Android编译系统分析大全

一、概述 自Android开源以来，引起了嵌入式行业一股热潮，很多嵌入式开发者表示对Android有很强的兴趣，并下载Android源码进行编译和移植。Android源码的巨大（repo下来，大概2G）给人以Android相当复杂的错觉。本文从Android编译系统的角度，让大家了解Android其实也是很纯真的。 Android编译系统（build system）集中于Android源码下的build/core下，其下有n多个*.mk文件，另外还有一些shell脚本，可谓相当庞大。为什么google将它的编译系统弄的如此复杂庞大呢？在build/core下的build-system.html中有以下讲述：

1. Multiple Targets

2. Non-Recursive Make

3. Rapid Compile-Test Cycles

4. Both Environment and Config File Based Settings

5. Object File Directory / make clean ......
基于以上目标，google Android开发人员将Android build system做成了现在的样子。在android.git.kernel.org上可以看到android build system作为一个项目一直在更新，因此，对于其编译系统的维护也是一个相当复杂的项目。为了实现Android在除ARM平台（x86、mips甚至一个全新的架构）上移植，必须深入了解Android编译系统。

二、 Android编译系统的架构

分析Android编译系统，你会发现，Android编译系统完成的并不仅仅是对目标（主机）系统二进制文件、java应用程序的编译、链接、打包等，而且还有包括生成各种依赖关系、确保某个模块的修改引起相依赖的文件的重新编译链接，甚至还包括目标文件系统的生成，配置文件的生成等，因此Android编译系统具有支持多架构（linux-x86、windows、arm等）、多语言（汇编、C、C++、Java等）、多目标、多编译方式。这些目标和结构决定其架构也很重要。

Android编译系统集中于build/core下，几个很重要的*.mk文件如下：

main.mk(主控Makefile)

base_rules.mk(对一些Makefile的变量规则化)

config.mk（关于编译参数、编译命令的一些配置）

definations.mk（定义了很多编译系统中用到的宏，相当于函数库）

Makefile（这个Makefile特指build/core下的Makefile，此文件主要控制生成system.img,ramdisk.img,userdata.img,以及recorvery image，sdk等）

Binary.mk(控制如何生成目标文件)

Clear_vars.mk（清除编译系统中用到的临时变量）

Combo/linux-arm.mk(控制如何生成linux-arm二进制文件，包括ARM相关的编译器，编译参数等的设置)

Copy_headers.mk（将头文件拷贝到指定目录）

分散于各个目录下的Android.mk(控制生成局部模块的源码，名称所需头文件路径，依赖库等特殊选项)

Build/envsetup.mk(编译环境初始化，定义一些实用的shell函数，方便编译使用)

以上几个主要的文件，可以按照社会分工打一个比方：

Main.mk是总统，是老大，承担了很多工作。

Makefile是副总统，辅佐老大Main.mk

Base_rules.mk是交警，让不规则的东西，变得规则。

Config.mk是省长，规定了各个人民群众该如何行事

Definations.mk是图书馆管理员

Binary.mk应该属于村长了，规定每个人该如何行事

Clear_vars.mk应该属于保洁公司的工人吧

Combo/linux-arm.mk应该属于社会公民了，他决定自己该如何去做 三、Main.mk分析 执行make，实际执行的是：build\core\main.mk Main.mk主要包含如下几个部分的内容

1. SHELL设置

2. 编译环境配置

3. 编译环境检查

4. 包含必要的宏

5. 根据make参数设置编译时的变量

6. 包含需要编译的Android.mk

7. 设置编译系统Target：prerequisites 控制整个编译流程

下面对上面几点进行必要解释：

有了前面小节对Android编译系统架构的分析，如果需要修改Android编译系统，就可以不至于盲目找问题，修改代码了。今天分析下main.mk，看它能为我们Android编译提供什么有价值的信息，以及如何自己定制我们的Android编译系统。

1 Main.mk 的第一句就根据ANDROID_BUILD_SHELL来包裹编译系统用到的Shell，如果我们不想使用bash，而想使用sh，那么就可以在它前面写上ANDROID_BUILD_SHELL := /bin/sh，或者在build/envsetup.sh中添加相关定义。 # this turns off the suffix rules built into make

.SUFFIXES:

# If a rule fails, delete $@.

.DELETE_ON_ERROR:

# Figure out where we are.

#TOP := $(dir $(word $(words $(MAKEFILE_LIST)),$(MAKEFILE_LIST)))

#TOP := $(patsubst %/,%,$(TOP))

# TOPDIR is the normal variable you should use, because

# if we are executing relative to the current directory

# it can be "", whereas TOP must be "." which causes

# pattern matching probles when make strips off the

# trailing "./" from paths in various places.

#ifeq ($(TOP),.)

