From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755677AbcK1W1Y (ORCPT ); Mon, 28 Nov 2016 17:27:24 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:35030 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755515AbcK1W1P (ORCPT ); Mon, 28 Nov 2016 17:27:15 -0500 Date: Tue, 29 Nov 2016 01:27:11 +0300 From: "Kirill A. Shutemov" To: Josh Poimboeuf Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Linus Torvalds , Sasha Levin , Konstantin Khlebnikov Subject: Re: [PATCH 2/4] x86/dumpstack: remove kernel text addresses from stack dump Message-ID: <20161128222711.GA32239@node.shutemov.name> References: <69329cb29b8f324bb5fcea14d61d224807fb6488.1477405374.git.jpoimboe@redhat.com> <20161125122604.GB3439@node.shutemov.name> <20161128204958.go7a6evhqm3usq7x@treble> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161128204958.go7a6evhqm3usq7x@treble> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 28, 2016 at 02:49:58PM -0600, Josh Poimboeuf wrote: > On Fri, Nov 25, 2016 at 03:26:04PM +0300, Kirill A. Shutemov wrote: > > On Tue, Oct 25, 2016 at 09:51:12AM -0500, Josh Poimboeuf wrote: > > > Printing kernel text addresses in stack dumps is of questionable value, > > > especially now that address randomization is becoming common. > > > > > > It can be a security issue because it leaks kernel addresses. It also > > > affects the usefulness of the stack dump. Linus says: > > > > > > "I actually spend time cleaning up commit messages in logs, because > > > useless data that isn't actually information (random hex numbers) is > > > actively detrimental. > > > > > > It makes commit logs less legible. > > > > > > It also makes it harder to parse dumps. > > > > > > It's not useful. That makes it actively bad. > > > > > > I probably look at more oops reports than most people. I have not > > > found the hex numbers useful for the last five years, because they are > > > just randomized crap. > > > > > > The stack content thing just makes code scroll off the screen etc, for > > > example." > > > > > > The only real downside to removing these addresses is that they can be > > > used to disambiguate duplicate symbol names. However such cases are > > > rare, and the context of the stack dump should be enough to be able to > > > figure it out. > > > > > > There's now a 'faddr2line' script which can be used to convert a > > > function address to a file name and line: > > > > > > $ ./scripts/faddr2line ~/k/vmlinux write_sysrq_trigger+0x51/0x60 > > > write_sysrq_trigger+0x51/0x60: > > > write_sysrq_trigger at drivers/tty/sysrq.c:1098 > > > > > > Or gdb can be used: > > > > > > $ echo "list *write_sysrq_trigger+0x51" |gdb ~/k/vmlinux |grep "is in" > > > (gdb) 0xffffffff815b5d83 is in driver_probe_device (/home/jpoimboe/git/linux/drivers/base/dd.c:378). > > > > > > (But note that when there are duplicate symbol names, gdb will only show > > > the first symbol it finds. faddr2line is recommended over gdb because > > > it handles duplicates and it also does function size checking.) > > > > The commit breaks scripts/decode_stacktrace.sh. > > > > Not sure if it's possible to fix it only on decode_stacktrace.sh side: we > > seems don't have a way to clearly distinguish stack trace line of any > > other. > > How about this bash regex? Seems to work for me with no false > positives. > > [[ $line =~ [^+\ ]+\+0x[0-9a-f]+/0x[0-9a-f]+ ]] Seems works fine to me. Thanks. Feel free to use my tested-by. -- Kirill A. Shutemov