Re: [Bpf] IETF BPF working group draft charter

[David Vernet <void@manifault.com>]

On Tue, May 23, 2023 at 12:15:35PM -0500, David Vernet wrote:
> On Tue, May 23, 2023 at 04:50:42PM +0000, Dave Thaler wrote:
> > > -----Original Message-----
> > > From: David Vernet <void@manifault.com>
> > > Sent: Tuesday, May 23, 2023 9:32 AM
> > > To: Dave Thaler <dthaler@microsoft.com>
> > > Cc: Jose E. Marchesi <jemarch@gnu.org>; bpf@ietf.org; bpf
> > > <bpf@vger.kernel.org>; Erik Kline <ek.ietf@gmail.com>; Suresh Krishnan
> > > (sureshk) <sureshk@cisco.com>; Christoph Hellwig <hch@infradead.org>;
> > > Alexei Starovoitov <ast@kernel.org>
> > > Subject: Re: [Bpf] IETF BPF working group draft charter
> > > 
> > > On Thu, May 18, 2023 at 07:42:11PM +0000, Dave Thaler wrote:
> > > > Jose E. Marchesi <jemarch@gnu.org> wrote:
> > > > > I would think that the way the x86_64, aarch64, risc-v, sparc, mips,
> > > > > powerpc architectures, along with their variants, handle their ELF
> > > > > extensions and psABI, ensures interoperability good enough for the
> > > problem at hand, but ok.
> > > > > I'm definitely not an expert in these matters.
> > > >
> > > > I am not familiar enough with those to make any comment about that.
> > > 
> > > Hi Dave,
> > > 
> > > Taking a step back here, perhaps we need to think about all of this more
> > > generically as "ABI", rather than ELF "extensions", "bindings", etc.  In my
> > > opinion this would include, at a minimum, the following items from the current
> > > proposed WG charter:
> > > 
> > > * the eBPF bindings for the ELF executable file format,
> > > 
> > > * the platform support ABI, including calling convention, linker
> > >   requirements, and relocations,
> > > 
> > > As far as I know (please correct me if I'm wrong), there isn't really a precedence
> > > for standardizing ABIs like this. For example, x86 calling conventions are not
> > > standardized.  Solaris, Linux, FreeBSD, macOS, etc all follow the System V
> > > AMD64 ABI, but Microsoft of course does not. As Jose pointed out, such
> > > standards extensions do not exist for psABI ELF extensions for various
> > > architectures either.
> > > 
> > > While it may be that we do end up needing to standardize these ABIs for BPF,
> > > I'm beginning to think that we should just remove them from the current WG
> > > charter, and consider standardizing them at a later time if it's clear that it's
> > > actually necessary. I think this is especially true given that we don't seem to be
> > > getting any closer to having consensus, and that we're very short on time given
> > > that Erik is going to be proposing the charter to the rest of the ADs in just two
> > > days on 5/25.
> > > 
> > > Thanks,
> > > David
> > 
> > I can tell you it's very important to those who work on the ebpf-for-windows project that the ELF format is common between Linux and Windows so that tools like
> > llvm-objdump and bpftool and other BPF-specific ELF parsing tools work for both
> > Linux and Windows.   We don't want Windows to diverge.
> 
> Be that as it may, as I said before, to my knowledge there's no
> precedence at all for standardizing ABI like this. Is there a reason
> that you think Windows would diverge if we didn't standardize the ABI?
> 
> I realize that I'm essentially saying, "Hey, pretend there's a standard
> and don't diverge", but if that's what the entire rest of the industry
> has done up until this point with all other psABIs, then it seems like a
> reasonable expectation.
> 
> > As such, I feel strongly that it is a requirement to be standardized right away.
> 
> I have to respectfully disagree. I think there are much bigger fish to
> fry, such as standardizing the ISA. Unless we really have a good reason
> for diverging from industry norms, standardizing on ABI now feels to me
> like we're putting the cart before the horse.

Hi Dave et al,

FYI, I just sent out a GitHub PR to remove these lines from the proposed
WG charter: https://github.com/ekline/bpf/pull/5/files. I thought it was
prudent to go ahead and open the PR now given how close we are to the
5/25 meeting, and that we don't seem to be any closer to getting
consensus here.

We can (and should) continue the discussion here, but my two cents is
that unless there's a strong reason to keep ABI standardization within
scope of the WG, that it makes sense to remove these bullets.

That said, if the discussion dies down and/or doesn't continue, IMHO it
would be prudent to merge the PR. I don't think our default position
should be to deviate from well-established industry-wide precedence,
with the onus being on those advocating for following industry norms to
prove that we don't need to discuss it. Again, I may be missing some
important context here, so apologies if that's the case.

Thanks,
David

> Just to be very clear: I could be totally wrong here, and it could be
> very important to deviate from industry norms and standardize ABI as
> part of the initial WG charter. However, IMHO, a positive claim like
> that needs to come with clear substantiation. The reality is that
> deviating from industry norms and standardizing on ABI will have its own
> costs and consequences.
> 
> > Hence I would not want this removed from the charter unless there's an effort
> > to do it somewhere else right away, which would seem to increase the coordination
> > burden.