[PATCH 2/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[PATCH 2/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[Yao Qi]

Hi,
Some tests in gdb.threads/multiple-step-overs.exp fail on arm target
when the displaced stepping on, but they pass when displaced stepping
is off.

 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: step: step
 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: next: next
 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: continue: continue
 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr1: continue to sigusr1_handler

when displaced stepping is on,

Sending packet: $vCont;c#a8...infrun: infrun_async(1)^M <--- [1]
infrun: prepare_to_wait^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   -1.0.0 [Thread 0],^M
infrun:   status->kind = ignore^M
infrun: TARGET_WAITKIND_IGNORE^M
infrun: prepare_to_wait^M
Packet received: T05swbreak:;0b:f8faffbe;0d:409ee7b6;0f:d0880000;thread:p635.636;core:0;^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   1589.1590.0 [Thread 1590],^M
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP^M
infrun: TARGET_WAITKIND_STOPPED^M
infrun: stop_pc = 0x88d0^M
infrun: context switch^M
infrun: Switching context from Thread 1591 to Thread 1590^

GDB resumes the whole process (all threads) rather than the specific
thread it wants to single step (as shown in [1]).  That is wrong.

when displaced stepping is off, GDB behaves correctly, only resumes
the specific thread (as shown in [2]).

Sending packet: $vCont;c:p611.613#b2...infrun: infrun_async(1)^M <-- [2]
infrun: prepare_to_wait^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   -1.0.0 [Thread 0],^M
infrun:   status->kind = ignore^M
infrun: TARGET_WAITKIND_IGNORE^M
infrun: prepare_to_wait^M
Packet received: T05swbreak:;0b:f8faffbe;0d:409e67b6;0f:48880000;thread:p611.613;core:1;^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   1553.1555.0 [Thread 1555],^M
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP^M
infrun: TARGET_WAITKIND_STOPPED^M
infrun: clear_step_over_info^M
infrun: stop_pc = 0x8848

The current logic in GDB on deciding the set of threads to resume is:

  /* Decide the set of threads to ask the target to resume.  */
  if ((step || thread_has_single_step_breakpoints_set (tp))
      && tp->control.trap_expected)
    {
      /* We're allowing a thread to run past a breakpoint it has
	 hit, by single-stepping the thread with the breakpoint
	 removed.  In which case, we need to single-step only this
	 thread, and keep others stopped, as they can miss this
	 breakpoint if allowed to run.  */
      resume_ptid = inferior_ptid;
    }
  else
    resume_ptid = internal_resume_ptid (user_step);

it doesn't handle the case correctly that GDB continue (instead of
single step) the thread for displaced stepping.

I also update the comment below to reflect the code.  I remove the
"with the breakpoint removed" comment, because GDB doesn't remove
breakpoints in displaced stepping, so we don't have to worry that
other threads may miss the breakpoint.

Patch is regression tested on both x86_64-linux and arm-linux.

gdb:

2015-10-28  Yao Qi  <yao.qi@linaro.org>

	* infrun.c (resume): Check displaced_step_in_progress_thread
	when deciding the set of threads to resume.
---
 gdb/infrun.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 0265d35..c619b61 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -2631,14 +2631,12 @@ resume (enum gdb_signal sig)
   gdb_assert (!(thread_has_single_step_breakpoints_set (tp) && step));
 
   /* Decide the set of threads to ask the target to resume.  */
-  if ((step || thread_has_single_step_breakpoints_set (tp))
+  if ((step || thread_has_single_step_breakpoints_set (tp)
+       || displaced_step_in_progress_thread (tp->ptid))
       && tp->control.trap_expected)
     {
       /* We're allowing a thread to run past a breakpoint it has
-	 hit, by single-stepping the thread with the breakpoint
-	 removed.  In which case, we need to single-step only this
-	 thread, and keep others stopped, as they can miss this
-	 breakpoint if allowed to run.  */
+	 hit, by single-stepping (in-line or out-of-line) the thread.  */
       resume_ptid = inferior_ptid;
     }
   else
-- 
1.9.1

[PATCH 0/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[Yao Qi]

Hi,
This patch series fixes fails in gdb.threads/multiple-step-overs.exp on
arm-linux.  Patch 1 adds a new function, and patch 2 is the main part.
See details in patch 2.

