Microsoft KB Archive/93594

= BUG: No Warning Moving Segment Register to Extended Reg. =

Article ID: 93594

Article Last Modified on 10/17/2003

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APPLIES TO


 * Microsoft Macro Assembler 5.1a
 * Microsoft Macro Assembler 6.0 Standard Edition
 * Microsoft Macro Assembler 6.0a
 * Microsoft Macro Assembler 6.0b
 * Microsoft Macro Assembler 6.1 Standard Edition
 * Microsoft Macro Assembler 6.1a
 * Microsoft Macro Assembler 6.11 Standard Edition

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This article was previously published under Q93594



SYMPTOMS
With the Microsoft Macro Assembler (MASM), an application can move data between one of the 16-bit segment registers and a 32-bit extended register. The assembler does not provide any error or warning message when an application makes such a move even though the high-order 16 bits of the 32-bit extended register are filled with a random value or are discarded in the move operation.



STATUS
Microsoft has confirmed this to be a problem in MASM versions 5.1, 5.1a, 6.0, 6.0a, 6.0b, 6.1, 6.1a, and 6.11. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.



MORE INFORMATION
Even though assembling the following code example should generate two assembler error or warning messages, it does not. The application runs; however, the EAX register is not restored to its original value as may be intended.

Sample Code
; Assembler options needed: /c /W3

.MODEL small .386 .STACK 4096

.CODE start: mov eax, 12345678h mov es, eax   ; this should generate a warning or an error mov eax, 87654321h mov eax, es   ; this should generate a warning or an error mov ax, 4C00h int 21h END start

Additional query words: 5.10 5.10a 6.00 6.00a 6.00b 6.10 6.10a buglist6.00a buglist6.00b buglist6.10 buglist6.10a buglist6.11

Keywords: KB93594

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