Kernel debugging

Kernel debugging

[Nikos Balkanas]

Hi,

I am developing a module for the Linux kernel. For that i have setup
the exact environment in Virtual Box and have loaded the (guest)
kernel with -g and removed the -frame-pointers. I will run gdb from
host and try to debug kernel on guest system.

What is the best approach for this scenario? GDBserver or gdbstubs?.
Gdb server is good only for userspace debugging. Will gdbstubs work?
Are they included in the recent gdb sources, or are the ones to use
since 2003 from sourceforge? I am also looking for instructions on how
to implement them. Any hints?

TIA,
Nikos

Re: Kernel debugging

[Mike Frysinger]

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On Thursday 19 December 2013 13:51:36 Nikos Balkanas wrote:
> I am developing a module for the Linux kernel. For that i have setup
> the exact environment in Virtual Box and have loaded the (guest)
> kernel with -g and removed the -frame-pointers. I will run gdb from
> host and try to debug kernel on guest system.
> 
> What is the best approach for this scenario? GDBserver or gdbstubs?.
> Gdb server is good only for userspace debugging. Will gdbstubs work?
> Are they included in the recent gdb sources, or are the ones to use
> since 2003 from sourceforge? I am also looking for instructions on how
> to implement them. Any hints?

the kernel has a built in gdb stub.  look for "kgdb" in the 
documentation/kconfig.
-mike

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Re: Kernel debugging

[Nikos Balkanas]

Ty mike,

I am aware of kdgb, but it doesn't have gdb's abilities. Besides I
know extensibly gdb, and I can never find the Sysreq key on my
keyboard :-(. I will try it next time, but for now I solved my problem
by reading the kernel source code. I have noticed the remote_vis.c in
gdb sources. Does this mean I can use gdb remotely to a virtual host?
How can i do it? Furthermore have gdbstubs incorporated into gdb
sources, or is it another abandoned project (since 2003 :-()?

Nikos

On Fri, Dec 20, 2013 at 9:41 PM, Mike Frysinger <vapier@gentoo.org> wrote:
> On Thursday 19 December 2013 13:51:36 Nikos Balkanas wrote:
>> I am developing a module for the Linux kernel. For that i have setup
>> the exact environment in Virtual Box and have loaded the (guest)
>> kernel with -g and removed the -frame-pointers. I will run gdb from
>> host and try to debug kernel on guest system.
>>
>> What is the best approach for this scenario? GDBserver or gdbstubs?.
>> Gdb server is good only for userspace debugging. Will gdbstubs work?
>> Are they included in the recent gdb sources, or are the ones to use
>> since 2003 from sourceforge? I am also looking for instructions on how
>> to implement them. Any hints?
>
> the kernel has a built in gdb stub.  look for "kgdb" in the
> documentation/kconfig.
> -mike

Re: Kernel debugging

[Mike Frysinger]

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On Saturday 21 December 2013 00:46:25 Nikos Balkanas wrote:
> Ty mike,

please don't top post in your replies

> I am aware of kdgb, but it doesn't have gdb's abilities. Besides I
> know extensibly gdb, and I can never find the Sysreq key on my
> keyboard :-(. I will try it next time, but for now I solved my problem
> by reading the kernel source code. I have noticed the remote_vis.c in
> gdb sources. Does this mean I can use gdb remotely to a virtual host?
> How can i do it? Furthermore have gdbstubs incorporated into gdb
> sources, or is it another abandoned project (since 2003 :-()?

are you confusing kdb and kgdb ?  kgdb is just a remote gdb stub.  you still 
need gdb running somewhere else to connect to it to do debugging.  which means 
you have full access to gdb's abilities.

note that QEMU also has a gdb stub in it.  so you could use one of its system 
binaries to boot a linux kernel and then connect your gdb client to it.
-mike

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