cross compile mingw

Windows 64bit binaries can be generated on 64bit Linux using the mingw compiler for cross-compilation.

The mingw cross-compiler should be at least version 8.2.0 (tested), but could be slightly older. Versions that are much older likely have faulty regex implementations.

Host setup
Run-time setup
Additional Notes / Workarounds
Known limitations (2020-11-25)

Host setup

openSUSE

On openSUSE use these packages for compilation:

zypper in mingw64-cross-binutils
zypper in mingw64-cross-cpp mingw64-cross-gcc mingw64-cross-gcc-c++
zypper in mingw64-filesystem mingw64-headers mingw64-runtime

zypper in mingw64-libwinpthread1 mingw64-winpthreads-devel
zypper in mingw64-libz mingw64-zlib-devel

# Note: can cross-compile FFTW from ThirdParty sources instead
zypper in mingw64-libfftw3 mingw64-fftw3-devel

CentOS/RedHat

For CentOS/RedHat, the cross-compiler is available under PowerTools

dnf config-manager --set-enabled PowerTools

The packages have slightly different names than the openSUSE ones:

dnf install mingw64-gcc-c++
dnf install mingw64-winpthreads mingw64-zlib

Notably, many of the development packages are simply rolled into the runtime ones. An FFTW package appears to be missing, but cross-compiling one from ThirdParty sources makes reasonable sense anyhow.

Caution

Cross-compiling on RedHat systems has not always be successful in the past. The runtime packages often lag behind the windows runtime environment and the cross-compiling packages simply do not run.

Configuration Files

Since the settings for cross-compilation will often differ from the native compilation, it is advisable to isolate the changes in a dedicated directory (OpenFOAM-v2006 and later). We normally create a etc-mingw directory as a convenient reminder to its purpose.

The overall preferences (etc-mingw/prefs.sh):

# Preferences for mingw cross-compiled

export FOAM_CONFIG_ETC="etc-mingw"
export WM_COMPILER=Mingw
export WM_MPLIB=MSMPI

To disable CGAL (etc-mingw/config.sh/CGAL):

boost_version=boost-none
cgal_version=CGAL-none

export BOOST_ARCH_PATH="/$boost_version"
export CGAL_ARCH_PATH="/$cgal_version"

For a system FFTW (etc-mingw/config.sh/FFTW):

fftw_version=fftw-system
export FFTW_ARCH_PATH=/usr/x86_64-w64-mingw32/sys-root/mingw

Since we have created the etc-mingw directory in OpenFOAM project directory, it is easiest to source the environment from there:

source etc/bashrc etc-mingw/prefs.sh

# With additional verbosity of the sourcing
FOAM_VERBOSE=true  source etc/bashrc etc-mingw/prefs.sh

Before a full compilation

Before spending a large amount of time and effort with cross-compiling and installing, it is advisable to verify that the simplest possible application works successfully on the target machine. This small test application/library suite is called Test-dummyLib and is located under

applications/test/00-dummy/Allwmake

Run-time setup

When running, the WM_PROJECT_DIR environment must be set. OpenFOAM will otherwise not be able to locate its files.

If running with MSYS2, make certain to set the following environmental control (preferrably for all users):

MSYS2_PATH_TYPE  inherit

For the cross-compiled executables and libraries to work, the corresponding runtime libraries are required. These will need to be copied across from the Linux host system to the target machine. On openSUSE these runtime libraries are provided by the packages:

mingw64-libgcc_s_seh1
mingw64-libstdc++6
mingw64-libz
mingw64-libwinpthread1

Both for CentOS/RedHat and for openSUSE, this roughly corresponds to the entire directory contents:

/usr/x86_64-w64-mingw32/sys-root/mingw/bin/*.dll

Additional Notes / Workarounds

Flex

Flex is used in a few locations within OpenFOAM for generating code. The generated C++ code requires the FlexLexer.h header file, but its /usr/include location will be ignored by the cross-compiler. As a moderately ugly workaround, a copy of this file can be made in a standard project include location as part of the compilation process. For example,

ln -s /usr/include/FlexLexer.h src/OSspecific/MSwindows

libz

If there are any issues with the system zlib, it is possible to download it manually and compile it as a static library.

CC="$(wmake -show-c)" CFLAGS="$(wmake -show-cflags)" ./configure --static
make

The resulting output files (zconf.h, zlib.h) and (libz.a) either need to be installed in system locations where OpenFOAM can find them, or if they are to be shipped directly with OpenFOAM, they can also be placed in the src/OpenFOAM/include and platforms/linux64Mingw*/lib paths.

If the header files are only needed during compilation, it can be a fairly convenient hack to simply place copies of them in the src/OSspecific/MSwindows directory.

The wmake toolchain

Always use the wmake/src/Allmake script (called automatically) to ensure that the wmake binary toolchain is built for the host platform where it is needed.

Known limitations (2020-11-25)

kahip does not build
ptscotch does not build
boost should build ok, but no CGAL support (ie, no foamyHexMesh)
no ParaView plugin, runTimePostProcessing