KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q87548: FIX: Upper Half of 32-bit Registers, GS, and FS Corrupt

Article: Q87548
Product(s): Microsoft Programming Utilities
Version(s): 
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 26-JUN-2001

-------------------------------------------------------------------------------
The information in this article applies to:

- Microsoft CodeView for MS-DOS 
- Microsoft CodeView for Windows 
-------------------------------------------------------------------------------

SYMPTOMS
========

When single-stepping or tracing through code in Microsoft CodeView versions 4.0,
4.01, and 4.05, the lower half of the 32-bit registers (eax, ebx, edi, etc.) is
always preserved, but the upper half may be corrupted. Other 386- specific
registers, such as the gs and fs registers, may also be corrupted. This problem
also occurs when animating. This problem does not occur if the instructions are
not executed one at a time.

STATUS
======

Microsoft has confirmed this to be a problem in CodeView version 4.0, 4.01, and
4.05. This problem was corrected in CodeView version 4.1.

MORE INFORMATION
================

The following sample code can be used to demonstrate this problem. The ebx
register will get the value FFFFFFFF, but single-stepping on the NOP will change
the value to 0000FFFF.

Sample Code
-----------

  ; Assemble options needed: /Zi

  _text SEGMENT para public 'code'
     ASSUME cs:_text, ds:_text
  main:
     .386

     MOV ebx, 0ffffffffh
     NOP

     MOV ah, 4ch
     INT 21h
  _text ENDS

  stack SEGMENT para stack 'stack'
     DW 64 dup( ? )
  stack ENDS

     END main

Additional query words: 4.00

======================================================================
Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbCodeView kbZNotKeyword3
Version           : :
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.