[samwho]

You’d need cooperation between your malloc implementation and the application code. It’s possible, but tricky. If your malloc returned a pointer to a pointer, and promised to keep the first level pointer up to date, and was able to lock your application whenever it moved things around, it could work.

Someone else already mentioned, but garbage collected languages do actually do this. Because they’re fully in control of memory (the language exposes no raw pointers), they’re able to create the layer of indirection you’ve suggested and move things around as they please. I know at minimum the JVM does this. The term to search for is “heap compaction.”

There’s also the weird and wonderful work of Emery Berger et al with their “Mesh” malloc implementation, which blows my mind: https://youtu.be/XRAP3lBivYM.