From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756537AbaEPMtv (ORCPT ); Fri, 16 May 2014 08:49:51 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:49636 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754550AbaEPMsY (ORCPT ); Fri, 16 May 2014 08:48:24 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Alex Wu" , "Xiangyu Lu" , "Dave Martin" , "Nicolas Pitre" , "Russell King" Date: Fri, 16 May 2014 13:47:21 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 20/34] ARM: 8027/1: fix do_div() bug in big-endian systems In-Reply-To: X-SA-Exim-Connect-IP: 2001:470:1f08:1539:3db0:c181:6526:5597 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.59-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Xiangyu Lu commit 80bb3ef109ff40a7593d9481c17de9bbc4d7c0e2 upstream. In big-endian systems, "%1" get the most significant part of the value, cause the instruction to get the wrong result. When viewing ftrace record in big-endian ARM systems, we found that the timestamp errors: swapper-0 [001] 1325.970000: 0:120:R ==> [001] 16:120:R events/1 events/1-16 [001] 1325.970000: 16:120:S ==> [001] 0:120:R swapper swapper-0 [000] 1325.1000000: 0:120:R + [000] 15:120:R events/0 swapper-0 [000] 1325.1000000: 0:120:R ==> [000] 15:120:R events/0 swapper-0 [000] 1326.030000: 0:120:R + [000] 1150:120:R sshd swapper-0 [000] 1326.030000: 0:120:R ==> [000] 1150:120:R sshd When viewed ftrace records, it will call the do_div(n, base) function, which achieved arch/arm/include/asm/div64.h in. When n = 10000000, base = 1000000, in do_div(n, base) will execute "umull %Q0, %R0, %1, %Q2". Reviewed-by: Dave Martin Reviewed-by: Nicolas Pitre Signed-off-by: Alex Wu Signed-off-by: Xiangyu Lu Signed-off-by: Russell King Signed-off-by: Ben Hutchings --- arch/arm/include/asm/div64.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/arm/include/asm/div64.h +++ b/arch/arm/include/asm/div64.h @@ -156,7 +156,7 @@ /* Select the best insn combination to perform the */ \ /* actual __m * __n / (__p << 64) operation. */ \ if (!__c) { \ - asm ( "umull %Q0, %R0, %1, %Q2\n\t" \ + asm ( "umull %Q0, %R0, %Q1, %Q2\n\t" \ "mov %Q0, #0" \ : "=&r" (__res) \ : "r" (__m), "r" (__n) \