FIX: MASM Generates Incorrect Code for Indirect Addressing (99239)

MORE INFORMATION

The evaluation order precedence of the operands in indirect addressing is left to right inside the brackets, followed by the label outside the brackets, if one is present. MASM generates incorrect code when the code uses any combination of 32-bit registers and a label to calculate an address when the label is located in a 16-bit segment and the label is listed as the first operand enclosed in brackets.

To work around this problem, make sure that the first operand MASM processes is a 32-bit register; then MASM calculates the address properly. You can do this by moving a 32-bit register to the beginning of the list in the brackets or moving the label outside the brackets. The code example below demonstrates both of these techniques.

Sample Code

; Assemble options needed:  /Zi
; Use CodeView to see the instructions generated by the assembler

.386
sseg SEGMENT STACK USE16 'STACK'
    BYTE 4096 dup (?)
sseg ENDS

cseg SEGMENT PUBLIC USE16 'CODE'
ASSUME cs:cseg, ds:cseg, es:cseg
filler WORD 0
alabel DWORD 2 dup (?)
start:
    mov eax, dword ptr [alabel+esi] ; assembles incorrectly
                                    ;  MOV EDI,DWORD PTR [BX+SI+0002]
    mov eax, dword ptr [esi+alabel] ; assembles correctly
                                    ;  MOV EAX,DWORD PTR [ESI+00000002]
    mov eax, dword ptr alabel[esi]  ; assembles correctly
                                    ;  MOV EAX,DWORD PTR [ESI+00000002]
    mov ax, 4C00h
    int 21h
cseg ENDS
END start