Not as is, but I think OpenBSD permits you to map the same memory twice, once as W and once as X (which would be a reasonable hoop to jump through for JITs etc.

Not as is, but I think OpenBSD permits you to map the same memory twice, once as W and once as X (which would be a reasonable hoop to jump through for JITs etc., except there’s no portable way to do it). ARM64 MacOS doesn’t even permit that, and you need to use OS-specific incantations[1] that essentially prohibit two JITs coexisting in the same process. [1] https://developer.apple.com/documentation/apple-silicon/porting-just-in-time-compilers-to-apple-silicon https://developer.apple.com/documentation/apple-silicon/port...