Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936495AbcKDQvI (ORCPT ); Fri, 4 Nov 2016 12:51:08 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:60917 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932511AbcKDQvH (ORCPT ); Fri, 4 Nov 2016 12:51:07 -0400 Date: Fri, 4 Nov 2016 09:50:47 -0700 From: Guenter Roeck To: "Maciej W. Rozycki" Cc: Matthew Fortune , Ralf Baechle , "linux-mips@linux-mips.org" , "linux-kernel@vger.kernel.org" , James Hogan Subject: Re: [PATCH] MIPS: VDSO: Always select -msoft-float Message-ID: <20161104165047.GA29628@roeck-us.net> References: <1477843551-21813-1-git-send-email-linux@roeck-us.net> <20161101233038.GA25472@roeck-us.net> <6D39441BF12EF246A7ABCE6654B0235380AB79B7@HHMAIL01.hh.imgtec.org> <20161104152603.GB12009@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: guenter@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: guenter@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1590 Lines: 33 On Fri, Nov 04, 2016 at 04:09:37PM +0000, Maciej W. Rozycki wrote: > On Fri, 4 Nov 2016, Guenter Roeck wrote: > > > > As above, unless absolutely critical to have floating point code then > > > the vDSO should just avoid all FP related issues and build soft-float. > > > > FWIW, my logic was quite simple: The rest of the kernel builds with > > -msoft-float, thus vDSO should do the same. Of course, I don't know the > > entire context, so there may well be a reason to handle it differently > > than the rest of the kernel. > > VDSO is not a part of the kernel, it's user mode code, made visible in > the user virtual memory, and implicitly loaded along the rest of the DSOs > on program startup by the dynamic loader (ld.so). It has to be PIC for > that reason, too, causing all the hassle we had with making it such that > it does not need a GOT. > > > Anyway, isn't the kernel supposed to not use floating point operations > > in the first place ? Is this different for vDSO ? > > This code is executed in the user mode so while floating-point code may > not be needed there, not at least right now, there's actually nothing > which should stop us from from adding some should such a need arise. > Just for my understanding - so the code is compiled with the kernel and part of the kernel source but executed in user mode ? If you ever add real floating point code, doesn't that also mean that you'll have to implement the necessary linker helper functions or wrappers (such as the wrappers needed for 64-bit integer divide operations in 32 bit code) ? Thanks, Guenter