Re: [RFC] build-many-glibcs: Add a rv64gcbv-on-rv64gc/lp64d sub-variant

[Michael Hudson-Doyle <michael.hudson@canonical.com>]

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On Wed, 17 Apr 2024 at 06:12, Palmer Dabbelt <palmer@rivosinc.com> wrote:

> On Tue, 16 Apr 2024 00:01:31 PDT (-0700), michael.hudson@canonical.com
> wrote:
> > On Tue, 16 Apr 2024 at 07:28, Palmer Dabbelt <palmer@rivosinc.com>
> wrote:
> >
> >> Unfortunately I don't think we can drop support for the other base ISAs:
> >> the distros appear to be targeting rv64gc and that's the only common
> >> base for most hardware that's out there.
> >>
> >
> > This is certainly the case for Ubuntu for now but I certainly hope that
> by
> > 26.04 we are able to be a bit more aggressive here, fwiw.
>
> That'd be awesome.  Any idea if something like this would help?


Well having the non baseline builds tested and so not having everything
explode as/when we shift the baseline would probably help, yes :-)


> I think we're all a bit worried about being stuck with a very small
> baseline and thus a bunch of vendor-specific behavior.


Yes. That would be unfortunate.


> That's certainly
> the way things are trending right now in RISC-V land, it's already super
> complicated to manage and it looks like it's going to get worse before
> it gets better.
>

I think for Ubuntu we are obviously not interested in supporting every
RISC-V core out there, we are only going to be aiming for what would be a
"cortex a" CPU in the ARM world and I think the baseline for those is
probably going to be a bit more than just rv64gc (like, we could almost
certainly just copy Google's baseline for Android).


> If we can pick up some extra testing burden now as a way to reduce
> fragmentation then it's probably a win in the long run, even if we have
> to go through a few generations of this before things calm down.  If
> you're planning on moving to something completely different, though,
> then maybe it's not worth the extra builds.
>

We certainly don't have any concrete plans beyond "we don't want to be
stuck on rv64gc forever". We also don't want to be building every package
in Ubuntu for every core either! It's obviously hard to see where things
are going but I can imagine a world where there are different baselines for
different application domains in practice (e.g. iot, routers, servers) with
different baselines in practice and it's worth building some core packages
to target those. But who knows!

Cheers,
mwh