Android编译过程详解（二）

作者：唐攀,华清远见嵌入式培训中心讲师。

通过上篇文章，我们分析了编译android时source build/envsetup.sh和lunch命令，在执行完上述两个命令后， 我们就可以进行编译android了。

1、 make

执行make命令的结果就是去执行当前目录下的Makefile文件，我们来看下它的内容：

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

呵呵，看到上面 的内容，我们都会笑，这是我见过最简单的Makefile了，我们再看下build/core/main.mk

在main.mk里，定义了变量TOPDIR，TOP为当前目录，BUILD_SYSTEM为build/core目录。

在49行，包含了build/core/config.mk文件。

后面的代码是check环境 变量，所有的Makefile都通过build/core/main.mk这个文件组织在一起，它定义了一个默认goals：droid，当我们在TOP目录下，敲Make实际上就等同于我们执行make droid。当Make include所有的文件，完成对所有make我文件的解析以后就会寻找生成droid的规则，依次生成它的依赖，直到所有满足的模块被编译好，然后使用相应的工具打包成相应的img。这儿不是我们的重点，不再多说。

2、 build/core/config.mk

该文件被main.mk包含。

定义了以下环境变量：

16 SRC_HEADERS := \
        17 $(TOPDIR)system/core/include \
        18 $(TOPDIR)hardware/libhardware/include \
        19 $(TOPDIR)hardware/libhardware_legacy/include \
        20 $(TOPDIR)hardware/ril/include \
        21 $(TOPDIR)dalvik/libnativehelper/include \
        22 $(TOPDIR)frameworks/base/include \
        23 $(TOPDIR)frameworks/base/opengl/include \
        24 $(TOPDIR)external/skia/include
        25 SRC_HOST_HEADERS:=$(TOPDIR)tools/include
        26 SRC_LIBRARIES:= $(TOPDIR)libs
        27 SRC_SERVERS:= $(TOPDIR)servers
        28 SRC_TARGET_DIR := $(TOPDIR)build/target
        29 SRC_API_DIR := $(TOPDIR)frameworks/base/api
        .....然后定义了下面几个重要的编译命令 43 CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mk
        44 BUILD_HOST_STATIC_LIBRARY:= $(BUILD_SYSTEM)/host_static_library.mk
        45 BUILD_HOST_SHARED_LIBRARY:= $(BUILD_SYSTEM)/host_shared_library.mk
        46 BUILD_STATIC_LIBRARY:= $(BUILD_SYSTEM)/static_library.mk
        47 BUILD_RAW_STATIC_LIBRARY := $(BUILD_SYSTEM)/raw_static_library.mk
        48 BUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.mk
        49 BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mk
        50 BUILD_RAW_EXECUTABLE:= $(BUILD_SYSTEM)/raw_executable.mk
        51 BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk
        52 BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk
        53 BUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mk
        54 BUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mk
        55 BUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mk
        56 BUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mk
        57 BUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mk
        58 BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk
        59 BUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mk
        60 BUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mk
        61 BUILD_KEY_CHAR_MAP := $(BUILD_SYSTEM)/key_char_map.mk

