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=-8.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,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 AC539C433FF for ; Sun, 28 Jul 2019 19:41:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 70AC020578 for ; Sun, 28 Jul 2019 19:41:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KWFF2mjN" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726291AbfG1Tl1 (ORCPT ); Sun, 28 Jul 2019 15:41:27 -0400 Received: from mail-qt1-f195.google.com ([209.85.160.195]:46986 "EHLO mail-qt1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726108AbfG1Tl0 (ORCPT ); Sun, 28 Jul 2019 15:41:26 -0400 Received: by mail-qt1-f195.google.com with SMTP id h21so57570171qtn.13; Sun, 28 Jul 2019 12:41:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=hw/FJV6kNbX3dJG9xz1ZqY6bUwNkBImddv944G3I5jU=; b=KWFF2mjNn41Vga7hU6YdR46+FUsGUX61tK4/Zxgf2GT01FJjx28cpAYBdbCg2uNuW/ uDJmj9DWNJRczTUUuhjjsTo0jnsQ3I+LyNyYTE03tY3VYrZVunepnzb/zlxtPF/qcq4h g0yoxHDjwbaPDD+zJv6ZKmE4zgtajsufTv2eTsvH2AnnP9rzSrIWD80RUFAEd8JJwvbp wOctnEjW19HzAXdYbZIo//nuUYw4EMnxXvip3Ul/USPqpcpwZPFaAPmUZ4o1Oxp8mQRr aI8dx35Rk9rH6FQxKiodroZz0JX84V5UTezmoacSFZTUtC7DMq+D49zK2oHI3L0E44KC coDg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=hw/FJV6kNbX3dJG9xz1ZqY6bUwNkBImddv944G3I5jU=; b=Q7tUgIl6AbReh+Qx8uVhGp4KJVtFfF1ohNrqAfh5XeKsCPttMAJ/u6kI1m8Bjf+QTx UhJxifKfHpvcg43Q6s2rb17CCZMXvFsNwHMpf1zC9O2Efjq/oDp4yhGhR4H0IEbHMpnl az4SD5UZinn9E2NKo6m5TxyEjMKBINuBriYSiu2FGdxIC+St8vyPBK/3geYmUaP8G4XI qWQGbTINzHmSTwhhQsmFDBFGait1hsjoGznNZU5zwjSPSv5Ebda42EOtNEvXMnUH0gE0 d1t/7QVsT502hxS0IIT4JKYaUweJZvE/deFFCnBlEtq/dEYWa3aBwkl4gLGgZa67kQTT Dq+A== X-Gm-Message-State: APjAAAVz/9vFBCpRITgB5im6Qk313Bp3//jf4+6HZhlIX1qx7SSVBG35 F8BqHqB5mUMy5+PxgpKrx+o= X-Google-Smtp-Source: APXvYqzbuUC9Ijr0q1lB3Uh0HyXwzMwxTDDVXBn4zgxhsxAzcNDkf7xNL4N/ewB363U9UpPOvGSfog== X-Received: by 2002:a0c:bd86:: with SMTP id n6mr77563621qvg.183.1564342885155; Sun, 28 Jul 2019 12:41:25 -0700 (PDT) Received: from localhost.localdomain ([2001:1284:f016:a0af:c6c5:7c31:69b:3f23]) by smtp.gmail.com with ESMTPSA id m5sm24797882qkb.117.2019.07.28.12.41.24 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sun, 28 Jul 2019 12:41:24 -0700 (PDT) Received: by localhost.localdomain (Postfix, from userid 1000) id 2031CC1BCD; Sun, 28 Jul 2019 16:41:22 -0300 (-03) Date: Sun, 28 Jul 2019 16:41:22 -0300 From: Marcelo Ricardo Leitner To: Qian Cai Cc: vyasevich@gmail.com, nhorman@tuxdriver.com, linux-sctp@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] net/sctp: fix GCC8+ -Wpacked-not-aligned warnings Message-ID: <20190728194122.GN6204@localhost.localdomain> References: <1564174659-21211-1-git-send-email-cai@lca.pw> <20190726213045.GL6204@localhost.localdomain> <4A42819C-32E5-4869-8A3B-0D4F9DF1B53C@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4A42819C-32E5-4869-8A3B-0D4F9DF1B53C@lca.pw> User-Agent: Mutt/1.12.0 (2019-05-25) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 28, 2019 at 01:05:25PM -0400, Qian Cai wrote: > > > > On Jul 26, 2019, at 5:30 PM, Marcelo Ricardo Leitner wrote: > > > > On Fri, Jul 26, 2019 at 04:57:39PM -0400, Qian Cai wrote: > >> There are a lot of those warnings with GCC8+ 64bit, > >> > >> In file included from ./include/linux/sctp.h:42, > >> from net/core/skbuff.c:47: > >> ./include/uapi/linux/sctp.h:395:1: warning: alignment 4 of 'struct > >> sctp_paddr_change' is less than 8 [-Wpacked-not-aligned] > >> } __attribute__((packed, aligned(4))); > >> ^ > >> ./include/uapi/linux/sctp.h:728:1: warning: alignment 4 of 'struct > >> sctp_setpeerprim' is less than 8 [-Wpacked-not-aligned] > >> } __attribute__((packed, aligned(4))); > >> ^ > >> ./include/uapi/linux/sctp.h:727:26: warning: 'sspp_addr' offset 4 in > >> 'struct sctp_setpeerprim' isn't aligned to 8 [-Wpacked-not-aligned] > >> struct sockaddr_storage sspp_addr; > >> ^~~~~~~~~ > >> ./include/uapi/linux/sctp.h:741:1: warning: alignment 4 of 'struct > >> sctp_prim' is less than 8 [-Wpacked-not-aligned] > >> } __attribute__((packed, aligned(4))); > >> ^ > >> ./include/uapi/linux/sctp.h:740:26: warning: 'ssp_addr' offset 4 in > >> 'struct sctp_prim' isn't aligned to 8 [-Wpacked-not-aligned] > >> struct sockaddr_storage ssp_addr; > >> ^~~~~~~~ > >> ./include/uapi/linux/sctp.h:792:1: warning: alignment 4 of 'struct > >> sctp_paddrparams' is less than 8 [-Wpacked-not-aligned] > >> } __attribute__((packed, aligned(4))); > >> ^ > >> ./include/uapi/linux/sctp.h:784:26: warning: 'spp_address' offset 4 in > >> 'struct sctp_paddrparams' isn't aligned to 8 [-Wpacked-not-aligned] > >> struct sockaddr_storage spp_address; > >> ^~~~~~~~~~~ > >> ./include/uapi/linux/sctp.h:905:1: warning: alignment 4 of 'struct > >> sctp_paddrinfo' is less than 8 [-Wpacked-not-aligned] > >> } __attribute__((packed, aligned(4))); > >> ^ > >> ./include/uapi/linux/sctp.h:899:26: warning: 'spinfo_address' offset 4 > >> in 'struct sctp_paddrinfo' isn't aligned to 8 [-Wpacked-not-aligned] > >> struct sockaddr_storage spinfo_address; > >> ^~~~~~~~~~~~~~ > >> Fix them by aligning the structures and fields to 8 bytes instead. > >> > >> Signed-off-by: Qian Cai > >> --- > >> include/uapi/linux/sctp.h | 18 +++++++++--------- > >> 1 file changed, 9 insertions(+), 9 deletions(-) > >> > >> diff --git a/include/uapi/linux/sctp.h b/include/uapi/linux/sctp.h > >> index b8f2c4d56532..e7bd71cde882 100644 > >> --- a/include/uapi/linux/sctp.h > >> +++ b/include/uapi/linux/sctp.h > > > > These changes gotta be more careful, if possible at all. As is, it's breaking UAPI. > > Could you please elaborate how this breaks userspace? I read through all the information > I can find about UAPI and still have no clue. All I can see if that some field alignments changed > which are expected, and it still take on 3 cachelines which should not hurt the performance. For example on the struct I pointed below, if an application is compiled using the old headers, sctp_paddrparams->spp_hbinterval is at offset 132. But with this patch, it will change to 136. Then with a kernel with this patch, it will look for the field at the wrong place. > > > > > -before > > +after patch > > > > struct sctp_paddrparams { > > sctp_assoc_t spp_assoc_id; /* 0 4 */ > > - struct __kernel_sockaddr_storage spp_address __attribute__((__aligned__(1))); /* 4 128 */ > > - /* --- cacheline 2 boundary (128 bytes) was 4 bytes ago --- */ > > - __u32 spp_hbinterval; /* 132 4 */ > > - __u16 spp_pathmaxrxt; /* 136 2 */ > > - __u32 spp_pathmtu; /* 138 4 */ > > - __u32 spp_sackdelay; /* 142 4 */ > > - __u32 spp_flags; /* 146 4 */ > > - __u32 