[snvzz]

As you say this, I realize I can't find anywhere that it does.

I do not know why I thought it did. Possibly as U74-MC[0] supports that option.

Interestingly, I also took a look at RVA22[1], and found it requires Zbb but not the whole B.

Your /proc/cpuinfo isn't listing Z* extensions. Maybe lscpu output would be more detailed?

0. https://www.sifive.com/cores/u74-mc

1. https://github.com/riscv/riscv-profiles/blob/main/profiles.a...

[zu2_]

Oh, I was mistaken. I've verified that at least the rev instruction works (tested on clang -march=rv64imafdcb0p94).

[snvzz]

It is quite possible it implements some B instructions (like the Za or Zb extensions) but not B as a whole.

[snvzz]

Got mine.

OpenSBI says:

Boot HART Base ISA : rv64imafdcbx