diff --git a/src/compiler.cpp b/src/compiler.cpp
index 9baa9b4c2f..6d6d63810a 100644
--- a/src/compiler.cpp
+++ b/src/compiler.cpp
@@ -120,12 +120,16 @@ class State {
 
 class LogicalInstruction {
  public:
+  LogicalInstruction() {
+    memset(this, 0, sizeof(LogicalInstruction));
+  }
+
   Event* firstEvent;
   Event* lastEvent;
   LogicalInstruction* immediatePredecessor;
   Stack* stack;
   Value** locals;
-  Promise* machineOffset;
+  Assembler::Offset* machineOffset;
   int index;
   bool stackSaved;
 };
@@ -226,6 +230,7 @@ class Context {
     lastConstant(0),
     machineCode(0),
     firstEvent(0),
+    lastEvent(0),
     logicalIp(-1),
     constantCount(0),
     nextSequence(0),
@@ -255,6 +260,7 @@ class Context {
   ConstantPoolNode* lastConstant;
   uint8_t* machineCode;
   Event* firstEvent;
+  Event* lastEvent;
   int logicalIp;
   unsigned constantCount;
   unsigned nextSequence;
@@ -369,9 +375,14 @@ class Event {
   {
     assert(c, c->logicalIp >= 0);
 
-    if (logicalInstruction->lastEvent) {
-      logicalInstruction->lastEvent->next = this;
+    if (c->lastEvent) {
+      c->lastEvent->next = this;
     } else {
+      c->firstEvent = this;
+    }
+    c->lastEvent = this;
+
+    if (logicalInstruction->firstEvent == 0) {
       logicalInstruction->firstEvent = this;
     }
     logicalInstruction->lastEvent = this;
@@ -2475,6 +2486,10 @@ compile(Context* c)
   for (Event* e = c->firstEvent; e; e = e->next) {
     e->block = block;
 
+    if (e->logicalInstruction->machineOffset == 0) {
+      e->logicalInstruction->machineOffset = a->offset();
+    }
+
     Event* predecessor = static_cast<Event*>(e->predecessors->value);
     if (e->predecessors->next) {
       setSites(c, e, predecessor->junctionSites);
diff --git a/src/x86.cpp b/src/x86.cpp
index cc833e0ab5..07737c3287 100644
--- a/src/x86.cpp
+++ b/src/x86.cpp
@@ -48,10 +48,19 @@ isInt32(intptr_t v)
 
 class Task;
 
+class Block {
+ public:
+  Block(unsigned offset): offset(offset), start(~0) { }
+
+  unsigned offset;
+  unsigned start;
+};
+
 class Context {
  public:
   Context(System* s, Allocator* a, Zone* zone):
-    s(s), zone(zone), client(0), code(s, a, 1024), tasks(0), result(0)
+    s(s), zone(zone), client(0), code(s, a, 1024), tasks(0), result(0),
+    block(0)
   { }
 
   System* s;
@@ -60,6 +69,7 @@ class Context {
   Vector code;
   Task* tasks;
   uint8_t* result;
+  Block* block;
 };
 
 typedef void (*OperationType)(Context*);
@@ -924,6 +934,31 @@ class MyArchitecture: public Assembler::Architecture {
   unsigned referenceCount;
 };
 
+class MyOffset: public Assembler::Offset {
+ public:
+  MyOffset(Context* c, Block* block, unsigned offset):
+    c(c), block(block), offset(offset)
+  { }
+
+  virtual unsigned resolve(unsigned start) {
+    block->start = start;
+    return value();
+  }
+
+  virtual bool resolved() {
+    return block->start != static_cast<unsigned>(~0);
+  }
+  
+  virtual unsigned value() {
+    assert(c, resolved());
+    return block->start + (offset - block->offset);
+  }
+
+  Context* c;
+  Block* block;
+  unsigned offset;
+};
+
 class MyAssembler: public Assembler {
  public:
   MyAssembler(System* s, Allocator* a, Zone* zone, MyArchitecture* arch):
@@ -1043,12 +1078,12 @@ class MyAssembler: public Assembler {
   }
 
   virtual Offset* offset() {
-    // todo
-    return 0;
+    return new (c.zone->allocate(sizeof(MyOffset)))
+      MyOffset(&c, c.block, c.code.length());
   }
 
   virtual void endBlock() {
-    // todo
+    c.block = new (c.zone->allocate(sizeof(Block))) Block(c.code.length());
   }
 
   virtual unsigned length() {