Quick introduction to reverse engineering for beginners

(_snprintf() function works just like printf(), but instead dumping result into stdout (e.g., to terminal
or console), write it to buf buffer. puts() copies buf contents to stdout. Of course, these two function calls
might be replaced by one printf() call, but I would like to illustrate small buffer usage.)
Let’s compile (MSVC 2010):
...
...
mov eax, 600 ; 00000258H
call __alloca_probe_16
mov esi, esp
push 3
push 2
push 1
push OFFSET $SG2672
push 600 ; 00000258H
push esi
call __snprintf
push esi
call _puts
add esp, 28 ; 0000001cH
The sole alloca() argument passed via EAX (instead of pushing into stack).
After alloca() call, ESP is now pointing to the block of 600 bytes and we can use it as memory for buf
array.
GCC 4.4.1 can do the same without calling external functions:
public f
f proc near ; CODE XREF: main+6
s = dword ptr -10h
var_C = dword ptr -0Ch
push ebp
mov ebp, esp
sub esp, 38h
mov eax, large gs:14h
mov [ebp+var_C], eax
xor eax, eax
sub esp, 624
lea eax, [esp+18h]
add eax, 0Fh
shr eax, 4 ; align pointer
shl eax, 4 ; by 16-byte border
mov [ebp+s], eax
mov eax, offset format ; "hi! %d, %d, %d\n"
mov dword ptr [esp+14h], 3
mov dword ptr [esp+10h], 2
mov dword ptr [esp+0Ch], 1
mov [esp+8], eax ; format
mov dword ptr [esp+4], 600 ; maxlen
mov eax, [ebp+s]
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