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{ "id": 169659, "web_url": "http://patches.dpdk.org/comment/169659/", "msgid": "<c3421da2-7394-45d3-b77d-b215882585a1@redhat.com>", "list_archive_url": "https://inbox.dpdk.org/dev/c3421da2-7394-45d3-b77d-b215882585a1@redhat.com", "date": "2024-04-25T13:44:37", "subject": "Re: [PATCH 1/1] vhost: fix GCC 13 build error", "submitter": { "id": 512, "url": "http://patches.dpdk.org/api/people/512/?format=api", "name": "Maxime Coquelin", "email": "maxime.coquelin@redhat.com" }, "content": "On 4/10/24 17:21, Luca Vizzarro wrote:\n> This patch resolves a build error with GCC 13 and arm/aarch32 as\n> targets:\n> \n> In function ‘mbuf_to_desc’,\n> inlined from ‘vhost_enqueue_async_packed’ at\n> ../lib/vhost/virtio_net.c:1828:6,\n> inlined from ‘virtio_dev_rx_async_packed’ at\n> ../lib/vhost/virtio_net.c:1842:6,\n> inlined from ‘virtio_dev_rx_async_submit_packed’ at\n> ../lib/vhost/virtio_net.c:1900:7:\n> ../lib/vhost/virtio_net.c:1159:18: error: ‘buf_vec[0].buf_addr’ may\n> be used uninitialized [-Werror=maybe-uninitialized]\n> 1159 | buf_addr = buf_vec[vec_idx].buf_addr;\n> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~\n> <snip>\n> ../lib/vhost/virtio_net.c:1160:18: error: ‘buf_vec[0].buf_iova’ may\n> be used uninitialized [-Werror=maybe-uninitialized]\n> 1160 | buf_iova = buf_vec[vec_idx].buf_iova;\n> | ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~\n> <snip>\n> ../lib/vhost/virtio_net.c:1161:35: error: ‘buf_vec[0].buf_len’ may\n> be used uninitialized [-Werror=maybe-uninitialized]\n> 1161 | buf_len = buf_vec[vec_idx].buf_len;\n> | ~~~~~~~~~~~~~~~~^~~~~~~~\n> \n> GCC complains about the possible runtime path where the while loop\n> which fills buf_vec (in vhost_enqueue_async_packed) is not run. As a\n> consequence it correctly thinks that buf_vec is not initialized while\n> being accessed anyways.\n> \n> This scenario is actually very unlikely as the only way this can occur\n> is if size has overflowed to 0. Meaning that the total packet length\n> would be close to UINT64_MAX (or actually UINT32_MAX). At first glance,\n> the code suggests that this may never happen as the type of size has\n> been changed to 64-bit. For a 32-bit architecture such as arm\n> (e.g. armv7-a) and aarch32, this still happens because the operand types\n> (pkt->pkt_len and sizeof) are 32-bit wide, performing 32-bit arithmetic\n> first (where the overflow can happen) and widening to 64-bit later.\n> \n> The proposed fix simply guarantees to the compiler that the scope which\n> fills buf_vec is accessed at least once, while not disrupting the actual\n> logic. This is based on the assumption that size will always be greater\n> than 0, as suggested by the sizeof, and the packet length will never be\n> as big as UINT32_MAX, and causing an overflow.\n> \n> Fixes: 873e8dad6f49 (\"vhost: support packed ring in async datapath\")\n> Cc: stable@dpdk.org\n> \n> Signed-off-by: Luca Vizzarro <luca.vizzarro@arm.com>\n> Reviewed-by: Paul Szczepanek <paul.szczepanek@arm.com>\n> Reviewed-by: Nick Connolly <nick.connolly@arm.com>\n> ---\n> lib/vhost/virtio_net.c | 4 ++--\n> 1 file changed, 2 insertions(+), 2 deletions(-)\n> \n\nReviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>\n\nThanks,\nMaxime", "headers": { "Return-Path": "<dev-bounces@dpdk.org>", "X-Original-To": "patchwork@inbox.dpdk.org", "Delivered-To": "patchwork@inbox.dpdk.org", "Received": [ "from mails.dpdk.org (mails.dpdk.org [217.70.189.124])\n\tby inbox.dpdk.org (Postfix) with ESMTP id B8FB943F01;\n\tThu, 25 Apr 2024 15:44:46 +0200 (CEST)", "from mails.dpdk.org (localhost [127.0.0.1])\n\tby mails.dpdk.org (Postfix) with ESMTP id A3DC9435F4;\n\tThu, 25 Apr 2024 15:44:46 +0200 (CEST)", "from us-smtp-delivery-124.mimecast.com\n (us-smtp-delivery-124.mimecast.com [170.10.129.124])\n by mails.dpdk.org (Postfix) with ESMTP id 1E37140284\n for <dev@dpdk.org>; Thu, 25 Apr 2024 15:44:45 +0200 (CEST)", "from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73])\n by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3,\n cipher=TLS_AES_256_GCM_SHA384) id us-mta-221-NP9XbV8wPwmav5kDpEi3aw-1; Thu,\n 25 Apr 2024 09:44:40 -0400", "from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com\n [10.11.54.9])\n (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest\n SHA256)\n (No client certificate requested)\n by mimecast-mx02.redhat.com (Postfix) with ESMTPS id BF56E2932480;\n Thu, 25 Apr 2024 13:44:39 +0000 (UTC)", "from [10.39.208.23] (unknown [10.39.208.23])\n by smtp.corp.redhat.com (Postfix) with ESMTPS id 776B65C5CC7;\n Thu, 25 Apr 2024 13:44:38 +0000 (UTC)" ], "DKIM-Signature": "v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com;\n s=mimecast20190719; t=1714052684;\n h=from:from:reply-to:subject:subject:date:date:message-id:message-id:\n to:to:cc:cc:mime-version:mime-version:content-type:content-type:\n content-transfer-encoding:content-transfer-encoding:\n in-reply-to:in-reply-to:references:references:autocrypt:autocrypt;\n bh=Nq3OJKOONSkNhh2+TnUs4BN4NAh/7c2GuKEjUsJAHVc=;\n b=OVaa96/7btKEIrMMYsBRUOuxckABc/QmbPpDr0lP+MicnG0PmvjAv6K4oHYXl7VuCYl85K\n fXZ71gNCISkDhk4fEvxymlG1a8KT0nR/cPJgLrRLf2K5A3qfmZzwtWqRqCQLPCFCVLugO2\n bDZiH4KPAA6PdKWa22UGsaMLeK8U644=", "X-MC-Unique": "NP9XbV8wPwmav5kDpEi3aw-1", "Message-ID": "<c3421da2-7394-45d3-b77d-b215882585a1@redhat.com>", "Date": "Thu, 25 Apr 2024 15:44:37 +0200", "MIME-Version": "1.0", "User-Agent": "Mozilla Thunderbird", "Subject": "Re: [PATCH 1/1] vhost: fix GCC 13 build error", "To": "Luca Vizzarro <luca.vizzarro@arm.com>, dev@dpdk.org", "Cc": "luca.boccassi@gmail.com, paul.szczepanek@arm.com, nick.connolly@arm.com,\n stable@dpdk.org", "References": "<20240410152101.3211244-1-luca.vizzarro@arm.com>\n <20240410152101.3211244-2-luca.vizzarro@arm.com>", "From": "Maxime Coquelin <maxime.coquelin@redhat.com>", "Autocrypt": "addr=maxime.coquelin@redhat.com; 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