linux-kernel - Re: [PATCH] [v2] printk: avoid -Wsometimes-uninitialized warning

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Date:   Mon, 4 Oct 2021 13:31:25 +0100
From:   Chris Down <chris@...isdown.name>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Arnd Bergmann <arnd@...nel.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Arnd Bergmann <arnd@...db.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        YueHaibing <yuehaibing@...wei.com>, Jessica Yu <jeyu@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] [v2] printk: avoid -Wsometimes-uninitialized warning

Petr Mladek writes:
>On Tue 2021-09-28 11:17:26, Chris Down wrote:
>> Arnd Bergmann writes:
>> > From: Arnd Bergmann <arnd@...db.de>
>> >
>> > clang notices that the pi_get_entry() function would use
>> > uninitialized data if it was called with a non-NULL module
>> > pointer on a kernel that does not support modules:
>> >
>> > kernel/printk/index.c:32:6: error: variable 'nr_entries' is used uninitialized whenever 'if' condition is false [-Werror,-Wsometimes-uninitialized]
>> >        if (!mod) {
>> >            ^~~~
>> > kernel/printk/index.c:38:13: note: uninitialized use occurs here
>> >        if (pos >= nr_entries)
>> >                   ^~~~~~~~~~
>> > kernel/printk/index.c:32:2: note: remove the 'if' if its condition is always true
>> >        if (!mod) {
>> >
>> > Rework the condition to make it clear to the compiler that we are always
>> > in the second case. Unfortunately the #ifdef is still required as the
>> > definition of 'struct module' is hidden when modules are disabled.
>> >
>> > Fixes: 337015573718 ("printk: Userspace format indexing support")
>>
>> This changelog should make it clear that this is theoretical and will never
>> actually happen, which is salient information for people who are considering
>> whether it should go in stable or similar.
>
>IMHO, the sentence "Rework the condition to make it clear that this
>is theoretical and will never actually happen" is rather clear.

Sounds good to me, thanks!

I guess it's unneeded at this point, but feel free to add:

Acked-by: Chris Down <chris@...isdown.name>

>Well, I am not a native speaker.
>
>Anyway, I have pushed the patch into printk/linux.git, branch
>for-5.16.
>
>Best Regards,
>Petr