Building System之编译前的准备工作

Android系统编译前的准备工作，我个人认为由如下三个步骤完成。接下来，我就逐一分析每一步骤都干了什么事情。

1、安装jdk、设置环境变量JAVA_HOME。

2、source build/envsetup.sh

3、lunch <product_name>-<build_variant>

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博文中出现的get_abs_build_var() 和 get_build_var()请移步到 这里

1、设置JAVA_HMOE环境变量

export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64

2、source build/envsetup.sh

该shell脚本实现了许多有用的shell函数，可通过执行hmm命令查看（hmm是envsetup.sh实现的第一个shell函数）。

下面是hmm命令显示的一部分：

Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:
- lunch:   lunch <product_name>-<build_variant>
- tapas:   tapas [<App1> <App2> ...] [arm|x86|mips|armv5|arm64|x86_64|mips64] [eng|userdebug|user]
- croot:   Changes directory to the top of the tree.
- m:       Makes from the top of the tree.
- mm:      Builds all of the modules in the current directory, but not their dependencies.
- mmm:     Builds all of the modules in the supplied directories, but not their dependencies.
           To limit the modules being built use the syntax: mmm dir/:target1,target2.
- mma:     Builds all of the modules in the current directory, and their dependencies.
- mmma:    Builds all of the modules in the supplied directories, and their dependencies.
- cgrep:   Greps on all local C/C++ files.
- ggrep:   Greps on all local Gradle files.
- jgrep:   Greps on all local Java files.
- resgrep: Greps on all local res/*.xml files.
- sgrep:   Greps on all local source files.
- godir:   Go to the directory containing a file.

除了上面实现的shell函数，envsetup.sh还把device和vendor目录下的所有vendorsetup.sh脚本包含进来了。最后，还调用shell函数addcompletions。

if [ "x$SHELL" != "x/bin/bash" ]; then
    case `ps -o command -p $$` in # $$属于Special Shell Variables,表示Process ID of shell
        *bash*)
            ;;
        *)
            echo "WARNING: Only bash is supported, use of other shell would lead to erroneous results"
            ;;
    esac
fi

# Execute the contents of any vendorsetup.sh files we can find.
for f in `test -d device && find -L device -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null` \
         `test -d vendor && find -L vendor -maxdepth 4 -name 'vendorsetup.sh' 2> /dev/null`
do
    echo "including $f"
    . $f # source找到的所有vendorsetup.sh文件
done
unset f

addcompletions # 检查bash版本，并source sdk/bash_completion目录下的所有[a-z]*.bash文件

$$ 请查看  Special Shell Variables

vendorsetup.sh的内容大多数是调用add_lunch_combo函数添加<product_name>-<build_variant>格式的lunch选项（也可以实现一些shell functions）。如：

add_lunch_combo aosp_flounder-userdebug

接下来，看一下add_lunch_combo函数的实现，File：build/envsetup.sh。

# Clear this variable.  It will be built up again when the vendorsetup.sh
# files are included at the end of this file.
unset LUNCH_MENU_CHOICES
function add_lunch_combo()
{
    local new_combo=$1
    local c
    for c in ${LUNCH_MENU_CHOICES[@]} ; do
        if [ "$new_combo" = "$c" ] ; then
            return
        fi
    done
    LUNCH_MENU_CHOICES=(${LUNCH_MENU_CHOICES[@]} $new_combo) # vendorsetup.sh中添加的combo选项都保存在数组LUNCH_MENU_CHOICES中
}

我们回到envsetup.sh脚本的最后一行，看一下addcompletions函数的实现，File：build/envsetup.sh。

function addcompletions()
{
    local T dir f

    # Keep us from trying to run in something that isn't bash.
    if [ -z "${BASH_VERSION}" ]; then
        return
    fi

    # Keep us from trying to run in bash that's too old.
    if [ ${BASH_VERSINFO[0]} -lt 3 ]; then
        return
    fi

    dir="sdk/bash_completion"
    if [ -d ${dir} ]; then
        for f in `/bin/ls ${dir}/[a-z]*.bash 2> /dev/null`; do
            echo ">>> including $f"
            . $f # source 所有[a-z]*.bash脚本
        done
    fi
}

