Q111877: BUG: SIZE and SIZEOF May Give Incorrect Values for Locals

Article: Q111877
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b,6.1,6.11,6.1a
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, 6.1, 6.1a, 6.11 
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SYMPTOMS
========

SIZEOF and SIZE drop the high byte of the size for LOCAL variables larger than
255 bytes. The SIZE and SIZEOF for global variables and data types is correct.
The TYPE operator works correctly for all variables.

RESOLUTION
==========

You can use the TYPE and LENGTHOF operators to obtain the correct size of local
variables.

STATUS
======

Microsoft has confirmed this to be a problem in MASM versions 6.x. We are
researching this problem and will post new information here in the Microsoft
Knowledge Base as it becomes available.

MORE INFORMATION
================

In the following example, structure junk1 is 255 bytes and junk2 is 256 bytes.
If local variables are used, SIZE and SIZEOF return 0 (zero) for the size of the
local variable j2L. This can be seen in the listing file or in CodeView if the
program is run in the debugger. Note that the TYPE operator works correctly for
single-element variables. To find the size of array types, use TYPE * LENGTHOF
as shown for j3L below.

Sample Code
-----------

  ; assembly options needed: /Zi /Fl /Sa
  .model large,c
  .386
   
  junktest PROTO
   
  junk1 struct
      a BYTE 255 DUP (?)
  junk1 ends

  junk2 struct
      a BYTE 256 DUP (?)
  junk2 ends

  .stack 10000
  .data
  j1 junk1 <>
  j2 junk2 <>

  .CODE
      .STARTUP
          mov ax, sizeof junk1  ; correct sizes here
          mov ax, sizeof j1
          mov ax, size j1
          mov ax, sizeof junk2
          mov ax, sizeof j2
          mov ax, size j2
          invoke junktest
      .EXIT

  junktest PROC
      LOCAL j1L:junk1     ; correct amount allocated 255 bytes
      LOCAL j2L:junk2     ; correct amount allocated 256 bytes
      LOCAL j3L[256]:BYTE ; correct amount allocated 256 bytes

      mov ax,0
      mov ax, sizeof junk1 ; correct -- 0FFh
      mov ax, sizeof j1L   ; correct -- 0FFh
      mov ax, size j1L     ; correct -- 0FFh
      mov ax, type j1L     ; correct -- 0FFh
      mov ax, sizeof junk2 ; correct -- 0100h
      mov ax, sizeof j2L   ; high byte lost -- returns 00h
      mov ax, size j2L     ; high byte lost -- returns 00h
      mov ax, type j2L     ; OK -- returns 0100h
      mov ax, sizeof j3L   ; high byte lost -- returns 00h
      mov ax, size j3L     ; high byte lost -- returns 00h
      mov ax, type j3L * lengthof j3L ; OK - returns 0100h
      ret
  junktest ENDP

  END

Additional query words: 6.00 6.00a 6.00b 6.10 6.10a 6.10b 6.11 ml buglist6.11

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM610 kbMASM611 kbMASM610a kbMASM600a kbMASM600b
Version           : :6.0,6.0a,6.0b,6.1,6.11,6.1a

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