Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758553Ab1EZVVv (ORCPT ); Thu, 26 May 2011 17:21:51 -0400 Received: from mx1.redhat.com ([209.132.183.28]:2867 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758210Ab1EZVVt (ORCPT ); Thu, 26 May 2011 17:21:49 -0400 Date: Thu, 26 May 2011 18:20:40 -0300 From: Arnaldo Carvalho de Melo To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, paulus@samba.org, hpa@zytor.com, mingo@redhat.com, eranian@google.com, tzanussi@gmail.com, penberg@cs.helsinki.fi, torvalds@linux-foundation.org, efault@gmx.de, peterz@infradead.org, davej@redhat.com, davem@davemloft.net, fweisbec@gmail.com, kees.cook@canonical.com, tglx@linutronix.de, linux-tip-commits@vger.kernel.org Subject: Re: [tip:perf/urgent] perf symbols: Handle /proc/sys/kernel/kptr_restrict Message-ID: <20110526212040.GA30593@ghostprotocols.net> References: <20110526193946.GA6363@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110526193946.GA6363@elte.hu> X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3904 Lines: 99 Em Thu, May 26, 2011 at 09:39:46PM +0200, Ingo Molnar escreveu: > > * tip-bot for Arnaldo Carvalho de Melo wrote: > > > Commit-ID: ec80fde746e3ccf93895d25ae1a7071c9af52585 > > Gitweb: http://git.kernel.org/tip/ec80fde746e3ccf93895d25ae1a7071c9af52585 > > Author: Arnaldo Carvalho de Melo > > AuthorDate: Thu, 26 May 2011 09:53:51 -0300 > > Committer: Arnaldo Carvalho de Melo > > CommitDate: Thu, 26 May 2011 11:15:25 -0300 > > > > perf symbols: Handle /proc/sys/kernel/kptr_restrict > > Ok, things are much better now with kptr_restrict turned on - but i > still see a few rough edges in practice. > > For example 'perf top' says: > > aldebaran:~/linux> perf top > [kernel.kallsyms] with build id 122214021a666675f6e5ff97d70a85ce7139c0e7 not found, continuing without symbols > The (null) file can't be used please wait a bit more, I completely forgot testing 'perf top' :-\ > Now we've confused the user, havent we? :-) > > Also, if i run 'perf top' with the proper vmlinux in the cwd, i do > not get any warning messages - despite both module symbols not being > available and potetial relocations not being considered. Right, it has to provide similar warning. > Secondly, even though i have the proper 'vmlinux' in cwd, i get half > a page long warnings on perf record warning me about the vmlinux: > > WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted, check /proc/sys/kernel/kptr_restrict. > > Samples in kernel functions may not be resolved if a suitable > vmlinux file is not found in the buildid cache or in the vmlinux > path. > > ... > > But a vmlinux file *is* in the cwd. > > One detail i noticed in the patch: > > > symbol__init(); > > > > + if (symbol_conf.kptr_restrict) > > + pr_warning("WARNING: Kernel address maps " > > + "(/proc/{kallsyms,modules}) are restricted, " > > + "check /proc/sys/kernel/kptr_restrict.\n\n" > > + "Samples in kernel functions may not be resolved " > > + "if a suitable vmlinux file is not found in the " > > + "buildid cache or in the vmlinux path.\n\n" > > + "Samples in kernel modules won't be resolved " > > + "at all.\n\n" > > + "If some relocation was applied (e.g. kexec) " > > + "symbols may be misresolved even with a suitable " > > + "vmlinux or kallsyms file.\n\n"); > > > messages broken mid-line just to make it look better is really bad > and can break git grep searches for the string as seen on the screen, > such as: > > git grep="are restricted, check" > > The solution i use in such cases is to deviate in a common-sense way > from the standard coding style: > > if (symbol_conf.kptr_restrict) { > pr_warning( > "WARNING: Kernel address maps (/proc/{kallsyms,modules}) are restricted, check /proc/sys/kernel/kptr_restrict.\n\n" > "Samples in kernel functions may not be resolved if a suitable vmlinux file is not found in the buildid cache or in the vmlinux path.\n\n" > "Samples in kernel modules won't be resolved at all.\n\n" > "If some relocation was applied (e.g. kexec) symbols may be misresolved even with a suitable vmlinux or kallsyms file.\n\n"); > } > > This has the big advantage that you can check how the *user* will see > this message. > > Had you done this you'd have immediately noticed that the individual > lines are *way* too large to fit on even large terminals. Please > break such messages in a much shorter fashion - we want the error > messages we output to be readable even on relatively small (80col) > terminals. But it would reflow, no? > Thanks, > > Ingo -- 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/