From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from elvis.franken.de (elvis.franken.de [193.175.24.41]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 32842824BC; Wed, 10 Jul 2024 07:40:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.175.24.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720597261; cv=none; b=jT/H8Iy8FKQ5s22o0uJ2th6qZPolcPugt+oLqebWItl0duaGphEjD+j/eJL/OUjXlVtKDsDMFWEP8y05VhEorK6ohmpTNO/dYoR1+FLA2jEQvrjLekbXNBIJtCiW2O+61OfRtazZZCgdOl+tFCTxWVmkbLMHTW/Ic8jdXuFVf8U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720597261; c=relaxed/simple; bh=ic/doOQaVCqp0tFw78Ip2mj0kPGzk2er21GSUClPl3Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=r2hKFGQNAYY69XvDIYK/hjNO0CgwL5haLJX8fCeffuOiAsOjTTH0r2pm+l/dTepE1c2XsdV9zXKLbfrviX4c29NzA01vtm3W0wMyw2DF1cWSXPvFdfUaet7C4KONvorQgZNenbe0Vz+yp/CxCjhrr9PSN2Cy0ONegNSfMsbfdRg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=alpha.franken.de; spf=pass smtp.mailfrom=alpha.franken.de; arc=none smtp.client-ip=193.175.24.41 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=alpha.franken.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=alpha.franken.de Received: from uucp by elvis.franken.de with local-rmail (Exim 3.36 #1) id 1sRRwG-0003DV-00; Wed, 10 Jul 2024 09:40:32 +0200 Received: by alpha.franken.de (Postfix, from userid 1000) id 6ED58C0120; Wed, 10 Jul 2024 09:36:13 +0200 (CEST) Date: Wed, 10 Jul 2024 09:36:13 +0200 From: Thomas Bogendoerfer To: Jiaxun Yang Cc: "Maciej W. Rozycki" , Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, "linux-mips@vger.kernel.org" , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= Subject: Re: [PATCH v3] MIPS: Implement ieee754 NAN2008 emulation mode Message-ID: References: <20240612-mips_ieee754_emul-v3-1-2c21b450abdb@flygoat.com> <9cc26415-9cbc-47fa-a132-7d8c000874a4@app.fastmail.com> <7797a7b2-1bb2-4c45-b65d-678f685dfa3d@app.fastmail.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7797a7b2-1bb2-4c45-b65d-678f685dfa3d@app.fastmail.com> On Wed, Jul 10, 2024 at 01:34:41PM +0800, Jiaxun Yang wrote: > > > 在2024年7月9日七月 下午4:55，Thomas Bogendoerfer写道： > > On Fri, Jun 28, 2024 at 01:33:06AM +0100, Jiaxun Yang wrote: > >> > >> > >> 在2024年6月27日六月 下午8:54，Maciej W. Rozycki写道： > >> > On Thu, 27 Jun 2024, Jiaxun Yang wrote: > >> > > >> >> >> @@ -318,6 +318,10 @@ void mips_set_personality_nan(struct arch_elf_state *state) > >> >> >> t->thread.fpu.fcr31 = c->fpu_csr31; > >> >> >> switch (state->nan_2008) { > >> >> >> case 0: > >> >> >> + if (!(c->fpu_msk31 & FPU_CSR_NAN2008)) > >> >> >> + t->thread.fpu.fcr31 &= ~FPU_CSR_NAN2008; > >> >> >> + if (!(c->fpu_msk31 & FPU_CSR_ABS2008)) > >> >> >> + t->thread.fpu.fcr31 &= ~FPU_CSR_ABS2008; > >> >> > > >> >> > why is this needed? > >> >> > >> >> Because t->thread.fpu.fcr31 comes from c->fpu_csr31, in this case we the default > >> >> value of c->fpu_csr31 is read from hardware and we don't know what would that be. > >> > > >> > But it has always been like this. What has changed with your patch that > >> > you need to mask the bit out now? > >> > >> After this patch kernel's copy of t->thread.fpu.fcr31 can disagree with hardware. > >> When disagree happens, we trigger emulation. > >> > >> Before that patch for nan legacy binary running on nan2008 CPU t->thread.fpu.fcr31 > >> will still be nan2008 (for ieee754=relaxed) so that's not relevant. > > > > I'm considering to apply your patch, how much testing/verification did > > this patch see ? Do have some test binaries ? > > It has been tested against Debian rootfs. There is no need to test againt special binary, > but you need NaN2008 hardware such as Loongson 3A4000. that's just one case, what about NaN2008 binaries on a legacy MIPS CPU ? Thomas. -- Crap can work. Given enough thrust pigs will fly, but it's not necessarily a good idea. [ RFC1925, 2.3 ]