Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754418AbbG0Pyt (ORCPT ); Mon, 27 Jul 2015 11:54:49 -0400 Received: from mail-wi0-f171.google.com ([209.85.212.171]:36066 "EHLO mail-wi0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752574AbbG0Pyr (ORCPT ); Mon, 27 Jul 2015 11:54:47 -0400 Date: Mon, 27 Jul 2015 17:54:43 +0200 From: Ingo Molnar To: Uros Bizjak Cc: Uros Bizjak , linux-kernel@vger.kernel.org, "x86@kernel.org" Subject: Re: [PATCH] x86: Introduce ASM flags to bitops Message-ID: <20150727155443.GA20896@gmail.com> References: <1437869262-3211-1-git-send-email-uros_bizjak1@t-2.net> <20150727154035.GA18213@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2619 Lines: 70 * Uros Bizjak wrote: > On Mon, Jul 27, 2015 at 5:40 PM, Ingo Molnar wrote: > > > > * Uros Bizjak wrote: > > > >> From: Uros Bizjak > >> > >> This patch introduces GCC ASM flags to bitops. Instead of e.g. > >> > >> 136d7: 48 0f a3 3d 00 00 00 bt %rdi,0x0(%rip) > >> 136de: 00 > >> 136df: 19 ff sbb %edi,%edi > >> 136e1: 85 ff test %edi,%edi > >> 136e3: 0f 95 c0 setne %al > >> > >> following code is generated: > >> > >> 13767: 48 0f a3 3d 00 00 00 bt %rdi,0x0(%rip) > >> 1376e: 00 > >> 1376f: 0f 92 c0 setb %al > >> > >> Similar improvement can be seen in following code: > >> > >> 7a6c: 48 0f a3 11 bt %rdx,(%rcx) > >> 7a70: 19 d2 sbb %edx,%edx > >> 7a72: 85 d2 test %edx,%edx > >> 7a74: 74 eb je 7a61 > >> > >> which becomes: > >> > >> 7a8c: 48 0f a3 11 bt %rdx,(%rcx) > >> 7a90: 73 ef jae 7a81 > >> > >> Signed-off-by: Uros Bizjak > >> --- > >> arch/x86/include/asm/bitops.h | 26 ++++++++++++++++++++++++-- > >> arch/x86/include/asm/percpu.h | 18 +++++++++++++++++- > >> arch/x86/include/asm/signal.h | 6 ++++++ > >> arch/x86/include/asm/sync_bitops.h | 18 ++++++++++++++++++ > >> 4 files changed, 65 insertions(+), 3 deletions(-) > > > > Nothing in your patch seems to be setting __GCC_ASM_FLAG_OUTPUTS__, and the patch > > does not seem to be mailed as part of a larger series ... > > > > So how is this supposed to work? > > GCC version 6+ will automatically define __GCC_ASM_FLAG_OUTPUTS__ when > this feature is supported. Please see [1] for RFC GCC patch series and > [2] for final committed patch. > > [1] https://gcc.gnu.org/ml/gcc-patches/2015-05/msg00594.html > [2] https://gcc.gnu.org/ml/gcc-patches/2015-06/msg02087.html Ok, great. This information should be part of the changelog and such, as it's not obvious. Does the GCC project treat this as an ABI kind of thing, i.e. can the kernel rely on it from now on, without the GCC side semantics of this feature not ever changing and breaking the kernel? Thanks, Ingo -- 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/