KnowledgeBase Archive

An Archive of Early Microsoft KnowledgeBase Articles

View on GitHub

Q95414: PRB: INVOKE Pushes SS to Convert NEAR PTR to FAR PTR

Article: Q95414
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b,6.1,6.11,6.1a
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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

- Microsoft Macro Assembler (MASM), versions 6.0, 6.0a, 6.0b, 6.1, 6.1a, 6.11 
-------------------------------------------------------------------------------

SYMPTOMS
========

When an application passes a parameter of type NEAR PTR to a routine that
expects an argument of type FAR PTR, the INVOKE directive converts the NEAR PTR
to a FAR PTR by pushing the SS segment register on the stack. The assembler does
not issue any warnings when it applies this conversion. In a situation where SS
does not equal DS, as in a Windows dynamic-link library (DLL), INVOKE may
generate incorrect code.

CAUSE
=====

When the assembler converts a NEAR PTR to a FAR PTR, it uses the SS segment
register when it has no other information about the appropriate segment value.

RESOLUTION
==========

When your application passes a NEAR PTR parameter to a function that expects a
FAR PTR, specify the segment register to use in the conversion by adding the
appropriate segment prefix (cs:, ds:, es:, or ss:) to the parameter. The code
example below demonstrates this method.

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

  ; Assemble options needed: none

  .MODEL small, C, farstack

  func1 PROTO arg1:FAR PTR BYTE

  .CODE
  func2 PROC, arg2:NEAR PTR BYTE
      INVOKE func1, arg2         ; This pushes ss:arg2
      ret
  func2 ENDP

  func3 PROC, arg2:NEAR PTR BYTE
      INVOKE func1, ds:arg2      ; This pushes ds:arg2
      ret
  func3 ENDP

  END

Additional query words: 6.00 6.00a 6.00b 6.10 6.10a

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM610 kbMASM611 kbMASM610a kbMASM600a kbMASM600b
Version           : :6.0,6.0a,6.0b,6.1,6.11,6.1a
Issue type        : kbprb

=============================================================================

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.