大家平时用虚拟机编译Android系统源码的时候，无非就是下面三个步骤：
<!--[if !supportLists]-->1、<!--[endif]-->执行source?build/envsetup.sh命令
<!--[if !supportLists]-->2、<!--[endif]-->执行lunch命令，选择需要编译的系统版本
<!--[if !supportLists]-->3、<!--[endif]-->执行make命令，然后就是编译你选择好的系统版本
那么研究Android的编译过程，无非也就是研究这三个步骤各自做了哪些操作。
接下来，将会对这三个步骤进行详细的分析。
source?build/envsetup.sh这个命令就是将envsetup.sh定义的所有命令加载到环境变量中，像后面要使用的lunch、make命令就是这里定义的。打开这个脚本文件，发现里面定义了很多函数（以function为开头），下面分析一下主要函数的一些功能：
function?hmm()：显示帮助信息，列出所有支持的命令，比如lunch、mm、mmm等
function?get_abs_build_var()：获取编译时一些变量的绝对路径（比如BUILD_SYSTEM）
function?get_build_var()：获取编译时一些变量的路径
function?check_product()：检查产品是否支持编译
function?check_variant()：检查变量variant是否有效，只能是user、userdebug、eng
function?setpaths()：设置一些文件路径，并将一些编译所需的路径添加到环境变量中去
function?printconfig()：打印配置信息
function?set_sequence_number()：设置BUILD_ENV_SEQUENCE_NUMBER的值
function?settitle()：设置PROMPT_COMMAND的值
function?set_java_home()：设置java主目录
function?set_stuff_for_environment()：调用setpaths、settitle、set_java_home、set_sequence_number函数，并设置ANDROID_BUILD_TOP值为Android源码目录
function?choosetype()：选择编译类型，release和debug中的一个
function?chooseproduct()：用户输入编译产品
function?choosevariant()：用户选择variant，只能是user、userdebug、eng中的一个
function?choosecombo()：调用choosetype、chooseproduct、choosevariant等函数
function?add_lunch_combo()：增加lunch命令的选择项
function?print_lunch_menu()：打印lunch命令可选择的项目列表
function?lunch()：lunch命令的执行逻辑
function?gettop()：获取Android源码根目录
function?m()：m命令的执行逻辑
function?findmakefile()：查找当前目录下Android.mk文件路径
function?mm()：mm命令的执行逻辑
function?mmm()：mmm命令的执行逻辑
function?croot()：进入Android源码根目录
function?pid()：查看某个进程的id
function?runtest()：执行测试脚本
function?godir?()：进入用户输入文件的所在目录
function?set_java_home()：设置环境变量JAVA_HOME
除了定义了很多函数之外，还执行了下面的操作：
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
done
unset?f
?
addcompletions
?
这里的操作就是查找vendor目录和device目录下的vendorsetup.sh文件，查找到之后就执行这些脚本文件。addcompletions函数主要是查找sdk/bash_completion目录下所有的.bash文件，找到之后执行这些文件。
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1.1、执行vendorsetup.sh
vendorsetup.sh脚本都是类似“add_lunch_combo?sp7731geaplus_dt-userdebug”这样的内容，也就是调用add_lunch_combo这个函数，将各自产品添加到LUNCH_MENU_CHOICES变量中去。
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1.2、执行.bash脚本
这些脚本主要是为命令提供tab支持，有了这些tab支持，输入命令后如果某个选项忘记了，只需要敲tab键，就能获得提示，使用命令更加方便。例如sdk/bash_completion/adb.bash就是为adb命令提供tab键提示功能。
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接下来就分析一下lunch命令的流程，找到envsetup.sh脚本中lunch函数：
function?lunch()
{
????local?answer
?
????if?[?"$1"?]?;?then
????????answer=$1
????else
#如果没有输入参数，则打印出产品列表，让用户选择
????????print_lunch_menu
????????echo?-n?"Which?would?you?like??[aosp_arm-eng]?"
????????read?answer
????fi
?
????local?selection=
?
????if?[?-z?"$answer"?]
????then
????????selection=aosp_arm-eng??#默认产品为aosp_arm-eng
?
????elif?(echo?-n?$answer?|?grep?-q?-e?"^[0-9][0-9]*$")?
#用户输入的是数字
????then
????????if?[?$answer?-le?${#LUNCH_MENU_CHOICES[@]}?]
????????then
????????????selection=${LUNCH_MENU_CHOICES[$(($answer-1))]}
????????fi
????elif?(echo?-n?$answer?|?grep?-q?-e?"^[^\-][^\-]*-[^\-][^\-]*$")
#用户输入的是文字
????then
????????selection=$answer
????fi
?
????if?[?-z?"$selection"?]
????then
????????echo
????????echo?"Invalid?lunch?combo:?$answer"
????????return?1
????fi
?
????export?TARGET_BUILD_APPS=
?
#从用户的选择中提取出product
????local?product=$(echo?-n?$selection?|?sed?-e?"s/-.*$//")
?
#检查产品是否支持
????check_product?$product
#如果不支持
????if?[?$??-ne?0?]
????then
????????echo
????????echo?"**?Don‘t?have?a?product?spec?for:?‘$product‘"
????????echo?"**?Do?you?have?the?right?repo?manifest?"
????????product=
????fi
#从用户选择中提取出variant
????local?variant=$(echo?-n?$selection?|?sed?-e?"s/^[^\-]*-//")
?
#检查variant是否支持
????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
?
#设置相关环境变量的属性
????export?TARGET_PRODUCT=$product
????export?TARGET_BUILD_VARIANT=$variant
????export?TARGET_BUILD_TYPE=release
?
????echo
?
#设置编译相关环境变量属性
????set_stuff_for_environment
?
#打印配置信息
????printconfig
}
Make命令就是去执行Android源码根目录下是Makefile脚本，脚本内容如下：
###?DO?NOT?EDIT?THIS?FILE?###
include?build/core/main.mk
###?DO?NOT?EDIT?THIS?FILE?###
意思就是去加载并执行build/core/main.mk脚本。
接下来分析main.mk脚本的执行流程：
<!--[if !supportLists]-->1、<!--[endif]-->根据ANDROID_BUILD_SHELL的定义来选择编译系统需要的SHELL，分别为/bin/sh和/bin/bash
ifdef?ANDROID_BUILD_SHELL
SHELL?:=?$(ANDROID_BUILD_SHELL)
else
SHELL?:=?/bin/bash
endif
?
<!--[if !supportLists]-->2、<!--[endif]-->检查MAKE_VERSION，必须大于或等于3.81
ifeq?(,$(findstring?CYGWIN,$(shell?uname?-sm)))
ifneq?(1,$(strip?$(shell?expr?$(MAKE_VERSION)?\>=?3.81)))
endif
endif
?
<!--[if !supportLists]-->3、<!--[endif]-->定义一些编译时所需的变量值和默认目标droid（make命令不加任何参数就执行这个）
PWD?:=?$(shell?pwd)
TOP?:=?.
TOPDIR?:=
BUILD_SYSTEM?:=?$(TOPDIR)build/core
BUILD_SYSTEM_VENDOR?:=?$(TOPDIR)build/vendor
.PHONY:?droid
DEFAULT_GOAL?:=?droid
$(DEFAULT_GOAL):
?
<!--[if !supportLists]-->4、<!--[endif]-->加载一些其他的.mk脚本
include?$(BUILD_SYSTEM)/help.mk
include?$(BUILD_SYSTEM)/config.mk
include?$(BUILD_SYSTEM)/cleanbuild.mk
?
<!--[if !supportLists]-->5、<!--[endif]-->检查java版本、jdk版本、javac版本
ifeq?($(LEGACY_USE_JAVA6),)
required_version?:=?"1.7.x"
required_javac_version?:=?"1.7"
java_version?:=?$(shell?echo?‘$(java_version_str)‘?|?grep?‘^java?.*[?"]1\.7[\.?"$$]‘)
javac_version?:=?$(shell?echo?‘$(javac_version_str)‘?|?grep?‘[?"]1\.7[\.?"$$]‘)
else?#?if?LEGACY_USE_JAVA6
required_version?:=?"1.6.x"
required_javac_version?:=?"1.6"
java_version?:=?$(shell?echo?‘$(java_version_str)‘?|?grep?‘^java?.*[?"]1\.6[\.?"$$]‘)
javac_version?:=?$(shell?echo?‘$(javac_version_str)‘?|?grep?‘[?"]1\.6[\.?"$$]‘)
endif?#?if?LEGACY_USE_JAVA6
?
ifeq?($(strip?$(java_version)),)
$(info?************************************************************)
$(info?You?are?attempting?to?build?with?the?incorrect?version)
$(info?of?java.)
$(info?$(space))
$(info?Your?version?is:?$(java_version_str).)
$(info?The?required?version?is:?$(required_version))
$(info?$(space))
$(info?Please?follow?the?machine?setup?instructions?at)
$(info?$(space)$(space)$(space)$(space)https://source.android.com/source/initializing.html)
$(info?************************************************************)
$(error?stop)
endif
ifeq?($(requires_openjdk),?true)
ifeq?($(shell?echo?‘$(java_version_str)‘?|?grep?-i?openjdk),)
$(info?************************************************************)
$(info?You?asked?for?an?OpenJDK?7?build?but?your?version?is)
$(info?$(java_version_str).)
$(info?************************************************************)
$(error?stop)
endif?#?java?version?is?not?OpenJdk
else?#?if?requires_openjdk
ifneq?($(shell?echo?‘$(java_version_str)‘?|?grep?-i?openjdk),)
$(info?************************************************************)
$(info?You?are?attempting?to?build?with?an?unsupported?JDK.)
$(info?$(space))
$(info?You?use?OpenJDK?but?only?Sun/Oracle?JDK?is?supported.)
$(info?Please?follow?the?machine?setup?instructions?at)
$(info?$(space)$(space)$(space)$(space)https://source.android.com/source/download.html)
$(info?************************************************************)
$(error?stop)
endif?#?java?version?is?not?Sun?Oracle?JDK
endif?#?if?requires_openjdk
?
ifeq?($(strip?$(javac_version)),)
$(info?************************************************************)
$(info?You?are?attempting?to?build?with?the?incorrect?version)
$(info?of?javac.)
$(info?$(space))
$(info?Your?version?is:?$(javac_version_str).)
$(info?The?required?version?is:?$(required_javac_version))
$(info?$(space))
$(info?Please?follow?the?machine?setup?instructions?at)
$(info?$(space)$(space)$(space)$(space)https://source.android.com/source/download.html)
$(info?************************************************************)
$(error?stop)
endif
6、加载一些.mk脚本，并确定好TARGET_BUILD_VARIANT变量的值（user/userdebug/eng）
include?$(BUILD_SYSTEM)/definitions.mk
include?$(BUILD_SYSTEM)/dex_preopt.mk
ifneq?($(filter?user?userdebug?eng,$(MAKECMDGOALS)),)
$(info?***************************************************************)
$(info?***************************************************************)
$(info?Do?not?pass?‘$(filter?user?userdebug?eng,$(MAKECMDGOALS))‘?on?\
???????the?make?command?line.)
$(info?Set?TARGET_BUILD_VARIANT?in?buildspec.mk,?or?use?lunch?or)
$(info?choosecombo.)
$(info?***************************************************************)
$(info?***************************************************************)
$(error?stopping)
endif
?
ifneq?($(filter-out?$(INTERNAL_VALID_VARIANTS),$(TARGET_BUILD_VARIANT)),)
$(info?***************************************************************)
$(info?***************************************************************)
$(info?Invalid?variant:?$(TARGET_BUILD_VARIANT)
$(info?Valid?values?are:?$(INTERNAL_VALID_VARIANTS)
$(info?***************************************************************)
$(info?***************************************************************)
$(error?stopping)
endif
?
?
<!--[if !supportLists]-->7、<!--[endif]-->确定is_sdk_build的值（后面需要用到）
is_sdk_build?:=
?
ifneq?($(filter?sdk?win_sdk?sdk_addon,$(MAKECMDGOALS)),)
is_sdk_build?:=?true
endif
?
<!--[if !supportLists]-->8、<!--[endif]-->根据TARGET_BUILD_VARIANT的值，设置不同的ro属性
user_variant?:=?$(filter?user?userdebug,$(TARGET_BUILD_VARIANT))
enable_target_debugging?:=?true
tags_to_install?:=
ifneq?(,$(user_variant))
??ADDITIONAL_DEFAULT_PROPERTIES?+=?ro.secure=1
?
??ifeq?($(user_variant),userdebug)
????tags_to_install?+=?debug
????ADDITIONAL_BUILD_PROPERTIES?+=?dalvik.vm.lockprof.threshold=500
??else
????enable_target_debugging?:=
??endif
?
??ifeq?(,$(WITH_DEXPREOPT))
????ifeq?($(DALVIK_VM_LIB),libdvm.so)
??????ifeq?($(user_variant),user)
????????ifeq?($(HOST_OS),linux)
??????????WITH_DEXPREOPT?:=?true
????????endif
??????endif
????endif
??endif
?
else?#?!user_variant
??ADDITIONAL_BUILD_PROPERTIES?+=?ro.kernel.android.checkjni=1
??ADDITIONAL_DEFAULT_PROPERTIES?+=?ro.secure=0
??ADDITIONAL_DEFAULT_PROPERTIES?+=?ro.allow.mock.location=1
endif?#?!user_variant
?
ifeq?(true,$(strip?$(enable_target_debugging)))
??ADDITIONAL_DEFAULT_PROPERTIES?+=?ro.debuggable=1
??INCLUDE_TEST_OTA_KEYS?:=?true
else?#?!enable_target_debugging
??ADDITIONAL_DEFAULT_PROPERTIES?+=?ro.debuggable=0
endif?#?!enable_target_debugging
?
ifeq?($(TARGET_BUILD_VARIANT),eng)
tags_to_install?:=?debug?eng
ifneq?($(filter?ro.setupwizard.mode=ENABLED,?$(call?collapse-pairs,?$(ADDITIONAL_BUILD_PROPERTIES))),)
??#?Don‘t?require?the?setup?wizard?on?eng?builds
??ADDITIONAL_BUILD_PROPERTIES?:=?$(filter-out?ro.setupwizard.mode=%,\
??????????$(call?collapse-pairs,?$(ADDITIONAL_BUILD_PROPERTIES)))?\
??????????ro.setupwizard.mode=OPTIONAL
endif
ifndef?is_sdk_build
??ADDITIONAL_BUILD_PROPERTIES?+=?dalvik.vm.image-dex2oat-filter=verify-none
??ADDITIONAL_BUILD_PROPERTIES?+=?dalvik.vm.dex2oat-filter=interpret-only
endif
endif
?
?
?
?
9、判断是否sdk编译，如果是则检查MAKECMDGOALS的值并设置一些属性的值
ifdef?is_sdk_build
sdk_repo_goal?:=?$(strip?$(filter?sdk_repo,$(MAKECMDGOALS)))
MAKECMDGOALS?:=?$(strip?$(filter-out?sdk_repo,$(MAKECMDGOALS)))
?
ifneq?($(words?$(filter-out?$(INTERNAL_MODIFIER_TARGETS)?checkbuild?emulator_tests?target-files-package,$(MAKECMDGOALS))),1)
$(error?The?‘sdk‘?target?may?not?be?specified?with?any?other?targets)
endif
tags_to_install?:=?debug?eng
ADDITIONAL_BUILD_PROPERTIES?+=?xmpp.auto-presence=true
ADDITIONAL_BUILD_PROPERTIES?+=?ro.config.nocheckin=yes
else?#?!sdk
endif
?
