Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751441AbdGZFmK (ORCPT ); Wed, 26 Jul 2017 01:42:10 -0400 Received: from mail-pg0-f52.google.com ([74.125.83.52]:38091 "EHLO mail-pg0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750816AbdGZFmI (ORCPT ); Wed, 26 Jul 2017 01:42:08 -0400 Subject: Re: [PATCH V2 1/4] hw_breakpoint: Add step_needed event attribute To: Will Deacon , mark.rutland@arm.com, Peter Zijlstra Cc: linux-arm-kernel@lists.infradead.org, Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , huawei.libin@huawei.com, linux-kernel@vger.kernel.org References: <9d4f76f3a0bffe93a6d5146c9b53ee7b985f22da.1499416107.git.panand@redhat.com> <20170725132737.GC28815@arm.com> From: Pratyush Anand Message-ID: <70b51184-dbe0-6d0b-c853-be5b556927f1@redhat.com> Date: Wed, 26 Jul 2017 11:12:03 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: <20170725132737.GC28815@arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2724 Lines: 69 On Tuesday 25 July 2017 06:57 PM, 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. >> >> Signed-off-by: Pratyush Anand >> --- >> include/linux/hw_breakpoint.h | 6 ++++++ >> include/uapi/linux/perf_event.h | 3 ++- >> kernel/events/core.c | 2 ++ >> tools/include/uapi/linux/perf_event.h | 3 ++- >> 4 files changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h >> index 0464c85e63fd..6173ae048cbc 100644 >> --- a/include/linux/hw_breakpoint.h >> +++ b/include/linux/hw_breakpoint.h >> @@ -38,6 +38,12 @@ static inline int hw_breakpoint_type(struct perf_event *bp) >> return bp->attr.bp_type; >> } >> >> +static inline bool >> +hw_breakpoint_needs_single_step(struct perf_event *bp) >> +{ >> + return bp->attr.step_needed; >> +} >> + >> static inline unsigned long hw_breakpoint_len(struct perf_event *bp) >> { >> return bp->attr.bp_len; >> 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. I too had thought to put it under include/linux/perf_event.h : struct perf_event. But, see hw_break_module_init() which does not have knowledge of this structure, and we need to have some way so that none-perf kernel module implementation can tell that it needs default arch step handler. Do you see any alternative? -- Regards Pratyush