From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f52.google.com (mail-ej1-f52.google.com [209.85.218.52]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 178EE1946B9 for ; Fri, 9 Aug 2024 15:40:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.52 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723218009; cv=none; b=NGouA1bfXpEnTj/lgwfxBVfxCFQPAGRKBc+Cbtu1SMag9Na8ZGGxTZ/OhRKK/0Te+BTvfd/HqBEUGUswE/JMcn/VGzgYX38Q6bIYyL9USH3NdpJ4VVCKhzMvFUxTe4XECoOeVR4cg4ixY6hg3YIHpdDTdj7LJVES/0MzKTen1Zo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723218009; c=relaxed/simple; bh=7uxpbX0dUiV2nAtAAnEFPVZf9an/qeChOgroY1rCZn8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XPVEIgA5N+4VCBvGr0EMcf6hCbuhSwHzLyLMWfuSJ6OOeQDnZomquOm5oYZMuSoziJWApZ0jGi1eSkM55fWOT7vFtGKO+lx67QC7HJAXQXtfmHuHKUhzXI7sdzhasw4OvT5ZyFjdiTwHeHgCCH7ibYmF5OiPQj51ZQU2jn3Nh5s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com; spf=pass smtp.mailfrom=suse.com; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b=CdMgFVBZ; arc=none smtp.client-ip=209.85.218.52 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=suse.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=suse.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=suse.com header.i=@suse.com header.b="CdMgFVBZ" Received: by mail-ej1-f52.google.com with SMTP id a640c23a62f3a-a7aa086b077so225286866b.0 for ; Fri, 09 Aug 2024 08:40:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=google; t=1723218005; x=1723822805; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=g9/gdXLxSnsU9nxoiw00oEcO7EcPaiVsBgSH221d6bo=; b=CdMgFVBZj9uRB6Hm+ZK6IAvIQd51ws0M+duKz3z1OCIT7NvOdmMEZ9uqDmXTdv2oG3 BKH43dITcFZhdqPo7pOW9EMNXM8VroSJGCzEBQZe3+H3Cu1Eni1rbUiEPud0pSIwkVS0 l5h35eSSleDacrFJQQQoB1UQmwSTA0EcLFzEs1kEeM+iH2/LrFdnYeX9ihwLW6EOPzF9 mbmsu1Hcda4pOPVI6EQpCR/GaGIc09oM3cz37duFUaOzMcYPbxgXuvXnvHE1yJybProF yKZrOSd8XpyPZtIRtdS7V2G5xUhlvLNPGSndqkdxAjzaYQ182jpGhf8yWGMazstZ71uO g/fA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723218005; x=1723822805; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=g9/gdXLxSnsU9nxoiw00oEcO7EcPaiVsBgSH221d6bo=; b=XmMNjcZVGJWf25G5vLGRru28GO0C9e3cL6qUCsfuW7d6wRd5EUFZc//yAKEln+3+7b qULDjHvIDh/HfCd+OOeAGYx/ZM8FXnUDfvWyjMnvPR2wigOgaIZoou9tOD1Xlrts/ZsO aGrt7sKTlT1JzOuCXnfNHH/gHu6OSyWvJjhlgCgUY6QMQM7JNeXClZBRaUjj6bcUFn7Z PjW39wjBHH3Rm+B9eE5cOYMxGq67rps4bFtDIwg2LV0328dH/SqjgClMcaoKkKA7PyWG a/jiqmelxbpxqzkqO5wSmOQexIqNE8p+9igM8ouadqp7jRBOJ1YOioRW+d5huHgsdtKy LyXQ== X-Forwarded-Encrypted: i=1; AJvYcCX/il+uYezckOVUubBydq2f1b90UpSerC4VvvF8lIB1utbiLVt5TCBLYPjH4FN3stvmj43YBfG5tkuw7P4iZ7rG8zF8NMWZcW2S9NOB X-Gm-Message-State: AOJu0YzhSoLPHGJv4TgIhhkD6umOwD0/qqyoxyzApHhDG/S2BG2VmJi8 k8CV2/7kzmGM0vqjxF9QOhHTkB+WXzqm4seni7+jJ8JfI7WxeGnaBQ2IGUfYbAo= X-Google-Smtp-Source: AGHT+IGaMJDQMYJCSNSGSCt/WttKifUKYpng5iXyE2ihkAwEcQvtfaW+DwlSQS3puMV/UUa3yUyaPg== X-Received: by 2002:a17:907:e6a4:b0:a7a:929f:c0cb with SMTP id a640c23a62f3a-a80aa5eb16amr149281466b.38.1723218005223; Fri, 09 Aug 2024 08:40:05 -0700 (PDT) Received: from pathway.suse.cz ([176.114.240.50]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a7dc9c12ad3sm851185966b.88.2024.08.09.08.40.