Re: [rfc] Fix PowerPC displaced stepping regression

["Ulrich Weigand" <uweigand@de.ibm.com>]

Pedro Alves wrote:

> On Sunday 27 September 2009 22:47:13, Ulrich Weigand wrote:
> > - In non-stop mode, we never want to use software single-step as
> >   common code does not support this in multiple threads at once.
> 
> Right.  Shouldn't we switch this particular predicate to
> check the non_stop global instead?

I'm not sure which "particular predicate" you're referring to, sorry ...

The check currently reads:

  if (use_displaced_stepping (gdbarch)
      && (tp->trap_expected
          || (step && gdbarch_software_single_step_p (gdbarch)))
      && sig == TARGET_SIGNAL_0)

that is, if we'd otherwise be about to issue a single step (potentially)
treat it like stepping over a breakpoint.  At what point would you
suggest to check for non_stop?

> Did you consider making the gdbarch_displaced_step_copy_insn
> callback itself return that it expects the target to be
> continued instead of stepped?

Yes, but this would have required changes to the existing gdbarch
interface that would have meant updating all existing users; and
I wanted to produce a patch that doesn't touch any platform I
cannot test at this point ...

In any case, the two interfaces should be pretty much identical:
a target can simply set a flag in its "closure" and return this
flag from the displaced_step_hw_singlestep routine.  That's why
I'm passing the closure in, even though PPC doesn't need it ...

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU Toolchain for Linux on System z and Cell BE
  Ulrich.Weigand@de.ibm.com