Do not use source map beyond function boundaries

Author: quantum5

src/source_map_support.js

@@ -55,7 +55,12 @@ function WasmSourceMap(sourceMap) {
 }
 
 WasmSourceMap.prototype.lookup = function (offset) {
-  var info = this.mapping[this.normalizeOffset(offset)];
+  var normalized = this.normalizeOffset(offset);
+#if 'emscripten_generate_pc' in addedLibraryItems
+  if (!wasmOffsetConverter.isSameFunc(offset, normalized))
+    return null;
+#endif
+  var info = this.mapping[normalized];
   if (!info)
     return null;
   return {

src/wasm_offset_converter.js

@@ -13,6 +13,7 @@ function WasmOffsetConverter(wasmBytes) {
   var idx = 0;
 
   this.map = {};
+  this.func_starts = [];
 
   function unsignedLEB128() {
     var result = 0;
@@ -69,6 +70,7 @@ function WasmOffsetConverter(wasmBytes) {
         while (count --> 0) {
           var size = unsignedLEB128();
           this.map[idx++] = offset;
+          this.func_starts.push(offset);
           offset += size;
         }
         return;
@@ -80,3 +82,23 @@ function WasmOffsetConverter(wasmBytes) {
 WasmOffsetConverter.prototype.convert = function (funcidx, offset) {
   return this.map[funcidx] + offset;
 }
+
+WasmOffsetConverter.prototype.isSameFunc = function (offset1, offset2) {
+  var array = this.func_starts;
+  function bisect(offset) {
+    var lo = 0;
+    var hi = array.length;
+    var mid;
+
+    while (lo < hi) {
+      mid = Math.floor((lo + hi) / 2);
+      if (array[mid] > offset) {
+        hi = mid;
+      } else {
+        lo = mid + 1;
+      }
+    }
+    return lo;
+  }
+  return bisect(offset1) == bisect(offset2);
+}