[RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL

[Scott Wood]

On 06/25/2013 01:00:23 AM, Joakim Tjernlund wrote:
> Scott Wood <scottwood at freescale.com> wrote on 2013/06/25 02:51:00:
> >
> > On Fri, Jul 20, 2012 at 10:37:17AM +0200, Joakim Tjernlund wrote:
> > > Zang Roy-R61911 <r61911 at freescale.com> wrote on 2012/07/20  
> 10:27:52:
> > > >
> > > >
> > > >
> > > > > -----Original Message-----
> > > > > From:
> linuxppc-dev-bounces+tie-fei.zang=freescale.com at lists.ozlabs.org
> > > > > [
> mailto:linuxppc-dev-bounces+tie-fei.zang=freescale.com at lists.ozlabs.org]
> > > > > On Behalf Of Joakim Tjernlund
> > > > > Sent: Friday, June 01, 2012 6:36 AM
> > > > > To: Wood Scott-B07421
> > > > > Cc: linuxppc-dev at ozlabs.org; Dan Malek; Bob Cochran; Support
> > > > > Subject: Re: [RFC] [PATCH] powerpc: Add MSR_DE to MSR_KERNEL
> > > > >
> > > > > It just occurred to me that you guys have this already in your
> Linux SDK so
> > > > > it can't be that bad.
> > > > No. MSR_DE is ONLY added when using CW debug in SDK.
> > > > Roy
> > > >
> > >
> > > Yes, and I later found that user space debugging is busted if you  
> turn
> on MSR_DE in
> > > kernel.
> >
> > So, how should we handle the CONFIG_BDI_SWITCH patch?  It seems  
> like it
> > should at least have a warning in the kconfig help text that it  
> breaks
> > userspace debugging (to the point of causing a kernel oops if it's
> > tried).  Or maybe it can deselect CONFIG_PPC_ADV_DEBUG_REGS?
> >
> > It'd also be nice to keep things like this, that are a consequence  
> of
> how
> > external debug works on e500, separate from the Abatron-specific  
> stuff.
> >
> 
> I was hoping the kernel would grow per context handling of MSR_DE.  
> Then
> one could have
> MSR_DE on in MSR_KERNEL but off in user space(unless gdb request it  
> on a
> per process basis).

What if the external debugger wants debugging to work when in userspace  
as well?  Plus, you wouldn't be able to debug from the very beginning  
of an exception handler if the exception came from userspace.

-Scott