Failed to cross-compile with some"undefined reference" errors

[lazylazypig]

System information (version)

• OpenCV => 3.4.1
• Operating System / Platform => Manjaro 17.1.10 (host)
• Compiler => arm-linux-gnueabi-g++ (ver 4.9.4)

Detailed description

I have failed to cross-compile opencv3.4.1 with several '### undefined reference' errors related to std::exception_ptr

Steps to reproduce

My configuration is as follow:
cmake -D CMAKE_BUILD_TYPE=RELEASE -D ENABLE_CXX11=ON -D ENABLE_NEON=ON -D ENABLE_VFPV3=ON -D BUILD_TESTS=OFF -D BUILD_EXAMPLES=OFF -D BUILD_opencv_world=ON -D WITH_TBB=ON -D BUILD_TBB=ON -D WITH_JPEG=ON -D BUILD_JPEG=ON -D WITH_PNG=ON -D BUILD_PNG=ON -D WITH_TIFF=ON -D BUILD_TIFF=ON -D WITH_FFMPEG=ON -D BUILD_opencv_apps=OFF -D CMAKE_TOOLCHAIN_FILE=mypath/toolchain.cmake ..

And, My toolchain.cmake file look like these:

set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)

set(CMAKE_C_COMPILER /opt/arm-hisiv600-linux/bin/arm-hisiv600-linux-gnueabi-gcc)
set(CMAKE_CXX_COMPILER /opt/arm-hisiv600-linux/bin/arm-hisiv600-linux-gnueabi-g++)

set(CMAKE_FIND_ROOT_PATH /opt/arm-hisiv600-linux/arm-hisiv600-linux-gnueabi)

set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)

add_definitions(-DENABLE_NEON=ON)
add_definitions(-DENABLE_VFPV3=ON)

set(CMAKE_C_FLAGS "-mcpu=cortex-a17.cortex-a7 -mfpu=neon-vfpv4 -mfp16-format=ieee -mfloat-abi=softfp -mno-unaligned-access -fno-aggressive-loop-optimizations")
set(CMAKE_CXX_FLAGS "-std=c++11 ${CMAKE_C_FLAGS}")

After several minutes, I got some errors as follow:
[ 88%] Built target opencv_ts
[ 89%] Building CXX object modules/world/CMakeFiles/opencv_perf_dnn.dir//dnn/perf/opencl/perf_convolution.cpp.o
[ 89%] Building CXX object modules/world/CMakeFiles/opencv_perf_dnn.dir//dnn/perf/perf_caffe.cpp.o
[ 89%] Building CXX object modules/world/CMakeFiles/opencv_perf_dnn.dir//dnn/perf/perf_convolution.cpp.o
[ 89%] Building CXX object modules/world/CMakeFiles/opencv_perf_dnn.dir//dnn/perf/perf_main.cpp.o
[ 89%] Building CXX object modules/world/CMakeFiles/opencv_perf_dnn.dir/__/dnn/perf/perf_net.cpp.o
[ 89%] Linking CXX executable ../../bin/opencv_perf_dnn
../../lib/libopencv_world.so.4.0.0: undefined reference to std::rethrow_exception(std::__exception_ptr::exception_ptr)' ../../lib/libopencv_world.so.4.0.0: undefined reference to std::__exception_ptr::exception_ptr::exception_ptr()'
../../lib/libopencv_world.so.4.0.0: undefined reference to std::current_exception()' ../../lib/libopencv_world.so.4.0.0: undefined reference to std::__exception_ptr::exception_ptr::exception_ptr(std::__exception_ptr::exception_ptr const&)'
../../lib/libopencv_world.so.4.0.0: undefined reference to std::__exception_ptr::exception_ptr::swap(std::__exception_ptr::exception_ptr&)' ../../lib/libopencv_world.so.4.0.0: undefined reference to std::__exception_ptr::exception_ptr::~exception_ptr()'
collect2: error: ld returned 1 exit status
make[2]: *** [modules/world/CMakeFiles/opencv_perf_dnn.dir/build.make:147：bin/opencv_perf_dnn] Error 1
make[1]: *** [CMakeFiles/Makefile2:1795：modules/world/CMakeFiles/opencv_perf_dnn.dir/all] Error 2
make: *** [Makefile:163：all] Error 2

I have set "-D ENABLE_CXX11=ON", and add "-std=c++11" to CMAKE_CXX_FLAGS (in the toolchain.cmake file), but still failed. Could anyone help me? Thanks :)

[alalek]

This is build configuration problem. std::exception_ptr is properly declared by compiler in headers, but final binary can't link - try adding something like -lstdc++ into linker flags.
If there is no such library with std::exception_ptr symbols, then used compiler setup is buggy - we can't help really here.
There is workaround in OpenCV to disable using std::exception_ptr via compiler definition:

• -D CV__EXCEPTION_PTR=0 (via CMAKE_CXX_FLAGS)

[lazylazypig]

@alalek thanks for the quick reply. but following your advice, i failed again:(
i don't think it's a bug of used compiler, because i have tried to build a very simple example about std::exception_ptr with the same toolchain.cmake file:

#include <iostream>
#include <string>
#include <exception>
#include <stdexcept>

void handle_eptr(std::exception_ptr eptr)
{
    try {
        if (eptr) {
            std::rethrow_exception(eptr);
        }
    } catch(const std::exception& e) {
        std::cout << "Caught exception \"" << e.what() << "\"\n";
    }
}
 
int main()
{
    std::exception_ptr eptr;
    try {
        std::string().at(1); // this generates an std::out_of_range
    } catch(...) {
        eptr = std::current_exception(); // capture
    }
    handle_eptr(eptr);
}

no errors occurred during build, and the built program run correctly on the target machine.
on the other hand, i found that the flags ENABLE_TBB and ENABLE_NEON can't be turned on at the same time (just as my original configuration). if I turned off either of them, the compiling of opencv was successful. I'm very confused.
thanks:)

[alalek]

Unfortunately we can't help on problems which we are not able to reproduce on our side (we don't have environment setup for this configuration).
But we can take a look on the clear reason of the problem and suggest some fix/workaround.

BTW, There two CMake lines seems wrong:

add_definitions(-DENABLE_NEON=ON)
add_definitions(-DENABLE_VFPV3=ON)

They should be CMake options (via set()), not for compiler.

Also take a look on OpenCV's cross-compiling GCC-based ARM toolchains here: https://github.com/opencv/opencv/tree/3.4/platforms/linux
We using them successfully on our CI: http://pullrequest.opencv.org/buildbot/waterfall?tag=arm