Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758817AbYFWQzX (ORCPT ); Mon, 23 Jun 2008 12:55:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752549AbYFWQzL (ORCPT ); Mon, 23 Jun 2008 12:55:11 -0400 Received: from relay2.sgi.com ([192.48.171.30]:51661 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751649AbYFWQzJ (ORCPT ); Mon, 23 Jun 2008 12:55:09 -0400 Message-ID: <485FD56B.1090303@sgi.com> Date: Mon, 23 Jun 2008 09:55:07 -0700 From: Mike Travis User-Agent: Thunderbird 2.0.0.6 (X11/20070801) MIME-Version: 1.0 To: "Eric W. Biederman" CC: Jeremy Fitzhardinge , Christoph Lameter , Linux Kernel Mailing List , "H. Peter Anvin" Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area References: <20080604003018.538497000@polaris-admin.engr.sgi.com> <20080605102222.GA21319@elte.hu> <484EF29C.7080100@sgi.com> <485947A8.8060801@goop.org> <4859511E.5050605@sgi.com> <48596315.6020104@goop.org> <48596893.4040908@sgi.com> <485AADAC.3070301@sgi.com> <485AB78B.5090904@goop.org> <485AC120.6010202@sgi.com> <485AC5D4.6040302@goop.org> <485ACA8F.10006@sgi.com> <485ACD92.8050109@sgi.com> <485AD138.4010404@goop.org> <485ADA12.5010505@sgi.com> <485ADC73.60009@goop.org> <485BDB04.4090709@sgi.com> <485BE80E.10209@goop.org> <485BF8F5.6010802@goop.org> <485BFFC5.6020404@sgi.com> In-Reply-To: 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 Content-Length: 3523 Lines: 76 Eric W. Biederman wrote: > Mike Travis writes: > >> Jeremy Fitzhardinge wrote: >>> >>> BTW, I think __per_cpu_load will cause trouble if you make a relocatable >>> kernel, being an absolute symbol. But I have relocation off at the moment. >>> >> ... >> Here's where it's defined (in include/asm-generic/vmlinux.lds.h): >> >> #ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU >> #define PERCPU(align) \ >> . = ALIGN(align); \ >> percpu : { } :percpu \ >> __per_cpu_load = .; \ >> .data.percpu 0 : AT(__per_cpu_load - LOAD_OFFSET) { \ >> *(.data.percpu.first) \ >> *(.data.percpu.shared_aligned) \ >> *(.data.percpu) \ >> *(.data.percpu.page_aligned) \ >> ____per_cpu_size = .; \ >> } \ >> . = __per_cpu_load + ____per_cpu_size; \ >> data : { } :data >> #else >> >> Can we generate a new symbol which would account for LOAD_OFFSET? > > Ouch. Absolute symbols indeed. On the 32bit kernel that may play havoc > with the relocatable kernel, although we have had similar absolute logic > for the last year. With __per_cpu_start and __per_cpu_end so it may > not be a problem. > > To initialize the percpu data you do want to talk to the virtual address > at __per_coup_load. But it is absolute Ugh. > > It might be worth saying something like. > .data.percpu.start : AT(.data.percpu.dummy - LOAD_OFFSET) { > DATA(0) > . = ALIGN(align); > __per_cpu_load = . ; > } > To make __per_cpu_load a relative symbol. ld has a bad habit of taking > symbols out of empty sections and making them absolute. Which is why > I added the DATA(0). > > Still I don't think that would be the 64bit problem. > > Eric I'm not sure I understand the linker lingo enough to fill in the rest of the blanks... I've tried various versions around this framework and none have been accepted yet. #ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU #define PERCPU(align) \ .data.percpu.start : AT(.data.percpu.dummy - LOAD_OFFSET) { \ DATA(0) \ . = ALIGN(align); \ __per_cpu_load = .; \ *(.data.percpu.first) \ *(.data.percpu.shared_aligned) \ *(.data.percpu) \ *(.data.percpu.page_aligned) \ ____per_cpu_size = . - __per_cpu_load \ } \ #else Thanks, Mike -- 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/