Tests Failures on PPC64

[Oleg Nesterov]

On 12/11, K.Prasad wrote:
>
> On Thu, Dec 10, 2009 at 08:24:36PM +0100, Oleg Nesterov wrote:
> >
> > 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)....

Thanks, please see another email, I cc'ed you.

> 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.

Yes. I straced gdb to be sure it really does PTRACE_SET_DEBUGREF to
use the hardware watchpoint.

There is something strange though. gdb does PTRACE_SINGLESTEP and only
then PTRACE_CONT after "watch xxx".

>    Where can one find the relevant piece of testcase?

http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/tests/ptrace-tests/tests/watchpoint.c?cvsroot=systemtap

Oleg.