From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Adrian Hunter <adrian.hunter@intel.com>, Arnd Bergmann <arnd@arndb.de>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
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" <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" <linuxppc-dev@lists.ozlabs.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG
Date: Thu, 11 Apr 2024 08:13:00 +0000 [thread overview]
Message-ID: <a434248a-1e9f-4f4f-8f90-d36d8e979f53@csgroup.eu> (raw)
In-Reply-To: <c9f382b2-cd96-4ee3-ad68-95381d9e09c0@intel.com>
Le 11/04/2024 à 09:16, Adrian Hunter a écrit :
> 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/
>
Looking at the report, I think the correct fix should be to use
BUILD_BUG() instead of BUG()
WARNING: multiple messages have this Message-ID (diff)
From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: Adrian Hunter <adrian.hunter@intel.com>, Arnd Bergmann <arnd@arndb.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
John Stultz <jstultz@google.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Alexander Gordeev <agordeev@linux.ibm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
"linux-s390@vger.kernel.org" <linux-s390@vger.kernel.org>,
Naresh Kamboju <naresh.kamboju@linaro.org>,
"x86@kernel.org" <x86@kernel.org>,
"Aneesh Kumar K.V" <aneesh.kumar@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Heiko Carstens <hca@linux.ibm.com>,
Nicholas Piggin <npiggin@gmail.com>,
Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
Bjorn Helgaas <bhelgaas@google.com>,
Thomas Gleixner <tglx@linutronix.de>,
Anna-Maria Gleixner <anna-maria@linutronix.de>,
Stephen Boyd <sboyd@kernel.org>,
Randy Dunlap <rdunlap@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Sven Schnelle <svens@linux.ibm.com>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG
Date: Thu, 11 Apr 2024 08:13:00 +0000 [thread overview]
Message-ID: <a434248a-1e9f-4f4f-8f90-d36d8e979f53@csgroup.eu> (raw)
In-Reply-To: <c9f382b2-cd96-4ee3-ad68-95381d9e09c0@intel.com>
Le 11/04/2024 à 09:16, Adrian Hunter a écrit :
> 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/
>
Looking at the report, I think the correct fix should be to use
BUILD_BUG() instead of BUG()
next prev parent reply other threads:[~2024-04-11 8:13 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-10 15:32 [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG Adrian Hunter
2024-04-10 15:32 ` Adrian Hunter
2024-04-10 17:02 ` Naresh Kamboju
2024-04-10 17:02 ` Naresh Kamboju
2024-04-10 20:05 ` [tip: timers/urgent] " tip-bot2 for Adrian Hunter
2024-04-11 7:04 ` [PATCH] " Arnd Bergmann
2024-04-11 7:04 ` Arnd Bergmann
2024-04-11 7:16 ` Adrian Hunter
2024-04-11 7:16 ` Adrian Hunter
2024-04-11 7:56 ` Arnd Bergmann
2024-04-11 9:03 ` Adrian Hunter
2024-04-11 10:27 ` David Laight
2024-04-11 8:13 ` Christophe Leroy [this message]
2024-04-11 8:13 ` Christophe Leroy
2024-04-11 8:22 ` Christophe Leroy
2024-04-11 8:22 ` Christophe Leroy
2024-04-11 9:27 ` Adrian Hunter
2024-04-11 9:27 ` Adrian Hunter
2024-04-11 11:26 ` Arnd Bergmann
2024-04-11 11:26 ` Arnd Bergmann
2024-04-15 2:19 ` Michael Ellerman
2024-04-15 15:35 ` Arnd Bergmann
2024-04-15 15:35 ` Arnd Bergmann
2024-04-15 17:07 ` Christophe Leroy
2024-04-15 17:32 ` Arnd Bergmann
2024-04-15 17:32 ` Arnd Bergmann
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