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爲full-eng,否則如果answer是數字就將其轉換爲對應的字符串表示
    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並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就比較複雜了，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.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

　　然後include進來了/build/core/envsetup.sh，在envsetup.sh中定義了HOST_OS，OUT_DIR等環境變量，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設置TARGET_DEVICE。

　　然後在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，然後通過make編譯droid（默認）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。