| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <CAP-5=fVWVHzJ6uzfPpM37p6ZNbFC2D51nmdJzmnyKXy4COwB_Q@mail.gmail.com>
Date: Wed, 19 Nov 2025 08:54:26 -0800
From: Ian Rogers <irogers@...gle.com>
To: Namhyung Kim <namhyung@...nel.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, James Clark <james.clark@...aro.org>,
Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>,
Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>,
LKML <linux-kernel@...r.kernel.org>, linux-perf-users@...r.kernel.org,
Steven Rostedt <rostedt@...dmis.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
Indu Bhagat <indu.bhagat@...cle.com>, Jens Remus <jremus@...ux.ibm.com>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, linux-trace-kernel@...r.kernel.org,
bpf@...r.kernel.org
Subject: Re: [PATCH v4 5/5] perf tools: Merge deferred user callchains
On Sat, Nov 15, 2025 at 3:41 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Save samples with deferred callchains in a separate list and deliver
> them after merging the user callchains. If users don't want to merge
> they can set tool->merge_deferred_callchains to false to prevent the
> behavior.
>
> With previous result, now perf script will show the merged callchains.
>
> $ 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])
> 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)
> ...
>
> The old output can be get using --no-merge-callchain option.
> Also perf report can get the user callchain entry at the end.
>
> $ perf report --no-children --stdio -q -S __build_id_parse.isra.0
> # symbol: __build_id_parse.isra.0
> 8.40% pwd [kernel.kallsyms]
> |
> ---__build_id_parse.isra.0
> perf_event_mmap
> mprotect_fixup
> do_mprotect_pkey
> __x64_sys_mprotect
> do_syscall_64
> entry_SYSCALL_64_after_hwframe
> mprotect
> _dl_sysdep_start
> _dl_start_user
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> tools/perf/Documentation/perf-script.txt | 5 ++
> tools/perf/builtin-inject.c | 1 +
> tools/perf/builtin-report.c | 1 +
> tools/perf/builtin-script.c | 4 ++
> tools/perf/util/callchain.c | 29 ++++++++++
> tools/perf/util/callchain.h | 3 ++
> tools/perf/util/evlist.c | 1 +
> tools/perf/util/evlist.h | 2 +
> tools/perf/util/session.c | 67 +++++++++++++++++++++++-
> tools/perf/util/tool.c | 1 +
> tools/perf/util/tool.h | 1 +
> 11 files changed, 114 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/Documentation/perf-script.txt b/tools/perf/Documentation/perf-script.txt
> index 28bec7e78bc858ba..03d1129606328d6d 100644
> --- a/tools/perf/Documentation/perf-script.txt
> +++ b/tools/perf/Documentation/perf-script.txt
> @@ -527,6 +527,11 @@ include::itrace.txt[]
> The known limitations include exception handing such as
> setjmp/longjmp will have calls/returns not match.
>
> +--merge-callchains::
> + Enable merging deferred user callchains if available. This is the
> + default behavior. If you want to see separate CALLCHAIN_DEFERRED
> + records for some reason, use --no-merge-callchains explicitly.
> +
> :GMEXAMPLECMD: script
> :GMEXAMPLESUBCMD:
> include::guest-files.txt[]
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index bd9245d2dd41aa48..51d2721b6db9dccb 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -2527,6 +2527,7 @@ int cmd_inject(int argc, const char **argv)
> inject.tool.auxtrace = perf_event__repipe_auxtrace;
> inject.tool.bpf_metadata = perf_event__repipe_op2_synth;
> inject.tool.dont_split_sample_group = true;
> + inject.tool.merge_deferred_callchains = false;
> inject.session = __perf_session__new(&data, &inject.tool,
> /*trace_event_repipe=*/inject.output.is_pipe,
> /*host_env=*/NULL);
> diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> index 2bc269f5fcef8023..add6b1c2aaf04270 100644
> --- a/tools/perf/builtin-report.c
> +++ b/tools/perf/builtin-report.c
> @@ -1614,6 +1614,7 @@ int cmd_report(int argc, const char **argv)
> report.tool.event_update = perf_event__process_event_update;
> report.tool.feature = process_feature_event;
> report.tool.ordering_requires_timestamps = true;
> + report.tool.merge_deferred_callchains = !dump_trace;
>
> session = perf_session__new(&data, &report.tool);
> if (IS_ERR(session)) {
> diff --git a/tools/perf/builtin-script.c b/tools/perf/builtin-script.c
