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

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Message-ID: <Z_gRR33vGZpIDXmH@surfacebook.localdomain>
Date: Thu, 10 Apr 2025 21:43:19 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>,
	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

Wed, Apr 09, 2025 at 10:16:40AM -0700, Dmitry Torokhov kirjoitti:
> 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/

How does it affect the BUG()?

>From your link:
"I tested using BUG() in lieu of unreachable() like the second change
 I mentioned above, which resolves the issue cleanly, ..."

-- 
With Best Regards,
Andy Shevchenko