3、lunch <product_name>-<build_variant>

lunch命令是一个shell函数，是在执行source  build/envsetup.sh时添加到shell环境中的。

function lunch()
{
    local answer

    if [ "$1" ] ; then
        answer=$1
    else
        print_lunch_menu # 3.1、循环打印LUNCH_MENU_CHOICES数组中的<product_name>-<build_variant>选项
        echo -n "Which would you like? [aosp_arm-eng] "
        read answer
    fi

    local selection=

    if [ -z "$answer" ]
    then
	# 3.2、如果lunch时没有指定或选中任何combo，就默认使用aosp_arm-eng，该combo是执行source build/envsetup.sh时添加到LUNCH_MENU_CHOICES中的
        selection=aosp_arm-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

    if [ -z "$selection" ]
    then
        echo
        echo "Invalid lunch combo: $answer"
        return 1
    fi

    export TARGET_BUILD_APPS=

    local product=$(echo -n $selection | sed -e "s/-.*$//") # 把<product_name>赋值给变量product
    check_product $product # 3.3、检查product是否存在
    if [ $? -ne 0 ]
    then
        echo
        echo "** Don't have a product spec for: '$product'"
        echo "** Do you have the right repo manifest?"
        product=
    fi

    local variant=$(echo -n $selection | sed -e "s/^[^\-]*-//") # 把<build_variant>赋值给变量variant
    check_variant $variant # 3.4、检查variant是否合法
    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

    export TARGET_PRODUCT=$product
    export TARGET_BUILD_VARIANT=$variant
    export TARGET_BUILD_TYPE=release

    echo

    set_stuff_for_environment # 3.5、设置编译所需的环境变量
    printconfig # 3.6、打印config
}

3.1、循环打印LUNCH_MENU_CHOICES数组中的<product_name>-<build_variant>选项。

function print_lunch_menu()
{
    local uname=$(uname)
    echo
    echo "You're building on" $uname
    echo
    echo "Lunch menu... pick a combo:"

    local i=1
    local choice
    for choice in ${LUNCH_MENU_CHOICES[@]} # 打印LUNCH_MENU_CHOICES数组中的所有元素
    do
        echo "     $i. $choice"
        i=$(($i+1))
    done

    echo
}

3.2、如果lunch时没有指定或选中任何combo，就默认使用aosp_arm-eng，该combo是执行source build/envsetup.sh时添加到LUNCH_MENU_CHOICES中的。

# add the default one here
add_lunch_combo aosp_arm-eng
add_lunch_combo aosp_arm64-eng
add_lunch_combo aosp_mips-eng
add_lunch_combo aosp_mips64-eng
add_lunch_combo aosp_x86-eng
add_lunch_combo aosp_x86_64-eng

3.3、检查product是否存在

# check to see if the supplied product is one we can build
function check_product()
{
    T=$(gettop)
    if [ ! "$T" ]; then
        echo "Couldn't locate the top of the tree.  Try setting TOP." >&2
        return
    fi
        TARGET_PRODUCT=$1 \
        TARGET_BUILD_VARIANT= \
        TARGET_BUILD_TYPE= \
        TARGET_BUILD_APPS= \
        get_build_var TARGET_DEVICE > /dev/null
    # hide successful answers, but allow the errors to show
}

3.4、检查variant是否合法

VARIANT_CHOICES=(user userdebug eng)

# check to see if the supplied variant is valid
function check_variant()
{
    for v in ${VARIANT_CHOICES[@]} # <build_variant>必须是（user userdebug eng）中的一个。
    do
        if [ "$v" = "$1" ]
        then
            return 0
        fi
    done
    return 1
}

3.5、设置编译所需的环境变量

function set_stuff_for_environment()
{
    settitle # 3.5.1、设置title
    set_java_home # 3.5.2、设置java home
    setpaths # 3.5.3、设置paths
    set_sequence_number # 3.5.4、设置sequence number

    export ANDROID_BUILD_TOP=$(gettop) # 该变量是android代码树根目录的绝对路径
    # With this environment variable new GCC can apply colors to warnings/errors
    export GCC_COLORS='error=01;31:warning=01;35:note=01;36:caret=01;32:locus=01:quote=01' # 设置gcc的警告和错误可以彩色显示
}

3.5.1、设置title

function settitle()
{
    if [ "$STAY_OFF_MY_LAWN" = "" ]; then # $STAY_OFF_MY_LAWN默认为空，走if分支
        local arch=$(gettargetarch)
        local product=$TARGET_PRODUCT # 即<product_name>
        local variant=$TARGET_BUILD_VARIANT # 即<build_name>
        local apps=$TARGET_BUILD_APPS # 默认为空
        if [ -z "$apps" ]; then # $apps默认为空，走if分会
            export PROMPT_COMMAND="echo -ne \"\033]0;[${arch}-${product}-${variant}] ${USER}@${HOSTNAME}: ${PWD}\007\""
        else
            export PROMPT_COMMAND="echo -ne \"\033]0;[$arch $apps $variant] ${USER}@${HOSTNAME}: ${PWD}\007\""
        fi
    fi
}

3.5.2、设置java home

# Force JAVA_HOME to point to java 1.7 or java 1.6  if it isn't already set.
#
# Note that the MacOS path for java 1.7 includes a minor revision number (sigh).
# For some reason, installing the JDK doesn't make it show up in the
# JavaVM.framework/Versions/1.7/ folder.
function set_java_home() {
    # Clear the existing JAVA_HOME value if we set it ourselves, so that
    # we can reset it later, depending on the version of java the build
    # system needs.
    #
    # If we don't do this, the JAVA_HOME value set by the first call to
    # build/envsetup.sh will persist forever.
    if [ -n "$ANDROID_SET_JAVA_HOME" ]; then # linux系统，$ANDROID_SET_JAVA_HOME默认为空，不走if分支。
      export JAVA_HOME=""
    fi

    if [ ! "$JAVA_HOME" ]; then # JAVA_HOME已经在第一步骤中export了。$JAVA_HOME不为空，不走if分支。
      if [ -n "$LEGACY_USE_JAVA6" ]; then
        case `uname -s` in
            Darwin)
                export JAVA_HOME=/System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home
                ;;
            *)
                export JAVA_HOME=/usr/lib/jvm/java-6-sun
                ;;
        esac
      else
        case `uname -s` in
            Darwin)
                export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)
                ;;
            *)
                export JAVA_HOME=/usr/lib/jvm/java-7-openjdk-amd64
                ;;
        esac
      fi

      # Keep track of the fact that we set JAVA_HOME ourselves, so that
      # we can change it on the next envsetup.sh, if required.
      export ANDROID_SET_JAVA_HOME=true
    fi
}

3.5.3、设置paths

function setpaths()
{
    T=$(gettop)
    if [ ! "$T" ]; then
        echo "Couldn't locate the top of the tree.  Try setting TOP."
        return
    fi

    ##################################################################
    #                                                                #
    #              Read me before you modify this code               #
    #                                                                #
    #   This function sets ANDROID_BUILD_PATHS to what it is adding  #
    #   to PATH, and the next time it is run, it removes that from   #
    #   PATH.  This is required so lunch can be run more than once   #
    #   and still have working paths.                                #
    #                                                                #
    ##################################################################

    # Note: on windows/cygwin, ANDROID_BUILD_PATHS will contain spaces
    # due to "C:\Program Files" being in the path.

    # out with the old
    if [ -n "$ANDROID_BUILD_PATHS" ] ; then
        export PATH=${PATH/$ANDROID_BUILD_PATHS/}
    fi
    if [ -n "$ANDROID_PRE_BUILD_PATHS" ] ; then
        export PATH=${PATH/$ANDROID_PRE_BUILD_PATHS/}
        # strip leading ':', if any
        export PATH=${PATH/:%/}
    fi

    # and in with the new
    prebuiltdir=$(getprebuilt)
    gccprebuiltdir=$(get_abs_build_var ANDROID_GCC_PREBUILTS)

    # defined in core/config.mk
    targetgccversion=$(get_build_var TARGET_GCC_VERSION)
    targetgccversion2=$(get_build_var 2ND_TARGET_GCC_VERSION)
    export TARGET_GCC_VERSION=$targetgccversion

    # The gcc toolchain does not exists for windows/cygwin. In this case, do not reference it.
    export ANDROID_TOOLCHAIN=
    export ANDROID_TOOLCHAIN_2ND_ARCH=
    local ARCH=$(get_build_var TARGET_ARCH)
    case $ARCH in
        x86) toolchaindir=x86/x86_64-linux-android-$targetgccversion/bin
            ;;
        x86_64) toolchaindir=x86/x86_64-linux-android-$targetgccversion/bin
            ;;
        arm) toolchaindir=arm/arm-linux-androideabi-$targetgccversion/bin;
               toolchaindir2=aarch64/aarch64-linux-android-$targetgccversion/bin
            ;;
        arm64) toolchaindir=aarch64/aarch64-linux-android-$targetgccversion/bin;
               toolchaindir2=arm/arm-linux-androideabi-$targetgccversion2/bin
            ;;
        mips|mips64) toolchaindir=mips/mips64el-linux-android-$targetgccversion/bin
            ;;
        *)
            echo "Can't find toolchain for unknown architecture: $ARCH"
            toolchaindir=xxxxxxxxx
            ;;
    esac
    if [ -d "$gccprebuiltdir/$toolchaindir" ]; then
        export ANDROID_TOOLCHAIN=$gccprebuiltdir/$toolchaindir
    fi

    if [ -d "$gccprebuiltdir/$toolchaindir2" ]; then
        export ANDROID_TOOLCHAIN_2ND_ARCH=$gccprebuiltdir/$toolchaindir2
    fi

