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 1C1A06F073 for ; Mon, 28 Apr 2025 21:39:46 +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=1745876388; cv=none; b=hE88lDR5b1W4dnzcsh5ZXmmt8NdV+9znKGmiwgGqgbJwkTpFWA3Oy/gcTXHBTyqi+eAZ6TvdLDMcgJzsZhQOW9ATAMi1DBgxlcLeXIlH68B6CLmQgArY0hR5wPLy18ji6fMYiuFc18Iqd0OrgfQacrN9Cy7uUUgXkFHK2KSUBIs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745876388; c=relaxed/simple; bh=IxZEGj0md+cpM4u952HviqymNhiVqc1HFmg2g9y45Xw=; h=Date:From:To:CC:Subject:In-Reply-To:References:Message-ID: MIME-Version:Content-Type; b=LqBdTBlGOsifHUrI8ZW5T7svGAE8HQjxkhqNb9JoMslNXgsVT2OBDCaZwpG+XPfqcI0Sf7PQD8mAPAm3hO+dKeK0G7+4wFfIPA/1E47P6oDymgBWSq9kRLSwYNAMEwmAXWyri2kZnARumfhI7xSJWTA6+9cwhn2VX8zVBnWBfSk= 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=Y6dnSHnX; 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="Y6dnSHnX" Received: from [IPv6:::1] ([172.59.161.110]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 53SLcqMl4064505 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Mon, 28 Apr 2025 14:38:53 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 53SLcqMl4064505 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2025042001; t=1745876335; bh=sQ20RzlhTI2OdKKrz143XBlONGa/0jFWo7zJXCXWAL0=; h=Date:From:To:CC:Subject:In-Reply-To:References:From; b=Y6dnSHnXkUStIgQVLFjFl/WxtubC4hEnVTp85eiu8hU/NXH7XMpJhcipi75ddaUXx /NgJZdBwG4YGgALW2ZBuc2ItVhSmmt6hLAaLrXrgK/va0SIroYA/dZXlbfOC88E16n ZH57S0ih6uCYhIIjqdhcg+zm2QALg0xS6Kn/ggUeXIpGMR1N1n6nxRZAXeLwRcS2PU +3eg0CL929Iy9x67h00wm229TzSUPUuBOjliEmd4xzgnb3s0obM8+coBaCMVyUcIqF bFChKrimnVYWirmjS9R+wtq1Tvf6r8kViKzsT3/5clVBlgSfFshY1zVI64ghckqW/p qvLCC7ylrKxUw== Date: Mon, 28 Apr 2025 14:38:46 -0700 From: "H. Peter Anvin" To: Linus Torvalds , Ingo Molnar CC: Andrew Cooper , Arnd Bergmann , Arnd Bergmann , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Juergen Gross , Boris Ostrovsky , Alexander Usyskin , Greg Kroah-Hartman , =?UTF-8?Q?Mateusz_Jo=C5=84czyk?= , Mike Rapoport , Ard Biesheuvel , Peter Zijlstra , linux-kernel@vger.kernel.org, xen-devel@lists.xenproject.org Subject: =?US-ASCII?Q?Re=3A_=5BPATCH=5D_bitops/32=3A_Convert_variable?= =?US-ASCII?Q?=5Fffs=28=29_and_fls=28=29_zero-case_handling_to_C?= User-Agent: K-9 Mail for Android In-Reply-To: References: <20250425141740.734030-1-arnd@kernel.org> Message-ID: 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=utf-8 Content-Transfer-Encoding: quoted-printable On April 28, 2025 9:14:45 AM PDT, Linus Torvalds wrote: >On Mon, 28 Apr 2025 at 00:05, Ingo Molnar wrote: >> >> And once we remove 486, I think we can do the optimization below to >> just assume the output doesn't get clobbered by BS*L in the zero-case, >> right? > >We probably can't, because who knows what "Pentium" CPU's are out there= =2E > >Or even if Pentium really does get it right=2E I doubt we have any >developers with an original Pentium around=2E > >So just leave the "we don't know what the CPU result is for zero" >unless we get some kind of official confirmation=2E > > Linus If anyone knows for sure, it is probably Christian Ludloff=2E However, the= re was a *huge* tightening of the formal ISA when the i686 was introduced (= family=3D6) and I really believe this was part of it=2E I also really don't trust that family=3D5 really means conforms to undocum= ented P5 behavior, e=2Eg=2E for Quark=2E