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
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