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 F358FC4321E for ; Wed, 30 Nov 2022 20:00:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229551AbiK3UA2 convert rfc822-to-8bit (ORCPT ); Wed, 30 Nov 2022 15:00:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36624 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229503AbiK3UA0 (ORCPT ); Wed, 30 Nov 2022 15:00:26 -0500 Received: from mx0a-00082601.pphosted.com (mx0a-00082601.pphosted.com [67.231.145.42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D05148C6B0 for ; Wed, 30 Nov 2022 12:00:25 -0800 (PST) Received: from pps.filterd (m0109334.ppops.net [127.0.0.1]) by mx0a-00082601.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 2AUJVjVH027883 for ; Wed, 30 Nov 2022 12:00:25 -0800 Received: from maileast.thefacebook.com ([163.114.130.16]) by mx0a-00082601.pphosted.com (PPS) with ESMTPS id 3m65bcn0bw-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NOT) for ; Wed, 30 Nov 2022 12:00:25 -0800 Received: from twshared13940.35.frc1.facebook.com (2620:10d:c0a8:1b::d) by mail.thefacebook.com (2620:10d:c0a8:83::5) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.31; Wed, 30 Nov 2022 12:00:24 -0800 Received: by devbig019.vll3.facebook.com (Postfix, from userid 137359) id F3EBA22AFC7F1; Wed, 30 Nov 2022 12:00:14 -0800 (PST) From: Andrii Nakryiko To: , , CC: , Subject: [PATCH bpf-next 1/2] libbpf: avoid enum forward-declarations in public API in C++ mode Date: Wed, 30 Nov 2022 12:00:12 -0800 Message-ID: <20221130200013.2997831-1-andrii@kernel.org> X-Mailer: git-send-email 2.30.2 X-FB-Internal: Safe Content-Type: text/plain X-Proofpoint-GUID: sEJHKoSpZtwRvjDIwpwKqcQh5cbQAHQ9 X-Proofpoint-ORIG-GUID: sEJHKoSpZtwRvjDIwpwKqcQh5cbQAHQ9 Content-Transfer-Encoding: 8BIT X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.219,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1 definitions=2022-11-30_04,2022-11-30_02,2022-06-22_01 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org C++ enum forward declarations are fundamentally not compatible with pure C enum definitions, and so libbpf's use of `enum bpf_stats_type;` forward declaration in libbpf/bpf.h public API header is causing C++ compilation issues. More details can be found in [0], but it comes down to C++ supporting enum forward declaration only with explicitly specified backing type: enum bpf_stats_type: int; In C (and I believe it's a GCC extension also), such forward declaration is simply: enum bpf_stats_type; Further, in Linux UAPI this enum is defined in pure C way: enum bpf_stats_type { BPF_STATS_RUN_TIME = 0; } And even though in both cases backing type is int, which can be confirmed by looking at DWARF information, for C++ compiler actual enum definition and forward declaration are incompatible. To eliminate this problem, for C++ mode define input argument as int, which makes enum unnecessary in libbpf public header. This solves the issue and as demonstrated by next patch doesn't cause any unwanted compiler warnings, at least with default warnings setting. [0] https://stackoverflow.com/questions/42766839/c11-enum-forward-causes-underlying-type-mismatch [1] Closes: https://github.com/libbpf/libbpf/issues/249 Signed-off-by: Andrii Nakryiko --- tools/lib/bpf/bpf.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h index a112e0ed1b19..7468978d3c27 100644 --- a/tools/lib/bpf/bpf.h +++ b/tools/lib/bpf/bpf.h @@ -409,8 +409,15 @@ LIBBPF_API int bpf_task_fd_query(int pid, int fd, __u32 flags, char *buf, __u32 *buf_len, __u32 *prog_id, __u32 *fd_type, __u64 *probe_offset, __u64 *probe_addr); +#ifdef __cplusplus +/* forward-declaring enums in C++ isn't compatible with pure C enums, so + * instead define bpf_enable_stats() as accepting int as an input + */ +LIBBPF_API int bpf_enable_stats(int type); +#else enum bpf_stats_type; /* defined in up-to-date linux/bpf.h */ LIBBPF_API int bpf_enable_stats(enum bpf_stats_type type); +#endif struct bpf_prog_bind_opts { size_t sz; /* size of this struct for forward/backward compatibility */ -- 2.30.2