From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751584AbaCVQmm (ORCPT ); Sat, 22 Mar 2014 12:42:42 -0400 Received: from bedivere.hansenpartnership.com ([66.63.167.143]:48348 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751199AbaCVQmj (ORCPT ); Sat, 22 Mar 2014 12:42:39 -0400 Message-ID: <1395506558.2143.18.camel@dabdike.int.hansenpartnership.com> Subject: Re: [PATCH v2] LLVMLinux: Remove warning about returning an uninitialized variable From: James Bottomley To: Behan Webster Cc: arnd@arndb.de, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, dwmw2@infradead.org, pageexec@freemail.hu, Mark Charlebois Date: Sat, 22 Mar 2014 09:42:38 -0700 In-Reply-To: <532DBC50.9040505@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> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.10.2 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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