[11/12] Use reinsert_breakpoint for vCont;s
Commit Message
Pedro Alves <palves@redhat.com> writes:
> That doesn't tell the reader why we need to stop _all_ threads. The
> threads that are about to be resumed are obviously stopped, and
> thus we could already _access_ inferior memory through them.
GDB may only resume some threads, and leave other threads running. In
order to access inferior memory safely, we must stop all threads.
>
> I guess this is about flushing instruction caches?
>
No, it is not about flushing instruction caches.
>>>> @@ -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.
>>
>> How about this
>>
>> /* On software single step target, we removed reinsert breakpoints
>> after we get any events from the inferior.
>
> Is that all events, even internal events? From the patch, it seemed
> like it was only before reporting an event to gdb.
>
You are right, I though too much about supporting range-stepping.
I rewrite the comments in the patch below,
>> If the client wants
>> thread step, re-install these reinsert breakpoints. */
>>
>
> If we only remove before reporting an event to gdb, then I don't
> understand this. We already insert single-step breakpoints when
> we process the resume request from gdb, no?
We insert single-step breakpoints when we process the resume requests
and threads are about to be resumed. If threads still have pending
status, single-step breakpoints are not installed, so we need to install
them in proceed_all_lwps.
Comments
On 06/15/2016 05:41 PM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
>
>> That doesn't tell the reader why we need to stop _all_ threads. The
>> threads that are about to be resumed are obviously stopped, and
>> thus we could already _access_ inferior memory through them.
>
> GDB may only resume some threads, and leave other threads running. In
> order to access inferior memory safely, we must stop all threads.
But what do you mean by "safely" ? What goes wrong if we
don't stop all threads?
>
>>
>> I guess this is about flushing instruction caches?
>>
>
> No, it is not about flushing instruction caches.
Then what is it about?
>
>>>>> @@ -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.
>>>
>>> How about this
>>>
>>> /* On software single step target, we removed reinsert breakpoints
>>> after we get any events from the inferior.
>>
>> Is that all events, even internal events? From the patch, it seemed
>> like it was only before reporting an event to gdb.
>>
>
> You are right, I though too much about supporting range-stepping.
> I rewrite the comments in the patch below,
>
>>> If the client wants
>>> thread step, re-install these reinsert breakpoints. */
>>>
>>
>> If we only remove before reporting an event to gdb, then I don't
>> understand this. We already insert single-step breakpoints when
>> we process the resume request from gdb, no?
>
> We insert single-step breakpoints when we process the resume requests
> and threads are about to be resumed. If threads still have pending
> status, single-step breakpoints are not installed, so we need to install
> them in proceed_all_lwps.
>
> @@ -3518,6 +3521,23 @@ linux_wait_1 (ptid_t ptid,
> return ignore_event (ourstatus);
> }
>
> + /* Remove reinsert breakpoints ... */
> + if (can_software_single_step ()
> + && has_reinsert_breakpoints (current_thread)
> + /*... if GDB requests this thread doing resume_step or ...*/
> + && (current_thread->last_resume_kind == resume_step
> + /* GDBserver has already started the step-over for vCont;s,
> + but it gets some other signal, like SIGSTOP sent by
> + GDBserver for vCont;t or other signal program received. */
> + || !maybe_internal_trap))
> + {
> + stop_all_lwps (1, event_child);
> +
> + delete_reinsert_breakpoints (current_thread);
> +
> + unstop_all_lwps (1, event_child);
> + }
I'm re-looking at this and wondering if this is really the
right place to do this. If the thread hits a breakpoint
that ends up not reported to gdb (e.g., condition evals false),
then we'll remove the reinsert breakpoints here, and then
later reinsert them in proceed_all_lwps. The extra
stopping/unstopping everything is best avoided if possible.
Thus, couldn't we move this to after:
/* We found no reason GDB would want us to stop. We either hit one
of our own breakpoints, or finished an internal step GDB
shouldn't know about. */
if (!report_to_gdb)
{
...
}
?
