[Vm-dev] Some protection missing (I guess in COG version)

[Bob Arning]

or just implement SmallInteger class>>new:, etc, to signal an error 
without bothering the primitive at all.

On 12/16/13 8:59 PM, Eliot Miranda wrote:
>   
>
>
> Hi Nicolas,
>
>     good catch.  thanks.
>
>
> On Mon, Dec 16, 2013 at 2:36 PM, Nicolas Cellier 
> <nicolas.cellier.aka.nice at gmail.com 
> <mailto:nicolas.cellier.aka.nice at gmail.com>> wrote:
>
>
>     (SmallInteger new: 0) can quickly lead to a VM crash.
>     This should better be intercepted as a primitive failure.
>
>
> greed.  But there are two obvious ways to go about this (at least in 
> Spur).  One is to explicitly test for the immediate classes in the new 
> and new: primitives.  This is poor as it introduces additional tests 
> on a critical path.  The other way is to give SmallInteger and 
> Character special formats and then the primitives would fail without 
> additional tests. The question is what format to use.  In Spur the 
> formats are
>
>  0 = 0 sized objects (UndefinedObject True False et al)
> 1 = non-indexable objects with inst vars (Point et al)
> 2 = indexable objects with no inst vars (Array et al)
> 3 = indexable objects with inst vars (MethodContext 
> AdditionalMethodState et al)
> 4 = weak indexable objects with inst vars (WeakArray et al)
> 5 = weak non-indexable objects with inst vars (ephemerons) (Ephemeron)
> 6 unused, reserved for exotic pointer objects?
> 7 Forwarded Object, 1st field is pointer, rest of fields are ignored
> 8 unused, reserved for exotic non-pointer objects?
> 9 (?) 64-bit indexable
> 10 - 11 32-bit indexable(11 unused in 32 bits)
> 12 - 15 16-bit indexable(14 & 15 unused in 32-bits)
> 16 - 23 byte indexable(20-23 unused in 32-bits)
> 24 - 31 compiled method(28-21 unused in 32-bits)
>
> Format 7 should never be valid for an instance as it is reserved by 
> the VM for forwarders.  So how about making 7 the format for immediate 
> classes?  Ten it will be easy to arrange that both new and new: will 
> fail naturally for this format.
>
>
>     I know that we cannot protect against all and every mistake, but
>     this one should be easy.
>
>     See
>     http://stackoverflow.com/questions/20621119/how-to-print-an-integer-to-transcript
>
>     I'm thinking of Spur where Character are immediate and where
>     archeo-code could lead to same kind of crash.
>
>
> -- 
> best,
> Eliot

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