Android build system note

很是有用的记录，感谢做者！
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1. Android编译系统分析
编译脚本及系统变量
build/envsetup.sh脚本分析
在编译源代码以前一般须要在android源代码顶层目录执行 . ./build/envsetup.sh 目的是为了使用
脚本 envsetup.sh 里面定义了一些函数：
function help()
function get_abs_build_var()
function get_build_var()
function check_product()
function check_variant()
function setpaths()
function printconfig()
function set_stuff_for_environment()
function set_sequence_number()
function settitle()
function choosetype()
function chooseproduct()
function choosevariant()
function tapas()
function choosecombo()
function print_lunch_menu()
function lunch()
function gettop
function m()
function findmakefile()
function mm()
function mmm()
function croot()
function pid()
function gdbclient()
function jgrep()
function cgrep()
function resgrep()
function getprebuilt
function tracedmdump()
function runhat()
function getbugreports()
function startviewserver()
function stopviewserver()
function isviewserverstarted()
function smoketest()
function runtest()
function runtest_py()
function godir ()

choosecombo 命令分析：
function choosecombo()
{
choosesim $1
echo
echo
choosetype $2

echo
echo
chooseproduct $3

echo
echo
choosevariant $4

echo
set_stuff_for_environment
printconfig
}
会依次进行以下选择：
Build for the simulator or the device?
1. Device
2. Simulator
Which would you like? [1] 

Build type choices are:
1. release
2. debug
Which would you like? [1] 

Product choices are:
1. emulator
2. generic
3. sim
4. littleton
You can also type the name of a product if you know it.
Which would you like? [littleton] 

Variant choices are:
1. user
2. userdebug
3. eng
Which would you like? [eng] user
默认选择之后会出现：
TARGET_PRODUCT=littleton
TARGET_BUILD_VARIANT=user
TARGET_SIMULATOR=false
TARGET_BUILD_TYPE=release
TARGET_ARCH=arm
HOST_ARCH=x86
HOST_OS=linux
HOST_BUILD_TYPE=release
BUILD_ID=
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function chooseproduct()函数分析：
choices=(`/bin/ls build/target/board/*/BoardConfig.mk vendor/*/*/BoardConfig.mk 2> /dev/null`)
读取 build/target/board/* 目录下的板配置文件：BoardConfig.mk
读取 vendor/*/*/目录下的板配置文件：BoardConfig.mk
choices 的值为：
build/target/board/emulator/BoardConfig.mk
build/target/board/generic/BoardConfig.mk
build/target/board/sim/BoardConfig.mk
vendor/marvell/littleton/BoardConfig.mk
通过：
for choice in ${choices[@]}
do
# The product name is the name of the directory containing
# the makefile we found, above.
prodlist=(${prodlist[@]} `dirname ${choice} | xargs basename`)
done
的处理，prodlist的值为：
emulator generic sim littleton
因此选择菜单为：
Product choices are:
1. emulator
2. generic
3. sim
4. littleton
若是选择 4，那么 TARGET_PRODUCT 被赋值为： littleton。


board_config_mk := \
$(strip $(wildcard \
$(SRC_TARGET_DIR)/board/$(TARGET_DEVICE)/BoardConfig.mk \
vendor/*/$(TARGET_DEVICE)/BoardConfig.mk \
))



怎样添加一个模块
LOCAL_PATH:= $(call my-dir)
#编译静态库
include $(CLEAR_VARS)
LOCAL_MODULE = libhellos
LOCAL_CFLAGS = $(L_CFLAGS)
LOCAL_SRC_FILES = hellos.c
LOCAL_C_INCLUDES = $(INCLUDES)
LOCAL_SHARED_LIBRARIES := libcutils
LOCAL_COPY_HEADERS_TO := libhellos
LOCAL_COPY_HEADERS := hellos.h
include $(BUILD_STATIC_LIBRARY)

#编译动态库
include $(CLEAR_VARS)
LOCAL_MODULE = libhellod
LOCAL_CFLAGS = $(L_CFLAGS)
LOCAL_SRC_FILES = hellod.c
LOCAL_C_INCLUDES = $(INCLUDES)
LOCAL_SHARED_LIBRARIES := libcutils
LOCAL_COPY_HEADERS_TO := libhellod
LOCAL_COPY_HEADERS := hellod.h
include $(BUILD_SHARED_LIBRARY)

