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 1585B2116FD for ; Tue, 8 Apr 2025 08:19:33 +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=1744100375; cv=none; b=vETHsQtRZg7jgtBSswXJ6HMRv9N/bJezg087Dmq7HH5hVvPGD1E+cHFiud6DwYn+2e8cEOly38iC8ZFZwNwx+XQzvKbfKPbZ2zDrczP7gHj455CA+PW7x+cXzmXyzFdm0VzxIiESYIssN/O664afDBejs1d+aR0Lk5FlJPUs+q4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1744100375; c=relaxed/simple; bh=RWDluSmvD0EtJvctRRT5CAy2qsHtkmsuPO3psGuGfu4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YQ5Wm6Ek2Zmm4rv9Wd7PiZhqRdS0NfDUNHUD2l5iWqhvPKu8QtemSjd0ET2U9VyzFEr+QSFirDtUxJUC0IHYDVpmXdtx5gRNd1fwAhzOfwzITOiMUDDYu0yYyrE/yVx92/Qgenc+slD1U0KuDRu/4JRrx2fCUFcYGXIAYLPbnqY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=N9fyQ3Gq; 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="N9fyQ3Gq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98A75C4CEE5; Tue, 8 Apr 2025 08:19:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744100373; bh=RWDluSmvD0EtJvctRRT5CAy2qsHtkmsuPO3psGuGfu4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=N9fyQ3GqpUgtbdKyXZ5kg7qfihhKGhrMj9B+li0orUu8ECTiBYoX8A7Ag09moZPEK jBF2Fu0YW/3aK5odPeKGsp180zLWjClPnR5os44/2upIxcGmj4NsL5PaPqLbgleNAQ e3jPwUh+tiiVrbdRXjP8flZpkagucKgwDQqSbsxZ9QYW9iVfDZ7dL/QC/qDyD4np3/ WnKhaVGlg93orolKq4yXYTbPmblttltWolA3CguR23J2KZzrwEd3nEznlfRDnLXgWV NHm1n7XQxFlcnBE4wW8r/E/y6mnz1APehNyqJj5YvSUNAV49Yq7rh1hIHbKo9w0r0i i8Q2o07ml7Gyw== Date: Tue, 8 Apr 2025 10:19:27 +0200 From: Ingo Molnar To: Nathan Chancellor 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: References: <20250404124931.2255618-1-david@redhat.com> <630caa8e-2ee2-4895-9e4e-8bf2fa079100@redhat.com> <4961949a-75db-4071-a478-fdc543c1dd28@stanley.mountain> <20250408025129.GA1168636@ax162> 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: <20250408025129.GA1168636@ax162> * Nathan Chancellor wrote: > 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 Cool, thanks for the explanation! Thanks, Ingo