Whole series is regression tested on x86_64-linux and arm-linux.

*** BLURB HERE ***

Yao Qi (2):
  New function displaced_step_in_progress_thread
  Fix gdb.threads/multiple-step-overs.exp fails on arm

 gdb/infrun.c | 30 ++++++++++++++++++++++--------
 1 file changed, 22 insertions(+), 8 deletions(-)

-- 
1.9.1

[PATCH 1/2] New function displaced_step_in_progress_thread

[Yao Qi]

This patch adds a new function displaced_step_in_progress_thread,
which returns whether the thread is in progress of displaced
stepping.

gdb:

2015-10-28  Yao Qi  <yao.qi@linaro.org>

	* infrun.c (displaced_step_in_progress_thread): New function.
	(handle_inferior_event_1): Call it.
---
 gdb/infrun.c | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 917f9be..0265d35 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1536,6 +1536,21 @@ displaced_step_in_progress_any_inferior (void)
   return 0;
 }
 
+/* Return true if thread represented by PTID is doing a displaced
+   step.  */
+
+static int
+displaced_step_in_progress_thread (ptid_t ptid)
+{
+  struct displaced_step_inferior_state *displaced;
+
+  gdb_assert (!ptid_equal (ptid, null_ptid));
+
+  displaced = get_displaced_stepping_state (ptid_get_pid (ptid));
+
+  return (displaced != NULL && ptid_equal (displaced->step_ptid, ptid));
+}
+
 /* Return true if process PID has a thread doing a displaced step.  */
 
 static int
@@ -4923,12 +4938,10 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
       {
 	struct regcache *regcache = get_thread_regcache (ecs->ptid);
 	struct gdbarch *gdbarch = get_regcache_arch (regcache);
-	struct displaced_step_inferior_state *displaced
-	  = get_displaced_stepping_state (ptid_get_pid (ecs->ptid));
 
 	/* If checking displaced stepping is supported, and thread
 	   ecs->ptid is displaced stepping.  */
-	if (displaced && ptid_equal (displaced->step_ptid, ecs->ptid))
+	if (displaced_step_in_progress_thread (ecs->ptid))
 	  {
 	    struct inferior *parent_inf
 	      = find_inferior_ptid (ecs->ptid);
@@ -4947,6 +4960,9 @@ Cannot fill $_exitsignal with the correct signal number.\n"));
 
 	    if (ecs->ws.kind == TARGET_WAITKIND_FORKED)
 	      {
+		struct displaced_step_inferior_state *displaced
+		  = get_displaced_stepping_state (ptid_get_pid (ecs->ptid));
+
 		/* Restore scratch pad for child process.  */
 		displaced_step_restore (displaced, ecs->ws.value.related_pid);
 	      }
-- 
1.9.1

Re: [PATCH 1/2] New function displaced_step_in_progress_thread

[Pedro Alves]

On 10/29/2015 03:01 PM, Yao Qi wrote:
> This patch adds a new function displaced_step_in_progress_thread,
> which returns whether the thread is in progress of displaced
> stepping.
> 
> gdb:
> 
> 2015-10-28  Yao Qi  <yao.qi@linaro.org>
> 
> 	* infrun.c (displaced_step_in_progress_thread): New function.
> 	(handle_inferior_event_1): Call it.

LGTM.

