Is it possible to build FORTRAN-only mex-files using GNU FORTRAN (gfortran) supplied with MinGW-w64 under Windows 10?

Hello all,

I have a question about compiler support for Mex with Matlab R2018a under 64-bit Windows 10. We have a Matlab mex function that uses mixed C and FORTRAN source code. The mex gateway is written in C. Using the mingw-w64 compilers found as an Add-On in Matlab, this function compiles, links and works fine.

On the supported compilers page it is stated that the mingw-w64 C/C++ compilers are supported and that you can get them here: MinGW-w64 at the File Exchange. It is not stated that the GNU FORTRAN compiler (gfortran) is supported, but it is actually part of the distribution and the experience with our mixed C/FORTRAN mex-file above confirms that it works.

In the "Comments and Ratings" part of the MinGW-w64 page on the File Exchange the "Mathworks Supported Compilers Team" on 2017-07-18 said GNU FORTRAN is supported.

Now to my problem and question. I am trying to build a FORTRAN-only mex-file, but without success. It compiles fine, but when linking it fails. Furthermore, trying one of the supplied sample files, timestwo.F, doesn't work either. When compiling,

mex -c timestwo.F

I get:

Warning: Selected compiler 'MinGW64 Compiler (FORTRAN)' is not supported and no other supported compiler was found. For options, visit https://www.mathworks.com/support/compilers.

Building with 'MinGW64 Compiler (FORTRAN)'.
MEX completed successfully.

So mex reports that the compiler is not supported, even though it is said to be supported on the file exchange as per above. Also, the file is compiled and I get a timestwo.obj.

Trying to build the mex-file,

mex timestwo.F

I get:

Warning: Selected compiler 'MinGW64 Compiler (FORTRAN)' is not supported and no other supported compiler was found. For options, visit https://www.mathworks.com/support/compilers.

Error using mex
Cannot export mexFunction: symbol not defined
timestwo.obj:timestwo.F:(.text+0x43): undefined reference to `mexerrmsgidandtxt'
timestwo.obj:timestwo.F:(.text+0x69): undefined reference to `mexerrmsgidandtxt'
timestwo.obj:timestwo.F:(.text+0x71): undefined reference to `mxisnumeric'
timestwo.obj:timestwo.F:(.text+0x94): undefined reference to `mexerrmsgidandtxt'
timestwo.obj:timestwo.F:(.text+0x9c): undefined reference to `mxgetm730'
timestwo.obj:timestwo.F:(.text+0xa7): undefined reference to `mxgetn730'
timestwo.obj:timestwo.F:(.text+0xb9): undefined reference to `mxgetpr'
timestwo.obj:timestwo.F:(.text+0xd0): undefined reference to `mxcopyptrtoreal8730'
timestwo.obj:timestwo.F:(.text+0xe4): undefined reference to `mxcreatedoublematrix730'
timestwo.obj:timestwo.F:(.text+0xee): undefined reference to `mxgetpr'
timestwo.obj:timestwo.F:(.text+0x10f): undefined reference to `mxcopyreal8toptr730'
collect2.exe: error: ld returned 1 exit status

So my question is, is it possible to use the MinGW-w64 compiler with FORTRAN-only mex-files? It would (of course) be fantastic if it did, and I would be very grateful if someone could point me in the right direction.

Thanks for any input on this!

Bernt

Answer 1

[Sid Jhaveri]

Hi Bernt,

Currently, MATLAB supports GNU FORTRAN only in Linux. MATLAB supports MinGW-w64 on Windows only for C/C++. For Windows, Intel Parallel studio XE and Intel Visual Fortran are supported Fortran compiler in MATLAB. For more information on supported compilers, you can visit https://www.mathworks.com/support/compilers.html

[Bernt Nilsson]

Ok, I accept that it is not supported, but is there anyone who has tried using MinGW-w64 gfortran on a pure FORTRAN mex-file with success? Having put together a working mexopts XML-file?

[Ammar Ali]

Hello,

I'm facing a similar issue but my MinGW-w64 compiler does not even recognise a FORTRAN compiler. I've installed Visual Studio 2017 and the Intel Parallel Studio XE 2017 For Fortran and MATLAB does not see them. Hopefully as you said someone would prepare a working mexopts XML-file. I'm wondering if your issue was resolved and if so, how you did it.

