Hi,
I was looking into the assembly code of a add function that I have written.
The function takes two integers as input and outputs an integer, which is
the sum of the two inputs. I am declaring 3 local varibles in the function,
2 to hold input and one for the output . The disassembly code shown for the
same in visual studio 6 is as follows.
-----------------------------------------------------------------------------
25: int add(int a, int b){
00401610 push ebp
00401611 mov ebp,esp
00401613 sub esp,44h *// allocating / reserving 68 bytes ?
*00401616 push ebx
00401617 push esi
00401618 push edi
00401619 lea edi,[ebp-44h]
0040161C mov ecx,11h
00401621 mov eax,0CCCCCCCCh
00401626 rep stos dword ptr [edi]
26:
27: int c;
28:
29: c= a+b;
00401628 mov eax,dword ptr [ebp+8]
0040162B add eax,dword ptr [ebp+0Ch]
0040162E mov dword ptr [ebp-4],eax
30: return c;
00401631 mov eax,dword ptr [ebp-4]
31:
32:
33: }
00401634 pop edi
00401635 pop esi
00401636 pop ebx
00401637 mov esp,ebp
00401639 pop ebp
0040163A ret
-----------------------------------------------------------------------------
1) My question is why did the compiler allocated 68 bytes while I have only
3 integer variables in my function = 3*4 = 12 bytes?
2) Though it allocates the 68 bytes instead of 12, it never refers to any
thing other than those 12 bytes?
Thanks in advance,
Sai.
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