linux-kernel - Re: [PATCH v6 05/12] regmap: irq: Remove unreachable goto

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Message-ID: <asjb2gjqpohtq2cyn3pll6nabbymd2o3jg723eloog6znwruo3@47wewlrtom5h>
Date: Wed, 9 Apr 2025 10:16:40 -0700
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Mark Brown <broonie@...nel.org>, 
	Mathieu Dubois-Briand <mathieu.dubois-briand@...tlin.com>, Lee Jones <lee@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Kamel Bouhara <kamel.bouhara@...tlin.com>, Linus Walleij <linus.walleij@...aro.org>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Uwe Kleine-König <ukleinek@...nel.org>, 
	Michael Walle <mwalle@...nel.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org, linux-input@...r.kernel.org, 
	linux-pwm@...r.kernel.org, Grégory Clement <gregory.clement@...tlin.com>, 
	Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v6 05/12] regmap: irq: Remove unreachable goto

On Wed, Apr 09, 2025 at 07:45:42PM +0300, Andy Shevchenko wrote:
> On Wed, Apr 09, 2025 at 05:32:55PM +0100, Mark Brown wrote:
> > On Wed, Apr 09, 2025 at 07:00:24PM +0300, Andy Shevchenko wrote:
> > > On Wed, Apr 09, 2025 at 04:46:04PM +0100, Mark Brown wrote:
> > 
> > > > unreachable() just annotates things, AFAICT it doesn't actually
> > > > guarantee to do anything in particular if the annotation turns out to be
> > > > incorrect.
> > 
> > > I;m not sure I follow. unreachable is a wrapper on top of
> > > __builtin_unreachable() which is intrinsic of the compiler.
> > 
> > > https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html#index-_005f_005fbuiltin_005funreachable
> > 
> > That just says that the program is undefined if we get to the
> > __builtin_undefined() and documents some behaviour around warnings.  One
> > example of undefined behaviour would be doing nothing.
> 
> Theoretically yes, practically return after a BUG() makes no sense. Note,
> that compiler effectively removes 'goto exit;' here (that's also mentioned
> in the documentation independently on the control flow behaviour), so
> I don't know what you expect from it.

So unreachable() sometimes lears to weird behavior from compiler, for
example as mentioned here where we ended up removing it to prevent
miscompilations:

https://lore.kernel.org/all/20241010222451.GA3571761@thelio-3990X/

Thanks.

-- 
Dmitry