上述命令变量其实是对应的mk文件名，所有的Android.mk文件里基本上都包含上述命令变量，如：

CLEAR_VARS：用来清除之前定义的环境变量

BUILD_SHARED_LIBRARY：用来指定编译动态库过程

109 # ---------------------------------------------------------------
        110 # Define most of the global variables. These are the ones that
        111 # are specific to the user's build configuration.
        112 include $(BUILD_SYSTEM)/envsetup.mk
        113
        114 # Boards may be defined under $(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)
        115 # or under vendor/*/$(TARGET_DEVICE). Search in both places, but
        116 # make sure only one exists.
        117 # Real boards should always be associated with an OEM vendor.
        118 board_config_mk := \
        119 $(strip $(wildcard \
        120 $(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)/BoardConfig.mk \
        121 vendor/*/$(TARGET_DEVICE)/BoardConfig.mk \
        122 ))
        123 ifeq ($(board_config_mk),)
        124 $(error No config file found for TARGET_DEVICE $(TARGET_DEVICE))
        125 endif
        126 ifneq ($(words $(board_config_mk)),1)
        127 $(error Multiple board config files for TARGET_DEVICE $(TARGET_DEVICE): $(board_config_mk))
        128 endif
        129 include $(board_config_mk)
        130 TARGET_DEVICE_DIR := $(patsubst %/,%,$(dir $(board_config_mk)))
        131 board_config_mk :=
        112行又包含了另外一个重要的mk文件envsetup.mk，我们来看一下。

3、envsetup.mk

25 ifeq ($(TARGET_PRODUCT),) #判断TARGET_PRODUCT是否为空，
        26 ifeq ($(TARGET_SIMULATOR),true)
        27 TARGET_PRODUCT := sim
        28 else
        29 TARGET_PRODUCT := generic
        30 endif
         31 endif

第25行，判断TARGET_PRODUCT是否为空，根据上一节分析可知，TARGET_PRODUCT=fs100
        34 # the variant -- the set of files that are included for a build
        35 ifeq ($(strip $(TARGET_BUILD_VARIANT)),)
         36 TARGET_BUILD_VARIANT := eng
        37 endif
         38
        39 # Read the product specs so we an get TARGET_DEVICE and other
        40 # variables that we need in order to locate the output files.
        41 include $(BUILD_SYSTEM)/product_config.mk

