[PATCH 2/4] Hardware accelerated watchpoint conditions

[Thiago Jung Bauermann]

On Fri, 2010-07-02 at 15:19 +0200, Ulrich Weigand wrote:
> Thiago Jung Bauermann wrote:
> > > > +  for (; v; v = value_next (v))
> > > > +    {
> > > > +      if (VALUE_LVAL (v) == lval_memory)
> > > > +	{
> > > > +	  /* A lazy memory lvalue is one that GDB never needed to fetch;
> > > > +	     we either just used its address (e.g., `a' in `a.b') or
> > > > +	     we never needed it at all (e.g., `a' in `a,b').  */
> > > > +	  if (!value_lazy (v))
> > > > +	    found_memory_cnt++;
> > > > +	}
> > > > +      else if (VALUE_LVAL (v) != not_lval
> > > > +	       && deprecated_value_modifiable (v) == 0)
> > > > +	return -1;	/* ??? What does this represent? */
> > > 
> > > These are values from the history (e.g. $1).  In this context, they
> > > should be treated as non-lvalues, so they should be fine ...
> > 
> > I removed that else if then. I'll submit a separate patch to replace
> > that comment in can_use_hardware_watchpoint.
> 
> Actually, thinking about this a bit more, the logic still does not
> seem quite correct.  What we really want is:
> 
> - not_lval values: these are fine
> - deprecated_value_modifiable (v) == 0 (history) values: treat just
>   like not_lval, no matter what their VALUE_LVAL says
> - lval_memory values: check whether they are lazy or not and count them
> - all other values (lval_computed, lval_internalvar ...): *not* OK
> 
> In particular, the missing check on lval_computed may become more important
> now that DWARF multi-piece values are always represented as lval_computed ...
> (This may also affect watchpoint code in breakpoint.c, but I guess that's
> a different issue.)

Ok, makes sense. That loop now reads:

  for (; v; v = value_next (v))
    {
      /* Constants and values from the history are fine.  */
      if (VALUE_LVAL (v) == not_lval || deprecated_value_modifiable (v) == 0)
        continue;
      else if (VALUE_LVAL (v) == lval_memory)
        {
          /* A lazy memory lvalue is one that GDB never needed to fetch;
             we either just used its address (e.g., `a' in `a.b') or
             we never needed it at all (e.g., `a' in `a,b').  */
          if (!value_lazy (v))
            found_memory_cnt++;
        }
      /* Other kinds of values are not fine. */
      else
        return -1;
    }

> Except for the num_memory_accesses logic discussed above, the patch
> is otherwise OK now.

Great! Except for the change in the loop above, the rest of the patch is
the same.

Thanks for your help with this work.


2010-07-06  Sergio Durigan Junior  <sergiodj@linux.vnet.ibm.com>
	    Thiago Jung Bauermann  <bauerman@br.ibm.com>

	* breakpoint.c (fetch_watchpoint_value): Rename to fetch_subexp_value
	and move to eval.c.  Change callers.
	(insert_bp_location): Pass watchpoint condition in
	target_insert_watchpoint.
	(remove_breakpoint_1) Pass watchpoint condition in
	target_remove_watchpoint.
	(watchpoint_locations_match): Call
	target_can_accel_watchpoint_condition.
	* eval.c: Include wrapper.h.
	(fetch_subexp_value): Moved from breakpoint.c.
	* ppc-linux-nat.c (ppc_linux_region_ok_for_hw_watchpoint):
	Formatting fix.
	(can_use_watchpoint_cond_accel): New function.
	(calculate_dvc): Likewise.
	(num_memory_accesses): Likewise.
	(check_condition): Likewise.
	(ppc_linux_can_accel_watchpoint_condition): Likewise
	(ppc_linux_insert_watchpoint): Call can_use_watchpoint_cond_accel,
	check_condition and calculate_dvc.
	(ppc_linux_remove_watchpoint): Likewise.
	(_initialize_ppc_linux_nat): Set to_can_accel_watchpoint_condition to
	ppc_linux_can_accel_watchpoint_condition
	* target.c (debug_to_insert_watchpoint): Add argument for watchpoint
	condition.
	(debug_to_remove_watchpoint): Likewise.
	(debug_to_can_accel_watchpoint_condition): New function.
	(update_current_target): Set to_can_accel_watchpoint_condition.
	(setup_target_debug): Set to_can_accel_watchpoint_condition.
	* target.h: Add opaque declaration for struct expression.
	(struct target_ops) <to_insert_watchpoint>,
	<to_remove_watchpoint>: Add new arguments to pass the watchpoint
	<to_can_accel_watchpoint_condition>: New member.
	condition.  Update all callers and implementations.
	(target_can_accel_watchpoint_condition): New macro.
	* value.c (free_value_chain): New function.
	* value.h (fetch_subexp_value): New prototype.
	(free_value_chain): Likewise.

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