Messages in this thread | | | From | Al Grant <> | Subject | RE: Question: perf dso support for /proc/kallsyms | Date | Fri, 2 Nov 2018 14:12:28 +0000 |
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> root@debian:~/coresight_test# perf buildid-list > 0242d9154c78df1d8fe1d0512c36a236d0861a18 [kernel.kallsyms] > b8c89e8ba41a2ea486c66a50c29c60d38c34a759 /root/coresight_test/main > 26b12a9d1a54ed2b0478cb0203435b76aabab3fb /usr/lib/aarch64-linux-gnu/ld- > 2.27.so > 8fca7ed524c9469b065af83bc8a529fe72858f53 [vdso] > 25829a59e21012cfde7850b30a310cd3a58f531c > /root/coresight_test/libcstest.so > 70512527439ef76c8802a7a2a546bde6a5a6e967 /usr/lib/aarch64-linux- > gnu/libc-2.27.so > root@debian:~/coresight_test# ls > ~/.debug/\[kernel.kallsyms\]/0242d9154c78df1d8fe1d0512c36a236d0861a18/ > kallsyms
What's in that last file? I've seen it happen that the copy of kallsyms in ~/.debug has the symbol addresses as zeroes - possibly because it was created when you didn't have permissions. That's really a bug in perf, as cacheing a copy of this file with the addresses zeroed out is kind of pointless. Again, this happens on Intel too.
Then, you can give yourself permissions - but perf's already cached the file and won't update it!
If you delete it, and then rerun perf record (either as sudo or now that you've got kptr_restrict=0) you should see it reappear, with correct kernel addresses.
Perhaps nobody spotted this on Intel because perf report goes directly to /proc/kallsyms. But it would be an issue if you ran a perf report on a perf.data from an older kernel and it had to go to ~/.debug. At that point the fact that ~/.debug/[kernel.kallsyms] had zeroes would mean you couldn't symbolicate any addresses.
Al
> > > Does it all work if you run perf record as sudo? Or if you do > > > > sudo sysctl kernel.kptr_restrict=0 > > > > before you run perf record? > > Yes, tested this on Juno board with Debian rootFS and logined in with 'root' user. > I suspected the pointer permission issue so checked with below command: > > root@debian:~/coresight_test# cat /proc/sys/kernel/kptr_restrict > 0 > > Thanks, > Leo Yan IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.
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