Add as_lval argument to expression evaluator

There are cases where the result of the expression evaluation is
expected to be in a form of a value and not location description.

One place that has this requirement is dwarf_entry_parameter_to_value
function, but more are expected in the future. Until now, this
requirement was fulfilled by extending the evaluated expression with
a DW_OP_stack_value operation at the end.

New implementation, introduces a new evaluation argument instead.

	* dwarf2/expr.c (dwarf_expr_context::fetch_result): Add as_lval
	argument.
	(dwarf_expr_context::eval_exp): Add as_lval argument.
	* dwarf2/expr.h (struct dwarf_expr_context): Add as_lval
	argument to fetch_result and eval_exp methods.
	* dwarf2/frame.c (execute_stack_op): Add as_lval argument.
	* dwarf2/loc.c (dwarf_entry_parameter_to_value): Remove
	DWARF expression extension.
	(dwarf2_evaluate_loc_desc_full): Add as_lval argument support.
	(dwarf2_evaluate_loc_desc): Add as_lval argument support.
	(dwarf2_locexpr_baton_eval): Add as_lval argument support.

1 files changed, 15 insertions, 7 deletions

diff --git a/gdb/dwarf2/expr.h b/gdb/dwarf2/expr.h
index a10fbac..16c5e71 100644
--- a/gdb/dwarf2/expr.h
+++ b/gdb/dwarf2/expr.h
@@ -126,11 +126,17 @@ struct dwarf_expr_context
   void push_address (CORE_ADDR value, bool in_stack_memory);
 
   /* Evaluate the expression at ADDR (LEN bytes long) in a given PER_CU
-     and FRAME context.  TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET describe
-     the expected struct value representation of the evaluation
-     result.  The ADDR_INFO property can be specified to override the
-     range of memory addresses with the passed in buffer.  */
-  value *evaluate (const gdb_byte *addr, size_t len,
+     and FRAME context.
+
+     AS_LVAL defines if the returned struct value is expected to be a
+     value (false) or a location description (true).
+
+     TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET describe the expected struct
+     value representation of the evaluation result.
+
+     The ADDR_INFO property can be specified to override the range of
+     memory addresses with the passed in buffer.  */
+  value *evaluate (const gdb_byte *addr, size_t len, bool as_lval,
 		   dwarf2_per_cu_data *per_cu, frame_info *frame,
 		   const struct property_addr_info *addr_info = nullptr,
 		   struct type *type = nullptr,
@@ -211,9 +217,11 @@ private:
 
   /* Fetch the result of the expression evaluation in a form of
      a struct value, where TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET
-     describe the source level representation of that result.  */
+     describe the source level representation of that result.
+     AS_LVAL defines if the fetched struct value is expected to
+     be a value or a location description.  */
   value *fetch_result (struct type *type, struct type *subobj_type,
-		       LONGEST subobj_offset);
+		       LONGEST subobj_offset, bool as_lval);
 
   /* Return the location expression for the frame base attribute, in
      START and LENGTH.  The result must be live until the current