Android编译流程

概述众所周知，Android系统其实就是一个运行在Linux系统上面的应用桌面程序，当然这样概括可能不是很准确，但是他们的编译确实异曲同工之妙。在Linux系统中，我们可以通过make命令来编译代码。执行Make命令默认会在当前目录找到一个Makefile文件，然后根据Makefile文件中的指令来对代码进行

众所周知，AndroID系统其实就是一个运行在linux系统上面的应用桌面程序，当然这样概括可能不是很准确，但是他们的编译确实异曲同工之妙。

在linux系统中，我们可以通过make命令来编译代码。执行Make命令默认会在当前目录找到一个Makefile文件，然后根据Makefile文件中的指令来对代码进行编译（makefile语法课参考《GNU make中文手册》）。也就是说make命令执行的是Makefile文件中的指令，Makefile文件中的指令可以是编译命令（例如gcc，也可以是其它命令）。

在AndroID系统中，随着源代码越来越复杂，光一个makefile在性能上已经满足不了，因此在该机制之上新增了自己的androID.mk和androID.bp方式，为了优雅的与makefile兼容，soong就此诞生了。

一、编译流程

Google已经给出了androID的原生编译流程：source build/envsetup.sh加载命令初始化环境、lunch选择平台、make执行编译命令。

1、初始化编译环境

进入androID源代码根目录执行命令source build/envsetup.sh即可初始化编译环境。其实该过程从source命令就可以看出主要是执行了envsetup.sh脚本且加载环境变量到当前终端。脚本envsetup.sh中其实定义了很多函数，如下：

//androID/build/envsetup.shfunction hmm() {cat <<EOFRun "m help" for help with the build system itself.Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:- lunch:      lunch <product_name>-<build_variant>              Selects <product_name> as the product to build, and <build_variant> as the variant to              build, and stores those selections in the environment to be read by subsequent              invocations of 'm' etc.- tapas:      tapas [<App1> <App2> ...] [arm|x86|mips|arm64|x86_64|mips64] [eng|userdeBUG|user]- croot:      Changes directory to the top of the tree, or a subdirectory thereof.- m:          Makes from the top of the tree.- mm:         Builds and installs all of the modules in the current directory, and their              dependencIEs.- mmm:        Builds and installs all of the modules in the supplIEd directorIEs, and their              dependencIEs.              To limit the modules being built use the Syntax: mmm dir/:target1,target2.- mma:        Same as 'mm'- mmma:       Same as 'mmm'- provision:  Flash device with all required partitions. Options will be passed on to fastboot.- cgrep:      Greps on all local C/C++ files.- ggrep:      Greps on all local Gradle files.- gogrep:     Greps on all local Go files.- jgrep:      Greps on all local Java files.- resgrep:    Greps on all local res/*.xml files.- mangrep:    Greps on all local AndroIDManifest.xml files.- mgrep:      Greps on all local Makefiles and *.bp files.- owngrep:    Greps on all local OWNERS files.- sepgrep:    Greps on all local sepolicy files.- sgrep:      Greps on all local source files.- godir:      Go to the directory containing a file.- allmod:     List all modules.- gomod:      Go to the directory containing a module.- pathmod:    Get the directory containing a module.- refreshmod: Refresh List of modules for allmod/gomod.Environment options:- SANITIZE_HOST: Set to 'address' to use ASAN for all host modules.- ANDROID_QUIET_BUILD: set to 'true' to display only the essential messages.Look at the source to vIEw more functions. The complete List is:EOF    local T=$(gettop)    local A=""    local i    for i in `cat $T/build/envsetup.sh | sed -n "/^[[:blank:]]*function /s/function \([a-z_]*\).*//p" | sort | uniq`; do      A="$A $i"    done    echo $A}# Get the exact value of a build variable.function get_build_var() { }# check to see if the supplIEd product is one we can buildfunction check_product() { }# 设置环境变量function setpaths() { }function chooseproduct() { }function add_lunch_combo() { }function print_lunch_menu() { }function lunch() { }function croot() { }function m() { }function mm() { }function make() { }# 加载执行产商定义vendorsetup.shfunction source_vendorsetup() {    unset vendOR_PYTHONPATH    allowed=    for f in $(find -L device vendor product -maxdepth 4 -name 'allowed-vendorsetup_sh-files' 2>/dev/null | sort); do        if [ -n "$allowed" ]; then            echo "More than one 'allowed_vendorsetup_sh-files' file found, not including any vendorsetup.sh files:"            echo "  $allowed"            echo "  $f"            return        fi        allowed="$f"    done    allowed_files=    [ -n "$allowed" ] && allowed_files=$(cat "$allowed")    for dir in device vendor product; do        for f in $(test -d $dir && \            find -L $dir -maxdepth 4 -name 'vendorsetup.sh' 2>/dev/null | sort); do            if [[ -z "$allowed" || "$allowed_files" =~ $f ]]; then                echo "including $f"; . "$f"            else                echo "ignoring $f, not in $allowed"            fi        done    done}valIDate_current_shellsource_vendorsetup  # 加载执行vendor分区的vendorsetup.sh  芯片产商通常会将自己的一些配置加载改文件addcompletions

source build/envsetup.sh执行之后，为当前终端加载了上面的这些函数，之后可以在该终端执行这些命令（函数名）来执行这些函数的内容，最后调用函数source_vendorsetup加载其他目录（device vendor product）下的vendorsetup.sh脚本。注意，该命令只在当前终端生效，如果未生效那么lunch和mm等命令是无法使用的。

2、选择编译平台3、开始编译 总结

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