From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 709AD346E7F; Fri, 27 Feb 2026 08:29:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772180966; cv=none; b=dZZtyuWhMxAexQe6u1MobniPEWXLgrhjTLu8Zc1AL205Y6sOXAhZgLHbNkRccYYfxLyBVEDEsOs2Mj/Ckq85GJDIm3iLZXZt6Kq4l1CtadYYLyEjWuE6enfduoHJW1rW76tKPv2/mRr48Ys/xYreVp8dsk28K1JQd6uBPXRElcE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772180966; c=relaxed/simple; bh=2iz8Rfwi3LCKHff7Q/EwnWY8qxUt8KKm0CS7VsO1S2M=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=K5XUaGNnCTG13aN/hb6HWzigWTb6eqfRtwmoIpHtFR1Im6Vobl7TgNWQfuhhNgyHuEHSJ0hzJhDPyreTXpQsCjQJZDVs0AnnQiZEumJRTb6Ox0q78taTNB9c+73R7TgUbh1MhFhXpt9DCf/KrSYFv5ZyAjEgpZFYaD1p2fKY5jE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=rhpdmz+F; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="rhpdmz+F" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=g651BAaPTh22OoeGP+PXuNzrraFm3BHATtRX6ifeu0M=; b=rhpdmz+FC4lsuUiYYSh0roYCbn DikRw1whb1a8/cs8F3RBfL9qPSv1zK68lpT5ZvQ3XaqPACuPnQ5TQV8U9WFojXXfclvGwO4L6FbM0 t1ZkSq7kYd93IfXTryVKJFwYT2bPOAWyIpn54alAPaJCs9Rhhl/kk3FqnZZWcYOCz54/e0ZI/cZro ylk+o0aVxNWuiP5GEbYpS/aDkiBKRF6YmnSpE+GtGk3hHOs6IKa07SPEm8c3X9LKN3PZONOAAS8bP H1TW9MlFKcULUZWv0GVF7oxr7KzAOe7QKWoFTm0IcyQHgVeiu8xBMSvOHRr7ztdrkADO/LITYvMEC +REprUWQ==; Received: from [172.31.31.148] (helo=u09cd745991455d.lumleys.internal) by desiato.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1vvtDj-0000000ChMj-2QKI; Fri, 27 Feb 2026 08:29:13 +0000 Message-ID: <718cbe24ffb546b97db8af94521da067d7437d70.camel@infradead.org> Subject: Re: [PATCH] KVM: x86: Fix C++ user API for structures with variable length arrays From: David Woodhouse To: Kees Cook Cc: "Gustavo A. R. Silva" , daniel@iogearbox.net, gustavoars@kernel.org, jgg@ziepe.ca, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Sean Christopherson , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" Date: Fri, 27 Feb 2026 08:29:11 +0000 In-Reply-To: <202602261053.78753BF1C@keescook> References: <97d40dd0e6abaf28f43d4d8ccf9c547a16c52e33.camel@infradead.org> <202602261053.78753BF1C@keescook> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-kniZVOuiD7hiypP9QK5+" User-Agent: Evolution 3.52.3-0ubuntu1.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-kniZVOuiD7hiypP9QK5+ Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2026-02-26 at 11:02 -0800, Kees Cook wrote: >=20 > > Also put the header fields into a struct_group() to provide (in C) a > > separate struct (e.g 'struct kvm_msrs_hdr') without the trailing VLA. >=20 > Right, my only worry is if C++ would want those header structs too. In > that case, you'd probably want to use a macro to include them (since not > all compilers are supporting transparent struct members yet): >=20 > #define __kvm_msrs_hdr \ > __u32 nmsrs; /* number of msrs in entries */ \ > __u32 pad >=20 > struct kvm_msrs_hdr { > __kvm_msrs_hdr; > }; >=20 > struct kvm_msrs { > __kvm_msrs_hdr; > __DECLARE_FLEX_ARRAY(struct kvm_msr_entry, entries); > }; Hm, does the struct_group() not also depend on the compiler supporting anonymous struct members? 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