From 9bca1a4ef5034f0a82861ac0375eb0272c5ce04e Mon Sep 17 00:00:00 2001 From: Adrian Hunter Date: Fri, 15 Nov 2019 14:42:13 +0200 Subject: [PATCH] perf record: Add a function to test for kernel support for AUX area sampling Architectures are expected to know if AUX area sampling is supported by the hardware. Add a function perf_can_aux_sample() which will determine whether the kernel supports it. Committer notes: I reported that this message was taking place on a kernel without the required bits: # perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' Error: The sys_perf_event_open() syscall returned with 7 (Argument list too long) for event (branch-misses:u). /bin/dmesg | grep -i perf may provide additional information. Adrian sent a patch addressing it, with this explanation: ---- perf_can_aux_sample_size() always returned true because it did not pass the attribute size to sys_perf_event_open, nor correctly check the return value and errno. ---- After applying it I get, later in the series, when --aux-sample is added: # perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' AUX area sampling is not supported by kernel Signed-off-by: Adrian Hunter Cc: Jiri Olsa Link: http://lore.kernel.org/lkml/20191115124225.5247-4-adrian.hunter@intel.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/util/evlist.h | 1 + tools/perf/util/record.c | 31 +++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h index 13051409fd22..3655b9ebb147 100644 --- a/tools/perf/util/evlist.h +++ b/tools/perf/util/evlist.h @@ -176,6 +176,7 @@ void perf_evlist__set_id_pos(struct evlist *evlist); bool perf_can_sample_identifier(void); bool perf_can_record_switch_events(void); bool perf_can_record_cpu_wide(void); +bool perf_can_aux_sample(void); void perf_evlist__config(struct evlist *evlist, struct record_opts *opts, struct callchain_param *callchain); int record_opts__config(struct record_opts *opts); diff --git a/tools/perf/util/record.c b/tools/perf/util/record.c index 8579505c29a4..7def66168503 100644 --- a/tools/perf/util/record.c +++ b/tools/perf/util/record.c @@ -136,6 +136,37 @@ bool perf_can_record_cpu_wide(void) return true; } +/* + * Architectures are expected to know if AUX area sampling is supported by the + * hardware. Here we check for kernel support. + */ +bool perf_can_aux_sample(void) +{ + struct perf_event_attr attr = { + .size = sizeof(struct perf_event_attr), + .exclude_kernel = 1, + /* + * Non-zero value causes the kernel to calculate the effective + * attribute size up to that byte. + */ + .aux_sample_size = 1, + }; + int fd; + + fd = sys_perf_event_open(&attr, -1, 0, -1, 0); + /* + * If the kernel attribute is big enough to contain aux_sample_size + * then we assume that it is supported. We are relying on the kernel to + * validate the attribute size before anything else that could be wrong. + */ + if (fd < 0 && errno == E2BIG) + return false; + if (fd >= 0) + close(fd); + + return true; +} + void perf_evlist__config(struct evlist *evlist, struct record_opts *opts, struct callchain_param *callchain) {