Precompilation: don't include an object header for instructions in the text section.

runtime/vm/raw_object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/raw_object.h"
 
 #include "vm/class_table.h"
 #include "vm/dart.h"
 #include "vm/freelist.h"
 #include "vm/isolate.h"
@@ skipping 517 matching lines @@
   return false;
 }
 
 
 intptr_t RawCode::VisitCodePointers(RawCode* raw_obj,
                                     ObjectPointerVisitor* visitor) {
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
 
   RawCode* obj = raw_obj->ptr();
   intptr_t length = Code::PtrOffBits::decode(obj->state_bits_);
+#if defined(TARGET_ARCH_IA32)
+  // On IA32 only we embed pointers to objects directly in the generated
+  // instructions. The variable portion of a Code object describes where to
+  // find those pointers for tracing.
   if (Code::AliveBit::decode(obj->state_bits_)) {
-    // Also visit all the embedded pointers in the corresponding instructions.
     uword entry_point = reinterpret_cast<uword>(obj->instructions_->ptr()) +
         Instructions::HeaderSize();
     for (intptr_t i = 0; i < length; i++) {
       int32_t offset = obj->data()[i];
       visitor->VisitPointer(
           reinterpret_cast<RawObject**>(entry_point + offset));
     }
   }
   return Code::InstanceSize(length);
+#else
+  // On all other architectures, objects are referenced indirectly through
+  // either an ObjectPool or Thread.
+  ASSERT(length == 0);
+  return Code::InstanceSize(0);
+#endif
 }
 
 
 intptr_t RawObjectPool::VisitObjectPoolPointers(
     RawObjectPool* raw_obj, ObjectPointerVisitor* visitor) {
   visitor->VisitPointer(
       reinterpret_cast<RawObject**>(&raw_obj->ptr()->info_array_));
   const intptr_t len = raw_obj->ptr()->length_;
   RawTypedData* info_array = raw_obj->ptr()->info_array_->ptr();
   Entry* first = raw_obj->first_entry();
@@ skipping 395 matching lines @@
 intptr_t RawUserTag::VisitUserTagPointers(
     RawUserTag* raw_obj, ObjectPointerVisitor* visitor) {
   // Make sure that we got here with the tagged pointer as this.
   ASSERT(raw_obj->IsHeapObject());
   visitor->VisitPointers(raw_obj->from(), raw_obj->to());
   return UserTag::InstanceSize();
 }
 
 
 }  // namespace dart