Android编译系统详解(三)——编译流程详解

原文：http://www.cloudchou.com/android/post-276.html

1.概述

编译Android的第三步是使用mka命令进行编译，当然我们也可以使用make –j4，但是推荐使用mka命令。因为mka将自动计算-j选项的数字，让我们不用纠结这个数字到底是多少(这个数字其实就是所有cpu的核心数)。在编译时我们可以带上我们需要编译的目标，假设你想生成recovery，那么使用mka recoveryimage，如果想生成ota包，那么需要使用mka otapackage，后续会介绍所有可以使用的目标。另外注意有一些目标只是起到修饰的作用，也就是说需要和其它目标一起使用，共有4个用于修饰的伪目标:

• 1) showcommands 显示编译过程中使用的命令
• 2) incrementaljavac用于增量编译java代码
• 3) checkbuild用于检验那些需要检验的模块
• 4) all如果使用all修饰编译目标，会编译所有模块

研究Android编译系统时最头疼的可能是变量，成百个变量我们无法记住其含义，也不知道这些变量会是什么值，为此我专门做了一个编译变量的参考网站android.cloudchou.com，你可以在该网站查找变量，它能告诉你变量的含义，也会给出你该变量的示例值，另外也详细解释了编译系统里每个Makefile的作用，这样你在看编译系统的代码时不至于一头雾水。

编译的核心文件是build/core/main.mk和build/core/makefile，main.mk主要作用是检查编译环境是否符合要求，确定产品配置，决定产品需要使用的模块，并定义了许多目标供开发者使用，比如droid，sdk等目标，但是生成这些目标的规则主要在Makefile里定义，而内核的编译规则放在build/core/task/kernel.mk

我们将先整体介绍main.mk的执行流程，然后再针对在Linux上编译默认目标时使用的关键代码进行分析。Makefile主要定义了各个目标的生成规则，因此不再详细介绍它的执行流程，若有兴趣看每个目标的生成规则，可查看http://android.cloudchou.com/build/core/Makefile.php

2. main.mk执行流程

2.1 检验编译环境并建立产品配置

• 1) 设置Shell变量为bash，不能使用其它shell
• 2) 关闭make的suffix规则，rcs/sccs规则，并设置一个规则: 当某个规则失败了，就删除所有目标
• 3) 检验make的版本，cygwin可使用任意版本make，但是linux或者mac只能使用3.81版本或者3.82版本
• 4) 设置PWD,TOP,TOPDIR，BUILD_SYSTEM等变量，定义了默认目标变量，但是暂时并未定义默认目标的生成规则
• 5) 包含build/core/help.mk，该makefile定义了两个目标help和out, help用于显示帮助，out用于检验编译系统是否正确
• 6) 包含build/core/config.mk，config.mk作了很多配置，包括产品配置，包含该makefile后，会建立输出目录系列的变量，还会建立PRODUCT系列变量，后续介绍产品配置时，对此会有更多详细介绍
• 7) 包含build/core/cleanbuild.mk，该makefile会包含所有工程的CleanSpec.mk，写了CleanSpec.mk的工程会定义每次编译前的特殊清理步骤，cleanbuild.mk会执行这些清除步骤
• 8) 检验编译环境，先检测上次编译结果，如果上次检验的版本和此次检验的版本一致，则不再检测，然后进行检测并将此次编译结果写入

2.2 包含其它makefile及编译目标检测

• 1) 如果目标里含有incrementaljavac， 那么编译目标时将用incremental javac进行增量编译
• 2) 设置EMMA_INSTRUMENT变量的值，emma是用于测试代码覆盖率的库
• 3) 包含build/core/definistions.mk，该makefile定义了许多辅助函数
• 4) 包含build/core/qcom_utils.mk，该makefile定义了高通板子的一些辅助函数及宏
• 5) 包含build/core/dex_preopt.mk，该makefile定义了优化dex代码的一些宏
• 6) 检测编译目标里是否有user,userdebug,eng，如果有则告诉用户放置在buildspec.mk或者使用lunch设置，检测TARGET_BUILD_VARIANT变量，看是否有效
• 7) 包含build/core/pdk_config.mk, PDK主要是能提高现有设备升级能力，帮助设备制造商能更快的适配新版本的android

