Undefined behaviour in `main` and 3.11

[matthiasgoergens]

I ran the sanitizers again, and found a few more instances of undefined behaviour, mostly around bit-shifting of signed integers and arithmetic with NULL pointers.

export CC="clang"
export ASAN_OPTIONS=detect_leaks=0
configure --with-assertions --with-address-sanitizer --with-trace-refs --with-undefined-behavior-sanitizer --with-pydebug
nice make -j8
make test

I put some asserts to demonstrate the undefined behaviour into pull requests for main (matthiasgoergens#18) and 3.11 (matthiasgoergens#19).

More information about my environment:

$ clang --version
clang version 14.0.6
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

[kumaraditya303]

Can you post a summary of "arithmetic with NULL pointers" here? Thanks

[matthiasgoergens]

@kumaraditya303 In ceval.c, the assert is my addition.

    /* Pack other positional arguments into the *args argument */
    if (co->co_flags & CO_VARARGS) {
        PyObject *u = NULL;
        assert(args != NULL);
        u = _PyTuple_FromArraySteal(args + n, argcount - n);
        if (u == NULL) {
            goto fail_post_positional;
        }
        assert(localsplus[total_args] == NULL);
        localsplus[total_args] = u;
    }

There's also an example in Modules/_testcapimodule.c but that's only a test, I guess.

[matthiasgoergens]

#96672 is also vaguely related.

[kumaraditya303]

cc @pablogsal This seems to be introduced in #89419

[pablogsal]

I am a bit surprised by this because we have a USAN buildbot that has not detected anything:

https://buildbot.python.org/all/#/builders/964

[pablogsal]

These are the parameters, just in case we want to compare:

https://github.com/python/buildmaster-config/blob/8484356e8a0854084e186d9c9eb47b3b0c6eb628/master/custom/factories.py#L311-L315

[matthiasgoergens]

@pablogsal I added some more info about what compiler I am using.