Hi i'm currently doing a binary bomb and am wondering if I am understanding some stuff correctly. I have this;
0x00000000004011d4 <+0>: sub $0x8,%rsp
0x00000000004011d8 <+4>: cmpb $0x59,(%rdi)
0x00000000004011db <+7>: jne 0x4011fd <phase_1+41>
0x00000000004011dd <+9>: cmpb $0x46,0x2(%rdi)
0x00000000004011e1 <+13>: jne 0x4011fd <phase_1+41>
0x00000000004011e3 <+15>: cmpb $0x68,0x1(%rdi)
0x00000000004011e7 <+19>: je 0x40120b <phase_1+55>
0x00000000004011e9 <+21>: movsbl 0x10(%rdi),%ecx
0x00000000004011ed <+25>: movsbl 0x5(%rdi),%edx
0x00000000004011f1 <+29>: add $0xb,%edx
0x00000000004011f4 <+32>: mov $0x1,%eax
0x00000000004011f9 <+37>: cmp %edx,%ecx
0x00000000004011fb <+39>: je 0x401210 <phase_1+60>
0x00000000004011fd <+41>: callq 0x401b20 <bomb_activation>
0x0000000000401202 <+46>: mov $0xffffffffffffffff,%rax
0x0000000000401209 <+53>: jmp 0x401210 <phase_1+60>
0x000000000040120b <+55>: mov $0x0,%eax
0x0000000000401210 <+60>: add $0x8,%rsp
0x0000000000401214 <+64>: retq
and so far I have translated it to this;
if(arr[0] != 'Y'){
bomb_activation();
}
if(arr[2] != 'F'){
bomb_activation();
}
if(arr[1] == 'h'){
bomb_activation();
}
int a = arr[10];
int b = arr[5];
b += 11;
status = 1;
if(t1 != t2){
bomb_activation();
}
return status;
}
As you can probably tell i'm really confused on how exactly to read these lines, I see it as moving the 10th element of the array into the ecx registry and filling the rest of the registry with 0s and the same logic to edx, however i'm not too sure how to determine what the value of arr[5] or arr[10] is just from this.
0x00000000004011e9 <+21>: movsbl 0x10(%rdi),%ecx
0x00000000004011ed <+25>: movsbl 0x5(%rdi),%edx
0x00000000004011f1 <+29>: add $0xb,%edx
0x00000000004011f4 <+32>: mov $0x1,%eax
0x00000000004011f9 <+37>: cmp %edx,%ecx
and more specifically how I am meant to determine the size of the array, maybe I am not understanding it at all though, any help would be great thanks.
Related
This is for one of my classes. We are given two files. One that contains C code:
guess_two_numbers.c
#include <stdio.h>
void print_error()
{
printf("\n Oooops, incorrect guess!\n");
exit(1);
}
int main()
{
int num1, num2;
printf("\n Guess my two secret numbers: ");
scanf("%d %d", &num1, &num2);
if(num1 > 11)
print_error();
if(num2 != num1 + 2)
print_error();
printf("\nCongratulations, you've found my two secret numbers!\n");
return 0;
}
And one that is Assembly Code:
0x08048462 <+0>: lea ecx,[esp+0x4]
0x08048466 <+4>: and esp,0xfffffff0
0x08048469 <+7>: push DWORD PTR [ecx-0x4]
0x0804846c <+10>: push ebp
0x0804846d <+11>: mov ebp,esp
0x0804846f <+13>: push ecx
0x08048470 <+14>: sub esp,0x24
0x08048473 <+17>: mov DWORD PTR [esp],0x80485c0
0x0804847a <+24>: call 0x8048360 <printf#plt>
0x0804847f <+29>: lea eax,[ebp-0xc]
