Add kern.features.cheri_purecap_kernel

[brooksdavis]

Rename misleading kern.features.cheriabi_kernel to kern.features.cheri_purecap_kernel and make clear that it's a pure-capaiblity kernel (not CheriABI which refers to userspace).

[brooksdavis]

Nothing in tree uses the old feature flag so I think it's safe to drop. Could keep it for a release instead, but we'd then need to remember to remove it.

[kwitaszczyk]

It might be worth renaming other features to match kernel config options and indicate that they refer to CHERI/Morello:

• kern.features.subobject_bounds to kern.features.cheri_subobject_bounds
• kern.features.cheri_revoke to kern.features.cheri_caprevoke
• kern.features.benchmark_abi_kernel to kern.features.morello_benchmarkabi_kernel.

That would be useful when listing features with sysctl kern.features | grep 'cheri\|morello'.

[jrtc27]

kern.features.morello_benchmarkabi_kernel

This doesn't say purecap in it. Given we have cheri_purecap_kernel, probably morello_purecap_benchmark_kernel is the best thing (with a possible _abi in there too if you want).

[jrtc27]

kern.features.cheri_caprevoke

This one is queried by bits of userspace, so an upgraded kernel would break them.

[jrtc27]

kern.features.cheri_subobject_bounds

This should say kernel in it too for the feature name?

[brooksdavis]

kern.features.cheri_caprevoke

This one is queried by bits of userspace, so an upgraded kernel would break them.

This would be mostly harmless and transient if we fixed userspace. It's used to suppress some warnings in libprocstat when the feature is missing and as well as skip some cheribsdtest tests so there would be a modest incompatibility between mismatched kernel and userspace but not critical breakage.