[New-bugs-announce] [issue35972] _xxsubinterpreters: channel_send() may truncate ints on 32-bit platforms

[Alexey Izbyshev]

New submission from Alexey Izbyshev <izbyshev at ispras.ru>:

Victor Stinner pointed out that on x86 Gentoo Installed with X 3.x buildbot, there is a compiler warning:

Python/pystate.c:1483:18: warning: cast to pointer from integer of
different size [-Wint-to-pointer-cast]

(https://buildbot.python.org/all/#/builders/103/builds/2067)

This warning reveals a bug:

static int
_long_shared(PyObject *obj, _PyCrossInterpreterData *data)
{
    int64_t value = PyLong_AsLongLong(obj);
    if (value == -1 && PyErr_Occurred()) {
        if (PyErr_ExceptionMatches(PyExc_OverflowError)) {
            PyErr_SetString(PyExc_OverflowError, "try sending as bytes");
        }
        return -1;
    }
    data->data = (void *)value;

A 64-bit value is converted to void *, which is 32-bit on 32-bit platforms.

I've implemented a PR that uses Py_ssize_t instead to match the pointer size and to preserve the ability to work with negative numbers.

----------
assignee: izbyshev
components: Extension Modules
messages: 335272
nosy: eric.snow, izbyshev, vstinner
priority: normal
severity: normal
status: open
title: _xxsubinterpreters: channel_send() may truncate ints on 32-bit platforms
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35972>
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