runtime library wrapper for program counter

[Vara Prasad]

William Cohen wrote:

> I like the wrapper for the return address in the systemtap runtime 
> libraries. Could there be a similar wrapper for the program 
> counter/instruction pointer?  There are three possible uses for it:
>
> 1) It would be use in the case where the same systemtap 
> instrumentation code is used to multiple points.  Allow the 
> instrumentation code to determine which probe fired.
>
> 2) Tracking destinations of calls. Have a post_handler instrumetation 
> look at the program counter to track the destination of indirect calls.
>
> 3) Tracking destination of jumps. For simple condition branch it would 
> probably be easier just to instrument the target and the fall through. 
> However for indirect jumps using jump tables, e.g. switch case, the 
> same post_handler as for destinations of calls could be done. Have a 
> probe that fires after executing the instruction.
>
> -Will
>

I like the PC/IP wrapper idea.

I also like the idea of wrapper function for process credentials. This 
call gives
process credentials like PID, PPID, UID, EUID, GID all filled into a 
structure.
This information will be useful filtering what probes get fired for 
which process like
process this probe only for my process kind of filter.

Another wrapper similarly would be print the call stack. For now we can 
limit to
kernel stack but in the future similar functions could exist for user 
stack and full stack.

bye,
Vara Prasad