Re: [Patch] PR python/15464 and python/16113

[Siva Chandra <sivachandra@google.com>]

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Attached is a newer version of the patch which an 'xfree' moved to a
more appropriate place.

2013-12-30  Siva Chandra Reddy  <sivachandra@google.com>

        PR python/15464
        PR python/16133
        * valops.c (value_struct_elt_bitpos): New function
        * python/py-value.c (valpy_getitem): Use 'bitpos' attribute to
        look for a field when 'name' is 'None' or empty.

        testsuite/
        * gdb.python/py-value-cc.cc: Enhance test case.
        * gdb.python/py-value-cc.exp: Add new tests.

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diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
index df25179..69194b0 100644
--- a/gdb/python/py-value.c
+++ b/gdb/python/py-value.c
@@ -573,6 +573,7 @@ valpy_getitem (PyObject *self, PyObject *key)
   value_object *self_value = (value_object *) self;
   char *field = NULL;
   PyObject *base_class_type_object = NULL;
+  long bitpos = -1;
   volatile struct gdb_exception except;
   PyObject *result = NULL;
 
@@ -614,10 +615,41 @@ valpy_getitem (PyObject *self, PyObject *key)
 	  if (name_obj == NULL)
 	    return NULL;
 
-	  field = python_string_to_host_string (name_obj);
-	  Py_DECREF (name_obj);
-	  if (field == NULL)
-	    return NULL;
+	  if (name_obj != Py_None)
+	    {
+	      field = python_string_to_host_string (name_obj);
+	      Py_DECREF (name_obj);
+	      name_obj = NULL;
+	      if (field == NULL)
+		return NULL;
+	    }
+
+	  if (name_obj == Py_None || field[0] == '\0')
+	    {
+	      PyObject *bitpos_obj;
+	      int valid;
+
+	      Py_XDECREF (name_obj);
+	      xfree (field);
+	      field = NULL;
+
+	      if (!PyObject_HasAttrString (key, "bitpos"))
+		{
+		  PyErr_SetString (PyExc_AttributeError,
+				   _("gdb.Field object has no name and no "
+                                     "'bitpos' attribute."));
+
+		  return NULL;
+		}
+	      bitpos_obj = PyObject_GetAttrString (key, "bitpos");
+	      if (bitpos_obj == NULL)
+		return NULL;
+
+	      valid = gdb_py_int_as_long (bitpos_obj, &bitpos);
+	      Py_DECREF (bitpos_obj);
+	      if (!valid)
+		return NULL;
+	    }
 	}
     }
 
@@ -629,6 +661,8 @@ valpy_getitem (PyObject *self, PyObject *key)
 
       if (field)
 	res_val = value_struct_elt (&tmp, NULL, field, 0, NULL);
+      else if (bitpos >= 0)
+	res_val = value_struct_elt_bitpos (&tmp, bitpos, "struct/class/union");
       else if (base_class_type_object != NULL)
 	{
 	  struct type *base_class_type, *val_type;
diff --git a/gdb/testsuite/gdb.python/py-value-cc.cc b/gdb/testsuite/gdb.python/py-value-cc.cc
index 80094ec..8b9aa5a 100644
--- a/gdb/testsuite/gdb.python/py-value-cc.cc
+++ b/gdb/testsuite/gdb.python/py-value-cc.cc
@@ -30,8 +30,15 @@ class B : public A {
   char a;
 };
 
+struct X
+{
+  union { int x; char y; };
+  union { int a; char b; };
+};
+
 typedef B Btd;
 typedef int *int_ptr;
+typedef X Xtd;
 
 int
 func (const A &a)
@@ -57,6 +64,13 @@ func (const A &a)
   U u;
   u.a = 99;
 
+  X x;
+  x.x = 101;
+  x.a = 102;
+
+  X *x_ptr = &x;
+  Xtd *xtd = &x;
+
   return 0; /* Break here.  */
 }
 
