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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 8CBEECDB465 for ; Thu, 19 Oct 2023 14:35:42 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.619397.964369 (Exim 4.92) (envelope-from ) id 1qtU7X-0001dC-DF; Thu, 19 Oct 2023 14:35:31 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 619397.964369; Thu, 19 Oct 2023 14:35:31 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1qtU7X-0001d5-AZ; Thu, 19 Oct 2023 14:35:31 +0000 Received: by outflank-mailman (input) for mailman id 619397; Thu, 19 Oct 2023 14:35:30 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1qtU7W-0001cy-BT for xen-devel@lists.xenproject.org; Thu, 19 Oct 2023 14:35:30 +0000 Received: from support.bugseng.com (mail.bugseng.com [162.55.131.47]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id bf63922d-6e8c-11ee-9b0e-b553b5be7939; Thu, 19 Oct 2023 16:35:28 +0200 (CEST) Received: from support.bugseng.com (support.bugseng.com [162.55.131.47]) by support.bugseng.com (Postfix) with ESMTPA id E69814EE073D; Thu, 19 Oct 2023 16:35:27 +0200 (CEST) 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" X-Inumbo-ID: bf63922d-6e8c-11ee-9b0e-b553b5be7939 MIME-Version: 1.0 Date: Thu, 19 Oct 2023 16:35:27 +0200 From: Nicola Vetrini To: Jan Beulich Cc: sstabellini@kernel.org, michal.orzel@amd.com, xenia.ragiadakou@amd.com, ayan.kumar.halder@amd.com, consulting@bugseng.com, andrew.cooper3@citrix.com, roger.pau@citrix.com, George Dunlap , Julien Grall , Wei Liu , xen-devel@lists.xenproject.org Subject: Re: [XEN PATCH][for-4.19 v2 8/8] xen/compat: use BUILD_BUG_ON in CHECK_SIZE macros In-Reply-To: <8546127f-9945-0175-4e11-e187233e13cb@suse.com> References: <6138e02935236afd51a5db98d3527e5e2602468d.1697123806.git.nicola.vetrini@bugseng.com> <8546127f-9945-0175-4e11-e187233e13cb@suse.com> User-Agent: Roundcube Webmail/1.4.3 Message-ID: <4e0c7d27b73fd00e8574547eff2a8da6@bugseng.com> X-Sender: nicola.vetrini@bugseng.com Organization: BUGSENG s.r.l. Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit On 17/10/2023 08:09, Jan Beulich wrote: > On 12.10.2023 17:28, Nicola Vetrini wrote: >> BUILD_BUG_ON is the preferred way to induce a build error >> upon statically determined incorrect conditions. >> >> This also fixes a MISRA C:2012 Rule 10.1 violation in the >> previous formulation. >> >> Signed-off-by: Nicola Vetrini > > Hmm, looking back it's indeed not clear why I didn't use BUILD_BUG_ON() > right > away. Perhaps just to avoid inline functions when things can be done > without. > And/or because originally the macros were intended to be usable in > function > bodies, not (just) at file scope. However, ... > >> --- a/xen/include/xen/compat.h >> +++ b/xen/include/xen/compat.h >> @@ -151,12 +151,20 @@ CHECK_NAME_(k, n, T)(k xen_ ## n *x, \ >> return x == c; \ >> } >> >> -#define CHECK_SIZE(name) \ >> - typedef int CHECK_NAME(name, S)[1 - (sizeof(xen_ ## name ## _t) >> != \ >> - sizeof(compat_ ## name ## >> _t)) * 2] >> +#define CHECK_SIZE(name) \ >> +static inline void __maybe_unused CHECK_SIZE_##name(void) \ >> +{ \ >> + typedef int CHECK_NAME(name, S)[1]; \ > > ... what's this and ... > >> + BUILD_BUG_ON(sizeof(xen_ ## name ## _t) != \ >> + sizeof(compat_ ## name ## _t)); \ >> +} >> #define CHECK_SIZE_(k, n) \ >> - typedef int CHECK_NAME_(k, n, S)[1 - (sizeof(k xen_ ## n) != \ >> - sizeof(k compat_ ## n)) * >> 2] >> +static inline void __maybe_unused CHECK_SIZE_##k_##n(void) \ >> +{ \ >> + typedef int CHECK_NAME_(k, n, S)[1]; \ > > ... this needed for? The types aren't used anywhere afaict. > > Jan > >> + BUILD_BUG_ON(sizeof(k xen_ ## n) != \ >> + sizeof(k compat_ ## n)); \ >> +} >> >> #define CHECK_FIELD_COMMON(name, t, f) \ >> static inline int __maybe_unused name(xen_ ## t ## _t *x, compat_ ## >> t ## _t *c) \ You're probably right. I was wondering the same thing when replacing the code with BUILD_BUG_ON. -- Nicola Vetrini, BSc Software Engineer, BUGSENG srl (https://bugseng.com)