FIX: Warning A4057 Generated Instead of Error A2019 (39373)

SYMPTOMS

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 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 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

;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
        end