<!--[if !supportLists]-->10、<!--[endif]-->判断PRODUCT_TAGS的值，然后设置虚拟机的一些参数
ifneq?($(filter?dalvik.gc.type-precise,$(PRODUCT_TAGS)),)??
??ADDITIONAL_BUILD_PROPERTIES?+=?dalvik.vm.dexopt-flags=m=y
endif
ADDITIONAL_BUILD_PROPERTIES?+=?net.bt.name=Android
ADDITIONAL_BUILD_PROPERTIES?+=?dalvik.vm.stack-trace-file=/data/anr/traces.txt
?
11、通过findleaves.py工具查找subdir下所有的mk文件
subdir_makefiles?:=?\
$(shell?build/tools/findleaves.py?--prune=$(OUT_DIR)?--prune=.repo?--prune=.git?$(subdirs)?Android.mk)
?
$(foreach?mk,?$(subdir_makefiles),?$(info?including?$(mk)?...)$(eval?include?$(mk)))
?
?
<!--[if !supportLists]-->12、<!--[endif]-->加载一些.mk文件
include?$(BUILD_SYSTEM)/post_clean.mk
?
ifeq?($(stash_product_vars),true)
??$(call?assert-product-vars,?__STASHED)
endif
?
include?$(BUILD_SYSTEM)/legacy_prebuilts.mk
ifneq?($(filter-out?$(GRANDFATHERED_ALL_PREBUILT),$(strip?$(notdir?$(ALL_PREBUILT)))),)
??$(warning?***?Some?files?have?been?added?to?ALL_PREBUILT.)
??$(warning?*)
??$(warning?*?ALL_PREBUILT?is?a?deprecated?mechanism?that)
??$(warning?*?should?not?be?used?for?new?files.)
??$(warning?*?As?an?alternative,?use?PRODUCT_COPY_FILES?in)
??$(warning?*?the?appropriate?product?definition.)
??$(warning?*?build/target/product/core.mk?is?the?product)
??$(warning?*?definition?used?in?all?products.)
??$(warning?*)
??$(foreach?bad_prebuilt,$(filter-out?$(GRANDFATHERED_ALL_PREBUILT),$(strip?$(notdir?$(ALL_PREBUILT)))),$(warning?*?unexpected?$(bad_prebuilt)?in?ALL_PREBUILT))
??$(warning?*)
??$(error?ALL_PREBUILT?contains?unexpected?files)
endif
?
<!--[if !supportLists]-->13、<!--[endif]-->处理编译依赖，包含32位/64位系统的编译
define?get-32-bit-modules
$(strip?$(foreach?m,$(1),\
??$(if?$(ALL_MODULES.$(m)$(TARGET_2ND_ARCH_MODULE_SUFFIX).CLASS),\
????$(m)$(TARGET_2ND_ARCH_MODULE_SUFFIX))))
endef
define?get-32-bit-modules-if-we-can
$(strip?$(foreach?m,$(1),\
??$(if?$(ALL_MODULES.$(m)$(TARGET_2ND_ARCH_MODULE_SUFFIX).CLASS),\
????$(m)$(TARGET_2ND_ARCH_MODULE_SUFFIX),
????$(m))))
endef
?
$(foreach?m,$(ALL_MODULES),\
??$(eval?r?:=?$(ALL_MODULES.$(m).REQUIRED))\
??$(if?$(r),\
????$(if?$(ALL_MODULES.$(m).FOR_2ND_ARCH),\
??????$(eval?r_r?:=?$(call?get-32-bit-modules-if-we-can,$(r))),\
??????$(if?$(filter?EXECUTABLES?SHARED_LIBRARIES,$(ALL_MODULES.$(m).CLASS)),\
????????$(eval?r_r?:=?$(r)),\
????????$(eval?r_r?:=?$(r)?$(call?get-32-bit-modules,$(r)))\
???????)\
?????)\
?????$(eval?ALL_MODULES.$(m).REQUIRED?:=?$(strip?$(r_r)))\
??)\
)
r_r?:=
?
define?add-required-deps
$(1):?|?$(2)
endef
?
?
?
14、根据FULL_BUILD的值，确定product_FILES和product_MODULES的值
ifdef?FULL_BUILD
??product_MODULES?:=?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES)
??#?Filter?out?the?overridden?packages?before?doing?expansion
??product_MODULES?:=?$(filter-out?$(foreach?p,?$(product_MODULES),?\
??????$(PACKAGES.$(p).OVERRIDES)),?$(product_MODULES))
?
??#?Resolve?the?:32?:64?module?name
??modules_32?:=?$(patsubst?%:32,%,$(filter?%:32,?$(product_MODULES)))
??modules_64?:=?$(patsubst?%:64,%,$(filter?%:64,?$(product_MODULES)))
??modules_rest?:=?$(filter-out?%:32?%:64,$(product_MODULES))
??#?Note?for?32-bit?product,?$(modules_32)?and?$(modules_64)?will?be
??#?added?as?their?original?module?names.
??product_MODULES?:=?$(call?get-32-bit-modules-if-we-can,?$(modules_32))
??product_MODULES?+=?$(modules_64)
??#?For?the?rest?we?add?both
??product_MODULES?+=?$(call?get-32-bit-modules,?$(modules_rest))
??product_MODULES?+=?$(modules_rest)
?
??$(call?expand-required-modules,product_MODULES,$(product_MODULES))
?
??product_FILES?:=?$(call?module-installed-files,?$(product_MODULES))
??ifeq?(0,1)
????$(info?product_FILES?for?$(TARGET_DEVICE)?($(INTERNAL_PRODUCT)):)
????$(foreach?p,$(product_FILES),$(info?:???$(p)))
????$(error?done)
??endif
else
??#?We‘re?not?doing?a?full?build,?and?are?probably?only?including
??#?a?subset?of?the?module?makefiles.??Don‘t?try?to?build?any?modules
??#?requested?by?the?product,?because?we?probably?won‘t?have?rules
??#?to?build?them.
??product_FILES?:=
endif
?
<!--[if !supportLists]-->15、<!--[endif]-->检查我们构建的模块是否冗余了
modules_to_check?:=?$(foreach?m,$(ALL_MODULES),$(ALL_MODULES.$(m).CHECKED))
ifneq?($(filter?all,$(MAKECMDGOALS)),)
modules_to_check?+=?$(foreach?m,$(ALL_MODULES),$(ALL_MODULES.$(m).BUILT))
endif
?
#?for?easier?debugging
modules_to_check?:=?$(sort?$(modules_to_check))
?
<!--[if !supportLists]-->16、<!--[endif]-->上面的都是配置操作，接下来就是整个项目的编译操作，确定好要生成的目标并开始编译。make默认执行droid，droid依赖于droidcore，droidcore依赖于files等等，这些依赖关系就控制着整个项目的编译流程。
.PHONY:?files
files:?prebuilt?\
????????$(modules_to_install)?\
????????$(INSTALLED_ANDROID_INFO_TXT_TARGET)
.PHONY:?droidcore
droidcore:?files?\
systemimage?\
$(INSTALLED_CHIPRAM_TARGET)?\
$(INSTALLED_UBOOT_TARGET)?\
$(INSTALLED_BOOTIMAGE_TARGET)?\
$(INSTALLED_RECOVERYIMAGE_TARGET)?\
$(INSTALLED_USERDATAIMAGE_TARGET)?\
$(INSTALLED_CACHEIMAGE_TARGET)?\
$(INSTALLED_PRODNVIMAGE_TARGET)?\
$(INSTALLED_VENDORIMAGE_TARGET)?\
$(INSTALLED_FILES_FILE)
?
?
?
