Porting deal.II to new systems

deal.II uses very few POSIX specific system features and is otherwise fairly ISO (2011) C++ Standard compliant. Consequently, there is a good chance that deal.II will run on a reasonably well behaved system besides the ones listed in the ReadMe. Nevertheless, there are cases where some adjustments are necessary.

Unknown compiler

Currently, the deal.II CMake build system recognizes gcc, clang, as well as icc, and sets up reasonable default compiler flags.

• To start porting to an unknown compiler, specify -DDEAL_II_SETUP_DEFAULT_COMPILER_FLAGS=OFF and set all necessary compiler flags by hand via

  DEAL_II_CXX_FLAGS         - used during all builds
  DEAL_II_CXX_FLAGS_DEBUG   - additional flags for the debug library
  DEAL_II_CXX_FLAGS_RELEASE - additional flags for the release library
  

  After that try to compile the library with minimal external dependencies (-DDEAL_II_ALLOW_AUTODETECTION=OFF, for further information see the deal.II CMake documentation).
• For adding permanent support for the unknown compiler to the build system, have a look at

  cmake/setup_compiler_flags.cmake
  cmake/setup_compiler_flags_gnu.cmake
  cmake/setup_compiler_flags_icc.cmake
  

  Patches are highly welcome! See here for information on how to get in contact with us.
• You might want to have a look at

  cmake/checks/check_01_for_compiler_features.cmake
  cmake/checks/check_01_for_cxx_features.cmake
  cmake/checks/check_03_for_compiler_bugs.cmake
  include/deal.II/base/config.h.in
  

  to see how compiler specific checks are done.

Porting to a new platform

deal.II should support almost all reasonably POSIX compliant platforms out of the box. Nevertheless, the following bits of information might help:

• The build system of deal.II uses CMake. So, in order to port deal.II to a new platform, it is obviously necessary that CMake supports the platform in question with at least one generator for a native build tool, see here.
• deal.II is mainly developed with gcc on GNU/Linux, so it is best to begin porting to a new platform with the help of gcc. After that a platform specific compiler might be tried.
• Almost all POSIX specific code is well guarded with fall-back code in case the specific POSIX function is not available. There is (currently) one exception, though: Routines that measure elapsed CPU time in source/base/timer.cc have implementations for POSIX and Windows and will not work correctly on other platforms.
• Have a look at

  cmake/checks/check_01_cxx_features.cmake
  cmake/checks/check_02_compiler_features.cmake
  cmake/checks/check_02_system_features.cmake
  cmake/checks/check_03_compiler_bugs.cmake
  include/deal.II/base/config.h.in
  

  to see how platform and compiler specific checks are done.
• Of course, we would be happy to hear about the changes you made for your system, so that we can include them into the next version of the library!

Cross compiling

It is possible to use CMake to cross compile deal.II for a foreign platform. Further information on that topic can be found at the CMake wiki.

You have to set up a native deal.II build directory first and run make expand_instantiations_exe in it. The executable is needed for the build system (and obviously the cross compiled version cannot be used). Locate the expand_instantiations executable (it usually resides under ${CMAKE_BINARY_DIR}/bin and export its location with the PATH environment variable.

Assuming you have a working cross compilation toolchain, the next step is to set up a toolchain file (or for for Windows64 using MinGW). After that invoke cmake with something like:

$ cmake -DCMAKE_TOOLCHAIN_FILE=<...>/Toolchain.sample \
        -DDEAL_II_FORCE_BUNDLED_BOOST=ON \
        -DDEAL_II_ALLOW_AUTODETECTION=OFF \
        ../deal.II