Dummy ecall circuit

[naure]

For some testing scenarios, implement any ecall as NOP instead of trap.

Adding a basic ecall

• Ref: Dummy Circuit - Basic ECALL #369.

Usage: Modify VMState.ecall to do whatever is needed. You can also optimize DummyConfig if some operations are not needed.

Adding arbitrary ecalls

• The current idea is to implement advanced functions in software and call these functions on ECALL as a trap handler.

Safe mode

• Make sure this cannot be used in production by mistake using some assertion or some compilation feature.