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=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 D5218C47257 for ; Thu, 7 May 2020 18:46:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AFF412145D for ; Thu, 7 May 2020 18:46:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877195; bh=8VacPoTbGjqVXDTwPuYe3Mg/26pmSYjPzGz8cwswqJk=; h=Date:From:To:Cc:Subject:List-ID:From; b=PkcL/VETsZ0sz/gp2pNoGE98fE/tUC1Zm7o/iBLyCOodlR9pQTkofYFScdMTr05A+ +tTOn58PIliOqhQ6N08cGnBj3QerojiZHL+dDeY2dOKU/hZ5hx/Nd01bQEbA3MuwZE Z7wGketPG7aK7GLk8u63n0mvEcoz8QyOCZVZYkys= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728404AbgEGSqd (ORCPT ); Thu, 7 May 2020 14:46:33 -0400 Received: from mail.kernel.org ([198.145.29.99]:47102 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726467AbgEGSqc (ORCPT ); Thu, 7 May 2020 14:46:32 -0400 Received: from embeddedor (unknown [189.207.59.248]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 159D8216FD; Thu, 7 May 2020 18:46:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588877192; bh=8VacPoTbGjqVXDTwPuYe3Mg/26pmSYjPzGz8cwswqJk=; h=Date:From:To:Cc:Subject:From; b=DedEP2mq6qrgUzakngn8r7xcVr2pM0OAetbvOrCdCURunFj9j6oKw6liEDu3jaFMc 7Xi0YhSgFEwnnm2wNZpibhKLlRtWfnsmN9RgFbAaOfIB7lBjmh46w4XTWJGbyCuAMb OS8MV6bw4czSSQxV0exZm1/fIuoApmNvHSn2tSlY= Date: Thu, 7 May 2020 13:50:57 -0500 From: "Gustavo A. R. Silva" To: Alexei Starovoitov , Daniel Borkmann Cc: Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , John Fastabend , KP Singh , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] libbpf: Replace zero-length array with flexible-array Message-ID: <20200507185057.GA13981@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.9.4 (2018-02-28) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org The current codebase makes use of the zero-length array language extension to the C90 standard, but the preferred mechanism to declare variable-length types such as these ones is a flexible array member[1][2], introduced in C99: struct foo { int stuff; struct boo array[]; }; By making use of the mechanism above, we will get a compiler warning in case the flexible array does not occur last in the structure, which will help us prevent some kind of undefined behavior bugs from being inadvertently introduced[3] to the codebase from now on. Also, notice that, dynamic memory allocations won't be affected by this change: "Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, sizeof evaluates to zero."[1] sizeof(flexible-array-member) triggers a warning because flexible array members have incomplete type[1]. There are some instances of code in which the sizeof operator is being incorrectly/erroneously applied to zero-length arrays and the result is zero. Such instances may be hiding some bugs. So, this work (flexible-array member conversions) will also help to get completely rid of those sorts of issues. This issue was found with the help of Coccinelle. [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html [2] https://github.com/KSPP/linux/issues/21 [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") Signed-off-by: Gustavo A. R. Silva --- kernel/bpf/queue_stack_maps.c | 2 +- tools/lib/bpf/libbpf.c | 2 +- tools/lib/bpf/libbpf_internal.h | 2 +- tools/testing/selftests/bpf/progs/core_reloc_types.h | 2 +- 4 files changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/queue_stack_maps.c b/kernel/bpf/queue_stack_maps.c index f697647ceb54..30e1373fd437 100644 --- a/kernel/bpf/queue_stack_maps.c +++ b/kernel/bpf/queue_stack_maps.c @@ -19,7 +19,7 @@ struct bpf_queue_stack { u32 head, tail; u32 size; /* max_entries + 1 */ - char elements[0] __aligned(8); + char elements[] __aligned(8); }; static struct bpf_queue_stack *bpf_queue_stack(struct bpf_map *map) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 8f480e29a6b0..b9335c686353 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -8035,7 +8035,7 @@ static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt, struct perf_sample_raw { struct perf_event_header header; uint32_t size; - char data[0]; + char data[]; }; struct perf_sample_lost { diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h index 8c3afbd97747..50d70e90d5f1 100644 --- a/tools/lib/bpf/libbpf_internal.h +++ b/tools/lib/bpf/libbpf_internal.h @@ -153,7 +153,7 @@ struct btf_ext_info_sec { __u32 sec_name_off; __u32 num_info; /* Followed by num_info * record_size number of bytes */ - __u8 data[0]; + __u8 data[]; }; /* The minimum bpf_func_info checked by the loader */ diff --git a/tools/testing/selftests/bpf/progs/core_reloc_types.h b/tools/testing/selftests/bpf/progs/core_reloc_types.h index 6d598cfbdb3e..34d84717c946 100644 --- a/tools/testing/selftests/bpf/progs/core_reloc_types.h +++ b/tools/testing/selftests/bpf/progs/core_reloc_types.h @@ -379,7 +379,7 @@ struct core_reloc_arrays___equiv_zero_sz_arr { struct core_reloc_arrays_substruct c[3]; struct core_reloc_arrays_substruct d[1][2]; /* equivalent to flexible array */ - struct core_reloc_arrays_substruct f[0][2]; + struct core_reloc_arrays_substruct f[][2]; }; struct core_reloc_arrays___fixed_arr {