[11/12] Use reinsert_breakpoint for vCont;s

Message ID 1464859846-15619-12-git-send-email-yao.qi@linaro.org
State New, archived
Headers

Commit Message

Yao Qi June 2, 2016, 9:30 a.m. UTC
  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.  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, call maybe_hw_step.
	(linux_wait_1): Stop all threads, remove reinsert breakpoints,
	and unstop them.
	(linux_resume_one_thread): If resume request is resume_step,
	call maybe_hw_step.
	(linux_resume): Install reinsert breakpoints if the thread is
	requested to resume_step.
	(proceed_one_lwp): If resume request is resume_step, call
	maybe_hw_step.
	(proceed_all_lwps): Install reinsert breakpoints if the thread is
	requested to resume_step.
---
 gdb/gdbserver/linux-low.c | 99 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 94 insertions(+), 5 deletions(-)
  

Comments

Pedro Alves June 13, 2016, 3:55 p.m. UTC | #1
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
  
Yao Qi June 14, 2016, 1:14 p.m. UTC | #2
Pedro Alves <palves@redhat.com> writes:

>> @@ -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.

If so, the assert won't be called for thread 1.

> The lwp->resume pointer is only meaningful within linux_resume
> and its callees.  (But this function is called in other contexts.)
>

When I wrote the patch, it took me a while to think about this condition
check.  I wanted to remove this condition and assert, but finally
decided to leave it there, as it is not harmful.  If lwp->resume is only
meaningful within linux_resume and its callees, how about remove the
condition check and assert here?

>> @@ -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.
>

How about this,

  /* Before we resume the threads, if resume_step is requested by GDB,
     we need to access the inferior memory to install reinsert
     breakpoints, so stop all 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.

How about this

  /* On software single step target, we removed reinsert breakpoints
     after we get any events from the inferior.  If the client wants
     thread step, re-install these reinsert breakpoints.  */
  
Pedro Alves June 14, 2016, 3:48 p.m. UTC | #3
On 06/14/2016 02:14 PM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
> 
>>> @@ -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.
> 
> If so, the assert won't be called for thread 1.
> 
>> The lwp->resume pointer is only meaningful within linux_resume
>> and its callees.  (But this function is called in other contexts.)
>>
> 
> When I wrote the patch, it took me a while to think about this condition
> check.  I wanted to remove this condition and assert, but finally
> decided to leave it there, as it is not harmful.  If lwp->resume is only
> meaningful within linux_resume and its callees, how about remove the
> condition check and assert here?

Yes, if it's only for the assert, then let's remove it.

> 
>>> @@ -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.
>>
> 
> How about this,
> 
>   /* Before we resume the threads, if resume_step is requested by GDB,
>      we need to access the inferior memory to install reinsert
>      breakpoints, so stop all threads.  */

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.

I guess this is 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.

> 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?

Thanks,
Pedro Alves
  

Patch

diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
index 6f32911..4e79ec1 100644
--- a/gdb/gdbserver/linux-low.c
+++ b/gdb/gdbserver/linux-low.c
@@ -2579,7 +2579,10 @@  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",
@@ -3530,6 +3533,23 @@  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_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);
@@ -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.  */
@@ -4853,7 +4873,6 @@  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;
 
@@ -4922,10 +4941,14 @@  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
@@ -4966,6 +4989,7 @@  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)
     {
@@ -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.  */
+  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 ())
+    {
+      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);
 }