linux-kernel - does gcc gives a false warning in kernel/trace/trace_events

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Message-ID: <50432132.90307@gmx.de>
Date:	Sun, 02 Sep 2012 11:04:50 +0200
From:	Toralf Förster <toralf.foerster@....de>
To:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: does gcc gives a false warning in kernel/trace/trace_events_filter.c
 ?

The current git tree of linux gave with gcc-4.6.3 :

kernel/trace/trace_events_filter.c: In function ‘ftrace_function_set_filter_cb’:
kernel/trace/trace_events_filter.c:2074:8: warning: ‘ret’ may be used uninitialized in this function [-Wuninitialized] 


which refers to this piece of code:


  2061  static int ftrace_function_set_filter_cb(enum move_type move,
  2062                                           struct filter_pred *pred,
  2063                                           int *err, void *data)
  2064  {
  2065          /* Checking the node is valid for function trace. */
  2066          if ((move != MOVE_DOWN) ||
  2067              (pred->left != FILTER_PRED_INVALID)) {
  2068                  *err = ftrace_function_check_pred(pred, 0);
  2069          } else {
  2070                  *err = ftrace_function_check_pred(pred, 1);
  2071                  if (*err)
  2072                          return WALK_PRED_ABORT;
  2073 
  2074                  *err = __ftrace_function_set_filter(pred->op == OP_EQ,
  2075                                                      pred->regex.pattern,
  2076                                                      pred->regex.len,
  2077                                                      data);
  2078          }
  2079 
  2080          return (*err) ? WALK_PRED_ABORT : WALK_PRED_DEFAULT;
  2081  }
  2082  


>From a Gentoo forum user I got a hint :

"Maybe it's some kind of a weird inlining issue? I think it's referring to the ret in __ftrace_function_set_filter(), which would be uninitialized if the for-loop does not run (re_cnt ≤ 0)"

Now I'm wondering if re_cnt can become zero or if gcc is wrong here ?

-- 
MfG/Sincerely
Toralf Förster
pgp finger print: 7B1A 07F4 EC82 0F90 D4C2 8936 872A E508 7DB6 9DA3
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