Android编译系统分析大全 终极总结篇
2014-05-16 18:09
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转自： http://blog.csdn.net/zjg555543/article/details/7804701
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
endif
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 ***************************************************************)
$(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 ***************************************************************)
$(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 ***************************************************************)
$(info Invalid variant: $(TARGET_BUILD_VARIANT)
$(info Valid values are: $(INTERNAL_VALID_VARIANTS)
$(info ***************************************************************)
$(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
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
endif
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
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 ************************************************************)
$(error Case-insensitive filesystems not supported)
endif
endif
endif
# Make sure that there are no spaces in the absolute path; the
# build system can't deal with them.
7检查当前编译的绝对路径是否纯在空格：ifneq ($(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 ***************************************************************)
$(info Don't pass '$(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 ***************************************************************)
$(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 ***************************************************************)
$(info Invalid variant: $(TARGET_BUILD_VARIANT)
$(info Valid values are: $(INTERNAL_VALID_VARIANTS)
$(info ***************************************************************)
$(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)),)
$(warning implicitly installing apns-conf_sdk.xml)
endif
endif
#(19)若是在test或eng的创建，且不是sdk那么要替换上面添加的apns-conf_sdk.xml。
# If we're on an eng or tests build, but not on the sdk, and we have
# a better one, use that instead.
ifneq ($(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
endif
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
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