linux-kernel - Re: [PATCH] rtc: ds1685: actually spin forever in poweroff error path

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Message-ID: <20160310224801.GP9868@piout.net>
Date:	Thu, 10 Mar 2016 23:48:01 +0100
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	Josh Poimboeuf <jpoimboe@...hat.com>
Cc:	Joshua Kinard <kumba@...too.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, linux-kernel@...r.kernel.org,
	kbuild test robot <fengguang.wu@...el.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH] rtc: ds1685: actually spin forever in poweroff error path

On 07/03/2016 at 09:03:02 -0600, Josh Poimboeuf wrote :
> objtool reports the following warnings:
> 
>   drivers/rtc/rtc-ds1685.o: warning: objtool: ds1685_rtc_work_queue()+0x0: duplicate frame pointer save
>   drivers/rtc/rtc-ds1685.o: warning: objtool: ds1685_rtc_work_queue()+0x3: duplicate frame pointer setup
>   drivers/rtc/rtc-ds1685.o: warning: objtool: ds1685_rtc_work_queue()+0x0: frame pointer state mismatch
> 
> The warning message needs to be improved, but what it really means in
> this case is that ds1685_rtc_poweroff() has a possible code path where
> it can actually fall through to the next function in the object code,
> ds1685_rtc_work_queue().
> 
> The bug is caused by the use of the unreachable() macro in a place which
> is actually reachable.  That causes gcc to assume that the printk()
> immediately before the unreachable() macro never returns, when in fact
> it does.  So gcc places the printk() at the very end of the function's
> object code.  When the printk() returns, the next function starts
> executing.
> 
> The surrounding comment and printk message state that the code should
> spin forever, which explains the unreachable() statement.  However the
> actual spin code is missing.
> 
> Reported-by: kbuild test robot <fengguang.wu@...el.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
> ---
>  drivers/rtc/rtc-ds1685.c | 1 +
>  1 file changed, 1 insertion(+)
> 
Applied, thanks.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com