Thanks.

[Bernt Nilsson]

Hello,

My experience with this is still the same. gfortran bundled with mingw-w64 works fine as long as the mex gateway is written in C. I have not been able to build a FORTRAN-only mex-file with mingw-w64.

To have the FORTRAN part of a mixed C/FORTRAN mex-file work I used the XML-file for (mingw-w64) C and made "obvious" changes to it (like defining CC as gfortran instead of gcc etc) and a maybe not so obvious change (add "-fno-underscoring" to CFLAGS), and saved it to a new file. This file is then used with the -f switch of the mex-command.

On my computer gfortran.exe is found in the following folder:

C:\ProgramData\MATLAB\SupportPackages\R2018a\3P.instrset\mingw_w64.instrset\bin

It is strange that Matlab does not find your compilers. I have no answer for that. Depending on your version of Matlab you can use

cc = mex.getCompilerConfigurations('FORTRAN')

to find out more, but I imagine you have already "been there".

[dpb]

"MATLAB supports GNU FORTRAN only in Linux. MATLAB supports MinGW-w64 on Windows only for C/C++."

This is totally rude and an unacceptable situation.

[Rylan]

I have met the same problems recently. I have to compile both the .c and .F90 file. What really bothered me is that the .F90 file cannot be compiled by ifort, but can be compiled by gfortran. However, only ifort is suppoted for windows platform.

[Robert]

Mathworks needs to get with the program and support gfortran via mingw-w64. Ever since Intel removed their non-commerical academic research licence option, it now appears to me that Mathworks is getting some sort of monetary incentive to not support any other FORTRAN compiler on windows or macos. This is the type of behavior that drives people away from from MATLAB to alternatives like Octave or Python. MATLAB days are numbered, I know of a number engineering and physics departments that have replaced their courses that used MATLAB with Python -- eventually all those students will bring this to their employers who will be more than happy to save money and drop MATLAB.

[dpb]

To have the FORTRAN part of a mixed C/FORTRAN mex-file work I used the XML-file for (mingw-w64) C and made "obvious" changes to it (like defining CC as gfortran instead of gcc etc) and a maybe not so obvious change (add "-fno-underscoring" to CFLAGS), and saved it to a new file. This file is then used with the -f switch of the mex-command."

But, with gfortran 6.3.0, adding -fno-underscoring then results in the exported entry names being append with "800" without the underscore.

Looking in, for example, libmex.lib, there are entry points exported with no trailing decoration or with _800, but none with only the trailing underscore gfortran emits by default nor with just "800".

That's a cursory look into trying to build "timestwo.F" from command line with the gfortran build included in the installed GCC that the MATLAB GCC link downloads.

gfortran runs just fine but I guess this linking issue is one TMW doesn't want to work through, although if they can do it for Linux/MacOS, doesn't seem as though should be any fundamental issue to include same for Windwoes since they can and do link C.

All in all, it still is an affront to their users and Fortran in general...there are other commerical Fortran compilers out there as well besides Intel although they are, granted, clearly the leader.

[dpb]

As a note for anybody else digging in the area who stumbles across this --

Indeed, the "trick" of using the MinGW XML file for GCC as the template did work and then (at least with R2020b) mex -setup FORTRAN will find and use it for mex compilation. That is a step forward although linking the Fortran generated code to the libraries is still an issue as outlined above for all Fortran.

However, it seems to me that since the libraries were built by TMW with and successfully link to the gcc C object files, one should be able to use the new C interop features of Fortran and build object fiies that will interoperate with the existing libraries. It would be far better if TMW would build/add the direct Fortran entry points/linkages, but it seems as though should be possible with the existing libraries.

At this point, however, I have not used gfortran sufficiently long nor am I yet familiar-enough with C interop features to be able to just throw something together; I'll have to research this at some length to give it a go.

Answer 2

[zhangbaby]

There is an old project called Gnumex which use MinGW to compile matlab mex file on windows platform. It is good at using gfortran for 32bit and in some cases for 64bit.