Introduce var_msym_value_operation

This adds class var_msym_value_operation, which implements
OP_VAR_MSYM_VALUE.  A new method is added to class operation in order
to support a special case in minsym evaluation.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* expression.h (class operation) <set_outermost>: New method.
	* expop.h (class var_msym_value_operation): New.
	* eval.c (eval_op_var_msym_value): No longer static.
	(var_msym_value_operation::evaluate_for_address)
	(var_msym_value_operation::evaluate_for_sizeof)
	(var_msym_value_operation::evaluate_for_cast): New methods.
	* ax-gdb.c (var_msym_value_operation::do_generate_ax): New
	method.

gdb/ChangeLog

@@ -1,3 +1,14 @@
+2021-03-08  Tom Tromey  <tom@tromey.com>
+
+	* expression.h (class operation) <set_outermost>: New method.
+	* expop.h (class var_msym_value_operation): New.
+	* eval.c (eval_op_var_msym_value): No longer static.
+	(var_msym_value_operation::evaluate_for_address)
+	(var_msym_value_operation::evaluate_for_sizeof)
+	(var_msym_value_operation::evaluate_for_cast): New methods.
+	* ax-gdb.c (var_msym_value_operation::do_generate_ax): New
+	method.
+
 2021-03-08  Tom Tromey  <tom@tromey.com>
 
 	* expop.h (class long_const_operation): New.

gdb/ax-gdb.c

@@ -2324,6 +2324,23 @@ long_const_operation::do_generate_ax (struct expression *exp,
 		   std::get<0> (m_storage));
 }
 
+void
+var_msym_value_operation::do_generate_ax (struct expression *exp,
+					  struct agent_expr *ax,
+					  struct axs_value *value,
+					  struct type *cast_type)
+{
+  gen_msym_var_ref (ax, value, std::get<0> (m_storage),
+		    std::get<1> (m_storage));
+
+  if (value->type->code () == TYPE_CODE_ERROR)
+    {
+      if (cast_type == nullptr)
+	error_unknown_type (std::get<0> (m_storage)->linkage_name ());
+      value->type = cast_type;
+    }
+}
+
 }
 
 /* This handles the middle-to-right-side of code generation for binary

gdb/eval.c

@@ -1221,7 +1221,7 @@ eval_op_var_entry_value (struct type *expect_type, struct expression *exp,
 
 /* Helper function that implements the body of OP_VAR_MSYM_VALUE.  */
 
-static struct value *
+struct value *
 eval_op_var_msym_value (struct type *expect_type, struct expression *exp,
 			enum noside noside, bool outermost_p,
 			minimal_symbol *msymbol, struct objfile *objfile)
@@ -3301,6 +3301,22 @@ scope_operation::evaluate_for_address (struct expression *exp,
   return x;
 }
 
+value *
+var_msym_value_operation::evaluate_for_address (struct expression *exp,
+						enum noside noside)
+{
+  value *val = evaluate_var_msym_value (noside,
+					std::get<1> (m_storage),
+					std::get<0> (m_storage));
+  if (noside == EVAL_AVOID_SIDE_EFFECTS)
+    {
+      struct type *type = lookup_pointer_type (value_type (val));
+      return value_zero (type, not_lval);
+    }
+  else
+    return value_addr (val);
+}
+
 }
 
 /* Evaluate like `evaluate_subexp' except coercing arrays to pointers.
@@ -3501,6 +3517,25 @@ operation::evaluate_for_sizeof (struct expression *exp, enum noside noside)
   return evaluate_subexp_for_sizeof_base (exp, value_type (val));
 }
 
