Q72727: PRB: No Error for Same Register Listed Twice in USES Clause

Article: Q72727
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b
Operating System(s): 
Keyword(s): 
Last Modified: 06-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), versions 6.0, 6.0a, 6.0b 
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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

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM600a kbMASM600b
Version           : :6.0,6.0a,6.0b

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