[U-Boot] [PATCH 21/21] RFC: Makefile: Build U-Boot as a library

[Simon Glass]

As an experiment, build U-Boot as a library, u-boot.o, so it can be used
by other open-source software. Update the sandbox build rules to suit.

This has not been tested in any meaningful way. It breaks sandbox_spl and
all x86 boards.

I am interested in feedback as to how useful this might be.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 Makefile               |  9 ++++++++-
 arch/sandbox/config.mk | 10 ++++------
 scripts/Makefile.spl   | 17 +++++++++++++++--
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index d82772e7786..c8236de1463 100644
--- a/Makefile
+++ b/Makefile
@@ -1379,7 +1379,14 @@ cmd_smap = \
 	$(CC) $(c_flags) -DSYSTEM_MAP="\"$${smap}\"" \
 		-c $(srctree)/common/system_map.c -o common/system_map.o
 
-u-boot:	$(u-boot-init) $(u-boot-main) u-boot.lds FORCE
+quiet_cmd_u-boot-lib ?= LIB     $@
+      cmd_u-boot-lib ?= $(LD) -r --exclude-libs ALL \
+		--start-group $(u-boot-main) --end-group -o $@
+
+u-boot.o: $(u-boot-init) $(u-boot-main) u-boot.lds FORCE
+	+$(call if_changed,u-boot-lib)
+
+u-boot: u-boot.o FORCE
 	+$(call if_changed,u-boot__)
 ifeq ($(CONFIG_KALLSYMS),y)
 	$(call cmd,smap)
diff --git a/arch/sandbox/config.mk b/arch/sandbox/config.mk
index 7226b7be428..0f30f9db0b2 100644
--- a/arch/sandbox/config.mk
+++ b/arch/sandbox/config.mk
@@ -17,14 +17,12 @@ PLATFORM_CPPFLAGS += $(shell sdl-config --cflags)
 endif
 endif
 
-cmd_u-boot__ = $(CC) -o $@ -Wl,-T u-boot.lds $(u-boot-init) \
-	-Wl,--start-group $(u-boot-main) -Wl,--end-group \
-	$(PLATFORM_LIBS) -Wl,-Map -Wl,u-boot.map
+cmd_u-boot__ = $(CC) -o $@ -Wl,-T u-boot.lds \
+	u-boot.o  $(u-boot-init) \
+	$(PLATFORM_LIBS) -Wl,-Map -Wl,u-boot.map \
 
 cmd_u-boot-spl = (cd $(obj) && $(CC) -o $(SPL_BIN) -Wl,-T u-boot-spl.lds \
-	$(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
-	-Wl,--start-group $(patsubst $(obj)/%,%,$(u-boot-spl-main)) \
-	$(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) -Wl,--end-group \
+	u-boot-spl.o $(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
 	$(PLATFORM_LIBS) -Wl,-Map -Wl,u-boot-spl.map -Wl,--gc-sections)
 
 CONFIG_ARCH_DEVICE_TREE := sandbox
diff --git a/scripts/Makefile.spl b/scripts/Makefile.spl
index 7416abec62e..17c44424ceb 100644
--- a/scripts/Makefile.spl
+++ b/scripts/Makefile.spl
@@ -349,6 +349,20 @@ cmd_sunxi_spl_image_builder = $(objtree)/tools/sunxi-spl-image-builder \
 $(obj)/sunxi-spl-with-ecc.bin: $(obj)/sunxi-spl.bin
 	$(call if_changed,sunxi_spl_image_builder)
 
+quiet_cmd_u-boot-spl-lib ?= LIB     $@
+      cmd_u-boot-spl-lib ?= $(LD) -r --start-group $(u-boot-spl-main) \
+		--end-group -o $@
+
+$(obj)/u-boot-spl.o: $(u-boot-spl-platdata) $(u-boot-spl-init) \
+		$(u-boot-spl-main) FORCE
+	(cd $(obj) && $(LD) -r $(patsubst $(obj)/%,%,$(u-boot-spl-init)) \
+			--start-group \
+		       $(patsubst $(obj)/%,%,$(u-boot-spl-main))  \
+		       $(patsubst $(obj)/%,%,$(u-boot-spl-platdata)) \
+		       --end-group \
+		       -o $(patsubst $(obj)/%,%,$@))
+	+$(call if_changed,u-boot-spl-lib)
+
 # Rule to link u-boot-spl
 # May be overridden by arch/$(ARCH)/config.mk
 quiet_cmd_u-boot-spl ?= LD      $@
@@ -359,8 +373,7 @@ quiet_cmd_u-boot-spl ?= LD      $@
 		       --end-group \
 		       $(PLATFORM_LIBS) -Map $(SPL_BIN).map -o $(SPL_BIN))
 
-$(obj)/$(SPL_BIN): $(u-boot-spl-platdata) $(u-boot-spl-init) \
-		$(u-boot-spl-main) $(obj)/u-boot-spl.lds FORCE
+$(obj)/$(SPL_BIN): $(obj)/u-boot-spl.o $(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) ;
-- 
2.20.0.rc0.387.gc7a69e6b6c-goog