Question

My plugin code crashes when I call the NPN_GetValue. Basically I created a scriptable object which has a ‘getDevice’ method that can return a device array to JavaScript. Below is the code snippet.

static bool mainNPObjectInvoke(NPObject *obj, NPIdentifier identifier, const NPVariant *args, uint32_t argCount, NPVariant *result)
{
    printf("create main object");
    MainNPObject *mainObject = (MainNPObject *)obj;

    if (identifier == methodIdentifiers[METHOD_ID_GET_DEVICES])
    {
        NPObject *windowObj = NULL;
        browser->getvalue(mainObject->npp, NPNVWindowNPObject, &windowObj);
        // it crashed here
    ....
    }
}

I created the MainNPObject instance with below method.

NPObject *createMainNPObject(NPP npp)
{
    MainNPObject *object = (MainNPObject *)browser->createobject(npp, &mainNPClass);
    object->npp = npp;

    theMainObject = object;

    return (NPObject *)object;
}

The createMainNPObject is called in the plugin function I provided to browser.

NPError NPP_GetValue(NPP instance, NPPVariable variable, void *value)
{
    PluginObject *obj = instance->pdata;

    switch (variable) {
        case NPPVpluginCoreAnimationLayer:
            if (!obj->rootLayer)
                setupLayerHierarchy(obj);

            *(CALayer **)value = obj->rootLayer;

            return NPERR_NO_ERROR;

        case NPPVpluginScriptableNPObject:

            if (!obj->mainObject)
            {
                obj->mainObject = createMainNPObject(instance);
            }
 ....
}

And the allocate function is as below.

static NPObject *mainNPObjectAllocate(NPP npp, NPClass *class)
{
    initializeIdentifiers();

    MainNPObject *mainObject = malloc(sizeof(MainNPObject));
    mainObject->deviceManager = [[DeviceManager alloc] init];

    return (NPObject *)mainObject;
}

Definition of MainNPObject:

typedef struct
{
    NPObject *npobject;
    NPP npp;
    DeviceManager *deviceManager;
} MainNPObject;

By debugging the code, I found that the system raised an EXC_BAD_ACCESS when calling the browser->getValue and it looks like the npp pointer is invalid.

0x00007fff83f82dab  <+0019>  je     0x7fff83f82db9 <_ZN6WebKit14NetscapePlugin7fromNPPEP4_NPP+33>
0x00007fff83f82dad  <+0021>  incl   0x8(%rax)

Can someone help me out?

Thanks!

Answer 1

Hmm; not seeing anything obvious. Try adding another parameter (an int?) to your structure and set it during allocate or immediately afterwords, then later on check to see if it’s still the value you set before you call getvalue. See if your struct is somehow getting corrupt. That happened to me once when I was casting the NPObject funny in a non-obvious way.