From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760326AbYEMNYX (ORCPT ); Tue, 13 May 2008 09:24:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756108AbYEMNYP (ORCPT ); Tue, 13 May 2008 09:24:15 -0400 Received: from out1.smtp.messagingengine.com ([66.111.4.25]:58231 "EHLO out1.smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755897AbYEMNYO (ORCPT ); Tue, 13 May 2008 09:24:14 -0400 Message-Id: <1210685053.13437.1252892061@webmail.messagingengine.com> X-Sasl-Enc: j/OZ41inK+ICsf6EcRiB6PLJKQq5qbBKmCjIhCWV1kqs 1210685053 From: "Alexander van Heukelum" To: "Nickolay Vinogradov" Cc: linux-kernel@vger.kernel.org, "Russell King" , "Andrew Morton" Content-Disposition: inline Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="ISO-8859-1" MIME-Version: 1.0 X-Mailer: MessagingEngine.com Webmail Interface References: <481E076A.8060302@protei.ru> <1210677433.22341.1252875863@webmail.messagingengine.com> <48298990.7040705@protei.ru> Subject: Re: [PATCH] asm-generic/bitops/fls64.h In-Reply-To: <48298990.7040705@protei.ru> Date: Tue, 13 May 2008 15:24:13 +0200 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 13 May 2008 16:29:04 +0400, "Nickolay Vinogradov" said: > Alexander van Heukelum пишет: > > > Hi Nickolay, > > > > The change is ok, I guess, but the cast should be a no-op (fls > > takes an int, which is always 32 bit in linux). What is the problem > > you are seeing? Does fls64() return a wrong value in some cases? If > > so, what cpu? Which values? > > > > Why would this be a bug on big endian systems only? There is no > > pointer magic involved, so the compiler should take care of the > > casts in a correct way. > > > > Maybe you see a compiler warning? Which compiler version? > > > > (also note that current (development) kernels now have separate > > versions for 32-bit and 64-bit environments.) > > Because fls() is a macro for asm-arm: > > #define fls(x) \ > ( __builtin_constant_p(x) ? constant_fls(x) : \ > ({ int __r; asm("clz\t%0, %1" : "=r"(__r) : "r"(x) : "cc"); > 32-__r; }) ) > > We can fix it right here: > > diff --git a/include/asm-arm/bitops.h b/include/asm-arm/bitops.h > index 5c60bfc..ce3fb6f 100644 > --- a/include/asm-arm/bitops.h > +++ b/include/asm-arm/bitops.h > @@ -279,7 +279,7 @@ static inline int constant_fls(int x) > > #define fls(x) \ > ( __builtin_constant_p(x) ? constant_fls(x) : \ > - ({ int __r; asm("clz\t%0, %1" : "=r"(__r) : "r"(x) : "cc"); > 32-__r; }) ) > + ({ int __r; asm("clz\t%0, %1" : "=r"(__r) : "r"((__u32)x) : > "cc"); 32-__r; }) ) > #define ffs(x) ({ unsigned long __t = (x); fls(__t & -__t); }) > #define __ffs(x) (ffs(x) - 1) > #define ffz(x) __ffs( ~(x) ) Hmm, indeed. Maybe: ({ int __r, __x = (x); asm("clz\t%0, %1" : "=r"(__r) : "r"(__x) : "cc"); 32-__r; }) ? This is a 32-bit machine, right? Doesn't the compiler complain about feeding a long long into a 32-bit register? Greetings, Alexander -- Alexander van Heukelum heukelum@fastmail.fm -- http://www.fastmail.fm - I mean, what is it about a decent email service?