Does that even work in W^X platforms? Context for my response has that assumption, we can't simply throw it out the window, right? I think I read somewhere about making two mappings to the same physical page (one W, one X), are you referring to that? (I'd still need to know how that works as it kinda defeats the protection, the OS should prohibit that, right?)

Oh, for sure what I said wouldn't work on a W^X system. I was just pointing out that one of the most widely used JIT software uses WX pages.

What OSes prohibit that? Linux doesn't (well, I think it can with SeLinux maybe?). OpenBSD might?

The question was about OSes with hardened runtime protections. The most basic of them all is W^X. All BSDs use it, and IIRC Linux is able to enforce it as well. I'd be surprised if it isn't the default in most distros, but I guess it's not impossible. I need to go for lunch so I won't check right now.