OpenWrt kernel install分析（2）
一. 前言
接下来分析make -C image compile install TARGET_BUILD=。
二. Makefile分析
1. 命令首先运行target/linux/mediatek/image/Makefile,该文件内容如下：
target/linux/mediatek/image/Makefile:
include $(TOPDIR)/rules.mk
include $(INCLUDE_DIR)/image.mk......# build signed fit
define Build/fit-sign$(TOPDIR)/scripts/mkits.sh \-D $(DEVICE_NAME) \-o $@.its \-k $@ \$(if $(word 2,$(1)),-d $(word 2,$(1))) -C $(word 1,$(1)) \-a $(KERNEL_LOADADDR) \-e $(if $(KERNEL_ENTRY),$(KERNEL_ENTRY),$(KERNEL_LOADADDR)) \-c $(if $(DEVICE_DTS_CONFIG),$(DEVICE_DTS_CONFIG),"config-1") \-A $(LINUX_KARCH) \-v $(LINUX_VERSION) \-s $(KDIR)/$(DEVICE_NAME)-u-boot-script \$(if $(FIT_KEY_NAME),-S $(FIT_KEY_NAME)) \$(if $(FW_AR_VER),-r $(FW_AR_VER))PATH=$(LINUX_DIR)/scripts/dtc:$(PATH) mkimage \-f $@.its \$(if $(FIT_KEY_DIR),-k $(FIT_KEY_DIR)) \-r \$@.new@mv $@.new $@
endef# default all platform image(fit) build
define Device/DefaultPROFILES = Default $$(DEVICE_NAME)KERNEL_NAME := ImageKERNEL = kernel-bin | lzma | \fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtbKERNEL_INITRAMFS = kernel-bin | lzma | \fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtbFILESYSTEMS := squashfsDEVICE_DTS_DIR := $(DTS_DIR)IMAGES := sysupgrade.binIMAGE/sysupgrade.bin := append-kernel | pad-to 128k | append-rootfs | \pad-rootfs | append-metadataFIT_KEY_DIR :=FIT_KEY_NAME :=
endefinclude $(SUBTARGET).mkdefine Image/Build$(call Image/Build/$(1),$(1))
endef$(eval $(call BuildImage))BuildImage在include/image.mk中定义，install目标在里面，代码如下：
include/image.mk:
define BuildImage......download:prepare:compile:clean:image_prepare:ifeq ($(IB),).PHONY: download prepare compile clean image_prepare kernel_prepare install install-imagescompile:$(call Build/Compile)clean:$(call Build/Clean)image_prepare: compilemkdir -p $(BIN_DIR) $(KDIR)/tmprm -rf $(BUILD_DIR)/json_info_files$(call Image/Prepare)elseimage_prepare:mkdir -p $(BIN_DIR) $(KDIR)/tmpendifkernel_prepare: image_prepare$(call Image/Build/targz)$(call Image/Build/cpiogz)$(call Image/BuildKernel)$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS),$(if $(IB),,$(call Image/BuildKernel/Initramfs)))$(call Image/InstallKernel)$(foreach device,$(TARGET_DEVICES),$(call Device,$(device)))install-images: kernel_prepare $(foreach fs,$(filter-out $(if $(UBIFS_OPTS),,ubifs),$(TARGET_FILESYSTEMS) $(fs-subtypes-y)),$(KDIR)/root.$(fs))$(foreach fs,$(TARGET_FILESYSTEMS),$(call Image/Build,$(fs)))install: install-images$(call Image/Manifest)endef由上可知，install依赖于install-images，install-images依赖于kernel_prepare，kernel_prepare依赖于image_prepare，由于IB未定义，所以image_prepare定义如下：
compile:$(call Build/Compile)clean:$(call Build/Clean)image_prepare: compilemkdir -p $(BIN_DIR) $(KDIR)/tmprm -rf $(BUILD_DIR)/json_info_files$(call Image/Prepare)image_prepare依赖于compile，这里，Build/Compile并未定义，所以什么都不干
注意：image_prepare在另一处也有定义，如下：
ifndef IB
define Device/Build/dtbifndef BUILD_DTS_$(1)BUILD_DTS_$(1) := 1$(KDIR)/image-$(1).dtb: FORCE$(call Image/BuildDTB,$(strip $(2))/$(strip $(3)).dts,$$@)image_prepare: $(KDIR)/image-$(1).dtbendifendef
