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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE5C5C54EBD for ; Sat, 7 Jan 2023 02:09:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236564AbjAGCJt (ORCPT ); Fri, 6 Jan 2023 21:09:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52308 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229552AbjAGCJr (ORCPT ); Fri, 6 Jan 2023 21:09:47 -0500 Received: from mail-qv1-f53.google.com (mail-qv1-f53.google.com [209.85.219.53]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B18C63224F; Fri, 6 Jan 2023 18:09:45 -0800 (PST) Received: by mail-qv1-f53.google.com with SMTP id p17so2252890qvn.1; Fri, 06 Jan 2023 18:09:45 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=user-agent:in-reply-to: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=ADJOnrT0to95tRJZIpNulRS9Rqms0FjnaYypouP2xC8=; b=PMQwBNt4iZk1UVn+kk6C2Lx+aVWaFHyp+35kScSFSILnX9XBXknauRHxgf5sVlQnNM 9NsQ9lL2n+M8bpxQ+8+CPfp2hBO2KjgsHQDa67q/U+gLCyikzriZNEovjnbIjhHmrD53 n/zysA4oQTcs/gGAQQTWyYGF2DaH2lrjsE4Zp3/n4JgQayvOCcq3VXn7SIB3xuX0C4n+ md8OQTt3LuQaSvGwqPzUKH1LuhVQvqIvQrE08PNh7JbH2qkYKx/qlSF1k7E7bXjQDeFU BuIYpVaSJHkgUIf+QFyx/RQ7mtFFf1VETJlyHBQN7mCngaBNSUJvbE3BTMgSDzHTO+SQ G30A== X-Gm-Message-State: AFqh2kr1iJBIK8uXgXtCl+jGp1uXi0pwe3xJKnbU0CkiuNz0jN1FS3ej z2FaA2IDxwJcqSkRZQ1/zJY= X-Google-Smtp-Source: AMrXdXtH++oYwIKBplmbiV7cBYZqZQi7FYNZiFHoFt8wTlWpN2zDpRWCHJW4QMheAVDjwZQ+MCvthA== X-Received: by 2002:a0c:bf03:0:b0:531:c5a5:6713 with SMTP id m3-20020a0cbf03000000b00531c5a56713mr26572538qvi.13.1673057384571; Fri, 06 Jan 2023 18:09:44 -0800 (PST) Received: from maniforge.lan ([2620:10d:c091:480::1:c7d8]) by smtp.gmail.com with ESMTPSA id t11-20020a05620a034b00b006fa31bf2f3dsm1450503qkm.47.2023.01.06.18.09.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Jan 2023 18:09:44 -0800 (PST) Date: Fri, 6 Jan 2023 20:09:44 -0600 From: David Vernet To: Alexei Starovoitov Cc: bpf , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , LKML , Kernel Team Subject: Re: [PATCH bpf-next 1/3] bpf: Add __bpf_kfunc tag for marking kernel functions as kfuncs Message-ID: References: <20230106195130.1216841-1-void@manifault.com> <20230106195130.1216841-2-void@manifault.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.9 (2022-11-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 06, 2023 at 05:04:02PM -0800, Alexei Starovoitov wrote: > On Fri, Jan 6, 2023 at 11:51 AM David Vernet wrote: > > > > kfuncs are functions defined in the kernel, which may be invoked by BPF > > programs. They may or may not also be used as regular kernel functions, > > implying that they may be static (in which case the compiler could e.g. > > inline it away), or it could have external linkage, but potentially be > > elided in an LTO build if a function is observed to never be used, and > > is stripped from the final kernel binary. > > > > We therefore require some convenience macro that kfunc developers can > > use just add to their kfuncs, and which will prevent all of the above > > issues from happening. This is in contrast with what we have today, > > where some kfunc definitions have "noinline", some have "__used", and > > others are static and have neither. > > > > In addition to providing the obvious correctness benefits, having such a > > macro / tag also provides the following advantages: > > > > - Giving an easy and intuitive thing to query for if people are looking > > for kfuncs, as Christoph suggested at the kernel maintainers summit > > (https://lwn.net/Articles/908464/). This is currently possible by > > grepping for BTF_ID_FLAGS(func, but having something more self > > describing would be useful as well. > > > > - In the future, the tag can be expanded with other useful things such > > as the ability to suppress -Wmissing-prototype for the kfuncs rather > > than requiring developers to surround the kfunc with __diags to > > suppress the warning (this requires compiler support that as far as I > > know currently does not exist). > > Have you considered doing bpf_kfunc_start/bpf_kfunc_end ? > The former would include: > __diag_push(); __diag_ignore_all(); __used noinline Yeah that's certainly an option. The downside is that all functions within scope of the __diag_push() will be affected, and sometimes we mix kfuncs with non-kfuncs (including e.g. static helper functions that are used by the kfuncs themselves). -Wmissing-prototypes isn't a big deal, but __used and noinline are kind of unfortunate. Not a big deal though, it'll just result in a few extra __bpf_kfuncs_start() and __bpf_kfuncs_end() sprinkled throughout to avoid them being included. The upside is of course that we can get rid of the __diag_push()'es we currently have to prevent -Wmissing-prototypes. Wdyt? I do like the idea of getting rid of those ugly __diag_push()'es. And we could always go back to using a __bpf_kfunc macro if and when compilers ever support using attributes to ignore warnings for specific functions. > > Also how about using bpf_kfunc on the same line ? > Then 'git grep' will be easier. Sure, if we keep this approach I'll do this in v2.