Cross compile with OpenCV (Raspberry Pi4)

Andrea_M

Hello to everyone,
I just set a Qt 5.15.2 for cross-compile (host is a Linux Mint 20.2 PC, target is a Raspberry 4 with Raspberry OS 32 bit).
I tested it with some Qt examples, an all seems to be ok.
As I need OpenCV, I installed on Raspberry (by apt-get) the libopencv*-dev, located on path:
usr/lib/arm-linux-gnueabihf
and synced directories and links on my host machine .The OpenCV path in sysroot is:
/home/myUser/raspi/sysroot/lib/arm-linux-gnueabihf

Compiling the code from my host I have:
i- undefined reference to cv::String::deallocate()' i- undefined reference to cv::String::deallocate()'
i- undefined reference to cv::VideoCapture::VideoCapture()' i- undefined reference to cv::VideoWriter::VideoWriter()'
i- undefined reference to `cv::VideoWriter::~VideoWriter()'
...

that is caused, in my opinion, by opencv libraries not found.
My *.pro file has this code

[...]
# FOR FEDORA
     LIBS += -L"/usr/local/lib64/"
# FOR UBUNTU
     LIBS += -L"/usr/local/lib/"
# FOR RASPBERRY
     LIBS += -L"usr/lib/arm-linux-gnueabihf"
     LIBS += -L"/home/myUser/raspi/sysroot/lib/arm-linux-gnueabihf"

     LIBS += -lopencv_calib3d
     LIBS += -lopencv_core
     LIBS += -lopencv_features2d
     LIBS += -lopencv_flann
     LIBS += -lopencv_highgui
     LIBS += -lopencv_imgcodecs
[...]

and compiling it under Linux OS with native Gcc, it does't give me any error (libs are located in /usr/local/lib/).
So, I suppose that I'm doing something wrong with OpenCv,but I can't understand what is the fault...

jsulm

@Andrea_M said in Cross compile with OpenCV (Raspberry Pi4):

-L"usr/lib/arm-linux-gnueabihf"

/ is missing at the beginning of the path.
Since you are using a sysroot you should not specify the whole path including the sysroot path as lib path! You specify the lib path as if you would build directly on RaspberryPi. There is also usually no need to specify the system lib folders explicetly as those are searched by linker by default.

Andrea_M

Thank you very much!
I tried with :

# FOR RASPBERRY
     LIBS += -L"/usr/local/"
     LIBS += -L"/lib/arm-linux-gnueabihf/"
     LIBS += -L"/usr/lib/arm-linux-gnueabihf/"

     LIBS += -lopencv_calib3d
     LIBS += -lopencv_core
     LIBS += -lopencv_features2d
     LIBS += -lopencv_flann
     LIBS += -lopencv_highgui

but without success. I tried to resolve creating a symbolic link into main program directory, in debug directory... nothing, I'm afraid it could be a different problem, so I'll try to compile openCV in Raspeberry device, and then sync it.
Compiling openCV in linux was rather simple, I hope in Rasperry would be the same!

jsulm

@Andrea_M Please post the whole build log, especially the linker part.

Andrea_M

I suppose it is a compatibility problem, because the compiler can find the opencv libs, but a problem accours. For example:

/home/myUser/raspi/sysroot/usr/include/opencv2/core/cvstd.inl.hpp:81: undefined reference to `cv::String::allocate(unsigned int)'

@jsulm
Sorry, I'm not sure about what do you mean with "build log"... is something like this?

