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From: Michael Ellerman <mpe@ellerman.id.au>
To: Arnd Bergmann <arnd@arndb.de>, Adrian Hunter <adrian.hunter@intel.com>,
 Christophe Leroy <christophe.leroy@csgroup.eu>
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Subject: Re: [PATCH] bug: Fix no-return-statement warning with !CONFIG_BUG
In-Reply-To: <dd6653b2-3a88-4b95-af13-c6fda5b27b39@app.fastmail.com>
References: <20240410153212.127477-1-adrian.hunter@intel.com>
 <87be83da-6102-483d-b1dc-a77eecc9f780@app.fastmail.com>
 <c9f382b2-cd96-4ee3-ad68-95381d9e09c0@intel.com>
 <a434248a-1e9f-4f4f-8f90-d36d8e979f53@csgroup.eu>
 <ff9d7032-a3b6-4ecd-ac26-d7d4a06a5c7f@csgroup.eu>
 <4d429a10-eb45-4262-8e74-69af810ef1ac@intel.com>
 <dd6653b2-3a88-4b95-af13-c6fda5b27b39@app.fastmail.com>
Date: Mon, 15 Apr 2024 12:19:50 +1000
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"Arnd Bergmann" <arnd@arndb.de> writes:
> On Thu, Apr 11, 2024, at 11:27, Adrian Hunter wrote:
>> On 11/04/24 11:22, Christophe Leroy wrote:
>>> Le 11/04/2024 =C3=A0 10:12, Christophe Leroy a =C3=A9crit=C2=A0:
>>>>
>>>> Looking at the report, I think the correct fix should be to use=20
>>>> BUILD_BUG() instead of BUG()
>>>=20
>>> I confirm the error goes away with the following change to next-2024041=
1=20
>>> on powerpc tinyconfig with gcc 13.2
>>>=20
>>> diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
>>> index 4e18db1819f8..3d5ac0cdd721 100644
>>> --- a/kernel/time/timekeeping.c
>>> +++ b/kernel/time/timekeeping.c
>>> @@ -282,7 +282,7 @@ static inline void timekeeping_check_update(struct=
=20
>>> timekeeper *tk, u64 offset)
>>>   }
>>>   static inline u64 timekeeping_debug_get_ns(const struct tk_read_base =
*tkr)
>>>   {
>>> -	BUG();
>>> +	BUILD_BUG();
>>>   }
>>>   #endif
>>>=20
>>
>> That is fragile because it depends on defined(__OPTIMIZE__),
>> so it should still be:
>
> If there is a function that is defined but that must never be
> called, I think we are doing something wrong.

It's a pretty inevitable result of using IS_ENABLED(), which the docs
encourage people to use.

In this case it could easily be turned into a build error by just making
it an extern rather than a static inline.

But I think Christophe's solution is actually better, because it's more
explicit, ie. this function should not be called and if it is that's a
build time error.

cheers