- Also, if in all-stop mode, if gdb does:
vCont;s:1;c
thus setting thread 1 stepping, and all others continuing,
and then some other thread but thread 1 hits a breakpoint,
what is removing the reinsert breakpoint of thread 1?
> +
> /* 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);
> @@ -4281,12 +4301,6 @@ 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)
> {
> @@ -4841,7 +4855,6 @@ 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;
>
> @@ -4910,10 +4923,14 @@ 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)
> + step = maybe_hw_step (thread);
> +
> linux_resume_one_lwp (lwp, step, lwp->resume->sig, NULL);
> }
> else
> @@ -4954,6 +4971,7 @@ 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)
> {
> @@ -4997,12 +5015,55 @@ linux_resume (struct thread_resume *resume_info, size_t n)
> debug_printf ("Resuming, no pending status or step over needed\n");
> }
>
> + /* If resume_step is requested by GDB, install reinsert breakpoints
> + when the thread is about to be actually resumed. IOW, we don't
> + insert reinsert breakpoints if any thread has pending status. */
> + 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)
> + {
> + /* We need to access the inferior memory to install
> + reinsert breakpoints, so stop all threads. */
> + 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)
> {
> @@ -5098,7 +5159,8 @@ 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)
> {
> @@ -5164,6 +5226,33 @@ proceed_all_lwps (void)
> if (debug_threads)
> debug_printf ("Proceeding, no step-over needed\n");
>
> + 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;
> +
> + /* On software single step target, we insert reinsert
> + breakpoints when the threads are about to be actually
> + resumed. IOW, we don't insert them if any thread has
> + pending status. Before we proceed threads, insert
> + reinsert breakpoints if the client wants it step. */
> + 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);
> }
>
Hmm, seeing that we need to handle installing the breakpoints in
both places, I wonder about making linux_resume just handle
setting up the last resume kind and queue signals, and then
end up calling proceed_all_lwps. If that works, I suspect it
would simplify things a good deal.
Thanks,
Pedro Alves
@@ -2567,7 +2567,10 @@ 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",
@@ -3518,6 +3521,23 @@ linux_wait_1 (ptid_t ptid,
return ignore_event (ourstatus);
}
+ /* Remove reinsert breakpoints ... */
+ if (can_software_single_step ()
+ && has_reinsert_breakpoints (current_thread)
+ /*... if GDB requests this thread doing resume_step or ...*/
+ && (current_thread->last_resume_kind == resume_step
+ /* GDBserver has already started the step-over for vCont;s,
+ but it gets some other signal, like SIGSTOP sent by
+ GDBserver for vCont;t or other signal program received. */
+ || !maybe_internal_trap))
+ {
+ stop_all_lwps (1, event_child);
+
+ delete_reinsert_breakpoints (current_thread);
+
+ 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);
@@ -4281,12 +4301,6 @@ 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)
{
@@ -4841,7 +4855,6 @@ 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;
@@ -4910,10 +4923,14 @@ 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)
+ step = maybe_hw_step (thread);
+
linux_resume_one_lwp (lwp, step, lwp->resume->sig, NULL);
}
else
@@ -4954,6 +4971,7 @@ 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)
{
@@ -4997,12 +5015,55 @@ linux_resume (struct thread_resume *resume_info, size_t n)
debug_printf ("Resuming, no pending status or step over needed\n");
}
+ /* If resume_step is requested by GDB, install reinsert breakpoints
+ when the thread is about to be actually resumed. IOW, we don't
+ insert reinsert breakpoints if any thread has pending status. */
+ 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)
+ {
+ /* We need to access the inferior memory to install
+ reinsert breakpoints, so stop all threads. */
+ 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)
{
@@ -5098,7 +5159,8 @@ 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)
{
@@ -5164,6 +5226,33 @@ proceed_all_lwps (void)
if (debug_threads)
debug_printf ("Proceeding, no step-over needed\n");
+ 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;
+
+ /* On software single step target, we insert reinsert
+ breakpoints when the threads are about to be actually
+ resumed. IOW, we don't insert them if any thread has
+ pending status. Before we proceed threads, insert
+ reinsert breakpoints if the client wants it step. */
+ 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);
}