BUILD_TEST=true
ifeq ($(BUILD_TEST),true)
#使用静态库
include $(CLEAR_VARS)
LOCAL_MODULE := hellos
LOCAL_STATIC_LIBRARIES := libhellos
LOCAL_SHARED_LIBRARIES :=
LOCAL_LDLIBS += -ldl
LOCAL_CFLAGS := $(L_CFLAGS)
LOCAL_SRC_FILES := mains.c
LOCAL_C_INCLUDES := $(INCLUDES)
include $(BUILD_EXECUTABLE)

#使用动态库
include $(CLEAR_VARS)
LOCAL_MODULE := hellod
LOCAL_MODULE_TAGS := debug
LOCAL_SHARED_LIBRARIES := libc libcutils libhellod
LOCAL_LDLIBS += -ldl
LOCAL_CFLAGS := $(L_CFLAGS)
LOCAL_SRC_FILES := maind.c
LOCAL_C_INCLUDES := $(INCLUDES)
include $(BUILD_EXECUTABLE)
endif # ifeq ($(WPA_BUILD_SUPPLICANT),true)

########################
#local_target_dir := $(TARGET_OUT)/etc/wifi
#include $(CLEAR_VARS)
#LOCAL_MODULE := wpa_supplicant.conf
#LOCAL_MODULE_TAGS := user
#LOCAL_MODULE_CLASS := ETC
#LOCAL_MODULE_PATH := $(local_target_dir)
#LOCAL_SRC_FILES := $(LOCAL_MODULE)
#include $(BUILD_PREBUILT)
########################
系统变量解析
LOCAL_MODULE － 编译的目标对象
LOCAL_SRC_FILES － 编译的源文件
LOCAL_C_INCLUDES － 须要包含的头文件目录
LOCAL_SHARED_LIBRARIES － 连接时须要的外部库
LOCAL_PRELINK_MODULE － 是否须要prelink处理
BUILD_SHARED_LIBRARY － 指明要编译成动态库


LOCAL_PATH - 编译时的目录
$(call 目录，目录….) 目录引入操做符
如该目录下有个文件夹名称 src，则能够这样写 $(call src)，那么就会获得 src 目录的完整路径

include $(CLEAR_VARS) -清除以前的一些系统变量
CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mk
在 build/core/config.mk 定义 CLEAR_VARS:= $(BUILD_SYSTEM)/clear_vars.mk
经过include 包含自定义的.mk文件（便是自定义编译规则）或是引用系统其余的.mk文件（系统定义的编译规则）。

LOCAL_SRC_FILES － 编译的源文件
能够是.c, .cpp, .java, .S（汇编文件）或是.aidl等格式
不一样的文件用空格隔开。若是编译目录子目录，采用相对路径，如子目录/文件名。也能够经过$(call 目录)，指明编译某目录
下全部.c/.cpp/.java/.S/ .aidl文件.追加文件 LOCAL_SRC_FILES += 文件

LOCAL_C_INCLUDES － 须要包含的头文件目录
能够是系统定义路径，也能够是相对路径. 如该编译目录下有个include目录，写法是include/*.h

LOCAL_SHARED_LIBRARIES － 连接时须要的外部共享库
LOCAL_STATIC_LIBRA RIES － 连接时须要的外部外部静态
LOCAL_JAVA_LIBRARIES 加入jar包

LOCAL_MODULE － 编译的目标对象
module 是指系统的 native code，一般针对c,c++代码
./system/core/sh/Android.mk:32:LOCAL_MODULE:= sh
./system/core/libcutils/Android.mk:71:LOCAL_MODULE := libcutils
./system/core/cpio/Android.mk:9:LOCAL_MODULE := mkbootfs
./system/core/mkbootimg/Android.mk:8:LOCAL_MODULE := mkbootimg
./system/core/toolbox/Android.mk:61:LOCAL_MODULE:= toolbox
./system/core/logcat/Android.mk:10:LOCAL_MODULE:= logcat
./system/core/adb/Android.mk:65:LOCAL_MODULE := adb
./system/core/adb/Android.mk:125:LOCAL_MODULE := adbd
./system/core/init/Android.mk:20:LOCAL_MODULE:= init
./system/core/vold/Android.mk:24:LOCAL_MODULE:= vold
./system/core/mountd/Android.mk:13:LOCAL_MODULE:= mountd

