Re: i386 int3 handling, running vs stepping

Daniel Jacobowitz
2009-02-02T21:49:23Z

On Mon, Feb 02, 2009 at 12:03:13PM -0800, Doug Evans wrote:
> On Sun, Feb 1, 2009 at 8:24 PM, Daniel Jacobowitz <drow@false.org> wrote:
> > On Sun, Feb 01, 2009 at 03:38:04PM -0800, Doug Evans wrote:
> >> I haven't looked into siginfo, but can gdb look at the insn? [akin to
> >> displaced stepping handling]
> >
> > I suppose, but I don't really see a point.
>
> Apologies, it's not clear what point you're referring to.
>
> I guess the issue is whether int3's in programs are supported by gdb,
> and by supported I mean users can rely on gdb flagging a SIGTRAP when
> they're executed. As you say, there are people who take advantage of
> this for hardwired breakpoints.

Since it works today, and we know that people use it, I think we have
no choice but to consider it supported.

> There are various situations where gdb itself will singlestep code
> (e.g., "step", "next", s/w watchpoints). Can users expect to see the
> SIGTRAP in these situations (and all others)? And if the program is
> being run by a script, can the script expect to see the SIGTRAP in all
> cases?

That's certainly not the case today. If you want to make it work, and
add a couple of tests for it, I've no objection - it seems a plausible
thing to do. But I would prefer that any solution did not involve
reading the instruction at every step; that's quite slow, on a target
where we otherwise do not need to.

--
Daniel Jacobowitz
CodeSourcery