1 files changed, 26 insertions, 0 deletions

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 498c6f70a747..99156c35bc62 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -116,6 +116,9 @@ static int process_sample_event(union perf_event *event,
         if (al.filtered || (hide_unresolved && al.sym == NULL))
                 return 0;
 
+        if (al.map != NULL)
+                al.map->dso->hit = 1;
+
         if (perf_session__add_hist_entry(session, &al, sample, evsel)) {
                 pr_debug("problem incrementing symbol period, skipping event\n");
                 return -1;
@@ -249,6 +252,8 @@ static int __cmd_report(void)
         u64 nr_samples;
         struct perf_session *session;
         struct perf_evsel *pos;
+        struct map *kernel_map;
+        struct kmap *kernel_kmap;
         const char *help = "For a higher level overview, try: perf report --sort comm,dso";
 
         signal(SIGINT, sig_handler);
@@ -268,6 +273,27 @@ static int __cmd_report(void)
         if (ret)
                 goto out_delete;
 
+        kernel_map = session->host_machine.vmlinux_maps[MAP__FUNCTION];
+        kernel_kmap = map__kmap(kernel_map);
+        if (kernel_map == NULL ||
+            (kernel_map->dso->hit &&
+             (kernel_kmap->ref_reloc_sym == NULL ||
+              kernel_kmap->ref_reloc_sym->addr == 0))) {
+                const struct dso *kdso = kernel_map->dso;
+
+                ui__warning("Kernel address maps "
+                            "(/proc/{kallsyms,modules}) were restricted, "
+                            "check /proc/sys/kernel/kptr_restrict before "
+                            "running 'perf record'.\n\n%s\n\n"
+                            "Samples in kernel modules can't be resolved "
+                            "as well.\n\n",
+                            RB_EMPTY_ROOT(&kdso->symbols[MAP__FUNCTION]) ?
+                            "As no suitable kallsyms nor vmlinux was found, "
+                            "kernel samples can't be resolved." :
+                            "If some relocation was applied (e.g. kexec) "
+                            "symbols may be misresolved.");
+        }
+
         if (dump_trace) {
                 perf_session__fprintf_nr_events(session, stdout);
                 goto out_delete;