diff -r dfce0539a77d -r 1aec996cde2d jitcraft/BytecodeEmitter.cpp
--- a/jitcraft/BytecodeEmitter.cpp	Wed Jul 11 01:12:54 2012 -0700
+++ b/jitcraft/BytecodeEmitter.cpp	Thu Jul 12 00:38:00 2012 -0700
@@ -32,6 +32,8 @@
     oom_(false),
     maxStackDepth_(0)
 {
+    lastCodePosition_ = 0;
+    firstLine_ = 1;
 }
 
 bool
@@ -95,3 +97,18 @@
     oom_ &= oopRecords_.append(record);
 }
 
+void
+BytecodeEmitter::note_position(const SourcePosition &pos)
+{
+    assert(pos.line > 0);
+    assert(unsigned(pos.line) >= firstLine_);
+
+    unsigned lineDelta = unsigned(pos.line) - firstLine_;
+    unsigned pcDelta = unsigned(position()) - lastCodePosition_;
+
+    sourcemap_.writeUint32(pcDelta);
+    sourcemap_.writeUint32(lineDelta);
+    sourcemap_.writeUint32(pos.col);
+
+    lastCodePosition_ = unsigned(position());
+}