Move 'h' from --isa to --priv

[chihminchao]

For some reason, the --isa string doesn't include big privilege extension and the privilege capability are specified by --priv. The convention is the same as the string in dts and match the "Subset Naming Convention" in user spec. However, the 'h', hypvervisor, extension is an exception at present. Do it need to be moved to --priv ?

[aswaterman]

I don't have an opinion yet, but I'll also offer an alternative: unify priv with isa. For example, --isa=rv64gc_sv39_h could imply M/S/U + H extension. (Sv39 implies S-mode, of course.)

The downside to this approach is that --isa=rv64gc would imply M-mode only, so we'd create a backwards incompatibility in the API (and, secondarily, ISA strings would get longer). But maybe it's desirable anyway, because it's arguably less hacky than the current scheme.

[a4lg]

:+1: for this proposal.

If (and only if) --priv and --isa should be merged (as proposed by @aswaterman), I would prefer ISA/privilege delimiter other than _ (which is already used by ISA naming conventions). How about :?

Edit: added "(and only if)" to avoid confusion a little.

[aswaterman]

We should not invent a new convention for Spike. We need to standardize this naming at RVI then adopt that convention.

Using a colon is really no different than the existing scheme, IMO: the problem is that it’s nonstandard.

[a4lg]

@aswaterman I agree that (it's just a bit better, but nothing more).