Android NDK error: undefined reference

Question

There have been some questions similar to mine, but it seems that their solutions don't work for me.

I'm trying to compile dumpsys source code using Android NDK. I have added a couple of lines to Android.mk to include the libraries. The final Android.mk file looks like this:

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

LOCAL_SRC_FILES:= \
        dumpsys.cpp

LOCAL_SHARED_LIBRARIES := \
        libutils \
        liblog \
        libbinders

ANDROID_SRC="my android source directory"
LOCAL_C_INCLUDES := ${ANDROID_SRC}/frameworks/native/include \
                        ${ANDROID_SRC}/system/core/include

#$(warning $(TARGET_C_INCLUDES))

LOCAL_MODULE:= dumpsys

TARGET_ARCH := arm

TARGET_ARCH_ABI := armeabi-v7a

include $(BUILD_EXECUTABLE)

when I execute ndk-build, I get the following errors:

/home/mahdi/university/androidsource/system/core/include/utils/TypeHelpers.h:144: error: undefined reference to 'android::String16::~String16()'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:240: error: undefined reference to 'android::VectorImpl::finish_vector()'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:241: error: undefined reference to 'android::VectorImpl::~VectorImpl()'
/home/mahdi/university/androidsource/system/core/include/utils/TypeHelpers.h:135: error: undefined reference to 'android::String16::String16()'
/home/mahdi/university/androidsource/system/core/include/utils/TypeHelpers.h:154: error: undefined reference to 'android::String16::String16(android::String16 const&)'
/home/mahdi/university/androidsource/system/core/include/utils/TypeHelpers.h:166: error: undefined reference to 'android::String16::String16(android::String16 const&)'
/home/mahdi/university/androidsource/system/core/include/utils/String16.h:178: error: undefined reference to 'strzcmp16'
/home/mahdi/university/androidsource/system/core/include/utils/StrongPointer.h:143: error: undefined reference to 'android::RefBase::decStrong(void const*) const'
jni/dumpsys.cpp:32: error: undefined reference to 'android::defaultServiceManager()'
jni/dumpsys.cpp:35: error: undefined reference to '__android_log_print'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:224: error: undefined reference to 'android::VectorImpl::VectorImpl(unsigned int, unsigned int)'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:224: error: undefined reference to 'android::VectorImpl::VectorImpl(unsigned int, unsigned int)'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:245: error: undefined reference to 'android::VectorImpl::operator=(android::VectorImpl const&)'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:378: error: undefined reference to 'android::VectorImpl::sort(int (*)(void const*, void const*))'
jni/dumpsys.cpp:49: error: undefined reference to 'android::String16::String16(char const*)'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:338: error: undefined reference to 'android::VectorImpl::add(void const*)'
jni/dumpsys.cpp:49: error: undefined reference to 'android::String16::~String16()'
jni/dumpsys.cpp:51: error: undefined reference to 'android::String16::String16(char const*)'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:338: error: undefined reference to 'android::VectorImpl::add(void const*)'
jni/dumpsys.cpp:51: error: undefined reference to 'android::String16::~String16()'
jni/dumpsys.cpp:53: error: undefined reference to 'android::String16::String16(char const*)'
/home/mahdi/university/androidsource/system/core/include/utils/Vector.h:338: error: undefined reference to 'android::VectorImpl::add(void const*)'
jni/dumpsys.cpp:53: error: undefined reference to 'android::String16::~String16()'
jni/dumpsys.cpp:66: error: undefined reference to 'android::operator<<(android::TextOutput&, android::String16 const&)'
jni/dumpsys.cpp:81: error: undefined reference to 'android::operator<<(android::TextOutput&, android::String16 const&)'
jni/dumpsys.cpp:89: error: undefined reference to 'android::operator<<(android::TextOutput&, android::String16 const&)'
/home/mahdi/university/androidsource/system/core/include/utils/StrongPointer.h:143: error: undefined reference to 'android::RefBase::decStrong(void const*) const'
jni/dumpsys.cpp:94: error: undefined reference to 'android::aerr'
jni/dumpsys.cpp:94: error: undefined reference to 'android::aout'
collect2: error: ld returned 1 exit status

How should I solve this issue?

Thanks in advance.

Answer 1

I'm working on a similar issue here.

Basically, dumpsys is an AOSP component and intended to be built with the AOSP toolchain. You will need to apply some tweaks to port it to NDK – including stuff from ${ANDROID_SRC} is the first step but not the whole story.

You've successfully included the headers and thus made the compiler happy. Now the linker is complaining because it cannot find the libraries you are linking against. The good news is that they are shared libraries, thus having the libraries around at build time isn't a strict requirement.

The NDK defines a stable API of libraries you can use, which is documented here. liblog is in that list and can be included by adding the following lines to Android.mk:

LOCAL_LDLIBS := \
  -llog \

The other two libraries are not part of the stable API. This essentially means that even if your code works on a particular version of Android, it may break on any later version because the API may have changed – you might want to bear this in mind.

Since these libraries are shared, all ld does is check if they actually provide the functions you're using. This question and its accepted answer have instructions for getting rid of the related error messages:

One way is to use something like:

LOCAL_LDFLAGS := -Wl,--unresolved-symbols=ignore-all

However, this will bypass all checks – so if you try to use a function that is indeed absent from the library, ld has no chance of warning you.

The cleaner, but more work-intensive approach, is to provide stub libraries. A stub library is essentially a dummy library which defines the same symbols (functions etc.) as the "real" thing but has no implementation (functions simply return without doing anything). It's enough to make the linker happy, but the libraries are not shipped and their "real" counterparts are used at runtime.

You would need to get the source code for the two libraries, which reside in the following directories: libutils and libbinders

system/core/libutils
frameworks/native/libs/binder

Copy these two dirs into your project's jni dir. Then strip the code down: * Edit Android.mk, removing all build targets other than BUILD_SHARED_LIBRARY. * Edit the source code files, replacing all function bodies with a simple return. It doesn't matter what you return, as long as you get the code to compile.

Eventually you will probably need to prevent the stub libraries from getting included in your .apk (I have yet to figure out how to do that).