loop-2{f,g} failures

[Joern Rennecke]

> Can anyone briefly comment on these failures?  Are these known to be
> fragile? In all the mmap voodoo in those test cases, have we perhaps
> introduced a dependence on library/mmap/vm behaviour?

The bug can only be shown if it is possible to obtain a piece of
memory where the sign of the address changes from positive to negative.

These tests only try the mmap approach; it is also possible to get such
memory in automatic arrays on the stack, but that needs root privileges to
raise the stack limit considerably.