Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932586Ab2JUTj5 (ORCPT ); Sun, 21 Oct 2012 15:39:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:29531 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932513Ab2JUTj4 (ORCPT ); Sun, 21 Oct 2012 15:39:56 -0400 Date: Sun, 21 Oct 2012 21:40:58 +0200 From: Oleg Nesterov To: Rabin Vincent 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: <20121021194058.GA29137@redhat.com> 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> <20121021181504.GA4840@ubuntu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20121021181504.GA4840@ubuntu> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1244 Lines: 30 On 10/21, Rabin Vincent wrote: > > On Wed, Oct 17, 2012 at 07:35:10PM +0200, Oleg Nesterov wrote: > > > > 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. OK, I see, thanks for your explanation. Oleg. -- 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/