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gh-104280: remove deprecated DTrace from docs #110571

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264 changes: 43 additions & 221 deletions Doc/howto/instrumentation.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@ domain-specific languages allowing a user to write scripts which:
- gather data from the processes of interest
- generate reports on the data

As of Python 3.6, CPython can be built with embedded "markers", also
As of Python 3.12, CPython can be built with embedded "markers", also
known as "probes", that can be observed by a DTrace or SystemTap script,
making it easier to monitor what the CPython processes on a system are
doing.
Expand Down Expand Up @@ -57,18 +57,14 @@ On macOS, you can list available DTrace probes by running a Python
process in the background and listing all probes made available by the
Python provider::

$ python3.6 -q &
$ sudo dtrace -l -P python$! # or: dtrace -l -m python3.6
$ python3.12 -q &
$ sudo dtrace -l -P python$! # or: dtrace -l -m python3.12

ID PROVIDER MODULE FUNCTION NAME
29564 python18035 python3.6 _PyEval_EvalFrameDefault function-entry
29565 python18035 python3.6 dtrace_function_entry function-entry
29566 python18035 python3.6 _PyEval_EvalFrameDefault function-return
29567 python18035 python3.6 dtrace_function_return function-return
29568 python18035 python3.6 collect gc-done
29569 python18035 python3.6 collect gc-start
29570 python18035 python3.6 _PyEval_EvalFrameDefault line
29571 python18035 python3.6 maybe_dtrace_line line
29568 python18035 python3.12 collect gc-done
29569 python18035 python3.12 collect gc-start
29570 python18035 python3.12 _PyEval_EvalFrameDefault line
29571 python18035 python3.12 maybe_dtrace_line line

On Linux, you can verify if the SystemTap static markers are present in
the built binary by seeing if it contains a ".note.stapsdt" section.
Expand All @@ -89,38 +85,38 @@ Sufficiently modern readelf can print the metadata::

$ readelf -n ./python

Displaying notes found at file offset 0x00000254 with length 0x00000020:
Owner Data size Description
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
OS: Linux, ABI: 2.6.32

Displaying notes found at file offset 0x00000274 with length 0x00000024:
Owner Data size Description
GNU 0x00000014 NT_GNU_BUILD_ID (unique build ID bitstring)
Build ID: df924a2b08a7e89f6e11251d4602022977af2670

Displaying notes found at file offset 0x002d6c30 with length 0x00000144:
Owner Data size Description
stapsdt 0x00000031 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: gc__start
Location: 0x00000000004371c3, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bf6
Arguments: -4@%ebx
stapsdt 0x00000030 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: gc__done
Location: 0x00000000004374e1, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bf8
Arguments: -8@%rax
stapsdt 0x00000045 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: function__entry
Location: 0x000000000053db6c, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6be8
Arguments: 8@%rbp 8@%r12 -4@%eax
stapsdt 0x00000046 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: function__return
Location: 0x000000000053dba8, Base: 0x0000000000630ce2, Semaphore: 0x00000000008d6bea
Arguments: 8@%rbp 8@%r12 -4@%eax
Displaying notes found in: .note.ABI-tag
Owner Data size Description
GNU 0x00000010 NT_GNU_ABI_TAG (ABI version tag)
OS: Linux, ABI: 4.4.0

Displaying notes found in: .note.stapsdt
Owner Data size Description
stapsdt 0x00000040 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: import__find__load__start
Location: 0x000000000024bb68, Base: 0x000000000041475d, Semaphore: 0x000000000059fa02
Arguments: 8@%rax
stapsdt 0x00000047 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: import__find__load__done
Location: 0x000000000024bb80, Base: 0x000000000041475d, Semaphore: 0x000000000059fa04
Arguments: 8@%rax -4@%edx
stapsdt 0x00000033 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: audit
Location: 0x0000000000283075, Base: 0x000000000041475d, Semaphore: 0x000000000059fa06
Arguments: 8@%rbp 8@%rbx
stapsdt 0x00000036 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: gc__start
Location: 0x000000000029e7ad, Base: 0x000000000041475d, Semaphore: 0x000000000059f9fe
Arguments: -4@120(%rsp)
stapsdt 0x00000030 NT_STAPSDT (SystemTap probe descriptors)
Provider: python
Name: gc__done
Location: 0x000000000029edd4, Base: 0x000000000041475d, Semaphore: 0x000000000059fa00
Arguments: -8@%rbx

The above metadata contains information for SystemTap describing how it
can patch strategically placed machine code instructions to enable the
Expand Down Expand Up @@ -171,7 +167,7 @@ invocations are not going to be listed:

It can be invoked like this::

$ sudo dtrace -q -s call_stack.d -c "python3.6 script.py"
$ sudo dtrace -q -s call_stack.d -c "python3.12 script.py"

The output looks like this:

Expand Down Expand Up @@ -204,108 +200,26 @@ The low-level way to use the SystemTap integration is to use the static
markers directly. This requires you to explicitly state the binary file
containing them.

