Quick introduction to reverse engineering for beginners

Let’s compile it in MSVC 2010 (I omitted some parts for the sake of brefity) with /Ox option:
__a$ = 8 ; size = 4
__b$ = 12 ; size = 4
_comp PROC
mov eax, DWORD PTR __a$[esp-4]
mov ecx, DWORD PTR __b$[esp-4]
mov eax, DWORD PTR [eax]
mov ecx, DWORD PTR [ecx]
cmp eax, ecx
jne SHORT $LN4@comp
xor eax, eax
ret 0
$LN4@comp:
xor edx, edx
cmp eax, ecx
setge dl
lea eax, DWORD PTR [edx+edx-1]
ret 0
_comp ENDP
...
_numbers$ = -44 ; size = 40
_i$ = -4 ; size = 4
_argc$ = 8 ; size = 4
_argv$ = 12 ; size = 4
_main PROC
push ebp
mov ebp, esp
sub esp, 44 ; 0000002cH
mov DWORD PTR _numbers$[ebp], 1892 ; 00000764H
mov DWORD PTR _numbers$[ebp+4], 45 ; 0000002dH
mov DWORD PTR _numbers$[ebp+8], 200 ; 000000c8H
mov DWORD PTR _numbers$[ebp+12], -98 ; ffffff9eH
mov DWORD PTR _numbers$[ebp+16], 4087 ; 00000ff7H
mov DWORD PTR _numbers$[ebp+20], 5
mov DWORD PTR _numbers$[ebp+24], -12345 ; ffffcfc7H
mov DWORD PTR _numbers$[ebp+28], 1087 ; 0000043fH
mov DWORD PTR _numbers$[ebp+32], 88 ; 00000058H
mov DWORD PTR _numbers$[ebp+36], -100000 ; fffe7960H
push OFFSET _comp
push 4
push 10 ; 0000000aH
lea eax, DWORD PTR _numbers$[ebp]
push eax
call _qsort
add esp, 16 ; 00000010H
...
Nothing surprising so far. As a fourth argument, an address of label _comp is passed, that’s just a place
where function comp() located.
How qsort() calling it?
Let’s take a look into this function located in MSVCR80.DLL (a MSVC DLL module with C standard
89