Never truncate the JS stack

Truncating it can lead to all sorts of crazy side effects, especially
as we'd be extending it again when leaving the function. When that happens
already freed JS objects could suddenly become visible to the GC again.

Fix this by copying the CallData to set up a new stack frame. This is not yet
ideal, as we're copying too much data, but that can be fixed separately.

Change-Id: I02a39ce479475bae326f9eddfe6654fbcf8e6d35
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

4 files changed, 34 insertions, 7 deletions

diff --git a/src/qml/jsruntime/qv4runtime.cpp b/src/qml/jsruntime/qv4runtime.cpp
index 2e97d8074a..97b0c5259f 100644
--- a/src/qml/jsruntime/qv4runtime.cpp
+++ b/src/qml/jsruntime/qv4runtime.cpp
@@ -1028,6 +1028,7 @@ ReturnedValue Runtime::method_callName(ExecutionEngine *engine, int nameIndex, C
 
 ReturnedValue Runtime::method_callProperty(ExecutionEngine *engine, int nameIndex, CallData *callData)
 {
+    Q_ASSERT(engine->jsStackTop >= callData->args + callData->argc());
     if (!callData->thisObject.isObject()) {
         Q_ASSERT(!callData->thisObject.isEmpty());
         if (callData->thisObject.isNullOrUndefined()) {
@@ -1058,6 +1059,7 @@ ReturnedValue Runtime::method_callProperty(ExecutionEngine *engine, int nameInde
 
 ReturnedValue Runtime::method_callPropertyLookup(ExecutionEngine *engine, uint index, CallData *callData)
 {
+    Q_ASSERT(engine->jsStackTop >= callData->args + callData->argc());
     Lookup *l = engine->currentStackFrame->v4Function->compilationUnit->runtimeLookups + index;
     callData->function = l->getter(l, engine, callData->thisObject);
 
diff --git a/src/qml/jsruntime/qv4vme_moth.cpp b/src/qml/jsruntime/qv4vme_moth.cpp
index f27a7d452c..4abd3582dd 100644
--- a/src/qml/jsruntime/qv4vme_moth.cpp
+++ b/src/qml/jsruntime/qv4vme_moth.cpp
@@ -509,6 +509,15 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
 
     Value *jsStackTop = engine->jsStackTop;
 
+    Q_ASSERT(engine->jsStackTop >= callData->args + callData->argc() - 1);
+    Value *stack = engine->jsStackTop;
+    engine->jsStackTop += sizeof(CallData)/sizeof(Value) - 1 + qMax(callData->argc(), int(function->compiledFunction->nRegisters));
+    memcpy(stack, callData, sizeof(CallData) - sizeof(Value) + callData->argc()*sizeof(Value));
+    // clear out remaining arguments and local registers
+    callData = reinterpret_cast<CallData *>(stack);
+    for (Value *v = callData->args + callData->argc(); v < engine->jsStackTop; ++v)
+        *v = Encode::undefined();
+
     CppStackFrame frame;
     frame.parent = engine->currentStackFrame;
     frame.v4Function = function;
@@ -516,12 +525,6 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     frame.jsFrame = callData;
     engine->currentStackFrame = &frame;
 
-    engine->jsStackTop = reinterpret_cast<QV4::Value *>(callData) + function->compiledFunction->nRegisters + 1;
-    // clear out remaining arguments and local registers
-    for (Value *v = callData->args + callData->argc(); v < jsStackTop; ++v)
-        *v = Encode::undefined();
-
-    QV4::Value *stack = reinterpret_cast<QV4::Value *>(callData);
     const uchar *exceptionHandler = 0;
 
