Re: Does DW_OP_deref work?

[Daniel Jacobowitz <drow at mvista dot com>]

On Thu, Jul 31, 2003 at 08:44:05AM -0700, H. J. Lu wrote:
> On Wed, Jul 30, 2003 at 08:27:53PM -0400, Daniel Jacobowitz wrote:
> > On Wed, Jul 30, 2003 at 05:23:06PM -0700, H. J. Lu wrote:
> > > On Wed, Jul 30, 2003 at 05:56:12PM -0400, Daniel Jacobowitz wrote:
> > > > On Wed, Jul 30, 2003 at 02:54:21PM -0700, H. J. Lu wrote:
> > > > > Does DW_OP_deref work correctly with gdb?
> > > > 
> > > > That depends on the context.  Things that use decode_locdesc, probably
> > > > not.  As we find time, things are being converted to the full
> > > > expression evaluator.  Location descriptions and frame bases should
> > > > work.
> > > 
> > > I don't think it does. Intel Fortran compiler generartes DW_OP_deref.
> > > I got
> > 
> > Location descriptions for parameters may not work fully.  Feel free to
> > fix it, or to investigate the reasons why more thoroughly - search for
> > LOC_COMPUTED_ARG, but I don't even think we generate those yet.
> > 
> 
> The problem is gdb has a different idea about DW_OP_deref than Intel
> compiler. From what I can tell in DWARF 3 draft, DW_OP_deref specifies
> an address. But dwarf2read.c and gdb doesn't support it at all. There
> is LOC_REF_ARG, which is an offset from the frame base register.
> new_symbol in dwarf2read.c has
> 
>               else if (offreg)
>                 {
>                   if (isderef)
>                     {
>                       if (basereg != frame_base_reg)
>                         dwarf2_complex_location_expr_complaint ();
>                       SYMBOL_CLASS (sym) = LOC_REF_ARG;
>                     }
>                   else
>                     {
>                       SYMBOL_CLASS (sym) = LOC_BASEREG_ARG;
>                       SYMBOL_BASEREG (sym) = DWARF2_REG_TO_REGNUM (basereg);
>                     }
>                 }
>               else
>                 {
>                   SYMBOL_CLASS (sym) = LOC_ARG;
>                 }
>  
> Since DW_OP_deref doesn't use basereg nor frame_base_reg, SYMBOL_CLASS
> is set to LOC_ARG. DW_OP_deref needs something like LOC_DEREF_ARG,
> which works on address instead of offset from a base register.

Please look more closely at what I suggested, and at how DW_OP_deref
works for DW_TAG_variable (as opposed to DW_TAG_formal_parameter).  All
of the above should be turned into LOC_COMPUTED_ARG.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer