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 or 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.

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 *attached thread state* is not required for these
APIs.

int PyUnstable_PerfMapState_Init(void)

   *This is Unstable API. It may change without warning in minor
   releases.*

   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 "PyUnstable_WritePerfMapEntry()").
   Normally, there’s no need to call this explicitly; just use
   "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.

int PyUnstable_WritePerfMapEntry(const void *code_addr, size_t code_size, const char *entry_name)

   *This is Unstable API. It may change without warning in minor
   releases.*

   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 "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
   "PyUnstable_PerfMapState_Init()" on failure.

void PyUnstable_PerfMapState_Fini(void)

   *This is Unstable API. It may change without warning in minor
   releases.*

   Close the perf map file opened by "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.

int PyUnstable_CopyPerfMapFile(const char *parent_filename)

   *This is Unstable API. It may change without warning in minor
   releases.*

   Open the "/tmp/perf-$pid.map" file and append the content of
   *parent_filename* to it.

   This function is available on all platforms but only generates
   output on platforms that support perf maps (currently only Linux).
   On other platforms, it does nothing.

   Added in version 3.13.

int PyUnstable_PerfTrampoline_CompileCode(PyCodeObject *code)

   *This is Unstable API. It may change without warning in minor
   releases.*

   Compile the given code object using the current perf trampoline.

   The “current” trampoline is the one set by the runtime or the most
   recent "PyUnstable_PerfTrampoline_SetPersistAfterFork()" call.

   If no trampoline is set, falls back to normal compilation (no perf
   map entry).

   Parameters:
      * **code** – The code object to compile.

   Returns:
      0 on success, -1 on failure.

   Added in version 3.13.

int PyUnstable_PerfTrampoline_SetPersistAfterFork(int enable)

   *This is Unstable API. It may change without warning in minor
   releases.*

   Set whether the perf trampoline should persist after a fork.

   * If "enable" is true (non-zero): perf map file remains open/valid
     post-fork. Child process inherits all existing perf map entries.

   * If "enable" is false (zero): perf map closes post-fork. Child
     process gets empty perf map.

   Default: false (clears on fork).

   Parameters:
      * **enable** – 1 to enable, 0 to disable.

   Returns:
      0 on success, -1 on failure.

   Added in version 3.13.
