From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (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 7664228F3 for ; Thu, 27 Feb 2025 15:28:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740670101; cv=none; b=BDm5uLHtzsVU8zUBk9q8VGIg/vk46Dn/Xn3xQMx9wF7U1opoai2tEdr6RB4RFkcEkz0FioZndxdH6O97AWdtwfkGJOAhdlzMuLCTgQEX6mT5tYlm8DI8WchG2+ns4eFyUbcnoximsy7P2cp17Gq0d84DV3CSyyBNpcZ1Ub3Z5bM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740670101; c=relaxed/simple; bh=o0UvjLqBNiIoXova2cJYX5uoNI9jFerQg1JWrk0OAsk=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=GHCQjpYSjjcBYWWxTJXPjfblzsmQ5C06+rDv1nxmyxdkCAGpS7MxOmWDYknJeYdDp9RW87UaNcpsDi9Sm+QILebpBOYp93tpYK/rgmS5zQG8eZGSBXZZcADQLNCz3g+6Ue3gqRC8WNspqeI4XIisJrpcYAgzivV9u3RhVhxteZA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=w8gd+D68; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="w8gd+D68" Received: from [127.0.0.1] ([76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 51RFRn4l2204046 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Thu, 27 Feb 2025 07:27:49 -0800 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 51RFRn4l2204046 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025021701; t=1740670071; bh=o0UvjLqBNiIoXova2cJYX5uoNI9jFerQg1JWrk0OAsk=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=w8gd+D686FERjp+qfzeIMQcKI8kUJJ94AXPZx/ikjhjHqb2nHRoFOXgA/1YD2biNY 9oI1ZUJFhat1YOiHgL/qSIhmSuW4OVxBvgNBNXNZiKAIIxmfrzw0xQTdfJaZdC11cw 29EjOCKplrI6Do4dE8PEUc/ViIlmcBnPXqSCRSWbY0R/gmYm59+k4BmVEnAA1A3tEv 7kD/4/ZaG8Nwd9PW/jbuRkLDKE7fUBnQIRVRBSvTtqg3DydyCKG1Mqb2tGJ+lQv5Qy z+IZa80n1AhnRRmSRRq2zAUxy4vPReygOALrlyczwhP5RPxJ75YSbLkjU61rnO62tJ 68/HdI+pV/RaQ== Date: Thu, 27 Feb 2025 07:27:48 -0800 From: "H. Peter Anvin" To: Ventura Jack , Martin Uecker CC: Linus Torvalds , Ralf Jung , "Paul E. McKenney" , Alice Ryhl , Kent Overstreet , Gary Guo , airlied@gmail.com, boqun.feng@gmail.com, david.laight.linux@gmail.com, ej@inai.de, gregkh@linuxfoundation.org, hch@infradead.org, ksummit@lists.linux.dev, linux-kernel@vger.kernel.org, miguel.ojeda.sandonis@gmail.com, rust-for-linux@vger.kernel.org Subject: Re: C aggregate passing (Rust kernel policy) User-Agent: K-9 Mail for Android In-Reply-To: References: <20250222141521.1fe24871@eugeo> <6pwjvkejyw2wjxobu6ffeyolkk2fppuuvyrzqpigchqzhclnhm@v5zhfpmirk2c> <5d7363b0-785c-4101-8047-27cb7afb0364@ralfj.de> Message-ID: <75F703D5-5ECD-4DF5-97AA-0CBD5965F470@zytor.com> Precedence: bulk X-Mailing-List: ksummit@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On February 27, 2025 6:21:24 AM PST, Ventura Jack wrote: >On Wed, Feb 26, 2025 at 1:00=E2=80=AFPM Martin Uecker wrote: >> >> I think C++ messed up a lot (including time-travel UB, uninitialized >> variables, aliasing ules and much more), but I do not see >> the problem here=2E > >C++26 actually changes the rules of reading uninitialized >variables from being undefined behavior to being >"erroneous behavior", for the purpose of decreasing instances >that can cause UB=2E Though programmers can still opt-into >the old behavior with UB, on a case by case basis, for the >sake of performance=2E > >Best, VJ=2E > > Of course, that is effectively what one gets if one treats the compiler wa= rning as binding=2E