Quick introduction to reverse engineering for beginners

mov DWORD PTR _a$[ebp+edx*4], ecx
jmp SHORT $LN2@main
$LN1@main:
mov eax, DWORD PTR _a$[ebp+400]
push eax
push OFFSET $SG2460
call _printf
add esp, 8
xor eax, eax
mov esp, ebp
pop ebp
ret 0
_main ENDP
I’m running it, and I got:
a[100]=760826203
It is just something, lying in the stack near to array, 400 bytes from its first element.
Indeed, how it could be done differently? Compiler may incorporate some code, checking index value
to be always in array’s bound, like in higher-level programming languages 39 , but this makes running code
slower.
OK, we read some values in stack illegally, but what if we could write something to it?
Here is what we will write:
#include
int main()
{
int a[20];
int i;
};
for (i=0; i