Q29570: PRB: Error "constant expected" with ORG Directive

Article: Q29570
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

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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
========

The statement 'ORG $+1' assembles without error, but the statements 'ORG $*2'
and 'ORG $/2' produce an error. Under MASM 5.0, 5.1, and 5.1a the error message
is:

  error A2042: Constant expected

Under MASM 6.0, 6.0a, and 6.0b the error message is:

  error A2026: constant expected

CAUSE
=====

The location counter ($) has the same attributes as a near label. Thus, MASM
emits an offset relative to the start of the current segment.

The linker must add the base address of the segment to do the fixup. When you use
$+1, MASM emits an offset equal to one more than the current value of $. When
you use $-1, MASM emits an offset equal to one less than the current value of
$.

When the linker adds the segment base address, the desired value is obtained.
Because the linker only adds the segment base address, there is no way to do
multiplicatiion or division; only addition and subtraction can be performed.
Since the Linker cannot multiply and divide, these operations cannot be applied
to symbols that are relocatable.

RESOLUTION
==========

This is the expected behavior of MASM.

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

  ; Assemble options needed: none

  .MODEL small

  .CODE
  start:
      mov ax,4C00h
      int 21h
  ORG $/2
  END start

Additional query words: 5.00 5.10 5.10a 6.00 6.00a 6.00b

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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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