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SubjectRe: [PATCH] pinctrl: ingenic: Make unreachable path more robust
Hi Josh,

Le lun., févr. 17, 2020 at 09:18, Josh Poimboeuf <jpoimboe@redhat.com>
a écrit :
> On Fri, Feb 14, 2020 at 11:37:04PM -0300, Paul Cercueil wrote:
>> > > I don't like the idea that you change this driver's code just
>> to
>> > > work around
>> > > a bug in objtool, and I don't like the idea of working around a
>> > > future bug
>> > > that shouldn't be introduced in the first place.
>> >
>> > It's not an objtool bug. It's a byproduct of the fact that GCC's
>> > undefined behavior is inscrutable, and there's no way to
>> determine that
>> > it actually *wants* to jump to a random function.
>> >
>> > And anyway, regardless of objtool, the patch is meant to make the
>> code
>> > more robust.
>> >
>> > Do you not agree that BUG (defined behavior) is more robust than
>> > unreachable (undefined behavior)?
>>
>> It's a dead code path. That would be an undefined behaviour, if it
>> was
>> taken, but it's not.
>
> Given your confidence that humans don't introduce bugs, would you
> recommend that we
>
> s/BUG()/unreachable()/
>
> tree-wide?

Of course not.

> Another option would be to remove the unreachable() statement, which
> would actually improve the generated code by making it more compact
> (16
> bytes of i-cache savings), on top of removing the "fallthrough to next
> function" nastiness.

I'd prefer that, yes.

-Paul

> diff --git a/drivers/pinctrl/pinctrl-ingenic.c
> b/drivers/pinctrl/pinctrl-ingenic.c
> index 96f04d121ebd..13c7d3351ed5 100644
> --- a/drivers/pinctrl/pinctrl-ingenic.c
> +++ b/drivers/pinctrl/pinctrl-ingenic.c
> @@ -2158,7 +2158,8 @@ static int ingenic_pinconf_set(struct
> pinctrl_dev *pctldev, unsigned int pin,
> break;
>
> default:
> - unreachable();
> + /* unreachable */
> + break;
> }
> }
>
>


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