#TOPDIR :=

#else

#TOPDIR := $(TOP)/

#endif

2 对MAKE_VERSION的检查。对这个项目的编译，需要make的版本大于或等于3.81。

# check for broken versions of make

ifeq (0,$(shell expr $$(echo $(MAKE_VERSION) | sed "s/[^0-9/.].*//") />= 3.81))

$(warning ********************************************************************************)

$(warning * You are using version $(MAKE_VERSION) of make.)

$(warning * You must upgrade to version 3.81 or greater.)

$(warning * see file://$(shell pwd)/docs/development-environment/machine-setup.html)

$(warning ********************************************************************************)

$(error stopping)

endif

TOP := .

TOPDIR :=

BUILD_SYSTEM := $(TOPDIR)build/core
3 设定第一个目标：DEFAULT_GOAL := droid,在用户输入make之后，如果不加任何参数，那么默认的目标就是

droid。虽然后面的include $(BUILD_SYSTEM)/config.mk写在默认目标droid依赖之后，但该目标之后的语句

# 都是要执行的，这由Makefile的语法决定的。

# This is the default target. It must be the first declared target.

DEFAULT_GOAL := droid

$(DEFAULT_GOAL):

# Set up various standard variables based on configuration

# and host information.

4 包含config.mk：include $(BUILD_SYSTEM)/config.mk,config.mk是一个总括性的文件，它里面定义了

# 各种module编译所需要使用的HOST工具以及如何来编译各种模块。

include $(BUILD_SYSTEM)/config.mk

# This allows us to force a clean build - included after the config.make

# environment setup is done, but before we generate any dependencies. This

# file does the rm -rf inline so the deps which are all done below will

# be generated correctly

5 包含cleanbuild.mk,cleanbuild.mk 完成三件事，一是载入所有的CleanSpec.mk，二是检查更新clean_steps.mk

# 和 previous_build_config.mk，避免不同编译间的互相干扰。最后是，定义installclean和dataclean。

include $(BUILD_SYSTEM)/cleanbuild.mk

VERSION_CHECK_SEQUENCE_NUMBER := 1

-include $(OUT_DIR)/versions_checked.mk

ifneq ($(VERSION_CHECK_SEQUENCE_NUMBER),$(VERSIONS_CHECKED))

$(info Checking build tools versions...)

6 编译环境若不是windows的话，会检查Case-insensitive filesystems。（这里好像无关紧要）

ifneq ($(HOST_OS),windows)

ifneq ($(HOST_OS)-$(HOST_ARCH),darwin-ppc)

# check for a case sensitive file system

ifneq (a,$(shell mkdir -p $(OUT_DIR) ; /

echo a > $(OUT_DIR)/casecheck.txt; /

echo B > $(OUT_DIR)/CaseCheck.txt; /

cat $(OUT_DIR)/casecheck.txt))

$(warning ************************************************************)

$(warning You are building on a case-insensitive filesystem.)

$(warning Please move your source tree to a case-sensitive filesystem.)

$(warning ************************************************************)

$(error Case-insensitive filesystems not supported)

endif

# Make sure that there are no spaces in the absolute path; the

# build system can't deal with them.

7 检查当前编译的绝对路径是否纯在空格：ifneq ($(words $(shell pwd)),1)若是存在空格，会抛出警告并退出。

ifneq ($(words $(shell pwd)),1)

$(warning ************************************************************)

$(warning You are building in a directory whose absolute path contains)

$(warning a space character:)

$(warning $(space))

$(warning "$(shell pwd)")

$(warning $(space))

$(warning Please move your source tree to a path that does not contain)

$(warning any spaces.)

$(warning ************************************************************)

$(error Directory names containing spaces not supported)

endif

# The windows build server currently uses 1.6. This will be fixed.

ifneq ($(HOST_OS),windows)

# Check for the correct version of java

java_version := $(shell java -version 2>&1 | head -n 1 | grep '[ "]1/.5[/. "$$]')

ifeq ($(strip $(java_version)),)

$(info ************************************************************)

$(info You are attempting to build with the incorrect version)

$(info of java.)

$(info $(space))

$(info Your version is: $(shell java -version 2>&1 | head -n 1).)

$(info The correct version is: 1.5.)

$(info $(space))

$(info Please follow the machine setup instructions at)

$(info $(space)$(space)$(space)$(space)http://source.android.com/download)

$(info ************************************************************)

$(error stop)

endif

# Check for the correct version of javac

8 对编译的java 版本的检查，在windows编译是使用1.6的，在别的平台上要使用1.5，如下。

javac_version := $(shell javac -version 2>&1 | head -n 1 | grep '[ "]1/.5[/. "$$]')

ifeq ($(strip $(javac_version)),)

$(info ************************************************************)

$(info You are attempting to build with the incorrect version)

$(info of javac.)

$(info $(space))

$(info Your version is: $(shell javac -version 2>&1 | head -n 1).)

$(info The correct version is: 1.5.)

$(info $(space))

$(info Please follow the machine setup instructions at)

$(info $(space)$(space)$(space)$(space)http://source.android.com/download)

$(info ************************************************************)

$(error stop)

endif

endif # windows

$(shell echo 'VERSIONS_CHECKED := $(VERSION_CHECK_SEQUENCE_NUMBER)' /

> $(OUT_DIR)/versions_checked.mk)

endif

# These are the modifier targets that don't do anything themselves, but

# change the behavior of the build.

# (must be defined before including definitions.make)

INTERNAL_MODIFIER_TARGETS := showcommands checkbuild

# Bring in standard build system definitions.

9 包含definition.mk: definations.mk中定义了很多编译系统中用到的宏，这些宏在编译时需要经常调用，

# 因此在编译的很靠前的阶段，就将之包含了进来。

include $(BUILD_SYSTEM)/definitions.mk

ifneq ($(filter eng user userdebug tests,$(MAKECMDGOALS)),)

$(info ***************************************************************)

$(info Don't pass '$(filter eng user userdebug tests,$(MAKECMDGOALS))' on /

the make command line.)

# XXX The single quote on this line fixes gvim's syntax highlighting.

# Without which, the rest of this file is impossible to read.

$(info Set TARGET_BUILD_VARIANT in buildspec.mk, or use lunch or)

$(info choosecombo.)

$(info ***************************************************************)

$(error stopping)

endif

10 TARGET_BUILD_VARIANT 在buildspec.mk设定,这个参数决定了要安装的模块。(重要，在后面会用到)

ifneq ($(filter-out $(INTERNAL_VALID_VARIANTS),$(TARGET_BUILD_VARIANT)),)

$(info ***************************************************************)

$(info Invalid variant: $(TARGET_BUILD_VARIANT)

$(info Valid values are: $(INTERNAL_VALID_VARIANTS)

$(info ***************************************************************)

$(error stopping)

endif

###

### In this section we set up the things that are different

### between the build variants

###

11 对is_sdk_build的设置，根据在主目录里执行make时，make后面的参数决定。

is_sdk_build :=

ifneq ($(filter sdk,$(MAKECMDGOALS)),)

is_sdk_build := true

endif

ifneq ($(filter sdk_addon,$(MAKECMDGOALS)),)

is_sdk_build := true

endif

## user/userdebug ##

12 查看buildspec.mk文件中定义的TARGET_BUILD_VARIANT是否已经定义有userdebug或user，将结果保存到user_variant

# user_variant这个参数在后面会用很多，关系到后面ADDITIONAL_DEFAULT_PROPERTIES，tags_to_install，enable_target_debugging

# 这些重要参数的设置。ADDITIONAL_BUILD_PROPERTIES用于指定被编译项的文件特性。

user_variant := $(filter userdebug user,$(TARGET_BUILD_VARIANT))

enable_target_debugging := true

ifneq (,$(user_variant))

# Target is secure in user builds.

ADDITIONAL_DEFAULT_PROPERTIES += ro.secure=1

tags_to_install := user

ifeq ($(user_variant),userdebug)

# Pick up some extra useful tools

tags_to_install += debug

else

# Disable debugging in plain user builds.

enable_target_debugging :=

endif

# TODO: Always set WITH_DEXPREOPT (for user builds) once it works on OSX.

# Also, remove the corresponding block in config/product_config.make.

ifeq ($(HOST_OS)-$(WITH_DEXPREOPT_buildbot),linux-true)

WITH_DEXPREOPT := true

endif

# Disallow mock locations by default for user builds

ADDITIONAL_DEFAULT_PROPERTIES += ro.allow.mock.location=0

else # !user_variant

# Turn on checkjni for non-user builds.

ADDITIONAL_BUILD_PROPERTIES += ro.kernel.android.checkjni=1

# Set device insecure for non-user builds.

ADDITIONAL_DEFAULT_PROPERTIES += ro.secure=0

# Allow mock locations by default for non user builds

ADDITIONAL_DEFAULT_PROPERTIES += ro.allow.mock.location=1

endif # !user_variant

13 根据enable_target_debugging的设置(在前面设定)，设置 DDITIONAL_DEFAULT_PROPERTIES的值。

ifeq (true,$(strip $(enable_target_debugging)))

# Target is more debuggable and adbd is on by default

ADDITIONAL_DEFAULT_PROPERTIES += ro.debuggable=1 persist.service.adb.enable=1

# Include the debugging/testing OTA keys in this build.

INCLUDE_TEST_OTA_KEYS := true

else # !enable_target_debugging

# Target is less debuggable and adbd is off by default

ADDITIONAL_DEFAULT_PROPERTIES += ro.debuggable=0 persist.service.adb.enable=0

endif # !enable_target_debugging

## eng ##

14 若是buildspec.mk文件中定义的TARGET_BUILD_VARIANT为eng,再对tags_to_install和ADDITIONAL_BUILD_PROPERTIES

# 进行设置。

ifeq ($(TARGET_BUILD_VARIANT),eng)

tags_to_install := user debug eng

# 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

## tests ##

15 若是buildspec.mk文件中定义的TARGET_BUILD_VARIANT为test,再对tags_to_install进行配置

ifeq ($(TARGET_BUILD_VARIANT),tests)

tags_to_install := user debug eng tests

endif

## sdk ##

16 若是对sdk的编译，会对MAKECMDGOALS的值进行检查，在编译sdk的时候，是不允许再另多其他中间目标的。

# 若是是sdk的边缘，还会tags_to_install，ADDITIONAL_BUILD_PROPERTIES添加一些值。

ifdef is_sdk_build

ifneq ($(words $(filter-out $(INTERNAL_MODIFIER_TARGETS),$(MAKECMDGOALS))),1)

$(error The 'sdk' target may not be specified with any other targets)

endif

# TODO: this should be eng I think. Since the sdk is built from the eng

# variant.

tags_to_install := user debug eng

ADDITIONAL_BUILD_PROPERTIES += xmpp.auto-presence=true

ADDITIONAL_BUILD_PROPERTIES += ro.config.nocheckin=yes

else # !sdk

endif

## precise GC ##

17 查看PRODUCT_TAGS是否有定义dalvik.gc.type-precise，PRODUCT_TAGS这个变量在product_config.mk定义。

# 若是有定义的话还要在ADDITIONAL_BUILD_PROPERTIES添加dalvik.vm.dexopt-flags这个配置信息。

ifneq ($(filter dalvik.gc.type-precise,$(PRODUCT_TAGS)),)

# Enabling type-precise GC results in larger optimized DEX files. The

# additional storage requirements for ".odex" files can cause /system

# to overflow on some devices, so this is configured separately for

# each product.

ADDITIONAL_BUILD_PROPERTIES += dalvik.vm.dexopt-flags=m=y

endif

#########################################################################################################

#(18)若是PRODUCT_COPY_FILES没有记录apns-conf.xml，要确保添加上去。

# 注意:这几个文件的作用如下：

# apns-conf_sdk.xml如：$ANDROID_SRC_HOME/development/data/etc/apns-conf_sdk.xml

# --主要用于生成system/etc/apns-conf.xml文件，生成过程本质上就是原文拷贝

# apns.xml 如：$ANDROID_SRC_HOME/frameworks/base/core/res/res/xml/apns.xml

# --该文件实际上在apn的设置方面没有实际意义，然而在android apn设置的逻辑方面却很重要，尤其是里面的version的值。

# apns-conf.xml 如： $ANDROID_SRC_HOME/out/target/product/generic/system/etc/apns-conf.xml

# --该文件里记录的内容最终打包到system.img中：

##########################################################################################################

# Install an apns-conf.xml file if one's not already being installed.

ifeq (,$(filter %:system/etc/apns-conf.xml, $(PRODUCT_COPY_FILES)))

PRODUCT_COPY_FILES += /

development/data/etc/apns-conf_sdk.xml:system/etc/apns-conf.xml

ifeq ($(filter eng tests,$(TARGET_BUILD_VARIANT)),)

$(warning implicitly installing apns-conf_sdk.xml)

endif

#(19)若是在test 或eng的创建，且不是sdk那么要替换上面添加的apns-conf_sdk.xml。

# If we're on an eng or tests build, but not on the sdk, and we have

# a better one, use that instead.

ifneq ($(filter eng tests,$(TARGET_BUILD_VARIANT)),)

ifndef is_sdk_build

apns_to_use := $(wildcard vendor/google/etc/apns-conf.xml)

ifneq ($(strip $(apns_to_use)),)

