[MLton] reason for mprotect with PROT_EXEC ?

[Henry Cejtin]

One  could  have  the  runtime code first check what the permissions on the C
stack memory are (I guess by  looking  at  /proc/self/maps  and  finding  the
permissions  for the piece that contains the address of a local variable) and
then setting the permissions for the signal stack to the same thing.

Mind you, the /proc/self/maps isn't going to work on other operating systems.

I actually don't know how one finds the permissions on a piece of memory that
is already allocated.