Re: Use of lval_register?

[Daniel Jacobowitz <drow@mvista.com>]

On Thu, Jun 05, 2003 at 12:12:50PM -0400, Andrew Cagney wrote:
> >On Thu, Jun 05, 2003 at 11:50:00AM -0400, Andrew Cagney wrote:
> >
> >>
> >
> >>>lval_reg_frame_relative is a relatively recent addition, I believe,
> >>>added to fix some particular problem with values stored in two places.
> >>>Probably around the HP merge?  But that's just a guess.
> >
> >>
> >>Ah.
> >>
> >
> >>>I think that lval_reg_frame_relative, lval_memory, and lval_register
> >>>should all be combined to an lval_location which takes the frame and a
> >>>description of a location, personally.
> >
> >>
> >>These will all need to live in harmony for a wile though.
> 
> Actually, these are separate but related problems:
> 
> - a location expression determines that a value is in REGNUM N in FRAME F.
> 
> - the CFI then determines that REGNUM N in frame F is actually in REGNUM 
> M in frame G.
> 
> Printing a variable relies on both mechanisms, printing $r1 uses just 
> the first.
> 
> >>The ``print $1''?  That output is correct.  GDB saves the value so that 
> >>it can be refered back to later without having it change.
> 
> >Oh right.  So the value is coming from the cache.
> 
> It's comming from GDB's infinite value history pool (the word cache 
> suggests that it is eventually flushed, which it isn't :-).
> 
> >
> >
> >>>I guess the question is, what _should_ happen if a variable moves? 
> >>>e.g. we switch to a different item on its location list.
> >
> >>
> >>From the users view point, the variable hasn't moved.  Hence the 
> >>assignment:
> >>
> >>	$1.argc = N
> >>
> >>should always work.  Should that assignment update the cached $1 value 
> >>as well, hmm....
> >
> >
> >I think it should update the cached copy.  I'm not so sure it should
> >update the in-memory copy, if the var has moved.  That would require
> >re-evaluating the expression that produced $1 wouldn't it?
> 
> Eventually.  For the moment I'm just worred about getting it to 
> re-evaluate the registers the value is assumed to reside in.
> 
> Or should it only modify the history pool (modifying memory is weird 
> here, but where to draw the line is also weird).

After some more thought, I suppose it should modify both the pool and
memory.  It's just not clear how to find out where in memory it should
be, now...

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer