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=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 77EC6C43381 for ; Tue, 12 Mar 2019 08:26:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 25C122147C for ; Tue, 12 Mar 2019 08:26:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1552379176; bh=l2HsO194GmzSjaZJ7s/9hf4Ym+X28F8Jw7yOi+Dx7sI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=F62eS6iUWe/5ctybCoitpXqaML1jKrHsBIVK4Lk045e0LF1wdPD58/CP11sQ6toYz X78tEEZp2yaXcQ8k6bHJf/xipL1gpNe+tE6xT8cOHkv0NJO17xSDdvW3lVxT1E0Wyb e41IaMCuWZA6wC0IGZpR1XLbrRz6PCPo8p72rVG0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727456AbfCLI0P (ORCPT ); Tue, 12 Mar 2019 04:26:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:46018 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725832AbfCLI0O (ORCPT ); Tue, 12 Mar 2019 04:26:14 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1BA30B157; Tue, 12 Mar 2019 08:26:13 +0000 (UTC) Date: Tue, 12 Mar 2019 09:26:12 +0100 From: Michal Hocko To: Pi-Hsun Shih Cc: Andrew Morton , Matthew Wilcox , Johannes Weiner , Stephen Rothwell , Minchan Kim , Huang Ying , Wei Yang , Yang Shi , Aaron Lu , Tejun Heo , Omar Sandoval , open list Subject: Re: [PATCH v2] mm/swap: Use offsetof instead of custom __swapoffset macro. Message-ID: <20190312082612.GH5721@dhcp22.suse.cz> References: <20190307094653.119425-1-pihsun@chromium.org> <20190312081902.223764-1-pihsun@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190312081902.223764-1-pihsun@chromium.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 12-03-19 16:18:59, Pi-Hsun Shih wrote: > Use offsetof to calculate offset of a field to take advantage of > compiler built-in version when possible, and avoid UBSAN warning when > compiling with Clang: > > UBSAN: Undefined behaviour in mm/swapfile.c:3010:38 > member access within null pointer of type 'union swap_header' > CPU: 6 PID: 1833 Comm: swapon Tainted: G S 4.19.23 #43 > Call trace: > dump_backtrace+0x0/0x194 > show_stack+0x20/0x2c > __dump_stack+0x20/0x28 > dump_stack+0x70/0x94 > ubsan_epilogue+0x14/0x44 > ubsan_type_mismatch_common+0xf4/0xfc > __ubsan_handle_type_mismatch_v1+0x34/0x54 > __se_sys_swapon+0x654/0x1084 > __arm64_sys_swapon+0x1c/0x24 > el0_svc_common+0xa8/0x150 > el0_svc_compat_handler+0x2c/0x38 > el0_svc_compat+0x8/0x18 > > Signed-off-by: Pi-Hsun Shih Yes this makes more sense. I still think the warning is bogus but whatever. A cleanup is worth it. Acked-by: Michal Hocko > --- > include/linux/swap.h | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index fc50e21b3b88..4bfb5c4ac108 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -157,9 +157,9 @@ struct swap_extent { > /* > * Max bad pages in the new format.. > */ > -#define __swapoffset(x) ((unsigned long)&((union swap_header *)0)->x) > #define MAX_SWAP_BADPAGES \ > - ((__swapoffset(magic.magic) - __swapoffset(info.badpages)) / sizeof(int)) > + ((offsetof(union swap_header, magic.magic) - \ > + offsetof(union swap_header, info.badpages)) / sizeof(int)) > > enum { > SWP_USED = (1 << 0), /* is slot in swap_info[] used? */ > -- > 2.21.0.360.g471c308f928-goog > -- Michal Hocko SUSE Labs