Add plumbing for building U-Boot with Link Time Optimizations (gcc
only).
Signed-off-by: Marek Behún <[email protected]>
---
Kbuild | 2 ++
Kconfig | 19 +++++++++++++++++++
Makefile | 26 ++++++++++++++++++++++++++
lib/efi_loader/Makefile | 2 +-
scripts/Makefile.lib | 3 +++
scripts/Makefile.spl | 13 +++++++++++++
6 files changed, 64 insertions(+), 1 deletion(-)
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
+ 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 33d0b80de8..88600ec101 100644
--- a/Makefile
+++ b/Makefile
@@ -677,6 +677,21 @@ else
KBUILD_CFLAGS += -O2
endif
+LTO_CFLAGS :=
+LTO_FINAL_LDFLAGS :=
+export LTO_CFLAGS LTO_FINAL_LDFLAGS
+ifdef CONFIG_LTO
+ # use plugin aware tools
+ AR = $(CROSS_COMPILE)gcc-ar
+ NM = $(CROSS_COMPILE)gcc-nm
+
+ LTO_CFLAGS := -flto
+ LTO_FINAL_LDFLAGS := -fuse-linker-plugin -flto=jobserver \
+ -fwhole-program
+
+ KBUILD_CFLAGS += $(LTO_CFLAGS)
+endif
+
KBUILD_CFLAGS += $(call cc-option,-fno-stack-protector)
KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks)
@@ -1748,11 +1763,22 @@ ARCH_POSTLINK := $(wildcard
$(srctree)/arch/$(ARCH)/Makefile.postlink)
# Rule to link u-boot
# May be overridden by arch/$(ARCH)/config.mk
quiet_cmd_u-boot__ ?= LD $@
+ifdef CONFIG_LTO
+ cmd_u-boot__ ?= $(CC) -nostdlib -nostartfiles
\
+ $(LTO_FINAL_CFLAGS) $(c_flags)
\
+ $(KBUILD_LDFLAGS:%=-Wl,%) $(LDFLAGS_u-boot:%=-Wl,%)
\
+ -o $@ -T u-boot.lds $(u-boot-init)
\
+ -Wl,--whole-archive
\
+ $(u-boot-main) $(PLATFORM_LIBS)
\
+ -Wl,--no-whole-archive -Wl,-Map,u-boot.map;
\
+ $(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
+else
cmd_u-boot__ ?= $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_u-boot) -o $@ \
-T u-boot.lds $(u-boot-init) \
--whole-archive $(u-boot-main) --no-whole-archive \
$(PLATFORM_LIBS) -Map u-boot.map; \
$(if $(ARCH_POSTLINK), $(MAKE) -f $(ARCH_POSTLINK) $@, true)
+endif
quiet_cmd_smap = GEN common/system_map.o
cmd_smap = \
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index 10b42e8847..a5a6639fd3 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -13,7 +13,7 @@ CFLAGS_efi_boottime.o += \
-DFW_VERSION="0x$(VERSION)" \
-DFW_PATCHLEVEL="0x$(PATCHLEVEL)"
CFLAGS_helloworld.o := $(CFLAGS_EFI) -Os -ffreestanding
-CFLAGS_REMOVE_helloworld.o := $(CFLAGS_NON_EFI)
+CFLAGS_REMOVE_helloworld.o := $(CFLAGS_NON_EFI) $(LTO_CFLAGS)
ifneq ($(CONFIG_CMD_BOOTEFI_HELLO_COMPILE),)
always += helloworld.efi
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 f9faf804de..b7cab2d302 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -420,11 +420,24 @@ $(obj)/$(SPL_BIN).sym: $(obj)/$(SPL_BIN) FORCE
# Rule to link u-boot-spl
# May be overridden by arch/$(ARCH)/config.mk
quiet_cmd_u-boot-spl ?= LD $@
+ifdef CONFIG_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,--whole-archive
\
+ $(patsubst $(obj)/%,%,$(u-boot-spl-main))
$(PLATFORM_LIBS) \
+ -Wl,--no-whole-archive
\
+ -Wl,--start-group $(patsubst $(obj)/%,%,$(u-boot-spl-platdata))
-Wl,--end-group \
+ -Wl,-Map,$(SPL_BIN).map -o $(SPL_BIN)
\
+ )
+else
cmd_u-boot-spl ?= (cd $(obj) && $(LD) $(KBUILD_LDFLAGS) $(LDFLAGS_$(@F))
\
$(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
--whole-archive $(patsubst
$(obj)/%,%,$(u-boot-spl-main)) --no-whole-archive \
--start-group $(patsubst
$(obj)/%,%,$(u-boot-spl-platdata)) --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
--
2.26.2
