NDK build编译的解析

从ndk-build命令开始解析：

1,ndk-build.sh:编译总脚本
a,获取make工具，找到makefile文件;
b,执行make -f makefile(or othername:build-local.mk);
2,build-local.mk:启动的makefile
a,检查NDK_ROOT的合法性;
b,初始化环境init.mk；
c,NDK_PROJECT_PATH：设法找到NDK工程所在的目录；找到NDK_APPLICATION_MK即Application.mk文件，以及输出目录：NDK_APP_OUT := $(NDK_PROJECT_PATH)/obj
d,Fake an application named 'local',虚拟app,并添加之include $(BUILD_SYSTEM)/add-application.mk;
Application.mk文件就是在这一步解析的，通过解析获取变量：APP_DEBUG，APP_MODULES，APP_PROJECT_PATH，APP_PLATFORM，APP_ABI，APP_BUILD_SCRIPT，APP_OPTIM
APP_CFLAGS，APP_STL，NDK_ALL_APPS,此处解析的是：/home/tony/workstation/android-ndk-r6b/build/core/default-application.mk这个文件；
e,开始编译：include $(BUILD_SYSTEM)/build-all.mk
3,init.mk:编译环境初始化
a,检查makefile版本(3.8.1以上);
b,再次检查NDK_ROOT的合法性;
c,检查NDKLOG;
d,设置主机的系统：HOST_OS和主机架构：HOST_ARCH，进而的到一个主机标签：HOST_TAG；如：HOST_OS = linux-HOST_ARCH =x86 --> HOST_TAG = linux-x86;
e,检查使用的awk工具和AWK脚本路径；
f,设置所有的编译脚本路径:BUILD_SYSTEM := $(NDK_ROOT)/build/core，以及公共定义$(BUILD_SYSTEM)/definitions.mk
g,添加交叉编译工具：$(BUILD_SYSTEM)/add-toolchain.mk，在目录$(wildcard $(NDK_ROOT)/toolchains/*/config.mk)下，有所有交叉编译工具的定义，每个工具通过
config.mk和setup.mk两个文件来定义；可以得到：
NDK_ALL_TOOLCHAINS： arm-linux-androideabi-4.4.3 x86-4.4.3
NDK_ALL_ABIS： armeabi armeabi-v7a x86
h,在NDK_PLATFORMS_ROOT下得到所有支持的platform($(NDK_PLATFORMS_ROOT)),
如：android-3 android-4 android-5 android-8 android-9，对于每种平台执行：include $(BUILD_SYSTEM)/add-platform.mk
添加之，并指定：SYSROOT所在，如$(NDK_PLATFORMS_ROOT)/$(_platform)/arch-$(_abi)) = /home/tony/workstation/android-ndk-r6b/platforms/android-9/arch-arm
然后找到各个level值以及最大值
4,build-all.mk,编译开始：
a,初始化各个脚本变量，这些都是Android文件中常用的：
CLEAR_VARS := $(BUILD_SYSTEM)/clear-vars.mk
BUILD_HOST_EXECUTABLE := $(BUILD_SYSTEM)/build-host-executable.mk
BUILD_HOST_STATIC_LIBRARY := $(BUILD_SYSTEM)/build-host-static-library.mk
BUILD_STATIC_LIBRARY := $(BUILD_SYSTEM)/build-static-library.mk
BUILD_SHARED_LIBRARY := $(BUILD_SYSTEM)/build-shared-library.mk
BUILD_EXECUTABLE := $(BUILD_SYSTEM)/build-executable.mk
PREBUILT_SHARED_LIBRARY := $(BUILD_SYSTEM)/prebuilt-shared-library.mk
PREBUILT_STATIC_LIBRARY := $(BUILD_SYSTEM)/prebuilt-static-library.mk
编译过程中会用的一些变量,伪目标，先把他们初始化了
ANDROID_MK_INCLUDED := \
$(CLEAR_VARS) \
$(BUILD_HOST_EXECUTABLE) \
$(BUILD_HOST_STATIC_LIBRARY) \
$(BUILD_STATIC_LIBRARY) \
$(BUILD_SHARED_LIBRARY) \
$(BUILD_EXECUTABLE) \
$(PREBUILT_SHARED_LIBRARY) \

# this is the list of directories containing dependency information
# generated during the build. It will be updated by build scripts
# when module definitions are parsed.
#
ALL_DEPENDENCY_DIRS :=

# this is the list of all generated files that we would need to clean
ALL_HOST_EXECUTABLES :=
ALL_HOST_STATIC_LIBRARIES :=
ALL_STATIC_LIBRARIES :=
ALL_SHARED_LIBRARIES :=
ALL_EXECUTABLES :=

WANTED_INSTALLED_MODULES :=
等等。。。
b,编译开始：
$(foreach _app,$(NDK_APPS),\
$(eval include $(BUILD_SYSTEM)/setup-app.mk)\
)
对每一个app循环，如Fake出来的app:local
5，setup-app.mk：
a,对与每个app,确定TARGET_PLATFORM和TARGET_ARCH_ABI，检查他们的合法性；
b,对于每个TARGET_ARCH_ABI，进行include $(BUILD_SYSTEM)/setup-abi.mk操作；
6,setup-abi.mk:
a,确定：TARGET_ARCH
b,确定：TARGET_OUT,TARGET_OBJS,TARGET_GDB_SETUP；
c,保存：TARGET_PLATFORM -->TARGET_PLATFORM_SAVED
d,include $(BUILD_SYSTEM)/setup-toolchain.mk,建立交叉编译；
//------------------------------------------------------以上涉及的关键控制(如app,abi)都在application.mk里面定义--------------------------------
7,setup-toolchain.mk:
a,获取TARGET_TOOLCHAIN，编译工具
b,获取TARGET_ABI，目标的指令集
c,SYSROOT,用于指定编译时所依赖的库和头文件。
d,统计$(__ndk_modules)模块，并计算每个模块的依赖
e,对于每个模块执行：build-binary.mk
8，build-binary.mk：
a,统计出每个模块里面的变量定义：include $(BUILD_SYSTEM)/import-locals.mk
计算出，LOCAL_CPP_EXTENSION，LOCAL_CFLAGS，LOCAL_OBJECTS，LOCAL_ARM_MODE，LOCAL_ARM_NEON，LOCAL_SRC_FILES，LOCAL_DEPENDENCY_DIRS
LOCAL_STATIC_LIBRARIES，LOCAL_SHARED_LIBRARIES ，LOCAL_WHOLE_STATIC_LIBRARIES， LOCAL_LDLIBS，分问库和源文件两类
b,根据是静态库，动态库或者可执行文件三种类型来进行5种情况的编译，
I,$(cmd-build-shared-library)：If this is a shared library module
II,$(cmd-build-executable)：If this is an executable module
III,$(cmd-build-static-library)：If this is a static library module
IV,Prebuilt：If this is a prebuilt module
V,cmd-strip：If this is an installable module
其中，I,II,III,三种情况使用的编译命令参数可在 $(NDK_ROOT)/toolchains/arm-linux-androideabi-4.4.3/setup.mk中找到定义，
系统中也有默认的(default-build-commands)

//------------------------------------------------------以上关键控制(如:LOCAL_XXX)都在Android.mk里面定义--------------------------------------

Note:
如果你的工程没有Application.mk文件，则系统会用默认的，$(NDK_ROOT)/build/core/default-application.mk

以上就是android-ndk编译文件make走过的全过程

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