gdb/python/python-value.c

/* Python interface to values.

   Copyright (C) 2008, 2009 Free Software Foundation, Inc.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "defs.h"
#include "gdb_assert.h"
#include "charset.h"
#include "value.h"
#include "exceptions.h"
#include "language.h"
#include "dfp.h"
#include "valprint.h"

/* List of all values which are currently exposed to Python. It is
   maintained so that when an objfile is discarded, preserve_values
   can copy the values' types if needed.  This is declared
   unconditionally to reduce the number of uses of HAVE_PYTHON in the
   generic code.  */
/* This variable is unnecessarily initialized to NULL in order to 
   work around a linker bug on MacOS.  */
struct value *values_in_python = NULL;

#ifdef HAVE_PYTHON

#include "python-internal.h"

/* Even though Python scalar types directly map to host types, we use
   target types here to remain consistent with the the values system in
   GDB (which uses target arithmetic).  */

/* Python's integer type corresponds to C's long type.  */
#define builtin_type_pyint builtin_type (python_gdbarch)->builtin_long

/* Python's float type corresponds to C's double type.  */
#define builtin_type_pyfloat builtin_type (python_gdbarch)->builtin_double

/* Python's long type corresponds to C's long long type.  */
#define builtin_type_pylong builtin_type (python_gdbarch)->builtin_long_long

#define builtin_type_pybool \
  language_bool_type (python_language, python_gdbarch)

#define builtin_type_pychar \
  language_string_char_type (python_language, python_gdbarch)

typedef struct {
  PyObject_HEAD
  struct value *value;
  PyObject *address;
  PyObject *type;
} value_object;

/* Called by the Python interpreter when deallocating a value object.  */
static void
valpy_dealloc (PyObject *obj)
{
  value_object *self = (value_object *) obj;

  value_remove_from_list (&values_in_python, self->value);

  value_free (self->value);

  if (self->address)
    /* Use braces to appease gcc warning.  *sigh*  */
    {
      Py_DECREF (self->address);
    }

  if (self->type)
    {
      Py_DECREF (self->type);
    }

  self->ob_type->tp_free (self);
}

/* Called when a new gdb.Value object needs to be allocated.  */
static PyObject *
valpy_new (PyTypeObject *subtype, PyObject *args, PyObject *keywords)
{
  struct value *value = NULL;   /* Initialize to appease gcc warning.  */
  value_object *value_obj;

  if (PyTuple_Size (args) != 1)
    {
      PyErr_SetString (PyExc_TypeError, _("Value object creation takes only "
					  "1 argument"));
      return NULL;
    }

  value_obj = (value_object *) subtype->tp_alloc (subtype, 1);
  if (value_obj == NULL)
    {
      PyErr_SetString (PyExc_MemoryError, _("Could not allocate memory to "
					    "create Value object."));
      return NULL;
    }

  value = convert_value_from_python (PyTuple_GetItem (args, 0));
  if (value == NULL)
    {
      subtype->tp_free (value_obj);
      return NULL;
    }

  value_obj->value = value;
  value_obj->address = NULL;
  value_obj->type = NULL;
  release_value (value);
  value_prepend_to_list (&values_in_python, value);

  return (PyObject *) value_obj;
}

/* Given a value of a pointer type, apply the C unary * operator to it.  */
static PyObject *
valpy_dereference (PyObject *self, PyObject *args)
{
  struct value *res_val = NULL;	  /* Initialize to appease gcc warning.  */
  volatile struct gdb_exception except;

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      res_val = value_ind (((value_object *) self)->value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return value_to_value_object (res_val);
}

/* Return "&value".  */
static PyObject *
valpy_get_address (PyObject *self, void *closure)
{
  struct value *res_val = NULL;	  /* Initialize to appease gcc warning.  */
  value_object *val_obj = (value_object *) self;
  volatile struct gdb_exception except;

  if (!val_obj->address)
    {
      TRY_CATCH (except, RETURN_MASK_ALL)
	{
	  res_val = value_addr (val_obj->value);
	}
      if (except.reason < 0)
	{
	  val_obj->address = Py_None;
	  Py_INCREF (Py_None);
	}
      else
	val_obj->address = value_to_value_object (res_val);
    }

