Re: [PATCH dwarves v2] btf: Add support for the floating-point types

[Ilya Leoshkevich <iii@linux.ibm.com>]

On Wed, 2021-03-10 at 10:37 -0300, Arnaldo Carvalho de Melo wrote:
> Em Tue, Mar 09, 2021 at 08:14:50PM -0800, Andrii Nakryiko escreveu:
> > On Tue, Mar 9, 2021 at 1:57 PM Ilya Leoshkevich <iii@linux.ibm.com>
> > wrote:
> > > On Tue, 2021-03-09 at 13:37 -0800, Andrii Nakryiko wrote:
> > > > On Tue, Mar 9, 2021 at 3:48 AM Arnaldo Carvalho de Melo
> > > > <acme@kernel.org> wrote:
> > > > > Em Tue, Mar 09, 2021 at 12:59:13AM +0100, Ilya Leoshkevich
> > > > > escreveu:
> > > > TBH, I think it's not exactly right to call out libbpf version
> > > > here.  It's BTF "version" (if we had such a thing) that
> > > > determines
> > > > the set of supported BTF kinds. There could be other libraries
> > > > that might want to parse BTF. So I don't know what this should
> > > > be
> > > > called, but libbpf_compat is probably a wrong name for it.
> 
> > > BTF version seems to exist: btf_header.version. Should we maybe
> > > bump
> > > this?
>  
> > That seems excessive. If the kernel doesn't use FLOATs, then no one
> > would even notice a difference. While if we bump this version, then
> > everything will automatically become incompatible.
> 
> > > > If we do want to teach pahole to not emit some parts of BTF, it
> > > > should
> > > > probably be a set of BPF features, not some arbitrary library
> > > > versions.
> 
> > > I thought about just adding --btf-allow-floats, but if new
> > > features
> > > will be added in the future, the list of options will become
> > > unwieldy.
> > > So I thought it would be good to settle for something that
> > > increases
> > > monotonically.
>  
> > BTF_KIND_FLOAT is the first extension in a long while. I'd worry
> > about
> > the proliferation of new options when we actually see some proof of
> > that being a problem in practice.
> 
> I tend to agree, Ilya, can you rework the patch in that direction?
> Something like --encode-btf-kind-float that starts disabled or other
> suitable name?
> 
> - Arnaldo

Sure, I'm actually testing v3 that does this right now. So far I went
with simply --btf_float, but I'll change it to the more explicit 
--encode_btf_kind_float.