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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 4F687C433E0 for ; Thu, 14 May 2020 22:04:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1056920709 for ; Thu, 14 May 2020 22:04:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589493899; bh=wVYlWHo32ix4biFnX8gPYhTJNt94qOjJRYKVMHTxriY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=OT1lMBM9qUMByGLkPzRECt9cSNM+S+qoKeXTAJXmWJ1qmPcn4twIIPOag6F3W8zCp wRClEs4kn06wiqaXiL32kGvhOQtZbpFyeqa+9ttvwSurYrVsC0EGFO+whFlTix8vwJ hj0cl75aMkFTZ8i3TrQpOoHosIYAe+3tGvJvNi0E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728060AbgENWE6 (ORCPT ); Thu, 14 May 2020 18:04:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:60352 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726046AbgENWE5 (ORCPT ); Thu, 14 May 2020 18:04:57 -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 351622065C; Thu, 14 May 2020 22:04:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589493897; bh=wVYlWHo32ix4biFnX8gPYhTJNt94qOjJRYKVMHTxriY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=yTzO9JVf0EPIEnb4lkoCCBtbx52fNb3IfBgx8VIupsRA4ajFa3DEORz6Vlgf21HVF Pqt0kPcIxYidQuySiG14cA6GXLkTd6p/0kzOusFFV22H4V1rD+8Ie2sGn4J78/700i xeB6ATQWwWv1dzqhagb6mYc2d/feorzN4rjmbrC8= Date: Thu, 14 May 2020 17:09:34 -0500 From: "Gustavo A. R. Silva" To: Ian Rogers Cc: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , LKML , "Gustavo A. R. Silva" Subject: Re: [PATCH perf/core] perf intel-pt: Fix clang build failure in intel_pt_synth_pebs_sample Message-ID: <20200514220934.GT4897@embeddedor> References: <20200513234738.GA21211@embeddedor> <20200514131030.GL5583@kernel.org> <20200514150601.GS4897@embeddedor> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 On Thu, May 14, 2020 at 12:06:48PM -0700, Ian Rogers wrote: > On Thu, May 14, 2020 at 8:01 AM Gustavo A. R. Silva > wrote: > > > > On Thu, May 14, 2020 at 10:10:30AM -0300, Arnaldo Carvalho de Melo wrote: > > > Em Wed, May 13, 2020 at 06:47:38PM -0500, Gustavo A. R. Silva escreveu: > > > > Fix the following build failure generated with command > > > > $ make CC=clang HOSTCC=clang -C tools/ perf: > > > > > > > > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > > > struct branch_stack br_stack; > > > > ^ > > > > 1 error generated. > > > > > > > > Fix this by reordering the members of struct br. > > > > > > Yeah, I noticed that as far back as with ubuntu 16.04's clang: > > > > > > clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final) > > > > > > util/intel-pt.c:1802:24: error: field 'br_stack' with variable sized type 'struct branch_stack' not at the end of a struct or class is a GNU > > > extension [-Werror,-Wgnu-variable-sized-type-not-at-end] > > > struct branch_stack br_stack; > > > ^ > > > 1 error generated. > > > > > > > > > Will fold this with the bug introducing the problem to avoid bisection > > > problems. > > > > > > > I agree. Also, the commit hash of the "Fixes" tag only applies to the > > perf/core branch and, I guess that might create confusion. > > > So while this fixes the warning I believe it breaks the intent of the code. > > tools/perf/util/branch.h: > struct branch_stack { > u64 nr; > u64 hw_idx; > struct branch_entry entries[]; > }; > > tools/perf/util/intel-pt.c: > struct { > struct branch_stack br_stack; > struct branch_entry entries[LBRS_MAX]; > } br; > > The array in br is trying to extend branch_stack's entries array. You > might have to do something like: > > alignas(alignof(branch_stack)) char storage[sizeof(branch_stack) + > sizeof(branch_entry) * LBRS_MAX]; > struct branch_stack *br = &storage; > > malloc/free may be nicer on the eyeballs. > Yep, I'd go for zalloc/free. There are a couple of places where dynamic memory is being allocated for struct branch_stack: tools/perf/util/cs-etm.c-256- if (etm->synth_opts.last_branch) { tools/perf/util/cs-etm.c:257: size_t sz = sizeof(struct branch_stack); tools/perf/util/cs-etm.c-258- tools/perf/util/cs-etm.c-259- sz += etm->synth_opts.last_branch_sz * tools/perf/util/cs-etm.c-260- sizeof(struct branch_entry); tools/perf/util/cs-etm.c-261- tidq->last_branch = zalloc(sz); tools/perf/util/thread-stack.c-148- if (br_stack_sz) { tools/perf/util/thread-stack.c:149: size_t sz = sizeof(struct branch_stack); tools/perf/util/thread-stack.c-150- tools/perf/util/thread-stack.c-151- sz += br_stack_sz * sizeof(struct branch_entry); tools/perf/util/thread-stack.c-152- ts->br_stack_rb = zalloc(sz); there is even function intel_pt_alloc_br_stack(). Just out of curiosity, why the need of such a hack in this case (the on-stack extension of branch_stack's entries array)? Thanks -- Gustavo