endif这里在执行完上面compile依赖，接下来会完成$(KDIR)/image-$(1).dtb这个依赖，也就是生成设备树文件。
这种有两个相同目标的执行过程，下面用一个简单案例解释，如下：
act1:@echo "act1"act2:@echo "act2"target:act1target:act2@echo "target finish"all: target@echo "all finish"这里有两个target目标，分别依赖act1和act2，注意，一个target是有执行动作的，一个没有，这里先执行act2依赖，再act1依赖，执行结果如下：
act2
act1
target finish
all finish回到分析，
ifndef IB
define Device/Build/dtbifndef BUILD_DTS_$(1)BUILD_DTS_$(1) := 1$(KDIR)/image-$(1).dtb: FORCE$(call Image/BuildDTB,$(strip $(2))/$(strip $(3)).dts,$$@)image_prepare: $(KDIR)/image-$(1).dtbendifendef
endif$(KDIR)/image-$(1).dtb也是一个目标，动作为$(call Image/BuildDTB,$(strip $(2))/$(strip $(3)).dts,$$@)，Image/BuildDTB定义如下，
define Image/BuildDTB$(TARGET_CROSS)cpp -nostdinc -x assembler-with-cpp \-I$(DTS_DIR) \-I$(DTS_DIR)/include \-I$(LINUX_DIR)/include/ \-undef -D__DTS__ $(3) \-o $(2).tmp $(1)$(LINUX_DIR)/scripts/dtc/dtc -O dtb \-i$(dir $(1)) $(DTC_FLAGS) $(4) \-o $(2) $(2).tmp$(RM) $(2).tmp
endef完整命令展开如下：
aarch64-openwrt-linux-musl-cpp -nostdinc -x assembler-with-cpp -I/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts -I/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts/include -I/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/include/ -undef -D__DTS__ -o /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/image-mt7981-spim-nor-rfb.dtb.tmp /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts/mediatek/mt7981-spim-nor-rfb.dts
aarch64-openwrt-linux-musl-cpp -nostdinc -x assembler-with-cpp -I/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts -I/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts/include -I/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/include/ -undef -D__DTS__ -o /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/image-mt7981-spim-nor-rfb.dtb.tmp /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts/mediatek/mt7981-spim-nor-rfb.dts
/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/scripts/dtc/dtc -O dtb -i/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/arch/arm64/boot/dts/mediatek/ -Wno-unit_address_vs_reg -Wno-simple_bus_reg -Wno-unit_address_format -Wno-pci_bridge -Wno-pci_device_bus_num -Wno-pci_device_reg -Wno-avoid_unnecessary_addr_size -Wno-alias_paths -Wno-graph_child_address -Wno-graph_port -Wno-unique_unit_address -o /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/image-mt7981-spim-nor-rfb.dtb /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/image-mt7981-spim-nor-rfb.dtb.tmp注意：
Device/Build/dtb是由下面代码展开得到的：
$(foreach device,$(TARGET_DEVICES),$(call Device,$(device)))TARGET_DEVICES定义在target/linux/mediatek/image/mt7981.mk 中，可以如下：
openwrt# grep -rn "TARGET_DEVICES" target/linux/mediatek/image/mt7981.mk
10:TARGET_DEVICES += mt7981-spim-nor-rfb
27:TARGET_DEVICES += mt7981-spim-nand-2500wan-gmac2
44:TARGET_DEVICES += mt7981-spim-nand-rfb
61:TARGET_DEVICES += mt7981-spim-nand-gsw
74:TARGET_DEVICES += mt7981-emmc-rfb
87:TARGET_DEVICES += mt7981-sd-rfb
104:TARGET_DEVICES += mt7981-snfi-nand-2500wan-p5
113:TARGET_DEVICES += mt7981-fpga-spim-nor
130:TARGET_DEVICES += mt7981-fpga-snfi-nand
147:TARGET_DEVICES += mt7981-fpga-spim-nand
