在build/envsetup.sh中主要完成了三件事。
添加编译目标的代码如下：
for f in `/bin/ls vendor/*/vendorsetup.sh vendor/*/*/vendorsetup.sh device/*/*/vendorsetup.sh 2> /dev/null`do echo "including $f" . $fdoneunset f
通过lunch选择编译目标，函数定义如下：
function lunch(){
local answer
//如果调用lunch时带参数就表示手动指定编译目标,否则打印选择编译目标的菜单 if [ "$1" ] ; then answer=$1 else print_lunch_menu echo -n "Which would you like? [full-eng] " read answer fi local selection=
//如果没有编译目标默认为full-eng,否则如果answer是数字就将其转换为对应的字符串表示 if [ -z "$answer" ] then selection=full-eng elif (echo -n $answer | grep -q -e "^[0-9][0-9]*$") then if [ $answer -le ${#LUNCH_MENU_CHOICES[@]} ] then selection=${LUNCH_MENU_CHOICES[$(($answer-1))]} fi elif (echo -n $answer | grep -q -e "^[^\-][^\-]*-[^\-][^\-]*$") then selection=$answer fi
//如果表示编译目标的字符串是空的表示非法选择,错误返回 if [ -z "$selection" ] then echo echo "Invalid lunch combo: $answer" return 1 fi export TARGET_BUILD_APPS=
//检测选择的product是否合法(只要在相应目录新建vendorsetup.sh并add_lunch_combo就可在lunch menu中显示相应项,但如果不配置product相关信息就会Invalid)
local product=$(echo -n $selection | sed -e "s/-.*$//") check_product $product if [ $? -ne 0 ] then echo echo "** Don't have a product spec for: '$product'" echo "** Do you have the right repo manifest?" product= fi
//从selection解析出product,variant local variant=$(echo -n $selection | sed -e "s/^[^\-]*-//") check_variant $variant if [ $? -ne 0 ] then echo echo "** Invalid variant: '$variant'" echo "** Must be one of ${VARIANT_CHOICES[@]}" variant= fi if [ -z "$product" -o -z "$variant" ] then echo return 1 fi
//导出TARGET_PRODECT,TARGET_BUILD_VARIANT与TARGET_BUILD_TYPE,比如若选择的是full-eng,那么TARGET_PRODUCT=full,TARGET_BUILD_VARIANT=eng export TARGET_PRODUCT=$product export TARGET_BUILD_VARIANT=$variant export TARGET_BUILD_TYPE=release echo set_stuff_for_environment printconfig}
要make肯定有Makefile，Android根目录的Makefile只是简单地include进来了一个文件：
1 ### DO NOT EDIT THIS FILE ### 2 include build/core/main.mk 3 ### DO NOT EDIT THIS FILE ###
而build/core/main.mk就比较复杂了，以下是main.mk的结构图：
在main.mk中首先定义了默认编译目标并做版本检查，然后include config.mk。
在config.mk中定义了在Android.mk中编译目标时会用到的常量
CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mkBUILD_HOST_STATIC_LIBRARY:= $(BUILD_SYSTEM)/host_static_library.mkBUILD_HOST_SHARED_LIBRARY:= $(BUILD_SYSTEM)/host_shared_library.mkBUILD_STATIC_LIBRARY:= $(BUILD_SYSTEM)/static_library.mkBUILD_RAW_STATIC_LIBRARY := $(BUILD_SYSTEM)/raw_static_library.mkBUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.mkBUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mkBUILD_RAW_EXECUTABLE:= $(BUILD_SYSTEM)/raw_executable.mkBUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mkBUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mkBUILD_PHONY_PACKAGE:= $(BUILD_SYSTEM)/phony_package.mkBUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mkBUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mkBUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mkBUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mkBUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mkBUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mkBUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mkBUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mkBUILD_NATIVE_TEST := $(BUILD_SYSTEM)/native_test.mkBUILD_HOST_NATIVE_TEST := $(BUILD_SYSTEM)/host_native_test.mk
然后include进来了/build/core/envsetup.sh，在envsetup.sh中定义了HOST_OS，OUT_DIR等环境变量，并通过include product_config.mk检索所有Product，并做有效性检查，然后根据lunch时选择的Product设置TARGET_DEVICE。
然后在envsetup.sh中根据TARGET_DEVICE查找BoardConfig.mk文件进行Board相关配置，查找KERNEL_HEADER，配置编译工具链。
在definitions.mk中定义了all_makefiles_under等用来检索文件的函数。
根据TARGET_BUILD_VARIANT设置ro.secure等系统属性，设定tags_to_install等变量。
接下来通过
subdir_makefiles := $(shell build/tools/findleaves.py --prune=out --prune=.repo --prune=.git $(subdirs) Android.mk) include $(subdir_makefiles)
找到所有子目录下的Android.mk文件并include进来，这样在Android.mk定义的LOCAL_PACKAGE_NAME与include $(BUILD_PACKAGE)就可以将相应的Android.mk中定义的目标包含进编译模块中，在config.mk中有如下定义：
BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk
而package.mk又包含base_rules.mk将LOCAL_MODULE添加到ALL_MODULES中。
post_clean.mk是跟Resource Overlay相关，使们们不需要修改framework中原来的资源文件就可以定义framework-res.apk中的资源。
接下来include build/core/Makefile文件，定义bootimage，systemimage等依赖目标，然后通过make编译droid（默认）目标就可以编译系统了。
Android采用检索所有子目录中的Android.mk将所有要编译的模块收集起来的方式编译系统，而不是进入到每个子目录执行make，这样就方便了我们添加自己的模块。
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