[Bug translator/4935] support on-the-fly probe enable/disable syntax

["fche at redhat dot com" <sourceware-bugzilla@sourceware.org>]

------- Additional Comments From fche at redhat dot com  2007-10-08 17:10 -------
> In that case, 
> ---
>  probe ALIAS=PROBEPOINT { stmt1; }
>  probe ALIAS if (expr) { stmt2; }
>  probe ALIAS { stmt3; }
> ---
> will be treated as
> ---
>  probe PROBEPOINT { if (!expr) next; stmt1; stmt2}
>  probe PROBEPOINT { stmt1; stmt3}
> ---
> Is that right?

That's right.  It wouldn't make sense to act as if the conditional
was within the probe handler block (after the prefix from aliases),
since that would require the underlying probe to still be active.

It also means that the variables in "expr" can in practice only involve
global script-level variables.  (Even pure embedded-C functions can
change their values frequently enough to make them impractical as
part of an automatic predicate.  In this sort of case, we could opt
to automatically translate the script to the "{ if (!expr) next; ... }"
form, which would run correctly but slowly.)


-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=4935

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