  Py_INCREF (val_obj->address);

  return val_obj->address;
}

/* Return type of the value.  */
static PyObject *
valpy_get_type (PyObject *self, void *closure)
{
  value_object *obj = (value_object *) self;
  if (!obj->type)
    {
      obj->type = type_to_type_object (value_type (obj->value));
      if (!obj->type)
	{
	  obj->type = Py_None;
	  Py_INCREF (obj->type);
	}
    }
  Py_INCREF (obj->type);
  return obj->type;
}

/* Implementation of gdb.Value.string ([encoding] [, errors]
   [, length]) -> string.  Return Unicode string with value contents.
   If ENCODING is not given, the string is assumed to be encoded in
   the target's charset.  If LENGTH is provided, only fetch string to
   the length provided.  */

static PyObject *
valpy_string (PyObject *self, PyObject *args, PyObject *kw)
{
  int length = -1, ret = 0;
  gdb_byte *buffer;
  struct value *value = ((value_object *) self)->value;
  volatile struct gdb_exception except;
  PyObject *unicode;
  const char *encoding = NULL;
  const char *errors = NULL;
  const char *user_encoding = NULL;
  const char *la_encoding = NULL;
  static char *keywords[] = { "encoding", "errors", "length" };

  if (!PyArg_ParseTupleAndKeywords (args, kw, "|ssi", keywords,
				    &user_encoding, &errors, &length))
    return NULL;

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      LA_GET_STRING (value, &buffer, &length, &la_encoding);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  encoding = (user_encoding && *user_encoding) ? user_encoding : la_encoding;
  unicode = PyUnicode_Decode (buffer, length, encoding, errors);
  xfree (buffer);

  return unicode;
}

/* Cast a value to a given type.  */
static PyObject *
valpy_cast (PyObject *self, PyObject *args)
{
  PyObject *type_obj;
  struct type *type;
  struct value *res_val = NULL;	  /* Initialize to appease gcc warning.  */
  volatile struct gdb_exception except;

  if (! PyArg_ParseTuple (args, "O", &type_obj))
    return NULL;

  type = type_object_to_type (type_obj);
  if (! type)
    {
      PyErr_SetString (PyExc_RuntimeError, "argument must be a Type");
      return NULL;
    }

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      res_val = value_cast (type, ((value_object *) self)->value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return value_to_value_object (res_val);
}

static Py_ssize_t
valpy_length (PyObject *self)
{
  /* We don't support getting the number of elements in a struct / class.  */
  PyErr_SetString (PyExc_NotImplementedError,
		   "Invalid operation on gdb.Value.");
  return -1;
}

/* Given string name of an element inside structure, return its value
   object.  */
static PyObject *
valpy_getitem (PyObject *self, PyObject *key)
{
  value_object *self_value = (value_object *) self;
  char *field = NULL;
  struct value *res_val = NULL;
  volatile struct gdb_exception except;

  if (gdbpy_is_string (key))
    {  
      field = python_string_to_host_string (key);
      if (field == NULL)
	return NULL;
    }

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      struct value *tmp = self_value->value;

      if (field)
	res_val = value_struct_elt (&tmp, NULL, field, 0, NULL);
      else
	{
	  /* Assume we are attempting an array access, and let the
	     value code throw an exception if the index has an invalid
	     type.  */
	  struct value *idx = convert_value_from_python (key);
	  if (idx != NULL)
	    res_val = value_subscript (tmp, value_as_long (idx));
	}
    }

  xfree (field);
  GDB_PY_HANDLE_EXCEPTION (except);

  return res_val ? value_to_value_object (res_val) : NULL;
}

static int
valpy_setitem (PyObject *self, PyObject *key, PyObject *value)
{
  PyErr_Format (PyExc_NotImplementedError,
		_("Setting of struct elements is not currently supported."));
  return -1;
}

