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=-17.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,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 E124BC433ED for ; Thu, 6 May 2021 14:40:00 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 1B9FE61176 for ; Thu, 6 May 2021 14:40:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1B9FE61176 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:41556 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lefAU-0005gc-VJ for qemu-devel@archiver.kernel.org; Thu, 06 May 2021 10:39:58 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42922) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leex8-0000v4-MN for qemu-devel@nongnu.org; Thu, 06 May 2021 10:26:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:26573) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1leex4-0003Ds-Sd for qemu-devel@nongnu.org; Thu, 06 May 2021 10:26:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1620311165; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=4iuE6eCW+gTRiFvl6fzIAuVjIl3+LmZF9xYYjhbaPYk=; b=QLggL/Kle0EorEYDdNTQw6rtwf8RCA9Y/zVqV3b/UYIcc6eJq+jD4eJTeafEAHQs6P2obq SXJmblmIrfjbbd/7lPDb82+l5osytK4q7vB2bpMDYqINIWmM9sXu9FwNK7v7xSf+I4p9Dx 4+36aZ1knWPe4eceW5ihmU0NuICSO4w= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-436-VUj96t0uOsKt2Yn_3ajXeQ-1; Thu, 06 May 2021 10:25:57 -0400 X-MC-Unique: VUj96t0uOsKt2Yn_3ajXeQ-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 4465818BA281; Thu, 6 May 2021 14:25:56 +0000 (UTC) Received: from [10.3.113.56] (ovpn-113-56.phx2.redhat.com [10.3.113.56]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E70A95D6D7; Thu, 6 May 2021 14:25:51 +0000 (UTC) Subject: Re: [PATCH v2 4/9] bsd-user/syscall: Replace alloca() by g_new() To: Warner Losh , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= References: <20210506133758.1749233-1-philmd@redhat.com> <20210506133758.1749233-5-philmd@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: <39f12704-af5c-2e4f-d872-a860d9a870d7@redhat.com> Date: Thu, 6 May 2021 09:25:51 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Received-SPF: pass client-ip=170.10.133.124; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.69, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, Kyle Evans , QEMU Developers , qemu-arm@nongnu.org, qemu-ppc@nongnu.org, Gerd Hoffmann , Paolo Bonzini , =?UTF-8?Q?Alex_Benn=c3=a9e?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/6/21 9:16 AM, Warner Losh wrote: > On Thu, May 6, 2021, 7:38 AM Philippe Mathieu-Daudé > wrote: > >> The ALLOCA(3) man-page mentions its "use is discouraged". >> >> Replace it by a g_new() call. >> >> Signed-off-by: Philippe Mathieu-Daudé >> --- >> bsd-user/syscall.c | 3 +-- >> 1 file changed, 1 insertion(+), 2 deletions(-) >> >> diff --git a/bsd-user/syscall.c b/bsd-user/syscall.c >> index 4abff796c76..dbee0385ceb 100644 >> --- a/bsd-user/syscall.c >> +++ b/bsd-user/syscall.c >> @@ -355,9 +355,8 @@ abi_long do_freebsd_syscall(void *cpu_env, int num, >> abi_long arg1, >> case TARGET_FREEBSD_NR_writev: >> { >> int count = arg3; >> - struct iovec *vec; >> + g_autofree struct iovec *vec = g_new(struct iovec, count); >> > > Where is this freed? Also, alloca just moves a stack pointer, where malloc > has complex interactions. Are you sure that's a safe change here? It's freed any time the g_autofree variable goes out of scope (that's what the g_autofree macro is for). Yes, the change is safe, although you are right that switching to malloc is going to be a bit more heavyweight than what alloca used. What's more, it adds safety: if count was under user control, a user could pass a value that could cause alloca to allocate more than 4k and accidentally mess up stack guard pages, while malloc() uses the heap and therefore cannot cause stack bugs. -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org