Android 系统编译

一、流程

根目录下的Makefile--->build/core/main.mk---->build/core/Makefile

1.1 根目录下的Makefile

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### DO NOT EDIT THIS FILE ### include build/core/main.mk ### DO NOT EDIT THIS FILE ###

1.2 main.mk

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.PHONY: droidcore droidcore:  kernelimage     \             kernelmodules    \             bootloader        \             files            \             systemimage        \             $(INSTALLED_BOOTIMAGE_TARGET)    \             $(INSTALLED_RECOVERY_TARGET)    \             $(INSTALLED_USRTDATAIAGE_TARGET) \             $(INSTALLED_CACHEIMAGE_TARGET)    \             $(INSTALLED_VERDORIMAGE_TARGET)    \             $(INSTALLED_FILES_FILE)            \             ubiimagesgenerate   include $(BUILD_SYSTEM)/Makefile   BUILD_SYSTEM := $(TOPDIR)build/core

可以看出，该编译目标为 android的核心编译目标。kernelimage即编译出的目标zImage，systemimage即编译出的system.img。

$(TOPDIR)即为Android源码的根目录。所以就把build/core/Makefile包含进去了。

1.3 build/core/Makefile

这个文件里定义了上文所有的目标

1.3.1 接下来分析目标 kernelimage ⇒ {kernel, dtb}

定义如下：

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.PHONY: kernelimage ifneq    ($(strip $(TARGET_NO_KERNEL)), true) KERNEL_CROSS_TOOLCHAIN  := `pwd`/prebuilts/gcc/linux-x86/arm/arm-linux-androideabi-4.9/bin/arm-linux-androideabi- KERNEL_CFLAGS             := KCFLAGS=-mno-android KERNEL_ENV                 := ARCH=arm CROSS_COMPILE=$(KERNEL_CROSS_TOOLCHAIN) LOADADDR=$(LOAD_KERNEL_ENTRY) $(KERNEL_CFLAGS) HOST_PROCESSOR             := $(shell cat /proc/cpuinfo | grep processor | wc -l) INSTALLED_KERNEL_TARGET := $(PRODUCT_OUT)kernel TARGET_PREBUILT_KERNEL  := $(PRODUCT_OUT)kernel KERNEL_CONFIGURE           := kernel_imx/.config TARGET_KERNEL_CONFIGURE := $(PRODUCT_OUT)/.config KERNEL_ZMAGE             := kernel_imx/arch/arm/boot/zImage KERNEL_OUT                :=$(TARGET_OUT_INTERMEDIATES/KERNEL_OBJ   .PHONY: $(TARGET_PREBUILT_KERNEL)    kernel.image:    $(TARGET_PREBUILT_KERNEL)   # 默认的内核配置文件 $(KERNEL_CONFIGURE): kernel_imx/arch/arm/configs/$(TARGET_KERNEL_DEFCONF)   # 配置内核 $(TARGET_KERNEL_CONFIGURE): kernel_imx/arch/arm/configs/$(TARGET_KERNEL_DEFCONF) $(KERNEL_CONFIGURE)         $(MAKE)    -C kernel_imx $(TARGET_KERNEL_DEFCONF) $(KERNEL_ENV)         install -D $(KERNEL_CONFIGURE) $(TARGET_KERNEL_CONFIGURE)   # 编译uImage 和 dtb，并安装到指定的目录 $(TARGET_PREBUILT_KERNEL): $(TARGET_KERNEL_CONFIGURE)         $(MAKE) -C kernel_imx -j$(HOST_PROCESSOR) uImage $(KERNEL_ENV)         $(MAKE) -C kernel_imx    dtbs $(KERNEL_ENV)         install -D $(KERNEL_ZIMAGE)     $(PRODUCT_OUT)/kernel         for dtsplat in $(TARGET_BOARD_DTS_CONFIG); do           \                 DTS_PLATFORM=`echo $$dtsplat | cut -d':' -f1`; \                 DTS_BOARD=`echo $$dtsplat | cut -d':' -f2`;        \                 install -D kernel_imx/arch/arm/boot/dts/$$DTS_BOARD $(PRODUCT_OUT)/$$DTS_BOARD; \         done else kernelimage: endif

