Bug 513065 - Part 3, Stay on trace when calculating scope in thisObject hook. r=mrbkap.

js/src/jsapi.cpp

@@ -1683,6 +1683,31 @@ JS_GetGlobalForObject(JSContext *cx, JSObject *obj)
     return obj->getGlobal();
 }
 
+JS_PUBLIC_API(JSObject *)
+JS_GetGlobalForScopeChain(JSContext *cx)
+{
+    /*
+     * This is essentially JS_GetScopeChain(cx)->getGlobal(), but without
+     * falling off trace.
+     *
+     * This use of cx->fp, possibly on trace, is deliberate:
+     * cx->fp->scopeChain->getGlobal() returns the same object whether we're on
+     * trace or not, since we do not trace calls across global objects.
+     */
+    VOUCH_DOES_NOT_REQUIRE_STACK();
+
+    if (cx->fp)
+        return cx->fp->scopeChain->getGlobal();
+
+    JSObject *scope = cx->globalObject;
+    if (!scope) {
+        JS_ReportErrorNumber(cx, js_GetErrorMessage, NULL, JSMSG_INACTIVE);
+        return NULL;
+    }
+    OBJ_TO_INNER_OBJECT(cx, scope);
+    return scope;
+}
+
 JS_PUBLIC_API(jsval)
 JS_ComputeThis(JSContext *cx, jsval *vp)
 {

js/src/jsapi.h

@@ -825,6 +825,9 @@ JS_GetScopeChain(JSContext *cx);
 extern JS_PUBLIC_API(JSObject *)
 JS_GetGlobalForObject(JSContext *cx, JSObject *obj);
 
+extern JS_PUBLIC_API(JSObject *)
+JS_GetGlobalForScopeChain(JSContext *cx);
+
 #ifdef JS_HAS_CTYPES
 /*
  * Initialize the 'ctypes' object on a global variable 'obj'. The 'ctypes'

js/src/xpconnect/src/xpcwrappednativejsops.cpp

@@ -1488,15 +1488,13 @@ XPC_WN_JSOp_ThisObject(JSContext *cx, JSObject *obj)
     if(!obj)
         return nsnull;
 
-    JSObject *scope = JS_GetScopeChain(cx);
+    JSObject *scope = JS_GetGlobalForScopeChain(cx);
     if(!scope)
     {
         XPCThrower::Throw(NS_ERROR_FAILURE, cx);
         return nsnull;
     }
 
-    scope = JS_GetGlobalForObject(cx, scope);
-
     XPCPerThreadData *threadData = XPCPerThreadData::GetData(cx);
     if(!threadData)
     {