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Aug 2024 08:40:04 -0700 (PDT) Date: Fri, 9 Aug 2024 17:40:02 +0200 From: Petr Mladek To: Song Liu Cc: Sami Tolvanen , Masami Hiramatsu , Steven Rostedt , Song Liu , "live-patching@vger.kernel.org" , LKML , "linux-trace-kernel@vger.kernel.org" , Josh Poimboeuf , Jiri Kosina , Miroslav Benes , Joe Lawrence , Nathan Chancellor , "morbo@google.com" , Justin Stitt , Luis Chamberlain , Leizhen , "kees@kernel.org" , Kernel Team , Matthew Maurer , "Alessandro Carminati (Red Hat)" Subject: Re: [PATCH v2 3/3] tracing/kprobes: Use APIs that matches symbols without .XXX suffix Message-ID: References: <20240806160049.617500de@gandalf.local.home> <20240806160149.48606a0b@gandalf.local.home> <6F6AC75C-89F9-45C3-98FF-07AD73C38078@fb.com> <20240807090146.88b38c2fbd1cd8db683be22c@kernel.org> <20240807190809.cd316e7f813400a209aae72a@kernel.org> <09ED7762-A464-45FF-9062-9560C59F304E@fb.com> 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-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Thu 2024-08-08 15:20:26, Song Liu wrote: > > > > On Aug 8, 2024, at 2:59 AM, Petr Mladek wrote: > > > > On Wed 2024-08-07 20:48:48, Song Liu wrote: > >> > >> > >>> On Aug 7, 2024, at 8:33 AM, Sami Tolvanen wrote: > >>> > >>> Hi, > >>> > >>> On Wed, Aug 7, 2024 at 3:08 AM Masami Hiramatsu wrote: > >>>> > >>>> On Wed, 7 Aug 2024 00:19:20 +0000 > >>>> Song Liu wrote: > >>>> > >>>>> 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? > >>> > >>> This was a few years ago when we were first adding LTO support, but > >>> the unexpected suffixes in tracing output broke systrace in Android, > >>> presumably because the tools expected to find specific function names > >>> without suffixes. I'm not sure if systrace would still be a problem > >>> today, but other tools might still make assumptions about the function > >>> name format. At the time, we decided to filter out the suffixes in all > >>> user space visible output to avoid these issues. > >>> > >>>> 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. > >>> > >>> The reports we received back then were about registering kprobes for > >>> static functions, which obviously failed if the compiler added a > >>> suffix to the function name. This was more of a problem with ThinLTO > >>> and Clang CFI at the time because the compiler used to rename _all_ > >>> static functions, but one can obviously run into the same issue with > >>> just LTO. > >> > >> I think newer LLVM/clang no longer add suffixes to all static functions > >> with LTO and CFI. So this may not be a real issue any more? > >> > >> If we still need to allow tracing without suffix, I think the approach > >> in this patch set is correct (sort syms based on full name, > > > > Yes, we should allow to find the symbols via the full name, definitely. > > > >> remove suffixes in special APIs during lookup). > > > > Just an idea. Alternative solution would be to make make an alias > > without the suffix when there is only one symbol with the same > > name. > > > > It would be complementary with the patch adding aliases for symbols > > with the same name, see > > https://lore.kernel.org/r/20231204214635.2916691-1-alessandro.carminati@gmail.com > > I guess v3 plus this work may work well together. > > > I would allow to find the symbols with and without the suffix using > > a single API. > > Could you please describe how this API would work? I tried some > idea in v1, but it turned out to be quite confusing. So I decided > to leave this logic to the users of kallsyms APIs in v2. If we create an alias without the suffix but only when there is only one symbol with such a name then we have, for example: klp_complete_transition.lwn.123456 klp_complete_transition [alias] init_once.lwn.2131221 init_once.lwn.3443243 init_once.lwn.4324322 init_once.lwn.5214121 init_once.lwn.2153121 init_once.lwn.4342343 This way, it will be possible to find the static symbol "klp_complete_transition" without the suffix via the alias. It will have the alias because it has an unique name. While "init_once" symbol must always be searched with the suffix because it is not unique. It looks like >99% of static symbols have unique name. Best Regards, Petr