return VM_SysCall.sysMMapErrno(address,size,prot,flag,fd,0);
return VM_SysCall.sysMMapErrno(address,size,prot,flag,fd,Offset.zero());
  public static Address mmapFile(Address address, Extent size, int fd, int prot) {    if (VM.VerifyAssertions)      VM._assert(isPageAligned(address) && isPageMultiple(size));    int flag = MAP_FILE | MAP_FIXED | MAP_SHARED;    return VM_SysCall.sysMMapErrno(address,size,prot,flag,fd,0);  }