rv32imc Lockstep Mismatches

[jordancarlin]

• Wally bugs
  • Illegal instructions don’t trap
• Imperas configuration issues or bugs
  • mstatus.SUM not read-only zero when SATP read only zero
    • The SUM bit should be read-only 0 when SATP is read-only 0. I've set --override cpu/Sv_modes=1, which should restrict virtual memory to bare mode only and therefore disable this bit.
• Other bugs
  • csrrs x5,satp,x0 is causing an illegal instruction exception on Wally and not on Imperas. Further investigation still needed to determine correct behavior.