Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753496AbaJGUDg (ORCPT ); Tue, 7 Oct 2014 16:03:36 -0400 Received: from mail-ig0-f180.google.com ([209.85.213.180]:42499 "EHLO mail-ig0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752318AbaJGUDf (ORCPT ); Tue, 7 Oct 2014 16:03:35 -0400 Message-ID: <54344714.1000600@gmail.com> Date: Tue, 07 Oct 2014 13:03:32 -0700 From: David Daney User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 MIME-Version: 1.0 To: Andy Lutomirski CC: Rich Felker , Leonid Yegoshin , Matthew Fortune , David Daney , David Daney , "libc-alpha@sourceware.org" , "linux-kernel@vger.kernel.org" , "linux-mips@linux-mips.org" , David Daney Subject: Re: [PATCH resend] MIPS: Allow FPU emulator to use non-stack area. References: <54332A64.5020605@caviumnetworks.com> <20141007000514.GD23797@brightrain.aerifal.cx> <543334CE.8060305@caviumnetworks.com> <20141007004915.GF23797@brightrain.aerifal.cx> <54337127.40806@gmail.com> <6D39441BF12EF246A7ABCE6654B0235320F1E173@LEMAIL01.le.imgtec.org> <543431DA.4090809@imgtec.com> <20141007190943.GM23797@brightrain.aerifal.cx> <54343C2B.2080801@imgtec.com> <20141007192107.GN23797@brightrain.aerifal.cx> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/07/2014 12:28 PM, Andy Lutomirski wrote: > On Tue, Oct 7, 2014 at 12:21 PM, Rich Felker wrote: >> On Tue, Oct 07, 2014 at 12:16:59PM -0700, Leonid Yegoshin wrote: >>> On 10/07/2014 12:09 PM, Rich Felker wrote: >>>> I agree completely here. We should not break things (or, as it >>>> seems, leave them broken) for common usage cases that affect >>>> everyone just to coddle proprietary vendor-specific instructions. >>>> The latter just should not be used in delay slots unless the chip >>>> vendor also promises to provide fpu branch in hardware. Rich >>> And what do you propose - remove a current in-stack emulation and >>> you still think it doesn't break a status-quo? >> >> The in-stack trampoline support could be left but used only for >> emulating instructions the kernel doesn't know. This would make all >> normal binaries immediately usable with non-executable stack, and >> would avoid the only potential source of regressions. Ultimately I >> think the "xol" stuff should be removed, but that could be a long term >> goal. > > Does anything break if the xol stuff is disabled for PT_GNU_STACK tasks? > The instructions must be executed, if you turn on a non-executable stack, you cannot execute them on the stack, so they must be handled in another way, which is the subject of this thread. Options: 1a) XOL kernel manages the memory 1b) XOL userspace manages the menory 2) Emulate the instructions. 3) I don't think there is a 3rd. option. As the imgtec people have said, you have to do #2 for their new r6 ISA, as it uses PC relative instructions. I really think we should bite the bullet and do #2 for everything, it will be the cleanest long term solutions. David Daney -- 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/