On Mar 21, 2011, at 2:57 PM, Toon Verwaest wrote:
> Yes you are right! Bytecode validation would be very important here. If you ask me, the VM should only allow verified bytecode to be executed. Here it could have a dual model, where bytecodes are "internalized" whenever you give them to the VM first. At that point they are validated. Once it's internalized, it can't be modified anymore from the outside, since the Smalltalk world doesn't have direct access to the internalized version. All changes to the bytecode "source", needs to be propagated to the VM by re-internalizing it.
>
> This is exactly the model I'm using in Pinocchio... and that allows us to not use bytecodes in the first place :) You just need a way to map the internal version back onto the highlevel version for debugging. (We don't verify the bytecode yet though).
>
> Bytecode verification btw shouldn't be too hard. You just need to make sure that all the codes are safe for the instance at hand, and for the method contexts you create. Anything else is just a runtime semantical error which you can't guarantee, since you don't know what the programmer is trying to do. We don't verify it yet since I'm still designing my register-based bytecodes; and since I atm have too much work at hand :)
>
> cheers,
> Toon
>
> On 03/21/2011 02:22 PM, Igor Stasenko wrote:
>> On 21 March 2011 13:14, Toon Verwaest<
[hidden email]> wrote:
>>> I couldn't agree more!
>>>
>>> However, here the problem is not that the format isn't a correct format. The
>>> problem is that a bytecode is activated that is incompatible with the
>>> instance format. So basically on every bytecode accessing an instance you
>>> would have to check if this is a valid access. And as we all know, Smalltalk
>>> avoids this; it makes things faster :)
>>>
>> In other words, a responsibility of having correct bytecode lies on
>> image side, not on VM side.
>>
>> Adding a bytecode verifier to VM will be a lot of work.. And of course
>> it could verify it only when you installing a method,
>> not when you activating it.
>>
>>> Toon
>>>
>>> On 03/21/2011 12:49 PM, Igor Stasenko wrote:
>>>> On 21 March 2011 11:29, Tudor Girba<
[hidden email]> wrote:
>>>>> Thanks, Toon!
>>>>>
>>>>> I changed the code to explicitly set the format, and it seems to fix the
>>>>> problem:
>>>>>
>>>>> cls := Class new superclass: MooseElement;
>>>>> setFormat: MooseElement format;
>>>>> yourself.
>>>>> cls compileSilently: 'mooseName ^ 1/0'.
>>>>> element := cls new.
>>>>>
>>>>> Is this correct?
>>>>>
>>>> Yes, you should pay attention to have correct format.
>>>> But of course VM could also be more cautios and verify if your class
>>>> are well formed before creating an instance of it..
>>>>
>>>>
>>>>
>>>>> Cheers,
>>>>> Doru
>>>>>
>>>>
>>>
>>>
>>
>>
>
>