static struct module *new_module(const char *modname)
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p[strlen(p) - 2] = '\0';
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mod->is_dot_o = 1;
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}
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/* strip trailing .lto */
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if (strends(p, ".lto"))
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p[strlen(p) - 4] = '\0';
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/* add to list */
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mod->name = p;
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@ -2000,6 +2003,10 @@ static char *remove_dot(char *s)
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size_t m = strspn(s + n + 1, "0123456789");
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if (m && (s[n + m] == '.' || s[n + m] == 0))
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s[n] = 0;
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/* strip trailing .lto */
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if (strends(s, ".lto"))
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s[strlen(s) - 4] = '\0';
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}
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return s;
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}
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