PROT_EXEC purity


POSIX has PROT_READ, PROT_WRITE, PROT_EXEC

In most systems, PROT_READ implies PROT_EXEC

BUT... we are permitted to do better

Needs hardware support in the MMU!

Perfect: sparc (sun4m), sparc64, alpha, hppa, (hammer in 64 bit mode)

Impossible: m68k, vax, mips

Very difficult... later work: m88k

Horrific hacks: i386, powerpc

No real overhead.  Making these changes sped up some architectures