Messages in this thread | | | Subject | Re: [PATCH 34/36] tty: serial: pmac_zilog: Make disposable variable __always_unused | From | Jiri Slaby <> | Date | Thu, 5 Nov 2020 09:55:21 +0100 |
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On 05. 11. 20, 9:36, Lee Jones wrote: > On Thu, 05 Nov 2020, Jiri Slaby wrote: > >> On 05. 11. 20, 8:04, Christophe Leroy wrote: >>> >>> >>> Le 04/11/2020 à 20:35, Lee Jones a écrit : >>>> Fixes the following W=1 kernel build warning(s): >>>> >>>> drivers/tty/serial/pmac_zilog.h:365:58: warning: variable >>>> ‘garbage’ set but not used [-Wunused-but-set-variable] >>> >>> Explain how you are fixing this warning. >>> >>> Setting __always_unused is usually not the good solution for fixing >>> this warning, but here I guess this is likely the good solution. But it >>> should be explained why. > > There are normally 3 ways to fix this warning; > > - Start using/checking the variable/result > - Remove the variable > - Mark it as __{always,maybe}_unused > > The later just tells the compiler that not checking the resultant > value is intentional. There are some functions (as Jiri mentions > below) which are marked as '__must_check' which *require* a dummy > (garbage) variable to be used. > >> Or, why is the "garbage =" needed in the first place? read_zsdata is not >> defined with __warn_unused_result__. > > I used '__always_used' here for fear of breaking something. > > However, if it's safe to remove it, then all the better.
Yes please -- this "garbage" is one of the examples of volatile misuses. If readb didn't work on volatile pointer, marking the return variable as volatile wouldn't save it.
>> And even if it was, would (void)!read_zsdata(port) fix it? > > That's hideous. :D
Sure, marking reads as must_check would be insane.
> *Much* better to just use '__always_used' in that use-case.
Then using a dummy variable to fool must_check must mean must_check is used incorrectly, no :)? But there are always exceptions…
thanks, -- js suse labs
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