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

From: Alexandre Belloni
Date: Thu Mar 10 2016 - 17:48:12 EST

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@xxxxxxxxx>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> ---
> drivers/rtc/rtc-ds1685.c | 1 +
> 1 file changed, 1 insertion(+)
Applied, thanks.

Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering