RE: [PATCH 08/10] btrace, python: Enable ptwrite listener registration.

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

Hello Felix,

> With this patch a default ptwrite listener is registered upon start of GDB.
> It prints the plain ptwrite payload as hex.  The default listener can be
> overwritten by registering a custom listener in python or by registering
> "None", for no output at all.  Registering a listener function creates per
> thread copies to allow unique internal states per thread.
> 
> 2019-05-29  Felix Willgerodt  <felix.willgerodt@intel.com>
> 
> gdb/ChangeLog:
> 	* btrace.c (ftrace_add_pt): Add call to
> 	apply_ext_lang_ptwrite_listener.
> 	* btrace.h (btrace_thread_info): New member ptw_listener.
> 	* data-directory/Makefile.in: Add ptwrite.py.
> 	* extension-priv.h (struct extension_language_ops): New member
> 	apply_ptwrite_listener.
> 	* extension.c (apply_ext_lang_ptwrite_listener): New function.
> 	* extension.h (apply_ext_lang_ptwrite_listener): New declaration.
> 	* guile/guile.c (guile_extension_ops): Add
> 	gdbscm_load_ptwrite_listener.
> 	* python/lib/gdb/ptwrite.py: New file.
> 	* python/py-record-btrace.c (recpy_initialize_listener,
> 	get_ptwrite_listener): New function.
> 	* python/py-record-btrace.h (recpy_initialize_listener): New
> 	declaration.
> 	* python/py-record.c (gdbpy_load_ptwrite_listener): New function.
> 	* python/python-internal.h (gdbpy_load_ptwrite_listener): New
> 	declaration.
> 	* python/python.c (python_extension_ops): New member
> 	gdbpy_load_ptwrite_listener.
> 
> ---
>  gdb/btrace.c                   |  3 ++
>  gdb/btrace.h                   |  3 ++
>  gdb/data-directory/Makefile.in |  1 +
>  gdb/extension-priv.h           |  4 ++
>  gdb/extension.c                | 24 ++++++++++
>  gdb/extension.h                |  3 ++
>  gdb/guile/guile.c              |  1 +
>  gdb/python/lib/gdb/ptwrite.py  | 83
> ++++++++++++++++++++++++++++++++++
>  gdb/python/py-record-btrace.c  | 40 ++++++++++++++++
>  gdb/python/py-record-btrace.h  |  3 ++
>  gdb/python/py-record.c         | 29 ++++++++++++
>  gdb/python/python-internal.h   |  3 ++
>  gdb/python/python.c            |  2 +
>  13 files changed, 199 insertions(+)
>  create mode 100644 gdb/python/lib/gdb/ptwrite.py

When registering a new PTWRITE listener, could GDB check the libipt version and give
an error if it does not support PTW?

> @@ -1308,6 +1309,8 @@ ftrace_add_pt (struct btrace_thread_info *btinfo,
>    uint64_t offset;
>    int status;
> 
> +  apply_ext_lang_ptwrite_listener (inferior_ptid);

We may decode the trace in chunks by calling ftrace_add_pt () multiple times.
This would need to preserve (the state of) the installed listener.

> @@ -0,0 +1,83 @@
> +# Ptwrite utilities.
> +# Copyright (C) 2018 Free Software Foundation, Inc.

It's 2019, meanwhile.

> +
> +# 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/>.
> +
> +"""Utilities for working with ptwrite listeners."""
> +
> +import gdb
> +from copy import deepcopy
> +
> +
> +def default_listener(payload, ip):

I somehow expected some PtwritePrinter class.

> +    """Default listener that is active upon starting GDB."""
> +    return "payload: {:#x}".format(payload)

Should we return the payload (in hex) without the prefix?

> @@ -735,3 +735,32 @@ gdbpy_stop_recording (PyObject *self, PyObject *args)
> 
>    Py_RETURN_NONE;
>  }
> +
> +/* Used for registering the default ptwrite listener to the current thread.  A
> +   pointer to this function is stored in the python extension interface.  */
> +
> +enum ext_lang_bt_status
> +gdbpy_load_ptwrite_listener (const struct extension_language_defn *extlang,
> +			     ptid_t inferior_ptid)

PTWRITE is very PT specific.  Any chance this could go into py-record-btrace.c?

> +{
> +  struct gdbarch *gdbarch = NULL;
> +
> +  if (!gdb_python_initialized)
> +    return EXT_LANG_BT_NO_FILTERS;
> +
> +  try
> +    {
> +      gdbarch = target_gdbarch ();
> +    }
> +  catch (const gdb_exception &except)
> +    {
> +      /* Let gdb try to print the stack trace.  */
> +      return EXT_LANG_BT_NO_FILTERS;

I fail to understand the comment.

> +    }
> +
> +  gdbpy_enter enter_py (gdbarch, current_language);
> +
> +  recpy_initialize_listener (inferior_ptid);
> +
> +  return EXT_LANG_BT_OK;
> +}

Thanks,
Markus.
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