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

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Message-ID: <35663517-26e1-c2a2-1554-5dd90be2747f@gmail.com>
Date:   Thu, 26 Jul 2018 03:27:01 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>, netdev@...r.kernel.org,
        Thomas Girard <thomas.g.girard@...e.fr>,
        Martin Cermak <mcermak@...hat.com>,
        linux-kernel@...r.kernel.org, acme@...nel.org
Subject: Re: pahole + BTF was: Re: [Question] bpf: about a new
 'tools/bpf/bpf_dwarf2btf'

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 ?

> BTW, Daniel, I just pushed to pahole's main repository at:
> 
>    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.. :'(