commit 802214c97d1661ad337aad0d011dded44f0b5ddd
Author: Tom Tromey <tromey@redhat.com>
Date:   Mon Apr 26 15:15:55 2010 -0600

    Fail gracefully if the _Unwind_DebugHook argument is optimized out

diff --git a/gdb/infrun.c b/gdb/infrun.c
index 2eea550..9a5b534 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -4925,20 +4925,24 @@ insert_exception_resume_breakpoint (struct thread_info *tp,
 
       vsym = lookup_symbol (SYMBOL_LINKAGE_NAME (sym), b, VAR_DOMAIN, NULL);
       value = read_var_value (vsym, frame);
-      handler = value_as_address (value);
+      /* If the value was optimized out, revert to the old behavior.  */
+      if (! value_optimized_out (value))
+	{
+	  handler = value_as_address (value);
 
-      /* We're going to replace the current step-resume breakpoint
-	 with an exception-resume breakpoint.  */
-      delete_step_resume_breakpoint (tp);
+	  /* We're going to replace the current step-resume breakpoint
+	     with an exception-resume breakpoint.  */
+	  delete_step_resume_breakpoint (tp);
 
-      if (debug_infrun)
-	fprintf_unfiltered (gdb_stdlog,
-			    "infrun: exception resume at %lx\n",
-			    (unsigned long) handler);
+	  if (debug_infrun)
+	    fprintf_unfiltered (gdb_stdlog,
+				"infrun: exception resume at %lx\n",
+				(unsigned long) handler);
 
-      bp = set_momentary_breakpoint_at_pc (get_frame_arch (frame),
-					   handler, bp_exception_resume);
-      inferior_thread ()->step_resume_breakpoint = bp;
+	  bp = set_momentary_breakpoint_at_pc (get_frame_arch (frame),
+					       handler, bp_exception_resume);
+	  inferior_thread ()->step_resume_breakpoint = bp;
+	}
     }
 }