160:TARGET_DEVICES += mt7981-fpga-emmc
173:TARGET_DEVICES += mt7981-fpga-sdDevice的定义如下：
define Device$(call Device/InitProfile,$(1))$(call Device/Init,$(1))$(call Device/Default,$(1))$(call Device/$(1),$(1))$(call Device/Check,$(1))$(call Device/$(if $(DUMP),Dump,Build),$(1))endefDevice/Default定义在target/linux/mediatek/image/Makefile，内容如下：
define Device/DefaultPROFILES = Default $$(DEVICE_NAME)KERNEL_NAME := ImageKERNEL = kernel-bin | lzma | \fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtbKERNEL_INITRAMFS = kernel-bin | lzma | \fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtbFILESYSTEMS := squashfsDEVICE_DTS_DIR := $(DTS_DIR)IMAGES := sysupgrade.binIMAGE/sysupgrade.bin := append-kernel | pad-to 128k | append-rootfs | \pad-rootfs | append-metadataFIT_KEY_DIR :=FIT_KEY_NAME :=
endefDevice/$(1)：由于$(1)=mt7981-spim-nor-rfb，表示Device/mt7981-spim-nor-rfb，定义在target/linux/mediatek/image/mt7981.mk，内容如下：
define Device/mt7981-spim-nor-rfbDEVICE_VENDOR := MediaTekDEVICE_MODEL := mt7981-spim-nor-rfbDEVICE_DTS := mt7981-spim-nor-rfbDEVICE_DTS_DIR := $(DTS_DIR)/mediatekSUPPORTED_DEVICES := mediatek,mt7981-spim-nor-rfb
endef
TARGET_DEVICES += mt7981-spim-nor-rfb由于DUMP未定义，$(call Device/$(if $(DUMP),Dump,Build),$(1))为Device/Build。
2. Device/Build展开如下
define Device/Build$$(eval $$(foreach image,$$(IMAGES), \$$(foreach fs,$$(filter $(TARGET_FILESYSTEMS),$$(FILESYSTEMS)), \$$(call Device/Build/per-device-fs,$$(fs),$$(image),$(1)))))$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS),$(call Device/Build/initramfs,$(1)))$(call Device/Build/kernel,$(1),$$(filter $(TARGET_FILESYSTEMS),$$(FILESYSTEMS)))$$(eval $$(foreach compile,$$(COMPILE), \$$(call Device/Build/compile,$$(compile),$(1))))$$(eval $$(foreach image,$$(IMAGES), \$$(foreach fs,$$(filter $(TARGET_FILESYSTEMS),$$(FILESYSTEMS)), \$$(call Device/Build/image,$$(fs),$$(image),$(1)))))$$(eval $$(foreach artifact,$$(ARTIFACTS), \$$(call Device/Build/artifact,$$(artifact))))endef注意：这里Device/Build/initramfs是关键，内存根文件系统只会执行到这个，Device/Build/initramfs，内容如下：
define split_args
$(foreach data, \$(subst |,$(space),\$(subst $(space),^,$(1))), \$(call $(2),$(strip $(subst ^,$(space),$(data)))))
endefdefine build_cmd
$(if $(Build/$(word 1,$(1))),,$(error Missing Build/$(word 1,$(1))))
$(call Build/$(word 1,$(1)),$(wordlist 2,$(words $(1)),$(1)))endefdefine concat_cmd
$(call split_args,$(1),build_cmd)
endefifndef IB
define Device/Build/initramfs$(call Device/Export,$(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE),$(1))$$(_TARGET): $$(if $$(KERNEL_INITRAMFS),$(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE) \$$(if $$(CONFIG_JSON_OVERVIEW_IMAGE_INFO), $(BUILD_DIR)/json_info_files/$$(KERNEL_INITRAMFS_IMAGE).json,))$(KDIR)/$$(KERNEL_INITRAMFS_NAME):: image_prepare$(BIN_DIR)/$$(KERNEL_INITRAMFS_IMAGE): $(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE)cp $$^ $$@$(KDIR)/tmp/$$(KERNEL_INITRAMFS_IMAGE): $(KDIR)/$$(KERNEL_INITRAMFS_NAME) $(CURDIR)/Makefile $$(KERNEL_DEPENDS) image_prepare@rm -f $$@$$(call concat_cmd,$$(KERNEL_INITRAMFS))......
