From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752259AbdGYOOi (ORCPT ); Tue, 25 Jul 2017 10:14:38 -0400 Received: from merlin.infradead.org ([205.233.59.134]:35552 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751799AbdGYOOf (ORCPT ); Tue, 25 Jul 2017 10:14:35 -0400 Date: Tue, 25 Jul 2017 16:14:23 +0200 From: Peter Zijlstra To: Will Deacon Cc: Pratyush Anand , linux-arm-kernel@lists.infradead.org, mark.rutland@arm.com, Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , huawei.libin@huawei.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2 1/4] hw_breakpoint: Add step_needed event attribute Message-ID: <20170725141423.ufucj2wl35bdxafh@hirez.programming.kicks-ass.net> References: <9d4f76f3a0bffe93a6d5146c9b53ee7b985f22da.1499416107.git.panand@redhat.com> <20170725132737.GC28815@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170725132737.GC28815@arm.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 25, 2017 at 02:27:38PM +0100, Will Deacon wrote: > On Fri, Jul 07, 2017 at 05:33:57PM +0530, Pratyush Anand wrote: > > Architecture like ARM64 currently allows to use default hw breakpoint > > single step handler only to perf. However, some other users like few > > systemtap tests or kernel test in > > samples/hw_breakpoint/data_breakpoint.c can also work with default step > > handler implementation. At the same time, some other like GDB/ptrace may > > implement their own step handler. > > > > Therefore, this patch introduces a new perf_event_attr bit field, so > > that arch specific code(specially on arm64) can make a decision to > > enable single stepping. > > > > Any architecture which is not using this field will not have any > > side effect. > > diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h > > index b1c0b187acfe..00935808de0d 100644 > > --- a/include/uapi/linux/perf_event.h > > +++ b/include/uapi/linux/perf_event.h > > @@ -345,7 +345,8 @@ struct perf_event_attr { > > context_switch : 1, /* context switch data */ > > write_backward : 1, /* Write ring buffer from end to beginning */ > > namespaces : 1, /* include namespaces data */ > > - __reserved_1 : 35; > > + step_needed : 1, /* Use arch step handler */ > > + __reserved_1 : 34; > > This needs documenting properly, as I really have no idea how userspace is > going to use it sensibley, especially as you silently overwrite it in some > cases below. This is not something userspace _can_ use sensibly afaict. Therefore it should probably not live here.