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- Subject: Re: Integer subtype and NaN trick
- From: Jay Carlson <nop@...>
- Date: Sun, 16 Jun 2013 15:28:25 -0400
On Jun 16, 2013, at 3:14 AM, Owen Shepherd wrote:
> Coda Highland wrote:
>>
>> Unless I'm wrong, ASLR isn't restricted to 48 bits. Virtual memory
>> allocation can use whatever addresses it wants.
>
>
> The hardware itself is physically limited to 48-bits. Each page is 4kB, plus there are 4 layers of page tables, bringing the total up to 48 bits.
>
> The processors throw an exception on a memory access if bits 63-48 don't match bit 47.
>
> This is all baked into silicon
Amusingly, 64-bit ARM is 49-bit. Twice as good as amd64!
64-bit ARM also has a mode which ignores the high 8 bits of addresses. Sadly, NaNs are still then in the high part of memory.
Jay
