linux-kernel - Re: drivers/net/can/usb/etas_es58x/es58x_fd.c:174:8: warning: Uninitialized variable: rx_event

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Date:   Wed, 2 Mar 2022 15:47:48 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     Vincent MAILHOL <mailhol.vincent@...adoo.fr>
Cc:     kernel test robot <yujie.liu@...el.com>, kbuild-all@...ts.01.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arunachalam Santhanam <Arunachalam.Santhanam@...bosch.com>,
        linux-can <linux-can@...r.kernel.org>
Subject: Re: drivers/net/can/usb/etas_es58x/es58x_fd.c:174:8: warning:
 Uninitialized variable: rx_event_msg [uninitvar]

On 02.03.2022 23:42:53, Vincent MAILHOL wrote:
> On Wed. 2 Mar 2022 at 22:04, Marc Kleine-Budde <mkl@...gutronix.de> wrote:
> > I was thinking of this:
> >
> > | void *foo = bar->baz;
> > |
> > | if (!bar)
> > |         return;
> > |
> > | printf("%p", foo);
> >
> > There were/are compilers that optimize the bar NULL pointer check away,
> > because bar has already been de-referenced.
> 
> Sorry, I do not get your example. If bar is NULL,
> | void *foo = bar->baz;
> would segfault and thus the check is not reached.

ACK

> If bar is not NULL, the check succeeds.
> 
> In both cases, the return statement of the if branch is never
> executed making this some dead code. So I do not see why this is
> an issue if the compiler removes it.

IIRC in some cases the code was shuffled around by the compiler and the
NULL pointer check was done....and with a new compiler version it
stopped working :)

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde           |
Embedded Linux                   | https://www.pengutronix.de  |
Vertretung West/Dortmund         | Phone: +49-231-2826-924     |
Amtsgericht Hildesheim, HRA 2686 | Fax:   +49-5121-206917-5555 |

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