CODEWITHSUNDEEP
cdebugginggdb
Da Mike
Da Mike

Reputation: 463

gdb showing different address for the same function?

So I want to practice doing a ret2libc attack and I'm playing around with gdb on this simple program

// File: retlib.c

#include <stdio.h>
#include <stdlib.h>

int main()
{
    printf("system = %p\n", system);
    char c[] = "echo 123";
    system(c);

    return 0;
}

Now notice this

Reading symbols from ./retlib...(no debugging symbols found)...done.
(gdb) p system
$1 = {<text variable, no debug info>} 0x4004b0 <system@plt>
(gdb) b main
Breakpoint 1 at 0x4005ea
(gdb) r
Starting program: /home/users/mickey/retlib 

Breakpoint 1, 0x00000000004005ea in main ()
(gdb) p system
$2 = {<text variable, no debug info>} 0x7ffff7a523a0 <__libc_system>
(gdb) c
Continuing.
system = 0x4004b0
123
[Inferior 1 (process 11593) exited normally]

My question is, why do I get 2 different outputs of the system function address. And even after I start running the program the gdb command says one thing, and printf says another. I notice that the tags for each address are different, but why is this happening? Any help would be appreciated!

Upvotes: 1

Views: 788

Answers (1)

Manuel
Manuel

Reputation: 2554

Before running the program, gdb will give you the procedure linkage table (.plt) address, after running, the libc function address.

Upvotes: 1

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