Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751130AbdGMGyL (ORCPT ); Thu, 13 Jul 2017 02:54:11 -0400 Received: from thoth.sbs.de ([192.35.17.2]:57404 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750807AbdGMGyJ (ORCPT ); Thu, 13 Jul 2017 02:54:09 -0400 Subject: Re: [PATCH v2 2/2] docs: disable KASLR when debugging kernel To: Zhouyi Zhou , corbet@lwn.net, kieran@ksquared.org.uk, akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kbingham@kernel.org References: <1499417505-31574-1-git-send-email-zhouzhouyi@gmail.com> From: Jan Kiszka Message-ID: <3eabc7d6-d19c-537e-5556-f8f155cc13f7@siemens.com> Date: Thu, 13 Jul 2017 08:53:59 +0200 User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 MIME-Version: 1.0 In-Reply-To: <1499417505-31574-1-git-send-email-zhouzhouyi@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1691 Lines: 43 On 2017-07-07 10:51, Zhouyi Zhou wrote: > commit 6807c84652b0 ("x86: Enable KASLR by default") enables KASLR > by default on x86. While KASLR will confuse gdb which resolve kernel > symbol address from symbol table of vmlinux. We should turn off KASLR for > kernel debugging. > > Signed-off-by: Zhouyi Zhou > Reviewed-by: Kieran Bingham > --- > Documentation/dev-tools/gdb-kernel-debugging.rst | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/Documentation/dev-tools/gdb-kernel-debugging.rst b/Documentation/dev-tools/gdb-kernel-debugging.rst > index 5e93c9b..60fec6d 100644 > --- a/Documentation/dev-tools/gdb-kernel-debugging.rst > +++ b/Documentation/dev-tools/gdb-kernel-debugging.rst > @@ -31,12 +31,13 @@ Setup > CONFIG_DEBUG_INFO_REDUCED off. If your architecture supports > CONFIG_FRAME_POINTER, keep it enabled. > > -- Install that kernel on the guest. > +- Install that kernel on the guest, turn off KASLR if necessary by adding > + "nokaslr" to the kernel command line. > Alternatively, QEMU allows to boot the kernel directly using -kernel, > -append, -initrd command line switches. This is generally only useful if > you do not depend on modules. See QEMU documentation for more details on > - this mode. > + this mode. In this case, you should build the kernel with > + CONFIG_RANDOMIZE_BASE disabled if the architecture supports KASLR. > > - Enable the gdb stub of QEMU/KVM, either > > FWIW: Acked-by: Jan Kiszka Who's taking this? Jon? Jan -- Siemens AG, Corporate Technology, CT RDA ITP SES-DE Corporate Competence Center Embedded Linux