[Bug runtime/10013] New: Support ENABLED sdt probe macro

["mjw at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

Currently there is no way for a user program that uses sdt.h for stap static
dynamic probes to know whether or not a probe has been enabled at runtime. This
might be beneficial when setting up probe arguments is expensive. This is an
issue for some interpreters that have to translate function names, classes or
methods to (pointers to) strings for example. They don't want to do that extra
argument setup unless the probe is enabled at that time. TCL for example uses a
facility like that. Java hotspot currently requires being started with an extra
flag that always translates all probe arguments when enabled. This causes a
performance hit and makes those probes only available in this "special mode"
which kind of defeats the purpose of "zero-impact, always on tracing".

This would also help with dtrace emulation for sdt. Currently our dtrace python
wrapper script just outputs "#define %s_ENABLED() 1" for every dtrace emulated
probe.

The ENABLED probe macro should return 1 when the associated probe is enabled
(the uprobe/mark set in the executable/library) and 0 otherwise.

-- 
           Summary: Support ENABLED sdt probe macro
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: mjw at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=10013

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