0x08048482 <+32>: mov DWORD PTR [esp+0x8],eax
0x08048486 <+36>: lea eax,[ebp-0x8]
0x08048489 <+39>: mov DWORD PTR [esp+0x4],eax
0x0804848d <+43>: mov DWORD PTR [esp],0x80485e0
0x08048494 <+50>: call 0x8048350 <scanf#plt>
0x08048499 <+55>: mov eax,DWORD PTR [ebp-0x8]
0x0804849c <+58>: cmp eax,0xb
0x0804849f <+61>: jle 0x80484a6 <main+68>
0x080484a1 <+63>: call 0x8048444 <print_error>
0x080484a6 <+68>: mov eax,DWORD PTR [ebp-0x8]
0x080484a9 <+71>: lea edx,[eax+0x2]
0x080484ac <+74>: mov eax,DWORD PTR [ebp-0xc]
0x080484af <+77>: cmp edx,eax
0x080484b1 <+79>: je 0x80484b8 <main+86>
0x080484b3 <+81>: call 0x8048444 <print_error>
0x080484b8 <+86>: mov DWORD PTR [esp],0x80485e8
0x080484bf <+93>: call 0x8048370 <puts#plt>
0x080484c4 <+98>: mov eax,0x0
0x080484c9 <+103>: add esp,0x24
0x080484cc <+106>: pop ecx
0x080484cd <+107>: pop ebp
0x080484ce <+108>: lea esp,[ecx-0x4]
0x080484d1 <+111>: ret
The question that I was asked was to identify which line/lines in the assembly code that match the secret number/numbers requirement, which are the first secret number is < 11, and the second secret number is within +2 of the first secret number.. Given these files, I said that the line containing the <+58> is one line, as it compares the eax to 0xb, which is 11 in hexademical. I also said that <+71> is also a line that contains it, as it adds +2 to eax to check the second requirement. Is this sufficient or should I add more detail?
I am having trouble this piece of code in assembly language.
Essentially I have to input 2 numbers that matches 2 numbers the code is comparing with.
On line 0x08048c47 in phase_4, it compares the first input with 2, so I know the first input has to be 2. It then moves 4 spaces from the first input to next input, which then gets 2 subtracted from it. Now the (input-2) is compared with 2. It will continue the instruction if the inputs are below than or equal to 2. I've tested this with numbers 2,3,4 which pass the comparison. Other numbers greater than 4 and less than 2 do not pass the comparison and will cause the bomb to explode.
I'm stuck on this part because the value being returned from func4 is not the same was the value represented at 0x08048c6e in phase_4, which is 8(%esp). On my computer when I debug it, it shows that it is 8, and the answers to my inputs 2,3,4 are 40, 60, 80 respectively.
disas func4
0x08048bda <+0>: push %edi
0x08048bdb <+1>: push %esi
0x08048bdc <+2>: push %ebx
0x08048bdd <+3>: mov 0x10(%esp),%ebx
0x08048be1 <+7>: mov 0x14(%esp),%edi
0x08048be5 <+11>: test %ebx,%ebx
0x08048be7 <+13>: jle 0x8048c14 <func4+58>
0x08048be9 <+15>: mov %edi,%eax
0x08048beb <+17>: cmp $0x1,%ebx
0x08048bee <+20>: je 0x8048c19 <func4+63>
0x08048bf0 <+22>: sub $0x8,%esp
0x08048bf3 <+25>: push %edi
0x08048bf4 <+26>: lea -0x1(%ebx),%eax
0x08048bf7 <+29>: push %eax
0x08048bf8 <+30>: call 0x8048bda <func4>
0x08048bfd <+35>: add $0x8,%esp
0x08048c00 <+38>: lea (%edi,%eax,1),%esi
0x08048c03 <+41>: push %edi
0x08048c04 <+42>: sub $0x2,%ebx
0x08048c07 <+45>: push %ebx
0x08048c08 <+46>: call 0x8048bda <func4>
0x08048c0d <+51>: add $0x10,%esp
0x08048c10 <+54>: add %esi,%eax
0x08048c12 <+56>: jmp 0x8048c19 <func4+63>
0x08048c14 <+58>: mov $0x0,%eax
0x08048c19 <+63>: pop %ebx
0x08048c1a <+64>: pop %esi
0x08048c1b <+65>: pop %edi
0x08048c1c <+66>: ret
disas phase_4
0x08048c1d <+0>: sub $0x1c,%esp
0x08048c20 <+3>: mov %gs:0x14,%eax
0x08048c26 <+9>: mov %eax,0xc(%esp)
0x08048c2a <+13>: xor %eax,%eax
0x08048c2c <+15>: lea 0x4(%esp),%eax
0x08048c30 <+19>: push %eax
0x08048c31 <+20>: lea 0xc(%esp),%eax
0x08048c35 <+24>: push %eax
0x08048c36 <+25>: push $0x804a25f
0x08048c3b <+30>: pushl 0x2c(%esp)
0x08048c3f <+34>: call 0x8048810 <__isoc99_sscanf#plt>
0x08048c44 <+39>: add $0x10,%esp
0x08048c47 <+42>: cmp $0x2,%eax
0x08048c4a <+45>: jne 0x8048c58 <phase_4+59>
0x08048c4c <+47>: mov 0x4(%esp),%eax
0x08048c50 <+51>: sub $0x2,%eax
0x08048c53 <+54>: cmp $0x2,%eax
0x08048c56 <+57>: jbe 0x8048c5d <phase_4+64>
0x08048c58 <+59>: call 0x8049123 <explode_bomb>
0x08048c5d <+64>: sub $0x8,%esp
0x08048c60 <+67>: pushl 0xc(%esp)
0x08048c64 <+71>: push $0x6
0x08048c66 <+73>: call 0x8048bda <func4>
0x08048c6b <+78>: add $0x10,%esp
0x08048c6e <+81>: cmp 0x8(%esp),%eax
0x08048c72 <+85>: je 0x8048c79 <phase_4+92>
0x08048c74 <+87>: call 0x8049123 <explode_bomb>
0x08048c79 <+92>: mov 0xc(%esp),%eax
0x08048c7d <+96>: xor %gs:0x14,%eax
0x08048c84 <+103>: je 0x8048c8b <phase_4+110>
0x08048c86 <+105>: call 0x8048790 <__stack_chk_fail#plt>
0x08048c8b <+110>: add $0x1c,%esp
0x08048c8e <+113>: ret
8(%esp) is the first number, under the framework of x86.
enter 40 2 or 60 3 or 80 4 should work.
Equivalent to the following logic
#include <stdio.h>
#include <stdlib.h>
void explode_bomb()
{
printf("explode bomb.\n");
exit(1);
}
unsigned func4(int val, unsigned num)
{
int ret;
if (val <= 0)
return 0;
if (num == 1)
return 1;
ret = func4(val - 1, num);
ret += num;
val -= 2;
ret += func4(val, num);
return ret;
}
void phase_4(const char *input)
{
unsigned num1, num2;
if (sscanf(input, "%u %u", &num1, &num2) != 2)
explode_bomb();
if (num2 - 2 > 2)
explode_bomb();
if (func4(6, num2) != num1)
explode_bomb();
}
int main()
{
phase_4("40 2");
phase_4("60 3");
phase_4("80 4");
printf("success.\n");
return 0;
}
I have to override a function's return address using buffer oveflow.
The function itself looks like this(I am passing the name argument):
void vuln(char *name)
{
int n = 20;
char buf[1024];
int f[n];
int i;
for (i=0; i<n; i++) {
f[i] = fib(i);
}
strcpy(buf, name);
...