在41行又包含了product_config.mk文件，等会我们再分析它，先看下面的

148 # ---------------------------------------------------------------
        149 # figure out the output directories
        150
        151 ifeq (,$(strip $(OUT_DIR)))
        152 OUT_DIR := $(TOPDIR)out
        153 endif
        154
        155 DEBUG_OUT_DIR := $(OUT_DIR)/debug
        156
        157 # Move the host or target under the debug/ directory
        158 # if necessary.
        159 TARGET_OUT_ROOT_release := $(OUT_DIR)/target
        160 TARGET_OUT_ROOT_debug := $(DEBUG_OUT_DIR)/target
        161 TARGET_OUT_ROOT := $(TARGET_OUT_ROOT_$(TARGET_BUILD_TYPE))
        162
        ...
        184 PRODUCT_OUT := $(TARGET_PRODUCT_OUT_ROOT)/$(TARGET_DEVICE)
        187
        188 HOST_OUT_EXECUTABLES:= $(HOST_OUT)/bin
        189 HOST_OUT_SHARED_LIBRARIES:= $(HOST_OUT)/lib
        190 HOST_OUT_JAVA_LIBRARIES:= $(HOST_OUT)/framework
        191 HOST_OUT_SDK_ADDON := $(HOST_OUT)/sdk_addon
        ...
        200 TARGET_OUT_INTERMEDIATES := $(PRODUCT_OUT)/obj
        201 TARGET_OUT_HEADERS:= $(TARGET_OUT_INTERMEDIATES)/include
        202 TARGET_OUT_INTERMEDIATE_LIBRARIES := $(TARGET_OUT_INTERMEDIATES)/lib
        203 TARGET_OUT_COMMON_INTERMEDIATES := $(TARGET_COMMON_OUT_ROOT)/obj
        204
        205 TARGET_OUT := $(PRODUCT_OUT)/system
        206 TARGET_OUT_EXECUTABLES:= $(TARGET_OUT)/bin
        207 TARGET_OUT_OPTIONAL_EXECUTABLES:= $(TARGET_OUT)/xbin
        208 TARGET_OUT_SHARED_LIBRARIES:= $(TARGET_OUT)/lib
        209 TARGET_OUT_JAVA_LIBRARIES:= $(TARGET_OUT)/framework
        210 TARGET_OUT_APPS:= $(TARGET_OUT)/app
        211 TARGET_OUT_KEYLAYOUT := $(TARGET_OUT)/usr/keylayout
        212 TARGET_OUT_KEYCHARS := $(TARGET_OUT)/usr/keychars
        213 TARGET_OUT_ETC := $(TARGET_OUT)/etc
        214 TARGET_OUT_STATIC_LIBRARIES:= $(TARGET_OUT_INTERMEDIATES)/lib
        215 TARGET_OUT_NOTICE_FILES:=$(TARGET_OUT_INTERMEDIATES)/NOTICE_FILES
        216
        217 TARGET_OUT_DATA := $(PRODUCT_OUT)/data
        218 TARGET_OUT_DATA_EXECUTABLES:= $(TARGET_OUT_EXECUTABLES)
        219 TARGET_OUT_DATA_SHARED_LIBRARIES:= $(TARGET_OUT_SHARED_LIBRARIES)
        220 TARGET_OUT_DATA_JAVA_LIBRARIES:= $(TARGET_OUT_JAVA_LIBRARIES)
        221 TARGET_OUT_DATA_APPS:= $(TARGET_OUT_DATA)/app
        222 TARGET_OUT_DATA_KEYLAYOUT := $(TARGET_OUT_KEYLAYOUT)
        223 TARGET_OUT_DATA_KEYCHARS := $(TARGET_OUT_KEYCHARS)
        224 TARGET_OUT_DATA_ETC := $(TARGET_OUT_ETC)
        225 TARGET_OUT_DATA_STATIC_LIBRARIES:= $(TARGET_OUT_STATIC_LIBRARIES)
        226
        227 TARGET_OUT_UNSTRIPPED := $(PRODUCT_OUT)/symbols
        228 TARGET_OUT_EXECUTABLES_UNSTRIPPED := $(TARGET_OUT_UNSTRIPPED)/system/bin
        229 TARGET_OUT_SHARED_LIBRARIES_UNSTRIPPED := $(TARGET_OUT_UNSTRIPPED)/system/lib
        230 TARGET_ROOT_OUT_UNSTRIPPED := $(TARGET_OUT_UNSTRIPPED)
        231 TARGET_ROOT_OUT_SBIN_UNSTRIPPED := $(TARGET_OUT_UNSTRIPPED)/sbin
        232 TARGET_ROOT_OUT_BIN_UNSTRIPPED := $(TARGET_OUT_UNSTRIPPED)/bin
        233
        234 TARGET_ROOT_OUT := $(PRODUCT_OUT)/root
        235 TARGET_ROOT_OUT_BIN := $(TARGET_ROOT_OUT)/bin
        236 TARGET_ROOT_OUT_SBIN := $(TARGET_ROOT_OUT)/sbin
        237 TARGET_ROOT_OUT_ETC := $(TARGET_ROOT_OUT)/etc
        238 TARGET_ROOT_OUT_USR := $(TARGET_ROOT_OUT)/usr
        239
        240 TARGET_RECOVERY_OUT := $(PRODUCT_OUT)/recovery
        241 TARGET_RECOVERY_ROOT_OUT := $(TARGET_RECOVERY_OUT)/root
        242
        243 TARGET_SYSLOADER_OUT := $(PRODUCT_OUT)/sysloader
        244 TARGET_SYSLOADER_ROOT_OUT := $(TARGET_SYSLOADER_OUT)/root
        245 TARGET_SYSLOADER_SYSTEM_OUT := $(TARGET_SYSLOADER_OUT)/root/system
        246
        247 TARGET_INSTALLER_OUT := $(PRODUCT_OUT)/installer
        248 TARGET_INSTALLER_DATA_OUT := $(TARGET_INSTALLER_OUT)/data
        249 TARGET_INSTALLER_ROOT_OUT := $(TARGET_INSTALLER_OUT)/root
        250 TARGET_INSTALLER_SYSTEM_OUT := $(TARGET_INSTALLER_OUT)/root/system

