CSC231 Homwork 2 Solution 2010
--D. Thiebaut 21:35, 6 October 2010 (UTC)
Contents
Mystery Program
- The program prints a quote attributed to Kurt Cobain: "Practice makes perfect... but nobody's perfect... so why practice?"
1 ;;; hw2c.asm
2 ;;; Alec Goebel
3 ;;;
4 ;;; reverse engineered from provided hex dump.
5 ;;; Prints "practice makes perfect...but nobody's perfect...so why practice?\n\n"
6 ;;;
7 ;;; to assemble:
8 ;;;
9 ;;; nasm -f elf -F stabs hw2c.asm
10 ;;; ld -o program hw2c.o
11 ;;;
12 ;;; to run
13 ;;; $ ./hw2c
14 ;;; practice makes perfect...but nobody's perfect...so why practice?
15 ;;;
16 ;;; $
17 ;;; -------------------------------------------------------------------
18
19 EXIT equ 1
20 WRITE equ 4
21 STDOUT equ 1
22
23 ;; ------------------------------------------------------------
24 ;; data areas
25 ;; ------------------------------------------------------------
26
27 section .data
28
29 00000000 206D616B657320 makes db " makes "
30 00000007 706572666563742E2E- prct db "perfect...practice"
31 00000010 2E7072616374696365
32 00000019 627574206E6F626F64- nbdy db "but nobody's so why "
33 00000022 79277320736F207768-
34 0000002B 7920
35 0000002D 3F0A0A qst db "?", 10, 10
36
37
38 ;; ------------------------------------------------------------
39 ;; code area
40 ;; ------------------------------------------------------------
41
42 section .text
43 global _start
44
45 _start:
46
47 ;; write 'practice' on STDOUT
48 00000000 B804000000 mov eax,WRITE
49 00000005 BB01000000 mov ebx,STDOUT
50 0000000A B9[11000000] mov ecx,prct+10
51 0000000F BA08000000 mov edx,8
52 00000014 CD80 int 0x80
53
54 ;; pointless instruction
55 00000016 B8FFFFFFFF mov eax,0xffffffff
56
57 ;; write ' makes ' on STDOUT
58 0000001B B804000000 mov eax,WRITE
59 00000020 BB01000000 mov ebx,STDOUT
60 00000025 B9[07000000] mov ecx,prct ;; pointless
61 0000002A B9[00000000] mov ecx,makes
62 0000002F BA07000000 mov edx,7
63 00000034 CD80 int 0x80
64
65 ;; write 'perfect...' on STDOUT
66 00000036 BA[11000000] mov edx,prct+10 ;; pointless
67 0000003B B801000000 mov eax,1 ;; pointless
68 00000040 B804000000 mov eax,WRITE
69 00000045 BB01000000 mov ebx,STDOUT
70 0000004A B9[07000000] mov ecx,prct
71 0000004F BA0A000000 mov edx,10
72 00000054 CD80 int 0x80
73
74 ;; write "but nobody's " on STDOUT
75 00000056 B804000000 mov eax,WRITE
76 0000005B BB01000000 mov ebx,STDOUT
77 00000060 B9[19000000] mov ecx,nbdy
78 00000065 BA0D000000 mov edx,13
79 0000006A CD80 int 0x80
80
81 ;; write "perfect..." to STDOUT
82 0000006C B804000000 mov eax,WRITE
83 00000071 BB01000000 mov ebx,STDOUT
84 00000076 B9[06000000] mov ecx,prct-1
85 0000007B BA0A000000 mov edx,10
86 00000080 41 inc ecx
87 00000081 CD80 int 0x80
88
89 ;; write "so why " to STDOUT
90 00000083 B804000000 mov eax,WRITE
91 00000088 BB01000000 mov ebx,STDOUT
92 0000008D B9[24000000] mov ecx,nbdy+11
93 00000092 41 inc ecx
94 00000093 BA07000000 mov edx,7
95 00000098 41 inc ecx
96 00000099 CD80 int 0x80
97
98 ;; write "practice" to STDOUT
99 0000009B B804000000 mov eax,WRITE
100 000000A0 BB01000000 mov ebx,STDOUT
101 000000A5 B9[11000000] mov ecx,prct+10
102 000000AA BA08000000 mov edx,8
103 000000AF CD80 int 0x80
104
105 ;; write "?\n\n"
106 000000B1 B804000000 mov eax,WRITE
107 000000B6 BB01000000 mov ebx,STDOUT
108 000000BB B9[2D000000] mov ecx,qst
109 000000C0 BA03000000 mov edx,3
110 000000C5 CD80 int 0x80
111
112 ;; exit()
113 000000C7 B801000000 mov eax,EXIT
114 000000CC BB00000000 mov ebx,0
115 000000D1 CD80 int 0x80 ; final system call
