What do those question marks mean in Windbg?

Question

I'm getting an access violation in a program. Windbg shows that the program is trying to read at 0x09015000. It shows question marks (??) next to the address. My question is, what do these question marks indicate. Do they mean the memory location was never allocated, i.e. it's not backed by any physical memory (or page file)? Or is it something else?

Answer 1

It means that the virtual address is bad. Possibly a bogus pointer (i.e. uninitialized garbage), freed memory, etc.

-scott