2010-12-20  Yao Qi  <yao@codesourcery.com>

	* infrun.c (displaced_step_prepare): Replace regcache_write_pc by
	regcache_cooked_write_unsigned to update PC without side effect.

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 1bc00a4..2711e19 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -1304,8 +1304,13 @@ displaced_step_prepare (ptid_t ptid)
 
   make_cleanup (displaced_step_clear_cleanup, displaced);
 
-  /* Resume execution at the copy.  */
-  regcache_write_pc (regcache, copy);
+  /* Resume execution at the copy.  Update PC without any side effects.  */
+  if (gdbarch_pc_regnum (gdbarch) >= 0)
+    regcache_cooked_write_unsigned (regcache,
+				    gdbarch_pc_regnum (gdbarch), copy);
+  else
+    internal_error (__FILE__, __LINE__,
+		    _("displaced: Unable to update PC"));
 
   discard_cleanups (ignore_cleanups);