Unix Programming - gdb break

Author

gdb break

sinbad

2008-03-15, 4:59 am

hi
how to make gdb to break ,with the change in some memory location.i
tried watchpoint but it's not working.
is there anyother way

thanks
sinbad

WANG Cong

2008-03-15, 8:11 am

On Fri, 14 Mar 2008 23:16:23 -0700，sinbad wrote：

> hi
> how to make gdb to break ,with the change in some memory location.i
> tried watchpoint but it's not working. is there anyother way
>

I think gnu.gcc.help is a more appropriate place to discuss this
problem.

I think 'watch' should work, what's wrong with it?

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Paul Pluzhnikov

2008-03-15, 7:28 pm

sinbad <sinbad.sinbad@gmail.com> writes:

> how to make gdb to break ,with the change in some memory location.

You'll do well to read this:
http://catb.org/esr/faqs/smart-questions.html
and ask a smarter question next time.

> i tried watchpoint but it's not working.

Since you didn't tell us what exactly you did, we can't tell you
what you did wrong. Gdb watchpoints work just fine. They are even
fast on some platforms.

> is there anyother way

No.

Here are precise instructions:
Suppose you have a global variable "count" and you want gdb to stop
every time it is updated.

$ cat t.c
#include <stdio.h>
int count;

int incr()
{
return count++;
}

int main()
{
int i;
while ((i = incr()) < 5)
printf("%d\n", i);
return 0;
}
$ gcc -g t.c && gdb -q ./a.out
Using host libthread_db library "/lib/tls/libthread_db.so.1".
(gdb) p &count
$1 = (int *) 0x804959c
(gdb) watch *$1
Hardware watchpoint 1: *$1
(gdb) r
Hardware watchpoint 1: *$1
Hardware watchpoint 1: *$1
Hardware watchpoint 1: *$1

Old value = 0
New value = 1
incr () at t.c:7
7 }
(gdb) bt
#0 incr () at t.c:7
#1 0x08048395 in main () at t.c:12
(gdb) c
0
Hardware watchpoint 1: *$1

Old value = 1
New value = 2
incr () at t.c:7
7 }
.... etc ...

Cheers,
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