Android編譯系統分析三：make完整編譯android系統
阿新 • • 發佈：2019-02-13
Android編譯系統分析系列文章：
這篇部落格的目標是摸清楚預設編譯整個android系統時程式碼的流程。
當我們執行make的時候，會查詢當前的Makefie檔案或者makefile檔案並且執行，在android頂級原始碼目錄下面，確實有個Makefile,它之後一行內容：
### DO NOT EDIT THIS FILE ###
include build/core/main.mk
### DO NOT EDIT THIS FILE ###一.依賴淺析
當我們執行make命令的時候，如果沒有傳入一個目標，那麼就會執行預設的目標。注意，我們在編譯android系統的時候，只需要執行make就可以了，那麼很顯然它會執行預設的目標了，那麼預設的目標是什麼呢？
在build/core/main.mk中：
# This is the default target. It must be the first declared target.
.PHONY: droid
DEFAULT_GOAL := droid
$(DEFAULT_GOAL):在main.mk開始不久，就出現了一個偽目標，即便你看不懂Makefile也沒有關係，註釋上說的很清楚了，他就是預設的目標了。而且這個預設的目標是一個偽目標。make工具遇到偽目標以後，會檢查解析偽目標的依賴，如果偽目標存在依賴，就會檢查這些依賴，如果這些依賴是偽目標，繼續檢查這個偽目標的依賴，如果不是偽目標，就會生成這個目標。
閱讀一個Makefile,理清目標的依賴關係很重，下圖列出了部分重要的以來關係：
在對依賴關係有個瞭解之後，我們開始順著make的載入流程，看看它到底做了什麼。
首先，我覺得很重要的就是載入特定產品的配置資訊。
二.配置產品資訊
首先，大致的流程如下圖所示：
在product_config.mk中：
1.AndoridProducts.mk 使用get-all-product-makefiles獲取所有的AndoridProducts.mk檔案：ifneq ($(strip $(TARGET_BUILD_APPS)),) # An unbundled app build needs only the core product makefiles. all_product_configs := $(call get-product-makefiles,\ $(SRC_TARGET_DIR)/product/AndroidProducts.mk) else # Read in all of the product definitions specified by the AndroidProducts.mk # files in the tree. all_product_configs := $(get-all-product-makefiles) endif
define get-all-product-makefiles
$(call get-product-makefiles,$(_find-android-products-files))
endefdefine _find-android-products-files
$(shell test -d device && find device -maxdepth 6 -name AndroidProducts.mk) \
$(shell test -d vendor && find vendor -maxdepth 6 -name AndroidProducts.mk) \
$(SRC_TARGET_DIR)/product/AndroidProducts.mk
endefdefine get-product-makefiles
$(sort \
$(foreach f,$(1), \
$(eval PRODUCT_MAKEFILES :=) \
$(eval LOCAL_DIR := $(patsubst %/,%,$(dir $(f)))) \
$(eval include $(f)) \
$(PRODUCT_MAKEFILES) \
) \
$(eval PRODUCT_MAKEFILES :=) \
$(eval LOCAL_DIR :=) \
)
endef這裡把所有的AndroidProducts.mk都載入進來了，但是我們只需要我們產品的配置資訊呀，所以接著做一個查詢，找到屬於我們產品的AndroidProducts.mk:
# Find the product config makefile for the current product.
# all_product_configs consists items like:
# <product_name>:<path_to_the_product_makefile>
# or just <path_to_the_product_makefile> in case the product name is the
# same as the base filename of the product config makefile.
current_product_makefile :=
all_product_makefiles :=
$(foreach f, $(all_product_configs),\
$(eval _cpm_words := $(subst :,$(space),$(f)))\
$(eval _cpm_word1 := $(word 1,$(_cpm_words)))\
$(eval _cpm_word2 := $(word 2,$(_cpm_words)))\
$(if $(_cpm_word2),\
$(eval all_product_makefiles += $(_cpm_word2))\
$(if $(filter $(TARGET_PRODUCT),$(_cpm_word1)),\
$(eval current_product_makefile += $(_cpm_word2)),),\
$(eval all_product_makefiles += $(f))\
$(if $(filter $(TARGET_PRODUCT),$(basename $(notdir $(f)))),\
$(eval current_product_makefile += $(f)),)))
_cpm_words :=
_cpm_word1 :=
_cpm_word2 :=
current_product_makefile := $(strip $(current_product_makefile))
all_product_makefiles := $(strip $(all_product_makefiles))2.current_product_makefile
最終找到的結果儲存在current_product_makefile中。關於它的值，這裡舉例說明：加入我們在lunch的時候選擇了 5：
1. aosp_arm-eng
2. aosp_arm64-eng
3. aosp_mips-eng
4. aosp_mips64-eng
5. aosp_x86-eng
6. aosp_x86_64-engifneq (,$(filter product-graph dump-products, $(MAKECMDGOALS)))
