Re: Workarounds for LuaJIT's 4GB limit
- From: Florian Weimer <fw@xxxxxxxxxxxxx>
- To: luajit@xxxxxxxxxxxxx
- Date: Tue, 21 Oct 2014 18:11:19 +0200
* Sean Conner:
> It was thus said that the Great Florian Weimer once stated:
>> * Mike Pall:
>>
>> > Florian Weimer wrote:
>> >> From this, I infer that all valid userspace pointers on x86_64 are
>> >> representable as lightuserdata values.
>> >
>> > Solaris also uses the negative x64 address space in user mode (for
>> > stacks and default mmap). I have no plans to deal with this oddity.
>>
>> Wow. I didn't know this was even supported by the silicon.
>
> Why not? Addresses presented to processes are virtual and as long as, for
> example, address $FFC0000012345670 is mapped into the process I don't see a
> problem with "negative" addresses.
The architecture is limited to 48 bits, and you can't map stuff at
arbitrary addresses (the topmost 16 bit must all be equal). I
mistakenly assumed that the negative addresses were reserved to kernel
data structures.
Anyway, rather soon, the 48 bit limit will fall, due to NVRAM.
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