Tests Failures on PPC64

[K.Prasad]

On Thu, Dec 10, 2009 at 08:24:36PM +0100, Oleg Nesterov wrote:
> On 12/09, CAI Qian wrote:
> >
> > ----- "Oleg Nesterov" <oleg at redhat.com> wrote:
> >
> > > Thanks, but it doesn't fail for me on this machine...
> >
> > Hmm, it failed for me.
> >
> > # cd /root/ptrace-tests
> >
> > # make check
> > ...
> > FAIL: watchpoint
> 
> OMG. Yet another test-case fails on powerpc ???? I didn't see this
> failure in the previous reports or missed it ...
> 
> I bet it fails without utrace too? (please don't tell it doesn't ;)
> 
> Did you see it fails on other ppc64 machines?
> 
> 
> Oh well. I spent this day grepping arch/powerpc to understand how
> PTRACE_SET_DEBUGREG works and what is the problem. But I am afraid
> this time I need a help from someone who understands the hardware
> magic on powerpc.
>

There's relatively less magic with PPC64 (with just one DABR) compared
to x86 :-)

I hope to offer a little help here (given that I work to tweak
ptrace_set_debugreg() in PPC64 to use the hw-breakpoint interfaces)....

Watchpoints (using DABR) through GDB can fail for many reasons....they
must ideally be set after the program has started execution - to enable
GDB know the size of the variable...else they would resort to
single-stepping to trap access to the target variable.

Cai,
   Where can one find the relevant piece of testcase?

Thanks,
K.Prasad