FIX: Prefix Bytes Are Order-Dependent in CodeView 4.0x

Last reviewed: September 16, 1997
Article ID: Q103721

4.00 4.01 MS-DOS kbtool kbfixlist kbbuglist

The information in this article applies to:

Microsoft CodeView for MS-DOS, versions 4.0 and 4.01

SYMPTOMS

The disassembler, which is used to display mixed source and assembly or assembly in CodeView, is sensitive to the order in which the 66h and 67h prefix bytes occur in 32-bit instructions. If the order is 67h 66h, then the instruction is disassembled as:

   67668B03      MOV     AX,WORD PTR [EBX]

CodeView incorrectly shows AX as the destination operand. However, if the order is 66h 67h, then the instruction is disassembled as:

   66678B03       MOV     EAX,DWORD PTR [EBX]

In this case, CodeView correctly shows EAX. The MASM version 6.x program shown below demonstrates the problem.

STATUS

Microsoft has confirmed this to be a problem in CodeView versions 4.0 and 4.01. The problem was corrected in CodeView version 4.1.

Sample Code

; Assemble options needed: /Zi

.MODEL small .386

.STACK 4096

.CODE

    .startup

loc1:

    mov eax, [ebx]

loc2:

    ORG loc1
    DB 66h, 67h    ; This forces the prefix bytes to 66h 67h
    ORG loc2

loc3:

    mov eax, [ebx]

loc4:

    ORG loc3
    DB 67h, 66h    ; This forces the prefix bytes to 67h 66h
    ORG loc4
    .exit 0

END

Additional reference words: reverse 4.00
KBCategory: kbtool kbfixlist kbbuglist
KBSubcategory: CvwIss
Keywords : kb16bitonly
Solution Type : kbfix

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Last reviewed: September 16, 1997
© 1998 Microsoft Corporation. All rights reserved. Terms of Use.