netdev - Re: [PATCH] flow_dissector: avoid uninitialized variable access

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Message-ID: <20161022065548.GA1625@nanopsycho.orion>
Date:   Sat, 22 Oct 2016 08:55:48 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>,
        Alexander Duyck <aduyck@...antis.com>,
        Tom Herbert <tom@...bertland.com>,
        Jiri Pirko <jiri@...lanox.com>,
        Hadar Hen Zion <hadarh@...lanox.com>,
        Gao Feng <fgao@...ai8.com>, Eric Garver <e@...g.me>,
        Amir Vadai <amir@...ai.me>,
        Network Development <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] flow_dissector: avoid uninitialized variable access

Sat, Oct 22, 2016 at 03:48:48AM CEST, torvalds@...ux-foundation.org wrote:
>On Fri, Oct 21, 2016 at 9:31 AM, Jiri Pirko <jiri@...nulli.us> wrote:
>>
>> I don't see how vlan could be used uninitialized. But I understand that
>> this is impossible for gcc to track it. Please just use uninitialized_var()
>
>Actually, I think we should never use "uninitialized_var()" except
>possibly for arrays or structures that gcc can complain about.
>
>It's a horrible thing to use, in that it adds extra cruft to the
>source code, and then shuts up a compiler warning (even the _reliable_
>warnings from gcc).
>
>It's much better to just initialize the variable, and if gcc some day
>gets smarter and sees that it  is unnecessary and always overwritten,
>so much the better. The cost of initializing a single word is
>basically zero.

On the other hand, I would agrue that initializing a var to "some" value
that is never used might confuse the reader. He would naturally try to
understand the reason for that exact value in initialization.