}
I am disassembling it using gdb which gives me the following
0x080485ae <+0>: push %ebp
0x080485af <+1>: mov %esp,%ebp
0x080485b1 <+3>: push %ebx
0x080485b2 <+4>: sub $0x414,%esp
0x080485b8 <+10>: mov %esp,%eax
0x080485ba <+12>: mov %eax,%ebx
0x080485bc <+14>: movl $0x14,-0x10(%ebp)
0x080485c3 <+21>: mov -0x10(%ebp),%eax
0x080485c6 <+24>: lea -0x1(%eax),%edx
0x080485c9 <+27>: mov %edx,-0x14(%ebp)
0x080485cc <+30>: shl $0x2,%eax
0x080485cf <+33>: lea 0x3(%eax),%edx
0x080485d2 <+36>: mov $0x10,%eax
0x080485d7 <+41>: sub $0x1,%eax
0x080485da <+44>: add %edx,%eax
0x080485dc <+46>: mov $0x10,%ecx
0x080485e1 <+51>: mov $0x0,%edx
0x080485e6 <+56>: div %ecx
0x080485e8 <+58>: imul $0x10,%eax,%eax
0x080485eb <+61>: sub %eax,%esp
0x080485ed <+63>: mov %esp,%eax
0x080485ef <+65>: add $0x3,%eax
0x080485f2 <+68>: shr $0x2,%eax
0x080485f5 <+71>: shl $0x2,%eax
0x080485f8 <+74>: mov %eax,-0x18(%ebp)
0x080485fb <+77>: movl $0x0,-0xc(%ebp)
0x08048602 <+84>: jmp 0x8048621 <vuln+115>
0x08048604 <+86>: sub $0xc,%esp
0x08048607 <+89>: pushl -0xc(%ebp)
0x0804860a <+92>: call 0x8048560 <fib>
0x0804860f <+97>: add $0x10,%esp
0x08048612 <+100>: mov %eax,%ecx
0x08048614 <+102>: mov -0x18(%ebp),%eax
0x08048617 <+105>: mov -0xc(%ebp),%edx
0x0804861a <+108>: mov %ecx,(%eax,%edx,4)
0x0804861d <+111>: addl $0x1,-0xc(%ebp)
0x08048621 <+115>: mov -0xc(%ebp),%eax
0x08048624 <+118>: cmp -0x10(%ebp),%eax
0x08048627 <+121>: jl 0x8048604 <vuln+86>
0x08048629 <+123>: sub $0x8,%esp
0x0804862c <+126>: pushl 0x8(%ebp)
0x0804862f <+129>: lea -0x418(%ebp),%eax
0x08048635 <+135>: push %eax
0x08048636 <+136>: call 0x80483c0 <strcpy#plt>
0x0804863b <+141>: add $0x10,%esp
0x0804863e <+144>: sub $0x8,%esp
0x08048641 <+147>: lea -0x418(%ebp),%eax
0x08048647 <+153>: push %eax
0x08048648 <+154>: push $0x80487b7
0x0804864d <+159>: call 0x80483a0 <printf#plt>
0x08048652 <+164>: add $0x10,%esp
0x08048655 <+167>: movl $0x0,-0xc(%ebp)
0x0804865c <+174>: jmp 0x804867f <vuln+209>
0x0804865e <+176>: mov -0x18(%ebp),%eax
0x08048661 <+179>: mov -0xc(%ebp),%edx
=> 0x08048664 <+182>: mov (%eax,%edx,4),%eax
0x08048667 <+185>: sub $0x4,%esp
0x0804866a <+188>: push %eax
0x0804866b <+189>: pushl -0xc(%ebp)
0x0804866e <+192>: push $0x80487c4
0x08048673 <+197>: call 0x80483a0 <printf#plt>
0x08048678 <+202>: add $0x10,%esp
0x0804867b <+205>: addl $0x1,-0xc(%ebp)
0x0804867f <+209>: cmpl $0x13,-0xc(%ebp)
0x08048683 <+213>: jle 0x804865e <vuln+176>
0x08048685 <+215>: mov %ebx,%esp
0x08048687 <+217>: nop
0x08048688 <+218>: mov -0x4(%ebp),%ebx
0x0804868b <+221>: leave
0x0804868c <+222>: ret
The address of the function which should be called with the return of vuln() is 0x804850b.
How am I supposed to know the amount of fillers until I reach the return address to be overwritten?
I guess the name argument should be in the form "a"*n + "\x0b\x85\x04\x08", where n is some number I am trying to guess. I suppose this should be basic stuff but I am still a beginner so please don't judge me...
How am I supposed to know ...
Your code is:
0x080485ae <+0>: push %ebp
0x080485af <+1>: mov %esp,%ebp
...
0x0804862f <+129>: lea -0x418(%ebp),%eax
0x08048635 <+135>: push %eax
0x08048636 <+136>: call 0x80483c0 <strcpy#plt>
Before you enter the function, the return address is at offset 0(%esp).
After the first push, it's at 4(%esp). Since %esp is next copied to %ebp, it's also at 4(%ebp).
Next you see that the location you start copying into is at -0x418(%ebp).
