1

I'm following Erickson 2008 Hacking the art of exploitation. The program is very simple.

#include <stdio.h> 
#include <string.h>
int main() {

char str_a[20];
strcpy(str_a, "Hello, world!\n");
printf(str_a); 
} 

I set a break at line 6

(gdb)break 6
(gdb)break strcpy

...which prompts

Function "strcpy" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y 
Breakpoint 2 (strcpy) pending.
(gdb) break 8 

Then I should be able to step through the program. With run or start and cont. However the program skips the break point 2. "info breakpoints" says breakpoint already hit 1 time at start. How do I make GDB stop at breakpoints even after being reached once? I thought this was the answer.

enable -- Enable all or some breakpoints.
enable breakpoints -- Enable all or some breakpoints.
enable breakpoints count -- Enable some breakpoints for COUNT hits.
enable breakpoints delete -- Enable some breakpoints and delete when hit.
enable breakpoints once -- Enable some breakpoints for one hit.
enable count -- Enable some breakpoints for COUNT hits.

GNU gdb (Ubuntu 9.2-0ubuntu1~20.04.1) 9.2 I'll keep digging trying to find the solution but for now it seems a mystery.

Edit: I believe the problem lies in gdb disabling my breakpoint at start. When I start the program, it disables breakpoint 2, then I run enable 2 check info breakpoints, and it's enabled, but it never stops there. I changed the addresses and "What" column for formatting.

Num     Type                 Disp Enb  Address          What.      .         .
1       breakpoint             keep y   0x0005 in main at **7.
        breakpoint already hit 1 time.                                .               .
2       STT_GNU_IFUNC resolver keep y   0x0007 <strcpy_ifunc>.        .      .
3       breakpoint             keep y   0x0005 in main at **8. 
        breakpoint already hit 1 time

1 Answer 1

2

If your output looks like this

(gdb) info breakpoints
Num     Type           Disp Enb Address            What
1       breakpoint     keep y   0x00005555554006c1 in main at x.c:6
        breakpoint already hit 1 time
2       breakpoint     keep y   0x00007ffff7a7f980 in strcpy_ifunc at ../sysdeps/x86_64/multiarch/ifunc-unaligned-ssse3.h:33

This means that only breakpoint 1 - the one for line 6 has been hit once. Not the one for strcpy

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.