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Message-ID: <c9f382b2-cd96-4ee3-ad68-95381d9e09c0@intel.com>
Date: Thu, 11 Apr 2024 10:16:16 +0300
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Subject: Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG
To: Arnd Bergmann <arnd@arndb.de>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
 Michael Ellerman <mpe@ellerman.id.au>, Nicholas Piggin <npiggin@gmail.com>,
 Christophe Leroy <christophe.leroy@csgroup.eu>,
 "Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
 "Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
 Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>,
 Alexander Gordeev <agordeev@linux.ibm.com>,
 Christian Borntraeger <borntraeger@linux.ibm.com>,
 Sven Schnelle <svens@linux.ibm.com>, Ingo Molnar <mingo@redhat.com>,
 Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>,
 x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
 Andy Lutomirski <luto@kernel.org>,
 Vincenzo Frascino <vincenzo.frascino@arm.com>,
 John Stultz <jstultz@google.com>, Stephen Boyd <sboyd@kernel.org>,
 Peter Zijlstra <peterz@infradead.org>, Randy Dunlap <rdunlap@infradead.org>,
 Bjorn Helgaas <bhelgaas@google.com>,
 Anna-Maria Gleixner <anna-maria@linutronix.de>,
 linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
 linux-s390@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>
References: <20240410153212.127477-1-adrian.hunter@intel.com>
 <87be83da-6102-483d-b1dc-a77eecc9f780@app.fastmail.com>
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From: Adrian Hunter <adrian.hunter@intel.com>
Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki,
 Business Identity Code: 0357606 - 4, Domiciled in Helsinki
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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/