这个脚本功能主要是打印出编译时的一些帮助信息
.PHONY:?help
help:
@echo
@echo?"Common?make?targets:"
@echo?"----------------------------------------------------------------------------------"
@echo?"droid???????????????????Default?target"
@echo?"clean???????????????????(aka?clobber)?equivalent?to?rm?-rf?out/"
@echo?"snod????????????????????Quickly?rebuild?the?system?image?from?built?packages"
@echo?"offline-sdk-docs????????Generate?the?HTML?for?the?developer?SDK?docs"
@echo?"doc-comment-check-docs??Check?HTML?doc?links?&?validity,?without?generating?HTML"
@echo?"libandroid_runtime??????All?the?JNI?framework?stuff"
@echo?"framework???????????????All?the?java?framework?stuff"
@echo?"services????????????????The?system?server?(Java)?and?friends"
@echo?"help????????????????????You‘re?reading?it?right?now"
?
.PHONY:?out
out:
@echo?"I‘m?sure?you‘re?nice?and?all,?but?no?thanks."
?
?
?
?
2.1、定义一些文件路径变量
SRC_DOCS:=?$(TOPDIR)docs
SRC_HEADERS?:=?\
$(TOPDIR)system/core/include?\
$(TOPDIR)hardware/libhardware/include?\
$(TOPDIR)hardware/libhardware_legacy/include?\
$(TOPDIR)hardware/ril/include?\
$(TOPDIR)libnativehelper/include?\
$(TOPDIR)frameworks/native/include?\
$(TOPDIR)frameworks/native/opengl/include?\
$(TOPDIR)frameworks/av/include?\
$(TOPDIR)frameworks/base/include
SRC_HOST_HEADERS:=$(TOPDIR)tools/include
SRC_LIBRARIES:=?$(TOPDIR)libs
SRC_SERVERS:=?$(TOPDIR)servers
SRC_TARGET_DIR?:=?$(TOPDIR)build/target
SRC_API_DIR?:=?$(TOPDIR)prebuilts/sdk/api
SRC_SYSTEM_API_DIR?:=?$(TOPDIR)prebuilts/sdk/system-api
SRC_DROIDDOC_DIR?:=?$(TOPDIR)build/tools/droiddoc
?
2.2、加载pathmap.mk脚本文件，这个文件主要定义了一些绝对路径变量，便于其他脚本调用。
include?$(BUILD_SYSTEM)/pathmap.mk
?
2.3、定义一些重要编译命令
BUILD_COMBOS:=?$(BUILD_SYSTEM)/combo
?
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?:=?$(BUILD_SYSTEM)/host_native_test.mk
?
BUILD_SHARED_TEST_LIBRARY?:=?$(BUILD_SYSTEM)/shared_test_lib.mk
BUILD_HOST_SHARED_TEST_LIBRARY?:=?$(BUILD_SYSTEM)/host_shared_test_lib.mk
BUILD_STATIC_TEST_LIBRARY?:=?$(BUILD_SYSTEM)/static_test_lib.mk
BUILD_HOST_STATIC_TEST_LIBRARY?:=?$(BUILD_SYSTEM)/host_static_test_lib.mk
?
BUILD_NOTICE_FILE?:=?$(BUILD_SYSTEM)/notice_files.mk
BUILD_HOST_DALVIK_JAVA_LIBRARY?:=?$(BUILD_SYSTEM)/host_dalvik_java_library.mk
BUILD_HOST_DALVIK_STATIC_JAVA_LIBRARY?:=?$(BUILD_SYSTEM)/host_dalvik_static_java_library.mk
?
#############?vendor?configs?################
BUILD_THEME_PACKAGE?:=?$(BUILD_SYSTEM_VENDOR)/themepackage.mk
BUILD_ADDON_PACKAGE?:=?$(BUILD_PACKAGE)
APPLY_PRODUCT_REVISION:=?build/vendor/product_config.mk
其中CLEAR_VARS：用来清除之前定义的环境变量
BUILD_SHARED_LIBRARY：用来指定编译动态库过程
?
?
2.4、打包后缀名的设置
COMMON_PACKAGE_SUFFIX?:=?.zip
COMMON_JAVA_PACKAGE_SUFFIX?:=?.jar
COMMON_ANDROID_PACKAGE_SUFFIX?:=?.apk
?
2.5、加载一些其他mk文件
ifndef?ANDROID_BUILDSPEC
ANDROID_BUILDSPEC?:=?$(TOPDIR)buildspec.mk
endif
-include?$(ANDROID_BUILDSPEC)
?
#?---------------------------------------------------------------
#?Define?most?of?the?global?variables.??These?are?the?ones?that
#?are?specific?to?the?user‘s?build?configuration.
include?$(BUILD_SYSTEM)/envsetup.mk
....
include?$(BUILD_SYSTEM)/combo/select.mk
?
2.6、判断支持32位编译还是64位编译
ifeq?(,$(TARGET_CPU_ABI_LIST))
??ifeq?($(TARGET_IS_64_BIT)|$(TARGET_PREFER_32_BIT_APPS),true|true)
????TARGET_CPU_ABI_LIST?:=?$(TARGET_CPU_ABI_LIST_32_BIT)?$(TARGET_CPU_ABI_LIST_64_BIT)
??else
????TARGET_CPU_ABI_LIST?:=?$(TARGET_CPU_ABI_LIST_64_BIT)?$(TARGET_CPU_ABI_LIST_32_BIT)
??endif
endif
?
2.7、加载javac.mk脚本
include?$(BUILD_SYSTEM)/combo/javac.mk
?
2.8、设置一些命令的变量（比如aapt、aidl等）
AAPT?:=?$(HOST_OUT_EXECUTABLES)/aapt$(HOST_EXECUTABLE_SUFFIX)
AIDL?:=?$(HOST_OUT_EXECUTABLES)/aidl$(HOST_EXECUTABLE_SUFFIX)
PROTOC?:=?$(HOST_OUT_EXECUTABLES)/aprotoc$(HOST_EXECUTABLE_SUFFIX)
SIGNAPK_JAR?:=?$(HOST_OUT_JAVA_LIBRARIES)/signapk$(COMMON_JAVA_PACKAGE_SUFFIX)
MKBOOTFS?:=?$(HOST_OUT_EXECUTABLES)/mkbootfs$(HOST_EXECUTABLE_SUFFIX)
MINIGZIP?:=?$(HOST_OUT_EXECUTABLES)/minigzip$(HOST_EXECUTABLE_SUFFIX)
ifeq?(,$(strip?$(BOARD_CUSTOM_MKBOOTIMG)))
MKBOOTIMG?:=?$(HOST_OUT_EXECUTABLES)/mkbootimg$(HOST_EXECUTABLE_SUFFIX)
else
MKBOOTIMG?:=?$(BOARD_CUSTOM_MKBOOTIMG)
endif
MKYAFFS2?:=?$(HOST_OUT_EXECUTABLES)/mkyaffs2image$(HOST_EXECUTABLE_SUFFIX)
APICHECK?:=?$(HOST_OUT_EXECUTABLES)/apicheck$(HOST_EXECUTABLE_SUFFIX)
FS_GET_STATS?:=?$(HOST_OUT_EXECUTABLES)/fs_get_stats$(HOST_EXECUTABLE_SUFFIX)
MKEXT2IMG?:=?$(HOST_OUT_EXECUTABLES)/genext2fs$(HOST_EXECUTABLE_SUFFIX)
MAKE_EXT4FS?:=?$(HOST_OUT_EXECUTABLES)/make_ext4fs$(HOST_EXECUTABLE_SUFFIX)
MKEXTUSERIMG?:=?$(HOST_OUT_EXECUTABLES)/mkuserimg.sh
MAKE_F2FS?:=?$(HOST_OUT_EXECUTABLES)/make_f2fs$(HOST_EXECUTABLE_SUFFIX)
MKF2FSUSERIMG?:=?$(HOST_OUT_EXECUTABLES)/mkf2fsuserimg.sh
MKEXT2BOOTIMG?:=?external/genext2fs/mkbootimg_ext2.sh
SIMG2IMG?:=?$(HOST_OUT_EXECUTABLES)/simg2img$(HOST_EXECUTABLE_SUFFIX)
E2FSCK?:=?$(HOST_OUT_EXECUTABLES)/e2fsck$(HOST_EXECUTABLE_SUFFIX)
MKTARBALL?:=?build/tools/mktarball.sh
TUNE2FS?:=?$(HOST_OUT_EXECUTABLES)/tune2fs$(HOST_EXECUTABLE_SUFFIX)
E2FSCK?:=?$(HOST_OUT_EXECUTABLES)/e2fsck$(HOST_EXECUTABLE_SUFFIX)
JARJAR?:=?$(HOST_OUT_JAVA_LIBRARIES)/jarjar.jar
PROGUARD?:=?external/proguard/bin/proguard.sh
JAVATAGS?:=?build/tools/java-event-log-tags.py
LLVM_RS_CC?:=?$(HOST_OUT_EXECUTABLES)/llvm-rs-cc$(HOST_EXECUTABLE_SUFFIX)
BCC_COMPAT?:=?$(HOST_OUT_EXECUTABLES)/bcc_compat$(HOST_EXECUTABLE_SUFFIX)
LINT?:=?prebuilts/sdk/tools/lint
RMTYPEDEFS?:=?$(HOST_OUT_EXECUTABLES)/rmtypedefs
APPEND2SIMG?:=?$(HOST_OUT_EXECUTABLES)/append2simg
VERITY_SIGNER?:=?$(HOST_OUT_EXECUTABLES)/verity_signer
BUILD_VERITY_TREE?:=?$(HOST_OUT_EXECUTABLES)/build_verity_tree
BOOT_SIGNER?:=?$(HOST_OUT_EXECUTABLES)/boot_signer
?
2.9、执行shell脚本去查找jdk的tools和jar，根据系统环境的不同（OS、32位和64位）执行不同的java操作
ifeq?($(HOST_OS),darwin)
ifeq?($(LEGACY_USE_JAVA6),)
HOST_JDK_TOOLS_JAR:=?$(shell?$(BUILD_SYSTEM)/find-jdk-tools-jar.sh)
else
#?Deliberately?set?to?blank?for?Java?6?installations?on?MacOS.?These
#?versions?allegedly?use?a?non-standard?directory?structure.
HOST_JDK_TOOLS_JAR?:=
endif
else
HOST_JDK_TOOLS_JAR:=?$(shell?$(BUILD_SYSTEM)/find-jdk-tools-jar.sh)
endif
?
ifneq?($(HOST_JDK_TOOLS_JAR),)
ifeq?($(wildcard?$(HOST_JDK_TOOLS_JAR)),)
$(error?Error:?could?not?find?jdk?tools.jar,?please?check?if?your?JDK?was?installed?correctly)
endif
endif
?
2.10、根据TARGET_BUILD_VARIANT（debug、user、userdebug）的不同，设置不同的签名
ifdef?PRODUCT_DEFAULT_DEV_CERTIFICATE
??DEFAULT_SYSTEM_DEV_CERTIFICATE?:=?$(PRODUCT_DEFAULT_DEV_CERTIFICATE)
else
ifeq?($(strip?$(TARGET_BUILD_VARIANT)),user)
??DEFAULT_SYSTEM_DEV_CERTIFICATE?:=?build/target/product/security/release/releasekey
??BUILD_KEYS?:=?release-keys
else
??DEFAULT_SYSTEM_DEV_CERTIFICATE?:=?build/target/product/security/testkey
endif
endif
?
?
?
2.11、DEX2OAT运行的一些变量配置
DEX2OAT_TARGET_ARCH?:=?$(TARGET_ARCH)
DEX2OAT_TARGET_CPU_VARIANT?:=?$(TARGET_CPU_VARIANT)
DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES?:=?default
ifneq?(,$(filter?$(DEX2OAT_TARGET_CPU_VARIANT),cortex-a7?cortex-a15?krait?denver))
??DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES?:=?div
endif
?
ifdef?TARGET_2ND_ARCH
$(TARGET_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_ARCH?:=?$(TARGET_2ND_ARCH)
$(TARGET_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_CPU_VARIANT?:=?$(TARGET_2ND_CPU_VARIANT)
$(TARGET_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES?:=?default
ifneq?(,$(filter?$($(TARGET_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_CPU_VARIANT),cortex-a7?cortex-a15?krait?denver))
??$(TARGET_2ND_ARCH_VAR_PREFIX)DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES?:=?div
endif
endif
?
3.1、加载version_defaults.mk脚本
include?$(BUILD_SYSTEM)/version_defaults.mk
?
3.2、设置一些变量的值
#?---------------------------------------------------------------
#?If?you?update?the?build?system?such?that?the?environment?setup
#?or?buildspec.mk?need?to?be?updated,?increment?this?number,?and
#?people?who?haven‘t?re-run?those?will?have?to?do?so?before?they
#?can?build.??Make?sure?to?also?update?the?corresponding?value?in
#?buildspec.mk.default?and?envsetup.sh.
CORRECT_BUILD_ENV_SEQUENCE_NUMBER?:=?10
?
#?---------------------------------------------------------------
#?The?product?defaults?to?generic?on?hardware
#?NOTE:?This?will?be?overridden?in?product_config.mk?if?make
#?was?invoked?with?a?PRODUCT-xxx-yyy?goal.
ifeq?($(TARGET_PRODUCT),)
TARGET_PRODUCT?:=?full
endif
?
?
#?the?variant?--?the?set?of?files?that?are?included?for?a?build
ifeq?($(strip?$(TARGET_BUILD_VARIANT)),)
TARGET_BUILD_VARIANT?:=?eng
endif
?
3.3、根据shell命令uname?-sm执行结果，也就是当前编译系统的环境，来设置一些变量的值，我这边虚拟机运行的结果是：Linux?x86_64
UNAME?:=?$(shell?uname?-sm)
?
#?HOST_OS
ifneq?(,$(findstring?Linux,$(UNAME)))
??HOST_OS?:=?linux
endif
ifneq?(,$(findstring?Darwin,$(UNAME)))
??HOST_OS?:=?darwin
endif
ifneq?(,$(findstring?Macintosh,$(UNAME)))
??HOST_OS?:=?darwin
endif
ifneq?(,$(findstring?CYGWIN,$(UNAME)))
??HOST_OS?:=?windows
endif
?
#?BUILD_OS?is?the?real?host?doing?the?build.
BUILD_OS?:=?$(HOST_OS)
?
#?Under?Linux,?if?USE_MINGW?is?set,?we?change?HOST_OS?to?Windows?to?build?the
#?Windows?SDK.?Only?a?subset?of?tools?and?SDK?will?manage?to?build?properly.
ifeq?($(HOST_OS),linux)
ifneq?($(USE_MINGW),)
??HOST_OS?:=?windows
endif
endif
?
ifeq?($(HOST_OS),)
$(error?Unable?to?determine?HOST_OS?from?uname?-sm:?$(UNAME)!)
endif
?
#?TODO:?Replace?BUILD_HOST_64bit?with?a?flag?that?forces?32-bit?build,
#?after?we?default?to?64-bit?host?build.
ifeq?(,$(BUILD_HOST_64bit))
#?Default?to?32-bit-by-default?multilib?host?build.
HOST_PREFER_32_BIT?:=?true
endif
?
#?HOST_ARCH
ifneq?(,$(findstring?x86_64,$(UNAME)))
??HOST_ARCH?:=?x86_64
??HOST_2ND_ARCH?:=?x86
??HOST_IS_64_BIT?:=?true
endif
?
ifeq?($(HOST_PREFER_32_BIT),true)
SDK_HOST_ARCH?:=?x86
else
SDK_HOST_ARCH?:=?$(HOST_ARCH)
endif
?
