Apparent kernel bug with GDB on ppc405

[Benjamin Herrenschmidt]

On Wed, 2007-10-24 at 16:40 -0600, Grant Likely wrote:
> On 10/24/07, Grant Likely <grant.likely at secretlab.ca> wrote:
> > > Not completely implausible, but a) why isn't this seen on basically
> > > every machine with software TLB? b) why does -local- GDB, which is
> > > presumably doing much less work than gdbserver + network stack, not fail?
> >
> > a) I don't know.... very odd.
> >
> > b) gdb is big.  It probably touches far more pages (via library calls)
> > than gdbserver.  The network stack is also big, but it's probably more
> > localized too.
> >
> > Niceing down the host also makes sense because if the PC is being slow
> > then the target may go off and run other things while between setting
> > the breakpoint and getting the 'go' command.
> >
> > Can you grab a snapshot of the TLB before and after setting the breakpoint?
> 
> Or; probably more relevant, before and after the page copy?

COW does ptep_clear_flush before setting the new TLB which does a
flush_tlb_page() so that should work.

Ben.