linux-kernel - Re: some help in kernel debugging

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Message-ID: <2625b9520611211256y4dbfaf1eyd95e2ca8fb94cec6@mail.gmail.com>
Date:	Tue, 21 Nov 2006 12:56:20 -0800
From:	"Thushara Wijeratna" <thushw@...il.com>
To:	"Samuel Korpi" <strontianite@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: some help in kernel debugging

Samuel, thanks much for the pointers, I'm following up on UML.
BTW, I fixed my earlier problem after realizing (a chat with a Linux
savvy friend had nothing to do with it...) Basically I made the initrd
image on the dev machine for the same kernel version and copied it
over to the test machine, it then booted.

I can now actually attach gdb and poke around and try to figure out
why it is throwing a SIGSEV. I have a stack like this:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 1]
0x00000000 in ?? ()
(gdb) bt
#0  0x00000000 in ?? ()
#1  0xc03051db in psmouse_interrupt (serio=0xc048cde0, data=250
'\uffff', flags=0,
    regs=0x0) at drivers/input/mouse/psmouse-base.c:206
#2  0xc030882a in i8042_interrupt (irq=0, dev_id=0x0, regs=0x0)
    at drivers/input/serio/i8042.c:433
#3  0xc03084f9 in i8042_aux_write (port=0x0, c=232 '\uffff')
    at drivers/input/serio/i8042.c:235
#4  0xc03053bb in psmouse_sendbyte (psmouse=0xf70aa7f8, byte=232 '\uffff')
    at include/linux/serio.h:77

and this is the code inside psmouse-base.c that is crashing:

	rc = psmouse->protocol_handler(psmouse, regs);

So I'm guessing I did't specify an option correctly in the `make
menuconfig` so that the kernel identifies my mouse and installs a
proper handler for it? It is a USB mouse and I thought I enabled it,
but I'm guessing I missed something.

Thanks a lot for all your help, at some point I want to contribute
testing builds, this is good training...

On 11/20/06, Samuel Korpi <strontianite@...il.com> wrote:
> Hi,
>
> I don't know what sort of debugging needs you have, exactly, but I
> would suggest you take a look at User Mode Linux (UML). UML provides a
> safe and pretty easy way to start you with kernel debugging and just
> looking into kernel internals. It is a virtual kernel running in user
> space, so it doesn't require a separate test machine, and you can
> debug it with normal gdb. Furthermore, it is included in current
> vanilla kernels, so you can get started without any extra patches.
>
> Main sources for information concerning UML are:
>
> Main page: http://www.user-mode-linux.org/
> HOWTO: http://user-mode-linux.sourceforge.net/UserModeLinux-HOWTO.html
> Wiki: http://uml.jfdi.org/
> Precompiled kernels and root file systems: http://uml.nagafix.co.uk/
>
> /Samuel Korpi
>
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