[devit]

No, you can of course allocate W+X pages from the OS and put multiple closures in them using a standard userspace memory allocator.

Or if the OS doesn't support W+X allocation at all, then you can have a bunch of tightly packed pregenerated trampolines in the binary.

[saagarjha]

Right, this is how Objective-C's implementation works, except it keeps around one page of trampolines and remaps that around when necessary to be able to "create" more trampolines on the fly, I believe.