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Message-ID: <CACqU3MVJ9Oj4pXH9O_2jnqDVBqKA+AgoWHwP-n2HGD4LU0pMHQ@mail.gmail.com>
Date: Mon, 25 Jul 2011 15:43:32 -0400
From: Arnaud Lacombe <lacombar@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: stufever@...il.com, linux-kernel@...r.kernel.org,
Wang Shaoyan <wangshaoyan.pt@...bao.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] TRACING: Fix a copmile warning
Hi,
On Mon, Jul 25, 2011 at 2:32 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Mon, 2011-07-18 at 17:40 +0800, stufever@...il.com wrote:
>> From: Wang Shaoyan <wangshaoyan.pt@...bao.com>
>>
>> It's harmless but annyoing.
>> kernel/trace/trace_printk.c: In function 'module_trace_bprintk_format_notify':
>> kernel/trace/trace_printk.c:52: warning: 'fmt' may be used uninitialized in this function
>
> I prefer not to add this patch. Fix gcc. Actually some gcc's do not warn
> on this, others do. Here's the code that confuses gcc:
>
> tb_fmt = kmalloc(sizeof(*tb_fmt), GFP_KERNEL);
> if (tb_fmt)
> fmt = kmalloc(strlen(*iter) + 1, GFP_KERNEL);
> if (tb_fmt && fmt) {
> list_add_tail(&tb_fmt->list, &trace_bprintk_fmt_list);
> strcpy(fmt, *iter);
> tb_fmt->fmt = fmt;
> *iter = tb_fmt->fmt;
>
>
> fmt will never be looked at if tb_fmt is NULL, and fmt is initialized if
> tb_fmt is not NULL.
>
Actually, we have a special uninitialized_var(x) macro to handle such
false positive. From include/linux/compiler-gcc.h:
/*
* A trick to suppress uninitialized variable warning without generating any
* code
*/
#define uninitialized_var(x) x = x
- Arnaud
> -- Steve
>
>>
>> Cc: Steven Rostedt <rostedt@...dmis.org>
>> Cc: Frederic Weisbecker <fweisbec@...il.com>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Signed-off-by: Wang Shaoyan <wangshaoyan.pt@...bao.com>
>>
>> ---
>> kernel/trace/trace_printk.c | 2 +-
>> 1 files changed, 1 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/trace/trace_printk.c b/kernel/trace/trace_printk.c
>> index 1f06468..1a5fff8 100644
>> --- a/kernel/trace/trace_printk.c
>> +++ b/kernel/trace/trace_printk.c
>> @@ -49,7 +49,7 @@ static
>> void hold_module_trace_bprintk_format(const char **start, const char **end)
>> {
>> const char **iter;
>> - char *fmt;
>> + char *fmt = NULL;
>>
>> mutex_lock(&btrace_mutex);
>> for (iter = start; iter < end; iter++) {
>
>
> --
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