Re: [RFC] [PATCH] Provide the ability to write the frame unwinder in Python

[Andy Wingo <wingo@igalia.com>]

On Tue 17 Mar 2015 22:37, Alexander Smundak <asmundak@google.com> writes:

> +/* The implementation of
> +   gdb.UnwindInfo.set_previous_frame_register (REG, VALUE) -> None.  */
> +
> +static PyObject *
> +unwind_infopy_set_previous_frame_register (PyObject *self, PyObject *args)
> +{
> +  unwind_info_object *unwind_info = (unwind_info_object *) self;
> +  sniffer_info_object *sniffer_info
> +      = (sniffer_info_object *) (unwind_info->sniffer_info);
> +  PyObject *pyo_reg_id;
> +  PyObject *pyo_reg_value;
> +  int regnum;
> +
> +  if (sniffer_info->frame_info == NULL)
> +    {
> +      PyErr_SetString (PyExc_ValueError,
> +                       "Attempting to read register from stale SnifferInfo");
> +      return NULL;
> +    }

Nit: we are setting the register here.

> +int
> +gdbpy_initialize_unwind (void)
> +{
> +  int rc;
> +  add_setshow_zuinteger_cmd
> +      ("py-unwind", class_maintenance, &pyuw_debug,
> +        _("Set Python unwinder debugging."),
> +        _("Show Python unwinder debugging."),
> +        _("When non-zero, Pythin unwinder debugging is enabled."),

"Python"

> +static PyMethodDef sniffer_info_object_methods[] =
> +{
> +  { "read_register", sniffer_infopy_read_register, METH_VARARGS,
> +    "read_register (REGNUM) -> gdb.Value\n"
> +    "Return the value of the REGNUM in the frame." },
> +  { "unwind_info_with_id",
> +    sniffer_infopy_unwind_info_with_id, METH_VARARGS,
> +    "unwind_info_with_id (SP, PC) -> gdb.UnwindInfo\n"
> +    "Construct UnwindInfo for this FrameData, using given SP and PC registers \n"
> +    "to identify the frame." },
> +  { "unwind_info_with_id_special",
> +    sniffer_infopy_unwind_info_with_id_special, METH_VARARGS,
> +    "unwind_info_with_id_special (SP, PC, SPECIAL) -> gdb.UnwindInfo\n"
> +    "Construct UnwindInfo for this FrameData, using given SP, PC, and SPECIAL "
> +    "registers to identify the frame." },
> +  { "unwind_info_with_id_wild",
> +    sniffer_infopy_unwind_info_with_id_wild, METH_VARARGS,
> +    "unwind_info_with_id_wild (SP) ->gdb.UnwindInfo\n"
> +    "Construct UnwindInfo for this FrameData, using given SP register to \n"
> +    "identify the frame." },
> +  {NULL}  /* Sentinel */
> +};

Still no support for register names.

> +import gdb
> +from gdb.sniffer import Sniffer
> +
> +class TestSniffer(Sniffer):

I still think it's much better to call these "unwinders".  You say that
it's the terminology that GDB uses but that's not really the case --
"sniffer" names part of the unwinder interface, which Python and Guile
implement the whole of.  You chose "unwinder" as the documentation
heading and the file name; why introduce a new term to the user?

Andy