Re: [PATCH v2 10/11] [PR gdb/14441] gdb: python: support rvalue references in the gdb module

[Keith Seitz <keiths at redhat dot com>]

On 01/19/2016 10:53 AM, Artemiy Volkov wrote:
> This patch adds the ability to inspect rvalue reference types and values using
> the gdb python module. Changes include the RvalueReferenceExplorer method
> providing mechanism to get a type and a referenced value for an rvalue
> reference object, and the valpy_rvalue_reference_value() function used
> to create an rvalue reference to an object of any type.
> 
> ./ChangeLog:
> 
> 2016-01-19  Artemiy Volkov  <artemiyv@acm.org>
> 
>         * gdb/python/lib/gdb/command/explore.py: Add
>         RvalueReferenceExplorer class.

The usual way to do this would be to mention the class first:

	* python/lib/gdb/command/explore.py
	(RvalueReferenceExplorer): New class.

But more on this later...

>         * gdb/python/lib/gdb/types.py: Implement get_basic_type() for
>         rvalue reference types.

Similarly,

	* python/lib/gdb/types.py (get_basic_type): Handle
	TYPE_CODE_RVALUE_REFERENCE.

>         * gdb/python/py-type.c: Add TYPE_CODE_RVALUE_REF to pyty_codes.

I would do the same here, too.

>         * gdb/python/py-value.c (valpy_rvalue_reference_value): Add value
>         getter function.
> ---
>  gdb/python/lib/gdb/command/explore.py | 21 +++++++++++++++++++++
>  gdb/python/lib/gdb/types.py           |  4 +++-
>  gdb/python/py-type.c                  |  1 +
>  gdb/python/py-value.c                 | 26 ++++++++++++++++++++++++++
>  4 files changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/gdb/python/lib/gdb/command/explore.py b/gdb/python/lib/gdb/command/explore.py
> index 6c9f17b..a980274 100644
> --- a/gdb/python/lib/gdb/command/explore.py
> +++ b/gdb/python/lib/gdb/command/explore.py
> @@ -318,6 +319,26 @@ class ReferenceExplorer(object):
>          Explorer.explore_type(name, target_type, is_child)
>          return False
>  
> +class RvalueReferenceExplorer(object):
> +    """Internal class used to explore rvalue reference (TYPE_CODE_RVALUE_REF) values."""
> +
> +    @staticmethod
> +    def explore_expr(expr, value, is_child):
> +        """Function to explore array values.
> +        See Explorer.explore_expr for more information.
> +        """
> +        referenced_value = value.referenced_value()
> +        Explorer.explore_expr(expr, referenced_value, is_child)
> +        return False
> +
> +    @staticmethod
> +    def explore_type(name, datatype, is_child):
> +        """Function to explore pointer types.
> +        See Explorer.explore_type for more information.
> +        """
> +        target_type = datatype.target()
> +        Explorer.explore_type(name, target_type, is_child)
> +        return False

I'm not all that familiar with python, but is there a reason for this to
be a new class? It looks identical to ReferenceExplorer?

>  class ArrayExplorer(object):
>      """Internal class used to explore arrays."""
> diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
> index 81d1225..dcc0cf9 100644
> --- a/gdb/python/py-value.c
> +++ b/gdb/python/py-value.c
> @@ -263,6 +263,30 @@ valpy_reference_value (PyObject *self, PyObject *args)
>    return result;
>  }
>  
> +/* Return a value which is an rvalue reference to the value.  */
> +
> +static PyObject *
> +valpy_rvalue_reference_value (PyObject *self, PyObject *args)
> +{
> +  PyObject *result = NULL;
> +
> +  TRY
> +    {
> +      struct value *self_val;
> +      struct cleanup *cleanup = make_cleanup_value_free_to_mark (value_mark ());
> +
> +      self_val = ((value_object *) self)->value;
> +      result = value_to_value_object (value_ref (self_val, TYPE_CODE_RVALUE_REF));
> +      do_cleanups (cleanup);
> +    }
> +  CATCH (except, RETURN_MASK_ALL)
> +    {
> +      GDB_PY_HANDLE_EXCEPTION (except);
> +    }
> +  END_CATCH
> +
> +  return result;
> +}
>  /* Return a "const" qualified version of the value.  */
>  
>  static PyObject *
> @@ -1778,6 +1802,8 @@ reinterpret_cast operator."
>      "Return the value referenced by a TYPE_CODE_REF or TYPE_CODE_PTR value." },
>    { "reference_value", valpy_reference_value, METH_NOARGS,
>      "Return a value of type TYPE_CODE_REF referencing this value." },
> +  { "rvalue_reference_value", valpy_rvalue_reference_value, METH_NOARGS,
> +    "Return a value of type TYPE_CODE_RVALUE_REF referencing this value." },
>    { "const_value", valpy_const_value, METH_NOARGS,
>      "Return a 'const' qualied version of the same value." },
>    { "lazy_string", (PyCFunction) valpy_lazy_string,

Same question here...

rvalue_reference_value/valpy_rvalue_reference_value have nearly
identical implementations as reference_value/valpy_reference_value.

Does TYPE_CODE (value_type (self_val)) not tell us which of the types we
are looking at? If so, I think it would be better to unify reference
handling into a common implementation, noting that the class handles
both types of references.

Keith