Re: Hashtable

[fche at redhat dot com (Frank Ch. Eigler)]

arkady.miasnikov wrote:


> I am trying to implement full bypass of the code generated by the
> SystemTap in some special cases. [...]

OK, interesting.


> My goal is to be able to write code like this:
> probe syscall.dup2
> {   /* bypass */  /* arg: oldfd */
>     printk(KERN_ALERT "tid=%d oldfd=%d\n", current->pid, l->l_oldfd);
> // Unmanaged C code
> }

So like an embedded-C probe handler?


> [...]  When generating the code I add the relevant dwarf_tvar_get_
> calls and initialize "local" variables in the context
> structure. Because the probes I am targeting are very short and simple
> and do not involve nested calls I shortcut lot of variables copying.

How much more efficient can this get, beyond

    function foo (l) %{
        STAP_PRINTF ("tid=%d oldfd=%d\n", current->pid, STAP_ARG_l); 
    %}
    probe syscall.dup2 { foo ($oldfd) }

?  Which parts of the latter can we elide?  Could we improve the
translator so that this elision can be done for general systemtap
scripts, not just your special case?


- FChE