/* Called by the Python interpreter to obtain string representation
   of the object.  */
static PyObject *
valpy_str (PyObject *self)
{
  char *s = NULL;
  long dummy;
  struct ui_file *stb;
  struct cleanup *old_chain;
  PyObject *result;
  struct value_print_options opts;
  volatile struct gdb_exception except;

  get_user_print_options (&opts);
  opts.deref_ref = 0;

  stb = mem_fileopen ();
  old_chain = make_cleanup_ui_file_delete (stb);

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      common_val_print (((value_object *) self)->value, stb, 0,
			&opts, python_language);
      s = ui_file_xstrdup (stb, &dummy);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  do_cleanups (old_chain);

  result = PyUnicode_Decode (s, strlen (s), host_charset (), NULL);
  xfree (s);

  return result;
}

/* Implements gdb.Value.is_optimized_out.  */
static PyObject *
valpy_get_is_optimized_out (PyObject *self, void *closure)
{
  struct value *value = ((value_object *) self)->value;

  if (value_optimized_out (value))
    Py_RETURN_TRUE;

  Py_RETURN_FALSE;
}

enum valpy_opcode
{
  VALPY_ADD,
  VALPY_SUB,
  VALPY_MUL,
  VALPY_DIV,
  VALPY_REM,
  VALPY_POW,
  VALPY_LSH,
  VALPY_RSH,
  VALPY_BITAND,
  VALPY_BITOR,
  VALPY_BITXOR
};

/* If TYPE is a reference, return the target; otherwise return TYPE.  */
#define STRIP_REFERENCE(TYPE) \
  ((TYPE_CODE (TYPE) == TYPE_CODE_REF) ? (TYPE_TARGET_TYPE (TYPE)) : (TYPE))

/* Returns a value object which is the result of applying the operation
   specified by OPCODE to the given arguments.  */
static PyObject *
valpy_binop (enum valpy_opcode opcode, PyObject *self, PyObject *other)
{
  struct value *res_val = NULL;	  /* Initialize to appease gcc warning.  */
  volatile struct gdb_exception except;

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      struct value *arg1, *arg2;

      /* If the gdb.Value object is the second operand, then it will be passed
	 to us as the OTHER argument, and SELF will be an entirely different
	 kind of object, altogether.  Because of this, we can't assume self is
	 a gdb.Value object and need to convert it from python as well.  */
      arg1 = convert_value_from_python (self);
      if (arg1 == NULL)
	break;

      arg2 = convert_value_from_python (other);
      if (arg2 == NULL)
	break;

      switch (opcode)
	{
	case VALPY_ADD:
	  {
	    struct type *ltype = value_type (arg1);
	    struct type *rtype = value_type (arg2);

	    CHECK_TYPEDEF (ltype);
	    ltype = STRIP_REFERENCE (ltype);
	    CHECK_TYPEDEF (rtype);
	    rtype = STRIP_REFERENCE (rtype);

	    if (TYPE_CODE (ltype) == TYPE_CODE_PTR
		&& is_integral_type (rtype))
	      res_val = value_ptradd (arg1, value_as_long (arg2));
	    else if (TYPE_CODE (rtype) == TYPE_CODE_PTR
		     && is_integral_type (ltype))
	      res_val = value_ptradd (arg2, value_as_long (arg1));
	    else
	      res_val = value_binop (arg1, arg2, BINOP_ADD);
	  }
	  break;
	case VALPY_SUB:
	  {
	    struct type *ltype = value_type (arg1);
	    struct type *rtype = value_type (arg2);

