perf report: Fix crash showing warning related to kernel maps

While testing https://lkml.org/lkml/2012/4/10/123 I hit this crash:

(gdb) bt
 0  0x000000000042000f in __cmd_report (rep=0x7fff80cec580) at builtin-report.c:380
 1  cmd_report (argc=0, argv=<optimized out>, prefix=<optimized out>) at builtin-report.c:759
 2  0x0000000000414513 in run_builtin (p=0x7724a8, argc=3, argv=0x7fff80ceca70) at perf.c:273
 3  0x0000000000413d41 in handle_internal_command (argv=0x7fff80ceca70, argc=3) at perf.c:345
 4  run_argv (argv=0x7fff80cec880, argcp=0x7fff80cec88c) at perf.c:389
 5  main (argc=3, argv=0x7fff80ceca70) at perf.c:487

kernel_map can be NULL, so need to handle it while dumping a warning
to user.

v2:
- fixed RB_EMPTY_ROOT check -- desc takes the altnerative output when RB_EMPTY_ROOT is false.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Link: http://lkml.kernel.org/r/1334544855-55021-1-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 2e31743..cdae9b2 100644 (file)
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -374,16 +374,23 @@ static int __cmd_report(struct perf_report *rep)
            (kernel_map->dso->hit &&
             (kernel_kmap->ref_reloc_sym == NULL ||
              kernel_kmap->ref_reloc_sym->addr == 0))) {
-               const struct dso *kdso = kernel_map->dso;
+               const char *desc =
+                   "As no suitable kallsyms nor vmlinux was found, kernel samples\n"
+                   "can't be resolved.";
+
+               if (kernel_map) {
+                       const struct dso *kdso = kernel_map->dso;
+                       if (!RB_EMPTY_ROOT(&kdso->symbols[MAP__FUNCTION])) {
+                               desc = "If some relocation was applied (e.g. "
+                                      "kexec) symbols may be misresolved.";
+                       }
+               }
 
                ui__warning(
 "Kernel address maps (/proc/{kallsyms,modules}) were restricted.\n\n"
 "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\n"
-"can't be resolved." :
-"If some relocation was applied (e.g. kexec) symbols may be misresolved.");
+               desc);
        }
 
        if (dump_trace) {