[Vm-dev] tracking WebAssembly

[Ryan Macnak]

On Mon, Mar 18, 2019 at 7:58 PM Eliot Miranda <eliot.miranda at gmail.com>
wrote:

> > On Mar 18, 2019, at 1:50 PM, Levente Uzonyi <leves at caesar.elte.hu>
> wrote:
> > Wouldn't it be easier to just use emscripten to compile the current C
> code directly to wasm?
> > I mean, it would probably be a smaller undertaking to create the
> necessary bindings/plugins for emscripten than to generate wasm code
> directly from VMMaker and rewrite the platform code.
>
> Sure, but running a stack machine virtually above another stack machine is
> going to be far less efficient than mapping the Cog Smalltalk stack to the
> WebAssembly stack.  So it’s an issue of performance and ambition.  I tend
> to choose the ambitious route, within affordability constraints.
>

The WebAssembly stack is too restrictive to directly host the Smalltalk
stack. By design, it's not possible to get an address into the stack. For C
code, Emscripten places locals that have their address taken into a shadow
stack that lives in WebAssembly memory. A direct translation from Slang to
WebAssembly would have to do the same.
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