From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933404AbaBAU3s (ORCPT ); Sat, 1 Feb 2014 15:29:48 -0500 Received: from terminus.zytor.com ([198.137.202.10]:33726 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932140AbaBAU3r (ORCPT ); Sat, 1 Feb 2014 15:29:47 -0500 Message-ID: <52ED590D.8090208@zytor.com> Date: Sat, 01 Feb 2014 12:29:01 -0800 From: "H. Peter Anvin" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: stefani@seibold.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de, mingo@redhat.com, ak@linux.intel.com, aarcange@redhat.com, john.stultz@linaro.org, luto@amacapital.net, xemul@parallels.com, gorcunov@openvz.org, andriy.shevchenko@linux.intel.com CC: Martin.Runge@rohde-schwarz.com, Andreas.Brief@rohde-schwarz.com Subject: Re: [PATCH 4/4] Add 32 bit VDSO time support for 64 bit kernel References: <1391268756-10766-1-git-send-email-stefani@seibold.net> <1391268756-10766-5-git-send-email-stefani@seibold.net> In-Reply-To: <1391268756-10766-5-git-send-email-stefani@seibold.net> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/01/2014 07:32 AM, stefani@seibold.net wrote: > > This kind of type hacking could be prevent in the future by doing a call to the > 64 bit code by the following sequence: > > - Compile the arch/x86/vdso/vclock_gettime.c as 64 bit, but only generate > the assembler output. > - Next compile a 32 bit object by including the 64 bit vclock_gettime.s > prefixed with .code64 > - At least we need a trampolin code which invokes the 64 bit code and do > the API conversation (64 bit longs to 32 bit longs), like the > followig snipped: > Honestly, I think the overhead of the mode switch would ruin a lot of the advantages with the vdso. -hpa