Resolve some disagreements between SIMARM and XARM on offsets used in compiled code.

runtime/vm/isolate.h

 // Copyright (c) 2013, 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.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 173 matching lines @@
     terminate_capability_ = value;
   }
   uint64_t terminate_capability() const { return terminate_capability_; }
 
   Heap* heap() const { return heap_; }
   void set_heap(Heap* value) { heap_ = value; }
   static intptr_t heap_offset() { return OFFSET_OF(Isolate, heap_); }
 
   ObjectStore* object_store() const { return object_store_; }
   void set_object_store(ObjectStore* value) { object_store_ = value; }
-  static intptr_t object_store_offset() {
-    return OFFSET_OF(Isolate, object_store_);
-  }
 
   // DEPRECATED: Use Thread's methods instead. During migration, these default
   // to using the mutator thread (which must also be the current thread).
   StackResource* top_resource() const {
     ASSERT(Thread::Current() == mutator_thread_);
     return mutator_thread_->top_resource();
   }
   void set_top_resource(StackResource* value) {
     ASSERT(Thread::Current() == mutator_thread_);
     mutator_thread_->set_top_resource(value);
@@ skipping 605 matching lines @@
     ASSERT(thread == Thread::Current());
     DEBUG_ASSERT(IsIsolateOf(thread));
     mutator_thread_ = thread;
   }
 #if defined(DEBUG)
   bool IsIsolateOf(Thread* thread);
 #endif  // DEBUG
 
   template<class T> T* AllocateReusableHandle();
 
-  uword vm_tag_;
+  // Accessed from generated code:
+  uword stack_limit_;

[Florian Schneider, 2015/09/30 09:38:13]

Add a COMPILE_ASSERT at for the first member, and maybe ALIGNx for the others to
make sure the offsets are consistent across compilers.

[rmacnak, 2015/10/01 22:00:49]

The compiler won't allow use of OFFSET_OF in a COMPILE_ASSERT.

runtime/vm/globals.h:54:69: error: a cast to a type other than an integral or
enumeration type cannot appear in a constant-expression
   (reinterpret_cast<intptr_t>(&(reinterpret_cast<type*>(kOffsetOfPtr)->field))

[Florian Schneider, 2015/10/02 13:41:09]

gcc has the offsetof macro which can appear as compile-time constant - Not sure
about MSVC, but the problem you're fixing here affects gcc, so we could use it
here under an #ifdef.

   StoreBuffer* store_buffer_;
   Heap* heap_;
+  uword vm_tag_;
+  uword user_tag_;
+  RawUserTag* current_tag_;
+  RawUserTag* default_tag_;
+  ClassTable class_table_;
+  bool single_step_;
+
   ThreadRegistry* thread_registry_;
-  ClassTable class_table_;
   Dart_MessageNotifyCallback message_notify_callback_;
   char* name_;
   char* debugger_name_;
   int64_t start_time_;
   Dart_Port main_port_;
   Dart_Port origin_id_;  // Isolates created by spawnFunc have some origin id.
   uint64_t pause_capability_;
   uint64_t terminate_capability_;
   bool errors_fatal_;
   ObjectStore* object_store_;
   uword top_exit_frame_info_;
   void* init_callback_data_;
   Dart_EnvironmentCallback environment_callback_;
   Dart_LibraryTagHandler library_tag_handler_;
   ApiState* api_state_;
   Debugger* debugger_;
-  bool single_step_;
   bool resume_request_;
   int64_t last_resume_timestamp_;
   bool has_compiled_;
   Flags flags_;
   Random random_;
   Simulator* simulator_;
   TimerList timer_list_;
   intptr_t deopt_id_;
   Mutex* mutex_;  // protects stack_limit_ and saved_stack_limit_.
-  uword stack_limit_;
   uword saved_stack_limit_;
   uword stack_base_;
   uword stack_overflow_flags_;
   int32_t stack_overflow_count_;
   MessageHandler* message_handler_;
   IsolateSpawnState* spawn_state_;
   bool is_runnable_;
   Dart_GcPrologueCallback gc_prologue_callback_;
   Dart_GcEpilogueCallback gc_epilogue_callback_;
   intptr_t defer_finalization_count_;
@@ skipping 15 matching lines @@
   // Ring buffer of objects assigned an id.
   ObjectIdRing* object_id_ring_;
 
   // Trace buffer support.
   TraceBuffer* trace_buffer_;
 
   IsolateProfilerData* profiler_data_;
   Mutex profiler_data_mutex_;
 
   VMTagCounters vm_tag_counters_;
-  uword user_tag_;
   RawGrowableObjectArray* tag_table_;
-  RawUserTag* current_tag_;
-  RawUserTag* default_tag_;
+
 
   RawGrowableObjectArray* collected_closures_;
   RawGrowableObjectArray* deoptimized_code_array_;
 
   // We use 6 list entries for each pending service extension calls.
   enum {
     kPendingHandlerIndex = 0,
     kPendingMethodNameIndex,
     kPendingKeysIndex,
     kPendingValuesIndex,
@@ skipping 224 matching lines @@
   uint8_t* serialized_message_;
   intptr_t serialized_message_len_;
   Isolate::Flags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_