From patchwork Thu Jun 22 08:24:50 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Nicola Vetrini X-Patchwork-Id: 13288409 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 CB98DEB64D8 for ; Thu, 22 Jun 2023 08:25:38 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.553366.863871 (Exim 4.92) (envelope-from ) id 1qCFd0-0006pU-Df; Thu, 22 Jun 2023 08:25:18 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 553366.863871; Thu, 22 Jun 2023 08:25:18 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1qCFd0-0006pN-9e; Thu, 22 Jun 2023 08:25:18 +0000 Received: by outflank-mailman (input) for mailman id 553366; Thu, 22 Jun 2023 08:25:16 +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 1qCFcy-0006pE-Nh for xen-devel@lists.xenproject.org; Thu, 22 Jun 2023 08:25:16 +0000 Received: from support.bugseng.com (mail.bugseng.com [162.55.131.47]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 4f69edcb-10d6-11ee-8611-37d641c3527e; Thu, 22 Jun 2023 10:25:13 +0200 (CEST) Received: from nico.bugseng.com (unknown [151.37.206.199]) by support.bugseng.com (Postfix) with ESMTPSA id 5AB224EE0737; Thu, 22 Jun 2023 10:25:11 +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: 4f69edcb-10d6-11ee-8611-37d641c3527e From: Nicola Vetrini To: xen-devel@lists.xenproject.org Cc: sstabellini@kernel.org, michal.orzel@amd.com, xenia.ragiadakou@amd.com, ayan.kumar.halder@amd.com, consulting@bugseng.com, jbeulich@suse.com, andrew.cooper3@citrix.com, roger.pau@citrix.com, bertrand.marquis@arm.com, julien@xen.org, Nicola Vetrini , George Dunlap , Wei Liu Subject: [XEN PATCH v3] xen/include: avoid using a compiler extension for BUILD_BUG_ON_ZERO. Date: Thu, 22 Jun 2023 10:24:50 +0200 Message-Id: X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Redefine BUILD_BUG_ON_ZERO to avoid using a compiler extension that gives an acceptable semantics to C99 undefined behavior 58 ("A structure or union is defined as containing no named members (6.7.2.1)"). The chosen ill-formed construct is a negative bitwidth in a bitfield within a struct containing at least one named member, which prevents the UB while keeping the semantics of the construct. Signed-off-by: Nicola Vetrini --- Changes in V2: - Avoid using a VLA as the compile-time assertion - Do not drop _Static_assert Changes in V3: - Changed the operation to bring the result to 0 when the construct does not lead to a compilation error --- xen/include/xen/lib.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/xen/include/xen/lib.h b/xen/include/xen/lib.h index 67fc7c1d7e..d5f9c4a18a 100644 --- a/xen/include/xen/lib.h +++ b/xen/include/xen/lib.h @@ -51,9 +51,10 @@ e.g. in a structure initializer (or where-ever else comma expressions aren't permitted). */ #define BUILD_BUG_ON_ZERO(cond) \ - sizeof(struct { _Static_assert(!(cond), "!(" #cond ")"); }) + (sizeof(struct { char c; _Static_assert(!(cond), "!(" #cond ")"); }) & 0U) #else -#define BUILD_BUG_ON_ZERO(cond) sizeof(struct { int:-!!(cond); }) +#define BUILD_BUG_ON_ZERO(cond) \ + (sizeof(struct { unsigned u : (cond) ? -1 : 1; }) & 0U) #define BUILD_BUG_ON(cond) ((void)BUILD_BUG_ON_ZERO(cond)) #endif