Re: [RFA]: LOC_COMPUTED + abstracted dwarf2 evaluator, again

Daniel Berlin
2002-07-09T22:47:36Z

On 9 Jul 2002, Jim Blandy wrote:

>
> Daniel Berlin <dberlin@dberlin.org> writes:
> > > > + if (ctx->in_reg)
> > > > + {
> > > > + store_typed_address (VALUE_CONTENTS_RAW (retval),
> > > > + SYMBOL_TYPE (var), dwarf_expr_fetch (ctx, 0));
> > > > + VALUE_LVAL (retval) = not_lval;
> > > > + }
> > > > + else
> > > > + {
> > > > + result = dwarf_expr_fetch (ctx, 0);
> > > > + VALUE_LAZY (retval) = 1;
> > > > + VALUE_ADDRESS (retval) = result;
> > > > + }
> > >
> > > This looks wrong. If evaluating the Dwarf location expression yields
> > > an `in_reg' result, shouldn't the value be an lval_register, with its
> > > the address set to the register number?
> >
> > This doesn't work, in reality.
> >
> > IIRC, you run into problems dereferencing the value, because it
> > thinks it *only* lives in a register (IE it's not really a memory
> > location), regardless of what you tell it.
> >
> > I may be misremembering the exact reason why, but I know things don't work
> > if you do this, even though it would seem to make sense (I had originally
> > written it to do what you suggest).
>
> The `in_reg' case needs to call value_from_register, not explicitly
> set the value's `lval' and `address' fields, as I implied. Calling
> value_from_register will take care of finding registers that have been
> spilled to the stack.

As you wish, but this is what i had tried next (or was it a cousin of
value_from_register).
I ran into problems with pointers vs non-pointer types, and pass by
reference vs pass by value.
I had to special case pointers and references, and do something slightly
difference or else it wouldn't let us deref them.
Though it looks like value_from_register handles this, so maybe it was a
sibling.
I wish i still had the old code to look at.

>
>