build: support building with Link Time Optimizations
Add plumbing for building U-Boot with Link Time Optimizations. When building with LTO, $(PLATFORM_LIBS) has to be in --whole-archive / --no-whole-archive group, otherwise some functions declared in assembly may not be resolved and linking may fail. Note: clang may throw away linker list symbols it thinks are unused when compiling with LTO. To force these symbols to be included, we refer to them via the __ADDRESSABLE macro in a C file generated from compiled built-in.o files before linking. Signed-off-by: Marek Behún <marek.behun@nic.cz> Reviewed-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Marek Behún
Tom Rini
parent
958f2e57ef
commit
c1094987d1
2
Kbuild
2
Kbuild
@ -10,6 +10,8 @@ generic-offsets-file := include/generated/generic-asm-offsets.h
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always := $(generic-offsets-file)
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targets := lib/asm-offsets.s
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CFLAGS_REMOVE_asm-offsets.o := $(LTO_CFLAGS)
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$(obj)/$(generic-offsets-file): $(obj)/lib/asm-offsets.s FORCE
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$(call filechk,offsets,__GENERIC_ASM_OFFSETS_H__)
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24
Kconfig
24
Kconfig
@ -85,6 +85,30 @@ config SPL_OPTIMIZE_INLINING
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do what it thinks is best, which is desirable in some cases for size
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reasons.
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config ARCH_SUPPORTS_LTO
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bool
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config LTO
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bool "Enable Link Time Optimizations"
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depends on ARCH_SUPPORTS_LTO
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default n
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help
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This option enables Link Time Optimization (LTO), a mechanism which
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allows the compiler to optimize between different compilation units.
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This can optimize away dead code paths, resulting in smaller binary
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size (if CC_OPTIMIZE_FOR_SIZE is enabled).
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This option is not available for every architecture and may
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introduce bugs.
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Currently, when compiling with GCC, due to a weird bug regarding
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jobserver, the final linking will not respect make's --jobs argument.
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Instead all available processors will be used (as reported by the
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nproc command).
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If unsure, say n.
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config TPL_OPTIMIZE_INLINING
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bool "Allow compiler to uninline functions marked 'inline' in TPL"
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depends on TPL
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67
Makefile
67
Makefile
@ -676,6 +676,31 @@ else
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KBUILD_CFLAGS += -O2
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endif
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LTO_CFLAGS :=
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LTO_FINAL_LDFLAGS :=
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export LTO_CFLAGS LTO_FINAL_LDFLAGS
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ifdef CONFIG_LTO
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ifeq ($(cc-name),clang)
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LTO_CFLAGS += -flto
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LTO_FINAL_LDFLAGS += -flto
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AR = $(shell $(CC) -print-prog-name=llvm-ar)
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NM = $(shell $(CC) -print-prog-name=llvm-nm)
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else
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NPROC := $(shell nproc 2>/dev/null || echo 1)
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LTO_CFLAGS += -flto=$(NPROC)
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LTO_FINAL_LDFLAGS += -fuse-linker-plugin -flto=$(NPROC)
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# use plugin aware tools
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AR = $(CROSS_COMPILE)gcc-ar
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NM = $(CROSS_COMPILE)gcc-nm
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endif
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CFLAGS_NON_EFI += $(LTO_CFLAGS)
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KBUILD_CFLAGS += $(LTO_CFLAGS)
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endif
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ifeq ($(CONFIG_STACKPROTECTOR),y)
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KBUILD_CFLAGS += $(call cc-option,-fstack-protector-strong)
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CFLAGS_EFI += $(call cc-option,-fno-stack-protector)
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@ -1708,8 +1733,45 @@ u-boot-swap.bin: u-boot.bin FORCE
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ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(ARCH)/Makefile.postlink)
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# Generate linker list symbols references to force compiler to not optimize
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# them away when compiling with LTO
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ifdef CONFIG_LTO
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u-boot-keep-syms-lto := keep-syms-lto.o
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u-boot-keep-syms-lto_c := $(patsubst %.o,%.c,$(u-boot-keep-syms-lto))
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quiet_cmd_keep_syms_lto = KSL $@
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cmd_keep_syms_lto = \
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NM=$(NM) $(srctree)/scripts/gen_ll_addressable_symbols.sh $^ >$@
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quiet_cmd_keep_syms_lto_cc = KSLCC $@
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cmd_keep_syms_lto_cc = \
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$(CC) $(filter-out $(LTO_CFLAGS),$(c_flags)) -c -o $@ $<
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$(u-boot-keep-syms-lto_c): $(u-boot-main)
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$(call if_changed,keep_syms_lto)
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$(u-boot-keep-syms-lto): $(u-boot-keep-syms-lto_c)
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$(call if_changed,keep_syms_lto_cc)
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else
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u-boot-keep-syms-lto :=
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endif
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# Rule to link u-boot
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# May be overridden by arch/$(ARCH)/config.mk
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ifdef CONFIG_LTO
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quiet_cmd_u-boot__ ?= LTO $@
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cmd_u-boot__ ?= \
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$(CC) -nostdlib -nostartfiles \
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$(LTO_FINAL_LDFLAGS) $(c_flags) \
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$(KBUILD_LDFLAGS:%=-Wl,%) $(LDFLAGS_u-boot:%=-Wl,%) -o $@ \
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-T u-boot.lds $(u-boot-init) \
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-Wl,--whole-archive \
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$(u-boot-main) \
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$(u-boot-keep-syms-lto) \
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$(PLATFORM_LIBS) \
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-Wl,--no-whole-archive \
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-Wl,-Map,u-boot.map; \
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$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
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else
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quiet_cmd_u-boot__ ?= LD $@
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cmd_u-boot__ ?= $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_u-boot) -o $@ \
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-T u-boot.lds $(u-boot-init) \
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@ -1718,6 +1780,7 @@ quiet_cmd_u-boot__ ?= LD $@
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--no-whole-archive \
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$(PLATFORM_LIBS) -Map u-boot.map; \
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$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
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endif
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quiet_cmd_smap = GEN common/system_map.o
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cmd_smap = \
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@ -1726,7 +1789,7 @@ cmd_smap = \
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$(CC) $(c_flags) -DSYSTEM_MAP="\"$${smap}\"" \
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-c $(srctree)/common/system_map.c -o common/system_map.o
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u-boot: $(u-boot-init) $(u-boot-main) u-boot.lds FORCE
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u-boot: $(u-boot-init) $(u-boot-main) $(u-boot-keep-syms-lto) u-boot.lds FORCE
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+$(call if_changed,u-boot__)
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ifeq ($(CONFIG_KALLSYMS),y)
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$(call cmd,smap)
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@ -2009,7 +2072,7 @@ CLEAN_FILES += include/bmp_logo.h include/bmp_logo_data.h tools/version.h \
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boot* u-boot* MLO* SPL System.map fit-dtb.blob* \
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u-boot-ivt.img.log u-boot-dtb.imx.log SPL.log u-boot.imx.log \
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lpc32xx-* bl31.c bl31.elf bl31_*.bin image.map tispl.bin* \
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idbloader.img flash.bin flash.log defconfig
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idbloader.img flash.bin flash.log defconfig keep-syms-lto.c
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# Directories & files removed with 'make mrproper'
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MRPROPER_DIRS += include/config include/generated spl tpl \
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@ -419,6 +419,9 @@ $(obj)/%_efi.so: $(obj)/%.o $(obj)/efi_crt0.o $(obj)/efi_reloc.o $(obj)/efi_free
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targets += $(obj)/efi_crt0.o $(obj)/efi_reloc.o $(obj)/efi_freestanding.o
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CFLAGS_REMOVE_efi_reloc.o := $(LTO_CFLAGS)
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CFLAGS_REMOVE_efi_freestanding.o := $(LTO_CFLAGS)
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# ACPI
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# ---------------------------------------------------------------------------
