Q59567

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Q59567: "A4100: Impure Memory Reference" Incorrectly Generated

Article: Q59567
Version(s): 5.00 5.10 5.10a | 5.00 5.10 5.10a
Operating System: MS-DOS          | OS/2
Flags: ENDUSER | buglist5.10
Last Modified: 29-MAR-1990

The /P option tells MASM to generate warning messages if data is
stored in the code segment when privileged instructions are in use.

Writing data to the code segment is acceptable in real mode; however,
it may cause problems in protected mode. If MASM is invoked with the
/P option and finds an impure memory reference, such as in the
following code

               .code
       c_word  DW        ?
               .
               .
               mov       cs:c_word,data

it will generate a warning similar to the following:

   filename.asm(???): warning A4100: Impure memory reference

MASM may incorrectly generate the warning message. The following
example demonstrates this problem:

        .model small
        .286p
        .code

        mov     al,cs:[bp]
        mul     word ptr cs:[bp+2]
        end

MASM incorrectly flags the line that does the multiplication. MASM
also incorrectly generates the A4100 warning message if the .286,
.386, and .386p directives are in effect.

Microsoft has confirmed this to be a problem in Version 5.10. We are
researching this problem and will post new information here as it
becomes available.