From 1c756cd429d8f3da33d31f2a970284b9d5260534 Mon Sep 17 00:00:00 2001 From: Al Grant Date: Fri, 13 Nov 2020 20:38:26 +0000 Subject: [PATCH] perf inject: Fix file corruption due to event deletion "perf inject" can create corrupt files when synthesizing sample events from AUX data. This happens when in the input file, the first event (for the AUX data) has a different sample_type from the second event (generally dummy). Specifically, they differ in the bits that indicate the standard fields appended to perf records in the mmap buffer. "perf inject" deletes the first event and moves up the second event to first position. The problem is with the synthetic PERF_RECORD_MMAP (etc.) events created by "perf record". Since these are synthetic versions of events which are normally produced by the kernel, they have to have the standard fields appended as described by sample_type. "perf record" fills these in with zeroes, including the IDENTIFIER field; perf readers interpret records with zero IDENTIFIER using the descriptor for the first event in the file. Since "perf inject" changes the first event, these synthetic records are then processed with the wrong value of sample_type, and the perf reader reads bad data, reports on incorrect length records etc. Mismatching sample_types are seen with "perf record -e cs_etm//", where the AUX event has TID|TIME|CPU|IDENTIFIER and the dummy event has TID|TIME|IDENTIFIER. Perhaps they could be the same, but it isn't normally a problem if they aren't - perf has no problems reading the file. The sample_types have to agree on the position of IDENTIFIER, because that's how perf finds the right event descriptor in the first place, but they don't normally have to agree on other fields, and perf doesn't check that they do. The problem is specific to the way "perf inject" reorganizes the events and the way synthetic MMAP events are recorded with a zero identifier. A simple solution is to stop "perf inject" deleting the tracing event. Committer testing Removed the now unused 'evsel' variable, update the comment about the evsel removal not being performed anymore, and apply the patch manually as it failed with this warning: warning: Patch sent with format=flowed; space at the end of lines might be lost. Testing it with: $ perf bench internals inject-build-id # Running 'internals/inject-build-id' benchmark: Average build-id injection took: 8.543 msec (+- 0.130 msec) Average time per event: 0.838 usec (+- 0.013 usec) Average memory usage: 12717 KB (+- 9 KB) Average build-id-all injection took: 5.710 msec (+- 0.058 msec) Average time per event: 0.560 usec (+- 0.006 usec) Average memory usage: 12079 KB (+- 7 KB) $ Signed-off-by: Al Grant Acked-by: Adrian Hunter Acked-by: Namhyung Kim Cc: Alexander Shishkin Cc: Jiri Olsa Cc: Mark Rutland Cc: Peter Zijlstra LPU-Reference: b9cf5611-daae-2390-3439-6617f8f0a34b@foss.arm.com Signed-off-by: Arnaldo Carvalho de Melo --- tools/perf/builtin-inject.c | 12 +----------- 1 file changed, 1 insertion(+), 11 deletions(-) diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c index 452a75fe68e5..0462dc8db2e3 100644 --- a/tools/perf/builtin-inject.c +++ b/tools/perf/builtin-inject.c @@ -779,25 +779,15 @@ static int __cmd_inject(struct perf_inject *inject) dsos__hit_all(session); /* * The AUX areas have been removed and replaced with - * synthesized hardware events, so clear the feature flag and - * remove the evsel. + * synthesized hardware events, so clear the feature flag. */ if (inject->itrace_synth_opts.set) { - struct evsel *evsel; - perf_header__clear_feat(&session->header, HEADER_AUXTRACE); if (inject->itrace_synth_opts.last_branch || inject->itrace_synth_opts.add_last_branch) perf_header__set_feat(&session->header, HEADER_BRANCH_STACK); - evsel = perf_evlist__id2evsel_strict(session->evlist, - inject->aux_id); - if (evsel) { - pr_debug("Deleting %s\n", evsel__name(evsel)); - evlist__remove(session->evlist, evsel); - evsel__delete(evsel); - } } session->header.data_offset = output_data_offset; session->header.data_size = inject->bytes_written;