Re: Instruction address catching

Kevin Buettner
2002-10-05T00:52:55Z

On Oct 5, 2:21am, Fredrik Tolf wrote:

> On Sat, 2002-10-05 at 02:11, Kevin Buettner wrote:
> > On Oct 5, 1:36am, Fredrik Tolf wrote:
> >
> > > Is it possible, with the current version of gdb, to make it detect every
> > > time an address is written to, and to make it stop only if the address
> > > of the instruction that wrote to that address isn't equal to a specific
> > > value.
> >
> > Do it like this:
> >
> > (gdb) watch foo
> > Hardware watchpoint 1: foo
> > (gdb) condition 1 $pc != 0x80484c8
> >
> > The address to compare $pc against should be the address of the
> > instruction *after* the one that writes to ``foo''. It's probably
> > easier to figure this out by simply setting a watchpoint on foo,
> > running 'til it's hit, and if that's not the one you're interested
> > in, add a condition so that it won't stop there again.
> >
> > > If it's possible, does it work in a multithreaded application?
> >
> > It should. If it doesn't, it's a bug.
>
> Are you sure? Wouldn't the pc it compares to be that of the selected
> thread and not that of the thread that wrote?

The thread that triggers the watchpoint becomes the selected thread
for the purposes of checking the condition. (At least, I think that's
the way it works.) I've just tried it with a simple (threaded) example
and it seems to work as expected...

Kevin