DOCUMENT:Q87548  26-JUN-2001  [utilities]
TITLE   :FIX: Upper Half of 32-bit Registers, GS, and FS Corrupt
PRODUCT :Microsoft Programming Utilities
PROD/VER::
OPER/SYS:
KEYWORDS:kb16bitonly

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The information in this article applies to:

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

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Keywords          : kb16bitonly 
Technology        : kbAudDeveloper kbCodeView kbZNotKeyword3
Version           : :
Solution Type     : kbfix

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