Re: nasty link problem with Gfortran and G++ (C++) ???

On 1/8/2025 3:37 AM, Thomas Koenig wrote:

Lynn McGuire <lynnmcguire5@gmail.com> schrieb:

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 turn off the trailing underscores in the Fortran code.  I build Win32
DLLs that are Excel VBA, C++, and Fortran callable.

 Just wondering... have you read the relevant gfortran documentation
regarding naming conventions and the attributes directive?

About three times now.  Still makes my head spin.
All of this F77 / C++ code was working with the Watcom F77 / C++ PCDOS / Win32 compilers for the last 32+ years and over 2,000 commercial users. The port has been the worst port ever.  But I blame that on the old Fortran code dating back to 1965 (Fortran II !!!).  I have ported the Fortran code to twelve different platforms over the years (mainframes, various Unix boxen, Vax VMS, Prime, PC DOS, Win32).
I was porting for the third attempt to the Intel Fortran / Visual C++ compilers and they obsoleted the Intel Fortran compiler on me about three months ago.  I am not going to port to an obsolete compiler.  The first two attempts in 2002 ? and 2010 ? to port to Intel Fortran ran into compiler bugs (crashed the linker table at 300,000 entries, the vector automatic zeroing code had a serious bug).
Lynn