Linker errors "undefined reference to 'ceres::internal::SchurEliminator...'" (etc) under Android

[Steffen Gauglitz]

Hello all,

I'm trying to use the Ceres solver for a project in Android. I've compiled the whole project successfully before for Linux x86-64, now trying to port it to Android, but I'm running into some "undefined reference" linker errors and I was hoping somebody could help me figure out what's wrong. I'm using ceres-solver-1.9.0.

I first compiled libceres.a via running ndk-build from ceres' jni folder (http://ceres-solver.org/building.html#android). No problems. I should add that I'm using APP_STL := gnustl_static (details below).
Then, I'm running ndk-build from my project's main folder. Compilation works fine, linking fails with the following error messages:

...
[armeabi-v7a] Compile++ arm  : _myproject <= slam.cpp
[armeabi-v7a] SharedLibrary  : lib_myproject.so
jni/../../ceres-solver-1.9.0/obj/local/armeabi-v7a/libceres.a(schur_eliminator.o):schur_eliminator.cc:vtable for ceres::internal::SchurEliminator<2, 4, 8>: error: undefined reference to 'ceres::internal::SchurEliminator<2, 4, 8>::~SchurEliminator()'
jni/../../ceres-solver-1.9.0/obj/local/armeabi-v7a/libceres.a(schur_eliminator.o):schur_eliminator.cc:vtable for ceres::internal::SchurEliminator<2, 4, 8>: error: undefined reference to 'ceres::internal::SchurEliminator<2, 4, 8>::~SchurEliminator()'
jni/../../ceres-solver-1.9.0/obj/local/armeabi-v7a/libceres.a(schur_eliminator.o):schur_eliminator.cc:vtable for ceres::internal::SchurEliminator<2, 4, 8>: error: undefined reference to 'ceres::internal::SchurEliminator<2, 4, 8>::Init(int, ceres::internal::CompressedRowBlockStructure const*)'
jni/../../ceres-solver-1.9.0/obj/local/armeabi-v7a/libceres.a(schur_eliminator.o):schur_eliminator.cc:vtable for ceres::internal::SchurEliminator<2, 4, 8>: error: undefined reference to 'ceres::internal::SchurEliminator<2, 4, 8>::Eliminate(ceres::internal::BlockSparseMatrix const*, double const*, double const*, ceres::internal::BlockRandomAccessMatrix*, double*)'
jni/../../ceres-solver-1.9.0/obj/local/armeabi-v7a/libceres.a(schur_eliminator.o):schur_eliminator.cc:vtable for ceres::internal::SchurEliminator<2, 4, 8>: error: undefined reference to 'ceres::internal::SchurEliminator<2, 4, 8>::BackSubstitute(ceres::internal::BlockSparseMatrix const*, double const*, double const*, double const*, double*)'
/<...>/ceres-solver-1.9.0/jni/../internal/ceres/partitioned_matrix_view.cc:118: error: undefined reference to 'ceres::internal::PartitionedMatrixView<2, 4, 8>::PartitionedMatrixView(ceres::internal::BlockSparseMatrix const&, int)'
collect2: error: ld returned 1 exit status
make: *** [obj/local/armeabi-v7a/lib_dtslam.so] Error 1

Here are the relevant parts of my project's Android.mk and Application.mk:

--- Application.mk: ---
APP_ABI := armeabi-v7a
APP_PLATFORM := android-16
APP_STL := gnustl_static
APP_CPPFLAGS := -frtti -fexceptions
APP_MODULES = lib_myproject

--- Android.mk: ---
LOCAL_PATH := $(call my-dir)

# Ceres as prebuilt library:
include $(CLEAR_VARS)
LOCAL_MODULE := ceres
LOCAL_SRC_FILES := ../../ceres-solver-1.9.0/obj/local/armeabi-v7a/libceres.a
include $(PREBUILT_STATIC_LIBRARY)

(...including OpenCV here...)

include $(CLEAR_VARS)

LOCAL_MODULE := lib_myproject

# enable C++11 support:
LOCAL_CFLAGS += -std=gnu++11

LOCAL_STATIC_LIBRARIES := \
    opencv_calib3d opencv_features2d opencv_flann opencv_imgproc opencv_core tbb \
    ceres \

LOCAL_SRC_FILES := \
    (list of local source files here)

LOCAL_C_INCLUDES := \
   (list of include paths here)

LOCAL_ARM_MODE := arm

include $(BUILD_SHARED_LIBRARY)

Not sure if this is relevant, but as stated above, I modified ceres' Application.mk and Android.mk to use APP_STL := gnustl_static, because the project *also* uses OpenCV, which appears to not like c++_static (see http://stackoverflow.com/questions/13037659/opencv-build-issue-cant-find-ext-atomicity-h).
The changes for that were: APP_STL := gnustl_static in Application.mk, and adding -std=gnu++11 -DCERES_TR1_MEMORY_HEADER -DCERES_TR1_SHARED_PTR to LOCAL_CFLAGS in Android.mk.

Any ideas what causes the linker errors?

Thanks a lot!
  Steffen

[Sameer Agarwal]

It is asking for the schur specializations but looks like they are not being built?

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[Alex Stewart]

It looks like: generated/schur_eliminator_2_4_8.cc got missed in the Android.mk in 1.9.0

Try adding:

$(CERES_SRC_PATH)/generated/schur_eliminator_2_4_8.cc

above line 187 in ceres/jni/Android.mk and rebuilding Ceres - note that this is fixed in master.

-Alex

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[Alex Stewart]

generated/partitioned_matrix_view_2_4_8.cc

also got missed it seems, so you should also add this above line 205:

$(CERES_SRC_PATH)/generated/partitioned_matrix_view_2_4_8.cc \

-Alex

(P.S. note of course that you also need the trailing backslash after line adding schur_eliminator_2_4_8.cc)

[Steffen Gauglitz]

That was it! Adding those two lines to Android.mk fixed it. Sorry, didn't think of checking the list of source files explicitly. Many thanks for the quick help!!