上面的代码是指定了目标输出代码的位置和主机输出代码的位置，重要的几个如下：

PRODUCT_OUT = 这个的结果要根据product_config.mk文件内容来决定，其实是out/target/product/fs100/
        TARGET_OUT = $(PRODUCT_OUT)/system
        TARGET_OUT_EXECUTABLES = $(PRODUCT_OUT)/system/bin
        TARGET_OUT_SHARED_LIBRARIES = $(PRODUCT_OUT)/system/lib
        TARGET_OUT_JAVA_LIBRARIES = $(PRODUCT_OUT)/system/framework
        TARGET_OUT_APPS = $(PRODUCT_OUT)/system/app
        TARGET_OUT_ETC = $(PRODUCT_OUT)/system/etc
        TARGET_OUT_STATIC_LIBRARIES = $(PRODUCT_OUT)/obj/lib
        TARGET_OUT_DATA = $(PRODUCT_OUT)/data
        TARGET_OUT_DATA_APPS = $(PRODUCT_OUT)/data/app
        TARGET_ROOT_OUT = $(PRODUCT_OUT)/root
        TARGET_ROOT_OUT_BIN = $(PRODUCT_OUT)/bin
        TARGET_ROOT_OUT_SBIN = $(PRODUCT_OUT)/system/sbin
        TARGET_ROOT_OUT_ETC = $(PRODUCT_OUT)/system/etc
        TARGET_ROOT_OUT_USR = $(PRODUCT_OUT)/system/usr

总结下：

envsetup.mk文件主要包含了product_config.mk文件，然后指定了编译时要输出的所有文件的OUT目录。

4、 build/core/product_config.mk

157 include $(BUILD_SYSTEM)/product.mk
        ...
        160 # Read in all of the product definitions specified by the AndroidProducts.mk
        161 # files in the tree.
        162 #
        163 #TODO: when we start allowing direct pointers to product files,
        164 # guarantee that they're in this list.
        165 $(call import-products, $(get-all-product-makefiles))
        166 $(check-all-products)
        ...
        170 # Convert a short name like "sooner" into the path to the product
        171 # file defining that product.
        172 #
        173 INTERNAL_PRODUCT := $(call resolve-short-product-name, $(TARGET_PRODUCT))
        ...
        176 # Find the device that this product maps to.
        177 TARGET_DEVICE := $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_DEVICE)157行，我靠，又包含了product.mk文件

165行，调用函数import-products, $(get-all-product-makefiles)，这儿我们看上面的注释：

Read in all of the product definitions specified by the AndroidProducts.mk files in the tree.
        TODO: when we start allowing direct pointers to product files, guarantee that they're in this list.

意思是说：读取指定的目录下所有的AndrodProducts.mk文件中定义的产品信息

其实get-all-product-makefiles返回所有的产品文件xxx.mk

import-products函数去验证这些产品配置文件是否都包含有必须的配置信息，细节后面分析。

173行调用了resolve-short-product-name函数，它将返回TARGET_PRODUCT产品的配置文件目录，并赋给INTERNAL_PRODUCT

也就是说：

INTERNAL_PRODUCT = vendor/farsight/products/fs100.mk

TARGET_DEVICE = fs100

如果调试看其结果，可以在167行，将#$(dump-product)取消注释

然后在175行添加： $(info $(INTERNAL_PRODUCT))

在178行添加： $(info $(TARGET_DEVICE ))，查看调试结果。

总结一下：

product_config.mk主要读取vendor目录下不同厂商自己定义的AndrodProducts.mk文件，从该文件里取得所有产品的配置文件，然后再根据lunch选择的编译项TARGET_PRODUCT，找到与之对应的配置文件，然后设置TARGET_DEVICE变量，用于后续编译。

