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>

diff --git a/Documentation/perf_counter/util/help.c b/Documentation/perf_counter/util/help.c
index 397487f..6653f7d 100644 (file)
--- 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");