Re: [rfc] Fix PowerPC displaced stepping regression

["Ulrich Weigand" <uweigand at de dot ibm dot com>]

Pedro Alves wrote:

> At the points where we decide to use displaced stepping because
> software single-stepping doesn't work with multiple pending
> simultaneous requests.  So, adding a non_stop check there in
> front of software_single_step_p,
> 
>   if (use_displaced_stepping (gdbarch)
>       && (tp->trap_expected
> -	  || (step && gdbarch_software_single_step_p (gdbarch)))
> +	  || (non_stop && step && gdbarch_software_single_step_p (gdbarch)))
> 
> 
> ... and in maybe_software_singlestep:
> 
> -      if (use_displaced_stepping (gdbarch))
> -      if (non_stop)
>         hw_step = 0;
> 
> (or make resume clear `step' if "non_stop && step && gdbarch_software_single_step_p (gdbarch))"
> so to we'd not reach maybe_software_singlestep at all.

Ah, now I've got it, thanks!

> But, let's ignore this.  The only benefit would be for
> all-stop + displaced stepping=on to not trigger displaced
> stepping all the way.

Agreed.

> > > 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 ...
> 
> True.  I like that!

OK, good :-)

Thanks,
Ulrich

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