I develop a game using cocos2d-x 2.1.2hotfix,
I test my game in iPod 4th, Ipad 2 and Iphone 5.
Ipod 4th and Ipad 2 works ok, but on Iphone 5 he game got black borders in both sides of the screen.
This is the code that I use in my app delegate, I get it from a old version of cocos2d-x.
CCDirector *pDirector = CCDirector::sharedDirector();
CCEGLView::sharedOpenGLView()->setDesignResolutionSize(480, 320, kResolutionExactFit);
// turn on display FPS
// set FPS. the default value is 1.0/60 if you don't call this
pDirector->setAnimationInterval(1.0 / 60);
// create a scene. it's an autorelease object
CCScene *pScene = MenuScene::scene();