Apple's latest CPUs, the M5 and the A19, have memory tagging.

Probably impractical for most server workloads (so not an alternative to Solaris on SPARC) but worth mentioning.

Does OpenBSD not do that? That feels like something OpenBSD could do, given their near paranoid level of exploit reduction and theos hardon for SPARC

Maybe, why use it on Oracle's hardware?

By the way Linux does it, but then again Oracle has its own distro.

So wait, sparc solaris is the only production unix with hardware memory tagging but also linux has it? Are we talking strict SUS compliant systems (current or former because for some reason solaris is no longer listed as such despite ostensibly still being compliant unless the SRUs have seriously FUBARed some things) or unices in general? because I'd argue anyone running SUS compliant systems out of anything other than their choice happening to be compliant is arguably even more niche than running AIX or Solaris for anything else

We are talking about SPARC ADI, still sold by Oracle and Fujistsu.

https://www.oracle.com/servers/sparc

Linux while not being UNIX, does support it as Oracle upstreamed SPARC ADI support during the brief time they had Oracle Linux support for SPARC.

https://docs.kernel.org/arch/sparc/adi.html

Now why someone would use unsupported OpenBSD on SPARC for the kinds of clients that pay for this stuff, beats me.

Assuming it does even support SPARC ADI.

Ohh ok I see.

Why would someone use unsupported OpenBSD on SPARC for the clients that pay for it? Probably the same reason so many servers run on Rocky or Alma instead of RHEL, money. Perhaps they bought the hardware without the support contract for Solaris, or they don't want to keep paying for it