Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1424353AbWKJFLc (ORCPT ); Fri, 10 Nov 2006 00:11:32 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1424309AbWKJFLc (ORCPT ); Fri, 10 Nov 2006 00:11:32 -0500 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:18134 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S1424353AbWKJFLb (ORCPT ); Fri, 10 Nov 2006 00:11:31 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: "Magnus Damm" Cc: "Magnus Damm" , linux-kernel@vger.kernel.org, "Vivek Goyal" , "Andi Kleen" , fastboot@lists.osdl.org, Horms , "Dave Anderson" Subject: Re: [PATCH 02/02] Elf: Align elf notes properly References: <20061102101942.452.73192.sendpatchset@localhost> <20061102101949.452.23441.sendpatchset@localhost> Date: Thu, 09 Nov 2006 22:09:26 -0700 In-Reply-To: (Magnus Damm's message of "Fri, 10 Nov 2006 12:52:40 +0900") Message-ID: User-Agent: Gnus/5.110004 (No Gnus v0.4) Emacs/21.4 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2659 Lines: 62 "Magnus Damm" writes: > I'm not sure you see all my points. The important parts are the > offsets - offset 0 and offset N2 in the description above. The should > be aligned somehow. Exactly how to align them depends on if the 64-bit > spec is valid or not. > > My points are: > > - Some kdump code rounds up the size of "elf note header" today. This > is unneccessary for 32 bit alignment and plain wrong for 64 bit > alignment. So I think that the code is strange and should be changed > regardless if the 64-bit spec is valid or not. Sure that is reasonable, if correct. > - Many implementations incorrectly calculate N2 as: roundup(sizeof(elf > note header)) + roundup(n_namesz). I am not certain that is incorrect. roundup(sizeof(elf note header), 4) + roundup(n_namesize, 4) will yield something that is properly 4 byte aligned. I do agree that implementation is not correct for 8 byte alignment. 8 byte alignment does not appear to be in widespread use in the wild. > - You say that the size of the notes do not vary and therefore this is > a non-issue. I agree that the size does not vary, but I believe that > the aligment _is_ an issue. One example is the N2 calculation above, > but more importantly the vmcore code that merges the elf note sections > into one. You know, if you have more than one cpu you will end up with > more than one crash note. And if you run Xen you will have even more > crash notes. Sure that is clearly an issue. > - On top of this I think it would be nice if all this code could be > unified to avoid code duplication. But we need to straighten out this > and agree on how the aligment should work before the code can be > merged into one implementation. Sure. To verify your claim that 8 byte alignment is correct I checked the core dump code in fs/binfmt_elf.c in the linux kernel. That always uses 4 byte alignment. Therefore it appears clear that only doing 4 byte alignment is not a local misreading of the spec, and is used in other implementations. If you can find an implementation that uses 8 byte alignment I am willing to consider it. The current situation is that the linux kernel generated application core dumps use 4 byte alignment so I expect that is what existing applications such as gdb expect. Therefore we use 4 byte alignment unless it can be shown that the linux core dumps are a fluke and should be fixed. Eric - 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/