NixOS on RISC-V

To boot the system in QEMU, first enter the development shell:

$ nix develop

Then run the boot script:

$ ./boot.sh

Use more than 1 CPU

With only 1 CPU some thigs are soo slow to work. For example, the ttyS0 device doesn't arrive on time and the login fails. Or the SSH daemon doesn't start until the third try. With -smp 32 seems to work ok.

Compressed instructions

To see if a binary has compressed instructions or not, you can use objdump:

hut% nix shell -vL nixpkgs#pkgsCross.riscv64.bintools
hut% objdump -M no-aliases -D result/u-boot | grep 'c\.' | head -5
    80200000:   822a                    c.mv    tp,a0
    80200002:   84ae                    c.mv    s1,a1
    80200018:   52c1                    c.li    t0,-16
    8020001e:   0356                    c.slli  t1,0x15
    80200024:   850a                    c.mv    a0,sp

To dump a ROM without the ELF header:

hut% objdump -b binary -m riscv:rv64 -M no-aliases -D result/u-boot.bin