PRODUCT_COPY_FILES := /

$(filter-out %:system/etc/apns-conf.xml,$(PRODUCT_COPY_FILES)) /

$(strip $(apns_to_use)):system/etc/apns-conf.xml

endif

#(20)再次配置ADDITIONAL_BUILD_PROPERTIES

ADDITIONAL_BUILD_PROPERTIES += net.bt.name=Android

ADDITIONAL_BUILD_PROPERTIES += ro.config.sync=yes

# enable vm tracing in files for now to help track

# the cause of ANRs in the content process

ADDITIONAL_BUILD_PROPERTIES += dalvik.vm.stack-trace-file=/data/anr/traces.txt

# ------------------------------------------------------------

# Define a function that, given a list of module tags, returns

# non-empty if that module should be installed in /system.

# For most goals, anything not tagged with the "tests" tag should

# be installed in /system.

define should-install-to-system

$(if $(filter tests,$(1)),,true)

endef

ifdef is_sdk_build

# For the sdk goal, anything with the "samples" tag should be

# installed in /data even if that module also has "eng"/"debug"/"user".

define should-install-to-system

$(if $(filter samples tests,$(1)),,true)

endef

endif

# If they only used the modifier goals (showcommands, checkbuild), we'll actually

# build the default target.

#(21)若make 后面的参数和INTERNAL_MODIFIER_TARGETS相同,那么就设定INTERNAL_MODIFIER_TARGETS对DEFAULT_GOAL的

# 依赖关系。

ifeq ($(filter-out $(INTERNAL_MODIFIER_TARGETS),$(MAKECMDGOALS)),)

.PHONY: $(INTERNAL_MODIFIER_TARGETS)

$(INTERNAL_MODIFIER_TARGETS): $(DEFAULT_GOAL)

endif

#(22)根据make 后面的参数设定 dont_bother这个变量。

# These targets are going to delete stuff, don't bother including

# the whole directory tree if that's all we're going to do

ifeq ($(MAKECMDGOALS),clean)

dont_bother := true

endif

ifeq ($(MAKECMDGOALS),clobber)

dont_bother := true

endif

ifeq ($(MAKECMDGOALS),dataclean)

dont_bother := true

endif

ifeq ($(MAKECMDGOALS),installclean)

dont_bother := true

endif

# Bring in all modules that need to be built.

ifneq ($(dont_bother),true)

ifeq ($(HOST_OS),windows)

SDK_ONLY := true

endif

ifeq ($(HOST_OS)-$(HOST_ARCH),darwin-ppc)

SDK_ONLY := true

endif

这个判断语句一直到这个语句块结束，都是对subdirs变量的设置，subdirs变量决定了哪些子文件夹最终被编译。

ifeq ($(SDK_ONLY),true)

# ----- SDK for Windows ------

# These configure the build targets that are available for the SDK under Cygwin.

# The first section defines all the C/C++ tools that can be compiled under Cygwin,

# the second section defines all the Java ones (assuming javac is available.)

#（23）确定subdirs，这里包含的文件目录下的文件最终被编译，其中第一部分决定了一些C/C++工具被编译的子目录。

# 第二部分为使用java编译器编译的目录。

#这是第一部分。

subdirs := /

prebuilt /

build/libs/host /

build/tools/zipalign /

dalvik/dexdump /

dalvik/libdex /

dalvik/tools/dmtracedump /

dalvik/tools/hprof-conv /

development/tools/line_endings /

development/tools/etc1tool /

sdk/emulator/mksdcard /

sdk/sdklauncher /

development/host /

external/expat /

external/libpng /

external/qemu /

external/sqlite/dist /

external/zlib /

frameworks/base/libs/utils /

frameworks/base/tools/aapt /

frameworks/base/tools/aidl /

frameworks/base/opengl/libs /

system/core/adb /

system/core/fastboot /

system/core/libcutils /

system/core/liblog /

system/core/libzipfile

# The following can only be built if "javac" is available.

# This check is used when building parts of the SDK under Cygwin.

#(24)调用which 命令查看在环境变量中是否有javac这个命令，若是有的话，说明java编译器是已经安装的了，

# 那么就包含这些目录，否则不包含这些目录，并抛出一个警告。

ifneq (,$(shell which javac 2>/dev/null))

$(warning sdk-only: javac available.)

#这是第二部分。

subdirs += /

build/tools/signapk /

dalvik/dx /

dalvik/libcore /

sdk/archquery /

sdk/androidprefs /

sdk/apkbuilder /

sdk/jarutils /

sdk/layoutlib_api /

sdk/layoutlib_utils /

sdk/ninepatch /

sdk/sdkstats /

sdk/sdkmanager /

sdk/layoutopt /

development/apps /

development/tools/mkstubs /

frameworks/base/tools/layoutlib /

external/googleclient /

packages

else

$(warning sdk-only: javac not available.)

endif

#(25)若当前HOST不是linux，那么还要要添加build/tools/acp这个目录。

# Exclude tools/acp when cross-compiling windows under linux

ifeq ($(findstring Linux,$(UNAME)),)

subdirs += build/tools/acp

endif

#(26)若SDK_ONLY不为真，且BUILD_TINY_ANDROID为真，那么添加一些文件，编译一个最小的系统.

