Issue 47208: Support libffi implementations that cannot support invocations with 1024 arguments (original) (raw)

Issue47208

Created on 2022-04-04 00:27 by hoodchatham, last changed 2022-04-11 14:59 by admin.

Messages (4)
msg416646 - (view)	Author: Hood Chatham (hoodchatham) *	Date: 2022-04-04 00:27
ctypes defines `CTYPES_MAX_ARGCOUNT` to be 1024: https://github.com/python/cpython/blob/6db2db91b96aaa1270c200ec931a2250fe2799c7/Modules/_ctypes/ctypes.h#L21 If a function call is attempted with more than 1024 arguments, it will fail. The libffi emscripten port github.com/hoodmane/libffi-emscripten can only support function calls with at most 122 arguments due to limitations in Emscripten / Wasm: https://github.com/emscripten-core/emscripten/pull/16653 I propose to allow the libffi port to define FFI_MAX_CLOSURE_ARGS and if this is defined then use this number instead for `CTYPES_MAX_ARGCOUNT`. https://github.com/libffi/libffi/issues/703 The test `test_callback_too_many_args` should also be updated to respect the value of `CTYPES_MAX_ARGCOUNT` rather than hardcoding 1024 into the test.
msg416677 - (view)	Author: Christian Heimes (christian.heimes) *	Date: 2022-04-04 17:13
New changeset d1b1c885d8f276a0b1ff2e327270916396a8b842 by Christian Heimes in branch 'main': bpo-47208: Allow vendors to override CTYPES_MAX_ARGCOUNT (GH-32297) https://github.com/python/cpython/commit/d1b1c885d8f276a0b1ff2e327270916396a8b842
msg416678 - (view)	Author: Christian Heimes (christian.heimes) *	Date: 2022-04-04 17:15
GH-32297 adds #ifndef CTYPES_MAX_ARGCOUNT and exposes the constant in the _ctypes extension module, so the test case can use the constant. It allows you to override CTYPES_MAX_ARGCOUNT until libffi upstream agrees on FFI_MAX_CLOSURE_ARGS.
msg416692 - (view)	Author: Hood Chatham (hoodchatham) *	Date: 2022-04-04 19:07
Ideally the library should be able to define a different macro, e.g., CTYPES_CUSTOM_MAX_ARGCOUNT. This way the libffi port can define CTYPES_CUSTOM_MAX_ARGCOUNT and it will be compatible with older Python versions without causing Warning: "CTYPES_MAX_ARGCOUNT redefined`.