r3 0x0 0 r4 0x9 9
Thus CFSocketEnableCallBacks is being passed a NULL pointer (and, for what it's worth, the flags are kCFSocketReadCallBack and kCFSocketWriteCallBack). Why it crashes in the spinlock, I'm not sure, but I imagine it might have to do with gdb not behaving nicely with threads.
In any case, since I don't see any registers getting overwritten with either 0x41 or 0x61 (since Safari converts it to lowercase), I don't really see an overflow. It's a crash which you might want to report to Apple, but it seems like it's probably just a case of dereferencing a NULL pointer.
I think what's happening is that some handler somewhere for the URL is seeing an overly large buffer and rejects it with a NULL pointer somewhere for the socket which isn't checked for appropriately.
Thanks, David