From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755901Ab3AERKU (ORCPT ); Sat, 5 Jan 2013 12:10:20 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:42752 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755825Ab3AERKK (ORCPT ); Sat, 5 Jan 2013 12:10:10 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@elte.hu, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu, dhowells@redhat.com, edumazet@google.com, darren@dvhart.com, fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 4/6] rcu: Silence compiler array out-of-bounds false positive Date: Sat, 5 Jan 2013 09:09:36 -0800 Message-Id: <1357405778-13903-4-git-send-email-paulmck@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.8 In-Reply-To: <1357405778-13903-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20130105170920.GA13766@linux.vnet.ibm.com> <1357405778-13903-1-git-send-email-paulmck@linux.vnet.ibm.com> X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13010517-5406-0000-0000-000003E57EE7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" It turns out that gcc 4.8 warns on array indexes being out of bounds unless it can prove otherwise. It gives this warning on some RCU initialization code. Because this is far from any fastpath, add an explicit check for array bounds and panic if so. This gives the compiler enough information to figure out that the array index is never out of bounds. However, if a similar false positive occurs on a fastpath, it will probably be necessary to tell the compiler to keep its array-index anxieties to itself. ;-) Markus Trippelsdorf Signed-off-by: Paul E. McKenney --- kernel/rcutree.c | 4 ++++ 1 files changed, 4 insertions(+), 0 deletions(-) diff --git a/kernel/rcutree.c b/kernel/rcutree.c index d145796..e0d9815 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -2938,6 +2938,10 @@ static void __init rcu_init_one(struct rcu_state *rsp, BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */ + /* Silence gcc 4.8 warning about array index out of range. */ + if (rcu_num_lvls > RCU_NUM_LVLS) + panic("rcu_init_one: rcu_num_lvls overflow"); + /* Initialize the level-tracking arrays. */ for (i = 0; i < rcu_num_lvls; i++) -- 1.7.8