2.3 根据TARGET_BUILD_VARIANT建立配置

• 1) 如果编译目标里有sdk，win_sdk或者sdk_addon，那么设置is_sdk_build为true
• 2) 如果定义了HAVE_SELINUX，那么编译时为build prop添加属性ro.build.selinux=1
• 3) 如果TARGET_BUILD_VARIANT是user或者userdebug，那么tags_to_install += debug 如果用户未定义DISABLE_DEXPREOPT为true，并且是user模式，那么将设置WITH_DEXPREOPT := true，该选项将开启apk的预优化，即将apk分成odex代码文件和apk资源文件
• 4) 判断enable_target_debugging变量，默认是true，当build_variant是user时，则它是false。如果该变量值为true，则设置Rom的编译属性ro.debuggable为1，否则设置ro.debuggable为0
• 5) 如果TARGET_BUILD_VARIANT是eng，那么tags_to_install为debug,eng， 并设置Rom的编译属性ro.setupwizard.mode为OPTIONAL，因为eng模式并不要安装向导
• 6) 如果TARGET_BUILD_VARIANT是tests，那么tags_to_install := debug eng tests
• 7) 设置sdk相关变量
• 8) 添加一些额外的编译属性
• 9) 定义should-install-to-system宏函数
• 10) 若除了修饰目标，没定义任何目标，那么将使用默认目标编译

2.4 包含所有要编译的模块的Makefile

如果编译目标是clean clobber installclean dataclean，那么设置dont_bother为true，若dont_bother为false，则将所有要编译的模块包含进来

1) 如果主机操作系统及体系结构为darwin-ppc(Mac电脑)，那么提示不支持编译Sdk，并将SDK_ONLY设置为true

2) 如果主机操作系统是windows，那么设置SDK_ONLY为true

3) 根据SDK_ONLY是否为true，编译主机操作系统类型，BUILD_TINY_ANDROID的值，设置sudbidrs变量

4) 将所有PRODUCT_*相关变量存储至stash_product_vars变量，稍后将验证它是否被修改

5) 根据ONE_SHOT_MAKEFILE的值是否为空，包含不同的makefile

6) 执行post_clean步骤，并确保产品相关变量没有变化

7) 检测是否有文件加入ALL_PREBUILT

8) 包含其它必须在所有Android.mk包含之后需要包含的makefile

9) 将known_custom_modules转化成安装路径得到变量CUSTOM_MODULES

10) 定义模块之间的依赖关系，$(ALL_MODULES.$(m).REQUIRED))变量指明了模块之间的依赖关系

11)计算下述变量的值：product_MODULES，debug_MODULES，eng_MODULES，tests_MODULES，modules_to_install，overridden_packages，target_gnu_MODULES，ALL_DEFAULT_INSTALLED_MODULES

12) 包含build/core/Makefile

13) 定义变量modules_to_check

2.5 定义多个目标

这一节定义了众多目标，prebuilt，all_copied_headers，files，checkbuild，ramdisk，factory_ramdisk，factory_bundle，systemtarball，boottarball，userdataimage，userdatatarball，cacheimage，bootimage，droidcore，dist_files，apps_only，all_modules，docs，sdk，lintall，samplecode，findbugs，clean，modules，showcommands，nothing。

后续文章将列出所有可用的目标

3 编译默认目标时的执行流程

在介绍编译默认目标时的执行流程之前，先介绍一下ALL_系列的变量，否则看代码时很难搞懂这些变量的出处，这些变量在包含所有模块后被建立，每个模块都有对应的用于编译的makefile，这些makefile会包含一个编译类型对应的makefile，比如package.mk，而这些makefile最终都会包含base_rules.mk，在base_rules.mk里会为ALL系列变量添加值。所有这些变量及其来源均可在android.cloudchou.com查看详细解释：

