delete your previously generated "obj" file from jni and then add android.mk file like below
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := "your shared library name"// while compile it will be generated as [.so]
LOCAL_SRC_FILES := \
Binder.cpp \
BpBinder.cpp \
CursorWindow.cpp \
IInterface.cpp \
IMemory.cpp \
IPCThreadState.cpp \
IPermissionController.cpp \
IServiceManager.cpp \
MemoryDealer.cpp \
MemoryBase.cpp \
MemoryHeapBase.cpp \
MemoryHeapPmem.cpp \
Parcel.cpp \
PermissionCache.cpp \
ProcessState.cpp \
Static.cpp
include $(BUILD_SHARED_LIBRARY)