FIX: DOSXNT DX1020 Error Using .WHILE and Processor Flag

MS-DOS     | OS/2

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, versions 6.1 and 6.1a
• Microsoft Macro Assembler for MS-DOS version 6.0, running under OS/2 version 1.21

SYMPTOMS

Microsoft Macro Assembler (MASM) version 6.1, and 6.1a may generate a DOSXNT DX1020 general protection fault when using the .WHILE directive to test the state of a processor flag (SIGN?, ZERO?, CARRY?, PARITY?, or OVERFLOW?). The error occurs if the processor flag is tested by itself or is negated and tested. For example:

   .WHILE SIGN?
   .WHILE !SIGN?

RESOLUTION

To work around this problem, OR the desired processor flag with zero. For example:

   .WHILE SIGN? || 0

STATUS

Microsoft has confirmed this to be a problem in MASM versions 6.0, 6.1, and 6.1a. This problem was corrected in MASM version 6.11.

MORE INFORMATION

The following sample code can be used to demonstrate the problem.

Sample Code

; Assemble options needed: none

.MODEL small .STACK 4096

.DATA

.CODE

    .startup
    .WHILE SIGN?       ; generates DOSXNT general protection fault
        nop
    .ENDW
    .WHILE SIGN? || 0  ; avoids the protection fault
        nop
    .ENDW
    .exit 0