Re: [Xen-devel] State of gdbsx in xen-4.0-testing.hg and debugger documentation.

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Tue, 28 Sep 2010 09:55:59 -0700
Bruce Edge <bruce.edge@xxxxxxxxx> wrote:

> On Wed, Jul 14, 2010 at 2:10 PM, Mukesh Rathor
> <mukesh.rathor@xxxxxxxxxx> wrote:
> >
> >
> > On Tue, 13 Jul 2010 22:29:48 -0700
> > Bruce Edge <bruce.edge@xxxxxxxxx> wrote:
> >> The docs for using gdbsx state:
> >>
> >> Â Â- Additionally, to debug loadable kernel modules, please do
> >> following: (gdb) p init_mm.pgd[3]
> >> Â Â Â $1 = {pgd = 0x1b874f027}
> >> Â Â Â (gdb) monitor pgd3 0x1b874f027 Â(Make sure value is in HEX)
> >> Â Â Â pgd3val set to: 0x1b874f027
> >>
> >> When I try to use this to access a module, I get:
> >>
> >> (gdb) p init_mm.pgd[3]
> >> $10 = {pgd = 0}
> >> (gdb)
> >>
> >> I assume that the value of pgd should not be 0 as the makes the
> >> next command it the docs meaningless.
> >>
> >> Is it possible that the field [3] offset has changed?
> >> What field are we after with this command?
> >>
> >
> > Bruce,
> >
> > This for 32bit domU kernel only. I guess the README is not updated
> > in all trees.. I'll submit patch to do this.
> >
> > Thanks,
> > Mukesh
> >
> >
> 
> Mukesh,
> I'm getting back to working on the debugger and have not been able to
> use it with any modules. How does one set breakpoints for modules that
> are not loaded?

You cannot.

> This may be a lack of experience with kernel/gdb context, but how does
> one go about setting a breakpoint in a module's init code?
> Is there any method to use to put in a symbolic function name as a
> breakpoint for a module that is not yet loaded?

Set breakpoint in kernel load module function, and step from there. 

> Are there any tutorials illustrating the use of gdbsx with a custom
> kernel module? This would be most helpful.

Nop, not at present.

Mukesh





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