On Mon, Feb 7, 2022 at 2:26 PM Victor Stinner <vstin...@python.org> wrote:
> CPython is also affected by these issues, but the benefits of PEP 674
> (alone) are too indirect, so I chose to avoid mentioning CPython
> issues directly, to avoid confusion.
A concrete example of problem caused by exposing structures in the C
API (unrelated to PEP 674). It's a tricky problem...
typedef struct {
PyObject_VAR_HEAD
Py_hash_t ob_shash;
char ob_sval[1];
} PyBytesObject;
The "char ob_sval[1];" syntax used to declare an array is an undefined
behavior if the array is longer in memory. On a bytes object of 4
bytes, accessing ob_sval[3] works, but is an undefined behavior.
=> see https://bugs.python.org/issue40120 for details
The problem can be solved by using "char ob_sval[];" syntax, but we
cannot use this syntax in the public C header, since it causes
compiler errors if the header is built with a C++ compiler (not to
build Python itself, but build a C++ extension using the Python C
API). Removing the structure from the public C API would solve the C++
issue.
Victor
--
Night gathers, and now my watch begins. It shall not end until my death.
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