spp_ipv6_flowlabel; /* 150 4 */ > > - __u8 spp_dscp; /* 154 1 */ > > > > - /* size: 156, cachelines: 3, members: 9 */ > > + /* XXX 4 bytes hole, try to pack */ > > + > > + struct __kernel_sockaddr_storage spp_address __attribute__((__aligned__(8))); /* 8 128 */ > > + /* --- cacheline 2 boundary (128 bytes) was 8 bytes ago --- */ > > + __u32 spp_hbinterval; /* 136 4 */ > > + __u16 spp_pathmaxrxt; /* 140 2 */ > > + __u32 spp_pathmtu; /* 142 4 */ > > + __u32 spp_sackdelay; /* 146 4 */ > > + __u32 spp_flags; /* 150 4 */ > > + __u32 spp_ipv6_flowlabel; /* 154 4 */ > > + __u8 spp_dscp; /* 158 1 */ > > + > > + /* size: 160, cachelines: 3, members: 9 */ > > + /* sum members: 155, holes: 1, sum holes: 4 */ > > /* padding: 1 */ > > - /* forced alignments: 1 */ > > - /* last cacheline: 28 bytes */ > > -} __attribute__((__aligned__(4))); > > + /* forced alignments: 1, forced holes: 1, sum forced holes: 4 */ > > + /* last cacheline: 32 bytes */ > > +} __attribute__((__aligned__(8))); > > > > > >> @@ -392,7 +392,7 @@ struct sctp_paddr_change { > >> int spc_state; > >> int spc_error; > >> sctp_assoc_t spc_assoc_id; > >> -} __attribute__((packed, aligned(4))); > >> +} __attribute__((packed, aligned(8))); > >> > >> /* > >> * spc_state: 32 bits (signed integer) > >> @@ -724,8 +724,8 @@ struct sctp_assocparams { > >> */ > >> struct sctp_setpeerprim { > >> sctp_assoc_t sspp_assoc_id; > >> - struct sockaddr_storage sspp_addr; > >> -} __attribute__((packed, aligned(4))); > >> + struct sockaddr_storage sspp_addr __attribute__((aligned(8))); > >> +} __attribute__((packed, aligned(8))); > >> > >> /* > >> * 7.1.10 Set Primary Address (SCTP_PRIMARY_ADDR) > >> @@ -737,8 +737,8 @@ struct sctp_setpeerprim { > >> */ > >> struct sctp_prim { > >> sctp_assoc_t ssp_assoc_id; > >> - struct sockaddr_storage ssp_addr; > >> -} __attribute__((packed, aligned(4))); > >> + struct sockaddr_storage ssp_addr __attribute__((aligned(8))); > >> +} __attribute__((packed, aligned(8))); > >> > >> /* For backward compatibility use, define the old name too */ > >> #define sctp_setprim sctp_prim > >> @@ -781,7 +781,7 @@ enum sctp_spp_flags { > >> > >> struct sctp_paddrparams { > >> sctp_assoc_t spp_assoc_id; > >> - struct sockaddr_storage spp_address; > >> + struct sockaddr_storage spp_address __attribute__((aligned(8))); > >> __u32 spp_hbinterval; > >> __u16 spp_pathmaxrxt; > >> __u32 spp_pathmtu; > >> @@ -789,7 +789,7 @@ struct sctp_paddrparams { > >> __u32 spp_flags; > >> __u32 spp_ipv6_flowlabel; > >> __u8 spp_dscp; > >> -} __attribute__((packed, aligned(4))); > >> +} __attribute__((packed, aligned(8))); > >> > >> /* > >> * 7.1.18. Add a chunk that must be authenticated (SCTP_AUTH_CHUNK) > >> @@ -896,13 +896,13 @@ struct sctp_stream_value { > >> */ > >> struct sctp_paddrinfo { > >> sctp_assoc_t spinfo_assoc_id; > >> - struct sockaddr_storage spinfo_address; > >> + struct sockaddr_storage spinfo_address __attribute__((aligned(8))); > >> __s32 spinfo_state; > >> __u32 spinfo_cwnd; > >> __u32 spinfo_srtt; > >> __u32 spinfo_rto; > >> __u32 spinfo_mtu; > >> -} __attribute__((packed, aligned(4))); > >> +} __attribute__((packed, aligned(8))); > >> > >> /* Peer addresses's state. */ > >> /* UNKNOWN: Peer address passed by the upper layer in sendmsg or connect[x] > >> -- > >> 1.8.3.1 >