ID Number: Q67513
6.00a 6.00ax | 6.00a
MS-DOS | OS/2
buglist6.00a buglist6.00ax
Summary:
When compiling with the /Fc option to produce a source and assembly
listing with the Microsoft C Compiler versions 6.0a and 6.0ax,
incorrect comments are produced in the code listing for the values
being pushed if the _fastcall keyword is used.
More Information:
The sample code below may be used to illustrate this problem. 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.
Microsoft has confirmed this to be a problem in C versions 6.0a and
6.0ax. We are researching this problem and will post new information
here as it becomes available.
Sample Code
-----------
/* Compile options needed: /Gs /Fc
*/
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);
}