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Q92609: PRB: SEGMENT AT Does Not Initialize Data at Absolute Address

Article: Q92609
Product(s): Microsoft Macro Assembler
Version(s): 5.0,5.1,5.1a,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 5.0, 5.1, 5.1a, 6.0, 6.0a, 6.0b 
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SYMPTOMS
========

When the SEGMENT directive is used with the AT combine type to place code or
initialized data at an absolute address, the generated executable file does not
initialize the segment at the specified absolute address. MASM versions 5.0,
5.1, and 5.1a do not generate any error or warning messages. MASM versions 6.0,
6.0a, and 6.0b generate the following warning message:

  A4014: instructions and initialized data not supported in AT

  segments

CAUSE
=====

This warning is expected and caused by the design of the Microsoft Linker.

The Microsoft Linker (LINK), distributed with Microsoft programming languages, is
designed to generate relocatable programs to run with MS-DOS, Microsoft Windows,
or OS/2. LINK does not generate code or data at absolute addresses. MASM
versions 6.0, 6.0a, and 6.0b generate a warning message because LINK does not
support SEGMENT AT in this manner.

RESOLUTION
==========

Link and locate tools that generate absolute addresses are available from
third-party vendors.

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

The SEGMENT AT directive is used to access a specified memory address, for
example, a code routine or data in the ROM BIOS. While SEGMENT AT allows an
application to create a template for memory at a fixed address, it does not
support initializing code or data at that address.

The code fragment below demonstrates the problem.

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


  ; Assembler options needed: none

  interrupt_table SEGMENT AT 0
  ORG 8*4
  irq0 DD 12345678h
  irq1 DD 9ABCDEF0h
  interrupt_table ENDS

  _text SEGMENT WORD PUBLIC 'CODE'
  ASSUME cs:_text
  start:
      mov ax, 4C00h
      int 21h
  _text ENDS

  END start

Additional query words: 5.00 5.10 5.10a 6.00 6.00a 6.00b romable code embedded systems

======================================================================
Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM500 kbMASM600a kbMASM510a kbMASM600b
Version           : :5.0,5.1,5.1a,6.0,6.0a,6.0b

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

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