2009/5/21 Dan Kegel <[email protected]>:
> On Thu, May 21, 2009 at 7:22 AM, Alex Bennee <[email protected]> wrote:
>> Is there any way I could mark an interesting location in memory with
>> the client mechanism and then get
>> Valgrind to show me a backtrace everytime the location was touched? If
>> not it would be a really useful tool :-)
>
> That would be cool. That said, have you tried a watchpoint in gdb?
> http://stackoverflow.com/questions/58851/can-i-set-a-breakpoint-on-memory-access-in-gdb
Yep I had been trying that. The main problem was not being able to do
ith progamatically:
b 869 if awatch (void *) *&n->timer
Would of been useful. But conditinal breakpoints aren't really
designed for setting newer breakpoints.
In the end I did solve it with a client request:
n->timer = NULL;
fprintf(stderr," 2:checking n=%p n->timer=%p\n", n, n->timer);
VALGRIND_MAKE_MEM_NOACCESS(&n->timer, sizeof(n->timer));
And almost imeadiatly Valgrind showed me an invalid write:
==31858== Invalid write of size 4
==31858== at 0x413B1D: function (snmp_interface.c:2699)
Which lead to:
n->vc_qam[us]++;
Which funnily enough was an incorrectly sized array just before n->timer
Time spent reading Valgrind's fine manual: 10 minutes, Time spent
hacking in the macro and running Valgrind 5 minutes, Time I *would
have* saved if I had done this earlier: 4 hours ;-)
--
Alex, homepage: http://www.bennee.com/~alex/
CV: http://www.bennee.com/~alex/cv.php
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