public static Address mmap(Address address, Extent size, int prot, int flags) {
public static Address mmap(Address address, int size, int prot, int flags, int fd, long offset) {
  public static Address mmap(Address address, Extent size, int prot, int flags) {    if (VM.VerifyAssertions)      VM._assert(isPageAligned(address) && isPageMultiple(size));    return VM_SysCall.sysMMapErrno(address,size,prot,flags,-1,0);  }