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SubjectRe: [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@landley.net>
>> CC: linux-doc@vger.kernel.org
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.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@suse.de>
>

Thanks!

Jan

--
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux


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