perf help: Fix bug when there's no perf-* command around

main_cmds can be empty - fix util/help.c to handle this case
without segfaulting.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 16 insertions, 12 deletions

diff --git a/Documentation/perf_counter/util/help.c b/Documentation/perf_counter/util/help.c
index 397487fb2bee..6653f7dd1d78 100644
--- a/Documentation/perf_counter/util/help.c
+++ b/Documentation/perf_counter/util/help.c
@@ -298,7 +298,7 @@ static void add_cmd_list(struct cmdnames *cmds, struct cmdnames *old)
 
 const char *help_unknown_cmd(const char *cmd)
 {
-        int i, n, best_similarity = 0;
+        int i, n = 0, best_similarity = 0;
         struct cmdnames main_cmds, other_cmds;
 
         memset(&main_cmds, 0, sizeof(main_cmds));
@@ -315,20 +315,24 @@ const char *help_unknown_cmd(const char *cmd)
               sizeof(main_cmds.names), cmdname_compare);
         uniq(&main_cmds);
 
-        /* This reuses cmdname->len for similarity index */
-        for (i = 0; i < main_cmds.cnt; ++i)
-                main_cmds.names[i]->len =
-                        levenshtein(cmd, main_cmds.names[i]->name, 0, 2, 1, 4);
+        if (main_cmds.cnt) {
+                /* This reuses cmdname->len for similarity index */
+                for (i = 0; i < main_cmds.cnt; ++i)
+                        main_cmds.names[i]->len =
+                                levenshtein(cmd, main_cmds.names[i]->name, 0, 2, 1, 4);
 
-        qsort(main_cmds.names, main_cmds.cnt,
-              sizeof(*main_cmds.names), levenshtein_compare);
+                qsort(main_cmds.names, main_cmds.cnt,
+                      sizeof(*main_cmds.names), levenshtein_compare);
+
+                best_similarity = main_cmds.names[0]->len;
+                n = 1;
+                while (n < main_cmds.cnt && best_similarity == main_cmds.names[n]->len)
+                        ++n;
+        }
 
-        best_similarity = main_cmds.names[0]->len;
-        n = 1;
-        while (n < main_cmds.cnt && best_similarity == main_cmds.names[n]->len)
-                ++n;
         if (autocorrect && n == 1) {
                 const char *assumed = main_cmds.names[0]->name;
+
                 main_cmds.names[0] = NULL;
                 clean_cmdnames(&main_cmds);
                 fprintf(stderr, "WARNING: You called a Git program named '%s', "
@@ -345,7 +349,7 @@ const char *help_unknown_cmd(const char *cmd)
 
         fprintf(stderr, "perf: '%s' is not a perf-command. See 'perf --help'.\n", cmd);
 
-        if (best_similarity < 6) {
+        if (main_cmds.cnt && best_similarity < 6) {
                 fprintf(stderr, "\nDid you mean %s?\n",
                         n < 2 ? "this": "one of these");