Force to insert software single step breakpoint

GDB doesn't insert software single step breakpoint if the instruction
branches to itself, so that the program can't stop after command "si".

(gdb) b 32
Breakpoint 2 at 0x8680: file git/gdb/testsuite/gdb.base/branch-to-self.c, line 32.
(gdb) c
Continuing.

Breakpoint 2, main () at gdb/git/gdb/testsuite/gdb.base/branch-to-self.c:32
32	  asm (".Lhere: " BRANCH_INSN " .Lhere"); /* loop-line */
(gdb) si
infrun: clear_proceed_status_thread (Thread 3991.3991)
infrun: proceed (addr=0xffffffff, signal=GDB_SIGNAL_DEFAULT)
infrun: step-over queue now empty
infrun: resuming [Thread 3991.3991] for step-over
infrun: skipping breakpoint: stepping past insn at: 0x8680
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sending packet: $Z0,8678,4#f3...Packet received: OK
infrun: skipping breakpoint: stepping past insn at: 0x8680
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Sending packet: $Z0,b6fe86c8,4#82...Packet received: OK
infrun: resume (step=1, signal=GDB_SIGNAL_0), trap_expected=1, current thread [Thread 3991.3991] at 0x868

breakpoint.c:should_be_inserted thinks the breakpoint shouldn't be
inserted, which is wrong.  This patch restrict the condition that
only skip the non-single-step breakpoints if they are inserted at
the place we are stepping over, however we don't want to skip
single-step breakpoint if its thread is the thread we are stepping
over, so in this patch, I add a thread num in 'struct step_over_info'
to record the thread we're stepping over.

gdb:

2016-04-25  Yao Qi  <yao.qi@linaro.org>

	* breakpoint.c (should_be_inserted): Return 0 if the location's
	owner is not single step breakpoint or single step breakpoint's
	thread isn't the thread which is stepping past a breakpoint.
	* gdbarch.sh (software_single_step): Update comments.
	* gdbarch.h: Regenerated.
	* infrun.c (struct step_over_info) <thread>: New field.
	(set_step_over_info): New argument 'thread'.  Callers updated.
	(clear_step_over_info): Set field thread to -1.
	(thread_is_stepping_over_breakpoint): New function.
	* infrun.h (thread_is_stepping_over_breakpoint): Declaration.

gdb/infrun.c

@@ -1296,6 +1296,9 @@ struct step_over_info
   /* The instruction being stepped over triggers a nonsteppable
      watchpoint.  If true, we'll skip inserting watchpoints.  */
   int nonsteppable_watchpoint_p;
+
+  /* The thread's global number.  */
+  int thread;
 };
 
 /* The step-over info of the location that is being stepped over.
@@ -1329,11 +1332,13 @@ static struct step_over_info step_over_info;
 
 static void
 set_step_over_info (struct address_space *aspace, CORE_ADDR address,
-		    int nonsteppable_watchpoint_p)
+		    int nonsteppable_watchpoint_p,
+		    int thread)
 {
   step_over_info.aspace = aspace;
   step_over_info.address = address;
   step_over_info.nonsteppable_watchpoint_p = nonsteppable_watchpoint_p;
+  step_over_info.thread = thread;
 }
 
 /* Called when we're not longer stepping over a breakpoint / an
@@ -1348,6 +1353,7 @@ clear_step_over_info (void)
   step_over_info.aspace = NULL;
   step_over_info.address = 0;
   step_over_info.nonsteppable_watchpoint_p = 0;
+  step_over_info.thread = -1;
 }
 
 /* See infrun.h.  */
@@ -1364,6 +1370,15 @@ stepping_past_instruction_at (struct address_space *aspace,
 
 /* See infrun.h.  */
 
+int
+thread_is_stepping_over_breakpoint (int thread)
+{
+  return (step_over_info.thread != -1
+	  && thread == step_over_info.thread);
+}
+
+/* See infrun.h.  */
+
 int
 stepping_past_nonsteppable_watchpoint (void)
 {
@@ -2579,7 +2594,7 @@ resume (enum gdb_signal sig)
 	    stop_all_threads ();
 
 	  set_step_over_info (get_regcache_aspace (regcache),
-			      regcache_read_pc (regcache), 0);
+			      regcache_read_pc (regcache), 0, tp->global_num);
 
 	  step = maybe_software_singlestep (gdbarch, pc);
 
@@ -7750,10 +7765,11 @@ keep_going_pass_signal (struct execution_control_state *ecs)
 	  && (remove_wps || !use_displaced_stepping (ecs->event_thread)))
 	{
 	  set_step_over_info (get_regcache_aspace (regcache),
-			      regcache_read_pc (regcache), remove_wps);
+			      regcache_read_pc (regcache), remove_wps,
+			      ecs->event_thread->global_num);
 	}
       else if (remove_wps)
-	set_step_over_info (NULL, 0, remove_wps);
+	set_step_over_info (NULL, 0, remove_wps, -1);
 
       /* If we now need to do an in-line step-over, we need to stop
 	 all other threads.  Note this must be done before