Re: pahole + BTF was: Re: [Question] bpf: about a new 'tools/bpf/bpf_dwarf2btf'

[Taeung Song]

On 07/26/2018 09:26 AM, Daniel Borkmann wrote:
> On 07/25/2018 10:11 PM, Martin KaFai Lau wrote:
> > On Thu, Jul 26, 2018 at 04:21:31AM +0900, Taeung Song wrote:
> > > On 07/26/2018 03:27 AM, Taeung Song wrote:
> > > > On 07/26/2018 02:52 AM, Arnaldo Carvalho de Melo wrote:
> > > > > Em Thu, Jul 26, 2018 at 02:23:32AM +0900, Taeung Song escreveu:
> > > > > > Hi,
> > > > > >
> > > > > > Building bpf programs with .BTF section,
> > > > > > I thought it'd be better to convert dwarf info to .BTF by
> > > > > > a new tool such as 'tools/bpf/bpf_dwarf2btf' instead of pahole
> > > > > > in the future.
> > > > > > Currently for bpf binary that have .BTF section,
> > > > > > we need to use pahole from https://github.com/iamkafai/pahole/tree/btf
> > > > > > with the command line such as "pahole -J bpf_prog.o".
> > > > > > I think it is great but if implementing new 'bpf_dwarf2btf'
> > > > > > (dwarf parsing + btf encoder code written by Martin KaFai Lau on
> > > > > > the pahole project i.e. btf.h, btf_encoder.c, btf_encoder.h,
> > > > > > libbtf.c, libbtf.h),
> > > > > > BPF developers would more easily use functionalities based on BTF.
> > > > >
> > > > > What would be easier exactly? Not having to install a package but build
> > > > > it from the kernel sources?
> > > > >
> > > > > Many kernel developers already have pahole installed for other uses, so
> > > > > no need to install anything.
> > > >
> > > > Understood, but I think there are many non-kernel developers
> > > > developing BPF programs and they mightn't have or use pahole.
> > > >
> > > > So, if providing the 'dwarf2btf' feature on tools/bpf or tools/bpf/bpftool,
> > > > non-kernel developers can also more easily build bpf prog with .BPF, no ?
> > Some quick thoughts,
> > IMO, I suspect if it is in the distro's pahole package,  it should be easy
> > enough for kernel and non kernel developer to install.
> > BTF usage is still evolving,  we might re-evaluate going forward but at this
> > point I think leveraging pahole's existing capability is a good option.
>
> Agree, if there will be a future use-case where pahole might not be well-fitting,
> we could add it to bpftool then so I wouldn't rule it out, but for the functionality
> right now it seems good to reuse it. Presumably BPF developers have it installed
> anyway to inspect struct padding from BPF obj files.
>
> Thanks,
> Daniel

OK, I got it, thanks for answering my question so detailedly

Thanks,
Taeung