[LLVMdev] Is address space 1 reserved?

Matt Arsenault
Wed, 07 Jan 2015 19:52:23 -0000

> On Jan 7, 2015, at 2:25 PM, Owen Anderson <resistor at mac.com>
wrote:
>
> I'm not aware of any such restriction, and I know of several LLVM based
systems that use address space 1 for something other than that.
>
> -Owen

Yes, this would be a problem for us. We use 1 for a normal address space where 0
is invalid. However, we also have a problem where some other address spaces do
want 0 to be a valid address, which just sort of don’t work correctly now.

-Matt



>
> On Jan 7, 2015, at 1:18 PM, Philip Reames <listmail at philipreames.com
<mailto:listmail at philipreames.com>> wrote:
>
>> On the review for http://reviews.llvm.org/D6808
<http://reviews.llvm.org/D6808>, majnemer
<http://reviews.llvm.org/p/majnemer/> commented that:
>> "Address space 1 has a special meaning in LLVM, it's identical
to address space 0 except for the fact that "null" may be
dereferenced. You might want to consider a different address space."
>>
>> This is the first I've heard of this and I can't find any
documentation about it being reserved, either in general, or specifically for
x86.  Can anyone clarify?
>>
>> The only address spaces with special meanings I know of are:
>> - 0 (the normal address space, null is not dereferencable)
>> - 256 - TLS, GS relative addressing
>> - 257 - FS relative addressing
>>
>> Philip
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