[Vm-dev] Push/pop considered harmful

Igor Stasenko siguctua at gmail.com
Tue Mar 3 18:52:30 UTC 2009

2009/3/3 Andreas Raab <andreas.raab at gmx.de>:
> Igor Stasenko wrote:
>> But it seems that it disabled by default.
>> Yes it would be nice to replace push/pops with single method, like
>> #primitiveArgumentAt: index
>> where index = 0 is receiver
>> 1 .. n - rest of arguments.
> I think that is a brilliant idea, right in line with what we were doing.
> Finally you can use left-to-right access to method args ;-)
>> Another thing, that most primitives never check a number of arguments
>> on stack. This is also a potential risk, when you calling primitive
>> with wrong number of arguments from a language side.
> Right. One thing we can do here is to add a check to primArgAt: that just
> fails the primitive if you try to access arguments that aren't provided.
yes, this check could be put in #primArgAt:
but i feel little unpleased that it will be performed more than once.
It would be better to have a slang directive, like:
self expectedArguments: 3.  " 1== receiver only, 2 == receiver +
single arg ... "

in primitie code, and put it as first check in primitive entry. Then
code generator could produce a code which checks the number of
arguments, and automatically fail primitive if they are not same as

>> Apart from this, what you suppose to do with primitives who switching
>> the active context (entering block closure,signaling semaphore,
>> scheduling etc)?
>> In this situation you shouldn't try to validate the stack pointer, as
>> well as primitive return value is useless.
> Yes. push and pop will still be there for internal use - it is only the
> plugins that will get updated. So anything that wants to munge the stack in
> such a way will have to be builtin VM primitive which seems fair to me.
> Cheers,
>  - Andreas

Best regards,
Igor Stasenko AKA sig.

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