[Mingw-cross-env-list] link to third party dll when cross compiling from linux?

[Richard Crozier]

Dear List,

I would like to cross compile C++ projects for Windows 64 bit from Linux 
using MXE. In my case the final step requires linking to several third 
party compiled dlls. I do not have the source code of these dlls, only 
the header files and compiled binary. Compiled using what? I do not know 
but likely Visual Studio.

To explain exactly what I am doing, I want to cross-compile Matlab mex 
files from Linux and need to link to the Matlab libraries libmex.dll, 
libmx.dll and libmat.dll.

As far as I am aware, I need to extract definitions from the dlls, into 
.def files, and create a link library to actually link to.

I have attempted both of these steps, first the creation of definition 
files for each library, which I did with the following command:

    gendef libmx.dll

Here's a snippet of the resulting definition file `libmx.def`

    ;
    ; Definition file of libmx.dll
    ; Automatic generated by gendef
    ; written by Kai Tietz 2008
    ;
    LIBRARY "libmx.dll"
    EXPORTS
    ; public: __cdecl <struct mxArray_tag,class 
Mprotected_mxArray_helper>::<struct mxArray_tag,class 
Mprotected_mxArray_helper>(class <struct mxArray_tag,class 
Mprotected_mxArray_helper> const &__ptr64 )__ptr64

address@hidden@@VMprotected_mxArray_helper@@@@address@hidden@@Z
    ; public: __cdecl <struct mxArray_tag,class 
Mprotected_mxArray_helper>::<struct mxArray_tag,class 
Mprotected_mxArray_helper>(struct mxArray_tag *__ptr64,bool)__ptr64

address@hidden@@VMprotected_mxArray_helper@@@@address@hidden@@address@hidden
    ; public: __cdecl <struct mxArray_tag,class 
Mprotected_mxArray_helper>::<struct mxArray_tag,class 
Mprotected_mxArray_helper>(void)__ptr64

address@hidden@@VMprotected_mxArray_helper@@@@address@hidden
    ; public: __cdecl matrix::serialize::Exception::Exception(class 
matrix::serialize::Exception const &__ptr64 )__ptr64
    address@hidden@matrix@@address@hidden@@Z
    ; public: __cdecl 
matrix::serialize::Exception::Exception(int,__int64)__ptr64
    address@hidden@matrix@@address@hidden@Z
    ; public: __cdecl matrix::serialize::FailedUCNV::FailedUCNV(class 
matrix::serialize::FailedUCNV const &__ptr64 )__ptr64
    address@hidden@matrix@@address@hidden@@Z
    ; public: __cdecl 
matrix::serialize::FailedUCNV::FailedUCNV(int,__int64,int)__ptr64
    address@hidden@matrix@@address@hidden@Z
    ; public: __cdecl Mprotected_mxArray::Mprotected_mxArray(class 
Mprotected_mxArray const &__ptr64 )__ptr64
    ??0Mprotected_mxArray@@address@hidden@@Z
    ; public: __cdecl Mprotected_mxArray::Mprotected_mxArray(struct 
mxArray_tag *__ptr64,bool)__ptr64
    ??0Mprotected_mxArray@@address@hidden@@address@hidden
    ; public: __cdecl Mprotected_mxArray::Mprotected_mxArray(void)__ptr64
    ??0Mprotected_mxArray@@address@hidden
    ; public: __cdecl RRTableVisitor::RRTableVisitor(class 
RRTableVisitor const &__ptr64 )__ptr64
    ??0RRTableVisitor@@address@hidden@@Z

I then attempted to create an import library based on the instructions 
provided for Mingw [here][1]. However, as I am using MXE my command was 
actually

    x86_64-w64-mingw32.static-dlltool -d libmx.def -l libmx.a

However, when I attempt to build a simple example linked to these 
libraries, I get an error. Here are the actual commands used to build 
and link the libs.

    /opt/mxe/usr/bin/x86_64-w64-mingw32.static-gcc -c 
-I/usr/local/MATLAB/R2015a/extern/include 
-I/usr/local/MATLAB/R2015a/simulink/include -DMATLAB_MEX_FILE -std=c99 
-D_GNU_SOURCE  -fexceptions -fPIC -fno-omit-frame-pointer -pthread 
-I/opt/mxe/usr/bin/include  -DMX_COMPAT_32 -O -DNDEBUG 
"/home/rcrozier/yprime.c"

    /opt/mxe/usr/bin/x86_64-w64-mingw32.static-gcc -O 
-L/home/rcrozier/Sync/work/matlab_windows_libs/r2013a 
-L/opt/mxe/usr/bin/lib -pthread 
-Wl,--version-script,/usr/local/MATLAB/R2015a/extern/lib/glnxa64/mexFunction.map 
-Wl,--no-undefined -I/usr/local/MATLAB/R2015a/extern/include -o 
"yprime.mexw64"  yprime.o  -Wl,-rpath-link 
-L/home/rcrozier/Sync/work/matlab_windows_libs/r2013a -lmx -lmex -lmat 
-L/opt/mxe/usr/bin/lib -lm -lstdc++

The compile step goes ok, but the linking step fails with the following 
error:

    yprime.o:yprime.c:(.text+0x53): undefined reference to `mxGetM'
    yprime.o:yprime.c:(.text+0x5f): undefined reference to `mxGetN'
    yprime.o:yprime.c:(.text+0x6b): undefined reference to `mxIsDouble'
    yprime.o:yprime.c:(.text+0x78): undefined reference to `mxIsComplex'
    yprime.o:yprime.c:(.text+0xbe): undefined reference to 
`mxCreateDoubleMatrix_700'
    yprime.o:yprime.c:(.text+0xca): undefined reference to `mxGetPr'
    yprime.o:yprime.c:(.text+0xd5): undefined reference to `mxGetPr'
    yprime.o:yprime.c:(.text+0xde): undefined reference to `mxGetPr'

/opt/mxe/usr/lib/gcc/x86_64-w64-mingw32.static/4.9.4/../../../../x86_64-w64-mingw32.static/lib/../lib/libmingw32.a(lib64_libmingw32_a-crt0_c.o): 
In function `main':

/opt/mxe/tmp-gcc-x86_64-w64-mingw32.static/gcc-4.9.4/mingw-w64-v4.0.6/mingw-w64-crt/crt/crt0_c.c:18: 
undefined reference to `WinMain'
    collect2: error: ld returned 1 exit status

I am happy for the result of this compilation to be statically linked.

So my question is, what exactly do I have to do to link to third party 
dlls when cross-compiling for Windows from Linux, and could you suggest 
why might the linking step be failing in this case?

I've put basically the same question up on StackOverflow here:

http://stackoverflow.com/questions/39472210/how-to-link-to-third-party-dll-when-cross-compiling-from-linux

where you can find the commands and things a bit more nicely formatted. 
I would really appreciate any advice on this, and will post any answer 
here to StackOverflow so others could benefit from a cross-build Matlab 
mex system.

Thanks,

Richard