SuSv3 says: "The mprotect() function shall fail if:

  [EACCES]
    The prot argument specifies a protection that violates the access
    permission the process has to the underlying memory object.

  [EAGAIN]
    The prot argument specifies PROT_WRITE over a MAP_PRIVATE mapping and
    there are insufficient memory resources to reserve for locking the
    private page.

  [EINVAL]
    The addr argument is not a multiple of the page size as returned by
    sysconf().

  [ENOMEM]
    Addresses in the range [addr,addr+len) are invalid for the address
    space of a process, or specify one or more pages which are not mapped.

  [ENOMEM]
    The prot argument specifies PROT_WRITE on a MAP_PRIVATE mapping, and
    it would require more space than the system is able to supply for
    locking the private pages, if required.

  [ENOTSUP]
    The implementation does not support the combination of accesses
    requested in the prot argument."

This fixes error code of mprotect() of the ENOMEM case.