Re: [RFA]: dwarf2expr.[ch]

[Daniel Berlin <dberlin at dberlin dot org>]

On 10 Jul 2002, Jim Blandy wrote:

> 
> Daniel Berlin <dberlin@dberlin.org> writes:
> > Just some questions and statements:
> > > > +   return ctx->stack[ctx->stack_len - (1+n)];
> > > > + 
> > > > + }     
> > > 
> > > This should check for underflow, too.  Look at what DW_OP_rot will do
> > > on an empty stack.
> > It does.
> > Look at the lines above it.
> > (Yours won't have internal_error, just (ctx->error))
> > if (ctx->stack_len < n)
> >      internal_error (__FILE__, __LINE__, "Asked for position %d of stack, 
> > stack only has %d elements on it\n",
> >                      n, ctx->stack_len);
> > 
> > If you ask for one item, and the stack has 0, this will catch it.
> 
> You're right, it does.  I misread 'n' as indexing from bottom to top,
> not top to bottom.
> 
> > > > + 
> > > > + 	  switch (op)
> > > > + 	    {
> > > > + 	    case DW_OP_deref:
> > > > + 	      {
> > > > + 		result = (CORE_ADDR) 
> > > > + 		  (ctx->read_mem) (ctx->read_mem_baton, 
> > > > + 				   result, 
> > > > + 				   TARGET_PTR_BIT / TARGET_CHAR_BIT);
> > > 
> > > Since CORE_ADDR may be wider than the target's address,
> > > I think this
> > > should mask off and/or sign extend as appropriate, depending on the
> > > current gdbarch.  Same anywhere we call ctx->read_mem, I think.
> > Shouldn't the read_mem function do this for us?
> > read_mem is returning a CORE_ADDR (the cast is pointless, i'll remove 
> > it) anyway, so it would seem to be *it's* job to make sure the 
> > CORE_ADDR it gives us is the right thing.
> 
> I'm worried about about strange addresses being produced because the
> evaluator is using stack elements wider than officially specified.
> Since the evaluator is the source of the behavior I'm concerned about,
> I think it's better to correct it there than to require the
> surrounding code in GDB to cope with it.
> 
> You're going to need a truncation function for all the operations that
> are sensitive to the upper bits anyway (divide, shift right, compare),
> so it doesn't seem a big deal to drop in an application here, too.

But i'm not, because i'm using the incredibly ugly transformation of

result = (LONGET) result2 / (LONGEST) result1

is

result = value_as_long (value_binop (value_from_pointer 
(builtin_type_CORE_ADDR,  result2), value_from_pointer 
(builtin_type_CORE_ADDR, result1), BINOP_DIV))


which handles it for us.
:)

 > 
>