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 E4A45C6FA83 for ; Tue, 27 Sep 2022 04:30:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229472AbiI0EaA convert rfc822-to-8bit (ORCPT ); Tue, 27 Sep 2022 00:30:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44714 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229470AbiI0E37 (ORCPT ); Tue, 27 Sep 2022 00:29:59 -0400 Received: from mx0b-00082601.pphosted.com (mx0b-00082601.pphosted.com [67.231.153.30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1557EDFAC for ; Mon, 26 Sep 2022 21:29:56 -0700 (PDT) Received: from pps.filterd (m0148460.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.5/8.17.1.5) with ESMTP id 28QLVicd019416 for ; Mon, 26 Sep 2022 21:29:56 -0700 Received: from mail.thefacebook.com ([163.114.132.120]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3jum2s9vdq-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Mon, 26 Sep 2022 21:29:55 -0700 Received: from twshared46966.41.prn1.facebook.com (2620:10d:c085:108::4) by mail.thefacebook.com (2620:10d:c085:21d::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Mon, 26 Sep 2022 21:29:54 -0700 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id 74CF41F65CC82; Mon, 26 Sep 2022 21:29:42 -0700 (PDT) From: Andrii Nakryiko To: , , CC: , , =?UTF-8?q?Toke=20H=C3=B8iland-J=C3=B8rgensen?= Subject: [PATCH bpf-next 1/2] libbpf: don't require full struct enum64 in UAPI headers Date: Mon, 26 Sep 2022 21:29:39 -0700 Message-ID: <20220927042940.147185-1-andrii@kernel.org> X-Mailer: git-send-email 2.30.2 Content-Type: text/plain; charset="UTF-8" X-FB-Internal: Safe X-Proofpoint-GUID: HipMKHEsHz2GBGrK-XSoX6iRIAt1c1fU X-Proofpoint-ORIG-GUID: HipMKHEsHz2GBGrK-XSoX6iRIAt1c1fU Content-Transfer-Encoding: 8BIT X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.528,FMLib:17.11.122.1 definitions=2022-09-26_11,2022-09-22_02,2022-06-22_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Drop the requirement for system-wide kernel UAPI headers to provide full struct btf_enum64 definition. This is an unexpected requirement that slipped in libbpf 1.0 and put unnecessary pressure ([0]) on users to have a bleeding-edge kernel UAPI header from unreleased Linux 6.0. To achieve this, we forward declare struct btf_enum64. But that's not enough as there is btf_enum64_value() helper that expects to know the layout of struct btf_enum64. So we get a bit creative with reinterpreting memory layout as array of __u32 and accesing lo32/hi32 fields as array elements. Alternative way would be to have a local pointer variable for anonymous struct with exactly the same layout as struct btf_enum64, but that gets us into C++ compiler errors complaining about invalid type casts. So play it safe, if ugly. [0] Closes: https://github.com/libbpf/libbpf/issues/562 Reported-by: Toke Høiland-Jørgensen Fixes: d90ec262b35b ("libbpf: Add enum64 support for btf_dump") Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/btf.h | 25 ++++++++++++++++++++++++- 1 file changed, 24 insertions(+), 1 deletion(-) diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h index ae543144ee30..8e6880d91c84 100644 --- a/tools/lib/bpf/btf.h +++ b/tools/lib/bpf/btf.h @@ -486,6 +486,8 @@ static inline struct btf_enum *btf_enum(const struct btf_type *t) return (struct btf_enum *)(t + 1); } +struct btf_enum64; + static inline struct btf_enum64 *btf_enum64(const struct btf_type *t) { return (struct btf_enum64 *)(t + 1); @@ -493,7 +495,28 @@ static inline struct btf_enum64 *btf_enum64(const struct btf_type *t) static inline __u64 btf_enum64_value(const struct btf_enum64 *e) { - return ((__u64)e->val_hi32 << 32) | e->val_lo32; + /* struct btf_enum64 is introduced in Linux 6.0, which is very + * bleeding-edge. Here we are avoiding relying on struct btf_enum64 + * definition coming from kernel UAPI headers to support wider range + * of system-wide kernel headers. + * + * Given this header can be also included from C++ applications, that + * further restricts C tricks we can use (like using compatible + * anonymous struct). So just treat struct btf_enum64 as + * a three-element array of u32 and access second (lo32) and third + * (hi32) elements directly. + * + * For reference, here is a struct btf_enum64 definition: + * + * const struct btf_enum64 { + * __u32 name_off; + * __u32 val_lo32; + * __u32 val_hi32; + * }; + */ + const __u32 *e64 = (const __u32 *)e; + + return ((__u64)e64[2] << 32) | e64[1]; } static inline struct btf_member *btf_members(const struct btf_type *t) -- 2.30.2