# Import all product makefiles.
$(call import-products, $(all_product_makefiles))
else
# Import just the current product.
ifndef current_product_makefile
$(error Can not locate config makefile for product "$(TARGET_PRODUCT)")
endif
ifneq (1,$(words $(current_product_makefile)))
$(error Product "$(TARGET_PRODUCT)" ambiguous: matches $(current_product_makefile))
endif
$(call import-products, $(current_product_makefile))
endif # Import all or just the current product makefile
# Sanity check
$(check-all-products)
4然後獲取TARGET_DEVICE的值：
# Find the device that this product maps to.
TARGET_DEVICE := $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_DEVICE)5獲取要拷貝的檔案
# A list of words like <source path>:<destination path>[:<owner>].
# The file at the source path should be copied to the destination path
# when building this product. <destination path> is relative to
# $(PRODUCT_OUT), so it should look like, e.g., "system/etc/file.xml".
# The rules for these copy steps are defined in build/core/Makefile.
# The optional :<owner> is used to indicate the owner of a vendor file.
PRODUCT_COPY_FILES := \
$(strip $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_COPY_FILES))這個變數也很重要，它儲存了需要拷貝的檔案。格式為 <source path>:<destination path>，在build/core/Makefile一開始就會先拷貝這個變數指定的檔案。
6.載入BoardConfig.mk
又回到envsetup.mk中：
# Boards may be defined under $(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)
# or under vendor/*/$(TARGET_DEVICE). Search in both places, but
# make sure only one exists.
# Real boards should always be associated with an OEM vendor.
board_config_mk := \
$(strip $(wildcard \
$(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)/BoardConfig.mk \
$(shell test -d device && find device -maxdepth 4 -path '*/$(TARGET_DEVICE)/BoardConfig.mk') \
$(shell test -d vendor && find vendor -maxdepth 4 -path '*/$(TARGET_DEVICE)/BoardConfig.mk') \
))
ifeq ($(board_config_mk),)
$(error No config file found for TARGET_DEVICE $(TARGET_DEVICE))
endif
ifneq ($(words $(board_config_mk)),1)
$(error Multiple board config files for TARGET_DEVICE $(TARGET_DEVICE): $(board_config_mk))
endif
include $(board_config_mk)
ifeq ($(TARGET_ARCH),)
$(error TARGET_ARCH not defined by board config: $(board_config_mk))
endifBoardConfig.mk中配置了重要的板級資訊，比如cpu架構等。
至此，配置一個產品所需的AndroidProducts.mk,具體產品的配置檔案，比如這裡的mini_x86.mk以及BoardConfig.mk都載入進來了。
三.載入所有模組
載入完單板資訊，make又回到main.mk中，不就就發現了ONE_SHOT_MAKEFILE變數的判斷：
1ONE_SHOT_MAKEFILE
ifneq ($(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.
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-%: ;
# A helper goal printing out install paths
.PHONY: GET-INSTALL-PATH
GET-INSTALL-PATH:
@$(foreach m, $(ALL_MODULES), $(if $(ALL_MODULES.$(m).INSTALLED), \
echo 'INSTALL-PATH: $(m) $(ALL_MODULES.$(m).INSTALLED)';))
else # ONE_SHOT_MAKEFILE
ifneq ($(dont_bother),true)
#
# 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_DIR) --prune=.repo --prune=.git $(subdirs) Android.mk)
$(foreach mk, $(subdir_makefiles), $(info including $(mk) ...)$(eval include $(mk)))
endif # dont_bother
endif # ONE_SHOT_MAKEFILEMAKECMDGOALS是make的一個環境變數，當我們執行make的時候並沒有設定它，因此它為空。所以dont_bother不等於true,因此，就會載入所有的Android.mk.這裡使用
一個python指令碼查詢系統中所有的Android.mk，然後Include進來。
四 收集所有要安裝的模組
在main.mk中繼續往下看：
3.1FULL_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.mk.
product_MODULES := $(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_PACKAGES)
# Filter out the overridden packages before doing expansion
product_MODULES := $(filter-out $(foreach p, $(product_MODULES), \
$(PACKAGES.$(p).OVERRIDES)), $(product_MODULES))
# Resolve the :32 :64 module name
modules_32 := $(patsubst %:32,%,$(filter %:32, $(product_MODULES)))
modules_64 := $(patsubst %:64,%,$(filter %:64, $(product_MODULES)))
modules_rest := $(filter-out %:32 %:64,$(product_MODULES))
# Note for 32-bit product, $(modules_32) and $(modules_64) will be
# added as their original module names.
product_MODULES := $(call get-32-bit-modules-if-we-can, $(modules_32))
product_MODULES += $(modules_64)
# For the rest we add both
product_MODULES += $(call get-32-bit-modules, $(modules_rest))
product_MODULES += $(modules_rest)
$(call expand-required-modules,product_MODULES,$(product_MODULES))
product_FILES := $(call module-installed-files, $(product_MODULES))
ifeq (0,1)
$(info product_FILES for $(TARGET_DEVICE) ($(INTERNAL_PRODUCT)):)
$(foreach p,$(product_FILES),$(info : $(p)))
$(error done)
endif
else
# We're not doing a full build, and are probably only including
# a subset of the module makefiles. Don't try to build any modules
# requested by the product, because we probably won't have rules
# to build them.
product_FILES :=
endifproduct_MODULES是所有產品配置檔案中新增的要打包進系統映象中的模組，它只是一個名字，比如上篇部落格分析過的screencap。
product_FILES獲取對應模組的.INSTALLED的值。
define module-installed-files
$(foreach module,$(1),$(ALL_MODULES.$(module).INSTALLED))
endef$(ALL_MODULES.$(target)).BUILT $(ALL_MODULES.$(target)).INSTALLED
它們在base_rule.mk中生成：
ALL_MODULES.$(my_register_name).BUILT := \
$(ALL_MODULES.$(my_register_name).BUILT) $(LOCAL_BUILT_MODULE)
ifneq (true,$(LOCAL_UNINSTALLABLE_MODULE))
ALL_MODULES.$(my_register_name).INSTALLED := \
$(strip $(ALL_MODULES.$(my_register_name).INSTALLED) $(LOCAL_INSTALLED_MODULE))
ALL_MODULES.$(my_register_name).BUILT_INSTALLED := \
$(strip $(ALL_MODULES.$(my_register_name).BUILT_INSTALLED) $(LOCAL_BUILT_MODULE):$(LOCAL_INSTALLED_MODULE))
endif$(ALL_MODULES.$(target)).BUILT代表的一般是out/target/product/xxx/obj下編譯生成的模組。
$(ALL_MODULES.$(target)).INSTALLED代表的是out/target/product/xxx/system下生成的模組。
3.2 全部安裝模組
modules_to_install := $(sort \
$(ALL_DEFAULT_INSTALLED_MODULES) \
$(product_FILES) \
$(foreach tag,$(tags_to_install),$($(tag)_MODULES)) \
$(CUSTOM_MODULES) \
)ALL_DEFAULT_INSTALLED_MODULES是系統預設要安裝的模組，product_FILES是特定產品附加的要安裝的模組，foreach找到的是特定
TAG的模組，以及加上CUSTOM_MODULES,這樣modules_to_install就是全部的要安裝的模組了。
ALL_DEFAULT_INSTALLED_MODULES := $(modules_to_install)
include $(BUILD_SYSTEM)/Makefile然後把modules_to_install的值全部賦給ALL_DEFAULT_INSTALLED_MODULES,接著載入build/core/Makefile。這個Makefile會使用
ALL_DEFAULT_INSTALLED_MODULES變數最終生成所有的映象檔案。生成映象檔案的過程放在下一節討論。
四.編譯所有模組
依賴關係我們在一開始就做了簡單的梳理，現在開始分析編譯所有模組的依賴關係。
從droid目標定義的地方來看，沒有看到它的依賴，但我們向下搜尋，就會發現：
.PHONY: apps_only
apps_only: $(unbundled_build_modules)
droid: apps_only# Building a full system-- the default is to build droidcore
droid: droidcore dist_files我們會發現它有出現了兩個依賴，那它到底依賴哪一個呢？
droid依賴哪一個取決於ifneq ($(TARGET_BUILD_APPS),)是否成立,也就是有沒有給TARGET_BUILD_APPS賦值過，原始碼如下：
ifneq ($(TARGET_BUILD_APPS),)
# If this build is just for apps, only build apps and not the full system by default.
unbundled_build_modules :=
ifneq ($(filter all,$(TARGET_BUILD_APPS)),)
# If they used the magic goal "all" then build all apps in the source tree.
unbundled_build_modules := $(foreach m,$(sort $(ALL_MODULES)),$(if $(filter APPS,$(ALL_MODULES.$(m).CLASS)),$(m)))
else
unbundled_build_modules := $(TARGET_BUILD_APPS)
endif
...
