Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755159AbYGALty (ORCPT ); Tue, 1 Jul 2008 07:49:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751534AbYGALtp (ORCPT ); Tue, 1 Jul 2008 07:49:45 -0400 Received: from relay2.sgi.com ([192.48.171.30]:54149 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751768AbYGALto (ORCPT ); Tue, 1 Jul 2008 07:49:44 -0400 Message-ID: <486A19D5.7010000@sgi.com> Date: Tue, 01 Jul 2008 04:49:41 -0700 From: Mike Travis User-Agent: Thunderbird 2.0.0.6 (X11/20070801) MIME-Version: 1.0 To: "Eric W. Biederman" CC: "H. Peter Anvin" , Jeremy Fitzhardinge , cl@linux-foundation.org, Linux Kernel Mailing List Subject: Re: [crash, bisected] Re: [PATCH 3/4] x86_64: Fold pda into per cpu area References: <20080604003018.538497000@polaris-admin.engr.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> <486912C4.8070705@sgi.com> <48691556.2080208@zytor.com> <48691E8B.4040605@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: 3897 Lines: 86 Eric W. Biederman wrote: > Mike Travis writes: > >> H. Peter Anvin wrote: >>> Mike Travis wrote: >>>> FYI, I did try this out and it caused the bootloader to scramble the >>>> loaded data. The first corruption I found was the .x86cpuvendor.init >>>> section contained all zeroes. >>>> >>> Explain what you mean with "the bootloader" in this context. >>> >>> -hpa >> >> After the code was loaded (the compressed code, it seems that my GRUB >> doesn't support uncompressed loading), the above section contained >> zeroes. I snapped it fairly early, around secondary_startup_64, and >> then printed it in x86_64_start_kernel. >> >> The object file had the correct data (as displayed by objdump) so I'm >> assuming that the bootloading process didn't load the section correctly. >> >> Below was the linker script I used: >> >> --- linux-2.6.tip.orig/include/asm-generic/vmlinux.lds.h >> +++ linux-2.6.tip/include/asm-generic/vmlinux.lds.h >> @@ -373,9 +373,13 @@ >> >> #ifdef CONFIG_HAVE_ZERO_BASED_PER_CPU >> #define PERCPU(align) \ >> - . = ALIGN(align); \ >> + .data.percpu.abs = .; \ >> percpu : { } :percpu \ >> - __per_cpu_load = .; \ >> + .data.percpu.rel : AT(.data.percpu.abs - LOAD_OFFSET) { \ >> + BYTE(0) \ >> + . = ALIGN(align); \ >> + __per_cpu_load = .; \ >> + } \ >> .data.percpu 0 : AT(__per_cpu_load - LOAD_OFFSET) { \ >> *(.data.percpu.first) \ >> *(.data.percpu.shared_aligned) \ >> @@ -383,8 +387,8 @@ >> *(.data.percpu.page_aligned) \ >> ____per_cpu_size = .; \ >> } \ >> - . = __per_cpu_load + ____per_cpu_size; \ >> - data : { } :data >> + . = __per_cpu_load + ____per_cpu_size; >> + >> #else >> #define PERCPU(align) \ >> . = ALIGN(align); \ >> >> It showed all the correct address in the map and __per_cpu_load was a >> relative symbol (which was the objective.) >> >> Btw, our simulator, which only loads uncompressed code, had the data correct, >> so it *may* only be a result of the code being compressed. > > Weird. Grub doesn't get involved in the decompression the kernel does it > all itself so we should be able to track where things go bad. > > Last I looked the compressed code was formed by essentially. > objcopy vmlinux -O binary vmlinux.bin > gzip vmlinux.bin > And then we take on a magic header to the gzip compressed file. > > Are things only bad with the change above? > > Eric Yes. The failure was "Unsupported CPU" (or some such) which clued me into the vendor section. I was able to get the zero-based variables working well for standard configs. It's getting tripped up now by some of Ingo's random configs, in very unusual places... And once again, it only fails on real h/w, not on our simulator, so catching the elusive bugger is tricky. 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/