Re: [RFA] Limited DW_OP_piece support

[Andrew Cagney <ac131313@redhat.com>]

> The patch below adds limited DW_OP_piece support to dwarf2expr.c.  I
> will post a patch to rs6000-tdep.c which illustrates what a
> ``dwarf2_compose_register_pieces'' method should look like.

I think GDB needs to just learn about location lists :-/

Andrew


> Index: dwarf2expr.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/dwarf2expr.c,v
> retrieving revision 1.7
> diff -u -p -r1.7 dwarf2expr.c
> --- dwarf2expr.c	14 May 2003 22:45:41 -0000	1.7
> +++ dwarf2expr.c	22 May 2003 16:39:14 -0000
> @@ -456,6 +456,98 @@ execute_stack_op (struct dwarf_expr_cont
>  	    ctx->in_reg = 0;
>  	  }
>  	  break;
> +
> +	case DW_OP_piece:
> +
> +	  if (!gdbarch_dwarf2_compose_register_pieces_p (current_gdbarch))
> +	    error ("DWARF-2 expression error: DW_OP_piece not supported for "
> +		   "this architecture.");
> +	  else
> +	    {
> +	      /* If the pieces consist of 2 or more registers in the
> +		 proper order, then gdb "will do the right thing" by
> +		 simply using the first register -- assuming, of course
> +		 that the corresponding type information is correct. 
> +		 Otherwise, complain.  
> +		 
> +		 For the case that we handle, there should already be
> +		 a register pushed on the stack.  Our strategy will
> +		 be to push the DW_OP_piece size information and then
> +		 push the next register and it's size information, etc.
> +		 Once that is done, an architecture specific method will
> +		 be called to determine which register should be used
> +		 to access the entire object described by the pieces.
> +		 
> +		 When we've finished the stack should look like this:
> +
> +		    reg num 1		Bottom of stack (index == 0)
> +		    size num 1
> +		    .
> +		    .
> +		    reg num N
> +		    size num N		Top of stack (index == 2*N-1)  */
> +
> +	      CORE_ADDR regnum;
> +
> +	      /* First check to make sure there's only one thing on the
> +		 stack and that's it's a register.  */
> +	      if (ctx->stack_len != 1 || !ctx->in_reg)
> +		error ("DWARF-2 expression error: DW_OP_piece expression "
> +		       "is too complicated.");
> +
> +	      while (1)
> +		{
> +		  long nextregnum;
> +
> +		  /* Fetch the number of bytes for this piece.  */
> +		  op_ptr = read_uleb128 (op_ptr, op_end, &uoffset);
> +		  dwarf_expr_push (ctx, uoffset);
> +
> +		  /* Break out if we're done.  */
> +		  if (op_ptr >= op_end)
> +		    break;
> +
> +		  /* We expect to see a register next.  */
> +		  op = *op_ptr++;
> +		  if (DW_OP_reg0 <= op && op <= DW_OP_reg31)
> +		    {
> +		      reg = op - DW_OP_reg0;
> +		      dwarf_expr_push (ctx, reg);
> +		    }
> +		  else if (op == DW_OP_regx)
> +		    {
> +		      op_ptr = read_uleb128 (op_ptr, op_end, &reg);
> +		      dwarf_expr_push (ctx, reg);
> +		    }
> +		  else
> +		    error ("DWARF-2 expression error: DW_OP_piece expression "
> +			   "is too complicated.");
> +
> +		  /* Make sure that we haven't read too far and that
> +		     a DW_OP_piece operator comes next.  */
> +
> +		  if (op_ptr >= op_end || (*op_ptr!= DW_OP_piece))
> +		    error ("DWARF-2 expression error: DW_OP_piece expression "
> +			   "is too complicated.");
> +
> +		  /* Skip over DW_OP_piece operator.  */
> +		  op_ptr++;
> +		}
> +
> +	      result = gdbarch_dwarf2_compose_register_pieces (
> +		         current_gdbarch, ctx->stack_len / 2, &ctx->stack[0]);
> +
> +	      if (result < 0)
> +		error ("DWARF-2 expression error: DW_OP_piece expression "
> +		       "is too complicated.");
> +
> +	      /* Note: ctx->in_reg is already set.  We want result to be the
> +	         only thing on the stack -- it will be pushed below.
> +		 Make the stack empty so that this will occur.  */
> +	      ctx->stack_len = 0;
> +	    }
> +	  break;
> +
>  	case DW_OP_dup:
>  	  result = dwarf_expr_fetch (ctx, 0);
>  	  break;
> Index: gdbarch.sh
> ===================================================================
> RCS file: /cvs/src/src/gdb/gdbarch.sh,v
> retrieving revision 1.237
> diff -u -p -r1.237 gdbarch.sh
> --- gdbarch.sh	17 May 2003 05:59:58 -0000	1.237
> +++ gdbarch.sh	22 May 2003 16:39:16 -0000
> @@ -471,6 +471,7 @@ f:2:DWARF_REG_TO_REGNUM:int:dwarf_reg_to
>  # to map one to one onto the sdb register numbers.
>  f:2:SDB_REG_TO_REGNUM:int:sdb_reg_to_regnum:int sdb_regnr:sdb_regnr:::no_op_reg_to_regnum::0
>  f:2:DWARF2_REG_TO_REGNUM:int:dwarf2_reg_to_regnum:int dwarf2_regnr:dwarf2_regnr:::no_op_reg_to_regnum::0
> +M:2:DWARF2_COMPOSE_REGISTER_PIECES:long:dwarf2_compose_register_pieces:int count, CORE_ADDR *piece_info:count, piece_info
>  f:2:REGISTER_NAME:const char *:register_name:int regnr:regnr:::legacy_register_name::0
>  v::DEPRECATED_REGISTER_SIZE:int:deprecated_register_size
>  v::DEPRECATED_REGISTER_BYTES:int:deprecated_register_bytes
> 
>