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=-13.8 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,USER_AGENT_SANE_1 autolearn=ham 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 EB5E7C47255 for ; Mon, 11 May 2020 20:07:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C8D6A20720 for ; Mon, 11 May 2020 20:07:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589227676; bh=/Oy/Sf2u70Yzd63mUcR8KEbAcs1JY1pR2AzcGOPrLA4=; h=Date:From:To:Cc:Subject:List-ID:From; b=CZ2o5sqm4pj/2Yhtq1dy1bbGLlj2rmzIQtmfXqYMeWUZxU7jZ7bj8qlTJKwRxcvD6 ZTOTnWd8ukqo3z9OyhEXT05pj2x1ToEkcSmwd67QNlnnwAfU5OtkNN8DBXdR4SsyAx AYiY6r2wwJmAxtZCBLFttNtLcYD/Z07sAUNbScjY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731556AbgEKUH4 (ORCPT ); Mon, 11 May 2020 16:07:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:49236 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727873AbgEKUHz (ORCPT ); Mon, 11 May 2020 16:07:55 -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 1F9ED206F5; Mon, 11 May 2020 20:07:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589227674; bh=/Oy/Sf2u70Yzd63mUcR8KEbAcs1JY1pR2AzcGOPrLA4=; h=Date:From:To:Cc:Subject:From; b=RxVbVM1go98ghgRmXsKhAPljplz/QBHdCeitk1fe1WOPCo3w6VLg/KUYs2uAX8Ac2 sahuyYyvVhljvswaAIiglR9itd+IHOPwQ5k8VXpa+ZevDvxsMxxp3tn71XIPReCLph AsS2Xd0UPrVEo9FvHopYfrp9mGtGHkZyUBOHK/pM= Date: Mon, 11 May 2020 15:12:27 -0500 From: "Gustavo A. R. Silva" To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim Cc: linux-kernel@vger.kernel.org, "Gustavo A. R. Silva" Subject: [PATCH] perf/core: Replace zero-length array with flexible-array Message-ID: <20200511201227.GA14041@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: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@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 --- include/linux/perf_event.h | 4 ++-- kernel/events/callchain.c | 2 +- kernel/events/internal.h | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-) diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h index 9c3e7619c929..306b07b56cc6 100644 --- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -61,7 +61,7 @@ struct perf_guest_info_callbacks { struct perf_callchain_entry { __u64 nr; - __u64 ip[0]; /* /proc/sys/kernel/perf_event_max_stack */ + __u64 ip[]; /* /proc/sys/kernel/perf_event_max_stack */ }; struct perf_callchain_entry_ctx { @@ -113,7 +113,7 @@ struct perf_raw_record { struct perf_branch_stack { __u64 nr; __u64 hw_idx; - struct perf_branch_entry entries[0]; + struct perf_branch_entry entries[]; }; struct task_struct; diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c index c2b41a263166..b1991043b7d8 100644 --- a/kernel/events/callchain.c +++ b/kernel/events/callchain.c @@ -16,7 +16,7 @@ struct callchain_cpus_entries { struct rcu_head rcu_head; - struct perf_callchain_entry *cpu_entries[0]; + struct perf_callchain_entry *cpu_entries[]; }; int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH; diff --git a/kernel/events/internal.h b/kernel/events/internal.h index f16f66b6b655..fcbf5616a441 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -55,7 +55,7 @@ struct perf_buffer { void *aux_priv; struct perf_event_mmap_page *user_page; - void *data_pages[0]; + void *data_pages[]; }; extern void rb_free(struct perf_buffer *rb); -- 2.26.2