From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754962Ab3L1BBF (ORCPT ); Fri, 27 Dec 2013 20:01:05 -0500 Received: from terminus.zytor.com ([198.137.202.10]:57983 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754603Ab3L1BBB (ORCPT ); Fri, 27 Dec 2013 20:01:01 -0500 Date: Fri, 27 Dec 2013 17:00:50 -0800 From: "tip-bot for H. Peter Anvin" Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, torvalds@linux-foundation.org, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, tglx@linutronix.de In-Reply-To: References: To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/asm] x86: Slightly tweak the access_ok() C variant for better code Git-Commit-ID: 34f873a773c59f738aff8f412fa59d528f1b3e3f X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.1 (terminus.zytor.com [127.0.0.1]); Fri, 27 Dec 2013 17:00:56 -0800 (PST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 34f873a773c59f738aff8f412fa59d528f1b3e3f Gitweb: http://git.kernel.org/tip/34f873a773c59f738aff8f412fa59d528f1b3e3f Author: H. Peter Anvin AuthorDate: Fri, 27 Dec 2013 16:52:47 -0800 Committer: H. Peter Anvin CommitDate: Fri, 27 Dec 2013 16:58:17 -0800 x86: Slightly tweak the access_ok() C variant for better code gcc can under very specific circumstances realize that the code sequence: foo += bar; if (foo < bar) ... ... is equivalent to a carry out from the addition. Tweak the implementation of access_ok() (specifically __chk_range_not_ok()) to make it more likely that gcc will make that connection. It isn't fool-proof (sometimes gcc seems to think it can make better code with lea, and ends up with a second comparison), still, but it seems to be able to connect the two more frequently this way. Cc: Linus Torvalds Link: http://lkml.kernel.org/r/CA%2B55aFzPBdbfKovMT8Edr4SmE2_=%2BOKJFac9XW2awegogTkVTA@mail.gmail.com Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/uaccess.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 84ecf1d..4f02113 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -41,7 +41,7 @@ * Test whether a block of memory is a valid user space address. * Returns 0 if the range is valid, nonzero otherwise. */ -static inline int __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit) +static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit) { /* * If we have used "sizeof()" for the size, @@ -55,7 +55,9 @@ static inline int __chk_range_not_ok(unsigned long addr, unsigned long size, uns /* Arbitrary sizes? Be careful about overflow */ addr += size; - return (addr < size) || (addr > limit); + if (addr < size) + return true; + return addr > limit; } #define __range_not_ok(addr, size, limit) \ @@ -84,7 +86,7 @@ static inline int __chk_range_not_ok(unsigned long addr, unsigned long size, uns * this function, memory access functions may still return -EFAULT. */ #define access_ok(type, addr, size) \ - (likely(__range_not_ok(addr, size, user_addr_max()) == 0)) + unlikely(!__range_not_ok(addr, size, user_addr_max())) /* * The exception table consists of pairs of addresses relative to the