From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752617AbeEOIJJ (ORCPT ); Tue, 15 May 2018 04:09:09 -0400 Received: from mga06.intel.com ([134.134.136.31]:28000 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752556AbeEOIJD (ORCPT ); Tue, 15 May 2018 04:09:03 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.49,403,1520924400"; d="scan'208";a="41032299" Subject: Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a sample To: Peter Zijlstra , Andy Lutomirski Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Andi Kleen , linux-kernel , linux-perf-users@vger.kernel.org References: <31205dc8-b756-e12b-0249-2ed06c2db9c9@linux.intel.com> <20180509145436.GV12217@hirez.programming.kicks-ass.net> From: Alexey Budankov Message-ID: Date: Tue, 15 May 2018 11:08:59 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180509145436.GV12217@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 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 Hi Andy, On 09.05.2018 17:54, Peter Zijlstra wrote: > On Tue, May 08, 2018 at 06:21:36PM +0300, Alexey Budankov wrote: >> >> Store user space frame-pointer value (BP register) into Perf trace >> on a sample for a process so the value becomes available when >> unwinding call stacks for functions gaining event samples. >> >> Signed-off-by: Alexey Budankov >> --- >> arch/x86/kernel/perf_regs.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c >> index e47b2dbbdef3..8d68658eff7f 100644 >> --- a/arch/x86/kernel/perf_regs.c >> +++ b/arch/x86/kernel/perf_regs.c >> @@ -156,7 +156,13 @@ void perf_get_regs_user(struct perf_regs *regs_user, > > >> * Most system calls don't save these registers, don't report them. > > ^^^ that worries me and is the reason for the '-1's below. However I > think with all the PTI rework this might no longer be true. > > The Changelog needs to state that user_regs->bp is in fact valid and > ideally point to the commits that makes it so. Also this patch should > update that comment. > > Cc Andy who keeps better track of all that than me. Are there any thoughts so far? Feedback on the matter above is highly appreciated. Thanks, Alexey > >> */ >> regs_user_copy->bx = -1; >> - regs_user_copy->bp = -1; >> + /* >> + * Store user space frame-pointer value on sample >> + * to facilitate stack unwinding for cases when >> + * user space executable code has such support >> + * enabled at compile time; >> + */ >> + regs_user_copy->bp = user_regs->bp; >> regs_user_copy->r12 = -1; >> regs_user_copy->r13 = -1; >> regs_user_copy->r14 = -1; >