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From: Lynn McGuire <lynnmcguire5@gmail.com>
Newsgroups: comp.lang.fortran
Subject: Re: nasty link problem with Gfortran and G++ (C++) ???
Date: Thu, 9 Jan 2025 22:43:24 -0600
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On 1/7/2025 4:18 PM, Thomas Koenig wrote:
> Lynn McGuire <lynnmcguire5@gmail.com> schrieb:
>> I just ran into a nasty problem with GFortran and G++ (C++).  Probably
>> not a bug ???  I am using GCC 14.1.
>>
>> I have a lot of code in C++ (over 100,000 lines).  I have 750,000 lines
>> of code in GFortran.  I have to extern "C" this code in C++ to make it
>> callable by GFortran code.
>>
>> I missed declaring a couple of C++ functions as extern "C" which means
>> that they kept their C++ mangled link names.  But these C++ functions
>> were declared as integer*8 and external in the GFortran code (old F77
>> code).
>>
>> So, the GCC linker did not report to me that it did not have a link for
>> the G++ functions.  This may be a bug, I am not sure.
> 
> Without having looked at the source code, I suspect
> it is probably something that you are not describing.
> 
> You can look into the object files with any number of utilities,
> for example "nm".  Here's an example:
> 
> subroutine foo
>    external bar
>    integer *8 bar
>    print *,bar(1234)
> end subroutine foo
> 
> Compiling to an object file and running nm on this will show you
> 
>                   U bar_
> 0000000000000000 T foo_
>                   U _gfortran_st_write
>                   U _gfortran_st_write_done
>                   U _gfortran_transfer_integer_write
> 
> which means you have a symbol "foo_" defined, it is a global (hence
> uppercase) symbol in the text section (hence T).  You also have
> several undefined symbols, among them bar_, plus some gfortran
> library routines, so all is fine.
> 
> If you do not find your undefined
>> When I ran the program, the C++ functions were not called by the
>> GFortran code.  Instead, the GFortran code treated the C++ functions as
>> integer*8 scalar variables.
> 
>>
>> If needful, I can probably put together a small code sample that
>> exhibits the problem.  Maybe.  It could be that the size of my code
>> affects the GCC linker.
> 
> That I would consider highly unlikely.

I cannot get a small code sample with or without a DLL to exhibit the 
problem.  Like I said, I thought it was something related to size of my 
DLL.  And this is the small DLL, only 3 MB.

Thanks,
Lynn