Q85508: PRB: No Warning for INVOKE Between 16-Bit and 32-Bit Segments

Article: Q85508
Product(s): Microsoft Macro Assembler
Version(s): MS-DOS:6.0,6.0a,6.0b
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 
-------------------------------------------------------------------------------

SYMPTOMS
========

The Microsoft Macro Assembler (MASM) version 6.0 does not support transfer of
control between 16-bit and 32-bit code segments through the INVOKE command. If
the assembler encounters an INVOKE in a 16-bit segment, it assumes that the
procedure being invoked is also in a 16-bit segment and places the parameters on
the stack using WORDs. On the other hand, if the assembler encounters an INVOKE
in a 32-bit code segment, the parameters are placed on the stack as DWORDs with
the assumption that the called routine will also be in a 32-bit code segment.
MASM does not generate warnings when the segment being called does not match the
calling segment.

CAUSE
=====

The INVOKE command, introduced in MASM 6.0, is not designed to support
transferring control between 16-bit and 32-bit code segments.

RESOLUTION
==========

You can work around this problem by pushing the necessary parameters on the
stack and making the appropriate call instead of using INVOKE.

STATUS
======

This feature is under review and will be considered for inclusion in a future
release.

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

It is important to note that, in order to run code in 32-bit segments, the
operating system that your program is running on must be able to support 32-bit
code segments. Most PC-based operating systems such as MS-DOS version 5.0,
Windows version 3.0, and OS/2 versions 1.x do not provide support for 32-bit
code segments. Newer operating systems and MS-DOS extender packages may provide
this support.

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

  ; Assemble options needed: none
  ; Note that this code does not work on present operating systems such
  ; as MS-DOS. This code is only provided to demonstrate how to replace
  ; an INVOKE statement with the appropriate push and call sequence.

  .MODEL small, pascal
  .386

  func PROTO FAR32 arg1:BYTE, arg2:WORD, arg3:DWORD

  .code
    .startup
    MOV dl, x
    MOV cx, y
    MOV ebx, z
    INVOKE func, dl, cx, ebx ; This doesn't work.

    ;MOV al, dl    ; Uncomment this code to set up the call to func.
    ;PUSH eax      ; Push DWORD instead of WORD.
    ;MOV ax, cx
    ;PUSH eax      ; Push DWORD instead of WORD.
    ;PUSH ebx
    ;CALL FAR32 PTR func

    .EXIT 0

  .DATA
    x DB 11h
    y DW 2222h
    z DD 33333333h

  _code32 SEGMENT DWORD PUBLIC USE32 'code'
  func PROC FAR32 arg1:BYTE, arg2:WORD, arg3:DWORD
    MOV bl, arg1   ; func assumes that all variables
    MOV cx, arg2   ; on the stack are DWORD aligned.
    MOV edx, arg3
    RET
  func ENDP
  _code32 ENDS

  END

Additional query words: 6.00 6.00a 6.00b

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM600a kbMASM600b
Version           : MS-DOS:6.0,6.0a,6.0b

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

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.

Copyright Microsoft Corporation 1986-2002.