Jump Table not found in Assembly code - c

Question

I'm learning Assembly. I wrote the below c program containing switch case, created the object file(gcc -o filename filename.c), then took the object dump. But I didn't find the Labels and jump tables in the object dump.
Can anybody tell me why the jump table is not getting generated ? Like the ones mention here
Link
Code
C file
int main() {
int i = 0;
int n = 9, z = 99 , p = 999;
switch( i )
{
case -1:
n++;
printf("value n=%d",n);
break;
case 0 :
z++;
printf("value z=%d",z);
break;
case 1 :
p++;
printf("value p=%d",p);
break;
case 2 :
p++;
printf("value p=%d",p);
break;
case 3 :
p++;
printf("value p=%d",p);
break;
case 4 :
p++;
printf("value p=%d",p);
break;
case 5 :
p++;
printf("value p=%d",p);
break;
}
printf("Values n=%d z=%d p=%d \n",n,z,p);
return 0;
}
Below is the main section
0804841d <main>:
804841d: 55 push %ebp
804841e: 89 e5 mov %esp,%ebp
8048420: 83 e4 f0 and $0xfffffff0,%esp
8048423: 83 ec 20 sub $0x20,%esp
8048426: c7 44 24 1c 00 00 00 movl $0x0,0x1c(%esp)
804842d: 00
804842e: c7 44 24 10 09 00 00 movl $0x9,0x10(%esp)
8048435: 00
8048436: c7 44 24 14 63 00 00 movl $0x63,0x14(%esp)
804843d: 00
804843e: c7 44 24 18 e7 03 00 movl $0x3e7,0x18(%esp)
8048445: 00
8048446: 8b 44 24 1c mov 0x1c(%esp),%eax
804844a: 83 c0 01 add $0x1,%eax
804844d: 83 f8 06 cmp $0x6,%eax
8048450: 0f 87 cb 00 00 00 ja 8048521 <main+0x104>
8048456: 8b 04 85 1c 86 04 08 mov 0x804861c(,%eax,4),%eax
804845d: ff e0 jmp *%eax
804845f: 83 44 24 10 01 addl $0x1,0x10(%esp)
8048464: 8b 44 24 10 mov 0x10(%esp),%eax
8048468: 89 44 24 04 mov %eax,0x4(%esp)
804846c: c7 04 24 e0 85 04 08 movl $0x80485e0,(%esp)
8048473: e8 78 fe ff ff call 80482f0 <printf#plt>
8048478: e9 a4 00 00 00 jmp 8048521 <main+0x104>
804847d: 83 44 24 14 01 addl $0x1,0x14(%esp)
8048482: 8b 44 24 14 mov 0x14(%esp),%eax
8048486: 89 44 24 04 mov %eax,0x4(%esp)
804848a: c7 04 24 eb 85 04 08 movl $0x80485eb,(%esp)
8048491: e8 5a fe ff ff call 80482f0 <printf#plt>
8048496: e9 86 00 00 00 jmp 8048521 <main+0x104>
804849b: 83 44 24 18 01 addl $0x1,0x18(%esp)
80484a0: 8b 44 24 18 mov 0x18(%esp),%eax
80484a4: 89 44 24 04 mov %eax,0x4(%esp)
80484a8: c7 04 24 f6 85 04 08 movl $0x80485f6,(%esp)
80484af: e8 3c fe ff ff call 80482f0 <printf#plt>
80484b4: eb 6b jmp 8048521 <main+0x104>
80484b6: 83 44 24 18 01 addl $0x1,0x18(%esp)
80484bb: 8b 44 24 18 mov 0x18(%esp),%eax
80484bf: 89 44 24 04 mov %eax,0x4(%esp)
80484c3: c7 04 24 f6 85 04 08 movl $0x80485f6,(%esp)
80484ca: e8 21 fe ff ff call 80482f0 <printf#plt>
80484cf: eb 50 jmp 8048521 <main+0x104>
80484d1: 83 44 24 18 01 addl $0x1,0x18(%esp)
80484d6: 8b 44 24 18 mov 0x18(%esp),%eax
80484da: 89 44 24 04 mov %eax,0x4(%esp)
80484de: c7 04 24 f6 85 04 08 movl $0x80485f6,(%esp)
80484e5: e8 06 fe ff ff call 80482f0 <printf#plt>
80484ea: eb 35 jmp 8048521 <main+0x104>
80484ec: 83 44 24 18 01 addl $0x1,0x18(%esp)
80484f1: 8b 44 24 18 mov 0x18(%esp),%eax
80484f5: 89 44 24 04 mov %eax,0x4(%esp)
80484f9: c7 04 24 f6 85 04 08 movl $0x80485f6,(%esp)
8048500: e8 eb fd ff ff call 80482f0 <printf#plt>
8048505: eb 1a jmp 8048521 <main+0x104>
8048507: 83 44 24 18 01 addl $0x1,0x18(%esp)
804850c: 8b 44 24 18 mov 0x18(%esp),%eax
8048510: 89 44 24 04 mov %eax,0x4(%esp)
8048514: c7 04 24 f6 85 04 08 movl $0x80485f6,(%esp)
804851b: e8 d0 fd ff ff call 80482f0 <printf#plt>
8048520: 90 nop
8048521: 8b 44 24 18 mov 0x18(%esp),%eax
8048525: 89 44 24 0c mov %eax,0xc(%esp)
8048529: 8b 44 24 14 mov 0x14(%esp),%eax
804852d: 89 44 24 08 mov %eax,0x8(%esp)
8048531: 8b 44 24 10 mov 0x10(%esp),%eax
8048535: 89 44 24 04 mov %eax,0x4(%esp)
8048539: c7 04 24 01 86 04 08 movl $0x8048601,(%esp)
8048540: e8 ab fd ff ff call 80482f0 <printf#plt>
8048545: b8 00 00 00 00 mov $0x0,%eax
804854a: c9 leave
804854b: c3 ret
804854c: 66 90 xchg %ax,%ax
804854e: 66 90 xchg %ax,%ax
Below is the .rodata section
Disassembly of section .rodata:
080485d8 <_fp_hw>:
80485d8: 03 00 add (%eax),%eax
...
Can anybody let me know why this is behaving like this?
Thanks in Advance

Answer 1

Your jump table is located at address 0x804861c. If you dump this address, I'm pretty sure, you'll find the values 0x804845f, 0x804847d, 0x804849b, etc. since these values correspond to the addresses of the branches of the switch statement.
What happens is that first it is ensured that the value of i (0x1c(%esp))is between 0 and 6 (and jump if above, ja, to last printf) and if it is between, uses its value multiplied by 4 (sizeof addresses on your architecture) as an offset into the jump table (0x804861c(,%eax,4),%eax).
I'm not sure what you're looking for exactly, or what you're trying to achieve, but as #Jens Gustedt pointed out, you should use the -S switch if you want to observe the assembly generated.
Additionally, beware that your code can easily be optimised by the compiler, i.e. as soon as you use the -O switch your assembly will probably shrink down to the last printf and the return statement, since the whole code execution can be predicted and useless parts can be omitted.