Setting kernel data breakpoints on x86

Setting kernel data breakpoints on x86

[Alan Stern]

I'm trying to debug a rather difficult data-overwriting problem, and it 
would be a big help to be able to use a data breakpoint.

Is there any easy way of doing this?  I'd prefer not to use a kernel 
debugger, because the address of the breakpoint and the time when it's 
needed are determined dynamically.

Does anybody have a little lightweight procedure for setting one of the 
x86's debug registers to point to a particular location in kernel memory 
space?  I don't care if the whole system crashes when the debug exception 
occurs, just so long as I can get a stack trace and find out where the 
overwrite comes from.

Alan Stern

Re: Setting kernel data breakpoints on x86

[Maneesh Soni]

On Tue, Nov 01, 2005 at 04:30:26PM -0500, Alan Stern wrote:
> I'm trying to debug a rather difficult data-overwriting problem, and it 
> would be a big help to be able to use a data breakpoint.
> 
> Is there any easy way of doing this?  I'd prefer not to use a kernel 
> debugger, because the address of the breakpoint and the time when it's 
> needed are determined dynamically.
> 
> Does anybody have a little lightweight procedure for setting one of the 
> x86's debug registers to point to a particular location in kernel memory 
> space?  I don't care if the whole system crashes when the debug exception 
> occurs, just so long as I can get a stack trace and find out where the 
> overwrite comes from.
> 
> 

Hi Alan

Probably watchpoint probes could be useful for this..

http://www.ussg.iu.edu/hypermail/linux/kernel/0508.3/1407.html

http://sourceware.org/ml/systemtap/2005-q3/msg00097.html

Thanks
Maneesh

-- 
Maneesh Soni
Linux Technology Center, 
IBM India Software Labs,
Bangalore, India
email: maneesh@in.ibm.com
Phone: 91-80-25044990

Re: Setting kernel data breakpoints on x86

[Alan Stern]

On Wed, 2 Nov 2005, Maneesh Soni wrote:

> On Tue, Nov 01, 2005 at 04:30:26PM -0500, Alan Stern wrote:
> > I'm trying to debug a rather difficult data-overwriting problem, and it 
> > would be a big help to be able to use a data breakpoint.
> > 
> > Is there any easy way of doing this?  I'd prefer not to use a kernel 
> > debugger, because the address of the breakpoint and the time when it's 
> > needed are determined dynamically.
> > 
> > Does anybody have a little lightweight procedure for setting one of the 
> > x86's debug registers to point to a particular location in kernel memory 
> > space?  I don't care if the whole system crashes when the debug exception 
> > occurs, just so long as I can get a stack trace and find out where the 
> > overwrite comes from.
> > 
> > 
> 
> Hi Alan
> 
> Probably watchpoint probes could be useful for this..
> 
> http://www.ussg.iu.edu/hypermail/linux/kernel/0508.3/1407.html
> 
> http://sourceware.org/ml/systemtap/2005-q3/msg00097.html

Hi Maneesh:

That's exactly what I was looking for.  Thanks!

Alan Stern