Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932525Ab2JUSQQ (ORCPT ); Sun, 21 Oct 2012 14:16:16 -0400 Received: from mail-la0-f46.google.com ([209.85.215.46]:36376 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932132Ab2JUSQO (ORCPT ); Sun, 21 Oct 2012 14:16:14 -0400 Date: Sun, 21 Oct 2012 20:15:53 +0200 From: Rabin Vincent To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Peter Zijlstra , Srikar Dronamraju Subject: Re: [PATCH 3/9] uprobes: allow ignoring of probe hits Message-ID: <20121021181504.GA4840@ubuntu> References: <1350242593-17761-1-git-send-email-rabin@rab.in> <1350242593-17761-3-git-send-email-rabin@rab.in> <20121015165218.GA10239@redhat.com> <20121017173510.GA11019@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121017173510.GA11019@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1525 Lines: 33 On Wed, Oct 17, 2012 at 07:35:10PM +0200, Oleg Nesterov wrote: > On 10/16, Rabin Vincent wrote: > > 2012/10/15 Oleg Nesterov : > > > Not sure I understand why we shouldn't call handlers in this case, > > > but OK, I know nothing about arm. > > > > This old discussion about kprobes should be useful: > > > > http://lists.infradead.org/pipermail/linux-arm-kernel/2011-March/045755.html > > Thanks... Not sure I understand this discussion... > > And, to clarify, I am not arguing. Just curious. > > So, is this like cmov on x86? And this patch allows to not report if > the condition is not true? Or there are other issues on arm? Yes, I guess this is like CMOV on x86. In the ARM instruction set most instructions can be conditionally executed. In order to set the probe on a conditional instruction, we use an undefined instruction with the same condition as the instruction we replace. However, it is implementation defined whether an undefined instruction with a failing condition code will trigger an undefined instruction exception or just be executed as a NOP. So for those processor implementations where we do get the undefined instruction exception even for a failing condition code, we have to ignore it in order to provide consistent behaviour. -- 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/