Thanks,
Pedro Alves

Re: [PATCH 2/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[Pedro Alves]

On 10/29/2015 03:01 PM, Yao Qi wrote:
> Hi,
> Some tests in gdb.threads/multiple-step-overs.exp fail on arm target
> when the displaced stepping on, but they pass when displaced stepping
> is off.
> 
>  FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: step: step
>  FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: next: next
>  FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: continue: continue
>  FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr1: continue to sigusr1_handler
> 
> when displaced stepping is on,
> 
> Sending packet: $vCont;c#a8...infrun: infrun_async(1)^M <--- [1]
> infrun: prepare_to_wait^M
> infrun: target_wait (-1.0.0, status) =^M
> infrun:   -1.0.0 [Thread 0],^M
> infrun:   status->kind = ignore^M
> infrun: TARGET_WAITKIND_IGNORE^M
> infrun: prepare_to_wait^M
> Packet received: T05swbreak:;0b:f8faffbe;0d:409ee7b6;0f:d0880000;thread:p635.636;core:0;^M
> infrun: target_wait (-1.0.0, status) =^M
> infrun:   1589.1590.0 [Thread 1590],^M
> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP^M
> infrun: TARGET_WAITKIND_STOPPED^M
> infrun: stop_pc = 0x88d0^M
> infrun: context switch^M
> infrun: Switching context from Thread 1591 to Thread 1590^
> 
> GDB resumes the whole process (all threads) rather than the specific
> thread it wants to single step (as shown in [1]).  That is wrong.

(I understand this, but I think it'd make it clearer to explicitly
state _why_ that is wrong.)

> 
> when displaced stepping is off, GDB behaves correctly, only resumes
> the specific thread (as shown in [2]).
> 
> Sending packet: $vCont;c:p611.613#b2...infrun: infrun_async(1)^M <-- [2]
> infrun: prepare_to_wait^M
> infrun: target_wait (-1.0.0, status) =^M
> infrun:   -1.0.0 [Thread 0],^M
> infrun:   status->kind = ignore^M
> infrun: TARGET_WAITKIND_IGNORE^M
> infrun: prepare_to_wait^M
> Packet received: T05swbreak:;0b:f8faffbe;0d:409e67b6;0f:48880000;thread:p611.613;core:1;^M
> infrun: target_wait (-1.0.0, status) =^M
> infrun:   1553.1555.0 [Thread 1555],^M
> infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP^M
> infrun: TARGET_WAITKIND_STOPPED^M
> infrun: clear_step_over_info^M
> infrun: stop_pc = 0x8848
> 
> The current logic in GDB on deciding the set of threads to resume is:
> 
>   /* Decide the set of threads to ask the target to resume.  */
>   if ((step || thread_has_single_step_breakpoints_set (tp))
>       && tp->control.trap_expected)
>     {
>       /* We're allowing a thread to run past a breakpoint it has
> 	 hit, by single-stepping the thread with the breakpoint
> 	 removed.  In which case, we need to single-step only this
> 	 thread, and keep others stopped, as they can miss this
> 	 breakpoint if allowed to run.  */
>       resume_ptid = inferior_ptid;
>     }
>   else
>     resume_ptid = internal_resume_ptid (user_step);
> 
> it doesn't handle the case correctly that GDB continue (instead of
> single step) the thread for displaced stepping.
> 
> I also update the comment below to reflect the code.  I remove the
> "with the breakpoint removed" comment, because GDB doesn't remove
> breakpoints in displaced stepping, so we don't have to worry that
> other threads may miss the breakpoint.
> 
> Patch is regression tested on both x86_64-linux and arm-linux.
> 
> gdb:
> 
> 2015-10-28  Yao Qi  <yao.qi@linaro.org>
> 
> 	* infrun.c (resume): Check displaced_step_in_progress_thread
> 	when deciding the set of threads to resume.
> ---
>  gdb/infrun.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/gdb/infrun.c b/gdb/infrun.c
> index 0265d35..c619b61 100644
> --- a/gdb/infrun.c
> +++ b/gdb/infrun.c
> @@ -2631,14 +2631,12 @@ resume (enum gdb_signal sig)
>    gdb_assert (!(thread_has_single_step_breakpoints_set (tp) && step));
>  
>    /* Decide the set of threads to ask the target to resume.  */
> -  if ((step || thread_has_single_step_breakpoints_set (tp))
> +  if ((step || thread_has_single_step_breakpoints_set (tp)
> +       || displaced_step_in_progress_thread (tp->ptid))
>        && tp->control.trap_expected)


