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SubjectRe: [PATCH] pinctrl: ingenic: Make unreachable path more robust
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?

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.

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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