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

[Pedro Alves <palves at redhat dot com>]

+Ulrich

Ulrich, any idea why cannot_step_breakpoint was ever needed?

Yao's change makes sense to me.

Thanks,
Pedro Alves

On 03/17/2015 02:52 PM, Yao Qi wrote:
> From: Yao Qi <yao.qi@linaro.org>
> 
> Nowadays, in infrun.c:resume, the setting to 'step' variable is like:
> 
>   if (use_displaced_stepping (gdbarch)
>       && tp->control.trap_expected
>       && sig == GDB_SIGNAL_0
>       && !current_inferior ()->waiting_for_vfork_done)
>     {
>     }
>   /* Do we need to do it the hard way, w/temp breakpoints?  */
>   else if (step)
>     step = maybe_software_singlestep (gdbarch, pc); <-- [1]
> 
>   ...
> 
>   if (execution_direction != EXEC_REVERSE
>       && step && breakpoint_inserted_here_p (aspace, pc))
>     {
>       ...
>       if (gdbarch_cannot_step_breakpoint (gdbarch)) <-- [2]
>         step = 0;
>     }
> 
> spu doesn't have displaced stepping and uses software single step,
> so 'step' is set to zero in [1], and [2] becomes unreachable as a
> result.  So don't have to call set_gdbarch_cannot_step_breakpoint
> in spu_gdbarch_init.
> 
> On the other hand, we either have hardware single step or software
> single step, do we still need gdbarch method cannot_step_breakpoint?
> CANNOT_STEP_BREAKPOINT was introduced in 1993 by commit
> cef4c2e7a5f2d3426a8255f74b6c7f4e795fd9a4 for alpha OSF/1 native
> support.
> 
> I don't have spu machine to test this patch.
> 
> gdb:
> 
> 2015-03-17  Yao Qi  <yao.qi@linaro.org>
> 
> 	* spu-tdep.c (spu_gdbarch_init): Don't call
> 	set_gdbarch_cannot_step_breakpoint.
> ---
>  gdb/spu-tdep.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/gdb/spu-tdep.c b/gdb/spu-tdep.c
> index 36ad312..870cf32 100644
> --- a/gdb/spu-tdep.c
> +++ b/gdb/spu-tdep.c
> @@ -2794,7 +2794,6 @@ spu_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>    set_gdbarch_decr_pc_after_break (gdbarch, 4);
>    set_gdbarch_breakpoint_from_pc (gdbarch, spu_breakpoint_from_pc);
>    set_gdbarch_memory_remove_breakpoint (gdbarch, spu_memory_remove_breakpoint);
> -  set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
>    set_gdbarch_software_single_step (gdbarch, spu_software_single_step);
>    set_gdbarch_get_longjmp_target (gdbarch, spu_get_longjmp_target);
>  
>