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

[Samuel Wu <wusamuel@google.com>]

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>