Red Hat Bugzilla – Bug 1279030
perf fails to access debug symbols for kernel modules
Last modified: 2016-07-19 15:59:03 EDT
Description of problem:
It appears that perf fails to load any symbol from loadable kernel modules, because a nonsensical path "./[modulename]" is tried.
Steps to Reproduce:
1. strace -e open perf top -e cycles --call-graph dwarf 2>files
2. grep <modulename> files
3. watch attempts to load file "[modulename]"
perf should be loading debug symbols from /usr/lib/debug/usr/lib/modules/`uname -r`/kernel/modulepath/modulename.ko.debug
Symlinking the bad module path to the right path workarounds the issue.
What version of perf?
Also, can you put a sample of the errors you are seeing here? I don't see this problem at all.
4.2.5, but I've seen this happening since I started using perf (2-3 years). I see it with "perf top" so I'm not sure what kind of samples you're asking for. Here's a screenshot of it happening http://i.imgur.com/n2CXbu8.png , and strace shows only "[iptable_raw]" was probed to read debug symbols: open("[iptable_raw]", O_RDONLY) = -1 ENOENT (No such file or directory)
Can you just attach your 'files' file that you've redirected output to? I'm still not seeing this.
Created attachment 1092393 [details]
strace output of perf
sudo strace perf top -e cycles:pp --call-graph dwarf 2>strace_perf
First instance of the faulty debug file resolution:
open("[tun]", O_RDONLY) = -1 ENOENT (No such file or directory)
Do you have the corresponding kernel debuginfo packages installed?
Also, the Fedora perf was built without xz compression support and could not read the xz compressed modules we install. It is likely worthwhile testing the 4.2.6 build once it is available.
Yes of course I do have the debuginfo package. Also as I said, symlinking the debug object file works, so it's not a problem of xz compression (the debug file is not compressed even).
Fedora 22 changed to end-of-life (EOL) status on 2016-07-19. Fedora 22 is
no longer maintained, which means that it will not receive any further
security or bug fix updates. As a result we are closing this bug.
If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
Thank you for reporting this bug and we are sorry it could not be fixed.