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

Pedro Alves
2016-06-13T15:55:35Z

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