+
ifeq ($(cc-name),clang)
ifneq ($(CROSS_COMPILE),)
CLANG_TARGET := --target=$(notdir $(CROSS_COMPILE:%-=%))
@@ -641,6 +644,11 @@ export CFLAGS_EFI # Compiler flags to add when building
EFI app
export CFLAGS_NON_EFI # Compiler flags to remove when building EFI app
export EFI_TARGET # binutils target if EFI is natively supported
+export LTO_ENABLE
+
+# This is y if LTO is enabled for this build
+LTO_ENABLE=$(if $(CONFIG_LTO),$(LTO_BUILD),)
+
# If board code explicitly specified LDSCRIPT or CONFIG_SYS_LDSCRIPT, use
# that (or fail if absent). Otherwise, search for a linker script in a
# standard location.
@@ -688,16 +696,16 @@ endif
LTO_CFLAGS :=
LTO_FINAL_LDFLAGS :=
export LTO_CFLAGS LTO_FINAL_LDFLAGS
-ifdef CONFIG_LTO
+ifeq ($(LTO_ENABLE),y)
ifeq ($(cc-name),clang)
- LTO_CFLAGS += -flto
+ LTO_CFLAGS += -DLTO_ENABLE -flto
LTO_FINAL_LDFLAGS += -flto
AR = $(shell $(CC)
-print-prog-name=llvm-ar)
NM = $(shell $(CC)
-print-prog-name=llvm-nm)
else
NPROC := $(shell nproc 2>/dev/null || echo 1)
- LTO_CFLAGS += -flto=$(NPROC)
+ LTO_CFLAGS += -DLTO_ENABLE -flto=$(NPROC)
LTO_FINAL_LDFLAGS += -fuse-linker-plugin -flto=$(NPROC)
# use plugin aware tools
@@ -1717,7 +1725,7 @@ ARCH_POSTLINK := $(wildcard
$(srctree)/arch/$(ARCH)/Makefile.postlink)
# Generate linker list symbols references to force compiler to not optimize
# them away when compiling with LTO
-ifdef CONFIG_LTO
+ifeq ($(LTO_ENABLE),y)
u-boot-keep-syms-lto := keep-syms-lto.o
u-boot-keep-syms-lto_c := $(patsubst %.o,%.c,$(u-boot-keep-syms-lto))
@@ -1739,7 +1747,7 @@ endif
# Rule to link u-boot
# May be overridden by arch/$(ARCH)/config.mk
-ifdef CONFIG_LTO
+ifeq ($(LTO_ENABLE),y)
quiet_cmd_u-boot__ ?= LTO $@
cmd_u-boot__ ?=
\
$(CC) -nostdlib -nostartfiles
\
diff --git a/arch/arm/config.mk b/arch/arm/config.mk
index b107b1af27a..065dbec4064 100644
--- a/arch/arm/config.mk
+++ b/arch/arm/config.mk
@@ -15,11 +15,11 @@ CFLAGS_NON_EFI := -fno-pic -ffixed-r9 -ffunction-sections
-fdata-sections \
-fstack-protector-strong
CFLAGS_EFI := -fpic -fshort-wchar
-ifneq ($(CONFIG_LTO)$(CONFIG_USE_PRIVATE_LIBGCC),yy)
+ifneq ($(LTO_ENABLE)$(CONFIG_USE_PRIVATE_LIBGCC),yy)
LDFLAGS_FINAL += --gc-sections
endif
-ifndef CONFIG_LTO
+ifneq ($(LTO_ENABLE),y)
PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections
endif
diff --git a/arch/arm/include/asm/global_data.h
b/arch/arm/include/asm/global_data.h
index 085e12b5d4d..b255b195aa0 100644
--- a/arch/arm/include/asm/global_data.h
+++ b/arch/arm/include/asm/global_data.h
@@ -98,7 +98,7 @@ struct arch_global_data {
#include <asm-generic/global_data.h>
-#if defined(__clang__) || defined(CONFIG_LTO)
+#if defined(__clang__) || defined(LTO_ENABLE)
#define DECLARE_GLOBAL_DATA_PTR
#define gd get_gd()
diff --git a/doc/build/gcc.rst b/doc/build/gcc.rst
index cdd79700326..136c318727d 100644
--- a/doc/build/gcc.rst
+++ b/doc/build/gcc.rst
@@ -141,6 +141,23 @@ of dtc is new enough. It also makes sure that pylibfdt is
present, if needed
Note that the :doc:`tools` are always built with the included version of
libfdt
so it is not possible to build U-Boot tools with a system libfdt, at present.
+Link-time optimisation (LTO)
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+U-Boot supports link-time optimisation which can reduce the size of the final
+U-Boot binaries, particularly with SPL.
+
+At present this can be enabled by ARM boards by adding `CONFIG_LTO=y` into the
+defconfig file. Other architectures are not supported. LTO is enabled by
default
+for sandbox.
+
+This does incur a link-time penalty of several seconds. For faster incremental
+builds during development, you can disable it by setting `LTO_BUILD` to `n`.
+
+.. code-block:: bash
+
+ LTO_BUILD=n make
+
Other build targets
~~~~~~~~~~~~~~~~~~~
--
2.33.0.1079.g6e70778dc9-goog
