OMP Cross compilation with x86_64-w64-mingw32-g++

Question

I have some trouble with crosscompiling C++ program which takes advantage of openMP library. I am using Linux Ubuntu 12.04 LTS. I want to obtain executable file runnable on Windows.

I have no problem with compiling my program with OMP with regular g++ command:

  g++ a.cpp b.cpp -o OMPres -pg -O3 -I./CBLAS/include -L./ -lcblas

Also when I try crosscompilation without OMP, everything runs perfectly fine:

 x86_64-w64-mingw32-g++ a.cpp b.cpp -O3 -I./CBLAS/include ./CBLAS/cblas_WIN64.a ./BLAS/blas_WIN64.a -o res.exe -l gfortran -static

But when I try to crosscompile it with OMP using following command:

x86_64-w64-mingw32-g++ a.cpp b.cpp -O3 -I./CBLAS/include ./CBLAS/cblas_WIN64.a ./BLAS/blas_WIN64.a -o OMPres.exe -l gfortran -static -fopenmp

I get this error: a.cpp:41:17: fatal error: omp.h: No such file or directory compilation terminated.

I found where omp.h file is located on my disk, and added the path to the command. After executing it:

x86_64-w64-mingw32-g++ a.cpp b.cpp -O3 -I./CBLAS/include -I/usr/lib/gcc/x86_64-linux-gnu/4.6/include ./CBLAS/cblas_WIN64.a ./BLAS/blas_WIN64.a -o OMPres.exe -l gfortran -static -fopenmp

I got another error: x86_64-w64-mingw32-g++: error: libgomp.spec: No such file or directory

As I also have this file on the disk I tried to copy it in various places and finaly it worked when I copied it directly into the directory where compilation takes place. Then it produced another error:

/usr/bin/x86_64-w64-mingw32-ld: cannot find -lgomp /usr/bin/x86_64-w64-mingw32-ld: cannot find -lrt collect2: ld returned 1 exit status

I don't have a good understanding of how compilers exactly work. I tried to update all mingw-w64 compilers that I could find with apt-cache search but nothing helped. I have no idea what more I can do :(.

Answer 1

Your x86_64-w64-mingw32 toolchain appears to have been build without libgomp .

• You could check your supplier/distribution if it there additional or variant packages that have libgomp .
• Or switch to a different supplier/distribution.
• Or you could rebuild (or build in the first place) a cross gcc with --enable-libgomp . This is kinda the hard way .

PS: Adding paths that do not correspond with your platform, like -I/usr/lib/gcc/x86_64-linux-gnu/4.6/include , is a bad idea in general, and will most certainly fail... This kinda creates a Franken-compiler.

Answer 2

First, @nmaier is completely correct in that the Ubuntu x86_64-w64-mingw32 toolchain is crippled, and that you can rebuild the toolchain yourself.

I, however, suggest that you use MXE , which saves you the time of manually compiling gcc and every dependency of it. The steps below should be enough for your purpose:

# Get MXE
git clone https://github.com/mxe/mxe.git && cd mxe

# Settings
cat <<EOF > settings.mk
MXE_TARGETS := x86_64-w64-mingw32.static
JOBS := 4
EOF

# Build gcc, libgomp, blas, and cblas. It will take a while
make -j2 libgomp cblas

# Add toolchain to PATH
# See http://htmlpreview.github.io/?https://github.com/mxe/mxe/blob/master/index.html#tutorial step 4
export PATH=`pwd`/usr/bin:$PATH

# You don't need -I./CBLAS/include ./CBLAS/cblas_WIN64.a ./BLAS/blas_WIN64.a
# because headers and libraries are installed to standard location and
# I already used `-lcblas -lblas`.
x86_64-w64-mingw32-g++ a.cpp b.cpp -fopenmp -O3 -o res.exe -lcblas -lblas -lgfortran -lquadmath