LOCAL_PACKAGE_NAME 
Java 应用程序的名字用该变量定义
./packages/apps/Music/Android.mk:9:LOCAL_PACKAGE_NAME := Music
./packages/apps/Browser/Android.mk:14:LOCAL_PACKAGE_NAME := Browser
./packages/apps/Settings/Android.mk:8:LOCAL_PACKAGE_NAME := Settings
./packages/apps/Stk/Android.mk:10:LOCAL_PACKAGE_NAME := Stk
./packages/apps/Contacts/Android.mk:10:LOCAL_PACKAGE_NAME := Contacts
./packages/apps/Mms/Android.mk:8:LOCAL_PACKAGE_NAME := Mms
./packages/apps/Camera/Android.mk:8:LOCAL_PACKAGE_NAME := Camera
./packages/apps/Phone/Android.mk:11:LOCAL_PACKAGE_NAME := Phone
./packages/apps/VoiceDialer/Android.mk:8:LOCAL_PACKAGE_NAME := VoiceDialer


BUILD_SHARED_LIBRARY － 指明要编译成动态库。
编译的目标，用include 操做符
UILD_STATIC_LIBRARY来指明要编译成静态库。
若是是java文件的话，会用到系统的编译脚本host_java_library.mk，用BUILD_PACKAGE来指明。三个编译
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include $(BUILD_STATIC_LIBRARY)
BUILD_STATIC_LIBRARY:= $(BUILD_SYSTEM)/static_library.mk
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include $(BUILD_SHARED_LIBRARY)
./build/core/config.mk:50:BUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.mk
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include $(BUILD_HOST_SHARED_LIBRARY)
BUILD_HOST_SHARED_LIBRARY:= $(BUILD_SYSTEM)/host_shared_library.mk
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include $(BUILD_EXECUTABLE)
build/core/config.mk:51:BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mk
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include $(BUILD_HOST_EXECUTABLE)
./build/core/config.mk:53:BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk
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BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk
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BUILD_JAVA_LIBRARY
./build/core/config.mk:58:BUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mk
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BUILD_STATIC_JAVA_LIBRARY 编译静态JAVA库
./build/core/config.mk:59:BUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mk
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BUILD_HOST_JAVA_LIBRARY 编译本机用的JAVA库
./build/core/config.mk:60:BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk
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BUILD_HOST_STATIC_LIBRARY:= $(BUILD_SYSTEM)/host_static_library.mk
BUILD_HOST_SHARED_LIBRARY:= $(BUILD_SYSTEM)/host_shared_library.mk
BUILD_STATIC_LIBRARY:= $(BUILD_SYSTEM)/static_library.mk
BUILD_RAW_STATIC_LIBRARY := $(BUILD_SYSTEM)/raw_static_library.mk
BUILD_SHARED_LIBRARY:= $(BUILD_SYSTEM)/shared_library.mk
BUILD_EXECUTABLE:= $(BUILD_SYSTEM)/executable.mk
BUILD_RAW_EXECUTABLE:= $(BUILD_SYSTEM)/raw_executable.mk
BUILD_HOST_EXECUTABLE:= $(BUILD_SYSTEM)/host_executable.mk
BUILD_PACKAGE:= $(BUILD_SYSTEM)/package.mk
BUILD_HOST_PREBUILT:= $(BUILD_SYSTEM)/host_prebuilt.mk
BUILD_PREBUILT:= $(BUILD_SYSTEM)/prebuilt.mk
BUILD_MULTI_PREBUILT:= $(BUILD_SYSTEM)/multi_prebuilt.mk
BUILD_JAVA_LIBRARY:= $(BUILD_SYSTEM)/java_library.mk
BUILD_STATIC_JAVA_LIBRARY:= $(BUILD_SYSTEM)/static_java_library.mk
BUILD_HOST_JAVA_LIBRARY:= $(BUILD_SYSTEM)/host_java_library.mk
BUILD_DROIDDOC:= $(BUILD_SYSTEM)/droiddoc.mk
BUILD_COPY_HEADERS := $(BUILD_SYSTEM)/copy_headers.mk
BUILD_KEY_CHAR_MAP := $(BUILD_SYSTEM)/key_char_map.mk

