From mboxrd@z Thu Jan 1 00:00:00 1970 From: Behan Webster Subject: Re: [PATCH v2] LLVMLinux: Remove warning about returning an uninitialized variable Date: Sat, 22 Mar 2014 23:32:21 -0700 Message-ID: <532E7FF5.9060806@converseincode.com> References: <201403221101.16961.arnd@arndb.de> <1395503299-15203-1-git-send-email-behanw@converseincode.com> <1395505786.2143.14.camel@dabdike.int.hansenpartnership.com> <532DBC50.9040505@converseincode.com> <1395506558.2143.18.camel@dabdike.int.hansenpartnership.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1395506558.2143.18.camel@dabdike.int.hansenpartnership.com> Sender: linux-kernel-owner@vger.kernel.org To: James Bottomley Cc: arnd@arndb.de, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, dwmw2@infradead.org, pageexec@freemail.hu, Mark Charlebois List-Id: linux-arch.vger.kernel.org On 03/22/14 09:42, James Bottomley wrote: > On Sat, 2014-03-22 at 09:37 -0700, Behan Webster wrote: >> On 03/22/14 09:29, James Bottomley wrote: >>> On Sat, 2014-03-22 at 08:48 -0700, behanw@converseincode.com wrote: >>>> From: Behan Webster >>>> >>>> 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 >>>> Signed-off-by: Mark Charlebois >>>> --- >>>> 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. > OK, but it's not supported by gcc-3. So gcc-3 would crap out seeing the > statement, which is why we have to wrapper it. Sorry. I wasn't clear. It is not merely a gcc-4 ism; it is also supported by clang. I'm not arguing it should be used. I understand (and agree with) your objection to its use since it isn't supported before gcc-4. >>> 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. > Great; This seems to work for me (but then my compiler doesn't see the > unreachable problem). > > James > > --- > diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h > index d8d4c89..70bef78 100644 > --- a/include/asm-generic/cmpxchg-local.h > +++ b/include/asm-generic/cmpxchg-local.h > @@ -4,7 +4,8 @@ > #include > #include > > -extern unsigned long wrong_size_cmpxchg(volatile void *ptr); > +extern unsigned long wrong_size_cmpxchg(volatile void *ptr) > + __noreturn; > > /* > * Generic version of __cmpxchg_local (disables interrupts). Takes an unsigned Nice. I'll give it a try. It looks like a much better solution. Behan -- Behan Webster behanw@converseincode.com From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f42.google.com ([209.85.220.42]:54363 "EHLO mail-pa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750817AbaCWGcZ (ORCPT ); Sun, 23 Mar 2014 02:32:25 -0400 Received: by mail-pa0-f42.google.com with SMTP id fb1so4113244pad.15 for ; Sat, 22 Mar 2014 23:32:24 -0700 (PDT) Message-ID: <532E7FF5.9060806@converseincode.com> Date: Sat, 22 Mar 2014 23:32:21 -0700 From: Behan Webster MIME-Version: 1.0 Subject: Re: [PATCH v2] LLVMLinux: Remove warning about returning an uninitialized variable References: <201403221101.16961.arnd@arndb.de> <1395503299-15203-1-git-send-email-behanw@converseincode.com> <1395505786.2143.14.camel@dabdike.int.hansenpartnership.com> <532DBC50.9040505@converseincode.com> <1395506558.2143.18.camel@dabdike.int.hansenpartnership.com> In-Reply-To: <1395506558.2143.18.camel@dabdike.int.hansenpartnership.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: James Bottomley Cc: arnd@arndb.de, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, dwmw2@infradead.org, pageexec@freemail.hu, Mark Charlebois Message-ID: <20140323063221.ymmqcQMSIbEuP8PNfVxQ9YfrgzEB8pD4b4hXPSQbEK0@z> On 03/22/14 09:42, James Bottomley wrote: > On Sat, 2014-03-22 at 09:37 -0700, Behan Webster wrote: >> On 03/22/14 09:29, James Bottomley wrote: >>> On Sat, 2014-03-22 at 08:48 -0700, behanw@converseincode.com wrote: >>>> From: Behan Webster >>>> >>>> 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 >>>> Signed-off-by: Mark Charlebois >>>> --- >>>> 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. > OK, but it's not supported by gcc-3. So gcc-3 would crap out seeing the > statement, which is why we have to wrapper it. Sorry. I wasn't clear. It is not merely a gcc-4 ism; it is also supported by clang. I'm not arguing it should be used. I understand (and agree with) your objection to its use since it isn't supported before gcc-4. >>> 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. > Great; This seems to work for me (but then my compiler doesn't see the > unreachable problem). > > James > > --- > diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h > index d8d4c89..70bef78 100644 > --- a/include/asm-generic/cmpxchg-local.h > +++ b/include/asm-generic/cmpxchg-local.h > @@ -4,7 +4,8 @@ > #include > #include > > -extern unsigned long wrong_size_cmpxchg(volatile void *ptr); > +extern unsigned long wrong_size_cmpxchg(volatile void *ptr) > + __noreturn; > > /* > * Generic version of __cmpxchg_local (disables interrupts). Takes an unsigned Nice. I'll give it a try. It looks like a much better solution. Behan -- Behan Webster behanw@converseincode.com