get_kprobe_functions() omits module functions

[markdrayton]

I noticed funccount and friends were unable to attach to NFS functions on my systems. E.g.:

$ sudo funccount nfs_opendir
No functions matched by pattern ^nfs_opendir$

There are two reasons for this:

1. Module functions are listed in kallsyms with an additional [module_name] column. The parsing code needs to be updated to handle the extra column (e.g. https://github.com/markdrayton/bcc/commit/9f0ab450e73ae299557ee0abfaeffa912dc57c79)

2. skip kprobe functions outside normal text section #1647 added excluding of symbols outside of [_stext, _etext]. It seems module functions are outside of this range:

$ sudo egrep '(_[es]text|nfs_opendir)' /proc/kallsyms 
ffffffff81000000 T _stext
ffffffff8196a69e T _etext
ffffffffa01f9df0 t nfs_opendir  [nfs]

I'm not sure how the second issue should be solved. @yonghong-song, any suggestions?

[yonghong-song]

Thanks for reporting. I think we can just exclude functions in init sections (__init_begin, __init_end). This should catch most of cases.
https://github.com/torvalds/linux/blob/4c3579f6cadd5eb8250a36e789e6df66f660237a/kernel/extable.c#L122

Will submit a patch soon.