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Wed, 25 Jul 2018 23:04:44 -0700 (PDT) Subject: Re: pahole + BTF was: Re: [Question] bpf: about a new 'tools/bpf/bpf_dwarf2btf' To: Daniel Borkmann , Martin KaFai Lau , Arnaldo Carvalho de Melo Cc: Alexei Starovoitov , netdev@vger.kernel.org, Thomas Girard , Martin Cermak , linux-kernel@vger.kernel.org, acme@kernel.org References: <47cfb90e-a9f4-8127-2b89-0e20d9fda2f0@gmail.com> <20180725175231.GA2121@redhat.com> <35663517-26e1-c2a2-1554-5dd90be2747f@gmail.com> <592c6325-23d0-771b-cc28-6a66842a1265@gmail.com> <20180725201122.h7ostqw3qtfvz7sn@kafai-mbp.dhcp.thefacebook.com> <96728b5e-8e41-a1df-be63-becbd9606307@iogearbox.net> From: Taeung Song Message-ID: Date: Thu, 26 Jul 2018 15:04:37 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <96728b5e-8e41-a1df-be63-becbd9606307@iogearbox.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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