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"    . $fdoneunset 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,否則列印選擇編譯目標的菜單    if [ "$1" ] ; then        answer=$1    else        print_lunch_menu        echo -n "Which would you like? [full-eng] "        read answer    fi    local selection=
　　//如果沒有編譯目標預設為full-eng,否則如果answer是數字就將其轉換為對應的字串表示    if [ -z "$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: $answer"        return 1    fi    export TARGET_BUILD_APPS=
   //檢測選擇的product是否合法(只要在相應目錄建立vendorsetup.sh並add_lunch_combo就可在lunch menu中顯示相應項,但如果不配置product相關資訊就會Invalid)
　　local product=$(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 "$variant" ]    then        echo        return 1    fi
　　//匯出TARGET_PRODECT,TARGET_BUILD_VARIANT與TARGET_BUILD_TYPE,比如若選擇的是full-eng,那麼TARGET_PRODUCT=full,TARGET_BUILD_VARIANT=eng    export TARGET_PRODUCT=$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進來了一個檔案：

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

　　而build/core/main.mk就比較複雜了，以下是main.mk的結構圖：

　　在main.mk中首先定義了預設編譯目標並做版本檢查，然後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.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

　　然後include進來了/build/core/envsetup.sh，在envsetup.sh中定義了HOST_OS，OUT_DIR等環境變數，並通過include product_config.mk檢索所有Product，並做有效性檢查，然後根據lunch時選擇的Product設定TARGET_DEVICE。

　　然後在envsetup.sh中根據TARGET_DEVICE尋找BoardConfig.mk檔案進行Board相關配置，尋找KERNEL_HEADER，配置編譯工具鏈。

　　在definitions.mk中定義了all_makefiles_under等用來檢索檔案的函數。

　　根據TARGET_BUILD_VARIANT設定ro.secure等系統屬性，設定tags_to_install等變數。

　　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檔案並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組中，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中原來的資源檔就可以定義framework-res.apk中的資源。

　　接下來include build/core/Makefile檔案，定義bootimage，systemimage等信賴目標，然後通過make編譯droid（預設）目標就可以編譯系統了。

　　Android採用檢索所有子目錄中的Android.mk將所有要編譯的模組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組。