Re: Question about extensions not mentioned in profiles
On Thu, Apr 6, 2023 at 3:29 PM David Weaver <david.weaver@...> wrote:
Krste, in this past week's CCM meeting, explained that the RVA profiles strongly suggest to trap unimplemented opcodes since they can't require that behavior - because that would prevent designs compatible with a future profile from still being compatible with a current profile. In other words, for the opcodes used by a new arch extension in that future profile, they would be required to be trapped in an implementation compatible with a current profile. Any given implementation can't simultaneously have both the old behavior and the new behavior for the same opcodes, and hence can't be compatible with both profiles.
To be able to mandate in RVA profiles that all unimplemented opcodes must be trapped, but without running into the preceding problem (so as to allow a new design implementing new extensions to be backward-compatible with a previous profile), it seems like the current wording:
Needs to change to something like this: