o BBL (Berkeley Boot Loader) provides no initial page tables
  anymore allowing us to choose VM, to build page tables manually
  and enable MMU in S-mode.
o SBI interface changed.
o GENERIC kernel.
  FDT is now chosen standard for RISC-V hardware description.
  DTB is now provided by Spike (golden model simulator). This
  allows us to introduce GENERIC kernel. However, description
  for console and timer devices is not provided in DTB, so move
  these devices temporary to nexus bus.
o Supervisor can't access userspace by default. Solution is to
  set SUM (permit Supervisor User Memory access) bit in sstatus
  register.
o Compressed extension is now turned on by default.
o External GCC 7.1 compiler used.
o _gp renamed to __global_pointer$
o Compiler -march= string is now in use allowing us to choose
  required extensions (compressed, FPU, atomic, etc).