[New-bugs-announce] [issue42688] ctypes memory error on Apple Silicon with external libffi

[Eli Rykoff]

New submission from Eli Rykoff <erykoff at stanford.edu>:

Building python 3.9.1 on Apple Silicon compiled against a external (non-os-provided) libffi makes the following code return a MemoryError:

Test:

import ctypes

@ctypes.CFUNCTYPE(None, ctypes.c_int, ctypes.c_char_p)
def error_handler(fif, message):
    pass

I have tracked this down to the following code in malloc_closure.c:

#if USING_APPLE_OS_LIBFFI && HAVE_FFI_CLOSURE_ALLOC
    if (__builtin_available(macos 10.15, ios 13, watchos 6, tvos 13, *)) {
        ffi_closure_free(p);
        return;
    }
#endif

and

#if USING_APPLE_OS_LIBFFI && HAVE_FFI_CLOSURE_ALLOC
    if (__builtin_available(macos 10.15, ios 13, watchos 6, tvos 13, *)) {
        return ffi_closure_alloc(size, codeloc);
    }
#endif

In fact, while the __builtin_available() call should be guarded by USING_APPLE_OS_LIBFFI, the call to ffi_closure_alloc() should only be guarded by HAVE_FFI_CLOSURE_ALLOC, as this is set as the result of an independent check in setup.py and should be used with external libffi when supported.

The following code does work instead:

#if HAVE_FFI_CLOSURE_ALLOC
#if USING_APPLE_OS_LIBFFI
    if (__builtin_available(macos 10.15, ios 13, watchos 6, tvos 13, *)) {
#endif
        ffi_closure_free(p);
        return;
#if USING_APPLE_OS_LIBFFI
    }
#endif
#endif


#if HAVE_FFI_CLOSURE_ALLOC
#if USING_APPLE_OS_LIBFFI
    if (__builtin_available(macos 10.15, ios 13, watchos 6, tvos 13, *)) {
#endif
        return ffi_closure_alloc(size, codeloc);
        return;
#if USING_APPLE_OS_LIBFFI
    }
#endif
#endif

----------
components: ctypes
messages: 383419
nosy: erykoff
priority: normal
severity: normal
status: open
title: ctypes memory error on Apple Silicon with external libffi
type: behavior
versions: Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42688>
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