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Date:   Mon, 17 Feb 2020 09:18:04 -0600
From:   Josh Poimboeuf <>
To:     Paul Cercueil <>
Cc:     Linus Walleij <>,,,
        Peter Zijlstra <>,
        Randy Dunlap <>
Subject: Re: [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



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,
-			unreachable();
+			/* unreachable */
+			break;

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