Feature implementation between Armv8.x versions
An Armv8.x-A processor can implement any features from the next .x extension. However, it cannot implement features from any .x extension after that.
For example, a processor described as implementing Armv8.1-A:
- Must implement all the mandatory features of Armv8.0-A and Armv8.1-A.
- Is permitted to implement some features from Armv8.2-A.
- Is not permitted to implement features from Armv8.3-A, Armv8.4-A, and so on.