Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756339Ab2EWQ3r (ORCPT ); Wed, 23 May 2012 12:29:47 -0400 Received: from merlin.infradead.org ([205.233.59.134]:41528 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751369Ab2EWQ3o (ORCPT ); Wed, 23 May 2012 12:29:44 -0400 Subject: Re: [tip:x86/mce] x86/bitops: Move BIT_64() for a wider use From: Peter Zijlstra To: Borislav Petkov Cc: "H. Peter Anvin" , mingo@kernel.org, linux-kernel@vger.kernel.org, frank.arnold@amd.com, akpm@linux-foundation.org, torvalds@linux-foundation.org, tglx@linutronix.de, linux-tip-commits@vger.kernel.org In-Reply-To: <20120523161932.GN14757@aftab.osrc.amd.com> References: <1337684026-19740-1-git-send-email-bp@amd64.org> <1337789429.9783.16.camel@laptop> <4FBD0C47.70600@zytor.com> <20120523161932.GN14757@aftab.osrc.amd.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 23 May 2012 18:29:31 +0200 Message-ID: <1337790571.9783.28.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 35 On Wed, 2012-05-23 at 18:19 +0200, Borislav Petkov wrote: > On Wed, May 23, 2012 at 09:11:51AM -0700, H. Peter Anvin wrote: > > On 05/23/2012 09:10 AM, Peter Zijlstra wrote: > > > On Wed, 2012-05-23 at 09:07 -0700, tip-bot for Borislav Petkov wrote: > > >> +#define BIT_64(n) (U64_C(1) << (n)) > > > > > > Because writing 1ULL << n is too much work? > > > > > > > Because writing 1ULL << n is broken in anything that needs to be used in > > assembly, for example. > > Actually we need a BIT() macro that works both > on 32- and 64-bit. But that won't be that easy: > http://lkml.indiana.edu/hypermail/linux/kernel/1010.1/02335.html > > And it should return UL for shift values < 32 and ULL otherwise. If I remember my type rules correctly you'll get something like that with: #define BIT(n) ({ typeof(n) __n = (n); (__n < 32) ? (1UL << __n) : (1ULL << __n); }) That said, having it do this might be unexpected, also hpa mentioned something about assembly magics which will obviously not work with the above either. Anyway, ignore me, I just thought the BIT_64() thing looked funny, but apparently there's good reasons for it. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/