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Date: Thu, 31 Jul 2003 15:44:00 -0000
From: "H. J. Lu" <hjl@lucon.org>
To: GDB <gdb@sources.redhat.com>
Subject: Re: Does DW_OP_deref work?
Message-ID: <20030731154405.GA11592@lucon.org>
References: <20030730215421.GA26408@lucon.org> <20030730215612.GB15640@nevyn.them.org> <20030731002306.GA28960@lucon.org> <20030731002753.GA18866@nevyn.them.org>
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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.


H.J.