BUILD_ARCH?:=?$(HOST_ARCH)
BUILD_2ND_ARCH?:=?$(HOST_2ND_ARCH)
?
ifeq?($(HOST_ARCH),)
$(error?Unable?to?determine?HOST_ARCH?from?uname?-sm:?$(UNAME)!)
endif
?
#?the?host?build?defaults?to?release,?and?it?must?be?release?or?debug
ifeq?($(HOST_BUILD_TYPE),)
HOST_BUILD_TYPE?:=?release
endif
?
ifneq?($(HOST_BUILD_TYPE),release)
ifneq?($(HOST_BUILD_TYPE),debug)
$(error?HOST_BUILD_TYPE?must?be?either?release?or?debug,?not?‘$(HOST_BUILD_TYPE)‘)
endif
endif
?
#?We?don‘t?want?to?move?all?the?prebuilt?host?tools?to?a?$(HOST_OS)-x86_64?dir.
HOST_PREBUILT_ARCH?:=?x86
#?This?is?the?standard?way?to?name?a?directory?containing?prebuilt?host
#?objects.?E.g.,?prebuilt/$(HOST_PREBUILT_TAG)/cc
ifeq?($(HOST_OS),windows)
??HOST_PREBUILT_TAG?:=?windows
else
??HOST_PREBUILT_TAG?:=?$(HOST_OS)-$(HOST_PREBUILT_ARCH)
endif
?
?
3.4、设置输出目录名称
TARGET_COPY_OUT_SYSTEM?:=?system
TARGET_COPY_OUT_DATA?:=?data
TARGET_COPY_OUT_OEM?:=?oem
TARGET_COPY_OUT_ROOT?:=?root
TARGET_COPY_OUT_RECOVERY?:=?recovery
?
3.5、加载product_config.mk脚本
include?$(BUILD_SYSTEM)/product_config.mk
?
3.6、根据TARGET_DEVICE的值寻找BoardConfig.mk脚本并加载
board_config_mk?:=?\
$(strip?$(wildcard?\
$(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)/BoardConfig.mk?\
$(shell?test?-d?device?&&?find?device?-maxdepth?4?-path?‘*/$(TARGET_DEVICE)/BoardConfig.mk‘)?\
$(shell?test?-d?vendor?&&?find?vendor?-maxdepth?4?-path?‘*/$(TARGET_DEVICE)/BoardConfig.mk‘)?\
))
ifeq?($(board_config_mk),)
??$(error?No?config?file?found?for?TARGET_DEVICE?$(TARGET_DEVICE))
endif
ifneq?($(words?$(board_config_mk)),1)
??$(error?Multiple?board?config?files?for?TARGET_DEVICE?$(TARGET_DEVICE):?$(board_config_mk))
endif
include?$(board_config_mk)
?
3.7、根据系统环境设置输出目录的路径
TARGET_OS?:=?linux
#?TARGET_ARCH?should?be?set?by?BoardConfig.mk?and?will?be?checked?later
ifneq?($(filter?%64,$(TARGET_ARCH)),)
TARGET_IS_64_BIT?:=?true
endif
?
#?the?target?build?type?defaults?to?release
ifneq?($(TARGET_BUILD_TYPE),debug)
TARGET_BUILD_TYPE?:=?release
endif
?
#?---------------------------------------------------------------
#?figure?out?the?output?directories
?
ifeq?(,$(strip?$(OUT_DIR)))
ifeq?(,$(strip?$(OUT_DIR_COMMON_BASE)))
OUT_DIR?:=?$(TOPDIR)out
else
OUT_DIR?:=?$(OUT_DIR_COMMON_BASE)/$(notdir?$(PWD))
endif
endif
?
DEBUG_OUT_DIR?:=?$(OUT_DIR)/debug
?
#?Move?the?host?or?target?under?the?debug/?directory
#?if?necessary.
TARGET_OUT_ROOT_release?:=?$(OUT_DIR)/target
TARGET_OUT_ROOT_debug?:=?$(DEBUG_OUT_DIR)/target
TARGET_OUT_ROOT?:=?$(TARGET_OUT_ROOT_$(TARGET_BUILD_TYPE))
?
HOST_OUT_ROOT_release?:=?$(OUT_DIR)/host
HOST_OUT_ROOT_debug?:=?$(DEBUG_OUT_DIR)/host
HOST_OUT_ROOT?:=?$(HOST_OUT_ROOT_$(HOST_BUILD_TYPE))
?
4.1、定义函数find-copy-subdir-files，执行shell命令查找子目录下指定文件用于PRODUCT_COPY_FILES和PRODUCT_SDK_ADDON_COPY_FILES
###########################################################
##?List?all?of?the?files?in?a?subdirectory?in?a?format
##?suitable?for?PRODUCT_COPY_FILES?and
##?PRODUCT_SDK_ADDON_COPY_FILES
##
##?$(1):?Glob?to?match?file?name
##?$(2):?Source?directory
##?$(3):?Target?base?directory
###########################################################
?
define?find-copy-subdir-files
$(shell?find?$(2)?-name?"$(1)"?|?$(SED_EXTENDED)?"s:($(2)/?(.*)):\\1\\:$(3)/\\2:"?|?sed?"s://:/:g")
endef
?
4.2、确定TARGET_BUILD_VARIANT和TARGET_PRODUCT的值
#?These?are?the?valid?values?of?TARGET_BUILD_VARIANT.??Also,?if?anything?else?is?passed
#?as?the?variant?in?the?PRODUCT-$TARGET_BUILD_PRODUCT-$TARGET_BUILD_VARIANT?form,
#?it?will?be?treated?as?a?goal,?and?the?eng?variant?will?be?used.
INTERNAL_VALID_VARIANTS?:=?user?userdebug?eng
?
#?---------------------------------------------------------------
#?Provide?"PRODUCT-<prodname>-<goal>"?targets,?which?lets?you?build
#?a?particular?configuration?without?needing?to?set?up?the?environment.
#
product_goals?:=?$(strip?$(filter?PRODUCT-%,$(MAKECMDGOALS)))
ifdef?product_goals
??#?Scrape?the?product?and?build?names?out?of?the?goal,
??#?which?should?be?of?the?form?PRODUCT-<productname>-<buildname>.
??#
??ifneq?($(words?$(product_goals)),1)
????$(error?Only?one?PRODUCT-*?goal?may?be?specified;?saw?"$(product_goals)")
??endif
??goal_name?:=?$(product_goals)
??product_goals?:=?$(patsubst?PRODUCT-%,%,$(product_goals))
??product_goals?:=?$(subst?-,?,$(product_goals))
??ifneq?($(words?$(product_goals)),2)
????$(error?Bad?PRODUCT-*?goal?"$(goal_name)")
??endif
?
??#?The?product?they?want
??TARGET_PRODUCT?:=?$(word?1,$(product_goals))
?
??#?The?variant?they?want
??TARGET_BUILD_VARIANT?:=?$(word?2,$(product_goals))
??ifeq?($(TARGET_BUILD_VARIANT),tests)
????$(error?"tests"?has?been?deprecated?as?a?build?variant.?Use?it?as?a?build?goal?instead.)
??endif
?
??#?The?build?server?wants?to?do?make?PRODUCT-dream-installclean
??#?which?really?means?TARGET_PRODUCT=dream?make?installclean.
??ifneq?($(filter-out?$(INTERNAL_VALID_VARIANTS),$(TARGET_BUILD_VARIANT)),)
????MAKECMDGOALS?:=?$(MAKECMDGOALS)?$(TARGET_BUILD_VARIANT)
????TARGET_BUILD_VARIANT?:=?eng
????default_goal_substitution?:=
??else
????default_goal_substitution?:=?$(DEFAULT_GOAL)
??endif
?
