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>
diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl
index ac2d203..7872cba 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -448,8 +448,48 @@
$(obj)/$(SPL_BIN).sym: $(obj)/$(SPL_BIN) FORCE
$(call if_changed,sym)
+# Generate linker list symbols references to force compiler to not optimize
+# them away when compiling with LTO
+ifdef CONFIG_LTO
+u-boot-spl-keep-syms-lto := $(obj)/keep-syms-lto.o
+u-boot-spl-keep-syms-lto_c := \
+ $(patsubst $(obj)/%.o,$(obj)/%.c,$(u-boot-spl-keep-syms-lto))
+
+quiet_cmd_keep_syms_lto = KSL $@
+ cmd_keep_syms_lto = \
+ NM=$(NM) $(srctree)/scripts/gen_ll_addressable_symbols.sh $^ >$@
+
+quiet_cmd_keep_syms_lto_cc = KSLCC $@
+ cmd_keep_syms_lto_cc = \
+ $(CC) $(filter-out $(LTO_CFLAGS),$(c_flags)) -c -o $@ $<
+
+$(u-boot-spl-keep-syms-lto_c): $(u-boot-spl-main) $(u-boot-spl-platdata)
+ $(call if_changed,keep_syms_lto)
+$(u-boot-spl-keep-syms-lto): $(u-boot-spl-keep-syms-lto_c)
+ $(call if_changed,keep_syms_lto_cc)
+else
+u-boot-spl-keep-syms-lto :=
+endif
+
# Rule to link u-boot-spl
# May be overridden by arch/$(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,--whole-archive \
+ $(patsubst $(obj)/%,%,$(u-boot-spl-main)) \
+ $(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) \
+ $(patsubst $(obj)/%,%,$(u-boot-spl-keep-syms-lto)) \
+ $(PLATFORM_LIBS) \
+ -Wl,--no-whole-archive \
+ -Wl,-Map,$(SPL_BIN).map -o $(SPL_BIN) \
+ )
+else
quiet_cmd_u-boot-spl ?= LD $@
cmd_u-boot-spl ?= \
( \
@@ -462,9 +502,11 @@
--no-whole-archive \
$(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
+ $(u-boot-spl-main) $(u-boot-spl-keep-syms-lto) \
+ $(obj)/u-boot-spl.lds FORCE
$(call if_changed,u-boot-spl)
$(sort $(u-boot-spl-init) $(u-boot-spl-main)): $(u-boot-spl-dirs) ;