11:45:03: Starting: "/usr/bin/make" -j4
Makefile:28197: warning: overriding recipe for target 'ui_session_database.h'
Makefile:20200: warning: ignoring old recipe for target 'ui_session_database.h'
/home/myUser/raspi/tools/gcc-linaro-7.4.1-2019.02-x86_64_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-g++ -mfloat-abi=hard --sysroot=/home/myUser/raspi/sysroot -Wl,-rpath,/usr/local/qt5pi/lib -Wl,-rpath-link,/home/myUser/raspi/qt5pi/lib -Wl,-rpath-link,/home/myUser/raspi/sysroot/usr/lib/arm-linux-gnueabihf -Wl,-rpath-link,/home/myUser/raspi/sysroot/lib/arm-linux-gnueabihf -o QtopenCV csv_output.o calibration.o create_test.o reportdb_exp.o resultdb_exp.o selection_export.o selectsession.o eye.o MyTimerClass.o editablesqlmodel.o fullscreen.o mediabrowser.o alarm.o send_data.o send_instruction.o [...all *.o file...]   /home/myUser/raspi/qt5pi/lib/libQt5PrintSupport.so /home/myUser/raspi/qt5pi/lib/libQt5MultimediaWidgets.so /home/myUser/raspi/qt5pi/lib/libQt5Widgets.so /home/myUser/raspi/qt5pi/lib/libQt5Multimedia.so /home/myUser/raspi/qt5pi/lib/libQt5Gui.so /home/myUser/raspi/qt5pi/lib/libQt5Sql.so /home/myUser/raspi/qt5pi/lib/libQt5Qml.so /home/myUser/raspi/qt5pi/lib/libQt5Network.so /home/myUser/raspi/qt5pi/lib/libQt5SerialPort.so /home/myUser/raspi/qt5pi/lib/libQt5Core.so -L/home/myUser/raspi/sysroot/usr/lib/arm-linux-gnueabihf -lGLESv2 -lpthread   
calibration.o: In function `cv::String::~String()':
/home/myUser/raspi/sysroot/usr/include/opencv2/core/cvstd.hpp:664: undefined reference to `cv::String::deallocate()'
calibration.o: In function `cv::String::operator=(cv::String const&)':
/home/myUser/raspi/sysroot/usr/include/opencv2/core/cvstd.hpp:672: undefined reference to `cv::String::deallocate()'
eye.o: In function `eye::eye(QWidget*)':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:42: undefined reference to `cv::VideoCapture::VideoCapture()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:42: undefined reference to `cv::VideoCapture::VideoCapture()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:42: undefined reference to `cv::VideoWriter::VideoWriter()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:42: undefined reference to `cv::VideoWriter::~VideoWriter()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:42: undefined reference to `cv::VideoCapture::~VideoCapture()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:42: undefined reference to `cv::VideoCapture::~VideoCapture()'
eye.o: In function `eye::~eye()':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:74: undefined reference to `cv::VideoWriter::~VideoWriter()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:74: undefined reference to `cv::VideoCapture::~VideoCapture()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:74: undefined reference to `cv::VideoCapture::~VideoCapture()'
eye.o: In function `eye::initCamera()':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:83: undefined reference to `cv::VideoCapture::open(int)'
eye.o: In function `eye::initVideo()':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:89: undefined reference to `cv::VideoCapture::read(cv::_OutputArray const&)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:105: undefined reference to `cv::VideoWriter::fourcc(char, char, char, char)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:108: undefined reference to `cv::VideoCapture::get(int) const'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:108: undefined reference to `cv::VideoCapture::get(int) const'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:109: undefined reference to `cv::VideoWriter::VideoWriter(cv::String const&, int, double, cv::Size_<int>, bool)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:109: undefined reference to `cv::VideoWriter::~VideoWriter()'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:109: undefined reference to `cv::VideoWriter::~VideoWriter()'
eye.o: In function `eye::processGui()':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:117: undefined reference to `cv::VideoCapture::read(cv::_OutputArray const&)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:120: undefined reference to `cv::VideoWriter::write(cv::Mat const&)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:121: undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:122: undefined reference to `cv::putText(cv::_InputOutputArray const&, cv::String const&, cv::Point_<int>, int, double, cv::Scalar_<double>, int, int, bool)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:125: undefined reference to `cv::cvtColor(cv::_InputArray const&, cv::_OutputArray const&, int, int)'
eye.o: In function `eye::on_record_clicked()':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:144: undefined reference to `cv::VideoCapture::isOpened() const'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:146: undefined reference to `cv::VideoCapture::release()'
eye.o: In function `eye::on_CaptureButton_clicked()':
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:177: undefined reference to `cv::VideoCapture::read(cv::_OutputArray const&)'
/home/myUser/Scrivania/build-Login-Raspberry_Pi4-Debug/../QT_2021_10_08/Program/Eye/eye.cpp:194: undefined reference to `cv::imwrite(cv::String const&, cv::_InputArray const&, std::vector<int, std::allocator<int> > const&)'
eye.o: In function `cv::String::String(char const*)':
/home/myUser/raspi/sysroot/usr/include/opencv2/core/cvstd.hpp:622: undefined reference to `cv::String::allocate(unsigned int)'
eye.o: In function `cv::Mat::~Mat()':
/home/myUser/raspi/sysroot/usr/include/opencv2/core/mat.inl.hpp:592: undefined reference to `cv::fastFree(void*)'
eye.o: In function `cv::Mat::release()':
/home/myUser/raspi/sysroot/usr/include/opencv2/core/mat.inl.hpp:704: undefined reference to `cv::Mat::deallocate()'
eye.o: In function `cv::String::String(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':
/home/myUser/raspi/sysroot/usr/include/opencv2/core/cvstd.inl.hpp:81: undefined reference to `cv::String::allocate(unsigned int)'
collect2: error: ld returned 1 exit status
make: *** [Makefile:642: QtopenCV] Error 1
11:45:09: The process "/usr/bin/make" exited with code 2.
Error while building/deploying project Login (kit: Raspberry Pi4 )
When executing step "Make"

This log appears not complete, because I need to do a clear after switching from a configuration to another... it's just an example.
I'll update this thread after compiling opencv on Raspberry.

jsulm

@Andrea_M It looks like the OpenCV libs are not passed to the linker.
Do a complete rebuild: delete build folder, run qmake and build.