use with mprotect(2), but without enabling them immediately.
Extend the mremap(2) interface to allow duplicating mappings, i.e.
create a second range of virtual addresses references the same physical
pages. Duplicated mappings can have different effective protections.
Adjust PAX mprotect logic to disallow effective protections of W&X, but
allow one mapping W and another X protections. This obsoletes using
temporary files for purposes like JIT.
Adjust PAX logic for mmap(2) and mprotect(2) to fail if W&X is requested
and not silently drop the X protection.
Improve test cases to ensure correct operation of the changed
interfaces.
4f77b889d0