[PATCH 4/7] perf list: fix a bug of segmentation fault

[Yunlong Song]

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 <yunlong.song@xxxxxxxxxx>
---
 tools/perf/util/parse-options.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/parse-options.c b/tools/perf/util/parse-options.c
index 4a015f7..4ee9a86 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] == '-') {
-- 
1.8.5.5

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