From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 296E1C433E0 for ; Wed, 27 Jan 2021 21:16:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D633C64DC4 for ; Wed, 27 Jan 2021 21:16:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233903AbhA0VQe (ORCPT ); Wed, 27 Jan 2021 16:16:34 -0500 Received: from elvis.franken.de ([193.175.24.41]:60530 "EHLO elvis.franken.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231927AbhA0VQb (ORCPT ); Wed, 27 Jan 2021 16:16:31 -0500 Received: from uucp (helo=alpha) by elvis.franken.de with local-bsmtp (Exim 3.36 #1) id 1l4s9k-0003fj-00; Wed, 27 Jan 2021 22:15:16 +0100 Received: by alpha.franken.de (Postfix, from userid 1000) id F222CC0AAF; Wed, 27 Jan 2021 22:15:06 +0100 (CET) Date: Wed, 27 Jan 2021 22:15:06 +0100 From: Thomas Bogendoerfer To: Peter Zijlstra Cc: Jiaxun Yang , Tiezhu Yang , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org, Xuefeng Li , David Daney , Ralf Baechle , Archer Yan , x86@kernel.org Subject: Re: [PATCH 1/3] MIPS: kernel: Support extracting off-line stack traces from user-space with perf Message-ID: <20210127211506.GA21163@alpha.franken.de> References: <1609246561-5474-1-git-send-email-yangtiezhu@loongson.cn> <1609246561-5474-2-git-send-email-yangtiezhu@loongson.cn> <20210104105904.GK3021@hirez.programming.kicks-ass.net> <0712b131-715a-a83a-bc9e-61405824ff0e@flygoat.com> <20210105101806.GG3040@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210105101806.GG3040@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 05, 2021 at 11:18:06AM +0100, Peter Zijlstra wrote: > On Tue, Jan 05, 2021 at 11:45:37AM +0800, Jiaxun Yang wrote: > > 在 2021/1/4 下午6:59, Peter Zijlstra 写道: > > > On Tue, Dec 29, 2020 at 08:55:59PM +0800, Tiezhu Yang wrote: > > > > +u64 perf_reg_abi(struct task_struct *tsk) > > > > +{ > > > > + if (test_tsk_thread_flag(tsk, TIF_32BIT_REGS)) > > > > + return PERF_SAMPLE_REGS_ABI_32; > > > > + else > > > > + return PERF_SAMPLE_REGS_ABI_64; > > > > +} > > > So we recently changed this on x86 to not rely on TIF flags. IIRC the > > > problem is that on x86 you can change the mode of a task without the > > > kernel being aware of it. Is something like that possible on MIPS as > > > well? > > > > Hi all, > > > > In MIPS world it's impossible to raise a thread to 64bit without kernel > > aware. > > Without STATUS.UX set it will trigger reserved instruction exception when > > trying > > to run 64bit instructions. > > The other way around is the case on x86, a 64bit program can create and > execute 32bit code sections without the kernel being aware. But if > clearing STATUS.UX has the same issue as setting it, that should not be > a problem for you. > > > However it may be possible to run with 32bit ABI without > > TIF_32BIT_REGS if user program didn't get ELF ABI right. I think > > that's out of our current consideration. > > Fair enough. > > > > The thing x86 does today is look at it's pt_regs state to determine the > > > actual state. > > It is possible to look at pt_regs Status.UX bit on MIPS. But it seems > > unnecessary > > as user can't change it. > > Ok, good. Then no objection, proceed! :-) this patch aims more to mips-next, while patch 2 and 3 are targeting tools/perf. Should I take them into mips-next, too ? Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]