Re: Detecting the Zbb extension on riscv64

Hi Michael,

Am Sun, Jun 02, 2024 at 03:05:09PM +0200 schrieb tuexen@freebsd.org:
> > Zbb is supported by the SiFive unmatched board for example.
> just double checking:
> According to
> https://sifive.cdn.prismic.io/sifive/d0556df9-55c6-47a8-b0f2-4b1521546543_hifive-unmatched-datasheet.pdf
> the processor supports RV64GC (RV64IMAFDC). I don't see a B there.
> So does it actually support Zbb? What about Zbr?

The board is based on the SiFive FU740-C000 SoC, which uses
a quad-core U74 CPU.  Reading the [U74 Core Complex Manual],
we find that it supports the Zba and Zbb instruction set
extensions.

[U74 Core Complex Manual]: https://starfivetech.com/uploads/u74_core_complex_manual_21G1.pdf

Though on the other hand, if I actually try to execute a program
using the CTZ instruction, I get a SIGILL... what's going on here?

Yours,
Robert Clausecker

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