linux-kernel - Re: [PATCH v9 perf,bpf 09/15] perf, bpf: save btf information as headers to perf.data

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Date:   Fri, 15 Mar 2019 19:31:45 +0000
From:   Song Liu <songliubraving@...com>
To:     Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
CC:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        "Jiri Olsa" <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
        "sdf@...ichev.me" <sdf@...ichev.me>
Subject: Re: [PATCH v9 perf,bpf 09/15] perf, bpf: save btf information as
 headers to perf.data

Sorry for replying from the phone.

Sent from my iPhone

> On Mar 15, 2019, at 12:26 PM, Arnaldo Carvalho de Melo <arnaldo.melo@...il.com> wrote:
> 
> Em Fri, Mar 15, 2019 at 04:06:51PM -0300, Arnaldo Carvalho de Melo escreveu:
>> And yes, there are BPF programs with BTF information associated:
> 
>> [root@...co perf]# bpftool map dump pids_filtered
>> [{
>>        "key": 2592,
>>        "value": true
>>    },{
>>        "key": 20511,
>>        "value": true
>>    }
>> ]
>> [root@...co perf]#
> 
>> I.e. bpftool can find the BTF info and thus is able to show the
>> 'pids_filtered' map keys and values pretty printed, not just as hex raw
>> data.
> 
>> I'm trying to find out why 'bpftool map dump' finds the BTF info while
>> perf_event__synthesize_one_bpf_prog() doesn't.
> 
> Humm, the BTF info above is for BPF _maps_ not for _programs_, I think
> you haven't added BTF info for maps in the perf.data header, right?
> 
> - Arnaldo

That’s right. We iterate all BPF programs, and fetch BTF referred by the programs.

Thanks,
Song