Re: [PATCH v3 4/5] perf script: Display PERF_RECORD_CALLCHAIN_DEFERRED

[Ian Rogers <irogers@google.com>]

On Thu, Nov 13, 2025 at 11:02 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> Handle the deferred callchains in the script output.
>
>   $ perf script
>   ...
>   pwd    2312   121.163435:     249113 cpu/cycles/P:
>           ffffffff845b78d8 __build_id_parse.isra.0+0x218 ([kernel.kallsyms])
>           ffffffff83bb5bf6 perf_event_mmap+0x2e6 ([kernel.kallsyms])
>           ffffffff83c31959 mprotect_fixup+0x1e9 ([kernel.kallsyms])
>           ffffffff83c31dc5 do_mprotect_pkey+0x2b5 ([kernel.kallsyms])
>           ffffffff83c3206f __x64_sys_mprotect+0x1f ([kernel.kallsyms])
>           ffffffff845e6692 do_syscall_64+0x62 ([kernel.kallsyms])
>           ffffffff8360012f entry_SYSCALL_64_after_hwframe+0x76 ([kernel.kallsyms])
>                  b00000006 [unknown] ([unknown])

Does this unknown value correspond to the cookie? Can the cookie and
deferred data be added to the kernel stack trace output?

>   pwd    2312   121.163447: DEFERRED CALLCHAIN
>               7f18fe337fa7 mprotect+0x7 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
>               7f18fe330e0f _dl_sysdep_start+0x7f (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)
>               7f18fe331448 _dl_start_user+0x0 (/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2)

Can we display the cookie here so that the user callchain can be
matched with the kernel part?

Thanks,
Ian

> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/perf/builtin-script.c | 89 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 89 insertions(+)
>
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index cf0040bbaba9cbc9..3b2896350bad2924 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -2719,6 +2719,93 @@ static int process_sample_event(const struct perf_tool *tool,
>         return ret;
>  }
>
> +static int process_deferred_sample_event(const struct perf_tool *tool,
> +                                        union perf_event *event,
> +                                        struct perf_sample *sample,
> +                                        struct evsel *evsel,
> +                                        struct machine *machine)
> +{
> +       struct perf_script *scr = container_of(tool, struct perf_script, tool);
> +       struct perf_event_attr *attr = &evsel->core.attr;
> +       struct evsel_script *es = evsel->priv;
> +       unsigned int type = output_type(attr->type);
> +       struct addr_location al;
> +       FILE *fp = es->fp;
> +       int ret = 0;
> +
> +       if (output[type].fields == 0)
> +               return 0;
> +
> +       /* Set thread to NULL to indicate addr_al and al are not initialized */
> +       addr_location__init(&al);
> +
> +       if (perf_time__ranges_skip_sample(scr->ptime_range, scr->range_num,
> +                                         sample->time)) {
> +               goto out_put;
> +       }
> +
> +       if (debug_mode) {
> +               if (sample->time < last_timestamp) {
> +                       pr_err("Samples misordered, previous: %" PRIu64
> +                               " this: %" PRIu64 "\n", last_timestamp,
> +                               sample->time);
> +                       nr_unordered++;
> +               }
> +               last_timestamp = sample->time;
> +               goto out_put;
> +       }
> +
> +       if (filter_cpu(sample))
> +               goto out_put;
> +
> +       if (machine__resolve(machine, &al, sample) < 0) {
> +               pr_err("problem processing %d event, skipping it.\n",
> +                      event->header.type);
> +               ret = -1;
> +               goto out_put;
> +       }
> +
> +       if (al.filtered)
> +               goto out_put;
> +
> +       if (!show_event(sample, evsel, al.thread, &al, NULL))
> +               goto out_put;
> +
> +       if (evswitch__discard(&scr->evswitch, evsel))
> +               goto out_put;
> +
> +       perf_sample__fprintf_start(scr, sample, al.thread, evsel,
> +                                  PERF_RECORD_CALLCHAIN_DEFERRED, fp);
> +       fprintf(fp, "DEFERRED CALLCHAIN");
> +
> +       if (PRINT_FIELD(IP)) {
> +               struct callchain_cursor *cursor = NULL;
> +
> +               if (symbol_conf.use_callchain && sample->callchain) {
> +                       cursor = get_tls_callchain_cursor();
> +                       if (thread__resolve_callchain(al.thread, cursor, evsel,
> +                                                     sample, NULL, NULL,
> +                                                     scripting_max_stack)) {
> +                               pr_info("cannot resolve deferred callchains\n");
> +                               cursor = NULL;
> +                       }
> +               }
> +
> +               fputc(cursor ? '\n' : ' ', fp);
> +               sample__fprintf_sym(sample, &al, 0, output[type].print_ip_opts,
> +                                   cursor, symbol_conf.bt_stop_list, fp);
> +       }
> +
> +       fprintf(fp, "\n");
> +
> +       if (verbose > 0)
> +               fflush(fp);
> +
> +out_put:
> +       addr_location__exit(&al);
> +       return ret;
> +}
> +
>  // Used when scr->per_event_dump is not set
>  static struct evsel_script es_stdout;
>
> @@ -4320,6 +4407,7 @@ int cmd_script(int argc, const char **argv)
>
>         perf_tool__init(&script.tool, !unsorted_dump);
>         script.tool.sample               = process_sample_event;
> +       script.tool.callchain_deferred   = process_deferred_sample_event;
>         script.tool.mmap                 = perf_event__process_mmap;
>         script.tool.mmap2                = perf_event__process_mmap2;
>         script.tool.comm                 = perf_event__process_comm;
> @@ -4346,6 +4434,7 @@ int cmd_script(int argc, const char **argv)
>         script.tool.throttle             = process_throttle_event;
>         script.tool.unthrottle           = process_throttle_event;
>         script.tool.ordering_requires_timestamps = true;
> +       script.tool.merge_deferred_callchains = false;
>         session = perf_session__new(&data, &script.tool);
>         if (IS_ERR(session))
>                 return PTR_ERR(session);
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
>