Re: [PATCH 11/12] Use reinsert_breakpoint for vCont;s

[Pedro Alves <palves at redhat dot com>]

On 06/02/2016 10:30 AM, Yao Qi wrote:

> @@ -4293,7 +4313,7 @@ linux_resume_one_lwp_throw (struct lwp_info *lwp,
>  
>        step = maybe_hw_step (thread);
>      }
> -  else
> +  else if (lwp->resume != NULL && lwp->resume->kind != resume_step)
>      {
>        /* If the thread isn't doing step-over, there shouldn't be any
>  	 reinsert breakpoints.  */

Consider (non-stop RSP):

 -> vCont;s:1
 <- OK
 -> vCont;s:2
 <- OK

The handling of the second vCont sets thread 1's lwp->resume to NULL.
The lwp->resume pointer is only meaningful within linux_resume
and its callees.  (But this function is called in other contexts.)

> @@ -5009,12 +5033,52 @@ linux_resume (struct thread_resume *resume_info, size_t n)
>  	debug_printf ("Resuming, no pending status or step over needed\n");
>      }
>  
> +  /* Before we resume the threads, if resume_step is requested by GDB,
> +     stop all threads and install reinsert breakpoints.  */

Looking again, I think the rationale for stopping threads should
be mentioned here, as it's not obvious.

> +  if (!leave_all_stopped && can_software_single_step ())
> +    {
> +      struct inferior_list_entry *inf, *tmp;
> +
> +      if (debug_threads)
> +	debug_printf ("Handle resume_step.\n");
> +
> +      ALL_INFERIORS (&all_threads, inf, tmp)
> +	{
> +	  struct thread_info *thread = (struct thread_info *) inf;
> +	  struct lwp_info *lwp = get_thread_lwp (thread);
> +
> +	  if (lwp->resume != NULL && lwp->resume->kind == resume_step)
> +	    {
> +	      if (!resume_step_is_handled)
> +		{
> +		  stop_all_lwps (0, NULL);
> +
> +		  if (debug_threads)
> +		    debug_printf ("Done stopping all threads.\n");
> +
> +		  resume_step_is_handled = 1;
> +		}
> +
> +	      install_software_single_step_breakpoints (lwp);
> +
> +	      if (debug_threads)
> +		debug_printf ("Insert breakpoint for resume_step LWP %ld\n",
> +			      lwpid_of (thread));
> +	    }
> +	}
> +
> +      if (debug_threads)
> +	debug_printf ("Handle resume_step.  Done\n");
> +    }
> +
>    /* Even if we're leaving threads stopped, queue all signals we'd
>       otherwise deliver.  */
>    find_inferior (&all_threads, linux_resume_one_thread, &leave_all_stopped);
>  
>    if (need_step_over)
>      start_step_over (get_thread_lwp (need_step_over));
> +  else if (resume_step_is_handled)
> +    unstop_all_lwps (0, NULL);
>  
>    if (debug_threads)
>      {
> @@ -5110,7 +5174,8 @@ proceed_one_lwp (struct inferior_list_entry *entry, void *except)
>        if (debug_threads)
>  	debug_printf ("   stepping LWP %ld, client wants it stepping\n",
>  		      lwpid_of (thread));
> -      step = 1;
> +
> +      step = maybe_hw_step (thread);
>      }
>    else if (lwp->bp_reinsert != 0)
>      {
> @@ -5176,6 +5241,30 @@ proceed_all_lwps (void)
>    if (debug_threads)
>      debug_printf ("Proceeding, no step-over needed\n");
>  
> +  /* Re-install the reinsert breakpoints on software single step target
> +     if the client wants it step.  */
> +  if (can_software_single_step ())

Not immediately obvious to why is this necessary.  Where were they
removed in the first place?  I'm it must be necessary, but maybe
extending the comment helps.

> +    {
> +      struct inferior_list_entry *inf, *tmp;
> +
> +      ALL_INFERIORS (&all_threads, inf, tmp)
> +	{
> +	  struct thread_info *thread = (struct thread_info *) inf;
> +
> +	  if (thread->last_resume_kind == resume_step)
> +	    {
> +	      struct lwp_info *lwp = get_thread_lwp (thread);
> +
> +	      if (!has_reinsert_breakpoints (thread))
> +		install_software_single_step_breakpoints (lwp);
> +
> +	      if (debug_threads)
> +		debug_printf ("Insert breakpoint for resume_step LWP %ld\n",
> +			      lwpid_of (thread));
> +	    }
> +	}
> +    }
> +
>    find_inferior (&all_threads, proceed_one_lwp, NULL);
>  }

Thanks,
Pedro Alves