    unset ANDROID_KERNEL_TOOLCHAIN_PATH
    case $ARCH in
        arm)
            # Legacy toolchain configuration used for ARM kernel compilation
            toolchaindir=arm/arm-eabi-$targetgccversion/bin
            if [ -d "$gccprebuiltdir/$toolchaindir" ]; then
                 export ARM_EABI_TOOLCHAIN="$gccprebuiltdir/$toolchaindir"
                 ANDROID_KERNEL_TOOLCHAIN_PATH="$ARM_EABI_TOOLCHAIN":
            fi
            ;;
        arm64)
            # Legacy toolchain configuration used for ARM kernel compilation
            toolchaindir=arm/arm-eabi-$targetgccversion2/bin
            if [ -d "$gccprebuiltdir/$toolchaindir" ]; then
                 export ARM_EABI_TOOLCHAIN="$gccprebuiltdir/$toolchaindir"
                 ANDROID_KERNEL_TOOLCHAIN_PATH="$ARM_EABI_TOOLCHAIN":
            fi
            ;;
        *)
            # No need to set ARM_EABI_TOOLCHAIN for other ARCHs
            ;;
    esac

    export ANDROID_DEV_SCRIPTS=$T/development/scripts:$T/prebuilts/devtools/tools
    export ANDROID_BUILD_PATHS=$(get_build_var ANDROID_BUILD_PATHS):$ANDROID_TOOLCHAIN:$ANDROID_TOOLCHAIN_2ND_ARCH:$ANDROID_KERNEL_TOOLCHAIN_PATH$ANDROID_DEV_SCRIPTS:

    # If prebuilts/android-emulator/<system>/ exists, prepend it to our PATH
    # to ensure that the corresponding 'emulator' binaries are used.
    case $(uname -s) in
        Darwin)
            ANDROID_EMULATOR_PREBUILTS=$T/prebuilts/android-emulator/darwin-x86_64
            ;;
        Linux)
            ANDROID_EMULATOR_PREBUILTS=$T/prebuilts/android-emulator/linux-x86_64
            ;;
        *)
            ANDROID_EMULATOR_PREBUILTS=
            ;;
    esac
    if [ -n "$ANDROID_EMULATOR_PREBUILTS" -a -d "$ANDROID_EMULATOR_PREBUILTS" ]; then
        ANDROID_BUILD_PATHS=$ANDROID_BUILD_PATHS$ANDROID_EMULATOR_PREBUILTS:
        export ANDROID_EMULATOR_PREBUILTS
    fi

    export PATH=$ANDROID_BUILD_PATHS$PATH

    unset ANDROID_JAVA_TOOLCHAIN
    unset ANDROID_PRE_BUILD_PATHS
    if [ -n "$JAVA_HOME" ]; then
        export ANDROID_JAVA_TOOLCHAIN=$JAVA_HOME/bin # 第1步骤设置的JAVA_HOME环境变量，就在这个地方被使用了。
        export ANDROID_PRE_BUILD_PATHS=$ANDROID_JAVA_TOOLCHAIN:
        export PATH=$ANDROID_PRE_BUILD_PATHS$PATH
    fi

    unset ANDROID_PRODUCT_OUT
    export ANDROID_PRODUCT_OUT=$(get_abs_build_var PRODUCT_OUT)
    export OUT=$ANDROID_PRODUCT_OUT

    unset ANDROID_HOST_OUT
    export ANDROID_HOST_OUT=$(get_abs_build_var HOST_OUT)

    # needed for building linux on MacOS
    # TODO: fix the path
    #export HOST_EXTRACFLAGS="-I "$T/system/kernel_headers/host_include
}

3.5.4、设置sequence number

function set_sequence_number()
{
    export BUILD_ENV_SEQUENCE_NUMBER=10
}

3.6、打印config

function printconfig()
{
    T=$(gettop)
    if [ ! "$T" ]; then
        echo "Couldn't locate the top of the tree.  Try setting TOP." >&2
        return
    fi
    get_build_var report_config
}

Example of printconfig
============================================
PLATFORM_VERSION_CODENAME=REL
PLATFORM_VERSION=5.1
TARGET_PRODUCT=aosp_oversea
TARGET_BUILD_VARIANT=userdebug
TARGET_BUILD_TYPE=release
TARGET_BUILD_APPS=
TARGET_ARCH=arm64
TARGET_ARCH_VARIANT=armv8-a
TARGET_CPU_VARIANT=generic
TARGET_2ND_ARCH=arm
TARGET_2ND_ARCH_VARIANT=armv7-a-neon
TARGET_2ND_CPU_VARIANT=cortex-a15
HOST_ARCH=x86_64
HOST_OS=linux
HOST_OS_EXTRA=Linux-3.5.0-23-generic-x86_64-with-Ubuntu-12.04-precise
HOST_BUILD_TYPE=release
BUILD_ID=LMY47D
OUT_DIR=out
============================================

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