Messages in this thread | | | Date | Wed, 6 Apr 2022 12:28:55 +0100 | Subject | Re: perf tool: About "perf arm64: Inject missing frames when using 'perf record --call-graph=fp'" | From | John Garry <> |
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On 06/04/2022 10:08, James Clark wrote: > > > On 05/04/2022 15:04, John Garry wrote: >> Hi Alexandre, >> >> I notice that with commit b9f6fbb3b2c2 ("perf arm64: Inject missing frames when using 'perf record --call-graph=fp'") that I get messages spewing the console when running perf record+report, as below: >> >> john@ubuntu:~/linux$sudo tools/perf/perf record -ag fio null12.fio >> john@ubuntu:~/linux$sudo tools/perf/perf report > report >> unwind: can't read reg 29 >> unwind: can't read reg 29 >> unwind: can't read reg 29 >> unwind: can't read reg 29 >> ... >> >> Do you know the possible cause? I haven't checked... > > Hi John, > > I'm going to look into this today.
Great
I expect the cause is because we only record >> the link register for this change and then do a best effort unwind to see if > we can get the return address just from that. So I don't think this is a major issue, > probably the outcome will be that I mask any of these errors just for this call > to libunwind that we added. The other main call to libunwind should still print > these errors. > > One thing that is interesting is why we didn't see this when we were testing > the patch before, and we've also found it a little bit difficult to reproduce here. > So there might be more to it than just masking the error, but I'm not sure yet. > > Either way, I don't expect that any unwinding is broken, just that it's > printing an annoying message.
Yeah, the actual ouput looks ok at a glance. I really didn't check much.
Thanks, John
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