Fix variadic calls on Apple platforms with a non-OS libffi

doc/source/whatsnew.rst

@@ -5,7 +5,12 @@ What's New
 v2.2.0.dev0
 ===========
 
-* TBD
+* Fixed variadic function calls on Apple platforms when ``_cffi_backend`` is
+  built against a libffi other than the one provided by the macOS SDK — that
+  is, the iOS/tvOS/watchOS wheels, or a macOS build using a Homebrew libffi.
+  (`#265`_).
+
+.. _`#265`: https://github.com/python-cffi/cffi/pull/265
 
 v2.1.0
 ======

src/c/_cffi_backend.c

@@ -117,6 +117,25 @@
 # define CFFI_CHECK_FFI_PREP_CIF_VAR __builtin_available(macos 10.15, ios 13, watchos 6, tvos 13, *)
 # define CFFI_CHECK_FFI_PREP_CIF_VAR_MAYBE 1
 
+#elif defined(__APPLE__)
+
+/* On Apple platforms, but built against a libffi whose headers do not
+ * define FFI_AVAILABLE_APPLE: not the OS-provided libffi, but e.g. the
+ * static libffi that iOS/tvOS/watchOS wheels are built against, or a
+ * Homebrew libffi on macOS.  There is no runtime-availability question
+ * there: whatever the linker resolved is present, so all three functions
+ * can be used unconditionally.  ffi_prep_cif_var() in particular must be
+ * used: on arm64 Apple platforms variadic arguments are passed on the
+ * stack, unlike regular arguments, so calling a variadic function through
+ * a cif prepared with ffi_prep_cif() silently passes garbage.
+ */
+# define CFFI_CHECK_FFI_CLOSURE_ALLOC 1
+# define CFFI_CHECK_FFI_CLOSURE_ALLOC_MAYBE 1
+# define CFFI_CHECK_FFI_PREP_CLOSURE_LOC 1
+# define CFFI_CHECK_FFI_PREP_CLOSURE_LOC_MAYBE 1
+# define CFFI_CHECK_FFI_PREP_CIF_VAR 1
+# define CFFI_CHECK_FFI_PREP_CIF_VAR_MAYBE 1
+
 #elif defined(__EMSCRIPTEN__)
 
 # define CFFI_CHECK_FFI_CLOSURE_ALLOC 1

src/c/test_c.py

@@ -1233,11 +1233,6 @@ def test_cannot_pass_struct_with_array_of_length_0():
     BFunc2 = new_function_type((BInt,), BStruct, False)
     pytest.raises(NotImplementedError, cast(BFunc2, 123), 123)
 
-@pytest.mark.xfail(
-    is_ios,
-    reason="For an unknown reason f(1, cast(BInt, 42)) returns 36792864",
-    raises=AssertionError,
-)
 def test_call_function_9():
     BInt = new_primitive_type("int")
     BFunc9 = new_function_type((BInt,), BInt, True)    # vararg
@@ -3022,11 +3017,6 @@ def test_string_assignment_to_byte_array():
     except ImportError:
         pass   # win32
 
-@pytest.mark.skipif(
-    is_ios,
-    reason="For an unknown reason fscanf() doesn't read anything on 3.14"
-           " and crashes on 3.13 (that's why it's not an xfail)",
-)
 def test_FILE():
     if sys.platform == "win32":
         pytest.skip("testing FILE not implemented")