Commit c72bf82f authored by Thomas Falcon's avatar Thomas Falcon Committed by Namhyung Kim
Browse files

perf top: populate PMU capabilities data in perf_env 

Calling perf top with branch filters enabled on Intel CPU's
with branch counters logging (A.K.A LBR event logging [1]) support
results in a segfault.

$ perf top  -e '{cpu_core/cpu-cycles/,cpu_core/event=0xc6,umask=0x3,frontend=0x11,name=frontend_retired_dsb_miss/}' -j any,counter
...
Thread 27 "perf" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffafff76c0 (LWP 949003)]
perf_env__find_br_cntr_info (env=0xf66dc0 <perf_env>, nr=0x0, width=0x7fffafff62c0) at util/env.c:653
653			*width = env->cpu_pmu_caps ? env->br_cntr_width :
(gdb) bt
 #0  perf_env__find_br_cntr_info (env=0xf66dc0 <perf_env>, nr=0x0, width=0x7fffafff62c0) at util/env.c:653
 #1  0x00000000005b1599 in symbol__account_br_cntr (branch=0x7fffcc3db580, evsel=0xfea2d0, offset=12, br_cntr=8) at util/annotate.c:345
 #2  0x00000000005b17fb in symbol__account_cycles (addr=5658172, start=5658160, sym=0x7fffcc0ee420, cycles=539, evsel=0xfea2d0, br_cntr=8) at util/annotate.c:389
 #3  0x00000000005b1976 in addr_map_symbol__account_cycles (ams=0x7fffcd7b01d0, start=0x7fffcd7b02b0, cycles=539, evsel=0xfea2d0, br_cntr=8) at util/annotate.c:422
 #4  0x000000000068d57f in hist__account_cycles (bs=0x110d288, al=0x7fffafff6540, sample=0x7fffafff6760, nonany_branch_mode=false, total_cycles=0x0, evsel=0xfea2d0) at util/hist.c:2850
 #5  0x0000000000446216 in hist_iter__top_callback (iter=0x7fffafff6590, al=0x7fffafff6540, single=true, arg=0x7fffffff9e00) at builtin-top.c:737
 #6  0x0000000000689787 in hist_entry_iter__add (iter=0x7fffafff6590, al=0x7fffafff6540, max_stack_depth=127, arg=0x7fffffff9e00) at util/hist.c:1359
 #7  0x0000000000446710 in perf_event__process_sample (tool=0x7fffffff9e00, event=0x110d250, evsel=0xfea2d0, sample=0x7fffafff6760, machine=0x108c968) at builtin-top.c:845
 #8  0x0000000000447735 in deliver_event (qe=0x7fffffffa120, qevent=0x10fc200) at builtin-top.c:1211
 #9  0x000000000064ccae in do_flush (oe=0x7fffffffa120, show_progress=false) at util/ordered-events.c:245
 #10 0x000000000064d005 in __ordered_events__flush (oe=0x7fffffffa120, how=OE_FLUSH__TOP, timestamp=0) at util/ordered-events.c:324
 #11 0x000000000064d0ef in ordered_events__flush (oe=0x7fffffffa120, how=OE_FLUSH__TOP) at util/ordered-events.c:342
 #12 0x00000000004472a9 in process_thread (arg=0x7fffffff9e00) at builtin-top.c:1120
 #13 0x00007ffff6e7dba8 in start_thread (arg=<optimized out>) at pthread_create.c:448
 #14 0x00007ffff6f01b8c in __GI___clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:78

The cause is that perf_env__find_br_cntr_info tries to access a
null pointer pmu_caps in the perf_env struct. A similar issue exists
for homogeneous core systems which use the cpu_pmu_caps structure.

Fix this by populating cpu_pmu_caps and pmu_caps structures with
values from sysfs when calling perf top with branch stack sampling
enabled.

[1], LBR event logging introduced here:
https://lore.kernel.org/all/20231025201626.3000228-5-kan.liang@linux.intel.com/



Reviewed-by: default avatarIan Rogers <irogers@google.com>
Signed-off-by: default avatarThomas Falcon <thomas.falcon@intel.com>
Link: https://lore.kernel.org/r/20250612163659.1357950-2-thomas.falcon@intel.com


Signed-off-by: default avatarNamhyung Kim <namhyung@kernel.org>
parent ac871873

tools/perf/builtin-top.c

+8 −0
Original line number Diff line number Diff line
@@ -1734,6 +1734,14 @@ int cmd_top(int argc, const char **argv) 
	if (opts->branch_stack && callchain_param.enabled)

		symbol_conf.show_branchflag_count = true;



	if (opts->branch_stack) {

		status = perf_env__read_core_pmu_caps(&perf_env);

		if (status) {

			pr_err("PMU capability data is not available\n");

			goto out_delete_evlist;

