linux-kernel - Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG

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Message-ID: <c9f382b2-cd96-4ee3-ad68-95381d9e09c0@intel.com>
Date: Thu, 11 Apr 2024 10:16:16 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Naresh Kamboju <naresh.kamboju@...aro.org>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Alexander Gordeev <agordeev@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Andy Lutomirski <luto@...nel.org>,
 Vincenzo Frascino <vincenzo.frascino@....com>,
 John Stultz <jstultz@...gle.com>, Stephen Boyd <sboyd@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Randy Dunlap <rdunlap@...radead.org>,
 Bjorn Helgaas <bhelgaas@...gle.com>,
 Anna-Maria Gleixner <anna-maria@...utronix.de>,
 linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
 linux-s390@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG

On 11/04/24 10:04, Arnd Bergmann wrote:
> On Wed, Apr 10, 2024, at 17:32, Adrian Hunter wrote:
>> BUG() does not return, and arch implementations of BUG() use unreachable()
>> or other non-returning code. However with !CONFIG_BUG, the default
>> implementation is often used instead, and that does not do that. x86 always
>> uses its own implementation, but powerpc with !CONFIG_BUG gives a build
>> error:
>>
>>   kernel/time/timekeeping.c: In function ‘timekeeping_debug_get_ns’:
>>   kernel/time/timekeeping.c:286:1: error: no return statement in function
>>   returning non-void [-Werror=return-type]
>>
>> Add unreachable() to default !CONFIG_BUG BUG() implementation.
> 
> I'm a bit worried about this patch, since we have had problems
> with unreachable() inside of BUG() in the past, and as far as I
> can remember, the current version was the only one that
> actually did the right thing on all compilers.
> 
> One problem with an unreachable() annotation here is that if
> a compiler misanalyses the endless loop, it can decide to
> throw out the entire code path leading up to it and just
> run into undefined behavior instead of printing a BUG()
> message.
> 
> Do you know which compiler version show the warning above?

Original report has a list

	https://lore.kernel.org/all/CA+G9fYvjdZCW=7ZGxS6A_3bysjQ56YF7S-+PNLQ_8a4DKh1Bhg@mail.gmail.com/