5、 build/core/product.mk

17 #
        18 # Functions for including AndroidProducts.mk files
        19 #
        20
        21 #
        22 # Returns the list of all AndroidProducts.mk files.
        23 # $(call ) isn't necessary.
        24 #
        25 define <strong>_find-android-products-files</strong>
        26 $(shell test -d vendor && find vendor -maxdepth 6 -name AndroidProducts.mk) \
        27 $(SRC_TARGET_DIR)/product/AndroidProducts.mk
        28 endef
        29
        30 #
        31 # Returns the sorted concatenation of all PRODUCT_MAKEFILES
        32 # variables set in all AndroidProducts.mk files.
        33 # $(call ) isn't necessary.
        34 #
        35 define <strong>get-all-product-makefiles</strong>
        36 $(sort \
        37 $(foreach f,$(_find-android-products-files), \
        38 $(eval PRODUCT_MAKEFILES :=) \
        39 $(eval LOCAL_DIR := $(patsubst %/,%,$(dir $(f)))) \
        40 $(eval include $(f)) \
        41 $(PRODUCT_MAKEFILES) \
        42 ) \
        43 $(eval PRODUCT_MAKEFILES :=) \
        44 $(eval LOCAL_DIR :=) \
        45 )
        46 endef通过注释可知，本文件中主要是一些用来处理AndroidProduct.mk的函数

 _find-android-products-files:

用来获得vendor目录下，所有名字为AndroidProduct.mk的文件列表。

get-all-product-makefiles：

用来获得所有AndroidProduct.mk文件里定义的PRODUCT_MAKEFILES的值（其实是产品文件路径名）。

在vendor目录下，每个公司目录下都会存在一个AndroidProduct.mk文件，这个文件是用来定义这个公司的产品列表，每个产品用<product_name>.mk来表示，  如Android给的示例：

vendor/sample/products/AndroidProduct.mk。其内容如下：

1 #
        2 # This file should set PRODUCT_MAKEFILES to a list of product makefiles
        3 # to expose to the build system. LOCAL_DIR will already be set to
        4 # the directory containing this file.
        5 #
        6 # This file may not rely on the value of any variable other than
        7 # LOCAL_DIR; do not use any conditionals, and do not look up the
         8 # value of any variable that isn't set in this file or in a file that
        9 # it includes.
        10 #
        11
         12 PRODUCT_MAKEFILES := \
         13 $(LOCAL_DIR)/sample_addon.mk里面只定义了一个产品配置文件，即当前目录下的sample_addon.mk：
        1 # List of apps and optional libraries (Java and native) to put in the add-on system image.
        2 PRODUCT_PACKAGES := \
        3 PlatformLibraryClient \
        4 com.example.android.platform_library \
        5 libplatform_library_jni

上述文件里定义了产品相关个性化信息，如，PRODUCT_PACKAGES表示要在当前产品里添加一些安装包。由此可见，get-all-product-makefiles函数，其实就是返回了当前公司里全部的产品对应的mk文件列表。

总结：

如果用户想个性定制自己的产品，应该有以下流程，包含上一节内容：

1. 创建公司目录

#mkdir vendor/farsight

2. 创建一个vendorsetup.sh文件，将当前产品编译项添加到lunch里，让lunch能找到用户个性定制编译项

#echo "add_lunch_combo fs100-eng" > vendor/farsight/vendorsetup.sh

3. 仿着Android示例代码，在公司目录下创建products目录

#mkdir -p vendor/farsight/products

4. 仿着Android示例代码，在products目录下创建两个mk文件

#touch vendor/farsight/products/AndroidProduct.mk vendor/farsight/products/fs100.mk

在AndroidProduct.mk里添加如下内容：

PRODUCT_MAKEFILES := $(LOCAL_DIR)/fs100.mk表示只有一个产品fs100，它对应的配置文件在当前目录下的fs100.mk。

5.在产品配置文件里添加最基本信息

1
        2 PRODUCT_PACKAGES := \
        3 IM \
        4 VoiceDialer
        5
        6 $(call inherit-product, build/target/product/generic.mk) ##从某一默认配置开始派生余下内容参考派生起点
        7
        8 # Overrides
        9 PRODUCT_MANUFACTURER := farsight
        10 PRODUCT_NAME := fs100
        11 PRODUCT_DEVICE := fs100

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