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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 AEC98C43331 for ; Fri, 6 Sep 2019 13:45:04 +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 83FE720650 for ; Fri, 6 Sep 2019 13:45:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 83FE720650 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]:56480 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i6EXv-0005tO-PP for qemu-devel@archiver.kernel.org; Fri, 06 Sep 2019 09:45:03 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42464) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i6EXA-0005Rz-Jp for qemu-devel@nongnu.org; Fri, 06 Sep 2019 09:44:17 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i6EX8-0006Z0-Vq for qemu-devel@nongnu.org; Fri, 06 Sep 2019 09:44:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42150) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i6EX8-0006Yi-OK for qemu-devel@nongnu.org; Fri, 06 Sep 2019 09:44:14 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C5B134E8AC; Fri, 6 Sep 2019 13:44:13 +0000 (UTC) Received: from [10.3.116.234] (ovpn-116-234.phx2.redhat.com [10.3.116.234]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F24885D9E5; Fri, 6 Sep 2019 13:44:08 +0000 (UTC) To: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , Tony Nguyen , qemu-devel@nongnu.org References: <20190902012647.1761-1-tony.nguyen@bt.com> <41e61c1c-15b0-d028-fc23-52e2c59319d2@redhat.com> <93172f42-7506-65d0-5754-248c3fc31aa1@redhat.com> <867bdb4b-3eef-0660-6db2-a2e6a0ab5a0e@redhat.com> From: Eric Blake Openpgp: preference=signencrypt Autocrypt: addr=eblake@redhat.com; keydata= xsBNBEvHyWwBCACw7DwsQIh0kAbUXyqhfiKAKOTVu6OiMGffw2w90Ggrp4bdVKmCaEXlrVLU xphBM8mb+wsFkU+pq9YR621WXo9REYVIl0FxKeQo9dyQBZ/XvmUMka4NOmHtFg74nvkpJFCD TUNzmqfcjdKhfFV0d7P/ixKQeZr2WP1xMcjmAQY5YvQ2lUoHP43m8TtpB1LkjyYBCodd+LkV GmCx2Bop1LSblbvbrOm2bKpZdBPjncRNob73eTpIXEutvEaHH72LzpzksfcKM+M18cyRH+nP sAd98xIbVjm3Jm4k4d5oQyE2HwOur+trk2EcxTgdp17QapuWPwMfhaNq3runaX7x34zhABEB AAHNHkVyaWMgQmxha2UgPGVibGFrZUByZWRoYXQuY29tPsLAegQTAQgAJAIbAwULCQgHAwUV CgkICwUWAgMBAAIeAQIXgAUCS8fL9QIZAQAKCRCnoWtKJSdDahBHCACbl/5FGkUqJ89GAjeX RjpAeJtdKhujir0iS4CMSIng7fCiGZ0fNJCpL5RpViSo03Q7l37ss+No+dJI8KtAp6ID+PMz wTJe5Egtv/KGUKSDvOLYJ9WIIbftEObekP+GBpWP2+KbpADsc7EsNd70sYxExD3liwVJYqLc Rw7so1PEIFp+Ni9A1DrBR5NaJBnno2PHzHPTS9nmZVYm/4I32qkLXOcdX0XElO8VPDoVobG6 gELf4v/vIImdmxLh/w5WctUpBhWWIfQDvSOW2VZDOihm7pzhQodr3QP/GDLfpK6wI7exeu3P pfPtqwa06s1pae3ad13mZGzkBdNKs1HEm8x6zsBNBEvHyWwBCADGkMFzFjmmyqAEn5D+Mt4P zPdO8NatsDw8Qit3Rmzu+kUygxyYbz52ZO40WUu7EgQ5kDTOeRPnTOd7awWDQcl1gGBXgrkR pAlQ0l0ReO57Q0eglFydLMi5bkwYhfY+TwDPMh3aOP5qBXkm4qIYSsxb8A+i00P72AqFb9Q7 3weG/flxSPApLYQE5qWGSXjOkXJv42NGS6o6gd4RmD6Ap5e8ACo1lSMPfTpGzXlt4aRkBfvb NCfNsQikLZzFYDLbQgKBA33BDeV6vNJ9Cj0SgEGOkYyed4I6AbU0kIy1hHAm1r6+sAnEdIKj cHi3xWH/UPrZW5flM8Kqo14OTDkI9EtlABEBAAHCwF8EGAEIAAkFAkvHyWwCGwwACgkQp6Fr SiUnQ2q03wgAmRFGDeXzc58NX0NrDijUu0zx3Lns/qZ9VrkSWbNZBFjpWKaeL1fdVeE4TDGm I5mRRIsStjQzc2R9b+2VBUhlAqY1nAiBDv0Qnt+9cLiuEICeUwlyl42YdwpmY0ELcy5+u6wz mK/jxrYOpzXKDwLq5k4X+hmGuSNWWAN3gHiJqmJZPkhFPUIozZUCeEc76pS/IUN72NfprZmF Dp6/QDjDFtfS39bHSWXKVZUbqaMPqlj/z6Ugk027/3GUjHHr8WkeL1ezWepYDY7WSoXwfoAL 