linux-kernel - Re: [PATCH v2] LLVMLinux: Remove warning about returning an uninitialized variable

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Message-ID: <532DBC50.9040505@converseincode.com>
Date:	Sat, 22 Mar 2014 09:37:36 -0700
From:	Behan Webster <behanw@...verseincode.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	arnd@...db.de, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, dwmw2@...radead.org,
	pageexec@...email.hu, Mark Charlebois <charlebm@...il.com>
Subject: Re: [PATCH v2] LLVMLinux: Remove warning about returning an uninitialized
 variable

On 03/22/14 09:29, James Bottomley wrote:
> On Sat, 2014-03-22 at 08:48 -0700, behanw@...verseincode.com wrote:
>> From: Behan Webster <behanw@...verseincode.com>
>>
>> Fix uninitialized return code in default case in cmpxchg-local.h
>>
>> This patch fixes the code to prevent an uninitialized return value that is detected
>> when compiling with clang. The bug produces numerous warnings when compiling the
>> Linux kernel with clang.
>>
>> Signed-off-by: Behan Webster <behanw@...verseincode.com>
>> Signed-off-by: Mark Charlebois <charlebm@...il.com>
>> ---
>>   include/asm-generic/cmpxchg-local.h | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h
>> index d8d4c89..9112111 100644
>> --- a/include/asm-generic/cmpxchg-local.h
>> +++ b/include/asm-generic/cmpxchg-local.h
>> @@ -41,6 +41,7 @@ static inline unsigned long __cmpxchg_local_generic(volatile void *ptr,
>>   		break;
>>   	default:
>>   		wrong_size_cmpxchg(ptr);
>> +		__builtin_unreachable();
> No, that's got to be unreachable() so that it works in all compilers,
> (__builtin_unreachable is a gcc-4 ism).
It is also supported by clang.

> Got to say this still looks wrong.  If wrong_size_cmpxchg() cannot
> return, the function should be annotated as such with __noreturn (like
> panic()) so the unreachable() should be superfluous.
Okay. I can try that instead.

Thanks,

Behan

-- 
Behan Webster
behanw@...verseincode.com

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