Add a new component into open source Android

The android build system is complicated. It is not easy to create a simple build script to build single component. But it is much easier to add a new component into the build system. Here is a sample to build the "Hello world!" for Android, and it is dynamic linked executable.

1. create a directory for the new component in $(YOUR_ANDROID)/external folder: $(YOUR_ANDROID)/external/hello
2. put the hello.c into the directory: $(YOUR_ANDROID)/external/hello/
3. create Android.mk in $(YOUR_ANDROID)/external/hello/ directory, the Android.mk likes the following:
   LOCAL_PATH:=$(call my-dir)
   include $(CLEAR_VARS)
   LOCAL_ARM_MODE := arm
   LOCAL_SRC_FILES:= \
   hello.c
   LOCAL_MODULE := hello
   include $(BUILD_EXECUTABLE)
4. add the following line into $(BUILD_SYSTEM)/main.mk,$(BUILD_SYSTEM) is in $(YOUR_ANDROID)/build/core:
   external/hello
5. launch the build command in $(YOUR_ANDROID): make hello

you will have the build target hello in $(YOUR_ANDROID)/out/target/product/generic/system/bin.
You can use include $(BUILD_SHARED_LIBRARY) to create shared library. Find more in $(YOUR_ANDROID)/build/core/config.mk.