Re: [PATCH 7/8] Use reinsert_breakpoint for vCont;s

Pedro Alves
2016-05-24T17:39:05Z

On 05/20/2016 04:12 PM, Yao Qi wrote:
> This patch is to teach GDBserver using software single step to handle
> vCont;s. Simply speaking, if the thread's resume request is resume_step,
> install reinsert breakpoint at the next pcs when GDBserver is about to
> resume threads. These reinsert breakpoints of a thread are removed,
> when GDBserver gets an event from that thread. Note that GDBserver may
> or may not report this event back to GDB.
>
> gdb/gdbserver:
>
> 2016-05-20 Yao Qi <yao.qi@linaro.org>
>
> * linux-low.c (resume_stopped_resumed_lwps): If resume request
> is resume_step, either set step to 1 or assert that reinsert
> breakpoints are installed.
> (linux_wait_1): Stop all threads, remove reinsert breakpoints,
> and unstop them.
> (linux_resume_one_thread): If resume request is resume_step,
> either set step to 1 or assert that reinsert breakpoints are
> installed.
> (linux_resume): Install reinsert breakpoints if the thread is
> requested to resume_step.
> (proceed_one_lwp): If resume request is resume_step,
> either set step to 1 or assert that reinsert breakpoints are
> installed.
> (proceed_all_lwps): Install reinsert breakpoints if the thread is
> requested to resume_step.

Spaces vs tabs, I think.

> ---
> gdb/gdbserver/linux-low.c | 125 ++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 121 insertions(+), 4 deletions(-)
>
> diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
> index d5f7097..22cf51a 100644
> --- a/gdb/gdbserver/linux-low.c
> +++ b/gdb/gdbserver/linux-low.c
> @@ -2526,7 +2526,18 @@ resume_stopped_resumed_lwps (struct inferior_list_entry *entry)
> && !lp->status_pending_p
> && thread->last_status.kind == TARGET_WAITKIND_IGNORE)
> {
> - int step = thread->last_resume_kind == resume_step;
> + int step = 0;
> +
> + if (thread->last_resume_kind == resume_step)
> + {

...

> + if (can_hardware_single_step ())
> + step = 1;
> + else
> + {
> + /* GDBserver must insert reinsert breakpoint for vCont;s. */
> + gdb_assert (has_reinsert_breakpoints (thread));
> + }

This pattern seems to appear in many places in the series.
Maybe we could add a function to wrap it? Something like:

static int
maybe_hw_step (struct thread_info *thread)
{
if (can_hardware_single_step ())
return 1;
else
{
gdb_assert (has_reinsert_breakpoints (thread));
return 0;
}
}

?

> + }
>
> if (debug_threads)
> debug_printf ("RSRL: resuming stopped-resumed LWP %s at %s: step=%d\n",
> @@ -3477,6 +3488,18 @@ linux_wait_1 (ptid_t ptid,
> return ignore_event (ourstatus);
> }
>
> + /* Remove reinsert breakpoints for resume_step. */
> + if (can_software_single_step ()
> + && current_thread->last_resume_kind == resume_step

What if a vCont;t came in after the step had started and
before it finished? Won't we have lost the resume_step
linux_set_resume_request then?

> + && has_reinsert_breakpoints (current_thread))
> + {
> + stop_all_lwps (1, event_child);
> +
> + delete_reinsert_breakpoints (current_ptid);
> +
> + unstop_all_lwps (1, event_child);
> + }
> +
> /* Note that all addresses are always "out of the step range" when
> there's no range to begin with. */
> in_step_range = lwp_in_step_range (event_child);
> @@ -4796,7 +4819,6 @@ linux_resume_one_thread (struct inferior_list_entry *entry, void *arg)
> {
> struct thread_info *thread = (struct thread_info *) entry;
> struct lwp_info *lwp = get_thread_lwp (thread);
> - int step;
> int leave_all_stopped = * (int *) arg;
> int leave_pending;
>
> @@ -4865,10 +4887,22 @@ linux_resume_one_thread (struct inferior_list_entry *entry, void *arg)
>
> if (!leave_pending)
> {
> + int step = 0;
> +
> if (debug_threads)
> debug_printf ("resuming LWP %ld\n", lwpid_of (thread));
>
> - step = (lwp->resume->kind == resume_step);
> + if (lwp->resume->kind == resume_step)
> + {
> + if (can_hardware_single_step ())
> + step = 1;
> + else
> + {
> + /* GDBserver must insert reinsert breakpoint for vCont;s. */
> + gdb_assert (has_reinsert_breakpoints (thread));
> + }
> + }
> +
> linux_resume_one_lwp (lwp, step, lwp->resume->sig, NULL);
> }
> else
> @@ -4909,6 +4943,7 @@ linux_resume (struct thread_resume *resume_info, size_t n)
> struct thread_info *need_step_over = NULL;
> int any_pending;
> int leave_all_stopped;
> + int resume_step_is_handled = 0;
>
> if (debug_threads)
> {
> @@ -4952,12 +4987,57 @@ 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. */
> + 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)
> + {
> + struct thread_info *saved_thread;
> +
> + 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;
> + }
> +
> + saved_thread = current_thread;
> + current_thread = thread;
> + install_software_single_step_breakpoints (lwp);
> + current_thread = saved_thread;
> +

This current thread save/restore should move to
install_software_single_step_breakpoints, as per the other patch.

> + 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)
> {
> @@ -5054,7 +5134,14 @@ 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;
> +
> + if (can_hardware_single_step ())
> + step = 1;
> + else
> + {
> + /* GDBserver must insert reinsert breakpoint for vCont;s. */
> + gdb_assert (has_reinsert_breakpoints (thread));
> + }
> }
> else if (lwp->bp_reinsert != 0)
> {
> @@ -5124,6 +5211,36 @@ 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 ())
> + {
> + 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);
> + struct thread_info *saved_thread;
> +
> + saved_thread = current_thread;
> + current_thread = thread;
> +
> + if (!has_reinsert_breakpoints (thread))
> + install_software_single_step_breakpoints (lwp);
> +
> + current_thread = saved_thread;

Ditto.

> +
> + 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