[dtrace-discuss] Error trying to count return points in functions.

[Darren.Reed at Sun.COM]

Brendan Gregg - Sun Microsystems wrote:

>G'Day Darren,
>
>On Tue, Jul 10, 2007 at 06:46:55PM -0700, Darren.Reed at Sun.COM wrote:
>
>>Whilst trying out some D to get an insight into what is the most
>>common reason for a given function to return, I have bumped
>>into an error I don't understand.
>>
>>The first take on what I was trying to do was:
>># dtrace -n 'fbt:ip:ip_input:return{@home[arg0] = count();}'
>>
>>and all was well.  The next step was:
>># dtrace -n 'fbt:ip::return{@home[strjoin(probefunc,(string)arg0)] = 
>>count();}'
>>
>>but the output was not quite so friendly:
>>dtrace: description 'fbt:ip::return' matched 1653 probes
>>dtrace: error on enabled probe ID 1574 (ID 23867: 
>>fbt:ip:ip_loopback_src_or_dst:return): invalid address (0x30) in action 
>>#2 at DIF offset 48
>>dtrace: error on enabled probe ID 769 (ID 25479: 
>>fbt:ip:ilm_lookup_ill:return): invalid address (0x52) in action #2 at 
>>DIF offset 48
>>...
>>
>>and all is not well.  I've also tried stringof(arg0) but the result is 
>>similar.
>>
>
>Both "(string)" and "stringof()" are attempting to dereference a "char *". 
>arg0 is a uint. If you wanted to append it to the probefunc using strjoin(),
>then you can turn it into a string using lltostr().
>

Yes, the lltostr() fixes the problem.
It would be nice if dtrace knew more about types and could
say that strjoin() was getting an argument that was the wrong
type rather than the above error.

>A better way may be to make it a 2-key hash,
>
># dtrace -n 'fbt:ip::return { @[probefunc, arg0] = count(); }
>    END { printa("   %32s+%#-8x %@8d\n", @); }
>

hmmm, yes, that works too and the END{...} solves the problem of
the default output being too wide for 80 columns.

thanks,
Darren