• 1) ALL_DOCS所有文档的全路径，ALL_DOCS的赋值在droiddoc.mk里, ALL_DOCS += $(full_target)
• 2)ALL_MODULES系统的所有模块的简单名字集合，编译系统还为每一个模块还定义了其它两个变量，ALL_MODULES.$(LOCAL_MODULE).BUILT 所有模块的生成路径ALL_MODULES.$(LOCAL_MODULE).INSTALLED 所有模块的各自安装路径，详情请见http://android.cloudchou.com/build/core/definitions.php#ALL_MODULES
• 3) ALL_DEFAULT_INSTALLED_MODULES 所有默认要安装的模块,在build/core/main.mk和build/core/makfile里设置
• 4) ALL_MODULE_TAGS 使用LOCAL_MODULE_TAGS定义的所有tag集合，每一个tag对应一个ALL_MODULE_TAGS.变量，详情请见http://android.cloudchou.com/build/core/definitions.php#ALL_MODULE_TAGS
• 5) ALL_MODULE_NAME_TAGS类似于ALL_MODULE_TAGS，但是它的值是 某个tag的所有模块的名称 详情请见http://android.cloudchou.com/build/core/definitions.php#ALL_MODULE_NAME_TAGS
• 6) ALL_HOST_INSTALLED_FILES 安装在pc上的程序集合
• 7) ALL_PREBUILT 将会被拷贝的预编译文件的安装全路径的集合
• 8) ALL_GENERATED_SOURCES 某些工具生成的源代码文件的集合，比如aidl会生成java源代码文件
• 9) ALL_C_CPP_ETC_OBJECTS 所有asm，c,c++,以及lex和yacc生成的c代码文件的全路径
• 10) ALL_ORIGINAL_DYNAMIC_BINARIES 没有被优化，也没有被压缩的动态链接库
• 11) ALL_SDK_FILES 将会放在sdk的文件
• 12) ALL_FINDBUGS_FILES 所有findbugs程序用的xml文件
• 13) ALL_GPL_MODULE_LICENSE_FILES GPL 模块的 许可文件
• 14) ANDROID_RESOURCE_GENERATED_CLASSES Android 资源文件生成的java代码编译后的类的类型

3.1 关键代码

定义默认目标的代码位于main.mk：

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.PHONY: droidDEFAULT_GOAL := droid$(DEFAULT_GOAL):

droid目标依赖的目标有：

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ifneq ($(TARGET_BUILD_APPS),)……droid: apps_only #如果编译app，那么droid依赖apps_only目标else……droid: droidcore dist_files #默认依赖droidcore目标和dist_files目标endif

dist_files目标依赖的目标主要是一些用于打包的工具，它们都是用dist-for-goals宏添加依赖关系的：

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$(call dist-for-goals, dist_files, $(EMMA_META_ZIP))system/core/mkbootimg/Android.mk$(call dist-for-goals, dist_files, $( LOCAL_BUILT_MODULE ))system/core/cpio/Android.mk:13:$(call dist-for-goals,dist_files,$(LOCAL_BUILT_MODULE))system/core/adb/Android.mk:88:$(call dist-for-goals,dist_files sdk,$(LOCAL_BUILT_MODULE))system/core/fastboot/Android.mk:68:$(call dist-for-goals,dist_files sdk,$(LOCAL_BUILT_MODULE))external/guava/Android.mk:26:$(call dist-for-goals, dist_files, $(LOCAL_BUILT_MODULE):guava.jar)external/yaffs2/Android.mk:28:$(call dist-for-goals, dist_files, $(LOCAL_BUILT_MODULE))external/mp4parser/Android.mk:26:$(call dist-for-goals, dist_files, $(LOCAL_BUILT_MODULE):mp4parser.jar)external/jsr305/Android.mk:25:$(call dist-for-goals, dist_files, $(LOCAL_BUILT_MODULE):jsr305.jar)frameworks/support/renderscript/v8/Android.mk:29:#$(call dist-for-goals, dist_files, $(LOCAL_BUILT_MODULE):volley.jar)frameworks/support/volley/Android.mk:29:#$(call dist-for-goals, dist_files, $(LOCAL_BUILT_MODULE):volley.jar)

