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.

5 files changed, 38 insertions, 30 deletions

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 1e67ffa..9e5a356 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -886,7 +886,7 @@ dwarf_expr_context::push_dwarf_reg_entry_value (call_site_parameter_kind kind,
 
 value *
 dwarf_expr_context::fetch_result (struct type *type, struct type *subobj_type,
-				  LONGEST subobj_offset)
+				  LONGEST subobj_offset, bool as_lval)
 {
   value *retval = nullptr;
   gdbarch *arch = this->m_per_objfile->objfile->arch ();
@@ -917,6 +917,11 @@ dwarf_expr_context::fetch_result (struct type *type, struct type *subobj_type,
     }
   else
     {
+      /* If AS_LVAL is false, means that the implicit conversion
+	 from a location description to value is expected.  */
+      if (!as_lval)
+	this->m_location = DWARF_VALUE_STACK;
+
       switch (this->m_location)
 	{
 	case DWARF_VALUE_REGISTER:
@@ -1037,7 +1042,7 @@ dwarf_expr_context::fetch_result (struct type *type, struct type *subobj_type,
 /* See expr.h.  */
 
 value *
-dwarf_expr_context::evaluate (const gdb_byte *addr, size_t len,
+dwarf_expr_context::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,
 			      struct type *type, struct type *subobj_type,
@@ -1048,7 +1053,7 @@ dwarf_expr_context::evaluate (const gdb_byte *addr, size_t len,
   this->m_addr_info = addr_info;
 
   eval (addr, len);
-  return fetch_result (type, subobj_type, subobj_offset);
+  return fetch_result (type, subobj_type, subobj_offset, as_lval);
 }
 
 /* Require that TYPE be an integral type; throw an exception if not.  */
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
diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
index ae26a88..f3d3877 100644
--- a/gdb/dwarf2/frame.c
+++ b/gdb/dwarf2/frame.c
@@ -233,7 +233,7 @@ execute_stack_op (const gdb_byte *exp, ULONGEST len, int addr_size,
   scoped_value_mark free_values;
 
   ctx.push_address (initial, initial_in_stack_memory);
-  value *result_val = ctx.evaluate (exp, len, nullptr, this_frame);
+  value *result_val = ctx.evaluate (exp, len, true, nullptr, this_frame);
 
   if (VALUE_LVAL (result_val) == lval_memory)
     return value_address (result_val);
diff --git a/gdb/dwarf2/loc.c b/gdb/dwarf2/loc.c
index d29fdcf..2322a01 100644
--- a/gdb/dwarf2/loc.c
+++ b/gdb/dwarf2/loc.c
@@ -50,7 +50,7 @@
 static struct value *dwarf2_evaluate_loc_desc_full
   (struct type *type, struct frame_info *frame, const gdb_byte *data,
    size_t size, dwarf2_per_cu_data *per_cu, dwarf2_per_objfile *per_objfile,
-   struct type *subobj_type, LONGEST subobj_byte_offset);
+   struct type *subobj_type, LONGEST subobj_byte_offset, bool as_lval = true);
 
 /* Until these have formal names, we define these here.
    ref: http://gcc.gnu.org/wiki/DebugFission
@@ -1214,7 +1214,6 @@ dwarf_entry_parameter_to_value (struct call_site_parameter *parameter,
 				dwarf2_per_objfile *per_objfile)
 {
   const gdb_byte *data_src;
-  gdb_byte *data;
   size_t size;
 
   data_src = deref_size == -1 ? parameter->value : parameter->data_value;
@@ -1225,15 +1224,8 @@ dwarf_entry_parameter_to_value (struct call_site_parameter *parameter,
     throw_error (NO_ENTRY_VALUE_ERROR,
 		 _("Cannot resolve DW_AT_call_data_value"));
 
-  /* DW_AT_call_value is a DWARF expression, not a DWARF
-     location.  Postprocessing of DWARF_VALUE_MEMORY would lose the type from
-     DWARF block.  */
-  data = (gdb_byte *) alloca (size + 1);
-  memcpy (data, data_src, size);
-  data[size] = DW_OP_stack_value;
-
-  return dwarf2_evaluate_loc_desc (type, caller_frame, data, size + 1, per_cu,
-				   per_objfile);
+  return dwarf2_evaluate_loc_desc (type, caller_frame, data_src, size, per_cu,
+				   per_objfile, false);
 }
 
 /* VALUE must be of type lval_computed with entry_data_value_funcs.  Perform
@@ -1459,7 +1451,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 			       dwarf2_per_cu_data *per_cu,
 			       dwarf2_per_objfile *per_objfile,
 			       struct type *subobj_type,
-			       LONGEST subobj_byte_offset)
+			       LONGEST subobj_byte_offset,
+			       bool as_lval)
 {
   if (subobj_type == NULL)
     {
@@ -1479,8 +1472,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 
   try
     {
-      retval = ctx.evaluate (data, size, per_cu, frame, nullptr, type,
-			     subobj_type, subobj_byte_offset);
+      retval = ctx.evaluate (data, size, as_lval, per_cu, frame, nullptr,
+			     type, subobj_type, subobj_byte_offset);
     }
   catch (const gdb_exception_error &ex)
     {
@@ -1521,10 +1514,10 @@ struct value *
 dwarf2_evaluate_loc_desc (struct type *type, struct frame_info *frame,
 			  const gdb_byte *data, size_t size,
 			  dwarf2_per_cu_data *per_cu,
-			  dwarf2_per_objfile *per_objfile)
+			  dwarf2_per_objfile *per_objfile, bool as_lval)
 {
   return dwarf2_evaluate_loc_desc_full (type, frame, data, size, per_cu,
-					per_objfile, NULL, 0);
+					per_objfile, NULL, 0, as_lval);
 }
 
 /* Evaluates a dwarf expression and stores the result in VAL,
@@ -1567,7 +1560,7 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
   try
     {
       result = ctx.evaluate (dlbaton->data, dlbaton->size,
-			     per_cu, frame, addr_stack);
+			     true, per_cu, frame, addr_stack);
     }
   catch (const gdb_exception_error &ex)
     {
diff --git a/gdb/dwarf2/loc.h b/gdb/dwarf2/loc.h
index 5d964b0..5ff061b 100644
--- a/gdb/dwarf2/loc.h
+++ b/gdb/dwarf2/loc.h
@@ -72,14 +72,16 @@ struct call_site_parameter *dwarf_expr_reg_to_entry_parameter
 
 /* Evaluate a location description, starting at DATA and with length
    SIZE, to find the current location of variable of TYPE in the context
-   of FRAME.  */
+   of FRAME.  AS_LVAL defines if the resulting struct value is expected to
+   be a value or a location description.  */
 
 struct value *dwarf2_evaluate_loc_desc (struct type *type,
 					struct frame_info *frame,
 					const gdb_byte *data,
 					size_t size,
 					dwarf2_per_cu_data *per_cu,
-					dwarf2_per_objfile *per_objfile);
+					dwarf2_per_objfile *per_objfile,
+					bool as_lval = true);
 
 /* A chain of addresses that might be needed to resolve a dynamic
    property.  */