Fix LookupCode for the DatePrototype_GetField builtin

src/builtins/s390/builtins-s390.cc

Index: src/builtins/s390/builtins-s390.cc
diff --git a/src/builtins/s390/builtins-s390.cc b/src/builtins/s390/builtins-s390.cc
index f9aebf935048f77121d58cc380c2bf648a91458c..eaf85866c25a2bf117af75bdb1117deed3ba58c7 100644
--- a/src/builtins/s390/builtins-s390.cc
+++ b/src/builtins/s390/builtins-s390.cc
@@ -1896,6 +1896,16 @@ void Builtins::Generate_DatePrototype_GetField(MacroAssembler* masm,
     __ LoadSmiLiteral(r2, Smi::FromInt(0));
     __ EnterBuiltinFrame(cp, r3, r2);
     __ CallRuntime(Runtime::kThrowNotDateError);
+
+    // It's far from obvious, but this final trailing instruction after the call
+    // is required for StackFrame::LookupCode to work correctly. To illustrate
+    // why: if call were the final instruction in the code object, then the pc
+    // (== return address) would point beyond the code object when the stack is
+    // traversed. When we then try to look up the code object through
+    // StackFrame::LookupCode, we actually return the next code object that
+    // happens to be on the same page in memory.
+    // TODO(jgruber): A proper fix for this would be nice.
+    __ nop();
   }
 }