From: Ingo Molnar <mingo@kernel.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] rcu: remove unused variable in boot_cpu_state_init
Date: Thu, 22 Jun 2017 09:51:04 +0200 [thread overview]
Message-ID: <20170622075104.dlajhtcx7p3sgacs@gmail.com> (raw)
In-Reply-To: <CAK8P3a1O4kxMNH00+ox44RMs_pdoQv6+tTvnJOe21eXezs-y_A@mail.gmail.com>
* Arnd Bergmann <arnd@arndb.de> wrote:
> > So I think we should consider it a syntactic construct to avoid.
>
> Unused variables are relatively harmless compared to used-uninitialized
> variables that are always bugs (though they are provably impossible to
> detect correctly in some cases).
So the thing I was most worried about was that old GCC used to not warn about:
long __maybe_unused error;
...
if (error)
return error;
... but recent GCC does warn if it's certain that the use is uninitialized, so the
scenario I outlined should not happen.
But it will supress the warning if the variable is uninitialized but GCC cannot
prove it for sure, so my point remains that it's a potentially dangerous
construct.
Thanks,
Ingo
next prev parent reply other threads:[~2017-06-22 7:51 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-21 21:57 [PATCH] rcu: remove unused variable in boot_cpu_state_init Arnd Bergmann
2017-06-21 22:10 ` Paul E. McKenney
2017-06-21 22:15 ` Arnd Bergmann
2017-06-22 14:36 ` Paul E. McKenney
2017-06-22 21:10 ` Paul E. McKenney
2017-06-22 7:26 ` Ingo Molnar
2017-06-22 7:41 ` Arnd Bergmann
2017-06-22 7:51 ` Ingo Molnar [this message]
2017-06-22 7:54 ` Ingo Molnar
2017-06-22 7:59 ` Ingo Molnar
2017-06-22 8:58 ` Arnd Bergmann
2017-06-22 9:02 ` Ingo Molnar
2017-06-22 9:44 ` Arnd Bergmann
2017-06-22 14:55 ` Paul E. McKenney
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