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Microsoft KB Archive/39373

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Knowledge Base

Article ID: 39373

Article Last Modified on 10/22/2003


  • Microsoft Macro Assembler 5.1 Standard Edition

This article was previously published under Q39373


The code below is correctly flagged as an error in the Microsoft Macro Assembler (MASM) versions 5.0, 6.0, 6.0a, 6.0b, but MASM 5.1 generates a warning and incorrect code.

The following is the error generated by MASM 5.0

A2019: Wrong type of register

Macro Assembler Version 5.1 fails to generate an error on the MOV instruction using the 8-bit registers (AH, BH, CH, DH, AL, BL, CL, DL) with segment registers (CS, DS, ES, SS). Instead, the following warning is generated

A4057: Illegal size for operand

The code generated is also in error. Each of the (8-bit) byte registers maps to the set (SP, DI, BP, SI, AX, BX, CX, DX).

The following is the error generated by MASM 6.0

A2024: invalid operand size for instruction


Microsoft has confirmed this to be a problem in MASM version 5.1. This problem was corrected in MASM version 6.0.


The following sample code demonstrates the problem:

Sample Code:

;Assemble options needed: none

_TEXT   segment word public 'CODE'
      ; instruction in source     Generated code shown in listing
        mov     ds, ah          ; mov   ds, sp
        mov     ds, bh          ; mov   ds, di
        mov     ds, ch          ; mov   ds, bp
        mov     ds, dh          ; mov   ds, si

        mov     ds, al          ; mov   ds, ax
        mov     ds, bl          ; mov   ds, bx
        mov     ds, cl          ; mov   ds, cx
        mov     ds, dl          ; mov   ds, dx

        mov     ah, 4ch
        int     21h
_TEXT   ends

Additional query words: 5.10 buglist5.10 fixlist6.00

Keywords: kbfix KB39373