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

[Brendan Gregg - Sun Microsystems]

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().

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", @); }'

no worries,

Brendan

-- 
Brendan
[CA, USA]