2UXYsMAr/uUncSKlfjvArhsej0S4zbqim2ZY6S8aRWw94J3bSvJR+Nwbs34GPTD4Pg== Organization: Red Hat, Inc. Message-ID: Date: Fri, 6 Sep 2019 08:44:08 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <867bdb4b-3eef-0660-6db2-a2e6a0ab5a0e@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 06 Sep 2019 13:44:13 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] memory: Set notdirty_mem_ops validator 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: Paolo Bonzini , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 9/6/19 8:24 AM, Philippe Mathieu-Daud=C3=A9 wrote: >>>> static const MemoryRegionOps notdirty_mem_ops =3D { >>>> .write =3D notdirty_mem_write, >>>> - .valid.accepts =3D notdirty_mem_accepts, >>>> .endianness =3D DEVICE_NATIVE_ENDIAN, >>>> .valid =3D { >>>> .min_access_size =3D 1, >>>> .max_access_size =3D 8, >>>> .unaligned =3D false, >>>> + .accepts =3D notdirty_mem_accepts, >>> >>> I'm surprised the compiler doesn't emit any warning... >> >> Same here. >> >> But reading >> https://en.cppreference.com/w/c/language/struct_initialization, this i= s >> compliant behavior: >> >> "However, when an initializer begins with a left open brace, its curre= nt >> object is fully re-initialized and any prior explicit initializers for >> any of its subobjects are ignored:" >> >> so it is worth filing a gcc bug asking for a QoI improvement in adding= a >> warning (since the code does not violate the C standard, but does caus= e >> surprises in the reinitialization of omitted members in the later {} t= o >> go back to 0 in spite of the earlier initialization by nested name). >=20 > Just remembered another case of (correct) reinitialization in > hw/arm/palm.c:101: We use nested reinitialization in multiple places. A gcc warning would have to be discriminating enough to NOT warn merely when something is listed twice...: >=20 > static struct { > int row; > int column; > } palmte_keymap[0x80] =3D { > [0 ... 0x7f] =3D { -1, -1 }, > [0x3b] =3D { 0, 0 }, /* F1 -> Calendar */ Here, [0x3b].row and [0x3b].column are listed twice, but both of the second listings are explicit. Similarly, in qobject/json-lexer.c: static const uint8_t json_lexer[][256] =3D { /* Relies on default initialization to IN_ERROR! */ ... /* * Two start states: * - IN_START recognizes JSON tokens with our string extensions * - IN_START_INTERP additionally recognizes interpolation. */ [IN_START ... IN_START_INTERP] =3D { ['"'] =3D IN_DQ_STRING, ... ['\n'] =3D IN_START, }, [IN_START_INTERP]['%'] =3D IN_INTERP, }; Done that way on purpose (I actually remember scratching my head on the best way to compress things while reviewing Markus' patch that ended up as 2cbd15aa6f; it took me a couple of tries off-list to end up at that override). ...rather, the gcc warning that I envision should ONLY be when a later partial =3D{} causes a zero-initialization override of an earlier explici= t .member, and NOT when a later complete =3D{} or explicit member overrides an earlier init (whether the earlier one was explicit due to .member or implicit due to partial =3D{}). --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org