else # !SDK_ONLY

ifeq ($(BUILD_TINY_ANDROID), true)

# TINY_ANDROID is a super-minimal build configuration, handy for board

# bringup and very low level debugging

subdirs := /

bionic /

system/core /

build/libs /

build/target /

build/tools/acp /

build/tools/apriori /

build/tools/kcm /

build/tools/soslim /

external/elfcopy /

external/elfutils /

external/yaffs2 /

external/zlib

else # !BUILD_TINY_ANDROID

#(27)若上面的两个条件(SDK_ONLY为真，BUILD_TINY_ANDROID为真)都不成了，那么就要包含$(TOP)下面

# 的所有android.mk文件了。这才是最典型的编译.

# Typical build; include any Android.mk files we can find.

subdirs := $(TOP)

FULL_BUILD := true

endif # !BUILD_TINY_ANDROID

endif # !SDK_ONLY

ifneq ($(ONE_SHOT_MAKEFILE),)

# We've probably been invoked by the "mm" shell function

# with a subdirectory's makefile.

include $(ONE_SHOT_MAKEFILE)

# Change CUSTOM_MODULES to include only modules that were

# defined by this makefile; this will install all of those

# modules as a side-effect. Do this after including ONE_SHOT_MAKEFILE

# so that the modules will be installed in the same place they

# would have been with a normal make.

#(28)设定CUSTOM_MODULES，在后面会涉及到。非常重要。

CUSTOM_MODULES := $(sort $(call get-tagged-modules,$(ALL_MODULE_TAGS),))

FULL_BUILD :=

# Stub out the notice targets, which probably aren't defined

# when using ONE_SHOT_MAKEFILE.

NOTICE-HOST-%: ;

NOTICE-TARGET-%: ;

else # ONE_SHOT_MAKEFILE

# Include all of the makefiles in the system

# Can't use first-makefiles-under here because

# --mindepth=2 makes the prunes not work.

#(29)在这里调用findleaves.py查找在subdirs的包含的子目录下所有的 Android.mk文件。

subdir_makefiles := /

$(shell build/tools/findleaves.py --prune=out --prune=.repo --prune=.git $(subdirs) Android.mk)

include $(subdir_makefiles)

endif # ONE_SHOT_MAKEFILE

# -------------------------------------------------------------------

# All module makefiles have been included at this point.

# -------------------------------------------------------------------

# Include any makefiles that must happen after the module makefiles

# have been included.

# TODO: have these files register themselves via a global var rather

# than hard-coding the list here.

ifdef FULL_BUILD

# Only include this during a full build, otherwise we can't be

# guaranteed that any policies were included.

-include frameworks/policies/base/PolicyConfig.mk

endif

# -------------------------------------------------------------------

# Fix up CUSTOM_MODULES to refer to installed files rather than

# just bare module names. Leave unknown modules alone in case

# they're actually full paths to a particular file.

#(30)提取用户定义的定义的模块，用户定义的模块，不一定在系统的所有模块中有定义，这里做了分类

#分为: known_custom_modules:用户定义了，并且在系统中有定义。

# unknown_custom_modules:用户没有定义，但系统系统中有定义。

known_custom_modules := $(filter $(ALL_MODULES),$(CUSTOM_MODULES))

unknown_custom_modules := $(filter-out $(ALL_MODULES),$(CUSTOM_MODULES))

CUSTOM_MODULES := /

$(call module-installed-files,$(known_custom_modules)) /

$(unknown_custom_modules)

# -------------------------------------------------------------------

# Define dependencies for modules that require other modules.

# This can only happen now, after we've read in all module makefiles.

# TODO: deal with the fact that a bare module name isn't

# unambiguous enough. Maybe declare short targets like

# APPS:Quake or HOST:SHARED_LIBRARIES:libutils.

# BUG: the system image won't know to depend on modules that are

# brought in as requirements of other modules.

define add-required-deps

#(31)这里调用了module-installed-files和add-required-deps函数，设定各个模块对各种库的依赖

$(1): $(2)

endef

$(foreach m,$(ALL_MODULES), /

$(eval r := $(ALL_MODULES.$(m).REQUIRED)) /

$(if $(r), /

$(eval r := $(call module-installed-files,$(r))) /

$(eval $(call add-required-deps,$(ALL_MODULES.$(m).INSTALLED),$(r))) /

) /

)

m :=

r :=

add-required-deps :=

# -------------------------------------------------------------------

# Figure out our module sets.

# Of the modules defined by the component makefiles,

# determine what we actually want to build.

# If a module has the "restricted" tag on it, it

# poisons the rest of the tags and shouldn't appear

# on any list.

#(32)设定Default_MODULES;