diff --git a/gdb/testsuite/gdb.python/py-value-cc.exp b/gdb/testsuite/gdb.python/py-value-cc.exp
index eacaf2e..08dc462 100644
--- a/gdb/testsuite/gdb.python/py-value-cc.exp
+++ b/gdb/testsuite/gdb.python/py-value-cc.exp
@@ -53,6 +53,12 @@ gdb_test_no_output "python b_ref = gdb.parse_and_eval('b_ref')" "init b_ref"
 gdb_test_no_output "python b_td = gdb.parse_and_eval('b_td')" "init b_td"
 gdb_test_no_output "python u = gdb.parse_and_eval('u')" "init u"
 gdb_test_no_output "python u_fields = u.type.fields()" "init u_fields"
+gdb_test_no_output "python x = gdb.parse_and_eval('x')" "init x"
+gdb_test_no_output "python x_fields = x.type.fields()" "init x_fields"
+gdb_test_no_output "python x_ptr = gdb.parse_and_eval('x_ptr')" "init x_ptr"
+gdb_test_no_output "python xtd = gdb.parse_and_eval('xtd')" "init xtd"
+
+gdb_test "python print(b\[b_fields\[1\]\])" "97 'a'" "b.a via field"
 
 gdb_test "python print(b\[b_fields\[1\]\])" "97 'a'" "b.a via field"
 gdb_test "python print(b\[b_fields\[0\]\].type)" "A" \
@@ -79,3 +85,11 @@ gdb_test "python print(b_td\[b_fields\[0\]\]\['a'\])" "100" \
 
 gdb_test "python print(u\[u_fields\[0\]\])" "99.*" "u's first field via field"
 gdb_test "python print(u\[u_fields\[1\]\])" "99.*" "u's second field via field"
+
+gdb_test "python print len(x_fields)" "2" "number for fields in u"
+gdb_test "python print x\[x_fields\[0\]\]\['x'\]" "101" "x.x via field"
+gdb_test "python print x\[x_fields\[1\]\]\['a'\]" "102" "x.a via field"
+gdb_test "python print x_ptr\[x_fields\[0\]\]\['x'\]" "101" "x_ptr->x via field"
+gdb_test "python print x_ptr\[x_fields\[1\]\]\['a'\]" "102" "x_ptr->a via field"
+gdb_test "python print xtd\[x_fields\[0\]\]\['x'\]" "101" "xtd->x via field"
+gdb_test "python print xtd\[x_fields\[1\]\]\['a'\]" "102" "xtd->a via field"
diff --git a/gdb/valops.c b/gdb/valops.c
index d43c758..f147854 100644
--- a/gdb/valops.c
+++ b/gdb/valops.c
@@ -2248,6 +2248,49 @@ value_struct_elt (struct value **argp, struct value **args,
   return v;
 }
 
+/* Given *ARGP, a value of type structure or union, or a pointer/reference
+   to a structure or union, extract and return its component (field) at the
+   specified BITPOS.
+   Returns NULL if BITPOS is invalid.  */
+
+struct value *
+value_struct_elt_bitpos (struct value **argp, int bitpos, const char *err)
+{
+  struct type *t;
+  struct value *v;
+  int i;
+  int nbases;
+
+  *argp = coerce_array (*argp);
+
+  t = check_typedef (value_type (*argp));
+
+  while (TYPE_CODE (t) == TYPE_CODE_PTR || TYPE_CODE (t) == TYPE_CODE_REF)
+    {
+      *argp = value_ind (*argp);
+      if (TYPE_CODE (check_typedef (value_type (*argp))) != TYPE_CODE_FUNC)
+	*argp = coerce_array (*argp);
+      t = check_typedef (value_type (*argp));
+    }
+
+  if (TYPE_CODE (t) != TYPE_CODE_STRUCT
+      && TYPE_CODE (t) != TYPE_CODE_UNION)
+    error (_("Attempt to extract a component of a value that is not a %s."),
+	   err);
+
+  for (i = TYPE_N_BASECLASSES (t); i < TYPE_NFIELDS (t); i++)
+    {
+      if (!field_is_static (&TYPE_FIELD (t, i))
+	  && bitpos == TYPE_FIELD_BITPOS (t, i))
+	return value_primitive_field (*argp, 0, i, t);
+    }
+
+  error (_("Attempt to extract a component with an invalid bitpos."));
+
+  /* Never hit.  */
+  return NULL;
+}
+
 /* Search through the methods of an object (and its bases) to find a
    specified method.  Return the pointer to the fn_field list of
    overloaded instances.
diff --git a/gdb/value.h b/gdb/value.h
index 6b158df..a279803 100644
--- a/gdb/value.h
+++ b/gdb/value.h
@@ -670,6 +670,10 @@ extern struct value *value_struct_elt (struct value **argp,
 				       const char *name, int *static_memfuncp,
 				       const char *err);
 
+extern struct value *value_struct_elt_bitpos (struct value **argp,
+					      int bitpos,
+					      const char *err);
+
 extern struct value *value_aggregate_elt (struct type *curtype,
 					  char *name,
 					  struct type *expect_type,