4.3、加载一些其他的mk脚本
include?$(BUILD_SYSTEM)/node_fns.mk
include?$(BUILD_SYSTEM)/product.mk
include?$(BUILD_SYSTEM)/device.mk
?
4.4、搜索所有的AndroidProducts.mk文件，找到当前产品的配置文件
ifneq?($(strip?$(TARGET_BUILD_APPS)),)
#?An?unbundled?app?build?needs?only?the?core?product?makefiles.
all_product_configs?:=?$(call?get-product-makefiles,\
????$(SRC_TARGET_DIR)/product/AndroidProducts.mk)
else
#?Read?in?all?of?the?product?definitions?specified?by?the?AndroidProducts.mk
#?files?in?the?tree.
all_product_configs?:=?$(get-all-product-makefiles)
endif
?
#?Find?the?product?config?makefile?for?the?current?product.
#?all_product_configs?consists?items?like:
#?<product_name>:<path_to_the_product_makefile>
#?or?just?<path_to_the_product_makefile>?in?case?the?product?name?is?the
#?same?as?the?base?filename?of?the?product?config?makefile.
current_product_makefile?:=
all_product_makefiles?:=
$(foreach?f,?$(all_product_configs),\
????$(eval?_cpm_words?:=?$(subst?:,$(space),$(f)))\
????$(eval?_cpm_word1?:=?$(word?1,$(_cpm_words)))\
????$(eval?_cpm_word2?:=?$(word?2,$(_cpm_words)))\
????$(if?$(_cpm_word2),\
????????$(eval?all_product_makefiles?+=?$(_cpm_word2))\
????????$(if?$(filter?$(TARGET_PRODUCT),$(_cpm_word1)),\
????????????$(eval?current_product_makefile?+=?$(_cpm_word2)),),\
????????$(eval?all_product_makefiles?+=?$(f))\
????????$(if?$(filter?$(TARGET_PRODUCT),$(basename?$(notdir?$(f)))),\
????????????$(eval?current_product_makefile?+=?$(f)),)))
_cpm_words?:=
_cpm_word1?:=
_cpm_word2?:=
current_product_makefile?:=?$(strip?$(current_product_makefile))
all_product_makefiles?:=?$(strip?$(all_product_makefiles))
?
4.5、调用clear-var-list函数去清除一些变量，并设置产品的运行时态product_runtimes
$(call?clear-var-list,?$(_product_var_list))
?
#?Set?PRODUCT_RUNTIMES,?allowing?buildspec?to?override?using?OVERRIDE_RUNTIMES
product_runtimes?:=?$(sort?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_RUNTIMES))
ifneq?($(OVERRIDE_RUNTIMES),)
??$(info?Overriding?PRODUCT_RUNTIMES=$(product_runtimes)?with?$(OVERRIDE_RUNTIMES))
??product_runtimes?:=?$(OVERRIDE_RUNTIMES)
endif
$(foreach?runtime,?$(product_runtimes),?$(eval?include?$(SRC_TARGET_DIR)/product/$(runtime).mk))
$(foreach?v,?$(_product_var_list),?$(if?$($(v)),\
????$(eval?PRODUCTS.$(INTERNAL_PRODUCT).$(v)?+=?$(sort?$($(v))))))
?
$(call?clear-var-list,?$(_product_var_list))
#?Now?we?can?assign?to?PRODUCT_RUNTIMES
PRODUCT_RUNTIMES?:=?$(product_runtimes)
product_runtimes?:=
?
PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PROPERTY_OVERRIDES?+=?persist.sys.dalvik.vm.lib.2=$(DALVIK_VM_LIB)
?
ifeq?($(words?$(PRODUCT_RUNTIMES)),1)
??#?If?we?only?have?one?runtime,?we?can?strip?classes.dex?by?default?during?dex_preopt
??DEX_PREOPT_DEFAULT?:=?true
else
??#?If?we?have?more?than?one,?we?leave?the?classes.dex?alone?for?post-boot?analysis
??DEX_PREOPT_DEFAULT?:=?nostripping
endif
?
4.6、获取BOOTCLASSPATH中的所有jar文件
#?A?list?of?module?names?of?BOOTCLASSPATH?(jar?files)
PRODUCT_BOOT_JARS?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_BOOT_JARS))
PRODUCT_SYSTEM_SERVER_JARS?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SYSTEM_SERVER_JARS))
?
?
?
?
4.7、设置TARGET_DEVICE和PRODUCT_LOCALES的值
#?Find?the?device?that?this?product?maps?to.
TARGET_DEVICE?:=?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_DEVICE)
?
#?Figure?out?which?resoure?configuration?options?to?use?for?this
#?product.
PRODUCT_LOCALES?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_LOCALES))
#?TODO:?also?keep?track?of?things?like?"port",?"land"?in?product?files.
?
#?If?CUSTOM_LOCALES?contains?any?locales?not?already?included
#?in?PRODUCT_LOCALES,?add?them?to?PRODUCT_LOCALES.
extra_locales?:=?$(filter-out?$(PRODUCT_LOCALES),$(CUSTOM_LOCALES))
ifneq?(,$(extra_locales))
??ifneq?($(CALLED_FROM_SETUP),true)
????#?Don‘t?spam?stdout,?because?envsetup.sh?may?be?scraping?values?from?it.
????$(info?Adding?CUSTOM_LOCALES?[$(extra_locales)]?to?PRODUCT_LOCALES?[$(PRODUCT_LOCALES)])
??endif
??PRODUCT_LOCALES?+=?$(extra_locales)
??extra_locales?:=
endif
?
4.8、配置aapt的相关属性
#?Add?PRODUCT_LOCALES?to?PRODUCT_AAPT_CONFIG
PRODUCT_AAPT_CONFIG?:=?$(strip?$(PRODUCT_LOCALES)?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_AAPT_CONFIG))
PRODUCT_AAPT_PREF_CONFIG?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_AAPT_PREF_CONFIG))
PRODUCT_AAPT_PREBUILT_DPI?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_AAPT_PREBUILT_DPI))
?
#?Keep?a?copy?of?the?space-separated?config
PRODUCT_AAPT_CONFIG_SP?:=?$(PRODUCT_AAPT_CONFIG)
?
#?Convert?spaces?to?commas.
PRODUCT_AAPT_CONFIG?:=?\
????$(subst?$(space),$(comma),$(strip?$(PRODUCT_AAPT_CONFIG)))
?
#?product-scoped?aapt?flags
PRODUCT_AAPT_FLAGS?:=
ifneq?($(filter?en_XA?ar_XB,$(PRODUCT_LOCALES)),)
#?Force?generating?resources?for?pseudo-locales.
PRODUCT_AAPT_FLAGS?+=?--pseudo-localize
endif
4.9、设置一些变量的值
PRODUCT_BRAND?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_BRAND))
?
PRODUCT_MODEL?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_MODEL))
ifndef?PRODUCT_MODEL
??PRODUCT_MODEL?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_NAME))
endif
?
PRODUCT_MANUFACTURER?:=?\
????$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_MANUFACTURER))
ifndef?PRODUCT_MANUFACTURER
??PRODUCT_MANUFACTURER?:=?unknown
endif
?
ifeq?($(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_CHARACTERISTICS),)
??TARGET_AAPT_CHARACTERISTICS?:=?default
else
??TARGET_AAPT_CHARACTERISTICS?:=?$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_CHARACTERISTICS))
endif
?
PRODUCT_DEFAULT_WIFI_CHANNELS?:=?\
????$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_DEFAULT_WIFI_CHANNELS))
?