endef
endif注意：这里concat_cmd非常重要，lzma压缩，mkits.sh制作its文件以及mkimage打包最终镜像都是这里完成。展开结果命令如下：
rm -f /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bincp /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/Image-initramfs /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin/home/work/openwrt/staging_dir/host/bin/lzma e /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin -lc1 -lp2 -pb2 /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin.new@mv /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin.new /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin/home/work/openwrt/scripts/mkits.sh -D mt7981-spim-nor-rfb -o /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin.its -k /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin -d /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/image-mt7981-spim-nor-rfb.dtb -C lzma -a 0x48080000 -e 0x48080000 -c "config-1" -A arm64 -v 5.4.203 PATH=/home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/linux-5.4.203/scripts/dtc:/home/work/openwrt/staging_dir/toolchain-aarch64_cortex-a53_gcc-8.4.0_musl/bin:/home/work/openwrt/staging_dir/toolchain-aarch64_cortex-a53_gcc-8.4.0_musl/bin:/home/work/openwrt/staging_dir/toolchain-aarch64_cortex-a53_gcc-8.4.0_musl/bin:/home/work/openwrt/staging_dir/host/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/work/openwrt/staging_dir/toolchain-aarch64_cortex-a53_gcc-8.4.0_musl/bin/ mkimage -f /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin.its /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin.new@mv /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin.new /home/work/openwrt/build_dir/target-aarch64_cortex-a53_musl/linux-mediatek_mt7981/tmp/openwrt-mediatek-mt7981-mt7981-spim-nor-rfb-initramfs-kernel.bin$$(eval $$(foreach compile,$$(COMPILE), $$(call Device/Build/compile,$$(compile),$(1))))展开如下：
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-spim-nor-rfb)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-spim-nand-2500wan-gmac2)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-spim-nand-rfb)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-spim-nand-gsw)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-emmc-rfb)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-sd-rfb)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-snfi-nand-2500wan-p5)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-fpga-spim-nor)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-fpga-snfi-nand)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-fpga-spim-nand)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-fpga-emmc)))
Makefile:91: $(eval $(foreach compile,$(COMPILE), $(call Device/Build/compile,$(compile),mt7981-fpga-sd)))由于$(COMPILE)为空，所以这块执行没有效果。
接下来，
$$(eval $$(foreach image,$$(IMAGES), \$$(foreach fs,$$(filter $(TARGET_FILESYSTEMS),$$(FILESYSTEMS)), \$$(call Device/Build/image,$$(fs),$$(image),$(1)))))由于TARGET_FILESYSTEMS是要编译的镜像格式类型，如下：
fs-types-$(CONFIG_TARGET_ROOTFS_SQUASHFS) += squashfs
fs-types-$(CONFIG_TARGET_ROOTFS_JFFS2) += $(addprefix jffs2-,$(JFFS2_BLOCKSIZE))
fs-types-$(CONFIG_TARGET_ROOTFS_JFFS2_NAND) += $(addprefix jffs2-nand-,$(NAND_BLOCKSIZE))
fs-types-$(CONFIG_TARGET_ROOTFS_EXT4FS) += ext4
fs-types-$(CONFIG_TARGET_ROOTFS_UBIFS) += ubifs
fs-subtypes-$(CONFIG_TARGET_ROOTFS_JFFS2) += $(addsuffix -raw,$(addprefix jffs2-,$(JFFS2_BLOCKSIZE)))TARGET_FILESYSTEMS := $(fs-types-y)由于CONFIG_TARGET_ROOTFS_SQUASHFS等我都没选，所以，TARGET_FILESYSTEMS为空，这里也是不执行的。可以看出Device/Build/image的作用是生成不同文件系统的镜像。
接下来，
$$(eval $$(foreach artifact,$$(ARTIFACTS), \$$(call Device/Build/artifact,$$(artifact))))由于ARTIFACTS变量为空，所以，这里Device/Build/artifact什么也不干。
三. 总结
这里需要注意的以下几点：
1. image_prepare有两个目标，有动作的这个目标做的事情很少，没有目标的依赖是用于编译设备树的，要非常注意。
2. 由于编译选项没选，Image/Build/targz，Image/Build/cpiogz这里什么也不做，Image/BuildKernel和Image/InstallKernel没有定义（可能是用于自定义的，这里没用到而已），这里什么也不做。
3. $(if $(CONFIG_TARGET_ROOTFS_INITRAMFS),$(if $(IB),,$(call Image/BuildKernel/Initramfs)))，这里结果为$(call Image/BuildKernel/Initramfs)，继续展开为$(call Image/Build/Initramfs)，但是Image/Build/Initramfs未定义，所以这里什么也不干，也是用于自定义的。
4. $(foreach device,$(TARGET_DEVICES),$(call Device,$(device)))，这里TARGET_DEVICES定义在mt7981.mk中，表示不同的镜像（spi-nor，spi-nand，emmc等等），Device宏里面要关注Device/Default和Device/Build，Device/Default定义在target/linux/mediatek/image/Makefile中，定义了一些镜像相关的变量，Device/Build中要关注$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS),$(call Device/Build/initramfs,$(1)))，结果是$(call Device/Build/initramfs,$(1))，重点要关注$$(call concat_cmd,$$(KERNEL_INITRAMFS))这里，这里面打包了最终的镜像（lzma压缩，its文件生成，mkimage都在这里执行）。