[LLVMdev] Is address space 1 reserved?

[Philip Reames]

On 01/07/2015 11:52 AM, Matt Arsenault wrote:
>
>> On Jan 7, 2015, at 2:25 PM, Owen Anderson <resistor at mac.com 
>> <mailto: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.
If you have an example with a null in a non-0 address space being 
mishandled, please file a bug.  We'll fix them as we find them.
>
> -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, 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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