Re: Variable identification (Was: [RFA] Don't reset watchpoint block on solib load.)

[Vladimir Prus <ghost@cs.msu.su>]

On Friday 30 November 2007 04:09:46 Michael Snyder wrote:
> On Thu, 2007-11-29 at 22:02 +0300, Vladimir Prus wrote:
> > Jim Blandy wrote:
> > >> This is probably good behaviour, indeed. Or maybe we should not
> > >> disable watchpoint, but mark it as pending, in the same sense of
> > >> "user wanted it to be enabled, but it won't trigger until a shared
> > >> lib is loaded" that is used for ordinary watchpoints.
> > >
> > > I think so, too.  I guess the key observation is that, while it's not
> > > meaningful to talk about a particular local variable "coming back
> > > alive", since each function call creates a distinct set of local
> > > variables, and you can have recursion, etc., it is meaningful to talk
> > > about a shared library being reloaded, and it's intuitive to identify
> > > the 'X' from the first loading with the 'X' in the second loading,
> > > even if they're at different addresses.
> >
> > Yes. I now recall this is more general problem with identification of
> > variables in GDB. Say, you're in function, and you have local variable
> > 'foo'. In GUI, you do something with 'foo' -- set display format to
> > hex, expand it, and so on. It's highly desirable to keep this
> > information for the next run of program, or even next run of the GUI --
> > even if variable is local, it's not likely that the display properties
> > user wants depend on frame.
> >
> > Unfortunately, there's no way to do that.
>
> I haven't followed the discussion closely, but
> shouldn't it be up to the GUI to keep such persistant
> info?  It's nothing to do with gdb, really.  It's the
> GUI's state.

It's GUI state, true. But to keep it, GUI needs some identifier for variables, 
that is is persistent across program restarts, preferably even if program 
changes. Presently, there's no such identifier provided by GDB.

- Volodya