From 5252ad2b646ee7bbcccee86a42cf48bbb321a6e2 Mon Sep 17 00:00:00 2001 From: "Miss Islington (bot)" <31488909+miss-islington@users.noreply.github.com> Date: Tue, 22 Nov 2022 10:57:45 -0800 Subject: GH-92892: Add section about variadic functions to ctypes documentation (GH-99529) On some platforms, and in particular macOS/arm64, the calling convention for variadic arguments is different from the regular calling convention. Add a section to the documentation to document this. (cherry picked from commit bc3a11d21ddef28047b18c0f6a5068fa9fb16da2) Co-authored-by: Ronald Oussoren --- Doc/library/ctypes.rst | 20 ++++++++++++++++++++ .../2022-11-16-12-52-23.gh-issue-92892.TS-P0j.rst | 1 + 2 files changed, 21 insertions(+) create mode 100644 Misc/NEWS.d/next/Documentation/2022-11-16-12-52-23.gh-issue-92892.TS-P0j.rst diff --git a/Doc/library/ctypes.rst b/Doc/library/ctypes.rst index 9f8737b..077a205 100644 --- a/Doc/library/ctypes.rst +++ b/Doc/library/ctypes.rst @@ -373,6 +373,26 @@ that they can be converted to the required C data type:: 31 >>> +.. _ctypes-calling-variadic-functions: + +Calling varadic functions +^^^^^^^^^^^^^^^^^^^^^^^^^ + +On a lot of platforms calling variadic functions through ctypes is exactly the same +as calling functions with a fixed number of parameters. On some platforms, and in +particular ARM64 for Apple Platforms, the calling convention for variadic functions +is different than that for regular functions. + +On those platforms it is required to specify the *argtypes* attribute for the +regular, non-variadic, function arguments: + +.. code-block:: python3 + + libc.printf.argtypes = [ctypes.c_char_p] + +Because specifying the attribute does inhibit portability it is adviced to always +specify ``argtypes`` for all variadic functions. + .. _ctypes-calling-functions-with-own-custom-data-types: diff --git a/Misc/NEWS.d/next/Documentation/2022-11-16-12-52-23.gh-issue-92892.TS-P0j.rst b/Misc/NEWS.d/next/Documentation/2022-11-16-12-52-23.gh-issue-92892.TS-P0j.rst new file mode 100644 index 0000000..54e421d --- /dev/null +++ b/Misc/NEWS.d/next/Documentation/2022-11-16-12-52-23.gh-issue-92892.TS-P0j.rst @@ -0,0 +1 @@ +Document that calling variadic functions with ctypes requires special care on macOS/arm64 (and possibly other platforms). -- cgit v0.12