Comment by Arnavion

Only tangentially related, but RISC-V intentionally makes any instruction starting with 0x0000 an illegal instruction instead of a NOP, for exactly the reason to prevent NOP-sleds. The official NOPs are 0x0001 (compressed 16-bit instruction) and 0x00000013 (regular 32-bit instruction; instructions are LE so 0x13 is the first byte in memory), both equivalent to addi x0, x0, 0, though many other instructions can act as NOPs by virtue of writing to the zero register.