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

Lancelot SIX via Gdb-patches
2021-06-15T23:42:04Z

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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> Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
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>

--
Lancelot SIX