Cross Compiling
===============

LibOSDP is written in C and does not depend on any other libraries. You can
compile it to pretty much any platform (even Windows). Follow the cross
compilation best practice for your platform. This document gives you some ideas
on how this can be done but is in no way conclusive.

Using Cmake
-----------

LibOSDP can be compiled with your cross compiler by passing a toolchain file to
cmake. This can be done by invoking cmake with the command line argument
``-DCMAKE_TOOLCHAIN_FILE=/path/to/toolchain-file.cmake``.

If your toolchain is installed in ``/opt/toolchain/armv8l-linux-gnueabihf/`` and
the sysroot is present in ``/opt/toolchain/armv8l-linux-gnueabihf/sysroot``, the
``toolchain-file.cmake`` file should look like this:

.. code:: cmake

    set(CMAKE_SYSTEM_NAME Linux)
    set(CMAKE_SYSTEM_PROCESSOR arm)

    # specify the cross compiler and sysroot
    set(TOOLCHAIN_INST_PATH /opt/toolchain/armv8l-linux-gnueabihf)
    set(CMAKE_C_COMPILER    ${TOOLCHAIN_INST_PATH}/bin/armv8l-linux-gnueabihf-gcc)
    set(CMAKE_CXX_COMPILER  ${TOOLCHAIN_INST_PATH}/bin/armv8l-linux-gnueabihf-g++)
    set(CMAKE_SYSROOT       ${TOOLCHAIN_INST_PATH}/sysroot)

    # don't search for programs in the build host directories
    set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)

    # search for libraries and headers in the target directories only
    set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
    set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
    set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

For convenience, the ``toolchain-file.cmake`` file can be placed in a common path
(probably where the toolchain is installed) and referenced from our build directory.

.. code:: sh

    mkdir build && cd build
    cmake -DCMAKE_TOOLCHAIN_FILE=/opt/toolchain/armv8l-linux-gnueabihf/toolchain-file.cmake ..
    make

Using make build
----------------

You could use the ``--cross-compile`` flag in configure.sh and then invoke make
to build the library.

.. code:: sh

    ./configure.sh --cross-compile arm-none-
    make
    make DESTDIR=/opt/arm-none-sysroot/ install