Re: [PATCH 03/24] perf: Add build id data in mmap2 event

From: Jiri Olsa
Date: Tue Nov 10 2020 - 13:23:49 EST

On Tue, Nov 10, 2020 at 11:10:46AM +0100, Jiri Olsa wrote:
> On Tue, Nov 10, 2020 at 09:28:51AM +0100, Peter Zijlstra wrote:
> > On Mon, Nov 09, 2020 at 10:53:54PM +0100, Jiri Olsa wrote:
> > > There's new misc bit for mmap2 to signal there's build
> > > id data in it:
> > >
> > > #define PERF_RECORD_MISC_BUILD_ID (1 << 14)
> >
> > PERF_RECORD_MISC_MMAP_BUILD_ID would be consistent with the existing
> > PERF_RECORD_MISC_MMAP_DATA naming.
>
> ok
>
> >
> > Also, AFAICT there's still a bunch of unused bits in misc.
> >
> > 012 CDEF
> > |||---------||||
> >
> > Where:
> > 0-2 CPUMODE_MASK
> >
> > C PROC_MAP_PARSE_TIMEOUT
> > D MMAP_DATA / COMM_EXEC / FORK_EXEC / SWITCH_OUT
> > E EXACT_IP / SCHED_OUT_PREEMPT
> > F (reserved)
> >
> > Maybe we should put in a comment to keep track of the hole ?
>
> ook

how about the change below.. I also switch the build_id with the size,
but I kept the build_id size 20, because I think there's bigger chance
we will use those reserved bytes for something, than that we will need
those extra 3 bytes in build_id array

struct {
u8 build_id_size;
u8 __reserved_1;
u16 __reserved_2;
u8 build_id[20];
};

jirka


---
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index b95d3c485d27..45a216bea048 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -384,7 +384,8 @@ struct perf_event_attr {
aux_output : 1, /* generate AUX records instead of events */
cgroup : 1, /* include cgroup events */
text_poke : 1, /* include text poke events */
- __reserved_1 : 30;
+ build_id : 1, /* use build id in mmap2 events */
+ __reserved_1 : 29;

union {
__u32 wakeup_events; /* wakeup every n events */
@@ -657,6 +658,22 @@ struct perf_event_mmap_page {
__u64 aux_size;
};

+/*
+ * The current state of perf_event_header::misc bits usage:
+ * ('|' used bit, '-' unused bit)
+ *
+ * 012 CDEF
+ * |||---------||||
+ *
+ * Where:
+ * 0-2 CPUMODE_MASK
+ *
+ * C PROC_MAP_PARSE_TIMEOUT
+ * D MMAP_DATA / COMM_EXEC / FORK_EXEC / SWITCH_OUT
+ * E MMAP_BUILD_ID / EXACT_IP / SCHED_OUT_PREEMPT
+ * F (reserved)
+ */
+
#define PERF_RECORD_MISC_CPUMODE_MASK (7 << 0)
#define PERF_RECORD_MISC_CPUMODE_UNKNOWN (0 << 0)
#define PERF_RECORD_MISC_KERNEL (1 << 0)
@@ -688,6 +705,7 @@ struct perf_event_mmap_page {
*
* PERF_RECORD_MISC_EXACT_IP - PERF_RECORD_SAMPLE of precise events
* PERF_RECORD_MISC_SWITCH_OUT_PREEMPT - PERF_RECORD_SWITCH* events
+ * PERF_RECORD_MISC_MMAP_BUILD_ID - PERF_RECORD_MMAP2 event
*
*
* PERF_RECORD_MISC_EXACT_IP:
@@ -697,9 +715,13 @@ struct perf_event_mmap_page {
*
* PERF_RECORD_MISC_SWITCH_OUT_PREEMPT:
* Indicates that thread was preempted in TASK_RUNNING state.
+ *
+ * PERF_RECORD_MISC_MMAP_BUILD_ID:
+ * Indicates that mmap2 event carries build id data.
*/
#define PERF_RECORD_MISC_EXACT_IP (1 << 14)
#define PERF_RECORD_MISC_SWITCH_OUT_PREEMPT (1 << 14)
+#define PERF_RECORD_MISC_MMAP_BUILD_ID (1 << 14)
/*
* Reserve the last bit to indicate some extended misc field
*/
@@ -911,10 +933,20 @@ enum perf_event_type {
* u64 addr;
* u64 len;
* u64 pgoff;
- * u32 maj;
- * u32 min;
- * u64 ino;
- * u64 ino_generation;
+ * union {
+ * struct {
+ * u32 maj;
+ * u32 min;
+ * u64 ino;
+ * u64 ino_generation;
+ * };
+ * struct {
+ * u8 build_id_size;
+ * u8 __reserved_1;
+ * u16 __reserved_2;
+ * u8 build_id[20];
+ * };
+ * };
* u32 prot, flags;
* char filename[];
* struct sample_id sample_id;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index da467e1dd49a..5b2b8ec82399 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -51,6 +51,7 @@
#include <linux/proc_ns.h>
#include <linux/mount.h>
#include <linux/min_heap.h>
+#include <linux/buildid.h>