Default_MODULES := $(sort $(ALL_DEFAULT_INSTALLED_MODULES) /

$(CUSTOM_MODULES))

# TODO: Remove the 3 places in the tree that use

# ALL_DEFAULT_INSTALLED_MODULES and get rid of it from this list.

ifdef FULL_BUILD

# The base list of modules to build for this product is specified

# by the appropriate product definition file, which was included

# by product_config.make.

#(33)设定user_PACKAGES获取这个product的所有的modules 的list，这份list定义的module选择定义在

# product_config.mk这个文件以及这个文件包含的子*.mk文件中。

user_PACKAGES := $(call module-installed-files, /

$(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES))

ifeq (0,1)

$(info user packages for $(TARGET_DEVICE) ($(INTERNAL_PRODUCT)):)

$(foreach p,$(user_PACKAGES),$(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.

user_PACKAGES :=

endif

#(34)模块设定:引擎类模块eng_MODULES，应用类模块user_MODULES,测试模块test_MODULES,调试模块debug_MOUDLE

# Use tags to get the non-APPS user modules. Use the product

# definition files to get the APPS user modules.

user_MODULES := $(sort $(call get-tagged-modules,user,_class@APPS restricted))

user_MODULES := $(user_MODULES) $(user_PACKAGES)

eng_MODULES := $(sort $(call get-tagged-modules,eng,restricted))

debug_MODULES := $(sort $(call get-tagged-modules,debug,restricted))

tests_MODULES := $(sort $(call get-tagged-modules,tests,restricted))

ifeq ($(strip $(tags_to_install)),)

$(error ASSERTION FAILED: tags_to_install should not be empty)

endif

#(35)从tags_to_install获取要安装的模块

# 获取关系如下:tags_to_install <- user_variant <- TARGET_BUILD_VARIANT,TARGET_BUILD_VARIANT在buildspec.mk设定

modules_to_install := $(sort $(Default_MODULES) /

$(foreach tag,$(tags_to_install),$($(tag)_MODULES)))

# Some packages may override others using LOCAL_OVERRIDES_PACKAGES.

# Filter out (do not install) any overridden packages.

overridden_packages := $(call get-package-overrides,$(modules_to_install))

ifdef overridden_packages

# old_modules_to_install := $(modules_to_install)

modules_to_install := /

$(filter-out $(foreach p,$(overridden_packages),$(p) %/$(p).apk), /

$(modules_to_install))

endif

#$(error filtered out

# $(filter-out $(modules_to_install),$(old_modules_to_install)))

# Don't include any GNU targets in the SDK. It's ok (and necessary)

# to build the host tools, but nothing that's going to be installed

# on the target (including static libraries).

#(36)剔除目标里包含的gnu里的tools，这是sdk里包含的工具类模块，是不能安装在目标里的。

ifdef is_sdk_build

target_gnu_MODULES := /

$(filter /

$(TARGET_OUT_INTERMEDIATES)/% /

$(TARGET_OUT)/% /

$(TARGET_OUT_DATA)/%, /

$(sort $(call get-tagged-modules,gnu)))

$(info Removing from sdk:)$(foreach d,$(target_gnu_MODULES),$(info : $(d)))

modules_to_install := /

$(filter-out $(target_gnu_MODULES),$(modules_to_install))

endif

# build/core/Makefile contains extra stuff that we don't want to pollute this

# top-level makefile with. It expects that ALL_DEFAULT_INSTALLED_MODULES

# contains everything that's built during the current make, but it also further

# extends ALL_DEFAULT_INSTALLED_MODULES.

#(37)对ALL_DEFAULT_INSTALLED_MODULES 的处理

ALL_DEFAULT_INSTALLED_MODULES := $(modules_to_install)

include $(BUILD_SYSTEM)/Makefile

modules_to_install := $(sort $(ALL_DEFAULT_INSTALLED_MODULES))

ALL_DEFAULT_INSTALLED_MODULES :=

endif # dont_bother

# These are additional goals that we build, in order to make sure that there

# is as little code as possible in the tree that doesn't build.

#(38)确保我们定义我们构建的模块是没有冗余的。

modules_to_check := $(foreach m,$(ALL_MODULES),$(ALL_MODULES.$(m).CHECKED))

# If you would like to build all goals, and not skip any intermediate

# steps, you can pass the "all" modifier goal on the commandline.

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))

#$(error modules_to_check $(modules_to_check))

# -------------------------------------------------------------------

# This is used to to get the ordering right, you can also use these,

# but they're considered undocumented, so don't complain if their

# behavior changes.

.PHONY: prebuilt

prebuilt: $(ALL_PREBUILT)

