ndk-build using amadillo (blas lapack) and vlfeat lib - android-ndk

Question

I am trying to compile c++ code written using armadillo that I have uncomment blas lapack in config.hpp and also vlfeat (vl.so) in Andriod make file.
In Jni folder I have the following Andriod.mk
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
PRODUCT_PACKAGES += \libblas
PRODUCT_PACKAGES += \liblapack
PRODUCT_PACKAGES += \libvl
include $(CLEAR_VARS)
LOCAL_MODULE+=mjni
LOCAL_SRC_FILES+=HelloJNI.cpp
LOCAL_SRC_FILES+=featureExtraction.cpp
LOCAL_C_INCLUDES:=$(LOCAL_PATH)/include
LOCAL_C_INCLUDES+=$(LOCAL_PATH)/include/externalInclude/
LOCAL_C_INCLUDES+=$(LOCAL_PATH)/include/externalInclude/armadillo_bits
#LOCAL_SHARED_LIBRARIES := blas lapack
LOCAL_LDLIBS += -llog -ldl
LOCAL_CPP_FEATURES += exceptions
LOCAL_CPPFLAGS += -fexceptions
include $(BUILD_SHARED_LIBRARY)
for each module blas, lapack, and vlfeat I used .so libraries as follows:
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := libvl
MY_LIBRARY_NAME := libvl
### export include path
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/../include/vl
LOCAL_EXPORT_C_INCLUDES += $(LOCAL_PATH)/../include/src
### path to library
LOCAL_SRC_FILES := libvl.so
### export dependency on the library
LOCAL_EXPORT_LDLIBS += -l$(MY_LIBRARY_NAME)
include $(PREBUILT_SHARED_LIBRARY)
and
LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := libblas
MY_LIBRARY_NAME := libblas
### export include path
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/../include/OpenBLAS/include
### path to library
LOCAL_SRC_FILES := libblas.so
### export dependency on the library
LOCAL_EXPORT_LDLIBS += -l$(MY_LIBRARY_NAME)
include $(PREBUILT_SHARED_LIBRARY)
I have got the following errors when I use ndk-build command:
jni/include/externalInclude/armadillo_bits/blas_wrapper.hpp:172: error: undefined reference to 'sdot_'
jni/include/externalInclude/armadillo_bits/blas_wrapper.hpp:98: error: undefined reference to 'ssyrk_'
jni/include/externalInclude/armadillo_bits/blas_wrapper.hpp:28: error: undefined reference to 'sgemv_'
jni/include/externalInclude/armadillo_bits/blas_wrapper.hpp:63: error: undefined reference to 'sgemm_'
error: undefined reference to 'vl_sift_new'
error: undefined reference to 'vl_sift_process_first_octave'
error: undefined reference to 'vl_sift_delete'
error: undefined reference to 'vl_sift_detect'
error: undefined reference to 'vl_sift_calc_keypoint_orientations'
error: undefined reference to 'vl_sift_calc_keypoint_descriptor'
error: undefined reference to 'vl_sift_process_next_octave'

Answer 1

i had the same problem and after some struggleing i found a sulotion
go to http://danilogiulianelli.blogspot.co.il/2013/02/how-to-build-gcc-fortran-cross-compiler.html and build the gcc cross compiler . i did it for ndk-8d.
make sure that after running the script you can see the 2 folders that the script created in
android-ndk-r8d\toolchains\arm-linux-androideabi-4.8.0
android-ndk-r8b\android-ndk-r8d\toolchains\x86-4.8.
download blas lib and update the following field in blas make.in:
instead of
FORTRAN = gfortran
FORTRAN = $(yourPath)/android-ndk-r8d/toolchains/x86-4.8.0/prebuilt/linux-x86/bin/i686-linux-android-gfortran
run the makefile.
add in you android.mk and add the following localflags
LOCAL_LDFLAGS := $(OPT) $(PROF) -lblas -llapack -lstdc++ -lgfortran
run ndk-build
i had problem with ndk-8d that had missing files of gcc 4.8, in order to solve it i copied the missing files from ndk-9 and it works.