[wasm] Patch trapping position into stack trace

test/mjsunit/wasm/trap-location.js

Index: test/mjsunit/wasm/trap-location.js
diff --git a/test/mjsunit/wasm/trap-location.js b/test/mjsunit/wasm/trap-location.js
new file mode 100644
index 0000000000000000000000000000000000000000..5e3661d122bca556ac8de45204b556b56b4c09bb
--- /dev/null
+++ b/test/mjsunit/wasm/trap-location.js
@@ -0,0 +1,78 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --expose-wasm
+
+load("test/mjsunit/wasm/wasm-constants.js");
+load("test/mjsunit/wasm/wasm-module-builder.js");
+
+// Collect the Callsite objects instead of just a string:
+Error.prepareStackTrace = function(error, frames) {
+  return frames;
+};
+
+var builder = new WasmModuleBuilder();
+
+var sig_index = builder.addSignature(kSig_i_v)
+
+// Build a function to resemble this code:
+//   if (idx < 2) {
+//     return load(-2 / idx);
+//   } else if (idx == 2) {
+//     unreachable;
+//   } else {
+//     return call_indirect(idx);
+//   }
+// There are four different traps which are triggered by different input values:
+// (0) division by zero; (1) mem oob; (2) unreachable; (3) invalid call target
+// Each of them also has a different location where it traps.
+builder.addFunction("main", kSig_i_i)
+  .addBody([
+      // offset 1
+      kExprBlock,
+            kExprGetLocal, 0,
+            kExprI32Const, 2,
+          kExprI32LtU,
+        kExprIf,
+        // offset 8
+              kExprI32Const, 0x7e /* -2 */,
+              kExprGetLocal, 0,
+            kExprI32DivU,
+          // offset 13
+          kExprI32LoadMem, 0, 0,
+          kExprBr, 1, 1,
+        kExprEnd,
+        // offset 20
+            kExprGetLocal, 0,
+            kExprI32Const, 2,
+          kExprI32Eq,
+        kExprIf,
+          kExprUnreachable,
+        kExprEnd,
+        // offset 28
+          kExprGetLocal, 0,
+        kExprCallIndirect, kArity0, sig_index,
+      kExprEnd,
+  ])
+  .exportAs("main");
+
+var module = builder.instantiate();
+
+function testWasmTrap(value, reason, position) {
+  try {
+    module.exports.main(value);
+    fail("expected wasm exception");
+  } catch (e) {
+    assertEquals(kTrapMsgs[reason], e.message, "trap reason");
+    assertEquals(3, e.stack.length, "number of frames");
+    assertEquals(0, e.stack[0].getLineNumber(), "wasmFunctionIndex");
+    assertEquals(position, e.stack[0].getPosition(), "position");
+  }
+}
+
+// The actual tests:
+testWasmTrap(0, kTrapDivByZero,      12);
+testWasmTrap(1, kTrapMemOutOfBounds, 13);
+testWasmTrap(2, kTrapUnreachable,    26);
+testWasmTrap(3, kTrapFuncInvalid,    30);