linux-kernel - Re: [PATCH v2 2/2] docs: disable KASLR when debugging kernel

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Message-ID: <3eabc7d6-d19c-537e-5556-f8f155cc13f7@siemens.com>
Date:   Thu, 13 Jul 2017 08:53:59 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Zhouyi Zhou <zhouzhouyi@...il.com>, corbet@....net,
        kieran@...uared.org.uk, akpm@...ux-foundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        kbingham@...nel.org
Subject: Re: [PATCH v2 2/2] docs: disable KASLR when debugging kernel

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 <zhouzhouyi@...il.com>
> Reviewed-by: Kieran Bingham <kbingham@...nel.org>
> ---
>  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 <jan.kiszka@...mens.com>

Who's taking this? Jon?

Jan

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