	    CHECK_TYPEDEF (ltype);
	    ltype = STRIP_REFERENCE (ltype);
	    CHECK_TYPEDEF (rtype);
	    rtype = STRIP_REFERENCE (rtype);

	    if (TYPE_CODE (ltype) == TYPE_CODE_PTR
		&& TYPE_CODE (rtype) == TYPE_CODE_PTR)
	      /* A ptrdiff_t for the target would be preferable here.  */
	      res_val = value_from_longest (builtin_type_pyint,
					    value_ptrdiff (arg1, arg2));
	    else if (TYPE_CODE (ltype) == TYPE_CODE_PTR
		     && is_integral_type (rtype))
	      res_val = value_ptradd (arg1, - value_as_long (arg2));
	    else
	      res_val = value_binop (arg1, arg2, BINOP_SUB);
	  }
	  break;
	case VALPY_MUL:
	  res_val = value_binop (arg1, arg2, BINOP_MUL);
	  break;
	case VALPY_DIV:
	  res_val = value_binop (arg1, arg2, BINOP_DIV);
	  break;
	case VALPY_REM:
	  res_val = value_binop (arg1, arg2, BINOP_REM);
	  break;
	case VALPY_POW:
	  res_val = value_binop (arg1, arg2, BINOP_EXP);
	  break;
	case VALPY_LSH:
	  res_val = value_binop (arg1, arg2, BINOP_LSH);
	  break;
	case VALPY_RSH:
	  res_val = value_binop (arg1, arg2, BINOP_RSH);
	  break;
	case VALPY_BITAND:
	  res_val = value_binop (arg1, arg2, BINOP_BITWISE_AND);
	  break;
	case VALPY_BITOR:
	  res_val = value_binop (arg1, arg2, BINOP_BITWISE_IOR);
	  break;
	case VALPY_BITXOR:
	  res_val = value_binop (arg1, arg2, BINOP_BITWISE_XOR);
	  break;
	}
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return res_val ? value_to_value_object (res_val) : NULL;
}

static PyObject *
valpy_add (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_ADD, self, other);
}

static PyObject *
valpy_subtract (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_SUB, self, other);
}

static PyObject *
valpy_multiply (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_MUL, self, other);
}

static PyObject *
valpy_divide (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_DIV, self, other);
}

static PyObject *
valpy_remainder (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_REM, self, other);
}

static PyObject *
valpy_power (PyObject *self, PyObject *other, PyObject *unused)
{
  /* We don't support the ternary form of pow.  I don't know how to express
     that, so let's just throw NotImplementedError to at least do something
     about it.  */
  if (unused != Py_None)
    {
      PyErr_SetString (PyExc_NotImplementedError,
		       "Invalid operation on gdb.Value.");
      return NULL;
    }

  return valpy_binop (VALPY_POW, self, other);
}

static PyObject *
valpy_negative (PyObject *self)
{
  struct value *val = NULL;
  volatile struct gdb_exception except;

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      val = value_neg (((value_object *) self)->value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return value_to_value_object (val);
}

static PyObject *
valpy_positive (PyObject *self)
{
  struct value *copy = value_copy (((value_object *) self)->value);

  return value_to_value_object (copy);
}

static PyObject *
valpy_absolute (PyObject *self)
{
  struct value *value = ((value_object *) self)->value;
  if (value_less (value, value_zero (value_type (value), not_lval)))
    return valpy_negative (self);
  else
    return valpy_positive (self);
}

/* Implements boolean evaluation of gdb.Value.  */
static int
valpy_nonzero (PyObject *self)
{
  value_object *self_value = (value_object *) self;
  struct type *type;

  type = check_typedef (value_type (self_value->value));

  if (is_integral_type (type) || TYPE_CODE (type) == TYPE_CODE_PTR)
    return !!value_as_long (self_value->value);
  else if (TYPE_CODE (type) == TYPE_CODE_FLT)
    return value_as_double (self_value->value) != 0;
  else if (TYPE_CODE (type) == TYPE_CODE_DECFLOAT)
    return !decimal_is_zero (value_contents (self_value->value),
			     TYPE_LENGTH (type),
			     gdbarch_byte_order (get_type_arch (type)));
  else
    {
      PyErr_SetString (PyExc_TypeError, _("Attempted truth testing on invalid "
					  "gdb.Value type."));
      return 0;
    }
}

/* Implements ~ for value objects.  */
static PyObject *
valpy_invert (PyObject *self)
{
  struct value *val = NULL;
  volatile struct gdb_exception except;

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      val = value_complement (((value_object *) self)->value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return value_to_value_object (val);
}

