Support for Perf Maps

.. highlight:: c

.. _perfmaps:

Support for Perf Maps

On supported platforms (Linux and macOS), the runtime can take advantage of perf map files to make Python functions visible to an external profiling tool (such as perf <https://perf.wiki.kernel.org/index.php/Main_Page>_ or samply <https://github.com/mstange/samply/>). A running process may create a file in the /tmp directory, which contains entries that can map a section of executable code to a name. This interface is described in the documentation of the Linux Perf tool <https://git.kernel.org/pub/scm/linux/ kernel/git/torvalds/linux.git/tree/tools/perf/Documentation/jit-interface.txt>.

In Python, these helper APIs can be used by libraries and features that rely on generating machine code on the fly.

Note that holding an :term:attached thread state is not required for these APIs.

.. c:function:: int PyUnstable_PerfMapState_Init(void)

Open the /tmp/perf-$pid.map file, unless it's already opened, and create a lock to ensure thread-safe writes to the file (provided the writes are done through :c:func:PyUnstable_WritePerfMapEntry). Normally, there's no need to call this explicitly; just use :c:func:PyUnstable_WritePerfMapEntry and it will initialize the state on first call.

Returns 0 on success, -1 on failure to create/open the perf map file, or -2 on failure to create a lock. Check errno for more information about the cause of a failure.

.. c:function:: int PyUnstable_WritePerfMapEntry(const void *code_addr, unsigned int code_size, const char *entry_name)

Write one single entry to the /tmp/perf-$pid.map file. This function is thread safe. Here is what an example entry looks like::

  # address      size  name
  7f3529fcf759 b     py::bar:/run/t.py

Will call :c:func:PyUnstable_PerfMapState_Init before writing the entry, if the perf map file is not already opened. Returns 0 on success, or the same error codes as :c:func:PyUnstable_PerfMapState_Init on failure.

.. c:function:: void PyUnstable_PerfMapState_Fini(void)

Close the perf map file opened by :c:func:PyUnstable_PerfMapState_Init. This is called by the runtime itself during interpreter shut-down. In general, there shouldn't be a reason to explicitly call this, except to handle specific scenarios such as forking.