[PATCH] perf python: Accept events larger than union perf_event

[PATCH] perf python: Accept events larger than union perf_event

[Lalit Maganti]

Samples recorded with --call-graph dwarf carry a copy of the user stack
and are larger than union perf_event, so session.process_events()
fails on the first one:

  $ perf record --call-graph dwarf -- ./workload
  $ python3 tools/perf/python/stackcollapse.py
  ...
  TypeError: Unexpected event size: 4168 < 8424

This makes all the standalone scripts unusable on such recordings.

pyrf_event__new() rejects events larger than union perf_event, which
guarded the copy into the union that pyrf_event used to embed. Since
commit 2c672ffdad4b ("perf python: Lazily copy events and samples from
process_events") the event is borrowed, or copied to a buffer of
header.size bytes when a callback keeps it, so nothing depends on the
event fitting in the union any more. Remove the check.

With this, stackcollapse.py and flamegraph.py process a DWARF recording
of a two-thread workload, with the same per-symbol sample counts as
perf script, also when the callback keeps the events after returning.

Assisted-by: LLM
Signed-off-by: Lalit Maganti <lalitmaganti@gmail.com>
---
 tools/perf/util/python.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
index 60dbe2dad5eb..8b4b2f3d0926 100644
--- a/tools/perf/util/python.c
+++ b/tools/perf/util/python.c
@@ -1792,11 +1792,6 @@ static PyObject *pyrf_event__new(const union perf_event *event, struct evsel *ev
 				    event->header.size, event->header.type);
 	}
 
-	if (event->header.size > sizeof(union perf_event)) {
-		return PyErr_Format(PyExc_TypeError, "Unexpected event size: %zu < %u",
-				    sizeof(union perf_event), event->header.size);
-	}
-
 	pevent = PyObject_New(struct pyrf_event, pyrf_event__type[event->header.type]);
 	if (pevent == NULL)
 		return PyErr_NoMemory();

base-commit: 1c90f0a3c8a1c4e38f9edd97af9e20848805a7fb
-- 
2.56.0

Re: [PATCH] perf python: Accept events larger than union perf_event

[Samuel Wu]

On Sun, Oct 18, 2026 at 12:45 AM Lalit Maganti <lalitmaganti@gmail.com> wrote:
>
> Samples recorded with --call-graph dwarf carry a copy of the user stack
> and are larger than union perf_event, so session.process_events()
> fails on the first one:
>
>   $ perf record --call-graph dwarf -- ./workload
>   $ python3 tools/perf/python/stackcollapse.py
>   ...
>   TypeError: Unexpected event size: 4168 < 8424
>
> This makes all the standalone scripts unusable on such recordings.
>
> pyrf_event__new() rejects events larger than union perf_event, which
> guarded the copy into the union that pyrf_event used to embed. Since
> commit 2c672ffdad4b ("perf python: Lazily copy events and samples from
> process_events") the event is borrowed, or copied to a buffer of
> header.size bytes when a callback keeps it, so nothing depends on the
> event fitting in the union any more. Remove the check.
>
> With this, stackcollapse.py and flamegraph.py process a DWARF recording
> of a two-thread workload, with the same per-symbol sample counts as
> perf script, also when the callback keeps the events after returning.
>
> Assisted-by: LLM
> Signed-off-by: Lalit Maganti <lalitmaganti@gmail.com>
> ---
>  tools/perf/util/python.c | 5 -----
>  1 file changed, 5 deletions(-)
>
> diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
> index 60dbe2dad5eb..8b4b2f3d0926 100644
> --- a/tools/perf/util/python.c
> +++ b/tools/perf/util/python.c
> @@ -1792,11 +1792,6 @@ static PyObject *pyrf_event__new(const union perf_event *event, struct evsel *ev
>                                     event->header.size, event->header.type);
>         }
>
> -       if (event->header.size > sizeof(union perf_event)) {
> -               return PyErr_Format(PyExc_TypeError, "Unexpected event size: %zu < %u",
> -                                   sizeof(union perf_event), event->header.size);
> -       }
> -
>         pevent = PyObject_New(struct pyrf_event, pyrf_event__type[event->header.type]);
>         if (pevent == NULL)
>                 return PyErr_NoMemory();
>
> base-commit: 1c90f0a3c8a1c4e38f9edd97af9e20848805a7fb
> --
> 2.56.0
>

Reviewed-by: Samuel Wu <wusamuel@google.com>

Re: [PATCH] perf python: Accept events larger than union perf_event

[Ian Rogers]

On Mon, Nov 9, 2026 at 9:58 AM Samuel Wu <wusamuel@google.com> wrote:
>
> On Sun, Oct 18, 2026 at 12:45 AM Lalit Maganti <lalitmaganti@gmail.com> wrote:
> >
> > Samples recorded with --call-graph dwarf carry a copy of the user stack
> > and are larger than union perf_event, so session.process_events()
> > fails on the first one:
> >
> >   $ perf record --call-graph dwarf -- ./workload
> >   $ python3 tools/perf/python/stackcollapse.py
> >   ...
> >   TypeError: Unexpected event size: 4168 < 8424
> >
> > This makes all the standalone scripts unusable on such recordings.
> >
> > pyrf_event__new() rejects events larger than union perf_event, which
> > guarded the copy into the union that pyrf_event used to embed. Since
> > commit 2c672ffdad4b ("perf python: Lazily copy events and samples from
> > process_events") the event is borrowed, or copied to a buffer of
> > header.size bytes when a callback keeps it, so nothing depends on the
> > event fitting in the union any more. Remove the check.
> >
> > With this, stackcollapse.py and flamegraph.py process a DWARF recording
> > of a two-thread workload, with the same per-symbol sample counts as
> > perf script, also when the callback keeps the events after returning.
> >
> > Assisted-by: LLM
> > Signed-off-by: Lalit Maganti <lalitmaganti@gmail.com>

