In python/py-registers.c we make use of PyObject_IsInstance. The
PyObject_IsInstance can return -1 for an error, 0 for false, or 1 for
true.
In py-registers.c we treat the return value from PyObject_IsInstance
as a boolean, which means both -1 and 1 will be treated as true.
If PyObject_IsInstance returns -1 for an error, this will be treated
as true, we will then invoke undefined behaviour as the pyo_reg_id
object will be treated as a gdb.RegisterDescriptor, even though it
might not be.
I noticed that the gdb.RegisterDescriptor class does not have the
Py_TPFLAGS_BASETYPE flag, and therefore cannot be inherited from. As
such, using PyObject_IsInstance is not necessary, we can use
PyObject_TypeCheck instead. The PyObject_TypeCheck function only
returns 0 or 1, so we don't need to worry about the error case.
Approved-By: Tom Tromey <tom@tromey.com>
1fc2d1491c