[Vm-dev] VM Maker: VMMaker.oscog-eem.267.mcz

[Frank Shearar]

On 21 February 2013 20:09, Eliot Miranda <eliot.miranda at gmail.com> wrote:
>
> On Thu, Feb 21, 2013 at 11:24 AM, tim Rowledge <tim at rowledge.org> wrote:
>>
>>
>> On 21-02-2013, at 11:10 AM, commits at source.squeak.org wrote:
>>> Implement unknownBytecode.
>>
>> If you implement all unknown bytecodes then you won't need to...
>
> First of all, in the Newspeak VM using the augmented SqueakV3 bytecode
> set all the bytecodes are implemented.
>
> Second of all, in the current newspeak VM we support two bytecode sets
> and that second set has bytecodes to spare, and were the same approach
> taken for Squeak there would be lots of bytecodes to spare for
> experimentation.
>
> Third, I can think of a couple of uses for unknownBytecode as
> implemented above.  My current idea is to use it for a basic-block
> coverage tool. Pepper a method with single-byte unknown bytecodes at
> the start of each basic block, storing the original bytecodes in
> properties. Now let the test suite run, and respond to unknownBytecode
> by recording the coverage, restoring the old bytecode and continuing.
> The same scheme can implement breakpoints.  But it depends crucially
> on having a single bytecode that raises an exception.  For example, at
> Cadence our current bytecode sequence is a clumsy three-bytecode one,
> push false, long jump true 0, which gets rewritten into push self,
> send breakpoint, pop.  Flipping a byte between a one-byte nop and a
> one-byte unknown bytecode would be nicer.

So this functions kind've like INT3 / CC?

frank

>> tim
>> --
>> tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
>> No one is listening until you make a mistake
>>
>>
>
>
>
> --
> best,
> Eliot