Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751201AbWIMVPU (ORCPT ); Wed, 13 Sep 2006 17:15:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751093AbWIMVPU (ORCPT ); Wed, 13 Sep 2006 17:15:20 -0400 Received: from gw.goop.org ([64.81.55.164]:24205 "EHLO mail.goop.org") by vger.kernel.org with ESMTP id S1751201AbWIMVPS (ORCPT ); Wed, 13 Sep 2006 17:15:18 -0400 Message-ID: <450874DD.8090109@goop.org> Date: Wed, 13 Sep 2006 14:15:09 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 1.5.0.5 (X11/20060907) MIME-Version: 1.0 To: Zachary Amsden CC: Arjan van de Ven , Linus Torvalds , Ingo Molnar , Andi Kleen , "Eric W. Biederman" , Linux Kernel Mailing List , Michael A Fetterman , Alan Cox Subject: Re: Assignment of GDT entries References: <450854F3.20603@goop.org> <1158175001.3054.7.camel@laptopd505.fenrus.org> <4508681E.3070708@goop.org> <4508711B.6060905@vmware.com> In-Reply-To: <4508711B.6060905@vmware.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1551 Lines: 42 Zachary Amsden wrote: > I believe 9,10,11 are reserved for future users like yourself or > expanded TLS segments. I think a bank of 3 TLS segments in the GDT is > working fine now (does NPTL even use more than one?). Nope. And there's a comment that wine uses one more. I think the third is completely unused. Does this mean that "reserved" is actually synonymous with "unused" in asm/segment.h? >> Otherwise line 1 would be ideal for putting 3 TLS, kernel+user >> code+data and PDA into, thereby making 99.999% of GDT descriptor uses >> come from one cache line. > > That change is visible to userspace, unfortunately. Don't think it matters much. 32-bit processes on x86-64 seem perfectly happy with the TLS being in a different place. I think the ABI is defined in terms of "use the selector for the entry that set_thread_area/clone returns", and so is not a constant. But I agree it would be better not to. Hm, moving user cs/ds would be pretty visible too... Hm, and it would have a greater chance of breaking stuff if they changed, compared to moving the TLS... So is there any reason for "kernel entries start at 12"? If there's no reason for it, then we can pack everything useful into 1-5. >> But anyway, what breaks if I put the PDA in 11? > > Nothing. OK then. J - 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/