Conclusion: the delta between &buf[0] and &return_address is 0x418 + 4 == 0x41C.
Alternative solution: fill name input with invalid addresses: 0x01010101, 0x01010102, ... 0x010102FF. Execute the code and observe on which address it crashed.
If my calculations are correct, it would crash when vuln tries to return to "slot" 0x41C / 4 == 0x107, which should contain 0x01010208.
I noticed that a code I'm working on uses conditionals like:
if(A != val) {
// code B
}
if(B != val) {
// code A
}
But to me, reading the same code like below is much easier. Maybe a personal preference.
if( B == val) {
//code B
}
if( A == val) {
//code A
}
This is a very latency sensitive code so is there a performance difference between the two? Is there a performance difference between != or == ? or > or < for that matter? Also, I realize that this code leaves room for a 3rd condition though I'm pretty sure the code leaves only 2 paths possible so an if/else is more appropriate.
Much appreciated.
Here is the assembly code when in the condition you use !=, note that I added a printf inside the if statement in order to have a better output from gdb:
0x0000000000400526 <+0>: push rbp
0x0000000000400527 <+1>: mov rbp,rsp
0x000000000040052a <+4>: sub rsp,0x10
0x000000000040052e <+8>: mov DWORD PTR [rbp-0xc],0x0
0x0000000000400535 <+15>: mov DWORD PTR [rbp-0x8],0x1
0x000000000040053c <+22>: mov DWORD PTR [rbp-0x4],0x1
0x0000000000400543 <+29>: mov eax,DWORD PTR [rbp-0xc]
0x0000000000400546 <+32>: cmp eax,DWORD PTR [rbp-0x4]
0x0000000000400549 <+35>: **je** 0x400555 <main+47>
0x000000000040054b <+37>: mov edi,0x4005f4
0x0000000000400550 <+42>: call 0x400400 <puts#plt>
0x0000000000400555 <+47>: mov eax,DWORD PTR [rbp-0x8]
0x0000000000400558 <+50>: cmp eax,DWORD PTR [rbp-0x4]
0x000000000040055b <+53>: **je** 0x400567 <main+65>
0x000000000040055d <+55>: mov edi,0x4005f4
0x0000000000400562 <+60>: call 0x400400 <puts#plt>
0x0000000000400567 <+65>: mov eax,0x0
0x000000000040056c <+70>: leave
0x000000000040056d <+71>: ret
While this is for ==:
0x0000000000400526 <+0>: push rbp
0x0000000000400527 <+1>: mov rbp,rsp
0x000000000040052a <+4>: sub rsp,0x10
0x000000000040052e <+8>: mov DWORD PTR [rbp-0xc],0x0
0x0000000000400535 <+15>: mov DWORD PTR [rbp-0x8],0x1
0x000000000040053c <+22>: mov DWORD PTR [rbp-0x4],0x1
0x0000000000400543 <+29>: mov eax,DWORD PTR [rbp-0x8]
0x0000000000400546 <+32>: cmp eax,DWORD PTR [rbp-0x4]
0x0000000000400549 <+35>: **jne** 0x400555 <main+47>
0x000000000040054b <+37>: mov edi,0x4005f4
0x0000000000400550 <+42>: call 0x400400 <puts#plt>
0x0000000000400555 <+47>: mov eax,DWORD PTR [rbp-0xc]
0x0000000000400558 <+50>: cmp eax,DWORD PTR [rbp-0x4]
0x000000000040055b <+53>: **jne** 0x400567 <main+65>
0x000000000040055d <+55>: mov edi,0x4005f4
0x0000000000400562 <+60>: call 0x400400 <puts#plt>
0x0000000000400567 <+65>: mov eax,0x0
0x000000000040056c <+70>: leave
0x000000000040056d <+71>: ret
As you may notice the only difference is the usage of je (jump if equal) or jne (jump if not equal) so in terms of performance you could say that it' exactly the same
You will have a conditional jump in your assembler code whether you check for equality or any kind of unequality. Performance difference should be marginal.
Though it can be beneficial to write branchless code, see e.g. Why is it faster to process a sorted array than an unsorted array?.
