Messages in this thread Patch in this message | | | Date | Wed, 15 Mar 2023 22:18:25 -0700 | From | Namhyung Kim <> | Subject | Re: [PATCH 02/10] perf bpf filter: Implement event sample filtering |
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On Wed, Mar 15, 2023 at 05:12:44PM -0300, Arnaldo Carvalho de Melo wrote: > Em Wed, Mar 15, 2023 at 09:51:03AM -0700, Namhyung Kim escreveu: > > On Wed, Mar 15, 2023 at 9:39 AM Arnaldo Carvalho de Melo > > <acme@kernel.org> wrote: > > > > > > Em Wed, Mar 15, 2023 at 01:24:37PM -0300, Arnaldo Carvalho de Melo escreveu: > > > > Em Tue, Mar 14, 2023 at 04:42:29PM -0700, Namhyung Kim escreveu: > > > > > The BPF program will be attached to a perf_event and be triggered when > > > > > it overflows. It'd iterate the filters map and compare the sample > > > > > value according to the expression. If any of them fails, the sample > > > > > would be dropped. > > > > > > > > > > Also it needs to have the corresponding sample data for the expression > > > > > so it compares data->sample_flags with the given value. To access the > > > > > sample data, it uses the bpf_cast_to_kern_ctx() kfunc which was added > > > > > in v6.2 kernel. > > > > > > > > > > Acked-by: Jiri Olsa <jolsa@kernel.org> > > > > > Signed-off-by: Namhyung Kim <namhyung@kernel.org> > > > > > > > > > > > > I'm noticing this while building on a debian:11 container: > > > > > > > > GENSKEL /tmp/build/perf/util/bpf_skel/bperf_leader.skel.h > > > > GENSKEL /tmp/build/perf/util/bpf_skel/bperf_follower.skel.h > > > > GENSKEL /tmp/build/perf/util/bpf_skel/func_latency.skel.h > > > > GENSKEL /tmp/build/perf/util/bpf_skel/bpf_prog_profiler.skel.h > > > > GENSKEL /tmp/build/perf/util/bpf_skel/kwork_trace.skel.h > > > > GENSKEL /tmp/build/perf/util/bpf_skel/sample_filter.skel.h > > > > libbpf: failed to find BTF for extern 'bpf_cast_to_kern_ctx' [21] section: -2 > > > > Error: failed to open BPF object file: No such file or directory > > > > make[2]: *** [Makefile.perf:1085: /tmp/build/perf/util/bpf_skel/sample_filter.skel.h] Error 254 > > > > make[2]: *** Deleting file '/tmp/build/perf/util/bpf_skel/sample_filter.skel.h' > > > > make[2]: *** Waiting for unfinished jobs.... > > > > make[1]: *** [Makefile.perf:236: sub-make] Error 2 > > > > make: *** [Makefile:70: all] Error 2 > > > > make: Leaving directory '/git/perf-6.3.0-rc1/tools/perf' > > > > + exit 1 > > > > [perfbuilder@five 11]$ > > > > > > Same thing on debian:10 > > > > Hmm.. I thought extern symbols with__ksym are runtime > > dependencies and it should build on old kernels too. > > > > BPF folks, any suggestions? > > Fedora 33 also fails, see below, but these work:
Maybe I can declare it as a weak symbol. How about this?
Thanks, Namhyung
---8<---
diff --git a/tools/perf/util/bpf_skel/sample_filter.bpf.c b/tools/perf/util/bpf_skel/sample_filter.bpf.c index 57e3c67d6d37..52cbdd1765cd 100644 --- a/tools/perf/util/bpf_skel/sample_filter.bpf.c +++ b/tools/perf/util/bpf_skel/sample_filter.bpf.c @@ -17,7 +17,7 @@ struct filters {
int dropped;
-void *bpf_cast_to_kern_ctx(void *) __ksym; +void *bpf_cast_to_kern_ctx(void *) __ksym __weak;
/* new kernel perf_sample_data definition */ struct perf_sample_data___new { @@ -118,6 +118,10 @@ int perf_sample_filter(void *ctx) int group_result = 0; int i;
+ /* no kernel context support, no filtering */ + if (!bpf_cast_to_kern_ctx) + return 1; + kctx = bpf_cast_to_kern_ctx(ctx);
for (i = 0; i < MAX_FILTERS; i++) {
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