From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935265AbeEIOyr (ORCPT ); Wed, 9 May 2018 10:54:47 -0400 Received: from merlin.infradead.org ([205.233.59.134]:56134 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934517AbeEIOyq (ORCPT ); Wed, 9 May 2018 10:54:46 -0400 Date: Wed, 9 May 2018 16:54:36 +0200 From: Peter Zijlstra To: Alexey Budankov Cc: Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Andi Kleen , linux-kernel , linux-perf-users@vger.kernel.org, Andy Lutomirski Subject: Re: [PATCH v2]: perf/x86: store user space frame-pointer value on a sample Message-ID: <20180509145436.GV12217@hirez.programming.kicks-ass.net> References: <31205dc8-b756-e12b-0249-2ed06c2db9c9@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <31205dc8-b756-e12b-0249-2ed06c2db9c9@linux.intel.com> User-Agent: Mutt/1.9.5 (2018-04-13) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > */ > 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;