gdb: Forward VALUE_LVAL when avoiding side effects for STRUCTOP_PTR

Assume that we have a C program like this:

  struct foo_type
  {
    int var;
  } foo;

  struct foo_type *foo_ptr = &foo;

  int
  main ()
  {
    return foo_ptr->var;
  }

Then GDB should be able to evaluate the following, however, it currently
does not:

  (gdb) start
  ...
  (gdb) whatis &(foo_ptr->var)
  Attempt to take address of value not located in memory.

The problem is that in EVAL_AVOID_SIDE_EFFECTS mode,
eval.c:evaluate_subexp_standard always returns a not_lval value as the
result for a STRUCTOP_PTR operation. As a consequence, the rest of
the code believes that one cannot take the address of the returned
value.

This patch fixes STRUCTOP_PTR handling so that the VALUE_LVAL
attribute for the returned value is properly initialized.  After this
change, the above session becomes:

  (gdb) start
  ...
  (gdb) whatis &(foo_ptr->var)
  type = int *

This commit is largely the same as commit 2520f728b7 (Forward
VALUE_LVAL when avoiding side effects for STRUCTOP_STRUCT) but applied
to STRUCTOP_PTR rather than STRUCTOP_STRUCT.  Both of these commits are
building on top of commit ac1ca910d7 (Fixes for PR exp/15364).

gdb/ChangeLog:

	* eval.c (evaluate_subexp_standard): If EVAL_AVOID_SIDE_EFFECTS
	mode, forward the VALUE_LVAL attribute to the returned value in
	the STRUCTOP_PTR case.

gdb/testsuite/ChangeLog:

	* gdb.base/whatis.c: Extend the test case.
	* gdb.base/whatis.exp: Add additional tests.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2016-05-27  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* eval.c (evaluate_subexp_standard): If EVAL_AVOID_SIDE_EFFECTS
+	mode, forward the VALUE_LVAL attribute to the returned value in
+	the STRUCTOP_PTR case.
+
 2016-05-25  Tom Tromey  <tom@tromey.com>
 
 	* python/py-value.c (value_object_as_number): Use correct spelling

gdb/eval.c

@@ -1917,7 +1917,7 @@ evaluate_subexp_standard (struct type *expect_type,
       arg3 = value_struct_elt (&arg1, NULL, &exp->elts[pc + 2].string,
 			       NULL, "structure pointer");
       if (noside == EVAL_AVOID_SIDE_EFFECTS)
-	arg3 = value_zero (value_type (arg3), not_lval);
+	arg3 = value_zero (value_type (arg3), VALUE_LVAL (arg3));
       return arg3;
 
     case STRUCTOP_MEMBER:

gdb/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2016-05-27  Andrew Burgess  <andrew.burgess@embecosm.com>
+
+	* gdb.base/whatis.c: Extend the test case.
+	* gdb.base/whatis.exp: Add additional tests.
+
 2016-05-25  Bernhard Heckel  <bernhard.heckel@intel.com>
 
 * gdb.fortran/type.f90: Add pointer variable.

gdb/testsuite/gdb.base/whatis.c

@@ -135,7 +135,7 @@ struct t_struct {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_struct1;
+} v_struct1, *v_struct_ptr1;
 
 struct {
     char	v_char_member;
@@ -147,7 +147,7 @@ struct {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_struct2;
+} v_struct2, *v_struct_ptr2;
 
 /**** unions *******/
 
@@ -161,7 +161,7 @@ union t_union {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_union;
+} v_union, *v_union_ptr;
 
 union {
     char	v_char_member;
@@ -173,7 +173,7 @@ union {
 #endif
     float	v_float_member;
     double	v_double_member;
-} v_union2;
+} v_union2, *v_union_ptr2;
 
 /*** Functions returning type ********/
 

gdb/testsuite/gdb.base/whatis.exp

@@ -294,6 +294,47 @@ gdb_test "whatis v_struct2" \
     "type = struct \{\.\.\.\}" \
     "whatis unnamed structure"
 
+gdb_test "whatis &v_struct1" \
+    "type = struct t_struct \\*"
+
+gdb_test "whatis &v_struct2" \
+    "type = struct {\\.\\.\\.} \\*"
+
+gdb_test "whatis v_struct_ptr1" \
+    "type = struct t_struct \\*"
+
+gdb_test "whatis v_struct_ptr2" \
+    "type = struct {\\.\\.\\.} \\*"
+
+gdb_test "whatis &v_struct_ptr1" \
+    "type = struct t_struct \\*\\*"
+
+gdb_test "whatis &v_struct_ptr2" \
+    "type = struct {\\.\\.\\.} \\*\\*"
+
+gdb_test "whatis v_struct1.v_char_member" \
+    "type = char"
+
+gdb_test "whatis v_struct2.v_char_member" \
+    "type = char"
+
+gdb_test "whatis v_struct_ptr1->v_char_member" \
+    "type = char"
+
+gdb_test "whatis v_struct_ptr2->v_char_member" \
+    "type = char"
+
+gdb_test "whatis &(v_struct1.v_char_member)" \
+    "type = char \\*"
+
+gdb_test "whatis &(v_struct2.v_char_member)" \
+    "type = char \\*"
+
+gdb_test "whatis &(v_struct_ptr1->v_char_member)" \
+    "type = char \\*"
+
+gdb_test "whatis &(v_struct_ptr2->v_char_member)" \
+    "type = char \\*"
 
 # test whatis command with union types
 gdb_test "whatis v_union" \
@@ -308,6 +349,48 @@ gdb_test "whatis v_union2" \
     "type = union \{\.\.\.\}" \
     "whatis unnamed union"
 
+gdb_test "whatis &v_union" \
+    "type = union t_union \\*"
+
+gdb_test "whatis &v_union2" \
+    "type = union {\\.\\.\\.} \\*"
+
+gdb_test "whatis v_union_ptr" \
+    "type = union t_union \\*"
+
+gdb_test "whatis v_union_ptr2" \
+    "type = union {\\.\\.\\.} \\*"
+
+gdb_test "whatis &v_union_ptr" \
+    "type = union t_union \\*\\*"
+
+gdb_test "whatis &v_union_ptr2" \
+    "type = union {\\.\\.\\.} \\*\\*"
+
+gdb_test "whatis v_union.v_char_member" \
+    "type = char"
+
+gdb_test "whatis v_union2.v_char_member" \
+    "type = char"
+
+gdb_test "whatis v_union_ptr->v_char_member" \
+    "type = char"
+
+gdb_test "whatis v_union_ptr2->v_char_member" \
+    "type = char"
+
+gdb_test "whatis &(v_union.v_char_member)" \
+    "type = char \\*"
+
+gdb_test "whatis &(v_union2.v_char_member)" \
+    "type = char \\*"
+
+gdb_test "whatis &(v_union_ptr->v_char_member)" \
+    "type = char \\*"
+
+gdb_test "whatis &(v_union_ptr2->v_char_member)" \
+    "type = char \\*"
+
 
 # Using stabs we will mark these functions as prototyped.  This
 # is harmless but causes an extra VOID to be printed.