netdev - Re: [PATCH 00/14] bpf: Add trampoline and dispatcher to /proc/kallsyms

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Date:   Mon, 10 Feb 2020 17:17:51 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Björn Töpel <bjorn.topel@...il.com>
Cc:     Jiri Olsa <jolsa@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Andrii Nakryiko <andriin@...com>, Yonghong Song <yhs@...com>,
        Song Liu <songliubraving@...com>,
        Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...hat.com>,
        Björn Töpel <bjorn.topel@...el.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>
Subject: Re: [PATCH 00/14] bpf: Add trampoline and dispatcher to
 /proc/kallsyms

On Mon, Feb 10, 2020 at 04:51:08PM +0100, Björn Töpel wrote:
> On Sat, 8 Feb 2020 at 16:42, Jiri Olsa <jolsa@...nel.org> wrote:
> >
> > hi,
> > this patchset adds trampoline and dispatcher objects
> > to be visible in /proc/kallsyms. The last patch also
> > adds sorting for all bpf objects in /proc/kallsyms.
> >
> 
> Thanks for working on this!
> 
> I'm probably missing something with my perf setup; I've applied your
> patches, and everything seem to work fine from an kallsyms
> perspective:
> 
> # grep bpf_dispatcher_xdp /proc/kallsyms
> ...
> ffffffffc0511000 t bpf_dispatcher_xdp   [bpf]
> 
> However, when I run
> # perf top
> 
> I still see the undecorated one:
> 0.90%  [unknown]                  [k] 0xffffffffc0511037
> 
> Any ideas?

yea strange.. it should be picked up from /proc/kallsyms as
fallback if there's no other source, I'll check on that
(might be the problem with perf depending on address going
only higher in /proc/kallsyms, while bpf symbols are at the
end and start over from the lowest bpf address)

anyway, in perf we enumerate bpf_progs via the perf events
PERF_BPF_EVENT_PROG_LOAD,PERF_BPF_EVENT_PROG_UNLOAD interface
together with PERF_RECORD_KSYMBOL_TYPE_BPF events

we might need to add something like:
  PERF_RECORD_KSYMBOL_TYPE_BPF_TRAMPOLINE
  PERF_RECORD_KSYMBOL_TYPE_BPF_DISPATCHER

to notify about the area, I'll check on that

however the /proc/kallsyms fallback should work in any
case.. thanks for report ;-)

jirka