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=-23.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_IN_DEF_DKIM_WL 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 13614C432BE for ; Thu, 12 Aug 2021 00:20:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF6FD61019 for ; Thu, 12 Aug 2021 00:20:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233034AbhHLAUj (ORCPT ); Wed, 11 Aug 2021 20:20:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52824 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230185AbhHLAUh (ORCPT ); Wed, 11 Aug 2021 20:20:37 -0400 Received: from mail-ed1-x52d.google.com (mail-ed1-x52d.google.com [IPv6:2a00:1450:4864:20::52d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3F59DC061765 for ; Wed, 11 Aug 2021 17:20:13 -0700 (PDT) Received: by mail-ed1-x52d.google.com with SMTP id bo19so6571278edb.9 for ; Wed, 11 Aug 2021 17:20:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ciNF9W+39aU1KfligFkasbssAwUB87TjLFIi4sKfemM=; b=Q/Xyt7pr8PpcaXXI/WFLYIo6GWhdgnu9a8MncUKdqxk0M22LyDtXUd3z/LHu59nN/J m6K3luOTMFEC4mMuVZpMNTRm+nXFDSfoB2CfyAUWM5QqJ3hiGl6mD3TgAZJQP7YygeII nVl9I4cljtvtT/v8yez9khnXaXZxHx59cjVs/Dtgp1MJRrQFormhC4G7JPJLDa6j9MuG TwpEQOsWaOoxzWAfPaWFr7d2CCjHCo9HbZubwtUyP08dHHMJCAD3NDueMi4vlC6W7mVd uyELL6eFzKCJGArr/s+PtcWbhiuJLBwdhtuTyPzdlg/d49T0Pb8b7ZRXAUNleX8sZajA Em1g== 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=ciNF9W+39aU1KfligFkasbssAwUB87TjLFIi4sKfemM=; b=tGkfMlEUDKUAPvZx/B7xCSWgo6Dfkzfnv1PGHGshfA+CB04Ma1BYbrL9IyFo0AAda8 sKaMDZvYQj97zQyPBoybX/Plpbj1O1r27AMkinbfL3fc++Mkd+P7nhtfA7it8Yp715xB /MwsIwV0WY1IjMcRAbtKEnwEUrayoBC7Hnyz1RECGE/2fnLtmHfkiF53hEEWxxXsfwnk DgS1+lgToZrsM4YKDZiWqrPIoGDfAo15+Sd8wIngABeD/hB4oQX6tVI1CQfFRgtcXPlm mHU+5jWaMEcYQfxoopJHcGQg9HiR0o+k6md3WcJbLS4/91IINa/tapw0IfnZzLQ+Ptn7 LM8Q== X-Gm-Message-State: AOAM5302o5yQHVMmHsb6GzcYNmWnXUJt2diHa1pysTs3nRYJ5fEvzL01 nV4IYT61JcZivp7LTnRMjBHYnOjEyx4CNJLwHddKvA== X-Google-Smtp-Source: ABdhPJybhf8Oq+5Fhh/V3kzdgpTQwfHdM36hP8tVVPUqorFzKOcI1KQIQKrl4yQdYp320z7ghsDvTyyKly2OFY6CMoc= X-Received: by 2002:a50:be81:: with SMTP id b1mr2032098edk.295.1628727611637; Wed, 11 Aug 2021 17:20:11 -0700 (PDT) MIME-Version: 1.0 References: <20210811224036.2416308-1-haoluo@google.com> In-Reply-To: From: Hao Luo Date: Wed, 11 Aug 2021 17:20:00 -0700 Message-ID: Subject: Re: [PATCH bpf-next v2] libbpf: support weak typed ksyms. To: Andrii Nakryiko Cc: Networking , bpf , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Aug 11, 2021 at 4:41 PM Andrii Nakryiko wrote: > > On Wed, Aug 11, 2021 at 3:40 PM Hao Luo wrote: > > > > Currently weak typeless ksyms have default value zero, when they don't > > exist in the kernel. However, weak typed ksyms are rejected by libbpf > > if they can not be resolved. This means that if a bpf object contains > > the declaration of a nonexistent weak typed ksym, it will be rejected > > even if there is no program that references the symbol. > > > > Nonexistent weak typed ksyms can also default to zero just like > > typeless ones. This allows programs that access weak typed ksyms to be > > accepted by verifier, if the accesses are guarded. For example, > > > > extern const int bpf_link_fops3 __ksym __weak; > > > > /* then in BPF program */ > > > > if (&bpf_link_fops3) { > > /* use bpf_link_fops3 */ > > } > > > > If actual use of nonexistent typed ksym is not guarded properly, > > verifier would see that register is not PTR_TO_BTF_ID and wouldn't > > allow to use it for direct memory reads or passing it to BPF helpers. > > > > Signed-off-by: Hao Luo > > --- Thanks for taking a look! All the comments seem reasonable. Let me fix them, test and send a new version. > > Changes since v1: > > - Weak typed symbols default to zero, as suggested by Andrii. > > - Use ASSERT_XXX() for tests. > > > > tools/lib/bpf/libbpf.c | 17 ++++-- > > .../selftests/bpf/prog_tests/ksyms_btf.c | 31 ++++++++++ > > .../selftests/bpf/progs/test_ksyms_weak.c | 57 +++++++++++++++++++ > > 3 files changed, 100 insertions(+), 5 deletions(-) > > create mode 100644 tools/testing/selftests/bpf/progs/test_ksyms_weak.c > > [...]