Android編譯系統
一、Android編譯步驟：
二、初始化編譯環境－－source build/envsetup.sh
在build/envsetup.sh中主要完成了三件事。
添加編譯目標的代碼如下：
for f in `/bin/ls vendor/*/vendorsetup.sh vendor/*/*/vendorsetup.sh device/*/*/vendorsetup.sh 2> /dev/null` do echo "including $f" . $f done unset f
三、選擇編譯目標－－lunch
通過lunch選擇編譯目標，函數定義如下：
function lunch(){
local answer
//如果調用lunch時帶參數就表示手動指定編譯目標,否則打印選擇編譯目標的菜單 if [ "$1" ] ; then answer=$1 else print_lunch_menu echo -n "Which would you like? [full-eng] " read answer fi local selection=
//如果沒有編譯目標默認為full-eng,否則如果answer是數字就將其轉換為對應的字符串表示 if [ -z "$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=$answer fi
//如果表示編譯目標的字符串是空的表示非法選擇,錯誤返回 if [ -z "$selection" ] then echo echo "Invalid lunch combo: $answer" return 1 fi export TARGET_BUILD_APPS=
//檢測選擇的product是否合法(只要在相應目錄新建vendorsetup.sh并add_lunch_combo就可在lunch menu中顯示相應項,但如果不配置product相關信息就會Invalid)
local product=$(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
//從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 "$variant" ] then echo return 1 fi
//導出TARGET_PRODECT,TARGET_BUILD_VARIANT與TARGET_BUILD_TYPE,比如若選擇的是full-eng,那么TARGET_PRODUCT=full,TARGET_BUILD_VARIANT=eng export TARGET_PRODUCT=$product export TARGET_BUILD_VARIANT=$variant export TARGET_BUILD_TYPE=release echo set_stuff_for_environment printconfig }
四、編譯－－make -j8
要make肯定有Makefile，Android根目錄的Makefile只是簡單地include進來了一個文件：
1 ### DO NOT EDIT THIS FILE ### 2 include build/core/main.mk 3 ### DO NOT EDIT THIS FILE ###
而build/core/main.mk就比較復雜了，以下是main.mk的結構圖：
在main.mk中首先定義了默認編譯目標并做版本檢查，然后include config.mk。
在config.mk中定義了在Android.mk中編譯目標時會用到的常量
CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mk BUILD_HOST_STATIC_LIBRARY:= $(BUILD_SYSTEM)/host_static_library.mk BUILD_HOST_SHARED_LIBRARY:= $(BUILD_SYSTEM)/host_shared_library.mk BUILD_STATIC_LIBRARY:= $(BUILD_SYSTEM)/static_library.mk BUILD_RAW_STATIC_LIBRARY := $(BUILD_SYSTEM)/raw_static_library.mk BUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.mk BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mk BUILD_RAW_EXECUTABLE:= $(BUILD_SYSTEM)/raw_executable.mk BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk BUILD_PHONY_PACKAGE:= $(BUILD_SYSTEM)/phony_package.mk BUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mk BUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mk BUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mk BUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mk BUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mk BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk BUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mk BUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mk BUILD_NATIVE_TEST := $(BUILD_SYSTEM)/native_test.mk BUILD_HOST_NATIVE_TEST := $(BUILD_SYSTEM)/host_native_test.mk
然后include進來了/build/core/envsetup.sh，在envsetup.sh中定義了HOST_OS，OUT_DIR等環境變量，并通過include product_config.mk檢索所有Product，并做有效性檢查，然后根據lunch時選擇的Product設置TARGET_DEVICE。
然后在envsetup.sh中根據TARGET_DEVICE查找BoardConfig.mk文件進行Board相關配置，查找KERNEL_HEADER，配置編譯工具鏈。
在definitions.mk中定義了all_makefiles_under等用來檢索文件的函數。
根據TARGET_BUILD_VARIANT設置ro.secure等系統屬性，設定tags_to_install等變量。
接下來通過
subdir_makefiles := \ $(shell build/tools/findleaves.py --prune=out --prune=.repo --prune=.git $(subdirs) Android.mk) include $(subdir_makefiles)
找到所有子目錄下的Android.mk文件并include進來，這樣在Android.mk定義的LOCAL_PACKAGE_NAME與include $(BUILD_PACKAGE)就可以將相應的Android.mk中定義的目標包含進編譯模塊中，在config.mk中有如下定義：
BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk
而package.mk又包含base_rules.mk將LOCAL_MODULE添加到ALL_MODULES中。
post_clean.mk是跟Resource Overlay相關，使們們不需要修改framework中原來的資源文件就可以定義framework-res.apk中的資源。
接下來include build/core/Makefile文件，定義bootimage，systemimage等依賴目標，然后通過make編譯droid（默認）目標就可以編譯系統了。
Android采用檢索所有子目錄中的Android.mk將所有要編譯的模塊收集起來的方式編譯系統，而不是進入到每個子目錄執行make，這樣就方便了我們添加自己的模塊。
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