> index 85b42205a71b3993..62e43d3c5ad731a0 100644
> --- a/tools/perf/builtin-script.c
> +++ b/tools/perf/builtin-script.c
> @@ -4009,6 +4009,7 @@ int cmd_script(int argc, const char **argv)
> bool header_only = false;
> bool script_started = false;
> bool unsorted_dump = false;
> + bool merge_deferred_callchains = true;
> char *rec_script_path = NULL;
> char *rep_script_path = NULL;
> struct perf_session *session;
> @@ -4162,6 +4163,8 @@ int cmd_script(int argc, const char **argv)
> "Guest code can be found in hypervisor process"),
> OPT_BOOLEAN('\0', "stitch-lbr", &script.stitch_lbr,
> "Enable LBR callgraph stitching approach"),
> + OPT_BOOLEAN('\0', "merge-callchains", &merge_deferred_callchains,
> + "Enable merge deferred user callchains"),
> OPTS_EVSWITCH(&script.evswitch),
> OPT_END()
> };
> @@ -4418,6 +4421,7 @@ 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 = merge_deferred_callchains;
> session = perf_session__new(&data, &script.tool);
> if (IS_ERR(session))
> return PTR_ERR(session);
> diff --git a/tools/perf/util/callchain.c b/tools/perf/util/callchain.c
> index 2884187ccbbecfdc..71dc5a070065dd2a 100644
> --- a/tools/perf/util/callchain.c
> +++ b/tools/perf/util/callchain.c
> @@ -1838,3 +1838,32 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
> }
> return 0;
> }
> +
> +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
> + struct perf_sample *sample_callchain)
> +{
> + u64 nr_orig = sample_orig->callchain->nr - 1;
> + u64 nr_deferred = sample_callchain->callchain->nr;
> + struct ip_callchain *callchain;
> +
> + if (sample_orig->callchain->nr < 2) {
> + sample_orig->deferred_callchain = false;
> + return -EINVAL;
> + }
> +
> + callchain = calloc(1 + nr_orig + nr_deferred, sizeof(u64));
> + if (callchain == NULL) {
> + sample_orig->deferred_callchain = false;
> + return -ENOMEM;
> + }
> +
> + callchain->nr = nr_orig + nr_deferred;
> + /* copy original including PERF_CONTEXT_USER_DEFERRED (but the cookie) */
> + memcpy(callchain->ips, sample_orig->callchain->ips, nr_orig * sizeof(u64));
> + /* copy deferred user callchains */
> + memcpy(&callchain->ips[nr_orig], sample_callchain->callchain->ips,
> + nr_deferred * sizeof(u64));
> +
> + sample_orig->callchain = callchain;
> + return 0;
> +}
> diff --git a/tools/perf/util/callchain.h b/tools/perf/util/callchain.h
> index d5ae4fbb7ce5fa44..2a52af8c80ace33c 100644
> --- a/tools/perf/util/callchain.h
> +++ b/tools/perf/util/callchain.h
> @@ -318,4 +318,7 @@ int sample__for_each_callchain_node(struct thread *thread, struct evsel *evsel,
> struct perf_sample *sample, int max_stack,
> bool symbols, callchain_iter_fn cb, void *data);
>
> +int sample__merge_deferred_callchain(struct perf_sample *sample_orig,
> + struct perf_sample *sample_callchain);
> +
> #endif /* __PERF_CALLCHAIN_H */
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index e8217efdda5323c6..03674d2cbd015e4f 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -85,6 +85,7 @@ void evlist__init(struct evlist *evlist, struct perf_cpu_map *cpus,
> evlist->ctl_fd.pos = -1;
> evlist->nr_br_cntr = -1;
> metricgroup__rblist_init(&evlist->metric_events);
> + INIT_LIST_HEAD(&evlist->deferred_samples);
> }
>
> struct evlist *evlist__new(void)
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 5e71e3dc60423079..911834ae7c2a6f76 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -92,6 +92,8 @@ struct evlist {
> * of struct metric_expr.
> */
> struct rblist metric_events;
> + /* samples with deferred_callchain would wait here. */
> + struct list_head deferred_samples;
> };
>
> struct evsel_str_handler {
> diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
> index 361e15c1f26a96d0..2e777fd1bcf6707b 100644
> --- a/tools/perf/util/session.c
> +++ b/tools/perf/util/session.c
> @@ -1285,6 +1285,60 @@ static int evlist__deliver_sample(struct evlist *evlist, const struct perf_tool
> per_thread);
> }
>
> +struct deferred_event {
> + struct list_head list;
> + union perf_event *event;
What's going on with the memory here? Doesn't the event need to be a
copy to avoid the memory going away in between processing events? It
is definitely worth commenting. Note, I don't see a copy being made
for the event here in machines__deliver_event.
