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perf probe: Report possible permission error for map__load() failure

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Report possible permission error including kptr_restrict setting
for map__load() failure. This can happen when non-superuser runs
perf probe.

With this patch, perf probe shows the following message.

 $ perf probe vfs_read
 Failed to load symbols from /proc/kallsyms
 Please ensure you can read the /proc/kallsyms symbol addresses.
 If the /proc/sys/kernel/kptr_restrict is '2', you can not read
 kernel symbol address even if you are a superuser. Please change
 it to '1'. If kptr_restrict is '1', the superuser can read the
 symbol addresses.
 In that case, please run this command again with sudo.
   Error: Failed to add events.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Link: http://lore.kernel.org/lkml/162282065877.448336.10047912688119745151.stgit@devnote2
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Masami Hiramatsu 2021-06-05 00:30:58 +09:00 committed by Arnaldo Carvalho de Melo
parent fe4f3eb1fd
commit f4f1c42953
1 changed files with 22 additions and 3 deletions
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25
tools/perf/util/probe-event.c
View file

@ -2936,7 +2936,7 @@ static int find_probe_functions(struct map *map, char *name,
bool cut_version = true;
if (map__load(map) < 0)
return 0;
return -EACCES; /* Possible permission error to load symbols */
/* If user gives a version, don't cut off the version from symbols */
if (strchr(name, '@'))
@ -2975,6 +2975,17 @@ void __weak arch__fix_tev_from_maps(struct perf_probe_event *pev __maybe_unused,
struct map *map __maybe_unused,
struct symbol *sym __maybe_unused) { }
static void pr_kallsyms_access_error(void)
{
pr_err("Please ensure you can read the /proc/kallsyms symbol addresses.\n"
"If /proc/sys/kernel/kptr_restrict is '2', you can not read\n"
"kernel symbol addresses even if you are a superuser. Please change\n"
"it to '1'. If kptr_restrict is '1', the superuser can read the\n"
"symbol addresses.\n"
"In that case, please run this command again with sudo.\n");
}
/*
* Find probe function addresses from map.
* Return an error or the number of found probe_trace_event
@ -3011,8 +3022,16 @@ static int find_probe_trace_events_from_map(struct perf_probe_event *pev,
*/
num_matched_functions = find_probe_functions(map, pp->function, syms);
if (num_matched_functions <= 0) {
pr_err("Failed to find symbol %s in %s\n", pp->function,
pev->target ? : "kernel");
if (num_matched_functions == -EACCES) {
pr_err("Failed to load symbols from %s\n",
pev->target ?: "/proc/kallsyms");
if (pev->target)
pr_err("Please ensure the file is not stripped.\n");
else
pr_kallsyms_access_error();
} else
pr_err("Failed to find symbol %s in %s\n", pp->function,
pev->target ? : "kernel");
ret = -ENOENT;
goto out;
} else if (num_matched_functions > probe_conf.max_probes) {