Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752155AbZL3V7L (ORCPT ); Wed, 30 Dec 2009 16:59:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752085AbZL3V7J (ORCPT ); Wed, 30 Dec 2009 16:59:09 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:42469 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751989AbZL3V7H (ORCPT ); Wed, 30 Dec 2009 16:59:07 -0500 Date: Wed, 30 Dec 2009 19:58:47 -0200 From: Arnaldo Carvalho de Melo To: "H. Peter Anvin" Cc: Xiao Guangrong , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Paul Mackerras , "Frank Ch. Eigler" , linux-kernel@vger.kernel.org, James Bottomley Subject: Re: [PATCH 1/3] x86: record relocation offset Message-ID: <20091230215847.GB2384@ghostprotocols.net> References: <4B3AC5CD.1000502@cn.fujitsu.com> <4B3AC629.4030504@cn.fujitsu.com> <20091230131518.GD2956@ghostprotocols.net> <4B3BADDA.8040102@zytor.com> <20091230203936.GA2384@ghostprotocols.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091230203936.GA2384@ghostprotocols.net> X-Url: http://oops.ghostprotocols.net:81/blog User-Agent: Mutt/1.5.20 (2009-08-17) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1423 Lines: 30 Em Wed, Dec 30, 2009 at 06:39:36PM -0200, Arnaldo Carvalho de Melo escreveu: > Em Wed, Dec 30, 2009 at 11:45:30AM -0800, H. Peter Anvin escreveu: > > The kernel already knows where it is loaded -- obviously, by sheer > > necessity -- and knows how it was itself configured, and as such we > > can do this calculation in C code without modifying boot_params or > > the early bootstrap. > > Problem is that at 'perf record' time we may not have access to the > vmlinux file, and thus not be able to figure out the relocation applied > in that boot. > > Then, at a later time, and possibly on another machine, on another arch, > we try to map back IPs to symbols, the /proc/kallsyms is completely > unrelated and we now have a vmlinux unrelocated... > > So we need a way to get the relocation applied at 'perf record' time and > encode it in the perf.data header. Ideas about how to do that? Well, I guess we could do the _stext trick again, storing its value, taken from /proc/kallsyms, into the perf.data header, then figuring out the relocation by looking at its value in the vmlinux symtab. There were concerns in the past about relying on _stext, IIRC, James? - Arnaldo -- 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/