So for my class project I am given a binary and what I have to do is bypass the security authentication. Now, once you change the binary to bypass the authentication, you have to create a C program that will replicate the "same" binary. Now, I have been struggling to understand what this area of the assembly code dump that I obtained does.
0x08048a59 <function8+54>: mov 0x8049e50,%eax
0x08048a5e <function8+59>: add $0x4,%eax
0x08048a61 <function8+62>: mov (%eax),%eax
0x08048a63 <function8+64>: movl $0x8048cd4,0x4(%esp)
I'm not very familiar with assembly, but I got most of it figured out. This is the original/entire assembly dump that I got using GDB.
0x08048a23 <function8+0>: push %ebp
0x08048a24 <function8+1>: mov %esp,%ebp
0x08048a26 <function8+3>: sub $0x28,%esp
0x08048a29 <function8+6>: movl $0xd6a1a,-0x18(%ebp)
0x08048a30 <function8+13>: mov 0x8(%ebp),%eax
0x08048a33 <function8+16>: mov %eax,-0x14(%ebp)
0x08048a36 <function8+19>: mov 0xc(%ebp),%eax
0x08048a39 <function8+22>: mov %eax,-0x10(%ebp)
0x08048a3c <function8+25>: movl $0x0,-0xc(%ebp)
0x08048a43 <function8+32>: mov -0xc(%ebp),%eax
0x08048a46 <function8+35>: mov %eax,%edx
0x08048a48 <function8+37>: sar $0x1f,%edx
0x08048a4b <function8+40>: idivl -0x18(%ebp)
0x08048a4e <function8+43>: imul -0x14(%ebp),%eax
0x08048a52 <function8+47>: imul -0x10(%ebp),%eax
0x08048a56 <function8+51>: mov %eax,-0xc(%ebp)
0x08048a59 <function8+54>: mov 0x8049e50,%eax
0x08048a5e <function8+59>: add $0x4,%eax
0x08048a61 <function8+62>: mov (%eax),%eax
0x08048a63 <function8+64>: movl $0x8048cd4,0x4(%esp)
0x08048a6b <function8+72>: mov %eax,(%esp)
0x08048a6e <function8+75>: call 0x8048434 <strcmp#plt>
0x08048a73 <function8+80>: test %eax,%eax
0x08048a75 <function8+82>: jne 0x8048a8d <function8+106>
0x08048a77 <function8+84>: mov $0x8048cdc,%eax
0x08048a7c <function8+89>: mov -0xc(%ebp),%edx
0x08048a7f <function8+92>: mov %edx,0x4(%esp)
0x08048a83 <function8+96>: mov %eax,(%esp)
0x08048a86 <function8+99>: call 0x8048414 <printf#plt>
0x08048a8b <function8+104>: jmp 0x8048a99 <function8+118>
0x08048a8d <function8+106>: movl $0x8048cfa,(%esp)
0x08048a94 <function8+113>: call 0x8048424 <puts#plt>
0x08048a99 <function8+118>: mov -0xc(%ebp),%eax
0x08048a9c <function8+121>: leave
0x08048a9d <function8+122>: ret
And so far I have managed to convert it to this in C:
int function8(one, two){
int a = 879130;
int b = one;
int c = two;
int d = 0;
d = (d / a * b * c);
if(strcmp(b, (d + 4)) == 0){
printf("You may enter using token %d", d);
}
else{
puts("You may not enter.");
}
return d;
}
int main(){
int one, two = 0;
function8(one, two);
}
I am know that
0x08048a59 <function8+54>: mov 0x8049e50,%eax
and
0x08048a63 <function8+64>: movl $0x8048cd4,0x4(%esp)
are pointing to a particular address and value respectively (correct me if I'm wrong), but don't know if I have to call it or not. If so, how do I call that particular address?
Any help would be appreciated!