整体过程就是配置交叉编译链，默认的配置文件，内核和设备树的输出目录和其他参数。这里用到了make 的 -C 参数，指定编译的源码路径编译。

1.3.2 kernelmodules

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.PHONY:    kernelmodules   kernel_modules_src_list := kernel_modules_dist_list :=   $(foreach cf, $(TARGET_KERNEL_MODULES),        \ $(eval _src := $(call word-colon,1,$(cf)))    \ $(eval _dest := $(call word-colon,2,$(cf)))    \ $(eval kernel_modules_src_list    += $(_src)) \ $(eval kernel_modules_dest_list    += $(call append-path, $(PRODUCT_OUT), $(_dest))))   ifneq ($(strip $(kernel_modules_src_list)),) # 编译模块，并拷贝到指定的目录 kernelmodules:    $(TARGET_PREBUILT_KERNEL) | $(ACP)         $(MAKE) -C kernel_imx modules $(KERNEL_ENV)         $(hide) $(foreach cf, $(TARGET_KERNEL_MODULES),        \         $(eval _src := $(call word-colon,1,$(cf)))            \         $(eval _dest := $(call word-colon,2,$(cf)))            \         $(eval _full_dest := $(call append-path, $(PRODUCT_OUT), $(_dest))) \         $(eval _dest_dir  := $(call dir, $(_full_dest)))         mkdir -p $(_dest_dir)                                \         $(ACP) $(_src) $(_full_dest);                        \         )         @echo "install kernel modules: $(kernel_modules_src_list)" else kernelmodules: endif

1.3.3 目标 $(INSTALLED_BOOTIMAGE_TARGET) ==> boot.img

==> {kernel, dtb, ramdisk}

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ifneq ($(strip $(TARGET_NO_KERNEL)), true) # 编译boot.img的参数 INTERNAL_BOOTIMAGE_ARGS :=    \         $(addprefix --second , $(INSTALLED_2NDBOOTLOADER_TARGET))    \         --kernel $(INSTALLED_KERNEL_TARGET) # ramdisk 参数 ifneq ($(BOARD_BUILD_SYSTEM_ROOT_IMAGE), true) INTERNAL_BOOTIMAGE_ARGS += --ramdisk $(INSTALLED_RAMDISK_TARGET) endif   INTERNAL_BOOTIMAGE_FILLES := $(filter-out --%, $(INTERNAL_BOOTIMAGE_ARGS)) # cmdline 参数 BOARD_KERNEL_CMDLINE := $(strip $(BOARD_KERNEL_CMDLINE)) ifdef BOARD_KERNEL_CMDLINE     INTERNAL_BOOTIMAGE_ARGS += --cmdline "$(BOARD_KERNEL_CMDLINE)" endif # base ? BOARD_KERNEL_BASE := $(strip $(BOARD_KERNEL_BASE)) ifdef BOARD_KERNEL_BASE     INTERNAL_BOOTIMAGE_ARGS += --base $(BOARD_KERNEL_BASE) endif # 页大小的参数 BOARD_KERNEL_PAGESIZE := $(strip $(BOARD_KERNEL_PAGESIZE)) ifdef BOARD_KERNEL_PAGESIZE     INTERNAL_BOOTIMAGE_ARGS += --pagesize $(BOARD_KERNEL_PAGESIZE) endif # 生成目标的完整路径文件名 INSTALLED_BOOTIMAGE_TARGET := $(PRODUCT_OUT)/boot.img   ifeq ($(TARGET_BOOTIMAGE_USE_EXT2),true) $(error TARGET_BOOTIMAGE_USE_EXT2 is not supports anymore) else ifeq (true, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_BOOT_SIGNER)) # 此处省略部分源码 本平台没用到 ..... else ifeq (true, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VBOOT)) # 此处省略部分源码 本平台没用到 ..... else $(INSTALLED_BOOTIMAGE_TARGET): $(MKBOOTIMG) $(INTERNAL_BOOTIMAGE_FILES)         $(call pretty, "Target boot image: $@")         for dtsplat in $(TARGET_BOARD_DTS_CONFIG); do     \             DTS_PLATFORM=`echo $$dtsplat | cut =d':' -f1`; \             DTS_BOARD=`echo $$dtsplat | cut =d':' -f2`; \             BOOT_IMAGE_BOATD=$(patsubst %.img,%-$$DTS_PLATFORM.img,$@);    \             $(MKBOOTIMG) $(INTERNAL_BOOTIMAGE_ARGS) --second $(PRODUCT_OUT)/$$DTS_BOARD $(BOARD_MKBOOTIMG_ARGS) --output $@;    \             cp  -f $@ $$BOOT_IMGAE_BOARD;    \         done   .PHONY:    bootimage-nodeps bootimage-nodeps: $(MKBOOTIMG)         @echo "make $@: ignoring dependencies"         $(hide) $(MKBOOTIMG) $(INTERNAL_BOOTIMAGE_ARGS) $(BOARD_MKBOOTIMG_ARGS) --output $(INSTALLED_BOOTIMAGE_TARGET)         $(hide) $(call assert-max-image-size, $(INSTALLED_BOOTIMAGE_TARGET),$(BOARD_BOOTIMAGE_PARTITION_SIZE)) endif

