Virtual memory and alignment - how do they factor together?

Question

I think I understand memory alignment, but what confuses me is that the address of a pointer on some systems is going to be in virtual memory, right? So most of the checking/ensuring of alignment I have seen seem to just use the pointer address. Is it not possible that the physical memory address will not be aligned? Isn't that problematic for things like SSE?

Answer 1

The physical address will be aligned because virtual memory only maps aligned pages to physical memory (and the pages are typically 4KB).

So unless you need alignment > page size, the physical memory will be aligned as per your requirements.

In the specific case of SSE, everything works fine because you only need 16 byte alignment.