From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 112D62575F; Wed, 7 Aug 2024 20:55:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723064154; cv=none; b=YjEX/+jELMQluf/LsLwjxZabetIrcKostuEvUdotqLtkoc7wK3ZTliioZXa5lEyDSN/ZMQigMFjhcpFrI0D7OgQh3pQjGKotxw6m8VRv7krxk0rTncOikhPgnYlhHJSiu3x5mW/U2H//zsW74coF2N8RSc0QDM8hxE7Kym2Bcqc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723064154; c=relaxed/simple; bh=EaZgcA3NtRAmtxQ7KZE96Vk2UBjW9UO69pLCY10zeOU=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=Ib9Fbx2Yiin7hmxrLsXAJiDyEpsfcN36t4hHCn4n3Y6wDOxJnMC4wM6OoVq/9aae5ghqaU3Bpjw4P6A4uuoBi55qvttFBfGXgnhnkGJvfMutnToQVtb2tkZeLZYzAYeGMSv0DaxRKR1XnAA53AzpYhG2bDl0aDte5aiW0ZciCA8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lPtmR41C; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lPtmR41C" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0A3EFC32781; Wed, 7 Aug 2024 20:55:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723064153; bh=EaZgcA3NtRAmtxQ7KZE96Vk2UBjW9UO69pLCY10zeOU=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=lPtmR41C4gg3atA2WrJ4WPsI4+3VjEXnkpMl/2QBNAD9rzgCm805CjQUYQIrVG4oI myMKNdhyxoMIRaiZep7hSjD1qYN598NiOe9vWsWZ5StkTgod1PQ3rYNHDgmYdgim1p CQabP3YQaQfw4qR1adoDmX/+2R0mZbWQiiuyiYtvbJg7O5XxGva++AMnYJQnrSdKtC 3aiFa7aO4yQhiK7VFAy0o87UPWGKpo+2DOdF50i/pHVJrIg+FWKKXuUtRTl/B4Gfc4 5h7WOXXs5H1cw7lMYniX81Vsa1GD24Uf/S8AVma0JmwOWo52fY0fm2g1e6HsW9MYg/ i77DTdIrALRgQ== Date: Thu, 8 Aug 2024 05:55:46 +0900 From: Masami Hiramatsu (Google) To: Song Liu Cc: Steven Rostedt , Song Liu , "live-patching@vger.kernel.org" , LKML , "linux-trace-kernel@vger.kernel.org" , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Petr Mladek , Joe Lawrence , Nathan Chancellor , "morbo@google.com" , Justin Stitt , Luis Chamberlain , Leizhen , "kees@kernel.org" , Kernel Team , Matthew Maurer , Sami Tolvanen Subject: Re: [PATCH v2 3/3] tracing/kprobes: Use APIs that matches symbols without .XXX suffix Message-Id: <20240808055546.9b7f8089a10713d83ba29a75@kernel.org> In-Reply-To: References: <20240802210836.2210140-1-song@kernel.org> <20240802210836.2210140-4-song@kernel.org> <20240806144426.00ed349f@gandalf.local.home> <20240806160049.617500de@gandalf.local.home> <20240806160149.48606a0b@gandalf.local.home> <6F6AC75C-89F9-45C3-98FF-07AD73C38078@fb.com> <20240807090146.88b38c2fbd1cd8db683be22c@kernel.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Wed, 7 Aug 2024 00:19:20 +0000 Song Liu wrote: > > > > On Aug 6, 2024, at 5:01 PM, Masami Hiramatsu wrote: > > > > On Tue, 6 Aug 2024 20:12:55 +0000 > > Song Liu wrote: > > > >> > >> > >>> On Aug 6, 2024, at 1:01 PM, Steven Rostedt wrote: > >>> > >>> On Tue, 6 Aug 2024 16:00:49 -0400 > >>> Steven Rostedt wrote: > >>> > >>>>>>> + if (IS_ENABLED(CONFIG_LTO_CLANG) && !addr) > >>>>>>> + addr = kallsyms_lookup_name_without_suffix(trace_kprobe_symbol(tk)); > >>>>>>> + > >>>>>> > >>>>>> So you do the lookup twice if this is enabled? > >>>>>> > >>>>>> Why not just use "kallsyms_lookup_name_without_suffix()" the entire time, > >>>>>> and it should work just the same as "kallsyms_lookup_name()" if it's not > >>>>>> needed? > >>>>> > >>>>> We still want to give priority to full match. For example, we have: > >>>>> > >>>>> [root@~]# grep c_next /proc/kallsyms > >>>>> ffffffff81419dc0 t c_next.llvm.7567888411731313343 > >>>>> ffffffff81680600 t c_next > >>>>> ffffffff81854380 t c_next.llvm.14337844803752139461 > >>>>> > >>>>> If the goal is to explicitly trace c_next.llvm.7567888411731313343, the > >>>>> user can provide the full name. If we always match _without_suffix, all > >>>>> of the 3 will match to the first one. > >>>>> > >>>>> Does this make sense? > >>>> > >>>> Yes. Sorry, I missed the "&& !addr)" after the "IS_ENABLED()", which looked > >>>> like you did the command twice. > >>> > >>> But that said, does this only have to be for llvm? Or should we do this for > >>> even gcc? As I believe gcc can give strange symbols too. > >> > >> I think most of the issue comes with LTO, as LTO promotes local static > >> functions to global functions. IIUC, we don't have GCC built, LTO enabled > >> kernel yet. > >> > >> In my GCC built, we have suffixes like ".constprop.0", ".part.0", ".isra.0", > >> and ".isra.0.cold". We didn't do anything about these before this set. So I > >> think we are OK not handling them now. We sure can enable it for GCC built > >> kernel in the future. > > > > Hmm, I think it should be handled as it is. This means it should do as > > livepatch does. Since I expected user will check kallsyms if gets error, > > we should keep this as it is. (if a symbol has suffix, it should accept > > symbol with suffix, or user will get confused because they can not find > > which symbol is kprobed.) > > > > Sorry about the conclusion (so I NAK this), but this is a good discussion. > > Do you mean we do not want patch 3/3, but would like to keep 1/3 and part > of 2/3 (remove the _without_suffix APIs)? If this is the case, we are > undoing the change by Sami in [1], and thus may break some tracing tools. BTW, I confirmed that the PATCH 1/3 and 2/3 fixes kprobes to probe on suffixed symbols correctly. (because 1/3 allows to search suffixed symbols) /sys/kernel/tracing # cat dynamic_events p:kprobes/p_c_stop_llvm_17132674095431275852_0 c_stop.llvm.17132674095431275852 p:kprobes/p_c_stop_llvm_8011538628216713357_0 c_stop.llvm.8011538628216713357 p:kprobes/p_c_stop_0 c_stop Thank you, > > Sami, could you please share your thoughts on this? > > If this works, I will send next version with 1/3 and part of 2/3. > > Thanks, > Song > > [1] https://lore.kernel.org/all/20210408182843.1754385-8-samitolvanen@google.com/ > -- Masami Hiramatsu (Google)