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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id ABAEFC27C76 for ; Wed, 25 Jan 2023 18:32:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235933AbjAYSci (ORCPT ); Wed, 25 Jan 2023 13:32:38 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234924AbjAYScg (ORCPT ); Wed, 25 Jan 2023 13:32:36 -0500 Received: from bee.birch.relay.mailchannels.net (bee.birch.relay.mailchannels.net [23.83.209.14]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77AB410423 for ; Wed, 25 Jan 2023 10:32:35 -0800 (PST) X-Sender-Id: dreamhost|x-authsender|kjlx@templeofstupid.com Received: from relay.mailchannels.net (localhost [127.0.0.1]) by relay.mailchannels.net (Postfix) with ESMTP id B2FFC920626 for ; Wed, 25 Jan 2023 18:32:34 +0000 (UTC) Received: from pdx1-sub0-mail-a306.dreamhost.com (unknown [127.0.0.6]) (Authenticated sender: dreamhost) by relay.mailchannels.net (Postfix) with ESMTPA id 002AB9212E7 for ; Wed, 25 Jan 2023 18:32:33 +0000 (UTC) ARC-Seal: i=1; s=arc-2022; d=mailchannels.net; t=1674671554; a=rsa-sha256; cv=none; b=BtDbI2R2XLd6eBw5G+IBNvb768fdQdkP1U5deNJT5N/PHVknUeePGej0IUuEWgo0PALBTK /02EIs5jNB8tpiCCO5wMSeLJxfestXiZXVwrfiIDXa1veUayNwhS4F80+MzdHAe8itf4gp jgSYeJLsSxhk21u09GlIu13JQ7xBQ3Dxm+mzUczU0L4rHIC+YedPpLlHYemY6xDcGv2UVa pj6/BexsAU+sNYi+GJaOo1QglDzlZG0qyZVdLdy8dKHlNSKpevTpQ3Nb5TUtKYYGrg2hk1 jn52dSCvz5Xctayj3HWPj330/Upi4Oi2UwjggCvfPTBRVXE3cPlnWuUSqkE/4g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=mailchannels.net; s=arc-2022; t=1674671554; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references:dkim-signature; bh=RklJeSBsXo3eoBMozqg37WAfagKIJsfsLub9jJTlyS0=; b=VLbPo2n/njUZrvXU3fIXRwPTcU1ObmSar48bwv10Rp/gl3v2SSUpf+oKd43PbKteq3X+kZ tNRn/2cHqGtg8A8EkbBqOlFnMmCnE0a9VqP45bpFkpPqW3rIUIeVP/bMAidcU0zlFnn0z3 iJFrWQJPgAQS3/vFELXPpYBXEfiINZiVOlOqr/GqXdj46c7bZi8CLv27HmdzXK7hhZQtPE MhRw0J/B7zfxrpP/RkqbWcWUukLcIr2YIXMrTLM4K8U4o3/d43EiHP9yBPca4LvV7J5NB2 82S8FQ+XRx8QhtcLWobGLw3yTtnZdXK6rPE9XgdXCD/fHlZCpEGpoaXb4FN3ow== ARC-Authentication-Results: i=1; rspamd-6989874cc5-4dw8b; auth=pass smtp.auth=dreamhost smtp.mailfrom=kjlx@templeofstupid.com X-Sender-Id: dreamhost|x-authsender|kjlx@templeofstupid.com X-MC-Relay: Neutral X-MailChannels-SenderId: dreamhost|x-authsender|kjlx@templeofstupid.com X-MailChannels-Auth-Id: dreamhost X-Shrill-Abaft: 611cd91253d2316a_1674671554254_2343272906 X-MC-Loop-Signature: 1674671554254:3707289730 X-MC-Ingress-Time: 1674671554254 Received: from pdx1-sub0-mail-a306.dreamhost.com (pop.dreamhost.com [64.90.62.162]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384) by 100.97.48.83 (trex/6.7.1); Wed, 25 Jan 2023 18:32:34 +0000 Received: from kmjvbox (c-76-102-200-71.hsd1.ca.comcast.net [76.102.200.71]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: kjlx@templeofstupid.com) by pdx1-sub0-mail-a306.dreamhost.com (Postfix) with ESMTPSA id 4P2CB93LKDzRn for ; Wed, 25 Jan 2023 10:32:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=templeofstupid.com; s=dreamhost; t=1674671553; bh=RklJeSBsXo3eoBMozqg37WAfagKIJsfsLub9jJTlyS0=; h=Date:From:To:Cc:Subject:Content-Type; b=N/714JzxOON/lNp5Lt6uyGnicVW6JvwaCA6YQbKmc4DCcuKtK3cTWOyDCGP0gW219 kLVElSeK0dBdv4Qry5EE10vpE/CaHFWD0JgR4g7GAHFLHpK9VE+ryBNWoJMIKg6it5 5JMtkc+4WV1psHPnlsxKGS9cK0mGd3GhoGVL4otA= Received: from johansen (uid 1000) (envelope-from kjlx@templeofstupid.com) id e00e2 by kmjvbox (DragonFly Mail Agent v0.12); Wed, 25 Jan 2023 10:32:31 -0800 Date: Wed, 25 Jan 2023 10:32:31 -0800 From: Krister Johansen To: Adrian Hunter Cc: Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Michael