Re: malloc() debugging

[Daniel Jacobowitz <drow at mvista dot com>]

On Wed, Oct 30, 2002 at 09:07:46PM +0100, Fredrik Tolf wrote:
> I'm trying to make a multithreaded program, but I've run into some
> problems. It appears as I am somehow modifying malloc's data
> structures (those in front of the allocated chunk, I'm using glibc),
> and thus the program crashes sometimes when the malloc related are
> called, most usually in free. The strangest thing, as I see it, is
> that (at least last time it crashed from this), the first word of
> that structure (prev_size) wasn't modified, but only the second word
> (size). The most probable reason I can see for an error of this kind
> would otherwise be a buffer overflow from the chunk before. Anyhow,
> the reason that I'm mailing to this list is that I'm wondering if
> it's possible to configure gdb to break whenever one of these
> structures is modified by an instruction outside the address range of
> the malloc related functions. If noone knows how this would be done,
> could you notify of any other good tool to find these conditions? Can
> valgrind detect it?

Nope, GDB can't do this.  You may want to try either Electric Fence or
dmalloc; dmalloc does work in multithreaded programs (although it needs
a little coaxing).

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer