[scialex]

It's not. It's trying to access unmapped or protected memory in its own process.

Basically what its used for is to implement an 'if' that's super fast on the most likely path but super slow on the less likely path.

It's not super clear what its being used for (this is often used for the GC but the fact that graal isn't affected means that likely still works). Possibly they are using this to detect attempts to use inline-cache entries that have been deleted.

[moonchild]

object.field is implemented as a direct load from the object; if the object turned out to be null, then the resultant signal is caught and turned into a NullPointerException

[moonchild]

sorry, I didn't read the linked post closely enough—from my reading, this case is not one of the ones that was broken