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SubjectRe: [PATCH v6 21/21] scripts/gdb: Add basic documentation
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 :)

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
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>

--
Regards/Gruss,
Boris.

Sent from a fat crate under my desk. Formatting is fine.
--


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