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.

Change-Id: I04000d8a506030c747a82cd14d1729a90339ebaf

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 5e99a98e1e3c6d473890226559e160fcb7f3f712..b1283e70df71773b046cd1f481de225de92b818a 100644 (file)
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -903,7 +903,8 @@ dwarf_expr_context::push_dwarf_reg_entry_value
 struct value *
 dwarf_expr_context::fetch_result (struct type *type,
                                  struct type *subobj_type,
-                                 LONGEST subobj_offset)
+                                 LONGEST subobj_offset,
+                                 bool as_lval)
 {
   struct value *retval = nullptr;
 
@@ -933,6 +934,11 @@ dwarf_expr_context::fetch_result (struct type *type,
     }
   else
     {
+      /* If AS_LVAL is false, means that the implicit conversion
+        from a location description to value is expected.  */
+      if (as_lval == false)
+       this->location = DWARF_VALUE_STACK;
+
       switch (this->location)
        {
        case DWARF_VALUE_REGISTER:
@@ -1057,7 +1063,7 @@ dwarf_expr_context::fetch_result (struct type *type,
 /* See expr.h.  */
 
 struct value *
-dwarf_expr_context::eval_exp (const gdb_byte *addr, size_t len,
+dwarf_expr_context::eval_exp (const gdb_byte *addr, size_t len, bool as_lval,
                              struct dwarf2_per_cu_data *per_cu,
                              struct frame_info *frame,
                              const struct property_addr_info *addr_info,
@@ -1073,7 +1079,7 @@ dwarf_expr_context::eval_exp (const gdb_byte *addr, size_t len,
     this->ref_addr_size = per_cu->ref_addr_size ();
 
   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 69a043da50efc74d2f0a45469040b24aa4b3da8a..1c06308f994f61ce5cc639fa7495d9d2e2c9c4a3 100644 (file)
--- a/gdb/dwarf2/expr.h
+++ b/gdb/dwarf2/expr.h
@@ -130,11 +130,13 @@ 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
-     FRAME context.  Where TYPE, SUBOBJ_TYPE and SUBOBJ_OFFSET describe
-     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.  */
-  struct value *eval_exp (const gdb_byte *addr, size_t len,
+     FRAME context.  AS_LVAL defines if the returned struct value is
+     expected to be a value or a location description.  Where TYPE,
+     SUBOBJ_TYPE and SUBOBJ_OFFSET describe 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.  */
+  struct value *eval_exp (const gdb_byte *addr, size_t len, bool as_lval,
                          struct dwarf2_per_cu_data *per_cu,
                          struct frame_info *frame,
                          const struct property_addr_info *addr_info = nullptr,
@@ -223,10 +225,13 @@ 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.  */
   struct 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 228c48f3877608591fe89764fe224d7acecafe52..4037653106702254931906799d590387831e788a 100644 (file)
--- a/gdb/dwarf2/frame.c
+++ b/gdb/dwarf2/frame.c
@@ -232,7 +232,7 @@ 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);
-  struct value *result_val = ctx.eval_exp (exp, len, nullptr, this_frame);
+  struct value *result_val = ctx.eval_exp (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 fdf8385933608bebc60b860c0d11bdaa21457d28..1a23e0b2da3632c81999396d20e959bc76147ae2 100644 (file)
--- 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
@@ -1183,7 +1183,6 @@ 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;
@@ -1194,15 +1193,8 @@ 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
@@ -1428,7 +1420,8 @@ 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)
     {
@@ -1448,8 +1441,8 @@ dwarf2_evaluate_loc_desc_full (struct type *type, struct frame_info *frame,
 
   try
     {
-      retval = ctx.eval_exp (data, size, per_cu, frame, nullptr, type,
-                            subobj_type, subobj_byte_offset);
+      retval = ctx.eval_exp (data, size, as_lval, per_cu, frame, nullptr,
+                            type, subobj_type, subobj_byte_offset);
     }
   catch (const gdb_exception_error &ex)
     {
@@ -1490,10 +1483,10 @@ 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,
@@ -1536,7 +1529,7 @@ dwarf2_locexpr_baton_eval (const struct dwarf2_locexpr_baton *dlbaton,
   try
     {
       result = ctx.eval_exp (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 1de36041940237dbdf6c2b2784a988598b118a99..c14ba8febd248ab68c11efb0386d2e8512501ddb 100644 (file)
--- a/gdb/dwarf2/loc.h
+++ b/gdb/dwarf2/loc.h
@@ -69,14 +69,16 @@ 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.  */