I wonder, can't we just remove the "step" check, like:

  if (tp->control.trap_expected)
    {



>      {
>        /* We're allowing a thread to run past a breakpoint it has
> -	 hit, by single-stepping the thread with the breakpoint
> -	 removed.  In which case, we need to single-step only this
> -	 thread, and keep others stopped, as they can miss this
> -	 breakpoint if allowed to run.  */
> +	 hit, by single-stepping (in-line or out-of-line) the thread.  */

The change looks good to me, though I think we should clarify
the comment here.  How about:

       /* We're allowing a thread to run past a breakpoint it has
	 hit, either by single-stepping the thread with the breakpoint
	 removed, or by displaced stepping, with the breakpoint inserted.
         In the former case, we need to single-step only this thread, and keep
         others stopped, as they can miss this breakpoint if allowed to run.
         That's not really a problem for displaced stepping, but, we still keep
         other threads stopped, in case another thread is also stopped for a
         breakpoint waiting for its turn in the displaced stepping queue.  */

I think we could optimize this by checking for
thread_step_over_chain_next (tp) == NULL, because if no other thread
is waiting for a step-over, then we could resume all threads, but
that's maybe not worth it.

>        resume_ptid = inferior_ptid;
>      }
>    else

Thanks,
Pedro Alves

Re: [PATCH 2/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[Yao Qi]

Pedro Alves <palves@redhat.com> writes:

Hi Pedro,

>> GDB resumes the whole process (all threads) rather than the specific
>> thread it wants to single step (as shown in [1]).  That is wrong.
>
> (I understand this, but I think it'd make it clearer to explicitly
> state _why_ that is wrong.)

I am not sure how to make the description clearer, how about this?

GDB resumes the whole process (all threads) rather than the specific
thread for which GDB wants to step over the breakpoint (as shown in [1]).
That is wrong.


>> diff --git a/gdb/infrun.c b/gdb/infrun.c
>> index 0265d35..c619b61 100644
>> --- a/gdb/infrun.c
>> +++ b/gdb/infrun.c
>> @@ -2631,14 +2631,12 @@ resume (enum gdb_signal sig)
>>    gdb_assert (!(thread_has_single_step_breakpoints_set (tp) && step));
>>  
>>    /* Decide the set of threads to ask the target to resume.  */
>> -  if ((step || thread_has_single_step_breakpoints_set (tp))
>> +  if ((step || thread_has_single_step_breakpoints_set (tp)
>> +       || displaced_step_in_progress_thread (tp->ptid))
>>        && tp->control.trap_expected)
>
>
> I wonder, can't we just remove the "step" check, like:
>
>   if (tp->control.trap_expected)
>     {
>

Yes, it works! as the patch below,

>
>
>>      {
>>        /* We're allowing a thread to run past a breakpoint it has
>> -	 hit, by single-stepping the thread with the breakpoint
>> -	 removed.  In which case, we need to single-step only this
>> -	 thread, and keep others stopped, as they can miss this
>> -	 breakpoint if allowed to run.  */
>> +	 hit, by single-stepping (in-line or out-of-line) the thread.  */
>
> The change looks good to me, though I think we should clarify
> the comment here.  How about:
>
>        /* We're allowing a thread to run past a breakpoint it has
> 	 hit, either by single-stepping the thread with the breakpoint
> 	 removed, or by displaced stepping, with the breakpoint inserted.
>          In the former case, we need to single-step only this thread, and keep
>          others stopped, as they can miss this breakpoint if allowed to run.
>          That's not really a problem for displaced stepping, but, we still keep
>          other threads stopped, in case another thread is also stopped for a
>          breakpoint waiting for its turn in the displaced stepping queue.  */
>

They are copied into the patch.