/* Implements left shift for value objects.  */
static PyObject *
valpy_lsh (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_LSH, self, other);
}

/* Implements right shift for value objects.  */
static PyObject *
valpy_rsh (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_RSH, self, other);
}

/* Implements bitwise and for value objects.  */
static PyObject *
valpy_and (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_BITAND, self, other);
}

/* Implements bitwise or for value objects.  */
static PyObject *
valpy_or (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_BITOR, self, other);
}

/* Implements bitwise xor for value objects.  */
static PyObject *
valpy_xor (PyObject *self, PyObject *other)
{
  return valpy_binop (VALPY_BITXOR, self, other);
}

/* Implements comparison operations for value objects.  */
static PyObject *
valpy_richcompare (PyObject *self, PyObject *other, int op)
{
  int result = 0;
  struct value *value_other;
  volatile struct gdb_exception except;

  if (other == Py_None)
    /* Comparing with None is special.  From what I can tell, in Python
       None is smaller than anything else.  */
    switch (op) {
      case Py_LT:
      case Py_LE:
      case Py_EQ:
	Py_RETURN_FALSE;
      case Py_NE:
      case Py_GT:
      case Py_GE:
	Py_RETURN_TRUE;
      default:
	/* Can't happen.  */
	PyErr_SetString (PyExc_NotImplementedError,
			 "Invalid operation on gdb.Value.");
	return NULL;
    }

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      value_other = convert_value_from_python (other);
      if (value_other == NULL)
	return NULL;

      switch (op) {
        case Py_LT:
	  result = value_less (((value_object *) self)->value, value_other);
	  break;
	case Py_LE:
	  result = value_less (((value_object *) self)->value, value_other)
	    || value_equal (((value_object *) self)->value, value_other);
	  break;
	case Py_EQ:
	  result = value_equal (((value_object *) self)->value, value_other);
	  break;
	case Py_NE:
	  result = !value_equal (((value_object *) self)->value, value_other);
	  break;
        case Py_GT:
	  result = value_less (value_other, ((value_object *) self)->value);
	  break;
	case Py_GE:
	  result = value_less (value_other, ((value_object *) self)->value)
	    || value_equal (((value_object *) self)->value, value_other);
	  break;
	default:
	  /* Can't happen.  */
	  PyErr_SetString (PyExc_NotImplementedError,
			   "Invalid operation on gdb.Value.");
	  return NULL;
      }
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  if (result == 1)
    Py_RETURN_TRUE;

  Py_RETURN_FALSE;
}

/* Helper function to determine if a type is "int-like".  */
static int
is_intlike (struct type *type, int ptr_ok)
{
  CHECK_TYPEDEF (type);
  return (TYPE_CODE (type) == TYPE_CODE_INT
	  || TYPE_CODE (type) == TYPE_CODE_ENUM
	  || TYPE_CODE (type) == TYPE_CODE_BOOL
	  || TYPE_CODE (type) == TYPE_CODE_CHAR
	  || (ptr_ok && TYPE_CODE (type) == TYPE_CODE_PTR));
}

/* Implements conversion to int.  */
static PyObject *
valpy_int (PyObject *self)
{
  struct value *value = ((value_object *) self)->value;
  struct type *type = value_type (value);
  LONGEST l = 0;
  volatile struct gdb_exception except;

  CHECK_TYPEDEF (type);
  if (!is_intlike (type, 0))
    {
      PyErr_SetString (PyExc_RuntimeError, "cannot convert value to int");
      return NULL;
    }

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      l = value_as_long (value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return PyInt_FromLong (l);
}

/* Implements conversion to long.  */
static PyObject *
valpy_long (PyObject *self)
{
  struct value *value = ((value_object *) self)->value;
  struct type *type = value_type (value);
  LONGEST l = 0;
  volatile struct gdb_exception except;

  if (!is_intlike (type, 1))
    {
      PyErr_SetString (PyExc_RuntimeError, "cannot convert value to long");
      return NULL;
    }

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      l = value_as_long (value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return PyLong_FromLong (l);
}

