Hi Mark:

 all the specs will have unique extension names. it is also possible to have rollup extension names like we have for crypto like Zk.

 I suggest we make the options match the extension names and if needed request a roll up extension name.

 ultimately we'd like users to use the profile names to select the whole set we know work together coupled with discovery as appropriate for native compiles. cross compiles will need more arguments if the target is different than the source system.

It sounds like we can expect all privilege stuff like machine-level
ISA, supervisor ISA will become several extensions at privilege spec
1.12,
and then those extensions can be controlled by profile and arch string.

For native compilation, I suppose there is no doubt we should use the
discover mechanism for that.
For cross compilation, ideally it can be covered by profile, but I am
concerned about backward compatibility,
existing RISC-V platforms are still using older privilege spec (<=
1.12), and didn't have the concept of profile yet,
so I think we should have an option for those users.

I guess this option might become less useful when we all transfer to
the world with the profile, but still useful
when we cross compile for the older RISC-V platform.