From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755556Ab2DNQ3H (ORCPT ); Sat, 14 Apr 2012 12:29:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:27434 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755407Ab2DNQ3F (ORCPT ); Sat, 14 Apr 2012 12:29:05 -0400 Date: Sat, 14 Apr 2012 13:28:51 -0300 From: Arnaldo Carvalho de Melo To: Ingo Molnar Cc: Linus Torvalds , hpa@zytor.com, paulus@samba.org, eranian@google.com, linux-kernel@vger.kernel.org, efault@gmx.de, peterz@infradead.org, namhyung@gmail.com, fweisbec@gmail.com, dsahern@gmail.com, Masami Hiramatsu , tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/core] perf ui annotate browser: Allow toggling addr offset view Message-ID: <20120414162851.GD22114@infradead.org> References: <20120414010410.GB22114@infradead.org> <20120414085519.GB28505@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20120414085519.GB28505@gmail.com> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Sat, Apr 14, 2012 at 10:55:19AM +0200, Ingo Molnar escreveu: > > * Arnaldo Carvalho de Melo wrote: > > > Em Fri, Apr 13, 2012 at 11:30:52AM -0700, Linus Torvalds escreveu: > > > On Fri, Apr 13, 2012 at 11:25 AM, Linus Torvalds > > > wrote: > > > > > > > > : > > > >    1.91 :          push   %rbp > > > > > > Oh, btw, talking about kmem_cache_free: that one uses altinstructions, > > > and so perf report shows the hottest instruction wrong (and I'm not > > > talking about "ugly"): > > > > Well, if we use Masami's disassembler we would use the actual > > code as it is being used and not the original DSO that was > > later patched by altinstructions. > > Key would be to use the kernel's live RAM image of instructions. Yeah, that is what I meant by "if we use Masami's disassembler" :-) > I.e. we should provide a live /proc/vmlinux image in essence: a > 'virtual' ELF binary image constructed out of the live kernel > RAM image - with no extra RAM overhead. (Maybe with modules > included in an intelligent way - although personally I don't use > modules when I instrument the kernel) > > That plus the always-available /proc/kallsyms would offer rather > powerful annotation already: without *any* debug info - out of > box, on any Linux installation. (This was always the main > advantage of /proc/profile and readprofile btw: it worked > everywhere while most other profiling solutions needed a > debuginfo, etc.) > > Doing /proc/vmlinux would be different from /dev/mem as it only > shows the kernel RAM image, and only in a read-only fashion. > > Default permissions of /proc/vmlinux should probably track > console permissions: it should be possible to allow people > sitting in front of the computer to read /proc/vmlinux, while > people logged in over the network wouldn't. > > Doing such a live kernel vmlinux would have other debugging and > instrumentation advantages as well: various code patching > effects could be checked and observed directly. I would say that even for userspace we would love to have such virtual ELF files, as code patching is become more common... - Arnaldo