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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8E338ECE59D for ; Tue, 15 Oct 2019 22:34:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 63EFE2064B for ; Tue, 15 Oct 2019 22:34:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KCJY/TuK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732524AbfJOWeR (ORCPT ); Tue, 15 Oct 2019 18:34:17 -0400 Received: from mail-qk1-f196.google.com ([209.85.222.196]:38645 "EHLO mail-qk1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732040AbfJOWeQ (ORCPT ); Tue, 15 Oct 2019 18:34:16 -0400 Received: by mail-qk1-f196.google.com with SMTP id p4so305186qkf.5; Tue, 15 Oct 2019 15:34:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=4AyMktzsTkv7aY4ZRJQAUNTUY8eMY0KqI0FaLqiE3Fo=; b=KCJY/TuKPwuRUnx6pza32kr3b4+favZGvpkv5SZACHhUlm3F5Hz6h5/zJBWbHKWw5F xKlfKx2GGUeR1SRfUGGHucF1kA9lTiqbLdG1+9upXsVCS0dCFCijqZMQLcYY8Kf6VKm3 ZN2CiodXpEtCZzxYCy+qmwzg3kEZmGAUPzexZiIBHpCqd8H7d/WgF7bcwZC4mmi2tkgg bMHBlG82Ea6b6X9EtmfMfGpmG6PLe//XzpDp4UP8PNbc7YCWuY7N7KprKDkEQRy52OsK EQiGwDfib+0FVyLZa9gywLIut0degBF4xWpB5DDSfmYpcerFq5uGLA1TNJrNVaoX4rSC T9Yg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=4AyMktzsTkv7aY4ZRJQAUNTUY8eMY0KqI0FaLqiE3Fo=; b=iqQnEWmtQnE5Q5p10L6CAp6GnzGWsQTPVFgpb3ZeFmyQfKD6LxXx5E9PQAb35j46e/ Kf7eVcphN16dye7Tpnq+53LnNwjI0k4wTHStm38RiiMIVO0kW6Iz/BqjEwehksrutuLl 1HaGPjZtu1xumNLQABbxoEbfi0cQIGdB7ucSsURT+du9Bq4u4t44HH7uz9MDmKAPTdsB lo0IJA1y2wVw3JqO6QSXb7MO/eFM11tioSbSyB2EIV3c+fa5fkR3t0tSUwyzHs8GkNO2 ECpNv7ipdB7xWP4AGscxiPlitKvN1Gd1lwD1HuYOQL241w7peVm1kg1ypxk9Kme97Mqg eYHQ== X-Gm-Message-State: APjAAAXmZgfFvdFPw2zXyAkhn9kPlAFOICZdH6i6tqWeDiMaBrWR9t5z hea5UOx67dOqGfbzrvYn5Xtu3he0JuETs0dy65dOQ+wN X-Google-Smtp-Source: APXvYqzIzcgB3Huzz14rqnHe/p4tutlP/9m/kZbwrhw1m/RlBiVbkl5OwlXF+3FRybhVeKxvc3ojWcxVoIAVkNcRnK4= X-Received: by 2002:a37:4c13:: with SMTP id z19mr39679360qka.449.1571178853685; Tue, 15 Oct 2019 15:34:13 -0700 (PDT) MIME-Version: 1.0 References: <20191011162124.52982-1-sdf@google.com> <20191012003819.GK2096@mini-arch> In-Reply-To: From: Andrii Nakryiko Date: Tue, 15 Oct 2019 15:33:58 -0700 Message-ID: Subject: Re: debug annotations for bpf progs. Was: [PATCH bpf-next 1/3] bpf: preserve command of the process that loaded the program To: Alexei Starovoitov Cc: Stanislav Fomichev , Stanislav Fomichev , Network Development , bpf , "David S. Miller" , Daniel Borkmann , Yonghong Song Content-Type: text/plain; charset="UTF-8" Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Oct 15, 2019 at 3:24 PM Alexei Starovoitov wrote: > > On Tue, Oct 15, 2019 at 3:14 PM Andrii Nakryiko > wrote: > > > > On Tue, Oct 15, 2019 at 2:22 PM Alexei Starovoitov > > wrote: > > > > > > On Fri, Oct 11, 2019 at 5:38 PM Stanislav Fomichev wrote: > > > > > > > > On 10/11, Alexei Starovoitov wrote: > > > > > On Fri, Oct 11, 2019 at 9:21 AM Stanislav Fomichev wrote: > > > > > > > > > > > > Even though we have the pointer to user_struct and can recover > > > > > > uid of the user who has created the program, it usually contains > > > > > > 0 (root) which is not very informative. Let's store the comm of the > > > > > > calling process and export it via bpf_prog_info. This should help > > > > > > answer the question "which process loaded this particular program". > > > > > > > > > > > > Signed-off-by: Stanislav Fomichev > > > > > > --- > > > > > > include/linux/bpf.h | 1 + > > > > > > include/uapi/linux/bpf.h | 2 ++ > > > > > > kernel/bpf/syscall.c | 4 ++++ > > > > > > 3 files changed, 7 insertions(+) > > > > > > > > > > > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > > > > > > index 5b9d22338606..b03ea396afe5 100644 > > > > > > --- a/include/linux/bpf.h > > > > > > +++ b/include/linux/bpf.h > > > > > > @@ -421,6 +421,7 @@ struct bpf_prog_aux { > > > > > > struct work_struct work; > > > > > > struct rcu_head rcu; > > > > > > }; > > > > > > + char created_by_comm[BPF_CREATED_COMM_LEN]; > > > > > > }; > > > > > > > > > > > > struct bpf_array { > > > > > > diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h > > > > > > index a65c3b0c6935..4e883ecbba1e 100644 > > > > > > --- a/include/uapi/linux/bpf.h > > > > > > +++ b/include/uapi/linux/bpf.h > > > > > > @@ -326,6 +326,7 @@ enum bpf_attach_type { > > > > > > #define BPF_F_NUMA_NODE (1U << 2) > > > > > > > > > > > > #define BPF_OBJ_NAME_LEN 16U > > > > > > +#define BPF_CREATED_COMM_LEN 16U > > > > > > > > > > Nack. > > > > > 16 bytes is going to be useless. > > > > > We found it the hard way with prog_name. > > > > > If you want to embed additional debug information > > > > > please use BTF for that. > > > > BTF was my natural choice initially, but then I saw created_by_uid and > > > > thought created_by_comm might have a chance :-) > > > > > > > > To clarify, by BTF you mean creating some unused global variable > > > > and use its name as the debugging info? Or there is some better way? > > > > > > I was thinking about adding new section to .btf.ext with this extra data, > > > but global variable is a better idea indeed. > > > We'd need to standardize such variables names, so that > > > bpftool can parse and print it while doing 'bpftool prog show'. > > > We see more and more cases where services use more than > > > one program in single .c file to accomplish their goals. > > > Tying such debug info (like 'created_by_comm') to each program > > > individually isn't quite right. > > > In that sense global variables are better, since they cover the > > > whole .c file. > > > Beyond 'created_by_comm' there are others things that people > > > will likely want to know. > > > Like which version of llvm was used to compile this .o file. > > > Which unix user name compiled it. > > > The name of service/daemon that will be using this .o > > > and so on. > > > May be some standard prefix to such global variables will do? > > > Like "bpftool prog show" can scan global data for > > > "__annotate_#name" and print both name and string contents ? > > > For folks who regularly ssh into servers to debug bpf progs > > > that will help a lot. > > > May be some annotations llvm can automatically add to .o. > > > Thoughts? > > > > We can dedicate separate ELF section for such variables, similar to > > license and version today, so that libbpf will know that those > > variables are not real variables and shouldn't be used from BPF > > program itself. But we can have many of them in single section, unlike > > version and license. :) With that, we'll have metadata and list of > > variables in BTF (DATASEC + VARs). The only downside - you'll need ELF > > itself to get the value of that variable, no? Is that acceptable? Do > > we always know where original ELF is? > > Having .o around is not acceptable. > That was already tried and didn't work with bcc. > I was proposing to have these special vars to be loaded into the kernel > as part of normal btf loading. BTF is just metadata for variables. We'll know name and type information about variable, but we need a string contents. That is stored in ELF, so without .o file we won't be able to extract it. Unless you have something else in mind? > Not sure what special section gives. It's a marker that libbpf doesn't have to allocate memory and create internal map for that section. We don't want those annotation variables to be backed by BPF map, do we?