`PyEval_GetFrame` crashes when it returns incomplete frames

[pablogsal]

Is it possible that PyEval_GetFrame returns incomplete frames. When this happens, Python segfaults in release mode or crashes in debug mode because of the check for incomplete frames in _PyFrame_GetFrameObject. This is reproducible in many ways involving C extensions, the easier one may be by installing a custom memory allocator for all the domains and calling PyEval_GetFrame from there. As the allocator can be called at random points of the eval loop (for example here) is perfectly possible that a legitimate call to PyEval_GetFrame returns an incomplete frame.

[pablogsal]

CC: @markshannon @brandtbucher @ericsnowcurrently @iritkatriel

[brandtbucher]

Typo? Are you asking us if it's possible, or telling us it is?

[pablogsal]

I am telling you

[pablogsal]

It may be easier to reproduce by using generators.

[brandtbucher]

It seems to me that the correct thing to do in this case is to walk back over the frames until we reach a "complete" one, like we do in other places. Not 100% sure yet.

[brandtbucher]

It may also be possible in sys._getframe(). The logic for skipping incomplete frames doesn't seem to happen anymore once you've walked back to the desired depth.

[brandtbucher]

Ah wait, I think sys._getframe() is okay actually. I don't think it can be called from an incomplete frame.