     QV4::Value &accumulator = frame.jsFrame->accumulator;
@@ -741,6 +744,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
         STORE_IP();
         STORE_ACC();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         acc = Runtime::method_callValue(engine, accumulator, cData);
         CHECK_EXCEPTION;
     MOTH_END_INSTR(CallValue)
@@ -748,6 +752,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(CallProperty)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         cData->thisObject = STACK_VALUE(base);
         acc = Runtime::method_callProperty(engine, name, cData);
         CHECK_EXCEPTION;
@@ -756,6 +761,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(CallPropertyLookup)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         cData->thisObject = STACK_VALUE(base);
         acc = Runtime::method_callPropertyLookup(engine, lookupIndex, cData);
         CHECK_EXCEPTION;
@@ -764,6 +770,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(CallElement)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         cData->thisObject = STACK_VALUE(base);
         acc = Runtime::method_callElement(engine, STACK_VALUE(index), cData);
         CHECK_EXCEPTION;
@@ -772,6 +779,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(CallName)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         acc = Runtime::method_callName(engine, name, cData);
         CHECK_EXCEPTION;
     MOTH_END_INSTR(CallName)
@@ -779,6 +787,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(CallPossiblyDirectEval)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         acc = Runtime::method_callPossiblyDirectEval(engine, cData);
         CHECK_EXCEPTION;
     MOTH_END_INSTR(CallPossiblyDirectEval)
@@ -786,6 +795,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(CallGlobalLookup)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         acc = Runtime::method_callGlobalLookup(engine, index, cData);
         CHECK_EXCEPTION;
     MOTH_END_INSTR(CallGlobalLookup)
@@ -934,6 +944,7 @@ QV4::ReturnedValue VME::exec(CallData *callData, QV4::Function *function)
     MOTH_BEGIN_INSTR(Construct)
         STORE_IP();
         QV4::CallData *cData = reinterpret_cast<QV4::CallData *>(stack + callData);
+        Q_ASSERT(cData->args + cData->argc() <= engine->jsStackTop);
         acc = Runtime::method_construct(engine, STACK_VALUE(func), cData);
         CHECK_EXCEPTION;
     MOTH_END_INSTR(Construct)
diff --git a/src/qml/memory/qv4mm.cpp b/src/qml/memory/qv4mm.cpp
index b9bc2c34a3..21c95bbe6e 100644
--- a/src/qml/memory/qv4mm.cpp
+++ b/src/qml/memory/qv4mm.cpp
@@ -1256,9 +1256,11 @@ void MemoryManager::collectFromJSStack(MarkStack *markStack) const
     Value *top = engine->jsStackTop;
     while (v < top) {
         Managed *m = v->managed();
-        if (m && m->inUse())
+        if (m) {
+            Q_ASSERT(m->inUse());
             // Skip pointers to already freed objects, they are bogus as well
             m->mark(markStack);
+        }
         ++v;
     }
 }
diff --git a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
index 899f14b51d..faab61cd3d 100644
--- a/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
+++ b/tests/auto/qml/qqmlecmascript/tst_qqmlecmascript.cpp
@@ -344,6 +344,7 @@ private slots:
     void singleBlockLoops();
     void qtbug_60547();
     void delayLoadingArgs();
+    void manyArguments();
 
 private:
 //    static void propertyVarWeakRefCallback(v8::Persistent<v8::Value> object, void* parameter);
@@ -8375,6 +8376,17 @@ void tst_qqmlecmascript::delayLoadingArgs()
     QCOMPARE(ret.toInt(), 42); // esp. not 44.
 }
 
+void tst_qqmlecmascript::manyArguments()
+{
+    const char *testCase =
+            "function x() { var sum; for (var i = 0; i < arguments.length; ++i) sum += arguments[i][0]; }"
+            "x([0],[1],[2],[3],[4],[5],[6],[7],[8],[9], [0],[1],[2],[3],[4],[5],[6],[7],[8],[9], [0],[1],[2],[3],[4],[5],[6],[7],[8],[9])";
+
+    QJSEngine engine;
+    engine.evaluate(testCase);
+}
+
+
 QTEST_MAIN(tst_qqmlecmascript)
 
 #include "tst_qqmlecmascript.moc"