Thanks,
Ian
> +};
> +
> +static int evlist__deliver_deferred_samples(struct evlist *evlist,
> + const struct perf_tool *tool,
> + union perf_event *event,
> + struct perf_sample *sample,
> + struct machine *machine)
> +{
> + struct deferred_event *de, *tmp;
> + struct evsel *evsel;
> + int ret = 0;
> +
> + if (!tool->merge_deferred_callchains) {
> + evsel = evlist__id2evsel(evlist, sample->id);
> + return tool->callchain_deferred(tool, event, sample,
> + evsel, machine);
> + }
> +
> + list_for_each_entry_safe(de, tmp, &evlist->deferred_samples, list) {
> + struct perf_sample orig_sample;
> +
> + ret = evlist__parse_sample(evlist, de->event, &orig_sample);
> + if (ret < 0) {
> + pr_err("failed to parse original sample\n");
> + break;
> + }
> +
> + if (sample->tid != orig_sample.tid)
> + continue;
> +
> + if (event->callchain_deferred.cookie == orig_sample.deferred_cookie)
> + sample__merge_deferred_callchain(&orig_sample, sample);
> + else
> + orig_sample.deferred_callchain = false;
> +
> + evsel = evlist__id2evsel(evlist, orig_sample.id);
> + ret = evlist__deliver_sample(evlist, tool, de->event,
> + &orig_sample, evsel, machine);
> +
> + if (orig_sample.deferred_callchain)
> + free(orig_sample.callchain);
> +
> + list_del(&de->list);
> + free(de);
> +
> + if (ret)
> + break;
> + }
> + return ret;
> +}
> +
> static int machines__deliver_event(struct machines *machines,
> struct evlist *evlist,
> union perf_event *event,
> @@ -1313,6 +1367,16 @@ static int machines__deliver_event(struct machines *machines,
> return 0;
> }
> dump_sample(evsel, event, sample, perf_env__arch(machine->env));
> + if (sample->deferred_callchain && tool->merge_deferred_callchains) {
> + struct deferred_event *de = malloc(sizeof(*de));
> +
> + if (de == NULL)
> + return -ENOMEM;
> +
> + de->event = event;
> + list_add_tail(&de->list, &evlist->deferred_samples);
> + return 0;
> + }
> return evlist__deliver_sample(evlist, tool, event, sample, evsel, machine);
> case PERF_RECORD_MMAP:
> return tool->mmap(tool, event, sample, machine);
> @@ -1372,7 +1436,8 @@ static int machines__deliver_event(struct machines *machines,
> return tool->aux_output_hw_id(tool, event, sample, machine);
> case PERF_RECORD_CALLCHAIN_DEFERRED:
> dump_deferred_callchain(evsel, event, sample);
> - return tool->callchain_deferred(tool, event, sample, evsel, machine);
> + return evlist__deliver_deferred_samples(evlist, tool, event,
> + sample, machine);
> default:
> ++evlist->stats.nr_unknown_events;
> return -1;
> diff --git a/tools/perf/util/tool.c b/tools/perf/util/tool.c
> index f732d33e7f895ed4..c5d3b464b2a433b3 100644
> --- a/tools/perf/util/tool.c
> +++ b/tools/perf/util/tool.c
> @@ -266,6 +266,7 @@ void perf_tool__init(struct perf_tool *tool, bool ordered_events)
> tool->cgroup_events = false;
> tool->no_warn = false;
> tool->show_feat_hdr = SHOW_FEAT_NO_HEADER;
> + tool->merge_deferred_callchains = true;
>
> tool->sample = process_event_sample_stub;
> tool->mmap = process_event_stub;
> diff --git a/tools/perf/util/tool.h b/tools/perf/util/tool.h
> index 9b9f0a8cbf3de4b5..e96b69d25a5b737d 100644
> --- a/tools/perf/util/tool.h
> +++ b/tools/perf/util/tool.h
> @@ -90,6 +90,7 @@ struct perf_tool {
> bool cgroup_events;
> bool no_warn;
> bool dont_split_sample_group;
> + bool merge_deferred_callchains;
> enum show_feature_header show_feat_hdr;
> };
>
> --
> 2.52.0.rc1.455.g30608eb744-goog
>
Powered by blists - more mailing lists