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LOCAL_PRELINK_MODULE
Prelink利用事先连接代替运行时连接的方法来加速共享库的加载，它不只能够加快起动速度，还能够减小部份内存开销，
是各类Linux架构上用于减小程序加载时间、缩短系统启动时间和加快应用程序启动的很受欢迎的一个工具。程序运行时的
动态连接尤为是重定位(relocation)的开销对于大型系统来讲是很大的。
动态连接和加载的过程开销很大，而且在大多数的系统上, 函数库并不会经常被更动, 每次程序被执行时所进行的连接
动做都是彻底相同的，对于嵌入式系统来讲尤为如此。所以，这一过程能够改在运行时以前就能够预先处理好，即花一些时间
利用Prelink工具对动态共享库和可执行文件进行处理，修改这些二进制文件并加入相应的重定位等信息，节约了原本在程序
启动时的比较耗时的查询函数地址等工做，这样能够减小程序启动的时间，同时也减小了内存的耗用。 
Prelink的这种作法固然也有代价：每次更新动态共享库时，相关的可执行文件都须要从新执行一遍Prelink才能保
证有效，由于新的共享库中的符号信息、地址等极可能与原来的已经不一样了，这就是为何 android framework代码一改动，
这时候就会致使相关的应用程序从新被编译。
这种代价对于嵌入式系统的开发者来讲可能稍微带来一些复杂度，不过好在对用户来讲几乎是能够忽略的。
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变量设置为false那么将不作prelink操做
LOCAL_PRELINK_MODULE := false
默认是须要prlink的，同时须要在 build/core/prelink-linux-arm.map 中加入
libhellod.so 0x96000000
这个map文件好像是制定动态库的地址的，在前面注释上面有一些地址范围的信息，注意库与库之间的间隔数，
若是指定很差的话编译的时候会提示说地址空间冲突的问题。另外，注意排序，这里要把数大的放到前面去，
按照大小降序排序。
解析 LOCAL_PRELINK_MODULE 变量
build/core/dynamic_binary.mk:94:ifeq ($(LOCAL_PRELINK_MODULE),true)
ifeq ($(LOCAL_PRELINK_MODULE),true)
$(prelink_output): $(prelink_input) $(TARGET_PRELINKER_MAP) $(APRIORI)
$(transform-to-prelinked)
transform-to-prelinked定义：
./build/core/definitions.mk:1002:define transform-to-prelinked
define transform-to-prelinked
@mkdir -p $(dir $@)
@echo "target Prelink: $(PRIVATE_MODULE) ($@)"
$(hide) $(APRIORI) \
--prelinkmap $(TARGET_PRELINKER_MAP) \
--locals-only \
--quiet \
$< \
--output $@
endef
./build/core/config.mk:183:APRIORI := $(HOST_OUT_EXECUTABLES)/apriori$(HOST_EXECUTABLE_SUFFIX)
prelink工具不是经常使用的prelink而是apriori，其源代码位于” <your_android>/build/tools/apriori”
参考文档：
动态库优化——Prelink（预链接）技术
http://www.eefocus.com/article/09-04/71629s.html


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LOCAL_ARM_MODE := arm
目前Android大部分都是基于Arm处理器的，Arm指令用两种模式Thumb(每条指令两个字节)和arm指令（每条指令四个字节）

LOCAL_CFLAGS += -O3 -fstrict-aliasing -fprefetch-loop-arrays
经过设定编译器操做，优化级别，-O0表示没有优化,-O1为缺省值，-O3优化级别最高
LOCAL_CFLAGS += -W -Wall
LOCAL_CFLAGS += -fPIC -DPIC
LOCAL_CFLAGS += -O2 -g -DADB_HOST=1 -Wall -Wno-unused-parameter
LOCAL_CFLAGS += -D_XOPEN_SOURCE -D_GNU_SOURCE -DSH_HISTORY
LOCAL_CFLAGS += -DUSEOVERLAY2
根据条件选择相应的编译参数
ifeq ($(TARGET_ARCH),arm)
LOCAL_CFLAGS += -DANDROID_GADGET=1
LOCAL_CFLAGS := $(PV_CFLAGS)
endif
ifeq ($(TARGET_BUILD_TYPE),release)
LOCAL_CFLAGS += -O2
endif

LOCAL_LDLIBS := -lpthread
LOCAL_LDLIBS += -ldl

ifdef USE_MARVELL_MVED
LOCAL_WHOLE_STATIC_LIBRARIES += lib_il_mpeg4aspdecmved_wmmx2lnx lib_il_h264decmved_wmmx2lnx
LOCAL_SHARED_LIBRARIES += libMrvlMVED
else
LOCAL_WHOLE_STATIC_LIBRARIES += lib_il_h264dec_wmmx2lnx lib_il_mpeg4aspdec_wmmx2lnx
endif
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