我们再看droidcore目标依赖的目标有：

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droidcore: files \systemimage \ #system.img$(INSTALLED_BOOTIMAGE_TARGET) \ #boot.img$(INSTALLED_RECOVERYIMAGE_TARGET) \#recovery.img$(INSTALLED_USERDATAIMAGE_TARGET) \#data.img$(INSTALLED_CACHEIMAGE_TARGET) \#cache.img$(INSTALLED_FILES_FILE)# installed-files.txtifneq ($(TARGET_BUILD_APPS),)….else$(call dist-for-goals, droidcore, \    $(INTERNAL_UPDATE_PACKAGE_TARGET) #cm_find5-img-eng.cloud.zip    $(INTERNAL_OTA_PACKAGE_TARGET) \ # cm_find5-ota-eng.cloud.zip    $(SYMBOLS_ZIP) \ # cm_find5-symbols-eng.cloud.zip    $(INSTALLED_FILES_FILE) \# installed-files.txt    $(INSTALLED_BUILD_PROP_TARGET) \# system/build.prop    $(BUILT_TARGET_FILES_PACKAGE) \# cm_find5-target_files-eng.cloud.zip    $(INSTALLED_ANDROID_INFO_TXT_TARGET) \# android-info.txt    $(INSTALLED_RAMDISK_TARGET) \# ramdisk.img    $(INSTALLED_FACTORY_RAMDISK_TARGET) \# factory_ramdisk.gz    $(INSTALLED_FACTORY_BUNDLE_TARGET) \# cm_find5-factory_bundle- eng.cloud.zip   )endif

system.img, boot.img, recovery.img, data.img,cache.img,installed_files.txt的生成规则在Makefile里定义, 在http://android.cloudchou.com/build/core/Makefile.php里可以看到详细的生成规则再看一下files目标所依赖的目标：

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files: prebuilt \        $(modules_to_install) \        $(INSTALLED_ANDROID_INFO_TXT_TARGET)

prebuilt目标依赖$(ALL_PREBUILT)，android-info.txt的生成规则在target/board/board.mk里定义，而$(modules_to_install)目标是所有要安装的模块的集合，计算比较复杂，现在以在linux下编译默认目标为例，将涉及到的代码组织如下：

