FIX: DOSXNT DX1020 Error Using .WHILE and Processor Flag

ID: Q97840

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS, versions 6.1, 6.1a
Microsoft Macro Assembler for MS-DOS and OS/2, version 6.0
on the following platforms: OS/2

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?

MASM version 6.0 running under OS/2 version 1.21 may generate a trap 13 in the above situation.

RESOLUTION

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

.WHILE SIGN? || 0

This work around will also work with ZERO?, CARRY?, PARITY?, and OVERFLOW?.

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
END

Additional query words: 6.00 6.10 6.10a unhandled exception buglist6.00 buglist6.10 buglist6.10a fixlist6.11

Keywords :
Version : :6.1,6.1a; MS-DOS:6.0
Platform : MS-DOS
Issue type :