		}

	}



	sort__mode = SORT_MODE__TOP;

	/* display thread wants entries to be collapsed in a different tree */

	perf_hpp_list.need_collapse = 1;

tools/perf/util/env.c

+110 −0
Original line number Diff line number Diff line
@@ -433,6 +433,116 @@ static int perf_env__read_nr_cpus_avail(struct perf_env *env) 
	return env->nr_cpus_avail ? 0 : -ENOENT;

}



static int __perf_env__read_core_pmu_caps(const struct perf_pmu *pmu,

					  int *nr_caps, char ***caps,

					  unsigned int *max_branches,

					  unsigned int *br_cntr_nr,

					  unsigned int *br_cntr_width)

{

	struct perf_pmu_caps *pcaps = NULL;

	char *ptr, **tmp;

	int ret = 0;



	*nr_caps = 0;

	*caps = NULL;



	if (!pmu->nr_caps)

		return 0;



	*caps = calloc(pmu->nr_caps, sizeof(char *));

	if (!*caps)

		return -ENOMEM;



	tmp = *caps;

	list_for_each_entry(pcaps, &pmu->caps, list) {

		if (asprintf(&ptr, "%s=%s", pcaps->name, pcaps->value) < 0) {

			ret = -ENOMEM;

			goto error;

		}



		*tmp++ = ptr;



		if (!strcmp(pcaps->name, "branches"))

			*max_branches = atoi(pcaps->value);

		else if (!strcmp(pcaps->name, "branch_counter_nr"))

			*br_cntr_nr = atoi(pcaps->value);

		else if (!strcmp(pcaps->name, "branch_counter_width"))

			*br_cntr_width = atoi(pcaps->value);

	}

	*nr_caps = pmu->nr_caps;

	return 0;

error:

	while (tmp-- != *caps)

		zfree(tmp);

	zfree(caps);

	*nr_caps = 0;

	return ret;

}



int perf_env__read_core_pmu_caps(struct perf_env *env)

{

	struct pmu_caps *pmu_caps;

	struct perf_pmu *pmu = NULL;

	int nr_pmu, i = 0, j;

	int ret;



	nr_pmu = perf_pmus__num_core_pmus();



	if (!nr_pmu)

		return -ENODEV;



	if (nr_pmu == 1) {

		pmu = perf_pmus__find_core_pmu();

		if (!pmu)

			return -ENODEV;

		ret = perf_pmu__caps_parse(pmu);

		if (ret < 0)

			return ret;

		return __perf_env__read_core_pmu_caps(pmu, &env->nr_cpu_pmu_caps,

						      &env->cpu_pmu_caps,

						      &env->max_branches,

						      &env->br_cntr_nr,

						      &env->br_cntr_width);

	}



	pmu_caps = calloc(nr_pmu, sizeof(*pmu_caps));

	if (!pmu_caps)

		return -ENOMEM;



	while ((pmu = perf_pmus__scan_core(pmu)) != NULL) {

		if (perf_pmu__caps_parse(pmu) <= 0)

			continue;

		ret = __perf_env__read_core_pmu_caps(pmu, &pmu_caps[i].nr_caps,

						     &pmu_caps[i].caps,

						     &pmu_caps[i].max_branches,

						     &pmu_caps[i].br_cntr_nr,

						     &pmu_caps[i].br_cntr_width);

		if (ret)

			goto error;



		pmu_caps[i].pmu_name = strdup(pmu->name);

		if (!pmu_caps[i].pmu_name) {

			ret = -ENOMEM;

			goto error;

		}

		i++;

	}



	env->nr_pmus_with_caps = nr_pmu;

	env->pmu_caps = pmu_caps;



	return 0;

error:

	for (i = 0; i < nr_pmu; i++) {

		for (j = 0; j < pmu_caps[i].nr_caps; j++)

			zfree(&pmu_caps[i].caps[j]);

		zfree(&pmu_caps[i].caps);

		zfree(&pmu_caps[i].pmu_name);

	}

	zfree(&pmu_caps);

	return ret;

}



const char *perf_env__raw_arch(struct perf_env *env)

{

	return env && !perf_env__read_arch(env) ? env->arch : "unknown";

tools/perf/util/env.h

+1 −0
Original line number Diff line number Diff line
@@ -152,6 +152,7 @@ struct btf_node; 


extern struct perf_env perf_env;



int perf_env__read_core_pmu_caps(struct perf_env *env);

void perf_env__exit(struct perf_env *env);



int perf_env__kernel_is_64_bit(struct perf_env *env);