+value *
+var_msym_value_operation::evaluate_for_sizeof (struct expression *exp,
+					       enum noside noside)
+
+{
+  minimal_symbol *msymbol = std::get<0> (m_storage);
+  value *mval = evaluate_var_msym_value (noside,
+					 std::get<1> (m_storage),
+					 msymbol);
+
+  struct type *type = value_type (mval);
+  if (type->code () == TYPE_CODE_ERROR)
+    error_unknown_type (msymbol->print_name ());
+
+  /* FIXME: This should be size_t.  */
+  struct type *size_type = builtin_type (exp->gdbarch)->builtin_int;
+  return value_from_longest (size_type, TYPE_LENGTH (type));
+}
+
 }
 
 /* Evaluate a subexpression of EXP, at index *POS, and return a value
@@ -3558,6 +3593,38 @@ evaluate_subexp_for_cast (expression *exp, int *pos,
   return value_cast (to_type, val);
 }
 
+namespace expr
+{
+
+value *
+var_msym_value_operation::evaluate_for_cast (struct type *to_type,
+					     struct expression *exp,
+					     enum noside noside)
+{
+  if (noside == EVAL_AVOID_SIDE_EFFECTS)
+    return value_zero (to_type, not_lval);
+
+  value *val = evaluate_var_msym_value (noside,
+					std::get<1> (m_storage),
+					std::get<0> (m_storage));
+
+  if (noside == EVAL_SKIP)
+    return eval_skip_value (exp);
+
+  val = value_cast (to_type, val);
+
+  /* Don't allow e.g. '&(int)var_with_no_debug_info'.  */
+  if (VALUE_LVAL (val) == lval_memory)
+    {
+      if (value_lazy (val))
+	value_fetch_lazy (val);
+      VALUE_LVAL (val) = not_lval;
+    }
+  return val;
+}
+
+}
+
 /* Parse a type expression in the string [P..P+LENGTH).  */
 
 struct type *

gdb/expop.h

@@ -45,6 +45,12 @@ extern struct value *eval_op_scope (struct type *expect_type,
 				    struct expression *exp,
 				    enum noside noside,
 				    struct type *type, const char *string);
+extern struct value *eval_op_var_msym_value (struct type *expect_type,
+					     struct expression *exp,
+					     enum noside noside,
+					     bool outermost_p,
+					     minimal_symbol *msymbol,
+					     struct objfile *objfile);
 
 namespace expr
 {
@@ -481,6 +487,52 @@ protected:
     override;
 };
 
+class var_msym_value_operation
+  : public maybe_constant_operation<minimal_symbol *, struct objfile *>
+{
+public:
+
+  using maybe_constant_operation::maybe_constant_operation;
+
+  value *evaluate (struct type *expect_type,
+		   struct expression *exp,
+		   enum noside noside) override
+  {
+    return eval_op_var_msym_value (expect_type, exp, noside, m_outermost,
+				   std::get<0> (m_storage),
+				   std::get<1> (m_storage));
+  }
+
+  value *evaluate_for_sizeof (struct expression *exp, enum noside noside)
+    override;
+
+  value *evaluate_for_address (struct expression *exp, enum noside noside)
+    override;
+
+  value *evaluate_for_cast (struct type *expect_type,
+			    struct expression *exp,
+			    enum noside noside) override;
+
+  enum exp_opcode opcode () const override
+  { return OP_VAR_MSYM_VALUE; }
+
+  void set_outermost () override
+  {
+    m_outermost = true;
+  }
+
+protected:
+
+  /* True if this is the outermost operation in the expression.  */
+  bool m_outermost = false;
+
+  void do_generate_ax (struct expression *exp,
+		       struct agent_expr *ax,
+		       struct axs_value *value,
+		       struct type *cast_type)
+    override;
+};
+
 } /* namespace expr */
 
 #endif /* EXPOP_H */

gdb/expression.h

@@ -165,6 +165,10 @@ public:
   /* Print this operation to STREAM.  */
   virtual void dump (struct ui_file *stream, int depth) const = 0;
 
+  /* Call to indicate that this is the outermost operation in the
+     expression.  This should almost never be overridden.  */
+  virtual void set_outermost () { }
+
 protected:
 
   /* Called by generate_ax to do the work for this particular