gemini: image: fix race condition when building copy-kernel.bin

Make treat copy-kernel.o as intermediate and delete it when it's no
longer needed.  This can fail when the same submake was triggered
multiple times for different devices.

	arm-openwrt-linux-muslgnueabi-as  -k -o copy-kernel.o copy-kernel.S
	export MAKEFLAGS= ;make -w -C copy-kernel CROSS_COMPILE=arm-openwrt-linux-muslgnueabi-
	arm-openwrt-linux-muslgnueabi-objcopy -O binary -S copy-kernel.o copy-kernel.bin
	make[5]: Entering directory '/builder/shared-workdir/build/target/linux/gemini/image/copy-kernel'
	arm-openwrt-linux-muslgnueabi-objcopy -O binary -S copy-kernel.o copy-kernel.bin
	rm copy-kernel.o
	make[5]: Leaving directory '/builder/shared-workdir/build/target/linux/gemini/image/copy-kernel'
	# "App" partition is the rootfs
	arm-openwrt-linux-muslgnueabi-objcopy: 'copy-kernel.o': No such file
	Makefile:27: recipe for target 'copy-kernel.bin' failed
	make[5]: Leaving directory '/builder/shared-workdir/build/target/linux/gemini/image/copy-kernel'
	make[5]: *** [copy-kernel.bin] Error 1
	Makefile:244: recipe for target '/builder/shared-workdir/build/build_dir/target-arm_fa526_musl_eabi/linux-gemini/tmp/openwrt-gemini-storlink_sl93512r-ext4-factory.bin' failed
	make[4]: *** [/builder/shared-workdir/build/build_dir/target-arm_fa526_musl_eabi/linux-gemini/tmp/openwrt-gemini-storlink_sl93512r-ext4-factory.bin] Error 2

With this change, output files are directed to $(KDIR)

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>

target/linux/gemini/image/Makefile

@@ -7,8 +7,8 @@
 include $(TOPDIR)/rules.mk
 include $(INCLUDE_DIR)/image.mk
 
-define Build/copy-kernel
-	$(MAKE) -C copy-kernel CROSS_COMPILE=$(TARGET_CROSS)
+define Build/copy-kernel.bin
+	$(call locked,$(MAKE) -C copy-kernel CROSS_COMPILE=$(TARGET_CROSS) O=$(KDIR),gemini-copy-kernel.bin)
 endef
 
 # Cook a "WRGG" image, this board is apparently one in the D-Link
@@ -93,11 +93,10 @@ endef
 define Build/storlink-default-images
 	mkdir -p $@.tmp
 
-	$(call Build/copy-kernel)
 	# "App" partition is the rootfs
 	mv $@ $@.tmp/hddapp.tgz
 	# 256 bytes copy routine
-	dd if=copy-kernel/copy-kernel.bin of=$@.tmp/zImage
+	dd if=$(KDIR)/copy-kernel.bin of=$@.tmp/zImage
 	$(call Image/pad-to,$@.tmp/zImage,512)
 	# Copy first part of the kernel into zImage
 	dd if=$(IMAGE_KERNEL) of=$@.tmp/zImage bs=1 seek=512 count=2096640
@@ -182,6 +181,8 @@ TARGET_DEVICES += dlink_dns-313
 
 # Default images setup used by the StorLink reference designs
 define Device/storlink-reference
+	COMPILE := copy-kernel-$(1).bin
+	COMPILE/copy-kernel-$(1).bin := copy-kernel.bin
 	IMAGES := factory.bin
 	IMAGE/factory.bin := append-rootfs | pad-rootfs | pad-to 6144k | \
 		storlink-default-images $(1)

target/linux/gemini/image/copy-kernel/Makefile

@@ -13,20 +13,26 @@ OBJCOPY		:= $(CROSS_COMPILE)objcopy
 
 BIN_FLAGS	:= -O binary -S
 
-all: copy-kernel.bin
+SRC_DIR		:= $(CURDIR)/
+OUT_DIR		:= $(if $(O),$(if $(patsubst %/,,$(O)),$(O)/,$(O)),$(SRC_DIR))
+
+all: $(OUT_DIR)copy-kernel.bin
 
 # Don't build dependencies, this may die if $(CC) isn't gcc
 dep:
 
 install:
 
-%.o : %.S
+$(OUT_DIR):
+	mkdir -p $(OUT_DIR)
+
+$(OUT_DIR)%.o : $(SRC_DIR)%.S | $(OUT_DIR)
 	$(AS) $(ASFLAGS) -k -o $@ $<
 
-%.bin: %.o
+$(OUT_DIR)%.bin: $(OUT_DIR)%.o
 	$(OBJCOPY) $(BIN_FLAGS) $< $@
 
 mrproper: clean
 
 clean:
-	rm -f copy-kernel.bin copy-kernel.o
+	rm -f $(OUT_DIR)copy-kernel.bin $(OUT_DIR)copy-kernel.o