dtrace discuss - Apr 2009 - Missing pid probes in OS X Python processes

I cannot seem to probe any of the Python interpreter''s C functions on
OS X.

$ sudo dtrace -n ''pid$target::PyEval_EvalFrameEx:entry''  -c
python
dtrace: invalid probe specifier pid$target::PyEval_EvalFrameEx:entry: probe 
description pid59706::PyEval_EvalFrameEx:entry does not match any probes

These functions show up in ustack()s, but they do not appear to be available for
probing. There do not appear to be any probes in the "a.out" module:

$ sudo dtrace -n ''pid$target:a.out::entry''  -c python
dtrace: invalid probe specifier pid$target:a.out::entry: probe description 
pid59714:python::entry does not match any probes

I suspect that part of the reason may be that these functions are in 
Python.framework rather than a shared library or the executable itself, but I 
don''t know how to get any farther than this.

Any suggestions?

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco

On Apr 22, 2009, at 1:52 PM, Robert Kern wrote:
> I cannot seem to probe any of the Python interpreter''s C functions
> on OS X.
>
> $ sudo dtrace -n ''pid$target::PyEval_EvalFrameEx:entry'' 
-c python
> dtrace: invalid probe specifier pid 
> $target::PyEval_EvalFrameEx:entry: probe description  
> pid59706::PyEval_EvalFrameEx:entry does not match any probes
>
> These functions show up in ustack()s, but they do not appear to be  
> available for probing. There do not appear to be any probes in the  
> "a.out" module:
>
> $ sudo dtrace -n ''pid$target:a.out::entry''  -c python
> dtrace: invalid probe specifier pid$target:a.out::entry: probe  
> description pid59714:python::entry does not match any probes
>
> I suspect that part of the reason may be that these functions are in  
> Python.framework rather than a shared library or the executable  
> itself, but I don''t know how to get any farther than this.
>
> Any suggestions?
Robert,

	Python seems to have multiple files that resolve to the same name,  
specifically Python.app/Contents/MacOS/Python and Python.framework/ 
Python.

	There is a bug in the OS X dtrace that when it looks for the "Python"
module, it only finds the first one. The Python.app executable has no  
symbols,
and happens to be the first one found.

	I filed <rdar://problem/6819690> dtrace cannot create probes when  
libraries have the same name

	James M

On 2009-04-23 03:39, James McIlree wrote:
>
> On Apr 22, 2009, at 1:52 PM, Robert Kern wrote:
>
>> I cannot seem to probe any of the Python interpreter''s C
functions on
>> OS X.
>>
>> $ sudo dtrace -n
''pid$target::PyEval_EvalFrameEx:entry'' -c python
>> dtrace: invalid probe specifier pid$target::PyEval_EvalFrameEx:entry:
>> probe description pid59706::PyEval_EvalFrameEx:entry does not match
>> any probes
>>
>> These functions show up in ustack()s, but they do not appear to be
>> available for probing. There do not appear to be any probes in the
>> "a.out" module:
>>
>> $ sudo dtrace -n ''pid$target:a.out::entry'' -c python
>> dtrace: invalid probe specifier pid$target:a.out::entry: probe
>> description pid59714:python::entry does not match any probes
>>
>> I suspect that part of the reason may be that these functions are in
>> Python.framework rather than a shared library or the executable
>> itself, but I don''t know how to get any farther than this.
>>
>> Any suggestions?
>
> Robert,
>
> Python seems to have multiple files that resolve to the same name,
> specifically Python.app/Contents/MacOS/Python and Python.framework/Python.
>
> There is a bug in the OS X dtrace that when it looks for the
"Python"
> module, it only finds the first one. The Python.app executable has no
> symbols,
> and happens to be the first one found.
>
> I filed <rdar://problem/6819690> dtrace cannot create probes when
> libraries have the same name
Thank you! I can verify that when I rebuild Python to use 
PythonApp.app/Contents/MacOS/PythonApp, I can now trace pid$target:Python::entry
probes.

What do you think the timeline is for getting that dtrace fix out? Is this in 
the userland dtrace tools? I.e. could a user build their own patched dtrace with
this fix, or do they have to wait for a new 10.5.x or even 10.6 update of the 
OS? I''m wondering whether it would be worthwhile to propose the
PythonApp
workaround, or something similar, in the upstream sources.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma
  that is made terrible by our own mad attempt to interpret it as though it had
  an underlying truth."
   -- Umberto Eco