[bwasti]

You can just try the instructions with an off-the-shelf assembler. They're not supported.

[saagarjha]

Unless you have to toggle an MSR, of course…

[andy_ppp]

I’m kind of interested about what happens if you throw random opcodes at processors now!

[aw1621107]

You might be interested in sandsifter [0], which does precisely that!

[0]: https://github.com/xoreaxeaxeax/sandsifter

[dirtypersian]

I would guess the processor would just cause an exception/interrupt and it would just call an OS level exception/interrupt handler which would probably tell the user what the exception/interrupt was that occured; in this case an unsupported instruction.

[nicoburns]

I believe most processors have undocumented opcodes. Often used for internal debugging or similar.

[grishka]

Your program will crash with SIGILL.