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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 1DC41C432C0 for ; Mon, 2 Dec 2019 19:54:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD43320848 for ; Mon, 2 Dec 2019 19:54:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="EvG48iMF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728218AbfLBTyl (ORCPT ); Mon, 2 Dec 2019 14:54:41 -0500 Received: from mail-qk1-f195.google.com ([209.85.222.195]:36514 "EHLO mail-qk1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727586AbfLBTyk (ORCPT ); Mon, 2 Dec 2019 14:54:40 -0500 Received: by mail-qk1-f195.google.com with SMTP id v19so864809qkv.3; Mon, 02 Dec 2019 11:54:39 -0800 (PST) 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:content-transfer-encoding; bh=2w/cy+utKSCOrRThhOlkaAEXscNjPmnC5jne6biM+7Y=; b=EvG48iMFy8TX2G9hixeC4PSXzFPCkkkDDIJ7UarL2ZhNPsfyxoHAgbqJSvN4Hqp4kb Ku82aJS5rxJ+kztooLXzL438Za5CxB+M0oh61lVpeVH4uFe3onXCfyXfX2nLIJmLwCKA tcu80y7xtd4qWhbuFGLinCiUTAkZAFT4r3FNpB1qymOB8Vx4m8bIe9aARTewO6o2x2bA 5D8ee7Js/52/9pc228hjnAtnhaVRLg9btwQkPtJZIRStjmysuyV+St1G40F2qF5tARH6 coK82FY0oM+bv0Ry1iOY4IcxuaVnUmMiFTwCThAz/rZajoczR5/4qoHM2gATcwftwAju hqxg== 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:content-transfer-encoding; bh=2w/cy+utKSCOrRThhOlkaAEXscNjPmnC5jne6biM+7Y=; b=m/dInyX6HgBNFYqOSNdgVDyUhWs/BrKA4t5MkrxnJZ7tvFVGTbuMofiOEOhlD33bjt vxY8Hstt/IMTg4tvlQWgk1/YY57MDjsVdx6iHmKuFHuGBTaRS65uUEUJ2AIjbaii9uhL Z2+++O/GKhiOGLijOjyyJUZk/C/UVsviFDO5p9R296S5lJhqnNUy6yVD88Xn9JCBtIr+ vkuKfH6HvMahJAY9uwXOA7s5nOz5Lr4qQQu4YxN/nmwRg20RN2kmVnhZjC1BChZJuabF wb+F5A7bHH25neOxgL8bxmNAlB3i7AVzjIvpzzXEOfMj5od8M/fKG2w4auieM4nJbdmB R8iQ== X-Gm-Message-State: APjAAAWT9nNasWBCA8t5nhBIZkG43mopxDL/4qxOUbeK7YM76gIL/284 UdmPocLuQgsYw2TFVOBMGCgPPWasuPO9zT1Es1c= X-Google-Smtp-Source: APXvYqwVOqsdllAQ3Vq04L95bqydtUe41aEkrFpnOUuic5MW9TGRlSKNp5OH8AqoD1boKD8FwFDfTukz5VDO1pN5Xb8= X-Received: by 2002:a37:a685:: with SMTP id p127mr665719qke.449.1575316478929; Mon, 02 Dec 2019 11:54:38 -0800 (PST) MIME-Version: 1.0 References: <20191127094837.4045-1-jolsa@kernel.org> <87zhgappl7.fsf@toke.dk> <20191202192122.GA22100@krava> In-Reply-To: <20191202192122.GA22100@krava> From: Andrii Nakryiko Date: Mon, 2 Dec 2019 11:54:27 -0800 Message-ID: Subject: Re: [PATCH 0/3] perf/bpftool: Allow to link libbpf dynamically To: Jiri Olsa Cc: =?UTF-8?B?VG9rZSBIw7hpbGFuZC1Kw7hyZ2Vuc2Vu?= , Jiri Olsa , Arnaldo Carvalho de Melo , lkml , Networking , bpf , Ingo Molnar , Namhyung Kim , Alexander Shishkin , Peter Zijlstra , Michael Petlan , Jesper Dangaard Brouer , Daniel Borkmann , Alexei Starovoitov , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Dec 2, 2019 at 11:21 AM Jiri Olsa wrote: > > On Mon, Dec 02, 2019 at 10:42:53AM -0800, Andrii Nakryiko wrote: > > On Mon, Dec 2, 2019 at 10:09 AM Toke H=C3=B8iland-J=C3=B8rgensen wrote: > > > > > > Andrii Nakryiko writes: > > > > > > > On Wed, Nov 27, 2019 at 1:49 AM Jiri Olsa wrote: > > > >> > > > >> hi, > > > >> adding support to link bpftool with libbpf dynamically, > > > >> and config change for perf. > > > >> > > > >> It's now possible to use: > > > >> $ make -C tools/bpf/bpftool/ LIBBPF_DYNAMIC=3D1 > > > > > > > > I wonder what's the motivation behind these changes, though? Why is > > > > linking bpftool dynamically with libbpf is necessary and important? > > > > They are both developed tightly within kernel repo, so I fail to se= e > > > > what are the huge advantages one can get from linking them > > > > dynamically. > > > > > > Well, all the regular reasons for using dynamic linking (memory usage= , > > > binary size, etc). > > > > bpftool is 327KB with statically linked libbpf. Hardly a huge problem > > for either binary size or memory usage. CPU instruction cache usage is > > also hardly a concern for bpftool specifically. > > > > > But in particular, the ability to update the libbpf > > > package if there's a serious bug, and have that be picked up by all > > > utilities making use of it. > > > > I agree, and that works only for utilities linking with libbpf > > dynamically. For tools that build statically, you'd have to update > > tools anyways. And if you can update libbpf, you can as well update > > bpftool at the same time, so I don't think linking bpftool statically > > with libbpf causes any new problems. > > it makes difference for us if we need to respin just one library > instead of several applications (bpftool and perf at the moment), > because of the bug in the library > > with the Toke's approach we compile some bits of libbpf statically into > bpftool, but there's still the official API in the dynamic libbpf that > we care about and that could carry on the fix without bpftool respin See my replies on v4 of your patchset. I have doubts this actually works as we hope it works. I also don't see how that is going to work in general. Imagine something like this: static int some_state =3D 123; LIBBPF_API void set_state(int x) { some_state =3D x; } int get_state() { return some_state; } If bpftool does: set_state(42); printf("%d\n", get_state()); How is this supposed to work with set_state() coming from libbpf.so, while get_state() being statically linked? Who "owns" memory of `int some_state` -- bpftool or libbpf.so? Can they magically share it? Or rather maybe some_state will be actually two different variables in two different memory regions? And set_state() would be setting one of them, while get_state() would be reading another one? It would be good to test this out. Do you mind checking? > > > > No reason why bpftool should be special in that respect. > > > > But I think bpftool is special and we actually want it to be special > > and tightly coupled to libbpf with sometimes very intimate knowledge > > of libbpf and access to "hidden" APIs. That allows us to experiment > > with new stuff that requires use of bpftool (e.g., code generation for > > BPF programs), without having to expose and seal public APIs. And I > > don't think it's a problem from the point of code maintenance, because > > both live in the same repository and are updated "atomically" when new > > features are added or changed. > > I thought we solved this by Toke's approach, so there' no need > to expose any new/experimental API .. also you guys will probably > continue using static linking I guess > > jirka > > > > > Beyond superficial binary size worries, I don't see any good reason > > why we should add more complexity and variables to libbpf and bpftool > > build processes just to have a "nice to have" option of linking > > bpftool dynamically with libbpf. >