FIX: Alternate Return Compiled with /Ox Can GPF at Run Time

The information in this article applies to:

• Microsoft FORTRAN PowerStation for MS-DOS, version 1.0

SYMPTOMS

The FORTRAN PowerStation optimizer may generate incorrect code when compiling routines containing alternate returns. If routines containing alternate returns are compiled with /Ox, the following errors may occur at run time:

   DOSXMSF : fatal error DX1020: unhandled exception: General
             protection fault;

   Fault occurred in a System Call

RESOLUTION

Altering code around the alternate return may alleviate this problem. If this doesn't work, then do not compile routines using alternate returns with /Ox. Note that other routines in the program can still be optimized.

STATUS

Microsoft has confirmed this to be a problem in FORTRAN PowerStation version 1.0 for MS-DOS. This problem has been resolved with FORTRAN PowerStation maintenance release version 1.0A for MS-DOS.

MORE INFORMATION

To duplicate the error, compile the sample code with /Ox and then run the program to get the DX1020 error. This problem is dependent on the surrounding code. Replacing "var=1.0" with "continue", or commenting out "goto 10" in the sample below removes the problem:

FORTRAN PowerStation version 1.0 can be differentiated from the maintenance release version 1.0A by invoking the linker. Typing "link32 | more" from /F32/BIN directory will show version 2.8 for FORTRAN Powerstation maintenance release version 1.0A for MS-DOS."

Sample Code

      call test(*10,*20)
   10 var=1.0
   20 if (var.ne.0) return
      goto 10
      end

      subroutine test(*,*)
      return 1
      end