how can i check bad pointer on asm?

[mcp]

@qkumba
Actually, that API is fundamentally broken because it is not free of side effects, e.g., consider the case where you use that API on a guard page. After using that API, that page won't be a guard page anymore!

Due to race conditions, there is no general safe way to test if a pointer is valid, other than making sure it is only obtained for safe addresses. Pretty much any address can become invalid after you tested the pointer, and vice versa.

The right question would be to ask: what are you actually trying to do?