Re: [PATCH 8/9] Use reinsert_breakpoint for vCont;s

Yao Qi
2016-07-21T08:38:38Z

Ping? I want this series go in before the release.

On Tue, Jul 5, 2016 at 9:14 AM, Yao Qi <qiyaoltc@gmail.com> wrote:
> Pedro Alves <palves@redhat.com> writes:
>
>>> if thread 1 doesn't hit the reinsert breakpoint, we don't have to
>>> remove them, because GDB will send vCont;s:1 next time, and GDBserver
>>
>> There's no guarantee GDB will send vCont;s:1 next time.
>> The user may do "continue" instead of "step".
>>
>>> can only install reinsert breakpoints if they are not installed yet.
>>
>> The user may even do "return + continue" or "jump", or an infcall,
>> all of which resume the thread at a different address from the address
>> the thread last stopped. So there's no guarantee that the
>> reinsert breakpoint address makes any sense for the next step request,
>> or even that the next resume request is a step in the first place.
>>
>> Basically the previous step request must be completely forgotten after
>> gdb has seen the thread stop. In all-stop, gdb "sees "all threads
>> stopped on each and every event reported to gdb, for any thread.
>> A stop reply cancels any and all previous resume requests.
>
> I add some code to delete all reinsert breakpoints for all threads in
> all-stop. See the patch below,
>
>>
>>> if thread hits the reinsert breakpoint, but the event is not reported.
>>> It becomes pending, and GDBserver will delete the reinsert breakpoints
>>> next time when this pending event is reported back to GDB.
>>
>> I don't follow. I'm talking about the case where the thread does _not_
>> hit the reinsert breakpoint. Instead some other thread hits some unrelated
>> event.
>
> In your review to V2, your words are about other threads hit a breakpoint, but
> doesn't mention "thread 1" (requested for resume_step) hits reinsert
> breakpoint or not. I just list two possible results (not hit vs
> hit). You didn't talk about the latter, so we don't have to follow it.
>
> --
> Yao (齐尧)
>
> From f4aa0593190e7e78831532c03177d8264b7dd1c1 Mon Sep 17 00:00:00 2001
> From: Yao Qi <yao.qi@linaro.org>
> Date: Thu, 19 May 2016 17:07:49 +0100
> Subject: [PATCH] Use reinsert_breakpoint for vCont;s
>
> V4: remove all reinsert breakpoints before sending event back to GDB
> in all-stop mode,
>
> V3: install breakpoints in proceed_one_lwp,
> no longer stop all threads when installing breakpoints,
> delete reinsert breakpoints when GDBserver wants to report event,
>
> V2: fix spaces in changelog entry,
> use maybe_hw_step,
> cancel step-over if signal arrives (!maybe_internal_trap),
>
> 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 and reports it back to
> GDB.
>
> gdb/gdbserver:
>
> 2016-07-05 Yao Qi <yao.qi@linaro.org>
>
> * linux-low.c (resume_stopped_resumed_lwps): If resume request
> is resume_step, call maybe_hw_step.
> (linux_wait_1): Stop all threads, remove reinsert breakpoints,
> and unstop them.
> (linux_resume_one_lwp_throw): Don't assert the thread has reinsert
> breakpoints or not.
> (proceed_one_lwp): If resume request is resume_step, install
> reinsert breakpoints and call maybe_hw_step.
>
> diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
> index abaf288..b579b4d 100644
> --- a/gdb/gdbserver/linux-low.c
> +++ b/gdb/gdbserver/linux-low.c
> @@ -2563,7 +2563,10 @@ 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)
> + step = maybe_hw_step (thread);
>
> if (debug_threads)
> debug_printf ("RSRL: resuming stopped-resumed LWP %s at %s: step=%d\n",
> @@ -3622,6 +3625,66 @@ linux_wait_1 (ptid_t ptid,
>
> /* Alright, we're going to report a stop. */
>
> + /* Remove reinsert breakpoints. */
> + if (can_software_single_step ())
> + {
> + /* Remove reinsert breakpoints or not. It it is true, stop all
> + lwps, so that other threads won't hit the breakpoint in the
> + staled memory. */
> + int remove_reinsert_breakpoints_p = 0;
> +
> + if (non_stop)
> + {
> + remove_reinsert_breakpoints_p
> + = has_reinsert_breakpoints (current_thread);
> + }
> + else
> + {
> + /* In all-stop, a stop reply cancels all previous resume
> + requests. Delete all reinsert breakpoints. */
> + struct inferior_list_entry *inf, *tmp;
> +
> + ALL_INFERIORS (&all_threads, inf, tmp)
> + {
> + struct thread_info *thread = (struct thread_info *) inf;
> +
> + if (has_reinsert_breakpoints (thread))
> + {
> + remove_reinsert_breakpoints_p = 1;
> + break;
> + }
> + }
> + }
> +
> + if (remove_reinsert_breakpoints_p)
> + {
> + /* If we remove reinsert breakpoints from memory, stop all lwps,
> + so that other threads won't hit the breakpoint in the staled
> + memory. */
> + stop_all_lwps (0, event_child);
> +
> + if (non_stop)
> + {
> + gdb_assert (has_reinsert_breakpoints (current_thread));
> + delete_reinsert_breakpoints (current_thread);
> + }
> + else
> + {
> + struct inferior_list_entry *inf, *tmp;
> +
> + ALL_INFERIORS (&all_threads, inf, tmp)
> + {
> + struct thread_info *thread = (struct thread_info *) inf;
> +
> + if (has_reinsert_breakpoints (thread))
> + delete_reinsert_breakpoints (thread);
> + }
> + }
> +
> + unstop_all_lwps (0, event_child);
> + }
> + }
> +
> if (!stabilizing_threads)
> {
> /* In all-stop, stop all threads. */
> @@ -4275,12 +4338,6 @@ linux_resume_one_lwp_throw (struct lwp_info *lwp,
>
> step = maybe_hw_step (thread);
> }
> - else
> - {
> - /* If the thread isn't doing step-over, there shouldn't be any
> - reinsert breakpoints. */
> - gdb_assert (!has_reinsert_breakpoints (thread));
> - }
>
> if (fast_tp_collecting == 1)
> {
> @@ -5088,7 +5145,14 @@ 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 resume_step is requested by GDB, install reinsert
> + breakpoints when the thread is about to be actually resumed if
> + the reinsert breakpoints weren't removed. */
> + if (can_software_single_step () && !has_reinsert_breakpoints (thread))
> + install_software_single_step_breakpoints (lwp);
> +
> + step = maybe_hw_step (thread);
> }
> else if (lwp->bp_reinsert != 0)
> {

--
Yao (齐尧)