> I think we could optimize this by checking for
> thread_step_over_chain_next (tp) == NULL, because if no other thread
> is waiting for a step-over, then we could resume all threads, but
> that's maybe not worth it.

'thread_step_over_chain_next (tp) == NULL' doesn't work on arm-linux,
however, I didn't investigate why it doesn't.

Patch below is regression tested on x86_64-linux and arm-linux.

-- 
Yao (齐尧)

From 9f1915b1d183b14286b1e785dec84d5c95f8ff5c Mon Sep 17 00:00:00 2001
From: Yao Qi <yao.qi@linaro.org>
Date: Wed, 28 Oct 2015 11:58:34 +0000
Subject: [PATCH] Fix gdb.threads/multiple-step-overs.exp fails on arm

Hi,
Some tests in gdb.threads/multiple-step-overs.exp fail on arm target
when the displaced stepping on, but they pass when displaced stepping
is off.

 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: step: step
 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: next: next
 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: continue: continue
 FAIL: gdb.threads/multiple-step-overs.exp: displaced=on: signal thr1: continue to sigusr1_handler

when displaced stepping is on,

Sending packet: $vCont;c#a8...infrun: infrun_async(1)^M <--- [1]
infrun: prepare_to_wait^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   -1.0.0 [Thread 0],^M
infrun:   status->kind = ignore^M
infrun: TARGET_WAITKIND_IGNORE^M
infrun: prepare_to_wait^M
Packet received: T05swbreak:;0b:f8faffbe;0d:409ee7b6;0f:d0880000;thread:p635.636;core:0;^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   1589.1590.0 [Thread 1590],^M
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP^M
infrun: TARGET_WAITKIND_STOPPED^M
infrun: stop_pc = 0x88d0^M
infrun: context switch^M
infrun: Switching context from Thread 1591 to Thread 1590^

GDB resumes the whole process (all threads) rather than the specific
thread for which GDB wants to step over the breakpoint (as shown in [1]).
That is wrong.

when displaced stepping is off, GDB behaves correctly, only resumes
the specific thread (as shown in [2]).

Sending packet: $vCont;c:p611.613#b2...infrun: infrun_async(1)^M <-- [2]
infrun: prepare_to_wait^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   -1.0.0 [Thread 0],^M
infrun:   status->kind = ignore^M
infrun: TARGET_WAITKIND_IGNORE^M
infrun: prepare_to_wait^M
Packet received: T05swbreak:;0b:f8faffbe;0d:409e67b6;0f:48880000;thread:p611.613;core:1;^M
infrun: target_wait (-1.0.0, status) =^M
infrun:   1553.1555.0 [Thread 1555],^M
infrun:   status->kind = stopped, signal = GDB_SIGNAL_TRAP^M
infrun: TARGET_WAITKIND_STOPPED^M
infrun: clear_step_over_info^M
infrun: stop_pc = 0x8848

The current logic in GDB on deciding the set of threads to resume is:

  /* Decide the set of threads to ask the target to resume.  */
  if ((step || thread_has_single_step_breakpoints_set (tp))
      && tp->control.trap_expected)
    {
      /* We're allowing a thread to run past a breakpoint it has
	 hit, by single-stepping the thread with the breakpoint
	 removed.  In which case, we need to single-step only this
	 thread, and keep others stopped, as they can miss this
	 breakpoint if allowed to run.  */
      resume_ptid = inferior_ptid;
    }
  else
    resume_ptid = internal_resume_ptid (user_step);

it doesn't handle the case correctly that GDB continue (instead of
single step) the thread for displaced stepping.

I also update the comment below to reflect the code.  I remove the
"with the breakpoint removed" comment, because GDB doesn't remove
breakpoints in displaced stepping, so we don't have to worry that
other threads may miss the breakpoint.

Patch is regression tested on both x86_64-linux and arm-linux.

gdb:

2015-11-09  Yao Qi  <yao.qi@linaro.org>

	* infrun.c (resume): Check control.trap_expected only
	when deciding the set of threads to resume.

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 185b79b..4a66d17 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -2654,14 +2654,17 @@ resume (enum gdb_signal sig)
   gdb_assert (!(thread_has_single_step_breakpoints_set (tp) && step));
 
   /* Decide the set of threads to ask the target to resume.  */
-  if ((step || thread_has_single_step_breakpoints_set (tp))
-      && tp->control.trap_expected)
+  if (tp->control.trap_expected)
     {
       /* We're allowing a thread to run past a breakpoint it has
-	 hit, by single-stepping the thread with the breakpoint
-	 removed.  In which case, we need to single-step only this
-	 thread, and keep others stopped, as they can miss this
-	 breakpoint if allowed to run.  */
+	 hit, either by single-stepping the thread with the breakpoint
+	 removed, or by displaced stepping, with the breakpoint inserted.
+	 In the former case, we need to single-step only this thread,
+	 and keep others stopped, as they can miss this breakpoint if
+	 allowed to run.  That's not really a problem for displaced
+	 stepping, but, we still keep other threads stopped, in case
+	 another thread is also stopped for a breakpoint waiting for
+	 its turn in the displaced stepping queue.  */
       resume_ptid = inferior_ptid;
     }
   else

Re: [PATCH 2/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[Pedro Alves]

On 11/09/2015 11:23 AM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
> 
> Hi Pedro,
> 
>>> GDB resumes the whole process (all threads) rather than the specific
>>> thread it wants to single step (as shown in [1]).  That is wrong.
>>
>> (I understand this, but I think it'd make it clearer to explicitly
>> state _why_ that is wrong.)
> 
> I am not sure how to make the description clearer, how about this?
> 
> GDB resumes the whole process (all threads) rather than the specific
> thread for which GDB wants to step over the breakpoint (as shown in [1]).
> That is wrong.

I think the _why_ is that wrong is still missing.  I was thinking
of something around this:

The reason we resume a single thread and leave others stopped when doing a
normal step over where we temporarily remove the breakpoint, single-step,
reinsert the breakpoint, is that if we let other threads run in the period
while the breakpoint is removed, then these other threads could miss
the breakpoint.  Since with displaced stepping, we don't ever remove the
breakpoint, it should be fine to let other threads run.  However, there's another
reason that we should not let other threads run: that is the case where some of
those threads are also stopped for a breakpoint that itself needs to be
stepped over.  If we just let those threads run, then they immediately re-trap
their breakpoint again.

> 
> Patch below is regression tested on x86_64-linux and arm-linux.
> 

LGTM.

Thanks,
Pedro Alves

Re: [PATCH 2/2] Fix gdb.threads/multiple-step-overs.exp fails on arm

[Yao Qi]

Pedro Alves <palves@redhat.com> writes:

> The reason we resume a single thread and leave others stopped when doing a
> normal step over where we temporarily remove the breakpoint, single-step,
> reinsert the breakpoint, is that if we let other threads run in the period
> while the breakpoint is removed, then these other threads could miss
> the breakpoint.  Since with displaced stepping, we don't ever remove the
> breakpoint, it should be fine to let other threads run.  However,
> there's another
> reason that we should not let other threads run: that is the case where some of
> those threads are also stopped for a breakpoint that itself needs to be
> stepped over.  If we just let those threads run, then they immediately re-trap
> their breakpoint again.
>

OK, copy them into the commit log.

>> 
>> Patch below is regression tested on x86_64-linux and arm-linux.
>> 
>
> LGTM.

Patch is pushed in.

-- 
Yao (齐尧)