_PyFrame_Copy() copied interpreter frames into generator and
frame-object storage without initializing the visited byte. Incremental
GC later reads frame->visited in mark_stacks() on non-start passes, so
copied frames could expose an uninitialized value once they became live
on a thread stack again.
Reset visited when copying a frame so copied frames start with defined
GC bookkeeping state. Preserve lltrace in Py_DEBUG builds.
faulthandler now detects if a frame or a code object is invalid or
freed.
Add helper functions:
* _PyCode_SafeAddr2Line()
* _PyFrame_SafeGetCode()
* _PyFrame_SafeGetLasti()
_PyMem_IsPtrFreed() now detects pointers in [-0xff, 0xff] range
as freed.
This tells TSAN not to sanitize `PyUnstable_InterpreterFrame_GetLine()`.
There's a possible data race on the access to the frame's `instr_ptr`
if the frame is currently executing. We don't really care about the
race. In theory, we could use relaxed atomics for every access to
`instr_ptr`, but that would create more code churn and current compilers
are overly conservative with optimizations around relaxed atomic
accesses.
We also don't sanitize `_PyFrame_IsIncomplete()` because it accesses
`instr_ptr` and is called from assertions within PyFrame_GetCode().
