Re: [PATCH u-boot 17/39] build: support building with Link Time Optimizations

On Sun, Mar 7, 2021 at 12:26 PM Marek Behún marek.behun@nic.cz wrote:

Add plumbing for building U-Boot with Link Time Optimizations.

Signed-off-by: Marek Behún marek.behun@nic.cz

Kbuild | 2 ++ Kconfig | 19 +++++++++++++++++++ Makefile | 36 ++++++++++++++++++++++++++++++++++++ scripts/Makefile.lib | 3 +++ scripts/Makefile.spl | 14 ++++++++++++++ 5 files changed, 74 insertions(+)

diff --git a/Kbuild b/Kbuild index 1eac091594..bf52e54051 100644 --- a/Kbuild +++ b/Kbuild @@ -10,6 +10,8 @@ generic-offsets-file := include/generated/generic-asm-offsets.h always := $(generic-offsets-file) targets := lib/asm-offsets.s

+CFLAGS_REMOVE_asm-offsets.o := $(LTO_CFLAGS)

$(obj)/$(generic-offsets-file): $(obj)/lib/asm-offsets.s FORCE $(call filechk,offsets,__GENERIC_ASM_OFFSETS_H__)

diff --git a/Kconfig b/Kconfig index 86f0a39bb0..ceba53926f 100644 --- a/Kconfig +++ b/Kconfig @@ -85,6 +85,25 @@ config SPL_OPTIMIZE_INLINING do what it thinks is best, which is desirable in some cases for size reasons.

+config ARCH_SUPPORTS_LTO

•   bool
  

+config LTO

•   bool "Enable Link Time Optimizations"
  

•   depends on ARCH_SUPPORTS_LTO
  

•   default n
  

nits: this line is not needed as the default value is n if omitted

•   help
  

•     This option enables Link Time Optimization (LTO), a mechanism which
  

•     allows the compiler to optimize between different compilation units.
  

•     This can optimize away dead code paths, resulting in smaller binary
  

•     size (if CC_OPTIMIZE_FOR_SIZE is enabled).
  

•     This option is not available for every architecture and may
  

•     introduce bugs.
  

•     If unsure, say n.
  

config TPL_OPTIMIZE_INLINING bool "Allow compiler to uninline functions marked 'inline' in TPL" depends on TPL diff --git a/Makefile b/Makefile index 6dc47810ea..4eee0c4196 100644 --- a/Makefile +++ b/Makefile @@ -677,6 +677,28 @@ else KBUILD_CFLAGS += -O2 endif

+LTO_CFLAGS := +LTO_FINAL_LDFLAGS := +export LTO_CFLAGS LTO_FINAL_LDFLAGS +ifdef CONFIG_LTO

•   LTO_CFLAGS                      := -flto
  

•   LTO_FINAL_LDFLAGS               := -fwhole-program
  

This one should not be necessary per my read of the GCC doc. Also in your patch, it is only used in the SPL build.

•   CFLAGS_NON_EFI                  += $(LTO_CFLAGS)
  

•   ifeq ($(cc-name),clang)
  

•           LTO_FINAL_LDFLAGS       += -flto
  

•   else
  

•           LTO_FINAL_LDFLAGS       += -fuse-linker-plugin -flto=jobserver
  

•           # use plugin aware tools
  

•           AR                      = $(CROSS_COMPILE)gcc-ar
  

•           NM                      = $(CROSS_COMPILE)gcc-nm
  

•   endif
  

•   KBUILD_CFLAGS                   += $(LTO_CFLAGS)
  

+endif

KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector) KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks)

@@ -1751,6 +1773,19 @@ ARCH_POSTLINK := $(wildcard $(srctree)/arch/$(ARCH)/Makefile.postlink)

# Rule to link u-boot # May be overridden by arch/$(ARCH)/config.mk +ifdef CONFIG_LTO +quiet_cmd_u-boot__ ?= LTO $@

•  cmd_u-boot__ ?=                                                          \
  

•           $(CC) -nostdlib -nostartfiles                                   \
  

•           $(LTO_FINAL_CFLAGS) $(c_flags)                                  \
  

LTO_FINAL_CFLAGS is not defined anywhere. I guess you wanted to use LTO_FINAL_LDFLAGS?

