Modern javascript engines (namely V8) avoid RWX, although last time I checked there's been a backslide as part of WASM implementation.

CPython also no longer appears to create RWX mappings even for ctypes, although you can of course still mmap them manually.

Wow. So V8 actually back to optimizing the entire bytecode region in one fell swoop?

I had thought that such V8 optimization were still occuring (as of Chrome Blink81/SparkPlug) during JavaScript execution of untouched bytecode as a form of overhead reduction of its startup.

https://egbert.net/blog/articles/javascript-jit-engines-time...

I don't know what V8 actually does, but one possible strategy is to have a pair of RW and RX mappings to the same physical pages (or just keep flipping permissions between the two)