Re: enable INVARIANT_SUPPORT in GENERIC in release builds

On Tue, Apr 16, 2024 at 8:35 PM Colin Percival <cperciva@tarsnap.com> wrote:

> 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.
>

I thought it had no overhead (despite the comments saying it does). It
only increases runtime from what I can see if INVARIANTS or WITNESS
are defined.


> > 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
>

I think that it just exports more functions, so that's something that could
be exported.

Warner