FIX: MASM 6.0 May Parse a Comment as a Conditional Directive

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, version 6.0
• Microsoft Macro Assembler for OS/2, version 6.0

SYMPTOMS

The Microsoft Macro Assembler (MASM) version 6.0 will incorrectly parse a comment as if it were a conditional-assembly directive if the following conditions are met:

1. There is a conditional-assembly directive (or word that is the same as a conditional directive) inside a comment block that does not directly follow the delimiter character and is the first thing on the line.

2. The comment block itself is contained in a conditional-assembly block, which will NOT be evaluated by the assembler.

CAUSE

When both of these conditions are true, the conditional-assembly directive is given precedence over the comment block. The conditional directive is treated as a keyword although it was not meant to be treated as such.

RESOLUTION

To work around the problem, make sure that the first word on the line inside the comment block is not the same as a conditional directive. For example, in the sample code, one solution is to change the line "If should be ignored in a comment" to "An if should be ignored in a comment."

STATUS

Microsoft has confirmed this to be a problem in MASM version 6.0. This problem was corrected in MASM version 6.0a.

MORE INFORMATION

If the conditional-assembly directive is either IF, IFE, IFB, IFNB, IFDEF, IFNDEF, IFIDN, or IFDIF and there is no associated ENDIF at the beginning of another line, then the following errors will be generated:

   error A2088 : END directive required at end of file
   fatal error : A1010 : unmatched block nesting : if-else

   error A2008 : syntax error : <the text following the ELSE>

   error A2008 : syntax error
   error A2081 : missing operand after unary operator

   error A2008 : syntax error
   error A2044 : invalid character in file

The sample code below illustrates this problem. It meets the above conditions, so it is parsed incorrectly and the following errors are generated:

   error A2088 : END directive required at end of file
   fatal error : A1010 : unmatched block nesting : if-else

Sample Code

; Assemble options needed: none

.MODEL small

.STACK 4096 .CODE

    .startup

IFDEF   xyz                ; xyz is not defined

        If should be ignored in this comment.
   ^

    .exit 0