[Vm-dev] InterpreterSimulator

[Eliot Miranda]

Hi Florin, 

   I believe the correct fix is for  ObjectMemory needs to decompose fetchLong64:ofObject: into two 32-but reads unless BytesPerWord = 8.  I'll commit asap (which is once I have 64-bit small float tagging converted).  But your fix should  keep you going until then.

_,,,^..^,,,_ (phone)

> On Mar 9, 2016, at 1:53 PM, Florin Mateoc <florin.mateoc at gmail.com> wrote:
> 
> 
>> On 3/9/2016 3:17 PM, Florin Mateoc wrote:
>> Hi again,
>> 
>> I think I found the bug: in method InterpreterPrimitives>>signed64BitValueOf: there seems to be an assumption (even
>> mentioned in the method comment) that (on 32bit machines) largeIntegers have to be either 4 or 8 bytes.
>> In this case we get a 5byte largeInteger, so we get the error. What I don't understand is where does this assumption
>> come from, because it does not seem limited to this method.
>> Also note that on BigEndian machines the code does not act upon this assumption, so it would not fail.
>> 
>> Actually, I suspect that the assumption comes from "generalizing" the 32-bit one, since the methods seem to be copied
>> and pasted.
>> For the 32bit variant, the comment stated that "The object may be either a positive SmallInteger or a four-byte
>> LargeInteger". But in this case it was correct, anything less than 4 bytes would not be a LargeInteger. When moving to
>> 64bit, the same does not hold true. We can have largeIntegers with 4,5,6,7 or 8 bytes fitting in 64 bits.
>> 
>> Also, speaking of BigEndian, it seems that, in the same class, the methods #magnitude64BitValueOf: and
>> #positive64BitValueOf: do not take care of the BigEndian case.
>> 
>> Cheers,
>> Florin
> 
> 
> For what it's worth, I did try the obvious (if what I suspect is correct) fix in #signed64BitValueOf: and it seemed to work:
> 
> 
>    ...
>    self cppIf: VMBIGENDIAN
>        ifTrue:
>            [value := objectMemory fetchByte: sz - 1 ofObject: oop.
>             sz - 2 to: 0 by: -1 do: [:i |
>                value := value << 8 + (objectMemory fetchByte: i ofObject: oop)]]
>        ifFalse:
>            [value := (objectMemory fetchLong32: 0 ofObject: oop) asUnsignedInteger.
>             4 to: sz - 1 do: [:i |
>                value := value << 8 + (objectMemory fetchByte: i ofObject: oop)]].
> 
> 
> instead of the original:
> 
> 
>    ...
>    self cppIf: VMBIGENDIAN
>        ifTrue:
>            [value := objectMemory fetchByte: sz - 1 ofObject: oop.
>             sz - 2 to: 0 by: -1 do: [:i |
>                value := value << 8 + (objectMemory fetchByte: i ofObject: oop)]]
>        ifFalse: [value := sz > 4
>                        ifTrue: [objectMemory fetchLong64: 0 ofObject: oop]
>                        ifFalse: [(objectMemory fetchLong32: 0 ofObject: oop) asUnsignedInteger]].
>