On Fri, Jul 25, 2025 at 1:03 PM Andrey Semashev wrote:
>
> There is only one pointer value that is guaranteed to not point at any
> object, and that's nullptr. If you want to add another one, that would
> have to go beyond just defining a new constant. The whole runtime
> (including but not limited to the memory allocator) would have to be
> updated with support for this new constant.
Not really. There isn't a computer in existence today -- I don't think
-- that uses more than 49 bits for a memory address. 64-Bit ARM uses
48 bits but it can be extended by 1 bit to 49 bits.
Since 2022, Intel has specified LA57, or 5-level paging, which uses a 57-bit virtual address. This is consistent with the design for the original amd64, which used the canonical address requirement to guard against userspace code being incompatible with further virtual address extensions. I believe Intel Server chips supporting this feature came out either this year, or will next year.