linux-kernel - Re: [PATCH v6 21/21] scripts/gdb: Add basic documentation

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Date:	Wed, 30 Oct 2013 12:22:15 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Jason Wessel <jason.wessel@...driver.com>,
	kgdb-bugreport@...ts.sourceforge.net,
	Andi Kleen <andi@...stfloor.org>,
	Tom Tromey <tromey@...hat.com>,
	Ben Widawsky <ben@...dawsk.net>, Borislav Petkov <bp@...e.de>,
	Tatiana Al-Chueyr Martins <tatiana.alchueyr@...il.com>,
	Rob Landley <rob@...dley.net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v6 21/21] scripts/gdb: Add basic documentation

On 2013-10-30 12:17, Borislav Petkov wrote:
> On Mon, Oct 28, 2013 at 09:58:58AM +0100, Jan Kiszka wrote:
>> CC: Rob Landley <rob@...dley.net>
>> CC: linux-doc@...r.kernel.org
>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
>> ---
>>  Documentation/gdb-kernel-debugging.txt | 159 +++++++++++++++++++++++++++++++++
>>  1 file changed, 159 insertions(+)
>>  create mode 100644 Documentation/gdb-kernel-debugging.txt
>>
>> diff --git a/Documentation/gdb-kernel-debugging.txt b/Documentation/gdb-kernel-debugging.txt
>> new file mode 100644
>> index 0000000..944f2d2
>> --- /dev/null
>> +++ b/Documentation/gdb-kernel-debugging.txt
>> @@ -0,0 +1,159 @@
>> +Debugging kernel and modules via gdb
>> +====================================
>> +
>> +The kernel debugger kgdb, hypervisors like QEMU or JTAG-based hardware
>> +interfaces allow to debug the Linux kernel and its modules during runtime
>> +using gdb. Gdb comes with a powerful scripting interface for python. The
>> +kernel provides a collection of helper scripts that can simplify typical
>> +kernel debugging steps. This is a short tutorial about how to enable and use
>> +them. It focuses on QEMU/KVM virtual machines as target, but the examples can
>> +be transferred to the other gdb stubs as well.
>> +
>> +
>> +Requirements
>> +------------
>> +
>> + o gdb 7.2+ (recommended: 7.4+) with python support enabled (typically true
>> +   for distributions)
>> +
>> +
>> +Setup
>> +-----
>> +
>> + o Create a virtual Linux machine for QEMU/KVM (see www.linux-kvm.org and
>> +   www.qemu.org for more details). For cross-development,
>> +   http://landley.net/aboriginal/bin keeps a pool of machine images and
>> +   toolchains that can be helpful to start from.
>> +
>> + o Build the kernel with CONFIG_DEBUG_INFO and CONFIG_KALLSYMS enabled, but
>> +   leave CONFIG_DEBUG_INFO_REDUCED off.
>> +
>> + o Install that kernel on the guest.
>> +
>> +   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.
>> +
>> + o Enable the gdb stub of QEMU/KVM, either
>> +    - at VM startup time by appending "-s" to the QEMU command line
>> +   or
>> +    - during runtime by issuing "gdbserver" from the QEMU monitor
>> +      console
>> +
>> + o cd /path/to/linux-build
>> +
>> + o Start gdb: gdb vmlinux
>> +
>> +   Note: Some distros may restrict auto-loading of gdb scripts to known safe
>> +   directories. In case gdb reports to refuse loading vmlinux-gdb.py, add
>> +
>> +    add-add-auto-load-safe-path /path/to/linux-build
> 
> Only one "add-" should be enough :)

Thanks, fixed. Need to update this file anyway.

> 
> Btw, gdb is nice enough to tell me:
> 
> $ gdb vmlinux
> Reading symbols from /w/kernel/linux-2.6/vmlinux...done.
> warning: File "/w/kernel/linux-2.6/scripts/gdb/vmlinux-gdb.py" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
> To enable execution of this file add
>         add-auto-load-safe-path /w/kernel/linux-2.6/scripts/gdb/vmlinux-gdb.py

Is that sufficient to be able to import all the sub-scripts as well?

> line to your configuration file "/home/boris/.gdbinit".
> To completely disable this security protection add
>         set auto-load safe-path /
> line to your configuration file "/home/boris/.gdbinit".
> For more information about this security protection see the
> "Auto-loading safe path" section in the GDB manual.  E.g., run from the shell:
>         info "(gdb)Auto-loading safe path"
> 
> Other than that, that's a very cool stuff and I'll make sure to be using
> it the next time.
> 
> Acked-by: Borislav Petkov <bp@...e.de>
> 

Thanks!

Jan

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Corporate Competence Center Embedded Linux
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