BUG: Access Violation Calling Exported Subroutine in DLL

• Microsoft Fortran PowerStation for Windows 95 and Windows NT, version 4.0

SYMPTOMS

When you use the !MS$ATTRIBUTES DLLEXPORT attribute to export a DLL's subroutine, and call that subroutine from another subroutine within the same DLL it causes the following Access Violation:

   The instruction at "0x00000000" referenced memory at "0x00000000".
   The memory could not be "written"

RESOLUTION

If you need to call an exported subroutine in a DLL, you should put this code into a non-exported helper subroutine and have the exported subroutine call the non-exported helper subroutine.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

Steps to Reproduce Problem

1. Build the DLL using the sub.for file listed below. At the MS-DOS command-line prompt, type:

   fl32 /LD sub.for

2. Build the MAIN program using the main.for file listed below, and link it to the DLL static library file created in Step 1. At the same MS-DOS command-line prompt, type:

   fl32 main.for sub.lib

Sample Code to Illustrate Problem

MAIN

! filename: main.for ! Compile options needed: none

      program fortapp
        interface
          subroutine thesub()
            !ms$attributes dllimport, stdcall :: thesub
          end subroutine
        end interface

   call thesub()
      end program fortapp

DLL

! filename: sub.for ! Compile options needed: /LD

      subroutine thesub()
        !ms$attributes dllexport, stdcall :: thesub
          interface
            subroutine othersub()
              !ms$attributes dllexport, stdcall :: othersub
            end subroutine othersub
     end interface

        call othersub()
      end subroutine

      subroutine othersub()
        !ms$attributes dllexport, stdcall :: othersub
      end subroutine