Microsoft KB Archive/78862

= FIX: Incorrect Code Generated If Operand Is [eax][eax] =

Article ID: 78862

Article Last Modified on 10/29/2003

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APPLIES TO


 * Microsoft Macro Assembler 6.0 Standard Edition

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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

Additional query words: 6.00 buglist6.00 fixlist6.00a

Keywords: kbfix KB78862

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