BUG: DPMI Function 0203h Does Not Report Error

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SYMPTOMS

Using the MS-DOS Protected Mode Interface (DPMI) function 0203h (set processor exception handler vector) to set an exception handler does not report an error (carry flag set) if the selector:offset pair is invalid.

RESOLUTION

The pointer to the exception handler must be validated with other means if it is necessary to check the pointer for validity. Other means of checking a code pointer for validity include using IsBadCodePtr() or the LAR (load access rights) protected-mode CPU instruction.

STATUS

Microsoft has confirmed this to be a bug in Windows version 3.1. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The problem with DPMI function 0203h can be illustrated with the following code segment:

   mov     edx, dword ptr BogusOffset
   mov     cx, word ptr BogusSelector
   ; Set Processor Exception Handler Vector
   mov     ax, 203h
   mov     bx, 7
   int     31h
   jc      Error       ; never jumps to Error

REFERENCE

The IsBadCodePtr() function is documented in the Windows 3.1 SDK "Programmer's Reference, Volume 2: Functions" manual. The LAR instruction is documented in the Intel 386 or 486 "Programmer's Reference" or in "Microsoft's 80386/80486 Programming Guide" by Microsoft Press.