1.3.4 ramdisk 是如何生成的？

跟踪 $(INSTALLED_BOOTIMAGE_TARGET)的依赖 $(INTERNAL_BOOTIMAGE_FILES)
$(INTERNAL_BOOTIMAGE_FILES) := $(filter-out --%, $(INTERNAL_BOOTIMAGE_ARGS))
然后有一句：
$(INTERNAL_BOOTIMAGE_ARGS) += --ramdisk $(INSTALLED_RAMDISK_TARGET)
所以 $(INSTALLED_RAMDISK_TARGET)会生成ramdisk。

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INTERNAL_RAMDISK_FILES := $(filter $(TARGET_ROOT_OUT)/%, \         $(ALL_PREBUILT)        \         $(ALL_COPIED_HEADERS)    \         $(ALL_GENERATED_SOURCES)    \         $(ALL_DEFAULT_INSTALLED_MODULES))               BUILT_RAMDISK_TARGET := $(PRODUCT_OUT)/ramdisk.img   INSTALLED_RAMDISK_TARGET := $(BUILT_RAMDISK_TARGET) $(INSTALLED_RAMDISK_TARGET): $(MKBOOTFS) $(INTERNAL_RAMDISK_FILES) | $(MINIGZIP)         $(call pretty, "Target ram disk: $@")         $(hide) $(MKBOOTFS) -d $(TARGET_OUT) $(TARGET_ROOT_OUT) | $(MINIGZIP) > $(INSTALLED_RAMDISK_TARGET)

1.3.5 目标 bootloader

即uboot的生成规则。
bootloader的生成规则相对比较简单，配置好交叉编译器，通过make **defconfig 配置源码，然后 make 就可以，接下来看Makefile:
build/core/main.mk的默认目标droidcore中包含了 bootloader目标，bootloader目标在build/core/Makefile中有定义：

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.PHONY: bootloader ifneq ($(strip $(TARGET_BOOTLOADER_CONFIG)),) BOOTLOADER_CROSS_TOOLCHAIN := `pwd`/prebuilts/gcc/linux-x86/arm/arm-linux-androideaib-4.9/bin/arm-linux BOOTLOADER_ENV    := ARCH=arm CROSS_COMPILE=$(BOOTLOADER_CROSS_TOOLCHAIN) HOST_PROCESSOR  := $(shell cat /proc/cpuinfo | grep processor | wc -l) TARGET_BOOTLODAER_IMAGE := $(PRODUCT_OUT)/u-boot.imx BOOTLOADER_PATH := bootable/bootloader/uboot/   bootloader: $(TARGET_BOOTLOADER_IMAGE) .PHONY    $(TARGET_BOOTLOADER_IMAGE) $(TARGET_BOOTLOADER_IMAGE):         for ubootplat in $(TARGET_BOOTLOADER_CONFIG); do    \             UBOOT_PLATFORM=`echo $$ubootplat | cut -d':' -f1`;    \             UBOOT_CONFIG=`echo $$ubootplat | cut -d':' -f2`;    \             $(MAKE) -C    $(BOOTLOADER_PATH) distclean $(BOOTLOADER_ENV);    \             $(MAKE) -C    $(BOOTLOADER_PATH) $$UBOOT_CONFIG $(BOOTLOADER_ENV);    \             $(MAKE) -C    $(BOOTLOADER_PATH) $(BOOTLOADER_ENV);    \             install -D    $(BOOTLOADER_PATH)/u-boot.imx $(PRODUCT_OUT)/u-boot-$$UBOOT_PLATFORM.imx;     \             install -D    $(BOOTLOADER_PATH)/u-boot.imx $@;     \         done else bootloader: endif

 二、编译运用

2.1 单独编译

我们要单独编译的时候，就可以在build 目录下搜索：grep -r "PHONY:"  -n

这样就可以列出所有目标的定义。比如：.PHONY: recoveryimage

我就可以通过 make  recoveryimage 来编译recovery.img，同时也可以查看recovery.img 在生成时要依赖哪些？编译过程是什么等？

2.2 lk的编译

我们通过上面的方式，找不到lk的定义，但是我们又可以通过make lk 来进行编译lk.bin呢？

因为，lk 这种不属于AOSP 的范畴了，所有它的定义是在：vendor/mediatek/proprietary/bootable/bootloader/lk/Android.mk 

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1 2	44 .PHONY: lk check-lk-config check-mtk-config include $(LOCAL_PATH)/build_lk.mk

需要在不同的平台下去找，Android 编译的时候会扫描mk文件，从而将lk 的目标添加到系统，这样我们就可以通过make lk的方式来编译lk 了。

 

参考连接：https://blog.csdn.net/qq_29897125/article/details/108880883