[Vm-dev] squeak decompiler

[karl ramberg]

Free books here:
http://stephane.ducasse.free.fr/FreeBooks.html

Early Squeak was pretty similar to the description in

http://sdmeta.gforge.inria.fr/FreeBooks/BlueBook/


Karl



On Mon, Oct 20, 2014 at 12:01 PM, Casey Ransberger <casey.obrien.r at gmail.com
> wrote:

>
> I don't know anything about how the Squeak decompiler works.
>
> One approach to translating code in one language to another is to build a
> parser for the source language in order to obtain an abstract syntax tree
> (AST) and then use a pretty-printer for the target language on the AST.
> That's the short, short version of an explanation of how we translate the
> Squeak VM from Slang to C.
>
> In the case of a decompiler for a byte compiled system, the source
> language (using the above approach) would be the bytecodes themselves, and
> the target language could be any language with sufficient facilities to
> support the semantics of the source language (in the case of a decompiler,
> the target language would be the original language used to compile the e.g.
> bytecode.)
>
> I hesitated to respond, because I definitely don't know anything about
> Squeak's decompiler, and also because what I've described is in some ways a
> massive oversimplification (if the compiler is optimizing things,
> deoptimization may be necessary to approach the intent and style of the
> original programmer's code, and that's just one thing I can think of.)
>
> We have available to us a couple of tools which make it (relatively) easy
> to play around with this idea and get a feel for it (OMeta/Squeak and
> PetitParser.)
>
> I'd recommend checking out PetitParser if you're messing with stuff to do
> with compilation, as OMeta's development seems to mostly have shifted to
> Javascript. PetitParser is actively maintained.
>
> Decompilation hasn't been an area of interest for me, and I don't know
> much about it, so I may be sending you down the primrose path. In the
> immortal words of LeVar Burton, "don't take my word for it."
>
> I know that several research papers have been written about OMeta, and I'd
> bet some have been written about PetitParser as well. The focus of these
> systems is on parsing expression grammars (PEGs,) but language to language
> translation is a thing, and it seems to me that a decompiler can be viewed
> as a special case of this thing. Following the references cited in such
> papers could prove valuable to whatever your cause is.
>
> For historical perspective on OMeta and PetitParser, it might be helpful
> looking into the meta language called Meta-2.
>
> Arguably, this question would be as well addressed on squeak-dev, as both
> the compiler and the decompiler are image-residents, and not built into the
> VM (though both are tied to the VM's behavior wrt interpreting bytecode.)
>
> HTH, sorry if it doesn't.
>
> Casey
>
> P.S.
>
> People who actually know how Squeak's decompiler works should still
> probably chime in here :D
>
> > On Oct 20, 2014, at 1:51 AM, Whiter Walt <whiter.walt at gmail.com> wrote:
> >
> > Hi,
> >
> > I am interested in the Squeak Decompiler class. Is there any technical
> information in the net, which explains the functionality? Or maybe it
> follows some common "rules", I can find in some paper or book?
> >
> > cheers
> > Walt
>
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