From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753516AbcFORnn (ORCPT ); Wed, 15 Jun 2016 13:43:43 -0400 Received: from mail.kernel.org ([198.145.29.136]:42176 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751884AbcFORnm (ORCPT ); Wed, 15 Jun 2016 13:43:42 -0400 Date: Wed, 15 Jun 2016 14:43:38 -0300 From: Arnaldo Carvalho de Melo To: Masami Hiramatsu Cc: Linux Kernel Mailing List Subject: Re: perf probe issues Message-ID: <20160615174338.GB4882@kernel.org> References: <20160614170504.GD3978@kernel.org> <20160615110201.c2838ec2291cd9caaaa93ce4@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160615110201.c2838ec2291cd9caaaa93ce4@kernel.org> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.6.1 (2016-04-27) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Wed, Jun 15, 2016 at 11:02:01AM +0900, Masami Hiramatsu escreveu: > On Tue, 14 Jun 2016 14:05:04 -0300 > Arnaldo Carvalho de Melo wrote: > > While investigating a problem in the annotation code reported by > > Linus, with "kaslr" on the kernel command line and this in .config: > > [root@jouet ~]# egrep 'CONFIG_(RANDOMIZE_BASE|DEBUG_INFO)' ~acme/git/build/v4.7.0-rc3/.config > > CONFIG_RANDOMIZE_BASE=y > > # CONFIG_DEBUG_INFO is not set > > [root@jouet ~]# > > [root@jouet ~]# grep -w vfs_write /proc/kallsyms > > ffffffffac2404c0 T vfs_write > > [root@jouet ~]# perf probe vfs_write > > vfs_write is out of .text, skip it. > > Error: Failed to add events. > > [root@jouet ~]# perf probe -v vfs_write > > probe-definition(0): vfs_write > > symbol:vfs_write file:(null) line:0 offset:0 return:0 lazy:(null) > > 0 arguments > > Looking at the vmlinux_path (8 entries long) > > Using /lib/modules/4.7.0-rc3/build/vmlinux for symbols > > Could not open debuginfo. Try to use symbols. > > vfs_write is out of .text, skip it. > > Error: Failed to add events. Reason: No such file or directory (Code: -2) > > [root@jouet ~]# > > Can you try to test with this config to investigate this problem? > Yes, I guess it missed to get start_text because of KASLR... > > We need to improve the error messages, for instance: > > "Could not open debuginfo. Try to use symbols." > > I think should be rewritten as: "Trying to use kallsyms", no? I.e. if it > > doesn't manage to find a vmlinux file, it will try to use kallsyms as a > > fallback, is that what is happening here? > Let me check that the perf symbol/map object uses kallsyms for kernel. > Anyway, if the target is not the kernel, do we change the message > as "trying to use symbols"? Well, it is _always_ trying to use "symbols" as in "information to map an address to a symbol", but this information can come from DWARF, kallsyms, ELF symbol tables, JIT /tmp/ maps, etc :-) So, if it is going to use kallsyms: "Trying to use kallsyms" ELF symtol tables: "Trying to use the ELF symbol table" etc. - Arnaldo