[pgeorgi]

Extensions are fair game, of course. As is not buying chips with closed extensions.

But designing the hooks for anti-user binary blobs into the ISA just encourages misbehavior as soon as they can get away with it.

RISC-V code in privileged and protected pockets of the systems is so much easier to design, maintain and update than ISA extensions that I consider that the bigger problem due to its future ubiquity.

[rwmj]

The machine mode is there for a very good reasons of microarchitecture design scalability, allowing the same machine model to be presented to the operating system with everything from tiny designs to everything-in-hardware. In all existing designs it is open source. It's quite reasonable to have this explicit layer, since in many other cases it has been hidden away (think: Transmeta, or many x86 emulators).