•           $(KBUILD_LDFLAGS:%=-Wl,%) $(LDFLAGS_u-boot:%=-Wl,%) -o $@       \
  

•           -T u-boot.lds $(u-boot-init)                                    \
  

•           -Wl,--start-group -Wl,--whole-archive                           \
  

--start-group should be dropped

•                   $(u-boot-main)                                          \
  

•           -Wl,--no-whole-archive -Wl,--end-group                          \
  

•           $(PLATFORM_LIBS) -Wl,-Map,u-boot.map;                           \
  

•           $(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
  

+else quiet_cmd_u-boot__ ?= LD $@ cmd_u-boot__ ?= $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_u-boot) -o $@ \ -T u-boot.lds $(u-boot-init) \ @@ -1759,6 +1794,7 @@ quiet_cmd_u-boot__ ?= LD $@ --no-whole-archive --end-group \ $(PLATFORM_LIBS) -Map u-boot.map; \ $(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true) +endif

quiet_cmd_smap = GEN common/system_map.o cmd_smap = \ diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib index 78543c6dd1..78bbebe7e9 100644 --- a/scripts/Makefile.lib +++ b/scripts/Makefile.lib @@ -419,6 +419,9 @@ $(obj)/%_efi.so: $(obj)/%.o $(obj)/efi_crt0.o $(obj)/efi_reloc.o $(obj)/efi_free

targets += $(obj)/efi_crt0.o $(obj)/efi_reloc.o $(obj)/efi_freestanding.o

+CFLAGS_REMOVE_efi_reloc.o := $(LTO_CFLAGS) +CFLAGS_REMOVE_efi_freestanding.o := $(LTO_CFLAGS)

# ACPI # --------------------------------------------------------------------------- # diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl index 889debb93c..6da5883442 100644 --- a/scripts/Makefile.spl +++ b/scripts/Makefile.spl @@ -419,6 +419,19 @@ $(obj)/$(SPL_BIN).sym: $(obj)/$(SPL_BIN) FORCE

# Rule to link u-boot-spl # May be overridden by arch/$(ARCH)/config.mk +ifdef CONFIG_LTO +quiet_cmd_u-boot-spl ?= LTO $@

•  cmd_u-boot-spl ?= (cd $(obj) &&                                          \
  

•           $(CC) -nostdlib -nostartfiles $(LTO_FINAL_LDFLAGS) $(c_flags)   \
  

•           $(KBUILD_LDFLAGS:%=-Wl,%) $(LDFLAGS_$(@F):%=-Wl,%)              \
  

•           $(patsubst $(obj)/%,%,$(u-boot-spl-init))                       \
  

•           -Wl,--start-group -Wl,--whole-archive                           \
  

•                   $(patsubst $(obj)/%,%,$(u-boot-spl-main))               \
  

•                   $(patsubst $(obj)/%,%,$(u-boot-spl-platdata))           \
  

•           -Wl,--no-whole-archive -Wl,--end-group                          \
  

•           $(PLATFORM_LIBS) -Wl,-Map,$(SPL_BIN).map -o $(SPL_BIN)          \
  

•                   )
  

+else quiet_cmd_u-boot-spl ?= LD $@ cmd_u-boot-spl ?= (cd $(obj) && \ $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_$(@F)) \ @@ -429,6 +442,7 @@ quiet_cmd_u-boot-spl ?= LD $@ --no-whole-archive --end-group \ $(PLATFORM_LIBS) -Map $(SPL_BIN).map -o $(SPL_BIN) \ ) +endif

$(obj)/$(SPL_BIN): $(u-boot-spl-platdata) $(u-boot-spl-init) \ $(u-boot-spl-main) $(obj)/u-boot-spl.lds FORCE --

Regards, Bin