#include "internal.h"

@@ -395,6 +396,7 @@ static atomic_t nr_ksymbol_events __read_mostly;
static atomic_t nr_bpf_events __read_mostly;
static atomic_t nr_cgroup_events __read_mostly;
static atomic_t nr_text_poke_events __read_mostly;
+static atomic_t nr_build_id_events __read_mostly;

static LIST_HEAD(pmus);
static DEFINE_MUTEX(pmus_lock);
@@ -4672,6 +4674,8 @@ static void unaccount_event(struct perf_event *event)
dec = true;
if (event->attr.mmap || event->attr.mmap_data)
atomic_dec(&nr_mmap_events);
+ if (event->attr.build_id)
+ atomic_dec(&nr_build_id_events);
if (event->attr.comm)
atomic_dec(&nr_comm_events);
if (event->attr.namespaces)
@@ -7942,6 +7946,8 @@ struct perf_mmap_event {
u64 ino;
u64 ino_generation;
u32 prot, flags;
+ u8 build_id[BUILD_ID_SIZE];
+ u32 build_id_size;

struct {
struct perf_event_header header;
@@ -7997,13 +8003,23 @@ static void perf_event_mmap_output(struct perf_event *event,
mmap_event->event_id.pid = perf_event_pid(event, current);
mmap_event->event_id.tid = perf_event_tid(event, current);

+ if (event->attr.mmap2 && event->attr.build_id)
+ mmap_event->event_id.header.misc |= PERF_RECORD_MISC_MMAP_BUILD_ID;
+
perf_output_put(&handle, mmap_event->event_id);

if (event->attr.mmap2) {
- perf_output_put(&handle, mmap_event->maj);
- perf_output_put(&handle, mmap_event->min);
- perf_output_put(&handle, mmap_event->ino);
- perf_output_put(&handle, mmap_event->ino_generation);
+ if (event->attr.build_id) {
+ u8 size[4] = { (u8) mmap_event->build_id_size, 0, 0, 0 };
+
+ __output_copy(&handle, size, 4);
+ __output_copy(&handle, mmap_event->build_id, BUILD_ID_SIZE);
+ } else {
+ perf_output_put(&handle, mmap_event->maj);
+ perf_output_put(&handle, mmap_event->min);
+ perf_output_put(&handle, mmap_event->ino);
+ perf_output_put(&handle, mmap_event->ino_generation);
+ }
perf_output_put(&handle, mmap_event->prot);
perf_output_put(&handle, mmap_event->flags);
}
@@ -8132,6 +8148,9 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)

mmap_event->event_id.header.size = sizeof(mmap_event->event_id) + size;

+ if (atomic_read(&nr_build_id_events))
+ build_id_parse(vma, mmap_event->build_id, &mmap_event->build_id_size);
+
perf_iterate_sb(perf_event_mmap_output,
mmap_event,
NULL);
@@ -11069,6 +11088,8 @@ static void account_event(struct perf_event *event)
inc = true;
if (event->attr.mmap || event->attr.mmap_data)
atomic_inc(&nr_mmap_events);
+ if (event->attr.build_id)
+ atomic_inc(&nr_build_id_events);
if (event->attr.comm)
atomic_inc(&nr_comm_events);
if (event->attr.namespaces)
diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 768888b9326a..1bcf51e24979 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -482,6 +482,9 @@ Specify vmlinux path which has debuginfo.
--buildid-all::
Record build-id of all DSOs regardless whether it's actually hit or not.

+--buildid-mmap::
+Record build ids in mmap2 events, disables build id cache (implies --no-buildid).
+
--aio[=n]::
Use <n> control blocks in asynchronous (Posix AIO) trace writing mode (default: 1, max: 4).
Asynchronous mode is supported only when linking Perf tool with libc library
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index adf311d15d3d..47bae9d82d43 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -102,6 +102,7 @@ struct record {
bool no_buildid_cache;
bool no_buildid_cache_set;
bool buildid_all;
+ bool buildid_mmap;
bool timestamp_filename;
bool timestamp_boundary;
struct switch_output switch_output;
@@ -2139,6 +2140,8 @@ static int perf_record_config(const char *var, const char *value, void *cb)
rec->no_buildid_cache = true;
else if (!strcmp(value, "skip"))
rec->no_buildid = true;
+ else if (!strcmp(value, "mmap"))
+ rec->buildid_mmap = true;
else
return -1;
return 0;
@@ -2554,6 +2557,8 @@ static struct option __record_options[] = {
"file", "vmlinux pathname"),
OPT_BOOLEAN(0, "buildid-all", &record.buildid_all,
"Record build-id of all DSOs regardless of hits"),
+ OPT_BOOLEAN(0, "buildid-mmap", &record.buildid_mmap,
+ "Record build-id in map events"),
OPT_BOOLEAN(0, "timestamp-filename", &record.timestamp_filename,
"append timestamp to output filename"),
OPT_BOOLEAN(0, "timestamp-boundary", &record.timestamp_boundary,
@@ -2657,6 +2662,21 @@ int cmd_record(int argc, const char **argv)

}

+ if (rec->buildid_mmap) {
+ if (!perf_can_record_build_id()) {
+ pr_err("Failed: no support to record build id in mmap events, update your kernel.\n");
+ err = -EINVAL;
+ goto out_opts;
+ }
+ pr_debug("Enabling build id in mmap2 events.\n");
+ /* Enable mmap build id synthesizing. */
+ symbol_conf.buildid_mmap2 = true;
+ /* Enable perf_event_attr::build_id bit. */
+ rec->opts.build_id = true;
+ /* Disable build id cache. */
+ rec->no_buildid = true;
+ }
+
if (rec->opts.kcore)
rec->data.is_dir = true;

diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index 1cad6051d8b0..749d806ee1d1 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1170,10 +1170,12 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
if (opts->sample_weight)
evsel__set_sample_bit(evsel, WEIGHT);

- attr->task = track;
- attr->mmap = track;
- attr->mmap2 = track && !perf_missing_features.mmap2;
- attr->comm = track;
+ attr->task = track;
+ attr->mmap = track;
+ attr->mmap2 = track && !perf_missing_features.mmap2;
+ attr->comm = track;
+ attr->build_id = track && opts->build_id;
+
/*
* ksymbol is tracked separately with text poke because it needs to be
* system wide and enabled immediately.
diff --git a/tools/perf/util/perf_api_probe.c b/tools/perf/util/perf_api_probe.c
index 3840d02f0f7b..829af17a0867 100644
--- a/tools/perf/util/perf_api_probe.c
+++ b/tools/perf/util/perf_api_probe.c
@@ -98,6 +98,11 @@ static void perf_probe_text_poke(struct evsel *evsel)
evsel->core.attr.text_poke = 1;
}

+static void perf_probe_build_id(struct evsel *evsel)
+{
+ evsel->core.attr.build_id = 1;
+}
+
bool perf_can_sample_identifier(void)
{
return perf_probe_api(perf_probe_sample_identifier);
@@ -172,3 +177,8 @@ bool perf_can_aux_sample(void)

return true;
}
+
+bool perf_can_record_build_id(void)
+{
+ return perf_probe_api(perf_probe_build_id);
+}
diff --git a/tools/perf/util/perf_api_probe.h b/tools/perf/util/perf_api_probe.h
index d5506a983a94..f12ca55f509a 100644
--- a/tools/perf/util/perf_api_probe.h
+++ b/tools/perf/util/perf_api_probe.h
@@ -11,5 +11,6 @@ bool perf_can_record_cpu_wide(void);
bool perf_can_record_switch_events(void);
bool perf_can_record_text_poke_events(void);
bool perf_can_sample_identifier(void);
+bool perf_can_record_build_id(void);

#endif // __PERF_API_PROBE_H
diff --git a/tools/perf/util/perf_event_attr_fprintf.c b/tools/perf/util/perf_event_attr_fprintf.c
index e67a227c0ce7..0f1c62d40a89 100644
--- a/tools/perf/util/perf_event_attr_fprintf.c
+++ b/tools/perf/util/perf_event_attr_fprintf.c
@@ -134,6 +134,7 @@ int perf_event_attr__fprintf(FILE *fp, struct perf_event_attr *attr,
PRINT_ATTRf(bpf_event, p_unsigned);
PRINT_ATTRf(aux_output, p_unsigned);
PRINT_ATTRf(cgroup, p_unsigned);
+ PRINT_ATTRf(build_id, p_unsigned);

PRINT_ATTRn("{ wakeup_events, wakeup_watermark }", wakeup_events, p_unsigned);
PRINT_ATTRf(bp_type, p_unsigned);
diff --git a/tools/perf/util/record.h b/tools/perf/util/record.h
index 266760ac9143..609e706f4282 100644
--- a/tools/perf/util/record.h
+++ b/tools/perf/util/record.h
@@ -49,6 +49,7 @@ struct record_opts {
bool no_bpf_event;
bool kcore;
bool text_poke;
+ bool build_id;
unsigned int freq;
unsigned int mmap_pages;
unsigned int auxtrace_mmap_pages;