Q67513: Comments in .COD Listing Are Wrong When Using _fastcall

Article: Q67513
Product(s): See article
Version(s): 6.00a  | 6.00a
Operating System(s): MS-DOS | OS/2
Keyword(s): ENDUSER | buglist6.00a fastcall | mspl13_c
Last Modified: 30-JAN-1991

When using the code below with the _fastcall keyword, and compiling
with the /Fc option for a code listing, the listing generates correct
code but incorrectly comments the values that are being pushed.

Using the /Gs (recommended for using _fastcall) and /Fc compile-line
options will generate a code listing that produces wrong comments for
the following statements:

   mov ch, byte ptr top
   mov cl, byte ptr left
   mov dh, byte ptr bot

The code listing below shows the incorrect comments that are
generated:

;|***                   mov al, byte ptr lines
; Line 13
        *** 000018   8a 46 06   mov     al,BYTE PTR [bp+6] ;lines
;|***                   mov bh, byte ptr attr
; Line 14
        *** 00001b   8a 7e fe   mov     bh,BYTE PTR [bp-2] ;attr
;|***                   mov ch, byte ptr top
; Line 15
        *** 00001e   8a 6e fe   mov     ch,BYTE PTR [bp-8]
;|***                   mov cl, byte ptr left
; Line 16
        *** 000021   8a 4e fa   mov     cl,BYTE PTR [bp-6] ;top
;|***                   mov dh, byte ptr bot
; Line 17
        *** 000024   8a 76 fc   mov     dh,BYTE PTR [bp-4] ;left
;|***                   mov dl, byte ptr right
; Line 18
        *** 000027   8a 56 08   mov     dl,BYTE PTR [bp+8] ;right

Notice that the comments after the ch, cl, dh mov statements are not
the same variable names that were actually moved into these registers.
For instance, the statement

    mov ch, byte ptr top

has no comment after it stating what variable was used. However, the
statement

    mov cl, byte ptr left

has a comment of ";top" stating that top was moved in. Obviously,
"top" was moved into the ch register in the previous statement.

Note: The generated code in this listing, as well as in the OBJ, is
correct.

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

static void _fastcall scr_scroll
          (int top, int left, int bot, int right, int lines, int dir)
{
        char attr = 7;

        _asm
                {
                        mov ah, byte ptr dir
                        or  ah, ah
                        mov ah, 7
                        jnz around
                        dec ah
                around:
                        mov al, byte ptr lines
                        mov bh, byte ptr attr
                        mov ch, byte ptr top
                        mov cl, byte ptr left
                        mov dh, byte ptr bot
                        mov dl, byte ptr right
                        int 0x10
                }
}

void main(void)
{
        int t=0,l=0,b=0,r=0,li=0,d=0;
        scr_scroll(t,l,b,r,li,d);
}

Microsoft has confirmed this to be a problem in the C version 6.00a.
We are researching this problem and will post new information here as
it becomes available.

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.