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……tags_to_install :=ifneq (,$(user_variant))…..  ifeq ($(user_variant),userdebug)  tags_to_install += debug  else  …  endifendififeq ($(TARGET_BUILD_VARIANT),eng)tags_to_install := debug eng…endififeq ($(TARGET_BUILD_VARIANT),tests)tags_to_install := debug eng testsendififdef is_sdk_buildtags_to_install := debug engelse # !sdkendif……# ------------------------------------------------------------# 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)endefifdef 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)endefendif…#接下来根据配置计算要查找的subdirs目录ifneq ($(dont_bother),true)…ifeq ($(SDK_ONLY),true)include $(TOPDIR)sdk/build/sdk_only_whitelist.mkinclude $(TOPDIR)development/build/sdk_only_whitelist.mk# Exclude tools/acp when cross-compiling windows under linuxifeq ($(findstring Linux,$(UNAME)),)subdirs += build/tools/acpendif else# !SDK_ONLYifeq ($(BUILD_TINY_ANDROID), true)subdirs := \bionic \system/core \system/extras/ext4_utils \system/extras/su \build/libs \build/target \build/tools/acp \external/gcc-demangle \external/mksh \external/openssl \external/yaffs2 \external/zlibelse# !BUILD_TINY_ANDROIDsubdirs := $(TOP) FULL_BUILD := trueendif# !BUILD_TINY_ANDROIDendif# Before we go and include all of the module makefiles, stash away# the PRODUCT_* values so that later we can verify they are not modified.stash_product_vars:=trueifeq ($(stash_product_vars),true)  $(call stash-product-vars, __STASHED)endif….ifneq ($(ONE_SHOT_MAKEFILE),)include $(ONE_SHOT_MAKEFILE)CUSTOM_MODULES := $(sort $(call get-tagged-modules,$(ALL_MODULE_TAGS)))FULL_BUILD :=…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.subdir_makefiles := \$(shell build/tools/findleaves.py --prune=out --prune=.repo --prune=.git $(subdirs) Android.mk) include $(subdir_makefiles) endif # ONE_SHOT_MAKEFILE……ifeq ($(stash_product_vars),true)  $(call assert-product-vars, __STASHED)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.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# -------------------------------------------------------------------# Figure out our module sets.## Of the modules defined by the component makefiles,# determine what we actually want to build. 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.  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))  $(call expand-required-modules,product_MODULES,$(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)  endifelse  # 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# When modules are tagged with debug eng or tests, they are installed# for those variants regardless of what the product spec says.debug_MODULES := $(sort \        $(call get-tagged-modules,debug) \        $(call module-installed-files, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES_DEBUG)) \    )eng_MODULES := $(sort \        $(call get-tagged-modules,eng) \        $(call module-installed-files, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES_ENG)) \    )tests_MODULES := $(sort \        $(call get-tagged-modules,tests) \        $(call module-installed-files, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES_TESTS)) \)# TODO: Remove the 3 places in the tree that use ALL_DEFAULT_INSTALLED_MODULES# and get rid of it from this list.# TODO: The shell is chosen by magic.  Do we still need this?modules_to_install := $(sort \    $(ALL_DEFAULT_INSTALLED_MODULES) \    $(product_FILES) \    $(foreach tag,$(tags_to_install),$($(tag)_MODULES)) \    $(call get-tagged-modules, shell_$(TARGET_SHELL)) \    $(CUSTOM_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).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))   # Ensure every module listed in PRODUCT_PACKAGES* gets something installed  # TODO: Should we do this for all builds and not just the sdk?  $(foreach m, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES), \    $(if $(strip $(ALL_MODULES.$(m).INSTALLED)),,\      $(warning $(ALL_MODULES.$(m).MAKEFILE): Module '$(m)' in PRODUCT_PACKAGES has nothing to install!)))  $(foreach m, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES_DEBUG), \    $(if $(strip $(ALL_MODULES.$(m).INSTALLED)),,\      $(warning $(ALL_MODULES.$(m).MAKEFILE): Module '$(m)' in PRODUCT_PACKAGES_DEBUG has nothing to install!)))  $(foreach m, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES_ENG), \    $(if $(strip $(ALL_MODULES.$(m).INSTALLED)),,\      $(warning $(ALL_MODULES.$(m).MAKEFILE): Module '$(m)' in PRODUCT_PACKAGES_ENG has nothing to install!)))  $(foreach m, $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES_TESTS), \    $(if $(strip $(ALL_MODULES.$(m).INSTALLED)),,\      $(warning $(ALL_MODULES.$(m).MAKEFILE): Module '$(m)' in PRODUCT_PACKAGES_TESTS has nothing to install!)))endif # Install all of the host modulesmodules_to_install += $(sort $(modules_to_install) $(ALL_HOST_INSTALLED_FILES)) # 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.ALL_DEFAULT_INSTALLED_MODULES := $(modules_to_install)include $(BUILD_SYSTEM)/Makefilemodules_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.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 debuggingmodules_to_check := $(sort $(modules_to_check))#$(error modules_to_check $(modules_to_check))