--- a/src/hotspot/share/code/compiledMethod.cpp	Mon Nov 05 12:53:55 2018 +0100
+++ b/src/hotspot/share/code/compiledMethod.cpp	Mon Nov 05 12:36:23 2018 +0100
@@ -293,6 +293,20 @@
   // first few bytes.  If an oop in the old code was there, that oop
   // should not get GC'd.  Skip the first few bytes of oops on
   // not-entrant methods.
+  if (frame_complete_offset() != CodeOffsets::frame_never_safe &&
+      code_begin() + frame_complete_offset() >
+      verified_entry_point() + NativeJump::instruction_size)
+  {
+    // If we have a frame_complete_offset after the native jump, then there
+    // is no point trying to look for oops before that. This is a requirement
+    // for being allowed to scan oops concurrently.
+    return code_begin() + frame_complete_offset();
+  }
+
+  // It is not safe to read oops concurrently using entry barriers, if their
+  // location depend on whether the nmethod is entrant or not.
+  assert(BarrierSet::barrier_set()->barrier_set_nmethod() == NULL, "Not safe oop scan");
+
   address low_boundary = verified_entry_point();
   if (!is_in_use() && is_nmethod()) {
     low_boundary += NativeJump::instruction_size;

--- a/src/hotspot/share/gc/z/zNMethodTable.cpp	Mon Nov 05 12:53:55 2018 +0100
+++ b/src/hotspot/share/gc/z/zNMethodTable.cpp	Mon Nov 05 12:36:23 2018 +0100
@@ -51,7 +51,6 @@
   nmethod* method() const;
   size_t immediate_oops_count() const;
   oop** immediate_oops_begin() const;
-  oop** immediate_oops_begin_safe() const;
   oop** immediate_oops_end() const;
 };
 
@@ -95,24 +94,6 @@
   return (oop**)((uintptr_t)this + header_size());
 }
 
-oop** ZNMethodWithImmediateOops::immediate_oops_begin_safe() const {
-  // Non-entrant nmethods have a jump instruction patched into the beginning
-  // of the verified entry point, which could have overwritten an immediate
-  // oop. If so, make sure we skip over that oop.
-  if (_nm->is_not_entrant()) {
-    oop* const first_immediate_oop = *immediate_oops_begin();
-    oop* const safe_begin = (oop*)(_nm->verified_entry_point() + NativeJump::instruction_size);
-    if (first_immediate_oop < safe_begin) {
-      // First immediate oop overwritten, skip it
-      return immediate_oops_begin() + 1;
-    }
-  }
-
-  // First immediate oop not overwritten
-  return immediate_oops_begin();
-}
-
-
 oop** ZNMethodWithImmediateOops::immediate_oops_end() const {
   return immediate_oops_begin() + immediate_oops_count();
 }
@@ -429,7 +410,7 @@
   if (entry.immediate_oops()) {
     // Process immediate oops
     const ZNMethodWithImmediateOops* const nmi = entry.method_with_immediate_oops();
-    oop** const begin = nmi->immediate_oops_begin_safe();
+    oop** const begin = nmi->immediate_oops_begin();
     oop** const end = nmi->immediate_oops_end();
     for (oop** p = begin; p < end; p++) {
       cl->do_oop(*p);