Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | From | Yang Jihong <> | Subject | [PATCH] perf top & record: Fix segfault when default cycles event is not supported | Date | Wed, 14 Jun 2023 15:16:25 +0000 |
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The perf-record and perf-top call parse_event() to add a cycles event to an empty evlist. For the system that does not support hardware cycles event, such as QEMU, the evlist is empty due to the following code process:
parse_event(evlist, "cycles:P" or ""cycles:Pu") parse_events(evlist, "cycles:P") __parse_events ... ret = parse_events__scanner(str, &parse_state); // ret = 0 ... ret2 = parse_events__sort_events_and_fix_groups() if (ret2 < 0) return ret; // The cycles event is not supported, here ret2 = -EINVAL, // Here return 0. ... evlist__splice_list_tail(evlist) // The code here does not execute to, so the evlist is still empty.
A null pointer occurs when the content in the evlist is accessed later.
Before:
# perf list hw
List of pre-defined events (to be used in -e or -M):
# perf record true libperf: Miscounted nr_mmaps 0 vs 1 WARNING: No sample_id_all support, falling back to unordered processing perf: Segmentation fault Obtained 1 stack frames. [0xc5beff] Segmentation fault
Solution: If cycles event is not supported, try to fall back to cpu-clock event.
After: # perf record true [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.006 MB perf.data ] #
Fixes: 7b100989b4f6 ("perf evlist: Remove __evlist__add_default") Signed-off-by: Yang Jihong <yangjihong1@huawei.com> --- tools/perf/builtin-record.c | 4 +--- tools/perf/builtin-top.c | 3 +-- tools/perf/util/evlist.c | 18 ++++++++++++++++++ tools/perf/util/evlist.h | 1 + 4 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index aec18db7ff23..29ae2b84a63a 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -4161,9 +4161,7 @@ int cmd_record(int argc, const char **argv) record.opts.tail_synthesize = true; if (rec->evlist->core.nr_entries == 0) { - bool can_profile_kernel = perf_event_paranoid_check(1); - - err = parse_event(rec->evlist, can_profile_kernel ? "cycles:P" : "cycles:Pu"); + err = evlist__add_default(rec->evlist); if (err) goto out; } diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c index c363c04e16df..798cb9252a5f 100644 --- a/tools/perf/builtin-top.c +++ b/tools/perf/builtin-top.c @@ -1665,8 +1665,7 @@ int cmd_top(int argc, const char **argv) goto out_delete_evlist; if (!top.evlist->core.nr_entries) { - bool can_profile_kernel = perf_event_paranoid_check(1); - int err = parse_event(top.evlist, can_profile_kernel ? "cycles:P" : "cycles:Pu"); + int err = evlist__add_default(top.evlist); if (err) goto out_delete_evlist; diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 7ef43f72098e..60efa762405e 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -287,6 +287,24 @@ struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide) return evsel; } +int evlist__add_default(struct evlist *evlist) +{ + bool can_profile_kernel; + int err; + + can_profile_kernel = perf_event_paranoid_check(1); + err = parse_event(evlist, can_profile_kernel ? "cycles:P" : "cycles:Pu"); + if (err) + return err; + + if (!evlist->core.nr_entries) { + pr_debug("The cycles event is not supported, trying to fall back to cpu-clock event\n"); + return parse_event(evlist, "cpu-clock"); + } + + return 0; +} + #ifdef HAVE_LIBTRACEEVENT struct evsel *evlist__add_sched_switch(struct evlist *evlist, bool system_wide) { diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h index 664c6bf7b3e0..47eea809ee91 100644 --- a/tools/perf/util/evlist.h +++ b/tools/perf/util/evlist.h @@ -116,6 +116,7 @@ int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs); int evlist__add_dummy(struct evlist *evlist); struct evsel *evlist__add_aux_dummy(struct evlist *evlist, bool system_wide); +int evlist__add_default(struct evlist *evlist); static inline struct evsel *evlist__add_dummy_on_all_cpus(struct evlist *evlist) { return evlist__add_aux_dummy(evlist, true); -- 2.30.GIT
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