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

[Pedro Alves <palves@redhat.com>]

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 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.

> 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?

Ulrich, any idea why cannot_step_breakpoint was ever needed
for the SPU?

Thanks,
Pedro Alves