android系统编写helloworld模块，编译以及adb运行

cd android4.0
mkdir external/hello
cd external/hello
vi hello.c Android.mk
cd ../..

LOCAL_PATH :=$(call my-dir)
$(info $(my-dir))
include $(CLEAR_VARS)
LOCAL_MODULE_TAGS :=optional

LOCAL_SRC_FILES := $(call all-subdir-c-files)
#LOCAL_SRC_FILES := hello.c
LOCAL_MODULE := hello
#LOCAL_SRC_FILES := $(call all-subdir-c-fiies)
include $(BUILD_EXECUTABLE)

#include <stdio.h>
int main()
{
printf("hello world!\n") ;
return 0 ;
}

mmm ./external/hello

adb push out/target/product/generic/system/bin/hello /data

adb shell
cd data
./hello