1. Bits and Bytes September 1, 2005 15-213 F’05 class02.ppt 15-213 “The Class That Gives CMU Its Zip!”

2. – 2 – 15-213, F’05 C Program #include char *buf[2] = {"Hello", "Goodbye"}; int main() { int i = random() & 1; printf("%s World!\n", buf[i]); return 0; }

3. – 3 – 15-213, F’05 Object Code (Window/Cygwin) 00401050 : 401050:55 push %ebp 401051:b8 10 00 00 00 mov $0x10,%eax 401056:89 e5 mov %esp,%ebp 401058:83 ec 08 sub $0x8,%esp 40105b:83 e4 f0 and $0xfffffff0,%esp 40105e:e8 2d 00 00 00 call 401090 401063:e8 b8 00 00 00 call 401120 401068:e8 d3 00 00 00 call 401140 40106d:c7 04 24 0e 30 40 00 movl $0x40300e,(%esp) 401074:83 e0 01 and $0x1,%eax 401077:8b 04 85 00 20 40 00 mov 0x402000(,%eax,4),%eax 40107e:89 44 24 04 mov %eax,0x4(%esp) 401082:e8 a9 00 00 00 call 401130 401087:c9 leave 401088:31 c0 xor %eax,%eax 40108a:c3 ret

4. – 4 – 15-213, F’05 Object Code (Linux/IA32) 080483b0 : 80483b0:55 push %ebp 80483b1:89 e5 mov %esp,%ebp 80483b3:83 ec 08 sub $0x8,%esp 80483b6:83 e4 f0 and $0xfffffff0,%esp 80483b9:83 ec 10 sub $0x10,%esp 80483bc:e8 07 ff ff ff call 80482c8 80483c1:83 e0 01 and $0x1,%eax 80483c4:c7 04 24 da 84 04 08 movl $0x80484da,(%esp) 80483cb:8b 04 85 f0 95 04 08 mov 0x80495f0(,%eax,4),%eax 80483d2:89 44 24 04 mov %eax,0x4(%esp) 80483d6:e8 0d ff ff ff call 80482e8 80483db:c9 leave 80483dc:31 c0 xor %eax,%eax 80483de:c3 ret

5. – 5 – 15-213, F’05 Object Code (Linux/x86-64) 0000000000400500 : 400500:48 83 ec 08 sub $0x8,%rsp 400504:e8 17 ff ff ff callq 400420 400509:83 e0 01 and $0x1,%eax 40050c:bf 2a 06 40 00 mov $0x40062a,%edi 400511:48 98 cltq 400513:48 8b 34 c5 10 09 50 mov 0x500910(,%rax,8),%rsi 40051a:00 40051b:31 c0 xor %eax,%eax 40051d:e8 0e ff ff ff callq 400430 400522:31 c0 xor %eax,%eax 400524:48 83 c4 08 add $0x8,%rsp 400528:c3 retq

6. – 6 – 15-213, F’05 Examining Data Representations typedef unsigned char *pointer; void show_bytes(pointer start, int len) { int i; for (i = 0; i < len; i++) printf("%.2x ", start[i]); printf("\n"); } int main(int argc, char *argv[]) { int i; for (i = 1; i < argc; i++) { long int v = strtol(argv[i], NULL, 0); show_bytes((pointer) &v, sizeof(long)); } return 0; }