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 E05251D1F73; Wed, 7 Aug 2024 10:08:15 +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=1723025296; cv=none; b=VAC0geUZsNeZ8GMH1H9cx8xkujfvZfSa6l0VgAiMxaqMbMZcjFHVy5hNXI5Qw5HFCMwbpfOYRavs+vMfHwM6tB/j38KOVdbiZ6ifegDh1XOGddJXvKjt0/6Kj5UUYbYG4l7MPeuR4ezfhP/21KNkS9u0c+dHgCex4rwReIiOmvA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723025296; c=relaxed/simple; bh=pbz9/mWikLj58LPIdHZGqQeOO3Hv+c3Hn1bmQqtGTqE=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=n/M3HFW6h9pFEvgDBhoRiAMLZ1GBRGTUPwr4gFKnW92NnigUCf9/WPv05jtazXY/nfZfkIXB2e9u3s+zsBEQG1DIBYAsJ7XEHYXLRVhC+qBUhDCOOwniMOgMaFT90XUzTgKy1nWCem//qDZxPXHYdjZtKywynMV28TLyAlV3uOQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=JGwv+vRz; 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="JGwv+vRz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 41E3CC32782; Wed, 7 Aug 2024 10:08:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723025295; bh=pbz9/mWikLj58LPIdHZGqQeOO3Hv+c3Hn1bmQqtGTqE=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=JGwv+vRzTcQ/uEot7V4X4z1XWtWOrbl9g9l//D1Nyh/AxgOt7LhAFiqLL8DBuyrsC 3INwE3Wn0kxGybNgy0/e2C8aF3fIld4pSPt4R1ZY1RybxNcL2I7BM8rJH5S68rBZtV E2Z0S8T55WUSOGxp+cHmdbMgeMWdNDwP/CAOc/wkbo1OhSKAH88I1y0mpdE9drrqRg zjUehHRCWdVufCGZVz1vJJbcqbrlR71U6AJy/DIXT6WhN/EGF90M3LZlaj/iFSllSV Dh45g7qpHLyXl1lt9aMTz5eYBnzTAclzE+xpZLZRDZt7VoMBbZ4YOijy6J5i8FpFM1 KW1eQv3GTbAtQ== Date: Wed, 7 Aug 2024 19:08:09 +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: <20240807190809.cd316e7f813400a209aae72a@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-trace-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. What tracing tools may be broke and why? For this suffix problem, I would like to add another patch to allow probing on suffixed symbols. (It seems suffixed symbols are not available at this point) The problem is that the suffixed symbols maybe a "part" of the original function, thus user has to carefully use it. > > Sami, could you please share your thoughts on this? Sami, I would like to know what problem you have on kprobes. Thank you, > > 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)