Microsoft KB Archive/72727

= PRB: No Error for Same Register Listed Twice in USES Clause =

Article ID: 72727

Article Last Modified on 10/29/2003

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APPLIES TO


 * Microsoft Macro Assembler 6.0 Standard Edition
 * Microsoft Macro Assembler 6.0a
 * Microsoft Macro Assembler 6.0b

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This article was previously published under Q72727



SYMPTOMS
The USES clause was added to the PROC directive with the release of the Microsoft Macro Assembler (MASM) version 6.0. With USES, it is possible to specify the registers that your procedure will use. The assembler will then save the registers on the stack at function entry and restore them upon exit, saving the programmer from having to do so.

If you mistakenly list the same register twice in the USES clause, MASM will not generate a warning. The assembler will generate code to push and pop the register twice.



CAUSE
This is correct behavior. It is the programmer's responsibility to catch this type of error.



MORE INFORMATION
The sample code below illustrates this situation. In this example, the ES, DI, DS, SI, and CX registers were meant to be saved. However, DI is inadvertently saved twice, and SI is not saved at all.

Sample Code
; Assemble Options Needed: /Fl /Sg /c

.MODEL small, c .STACK 4096 .DATA

.CODE StrCmp PROC USES es di ds di cx, string1:FAR PTR, string2:FAR PTR, len:WORD CLD MOV  cx, len LES  di, string1 LDS  si, string2 REPE cmpsb MOV  ax, cx StrCmp  ENDP END

Additional query words: 6.00

Keywords: KB72727

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