From mboxrd@z Thu Jan 1 00:00:00 1970 From: Frederic Weisbecker Subject: Re: [PATCH] perf, x86: Disable sanity check Date: Thu, 19 Apr 2012 07:22:11 +0200 Message-ID: <20120419052208.GA29875@somewhere.redhat.com> References: <1334791449-402-1-git-send-email-asharma@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-qa0-f42.google.com ([209.85.216.42]:40260 "EHLO mail-qa0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751315Ab2DSFWR (ORCPT ); Thu, 19 Apr 2012 01:22:17 -0400 Content-Disposition: inline In-Reply-To: <1334791449-402-1-git-send-email-asharma@fb.com> Sender: linux-perf-users-owner@vger.kernel.org List-ID: To: Arun Sharma Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Arnaldo Carvalho de Melo , Mike Galbraith , Paul Mackerras , Peter Zijlstra , Stephane Eranian , Namhyung Kim , Tom Zanussi , linux-perf-users@vger.kernel.org On Wed, Apr 18, 2012 at 04:24:09PM -0700, Arun Sharma wrote: > Without this patch, applications with two different stack > regions (eg: native stack vs JIT stack) get truncated > callchains even when RBP chaining is present. GDB shows proper > stack traces and the frame pointer chaining is intact. > > This patch disables the (fp < RSP) check, hoping that other checks > in the code save the day for us. In our limited testing, this > didn't seem to break anything. > > In the long term, we could potentially have userspace advise > the kernel on the range of valid stack addresses, so we don't > spend a lot of time unwinding from bogus addresses. So rbp is part of the JIT stack but not rsp? Do you have a practical example of that? I must confess I don't know much about JIT stack. Thanks. > > Signed-off-by: Arun Sharma > Cc: Ingo Molnar > CC: Arnaldo Carvalho de Melo > Cc: Frederic Weisbecker > Cc: Mike Galbraith > Cc: Paul Mackerras > Cc: Peter Zijlstra > Cc: Stephane Eranian > Cc: Namhyung Kim > Cc: Tom Zanussi > Cc: linux-kernel@vger.kernel.org > Cc: linux-perf-users@vger.kernel.org > > --- > arch/x86/kernel/cpu/perf_event.c | 3 --- > 1 files changed, 0 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c > index 07f46ba..87d9abd 100644 > --- a/arch/x86/kernel/cpu/perf_event.c > +++ b/arch/x86/kernel/cpu/perf_event.c > @@ -1596,9 +1596,6 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs) > if (bytes != sizeof(frame)) > break; > > - if ((unsigned long)fp < regs->sp) > - break; > - > perf_callchain_store(entry, frame.return_address); > fp = frame.next_frame; > } > -- > 1.7.8.4 >