RE: [PATCH 09/10] btrace, python: Enable calling the ptwrite listener.

["Metzger, Markus T" <markus dot t dot metzger at intel dot com>]

Hello Felix,

> diff --git a/gdb/btrace.h b/gdb/btrace.h
> index 7a80f5a44e1..7ad3cb65a28 100644
> --- a/gdb/btrace.h
> +++ b/gdb/btrace.h
> @@ -354,6 +354,14 @@ struct btrace_thread_info
>       stepping through the execution history.  */
>    std::vector<std::string> aux_data;
> 
> +  /* Function pointer to the ptwrite callback.  Returns the string returned
> +     by the ptwrite listener function or nullptr if no string is supposed to
> +     be printed.  */
> +  gdb::unique_xmalloc_ptr<char> (*ptw_callback_fun) (
> +						const uint64_t *payload,
> +						const uint64_t *ip,
> +						const void *ptw_listener);
> +
>    /* PyObject pointer to the ptwrite listener function.  */
>    void *ptw_listener = nullptr;
> 
> diff --git a/gdb/python/py-record-btrace.c b/gdb/python/py-record-btrace.c
> index c7ad47d64a0..42a0c29a348 100644
> --- a/gdb/python/py-record-btrace.c
> +++ b/gdb/python/py-record-btrace.c
> @@ -772,6 +772,68 @@ recpy_bt_function_call_history (PyObject *self, void
> *closure)
>    return btpy_list_new (tinfo, first, last, 1, &recpy_func_type);
>  }
> 
> +/* Calling the ptwrite listener.  Returns a pointer to the string that will be
> +   printed or nullptr if nothing should be printed.  */
> +gdb::unique_xmalloc_ptr<char>
> +recpy_call_listener (const uint64_t *payload, const uint64_t *ip,
> +		     const void *ptw_listener)
> +{
> +  if ((PyObject *) ptw_listener == Py_None)
> +    return nullptr;
> +  else if ((PyObject *) ptw_listener == nullptr)
> +    error (_("No valid ptwrite listener."));

PTW_LISTENER is declared void * in struct btrace_info.  Couldn't we treat nullptr
as not-present?

> +
> +  /* As Python is started as a seperate thread, we need to
> +     acquire the GIL to safely call the listener function.  */
> +  PyGILState_STATE gstate = PyGILState_Ensure ();
> +
> +  PyObject *py_ip = Py_None;
> +  PyObject *py_payload = PyLong_FromUnsignedLongLong (*payload);
> +  Py_INCREF (Py_None);

Are we dropping that reference again in the case that PY_IP gets overwritten?

> +
> +  if (ip != nullptr)
> +    py_ip = PyLong_FromUnsignedLongLong (*ip);

It wouldn't hurt to document that IP can be NULL whereas PAYLOAD cannot
in the function's comment.

> +
> +  PyObject *py_result = PyObject_CallFunctionObjArgs ((PyObject *)
> ptw_listener,
> +						      py_payload, py_ip, NULL);
> +
> +  if (PyErr_Occurred ())
> +    {
> +      gdbpy_print_stack ();
> +      gdb_Py_DECREF (py_ip);
> +      gdb_Py_DECREF (py_payload);
> +      gdb_Py_DECREF (py_result);
> +      PyGILState_Release (gstate);
> +      error (_("Error while executing Python code."));
> +    }
> +
> +  gdb_Py_DECREF (py_ip);
> +  gdb_Py_DECREF (py_payload);
> +
> +  if (py_result == Py_None)
> +    {
> +      gdb_Py_DECREF (py_result);
> +      PyGILState_Release (gstate);
> +      return nullptr;
> +    }
> +
> +  gdb::unique_xmalloc_ptr<char> resultstring = gdbpy_obj_to_string
> (py_result);
> +
> +  if (PyErr_Occurred ())
> +    {
> +      gdbpy_print_stack ();
> +      gdb_Py_DECREF (py_result);
> +      PyGILState_Release (gstate);
> +      error (_("Error while executing Python code."));
> +    }
> +
> +  if (py_result != nullptr)
> +    gdb_Py_DECREF (py_result);

Shouldn't we check that before using PY_RESULT above?

> +  PyGILState_Release (gstate);
> +
> +  return resultstring;
> +}
> +
>  /* Helper function returning the current ptwrite listener.  Returns nullptr
>     in case of errors.  */
> 
> @@ -807,6 +869,7 @@ recpy_initialize_listener (ptid_t inferior_ptid)
> 
>    gdb_assert (tinfo != nullptr);
> 
> +  tinfo->btrace.ptw_callback_fun = &recpy_call_listener;
>    tinfo->btrace.ptw_listener = get_ptwrite_listener ();
> 
>    return (PyObject *) tinfo->btrace.ptw_listener;
> --
> 2.20.1

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