/* Implements conversion to float.  */
static PyObject *
valpy_float (PyObject *self)
{
  struct value *value = ((value_object *) self)->value;
  struct type *type = value_type (value);
  double d = 0;
  volatile struct gdb_exception except;

  CHECK_TYPEDEF (type);
  if (TYPE_CODE (type) != TYPE_CODE_FLT)
    {
      PyErr_SetString (PyExc_RuntimeError, "cannot convert value to float");
      return NULL;
    }

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      d = value_as_double (value);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return PyFloat_FromDouble (d);
}

/* Returns an object for a value which is released from the all_values chain,
   so its lifetime is not bound to the execution of a command.  */
PyObject *
value_to_value_object (struct value *val)
{
  value_object *val_obj;

  val_obj = PyObject_New (value_object, &value_object_type);
  if (val_obj != NULL)
    {
      val_obj->value = val;
      val_obj->address = NULL;
      val_obj->type = NULL;
      release_value (val);
      value_prepend_to_list (&values_in_python, val);
    }

  return (PyObject *) val_obj;
}

/* Returns value structure corresponding to the given value object.  */
struct value *
value_object_to_value (PyObject *self)
{
  value_object *real;
  if (! PyObject_TypeCheck (self, &value_object_type))
    return NULL;
  real = (value_object *) self;
  return real->value;
}

/* Try to convert a Python value to a gdb value.  If the value cannot
   be converted, set a Python exception and return NULL.  */

struct value *
convert_value_from_python (PyObject *obj)
{
  struct value *value = NULL; /* -Wall */
  PyObject *target_str, *unicode_str;
  struct cleanup *old;
  volatile struct gdb_exception except;
  int cmp;

  gdb_assert (obj != NULL);

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      if (PyBool_Check (obj)) 
	{
	  cmp = PyObject_IsTrue (obj);
	  if (cmp >= 0)
	    value = value_from_longest (builtin_type_pybool, cmp);
	}
      else if (PyInt_Check (obj))
	{
	  long l = PyInt_AsLong (obj);

	  if (! PyErr_Occurred ())
	    value = value_from_longest (builtin_type_pyint, l);
	}
      else if (PyLong_Check (obj))
	{
	  LONGEST l = PyLong_AsLongLong (obj);

	  if (! PyErr_Occurred ())
	    value = value_from_longest (builtin_type_pylong, l);
	}
      else if (PyFloat_Check (obj))
	{
	  double d = PyFloat_AsDouble (obj);

	  if (! PyErr_Occurred ())
	    value = value_from_double (builtin_type_pyfloat, d);
	}
      else if (gdbpy_is_string (obj))
	{
	  char *s;

	  s = python_string_to_target_string (obj);
	  if (s != NULL)
	    {
	      old = make_cleanup (xfree, s);
	      value = value_cstring (s, strlen (s), builtin_type_pychar);
	      do_cleanups (old);
	    }
	}
      else if (PyObject_TypeCheck (obj, &value_object_type))
	value = value_copy (((value_object *) obj)->value);
      else
	PyErr_Format (PyExc_TypeError, _("Could not convert Python object: %s"),
		      PyString_AsString (PyObject_Str (obj)));
    }
  if (except.reason < 0)
    {
      PyErr_Format (except.reason == RETURN_QUIT
		    ? PyExc_KeyboardInterrupt : PyExc_RuntimeError,
		    "%s", except.message);
      return NULL;
    }

  return value;
}

/* Returns value object in the ARGth position in GDB's history.  */
PyObject *
gdbpy_history (PyObject *self, PyObject *args)
{
  int i;
  struct value *res_val = NULL;	  /* Initialize to appease gcc warning.  */
  volatile struct gdb_exception except;

  if (!PyArg_ParseTuple (args, "i", &i))
    return NULL;

  TRY_CATCH (except, RETURN_MASK_ALL)
    {
      res_val = access_value_history (i);
    }
  GDB_PY_HANDLE_EXCEPTION (except);

  return value_to_value_object (res_val);
}

void
gdbpy_initialize_values (void)
{
  if (PyType_Ready (&value_object_type) < 0)
    return;

