Re: does gcc gives a false warning in kernel/trace/trace_events_filter.c ?

Steven Rostedt
2012-09-05T17:08:07Z

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