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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C1C3FC433EF for ; Thu, 28 Oct 2021 08:43:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9F60F610C7 for ; Thu, 28 Oct 2021 08:43:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229791AbhJ1Ip1 (ORCPT ); Thu, 28 Oct 2021 04:45:27 -0400 Received: from foss.arm.com ([217.140.110.172]:52330 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229626AbhJ1Ip0 (ORCPT ); Thu, 28 Oct 2021 04:45:26 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 91E321FB; Thu, 28 Oct 2021 01:42:59 -0700 (PDT) Received: from [10.32.36.26] (e121896.Emea.Arm.com [10.32.36.26]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8987D3F70D; Thu, 28 Oct 2021 01:42:57 -0700 (PDT) Subject: Re: [PATCH] perf symbol: ignore $a/$d symbols for ARM modules To: Lexi Shao Cc: acme@kernel.org, alexander.shishkin@linux.intel.com, jolsa@redhat.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, mark.rutland@arm.com, mingo@redhat.com, namhyung@kernel.org, nixiaoming@huawei.com, peterz@infradead.org, qiuxi1@huawei.com, wangbing6@huawei.com References: <20211028020509.39082-1-shaolexi@huawei.com> From: James Clark Message-ID: Date: Thu, 28 Oct 2021 09:42:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211028020509.39082-1-shaolexi@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On 28/10/2021 03:05, Lexi Shao wrote: > On 27/10/2021 23:10, James Clark wrote: >> On 27/10/2021 13:31, Lexi Shao wrote: >>> On 27/10/2021 18:24, James Clark wrote: >>>> On 27/10/2021 10:52, Lexi Shao wrote: >>>>> On ARM machine, kernel symbols from modules can be resolved to $a >>>>> instead of printing the actual symbol name. Ignore symbols starting with >>>>> "$" when building kallsyms rbtree. >>>>> >>>>> A sample stacktrace is shown as follows: >>>>> >>>>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>>>> bf4a66d8 $a+0x78 ([test_module]) >>>>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>>>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>>>> >>>>> On ARM machine, $a/$d symbols are used by the compiler to mark the >>>>> beginning of code/data part in code section. These symbols are filtered >>>>> out when linking vmlinux(see scripts/kallsyms.c ignored_prefixes), but >>>>> are left on modules. So there are $a symbols in /proc/kallsyms which >>>>> share the same addresses with the actual module symbols and confuses perf >>>>> when resolving symbols. >>>> >>>> Hi Lexi, >>>> >>>> Is it worth using or re-implementing the entire is_ignored_symbol() function >>> >from scripts/kallsyms.c? It seems like this change only fixes one occurrence, >>>> but is_ignored_symbol() has a big list of other cases. >>>> >>>> Unless those cases are different? >>>> >>>> Thanks >>>> James >>> >>> Hi James, >>> >>> I don't think it's necessary to cover all the cases listed in >>> is_ignored_symbol(). As long as the symbols are unique and not overlapping >>> with each other, they should't cause problems in resolving symbols. So most >>> of the cases in is_ignored_symbol() should be irrelevant. >> >> Is it possible to do the filtering of the module symbols somewhere else like >> in kernel/kallsyms.c? I'm not that familiar with it but it seems like >> at one point when populating kallsyms '$...' functions are filtered out, but >> when modules are loaded the symbols are not filtered because another code path is >> used? >> >> If kallsyms has some duplicate addresses in there then isn't the bug in kallsyms >> rather than perf? And another tool could get confused too. >> >> James > > Yes we can filter these symbols out when adding module symbols to the kallsyms > list. I will send another patch that modifies module.c to ignore '$' symbols > when loading module. > That sounds great thanks. > I think it's worth applying this patch in the sense that perf userspace tool > can be used on all 5.x kernels, and people don't have to update the kernel > to fix it. Yes you are right. In that case I will add a review tag to this change. Thanks James > > Lexi > >> >>> >>> Lexi >>> >>>> >>>>> >>>>> After this patch, the module symbol name is printed: >>>>> >>>>> c0f2e39c schedule_hrtimeout+0x14 ([kernel.kallsyms]) >>>>> bf4a66d8 test_func+0x78 ([test_module]) >>>>> c0a4f5f4 kthread+0x15c ([kernel.kallsyms]) >>>>> c0a001f8 ret_from_fork+0x14 ([kernel.kallsyms]) >>>>> >>>>> Signed-off-by: Lexi Shao >>>>> --- >>>>> tools/perf/util/symbol.c | 4 ++++ >>>>> 1 file changed, 4 insertions(+) >>>>> >>>>> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c >>>>> index 0fc9a5410739..35116aed74eb 100644 >>>>> --- a/tools/perf/util/symbol.c >>>>> +++ b/tools/perf/util/symbol.c >>>>> @@ -702,6 +702,10 @@ static int map__process_kallsym_symbol(void *arg, const char *name, >>>>> if (!symbol_type__filter(type)) >>>>> return 0; >>>>> >>>>> + /* Ignore local symbols for ARM modules */ >>>>> + if (name[0] == '$') >>>>> + return 0; >>>>> + >>>>> /* >>>>> * module symbols are not sorted so we add all >>>>> * symbols, setting length to 0, and rely on >>>>> >>>> >