  Py_INCREF (&value_object_type);
  PyModule_AddObject (gdb_module, "Value", (PyObject *) &value_object_type);

  values_in_python = NULL;
}



static PyGetSetDef value_object_getset[] = {
  { "address", valpy_get_address, NULL, "The address of the value.",
    NULL },
  { "is_optimized_out", valpy_get_is_optimized_out, NULL,
    "Boolean telling whether the value is optimized out (i.e., not available).",
    NULL },
  { "type", valpy_get_type, NULL, "Type of the value.", NULL },
  {NULL}  /* Sentinel */
};

static PyMethodDef value_object_methods[] = {
  { "cast", valpy_cast, METH_VARARGS, "Cast the value to the supplied type." },
  { "dereference", valpy_dereference, METH_NOARGS, "Dereferences the value." },
  { "string", (PyCFunction) valpy_string, METH_VARARGS | METH_KEYWORDS,
    "string ([encoding] [, errors] [, length]) -> string\n\
Return Unicode string representation of the value." },
  {NULL}  /* Sentinel */
};

static PyNumberMethods value_object_as_number = {
  valpy_add,
  valpy_subtract,
  valpy_multiply,
  valpy_divide,
  valpy_remainder,
  NULL,			      /* nb_divmod */
  valpy_power,		      /* nb_power */
  valpy_negative,	      /* nb_negative */
  valpy_positive,	      /* nb_positive */
  valpy_absolute,	      /* nb_absolute */
  valpy_nonzero,	      /* nb_nonzero */
  valpy_invert,		      /* nb_invert */
  valpy_lsh,		      /* nb_lshift */
  valpy_rsh,		      /* nb_rshift */
  valpy_and,		      /* nb_and */
  valpy_xor,		      /* nb_xor */
  valpy_or,		      /* nb_or */
  NULL,			      /* nb_coerce */
  valpy_int,		      /* nb_int */
  valpy_long,		      /* nb_long */
  valpy_float,		      /* nb_float */
  NULL,			      /* nb_oct */
  NULL			      /* nb_hex */
};

static PyMappingMethods value_object_as_mapping = {
  valpy_length,
  valpy_getitem,
  valpy_setitem
};

PyTypeObject value_object_type = {
  PyObject_HEAD_INIT (NULL)
  0,				  /*ob_size*/
  "gdb.Value",			  /*tp_name*/
  sizeof (value_object),	  /*tp_basicsize*/
  0,				  /*tp_itemsize*/
  valpy_dealloc,		  /*tp_dealloc*/
  0,				  /*tp_print*/
  0,				  /*tp_getattr*/
  0,				  /*tp_setattr*/
  0,				  /*tp_compare*/
  0,				  /*tp_repr*/
  &value_object_as_number,	  /*tp_as_number*/
  0,				  /*tp_as_sequence*/
  &value_object_as_mapping,	  /*tp_as_mapping*/
  0,				  /*tp_hash */
  0,				  /*tp_call*/
  valpy_str,			  /*tp_str*/
  0,				  /*tp_getattro*/
  0,				  /*tp_setattro*/
  0,				  /*tp_as_buffer*/
  Py_TPFLAGS_DEFAULT | Py_TPFLAGS_CHECKTYPES,	/*tp_flags*/
  "GDB value object",		  /* tp_doc */
  0,				  /* tp_traverse */
  0,				  /* tp_clear */
  valpy_richcompare,		  /* tp_richcompare */
  0,				  /* tp_weaklistoffset */
  0,				  /* tp_iter */
  0,				  /* tp_iternext */
  value_object_methods,		  /* tp_methods */
  0,				  /* tp_members */
  value_object_getset,		  /* tp_getset */
  0,				  /* tp_base */
  0,				  /* tp_dict */
  0,				  /* tp_descr_get */
  0,				  /* tp_descr_set */
  0,				  /* tp_dictoffset */
  0,				  /* tp_init */
  0,				  /* tp_alloc */
  valpy_new			  /* tp_new */
};

#endif /* HAVE_PYTHON */