diff --git a/gdb/gdbserver/remote-utils.c b/gdb/gdbserver/remote-utils.c
index d638a3f..76953ae 100644
--- a/gdb/gdbserver/remote-utils.c
+++ b/gdb/gdbserver/remote-utils.c
@@ -1181,8 +1181,8 @@ prepare_resume_reply (char *buf, ptid_t ptid,
 		strcat (buf, ";");
 		buf += strlen (buf);
 
-		if (the_target->core_for_thread)
-		  core = (*the_target->core_for_thread) (ptid);
+		if (the_target->core_of_thread)
+		  core = (*the_target->core_of_thread) (ptid);
 		if (core != -1)
 		  {
 		    sprintf (buf, "core:");
diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
index dfc92a8..c781552 100644
--- a/gdb/gdbserver/server.c
+++ b/gdb/gdbserver/server.c
@@ -723,8 +723,8 @@ handle_threads_qxfer_proper (struct buffer *buffer)
 
       write_ptid (ptid_s, ptid);
 
-      if (the_target->core_for_thread)
-	core = (*the_target->core_for_thread) (ptid);
+      if (the_target->core_of_thread)
+	core = (*the_target->core_of_thread) (ptid);
 
       if (core != -1)
 	{
diff --git a/gdb/gdbserver/target.h b/gdb/gdbserver/target.h
index 0ee0d41..0c761e9 100644
--- a/gdb/gdbserver/target.h
+++ b/gdb/gdbserver/target.h
@@ -285,7 +285,7 @@ struct target_ops
   int (*handle_monitor_command) (char *);
 
   /* Returns the core given a thread, or -1 if not known.  */
-  int (*core_for_thread) (ptid_t);
+  int (*core_of_thread) (ptid_t);
 };
 
 extern struct target_ops *the_target;
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 717f78c..bf0a5f1 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -1184,6 +1184,7 @@ add_lwp (ptid_t ptid)
   lp->waitstatus.kind = TARGET_WAITKIND_IGNORE;
 
   lp->ptid = ptid;
+  lp->core = -1;
 
   lp->next = lwp_list;
   lwp_list = lp;
@@ -3642,6 +3643,7 @@ retry:
     fprintf_unfiltered (gdb_stdlog, "LLW: exit\n");
 
   restore_child_signals_mask (&prev_mask);
+  lp->core = linux_nat_core_of_thread_1 (lp->ptid);
   return lp->ptid;
 }
 
@@ -5423,10 +5425,8 @@ linux_nat_thread_address_space (struct target_ops *t, ptid_t ptid)
   return inf->aspace;
 }
 
-/* Return the core for a thread.  */
-
-static int
-linux_nat_core_of_thread (struct target_ops *ops, ptid_t ptid)
+int
+linux_nat_core_of_thread_1 (ptid_t ptid)
 {
   struct cleanup *back_to;
   char *filename;
@@ -5483,6 +5483,17 @@ linux_nat_core_of_thread (struct target_ops *ops, ptid_t ptid)
   return core;
 }
 
+/* Return the cached value of the processor core for thread PTID.  */
+
+int
+linux_nat_core_of_thread (struct target_ops *ops, ptid_t ptid)
+{
+  struct lwp_info *info = find_lwp_pid (ptid);
+  if (info)
+    return info->core;
+  return -1;
+}
+
 void
 linux_nat_add_target (struct target_ops *t)
 {
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index 9537740..5aba089 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -89,6 +89,9 @@ struct lwp_info
      - TARGET_WAITKIND_SYSCALL_RETURN */
   int syscall_state;
 
+  /* The processor core this LWP was last seen on.  */
+  int core;
+
   /* Next LWP in list.  */
   struct lwp_info *next;
 };
@@ -163,3 +166,6 @@ void linux_nat_switch_fork (ptid_t new_ptid);
 
 /* Return the saved siginfo associated with PTID.  */
 struct siginfo *linux_nat_get_siginfo (ptid_t ptid);
+
+/* Compute and return the processor core of a given thread.  */
+int linux_nat_core_of_thread_1 (ptid_t ptid);
diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index 659d99d..2c66da7 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -1454,6 +1454,12 @@ thread_db_find_new_threads_1 (ptid_t ptid)
   thread_db_find_new_threads_2 (ptid, 0);
 }
 
+static int
+update_thread_core (struct lwp_info *info, void *closure)
+{
+  info->core = linux_nat_core_of_thread_1 (info->ptid);
+  return 0;
+}
 
 static void
 thread_db_find_new_threads (struct target_ops *ops)
@@ -1466,6 +1472,9 @@ thread_db_find_new_threads (struct target_ops *ops)
     return;
 
   thread_db_find_new_threads_1 (inferior_ptid);
+
+  iterate_over_lwps (minus_one_ptid /* iterate over all */,
+		     update_thread_core, NULL);
 }
 
 static char *
diff --git a/gdb/remote.c b/gdb/remote.c
index 992ef9a..beb585e 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -1411,7 +1411,7 @@ remote_notice_new_inferior (ptid_t currthread, int running)
 	      remote_add_thread (currthread, running);
 	      inferior_ptid = currthread;
 	    }
- 	  return;
+	  return;
 	}
 
       if (ptid_equal (magic_null_ptid, inferior_ptid))
@@ -1421,7 +1421,7 @@ remote_notice_new_inferior (ptid_t currthread, int running)
 	     doesn't support qC.  This is the first stop reported
 	     after an attach, so this is the main thread.  Update the
 	     ptid in the thread list.  */
-  	  thread_change_ptid (inferior_ptid, currthread);
+	  thread_change_ptid (inferior_ptid, currthread);
 	  return;
 	}
 
@@ -1452,12 +1452,12 @@ demand_private_info (ptid_t ptid)
 
   gdb_assert (info);
 
-  if (!info->private) 
+  if (!info->private)
     {
       info->private = xmalloc (sizeof (*(info->private)));
       info->private_dtor = free_private_thread_info;
     }
-  
+
   return info->private;
 }
 
diff --git a/gdb/target.h b/gdb/target.h
index 9725375..a020bf7 100644
--- a/gdb/target.h
+++ b/gdb/target.h
@@ -653,11 +653,10 @@ struct target_ops
        disconnection - set VAL to 1 to keep tracing, 0 to stop.  */
     void (*to_set_disconnected_tracing) (int val);
 
-    /* Return the core that thread PTID is on.  For a stopped thread, should
-       return the core the thread was last running on.  For a running thread,
-       should return one of the cores that the thread was running between
-       the call to this function and return -- and if it was running on
-       several cores, any other may be returned.
+    /* Return the processor core that thread PTID was last seen on.
+       This information is updated only when:
+       - update_thread_list is called
+       - thread stops
        If the core cannot be determined -- either for the specified thread, or
        right now, or in this debug session, or for this target -- return -1.  */
     int (*to_core_of_thread) (struct target_ops *, ptid_t ptid);