====== Ubuntu cross compiling with libraries ======
This guide describes how to cross compile for aarch64 targets with linking to external libraries from a Ubuntu host. The cross compilation is tested on a x86_64 host running Ubuntu 20.04, a target running Ubuntu Server 20.04 aarch64 (Raspberry Pi 4B) and using the cmake build tool. It links external libraries by mounting the target filesystem over ''sshfs''.


===== On target =====

Install external libraries (OMPL: lib-eigen3-dev, boost libraries)

===== On host =====
  * Unordered List ItemInstall aarch64 compiler
    * ''sudo apt-get install g++-aarch64-linux-gnu''

  * Mount target filesystem
    * ''sudo mkdir /mnt/rpi''
    * ''sudo sshfs -o allow_other,default_permissions [target_username]@[target_ip]:/ /mnt/rpi''

  * Create ''toolchain.cmake'' file, see section below.
  * Configure cmake to use toolchain file
    * ''cmake -DCMAKE_TOOLCHAIN_FILE=..[toolchain_file] [project_location]''
    * ''make -j[threads_to_use]''

==== Toolchain file ====
  set(CMAKE_SYSTEM_NAME Linux)
  set(CMAKE_SYSTEM_PROCESSOR aarch64)
  
  set(tools /usr/bin)
  set(CMAKE_C_COMPILER ${tools}/aarch64-linux-gnu-gcc-9)
  set(CMAKE_CXX_COMPILER ${tools}/aarch64-linux-gnu-g++-9)
  
  set(CMAKE_SYSROOT /mnt/rpi)
  
  set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
  set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
  set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
  set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)