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

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Date:	Wed, 05 Sep 2012 13:08:03 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Toralf Förster <toralf.foerster@....de>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: does gcc gives a false warning in
 kernel/trace/trace_events_filter.c ?

On Sun, 2012-09-02 at 11:04 +0200, Toralf Förster wrote:
> 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 ?
> 

Strange, as ret is initialized to 'ret = -EINVAL;' in
__ftrace_function_set_filter(). I'm thinking that gcc got confused here.
Maybe report it to the gcc maintainers?

-- Steve


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