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#
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@ -448,8 +448,48 @@ quiet_cmd_sym ?= SYM $@
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$(obj)/$(SPL_BIN).sym: $(obj)/$(SPL_BIN) FORCE
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$(call if_changed,sym)
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# Generate linker list symbols references to force compiler to not optimize
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# them away when compiling with LTO
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ifdef CONFIG_LTO
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u-boot-spl-keep-syms-lto := $(obj)/keep-syms-lto.o
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u-boot-spl-keep-syms-lto_c := \
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$(patsubst $(obj)/%.o,$(obj)/%.c,$(u-boot-spl-keep-syms-lto))
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quiet_cmd_keep_syms_lto = KSL $@
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cmd_keep_syms_lto = \
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NM=$(NM) $(srctree)/scripts/gen_ll_addressable_symbols.sh $^ >$@
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quiet_cmd_keep_syms_lto_cc = KSLCC $@
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cmd_keep_syms_lto_cc = \
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$(CC) $(filter-out $(LTO_CFLAGS),$(c_flags)) -c -o $@ $<
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$(u-boot-spl-keep-syms-lto_c): $(u-boot-spl-main) $(u-boot-spl-platdata)
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$(call if_changed,keep_syms_lto)
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$(u-boot-spl-keep-syms-lto): $(u-boot-spl-keep-syms-lto_c)
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$(call if_changed,keep_syms_lto_cc)
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else
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u-boot-spl-keep-syms-lto :=
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endif
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# Rule to link u-boot-spl
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# May be overridden by arch/$(ARCH)/config.mk
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ifdef CONFIG_LTO
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quiet_cmd_u-boot-spl ?= LTO $@
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cmd_u-boot-spl ?= \
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( \
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cd $(obj) && \
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$(CC) -nostdlib -nostartfiles $(LTO_FINAL_LDFLAGS) $(c_flags) \
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$(KBUILD_LDFLAGS:%=-Wl,%) $(LDFLAGS_$(@F):%=-Wl,%) \
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$(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
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-Wl,--whole-archive \
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$(patsubst $(obj)/%,%,$(u-boot-spl-main)) \
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$(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) \
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$(patsubst $(obj)/%,%,$(u-boot-spl-keep-syms-lto)) \
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$(PLATFORM_LIBS) \
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-Wl,--no-whole-archive \
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-Wl,-Map,$(SPL_BIN).map -o $(SPL_BIN) \
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)
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else
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quiet_cmd_u-boot-spl ?= LD $@
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cmd_u-boot-spl ?= \
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( \
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@ -462,9 +502,11 @@ quiet_cmd_u-boot-spl ?= LD $@
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--no-whole-archive \
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$(PLATFORM_LIBS) -Map $(SPL_BIN).map -o $(SPL_BIN) \
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)
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endif
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$(obj)/$(SPL_BIN): $(u-boot-spl-platdata) $(u-boot-spl-init) \
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$(u-boot-spl-main) $(obj)/u-boot-spl.lds FORCE
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$(u-boot-spl-main) $(u-boot-spl-keep-syms-lto) \
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$(obj)/u-boot-spl.lds FORCE
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$(call if_changed,u-boot-spl)
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$(sort $(u-boot-spl-init) $(u-boot-spl-main)): $(u-boot-spl-dirs) ;
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12
scripts/gen_ll_addressable_symbols.sh
Executable file
12
scripts/gen_ll_addressable_symbols.sh
Executable file
@ -0,0 +1,12 @@
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#!/bin/bash
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# SPDX-License-Identifier: GPL-2.0+
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# Copyright (C) 2020 Marek Behún <marek.behun@nic.cz>
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# Generate __ADDRESSABLE(symbol) for every linker list entry symbol, so that LTO
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# does not optimize these symbols away
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set -e
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echo '#include <common.h>'
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$NM "$@" 2>/dev/null | grep -oe '_u_boot_list_2_[a-zA-Z0-9_]*_2_[a-zA-Z0-9_]*' | \
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sort -u | sed -e 's/^\(.*\)/extern char \1[];\n__ADDRESSABLE(\1);/'
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