For example, this SystemTap script can be used to show the call/return
hierarchy of a Python script:

.. code-block:: none

probe process("python").mark("function__entry") {
filename = user_string($arg1);
funcname = user_string($arg2);
lineno = $arg3;

printf("%s => %s in %s:%d\\n",
thread_indent(1), funcname, filename, lineno);
}

probe process("python").mark("function__return") {
filename = user_string($arg1);
funcname = user_string($arg2);
lineno = $arg3;

printf("%s <= %s in %s:%d\\n",
thread_indent(-1), funcname, filename, lineno);
}

It can be invoked like this::

$ stap \
show-call-hierarchy.stp \
-c "./python test.py"

The output looks like this:

.. code-block:: none

11408 python(8274): => __contains__ in Lib/_abcoll.py:362
11414 python(8274): => __getitem__ in Lib/os.py:425
11418 python(8274): => encode in Lib/os.py:490
11424 python(8274): <= encode in Lib/os.py:493
11428 python(8274): <= __getitem__ in Lib/os.py:426
11433 python(8274): <= __contains__ in Lib/_abcoll.py:366

where the columns are:

- time in microseconds since start of script

- name of executable

- PID of process

and the remainder indicates the call/return hierarchy as the script executes.

For a :option:`--enable-shared` build of CPython, the markers are contained within the
libpython shared library, and the probe's dotted path needs to reflect this. For
example, this line from the above example:

.. code-block:: none

probe process("python").mark("function__entry") {
probe process("python").mark("import__find__load__start") {

should instead read:

.. code-block:: none

probe process("python").library("libpython3.6dm.so.1.0").mark("function__entry") {
probe process("python").library("libpython3.12dm.so.1.0").mark("import__find__load__start") {

(assuming a :ref:`debug build <debug-build>` of CPython 3.6)
(assuming a :ref:`debug build <debug-build>` of CPython 3.12)


Available static markers
------------------------

.. object:: function__entry(str filename, str funcname, int lineno)

This marker indicates that execution of a Python function has begun.
It is only triggered for pure-Python (bytecode) functions.

The filename, function name, and line number are provided back to the
tracing script as positional arguments, which must be accessed using
``$arg1``, ``$arg2``, ``$arg3``:

* ``$arg1`` : ``(const char *)`` filename, accessible using ``user_string($arg1)``

* ``$arg2`` : ``(const char *)`` function name, accessible using
``user_string($arg2)``

* ``$arg3`` : ``int`` line number

.. object:: function__return(str filename, str funcname, int lineno)

This marker is the converse of :c:func:`!function__entry`, and indicates that
execution of a Python function has ended (either via ``return``, or via an
exception). It is only triggered for pure-Python (bytecode) functions.

The arguments are the same as for :c:func:`!function__entry`

.. object:: line(str filename, str funcname, int lineno)

This marker indicates a Python line is about to be executed. It is
the equivalent of line-by-line tracing with a Python profiler. It is
not triggered within C functions.

The arguments are the same as for :c:func:`!function__entry`.

.. object:: gc__start(int generation)

Fires when the Python interpreter starts a garbage collection cycle.
Expand Down Expand Up @@ -341,96 +255,4 @@ Available static markers
.. versionadded:: 3.8


SystemTap Tapsets
-----------------

The higher-level way to use the SystemTap integration is to use a "tapset":
SystemTap's equivalent of a library, which hides some of the lower-level
details of the static markers.

Here is a tapset file, based on a non-shared build of CPython:

.. code-block:: none

/*
Provide a higher-level wrapping around the function__entry and
function__return markers:
\*/
probe python.function.entry = process("python").mark("function__entry")
{
filename = user_string($arg1);
funcname = user_string($arg2);
lineno = $arg3;
frameptr = $arg4
}
probe python.function.return = process("python").mark("function__return")
{
filename = user_string($arg1);
funcname = user_string($arg2);
lineno = $arg3;
frameptr = $arg4
}

If this file is installed in SystemTap's tapset directory (e.g.
``/usr/share/systemtap/tapset``), then these additional probepoints become
available:

.. object:: python.function.entry(str filename, str funcname, int lineno, frameptr)

This probe point indicates that execution of a Python function has begun.
It is only triggered for pure-Python (bytecode) functions.

.. object:: python.function.return(str filename, str funcname, int lineno, frameptr)

This probe point is the converse of ``python.function.return``, and
indicates that execution of a Python function has ended (either via
``return``, or via an exception). It is only triggered for pure-Python
(bytecode) functions.


Examples
--------
This SystemTap script uses the tapset above to more cleanly implement the
example given above of tracing the Python function-call hierarchy, without
needing to directly name the static markers:

.. code-block:: none

probe python.function.entry
{
printf("%s => %s in %s:%d\n",
thread_indent(1), funcname, filename, lineno);
}

probe python.function.return
{
printf("%s <= %s in %s:%d\n",
thread_indent(-1), funcname, filename, lineno);
}


The following script uses the tapset above to provide a top-like view of all
running CPython code, showing the top 20 most frequently entered bytecode
frames, each second, across the whole system:

.. code-block:: none

global fn_calls;

probe python.function.entry
{
fn_calls[pid(), filename, funcname, lineno] += 1;
}

probe timer.ms(1000) {
printf("\033[2J\033[1;1H") /* clear screen \*/
printf("%6s %80s %6s %30s %6s\n",
"PID", "FILENAME", "LINE", "FUNCTION", "CALLS")
foreach ([pid, filename, funcname, lineno] in fn_calls- limit 20) {
printf("%6d %80s %6d %30s %6d\n",
pid, filename, lineno, funcname,
fn_calls[pid, filename, funcname, lineno]);
}
delete fn_calls;
}