FIX: Incorrect Code Generated If Operand Is [eax][eax] (78862)


The information in this article applies to:

  • Microsoft Macro Assembler (MASM) 6.0
This article was previously published under Q78862

SYMPTOMS

In the Microsoft Macro Assembler (MASM) version 6.0, incorrect code is generated for instructions, such as the following, using the operand [eax][eax]:

lea edi, [eax][eax]
mov edi, [eax][eax]

RESOLUTION

A workaround for this problem is to embed the opcode for the instruction directly in the code. The sample code below demonstrates this method.

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

A listing file from the following program will show that the instruction lea edi, [eax][eax] is encoded as 8D 3C 3A. However, the code actually placed into the executable is 8D 3C. The correct code in the case of lea edi, [eax][eax] is 8D 3C 00. Note that the operand [eax][eax] is available only when using the .386 or .486 directives.

Sample Code

; Assembler options needed: none

.386
.MODEL small

CODE32 SEGMENT DWORD PUBLIC USE32 'CODE'
ASSUME CS:CODE32
main PROC
    lea edi, [eax][eax] ; Replace this by BYTE 8Dh, 3Ch, 00h
                        ; since the code generated by it is
                        ; 8D 3C 3A, which is incorrect.
    mov edi, [eax][eax] ; Replace this by BYTE 8Bh, 3Ch, 00h
                        ; since the code generated by it is
                        ; 8B 3C 3A, which is incorrect.
    ret
main ENDP
CODE32 ENDS

END main
Modification Type:MinorLast Reviewed:10/29/2003
Keywords:kbfix KB78862
©2003 Microsoft Corporation. All rights reserved.