OpenBSD malloc gist

gistfile1.txt

     Allocation of a zero size object returns a pointer to a zero size object.
     This zero size object is access protected, so any access to it will
     generate an exception (SIGSEGV).  Many zero-sized objects can be placed
     consecutively in shared protected pages.  The minimum size of the
     protection on each object is suitably aligned and sized as previously
     stated, but the protection may extend further depending on where in a
     protected zone the object lands.