Just in case you guys need it, this is my current output when I create a binary using GCC and then run GDB to get the dump:
0x08048434 <function8+0>: push %ebp
0x08048435 <function8+1>: mov %esp,%ebp
0x08048437 <function8+3>: sub $0x28,%esp
0x0804843a <function8+6>: movl $0xd6a1a,-0x18(%ebp)
0x08048441 <function8+13>: mov 0x8(%ebp),%eax
0x08048444 <function8+16>: mov %eax,-0x14(%ebp)
0x08048447 <function8+19>: mov 0xc(%ebp),%eax
0x0804844a <function8+22>: mov %eax,-0x10(%ebp)
0x0804844d <function8+25>: movl $0x0,-0xc(%ebp)
0x08048454 <function8+32>: mov -0xc(%ebp),%eax
0x08048457 <function8+35>: mov %eax,%edx
0x08048459 <function8+37>: sar $0x1f,%edx
0x0804845c <function8+40>: idivl -0x18(%ebp)
0x0804845f <function8+43>: imul -0x14(%ebp),%eax
0x08048463 <function8+47>: imul -0x10(%ebp),%eax
0x08048467 <function8+51>: mov %eax,-0xc(%ebp)
0x0804846a <function8+54>: mov -0xc(%ebp),%eax
0x0804846d <function8+57>: add $0x4,%eax
0x08048470 <function8+60>: mov %eax,0x4(%esp)
0x08048474 <function8+64>: mov -0x14(%ebp),%eax
0x08048477 <function8+67>: mov %eax,(%esp)
0x0804847a <function8+70>: call 0x8048364 <strcmp#plt>
0x0804847f <function8+75>: test %eax,%eax
0x08048481 <function8+77>: jne 0x8048499 <function8+101>
0x08048483 <function8+79>: mov $0x80485a0,%eax
0x08048488 <function8+84>: mov -0xc(%ebp),%edx
0x0804848b <function8+87>: mov %edx,0x4(%esp)
0x0804848f <function8+91>: mov %eax,(%esp)
0x08048492 <function8+94>: call 0x8048344 <printf#plt>
0x08048497 <function8+99>: jmp 0x80484a5 <function8+113>
0x08048499 <function8+101>: movl $0x80485bd,(%esp)
0x080484a0 <function8+108>: call 0x8048354 <puts#plt>
0x080484a5 <function8+113>: mov -0xc(%ebp),%eax
0x080484a8 <function8+116>: leave
0x080484a9 <function8+117>: ret
strcmp compares two strings that are passed in as pointers. The code here :
0x08048a59 <function8+54>: mov 0x8049e50,%eax
0x08048a5e <function8+59>: add $0x4,%eax
0x08048a61 <function8+62>: mov (%eax),%eax
0x08048a63 <function8+64>: movl $0x8048cd4,0x4(%esp)
0x08048a6b <function8+72>: mov %eax,(%esp)
0x08048a6e <function8+75>: call 0x8048434 <strcmp#plt>
is passing two pointers to strcmp, both of which are static/global data (not local, like you have in your C code). One is at 0x8048cd4 (that's the address of the string.. it's probably something in quotes : "example"). The other is a pointer load + 4 that's dereferenced. I'd recommend : (1) look at those addresses to see what's stored in them, and (2) if you're confused by the assembly pointer chasing, try writing simple C programs that call strcmp and seeing the resulting assembly.
good luck.
This is the part who is calling the strcmp as drivingon9 pointed.
0x08048a59 <function8+54>: mov 0x8049e50,%eax
0x08048a5e <function8+59>: add $0x4,%eax
0x08048a61 <function8+62>: mov (%eax),%eax
0x08048a63 <function8+64>: movl $0x8048cd4,0x4(%esp)
0x08048a6b <function8+72>: mov %eax,(%esp)
0x08048a6e <function8+75>: call 0x8048434 <strcmp#plt>
The result value of the strcmp will be stored in the register EAX.
Thats why we have a test eax,eax in the code bellow:
0x0804847f <function8+75>: test %eax,%eax
0x08048481 <function8+77>: jne 0x8048499 <function8+101>
0x08048483 <function8+79>: mov $0x80485a0,%eax
0x08048488 <function8+84>: mov -0xc(%ebp),%edx
The test eax, eax tests if eax register is equal to 0.
i'm not sure what part of the code will let you do what you want, but you can try change the line
0x08048481 <function8+77>: jne 0x8048499 <function8+101>
and change the instruction to a je(JUMP IF EQUAL) or a incondicional jump(JMP)