Petlan , David Reaver , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo Subject: Re: [PATCH] perf/util: Symbol lookup can fail if multiple segmets match stext Message-ID: <20230125183231.GB1963@templeofstupid.com> References: <20230124223531.GB1962@templeofstupid.com> <65cb75e0-4c0b-9384-1f6b-77a0053d8109@intel.com> <231b238b-d464-464e-01d1-a2d5374a79ea@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <231b238b-d464-464e-01d1-a2d5374a79ea@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Adrian, On Wed, Jan 25, 2023 at 09:37:59AM +0200, Adrian Hunter wrote: > On 25/01/23 09:29, Adrian Hunter wrote: > > Also subject line has spelling mistake, and should identify kcore > as the issue e.g. > > perf symbol: Symbol lookup with kcore can fail if multiple segments match stext > > > On 25/01/23 00:35, Krister Johansen wrote: > >> This problem was encountered on an arm64 system with a lot of memory. > >> Without kernel debug symbols installed, and with both kcore and kallsyms > >> available, perf managed to get confused and returned "unknown" for all > >> of the kernel symbols that it tried to look up. > >> > >> On this system, stext fell within the vmalloc segment. The kcore symbol > >> matching code tries to find the first segment that contains stext and > >> uses that to replace the segment generated from just the kallsyms > >> information. In this case, however, there were two: a very large > >> vmalloc segment, and the text segment. This caused perf to get confused > >> because multiple overlapping segments were inserted into the RB tree > >> that holds the discovered segments. However, that alone wasn't > >> sufficient to cause the problem. Even when we could find the segment, > >> the offsets were adjusted in such a way that the newly generated symbols > >> didn't line up with the instruction addresses in the trace. The most > >> obvious solution would be to consult which segment type is text from > >> kcore, but this information is not exposed to users. > >> > >> Instead, select the smallest matching segment that contains stext > >> instead of the first matching segment. This allows us to match the text > >> segment instead of vmalloc, if one is contained within the other. > >> > >> Signed-off-by: Krister Johansen > >> --- > >> tools/perf/util/symbol.c | 10 ++++++++-- > >> 1 file changed, 8 insertions(+), 2 deletions(-) > >> > >> diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c > >> index a3a165ae933a..14ac4189eaff 100644 > >> --- a/tools/perf/util/symbol.c > >> +++ b/tools/perf/util/symbol.c > >> @@ -1368,10 +1368,16 @@ static int dso__load_kcore(struct dso *dso, struct map *map, > >> > >> /* Find the kernel map using the '_stext' symbol */ > >> if (!kallsyms__get_function_start(kallsyms_filename, "_stext", &stext)) { > >> + u64 replacement_size = 0; > > > > We'd usually put a blank line here > > > >> list_for_each_entry(new_map, &md.maps, node) { > >> - if (stext >= new_map->start && stext < new_map->end) { > >> + u64 new_size = new_map->end - new_map->start; > >> + > >> + if (!(stext >= new_map->start && stext < new_map->end)) > >> + continue; > >> + > > > > Really needs a comment, and please be specific e.g. > > > > ARM64 vmalloc segment overlaps the kernel text segment, so > > choosing the smaller segment will get the kernel text. > > > > > > > >> + if (!replacement_map || new_size < replacement_size) { > >> replacement_map = new_map; > >> - break; > >> + replacement_size = new_size; > >> } > >> } > >> } Thanks for all the feedback. I'll incorporate these changes and send out a v2 shortly. -K