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 [off-list ref] wrote:

quoted

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