PRODUCT_DEFAULT_DEV_CERTIFICATE?:=?\
????$(strip?$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_DEFAULT_DEV_CERTIFICATE))
ifdef?PRODUCT_DEFAULT_DEV_CERTIFICATE
ifneq?(1,$(words?$(PRODUCT_DEFAULT_DEV_CERTIFICATE)))
????$(error?PRODUCT_DEFAULT_DEV_CERTIFICATE=‘$(PRODUCT_DEFAULT_DEV_CERTIFICATE)‘,?\
??????only?1?certificate?is?allowed.)
endif
endif
?
这个脚本主要是定义了很多函数，相当于一个函数库用于编译所需
define?print-vars
$(foreach?var,$(1),?\
??$(info?$(var):)?\
??$(foreach?word,$($(var)),?\
????$(info?$(space)$(space)$(word))?\
???)?\
?)
endef
?
define?true-or-empty
$(filter?true,?$(1))
endef
?
define?my-dir
$(strip?\
??$(eval?LOCAL_MODULE_MAKEFILE?:=?$$(lastword?$$(MAKEFILE_LIST)))?\
??$(if?$(filter?$(BUILD_SYSTEM)/%?$(OUT_DIR)/%,$(LOCAL_MODULE_MAKEFILE)),?\
????$(error?my-dir?must?be?called?before?including?any?other?makefile.)?\
???,?\
????$(patsubst?%/,%,$(dir?$(LOCAL_MODULE_MAKEFILE)))?\
???)?\
?)
endef
?
Android.mk是用来向编译系统描述你的源代码，也就是告诉编译系统你的源代码需要编译成什么样。你可以在一个Android.mk文件中定义一个或者多个模块，模块的类型包括：
???1）APK程序，一般的Android程序，编译打包生成apk文件
???2）Java库，java类库，编译打包生成jar文件
???3)??C\C++应用程序，可执行的C\C++应用程序
???4）C\C++静态库，编译生成C\C++静态库，并打包成.a文件
???5）C\C++共享库，?编译生成共享库（动态链接库），并打包成.so文件，有且只有共享库才能被安装/复制到您的应用软件（APK）包中。
下面是一个Android.mk的例子：
LOCAL_PATH?:=?$(call?my-dir)
include?$(CLEAR_VARS)
LOCAL_MODULE????????:=?settings_talpa
LOCAL_MODULE_TAGS???:=?optional
LOCAL_MODULE_CLASS??:=?APPS
LOCAL_MODULE_SUFFIX?:=?.apk
LOCAL_SRC_FILES?????:=?Settings.apk
LOCAL_MODULE_PATH???:=?$(TARGET_OUT_APPS_PRIVILEGED)
LOCAL_CERTIFICATE???:=?platform
LOCAL_OVERRIDES_PACKAGES?:=?Settings
include?$(BUILD_PREBUILT)
接下来根据这个例子来解释每一行代码
<!--[if !supportLists]-->1、<!--[endif]-->LOCAL_PATH?:=?$(call?my-dir)
每个Android.mk必须定义LOCAL_PATH这个变量，它用于在开发树中查找源文件。my-dir是一个函数名，由编译系统提供，用于返回当前Android.mk的目录路径。$(call?my-dir)表示的就是去调用my-dir这个函数
?
2、include?$(CLEAR_VARS)
CLEAR_VARS是由编译系统提供的变量，config.mk文件中能找到其定义，前面也提到过，它的值是$(BUILD_SYSTEM)/clear_vars.mk，这句代码表示去加载并执行这个mk脚本，清理掉local_xxx这样的一些变量。
?
<!--[if !supportLists]-->3、<!--[endif]-->LOCAL_MODULE????????:=?settings_talpa
LOCAL_MODULE也是必须定义的变量，表示模块的名字，这个名字必须唯一且不包含空格。编译系统会自动添加适当的前缀和后缀。
?
4、LOCAL_MODULE_TAGS???:=?optional
LOCAL_MODULE_TAGS表示当前模块在哪种模式下编译，模式包含user?eng?tests?optional。
user:?指该模块只在user版本下才编译
eng:?指该模块只在eng版本下才编译
tests:?指该模块只在tests版本下才编译
optional:指该模块在所有版本下都编译
?
5、LOCAL_MODULE_CLASS??:=?APPS
LOCAL_MODULE_CLASS?指定模块的文件类型，apk文件用APPS,?并且?会检查?是否是apk文件，动态库so文件用SHARED_LIBRARIES?，bin文件用EXECUTABLES，其他文件?用ETC
?
6、LOCAL_MODULE_SUFFIX?:=?.apk
LOCAL_MODULE_SUFFIX指定模块的后缀
?
<!--[if !supportLists]-->7、<!--[endif]-->LOCAL_SRC_FILES
LOCAL_SRC_FILES指定需要打包进模块的文件
?
<!--[if !supportLists]-->8、<!--[endif]-->LOCAL_MODULE_PATH
LOCAL_MODULE_PATH指定模块的安装路径
$(TARGET_OUT_APPS_PRIVILEGED):system/priv-app/
$(TARGET_OUT_APPS):system/app/
?
9、LOCAL_CERTIFICATE???:=?platform
LOCAL_CERTIFICATE指定模块的签名key值，包含media、shared、platform、PRESIGNED（表示已经签过名，不需要签名）
?
<!--[if !supportLists]-->10、<!--[endif]-->LOCAL_OVERRIDES_PACKAGES?:=?Settings
LOCAL_OVERRIDES_PACKAGES表示当前模块需要覆盖系统原有的哪个模块名
?
11、include?$(BUILD_PREBUILT)
这句代码同样也是加载其他的脚本
BUILD_PACKAGE：指向build/core/package.mk，用来编译APK文件。
?????BUILD_JAVA_LIBRARY：指向build/core/java_library.mk，用来编译Java库文件。
???????BUILD_STATIC_JAVA_LIBRARY：指向build/core/tatic_java_library.mk，用来编译Java静态库文件。
???????BUILD_STATIC_LIBRARY：指向build/core/static_library.mk，用来编译静态库文件。也就是.a文件。
???????BUILD_EXECUTABLE：指向build/core/executable.mk，用来编译可执行文件。
???????BUILD_PREBUILT：指向build/core/prebuilt.mk。用来编译已经预编译好的第三方库文件，实际上是将这些预编译好的第三方库文件拷贝到合适的位置去，以便可以让其它模块引用。
?
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我们知道Android平台分为四层架构，分别是应用程序层、应用框架层、运行库层和Linux内核层，这四层架构和Android源码目录的对应关系如下：
<!--[if !supportLists]-->1、<!--[endif]-->应用程序层对应的是packages/apps
<!--[if !supportLists]-->2、<!--[endif]-->应用框架层对应的是frameworks
<!--[if !supportLists]-->3、<!--[endif]-->运行库层对应的是libcore、dalvik
<!--[if !supportLists]-->4、<!--[endif]-->Linux内核层对应的是kernel
下面详细介绍Android源码的目录结构：
Bionic：包含一些C语言库，比如内核层的一些头文件、时区的相关代码等等
Bootable：启动引导的相关代码，包含bootloader、ota、recovery等等
Build：存放系统编译规则以及编译所需的基础包和相关工具
Cts：Android兼容性测试套件标准
Dalvik：dalvik虚拟机的相关代码
Development：应用程序开发所需的一些例子源码和相关工具
External：Android的一些开源模块，比如加密、xml解析、压缩、数据库等等
Frameworks：Android的核心框架（Java和C++语言），比如WiFi、蓝牙、通讯等等
Hardware：部分厂家开源的硬解适配层HAL代码
Packages：Android应用程序包，比如浏览器、计算器、相机、多媒体应用等等
Prebuilt：x86和arm架构下预编译的一些资源
Sdk：Android的SDK和模拟器
System：底层文件系统库、应用及组件
Vendor：厂商定制代码
Kernel：Linux内核相关代码和脚本
Out：系统编译输出目录，包含相关基础包以及相关镜像文件
Device：产品的相关描述文件（与编译系统有关）
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原文：http://yaolinnan.iteye.com/blog/2299491