Re: [PATCH v2 09/12] btrace, python: Enable ptwrite listener registration.

[Lancelot SIX <lsix@lancelotsix.com>]

Hi

I have few remarks later in the patch.

On Mon, Jun 14, 2021 at 04:54:08PM +0200, Felix Willgerodt via Gdb-patches wrote:
> 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.
> 
> gdb/ChangeLog:
> 2021-06-14  Felix Willgerodt  <felix.willgerodt@intel.com>
> 
> 	* 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                | 21 +++++++++
>  gdb/extension.h                |  3 ++
>  gdb/guile/guile.c              |  1 +
>  gdb/python/lib/gdb/ptwrite.py  | 86 ++++++++++++++++++++++++++++++++++
>  gdb/python/py-record-btrace.c  | 67 ++++++++++++++++++++++++++
>  gdb/python/py-record-btrace.h  |  6 +++
>  gdb/python/python-internal.h   |  3 ++
>  gdb/python/python.c            |  2 +
>  12 files changed, 200 insertions(+)
>  create mode 100644 gdb/python/lib/gdb/ptwrite.py
> 
> diff --git a/gdb/btrace.c b/gdb/btrace.c
> index 2c4f3f67c6b..d66c3e21f11 100644
> --- a/gdb/btrace.c
> +++ b/gdb/btrace.c
> @@ -34,6 +34,7 @@
>  #include "gdbsupport/rsp-low.h"
>  #include "gdbcmd.h"
>  #include "cli/cli-utils.h"
> +#include "extension.h"
>  #include "gdbarch.h"
>  
>  /* For maintenance commands.  */
> @@ -1311,6 +1312,8 @@ ftrace_add_pt (struct btrace_thread_info *btinfo,
>    uint64_t offset;
>    int status;
>  
> +  apply_ext_lang_ptwrite_listener (inferior_ptid);
> +
>    for (;;)
>      {
>        struct pt_insn insn;
> diff --git a/gdb/btrace.h b/gdb/btrace.h
> index e6694551c70..b15efcd147c 100644
> --- a/gdb/btrace.h
> +++ b/gdb/btrace.h
> @@ -352,6 +352,9 @@ struct btrace_thread_info
>       stepping through the execution history.  */
>    std::vector<std::string> aux_data;
>  
> +  /* PyObject pointer to the ptwrite listener function.  */
> +  void *ptw_listener = nullptr;
> +
>    /* The function level offset.  When added to each function's LEVEL,
>       this normalizes the function levels such that the smallest level
>       becomes zero.  */
> diff --git a/gdb/data-directory/Makefile.in b/gdb/data-directory/Makefile.in
> index 888325f974e..c759920a343 100644
> --- a/gdb/data-directory/Makefile.in
> +++ b/gdb/data-directory/Makefile.in
> @@ -74,6 +74,7 @@ PYTHON_FILE_LIST = \
>  	gdb/frames.py \
>  	gdb/printing.py \
>  	gdb/prompt.py \
> +	gdb/ptwrite.py \
>  	gdb/types.py \
>  	gdb/unwinder.py \
>  	gdb/xmethod.py \
> diff --git a/gdb/extension-priv.h b/gdb/extension-priv.h
> index 77f23e0f911..36da4211738 100644
> --- a/gdb/extension-priv.h
> +++ b/gdb/extension-priv.h
> @@ -183,6 +183,10 @@ struct extension_language_ops
>       enum ext_lang_frame_args args_type,
>       struct ui_out *out, int frame_low, int frame_high);
>  
> +  /* Used for registering the ptwrite listener to the current thread.  */
> +  enum ext_lang_bt_status (*apply_ptwrite_listener)
> +    (const struct extension_language_defn *, ptid_t inferior_ptid);
> +
>    /* Update values held by the extension language when OBJFILE is discarded.
>       New global types must be created for every such value, which must then be
>       updated to use the new types.
> diff --git a/gdb/extension.c b/gdb/extension.c
> index 27dce9befa0..826cb0285c3 100644
> --- a/gdb/extension.c
> +++ b/gdb/extension.c
> @@ -550,6 +550,27 @@ apply_ext_lang_frame_filter (struct frame_info *frame,
>    return EXT_LANG_BT_NO_FILTERS;
>  }
>  
> +/* Used for registering the ptwrite listener to the current thread.  */
> +
> +enum ext_lang_bt_status
> +apply_ext_lang_ptwrite_listener (ptid_t inferior_ptid)
> +{
> +  for (const struct extension_language_defn *extlang : extension_languages)
> +    {
> +      enum ext_lang_bt_status status;
> +
> +      if (extlang->ops == nullptr
> +	  || extlang->ops->apply_ptwrite_listener == NULL)
> +	continue;
> +      status = extlang->ops->apply_ptwrite_listener (extlang, inferior_ptid);
> +
> +      if (status != EXT_LANG_BT_NO_FILTERS)
> +	return status;
> +    }
> +
> +  return EXT_LANG_BT_NO_FILTERS;
> +}
> +
>  /* Update values held by the extension language when OBJFILE is discarded.
>     New global types must be created for every such value, which must then be
>     updated to use the new types.
> diff --git a/gdb/extension.h b/gdb/extension.h
> index 56f57560de3..97562304ae4 100644
> --- a/gdb/extension.h
> +++ b/gdb/extension.h
> @@ -295,6 +295,9 @@ extern enum ext_lang_bt_status apply_ext_lang_frame_filter
>     enum ext_lang_frame_args args_type,
>     struct ui_out *out, int frame_low, int frame_high);
>  
> +enum ext_lang_bt_status apply_ext_lang_ptwrite_listener
> +  (ptid_t inferior_ptid);
> +
>  extern void preserve_ext_lang_values (struct objfile *, htab_t copied_types);
>  
>  extern const struct extension_language_defn *get_breakpoint_cond_ext_lang
> diff --git a/gdb/guile/guile.c b/gdb/guile/guile.c
> index a28dee37ed8..ef784885e87 100644
> --- a/gdb/guile/guile.c
> +++ b/gdb/guile/guile.c
> @@ -124,6 +124,7 @@ static const struct extension_language_ops guile_extension_ops =
>    gdbscm_apply_val_pretty_printer,
>  
>    NULL, /* gdbscm_apply_frame_filter, */
> +  NULL, /* gdbscm_load_ptwrite_listener, */
>  
>    gdbscm_preserve_values,
>  
> diff --git a/gdb/python/lib/gdb/ptwrite.py b/gdb/python/lib/gdb/ptwrite.py
> new file mode 100644
> index 00000000000..e52b1e7c88e
> --- /dev/null
> +++ b/gdb/python/lib/gdb/ptwrite.py
> @@ -0,0 +1,86 @@
> +# Ptwrite utilities.
> +# Copyright (C) 2020 Free Software Foundation, Inc.
> +
> +# 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):
> +    """Default listener that is active upon starting GDB."""
> +    return "{:x}".format(payload)
> +
> +# This dict contains the per thread copies of the listener function and the
> +# global template listener, from which the copies are created.
> +_ptwrite_listener = {"global" : default_listener}
> +
> +
> +def _update_listener_dict(thread_list):
> +    """Helper function to update the listener dict.
> +
> +    Discards listener copies of threads that already exited and registers
> +    copies of the listener for new threads."""
> +    # thread_list[x].ptid returns the tuple (pid, lwp, tid)
> +    lwp_list = [i.ptid[1] for i in thread_list]
> +
> +    # clean-up old listeners
> +    for key in _ptwrite_listener.keys():
> +      if key not in lwp_list and not "global":
> +        _ptwrite_listener.pop(key)

Did you mean

    if key not in lwp_list and key != "global":

?

Otherwise, `not "global"` will always evaluate to `False`, and the pop
call will never be evaluated.

> +
> +    # Register listener for new threads
> +    for key in lwp_list:
> +        if key not in _ptwrite_listener.keys():
> +            _ptwrite_listener[key] = deepcopy(_ptwrite_listener["global"])
> +
> +
> +def _clear_traces(thread_list):
> +    """Helper function to clear the trace of all threads."""
> +    current_thread = gdb.selected_thread()
> +
> +    recording = gdb.current_recording()
> +
> +    if (recording is not None):
> +        for thread in thread_list:
> +            thread.switch()
> +            recording.clear()
> +
> +        current_thread.switch()
> +
> +
> +def register_listener(listener):
> +    """Register the ptwrite listener function."""
> +    global _ptwrite_listener

Since _ptwrite_listener is never (re)assigned in this function, the
global statement is not necessary.  It could be dropped.  I guess at
some point a new dict was assigned to _ptwrite_listener, it eventually
got replaced with the `clear` call and the `global` remained.

Best,
Lancelot.

> +
> +    if listener is not None and not callable(listener):
> +        raise TypeError("Listener must be callable!")
> +
> +    thread_list = gdb.Inferior.threads(gdb.selected_inferior())
> +    _clear_traces(thread_list)
> +
> +    _ptwrite_listener.clear()
> +    _ptwrite_listener["global"] = listener
> +
> +    _update_listener_dict(thread_list)
> +
> +
> +def get_listener():
> +    """Returns the listeners of the current thread."""
> +    thread_list = gdb.Inferior.threads(gdb.selected_inferior())
> +    _update_listener_dict(thread_list)
> +
> +    return _ptwrite_listener[gdb.selected_thread().ptid[1]]
> diff --git a/gdb/python/py-record-btrace.c b/gdb/python/py-record-btrace.c
> index 97649b206a5..82f0e00d675 100644
> --- a/gdb/python/py-record-btrace.c
> +++ b/gdb/python/py-record-btrace.c
> @@ -776,6 +776,73 @@ recpy_bt_function_call_history (PyObject *self, void *closure)
>    return btpy_list_new (tinfo, first, last, 1, &recpy_func_type);
>  }
>  
> +/* Helper function returning the current ptwrite listener.  Returns nullptr
> +   in case of errors.  */
> +
> +PyObject *
> +get_ptwrite_listener ()
> +{
> +  PyObject *module = PyImport_ImportModule ("gdb.ptwrite");
> +
> +  if (PyErr_Occurred ())
> +  {
> +    gdbpy_print_stack ();
> +    return nullptr;
> +  }
> +
> +  PyObject *default_ptw_listener = PyObject_CallMethod (module,	"get_listener",
> +							NULL);
> +
> +  gdb_Py_DECREF (module);
> +
> +  if (PyErr_Occurred ())
> +    gdbpy_print_stack ();
> +
> +  return default_ptw_listener;
> +}
> +
> +/* Helper function to initialize the ptwrite listener.  Returns nullptr in
> +   case of errors.  */
> +
> +PyObject *
> +recpy_initialize_listener (ptid_t inferior_ptid)
> +{
> +  process_stratum_target *proc_target = current_inferior ()->process_target ();
> +  struct thread_info * const tinfo = find_thread_ptid (proc_target, inferior_ptid);
> +
> +  tinfo->btrace.ptw_listener = get_ptwrite_listener ();
> +
> +  return (PyObject *) tinfo->btrace.ptw_listener;
> +}
> +
> +/* 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)
> +{
> +  struct gdbarch *gdbarch = NULL;
> +
> +  if (!gdb_python_initialized)
> +    return EXT_LANG_BT_NO_FILTERS;
> +
> +  try
> +    {
> +      gdbarch = target_gdbarch ();
> +    }
> +  catch (const gdb_exception &except)
> +    {
> +      return EXT_LANG_BT_NO_FILTERS;
> +    }
> +
> +  gdbpy_enter enter_py (gdbarch, current_language);
> +
> +  recpy_initialize_listener (inferior_ptid);
> +
> +  return EXT_LANG_BT_OK;
> +}
> +
>  /* Implementation of BtraceRecord.goto (self, BtraceInstruction) -> None.  */
>  
>  PyObject *
> diff --git a/gdb/python/py-record-btrace.h b/gdb/python/py-record-btrace.h
> index adb03c5eab4..36389e99ab8 100644
> --- a/gdb/python/py-record-btrace.h
> +++ b/gdb/python/py-record-btrace.h
> @@ -91,4 +91,10 @@ extern PyObject *recpy_bt_func_prev (PyObject *self, void *closure);
>  /* Implementation of RecordFunctionSegment.next [RecordFunctionSegment].  */
>  extern PyObject *recpy_bt_func_next (PyObject *self, void *closure);
>  
> +/* Helper function to initialize the ptwrite listener.  */
> +extern PyObject *recpy_initialize_listener (ptid_t inferior_ptid);
> +
> +/* Helper function returning the current ptwrite listener.  */
> +extern PyObject *get_ptwrite_listener ();
> +
>  #endif /* PYTHON_PY_RECORD_BTRACE_H */
> diff --git a/gdb/python/python-internal.h b/gdb/python/python-internal.h
> index 690d2fb43c0..fcbd7a0b1b8 100644
> --- a/gdb/python/python-internal.h
> +++ b/gdb/python/python-internal.h
> @@ -392,6 +392,9 @@ extern enum ext_lang_rc gdbpy_apply_val_pretty_printer
>     struct ui_file *stream, int recurse,
>     const struct value_print_options *options,
>     const struct language_defn *language);
> +extern enum ext_lang_bt_status gdbpy_load_ptwrite_listener
> +  (const struct extension_language_defn *extlang,
> +   ptid_t inferior_ptid);
>  extern enum ext_lang_bt_status gdbpy_apply_frame_filter
>    (const struct extension_language_defn *,
>     struct frame_info *frame, frame_filter_flags flags,
> diff --git a/gdb/python/python.c b/gdb/python/python.c
> index e42cbc4fd5e..ad23532f9d8 100644
> --- a/gdb/python/python.c
> +++ b/gdb/python/python.c
> @@ -174,6 +174,8 @@ const struct extension_language_ops python_extension_ops =
>  
>    gdbpy_apply_frame_filter,
>  
> +  gdbpy_load_ptwrite_listener,
> +
>    gdbpy_preserve_values,
>  
>    gdbpy_breakpoint_has_cond,
> -- 
> 2.25.4
> 
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> 

-- 
Lancelot SIX