Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752317AbbHRF5P (ORCPT ); Tue, 18 Aug 2015 01:57:15 -0400 Received: from terminus.zytor.com ([198.137.202.10]:59559 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751399AbbHRF5O (ORCPT ); Tue, 18 Aug 2015 01:57:14 -0400 User-Agent: K-9 Mail for Android In-Reply-To: References: <20150814071500.GA2678@gmail.com> <20150817080143.GA16928@gmail.com> <3019C0BF-A7B4-4058-8F92-A6104FE41E1D@zytor.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Subject: Re: [GIT PULL] x86 fixes From: "H. Peter Anvin" Date: Mon, 17 Aug 2015 22:56:35 -0700 To: Andy Lutomirski CC: Ingo Molnar , Linus Torvalds , Juergen Gross , Andy Lutomirski , Linux Kernel Mailing List , Thomas Gleixner , Peter Zijlstra , Brian Gerst , Denys Vlasenko , Andrew Morton Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1470 Lines: 28 I used a very old userspace, and embedded systems are much more likely to use uclibc than glibc. However, if they try to use SSE without checking they will break on a hell of a lot more hardware. On August 17, 2015 5:19:10 PM PDT, Andy Lutomirski wrote: >On Mon, Aug 17, 2015 at 5:06 PM, H. Peter Anvin wrote: >> User space does not need to treat for FPU instructions, except for >performance reasons, because the kernel emulates the full x87 FPU. So >it is localized to the kernel. > >But user space needs to avoid SSE2 and such, I suspect. In general, >I'd be surprised if things work well if we emulate the FPU (and set >CR0.em? I haven't checked out Linux's FPU emulation works) if user >code sees fancy instruction sets exposed and possibly even OSXSAVE. > >None of this matters except for testing, since it's very unlikely that >any CPU exists that supports XSAVE, XMM, SSE2, etc but uses emulated >x87. But if we emulate such a beast, things could break, and I bet >that's what Ingo's seeing. (Also, lots of distros target "i686" these >days, and that might cause its own set of problems.) > >--Andy -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/