CrossBuilder

This contains several utilities for cross compiling native projects on a Windows based host.

Highlights

• Dependency fetcher that emulates apt-get
  • Downloads packages directly to the host computer instead of downloading them first to the target and copying them over.
  • Prevents having to install dev packages on the target machine.
• File catcher that tracks file modifications when using commands such as make install
  • Most cmake projects don't respect the install directory and instead write their files to all different directories.
  • Allows you to copy captured files to your sysroot or staging directory.

Finding a sysroot to use

1. On the physical device, you'll want to find out what version of GCC you have. Do so by typing gcc -v and you should see something similar to the following:

   debian@beaglebone:~$ gcc -v
   Using built-in specs.
   COLLECT_GCC=gcc
   COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-linux-gnueabihf/6/lto-wrapper
   ---> Target: arm-linux-gnueabihf
   Configured with: ../src/configure -v --with-pkgversion='Debian 6.3.0-18+deb9u1' --with-bugurl=file:///usr/share/doc/gcc-6/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-6 --program-prefix=arm-linux-gnueabihf- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-libitm --disable-libquadmath --enable-plugin --enable-default-pie --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-6-armhf/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-6-armhf --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-6-armhf --with-arch-directory=arm --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --with-target-system-zlib --enable-objc-gc=auto --enable-multiarch --disable-sjlj-exceptions --with-arch=armv7-a --with-fpu=vfpv3-d16 --with-float=hard --with-mode=thumb --enable-checking=release --build=arm-linux-gnueabihf --host=arm-linux-gnueabihf --target=arm-linux-gnueabihf
   Thread model: posix
   ---> gcc version 6.3.0 20170516 (Debian 6.3.0-18+deb9u1)

2. Now, if you have an ARM device this next step is easy since Linaro has a slew of sysroots available as well as compilers for all different platforms. To find the one you need, navigate to https://releases.linaro.org/components/toolchain/binaries/ and you'll see a list of GCC versions.

3. Choose the version closest to the version installed on the physical device, in my case the version on my device is gcc version 6.3.0 20170516 (Debian 6.3.0-18+deb9u1) and the closest version from Linaro is 6.3-2017.05.

4. Now select the appropriate target where mine is arm-linux-gnueabihf as determined by the GCC version command above.

5. Download and extract the GCC compiler that's appropriate for your host machine. In my case, I would download gcc-linaro-6.3.1-2017.05-i686-mingw32_arm-linux-gnueabihf.tar.xz since I am running windows and using mingw. (TODO: how to determine the exact binaries and setup for mingw)

6. Download and extract the sysroot, in my case it's sysroot-glibc-linaro-2.23-2017.05-arm-linux-gnueabihf.tar.xz.

7. Create a CMake toolchain for your new compiler and sysroot. An example one is shown below for my environment:

   set(CMAKE_SYSTEM_NAME Linux)
   
   set(CMAKE_C_COMPILER "D:/Toolchains/gcc-linaro-6.5.0-2018.12-i686-mingw32_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-gcc.exe")
   set(CMAKE_CXX_COMPILER "D:/Toolchains/gcc-linaro-6.5.0-2018.12-i686-mingw32_arm-linux-gnueabihf/bin/arm-linux-gnueabihf-g++.exe")
   
   set(CMAKE_SYSROOT "D:/Toolchains/sysroot-glibc-linaro-2.23-2017.05-arm-linux-gnueabihf")
   set(CMAKE_PREFIX_PATH "D:/Toolchains/sysroot-glibc-linaro-2.23-2017.05-arm-linux-gnueabihf")
   
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -L=/usr/lib -L=/lib")
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -L=/usr/lib -L=/lib")

Building OpenCV

1. Install dependencies

   CrossBuilder.exe install -s "D:\Toolchains\sysroot-glibc-linaro-2.23-2017.05-arm-linux-gnueabihf" libavcodec-dev libavformat-dev libswscale-dev libgstreamer1.0-0 gstreamer1.0-plugins-base gstreamer1.0-plugins-good gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly gstreamer1.0-libav gstreamer1.0-tools libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev libusb-1.0-0-dev libgtk-3-dev ffmpeg libgtk2.0-dev

2. Clone the OpenCV project and run CMake inside build directory:

   cmake -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE=D:\Git\CrossBuilder\armhf.toolchain.cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_EXAMPLES=OFF -DBUILD_DOCS=OFF -DBUILD_PERF_TESTS=OFF -DBUILD_TESTS=OFF -DWITH_GSTREAMER=ON -DWITH_GTK=ON ..

3. Build the project:

   make -j10

4. Capture the installed files to be used in the sysroot:

   FileCatcher.exe make install

Building RealSense

1. Install dependencies

   CrossBuilder.exe install -s "D:\Toolchains\sysroot-glibc-linaro-2.23-2017.05-arm-linux-gnueabihf" libusb-1.0-0-dev libglfw3-dev

2. Clone the librealsense project and run CMake inside build directory:

   cmake -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE=D:\Git\CrossBuilder\armhf.toolchain.cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_EXAMPLES=OFF -DBUILD_DOCS=OFF -DBUILD_PERF_TESTS=OFF -DBUILD_TESTS=OFF -DWITH_GSTREAMER=ON -DWITH_GTK=ON ..

3. Build the project:

   make -j10

4. Capture the installed files to be used in the sysroot:

   FileCatcher.exe make install

Building the example app

1. Install dependencies

   CrossBuilder.exe install -s "D:\Toolchains\sysroot-glibc-linaro-2.23-2017.05-arm-linux-gnueabihf" ti-tidl python3-dev

Troubleshooting

undefined reference to `__dlsym'

You probably don't have libdl.so or librt.so. Try installing libc6-dev

ld.exe: cannot find /lib/arm-linux-gnueabihf/libc.so.6 inside

Probably didn't update and remove absolute paths in .so files

libm.a: error adding symbols: Bad value

Cannot find libm.so and resorts to using libm.a which is BAD. Create libm.so