From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4574A78F5E for ; Tue, 8 Apr 2025 02:51:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744080696; cv=none; b=L78rqam2SOw/kCs93rGwiw3SIsQW7LWjq+IqP5pdNKzi6BVAbMIHOPUbjI7l5Rz+/mQW2dv0oGiHOCQ8YrVgs8EFWXukv+5qXB0bmcTpXZoPF6J8mwPnNtK40a0jfV/MzX+4pMHuIA1sCVveeyW0X1gA5uuG/hVkOBBVDesbyAY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744080696; c=relaxed/simple; bh=Ik+LdWMaF8o8H1avWZeByXTNmquKpNLMRhUEWBst4T4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rflcerpuXwaF7KwAGQVmK6DgTcNx1PSTU27tPGm0ntpdzOEzeL3t3VOwTddu1lBSnbbiyBsRUDxtaUH+e5H/8mW42ES/OP8WYsrscMXwef5dAFzjm5af2nw/tRdX63UQlz2QKIAcT+xMrsCPsp+t4XmyQd9oarF89f6YglWwxHI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PC1fIXQC; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PC1fIXQC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4357EC4CEDD; Tue, 8 Apr 2025 02:51:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744080695; bh=Ik+LdWMaF8o8H1avWZeByXTNmquKpNLMRhUEWBst4T4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=PC1fIXQCXYEacT6zxhs1TsW0HQYiirNw6s54m4/dQyebZkf8hUrQ7mT1HkOKH45IM O0mmAPJYVU9bWJnvg5UpDr9MvfNvDbkydxtNnDrOeCJInLJE3064POSnk3n5SQdrUd B1fFKS+SXB2yffVEiJQ4XTIixi8OHTUQVXphmhqOJj2NI1LoXRQJEo+CPPs/O1ev2F v4ii/2/gDkpYGt9naptpUIcXVtxOdCpNf6RAmFHj+0EIsKQYJedd39T5+0QYIe8AfC 41dYtUL6yDFnvxkdclZIEZFG/vTMeoN2Rkror3f6YI4PSjFRR2O74YM1nnuYmR/x+E mTQRD5CmKqlxg== Date: Mon, 7 Apr 2025 19:51:29 -0700 From: Nathan Chancellor To: Ingo Molnar Cc: Dan Carpenter , David Hildenbrand , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, kernel test robot , Dan Carpenter , Andrew Morton , Lorenzo Stoakes , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Rik van Riel , "H. Peter Anvin" , Linus Torvalds Subject: Re: [PATCH v1] x86/mm/pat: (un)track_pfn_copy() fix + improvements Message-ID: <20250408025129.GA1168636@ax162> References: <20250404124931.2255618-1-david@redhat.com> <630caa8e-2ee2-4895-9e4e-8bf2fa079100@redhat.com> <4961949a-75db-4071-a478-fdc543c1dd28@stanley.mountain> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Apr 07, 2025 at 08:59:44PM +0200, Ingo Molnar wrote: > Good, although why is this compiler option named so weirdly in Clang: > > CC_AUTO_VAR_INIT_ZERO_ENABLER := -enable-trivial-auto-var-init-zero-knowing-it-will-be-removed-from-clang > > Hopefully it is named thusly because Clang has adopted GCC's > -ftrivial-auto-var-init=zero? Clang did -ftrivial-auto-var-init first, where the original author added both pattern and zero but intended to remove zero once pattern has been optimized enough compared to zero (if I remember and understand correctly), so the "enabler" flag was added to try and make that clear. Eventually, Kees leveraged both Linus's stated desire for initializing stack variables [1] and GCC 12 landing -ftrivial-auto-var-init=zero without a separate enable option to deprecate the "enabler" flag in clang 16 [2] and remove it altogether in clang 18 [3]. [1]: https://lore.kernel.org/CAHk-=wgTM+cN7zyUZacGQDv3DuuoA4LORNPWgb1Y_Z1p4iedNQ@mail.gmail.com/ [2]: https://github.com/llvm/llvm-project/commit/aef03c9b3bed5cef5a1940774b80128aefcb4095 [3]: https://github.com/llvm/llvm-project/commit/00e54d04ae2802d498741097d4b83e898bc99c5b Cheers, Nathan