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 E1440C433F5 for ; Fri, 8 Apr 2022 18:14:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229677AbiDHSQr convert rfc822-to-8bit (ORCPT ); Fri, 8 Apr 2022 14:16:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39608 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229836AbiDHSQq (ORCPT ); Fri, 8 Apr 2022 14:16:46 -0400 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B02DF13F2E for ; Fri, 8 Apr 2022 11:14:42 -0700 (PDT) Received: from pps.filterd (m0109333.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.16.1.2/8.16.1.2) with ESMTP id 238GqqC3022002 for ; Fri, 8 Apr 2022 11:14:42 -0700 Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3fad7yvyt1-4 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Fri, 08 Apr 2022 11:14:36 -0700 Received: from twshared27284.14.frc2.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::4) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Fri, 8 Apr 2022 11:14:33 -0700 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id DDA9216F8734C; Fri, 8 Apr 2022 11:14:28 -0700 (PDT) From: Andrii Nakryiko To: , , CC: , Subject: [PATCH bpf-next 1/3] libbpf: don't error out on CO-RE relos for overriden weak subprogs Date: Fri, 8 Apr 2022 11:14:23 -0700 Message-ID: <20220408181425.2287230-2-andrii@kernel.org> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20220408181425.2287230-1-andrii@kernel.org> References: <20220408181425.2287230-1-andrii@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8BIT X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-ORIG-GUID: ABlcz39Y9Q077BqA-vvqwJhZVkrmSnMd X-Proofpoint-GUID: ABlcz39Y9Q077BqA-vvqwJhZVkrmSnMd X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.858,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-04-08_05,2022-04-08_01,2022-02-23_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org During BPF static linking, all the ELF relocations and .BTF.ext information (including CO-RE relocations) are preserved for __weak subprograms that were logically overriden by either previous weak subprogram instance or by corresponding "strong" (non-weak) subprogram. This is just how native user-space linkers work, nothing new. But libbpf is over-zealous when processing CO-RE relocation to error out when CO-RE relocation belonging to such eliminated weak subprogram is encountered. Instead of erroring out on this expected situation, log debug-level message and skip the relocation. Fixes: db2b8b06423c ("libbpf: Support CO-RE relocations for multi-prog sections") Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/libbpf.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 9deb1fc67f19..465b7c0996f1 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -5687,10 +5687,17 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path) insn_idx = rec->insn_off / BPF_INSN_SZ; prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx); if (!prog) { - pr_warn("sec '%s': failed to find program at insn #%d for CO-RE offset relocation #%d\n", - sec_name, insn_idx, i); - err = -EINVAL; - goto out; + /* When __weak subprog is "overridden" by another instance + * of the subprog from a different object file, linker still + * appends all the .BTF.ext info that used to belong to that + * eliminated subprogram. + * This is similar to what x86-64 linker does for relocations. + * So just ignore such relocations just like we ignore + * subprog instructions when discovering subprograms. + */ + pr_debug("sec '%s': skipping CO-RE relocation #%d for insn #%d belonging to eliminated weak subprogram\n", + sec_name, i, insn_idx); + continue; } /* no need to apply CO-RE relocation if the program is * not going to be loaded -- 2.30.2