Re: [PATCH] Allow conversion of 128-bit integers to Python

[Simon Marchi <simark@simark.ca>]

On 9/5/25 9:29 AM, Tom Tromey wrote:
> Currently, trying to convert a 128-bit integer from a gdb.Value to a
> Python integer will fail.  This is surprising because Python uses
> bigints internally.
> 
> The bug here is that valpy_long uses value_as_long, which fails for
> anything wider than LONGEST.  This patch fixes the problem by using
> the recommended Python API.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=33366
> ---
>  gdb/python/py-value.c                 | 41 +++++++++++++++++++++++----
>  gdb/testsuite/gdb.python/py-value.exp | 12 ++++++++
>  2 files changed, 47 insertions(+), 6 deletions(-)
> 
> diff --git a/gdb/python/py-value.c b/gdb/python/py-value.c
> index 833ce26d5a3..973785b5e4a 100644
> --- a/gdb/python/py-value.c
> +++ b/gdb/python/py-value.c
> @@ -1866,7 +1866,7 @@ valpy_long (PyObject *self)
>  {
>    struct value *value = ((value_object *) self)->value;
>    struct type *type = value->type ();
> -  LONGEST l = 0;
> +  PyObject *result;
>  
>    try
>      {
> @@ -1882,17 +1882,46 @@ valpy_long (PyObject *self)
>  	  && type->code () != TYPE_CODE_PTR)
>  	error (_("Cannot convert value to long."));
>  
> -      l = value_as_long (value);
> +      gdb::array_view<const gdb_byte> contents = value->contents ();
> +#if PY_VERSION_HEX >= 0x030d0000
> +      int flags = (type_byte_order (type) == BFD_ENDIAN_BIG
> +		   ? Py_ASNATIVEBYTES_BIG_ENDIAN
> +		   : Py_ASNATIVEBYTES_LITTLE_ENDIAN);
> +      if (type->is_unsigned ())
> +	flags |= Py_ASNATIVEBYTES_UNSIGNED_BUFFER;
> +      result = PyLong_FromNativeBytes (contents.data (), contents.size (),
> +				       flags);
> +#else
> +      /* We need this roundabout approach because int.from_bytes
> +	 requires "signed" to be a keyword arg.  */
> +      gdbpy_ref<> args
> +	(Py_BuildValue ("(y#s)", contents.data (),
> +			(Py_ssize_t) contents.size (),
> +			(type_byte_order (type) == BFD_ENDIAN_BIG
> +			 ? "big" : "little")));
> +      if (args == nullptr)
> +	return nullptr;
> +
> +      gdbpy_ref<> kwargs (Py_BuildValue ("{sO}", "signed",
> +					 type->is_unsigned ()
> +					 ? Py_False : Py_True));
> +      if (kwargs == nullptr)
> +	return nullptr;
> +
> +      gdbpy_ref<> callable (PyObject_GetAttrString ((PyObject *) &PyLong_Type,
> +						    "from_bytes"));
> +      if (callable == nullptr)
> +	return nullptr;

If we are forced to use kwargs, I think we might as well just use kwargs
for all the args.

Can you add some comments above the Python API calls, just to explain at
a high level what this is doing, so that someone who doesn't know the
Python API by heart can follow what is happening?  Something like:

      /* args = (bytes, byteorder) */
      gdbpy_ref<> args
	(Py_BuildValue ("(y#s)", contents.data (),
			(Py_ssize_t) contents.size (),
			(type_byte_order (type) == BFD_ENDIAN_BIG
			 ? "big" : "little")));
      if (args == nullptr)
	return nullptr;

      /* kwargs = {"signed": signed} */
      gdbpy_ref<> kwargs (Py_BuildValue ("{sO}", "signed",
					 type->is_unsigned ()
					 ? Py_False : Py_True));
      if (kwargs == nullptr)
	return nullptr;

      /* Get `int.from_bytes`.  */
      gdbpy_ref<> callable (PyObject_GetAttrString ((PyObject *) &PyLong_Type,
						    "from_bytes"));
      if (callable == nullptr)
	return nullptr;

      /* Call `int.from_byte(*args, **kwargs)`.  */
      result = PyObject_Call (callable.get (), args.get (), kwargs.get ());

Approved-By: Simon Marchi <simon.marchi@efficios.com>

Simon