Hello All !
I wrote the following C program and
obtained its assembly version , using command :
cc -S temp.c
< on an x-86 Linux machine >
/* File Name - temp.c */
void function(int a, int b, int c) {
char buffer[SIZE]; -------------------> SIZE=51
}
void main() {
function(1,2,3);
}
The Assembly File is as below :-
.file "temp.c"
.version "01.01"
gcc2_compiled.:
.text
.align 4
.globl function
.type function,@function
function:
pushl %ebp
movl %esp, %ebp
subl $72, %esp -----------> Stack allocation
leave
ret
.Lfe1:
.size function,.Lfe1-function
.align 4
.globl main
.type main,@function
main:
pushl %ebp
movl %esp, %ebp
subl $8, %esp
subl $4, %esp
pushl $3
pushl $2
pushl $1
call function
addl $16, %esp
leave
ret
.Lfe2:
.size main,.Lfe2-main
.ident "GCC: (GNU) 2.96 20000731 (Red Hat Linux 7.1
2.96-81)"
In the function part of the assembly
file , I noticed that the depending on
the "SIZE" of the array , it allocates
memory on stack as shown in the below
table .
Array Size Actual stack allocation
0 - 4 = 4
5 - 16 = 24
17 - 32 = 40
33 - 48 = 56
49 - 64 = 72
Can anybody please explain me ,
what is the reason behind this ?
Why is it that only the required
amount of stack is not allocated ?
Harmony !
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