PRB: Line Parsing Order: Looks Up Second Token First

ID: Q35128

The information in this article applies to:

Microsoft Macro Assembler for MS-DOS, versions 5.1, 5.1a, 6.0, 6.0a, 6.0b
Microsoft Macro Assembler for OS/2, versions 5.1, 5.1a, 6.0, 6.0a, 6.0b

SYMPTOMS

The example below will generate the warning:

warning A4016: Reserved word used as symbol: MOV

when assembled with Microsoft Macro Assembler (MASM) 5.1 and 5.1a. This warning is misleading. MASM 6.0, 6.0a, and 6.0b generate the more specific error message:

error A2001: immediate operand not allowed

CAUSE

The reference to a_struc.a in the example below is a reference to a structure template and not to a variable stored in memory. Thus, a_struc.a is a constant or immediate operand. MASM 5.1 and 5.1a always looks up the second token on the line first. In the case below, it sees "a_struc". Because a_struc is a structure declaration, MASM assumes the line declares a structure instance with "MOV" being the label. At this point, MASM errors on trying to use reserved symbol "MOV" as a structure instance label.

RESOLUTION

This is the expected behavior of MASM.

MORE INFORMATION

Sample Code


; Assemble options needed: none

a_struc STRUC
    a DW ?
a_struc ENDS

_TEXT SEGMENT 'CODE'
ASSUME CS:_TEXT
start:
    mov a_struc.a, ax
    mov ax, 4C00h
    int 21h
_TEXT ENDS

END start

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

Keywords :
Version : :5.1,5.1a,6.0,6.0a,6.0b
Platform :
Issue type :