Re: Patch: Dwarf2 reader -vs- DW_OP_piece

[Jim Blandy <jimb@redhat.com>]

Can you explain what sorts of location expressions this is supposed to
help GDB handle?

Tom Tromey <tromey@redhat.com> writes:

> I just submitted a change that changes gcc's Dwarf-2 output.
> It hasn't been approved yet, but of course I'm hoping it will be.
> With this change gcc will now generate DW_OP_piece when a value spans
> multiple registers.
> 
> I came up with a somewhat hacky gdb patch to ignore DW_OP_piece.
> 
> I'm hoping this patch is just a stopgap until someone adds real
> Dwarf-2 location expression support to gdb.
> 
> Ok?
> 
> Tom
> 
> 
> Index: ChangeLog
> from  Tom Tromey  <tromey@redhat.com>
> 
> 	* dwarf2read.c (decode_locdesc): Recognize DW_OP_piece.
> 
> Index: dwarf2read.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/dwarf2read.c,v
> retrieving revision 1.48
> diff -u -r1.48 dwarf2read.c
> --- dwarf2read.c 2002/02/15 22:42:33 1.48
> +++ dwarf2read.c 2002/02/21 18:49:43
> @@ -5808,6 +5808,7 @@
>    int stacki;
>    unsigned int bytes_read, unsnd;
>    unsigned char op;
> +  int last_was_piece = 0;
>  
>    i = 0;
>    stacki = 0;
> @@ -5891,8 +5892,13 @@
>  	case DW_OP_reg29:
>  	case DW_OP_reg30:
>  	case DW_OP_reg31:
> -	  isreg = 1;
> -	  stack[++stacki] = op - DW_OP_reg0;
> +	  if (last_was_piece)
> +	    last_was_piece = 0;
> +	  else
> +	    {
> +	      isreg = 1;
> +	      stack[++stacki] = op - DW_OP_reg0;
> +	    }
>  	  break;
>  
>  	case DW_OP_regx:
> @@ -6043,6 +6049,14 @@
>  	     this using GDB's address_class enum.  */
>  	  if (i < size)
>  	    complain (&dwarf2_complex_location_expr);
> +	  break;
> +
> +	case DW_OP_piece:
> +	  /* For now we essentially ignore this.  We assume it only
> +	     occurs when a value spans multiple registers.  */
> +	  read_unsigned_leb128 (NULL, (data + i), &bytes_read);
> +	  i += bytes_read;
> +	  last_was_piece = 1;
>  	  break;
>  
>  	default: