perf tools: Fix a bug of segmentation fault

Fix the 'segmentation fault' bug of 'perf list --list-cmds', which also
happens in other cases (e.g. record, report ...). This bug happens when
there are no cmds to list at all.

Example:

Before this patch:

  $ perf list --list-cmds
  Segmentation fault
  $

  After this patch:
  $ perf list --list-cmds
  $

As shown above, the result prints nothing rather than a segmentation
fault. The null result means 'perf list' has no cmds to display at this
time.

Signed-off-by: Yunlong Song <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Wang Nan <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

1 files changed, 4 insertions, 2 deletions

diff --git a/tools/perf/util/parse-options.c b/tools/perf/util/parse-options.c
index 4a015f77e2b5..4ee9a86705ed 100644
--- a/tools/perf/util/parse-options.c
+++ b/tools/perf/util/parse-options.c
@@ -510,8 +510,10 @@ int parse_options_subcommand(int argc, const char **argv, const struct option *o
 		}
 		exit(130);
 	case PARSE_OPT_LIST_SUBCMDS:
-		for (int i = 0; subcommands[i]; i++)
-			printf("%s ", subcommands[i]);
+		if (subcommands) {
+			for (int i = 0; subcommands[i]; i++)
+				printf("%s ", subcommands[i]);
+		}
 		exit(130);
 	default: /* PARSE_OPT_UNKNOWN */
 		if (ctx.argv[0][1] == '-') {