visit_target_symbol() for derived_probes

[William Cohen]

William Cohen wrote:
> I have tried to replicate what the dwarf and mark probes do as far as 
> handling target variable ($variable) for $counter in the perfmon probes. 
>  The perfmon probe needs a read only value indicating which counter is 
> being used for that event. From what I understand discussing this with 
> Frank and examining the code here are the things that need to be done:
> 
> -allocate space for the variable
> -generate a declaration for the synthesized function
> -generate C code for the synthesized function
> -replace the $target var use with a call to the synthesized function
> 
> It appears that I am not getting the function built in the latest patch 
> that is saved in bz#909. Where exactly does the creation of the 
> synthesized function occur for the dwarf and mark probes? I seem to be 
> missing the corresponding operation. Later the code gets a seg fault in 
> symresolution_info::visit_symbol(). Thus, for the this short example:

I tracked down my problem to a missing '&' so the systemtap_session 
wasn't passed by reference to perfmon_var_expanding_copy_visitory 
constructor. It looks I have something that generates a $counter handle 
for each of the probes so the script writer doesn't need to know which 
registers are used.

-Will