Re: [PATCH v1] gdb/python: fix memory leak in gdb_py_tp_name

[Andrew Burgess <aburgess@redhat.com>]

Matthieu Longo <matthieu.longo@arm.com> writes:

> On 29/05/2026 14:09, Tom Tromey wrote:
>>>>>>> "Andrew" == Andrew Burgess <aburgess@redhat.com> writes:
>> 
>> Andrew> isn't throwing an error here going to be problematic as gdb_py_tp_name
>> Andrew> is called from Python callbacks?  Unless these are catching and handling
>> Andrew> exceptions then the error is going to end up trying to pass through
>> Andrew> Python's C code.
>> 
>> Yeah.
>> 
>> I guess maybe it isn't explicitly stated anywhere (not sure) but the
>> rule in gdb's Python layer is that gdb exceptions can't propagate into
>> Python itself.  So if a function is called from Python (say like a
>> __repr__ implementation), then that function has to be sure that it does
>> not throw.  And since most things in gdb can throw, this is why at
>> present we wrap calls into gdb's core in try/catch.
>> 
>> Andrew> So maybe just returning something like "<type name unavailable>" would
>> Andrew> be better?  This might be better even when the safety work _is_ merged;
>> Andrew> if gdb_py_tp_name is called as part of logging then we'd probably rather
>> Andrew> log "<type name unavailable>" than have GDB throw an exception?
>> 
>> Yeah, I think this is what should be done, since IIUC the cases where
>> this can set the Python exception are pathological in nature.
>> 
>> Or just propagating the Python exception.  Though this would mean using
>> a return type other than std::string.
>> 
>> Tom
>
> Adopting the approach proposed by Andrew.
>
> Matthieu
>
>   /* Return the type's fully qualified name from a PyTypeObject.  */
> -const char *
> +std::string
>   gdb_py_tp_name (PyTypeObject *py_type) noexcept
>   {
> +  static const std::string NO_TYPE_NAME = "<type name unavailable>";
> +
> +  auto pyobj_to_str = [&](PyObject *name) -> std::string
> +  {
> +    const char *s = PyUnicode_AsUTF8AndSize (name, nullptr);
> +    if (s == nullptr)
> +      return NO_TYPE_NAME;

If PyUnicode_AsUTF8AndSize fails then a Python exception will be set.
As we're not going to propagate that back to the actual Python
interpreter, should we not clear the exception at this point?

And the same question each time NO_TYPE_NAME is injected instead of an
error?

Thanks,
Andrew