Hi All
I don't know whether I should post this thing to compiler group or
this group.
Anyway, I decided to post to this group. (I'm sorry if you think I
post in wrong group)
My question is...
I wrote the program like this.
void func()
{
char a[8];
}
And then compile to asm code (gcc with -S option)
I've got this line of code.
......
subl $8 %esp
......
That makes sense, It moves stack pointer down 8 bytes for local
variable.
But the problem is, when I change size of array to 9 or 7 the asm code
turn
to this.
.....
subl $24 %esp
.....
It doesn't make any sense to me. Why it allocates 24 bytes for 9 or 7
bytes variable.
Does anybody has any explaination?
Thank in advance.
Prawit C. 6 1351 ar*********@hot mail.com (Prawit Chaivong) typa: Hi All I don't know whether I should post this thing to compiler group or this group. Anyway, I decided to post to this group. (I'm sorry if you think I post in wrong group)
My question is... I wrote the program like this.
void func() { char a[8]; }
And then compile to asm code (gcc with -S option) I've got this line of code.
..... subl $8 %esp .....
That makes sense, It moves stack pointer down 8 bytes for local variable. But the problem is, when I change size of array to 9 or 7 the asm code turn to this.
.... subl $24 %esp ....
Same think for me with asm output and CPU debug trace.
On the same IDE, with Borland bc++5.6 and gcc 3.2, i tried :
void func()
{
int i;
char a[??];
printf("%d\n", (int)&i - (int)&a[0]);
}
Results accords tou yours:
?? output bc++5.6 output gcc 3.2
-------------------------------------------
0 no compile 28
1 1 1
2 2 2
3 3 28
4 4 4
5 8 28
6 8 28
7 8 28
8 8 12
9 12 28
10 12 28
11 12 28
12 12 28
13 16 28
14 16 28
15 16 28
16 16 28
17 20 44
18 20 44
gcc seems crazy (bug ?).
bc++5.6 does not support VLAs. But wit gcc i tried:
void func(int N)
{
int i;
char a[N];
printf("%d\n", (int)&i - (int)&a[0]);
}
int main(void)
{
for(int i = 0; i <= 32; i++)
{
printf("%d\t", i);
func(i);
}
return 0;
}
The output is:
0 16
1 32
2 32
3 32
4 32
5 32
6 32
7 32
8 32
9 32
10 32
11 32
12 32
13 32
14 32
15 32
16 32
17 48
18 48
19 48
20 48
21 48
22 48
23 48
24 48
25 48
26 48
27 48
28 48
29 48
30 48
31 48
32 48
It doesn't make any sense to me. Why it allocates 24 bytes for 9 or 7 bytes variable.
Does anybody has any explaination?
Not any sensible ....
--
Pierre
Emmanuel Delahaye <em**********@n oos.fr> typa: In 'comp.lang.c', Pierre Maurette <ma************ *@free.fr> wrote:
Results accords tou yours:
Results comply with yours:
(well, I think)
"tou" instead of "to" was a typo.
For the rest, my english is even worse than my C style ;-)
--
Pierre
Emmanuel Delahaye <em**********@n oos.fr> wrote: In 'comp.lang.c', Pierre Maurette <ma************ *@free.fr> wrote:
Results accords tou yours:
Results comply with yours:
"Agree with" is, AFAICT (not being Anglophone myself either, after all)
more idiomatically correct. "Comply with" would be used for rules, not
for observations.
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