Android NDK - Including prebuilt static libraries gives undefined reference errors

Question

I am trying to build a shared library using a prebuilt static library. For some reason, building always fails giving undefined reference errors. If I add LOCAL_ALLOW_UNDEFINED_SYMBOLS := true, building succeeds but the shared library is only a few kilobytes while the static library is about 3 megabytes... So it seems something went wrong in linking the static library. I have no idea what it could be. I am only using C++ code.

Android.mk:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

LOCAL_MODULE    := kes
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include
LOCAL_SRC_FILES := libkes.a

include $(PREBUILT_STATIC_LIBRARY)

include $(CLEAR_VARS)

LOCAL_MODULE    := PortaKES
LOCAL_SRC_FILES := PortaKES.cpp
LOCAL_STATIC_LIBARIES := kes

include $(BUILD_SHARED_LIBRARY)

Application.mk:

APP_ABI := all
APP_STL := stlport_static

JNI directory structure:

Output:

./obj/local/arm64-v8a/objs/PortaKES/PortaKES.o: In function `Java_com_kurzweil_portakes_KESFile_createPOLEFile':
C:\Users\niels.mylle\Documents\Kurzweil Mobile Android\PortaKES/jni/PortaKES.cpp:18: undefined reference to `CPoleFile::CPoleFile(char const*, bool, bool, CEncrypter*)'
./obj/local/arm64-v8a/objs/PortaKES/PortaKES.o: In function `Java_com_kurzweil_portakes_KESFile_createKSection':
C:\Users\niels.mylle\Documents\Kurzweil Mobile Android\PortaKES/jni/PortaKES.cpp:33: undefined reference to `CKSection::CKSection(char const*, CPoleFile*, CPoleLeaf*)'
./obj/local/arm64-v8a/objs/PortaKES/PortaKES.o: In function `Java_com_kurzweil_portakes_POLEFile_destroy':
C:\Users\niels.mylle\Documents\Kurzweil Mobile Android\PortaKES/jni/PortaKES.cpp:48: undefined reference to `CPoleFile::~CPoleFile()'
./obj/local/arm64-v8a/objs/PortaKES/PortaKES.o: In function `Java_com_kurzweil_portakes_POLEFile_exists':
C:\Users\niels.mylle\Documents\Kurzweil Mobile Android\PortaKES/jni/PortaKES.cpp:100: undefined reference to `CPoleFile::exists(char const*)'
collect2.exe: error: ld returned 1 exit status
make.exe: *** [obj/local/arm64-v8a/libPortaKES.so] Error 1

Answer 1

Maybe it's just part of the problem, but at least this reference is wrong:

LOCAL_SRC_FILES := libkes.a

You're building for all the ndk compatible architectures, but always referencing the same static prebuilt for each of them, which cannot work.

You should have a different .a for each architecture you're targeting, ie ./armeabi/libkes.a, ./x86/libkes.a, ./armeabi-v7a/libkes.a, etc. In that case you'll be able to reference your .a using TARGET_ARCH_ABI variable, like so:

LOCAL_SRC_FILES := $(TARGET_ARCH_ABI)/libkes.a