Re: [PATCH v2 0/1] update riscv prctl for discovering V extension

Samuel Holland
2026-03-14T02:01:11Z

Hi,

On 2026-03-13 4:19 AM, Yao Zihong wrote:
> It has been a while since the last activity on this thread,
> so I would like to gently ping for comments.

There was some off-list discussion about this around this time (anyone involved
please correct me, it has been several weeks), and my understanding of the
sentiment was that:

1) These sysctl and prctl() interfaces were introduced because adding vector
state to the signal frame was technically an ABI break, due to increasing the
minimum signal stack size. The prctl() provided an escape hatch for users to run
existing software that used a smaller signal stack size. Notably, this existing
software necessarily did not use RVV, because any C runtime that supported RVV
would have enforced a larger minimum signal stack size.

2) Using these interfaces for another reason is unsupported, and anyone doing so
gets to keep both pieces. Software that was aware of RVV at compile time is not
expected to ever run with the sysctl/prctl() disabled at runtime.

3) Therefore, hwprobe() is sufficient for detecting the presence of the various
vector extensions. The case where hwprobe() says RVV is available, but its usage
traps, is considered a configuration error.

Regards,
Samuel