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

[Taeung Song]

On 07/26/2018 03:27 AM, Taeung Song wrote:
> Hi Arnaldo,
>
> 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 ?

Or, if tools/lib/bpf/ have the 'dwarf2btf' feature,
I think BPF developers can just use bpf programs that have dwarf info
after compiling with clang '-g' and llc '-mattr=dwarfris', even though 
not using pahole.
Isn't it good way ?

> > BTW, Daniel, I just pushed to pahole's main repository at:
> >
> > ÂÂ git://git.kernel.org/pub/scm/devel/pahole/pahole.git
> >
> > with the Martin's BTF patch, so no need to pull from the github one,
> > I'll tag v1.12 and announce the release so that distro package
> > maintainers can update their packages.
> > > What do you think about this ? Do you think this is needed ?
> > > Or, already implementing something like this ?
> > > If it is needed, I want to try to make 'tools/bpf/bpf_dwarf2btf'
> > > based on the pahole code. I'd appreciate it, if you reply to this
> >
> > The way Martin took advantage of the work done a long time ago to
> > support CTF out of the same DWARF reading codebase was really cool, not
> > that much work to do, just add a new format to pahole's codebase making
> > it more useful.
>
> I got it !
>
> Thanks,
> Taeung
>
> > I was just so far overly picky with testing it and kept leaving for
> > later to have a good documentation about testing it, vacation and perf
> > maintainership duties kept making this take like forever, grumble :-\
> >
> > - Arnaldo
>
> --
> oh.. :'(