Re: enable INVARIANT_SUPPORT in GENERIC in release builds

On 4/16/24 14:00, Lexi Winter wrote:
> currently release version of GENERIC (or GENERIC-NODEBUG in main) does
> not have INVARIANT_SUPPORT enabled.
> 
> unfortunately, the presence or absense of this option breaks the KABI
> because, as i understand it, modules built with INVARIANTS won't load on
> a kernel without INVARIANT_SUPPORT.
> 
> is there a reason INVARIANT_SUPPORT can't just be enabled by default?

I think while it had much lower overhead than INVARIANTS, there was still
a significant overhead cost at least in the early days.  Maybe that's no
longer the case.

> this would remove one roadblock to separating kernel modules from the
> kernel config in both pkgbase and ports, because there would be no need
> to build a KABI-incompatible kernel just to build a single module with
> INVARIANTS.

If the overhead cost of INVARIANT_SUPPORT is no longer relevant, I'd be
fine with including it in stable/15.  Of course we can't turn it on for
stable/1[34] for the ABI reasons you just mentioned.

-- 
Colin Percival
FreeBSD Release Engineering Lead & EC2 platform maintainer
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid