PR threads/18127 - threads spawned by infcall end up stuck in "running" state

Refs:
 https://sourceware.org/ml/gdb/2015-03/msg00024.html
 https://sourceware.org/ml/gdb/2015-06/msg00005.html

On GNU/Linux, if an infcall spawns a thread, that thread ends up with
stuck running state.  This happens because:

 - when linux-nat.c detects a new thread, it marks them as running,
   and does not report anything to the core.

 - we skip finish_thread_state when the thread that is running the
   infcall stops.

As result, that new thread ends up with stuck "running" state, even
though it really is stopped.

On Windows, _all_ threads end up stuck in running state, not just the
one that was spawned.  That happens because when a new thread is
detected, unlike linux-nat.c, windows-nat.c reports
TARGET_WAITKIND_SPURIOUS to infrun.  It's the fact that that event
does not cause a user-visible stop that triggers the problem.  When
the target is re-resumed, we call set_running with a wildcard ptid,
which marks all thread as running.  That set_running is not suppressed
because the (leader) thread being resumed does not have in_infcall
set.  Later, when the infcall finally finishes successfully, nothing
marks all threads back to stopped.

We can trigger the same problem on all targets by having a thread
other than the one that is running the infcall report a breakpoint hit
to infrun, and then have that breakpoint not cause a stop.  That's
what the included test does.

The fix is to stop GDB from suppressing the set_running calls while
doing an infcall, and then set the threads back to stopped when the
call finishes, iff they were originally stopped before the infcall
started.  (Note the MI *running/*stopped event suppression isn't
affected.)

Tested on x86_64 GNU/Linux.

gdb/ChangeLog:
2015-06-29  Pedro Alves  <palves@redhat.com>

	PR threads/18127
	* infcall.c (run_inferior_call): On infcall success, if the thread
	was marked stopped before, reset it back to stopped.
	* infrun.c (resume): Don't suppress the set_running calls when
	doing an infcall.
	(normal_stop): Only discard the finish_thread_state cleanup if the
	infcall succeeded.

gdb/testsuite/ChangeLog:
2015-06-29  Pedro Alves  <palves@redhat.com>

	PR threads/18127
	* gdb.threads/hand-call-new-thread.c: New file.
	* gdb.threads/hand-call-new-thread.c: New file.

1 files changed, 21 insertions, 0 deletions

diff --git a/gdb/infcall.c b/gdb/infcall.c
index f79afea..e3bd72a 100644
--- a/gdb/infcall.c
+++ b/gdb/infcall.c
@@ -387,6 +387,7 @@ run_inferior_call (struct thread_info *call_thread, CORE_ADDR real_pc)
   int saved_in_infcall = call_thread->control.in_infcall;
   ptid_t call_thread_ptid = call_thread->ptid;
   int saved_sync_execution = sync_execution;
+  int was_running = call_thread->state == THREAD_RUNNING;
 
   /* Infcalls run synchronously, in the foreground.  */
   if (target_can_async_p ())
@@ -433,6 +434,26 @@ run_inferior_call (struct thread_info *call_thread, CORE_ADDR real_pc)
      CALL_THREAD as it could be invalid if its thread has exited.  */
   call_thread = find_thread_ptid (call_thread_ptid);
 
+  /* If the infcall does NOT succeed, normal_stop will have already
+     finished the thread states.  However, on success, normal_stop
+     defers here, so that we can set back the thread states to what
+     they were before the call.  Note that we must also finish the
+     state of new threads that might have spawned while the call was
+     running.  The main cases to handle are:
+
+     - "(gdb) print foo ()", or any other command that evaluates an
+     expression at the prompt.  (The thread was marked stopped before.)
+
+     - "(gdb) break foo if return_false()" or similar cases where we
+     do an infcall while handling an event (while the thread is still
+     marked running).  In this example, whether the condition
+     evaluates true and thus we'll present a user-visible stop is
+     decided elsewhere.  */
+  if (!was_running
+      && ptid_equal (call_thread_ptid, inferior_ptid)
+      && stop_stack_dummy == STOP_STACK_DUMMY)
+    finish_thread_state (user_visible_resume_ptid (0));
+
   enable_watchpoints_after_interactive_call_stop ();
 
   /* Call breakpoint_auto_delete on the current contents of the bpstat