Re: DWARF-2 expression error in location list entries

[Daniel Jacobowitz <drow@false.org>]

On Tue, May 08, 2007 at 01:22:25PM -0700, Carl Burch wrote:
>    In dwarf2expr.c function execute_stack_op() there are two occurrences of
> error() calls asserting :
> 
>          if (op_ptr != op_end && *op_ptr != DW_OP_piece)
>             error (_("DWARF-2 expression error: DW_OP_reg operations must be "
>                    "used either alone or in conjuction with DW_OP_piece."));
> 
>    A couple of us have looked for that first restriction in the DWARF3
> standard and not found it.  I also went back to the DWARF2 standard
> literally cited by the message and failed to find it there as well.  Can
> anyone point out where to read the restriction these error() calls refer to?

I believe the language was recently discussed on the dwarf workgroup
list.  It's unclear, but the error is correct.  DW_OP_regx describes
a location ("the value is in this register"), not a value ("the value is
the contents of this register").  Therefore the value may not be
stack-sized, and is not pushed on to the expression stack, so there's
nothing for you to DW_OP_deref later.

>    The expression we have in mind to add is to describe Fortran reference
> parameters in location list entries like :
> 
> { 0x4022720--0x4022724: DW_OP_regx  32 DW_OP_deref   }

Isn't that just "DW_OP_bregx 32 0"?

-- 
Daniel Jacobowitz
CodeSourcery