Probably worth having:

Fixes: 2c672ffdad4b ("perf python: Lazily copy events and samples from
process_events")

Reviewed-by: Ian Rogers <irogers@google.com>

Thanks,
Ian

> > ---
> >  tools/perf/util/python.c | 5 -----
> >  1 file changed, 5 deletions(-)
> >
> > diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
> > index 60dbe2dad5eb..8b4b2f3d0926 100644
> > --- a/tools/perf/util/python.c
> > +++ b/tools/perf/util/python.c
> > @@ -1792,11 +1792,6 @@ static PyObject *pyrf_event__new(const union perf_event *event, struct evsel *ev
> >                                     event->header.size, event->header.type);
> >         }
> >
> > -       if (event->header.size > sizeof(union perf_event)) {
> > -               return PyErr_Format(PyExc_TypeError, "Unexpected event size: %zu < %u",
> > -                                   sizeof(union perf_event), event->header.size);
> > -       }
> > -
> >         pevent = PyObject_New(struct pyrf_event, pyrf_event__type[event->header.type]);
> >         if (pevent == NULL)
> >                 return PyErr_NoMemory();
> >
> > base-commit: 1c90f0a3c8a1c4e38f9edd97af9e20848805a7fb
> > --
> > 2.56.0
> >
>
> Reviewed-by: Samuel Wu <wusamuel@google.com>

Re: [PATCH] perf python: Accept events larger than union perf_event

[Arnaldo Melo]

On November 9, 2026 3:27:56 PM GMT-03:00, Ian Rogers <irogers@google.com> wrote:
>On Mon, Nov 9, 2026 at 9:58 AM Samuel Wu <wusamuel@google.com> wrote:
>>
>> On Sun, Oct 18, 2026 at 12:45 AM Lalit Maganti <lalitmaganti@gmail.com> wrote:
>> >
>> > Samples recorded with --call-graph dwarf carry a copy of the user stack
>> > and are larger than union perf_event, so session.process_events()
>> > fails on the first one:
>> >
>> >   $ perf record --call-graph dwarf -- ./workload
>> >   $ python3 tools/perf/python/stackcollapse.py
>> >   ...
>> >   TypeError: Unexpected event size: 4168 < 8424
>> >
>> > This makes all the standalone scripts unusable on such recordings.
>> >
>> > pyrf_event__new() rejects events larger than union perf_event, which
>> > guarded the copy into the union that pyrf_event used to embed. Since
>> > commit 2c672ffdad4b ("perf python: Lazily copy events and samples from
>> > process_events") the event is borrowed, or copied to a buffer of
>> > header.size bytes when a callback keeps it, so nothing depends on the
>> > event fitting in the union any more. Remove the check.
>> >
>> > With this, stackcollapse.py and flamegraph.py process a DWARF recording
>> > of a two-thread workload, with the same per-symbol sample counts as
>> > perf script, also when the callback keeps the events after returning.
>> >
>> > Assisted-by: LLM
>> > Signed-off-by: Lalit Maganti <lalitmaganti@gmail.com>
>
>Probably worth having:
>
>Fixes: 2c672ffdad4b ("perf python: Lazily copy events and samples from
>process_events")
>
>Reviewed-by: Ian Rogers <irogers@google.com>


I'll pick it for v7.4,

Thanks,

- Arnaldo 
>
>Thanks,
>Ian
>
>> > ---
>> >  tools/perf/util/python.c | 5 -----
>> >  1 file changed, 5 deletions(-)
>> >
>> > diff --git a/tools/perf/util/python.c b/tools/perf/util/python.c
>> > index 60dbe2dad5eb..8b4b2f3d0926 100644
>> > --- a/tools/perf/util/python.c
>> > +++ b/tools/perf/util/python.c
>> > @@ -1792,11 +1792,6 @@ static PyObject *pyrf_event__new(const union perf_event *event, struct evsel *ev
>> >                                     event->header.size, event->header.type);
>> >         }
>> >
>> > -       if (event->header.size > sizeof(union perf_event)) {
>> > -               return PyErr_Format(PyExc_TypeError, "Unexpected event size: %zu < %u",
>> > -                                   sizeof(union perf_event), event->header.size);
>> > -       }
>> > -
>> >         pevent = PyObject_New(struct pyrf_event, pyrf_event__type[event->header.type]);
>> >         if (pevent == NULL)
>> >                 return PyErr_NoMemory();
>> >
>> > base-commit: 1c90f0a3c8a1c4e38f9edd97af9e20848805a7fb
>> > --
>> > 2.56.0
>> >
>>
>> Reviewed-by: Samuel Wu <wusamuel@google.com>
>

- Arnaldo