Defined illegal instruction

[jacob navia]

The riscv processor defines an illegal instruction (all zeroes). I do not find the mnemonic used by gas for this. As far as I remember, the x86 also has a defined illegal instruction.

I find an instruction called « unimp » . It generates something else (an attempt to write into a read only special register). Is that the « defined illegal instruction » for risk?

Thanks for any answers

Jacob