FIX: A1010 from Unclosed Segment in MASM @ShowStr Macro

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS, version 6.0

SYMPTOMS

The Microsoft Macro Assembler (MASM) version 6.0 includes a predefined macro in DOS.INC called @ShowStr that displays a $-terminated string. When the argument to @ShowStr is a string literal and there are no segment directives or ends directives following the occurrence of @ShowStr, the assembler will generate the following error:

   fatal error A1010: unmatched block nesting: _DATA

RESOLUTION

To work around this problem, make sure that a simplified segment directive or ends directive follows the @ShowStr macro.

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

When @ShowStr is passed a string literal, the macro generates the following code:

   sseg    TEXTEQU @CurSeg        ; save current segment
   .DATA                          ; change segment
   msg     BYTE    ofset, "$"     ; terminate string with a '$'
   sseg    SEGMENT                ; restore segment
   mov     dx,     OFFSET msg
   mov     ah,     9
   int     21h                    ; display '$' terminated string

In the sample code below, @ShowStr is in a segment started with .CODE. In the macro expansion, that segment is ended and the next segment begun with .DATA. The code segment is restored with the statement _TEXT SEGMENT. This segment is not closed in the macro or in the subsequent code, so the A1010 error is produced. The error can be eliminated by uncommenting either of the commented lines.

Sample Code

; Assemble options needed: none

.MODEL small

INCLUDE dos.inc

.STACK 4096 .CODE

    .startup
    @ShowStr "Hello"
    .exit 0

END