.PHONY: apps_only
apps_only: $(unbundled_build_modules)
droid: apps_only
else # TARGET_BUILD_APPS
$(call dist-for-goals, droidcore, \
$(INTERNAL_UPDATE_PACKAGE_TARGET) \
$(INTERNAL_OTA_PACKAGE_TARGET) \
$(BUILT_OTATOOLS_PACKAGE) \
$(SYMBOLS_ZIP) \
$(INSTALLED_FILES_FILE) \
$(INSTALLED_BUILD_PROP_TARGET) \
$(BUILT_TARGET_FILES_PACKAGE) \
$(INSTALLED_ANDROID_INFO_TXT_TARGET) \
$(INSTALLED_RAMDISK_TARGET) \
)
# Building a full system-- the default is to build droidcore
droid: droidcore dist_files
endif # TARGET_BUILD_APPS
我們期望的是整個系統的編譯，所以，droid依賴的是droidcore 和 dist_files
4.1droidcore的定義：
# 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_CACHEIMAGE_TARGET) \
$(INSTALLED_VENDORIMAGE_TARGET) \
$(INSTALLED_FILES_FILE)可以droidcore又是一個偽目標，它又依賴於files 等一系列目標，從名字來看，這些目標應該是systemimage,userdataimage,recoryimage等，也就是說，droidcore的最終目的就是生成system.img,userdata.img等系統映象檔案。
看到變數的定義就明白了：
1.boot.img:
INSTALLED_BOOTIMAGE_TARGET := $(PRODUCT_OUT)/boot.img
2.recovery.img:
INSTALLED_RECOVERYIMAGE_TARGET := $(PRODUCT_OUT)/recovery.img
3.userdata.img:
INSTALLED_USERDATAIMAGE_TARGET := $(BUILT_USERDATAIMAGE_TARGET)
--->BUILT_USERDATAIMAGE_TARGET := $(PRODUCT_OUT)/userdata.img
4.cache.img
INSTALLED_CACHEIMAGE_TARGET := $(BUILT_CACHEIMAGE_TARGET)
--->BUILT_CACHEIMAGE_TARGET := $(PRODUCT_OUT)/cache.img
5.vendor.img
INSTALLED_VENDORIMAGE_TARGET := $(BUILT_VENDORIMAGE_TARGET)
BUILT_VENDORIMAGE_TARGET := $(PRODUCT_OUT)/vendor.img
因此，droidcore的最終目的就是生成這些.Img檔案。
dist_files的定義：
# dist_files only for putting your library into the dist directory with a full build.
.PHONY: dist_files4.2.files
它的第一個目標是files:
# All the droid stuff, in directories
.PHONY: files
files: prebuilt \
$(modules_to_install) \
$(INSTALLED_ANDROID_INFO_TXT_TARGET)、1.1files又依賴了三個目標，第一個是prebuilt:
# -------------------------------------------------------------------
# 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）prebuilt又是一個偽目標，它又依賴於ALL_PREBUILT變數指向的目標，ALL_PREBUILT是一些預編譯模組：
Android.mk (makefile\frameworks\base\cmds\bmgr):ALL_PREBUILT += $(TARGET_OUT)/bin/bmgr
Android.mk (makefile\frameworks\base\cmds\ime):ALL_PREBUILT += $(TARGET_OUT)/bin/ime
Android.mk (makefile\frameworks\base\cmds\input):ALL_PREBUILT += $(TARGET_OUT)/bin/input
Android.mk (makefile\frameworks\base\cmds\pm):ALL_PREBUILT += $(TARGET_OUT)/bin/pm
Android.mk (makefile\frameworks\base\cmds\svc):ALL_PREBUILT += $(TARGET_OUT)/bin/svc4.3modules_to_install
modules_to_install := $(sort \
$(ALL_DEFAULT_INSTALLED_MODULES) \
$(product_FILES) \
$(foreach tag,$(tags_to_install),$($(tag)_MODULES)) \
$(CUSTOM_MODULES) \
)
這個變數之前已經分析過，它包含所有的要安裝的模組，make會為這個目標生成依賴關係鏈，也就是會給其中的每一個模組生成依賴關係鏈，然後編譯每一個模組，這個過程在上一節中已經說過了。
至此，所有應該編譯的模組都已經被編譯，剩下的就是打包映象檔案了。這將在下一節討論。