PRB: Line Parsing Order: Looks Up Second Token First

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

SYMPTOMS

The example below will generate the warning:

   warning A4016: Reserved word used as symbol: MOV

   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 ?

_TEXT SEGMENT 'CODE' ASSUME CS:_TEXT start:

    mov a_struc.a, ax
    mov ax, 4C00h
    int 21h

END start