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=-17.3 required=3.0 tests=BAYES_00,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, URIBL_BLOCKED,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 078A0C433E0 for ; Wed, 10 Mar 2021 14:58:47 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 A986164EFE for ; Wed, 10 Mar 2021 14:58:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A986164EFE Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=xen.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.96165.181700 (Exim 4.92) (envelope-from ) id 1lK0IG-0004qH-0G; Wed, 10 Mar 2021 14:58:36 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 96165.181700; Wed, 10 Mar 2021 14:58:35 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lK0IF-0004qA-S9; Wed, 10 Mar 2021 14:58:35 +0000 Received: by outflank-mailman (input) for mailman id 96165; Wed, 10 Mar 2021 14:58:34 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lK0IE-0004q2-Fy for xen-devel@lists.xenproject.org; Wed, 10 Mar 2021 14:58:34 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1lK0IC-00044f-Qy; Wed, 10 Mar 2021 14:58:32 +0000 Received: from 54-240-197-234.amazon.com ([54.240.197.234] helo=a483e7b01a66.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) (Exim 4.92) (envelope-from ) id 1lK0IC-0002OO-Fo; Wed, 10 Mar 2021 14:58:32 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=Content-Transfer-Encoding:Content-Type:In-Reply-To: MIME-Version:Date:Message-ID:From:References:Cc:To:Subject; bh=lodQ7FG7ZXZ4/aX0c5msg2K6xV7OPC6YGi3udVI9Da8=; b=M6RZIVEsNY+4LeQi8nqbm0qlrh 45ZOro3r2r+Kc7zWzDCLXK2F1rpCd47uv+aaa6DswVFAni9+BoPeATPx7ZicMKYYQiglYFBccEJkO 4jH6K9hzDa1N097t34RLWlcvlvgephc5Tij8q7npla1caIiZt8dFGPoEZL0qUhm0wGJc=; Subject: Re: [PATCH][4.15] gnttab: work around "may be used uninitialized" warning To: Jan Beulich , "xen-devel@lists.xenproject.org" Cc: Andrew Cooper , George Dunlap , Ian Jackson , Stefano Stabellini , Wei Liu References: From: Julien Grall Message-ID: Date: Wed, 10 Mar 2021 14:58:30 +0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Hi Jan, On 10/03/2021 10:13, Jan Beulich wrote: > Sadly I was wrong to suggest dropping vaddrs' initializer during review > of v2 of the patch introducing this code. gcc 4.3 can't cope. What's the error? Are you sure this is not going to hiding a potential miscompilation of the function? > > Fixes: 52531c734ea1 ("xen/gnttab: Rework resource acquisition") > Signed-off-by: Jan Beulich > > --- a/xen/common/grant_table.c > +++ b/xen/common/grant_table.c > @@ -4026,7 +4026,7 @@ int gnttab_acquire_resource( > struct grant_table *gt = d->grant_table; > unsigned int i, final_frame; > mfn_t tmp; > - void **vaddrs; > + void **vaddrs = NULL; I am a bit nervous to inialize vaddrs to NULL for a few reasons: 1) It is not 100% obvious (e.g. it takes more than a second) that vaddrs will always be initialized. 2) A compiler will not be able to help us if we are adding code without initialized vaddrs. It also feels wrong to me to try to write Xen in a way that will make a 10 years compiler happy... If we still want to support them, then maybe a better approach would be to turn off to turn off -Werror for some version of GCC. So we can continue to benefit from the newer compiler diagnostics. Cheers, -- Julien Grall