# An internal target that depends on all copied headers

# (see copy_headers.make). Other targets that need the

# headers to be copied first can depend on this target.

.PHONY: all_copied_headers

all_copied_headers: ;

$(ALL_C_CPP_ETC_OBJECTS): | all_copied_headers

#(39)files 这个目标在这里是一个非常大的目标，包括moudules_to_install,modules_to_check,prebuilt等等

# 前面所做的就是为这几个目标的正确生成。关系如下:droid依赖于droidcore,而droidcore依赖于files,如下，

# 就是这几项的依赖的关系控制着整个项目的编译流程。

# All the droid stuff, in directories

.PHONY: files

files: prebuilt /

$(modules_to_install) /

$(modules_to_check) /

$(INSTALLED_ANDROID_INFO_TXT_TARGET)

# -------------------------------------------------------------------

.PHONY: checkbuild

checkbuild: $(modules_to_check)

.PHONY: ramdisk

ramdisk: $(INSTALLED_RAMDISK_TARGET)

.PHONY: systemtarball

systemtarball: $(INSTALLED_SYSTEMTARBALL_TARGET)

.PHONY: userdataimage

userdataimage: $(INSTALLED_USERDATAIMAGE_TARGET)

.PHONY: userdatatarball

userdatatarball: $(INSTALLED_USERDATATARBALL_TARGET)

.PHONY: bootimage

bootimage: $(INSTALLED_BOOTIMAGE_TARGET)

ifeq ($(BUILD_TINY_ANDROID), true)

INSTALLED_RECOVERYIMAGE_TARGET :=

endif

#（40）一下是整改项目的build动作，如果要把整个编译过程分成：配置和编译两部分的话，

# 上面的所有的都是配置过程，下面的为编译过程。

# 这里确定好要生成的子目标。

# Build files and then package it into the rom formats

.PHONY: droidcore

droidcore: files /

systemimage /

$(INSTALLED_BOOTIMAGE_TARGET) /

$(INSTALLED_RECOVERYIMAGE_TARGET) /

$(INSTALLED_USERDATAIMAGE_TARGET) /

$(INSTALLED_FILES_FILE)

# The actual files built by the droidcore target changes depending

# on the build variant.

#这里开始编译。

.PHONY: droid tests

droid tests: droidcore

$(call dist-for-goals, droid, /

$(INTERNAL_UPDATE_PACKAGE_TARGET) /

$(INTERNAL_OTA_PACKAGE_TARGET) /

$(SYMBOLS_ZIP) /

$(APPS_ZIP) /

$(INTERNAL_EMULATOR_PACKAGE_TARGET) /

$(PACKAGE_STATS_FILE) /

$(INSTALLED_FILES_FILE) /

$(INSTALLED_BUILD_PROP_TARGET) /

$(BUILT_TARGET_FILES_PACKAGE) /

)

# Tests are installed in userdata.img. If we're building the tests

# variant, copy it for "make tests dist". Also copy a zip of the

# contents of userdata.img, so that people can easily extract a

# single .apk.

ifeq ($(TARGET_BUILD_VARIANT),tests)

$(call dist-for-goals, droid, /

$(INSTALLED_USERDATAIMAGE_TARGET) /

$(BUILT_TESTS_ZIP_PACKAGE) /

)

endif

.PHONY: docs

docs: $(ALL_DOCS)

.PHONY: sdk

ALL_SDK_TARGETS := $(INTERNAL_SDK_TARGET)

sdk: $(ALL_SDK_TARGETS)

$(call dist-for-goals,sdk,$(ALL_SDK_TARGETS))

.PHONY: findbugs

findbugs: $(INTERNAL_FINDBUGS_HTML_TARGET) $(INTERNAL_FINDBUGS_XML_TARGET)

.PHONY: clean

dirs_to_clean := /

$(PRODUCT_OUT) /

$(TARGET_COMMON_OUT_ROOT) /

$(HOST_OUT) /

$(HOST_COMMON_OUT_ROOT)

clean:

@for dir in $(dirs_to_clean) ; do /

echo "Cleaning $$dir..."; /

rm -rf $$dir; /

done

@echo "Clean."; /

.PHONY: clobber

clobber:

@rm -rf $(OUT_DIR)

@echo "Entire build directory removed."

# The rules for dataclean and installclean are defined in cleanbuild.mk.

#xxx scrape this from ALL_MODULE_NAME_TAGS

.PHONY: modules

modules:

@echo "Available sub-modules:"

@echo "$(call module-names-for-tag-list,$(ALL_MODULE_TAGS))" | /

sed -e 's/ *//n/g' | sort -u | $(COLUMN)

.PHONY: showcommands

showcommands:

@echo >/dev/null

更多相关文章

随机推荐