[DTrace-devel] unaddable kprobes

[Eugene Loh]

I guess one way to do kprobes is go to /sys/kernel/debug/tracing, read 
through available_filter_functions, and then write whichever probes you 
want to kprobe_events.  The problem is that not every probe in 
available_filter_functions can be added.  (I do not know why.)  Some of 
these unaddable probes have names like *.constprop.*, *.isra.*, 
*.part.*, but some have names that do not look very special.  When you 
try to "echo $name >> kprobe_events", the command fails.

What this means for us is that if we populate fbt probes based on 
available_filter_functions, then "fbt:vmlinux::entry" will fail. So 
there are a variety of options:

*)  If we try to add a probe and it fails, keep going anyhow.

*)  When we populate fbt probes, check to make sure they can be added.  
(This turns fbt populate from about a second to several minutes.)

*)  See if we can figure out which probes are not addable.

Suggestions?