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 [email protected] \
		-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 [email protected] \
		$(if $(FIT_KEY_DIR),-k $(FIT_KEY_DIR)) \
		-r \
		[email protected]
	@mv [email protected] $@
endef

# default all platform image(fit) build 
define Device/Default
  PROFILES = Default $$(DEVICE_NAME)
  KERNEL_NAME := Image
  KERNEL = kernel-bin | lzma | \
	fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
  KERNEL_INITRAMFS = kernel-bin | lzma | \
	fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
  FILESYSTEMS := squashfs
  DEVICE_DTS_DIR := $(DTS_DIR)
  IMAGES := sysupgrade.bin
  IMAGE/sysupgrade.bin := append-kernel | pad-to 128k | append-rootfs | \
	pad-rootfs | append-metadata
  FIT_KEY_DIR :=
  FIT_KEY_NAME :=
endef

include $(SUBTARGET).mk

define 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-images
    compile:
		$(call Build/Compile)

    clean:
		$(call Build/Clean)

    image_prepare: compile
		mkdir -p $(BIN_DIR) $(KDIR)/tmp
		rm -rf $(BUILD_DIR)/json_info_files
		$(call Image/Prepare)

  else
    image_prepare:
		mkdir -p $(BIN_DIR) $(KDIR)/tmp
  endif

  kernel_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: compile
		mkdir -p $(BIN_DIR) $(KDIR)/tmp
		rm -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/dtb
  ifndef 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).dtb
  endif

endef
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:act1

target: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/dtb
  ifndef 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).dtb
  endif

endef
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-sd

Device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))

endef

        Device/Default定义在target/linux/mediatek/image/Makefile,内容如下:

define Device/Default
  PROFILES = Default $$(DEVICE_NAME)
  KERNEL_NAME := Image
  KERNEL = kernel-bin | lzma | \
	fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
  KERNEL_INITRAMFS = kernel-bin | lzma | \
	fit lzma $$(KDIR)/image-$$(firstword $$(DEVICE_DTS)).dtb
  FILESYSTEMS := squashfs
  DEVICE_DTS_DIR := $(DTS_DIR)
  IMAGES := sysupgrade.bin
  IMAGE/sysupgrade.bin := append-kernel | pad-to 128k | append-rootfs | \
	pad-rootfs | append-metadata
  FIT_KEY_DIR :=
  FIT_KEY_NAME :=
endef

        Device/$(1):由于$(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-rfb
  DEVICE_VENDOR := MediaTek
  DEVICE_MODEL := mt7981-spim-nor-rfb
  DEVICE_DTS := mt7981-spim-nor-rfb
  DEVICE_DTS_DIR := $(DTS_DIR)/mediatek
  SUPPORTED_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)))))
endef

define build_cmd
$(if $(Build/$(word 1,$(1))),,$(error Missing Build/$(word 1,$(1))))
$(call Build/$(word 1,$(1)),$(wordlist 2,$(words $(1)),$(1)))

endef

define concat_cmd
$(call split_args,$(1),build_cmd)
endef

ifndef 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.bin
        cp /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/BuildKernelImage/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)。

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