Re: [rfc, spu] Don't call set_gdbarch_cannot_step_breakpoint in spu_gdbarch_init

[Peter Schauer <peterschauer@gmx.net>]

> On 04/01/2015 09:35 PM, Peter Schauer wrote:
> 
> > This was needed for alpha OSF/1.
> > 
> > Back then it was the only architecture which would not ptrace step
> > over an inserted breakpoint, causing an infinite loop while trying
> > to single step over an inserted breakpoint.
> 
> OOC, do you recall whether the infinite loop was that the step didn't
> make progress, and gdb would continuously issue a single-step forever,
> or whether the infinite loop was all in the kernel?

The step didn't make progress and GDB would have continuously issued
a single-step forever.

> > The diff back then was
> > 
> > + #ifdef CANNOT_STEP_BREAKPOINT
> > +   /* If the target doesn't support stepping over a breakpoint, simply
> > +      continue, we will then hit the breakpoint anyway.  */
> > +   if (step && breakpoints_inserted && breakpoint_here_p (read_pc ()))
> > +     step = 0;
> > + #endif
> > 
> > I do not know if GDB ever tries to ptrace step over an inserted
> > breakpoint nowadays, sorry.
> 
> It does in some cases when we have a signal to deliver at the
> same time we are trying to step over a breakpoint.  Look for
> "signal arrived while stepping over" in infrun.c.

Yeah, that was also the reason why we had to keep the breakpoint
inserted back then.

> > Meanwhile the alpha OSF/1 port is dead anyways...
> 
> The setting ended up done for all alpha ports today though, in:
> 
>   alpha-tdep.c:  set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
> 
> OSF/1 is gone, but we still support Alpha GNU/Linux, which is also
> taking that code path,. If this was OSF/1 specific, then we could
> get rid of that too, and then get rid of gdbarch_cannot_step_breakpoint
> completely.  Anyone have access to Alpha GNU/Linux to try that out?

If it really happens on Alpha GNU/Linux, we could request a fix from the
kernel folks and phase out this ugly gdbarch_cannot_step_breakpoint hack
slowly.

> Ulrich, any idea why cannot_step_breakpoint was ever needed
> for the SPU?
> 
> Thanks,
> Pedro Alves

-- 
Peter Schauer			Peter.Schauer@mytum.de