[Bug translator/6594] New: investigate ftrace interface

[Bug translator/6594] New: investigate ftrace interface

[fche at redhat dot com]

see git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched-devel.git
branch tracing/ftrace
functions in include/linux/ftrace.h, [...]register_ftrace_function()

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           Summary: investigate ftrace interface
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: fche at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=6594

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[Bug translator/6594] investigate ftrace interface

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2008-06-05 02:11 -------
probably needs kernel changes for:
... module-friendly ftrace registration api
... and a data (argument) passing mechanism


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[Bug translator/6594] investigate ftrace interface

[mhiramat at redhat dot com]

------- Additional Comments From mhiramat at redhat dot com  2008-06-05 02:15 -------
(In reply to comment #0)
> see git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched-devel.git

FYI, recently, Ingo changed name of his tree.

http://www.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-ftrace.git



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[Bug translator/6594] investigate ftrace interface

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2008-07-07 20:27 -------
Anonymous word-of-mouth from a colleague of the ftrace team suggests
an intention on their part to produce a module-facing interface for
the widget.  Once that exists, we can make systemtap work with it.


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             Status|NEW                         |SUSPENDED


http://sourceware.org/bugzilla/show_bug.cgi?id=6594

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[Bug translator/6594] investigate ftrace interface

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2008-07-20 18:59 -------
https://bugzilla.redhat.com/show_bug.cgi?id=454694

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[Bug translator/6594] investigate ftrace interface

[dsmith at redhat dot com]

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                 CC|                            |dsmith at redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=6594

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[Bug translator/6594] investigate ftrace interface

[mhiramat at redhat dot com]

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http://sourceware.org/bugzilla/show_bug.cgi?id=6594

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[Bug translator/6594] investigate ftrace interface

[prasad at linux dot vnet dot ibm dot com]

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http://sourceware.org/bugzilla/show_bug.cgi?id=6594

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[Bug translator/6594] investigate ftrace interface

[mhiramat at redhat dot com]

------- Additional Comments From mhiramat at redhat dot com  2008-10-02 15:27 -------
(In reply to comment #1)
> probably needs kernel changes for:
> ... module-friendly ftrace registration api

I think this should be done by simply exporting
register/unregister_ftrace_function().

> ... and a data (argument) passing mechanism

Arguments passing is hard because of mcount implementation.
It will give us just caller ip and callee ip.
So, in the first phase, might we support only $caller and $callee in
ftrace-based probe?



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[Bug translator/6594] investigate ftrace interface

[fche at redhat dot com]

------- Additional Comments From fche at redhat dot com  2008-10-02 16:56 -------
> > probably needs kernel changes for:
> > ... module-friendly ftrace registration api
> I think this should be done by simply exporting
> register/unregister_ftrace_function().

Hooking into the "dyn-ftrace" functionality seems more relevant,
since that is what we'd need to choose only subsets of kernel
functions to probe.  The register_ftrace_function widget seems
to be suited only for a separate abstract event source that traps\*all* function
entries.


> > ... and a data (argument) passing mechanism
> 
> Arguments passing is hard because of mcount implementation.
> It will give us just caller ip and callee ip.
> So, in the first phase, might we support only $caller and $callee in
> ftrace-based probe?

I was not talking about accessing contextual data registers via ftrace.
We'll have to work somewhat hard to make that work at all.  What I
was referring to was a callback void* parameter that allows us
to tell apart potentially multiple registrations -- like the kprobe*
pointer we get back from kprobe callbacks.


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