Messages in this thread | | | Date | Tue, 17 Nov 2020 14:43:33 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH 13/24] perf tools: Allow mmap2 event to synthesize kernel image |
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Em Tue, Nov 17, 2020 at 04:16:51PM +0100, Jiri Olsa escreveu: > On Tue, Nov 17, 2020 at 09:44:37AM -0300, Arnaldo Carvalho de Melo wrote: > > Em Tue, Nov 17, 2020 at 12:00:42PM +0100, Jiri Olsa escreveu: > > > Allow mmap2 event to synthesize kernel image, > > > so we can synthesize kernel build id data in > > > following changes. > > > > > > It's enabled by new symbol_conf.buildid_mmap2 > > > bool, which will be switched in following > > > changes. > > > > Why make this an option? MMAP2 goes back years: > > > > 13d7a2410fa637f45 (Stephane Eranian 2013-08-21 12:10:24 +0200 904) * The MMAP2 records are an augmented version of MMAP, they add > > 13d7a2410fa637f45 (Stephane Eranian 2013-08-21 12:10:24 +0200 905) * maj, min, ino numbers to be used to uniquely identify each mapping > > > > Also we unconditionally generate MMAP2 events if the kernel supports it, > > from evsel__config(): > > > > attr->mmap = track; > > attr->mmap2 = track && !perf_missing_features.mmap2; > > > > So perhaps we should reuse that logic? I.e. use mmap2 if the kernel > > supports it? > > mmap2 itself is not a problem, the problem is the new > bit (PERF_RECORD_MISC_MMAP_BUILD_ID) that says there's > build id in mmap2.. older perf tool won't understand > that and report will crash
Is this theoretical or have you experienced it?
Would be good to tweak the perf.data reader code to not crash on unknown bits like that :-\
But by looking at machine__process_mmap2_event() I couldn't imagine how that would crash.
It would get bogus maj, min, ino, ino_generation, but probably that wouldn't make it crash.
- Arnaldo
int machine__process_mmap2_event(struct machine *machine, union perf_event *event, struct perf_sample *sample) { struct thread *thread; struct map *map; struct dso_id dso_id = { .maj = event->mmap2.maj, .min = event->mmap2.min, .ino = event->mmap2.ino, .ino_generation = event->mmap2.ino_generation, }; int ret = 0;
if (dump_trace) perf_event__fprintf_mmap2(event, stdout); if (sample->cpumode == PERF_RECORD_MISC_GUEST_KERNEL || sample->cpumode == PERF_RECORD_MISC_KERNEL) { ret = machine__process_kernel_mmap_event(machine, event); if (ret < 0) goto out_problem; return 0; } thread = machine__findnew_thread(machine, event->mmap2.pid, event->mmap2.tid); if (thread == NULL) goto out_problem;
map = map__new(machine, event->mmap2.start, event->mmap2.len, event->mmap2.pgoff, &dso_id, event->mmap2.prot, event->mmap2.flags, event->mmap2.filename, thread);
if (map == NULL) goto out_problem_map;
ret = thread__insert_map(thread, map); if (ret) goto out_problem_insert;
thread__put(thread); map__put(map); return 0;
out_problem_insert: map__put(map); out_problem_map: thread__put(thread); out_problem: dump_printf("problem processing PERF_RECORD_MMAP2, skipping event.\n"); return 0; }
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