Re: some questions about ranged breakpoints

[Pedro Alves <pedro at codesourcery dot com>]

On Tuesday 11 October 2011 15:50:21, Tom Tromey wrote:
> >>>>> "Pedro" == Pedro Alves <pedro@codesourcery.com> writes:
> 
> Tom> What should actually happen here?
> 
> Pedro> I think we should remove the assertion, and have each location map to a
> Pedro> hardware accelerated ranged breakpoint, instead of assuming there can
> Pedro> be only one.  This isn't much different from creating a regular
> Pedro> (non-range) hardware breakpoint that ends up mapping to more than
> Pedro> one location.
> 
> Ok, that makes sense, but unfortunately I think it yields other weird
> behavior.  The problem is that you must somehow pair start and end
> locations; you might even see more of one than the other.

Gross, you're right.

> I thought that pairing could perhaps be done by sorting the addresses
> and, for each address in the first list, choose the nearest greater
> address from the second list.  However, my worry with any heuristic like
> this is that a re-set could cause the breakpoint to change in an
> unforseen way, yielding wrong results for the user.
> 
> Also the parsing is a pain when you have multiple matches.
> Consider the difference between a relative linespec (break-range
> file.c:73, +5) and an absolute one (break-range file.c:73, file.c:78).
> We don't know before parsing whether a linespec is relative.
> So, I think we have to reparse the second linespec in the context of
> each result from the first linespec, then eliminate dups... gross, but I
> guess doable.

Hmm, that's sounding too complicated and hard to both explain
and understand, and probably ends up not being useful...
I'm liking your "deactivate if resetting introduces ambiguity"
idea more.

I think we'll still need to handle multiple locations though,
though I'm not familiar with your code enough to be know how to
express it in a way that makes the ambiguity a different kind
of ambiguity (or if it's expressable even) from the inline cases.
E.g., if you're debugging two inferiors, "file.c:73, +5", may mean
different addresses for each inferior, just because they loaded the
code at different addresses.  But for each inferior, or
each objfile, "file.c:73, +5" was not ambiguous, so I'd
expect to end with two range locations, one for each
inferior or objfile.

-- 
Pedro Alves