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

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Message-ID: <bcabe9a0-df3d-d57a-92aa-63267b3b7dd5@gmail.com>
Date:   Thu, 26 Jul 2018 15:04:37 +0900
From:   Taeung Song <treeze.taeung@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>, 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'



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